north atlantic-arctic region: Topics by Science.gov

Sample records for north atlantic-arctic region

Building International Research Partnerships in the North Atlantic-Arctic Region

NASA Astrophysics Data System (ADS)

Benway, Heather M.; Hofmann, Eileen; St. John, Michael

2014-09-01

The North Atlantic-Arctic region, which is critical to the health and socioeconomic well being of North America and Europe, is susceptible to climate-driven changes in circulation, biogeochemistry, and marine ecosystems. The need for strong investment in the study of biogeochemical and ecosystem processes and interactions with physical processes over a range of time and space scales in this region was clearly stated in the 2013 Galway Declaration, an intergovernmental statement on Atlantic Ocean cooperation (http://europa.eu/rapid/press-release_IP-13-459_en.htm). Subsequently, a workshop was held to bring together researchers from the United States, Canada, and Europe with expertise across multiple disciplines to discuss an international research initiative focused on key features, processes, and ecosystem services (e.g., Atlantic Meridional Overturning Circulation, spring bloom dynamics, fisheries, etc.) and associated sensitivities to climate changes.
Arctic Contribution to Upper-Ocean Variability in the North Atlantic.

NASA Astrophysics Data System (ADS)

Walsh, John E.; Chapman, William L.

1990-12-01

Because much of the deep water of the world's oceans forms in the high-latitude North Atlantic, the potential climatic leverage of salinity and temperature anomalies in this region is large. Substantial variations of sea ice have accompanied North Atlantic salinity and temperature anomalies, especially the extreme and long-lived `Great Salinity Anomaly' of the late 1960s and early 1970s. Atmospheric pressure data are used hem to show that the local forcing of high-latitude North Atlantic Ocean fluctuations is augmented by antecedent atmospheric circulation anomalies over the central Arctic. These circulation anomalies are consistent with enhanced wind-forcing of thicker, older ice into the Transpolar Drift Stream and an enhanced export of sea ice (fresh water) from the Arctic into the Greenland Sea prior to major episodes of ice severity in the Greenland and Iceland seas. An index of the pressure difference between southern Greenland and the Arctic-Asian coast reached its highest value of the twentieth century during the middle-to-late 1960s, the approximate time of the earliest observation documentation of the Great Salinity Anomaly.
Ocean Dynamics in the Key Regions of North Atlantic-Arctic Exchanges: Evaluation of Global Multi-Resolution FESOM and CMIP-type INMCM Models with Long-Term Observations

NASA Astrophysics Data System (ADS)

Beszczynska-Moeller, A.; Gürses, Ö.; Sidorenko, D.; Goessling, H.; Volodin, E. M.; Gritsun, A.; Iakovlev, N. G.; Andrzejewski, J.

2017-12-01

Enhancing the fidelity of climate models in the Arctic and North Atlantic in order to improve Arctic predictions requires better understanding of the underlying causes of common biases. The main focus of the ERA.Net project NAtMAP (Amending North Atlantic Model Biases to Improve Arctic Predictions) is on the dynamics of the key regions connecting the Arctic and the North Atlantic climate. The study aims not only at increased model realism, but also at a deeper understanding of North Atlantic-Arctic links and their contribution to Arctic predictability. Two complementary approaches employing different global coupled climate models, ECHAM6-FESOM and INMCM4/5, were adopted. The first approach is based on a recent development of climate models with ocean components based on unstructured meshes, allowing to resolve eddies and narrow boundary currents in the most crucial regions while keeping a moderate resolution elsewhere. The multi-resolution sea ice-ocean component of ECHAM6-FESOM allows studying the benefits of very high resolution in key areas of the North Atlantic. An alternative approach to address the North Atlantic and Arctic biases is also tried by tuning the performance of the relevant sub-grid-scale parameterizations in eddy resolving version the CMIP5 climate model INMCM4. Using long-term in situ and satellite observations and available climatologies we attempt to evaluate to what extent a higher resolution, allowing the explicit representation of eddies and narrow boundary currents in the North Atlantic and Nordic Seas, can alleviate the common model errors. The effects of better resolving the Labrador Sea area on reducing the model bias in surface hydrography and improved representation of ocean currents are addressed. Resolving eddy field in the Greenland Sea is assessed in terms of reducing the deep thermocline bias. The impact of increased resolution on the modeled characteristics of Atlantic water transport into the Arctic is examined with a special
Amplified North Atlantic warming in the late Pliocene by changes in Arctic gateways

DOE PAGES

Otto-Bliesner, Bette L.; Jahn, Alexandra; Feng, Ran; ...

2016-12-26

Under previous reconstructions of late Pliocene boundary conditions, climate models have failed to reproduce the warm sea surface temperatures reconstructed in the North Atlantic. Using a reconstruction of mid-Piacenzian paleogeography that has the Bering Strait and Canadian Arctic Archipelago Straits closed, however, improves the simulation of the proxy-indicated warm sea surface temperatures in the North Atlantic in the Community Climate System Model. We find that the closure of these small Arctic gateways strengthens the Atlantic Meridional Overturning Circulation, by inhibiting freshwater transport from the Pacific to the Arctic Ocean and from the Arctic Ocean to the Labrador Sea, leading tomore » warmer sea surface temperatures in the North Atlantic. In conclusion, this indicates that the state of the Arctic gateways may influence the sensitivity of the North Atlantic climate in complex ways, and better understanding of the state of these Arctic gateways for past time periods is needed.« less
North Atlantic Deep Water formation inhibits high Arctic contamination by continental perfluorooctane sulfonate discharges

NASA Astrophysics Data System (ADS)

Zhang, Xianming; Zhang, Yanxu; Dassuncao, Clifton; Lohmann, Rainer; Sunderland, Elsie M.

2017-08-01

Perfluorooctane sulfonate (PFOS) is an aliphatic fluorinated compound with eight carbon atoms that is extremely persistent in the environment and can adversely affect human and ecological health. The stability, low reactivity, and high water solubility of PFOS combined with the North American phaseout in production around the year 2000 make it a potentially useful new tracer for ocean circulation. Here we characterize processes affecting the lifetime and accumulation of PFOS in the North Atlantic Ocean and transport to sensitive Arctic regions by developing a 3-D simulation within the MITgcm. The model captures variability in measurements across biogeographical provinces (R2 = 0.90, p = 0.01). In 2015, the North Atlantic PFOS reservoir was equivalent to 60% of cumulative inputs from the North American and European continents (1400 Mg). Cumulative inputs to the Arctic accounted for 30% of continental discharges, while the remaining 10% was transported to the tropical Atlantic and other regions. PFOS concentrations declined rapidly after 2002 in the surface mixed layer (half-life: 1-2 years) but are still increasing below 1000 m depth. During peak production years (1980-2000), plumes of PFOS-enriched seawater were transported to the sub-Arctic in energetic surface ocean currents. However, Atlantic Meridional Overturning Circulation (AMOC) and deep ocean transport returned a substantial fraction of this northward transport (20%, 530 Mg) to southern latitudes and reduced cumulative inputs to the Arctic (730 Mg) by 70%. Weakened AMOC due to climate change is thus likely to increase the magnitude of persistent bioaccumulative pollutants entering the Arctic Ocean.
Arctic climatechange and its impacts on the ecology of the North Atlantic.

PubMed

Greene, Charles H; Pershing, Andrew J; Cronin, Thomas M; Ceci, Nicole

2008-11-01

Arctic climate change from the Paleocene epoch to the present is reconstructed with the objective of assessing its recent and future impacts on the ecology of the North Atlantic. A recurring theme in Earth's paleoclimate record is the importance of the Arctic atmosphere, ocean, and cryosphere in regulating global climate on a variety of spatial and temporal scales. A second recurring theme in this record is the importance of freshwater export from the Arctic in regulating global- to basin-scale ocean circulation patterns and climate. Since the 1970s, historically unprecedented changes have been observed in the Arctic as climate warming has increased precipitation, river discharge, and glacial as well as sea-ice melting. In addition, modal shifts in the atmosphere have altered Arctic Ocean circulation patterns and the export of freshwater into the North Atlantic. The combination of these processes has resulted in variable patterns of freshwater export from the Arctic Ocean and the emergence of salinity anomalies that have periodically freshened waters in the North Atlantic. Since the early 1990s, changes in Arctic Ocean circulation patterns and freshwater export have been associated with two types of ecological responses in the North Atlantic. The first of these responses has been an ongoing series of biogeographic range expansions by boreal plankton, including renewal of the trans-Arctic exchanges of Pacific species with the Atlantic. The second response was a dramatic regime shift in the shelf ecosystems of the Northwest Atlantic that occurred during the early 1990s. This regime shift resulted from freshening and stratification of the shelf waters, which in turn could be linked to changes in the abundances and seasonal cycles of phytoplankton, zooplankton, and higher trophic-level consumer populations. It is predicted that the recently observed ecological responses to Arctic climate change in the North Atlantic will continue into the near future if current trends
Meltwater and precipitation runoff to the North Atlantic, Arctic, and Gulf of Mexico from the Laurentide Ice Sheet and adjacent regions during the Younger Dryas

NASA Astrophysics Data System (ADS)

Teller, James T.

1990-12-01

Runoff from North America may have played a significant role in ocean circulation and climate change during the last deglaciation. Because the driving force behind such changes may have been related to salinity of the north flowing Atlantic Ocean conveyor circulation, it is critical to know the volume, timing, and location of fresh water entering the North Atlantic from the melting Laurentide Ice Sheet. During the Younger Dryas cold episode, 11,000-10,000 years B.P., there was a two-fold increase in the volume of meltwater plus precipitation runoff, to more than 1700 km³ yr-1, flowing through the St. Lawrence valley to the North Atlantic, mainly because retreating ice allowed the glacial Lake Agassiz basin to drain eastward into the Great Lakes at this time. There was a corresponding decline in discharge from Lake Agassiz through the Mississippi River to the Gulf of Mexico. Runoff to the Arctic Ocean also increased at about the beginning of the Younger Dryas, from 740 to 900 km³ yr-1, because of the capture of what is now the headwater region of the Mackenzie River watershed. This, in combination with rising sea level and warming climate, may have increased the amount of pack ice reaching the North Atlantic through the Norwegian Sea from the Arctic Ocean. At 10,000 years B.P., eastward overflow from the western interior of North America was blocked by advancing ice, again forcing overflow to the Gulf of Mexico and, possibly, to the northwest into the Arctic Ocean. Although total runoff to the oceans from all regions draining from the Laurentide Ice Sheet did not vary substantially between 12,000 and 9000 years B.P., if discharge to the Gulf of Mexico is excluded, fresh water reaching the North Atlantic averaged 4000 km³ yr-1 during the Younger Dryas, in contrast to 2870 km³ yr-1 just before this cold episode and 3440 km³ yr-1 just after it.
Amplified North Atlantic Warming in the Late Pliocene by Changes in Arctic Gateways

NASA Astrophysics Data System (ADS)

Otto-Bliesner, B. L.; Jahn, A.; Feng, R.; Brady, E. C.; Hu, A.; Lofverstrom, M.

2017-12-01

Reconstructions of the late Pliocene (mid-Piacenzian, 3.3 - 3.0 million years ago) sea surface temperature (SST) find much warmer conditions in the North Atlantic than modern. The much warmer SSTs, up to 8.8°C from sites with good dating and replicates from several different types of proxies, have been difficult for climate models to reproduce. Even with the slow feedbacks of a reduced Greenland ice sheet and expansion of boreal forests to the Arctic Ocean over Canada and Eurasia, models cannot warm the North Atlantic sufficiently to match the reconstructed SSTs. An enhancement of the Atlantic Meridional Overturning Circulation (AMOC) during the late Pliocene, proposed as a possible mechanism based on ocean core records of δ13C, also is not present in the model simulations. Here, we present CESM simulations using a new reconstruction of late Pliocene paleogeography that has the Bering Strait (BS) and Canadian Arctic Archipelago (CAA) Straits closed. We find that the closure of these small Arctic gateways strengthens the AMOC, by inhibiting freshwater (FW) transport from the Pacific to the Arctic Ocean and from the Arctic Ocean to the Labrador Sea, leading to warmer sea surface temperatures in the North Atlantic. The cutoff of the short export route through the CAA results in a more saline Labrador and south Greenland Sea with increased deep convection. At the same time, as all FW now leaves the Arctic east of Greenland, there is a freshening of and decreased deepwater formation in the Norwegian Sea. Overall, the AMOC strengthens. This past time period has implications for a future Earth under more responsible scenarios of emissions. Late Pliocene atmospheric carbon dioxide concentrations are estimated to have ranged between 350 and 450 ppmv and the paleogeography is relatively similar to modern. Our study indicates that the state of the Arctic gateways may influence the sensitivity of the North Atlantic climate in complex ways, and better understanding of the
Arctic Sovereignty Disputes: International Relations Theory in the High North

DTIC Science & Technology

2011-12-01

ARCTIC REGION.............................20 D. INSTITUTIONS FOR ARCTIC SECURITY COOPERATION .............22 1. The United Nations and The Law of...39 1. The Law of the Sea .............................................................................39 2. The Arctic Council as an...Change IR International Relations NAFTA North American Free Trade Agreement NATO North Atlantic Treaty Organization NORAD North American
Future change in ocean productivity: Is the Arctic the new Atlantic?

NASA Astrophysics Data System (ADS)

Yool, A.; Popova, E. E.; Coward, A. C.

2015-12-01

One of the most characteristic features in ocean productivity is the North Atlantic spring bloom. Responding to seasonal increases in irradiance and stratification, surface phytopopulations rise significantly, a pattern that visibly tracks poleward into summer. While blooms also occur in the Arctic Ocean, they are constrained by the sea-ice and strong vertical stratification that characterize this region. However, Arctic sea-ice is currently declining, and forecasts suggest this may lead to completely ice-free summers by the mid-21st century. Such change may open the Arctic up to Atlantic-style spring blooms, and do so at the same time as Atlantic productivity is threatened by climate change-driven ocean stratification. Here we use low and high-resolution instances of a coupled ocean-biogeochemistry model, NEMO-MEDUSA, to investigate productivity. Drivers of present-day patterns are identified, and changes in these across a climate change scenario (IPCC RCP 8.5) are analyzed. We find a globally significant decline in North Atlantic productivity (> -20%) by 2100, and a correspondingly significant rise in the Arctic (> +50%). However, rather than the future Arctic coming to resemble the current Atlantic, both regions are instead transitioning to a common, low nutrient regime. The North Pacific provides a counterexample where nutrients remain high and productivity increases with elevated temperature. These responses to climate change in the Atlantic and Arctic are common between model resolutions, suggesting an independence from resolution for key impacts. However, some responses, such as those in the North Pacific, differ between the simulations, suggesting the reverse and supporting the drive to more fine-scale resolutions. This article was corrected on 5 JAN 2016. See the end of the full text for details.
Bathymetric controls on Pliocene North Atlantic and Arctic sea surface temperature and deepwater production

USGS Publications Warehouse

Robinson, M.M.; Valdes, P.J.; Haywood, A.M.; Dowsett, H.J.; Hill, D.J.; Jones, S.M.

2011-01-01

The mid-Pliocene warm period (MPWP; ~. 3.3 to 3.0. Ma) is the most recent interval in Earth's history in which global temperatures reached and remained at levels similar to those projected for the near future. The distribution of global warmth, however, was different than today in that the high latitudes warmed more than the tropics. Multiple temperature proxies indicate significant sea surface warming in the North Atlantic and Arctic Oceans during the MPWP, but predictions from a fully coupled ocean-atmosphere model (HadCM3) have so far been unable to fully predict the large scale of sea surface warming in the high latitudes. If climate proxies accurately represent Pliocene conditions, and if no weakness exists in the physics of the model, then model boundary conditions may be in error. Here we alter a single boundary condition (bathymetry) to examine if Pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of North Atlantic Ocean ridges. We find an increase in both Arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened Greenland-Scotland Ridge. These results offer both a mechanism for the warming in the North Atlantic and Arctic Oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of Pliocene northern North Atlantic and Arctic Ocean conditions. Determining the causes of Pliocene warmth remains critical to fully understanding comparisons of the Pliocene warm period to possible future climate change scenarios. ?? 2011.
Early 20th Century Arctic Warming Intensified by Pacific and Atlantic Multidecadal Variability

NASA Astrophysics Data System (ADS)

Tokinaga, H.; Xie, S. P.; Mukougawa, H.

2017-12-01

We investigate the influence of Pacific and Atlantic multidecadal variability on the Arctic temperature, with a particular focus on the early 20th century Arctic warming. Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing than at present. We find that the concurrent phase shift of Pacific and Atlantic multidecadal variability is the major driver for the early 20th century Arctic warming. Atmospheric model simulations reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early Arctic warming is associated with the cold-to-warm phase shifts of Atlantic and Pacific multidecadal variability modes, a SST pattern reminiscent of the positive phase of the Pacific decadal and Atlantic multidecadal oscillations. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. The equatorial Pacific warming deepens the Aleutian low, advecting warm air to the North American Arctic. Coupled ocean-atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, cold-to-warm phase shift of the Pacific and Atlantic multidecadal variability. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.
Freshwater fluxes into the subpolar North Atlantic from secular trends in Arctic land ice mass balance

NASA Astrophysics Data System (ADS)

Bamber, J. L.; Enderlin, E. M.; Howat, I. M.; Wouters, B.; van den Broeke, M.

2015-12-01

Freshwater fluxes (FWF) from river runoff and precipitation minus evaporation for the pan Arctic seas are relatively well documented and prescribed in ocean GCMs. Fluxes from Greenland and Arctic glaciers and ice caps on the other hand are generally ignored, despite their potential impacts on ocean circulation and marine biology and growing evidence for changes to the hydrography of parts of the subpolar North Atlantic. In a previous study we determined the FWF from Greenland for the period 1958-2010 using a combination of observations and regional climate modeling. Here, we update the analysis with data from new satellite observations to extend the record both in space and time. The new FWF estimates cover the period 1958-2014 and include the Canadian, Russian and Norwegian Arctic (Svalbard) in addition to the contributions from Greenland. We combine satellite altimetry (including CryoSat 2) with grounding line flux data, regional climate modeling of surface mass balance and gravimetry to produce consistent estimates of solid ice and liquid FWF into the Arctic and North Atlantic Oceans. The total cumulative FWF anomaly from land ice mass loss started to increase significantly in the mid 1990s and now exceeds 5000 km^3, a value that is about half of the Great Salinity Anomaly of the 1970s. The majority of the anomaly is entering two key areas of deep water overturning in the Labrador and Irminger Seas, at a rate that has been increasing steadily over the last ~20 years. Since the mid 2000s, however, the Canadian Arctic archipelago has been making a significant contribution to the FW anomaly entering Baffin Bay. Tracer experiments with eddy-permitting ocean GCMs suggest that the FW input from southern Greenland and the Canadian Arctic should accumulate in Baffin Bay with the potential to affect geostrophic circulation, stratification in the region and possibly the strength of the Atlantic Meridional Overturning Circulation. We also examine the trajectory of
Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

PubMed Central

Tokinaga, Hiroki; Xie, Shang-Ping; Mukougawa, Hitoshi

2017-01-01

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean–atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region. PMID:28559341
Early 20th-century Arctic warming intensified by Pacific and Atlantic multidecadal variability

NASA Astrophysics Data System (ADS)

Tokinaga, Hiroki; Xie, Shang-Ping; Mukougawa, Hitoshi

2017-06-01

With amplified warming and record sea ice loss, the Arctic is the canary of global warming. The historical Arctic warming is poorly understood, limiting our confidence in model projections. Specifically, Arctic surface air temperature increased rapidly over the early 20th century, at rates comparable to those of recent decades despite much weaker greenhouse gas forcing. Here, we show that the concurrent phase shift of Pacific and Atlantic interdecadal variability modes is the major driver for the rapid early 20th-century Arctic warming. Atmospheric model simulations successfully reproduce the early Arctic warming when the interdecadal variability of sea surface temperature (SST) is properly prescribed. The early 20th-century Arctic warming is associated with positive SST anomalies over the tropical and North Atlantic and a Pacific SST pattern reminiscent of the positive phase of the Pacific decadal oscillation. Atmospheric circulation changes are important for the early 20th-century Arctic warming. The equatorial Pacific warming deepens the Aleutian low, advecting warm air into the North American Arctic. The extratropical North Atlantic and North Pacific SST warming strengthens surface westerly winds over northern Eurasia, intensifying the warming there. Coupled ocean-atmosphere simulations support the constructive intensification of Arctic warming by a concurrent, negative-to-positive phase shift of the Pacific and Atlantic interdecadal modes. Our results aid attributing the historical Arctic warming and thereby constrain the amplified warming projected for this important region.
A new collective view of oceanography of the Arctic and North Atlantic basins

NASA Astrophysics Data System (ADS)

Yashayaev, Igor; Seidov, Dan; Demirov, Entcho

2015-03-01

We review some historical aspects of the major observational programs in the North Atlantic and adjacent regions that contributed to establishing and maintaining the global ocean climate monitoring network. The paper also presents the oceanic perspectives of climate change and touches the important issues of ocean climate variability on time scales from years to decades. Some elements of the improved understanding of the causes and mechanisms of variability in the subpolar North Atlantic and adjacent seas are discussed in detail. The sophistication of current oceanographic analysis, especially in connection with the most recent technological breakthroughs - notably the launch of the global array of profiling Argo floats - allows us to approach new challenges in ocean research. We demonstrate how the ocean-climate changes in the subpolar basins and polar seas correlate with variations in the major climate indices such as the North Atlantic Oscillation and Atlantic Multidecadal Oscillation, and discuss possible connections between the unprecedented changes in the Arctic and Greenland ice-melt rates observed over the past decade and variability of hydrographic conditions in the Labrador Sea. Furthermore, a synthesis of shipboard and Argo measurements in the Labrador Sea reveals the effects of the regional climate trends such as freshening of the upper layer - possible causes of which are also discussed - on the winter convection in the Labrador Sea including its strength, duration and spatial extent. These changes could have a profound impact on the regional and planetary climates. A section with the highlights of all papers comprising the Special Issue concludes the Preface.
Mercury in the atmosphere, snow and melt water ponds in the North Atlantic Ocean during Arctic summer.

