Holocene deglacial history of the northeast Antarctic Peninsula - A review and new chronological constraints

NASA Astrophysics Data System (ADS)

Johnson, Joanne S.; Bentley, Michael J.; Roberts, Stephen J.; Binnie, Steven A.; Freeman, Stewart P. H. T.

2011-12-01

The northeast Antarctic Peninsula (NEAP) region is currently showing signs of significant environmental change, evidenced by acceleration of glacial retreat and collapse of both Larsen-A and -B ice shelves within the past 15 years. However, data on the past extent of the eastern margin of the Antarctic Peninsula Ice Sheet (APIS) and its Holocene retreat history are sparse, and hence we cannot yet put the recent changes into a long-term context. In order to investigate the timing of deglaciation, we present 16 new cosmogenic 10Be surface exposure ages from sites on northern James Ross Island (Cape Lachman, Johnson Mesa and Terrapin Hill) and Seymour Island. The majority of the ages cluster around 6-10 ka, with three significantly older (25-31 ka). We combine these ages with existing terrestrial and marine radiocarbon deglaciation ages, and a compilation of existing swath bathymetry data, to quantify the temporal and spatial character of the regional glacial history. Ice had begun to retreat from the outer shelf by 18.3 ka, reaching Seymour Island by ˜8 ka. Northern James Ross Island began to deglaciate around the time of the Early Holocene Climatic Optimum (c. 11-9.5 ka). Deglaciation continued, and a transition from grounded to floating ice in Prince Gustav Channel occurred around 8 ka, separating the James Ross Island ice cap from the APIS. This occurred shortly before Prince Gustav Channel ice shelf began to disintegrate at 6.2 ka. Our results suggest there may be a bathymetric control on the spatial pattern of deglaciation in the NEAP.

The Earth's Cryosphere: Current State and Recent Changes

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.

2006-01-01

The Earth continues to have a third of the ice that it had at the peak of the last ice age, although that ice continues to decrease, as it has, overall, for the past 18,000 years. Over the last 100 years, the retreat signal has been especially strong in ice shelves of the Arctic and along the Antarctic Peninsula, with a more mixed signal elsewhere. For instance, since the early 1990s the massive Greenland and Antarctic ice sheets have thinned along the coasts but thickened in the interior, and since the late 1970s sea ice has decreased in the Arctic but increased (slightly) in the Antarctic. Major difficulties in the interpretations of the climate record come from the high interannual variability of most cryosphere components and the lack of consistent long-term global data records, the latter problem now being slowly remedied, in part, through satellite technology.

Quantifying the sources of atmospheric ice nuclei from carbonaceous combustion aerosol

NASA Astrophysics Data System (ADS)

Schill, G. P.; Jathar, S.; Galang, A.; Farmer, D.; Friedman, B.; Levin, E. J.; DeMott, P. J.; Kreidenweis, S. M.

2015-12-01

Ice nucleation on particles is a fundamental atmospheric process, which governs precipitation, cloud lifetimes, and climate. Despite being a basic atmospheric process, our current understanding of ice nucleation in the atmosphere is low. One reason for this low understanding is that ice nuclei concentrations are low (only ~1 in 105 particles in the free troposphere nucleate ice), making it challenging to identify both the composition and sources of ambient ice nuclei. Carbonaceous combustion aerosol produced from biomass and fossil fuel combustion are one potential source of these ice nuclei, as they contribute to over one-third of all aerosol in the North American free troposphere. Unfortunately, previous results from field measurements in-cloud, aircraft measurements, and laboratory studies are in conflict, with estimates of the impact of combustion aerosol ranging from no effect to rivaling the well-known atmospheric ice nuclei mineral dust. It is, however, becoming clear that aerosols from combustion processes are more complex than model particles, and their ice activity depends greatly on both fuel type and combustion conditions. Given these dependencies, we propose that sampling from real-world biomass burning and fossil fuel sources would provide the most useful new information on the contribution of carbonaceous combustion aerosols to atmospheric ice nuclei particles. To determine the specific contribution of refractory black carbon (rBC) to ice nuclei concentrations, we have coupled the Single Particle Soot Photometer (SP2) to the Colorado State University Continuous Flow Diffusion Chamber (CFDC). The SP2 utilizes laser-induced incandescence to quantify rBC mass on a particle-by-particle basis; in doing so, it also selectively destroys rBC particles by heating them to their vaporization temperature. Thus, the SP2 can be used as a selective pre-filter for rBC into the CFDC. In this work, we will present recent results looking at contribution of diesel engine exhaust to ice nuclei concentrations. Sampling was done for both diesel and biodiesel on fresh emissions and emissions aged up to 18 days equivalent photochemical aging with a Potential Aerosol Mass chamber. Our results show that, for mixed-phase clouds, both fresh and aged (bio)diesel are not likely a significant source of ice nuclei.

The last glaciation of Bear Peninsula, central Amundsen Sea Embayment of Antarctica: Constraints on timing and duration revealed by in situ cosmogenic 14C and 10Be dating

NASA Astrophysics Data System (ADS)

Johnson, Joanne S.; Smith, James A.; Schaefer, Joerg M.; Young, Nicolás E.; Goehring, Brent M.; Hillenbrand, Claus-Dieter; Lamp, Jennifer L.; Finkel, Robert C.; Gohl, Karsten

2017-12-01

Ice streams in the Pine Island-Thwaites region of West Antarctica currently dominate contributions to sea level rise from the Antarctic ice sheet. Predictions of future ice-mass loss from this area rely on physical models that are validated with geological constraints on past extent, thickness and timing of ice cover. However, terrestrial records of ice sheet history from the region remain sparse, resulting in significant model uncertainties. We report glacial-geological evidence for the duration and timing of the last glaciation of Hunt Bluff, in the central Amundsen Sea Embayment. A multi-nuclide approach was used, measuring cosmogenic 10Be and in situ14C in bedrock surfaces and a perched erratic cobble. Bedrock 10Be ages (118-144 ka) reflect multiple periods of exposure and ice-cover, not continuous exposure since the last interglacial as had previously been hypothesized. In situ14C dating suggests that the last glaciation of Hunt Bluff did not start until 21.1 ± 5.8 ka - probably during the Last Glacial Maximum - and finished by 9.6 ± 0.9 ka, at the same time as ice sheet retreat from the continental shelf was complete. Thickening of ice at Hunt Bluff most likely post-dated the maximum extent of grounded ice on the outer continental shelf. Flow re-organisation provides a possible explanation for this, with the date for onset of ice-cover at Hunt Bluff providing a minimum age for the timing of convergence of the Dotson and Getz tributaries to form a single palaeo-ice stream. This is the first time that timing of onset of ice cover has been constrained in the Amundsen Sea Embayment.

Large Fluctuations in Speed on Jakobshavn Isbrae, Greenland

NASA Technical Reports Server (NTRS)

Joughin, Ian; Abdalati, Waleed; Fahnestock, Mark

2003-01-01

We have assembled an 18-year velocity record for Jakobshavn Isbrae, Greenland. From a 1985 speed of approx. 7000 m/yr, the glacier had slowed by approx. 1000 m/ yr in 1992, which coincided with independently observed thickening in the early 1990s . The glacier then sped up by approx. 4000 m/yr between 1997 and 2000, during which time other measurements show rapid thinning . From 2000 to 2003, the glacier s floating ice tongue almost entirely disintegrated, as speed increased to 12,600 m/yr. If the retreat of the ice tongue caused the acceleration, then similar losses of floating ice tongues since the Little Ice Age may explain the current rapid thinning observed for many of Greenland s outlet glaciers.

PHYSICAL THERAPY MANAGEMENT OF ICE HOCKEY ATHLETES: FROM THE RINK TO THE CLINIC AND BACK

PubMed Central

Davenport, Todd E.

2016-01-01

ABSTRACT Background The increasing number of athletes playing hockey compels rehabilitation professionals working in orthopedic and sports settings to understand the unique functional demands of ice hockey and the patterns of injuries they may promote. Purpose The purpose of this clinical perspective is to: (1) discuss the functional implications of different positions and age levels on injury prevalence within the sport; (2) summarize the seven most common injuries sustained by ice hockey athletes; and (3) present a conceptual model for the clinical management and prevention of these injuries by rehabilitation professionals. Methods A narrative review and synthesis was conducted of currently available literature on prevalence, etiology, rehabilitative intervention, prognosis, and prevention of ice hockey injuries. Results Research evidence is available to support the prevalence of injuries sustained while participating in ice hockey, as well as the most effective clinical treatment protocols to treat them. Most of the existing protocols are based on clinical and sports experience with incorporation of scientific data. Conclusion This clinical commentary reviews the current concepts of ice hockey injury care and prevention, based on scientific information regarding the incidence, mechanism, rehabilitation protocols, prognosis, and prevention of injuries. Science-based, patient-centered reasoning is integral to provide the highest quality of rehabilitative and preventative care for ice hockey athletes by physical therapists. Level of Evidence 5 PMID:27274432

The current evolution of complex high mountain debris-covered glacier systems and its relation with ground ice nature and distribution: the case of Rognes and Pierre Ronde area (Mont-Blanc range, France).

NASA Astrophysics Data System (ADS)

Bosson, Jean-Baptiste; Lambiel, Christophe

2014-05-01

The current climate forcing, through negative glacier mass balance and rockfall intensification, is leading to the rapid burring of many small glacier systems. When the debris mantle exceeds some centimeters of thickness, the climate control on ice melt is mitigated and delayed. As well, debris-covered glaciers respond to climate forcing in a complex way. This situation is emphasised in high mountain environments, where topo-climatic conditions, such as cold temperatures, amount of solid precipitation, duration of snow cover, nebulosity or shadow effect of rockwalls, limit the influence of rising air temperatures in the ground. Beside, due to Holocene climate history, glacier-permafrost interactions are not rare within the periglacial belt. Glacier recurrence may have removed and assimilated former ice-cemented sediments, the negative mass balance may have led to the formation of ice-cored rock glaciers and neopermafrost may have formed recently under cold climate conditions. Hence, in addition to sedimentary ice, high mountain debris-covered glacier systems can contain interstitial magmatic ice. Especially because of their position at the top of alpine cascade systems and of the amount of water and (unconsolidated) sediment involved, it is important to understand and anticipate the evolution of these complex landforms. Due to the continuous and thick debris mantle and to the common existence of dead ice in deglaciated areas, the current extent of debris-covered glacier can be difficult to point out. Thus, the whole system, according to Little Ice Age (LIA) extent, has sometimes to be investigated to understand the current response of glacier systems to the climate warming. In this context, two neighbouring sites, Rognes and Pierre Ronde systems (45°51'38''N, 6°48'40''E; 2600-3100m a.s.l), have been studied since 2011. These sites are almost completely debris-covered and only few ice outcrops in the upper slopes still witness the existence of former glaciers. Electrical resistivity tomographies, kinematic data and ground surface temperature show that heterogeneous responses to climate forcing are occurring despites their small areas (> 0.3 km2). This complex situation is related to Holocene climate history and especially to glacier systems evolution since LIA. The current dynamics depend of ground ice nature and distribution. Five main behaviours can be highlighted: - Debris covered glacier areas are the most active. Their responses to climate forcing are relatively fast, especially through massive ice melt-out each summer. - Ice-cored rock glacier areas are quite active. The existence of massive glacier ice under few meters of debris explain the important surface lowering during the snow free period . - Ice-cemented rock glacier areas are characterised by winter and summer subhorizontal downslope creeping. - Moraine areas containing dead ice have heterogeneous activities (directions and values of detected movements) related to the ice vanishing. - Deglaciated moraine areas are almost inactive, except modest superficial paraglacial rebalancing.

Ice Age Sea Level Change on a Dynamic Earth

NASA Astrophysics Data System (ADS)

Austermann, J.; Mitrovica, J. X.; Latychev, K.; Rovere, A.; Moucha, R.

2014-12-01

Changes in global mean sea level (GMSL) are a sensitive indicator of climate variability during the current ice age. Reconstructions are largely based on local sea level records, and the mapping to GMSL is computed from simulations of glacial isostatic adjustment (GIA) on 1-D Earth models. We argue, using two case studies, that resolving important, outstanding issues in ice age paleoclimate requires a more sophisticated consideration of mantle structure and dynamics. First, we consider the coral record from Barbados, which is widely used to constrain global ice volume changes since the Last Glacial Maximum (LGM, ~21 ka). Analyses of the record using 1-D viscoelastic Earth models have estimated a GMSL change since LGM of ~120 m, a value at odds with analyses of other far field records, which range from 130-135 m. We revisit the Barbados case using a GIA model that includes laterally varying Earth structure (Austermann et al., Nature Geo., 2013) and demonstrate that neglecting this structure, in particular the high-viscosity slab in the mantle linked to the subduction of the South American plate, has biased (low) previous estimates of GMSL change since LGM by ~10 m. Our analysis brings the Barbados estimate into accord with studies from other far-field sites. Second, we revisit estimates of GMSL during the mid-Pliocene warm period (MPWP, ~3 Ma), which was characterized by temperatures 2-3°C higher than present. The ice volume deficit during this period is a source of contention, with estimates ranging from 0-40 m GMSL equivalent. We argue that refining estimates of ice volume during MPWP requires a correction for mantle flow induced dynamic topography (DT; Rowley et al., Science, 2013), a signal neglected in previous studies of ice age sea level change. We present estimates of GIA- and DT-corrected elevations of MPWP shorelines from the U.S. east coast, Australia and South Africa in an attempt to reconcile these records with a single GMSL value.

Surface Exposure Dating of the Huancané III Moraines in Peru: A Record of Quelccaya Ice Cap's Maximum Extent during the Last Glacial Period

NASA Astrophysics Data System (ADS)

Baranes, H. E.; Kelly, M. A.; Stroup, J. S.; Howley, J. A.; Lowell, T. V.

2012-12-01

The climatic conditions that influenced the tropics during the height of the last glacial period are not well defined and controversial. There are disparities in estimates of temperature anomalies (e.g., MARGO, 2009; Rind and Peteet, 1985; CLIMAP, 1976), and critical terrestrial paleotemperature proxy records in tropical regions are poorly dated (e.g., Porter, 2001). Defining these conditions is important for understanding the mechanisms that cause major shifts in climate, as the tropics are a primary driver of atmospheric and oceanic circulation. This study aims to constrain the timing of maximum glacier extents in the Cordillera Oriental in southern Peru during the last glacial period by applying surface exposure (beryllium-10) dating to the Huancané III (Hu-III) moraines. The Hu-III moraines mark the maximum extent of Quelccaya Ice Cap (QIC) (13.93°S, 70.83°W), the largest tropical ice cap, during the last ice age. The eight beryllium-10 ages presented here yield 17,056 ± 520 yrs ago as a minimum age for the onset of recession from the ice cap advance marked by the Hu-III moraines. Comparing this age to other paleoclimate records indicates that the ice cap advance marked by the Hu-III moraines is more likely associated with a North Atlantic climate event known as Heinrich I (H1; 16,800 yrs ago, Bond et al., 1992, 1993) than with global cooling at the Last Glacial Maximum (LGM; ~21,000 yrs ago, Denton and Hughes, 1981). This result suggests that climate processes in the North Atlantic region are linked to climatic conditions in the tropical Andes. A mesoscale climate model and an ice-flow model are currently being developed for QIC. The moraine data presented in this study will be used with these two models to test response of QIC to North Atlantic and global climate events.

High-resolution 129I bomb peak profile in an ice core from SE-Dome site, Greenland.

PubMed

Bautista, Angel T; Miyake, Yasuto; Matsuzaki, Hiroyuki; Iizuka, Yoshinori; Horiuchi, Kazuho

2018-04-01

129 I in natural archives, such as ice cores, can be used as a proxy for human nuclear activities, age marker, and environmental tracer. Currently, there is only one published record of 129 I in ice core (i.e., from Fiescherhorn Glacier, Swiss Alps) and its limited time resolution (1-2 years) prevents the full use of 129 I for the mentioned applications. Here we show 129 I concentrations in an ice core from SE-Dome, Greenland, covering years 1956-1976 at a time resolution of ∼6 months, the most detailed record to date. Results revealed 129 I bomb peaks in years 1959, 1962, and 1963, associated to tests performed by the former Soviet Union, one year prior, in its Novaya Zemlya test site. All 129 I bomb peaks were observed in winter (1958.9, 1962.1, and 1963.0), while tritium bomb peaks, another prominent radionuclide associated with nuclear bomb testing, were observed in spring or summer (1959.3, and 1963.6; Iizuka et al., 2017). These results indicate that 129 I bomb peaks can be used as annual and seasonal age markers for these years. Furthermore, we found that 129 I recorded nuclear fuel reprocessing signals and that these can be potentially used to correct timing of estimated 129 I releases during years 1964-1976. Comparisons with other published records of 129 I in natural archives showed that 129 I can be used as common age marker and tracer for different types of records. Most notably, the 1963 129 I bomb peak can be used as common age marker for ice and coral cores, providing the means to reconcile age models and associated trends from the polar and tropical regions, respectively. Copyright © 2017 Elsevier Ltd. All rights reserved.

The extent and timing of the last British-Irish Ice Sheet offshore of west Ireland-preliminary findings

NASA Astrophysics Data System (ADS)

Peters, Jared; Benetti, Sara; Dunlop, Paul; Cofaigh, Colm Ó.

2014-05-01

Recently interpreted marine geophysical data from the western Irish shelf has provided the first direct evidence that the last British-Irish Ice Sheet (BIIS) extended westwards onto the Irish continental shelf as a grounded ice mass composed of several lobes with marine-terminating margins. Marine terminating ice margins are known to be sensitive to external forcing mechanisms and currently there is concern regarding the future stability of marine based ice sheets, such as the West Antarctic Ice Sheet, in a warming world. Given its position, the glaciated western Irish continental shelf is a prime location to investigate the processes of how marine-based ice sheets responded to past climatic and oceanic events, which may in turn help us better predict the future trajectory of the marine sectors of modern Ice Sheets. However, despite the potential importance of the former Irish ice margin to our understanding of ice sheet behaviour, the timing and nature of its advance and retreat is currently poorly understood. This study aims to describe the depositional history of the last BIIS on the continental shelf west of Ireland and age-constrain the rate of retreat of two ice lobes that extended from Galway Bay and Clew Bay. This is being accomplished through a multifaceted analysis of at least 29 sediment cores gathered across the continental shelf offshore of counties Galway and Mayo, Ireland. This poster shows results from initial sedimentological descriptions of cores from the mid to outer shelf, which support previous geomorphic interpretations of BIIS history. Preliminary palaeoenvironmental results from ongoing micropaleontological analyses are also discussed and provide new data that verifies sedimentary interpretations on ice proximity. Finally, results from several radiocarbon dates are discussed, which limit these deposits to the last glacial maximum and constrain the timings of ice advance and retreat on the continental shelf west of Ireland.

77 FR 14567 - Draft General Management Plan/Environmental Impact Statement for the Ice Age Complex at Cross...

Federal Register 2010, 2011, 2012, 2013, 2014

2012-03-12

... Impact Statement for the Ice Age Complex at Cross Plains, Cross Plains, Wisconsin AGENCY: National Park... General Management Plan/Environmental Impact Statement for the Ice Age Complex at Cross Plains, Wisconsin... also send comments to Superintendent, Ice Age National Scenic Trail, 700 Rayovac Drive, Suite 100...

The isotopic composition of methane in polar ice cores

NASA Technical Reports Server (NTRS)

Craig, H.; Chou, C. C.; Welhan, J. A.; Stevens, C. M.; Engelkemeir, A.

1988-01-01

Air bubbles in polar ice cores indicate that about 300 years ago the atmospheric mixing ratio of methane began to increase rapidly. Today the mixing ratio is about 1.7 parts per million by volume, and, having doubled once in the past several hundred years, it will double again in the next 60 years if current rates continue. Carbon isotope ratios in methane up to 350 years in age have been measured with as little as 25 kilograms of polar ice recovered in 4-meter-long ice-core segments. The data show that: (1) in situ microbiology or chemistry has not altered the ice-core methane concentrations, and (2) that the carbon-13 to carbon-12 ratio of atmospheric CH4 in ice from 100 years and 300 years ago was about 2 per mil lower than at present. Atmospheric methane has a rich spectrum of isotopic sources: the ice-core data indicate that anthropogenic burning of the earth's biomass is the principal cause of the recent C-13H4 enrichment, although other factors may also contribute.

Toward unified ice core chronologies with the DatIce tool

NASA Astrophysics Data System (ADS)

Toye Mahamadou Kele, H.; Lemieux-Dudon, B.; Blayo, E.

2012-04-01

Antarctic and Greenland ice cores provide a means to study the phase relationships of climate changes in both hemispheres. They also enable to study the timing between climate, and greenhouse gases or orbital forcings. One key step for such studies is to improve the absolute and relative precisions of ice core age scales (for ice and trapped gas), and beyond that, to try to reach the best consistency between chronologies of paleo records of any kind. The DatIce tool is designed to increase the consistency between pre-existing (also called background) core chronologies. It formulates a variational inverse problem which aims at correcting three key quantities that uniquely define the core age scales: the accumulation rate, the total thinning function, and the close-off depth. For that purpose, it integrates paleo data constraints of many types among which age markers (with for instance documented volcanoes eruptions), and stratigraphic links (with for instance abrupt changes in methane concentration). A cost function is built that enables to calculate new chronologies by making a trade-off between all the constraints (background chronologies and paleo data). The method presented in Lemieux-Dudon et al (2010) has already been applied simultaneously to EPICA EDML and EDC, Vostok and NGRIP. Currently, on going works are conducted at LSCE Saclay and LGGE Grenoble laboratories to construct unified Antarctic chronologies by applying the DatIce tool with new ice cores and new sets of paleo measurements. We here present the DatIce tool, the underlying methodology, and its potential applications. We further show some improvements that have been made recently. We especially adress the issue related to the calibration of the error of pre-existing core chronologies. They are inputs that may have a strong impact on the results. However these uncertainties are uneasy to analyze, since prior chronologies are most of the time assessed on the basis of glaciological models (firn densification and ice flow models) which still face large uncertainties (forcing fields, model parameters, mechanic and physic formulation). For that reason, we chose to calibrate errors by applying consistency diagnostics, a classical method in data assimilation (Desrozier et al, 2009).

Centuries of intense surface melt on Larsen C Ice Shelf

NASA Astrophysics Data System (ADS)

Bevan, Suzanne L.; Luckman, Adrian; Hubbard, Bryn; Kulessa, Bernd; Ashmore, David; Kuipers Munneke, Peter; O'Leary, Martin; Booth, Adam; Sevestre, Heidi; McGrath, Daniel

2017-12-01

Following a southward progression of ice-shelf disintegration along the Antarctic Peninsula (AP), Larsen C Ice Shelf (LCIS) has become the focus of ongoing investigation regarding its future stability. The ice shelf experiences surface melt and commonly features surface meltwater ponds. Here, we use a flow-line model and a firn density model (FDM) to date and interpret observations of melt-affected ice layers found within five 90 m boreholes distributed across the ice shelf. We find that units of ice within the boreholes, which have densities exceeding those expected under normal dry compaction metamorphism, correspond to two climatic warm periods within the last 300 years on the Antarctic Peninsula. The more recent warm period, from the 1960s onwards, has generated distinct sections of dense ice measured in two boreholes in Cabinet Inlet, which is close to the Antarctic Peninsula mountains - a region affected by föhn winds. Previous work has classified these layers as refrozen pond ice, requiring large quantities of mobile liquid water to form. Our flow-line model shows that, whilst preconditioning of the snow began in the late 1960s, it was probably not until the early 1990s that the modern period of ponding began. The earlier warm period occurred during the 18th century and resulted in two additional sections of anomalously dense ice deep within the boreholes. The first, at 61 m in one of our Cabinet Inlet boreholes, consists of ice characteristic of refrozen ponds and must have formed in an area currently featuring ponding. The second, at 69 m in a mid-shelf borehole, formed at the same time on the edge of the pond area. Further south, the boreholes sample ice that is of an equivalent age but which does not exhibit the same degree of melt influence. This west-east and north-south gradient in the past melt distribution resembles current spatial patterns of surface melt intensity.

The Holocene Minimum of the West Antarctic Ice Sheet: Radiocarbon Model Ages for Subglacial Sediments

NASA Astrophysics Data System (ADS)

Tulaczyk, S. M.; Stansell, N.; Scherer, R. P.; Powell, R. D.

2017-12-01

It is commonly assumed that the West Antarctic Ice Sheet (WAIS) is at the present time as small as it has been since at least the last interglacial period about 125,000 years ago. Yet, our recent analyses of subglacial sediments recovered from beneath the ice sheet indicate regionally widespread presence of radiocarbon. This unstable isotope with half life of 5,730 years should decay to nil if the analyzed subglacial sediment samples have been isolated beneath the ice sheet from the atmosphere and the ocean for 125,000 years (over 20 half lives). However, the apparent radiocarbon ages for these samples are in the range of about 20,000-30,000 years BP, based on radiocarbon Fraction Modern (FM) of a few to several percent. The apparent sediment ages cannot be taken at face value because: (1) they overlap with the Last Glacial Maximum (LGM) when WAIS is known to have extended over 1,000 km past the sediment sampling locations, and (2) Antarctic glacigenic sediments commonly contain significant admixture of old, radiocarbon-dead organic matter. The latter biases apparent radiocarbon ages because it violates the assumption that the initial radiocarbon fraction in a sample was equal to FM. To mitigate the problem with apparent ages, we assume that initial radiocarbon fraction in subglacial sediments was equal to that determined by us independently in J-9 sediments from beneath the Ross Ice Shelf (RIS) and calculate radiocarbon 'model ages' between 1,000 and 6,000 years BP. This period of time overlaps with a regional climatic optimum and with late phases of post-LGM glacioisostatic adjustment in the region (e.g., Kingslake et al., this session). We propose that the grounding line of WAIS, at least on the RIS side, retreated in mid/late Holocene more than 300 km beyond its current position and then re-advanced to reach its modern geometry. This implies that the main body of WAIS was significantly smaller than today in mid/late Holocene and that the ice sheet is capable of large fluctuations on timescales much shorter than previously expected.

Biomarker-based reconstruction of late Holocene sea-ice variability: East versus West Greenland continental shelf.

NASA Astrophysics Data System (ADS)

Kolling, H. M.; Stein, R. H.; Fahl, K.

2016-12-01

Sea is a critical component of the climate system and its role is not yet fully understood e.g. the recent rapid decrease in sea ice is not clearly reflected in climate models. This illustrates the need for high-resolution proxy-based sea-ice reconstructions going beyond the time scale of direct measurements in order to understand the processes controlling present and past natural variability of sea ice on short time scales. Here we present the first comparison of two high-resolution biomarker records from the East and West Greenland Shelf for the late Holocene. Both areas are highly sensitive to sea-ice changes as they are influenced by the East Greenland Current, the main exporter of Arctic freshwater and sea ice. On the East Greenland Shelf, we do not find any clear evidence for a long-term increase of sea ice during the late Holocene Neoglacial. This sea-ice record seems to be more sensitive to short-term climate events, such as the Roman Warm Period, the Dark Ages, the Medieval Warm Period and the Little Ice Age. In contrary, the West Greenland Shelf record shows a strong and gradual increase in sea ice concentration and a reduction in marine productivity markers starting near 1.6 ka. In general, the increase in sea ice seems to follow the decreasing solar insolation trend. Short-term events are not as clearly pronounced as on the East Greenland Shelf. A comparison to recently published foraminiferal records from the same cores (Perner et al., 2011, 2015) illuminates the differences of biomarker and micropaleontoligical proxies. It seems that the general trend is reflected in both proxies but the signal of small-scale events is preserved rather differently, pointing towards different environmental requirements of the species behind both proxies. References: Perner, K., et al., 2011. Quat. Sci. Revs. 30, 2815-2826 Perner, K., et al., 2015. Quat. Sci. Revs. 129, 296-307

Kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central Lower Michigan, USA

NASA Astrophysics Data System (ADS)

Schaetzl, Randall J.; Lepper, Kenneth; Thomas, Sarah E.; Grove, Leslie; Treiber, Emma; Farmer, Alison; Fillmore, Austin; Lee, Jordan; Dickerson, Bethany; Alme, Kayleigh

2017-03-01

In association with an undergraduate Honors Seminar at Michigan State University, we studied two small kame deltas in north-central Lower Michigan. These recently identified deltas provide clear evidence for a previously unknown proglacial lake (Glacial Lake Roscommon) in this large basin located in an interlobate upland. Our first goal was to document and characterize the geomorphology of these deltas. Because both deltas are tied to ice-contact ridges that mark the former position of the retreating ice margin within the lake, our second goal was to establish the age of one of the deltas, thereby constraining the timing of ice retreat in this part of Michigan, for which little information currently exists. Both deltas are composed of well-sorted fine and medium sands with little gravel, and have broad, nearly flat surfaces and comparatively steep fronts. Samples taken from the upper 1.5 m of the deltas show little spatial variation in texture, aside from a general fining toward their outer margins. Gullies on the outer margins of both deltas probably postdate the formation of the deltas proper; we suggest that they formed by runoff during a permafrost period, subsequent to lake drawdown. We named the ice lobe that once covered this area the Mackinac Lobe, because it had likely advanced into the region across the Mackinac Straits area. Five of six optically stimulated luminescence (OSL) ages from one of the deltas had minimal scatter and were within ± 1000 years of one another, with a mean age of 23.1 ± 0.4 ka. These ages suggest that the Mackinac Lobe had started to retreat from the region considerably earlier than previously thought, even while ice was near its maximum extent in Illinois and Indiana, and the remainder of Michigan was ice-covered. This early retreat, which appears to coincide with a short-lived warm period indicated from the Greenland ice core, formed an "opening" that was at least occasionally flooded. Thick and deep, fine-textured deposits, which underlie much of the region, probably date to this time. Our work provides the first evidence of this extremely early ice retreat from central Lower Michigan, occurring almost 4000 years before the southern margin of the ice (Saginaw Lobe) had started its retreat from the state.

Effect of photochemical aging on the ice nucleation properties of diesel and wood burning particles

NASA Astrophysics Data System (ADS)

Chou, C.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Kanji, Z. A.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

2012-06-01

A measurement campaign (IMBALANCE) was conducted in 2009 and aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro with no emission after-treatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical aging did not play a role in modifying their ice nucleation behavior. Only one diesel experiment where α-pinene was added, showed an ice nucleation enhancement after the aging at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical aging did also not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C with no ice nucleation observed at -30 °C for wood burning particles. Photochemical aging did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -30 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical aging on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

Effect of photochemical ageing on the ice nucleation properties of diesel and wood burning particles

NASA Astrophysics Data System (ADS)

Chou, C.; Kanji, Z. A.; Stetzer, O.; Tritscher, T.; Chirico, R.; Heringa, M. F.; Weingartner, E.; Prévôt, A. S. H.; Baltensperger, U.; Lohmann, U.

2013-01-01

A measurement campaign (IMBALANCE) conducted in 2009 was aimed at characterizing the physical and chemical properties of freshly emitted and photochemically aged combustion particles emitted from a log wood burner and diesel vehicles: a EURO3 Opel Astra with a diesel oxidation catalyst (DOC) but no particle filter and a EURO2 Volkswagen Transporter TDI Syncro without emission aftertreatment. Ice nucleation experiments in the deposition and condensation freezing modes were conducted with the Portable Ice Nucleation Chamber (PINC) at three nominal temperatures, -30 °C, -35 °C and -40 °C. Freshly emitted diesel particles showed ice formation only at -40 °C in the deposition mode at 137% relative humidity with respect to ice (RHi) and 92% relative humidity with respect to water (RHw), and photochemical ageing did not play a role in modifying their ice nucleation behaviour. Only one diesel experiment where α-pinene was added for the ageing process, showed an ice nucleation enhancement at -35 °C. Wood burning particles also act as ice nuclei (IN) at -40 °C in the deposition mode at the same conditions as for diesel particles and photochemical ageing also did not alter the ice formation properties of the wood burning particles. Unlike diesel particles, wood burning particles form ice via condensation freezing at -35 °C whereas no ice nucleation was observed at -30 °C. Photochemical ageing did not affect the ice nucleation ability of the diesel and wood burning particles at the three different temperatures investigated but a broader range of temperatures below -40 °C need to be investigated in order to draw an overall conclusion on the effect of photochemical ageing on deposition/condensation ice nucleation across the entire temperature range relevant to cold clouds.

Taste CREp: the Cosmic-Ray Exposure program

NASA Astrophysics Data System (ADS)

Martin, Léo; Blard, Pierre-Henri; Balco, Greg; Lavé, Jérôme; Delunel, Romain; Lifton, Nathaniel

2017-04-01

We present here the CREp program and the ICE-D production rate database, an online system to compute Cosmic Ray Exposure (CRE) ages with cosmogenic 3He and 10Be (crep.crpg.cnrs-nancy.fr). The CREp calculator is designed to automatically reflect the current state of the global calibration database production rate stored in ICE-D (http://calibration.ice-d.org). ICE-D will be regularly updated in order to incorporate new calibration data and reflect the current state of the available literature. The CREp program permits to calculate ages in a flexible way: 1) Two scaling models are available, i.e. i) the empirical Lal-Stone time-dependent model (Balco et al., 2008; Lal, 1991; Stone, 2000) with the muon parameters of Braucher et al. (2011), and ii) the Lifton-Sato-Dunai (LSD) theoretical model (Lifton et al., 2014). 2) Users may also test the impact of the atmosphere model, using either i) the ERA-40 database (Uppala et al., 2005), or ii) the standard atmosphere (N.O.A.A., 1976). 3) For the time-dependent correction, users or choose among the three proposed geomagnetic datasets (Lifton, 2016; Lifton et al., 2014; Muscheler et al., 2005) or import their own database. 4) For the important choice of the production rate, CREp is linked to a database of production rate calibration data, ICE-D. This database includes published empirical calibration rate studies that are publicly available at present, including those of the CRONUS-Earth and CRONUS-EU projects, as well as studies from other projects. Users may select the production rates either: i) using a worldwide mean value, ii) a regionally averaged value (not available in regions with no data), iii) a local unique value, which can be chosen among the existing dataset or imported by the user, or iv) any combination of single or multiple calibration data. We tested the efficacy of the different scaling models by looking at the statistical dispersion of the computed Sea Level High Latitude (SLHL) calibrated production rates. Lal/Stone and LSD models have comparable efficacies, and the impact of the tested atmospheric model and the geomagnetic database is also limited. If a global mean is chosen, the 1σ uncertainty arising from the production rate is about 5% for 10Be and 10% for 3He. If a regional production rate is picked, these uncertainties are potentially lower.

Holocene history of drift ice in the northern North Atlantic: Evidence for different spatial and temporal modes

USGS Publications Warehouse

Moros, M.; Andrews, John T.; Eberl, D.D.; Jansen, E.

2006-01-01

We present new high-resolution proxy data for the Holocene history of drift ice off Iceland based on the mineralogy of the <2-mm sediment fraction using quantitative X-ray diffraction. These new data, bolstered by a comparison with published proxy records, point to a long-term increasing trend in drift ice input into the North Atlantic from 6 to 5 ka toward the present day at sites influenced by the cold east Greenland Current. This feature reflects the late Holocene Neoglacial or cooling period recorded in ice cores and further terrestrial archives on Greenland. In contrast, a decrease in drift ice during the same period is recorded at sites underlying the North Atlantic Drift, which may reflect a warming of this region. The results document that Holocene changes in iceberg rafting and sea ice advection did not occur uniformly across the North Atlantic. Centennial-scale climate variability in the North Atlantic region over the last ???4 kyr is linked to the observed changes in drift ice input. Increased drift ice may have played a role in the increase of cold intervals during the late Holocene, e.g., the Little Ice Age cooling. Copyright 2006 by the American Geophysical Union.

Reconstruction of Plio-Pleistocene paleoceanographic conditions in the western Arctic Ocean based on a Northwind Ridge sediment record.

NASA Astrophysics Data System (ADS)

Dipre, G.; Polyak, L.; Ortiz, J. D.; Oti, E.; Kuznetsov, A.

2017-12-01

The rapid loss of sea ice in the Arctic Ocean is expected to result in major climatic and hydrographic changes, some of which are already being observed. To better understand these changes, it is necessary to investigate paleoclimatic conditions during times when the Arctic had similarly reduced sea-ice cover. The Pliocene to early Pleistocene period ( 1-5 Ma) may represent the best analog, as the modern Arctic geography had developed with the opening of the Bering Strait (ca. 5-6 Ma), but major Northern Hemisphere glaciations other than Greenland had not fully begun. Here we present an investigation of sediment core HLY0503-03JPC from top of the Northwind Ridge, western Arctic Ocean. This sedimentary record contains uniquely preserved calcareous microfossils through the early Pleistocene according to strontium isotope ages. Based on extrapolation of these ages, the record extends to at least the late Pliocene. We evaluate paleo-sea ice conditions using benthic foraminifera assemblages, similar to a prior study of a nearby core (Polyak et al., 2013), along with physical (sediment optical properties, density, grain size) and chemical (XRF, δ18O, δ13C) proxies to reconstruct paleo-circulation and sediment transport processes. Based on these proxies, the record exhibits a distinct tripartite stratigraphic division. The top unit, recovering the middle to late Quaternary, shows sedimentary impacts of major glaciations and mostly perennial sea ice conditions. The second unit, dated to the early Pleistocene, indicates reduced glacial inputs, mostly seasonal sea ice, and potentially intensified current conditions. Finally, preliminary results for the oldest unit, presumably representing the late Pliocene, suggest a more acidic ocean characterized by low, if any, sea ice presence and increased current activity. As similar conditions (acidification, storminess) are starting to be observed in the changing modern environment, this third unit may provide especially valuable insight for understanding the projected changes for the western Arctic Ocean.

Rapid Holocene thinning of outlet glaciers followed by readvance in the western Ross Embayment, Antarctica

NASA Astrophysics Data System (ADS)

Jones, R. S.; Whitmore, R.; Mackintosh, A.; Norton, K. P.; Eaves, S.; Stutz, J.

2017-12-01

Investigating Antarctic deglaciation following the LGM provides an opportunity to better understand patterns, mechanisms and drivers of ice sheet retreat. In the Ross Sea sector, geomorphic features preserved on the seafloor indicate that streaming East Antarctic outlet glaciers once extended >100 km offshore of South Victoria Land prior to back-stepping towards their modern configurations. In order to adequately interpret the style and causes of this retreat, the timing and magnitude of corresponding ice thickness change is required. We present new constraints on ice surface lowering from Mawson Glacier, an outlet of the East Antarctic Ice Sheet that flows into the western Ross Sea. Surface-exposure (10Be) ages from samples collected in elevation transects above the modern ice surface reveal that rapid thinning occurred at 5-8 ka, broadly coeval with new ages of grounding-line retreat at 6 ka and rapid thinning recorded at nearby Mackay Glacier at 7 ka. Our data also show that a moraine formed near to the modern ice margin of Mawson Glacier at 0.8 ka, which, together with historical observations, indicates that glaciers in this region readvanced during the last thousand years. We argue that 1) the accelerated thinning of outlet glaciers was driven by local grounding-line retreat through overdeepened basins during the early-mid Holocene, and 2) the glaciers subsequently readvanced, possibly linked to late Holocene sea-ice expansion, before retreating to their current positions. Our work demonstrates that these outlet glaciers were closely coupled to environmental and topography-induced perturbations near their termini throughout the Holocene.

Late Noachian and early Hesperian ridge systems in the south circumpolar Dorsa Argentea Formation, Mars: Evidence for two stages of melting of an extensive late Noachian ice sheet

NASA Astrophysics Data System (ADS)

Kress, Ailish M.; Head, James W.

2015-05-01

The Dorsa Argentea Formation (DAF), extending from 270°-100° E and 70°-90° S, is a huge circumpolar deposit surrounding and underlying the Late Amazonian South Polar Layered Deposits (SPLD) of Mars. Currently mapped as Early-Late Hesperian in age, the Dorsa Argentea Formation has been interpreted as volatile-rich, possibly representing the remnants of an ancient polar ice cap. Uncertain are its age (due to the possibility of poor crater retention in ice-related deposits), its mode of origin, the origin of the distinctive sinuous ridges and cavi that characterize the unit, and its significance in the climate history of Mars. In order to assess the age of activity associated with the DAF, we examined the ridge populations within the Dorsa Argentea Formation, mapping and characterizing seven different ridge systems (composed of nearly 4,000 ridges covering a total area of ~300,000 km2, with a cumulative length of ridges of ~51,000 km) and performing crater counts on them using the method of buffered crater counting to determine crater retention ages of the ridge populations. We examined the major characteristics of the ridge systems and found that the majority of them were consistent with an origin as eskers, sediment-filled subglacial drainage channels. Ridge morphologies reflect both distributed and channelized esker systems, and evidence is also seen that some ridges form looping moraine-like termini distal to some distributed systems. The ridge populations fall into two age groups: ridge systems between 270° and 0° E date to the Early Hesperian, but to the east, the Promethei Planum and the Chasmata ridge systems date to the Late Noachian. Thus, these ages, and esker and moraine-like morphologies, support the interpretation that the DAF is a remnant ice sheet deposit, and that the esker systems represent evidence of significant melting and drainage of meltwater from portions of this ice sheet, thus indicating at least some regions and/or periods of wet-based glaciation. The Late Noachian and Early Hesperian ages of the ridge systems closely correspond to the ages of valley network/open basin lake systems, representing runoff, drainage and storage of liquid water in non-polar regions of the surface of Mars. Potential causes of such wet-based conditions in the DAF include: 1) top-down melting due to atmospheric warming, 2) enhanced snow and ice accumulation and raising of the melting isotherm to the base of the ice sheet, or 3) basal melting associated with intrusive volcanism (volcano-ice interactions). The early phase of melting is closely correlated in time with valley network formation and thus may be due to global atmospheric warming, while the later phase of melting may be linked to Early Hesperian global volcanism and specific volcano-ice interactions (table mountains) in the DAF. Crater ages indicate that these wet-based conditions ceased by the Late Hesperian, and that further retreat of the DAF to its present configuration occurred largely through sublimation, not melting, thus preserving the extensive ridge systems. MARSIS radar data suggest that significant areas of layered, potentially ice-rich parts of the Dorsa Argentea Formation remain today.

Cosmogenic exposure age constraints on deglaciation and flow behaviour of a marine-based ice stream in western Scotland, 21-16 ka

NASA Astrophysics Data System (ADS)

Small, David; Benetti, Sara; Dove, Dayton; Ballantyne, Colin K.; Fabel, Derek; Clark, Chris D.; Gheorghiu, Delia M.; Newall, Jennifer; Xu, Sheng

2017-07-01

Understanding how marine-based ice streams operated during episodes of deglaciation requires geochronological data that constrain both timing of deglaciation and changes in their flow behaviour, such as that from unconstrained ice streaming to topographically restricted flow. We present seventeen new 10Be exposure ages from glacial boulders and bedrock at sites in western Scotland within the area drained by the Hebrides Ice Stream, a marine-based ice stream that drained a large proportion of the former British-Irish Ice Sheet. Exposure ages from Tiree constrain deglaciation of a topographic high within the central zone of the ice stream, from which convergent flowsets were produced during ice streaming. These ages thus constrain thinning of the Hebrides Ice Stream, which, on the basis of supporting information, we infer to represent cessation of ice streaming at 20.6 ± 1.2 ka, 3-4 ka earlier than previously inferred. A period of more topographically restricted flow produced flow indicators superimposed on those relating to full ice stream conditions, and exposure ages from up-stream of these constrain deglaciation to 17.5 ± 1.0 ka. Complete deglaciation of the marine sector of the Hebrides Ice Stream occurred by 17-16 ka at which time the ice margin was located near the present coastline. Exposure ages from the southernmost Outer Hebrides (Mingulay and Barra) indicate deglaciation at 18.9 ± 1.0 and 17.1 ± 1.0 ka respectively, demonstrating that an independent ice cap persisted on the southern Outer Hebrides for 3-4 ka after initial ice stream deglaciation. This suggests that deglaciation of the Hebrides Ice Stream was focused along major submarine troughs. Collectively, our data constrain initial deglaciation and changes in flow regime of the Hebrides Ice Stream, final deglaciation of its marine sector, and deglaciation of the southern portion of the independent Outer Hebrides Ice Cap, providing chronological constraints on future numerical reconstructions of this key sector of the former British-Irish Ice Sheet.

Unsweetened ice popsicles impart a positive feeling and reduce self-mutilation after paediatric dental treatment with local anaesthesia.

PubMed

Ram, Diana; Berson, Tamar; Moskovitz, Moti; Efrat, Jacob

2010-09-01

The purpose of the current study was to assess whether an unsweetened ice-popsicle imparts a positive feeling to children after dental treatment in which local anaesthesia is administered, and whether it reduces the tendency of children to self-mutilate (bite the lip, cheek or tongue) after the administration of local anaesthesia. Crossover study of 31 children aged 4-11 years old who needed similar dental treatments on both sides of the mandible or maxilla under local anaesthesia. At the end of each appointment the child received a toy or an ice-popsicle especially made for this study. Patients and parents answered a questionnaire regarding the children's behaviour and feeling immediately after the treatment, and 10 and 30 min after receiving the ice-popsicle or toy. Children who received ice-popsicles after dental treatment under local anaesthesia felt less discomfort and suffered less soft tissue trauma than they did when they received a toy. Reduction in soft tissue trauma was evident 10 min after receiving the ice-popsicles. Licking of an ice-popsicle after dental treatment with local anaesthesia reduces the feeling of discomfort and the biting of soft tissue and self- mutilation.

Could a new ice core offer an insight into the stability of the West Antarctic Ice Sheet during the last interglacial?

NASA Astrophysics Data System (ADS)

Mulvaney, R.; Hindmarsh, R. C.

2013-12-01

Vaughan et al., in their 2011 paper 'Potential Seaways across West Antarctica' (Geochem. Geophys. Geosyst., 12, Q10004, doi:10.1029/2011GC003688), offer the intriguing prospect that substantial ice loss from the West Antarctic Ice Sheet during the previous interglacial period might have resulted in the opening of a seaway between the Weddell Sea and the Amundsen Sea. One of their potential seaways passes between the south western corner of the present Ronne Ice Shelf and the Pine Island Bay, through what is currently the course of the Rutford Ice Stream, between the Ellsworth Mountains and the Fletcher Promontory. To investigate whether this seaway could have existed (and to recover a paleoclimate and ice sheet history from the Weddell Sea), a team from the British Antarctic Survey and the Laboratoire de Glaciologie et Géophysique de l'Environnement drilled an ice core from a close to a topographic dome in the ice surface on the Fletcher Promontory in January 2012, reaching the bedrock at 654.3m depth from the surface. The site was selected to penetrate directly through the centre of a Raymond cupola observed in internal radar reflections from the ice sheet, with the intention that this would ensure we obtained the oldest ice available from the Fletcher Promontory. The basal ice sheet temperature measured was -18°C, implying the oldest ice would not have melted away from the base, while the configuration of the Raymond cupola in the radar horizons suggested stability in the ice dome topography during the majority of the Holocene. Our hypothesis is that chemical analysis of the ice core will reveal whether the site was ever relatively close to open sea water or ice shelf in the Rutford channel 20 km distant, rather than the current 700 km distance to sea ice/open water in either the Weddell Sea or the Amundsen Sea. While we do not yet have the chemistry data to test this hypothesis, in this poster we will discuss whether there is in reality any potential local meteoric ice remaining from the previous interglacial that could provide the evidence we need. We show likely age-depth models in an ice dome with a pronounced Raymond cupola and flat bedrock. The evidence from the stable water isotope temperature history from the site shows the Last Glacial Maximum/Holocene boundary substantially above the bedrock, implying the possibility of much older ice in the lowest ice layers.

Saving Humanity from Catastrophic Cooling with Geo-Engineering

NASA Astrophysics Data System (ADS)

Haapala, K.; Singer, S. F.

2016-02-01

There are two kinds of ice ages; they are fundamentally different and therefore require different methods of mitigation: (i) Major (Milankovitch-style) glaciations occur on a 100,000-year time-scale and are controlled astronomically. (ii) "Little" ice ages were discovered in ice cores; they have been occurring on an approx. 1000-1500-yr cycle and are likely controlled by the Sun [Ref: Singer & Avery 2007. Unstoppable Global Warming: Every 1500 years]. The current cycle's cooling phase may be imminent - hence there may be urgent need for action. To stop onset of a major (Milankovitch) glaciation 1. Locate a "trigger" - a growing perennial snow/ice field - using satellites 2. Spread soot, to lower the albedo, and use Sun to melt 3. How much soot? How to apply soot? Learn by experimentation To lessen (regional, intermittent) cooling of DOB (Dansgaard-Oeschger-Bond) cycles1. Use greenhouse effect of manmade cirrus (ice particles) [Ref: Singer 1988. Meteorology and Atmospheric Physics 38:228 - 239]2. Inject water droplets (mist) near tropopause 3. Trace dispersion of cirrus cloud by satellite and observe warming at surface 4. How much water; over what area? How often to inject? Learn by experimentation Many scientific questions remain. While certainly interesting and important, there is really no need to delay the crucial and urgent tests of geo-engineering, designed to validate schemes of mitigation. Such proposed tests involve only minor costs and present negligible risks to the environment.

Rapid Access Ice Drill: A New Tool for Exploration of the Deep Antarctic Ice Sheets and Subglacial Geology

NASA Astrophysics Data System (ADS)

Goodge, J. W.; Severinghaus, J. P.

2014-12-01

The Rapid Access Ice Drill (RAID) will penetrate the Antarctic ice sheets in order to core through deep ice, the glacial bed, and into bedrock below. This new technology will provide a critical first look at the interface between major ice caps and their subglacial geology. Currently in construction, RAID is a mobile drilling system capable of making several long boreholes in a single field season in Antarctica. RAID is interdisciplinary and will allow access to polar paleoclimate records in ice >1 Ma, direct observation at the base of the ice sheets, and recovery of rock cores from the ice-covered East Antarctic craton. RAID uses a diamond rock-coring system as in mineral exploration. Threaded drill-pipe with hardened metal bits will cut through ice using reverse circulation of Estisol for pressure-compensation, maintenance of temperature, and removal of ice cuttings. Near the bottom of the ice sheet, a wireline bottom-hole assembly will enable diamond coring of ice, the glacial bed, and bedrock below. Once complete, boreholes will be kept open with fluid, capped, and made available for future down-hole measurement of thermal gradient, heat flow, ice chronology, and ice deformation. RAID will also sample for extremophile microorganisms. RAID is designed to penetrate up to 3,300 meters of ice and take sample cores in less than 200 hours. This rapid performance will allow completion of a borehole in about 10 days before moving to the next drilling site. RAID is unique because it can provide fast borehole access through thick ice; take short ice cores for paleoclimate study; sample the glacial bed to determine ice-flow conditions; take cores of subglacial bedrock for age dating and crustal history; and create boreholes for use as an observatory in the ice sheets. Together, the rapid drilling capability and mobility of the drilling system, along with ice-penetrating imaging methods, will provide a unique 3D picture of the interior Antarctic ice sheets.

Stationary Waves of the Ice Age Climate.

NASA Astrophysics Data System (ADS)

Cook, Kerry H.; Held, Isaac M.

1988-08-01

A linearized, steady state, primitive equation model is used to simulate the climatological zonal asymmetries (stationary eddies) in the wind and temperature fields of the 18 000 YBP climate during winter. We compare these results with the eddies simulated in the ice age experiments of Broccoli and Manabe, who used CLIMAP boundary conditions and reduced atmospheric CO2 in an atmospheric general circulation model (GCM) coupled with a static mixed layer ocean model. The agreement between the models is good, indicating that the linear model can be used to evaluate the relative influences of orography, diabatic heating, and transient eddy heat and momentum transports in generating stationary waves. We find that orographic forcing dominates in the ice age climate. The mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies. This concept of the ice age climate is complicated by the sensitivity of the stationary eddies to the large increase in the magnitude of the zonal mean meridional temperature gradient simulated in the ice age GCM.

Capabilities and performance of Elmer/Ice, a new-generation ice sheet model

NASA Astrophysics Data System (ADS)

Gagliardini, O.; Zwinger, T.; Gillet-Chaulet, F.; Durand, G.; Favier, L.; de Fleurian, B.; Greve, R.; Malinen, M.; Martín, C.; Råback, P.; Ruokolainen, J.; Sacchettini, M.; Schäfer, M.; Seddik, H.; Thies, J.

2013-08-01

The Fourth IPCC Assessment Report concluded that ice sheet flow models, in their current state, were unable to provide accurate forecast for the increase of polar ice sheet discharge and the associated contribution to sea level rise. Since then, the glaciological community has undertaken a huge effort to develop and improve a new generation of ice flow models, and as a result a significant number of new ice sheet models have emerged. Among them is the parallel finite-element model Elmer/Ice, based on the open-source multi-physics code Elmer. It was one of the first full-Stokes models used to make projections for the evolution of the whole Greenland ice sheet for the coming two centuries. Originally developed to solve local ice flow problems of high mechanical and physical complexity, Elmer/Ice has today reached the maturity to solve larger-scale problems, earning the status of an ice sheet model. Here, we summarise almost 10 yr of development performed by different groups. Elmer/Ice solves the full-Stokes equations, for isotropic but also anisotropic ice rheology, resolves the grounding line dynamics as a contact problem, and contains various basal friction laws. Derived fields, like the age of the ice, the strain rate or stress, can also be computed. Elmer/Ice includes two recently proposed inverse methods to infer badly known parameters. Elmer is a highly parallelised code thanks to recent developments and the implementation of a block preconditioned solver for the Stokes system. In this paper, all these components are presented in detail, as well as the numerical performance of the Stokes solver and developments planned for the future.

High-frequency and meso-scale winter sea-ice variability in the Southern Ocean in a high-resolution global ocean model

NASA Astrophysics Data System (ADS)

Stössel, Achim; von Storch, Jin-Song; Notz, Dirk; Haak, Helmuth; Gerdes, Rüdiger

2018-03-01

This study is on high-frequency temporal variability (HFV) and meso-scale spatial variability (MSV) of winter sea-ice drift in the Southern Ocean simulated with a global high-resolution (0.1°) sea ice-ocean model. Hourly model output is used to distinguish MSV characteristics via patterns of mean kinetic energy (MKE) and turbulent kinetic energy (TKE) of ice drift, surface currents, and wind stress, and HFV characteristics via time series of raw variables and correlations. We find that (1) along the ice edge, the MSV of ice drift coincides with that of surface currents, in particular such due to ocean eddies; (2) along the coast, the MKE of ice drift is substantially larger than its TKE and coincides with the MKE of wind stress; (3) in the interior of the ice pack, the TKE of ice drift is larger than its MKE, mostly following the TKE pattern of wind stress; (4) the HFV of ice drift is dominated by weather events, and, in the absence of tidal currents, locally and to a much smaller degree by inertial oscillations; (5) along the ice edge, the curl of the ice drift is highly correlated with that of surface currents, mostly reflecting the impact of ocean eddies. Where ocean eddies occur and the ice is relatively thin, ice velocity is characterized by enhanced relative vorticity, largely matching that of surface currents. Along the ice edge, ocean eddies produce distinct ice filaments, the realism of which is largely confirmed by high-resolution satellite passive-microwave data.

Effectiveness of Rapid Cooling as a Method of Euthanasia for Young Zebrafish (Danio rerio).

PubMed

Wallace, Chelsea K; Bright, Lauren A; Marx, James O; Andersen, Robert P; Mullins, Mary C; Carty, Anthony J

2018-01-01

Despite increased use of zebrafish (Danio rerio) in biomedical research, consistent information regarding appropriate euthanasia methods, particularly for embryos, is sparse. Current literature indicates that rapid cooling is an effective method of euthanasia for adult zebrafish, yet consistent guidelines regarding zebrafish younger than 6 mo are unavailable. This study was performed to distinguish the age at which rapid cooling is an effective method of euthanasia for zebrafish and the exposure times necessary to reliably euthanize zebrafish using this method. Zebrafish at 3, 4, 7, 14, 16, 19, 21, 28, 60, and 90 d postfertilization (dpf) were placed into an ice water bath for 5, 10, 30, 45, or 60 min (n = 12 to 40 per group). In addition, zebrafish were placed in ice water for 12 h (age ≤14 dpf) or 30 s (age ≥14 dpf). After rapid cooling, fish were transferred to a recovery tank and the number of fish alive at 1, 4, and 12-24 h after removal from ice water was documented. Euthanasia was defined as a failure when evidence of recovery was observed at any point after removal from ice water. Results showed that younger fish required prolonged exposure to rapid cooling for effective euthanasia, with the required exposure time decreasing as fish age. Although younger fish required long exposure times, animals became immobilized immediately upon exposure to the cold water, and behavioral indicators of pain or distress rarely occurred. We conclude that zebrafish 14 dpf and younger require as long as 12 h, those 16 to 28 dpf of age require 5 min, and those older than 28 dpf require 30 s minimal exposure to rapid cooling for reliable euthanasia.

There goes the sea ice: following Arctic sea ice parcels and their properties.

NASA Astrophysics Data System (ADS)

Tschudi, M. A.; Tooth, M.; Meier, W.; Stewart, S.

2017-12-01

Arctic sea ice distribution has changed considerably over the last couple of decades. Sea ice extent record minimums have been observed in recent years, the distribution of ice age now heavily favors younger ice, and sea ice is likely thinning. This new state of the Arctic sea ice cover has several impacts, including effects on marine life, feedback on the warming of the ocean and atmosphere, and on the future evolution of the ice pack. The shift in the state of the ice cover, from a pack dominated by older ice, to the current state of a pack with mostly young ice, impacts specific properties of the ice pack, and consequently the pack's response to the changing Arctic climate. For example, younger ice typically contains more numerous melt ponds during the melt season, resulting in a lower albedo. First-year ice is typically thinner and more fragile than multi-year ice, making it more susceptible to dynamic and thermodynamic forcing. To investigate the response of the ice pack to climate forcing during summertime melt, we have developed a database that tracks individual Arctic sea ice parcels along with associated properties as these parcels advect during the summer. Our database tracks parcels in the Beaufort Sea, from 1985 - present, along with variables such as ice surface temperature, albedo, ice concentration, and convergence. We are using this database to deduce how these thousands of tracked parcels fare during summer melt, i.e. what fraction of the parcels advect through the Beaufort, and what fraction melts out? The tracked variables describe the thermodynamic and dynamic forcing on these parcels during their journey. This database will also be made available to all interested investigators, after it is published in the near future. The attached image shows the ice surface temperature of all parcels (right) that advected through the Beaufort Sea region (left) in 2014.

Preservation of Late Amazonian Mars ice and water-related deposits in a unique crater environment in Noachis Terra: Age relationships between lobate debris tongues and gullies

NASA Astrophysics Data System (ADS)

Morgan, Gareth A.; Head, James W.; Marchant, David R.

2011-01-01

The Amazonian period of Mars has been described as static, cold, and dry. Recent analysis of high-resolution imagery of equatorial and mid-latitude regions has revealed an array of young landforms produced in association with ice and liquid water; because near-surface ice in these regions is currently unstable, these ice-and-water-related landforms suggest one or more episodes of martian climate change during the Amazonian. Here we report on the origin and evolution of valley systems within a degraded crater in Noachis Terra, Asimov Crater. The valleys have produced a unique environment in which to study the geomorphic signals of Amazonian climate change. New high-resolution images reveal Hesperian-aged layered basalt with distinctive columnar jointing capping interior crater fill and providing debris, via mass wasting, for the surrounding annular valleys. The occurrence of steep slopes (>20°), relatively narrow (sheltered) valleys, and a source of debris have provided favorable conditions for the preservation of shallow-ice deposits. Detailed mapping reveals morphological evidence for viscous ice flow, in the form of several lobate debris tongues (LDT). Superimposed on LDT are a series of fresh-appearing gullies, with typical alcove, channel, and fan morphologies. The shift from ice-rich viscous-flow formation to gully erosion is best explained as a shift in martian climate, from one compatible with excess snowfall and flow of ice-rich deposits, to one consistent with minor snow and gully formation. Available dating suggests that the climate transition occurred >8 Ma, prior to the formation of other small-scale ice-rich flow features identified elsewhere on Mars that have been interpreted to have formed during the most recent phases of high obliquity. Taken together, these older deposits suggest that multiple climatic shifts have occurred over the last tens of millions of years of martian history.

Visual-Stratigraphic Dating of the GISP2 Ice Core: Basis, Reproducibility, and Application

NASA Technical Reports Server (NTRS)

Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.;

Visual-stratigraphic dating of the GISP2 ice core: Basis, reproducibility, and application

NASA Astrophysics Data System (ADS)

Alley, R. B.; Shuman, C. A.; Meese, D. A.; Gow, A. J.; Taylor, K. C.; Cuffey, K. M.; Fitzpatrick, J. J.; Grootes, P. M.; Zielinski, G. A.; Ram, M.; Spinelli, G.; Elder, B.

1997-11-01

Annual layers are visible in the Greenland Ice Sheet Project 2 ice core from central Greenland, allowing rapid dating of the core. Changes in bubble and grain structure caused by near-surface, primarily summertime formation of hoar complexes provide the main visible annual marker in the Holocene, and changes in "cloudiness" of the ice correlated with dustiness mark Wisconsinan annual cycles; both markers are evident and have been intercalibrated in early Holocene ice. Layer counts are reproducible between different workers and for one worker at different times, with 1% error over century-length times in the Holocene. Reproducibility is typically 5% in Wisconsinan ice-age ice and decreases with increasing age and depth. Cumulative ages from visible stratigraphy are not significantly different from independent ages of prominent events for ice older than the historical record and younger than approximately 50,000 years. Visible observations are not greatly degraded by "brittle ice" or many other core-quality problems, allowing construction of long, consistently sampled time series. High accuracy requires careful study of the core by dedicated observers.

Using U-Pb Detrital Zircon Geochronology to Study Ice Streams in the Weddell Sea Embayment, Antarctica

NASA Astrophysics Data System (ADS)

Agrios, L.; Licht, K.; Hemming, S. R.; Williams, T.

2016-12-01

Till from major ice streams of the Weddell Sea Embayment contain detrital zircons with distinct U-Pb age populations that can be used as a provenance tool to better understand ice stream dynamics. The ice streams in this study include the Foundation Ice Stream, and Academy, Slessor, and Recovery glaciers, all of which drain ice from the continent's interior into the Weddell Sea. Characterizing the U-Pb detrital zircon ages in till and rocks will (1) provide the zircon provenance signatures of the material carried by the ice stream - when these signatures are found in LGM and older deposits downstream they can enable interpretation of past ice flow history; and (2) constrain ice-covered upstream bedrock geology that supplies the till carried by ice streams and glaciers. U-Pb ages of detrital zircons were measured in 21 samples of onshore till, erratics, and bedrock of potential source rocks. Grains were analyzed by LA-ICPMS at the University of Arizona (n=300). Relative probability U-Pb age density plots of till in moraines along the Foundation Ice Stream and Academy Glacier show prominent peaks at 500-530 and 615-650 Ma, which overlap with the timing of the Ross and Pan-African orogenies. Zircon ages of 1000-1095 Ma are also present. Local bedrock in the Patuxent Range has the most prominent peak at 510 Ma, suggesting the till is predominantly derived from local Patuxent Formation. However, local bedrock also has fewer grains at 1030 Ma which suggests that this age population is carried in the till as well. Prominent peaks in U-Pb ages from till transported by the Recovery Glacier are 530, 635, 1610 and 1770 Ma. Bedrock of this area contains similar age peaks, with the exception of the 635 Ma peak, suggesting that this ice stream is carrying a signature from an unexposed source of this age completely buried by ice. The Slessor Glacier carries zircons with prominent populations at 1710 and 2260-2420 Ma, which overlap with a high-grade metamorphic event in the Shackleton Range between 1710-1680 Ma. In order to gain the offshore signature of ice streams, these data will be compared to 40Ar/39Ar hornblende and biotite thermochronological data, and U-Pb geochronology data from subglacial till and proximal glaciomarine sediment from existing core sites located at the edge of the Ronne-Filchner Ice Shelf.

New age constraints for the Saalian glaciation in northern central Europe: Implications for the extent of ice sheets and related proglacial lake systems

NASA Astrophysics Data System (ADS)

Lang, Jörg; Lauer, Tobias; Winsemann, Jutta

2018-01-01

A comprehensive palaeogeographic reconstruction of ice sheets and related proglacial lake systems for the older Saalian glaciation in northern central Europe is presented, which is based on the integration of palaeo-ice flow data, till provenance, facies analysis, geomorphology and new luminescence ages of ice-marginal deposits. Three major ice advances with different ice-advance directions and source areas are indicated by palaeo-ice flow directions and till provenance. The first ice advance was characterised by a southwards directed ice flow and a dominance of clasts derived from southern Sweden. The second ice advance was initially characterised by an ice flow towards the southwest. Clasts are mainly derived from southern and central Sweden. The latest stage in the study area (third ice advance) was characterised by ice streaming (Hondsrug ice stream) in the west and a re-advance in the east. Clasts of this stage are mainly derived from eastern Fennoscandia. Numerical ages for the first ice advance are sparse, but may indicate a correlation with MIS 8 or early MIS 6. New pIRIR290 luminescence ages of ice-marginal deposits attributed to the second ice advance range from 175 ± 10 to 156 ± 24 ka and correlate with MIS 6. The ice sheets repeatedly blocked the main river-drainage pathways and led to the formation of extensive ice-dammed lakes. The formation of proglacial lakes was mainly controlled by ice-damming of river valleys and major bedrock spillways; therefore the lake levels and extends were very similar throughout the repeated ice advances. During deglaciation the lakes commonly increased in size and eventually drained successively towards the west and northwest into the Lower Rhine Embayment and the North Sea. Catastrophic lake-drainage events occurred when large overspill channels were suddenly opened. Ice-streaming at the end of the older Saalian glaciation was probably triggered by major lake-drainage events.

A high altitude paleoclimate record from an ice core retrieved at the northern margin of the Mediterranean basin

NASA Astrophysics Data System (ADS)

Gabrielli, P.; Barbante, C.; Carturan, L.; Davis, M. E.; Dalla Fontana, G.; Dreossi, G.; Dinale, R.; Draga, G.; Gabrieli, J.; Kehrwald, N. M.; Mair, V.; Mikhalenko, V.; Oeggl, K.; Schotterer, U.; Seppi, R.; Spolaor, A.; Stenni, B.; Thompson, L. G.; Tonidandel, D.

2013-12-01

Atmospheric temperatures in the Alps are increasing at twice the global rate and this change may be amplified at the highest elevations. There is a scarcity of paleo-climate information from high altitudes to place this current rapid climate change in a paleo-perspective. The 'Ortles Project' is an international scientific effort gathering institutes from six nations with the primary goal of obtaining a high altitude paleo-climate record in the Mediterranean area. In 2011 four ice cores were extracted from Alto dell'Ortles (3859 m, South Tyrol, Italy) the highest glacier in the eastern Alps. This site is located ~30 km away from where the famous ~5.2 kyr old Tyrolean Ice Man was discovered emerging from an ablating ice field (Hauslabjoch, 3210 m) in 1991. The good state of conservation of this mummy suggested that the current warming trend is unprecedented in South Tyrol during the late Holocene and that unique prehistoric ice was still present in this region. During the ice core drilling operations we found that the glacier Alto dell'Ortles shows a very unusual thermic behavior as it is transitioning from a cold to a temperate state. In fact, below a 30 meter thick temperate firn portion, we observed cold ice layers sitting on a frozen bedrock (-2.8 C). These represent remnants of the colder climate before ~1980 AD, when an instrumental record indicates a ~2 C lower temperature in this area during the period 1864-1980 AD. By analyzing one of the Ortles cores for stable isotopes, dust and major ions, we found an annually preserved climatic signal embedded in the deep cold ice of this glacier. Alto dell'Ortles is therefore the first low-accumulation (850 mm w.e. per year) alpine drilling site where both winter and summer layers can be identified. Preliminary annual layer counting and two absolute time markers suggest that the time period covered by the Ortles ice cores spans from several centuries to a few millennia. In particular, a Larix (larch) leaf discovered at 74 m depth suggests a 14C bottom ice age of 2664 ×166 years (early European Iron Age) supporting the idea that exceptional prehistoric ice is still present at the highest elevations of South Tyrol. Here we present the records of the first Ortles core analyzed in terms of δ18O (proxy of mid-tropospheric temperature), major ions and dust. We found that δ18O measured in the shallowest layers of this glacier exceeds the average deeper values indicating that the Ortles cores capture the recent increase in atmospheric temperatures at high elevation and that this is anomalous over a time scale that extends from hundreds to thousands of years.

Ice erosion of a sea-floor knickpoint at the inner edge of the stamukhi zone, Beaufort Sea, Alaska

USGS Publications Warehouse

Barnes, P.W.; Asbury, J.L.; Rearic, D.M.; Ross, C.R.

1987-01-01

In 1981 and 1982, detailed bathymetric and side-scan sonar surveys were made of an area of the sea floor north of Prudhoe Bay, Alaska, to study the changing characteristics of the seabed at the inner boundary of the stamukhi zone, the coast-parallel zone of grounded ice ridges that occurs in water depths between 15 and 50 m in the arctic. The fathograms and sonographs resolved 10-cm features and electronic navigation gave relocations accurate to about 10 m. Year after year an ice boundary develops at the inner edge of the stamukhi zone where major shear and pressure deformation occur in about the same location. Associated with this ice boundary, the bathymetry shows a pronounced break in slope - the knickpoint - on the shelf profile at about 20 m depth. The 2-3 m-high knickpoint is cut in a consolidated gravelly mud of pre-Holocene age. A well-defined gravel and cobble shoal a few meters high usually occurs at the inshore edge of the knickpoint. The sonograph mosaic shows that seaward of the knickpoint, ice gouges saturate the sea floor and are well defined; inshore the gouges are fewer in number and are poorly defined on the records. Few gouges can be traced from the seaward side of the knickpoint across the shoals to the inshore side of the knickpoint. Studies of ice gouging rates in two seabed corridors that cross the stamukhi zone reveal the highest rates of gouging seaward of the knickpoint. We believe that the knickpoint results from ice erosion at the inner boundary of the stamukhi zone. Intensified currents associated with this boundary winnow away fine sediments. Ice bulldozing and currents shape the shoals, which perch atop the knickpoint. The knickpoint helps to limit ice forces on the seabed inshore of the stamukhi zone. ?? 1987.

Dating an 800,000 year Antarctic ice core record using the isotopic composition of trapped air

NASA Astrophysics Data System (ADS)

Dreyfus, Gabrielle Boissier

Here we measure the isotopic composition of air trapped in the European Project for Ice Coring in Antarctica Dome C (EDC) ice core, and use this geochemical information to improve the ice core agescale and our understanding of air enclosure processes. A first result is the detection of a flow anomaly in the bottom 500m of the EDC ice core using the delta18O of atmospheric oxygen (noted delta18Oatm). By tuning the measured delta18Oatm to the orbital precession signal, we correct the EDC agescale over 400-800 ka for flow-induced distortions in the duration of events. Uncertainty in delta 18Oatm phasing with respect to precession limits the accuracy of the tuned agescale to +/-6 ka. We use this improved agescale to date two 10Be peaks detected in the EDC ice core and associated with the Matuyama-Brunhes geomagnetic boundary. While the ice age of the "precursor" event agrees within uncertainty with the age of radioisotopically dated lavas, the volcanic age for the younger reversal is approximately 10 ka older than the mid-point of the 10 Be peak in the ice. Since 80% of the lavas recording the Matuyama-Brunhes reversal are located in the Central Pacific, the observed age difference may indicate that the magnetic field orientation at this location changed prior to the dipole intensity minimum recorded by the ice core 10Be, as suggested by recent geodynamo modeling. A particular challenge for ice core dating is accurately accounting for the age difference between the trapped air and surrounding ice. This gas age - ice age difference (noted Deltaage) depends on the age of the ice at the bottom of the firn. delta15N of N2 is constant in the atmosphere over the timescales considered here, so any deviation from atmospheric composition reflects fractionation processes in the firn. We show that delta15N is positively correlated with the ice deuterium content, a proxy for temperature, over the entire EDC record, and propose an accumulation-permeability-convection mechanism. While temporal resolution and noise in the available data limit our ability to constrain glacial Deltaage, these data suggest that delta15N may be used as a gas-phase climate proxy at EDC.

Where is the 1-million-year-old ice at Dome A?

NASA Astrophysics Data System (ADS)

Zhao, Liyun; Moore, John C.; Sun, Bo; Tang, Xueyuan; Guo, Xiaoran

2018-05-01

Ice fabric influences the rheology of ice, and hence the age-depth profile at ice core drilling sites. To investigate the age-depth profile to be expected of the ongoing deep ice coring at Kunlun station, Dome A, we use the depth-varying anisotropic fabric suggested by the recent polarimetric measurements around Dome A along with prescribed fabrics ranging from isotropic through girdle to single maximum in a three-dimensional, thermo-mechanically coupled full-Stokes model of a 70 × 70 km2 domain around Kunlun station. This model allows for the simulation of the near basal ice temperature and age, and ice flow around the location of the Chinese deep ice coring site. Ice fabrics and geothermal heat flux strongly affect the vertical advection and basal temperature which consequently control the age profile. Constraining modeled age-depth profiles with dated radar isochrones to 2/3 ice depth, the surface vertical velocity, and also the spatial variability of a radar isochrones dated to 153.3 ka BP, limits the age of the deep ice at Kunlun to between 649 and 831 ka, a much smaller range than previously inferred. The simple interpretation of the polarimetric radar fabric data that we use produces best fits with a geothermal heat flux of 55 mW m-2. A heat flux of 50 mW m-2 is too low to fit the deeper radar layers, and 60 mW m-2 leads to unrealistic surface velocities. The modeled basal temperature at Kunlun reaches the pressure melting point with a basal melting rate of 2.2-2.7 mm a-1. Using the spatial distribution of basal temperatures and the best fit fabric suggests that within 400 m of Kunlun station, 1-million-year-old ice may be found 200 m above the bed, and that there are large regions where even older ice is well above the bedrock within 5-6 km of the Kunlun station.

Earth and Aurora Observations taken by the Expedition 39 Crew

NASA Image and Video Library

2014-04-14

ISS039-E-11773 (14 April 2014) --- Photographed with a camera equipped with an 80mm lens from the International Space Station, patterns of sea ice in the Sea of Okhotsk reveal the dynamics of ocean currents that could otherwise only be seen in sunglint. In this Expedition 39 photo, one can see nearly 1,000 kilometers (600 miles) of the East Sakhalin Current, which is carrying winter ice south toward Japan’s Hokkaido Island. The current is marked by the narrow corridor of dense ice that hugs the coast of Russia’s Sakhalin Island. As it approaches Hokkaido, the ice patterns show a series of eddies and swirls. The East Sakhalin Current wanes in summer when the Soya Current begins to enter the Sea of Okhotsk. This inrush of summer water starts in April and, according to NASA scientists, probably expresses itself in this image as ice pattern to the east above Hokkaido. The Sakhalin current turns east and transports ice toward the Kuril Island chain. Some ice can spill through gaps in the islands, where it is swept southwest by the Kuril Current (lower right).

The last forests in Greenland, and the age of the ice sheet

NASA Astrophysics Data System (ADS)

Funder, Svend; Schmidt, Astrid M. Z.; Dahl-Jensen, Dorthe; Steffensen, Jørgen Peder; Willerslev, Eske

2014-05-01

Recently ancient DNA (aDNA) studies of the basal ice in the Camp Century ice core, northern Greenland, have shown that mixed coniferous-deciduous forest grew here before the area was invaded and permanently covered by the ice sheet. The coring site is situated only 100 km from the present ice margin and more than 500 km from the ice divide, indicating that since this last inception the northern part of the ice sheet never receded more than 100 km from its present margin. Dating of the basal ice and obtaining an age for the forest and for the beginning of the ice sheet's permanency has been attempted by analyzing for optically stimulated luminescence (OSL), meteoric 10Be/36Cl cosmogenic nuclides, 234U/238U recoil. These methods all provide only minimum ages and show that the forest at Cap Century is older than 500 ka. Comparison with other Pleistocene "forest sites" in Greenland - the Kap København Formation in northernmost Greenland, the DYE-3 ice core in the south, the ODP boring 646 south of Greenland, as well as results from basal ice in the GRIP ice core - extends the minimum age to c. 1 ma. The maximum age is provided by the Kap København Formation, which must be older - or contemporaneous. The formation has recently been confirmed to date within the interval 2-2.5 ma, with a preferred age of 2.3-2.4 ma. Surprisingly, application of the molecular clock of insect COI sequences on the Camp Century aDNA now seem to push the minimum age just as far back - to 2.4 ma, suggesting that the timberline boreal forest at Kap København is contemporaneous with the mixed forest at Camp Century, 600 km to the south. From this we conclude that the northern ice sheet dome, which today contains 85% of the total ice sheet volume, has remained within 100 km of its present margin for at least 1 ma, and possibly may go back as far as 2.4 ma. The ice sheet has therefore survived both interglacials and "super interglacials" that were both warmer and longer than the present. This may give us some hope for the future.

Glacial-Geomorphological Evidence for Past Ice Cover in the Western Amundsen Sea Embayment of Antarctica

NASA Astrophysics Data System (ADS)

Roberts, S. J.; Johnson, J.; Ireland, L.; Rood, D. H.; Schaefer, J. M.; Whitehouse, P. L.; Pollard, D.

2016-12-01

Reliable model predictions of the future evolution of the West Antarctic Ice Sheet in the Amundsen Sea Embayment of Antarctica are currently hindered by a lack of data on the regional thinning history, particularly to the west of Thwaites Glacier. Our project will fill this critical gap by acquiring glacial-geological data, in particular, a high density of cosmogenic exposure ages that record ice sheet changes in the western Amundsen Sea Embayment over the past 20,000 years. In 2015/6, during the first of two field seasons in the region, we collected glacial-geomorphological evidence and cosmogenic surface exposure dating samples to constrain past ice cover of nunataks around Mt Murphy, which are adjacent to the Pope Glacier. The presence of abundant rounded granite and gneiss cobbles perched on bedrock ridges and terraces up to 885 m asl, as well as extensive striated bedrock above this height, indicate that ice was much thicker in the past. We also present preliminary results from a novel study on Turtle Rock, a key site for understanding past fluctuations of Pope Glacier. We used an unmanned aerial vehicle (UAV) to map the geomorphology of selected areas in greater detail than is currently possible from high-resolution satellite imagery, and ground-truthed the data by measuring the size, orientation and lithological composition of erratic cobbles and boulders. Combined with surface exposure dating, we will use these datasets to determine whether there were multiple phases of ice overriding, and the timing of thinning of Pope Glacier since the Last Glacial Maximum.

The Svalbard-Barents Sea ice-sheet - Historical, current and future perspectives

NASA Astrophysics Data System (ADS)

Ingólfsson, Ólafur; Landvik, Jon Y.

2013-03-01

The history of research on the Late Quaternary Svalbard-Barents Sea ice sheet mirrors the developments of ideas and the shifts of paradigms in glacial theory over the past 150 years. Since the onset of scientific research there in the early 19th Century, Svalbard has been a natural laboratory where ideas and concepts have been tested, and played an important (but rarely acknowledged) role in the break-through of the Ice Age theory in the 1870's. The history of how the scientific perception of the Svalbard-Barents sea ice sheet developed in the mid-20th Century also tells a story of how a combination of fairly scattered and often contradictory observational data, and through both deductive and inductive reasoning, could outline a major ice sheet that had left but few tangible fingerprints. Since the 1980's, with increased terrestrial stratigraphical data, ever more marine geological evidence and better chronological control of glacial events, our perception of the Svalbard-Barents Sea ice sheet has changed. The first reconstructions depicted it as a static, concentric, single-domed ice sheet, with ice flowing from an ice divide over the central northern Barents Sea that expanded and declined in response to large-scale, Late Quaternary climate fluctuations, and which was more or less in tune with other major Northern Hemisphere ice sheets. We now increasingly perceive it as a very dynamic, multidomed ice sheet, controlled by climate fluctuations, relative sea-level change, as well as subglacial topography, substrate properties and basal temperature. In this respect, the Svalbard-Barents Sea ice sheet will increasingly hold the key for understanding the dynamics and processes of how marine-based ice sheets build-up and decay.

Differences Between Surface Ice Deposits at the Poles of Mercury and the Moon: Insights into Ages of the Ice

NASA Astrophysics Data System (ADS)

Deutsch, A. N.; Head, J. W.; Neumann, G. A.

2018-05-01

The poles of Mercury and the Moon both show evidence for water ice, but the deposits on Mercury have a greater areal distribution and a more pure concentration. We explore how these differences may be related to the ages of the ice.

Oceanographic influences on the sea ice cover in the Sea of Okhotsk

NASA Technical Reports Server (NTRS)

Gratz, A. J.; Parkinson, C. L.

1981-01-01

Sea ice conditions in the Sea of Okhotsk, as determined by satellite images from the electrically scanning microwave radiometer on board Nimbus 5, were analyzed in conjunction with the known oceanography. In particular, the sea ice coverage was compared with the bottom bathymetry and the surface currents, water temperatures, and salinity. It is found that ice forms first in cold, shallow, low salinity waters. Once formed, the ice seems to drift in a direction approximating the Okhotsk-Kuril current system. Two basic patterns of ice edge positioning which persist for significant periods were identified as a rectangular structure and a wedge structure. Each of these is strongly correlated with the bathymetry of the region and with the known current system, suggesting that convective depth and ocean currents play an important role in determining ice patterns.

Icing simulation: A survey of computer models and experimental facilities

NASA Technical Reports Server (NTRS)

Potapczuk, M. G.; Reinmann, J. J.

1991-01-01

A survey of the current methods for simulation of the response of an aircraft or aircraft subsystem to an icing encounter is presented. The topics discussed include a computer code modeling of aircraft icing and performance degradation, an evaluation of experimental facility simulation capabilities, and ice protection system evaluation tests in simulated icing conditions. Current research focussed on upgrading simulation fidelity of both experimental and computational methods is discussed. The need for increased understanding of the physical processes governing ice accretion, ice shedding, and iced airfoil aerodynamics is examined.

Icing simulation: A survey of computer models and experimental facilities

NASA Technical Reports Server (NTRS)

Potapczuk, M. G.; Reinmann, J. J.

1991-01-01

A survey of the current methods for simulation of the response of an aircraft or aircraft subsystem to an icing encounter is presented. The topics discussed include a computer code modeling of aircraft icing and performance degradation, an evaluation of experimental facility simulation capabilities, and ice protection system evaluation tests in simulated icing conditions. Current research focused on upgrading simulation fidelity of both experimental and computational methods is discussed. The need for the increased understanding of the physical processes governing ice accretion, ice shedding, and iced aerodynamics is examined.

Radiostratigraphy and age structure of the Greenland Ice Sheet

PubMed Central

MacGregor, Joseph A; Fahnestock, Mark A; Catania, Ginny A; Paden, John D; Prasad Gogineni, S; Young, S Keith; Rybarski, Susan C; Mabrey, Alexandria N; Wagman, Benjamin M; Morlighem, Mathieu

2015-01-01

Several decades of ice-penetrating radar surveys of the Greenland and Antarctic ice sheets have observed numerous widespread internal reflections. Analysis of this radiostratigraphy has produced valuable insights into ice sheet dynamics and motivates additional mapping of these reflections. Here we present a comprehensive deep radiostratigraphy of the Greenland Ice Sheet from airborne deep ice-penetrating radar data collected over Greenland by The University of Kansas between 1993 and 2013. To map this radiostratigraphy efficiently, we developed new techniques for predicting reflection slope from the phase recorded by coherent radars. When integrated along track, these slope fields predict the radiostratigraphy and simplify semiautomatic reflection tracing. Core-intersecting reflections were dated using synchronized depth-age relationships for six deep ice cores. Additional reflections were dated by matching reflections between transects and by extending reflection-inferred depth-age relationships using the local effective vertical strain rate. The oldest reflections, dating to the Eemian period, are found mostly in the northern part of the ice sheet. Within the onset regions of several fast-flowing outlet glaciers and ice streams, reflections typically do not conform to the bed topography. Disrupted radiostratigraphy is also observed in a region north of the Northeast Greenland Ice Stream that is not presently flowing rapidly. Dated reflections are used to generate a gridded age volume for most of the ice sheet and also to determine the depths of key climate transitions that were not observed directly. This radiostratigraphy provides a new constraint on the dynamics and history of the Greenland Ice Sheet. Key Points Phase information predicts reflection slope and simplifies reflection tracing Reflections can be dated away from ice cores using a simple ice flow model Radiostratigraphy is often disrupted near the onset of fast ice flow PMID:26213664

Constraints on martian lobate debris apron evolution and rheology from numerical modeling of ice flow

NASA Astrophysics Data System (ADS)

Parsons, Reid A.; Nimmo, Francis; Miyamoto, Hideaki

2011-07-01

Radar observations in the Deuteronilus Mensae region by Mars Reconnaissance Orbiter have constrained the thickness and dust concentration found within mid-latitude ice deposits, providing an opportunity to more accurately estimate the rheology of ice responsible for the formation of lobate debris aprons based on their apparent age of ˜100 Myr. We developed a numerical model simulating ice flow under martian conditions using results from ice deformation experiments, theory of ice grain growth based on terrestrial ice cores, and observational constraints from radar profiles and laser altimetry. By varying the ice grain size, the ice temperature, the subsurface slope, and the initial ice volume we determine the combination of parameters that best reproduce the observed LDA lengths and thicknesses over a period of time comparable to the apparent ages of LDA surfaces (90-300 Myr). We find that an ice temperature of 205 K, an ice grain size of 5 mm, and a flat subsurface slope give reasonable ages for many LDAs in the northern mid-latitudes of Mars. Assuming that the ice grain size is limited by the grain boundary pinning effect of incorporated dust, these results limit the dust volume concentration to less than 4%. However, assuming all LDAs were emplaced by a single event, we find that there is no single combination of grain size, temperature, and subsurface slope which can give realistic ages for all LDAs, suggesting that some or all of these variables are spatially heterogeneous. Based on our model we conclude that the majority of northern mid-latitude LDAs are composed of clean (⩽4 vol%), coarse (⩾1 mm) grained ice, but regional differences in either the amount of dust mixed in with the ice, or in the presence of a basal slope below the LDA ice must be invoked. Alternatively, the ice temperature and/or timing of ice deposition may vary significantly between different mid-latitude regions. Either eventuality can be tested with future observations.

Glaciological constraints on current ice mass changes from modelling the ice sheets over the glacial cycles

NASA Astrophysics Data System (ADS)

Huybrechts, P.