PubMed

Aspmo, Katrine; Temme, Christian; Berg, Torunn; Ferrari, Christophe; Gauchard, L Pierre-Alexis; Fain, Xavier; Wibetoe, Grethe

2006-07-01

Atmospheric mercury speciation measurements were performed during a 10 week Arctic summer expedition in the North Atlantic Ocean onboard the German research vessel RV Polarstern between June 15 and August 29, 2004. This expedition covered large areas of the North Atlantic and Arctic Oceans between latitudes 54 degrees N and 85 degrees N and longitudes 16 degrees W and 16 degrees E. Gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and mercury associated with particles (Hg-P) were measured during this study. In addition, total mercury in surface snow and meltwater ponds located on sea ice floes was measured. GEM showed a homogeneous distribution over the open North Atlantic Ocean (median 1.53 +/- 0.12 ng/m3), which is in contrast to the higher concentrations of GEM observed over sea ice (median 1.82 +/- 0.24 ng/m3). It is hypothesized that this results from either (re-) emission of mercury contained in snow and ice surfaces that was previously deposited during atmospheric mercury depletion events (AMDE) in the spring or evasion from the ocean due to increased reduction potential at high latitudes during Arctic summer. Measured concentrations of total mercury in surface snow and meltwater ponds were low (all samples <10 ng/L), indicating that marginal accumulation of mercury occurs in these environmental compartments. Results also reveal low concentrations of RGM and Hg-P without a significant diurnal variability. These results indicate that the production and deposition of these reactive mercury species do not significantly contribute to the atmospheric mercury cycle in the North Atlantic Ocean during the Arctic summer.
Arctic sea-ice decline weakens the Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Sévellec, Florian; Fedorov, Alexey V.; Liu, Wei

2017-08-01

The ongoing decline of Arctic sea ice exposes the ocean to anomalous surface heat and freshwater fluxes, resulting in positive buoyancy anomalies that can affect ocean circulation. In this study, we use an optimal flux perturbation framework and comprehensive climate model simulations to estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to such buoyancy forcing over the Arctic and globally, and more generally to sea-ice decline. It is found that on decadal timescales, flux anomalies over the subpolar North Atlantic have the largest impact on the AMOC, while on multi-decadal timescales (longer than 20 years), flux anomalies in the Arctic become more important. These positive buoyancy anomalies spread to the North Atlantic, weakening the AMOC and its poleward heat transport. Therefore, the Arctic sea-ice decline may explain the suggested slow-down of the AMOC and the `Warming Hole’ persisting in the subpolar North Atlantic.
Climate drift of AMOC, North Atlantic salinity and arctic sea ice in CFSv2 decadal predictions

NASA Astrophysics Data System (ADS)

Huang, Bohua; Zhu, Jieshun; Marx, Lawrence; Wu, Xingren; Kumar, Arun; Hu, Zeng-Zhen; Balmaseda, Magdalena A.; Zhang, Shaoqing; Lu, Jian; Schneider, Edwin K.; Kinter, James L., III

2015-01-01

There are potential advantages to extending operational seasonal forecast models to predict decadal variability but major efforts are required to assess the model fidelity for this task. In this study, we examine the North Atlantic climate simulated by the NCEP Climate Forecast System, version 2 (CFSv2), using a set of ensemble decadal hindcasts and several 30-year simulations initialized from realistic ocean-atmosphere states. It is found that a substantial climate drift occurs in the first few years of the CFSv2 hindcasts, which represents a major systematic bias and may seriously affect the model's fidelity for decadal prediction. In particular, it is noted that a major reduction of the upper ocean salinity in the northern North Atlantic weakens the Atlantic meridional overturning circulation (AMOC) significantly. This freshening is likely caused by the excessive freshwater transport from the Arctic Ocean and weakened subtropical water transport by the North Atlantic Current. A potential source of the excessive freshwater is the quick melting of sea ice, which also causes unrealistically thin ice cover in the Arctic Ocean. Our sensitivity experiments with adjusted sea ice albedo parameters produce a sustainable ice cover with realistic thickness distribution. It also leads to a moderate increase of the AMOC strength. This study suggests that a realistic freshwater balance, including a proper sea ice feedback, is crucial for simulating the North Atlantic climate and its variability.
Variations in freshwater pathways from the Arctic Ocean into the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Wang, Zeliang; Hamilton, James; Su, Jie

2017-06-01

Understanding the mechanisms that drive exchanges between the Arctic Ocean and adjacent oceans is critical to building our knowledge of how the Arctic is reacting to a warming climate, and how potential changes in Arctic Ocean freshwater export may impact the AMOC (Atlantic Meridional Overturning Circulation). Here, freshwater pathways from the Arctic Ocean to the North Atlantic are investigated using a 1 degree global model. An EOF analysis of modeled sea surface height (SSH) demonstrates that while the second mode accounts for only 15% of the variability, the associated geostrophic currents are strongly correlated with freshwater exports through CAA (Canadian Arctic Archipelago; r = 0.75), Nares Strait (r = 0.77) and Fram Strait (r = -0.60). Separation of sea level into contributing parts allows us to show that the EOF1 is primarily a barotropic mode reflecting variability in bottom pressure equivalent sea level, while the EOF2 mode reflects changes in steric height in the Arctic Basin. This second mode is linked to momentum wind driven surface current, and dominates the Arctic Ocean freshwater exports. Both the Arctic Oscillation and Arctic Dipole atmospheric indices are shown to be linked to Arctic Ocean freshwater exports, with the forcing associated with the Arctic Dipole reflecting the out-of-phase relationship between transports through the CAA and those through Fram Strait. Finally, observed freshwater transport variation through the CAA is found to be strongly correlated with tide gauge data from the Beaufort Sea coast (r = 0.81), and with the EOF2 mode of GRACE bottom pressure data (r = 0.85) on inter-annual timescales.

Can Arctic Sea Ice Decline Weaken the Atlantic Meridional Overturning Circulation?

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; Sevellec, F.; Liu, W.

2017-12-01

The ongoing decline of Arctic sea ice exposes the ocean to anomalous surface heat and freshwater fluxes, resulting in positive buoyancy anomalies that can affect ocean circulation. In this study (detailed in Sevellec, Fedorov, Liu 2017, Nature Climate Change) we apply an optimal flux perturbation framework and comprehensive climate model simulations (using CESM) to estimate the sensitivity of the Atlantic meridional overturning circulation (AMOC) to such buoyancy forcing over the Arctic and globally, and more generally AMOC sensitivity to sea ice decline. We find that on decadal timescales flux anomalies over the subpolar North Atlantic have the largest impact on the AMOC; however, on multi-decadal timescales (longer than 20 years), anomalies in the Arctic become more important. These positive buoyancy anomalies from the Arctic spread to the North Atlantic, weakening the AMOC and its poleward heat transport after several decades. Therefore, the Arctic sea ice decline may explain the suggested slow-down of the AMOC and the "Warming Hole" persisting in the subpolar North Atlantic. Further, we discuss how the proposed connection, i.e. Arctic sea ice contraction would lead to an AMOC slow-down, varies across different earth system models. Overall, this study demonstrates that Arctic sea ice decline can play an active role in ocean and climate change.
Warming in the Nordic Seas, North Atlantic storms and thinning Arctic sea ice

NASA Astrophysics Data System (ADS)

Alexeev, Vladimir A.; Walsh, John E.; Ivanov, Vladimir V.; Semenov, Vladimir A.; Smirnov, Alexander V.

2017-08-01

Arctic sea ice over the last few decades has experienced a significant decline in coverage both in summer and winter. The currently warming Atlantic Water layer has a pronounced impact on sea ice in the Nordic Seas (including the Barents Sea). More open water combined with the prevailing atmospheric pattern of airflow from the southeast, and persistent North Atlantic storms such as the recent extremely strong Storm Frank in December 2015, lead to increased energy transport to the high Arctic. Each of these storms brings sizeable anomalies of heat to the high Arctic, resulting in significant warming and slowing down of sea ice growth or even melting. Our analysis indicates that the recently observed sea ice decline in the Nordic Seas during the cold season around Svalbard, Franz Joseph Land and Novaya Zemlya, and the associated heat release from open water into the atmosphere, contributed significantly to the increase in the downward longwave radiation throughout the entire Arctic. Added to other changes in the surface energy budget, this increase since the 1960s to the present is estimated to be at least 10 W m-2, which can result in thinner (up to at least 15-20 cm) Arctic ice at the end of the winter. This change in the surface budget is an important contributing factor accelerating the thinning of Arctic sea ice.
The relationship between Arctic sea ice and the Atlantic meridional overturning circulation in a warming climate

NASA Astrophysics Data System (ADS)

Liu, W.; Fedorov, A. V.

2017-12-01

A recent study (Sevellec, Fedorov, Liu 2017, Nature Climate Change) has suggested that Arctic sea ice decline can lead to a slow-down of the Atlantic meridional overturning circulation (AMOC). Here, we build on this previous work and explore the relationship between Arctic sea ice and the AMOC in climate models. We find that the current Arctic sea ice decline can contribute about 40% to the AMOC weakening over the next 60 years. This effect is related to the warming and freshening of the upper ocean in the Arctic, and the subsequent spread of generated buoyancy anomalies downstream where they affect the North Atlantic deep convection sites and hence the AMOC on multi-decadal timescales. The weakening of the AMOC and its poleward heat transport, in turn, sustains the "Warming Hole" - a region in the North Atlantic with anomalously weak (or even negative) warming trends. We discuss the key factors that control this robust AMOC response to changes in Arctic sea ice.
Regional and inter-annual variability in Atlantic zooplankton en route to the Arctic Ocean: potential effects of multi-path Atlantic water advection through Fram Strait and the Barents Sea

NASA Astrophysics Data System (ADS)

Kwasniewski, Slawomir; Gluchowska, Marta; Trudnowska, Emilia; Ormanczyk, Mateusz; Walczowski, Waldemar; Beszczynska-Moeller, Agnieszka

2016-04-01

The Arctic is among the regions where the climate change effects on ecosystem will be the most rapid and consequential, with Arctic amplification recognized as an integral part of the process. Great part of the changes are forced by advection of warm waters from the North Atlantic and the expected modifications of Arctic marine ecosystem will be induced not only by changing environmental conditions but also as a result of introducing Atlantic biota. Thus, the knowledge of physical and biological heterogeneity of Atlantic inflow is requisite for understanding the effects of climate change on biological diversity and ecosystem functioning in the Arctic. The complex and variable two-branched structure of the Atlantic Water flow via Fram Strait and the Barents Sea most likely has a strong influence on the ocean biology in these regions, especially in the pelagic realm. Zooplankton are key components of marine ecosystems which form essential links between primary producers and grazer/predator consumers, thus they are important for functioning of the biological carbon pump. Changes in zooplankton distribution and abundance may have cascading effects on ecosystem functioning, with regulatory effects on climate. Based on data collected in summers of 2012-2014, within the scope of the Polish-Norwegian PAVE research project, we investigate zooplankton distribution, abundance and selected structural characteristics of communities, in relation to water mass properties in the Atlantic Water complex flow to the Arctic Ocean. The main questions addressed here are: what are the differences in zooplankton patterns between the Fram Strait and Barents Sea branches, and how does the inter-annual variability of Atlantic Water advection relate to changes in zooplankton? The results of the investigation are precondition for foreseeing changes in the pelagic realm in the Arctic Ocean and are necessary for constructing and tuning plankton components of ecosystem models.
Impact of ship emissions on air pollution and AOD over North Atlantic and European Arctic

NASA Astrophysics Data System (ADS)

Kaminski, Jacek W.; Struzewska, Joanna; Jefimow, Maciej; Durka, Pawel

2016-04-01

The iAREA project is combined of experimental and theoretical research in order to contribute to the new knowledge on the impact of absorbing aerosols on the climate system in the European Arctic (http://www.igf.fuw.edu.pl/iAREA). A tropospheric chemistry model GEM-AQ (Global Environmental Multiscale Air Quality) was used as a computational tool. The core of the model is based on a weather prediction model with environmental processes (chemistry and aerosols) implanted on-line and are interactive (i.e. providing feedback of chemistry on radiation and dynamics). The numerical grid covered the Euro-Atlantic region with the resolution of 50 km. Emissions developed by NILU in the ECLIPSE project was used (Klimont et al., 2013). The model was run for two 1-year scenarios. 2014 was chosen as a base year for simulations and analysis. Scenarios include a base run with most up-to-date emissions and a run without maritime emissions. The analysis will focus on the contribution of maritime emissions on levels of particulate matter and gaseous pollutants over the European Arctic, North Atlantic and coastal areas. The annual variability will be assessed based on monthly mean near-surface concentration fields. Analysis of shipping transport on near-surface air pollution over the Euro-Atlantic region will be assessed for ozone, NO2, SO2, CO, PM10, PM2.5. Also, a contribution of ship emissions to AOD will be analysed.
Can preferred atmospheric circulation patterns over the North-Atlantic-Eurasian region be associated with arctic sea ice loss?

NASA Astrophysics Data System (ADS)

Crasemann, Berit; Handorf, Dörthe; Jaiser, Ralf; Dethloff, Klaus; Nakamura, Tetsu; Ukita, Jinro; Yamazaki, Koji

2017-12-01

In the framework of atmospheric circulation regimes, we study whether the recent Arctic sea ice loss and Arctic Amplification are associated with changes in the frequency of occurrence of preferred atmospheric circulation patterns during the extended winter season from December to March. To determine regimes we applied a cluster analysis to sea-level pressure fields from reanalysis data and output from an atmospheric general circulation model. The specific set up of the two analyzed model simulations for low and high ice conditions allows for attributing differences between the simulations to the prescribed sea ice changes only. The reanalysis data revealed two circulation patterns that occur more frequently for low Arctic sea ice conditions: a Scandinavian blocking in December and January and a negative North Atlantic Oscillation pattern in February and March. An analysis of related patterns of synoptic-scale activity and 2 m temperatures provides a synoptic interpretation of the corresponding large-scale regimes. The regimes that occur more frequently for low sea ice conditions are resembled reasonably well by the model simulations. Based on those results we conclude that the detected changes in the frequency of occurrence of large-scale circulation patterns can be associated with changes in Arctic sea ice conditions.
Anomalous Structure of Oceanic Lithosphere in the North Atlantic and Arctic Oceans: A Preliminary Analysis Based on Bathymetry, Gravity and Crustal Structure

NASA Astrophysics Data System (ADS)

Barantsrva, O.

2014-12-01

We present a preliminary analysis of the crustal and upper mantle structure for off-shore regions in the North Atlantic and Arctic oceans. These regions have anomalous oceanic lithosphere: the upper mantle of the North Atlantic ocean is affected by the Iceland plume, while the Arctic ocean has some of the slowest spreading rates. Our specific goal is to constrain the density structure of the upper mantle in order to understand the links between the deep lithosphere dynamics, ocean spreading, ocean floor bathymetry, heat flow and structure of the oceanic lithosphere in the regions where classical models of evolution of the oceanic lithosphere may not be valid. The major focus is on the oceanic lithosphere, but the Arctic shelves with a sufficient data coverage are also included into the analysis. Out major interest is the density structure of the upper mantle, and the analysis is based on the interpretation of GOCE satellite gravity data. To separate gravity anomalies caused by subcrustal anomalous masses, the gravitational effect of water, crust and the deep mantle is removed from the observed gravity field. For bathymetry we use the global NOAA database ETOPO1. The crustal correction to gravity is based on two crustal models: (1) global model CRUST1.0 (Laske, 2013) and, for a comparison, (2) a regional seismic model EUNAseis (Artemieva and Thybo, 2013). The crustal density structure required for the crustal correction is constrained from Vp data. Previous studies have shown that a large range of density values corresponds to any Vp value. To overcome this problem and to reduce uncertainty associated with the velocity-density conversion, we account for regional tectonic variations in the Northern Atlantics as constrained by numerous published seismic profiles and potential-field models across the Norwegian off-shore crust (e.g. Breivik et al., 2005, 2007), and apply different Vp-density conversions for different parts of the region. We present preliminary results
Influence of Sea Ice on the Thermohaline Circulation in the Arctic-North Atlantic Ocean

NASA Technical Reports Server (NTRS)

Mauritzen, Cecilie; Haekkinen, Sirpa

1997-01-01

A fully prognostic coupled ocean-ice model is used to study the sensitivity of the overturning cell of the Arctic-North-Atlantic system to sea ice forcing. The strength of the thermohaline cell will be shown to depend on the amount of sea ice transported from the Arctic to the Greenland Sea and further to the subpolar gyre. The model produces a 2-3 Sv increase of the meridional circulation cell at 25N (at the simulation year 15) corresponding to a decrease of 800 cu km in the sea ice export from the Arctic. Previous modeling studies suggest that interannual and decadal variability in sea ice export of this magnitude is realistic, implying that sea ice induced variability in the overturning cell can reach 5-6 Sv from peak to peak.
Arctic and N Atlantic Crustal Thickness and Oceanic Lithosphere Distribution from Gravity Inversion

NASA Astrophysics Data System (ADS)

Kusznir, Nick; Alvey, Andy

2014-05-01

The ocean basins of the Arctic and N. Atlantic formed during the Mesozoic and Cenozoic as a series of distinct ocean basins, both small and large, leading to a complex distribution of oceanic crust, thinned continental crust and rifted continental margins. The plate tectonic framework of this region was demonstrated by the pioneering work of Peter Ziegler in AAPG Memoir 43 " Evolution of the Arctic-North Atlantic and the Western Tethys" published in 1988. The spatial evolution of Arctic Ocean and N Atlantic ocean basin geometry and bathymetry are critical not only for hydrocarbon exploration but also for understanding regional palaeo-oceanography and ocean gateway connectivity, and its influence on global climate. Mapping crustal thickness and oceanic lithosphere distribution represents a substantial challenge for the Polar Regions. Using gravity anomaly inversion we have produced comprehensive maps of crustal thickness and oceanic lithosphere distribution for the Arctic and N Atlantic region, We determine Moho depth, crustal basement thickness, continental lithosphere thinning and ocean-continent transition location using a 3D spectral domain gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction (Chappell & Kusznir 2008). Gravity anomaly and bathymetry data used in the gravity inversion are from the NGA (U) Arctic Gravity Project and IBCAO respectively; sediment thickness is from a new regional compilation. The resulting maps of crustal thickness and continental lithosphere thinning factor are used to determine continent-ocean boundary location and the distribution of oceanic lithosphere. Crustal cross-sections using Moho depth from the gravity inversion allow continent-ocean transition structure to be determined and magmatic type (magma poor, "normal" or magma rich). Our gravity inversion predicts thin crust and high continental lithosphere thinning factors in the Eurasia, Canada, Makarov, Podvodnikov and Baffin Basins
Evolution of the Arctic-North Atlantic and the Western Tethys

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

Ziegler, P.A.