2003-04-01

The evolution of continental ice sheets introduces a long time scale in the climate system. Large ice sheets have a memory of millenia, hence the present-day ice sheets of Greenland and Antarctica are still adjusting to climatic variations extending back to the last glacial period. This trend is separate from the direct response to mass-balance changes on decadal time scales and needs to be correctly accounted for when assessing current and future contributions to sea level. One way to obtain estimates of current ice mass changes is to model the past history of the ice sheets and their underlying beds over the glacial cycles. Such calculations assist to distinguish between the longer-term ice-dynamic evolution and short-term mass-balance changes when interpreting altimetry data, and are helpful to isolate the effects of postglacial rebound from gravity and altimetry trends. The presentation will discuss results obtained from 3-D thermomechanical ice-sheet/lithosphere/bedrock models applied to the Antarctic and Greenland ice sheets. The simulations are forced by time-dependent boundary conditions derived from sediment and ice core records and are constrained by geomorphological and glacial-geological data of past ice sheet and sea-level stands. Current simulations suggest that the Greenland ice sheet is close to balance, while the Antarctic ice sheet is still losing mass, mainly due to incomplete grounding-line retreat of the West Antarctic ice sheet since the LGM. The results indicate that altimetry trends are likely dominated by ice thickness changes but that the gravitational signal mainly reflects postglacial rebound.

Rapid changes in ice core gas records - Part 1: On the accuracy of methane synchronisation of ice cores

NASA Astrophysics Data System (ADS)

Köhler, P.

2010-08-01

Methane synchronisation is a concept to align ice core records during rapid climate changes of the Dansgaard/Oeschger (D/O) events onto a common age scale. However, atmospheric gases are recorded in ice cores with a log-normal-shaped age distribution probability density function, whose exact shape depends mainly on the accumulation rate on the drilling site. This age distribution effectively shifts the mid-transition points of rapid changes in CH4 measured in situ in ice by about 58% of the width of the age distribution with respect to the atmospheric signal. A minimum dating uncertainty, or artefact, in the CH4 synchronisation is therefore embedded in the concept itself, which was not accounted for in previous error estimates. This synchronisation artefact between Greenland and Antarctic ice cores is for GRIP and Byrd less than 40 years, well within the dating uncertainty of CH4, and therefore does not calls the overall concept of the bipolar seesaw into question. However, if the EPICA Dome C ice core is aligned via CH4 to NGRIP this synchronisation artefact is in the most recent unified ice core age scale (Lemieux-Dudon et al., 2010) for LGM climate conditions of the order of three centuries and might need consideration in future gas chronologies.

Investigating cold based summit glaciers through direct access to the glacier base: a case study constraining the maximum age of Chli Titlis glacier, Switzerland

NASA Astrophysics Data System (ADS)

Bohleber, Pascal; Hoffmann, Helene; Kerch, Johanna; Sold, Leo; Fischer, Andrea

2018-01-01

Cold glaciers at the highest locations of the European Alps have been investigated by drilling ice cores to retrieve their stratigraphic climate records. Findings like the Oetztal ice man have demonstrated that small ice bodies at summit locations of comparatively lower altitudes may also contain old ice if locally frozen to the underlying bedrock. In this case, constraining the maximum age of their lowermost ice part may help to identify past periods with minimum ice extent in the Alps. However, with recent warming and consequent glacier mass loss, these sites may not preserve their unique climate information for much longer. Here we utilized an existing ice cave at Chli Titlis (3030 m), central Switzerland, to perform a case study for investigating the maximum age of cold-based summit glaciers in the Alps. The cave offers direct access to the glacier stratigraphy without the logistical effort required in ice core drilling. In addition, a pioneering exploration had already demonstrated stagnant cold ice conditions at Chli Titlis, albeit more than 25 years ago. Our englacial temperature measurements and the analysis of the isotopic and physical properties of ice blocks sampled at three locations within the ice cave show that cold ice still exists fairly unchanged today. State-of-the-art micro-radiocarbon analysis constrains the maximum age of the ice at Chli Titlis to about 5000 years before present. By this means, the approach presented here will contribute to a future systematic investigation of cold-based summit glaciers, also in the Eastern Alps.

One Isotope, Two Tales: using plant and cosmogenic 14C to constrain Holocene glacier activity on Baffin Island.

NASA Astrophysics Data System (ADS)

Pendleton, S.; Miller, G. H.; Lifton, N. A.; Young, N. E.

2017-12-01

As the cryosphere continues to undergo rapid and accelerating change, it is more important than ever to understand past glacier activity to predict the future of the cryosphere. However, continuous Holocene glacier records are notoriously difficult to reconstruct because an advancing glacier will re-incorporate previous deposits so that moraines typically only record the farthest downvalley glacier expansion. Here we combine dates of ice margin advance from in situ dead vegetation with in situ cosmogenic 14C (in situ 14C) from preserved bedrock surfaces at the same locations to further constrain the timing of ice-free episodes during the Holocene following deglaciation on southern Baffin Island. Radiocarbon ages from recently exposed in situ plants suggest that ice last advanced over sample locations at 9.4, 9.2, 9.0, and 3.7 ka and that they remained ice covered until modern times. Associated in situ 14C inventories are variable, but well above background levels, suggesting some amount of Holocene in situ 14C production. Using plant 14C ages representing the beginning of ice coverage and in situ 14C inventories representative of exposure prior to ice coverage, a simple model of cosmogenic in situ 14C production (accounting for muon production through ice) provides constraints timing and duration of ice-free times at sample locations prior to their most recent burial. Using conservative Holocene ice thicknesses, the locations buried at 9.4, 9.2, and 9.0 ka require, at minimum, 1000 years of pre-burial exposure to match the observed in situ 14C inventory. This suggests these locations were ice free by at least 10 ka and likely earlier. The in situ 14C inventory at the location buried at 3.7 ka limits prior exposure to 2000 years, suggesting that this location experienced more complex Holocene ice cover/burial history. These pilot data show that valuable information regarding periods of exposure is contained within in situ 14C inventories. Additional paired plant and in situ 14C analyses currently underway will provide further constraints on the timing and duration of Holocene exposure. The combination of these two dating techniques supplies some of the first constraints on both ice cover and exposure and provides much needed information about the evolution of glaciers on southern Baffin Island following deglaciation.

Methane seeps along boundaries of arctic permafrost thaw and melting glaciers

NASA Astrophysics Data System (ADS)

Anthony, P.; Walter Anthony, K. M.; Grosse, G.; Chanton, J.

2014-12-01

Methane, a potent greenhouse gas, accumulates in subsurface hydrocarbon reservoirs. In the Arctic, impermeable icy permafrost and glacial overburden form a 'cryosphere cap' that traps gas leaking from these reservoirs, restricting flow to the atmosphere. We document the release of geologic methane to the atmosphere from abundant gas seeps concentrated along boundaries of permafrost thaw and receding glaciers in Alaska. Through aerial and ground surveys we mapped >150,000 seeps identified as bubbling-induced open holes in lake ice. Subcap methane seeps had anomalously high fluxes, 14C-depletion, and stable isotope values matching known coalbed and thermogenic methane accumulations in Alaska. Additionally, we observed younger subcap methane seeps in Greenland that were associated with ice-sheet retreat since the Little Ice Age. These correlations suggest that in a warming climate, continued disintegration of permafrost, glaciers, and parts of the polar ice sheets will relax pressure on subsurface seals and further open conduits, allowing a transient expulsion of geologic methane currently trapped by the cryosphere cap.

Viscous grounding lines

NASA Astrophysics Data System (ADS)

Worster, Grae; Huppert, Herbert; Robison, Rosalyn; Nandkishore, Rahul; Rajah, Luke

2008-11-01

We have used simple laboratory experiments with viscous fluids to explore the dynamics of grounding lines between Antarctic marine ice sheets and the freely floating ice shelves into which they develop. Ice sheets are shear-dominated gravity currents, while ice shelves are extensional gravity currents with zero shear to leading order. Though ice sheets have non-Newtonian rheology, fundamental aspects of their flow can be explored using Newtonian fluid mechanics. We have derived a mathematical model of this flow that incorporates a new dynamic boundary condition for the position of the grounding line, where the gravity current loses contact with the solid base. Good agreement between our theoretical predictions and our experimental measurements, made using gravity currents of syrup flowing down a rigid slope into a deep, dense salt solution, gives confidence in the fundamental assumptions of our model, which can be incorporated into shallow-ice models to make important predictions regarding the dynamical stability of marine ice sheets.

Polar process and world climate /A brief overview/

NASA Technical Reports Server (NTRS)

Goody, R.

1980-01-01

A review is presented of events relating polar regions to the world climate, the mechanisms of sea ice and polar ice sheets, and of two theories of the Pleistocene Ice Ages. The sea ice which varies over time scales of one or two years and the polar ice sheets with time changes measured in tens or hundreds of thousands of years introduce two distinct time constants into global time changes; the yearly Arctic sea ice variations affect northern Europe and have some effect over the entire Northern Hemisphere; the ice-albedo coupling in the polar ice sheets is involved in major climatic events such as the Pleistocene ice ages. It is concluded that climate problems require a global approach including the atmosphere, the oceans, and the cryosphere.

Sub-Antarctic glacier extensions in the Kerguelen region (49°S, Indian Ocean) over the past 24,000 years constrained by 36Cl moraine dating

NASA Astrophysics Data System (ADS)

Jomelli, Vincent; Mokadem, Fatima; Schimmelpfennig, Irene; Chapron, Emmanuel; Rinterknecht, Vincent; Favier, Vincent; Verfaillie, Deborah; Brunstein, Daniel; Legentil, Claude; Michel, Elisabeth; Swingedouw, Didier; Jaouen, Alain; Aumaitre, Georges; Bourlès, Didier L.; Keddadouche, Karim

2017-04-01

Similar to many other regions in the world, glaciers in the southern sub-polar regions are currently retreating. In the Kerguelen Islands (49°S, 69°E), the mass balance of the Cook Ice Cap (CIC), the largest ice cap in this region, experienced dramatic shrinking between 1960 and 2013 with retreat rates among the highest in the world. This observation needs to be evaluated in a long-term context. However, data on the past glacier extents are sparse in the sub-Antarctic regions. To investigate the deglaciation pattern since the Last Glacial Maximum (LGM) period, we present the first 13 cosmogenic 36Cl surface exposure ages from four sites in the Kerguelen Islands. The 36Cl ages from erratic and moraine boulders span from 24.4 ± 2.7 ka to 0.3 ± 0.1 ka. We combined these ages with existing glacio-marine radiocarbon ages and bathymetric data to document the temporal and spatial changes of the island's glacial history. Ice began to retreat on the main island before 24.4 ± 2.7 ka until around the time of the Antarctic Cold Reversal (ACR) period (∼14.5-12.9 ka), during which the Bontemps moraine was formed by the advance of a CIC outlet glacier. Deglaciation continued during the Holocene probably until 3 ka with evidence of minor advances during the last millennium. This chronology is in pace with major changes in δ18O in a recent West Antarctica ice core record, showing that Kerguelen Islands glaciers are particularly sensitive and relevant to document climate change in the southern polar regions.

Remote sensing of the marginal ice zone during Marginal Ice Zone Experiment (MIZEX) 83

NASA Technical Reports Server (NTRS)

Shuchman, R. A.; Campbell, W. J.; Burns, B. A.; Ellingsen, E.; Farrelly, B. A.; Gloersen, P.; Grenfell, T. C.; Hollinger, J.; Horn, D.; Johannessen, J. A.

1984-01-01

The remote sensing techniques utilized in the Marginal Ice Zone Experiment (MIZEX) to study the physical characteristics and geophysical processes of the Fram Strait Region of the Greenland Sea are described. The studies, which utilized satellites, aircraft, helicopters, and ship and ground-based remote sensors, focused on the use of microwave remote sensors. Results indicate that remote sensors can provide marginal ice zone characteristics which include ice edge and ice boundary locations, ice types and concentration, ice deformation, ice kinematics, gravity waves and swell (in the water and the ice), location of internal wave fields, location of eddies and current boundaries, surface currents and sea surface winds.

On Quaternary glaciations, observations and theories

NASA Astrophysics Data System (ADS)

Paillard, D.

2015-07-01

In a recent paper, Paillard (2015) presents a rapid overview of both major theoretical and empirical studies of Pleistocene glaciations. In particular, it is explained how, over the last 150 years, astronomical theories were confronted to observational constraints and why the "100-kyr problem" is still the major unsolved issue of Quaternary ice ages. This paper also discusses the main alternative theory, which involves changes in atmospheric carbon dioxide concentration. It is then argued that a synthesis of both theories would better account for empirical evidences, as well as for our current knowledge of climate physics. Indeed, if there is no doubt that ice ages are "paced" by the astronomy as evidenced in Hays et al. (1976), the cause of terminations, and therefore the dynamics of the 100-kyr cycles, appears to be closely linked to Southern Ocean climate and atmospheric pCO2.

Extensive Holocene ice sheet grounding line retreat and uplift-driven readvance in West Antarctica

NASA Astrophysics Data System (ADS)

Kingslake, J.; Scherer, R. P.; Albrecht, T.; Coenen, J. J.; Powell, R. D.; Reese, R.; Stansell, N.; Tulaczyk, S. M.; Whitehouse, P. L.

2017-12-01

The West Antarctic Ice Sheet (WAIS) reached its Last Glacial Maximum (LGM) extent 29-14 kyr before present. Numerical models used to project future ice-sheet contributions to sea-level rise exploit reconstructions of post-LGM ice mass loss to tune model parameterizations. Ice-sheet reconstructions are poorly constrained in areas where floating ice shelves or a lack of exposed geology obstruct conventional glacial-geological techniques. In the Weddell and Ross Sea sectors, ice-sheet reconstructions have traditionally assumed progressive grounding line (GL) retreat throughout the Holocene. Contrasting this view, using three distinct lines of evidence, we show that the GL retreated hundreds of kilometers inland of its present position, before glacial isostatic rebound during the Mid to Late Holocene caused the GL to readvance to its current position. Evidence for retreat and readvance during the last glacial termination includes (1) widespread radiocarbon in sediment cores recovered from beneath ice streams along the Siple and Gould Coasts, indicating marine exposure at least 200 km inland of the current GL, (2) ice-penetrating radar observations of relic crevasses and other englacial structures preserved in slow-moving grounded ice, indicating ice-shelf grounding and (3) an ensemble of new ice-sheet simulations showing widespread post-LGM retreat of the GL inland of its current location and later readvance. The model indicates that GL readvance across low slope ice-stream troughs requires uplift-driven grounding of the ice shelf on topographic highs (ice rises). Our findings highlight ice-shelf pinning points and lithospheric response to unloading as drivers of major ice-sheet fluctuations. Full WAIS collapse likely requires GL retreat well beyond its current position in the Ronne and Ross Sectors and linkage via Amundsen Sea sector glaciers.

Last Glacial Maximum cirque glaciation in Ireland and implications for reconstructions of the Irish Ice Sheet

NASA Astrophysics Data System (ADS)

Barth, Aaron M.; Clark, Peter U.; Clark, Jorie; McCabe, A. Marshall; Caffee, Marc

2016-06-01

Reconstructions of the extent and height of the Irish Ice Sheet (IIS) during the Last Glacial Maximum (LGM, ∼19-26 ka) are widely debated, in large part due to limited age constraints on former ice margins and due to uncertainties in the origin of the trimlines. A key area is southwestern Ireland, where various LGM reconstructions range from complete coverage by a contiguous IIS that extends to the continental shelf edge to a separate, more restricted southern-sourced Kerry-Cork Ice Cap (KCIC). We present new 10Be surface exposure ages from two moraines in a cirque basin in the Macgillycuddy's Reeks that provide a unique and unequivocal constraint on ice thickness for this region. Nine 10Be ages from an outer moraine yield a mean age of 24.5 ± 1.4 ka while six ages from an inner moraine yield a mean age of 20.4 ± 1.2 ka. These ages show that the northern flanks of the Macgillycuddy's Reeks were not covered by the IIS or a KCIC since at least 24.5 ± 1.4 ka. If there was more extensive ice coverage over the Macgillycuddy's Reeks during the LGM, it occurred prior to our oldest ages.

78 FR 46604 - Notice of Availability of the Record of Decision for the General Management Plan/Environmental...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-08-01

... Statement for the Ice Age National Scenic Trail Interpretive Site, Wisconsin AGENCY: National Park Service... (GMP/EIS) for the Ice Age National Scenic Trail (Trail) Interpretive Site, Wisconsin. ADDRESSES: Copies may be picked up in person or by mailing a request in writing to the Ice Age National Scenic Trail...

Arctic Ice-Ocean Coupling and Gyre Equilibration Observed With Remote Sensing

NASA Astrophysics Data System (ADS)

Dewey, Sarah; Morison, James; Kwok, Ronald; Dickinson, Suzanne; Morison, David; Andersen, Roger

2018-02-01

Model and observational evidence has shown that ocean current speeds in the Beaufort Gyre have increased and recently stabilized. Because these currents rival ice drift speeds, we examine the potential for the Beaufort Gyre's shift from a system in which the wind drives the ice and the ice drives a passive ocean to one in which the ocean often, in the absence of high winds, drives the ice. The resultant stress exerted on the ocean by the ice and the resultant Ekman pumping are reversed, without any change in average wind stress curl. Through these curl reversals, the ice-ocean stress provides a key feedback in Beaufort Gyre stabilization. This manuscript constitutes one of the first observational studies of ice-ocean stress inclusive of geostrophic ocean currents, by making use of recently available remote sensing data.

Detrital Carbonate Events on the Labrador Shelf, a 13 to 7 kyr Template for Freshwater Forcing From the Laurentide Ice Sheet

NASA Astrophysics Data System (ADS)

Jennings, A. E.; Andrews, J. T.

2008-12-01

A complex sequence of abrupt glacial advances and retreats punctuate the late phases of Laurentide Ice Sheet deglaciation. These episodes have been reconstructed from interpretation and mapping of glacial deposits on land and in marine basins proximal to the former ice margins in Hudson Strait, Hudson Bay, and the SE Baffin Island shelf. As these events likely produced pulses of freshwater discharge into the North Altantic, which may be responsible for rapid climate change, their timing and magnitude need to be understood. The timing of these events is well constrained by radiocarbon ages, but the ocean reservoir age in ice proximal areas is subject to very large uncertainties, making it difficult to determine calibrated ages for the glacial events so that they can be compared to other climate records. We suggest that the sequence of high detrital carbonate peaks in Holocene and Late Glacial sediments in the Cartwright Saddle of the Labrador shelf provides a template of the abrupt glacial events of the NE margin of the Laurentide Ice Sheet, particularly events that issued from Hudson Strait and Hudson Bay, but possibly including events in Baffin Bay. Once the Labrador Shelf was deglaciated and the local ice had retreated inland, the Cartwright Saddle was a distal trap for sediments released from Hudson Strait and other ice sheet outlets farther north as their sediments and meltwater were carried southwards by surface currents. Core MD99-2236 contains a sediment record beginning c. 13.9 cal ka. We assume a marine reservoir age for the Cartwright Saddle of 450 yrs, which is reasonable given the ice distal and oceanic position of the site. Carbonate was measured on average at a 30 yr time resolution. Carbonate values are elevated between 11.7 and 7 cal kyr BP, with six spikes exceeding 30 percent. Each spike corresponds to a light isotope spike in foraminifers, suggesting that each major spike is associated with a pulse of glacial meltwater. Elevated IRD counts associated with the carbonate spikes suggest that at least some of the meltwater was released by icebergs. Age estimates of these peaks are: 11.5, 10.6, 9.5, 9.1, 8.7, and 8.2 cal kyr BP, and their duration ranges between 50 and 200 years. A 'red bed' is associated with a subsidiary carbonate spike 8.57 cal ka, very close to the estimated age of the timing of the final outburst drainage of lakes Agassiz and Ojibway: about 8.47 cal ka BP. A lower carbonate spike at 11.1 cal ka is associated with a light isotope event. The carbonate record of MD99-2236 promises to be an important key to the timing and role of deglacial episodes in freshwater forcing on North Altantic climate.

An investigation of the astronomical theory of the ice ages using a simple climate-ice sheet model

NASA Technical Reports Server (NTRS)

Pollard, D.

1978-01-01

The astronomical theory of the Quaternary ice ages is incorporated into a simple climate model for global weather; important features of the model include the albedo feedback, topography and dynamics of the ice sheets. For various parameterizations of the orbital elements, the model yields realistic assessments of the northern ice sheet. Lack of a land-sea heat capacity contrast represents one of the chief difficulties of the model.

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica

PubMed Central

Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V.; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P.; Brook, Edward J.

2014-01-01

We present successful 81Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The 81Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) 85Kr and 39Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the 81Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130–115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA 81Kr analysis requires a 40–80-kg ice sample; as sample requirements continue to decrease, 81Kr dating of ice cores is a future possibility. PMID:24753606

Radiometric 81Kr dating identifies 120,000-year-old ice at Taylor Glacier, Antarctica.

PubMed

Buizert, Christo; Baggenstos, Daniel; Jiang, Wei; Purtschert, Roland; Petrenko, Vasilii V; Lu, Zheng-Tian; Müller, Peter; Kuhl, Tanner; Lee, James; Severinghaus, Jeffrey P; Brook, Edward J

2014-05-13

We present successful (81)Kr-Kr radiometric dating of ancient polar ice. Krypton was extracted from the air bubbles in four ∼350-kg polar ice samples from Taylor Glacier in the McMurdo Dry Valleys, Antarctica, and dated using Atom Trap Trace Analysis (ATTA). The (81)Kr radiometric ages agree with independent age estimates obtained from stratigraphic dating techniques with a mean absolute age offset of 6 ± 2.5 ka. Our experimental methods and sampling strategy are validated by (i) (85)Kr and (39)Ar analyses that show the samples to be free of modern air contamination and (ii) air content measurements that show the ice did not experience gas loss. We estimate the error in the (81)Kr ages due to past geomagnetic variability to be below 3 ka. We show that ice from the previous interglacial period (Marine Isotope Stage 5e, 130-115 ka before present) can be found in abundance near the surface of Taylor Glacier. Our study paves the way for reliable radiometric dating of ancient ice in blue ice areas and margin sites where large samples are available, greatly enhancing their scientific value as archives of old ice and meteorites. At present, ATTA (81)Kr analysis requires a 40-80-kg ice sample; as sample requirements continue to decrease, (81)Kr dating of ice cores is a future possibility.

GIA Modeling with 3D Rheology and Recent Ice Thickness Changes in Polar Regions

NASA Astrophysics Data System (ADS)

Van Der Wal, W.; Wu, P. P.

2012-12-01

Models for Glacial Isostatic Adjustment (GIA) mainly focus on the response of the solid Earth to ice thickness changes on the scale of thousands of years. However, some of the fastest vertical movement in former glaciated regions is due to changes in ice thickness that occurred within the last 1,000 years. Similar studies for the polar regions are limited, possibly due to a lack of knowledge on past ice sheet thicknesses there. Still, predictions of uplift rate and mass change due to recent ice thickness changes need to improve in order to provide accurate estimates of current mass loss. In order to obtain a measurable response to variations in ice thickness in the last 1,000 years, viscosity in the lithosphere or top of the upper mantle needs to be lower than the mantle viscosity values in conventional GIA models. In the absence of reliable models for recent ice thickness changes we aim to bracket the predicted uplift rates and gravity rates for such changes by assuming simplified past ice growth and melt patterns. Instead of adding a low-viscous layer in the mantle a priori, creep parameters are based on information from experimental constraints, seismology and heatflow measurements. Thus the model includes viscosity varying in space and time. The simulations are performed on a finite element model of a spherical, self-gravitating, incompressible Earth using the commercial software Abaqus. 3D composite rheology is implemented based on temperature fields from heatflow measurements or seismic velocity anomalies. The lithospheric thickness does not need to be specified as the effective elastic thickness is determined by the local effective viscosity. ICE-5G is used as ice loading history while ice changes during and around the Little Ice Age in Greenland are assumed to take place near the coast. A 3D composite rheology has been shown to match historic sea levels well, but uplift rates are somewhat underestimated. With the GIA models that best match uplift rates in Fennoscandia and North America we find that ice thickness increase during the Little Ice Age in Greenland can make up a significant part of the mass change signal observed by the GRACE satellites (locally up to 10%). 3D non-linear rheology models introduce variation of up to 30% of the maximum signal observed with GRACE, compared to about 20% for conventional GIA models with 1D viscosity.

Early glaciation already during the Early Miocene in the Amundsen Sea, Southern Pacific: Indications from the distribution of sedimentary sequences

NASA Astrophysics Data System (ADS)

Uenzelmann-Neben, Gabriele; Gohl, Karsten

2014-09-01

The distribution and internal architecture of seismostratigraphic sequences observed on the Antarctic continental slope and rise are results of sediment transport and deposition by bottom currents and ice sheets. Analysis of seismic reflection data allows to reconstruct sediment input and sediment transport patterns and to infer past changes in climate and oceanography. We observe four seismostratigraphic units which show distinct differences in location and shape of their depocentres and which accumulated at variable sedimentation rates. We used an age-depth model based on DSDP Leg 35 Site 324 for the Plio/Pleistocene and a correlation with seismic reflection characteristics from the Ross and Bellingshausen Seas, which unfortunately has large uncertainties. For the period before 21 Ma, we interpret low energy input of detritus via a palaeo-delta originating in an area of the Amundsen Sea shelf, where a palaeo-ice stream trough (Pine Island Trough East, PITE) is located today, and deposition of this material on the continental rise under sea ice coverage. For the period 21-14.1 Ma we postulate glacial erosion for the hinterland of this part of West Antarctica, which resulted in a larger depocentre and an increase in mass transport deposits. Warming during the Mid Miocene Climatic Optimum resulted in a polythermal ice sheet and led to a higher sediment supply along a broad front but with a focus via two palaeo-ice stream troughs, PITE and Abbot Trough (AT). Most of the glaciogenic debris was transported onto the eastern Amundsen Sea rise where it was shaped into levee-drifts by a re-circulating bottom current. A reduced sediment accumulation in the deep-sea subsequent to the onset of climatic cooling after 14 Ma indicates a reduced sediment supply probably in response to a colder and drier ice sheet. A dynamic ice sheet since 4 Ma delivered material offshore mainly via AT and Pine Island Trough West (PITW). Interaction of this glaciogenic detritus with a west-setting bottom current resulted in the continued formation of levee-drifts in the eastern and central Amundsen Sea.

Oceanographic Influences on Ice Shelves and Drainage in the Amundsen Sea

NASA Astrophysics Data System (ADS)

Minzoni, R. T.; Anderson, J. B.; Majewski, W.; Yokoyama, Y.; Fernandez, R.; Jakobsson, M.

2016-12-01

Marine sediment cores collected during the IB OdenSouthern Ocean 2009-2010 cruise are used to reconstruct the Holocene history of the Cosgrove Ice Shelf, which today occupies Ferrero Bay, a large embayment of eastern Pine Island Bay. Detailed sedimentology, geochemistry, and micropaleontology of cores, in conjunction with subbottom profiles, reveal an unexpected history of recession. Presence of planktic foraminifera at the base of Kasten Core-15 suggests an episode of enhanced circulation beneath a large ice shelf that covered the Amundsen Sea during the Early Holocene, and relatively warm water incursion has been interpreted as a potential culprit for major recession and ice mass loss by 10.7 cal kyr BP from radiocarbon dating. Fine sediment deposition and low productivity throughout the Mid Holocene indicate long-lived stability of the Cosgrove Ice Shelf in Ferrero Bay, despite regional warming evident from ice core data and ice shelf loss in the Antarctic Peninsula. High productivity and diatom abundance signify opening of Ferrero Bay and recession of the Cosgrove Ice Shelf to its present day configuration by 2.0 cal kyr BP. This coincides with deglaciation of an island near Canisteo Peninsula according to published cosmogenic exposure ages. Presence of benthic foraminifera imply that warm deep water influx beneath the extended Cosgrove Ice Shelf was a mechanism for under-melting the ice shelf and destabilizing the grounding line. Major ice shelf recession may also entail continental ice mass loss from the eastern sector of the Amundsen Sea during the Late Holocene. Oceanographic forcing remains a key concern for the current stability of the Antarctic Ice Sheet, especially along the tidewater margins of West Antarctica. Ongoing work on diatom and foraminiferal assemblages of the Late Holocene in Ferrero Bay and other fjord settings will improve our understanding of recent oceanographic changes and their potential influence on ice shelves and outlet glaciers that contribute to the mass balance of the West Antarctic Ice Sheet.

Out of Tibet: Pliocene woolly rhino suggests high-plateau origin of Ice Age megaherbivores.

PubMed

Deng, Tao; Wang, Xiaoming; Fortelius, Mikael; Li, Qiang; Wang, Yang; Tseng, Zhijie J; Takeuchi, Gary T; Saylor, Joel E; Säilä, Laura K; Xie, Guangpu

2011-09-02

Ice Age megafauna have long been known to be associated with global cooling during the Pleistocene, and their adaptations to cold environments, such as large body size, long hair, and snow-sweeping structures, are best exemplified by the woolly mammoths and woolly rhinos. These traits were assumed to have evolved as a response to the ice sheet expansion. We report a new Pliocene mammal assemblage from a high-altitude basin in the western Himalayas, including a primitive woolly rhino. These new Tibetan fossils suggest that some megaherbivores first evolved in Tibet before the beginning of the Ice Age. The cold winters in high Tibet served as a habituation ground for the megaherbivores, which became preadapted for the Ice Age, successfully expanding to the Eurasian mammoth steppe.

Siple Dome ice reveals two modes of millennial CO2 change during the last ice age

PubMed Central

Ahn, Jinho; Brook, Edward J.

2014-01-01

Reconstruction of atmospheric CO2 during times of past abrupt climate change may help us better understand climate-carbon cycle feedbacks. Previous ice core studies reveal simultaneous increases in atmospheric CO2 and Antarctic temperature during times when Greenland and the northern hemisphere experienced very long, cold stadial conditions during the last ice age. Whether this relationship extends to all of the numerous stadial events in the Greenland ice core record has not been clear. Here we present a high-resolution record of atmospheric CO2 from the Siple Dome ice core, Antarctica for part of the last ice age. We find that CO2 does not significantly change during the short Greenlandic stadial events, implying that the climate system perturbation that produced the short stadials was not strong enough to substantially alter the carbon cycle. PMID:24781344

Exposure age and ice-sheet model constraints on Pliocene East Antarctic ice sheet dynamics.

PubMed

Yamane, Masako; Yokoyama, Yusuke; Abe-Ouchi, Ayako; Obrochta, Stephen; Saito, Fuyuki; Moriwaki, Kiichi; Matsuzaki, Hiroyuki

2015-04-24

The Late Pliocene epoch is a potential analogue for future climate in a warming world. Here we reconstruct Plio-Pleistocene East Antarctic Ice Sheet (EAIS) variability using cosmogenic nuclide exposure ages and model simulations to better understand ice sheet behaviour under such warm conditions. New and previously published exposure ages indicate interior-thickening during the Pliocene. An ice sheet model with mid-Pliocene boundary conditions also results in interior thickening and suggests that both the Wilkes Subglacial and Aurora Basins largely melted, offsetting increased ice volume. Considering contributions from West Antarctica and Greenland, this is consistent with the most recent IPCC AR5 estimate, which indicates that the Pliocene sea level likely did not exceed +20 m on Milankovitch timescales. The inception of colder climate since ∼3 Myr has increased the sea ice cover and inhibited active moisture transport to Antarctica, resulting in reduced ice sheet thickness, at least in coastal areas.

Cool Science Explains a Warming World: Using Ice Core Science to Bridge the Gap Between Researchers and the K-12 Classroom

NASA Astrophysics Data System (ADS)

Huffman, L. T.

2017-12-01

Changing ice has urgent implications for people around the world. The Ice Drilling Program Office (IDPO) provides scientific leadership and oversight of ice coring and drilling activities funded by the US National Science Foundation and also has goals to enhance education and communication of current research information. In a time when misinformation is rampant and climate change science is suspect, it is essential that students receive accurate scientific information and engage in learning activities that model complex ideas through engaging and age appropriate ways, while also learning to validate and recognize reliable sources. The IDPO Education and Outreach (EO) office works to create resources, activities and professional development that bridge the gap between ice core science research and educators and their students. Ice core science is on the cutting edge of new discoveries about climate change and understanding better the past to predict the future. Hands-on inquiry activities based on ice core data allow teachers to lead their students to new discoveries about climate secrets hidden deep in the ice. Capitalizing on the inherent interest in the extremes of the Polar Regions, IDPO materials engage students in activities aligned with NGSS standards. Ice drilling technologies make an ideal platform for intertwining engineering concepts and practices with science research to meet the SEP (Science and Engineering Practices) in the NGSS. This session will highlight how the IDPO EO office has built a community of ice core scientists willing to take part in education and outreach projects and events and share some of the resources available to K-12 educators. We will highlight some of the successes and lessons learned as we continually evolve our work toward more effective science education and communication highlighting ice core and climate change science.

Space/Time Statistics of Polar Ice Motion

NASA Technical Reports Server (NTRS)

Emery, William J.; Fowler, Charles; Maslanik, James A.

2003-01-01

Ice motions have been computed from passive microwave imagery (SMMR and SSM/I) on a daily basis for both Polar Regions. In the Arctic these daily motions have been merged with daily motions from AVHRR imagery and the Arctic buoy program. In the Antarctic motion only from the AVHRR were available for merging with the passive microwave vectors. Long-term means, monthly means and weekly means have all been computed from the resulting 22-year time series of polar ice motion. Papers are in preparation that present the long term (22 year) means, their variability and show animations of the monthly means over this time period for both Polar Regions. These papers will have links to "enhanced objects" that allow the reader to view the animations as part of the paper. The first paper presents the ice motion results from each of the Polar Regions. The second paper looks only at ice motion in the Arctic in order to develop a time series of ice age in the Arctic. Starting with the first full SMMR year in 1979 we keep track of each individual "ice element" (resolution of the sensor) and track it in the subsequent monthly time series. After a year we "age" each "particle" and we thus can keep track of the age of the ice starting in 1979. We keep track of ice age classes between one and five years and thus we can see the evolution of the ice as it ages after the initial 5-year period. This calculation shows how we are losing the older ice through Fram Strait at a rather alarming rate particularly in the past 15 years. This loss of older ice has resulted in an overall decrease in the thickest, oldest ice, which is now limited to a region just north of the Canadian Archipelago with tongues extending out across the pole towards the Siberian Shelf. This loss of old ice is consistent with the effects of global warming which provides the heat needed to melt, move and disperse this oldest ice through Fram Strait. This is the first step in a progression that may eventually open the Arctic ice pack and lead to an ice-free Arctic Ocean.

Alternating current breakdown voltage of ice electret

NASA Astrophysics Data System (ADS)

Oshika, Y.; Tsuchiya, Y.; Okumura, T.; Muramoto, Y.

2017-09-01

Ice has low environmental impact. Our research objectives are to study the availability of ice as a dielectric insulating material at cryogenic temperatures. We focus on ferroelectric ice (iceXI) at cryogenic temperatures. The properties of iceXI, including its formation, are not clear. We attempted to obtain the polarized ice that was similar to iceXI under the applied voltage and cooling to 77 K. The polarized ice have a wide range of engineering applications as electronic materials at cryogenic temperatures. This polarized ice is called ice electret. The structural difference between ice electret and normal ice is only the positions of protons. The effects of the proton arrangement on the breakdown voltage of ice electret were shown because electrical properties are influenced by the structure of ice. We observed an alternating current (ac) breakdown voltage of ice electret and normal ice at 77 K. The mean and minimum ac breakdown voltage values of ice electret were higher than those of normal ice. We considered that the electrically weak part of the normal ice was improved by applied a direct electric field.

Greenland ice sheet retreat since the Little Ice Age

NASA Astrophysics Data System (ADS)

Beitch, Marci J.

Late 20th century and 21st century satellite imagery of the perimeter of the Greenland Ice Sheet (GrIS) provide high resolution observations of the ice sheet margins. Examining changes in ice margin positions over time yield measurements of GrIS area change and rates of margin retreat. However, longer records of ice sheet margin change are needed to establish more accurate predictions of the ice sheet's future response to global conditions. In this study, the trimzone, the area of deglaciated terrain along the ice sheet edge that lacks mature vegetation cover, is used as a marker of the maximum extent of the ice from its most recent major advance during the Little Ice Age. We compile recently acquired Landsat ETM+ scenes covering the perimeter of the GrIS on which we map area loss on land-, lake-, and marine-terminating margins. We measure an area loss of 13,327 +/- 830 km2, which corresponds to 0.8% shrinkage of the ice sheet. This equates to an averaged horizontal retreat of 363 +/- 69 m across the entire GrIS margin. Mapping the areas exposed since the Little Ice Age maximum, circa 1900 C.E., yields a century-scale rate of change. On average the ice sheet lost an area of 120 +/- 16 km 2/yr, or retreated at a rate of 3.3 +/- 0.7 m/yr since the LIA maximum.

Latest Pleistocene and Holocene Glacier Fluctuations in southernmost Patagonia

NASA Astrophysics Data System (ADS)

Menounos, B.; Maurer, M.; Clague, J. J.; osborn, G.; Ponce, F.; Davis, P. T.; Rabassa, J.; Coronato, A.; Marr, R.

2011-12-01

Summer insolation has been proposed to explain long-term glacier fluctuations during the Holocene. If correct, the record of glacier fluctuations at high latitudes in the Southern Hemisphere should differ from that in the Northern Hemisphere. Testing this insolation hypothesis has been hampered by dating uncertainties of many Holocene glacier chronologies from Patagonia. We report on our ongoing research aimed at developing a regional glacier chronology at the southern end of the Andes north and west of Ushuaia, Argentina. We have found evidence for an advance of cirque glaciers at the end of the Pleistocene; one or locally two closely spaced moraines extend up to 2 km beyond Little Ice Age moraines. Radiocarbon dating of terrestrial macrofossils recovered from basal sediments behind two of these moraines yielded ages of 10,320 ± 25 and 10,330 ± 30 14C yr BP. These moraines may record glacier advances coeval with the Antarctic Cold Reversal; surface exposure dating of these moraines is currently in progress to test this hypothesis. We find no evidence of Holocene moraines older than 6800 14C yr BP, based on the distribution of Hudson tephra of that age. At some sites, there is evidence for an early Neoglacial advance of glaciers slightly beyond (< 0.5 km) Little Ice Age limits. Terrestrial macrofossils at the upper contact of basal till from one site yielded an age of 4505 ± 30 14C yr BP; this age overlaps the most probable age range of early Neoglacial ice expansion in southern Patagonia reported by Porter (2000) and the age of plants killed by expansion of the Quelccaya Ice Cap in Peru. We have documented multiple wood mats with stumps in growth position separated by till units in a 100 m section of the northeast lateral moraine at Stoppani Glacier (54.78 S, 68.98 W), 50 km west of Ushuaia. Ten radiocarbon ages on these wood mats range in age from 3510 ± 15 to 135 ± 15 14C yr BP. The mats decrease in age up-section; many overlap with published age ranges for Neoglacial advances in western Canada. Taken together, these data: a) do not support the summer insolation hypothesis for Holocene glacier fluctuations in southernmost Patagonia; b) confirm paleobotanical evidence for a warm, dry early Holocene; and c) suggest that many Neoglacial advances in southernmost Patagonia and western North America were synchronous.

Students' Conceptions of Glaciers and Ice Ages: Applying the Model of Educational Reconstruction to Improve Learning

ERIC Educational Resources Information Center

Felzmann, Dirk

2017-01-01

Glaciers and ice ages are important topics in teaching geomorphology, earth history, and climate change. As with many geoscience topics, glacier formation, glacier movement, glacial morphology, and ice ages consist of a wide variety of processes and phenomena. Accordingly, it must be decided which of those processes and phenomena should be part of…

Sunlight, Sea Ice, and the Ice Albedo Feedback in a Changing Artic Sea Ice Cover

DTIC Science & Technology

2015-11-30

information from the PIOMAS model [J. Zhang], melt pond coverage from MODIS [Rösel et al., 2012], and ice-age estimates [Maslanik et al., 2011] to...determined from MODIS satellite data using an artificial neural network, Cryosph., 6(2), 431–446, doi:10.5194/tc- 6-431-2012. PUBLICATIONS Carmack...from MODIS , and ice-age estimates to this dataset. We have used this extented dataset to build a climatology of the partitioning of solar heat between

The Influence of Non-linear 3-D Mantle Rheology on Predictions of Glacial Isostatic Adjustment Models

NASA Astrophysics Data System (ADS)

Van Der Wal, W.; Barnhoorn, A.; Stocchi, P.; Drury, M. R.; Wu, P. P.; Vermeersen, B. L.

2011-12-01

Ice melting in Greenland and Antarctica can be estimated from GRACE satellite measurements. The largest source of error in these estimates is uncertainty in models for Glacial Isostatic Adjustment (GIA). GIA models that are used to correct the GRACE data have several shortcomings, including (i) mantle viscosity is only varied with depth, and (ii) stress-dependence of viscosity is ignored. Here we attempt to improve on these two issues with the ultimate goal of providing more realistic GIA predictions in areas that are currently ice covered. The improved model is first tested against observations in Fennoscandia, where there is good coverage with GIA observations, before applying it to Greenland. Deformation laws for diffusion and dislocation creep in olivine are taken from a compilation of laboratory experiments. Temperature is obtained from two different sources: surface heatflow maps as input for the heat transfer equation, and seismic velocity anomalies converted to upper mantle temperatures. Grain size and olivine water content are kept as free parameters. Surface loading is provided by an ice loading history that is constructed from constraints on past ice margins and input from climatology. The finite element model includes self-gravitation but not compressibility and background stresses. It is found that the viscosity in Fennoscandia changes in time by two orders of magnitude for a wet rheology with large grain size. The wet rheology provides the best fit to historic sea level data. However, present-day uplift and gravity rates are too low for such a rheology. We apply a wet rheology on Greenland, and simulate a Little Ice Age (LIA) increase in thickness on top of the ICE-5G ice loading history. Preliminary results show a negative geoid rate of magnitude more than 0.5 mm/year due to the LIA increase in ice thickness in combination with the non-linear upper mantle rheology. More tests are necessary to determine the influence of mantle rheology on GIA model predictions in areas of current ice sheet melting.

Debris supply to mountain glaciers and how it effects their sensitivity to climate change - A case study from the Chhota Shigri Glacier, India

NASA Astrophysics Data System (ADS)

Scherler, D.; Egholm, D. L.

2017-12-01

Debris-covered glaciers are widespread in the Himalaya and other steep mountain ranges. They testify to active erosion of ice-free bedrock hillslopes that tower above valley glaciers, sometimes more than a kilometer high. It is well known that supraglacial debris cover significantly reduces surface ablation rates and thereby influences glacial mass balances and runoff. However, the dynamic evolution of debris cover along with climatic and topographic changes is poorly understood. Here, we present ice-free hillslope erosion rates derived from 10Be concentrations in the ablation-dominated medial moraine of the Chhota Shigri Glacier, Indian Himalaya. We combine our empirical, field-based approach with a numerical model of frost-related sediment production and glacial debris transport to (1) assess patterns of ice-free hillslope erosion that are permissible with observed patterns of debris cover, and (2) explore the coupled response of glaciers and ice-free hillslopes to climatic changes. Measured 10Be concentrations increase downglacier from 3×104 to 6×104 atoms (g quartz) -1, yielding hillslope erosion rates of 1.3-0.6 mm yr-1. The accumulation of 10Be during debris residence on the ice surface can only account for a small fraction (<20%) of the downglacier increase. Other potential explanations include (1) heterogeneous source areas with different average productions rates, and (2) homogeneous source areas but temporally variable erosion rates. We used the 10Be-derived hillslope erosion rates to define debris supply rates from ice-free bedrock hillslopes in the numerical ice and landscape evolution model iSOSIA. Based on available mass balance and ice thickness data, the calibrated model reproduces the medial moraine of the Chhota Shogri Glacier quite well, although uncertainties exist due to the transient disequilibrium of the glacier, i.e., the current debris cover was fed into the glacier during the Little Ice Age (LIA), and thus under different boundary conditions. We currently perform transient experiments during warming and cooling periods for testing models of frost-related and temperature-sensitive debris production, and for assessing the coupled sensitivity of hillslopes and glaciers to climate change.

Current Status and Future Plan of Arctic Sea Ice monitoring in South Korea

NASA Astrophysics Data System (ADS)

Shin, J.; Park, J.

2016-12-01

Arctic sea ice is one of the most important parameters in climate. For monitoring of sea ice changes, the National Meteorological Satellite Center (NMSC) of Korea Metrological Administration has developed the "Arctic sea ice monitoring system" to retrieve the sea ice extent and surface roughness using microwave sensor data, and statistical prediction model for Arctic sea ice extent. This system has been implemented to the web site for real-time public service. The sea ice information can be retrieved using the spaceborne microwave sensor-Special Sensor Microwave Imager/Sounder (SSMI/S). The sea ice information like sea ice extent, sea ice surface roughness, and predictive sea ice extent are produced weekly base since 2007. We also publish the "Analysis report of the Arctic sea ice" twice a year. We are trying to add more sea ice information into this system. Details of current status and future plan of Arctic sea ice monitoring and the methodology of the sea ice information retrievals will be presented in the meeting.

Aerodynamic Classification of Swept-Wing Ice Accretion

NASA Technical Reports Server (NTRS)

Broeren, Andy; Diebold, Jeff; Bragg, Mike

2013-01-01

The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current state-of-the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice, and spanwise-ridge ice. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.

Cumulative estrogen exposure and prospective memory in older women.

PubMed

Hesson, Jacqueline

2012-10-01

This study looked at cumulative lifetime estrogen exposure, as estimated with a mathematical index (Index of Cumulative Estrogen Exposure (ICEE)) that included variables (length of time on estrogen therapy, age at menarche and menopause, postmenopausal body mass index, time since menopause, nulliparity and duration of breastfeeding) known to influence estrogen levels across the life span, and performance on prospective and retrospective memory measures in a group of 50 postmenopausal women (mean age=69.3years) who, if they were current or former users of estrogen therapy, had started therapy within 5years of menopause. The ICEE was found to be a significant predictor of performance on the Prospective Memory task (F(1)=4.21, p=.046, η(p)(2)=.084). No significant relationship was noted between the ICEE and performance on measures of retrospective memory. The results suggest that the level of cumulative lifetime exposure to estrogen a woman has influences her prospective memory performance later in life and that the influence of reproductive and biological markers of endogenous estrogen exposure are relevant factors to consider when studying the effect of estrogen therapy on cognitive functioning in postmenopausal women. In addition, the finding that performance on a measure of prospective memory, but not performance on measures of retrospective memory, was associated with the ICEE adds further support to the theory that the frontal cortex may be especially sensitive to estrogen. Copyright © 2012 Elsevier Inc. All rights reserved.

Explosive ice age diversification of kiwi.

PubMed

Weir, Jason T; Haddrath, Oliver; Robertson, Hugh A; Colbourne, Rogan M; Baker, Allan J

2016-09-20

Molecular dating largely overturned the paradigm that global cooling during recent Pleistocene glacial cycles resulted in a burst of species diversification although some evidence exists that speciation was commonly promoted in habitats near the expanding and retracting ice sheets. Here, we used a genome-wide dataset of more than half a million base pairs of DNA to test for a glacially induced burst of diversification in kiwi, an avian family distributed within several hundred kilometers of the expanding and retracting glaciers of the Southern Alps of New Zealand. By sampling across the geographic range of the five kiwi species, we discovered many cryptic lineages, bringing the total number of kiwi taxa that currently exist to 11 and the number that existed just before human arrival to 16 or 17. We found that 80% of kiwi diversification events date to the major glacial advances of the Middle and Late Pleistocene. During this period, New Zealand was repeatedly fragmented by glaciers into a series of refugia, with the tiny geographic ranges of many kiwi lineages currently distributed in areas adjacent to these refugia. Estimates of effective population size through time show a dramatic bottleneck during the last glacial cycle in all but one kiwi lineage, as expected if kiwi were isolated in glacially induced refugia. Our results support a fivefold increase in diversification rates during key glacial periods, comparable with levels observed in classic adaptive radiations, and confirm that at least some lineages distributed near glaciated regions underwent rapid ice age diversification.

Vostok Subglacial Lake: A Review of Geophysical Data Regarding Its Discovery and Topographic Setting

NASA Technical Reports Server (NTRS)

Siegert, Martin J.; Popov, Sergey; Studinger, Michael

2011-01-01

Vostok Subglacial Lake is the largest and best known sub-ice lake in Antarctica. The establishment of its water depth (>500 m) led to an appreciation that such environments may be habitats for life and could contain ancient records of ice sheet change, which catalyzed plans for exploration and research. Here we discuss geophysical data used to identify the lake and the likely physical, chemical, and biological processes that occur in it. The lake is more than 250 km long and around 80 km wide in one place. It lies beneath 4.2 to 3.7 km of ice and exists because background levels of geothermal heating are sufficient to warm the ice base to the pressure melting value. Seismic and gravity measurements show the lake has two distinct basins. The Vostok ice core extracted >200 m of ice accreted from the lake to the ice sheet base. Analysis of this ice has given valuable insights into the lake s biological and chemical setting. The inclination of the ice-water interface leads to differential basal melting in the north versus freezing in the south, which excites circulation and potential mixing of the water. The exact nature of circulation depends on hydrochemical properties, which are not known at this stage. The age of the subglacial lake is likely to be as old as the ice sheet (approx.14 Ma). The age of the water within the lake will be related to the age of the ice melting into it and the level of mixing. Rough estimates put that combined age as approx.1 Ma.

The diatom record from beneath the West Antarctic Ice Sheet and the global proxy perspective

NASA Technical Reports Server (NTRS)

Scherer, Reed P.

1993-01-01

Recent glaciological evaluation and modeling of the marine-based West Antarctic Ice Sheet (WAIS) support the possibility that the WAIS disintegrated during one or more Pleistocene interglacial period(s). The magnitude of sea level and oxygen isotope variation during certain late-Pleistocene interglacial periods is also consistent with the possibility of major retreat of the WAIS. Although oxygen isotopes from deep-sea sediments provide the best available proxy record for global ice volume (despite the ambiguities in the record), the source of ice volume changes must be hypothesized. Based on the intensity of interglacial isotopic shifts recorded in Southern Ocean marine sedimentary records, stage 11 (400,000 years ago) is the strongest candidate for WAIS collapse, but the records for stages 9, 7, and 5.5 are all consistent with the possibility of multiple late-Pleistocene collapses. Seismic reflection studies through the WAIS have revealed thick successions of strata with seismic characteristics comparable to upper Tertiary marine sediments. Small samples of glacial diamictons from beneath the ice sheet have been collected via hot-water drilled access holes. These sediments include mixed diatom assemblages of varying ages. Late-Miocene diatoms dominate many samples, probably reflecting marine deposition in West Antarctic basins prior to development of a dominantly glacial phase in West Antarctica. In addition to late-Miocene diatoms, samples from Upstream B (1988/89) contain rare post-Miocene diatoms, many of which imply deposition in the West Antarctic interior during one or more Pleistocene deglaciation periods. Age-diagnostic fossils in glacial sediments beneath ice sheets provide relatively coarse chronostratigraphic control, but they do contain direct evidence of regional deglaciation. Thus, sub-glacial till samples provide the evidence regarding the source of ice sheet variability seen in well-dated proxy records. Combined, these independent data sets can provide a more comprehensive and less speculative interpretation of the history of past glacial minima in currently glaciated polar regions.

The Depth of Ice Inside the Smallest Cold-Traps on Mercury: Implications for Age and Origin

NASA Astrophysics Data System (ADS)

Rubanenko, L.; Mazarico, E.; Neumann, G. A.; Paige, D. A.

2018-05-01

We use Mercury Laser Altimeter data and an illumination model to constrain the depth of the smallest ice deposits on Mercury. By comparing this depth to modeled gardening rates, we estimate the age and delivery method of this ice.

Chronological framework for the deglaciation of the Lake Michigan lobe of the Laurentide ice sheet from ice-walled lake deposits

USGS Publications Warehouse

Curry, B.; Petras, J.

2011-01-01

A revised chronological framework for the deglaciation of the Lake Michigan lobe of the south-central Laurentide Ice Sheet is presented based on radiocarbon ages of plant macrofossils archived in the sediments of low-relief ice-walled lakes. We analyze the precision and accuracy of 15 AMS 14C ages of plant macrofossils obtained from a single ice-walled lake deposit. The semi-circular basin is about 0.72km wide and formed of a 4- to 16-m-thick succession of loess and lacustrine sediment inset into till. The assayed material was leaves, buds and stems of Salix herbacea (snowbed willow). The pooled mean of three ages from the basal lag facies was 18 270??50 14C a BP (21 810cal. a BP), an age that approximates the switch from active ice to stagnating conditions. The pooled mean of four ages for the youngest fossil-bearing horizon was 17 770??40 14C a BP (21 180cal. a BP). Material yielding the oldest and youngest ages may be obtained from sediment cores located at any place within the landform. Based on the estimated settling times of overlying barren, rhythmically bedded sand and silt, the lacustrine environment persisted for about 50 more years. At a 67% confidence level, the dated part of the ice-walled lake succession persisted for between 210 and 860cal. a (modal value: 610cal. a). The deglacial age of five moraines or morainal complexes formed by the fluctuating margin of the Lake Michigan lobe have been assessed using this method. There is no overlap of time intervals documenting when ice-walled lakes persisted on these landforms. The rapid readvances of the lobe during deglaciation after the last glacial maximum probably occurred at some point between the periods of ice-walled lake sedimentation. ?? 2011 John Wiley & Sons, Ltd.

Climate change alters the reproductive phenology and investment of a lacustrine fish, the three-spine stickleback.

PubMed

Hovel, Rachel A; Carlson, Stephanie M; Quinn, Thomas P

2017-06-01

High-latitude lakes are particularly sensitive to the effects of global climate change, demonstrating earlier ice breakup, longer ice-free seasons, and increased water temperatures. Such physical changes have implications for diverse life-history traits in taxa across entire lake food webs. Here, we use a five-decade time series from an Alaskan lake to explore effects of climate change on growth and reproduction of a widely distributed lacustrine fish, the three-spine stickleback (Gasterosteus aculeatus). We used multivariate autoregressive state-space (MARSS) models to describe trends in the mean length for multiple size classes and to explore the influence of physical (date of ice breakup, surface water temperature) and biological (density of con- and heterospecifics) factors. As predicted, mean size of age 1 and older fish at the end of the growing season increased across years with earlier ice breakup and warmer temperatures. In contrast, mean size of age 0 fish decreased over time. Overall, lower fish density and warmer water temperatures were associated with larger size for all cohorts. Earlier ice breakup was associated with larger size for age 1 and older fish but, paradoxically, with smaller size of age 0 fish. To explore this latter result, we used mixing models on age 0 size distributions, which revealed an additional cohort in years with early ice breakup, lowering the mean size of age 0 fish. Moreover, early ice breakup was associated with earlier breeding, evidenced by earlier capture of age 0 fish. Our results suggest that early ice breakup altered both timing and frequency of breeding; three-spine stickleback spawned earlier and more often in response to earlier ice breakup date. While previous studies have shown the influence of changing conditions in northern lakes on breeding timing and growth, this is the first to document increased breeding frequency, highlighting another pathway by which climate change can alter the ecology of northern lakes. © 2016 John Wiley & Sons Ltd.

Possible contribution of ice-sheet/lithosphere interactions to past glaciological changes in Greenland

NASA Astrophysics Data System (ADS)

Alley, R. B.; Parizek, B. R.; Anandakrishnan, S.; Pollard, D.; Stevens, N. T.; Pourpoint, M.

2017-12-01

Ice-lithosphere interactions may have influenced the history of ice-sheet sensitivity to climate change. The Greenland ice sheet (GIS) is sensitive to warming, and is likely to be largely removed if subjected to relatively small additional temperature increases. The recent report (Schaefer et al., 2016, Nature) of near-complete GIS removal under modest Pleistocene forcing suggests that GIS sensitivity may be even greater than generally modeled, but lack of major Holocene retreat is more consistent with existing models. As shown by Stevens et al. (2016, JGR), peak lithospheric flexural stresses associated with ice-age GIS cycling are of the same order as dike-driving stresses in plutonic systems, and migrate over ice-age cycles. The full analysis by Stevens et al. suggests the possibility that the onset of cyclic ice-sheet loading allowed deep melt associated with the passage of the Icelandic hot spot beneath Greenland to work up though the crust to or near the base of the ice sheet, helping explain the anomalous geothermal heat fluxes observed at the head of the Northeast Greenland Ice Stream and elsewhere in the northern part of GIS. If ice-age cycling aided extraction of an existing reservoir of melted rock, then geothermal heat flux would have risen with the onset of extraction and migration, but with a subsequent fall associated with reservoir depletion. Simple parameterized flow-model simulations confirm intuition that a higher geothermal flux makes deglaciation easier, with the northern part of the ice sheet especially important. Large uncertainties remain in quantification, but we suggest the hypothesis that, following the onset of ice-age cycling, deglaciation of the GIS first became easier and then more difficult in response to feedbacks involving the ice sheet and the geological system beneath. In turn, this suggests that evidence of past deglaciation under moderate forcing is consistent with existing ice-sheet models.

The NASA Altitude Wind Tunnel (AWT): Its role in advanced icing research and development

NASA Technical Reports Server (NTRS)

Blaha, B. J.; Shaw, R. J.

1985-01-01

Currently experimental aircraft icing research is severely hampered by limitations of ground icing simulation facilities. Existing icing facilities do not have the size, speed, altitude, and icing environment simulation capabilities to allow accurate studies to be made of icing problems occurring for high speed fixed wing aircraft and rotorcraft. Use of the currently dormant NASA Lewis Altitude Wind Tunnel (AWT), as a proposed high speed propulsion and adverse weather facility, would allow many such problems to be studied. The characteristics of the AWT related to adverse weather simulation and in particular to icing simulation are discussed, and potential icing research programs using the AWT are also included.

NASA Iced Aerodynamics and Controls Current Research

NASA Technical Reports Server (NTRS)

Addy, Gene

2009-01-01

This slide presentation reviews the state of current research in the area of aerodynamics and aircraft control with ice conditions by the Aviation Safety Program, part of the Integrated Resilient Aircraft Controls Project (IRAC). Included in the presentation is a overview of the modeling efforts. The objective of the modeling is to develop experimental and computational methods to model and predict aircraft response during adverse flight conditions, including icing. The Aircraft icing modeling efforts includes the Ice-Contaminated Aerodynamics Modeling, which examines the effects of ice contamination on aircraft aerodynamics, and CFD modeling of ice-contaminated aircraft aerodynamics, and Advanced Ice Accretion Process Modeling which examines the physics of ice accretion, and works on computational modeling of ice accretions. The IRAC testbed, a Generic Transport Model (GTM) and its use in the investigation of the effects of icing on its aerodynamics is also reviewed. This has led to a more thorough understanding and models, both theoretical and empirical of icing physics and ice accretion for airframes, advanced 3D ice accretion prediction codes, CFD methods for iced aerodynamics and better understanding of aircraft iced aerodynamics and its effects on control surface effectiveness.

The deglacial history of NW Alexander Island, Antarctica, from surface exposure dating

NASA Astrophysics Data System (ADS)

Johnson, Joanne S.; Everest, Jeremy D.; Leat, Philip T.; Golledge, Nicholas R.; Rood, Dylan H.; Stuart, Finlay M.

2012-03-01

Recent changes along the margins of the Antarctic Peninsula, such as the collapse of the Wilkins Ice Shelf, have highlighted the effects of climatic warming on the Antarctic Peninsula Ice Sheet (APIS). However, such changes must be viewed in a long-term (millennial-scale) context if we are to understand their significance for future stability of the Antarctic ice sheets. To address this, we present nine new cosmogenic 10Be exposure ages from sites on NW Alexander Island and Rothschild Island (adjacent to the Wilkins Ice Shelf) that provide constraints on the timing of thinning of the Alexander Island ice cap since the last glacial maximum. All but one of the 10Be ages are in the range 10.2-21.7 ka, showing a general trend of progressive ice-sheet thinning since at least 22 ka until 10 ka. The data also provide a minimum estimate (490 m) for ice-cap thickness on NW Alexander Island at the last glacial maximum. Cosmogenic 3He ages from a rare occurrence of mantle xenoliths on Rothschild Island yield variable ages up to 46 ka, probably reflecting exhumation by periglacial processes.

500,000-year temperature record challenges ice age theory

USGS Publications Warehouse

Snow, K. Mitchell

1994-01-01

Just outside the searing heat of Death Valley lies Devils Hole (fig. 1), a fault-created cave that harbors two remnants of the Earth's great ice ages. The endangered desert pupfish (Cyprinodon diabolis) has long made its home in the cave. A 500,000-year record of the planet's climate that challenges a widely accepted theory explaining the ice ages also has been preserved in Devils Hole.

Past and future ice age initiation: the role of an intrinsic deep-ocean millennial oscillation

NASA Astrophysics Data System (ADS)

Johnson, R. G.

2014-05-01

This paper offers three interdependent contributions to studies of climate variation: (1) the recognition and analysis of an intrinsic millennial oceanic oscillation that affects both Northern and Southern high latitude climates, (2) The recognition of an oceanographic switch to ice-free seas west of Greenland that explains the initiation of the Last Ice Age, and (3) an analysis of the effect of increasing salinity in the seas east of Greenland that suggests the possibility of the initiation of an ice age threshold climate in the near future. In the first contribution the millennial oscillation in the flow of the North Atlantic Drift reported by Bond et al. (1997) is proposed to be part of a 1500 yr intrinsic deep ocean oscillation. This oscillation involves the exchange of North Atlantic intermediate-level deep water (NADW) formed in the seas east of Greenland with Antarctic Bottom Water formed in a shallow-water zone at the edge of the Antarctic continent. The concept of NADW formation is already well known, with details of the sinking water flowing out of the Greenland Sea observed by Smethie et al. (2000) using chlorofluorocarbon tracers. The concept of Antarctic Bottom Water formation is also already well established. However, its modulation by the changing fraction of NADW in the Southern Ocean, which I infer from the analysis of Weyl (1968), has not been previously discussed. The modulated lower-salinity Antarctic Bottom Water that reaches the northern North Atlantic then provides negative feedback for the cyclic variation of NADW formation as proposed here. This causes the 1500 yr bipolar oscillation. The feedback suggests the possible sinusoidal character of the proposed oscillation model. The model is consistent with the cooling of the Little Ice Age (Lamb, 1972, 1995), and it also correctly predicts NASA's observation of today's record maximum area of winter sea ice on the Southern Ocean and the present observed record low rate of Antarctic Bottom Water production cited by Broecker (2000). The sinusoidal form of this conceptual model is therefore reinforced by both old and new data, and provides insights into world-wide climate change. The second contribution of this paper is a hypothesis for the initiation of Pleistocene ice ages, typified by the Last Ice Age that began 120 000 yr BP. Instead of the classical Northern high-latitude summer cooling caused by orbital precession and changes in Earth's axis inclination, this hypothesis proposes the sudden onset of year-round ice-free seas west of Greenland, with greatly increased precipitation in the ice sheet nucleation regions of Baffin Island, northern Quebec, and Labrador. Devon Island ice-core studies by Koerner at al. (1988) and deep-sea sediment data reported by Fillon (1985) support the concept of ice-free seas west of Greenland and imply the initial meteorological conditions that are proposed here. These conditions are consistent with the heavy precipitation inferred by Adkins et al. (1997) from deep-sea sediment data. The changes in northeastern Canada were accompanied by quite cold conditions in northern Europe, inferred by Field et al. (1994) from tree pollen data. The European cooling was probably caused by loss of the recurring Iceland low-pressure system due to the dominant effect of a frequent stronger low-pressure system over the Labrador Sea, as postulated in this paper. The key to ice-free seas west of Greenland is the loss of the near-surface stratification that normally enables sea ice to freeze. Using the high-resolution European Space Agency's ENVISAT system, I have monitored the flows through the Nares Strait and found that the dominant southward flow of lower density polar water into Baffin Bay correlated with the growing area of seasonal sea ice forming early in the winter in the Bay near the southern end of the Strait. This implies that low-salinity polar water was the cause of the stratification. A search for the cause of the stratification loss then became a search for the cause of the loss of the southward flow of polar water. The loss could have occurred if denser and more saline Atlantic water replaced the polar water in-flow. Medieval historical records suggest that an analogous partial replacement probably did occur during the early medieval climatic optimum, with some warmer Atlantic water removing the thick perennial sea ice along Greenland's north coast. The NADW formation rate and the Spitsbergen-Atlantic Current (SAC) flow were then near maximum values. I hypothesize that enough of the thick perennial sea ice along Greenland's north coast was removed by the penetration of the SAC flow into the polar ocean to enable a medieval voyage eastward along the coast in AD 1118. This voyage is implied by an old map record showing Greenland realistically as an island. An even stronger SAC flow associated with a stronger maximum in the 1500 yr intrinsic oscillation of the oceanic system was the likely trigger for the initial conditions of ice-sheet growth when the Last Ice Age began. The third contribution of this paper is the hypothesis that modern society's activities might cause a repetition of the transition to an ice age threshold climate within one or two decades from 2013. This possibility depends on a continuing increase of salinity in the seas east of Greenland, with a corresponding increase of NADW formation and the SAC flow. The increase is currently being driven by the increasing rate of the saline Mediterranean outflow that contributes to the North Atlantic Drift. The rate increase is a consequence of the increasing salinity of the Mediterranean Sea as reported by European oceanographers (Science, 279, 483-484, 1998). The rising salinity of the Mediterranean and its increasing outflow is attributed to the diversion of nearly all the in-flowing rivers for irrigation. A further substantial salinity increase should occur with the loss of all perennial polar sea ice possibly within one or two decades from 2013 if the present trend of loss continues. The trend is displayed on the University of Illinois internet site: http://arctic.atmos.uiuc.edu/cryosphere/. The increasing salinity of the Greenland Sea is now reflected in an increasing northward winter penetration by the SAC flow. According to Lamb (1972), during the early 20th century at the time of maximum extension of sea ice in April, open water normally extended only as far north as the southern cape of Spitsbergen at about 76.6° N. But in Aprils of 2013 and 2014, open water extended 380 km farther northward to the north coast of Spitsbergen. When the SAC was running strongly to replace sinking NADW in February of 2014, I observed open water extending about 730 km north from the cape into the polar ocean to latitude 83° N, where the penetration of the SAC flow was beginning to obstruct the southward flow of polar water. Even greater seasonal extensions of the SAC flow are expected with an additional Greenland Sea salinity increase after the loss of all perennial polar sea ice. This could cut off southward movement of polar water through the Fram Strait during much of the winter, and send annual pulses of the denser Atlantic water of the SAC flow into the sea north of Greenland. If these annual pulses begin to occur and allow enough denser Atlantic water to flow southward through the Nares Strait, the Baffin Bay stratification would be lost and a switch to an ice age threshold would occur. The severity of the resulting cold regional climate might have a disruptive effect on higher-latitude societies.

Aerodynamic Classification of Swept-Wing Ice Accretion

NASA Technical Reports Server (NTRS)

Diebold, Jeff M.; Broeren, Andy P.; Bragg, Michael B.

2013-01-01

The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current stateof- the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice and spanwise-ridge ice. In the case of horn ice it is shown that a further subclassification of "nominally 3D" or "highly 3D" horn ice may be necessary. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.

Aerodynamic Classification of Swept-Wing Ice Accretion

NASA Technical Reports Server (NTRS)

Diebold, Jeff M.; Broeren, Andy P.; Bragg, Michael B.

2013-01-01

The continued design, certification and safe operation of swept-wing airplanes in icing conditions rely on the advancement of computational and experimental simulation methods for higher fidelity results over an increasing range of aircraft configurations and performance, and icing conditions. The current state-of-the-art in icing aerodynamics is mainly built upon a comprehensive understanding of two-dimensional geometries that does not currently exist for fundamentally three-dimensional geometries such as swept wings. The purpose of this report is to describe what is known of iced-swept-wing aerodynamics and to identify the type of research that is required to improve the current understanding. Following the method used in a previous review of iced-airfoil aerodynamics, this report proposes a classification of swept-wing ice accretion into four groups based upon unique flowfield attributes. These four groups are: ice roughness, horn ice, streamwise ice and spanwise-ridge ice. In the case of horn ice it is shown that a further subclassification of nominally 3D or highly 3D horn ice may be necessary. For all of the proposed ice-shape classifications, relatively little is known about the three-dimensional flowfield and even less about the effect of Reynolds number and Mach number on these flowfields. The classifications and supporting data presented in this report can serve as a starting point as new research explores swept-wing aerodynamics with ice shapes. As further results are available, it is expected that these classifications will need to be updated and revised.

Millennial-scale variability in dust deposition, marine export production, and nutrient consumption in the glacial subantarctic ocean (Invited)

NASA Astrophysics Data System (ADS)

Martinez-Garcia, A.; Sigman, D. M.; Anderson, R. F.; Ren, H. A.; Hodell, D. A.; Straub, M.; Jaccard, S.; Eglinton, T. I.; Haug, G. H.

2013-12-01

Based on the limitation of modern Southern Ocean phytoplankton by iron and the evidence of higher iron-bearing dust fluxes to the ocean during ice ages, it has been proposed that iron fertilization of Southern Ocean phytoplankton contributed to the reduction in atmospheric CO2 during ice ages. In the Subantarctic zone of the Atlantic Southern Ocean, glacial increases in dust flux and export production have been documented, supporting the iron fertilization hypothesis. However, these observations could be interpreted alternatively as resulting from the equatorward migration of Southern Ocean fronts during ice ages if the observed productivity rise was not accompanied by an increase in major nutrient consumption. Here, new 230Th-normalized lithogenic and opal fluxes are combined with high-resolution biomarker measurements to reconstruct millennial-scale changes in dust deposition and marine export production in the subantarctic Atlantic over the last glacial cycle. In the same record foraminifera-bound nitrogen isotopes are used to reconstruct ice age changes in surface nitrate utilization, providing a comprehensive test of the iron fertilization hypothesis. Elevation in foraminifera-bound δ15N, indicating more complete nitrate consumption, coincides with times of surface cooling and greater dust flux and export production. These observations indicate that the ice age Subantarctic was characterized by iron fertilized phytoplankton growth. The resulting strengthening of the Southern Ocean's biological pump can explain the ~40 ppm lowering of CO2 that characterizes the transitions from mid-climate states to full ice age conditions as well as the millennial-scale atmospheric CO2 fluctuations observed within the last ice age

Do physical maturity and birth date predict talent in male youth ice hockey players?

PubMed

Sherar, Lauren B; Baxter-Jones, Adam D G; Faulkner, Robert A; Russell, Keith W

2007-06-01

The aim of this study was to examine the relationships among biological maturity, physical size, relative age (i.e. birth date), and selection into a male Canadian provincial age-banded ice hockey team. In 2003, 619 male ice hockey players aged 14-15 years attended Saskatchewan provincial team selection camps, 281 of whom participated in the present study. Data from 93 age-matched controls were obtained from the Saskatchewan Pediatric Bone Mineral Accrual Study (1991-1997). During the initial selection camps, birth dates, heights, sitting heights, and body masses were recorded. Age at peak height velocity, an indicator of biological maturity, was determined in the controls and predicted in the ice hockey players. Data were analysed using one-way analysis of variance, logistic regression, and a Kolmogorov-Smirnov test. The ice hockey players selected for the final team were taller, heavier, and more mature (P < 0.05) than both the unselected players and the age-matched controls. Furthermore, age at peak height velocity predicted (P < 0.05) being selected at the first and second selection camps. The birth dates of those players selected for the team were positively skewed, with the majority of those selected being born in the months January to June. In conclusion, team selectors appear to preferentially select early maturing male ice hockey players who have birth dates early in the selection year.

Cosmogenic nuclide age estimate for Laurentide Ice Sheet recession from the terminal moraine, New Jersey, USA, and constraints on latest Pleistocene ice sheet history

USGS Publications Warehouse

Corbett, Lee B.; Bierman, Paul R.; Stone, Byron D.; Caffee, Marc W.; Larsen, Patrick L.

2017-01-01

The time at which the Laurentide Ice Sheet reached its maximum extent and subsequently retreated from its terminal moraine in New Jersey has been constrained by bracketing radiocarbon ages on preglacial and postglacial sediments. Here, we present measurements of in situ produced 10Be and 26Al in 16 quartz-bearing samples collected from bedrock outcrops and glacial erratics just north of the terminal moraine in north-central New Jersey; as such, our ages represent a minimum limit on the timing of ice recession from the moraine. The data set includes field and laboratory replicates, as well as replication of the entire data set five years after initial measurement. We find that recession of the Laurentide Ice Sheet from the terminal moraine in New Jersey began before 25.2±2.1 ka (10Be, n=16, average, 1 standard deviation). This cosmogenic nuclide exposure age is consistent with existing limiting radiocarbon ages in the study area and cosmogenic nuclide exposure ages from the terminal moraine on Martha’s Vineyard ~300 km to the northeast. The age we propose for Laurentide Ice Sheet retreat from the New Jersey terminal position is broadly consistent with regional and global climate records of the last glacial maximum termination and records of fluvial incision.

Leads and lags between the Antarctic temperature and carbon dioxide during the last deglaciation

NASA Astrophysics Data System (ADS)

Gest, Léa; Parrenin, Frédéric; Raynaud, Dominique; Fudge, Tyler J.

2017-04-01

To understand causal relationships in past climate variations, it is essential to have accurate chronologies of paleoclimate records. Ice cores in Antarctica provide important paleoclimate variables, such as local temperature and global atmospheric CO2. Unfortunately, temperature is recorded in the ice while CO2 is recorded in the enclosed air bubbles. The ages of the former and of the latter are different since air is trapped at 50-120 m below the surface. For the last deglacial warming, 18,000 to 11,000 years ago, Parrenin et al. (Science, 2013) inferred that CO2 and Antarctic temperature started to increase in phase while CO2 lagged temperature at the beginning of the Holocene period. However, this study suffers from various uncertainties that we tried to address in the current study. First, Antarctic temperature was inferred from a stack of 5 Antarctic ice cores that were not always accurately synchronized. Here we use a stack of 4 Antarctic ice cores which are all accurately synchronized thanks to volcanic peak matching. Second, Parrenin et al. (Science, 2013) used a relatively low-resolution CO2 record from the EPICA Dome C ice core. Here, we use the more recent and higher resolution CO2 record from the West Antarctic Ice Sheet Divide ice core. Third, the air trapping depth was deduced on the low accumulation EPICA Dome C ice core using the gravitational enrichment of the δ15N isotopes and assuming a zero convective depth, a hypothesis that was not proved. Here, we use the higher accumulation WAIS Divide ice core, where the ice-air age shift is one order of magnitude smaller, and therefore better constrained. Finally, we use an improved mathematical method to infer break points in the Antarctic temperature and atmospheric CO2 records. We find that, at the onset of the last deglaciation and the onset of the Bølling-Allerød period, the phasing between CO2 and Antarctic temperature is negligible within a range of 130 years. Then CO2 slightly leads by 200 ± 90 years at the onset of the Younger-Dryas period. Finally, Antarctic temperature significantly leads by 460 ± 95 years at the onset of the Holocene period. Our results further supports the hypothesis of no convective zone at EPICA Dome C during the last deglaciation, as assumed by Parrenin et al. (Climate of the past, 2012, On the gas-ice depth difference (Delta depth) along the EPICA Dome C ice core)

Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water.

PubMed

Darelius, E; Fer, I; Nicholls, K W

2016-08-02

The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing.

Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water

PubMed Central

Darelius, E.; Fer, I.; Nicholls, K. W.

2016-01-01

The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing. PMID:27481659

Geomorphic influences of the Little Ice Age glacial advance on selected hillslope systems in Nordfjord, Western Norway (Erdalen and Bødalen valleys)

NASA Astrophysics Data System (ADS)

Laute, Katja; Beylich, Achim A.

2010-05-01

Hillslopes in glacially formed landscapes are typically characterized by talus cones developed beneath free rock faces. Studying hillslopes as sedimentary source, storage and transfer zones as well as surface processes acting on hillslopes since the end of the deglaciation is of importance in order to gain a better understanding of the complex sedimentary source-to-sink fluxes in cold climate environments. Hillslopes function as a key component within the geomorphic process response system. Large areas of the Norwegian fjord landscapes are covered by hillslopes and are characterized by the influences of the glacial inheritance. This PhD project is part of the NFR funded SedyMONT-Norway project within the ESF TOPO-EUROPE SedyMONT (Timescales of sediment dynamics, climate and topographic change in mountain landscapes) programme. The focus of this study is on geomorphic influences of the Little Ice Age glacial advance on postglacial hillslope systems in four distinct headwater areas of the Erdalen and Bødalen valleys in the Nordfjord valley-fjord system (inner Nordfjord, Western Norway). Both valleys can be described as steep, U-shaped and glacier-fed, subarctic tributary valleys. Approximately 14% of the 49 km2 large headwater areas of Erdalen are occupied by hillslope deposits and 41% by rock surfaces; in Bødalen hillslope deposits occupy 12% and rock surfaces occupy 38% of the 42 km2 large headwater areas. The main aims of this study are (i) to analyze and compare the morphometric characteristics as well as the composition of hillslope systems inside and outside of the Little Ice Age glacial limit, (ii) to detect possible changes within the mass balances of these hillslope systems, (iii) to identify the type and intensity of currently acting hillslope processes as well as (iv) to determine possible sediment sources and delivery pathways within the headwater areas of the catchments. The process-based approach includes orthophoto- and topographical map interpretation, hillslope profile surveying, photo monitoring, geomorphological mapping as well as GIS and DEM computing. Two appropriate hillslope test sites within each headwater area are selected in order to follow the main aims of this study. The designed monitoring instrumentation of the slope test sites includes nets for collecting freshly accumulated rockfall debris, stone tracer lines for measuring surface movements, wooden sticks for monitoring of slow surface creep movements and peg lines for depth-integrated measurements of slow mass movements. In addition, remote site cameras for monitoring rapid mass movement events (avalanches, slush- and debris flows) and slope wash traps for analyzing slope wash denudation are installed and measurements of solute concentrations at small hillslope drainage creeks for investigating the role of chemical denudation are conducted. Measurements of morphometric characteristics and longitudinal profiles along the main axis of the talus cones are carried out at each test site. The manually obtained longitudinal profile data are combined with data derived from a DEM in order to generate complete longitudinal hillslope profiles reaching from the apex until the slope foot. Preliminary results show a steepening trend of the talus cones located inside the Little Ice Age glacier limit which is due to erosion during the Little Ice Age glacial advance. In addition, some of these talus cones are characterized by a recognizable more complex talus cone morphometry and composition, resulting from implementation of Little Ice Age glacier side moraines. The combination of (i) steepened talus cones and (ii) complex composition seems to increase currently acting hillslope processes which leads to a higher sediment delivery from these slopes as compared to hillslopes outside the Little Ice Age glacier limit. The implementation of moraine material but also the increased intensity of denudative processes has a recognizable influence on the mass balance of the hillslope systems inside the Little Ice Age glacier limit. Research on the complex development of hillslope systems from a postglacial to contemporary time perspective in combination with analyses of contemporary sedimentary fluxes contributes to a better understanding of hillslopes acting as source, storage and transfer zones in cold climate environments (paraglacial systems).

Multi-Decadal Averages of Basal Melt for Ross Ice Shelf, Antarctica Using Airborne Observations

NASA Astrophysics Data System (ADS)

Das, I.; Bell, R. E.; Tinto, K. J.; Frearson, N.; Kingslake, J.; Padman, L.; Siddoway, C. S.; Fricker, H. A.

2017-12-01

Changes in ice shelf mass balance are key to the long term stability of the Antarctic Ice Sheet. Although the most extensive ice shelf mass loss currently is occurring in the Amundsen Sea sector of West Antarctica, many other ice shelves experience changes in thickness on time scales from annual to ice age cycles. Here, we focus on the Ross Ice Shelf. An 18-year record (1994-2012) of satellite radar altimetry shows substantial variability in Ross Ice Shelf height on interannual time scales, complicating detection of potential long-term climate-change signals in the mass budget of this ice shelf. Variability of radar signal penetration into the ice-shelf surface snow and firn layers further complicates assessment of mass changes. We investigate Ross Ice Shelf mass balance using aerogeophysical data from the ROSETTA-Ice surveys using IcePod. We use two ice-penetrating radars; a 2 GHz unit that images fine-structure in the upper 400 m of the ice surface and a 360 MHz radar to identify the ice shelf base. We have identified internal layers that are continuous along flow from the grounding line to the ice shelf front. Based on layer continuity, we conclude that these layers must be the horizons between the continental ice of the outlet glaciers and snow accumulation once the ice is afloat. We use the Lagrangian change in thickness of these layers, after correcting for strain rates derived using modern day InSAR velocities, to estimate multidecadal averaged basal melt rates. This method provides a novel way to quantify basal melt, avoiding the confounding impacts of spatial and short-timescale variability in surface accumulation and firn densification processes. Our estimates show elevated basal melt rates (> -1m/yr) around Byrd and Mullock glaciers within 100 km from the ice shelf front. We also compare modern InSAR velocity derived strain rates with estimates from the comprehensive ground-based RIGGS observations during 1973-1978 to estimate the potential magnitude of strain-driven thickness changes over four decades. Combining maps of basal melt rate with radar derived basal reflectivity, we identify regions that are undergoing melting and freezing and provide a comprehensive understanding of how ocean processes may be changing the base of Ross Ice Shelf in recent decades.

Little Ice Age Fluctuations of Quelccaya Ice Cap, Peru

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T.

2009-12-01

A record of the past extents of Quelccaya Ice Cap (QIC) provides valuable information about tropical climate change from late glacial to recent time. Here, we examine the timing and regional significance of fluctuations of QIC during the Little Ice Age (LIA; ~1300-1850 AD). One prominent set of moraines, known as the Huancane I moraines, is located ~1 km from the present-day western ice cap margin and provides a near-continuous outline of the most recent advance of QIC. This moraine set was radiocarbon dated (~298 ± 134 and 831 ± 87 yr BP) by Mercer and Palacios (1977) and presented as some of the first evidence for cooling in the tropics during the Little Ice Age. Recent field investigations in the QIC region focused on refining the chronology of the Huancane I moraines. In 2008, new stratigraphic sections exposed by local lake-flooding events revealed multiple layers of peat within the Huancane I moraines. In both 2008 and 2009, samples were obtained for 10Be dating of boulders on Huancane I moraines. A combination of radiocarbon and 10Be ages indicate that the Huancane I moraines were deposited by ice cap expansion after ~3800 yr BP and likely by multiple advances at approximately 1000, 600, 400, and 200 yr BP. Radiocarbon and 10Be chronologies of the Huancane I moraines are compared with the Quelccaya ice core records (Thompson et al., 1985; 1986; 2006). Accumulation data from the ice core records are interpreted to indicate a significant wet period at ~1500-1700 AD followed by a significant drought at ~1720-1860 AD. We examine ice marginal fluctuations during these times to determine influence of such events on the ice cap extent.

Seismic stratigraphic interpretations suggest that sectors of the central and western Ross Sea were near or above sea level during earliest Oligocene time

NASA Astrophysics Data System (ADS)

Sorlien, C. C.; Sauli, C.; De Santis, L.; Luyendyk, B. P.; Wardell, N.; Davis, S. M.; Wilson, D. S.; Brazell, S.; Bartek, L., III; Bart, P. J.

2016-12-01

Most of West Antarctica has been interpreted as a high-elevation plateau that has subsided between about 100 Ma and present. Ross Sea was characterized by subaerial ridges and islands up to mid-Cenozoic time. It was in such an environment that Oligocene ice sheets and glaciers advanced and retreated within Ross Embayment. The extent to which Oligocene ice affected the embayment north of the current ice shelf has not been established, with either ice caps on islands, or broad glaciers affecting basins having been proposed. We used all available data from the Seismic Data Library System to interpret stratigraphic horizons through most of Ross Sea. A new 3D velocity model was constructed for the western 2/3 of Ross Sea. Stratigraphic age control was provided by deep scientific coring, including Deep Sea Drilling Program sites, the Cape Roberts Drilling Program, and published correlations to ANDRILL sites. The correlation with recent drill records and much additional seismic reflection data allowed a new interpretation of Ross Sea, which differs from the previous comprehensive seismic stratigraphic interpretation (ANTOSTRAT 1995). Sedimentary rocks of given ages are twice as deep within Terror Rift in westernmost Ross Sea in our interpretation. In contrast, acoustic basement is 1 km shallower in part of Central Trough. The 200 km-wide smooth acoustic basement on Central High eroded sub-aerially until it subsided differentially through sea level toward the centers of Cretaceous and Cenozoic rifts. If the subsiding basins were kept filled with sediment eroded by Oligocene ice sheets, then the age the strata aggrading above the planar rock platform date subsidence through sea level at each location. Using such an assumption, much of central and western Ross Sea was near or above sea level during earliest Oligocene time. These assumptions will be tested by backstripping and thermal subsidence models.

Rate and style of ice stream retreat constrained by new surface-exposure ages: The Minch, NW Scotland

NASA Astrophysics Data System (ADS)

Bradwell, Tom; Small, David; Fabel, Derek; Dove, Dayton; Cofaigh, Colm O.; Clark, Chris; Consortium, Britice-Chrono

2016-04-01

Chronologically constrained studies of former ice-sheet extents and dynamics are important for understanding past cryospheric responses and modelling future ice-sheet and sea-level change. As part of the BRITICE-CHRONO project, we present new geomorphological and chronological data from a marine-terminating ice stream system in NW Europe that operated during the Late Weichselian Glaciation. A suite of 51 cosmogenic-nuclide exposure ages from ice sheet moraines and glacially transported boulders constrain the maximum extent of the ice sheet on the continental shelf (~28 ka BP) and its subsequent retreat, between ~27 and 16 ka BP, into a large marine embayment (ca. 7000 km2; the Minch, NW Scotland). Recently acquired swath bathymetry and acoustic sub-bottom profiler data reveal several large transverse grounding-zone wedges up to 40 m thick and 5 km wide with diagnostic acoustic-facies architecture. These seabed sediment wedges mark former quasi-stable positions of grounded marine-terminating ice-stream fronts; their size and thickness suggest long-lived stillstands of the order of centuries. Statistically significant clusters of exposure ages from glacial deposits on islands and intervening headlands shed important new light on the age of these marine grounding-zone wedges and, by inference, the rate and timing of Minch palaeo-ice stream retreat. We find strong evidence for episodic ice stream retreat on the continental shelf between ~28-24 ka BP, in the outer Minch between ~24-22 ka BP, and in the central Minch between 22-18.5 ka BP. In contrast, final ice stream deglaciation (<18 ka) across the deepest parts of the inner Minch embayment, was probably rapid and uninterrupted - with the ice sheet margin at or close to the present-day coastline in NW Scotland by 16.1 ka BP. It is hoped that these results will form the empirical basis for future ice-sheet modelling of this dynamically sensitive sector of the British-Irish Ice Sheet.

Reassessment of ice-age cooling of the tropical ocean and atmosphere

USGS Publications Warehouse

Hostetler, S.W.; Mix, A.C.

1999-01-01

The CLIMAP project's reconstruction of past sea surface temperature inferred limited ice-age cooling in the tropical oceans. This conclusion has been controversial, however, because of the greater cooling indicated by other terrestrial and ocean proxy data. A new faunal sea surface temperature reconstruction, calibrated using the variation of foraminiferal species through time, better represents ice-age faunal assemblages and so reveals greater cooling than CLIMAP in the equatorial current systems of the eastern Pacific and tropical Atlantic oceans. Here we explore the climatic implications of this revised sea surface temperature field for the Last Glacial Maximum using an atmospheric general circulation model. Relative to model results obtained using CLIMAP sea surface temperatures, the cooler equatorial oceans modify seasonal air temperatures by 1-2??C or more across parts of South America, Africa and southeast Asia and cause attendant changes in regional moisture patterns. In our simulation of the Last Glacial Maximum, the Amazon lowlands, for example, are cooler and drier, whereas the Andean highlands are cooler and wetter than the control simulation. Our results may help to resolve some of the apparent disagreements between oceanic and continental proxy climate data. Moreover, they suggest a wind-related mechanism for enhancing the export of water vapour from the Atlantic to the Indo-Pacific oceans, which may link variations in deep-water production and high-latitude climate changes to equatorial sea surface temperatures.

Transient and asymptotic behavior in a regular network model for the ice-albedo feedback under thermal forcing

NASA Astrophysics Data System (ADS)

Mueller-Stoffels, M.; Wackerbauer, R.

2010-12-01

The Arctic ocean and sea ice form a feedback system which plays an important role in the global climate. Variations of the global ice and snow distribution have a significant effect on the planetary albedo which governs the absorption of shortwave radiation. The complexity of highly parametrized GCMs makes it very difficult to assess single feedback processes in the climate system without the concurrent use of simple models where the physics are understood [1][2][3]. We introduce a complex systems model to investigate thermodynamic feedback processes in an Arctic ice-ocean layer. The ice-ocean layer is represented as a regular network of coupled cells. The state of each cell is determined by its energy content, which also defines the phase of the cell. The energy transport between cells is described with nonlinear and heterogeneous diffusion constants. And the time-evolution of the ice-ocean is driven by shortwave, longwave and lateral oceanic and atmospheric thermal forcing. This model is designed to study the stability of an ice cover under various heat intake scenarios. The network structure of the model allows to easily introduce albedo heterogeneities due to aging ice, wind blown snow cover, and ice movement to explore the time-evolution and pattern formation (melt ponds) processes in the Arctic sea ice. The solely thermodynamic model exhibits two stable states; one in the perennially ice covered domain and one in the perennially open water domain. Their existence is due to the temperature dependence of the longwave radiative budget. Transition between these states can be forced via lateral heat fluxes. During the transition from the ice covered to the open water stable state the ice albedo feedback effects are manifested as an increased warming rate of the ice cover together with enhanced seasonal energy oscillations. In the current model realization seasonal ice cover is present as a transient state only. Furthermore, the model exhibits hysteresis between the ice covered and the open water state when varying the lateral atmospheric (or oceanic) heat intake. Once the ice-ocean layer has transitioned from the ice covered to the open water stable state significant cooling (reduction of lateral fluxes) is necessary to return to the ice covered stable state. We also find that ocean heat fluxes are more efficient than atmospheric heat fluxes to melt Arctic sea ice; only small portions of heat entering from the bottom of the ice-ocean layer induce already a transition to the stable asymptotic state with perennial open water. This indicates that ocean currents, understood as heat conveyors, can play a significant role in melting continuous ice covers. This is consistent with the findings of Shimada et al. for the Canada basin [4]. References: [1] S. Bony et al., How well do we understand and evaluate climate change feedback processes?, J of Climate 19, 3445 (2006). [2]I. Eisenman and J.S. Wettlaufer, Nonlinear threshold behavior during the loss of Arctic sea ice, PNAS 106, 28 (2009). [3]A.S. Thorndike, A Toy Model Linking Atmospheric and Thermal Radiation and Sea Ice Growth, JGR 97, 9401 (1992). [4] K. Shimada et al., Paci[|#12#|]c Ocean inflow: Influence on catastrophic reduction of sea ice cover in the Arctic Ocean, GRL 33, L08605 (2006).

Late-glacial and Holocene history of changes in Quelccaya Ice Cap, Peru

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.; Finkel, R. C.

2008-12-01

Quelccaya Ice Cap in the southeastern Peruvian Andes (~13-14° S latitude) is an icon for climate change. Its rapidly receding outlet, Qori Kalis Glacier, has been monitored since the 1970's. Cores from Quelccaya Ice Cap provide high-resolution information about temperature and precipitation during the past 1,500 years. We extend the understanding of past changes in Quelccaya Ice Cap based on mapping and dating of glacial moraines and associated deposits. Our results include fifty 10Be ages of moraines and bedrock as well as twenty-nine 14C ages of organic material associated with moraines. These results form the basis of a chronology of changes in Quelccaya Ice Cap from ~16,000 yr BP to late Holocene time. Results from 10Be and 14C dating indicate that Quelccaya Ice Cap experienced a significant advance at 12,700-11,400 yr BP. Subsequent to this advance, the ice margin deposited at least three recessional moraine sets. Quelccaya Ice Cap receded to near its present-day margin by ~10,000 yr BP. Neoglacial advances began by ~3,000 yr BP and culminated with a maximum advance during the Little Ice Age. This chronology fits well with prior work which indicates a restricted Quelccaya Ice Cap during middle Holocene time. Moreover, the overlap between moraine and ice core data for the last 1,500 years provides a unique opportunity to assess the influences of temperature and precipitation on past ice cap extents.

Development of 3D Ice Accretion Measurement Method

NASA Technical Reports Server (NTRS)

Lee, Sam; Broeren, Andy P.; Addy, Harold E., Jr.; Sills, Robert; Pifer, Ellen M.

2012-01-01

Icing wind tunnels are designed to simulate in-flight icing environments. The chief product of such facilities is the ice accretion that forms on various test articles. Documentation of the resulting ice accretion key piece of data in icing-wind-tunnel tests. Number of currently used options for documenting ice accretion in icing-wind-tunnel testing.

Constraints on Lobate Debris Apron Evolution and Rheology from Numerical Modeling of Ice Flow

NASA Astrophysics Data System (ADS)

Parsons, R.; Nimmo, F.

2010-12-01

Recent radar observations of mid-latitude lobate debris aprons (LDAs) have confirmed the presence of ice within these deposits. Radar observations in Deuteronilus Mensae have constrained the concentration of dust found within the ice deposits to <30% by volume based on the strength of the returned signal. In addition to constraining the dust fraction, these radar observations can measure the ice thickness - providing an opportunity to more accurately estimate the flow behavior of ice responsible for the formation of LDAs. In order to further constrain the age and rheology of LDA ice, we developed a numerical model simulating ice flow under Martian conditions using results from ice deformation experiments, theory of ice grain growth based on terrestrial ice cores, and observational constraints from radar profiles and laser altimetry. This finite difference model calculates the LDA profile shape as it flows over time assuming no basal slip. In our model, the ice rheology is determined by the concentration of dust which influences the ice grain size by pinning the ice grain boundaries and halting ice grain growth. By varying the dust fraction (and therefore the ice grain size), the ice temperature, the subsurface slope, and the initial ice volume we are able to determine the combination of parameters that best reproduce the observed LDA lengths and thicknesses over a period of time comparable to crater age dates of LDA surfaces (90 - 300 My, see figure). Based on simulations using different combinations of ice temperature, ice grain size, and basal slope, we find that an ice temperature of 205 K, a dust volume fraction of 0.5% (resulting in an ice grain size of 5 mm), and a flat subsurface slope give reasonable model LDA ages for many LDAs in the northern mid-latitudes of Mars. However, we find that there is no single combination of dust fraction, temperature, and subsurface slope which can give realistic ages for all LDAs suggesting that all or some of these variables are spatially heterogeneous. We conclude that there are important regional differences in either the amount of dust mixed in with the ice, or in the presence of a basal slope below the LDA ice. Alternatively, the ice temperature and/or timing of ice deposition may vary significantly between different mid-latitude regions. a) Topographic profiles plotted every 200 My (thin, solid lines) from a 1 Gy simulation of ice flow for an initial ice deposit (thick, solid line) 5 km long and 1 km thick using an ice temperature of 205 K and a dust fraction, φ, of 0.047%. A MOLA profile of an LDA at 38.6oN, 24.3oE (dashed line) is shown for comparison. b) Final profiles for simulations lasting 100 My using temperatures of 195, 205 and 215 K illustrate the effect of both temperature and increasing the dust volume fraction to 1.2% (resulting in an ice grain size of 1 mm).

Rotorcraft aviation icing research requirements: Research review and recommendations

NASA Technical Reports Server (NTRS)

Peterson, A. A.; Dadone, L.; Bevan, A.

1981-01-01

The status of rotorcraft icing evaluation techniques and ice protection technology was assessed. Recommendations are made for near and long term icing programs that describe the needs of industry. These recommended programs are based on a consensus of the major U.S. helicopter companies. Specific activities currently planned or underway by NASA, FAA and DOD are reviewed to determine relevance to the overall research requirements. New programs, taking advantage of current activities, are recommended to meet the long term needs for rotorcraft icing certification.

Evidence for stabilization of the ice-cemented cryosphere in earlier martian history: Implications for the current abundance of groundwater at depth on Mars

NASA Astrophysics Data System (ADS)

Weiss, David K.; Head, James W.

2017-05-01

The present-day martian mean annual surface temperature is well below freezing at all latitudes; this produces a near-surface portion of the crust that is below the freezing point of water for > 2 consecutive years (defined as permafrost). This permafrost layer (i.e., the cryosphere) is a few to tens of km thick depending on latitude. Below the base of the permafrost (i.e., the cryosphere), groundwater is stable if it exists, and can increase and decrease in abundance as the freezing isotherm rises and falls. Where water is available, ice fills the pore space within the cryosphere; this region is known as the ice-cemented cryosphere (ICC). The potential for a large reservoir of pore ice beneath the surface has been the subject of much discussion: previous studies have demonstrated that the theoretical thickness of the martian cryosphere in the Amazonian period ranges from up to ∼9 km at the equator to ∼10-22 km at the poles. The total thickness of ice that might fill the pore space within the cryosphere (the ICC), however, remains unknown. A class of martian crater, the Hesperian-Amazonian-aged single-layered ejecta crater, is widely accepted as having formed by impact into an ice-cemented target. Although the target structure related to the larger multiple-layered ejecta craters remains uncertain, they have recently been interpreted to be formed by impact crater excavation below the ice-cemented target, and here we tentatively adopt this interpretation in order to infer the thickness of the ice-cemented cryosphere. Our global examination of the excavation depths of these crater populations points to a Hesperian-Amazonian-aged ice-cemented cryosphere that is ∼1.3 km thick at the equator, and ∼2.3 km thick at the poles (corresponding to a global equivalent water layer of ∼200 m assuming ∼20% pore ice at the surface). To explore the implications of this result on the martian climatic and hydrologic evolution, we then assess the surface temperature, atmospheric pressure, obliquity, and surface heat flux conditions under which the downward-propagating cryosphere freezing front matches the inferred ice-cemented cryosphere. The thermal models which can best reproduce the inferred ice-cemented cryosphere occur for obliquities between 25° and 45° and CO2 atmospheric pressures ≤600 mbar, but require increased heat fluxes and surface temperatures/pressures relative to the Amazonian period. Because the inferred ice-cemented cryosphere is much thinner compared with Amazonian-aged cryosphere thermal models, we suggest that the ice-cemented cryosphere ceased growing when it exhausted the underlying groundwater supply (i.e., ICC stabilization) in a more ancient period in Mars geologic history. Our thermal analysis suggests that this ICC stabilization likely occurred sometime before or at ∼3.0-3.3 Ga (during or before the Late Hesperian or Early Amazonian period). If groundwater remained below the ICC during the earlier Late Noachian period, our models predict that mean annual surface temperatures during this time were ≥212-227 K. If the Late Noachian had a pure CO2 atmosphere, this places a minimum bound on the Late Noachian atmospheric pressure of ≥390-850 mbar. These models suggest that deep groundwater is not abundant or does not persist in the subsurface of Mars today, and that diffusive loss of ice from the subsurface has been minimal.

Deglacial and Holocene sea-ice variability north of Iceland and response to ocean circulation changes

NASA Astrophysics Data System (ADS)

Xiao, Xiaotong; Zhao, Meixun; Knudsen, Karen Luise; Sha, Longbin; Eiríksson, Jón; Gudmundsdóttir, Esther; Jiang, Hui; Guo, Zhigang

2017-08-01

Sea-ice conditions on the North Icelandic shelf constitute a key component for the study of the climatic gradients between the Arctic and the North Atlantic Oceans at the Polar Front between the cold East Icelandic Current delivering Polar surface water and the relatively warm Irminger Current derived from the North Atlantic Current. The variability of sea ice contributes to heat reduction (albedo) and gas exchange between the ocean and the atmosphere, and further affects the deep-water formation. However, lack of long-term and high-resolution sea-ice records in the region hinders the understanding of palaeoceanographic change mechanisms during the last glacial-interglacial cycle. Here, we present a sea-ice record back to 15 ka (cal. ka BP) based on the sea-ice biomarker IP25, phytoplankton biomarker brassicasterol and terrestrial biomarker long-chain n-alkanols in piston core MD99-2272 from the North Icelandic shelf. During the Bølling/Allerød (14.7-12.9 ka), the North Icelandic shelf was characterized by extensive spring sea-ice cover linked to reduced flow of warm Atlantic Water and dominant Polar water influence, as well as strong meltwater input in the area. This pattern showed an anti-phase relationship with the ice-free/less ice conditions in marginal areas of the eastern Nordic Seas, where the Atlantic Water inflow was strong, and contributed to an enhanced deep-water formation. Prolonged sea-ice cover with occasional occurrence of seasonal sea ice prevailed during the Younger Dryas (12.9-11.7 ka) interrupted by a brief interval of enhanced Irminger Current and deposition of the Vedde Ash, as opposed to abruptly increased sea-ice conditions in the eastern Nordic Seas. The seasonal sea ice decreased gradually from the Younger Dryas to the onset of the Holocene corresponding to increasing insolation. Ice-free conditions and sea surface warming were observed for the Early Holocene, followed by expansion of sea ice during the Mid-Holocene.

Impact of the Agulhas Return Current on the glacial Subantarctic region in the South Indian Ocean

NASA Astrophysics Data System (ADS)

Ikehara, M.; Crosta, X.; Manoj, M. C.

2017-12-01

The Southern Ocean has played an important role in the evolution of the global climate system. The Southern Ocean circulation is dominated by the Antarctic Circumpolar Current (ACC), the world's longest and largest current system. Sea ice coverage on sea surface strongly affects the climate of the Southern Hemisphere through its impacts on the energy and gas budget, on the atmospheric circulation, on the hydrological cycle, and on the biological productivity. The Agulhas Return Current (ARC) originates from the Agulhas Current, the major western boundary current in the Indian Ocean, and transports heat from subtropical to subantarctic region. It's thought that the Agulhas leakage from the Indian Ocean to the Atlantic was reduced for the last glacial due to a northward shift of the westerlies and ACC, however, there are still unknown yet how the ARC was responded to the reduced Agulhas leakage. A piston core DCR-1PC was collected from the Del Caño Rise (46°S, 44°E, 2632m), Indian sector of the Southern Ocean. Core site located in the Subantarctic region between the Subtropical Front (STF) and Subantarctic Front (SAF). Age model of the core was established by radiocarbon dating of planktic foraminifer Globorotalia bulloides and oxygen isotope stratigraphy of benthic foraminifers Cibicidoides wuellerstorfi and Melonis bareelanus. Sediment of DCR-1PC show the cyclic changes of diatom/carbonate ooze sedimentation corresponding to Southern Ocean fronts' migrations on glacial-interglacial timescales. Records of ice-rafted debris (IRD) and oxygen isotope in planktic foraminfer G. bulloides suggest that the melting of sea ice was significantly increased during the last glacial maximum (LGM) in the Subantarctic surface water. Diatom assemblage based summer SST also shows the relative warmer condition in the Subantarctic during the LGM. These results might be explained by the strong influence of the Agulhas Return Current during the LGM in the Subantarctic. The reduced Agulhas leakage due to a northward shift of the westerlies and ACC impacted significantly on sea ice melting in the glacial Subantarctic region in the South Indian Ocean.

Studies of Antarctic Sea Ice Concentrations from Satellite Data and Their Applications

NASA Technical Reports Server (NTRS)

Comiso, Josefino C.; Steffen, Konrad; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

Large changes in the sea ice cover have been observed recently. Because of the relevance of such changes to climate change studies it is important that key ice concentration data sets used for evaluating such changes are interpreted properly. High and medium resolution visible and infrared satellite data are used in conjunction with passive microwave data to study the true characteristics of the Antarctic sea ice cover, assess errors in currently available ice concentration products, and evaluate the applications and limitations of the latter in polar process studies. Cloud-free high resolution data provide valuable information about the natural distribution, stage of formation, and composition of the ice cover that enables interpretation of the large spatial and temporal variability of the microwave emissivity of Antarctic sea ice. Comparative analyses of co-registered visible, infrared and microwave data were used to evaluate ice concentrations derived from standard ice algorithms (i.e., Bootstrap and Team) and investigate the 10 to 35% difference in derived values from large areas within the ice pack, especially in the Weddell Sea, Amundsen Sea, and Ross Sea regions. Landsat and OLS data show a predominance of thick consolidated ice in these areas and show good agreement with the Bootstrap Algorithm. While direct measurements were not possible, the lower values from the Team Algorithm results are likely due to layering within the ice and snow and/or surface flooding, which are known to affect the polarization ratio. In predominantly new ice regions, the derived ice concentration from passive microwave data is usually lower than the true percentage because the emissivity of new ice changes with age and thickness and is lower than that of thick ice. However, the product provides a more realistic characterization of the sea ice cover, and are more useful in polar process studies since it allows for the identification of areas of significant divergence and polynya activities. Also, heat and salinity fluxes are proportionately increased in these areas compared to those from the thicker ice areas. A slight positive trend in ice extent and area from 1978 through 2000 is observed consistent with slight continental cooling during the period. However, the confidence in this result is only moderate because the overlap period for key instruments is just one month and the sensitivity to changes in sensor characteristics, calibration and threshold for the ice edge is quite high.

The Sea Level Fingerprints of Global Change

NASA Astrophysics Data System (ADS)

Mitrovica, J. X.; Hay, C.; Kopp, R. E., III; Morrow, E.

2014-12-01

It may be difficult to persuade those living in northern Europe that the sea level changes that their coastal communities face depends less on the total melting of polar ice sheets and glaciers than on the individual contributions to this total. In particular, melting of a specific ice sheet or mountain glacier drives deformational, gravitational and rotational perturbations to the Earth system that are manifest in a unique geometry, or fingerprint, of global sea level change. For example, melting from the Greenland Ice Sheet equivalent to 1 mm/yr of global mean sea level (GMSL) rise will lead to sea level rise of ~0 mm/yr in Dublin, ~0.2 mm/yr in Amsterdam, ~0.4 mm/yr in Boston and ~1.2 mm/yr in Cape Town. In contrast, if the same volume of ice melted from the West Antarctic Ice Sheet, all of the above sites would experience a sea level rise in the range 1.1-1.2 mm/yr. These fingerprints of modern ice melting, together with ocean thermal expansion and dynamic effects, and the ongoing signal from glacial isostatic adjustment in response to the last ice age, combine to produce a sea level field with significant geographic variability. In this talk I will highlight an analysis of global tide gauge records that takes full advantage of this variability to estimate both GMSL and the sources of meltwater over the last century, and to project GMSL to the end of the current century.

The usefulness and reliability of fitness testing protocols for ice hockey players: a literature review.

PubMed

Nightingale, Steven C; Miller, Stuart; Turner, Anthony

2013-06-01

Ice hockey, like most sports, uses fitness testing to assess athletes. This study reviews the current commonly used fitness testing protocols for ice hockey players, discussing their predictive values and reliability. It also discusses a range of less commonly used measures and limitations in current testing protocols. The article concludes with a proposed testing program suitable for ice hockey players.

Morphological, Physiological and Skating Performance Profiles of Male Age-Group Elite Ice Hockey Players.

PubMed

Allisse, Maxime; Sercia, Pierre; Comtois, Alain-Steve; Leone, Mario

2017-09-01

The purpose of this study was to describe the evolution of morphological, physiological and skating performance profiles of elite age-group ice hockey players based on repeated measures spread over one season. In addition, the results of fitness tests and training programs performed in off-ice conditions and their relationship with skating performance were analyzed. Eighteen high level age-group ice hockey players (13.1 ± 0.6 years) were assessed off and on-ice at the beginning and at the end of the hockey season. A third evaluation was also conducted at the beginning of the following hockey season. The players were taller, heavier, and showed bone breadths and muscle girths above the reference population of the same age. Muscular variables improved significantly during and between the two hockey seasons (p < 0.05). However, maximal aerobic power improved only during the off-season. All skating performance tests exhibited significant enhancements during the hockey season, but not during the off-season where some degradation was observed. Finally, weak observed variances (generally <20% of the explained variance) between physiological variables measured off-ice and on-ice skating performance tests indicated important gaps, both in the choice of the off-ice assessment tools as well as in training methods conventionally used. The reflection on the best way to assess and train hockey players certainly deserves to be continued.

Morphological, Physiological and Skating Performance Profiles of Male Age-Group Elite Ice Hockey Players

PubMed Central

Allisse, Maxime; Sercia, Pierre; Comtois, Alain-Steve; Leone, Mario

2017-01-01

Abstract The purpose of this study was to describe the evolution of morphological, physiological and skating performance profiles of elite age-group ice hockey players based on repeated measures spread over one season. In addition, the results of fitness tests and training programs performed in off-ice conditions and their relationship with skating performance were analyzed. Eighteen high level age-group ice hockey players (13.1 ± 0.6 years) were assessed off and on-ice at the beginning and at the end of the hockey season. A third evaluation was also conducted at the beginning of the following hockey season. The players were taller, heavier, and showed bone breadths and muscle girths above the reference population of the same age. Muscular variables improved significantly during and between the two hockey seasons (p < 0.05). However, maximal aerobic power improved only during the off-season. All skating performance tests exhibited significant enhancements during the hockey season, but not during the off-season where some degradation was observed. Finally, weak observed variances (generally <20% of the explained variance) between physiological variables measured off-ice and on-ice skating performance tests indicated important gaps, both in the choice of the off-ice assessment tools as well as in training methods conventionally used. The reflection on the best way to assess and train hockey players certainly deserves to be continued. PMID:28828080

Spontaneous abrupt climate change due to an atmospheric blocking-sea-ice-ocean feedback in an unforced climate model simulation.

PubMed

Drijfhout, Sybren; Gleeson, Emily; Dijkstra, Henk A; Livina, Valerie

2013-12-03

Abrupt climate change is abundant in geological records, but climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70 °N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds changed from north to south, terminating the event with similar abruptness to its onset. Our results imply that only climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of abrupt climate change.

SEA-ICE INFLUENCE ON ARCTIC COASTAL RETREAT.

USGS Publications Warehouse

Reimnitz, Erk; Barnes, P.W.

1987-01-01

Recent studies document the effectiveness of sea ice in reshaping the seafloor of the inner shelf into sharp-relief features, including ice gouges with jagged flanking ridges, ice-wallow relief, and 2- to 6-m-deep strudel-scour craters. These ice-related relief forms are in disequilibrium with classic open-water hydraulic processes and thus are smoothed over by waves and currents in one to two years. Such alternate reworking of the shelf by ice and currents - two diverse types of processes, which in the case of ice wallow act in unison-contributes to sediment mobility and, thus, to sediment loss from the coast and inner shelf. The bulldozing action by ice results in coast-parallel sediment displacement. Additionally, suspension of sediment by frazil and anchor ice, followed by ice rafting, can move large amounts of bottom-derived materials. Our understanding of all these processes is insufficient to model Arctic coastal processes.

Correlating Ice Cores from Quelccaya Ice Cap with Chronology from Little Ice Age Glacial Extents

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.

2010-12-01

Proxy records indicate Southern Hemisphere climatic changes during the Little Ice Age (LIA; ~1300-1850 AD). In particular, records of change in and around the tropical latitudes require attention because these areas are sensitive to climatic change and record the dynamic interplay between hemispheres (Oerlemans, 2005). Despite this significance, relatively few records exist for the southern tropics. Here we present a reconstruction of glacial fluctuations of Quelccaya Ice Cap (QIC), Peruvian Andes, from pre-LIA up to the present day. In the Qori Kalis valley, extensive sets of moraines exist beginning with the 1963 AD ice margin (Thompson et al., 2006) and getting progressively older down valley. Several of these older moraines can be traced and are continuous with moraines in the Challpa Cocha valley. These moraines have been dated at <1050-1350-AD (Mercer and Palacios, 1977) and interpreted to have been deposited during the Little Ice Age. We present a new suite of surface exposure and radiocarbon dates collected in 2008 and 2009 that constrain the ages of these moraines. Preliminary 10Be ages of boulder surfaces atop the moraines range from ~350-1370 AD. Maximum and minimum-limiting radiocarbon ages bracketing the moraines are ~0-1800 AD. The chronology of past ice cap extents are correlated with ice core records from QIC which show an accumulation increase during ~1500-1700 AD and an accumulation decrease during ~1720-1860 AD (Thompson et al., 1985; 1986; 2006). In addition, other proxy records from Peru and the tropics are correlated with the records at QIC as a means to understand climate conditions during the LIA. This work forms the basis for future modeling of the glacial system during the LIA at QIC and for modeling of past temperature and precipitation regimes at high altitude in the tropics.

The little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap.

PubMed

Thompson, L G; Mosley-Thompson, E; Dansgaard, W; Grootes, P M

1986-10-17

The analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent. Annual variations in visible dust layers, oxygen isotopes, microparticle concentrations, conductivity, and identification of the historical (A.D. 1600) Huaynaputina ash permit accurate dating and time-scale verification. The fact that the Little Ice Age (about A.D. 1500 to 1900) stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event.

Comparison of In-Situ, Model and Ground Based In-Flight Icing Severity

NASA Technical Reports Server (NTRS)

Serke, David J.; Johnston, Christopher J.; Adriaansen, Daniel R.; Reehorst, Andrew L.; Politovich, Marcia K.; Wolff, Cory A.; McDonough, Frank

2011-01-01

Currently there are two systems that are being developed for the detection of in-flight icing: NASA Icing Remote Sensing System (NIRSS) and current Icing Product (CIP). In-flight icing (IFI) is a significant hazard for the aviation industry. IFI occurs when supercooled liquid water (SLW) comes in contact with, and freezes to, the leading surfaces of an aircraft. Significantly alters aircraft aerodynamic properties: increases the amount of drag on an aircraft and reduces the lift. The objective of this study is to examine how the testbed NIRSS icing severity product and the operational CIP severity product compare to PIREPs of icing severity, and how the NIRSS and CIP compare to each other.

Tropical Andean and African glacier extent through the Holocene assessed with proglacial in situ 14C and 10Be measurements

NASA Astrophysics Data System (ADS)

Vickers, A. C.; Shakun, J. D.; Goehring, B. M.; Kelly, M. A.; Jackson, M. S.; Jomelli, V.

2017-12-01

We present measurements of the in situ cosmogenic radionuclides 14C and 10Be from recently exposed proglacial bedrock samples at the margin of the Quelccaya Ice Cap in Peru (n=5) and the Rwenzori mountains in Africa (n=3) to calculate cumulative exposure, burial, and erosion histories at these sites over the Holocene. The Holocene history (11 ka - present) of tropical glaciers gives important context to their observed retreat over the last century, insight into their sensitivity to climate forcing, and constraints on past climate change. Paired in situ 14C/10Be methods are used to exploit the multiple controls on nuclide concentrations and their differing half-lives (5730 years vs 1.38 Myr). In particular, the concentrations of both 14C and 10Be increase with exposure and decrease with glacial erosion; however,14C decreases not only due to glacial erosion, but also in appreciable amounts due to radio-decay during periods of burial as short as 800 years. Our results show similarities at both sites, with moderately high 10Be concentrations but 14C/10Be ratios approximately one-third of the production value, suggesting that both sites experienced several thousand years of exposure followed by burial during the mid-to-late Holocene. Our results are consistent with recently exposed subfossil plant remains at the Quelccaya margin that imply ice extended beyond its current position since 5.2 ka We will also present 10Be ages of several boulders from probable Little Ice Age moraines of the Charquini Sur Glacier in Bolivia (n=2) and Ritacuba Negro Glacier in Colombia (n=4) to better understand the timing of Little Ice Age advances in the tropical Andes.

The Holocene history of Nares Strait: Transition from glacial bay to Arctic-Atlantic throughflow

USGS Publications Warehouse

Jennings, Anne E.; Sheldon, Christina; Cronin, Thomas M.; Francus, Pierre; Stoner, Joseph; Andrews, John

2011-01-01

Retreat of glacier ice from Nares Strait and other straits in the Canadian Arctic Archipelago after the end of the last Ice Age initiated an important connection between the Arctic and the North Atlantic Oceans, allowing development of modern ocean circulation in Baffin Bay and the Labrador Sea. As low-salinity, nutrient-rich Arctic Water began to enter Baffin Bay, it contributed to the Baffin and Labrador currents flowing southward. This enhanced freshwater inflow must have influenced the sea ice regime and likely is responsible for poor calcium carbonate preservation that characterizes the Baffin Island margin today. Sedimentologic and paleoceanographic data from radiocarbon-dated core HLY03-05GC, Hall Basin, northern Nares Strait, document the timing and paleoenvironments surrounding the retreat of waning ice sheets from Nares Strait and opening of this connection between the Arctic Ocean and Baffin Bay. Hall Basin was deglaciated soon before 10,300 cal BP (calibrated years before present) and records ice-distal sedimentation in a glacial bay facing the Arctic Ocean until about 9,000 cal BP. Atlantic Water was present in Hall Basin during deglaciation, suggesting that it may have promoted ice retreat. A transitional unit with high ice-rafted debris content records the opening of Nares Strait at approximately 9,000 cal BP. High productivity in Hall Basin between 9,000 and 6,000 cal BP reflects reduced sea ice cover and duration as well as throughflow of nutrient-rich Pacific Water. The later Holocene is poorly resolved in the core, but slow sedimentation rates and heavier carbon isotope values support an interpretation of increased sea ice cover and decreased productivity during the Neoglacial period.

Ice-dammed lateral lake and epishelf lake insights into Holocene dynamics of Marguerite Trough Ice Stream and George VI Ice Shelf, Alexander Island, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Davies, Bethan J.; Hambrey, Michael J.; Glasser, Neil F.; Holt, Tom; Rodés, Angél; Smellie, John L.; Carrivick, Jonathan L.; Blockley, Simon P. E.

2017-12-01

We present new data regarding the past dynamics of Marguerite Trough Ice Stream, George VI Ice Shelf and valley glaciers from Ablation Point Massif on Alexander Island, Antarctic Peninsula. This ice-free oasis preserves a geological record of ice stream lateral moraines, ice-dammed lakes, ice-shelf moraines and valley glacier moraines, which we dated using cosmogenic nuclide ages. We provide one of the first detailed sediment-landform assemblage descriptions of epishelf lake shorelines. Marguerite Trough Ice Stream imprinted lateral moraines against eastern Alexander Island at 120 m at Ablation Point Massif. During deglaciation, lateral lakes formed in the Ablation and Moutonnée valleys, dammed against the ice stream in George VI Sound. Exposure ages from boulders on these shorelines yielded ages of 13.9 to 9.7 ka. Following recession of the ice stream, George VI Ice Shelf formed in George VI Sound. An epishelf lake formed at 15-20 m asl in Ablation and Moutonnée valleys, dated from 9.4 to 4.6 ka, suggesting that the lake was stable and persistent for some 5000 years. Lake-level lowering occurred after this, with the lake level at 12 m at 3.1 ± 0.4 ka and at 5 m asl today. A readvance of the valley glaciers on Alexander Island at 4.4 ± 0.7 ka is recorded by valley glacier moraines overlying epishelf lake sediments. We speculate that the glacier readvance, which occurred during a period of warmth, may have been caused by a dynamic response of the glaciers to a lowering in surface elevation of George VI Ice Shelf.

Circulation and water properties in the landfast ice zone of the Alaskan Beaufort Sea

NASA Astrophysics Data System (ADS)

Weingartner, Thomas J.; Danielson, Seth L.; Potter, Rachel A.; Trefry, John H.; Mahoney, Andy; Savoie, Mark; Irvine, Cayman; Sousa, Leandra

2017-09-01

Moorings, hydrography, satellite-tracked drifters, and high-frequency radar data describe the annual cycle in circulation and water properties in the landfast ice zone (LIZ) of the Alaskan Beaufort Sea. Three seasons, whose duration and characteristics are controlled by landfast ice formation and ablation, define the LIZ: ;winter;, ;break-up;, and ;open-water;. Winter begins in October with ice formation and ends in June when rivers commence discharging. Winter LIZ ice velocities are zero, under-ice currents are weak ( 5 cm s-1), and poorly correlated with winds and local sea level. The along-shore momentum balance is between along-shore pressure gradients and bottom and ice-ocean friction. Currents at the landfast ice-edge are swift ( 35 cm s-1), wind-driven, with large horizontal shears, and potentially unstable. Weak cross-shore velocities ( 1 cm s-1) imply limited exchanges between the LIZ and the outer shelf in winter. The month-long break-up season (June) begins with the spring freshet and concludes when landfast ice detaches from the bottom. Cross-shore currents increase, and the LIZ hosts shallow ( 2 m), strongly-stratified, buoyant and sediment-laden, under-ice river plumes that overlie a sharp, 1 m thick, pycnocline across which salinity increases by 30. The plume salt balance is between entrainment and cross-shore advection. Break-up is followed by the 3-month long open-water season when currents are swift (≥20 cm s-1) and predominantly wind-driven. Winter water properties are initialized by fall advection and evolve slowly due to salt rejection from ice. Fall waters and ice within the LIZ derive from local rivers, the Mackenzie and/or Chukchi shelves, and the Arctic basin.

A common and optimized age scale for Antarctic ice cores

NASA Astrophysics Data System (ADS)

Parrenin, F.; Veres, D.; Landais, A.; Bazin, L.; Lemieux-Dudon, B.; Toye Mahamadou Kele, H.; Wolff, E.; Martinerie, P.

2012-04-01

Dating ice cores is a complex problem because 1) there is a age shift between the gas bubbles and the surrounding ice 2) there are many different ice cores which can be synchronized with various proxies and 3) there are many methods to date the ice and the gas bubbles, each with advantages and drawbacks. These methods fall into the following categories: 1) Ice flow (for the ice) and firn densification modelling (for the gas bubbles); 2) Comparison of ice core proxies with insolation variations (so-called orbital tuning methods); 3) Comparison of ice core proxies with other well dated archives; 4) Identification of well-dated horizons, such as tephra layers or geomagnetic anomalies. Recently, an new dating tool has been developped (DATICE, Lemieux-Dudon et al., 2010), to take into account all the different dating information into account and produce a common and optimal chronology for ice cores with estimated confidence intervals. In this talk we will review the different dating information for Antarctic ice cores and show how the DATICE tool can be applied.

Dynamic ocean topography from CryoSat-2: examining recent changes in ice-ocean stress and advancing a theory for Beaufort Gyre stabilization

NASA Astrophysics Data System (ADS)

Dewey, S.; Morison, J.; Kwok, R.; Dickinson, S.; Morison, D.; Andersen, R.

2017-12-01

Model and sparse observational evidence has shown the ocean current speed in the Beaufort Gyre to have increased and recently stabilized. However, full-basin altimetric observations of dynamic ocean topography (DOT) and ocean surface currents have yet to be applied to the dynamics of gyre stabilization. DOT fields from retracked CryoSat-2 retrievals in Arctic Ocean leads have enabled us to calculate 2-month average ocean geostrophic currents. These currents are crucial to accurately computing ice-ocean stress, especially because they have accelerated so that their speed rivals that of the overlying sea ice. Given these observations, we can shift our view of the Beaufort Gyre as a system in which the wind drives the ice and the ice drives a passive ocean to a system with the following feedback: After initial input of energy by wind, ice velocity decreases due to water drag and internal ice stress and the ocean drives the ice, reversing Ekman pumping and decelerating the gyre. This reversal changes the system from a persistently convergent regime to one in which freshwater is released from the gyre and doming of the gyre decreases, without any change in long-term average wind stress curl. Through these processes, the ice-ocean stress provides a key feedback in Beaufort Gyre stabilization.

Climate hazards, adaptation and "resilience" of societies (early Little Ice Age, west of France).

NASA Astrophysics Data System (ADS)

Athimon, Emmanuelle; Maanan, Mohamed

2016-04-01

Over the past ten to fifteen years, climate hazards and adaptation have received more attention due to the current climate change. Climate historians have gathered strong evidence that the world's climate has evolved over the past millennium and one of the most significant changes took place during the Little Ice Age. Recently, a set of questions has emerged: what were the effects of the Little Ice Age on human's societies? How did humans adapt to these climate changes? How did they react to extreme weather-related events? Using examples of climate hazards from the West of France during the beginning of the Little Ice Age (xivth-xviith centuries) such as storms, flooding, drought, harsh winters, the poster aims at showing how the past societies can constitute a source of inspiration for present ones. Through schemas, this research exposes the system's rebound capacity, points out the importance of the historical depth in research on human's adaptation and resilience and shows the value of integrating a historical approach. It reveals that History contributes to the knowledge of the relationship between societies and climate hazards. Data on climate hazards and adaptation of societies stem from historical sources such as chronicles, diaries, books of accounts, records of cities repairs. To protect themselves and their goods, medieval and modern societies had developed specific skills, practices and strategies. From the xivth to the xviiith century, there is an increase of defense by dikes in the low Loire, as for example the construction of those amongst Longué and Ponts-de-Cé between the early xivth century and 1407. The French kingdom's authorities also tried increasingly to provide technical, material, logistical and fiscal support: for instance, during the winter 1564-1565, several bridges have been destroyed by a river flooding in Nantes. The King Charles IX then offered to people of Nantes part of the funds from taxes on the main activities such as the exports of wine or salt to finance the restoration of the bridges. So it appears that these societies have been able to adapt through a collective memory, a lifestyle, a significant perception of risks, a territory management, the construction of infrastructures, etc. Key words : Little Ice Age, West of France, climate hazards, resilience, adaptation. This work was supported by grants from the Fondation de France through the research program « Quels littoraux pour demain? ».

Did glacially induced TPW end the ice age? A reanalysis

NASA Astrophysics Data System (ADS)

Chan, Ngai-Ham; Mitrovica, Jerry X.; Daradich, Amy

2015-09-01

Previous studies of Earth rotation perturbations due to ice-age loading have predicted a slow secular drift of the rotation axis relative to the surface geography (i.e. true polar wander, TPW) of order of several degrees over the Plio-Pleistocene. It has been argued that this drift and the change in the geographic distribution of solar insolation that it implies may have been responsible for important transitions in ice-age climate, including the termination of ice-age cycles.We use a revised rotational stability theory that incorporates a more accurate treatment of the Earth's background ellipticity to reconsider this issue, and demonstrate that the net displacement of the pole predicted in earlier studies disappears. This more muted polar motion is due to two factors: first, the revised theory no longer predicts the permanent shift in the rotation axis, or the so-called `unidirectional TPW', that appears in the traditional stability theory; and, second, the increased background ellipticity incorporated in the revised predictions acts to reduce the normal mode amplitudes governing the motion of the pole. We conclude that ice-age-induced TPW was not responsible for the termination of the ice age. This does not preclude the possibility that TPW induced by mantle convective flow may have played a role in major Plio-Pleistocene climate transitions, including the onset of Northern Hemisphere glaciation.

Deep Radiostratigraphy of the East Antarctic Plateau: Connecting the Dome C and Vostok Ice Core Sites

NASA Technical Reports Server (NTRS)

Cavitte, Marie G. P.; Blankenship, Donald D.; Young, Duncan A.; Schroeder, Dustin M.; Parrenin, Frederic; Lemeur, Emmanuel; Macgregor, Joseph A.; Siegert, Martin J.

2016-01-01

Several airborne radar-sounding surveys are used to trace internal reflections around the European Project for Ice Coring in Antarctica Dome C and Vostok ice core sites. Thirteen reflections, spanning the last two glacial cycles, are traced within 200 km of Dome C, a promising region for million-year-old ice, using the University of Texas Institute for Geophysics High-Capacity Radar Sounder. This provides a dated stratigraphy to 2318 m depth at Dome C. Reflection age uncertainties are calculated from the radar range precision and signal-to-noise ratio of the internal reflections. The radar stratigraphy matches well with the Multichannel Coherent Radar Depth Sounder (MCoRDS) radar stratigraphy obtained independently. We show that radar sounding enables the extension of ice core ages through the ice sheet with an additional radar-related age uncertainty of approximately 1/3-1/2 that of the ice cores. Reflections are extended along the Byrd-Totten Glacier divide, using University of Texas/Technical University of Denmark and MCoRDS surveys. However, core-to-core connection is impeded by pervasive aeolian terranes, and Lake Vostok's influence on reflection geometry. Poor radar connection of the two ice cores is attributed to these effects and suboptimal survey design in affected areas. We demonstrate that, while ice sheet internal radar reflections are generally isochronal and can be mapped over large distances, careful survey planning is necessary to extend ice core chronologies to distant regions of the East Antarctic ice sheet.

Retention of ice-associated amphipods: possible consequences for an ice-free Arctic Ocean.

PubMed

Berge, J; Varpe, O; Moline, M A; Wold, A; Renaud, P E; Daase, M; Falk-Petersen, S

2012-12-23

Recent studies predict that the Arctic Ocean will have ice-free summers within the next 30 years. This poses a significant challenge for the marine organisms associated with the Arctic sea ice, such as marine mammals and, not least, the ice-associated crustaceans generally considered to spend their entire life on the underside of the Arctic sea ice. Based upon unique samples collected within the Arctic Ocean during the polar night, we provide a new conceptual understanding of an intimate connection between these under-ice crustaceans and the deep Arctic Ocean currents. We suggest that downwards vertical migrations, followed by polewards transport in deep ocean currents, are an adaptive trait of ice fauna that both increases survival during ice-free periods of the year and enables re-colonization of sea ice when they ascend within the Arctic Ocean. From an evolutionary perspective, this may have been an adaptation allowing success in a seasonally ice-covered Arctic. Our findings may ultimately change the perception of ice fauna as a biota imminently threatened by the predicted disappearance of perennial sea ice.

Satellite imagery of the onset of streaming flow of ice streams C and D, West Antarctica

USGS Publications Warehouse

Hodge, S.M.; Doppelhammer, S.K.

1996-01-01

Five overlapping Landsat multispectral scanner satellite images of the interior of the West Antarctic ice sheet were enhanced with principal component analysis, high-pass filtering, and linear contrast stretching and merged into a mosaic by aligning surface features in the overlap areas. The mosaic was registered to geodetic coordinates, to an accuracy of about 1 km, using the five scene centers as control points. The onset of streaming flow of two tributaries of ice stream C and one tributary of ice stream D is visible in the mosaic. The onset appears to occur within a relatively short distance, less than the width of the ice stream, typically at a subglacial topographic feature such as a step or ridge. The ice streams extend farther up into the interior than previously mapped. Ice stream D starts about 150 km from the ice divide, at an altitude of about 1500 m, approximately halfway up the convex-upward dome shape of the interior ice sheet. Ice stream D is relatively much longer than ice stream C, possibly because ice stream D is currently active whereas ice stream C is currently inactive. The grounded portion of the West Antarctic ice sheet is perhaps best conceptualized as an ice sheet in which ice streams are embedded over most of its area, with slow moving ice converging into fast moving ice streams in a widely distributed pattern, much like that of streams and rivers in a hydrologic basin. A relic margin appears to parallel most of the south margin of the tributary of ice stream D, separated from the active shear margin by about 10 km or less for a distance of over 200 km. This means there is now evidence for recent changes having occurred in three of the five major ice streams which drain most of West Antarctica (B, C, and D), two of which (B and D) are currently active.

Polar oceans in a changing climate.

PubMed

Barnes, David K A; Tarling, Geraint A

2017-06-05

Most of Earth's surface is blue or white, but how much of each would depend on the time of observation. Our planet has been through phases of snowball (all frozen), greenhouse (all liquid seas) and icehouse (frozen and liquid). Even during current icehouse conditions, the extent of ice versus water has changed considerably between ice ages and interglacial periods. Water has been vital for life on Earth and has driven and been influenced by transitions between greenhouse and icehouse. However, neither the possession of water nor having liquid and frozen seas are unique to Earth (Figure 1). Frozen water oceans on the moons Enceladus and Europa (and possibly others) and the liquid and frozen hydrocarbon oceans on Titan probably represent the most likely areas to find extraterrestrial life. We know very little about life in Earth's polar oceans, yet they are the engine of the thermohaline 'conveyor-belt', driving global circulation of heat, oxygen, carbon and nutrients as well as setting sea level through change in ice-mass balance. In regions of polar seas, where surface water is particularly cold and dense, it sinks to generate a tropic-ward flow on the ocean floor of the Pacific, Atlantic and Indian Oceans. Cold water holds more gas, so this sinking water exports O 2 and nutrients, thereby supporting life in the deep sea, as well as soaking up CO 2 from the atmosphere. Water from mid-depths at lower latitudes flows in to replace the sinking polar surface water. This brings heat. The poles are cold because they receive the least energy from the sun, and this extreme light climate varies on many different time scales. To us, the current warm, interglacial conditions seem normal, yet such phases have represented only ∼10% of Homo sapiens' existence. Variations in Earth's orbit (so called 'Milankovitch cycles') have driven cyclical alternation of glaciations (ice ages) and warmer interglacials. Despite this, Earth's polar regions have been our planet's most environmentally constant surface regions for several millions of years, with most land ice-covered and much of the ocean seasonally freezing. The two poles have much in common, such as light climate, temperature and water viscosity, winter calm and summer (iceberg and storm) disturbance and resources. However, they are also regions of striking contrasts: the Arctic Ocean is near surrounded by land compared with the Antarctic continent, which is surrounded by the Southern Ocean. Polar oceans contrast in size, age, isolation, depth, oceanography, biology and human factors, such as governance and human habitation. The simplest foodwebs with the smallest residents live on the 1% of Antarctica that is ice free, whilst the largest animals that have ever lived on Earth (Blue and Fin whales) feed in the Arctic and Southern Oceans. Copyright © 2017 Elsevier Ltd. All rights reserved.

Evidence for late Pliocene deglacial megafloods in the Gulf of Mexico

NASA Astrophysics Data System (ADS)

Wang, Z.; Gani, M. R.

2017-12-01

The paleoclimatic significance of giant sedimentary structures developed under unconfined Froude-supercritical sediment gravity flows in subaqueous settings is considerably under-examined. This research, for the first time, extensively documents >20-km-wide and 200-m-thick Plio-Pleistocene giant sediment waves in the northern Gulf of Mexico continental slope using 3D seismic data, showing waveform morphology in unprecedented detail. Published biostratigraphic data help constraining the geologic age of these deposits. The results of numerical and morphological analyses suggest that such large-scale bedforms were formed under sheet-like unconfined Froude-supercritical turbidity currents as cyclic steps. Paleohydraulic reconstruction (e.g., flow velocity, discharge, and unit flux), in association with other evidence like geologic age, published stable isotope records, and temporal rarity, points out that the responsible Froude-supercritical turbidity currents were most likely triggered by deglacial catastrophic outburst floods during the late Pliocene to early Pleistocene. Laurentide Ice Sheet outburst floods to the Gulf of Mexico have previously been documented based mainly on deep-sea cores during the last several interglacial episodes in the late Pleistocene. Our megaflood events constitute, by far, the oldest record of the glacial outburst floods during the Quaternary Ice Age anywhere in the world. This study suggests that such pervasive occurrence of large-scale sediment waves likely serve as a proxy for extreme events like catastrophic megafloods.

Protective role of vitamins E and C against oxidative stress caused by intermittent cold exposure in aging rat's frontoparietal cortex.

PubMed

Asha Devi, S; Manjula, K R; Subramanyam, M V V

2012-11-07

This study examined the role of vitamins E and C in combating oxidative stress (OS) caused by intermittent cold exposure (ICE) in the frontoparietal cortex (FPC) of adult (3 months), late-adult (12 months), middle-aged (18 months) and old (24 months) male Wistar rats. Each age group was divided into sub-groups, control (CON), cold-exposed at 5°C (C5), control supplementees (CON+S) and cold-exposed supplementees (C5+S). The supplement was a daily dose of 400mg vitamin C and 50I.U.of vitamin E/kg body weight. Cold exposure lasted 2h/day for 4 weeks. All age groups except the old showed an increase in the final body mass in the cold-exposed. The feeding efficiency was higher in the cold-exposed irrespective of age. OS as reflected in age-related increased levels of hydrogen peroxide, protein carbonyl, advanced oxidation protein products and malondialdehyde showed further increase with ICE in the FPC. However, vitamins E and C supplementation attenuated the ICE-induced OS. ICE depleted the levels of tissue vitamins E and C while supplementation resulted in increased levels. Further age emerged as a significant factor in ICE-induced stress and also the response to vitamins E and C supplementation. Behavioral studies are underway to examine the findings on ICE-induced oxidative injury in the FPC, and the prospects for using vitamins E and C in cold exposures in the aged. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

How and when to terminate the Pleistocene ice ages?

NASA Astrophysics Data System (ADS)

Abe-Ouchi, A.; Saito, F.; Kawamura, K.; Takahashi, K.; Raymo, M. E.; Okuno, J.; Blatter, H.

2015-12-01

Climate change with wax and wane of large Northern Hemisphere ice sheet occurred in the past 800 thousand years characterized by 100 thousand year cycle with a large amplitude of sawtooth pattern, following a transition from a period of 40 thousand years cycle with small amplitude of ice sheet change at about 1 million years ago. Although the importance of insolation as the ultimate driver is now appreciated, the mechanism what determines timing and strength of terminations are far from clearly understood. Here we show, using comprehensive climate and ice-sheet models, that insolation and internal feedbacks between the climate, the ice sheets and the lithosphere-asthenosphere system explain the 100,000-year periodicity. The responses of equilibrium states of ice sheets to summer insolation show hysteresis, with the shape and position of the hysteresis loop playing a key part in determining the periodicities of glacial cycles. The hysteresis loop of the North American ice sheet is such that after inception of the ice sheet, its mass balance remains mostly positive through several precession cycles, whose amplitudes decrease towards an eccentricity minimum. The larger the ice sheet grows and extends towards lower latitudes, the smaller is the insolation required to make the mass balance negative. Therefore, once a large ice sheet is established, a moderate increase in insolation is sufficient to trigger a negative mass balance, leading to an almost complete retreat of the ice sheet within several thousand years. We discuss further the mechanism which determine the timing of ice age terminations by examining the role of astronomical forcing and change of atmospheric carbon dioxide contents through sensitivity experiments and comparison of several ice age cycles with different settings of astronomical forcings.

Timing of the Late Paleozoic Ice Age: A Review of the Status Quo and New U-Pb Zircon Ages From Southern Gondwana

NASA Astrophysics Data System (ADS)

Mundil, R.; Griffis, N. P.; Keller, C. B.; Fedorchuk, N.; Montanez, I. P.; Isbell, J.; Vesely, F.; Iannuzzi, R.

2017-12-01

Throughout the Carboniferous and Permian Late Paleozoic Ice Age (LPIA), glaciations in southern Gondwana exerted a profound influence on global climate and environment, ocean chemistry, and the nature of sedimentary processes. The LPIA is widely regarded as an analogue for Pleistocene glaciations. Our understanding of the latter, as well as the validity of predictions for the future global climate and environment, depends therefore on our ability to reconstruct the LPIA. A robust chronostratigraphic framework built on high precision/high accuracy geochronology is crucial for the reconstruction of events and processes that occurred during the LPIA, particularly in the absence of high-resolution terrestrial biostratigraphic constraints that apply to both near- and far-field proxy records. The occurrence of volcaniclastic layers containing primary volcanic zircon at many levels throughout southern Gondwana makes such a reconstruction feasible, but complications inevitably arise due to the mixing of older age components with primary volcanic crystals, as well as the potential of unrecognized open system behavior to produce spurious younger ages. These pitfalls cause age dispersion that may be difficult to interpret, or is unrecognized if low precision geochronological techniques are used, resulting in inaccurate radioisotopic ages. Our current efforts in the Parana Basin (Southern Brazil) and the Karoo Basin (South Africa/Namibia) concentrate on building a robust and exportable chronostratigraphic framework based on U-Pb zircon CA-TIMS ages with sub-permil level precision combined with Bayesian approaches for resolving the eruption age of dispersed age spectra to facilitate the reconstruction of glaciogenic processes through the Carboniferous-Permian transition, as well as their implications for global sea level, atmospheric pCO2 and ocean chemistry. We will also review currently available geochronological data from contemporaneous Australian successions and their potential for robust correlations and paleo-environmental reconstruction.

A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea

NASA Astrophysics Data System (ADS)

Rabenstein, L.; Krumpen, T.; Hendricks, S.; Koeberle, C.; Haas, C.; Hoelemann, J. A.

2013-06-01

A combined interpretation of synthetic aperture radar (SAR) satellite images and helicopter electromagnetic (HEM) sea-ice thickness data has provided an estimate of sea-ice volume formed in Laptev Sea polynyas during the winter of 2007/08. The evolution of the surveyed sea-ice areas, which were formed between late December 2007 and middle April 2008, was tracked using a series of SAR images with a sampling interval of 2-3 days. Approximately 160 km of HEM data recorded in April 2008 provided sea-ice thicknesses along profiles that transected sea ice varying in age from 1 to 116 days. For the volume estimates, thickness information along the HEM profiles was extrapolated to zones of the same age. The error of areal mean thickness information was estimated to be between 0.2 m for younger ice and up to 1.55 m for older ice, with the primary error source being the spatially limited HEM coverage. Our results have demonstrated that the modal thicknesses and mean thicknesses of level ice correlated with the sea-ice age, but that varying dynamic and thermodynamic sea-ice growth conditions resulted in a rather heterogeneous sea-ice thickness distribution on scales of tens of kilometers. Taking all uncertainties into account, total sea-ice area and volume produced within the entire surveyed area were 52 650 km2 and 93.6 ± 26.6 km3. The surveyed polynya contributed 2.0 ± 0.5% of the sea-ice produced throughout the Arctic during the 2007/08 winter. The SAR-HEM volume estimate compares well with the 112 km3 ice production calculated with a~high-resolution ocean sea-ice model. Measured modal and mean-level ice thicknesses correlate with calculated freezing-degree-day thicknesses with a factor of 0.87-0.89, which was too low to justify the assumption of homogeneous thermodynamic growth conditions in the area, or indicates a strong dynamic thickening of level ice by rafting of even thicker ice.

A combined approach of remote sensing and airborne electromagnetics to determine the volume of polynya sea ice in the Laptev Sea

NASA Astrophysics Data System (ADS)

Rabenstein, L.; Krumpen, T.; Hendricks, S.; Koeberle, C.; Haas, C.; Hoelemann, J. A.

2013-02-01

A combined interpretation of synthetic aperture radar (SAR) satellite images and helicopter electromagnetic (HEM) sea-ice thickness data has provided an estimate of sea-ice volume formed in Laptev Sea polynyas during the winter of 2007/08. The evolution of the surveyed sea-ice areas, which were formed between late December 2007 and middle April 2008, was tracked using a series of SAR images with a sampling interval of 2-3 days. Approximately 160 km of HEM data recorded in April 2008 provided sea-ice thicknesses along profiles that transected sea-ice varying in age from 1-116 days. For the volume estimates, thickness information along the HEM profiles was extrapolated to zones of the same age. The error of areal mean thickness information was estimated to be between 0.2 m for younger ice and up to 1.55 m for older ice, with the primary error source being the spatially limited HEM coverage. Our results have demonstrated that the modal thicknesses and mean thicknesses of level ice correlated with the sea-ice age, but that varying dynamic and thermodynamic sea-ice growth conditions resulted in a rather heterogeneous sea-ice thickness distribution on scales of tens of kilometers. Taking all uncertainties into account, total sea-ice area and volume produced within the entire surveyed area were 52 650 km2 and 93.6 ± 26.6 km3. The surveyed polynya contributed 2.0 ± 0.5% of the sea-ice produced throughout the Arctic during the 2007/08 winter. The SAR-HEM volume estimate compares well with the 112 km3 ice production calculated with a high resolution ocean sea-ice model. Measured modal and mean-level ice thicknesses correlate with calculated freezing-degree-day thicknesses with a factor of 0.87-0.89, which was too low to justify the assumption of homogeneous thermodynamic growth conditions in the area, or indicates a strong dynamic thickening of level ice by rafting of even thicker ice.

Thin film eddy current impulse deicer

NASA Technical Reports Server (NTRS)

Smith, Samuel O.; Zieve, Peter B.

1990-01-01

Two new styles of electrical impulse deicers has been developed and tested in NASA's Icing Research Tunnel. With the Eddy Current Repulsion Deicing Boot (EDB), a thin and flexible spiral coil is encapsulated between two thicknesses of elastomer. The coil, made by an industrial printed circuit board manufacturer, is bonded to the aluminum aircraft leading edge. A capacitor bank is discharged through the coil. Induced eddy currents repel the coil from the aluminum aircraft structure and shed accumulated ice. A second configuration, the Eddy Current Repulsion Deicing-Strip (EDS) uses an outer metal erosion strip fastened over the coil. Opposite flowing eddy currents repel the strip and create the impulse deicing force. The outer strip serves as a surface for the collection and shedding of ice and does not require any structural properties. The EDS is suitable for composite aircraft structures. Both systems successfully dispelled over 95 percent of the accumulated ice from airfoils over the range of the FAA icing envelope.

Low-latitude ice cores and freshwater availability

NASA Astrophysics Data System (ADS)

Kehrwald, Natalie Marie

2009-12-01

Recent retreat of Tibetan Plateau glaciers affects at least half a billion people. Himalayan glaciers seasonally release meltwater into tributaries of the Indus, Ganges, and Brahmaputra Rivers and supply freshwater necessary to support agricultural and economic practices. Tibetan Plateau glaciers are retreating more rapidly than mountain glaciers elsewhere in the world, and this retreat is accelerating. The Naimona'nyi (30°27'N; 81°91'E, 6050 m a.s.l), Guliya (35°17'N; 81°29'E, 6710 m a.s.l.) and Dasuopu (28°23'N; 85°43'E, 7200 m a.s.l.) ice cores place this recent retreat into a longer time perspective through quantifying climate parameters such as past temperature, aridity, and atmospheric chemistry. Naimona'nyi has not accumulated mass since at least 1950, as evidenced by the virtual lack of radiogenic isotopes (36Cl, 3 H, and beta radioactivity) present in the ice core. These isotopes were produced by U.S. and Soviet atmospheric thermonuclear bomb tests conducted in the 1950s and 1960s and provide independent dating horizons for the ice cores. Lead-210 dates imply that the uppermost preserved glacial ice on Naimona'nyi formed during the 1940s. While this is the highest documented glacial thinning in the world other glaciers at elevations similar to that of Naimona'nyi, such as Kilimanjaro (3°4'S; 37°21'E, 5893 m a.s.l.), are also losing mass at their summits. The global scope of high-elevation glacial thinning suggests that ablation on the Earth's highest ice fields may be more prevalent as global mean temperatures continue to increase. Glacial thinning has not been taken into account in future projections of regional freshwater availability, and the net mass loss indicates that Himalayan glaciers currently store less freshwater than assumed in models. The acceleration of Tibetan Plateau glacial retreat has been hypothesized to be due in part to deposition of black carbon (BC) from biomass burning on to ice fields, thereby lowering the reflectivity of the glacier surface and melting the upper ice. The application of a novel technique of measuring and radiocarbon-dating ultra-small samples (< 100mug) of the BC and total organic carbon (TOC) fractions of Naimona'nyi demonstrates a decrease (˜12 to 14 ka versus ˜7 ka) in the composite age of BC in the upper 40 m and lowest 20 m of the 137 m ice core, suggesting the incorporation of radiocarbon-dead BC. Precambrian black shale in the Lesser Himalaya provide a natural source material which may be operationally defined as black carbon and which may incorporate radiocarbon-dead sediments into the bulk 14C measurements, yet as the mean 14C age is ˜10 ka, modern BC from biomass burning must also be incorporated into the ice core record. While the uppermost sample (5 m) contains 38% BC, 210 Pb dates show that this depth corresponds to an age before 1850 AD, or before the regional Industrial Revolution. As BC is a hydrophobic substance, the BC is unlikely to have migrated through the firn and glacial ice. Therefore, the high-elevation thinning on Naimona'nyi appears to be a response to increased temperatures rather than primarily driven by changes in surface albedo. This technique was applied to the annually-dated ice core from the accumulating summit of the Quleccaya ice cap, Peru (13'56'S; 70°50'W; 5670 m a.s.l.). A marked increase in modern BC and TOC was measured since 1880 AD. No increase in radiocarbon-dead (> 60,000 ka) BC or TOC was noted, suggesting that the source of the carbon was from biomass burning, with a possible contribution of Amazon slash and burn clearing, rather than the input of fossil fuel combustion. The age of the BC and TOC is thousands of years older than the age of the surrounding ice, and should not be used to date the ice core. Although Naimona'nyi provides challenges for constructing an ice core chronology due to its lack of independent horizons such as volcanic activity, methane gas measurements, 14C dates, 3H, 36Cl, or beta radioactivity, the oxygen isotopic record can be correlated with the neighboring Dasuopu and Guliya ice cores. Naimona'nyi contains a pronounced positive ˜10‰ shift in delta18O in the basal 37 m of the core which mimics similar isotopic shifts in regional speleothems, lacustrian sediments, and planktonic foraminifera proxy records. This distinct shift is attributed to amplified monsoon intensity caused by increased summer insolation at 30°N. This correlation between regional proxy records results in a basal age of ˜8.6 ka for Naimona'nyi, suggesting that the ice field grew as a response to tropical rather than polar climate forcings.

Glacial/interglacial changes in subarctic north pacific stratification.

PubMed

Jaccard, S L; Haug, G H; Sigman, D M; Pedersen, T F; Thierstein, H R; Röhl, U

2005-05-13

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.

The Antarctica component of postglacial rebound model ICE-6G_C (VM5a) based on GPS positioning, exposure age dating of ice thicknesses, and relative sea level histories

NASA Astrophysics Data System (ADS)

Argus, Donald F.; Peltier, W. R.; Drummond, R.; Moore, Angelyn W.

2014-07-01

A new model of the deglaciation history of Antarctica over the past 25 kyr has been developed, which we refer to herein as ICE-6G_C (VM5a). This revision of its predecessor ICE-5G (VM2) has been constrained to fit all available geological and geodetic observations, consisting of: (1) the present day uplift rates at 42 sites estimated from GPS measurements, (2) ice thickness change at 62 locations estimated from exposure-age dating, (3) Holocene relative sea level histories from 12 locations estimated on the basis of radiocarbon dating and (4) age of the onset of marine sedimentation at nine locations along the Antarctic shelf also estimated on the basis of 14C dating. Our new model fits the totality of these data well. An additional nine GPS-determined site velocities are also estimated for locations known to be influenced by modern ice loss from the Pine Island Bay and Northern Antarctic Peninsula regions. At the 42 locations not influenced by modern ice loss, the quality of the fit of postglacial rebound model ICE-6G_C (VM5A) is characterized by a weighted root mean square residual of 0.9 mm yr-1. The Southern Antarctic Peninsula is inferred to be rising at 2 mm yr-1, requiring there to be less Holocene ice loss there than in the prior model ICE-5G (VM2). The East Antarctica coast is rising at approximately 1 mm yr-1, requiring ice loss from this region to have been small since Last Glacial Maximum. The Ellsworth Mountains, at the base of the Antarctic Peninsula, are inferred to be rising at 5-8 mm yr-1, indicating large ice loss from this area during deglaciation that is poorly sampled by geological data. Horizontal deformation of the Antarctic Plate is minor with two exceptions. First, O'Higgins, at the tip of the Antarctic Peninsula, is moving southeast at a significant 2 mm yr-1 relative to the Antarctic Plate. Secondly, the margins of the Ronne and Ross Ice Shelves are moving horizontally away from the shelf centres at an approximate rate of 0.8 mm yr-1, in viscous response to the early Holocene unloading of ice from the current locations of the ice shelf centers. ICE-6G_C (VM5A) fits the horizontal observations well (wrms residual speed of 0.7 mm yr-1), there being no need to invoke any influence of lateral variation in mantle viscosity. ICE-6G_C (VM5A) differs in several respects from the recently published W12A model of Whitehouse et al. First, the upper-mantle viscosity in VM5a is 5 × 1020 Pa s, half that in W12A. The VM5a profile, which is identical to that inferred on the basis of the Fennoscandian relaxation spectrum, North American relative sea level histories and Earth rotation constraints, when coupled with the revised ICE-6G_C deglaciation history, fits all of the available constraints. Secondly, the net contribution of Antarctica ice loss to global sea level rise is 13.6 m, 2/3 greater than the 8 m in W12A. Thirdly, ice loss occurs quickly from 12 to 5 ka, and the contribution to global sea level rise during Meltwater Pulse 1B (11.5 ka) is large (5 m), consistent with sedimentation constraints from cores from the Antarctica ice shelf. Fourthly, in ICE-6G_C there is no ice gain in the East Antarctica interior, as there is in W12A. Finally, the new model of Antarctic deglaciation reconciles the global constraint upon the global mass loss during deglaciation provided by the Barbados record of relative sea level history when coupled with the Northern Hemisphere counterpart of this new model.

Firn-air Properties and Influences at the West Antarctic Ice Sheet Divide

NASA Astrophysics Data System (ADS)

Battle, M. O.; Severinghaus, J. P.; Montzka, S. A.; Sofen, E. D.; Tans, P. P.

2007-12-01

In December 2005, we collected samples of firn air from a pair of dedicated boreholes drilled at the West Antarctic Ice Sheet Divide (WAIS-D), immediately adjacent to the WAIS-D deep ice coring effort currently underway at 79° 28'S, 112° 7'W at an elevation of ~1800m. The site is characterized by moderate temperatures (annual mean of -31°C) and moderate accumulation (24 cm/yr ice-equivalent). These samples were analyzed for a wide variety of atmospheric species by laboratories at the Scripps Institution of Oceanography, NOAA-ESRL, University of Colorado/INSTAAR, UC Irvine and Penn. State University. In this presentation, we focus on general properties of the firn air at this site and the influences on its composition, as inferred from concentration data for CO2, CH4, and a range of halogenated species, as well as the stable isotope ratios of N2 and several noble gases. Preliminary analyses indicate the presence of a shallow convective zone (a few meters or less), a diffusive region extending down to roughly 65m and a lock-in zone from 65m to the firn-ice transition at 76.5m. There is also evidence of a thermally-driven seasonal cycle in composition in the upper 25m of the firn. Modeling studies indicate that the accumulation rate at this site is low enough that the downward advection of air accompanying firn compression has a very small influence on the firn air profile. Air at the bottom of the diffusive column has a CO2-based age of 10-15 years (depending on the definition of "mean age"), while the air at the firn-ice transition is ~38 years old. Concentrations of halogenated species in the samples collected imply atmospheric histories that are generally consistent with those derived from direct atmospheric measurements and from firn air collected at other sites. Additional properties of the air, and their controlling processes will also be presented.

Fram Strait: Atmospheric Forcing of The Sea Ice Flux

NASA Astrophysics Data System (ADS)

Widell, K.; Østerhus, S.; Gammelsrød, T.

Measuring the magnitude and variability of the ice and freshwater flux through Fram Strait is an important element in understanding climate variability in the Arctic. Since the major part of the ice and freshwater that leaves the Arctic passes through Fram Strait, this passage can be considered a key area for estimating the net ice production in the Arctic Ocean. In 1990, the Norwegian Polar Institute (NPI) started a monitoring program in the strait, most years by means of two moorings with Upward Looking Sonars (ULS) measuring ice draft. From 1995 and on, these moorings were also equipped with Doppler Current Meters (DCM) to measure the ice velocity. These measurements give an opportunity to investigate the different forces affecting ice motion in the strait. Maximum correlation coefficient between atmospheric sea level pressure (from NCEP/NCAR reanalysed data) and southward ice velocity is found when using the cross strait pressure difference along 80N between 10W and 5E (R = 0.72) consider- ing monthly means. Subtracting current velocity at 50 m depth (also measured by the DCM) from ice velocity improves the correlation to R = 0.84. This gives insight in the relative importance of current and wind on the ice motion, and indicates that pressure data can be used to make fairly good estimates of the ice velocity in the strait. In combination with data on ice thickness and ice stream width, this result is used to calculate the ice volume transport. By making assumptions on the parameters in- volved, the time series is extended back to 1948, the start of the pressure record. This time series will be presented and compared to literature, and annual and seasonal vari- ation of the ice flux will be discussed.

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments.

PubMed

La Farge, Catherine; Williams, Krista H; England, John H

2013-06-11

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550-1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems.

Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments

PubMed Central

La Farge, Catherine; Williams, Krista H.; England, John H.

2013-01-01

Across the Canadian Arctic Archipelago, widespread ice retreat during the 20th century has sharply accelerated since 2004. In Sverdrup Pass, central Ellesmere Island, rapid glacier retreat is exposing intact plant communities whose radiocarbon dates demonstrate entombment during the Little Ice Age (1550–1850 AD). The exhumed bryophyte assemblages have exceptional structural integrity (i.e., setae, stem structures, leaf hair points) and have remarkable species richness (60 of 144 extant taxa in Sverdrup Pass). Although the populations are often discolored (blackened), some have developed green stem apices or lateral branches suggesting in vivo regrowth. To test their biological viability, Little Ice Age populations emerging from the ice margin were collected for in vitro growth experiments. Our results include a unique successful regeneration of subglacial bryophytes following 400 y of ice entombment. This finding demonstrates the totipotent capacity of bryophytes, the ability of a cell to dedifferentiate into a meristematic state (analogous to stem cells) and develop a new plant. In polar ecosystems, regrowth of bryophyte tissue buried by ice for 400 y significantly expands our understanding of their role in recolonization of polar landscapes (past or present). Regeneration of subglacial bryophytes broadens the concept of Ice Age refugia, traditionally confined to survival of land plants to sites above and beyond glacier margins. Our results emphasize the unrecognized resilience of bryophytes, which are commonly overlooked vis-a-vis their contribution to the establishment, colonization, and maintenance of polar terrestrial ecosystems. PMID:23716658

Volcano-ice age link discounted

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kerr, R.A.

1996-05-10

Speculation that huge volcanic eruptions may have caused an immediate `volcanic winter` that devastated early humans and accelerated a slide into the Ice Age. However, further information from the Greenland ice sheet about the Toba errumption on the island of Sumatra 70,000 years ago, seems to indicate that such volcanic actions wasn`t a major climatic catalyst. This article discusses the evidence and further possibilities.

Wind, current and swell influences on the ice extent and flux in the Grand Banks-Labrador sea area as observed in the LIMEX '87 experiment

NASA Technical Reports Server (NTRS)

Argus, Susan Digby; Carsey, Frank; Holt, Benjamin

1988-01-01

This paper presents data collected by airborne and satellite instruments during the Labrador Ice Margin Experiment, that demonstrate the effects of oceanic and atmospheric processes on the ice conditions in the Grand Banks-Labrador sea area. Special consideration is given to the development of algorithms for extracting information from SAR data. It is shown that SAR data can be used to monitor ice extent, determine ice motion, locate shear zones, monitor the penetration of swell into the ice, estimate floe sizes, and establish the dimensions of the ice velocity zones. It is also shown that the complex interaction of the ice cover with winds, currents, swell, and coastlines is similar to the dynamics established for a number of sites in both polar regions.

Deglaciation of Antarctica since the Last Glacial Maximum - what can we learn from cosmogenic 10Be and 26Al exposure ages?

NASA Astrophysics Data System (ADS)

Fink, David

2015-04-01

Ice volume changes at the coastal margins of Antarctica during the global LGM are uncertain. The little evidence available suggests that behaviour of the East and West Antarctic Ice Sheets are markedly different and complex. It is hypothesised that during interglacials, thinning of the Ross Ice Shelf, a more open-water environment and increased precipitation, allowed outlet glaciers draining the Transantarctic Mnts and fed by interior Ice Sheets to advance during moist warmer periods, out of phase with colder arid periods. In contrast, glacier dynamics along the vast coastal perimeter of East Antarctica is strongly influenced by Southern Ocean conditions. Cosmogenic 10Be and 26Al chronologies, although restricted to ice-free oasis and mountains flanking drainage glaciers, has become an invaluable, if not unique, tool to quantify spatial and temporal Pleistocene ice sheet variability over the past 2 Ma. Despite an increasing number of well documented areas, extracting reliable ages from glacial deposits in polar regions is problematic. Recycling of previously exposed/ buried debris and continual post-depositional modification leads to age ambiguities for a coeval glacial landform. More importantly, passage of cold-based ice can leave a landform unmodified resulting in young erratics deposited on ancient bedrock. Advances in delivering in-situ radiocarbon to routine application offer some relief. Exposure ages from different localities throughout East Antarctica (Framnes Mnts, Lutzow-Holm Bay, Vestfold Hills) and West Antarctica (Denton Ranges, Hatherton Glacier, Shackleton Range) highlight some of the new findings. This talk presents results which quantify the magnitude and timing of paleo-ice sheet thickness changes, questions the validity of an Antarctic LGM and discusses the complexities encountered in the often excessive spread in exposure ages.

Reconstruction of sea-ice cover and primary production on the East Greenland Shelf (73°N) during the last 5200 years

NASA Astrophysics Data System (ADS)

Kolling, Henriette Marie; Stein, Rüdiger; Fahl, Kirsten; Perner, Kerstin; Moros, Matthias

2016-04-01

Over the last decades the extent and thickness of Arctic sea ice has changed dramatically and much more rapidly than predicted by climate models. Thus, high-resolution sea-ice reconstructions from pre-anthropogenic times are useful and needed in order to better understand the processes controlling the natural sea-ice variability. Here, we present the first high-resolution biomarker (IP25, sterols) approach over the last 5.2 ka from the East Greenland Shelf (for background about the biomarker approach see Belt et al., 2007; Müller et al., 2009, 2011). This area is highly sensitive to sea-ice changes, as it underlies the pathway of the East Greenland Current, the main exporter of Arctic freshwater and sea ice that affects the environmental conditions on the East Greenland Shelf and deep-water formation/ convection in the Northern North Atlantic. After rather stable sea-ice conditions in the mid-Holocene we found a strong increase in sea ice, cumulating around 1.5 ka and associated with the Neoglacial cooling. The general trend especially during the last 1ka is interrupted by several short-lived events such as the prominent Medieval Warm Period and Little Ice Age, characterized by minimum and maximum sea-ice extent, respectively. Using a spectral analysis, we could identify several cyclicites, e.g. a 45-year cyclicity for cold events. A comparison to similar records from the eastern Fram Strait revealed a slight time lag in the onset of the Neoglacial, but also suggesting the direct link of the East Greenland Shelf area to the Arctic sea-ice/freahwater outflow. A comparison of the biomarker data with a new foraminiferal record obtained from the same site (Perner et al., 2015) suggests that IP25 and foraminifera assemblages are probably controlled by rather different processes within the oceanographic systems, such as the sea-ice conditions and, for the foraminifera, water-mass changes and nutrient supply. References: Belt. S.T., Massé, G., Rowland, S.J., Poulin, M., Michel, C., LeBlanc B., 2007. A novel chemical fossil of palaeo sea ice: IP25. Organic Geochemistry 38 (2007) 16-27 Müller, J., Massé, G., Stein, R., Belt, S.T., 2009. Variability of sea-ice conditons in the Fram Strait over the past 30,000 years. Nature Geoscience Vol 2 (2009), 772-776 Müller, J., Wagner, A., Fahl, K., Stein, R., Prange, M., Lohmann, G., 2011. Towards quantitative sea ice reconstructions in the northern North Atlantic: A combines biomarker and numerical modelling approach. East and Planetrary Science Letters 306 (2011) 137-148 Perner, K., Moros, M., Lloyd, J.M., Jansen, E., Stein, R., 2015. Mid to late Holocene strengthening of the East Greenland Current linked to warm subsurface Atlantic water. Quaternary Science Reviews 129 (2015) 296-307

Expanded secondary craters in the Arcadia Planitia region, Mars: evidence for tens of Myr-old shallow subsurface ice

USGS Publications Warehouse

Viola, Donna; McEwen, Alfred S.; Dundas, Colin M.; Byrne, Shane

2015-01-01

A range of observations indicates widespread subsurface ice throughout the mid and high latitudes of Mars in the form of both pore-filling and excess ice. It is generally thought that this ice was recently emplaced and is not older than a hundred thousand to a few millions of years old based on ice stability and orbital-induced climate change. We analyze the distribution of subsurface ice in Arcadia Planitia, located in the northern mid latitudes, by mapping thermokarstically expanded secondary craters, providing additional evidence for extensive excess ice down to fairly low latitudes (less than 40°N). We further infer the minimum age of this subsurface ice based on the ages of the four primary craters that are thought to be the source of a large portion of these secondaries, which yields estimates on the order of tens of millions of years old – much more ancient than anticipated. This estimated ancient age suggests that ice can be preserved in the shallow subsurface for long periods of time, at least in some parts of Arcadia Planitia where expanded secondary craters are especially abundant. We estimate the amount of ice lost to sublimation during crater expansion based on measurements of expanded secondary craters in HiRISE Digital Terrain Models. The loss is equivalent to a volume of ice between ∼140 and 360 km3, which would correspond to a global layer of 1–2.5 mm thick. We further argue that much more ice (at least 6000 km3) is likely preserved beneath the un-cratered regions of Arcadia Planitia since significant loss of this excess ice would have caused extensive terrain dissection and the removal of the expanded secondary craters. Both the loss of ice due to secondary crater expansion and the presence of this ice today have implications for the martian climate.

The Relationship Between Arctic Sea Ice Albedo and the Geophysical Parameters of the Ice Cover

NASA Astrophysics Data System (ADS)

Riihelä, A.

2015-12-01

The Arctic sea ice cover is thinning and retreating. Remote sensing observations have also shown that the mean albedo of the remaining ice cover is decreasing on decadal time scales, albeit with significant annual variability (Riihelä et al., 2013, Pistone et al., 2014). Attribution of the albedo decrease between its different drivers, such as decreasing ice concentration and enhanced surface melt of the ice, remains an important research question for the forecasting of future conditions of the ice cover. A necessary step towards this goal is understanding the relationships between Arctic sea ice albedo and the geophysical parameters of the ice cover. Particularly the question of the relationship between sea ice albedo and ice age is both interesting and not widely studied. The recent changes in the Arctic sea ice zone have led to a substantial decrease of its multi-year sea ice, as old ice melts and is replaced by first-year ice during the next freezing season. It is generally known that younger sea ice tends to have a lower albedo than older ice because of several reasons, such as wetter snow cover and enhanced melt ponding. However, the quantitative correlation between sea ice age and sea ice albedo has not been extensively studied to date, excepting in-situ measurement based studies which are, by necessity, focused on a limited area of the Arctic Ocean (Perovich and Polashenski, 2012).In this study, I analyze the dependencies of Arctic sea ice albedo relative to the geophysical parameters of the ice field. I use remote sensing datasets such as the CM SAF CLARA-A1 (Karlsson et al., 2013) and the NASA MeaSUREs (Anderson et al., 2014) as data sources for the analysis. The studied period is 1982-2009. The datasets are spatiotemporally collocated and analysed. The changes in sea ice albedo as a function of sea ice age are presented for the whole Arctic Ocean and for potentially interesting marginal sea cases. This allows us to see if the the albedo of the older sea ice in the central parts of the Arctic Ocean is resistant to the decreasing overall trend.A similar analysis is also extended to ice concentration, melt season length and other appropriate parameters describing the surface conditions. The results of the analyses are summed up to provide an assessment of the relative impact strengths of the ice field parameters on the albedo.

iss012e15918

NASA Image and Video Library

2006-01-24

ISS012-E-15918 (24 Jan. 2006) --- Belle Isle and a portion of Newfoundland, Canada are featured in this image photographed by an Expedition 12 crew member on the International Space Station. Belle Isle (center) is surrounded by sea ice in this recent winter view. Belle Isle lies in the strait between the Island of Newfoundland and Labrador (the mainland portion of Canada’s province of Newfoundland). Small islands along the coast of Labrador appear in the top left corner. In this key location Belle Isle lies on the shortest shipping lanes between the Great Lakes and Europe, and also on the main north-south shipping route to Hudson Bay and the Northwest Territories. Snow and ice in this recent winter view obliterate the dozens of glacier-scoured lakes that dot the surface of the island. The single community of Belle Isle Landing on the southeast tip is equally hard to see. Ice patterns also show that the island lies at the meeting point of two sea currents. The Labrador Current flows from the northwest (top left), and a smaller current, driven by dominant westerly winds, flows from the southwest (lower left) out of the narrow Belle Isle Strait (out of frame lower left). Flow lines in sea ice indicate the sense of movement of the ice. Ice floes embedded in the Labrador Current appear in the upper part of the image as a relatively open pattern. Sea ice with a denser pattern enters from the lower left corner, banking against the west side of Belle Isle. Tendrils flow around capes at either end of the island, with an ice-free “shadow” on the opposite, downstream side. Eddies (center) in the ice patterns show where the currents interact, north and west of the island.

A Chronology of Late-Glacial and Holocene Advances of Quelccaya Ice Cap, Peru, Based on 10Be and Radiocarbon Dating

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Lowell, T. V.; Schaefer, J. M.

2007-12-01

The Quelccaya Ice Cap region in the southeastern Peruvian Andes (~13-14°S latitude) is a key location for the development of late-glacial and Holocene terrestrial paleoclimate records in the tropics. We present a chronology of past extents of Quelccaya Ice Cap based on ~thirty internally consistent 10Be dates of boulders on moraines and bedrock as well as twenty radiocarbon dates of organic material associated with moraines. Based on results from both dating methods, we suggest that significant advances of Quelccaya Ice Cap occurred during late-glacial time, at ~12,700-11,400 yr BP, and during Late Holocene time ~400-300 yr BP. Radiocarbon dating of organic material associated with moraines provides maximum and minimum ages for ice advances and recessions, respectively, thus providing an independent check on 10Be dates of boulders on moraines. The opportunity to use both 10Be and radiocarbon dating makes the Quelccaya Ice Cap region a potentially important low-latitude calibration site for production rates of cosmogenic nuclides. Our radiocarbon chronology provides a tighter constraint on maximum ages of late-glacial and Late Holocene ice advances. Upcoming field research will obtain organic material for radiocarbon dating to improve minimum age constrains for late-glacial and Late Holocene ice recessions.

Effect of aging and ice structuring proteins on the morphology of frozen hydrated gluten networks.

PubMed

Kontogiorgos, Vassilis; Goff, H Douglas; Kasapis, Stefan

2007-04-01

The present investigation constitutes an attempt to rationalize the effect of aging and ice structuring proteins (ISPs) on the network morphology of frozen hydrated gluten. In doing so, it employs differential scanning calorimetry, time-domain NMR, dynamic oscillation on shear, creep testing, and electron microscopy. Experimentation and first principles modeling allows identification and description of the processes of ice formation and recrystallization in molecular terms. It is demonstrated that in the absence of a readily discernible glass transition temperature in gluten-ice composites, the approach of considering the melting point and aging at constant or fluctuating temperature conditions in the vicinity of this point can provide a valid index of functional quality. A theoretical framework supporting the concept of capillary confined frozen water in the gluten matrix was advanced, and it was found that ISPs were effective in controlling recrystallization both within these confines and within ice in the bulk.

NASA Airframe Icing Research Overview Past and Current

NASA Technical Reports Server (NTRS)

Potapczuk, Mark

2009-01-01

This slide presentation reviews the past and current research that NASA has done in the area of airframe icing. Both the history experimental efforts and model development to understand the process and problem of ice formation are reviewed. This has resulted in the development of new experimental methods, advanced icing simulation software, flight dynamics and experimental databases that have an impact on design, testing, construction and certification and qualification of the aircraft and its sub-systems.

Simulating hydrodynamics and ice cover in Lake Erie using an unstructured grid model

NASA Astrophysics Data System (ADS)

Fujisaki-Manome, A.; Wang, J.

2016-02-01

An unstructured grid Finite-Volume Coastal Ocean Model (FVCOM) is applied to Lake Erie to simulate seasonal ice cover. The model is coupled with an unstructured-grid, finite-volume version of the Los Alamos Sea Ice Model (UG-CICE). We replaced the original 2-time-step Euler forward scheme in time integration by the central difference (i.e., leapfrog) scheme to assure a neutrally inertial stability. The modified version of FVCOM coupled with the ice model is applied to the shallow freshwater lake in this study using unstructured grids to represent the complicated coastline in the Laurentian Great Lakes and refining the spatial resolution locally. We conducted multi-year simulations in Lake Erie from 2002 to 2013. The results were compared with the observed ice extent, water surface temperature, ice thickness, currents, and water temperature profiles. Seasonal and interannual variation of ice extent and water temperature was captured reasonably, while the modeled thermocline was somewhat diffusive. The modeled ice thickness tends to be systematically thinner than the observed values. The modeled lake currents compared well with measurements obtained from an Acoustic Doppler Current Profiler located in the deep part of the lake, whereas the simulated currents deviated from measurements near the surface, possibly due to the model's inability to reproduce the sharp thermocline during the summer and the lack of detailed representation of offshore wind fields in the interpolated meteorological forcing.

Proceedings of oceans 87. The ocean - an international workplace

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1987-01-01

This book includes proceedings containing 347 papers. Some of the topics are: ICE -Cold ocean and ice research; ICE-1-Icebergs; ICE-2-Sea ice and structures; IE-3-Cold ocean instrumentation; ICE-4-Ocean and ice; INS-Oceanographic instrumentation; INS-1-Acoustic Doppler Current profilers; ENG-1-New solutions to old problems; ENG-2-energy from the ocean; ENG-3-Cables and connectors; POL-Policy, education and technology transfer; POL-1-International issues; POL-2-Ocean space utilization; POL-3-Economics, planning and management; SCI-6-fish stock assessment; ACI-7-Coastal currents and sediment; SCI-9-Satellite navigation; SCI-10-Deep sea minerals and methods of recovery; ODS-Fifth working symposium on oceanographic data system; ODS-1-Data base management; UND-Underwater work systems; UND-1-Diving for science.