1988-01-01

This volume provides an overview of the late Paleozoic to recent geological evolution of the continents and shelves bordering the North Atlantic Ocean, the Norwegian-Greenland Sea, the Arctic Ocean, and the Mediterranean Sea. The evolution of these seas has been the subject of many studies and compilations, which discuss the evolution of oceanic basins on the basis of their magnetic sea-floor anomalies. The volume presented combines this information with geological data from the adjacent shelf and onshore areas. It retraces the evolution of sedimentary basins developed during the rifting phases that preceded the opening of these oceans and highlights themore » scope of the associated intra-plate phenomena. The author presents a reconstruction of the late Paleozoic and early Mesozoic development of Europe, northernmost Africa and northeastern North America-Greenland and discusses the different orogenic cycles that accompanied the stepwise assembly of Pangea and the early rifting phases heralding its break-up.« less
Land Ice Freshwater Budget of the Arctic and North Atlantic Oceans: 1. Data, Methods, and Results

NASA Astrophysics Data System (ADS)

Bamber, J. L.; Tedstone, A. J.; King, M. D.; Howat, I. M.; Enderlin, E. M.; van den Broeke, M. R.; Noel, B.

2018-03-01

The freshwater budget of the Arctic and sub-polar North Atlantic Oceans has been changing due, primarily, to increased river runoff, declining sea ice and enhanced melting of Arctic land ice. Since the mid-1990s this latter component has experienced a pronounced increase. We use a combination of satellite observations of glacier flow speed and regional climate modeling to reconstruct the land ice freshwater flux from the Greenland ice sheet and Arctic glaciers and ice caps for the period 1958-2016. The cumulative freshwater flux anomaly exceeded 6,300 ± 316 km3 by 2016. This is roughly twice the estimate of a previous analysis that did not include glaciers and ice caps outside of Greenland and which extended only to 2010. From 2010 onward, the total freshwater flux is about 1,300 km3/yr, equivalent to 0.04 Sv, which is roughly 40% of the estimated total runoff to the Arctic for the same time period. Not all of this flux will reach areas of deep convection or Arctic and Sub-Arctic seas. We note, however, that the largest freshwater flux anomalies, grouped by ocean basin, are located in Baffin Bay and Davis Strait. The land ice freshwater flux displays a strong seasonal cycle with summer time values typically around five times larger than the annual mean. This will be important for understanding the impact of these fluxes on fjord circulation, stratification, and the biogeochemistry of, and nutrient delivery to, coastal waters.
North Atlantic Origin of Interdecadal variability of Siberian High

NASA Astrophysics Data System (ADS)

Kim, Seon-Hwa; Sung, Mi-Kyung; Kim, Baek-Min

2017-04-01

We suggest that the changes in the mean atmospheric circulation structure in the North Atlantic Ocean upstream region of Eurasian continent play an important role in the interdecadal variability of Siberian High (SH) through the modulation of Ural blocking frequency. Previous studies suggested that the interdecadal variability of SH is partly explained by the Arctic Oscillation. However, in this study, we emphasize the role of 'Warm Arctic and Cold Eurasia (WACE)', which is the second mode of winter surface air temperature variability over Eurasia. We show that the correlation between SH and WACE is high in general compared to that between SH and AO. However, the correlation between SH and WACE does not always exhibit high constant value. It shows a distinctive interdecadal fluctuation in the correlation. We found that this fluctuation in the correlation is due to the interdecadal fluctuation of the continental trough over the North Atlantic and the resultant strengthening of in-situ atmospheric baroclinicity. This accompanies changes in the transient vorticity flux divergence which leads to the downstream wave development and anomalous anticyclonic flow near Ural region. Obviously, the existence of anticyclonic flow over Ural region helps more frequent occurrence of Ural blocking and it is shown that this condition favors positive WACE event, which links to an intensified SH.
The summer North Atlantic Oscillation (SNAO) variability on decadal to paleoclimate time scales

NASA Astrophysics Data System (ADS)

Linderholm, H. W.; Folland, C. K.; Zhang, P.; Gunnarson, B. E.; Jeong, J. H.; Ren, H.

2017-12-01

The summer North Atlantic Oscillation (SNAO), strongly related to the latitude of the North Atlantic and European summer storm tracks, exerts a considerable influence on European summer climate variability and extremes. Here we extend the period covered by the SNAO from July and August to June, July and August (JJA). As well as marked interannual variability, the JJA SNAO has shown a large inter-decadal change since the 1970s. Decadally averaged, there has been a change from a very positive to a rather negative SNAO phase. This change in SNAO phase is opposite in sign from that expected by a number of climate models under enhanced greenhouse forcing by the late twenty first century. It has led to noticeably wetter summers in North West Europe in the last decade. On interannual to multidecadal timescales, SNAO variability is linked to variations in North Atlantic sea surface temperature (SST): observations and models indicate an association between the Atlantic Multi-decadal Oscillation (AMO) where the cold (warm) phase of the AMO corresponds a positive (negative) phase of the SNAO. Observations also indicate a link with SST in the Gulf Stream region of the North Atlantic where, particularly on decadal time scales, SST warming may favour a more positive phase of the SNAO. Influences of Arctic climate change on North Atlantic and European atmospheric circulation may also exist, particularly reduced sea ice coverage, perhaps favouring the negative phase of the SNAO. A new tree-ring data based JJA SNAO reconstruction extending over the last millennium, as well as climate model output for the same period, enables us to examine the influence of North Atlantic SST and Arctic sea-ice coverage, as well as SNAO impacts on European summer climate, in a long-term, pre-industrial context.
Interannual Variability of the Atlantic Water in the Arctic Basin

DTIC Science & Technology

1996-01-01

3778-3784, 1987. 4. Anderson L.G., Bjork G., Holby 0., Jones E.P., Kattner G., Kolterman K.P., Liljebad B ., Lindegren R., Rudels B ., Swift J. Water...Res., part A, 36, pp. 475 - 482 , 1989. 6. Antonov J. Recent climatic changes of the vertical thermal structure of the North Atlantic Ocean and the...North Pacific Ocean. - J. of Climate, v.6, pp.1928-1942, 1993. 7. Blinov N.I. and Popkov S.N. About the heat exchange of Atlantic Waters in the Arctic
Arctic warming will promote Atlantic-Pacific fish interchange

NASA Astrophysics Data System (ADS)

Wisz, M. S.; Broennimann, O.; Grønkjær, P.; Møller, P. R.; Olsen, S. M.; Swingedouw, D.; Hedeholm, R. B.; Nielsen, E. E.; Guisan, A.; Pellissier, L.

2015-03-01

Throughout much of the Quaternary Period, inhospitable environmental conditions above the Arctic Circle have been a formidable barrier separating most marine organisms in the North Atlantic from those in the North Pacific. Rapid warming has begun to lift this barrier, potentially facilitating the interchange of marine biota between the two seas. Here, we forecast the potential northward progression of 515 fish species following climate change, and report the rate of potential species interchange between the Atlantic and the Pacific via the Northwest Passage and the Northeast Passage. For this, we projected niche-based models under climate change scenarios and simulated the spread of species through the passages when climatic conditions became suitable. Results reveal a complex range of responses during this century, and accelerated interchange after 2050. By 2100 up to 41 species could enter the Pacific and 44 species could enter the Atlantic, via one or both passages. Consistent with historical and recent biodiversity interchanges, this exchange of fish species may trigger changes for biodiversity and food webs in the North Atlantic and North Pacific, with ecological and economic consequences to ecosystems that at present contribute 39% to global marine fish landings.
An early to mid-Pleistocene deep Arctic Ocean ostracode fauna with North Atlantic affinities

USGS Publications Warehouse

DeNinno, Lauren H.; Cronin, Thomas M.; Rodriquez-Lazaro, J.; Brenner, Alec R.

2015-01-01

An early to middle Pleistocene ostracode fauna was discovered in sediment core P1-93-AR-23 (P23, 76.95°N, 155.07°W) from 951 meter water depth from the Northwind Ridge, western Arctic Ocean. Piston core P23 yielded more than 30,000 specimens and a total of about 30 species. Several early to mid-Pleistocene species in the genera Krithe,Echinocythereis, Pterygocythereis, and Arcacythere are now extinct in the Arctic and show taxonomic affinities to North Atlantic Ocean species. Our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the Mid-Pleistocene Transition (MPT, ~ 1.2 to 0.7 Ma) and the Mid-Brunhes Event (MBE, ~ 400 ka) reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400,000 years.
Post-1980 shifts in the sensitivity of boreal tree growth to North Atlantic Ocean dynamics and seasonal climate. Tree growth responses to North Atlantic Ocean dynamics

NASA Astrophysics Data System (ADS)

Ols, Clémentine; Trouet, Valerie; Girardin, Martin P.; Hofgaard, Annika; Bergeron, Yves; Drobyshev, Igor

2018-06-01

The mid-20th century changes in North Atlantic Ocean dynamics, e.g. slow-down of the Atlantic meridional overturning thermohaline circulation (AMOC), have been considered as early signs of tipping points in the Earth climate system. We hypothesized that these changes have significantly altered boreal forest growth dynamics in northeastern North America (NA) and northern Europe (NE), two areas geographically adjacent to the North Atlantic Ocean. To test our hypothesis, we investigated tree growth responses to seasonal large-scale oceanic and atmospheric indices (the AMOC, North Atlantic Oscillation (NAO), and Arctic Oscillation (AO)) and climate (temperature and precipitation) from 1950 onwards, both at the regional and local levels. We developed a network of 6876 black spruce (NA) and 14437 Norway spruce (NE) tree-ring width series, extracted from forest inventory databases. Analyses revealed post-1980 shifts from insignificant to significant tree growth responses to summer oceanic and atmospheric dynamics both in NA (negative responses to NAO and AO indices) and NE (positive response to NAO and AMOC indices). The strength and sign of these responses varied, however, through space with stronger responses in western and central boreal Quebec and in central and northern boreal Sweden, and across scales with stronger responses at the regional level than at the local level. Emerging post-1980 associations with North Atlantic Ocean dynamics synchronized with stronger tree growth responses to local seasonal climate, particularly to winter temperatures. Our results suggest that ongoing and future anomalies in oceanic and atmospheric dynamics may impact forest growth and carbon sequestration to a greater extent than previously thought. Cross-scale differences in responses to North Atlantic Ocean dynamics highlight complex interplays in the effects of local climate and ocean-atmosphere dynamics on tree growth processes and advocate for the use of different spatial scales in
Building Partnerships and Research Collaborations to Address the Impacts of Arctic Change: The North Atlantic Climate Change Collaboration (NAC3)

NASA Astrophysics Data System (ADS)

Polk, J.; North, L. A.; Strenecky, B.

2015-12-01

Changes in Arctic warming influence the various atmospheric and oceanic patterns that drive Caribbean and mid-latitude climate events, including extreme events like drought, tornadoes, and flooding in Kentucky and the surrounding region. Recently, the establishment of the North Atlantic Climate Change Collaboration (NAC3) project at Western Kentucky University (WKU) in partnership with the University of Akureyri (UNAK), Iceland Arctic Cooperation Network (IACN), and Caribbean Community Climate Change Centre (CCCCC) provides a foundation from which to engage students in applied research from the local to global levels and more clearly understand the many tenets of climate change impacts in the Arctic within both a global and local community context. The NAC3 project encompasses many facets, including joint international courses, student internships, economic development, service learning, and applied research. In its first phase, the project has generated myriad outcomes and opportunities for bridging STEM disciplines with other fields to holistically and collaboratively address specific human-environmental issues falling under the broad umbrella of climate change. WKU and UNAK students desire interaction and exposure to other cultures and regions that are threatened by climate change and Iceland presents a unique opportunity to study influences such as oceanic processes, island economies, sustainable harvest of fisheries, and Arctic influences on climate change. The project aims to develop a model to bring partners together to conduct applied research on the complex subject of global environmental change, particularly in the Arctic, while simultaneously focusing on changing how we learn, develop community, and engage internationally to understand the impacts and find solutions.
Hydrographic changes in the subpolar North Atlantic at the MCA to LIA transition

NASA Astrophysics Data System (ADS)

Divine, Dmitry; Miettinen, Arto; Husum, Katrine; Koc, Nalan

2016-04-01

A network of four marine sediment cores from the northern North Atlantic is used to study hydrographic changes in surface water masses during the last 2000 years with a special focus on the Medieval Climate Anomaly (MCA) to the Little Ice Age (LIA) transition. Three of the cores are recovered from the sites located on main pathways of warm Atlantic water to the Arctic: M95-2011 (Vøring plateau, Norwegian Sea), Rapid-21 COM and LO-14 (Reykjanes Ridge, south of Iceland). The fourth core MD99-2322 is from the SE Greenland shelf (Denmark Strait), and it is influenced by the cold water outflow from the Arctic. The cores were analyzed continuously for planktonic diatoms with a high decadal to subdecadal temporal resolution. Past changes in the spatial distribution of surface water masses have been studied identifying factors, or typical species compositions, in downcore diatom assemblages. To derive the factors a Q-mode factor analysis has been applied to the extended modern calibration data set of 184 surface sediment samples from the North Atlantic, the Labrador Sea, the Nordic Seas, and Baffin Bay. SSTs have also been reconstructed using transfer functions. Variations of the reconstructed SSTs and loadings of major contributing factors reveal a complex regional pattern of changes in the structure of circulation during the MCA/LIA transition (1200-1400 AD). In the Norwegian Sea, the factors associated with assemblages typical for warmer and saline North Atlantic waters are partly displaced by colder and fresher water dwelling diatoms suggesting an eastward migration of mixed Arctic/Atlantic water masses into the Norwegian Sea. The two cores south of Iceland show a westward propagation of a warm water pulse as evidenced by the dominance of assemblages, which today are typical for the waters ca 5° further south than the current study sites. At the SE Greenland shelf an abrupt shift (ca. 50 years) in factors associated with different sea ice zone dwelling diatoms
Regime shifts in the Arctic North Atlantic during the Neoglacial revealed by seabirds and precipitation isotopes on Bjørnøya, Svalbard

NASA Astrophysics Data System (ADS)

D'Andrea, William J.; Hormes, Anne; Bakke, Jostein; Nicolaisen, Line

2016-04-01

The northeastern North Atlantic Ocean, and the Norwegian and Greenland Seas are subject to large hydrographic changes. These variations can influence oceanic heat transport to the Arctic, meridional overturning circulation, and atmospheric circulation patterns and thereby impact global climate patterns. Marine records suggest that numerous large-scale changes in the hydrography of the northern North Atlantic took place during the middle to late Holocene. We report a record of nitrogen and hydrogen isotope measurements from a lake sediment core from Bjørnøya, Svalbard (74.38°N, 19.02°E) that documents major regime shifts in the climate of the northern North Atlantic during the past 6,000 years. Bjørnøya is the nesting ground for one of the largest seabird populations in the North Atlantic. As top predators in the marine ecosystem, seabirds (and their guano) are enriched in 15N; during spring and summer months they deliver isotopically enriched nitrogen to nesting areas. We developed a record of seabird population changes on Bjørnøya based on the nitrogen isotope composition of sediments in a core collected from lake Ellasjøen. The record reveals multiple multicentennial scale changes in δ15N values (varying between ~8-12‰) that track past changes in the size of seabird populations. From the same sediment core, we also developed a record of δD of precipitation, using δD values of sedimentary n-alkanes. Past intervals with the largest inferred bird populations correspond with the most enriched δD of precipitation, which we interpret to represent a more Atlantic climate. Periods with reduced seabird populations correspond with intervals with more negative δD of precipitation and representing a more Arctic climate. Together, the nitrogen and hydrogen isotope records signify regime shifts in the oceanography, marine ecosystem, and atmospheric circulation of the northern North Atlantic that are related to variations in the strength of the subpolar gyre.

Mid-Holocene Strengthening of the Bering Strait Inflow to the Arctic and its Linkage With the North Atlantic Subpolar Gyre Circulation

NASA Astrophysics Data System (ADS)

Yamamoto, M.; Nam, S. I.; Polyak, L.; Kobayashi, D.; Suzuki, K.; Irino, T.; Shimada, K.

2017-12-01

The Bering Strait inflow (BSI) is an important element of the Arctic Ocean circulation system. We report records of the chlorite/illite ratios in three sediment cores from the northern Chukchi Sea providing insights into the long-term dynamics of the BSI during the Holocene. The BSI approximation by the chlorite/illite record, despite a considerable geographic variability, consistently shows intensified flow from the Bering Sea to the Arctic during the middle Holocene, which is attributed primarily to the effect of higher atmospheric pressure over the Aleutian Basin. The intensified BSI was associated with decrease in sea-ice concentrations and increase in marine production, as indicated by biomarker concentrations, suggesting a major influence of the BSI on sea-ice and biological conditions in the Chukchi Sea. Multi-century to millennial fluctuations, presumably controlled by solar activity, were also identified. This middle Holocene strengthening of the BSI was coeval with intense subpolar gyre circulation in the North Atlantic. We propose that the BSI is linked with the North Atlantic circulation via an atmospheric teleconnection between the Aleutian and Icelandic Lows.
Observations of elevated Atlantic water heat fluxes at the boundary of the Arctic Basin.

NASA Astrophysics Data System (ADS)

Lincoln, Benjamin; Rippeth, Tom; Lenn, Yueng; Bacon, Sheldon

2014-05-01

The well documented decline in Arctic Sea Ice cover over the past 30 years has outpaced global models as warming in Polar Regions occurs faster than the global mean. The thermohaline circulation brings warm water from the Atlantic Ocean into the Arctic basin. This Atlantic water circulates at depth and contains sufficient heat to melt the sea ice cover several times over. Recent studies have shown that this Atlantic water has warmed and shoaled over recent decades (Polyakov et al, 2010). The stability of the upper Arctic Ocean has also changed, with stratification reduced in the Eurasian basin but increased in the Canada basin. Along with an increased availability of heat the reduction in sea ice cover allows greater potential for wind to input energy to the ocean to vertically mix heat to the surface and further melt sea ice. Direct measurements of vertical mixing rates across the Arctic are essential to understanding the changes in this supply of heat from below, but are scarce due to the challenges of making such measurements in the harsh Arctic environment. We present measurements of turbulent kinetic energy dissipation (ɛ) within the top 500 m of the water column using microstructure measurements made both in open water and under ice during 4 different years. Mean rates of dissipation in the Atlantic water thermocline are calculated and compared for data collected in the European, Siberian and Canadian Arctic, including measurements from 2007 and 2012 when record minimum sea ice extents were recorded. Diapycnal heat fluxes from the mean Atlantic water dissipation rates were calculated from these mean dissipation rates and show significant variation across the Arctic Basin. Profiles in the deep basin generally revealed very low rates of dissipation were low ɛ<10-9Wkg-1 and as such heat fluxes of AW were correspondingly low Fh=0.1-0.5Wm-2. However double diffusive staircases were present in all such casts and so vertical transfer of heat may be increased by
Bottom melting of Arctic Sea Ice in the Nansen Basin due to Atlantic Water influence

NASA Astrophysics Data System (ADS)

Muilwijk, Morven; Smedsrud, Lars H.; Meyer, Amelie

2016-04-01

Our global climate is warming, and a shrinking Arctic sea ice cover remains one of the most visible signs of this warming. Sea Ice loss is now visible for all months in all regions of the Arctic. Hydrographic and current observations from a region north of Svalbard collected during the Norwegian Young Sea Ice Cruise (N-ICE2015) are presented here. Comparison with historical data shows that the new observations from January through June fill major gaps in available observations, and help describing important processes linking changes in regional Atlantic Water (AW) heat transport and sea ice. Warm and salty AW originating in the North Atlantic enters the Arctic Ocean through the Fram Strait and is present below the Arctic Sea Ice cover throughout the Arctic. However, the depth of AW varies by region and over time. In the region north of Svalbard, we assume that depth could be governed primarily by local processes, by upstream conditions of the ice cover (Northwards), or by upstream conditions of the AW (Southwards). AW carries heat corresponding to the volume transport of approximately 9 SV through Fram Strait, varying seasonally from 28 TW in winter to 46 TW in summer. Some heat is recirculated, but the net annual heat flux into the Arctic Ocean from AW is estimated to be around 40 TW. The Atlantic Water layer temperature at intermediate depths (150-900m) has increased in recent years. Until recently, maximum temperatures have been found to be 2-3 C in the Nansen Basin. Studies have shown that for example, in the West Spitsbergen Current the upper 50-200m shows an overall AW warming of 1.1 C since 1979. In general we expect efficient melting when AW is close to the surface. Previously the AW entering through Fram Strait has been considered as less important because changes in the sea ice cover have been connected to greater inflow of Pacific Water through Bering Strait and atmospheric forcing. Conversely it is now suggested that AW has direct impact on melting of
On the Freshwater Sensitivity of the Arctic-Atlantic Thermohaline Circulation

NASA Astrophysics Data System (ADS)

Lambert, E.; Eldevik, T.; Haugan, P.

2016-02-01

The North Atlantic thermohaline circulation (THC) carries heat and salt toward the Arctic. This circulation is generally believed to be inhibited by northern freshwater input as indicated by the `box-model' of Stommel (1961). The inferred freshwater-sensitivity of the THC, however, varies considerably between studies, both quantitatively and qualitatively. The northernmost branch of the Atlantic THC, which forms a double estuarine circulation in the Arctic Mediterranean, is one example where both strengthening and weakening of the circulation may occur due to increased freshwater input. We have accordingly built on Stommel's original concept to accomodate a THC similar to that in the Arctic Mediterranean. This model consists of three idealized basins, or boxes, connected by two coupled branches of circulation - the double estuary. The net transport of these two branches represents the extension of the Gulf Stream toward the Arctic. Its sensitivity to a change in freshwater forcing depends largely on the distribution of freshwater over the two northern basins. Varying this distribution opens a spectrum of qualitative behaviours ranging from Stommel's original freshwater-inhibited overturning circulation to a freshwater-facilitated estuarine circulation. Between these limiting cases, a Hopf and a cusp bifurcation divide the spectrum into three qualitative regions. In the first region, the circulation behaves similarly to Stommel's circulation, and sufficient freshwater input can induce an abrupt transition into a reversed flow; in the second, a similar transition can be found, although it does not reverse the circulation; in the third, no transition can occur and the circulation is generally facilitated by the northern freshwater input. Overall, the northern THC appears more stable than what would be inferred based on Stommel's model; it requires a larger amount and more localized freshwater input to `collapse' it, and a double estuary circulation is less prone to
On the Flow of Atlantic Water Towards the Arctic Ocean; a Synergy Between Altimetry and Hydrography.

NASA Astrophysics Data System (ADS)

Chafik, L.; Nilsson, J.; Skagseth, O.; Lundberg, P.

2015-12-01

The Arctic climate is strongly influenced by the inflow of warm Atlantic water conveyed by the Norwegian Atlantic Slope Current (NwASC); the main heat conveyor into the Arctic Ocean. Based on sea surface height (SSH) data from altimetry, we develop a dynamical measure of the NwASC transport to diagnose its spatio-temporal variability. This supports a dynamical division of the NwASC into two flow regimes; the Svinøy Branch (SvB) in the Norwegian Sea, and the Fram Strait Branch (FSB) west of Spitsbergen. The SvB transport is well correlated with the SSH and atmospheric variability within the Nordic Seas, factors that also affect the inflow to the Barents Sea. In contrast, the FSB is regulated by regional atmospheric patterns around Svalbard and northern Barents Sea. We further relate anomalous flow events to temperature fluctuations of Atlantic water. A warm anomaly is found to propagate northwards, with a tendency to amplify enroute, after events of strong flow in the Norwegian Sea. A roughly 12-months delayed temperature signal is identified in the FSB. This suggests that hydrographic anomalies both upstream from the North Atlantic, and locally generated in the Norwegian Sea, are important for the oceanic heat and salt transport that eventually enters into the Arctic. We believe that the combination of the flow from altimetry and temperature fluctuations in the Nordic Seas can be used to qualitatively predict warm anomalies towards the Arctic Ocean, which could be a valuable addition to the forecast skill of the statistical Arctic sea-ice models.
Salinity Trends within the Upper Layers of the Subpolar North Atlantic

NASA Astrophysics Data System (ADS)

Tesdal, J. E.; Abernathey, R.; Goes, J. I.; Gordon, A. L.; Haine, T. W. N.

2017-12-01

Examination of a range of salinity products collectively suggest widespread freshening of the North Atlantic from the mid-2000 to the present. Monthly salinity fields reveal negative trends that differ in magnitude and significance between western and eastern regions of the North Atlantic. These differences can be attributed to the large negative interannual excursions in salinity in the western subpolar gyre and the Labrador Sea, which are not apparent in the central or eastern subpolar gyre. This study demonstrates that temporal trends in salinity in the northwest (including the Labrador Sea) are subject to mechanisms that are distinct from those responsible for the salinity trends in central and eastern North Atlantic. In the western subpolar gyre a negative correlation between near surface salinity and the circulation strength of the subpolar gyre suggests that negative salinity anomalies are connected to an intensification of the subpolar gyre, which is causing increased flux of freshwater from the East Greenland Current and subsequent transport into the Labrador Sea during the melting season. Analyses of sea surface wind fields suggest that the strength of the subpolar gyre is linked to the North Atlantic Oscillation and Arctic Oscillation-driven changes in wind stress curl in the eastern subpolar gyre. If this trend of decreasing salinity continues, it has the potential to enhance water column stratification, reduce vertical fluxes of nutrients and cause a decline in biological production and carbon export in the North Atlantic Ocean.
Genetic discontinuity among regional populations of Lophelia pertusa in the North Atlantic Ocean

USGS Publications Warehouse

Morrison, C.L.; Ross, Steve W.; Nizinski, M.S.; Brooke, S.; Jarnegren, J.; Waller, R.G.; Johnson, Robin L.; King, T.L.

2011-01-01

Knowledge of the degree to which populations are connected through larval dispersal is imperative to effective management, yet little is known about larval dispersal ability or population connectivity in Lophelia pertusa, the dominant framework-forming coral on the continental slope in the North Atlantic Ocean. Using nine microsatellite DNA markers, we assessed the spatial scale and pattern of genetic connectivity across a large portion of the range of L. pertusa in the North Atlantic Ocean. A Bayesian modeling approach found four distinct genetic groupings corresponding to ocean regions: Gulf of Mexico, coastal southeastern U.S., New England Seamounts, and eastern North Atlantic Ocean. An isolation-by-distance pattern was supported across the study area. Estimates of pairwise population differentiation were greatest with the deepest populations, the New England Seamounts (average F ST = 0.156). Differentiation was intermediate with the eastern North Atlantic populations (F ST = 0.085), and smallest between southeastern U.S. and Gulf of Mexico populations (F ST = 0.019), with evidence of admixture off the southeastern Florida peninsula. Connectivity across larger geographic distances within regions suggests that some larvae are broadly dispersed. Heterozygote deficiencies were detected within the majority of localities suggesting deviation from random mating. Gene flow between ocean regions appears restricted, thus, the most effective management scheme for L. pertusa involves regional reserve networks.
Initializing decadal climate predictions over the North Atlantic region

NASA Astrophysics Data System (ADS)

Matei, Daniela Mihaela; Pohlmann, Holger; Jungclaus, Johann; Müller, Wolfgang; Haak, Helmuth; Marotzke, Jochem

2010-05-01

Decadal climate prediction aims to predict the internally-generated decadal climate variability in addition to externally-forced climate change signal. In order to achieve this it is necessary to start the predictions from the current climate state. In this study we investigate the forecast skill of the North Atlantic decadal climate predictions using two different ocean initialization strategies. First we apply an assimilation of ocean synthesis data provided by the GECCO project (Köhl and Stammer, 2008) as initial conditions for the coupled model ECHAM5/MPI-OM. Hindcast experiments are then performed over the period 1952-2001. An alternative approach is one in which the subsurface ocean temperature and salinity are diagnosed from an ensemble of ocean model runs forced by the NCEP-NCAR atmospheric reanalyzes for the period 1948-2007, then nudge into the coupled model to produce initial conditions for the hindcast experiments. An anomaly coupling scheme is used in both approaches to avoid the hindcast drift and the associated initial shock. Differences between the two assimilation approaches are discussed by comparing them with the observational data in key regions and processes. We asses the skill of the initialized decadal hindcast experiments against the prediction skill of the non-initialized hindcasts simulation. We obtain an overview of the regions with the highest predictability from the regional distribution of the anomaly correlation coefficients and RMSE for the SAT. For the first year the hindcast skill is increased over almost all ocean regions in the NCEP-forced approach. This increase in the hindcast skill for the 1 year lead time is somewhat reduced in the GECCO approach. At lead time 5yr and 10yr, the skill enhancement is still found over the North Atlantic and North Pacific regions. We also consider the potential predictability of the Atlantic Meridional Overturning Circulation (AMOC) and Nordic Seas Overflow by comparing the predicted values to
Pliocene shallow water paleoceanography of the North Atlantic ocean based on marine ostracodes

USGS Publications Warehouse

Cronin, T. M.

1991-01-01

Middle Pliocene marine ostracodes from coastal and shelf deposits of North and Central America and Iceland were studied to reconstruct paleotemperatures of shelf waters bordering portions of the Western Boundary Current System (including the Gulf Loop Current, Florida Current, Gulf Stream and North Atlantic Drift). Factor analytic transfer functions provided Pliocene August and February bottom-water temperatures of eight regions from the tropics to the subfrigid. The results indicate: (1) meridional temperature gradients in the western North Atlantic were less steep during the Pliocene than either today or during Late Pleistocene Isotope Stage 5e; (2) tropical and subtropical shelf waters during the Middle Pliocene were as warm as, or slightly cooler than today; (3) slightly cooler water was on the outer shelf off the southeastern and mid-Atlantic coast of the U.S., possibly due to summer upwelling of Gulf Stream water; (4) the shelf north of Cape Hatteras, North Carolina may have been influenced by warm water incursions from the western edge of the Gulf Stream, especially in summer; (5) the northeast branch of the North Atlantic Drift brought warm water to northern Iceland between 4 and 3 Ma; evidence from the Iceland record indicates that cold East Greenland Current water did not affect coastal Iceland between 4 and 3 Ma; (6) Middle Pliocene North Atlantic circulation may have been intensified, transporting more heat from the tropics to the Arctic than it does today. ?? 1991.
North Atlantic Regional Water Resources Study. Main Report

DTIC Science & Technology

1972-06-01

Areas of the Rgion are found in Annex 1 to this Report. These Area Programs have The NAR is presently growing at a slower rate been reformu!ld into...Physical Characteristics of The Region double to 86.2 million by the year 2020. The rate of growth is about 80 percent of that The North Atlantic Region...Use of 141 and Delaware River Basin (Area 15). wells and of waste water intakes, while small, is growing at an increased rate . Publicly supplied and
Threshold in North Atlantic-Arctic Ocean circulation controlled by the subsidence of the Greenland-Scotland Ridge

PubMed Central

Stärz, Michael; Jokat, Wilfried; Knorr, Gregor; Lohmann, Gerrit

2017-01-01

High latitude ocean gateway changes are thought to play a key role in Cenozoic climate evolution. However, the underlying ocean dynamics are poorly understood. Here we use a fully coupled atmosphere-ocean model to investigate the effect of ocean gateway formation that is associated with the subsidence of the Greenland–Scotland Ridge. We find a threshold in sill depth (∼50 m) that is linked to the influence of wind mixing. Sill depth changes within the wind mixed layer establish lagoonal and estuarine conditions with limited exchange across the sill resulting in brackish or even fresher Arctic conditions. Close to the threshold the ocean regime is highly sensitive to changes in atmospheric CO2 and the associated modulation in the hydrological cycle. For larger sill depths a bi-directional flow regime across the ridge develops, providing a baseline for the final step towards the establishment of a modern prototype North Atlantic-Arctic water exchange. PMID:28580952
The relation between AMOC, gyre circulation, and meridional heat transports in the North Atlantic in model simulations of the last millennium

NASA Astrophysics Data System (ADS)

Jungclaus, J. H.; Moreno-Chamarro, E.; Lohmann, K.; Zanchettin, D.

2016-02-01

While it is clear that the Atlantic Meridional Overturning Circulation (AMOC) is responsible for meridional heat transfer from the South Atlantic and the tropics to the North Atlantic, the majority of the heat transport in the northern North Atlantic and the Nordic seas is carried by the gyre system. However, the detailed mechanisms determining the interaction between and the temporal modulation of the components of the northward heat transport system are not clear. Long-term climate records and model simulations can help to identify important processes and to provide background for the changes that are presently observed. Multi-centennial proxy records from the subpolar North Atlantic and the Nordic Seas indicate, for example, an out-of-phase behavior of sea surface temperature and gyre circulation between the two regions with consequences for regional climate. Paleoceanographic evidence from Fram Strait shows a pronounced modulation of heat transfer to the Arctic by the Atlantic Water layer during the last 2000 years and reconstructions from the Subpolar North Atlantic suggest a role of ocean circulation in the transition between the Medieval Climate Anomaly and the Little Ice Age. Here we explore a small ensemble of last millennium simulations, carried out with the Max Planck Institute Earth System Model, and analyze mechanisms connecting the AMOC and gyre circulation and their relation to external forcing. Our results support the important role of the Subpolar Gyre strength and the related meridional mass and temperature fluxes. We find that the modulation of the northward heat transport into the Nordic Seas and the Arctic has pronounced impact on sea-ice distribution, ocean-atmosphere interaction, and the surface climate in Scandinavia and Western Europe.
The relation between AMOC, gyre circulation, and meridional heat transports in the North Atlantic in model simulations of the last millennium

NASA Astrophysics Data System (ADS)

Jungclaus, Johann; Moreno-Chamarro, Eduardo; Lohmann, Katja

2016-04-01

While it is clear that the Atlantic Meridional Overturning Circulation (AMOC) is responsible for meridional heat transfer from the South Atlantic and the tropics to the North Atlantic, the majority of the heat transport in the northern North Atlantic and the Nordic seas is carried by the gyre system. However, the detailed mechanisms determining the interaction between and the temporal modulation of the components of the northward heat transport system are not clear. Long-term climate records and model simulations can help to identify important processes and to provide background for the changes that are presently observed. Multi-centennial proxy records from the subpolar North Atlantic and the Nordic Seas indicate, for example, an out-of-phase behavior of sea surface temperature and gyre circulation between the two regions with consequences for regional climate. Paleoceanographic evidence from Fram Strait shows a pronounced modulation of heat transfer to the Arctic by the Atlantic Water layer during the last 2000 years and reconstructions from the Subpolar North Atlantic suggest a role of ocean circulation in the transition between the Medieval Climate Anomaly and the Little Ice Age. Here we explore a small ensemble of last millennium simulations, carried out with the Max Planck Institute Earth System Model, and analyze mechanisms connecting the AMOC and gyre circulation and their relation to external forcing. Our results support the important role of the Subpolar Gyre strength and the related meridional mass and temperature fluxes. We find that the modulation of the northward heat transport into the Nordic Seas and the Arctic has pronounced impact on sea-ice distribution, ocean-atmosphere interaction, and the surface climate in Scandinavia and Western Europe.
An interannual link between Arctic sea-ice cover and the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Caian, Mihaela; Koenigk, Torben; Döscher, Ralf; Devasthale, Abhay

2018-01-01

This work investigates links between Arctic surface variability and the phases of the winter (DJF) North Atlantic Oscillation (NAO) on interannual time-scales. The analysis is based on ERA-reanalysis and model data from the EC-Earth global climate model. Our study emphasizes a mode of sea-ice cover variability that leads the NAO index by 1 year. The mechanism of this leading is based on persistent surface forcing by quasi-stationary meridional thermal gradients. Associated thermal winds lead a slow adjustment of the pressure in the following winter, which in turn feeds-back on the propagation of sea-ice anomalies. The pattern of the sea-ice mode leading NAO has positive anomalies over key areas of South-Davis Strait-Labrador Sea, the Barents Sea and the Laptev-Ohkostsk seas, associated to a high pressure anomaly over the Canadian Archipelago-Baffin Bay and the Laptev-East-Siberian seas. These anomalies create a quasi-annular, quasi-steady, positive gradient of sea-ice anomalies about coastal line (when leading the positive NAO phase) and force a cyclonic vorticity anomaly over the Arctic in the following winter. During recent decades in spite of slight shifts in the modes' spectral properties, the same leading mechanism remains valid. Encouraging, actual models appear to reproduce the same mechanism leading model's NAO, relative to model areas of persistent surface forcing. This indicates that the link between sea-ice and NAO could be exploited as a potential skill-source for multi-year prediction by addressing the key problem of initializing the phase of the NAO/AO (Arctic Oscillation).
North Atlantic climate variability: The role of the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Hurrell, James W.; Deser, Clara

2009-08-01

Marine ecosystems are undergoing rapid change at local and global scales. To understand these changes, including the relative roles of natural variability and anthropogenic effects, and to predict the future state of marine ecosystems requires quantitative understanding of the physics, biogeochemistry and ecology of oceanic systems at mechanistic levels. Central to this understanding is the role played by dominant patterns or "modes" of atmospheric and oceanic variability, which orchestrate coherent variations in climate over large regions with profound impacts on ecosystems. We review the spatial structure of extratropical climate variability over the Northern Hemisphere and, specifically, focus on modes of climate variability over the extratropical North Atlantic. A leading pattern of weather and climate variability over the Northern Hemisphere is the North Atlantic Oscillation (NAO). The NAO refers to a redistribution of atmospheric mass between the Arctic and the subtropical Atlantic, and swings from one phase to another producing large changes in surface air temperature, winds, storminess and precipitation over the Atlantic as well as the adjacent continents. The NAO also affects the ocean through changes in heat content, gyre circulations, mixed layer depth, salinity, high latitude deep water formation and sea ice cover. Thus, indices of the NAO have become widely used to document and understand how this mode of variability alters the structure and functioning of marine ecosystems. There is no unique way, however, to define the NAO. Several approaches are discussed including both linear (e.g., principal component analysis) and nonlinear (e.g., cluster analysis) techniques. The former, which have been most widely used, assume preferred atmospheric circulation states come in pairs, in which anomalies of opposite polarity have the same spatial structure. In contrast, nonlinear techniques search for recurrent patterns of a specific amplitude and sign. They reveal
North Atlantic climate variability: The role of the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Hurrell, James W.; Deser, Clara

2010-02-01

Marine ecosystems are undergoing rapid change at local and global scales. To understand these changes, including the relative roles of natural variability and anthropogenic effects, and to predict the future state of marine ecosystems requires quantitative understanding of the physics, biogeochemistry and ecology of oceanic systems at mechanistic levels. Central to this understanding is the role played by dominant patterns or "modes" of atmospheric and oceanic variability, which orchestrate coherent variations in climate over large regions with profound impacts on ecosystems. We review the spatial structure of extratropical climate variability over the Northern Hemisphere and, specifically, focus on modes of climate variability over the extratropical North Atlantic. A leading pattern of weather and climate variability over the Northern Hemisphere is the North Atlantic Oscillation (NAO). The NAO refers to a redistribution of atmospheric mass between the Arctic and the subtropical Atlantic, and swings from one phase to another producing large changes in surface air temperature, winds, storminess and precipitation over the Atlantic as well as the adjacent continents. The NAO also affects the ocean through changes in heat content, gyre circulations, mixed layer depth, salinity, high latitude deep water formation and sea ice cover. Thus, indices of the NAO have become widely used to document and understand how this mode of variability alters the structure and functioning of marine ecosystems. There is no unique way, however, to define the NAO. Several approaches are discussed including both linear (e.g., principal component analysis) and nonlinear (e.g., cluster analysis) techniques. The former, which have been most widely used, assume preferred atmospheric circulation states come in pairs, in which anomalies of opposite polarity have the same spatial structure. In contrast, nonlinear techniques search for recurrent patterns of a specific amplitude and sign. They reveal
Exploring Arctic history through scientific drilling

NASA Astrophysics Data System (ADS)

ODP Leg 151 Shipboard Scientific Party

During the brief Arctic summer of 1993, the Ocean Drilling Program's research vessel JOIDES Resolution recovered the first scientific drill cores from the eastern Arctic Ocean. Dodging rafts of pack ice shed from the Arctic ice cap, the science party sampled sediments north of 80°N latitude from the Yermak Plateau, as well as from sites in Fram Strait, the northeastern Greenland margin, and the Iceland Plateau (Figure 1).The sediments collected reveal the earliest history of the connection between the North Atlantic and Arctic Oceans through the Nordic Seas. The region between Greenland and Norway first formed a series of isolated basins, sometimes with restricted deep circulation, that eventually joined and allowed deep and surface Arctic Ocean water to invade the region. A record was also retrieved that shows major glaciation in the region began about 2.5 m.y.a.
Influence of ENSO on Gulf Stream cyclogenesis and the North Atlantic storm track

NASA Astrophysics Data System (ADS)

Li, C.; Schemm, S.; Ciasto, L.; Kvamsto, N. G.