Spontaneous abrupt climate change due to an atmospheric blocking–sea-ice–ocean feedback in an unforced climate model simulation

PubMed Central

Drijfhout, Sybren; Gleeson, Emily; Dijkstra, Henk A.; Livina, Valerie

2013-01-01

Abrupt climate change is abundant in geological records, but climate models rarely have been able to simulate such events in response to realistic forcing. Here we report on a spontaneous abrupt cooling event, lasting for more than a century, with a temperature anomaly similar to that of the Little Ice Age. The event was simulated in the preindustrial control run of a high-resolution climate model, without imposing external perturbations. Initial cooling started with a period of enhanced atmospheric blocking over the eastern subpolar gyre. In response, a southward progression of the sea-ice margin occurred, and the sea-level pressure anomaly was locked to the sea-ice margin through thermal forcing. The cold-core high steered more cold air to the area, reinforcing the sea-ice concentration anomaly east of Greenland. The sea-ice surplus was carried southward by ocean currents around the tip of Greenland. South of 70°N, sea ice already started melting and the associated freshwater anomaly was carried to the Labrador Sea, shutting off deep convection. There, surface waters were exposed longer to atmospheric cooling and sea surface temperature dropped, causing an even larger thermally forced high above the Labrador Sea. In consequence, east of Greenland, anomalous winds changed from north to south, terminating the event with similar abruptness to its onset. Our results imply that only climate models that possess sufficient resolution to correctly represent atmospheric blocking, in combination with a sensitive sea-ice model, are able to simulate this kind of abrupt climate change. PMID:24248352

The Ross Sea Dipole - temperature, snow accumulation and sea ice variability in the Ross Sea region, Antarctica, over the past 2700 years

NASA Astrophysics Data System (ADS)

Bertler, Nancy A. N.; Conway, Howard; Dahl-Jensen, Dorthe; Emanuelsson, Daniel B.; Winstrup, Mai; Vallelonga, Paul T.; Lee, James E.; Brook, Ed J.; Severinghaus, Jeffrey P.; Fudge, Taylor J.; Keller, Elizabeth D.; Baisden, W. Troy; Hindmarsh, Richard C. A.; Neff, Peter D.; Blunier, Thomas; Edwards, Ross; Mayewski, Paul A.; Kipfstuhl, Sepp; Buizert, Christo; Canessa, Silvia; Dadic, Ruzica; Kjær, Helle A.; Kurbatov, Andrei; Zhang, Dongqi; Waddington, Edwin D.; Baccolo, Giovanni; Beers, Thomas; Brightley, Hannah J.; Carter, Lionel; Clemens-Sewall, David; Ciobanu, Viorela G.; Delmonte, Barbara; Eling, Lukas; Ellis, Aja; Ganesh, Shruthi; Golledge, Nicholas R.; Haines, Skylar; Handley, Michael; Hawley, Robert L.; Hogan, Chad M.; Johnson, Katelyn M.; Korotkikh, Elena; Lowry, Daniel P.; Mandeno, Darcy; McKay, Robert M.; Menking, James A.; Naish, Timothy R.; Noerling, Caroline; Ollive, Agathe; Orsi, Anaïs; Proemse, Bernadette C.; Pyne, Alexander R.; Pyne, Rebecca L.; Renwick, James; Scherer, Reed P.; Semper, Stefanie; Simonsen, Marius; Sneed, Sharon B.; Steig, Eric J.; Tuohy, Andrea; Ulayottil Venugopal, Abhijith; Valero-Delgado, Fernando; Venkatesh, Janani; Wang, Feitang; Wang, Shimeng; Winski, Dominic A.; Winton, V. Holly L.; Whiteford, Arran; Xiao, Cunde; Yang, Jiao; Zhang, Xin

2018-02-01

High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually dated ice core record from the eastern Ross Sea, named the Roosevelt Island Climate Evolution (RICE) ice core. Comparison of this record with climate reanalysis data for the 1979-2012 interval shows that RICE reliably captures temperature and snow precipitation variability in the region. Trends over the past 2700 years in RICE are shown to be distinct from those in West Antarctica and the western Ross Sea captured by other ice cores. For most of this interval, the eastern Ross Sea was warming (or showing isotopic enrichment for other reasons), with increased snow accumulation and perhaps decreased sea ice concentration. However, West Antarctica cooled and the western Ross Sea showed no significant isotope temperature trend. This pattern here is referred to as the Ross Sea Dipole. Notably, during the Little Ice Age, West Antarctica and the western Ross Sea experienced colder than average temperatures, while the eastern Ross Sea underwent a period of warming or increased isotopic enrichment. From the 17th century onwards, this dipole relationship changed. All three regions show current warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea but increasing in the western Ross Sea. We interpret this pattern as reflecting an increase in sea ice in the eastern Ross Sea with perhaps the establishment of a modern Roosevelt Island polynya as a local moisture source for RICE.

Development of lysozyme-combined antibacterial system to reduce sulfur dioxide and to stabilize Italian Riesling ice wine during aging process

PubMed Central

Chen, Kai; Han, Shun-yu; Zhang, Bo; Li, Min; Sheng, Wen-jun

2015-01-01

For the purpose of SO2 reduction and stabilizing ice wine, a new antibacterial technique was developed and verified in order to reduce the content of sulfur dioxide (SO2) and simultaneously maintain protein stability during ice wine aging process. Hazardous bacterial strain (lactic acid bacteria, LAB) and protein stability of Italian Riesling ice wine were evaluated in terms of different amounts of lysozyme, SO2, polyphenols, and wine pH by single-factor experiments. Subsequently, a quadratic rotation-orthogonal composite design with four variables was conducted to establish the multiple linear regression model that demonstrated the influence of different treatments on synthesis score between LAB inhibition and protein stability of ice wine. The results showed that, synthesis score can be influenced by lysozyme and SO2 concentrations on an extremely significant level (P < 0.01). Furthermore, the lysozyme-combined antibacterial system, which is specially designed for ice wine aging, was optimized step by step by response surface methodology and ridge analysis. As a result, the optimal proportion should be control in ice wine as follows: 179.31 mg L−1 lysozyme, 177.14 mg L−1 SO2, 0.60 g L−1 polyphenols, and 4.01 ice wine pH. Based on this system, the normalized synthesis score between LAB inhibition and protein stability can reach the highest point 0.920. Finally, by the experiments of verification and comparison, it was indicated that lysozyme-combined antibacterial system, which was a practical and prospective method to reduce SO2 concentration and effectively prevent contamination from hazardous LAB, can be used to stabilize ice wine during aging process. PMID:26405531

High-resolution chronology for deglaciation of the Patagonian Ice Sheet at Lago Buenos Aires (46.5°S) revealed through varve chronology and Bayesian age modelling

NASA Astrophysics Data System (ADS)

Bendle, Jacob M.; Palmer, Adrian P.; Thorndycraft, Varyl R.; Matthews, Ian P.

2017-12-01

Glaciolacustrine varves offer the potential to construct continuous, annually-resolved chronologies for ice-sheet deglaciation, and improved understanding of glacier retreat dynamics. This paper investigates laminated glaciolacustrine sediments deposited around the waning margins of the Patagonian Ice Sheet, following the local Last Glacial Maximum (LGM). Detailed macro- and microfacies analyses confirm an annual (varve) structure within these sediments. The correlation of annual layers (varves) across five sites in eastern Lago Buenos Aires yields a 994 ± 36 varve-year (vyr) chronology and thickness record. The floating chronology has been anchored to the calendar-year timescale through identification of the Ho tephra (17,378 ± 118 cal a BP) in the varve sequences. Using a Bayesian age model to integrate the new varve chronology with published moraine ages, the onset of deglaciation at 46.5°S is dated to 18,086 ± 214 cal a BP. New age estimates for deglacial events are combined with high-resolution analysis of varve thickness trends, and new lithostratigraphic data on ice-margin position(s), to reconstruct ice-margin retreat rates for the earliest ca. 1000 years of ice-sheet demise. Glacier retreat rates were moderate (5.3-10.3 m yr-1) until 17,322 ± 115 cal a BP, but subsequently accelerated (15.4-18.0 m yr-1). Sustained influxes of ice-rafted debris (IRD) after 17,145 ± 122 cal a BP suggest retreat rates were enhanced by calving after ice contracted into deeper lake waters. Ice persisted in eastern Lago Buenos Aires until at least 16,934 ± 116 cal a BP, after which the glacier started to retreat towards the Patagonian mountains.

Volcanic Eruptions as the Cause of the Little Ice Age

NASA Astrophysics Data System (ADS)

Zambri, B.; Robock, A.

2017-12-01

Both external forcing (solar radiation, volcanic eruptions) and internal fluctuations have been proposed to explain such multi-centennial perturbations as the Little Ice Age. Confidence in these hypotheses is limited due to the limited number of proxies, as well as only one observed realization of the Last Millennium. Here, we evaluate different hypotheses on the origin of Little Ice Age-like anomalies, focusing in particular on the long-term response of North Atlantic and Arctic climate perturbations to solar and volcanic perturbations. For that, we conduct a range of sensitivity tests carried out with the Community Earth System Model (CESM) at the National Center for Atmospheric Research, focusing in particular on the sensitivity to initial conditions and the strength of solar and volcanic forcing. By comparing the climate response to various combinations of external perturbations, we demonstrate nonlinear interactions that are necessary to explain trends observed in the fully coupled system and discuss physical mechanisms through which these external forcings can trigger multidecadal modes of the Atlantic Multidecadal Oscillation and subsequently lead to a Little-Ice-Age-like regime. For that, we capture and compare patterns of the coupled atmosphere-sea-ice-ocean response as revealed through a range of data analysis techniques. We show that the large 1257 Samalas, 1452 Kuwae, and 1600 Huaynaputina volcanic eruptions were the main causes of the multi-centennial glaciation associated with the Little Ice Age.

Immersion in Cold-Water Evaluation (ICE) and self-reported cold intolerance are reliable but unrelated measures.

PubMed

Traynor, Robyn; MacDermid, Joy C

2008-09-01

Intolerance to the cold is common following peripheral nerve injury and surgery of the upper extremity. Despite its prevalence, the exact pathophysiology and natural history of this condition are not well understood. Subjective, self-report questionnaires have been created and validated as reliable measures of post-traumatic cold intolerance. The difficulty currently lies in assigning an objective measure to this predominantly subjective phenomenon. The present study evaluated the test-retest reliability of a proposed objective measure of cold intolerance, the Immersion in Cold-water Evaluation (ICE), and its correlation with subjective measures in healthy control subjects. Two age groups were also compared to investigate the effect of age on cold intolerance and temperature recovery. On two separate testing days, subjects completed three health-related questionnaires and submersed their dominant hands in cold water. The temperature of their second and fifth digits was monitored during recovery. Both the objective cold-provocation testing and the subjective self-report questionnaires were highly reliable albeit not significantly correlated. No significant temperature recovery trend was noted between the age groups. Post-traumatic cold intolerance is postulated to have both a vascular and neural etiology among other contributing causes. The protocol studied here was centered predominantly on the former etiology, examining peripheral blood flow and associated temperature recovery. This study established ICE as a reliable means to objectively measure cold response, supplementing information provided by previously validated self-report methods.

Ice nucleation activity of diesel soot particles at Cirrus relevant conditions: Effects of hydration, secondary organics coating, hydration, soot morphology, and coagulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kulkarni, Gourihar R.; China, Swarup; Liu, Shang

The role of atmospheric relevant soot particles that are processed in the atmosphere toward ice nucleation at cirrus cloud condition is poorly understood. In this study, the ice nucleating properties of diesel soot particles subjected to various physical and chemical aging treatments were investigated at temperatures ranging from -40 to -50 °C. We show that bare soot particles nucleate ice in deposition mode, but coating with secondary organics suppresses the heterogeneous ice nucleation potential of soot particles requiring homogeneous freezing threshold conditions. However, the ice nucleation efficiency of soot particles coated with an aqueous organic layer was similar to baremore » soot particles. Hydration of bare soot particles slightly enhanced the ice nucleation efficiency, and the IN abilities of compact soot particles (roundness = ~ 0.6) were similar to bare lacey soot particles (roundness = ~ 0.4). These results indicate that ice nucleation properties are sensitive to the various aging treatments.« less

Marine sources of ice nucleating particles: results from phytoplankton cultures and samples collected at sea

NASA Astrophysics Data System (ADS)

Wilbourn, E.; Thornton, D.; Brooks, S. D.; Graff, J.

2016-12-01

The role of marine aerosols as ice nucleating particles is currently poorly understood. Despite growing interest, there are remarkably few ice nucleation measurements on representative marine samples. Here we present results of heterogeneous ice nucleation from laboratory studies and in-situ air and sea water samples collected during NAAMES (North Atlantic Aerosol and Marine Ecosystems Study). Thalassiosira weissflogii (CCMP 1051) was grown under controlled conditions in batch cultures and the ice nucleating activity depended on the growth phase of the cultures. Immersion freezing temperatures of the lab-grown diatoms were determined daily using a custom ice nucleation apparatus cooled at a set rate. Our results show that the age of the culture had a significant impact on ice nucleation temperature, with samples in stationary phase causing nucleation at -19.9 °C, approximately nine degrees warmer than the freezing temperature during exponential growth phase. Field samples gathered during the NAAMES II cruise in May 2016 were also tested for ice nucleating ability. Two types of samples were gathered. Firstly, whole cells were fractionated by size from surface seawater using a BD Biosciences Influx Cell Sorter (BD BS ISD). Secondly, aerosols were generated using the SeaSweep and subsequently size-selected using a PIXE Cascade Impactor. Samples were tested for the presence of ice nucleating particles (INP) using the technique described above. There were significant differences in the freezing temperature of the different samples; of the three sample types the lab-grown cultures tested during stationary phase froze at the warmest temperatures, followed by the SeaSweep samples (-25.6 °C) and the size-fractionated cell samples (-31.3 °C). Differences in ice nucleation ability may be due to size differences between the INP, differences in chemical composition of the sample, or some combination of these two factors. Results will be presented and atmospheric implications discussed.

Layered, massive and thin sediments on Mars: Possible Late Noachian to Late Amazonian tephra?

USGS Publications Warehouse

Chapman, M.G.

2002-01-01

Data from instruments on the currently orbiting Mars Global Surveyor (MGS) suggest that as an alternative interpretation to lacustrine deposits, widespread sediments on Mars may be tephra deposits of variable age, formed in part by volcano-ice interactions. The materials are often associated with outcrops of mapped geological units that have each been previously interpreted as volcanic ash deposits with identified, but unconfirmed possible volcanic vents. Spectral investigation indicates that although some outcrops are basaltic, many show moderate to high concentrations of andesite, a composition at which large explosive eruptions may be possible. In addition, many outcrops are in areas suspected to be water/ice rich. On Earth, magma and groundwater can react to create violent explosive eruptions. Observations from MGS support a pyroclastic mechanism of deposition and show some morphologies consistent with volcano-ice interactions, including subaqueous eruptions. Perhaps MGS data are finally producing more definitive evidence of the widespread tephra that were predicted to be likely in the reduced atmospheric pressure of Mars.

The contemporary degassing rate of 40Ar from the solid Earth.

PubMed

Bender, Michael L; Barnett, Bruce; Dreyfus, Gabrielle; Jouzel, Jean; Porcelli, Don

2008-06-17

Knowledge of the outgassing history of radiogenic (40)Ar, derived over geologic time from the radioactive decay of (40)K, contributes to our understanding of the geodynamic history of the planet and the origin of volatiles on Earth's surface. The (40)Ar inventory of the atmosphere equals total (40)Ar outgassing during Earth history. Here, we report the current rate of (40)Ar outgassing, accessed by measuring the Ar isotope composition of trapped gases in samples of the Vostok and Dome C deep ice cores dating back to almost 800 ka. The modern outgassing rate (1.1 +/- 0.1 x 10(8) mol/yr) is in the range of values expected by summing outgassing from the continental crust and the upper mantle, as estimated from simple calculations and models. The measured outgassing rate is also of interest because it allows dating of air trapped in ancient ice core samples of unknown age, although uncertainties are large (+/-180 kyr for a single sample or +/-11% of the calculated age, whichever is greater).

The Great Ice Age

USGS Publications Warehouse

Ray, Louis L.

1992-01-01

The Great Ice Age, a recent chapter in the Earth's history, was a period of recurring widespread glaciations. During the Pleistocene Epoch of the geologic time scale, which began about a million or more years ago, mountain glaciers formed on all continents, the icecaps of Antarctica and Greenland were more extensive and thicker than today, and vast glaciers, in places as much as several thousand feet thick, spread across northern North America and Eurasia. So extensive were these glaciers that almost a third of the present land surface of the Earth was intermittently covered by ice. Even today remnants of the great glaciers cover almost a tenth of the land, indicating that conditions somewhat similar to those which produced the Great Ice Age are still operating in polar and subpolar climates.

Methodological synergies for glaciological constraints to find Oldest Ice

NASA Astrophysics Data System (ADS)

Eisen, Olaf

2017-04-01

The Beyond EPICA - Oldest Ice (BE-OI) consortium and its international partners unite a globally unique concentration of scientific expertise and infrastructure for ice-core investigations. It delivers the technical, scientific and financial basis for a comprehensive plan to retrieve an ice core up to 1.5 million years old. The consortium takes care of the pre-site surveys for site selection around Dome C and Dome Fuji, both potentially appropriate regions in East Antarctica. Other science consortia will investigate other regions under the umbrella of the International Partnerships in Ice Core Sciences (IPICS). Of major importance to obtain reliable estimates of the age of the ice in the basal layers of the ice sheet are the physical boundary conditions and ice-flow dynamics: geothermal heat flux, advection and layer integrity to avoid layer overturning and the formation of folds. The project completed the first field season at both regions of interest. This contribution will give an overview how the combined application of various geophysical, geodetical and glaciological methods applied in the field in combination with ice-flow modelling can constrain the glaciological boundary conditions and thus age at depth.

Emergent Dead Vegetation and Paired Cosmogenic Isotope Constraints on Ice Cap Activity, Baffin Island, Arctic Canada

NASA Astrophysics Data System (ADS)

Pendleton, S.; Miller, G. H.

2014-12-01

Recent summer warming has now raised the equilibrium line above almost all ice caps on Baffin Island, resulting in surface lowering and marginal recession everywhere. As cold-based ice recedes it frequently exposes in situ tundra plants that were living at the time ice expanded across the site. Radiocarbon dates for each plant records when cold summers dropped regional snowline below the site, killing the plants, and snowline remained below the site until the collection date. The kill dates also represent the last time that the climate was warm enough to expose the sampling location. Seventy-six vegetation samples collected in 2013 from the Penny Ice Cap region have been dated, with significant age populations at ~0.5, 1.8, 2.3, and 3.6 ka. The absence of ages around ~1, 2, 3, 4.5, and 5.5 ka suggest periods of either no snowline depression or stability. Sixteen vegetation samples returned ages of >45 ka (2 revisited sites from 2010, 14 new). It is postulated that these radiocarbon dead samples were last exposed during the last interglaciation (~120 ka), the last time climate was as warm as present. In addition to plant collections, bedrock exposures at the ice margins were sampled for 26Al/10Be cosmogenic nuclide dating. Seven samples from and around the Penny Ice cap have returned maximum exposure ages from ~ 0.6-0.9 ma and total histories of ~0.6-1.5 ma. In general, samples from the larger Penny Ice Cap exhibited lower amounts of exposure (~20% of total history) than those samples from smaller, localized ice caps (~55%). Radiocarbon dead sites north of the Penny Ice cap experienced significantly more exposure over their lifetimes than their counterparts east of the Penny Ice cap, suggesting significant differences in local and regional land ice fluctuations over the last 2 million years. Utilizing both the method of in situ moss and 26Al/10Be dating provides new insight into both the recent activity and long-term evolution of ice on Baffin Island. In particular these new data help to shed light on how late Holocene coolings affect both large and small ice bodies and how this behavior is represented in the longer-term burial/exposure record contained within the rock surface.

Rapid onset of Little Ice Age summer cold in the northern North Atlantic derived from precisely dated ice cap records (Invited)

NASA Astrophysics Data System (ADS)

Miller, G. H.; Larsen, D.; Geirsdottir, A.; Refsnider, K. A.; Anderson, C.

2009-12-01

Precise radiocarbon dates on dead vegetation emerging beneath retreating non-erosive ice caps in NE Arctic Canada define the onset of ice cap growth, and provide a Holocene context for 20th Century warming. Although most plateau ice caps melted during the Medieval Warm Period, a few that are now disappearing remained intact since at least 350 AD. Little Ice Age ice cap inception occurred in two pulses, centered on 1250-1300 AD and around 1450 AD, with ice caps remaining in an expanded state until the warming of the past few decades. Ice cap inception occurred simultaneously (±10 years) over a 200 m elevational range, suggesting an abrupt onset of Little Ice Age cold, rather than a slow cooling over many decades. Similarly, a 3000 year annually resolved lacustrine record of glacier power and a complementary independent proxy for landscape instability in the highlands of central Iceland show an initial jump in both glacier power and landscape instability between 1250 and 1300 AD, with a second step-increase around 1450 AD, and dramatic increases in both proxies around 1800 AD, retracting in the 20th Century. A sub-decadal record of hillslope stability and within-lake primary productivity in sediments from a low-elevation lake in northern Iceland shows parallel changes at similar times. Sea ice proxies and historical records document the first appearance of sea ice around Iceland following Medieval time about 1250 AD. The similarity in the onset and intensification of Little Ice Age cold-weather proxies across a wide region of the northern North Atlantic suggests at least a regional driver of abrupt climate change. The time intervals for which these abrupt changes occur coincide with the three most intense episodes of multiple explosive volcanic eruptions that introduced large volumes of sulfate aerosols into the stratosphere during the past millennium. Although the direct impacts of volcanic aerosols have a duration of only a few years, the memory stored by the cooled ocean surface waters allows a cumulative effect to have a longer-term impact. To explain the apparent irreversible shift to colder summers following volcanic eruptions requires additional strong positive feedbacks, most likely a consequence of expanded sea ice cover.

Importance of Sea Ice for Validating Global Climate Models

NASA Technical Reports Server (NTRS)

Geiger, Cathleen A.

1997-01-01

Reproduction of current day large-scale physical features and processes is a critical test of global climate model performance. Without this benchmark, prognoses of future climate conditions are at best speculation. A fundamental question relevant to this issue is, which processes and observations are both robust and sensitive enough to be used for model validation and furthermore are they also indicators of the problem at hand? In the case of global climate, one of the problems at hand is to distinguish between anthropogenic and naturally occuring climate responses. The polar regions provide an excellent testing ground to examine this problem because few humans make their livelihood there, such that anthropogenic influences in the polar regions usually spawn from global redistribution of a source originating elsewhere. Concomitantly, polar regions are one of the few places where responses to climate are non-anthropogenic. Thus, if an anthropogenic effect has reached the polar regions (e.g. the case of upper atmospheric ozone sensitivity to CFCs), it has most likely had an impact globally but is more difficult to sort out from local effects in areas where anthropogenic activity is high. Within this context, sea ice has served as both a monitoring platform and sensitivity parameter of polar climate response since the time of Fridtjof Nansen. Sea ice resides in the polar regions at the air-sea interface such that changes in either the global atmospheric or oceanic circulation set up complex non-linear responses in sea ice which are uniquely determined. Sea ice currently covers a maximum of about 7% of the earth's surface but was completely absent during the Jurassic Period and far more extensive during the various ice ages. It is also geophysically very thin (typically <10 m in Arctic, <3 m in Antarctic) compared to the troposphere (roughly 10 km) and deep ocean (roughly 3 to 4 km). Because of these unique conditions, polar researchers regard sea ice as one of the more important features to monitor in terms of heat, mass, and momentum transfer between the air and sea and furthermore, the impact of such responses to global climate.

Episodic Neoglacial snowline descent and glacier expansion on Svalbard reconstructed from the 14C ages of ice-entombed plants

NASA Astrophysics Data System (ADS)

Miller, Gifford H.; Landvik, Jon Y.; Lehman, Scott J.; Southon, John R.

2017-01-01

The response of the Northern Hemisphere cryosphere to the monotonic decline in summer insolation and variable radiative forcing during the Holocene has been one of irregular expansion culminating in the Little Ice Age, when most glaciers attained their maximum late Holocene dimensions. Although periods of intervening still-stand or ice-retreat can be reconstructed by direct dating of ice-recessional features, defining times of Neoglacial ice growth has been limited to indirect proxies preserved in distal archives. Here we report 45 precise radiocarbon dates on in situ plants emerging from beneath receding glaciers on Svalbard that directly date the onset of snowline descent and glacier expansion, entombing the plants. Persistent snowline lowering occurred between 4.0 and 3.4 ka, but with little additional persistent lowering until early in the first millennium AD. Populations of individual 14C calendar age results and their aggregate calendar age probabilities define discrete episodes of vegetation kill and snowline lowering 240-340 AD, 410-540 AD and 670-750 AD, each with a lower snowline than the preceding episode, followed by additional snowline lowering between 1000 and 1220 AD, and between 1300 and 1450 AD. Snowline changes after 1450 AD, including the maximum ice extent of the Little Ice Age are not resolved by our collections, although snowlines remained lower than their 1450 AD level until the onset of modern warming. A time-distance diagram derived from a 250-m-long transect of dated ice-killed plants documents ice-margin advances ∼750, ∼1100 and after ∼1500 AD, concordant with distributed vegetation kill ages seen in the aggregate data set, supporting our central thesis that vegetation kill ages provide direct evidence of snowline lowering and cryospheric expansion. The mid- to late-Holocene history of snowline lowering on Svalbard is similar to ELA reconstructions of Norwegian and Svalbard cirque glaciers, and consistent with a cryospheric response to the secular decline of regional summertime insolation and stepped changes in nearby surface ocean environments. The widespread exposure of entombed plants dating from the first millennium AD suggests that Svalbard's average summer temperatures of the past century now exceed those of any century since at least 700 AD, including medieval times.

Delayed deglaciation or extreme Arctic conditions 21-16 cal. kyr at southeastern Laurentide Ice Sheet margin?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peteet, D. M.; Beh, M.; Orr, C.

The conventionally accepted ages of the Last Glacial Maximum (LGM) retreat of the southeastern Laurentide Ice Sheet (LIS) are 26–21 cal. kyr (derived from bulk-sediment radiocarbon ages) and 28–23 cal. kyr (varve estimates). By utilizing accelerator mass spectrometry (AMS) 14C dating of earliest macrofossils in 13 lake/bog inorganic clays, we find that vegetation first appeared on the landscape at 16–15 cal. kyr, suggesting ice had not retreated until that time. The gap between previous age estimates and ours is significant and has large implications for our understanding of ocean-atmosphere linkages. Older ages imply extreme Arctic conditions for 9–5 cal kyr;more » a landscape with no ice, yet no deposition in lakes. Also, our new AMS chronology of LIS retreat is consistent with marine evidence of deglaciation from the N. Atlantic, showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid, perhaps delaying ice melt.« less

Delayed deglaciation or extreme Arctic conditions 21-16 cal. kyr at southeastern Laurentide Ice Sheet margin?

DOE PAGES

Peteet, D. M.; Beh, M.; Orr, C.; ...

2012-06-15

The conventionally accepted ages of the Last Glacial Maximum (LGM) retreat of the southeastern Laurentide Ice Sheet (LIS) are 26–21 cal. kyr (derived from bulk-sediment radiocarbon ages) and 28–23 cal. kyr (varve estimates). By utilizing accelerator mass spectrometry (AMS) 14C dating of earliest macrofossils in 13 lake/bog inorganic clays, we find that vegetation first appeared on the landscape at 16–15 cal. kyr, suggesting ice had not retreated until that time. The gap between previous age estimates and ours is significant and has large implications for our understanding of ocean-atmosphere linkages. Older ages imply extreme Arctic conditions for 9–5 cal kyr;more » a landscape with no ice, yet no deposition in lakes. Also, our new AMS chronology of LIS retreat is consistent with marine evidence of deglaciation from the N. Atlantic, showing significant freshwater input and sea level rise only after 19 cal kyr with a cold meltwater lid, perhaps delaying ice melt.« less

Ice cores and SeaRISE: What we do (and don't) know

NASA Technical Reports Server (NTRS)

Alley, Richard B.

1991-01-01

Ice core analyses are needed in SeaRISE to learn what the West Antarctic ice sheet and other marine ice sheets were like in the past, what climate changes led to their present states, and how they behave. The major results of interest to SeaRISE from previous ice core analyses in West Antarctic are that the end of the last ice age caused temperature and accumulation rate increases in inland regions, leading to ice sheet thickening followed by thinning to the present.

Age of the Pineo Ridge System: Implications for behavior of the Laurentide Ice Sheet in eastern Maine, U.S.A., during the last deglaciation

NASA Astrophysics Data System (ADS)

Hall, Brenda L.; Borns, Harold W.; Bromley, Gordon R. M.; Lowell, Thomas V.

2017-08-01

The Laurentide Ice Sheet was a major driver of global sea-level change during the last deglaciation and may have impacted both atmospheric and oceanic circulation. An understanding of past changes in the ice sheet is important for constraining its interaction with other components of the climate system. Here, we present the geologic context and chronology for ice-sheet fluctuations in eastern Maine, adjacent to the North Atlantic Ocean, thought to be a key player in the termination of the last ice age. Retreat of the Laurentide Ice Sheet through coastal Maine first produced a series of lobate grounding-line moraines, followed by deposition of the prominent Pineo Ridge System, which crosscut the earlier moraine set and which is characterized by extensive ice-contact deltas, closely spaced parallel moraines, and association with eskers. Our new 10Be surface exposure ages indicate that the Pineo Ridge System, which extends for more than 100 km in eastern Maine and Atlantic Canada, dates to ∼15.3 ka, ∼800 years older than recent estimates. Our data are in accord with inboard minimum-limiting radiocarbon ages of terrestrial materials, which indicate deglaciation as early as 15.3 ka, as well as of marine shells that are as old as 15.0 ka. Both the deglaciation that produced the lobate moraines and the short-lived readvance that led to the Pineo Ridge System occurred during Heinrich Stadial 1. Given that faunal and isotopic evidence indicates that the ocean remained cold during deglaciation of coastal Maine, we infer that ice recession was due to rising summer air temperatures that gave way briefly to cooling to allow minor readvance. Glacial deposits north of the Pineo Ridge System display evidence of ice stagnation and downwasting, suggesting rapid ice retreat following deposition of the delta-moraine complex, coincident with the onset of the Bølling.

Age and origin of ice-rich Yedoma silts at Duvanny Yar, northeast Siberia: a record of Beringian environmental change since the last interglacial

NASA Astrophysics Data System (ADS)

Murton, J.; Edwards, M. E.; Murton, D.; Bateman, M.; Haile, J.

2010-12-01

Silty Yedoma deposits at the important Beringian site of Duvanny Yar (68o,37’ N; 159o08’ E) in northeast Siberia, have been interpreted before as both loess and nival deposits. The yedoma deposits form a stratigraphic unit more than 30 m thick that comprises sandy silts which are generally massive and rich in ground ice and organic material. The ground ice includes pore ice, segregated ice and wedge ice (both syngenetic and epigenetic), and much of it accumulated more or less coevally with deposition of the silt and upward growth of permafrost. Organic material includes pervasive rootlets of former steppe-tundra vegetation (e.g. grasses), vertebrate bones (e.g. mammoth, bison, horse), pollen, insect remains, and plant macrofossils. A number of cryoturbated organic horizons within the silts are interpreted as incipient palaeosols. The sedimentary properties of the silts (particle size and magnetic susceptibility) and the palaeocological characteristics of the contained organic material are both consistent with deposition of silts primarily as loess and loess-sand intergrades, sedimentologically similar to known aeolian deposits in northwest Europe (e.g. Pegwell Bay, UK). Deposition primarily by snow meltwater is unlikely because the nearest uplands where snow could have accumulated and hillslopes could have provided runoff sites are many kilometers distant. The remnants of the original landsurface—prior to thermokarst activity during the late-glacial and Holocene—indicate an essentially flat landscape during dust deposition. Radiocarbon dating of mainly in situ rootlets indicates a complete record of dust deposition during the Last Glacial Maximum (LGM), potentially one of the best terrestrial records of LGM palaeoenvironments. Older radiocarbon dates suggest at least two periods of soil formation between the LGM and about 40,000 radiocarbon years BP (within Marine Isotope Stage 3). Optical dating is currently being undertaken to constrain the ages of older dust deposits and palaeosols. U-series dating of wood contained within thaw-lake deposits at the base of the sequence provides an age from the Last Interglacial. Overall, dating of the yedoma sequence constrains interpretation of ancient soil DNA contained within the silts and provides a basis for reconstructing LGM palaeo-wind conditions associated with the Siberian high-pressure cell.

How will melting of ice affect volcanic hazards in the twenty-first century?

PubMed

Tuffen, Hugh

2010-05-28

Glaciers and ice sheets on many active volcanoes are rapidly receding. There is compelling evidence that melting of ice during the last deglaciation triggered a dramatic acceleration in volcanic activity. Will melting of ice this century, which is associated with climate change, similarly affect volcanic activity and associated hazards? This paper provides a critical overview of the evidence that current melting of ice will increase the frequency or size of hazardous volcanic eruptions. Many aspects of the link between ice recession and accelerated volcanic activity remain poorly understood. Key questions include how rapidly volcanic systems react to melting of ice, whether volcanoes are sensitive to small changes in ice thickness and how recession of ice affects the generation, storage and eruption of magma at stratovolcanoes. A greater frequency of collapse events at glaciated stratovolcanoes can be expected in the near future, and there is strong potential for positive feedbacks between melting of ice and enhanced volcanism. Nonetheless, much further research is required to remove current uncertainties about the implications of climate change for volcanic hazards in the twenty-first century.

A middle Pleistocene through middle Miocene moraine sequence in the central Transantarctic Mountains, Antarctica

NASA Astrophysics Data System (ADS)

Balter, A.; Bromley, G. R.; Balco, G.; Thomas, H.; Jackson, M. S.

2017-12-01

Ice-free areas at high elevation in the central Transantarctic Mountains preserve extensive moraine sequences and drift deposits that comprise a geologic record of former East Antarctic Ice Sheet thickness and extent. We are applying cosmogenic-nuclide exposure dating to determine the ages of these moraine sequences at Roberts Massif and Otway Massif, at the heads of the Shackleton and Beardmore Glaciers, respectively. Moraines at these sites are for the most part openwork boulder belts characteristic of deposition by cold-based ice, which is consistent with present climate and glaciological conditions. To develop our chronology, we collected samples from 30 distinct ice-marginal landforms and have so far measured >100 3He, 10Be, and 21Ne exposure ages. Apparent exposure ages range from 1-14 Ma, which shows that these landforms record glacial events between the middle Pleistocene and middle Miocene. These data show that the thickness of the East Antarctic Ice Sheet in this region was similar to or thicker than present for long periods between the middle Miocene and today. The time range represented by these moraine sequences indicates that they may also provide direct geologic evidence for East Antarctic Ice Sheet behavior during past periods of warmer-than-present climate, specifically the Miocene and Pliocene. As the East Antarctic Ice Sheet is the largest ice sheet on earth, understanding its sensitivity to warm-climate conditions is critical for projections of ice sheet behavior and sea-level rise in future warm climates.

Icing: Accretion, Detection, Protection

NASA Technical Reports Server (NTRS)

Reinmann, John J.

1994-01-01

The global aircraft industry and its regulatory agencies are currently involved in three major icing efforts: ground icing; advanced technologies for in-flight icing; and tailplane icing. These three major icing topics correspondingly support the three major segments of any aircraft flight profile: takeoff; cruise and hold; and approach and land. This lecture addressess these three topics in the same sequence as they appear in flight, starting with ground deicing, followed by advanced technologies for in-flight ice protection, and ending with tailplane icing.

Pilots' Information Needs and Strategies for Operating in Icing Conditions

NASA Technical Reports Server (NTRS)

Vigeant-Langlois, Laurence N.; Hansman, R. John

2003-01-01

Pilot current use of icing information, pilot encounters and strategies for dealing with in-flight aircraft structural icing situations, and desired attributes of new icing information systems were investigated through a survey of pilots of several operational categories. The survey identified important information elements and fiequently used information paths for obtaining icing-related information. Free- response questions solicited descriptions of significant , icing encounters, and probed key icing-related decision and information criteria. Results indicated the information needs for the horizontal and vertical location of icing conditions and the identification of icing-free zones.

Causes of ice age intensification across the Mid-Pleistocene Transition

PubMed Central

Foster, Gavin L.; Rohling, Eelco J.; Sexton, Philip F.; Cherry, Soraya G.; Hasenfratz, Adam P.; Haug, Gerald H.; Martínez-García, Alfredo; Pälike, Heiko; Pancost, Richard D.; Wilson, Paul A.

2017-01-01

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth’s orbitally paced ice age cycles intensified, lengthened from ∼40,000 (∼40 ky) to ∼100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ∼43 to ∼75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets. PMID:29180424

Causes of ice age intensification across the Mid-Pleistocene Transition

NASA Astrophysics Data System (ADS)

Chalk, Thomas B.; Hain, Mathis P.; Foster, Gavin L.; Rohling, Eelco J.; Sexton, Philip F.; Badger, Marcus P. S.; Cherry, Soraya G.; Hasenfratz, Adam P.; Haug, Gerald H.; Jaccard, Samuel L.; Martínez-García, Alfredo; Pälike, Heiko; Pancost, Richard D.; Wilson, Paul A.

2017-12-01

During the Mid-Pleistocene Transition (MPT; 1,200–800 kya), Earth's orbitally paced ice age cycles intensified, lengthened from ˜40,000 (˜40 ky) to ˜100 ky, and became distinctly asymmetrical. Testing hypotheses that implicate changing atmospheric CO2 levels as a driver of the MPT has proven difficult with available observations. Here, we use orbitally resolved, boron isotope CO2 data to show that the glacial to interglacial CO2 difference increased from ˜43 to ˜75 μatm across the MPT, mainly because of lower glacial CO2 levels. Through carbon cycle modeling, we attribute this decline primarily to the initiation of substantive dust-borne iron fertilization of the Southern Ocean during peak glacial stages. We also observe a twofold steepening of the relationship between sea level and CO2-related climate forcing that is suggestive of a change in the dynamics that govern ice sheet stability, such as that expected from the removal of subglacial regolith or interhemispheric ice sheet phase-locking. We argue that neither ice sheet dynamics nor CO2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets.

Overview of Sea-Ice Properties, Distribution and Temporal Variations, for Application to Ice-Atmosphere Chemical Processes.

NASA Astrophysics Data System (ADS)

Moritz, R. E.

2005-12-01

The properties, distribution and temporal variation of sea-ice are reviewed for application to problems of ice-atmosphere chemical processes. Typical vertical structure of sea-ice is presented for different ice types, including young ice, first-year ice and multi-year ice, emphasizing factors relevant to surface chemistry and gas exchange. Time average annual cycles of large scale variables are presented, including ice concentration, ice extent, ice thickness and ice age. Spatial and temporal variability of these large scale quantities is considered on time scales of 1-50 years, emphasizing recent and projected changes in the Arctic pack ice. The amount and time evolution of open water and thin ice are important factors that influence ocean-ice-atmosphere chemical processes. Observations and modeling of the sea-ice thickness distribution function are presented to characterize the range of variability in open water and thin ice.

Challenges in validating model results for first year ice

NASA Astrophysics Data System (ADS)

Melsom, Arne; Eastwood, Steinar; Xie, Jiping; Aaboe, Signe; Bertino, Laurent

2017-04-01

In order to assess the quality of model results for the distribution of first year ice, a comparison with a product based on observations from satellite-borne instruments has been performed. Such a comparison is not straightforward due to the contrasting algorithms that are used in the model product and the remote sensing product. The implementation of the validation is discussed in light of the differences between this set of products, and validation results are presented. The model product is the daily updated 10-day forecast from the Arctic Monitoring and Forecasting Centre in CMEMS. The forecasts are produced with the assimilative ocean prediction system TOPAZ. Presently, observations of sea ice concentration and sea ice drift are introduced in the assimilation step, but data for sea ice thickness and ice age (or roughness) are not included. The model computes the age of the ice by recording and updating the time passed after ice formation as sea ice grows and deteriorates as it is advected inside the model domain. Ice that is younger than 365 days is classified as first year ice. The fraction of first-year ice is recorded as a tracer in each grid cell. The Ocean and Sea Ice Thematic Assembly Centre in CMEMS redistributes a daily product from the EUMETSAT OSI SAF of gridded sea ice conditions which include "ice type", a representation of the separation of regions between those infested by first year ice, and those infested by multi-year ice. The ice type is parameterized based on data for the gradient ratio GR(19,37) from SSMIS observations, and from the ASCAT backscatter parameter. This product also includes information on ambiguity in the processing of the remote sensing data, and the product's confidence level, which have a strong seasonal dependency.

Validation of the FAST skating protocol to predict aerobic power in ice hockey players.

PubMed

Petrella, Nicholas J; Montelpare, William J; Nystrom, Murray; Plyley, Michael; Faught, Brent E

2007-08-01

Few studies have reported a sport-specific protocol to measure the aerobic power of ice hockey players using a predictive process. The purpose of our study was to validate an ice hockey aerobic field test on players of varying ages, abilities, and levels. The Faught Aerobic Skating Test (FAST) uses an on-ice continuous skating protocol on a course measuring 160 feet (48.8 m) using a CD to pace the skater with a beep signal to cross the starting line at each end of the course. The FAST incorporates the principle of increasing workload at measured time intervals during a continuous skating exercise. Step-wise multiple regression modelling was used to determine the estimate of aerobic power. Participants completed a maximal aerobic power test using a modified Bruce incremental treadmill protocol, as well as the on-ice FAST. Normative data were collected on 406 ice hockey players (291 males, 115 females) ranging in age from 9 to 25 y. A regression to predict maximum aerobic power was developed using body mass (kg), height (m), age (y), and maximum completed lengths of the FAST as the significant predictors of skating aerobic power (adjusted R2 = 0.387, SEE = 7.25 mL.kg-1.min-1, p < 0.0001). These results support the application of the FAST in estimating aerobic power among male and female competitive ice hockey players between the ages of 9 and 25 years.

Recent low-latitude freeze thaw on Mars

NASA Astrophysics Data System (ADS)

Page, David P.

2007-07-01

Outside polar latitudes, features corresponding to surface thaw have yet to be identified on Mars. The youthful gully landforms observed at mid-high latitude [Malin, M., Edgett, K., 2000. Science 288, 2330-2335] are the nearest candidate, but the source (and nature) of the gully carving agent remains controversial [e.g., Musselwhite, D.S., Swindle, T.D., Lunine, J.I., 2001. Geophys. Res. Lett. 28, 1283-1285; Mellon, M.T., Phillips, R.J., 2001. J. Geophys. Res. 106, 1-15; Knauth, L.P., Burt, D.M., 2002. Icarus 158, 267-271; Costard, F., Forget, F., Mangold, N., Peulvast, J.P., 2002. Science 295, 110-113; Christensen, P.R., 2003. Nature 422, 45-48; Treiman, A.H., 2003. J. Geophys. Res. 108]. At higher obliquity than the present epoch, near-surface ground ice should be present globally [Mellon, M.T., Jakosky, B.M., 1995. J. Geophys. Res. 100 (E6), 11781-11799], populated by condensation of atmospheric water vapour in the top few metres of the regolith, or emplaced as dusty ice sheets reaching down towards the equator. The latitudinal restriction of these gullies to regions poleward of ±30° appears to argue against a thaw component to their formation—since ground ice is present and stable at all latitudes at high obliquity, the current (low) obliquity regime should result in ground ice thaw at low latitudes, where insolation and daytime temperatures are currently greatest, and this is not observed. A previously undescribed meltwater sequence in the Cerberus plains, at 20° N/187° E, shows that comparable, but much more continuous, and mappable melting and surface runoff have occurred in the geologically recent past at near-equatorial latitudes on Mars. Polygonal ground in the Cerberus plains is seen by the Mars Global Surveyor Mars Orbiter Camera (MOC) to suffer sequential, regional-scale volatile-loss consistent with thaw of near-surface ground ice under periglacial conditions. This degradation is continuously sampled by a single MOC strip, showing an icy landscape undergoing thaw modification and collapse, and may form the first evidence of equatorial wet-based glaciation during late Amazonian time, with indications of melting within the last million years. The dissolution and re-formation of polygonal ground links this landform to freeze-thaw processes, providing the conclusion to a question that has been the subject of debate for three decades—whether Mars' polygonal grounds require ice to form—and a consistent explanation for the fate of the water that carved the great outflow channels, much of which may still reside as ground ice in the regolith. This thaw occurs in the Cerberus Formation; deposits that are considered to be magmatic in origin, and the type formation for late-stage, "plains-style" volcanism on Mars [Keszthelyi, L., McEwen, A.S., Thordarson T., 2000. J. Geophys. Res. 105, 15027-15049]. By superposing large numbers of small impact craters, polygonal ground in the Cerberus plains sustains previous suggestions of a non-magmatic origin for this and other landforms in the region [Page, D.P., Murray, J.B., 2006. Icarus 183, 46-54]. Together, these periglacial landforms document evidence of climate change much younger than is currently recognised by crater counts, with important implications for age constraints on young surfaces and absolute age determinations by this method. It is tentatively suggested that this melting may be occurring today, with a striking correspondence between permafrost thaw in the Cerberus plains, the high atmospheric methane flux currently observed over this region [Mumma, M.J., Novak, R.E., DiSanti, M.A., Bonev, B.P., Dello Russo, N., 2004. Bull. Am. Astron. Soc. 36, 1127; Krasnopolsky, V.A., Maillard, J.P., Owen, T.C., 2004. Icarus 172, 537-547; Formisano, V., Atreya, S., Encrenaz, T., Ignatiev, N., Giuranna, M., 2004. Science 306, 1758-1761], and the only latitude zone on Mars—equatorward of 30° N—where melting of ground ice is thought possible in the current climate [Haberle, R.M., McKay, C.P., Schaeffer, J., Cabrol, N.A., Grin, E.A., Zent, A.P., Quinn, R., 2001. J. Geophys. Res. 106 (E10), 23317-23326; Lobitz, B., Wood, B.L., Averner, M.M., McKay, C.P., 2001. Proc. Natl. Acad. Sci. 98, 2132-2137]. Low-latitude polygonal ground as transient, and hydrologically active over wide areas transforms our understanding of the recent climatic evolution of Mars, supporting models of atmospheric water-ice migration [Mischna, M., Richardson, M.I., Wilson, R.J., McCleese, D.J., 2003. J. Geophys. Res. 108 (E6). 5062], complex, volatile stratigraphies [Clifford, S.M., Parker, T.J., 2001. Icarus 154, 40-79], and hypothesised, geologically recent 'ice ages' [Head, J.W., Mustard, J.F., Kreslavsky, M.A., Milliken, R.E., Marchant, D.R., 2003. Nature 426, 797-802]. The temporal coincidence of glacial epochs on the Earth and Mars during the Quaternary and latest Amazonian would suggest a coupled system linking both [Sagan, C., Young, A.T., 1973. Nature 243, 459].

Evidence for smaller extents of the northwestern Greenland Ice Sheet and North Ice Cap during the Holocene

NASA Astrophysics Data System (ADS)

Kelly, M. A.; Osterberg, E. C.; Axford, Y.; Bigl, M.; Birkel, S. D.; Corbett, L. B.; Roy, E. P.; Thompson, J. T.; Whitecloud, S.

2013-12-01

The Greenland Ice Sheet (GrIS) and local glaciers on Greenland are responding dynamically to warming temperatures with widespread retreat. GRACE satellite data (e.g., Kahn et al., 2010) and the Petermann Glacier calving events document the recent expansion of ice loss into northwestern Greenland. To improve the ability to estimate future ice loss in a warming climate, we are developing records of the response of the northwestern Greenlandic cryosphere to Holocene climatic conditions, with a focus on past warm periods. Our ongoing research includes analyses of glacial geology, sub-fossil vegetation, lake sediment cores, chironomid assemblages and ice cores combined with glaciological modeling. To constrain past ice extents that were as small as, or smaller than, at present, we recovered sub-fossil vegetation exposed at the receding margins of the GrIS and North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W) and of the GrIS near Thule (~76.5°N, 68.7°W). We present vegetation types and radiocarbon ages of 30 plant samples collected in August 2012. In the Nunatarssuaq region, five ages of in situ (rooted) vegetation including Polytrichum moss, Saxifraga nathorstii and grasses located <5 m outboard of the GrIS margin are ~120-200 cal yr BP (range of medians of the 2-sigma calibrated age ranges). Nine ages of in situ Polytrichum, Saxifraga oppositafolia and grasses from ~1-5 m inboard of the NIC margin (excavated from beneath ice) range from ~50 to 310 cal yr BP. The growth of these plants occurred when the GrIS and NIC were at least as small as at present and their ages suggest that ice advances occurred in the last 50-120 yrs. In addition to the in situ samples, we collected plants from well-preserved ground material exposed along shear planes in the GrIS margins. In Nunatarssuaq, two Polytrichum mosses rooted in ground material and exposed along a shear plane in the GrIS margin date to 4680 and 4730 cal yr BP. Near Thule, three ages of Salix arctica rooted in ground material and exposed along a shear plane in the GrIS are ~170-390 cal yr BP. Four ages of plant fragments within ice in a shear plane in the NIC margin are ~600-950 cal yr BP. Since these organic remains have been transported from beneath the GrIS and NIC, respectively, they indicate times of smaller than present ice extents. Together these plants provide evidence that the northwestern GrIS was smaller than at present at ~4600-4800 and ~170-390 cal yr BP. Advance to the modern GrIS extent was likely underway at of after ~170 cal yr BP. NIC was smaller than at present at ~600-950 cal yr. Our ongoing research is investigating the climatic conditions during these times and the relationship of these restricted ice extents to those documented elsewhere on Greenland as well as on Baffin Island.

The Little Ice Age and Solar Activity

NASA Astrophysics Data System (ADS)

Velasco Herrera, Victor Manuel; Leal Silva, C. M. Carmen; Velasco Herrera, Graciela

We analyze the ice winter severity index on the Baltic region since 1501-1995. We found that the variability of this index is modulated among other factors by the secular solar activity. The little ice ages that have appeared in the North Hemisphere occurred during periods of low solar activity. Seemingly our star is experiencing a new quiet stage compared with Maunder or Dalton minimum, this is important because it is estimated that even small changes in weather can represent a great impact in ice index. These results are relevant since ice is a very important element in the climate system of the Baltic region and it can affect directly or indirectly many of the oceanographic, climatic, eco-logical, economical and cultural patterns.

Proceedings of the Airframe Icing Workshop

NASA Technical Reports Server (NTRS)

Colantonio, Ron O. (Editor)

2009-01-01

The NASA Glenn Research Center (GRC) has a long history of working with its partners towards the understanding of ice accretion formation and its associated degradation of aerodynamic performance. The June 9, 2009, Airframe Icing Workshop held at GRC provided an opportunity to examine the current NASA airframe icing research program and to dialogue on remaining and emerging airframe icing issues and research with the external community. Some of the airframe icing gaps identified included, but are not limited to, ice accretion simulation enhancements, three-dimensional benchmark icing database development, three-dimensional iced aerodynamics modeling, and technology development for a smart icing system.

Lichenometry in the Cordillera Blanca, Peru: “Little Ice Age” moraine chronology

NASA Astrophysics Data System (ADS)

Solomina, Olga; Jomelli, Vincent; Kaser, Georg; Ames, Alcides; Berger, Bernhard; Pouyaud, Bernard

2007-10-01

This paper is a comparison and compilation of lichenometric and geomorphic studies performed by two independent teams in the Cordillera Blanca, Peru, in 1996 and 2002 on 66 "Little Ice Age" moraines of 14 glaciers. Using eleven new control points, we recalibrated the initial rapid growth phase of the previously established Rhizocarpon subgenus Rhizocarpon growth curve. This curve was then used to estimate the age of "Little Ice Age" moraines. The time of deposition of the most prominent and numerous terminal and lateral moraines on the Pacific-facing side of the Cordillera Blanca (between AD 1590 and AD 1720) corresponds to the coldest and wettest phase in the tropical Andes as revealed by ice-core data. Less prominent advances occurred between AD 1780 and 1880.

Erosion patterns produced by the paleo Haizishan ice cap, SE Tibetan Plateau

NASA Astrophysics Data System (ADS)

Fu, P.; Stroeven, A. P.; Harbor, J.; Hättestrand, C.; Heyman, J.; Caffee, M. W.

2017-12-01

Erosion is a primary driver of landscape evolution, topographic relief production, geochemical cycles, and climate change. Combining in situ 10Be and 26Al exposure age dating, geomorphological mapping, and field investigations, we examine glacial erosion patterns of the almost 4,000 km2 paleo Haizishan ice cap on the southeastern Tibetan Plateau. Our results show that ice caps on the low relief Haizishan Plateau produced a zonal pattern of landscape modification. In locations where apparent exposure ages on bedrock are consistent with the last deglaciation, complete resetting of the cosmogenic exposure age clock indicates glacial erosion of at least a few meters. However, older apparent exposure ages on bedrock in areas known to have been covered by the paleo ice cap during the Last Glacial Maximum indicate inheritance and thus limited glacial erosion. Inferred surface exposure ages from cosmogenic depth profiles through two saprolites vary from resetting and thus saprolite profile truncation to nuclide inheritance indicating limited erosion. Finally, significant nuclide inheritance in river sand samples from basins on the scoured plateau surface also indicate limited glacial erosion during the last glaciation. Hence, for the first time, our study shows clear evidence of preservation under non-erosive ice on the Tibetan Plateau. As patterns of glacial erosion intensity are largely driven by the basal thermal regime, our results confirm earlier inferences from geomorphology for a concentric basal thermal pattern for the paleo Haizishan ice cap during the LGM.

NWS Alaska Sea Ice Program: Operations and Decision Support Services

NASA Astrophysics Data System (ADS)

Schreck, M. B.; Nelson, J. A., Jr.; Heim, R.

2015-12-01

The National Weather Service's Alaska Sea Ice Program is designed to service customers and partners operating and planning operations within Alaska waters. The Alaska Sea Ice Program offers daily sea ice and sea surface temperature analysis products. The program also delivers a five day sea ice forecast 3 times each week, provides a 3 month sea ice outlook at the end of each month, and has staff available to respond to sea ice related information inquiries. These analysis and forecast products are utilized by many entities around the state of Alaska and nationally for safety of navigation and community strategic planning. The list of current customers stem from academia and research institutions, to local state and federal agencies, to resupply barges, to coastal subsistence hunters, to gold dredgers, to fisheries, to the general public. Due to a longer sea ice free season over recent years, activity in the waters around Alaska has increased. This has led to a rise in decision support services from the Alaska Sea Ice Program. The ASIP is in constant contact with the National Ice Center as well as the United States Coast Guard (USCG) for safety of navigation. In the past, the ASIP provided briefings to the USCG when in support of search and rescue efforts. Currently, not only does that support remain, but our team is also briefing on sea ice outlooks into the next few months. As traffic in the Arctic increases, the ASIP will be called upon to provide more and more services on varying time scales to meet customer needs. This talk will address the many facets of the current Alaska Sea Ice Program as well as delve into what we see as the future of the ASIP.

NWS Alaska Sea Ice Program: Operations, Customer Support & Challenges

NASA Astrophysics Data System (ADS)

Heim, R.; Schreck, M. B.

2016-12-01

The National Weather Service's Alaska Sea Ice Program is designed to service customers and partners operating and planning operations within Alaska waters. The Alaska Sea Ice Program offers daily sea ice and sea surface temperature analysis products. The program also delivers a five day sea ice forecast 3 times each week, provides a 3 month sea ice outlook at the end of each month, and has staff available to respond to sea ice related information inquiries. These analysis and forecast products are utilized by many entities around the state of Alaska and nationally for safety of navigation and community strategic planning. The list of current customers stem from academia and research institutions, to local state and federal agencies, to resupply barges, to coastal subsistence hunters, to gold dredgers, to fisheries, to the general public. Due to a longer sea ice free season over recent years, activity in the waters around Alaska has increased. This has led to a rise in decision support services from the Alaska Sea Ice Program. The ASIP is in constant contact with the National Ice Center as well as the United States Coast Guard (USCG) for safety of navigation. In the past, the ASIP provided briefings to the USCG when in support of search and rescue efforts. Currently, not only does that support remain, but our team is also briefing on sea ice outlooks into the next few months. As traffic in the Arctic increases, the ASIP will be called upon to provide more and more services on varying time scales to meet customer needs. This talk will address the many facets of the current Alaska Sea Ice Program as well as delve into what we see as the future of the ASIP.

Crystal alignments in the Fast ice of arctic Alaska

NASA Astrophysics Data System (ADS)

Weeks, W. F.; Gow, A. J.

1980-02-01

Field observations at 60 sites located in the fast or near-fast ice along a 1200-km stretch of the north coast of Alaska between the Bering Strait and Barter Island have shown that the great majority of the ice samples (95%) exhibit striking c axis alignments within the horizontal plane. In all cases the degree of preferred orientation increased with depth in the ice. Representative standard deviations around a mean direction in the horizontal plane are commonly less than ±10° for samples collected near the bottom of the ice. At a given site the mean c axis direction ?0 may vary as much as 20° with vertical location in the ice sheet. The c axis allignments in the nearshore region generally parallel the coast, with strong alignments occurring in the lagoon systems between the barrier islands and the coast and seaward of the barrier islands. In passes between islands and in entrances such as the opening to Kotzebue Sound the alignment is parallel to the channel. Only limited observations are available farther seaward over the inner (10- to 50-m isobaths) and outer (50-m isobath to shelf break) shelf regions. These indicate NE-SW and E-W alignments, respectively, in the Beaufort Sea north of Prudhoe Bay. The general patterns of the alignments support the correlation between the preferred c axis direction and the current direction at the ice/water interface suggested by Weeks and Gow (1978). A comparison between c axis alignments and instantaneous current measurements made at 42 locations shows that the most frequent current direction coincides with ?0. At the one site where we were able to determine the current direction (52°T) over a longer period (7 hours), the agreement with ?0. (48°T) was excellent. Similarly, if only ?0. values determined in the nearshore region are considered, the most frequent deviation is 10° or less between ?0. and the trend of the adjacent shoreline, which is presumably parallel to the prevailing longshore currents. The c axis alignments are believed to be the result of geometric selection, with the most favored orientation being that in which the current flows normal to the (0001) plates of ice that comprise the dendritic sea ice/seawater interface. The instantaneous current observations suggest SW nearshore currents along the Chukchi coast between SW of Point Lay and SW of the Rogers-Post Monument. In the vicinity of Barrow all currents measured along the Chukchi coast were toward the NE. Current directions along the Beaufort coast in the nearshore region were generally parallel to the coast, with 45% of the observations indicating currents toward the E and 55% currents toward the W.

Pack ice along the Kamchatka Peninsula, Russia as seen from STS-60

NASA Technical Reports Server (NTRS)

1994-01-01

Pack ice is documented in this photograph along the coast of the Kamchatka Peninsula of Russia in Zaliv Ozernoj. Detailed photographs of the ice provide information to scientists in both Russia and the United States about the location and fluctuation of ice edges, and how this new sea ice interacts with ocean and littoral currents.

Ice core carbonyl sulfide measurements from a new South Pole ice core (SPICECORE)

NASA Astrophysics Data System (ADS)

Aydin, M.; Nicewonger, M. R.; Saltzman, E. S.

2017-12-01

Carbonyl sulfide (COS) is the most abundant sulfur gas in the troposphere with a present-day mixing ratio of about 500 ppt. Direct and indirect emissions from the oceans are the predominant sources of atmospheric COS. The primary removal mechanism is uptake by terrestrial plants during photosynthesis. Because plants do not respire COS, atmospheric COS levels are linked to terrestrial gross primary productivity (GPP). Ancient air trapped in polar ice cores has been used to reconstruct COS records of the past atmosphere, which can be used to infer past GPP variability and potential changes in oceanic COS emission. We are currently analyzing samples from a newly drilled intermediate depth ice core from South Pole, Antarctica (SPICECORE). This core is advantageous for studying COS because the cold temperatures of South Pole ice lead to very slow rates of in situ loss due to hydrolysis. One hundred and eighty-four bubbly ice core samples have been analyzed to date with gas ages ranging from about 9.2 thousand (733 m depth) to 75 years (126 m depth) before present. After a 2% correction for gravitational enrichment in the firn, the mean COS mixing ratio for the data set is 312±15 ppt (±1s), with the data set median also equal to 312 ppt. The only significant long-term trend in the record is a 5-10% increase in COS during the last 2-3 thousand years of the Holocene. The SPICECORE data agree with previously published ice core COS records from other Antarctic sites during times of overlap, confirming earlier estimates of COS loss rates to in situ hydrolysis in ice cores. Antarctic ice core data place strict constraints on the COS mixing ratio and its range of variability in the southern hemisphere atmosphere during the last several millennia. Implications for the atmospheric COS budget will be discussed.

Modelled non-linear response to climate of Hardangerjøkulen ice cap, southern Norway, since the mid-Holocene

NASA Astrophysics Data System (ADS)

Åkesson, Henning; Nisancioglu, Kerim H.; Giesen, Rianne H.; Morlighem, Mathieu

2016-04-01

Glacier and ice cap volume changes currently amount to half of the total cryospheric contribution to sea-level rise and are projected to remain substantial throughout the 21st century. To simulate glacier behavior on centennial and longer time scales, models rely on simplified dynamics and tunable parameters for processes not well understood. Model calibration is often done using present-day observations, even though the relationship between parameters and parametrized processes may be altered for significantly different glacier states. In this study, we simulate the Hardangerjøkulen ice cap in southern Norway since the mid-Holocene, through the Little Ice Age (LIA) and into the future. We run an ensemble for both calibration and transient experiments, using a two-dimensional ice flow model with mesh refinement. For the Holocene, we apply a simple mass balance forcing based on climate reconstructions. For the LIA until 1962, we use geomorphological evidence and measured outlet glacier positions to find a mass balance history, while we use direct mass balance measurements from 1963 until today. Given a linear climate forcing, we show that Hardangerøkulen grew from ice-free conditions in the mid-Holocene, to its maximum LIA extent in a highly non-linear fashion. We relate this to local bed topography and demonstrate that volume and area of some but not all outlet glaciers, as well as the entire ice cap, become decoupled for several centuries during our simulation of the late Holocene, before co-varying approaching the LIA. Our model is able to simulate most recorded ice cap and outlet glacier changes from the LIA until today. We show that present-day Hardangerøkulen is highly sensitive to mass balance changes, and estimate that the ice cap will melt completely by the year 2100.

Smart skin technology development for measuring ice accretion, stall, and high AOA aircraft performance. Part 1: Capacitive ice detector development

NASA Technical Reports Server (NTRS)

Pruzan, Daniel A.; Khatkhate, Ateen A.; Gerardi, Joseph J.; Hickman, Gail A.

1993-01-01

A reliable way to detect and measure ice accretion during flight is required to reduce the hazards of icing currently threatening present day aircraft. Many of the sensors used for this purpose are invasive (probe) sensors which must be placed in areas of the airframe where ice does not naturally form. Due to the difference in capture efficiency of the exposed surface, difficulties result in correlating the ice accretion on the probe to what is happening on a number of vastly different airfoil sections. Most flush mounted sensors in use must be integrated into the aircraft surface by cutting or drilling the aircraft surface. An alternate type of ice detector which is based on a NASA patent is currently being investigated at Innovative Dynamics, Inc. (IDI). Results of the investigation into the performance of different capacitive type sensor designs, both rigid as well as elastic, are presented.

Seasonal to interannual Arctic sea ice predictability in current global climate models

NASA Astrophysics Data System (ADS)

Tietsche, S.; Day, J. J.; Guemas, V.; Hurlin, W. J.; Keeley, S. P. E.; Matei, D.; Msadek, R.; Collins, M.; Hawkins, E.

2014-02-01

We establish the first intermodel comparison of seasonal to interannual predictability of present-day Arctic climate by performing coordinated sets of idealized ensemble predictions with four state-of-the-art global climate models. For Arctic sea ice extent and volume, there is potential predictive skill for lead times of up to 3 years, and potential prediction errors have similar growth rates and magnitudes across the models. Spatial patterns of potential prediction errors differ substantially between the models, but some features are robust. Sea ice concentration errors are largest in the marginal ice zone, and in winter they are almost zero away from the ice edge. Sea ice thickness errors are amplified along the coasts of the Arctic Ocean, an effect that is dominated by sea ice advection. These results give an upper bound on the ability of current global climate models to predict important aspects of Arctic climate.

Does hydrophilicity of carbon particles improve their ice nucleation ability?

PubMed

Lupi, Laura; Molinero, Valeria

2014-09-04

Carbonaceous particles account for 10% of the particulate matter in the atmosphere. Atmospheric oxidation and aging of soot modulates its ice nucleation ability. It has been suggested that an increase in the ice nucleation ability of aged soot results from an increase in the hydrophilicity of the surfaces upon oxidation. Oxidation, however, also impacts the nanostructure of soot, making it difficult to assess the separate effects of soot nanostructure and hydrophilicity in experiments. Here we use molecular dynamics simulations to investigate the effect of changes in hydrophilicity of model graphitic surfaces on the freezing temperature of ice. Our results indicate that the hydrophilicity of the surface is not in general a good predictor of ice nucleation ability. We find a correlation between the ability of a surface to promote nucleation of ice and the layering of liquid water at the surface. The results of this work suggest that ordering of liquid water in contact with the surface plays an important role in the heterogeneous ice nucleation mechanism.

On the Importance of High Frequency Gravity Waves for Ice Nucleation in the Tropical Tropopause Layer

NASA Technical Reports Server (NTRS)

Jensen, Eric J.

2016-01-01

Recent investigations of the influence of atmospheric waves on ice nucleation in cirrus have identified a number of key processes and sensitivities: (1) ice concentrations produced by homogeneous freezing are strongly dependent on cooling rates, with gravity waves dominating upper tropospheric cooling rates; (2) rapid cooling driven by high-frequency waves are likely responsible for the rare occurrences of very high ice concentrations in cirrus; (3) sedimentation and entrainment tend to decrease ice concentrations as cirrus age; and (4) in some situations, changes in temperature tendency driven by high-frequency waves can quench ice nucleation events and limit ice concentrations. Here we use parcel-model simulations of ice nucleation driven by long-duration, constant-pressure balloon temperature time series, along with an extensive dataset of cold cirrus microphysical properties from the recent ATTREX high-altitude aircraft campaign, to statistically examine the importance of high-frequency waves as well as the consistency between our theoretical understanding of ice nucleation and observed ice concentrations. The parcel-model simulations indicate common occurrence of peak ice concentrations exceeding several hundred per liter. Sedimentation and entrainment would reduce ice concentrations as clouds age, but 1-D simulations using a wave parameterization (which underestimates rapid cooling events) still produce ice concentrations higher than indicated by observations. We find that quenching of nucleation events by high-frequency waves occurs infrequently and does not prevent occurrences of large ice concentrations in parcel simulations of homogeneous freezing. In fact, the high-frequency variability in the balloon temperature data is entirely responsible for production of these high ice concentrations in the simulations.

Variation in annual production of copepods, euphausiids, and juvenile walleye pollock in the southeastern Bering Sea

NASA Astrophysics Data System (ADS)

Sigler, Michael F.; Napp, Jeffrey M.; Stabeno, Phyllis J.; Heintz, Ronald A.; Lomas, Michael W.; Hunt, George L.

2016-12-01

We synthesize recent research on variation in annual production of copepods (Calanus spp.), euphausiids (Thysanoessa spp.), and juvenile walleye pollock (Gadus chalcogrammus) in the southeastern Bering Sea. We reach five conclusions: 1) the timing of the spring bloom is more important than the amount of annual primary production for the transfer of primary to secondary production (i.e., timing matters); 2) summer and fall, not just spring, matter: organisms must maximize energy intake devoted to somatic growth and storage of lipids and minimize energy expenditures during each season; 3) stored lipids are important for the overwinter survival of both zooplankton and age-0 walleye pollock; 4) variation in ice extent and timing of ice retreat affect the spatial distributions of phytoplankton, zooplankton, and age-0 walleye pollock; when these spatial distributions match in late-ice-retreat years, the annual production of copepods, euphausiids, and juvenile walleye pollock often increases (i.e., location matters); 5) if years with late ice retreat, which favor copepod, euphausiid, and juvenile walleye pollock production, occur in succession, top-down control increases. These conclusions help to explain annual variation in production of copepods, euphausiids and juvenile walleye pollock. Copepods and euphausiids often are more abundant in cold years with late ice retreat than in warm years with early ice retreat due to bloom timing and the availability of ice algae during years with late ice retreat. As a consequence, age-0 walleye pollock consume lipid-enriched prey in cold years, better preparing them for their first winter and their overwinter survival is greater. In addition, there is a spatial match of primary production, zooplankton, and age-0 walleye pollock in cold years and a mismatch in warm years.

Trends in reporting of mechanisms and incidence of hip injuries in males playing minor ice hockey in Canada: a cross-sectional study.

PubMed

Ayeni, Olufemi R; Kowalczuk, Marcin; Farag, Jordan; Farrokhyar, Forough; Chu, Raymond; Bedi, Asheesh; Willits, Kevin; Bhandari, Mohit

2014-01-01

There has been a noted increase in the diagnosis and reporting of sporting hip injuries and conditions in the medical literature but reporting at the minor hockey level is unknown. The purpose of this study is to investigate the trend of reporting hip injuries in amateur ice hockey players in Canada with a focus on injury type and mechanism. A retrospective review of the Hockey Canada insurance database was performed and data on ice hockey hip injuries reported between January 2005 and June 2011 were collected. The study population included all male hockey players from Peewee (aged 11-12 years) to Senior (aged 20+ years) participating in amateur level competition sanctioned by Hockey Canada. Reported cases of ice hockey hip injuries were analyzed according to age, mechanism of injury, and injury subtype. Annual injury reporting rates were determined and using a linear regression analysis trended to determine the change in ice hockey hip injury reporting rate over time. One hundred and six cases of ice hockey-related hip injuries were reported in total. The majority of injuries (75.5%) occurred in players aged 15-20 years playing at the Junior level. Most injuries were caused by a noncontact mechanism (40.6%) and strains were the most common subtype (50.0%). From 2005 to 2010, the number of reported hip injuries increased by 5.31 cases per year and the rate of reported hip injury per 1,000 registered players increased by 0.02 cases annually. Reporting of hip injuries in amateur ice hockey players is increasing. A more accurate injury reporting system is critical for future epidemiologic studies to accurately document the rate and mechanism of hip injury in amateur ice hockey players.

Volcanic synchronisation of the EPICA-DC and TALDICE ice cores for the last 42 kyr BP

NASA Astrophysics Data System (ADS)

Severi, M.; Udisti, R.; Becagli, S.; Stenni, B.; Traversi, R.

2012-04-01

An age scale synchronisation between the Talos Dome and the EPICA Dome C ice cores was carried on through the identification of several common volcanic signatures for the last 42 kyr. Using this tight stratigraphic link we transferred the EDC age scale to the Talos Dome ice core producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modeled TALDICE-1 age scale and the new one during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. Except for a very few cases, R ranges between 0.8 and 1.2 corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. At this stage our approach does not allow us unequivocally to find out which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to 200 years appears in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Thus, we propose for the Talos Dome ice core a new age scale (covering the whole Holocene) obtained by a direct transfer, via our stratigraphic link, from the EDC modelled age scale by Lemieux-Dudon et al. (2010).

Modelling the long-term evolution of worst-case Arctic oil spills.

PubMed

Blanken, Hauke; Tremblay, Louis Bruno; Gaskin, Susan; Slavin, Alexander

2017-03-15

We present worst-case assessments of contamination in sea ice and surface waters resulting from hypothetical well blowout oil spills at ten sites in the Arctic Ocean basin. Spill extents are estimated by considering Eulerian passive tracers in the surface ocean of the MITgcm (a hydrostatic, coupled ice-ocean model). Oil in sea ice, and contamination resulting from melting of oiled ice, is tracked using an offline Lagrangian scheme. Spills are initialized on November 1st 1980-2010 and tracked for one year. An average spill was transported 1100km and potentially affected 1.1 million km 2 . The direction and magnitude of simulated oil trajectories are consistent with known large-scale current and sea ice circulation patterns, and trajectories frequently cross international boundaries. The simulated trajectories of oil in sea ice match observed ice drift trajectories well. During the winter oil transport by drifting sea ice is more significant than transport with surface currents. Copyright © 2017 Elsevier Ltd. All rights reserved.

On the nature of the dirty ice at the bottom of the GISP2 ice core

USGS Publications Warehouse

Bender, Michael L.; Burgess, Edward; Alley, Richard B.; Barnett, Bruce; Clow, Gary D.

2010-01-01

We present data on the triple Ar isotope composition in trapped gas from clean, stratigraphically disturbed ice between 2800 and 3040m depth in the GISP2 ice core, and from basal dirty ice from 3040 to 3053m depth. We also present data for the abundance and isotopic composition of O2 and N2, and abundance of Ar, in the basal dirty ice. The Ar/N2 ratio of dirty basal ice, the heavy isotope enrichment (reflecting gravitational fractionation), and the total gas content all indicate that the gases in basal dirty ice originate from the assimilation of clean ice of the overlying glacier, which comprises most of the ice in the dirty bottom layer. O2 is partly to completely depleted in basal ice, reflecting active metabolism. The gravitationally corrected ratio of 40Ar/38Ar, which decreases with age in the global atmosphere, is compatible with an age of 100-250ka for clean disturbed ice. In basal ice, 40Ar is present in excess due to injection of radiogenic 40Ar produced in the underlying continental crust. The weak depth gradient of 40Ar in the dirty basal ice, and the distribution of dirt, indicate mixing within the basal ice, while various published lines of evidence indicate mixing within the overlying clean, disturbed ice. Excess CH4, which reaches thousands of ppm in basal dirty ice at GRIP, is virtually absent in overlying clean disturbed ice, demonstrating that mixing of dirty basal ice into the overlying clean ice, if it occurs at all, is very slow. Order-of-magnitude estimates indicate that the mixing rate of clean ice into dirty ice is sufficient to maintain a steady thickness of dirty ice against thinning from the mean ice flow. The dirty ice appears to consist of two or more basal components in addition to clean glacial ice. A small amount of soil or permafrost, plus preglacial snow, lake or ground ice could explain the observations.

Sea ice motions in the Central Arctic pack ice as inferred from AVHRR imagery

NASA Technical Reports Server (NTRS)

Emery, William; Maslanik, James; Fowler, Charles

1995-01-01

Synoptic observations of ice motion in the Arctic Basin are currently limited to those acquired by drifting buoys and, more recently, radar data from ERS-1. Buoys are not uniformly distributed throughout the Arctic, and SAR coverage is currently limited regionally and temporally due to the data volume, swath width, processing requirements, and power needs of the SAR. Additional ice-motion observations that can map ice responses simultaneously over large portions of the Arctic on daily to weekly time intervals are thus needed to augment the SAR and buoys data and to provide an intermediate-scale measure of ice drift suitable for climatological analyses and ice modeling. Principal objectives of this project were to: (1) demonstrate whether sufficient ice features and ice motion existed within the consolidated ice pack to permit motion tracking using AVHRR imagery; (2) determine the limits imposed on AVHRR mapping by cloud cover; and (3) test the applicability of AVHRR-derived motions in studies of ice-atmosphere interactions. Each of these main objectives was addressed. We conclude that AVHRR data, particularly when blended with other available observations, provide a valuable data set for studying sea ice processes. In a follow-on project, we are now extending this work to cover larger areas and to address science questions in more detail.

Ice nucleation activity of diesel soot particles at cirrus relevant temperature conditions: Effects of hydration, secondary organics coating, soot morphology, and coagulation

NASA Astrophysics Data System (ADS)

Kulkarni, Gourihar; China, Swarup; Liu, Shang; Nandasiri, Manjula; Sharma, Noopur; Wilson, Jacqueline; Aiken, Allison C.; Chand, Duli; Laskin, Alexander; Mazzoleni, Claudio; Pekour, Mikhail; Shilling, John; Shutthanandan, Vaithiyalingam; Zelenyuk, Alla; Zaveri, Rahul A.

2016-04-01

Ice formation by diesel soot particles was investigated at temperatures ranging from -40 to -50°C. Size-selected soot particles were physically and chemically aged in an environmental chamber, and their ice nucleating properties were determined using a continuous flow diffusion type ice nucleation chamber. Bare (freshly formed), hydrated, and compacted soot particles, as well as α-pinene secondary organic aerosol (SOA)-coated soot particles at high relative humidity conditions, showed ice formation activity at subsaturation conditions with respect to water but below the homogeneous freezing threshold conditions. However, SOA-coated soot particles at dry conditions were observed to freeze at homogeneous freezing threshold conditions. Overall, our results suggest that heterogeneous ice nucleation activity of freshly emitted diesel soot particles are sensitive to some of the aging processes that soot can undergo in the atmosphere.

Sensitivity of the marine-terminating margins to Holocene climate change in south and southeast Greenland

NASA Astrophysics Data System (ADS)

Levy, L.; Larsen, N. K.; Kjaer, K. H.; Bjork, A. A.; Kjeldsen, K. K.; Funder, S.; Kelly, M. A.; Howley, J. A.

2016-12-01

The marine-terminating glaciers of the Greenland Ice Sheet (GrIS) are responding rapidly to present-day climate change. More than one-third of the GrIS's discharge flows to the ocean through the marine-terminating outlet glaciers of southeastern Greenland, making it a potentially important region of the ice sheet. Documenting how these outlet glaciers have responded to longer-term past climate change (i.e. the Holocene) allows for more accurate predictions of their response to future climate changes. Here, we present 36 new 10Be ages on boulders perched on bedrock and on bedrock that record the timing of ice marginal fluctuations in several fjords in southeast and south Greenland, a region where little is known about past ice fluctuations due to its relative inaccessibility. We show that at Skjoldungen Sund (63.4N), deglaciation was rapid, beginning by 10.1 ± 0.4 ka. Deglaciation occurred concurrently at Timmiarmiut Fjord (62.7N), 100 km to the south, at 10.3 ± 0.4 ka. We suggest that this was in response to the warming ocean and air temperatures of the early Holocene. Additionally, 10Be ages on boulders perched on bedrock just distal to the historic­ moraines in Timmiarmiut Fjord date to 1.7 ± 0.1 ka, indicating the presence of a late Holocene advance prior to the Little Ice Age. In southern Greenland, deglaciation at Lindenow Fjord (60.6N), which drains the Julienhåb ice cap, occurred at 11.2 ± 0.4 ka. The ice then retreated up-fjord at a rate of 70-100 m yr-1, comparable with modern retreat rates of 30-100 m yr-1. We hypothesize that the earlier deglaciation at Lindenow Fjord by 1 ka may indicate that the Julienhåb ice cap was more sensitive to early Holocene warming than the GrIS. Additional 10Be ages from Prins Christen Fjord and near Qaqortoq are forthcoming. These new 10Be ages provide a longer-term perspective of marine-terminating outlet glacier fluctuations in Greenland and show that the ice sheet responded sensitively to Holocene climate change.

"Crystals within Crystals: The Story of Sea Ice". A Classroom-Based Outreach Project Communicating Cutting-Edge Ocean Science to School Pupils

NASA Astrophysics Data System (ADS)

Butler, B.

2016-02-01

'Crystals within Crystals: The story of sea ice' is a UK based outreach project based that uses a range practical tools to engage school students with cutting edge scientific research that relates to the use of some of the world's most powerful X-rays in sea ice research. The project is delivered in the form of a classroom workshop that first introduces school pupils (aged 11-14) to seawater and the salts that give it a salinity. The pupils are then shown how the presence of salts within seawater results in very important physical changes when the liquid freezes, which includes different structural and optical properties of the ice. The properties of the ice are then linked to the presence of countless microscopic salt crystals that are trapped within the microstructure of the frozen seawater, which is explained with use of a novel crystal growth demonstration. Given that there is currently no way of successfully removing these salt crystals from the ice, the workshop culminates in explaining how some of the worlds most powerful X-rays can be used to investigate processes that otherwise remain elusive. The workshop introduces students to the fundamental principles of scientific enquiry, the sea ice environment, and the power of X-rays in investigating the properties of crystals. Here we present information that outlines a host of practical and project management tools that are applicacble to outreach projects in the the field of ocean sciences, with the aim of seeding ideas and interest for other graduate student to enage with the public during their studies.

Periodic fluctuations in deep water formation due to sea ice

NASA Astrophysics Data System (ADS)

Saha, R.

2012-12-01

During the last ice age, several abrupt warming events took place, known as Dansgaard-Oeschger (D-O) events. Their effects were felt globally, although the North Atlantic experienced the largest temperature increase. The leading hypothesis to explain their occurrence postulates that the warming was caused by abrupt disruptions of the North Atlantic Current due to meltwater discharge from destabilized ice sheets (Heinrich events). However, the number of warming events outnumber the those of ice-sheet collapse. Thus, the majority of D-O events are not attributed to surface freshwater anomalies, and the underlying mechanism behind their occurrence remain unexplained. Using a simple dynamical model of sea ice and an overturning circulation, I show the existence of self-sustained relaxation oscillations in the overturning circulation. The insulating effect of sea ice is shown to paradoxically lead to a net loss of heat from the top layer of the polar ocean when sea ice retreats. Repeated heat loss results in a denser top layer and a destabilized water column, which triggers convection. The convective state pulls the system out of its preferred mode of circulation, setting up relaxation oscillations. The period of oscillations in this case is linked to the geometry of the ocean basin, if solar forcing is assumed to remain constant. If appropriate glacial freshwater forcing is applied to the model, a pattern of oscillation is produced that bears remarkable similarity to the observed fluctuations in North Atlantic climate between 50,000 and 30,000 years before present.; Comparison of NGRIP δ 18-O (proxy for near surface air temperature) between 50,000 and 30,000 years before present, showing Bond cycles (left) with the model output when forced with appropriate glacial freshwater forcing (right).

Update and Overview of Spinal Injuries in Canadian Ice Hockey, 1943 to 2011: The Continuing Need for Injury Prevention and Education.

PubMed

Tator, Charles H; Provvidenza, Christine; Cassidy, J David

2016-05-01

To identify spinal injuries in Canadian ice hockey from 2006 to 2011 and to discuss data from 1943 to 2011 and impact of injury prevention programs. Data about spinal injuries with and without spinal cord injury in ice hockey have been collected by ThinkFirst's (now Parachute Canada) Canadian Ice Hockey Spinal Injuries Registry since 1981 through questionnaires from practitioners, ice hockey organizations, and media. All Canadian provinces and territories. All registered Canadian ice hockey players. Age, gender, level of play, location, mechanism of injury. Incidence, incidence rate, prevalence, and nature (morbidity) of the injuries. Between 2006 and 2011, 44 cases occurred, 4 (9.1%) of which were severe. The incidence in the recent years continues to be lower than the peak years. From 1943 to 2011, 355 cases have been documented, primarily males (97.7%) and cervical spine injuries (78.9%), resulting from impact with the boards (64.2%). Check or push from behind (36.0%) was still the most common cause of injury, although slightly lower during 2006 to 2011. From 1943 to 2011, Prince Edward Island, New Brunswick, and British Columbia/Yukon had the highest injury rates. Ontario and Quebec continued to show markedly different injury rates, with Ontario more than twice that of Quebec. Current data for 2006 to 2011 indicate that spinal injuries in ice hockey continue to occur, although still at lower rates than the peak years 1982 to 1995. It is imperative to continue educating players and team officials about spinal injury prevention and to reinforce the rules against checking or pushing from behind to reduce the incidence of these serious injuries.

Marine sedimentary provenance evidence for massive discharges of icebergs from the Aurora and Wilkes sub-glacial basins

NASA Astrophysics Data System (ADS)

Pierce, E. L.; Williams, T.; van de Flierdt, T.; Hemming, S. R.; Brachfeld, S. A.; Goldstein, S. L.

2010-12-01

Understanding the evolution of the East Antarctic Ice Sheet (EAIS) is a fundamental goal in the field of paleoclimate today. Given the current and projected state of global warming, it is important to know how an ice sheet that holds over 50 m of sea-level has behaved under warmer conditions in the past. Despite the fact that over 98% of the East Antarctica continent is covered by thick (2.1 km on average) ice, the chronological characterization of glaciogenic detrital hornblende grains has been proven an excellent provenance tool in the investigation of the source areas for ice rafted detritus around Antarctica (Roy et al., 2007, Chem. Geo.). A circum-Antarctica core-top survey of Ar-Ar ages in hornblende grains demonstrates that East Antarctica can be simply divided into several sectors that correspond to modern ice divides and published geochronological evidence from sparse outcrops around the margins of the continent. Williams et al., (2010, EPSL) found evidence in ice rafted detritus layers in ODP Site 1165 from the Wilde drift off Prydz Bay for large discharges of icebergs from the Adélie and Wilkes Land coasts occurring during the late Miocene and early Pliocene. Sourcing from the Adélie and Wilkes Land coasts requires iceberg transport more than 1500 km around the Antarctic perimeter, and this is therefore evidence for massive discharges of icebergs from these sectors. In the Aurora and Wilkes Basins in these sectors, the ice sheet is grounded well below sea level, and is therefore thought to be potentially unstable under warmer conditions. Such long distant transport of sediments with distinctive sources is reminiscent of Heinrich Events in the North Atlantic. A model often invoked as the cause of these events is the collapse and retreat of ice-streams, which leads to massive discharges of icebergs, laden with sediment, into the ocean. The importance of this interpretation, if true, has led us to make more detailed studies of Quaternary sediments from the Adélie and Wilkes Land coasts as well as glaciogenic sediments throughout the Cenozoic in Prydz Bay. We will present Ar-Ar ages of detrital hornblende and biotite grains (>150 µm), as well as epsilon-Nd values measured on the terrigenous fine fraction (<63 µm), from 9 marine sediment cores along the Adélie and Wilkes Land coasts of East Antarctica (95° to 165°E), and compare them and proximal Prydz Bay data with IRD layers in ODP Site 1165. We have also compared the Ar-Ar biotite age populations from the same IRD layers in ODP site 1165 that Williams et al., (2010, EPSL) examined to explore the use of Ar-Ar biotite ages as a tracer of IRD; given the high K content in biotite, it may be possible to use the 63-150 µm fraction for provenance studies which may be particularly useful for tracing sources of IRD into the Southern Ocean where IRD abundances are low and thus grain sizes tend to be finer. The combined application of these tracers will allow interpretation of the average crust formation age of the sources, as well as provide information on major tectonothermal pulses and cooling through approximately 300°C.

Using Ice Predictions to Guide Submarines

DTIC Science & Technology

2016-01-01

the Arctic Cap Nowcast/ Forecast System (ACNFS) in September 2013. The ACNFS consists of a coupled ice -ocean model that assimilates available real...of the ice cover. The age of the sea ice serves as an indicator of its physical properties including surface roughness, melt pond coverage, and...the Arctic Cap Nowcast/Forecast System (ACNFS). Ice thickness is in meters for 11 September 2015. Thickness ranges from zero to five meters as shown

Estimating the extent of Antarctic summer sea ice during the Heroic Age of Antarctic Exploration

NASA Astrophysics Data System (ADS)

Edinburgh, Tom; Day, Jonathan J.