2015-12-01

There is emerging evidence that climate in the North Atlantic-European sector is sensitive to vacillations of tropical Pacific sea surface temperatures, in particular, the central Pacific flavour of the El Nino Southern Oscillation (ENSO) and concomitant trends in atmospheric heating. The frequency of central Pacific ENSOs appears to have increased over the last decades and some studies suggest it may continue increasing in the future, but the precise mechanisms by which these events affect the North Atlantic synoptic scale circulation are poorly understood. Here, we show that central Pacific ENSOs influence where midlatitude cyclogenesis occurs over the Gulf Stream, producing more cyclogenesis in the jet exit region rather than in the climatologically preferred jet entrance region. The cyclones forming over the Gulf Stream in central Pacific ENSO seasons tend to veer north, penetrating deeper into the Arctic rather than into continental Europe. The shift in cyclogenesis is linked to changes in the large scale circulation, namely, the upper-level trough formed in the lee of the Rocky Mountains.
The North Atlantic Oscillation as a driver of multidecadal variability of the AMOC, the AMO, and Northern Hemisphere climate

NASA Astrophysics Data System (ADS)

Delworth, T. L.; Zeng, F. J.; Yang, X.; Zhang, L.

2017-12-01

We use suites of simulations with coupled ocean-atmosphere models to show that multidecadal changes in the North Atlantic Oscillation (NAO) can drive multidecadal changes in the Atlantic Meridional Overturning Circulation (AMOC) and the Atlantic Multidecadal Oscillation (AMO), with associated hemispheric climatic impacts. These impacts include rapid changes in Arctic sea ice, hemispheric temperature, and modulation of Atlantic hurricane activity. We use models that incorporate either a fully dynamic ocean or a simple slab ocean to explore the role of ocean dynamics and ocean-atmosphere interactions. A positive phase of the NAO is associated with strengthened westerly winds over the North Atlantic. These winds extract more heat than normal from the subpolar ocean, thereby increasing upper ocean density, deepwater formation, and the strength of the AMOC and associated poleward ocean heat transport. This warming leads to a positive phase of the AMO. The enhanced oceanic heat transport extends to the Arctic where it causes a reduction of Arctic sea ice. Large-scale atmospheric warming reduces vertical wind shear in the tropical North Atlantic, creating an environment more favorable for tropical storms. We use models to further show that observed multidecadal variations of the NAO over the 20th and early 21st centuries may have led to multidecadal variations of simulated AMOC and the AMO. Specifically, negative NAO values from the late 1960s through the early 1980s led to a weakened AMOC/cold North Atlantic, whereas increasing NAO values from the late 1980s through the late 1990s increased the model AMOC and led to a positive (warm) phase of the AMO. The warm phase contributed to increases in tropical storm activity and decreases in Arctic sea ice after the mid 1990s. Ocean dynamics are essential for translating the observed NAO variations into ocean heat content variations for the extratropical North Atlantic, but appear less important in the tropical North Atlantic
Inter-Relationship Between Subtropical Pacific Sea Surface Temperature, Arctic Sea Ice Concentration, and the North Atlantic Oscillation in Recent Summers and Winters

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon; Cullather, Richard I.; Nowicki, Sophie M.; Kim, Kyu-Myong

2017-01-01

The inter-relationship between subtropical western-central Pacific sea surface temperatures (STWCPSST), sea ice concentration in the Beaufort Sea (SICBS), and the North Atlantic Oscillation (NAO) are investigated for the last 37 summers and winters (1980-2016). Lag-correlation of the STWCPSST×(-1) in spring with the NAO phase and SICBS in summer increases over the last two decades, reaching r = 0.4-0.5 with significance at 5 percent, while winter has strong correlations in approximately 1985-2005. Observational analysis and the atmospheric general circulation model experiments both suggest that STWCPSST warming acts to increase the Arctic geopotential height and temperature in the following season. This atmospheric response extends to Greenland, providing favorable conditions for developing the negative phase of the NAO. SIC and surface albedo tend to decrease over the Beaufort Sea in summer, linked to the positive surface net shortwave flux. Energy balance considering radiative and turbulent fluxes reveal that available energy that can heat surface is larger over the Arctic and Greenland and smaller over the south of Greenland, in response to the STWCPSST warming in spring. XXXX Arctic & Atlantic: Positive upper-level height/T anomaly over the Arctic and Greenland, and a negative anomaly over the central-eastern Atlantic, resembling the (-) phase of the NAO. Pacific: The negative height/T anomaly over the mid-latitudes, along with the positive anomaly over the STWCP, where 1degC warming above climatology is prescribed. Discussion: It is likely that the Arctic gets warm and the NAO is in the negative phase in response to the STWCP warming. But, there are other factors (e.g., internal variability) that contribute to determination of the NAO phase: not always the negative phase of the NAO in the event of STWCP warming (e.g.: recent winters and near neutral NAO in 2017 summer).

New tectonic concept of the Arctic region evolution

NASA Astrophysics Data System (ADS)

Petrov, O. V.; Morozov, A.; Grikurov, G.; Shokalsky, S.; Kashubin, S.; Sobolev, N. V.; Petrov, E.

2012-12-01

-Early Cretaceous continental rifting and volcanic activity. Reactivation of rifting in the Central Arctic at the beginning of Cenozoic led to the onset of spreading 56 million years ago along the emerging Gakkel Ridge and to the subsequent formation of the Eurasian Basin. Approximately 33 million years ago, the newly formed Eurasian oceanic basin connected with the Norwegian-Greenland Basin of the North Atlantic. Combined interpretation of seismostratigraphic data and drilling results suggests that during the Paleogene shallow-water sedimentation in the Central Arctic occurred, which indicates the high-standing sea level. Only in the Early Miocene (about 20 million years ago) the sea bottom sank sharply reaching its present-day depth and causing transition to deep-water deposition. This essential tectonic event is recorded throughout the Central Arctic elevations by a regional unconformity in seismostratigraphic sections. The Cenozoic expansion of the North Atlantic into the Central Arctic occurred across the structural assemblages whose formation was controlled by the preceding evolution of the Asian paleo-ocean.
Role of the North Atlantic Ocean in Low Frequency Climate Variability

NASA Astrophysics Data System (ADS)

Danabasoglu, G.; Yeager, S. G.; Kim, W. M.; Castruccio, F. S.

2017-12-01

The Atlantic Ocean is a unique basin with its extensive, North - South overturning circulation, referred to as the Atlantic meridional overturning circulation (AMOC). AMOC is thought to represent the dynamical memory of the climate system, playing an important role in decadal and longer time scale climate variability as well as prediction of the earth's future climate on these time scales via its large heat and salt transports. This oceanic memory is communicated to the atmosphere primarily through the influence of persistent sea surface temperature (SST) variations. Indeed, many modeling studies suggest that ocean circulation, i.e., AMOC, is largely responsible for the creation of coherent SST variability in the North Atlantic, referred to as Atlantic Multidecadal Variability (AMV). AMV has been linked to many (multi)decadal climate variations in, e.g., Sahel and Brazilian rainfall, Atlantic hurricane activity, and Arctic sea-ice extent. In the absence of long, continuous observations, much of the evidence for the ocean's role in (multi)decadal variability comes from model simulations. Although models tend to agree on the role of the North Atlantic Oscillation in creating the density anomalies that proceed the changes in ocean circulation, model fidelity in representing variability characteristics, mechanisms, and air-sea interactions remains a serious concern. In particular, there is increasing evidence that models significantly underestimate low frequency variability in the North Atlantic compared to available observations. Such model deficiencies can amplify the relative influence of external or stochastic atmospheric forcing in generating (multi)decadal variability, i.e., AMV, at the expense of ocean dynamics. Here, a succinct overview of the current understanding of the (North) Atlantic Ocean's role on the regional and global climate, including some outstanding questions, will be presented. In addition, a few examples of the climate impacts of the AMV via
Synoptic Drivers of Precipitation in the Atlantic Sector of the Arctic

NASA Astrophysics Data System (ADS)

Cohen, L.; Hudson, S.; Graham, R.; Renwick, J. A.

2017-12-01

Precipitation in the Arctic has been shown to be increasing in recent decades, from both observational and modelling studies, with largest trends seen in autumn and winter. This trend is attributed to a combination of the warming atmosphere and reduced sea ice extent. The seasonality of precipitation in the Arctic is important as it largely determines whether the precipitation falls as snow or rain. This study assesses the spatial and temporal variability of the synoptic drivers of precipitation in the Atlantic (European) sector of the Arctic. This region of the Arctic is of particular interest as it has the largest inter-annual variability in sea ice extent and is the primary pathway for moisture transport into the Arctic from lower latitudes. This study uses the ECMWF ERA-I reanalysis total precipitation to compare to long-term precipitation observations from Ny Ålesund, Svalbard to show that the reanalysis captures the synoptic variability of precipitation well and that most precipitation in this region is synoptically driven. The annual variability of precipitation in the Atlantic Arctic shows strong regionality. In the Svalbard and Barents Sea region, most of the annual total precipitation occurs during autumn and winter (Oct-Mar) (>60% of annual total), while the high-Arctic (> 80N) and Kara Sea receives most of the annual precipitation ( 60% of annual total) during summer (July-Sept). Using a synoptic classification developed for this region, this study shows that winter precipitation is driven by winter cyclone occurrence, with strong correlations to the AO and NAO indices. High precipitation over Svalbard is also strongly correlated with the Scandinavian blocking pattern, which produces a southerly flow in the Greenland Sea/Svalbard area. An increasing occurrence of these synoptic patterns are seen for winter months (Nov and Jan), which may explain much of the observed winter increase in precipitation.
Why different gas flux velocity parameterizations result in so similar flux results in the North Atlantic?

NASA Astrophysics Data System (ADS)

Piskozub, Jacek; Wróbel, Iwona

2016-04-01

The North Atlantic is a crucial region for both ocean circulation and the carbon cycle. Most of ocean deep waters are produced in the basin making it a large CO2 sink. The region, close to the major oceanographic centres has been well covered with cruises. This is why we have performed a study of net CO2 flux dependence upon the choice of gas transfer velocity k parameterization for this very region: the North Atlantic including European Arctic Seas. The study has been a part of a ESA funded OceanFlux GHG Evolution project and, at the same time, a PhD thesis (of I.W) funded by Centre of Polar Studies "POLAR-KNOW" (a project of the Polish Ministry of Science). Early results have been presented last year at EGU 2015 as a PICO presentation EGU2015-11206-1. We have used FluxEngine, a tool created within an earlier ESA funded project (OceanFlux Greenhouse Gases) to calculate the North Atlantic and global fluxes with different gas transfer velocity formulas. During the processing of the data, we have noticed that the North Atlantic results for different k formulas are more similar (in the sense of relative error) that global ones. This was true both for parameterizations using the same power of wind speed and when comparing wind squared and wind cubed parameterizations. This result was interesting because North Atlantic winds are stronger than the global average ones. Was the flux result similarity caused by the fact that the parameterizations were tuned to the North Atlantic area where many of the early cruises measuring CO2 fugacities were performed? A closer look at the parameterizations and their history showed that not all of them were based on North Atlantic data. Some of them were tuned to the South Ocean with even stronger winds while some were based on global budgets of 14C. However we have found two reasons, not reported before in the literature, for North Atlantic fluxes being more similar than global ones for different gas transfer velocity parametrizations
Climate change impact on seaweed meadow distribution in the North Atlantic rocky intertidal

PubMed Central

Jueterbock, Alexander; Tyberghein, Lennert; Verbruggen, Heroen; Coyer, James A; Olsen, Jeanine L; Hoarau, Galice

2013-01-01

The North-Atlantic has warmed faster than all other ocean basins and climate change scenarios predict sea surface temperature isotherms to shift up to 600 km northwards by the end of the 21st century. The pole-ward shift has already begun for many temperate seaweed species that are important intertidal foundation species. We asked the question: Where will climate change have the greatest impact on three foundational, macroalgal species that occur along North-Atlantic shores: Fucus serratus, Fucus vesiculosus, and Ascophyllum nodosum? To predict distributional changes of these key species under three IPCC (Intergovernmental Panel on Climate Change) climate change scenarios (A2, A1B, and B1) over the coming two centuries, we generated Ecological Niche Models with the program MAXENT. Model predictions suggest that these three species will shift northwards as an assemblage or “unit” and that phytogeographic changes will be most pronounced in the southern Arctic and the southern temperate provinces. Our models predict that Arctic shores in Canada, Greenland, and Spitsbergen will become suitable for all three species by 2100. Shores south of 45° North will become unsuitable for at least two of the three focal species on both the Northwest- and Northeast-Atlantic coasts by 2200. If these foundational species are unable to adapt to the rising temperatures, they will lose their centers of genetic diversity and their loss will trigger an unpredictable shift in the North-Atlantic intertidal ecosystem. PMID:23762521
Atlantic water heat transfer through the Arctic Gateway (Fram Strait) during the Last Interglacial

NASA Astrophysics Data System (ADS)

Zhuravleva, Anastasia; Bauch, Henning A.; Spielhagen, Robert F.

2017-10-01

The Last Interglacial in the Arctic region is often described as a time with warmer conditions and significantly less summer sea ice than today. The role of Atlantic water (AW) as the main oceanic heat flux agent into the Arctic Ocean remains, however, unclear. Using high-resolution stable isotope and faunal records from the only deep Arctic Gateway, the Fram Strait, we note for the upper water column a diminished influence of AW and generally colder-than-Holocene surface ocean conditions. After the main Saalian deglaciation had terminated, a first intensification of northward-advected AW happened ( 124 ka). However, an intermittent sea surface cooling, triggered by meltwater release at 122 ka, caused a regional delay in the further development towards peak interglacial conditions. Maximum AW heat advection occurred during late MIS 5e (118.5-116 ka) and interrupted a longer-term cooling trend at the sea surface that started from about 120 ka on. Such a late occurrence of the major AW-derived near-surface warming in the Fram Strait - this is in stark contrast to an early warm peak in the Holocene - compares well in time with upstream records from the Norwegian Sea, altogether implying a coherent development of south-to-north ocean heat transfer through the eastern Nordic Seas and into the high Arctic during the Last Interglacial.
Influence of the North Atlantic Oscillation on European tropospheric composition: an observational and modelling study

NASA Astrophysics Data System (ADS)

Pope, R.; Chipperfield, M.

2017-12-01

The North Atlantic Oscillation (NAO) has a strong influence on winter-time North Atlantic and European circulation patterns. Under the positive phase of the NAO (NAO+), intensification of the climatological Icelandic low and Azores high pressure systems results in strong westerly flow across the Atlantic into Europe. Under the NAO negative phase (NAO-), there is a weakening of this meridional pressure gradient resulting in a southerly shift in the westerlies flow towards the sub-tropical Atlantic. Therefore, NAO+ and NAO- introduce unstable stormy and drier stable conditions into Europe, respectively. Under NAO+ conditions, the strong westerlies tend to enhance transport of European pollution (e.g. nitrogen oxides) away from anthropogenic source regions. While during NAO-, the more stable conditions lead to a build up of pollutants. However, secondary pollutants (i.e. tropospheric ozone) show the opposite signal where NAO+, while transporting primary pollutants away, introduces Atlantic ozone enriched air into Europe. Here ozone can form downwind of pollution from continental North America and be transported into Europe via the westerly flow. Under NAO-, this westerly ozone transport is reduced yielding lower European ozone concentrations also depleted further by ozone loss through the reaction with NOx, which has accumulated over the continent. Peroxyacetyl nitrate (PAN), observed in the upper troposphere - lower stratosphere (UTLS) by satellite, peaks over Iceland/Southern Greenland in NAO-, between 200-100 hPa, consistent with trapping by an anticyclone at this altitude. During NAO+, PAN is enhanced over the sub-tropical Atlantic and Arctic. Model simulations show that enhanced PAN over Iceland/Southern Greenland in NAO- is associated with vertical transport from the troposphere into the UTLS, while peak Arctic PAN in NAO+ is its accumulation given the strong northerly meridional transport in the UTLS. UTLS ozone spatial anomalies, relative to the winter
Experiences in multiyear combined state-parameter estimation with an ecosystem model of the North Atlantic and Arctic Oceans using the Ensemble Kalman Filter

NASA Astrophysics Data System (ADS)

Simon, Ehouarn; Samuelsen, Annette; Bertino, Laurent; Mouysset, Sandrine

2015-12-01

A sequence of one-year combined state-parameter estimation experiments has been conducted in a North Atlantic and Arctic Ocean configuration of the coupled physical-biogeochemical model HYCOM-NORWECOM over the period 2007-2010. The aim is to evaluate the ability of an ensemble-based data assimilation method to calibrate ecosystem model parameters in a pre-operational setting, namely the production of the MyOcean pilot reanalysis of the Arctic biology. For that purpose, four biological parameters (two phyto- and two zooplankton mortality rates) are estimated by assimilating weekly data such as, satellite-derived Sea Surface Temperature, along-track Sea Level Anomalies, ice concentrations and chlorophyll-a concentrations with an Ensemble Kalman Filter. The set of optimized parameters locally exhibits seasonal variations suggesting that time-dependent parameters should be used in ocean ecosystem models. A clustering analysis of the optimized parameters is performed in order to identify consistent ecosystem regions. In the north part of the domain, where the ecosystem model is the most reliable, most of them can be associated with Longhurst provinces and new provinces emerge in the Arctic Ocean. However, the clusters do not coincide anymore with the Longhurst provinces in the Tropics due to large model errors. Regarding the ecosystem state variables, the assimilation of satellite-derived chlorophyll concentration leads to significant reduction of the RMS errors in the observed variables during the first year, i.e. 2008, compared to a free run simulation. However, local filter divergences of the parameter component occur in 2009 and result in an increase in the RMS error at the time of the spring bloom.
Dynamical mechanisms of Arctic amplification.

PubMed

Dethloff, Klaus; Handorf, Dörthe; Jaiser, Ralf; Rinke, Annette; Klinghammer, Pia

2018-05-12

The Arctic has become a hot spot of climate change, but the nonlinear interactions between regional and global scales in the coupled climate system responsible for Arctic amplification are not well understood and insufficiently described in climate models. Here, we compare reanalysis data with model simulations for low and high Arctic sea ice conditions to identify model biases with respect to atmospheric Arctic-mid-latitude linkages. We show that an appropriate description of Arctic sea ice forcing is able to reproduce the observed winter cooling in mid-latitudes as result of improved tropospheric-stratospheric planetary wave propagation triggering a negative phase of the Arctic Oscillation/North Atlantic Oscillation in late winter. © 2018 New York Academy of Sciences.
Flood events across the North Atlantic region - past development and future perspectives

NASA Astrophysics Data System (ADS)

Matti, Bettina; Dieppois, Bastien; Lawler, Damian; Dahlke, Helen E.; Lyon, Steve W.

2016-04-01

Flood events have a large impact on humans, both socially and economically. An increase in winter and spring flooding across much of northern Europe in recent years opened up the question of changing underlying hydro-climatic drivers of flood events. Predicting the manifestation of such changes is difficult due to the natural variability and fluctuations in northern hydrological systems caused by large-scale atmospheric circulations, especially under altered climate conditions. Improving knowledge on the complexity of these hydrological systems and their interactions with climate is essential to be able to determine drivers of flood events and to predict changes in these drivers under altered climate conditions. This is particularly true for the North Atlantic region where both physical catchment properties and large-scale atmospheric circulations have a profound influence on floods. This study explores changes in streamflow across North Atlantic region catchments. An emphasis is placed on high-flow events, namely the timing and magnitude of past flood events, and selected flood percentiles were tested for stationarity by applying a flood frequency analysis. The issue of non-stationarity of flood return periods is important when linking streamflow to large-scale atmospheric circulations. Natural fluctuations in these circulations are found to have a strong influence on the outcome causing natural variability in streamflow records. Long time series and a multi-temporal approach allows for determining drivers of floods and linking streamflow to large-scale atmospheric circulations. Exploring changes in selected hydrological signatures consistency was found across much of the North Atlantic region suggesting a shift in flow regime. The lack of an overall regional pattern suggests that how catchments respond to changes in climatic drivers is strongly influenced by their physical characteristics. A better understanding of hydrological response to climate drivers is
Impact of the North Atlantic circulation on the climate change patterns of North Sea.

NASA Astrophysics Data System (ADS)

Narayan, Nikesh; Mathis, Mortiz; Klein, Birgit; Klein, Holger; Mikolajewicz, Uwe

2017-04-01

The physical properties of the North Sea are characterized by the exchange of water masses with the North Atlantic at the northern boundary and Baltic Sea to the east. The combined effects of localized forcing, tidal mixing and advection of water masses make the North Sea a challenging study area. Previous investigations indicated a possibility that the variability of the North Atlantic circulation and the strength of the sub-polar gyre (SPG) might influence the physical properties of the North Sea. The assessment of the complex interaction between the North Atlantic and the North Sea in a climate change scenario requires regionally coupled global RCP simulations with enhanced resolution of the North Sea and the North Atlantic. In this study we analyzed result from the regionally coupled ocean-atmosphere-biogeochemistry model system (MPIOM-REMO-HAMOCC) with a hydrodynamic (HD) model. The ocean model has a zoomed grid which provides the highest resolution over the West European Shelf by shifting its poles over Chicago and Central Europe. An index for the intensity of SPG was estimated by averaging the barotropic stream function (ψ) over the North Atlantic. Various threshold values for ψ were tested to define the strength of the SPG. These SPG indices have been correlated with North Sea hydrographic parameters at various levels to identify areas affected by SPG variability. The influence of the Atlantic's eastern boundary current, contributing more saline waters to the North West European shelf area is also investigated.
Overview of the 1988 GCE/CASE/WATOX Studies of biogeochemical cycles in the North Atlantic region

NASA Astrophysics Data System (ADS)

Pszenny, Alexander A. P.; Galloway, James N.; Artz, Richard S.; Boatman, Joseph F.

1990-06-01

The 1988 Global Change Expedition/Coordinated Air-Sea Experiment/Western Atlantic Ocean Experiment (GCE/CASE/WATOX) was a multifaceted research program designed to study atmospheric and oceanic processes affecting the biogeochemical cycles of carbon, nitrogen, sulfur, and trace metals in the North Atlantic Ocean region. Field work included (1) a 49-day research cruise aboard NOAA ship Mt. Mitchell (Global Change Expedition) from Norfolk, Virginia, to Bermuda, Iceland, the Azores, and Barbados, (2) eight flights of the NOAA King Air research aircraft, four off the Virginia Capes and four near Bermuda (CASE/WATOX), and (3) a research cruise aboard the yacht Fleurtie near Bermuda (WATOX). Objectives of GCE/CASE/WATOX were (1) to examine processes controlling the mesoscale distributions of productivity, chlorophyll, and phytoplankton growth rates in Atlantic surface waters, (2) to identify factors controlling the distribution of ozone in the North Atlantic marine boundary layer, and (3) to estimate the contributions of sources on surrounding continents to the biogeochemical cycles of sulfur, nitrogen, and trace metals over the North Atlantic region during the boreal summer season. The individual papers in this and the next two issues of Global Biogeochemical Cycles provide details on the results and analyses of the individual measurement efforts. This paper provides a brief overview of GCE/CASE/WATOX.
Water Mass Variability at the Mid-Atlantic Ridge and in the Eastern North Atlantic

NASA Astrophysics Data System (ADS)

Köllner, Manuela; Klein, Birgit; Kieke, Dagmar; Klein, Holger; Roessler, Achim; Rhein, Monika

2017-04-01

The strong warming and salinification of the Eastern North Atlantic starting in the mid 1990s has been attributed to a westward contraction of the sub-polar gyre and stronger inflow of waters from the sub-tropical gyre. Temporal changes in the shape and strength of the two gyres have been related to the major mode of atmospheric variability in the Atlantic sector, the NAO. Hydrographic conditions along the Northwest European shelf are thus the result of different processes such as variations in transports, varying relative contributions of water masses from the two gyres and property trends in the source water masses. The North Atlantic Current (NAC) can be regarded as the southern border of the sub-polar gyre transporting water from the tropical regions northward. On its way towards the Mid Atlantic Ridge (MAR) the NAC has partly mixed with waters from the sub-polar gyre and crosses the MAR split into several branches. For the study we analyzed data of water mass variability and transport fluctuations from the RACE (Regional circulation and Global change) project (2012-2015) which provided time series of transports and hydrographic anomalies from moored instruments at the western flank of the MAR. The time depending positions of the NAC branches over the MAR were obtained from mooring time series and compared to sea surface velocities from altimeter data. The results show a high variability of NAC pathways over the MAR. Transition regimes with strong meandering and eddies could be observed as well as periods of strong NAC branches over the Fracture Zones affecting water mass exchange at all depth levels. A positive temperature trend at depths between 1000-2000 m was found at the Faraday Fracture Zone (FFZ). This warming trend was also detected by Argo floats crossing the MAR close to the FFZ region. During the second phase of RACE (RACE-II, 2016-2018) a mooring array across the eastern shelf break at Goban Spur was deployed to monitor the poleward Eastern Boundary
Sea level anomaly in the North Atlantic and seas around Europe: Long-term variability and response to North Atlantic teleconnection patterns.

PubMed

Iglesias, Isabel; Lorenzo, M Nieves; Lázaro, Clara; Fernandes, M Joana; Bastos, Luísa

2017-12-31

Sea level anomaly (SLA), provided globally by satellite altimetry, is considered a valuable proxy for detecting long-term changes of the global ocean, as well as short-term and annual variations. In this manuscript, monthly sea level anomaly grids for the period 1993-2013 are used to characterise the North Atlantic Ocean variability at inter-annual timescales and its response to the North Atlantic main patterns of atmospheric circulation variability (North Atlantic Oscillation, Eastern Atlantic, Eastern Atlantic/Western Russia, Scandinavian and Polar/Eurasia) and main driven factors as sea level pressure, sea surface temperature and wind fields. SLA variability and long-term trends are analysed for the North Atlantic Ocean and several sub-regions (North, Baltic and Mediterranean and Black seas, Bay of Biscay extended to the west coast of the Iberian Peninsula, and the northern North Atlantic Ocean), depicting the SLA fluctuations at basin and sub-basin scales, aiming at representing the regions of maximum sea level variability. A significant correlation between SLA and the different phases of the teleconnection patterns due to the generated winds, sea level pressure and sea surface temperature anomalies, with a strong variability on temporal and spatial scales, has been identified. Long-term analysis reveals the existence of non-stationary inter-annual SLA fluctuations in terms of the temporal scale. Spectral density analysis has shown the existence of long-period signals in the SLA inter-annual component, with periods of ~10, 5, 4 and 2years, depending on the analysed sub-region. Also, a non-uniform increase in sea level since 1993 is identified for all sub-regions, with trend values between 2.05mm/year, for the Bay of Biscay region, and 3.98mm/year for the Baltic Sea (no GIA correction considered). The obtained results demonstrated a strong link between the atmospheric patterns and SLA, as well as strong long-period fluctuations of this variable in spatial and
Historic Storminess Changes in North Atlantic Region

NASA Astrophysics Data System (ADS)

Dawson, A. G.; Elliott, L.; Noone, S.; Hickey, K.; Foster, I.; Wadhams, P.; Mayewski, P.

2001-05-01

Reconstructed patterns of historic storminess (1870-1990 AD) for North Atlantic region as indicated by measurements from selected stations in Iceland, Faeroes, Scotland and Ireland show clear links with the climate "seesaw" winters first described by Van Loon and Rogers. The stormiest winters appear to have occurred during periods when measured Greenland air temperatures at Jacobshavn and reconstructed air temperatures from the Summit ice core site have been exceptionally low and when air temperature across northern Europe have been well above average. Maxima and minima of recorded winter storms for the various stations are also in agreement with the Sodium chronology from GISP2 that points to increased sea salt precipitation on Greenland ice at Summit during Greenland "below" periods of the climate seesaw.
Nature Run for the North Atlantic Ocean Hurricane Region: System Evaluation and Regional Applications

NASA Astrophysics Data System (ADS)

Kourafalou, V.; Androulidakis, I.; Halliwell, G. R., Jr.; Kang, H.; Mehari, M. F.; Atlas, R. M.

2016-02-01

A prototype ocean Observing System Simulation Experiments (OSSE) system, first developed and data validated in the Gulf of Mexico, has been applied on the extended North Atlantic Ocean hurricane region. The main objectives of this study are: a) to contribute toward a fully relocatable ocean OSSE system by expanding the Gulf of Mexico OSSE to the North Atlantic Ocean; b) demonstrate and quantify improvements in hurricane forecasting when the ocean component of coupled hurricane models is advanced through targeted observations and assimilation. The system is based on the Hybrid Coordinate Ocean Model (HYCOM) and has been applied on a 1/250 Mercator mesh for the free-running Nature Run (NR) and on a 1/120 Mercator mesh for the data assimilative forecast model (FM). A "fraternal twin" system is employed, using two different realizations for NR and FM, each configured to produce substantially different physics and truncation errors. The NR has been evaluated using a variety of available observations, such as from AVISO, GDEM climatology and GHRSST observations, plus specific regional products (upper ocean profiles from air-borne instruments, surface velocity maps derived from the historical drifter data set and tropical cyclone heat potential maps derived from altimetry observations). The utility of the OSSE system to advance the knowledge of regional air-sea interaction processes related to hurricane activity is demonstrated in the Amazon region (salinity induced surface barrier layer) and the Gulf Stream region (hurricane impact on the Gulf Stream extension).
North Atlantic deep water formation and AMOC in CMIP5 models

NASA Astrophysics Data System (ADS)

Heuzé, Céline

2017-07-01

Deep water formation in climate models is indicative of their ability to simulate future ocean circulation, carbon and heat uptake, and sea level rise. Present-day temperature, salinity, sea ice concentration and ocean transport in the North Atlantic subpolar gyre and Nordic Seas from 23 CMIP5 (Climate Model Intercomparison Project, phase 5) models are compared with observations to assess the biases, causes and consequences of North Atlantic deep convection in models. The majority of models convect too deep, over too large an area, too often and too far south. Deep convection occurs at the sea ice edge and is most realistic in models with accurate sea ice extent, mostly those using the CICE model. Half of the models convect in response to local cooling or salinification of the surface waters; only a third have a dynamic relationship between freshwater coming from the Arctic and deep convection. The models with the most intense deep convection have the warmest deep waters, due to a redistribution of heat through the water column. For the majority of models, the variability of the Atlantic Meridional Overturning Circulation (AMOC) is explained by the volumes of deep water produced in the subpolar gyre and Nordic Seas up to 2 years before. In turn, models with the strongest AMOC have the largest heat export to the Arctic. Understanding the dynamical drivers of deep convection and AMOC in models is hence key to realistically forecasting Arctic oceanic warming and its consequences for the global ocean circulation, cryosphere and marine life.
Parasites as biological tags of marine, freshwater and anadromous fishes in North America from the Tropics to the Arctic.

PubMed

Marcogliese, David J; Jacobson, Kym C

2015-01-01

Parasites have been considered as natural biological tags of marine fish populations in North America for almost 75 years. In the Northwest Atlantic, the most studied species include Atlantic cod (Gadus morhua), Atlantic herring (Clupea harengus) and the redfishes (Sebastes spp.). In the North Pacific, research has centred primarily on salmonids (Oncorhynchus spp.). However, parasites have been applied as tags for numerous other pelagic and demersal species on both the Atlantic and Pacific coasts. Relatively few studies have been undertaken in the Arctic, and these were designed to discriminate anadromous and resident salmonids (Salvelinus spp.). Although rarely applied in fresh waters, parasites have been used to delineate certain fish stocks within the Great Lakes-St Lawrence River basin. Anisakid nematodes and the copepod Sphyrion lumpi frequently prove useful indicators in the Northwest Atlantic, while myxozoan parasites prove very effective on the coast and open seas of the Pacific Ocean. Relative differences in the ability of parasites to discriminate between fish stocks on the Pacific and Atlantic coasts may be due to oceanographic and bathymetric differences between regions. Molecular techniques used to differentiate populations and species of parasites show promise in future applications in the field.
The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation

PubMed Central

Cózar, Andrés; Martí, Elisa; Duarte, Carlos M.; García-de-Lomas, Juan; van Sebille, Erik; Ballatore, Thomas J.; Eguíluz, Victor M.; González-Gordillo, J. Ignacio; Pedrotti, Maria L.; Echevarría, Fidel; Troublè, Romain; Irigoien, Xabier

2017-01-01

The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris. PMID:28439534
The Arctic Ocean as a dead end for floating plastics in the North Atlantic branch of the Thermohaline Circulation.

PubMed

Cózar, Andrés; Martí, Elisa; Duarte, Carlos M; García-de-Lomas, Juan; van Sebille, Erik; Ballatore, Thomas J; Eguíluz, Victor M; González-Gordillo, J Ignacio; Pedrotti, Maria L; Echevarría, Fidel; Troublè, Romain; Irigoien, Xabier

2017-04-01

The subtropical ocean gyres are recognized as great marine accummulation zones of floating plastic debris; however, the possibility of plastic accumulation at polar latitudes has been overlooked because of the lack of nearby pollution sources. In the present study, the Arctic Ocean was extensively sampled for floating plastic debris from the Tara Oceans circumpolar expedition. Although plastic debris was scarce or absent in most of the Arctic waters, it reached high concentrations (hundreds of thousands of pieces per square kilometer) in the northernmost and easternmost areas of the Greenland and Barents seas. The fragmentation and typology of the plastic suggested an abundant presence of aged debris that originated from distant sources. This hypothesis was corroborated by the relatively high ratios of marine surface plastic to local pollution sources. Surface circulation models and field data showed that the poleward branch of the Thermohaline Circulation transfers floating debris from the North Atlantic to the Greenland and Barents seas, which would be a dead end for this plastic conveyor belt. Given the limited surface transport of the plastic that accumulated here and the mechanisms acting for the downward transport, the seafloor beneath this Arctic sector is hypothesized as an important sink of plastic debris.

Potential Impact of North Atlantic Climate Variability on Ocean Biogeochemical Processes

NASA Astrophysics Data System (ADS)

Liu, Y.; Muhling, B.; Lee, S. K.; Muller-Karger, F. E.; Enfield, D. B.; Lamkin, J. T.; Roffer, M. A.

2016-02-01

Previous studies have shown that upper ocean circulations largely determine primary production in the euphotic layers, here the global ocean model with biogeochemistry (GFDL's Modular Ocean Model with TOPAZ biogeochemistry) forced with the ERA-Interim is used to simulate the natural variability of biogeochemical processes in global ocean during 1979-present. Preliminary results show that the surface chlorophyll is overall underestimated in MOM-TOPAZ, but its spatial pattern is fairly realistic. Relatively high chlorophyll variability is shown in the subpolar North Atlantic, northeastern tropical Atlantic, and equatorial Atlantic. Further analysis suggests that the chlorophyll variability in the North Atlantic Ocean is affected by long-term climate variability. For the subpolar North Atlantic region, the chlorophyll variability is light-limited and is significantly correlated with North Atlantic Oscillation. A dipole pattern of chlorophyll variability is found between the northeastern tropical Atlantic and equatorial Atlantic. For the northeastern North Atlantic, the chlorophyll variability is significantly correlated with Atlantic Meridional Mode (AMM) and Atlantic Multidecadal Oscillation (AMO). During the negative phase of AMM and AMO, the increased trade wind in the northeast North Atlantic can lead to increased upwelling of nutrients. In the equatorial Atlantic region, the chlorophyll variability is largely link to Atlantic-Niño and associated equatorial upwelling of nutrients. The potential impact of climate variability on the distribution of pelagic fishes (i.e. yellowfin tuna) are discussed.
Synoptic Scale North American Weather Tracks and the Formation of North Atlantic Windstorms

NASA Astrophysics Data System (ADS)

Baum, A. J.; Godek, M. L.

2014-12-01

Each winter, dozens of fatalities occur when intense North Atlantic windstorms impact Western Europe. Forecasting the tracks of these storms in the short term is often problematic, but long term forecasts provide an even greater challenge. Improved prediction necessitates the ability to identify these low pressure areas at formation and understand commonalities that distinguish these storms from other systems crossing the Atlantic, such as where they develop. There is some evidence that indicates the majority of intense windstorms that reach Europe have origins far west, as low pressure systems that develop over the North American continent. This project aims to identify the specific cyclogenesis regions in North America that produce a significantly greater number of dangerous storms. NOAA Ocean Prediction Center surface pressure reanalysis maps are used to examine the tracks of storms. Strong windstorms are characterized by those with a central pressure of less than 965 hPa at any point in their life cycle. Tracks are recorded using a coding system based on source region, storm track and dissipation region. The codes are analyzed to determine which region contains the most statistical significance with respect to strong Atlantic windstorm generation. The resultant set of codes also serves as a climatology of North Atlantic extratropical cyclones. Results indicate that a number of windstorms favor cyclogenesis regions off the east coast of the United States. A large number of strong storms that encounter east coast cyclogenesis zones originate in the central mountain region, around Colorado. These storms follow a path that exits North America around New England and subsequently travel along the Canadian coast. Some of these are then primed to become "bombs" over the open Atlantic Ocean.
An atmosphere-ocean GCM modelling study of the climate response to changing Arctic seaways in the early Cenozoic.