2016-11-01

In stark contrast to the sharp decline in Arctic sea ice, there has been a steady increase in ice extent around Antarctica during the last three decades, especially in the Weddell and Ross seas. In general, climate models do not to capture this trend and a lack of information about sea ice coverage in the pre-satellite period limits our ability to quantify the sensitivity of sea ice to climate change and robustly validate climate models. However, evidence of the presence and nature of sea ice was often recorded during early Antarctic exploration, though these sources have not previously been explored or exploited until now. We have analysed observations of the summer sea ice edge from the ship logbooks of explorers such as Robert Falcon Scott, Ernest Shackleton and their contemporaries during the Heroic Age of Antarctic Exploration (1897-1917), and in this study we compare these to satellite observations from the period 1989-2014, offering insight into the ice conditions of this period, from direct observations, for the first time. This comparison shows that the summer sea ice edge was between 1.0 and 1.7° further north in the Weddell Sea during this period but that ice conditions were surprisingly comparable to the present day in other sectors.

Antarctic ice discharge due to warm water intrusion into shelf cavities

NASA Astrophysics Data System (ADS)

Winkelmann, R.; Reese, R.; Albrecht, T.; Mengel, M.; Asay-Davis, X.

2017-12-01

Ocean-induced melting below ice shelves is the dominant driver for mass loss from the Antarctic Ice Sheet at present. Observations show that many Antarctic ice shelves are thinning which reduces their buttressing potential and can lead to increased ice discharge from the glaciers upstream. Melt rates from Antarctic ice shelves are determined by the temperature and salinity of the ambient ocean. In many parts, ice shelves are shielded by clearly defined density fronts which keep relatively warm Northern water from entering the cavity underneath the ice shelves. Projections show that a redirection of coastal currents might allow these warmer waters to intrude into ice shelf cavities, for instance in the Weddell Sea, and thereby cause a strong increase in sub-shelf melt rates. Using the Potsdam Ice-shelf Cavity mOdel (PICO), we assess how such a change would influence the dynamic ice loss from Antarctica. PICO is implemented as part of the Parallel Ice Sheet Model (PISM) and mimics the vertical overturning circulation in ice-shelf cavities. The model is capable of capturing the wide range of melt rates currently observed for Antarctic ice shelves and reproduces the typical pattern of comparably high melting near the grounding line and lower melting or refreezing towards the calving front. Based on regional observations of ocean temperatures, we use PISM-PICO to estimate an upper limit for ice discharge resulting from the potential erosion of ocean fronts around Antarctica.

Uranium isotopes and dissolved organic carbon in loess permafrost: Modeling the age of ancient ice

USGS Publications Warehouse

Ewing, Stephanie A.; Paces, James B.; O'Donnell, J.A.; Jorgenson, M.T.; Kanevskiy, M.Z.; Aiken, George R.; Shur, Y.; Harden, Jennifer W.; Striegl, Robert G.

2015-01-01

The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of the circumstances and evidence of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium isotopes to evaluate the residence time of segregated ground ice from ice-rich loess permafrost cores in central Alaska. Activity ratios of 234U vs. 238U (234U/238U) in water from thawed core sections ranged between 1.163 and 1.904 due to contact of ice and associated liquid water with mineral surfaces over time. Measured (234U/238U) values in ground ice showed an overall increase with depth in a series of five neighboring cores up to 21 m deep. This is consistent with increasing residence time of ice with depth as a result of accumulation of loess over time, as well as characteristic ice morphologies, high segregated ice content, and wedge ice, all of which support an interpretation of syngenetic permafrost formation associated with loess deposition. At the same time, stratigraphic evidence indicates some past sediment redistribution and possibly shallow thaw among cores, with local mixing of aged thaw waters. Using measures of surface area and a leaching experiment to determine U distribution, a geometric model of (234U/238U) evolution suggests mean ages of up to ∼200 ky BP in the deepest core, with estimated uncertainties of up to an order of magnitude. Evidence of secondary coatings on loess grains with elevated (234U/238U) values and U concentrations suggests that refinement of the geometric model to account for weathering processes is needed to reduce uncertainty. We suggest that in this area of deep ice-rich loess permafrost, ice bodies have been preserved from the last glacial period (10–100 ky BP), despite subsequent fluctuations in climate, fire disturbance and vegetation. Radiocarbon (14C) analysis of dissolved organic carbon (DOC) in thaw waters supports ages greater than ∼40 ky BP below 10 m. DOC concentrations in thaw waters increased with depth to maxima of >1000 ppm, despite little change in ice content or cryostructures. These relations suggest time-dependent production of old DOC that will be released upon permafrost thaw at a rate that is mediated by sediment transport, among other factors.

The mass balance of the ice plain of Ice Stream B and Crary Ice Rise

NASA Technical Reports Server (NTRS)

Bindschadler, Robert

1993-01-01

The region in the mouth of Ice Stream B (the ice plain) and that in the vicinity of Crary Ice Rise are experiencing large and rapid changes. Based on velocity, ice thickness, and accumulation rate data, the patterns of net mass balance in these regions were calculated. Net mass balance, or the rate of ice thickness change, was calculated as the residual of all mass fluxes into and out of subregions (or boxes). Net mass balance provides a measure of the state of health of the ice sheet and clues to the current dynamics.

Assimilating the ICE-6G_C Reconstruction of the Latest Quaternary Ice Age Cycle Into Numerical Simulations of the Laurentide and Fennoscandian Ice Sheets

NASA Astrophysics Data System (ADS)

Stuhne, G. R.; Peltier, W. R.

2017-12-01

We analyze the effects of nudging 100 kyr numerical simulations of the Laurentide and Fennoscandian ice sheets toward the glacial isostatic adjustment-based (GIA-based) ICE-6G_C reconstruction of the most recent ice age cycle. Starting with the ice physics approximations of the PISM ice sheet model and the SeaRISE simulation protocols, we incorporate nudging at characteristic time scales, τf, through anomalous mass balance terms in the ice mass conservation equation. As should be expected, these mass balances exhibit physically unrealistic details arising from pure GIA-based reconstruction geometry when nudging is very strong (τf=20 years for North America), while weakly nudged (τf=1,000 years) solutions deviate from ICE-6G_C sufficiently to degrade its observational fit quality. For reasonable intermediate time scales (τf=100 years and 200 years), we perturbatively analyze nudged ice dynamics as a superposition of "leading-order smoothing" that diffuses ICE-6G_C in a physically and observationally consistent manner and "higher-order" deviations arising, for instance, from biases in the time dependence of surface climate boundary conditions. Based upon the relative deviations between respective nudged simulations in which these biases follow surface temperature from ice cores and eustatic sea level from marine sediment cores, we compute "ice core climate adjustments" that suggest how local paleoclimate observations may be applied to the systematic refinement of ICE-6G_C. Our results are consistent with a growing body of evidence suggesting that the geographical origins of Meltwater Pulse 1B (MWP1b) may lie primarily in North America as opposed to Antarctica (as reconstructed in ICE-6G_C).

On the Revealing Firsthand Probing of Ocean-Ice-Atmosphere Interactions off Sabrina Coast During NBP1402

NASA Astrophysics Data System (ADS)

Huber, B. A.; Orsi, A. H.; Zielinski, N. J.; Durkin, W. J., IV; Clark, P.; Wiederwohl, C. L.; Rosenberg, M. A.; Gwyther, D.; Greenbaum, J. S.; Lavoie, C.; Shevenell, A.; Leventer, A.; Blankenship, D. D.; Gulick, S. P. S.; Domack, E. W.

2014-12-01

Diverse interactions of winds, currents and ice around Antarctica dictate how, where and when the world's densest waters form and massive floating ice shelves and glaciers melt, as well as control sea surface gas exchange and primary productivity. Compelled by recent rate estimates of East Antarctic Ice Sheet mass loss, we contrast the paths and mixing histories of oceanic waters reaching the continental ice edge off the Sabrina and Adelie coasts relying on the unique set of synoptic shipboard measurements from NBP1402 (swath bathymetry, ADCP, underway CTD). Analysis of historical hydrography and sea ice concentration fields within the Mertz Polynya indicates the apparent effect of evolving ocean-ice-atmosphere interactions on the characteristics of local Shelf Water (SW) sources to current outflow of newly formed Antarctic Bottom Water (AABW). A polynya dominated water mass structure similar to that observed off the Adelie Coast before the removal of the Mertz Ice Tongue was expected to the west of the Dalton Ice Tongue (DIT). However, we found no evidence of dense SW off Sabrina Coast, which may lessen the region's preconceived influence to global meridional overturning. Present sea ice production within the eastern Dalton Polynya is overshadowed by freshwater input to relatively stable interior upper waters. The Antarctic Coastal Current (ACoC) picks up distinct meltwater contributions along the DIT western flank and in front of the Moscow University Ice Shelf (MUIS) and Totten Glacier (TG). Unlike over other highly influential margins to global sea level rise, there is no evidence of local cross-shelf inflow and mixing of warm Circumpolar Deep Water. Relatively cold thermocline waters from the continental slope enter the eastern trough off Sabrina Coast, and they are swiftly steered poleward by complex underlying topography. Meltwater export from beneath the MUIS and TG is observed at newly discovered trenches that effectively constrain sub-cavity inflow to low salinity near-freezing waters drawn from intermediate levels of the adjacent westward flowing ACoC. Winds, currents and ice interactions observed off Sabrina Coast during NBP1402 are most likely widespread, in view of reported decadal freshening of upper waters over the Antarctic continental shelf and their localized AABW outflows.

Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean

NASA Astrophysics Data System (ADS)

China, Swarup; Alpert, Peter A.; Zhang, Bo; Schum, Simeon; Dzepina, Katja; Wright, Kendra; Owen, R. Chris; Fialho, Paulo; Mazzoleni, Lynn R.; Mazzoleni, Claudio; Knopf, Daniel A.

2017-03-01

Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition between samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity (RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. This study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.

Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean

DOE PAGES

China, Swarup; Alpert, Peter A.; Zhang, Bo; ...

2017-02-27

Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition betweenmore » samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity ( RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. Finally, this study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.« less

Ice cloud formation potential by free tropospheric particles from long-range transport over the Northern Atlantic Ocean

DOE Office of Scientific and Technical Information (OSTI.GOV)

China, Swarup; Alpert, Peter A.; Zhang, Bo

Long-range transported free tropospheric particles can play a significant role on heterogeneous ice nucleation. Using optical and electron microscopy we examine the physicochemical characteristics of ice nucleating particles (INPs). Particles were collected on substrates from the free troposphere at the remote Pico Mountain Observatory in the Azores Islands, after long-range transport and aging over the Atlantic Ocean. We investigate four specific events to study the ice formation potential by the collected particles with different ages and transport patterns. We use single-particle analysis, as well as bulk analysis to characterize particle populations. Both analyses show substantial differences in particle composition betweenmore » samples from the four events; in addition, single-particle microscopy analysis indicates that most particles are coated by organic material. The identified INPs contained mixtures of dust, aged sea salt and soot, and organic material acquired either at the source or during transport. The temperature and relative humidity ( RH) at which ice formed, varied only by 5% between samples, despite differences in particle composition, sources, and transport patterns. We hypothesize that this small variation in the onset RH may be due to the coating material on the particles. Finally, this study underscores and motivates the need to further investigate how long-range transported and atmospherically aged free tropospheric particles impact ice cloud formation.« less

Experimental evidence for modifying the current physical model for ice accretion on aircraft surfaces

NASA Technical Reports Server (NTRS)

Olsen, W.; Walker, E.

1986-01-01

Closeup movies, still photographs, and other experimental data suggest that the current physical model for ice accretion needs significant modification. At aircraft airspeeds there was no flow of liquid over the surface of the ice after a short initial flow, even at barely subfreezing temperatures. Instead, there were very large stationary drops on the ice surface that lose water from their bottoms by freezing and replenish their liquid by catching the microscopic cloud droplets. This observation disagrees with the existing physical model, which assumes there is a thin liquid film continuously flowing over the ice surface. With no such flow, the freezing-fraction concept of the model fails when a mass balance is performed on the surface water. Rime ice does, as the model predicts, form when the air temperature is low enough to cause the cloud droplets to freeze almost immediately on impact. However, the characteristic shapes of horn-glaze ice or rime ice are primarily caused by the ice shape affecting the airflow locally and consequently the droplet catch and the resulting ice shape. Ice roughness greatly increases the heat transfer coefficient, stops the movement of drops along the surface, and may also affect the airflow initially and thereby the droplet catch. At high subreezing temperatures the initial flow and shedding of surface drops have a large effect on the ice shape. At the incipient freezing limit, no ice forms.

Core drilling through the ross ice shelf (antarctica) confirmed Basal freezing.

PubMed

Zotikov, I A; Zagorodnov, V S; Raikovsky, J V

1980-03-28

New techniques that have been used to obtain a continuous ice core through the whole 416-meter thickness of the Ross Ice Shelf at Camp J-9 have demonstrated that the bottom 6 meters of the ice shelf consists of sea ice. The rate of basal freezing that is forming this ice is estimated by different methods to be 2 centimeters of ice per year. The sea ice is composed of large vertical crystals, which form the waffle-like lower boundary of the shelf. A distinct alignment of the crystals throughout the sea ice layer suggests the presence of persistent long-term currents beneath the ice shelf.

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120-800 ka

NASA Astrophysics Data System (ADS)

Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Veres, D.; Parrenin, F.; Martinerie, P.; Ritz, C.; Capron, E.; Lipenkov, V.; Loutre, M.-F.; Raynaud, D.; Vinther, B.; Svensson, A.; Rasmussen, S. O.; Severi, M.; Blunier, T.; Leuenberger, M.; Fischer, H.; Masson-Delmotte, V.; Chappellaz, J.; Wolff, E.

2013-08-01

An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale had been developed based on an inverse dating method (Datice), combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousands of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2013), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120-800 ka. In this framework, new measurements of δ18Oatm over Marine Isotope Stage (MIS) 11-12 on EDC and a complete δ18Oatm record of the TALDICE ice cores permit us to derive additional orbital gas age constraints. The coherency of the different orbitally deduced ages (from δ18Oatm, δO2/N2 and air content) has been verified before implementation in AICC2012. The new chronology is now independent of other archives and shows only small differences, most of the time within the original uncertainty range calculated by Datice, when compared with the previous ice core reference age scale EDC3, the Dome F chronology, or using a comparison between speleothems and methane. For instance, the largest deviation between AICC2012 and EDC3 (5.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

An optimized multi-proxy, multi-site Antarctic ice and gas orbital chronology (AICC2012): 120-800 ka

NASA Astrophysics Data System (ADS)

Bazin, L.; Landais, A.; Lemieux-Dudon, B.; Toyé Mahamadou Kele, H.; Veres, D.; Parrenin, F.; Martinerie, P.; Ritz, C.; Capron, E.; Lipenkov, V.; Loutre, M.-F.; Raynaud, D.; Vinther, B.; Svensson, A.; Rasmussen, S. O.; Severi, M.; Blunier, T.; Leuenberger, M.; Fischer, H.; Masson-Delmotte, V.; Chappellaz, J.; Wolff, E.

2012-11-01

An accurate and coherent chronological framework is essential for the interpretation of climatic and environmental records obtained from deep polar ice cores. Until now, one common ice core age scale has been developed based on an inverse dating method (Datice) combining glaciological modelling with absolute and stratigraphic markers between 4 ice cores covering the last 50 ka (thousand of years before present) (Lemieux-Dudon et al., 2010). In this paper, together with the companion paper of Veres et al. (2012), we present an extension of this work back to 800 ka for the NGRIP, TALDICE, EDML, Vostok and EDC ice cores using an improved version of the Datice tool. The AICC2012 (Antarctic Ice Core Chronology 2012) chronology includes numerous new gas and ice stratigraphic links as well as improved evaluation of background and associated variance scenarios. This paper concentrates on the long timescales between 120-800 ka. In this frame, new measurements of δ18Oatm over Marine Isotope Stage (MIS) 11-12 on EDC and a complete δ18Oatm record of the TALDICE ice cores permit us to derive new orbital gas age constraints. The coherency of the different orbitally deduced ages (from δ18Oatm, δO2/N2 and air content) has been verified before implementation in AICC2012. The new chronology shows only small differences, well within the original uncertainty range, when compared with the previous ice core reference age scale EDC3. For instance, the duration of the last four interglacial periods is not affected by more than 5%. The largest deviation between AICC2012 and EDC3 (4.4 ka) is obtained around MIS 12. Despite significant modifications of the chronological constraints around MIS 5, now independent of speleothem records in AICC2012, the date of Termination II is very close to the EDC3 one.

Timing of the Northern Prince Gustav Ice Stream retreat and the deglaciation of northern James Ross Island, Antarctic Peninsula during the last glacial-interglacial transition

NASA Astrophysics Data System (ADS)

Nývlt, Daniel; Braucher, Régis; Engel, Zbyněk; Mlčoch, Bedřich

2014-09-01

The Northern Prince Gustav Ice Stream located in Prince Gustav Channel, drained the northeastern portion of the Antarctic Peninsula Ice Sheet during the last glacial maximum. Here we present a chronology of its retreat based on in situ produced cosmogenic 10Be from erratic boulders at Cape Lachman, northern James Ross Island. Schmidt hammer testing was adopted to assess the weathering state of erratic boulders in order to better interpret excess cosmogenic 10Be from cumulative periods of pre-exposure or earlier release from the glacier. The weighted mean exposure age of five boulders based on Schmidt hammer data is 12.9 ± 1.2 ka representing the beginning of the deglaciation of lower-lying areas (< 60 m a.s.l.) of the northern James Ross Island, when Northern Prince Gustav Ice Stream split from the remaining James Ross Island ice cover. This age represents the minimum age of the transition from grounded ice stream to floating ice shelf in the middle continental shelf areas of the northern Prince Gustav Channel. The remaining ice cover located at higher elevations of northern James Ross Island retreated during the early Holocene due to gradual decay of terrestrial ice and increase of equilibrium line altitude. Schmidt hammer R-values are inversely correlated with 10Be exposure ages and could be used as a proxy for exposure history of individual granite boulders in this region and favour the hypothesis of earlier release of boulders with excessive 10Be concentrations from glacier directly at this site. These data provide evidences for an earlier deglaciation of northern James Ross Island when compared with other recently presented cosmogenic nuclide based deglaciation chronologies, but this timing coincides with rapid increase of atmospheric temperature in this marginal part of Antarctica.

Countering Ice Ages: Re-directing Public Concern from Global Warming (GW) to Global Cooling (GC)

NASA Astrophysics Data System (ADS)

Singer, S. F.

2016-02-01

I present here three arguments in favor of such a drastic shift - which involves also a shift in current policies, such as mitigation of the greenhouse (GH) gas carbon dioxide. 1. Historical evidence shows that cooling, even on a regional or local scale, is much more damaging than warming. The key threat is to agriculture, leading to failure of harvests, followed by famine, starvation, disease, and mass deaths. 2. Also, GC is reasonably sure, while GW is iffy. The evidence from deep-sea sediment cores and ice cores shows some 17 (Milankovitch-style) glaciations in the past 2 million years, each typically lasting 100,000 years, interrupted by warm inter-glacials, typically around 10,000-yr duration. The most recent glaciation ended rather suddenly about 12,000 years ago. We are now in the warm Holocene, which is expected to end soon. Most of humanity may not survive the next, inevitable glaciation. We need to consider also the warming-cooling (Dansgaard-Oeschger-Bond - DOB) cycles, which seem solar-controlled and have a period of approx 1000-1500 years; its most recent cooling phase, the "Little Ice Age" (LIA), ended about 200 years ago. For details, see Unstoppable Global Warming: Every 1500 years by Singer &Avery [2007]. 3. Available technology seems adequate to assure human survival - at least in industrialized nations. The main threat is warfare, driven by competition for food and other essential resources. With nuclear weapons and delivery systems widely dispersed, the outcome of future wars is difficult to predict. Using geo-engineering to overcome a future cooling looks promising for both types of ice ages - with relatively low cost and low risk to the physical and biological environment. I will describe how to neutralize the "trigger" of major glaciations, and propose a particular greenhouse scheme that may counter the cooling phase of DOB cycles.

Extreme aridity and mild temperatures in the Middle East during the late Little Ice Age indicated by paired coral Sr/Ca and δ18O from the northern Red Sea

NASA Astrophysics Data System (ADS)

Felis, T.; Ionita, M.; Rimbu, N.; Lohmann, G.; Kölling, M.

2016-12-01

Throughout the global deserts, annually resolved reconstructions of temperature that extend the short instrumental record are virtually absent, and proxy records of aridity are difficult to obtain. The Little Ice Age ( 1450-1850) is thought to have been characterized by generally cold conditions in many regions of the globe with little commonality regarding the hydroclimate. However, due to a lack of annually resolved natural archives in the Sahara and Arabian Desert, the precise characteristics of Middle Eastern climate during the Little Ice Age are unknown. Here we show, based on subseasonally resolved proxy records using corals from the northern Red Sea that the Middle East did not experience pronounced cooling during the late Little Ice Age (1751-1850). Instead, it was characterised by an even more arid climate than today. From our coral records and early instrumental data we conclude that Middle Eastern aridity resulted from a blocking-like atmospheric circulation over central Europe that weakened the moist Mediterranean westerlies and favoured the advection of dry continental air from Eurasia. We find that this extreme aridity terminated abruptly between 1850 and 1855 due to an atmospheric circulation change over the European-Middle East area at the end of the Little Ice Age with profound impacts on regional hydroclimate. Our results provide a hydroclimatic perspective on the resettlement of abandoned areas of the historical Fertile Crescent following the Little Ice Age. Furthermore, we speculate such an atmospheric blocking could have prevailed during other North Atlantic-European cold events of the Holocene epoch, and may explain the northern Mesopotamian aridification at 4,200 years ago that is thought to have led to the collapse of ancient civilizations.

Effects of elevated temperatures and rising sea level on Arctic Coast

USGS Publications Warehouse

Barnes, Peter W.

1990-01-01

Ice is a major agent on the inner shelf, gouging the bottom, increasing hydraulic scour, transporting sediment, and influencing river flood patterns. Rapid coastal retreat is common and low barrier islands and beaches are constantly changing due to the influence of permafrost, ice-push, waves, and currents. Coastal processes are presently a balance between the influence of ice and the action of waves and currents. Quantitative values for processes are poorly known, however our qualitative understanding is nearly complete. Climatic warming and rising sea levels would decrease the temporal and aerial extent of coastal ice thereby expanding the role of waves and currents. As a result, shoreline retreat rates would increase, producing a transgressive erosional surface on the low coastal plain. With increased wave activity, beaches and barrier islands presently nourished by ice push processes would decay and disappear. Increased sediment supply from a deeply thawed, active layer would release more sediments to rivers and coasts. Additional research should be focused on permafrost and sea ice processes active during freeze up and breakup; the two seasons of most vigorous activity and change.

Atmospheric and oceanic forcing of Weddell Sea ice motion

NASA Astrophysics Data System (ADS)

Kottmeier, C.; Sellmann, Lutz

1996-09-01

The data from sea ice buoys, which were deployed during the Winter Weddell Sea Project 1986, the Winter Weddell Gyre Studies 1989 and 1992, the Ice Station Weddell in 1992, the Antarctic Zone Flux Experiment in 1994, and several ship cruises in Austral summers, are uniformly reanalyzed by the same objective methods. Geostrophic winds are derived after matching of the buoy pressure data with the surface pressure fields of the European Centre for Medium Range Weather Forecasts. The ratio between ice drift and geostrophic wind speeds is reduced when winds and currents oppose each other, when the atmospheric surface layer is stably stratified, and when the ice is under pressure near coasts. Over the continental shelves, the spatial inhomogeneity of tidal and inertial motion effectively controls the variability of divergence for periods below 36 hours. Far from coasts, speed ratios, which presumably reflect internal stress variations in the ice cover, are independent of drift divergence on the spatial scale of 100 km. To study basin-scale ice dynamics, all ice drift data are related to the geostrophic winds based on the complex linear model [Thorndike and Colony, 1982] for daily averaged data. The composite patterns of mean ice motion, geostrophic winds, and geostrophic surface currents document cyclonic basin-wide circulations. Geostrophic ocean currents are generally small in the Weddell Sea. Significant features are the coastal current near the southeastern coasts and the bands of larger velocities of ≈6 cm s-1 following the northward and eastward orientation of the continental shelf breaks in the western and northwestern Weddell Sea. In the southwestern Weddell Sea the mean ice drift speed is reduced to less than 0.5% of the geostrophic wind speed and increases rather continuously to 1.5% in the northern, central, and eastern Weddell Sea. The linear model accounts for less than 50% of the total variance of drift speeds in the southwestern Weddell Sea and up to 80% in the northern and eastern Weddell Sea.

Lake Sediment Records as an Indicator of Holocene Fluctuations of Quelccaya Ice Cap, Peru and Regional Climate

NASA Astrophysics Data System (ADS)

Stroup, J. S.; Kelly, M. A.; Lowell, T. V.; Beal, S. A.; Smith, C. A.; Baranes, H. E.

2012-12-01

The past fluctuations of Quelccaya Ice Cap, (QIC; 13°S, 70°W, 5200 m asl) located in the southeastern Peruvian Andes, provide a record of tropical climate since the last glacial-interglacial transition. A detailed surficial geomorphic record of past glacial extents developed over the last several decades (e.g. Mercer and Palacios 1977; Buffen et al. 2009; Kelly et al. 2012 accepted) demonstrates that QIC is a dynamic glacial system. These records show that the ice cap was larger than present and retreating by ~11,500 yr BP, and smaller than present between ~7,000 and ~4,600 yr BP. The most recent advance occurred during the late Holocene (Little Ice Age;LIA), dated with 10Be surface exposure ages (510±90 yrs (n = 8)) (Stroup et al. in prep.). This overrode earlier deposits obscuring a complete Holocene record; we aim to address the gaps in glacial chronology using the sedimentary record archived in lakes. We retrieved two sets cores (8 and 5 m-long) from Laguna Challpacocha (13.91°S, 70.86°W, 5040 m asl), a lake that currently receives meltwater from QIC. Four radiocarbon ages from the cores suggest a continuous record dating to at least ~10,500 cal. yr BP. Variations in magnetic susceptibility, percent organic and inorganic carbon, bulk density, grayscale and X-ray fluorescence chemistry indicate changes in the amount of clastic sediment deposition. We interpret clastic sediments to have been deposited from ice cap meltwater, thus indicating more extensive ice. Clastic sediments compose the top of the core from 4 to 30 cm depth, below there is a sharp transition to organic sediments radiocarbon dated to (500±30 and 550±20 cal. yr BP). The radiocarbon ages are similar to the 10Be dated (LIA) glacial position. At least three other clastic units exist in the core; dating to ~2600-4300, ~4800-7300 and older then ~10,500 cal. yr BP based on a linear age model with four radiocarbon dates. We obtained two, ~4 m long, cores from Laguna Yanacocha (13.95°S,70.87°W, 4910 m asl), a lake that has not received glacial meltwater since late glacial time. We used the clastic sediment record to determine the input from non-glacial sources, representing ambient climate. This information tests our hypothesis that increased clastic sediment is from a glacial source in the Challpacocha record. The Yanacocha cores are composed primarily of organic-rich sediment with little clastic sediment. Eight radiocarbon ages in stratigraphic order indicate a continuous sedimentation in the lake since 11,240±90 cal. yr BP. Till at the base of the core indicates likely ice recession from the basin at this time. Variations in magnetic susceptibility, percent organic and inorganic carbon, bulk density, and gray scale suggest only minor changes in sedimentation relative to those in the Challpacocha core. Our new continuous lake sediment record provides complementary data to the discontinuous records of QIC Holocene extents as marked by moraines and exposed sections (e.g. Buffen et al. 2009; Thompson et al. 2006). Our record has some similarities with the nearby lacustrine record from Laguna Pacococha, which also receives meltwater from QIC (Rodbell and Seltzer, 2000; Abbott et al., 2003).

Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow

PubMed Central

Kulessa, Bernd; Hubbard, Alun L.; Booth, Adam D.; Bougamont, Marion; Dow, Christine F.; Doyle, Samuel H.; Christoffersen, Poul; Lindbäck, Katrin; Pettersson, Rickard; Fitzpatrick, Andrew A. W.; Jones, Glenn A.

2017-01-01

The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms. PMID:28835915

Seismic evidence for complex sedimentary control of Greenland Ice Sheet flow.

PubMed

Kulessa, Bernd; Hubbard, Alun L; Booth, Adam D; Bougamont, Marion; Dow, Christine F; Doyle, Samuel H; Christoffersen, Poul; Lindbäck, Katrin; Pettersson, Rickard; Fitzpatrick, Andrew A W; Jones, Glenn A

2017-08-01

The land-terminating margin of the Greenland Ice Sheet has slowed down in recent decades, although the causes and implications for future ice flow are unclear. Explained originally by a self-regulating mechanism where basal slip reduces as drainage evolves from low to high efficiency, recent numerical modeling invokes a sedimentary control of ice sheet flow as an alternative hypothesis. Although both hypotheses can explain the recent slowdown, their respective forecasts of a long-term deceleration versus an acceleration of ice flow are contradictory. We present amplitude-versus-angle seismic data as the first observational test of the alternative hypothesis. We document transient modifications of basal sediment strengths by rapid subglacial drainages of supraglacial lakes, the primary current control on summer ice sheet flow according to our numerical model. Our observations agree with simulations of initial postdrainage sediment weakening and ice flow accelerations, and subsequent sediment restrengthening and ice flow decelerations, and thus confirm the alternative hypothesis. Although simulated melt season acceleration of ice flow due to weakening of subglacial sediments does not currently outweigh winter slowdown forced by self-regulation, they could dominate over the longer term. Subglacial sediments beneath the Greenland Ice Sheet must therefore be mapped and characterized, and a sedimentary control of ice flow must be evaluated against competing self-regulation mechanisms.

Antarctic Ice-Sheet Mass Balance from Satellite Altimetry 1992 to 2001

NASA Technical Reports Server (NTRS)

Zwally, H. Jay; Brenner, Anita C.; Cornejo, Helen; Giovinetto, Mario; Saba, Jack L.; Yi, Donghui

2003-01-01

A major uncertainty in understanding the causes of the current rate of sea level rise is the potential contributions from mass imbalances of the Greenland and Antarctic ice sheets. Estimates of the current mass balance of the Antarctic ice sheet are derived from surface- elevation changes obtained from 9 years of ERS - 1 & 2 radar altimeter data. Elevation time-series are created from altimeter crossovers among 90-day data periods on a 50 km grid to 81.5 S. The time series are fit with a multivariate linear/sinusoidal function to give the average rate of elevation change (dH/dt). On the major Rome-Filchner, Ross, and Amery ice shelves, the W d t are small or near zero. In contrast, the ice shelves of the Antarctic Peninsula and along the West Antarctic coast appear to be thinning significantly, with a 23 +/- 3 cm per year surface elevation decrease on the Larsen ice shelf and a 65 +/- 4 cm per year decrease on the Dotson ice shelf. On the grounded ice, significant elevation decreases are obtained over most of the drainage basins of the Pine Island and Thwaites glaciers in West Antarctica and inland of Law Dome in East Antarctica. Significant elevation increases are observed within about 200 km of the coast around much of the rest of the ice sheet. Farther inland, the changes are a mixed pattern of increases and decreases with increases of a few centimeters per year at the highest elevations of the East Antarctic plateau. The derived elevation changes are combined with estimates of the bedrock uplift from several models to provide maps of ice thickness change. The ice thickness changes enable estimates of the ice mass balances for the major drainage basins, the overall mass balance, and the current contribution of the ice sheet to global sea level change.

Fram-2014/2015: A 400 Day Investigation of the Arctic's Oldest Sediments over the Alpha Ridge with a Research Hovercraft

NASA Astrophysics Data System (ADS)

Hall, J. K.; Kristoffersen, Y.

2014-12-01

The thickest multi-year ice in the Arctic covers a secret. Four short cores raised from the Alpha Ridge in the 1970s and 1980s from drift stations T-3 and CESAR showed ages between 45 and 76 my. The reason for these old ages became clear when examination of legacy seismic data from T-3 showed that in some places up to 500 m of sediments had been removed within an area of some 200 by 600 km, presumably by an impact of asteroid fragments. To investigate the impact area, the authors conceived an innovative research platform in 2007. Named the R/H SABVABAA, this 12m by 6m hovercraft has been home-based in Svalbard since June 2008. During the following 6 years the craft and its evolving innovative light-weight equipment have made 18 trips to the summer ice pack, traveling some 4410 km over ice during some six months of scientific investigations. An opportunity to get a lift to this area, some 1500 km from Svalbard, came in a 2011 invitation to join AWI's icebreaker POLARSTERN in its ARK-XXVIII/4 expedition departing Tromsö August 5, 2014. The 400 day drift will be the first wintering over, ever, of a mobile research platform with geophysical, geological, and oceanographic capabilities. The Arctic ice pack continually moves due to winds and currents. While at the main camp, observations will consist of marine geophysics (seismic profiling with four element CHIRP, a 20 in³ airgun with single hydrophone, as well as 12 kHz bathymetry and 200 kHz sounding of the deep scattering layer), marine geology (coring with a hydrostatically-boosted 3 or 6 m corer; bottom photography; and two rock dredges), and oceanography. Deployed away from the camp, four sonobuoys will allow 3-D seismic acquisition. Access to the depths below the ice is via a hydraulic capstan winch, with 6500 m of Kevlar aramid fiber rope with 2.8 ton breaking strength. Ice thickness monitoring of the local 100 km² will be made with the craft's EM-31 probe when away from the camp, moving to choice locations for taking cores, and deformation of the ice pack monitored by 5 remote GPS data loggers. A meteorological station including radiation flux measurements will be operated. Several cameras will be used to observe under-ice conditions (ice formation, biology) as well as time-lapse local ice movement. The talk will summarize the operations up to the time of the GEBCO 2014 Science Day at the AGU Fall Meeting.

Cosmogenic 10Be ages from the Meirs and Garwood Valleys, Denton Hills, West Antarctica, suggest an absence in LGM Ice Sheet expansion.

NASA Astrophysics Data System (ADS)

Fink, David; Joy, Kurt; Storey, Bryan

2014-05-01

It has been hypothesised that during interglacials, thinning of the Ross Ice Shelf allowed a more open water environment with increased local precipitation. This resulted in outlet glaciers, which drain the Transantarctic Mountains and fed by the East Antarctic Ice Sheet, advancing during moist warmer periods, apparently out of phase with colder arid dry periods. Significantly the ice core record during these warm periods also shows increased accumulation continent wide The geomorphology of the Denton Hills in the Royal Society Range, West Antarctica, is a result of Miocene fluvial incision reworked by subsequent glacial advances throughout the Quaternary. The Garwood and Miers glacial valleys drain ice across the Denton Hills into the Shelf, and should thus show maximum extent during interstadials. To understand the chronology of late Quaternary glaciations, 15 granitic boulders from terminal moraines were sampled for 10Be and 26Al cosmogenic dating. Obtaining reliable exposure ages of erratics within moraines that represent timing of deposition (i.e. glacial advances) is problematic in polar regions, where glacial activity is principally controlled by ice sheet dynamics. Recycling of previously exposed debris, uncertainty in provenance of glacially transported boulders and a lack of a post-depositional hydrologic process to remove previously exposed material from a valley system, leads to ambiguities in multiple exposure ages from a single coeval glacial landform. More importantly, cold-based ice advance can leave a landform unmodified resulting in young erratics deposited on bedrock that shows weathering and/or inconsistent age-altitude relationships. Primarily, inheritance becomes a difficulty in qualifying exposure ages from polar regions. Preliminary results from the Garwood and Miers Valleys indicate that glaciers in the Denton Hills had begun to retreat from their last maximum positions no later than 23-37 ka, and thus the local last glacial maximum occurred prior to the Antarctic LGM (18-22 ka). No evidence based on cosmogenic ages for post-LGM or Holocene advances were found. These results support an extensive exposure age data set from the nearby Darwin-Hatherton Glacier system that indicates an absence of EAIS expansion across the Transantarctic Mnts during the global LGM period.

Paraglacial dynamics in Little Ice Age glaciated environments in the Iberian Peninsula

NASA Astrophysics Data System (ADS)

Oliva, Marc; Serrano, Enrique; Ruiz-Fernández, Jesús; Gómez-Ortiz, Antonio; Palacios, David

2017-04-01

Three Iberian mountain ranges encompassed glaciers during the Little Ice Age (LIA): the Pyrenees, Cantabrian Mountains and Sierra Nevada. The gradual warming trend initiated during the second half of the XIX century promoted the progressive shrinking of these glaciers, which completely melted during the first half of the 20th century in the Cantabrian Mountains and Sierra Nevada and reduced by 80% of their LIA extent in the Pyrenees. Currently, the formerly glaciated environments are located within the periglacial belt and still present to a major or lesser degree signs of paraglacial activity. LIA moraines are devoid of vegetation and composed of highly unstable sediments that are being intensely mobilized by slope processes. Inside the moraines, different landforms and processes generated following LIA glacial retreat have generated: (i) buried ice trapped within rock debris supplied from the cirque walls, which has also generated rock glaciers and protalus lobes; (ii) semi-permanent snow fields distributed above the ice-patches remnants of the LIA glaciers, and (iii) small periglacial features such as frost mounds, sorted circles and solifluction landforms generated by processes such as solifluction and cryoturbation. Present-day morphodynamics is mostly related to seasonal frost conditions, though patches of permafrost have formed in some areas in contact with the buried ice. This 'geomorphic permafrost' is undergoing a process of degradation since it is not balanced with present-day climate conditions. This is reflected in the occurrence of multiple collapses and subsidences of the debris cover where the frozen bodies sit. In the highest areas of the Pyrenees there is a permafrost belt next to the small glaciated environments in the highest massifs. Finally, we propose a model for paraglacial activity in Iberian mountain ranges and compare it to other mid-latitude mountain environments as well as to other past deglaciation stages.

Sports-related eye injuries: the current picture.

PubMed

Leivo, Tiina; Haavisto, Anna-Kaisa; Sahraravand, Ahmad

2015-05-01

This study aims to represent the epidemiologies, findings, treatments, use of resources, outcomes and protective-eyewear-use recommendations in sports-related eye injuries by sport type. The study population is comprised of all new eye injury patients in 1 year in Helsinki University Eye Hospital. Data were collected from patient questionnaires and hospital records. The follow-up period was 3 months. 149/1151 (12.9%) of eye injuries were sports-related. Thirty two percent were related to floorball (type of hockey played on a mat with a stick and a ball); football, tennis and ice hockey were the next most common eye-injury-causing sports. Relatively, the most dangerous sports were rink bandy, (bandy played on ice hockey rink with a stick and a ball) (0.50 injuries in 12 months/1000 participants, CI 0.10-1.46), floorball (0.47, CI 0.34-0.62) and tennis (0.47, CI 0.26-0.77). Contusion was the primary diagnosis in 77% of cases; 41% of contusion patients had severe, mainly retinal findings. The number of outpatient visits was 459; inpatient days 25 and major surgeries 31. One hundred and eight patients were estimated to need life-long follow-up. Seventeen patients had a permanent functional impairment, 4 in ice hockey, 3 in floorball, 2 each in tennis and badminton. Compared to a previous study, ice hockey eye injuries are increasing and relatively severe, and a third of these injuries occurred despite visor use. Floorball eye injury incidence has significantly declined, mainly due to recently enforced mandatory protective eyewear for younger age groups. Based on these findings, we recommend, in floorball, that protective eyewear should be mandatory in all age groups. Universally in ice hockey, the proper use of a visor should be emphasised. © 2015 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

In Situ Airborne Instrumentation: Addressing and Solving Measurement Problems in Ice Clouds

DOE PAGES

Baumgardner, Darrel; Kok, Greg; Avallone, L.; ...

2012-02-01

A meeting of 31 international experts on in situ measurements from aircraft was held to identify unresolved questions concerning ice formation and evolution in ice clouds, assess the current state of instrumentation that can address these problems, introduce emerging technology that may overcome current measurement issues and recommend future courses of action that can improve our understanding of ice cloud microphysical processes and their impact on the environment. The meeting proceedings and outcome has been described in detail in a manuscript submitted to the Bulletin of the American Meteorological Society (BAMS) on March 24, 2011. This paper is currently undermore » review. The remainder of this summary, in the following pages, is the text of the BAMS article. A technical note that will be published by the National Center for Atmospheric Research is currently underway and is expected to be published before the end of the year.« less

Reconstructing the history of major Greenland glaciers since the Little Ice Age

NASA Astrophysics Data System (ADS)

Csatho, B. M.; Schenk, A. F.; van der Veen, C. J.; Stearns, L.; Babonis, G. S.

2008-12-01

The Greenland Ice Sheet may have been responsible for rapid sea level rise during the last interglacial period and recent studies indicate that it is likely to make a faster contribution to sea-level rise than previously believed. Rapid thinning and velocity increase has been observed on most major outlet glaciers with terminus retreat that might lead to increased discharge from the interior and consequent further thinning and retreat. Potentially, such behavior could have serious implications for global sea level. However, the current thinning may simply be a manifestation of longer-term behavior of the ice sheet as it responds to the general warming following the Little Ice Age (LIA). Although Greenland outlet glaciers have been comprehensively monitored since the 1980s, studies of long-term changes mostly rely on records of the calving front position. Such records can be misleading because the glacier terminus, particularly if it is afloat, can either advance or retreat as ice further upstream thins and accelerates. To assess whether recent trends deviate from longer-term behavior, we examined three rapidly thinning and retreating outlet glaciers, Jakobshavn Isbrae in west, Kangerdlussuaq Glacier in east and Petermann Glacier in northwest Greenland. Glacier surface and trimline elevations, as well as terminus positions were measured using historical photographs and declassified satellite imagery acquired between the 1940s and 1985. These results were combined with data from historical records, ground surveys, airborne laser altimetry, satellite observations and field mapping of lateral moraines and trimlines, to reconstruct the history of changes since the (LIA) up to the present. We identified several episodes of rapid thinning and ice shelf break-up, including thinning episodes that occurred when the calving front was stationary. Coastal weather station data are used to assess the influence of air temperatures and intensity of surface melting, and to isolate glacier changes likely associated with changes in glacier dynamics. We also examined the potential influence of geologic control, including the effect of increased heat flux and high rates of subglacial melt suggested by geophysical data.

Modelling MIZ dynamics in a global model

NASA Astrophysics Data System (ADS)

Rynders, Stefanie; Aksenov, Yevgeny; Feltham, Daniel; Nurser, George; Naveira Garabato, Alberto

2016-04-01

Exposure of large, previously ice-covered areas of the Arctic Ocean to the wind and surface ocean waves results in the Arctic pack ice cover becoming more fragmented and mobile, with large regions of ice cover evolving into the Marginal Ice Zone (MIZ). The need for better climate predictions, along with growing economic activity in the Polar Oceans, necessitates climate and forecasting models that can simulate fragmented sea ice with a greater fidelity. Current models are not fully fit for the purpose, since they neither model surface ocean waves in the MIZ, nor account for the effect of floe fragmentation on drag, nor include sea ice rheology that represents both the now thinner pack ice and MIZ ice dynamics. All these processes affect the momentum transfer to the ocean. We present initial results from a global ocean model NEMO (Nucleus for European Modelling of the Ocean) coupled to the Los Alamos sea ice model CICE. The model setup implements a novel rheological formulation for sea ice dynamics, accounting for ice floe collisions, thus offering a seamless framework for pack ice and MIZ simulations. The effect of surface waves on ice motion is included through wave pressure and the turbulent kinetic energy of ice floes. In the multidecadal model integrations we examine MIZ and basin scale sea ice and oceanic responses to the changes in ice dynamics. We analyse model sensitivities and attribute them to key sea ice and ocean dynamical mechanisms. The results suggest that the effect of the new ice rheology is confined to the MIZ. However with the current increase in summer MIZ area, which is projected to continue and may become the dominant type of sea ice in the Arctic, we argue that the effects of the combined sea ice rheology will be noticeable in large areas of the Arctic Ocean, affecting sea ice and ocean. With this study we assert that to make more accurate sea ice predictions in the changing Arctic, models need to include MIZ dynamics and physics.

Geothermal Heat Flux and Upper Mantle Viscosity across West Antarctica: Insights from the UKANET and POLENET Seismic Networks

NASA Astrophysics Data System (ADS)

O'Donnell, J. P.; Dunham, C.; Stuart, G. W.; Brisbourne, A.; Nield, G. A.; Whitehouse, P. L.; Hooper, A. J.; Nyblade, A.; Wiens, D.; Aster, R. C.; Anandakrishnan, S.; Huerta, A. D.; Wilson, T. J.; Winberry, J. P.

2017-12-01

Quantifying the geothermal heat flux at the base of ice sheets is necessary to understand their dynamics and evolution. The heat flux is a composite function of concentration of upper crustal radiogenic elements and flow of heat from the mantle into the crust. Radiogenic element concentration varies with tectonothermal age, while heat flow across the crust-mantle boundary depends on crustal and lithospheric thicknesses. Meanwhile, accurately monitoring current ice mass loss via satellite gravimetry or altimetry hinges on knowing the upper mantle viscosity structure needed to account for the superimposed glacial isostatic adjustment (GIA) signal in the satellite data. In early 2016 the UK Antarctic Network (UKANET) of 10 broadband seismometers was deployed for two years across the southern Antarctic Peninsula and Ellsworth Land. Using UKANET data in conjunction with seismic records from our partner US Polar Earth Observing Network (POLENET) and the Antarctic Seismographic Argentinian Italian Network (ASAIN), we have developed a 3D shear wave velocity model of the West Antarctic crust and uppermost mantle based on Rayleigh and Love wave phase velocity dispersion curves extracted from ambient noise cross-correlograms. We combine seismic receiver functions with the shear wave model to help constrain the depth to the crust-mantle boundary across West Antarctica and delineate tectonic domains. The shear wave model is subsequently converted to temperature using a database of densities and elastic properties of minerals common in crustal and mantle rocks, while the various tectonic domains are assigned upper crustal radiogenic element concentrations based on their inferred tectonothermal ages. We combine this information to map the basal geothermal heat flux variation across West Antarctica. Mantle viscosity depends on factors including temperature, grain size, the hydrogen content of olivine and the presence of melt. Using published mantle xenolith and magnetotelluric data to constrain grain size and hydrogen content, respectively, we use the temperature model to estimate the regional upper mantle viscosity structure. The viscosity information will be incorporated in a 3D GIA model that will better constrain estimates of current ice loss from the West Antarctic Ice Sheet.

Bacterial Ice Crystal Controlling Proteins

PubMed Central

Lorv, Janet S. H.; Rose, David R.; Glick, Bernard R.

2014-01-01

Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions. PMID:24579057

Bacterial ice crystal controlling proteins.

PubMed

Lorv, Janet S H; Rose, David R; Glick, Bernard R

2014-01-01

Across the world, many ice active bacteria utilize ice crystal controlling proteins for aid in freezing tolerance at subzero temperatures. Ice crystal controlling proteins include both antifreeze and ice nucleation proteins. Antifreeze proteins minimize freezing damage by inhibiting growth of large ice crystals, while ice nucleation proteins induce formation of embryonic ice crystals. Although both protein classes have differing functions, these proteins use the same ice binding mechanisms. Rather than direct binding, it is probable that these protein classes create an ice surface prior to ice crystal surface adsorption. Function is differentiated by molecular size of the protein. This paper reviews the similar and different aspects of bacterial antifreeze and ice nucleation proteins, the role of these proteins in freezing tolerance, prevalence of these proteins in psychrophiles, and current mechanisms of protein-ice interactions.

How Many Seals Were There? The Global Shelf Loss during the Last Glacial Maximum and Its Effect on the Size and Distribution of Grey Seal Populations

PubMed Central

Boehme, Lars; Thompson, Dave; Fedak, Mike; Bowen, Don; Hammill, Mike O.; Stenson, Garry B.

2012-01-01

Predicting how marine mammal populations respond to habitat changes will be essential for developing conservation management strategies in the 21st century. Responses to previous environmental change may be informative in the development of predictive models. Here we describe the likely effects of the last ice age on grey seal population size and distribution. We use satellite telemetry data to define grey seal foraging habitat in terms of the temperature and depth ranges exploited by the contemporary populations. We estimate the available extent of such habitat in the North Atlantic at present (between 1.42·106 km2 and 2.07·106 km2) and at the last glacial maximum (between 4.74·104 km2 and 2.11·105 km2); taking account of glacial and seasonal sea-ice coverage, estimated reductions of sea-level (123 m) and sea surface temperature hind-casts. Most of the extensive continental shelf waters (North Sea, Baltic Sea and Scotian Shelf), currently supporting >95% of grey seals, were unavailable during the last glacial maximum. A combination of lower sea-level and extensive ice-sheets, massively increased seasonal sea-ice coverage and southerly extent of cold water would have pushed grey seals into areas with no significant shelf waters. The habitat during the last glacial maximum might have been as small as 3% of today's extent and grey seal populations may have fallen to similarly low numbers. An alternative scenario involving a major change to a pelagic or bathy-pelagic foraging niche cannot be discounted. However, hooded seals currently dominate that niche and may have excluded grey seals from such habitat. If as seems likely, the grey seal population fell to very low levels it would have remained low for several thousand years before expanding into current habitats over the past 12,000 years or so. PMID:23300843

First High-Resolution Record of Late Quaternary Environmental Changes in the Amundsen Sea, West Antarctica, Revealed by Multi-proxy Analysis of Drift Sediments

NASA Astrophysics Data System (ADS)

Horrocks, J.; Ó Cofaigh, C.; Lloyd, J. M.; Hillenbrand, C. D.; Kuhn, G.; Smith, J.; Ehrmann, W. U.; Esper, O.

2015-12-01

The Amundsen Sea sector of the West Antarctic Ice Sheet (WAIS) is experiencing rapid mass loss and there is a pressing need to place the contemporary ice-sheet changes into a longer term context. The continental rise in this region is characterised by large sediment mounds that are shaped by westward flowing bottom currents and that resemble contouritic drifts existing offshore from the Antarctic Peninsula. Similar to the Antarctic Peninsula drifts, marine sediment cores from the poorly studied sediment mounds in the Amundsen Sea have the potential to provide reliable records of dynamical ice-sheet behaviour in West Antarctica and palaeoceanographic changes in the Southern Ocean during the Late Quaternary that can be reconstructed from their terrestrial, biogenic and authigenic components. Here we use multi-proxy data from three sediment cores recovered from two of the Amundsen Sea mounds to present the first high-resolution study of environmental changes on this part of the West Antarctic continental margin over the glacial-interglacial cycles of the Late Quaternary. Age constraints for the records are derived from biostratigraphy, AMS 14C dates and lithostratigraphy. We focus on the investigation of processes for drift formation, thereby using grain size and sortable silt data to reconstruct changes in bottom current speed and to identify episodes of current winnowing. Data on geochemical and mineralogical sediment composition and physical properties are used to infer both changes in terrigenous sediment supply in response to the advance and retreat of the WAIS across the Amundsen Sea shelf and changes in biological productivity that are mainly controlled by the duration of annual sea-ice coverage. We compare our data sets from the Amundsen Sea mounds to those from the well-studied Antarctic Peninsula drifts, thereby highlighting similarities and discrepancies in depositional processes and climatically-driven environmental changes.

Ocean-ice interaction in the marginal ice zone

NASA Technical Reports Server (NTRS)

Liu, Antony K.; Peng, Chich Y.

1994-01-01

Ocean ice interaction processes in the Marginal Ice Zone (MIZ) by wind, waves, and mesoscale features, such as upwelling and eddies, are studied using ERS-1 Synthetic Aperture Radar (SAR) images and ocean ice interaction model. A sequence of SAR images of the Chukchi Sea MIZ with three days interval are studied for ice edge advance/retreat. Simultaneous current measurements from the northeast Chukchi Sea as well as the Barrow wind record are used to interpret the MIZ dynamics.

Changes in the seasonality of Arctic sea ice and temperature

NASA Astrophysics Data System (ADS)

Bintanja, R.

2012-04-01

Observations show that the Arctic sea ice cover is currently declining as a result of climate warming. According to climate models, this retreat will continue and possibly accelerate in the near-future. However, the magnitude of this decline is not the same throughout the year. With temperatures near or above the freezing point, summertime Arctic sea ice will quickly diminish. However, at temperatures well below freezing, the sea ice cover during winter will exhibit a much weaker decline. In the future, the sea ice seasonal cycle will be no ice in summer, and thin one-year ice in winter. Hence, the seasonal cycle in sea ice cover will increase with ongoing climate warming. This in itself leads to an increased summer-winter contrast in surface air temperature, because changes in sea ice have a dominant influence on Arctic temperature and its seasonality. Currently, the annual amplitude in air temperature is decreasing, however, because winters warm faster than summer. With ongoing summer sea ice reductions there will come a time when the annual temperature amplitude will increase again because of the large seasonal changes in sea ice. This suggests that changes in the seasonal cycle in Arctic sea ice and temperature are closely, and intricately, connected. Future changes in Arctic seasonality (will) have an profound effect on flora, fauna, humans and economic activities.

Global ice-sheet system interlocked by sea level

NASA Astrophysics Data System (ADS)

Denton, George H.; Hughes, Terence J.; Karlén, Wibjörn

1986-07-01

Denton and Hughes (1983, Quaternary Research20, 125-144) postulated that sea level linked a global ice-sheet system with both terrestrial and grounded marine components during late Quaternary ice ages. Summer temperature changes near Northern Hemisphere melting margins initiated sea-level fluctuations that controlled marine components in both polar hemispheres. It was further proposed that variations of this ice-sheet system amplified and transmitted Milankovitch summer half-year insolation changes between 45 and 75°N into global climatic changes. New tests of this hypothesis implicate sea level as a major control of the areal extent of grounded portions of the Antarctic Ice Sheet, thus fitting the concept of a globally interlocked ice-sheet system. But recent atmospheric modeling results ( Manabe and Broccoli, 1985, Journal of Geophysical Research90, 2167-2190) suggest that factors other than areal changes of the grounded Antarctic Ice Sheet strongly influenced Southern Hemisphere climate and terminated the last ice age simultaneously in both polar hemispheres. Atmospheric carbon dioxide linked to high-latitude oceans is the most likely candidate ( Shackleton and Pisias, 1985, Atmospheric carbon dioxide, orbital forcing, and climate. In "The Carbon Cycle and Atmospheric CO 2: Natural Variations Archean to Present" (E. T. Sundquest and W. S. Broecker, Eds.), pp. 303-318. Geophysical Monograph 32, American Geophysical Union, Washington, D.C.), but another potential influence was high-frequency climatic oscillations (2500 yr). It is postulated that variations in atmospheric carbon dioxide acted through an Antarctic ice shelf linked to the grounded ice sheet to produce and terminate Southern Hemisphere ice-age climate. It is further postulated that Milankovitch summer insolation combined with a warm high-frequency oscillation caused marked recession of Northern Hemisphere ice-sheet melting margins and the North Atlantic polar front about 14,000 14C yr B.P. This permitted renewed formation of North Atlantic Deep Water, which could well have controlled atmospheric carbon dioxide ( W. S. Broecker, D. M. Peteet, and D. Rind, 1985, Nature ( London) 315, 21-26). Combined melting and consequent sea-level rise from the three warming factors initiated irreversible collapse of the interlocked global ice-sheet system, which was at its largest but most vulnerable configuration.

Incidence of Concussion in Youth Ice Hockey Players

PubMed Central

Elbin, R.J.; Sufrinko, Alicia; Dakan, Scott; Bookwalter, Kylie; Price, Ali; Meehan, William P.; Collins, Michael W.

2016-01-01

BACKGROUND: Ice hockey is a fast-paced collision sport that entails both intentional (ie, body checking) and incidental contact that may involve the head. The objective of this study was to determine the incidence of concussions in relation to games/practices and age among competition-level youth ice hockey players (ages 12–18 years). METHODS: Participants included 397 youth ice hockey players from Western Pennsylvania; Boston, Massachusetts; and Birmingham, Alabama, during the 2012–2013 and 2013–2014 youth ice hockey seasons. Incidence rates (IRs) and incidence rate ratios (IRRs) of concussion were calculated for games/practices and age groups. RESULTS: A total of 23 369 (12 784 practice/10 585 game) athletic exposures (AEs) involving 37 medically diagnosed concussions occurred. More than 40% of concussions involved illegal contact. The combined IR for games and practices was 1.58 concussions per 1000 AEs. The IRR was 2.86 times (95% confidence interval 0.68–4.42) higher during games (2.49 per 1000 AEs) than practices (1.04 per 1000 AEs). CONCLUSIONS: The overall IR for concussion in youth ice hockey was comparable to those reported in other youth collision sports. The game-to-practice IRR was lower than previously reported in ice hockey and other youth sports, although more concussions per exposure occurred in games compared with practices. Younger players had a higher rate of concussions than older players. PMID:26746405

Incidence of Concussion in Youth Ice Hockey Players.

PubMed

Kontos, Anthony P; Elbin, R J; Sufrinko, Alicia; Dakan, Scott; Bookwalter, Kylie; Price, Ali; Meehan, William P; Collins, Michael W

2016-02-01

Ice hockey is a fast-paced collision sport that entails both intentional (ie, body checking) and incidental contact that may involve the head. The objective of this study was to determine the incidence of concussions in relation to games/practices and age among competition-level youth ice hockey players (ages 12-18 years). Participants included 397 youth ice hockey players from Western Pennsylvania; Boston, Massachusetts; and Birmingham, Alabama, during the 2012-2013 and 2013-2014 youth ice hockey seasons. Incidence rates (IRs) and incidence rate ratios (IRRs) of concussion were calculated for games/practices and age groups. A total of 23 369 (12 784 practice/10 585 game) athletic exposures (AEs) involving 37 medically diagnosed concussions occurred. More than 40% of concussions involved illegal contact. The combined IR for games and practices was 1.58 concussions per 1000 AEs. The IRR was 2.86 times (95% confidence interval 0.68-4.42) higher during games (2.49 per 1000 AEs) than practices (1.04 per 1000 AEs). The overall IR for concussion in youth ice hockey was comparable to those reported in other youth collision sports. The game-to-practice IRR was lower than previously reported in ice hockey and other youth sports, although more concussions per exposure occurred in games compared with practices. Younger players had a higher rate of concussions than older players. Copyright © 2016 by the American Academy of Pediatrics.

A survey of anti-icing practice in Virginia.

DOT National Transportation Integrated Search

1997-01-01

This study documents the current Virginia Department of Transportation's anti-icing practice so that development of a coordinated statewide plan for implementing anti-icing technology can be considered. The researcher surveyed VDOT managers to determ...

Volcanic synchronisation of the EPICA-DC and TALDICE ice cores for the last 42 kyr BP

NASA Astrophysics Data System (ADS)

Severi, M.; Udisti, R.; Becagli, S.; Stenni, B.; Traversi, R.

2012-03-01

The age scale synchronisation between the Talos Dome and the EPICA Dome C ice cores was carried on through the identification of several common volcanic signatures. This paper describes the rigorous method, using the signature of volcanic sulphate, which was employed for the last 42 kyr of the record. Using this tight stratigraphic link, we transferred the EDC age scale to the Talos Dome ice core, producing a new age scale for the last 12 kyr. We estimated the discrepancies between the modelled TALDICE-1 age scale and the new scale during the studied period, by evaluating the ratio R of the apparent duration of temporal intervals between pairs of isochrones. Except for a very few cases, R ranges between 0.8 and 1.2, corresponding to an uncertainty of up to 20% in the estimate of the time duration in at least one of the two ice cores. At this stage our approach does not allow us to unequivocally identify which of the models is affected by errors, but, taking into account only the historically known volcanic events, we found that discrepancies up to 200 yr appear in the last two millennia in the TALDICE-1 model, while our new age scale shows a much better agreement with the volcanic absolute horizons. Thus, we propose for the Talos Dome ice core a new age scale (covering the whole Holocene) obtained by a direct transfer, via our stratigraphic link, from the EDC modelled age scale by Lemieux-Dudon et al. (2010).

Ice Accretion Test Results for Three Large-Scale Swept-Wing Models in the NASA Icing Research Tunnel

NASA Technical Reports Server (NTRS)

Broeren, Andy; Potapczuk, Mark; Lee, Sam; Malone, Adam; Paul, Ben; Woodard, Brian

2016-01-01

The design and certification of modern transport airplanes for flight in icing conditions increasing relies on three-dimensional numerical simulation tools for ice accretion prediction. There is currently no publically available, high-quality, ice accretion database upon which to evaluate the performance of icing simulation tools for large-scale swept wings that are representative of modern commercial transport airplanes. The purpose of this presentation is to present the results of a series of icing wind tunnel test campaigns whose aim was to provide an ice accretion database for large-scale, swept wings.

Ocean Tide Influences on the Antarctic and Greenland Ice Sheets

NASA Astrophysics Data System (ADS)

Padman, Laurie; Siegfried, Matthew R.; Fricker, Helen A.

2018-03-01

Ocean tides are the main source of high-frequency variability in the vertical and horizontal motion of ice sheets near their marine margins. Floating ice shelves, which occupy about three quarters of the perimeter of Antarctica and the termini of four outlet glaciers in northern Greenland, rise and fall in synchrony with the ocean tide. Lateral motion of floating and grounded portions of ice sheets near their marine margins can also include a tidal component. These tide-induced signals provide insight into the processes by which the oceans can affect ice sheet mass balance and dynamics. In this review, we summarize in situ and satellite-based measurements of the tidal response of ice shelves and grounded ice, and spatial variability of ocean tide heights and currents around the ice sheets. We review sensitivity of tide heights and currents as ocean geometry responds to variations in sea level, ice shelf thickness, and ice sheet mass and extent. We then describe coupled ice-ocean models and analytical glacier models that quantify the effect of ocean tides on lower-frequency ice sheet mass loss and motion. We suggest new observations and model developments to improve the representation of tides in coupled models that are used to predict future ice sheet mass loss and the associated contribution to sea level change. The most critical need is for new data to improve maps of bathymetry, ice shelf draft, spatial variability of the drag coefficient at the ice-ocean interface, and higher-resolution models with improved representation of tidal energy sinks.

Relative influences of the metocean forcings on the drifting ice pack and estimation of internal ice stress gradients in the Labrador Sea

NASA Astrophysics Data System (ADS)

Turnbull, I. D.; Torbati, R. Z.; Taylor, R. S.

2017-07-01

Understanding the relative influences of the metocean forcings on the drift of sea ice floes is a crucial component to the overall characterization of an ice environment and to developing an understanding of the factors controlling the ice dynamics. In addition, estimating the magnitude of the internal stress gradients on drifting sea ice floes generated by surrounding ice cover is important for modeling operations, informing the design of offshore structures and vessels in ice environments, and for the proper calibration of Discrete Element Models (DEM) of fields of drifting ice floes. In the spring of 2015 and 2016, four sea ice floes offshore Makkovik, Labrador were tagged with satellite-linked ice tracking buoys along with one satellite-linked weather station on each floe to transmit wind speed and direction. Twenty satellite-linked Lagrangian surface ocean current tracking buoys were also deployed in the open water adjacent to the targeted ice floes. In this paper, the dynamics of the four ice floes are explored in terms of the relative proportions which were forced by the wind, current, sea surface topography, Coriolis, and internal stress gradients. The internal ice stress gradients are calculated as residuals between the observed accelerations of the floes as measured by the tracking buoys and the sums of the other metocean forcings. Results show that internal ice stress gradients accounted for up to 50% of the observed forcing on the floes, and may have reached up to around 0.19 kPa.

Mixed Phase Modeling in GlennICE with Application to Engine Icing

NASA Technical Reports Server (NTRS)

Wright, William B.; Jorgenson, Philip C. E.; Veres, Joseph P.

2011-01-01

A capability for modeling ice crystals and mixed phase icing has been added to GlennICE. Modifications have been made to the particle trajectory algorithm and energy balance to model this behavior. This capability has been added as part of a larger effort to model ice crystal ingestion in aircraft engines. Comparisons have been made to four mixed phase ice accretions performed in the Cox icing tunnel in order to calibrate an ice erosion model. A sample ice ingestion case was performed using the Energy Efficient Engine (E3) model in order to illustrate current capabilities. Engine performance characteristics were supplied using the Numerical Propulsion System Simulation (NPSS) model for this test case.

Skylab floating ice experiment

NASA Technical Reports Server (NTRS)

Campbell, W. J. (Principal Investigator); Ramseier, R. O.; Weaver, R. J.; Weeks, W. F.

1975-01-01

The author has identified the following significant results. Coupling of the aircraft data with the ground truth observations proved to be highly successful with interesting results being obtained with IR and SLAR passive microwave techniques, and standard photography. Of particular interest were the results of the PMIS system which operated at 10.69 GHz with both vertical and horizontal polarizations. This was the first time that dual polarized images were obtained from floating ice. In both sea and lake ice, it was possible to distinguish a wide variety of thin ice types because of their large differences in brightness temperatures. It was found that the higher brightness temperature was invariably obtained in the vertically polarized mode, and as the age of the ice increases the brightness temperature increases in both polarizations. Associated with this change in age, the difference in temperature was observed as the different polarizations decreased. It appears that the horizontally polarized data is the most sensitive to variations in ice type for both fresh water and sea ice. The study also showed the great amount of information on ice surface roughness and deformation patterns that can be obtained from X-band SLAR observations.

Aviation Safety Program Atmospheric Environment Safety Technologies (AEST) Project

NASA Technical Reports Server (NTRS)

Colantonio, Ron

2011-01-01

Engine Icing: Characterization and Simulation Capability: Develop knowledge bases, analysis methods, and simulation tools needed to address the problem of engine icing; in particular, ice-crystal icing Airframe Icing Simulation and Engineering Tool Capability: Develop and demonstrate 3-D capability to simulate and model airframe ice accretion and related aerodynamic performance degradation for current and future aircraft configurations in an expanded icing environment that includes freezing drizzle/rain Atmospheric Hazard Sensing and Mitigation Technology Capability: Improve and expand remote sensing and mitigation of hazardous atmospheric environments and phenomena

Brine Pockets in the Icy Shell on Europa: Distribution, Chemistry, and Habitability

NASA Technical Reports Server (NTRS)

Zolotov, M. Yu; Shock, E. L.; Barr, A. C.; Pappalardo, R. T.

2004-01-01

On Earth, sea ice is rich in brine, salt, and gas inclusions that form through capturing of seawater during ice formation. Cooling of the ice over time leads to sequential freezing of captured sea-water, precipitation of salts, exsolution of gases, and formation of brine channels and pockets. Distribution and composition of brines in sea ice depend on the rate of ice formation, vertical temperature gradient, and the age of the ice. With aging, the abundance of brine pockets decreases through downward migration. De- spite low temperatures and elevated salinities, brines in sea ice provide a habitat for photosynthetic and chemosynthetic organisms. On Europa, brine pockets and channels could exist in the icy shell that may be from a few km to a few tens of km thick and is probably underlain by a water ocean. If the icy shell is relatively thick, convection could develop, affecting the temperature pattern in the ice. To predict the distribution and chemistry of brine pockets in the icy shell we have combined numerical models of the temperature distribution within a convecting shell, a model for oceanic chemistry, and a model for freezing of Europan oceanic water. Possible effects of brine and gas inclusions on ice rheology and tectonics are discussed.

Overview of Icing Research at NASA Glenn

NASA Technical Reports Server (NTRS)

Kreeger, Richard E.

2013-01-01

The aviation industry continues to deal with icing-related incidents and accidents on a regular basis. Air traffic continues to increase, placing more aircraft in adverse icing conditions more frequently and for longer periods. Icing conditions once considered rare or of little consequence, such as super-cooled large droplet icing or high altitude ice crystals, have emerged as major concerns for modern aviation. Because of this, there is a need to better understand the atmospheric environment, the fundamental mechanisms and characteristics of ice growth, and the aerodynamic effects due to icing, as well as how best to protect these aircraft. The icing branch at NASA Glenn continues to develop icing simulation methods and engineering tools to address current aviation safety issues in airframe, engine and rotorcraft icing.

The Extreme Ice Survey: Capturing and Conveying Glacial Processes Through Time-Lapse Imagery and Narration

NASA Astrophysics Data System (ADS)

Balog, J. D.; Box, J. E.; Pfeffer, W. T.; Hood, E. W.; Fagre, D. B.; Anker, C.; O'Neel, S.

2010-12-01

The Extreme Ice Survey (EIS) uses time-lapse photography, conventional photography, and video to document rapid change in the Earth's glacial ice. The EIS team currently has 38 time-lapse cameras at sites in Greenland, Iceland, Alaska, the Rocky Mountains and Nepal. EIS supplements this ongoing record with annual repeat photography in British Columbia, Iceland, the Alps, and Bolivia. EIS imagery supplies basic knowledge in glacier dynamics to the science community, as well as compelling, engaging narratives to the general public about the immediacy of the Anthropocene and climate change. Visual materials from EIS have impacted more than 150 million people, ranging from White House staff, the U. S. Congress and government agency officials to globally influential corporate officers and all age strata of the general public. Media products include a National Geographic/NOVA special, two National Geographic magazine articles, a feature in Parade magazine (circulation 71 million), and numerous presentations on CNN, NBC, BBC and National Public Radio. Columbia Glacier, Alaska, June 2006, May 2007, June 2008 terminus indicated.

Introducing the North Water: Histories of exploration, ice dynamics, living resources, and human settlement in the Thule Region.

PubMed

Hastrup, Kirsten; Mosbech, Anders; Grønnow, Bjarne

2018-04-01

The North Water is a recurrent polynya in the High Arctic situated between Northwest Greenland and Ellesmere Island of Canada. The North Water makes a dynamic space, where various processes may enhance or obstruct each other, accelerating or halting particular modes of human-animal relations in the region, where life itself depends on the North Water. This will be discussed in four steps. The first step posits the North Water as a perceived oasis for explorers and whalers hailing from Europe or America in the nineteenth century. The second step concentrates on the diverse rhythms inherent in the ice conditions, as affected by trends that are set in motion elsewhere. The third step highlights the implications of the dynamics of the ice and sea currents for animal life in the region. The fourth step gives an overview of human settlement patterns around the North Water across the ages. The article shows how natural and social features are deeply implicated in each other, even if they are not directly co-variant.

Effect of Probiotic Containing Ice-cream on Salivary Mutans Streptococci (SMS) Levels in Children of 6-12 Years of Age: A Randomized Controlled Double Blind Study with Six-months Follow Up.

PubMed

Ashwin, Devasya; Ke, Vijayaprasad; Taranath, Mahanthesh; Ramagoni, Naveen Kumar; Nara, Asha; Sarpangala, Mythri

2015-02-01

To evaluate the caries risk based on the salivary levels of streptococcus mutans in children of 6-12 years of age group before and after consuming probiotic ice-cream containing Bifidobacterium lactis Bb-12 and Lactobacillus acidophilus La-5. A double blind, placebo controlled trial was carried out in 60 children aged between 6 to 12 years with zero decayed, missing, and filled teeth (DMFT). They were randomly divided into two equal groups. Saliva sample were collected before the consumption of ice-cream and Streptococcus mutans count was calculated and recorded as baseline data. For the next seven days both the groups were given ice creams marked as A and B. Saliva samples were collected after ice-cream consumption at the end of study period and also after a washout period of 30 days and again after six months. Samples were inoculated and colonies were counted. On statistical evaluation by students paired t-test, probiotic ice-cream brought significant reduction in the Streptococcus mutans count after seven days of ice-cream ingestion (p<0.001) and also after 30 d of washout period (p<0.001). There was no significant reduction (p=0.076) by normal ice-cream consumption. After six months of the study period in both the groups the salivary levels of Streptococcus mutans was similar to the baseline. Probiotic ice-cream containing Bifidobacterium lactis Bb-12 and Lactobacillus acidophilus La-5 can cause reduction in caries causative organism. The dosage of the probiotic organisms for the long term or synergetic effect on the oral health are still needed to be explored.

Effect of Probiotic Containing Ice-cream on Salivary Mutans Streptococci (SMS) Levels in Children of 6-12 Years of Age: A Randomized Controlled Double Blind Study with Six-months Follow Up

PubMed Central

KE, Vijayaprasad; Taranath, Mahanthesh; Ramagoni, Naveen Kumar; Nara, Asha; Sarpangala, Mythri

2015-01-01

Introduction: To evaluate the caries risk based on the salivary levels of streptococcus mutans in children of 6-12 years of age group before and after consuming probiotic ice-cream containing Bifidobacterium lactis Bb-12 and Lactobacillus acidophilus La-5. Materials and Methods: A double blind, placebo controlled trial was carried out in 60 children aged between 6 to 12 years with zero decayed, missing, and filled teeth (DMFT). They were randomly divided into two equal groups. Saliva sample were collected before the consumption of ice-cream and Streptococcus mutans count was calculated and recorded as baseline data. For the next seven days both the groups were given ice creams marked as A and B. Saliva samples were collected after ice-cream consumption at the end of study period and also after a washout period of 30 days and again after six months. Samples were inoculated and colonies were counted. Results: On statistical evaluation by students paired t-test, probiotic ice-cream brought significant reduction in the Streptococcus mutans count after seven days of ice-cream ingestion (p<0.001) and also after 30 d of washout period (p<0.001). There was no significant reduction (p=0.076) by normal ice-cream consumption. After six months of the study period in both the groups the salivary levels of Streptococcus mutans was similar to the baseline. Conclusion: Probiotic ice-cream containing Bifidobacterium lactis Bb-12 and Lactobacillus acidophilus La-5 can cause reduction in caries causative organism. The dosage of the probiotic organisms for the long term or synergetic effect on the oral health are still needed to be explored. PMID:25859515

Ice Detection and Mitigation Device

NASA Technical Reports Server (NTRS)

Gambino, Richard J. (Inventor); Gouldstone, Christopher (Inventor); Gutleber, Jonathan (Inventor); Hubble, David (Inventor); Trelewicz, Jason (Inventor)

2016-01-01

A method for deicing an aerostructure includes driving a sensing current through a heater element coated to an aerostructure, the heater element having a resistance that is temperature dependent. A resistance of the heater element is monitored. It is determined whether there is icing at the heater element using the monitored resistance of the heater element. A melting current is driven through the heater element when it is determined that there is icing at the heater element.

Marine biological controls on atmospheric CO2 and climate

NASA Technical Reports Server (NTRS)

Mcelroy, M. B.

1983-01-01

It is argued that the ocean is losing N gas faster than N is being returned to the ocean, and that replenishment of the N supply in the ocean usually occurs during ice ages. Available N from river and estruarine transport and from rainfall after formation by lightning are shown to be at a rate too low to compensate for the 10,000 yr oceanic lifetime of N. Ice sheets advance and transfer moraine N to the ocean, lower the sea levels, erode the ocean beds, promote greater biological productivity, and reduce CO2. Ice core samples have indicated a variability in the atmospheric N content that could be attributed to the ice age scenario.

75 FR 7536 - Culturally Significant Objects Imported for Exhibition Determinations: “Hendrick Avercamp (1585...

Federal Register 2010, 2011, 2012, 2013, 2014

2010-02-19

... DEPARTMENT OF STATE [Public Notice 6897] Culturally Significant Objects Imported for Exhibition Determinations: ``Hendrick Avercamp (1585-1634): The Little Ice Age'' SUMMARY: Notice is hereby given of the... included in the exhibition ``Hendrick Avercamp (1585-1634): The Little Ice Age,'' imported from abroad for...

Global Warming: Understanding and Teaching the Forecast.

ERIC Educational Resources Information Center

Andrews, Bill

1994-01-01

A resource for the teaching of the history and causes of climate change. Discusses evidence of climate change from the Viking era, early ice ages, the most recent ice age, natural causes of climate change, human-made causes of climate change, projections of global warming, and unequal warming. (LZ)

The contemporary degassing rate of 40Ar from the solid Earth

PubMed Central

Bender, Michael L.; Barnett, Bruce; Dreyfus, Gabrielle; Jouzel, Jean; Porcelli, Don

2008-01-01

Knowledge of the outgassing history of radiogenic 40Ar, derived over geologic time from the radioactive decay of 40K, contributes to our understanding of the geodynamic history of the planet and the origin of volatiles on Earth's surface. The 40Ar inventory of the atmosphere equals total 40Ar outgassing during Earth history. Here, we report the current rate of 40Ar outgassing, accessed by measuring the Ar isotope composition of trapped gases in samples of the Vostok and Dome C deep ice cores dating back to almost 800 ka. The modern outgassing rate (1.1 ± 0.1 × 108 mol/yr) is in the range of values expected by summing outgassing from the continental crust and the upper mantle, as estimated from simple calculations and models. The measured outgassing rate is also of interest because it allows dating of air trapped in ancient ice core samples of unknown age, although uncertainties are large (±180 kyr for a single sample or ±11% of the calculated age, whichever is greater). PMID:18550816

Global Warming and Ice Ages: I. Prospects For Physics Based Modulation of Global Change

DOE R&D Accomplishments Database

Teller, E.; Wood, L.; Hyde, R.

1996-08-15

It has been suggested that large-scale climate changes, mostly due to atmospheric injection of greenhouse gases connected with fossil-fired energy production, should be forestalled by internationally-agreed reductions in, e.g., electricity generation. The potential economic impacts of such limitations are obviously large: greater than or equal to $10{sup 11}/year. We propose that for far smaller - less than 1% - the mean thermal effects of greenhouse gases may be obviated in any of several distinct ways, some of them novel. These suggestions are all based on scatterers that prevent a small fraction of solar radiation from reaching all or part of the Earth. We propose research directed to quite near-term realization of one or more of these inexpensive approaches to cancel the effects of the greenhouse gas injection. While the magnitude of the climatic impact of greenhouse gases is currently uncertain, the prospect of severe failure of the climate, for instance at the onset of the next Ice Age, is undeniable. The proposals in this paper may lead to quite practical methods to reduce or eliminate all climate failures.

NASA Lewis Research Center's Program on Icing Research

NASA Technical Reports Server (NTRS)

Reinmann, J. J.; Shaw, R. J.; Olsen, W. A., Jr.

1982-01-01

The helicopter and general aviation, light transport, and commercial transport aircraft share common icing requirements: highly effective, lightweight, low power consuming deicing systems, and detailed knowledge of the aeropenalties due to ice on aircraft surfaces. To meet current and future needs, NASA has a broadbased icing research program which covers both research and engineering applications, and is well coordinated with the FAA, DOD, universities, industry, and some foreign governments. Research activity in ice protection systems, icing instrumentation, experimental methods, analytical modeling, and in-flight research are described.

A new characterization of the icing environment below 10,000 feet AGL from 7,000 miles of measurements in supercooled clouds

NASA Technical Reports Server (NTRS)

Jeck, R. K.

1985-01-01

A growing requirement over the past decade for a new assessment of aircraft icing conditions in wintertime clouds at altitudes up to about 10,000 feet is discussed. The requirement was documented in past workshops and comes primarily from the helicopter community which wants ice-protected rotorcraft to meet increasing demands for all-weather operations. Currently, only a few of the larger helicopters are equipped with certification of ice-protection devices. This is because the current FAA criteria for design and certification of ice-protection equipment results in power and payload penalties that smaller rotorcraft cannot tolerate. The FAA criteria were actually designed for large, transport-category aircraft capable of flying to 20,000 feet or more. For this reason, there have been concerns that the current criteria may be too severe for low-performance aircraft, such as helicopters, which generally operate at altitudes below 10,000 feet.

Sensitivity of open-water ice growth and ice concentration evolution in a coupled atmosphere-ocean-sea ice model

NASA Astrophysics Data System (ADS)

Shi, Xiaoxu; Lohmann, Gerrit

2017-09-01

A coupled atmosphere-ocean-sea ice model is applied to investigate to what degree the area-thickness distribution of new ice formed in open water affects the ice and ocean properties. Two sensitivity experiments are performed which modify the horizontal-to-vertical aspect ratio of open-water ice growth. The resulting changes in the Arctic sea-ice concentration strongly affect the surface albedo, the ocean heat release to the atmosphere, and the sea-ice production. The changes are further amplified through a positive feedback mechanism among the Arctic sea ice, the Atlantic Meridional Overturning Circulation (AMOC), and the surface air temperature in the Arctic, as the Fram Strait sea ice import influences the freshwater budget in the North Atlantic Ocean. Anomalies in sea-ice transport lead to changes in sea surface properties of the North Atlantic and the strength of AMOC. For the Southern Ocean, the most pronounced change is a warming along the Antarctic Circumpolar Current (ACC), owing to the interhemispheric bipolar seasaw linked to AMOC weakening. Another insight of this study lies on the improvement of our climate model. The ocean component FESOM is a newly developed ocean-sea ice model with an unstructured mesh and multi-resolution. We find that the subpolar sea-ice boundary in the Northern Hemisphere can be improved by tuning the process of open-water ice growth, which strongly influences the sea ice concentration in the marginal ice zone, the North Atlantic circulation, salinity and Arctic sea ice volume. Since the distribution of new ice on open water relies on many uncertain parameters and the knowledge of the detailed processes is currently too crude, it is a challenge to implement the processes realistically into models. Based on our sensitivity experiments, we conclude a pronounced uncertainty related to open-water sea ice growth which could significantly affect the climate system sensitivity.

Experimental Analysis of Sublimation Dynamics for Buried Glacier Ice in Beacon Valley, Antarctica

NASA Astrophysics Data System (ADS)

Ehrenfeucht, S.; Dennis, D. P.; Marchant, D. R.

2017-12-01

The age of the oldest known buried ice in Beacon Valley, McMurdo Dry Valleys (MDV) Antarctica is a topic of active debate due to its implications for the stability of the East Antarctic Ice Sheet. Published age estimates range from as young as 300 ka to as old as 8.1 Ma. In the upland MDV, ablation occurs predominantly via sublimation. The relict ice in question (ancient ice from Taylor Glacier) lies buried beneath a thin ( 30-70 cm) layer of sublimation till, which forms as a lag deposit as underlying debris-rich ice sublimes. As the ice sublimates, the debris held within the ice accumulates slowly on the surface, creating a porous boundary between the buried-ice surface and the atmosphere, which in turn influences gas exchange between the ice and the atmosphere. Additionally, englacial debris adds several salt species that are ultimately concentrated on the ice surface. It is well documented the rate of ice sublimation varies as a function of overlying till thickness. However, the rate-limiting dynamics under varying environmental conditions, including the threshold thicknesses at which sublimation is strongly retarded, are not yet defined. To better understand the relationships between sublimation rate, till thickness, and long-term surface evolution, we build on previous studies by Lamp and Marchant (2017) and evaluate the role of till thickness as a control on ice loss in an environmental chamber capable of replicating the extreme cold desert conditions observed in the MDV. Previous work has shown that this relationship exhibits exponential decay behavior, with sublimation rate significantly dampened under less than 10 cm of till. In our experiments we pay particular attention to the effect of the first several cm of till in order to quantify the dynamics that govern the transition from bare ice to debris-covered ice. We also examine this transition for various forms of glacier ice, including ice with various salt species.

Forecasting Future Sea Ice Conditions in the MIZ: A Lagrangian Approach

DTIC Science & Technology

2013-09-30

www.mcgill.ca/meteo/people/tremblay LONG-TERM GOALS 1- Determine the source regions for sea ice in the seasonally ice-covered zones (SIZs...distribution of sea ice cover and transport pathways. 2- Improve our understanding of the strengths and/or limitations of GCM predictions of future...ocean currents, RGPS sea ice deformation, Reanalysis surface wind , surface radiative fluxes, etc. Processing the large datasets involved is a tedious

Late mid-Holocene sea-level oscillation: A possible cause

NASA Astrophysics Data System (ADS)

Scott, D. B.; Collins, E. S.

Sea level oscillated between 5500 and 3500 years ago at Murrells Inlet, South Carolina, Chezzetcook and Baie Verte, Nova Scotia and Montmagny, Quebec. The oscillation is well constrained by foraminiferal marsh zonations in three locations and by diatoms in the fourth one. The implications are: (1) there was a eustatic sea-level oscillation of about 2-10 m in the late mid-Holocene on the southeast coast of North America (South Carolina to Quebec) that is not predicted by present geophysical models of relative sea-level change; (2) this oscillation coincides with oceanographic cooling on the east coast of Canada that we associate with melting ice; and (3) this sea- level oscillation/climatic event coincides exactly with the end of pyramid building in Egypt which is suggested to have resulted from a climate change (i.e. drought, cooling). This sea-level/climatic change is a prime example of feedback where climatic warming in the mid-Holocene promoted ice melt in the Arctic which subsequently caused climatic cooling by opening up Arctic channels releasing cold water into the Inner Labrador Current that continued to intensify until 4000 years ago. This sea-level event may also be the best way of measuring when the final ice melted since most estimates of the ages of the last melting are based on end moraine dates in the Arctic which may not coincide with when the last ice actually melted out, since there is no way of dating the final ice positions.

Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

USGS Publications Warehouse

Jakobsson, Martin; Nilsson, Johan; Anderson, Leif G.; Backman, Jan; Bjork, Goran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Macho, Natalia Barrientos; Cherniykh, Dennis; Coxall, Helen; Eriksson, Bjorn; Floden, Tom; Gemery, Laura; Gustafsson, Orjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor

2016-01-01

The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (~140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening.

Comprehensive Examination of Bottom Ash, Soil Dust, and Direct Emissions and Aging of Laboratory Biomass Burning as Potential Sources of Ice Nucleating Particles

NASA Astrophysics Data System (ADS)

Polen, M.; Jahl, L.; Jahn, L.; Somers, J.; Sullivan, R. C.

2017-12-01

Recent laboratory and field studies have found that biomass burning can produce ice nucleating particles (INP) with varying efficiencies depending on fuel and burn conditions. Few studies have examined the ice nucleating potential of bottom ash, which has the potential to be lofted during intense burning events. To date, no publications have examined the impact of atmospheric aging or lofted soil particles on INP emitted from biomass burning. This study investigated each of these aspects through laboratory biomass fuel combustion studies. We burned a number of grasses from different locations, and collected filter samples of fresh and photochemically aged biomass burning aerosol, as well as bottom ash collected after the burn. Some burns included soil that the grasses grew in to test for the importance of soil dust to INP emissions lofting during intense fires. The composition and mixing state of the aerosol was determined using a suite of online and offline single-particle techniques. Our findings suggest that bottom ash is a relatively weak INP, but all samples froze consistently at -20 °C < T < -25 °C. We also found that oxidation of the biomass burning aerosol typically enhances ice nucleating activity over fresh, unaged particles, increasing the ice active site surface density by up to a factor of 3 at T = -25 °C. Lastly, the presence of soil dust can greatly enhance INP concentrations for biomass burning events with an increase in the freezing temperature spectrum by > 3 °C. Detailed analysis of these samples aims to provide a clearer understanding of what components of biomass burning increase the ambient concentrations of ice nucleation active particles, and how their ice nucleation properties evolve during atmospheric aging.