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

2008-12-01

The report of fossil Azolla (a freshwater aquatic fern) in sediments from the Lomonosov Ridge suggests low salinity conditions occurred in the Arctic Ocean in the early Eocene. Restricted passages between the Arctic Ocean and the surrounding oceans are hypothesized to have caused this Arctic freshening. We investigate this scenario using a water-isotope enabled atmosphere-ocean general circulation model with Eocene boundary conditions including 4xCO2, 7xCH4, altered bathymetry and topography, and an estimated distribution of Eocene vegetational types. In one experiment, oceanic exchange between the Arctic Ocean and other ocean basins was restricted to two shallow (~250 m) seaways, one in the North Atlantic, the Greenland-Norwegian seaway, and the second connecting the Arctic Ocean with the Tethys Ocean, the Turgai Straits. In the restricted configuration, the Greenland-Norwegian seaway was closed and exchange through the Turgai Straits was limited to a depth of ~60 m. The simulations suggest that the severe restriction of Arctic seaways in the early Eocene may have been sufficient to freshen Arctic Ocean surface waters, conducive to Azolla blooms. When exchange with the Arctic Ocean is limited, salinities in the upper several hundred meters of the water column decrease by ~10 psu. In some regions, surface salinity is within 2-3 psu of the reported maximum modern conditions tolerated by Azolla (~5 psu). In the restricted scenario, salt is stored preferentially in the North Atlantic and Tethys oceans, resulting in enhanced meridional overturning, increased poleward heat transport in the North Atlantic western boundary current, and warming of surface and intermediate waters in the North Atlantic by several degrees. Increased sensible and latent heat fluxes from the North Atlantic Ocean, combined with a reduction in cloud albedo, also lead to an increase in surface air temperature of over much of North America, Greenland and Eurasia. Our work is consistent with
Reconstructing the leading mode of multi-decadal North Atlantic variability over the last two millenia using functional paleoclimate networks

NASA Astrophysics Data System (ADS)

Franke, Jasper G.; Werner, Johannes; Donner, Reik V.

2017-04-01

The increasing availability of high-resolution North Atlantic paleoclimate proxies allows to not only study local climate variations in time, but also temporal changes in spatial variability patterns across the entire region possibly controlled by large-scale coherent variability modes such as the North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation. In this study, we use functional paleoclimate network analysis [1,2] to investigate changes in the statistical similarity patterns among an ensemble of high-resolution terrestrial paleoclimate records from Northern Europe included in the Arctic 2k data base. Specifically, we construct complex networks capturing the mutual statistical similarity of inter-annual temperature variability recorded in tree ring records, ice cores and lake sediments for multidecadal time windows covering the last two millenia. The observed patterns of co-variability are ultimately connected to the North Atlantic atmospheric circulation and most prominently to multidecadal variations of the NAO. Based on the inferred networks, we study the dynamical similarity between regional clusters of archives defined according to present-day inter-annual temperature variations across the study region. This analysis identifies those time-dependent inter-regional linkages that are most informative about the leading-order North Atlantic climate variability according to a recent NAO reconstruction for the last millenium [3]. Based on these linkages, we extend the existing reconstruction to obtain qualitative information on multidecadal to centennial scale North Atlantic climate variability over the last two millenia. In general, we find a tendency towards a dominating positive NAO phase interrupted by pronounced and extended intervals of negative NAO. Relatively rapid transitions between both types of behaviour are present during distinct periods including the Little Ice Age, the Medieval Climate Anomaly and for the Dark Ages Little Ice Age
Surface changes in the North Atlantic meridional overturning circulation during the last millennium

PubMed Central

Wanamaker, Alan D.; Butler, Paul G.; Scourse, James D.; Heinemeier, Jan; Eiríksson, Jón; Knudsen, Karen Luise; Richardson, Christopher A.

2012-01-01

Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector. PMID:22692542
Surface changes in the North Atlantic meridional overturning circulation during the last millennium.

PubMed

Wanamaker, Alan D; Butler, Paul G; Scourse, James D; Heinemeier, Jan; Eiríksson, Jón; Knudsen, Karen Luise; Richardson, Christopher A

2012-06-12

Despite numerous investigations, the dynamical origins of the Medieval Climate Anomaly and the Little Ice Age remain uncertain. A major unresolved issue relating to internal climate dynamics is the mode and tempo of Atlantic meridional overturning circulation variability, and the significance of decadal-to-centennial scale changes in Atlantic meridional overturning circulation strength in regulating the climate of the last millennium. Here we use the time-constrained high-resolution local radiocarbon reservoir age offset derived from an absolutely dated annually resolved shell chronology spanning the past 1,350 years, to reconstruct changes in surface ocean circulation and climate. The water mass tracer data presented here from the North Icelandic shelf, combined with previously published data from the Arctic and subtropical Atlantic, show that surface Atlantic meridional overturning circulation dynamics likely amplified the relatively warm conditions during the Medieval Climate Anomaly and the relatively cool conditions during the Little Ice Age within the North Atlantic sector.
The behaviour of ¹²⁹I released from nuclear fuel reprocessing factories in the North Atlantic Ocean and transport to the Arctic assessed from numerical modelling.

PubMed

Villa, M; López-Gutiérrez, J M; Suh, Kyung-Suk; Min, Byung-Il; Periáñez, R

2015-01-15

A quantitative evaluation of the fate of (129)I, released from the European reprocessing plants of Sellafield (UK) and La Hague (France), has been made by means of a Lagrangian dispersion model. Transport of radionuclides to the Arctic Ocean has been determined. Thus, 5.1 and 16.6 TBq of (129)I have been introduced in the Arctic from Sellafield and La Hague respectively from 1966 to 2012. These figures represent, respectively, 48% and 55% of the cumulative discharge to that time. Inventories in the North Atlantic, including shelf seas, are 4.4 and 13.8 TBq coming from Sellafield and La Hague respectively. These figures are significantly different from previous estimations based on field data. The distribution of these inventories among several shelf seas and regions has been evaluated as well. Mean ages of tracers have been finally obtained, making use of the age-averaging hypothesis. It has been found that mean ages for Sellafield releases are about 3.5 year larger than for La Hague releases. Copyright © 2014 Elsevier Ltd. All rights reserved.
Palynological evidence for a southward shift of the North Atlantic Current at 2.6 Ma during the intensification of late Cenozoic Northern Hemisphere glaciation

NASA Astrophysics Data System (ADS)

Hennissen, Jan A. I.; Head, Martin J.; De Schepper, Stijn; Groeneveld, Jeroen

2014-06-01

The position of the North Atlantic Current (NAC) during the intensification of Northern Hemisphere glaciation (iNHG) has been evaluated using dinoflagellate cyst assemblages and foraminiferal geochemistry from a 260 kyr interval straddling the base of the Quaternary System from two sites: eastern North Atlantic Deep Sea Drilling Project Site 610 in the path of the present NAC and central North Atlantic Integrated Ocean Drilling Program Site U1313 in the subtropical gyre. Stable isotope and foraminiferal Mg/Ca analyses confirm cooling near the marine isotope stage (MIS) G7-G6 transition (2.74 Ma). However, a continued dominance of the dinoflagellate cyst Operculodinium centrocarpum sensu Wall and Dale (1966) indicates an active NAC in the eastern North Atlantic for a further 140 kyr. At MIS 104 ( 2.60 Ma), a profound dinoflagellate cyst assemblage turnover indicates NAC shutdown in the eastern North Atlantic, implying elevated atmospheric pressure over the Arctic and a resulting shift in the westerlies that would have driven the NAC. These findings challenge recent suggestions that there was no significant southward shift of the NAC or the Arctic Front during iNHG, and reveal a fundamental climatic reorganization near the base of the Quaternary.
Regional Modelling of Air Quality in the Canadian Arctic: Impact of marine shipping and North American wild fire emissions

NASA Astrophysics Data System (ADS)

Gong, W.; Beagley, S. R.; Zhang, J.; Cousineau, S.; Sassi, M.; Munoz-Alpizar, R.; Racine, J.; Menard, S.; Chen, J.

2015-12-01

Arctic atmospheric composition is strongly influenced by long-range transport from mid-latitudes as well as processes occurring in the Arctic locally. Using an on-line air quality prediction model GEM-MACH, simulations were carried out for the 2010 northern shipping season (April - October) over a regional Arctic domain. North American wildfire emissions and Arctic shipping emissions were represented, along with other anthropogenic and biogenic emissions. Sensitivity studies were carried out to investigate the principal sources and processes affecting air quality in the Canadian Northern and Arctic regions. In this paper, we present an analysis of sources, transport, and removal processes on the ambient concentrations and atmospheric loading of various pollutants with air quality and climate implications, such as, O3, NOx, SO2, CO, and aerosols (sulfate, black carbon, and organic carbon components). Preliminary results from a model simulation of a recent summertime Arctic field campaign will also be presented.
Impacts of the north and tropical Atlantic Ocean on the Antarctic Peninsula and sea ice.

PubMed

Li, Xichen; Holland, David M; Gerber, Edwin P; Yoo, Changhyun

2014-01-23

In recent decades, Antarctica has experienced pronounced climate changes. The Antarctic Peninsula exhibited the strongest warming of any region on the planet, causing rapid changes in land ice. Additionally, in contrast to the sea-ice decline over the Arctic, Antarctic sea ice has not declined, but has instead undergone a perplexing redistribution. Antarctic climate is influenced by, among other factors, changes in radiative forcing and remote Pacific climate variability, but none explains the observed Antarctic Peninsula warming or the sea-ice redistribution in austral winter. However, in the north and tropical Atlantic Ocean, the Atlantic Multidecadal Oscillation (a leading mode of sea surface temperature variability) has been overlooked in this context. Here we show that sea surface warming related to the Atlantic Multidecadal Oscillation reduces the surface pressure in the Amundsen Sea and contributes to the observed dipole-like sea-ice redistribution between the Ross and Amundsen-Bellingshausen-Weddell seas and to the Antarctic Peninsula warming. Support for these findings comes from analysis of observational and reanalysis data, and independently from both comprehensive and idealized atmospheric model simulations. We suggest that the north and tropical Atlantic is important for projections of future climate change in Antarctica, and has the potential to affect the global thermohaline circulation and sea-level change.
Decadal predictions of the North Atlantic CO2 uptake.

PubMed

Li, Hongmei; Ilyina, Tatiana; Müller, Wolfgang A; Sienz, Frank

2016-03-30

As a major CO2 sink, the North Atlantic, especially its subpolar gyre region, is essential for the global carbon cycle. Decadal fluctuations of CO2 uptake in the North Atlantic subpolar gyre region are associated with the evolution of the North Atlantic Oscillation, the Atlantic meridional overturning circulation, ocean mixing and sea surface temperature anomalies. While variations in the physical state of the ocean can be predicted several years in advance by initialization of Earth system models, predictability of CO2 uptake has remained unexplored. Here we investigate the predictability of CO2 uptake variations by initialization of the MPI-ESM decadal prediction system. We find large multi-year variability in oceanic CO2 uptake and demonstrate that its potential predictive skill in the western subpolar gyre region is up to 4-7 years. The predictive skill is mainly maintained in winter and is attributed to the improved physical state of the ocean.
Information security of power enterprises of North-Arctic region

NASA Astrophysics Data System (ADS)

Sushko, O. P.

2018-05-01

The role of information technologies in providing technological security for energy enterprises is a component of the economic security for the northern Arctic region in general. Applying instruments and methods of information protection modelling of the energy enterprises' business process in the northern Arctic region (such as Arkhenergo and Komienergo), the authors analysed and identified most frequent risks of information security. With the analytic hierarchy process based on weighting factor estimations, information risks of energy enterprises' technological processes were ranked. The economic estimation of the information security within an energy enterprise considers weighting factor-adjusted variables (risks). Investments in information security systems of energy enterprises in the northern Arctic region are related to necessary security elements installation; current operating expenses on business process protection systems become materialized economic damage.
Refining plate reconstructions of the North Atlantic and Ellesmerian domains

NASA Astrophysics Data System (ADS)

Shephard, Grace E.; Abdelmalak, Mansour M.; Buiter, Susanne; Piepjohn, Karsten; Jones, Morgan; Torsvik, Trond; Faleide, Jan Inge; Gaina, Carmen

2017-04-01

Located at the intersection of major tectonic plates, the North Atlantic and western Arctic domains have experienced both widespread and localized deformation since the Paleozoic. In conventional tectonic reconstructions, the plates of Greenland, Eurasia and North America are assumed to be rigid. However, prior to the onset of seafloor spreading, rifting lithosphere experiences significant thinning that is usually not accounted for. This leads to significant (in excess of 300 km in places) over- and under-laps between conjugate continent-ocean boundaries, an incomplete history of basin evolution, and loose correlations between climatic, volcanic, oceanographic and, geologic events. Furthermore, a handful of alternative regional reconstructions now exist, which predict different timings, rates and locations of relative motion and associated deformation. Assumptions of reference crustal thicknesses and the nature of lower crustal bodies, as well as the location of basin hinge lines have to-date not yet been incorporated into a consistent regional kinematic model. Notably, the alternative models predict varying episodes of compression or quiescence, not just orthogonal or oblique rifting. Here, we present new temporal and spatial-dependent results related to (1) the dominant rifting episodes across the North Atlantic (Carboniferous, Late Permian, Late Jurassic-Early Cenozoic and Late Cretaceous-Paleogene), and (2) restoration of compression and strike-slip motion between northern Greenland, Ellesmere Island (North America) and Spitsbergen (Eurasia) related to the Eurekan Orogeny. We achieve this by integrating a series of conjugate seismic profiles, calculated stretching factors, dated volcanic events, structural mapping and mass-balanced restorations into a global plate motion model via GPlates software. We also test alternative models of rift velocities (as kinematic boundary conditions) with 2-D lithosphere and mantle numerical models, and explore the importance of
Holocene oscillations in temperature and salinity of the surface subpolar North Atlantic.

PubMed

Thornalley, David J R; Elderfield, Harry; McCave, I Nick

2009-02-05

The Atlantic meridional overturning circulation (AMOC) transports warm salty surface waters to high latitudes, where they cool, sink and return southwards at depth. Through its attendant meridional heat transport, the AMOC helps maintain a warm northwestern European climate, and acts as a control on the global climate. Past climate fluctuations during the Holocene epoch ( approximately 11,700 years ago to the present) have been linked with changes in North Atlantic Ocean circulation. The behaviour of the surface flowing salty water that helped drive overturning during past climatic changes is, however, not well known. Here we investigate the temperature and salinity changes of a substantial surface inflow to a region of deep-water formation throughout the Holocene. We find that the inflow has undergone millennial-scale variations in temperature and salinity ( approximately 3.5 degrees C and approximately 1.5 practical salinity units, respectively) most probably controlled by subpolar gyre dynamics. The temperature and salinity variations correlate with previously reported periods of rapid climate change. The inflow becomes more saline during enhanced freshwater flux to the subpolar North Atlantic. Model studies predict a weakening of AMOC in response to enhanced Arctic freshwater fluxes, although the inflow can compensate on decadal timescales by becoming more saline. Our data suggest that such a negative feedback mechanism may have operated during past intervals of climate change.
Regional Arctic and Hemispheric Teleconnections expressed in the paleoenvironmental record of El'gygytgyn Lake, NE Russia

NASA Astrophysics Data System (ADS)

Brigham-Grette, J.; Melles, M.; Deconto, R.; Koenig, S.

2007-12-01

The common goal of recovering long high-resolution records is in testing relevant questions of Earth system dynamics, as well as documenting the drivers of regional and global scale change. Lake El'gygytgyn, located 100 km north of the Arctic Circle in NE Russia is a target for deep drilling a continuous record back to ~3.6 My in Spring 2009. Pilot cores dating to 250ka to 300 ka provide the impetus for evaluating the sensitivity of the Arctic to regional and global climate events on millennial timescales. A clear record of the Younger Dryas, rapid change within MIS 3, and events including interstadials 19, 20, events within Stage 5, and at the end of stage 6 seen in Greenland and marine records suggest that oceanographic and atmospheric changes over the North Atlantic are reflected in hydrologic and seasonal temperature proxies. Rapid events are recorded despite demonstrated precessional influences and the suggested upwind influence of the Eurasian Ice sheet and dramatic changes in continentality due to changes in sea level across the Bering/Chukchi shelves and the extent and seasonal persistence of sea ice in the Arctic Ocean and deeper Bering Sea. Regionally, lake cores throughout Beringia reflect patterns of precipitation and temperature that point to persistent zonal differences in the response of the landscape to environmental change.
Anthropogenic 129I in the North Pacific, Bering and Chukchi Seas, and Arctic Ocean in 2012-2013

NASA Astrophysics Data System (ADS)

Nagai, H.; Hasegawa, A.; Yamagata, T.; Kumamoto, Y.; Nishino, S.; Matsuzaki, H.

2015-10-01

Most of anthropogenic 129I in marine environment are due to discharge from the nuclear fuel reprocessing facilities at Sellafield (U.K.) and La Hague (France) for past few decades. The discharge raised 129I concentration in seawaters in the North Atlantic and Arctic Oceans to more than 109 atoms L-1, which is two orders of magnitude higher than that in other region. Recently, in March 2011, a large quantity of 129I was released into the western North Pacific due to the Fukushima Daiichi Nuclear Power Plant (F1NPP) accident. To evaluate the influence of these events, we have measured 129I concentration in seawaters in the northern North Pacific Ocean, Bering and Chukchi Seas, and Arctic Ocean in 2012-2013. The 129I concentrations were 1.0-1.8 × 107 atoms L-1 in the surface waters in the vicinity of 47°N 150°E-130°W North Pacific Ocean, Bering Sea, and Chukchi Sea (<74°N), which are equal to or lower than the 129I concentration level in surface water in the North Pacific Ocean before the F1NPP accident. The vertical profiles in the North Pacific were almost same as that observed in the western North Pacific before the F1NPP accident. The 129I distribution in seawater in the North Pacific to the Chukchi Sea revealed no significant increase of 129I concentration caused by the F1NPP accident. The 129I concentrations were 13-14 × 107 atoms L-1 in surface waters and 80 × 107 atoms L-1 at depths of 300 and 800 m in the Arctic Ocean.
The late Wisconsinan and Holocene record of Walrus (Odobenus rosmarus) from North America: A review with new data from Arctic and Atlantic Canada

USGS Publications Warehouse

Dyke, A.S.; Hooper, J.; Harington, C.R.; Savelle, J.M.

1999-01-01

The Late Wisconsinan and Holocene record of the Atlantic walrus is known from numerous collections of bones and tusks from Arctic Canada and south to North Carolina, as well as from many archaeological sites in the Arctic and Subarctic. In contrast, the Pacific walrus has no dated Late Wisconsinan or early Holocene record in North America, and it may have been displaced into the northwest Pacific at Last Glacial Maximum (LGM). The Atlantic walrus rapidly exploited newly deglaciated territory, moving northward from its LGM refugium and reaching the Bay of Fundy by 12800 B.P., the Grand Banks by 12500 B.P., southern Labrador by 11500 B.P., and the central Canadian Arctic Archipelago (CAA) by 9700 B.P. Its southern range limit may have retracted to the Bay of Fundy by ca. 7500 B.P. Within the CAA, walrus remains cluster in two main age groups: 9700 to 8500 B.P. and 5000 to 4/3000 B.P. This pattern strongly resembles the distribution of bowhead whale radiocarbon ages from the same area, which suggests a common control by sea-ice conditions. Walrus remains occur in Indian culture archaeological sites as old as 7500 B.P. and, in some cases (Namu, British Columbia, and Mackinac Island, Michigan), they evidently represent long-distance human transport. They are much more common in Paleoeskimo and Neoeskimo culture sites. However, they occur in very low abundances, and generally as debitage, in sites older than Dorset (2500 B.P.). The walrus, therefore, may not have been hunted by early Paleoeskimos. Beginning with Early Dorset, walrus remains occur in definite diet-related contexts. Middle Dorset (2300 to 1500 B.P.) and late Thule (<400 B.P.) sites are missing from the High Arctic, and there may be a similar gap in the middle Pre-Dorset (3400 to 2600 B.P.). Sea-ice conditions at these times may have adversely affected availability of walrus and other marine mammal resources. Walrus is a prominent faunal element in Middle Dorset sites on the Labrador coast; this is
Molecular epidemiological study of Arctic rabies virus isolates from Greenland and comparison with isolates from throughout the Arctic and Baltic regions.