Glacier History of the Northern Antarctic Peninsula Region Since the End of the Last Ice Age and Implications for Southern Hemisphere Westerly-Climate Changes

NASA Astrophysics Data System (ADS)

Kaplan, M. R.; Schaefer, J. M.; Strelin, J. A.; Peltier, C.; Southon, J. R.; Lepper, K. E.; Winckler, G.

2017-12-01

For the area around James Ross Island, we present new cosmogenic 10Be exposure ages on glacial deposits, and 14C ages on associated fossil materials. These data allow us to reconstruct in detail when and how the Antarctic Peninsula Ice Sheet retreated around the Island as the last Ice Age ended, and afterward when local land-based glaciers fluctuated. Similar to other studies, we found widespread deglaciation during the earliest Holocene, with fjords and bays becoming ice free between about 11,000 and 8,000 years ago. After 7,000 years ago, neoglacial type advances initiated. Then, both expansions and ice free periods occurred from the middle to late Holocene. We compare the new glacier record to those in southern Patagonia, which is on the other side of the Drake Passage, and published Southern Ocean marine records, in order to infer past middle to high latitude changes in the Southern Hemisphere Westerlies. Widespread warmth in the earliest Holocene, to the north and south of the Drake Passage, led to small glacier systems in Patagonia and wide-ranging glacier recession around the northern Antarctic Peninsula. We infer that this early Holocene period of overall glacier recession - from Patagonia to the northern Peninsula - was caused by a persistent far-southerly setting of the westerlies and accompanying warm climates. Subsequently, during the middle Holocene renewed glacier expansions occurred on both sides of the Drake Passage, which reflects that the Westerlies and associated colder climate systems were generally more equatorward. From the middle to late Holocene, glacier expansions and ice free periods (and likely related ice shelf behavior) document how the Westerlies and associated higher-latitude climate systems varied.

Methane seeps along boundaries of receding glaciers in Alaska and Greenland

NASA Astrophysics Data System (ADS)

Walter Anthony, K. M.; Anthony, P. M.; Grosse, G.; Chanton, J.

2012-12-01

Glaciers, ice sheets, and permafrost form a 'cryosphere cap' that traps methane formed in the subsurface, restricting its flow to the Earth's surface and atmosphere. Despite model predictions that glacier melt and degradation of permafrost open conduits for methane's escape, there has been a paucity of field evidence for 'subcap' methane seepage to the atmosphere as a direct result of cryosphere disintegration in the terrestrial Arctic. Here, we document for the first time the release of sub-cryosphere methane to lakes, rivers, shallow marine fjords and the atmosphere from abundant gas seeps concentrated along boundaries of receding glaciers and permafrost thaw in Alaska and Greenland. Through aerial and ground surveys of 6,700 lakes and fjords in Alaska we mapped >150,000 gas seeps identified as bubbling-induced open holes in seasonal ice. Using gas flow rates, stable isotopes, and radiocarbon dating, we distinguished recent ecological methane from subcap, geologic methane. Subcap seeps had anomalously high bubbling rates, 14C-depletion, and stable isotope values matching microbial sources associated with sedimentary deposits and coal beds as well as thermogenic methane accumulations in Alaska. Since differential ice loading can overpressurize fluid reservoirs and cause sediment fracturing beneath ice sheets, and since the loss of glacial ice reduces normal stress on ground, opens joints, and activates faults and fissures, thereby increasing permeability of the crust to fluid flow, we hypothesized that in the previously glaciated region of Southcentral Alaska, where glacial wastage continues presently, subcap seeps should be disproportionately associated with neotectonic faults. Geospatial analysis confirmed that subcap seep sites were associated with faults within a 7 km belt from the modern glacial extent. The majority of seeps were located in areas affected by seismicity from isostatic rebound associated with deglaciation following the Little Ice Age (LIA; ca. 1650-1850 C.E.). Across Alaska, we found a relationship between methane stable isotopes, radiocarbon age, and distance to faults. Faults appear to allow the escape of deeper, more 14C-depleted methane to the atmosphere, whereas seeps away from faults entrained 14C-enriched methane formed in shallower sediments from microbial decomposition of younger organic matter. Additionally, we observed younger subcap methane seeps in lakes of Greenland's Sondrestrom Fjord that were associated with ice-sheet retreat since the LIA. These correlations suggest that in a warming climate, continued disintegration of glaciers, permafrost, and parts of the polar ice sheets will weaken subsurface seals and further open conduits, allowing a transient expulsion of methane currently trapped by the cryosphere cap.

Understanding the Sea Ice Zone: Scientists and Communities Partnering to Archive, Analyze and Disseminate Local Ice Observations

NASA Astrophysics Data System (ADS)

Collins, J. A.; Oldenburg, J.; Liu, M.; Pulsifer, P. L.; Kaufman, M.; Eicken, H.; Parsons, M. A.

2012-12-01

Knowledge of sea ice is critical to the hunting, whaling, and cultural activities of many Indigenous communities in Northern and Western Alaska. Experienced hunters have monitored seasonal changes of the sea ice over many years, giving them a unique expertise in assessing the current state of the sea ice as well as any anomalies in seasonal sea ice conditions. The Seasonal Ice Zone Observing Network (SIZONet), in collaboration with the Exchange for Local Observations and Knowledge of the Arctic (ELOKA), has developed an online application for collecting, storing, and analyzing sea ice observations contributed by local experts from coastal Alaskan communities. Here we present the current iteration of the application, outline future plans and discuss how the development process and resulting system have improved our collective understanding of sea ice processes and changes. The SIZONet application design is based on the needs of the research scientists responsible for entering observation data into the database, the needs of local sea ice experts contributing their observations and knowledge, and the information needs of Alaska coastal communities. Entry forms provide a variety of input methods, including menus, check boxes, and free text input. Input options strive to balance flexibility in capturing concepts and details with the need for analytical consistency. Currently, research staff at the University of Alaska Fairbanks use the application to enter observations received via written or electronic communications from local sea ice experts. Observation data include current weather conditions, snow and ice quantity and quality, and wildlife sighted or taken. Future plans call for direct use of the SIZONet interface by local sea ice experts as well as students, both as contributors to the data collection and as users seeking meaning in the data. This functionality is currently available to a limited number of community members as we extend the application to support specific roles for particular users (or groups of users); this role-based access will be necessary to support a diverse user population while maintaining the integrity of the data and protecting personal information, or the location of sensitive sites, captured in the data records. Additionally, future improvements to the interface will include the ability to upload photos and videos to capture visual records of the environment. The SIZONet application was developed to provide a robust interface for working with observational data. The contributed nature of the data, however, presents a unique set of collaborative benefits and challenges as we work towards the final implementation of the application. The successful partnership supporting the observation network is a direct function of the long-term relationships established between university-based researchers and community members.

Large-scale evolution of the central-east Greenland margin: New insights to the North Atlantic glaciation history

NASA Astrophysics Data System (ADS)

Pérez, Lara F.; Nielsen, Tove; Knutz, Paul C.; Kuijpers, Antoon; Damm, Volkmar

2018-04-01

The continental shelf of central-east Greenland is shaped by several glacially carved transverse troughs that form the oceanward extension of the major fjord systems. The evolution of these troughs through time, and their relation with the large-scale glaciation of the Northern Hemisphere, is poorly understood. In this study seismostratigraphic analyses have been carried out to determine the morphological and structural development of this important sector of the East Greenland glaciated margin. The age of major stratigraphic discontinuities has been constrained by a direct tie to ODP site 987 drilled in the Greenland Sea basin plain off Scoresby Sund fan system. The areal distribution and internal facies of the identified seismic units reveal the large-scale depositional pattern formed by ice-streams draining a major part of the central-east Greenland ice sheet. Initial sedimentation along the margin was, however, mainly controlled by tectonic processes related to the margin construction, continental uplift, and fluvial processes. From late Miocene to present, progradational and erosional patterns point to repeated glacial advances across the shelf. The evolution of depo-centres suggests that ice sheet advances over the continental shelf have occurred since late Miocene, about 2 Myr earlier than previously assumed. This cross-shelf glaciation is more pronounced during late Miocene and early Pliocene along Blosseville Kyst and around the Pliocene/Pleistocene boundary off Scoresby Sund; indicating a northward migration of the glacial advance. The two main periods of glaciation were separated by a major retreat of the ice sheet to an inland position during middle Pliocene. Mounded-wavy deposits interpreted as current-related deposits suggest the presence of changing along-slope current dynamics in concert with the development of the modern North Atlantic oceanographic pattern.

Geochronology and paleoclimatic implications of the last deglaciation of the Mauna Kea Ice Cap, Hawaii

USGS Publications Warehouse

Anslow, Faron S.; Clark, P.U.; Kurz, M.D.; Hostetler, S.W.

2010-01-01

We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5??2.5ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3km upslope for ~4.5-5.0kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ~15.4ka corresponds to a large reduction of the Atlantic meridional overturning circulation (AMOC) following Heinrich Event 1. Subsequent ice-margin retreat began at 14.6??1.9ka, corresponding to a rapid resumption of the AMOC and onset of the B??lling warm interval, with the ice cap melting rapidly to complete deglaciation. Additional 3He ages obtained from a flood deposit date the catastrophic outburst of a moraine-dammed lake roughly coeval with the Younger Dryas cold interval, suggesting a more active hydrological cycle on Mauna Kea at this time. A coupled mass balance and ice dynamics model is used to constrain the climate required to generate ice caps of LLGM and readvance sizes. The depression of the LLGM equilibrium line altitude requires atmospheric cooling of 4.5??1??C, whereas the mass balance modeling indicates an accompanying increase in precipitation of as much as three times that of present. We hypothesize (1) that the LLGM temperature depression was associated with global cooling, (2) that the temperature depression that contributed to the readvance occurred in response to an atmospheric teleconnection to the North Atlantic, and (3) that the precipitation enhancement associated with both events occurred in response to a southward shift in the position of the inter-tropical convergence zone (ITCZ). Such a shift in the ITCZ would have allowed midlatitude cyclones to reach Mauna Kea more frequently which would have increased precipitation at high elevations and caused additional cooling. ?? 2010 Elsevier B.V.

Chronological refinement of an ice core record at Upper Fremont Glacier in south central North America

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schuster, Paul F.; White, David E.; Naftz, David L.

2000-02-27

The potential to use ice cores from alpine glaciers in the midlatitudes to reconstruct paleoclimatic records has not been widely recognized. Although excellent paleoclimatic records exist for the polar regions, paleoclimatic ice core records are not common from midlatitude locations. An ice core removed from the Upper Fremont Glacier in Wyoming provides evidence for abrupt climate change during the mid-1800s. Volcanic events (Krakatau and Tambora) identified from electrical conductivity measurements (ECM) and isotopic and chemical data from the Upper Fremont Glacier were reexamined to confirm and refine previous chronological estimates of the ice core. At a depth of 152 mmore » the refined age-depth profile shows good agreement (1736{+-}10 A.D.) with the {sup 14}C age date (1729{+-}95 A.D.). The {delta}{sup 18}O profile of the Upper Fremont Glacier (UFG) ice core indicates a change in climate known as the Little Ice Age (LIA). However, the sampling interval for {delta}{sup 18}O is sufficiently large (20 cm) such that it is difficult to pinpoint the LIA termination on the basis of {delta}{sup 18}O data alone. Other research has shown that changes in the {delta}{sup 18}O variance are generally coincident with changes in ECM variance. The ECM data set contains over 125,000 data points at a resolution of 1 data point per millimeter of ice core. A 999-point running average of the ECM data set and results from f tests indicates that the variance of the ECM data decreases significantly at about 108 m. At this depth, the age-depth profile predicts an age of 1845 A.D. Results indicate the termination of the LIA was abrupt with a major climatic shift to warmer temperatures around 1845 A.D. and continuing to present day. Prediction limits (error bars) calculated for the profile ages are {+-}10 years (90% confidence level). Thus a conservative estimate for the time taken to complete the LIA climatic shift to present-day climate is about 10 years, suggesting the LIA termination in alpine regions of central North America may have occurred on a relatively short (decadal) timescale. (c) 2000 American Geophysical Union.« less

Computational Simulation of Large Droplet Icing

DOT National Transportation Integrated Search

1996-01-01

Certification for flight into known icing remains one of the more challenging goals for aircraft manufacturers. This activity has been further complicated by the current interest in large droplet icing. Due to the lack of data available on the meteor...

A novel ice storm manipulation experiment in a northern hardwood forest

Treesearch

Lindsey E. Rustad; John L. Campbell

2012-01-01

Ice storms are an important natural disturbance within forest ecosystems of the northeastern United States. Current models suggest that the frequency and severity of ice storms may increase in the coming decades in response to changes in climate. Because of the stochastic nature of ice storms and difficulties in predicting their occurrence, most past investigations of...

Northeast Coast, Hokkaido, Japan

NASA Image and Video Library

1992-04-02

The northeast coast of Hokkaido and Kunashir Island, Japan (44.0N, 143.0E) are seen bordered by drifting sea ice. The sea ice has formed a complex pattern of eddies in response to surface water currents and winds. Photos of this kind aid researchers in describing local ocean current patterns and the effects of wind speed and direction on the drift of surface material, such as ice floes or oil. Kunashir is the southernmost of the Kuril Islands.

Durability of Polymer Electrolyte Membrane Fuel Cells Operated at Subfreezing Temperatures

DOE PAGES

Macauley, Natalia; Lujan, Roger W.; Spernjak, Dusan; ...

2016-09-15

The structure, composition, and interfaces of membrane electrode assemblies (MEA) and gas-diffusion layers (GDLs) have a significant effect on the performance of single-proton-exchange-membrane (PEM) fuel cells operated isothermally at subfreezing temperatures. During isothermal constant-current operation at subfreezing temperatures, water forming at the cathode initially hydrates the membrane, then forms ice in the catalyst layer and/or GDL. This ice formation results in a gradual decay in voltage. High-frequency resistance initially decreases due to an increase in membrane water content and then increases over time as the contact resistance increases. The water/ice holding capacity of a fuel cell decreases with decreasing subfreezingmore » temperature (-10°C vs. -20°C vs. -30°C) and increasing current density (0.02 A cm -2 vs. 0.04 A cm -2). Ice formation monitored using in-situ high-resolution neutron radiography indicated that the ice was concentrated near the cathode catalyst layer at low operating temperatures (≈-20°C) and high current densities (0.04 A cm -2). Significant ice formation was also observed in the GDLs at higher subfreezing temperatures (≈-10°C) and lower current densities (0.02 A cm -2). These results are in good agreement with the long-term durability observations that show more severe degradation at lower temperatures (-20°C and -30°C).« less

Life and extinction of megafauna in the ice-age Arctic

PubMed Central

Mann, Daniel H.; Groves, Pamela; Reanier, Richard E.; Gaglioti, Benjamin V.; Kunz, Michael L.; Shapiro, Beth

2015-01-01

Understanding the population dynamics of megafauna that inhabited the mammoth steppe provides insights into the causes of extinctions during both the terminal Pleistocene and today. Our study area is Alaska's North Slope, a place where humans were rare when these extinctions occurred. After developing a statistical approach to remove the age artifacts caused by radiocarbon calibration from a large series of dated megafaunal bones, we compare the temporal patterns of bone abundance with climate records. Megafaunal abundance tracked ice age climate, peaking during transitions from cold to warm periods. These results suggest that a defining characteristic of the mammoth steppe was its temporal instability and imply that regional extinctions followed by population reestablishment from distant refugia were characteristic features of ice-age biogeography at high latitudes. It follows that long-distance dispersal was crucial for the long-term persistence of megafaunal species living in the Arctic. Such dispersal was only possible when their rapidly shifting range lands were geographically interconnected. The end of the last ice age was fatally unique because the geographic ranges of arctic megafauna became permanently fragmented after stable, interglacial climate engendered the spread of peatlands at the same time that rising sea level severed former dispersal routes. PMID:26578776

Seasonal sea ice cover during the warm Pliocene: Evidence from the Iceland Sea (ODP Site 907)

NASA Astrophysics Data System (ADS)

Clotten, Caroline; Stein, Ruediger; Fahl, Kirsten; De Schepper, Stijn

2018-01-01

Sea ice is a critical component in the Arctic and global climate system, yet little is known about its extent and variability during past warm intervals, such as the Pliocene (5.33-2.58 Ma). Here, we present the first multi-proxy (IP25, sterols, alkenones, palynology) sea ice reconstructions for the Late Pliocene Iceland Sea (ODP Site 907). Our interpretation of a seasonal sea ice cover with occasional ice-free intervals between 3.50-3.00 Ma is supported by reconstructed alkenone-based summer sea surface temperatures. As evidenced from brassicasterol and dinosterol, primary productivity was low between 3.50 and 3.00 Ma and the site experienced generally oligotrophic conditions. The East Greenland Current (and East Icelandic Current) may have transported sea ice into the Iceland Sea and/or brought cooler and fresher waters favoring local sea ice formation. Between 3.00 and 2.40 Ma, the Iceland Sea is mainly sea ice-free, but seasonal sea ice occurred between 2.81 and 2.74 Ma. Sea ice extending into the Iceland Sea at this time may have acted as a positive feedback for the build-up of the Greenland Ice Sheet (GIS), which underwent a major expansion ∼2.75 Ma. Thereafter, most likely a stable sea ice edge developed close to Greenland, possibly changing together with the expansion and retreat of the GIS and affecting the productivity in the Iceland Sea.

Effects of micro electric current load during cooling of plant tissues on intracellular ice crystal formation behavior and pH.

PubMed

Ninagawa, Takako; Kawamura, Yukio; Konishi, Tadashi; Narumi, Akira

2016-08-01

Cryopreservation techniques are expected to evolve further to preserve biomaterials and foods in a fresh state for extended periods of time. Long-term cryopreservation of living materials such as food and biological tissue is generally achieved by freezing; thus, intracellular freezing occurs. Intracellular freezing injures the cells and leads to cell death. Therefore, a dream cryopreservation technique would preserve the living materials without internal ice crystal formation at a temperature low enough to prevent bacterial activity. This study was performed to investigate the effect of micro electrical current loading during cooling as a new cryopreservation technique. The behavior of intracellular ice crystal formation in plant tissues with or without an electric current load was evaluated using the degree of supercooling, degree of cell deformation, and grain size and growing rate of intracellular ice crystal. Moreover, the transition of intracellular pH during plant tissue cooling with or without electric current loading was also examined using the fluorescence intensity ratio to comprehend cell activity at lower temperatures. The results indicated that micro electric current load did not only decrease the degree of cell deformation and grain size of intracellular ice crystal but also reduced the decline in intracellular pH due to temperature lowering, compared with tissues subjected to the same cooling rate without an electric current load. Thus, the effect of electric current load on cryopreservation and the potential of a new cryopreservation technique using electric current load were discussed based on these results. Copyright © 2016 Elsevier Inc. All rights reserved.

A 62 ka record from the WAIS Divide ice core with annual resolution to 30 ka (so far)

NASA Astrophysics Data System (ADS)

Fudge, T. J.; Taylor, K.; McGwire, K.; Brook, E.; Sowers, T.; Steig, E.; White, J.; Vaughn, B.; Bay, R.; McConnell, J.; Waddington, E.; Conway, H.; Clow, G.; Cuffey, K.; Cole-Dai, J.; Ferris, D.; Severinghaus, J.

2012-04-01

Drilling of the West Antarctic Ice Sheet (WAIS) Divide ice core has been completed to a depth of 3400 m, about 60 meters above the bed. We present an annually resolved time scale for the most recent 30ka (to 2800 m) based on electrical conductivity measurements, called "timescale WDC06A-5". Below 2800 m the ice is dated by matching isotopes, methane, and/or dust records to other ice cores. Optical borehole logging provides stratigraphic ties to other cores for the bottom-most 75 m that was drilled in December 2011, and indicates the bottom-most ice has an age of 62 ka. The relatively young ice at depth is likely the result of basal melting. The inferred annual layer thickness of the deep ice is >1 cm, suggesting that annual layer counting throughout the entire core may be possible with continuous flow analysis of the ice core chemistry; however, the annual signal in the electrical measurements fades at about 30 ka. We compare the WDC06A-5 timescale through the glacial-interglacial transition with the Greenland GICC05 and GISP2 timescales via rapid variations in methane. We calculate a preliminary delta-age with: 1) accumulation rate inferred from the annual layer thicknesses and thinning functions computed with a 1-D ice flow model, and 2) surface temperature inferred from the low resolution d18O record and a preliminary borehole temperature profile. The WDC06A-5 timescale agrees with the GICC05 and GISP2 timescales to within decades at the 8.2k event and the ACR termination (Younger Dryas/Preboreal transition, 11.7 ka). This is within the delta-age and correlation uncertainties. At the rapid methane drop at ~12.8 ka, the WDC06A-5 timescale is ~150 years older than GICC05 and ~90 older than GISP2; while at ~14.8 ka, the timescales once again agree within the delta-age and correlation uncertainties. The cause of the age discrepancy at 12.8 ka is unclear. We also compare the WDC06A-5 timescale at Dansgaard-Oeschger events 3 and 4 (~27.5 and 29 ka) to the radiometrically-dated speolethem records from Hulu Cave, China (Larry Edwards and Hai Cheng, personal communication). To make such a comparison, we assume that the rapid variations in methane from the WAIS Divide core are synchronous with the rapid variations in d18O in the speleothem record. We find that the WDC06A-5 timescale is multiple hundreds of years older than the Hulu Cave record. As the GICC05 timescale is younger than the Hulu timescale, this puts the WDC06A-5 timescale even older than the GICC05. The uncertainties in the comparison are large both because of the uncertainty in the synchroneity of the ice core methane and speleothem isotope variations and because of the larger delta-age for the ice core in the glacial period. The timescale for the WAIS Divide core will be revised when the CFA results become available.

Establishing a Reliable Depth-Age Relationship for the Denali Ice Core

NASA Astrophysics Data System (ADS)

Wake, C. P.; Osterberg, E. C.; Winski, D.; Ferris, D.; Kreutz, K. J.; Introne, D.; Dalton, M.

2015-12-01

Reliable climate reconstruction from ice core records requires the development of a reliable depth-age relationship. We have established a sub-annual resolution depth-age relationship for the upper 198 meters of a 208 m ice core recovered in 2013 from Mt. Hunter (3,900 m asl), Denali National Park, central Alaska. The dating of the ice core was accomplished via annual layer counting of glaciochemical time-series combined with identification of reference horizons from volcanic eruptions and atmospheric nuclear weapons testing. Using the continuous ice core melter system at Dartmouth College, sub-seasonal samples have been collected and analyzed for major ions, liquid conductivity, particle size and concentration, and stable isotope ratios. Annual signals are apparent in several of the chemical species measured in the ice core samples. Calcium and magnesium peak in the spring, ammonium peaks in the summer, methanesulfonic acid (MSA) peaks in the autumn, and stable isotopes display a strong seasonal cycle with the most depleted values occurring during the winter. Thin ice layers representing infrequent summertime melt were also used to identify summer layers in the core. Analysis of approximately one meter sections of the core via nondestructive gamma spectrometry over depths from 84 to 124 m identified a strong radioactive cesium-137 peak at 89 m which corresponds to the 1963 layer deposited during extensive atmospheric nuclear weapons testing. Peaks in the sulfate and chloride record have been used for the preliminary identification of volcanic signals preserved in the ice core, including ten events since 1883. We are confident that the combination of robust annual layers combined with reference horizons provides a timescale for the 20th century that has an error of less than 0.5 years, making calibrations between ice core records and the instrumental climate data particularly robust. Initial annual layer counting through the entire 198 m suggests the Denali Ice Core record will span the past 1000 years.

Acquisition of Ice-Tethered Profilers with Velocity (ITP-V) Instruments for Future Arctic Studies

DTIC Science & Technology

2015-09-30

jacketed wire rope tether and end weight should the ice fracture or melt , and to provide modest protection in the event of ice ridging. The profiler...1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Acquisition of Ice -Tethered Profilers with Velocity (ITP...evolving thermohaline stratification, the ocean currents and air- ice -sea interactions on time scales of minutes to seasonal and longer. OBJECTIVES

Systems and Techniques for Identifying and Avoiding Ice

NASA Technical Reports Server (NTRS)

Hansman, R. John

1995-01-01

In-flight icing is one of the most difficult aviation weather hazards facing general aviation. Because most aircraft in the general aviation category are not certified for flight into known icing conditions, techniques for identifying and avoiding in-flight ice are important to maintain safety while increasing the utility and dispatch capability which is part of the AGATE vision. This report summarizes a brief study effort which: (1) Reviewed current ice identification, forecasting, and avoidance techniques; (2) Assessed feasibility of improved forecasting and ice avoidance procedures; and (3) Identified key issues for the development of improved capability with regard to in-flight icing.

A New Chronology of Late Quaternary Sequences From the Central Arctic Ocean Based on "Extinction Ages" of Their Excesses in 231Pa and 230Th

NASA Astrophysics Data System (ADS)

Hillaire-Marcel, C.; Ghaleb, B.; de Vernal, A.; Maccali, J.; Cuny, K.; Jacobel, A.; Le Duc, C.; McManus, J.

2017-12-01

Merging the late Quaternary Arctic paleoceanography into the Earth's global climate history remains challenging due to the lack of robust marine chronostratigraphies. Over ridges notably, low and variable sedimentation rates, scarce biogenic remains ensuing from low productivity and/or poor preservation, and oxygen isotope and paleomagnetic records differing from global stacks represent major impediments. However, as illustrate here based on consistent records from Mendeleev-Alpha and Lomonosov Ridges, disequilibria between U-series isotopes can provide benchmark ages. In such settings, fluxes of the particle-reactive U-daughter isotopes 230Th and 231Pa from the water column, are not unequivocally linked to sedimentation rates, but rather to sea-ice rafting and brine production histories, thus to the development of sea-ice factories over shelves during intervals of high relative sea level. The excesses in 230Th and 231Pa over fractions supported by their parent U-isotopes, collapse down sedimentary sequences, due to radioactive decay, and provide radiometric benchmark ages of approximately 300 and 140 ka, respectively. These "extinction ages" point to mean sedimentation rates of ˜4.3 and ˜1.7 mm/ka, respectively, over the Lomonosov and Mendeleev Ridges, which are significantly lower than assumed in most recent studies, thus highlighting the need for revisiting current interpretations of Arctic lithostratigraphies in relation to the global-scale late Quaternary climatostratigraphy.

BrightFocus Foundation

MedlinePlus

... treatment for geographic atrophy, the advanced form of dry age-related macular degeneration. Thursday, September 28, 2017 ... and ICE Syndrome Iridocorneal endothelial syndrome, or ICE syndrome, is a ...

Measuring Greenland Ice Mass Variation With Gravity Recovery and the Climate Experiment Gravity and GPS

NASA Technical Reports Server (NTRS)

Wu, Xiao-Ping

1999-01-01

The response of the Greenland ice sheet to climate change could significantly alter sea level. The ice sheet was much thicker at the last glacial maximum. To gain insight into the global change process and the future trend, it is important to evaluate the ice mass variation as a function of time and space. The Gravity Recovery and Climate Experiment (GRACE) mission to fly in 2001 for 5 years will measure gravity changes associated with the current ice variation and the solid earth's response to past variations. Our objective is to assess the separability of different change sources, accuracy and resolution in the mass variation determination by the new gravity data and possible Global Positioning System (GPS) bedrock uplift measurements. We use a reference parameter state that follows a dynamic ice model for current mass variation and a variant of the Tushingham and Peltier ICE-3G deglaciation model for historical deglaciation. The current linear trend is also assumed to have started 5 kyr ago. The Earth model is fixed as preliminary reference Earth model (PREM) with four viscoelastic layers. A discrete Bayesian inverse algorithm is developed employing an isotropic Gaussian a priori covariance function over the ice sheet and time. We use data noise predicted by the University of Texas and JPL for major GRACE error sources. A 2 mm/yr uplift uncertainty is assumed for GPS occupation time of 5 years. We then carry out covariance analysis and inverse simulation using GRACE geoid coefficients up to degree 180 in conjunction with a number of GPS uplift rates. Present-day ice mass variation and historical deglaciation are solved simultaneously over 146 grids of roughly 110 km x 110 km and with 6 time increments of 3 kyr each, along with a common starting epoch of the current trend. For present-day ice thickness change, the covariance analysis using GRACE geoid data alone results in a root mean square (RMS) posterior root variance of 2.6 cm/yr, with fairly large a priori uncertainties in the parameters and a Gaussian correlation length of 350 km. Simulated inverse can successfully recover most features in the reference present-day change. The RMS difference between them over the grids is 2.8 cm/yr. The RMS difference becomes 1.1 cm/yr when both are averaged with a half Gaussian wavelength of 150 km. With a fixed Earth model, GRACE alone can separate the geoid signals due to past and current load fairly well. Shown are the reference geoid signatures of direct and elastic effects of the current trend, the viscoelastic effect of the same trend starting from 5 kyr ago, the Post Glacial Rebound (PGR), and the predicted GRACE geoid error. The difference between the reference and inverse modeled total viscoelastic signatures is also shown. Although past and current ice mass variations are allowed the same spatial scale, their geoid signals have different spatial patterns. GPS data can contribute to the ice mass determination as well. Additional information is contained in the original.

The New ICE-Age: Frozen and Thawing Perceptions of Imagination

ERIC Educational Resources Information Center

Hatt, Blaine E.

2018-01-01

The article examines the importance of imagination in adult-child relationships in 21st-century experiential learning, where ICE is an acronym for Imagination Creativity Education. It explores, through hermeneutic phenomenology, the impact of imagination in the life-experiences of three school-aged children through the wonder of toying, through…

Integrating Teaching about the Little Ice Age with History, Art, and Literature.

ERIC Educational Resources Information Center

Glenn, William Harold

1996-01-01

Discusses climate change during the Little Ice Age as experienced during several historical events, including the settlement and demise of the Norse Greenland colonies, the landing of the Pilgrims at Plymouth, and both the Battle of Trenton and Washington's encampment at Valley Forge during the American Revolution. Associated artistic and literary…

Greenhouse Gas Concentration Records Extended Back to 800,000 Years From the EPICA Dome C Ice Core

NASA Astrophysics Data System (ADS)

Chappellaz, J.; Luethi, D.; Loulergue, L.; Barnola, J.; Bereiter, B.; Blunier, T.; Jouzel, J.; Lefloch, M.; Lemieux, B.; Masson-Delmotte, V.; Raynaud, D.; Schilt, A.; Siegenthaler, U.; Spahni, R.; Stocker, T.

2007-12-01

The deep ice core recovered from Dome Concordia in the framework of EPICA, the European Project for Ice Coring in Antarctica, has extended the record of Antarctic climate history back to 800,000 years [Jouzel et al., 2007]. We present the current status of measurements of CO2, CH4 and N2O on air trapped in the bubbles of the Dome C ice core. CO2 is measured in two laboratories using different techniques (laser absorption spectroscopy or gas chromatography on samples of 8 and 40 g of ice which are mechanically crushed or milled, respectively). CH4 and N2O are extracted using a melt-refreeze technique and then measured by gas chromatography (in two laboratories for CH4). The greenhouse gas concentrations have now been measured on the lowest 200 m of the Dome C core, going back to Marine Isotope Stage 20 (MIS 20) as verified by a consistent gas age/ice age difference determined at termination IX [Jouzel et al., 2007]. The atmospheric CO2 concentration mostly lagged the Antarctic temperature with a rather strong correlation throughout the eight and a half glacial cycles, but with significantly lower CO2 values between 650 and 750 kyr BP. Its lowest level ever measured in ice cores (172 ppmv) is observed during MIS 16 (minimum centered at 667 kyr BP according to the EDC3 chronology) redetermining the natural span of CO2 to 172-300 ppmv. With 2245 individual measurements, the CH4 concentration is now reconstructed over 800,000 years from a single core, with an average time resolution of 380 years. Spectral analyses of the CH4 signal show an increasing contribution of precession during the last four climatic cycles compared with the four older ones, suggesting an increasing impact of low latitudes sources/sinks. Millennial scale features in this very detailed signal allows us to compare their occurrence with ice volume reconstructions and the isotopic composition of precipitation over the East Antarctic plateau. N2O is still affected by glaciological artefacts involving dust content in the ice, and its exact temporal evolution remains to be deciphered. These measurements represent the basis of the so-called "EPICA Challenge" [Wolff et al., 2005]: they will put the climate and carbon cycle modelers under the challenge of fully understanding how orbital parameters and climate system configurations could have built such tight coupling between atmospheric composition and natural climate change during the late Quaternary. Jouzel et al., Science 317, 793-796, 10 August 2007 Wolff et al., EOS 86, N°38, 341-345, 20 September 2005

Skin Temperature Processes in the Presence of Sea Ice

NASA Astrophysics Data System (ADS)

Brumer, S. E.; Zappa, C. J.; Brown, S.; McGillis, W. R.; Loose, B.

2013-12-01

Monitoring the sea-ice margins of polar oceans and understanding the physical processes at play at the ice-ocean-air interface is essential in the perspective of a changing climate in which we face an accelerated decline of ice caps and sea ice. Remote sensing and in particular InfraRed (IR) imaging offer a unique opportunity not only to observe physical processes at sea-ice margins, but also to measure air-sea exchanges near ice. It permits monitoring ice and ocean temperature variability, and can be used for derivation of surface flow field allowing investigating turbulence and shearing at the ice-ocean interface as well as ocean-atmosphere gas transfer. Here we present experiments conducted with the aim of gaining an insight on how the presence of sea ice affects the momentum exchange between the atmosphere and ocean and investigate turbulence production in the interplay of ice-water shear, convection, waves and wind. A set of over 200 high resolution IR imagery records was taken at the US Army Cold Regions Research and Engineering Laboratory (CRREL, Hanover NH) under varying ice coverage, fan and pump settings. In situ instruments provided air and water temperature, salinity, subsurface currents and wave height. Air side profiling provided environmental parameters such as wind speed, humidity and heat fluxes. The study aims to investigate what can be gained from small-scale high-resolution IR imaging of the ice-ocean-air interface; in particular how sea ice modulates local physics and gas transfer. The relationship between water and ice temperatures with current and wind will be addressed looking at the ocean and ice temperature variance. Various skin temperature and gas transfer parameterizations will be evaluated at ice margins under varying environmental conditions. Furthermore the accuracy of various techniques used to determine surface flow will be assessed from which turbulence statistics will be determined. This will give an insight on how ice presence may affect the dissipation of turbulent kinetic energy.

Glacier loss on Kilimanjaro continues unabated

PubMed Central

Thompson, L. G.; Brecher, H. H.; Mosley-Thompson, E.; Hardy, D. R.; Mark, B. G.

2009-01-01

The dramatic loss of Kilimanjaro's ice cover has attracted global attention. The three remaining ice fields on the plateau and the slopes are both shrinking laterally and rapidly thinning. Summit ice cover (areal extent) decreased ≈1% per year from 1912 to 1953 and ≈2.5% per year from 1989 to 2007. Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone. From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was ≈1.9 and ≈5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of ≈3.6% and ≈24%, respectively. Furtwängler Glacier thinned ≈50% at the drill site between 2000 and 2009. Ice volume changes (2000–2007) calculated for two ice fields reveal that nearly equivalent ice volumes are now being lost to thinning and lateral shrinking. The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration. Kilimanjaro's ice loss is contemporaneous with widespread glacier retreat in mid to low latitudes. The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought ≈4,200 years ago that lasted ≈300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro's ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades. PMID:19884500

Glacier loss on Kilimanjaro continues unabated.

PubMed

Thompson, L G; Brecher, H H; Mosley-Thompson, E; Hardy, D R; Mark, B G

2009-11-24

The dramatic loss of Kilimanjaro's ice cover has attracted global attention. The three remaining ice fields on the plateau and the slopes are both shrinking laterally and rapidly thinning. Summit ice cover (areal extent) decreased approximately 1% per year from 1912 to 1953 and approximately 2.5% per year from 1989 to 2007. Of the ice cover present in 1912, 85% has disappeared and 26% of that present in 2000 is now gone. From 2000 to 2007 thinning (surface lowering) at the summits of the Northern and Southern Ice Fields was approximately 1.9 and approximately 5.1 m, respectively, which based on ice thicknesses at the summit drill sites in 2000 represents a thinning of approximately 3.6% and approximately 24%, respectively. Furtwängler Glacier thinned approximately 50% at the drill site between 2000 and 2009. Ice volume changes (2000-2007) calculated for two ice fields reveal that nearly equivalent ice volumes are now being lost to thinning and lateral shrinking. The relative importance of different climatological drivers remains an area of active inquiry, yet several points bear consideration. Kilimanjaro's ice loss is contemporaneous with widespread glacier retreat in mid to low latitudes. The Northern Ice Field has persisted at least 11,700 years and survived a widespread drought approximately 4,200 years ago that lasted approximately 300 years. We present additional evidence that the combination of processes driving the current shrinking and thinning of Kilimanjaro's ice fields is unique within an 11,700-year perspective. If current climatological conditions are sustained, the ice fields atop Kilimanjaro and on its flanks will likely disappear within several decades.

Shifting Climate Modes and a Warm Little Ice Age: Paleo Productivity and Temperature Determinations from the Southern California Current Over the Last Millennium

NASA Astrophysics Data System (ADS)

Kelly, C. S.; Herbert, T.; O'Mara, N. A.; Abella-Gutiérrez, J. L.; Herguera, J. C.

2016-12-01

The ocean dynamical thermostat hypothesis predicts that stronger [weaker] equatorial radiation forces warmer [cooler] western Pacific sea surface temperatures (SSTs) and a cooler [warmer] Eastern Equatorial Pacific (EEP) through air-sea coupling of the Walker circulation. Although proxy data offers some support for this prediction, recent SST reconstructions from the EEP suggest complex relationships between Northern Hemisphere (NH) and EEP temperature during the last millennium (Rustic et al. 2015), with EEP SSTs positively covarying with NH temperature during the Medieval Warm Period but negatively covarying during the Little Ice Age (LIA). Whereas most proxy reconstructions have focused on the EEP upwelling zone, few high-resolution studies exist from the California Current (CC)—a region whose oceanography displays exceptional fidelity to the El Niño Southern Oscillation and the Pacific Decadal Oscillation. In particular, southern CC oceanography reflects a balance between tropically-sourced and more northerly, temperate waters. Teasing these signals apart across past centuries can provide insight as to how a more complex dynamical thermostat affects the subtropics. Does the subtropical eastern Pacific track EEP SST across multiple centuries and climatic transitions? We present a record from the San Lazaro Basin (25N, 112.5W) in the subtropical eastern Pacific off Baja, Mexico of SST and marine paleoproductivity based upon alkenone saturation and concentrations (C37tot) over the last millennium. By combining these analyses on laminated sediment cores with newly published productivity records from the same site, we provide the first sub decadal paleoceanographic record from the southern California upwelling zone. We observe quasi-periodic short-lived cold excursions, centennial modulation of multidecadal periodicities, and an inverse relationship between C37tot and SST at lower frequencies. Our SST record displays a warm Little Ice Age, similar to but 100 years earlier than EEP warmth observed at 1500 CE (Rustic et al. 2015). In spite of this mismatch, the similarity between these records and the correlation of LIA warmth with NH cooling offers support for the dynamical thermostat's application in subtropical settings, provided they are plumbed to the equatorial climatology.

Map Showing Limits of Tahoe Glaciation in Sequoia and Kings Canyon National Parks, California

USGS Publications Warehouse

Moore, James Gregory; Mack, Gregory S.

2008-01-01

The latest periods of extensive ice cover in the Sierra Nevada include the Tahoe glaciation followed by the Tioga glaciation, and evidence for these ice ages is widespread in the Sequoia and Kings Canyon National Parks area. However, the timing of the advances and retreats of the glaciers during the periods of glaciation continues to be a matter of debate. A compilation of existing work (Clark and others, 2003) defines the Tioga glaciation at 14-25 thousand years ago and splits the Tahoe glaciation into two stages that range from 42-50 and 140-200 thousand years ago. The extent of the Tahoe ice mass shown in the map area is considered to represent the younger Tahoe stage, 42-50 thousand years ago. Evidence of glaciations older than the Tahoe is limited in the southern Sierra Nevada. After the Tioga glaciation, only minor events with considerably less ice cover occurred. The Tioga glaciation was slightly less extensive than the Tahoe glaciation, and each covered about half of the area of Sequoia and Kings Canyon National Parks. The Tahoe glaciers extended 500-1,000 ft lower and 0.5-1.2 mi farther down valleys. Evidence for the Tahoe glacial limits is not as robust as that for Tioga, but the extent of the Tahoe ice is mapped because it covered a larger area and the ice did leave prominent moraines (piles of sediment and boulders deposited by glaciers as they melted at their margins) lower on the east front of the range. Current Sierra redwood (Sequoiadendron giganteum) groves occur in a belt on the west side of the Sierra Nevada, generally west of the area of Tahoe glaciation.

Ross Sea paleo-ice sheet drainage and deglacial history during and since the LGM

NASA Astrophysics Data System (ADS)

Anderson, John B.; Conway, Howard; Bart, Philip J.; Witus, Alexandra E.; Greenwood, Sarah L.; McKay, Robert M.; Hall, Brenda L.; Ackert, Robert P.; Licht, Kathy; Jakobsson, Martin; Stone, John O.

2014-09-01

Onshore and offshore studies show that an expanded, grounded ice sheet occupied the Ross Sea Embayment during the Last Glacial Maximum (LGM). Results from studies of till provenance and the orientation of geomorphic features on the continental shelf show that more than half of the grounded ice sheet consisted of East Antarctic ice flowing through Transantarctic Mountain (TAM) outlet glaciers; the remainder came from West Antarctica. Terrestrial data indicate little or no thickening in the upper catchment regions in both West and East Antarctica during the LGM. In contrast, evidence from the mouths of the southern and central TAM outlet glaciers indicate surface elevations between 1000 m and 1100 m (above present-day sea level). Farther north along the western margin of the Ross Ice Sheet, surface elevations reached 720 m on Ross Island, and 400 m at Terra Nova Bay. Evidence from Marie Byrd Land at the eastern margin of the ice sheet indicates that the elevation near the present-day grounding line was more than 800 m asl, while at Siple Dome in the central Ross Embayment, the surface elevation was about 950 m asl. Farther north, evidence that the ice sheet was grounded on the middle and the outer continental shelf during the LGM implies that surface elevations had to be at least 100 m above the LGM sea level. The apparent low surface profile and implied low basal shear stress in the central and eastern embayment suggests that although the ice streams may have slowed during the LGM, they remained active. Ice-sheet retreat from the western Ross Embayment during the Holocene is constrained by marine and terrestrial data. Ages from marine sediments suggest that the grounding line had retreated from its LGM outer shelf location only a few tens of kilometer to a location south of Coulman Island by ˜13 ka BP. The ice sheet margin was located in the vicinity of the Drygalski Ice Tongue by ˜11 ka BP, just north of Ross Island by ˜7.8 ka BP, and near Hatherton Glacier by ˜6.8 ka BP. Farther south, 10Be exposure ages from glacial erratics on nunataks near the mouths of Reedy, Scott and Beardmore Glaciers indicate thinning during the mid to late Holocene, but the grounding line did not reach its present position until 2 to 3 ka BP. Marine dates, which are almost exclusively Acid Insoluble Organic (AIO) dates, are consistently older than those derived from terrestrial data. However, even these ages indicate that the ice sheet experienced significant retreat after ˜13 ka BP. Geomorphic features indicate that during the final stages of ice sheet retreat ice flowing through the TAM remained grounded on the shallow western margin of Ross Sea. The timing of retreat from the central Ross Sea remains unresolved; the simplest reconstruction is to assume that the grounding line here started to retreat from the continental shelf more or less in step with the retreat from the western and eastern sectors. An alternative hypothesis, which relies on the validity of radiocarbon ages from marine sediments, is that grounded ice had retreated from the outer continental shelf prior to the LGM. More reliable ages from marine sediments in the central Ross Embayment are needed to test and validate this hypothesis.

Antarctic Circumpolar Current Dynamics and Their Relation to Antarctic Ice Sheet and Perennial Sea-Ice Variability in the Central Drake Passage During the Last Climate Cycle

NASA Astrophysics Data System (ADS)

Kuhn, G.; Wu, S.; Hass, H. C.; Klages, J. P.; Zheng, X.; Arz, H. W.; Esper, O.; Hillenbrand, C. D.; Lange, C.; Lamy, F.; Lohmann, G.; Müller, J.; McCave, I. N. N.; Nürnberg, D.; Roberts, J.; Tiedemann, R.; Timmermann, A.; Titschack, J.; Zhang, X.

2017-12-01

The evolution of the Antarctic Ice Sheet during the last climate cycle and the interrelation to global atmospheric and ocean circulation remains controversial and plays an important role for our understanding of ice sheet response to modern global warming. The timing and sequence of deglacial warming is relevant for understanding the variability and sensitivity of the Antarctic Ice Sheet to climatic changes, and the continuing rise of atmospheric greenhouse gas concentrations. The Antarctic Ice Sheet is a pivotal component of the global water budget. Freshwater fluxes from the ice sheet may affect the Antarctic Circumpolar Current (ACC), which is strongly impacted by the westerly wind belt in the Southern Hemisphere (SHWW) and constricted to its narrowest extent in the Drake Passage. The flow of ACC water masses through Drake Passage is, therefore, crucial for advancing our understanding of the Southern Ocean's role in global meridional overturning circulation and global climate change. In order to address orbital and millennial-scale variability of the Antarctic ice sheet and the ACC, we applied a multi-proxy approach on a sediment core from the central Drake Passage including grain size, iceberg-rafted debris, mineral dust, bulk chemical and mineralogical composition, and physical properties. In combination with already published and new sediment records from the Drake Passage and Scotia Sea, as well as high-resolution data from Antarctic ice cores (WDC, EDML), we now have evidence that during glacial times a more northerly extent of the perennial sea-ice zone decreased ACC current velocities in the central Drake Passage. During deglaciation the SHWW shifted southwards due to a decreasing temperature gradient between subtropical and polar latitudes caused by sea ice and ice sheet decline. This in turn caused Southern Hemisphere warming, a more vigorous ACC, stronger Southern Ocean ventilation, and warm Circumpolar Deep Water (CDW) upwelling on Antarctic shelves resulting in increased ice shelf melting. Stronger upwelling is associated with a rise in atmospheric carbon dioxide to reach a threshold at which full deglaciation could become inevitable.

Does Relative Age Affect Career Length in North American Professional Sports?

PubMed

Steingröver, C; Wattie, N; Baker, J; Schorer, J

Relative age effects (RAEs) typically favour older members within a cohort; however, research suggests that younger players may experience some long-term advantages, such as longer career length. The purposes of this study were to replicate previous findings on RAEs among National Hockey League (NHL) ice hockey players, National Basketball Association (NBA) basketball players and National Football League (NFL) football players and to investigate the influence of relative age on career length in all three sports. Using official archives, birthdates and number of games played were collected for players drafted into the NBA ( N  = 407), NFL ( N  = 2380) and NHL ( N  = 1028) from 1980 to 1989. We investigated the possibility that younger players might be able to maximize their career length by operationalizing career length as players' number of games played throughout their careers. There was a clear RAE for the NHL, but effects were not significant for the NBA or NFL. Moreover, there was a significant difference in matches played between birth quartiles in the NHL favouring relatively younger players. There were no significant quartiles by career length effects in the NBA or NFL. The significant relationship between relative age and career length provides further support for relative age as an important constraint on expertise development in ice hockey but not basketball or football. Currently, the reason why relatively younger players have longer careers is not known. However, it may be worth exploring the influence of injury risk or the development of better playing skills.

Allan Hills Pleistocene Ice Project (PIP)

NASA Astrophysics Data System (ADS)

Kurbatov, A.; Brook, E.; Campbell, S. W.; Conway, H.; Dunbar, N. W.; Higgins, J. A.; Iverson, N. A.; Kehrl, L. M.; McIntosh, W. C.; Spaulding, N. E.; Yan, Y.; Mayewski, P. A.

2016-12-01

A major international effort to identify at least 1.5 Ma old ice for paleoclimate reconstructions has successfully resulted in the selection of several potential drill sites in East Antarctica. At this point it is indisputable that the Antarctic ice sheet captures a continuous envinronmental record of the Earth that spans the Mid Pleistocene Transition (MPT). In addition to traditional ice coring approaches, the oldest ice can also be recovered in Antarctic Blue Ice Areas (BIA). We have already successfully demonstrated that the Allan Hills (AH) BIA captures a regional climate signal and robust record of 1Ma atmosphere that can be studied with a relatively uncomplicated logistical imprint and essentially unlimited sampling volume. The attractiveness of unlimited sampling of known age ice is the basis for the "ice park" concept proposed earlier by our research team. The idea is that, once the age of ice exposed along the flow line at the surface of BIA is mapped, it could be sampled for numerous research projects as needed. Here we propose an intermediate ( 1,150 m deep) ice core drill site, located only 240 km away from McMurdo base that will help to develop a, continuous, high quality regional paleoclimate record that is at least 1Ma old. We will introduce and discuss the glaciological settings, paleoclimate signals and possible limitations and advantages of the 1 Ma AH BIA regional paleoclimate record. The research was funded by NSF Division of Polar Programs.

SIPEX 2012: Extreme sea-ice and atmospheric conditions off East Antarctica

NASA Astrophysics Data System (ADS)

Heil, P.; Stammerjohn, S.; Reid, P.; Massom, R. A.; Hutchings, J. K.

2016-09-01

In 2012, Antarctic sea-ice coverage was marked by weak annual-mean climate anomalies that consisted of opposing anomalies early and late in the year (some setting new records) which were interspersed by near-average conditions for most of the austral autumn and winter. Here, we investigate the ocean-ice-atmosphere system off East Antarctica, prior to and during the Sea Ice Physics and Ecosystems eXperiment [SIPEX] 2012, by exploring relationships between atmospheric and oceanic forcing together with the sea-ice and snow characteristics. During August and September 2012, just prior to SIPEX 2012, atmospheric circulation over the Southern Ocean was near-average, setting up the ocean-ice-atmosphere system for near-average conditions. However, below-average surface pressure and temperature as well as strengthened circumpolar winds prevailed during June and July 2012. This led to a new record (19.48×106 km2) in maximum Antarctic sea-ice extent recorded in late September. In contrast to the weak circum-Antarctic conditions, the East Antarctic sector (including the SIPEX 2012 region) experienced positive sea-ice extent and concentration anomalies during most of 2012, coincident with negative atmospheric pressure and sea-surface temperature anomalies. Heavily deformed sea ice appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea ice from the east. This increased westward ice flux is likely linked to the break-up of nearly 80% of the Mertz Glacier Tongue in 2010, which strongly modified the coastal configuration and hence the width of the westward coastal current. Combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea ice to remain within the coastal current at the expense of a reduced northward flow in the region around 141°-145°E. In addition a westward propagating positive anomaly of sea-ice extent from the western Ross Sea during austral winter 2012 has been identified to have fed into the westward current of the SIPEX 2012 region. A pair of large grounded icebergs appears to have modified the local stress state as well as the structure of the ice pack upstream and also towards the Dalton Glacier Tongue. Together with the increased influx of sea ice into the regions, this contributed to the difficulties in navigating the SIPEX 2012 region.

Ice age True Polar Wander: raising debates and new analyses

NASA Astrophysics Data System (ADS)

Sabadini, Roberto; Cambiotti, Gabriele; Ricard, Yanick

2010-05-01

Issues related to long time scale instability in the Earth's rotation, named True Polar Wander (TPW), have continuously been debated, after the pioneering works of the sixties. Since Maxwell Earth models with elastic or high viscosity viscoelastic lithospheres predict different ice-age TPW in the lower mantle viscosity range 1021 - 1022 Pa s, it has been recently suggested that the observed fluid Love number should be used to describe the initial equatorial bulge rather than the tidal fluid limit resulting from the viscoelastic modelling itself. We show that different ice-age TPW predictions have to be expected due to the dependence of TPW on the Earth's initial state, characterized by a larger and stress-free equatorial bulge for the viscoelastic lithosphere, compared to the elastic one, and that there is no shortcomings or errors in the traditional approach based on the use of tidal Love number from the model. The use of the observed fluid Love number represents in fact a simplified attempt to couple the effects on TPW from mantle convection and glacial forcing, by including the non-hydrostatic flattening due to mantle convection but not its driving part. This partial coupling freezes in space the non-hydrostatic contribution due to mantle convection, thus damping the present-day ice-age TPW and forcing the axis of instantaneous rotation to come back to its initial position when ice ages started. In this perspective, we discuss the implication of self-consistent convection calculations of the non-hydrostatic contribution and its impact on the long-term Earth's rotation stability during ice-age. We develop a full compressible model, based on the numerical integration in the radial variable of the momentum and Poisson equations and on the contour integration in the Laplace domain, which allows us to deal with the non-modal contribution from continuous radial rheological variations. We quantify the effects of the compressible rheology, compared to the widely used incompressible ones

Remotely Operated Vehicles under sea ice - Experiences and results from five years of polar operations

NASA Astrophysics Data System (ADS)

Katlein, Christian; Arndt, Stefanie; Lange, Benjamin; Belter, Hans Jakob; Schiller, Martin; Nicolaus, Marcel

2016-04-01

The availability of advanced robotic technologies to the Earth Science community has largely increased in the last decade. Remotely operated vehicles (ROV) enable spatially extensive scientific investigations underneath the sea ice of the polar oceans, covering a larger range and longer diving times than divers with significantly lower risks. Here we present our experiences and scientific results acquired from ROV operations during the last five years in the Arctic and Antarctic sea ice region. Working under the sea ice means to have all obstacles and investigated objects above the vehicle, and thus changes several paradigms of ROV operations as compared to blue water applications. Observations of downwelling spectral irradiance and radiance allow a characterization of the optical properties of sea ice and the spatial variability of the energy partitioning across the atmosphere-ice-ocean boundary. Our results show that the decreasing thickness and age of the sea ice have led to a significant increase in light transmission during summer over the last three decades. Spatially extensive measurements from ROV surveys generally provide more information on the light field variability than single spot measurements. The large number of sampled ice conditions during five cruises with the German research icebreaker RV Polarstern allows for the investigations of the seasonal evolution of light transmittance. Both, measurements of hyperspectral light transmittance through sea ice, as well as classification of upward-looking camera images were used to investigate the spatial distribution of ice-algal biomass. Buoyant ice-algal aggregates were found to be positioned in the stretches of level ice, rather than pressure ridges due to a physical interaction of aggregate-buoyancy and under-ice currents. Synchronous measurements of sea ice thickness by upward looking sonar provides crucial additional information to put light-transmittance and biological observations into context. Observations of under-ice topography by upward-looking multibeam sonar combined with aerial images provide a unique three dimensional picture of the complexity of the non-uniform sea ice layer. ROV surveys cover the scale of an entire ice floe and are an excellent tool to bridge the scale gap between isolated point measurements and larger scale surveys, such as specifically designed under-ice nets with sensor arrays or surveys by autonomous underwater vehicles (AUV). In the framework of the infrastructure project FRAM (Frontiers in Arctic Marine Monitoring), the Alfred Wegener Institute is in the process of commissioning a new lightweight mobile ROV system for interdisciplinary research underneath sea ice. This new system profits from the acquired experiences and will receive a significantly upgraded suite of scientific sensors, maintaining the rugged and reliable characteristics of the past systems. The interdisciplinary sensor suite will be extended towards the measurement of more oceanographic and biological parameters with a CTD, different fluorometers, and biogeochemical sensors. While basic intervention capabilities are already available, the system can be extended with advanced manipulation and sampling capabilities in the future.

The Little Ice Age in the tropical Andes

NASA Astrophysics Data System (ADS)

Jomelli, V.; Cooley, D.; Naveau, P.; Rabatel, A.

2003-12-01

The period known as the Little Ice Age, from the 17th to the 19th century, brought a cooling of around 0.5 degrees Celsius as well as varyingly humid episodes Eurasia and North America. Because of a lack of long paleoclimatic time series in the tropical Andes, it is still unclear if similar cooling occurred over these tropical and Southern Hemisphere regions. Furthermore, if changes did take place, it is currently not well established if they were temporally synchronous or shifted with respect of the variations in the Northern Hemisphere or the globe. To look into this important climatic question and for advancing our understanding of the past climate links between the tropics and higher latitudes, 25 glaciers located in Bolivia and in Peru were carefully selected. Glacial activity and environmental changes were analyzed using lichenometry. Largest lichen diameters were measured in the different glacial basins. To better analyze these maximum diameters and to more appropriately represent uncertainty and the character of this collected data, age estimates of the different moraine systems were derived using extreme value theory rather than the traditional averaging. The results reveal two particular phases of glacier growth, 1550-1600 and 1800-1850. These two phases have also been identified in other proxy records, such as ice-cores and documentary data (particularly from church chronicles). In order to understand the climatic changes that could have contributed to the glacial variations, a simple model based on both precipitations and temperatures is applied to estimate mass balance questions in the basins. A cooling of the order of 0.5 C seems to be the most consistent with the data. Finally, these findings are compared with the better-known histories of Northern Hemisphere mid-latitude glaciers.

Modelled rainfall skill assessment against a 1000-year time/space isotope dendro-climatology for southern Africa

NASA Astrophysics Data System (ADS)

Woodborne, Stephan; Hall, Grant; Zhang, Qiong

2016-04-01

Palaeoclimate reconstruction using isotopic analysis of tree growth increments has yielded a 1000-year record of rainfall variability in southern Africa. Isotope dendro-climatology reconstructions from baobab trees (Adansonia digitata) provide evidence for rainfall variability from the arid Namib Desert and the Limpopo River Valley. Isotopic analysis of a museum specimen of a yellowwood tree (Podocarps falcatus) yields another record from the southwestern part of the subcontinent. Combined with the limited classic denro-climatologies available in the region these records yield palaeo-rainfall variability in the summer and winter rainfall zones as well as the hyper-arid zone over the last 1000 years. Coherent shifts in all of the records indicate synoptic changes in the westerlies, the inter-tropical convergence zone, and the Congo air boundary. The most substantial rainfall shift takes place at about 1600 CE at the onset of the Little Ice Age. Another distinctive feature of the record is a widespread phenomenon that occurs shortly after 1810 CE that in southern Africa corresponds with a widespread social upheaval known as the Difequane or Mfekane. Large scale forcing of the system includes sea-surface temperatures in the Agulhas Current, the El Nino Southern Oscillation and the Southern Annular Mode. The Little Ice Age and Mfekane climate shifts result from different forcing mechanisms, and the rainfall response in the different regions at these times do not have a fixed phase relationship. This complexity provides a good scenario to test climate models. A first order (wetter versus drier) comparison between each of the tree records and a 1000-year palaeoclimate model simulation for the Little Ice Age and Mfekane transitions demonstrates a generally good correspondence.

Lake carbonate-δ18 records from the Yukon Territory, Canada: Little Ice Age moisture variability and patterns

USGS Publications Warehouse

Anderson, Lesleigh; Finney, Bruce P.; Shapley, Mark D.

2011-01-01

A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water δ18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake’s hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water δ18O values decrease. Past lake-water δ18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate δ18O, supplemented by those in carbonate and organic δ13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ∼AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ∼AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake δ18O, a similarly small, stratified, alkaline lake located ∼250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances.

Mitochondrial phylogeography of moose (Alces alces): Late Pleistocene divergence and population expansion

USGS Publications Warehouse

Hundertmark, Kris J.; Shields, Gerald F.; Udina, Irina G.; Bowyer, R. Terry; Danilkin, Alexei A.; Schwartz, Charles C.

2002-01-01

We examined phylogeographic relationships of moose (Alces alces) worldwide to test the proposed existence of two geographic races and to infer the timing and extent of demographic processes underpinning the expansion of this species across the Northern Hemisphere in the late Pleistocene. Sequence variation within the left hypervariable domain of the control region occurred at low or moderate levels worldwide and was structured geographically. Partitioning of genetic variance among regions indicated that isolation by distance was the primary agent for differentiation of moose populations but does not support the existence of distinct eastern and western races. Levels of genetic variation and structure of phylogenetic trees identify Asia as the origin of all extant mitochondrial lineages. A recent coalescence is indicated, with the most recent common ancestor dating to the last ice age. Moose have undergone two episodes of population expansion, likely corresponding to the final interstade of the most recent ice age and the onset of the current interglacial. Timing of expansion for the population in the Yakutia–Manchuria region of eastern Asia indicates that it is one of the oldest populations of moose and may represent the source of founders of extant populations in North America, which were colonized within the last 15,000 years. Our data suggest an extended period of low population size or a severe bottleneck prior to the divergence and expansion of extant lineages and a recent, less-severe bottleneck among European lineages. Climate change during the last ice age, acting through contraction and expansion of moose habitat and the flooding of the Bering land bridge, undoubtedly was a key factor influencing the divergence and expansion of moose populations.

Lake carbonate-δ 18O records from the Yukon Territory, Canada: Little Ice Age moisture variability and patterns

NASA Astrophysics Data System (ADS)

Anderson, Lesleigh; Finney, Bruce P.; Shapley, Mark D.

2011-04-01

A 1000-yr history of climate change in the central Yukon Territory, Canada, is inferred from sediment composition and isotope geochemistry from small, groundwater fed, Seven Mile Lake. Recent observations of lake-water δ 18O, lake level, river discharge, and climate variations, suggest that changes in regional effective moisture (precipitation minus evaporation) are reflected by the lake's hydrologic balance. The observations indicate that the lake is currently 18O-enriched by summer evaporation and that during years of increased precipitation, when groundwater inflow rates to the lake increase, lake-water δ 18O values decrease. Past lake-water δ 18O values are inferred from oxygen isotope ratios of fine-grained sedimentary endogenic carbonate. Variations in carbonate δ 18O, supplemented by those in carbonate and organic δ 13C, C/N ratios, and organic carbon, carbonate and biogenic silica accumulation rates, document changes in effective moisture at decadal time scales during the early Little Ice Age period to present. Results indicate that between ˜AD 1000 and 1600, effective moisture was higher than today. A shift to more arid climate conditions occurred after ˜AD 1650. The 19th and 20th centuries have been the driest of the past millennium. Temporal variations correspond with inferred shifts in summer evaporation from Marcella Lake δ 18O, a similarly small, stratified, alkaline lake located ˜250 km to the southwest, suggesting that the combined reconstructions accurately document the regional paleoclimate of the east-central interior. Comparison with regional glacial activity suggests differing regional moisture patterns during early and late Little Ice Age advances.

Pack ice along the Kamchatka Peninsula, Russia as seen from STS-60

NASA Image and Video Library

1994-02-09

STS060-73-038 (3-11 Feb 1994) --- Pack ice is documented in this photograph along the coast of the Kamchatka Peninsula of Russia in Zaliv Ozernoj. Newly formed ice continually breaks away from the land and takes the form imposed by coastal currents. Detailed photographs of the ice provide information to scientists in both Russia and the united States about the location and fluctuation of ice edges, and how this new sea ice interacts with ocean and littoral currents. This information results in better ice warnings to shipping traffic and provides data points for long-range climate change research for both the Mission-To-Planet Earth and the Russian Priroda ("Nature") monitoring and assessment programs that are respectively coordinated by NASA and the Russian Academy of Sciences. This photography of ice development in the North Pacific, North Atlantic, the Southern Ocean, the Baltic and North Seas, and the Great Lakes is of great interest to the international scientific community. NASA scientists feel high-resolution analog and digital photography from the Space Shuttle and future craft can be a particularly important component in satisfying their data needs on both an operational and a long-term research basis.

Transport of contaminants by Arctic sea ice and surface ocean currents

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pfirman, S.

1995-12-31

Sea ice and ocean currents transport contaminants in the Arctic from source areas on the shelves, to biologically active regions often more than a thousand kilometers away. Coastal regions along the Siberian margin are polluted by discharges of agricultural, industrial and military wastes in river runoff, from atmospheric deposition and ocean dumping. The Kara Sea is of particular concern because of deliberate dumping of radioactive waste, as well as the large input of polluted river water. Contaminants are incorporated in ice during suspension freezing on the shelves, and by atmospheric deposition during drift. Ice releases its contaminant load through brinemore » drainage, surface runoff of snow and meltwater, and when the floe disintegrates. The marginal ice zone, a region of intense biological activity, may also be the site of major contaminant release. Potentially contaminated ice from the Kara Sea is likely to influence the marginal ice zones of the Barents and Greenland seas. From studies conducted to date it appears that sea ice from the Kara Sea does not typically enter the Beaufort Gyre, and thus is unlikely to affect the northern Canadian and Alaskan margins.« less

Southern Ocean biogeochemical control of glacial/interglacial carbon dioxide change

NASA Astrophysics Data System (ADS)

Sigman, D. M.

2014-12-01

In the effort to explain the lower atmospheric CO2 concentrations observed during ice ages, two of the first hypotheses involved redistributing dissolved inorganic carbon (DIC) within the ocean. Broecker (1982) proposed a strengthening of the ocean's biological pump during ice ages, which increased the dissolved inorganic carbon gradient between the dark, voluminous ocean interior and the surface ocean's sun-lit, wind-mixed layer. Boyle (1988) proposed a deepening in the ocean interior's pool of DIC associated with organic carbon regeneration, with its concentration maximum shifting from intermediate to abyssal depths. While not irrefutable, evidence has arisen that these mechanisms can explain much of the ice age CO2 reduction and that both were activated by changes in the Southern Ocean. In the Antarctic Zone, reduced exchange of water between the surface and the underlying ocean sequestered more DIC in the ocean interior (the biological pump mechanism). Dust-borne iron fertilization of the Subantarctic surface lowered CO2 partly by the biological pump mechanism and partly by Boyle's carbon deepening. Each mechanism owes a part of its CO2 effect to a transient increase in seafloor calcium carbonate dissolution, which raised the ice age ocean's alkalinity, causing it to absorb more CO2. However, calcium carbonate cycling also sets limits on these mechanisms and their CO2 effects, such that the combination of Antarctic and Subantarctic changes is needed to achieve the full (80-100 ppm) ice age CO2 decline. Data suggest that these changes began at different phases in the development of the last ice age, 110 and 70 ka, respectively, explaining a 40 ppm CO2 drop at each time. We lack a robust understanding of the potential causes for both the implied reduction in Antarctic surface/deep exchange and the increase in Subantarctic dust supply during ice ages. Thus, even if the evidence for these Southern Ocean changes were to become incontrovertible, conceptual gaps stand in the way of a theory of glacial cycles that includes Southern Ocean-driven CO2 change. There are more compelling proposals for the causes of deglacial change, with a sharp reduction in North Atlantic deep water formation implicated as a trigger of increased surface/deep exchange in the Antarctic and the resulting release of CO2 to the atmosphere.

Rheological properties of reduced fat ice cream mix containing octenyl succinylated pearl millet starch.

PubMed

Sharma, Monika; Singh, Ashish K; Yadav, Deep N

2017-05-01

The octenyl succinyl anhydride (OSA) esterified pearl millet ( Pennisetum typhoides ) starch was evaluated as fat replacer in soft serve ice cream in comparison to other fat replacers viz. inulin, whey protein concentrate-70 and commercial starch. During temperature sweep test, the yield stress and flow behaviour index of un-pasteurized ice cream mixes increased as the temperature increased from 40 to 80 °C, while the consistency index decreased. Consistency index of aged ice cream mixes containing 2% fat replacer was higher as compared to mixes with 1% level. The aged ice cream mixes exhibited non-Newtonian behaviour as flow behaviour index values were less than one. Apparent viscosity (at 50 s -1 shear rate) of control as well as ice cream mix containing 1% OSA-esterified pearl millet starch samples was 417 and 415 mPas, respectively and did not differ significantly. The overrun of the ice cream (with 5 and 7.5% fat) containing 1 and 2% of above fat replacers ranged between 29.7 and 34.3% and was significantly lower than control (40.3%). The percent melted ice cream was also low for the ice creams containing 2% of above fat replacers at 5% fat content as compared to control. However, sensory acceptability and rheological characteristics of reduced fat ice creams containing 1.0 and 2.0% OSA-esterified pearl millet starch were at par with other fat replacers under the study. Thus, OSA-esterified pearl millet starch has potential to be used as fat replacer in reduced fat ice cream.

Cloud Response to Arctic Sea Ice Loss and Implications for Feedbacks in the CESM1 Climate Model

NASA Astrophysics Data System (ADS)

Morrison, A.; Kay, J. E.; Chepfer, H.; Guzman, R.; Bonazzola, M.

2017-12-01

Clouds have the potential to accelerate or slow the rate of Arctic sea ice loss through their radiative influence on the surface. Cloud feedbacks can therefore play into Arctic warming as clouds respond to changes in sea ice cover. As the Arctic moves toward an ice-free state, understanding how cloud - sea ice relationships change in response to sea ice loss is critical for predicting the future climate trajectory. From satellite observations we know the effect of present-day sea ice cover on clouds, but how will clouds respond to sea ice loss as the Arctic transitions to a seasonally open water state? In this study we use a lidar simulator to first evaluate cloud - sea ice relationships in the Community Earth System Model (CESM1) against present-day observations (2006-2015). In the current climate, the cloud response to sea ice is well-represented in CESM1: we see no summer cloud response to changes in sea ice cover, but more fall clouds over open water than over sea ice. Since CESM1 is credible for the current Arctic climate, we next assess if our process-based understanding of Arctic cloud feedbacks related to sea ice loss is relevant for understanding future Arctic clouds. In the future Arctic, summer cloud structure continues to be insensitive to surface conditions. As the Arctic warms in the fall, however, the boundary layer deepens and cloud fraction increases over open ocean during each consecutive decade from 2020 - 2100. This study will also explore seasonal changes in cloud properties such as opacity and liquid water path. Results thus far suggest that a positive fall cloud - sea ice feedback exists in the present-day and future Arctic climate.

The distribution of ground ice on Mars

NASA Technical Reports Server (NTRS)

Mellon, M. T.; Jakosky, B. M.

1993-01-01

A wealth of geologic evidence indicates that subsurface water ice has played an important role in the evolution of Martian landforms. Theoretical models of the stability of ground ice show that in the near-surface regolith ice is currently stable at latitudes poleward of about +/- 40 deg and below a depth of a few centimeters to a meter, with some variations with longitude. If ice is not previously present at a particular location where it is stable, atmospheric water will diffuse into the regolith and condense as ice, driven by the annual subsurface thermal oscillations. The lower boundary of this ice deposit is found to occur at a depth (typically a few meters) where the annual thermal oscillations give way to the geothermal gradient. In the equatorial regions near-surface ice is currently not stable, resulting in the sublimation of any existing ice and subsequent loss to the atmosphere. However, subliming ice might be maintained at a steady-state depth, where diffusion and loss to the atmosphere are balanced by resupply from a possible deeper source of water (either deeper, not yet depleted, ice deposits or ground water). This depth is typically a few tens to hundreds of meters and depends primarily on the surface temperature and the nature of the geothermal gradient, being deeper for a higher surface temperature and a lower geothermal gradient. Such an equatorial deposit is characterized by the regolith ice content being low nearer the surface and increasing with depth in the deposit. Oscillations in the orbit will affect this picture of ground ice in two ways: by causing periodic changes in the pattern of near-surface stability and by producing subsurface thermal waves that may be capable of driving water ice deeper into the regolith.

Detrital zircon fission track analysis reveals the thermotectonic history of ice-covered rocks of the Chugach-St. Elias orogen, SE-Alaska

NASA Astrophysics Data System (ADS)

Enkelmann, E.; Garver, J. I.; Pavlis, T. L.; Bruhn, R. L.; Chapman, J. B.

2007-12-01

Investigating the exhumation history of the Chugach-St. Elias orogen (SE Alaska) using low-temperature thermochronometers is challenged by significant ice cover. Assuming exhumation drove cooling, cooling ages increase with elevation in an orogenic belt, and as such the youngest ages occur in valley bottoms. Cooling and exhumation rates are expected to be very high in the Chugach-St. Elias orogen due to efficient glacial erosion and the most intense erosion occurs under the major ice fields. To study the cooling history of rapidly exhuming rocks underneath this ice cover, we analyzed detrital zircon fission track (DZFT) ages of Recent sand samples from modern rivers that drain the central Bagley Ice field and smaller glaciers draining north (Chitina valley) and south (Pacific) of the mountain range. A distinct advantage of DZFT is that it allows one to sample a landscape regardless of accessibility. The youngest ZFT component populations of samples north and south of the Bagley Ice field record a Late Miocene (5-13 Ma) cooling of the orogen. The pattern of cooling ages shows symmetry across the orogen predates the earliest record of the collision of the Yakutat terrane with Alaska. This result contrasts with the asymmetric cooling pattern displayed by low- temperature thermochronological ages (AFT and AHe) of the exposed bedrock within the range. Apatite FT and U- Th/He ages of bedrock samples south of the Bagley Ice field record the syn-collisional (<5 Ma) fast exhumation whereas apatite ages to the north reveal more heterogeneous exhumation and vary widely from Miocene to Eocene. The bedrock samples from throughout the orogenic belt thus display predominantly the effects of the recent climatic situation of the mountain range with very high precipitation on the south, seaward side versus a more arid north side. Our ZFT results from the northern drainages highlight the relative sense and timing of two important fault zones, both accommodate south-side-up exhumation. The Steward Creek fault zone, located north of the Bagley Ice field, limits the Late Miocene exhumation, whereby samples north of it yielded age populations that are Late Eocene to Cretaceous (30-120 Ma) or older. The Border Ranges fault zone, located farther north, limits the Late Eocene cooling and exhumation of the low-P and high-T Chugach Metamorphic Complex that is inferred to have formed during Eocene ridge subduction. This study provides the first insights on the exhumation history of the Chugach- St. Elias orogen between the time of Eocene ridge subduction and full collision of the Yakutat terrane with North America in the latest Miocene.

Ice electrode electrolytic cell

DOEpatents

Glenn, D.F.; Suciu, D.F.; Harris, T.L.; Ingram, J.C.

1993-04-06

This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

Ice electrode electrolytic cell

DOEpatents

Glenn, David F.; Suciu, Dan F.; Harris, Taryl L.; Ingram, Jani C.

1993-01-01

This invention relates to a method and apparatus for removing heavy metals from waste water, soils, or process streams by electrolytic cell means. The method includes cooling a cell cathode to form an ice layer over the cathode and then applying an electric current to deposit a layer of the heavy metal over the ice. The metal is then easily removed after melting the ice. In a second embodiment, the same ice-covered electrode can be employed to form powdered metals.

The diversity of ice algal communities on the Greenland Ice Sheet as revealed by oligotyping

PubMed Central

Lutz, Stefanie; McCutcheon, Jenine; McQuaid, James B.; Benning, Liane G.

2018-01-01

The Arctic is being disproportionally affected by climate change compared with other geographic locations, and is currently experiencing unprecedented melt rates. The Greenland Ice Sheet (GrIS) can be regarded as the largest supraglacial ecosystem on Earth, and ice algae are the dominant primary producers on bare ice surfaces throughout the course of a melt season. Ice-algal-derived pigments cause a darkening of the ice surface, which in turn decreases albedo and increases melt rates. The important role of ice algae in changing melt rates has only recently been recognized, and we currently know little about their community compositions and functions. Here, we present the first analysis of ice algal communities across a 100 km transect on the GrIS by high-throughput sequencing and subsequent oligotyping of the most abundant taxa. Our data reveal an extremely low algal diversity with Ancylonema nordenskiöldii and a Mesotaenium species being by far the dominant taxa at all sites. We employed an oligotyping approach and revealed a hidden diversity not detectable by conventional clustering of operational taxonomic units and taxonomic classification. Oligotypes of the dominant taxa exhibit a site-specific distribution, which may be linked to differences in temperatures and subsequently the extent of the melting. Our results help to better understand the distribution patterns of ice algal communities that play a crucial role in the GrIS ecosystem. PMID:29547098

Antarctic glacial history from numerical models and continental margin sediments

USGS Publications Warehouse

Barker, P.F.; Barrett, P.J.; Cooper, A. K.; Huybrechts, P.

1999-01-01

The climate record of glacially transported sediments in prograded wedges around the Antarctic outer continental shelf, and their derivatives in continental rise drifts, may be combined to produce an Antarctic ice sheet history, using numerical models of ice sheet response to temperature and sea-level change. Examination of published models suggests several preliminary conclusions about ice sheet history. The ice sheet's present high sensitivity to sea-level change at short (orbital) periods was developed gradually as its size increased, replacing a declining sensitivity to temperature. Models suggest that the ice sheet grew abruptly to 40% (or possibly more) of its present size at the Eocene-Oligocene boundary, mainly as a result of its own temperature sensitivity. A large but more gradual middle Miocene change was externally driven, probably by development of the Antarctic Circumpolar Current (ACC) and Polar Front, provided that a few million years' delay can be explained. The Oligocene ice sheet varied considerably in size and areal extent, but the late Miocene ice sheet was more stable, though significantly warmer than today's. This difference probably relates to the confining effect of the Antarctic continental margin. Present-day numerical models of ice sheet development are sufficient to guide current sampling plans, but sea-ice formation, polar wander, basal topography and ice streaming can be identified as factors meriting additional modelling effort in the future.

How sea ice could be the cold beating heart of European weather

NASA Astrophysics Data System (ADS)

Margrethe Ringgaard, Ida; Yang, Shuting; Hesselbjerg Christensen, Jens; Kaas, Eigil

2017-04-01

The possibility that the ongoing rapid demise of Arctic sea ice may instigate abrupt changes is, however, not tackled by current research in general. Ice cores from the Greenland Ice Sheet (GIS) show clear evidence of past abrupt warm events with up to 15 degrees warming in less than a decade, most likely triggered by rapid disappearance of Nordic Seas sea ice. At present, both Arctic Sea ice and the GIS are in strong transformation: Arctic sea-ice cover has been retreating during most of the satellite era and in recent years, Arctic sea ice experienced a dramatic reduction and the summer extent was in 2012 and 2016 only half of the 1979-2000 average. With such dramatic change in the current sea ice coverage as a point of departure, several studies have linked reduction in wintertime sea ice in the Barents-Kara seas to cold weather anomalies over Europe and through large scale tele-connections to regional warming elsewhere. Here we aim to investigate if, and how, Arctic sea ice impacts European weather, i.e. if the Arctic sea ice works as the 'cold heart' of European weather. To understand the effects of the sea ice reduction on the full climate system, a fully-coupled global climate model, EC-Earth, is used. A new energy-conserving method for assimilating sea ice using the sensible heat flux is implemented in the coupled climate model and compared to the traditional, non-conserving, method of assimilating sea ice. Using this new method, experiments are performed with reduced sea ice cover in the Barents-Kara seas under both warm and cold conditions in Europe. These experiments are used to evaluate how the Arctic sea ice modulates European winter weather under present climate conditions with a view towards favouring both relatively cold and warm conditions.

Luminescence dating of paleolake deltas and glacial deposits in Garwood Valley, Antarctica: Implications for climate, Ross ice sheet dynamics, and paleolake duration

USGS Publications Warehouse

Levy, Joseph S.; Rittenour, Tammy M.; Fountain, Andrew G.; O'Connor, Jim E.

2017-01-01

The formation of perched deltas and other lacustrine deposits in the McMurdo Dry Valleys of Antarctica is widely considered to be evidence of valley-filling lakes dammed by the grounded Ross Sea ice sheet during the local Last Glacial Maximum, with lake drainage interpreted as a record of grounding line retreat. We used luminescence dating to determine the age of paleolake deltas and glacial tills in Garwood Valley, a coastal dry valley that opens to the Ross Sea. Luminescence ages are stratigraphically consistent with radiocarbon results from algal mats within the same delta deposits but suggest radiocarbon dates from lacustrine carbonates may overestimate deposit ages by thousands of years. Results suggest that late Holocene delta deposition into paleolake Howard in Garwood Valley persisted until ca. 3.5 ka. This is significantly younger than the date when grounded ice is thought to have retreated from the Ross Sea. Our evidence suggests that the local, stranded ice-cored till topography in Garwood Valley, rather than regional ice-sheet dynamics, may have controlled lake levels for some McMurdo Dry Valleys paleolakes. Age control from the supraglacial Ross Sea drift suggests grounding and up-valley advance of the Ross Sea ice sheet into Garwood valley during marine oxygen isotope stage (MIS) 4 (71–78 ka) and the local Last Glacial Maximum (9–10 ka). This work demonstrates the power of combining luminescence dating with existing radiocarbon data sets to improve understanding of the relationships among paleolake formation, glacial position, and stream discharge in response to climate change.

Development of a novel nanoscratch technique for quantitative measurement of ice adhesion strength

NASA Astrophysics Data System (ADS)

Loho, T.; Dickinson, M.

2018-04-01

The mechanism for the way that ice adheres to surfaces is still not well understood. Currently there is no standard method to quantitatively measure how ice adheres to surfaces which makes ice surface studies difficult to compare. A novel quantitative lateral force adhesion measurement at the micro-nano scale for ice was created which shears micro-nano sized ice droplets (less than 3 μm in diameter and 100nm in height) using a nanoindenter. By using small ice droplets, the variables associated with bulk ice measurements were minimised which increased data repeatability compared to bulk testing. The technique provided post- testing surface scans to confirm that the ice had been removed and that measurements were of ice adhesion strength. Results show that the ice adhesion strength of a material is greatly affected by the nano-scale surface roughness of the material with rougher surfaces having higher ice adhesion strength.

Implications of 36Cl exposure ages from Skye, northwest Scotland for the timing of ice stream deglaciation and deglacial ice dynamics

NASA Astrophysics Data System (ADS)

Small, David; Rinterknecht, Vincent; Austin, William E. N.; Bates, Richard; Benn, Douglas I.; Scourse, James D.; Bourlès, Didier L.; Hibbert, Fiona D.

2016-10-01

Geochronological constraints on the deglaciation of former marine based ice streams provide information on the rates and modes by which marine based ice sheets have responded to external forcing factors such as climate change. This paper presents new 36Cl cosmic ray exposure dating from boulders located on two moraines (Glen Brittle and Loch Scavaig) in southern Skye, northwest Scotland. Ages from the Glen Brittle moraines constrain deglaciation of a major marine terminating ice stream, the Barra-Donegal Ice Stream that drained the former British-Irish Ice Sheet, depending on choice of production method and scaling model this occurred 19.9 ± 1.5-17.6 ± 1.3 ka ago. We compare this timing of deglaciation to existing geochronological data and changes in a variety of potential forcing factors constrained through proxy records and numerical models to determine what deglaciation age is most consistent with existing evidence. Another small section of moraine, the Scavaig moraine, is traced offshore through multibeam swath-bathymetry and interpreted as delimiting a later stillstand/readvance stage following ice stream deglaciation. Additional cosmic ray exposure dating from the onshore portion of this moraine indicate that it was deposited 16.3 ± 1.3-15.2 ± 0.9 ka ago. When calculated using the most up-to-date scaling scheme this time of deposition is, within uncertainty, the same as the timing of a widely identified readvance, the Wester Ross Readvance, observed elsewhere in northwest Scotland. This extends the area over which this readvance has potentially occurred, reinforcing the view that it was climatically forced.

Lateglacial retreat chronology of the Scandinavian Ice Sheet in Finnmark, northern Norway, reconstructed from surface exposure dating of major end moraines

NASA Astrophysics Data System (ADS)

Romundset, Anders; Akçar, Naki; Fredin, Ola; Tikhomirov, Dmitry; Reber, Regina; Vockenhuber, Christof; Christl, Marcus; Schlüchter, Christian

2017-12-01

We report results from a comprehensive surface exposure dating campaign in eastern Finnmark, located in the northernmost part of Norway and close to the Norwegian-Russian border. This is a palaeo-glaciologically important region as it sits near the proposed border-zone between the former Scandinavian and Barents Sea Ice Sheets. However, until now the deglaciation history has few direct dates onshore and the chronology of ice front retreat is instead found by correlating ice-marginal deposits with isostatically raised shorelines and marine sediment cores. We measured the content of 10Be (N = 22) and 36Cl (N = 17) from boulders located at the crest of major moraine ridges at four localities; Kjæs, Kongsfjorden, Vardø and Kirkenes. These are key localities of existing regional reconstructions of ice recession in this area. Despite some spread in age results from each locality due to methodological challenges associated with surface exposure dating, the large numbers of samples from each site except Kjæs still allow for obtaining clusters of similar ages which are used for arriving at a likely chronology of ice front retreat. Our results show that the Kongsfjorden and Vardø moraines were deposited 14.3 ± 1.7 ka and 13.6 ± 1.4 ka, respectively, and thus point to a Older Dryas age of the proposed 'Outer Porsanger' deglaciation sub-stage. Moraine ridges belonging to the 'Main' sub-stage near Kirkenes were dated to 11.9 ± 1.2 ka, corresponding well with the ice retreat chronology farther west in northern Norway and suggesting that the maximum Younger Dryas ice sheet extent was attained in the late Younger Dryas along a more than 500 km long stretch in northernmost Scandinavia.

Subsonic Aircraft Safety Icing Study

NASA Technical Reports Server (NTRS)

Jones, Sharon Monica; Reveley, Mary S.; Evans, Joni K.; Barrientos, Francesca A.

2008-01-01

NASA's Integrated Resilient Aircraft Control (IRAC) Project is one of four projects within the agency s Aviation Safety Program (AvSafe) in the Aeronautics Research Mission Directorate (ARMD). The IRAC Project, which was redesigned in the first half of 2007, conducts research to advance the state of the art in aircraft control design tools and techniques. A "Key Decision Point" was established for fiscal year 2007 with the following expected outcomes: document the most currently available statistical/prognostic data associated with icing for subsonic transport, summarize reports by subject matter experts in icing research on current knowledge of icing effects on control parameters and establish future requirements for icing research for subsonic transports including the appropriate alignment. This study contains: (1) statistical analyses of accident and incident data conducted by NASA researchers for this "Key Decision Point", (2) an examination of icing in other recent statistically based studies, (3) a summary of aviation safety priority lists that have been developed by various subject-matter experts, including the significance of aircraft icing research in these lists and (4) suggested future requirements for NASA icing research. The review of several studies by subject-matter experts was summarized into four high-priority icing research areas. Based on the Integrated Resilient Aircraft Control (IRAC) Project goals and objectives, the IRAC project was encouraged to conduct work in all of the high-priority icing research areas that were identified, with the exception of the developing of methods to sense and document actual icing conditions.

NASA,FAA,ONERA Swept-Wing Icing and Aerodynamics: Summary of Research and Current Status

NASA Technical Reports Server (NTRS)

Broeren, Andy

2015-01-01

NASA, FAA, ONERA, and other partner organizations have embarked on a significant, collaborative research effort to address the technical challenges associated with icing on large scale, three-dimensional swept wings. These are extremely complex phenomena important to the design, certification and safe operation of small and large transport aircraft. There is increasing demand to balance trade-offs in aircraft efficiency, cost and noise that tend to compete directly with allowable performance degradations over an increasing range of icing conditions. Computational fluid dynamics codes have reached a level of maturity that they are being proposed by manufacturers for use in certification of aircraft for flight in icing. However, sufficient high-quality data to evaluate their performance on iced swept wings are not currently available in the public domain and significant knowledge gaps remain.

Evidence for an ice shelf covering the central Arctic Ocean during the penultimate glaciation

PubMed Central

Jakobsson, Martin; Nilsson, Johan; Anderson, Leif; Backman, Jan; Björk, Göran; Cronin, Thomas M.; Kirchner, Nina; Koshurnikov, Andrey; Mayer, Larry; Noormets, Riko; O'Regan, Matthew; Stranne, Christian; Ananiev, Roman; Barrientos Macho, Natalia; Cherniykh, Denis; Coxall, Helen; Eriksson, Björn; Flodén, Tom; Gemery, Laura; Gustafsson, Örjan; Jerram, Kevin; Johansson, Carina; Khortov, Alexey; Mohammad, Rezwan; Semiletov, Igor

2016-01-01

The hypothesis of a km-thick ice shelf covering the entire Arctic Ocean during peak glacial conditions was proposed nearly half a century ago. Floating ice shelves preserve few direct traces after their disappearance, making reconstructions difficult. Seafloor imprints of ice shelves should, however, exist where ice grounded along their flow paths. Here we present new evidence of ice-shelf groundings on bathymetric highs in the central Arctic Ocean, resurrecting the concept of an ice shelf extending over the entire central Arctic Ocean during at least one previous ice age. New and previously mapped glacial landforms together reveal flow of a spatially coherent, in some regions >1-km thick, central Arctic Ocean ice shelf dated to marine isotope stage 6 (∼140 ka). Bathymetric highs were likely critical in the ice-shelf development by acting as pinning points where stabilizing ice rises formed, thereby providing sufficient back stress to allow ice shelf thickening. PMID:26778247

The Holocene and the Late Deglaciation: timing and development on the northern Svalbard margin

NASA Astrophysics Data System (ADS)

Slubowska, M. A.; Koc, N.; Rasmussen, T. L.

2002-12-01

Svalbard is located in the high Arctic (76§ to 81§ N and 10§ to 28§ E) at the northernmost reach of the warmer West Spitsbergen Current, which forms the continuation of the North Atlantic Current. At this position, close to the Polar Front, even small variations in the current are expected to have large effects on the regional climate. Therefore, the Svalbard area is ideal for monitoring past changes in the ocean circulation as well as the timing and the nature of the Svalbard ice sheet disintegration. We have investigated core NP94-51 SC2 (80§ 21,346 N, 16§ 17,970 E, 400m water depth and 714 cm long) retrieved from the mouth of the Hinlopen Strait in the Arctic Ocean, north of Svalbard. The main objective of this study is to document a) the deglaciation history of the area, b) the Holocene climate variability on the decadal time scales using sedimentological, physical and biological analysis. AMS-14C dating gives the age of approximately 14,000 BP for the bottom of the core. The Holocene interglacial is represented by c. 5 m. A detailed analysis of different oceanographic proxies such as: ice rafted debris, magnetic susceptibility, spectral reflectance (L*a*b scale), benthic and planktic foraminiferal fauna, diatom flora, grain size and radiocarbon dates (AMS-14C) were used to reconstruct the paleoceanographic evolution of the area. The results show that disintegration of the Hinlopen Strait ice sheet and, possibly, the northern margin of the Svalbard ice sheet began at 14,000 BP. The influx of the subsurface Atlantic waters into the area began during the Bolling interstadial at 12,600 BP, while the surface waters were still cold and of low salinity. The retreat of the sea ice cover occurred together with the opening of the surface waters at 10,800 BP. During major part of the Younger Dryas (10,800 - 10,000 BP) the Polar Front was located close to the core site. At 10,100 BP the Polar Front retreated from that area. In comparison to the deglaciation, preliminary results of grain sizes, magnetic susceptibility and reflectance from the Holocene period indicate relatively low variability in the environmental conditions.

The little ice age and medieval warm period in the Sargasso Sea

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keigwin, L.D.

1996-11-29

Sea surface temperature (SST), salinity, and flux of terrigenous material oscillated on millennial time scales in the Pleistocene North Atlantic, but there are few records of Holocene variability. Because of high rates of sediment accumulation, Holocene oscillations are well documented in the northern Sargasso Sea. Results from a radiocarbondated box core show that SST was {approximately} 1{degree}C cooler than today {approximately} 400 years ago (the Little Ice Age) and 1700 years ago, and {approximately} 1{degree}C warmer than today 1000 years ago (the Medieval Warm Period). Thus, at least some of the warming since the Little Ice Age appears to bemore » part of a natural oscillation. 39 refs., 4 figs., 1 tab.« less

Ice Accretions and Icing Effects for Modern Airfoils

NASA Technical Reports Server (NTRS)

Addy, Harold E., Jr.

2000-01-01

Icing tests were conducted to document ice shapes formed on three different two-dimensional airfoils and to study the effects of the accreted ice on aerodynamic performance. The models tested were representative of airfoil designs in current use for each of the commercial transport, business jet, and general aviation categories of aircraft. The models were subjected to a range of icing conditions in an icing wind tunnel. The conditions were selected primarily from the Federal Aviation Administration's Federal Aviation Regulations 25 Appendix C atmospheric icing conditions. A few large droplet icing conditions were included. To verify the aerodynamic performance measurements, molds were made of selected ice shapes formed in the icing tunnel. Castings of the ice were made from the molds and placed on a model in a dry, low-turbulence wind tunnel where precision aerodynamic performance measurements were made. Documentation of all the ice shapes and the aerodynamic performance measurements made during the icing tunnel tests is included in this report. Results from the dry, low-turbulence wind tunnel tests are also presented.

Mechanisms resulting in accreted ice roughness

NASA Technical Reports Server (NTRS)

Bilanin, Alan J.; Chua, Kiat

1992-01-01

Icing tests conducted on rotating cylinders in the BF Goodrich's Icing Research Facility indicate that a regular, deterministic, icing roughness pattern is typical. The roughness pattern is similar to kernels of corn on a cob for cylinders of diameter typical of a cob. An analysis is undertaken to determine the mechanisms which result in this roughness to ascertain surface scale and amplitude of roughness. Since roughness and the resulting augmentation of the convected heat transfer coefficient has been determined to most strongly control the accreted ice in ice prediction codes, the ability to predict a priori, location, amplitude and surface scale of roughness would greatly augment the capabilities of current ice accretion models.

Ice-sheet mass balance and climate change.

PubMed

Hanna, Edward; Navarro, Francisco J; Pattyn, Frank; Domingues, Catia M; Fettweis, Xavier; Ivins, Erik R; Nicholls, Robert J; Ritz, Catherine; Smith, Ben; Tulaczyk, Slawek; Whitehouse, Pippa L; Zwally, H Jay

2013-06-06

Since the 2007 Intergovernmental Panel on Climate Change Fourth Assessment Report, new observations of ice-sheet mass balance and improved computer simulations of ice-sheet response to continuing climate change have been published. Whereas Greenland is losing ice mass at an increasing pace, current Antarctic ice loss is likely to be less than some recently published estimates. It remains unclear whether East Antarctica has been gaining or losing ice mass over the past 20 years, and uncertainties in ice-mass change for West Antarctica and the Antarctic Peninsula remain large. We discuss the past six years of progress and examine the key problems that remain.

Instructional Basics: Oppelt Standard Method of Therapeutic and Recreational Ice Skating.

ERIC Educational Resources Information Center

Oppelt, Kurt

Detailed in the booklet is the standard ice skating method and considered are the benefits of therapeutic ice skating for the handicapped and aged. Values for the mentally retarded and physically handicapped are seen to include physiological (such as increased flexibility and improved posture), psychological (including satifaction and enhanced…

Seasonal surface layer dynamics and sensitivity to runoff in a high Arctic fjord (Young Sound/Tyrolerfjord, 74°N)

NASA Astrophysics Data System (ADS)

Bendtsen, Jørgen; Mortensen, John; Rysgaard, Søren

2014-09-01

Runoff from the Greenland Ice Sheet, local glaciers, and snowmelt along the northeastern Greenland coastline has a significant impact on coastal water masses flowing south toward Denmark Strait. Very few direct measurements of runoff currently exist in this large area, and the water masses near the coast are also difficult to measure due to the presence of icebergs and sea ice. Measurements from the Zackenberg Research station, located in Young Sound/Tyrolerfjord in northeast Greenland (74°N), provide some of the few observations of hydrographic, hydrologic, and atmospheric parameters from this remote area. Here we analyze measurements from the fjord and also measurements in the ambient water masses, which are found in the outer fjord and between the fjord and the East Greenland Current and validate and apply a numerical model of the fjord. A model sensitivity study allows us to constrain runoff estimates for the area. We also show that a total runoff between 0.9 and 1.4 km3 in 2006 is in accordance with observed surface salinities and calculated freshwater content in the fjord. This indicates that earlier reported runoff to the area is significantly underestimated and that melt from glaciers and the Greenland Ice Sheet in this region may be up to 50% larger than the current estimate. Model simulations indicate the presence of a cold low-saline coastal water mass formed by runoff from fjords north of the Young Sound/Tyrolerfjord system. Simulations of passive and age tracers show that residence time of river water during the summer period is about 1 month in the inner part of the fjord. This article was corrected on 10 OCT 2014. See the end of the full text for details.

Ice stream behaviour in the western sector of the North Sea during the end of the last glacial cycle

NASA Astrophysics Data System (ADS)

Roberts, David; Evans, David; Clark, Chris; Bateman, Mark; Livingstone, Stephen; Medialdea, Alicia; Cofaigh, Colm O.; Grimoldi, Elena; Callard, Louise; Dove, Dayton; Stewart, Heather; Davies, Bethan; Chiverell, Richard

2016-04-01

During the last glacial cycle the East coast of the UK was overrun by the British-Irish Ice Sheet (BIIS) flowing eastwards and southwards. In recent years it has become evident that several ice streams including the Tweed, Tyne, and Stainmore Gap ice streams, as well as the late stage North Sea Lobe (NSL), all played a role in shaping the glacial landscape during this period, but understanding the flow phasing of these ice streams during advance and collapse has proved challenging. Here we present new data from the seafloor collected during recent work undertaken by the Britice Chrono and Glanam project teams during cruise JC123 in the North Sea. Sub-bottom seafloor data together with new swath data clearly show that the final phases of the collapse of the NSL were controlled by ice sourced from the Firth of Forth ice stream which deglaciated in a NNW trajectory. Other ice streams being fed from the west (e.g. Stainmore, Tyne, Tweed) were not influential in final phase ice retreat from the southern North Sea. The Forth ice imprint is characterised by several grounding zone/till wedges marking dynamic, oscillatory retreat of the ice as it retreated along an offshore corridor between North Yorkshire and Northumberland. Repeated packages of tills, ice marginal and glaciomarine sediments, which drape glacially scoured bedrock terrain and drumlins along this corridor, point to marine inundation accompanying ice retreat. New TCN ages suggest decoupling of the Tyne Gap ice stream and NSL between 17.8 and 16.5 ka and this coincides with rapid, regional collapse of the NSL between 17.2 and 16.0 ka along the Yorkshire and Durham coasts (new OSL ages; Britice Chrono). Hence, both the central and northern sectors of the BIIS were being strongly influenced by marine margin instability during the latter phases of the last glacial cycle.

Debris-Covered Glaciers in Antarctica: Analogs for Viscous-Flow Features on Mars

NASA Astrophysics Data System (ADS)

Marchant, D. R.; Phillips, W. M.; Schaefer, J.; Fastook, J.; Landis, G.

2007-12-01

The McMurdo Dry Valleys (MDV) are generally classified as a hyper-arid, cold-polar desert. Subtle variations in climate parameters throughout the region result in considerable differences in the distribution, origin, and morphology of buried ice. In the coastal thaw zone, near-surface buried ice experiences seasonal melt and may have formed where pore water from surface snowmelt freezes underground (segregation ice). Characteristic landforms associated with this type of buried ice include thermokarst, shallow planar slides, and solifluction. In contrast, in the coldest and driest regions of the MDV, the stable upland zone, there is insufficient meltwater to produce extensive segregation ice. Rather, widespread buried ice in this zone is typically glacier ice. Temperature data indicate that ice remains frozen in this zone if buried beneath ~15 cm of debris. The Mullins-valley debris-covered glacier, which lies within the stable upland zone, contains ancient glacier ice beneath a thin layer of sublimation till. Four independent dating techniques confirm that the glacier age ranges from ~10 ka near the valley head, to >8 Ma at its diffuse terminus in central Beacon Valley. The dating methods include cosmogenic-nuclide analyses of surface boulders; horizontal ice-flow velocities as determined from synthetic aperture radar interferometry; 40Ar/39Ar analyses of in-situ ash fall in relict polygon troughs at the till surface; and numerical ice-flow models. Age results so derived are in accord with measured variations in ancient community DNA extracted from pristine ice samples along the length of the glacier. Multi- channel seismic and ground-penetrating radar surveys demonstrate that the ice is relatively clean and that it averages from ~45 m to ~150 m thick. Morphologic comparisons of the Mullins Valley debris-covered glacier are used to shed light on the origin and modification of near-surface ice on Mars.

Interaction of ice storms and management practices on current carbon sequestration in forests with potential mitigation under future CO2 atmosphere

Treesearch

Heather R. McCarthy; Ram Oren; Hyun-Seok Kim; Kurt H. Johnsen; Chris Maier; Seth G. Pritchard; Michael A. Davis

2006-01-01

Ice storms are disturbance events with potential impacts on carbon sequestration. Common forest management practices, such as fertilization and thinning, can change wood and stand properties and thus may change vulnerability to ice storm damage. At the same time, increasing atmospheric CO2 levels may also influence ice storm vulnerability. Here...

Ice sheet systems and sea level change.

NASA Astrophysics Data System (ADS)

Rignot, E. J.

2015-12-01

Modern views of ice sheets provided by satellites, airborne surveys, in situ data and paleoclimate records while transformative of glaciology have not fundamentally changed concerns about ice sheet stability and collapse that emerged in the 1970's. Motivated by the desire to learn more about ice sheets using new technologies, we stumbled on an unexplored field of science and witnessed surprising changes before realizing that most were coming too fast, soon and large. Ice sheets are integrant part of the Earth system; they interact vigorously with the atmosphere and the oceans, yet most of this interaction is not part of current global climate models. Since we have never witnessed the collapse of a marine ice sheet, observations and exploration remain critical sentinels. At present, these observations suggest that Antarctica and Greenland have been launched into a path of multi-meter sea level rise caused by rapid climate warming. While the current loss of ice sheet mass to the ocean remains a trickle, every mm of sea level change will take centuries of climate reversal to get back, several major marine-terminating sectors have been pushed out of equilibrium, and ice shelves are irremediably being lost. As glaciers retreat from their salty, warm, oceanic margins, they will melt away and retreat slower, but concerns remain about sea level change from vastly marine-based sectors: 2-m sea level equivalent in Greenland and 23-m in Antarctica. Significant changes affect 2/4 marine-based sectors in Greenland - Jakobshavn Isb. and the northeast stream - with Petermann Gl. not far behind. Major changes have affected the Amundsen Sea sector of West Antarctica since the 1980s. Smaller yet significant changes affect the marine-based Wilkes Land sector of East Antarctica, a reminder that not all marine-based ice is in West Antarctica. Major advances in reducing uncertainties in sea level projections will require massive, interdisciplinary efforts that are not currently in place but are getting there. Projection scenarios are overwhelmingly conservative, pushed up by observations, awaiting more detailed knowledge of ocean circulation, winds, ice-ocean interaction, and mechanics of rapid ice fracture, not to mention the mere definition of static boundaries (ice thickness and sea floor bathymetry).

Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages.

USGS Publications Warehouse

Croft, S.K.; Kieffer, S.W.; Ahrens, T.J.

1979-01-01

We produced a series of decimeter-sized impact craters in blocks of ice near 0oC and -70oC and in ice-saturated sand near -70oC as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar satellites. Crater diameters in the ice-saturated sand were 2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were c.3 times larger. Martian impact crater energy versus diameter scaling may thus be a function of latitude. -from Authors

Glaciers of Greenland

USGS Publications Warehouse

Williams, Richard S.; Ferrigno, Jane G.

1995-01-01

Landsat imagery, combined with aerial photography, sketch maps, and diagrams, is used as the basis for a description of the geography, climatology, and glaciology, including mass balance, variation, and hazards, of the Greenland ice sheet and local ice caps and glaciers. The Greenland ice sheet, with an estimated area of 1,736,095+/-100 km2 and volume of 2,600,000 km3, is the second largest glacier on the planet and the largest relict of the Ice Age in the Northern Hemisphere. Greenland also has 48,599+/-100 km2 of local ice caps and other types of glaciers in coastal areas and islands beyond the margin of the ice sheet.

A comparison of ringed and bearded seal diet, condition and productivity between historical (1975-1984) and recent (2003-2012) periods in the Alaskan Bering and Chukchi seas

NASA Astrophysics Data System (ADS)

Crawford, Justin A.; Quakenbush, Lori T.; Citta, John J.

2015-08-01

Reductions in summer sea ice in the Chukchi and Beaufort seas are expected to affect what has been an ice-adapted marine food web in the Pacific Arctic. To determine whether recent decreases in sea ice have affected ice-associated marine predators (i.e., ringed, Pusa hispida, and bearded seals, Erignathus barbatus) in the Bering and Chukchi seas we compared diet, body condition, growth, productivity, and the proportion of pups harvested (an index of weaning success) for seals of each species harvested by 11 Alaskan villages during two periods; a historical (1975-1984) and a recent period (2003-2012). We also examined how changes in indices of seal health may be correlated with the reduction of sea ice characteristic of the recent period. For ringed seals ⩾1 year of age, the % frequency of occurrence (%FO) of Arctic cod (Boreogadus saida), walleye pollock (Gadus chalcogramma), rainbow smelt (Osmerus mordax), and Pacific herring (Clupea pallasi) increased from the historic to the recent period, while the %FO of invertebrates decreased for both pups and seals ⩾1 year of age. For bearded seals ⩾1 year of age, the %FO of Arctic cod, pricklebacks, and flatfish increased during the recent period, while the %FO of saffron cod (Eleginus gracilis) decreased for pups. Although invertebrates did not change overall for either age class, decreases occurred in 10 of 24 specific prey categories, for bearded seals ⩾1 year of age; only echiurids increased. The %FO of gastropods and bivalves increased for pups while isopods and one species of shrimp and crab decreased in occurrence. During the recent period ringed seals grew faster, had thicker blubber, had no change in pregnancy rate, matured 2 years earlier, and a larger proportion of pups was harvested than during the historical period. Correlations with spring ice concentration showed that the growth and blubber thickness of seals ⩾1 year of age, blubber thickness of pups, and the proportion of pups in the harvest all declined for ringed seals when ice concentrations were higher in the historic period. However, only the correlations between high ice concentrations and growth of ringed seals ⩾1 year of age and the proportion of ringed seal pups in the harvest were statistically significant. Although growth of bearded seals ⩾1 year of age was slower during the recent period, it was similar to the average over the entire time series, and blubber thickness increased. Pup growth and blubber thickness did not change between periods. There was no change in pregnancy rate, but females matured 1.6 years earlier, and a larger proportion of pups were harvested. Correlations with spring ice concentration showed that the growth of seals ⩾1 year of age, the growth of pups, blubber thickness of pups, and proportion of pups in the harvest also declined for bearded seals when sea ice concentrations were higher. However, no relationships between bearded seals and sea ice were statistically significant. Overall, our results suggest that ringed seals in the Alaskan Bering and Chukchi seas have adjusted to changes in diet, are growing faster and possibly weaning more pups in the recent compared to the historic period. These patterns are less evident for bearded seals. Although the ringed and bearded seals we examined have not exhibited the declines in body condition, growth, or reproduction observed in other populations, continued monitoring and comparison among seal populations is vital to understanding the effects of changing environmental conditions in the Pacific Arctic region.

Towards multi-decadal to multi-millennial ice core records from coastal west Greenland ice caps

NASA Astrophysics Data System (ADS)

Das, Sarah B.; Osman, Matthew B.; Trusel, Luke D.; McConnell, Joseph R.; Smith, Ben E.; Evans, Matthew J.; Frey, Karen E.; Arienzo, Monica; Chellman, Nathan

2017-04-01

The Arctic region, and Greenland in particular, is undergoing dramatic change as characterized by atmospheric warming, decreasing sea ice, shifting ocean circulation patterns, and rapid ice sheet mass loss, but longer records are needed to put these changes into context. Ice core records from the Greenland ice sheet have yielded invaluable insight into past climate change both regionally and globally, and provided important constraints on past surface mass balance more directly, but these ice cores are most often from the interior ice sheet accumulation zone, at high altitude and hundreds of kilometers from the coast. Coastal ice caps, situated around the margins of Greenland, have the potential to provide novel high-resolution records of local and regional maritime climate and sea surface conditions, as well as contemporaneous glaciological changes (such as accumulation and surface melt history). But obtaining these records is extremely challenging. Most of these ice caps are unexplored, and thus their thickness, age, stratigraphy, and utility as sites of new and unique paleoclimate records is largely unknown. Access is severely limited due to their high altitude, steep relief, small surface area, and inclement weather. Furthermore, their relatively low elevation and marine moderated climate can contribute to significant surface melting and degradation of the ice stratigraphy. We recently targeted areas near the Disko Bay region of central west Greenland where maritime ice caps are prevalent but unsampled, as potential sites for new multi-decadal to multi-millennial ice core records. In 2014 & 2015 we identified two promising ice caps, one on Disko Island (1250 m. asl) and one on Nuussuaq Peninsula (1980 m. asl) based on airborne and ground-based geophysical observations and physical and glaciochemical stratigraphy from shallow firn cores. In spring 2015 we collected ice cores at both sites using the Badger-Eclipse electromechanical drill, transported by a medley of small fixed wing and helicopter aircraft, and working out of small tent camps. On Disko Island, despite high accumulation rates and ice thickness of 250 meters, drilling was halted twice due to the encounter of liquid water at depths ranging from 18-20 meters, limiting the depth of the final core to 21 m, providing a multi-decadal record (1980-2015.) On Nuussuaq Peninsula, we collected a 138 m ice core, almost to bedrock, representing a 2500 year record. The ice cores were subsequently analyzed using a continuous flow analysis system (CFA). Age-depth profiles and accumulation histories were determined by combining annual layer counting and an ice flow thinning model, both constrained by glaciochemical tie points to other well-dated Greenland ice core records (e.g. volcanic horizons and continuous heavy metal records). Here we will briefly provide an overview of the project and the new sites, and the novel dating methodology, and describe the latest stratigraphic, isotopic and glaciochemical results. We will also provide a particular focus on new regional climatological insight gained from our records during three climatically sensitive time periods: the late 20th & early 21st centuries; the Little Ice Age; and the Medieval Climate Anomaly.

Subdivision of Glacial Deposits in Southeastern Peru Based on Pedogenic Development and Radiometric Ages

NASA Astrophysics Data System (ADS)

Goodman, Adam Y.; Rodbell, Donald T.; Seltzer, Geoffrey O.; Mark, Bryan G.

2001-07-01

The Cordillera Vilcanota and Quelccaya Ice Cap region of southern Peru (13°30‧-14°00‧S; 70°40‧-71°25‧W) contains a detailed record of late Quaternary glaciation in the tropical Andes. Quantification of soil development on 19 moraine crests and radiocarbon ages are used to reconstruct the glacial history. Secondary iron and clay increase linearly in Quelccaya soils and clay accumulates at a linear rate in Vilcanota soils, which may reflect the semicontinuous addition of eolian dust enriched in secondary iron to all soils. In contrast, logarithmic rates of iron buildup in soils in the Cordillera Vilcanota reflect chemical weathering; high concentrations of secondary iron in Vilcanota tills may mask the role of eolian input to these soils. Soil-age estimates from extrapolation of field and laboratory data suggest that the most extensive late Quaternary glaciation occurred >70,000 yr B.P. This provides one of the first semiquantitative age estimates for maximum ice extent in southern Peru and is supported by a minimum-limiting age of ∼41,520 14C yr B.P. A late glacial readvance culminated ∼16,650 cal yr B.P. in the Cordillera Vilcanota. Following rapid deglaciation of unknown extent, an advance of the Quelccaya Ice Cap occurred between ∼13,090 and 12,800 cal yr B.P., which coincides approximately with the onset of the Younger Dryas cooling in the North Atlantic region. Moraines deposited <394 cal yr B.P. in the Cordillera Vilcanota and <300 cal yr B.P. on the west side of the Quelccaya Ice Cap correlate with Little Ice Age moraines of other regions.

Insights into accumulation variability over the last 2000 years at James Ross Island, Antarctic Peninsula

NASA Astrophysics Data System (ADS)

Massam, A.; Mulvaney, R.; McConnell, J.; Abram, N.; Arienzo, M. M.; Whitehouse, P. L.

2016-12-01

The James Ross Island ice core, drilled to 364 m on the northern tip of the Antarctic Peninsula, preserves a climate record that spans beyond the Holocene period to the end of the last glacial maximum (LGM). Reanalysis of the ice core using high-resolution continuous flow analysis (CFA) highlighted errors in the identification of events of known age that had been used to constrain the earlier chronology. The new JRI2 chronology is annual layer counted to 300 years, with the remaining profile reconstructed using a new age-depth model that is tied to age horizons identified in the annual-layer counted WAIS Divide ice core record. An accurate age-depth profile requires reliable known-age horizons along the ice core profile. In addition, these allow us to determine a solution for the accumulation history and rate of compaction due to vertical strain. The accuracy of the known-age constraints used in JRI2 allows only a small uncertainty in the reconstruction of the most recent 2000 years of accumulation variability. Independently, the surface temperature profile has been estimated from the stable water isotope profile and calibrated to borehole temperature observations. We present the accumulation, vertical thinning and temperature history interpreted from the James Ross Island ice core for the most recent 2000 years. JRI2 reconstructions show accumulation variability on a decadal to centennial timescale up to 20% from the present-day mean annual accumulation rate of 0.63 m yr-1. Analysis of the accumulation profile for James Ross Island offers insight into the sensitivity of accumulation to a change in surface temperature, as well as the reliability of the assumed relationship between accumulation and surface temperature in climate reconstructions using stable water isotope proxies.

Improvements in the chronology, geochemistry and correlation techniques of tephra in Antarctic ice

NASA Astrophysics Data System (ADS)

Iverson, N. A.; Dunbar, N. W.; McIntosh, W. C.; Pearce, N. J.; Kyle, P. R.

2013-12-01

Visible and crypto tephra layers found in West Antarctic ice provide an excellent record of Antarctic volcanism over the past 100ka. Tephra layers are deposited almost instantaneously across wide areas creating horizons that, if found in several locations, provide 'pinning points' to adjust ice time scales that may otherwise be lacking detailed chronology. Individual tephra layers can have distinct chemical fingerprints allowing them to correlate over great distances. Advances in sample preparation, geochemical analyses (major and trace elements) of fine grained tephra and higher precision 40Ar/39Ar dating of young (<100ka) proximal volcanic deposits are improving an already established tephra record in West Antarctica. Forty three of the potential hundreds of silicate layers found in a recently drilled deep West Antarctic Ice Sheet Divide core (WDC06A) have been analyzed for major elements and a subset for trace elements. Of these layers, at least 16 are homogenous tephra that could be correlated to other ice cores (e.g. Siple Dome, SDMA) and/or to source volcanoes found throughout Antarctica and even extra-continental eruptions (e.g. Sub-Antarctic islands and South America). Combining ice core tephra with those exposed in blue ice areas provide more locations to correlate widespread eruptions. For example, a period of heightened eruptive activity at Mt. Berlin, West Antarctica between 24 and 28ka produced a set of tephra layers that are found in WDC06A and SDMA ice cores, as well as at a nearby blue ice area at Mt. Moulton (BIT-151 and BIT-152). Possible correlative tephra layers are found at ice ages of 26.4, 26.9 and 28.8ka in WDC06A and 26.5, 27.0, and 28.7ka in SDMA cores. The geochemical similarities of major elements in these layers mean that ongoing trace element analyses will be vital to decipher the sequence of events during this phase of activity at Mt. Berlin. Sample WDC06A-2767.117 (ice age of 28.6×1.0ka) appears to correlate to blue ice tephra BIT-152 and to tephra layer SDMA-5683 (ice age of 28.5ka). This tephra layer also appears to be present in blue ice at Mt. Terra Nova on Ross Island, 1400km away, suggesting that it may be a possible to link ice cores in East Antarctica (e.g. Talos Dome and Law Dome). The amount of feldspar in ice core tephra is typically too small to be directly dated by 40Ar/39Ar method, making it very important to geochemically correlate these layers to proximal deposits where more and larger feldspar can be sampled. The correlation of WDC06A-2767.117 to the coarse, proximal BIT-152 provides one such link. The New Mexico Geochronology Research Lab (NMGRL) has two new multi-collector ARGUS VI mass spectrometers that can provide single crystal laser fusion ages that are approximately an order of magnitude more precise than the previous determinations. With these advancements in analytical technology, we hope to improve precision on 'pinning points' in the deep ice cores where annual layer counting becomes less precise.

The Geology of Pluto and Charon Through the Eyes of New Horizons

NASA Technical Reports Server (NTRS)

Moore, J. M.; McKinnon, W. B.; Spencer, J. R.; Howard, A. D.; Schenk, P. M.; Beyer, R. A.; Nimmo, F.; Singer, K. N.; Umurhan, O. M.; White, O. L.;

On a new species of Amphilochus from deep and cold Atlantic waters, with a note on the genus Amphilochopsis (Amphipoda, Gammaridea, Amphilochidae)

PubMed Central

Tandberg, Anne Helene S.; Vader, Wim

2018-01-01

Abstract Amphilochus manudens and Amphilochopsis hamatus are redescribed based on specimens from the BioIce, Mareano, and IceAGE programmes. The new species Amphilochus anoculus sp. n. is described based on material from the IceAGE programme and the preceding BioIce programme; it is separated from the closely related Amphilochus manudens by the absence of eyes, a symmetrically bilobed labrum, four setae on the maxilla 2 outer plate, a rounded corner of epimeral plate 3, and a robust seta at the tip of the telson. There are also clear differences in depth and temperature ranges. Amphilochopsis hamatus is shown to be closely related to Amphilochus manudens and A. anoculus and transferred to Amphilochus s. str. PMID:29416401

Comparative Study of Probiotic Ice Cream and Probiotic Drink on Salivary Streptococcus mutans Levels in 6-12 Years Age Group Children.

PubMed

Mahantesha, Taranatha; Reddy, K M Parveen; Kumar, N H Praveen; Nara, Asha; Ashwin, Devasya; Buddiga, Vinutna

2015-09-01

Dental caries is one of the most common health problems in the world. Probiotics are one the various preventive methods to reduce dental caries. The aim of this study is to compare the effectiveness of probiotic ice cream and drink on salivary Streptococcus mutans levels in children of 6-12 years age group. A three phase study was carried out in children (n = 50) of 6-12 years age with zero decayed missing filled teeth (dmft)/DMFT. They were randomly divided into two equal groups. Saliva samples were collected before the consumptions of probiotic ice cream and probiotic drink. Colony count obtained was recorded as baseline data. For both groups probiotic ice cream and drink was given randomly for 7 days and a washout period of 90 days were given and then the saliva samples were collected and colony counting was done. Statistical analysis was performed using Student's paired t-test and multiple comparisons by Tukey's honest significant difference test which showed, there is a significant reduction in salivary S. mutans level in both groups after 7 days period. However, after washout period only probiotic ice cream showed reduction whereas drink did not. Also, there was no significant difference between probiotic ice cream and drink. Probiotic organisms definitely have a role in reducing the salivary S. mutans level and ice cream would be a better choice than drink. However, the prolonged use of the agents and their effects on caries is still to be determined.

NASA/FAA Tailplane Icing Program Overview

NASA Technical Reports Server (NTRS)

Ratvasky, Thomas P.; VanZante, Judith Foss; Riley, James T.

1999-01-01

The effects of tailplane icing were investigated in a four-year NASA/FAA Tailplane Icing, Program (TIP). This research program was developed to improve the understanding, of iced tailplane aeroperformance and aircraft aerodynamics, and to develop design and training aides to help reduce the number of incidents and accidents caused by tailplane icing. To do this, the TIP was constructed with elements that included icing, wind tunnel testing, dry-air aerodynamic wind tunnel testing, flight tests, and analytical code development. This paper provides an overview of the entire program demonstrating the interconnectivity of the program elements and reports on current accomplishments.

Snow and ice in a changing hydrological world.

USGS Publications Warehouse

Meier, M.F.

1983-01-01

Snow cover on land (especially in the Northern Hemisphere) and sea ice (especially in the Southern Hemisphere) vary seasonally, and this seasonal change has an important affect on the world climate because snow and sea ice reflect solar radiation efficiently and affect other heat flow processes between atmosphere and land or ocean. Glaciers, including ice sheets, store most of the fresh water on Earth, but change dimensions relatively slowly. There is no clear evidence that the glacier ice volume currently is declining, but more needs to be known about mountain glacier and ice sheet mass balances. -from Author

Anti-icing Behavior of Thermally Sprayed Polymer Coatings

NASA Astrophysics Data System (ADS)

Koivuluoto, Heli; Stenroos, Christian; Kylmälahti, Mikko; Apostol, Marian; Kiilakoski, Jarkko; Vuoristo, Petri

2017-01-01

Surface engineering shows an increasing potential to provide a sustainable approach to icing problems. Currently, several passive anti-ice properties adoptable to coatings are known, but further research is required to proceed for practical applications. This is due to the fact that icing reduces safety, operational tempo, productivity and reliability of logistics, industry and infrastructure. An icing wind tunnel and a centrifugal ice adhesion test equipment can be used to evaluate and develop anti-icing and icephobic coatings for a potential use in various arctic environments, e.g., in wind power generation, oil drilling, mining and logistic industries. The present study deals with evaluation of icing properties of flame-sprayed polyethylene (PE)-based polymer coatings. In the laboratory-scale icing tests, thermally sprayed polymer coatings showed low ice adhesion compared with metals such as aluminum and stainless steel. The ice adhesion strength of the flame-sprayed PE coating was found to have approximately seven times lower ice adhesion values compared with metallic aluminum, indicating a very promising anti-icing behavior.

Timing and Rate of Deglaciation of the MIS 2 Cordilleran Ice Sheet in Yukon Territory

NASA Astrophysics Data System (ADS)

Ward, B. C.; Bond, J. D.; Gosse, J. C.; Turner, D. G.

2015-12-01

The northern Cordilleran ice sheet (CIS) consisted of a series of quasi-independent ice lobes that coalesced during the last glacial maximum (LGM) to form a continuous carapace of precipitation limited ice over southern Yukon. Variations in effective precipitation to different source areas of these ice lobes have been used to explain disparities in glacier extents in marine oxygen isotope stages (MIS) 4 and 6. Deglaciation of the northern margin of the CIS and its rate of recession from the LGM are poorly understood. We use cosmogenic nuclide exposure dating (10Be and 36Cl) on groups of 3-4 glacial erratics to reconstruct the timing and rate of deglaciation. Our sampling concentrated on the St. Elias, Cassiar and Selwyn lobes, as well an independent glacier from the Ogilvie Mountains. Boulders sampled up-ice from terminal moraines show that the initiation of deglaciation varied regionally. 36Cl ages from the Ogilvie Mountains indicate that deglaciation initiated by 24.8 ka. Further south in the Selwyn Lobe, two sites separated by ~150 km returned ages of 15.2 and 16.1 ka. To the south-west, three boulders from the Cassiar Lobe are 13.6 ka. Rates of deglaciation are best constrained for the Cassiar Lobe with two transects along different flow lines. Multiple valley bottom samples in the mid-deglaciation setting at Whitehorse yielded ages of 12.0 ka, while one boulder from the adjacent ridge top 600 m above is 13.5 ka. In the accumulation zone, ice-free conditions occurred by 10.8 ka. The other transect has higher elevation samples in a mid-deglaciation setting in the Pelly Mountains that indicate deglaciation occurred by 13.0 ka. Samples taken from high elevation and valley bottom sites close to accumulation zones of the Cassiar Lobe yielded ages of 13.6 and 11.0 ka, respectively. These results provide a chronology for the style of deglaciation interpreted from regional mapping throughout Yukon: gradual initial retreat and thinning marked by moraines, followed by rapid downwasting and regional stagnation. Thinning of the ice to expose uplands in the Cassiar lobe was coincident with margin retreat. The increase in rates of deglaciation after 12 ka fits well with mapped evidence of regional stagnation. These ages correspond to evidence in the north Pacific of rapid warming immediately after the Younger Dryas in the pre-Boreal.

Improved age constraints for the retreat of the Irish Sea Ice Stream

NASA Astrophysics Data System (ADS)

Smedley, Rachel; Chiverrell, Richard; Duller, Geoff; Scourse, James; Small, David; Fabel, Derek; Burke, Matthew; Clarke, Chris; McCarroll, Danny; McCarron, Stephen; O'Cofaigh, Colm; Roberts, David

2016-04-01

BRITICE-CHRONO is a large (> 45 researchers) consortium project working to provide an extensive geochronological dataset constraining the rate of retreat of a number of ice streams of the British-Irish Ice Sheet following the Last Glacial Maximum. When complete, the large empirical dataset produced by BRITICE-CHRONO will be integrated into model simulations to better understand the behaviour of the British-Irish Ice Sheet in response to past climate change, and provide an analogue for contemporary ice sheets. A major feature of the British-Irish Ice Sheet was the dynamic Irish Sea Ice Stream, which drained a large proportion of the ice sheet and extended to the proposed southern limit of glaciation upon the Isles of Scilly (Scourse, 1991). This study will focus on a large suite of terrestrial samples that were collected along a transect of the Irish Sea basin, covering the line of ice retreat from the Isles of Scilly (50°N) in the south, to the Isle of Man (54°N) in the north; a distance of 500 km. Ages are determined for both the eastern and western margins of the Irish Sea using single-grain luminescence dating (39 samples) and terrestrial cosmogenic nuclide dating (10 samples). A Bayesian sequence model is then used in combination with the prior information determined for deglaciation to integrate the geochronological datasets, and assess retreat rates for the Irish Sea Ice Stream. Scourse, J.D., 1991. Late Pleistocene stratigraphy and palaeobotany of the Isles of Scilly. Philosophical Transactions of the Royal Society of London B334, 405 - 448.

Modeling Pluto's Ice-Rich Surface and Its Interaction with Atmosphere

NASA Astrophysics Data System (ADS)

Wei, Q.; Hu, Y.

2016-12-01

Recent discoveries made available through NASA's New Horizon mission revealed a new world on Pluto with a plateau of "young" surface, the Sputnik Planum. It is a gigantic reservoir of volatile ice on top of an impact basin. The reason of such a high level of concentration of volatile ice is yet unknown. We are actively looking into explanations through atmospheric models and ice sheet models. Apart from the quantity of ice on SP, its surface age constrained by impact flux models to under 10Myr is significantly different from other parts of Pluto. Convection of solid nitrogen ice has been proposed as a viable cause. We endeavor to explore other possibilities that may have jointly contributed to this phenomena, including atmospheric condensation, ice sheet evolution, etc. Unique rheological properties of nitrogen ice, which is thought to dominate the Sputnik Planum, may hold the key to answering our questions. They are soft and easy to deform under its own weight even at Pluto's surface temperature of around 40K. Based on our initial simulations with numerical ice sheet models, we propose that once a crater is created on the Sputnik Planum, deformation under internal stress kicks in as a primary mechanism to flatten out craters. This could be done in a time scale of 100,000 years, significantly shorter than the maximum surface age contrained by crater densitiess models. As the surface arpproaches a flat state, such mechanism becomes weaker. The surface feature is then dominated by convection.

High response speed microfluidic ice valves with enhanced thermal conductivity and a movable refrigeration source

PubMed Central

Si, Chaorun; Hu, Songtao; Cao, Xiaobao; Wu, Weichao

2017-01-01

Due to their ease of fabrication, facile use and low cost, ice valves have great potential for use in microfluidic platforms. For this to be possible, a rapid response speed is key and hence there is still much scope for improvement in current ice valve technology. Therefore, in this study, an ice valve with enhanced thermal conductivity and a movable refrigeration source has been developed. An embedded aluminium cylinder is used to dramatically enhance the heat conduction performance of the microfluidic platform and a movable thermoelectric unit eliminates the thermal inertia, resulting in a faster cooling process. The proposed ice valve achieves very short closing times (0.37 s at 10 μL/min) and also operates at high flow rates (1150 μL/min). Furthermore, the response time of the valve decreased by a factor of 8 when compared to current state of the art technology. PMID:28084447

High response speed microfluidic ice valves with enhanced thermal conductivity and a movable refrigeration source

NASA Astrophysics Data System (ADS)

Si, Chaorun; Hu, Songtao; Cao, Xiaobao; Wu, Weichao

2017-01-01

Due to their ease of fabrication, facile use and low cost, ice valves have great potential for use in microfluidic platforms. For this to be possible, a rapid response speed is key and hence there is still much scope for improvement in current ice valve technology. Therefore, in this study, an ice valve with enhanced thermal conductivity and a movable refrigeration source has been developed. An embedded aluminium cylinder is used to dramatically enhance the heat conduction performance of the microfluidic platform and a movable thermoelectric unit eliminates the thermal inertia, resulting in a faster cooling process. The proposed ice valve achieves very short closing times (0.37 s at 10 μL/min) and also operates at high flow rates (1150 μL/min). Furthermore, the response time of the valve decreased by a factor of 8 when compared to current state of the art technology.

Surface-exposure ages of Front Range moraines that may have formed during the Younger Dryas, 8.2 cal ka, and Little Ice Age events

USGS Publications Warehouse

Benson, L.; Madole, R.; Kubik, P.; McDonald, R.

2007-01-01

Surface-exposure (10Be) ages have been obtained on boulders from three post-Pinedale end-moraine complexes in the Front Range, Colorado. Boulder rounding appears related to the cirque-to-moraine transport distance at each site with subrounded boulders being typical of the 2-km-long Chicago Lakes Glacier, subangular boulders being typical of the 1-km-long Butler Gulch Glacier, and angular boulders being typical of the few-hundred-m-long Isabelle Glacier. Surface-exposure ages of angular boulders from the Isabelle Glacier moraine, which formed during the Little Ice Age (LIA) according to previous lichenometric dating, indicate cosmogenic inheritance values ranging from 0 to ???3.0 10Be ka.11Surface-exposure ages in this paper are labeled 10Be; radiocarbon ages are labeled 14C ka, calendar and calibrated radiocarbon ages are labeled cal ka, and layer-based ice-core ages are labeled ka. 14C ages, calibrated 14C ages, and ice core ages are given relative to AD 1950, whereas 10Be ages are given relative to the sampling date. Radiocarbon ages were calibrated using CALIB 5.01 and the INTCAL04 data base Stuiver et al. (2005). Ages estimated using CALIB 5.01 are shown in terms of their 1-sigma range. Subangular boulders from the Butler Gulch end moraine yielded surface-exposure ages ranging from 5 to 10.2 10Be ka. We suggest that this moraine was deposited during the 8.2 cal ka event, which has been associated with outburst floods from Lake Agassiz and Lake Ojibway, and that the large age range associated with the Butler Gulch end moraine is caused by cosmogenic shielding of and(or) spalling from boulders that have ages in the younger part of the range and by cosmogenic inheritance in boulders that have ages in the older part of the range. The surface-exposure ages of eight of nine subrounded boulders from the Chicago Lakes area fall within the 13.0-11.7 10Be ka age range, and appear to have been deposited during the Younger Dryas interval. The general lack of inheritance in the eight samples probably stems from the fact that only a few thousand years intervened between the retreat of the Pinedale glacier and the advance of the Chicago Lakes glacier; in addition, bedrock in the Chicago Lakes cirque area may have remained covered with snow and ice during that interval, thus partially shielding the bedrock from cosmogenic radiation.

Progress Towards the Remote Sensing of Aircraft Icing Hazards

NASA Technical Reports Server (NTRS)

Reehorst, Andrew; Brinker, David; Politovich, Marcia; Serke, David; Ryerson, Charles; Pazmany, Andrew; Solheim, Fredrick

2009-01-01

NASA has teamed with the FAA, DoD, industry, and academia for research into the remote detection and measurement of atmospheric conditions leading to aircraft icing hazards. The ultimate goal of this effort is to provide pilots, controllers, and dispatchers sufficient information to allow aircraft to avoid or minimize their exposure to the hazards of in-flight icing. Since the hazard of in-flight icing is the outcome of aircraft flight through clouds containing supercooled liquid water and strongly influenced by the aircraft s speed and configuration and by the length of exposure, the hazard cannot be directly detected, but must be inferred based upon the measurement of conducive atmospheric conditions. Therefore, icing hazard detection is accomplished through the detection and measurement of liquid water in regions of measured sub-freezing air temperatures. The icing environment is currently remotely measured from the ground with a system fusing radar, lidar, and multifrequency microwave radiometer sensors. Based upon expected ice accretion severity for the measured environment, a resultant aircraft hazard is then calculated. Because of the power, size, weight, and view angle constraints of airborne platforms, the current ground-based solution is not applicable for flight. Two current airborne concepts are based upon the use of either multifrequency radiometers or multifrequency radar. Both ground-based and airborne solutions are required for the future since groundbased systems can provide hazard detection for all aircraft in airport terminal regions while airborne systems will be needed to provide equipped aircraft with flight path coverage between terminal regions.

A revised surface age for the North Polar Layered Deposits of Mars

USGS Publications Warehouse

Landis, Margaret E.; Byrne, Shane; Daubar, Ingrid J.; Herkenhoff, Kenneth E.; Dundas, Colin M.

2016-01-01

The North Polar Layered Deposits (NPLD) of Mars contain a complex stratigraphy that has been suggested to retain a record of past eccentricity- and obliquity-forced climate changes. The surface accumulation rate in the current climate can be constrained by the crater retention age. We scale NPLD crater diameters to account for icy target strength and compare surface age using a new production function for recent small impacts on Mars to the previously used model of Hartmann (2005). Our results indicate that ice is accumulating in these craters several times faster than previously thought, with a 100 m diameter crater being completely infilled within centuries. Craters appear to have a diameter-dependent lifetime, but the data also permit a complete resurfacing of the NPLD at ~1.5 ka.

Pyroclastic density current dynamics and associated hazards at ice-covered volcanoes

NASA Astrophysics Data System (ADS)

Dufek, J.; Cowlyn, J.; Kennedy, B.; McAdams, J.

2015-12-01

Understanding the processes by which pyroclastic density currents (PDCs) are emplaced is crucial for volcanic hazard prediction and assessment. Snow and ice can facilitate PDC generation by lowering the coefficient of friction and by causing secondary hydrovolcanic explosions, promoting remobilisation of proximally deposited material. Where PDCs travel over snow or ice, the reduction in surface roughness and addition of steam and meltwater signficantly changes the flow dynamics, affecting PDC velocities and runout distances. Additionally, meltwater generated during transit and after the flow has come to rest presents an immediate secondary lahar hazard that can impact areas many tens of kilometers beyond the intial PDC. This, together with the fact that deposits emplaced on ice are rarely preserved means that PDCs over ice have been little studied despite the prevalence of summit ice at many tall stratovolcanoes. At Ruapehu volcano in the North Island of New Zealand, a monolithologic welded PDC deposit with unusually rounded clasts provides textural evidence for having been transported over glacial ice. Here, we present the results of high-resolution multiphase numerical PDC modeling coupled with experimentaly determined rates of water and steam production for the Ruapehu deposits in order to assess the effect of ice on the Ruapehu PDC. The results suggest that the presence of ice significantly modified the PDC dynamics, with implications for assessing the PDC and associated lahar hazards at Ruapehu and other glaciated volcanoes worldwide.

Nonlinear threshold behavior during the loss of Arctic sea ice.

PubMed

Eisenman, I; Wettlaufer, J S

2009-01-06

In light of the rapid recent retreat of Arctic sea ice, a number of studies have discussed the possibility of a critical threshold (or "tipping point") beyond which the ice-albedo feedback causes the ice cover to melt away in an irreversible process. The focus has typically been centered on the annual minimum (September) ice cover, which is often seen as particularly susceptible to destabilization by the ice-albedo feedback. Here, we examine the central physical processes associated with the transition from ice-covered to ice-free Arctic Ocean conditions. We show that although the ice-albedo feedback promotes the existence of multiple ice-cover states, the stabilizing thermodynamic effects of sea ice mitigate this when the Arctic Ocean is ice covered during a sufficiently large fraction of the year. These results suggest that critical threshold behavior is unlikely during the approach from current perennial sea-ice conditions to seasonally ice-free conditions. In a further warmed climate, however, we find that a critical threshold associated with the sudden loss of the remaining wintertime-only sea ice cover may be likely.

Analysis of Ice-Related Intra-Crater Facies in Promethei Terra, Mars

NASA Astrophysics Data System (ADS)

Orgel, Csilla; Kereszturi, Ákos; van Gasselt, Stephan

2014-05-01

On Mars ice-related landforms have been identified at mid-latitudes between 30° and 50° in both hemispheres including the areas of Tempe Terra, Deuteronilus-Protonilus Mensae, Phlegra Montes and the rims of the southern-hemispheric impact basins Argyre and Hellas [1-7]. Our study area - informally termed hourglass-shaped crater [8] - is located near Reull Vallis on the eastern rim of the Hellas impact basin (39.0°S, 102.8°E). Impact-crater infill was described as debris-covered piedmont-type glacier [8] based on analysis of High Resolution Stereo Camera (HRSC) data, and implies a glacial origin with precipitation of ice during higher obliquity phases. Recent, higher-resolution image data such as data of the High Resolution Imaging Science Experiment (HiRISE) and the Context Imager (CTX) provide a more detailed picture of the lateral distribution of different small-scale surface features indicative of periglacial and/or glacial origin. The aim of this study is to identify qualitative and quantitative characteristics of these ice-related landforms and to separate sources of water ice and related processes. Initial age determinations based on impact-crater size-frequency statistics indicate an age of 3.4 Gyr for the impact-crater and an age of approximately 75 Myr for the infill [8]. In order to identify a possible sequence of surface-feature evolution we calculated the age distribution of four major surface units which span ages ages between 1-47 Myr. Along with detailed age information and a separation of different processes at this confined type location of Mars young-Amazonian landscape evolution and potential cyclic signals are being reconstructed to constrain climate evolution. Carr, M. H. & Schaber, G. G. 1977: Martian permafrost features.- J. Geophys. Res. 82, 4039-4054. Squyres, S. W. 1978: Martian fretted terrain: flow of erosional debris.- Icarus 34, 600-613. Squyres, S. W. 1979: The distribution of lobate debris aprons and similar flows on Mars.- J. Geophys. Res. 84, 8087-8096. Lucchitta, B. K. 1981: Mars and Earth: comparison of cold-climate features.- Icarus 45, 264-303. Lucchitta, B. K. 1984: Ice and debris in the fretted terrain, Mars.- J. Geophys. Res. 89, B409-B418. Squyres, S. W. & Carr, M. H. 1986: Geomorphic evidence for the distribution of ground ice on Mars.- Science 231, 249-252. Kargel, J. S. & Strom, R. G. 1992: Ancient glaciation on Mars.- Geology 20, 3-7. Head, J. W., Neukum, G., Jaumann, R., Hiesinger, H., Hauber, E., Carr, M., Masson, P., Foing, B., Hoffmann, H., Kreslavsky, M., Werner, S., Milkovich, S., van Gasselt, S. & the HRSC Co-Investigator Team 2005: Tropical and mid-latitude snow and ice accumulation, flow and glaciation on Mars.- Nature 434, 346-351.

Effects of Orbital Evolution on Lunar Ice Stability

NASA Astrophysics Data System (ADS)

Siegler, M. A.; Bills, B. G.; Paige, D. A.

2010-12-01

Permanently shadowed regions of the Moon have complex thermal histories that influence their ability to act as traps for water ice. Though many areas are now cold enough that surface water ice would be stable from sublimation losses for billions of years, this has not always been the case. Here we examine the effects of the long term orbital and rotational evolution of the Moon on polar thermal history, volatile stability and mobility. Using data from the Diviner Lunar Radiometer, aboard the Lunar Reconnaissance Orbiter, we validate models of the current temperature in the lunar polar region. This model includes the effects of topography, scattering, re-radiation, and regolith thermal properties. Then, integrating the effects of tidal torques backward from the present, we reconstruct past orbital and rotational states and use them as input to the thermal model to estimate the thermal environment of the distant lunar past. The rate of tidal evolution of the lunar orbit is quite uncertain, thus use orbital semimajor axis as independent variable, rather than time, in the reconstruction. The orbital integration results in a high obliquity period which occurred when the Moon was at about half its present distance from the Earth. This period, which caused half a year of direct sunlight on the polar region, is due to a transition between two Cassini States, spin-orbit configurations resulting from internal dissipation within the Moon. Since this event, the tilt of the Moon (with respect to the ecliptic) has slowly decreased to the current 1.54 degree. Prior to this transition, due to the relatively small Earth-Moon distance, large amplitude variations in the inclination of the orbital plain were also important. We examine the stability of polar volatiles in response to the evolving lunar orbit, and apply simple models to describe when in the Moon’s history supplied volatiles would have been most likely to be buried by thermal diffusion. When temperatures are much below 95K, ice delivered to the lunar surface is immobile in terms of thermal diffusion. Unless buried on relatively short time scales, most of the current polar environments are currently too cold to efficiently drive ice downward along thermal gradients and protect it from other surface loss processes. In the past, these same locations went through “ice trap” periods, where they were warm enough that supplied volatiles might have been buried by on short time scales, but cold enough that they would not be lost quickly, supplying the subsurface with volatiles that could still be stable today. The Cassini state transition was so warm that ice would either have been driven out into space, or possibly deep into the lunar subsurface. If a present lunar cold trap is ice bearing, that ice is likely to be representative of these “ice trap” periods and have little to do with the early Moon. As each current cold trap had a period where it was most efficient at thermal ice burial, the location of current ground ice on the Moon might also constrain the obliquity and time at which it was deposited. The presence of ice in a specific crater may imply either an increase in water flux or large comet impact during that period.

Icing Management for Coast Guard Assets

DTIC Science & Technology

2013-04-01

Homola et al. (2006) summarized many ice detection concepts and assessed their near-term application potential to wind turbines . This re- port will...is attached, using adhe- sive, to the leading edge of an airfoil, aircraft or wind turbine , or any other surface that must be protected from icing...for ap- plication to wind turbines . ERDC/CRREL TR-13-7 287 Five optical ice detectors are currently mature technologies, but not all are

Sea Ice Biogeochemistry: A Guide for Modellers

PubMed Central

Tedesco, Letizia; Vichi, Marcello

2014-01-01

Sea ice is a fundamental component of the climate system and plays a key role in polar trophic food webs. Nonetheless sea ice biogeochemical dynamics at large temporal and spatial scales are still rarely described. Numerical models may potentially contribute integrating among sparse observations, but available models of sea ice biogeochemistry are still scarce, whether their relevance for properly describing the current and future state of the polar oceans has been recently addressed. A general methodology to develop a sea ice biogeochemical model is presented, deriving it from an existing validated model application by extension of generic pelagic biogeochemistry model parameterizations. The described methodology is flexible and considers different levels of ecosystem complexity and vertical representation, while adopting a strategy of coupling that ensures mass conservation. We show how to apply this methodology step by step by building an intermediate complexity model from a published realistic application and applying it to analyze theoretically a typical season of first-year sea ice in the Arctic, the one currently needing the most urgent understanding. The aim is to (1) introduce sea ice biogeochemistry and address its relevance to ocean modelers of polar regions, supporting them in adding a new sea ice component to their modelling framework for a more adequate representation of the sea ice-covered ocean ecosystem as a whole, and (2) extend our knowledge on the relevant controlling factors of sea ice algal production, showing that beyond the light and nutrient availability, the duration of the sea ice season may play a key-role shaping the algal production during the on going and upcoming projected changes. PMID:24586604

Evaluating Antarctic sea ice predictability at seasonal to interannual timescales in global climate models

NASA Astrophysics Data System (ADS)

Marchi, Sylvain; Fichefet, Thierry; Goosse, Hugues; Zunz, Violette; Tietsche, Steffen; Day, Jonny; Hawkins, Ed

2016-04-01

Unlike the rapid sea ice losses reported in the Arctic, satellite observations show an overall increase in Antarctic sea ice extent over recent decades. Although many processes have already been suggested to explain this positive trend, it remains the subject of current investigations. Understanding the evolution of the Antarctic sea ice turns out to be more complicated than for the Arctic for two reasons: the lack of observations and the well-known biases of climate models in the Southern Ocean. Irrespective of those issues, another one is to determine whether the positive trend in sea ice extent would have been predictable if adequate observations and models were available some decades ago. This study of Antarctic sea ice predictability is carried out using 6 global climate models (HadGEM1.2, MPI-ESM-LR, GFDL CM3, EC-Earth V2, MIROC 5.2 and ECHAM 6-FESOM) which are all part of the APPOSITE project. These models are used to perform hindcast simulations in a perfect model approach. The predictive skill is estimated thanks to the PPP (Potential Prognostic Predictability) and the ACC (Anomaly Correlation Coefficient). The former is a measure of the uncertainty of the ensemble while the latter assesses the accuracy of the prediction. These two indicators are applied to different variables related to sea ice, in particular the total sea ice extent and the ice edge location. This first model intercomparison study about sea ice predictability in the Southern Ocean aims at giving a general overview of Antarctic sea ice predictability in current global climate models.

Retreat of the Southwest Labrador Sector of the Laurentide Ice Sheet During the Last Termination

NASA Astrophysics Data System (ADS)

Lowell, T. V.; Kelly, M. A.; Fisher, T. G.; Barnett, P. J.; Howley, J. A.; Zimmerman, S. R. H.

2016-12-01

Large ice sheets are suspected to have played a major role in forcing the transitions from glacial to interglacial conditions, known as terminations. To improve the understanding of the role of the Laurentide Ice Sheet in the last termination, we present a chronology of ice sheet recession from just subsequent to end of the Last Glacial Maximum (LGM) to the early Holocene. We focus on the retreat of the southwest Labrador Sector of the ice sheet in northern Minnesota and adjacent Ontario. Multiple moraines in this region mark an overall pattern of ice recession interrupted by stillstands and/or minor readvances. Radiocarbon and 10Be ages from 50 sites along this 400 km-long transect indicate that the oldest moraine complex, the Vermillion moraine, formed at 17.0 ka. Subsequently, the ice margin retreated with minor standstills until the Dog Lake moraine was deposited between 12.7 and 12.3 ka. Recession from the Dog Lake moraine began by 12.3 ka the ice margin receded 150 km to the north-northeast by 10.7 ka. In general, the radiocarbon and 10Be ages define a pattern of near-continuous ice sheet retreat. Deposition of the Vermillion and Dog Lake moraines occurred at the beginning of Heinrich stadials 1 ( 17.5-14.5 ka) and 0 ( 12.9-11.7 ka), respectively, but ice recession occurred throughout the remainder of these stadials. This pattern is different from climate conditions registered by Greenland ice cores which show cold conditions from the end of the LGM until the Bølling warming at 14.5 ka, and throughout the Younger Dryas ( 12.9-11.7 ka). We suggest that the pattern of ice sheet recession is more similar to mountain glaciers in the southern mid-latitudes and tropics, and that Heinrich stadials may have been characterized by warming at least in the summertime that influenced near global ice recession.

The impact of past climate change on genetic variation and population connectivity in the Icelandic arctic fox

PubMed Central

Mellows, Andrew; Barnett, Ross; Dalén, Love; Sandoval-Castellanos, Edson; Linderholm, Anna; McGovern, Thomas H.; Church, Mike J.; Larson, Greger

2012-01-01

Previous studies have suggested that the presence of sea ice is an important factor in facilitating migration and determining the degree of genetic isolation among contemporary arctic fox populations. Because the extent of sea ice is dependent upon global temperatures, periods of significant cooling would have had a major impact on fox population connectivity and genetic variation. We tested this hypothesis by extracting and sequencing mitochondrial control region sequences from 17 arctic foxes excavated from two late-ninth-century to twelfth-century AD archaeological sites in northeast Iceland, both of which predate the Little Ice Age (approx. sixteenth to nineteenth century). Despite the fact that five haplotypes have been observed in modern Icelandic foxes, a single haplotype was shared among all of the ancient individuals. Results from simulations within an approximate Bayesian computation framework suggest that the rapid increase in Icelandic arctic fox haplotype diversity can only be explained by sea-ice-mediated fox immigration facilitated by the Little Ice Age. PMID:22977155

County-Level Climate Uncertainty for Risk Assessments: Volume 24 Appendix W - Historical Sea Ice Age.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Backus, George A.; Lowry, Thomas Stephen; Jones, Shannon M

2017-05-01

This report uses the CMIP5 series of climate model simulations to produce country- level uncertainty distributions for use in socioeconomic risk assessments of climate change impacts. It provides appropriate probability distributions, by month, for 169 countries and autonomous-areas on temperature, precipitation, maximum temperature, maximum wind speed, humidity, runoff, soil moisture and evaporation for the historical period (1976-2005), and for decadal time periods to 2100. It also provides historical and future distributions for the Arctic region on ice concentration, ice thickness, age of ice, and ice ridging in 15-degree longitude arc segments from the Arctic Circle to 80 degrees latitude, plusmore » two polar semicircular regions from 80 to 90 degrees latitude. The uncertainty is meant to describe the lack of knowledge rather than imprecision in the physical simulation because the emphasis is on unfalsified risk and its use to determine potential socioeconomic impacts. The full report is contained in 27 volumes.« less

County-Level Climate Uncertainty for Risk Assessments: Volume 25 Appendix X - Forecast Sea Ice Age.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Backus, George A.; Lowry, Thomas Stephen; Jones, Shannon M.

2017-05-01

This report uses the CMIP5 series of climate model simulations to produce country- level uncertainty distributions for use in socioeconomic risk assessments of climate change impacts. It provides appropriate probability distributions, by month, for 169 countries and autonomous-areas on temperature, precipitation, maximum temperature, maximum wind speed, humidity, runoff, soil moisture and evaporation for the historical period (1976-2005), and for decadal time periods to 2100. It also provides historical and future distributions for the Arctic region on ice concentration, ice thickness, age of ice, and ice ridging in 15-degree longitude arc segments from the Arctic Circle to 80 degrees latitude, plusmore » two polar semicircular regions from 80 to 90 degrees latitude. The uncertainty is meant to describe the lack of knowledge rather than imprecision in the physical simulation because the emphasis is on unfalsified risk and its use to determine potential socioeconomic impacts. The full report is contained in 27 volumes.« less

Geologic and hydrologic hazards in glacierized basins in North America resulting from 19th and 20th century global warming

USGS Publications Warehouse

O'Connor, J. E.; Costa, J.E.

1993-01-01

Alpine glacier retreat resulting from global warming since the close of the Little Ice Age in the 19th and 20th centuries has increased the risk and incidence of some geologic and hydrologic hazards in mountainous alpine regions of North America. Abundant loose debris in recently deglaciated areas at the toe of alpine glaciers provides a ready source of sediment during rainstorms or outburst floods. This sediment can cause debris flows and sedimentation problems in downstream areas. Moraines built during the Little Ice Age can trap and store large volumes of water. These natural dams have no controlled outlets and can fail without warning. Many glacier-dammed lakes have grown in size, while ice dams have shrunk, resulting in greater risks of ice-dam failure. The retreat and thinning of glacier ice has left oversteepened, unstable valley walls and has led to increased incidence of rock and debris avalanches. ?? 1993 Kluwer Academic Publishers.

The impact of past climate change on genetic variation and population connectivity in the Icelandic arctic fox.

PubMed

Mellows, Andrew; Barnett, Ross; Dalén, Love; Sandoval-Castellanos, Edson; Linderholm, Anna; McGovern, Thomas H; Church, Mike J; Larson, Greger

2012-11-22

Previous studies have suggested that the presence of sea ice is an important factor in facilitating migration and determining the degree of genetic isolation among contemporary arctic fox populations. Because the extent of sea ice is dependent upon global temperatures, periods of significant cooling would have had a major impact on fox population connectivity and genetic variation. We tested this hypothesis by extracting and sequencing mitochondrial control region sequences from 17 arctic foxes excavated from two late-ninth-century to twelfth-century AD archaeological sites in northeast Iceland, both of which predate the Little Ice Age (approx. sixteenth to nineteenth century). Despite the fact that five haplotypes have been observed in modern Icelandic foxes, a single haplotype was shared among all of the ancient individuals. Results from simulations within an approximate Bayesian computation framework suggest that the rapid increase in Icelandic arctic fox haplotype diversity can only be explained by sea-ice-mediated fox immigration facilitated by the Little Ice Age.

Application of ground-penetrating radar imagery for three-dimensional visualisation of near-surface structures in ice-rich permafrost, Barrow, Alaska

USGS Publications Warehouse

Munroe, Jeffrey S.; Doolittle, James A.; Kanevskiy, Mikhail; Hinkel, Kenneth M.; Nelson, Frederick E.; Jones, Benjamin M.; Shur, Yuri; Kimble, John M.

2007-01-01

Three-dimensional ground-penetrating radar (3D GPR) was used to investigate the subsurface structure of ice-wedge polygons and other features of the frozen active layer and near-surface permafrost near Barrow, Alaska. Surveys were conducted at three sites located on landscapes of different geomorphic age. At each site, sediment cores were collected and characterised to aid interpretation of GPR data. At two sites, 3D GPR was able to delineate subsurface ice-wedge networks with high fidelity. Three-dimensional GPR data also revealed a fundamental difference in ice-wedge morphology between these two sites that is consistent with differences in landscape age. At a third site, the combination of two-dimensional and 3D GPR revealed the location of an active frost boil with ataxitic cryostructure. When supplemented by analysis of soil cores, 3D GPR offers considerable potential for imaging, interpreting and 3D mapping of near-surface soil and ice structures in permafrost environments.

Icing Test Results on an Advanced Two-Dimensional High-Lift Multi-Element Airfoil

NASA Technical Reports Server (NTRS)

Shin, Jaiwon; Wilcox, Peter; Chin, Vincent; Sheldon, David

1994-01-01

An experimental study has been conducted to investigate ice accretions on a high-lift, multi-element airfoil in the Icing Research Tunnel at the NASA Lewis Research Center. The airfoil is representative of an advanced transport wing design. The experimental work was conducted as part of a cooperative program between McDonnell Douglas Aerospace and the NASA Lewis Research Center to improve current understanding of ice accretion characteristics on the multi-element airfoil. The experimental effort also provided ice shapes for future aerodynamic tests at flight Reynolds numbers to ascertain high-lift performance effects. Ice shapes documented for a landing configuration over a variety of icing conditions are presented along with analyses.

Probing the Origin and Evolution of Interstellar and Protoplanetary Biogenic Ices with SPHEREx

NASA Astrophysics Data System (ADS)

Melnick, Gary; SPHEREx Science Team

2018-01-01

Many of the most important building blocks of life are locked in interstellar and protoplanetary ices. Examples include H2O, CO, CO2, and CH3OH, among others. There is growing evidence that within the cores of dense molecular clouds and the mid-plane of protoplanetary disks the abundance of these species in ices far exceeds that in the gas phase. As a result, collisions between ice-bearing bodies and newly forming planets are thought to be a major means of delivering these key species to young planets. There currently exist fewer than 250 ice absorption spectra toward Galactic molecular clouds, which is insufficient to reliably trace the ice content of clouds through the various evolutionary stages of collapse to form stars and planets. Likewise, the current number of spectra is inadequate to assess the effects of environment, such as cloud density and temperature, presence or absence of embedded sources, external FUV and X-ray radiation, gas-phase composition, or cosmic-ray ionization rate, on the ice composition of clouds at similar stages of evolution. Ultimately, our goal is to understand how these findings connect to our own Solar System.SPHEREx will be a game changer for the study of interstellar, circumstellar, and protoplanetary disk ices. SPHEREx will obtain spectra over the entire sky in the optical and near-IR, including the 2.5 to 5.0 micron region, which contains the above biogenic ice features. SPHEREx will detect millions of potential background continuum point sources already catalogued by NASA’s Wide-field Infrared Survey Explorer (WISE) at 3.4 and 4.6 microns for which there is evidence for intervening gas and dust based on the 2MASS+WISE colors with sufficient sensitivity to yield ice absorption spectra with SNR ≥ 100 per spectral resolution element. The resulting > 100-fold increase in the number of high-quality ice absorption spectra toward a wide variety of regions distributed throughout the Galaxy will reveal correlations between ice content and environment not possible with current spectra or the limited number that will be obtained with JWST. Finally, because SPHEREx and JWST will overlap beyond 2022, SPHEREx will provide JWST with a complete ice source catalog for follow-up.

Radar Interferometry Studies of the Mass Balance of Polar Ice Sheets

NASA Technical Reports Server (NTRS)

Rignot, Eric (Editor)

1999-01-01

The objectives of this work are to determine the current state of mass balance of the Greenland and Antarctic Ice Sheets. Our approach combines different techniques, which include satellite synthetic-aperture radar interferometry (InSAR), radar and laser altimetry, radar ice sounding, and finite-element modeling. In Greenland, we found that 3.5 times more ice flows out of the northern part of the Greenland Ice Sheet than previously accounted for. The discrepancy between current and past estimates is explained by extensive basal melting of the glacier floating sections in the proximity of the grounding line where the glacier detaches from its bed and becomes afloat in the ocean. The inferred basal melt rates are very large, which means that the glaciers are very sensitive to changes in ocean conditions. Currently, it appears that the northern Greenland glaciers discharge more ice than is being accumulated in the deep interior, and hence are thinning. Studies of temporal changes in grounding line position using InSAR confirm the state of retreat of northern glaciers and suggest that thinning is concentrated at the lower elevations. Ongoing work along the coast of East Greenland reveals an even larger mass deficit for eastern Greenland glaciers, with thinning affecting the deep interior of the ice sheet. In Antarctica, we found that glaciers flowing into a large ice shelf system, such as the Ronne Ice Shelf in the Weddell Sea, exhibit an ice discharge in remarkable agreement with mass accumulation in the interior, and the glacier grounding line positions do not migrate with time. Glaciers flowing rapidly into the Amudsen Sea, unrestrained by a major ice shelf, are in contrast discharging more ice than required to maintain a state of mass balance and are thinning quite rapidly near the coast. The grounding line of Pine Island glacier (see diagram) retreated 5 km in 4 years, which corresponds to a glacier thinning rate of 3.5 m/yr. Mass imbalance is even more negative on Thwaites Glacier. This sector of West Antarctica probably initiated its collapse decades or centuries ago, once the embaying ice shelves in front of them started to melt because of enhanced basal melting from warmer ocean waters. Additional information is contained in the original.

Extensive Ice Fractures in the Beaufort Sea

NASA Image and Video Library

2017-12-08

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013. Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice. That was what was happening on the left side of the animation (seen here: bit.ly/10kE7sh) in late January. A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea. “A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.” In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles). The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible. While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.” NASA Earth Observatory images by Jesse Allen using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland. Instrument: Suomi NPP - VIIRS For more info go to: earthobservatory.nasa.gov/IOTD/view.php?id=80752 Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Extensive Ice Fractures in the Beaufort Sea [detail

NASA Image and Video Library

2017-12-08

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013. Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice. That was what was happening on the left side of the animation (seen here: bit.ly/10kE7sh) in late January. A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea. “A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.” In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles). The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible. While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.” NASA Earth Observatory images by Jesse Allen using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland. Instrument: Suomi NPP - VIIRS For more info go to: earthobservatory.nasa.gov/IOTD/view.php?id=80752 Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Extensive Ice Fractures in the Beaufort Sea [annotated

NASA Image and Video Library

2017-12-08

The Visible Infrared Imaging Radiometer Suite (VIIRS) on the Suomi NPP satellite captured this view of extensive sea-ice fracturing off the northern coast of Alaska. The event began in late-January and spread west toward Banks Island throughout February and March 2013. Visualizations of the Arctic often give the impression that the ice cap is a continuous sheet of stationary, floating ice. In fact, it is a collection of smaller pieces that constantly shift, crack, and grind against one another as they are jostled by winds and ocean currents. Especially during the summer—but even during the height of winter—cracks—or leads—open up between pieces of ice. That was what was happening on the left side of the animation (seen here: bit.ly/10kE7sh) in late January. A high-pressure weather system was parked over the region, producing warmer temperatures and winds that flowed in a southwesterly direction. That fueled the Beaufort Gyre, a wind-driven ocean current that flows clockwise. The gyre was the key force pulling pieces of ice west past Point Barrow, the northern nub of Alaska that protrudes into the Beaufort Sea. “A fracturing event in this area is not unusual because the Beaufort Gyre tends to push ice away from Banks Island and the Canadian Archipelago,” explained Walt Meier of the National Snow & Ice Data Center (NSIDC). “Point Barrow can act like a ‘pin point’ where the ice catches and fractures to the north and east.” In February, however, a series of storms passing over central Alaska exacerbated the fracturing. Strong westerly winds prompted several large pieces of ice to break away in an arc-shaped wave that moved progressively east. By the end of February, large pieces of ice had fractured all the way to the western coast of Banks Island, a distance of about 1,000 kilometers (600 miles). The data used to create the animation came from the longwave infrared (thermal) portion of the electromagnetic spectrum, so the animation illustrates how much heat the surface was emitting as VIIRS surveyed the area. Cooler areas (sea ice) appear white, while warmer areas (open water) are dark. The light gray plume near the cracks is warmer, moister air escaping from the ocean and blowing downwind. Clouds do not show up well in the VIIRS thermal band, so the storms that fueled the fracturing are not readily visible. While fracturing events are common, few events sprawl across such a large area or produce cracks as long and wide as those seen here. The age of the sea ice in this area was one of the key reasons this event became so widespread. “The region is covered almost completely by seasonal or first-year ice—ice that has formed since last September,” said Meier. “This ice is thinner and weaker than the older, multi-year ice, so it responds more readily to winds and is more easily broken up.” NASA Earth Observatory images by Jesse Allen using VIIRS day-night band data from the Suomi National Polar-orbiting Partnership. Suomi NPP is the result of a partnership between NASA, the National Oceanic and Atmospheric Administration, and the Department of Defense. Caption by Adam Voiland. Instrument: Suomi NPP - VIIRS For more info go to: earthobservatory.nasa.gov/IOTD/view.php?id=80752 Credit: NASA Earth Observatory NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

Implication of azelaic acid in a Greenland Ice Core for oceanic and atmospheric changes in high latitudes

NASA Astrophysics Data System (ADS)

Kawamura, K.; Yokoyama, K.; Fujii, Y.; Watanabe, O.

A Greenland ice core (450 years) has been studied for low molecular weight dicarboxylic acids (C2-C10) using a capillary gas chromatography and mass spectrometer. Their molecular distribution generally showed a predominance of succinic acid (C4) followed by oxalic (C2), malonic (C3), glutaric (C5), adipic (C6), and azelaic (C9) acids. Azelaic acid, that is a specific photochemical reaction product of biogenic unsaturated fatty acids, gave a characteristic historical trend in the ice core; i.e., the concentrations are relatively low during late 16th to 19th century (Little Ice Age) but become very high in late 19th to 20th century (warmer periods) with a large peak in 1940s AD. Lower concentrations of azelaic acid may have been caused by a depressed emission of unsaturated fatty acids from seawater microlayers due to enhanced sea ice coverage during Little Ice Age. Inversely, increased concentrations of azelaic acid in late 19th to 20th century are likely interpreted by an enhanced sea-to-air emission of the precursor unsaturated fatty acids due to a retreat of sea ice and/or by the enhanced production due to a potentially increased oxidizing capability of the atmosphere.

The Isfahan Comprehensive Elderly Study: Objectives, research design, methodology, and preliminary results.

PubMed

Heidari, Zahra; Feizi, Awat

2017-01-01

This paper presents the objectives, research design, methodology, and primary findings of the Isfahan Comprehensive Elderly Study (ICES). In this cross-sectional study, 603 elderly persons (aged 60 and over) were selected by multistage cluster sampling method from Isfahan, Iran, in 2016 comprehensive questionnaires along with a detailed interview were used to collect information on personal, family, socioeconomic, health and social services characteristics, life styles, physical illnesses and chronic diseases, mental, emotional and cognition disorders, quality of life, disabilities, sleep quality, social supports, life satisfaction, self-efficacy, and of participants. The mean ± standard deviation (SD) age of participants was 69.66 ± 6.31 years, consisting of 50.75% females. About 23% of elderly persons were at the risk of malnutrition and 4.5% were current smoker. Severe and mild depression were documented in 9.3% and 30.2% among included study subjects, respectively. About half of the participants had hypertension, and 26.8% suffered from cardiovascular disease. The mean ± SD of total score of Geriatric Depression Scale, Perceived Stress Scale, Older People's Quality of Life, Physical Activity Scale for the Elderly and Pittsburg Sleep Quality Index was 8.84 ± 6.79, 14.76 ± 5.92, 133.99 ± 10.55, 142.04 ± 120.53, and 6.17 ± 3.44, respectively. Elderly males had significantly higher life satisfaction and self-efficacy and better cognitive function than females ( P < 0.01). The findings of current study provided a comprehensive overview of the current health status and lifestyle of older adults in Isfahan city. The ICES could help policy makers to design appropriate prevention and interventional programs and policies to cover the specific needs of the elderly population.

The Isfahan Comprehensive Elderly Study: Objectives, research design, methodology, and preliminary results

PubMed Central

Heidari, Zahra; Feizi, Awat

2017-01-01

Background: This paper presents the objectives, research design, methodology, and primary findings of the Isfahan Comprehensive Elderly Study (ICES). Materials and Methods: In this cross-sectional study, 603 elderly persons (aged 60 and over) were selected by multistage cluster sampling method from Isfahan, Iran, in 2016 comprehensive questionnaires along with a detailed interview were used to collect information on personal, family, socioeconomic, health and social services characteristics, life styles, physical illnesses and chronic diseases, mental, emotional and cognition disorders, quality of life, disabilities, sleep quality, social supports, life satisfaction, self-efficacy, and of participants. Results: The mean ± standard deviation (SD) age of participants was 69.66 ± 6.31 years, consisting of 50.75% females. About 23% of elderly persons were at the risk of malnutrition and 4.5% were current smoker. Severe and mild depression were documented in 9.3% and 30.2% among included study subjects, respectively. About half of the participants had hypertension, and 26.8% suffered from cardiovascular disease. The mean ± SD of total score of Geriatric Depression Scale, Perceived Stress Scale, Older People's Quality of Life, Physical Activity Scale for the Elderly and Pittsburg Sleep Quality Index was 8.84 ± 6.79, 14.76 ± 5.92, 133.99 ± 10.55, 142.04 ± 120.53, and 6.17 ± 3.44, respectively. Elderly males had significantly higher life satisfaction and self-efficacy and better cognitive function than females (P < 0.01). Conclusion: The findings of current study provided a comprehensive overview of the current health status and lifestyle of older adults in Isfahan city. The ICES could help policy makers to design appropriate prevention and interventional programs and policies to cover the specific needs of the elderly population. PMID:28919912

A new approach to driving and controlling precision lasers for cold-atom science

NASA Astrophysics Data System (ADS)

Luey, Ben; Shugrue, Jeremy; Anderson, Mike

2014-05-01

Vescent's Integrated Control Electronics (ICE) Platform is a new approach to controlling and driving lasers and other electoral devices in complex atomic and optical experiments. By employing low-noise, high-bandwidth analog electronics with digital control, ICE combines the performance of analog design with the convenience of the digital world. Utilizing a simple USB COM port interface, ICE can easily be controlled via LabView, Python, or an FPGA. High-speed TTL inputs enable precise external timing or triggering. ICE is capable of generating complex timing internally, enabling ICE to drive an entire experiment or it can be directed by an external control program. The system is capable of controlling up to 8 unique ICE slave boards providing flexibility to tailor an assortment of electronics hardware to the needs of a specific experiment. Examples of ICE slave boards are: a current controller and peak-lock laser servo, a four channel temperature controller, a current controller and offset phase lock servo. A single ensemble can drive, stabilize, and frequency lock 3 lasers in addition to powering an optical amplifier, while still leaving 2 remaining slots for further control needs. Staff Scientist

Effect of Common Cryoprotectants on Critical Warming Rates and Ice Formation in Aqueous Solutions

PubMed Central

Hopkins, Jesse B.; Badeau, Ryan; Warkentin, Matthew; Thorne, Robert E.

2012-01-01

Ice formation on warming is of comparable or greater importance to ice formation on cooling in determining survival of cryopreserved samples. Critical warming rates required for ice-free warming of vitrified aqueous solutions of glycerol, dimethyl sulfoxide, ethylene glycol, polyethylene glycol 200 and sucrose have been measured for warming rates of order 10 to 104 K/s. Critical warming rates are typically one to three orders of magnitude larger than critical cooling rates. Warming rates vary strongly with cooling rates, perhaps due to the presence of small ice fractions in nominally vitrified samples. Critical warming and cooling rate data spanning orders of magnitude in rates provide rigorous tests of ice nucleation and growth models and their assumed input parameters. Current models with current best estimates for input parameters provide a reasonable account of critical warming rates for glycerol solutions at high concentrations/low rates, but overestimate both critical warming and cooling rates by orders of magnitude at lower concentrations and larger rates. In vitrification protocols, minimizing concentrations of potentially damaging cryoprotectants while minimizing ice formation will require ultrafast warming rates, as well as fast cooling rates to minimize the required warming rates. PMID:22728046

Tidal bending of ice shelves as a mechanism for large-scale temporal variations in ice flow

NASA Astrophysics Data System (ADS)

Rosier, Sebastian H. R.; Hilmar Gudmundsson, G.

2018-05-01

GPS measurements reveal strong modulation of horizontal ice shelf and ice stream flow at a variety of tidal frequencies, most notably a fortnightly (Msf) frequency not present in the vertical tides themselves. Current theories largely fail to explain the strength and prevalence of this signal over floating ice shelves. We show how well-known non-linear aspects of ice rheology can give rise to widespread, long-periodic tidal modulation in ice shelf flow, generated within ice shelves themselves through tidal flexure acting at diurnal and semidiurnal frequencies. Using full-Stokes viscoelastic modelling, we show that inclusion of tidal bending within the model accounts for much of the observed tidal modulation of ice shelf flow. Furthermore, our model shows that, in the absence of vertical tidal forcing, the mean flow of the ice shelf is reduced by almost 30 % for the geometry that we consider.

Airborne Tomographic Swath Ice Sounding Processing System

NASA Technical Reports Server (NTRS)

Wu, Xiaoqing; Rodriquez, Ernesto; Freeman, Anthony; Jezek, Ken

2013-01-01

Glaciers and ice sheets modulate global sea level by storing water deposited as snow on the surface, and discharging water back into the ocean through melting. Their physical state can be characterized in terms of their mass balance and dynamics. To estimate the current ice mass balance, and to predict future changes in the motion of the Greenland and Antarctic ice sheets, it is necessary to know the ice sheet thickness and the physical conditions of the ice sheet surface and bed. This information is required at fine resolution and over extensive portions of the ice sheets. A tomographic algorithm has been developed to take raw data collected by a multiple-channel synthetic aperture sounding radar system over a polar ice sheet and convert those data into two-dimensional (2D) ice thickness measurements. Prior to this work, conventional processing techniques only provided one-dimensional ice thickness measurements along profiles.

Airframe Icing Research Gaps: NASA Perspective

NASA Technical Reports Server (NTRS)

Potapczuk, Mark

2009-01-01

qCurrent Airframe Icing Technology Gaps: Development of a full 3D ice accretion simulation model. Development of an improved simulation model for SLD conditions. CFD modeling of stall behavior for ice-contaminated wings/tails. Computational methods for simulation of stability and control parameters. Analysis of thermal ice protection system performance. Quantification of 3D ice shape geometric characteristics Development of accurate ground-based simulation of SLD conditions. Development of scaling methods for SLD conditions. Development of advanced diagnostic techniques for assessment of tunnel cloud conditions. Identification of critical ice shapes for aerodynamic performance degradation. Aerodynamic scaling issues associated with testing scale model ice shape geometries. Development of altitude scaling methods for thermal ice protections systems. Development of accurate parameter identification methods. Measurement of stability and control parameters for an ice-contaminated swept wing aircraft. Creation of control law modifications to prevent loss of control during icing encounters. 3D ice shape geometries. Collection efficiency data for ice shape geometries. SLD ice shape data, in-flight and ground-based, for simulation verification. Aerodynamic performance data for 3D geometries and various icing conditions. Stability and control parameter data for iced aircraft configurations. Thermal ice protection system data for simulation validation.

CRN Dating and Numerical Glacier Modeling to Investigate Climate During the Last Glacial Maximum, and the Subsequent Deglaciation, Sawatch Range, Colorado

NASA Astrophysics Data System (ADS)

Russell, C.; Leonard, E. M.

2016-12-01

The current study employs a combination of cosmogenic radionuclide (CRN) surface-exposure dating and numerical glacier modeling to investigate the climate during and following the last glacial maximum (LGM) in the Sawatch Range of Colorado. A coupled 2-D energy/mass balance and flow model is used to asses the combinations of temperature and precipitation change that could have sustained glaciers in the range at their LGM extents in five valleys along the eastern flank of the range, by matching modeled ice extent to the well-preserved LGM moraines in each valley. In addition, the study couples modeling with CRN geochronology of post-LGM ice recession to try to understand the dynamics of deglaciation and the magnitudes and rates of the climate changes that drove it. Results to date include an equilibrium glacier model that fits LGM moraines in all five valleys with a 5.4°C temperature depression and no change from modern precipitation amounts or seasonality. Modeling of deglaciation indicates, however, that the response of individual glacier systems is strongly influenced by valley hypsometry as was suggested by previous workers. Low-gradient glacier systems in the range, including the Lake Creek and Clear Creek glaciers, respond dramatically to even small temperature increases, while much steeper systems, such as the Pine Creek glacier, experience much more limited retreat in response to the same climate forcing A CRN-based deglaciation chronology is available for the Lake Creek glacier, the largest of five paleoglaciers studied. The ages show that portions of the valley floor were ice-covered for several hundred years longer than the cirques above. The numerical model is currently being used to investigate two possible explanations for this. One possibility is that climate ameliorated and deglaciation proceeded so fast that thin ice in the cirques melted out before much thicker stagnant ice melted in the valley. A second possibility is that cross-divide flow from the wetter west side of the range maintained small east-side valley glaciers even as the east-side cirques deglaciated. Ongoing work will model a larger area of range to gain a better understanding of range-wide patterns of ice flow that could have affected deglaciation of the Lake Creek valley.

Medieval Warm Period and Little Ice Age Impacts on Prehistoric Human Migrations in the Eastern North American Arctic

NASA Astrophysics Data System (ADS)

Friesen, M.; Finkelstein, S. A.

2014-12-01

The eastern North American Arctic has a complex 5,000-year prehistory, during which many human population movements occurred over large distances. Archaeologists have interpreted these movements as resulting from many factors, however the effects of climate change are often hypothesized as primary drivers that can "push" human groups to leave some regions, or "pull" them to move to others. In this paper, we will examine climate change over the past millennium-and-a-half, and in particular at the two widespread, though variable, climate change events known as the Medieval Warm Period and Little Ice Age. We synthesize the latest paleoclimatological information on the timing and magnitude of these periods across the eastern Arctic, and assess the degree to which they coincide with current understanding of major population movements. In particular, we assess climate's potential impact on 1) the expansion of Late Dorset Paleo-Inuit to the High Arctic; 2) the migration of Thule Inuit from Alaska to the eastern Arctic; and 3) the abandonment of northern regions and new settlement of southern regions by Inuit in the mid-second millennium AD.

Conference Summary: First International Conference on Global Warming and the Next Ice Age

NASA Technical Reports Server (NTRS)

Wetzel, Peter J.; Chylek, Petr; Lesins, Glen; Starr, David OC. (Technical Monitor)

2002-01-01

The First International Conference on Global Warming and the Next Ice Age was convened in Halifax, Nova Scotia, August 19-24, 2001. The conference program began each day with a 30 minute live classical music performances of truly international quality before the beginning business. Ample time for panel discussions was also scheduled. The general public was invited to attend and participate in a special evening panel session on the last day of the conference. The unusual and somewhat provocative title of the conference was designed to attract diverse views on global climate change. This summary attempts to accurately reflect the tone and flavor of the lively discussions which resulted. Presentations ranged from factors forcing current climate to those in effect across the span of time from the Proterozoic "snowball Earth" epoch to 50,000 years in the future. Although, as should be expected, attendees at the conference arrived with opinions on some of the controversial issues regarding climate change, and no-one openly admitted to a 'conversion' from their initial point of view, the interdisciplinary nature of the formal presentations, poster discussions, panels, and abundant informal discourse helped to place the attendees' personal perspectives into a broader, more diversified context.

Heat sources within the Greenland Ice Sheet: dissipation, temperate paleo-firn and cryo-hydrologic warming

DOE PAGES

Lüthi, M. P.; Ryser, C.; Andrews, L. C.; ...

2015-01-01

Ice temperature profiles from the Greenland Ice Sheet contain information on the deformation history, past climates and recent warming. We present full-depth temperature profiles from two drill sites on a flow line passing through Swiss Camp, West Greenland. Numerical modeling reveals that ice temperatures are considerably higher than would be expected from heat diffusion and dissipation alone. The possible causes for this extra heat are evaluated using a Lagrangian heat flow model. The model results reveal that the observations can be explained with a combination of different processes: enhanced dissipation (strain heating) in ice-age ice, temperate paleo-firn, and cryo-hydrologic warmingmore » in deep crevasses.« less

First Younger Dryas moraines in Greenland

NASA Astrophysics Data System (ADS)

Funder, Svend; Larsen, Nicolaj K.; Linge, Henriette; Möller, Per; Schomacker, Anders; Fabel, Derek; Kjær, Kurt H.; Xu, Sheng

2016-04-01

Over the Greenland ice sheet the Younger Dryas (YD) cold climate oscillation (12.9-11.7 kaBP) began with up to 10°C drop in temperatures and ended with up to 12°C abrupt warming. In the light of the present warming and melting of the ice sheet, and its importance for future climate change, the ice sheet's response to these dramatic changes in the past is of great interest. However, even though much effort has gone into charting YD ice margin behaviour around Greenland in recent years, no clear-cut signal of response to the oscillation has been uncovered. Here we show evidence to suggest that three major outlets from a local ice cap at Greenland's north coast advanced and retreated synchronously during YD. The evidence comprises OSL (optically stimulated luminescence) dates from a marine transgression of the coastal valleys that preceded the advance, and exposure ages from boulders on the moraines, formed by glaciers that overrode the marine sediment. The OSL ages suggest a maximum age of 12.4 ±0.6 kaBP for the marine incursion, and 10 exposure ages on boulders from the three moraines provide an average minimum age of 12.5 ±0.7 kaBP for the moraines, implying that the moraines were formed within the interval 11.8-13.0 kaBP. Elsewhere in Greenland evidence for readvance has been recorded in two areas. Most notably, in the East Greenland fjord zone outlet glaciers over a stretch of 800 km coast advanced through the fjords. In Scoresby Sund, where the moraines form a wide belt, an extensive 14C and exposure dating programme has shown that the readvance here probably culminated before YD, while cessation of moraine formation and rapid retreat from the moraine belt did not commence until c. 11.5 kaBP, but no moraines have so far been dated to YD. Readvance is also seen in Disko Bugt, the largest ice sheet outlet in West Greenland. However, here the advance and retreat of the ice stream took place in mid YD times, and lasted only a few hundred years, while YD in general was characterised by large scale, more than 200 km, retreat on the shelf. Therefore, although readvance and retreat occurred in both areas, the readvance was apparently not triggered by the initial YD cooling nor was the retreat caused by the abrupt warming at the end. At all other sites with a record that run through or into YD - Southeast Greenland, South Greenland, northern West Greenland - the ice margins were apparently retreating through YD, leaving the north coast as the only area with evidence for a climatically conditioned YD readvance/retreat. The apparent mismatch between ice core temperatures and ice margin behaviour is generally seen as a function of reduced AMOC (Atlantic Meridional Overturning Circulation), inducing both higher seasonality with very cold winters and warm summers, and also occurrence of warm subsurface water to melt the ice sheet margin along some coasts. Therefore the ice margin response to the cold oscillation was to some extent determined by the nearness to the North Atlantic - with North Greenland being the farthest away. Although this may explain why glaciers advanced in North Greenland, while they melted in more southerly parts, it still leaves the question with a bearing on the future: why don't we see any ice margin response neither to the initial YD cooling, nor to the abrupt warming at the end?

Spatial and temporal scales of sea ice protists and phytoplankton distribution from the gateway Fram Strait into the Central Arctic Ocean

NASA Astrophysics Data System (ADS)

Peeken, I.; Hardge, K.; Krumpen, T.; Metfies, K.; Nöthig, E. M.; Rabe, B.; von Appen, W. J.; Vernet, M.

2016-02-01

The Arctic Ocean is currently one of the key regions where the effect of climate change is most pronounced. Sea ice is an important interface in this region by representing a unique habitat for many organisms. Massive reduction of sea ice thickness and extent, which have been recorded over the last twenty years, is anticipated to cause large cascading changes in the entire Arctic ecosystem. Most sea ice is formed on the Eurasian shelves and transported via the Transpolardrift to the western Fram Strait and out of the Arctic Ocean with the cold East Greenland Current (EGC). Warm Atlantic water enters the Arctic Ocean with the West Spitsbergen Current (WSC) via eastern Fram Strait. Here, we focus on the spatial spreading of protists from the Atlantic water masses, and their occurrences over the deep basins of the Central Arctic and the relationship amongst them in water and sea ice. Communities were analyzed by using pigments, flow cytometer and ARISA fingerprints during several cruises with the RV Polarstern to the Fram Strait, the Greenland Sea and the Central Arctic Ocean. By comparing these data sets we are able to demonstrate that the origin of the studied sea ice floes is more important for the biodiversity found in the sea ice communities then the respective underlying water mass. In contrast, biodiversity in the water column is mainly governed by the occurring water masses and the presence or absence of sea ice. However, overall the development of standing stocks in both biomes was governed by the availability of nutrients. To get a temporal perspective of the recent results, the study will be embedded in a long-term data set of phytoplankton biomass obtained during several cruises over the last twenty years.

Volcanic ash layers in blue ice fields (Beardmore Glacier Area, Antarctica): Iridium enrichments

NASA Technical Reports Server (NTRS)

Koeberl, Christian

1988-01-01

Dust bands on blue ice fields in Antarctica have been studied and have been identified to originate from two main sources: bedrock debris scraped up from the ground by the glacial movement (these bands are found predominantly at fractures and shear zones in the ice near moraines), and volcanic debris deposited on and incorporated in the ice by large-scale eruptions of Antarctic (or sub-Antractic) volcanoes. Ice core studies have revealed that most of the dust layers in the ice cores are volcanic (tephra) deposits which may be related to some specific volcanic eruptions. These eruptions have to be related to some specific volcanic eruptions. These eruptions have to be relatively recent (a few thousand years old) since ice cores usually incorporate younger ice. In contrast, dust bands on bare blue ice fields are much older, up to a few hundred thousand years, which may be inferred from the rather high terrestrial age of meteorites found on the ice and from dating the ice using the uranium series method. Also for the volcanic ash layers found on blue ice fields correlations between some specific volcanoes (late Cenozoic) and the volcanic debris have been inferred, mainly using chemical arguments. During a recent field expedition samples of several dust bands found on blue ice fields at the Lewis Cliff Ice Tongue were taken. These dust band samples were divided for age determination using the uranium series method, and chemical investigations to determine the source and origin of the dust bands. The investigations have shown that most of the dust bands found at the Ice Tongue are of volcanic origin and, for chemical and petrological reasons, may be correlated with Cenozoic volcanoes in the Melbourne volcanic province, Northern Victoria Land, which is at least 1500 km away. Major and trace element data have been obtained and have been used for identification and correlation purposes. Recently, some additional trace elements were determined in some of the dust band samples, including Ir. Iridium determinations were made using INAA, with synthetical and natural (meteorite) standards. These findings are discussed.

The microphysical and radiative properties of tropical cirrus from the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE)

NASA Astrophysics Data System (ADS)

Um, Jun Shik

During the 2006 Tropical Warm Pool International Cloud Experiment conducted in the region near Darwin, Australia, the Scaled Composites Proteus aircraft executed spiral profiles and flew horizontal legs through aging cirrus, fresh anvils, and cirrus of unknown origin. Data from 27 Jan., 29 Jan., and 2 Feb., when all the microphysical probes a Cloud and Aerosol Spectrometer (CAS), a Cloud Droplet Probe (CDP), a Cloud Imaging Probe (CIP), and a Cloud Particle Imager (CPI) were working, are used to investigate whether a single parameterization can be used to characterize tropical cirrus in terms of prognostic variables used in large-scale models, to calculate the single-scattering properties (scattering phase function P11 and asymmetry parameter g) of aggregates and small ice crystals that more closely match observed ice crystals, and to quantify the influences of small ice crystals on the bulk scattering properties of tropical cirrus. A combination of CDP (D < 50 mum), fits (50 < D < 125 microm), and CIP (D > 125 mum) distributions is used to represent ice crystal size distributions. The CDP measurements are used for small ice crystals because comparison between the CAS and CDP suggested the CAS was artificially amplifying small ice crystal concentrations by detecting remnants of shattered large ice crystals. Artifacts in CIP images are removed or corrected and then CIP measurements are used to represent large ice crystals. Because of the uncertainties in both the CPI and CIP for 50 < D < 125 mum, the incomplete gamma fitting method with the CDP (D < 50 mum) and CIP (D > 125 mum) measurements as input is used to characterize these distributions. A new quasi-automatic habit classification scheme is developed. For all days, small quasi-spheres dominated the contributions from all ice crystal sizes (D > 0 mum, by number) for all 3 days. The areal fraction (D > 200 mum) from bullet rosettes and their aggregates was 48% and 60% for 27 and 29 Jan., respectively, but only 7% for 2 Feb, whereas the fraction of aggregates of plates was 46.2% for 2 Feb. and only 7.2% and 1% for 27 and 29 Jan., respectively. The difference in ice crystal habits sampled on the different days is likely associated with the difference between fresh anvil cirrus on 2 Feb. and aged cirrus bands on the 27 and 29 of Jan. Because of variations in microphysical properties (i.e., number concentration, median mass dimension, and fit variables of gamma distributions) it is also shown that variables in addition to ice water content and temperature are required to represent the characteristics of cirrus with different origins in large-scale models. Aggregates of bullet rosettes and aggregates of plates are shown to scatter more light in the lateral and backward scattering region and less light in the forward scattering region compared to their component crystals, leading to a decrease in g for aggregates. To represent the three-dimensional shape of aggregates of plates, three parameters, the aggregation index ( AI), the area ratio (AR), and the normalized projected area (An), are introduced and the single-scattering properties of aggregates of plates are shown to depend heavily on AI. A new model (budding Bucky ball, 3B) for the shape of small ice crystals is developed based on the shapes of ice analogues grown in laboratory experiments. The 3B scatters more light in the lateral, and backward direction and less in the forward direction compared with other existing models currently used to describe small crystal shape (i.e., Gaussian random sphere and droxtal). The combination of the reduction in the forward scattering and enhancement in the lateral and backward scattering causes 11.13% and 8.74% decreases in g for the 3B compared with that for Gaussian random sphere and droxtal, respectively. The impacts of variations in small ice crystal shapes and concentrations on bulk scattering properties of tropical cirrus are quantified. The calculated mean asymmetry parameter ḡ for the fresh anvil (i.e., 2 Feb) is larger than that for cirrus bands of varying ages (i.e., 27 and 29 Jan.) for -60 < T < -45°C and -45 < T < -30°C where the fractional contributions of small ice crystals to total cross sectional area are small. The impact using different models for small ice crystals on ḡ is largest at lower temperatures (T < -60°C). The impact of enhanced number concentrations of small ice crystals on the bulk scattering properties depends on the assumed shapes of small ice crystals, which is largest (smallest) in the temperature ranges of -45 < T < -30 T (T < -60°C) where the CAS/CDP ratio of N of small ice crystals is maximum (minimum).

Simulating LGM retreat of the Uummannaq Ice Stream and Rinks Isbrae, Western Greenland using a 1-D ice-stream model constrained by a suite of marine and terrestrial data

NASA Astrophysics Data System (ADS)

Jamieson, Stewart; Roberts, Dave; Rea, Brice; Lane, Timothy; Vieli, Andreas; Cofaigh, Colm Ó.

2014-05-01

We aim to understand what controlled the retreat pattern of the Uummannaq Ice Stream (UIS) during the last deglaciation. Evidence for the pattern of retreat is found in both the marine and terrestrial realms, but because the evidence is temporally and spatially discontinuous, it is challenging to coherently reconstruct both grounding-line retreat and ice-surface thinning such that they are in agreement. Marine stratigraphic and geophysical evidence indicates that the ice stream was grounded close to the continental shelf edge at the Last Glacial Maximum, and retreated rapidly and nonlinearly after 14.8 ka. Cosmogenic nuclide exposure dating on Ubekendt Island at the convergence zone of multiple feeder ice streams show that the ice surface thinned progressively and that the island became ice-free by ca. 12.4 ka. The ice stream then collapsed over the next 1-1.6 kyrs and the ice stream separated into a series of distinct inland arms. In the northernmost Rinks system, there is a 'staircase' of evidence showing ice surface thinning over time, but it is unclear where the grounding line was located during this phase of thinning. Furthermore, it is currently unclear what controlled the nonlinear retreat pattern identified in the Uummannaq system. We develop a numerical model of ice-stream retreat using the marine geophysical data and measurements of sediment strength on the continental shelf to control the boundary conditions. The model has the capability to dynamically and robustly simulate grounding line-retreat behaviour over millennial timescales. We simulate the retreat of the UIS grounding line into the northernmost Rinks system in response to enhanced ocean warming, rising sea level and warming climate. We compare the simulated dynamic behaviour of the UIS against the geomorphological and cosmogenic exposure evidence for ice surface thinning onshore and against dated marine grounding line positions. Our model results enable us to match grounding-line positions in the marine trough to distinct onshore ice-surface heights, and therefore provide a 2-dimensional reconstruction of the geometry of the UIS as it retreated after the LGM. We find that the nonlinearity in retreat rate is conditioned by the locations of vertical and lateral constrictions in the Uummannaq/Rink trough which provide temporary pinning points for the grounding line. When the grounding line retreats rapidly between pinning points, the ice surface thins rapidly inland. When the grounding line is pinned, thinning of the ice surface becomes much slower in locations corresponding to the deposition of moraines. We suggest that the slowdowns in retreat identified in the marine domain are therefore reflected by the generation of moraines in the terrestrial domain. Finally, we generate hypotheses about the timing of marine grounding-line retreat based upon the published terrestrial cosmogenic exposure ages.

Experimental Study of Supercooled Large Droplet Impingement Effects

NASA Technical Reports Server (NTRS)

Papadakis, M.; Rachman, A.; Wong, S. C.; Hung, K. E.; Vu, G. T.

2003-01-01

Typically, ice accretion results from small supercooled droplets (droplets cooled below freezing), usually 5 to 50 microns in diameter, which can freeze upon impact with an aircraft surface. Recently, ice accretions resulting from supercooled large droplet (SLD) conditions have become a safety concern. Current ice accretion codes have been extensively tested for Title 14 Code of Federal Regulations Part 25, Appendix C icing conditions but have not been validated for SLD icing conditions. This report presents experimental methods for investigating large droplet impingement dynamics and for obtaining small and large water droplet impingement data.

Expanding research capabilities with sea ice climate records for analysis of long-term climate change and short-term variability

NASA Astrophysics Data System (ADS)

Scott, D. J.; Meier, W. N.

2008-12-01

Recent sea ice analysis is leading to predictions of a sea ice-free summertime in the Arctic within 20 years, or even sooner. Sea ice topics, such as concentration, extent, motion, and age, are predominately studied using satellite data. At the National Snow and Ice Data Center (NSIDC), passive microwave sea ice data sets provide timely assessments of seasonal-scale variability as well as consistent long-term climate data records. Such data sets are crucial to understanding changes and assessing their impacts. Noticeable impacts of changing sea ice conditions on native cultures and wildlife in the Arctic region are now being documented. With continued deterioration in Arctic sea ice, global economic impacts will be seen as new shipping routes open. NSIDC is at the forefront of making climate data records available to address the changes in sea ice and its global impacts. By focusing on integrated data sets, NSIDC leads the way by broadening the studies of sea ice beyond the traditional cryospheric community.

The Geology and Astrobiology of Europa (Invited)

NASA Astrophysics Data System (ADS)

Chyba, C. F.; Hand, K. P.

2009-12-01

Galileo’s discovery of the jovian moons was a crucial step in the process, completed by Newton, that overthrew the Aristotelian dichotomy between the physics of the terrestrial realm and the physics of the heavens. Now, 400 years later, we know of one kind of biology, Earth biology (DNA-protein life) and have glimpses of other possibilities more closely or distantly related (e.g., the RNA world). The galilean satellite Europa is one of the most likely venues in our solar system for presenting us with another example of life, and life likely from an entirely separate origin. Europa therefore gives us a chance to extend our understanding of biology beyond Earth biology to a more generalized biology, providing a biological counterpart to the galilean/newtonian revolution. This possibility is the reason that Europa is one of the highest priorities in solar system exploration. It is a still entirely speculative but credible possibility, because of Europa’s extraordinary geophysics and chemistry. First, radiogenic decay and tidal energy appear sufficient to maintain a subsurface liquid water ocean on Europa that resides between an ice shell and a rocky mantle. Gravity measurements confirm this differentiation, and magnetometer measurements seem to confirm the liquidity of the ocean. Magnetometer measurements further put strong limits on the thickness of the ice shell overlying the ocean and on the salinity of the ocean itself. Because the ocean is covered by kilometers of ice, the enormous free energy of sunlight is rarely available for chemistry or possible biology, but radiolytic chemistry at the surface ice may provide a powerful oxidizing arrow for the ocean that, coupled with deep hydrothermal activity, maintains a supply of electron acceptor and donor pairs that could be used by life. The details of this scenario depend on surface impact gardening and sputtering rates, and on the interaction of the ice shell with the ocean. Current estimates based on cratering rates suggest an ice shell age 1-2 orders of magnitude less than the age of the solar system; sufficiently frequent melting into the ocean could lead to an oxidized, rather than a reduced ocean. Europa likely formed with a chondritic composition and, in addition, accumulated some material (while losing much in erosion) from impacts over the age of the solar system, so that the biologically essential elements should all be present. It is this combination of liquid water, essential elements, and available energy, all in contact with potentially catalytic mineral surfaces, that makes Europa so biologically attractive and gives its ocean the appearance of habitability, at least for some potential Earth-analog organisms. Of course, habitability for life and prospects for the origin of life are two distinct issues.

Assessing the Response of Alaska's Glaciers to Post-Little Ice Age Climate Change

NASA Astrophysics Data System (ADS)

Molnia, B. F.

2001-12-01

A comprehensive survey of the eleven mountain ranges and three island areas in Alaska that presently support glaciers was conducted to determine how glaciers in each area have responded to post-Little Ice Age (LIA) climate change. Today, glaciers cover 5 percent of Alaska, about 75,000 sq. km., range in elevation from 6,000 m to below sea level, and span latitudes from south of 55 degrees N to north of 69 degrees N. During the LIA, Alaskan glaciers expanded significantly, covering 10 percent more area than today. Many different types of data were used to construct baselines and determine glacier change. These include: published descriptions of glaciers (1794 - 2000), historic and modern maps (1794 - 2000), aerial photography (1926 - 2001), ground photography (1884 - 2001), airborne radar (1981 - 1991), satellite radar (1978 - 1998), space photography (1984 - 1994), multi-spectral satellite imagery (1972 - 2001), aerial reconnaissance and field observations by the author (1968 - 2001), and various types of proxy data. Data available varied for each region and glacier. Every mountain range and island group investigated is characterized by significant glacier retreat, thinning, and/or stagnation, especially at lower elevations. At some locations, glaciers have completely disappeared during the twentieth century. In other areas, retreat that started as early as the early eighteenth century, has continued into the twenty-first century. Ironically, in several areas, retreat is resulting in the number of glaciers is actually increasing, but the volume and area of ice is decreasing. The key survey findings are: ALEXANDER ARCHIPELAGO, KODIAK ISLAND, ALEUTIAN ISLANDS: every glacier examined showed evidence of thinning and retreat. Some have disappeared since last being mapped in the mid-twentieth century; COAST MOUNTAINS, ST. ELIAS MOUNTAINS, CHUGACH MOUNTAINS, KENAI MOUNTAINS, WRANGELL MOUNTAINS, ALASKA RANGE, AND THE ALEUTIAN RANGE: more than 95 percent of glaciers ending below an elevation of 1,500 m are retreating, thinning, and/or stagnating. Some advancing glaciers have tidewater termini. The two largest glaciers, Bering and Malaspina Glaciers, are thinning and retreating, losing several cubic kilometers of ice each year to melting and calving; TALKEETNA MOUNTAINS, AHKLUN-WOOD RIVER MOUNTAINS, KIGLUAIK MOUNTAINS, AND THE BROOKS RANGE: every glacier examined is retreating. Some disappeared during the twentieth century. Glaciers at higher elevations show little or no change. Perhaps, at these locations, regional climate change has not resulted in temperatures being elevated to a level where they impact existing glacier ice. Increases in precipitation may also be compensating for increases in melting. Throughout Alaska, in response to post-Little Ice Age climate change, all but a few glaciers that descent below an elevation of 1,500 m have thinned, stagnated, and/or retreated. Of the nearly 700 named Alaskan glaciers, less than a dozen are currently advancing.

Light transport and general aviation aircraft icing research requirements

NASA Technical Reports Server (NTRS)

Breeze, R. K.; Clark, G. M.

1981-01-01

A short term and a long term icing research and technology program plan was drafted for NASA LeRC based on 33 separate research items. The specific items listed resulted from a comprehensive literature search, organized and assisted by a computer management file and an industry/Government agency survey. Assessment of the current facilities and icing technology was accomplished by presenting summaries of ice sensitive components and protection methods; and assessments of penalty evaluation, the experimental data base, ice accretion prediction methods, research facilities, new protection methods, ice protection requirements, and icing instrumentation. The intent of the research plan was to determine what icing research NASA LeRC must do or sponsor to ultimately provide for increased utilization and safety of light transport and general aviation aircraft.

Glacier Instability, Rapid Glacier Lake Growth and Related Hazards at Belvedere Glacier, Macugnaga, Italy

NASA Astrophysics Data System (ADS)

Huggel, C.; Kaeaeb, A.; Haeberli, W.; Mortara, G.; Chiarle, M.; Epifani, F.

2002-12-01

Starting in summer 2000, Belvedere Glacier, near Macugnaga, Italian Alps, developed an extraordinary change in flow, geometry and surface appearance. A surge-type flow acceleration started in the lower parts of the Monte-Rosa east face, leading to strong crevassing and deformation of Belvedere Glacier, accompanied by bulging of its orographic right margin. In September 2001, a small supraglacial lake developed on the glacier. High water pressure and accelerated movement lasted into winter 2001/2002. The ice, in places, started to override moraines from the Little Ice Age. In late spring and early summer 2002, the supraglacial lake grew at extraordinary rates reaching a maximum area of more than 150'000 m2 by end of June. The evolution of such a large supraglacial lake, a rather unique feature in the Alps, was probably enabled by changes in the subglacial drainage system in the course of the surge-like developments with high water pressure in the glacier. At the end of June, an enhanced growth of the lake level with a rise of about 1 m per day was observed such that the supraglacial lake became a urgent hazard problem for the community of Macugnaga. Emergency measures had to be taken by the Italian Civil Protection. The authors thereby acted as the official expert advisers. Temporal evacuations were ordered and a permanent monitoring and alarm system was installed. Pumps with a maximum output of 1 m3/s were brought to the lake. Bathymetric studies yielded a maximum lake depth of 55 m and a volume of 3.3 millions of cubic meters of water. Aerial photography of 1995, 1999, September 2001 and October 2001 was used to calculate ice flow velocities and changes in surface altitude. Compared to the period of 1995 to 1999, the flow accelerated by about five times in 2001 (max. speeds up to 200 m/yr). Surface uplift measured was about 10-15 m/yr. The results of the photogrammetric studies were used to evaluate different possible lake-outburst scenarios, in particular overtopping and failure of ice dam with catastrophic subglacial drainage. In consideration of the current bathymetric studies and ice thickness measurements from the 1980ies, it was assumed that the floatation equilibrium was possibly reached by end of June. In case of an ice dam, the maximum discharge of a related subglacial drainage was estimated at 200 m3/s, probably involving a large debris flow. Extension and nature of thermokarst processes of the lake/ice interface are currently studied by repeated bathymetric measurements and adaption of corresponding models. In July/August 2002, geodetic ice flow velocity measurements showed that the enhanced flow velocities have decreased probably indicat ing the end of the surge-like movement. In conclusion, the developments at Macugnaga are an excellent example illustrating the need for inte grated hazard assessments in consideration of complex process chains. The current situation requires studies on different aspects, such as rock instabilities, glacier dynamics and hydrology, geomorphody namics, and mitigation-construction planning.

White Arctic vs. Blue Arctic: A case study of diverging stakeholder responses to environmental change

NASA Astrophysics Data System (ADS)

Newton, Robert; Pfirman, Stephanie; Schlosser, Peter; Tremblay, Bruno; Murray, Maribeth; Pomerance, Rafe

2016-08-01

Recent trends and climate models suggest that the Arctic summer sea ice cover is likely to be lost before climate interventions can stabilize it. There are environmental, socioeconomic, and sociocultural arguments for, but also against, restoring and sustaining current conditions. Even if global warming can be reversed, some people will experience ice-free summers before perennial sea ice begins to return. We ask: How will future generations feel about bringing sea ice back where they have not experienced it before? How will conflicted interests in ice-covered vs. ice-free conditions be resolved? What role will science play in these debates?

Investigation of surface water behavior during glaze ice accretion

NASA Technical Reports Server (NTRS)

Hansman, R. John, Jr.; Turnock, Stephen R.

1988-01-01

Microvideo observations of glaze ice accretions on 1-in-diameter cylinders in a closed-loop refrigerated wind tunnel were obtained to study factors controlling the behavior of unfrozen surface water during glaze ice accretion. Three zones of surface water behavior were noted, each with a characteristic roughness. The effect of substrate thermal and roughness properties on ice accretions was also studied. The contact angle and hysteresis were found to increase sharply at temperatures just below 0 C, explaining the high resistance to motion of water beads observed on accreting glaze ice surfaces. Based on the results, a simple multizone modification to the current glaze ice accretion model is proposed.

Ice-skating and roller disco injuries in Dublin.

PubMed Central

Horner, C.; McCabe, M. J.

1984-01-01

A comparative study was carried out on a series of 72 ice-skating and 57 roller skating injuries over a sixteen month period. The average patient age was 20.5 years in the ice-skating group and 16.5 years in the roller skating group. Females predominated in both groups accounting for 72% of ice-skaters injured and 77% of roller skaters injured. Ice-skaters sustained more serious injuries than roller skaters as was evident from the significant difference in fracture numbers in the two groups. Ice-skating fractures accounted for 40% of all injuries while roller skating fractures were only 14% of their total injuries. The majority of ice-skating fractures occurred in females. As a result of our study we recommended several preventative measures. Images p207-a p207-b PMID:6487948

Interhemispheric ice-sheet synchronicity during the last glacial maximum

USGS Publications Warehouse

Weber, Michael E.; Clark, Peter U.; Ricken, Werner; Mitrovica, Jerry X.; Hostetler, Steven W.; Kuhn, Gerhard

2011-01-01

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.

Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum.

PubMed

Weber, Michael E; Clark, Peter U; Ricken, Werner; Mitrovica, Jerry X; Hostetler, Steven W; Kuhn, Gerhard

2011-12-02

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.

High Resolution Continuous Flow Analysis System for Polar Ice Cores

NASA Astrophysics Data System (ADS)

Dallmayr, Remi; Azuma, Kumiko; Yamada, Hironobu; Kjær, Helle Astrid; Vallelonga, Paul; Azuma, Nobuhiko; Takata, Morimasa

2014-05-01

In the last decades, Continuous Flow Analysis (CFA) technology for ice core analyses has been developed to reconstruct the past changes of the climate system 1), 2). Compared with traditional analyses of discrete samples, a CFA system offers much faster and higher depth resolution analyses. It also generates a decontaminated sample stream without time-consuming sample processing procedure by using the inner area of an ice-core sample.. The CFA system that we have been developing is currently able to continuously measure stable water isotopes 3) and electrolytic conductivity, as well as to collect discrete samples for the both inner and outer areas with variable depth resolutions. Chemistry analyses4) and methane-gas analysis 5) are planned to be added using the continuous water stream system 5). In order to optimize the resolution of the current system with minimal sample volumes necessary for different analyses, our CFA system typically melts an ice core at 1.6 cm/min. Instead of using a wire position encoder with typical 1mm positioning resolution 6), we decided to use a high-accuracy CCD Laser displacement sensor (LKG-G505, Keyence). At the 1.6 cm/min melt rate, the positioning resolution was increased to 0.27mm. Also, the mixing volume that occurs in our open split debubbler is regulated using its weight. The overflow pumping rate is smoothly PID controlled to maintain the weight as low as possible, while keeping a safety buffer of water to avoid air bubbles downstream. To evaluate the system's depth-resolution, we will present the preliminary data of electrolytic conductivity obtained by melting 12 bags of the North Greenland Eemian Ice Drilling (NEEM) ice core. The samples correspond to different climate intervals (Greenland Stadial 21, 22, Greenland Stadial 5, Greenland Interstadial 5, Greenland Interstadial 7, Greenland Stadial 8). We will present results for the Greenland Stadial -8, whose depths and ages are between 1723.7 and 1724.8 meters, and 35.520 to 35.636 kyr b2k 7), respectively. The results show the conductivity measured upstream and downstream of the debubbler. We will calculate the depth resolution of our system and compare it with earlier studies. 1) Bigler at al, "Optimization of High-Resolution Continuous Flow Analysis For Transient Climate Signals in Ice Cores". Environ. Sci. Technol. 2011, 45, 4483-4489 2) Kaufmann et al, "An Improved Continuous Flow Analysis System for High Resolution Field Measurements on Ice Cores". Environmental Environ. Sci. Technol. 2008, 42, 8044-8050 3) Gkinis, V., T. J. Popp, S. J. Johnsen and T, Blunier, 2010: A continuous stream flash evaporator for the calibration of an IR cavity ring down spectrometer for the isotopic analysis of water. Isotopes in Environmental and Health Studies, 46(4), 463-475. 4) McConnell et al, "Continuous ice-core chemical analyses using inductively coupled plasma mass spectrometry. Environ. Sci. Technol. 2002, 36, 7-11 5) Rhodes et al, "Continuous methane measurements from a late Holocene Greenland ice core : Atmospheric and in-situ signals" Earth and Planetary Science Letters. 2013, 368, 9-19 6) Breton et al, "Quantifying Signal Dispersion in a Hybrid Ice Core Melting System". Environ. Sci. Technol. 2012, 46, 11922-11928 7) Rasmussen et al, " A first chronology for the NEEM ice core". Climate of the Past. 2013, 9, 2967--3013

78 FR 9088 - Self-Regulatory Organizations; ICE Clear Europe Limited; Order Approving Proposed Rule Change To...

Federal Register 2010, 2011, 2012, 2013, 2014

2013-02-07

... Customer Clearing Model for CDS Products and To Amend, Clarify, and Consolidate Certain Rules and... the proposed rule change is to provide for a Customer CDS Clearing Model whereby customers of ICE... changes that are unrelated to Customer CDS Clearing Model. Currently, ICE Clear Europe Clearing Members...

IceCube

Science.gov Websites

the IEEE Spectrum reflects on the deployment of IceCube's last string. (February 2011). From the Daily Californian (January 26, 2011) includes current group photo. From the Guardian and Observer (UK) (January 23 , 2011) NSF Press Release (December 2010) Major Milestone - Completion of the IceCube Detector December

Academic Airframe Icing Perspective

NASA Technical Reports Server (NTRS)

Bragg, Mike; Rothmayer, Alric; Thompson, David

2009-01-01

2-D ice accretion and aerodynamics reasonably well understood for engineering applications To significantly improve our current capabilities we need to understand 3-D: a) Important ice accretion physics and modeling not well understood in 3-D; and b) Aerodynamics unsteady and 3-D especially near stall. Larger systems issues important and require multidisciplinary team approach

Gold Nanoparticle Aggregation as a Probe of Antifreeze (Glyco) Protein-Inspired Ice Recrystallization Inhibition and Identification of New IRI Active Macromolecules

NASA Astrophysics Data System (ADS)

Mitchell, Daniel E.; Congdon, Thomas; Rodger, Alison; Gibson, Matthew I.

2015-10-01

Antifreeze (glyco)proteins are found in polar fish species and act to slow the rate of growth of ice crystals; a property known as ice recrystallization inhibition. The ability to slow ice growth is of huge technological importance especially in the cryopreservation of donor cells and tissue, but native antifreeze proteins are often not suitable, nor easily available. Therefore, the search for new materials that mimic this function is important, but currently limited by the low-throughout assays associated with the antifreeze properties. Here 30 nm gold nanoparticles are demonstrated to be useful colorimetric probes for ice recrystallization inhibition, giving a visible optical response and is compatible with 96 well plates for high-throughout studies. This method is faster, requires less infrastructure, and has easier interpretation than the currently used ‘splat’ methods. Using this method, a series of serum proteins were identified to have weak, but specific ice recrystallization inhibition activity, which was removed upon denaturation. It is hoped that high-throughput tools such as this will accelerate the discovery of new antifreeze mimics.

Gold Nanoparticle Aggregation as a Probe of Antifreeze (Glyco) Protein-Inspired Ice Recrystallization Inhibition and Identification of New IRI Active Macromolecules

PubMed Central

Mitchell, Daniel E.; Congdon, Thomas; Rodger, Alison; Gibson, Matthew I.

2015-01-01

Antifreeze (glyco)proteins are found in polar fish species and act to slow the rate of growth of ice crystals; a property known as ice recrystallization inhibition. The ability to slow ice growth is of huge technological importance especially in the cryopreservation of donor cells and tissue, but native antifreeze proteins are often not suitable, nor easily available. Therefore, the search for new materials that mimic this function is important, but currently limited by the low-throughout assays associated with the antifreeze properties. Here 30 nm gold nanoparticles are demonstrated to be useful colorimetric probes for ice recrystallization inhibition, giving a visible optical response and is compatible with 96 well plates for high-throughout studies. This method is faster, requires less infrastructure, and has easier interpretation than the currently used ‘splat’ methods. Using this method, a series of serum proteins were identified to have weak, but specific ice recrystallization inhibition activity, which was removed upon denaturation. It is hoped that high-throughput tools such as this will accelerate the discovery of new antifreeze mimics. PMID:26499135

Gold Nanoparticle Aggregation as a Probe of Antifreeze (Glyco) Protein-Inspired Ice Recrystallization Inhibition and Identification of New IRI Active Macromolecules.

PubMed

Mitchell, Daniel E; Congdon, Thomas; Rodger, Alison; Gibson, Matthew I

2015-10-26

Antifreeze (glyco)proteins are found in polar fish species and act to slow the rate of growth of ice crystals; a property known as ice recrystallization inhibition. The ability to slow ice growth is of huge technological importance especially in the cryopreservation of donor cells and tissue, but native antifreeze proteins are often not suitable, nor easily available. Therefore, the search for new materials that mimic this function is important, but currently limited by the low-throughout assays associated with the antifreeze properties. Here 30 nm gold nanoparticles are demonstrated to be useful colorimetric probes for ice recrystallization inhibition, giving a visible optical response and is compatible with 96 well plates for high-throughout studies. This method is faster, requires less infrastructure, and has easier interpretation than the currently used 'splat' methods. Using this method, a series of serum proteins were identified to have weak, but specific ice recrystallization inhibition activity, which was removed upon denaturation. It is hoped that high-throughput tools such as this will accelerate the discovery of new antifreeze mimics.

Ice Cores Dating With a New Inverse Method Taking Account of the Flow Modeling Errors

NASA Astrophysics Data System (ADS)

Lemieux-Dudon, B.; Parrenin, F.; Blayo, E.

2007-12-01

Deep ice cores extracted from Antarctica or Greenland recorded a wide range of past climatic events. In order to contribute to the Quaternary climate system understanding, the calculation of an accurate depth-age relationship is a crucial point. Up to now ice chronologies for deep ice cores estimated with inverse approaches are based on quite simplified ice-flow models that fail to reproduce flow irregularities and consequently to respect all available set of age markers. We describe in this paper, a new inverse method that takes into account the model uncertainty in order to circumvent the restrictions linked to the use of simplified flow models. This method uses first guesses on two flow physical entities, the ice thinning function and the accumulation rate and then identifies correction functions on both flow entities. We highlight two major benefits brought by this new method: first of all the ability to respect large set of observations and as a consequence, the feasibility to estimate a synchronized common ice chronology for several cores at the same time. This inverse approach relies on a bayesian framework. To respect the positive constraint on the searched correction functions, we assume lognormal probability distribution on one hand for the background errors, but also for one particular set of the observation errors. We test this new inversion method on three cores simultaneously (the two EPICA cores : DC and DML and the Vostok core) and we assimilate more than 150 observations (e.g.: age markers, stratigraphic links,...). We analyze the sensitivity of the solution with respect to the background information, especially the prior error covariance matrix. The confidence intervals based on the posterior covariance matrix calculation, are estimated on the correction functions and for the first time on the overall output chronologies.

Are There Differences in Ice Hockey Injuries Between Sexes?: A Systematic Review.

PubMed

MacCormick, Lauren; Best, Thomas M; Flanigan, David C

2014-01-01

Men's ice hockey allows for body checking, and women's ice hockey prohibits it. Studies have reported injury data on both sexes, but no systematic reviews have compared the injury patterns between male and female ice hockey players. Men's and women's ice hockey would have different types of injuries, and this difference would extend across the different age groups and levels of play. Systematic review; Level of evidence, 4. Three databases, 3 scientific journals, and selected bibliographies were searched to identify articles relevant to this study. Articles were further screened by the use of predetermined inclusion and exclusion criteria. Twenty-two studies met these criteria and were subsequently reviewed. Men sustained higher rates of injuries than women at all age levels, and both sexes sustained at least twice as many injuries in games than practices. Both sexes sustained most of their injuries from player contact. Men and women in college sustained most injuries to the head and face, and women suffered from higher percentages of concussion. At all ages and levels of play, men had higher rates of upper extremity injuries (shoulder), while women were found to sustain more injuries to the lower extremity (thigh, knee). Although findings showed men sustaining higher rates of injuries than women, the predominant mechanism of player contact was the same. The most common locations and types of injuries in female ice hockey players are comparable to other sports played by women, and similar interventions could offer protection against injury. Further studies that report injury data for women playing ice hockey at all levels will assist in understanding what prevention strategies should be implemented.

Science support for the Earth radiation budget sensor on the Nimbus-7 spacecraft

NASA Technical Reports Server (NTRS)

Ingersoll, A. P.

1982-01-01

Experimental data supporting the Earth radiation budget sensor on the Nimbus 7 Satellite is given. The data deals with the empirical relations between radiative flux, cloudiness, and other meteorological parameters; response of a zonal climate ice sheet model to the orbital perturbations during the quaternary ice ages; and a simple parameterization for ice sheet ablation rate.

Holocene glacier and climate variations in Vestfirðir, Iceland, from the modeling of Drangajökull ice cap

NASA Astrophysics Data System (ADS)

Anderson, Leif S.; Flowers, Gwenn E.; Jarosch, Alexander H.; Aðalgeirsdóttir, Guðfinna Th; Geirsdóttir, Áslaug; Miller, Gifford H.; Harning, David J.; Thorsteinsson, Thorsteinn; Magnússon, Eyjólfur; Pálsson, Finnur

2018-06-01

Drangajökull is a maritime ice cap located in northwest (Vestfirðir) Iceland. Drangajökull's evolution is therefore closely linked to atmospheric and ocean variability. In order to better constrain the Holocene climate and glacier history of Vestfirðir we model the past evolution of Drangajökull ice cap. Simulations from 10 ka to present are forced by general circulation model output, ice-core-based temperature reconstructions, and sea-surface temperature reconstructions. Based on these 10-thousand year simulations, Drangajökull did not persist through the Holocene. We estimate that air temperatures were 2.5-3.0 °C higher during the Holocene Thermal Maximum than the local 1960-1990 average. Simulations support Drangajökull's late Holocene inception between 2 and 1 ka, though intermittent ice likely occupied cirques as early as 2.6 ka. Drangajökull is primarily a Little Ice Age ice cap: it expanded between 1300 and 1750 CE, with the most rapid growth occurring between 1600 and 1750 CE. The maximum Holocene extent of Drangajökull occurred between 1700 and 1925 CE, despite the lowest late Holocene temperatures, occurring between 1650 and 1720 CE. Between 1700 and 1925 CE temperatures were likely 0.6-0.8 °C lower than the 1950-2015 reference temperature. The modern equilibrium line altitude (ELA) is bracketed by topographic thresholds: a 1 °C temperature increase from the modern ELA would eliminate the ice cap's accumulation area, while a reduction of 0.5 °C would lead to the rapid expansion of the ice cap across Vestfirðir. The proximity of Drangajökull to topographic thresholds may explain its late inception and rapid expansion during the Little Ice Age.

Timing and east-west correlation of south Swedish ice marginal lines during the Late Weichselian

NASA Astrophysics Data System (ADS)

Lundqvist, Jan; Wohlfarth, Barbara

2000-01-01

The retreat of the Late Weichselian ice sheet over the southern part of Sweden is marked along the southwest coast by distinct marginal moraine ridges. Their timing can directly and indirectly be assessed based on a number of radiocarbon dates and pollen stratigraphic investigations on lake sediment sequences adjacent to the ice marginal lines. Along the southeastern side of the peninsula, the ice recession has been reconstructed based on a combination of clay-varve chronology, pollen and radiocarbon stratigraphy. A morphological correlation of ice marginal lines between the west and east coast is problematic since the distinct west-coast moraines cannot be followed through the central part of the peninsula towards the east coast. This paper is an attempt to reconstruct an age-equivalent west-east extension of the ice-recession lines on the basis of existing data sets. For our correlation we use calibrated radiocarbon ages for ice marginal deposits on the west coast and compare these with a partly radiocarbon-dated clay-varve chronology on the east coast. We conclude that the two oldest moraines on the west coast formed at ˜18,000-16,000 and ˜15,400-14,500 cal yr BP, respectively. During the following rapid deglaciation, which may have coincided with the beginning of the Bølling pollen zone, large parts of southernmost Sweden became ice free, except for higher elevated areas, where stagnant ice remained for another 400-500 yr. A best guess is that the formation of the next younger ice marginal lines may have occurred at ˜14,400-14,200, ˜14,200 and ˜13,400 cal yr BP and during the Younger Dryas cold event.

On the use of δ18Oatm for ice core dating

NASA Astrophysics Data System (ADS)

Extier, Thomas; Landais, Amaelle; Bréant, Camille; Prié, Frédéric; Bazin, Lucie; Dreyfus, Gabrielle; Roche, Didier M.; Leuenberger, Markus

2018-04-01

Deep ice core chronologies have been improved over the past years through the addition of new age constraints. However, dating methods are still associated with large uncertainties for ice cores from the East Antarctic plateau where layer counting is not possible. Indeed, an uncertainty up to 6 ka is associated with AICC2012 chronology of EPICA Dome C (EDC) ice core, which mostly arises from uncertainty on the delay between changes recorded in δ18Oatm and in June 21st insolation variations at 65°N used for ice core orbital dating. Consequently, we need to enhance the knowledge of this delay to improve ice core chronologies. We present new high-resolution EDC δ18Oatm record (153-374 ka) and δO2/N2 measurements (163-332 ka) performed on well-stored ice to provide continuous records of δ18Oatm and δO2/N2 between 100 and 800 ka. The comparison of δ18Oatm with the δ18Ocalcite from East Asian speleothems shows that both signals present similar orbital and millennial variabilities, which may represent shifts in the InterTropical Convergence Zone position, themselves associated with Heinrich events. We thus propose to use the δ18Ocalcite as target for δ18Oatm orbital dating. Such a tuning method improves the ice core chronology of the last glacial inception compared to AICC2012 by reconciling NGRIP and mid-latitude climatic records. It is especially marked during Dansgaard-Oeschger 25 where the proposed chronology is 2.2 ka older than AICC2012. This δ18Oatm - δ18Ocalcite alignment method applied between 100 and 640 ka improves the EDC ice core chronology, especially over MIS 11, and leads to lower ice age uncertainties compared to AICC2012.

Thinning History of the Weddell Sea Embayment Using in situ 14C Exposure Ages from the Lassiter Coast

NASA Astrophysics Data System (ADS)

Nichols, K. A.; Johnson, J.; Goehring, B. M.; Balco, G.

2017-12-01

We present a suite of in situ 14C cosmogenic nuclide exposure ages from nunataks at the Lassiter Coast in West Antarctica on the west side of the Weddell Sea Embayment (WSE) to constrain the thinning history of the Ronne-Filchner Ice Shelf. Constraints on past ice extents in the WSE remain relatively understudied, despite the WSE draining 22% of the Antarctic Ice Sheet (AIS). Information lacking includes unambiguous geological evidence for the maximum Last Glacial Maximum (LGM) ice thickness and the timing of subsequent ice retreat in key peripheral locations. Past studies using long-lived cosmogenic nuclides have shown that, due to the cold-based nature of the AIS, inheritance of nuclide concentrations from previous periods of exposure is a common problem. We utilised the cosmogenic nuclide 14C to circumvent the issue of inheritance. The short half-life of 14C means measured concentrations are largely insensitive to inheritance, as relatively short periods of ice cover (20-30 kyr) result in significant 14C decay. Furthermore, samples saturated in 14C will demonstrate that their location was above the maximum LGM thickness of the ice sheet and exposed for at least the past ca. 35 kyr. Preliminary results from four samples indicate elevations between 63 and 360 m above the present-day ice surface elevations were deglaciated between 7 and 6 ka. With little exposed rock above these elevations (ca. 70 m), this may indicate that the locality was entirely covered by ice during the LGM. Additional 14C measurements will form a full elevation transect of samples to decipher the post-LGM thinning history of ice at this location.

Asynchronous behavior of the Antarctic Ice Sheet and local glaciers during and since Termination 1, Salmon Valley, Antarctica

NASA Astrophysics Data System (ADS)

Jackson, Margaret S.; Hall, Brenda L.; Denton, George H.

2018-01-01

The stability of the Antarctic Ice Sheet under future warming remains an open question with broad implications for sea-level prediction and adaptation. In particular, knowledge of whether the ice sheet has the capacity for rapid drawdown or collapse, or whether it can remain stable during periods of warming, is essential for predicting its future behavior. Here we use 55 radiocarbon dates, coupled with geomorphologic mapping, to reconstruct the timing of changes in ice extent and elevation during the last ice-age termination in Salmon Valley, adjacent to McMurdo Sound in the western Ross Sea Embayment. Results indicate that a grounded ice sheet in the Ross Sea Embayment achieved its maximum elevation and extent along the headlands of Salmon Valley at ∼18,000 yr BP, during a period of increasing temperatures and accumulation over the Antarctic continent. This ice remained at or near its maximum on the headlands near the valley mouth until after ∼14,000 yr BP. Removal of grounded Ross Sea ice from Salmon Valley was complete shortly after ∼7900 yr BP, indicating that the grounding line had retreated through southern McMurdo Sound by that time. We suggest the primary driver of Ross Sea ice removal from McMurdo Sound was marine-based, either through basal melting or calving due to sea-level rise. When combined with regional data, the Salmon Valley record suggests that this sector of the Antarctic Ice Sheet did not contribute in a significant way to deglacial meltwater pulses, such as meltwater pulse 1a. In contrast to the Ross Sea ice, our work also shows that local, independent alpine glaciers in Salmon Valley have advanced through the Holocene. Land-terminating glaciers such as these elsewhere in the region show a similar pattern, and may reflect the continued influence of increased accumulation following the termination of the last ice age.

Brief Communication: Mapping river ice using drones and structure from motion

NASA Astrophysics Data System (ADS)

Alfredsen, Knut; Haas, Christian; Tuhtan, Jeffrey A.; Zinke, Peggy

2018-02-01

In cold climate regions, the formation and break-up of river ice is important for river morphology, winter water supply, and riparian and instream ecology as well as for hydraulic engineering. Data on river ice is therefore significant, both to understand river ice processes directly and to assess ice effects on other systems. Ice measurement is complicated due to difficult site access, the inherent complexity of ice formations, and the potential danger involved in carrying out on-ice measurements. Remote sensing methods are therefore highly useful, and data from satellite-based sensors and, increasingly, aerial and terrestrial imagery are currently applied. Access to low cost drone systems with quality cameras and structure from motion software opens up a new possibility for mapping complex ice formations. Through this method, a georeferenced surface model can be built and data on ice thickness, spatial distribution, and volume can be extracted without accessing the ice, and with considerably fewer measurement efforts compared to traditional surveying methods. A methodology applied to ice mapping is outlined here, and examples are shown of how to successfully derive quantitative data on ice processes.

Effect of Ice Shape Fidelity on Swept-Wing Aerodynamic Performance

NASA Technical Reports Server (NTRS)

Camello, Stephanie C.; Bragg, Michael B.; Broeren, Andy P.; Lum, Christopher W.; Woodard, Brian S.; Lee, Sam

2017-01-01

Low-Reynolds number testing was conducted at the 7 ft. x 10 ft. Walter H. Beech Memorial Wind Tunnel at Wichita State University to study the aerodynamic effects of ice shapes on a swept wing. A total of 17 ice shape configurations of varying geometric detail were tested. Simplified versions of an ice shape may help improve current ice accretion simulation methods and therefore aircraft design, certification, and testing. For each configuration, surface pressure, force balance, and fluorescent mini-tuft data were collected and for a selected subset of configurations oil-flow visualization and wake survey data were collected. A comparison of two ice shape geometries and two configurations with simplified geometric detail for each ice shape geometry is presented in this paper.

Eastern Ross Ice Sheet Deglacial History inferred from the Roosevelt Island Ice Core

NASA Astrophysics Data System (ADS)

Fudge, T. J.; Buizert, C.; Lee, J.; Waddington, E. D.; Bertler, N. A. N.; Conway, H.; Brook, E.; Severinghaus, J. P.

2017-12-01

The Ross Ice Sheet drains large portions of both West and East Antarctica. Understanding the retreat of the Ross Ice Sheet following the Last Glacial Maximum is particularly difficult in the eastern Ross area where there is no exposed rock and the Ross Ice Shelf prevents extensive bathymetric mapping. Coastal domes, by preserving old ice, can be used to infer the establishment of grounded ice and be used to infer past ice thickness. Here we focus on Roosevelt Island, in the eastern Ross Sea, where the Roosevelt Island Climate Evolution project recently completed an ice core to bedrock. Using ice-flow modeling constrained by the depth-age relationship and an independent estimate of accumulation rate from firn-densification measurements and modeling, we infer ice thickness histories for the LGM (20ka) to present. Preliminary results indicate thinning of 300m between 15ka and 12ka is required. This is similar to the amount and timing of thinning inferred at Siple Dome, in the central Ross Sea (Waddington et al., 2005; Price et al., 2007) and supports the presence of active ice streams throughout the Ross Ice Sheet advance during the LGM.

The implementation of a municipal indoor ice skating helmet policy: effects on helmet use, participation and attitudes.

PubMed

O'Mahony-Menton, Colleen; Willmore, Jacqueline; Russell, Katherine

2015-12-01

In Ottawa, between 2005 and 2009 there was an annual average of 47.2 head injuries due to ice skating in children and youth (1-19 years of age) requiring a visit to the emergency department, with the highest rates among those aged 5-14 years. Between 2002 and 2007, only 6% of children were wearing a helmet during ice skating when the head injury occurred. During indoor public skating sessions, 93% of children (<10 years)-57% aged 10-12 years, 20% aged 13-17 years and 9% adults-wore helmets in the absence of a policy. Support for a helmet policy was high from public health, medical, political and community perspectives. Helmet policies in relation to cycling have demonstrated increases in helmet use and reduction of head injuries without decreasing physical activity. However, no known studies have examined the effect of indoor ice skating helmet policy coupled with education and promotional activities on helmet use, participation and attitudes towards helmet use. An ice skating helmet policy for children (<11 years of age) and those with limited skating experience at indoor rinks during public skating sessions was developed, implemented and evaluated. Supportive activities such as discount coupons, promotional materials, a media launch, social marketing and staff training are described. The helmet policy was associated with increased helmet use for young children and for older children, youth and adults not included in the policy, without decreasing attendance to public skating sessions. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

USGS Publications Warehouse

Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

2013-01-01

Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

Geochronological (OSL) and geomorphological investigations at the presumed Frankfurt ice marginal position in northeast Germany

NASA Astrophysics Data System (ADS)

Hardt, Jacob; Lüthgens, Christopher; Hebenstreit, Robert; Böse, Margot

2016-12-01

The Weichselian Frankfurt ice marginal position in northeast Germany has been critically discussed in the past owing to weak morphological evidence and a lack of clear sedimentological records. This study aims to contribute to this discussion with new geochronological and geomorphological results. Apart from very few cosmogenic exposure ages, the time frame is to date still based on long distance correlation with radiocarbon chronologies. We selected a study site in a key position regarding the classic location of the Frankfurt ice marginal position and the recently described arcuate ridge structures on the Barnim plateau. For the first time we present Optically Stimulated Luminescence (OSL) ages of quartz from glaciofluvial deposits for this Weichselian phase. Our results indicate an advance of the Scandinavian Ice Sheet (SIS) at around 34.1 ± 4.6 ka. This is in agreement with OSL ages from sandur deposits at the Brandenburg ice marginal position located farther south and could also be correlated with the Klintholm advance in Denmark. The subsequent meltdown phase lasted until around 26.3 ± 3.7 ka. During the meltdown phase a minor oscillation of the SIS caused the formation of the recently described arcuate ridges on the Barnim till plain. Recalculated surface exposure ages of glacigenic boulders with an updated global production rate indicate a landscape stabilization phase at around 22.7 ± 1.6 ka, which is in agreement with our ages. A phase of strong aeolian activity has been dated with OSL to 1 ± 0.1 ka; this may have been triggered by human activities that are documented in this region for the medieval period.

Ice-age megafauna in Arctic Alaska: extinction, invasion, survival

NASA Astrophysics Data System (ADS)

Mann, Daniel H.; Groves, Pamela; Kunz, Michael L.; Reanier, Richard E.; Gaglioti, Benjamin V.

2013-06-01

Radical restructuring of the terrestrial, large mammal fauna living in arctic Alaska occurred between 14,000 and 10,000 years ago at the end of the last ice age. Steppe bison, horse, and woolly mammoth became extinct, moose and humans invaded, while muskox and caribou persisted. The ice age megafauna was more diverse in species and possibly contained 6× more individual animals than live in the region today. Megafaunal biomass during the last ice age may have been 30× greater than present. Horse was the dominant species in terms of number of individuals. Lions, short-faced bears, wolves, and possibly grizzly bears comprised the predator/scavenger guild. The youngest mammoth so far discovered lived ca 13,800 years ago, while horses and bison persisted on the North Slope until at least 12,500 years ago during the Younger Dryas cold interval. The first people arrived on the North Slope ca 13,500 years ago. Bone-isotope measurements and foot-loading characteristics suggest megafaunal niches were segregated along a moisture gradient, with the surviving species (muskox and caribou) utilizing the warmer and moister portions of the vegetation mosaic. As the ice age ended, the moisture gradient shifted and eliminated habitats utilized by the dryland, grazing species (bison, horse, mammoth). The proximate cause for this change was regional paludification, the spread of organic soil horizons and peat. End-Pleistocene extinctions in arctic Alaska represent local, not global extinctions since the megafaunal species lost there persisted to later times elsewhere. Hunting seems unlikely as the cause of these extinctions, but it cannot be ruled out as the final blow to megafaunal populations that were already functionally extinct by the time humans arrived in the region.

Late Quaternary deglacial history across the Larsen B embayment, Antarctica

NASA Astrophysics Data System (ADS)

Jeong, Ara; Lee, Jae Il; Seong, Yeong Bae; Balco, Greg; Yoo, Kyu-Cheul; Yoon, Ho Il; Domack, Eugene; Rhee, Hyun Hee; Yu, Byung Yong

2018-06-01

We measured meteoric 10Be variation throughout a marine sediment core from the Larsen B embayment (LBE) of the Antarctic Peninsula, and collected in situ 10Be and 14C exposure ages on terrestrial glacial deposits from the northern and southern margins of the LBE. We use these data to reconstruct Last Glacial Maximum (LGM) to present deglaciation and ice shelf change in the LBE. Core sedimentary facies and meteoric 10Be data show a monotonic progression from subglacial deposits to sub-ice-shelf deposits to open-marine conditions, indicating that its collapse in 2002 was unprecedented since the LGM. Exposure-age data from the southern LBE indicate 40 m of ice surface lowering between 14 and 6 ka, then little change between 6 ka and the 2002 collapse. Exposure-age data from the northern LBE show a bimodal distribution in which clusters of apparent exposure ages in the ranges 4.9-5.1 ka and 1.0-2.0 ka coexist near 50 m elevation. Based on these results, other published terrestrial and marine deglaciation ages, and a compilation of sea bed imagery, we suggest a north-to-south progression of deglaciation in the northeast Antarctic Peninsula in response to Holocene atmospheric and oceanic warming. We argue that local topography and ice configuration inherited from the LGM, in addition to climate change, are important in controlling the deglaciation history in this region.

Ocean-Ice-Atmosphere Interactions off Sabrina and Adelie Coasts During NBP1402 and AU1402

NASA Astrophysics Data System (ADS)

Orsi, A. H.; Zielinski, N. J.; Webb, C.; Huber, B. A.

2015-12-01

Diverse interactions of winds, currents and ice around Antarctica dictate how, where and when the world's densest waters form, massive floating ice shelves and glaciers melt, gases are exchanged at the sea surface, and primary productivity. Compelled by recent rate estimates of East Antarctic Ice Sheet mass loss, we contrast the paths and mixing histories of oceanic waters reaching the continental ice edge off the Sabrina and Adelie coasts relying on a the first synoptic shipboard measurements made by U.S. (NBP1402) and Australian (AU1402) scientists. Analysis of historical hydrography and sea ice concentration fields within the Mertz Polynya indicates the apparent effect of evolving ocean-ice- atmosphere interactions on the characteristics of local Shelf Water (SW) sources. A polynya dominated water mass structure similar to that observed off the Adelie Coast before the removal of the Mertz Ice Tongue was expected to the west of the Dalton Ice Tongue (DIT). However, there was no evidence of dense SW off Sabrina Coast during both summer cruises of 2014 and 2015, thus lessening the region's preconceived influence to global meridional overturning. Present sea ice production within the eastern Dalton Polynya is overshadowed by freshwater input to relatively stable interior upper waters. The Antarctic Coastal Current (ACoC) picks up distinct meltwater contributions along the DIT western flank and in front of the Moscow University Ice Shelf (MUIS) and Totten Glacier (TG). Unlike over other highly influential margins to global sea level rise, the main evidence of inflow and mixing of relatively warm oceanic waters is reduced to relatively cold thermocline water (< 0.3°C) from the continental slope. This source water enters the eastern trough off Sabrina Coast and is swiftly steered poleward by complex underlying topography. Meltwater export from beneath the MUIS and TG is observed at newly discovered trenches that effectively constrain sub-cavity inflow to low salinity near-freezing waters drawn from intermediate levels of the adjacent westward flowing ACoC.
Winds, currents and ice interactions observed off Sabrina Coast during NBP1402 and AU1402 are most likely widespread, in view of reported decadal freshening of upper waters over the Antarctic continental shelf and their localized AABW outflows.

Reconstructing lake ice cover in subarctic lakes using a diatom-based inference model

NASA Astrophysics Data System (ADS)

Weckström, Jan; Hanhijärvi, Sami; Forsström, Laura; Kuusisto, Esko; Korhola, Atte

2014-03-01

A new quantitative diatom-based lake ice cover inference model was developed to reconstruct past ice cover histories and applied to four subarctic lakes. The used ice cover model is based on a calculated melting degree day value of +130 and a freezing degree day value of -30 for each lake. The reconstructed Holocene ice cover duration histories show similar trends to the independently reconstructed regional air temperature history. The ice cover duration was around 7 days shorter than the average ice cover duration during the warmer early Holocene (approximately 10 to 6.5 calibrated kyr B.P.) and around 3-5 days longer during the cool Little Ice Age (approximately 500 to 100 calibrated yr B.P.). Although the recent climate warming is represented by only 2-3 samples in the sediment series, these show a rising trend in the prolonged ice-free periods of up to 2 days. Diatom-based ice cover inference models can provide a powerful tool to reconstruct past ice cover histories in remote and sensitive areas where no measured data are available.

Atmospheric form drag over Arctic sea ice derived from high-resolution IceBridge elevation data

NASA Astrophysics Data System (ADS)

Petty, A.; Tsamados, M.; Kurtz, N. T.

2016-02-01

Here we present a detailed analysis of atmospheric form drag over Arctic sea ice, using high resolution, three-dimensional surface elevation data from the NASA Operation IceBridge Airborne Topographic Mapper (ATM) laser altimeter. Surface features in the sea ice cover are detected using a novel feature-picking algorithm. We derive information regarding the height, spacing and orientation of unique surface features from 2009-2014 across both first-year and multiyear ice regimes. The topography results are used to explicitly calculate atmospheric form drag coefficients; utilizing existing form drag parameterizations. The atmospheric form drag coefficients show strong regional variability, mainly due to variability in ice type/age. The transition from a perennial to a seasonal ice cover therefore suggest a decrease in the atmospheric form drag coefficients over Arctic sea ice in recent decades. These results are also being used to calibrate a recent form drag parameterization scheme included in the sea ice model CICE, to improve the representation of form drag over Arctic sea ice in global climate models.

Glaciological studies in the central Andes using AIRSAR/TOPSAR

NASA Technical Reports Server (NTRS)

Forster, Richard R.; Klein, Andrew G.; Blodgett, Troy A.; Isacks, Bryan L.

1993-01-01

The interaction of climate and topography in mountainous regions is dramatically expressed in the spatial distribution of glaciers and snowcover. Monitoring existing alpine glaciers and snow extent provides insight into the present mountain climate system and how it is changing, while mapping the positions of former glaciers as recorded in landforms such as cirques and moraines provide a record of the large past climate change associated with the last glacial maximum. The Andes are an ideal mountain range in which to study the response of snow and ice to past and present climate change. Their expansive latitudinal extent offers the opportunity to study glaciers in diverse climate settings from the tropical glaciers of Peru and Bolivia to the ice caps and tide-water glaciers of sub-polar Patagonia. SAR has advantages over traditional passive remote sensing instruments for monitoring present snow and ice and differentiating moraine relative ages. The cloud penetrating ability of SAR is indispensable for perennially cloud covered mountains. Snow and ice facies can be distinguished from SAR's response to surface roughness, liquid water content and grain size distribution. The combination of SAR with a coregestered high-resolution DEM (TOPSAR) provides a promising tool for measuring glacier change in three dimensions, thus allowing ice volume change to be measured directly. The change in moraine surface roughness over time enables SAR to differentiate older from younger moraines. Polarimetric SAR data have been used to distinguish snow and ice facies and relatively date moraines. However, both algorithms are still experimental and require ground truth verification. We plan to extend the SAR classification of snow and ice facies and moraine age beyond the ground truth sites to throughout the Cordillera Real to provide a regional view of past and present snow and ice. The high resolution DEM will enhance the SAR moraine dating technique by discriminating relative ages based on moraine slope degradation.

The Unexpected Re-Growth of Ice-Entombed Bryophytes in the Canadian High Arctic

NASA Astrophysics Data System (ADS)

La Farge, C.

2014-12-01

The rapid retreat of glaciers and ice caps throughout the Canadian Arctic is exposing pristine vegetation preserved beneath cold-based ice. For the past half century this vegetation has been consistently reported as dead. This interpretation has been overturned by the successful re-growth of Little Ice Age (1550-1850 AD) bryophytes emerging from the Teardrop Glacier, Sverdrup Pass, Ellesmere Island (79° N) collected in 2009. Some populations showed regeneration in the field and lab experiments confirmed their capacity to regrow. The species richness of these subglacial populations is exceptional, comprising >62 species that represent 44% of the extant bryophyte flora of Sverdrup Pass. Cold-based glaciers are known to provide critical habitats for a variety of microbiota (i.e., fungi, algae, cyanobacteria, bacteria and viruses) in high latitude ecosystems. The regeneration of Little Ice Age bryophytes fundamentally expands the concept of biological refugia to land plants that was previously restricted to survival above and beyond glacial margins. Given this novel understanding of subglacial ecosystems, fieldwork is now being extended southward to plateau ice caps on Baffin Island, Nunavut, where ice retreat is exposing subglacial populations of greater antiquity (thousands to tens of thousands of radiocarbon years before present). Bryophytes by nature are totipotent (stem cell equivalency) and poikilohydric (desiccation tolerance), which facilitate their unique adaptation to extreme environments. Continuity of the Arctic bryophyte flora extends back through the Holocene to the late Tertiary [Beaufort Fm, 2-5 Ma], when the majority of taxa were the same, based on records spanning the archipelago from Ellesmere to Banks Island. This record contrasts with that of vascular plants, which have had a number of extinctions, necessitating recolonization of arctic populations from outside the region. The biological significance of a stable bryophyte element highlights their capacity, resilience and persistence throughout arctic climate fluctuations, suggesting they - like those entombed during the Little Ice Age - have survived glaciation in situ, frozen in time.

Preliminary Results From a Heavily Instrumented Engine Ice Crystal Icing Test in a Ground Based Altitude Test Facility

NASA Technical Reports Server (NTRS)

Flegel, Ashlie B.; Oliver, Michael J.

2016-01-01

Preliminary results from the Heavily Instrumented ALF503R-5 Engine test conducted in the NASA Glenn Research Center Propulsion Systems Laboratory will be discussed. The effects of ice crystal icing on a full scale engine is examined and documented. This model engine, serial number LF01, was used during the inaugural icing test in the PSL facility. The reduction of thrust (rollback) events experienced by this engine in flight were replicated in the facility. Limited instrumentation was used to detect icing. Metal temperature on the exit guide vanes and outer shroud and the load measurement were the only indicators of ice formation. The current study features a similar engine, serial number LF11, which is instrumented to characterize the cloud entering the engine, detect characterize ice accretion, and visualize the ice accretion in the region of interest.

Large-scale oil-in-ice experiment in the Barents Sea: monitoring of oil in water and MetOcean interactions.

PubMed

Faksness, Liv-Guri; Brandvik, Per Johan; Daae, Ragnhild L; Leirvik, Frode; Børseth, Jan Fredrik

2011-05-01

A large-scale field experiment took place in the marginal ice zone in the Barents Sea in May 2009. Fresh oil (7000 L) was released uncontained between the ice floes to study oil weathering and spreading in ice and surface water. A detailed monitoring of oil-in-water and ice interactions was performed throughout the six-day experiment. In addition, meteorological and oceanographic data were recorded for monitoring of the wind speed and direction, air temperature, currents and ice floe movements. The monitoring showed low concentrations of dissolved hydrocarbons and the predicted acute toxicity indicated that the acute toxicity was low. The ice field drifted nearly 80 km during the experimental period, and although the oil drifted with the ice, it remained contained between the ice floes. Copyright © 2011 Elsevier Ltd. All rights reserved.

Representation of Ice Geometry by Parametric Functions: Construction of Approximating NURBS Curves and Quantification of Ice Roughness--Year 1: Approximating NURBS Curves

NASA Technical Reports Server (NTRS)

Dill, Loren H.; Choo, Yung K. (Technical Monitor)

2004-01-01

Software was developed to construct approximating NURBS curves for iced airfoil geometries. Users specify a tolerance that determines the extent to which the approximating curve follows the rough ice. The user can therefore smooth the ice geometry in a controlled manner, thereby enabling the generation of grids suitable for numerical aerodynamic simulations. Ultimately, this ability to smooth the ice geometry will permit studies of the effects of smoothing upon the aerodynamics of iced airfoils. The software was applied to several different types of iced airfoil data collected in the Icing Research Tunnel at NASA Glenn Research Center, and in all cases was found to efficiently generate suitable approximating NURBS curves. This method is an improvement over the current "control point formulation" of Smaggice (v.1.2). In this report, we present the relevant theory of approximating NURBS curves and discuss typical results of the software.

Will sea ice thickness initialisation improve Arctic seasonal-to-interannual forecast skill?

NASA Astrophysics Data System (ADS)

Day, J. J.; Hawkins, E.; Tietsche, S.

2014-12-01

A number of recent studies have suggested that Arctic sea ice thickness is an important predictor of Arctic sea ice extent. However, coupled forecast systems do not currently use sea ice thickness observations in their initialization and are therefore missing a potentially important source of additional skill. A set of ensemble potential predictability experiments, with a global climate model, initialized with and without knowledge of the sea ice thickness initial state, have been run to investigate this. These experiments show that accurate knowledge of the sea ice thickness field is crucially important for sea ice concentration and extent forecasts up to eight months ahead. Perturbing sea ice thickness also has a significant impact on the forecast error in the 2m temperature and surface pressure fields a few months ahead. These results show that advancing capabilities to observe and assimilate sea ice thickness into coupled forecast systems could significantly increase skill.

Icing Branch Current Research Activities in Icing Physics

NASA Technical Reports Server (NTRS)

Vargas, Mario

2009-01-01

Current development: A grid block transformation scheme which allows the input of grids in arbitrary reference frames, the use of mirror planes, and grids with relative velocities has been developed. A simple ice crystal and sand particle bouncing scheme has been included. Added an SLD splashing model based on that developed by William Wright for the LEWICE 3.2.2 software. A new area based collection efficiency algorithm will be incorporated which calculates trajectories from inflow block boundaries to outflow block boundaries. This method will be used for calculating and passing collection efficiency data between blade rows for turbo-machinery calculations.

Arctic ice shelves and ice islands: Origin, growth and disintegration, physical characteristics, structural-stratigraphic variability, and dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jeffries, M.O.

1992-08-01

Ice shelves are thick, floating ice masses most often associated with Antarctica where they are seaward extensions of the grounded Antarctic ice sheet and sources of many icebergs. However, there are also ice shelves in the Arctic, primarily located along the north coast of Ellesmere Island in the Canadian High Arctic. The only ice shelves in North America and the most extensive in the north polar region, the Ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands, the tabular icebergs of the Arctic Ocean. The present state of knowledge and understanding ofmore » these ice features is summarized in this paper. It includes historical background to the discovery and early study of ice shelves and ice islands, including the use of ice islands as floating laboratories for polar geophysical research. Growth mechanisms and age, the former extent and the twentieth century disintegration of the Ellesmere ice shelves, and the processes and mechanisms of ice island calving are summarized. Surface features, thickness, thermal regime, and the size, shape, and numbers of ice islands are discussed. The structural-stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described. Large-scale and small-scale dynamics of ice islands are described, and the results of modeling their drift and recurrence intervals are presented. The conclusion identifies some unanswered questions and future research opportunities and needs. 97 refs., 18 figs.« less

Sea-Ice Conditions in the Norwegian, Barents, and White Seas

DTIC Science & Technology

1976-08-01

pack, aided by relatively warm water from the Murman coast current, would reduce the maximum ice thickness predicted by the equation used for...THICKNESS With the aid of the ice growth model in the appendix, it is pos- sible to relate the maximum ice thickness attained during a winter season to a...inserted merely to aid the reader in discerning differences between individual winter seasons. As was the case for the 12-month mean temperatures

Data Assimilation as it Relates to the Sea Ice Outlook (SIO) and Prospects for Improvement

NASA Technical Reports Server (NTRS)

Cullather, Richard

2017-01-01

Improved seasonal forecasts of Arctic sea ice are important for regional stakeholders, but also for obtaining a better understanding of the Arctic climate system. An important part of the forecasts is the initial sea ice, ocean, and atmosphere initial conditions. I briefly give an overview of the initial conditions currently being used in seasonal sea ice predictions. I also identify available sources of observational data and prospects for coupled atmosphere/ocean reanalyses.

Wave Climate and Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling

DTIC Science & Technology

2014-09-30

At the same time, the PIs participate in Australian efforts of developing wave-ocean- ice coupled models for Antarctica . Specific new physics modules...Wave Mixing in the Marginal Ice Zones of Arctic Seas, Observations and Modelling Alexander V. Babanin Swinburne University of Technology, PO Box...operational forecast. Altimeter climatology and the wave models will be used to study the current and future wind/wave and ice trends. APPROACH

Cirrus Susceptibility to Changes in Ice Nuclei: Physical Processes, Model Uncertainties, and Measurement Needs

NASA Technical Reports Server (NTRS)

Jensen, Eric

2018-01-01

One of the proposed concepts for mitigating the warming effect of increasing greenhouse gases is seeding cirrus cloud with ice nuclei (IN) in order to reduce the lifetime and coverage of cold cirrus that have a net warming impact on the earth's surface. Global model simulations of the net impact of changing upper tropospheric IN have given widely disparate results, partly as a result of poor understanding of ice nucleation processes in the current atmosphere, and partly as a result of poor representation of these processes in global models. Here, we present detailed process-model simulations of tropical tropopause layer (TTL) transport and cirrus formation with ice nuclei properties based on recent laboratory nucleation experiments and field measurements of aerosol composition. The model is used to assess the sensitivity of TTL cirrus occurrence frequency and microphysical properties to the abundance and efficacy of ice nuclei. The simulated cloud properties compared with recent high-altitude aircraft measurements of TTL cirrus and ice supersaturation. We find that abundant effective IN (either from glassy organic aerosols or crystalline ammonium sulfate with concentrations greater than about 100/L) prevent the occurrences of large ice concentration and large ice supersaturations, both of which are clearly indicated by the in situ observations. We find that concentrations of effective ice nuclei larger than about 50/L can drive significant changes in cirrus microphysical properties and occurrence frequency. However, the cloud occurrence frequency can either increase or decrease, depending on the efficacy and abundance of IN added to the TTL. We suggest that our lack of information about ice nuclei properties in the current atmosphere, as well as uncertainties in ice nucleation processes and their representations in global models, preclude meaningful estimates of climate impacts associated with addition of ice nuclei in the upper troposphere. We will briefly discuss the key field measurements needed to constrain ice nucleation processes.

Ice2sea - the future glacial contribution to sea-level rise

NASA Astrophysics Data System (ADS)

Vaughan, D. G.; Ice2sea Consortium

2009-04-01

The melting of continental ice (glaciers, ice caps and ice sheets) is a substantial source of current sea-level rise, and one that is accelerating more rapidly than was predicted even a few years ago. Indeed, the most recent report from Intergovernmental Panel on Climate Change highlighted that the uncertainty in projections of future sea-level rise is dominated by uncertainty concerning continental ice, and that understanding of the key processes that will lead to loss of continental ice must be improved before reliable projections of sea-level rise can be produced. Such projections are urgently required for effective sea-defence management and coastal adaptation planning. Ice2sea is a consortium of European institutes and international partners seeking European funding to support an integrated scientific programme to improve understanding concerning the future glacial contribution to sea-level rise. This includes improving understanding of the processes that control, past, current and future sea-level rise, and generation of improved estimates of the contribution of glacial components to sea-level rise over the next 200 years. The programme will include targeted studies of key processes in mountain glacier systems and ice caps (e.g. Svalbard), and in ice sheets in both polar regions (Greenland and Antarctica) to improve understanding of how these systems will respond to future climate change. It will include fieldwork and remote sensing studies, and develop a suite of new, cross-validated glacier and ice-sheet model. Ice2sea will deliver these results in forms accessible to scientists, policy-makers and the general public, which will include clear presentations of the sources of uncertainty. Our aim is both, to provide improved projections of the glacial contribution to sea-level rise, and to leave a legacy of improved tools and techniques that will form the basis of ongoing refinements in sea-level projection. Ice2sea will provide exciting opportunities for many early-career glaciologists and ice-modellers in a variety of host institutes.

Europa's shallow subsurface: lakes, layers and life? (Invited)

NASA Astrophysics Data System (ADS)

Schmidt, B. E.; Soderlund, K. M.; Gooch, B. T.; Blankenship, D. D.

2013-12-01

With an icy exterior covering a global ocean, Europa has long been a target of interest in the search for life beyond Earth. A critical question related to the habitability of this icy world is: how does the ice shell recycle? Recent detection of shallow subsurface water lenses or "lakes" joins the evidence that implies Europa is currently active, recycling its ice shell. This new perspective has important astrobiological implications. At a surface age of 40-90 Myr, and about 50% covered by chaos terrain, Europa's resurfacing rate is likely to be very high if water does play a significant role in their formation. Because of the vigor of overturn implied if chaos does form by the collapse of ice above subsurface lenses, it is likely that surface and subsurface materials are well-mixed within the largest and deepest lenses, providing a mechanism for bringing oxidants and other surface contaminants to the deeper ice shell where it can reach the ocean by convective or compositional effects. The timescales over which large lenses refreeze (a few hundred thousand years) are large compared to the timescales for vertical transport (a few tens of thousands of years), while the timescales for smaller lenses are comparable to or shorter than convective timescales but involving smaller impurity loads than for larger more well-mixed sources. Melt lenses are intriguing potential habitats, particularly the larger features. Moreover, their formation likely requires the existence of impurities within the upper ice shell that may be sources of energy for microorganisms. Geomorphic evidence also exists for brine percolation that can disperse fluids both vertically and horizontally through pores and fractures. This process, observed in terrestrial ice shelves, may preserve liquid water within the ice matrix over many kilometers from the source. Horizontal transport of material may produce interconnectivity between distinct regions of Europa, providing a pathway for transferring nutrients and biomass, thus preserving habitable conditions within the ice over a longer duration. From this point of view, we evaluate the habitability of Europa's ice and ocean in light of active processes, including the lifetime of liquid reservoirs, vertical and horizontal material transport, and the resurfacing rate of the body that may be responsible both for reenergizing and destroying shallow habitats.

Stationary spiraling eddies in presence of polar amplification of global warming as a governing factor of ecology of Greenland seals White Sea population: results of verification study

NASA Astrophysics Data System (ADS)

Melentyev, K.; Chernook, V.; Melentyev, V.

2003-04-01

Ice-associated forms of marine mammals are representatives of a high level of fodder chains in the ocean and taxation of population number for different group, as assessment of ecology and animal welfare are the important tasks for marine biology, ecology, fishery and other application uses. Many problems create a global warming and antropogenical impact on marine and coastal ecosystem. In order to investigate ice covered Arctic Ocean and charting the number of seals were performed annual inspections onboard research aircraft PINRO "Arktika". Multi-spectral airborne and satellite observations were fulfilled regularly from Barents and White Sea to the Bering and Okhotsk Sea (1996-2002). A contemporary status of different group of sea mammals was evaluated, where number of adults and pups were checked separately. In situ observations were provided with using helicopter and icebreaker for gathering a water samples and ice cores (with following biochemical and toxicological analysis). A prevailing part of life cycle of Greenland seals (harp seal) is strongly depended from winter hydrology (water masses, stable currents, meandering fronts, stationary eddies) and closely connected with type of ice (pack, fast ice) and other parameters of ice (age, origin, salinity, ice edge.). First-year ice floes which has a specific properties and distinctive features are used by harp seals for pupping, lactation, molting, pairing and resting. Ringed seals, inversely, use for corresponding purposes only fast-ice. Different aspects of ecology, and migration features of harp seals were analyzed in frame of verification study. It was revealed a scale of influence of winter severity and wind regime, but stationary eddies in the White Sea is most effective governing factor (novelty). Following relationship " eddies - ecology of Greenland seal White Sea population " will be discussed: A) regularities of eddies formation and their spatial arrangement, temporal (seasonal and annual) modification; B) eddies displacement and parameters modification (type of eddy, intensity and sign of rotation) as result of climate change; C) relationship between eddies location and whelping rookeries arrangement, climate change and variety of the type of migration; D) stationary eddy as zone of concentration of polluted waters and toxically hazard, climate change and self-cleaning ability; E) spiraling eddies in changing climate and prediction of modification of marine animal welfare.

Late nineteenth to early twenty-first century behavior of Alaskan glaciers as indicators of changing regional climate

USGS Publications Warehouse

Molnia, B.F.

2007-01-01

Alaska's climate is changing and one of the most significant indications of this change has been the late 19th to early 21st century behavior of Alaskan glaciers. Weather station temperature data document that air temperatures throughout Alaska have been increasing for many decades. Since the mid-20th century, the average change is an increase of ?????2.0????C. In order to determine the magnitude and pattern of response of glaciers to this regional climate change, a comprehensive analysis was made of the recent behavior of hundreds of glaciers located in the eleven Alaskan mountain ranges and three island areas that currently support glaciers. Data analyzed included maps, historical observations, thousands of ground-and-aerial photographs and satellite images, and vegetation proxy data. Results were synthesized to determine changes in length and area of individual glaciers. Alaskan ground photography dates from 1883, aerial photography dates from 1926, and satellite photography and imagery dates from the early 1960s. Unfortunately, very few Alaskan glaciers have any mass balance observations. In most areas analyzed, every glacier that descends below an elevation of ?????1500??m is currently thinning and/or retreating. Many glaciers have an uninterrupted history of continuous post-Little-Ice-Age retreat that spans more than 250??years. Others are characterized by multiple late 19th to early 21st century fluctuations. Today, retreating and/or thinning glaciers represent more than 98% of the glaciers examined. However, in the Coast Mountains, St. Elias Mountains, Chugach Mountains, and the Aleutian Range more than a dozen glaciers are currently advancing and thickening. Many currently advancing glaciers are or were formerly tidewater glaciers. Some of these glaciers have been expanding for more than two centuries. This presentation documents the post-Little-Ice-Age behavior and variability of the response of many Alaskan glaciers to changing regional climate. ?? 2006.

The Antarctic ice core chronology (AICC2012): an optimized multi-parameter and multi-site dating approach for the last 120 thousand years

NASA Astrophysics Data System (ADS)

Veres, D.; Bazin, L.; Landais, A.; Toyé Mahamadou Kele, H.; Lemieux-Dudon, B.; Parrenin, F.; Martinerie, P.; Blayo, E.; Blunier, T.; Capron, E.; Chappellaz, J.; Rasmussen, S. O.; Severi, M.; Svensson, A.; Vinther, B.; Wolff, E. W.

2013-08-01

The deep polar ice cores provide reference records commonly employed in global correlation of past climate events. However, temporal divergences reaching up to several thousand years (ka) exist between ice cores over the last climatic cycle. In this context, we are hereby introducing the Antarctic Ice Core Chronology 2012 (AICC2012), a new and coherent timescale developed for four Antarctic ice cores, namely Vostok, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML) and Talos Dome (TALDICE), alongside the Greenlandic NGRIP record. The AICC2012 timescale has been constructed using the Bayesian tool Datice (Lemieux-Dudon et al., 2010) that combines glaciological inputs and data constraints, including a wide range of relative and absolute gas and ice stratigraphic markers. We focus here on the last 120 ka, whereas the companion paper by Bazin et al. (2013) focuses on the interval 120-800 ka. Compared to previous timescales, AICC2012 presents an improved timing for the last glacial inception, respecting the glaciological constraints of all analyzed records. Moreover, with the addition of numerous new stratigraphic markers and improved calculation of the lock-in depth (LID) based on δ15N data employed as the Datice background scenario, the AICC2012 presents a slightly improved timing for the bipolar sequence of events over Marine Isotope Stage 3 associated with the seesaw mechanism, with maximum differences of about 600 yr with respect to the previous Datice-derived chronology of Lemieux-Dudon et al. (2010), hereafter denoted LD2010. Our improved scenario confirms the regional differences for the millennial scale variability over the last glacial period: while the EDC isotopic record (events of triangular shape) displays peaks roughly at the same time as the NGRIP abrupt isotopic increases, the EDML isotopic record (events characterized by broader peaks or even extended periods of high isotope values) reached the isotopic maximum several centuries before. It is expected that the future contribution of both other long ice core records and other types of chronological constraints to the Datice tool will lead to further refinements in the ice core chronologies beyond the AICC2012 chronology. For the time being however, we recommend that AICC2012 be used as the preferred chronology for the Vostok, EDC, EDML and TALDICE ice core records, both over the last glacial cycle (this study), and beyond (following Bazin et al., 2013). The ages for NGRIP in AICC2012 are virtually identical to those of GICC05 for the last 60.2 ka, whereas the ages beyond are independent of those in GICC05modelext (as in the construction of AICC2012, the GICC05modelext was included only via the background scenarios and not as age markers). As such, where issues of phasing between Antarctic records included in AICC2012 and NGRIP are involved, the NGRIP ages in AICC2012 should therefore be taken to avoid introducing false offsets. However for issues involving only Greenland ice cores, there is not yet a strong basis to recommend superseding GICC05modelext as the recommended age scale for Greenland ice cores.