PubMed

Mansfield, K L; Racloz, V; McElhinney, L M; Marston, D A; Johnson, N; Rønsholt, L; Christensen, L S; Neuvonen, E; Botvinkin, A D; Rupprecht, C E; Fooks, A R

2006-03-01

We report a molecular epidemiological study of rabies in Arctic countries by comparing a panel of novel Greenland isolates to a larger cohort of viral sequences from both Arctic and Baltic regions. Rabies virus isolates originating from wildlife (Arctic/red foxes, raccoon-dogs and reindeer), from domestic animals (dogs/cats) and from two human cases were investigated. The resulting 400 bp N-gene sequences were compared with isolates representing neighbouring Arctic or Baltic countries from North America, the former Soviet Union and Europe. Phylogenetic analysis demonstrated similarities between sequences from the Arctic and Arctic-like viruses, which were distinct from rabies isolates originating in the Baltic region of Europe, the Steppes in Russia and from North America. The Arctic-like group consist of isolates from India, Pakistan, southeast Siberia and Japan. The Arctic group was differentiated into two lineages, Arctic 1 and Arctic 2, with good bootstrap support. Arctic 1 is mainly comprised of Canadian isolates with a single fox isolate from Maine in the USA. Arctic 2 was further divided into sub-lineages: 2a/2b. Arctic 2a comprises isolates from the Arctic regions of Yakutia in northeast Siberia and Alaska. Arctic 2b isolates represent a biotype, which is dispersed throughout the Arctic region. The broad distribution of rabies in the Arctic regions including Greenland, Canada and Alaska provides evidence for the movement of rabies across borders.
The Response of the North Atlantic Bloom to NAO Forcing

NASA Technical Reports Server (NTRS)

Mizoguchi, Ken-Ichi; Worthen, Denise L.; Hakkinen, Sirpa; Gregg, Watson W.

2004-01-01

Results from the climatologically forced coupled ice/ocean/biogeochemical model that covers the Arctic and North Atlantic Oceans are presented and compared to the chlorophyll fields of satellite-derived ocean color measurements. Biogeochemical processes in the model are determined from the interactions among four phytoplankton functional groups (diatoms, chlorophytes, cyanobacteria and coccolithophores) and four nutrients (nitrate, ammonium, silicate and dissolved iron). The model simulates the general large-scale pattern in April, May and June, when compared to both satellite-derived and in situ observations. The subpolar North Atlantic was cool in the 1980s and warm in the latter 1990s, corresponding to the CZCS and SeaWiFS satellite observing periods, respectively. The oceanographic conditions during these periods resemble the typical subpolar upper ocean response to the NAO+ and NAO-phases, respectively. Thus, we use the atmospheric forcing composites from the two NAO phases to simulate the variability of the mid-ocean bloom during the satellite observing periods. The model results show that when the subpolar North Atlantic is cool, the NAO+ case, more nutrients are available in early spring than when the North Atlantic is warm, the NAO-case. However, the NAO+ simulation produces a later bloom than the NAO-simulation. This difference in the bloom times is also identified in SeaWiFS and CZCS satellite measurements. In the model results, we can trace the difference to the early diatom bloom due to a warmer upper ocean. The higher nutrient abundance in the NAO+ case did not provide larger total production than in the NAO- case, instead the two cases had a comparable area averaged amplitude. This leads us to conclude that in the subpolar North Atlantic, the timing of the spring phytoplankton bloom depends on surface temperature and the magnitude of the bloom is not significantly impacted by the nutrient abundance.
The Influence of the North Atlantic Oscillation on Tropospheric Distributions of Ozone and Carbon Monoxide.

NASA Astrophysics Data System (ADS)

Knowland, K. E.; Doherty, R. M.; Hodges, K.

2015-12-01

The influence of the North Atlantic Oscillation (NAO) on the tropospheric distributions of ozone (O3) and carbon monoxide (CO) has been quantified. The Monitoring Atmospheric Composition and Climate (MACC) Reanalysis, a combined meteorology and composition dataset for the period 2003-2012 (Innes et al., 2013), is used to investigate the composition of the troposphere and lower stratosphere in relation to the location of the storm track as well as other meteorological parameters over the North Atlantic associated with the different NAO phases. Cyclone tracks in the MACC Reanalysis compare well to the cyclone tracks in the widely-used ERA-Interim Reanalysis for the same 10-year period (cyclone tracking performed using the tracking algorithm of Hodges (1995, 1999)), as both are based on the European Centre for Medium-Range Weather Forecasts' (ECMWF) Integrated Forecast System (IFS). A seasonal analysis is performed whereby the MACC reanalysis meteorological fields, O3 and CO mixing ratios are weighted by the monthly NAO index values. The location of the main storm track, which tilts towards high latitudes (toward the Arctic) during positive NAO phases to a more zonal location in the mid-latitudes (toward Europe) during negative NAO phases, impacts the location of both horizontal and vertical transport across the North Atlantic and into the Arctic. During positive NAO seasons, the persistence of cyclones over the North Atlantic coupled with a stronger Azores High promotes strong horizontal transport across the North Atlantic throughout the troposphere. In all seasons, significantly more intense cyclones occur at higher latitudes (north of ~50°C) during the positive phase of the NAO and in the southern mid-latitudes during the negative NAO phase. This impacts the location of stratospheric intrusions within the descending dry airstream behind the associated cold front of the extratropical cyclone and the venting of low-level pollution up into the free troposphere within

Remarkable link between projected uncertainties of Arctic sea-ice decline and winter Eurasian climate

NASA Astrophysics Data System (ADS)

Cheung, Hoffman H. N.; Keenlyside, Noel; Omrani, Nour-Eddine; Zhou, Wen

2018-01-01

We identify that the projected uncertainty of the pan-Arctic sea-ice concentration (SIC) is strongly coupled with the Eurasian circulation in the boreal winter (December-March; DJFM), based on a singular value decomposition (SVD) analysis of the forced response of 11 CMIP5 models. In the models showing a stronger sea-ice decline, the Polar cell becomes weaker and there is an anomalous increase in the sea level pressure (SLP) along 60°N, including the Urals-Siberia region and the Iceland low region. There is an accompanying weakening of both the midlatitude westerly winds and the Ferrell cell, where the SVD signals are also related to anomalous sea surface temperature warming in the midlatitude North Atlantic. In the Mediterranean region, the anomalous circulation response shows a decreasing SLP and increasing precipitation. The anomalous SLP responses over the Euro-Atlantic region project on to the negative North Atlantic Oscillation-like pattern. Altogether, pan-Arctic SIC decline could strongly impact the winter Eurasian climate, but we should be cautious about the causality of their linkage.
Climate variability and marine ecosystem impacts: a North Atlantic perspective

NASA Astrophysics Data System (ADS)

Parsons, L. S.; Lear, W. H.

In recent decades it has been recognized that in the North Atlantic climatic variability has been largely driven by atmospheric forcing related to the North Atlantic Oscillation (NAO). The NAO index began a pronounced decline around 1950 to a low in the 1960s. From 1970 onward the NAO index increased to its most extreme and persistent positive phase during the late 1980s and early 1990s. Changes in the pattern of the NAO have differential impacts on the opposite sides of the North Atlantic and differential impacts in the north and south. The changes in climate resulting from changes in the NAO appear to have had substantial impacts on marine ecosystems, in particular, on fish productivity, with the effects varying from region to region. An examination of several species and stocks, e.g. gadoids, herring and plankton in the Northeast Atlantic and cod and shellfish in the Northwest Atlantic, indicates that there is a link between long-term trends in the NAO and the productivity of various components of the marine ecosystem. While broad trends are evident, the mechanisms are poorly understood. Further research is needed to improve our understanding of how this climate variability affects the productivity of various components of the North Atlantic marine ecosystem.
Surface-Wind Anomalies in North-Atlantic and North Pacific from SSM/I Observations: Influence on Temperature of Adjoining Land Regions

NASA Technical Reports Server (NTRS)

Otterman, Joseph; Atlas, R.; Ingraham, J.; Ardizzone, J.; Starr, D.; Terry, J.

1998-01-01

Surface winds over the oceans are derived from Special Sensor Microwave Imager (SSM/I) measurements, assigning direction by Variational Analysis Method (VAM). Validations by comparison with other measurements indicate highly-satisfactory data quality. Providing global coverage from 1988, the dataset is a convenient source for surface-wind climatology. In this study, the interannual variability of zonal winds is analyzed concentrating on the westerlies in North Atlantic and North Pacific, above 30 N. Interannual differences in the westerlies exceeding 10 m sec (exp -1) are observed over large regions, often accompanied by changes of the same magnitude in the easterlies below 30 N. We concentrate on February/March, since elevated temperatures, by advancing snow-melt, can produce early spring. The extremely strong westerlies in 1997 observed in these months over North Atlantic (and also North Pacific) apparently contributed to large surface-temperature anomalies in western Europe, on the order of +3 C above the climatic monthly average for England and France. At these latitudes strong positive anomalies extended in a ring around the globe. We formulated an Index of South westerlies for the North Atlantic, which can serve as an indicator for day-by-day advection effects into Europe. In comparing 1997 and 1998 with the previous years, we establish significant correlations with the temperature anomalies (one to five days later, depending on the region, and on the season). This variability of the ocean-surface winds and of the temperature anomalies on land may be related to the El Nino/La Nina oscillations. Such large temperature fluctuations over large areas, whatever the cause, can be regarded as noise in attempts to assess long-term trends in global temperature.
The dominant role of Arctic surface buoyancy fluxes for AMOC slow-down on multi-decadal timescales

NASA Astrophysics Data System (ADS)

Fedorov, A. V.; Sevellec, F.

2016-12-01

One of the most dramatic consequences of the ongoing climate change is the reduction in the Arctic sea ice cover observed over the past few decades. This sea ice loss increases net heat flux into the ocean and at the same time exposes the ocean to additional freshwater flux from the atmosphere. These two effects imply positive anomalies in surface buoyancy fluxes over the Arctic ocean. In this study we estimate the sensitivity of the Atlantic Meridional Overturning Circulation (AMOC) to global changes in surface buoyancy forcing, especially in the context of changes in the Arctic. We find that, whereas on decadal timescale the subpolar region (especially east and south of Greenland) is the primarily driver of AMOC weakening due to positive buoyancy fluxes, on multidecadal timescales (longer than 20 years) it is the Arctic region that largely controls the AMOC slow-down. On timescales close to one century surface buoyancy fluxes over the Arctic ocean are nearly twice as effective for weakening the AMOC than those in the subpolar North Atlantic. We also find that the anomalous surface buoyancy fluxes in the Arctic can efficiently weaken poleward heat transport in the North Atlantic on a basin scale (i.e., between 25oN and 50oN). We conclude that such remote control of the AMOC intensity and heat transport by the Arctic ocean is a robust feature of climate change on multi-decadal timescales.
Size Scaling in Western North Atlantic Loggerhead Turtles Permits Extrapolation between Regions, but Not Life Stages.

PubMed

Marn, Nina; Klanjscek, Tin; Stokes, Lesley; Jusup, Marko

2015-01-01

Sea turtles face threats globally and are protected by national and international laws. Allometry and scaling models greatly aid sea turtle conservation and research, and help to better understand the biology of sea turtles. Scaling, however, may differ between regions and/or life stages. We analyze differences between (i) two different regional subsets and (ii) three different life stage subsets of the western North Atlantic loggerhead turtles by comparing the relative growth of body width and depth in relation to body length, and discuss the implications. Results suggest that the differences between scaling relationships of different regional subsets are negligible, and models fitted on data from one region of the western North Atlantic can safely be used on data for the same life stage from another North Atlantic region. On the other hand, using models fitted on data for one life stage to describe other life stages is not recommended if accuracy is of paramount importance. In particular, young loggerhead turtles that have not recruited to neritic habitats should be studied and modeled separately whenever practical, while neritic juveniles and adults can be modeled together as one group. Even though morphometric scaling varies among life stages, a common model for all life stages can be used as a general description of scaling, and assuming isometric growth as a simplification is justified. In addition to linear models traditionally used for scaling on log-log axes, we test the performance of a saturating (curvilinear) model. The saturating model is statistically preferred in some cases, but the accuracy gained by the saturating model is marginal.
Eocene climate and Arctic paleobathymetry: A tectonic sensitivity study using GISS ModelE-R

NASA Astrophysics Data System (ADS)

Roberts, C. D.; Legrande, A. N.; Tripati, A. K.

2009-12-01

The early Paleogene (65-45 million years ago, Ma) was a ‘greenhouse’ interval with global temperatures warmer than any other time in the last 65 Ma. This period was characterized by high levels of CO2, warm high-latitudes, warm surface-and-deep oceans, and an intensified hydrological cycle. Sediments from the Arctic suggest that the Eocene surface Arctic Ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions remain uncertain. We present equilibrium climate conditions derived from a fully-coupled, water-isotope enabled, general circulation model (GISS ModelE-R) configured for the early Eocene. We also present model-data comparison plots for key climatic variables (SST and δ18O) and analyses of the leading modes of variability in the tropical Pacific and North Atlantic regions. Our tectonic sensitivity study indicates that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the seaways connecting the Arctic to the Atlantic and Tethys. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~6 psu and warming of sea-surface temperatures by 2°C in the North Atlantic and 5-10°C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We also suggest that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates in the Atlantic.
Gravity model for the North Atlantic ocean mantle: results, uncertainties and links to regional geodynamics

NASA Astrophysics Data System (ADS)

Barantsrva, O.; Artemieva, I. M.; Thybo, H.

2015-12-01

We present the results of gravity modeling for the North Atlantic region based on interpretation of GOCE gravity satellite data. First, to separate the gravity signal caused by density anomalies within the crust and the upper mantle, we subtract the lower harmonics in the gravity field, which are presumably caused by deep density structure of the Earth (the core and the lower mantle). Next, the gravity effect of the upper mantle is calculated by subtracting the gravity effect of the crustal model. Our "basic model" is constrained by a recent regional seismic model EUNAseis for the crustal structure (Artemieva and Thybo, 2013); for bathymetry and topography we use a global ETOPO1 model by NOAA. We test sensitivity of the results to different input parameters, such as bathymetry, crustal structure, and gravity field. For bathymetry, we additionally use GEBCO data; for crustal correction - a global model CRUST 1.0 (Laske, 2013); for gravity - EGM2008 (Pavlis, 2012). Sensitivity analysis shows that uncertainty in the crustal structure produces the largest deviation from "the basic model". Use of different bathymetry data has little effect on the final results, comparable to the interpolation error. The difference in mantle residual gravity models based on GOCE and EMG2008 gravity data is 5-10 mGal. The results based on two crustal models have a similar pattern, but differ significantly in amplitude (ca. 250 mGal) for the Greenland-Faroe Ridge. The results demonstrate the presence of a strong gravity and density heterogeneity in the upper mantle in the North Atlantic region. A number of mantle residual gravity anomalies are robust features, independent of the choice of model parameters. This include (i) a sharp contrast at the continent-ocean transition, (ii) positive mantle gravity anomalies associated with continental fragments (microcontinents) in the North Atlantic ocean; (iii) negative mantle gravity anomalies which mark regions with anomalous oceanic mantle and
Recent intensified impact of December Arctic Oscillation on subsequent January temperature in Eurasia and North Africa

NASA Astrophysics Data System (ADS)

He, Shengping; Wang, Huijun; Gao, Yongqi; Li, Fei

2018-03-01

This study reveals an intensified influence of December Arctic Oscillation (AO) on the subsequent January surface air temperature (SAT) over Eurasia and North Africa in recent decades. The connection is statistically insignificant during 1957/58-1979/80 (P1), which becomes statistically significant during 1989/90-2011/12 (P2). The possible causes are further investigated. Associated with positive December AO during P2, significant anomalous anticyclone emerges over the central North Atlantic, which is accompanied with significant westerly and easterly anomalies along 45°-65°N and 20°-40°N, respectively. This favors the significant influence of December AO on the subsequent January SAT and atmospheric circulation over Eurasia and North Africa via triggering the North Atlantic tripole sea surface temperature (SST) anomaly that persists into the subsequent January. By contrast, the December AO-related anomalous anticyclone during P1 is weak and is characterized by two separate centers located in the eastern and western North Atlantic. Correspondingly, the westerly and easterly anomalies over the North Atlantic Ocean are weak and the-related tripole SST anomaly is not well formed, unfavorable for the persistent impact of the December AO into the subsequent January. Further analyses indicate that the different anomalous anticyclone associated with the December AO over the North Atlantic may be induced by the strengthened synoptic-scale eddy feedbacks over the North Atlantic, which may be related to the interdecadal intensification of the storm track activity. Additionally, the planetary stationary wave related to the December AO propagates from surface into upper stratosphere at mid-latitudes during P2, which further propagates downward to the troposphere and causes anomalous atmospheric circulation in the subsequent January.
Sensitivity of the Arctic Ocean gas hydrate to climate changes in the period of 1948-2015

NASA Astrophysics Data System (ADS)

Malakhova, Valentina V.; Golubeva, Elena N.; Iakshina, Dina F.

2017-11-01

The objective of the present study is to analyze the interactions between a methane hydrates stability zone and the ocean temperature variations and to define the hydrate sensitivity to the contemporary warming in the Arctic Ocean. To obtain the spatial-temporary variability of the ocean bottom temperature we employ the ICMMG regional Arctic-North Atlantic ocean model that has been developed in the Institute of Computational Mathematics and Mathematical Geophysics. With the ice-ocean model the Arctic bottom water temperatures were analyzed. The resulting warming ocean bottom water is spatially inhomogeneous, with a strong impact by the Atlantic inflow on shallow regions of 200-500 m depth. Results of the mathematical modeling of the dynamics of methane hydrate stability zone in the Arctic Ocean sediment are reported. We find that the reduction of the methane hydrate stability zone occurs in the Arctic Ocean between 250 and 400 m water depths within the upper 100 m of sediment in the area influenced by the Atlantic inflow. We have identified the areas of the Arctic Ocean where an increase in methane release is probable to occur at the present time.
Enhanced sea-ice export from the Arctic during the Younger Dryas.

PubMed

Not, Christelle; Hillaire-Marcel, Claude

2012-01-31

The Younger Dryas cold spell of the last deglaciation and related slowing of the Atlantic meridional overturning circulation have been linked to a large array of processes, notably an influx of fresh water into the North Atlantic related to partial drainage of glacial Lake Agassiz. Here we observe a major drainage event, in marine sediment cores raised from the Lomonosov Ridge, in the central Arctic Ocean marked by a pulse in detrital dolomitic-limestones. This points to an Arctic-Canadian sediment source area with about fivefold higher Younger Dryas ice-rafting deposition rate, in comparison with the Holocene. Our findings thus support the hypothesis of a glacial drainage event in the Canadian Arctic area, at the onset of the Younger Dryas, enhancing sea-ice production and drifting through the Arctic, then export through Fram Strait, towards Atlantic meridional overturning circulation sites of the northern North Atlantic.
Recent changes in the North Atlantic.

PubMed

Dickson, Robert R; Curry, Ruth; Yashayaev, Igor

2003-09-15

It has long been recognized that the Atlantic meridional overturning circulation (MOC) is potentially sensitive to greenhouse-gas and other climate forcing, and that changes in the MOC have the potential to cause abrupt climate change. However, the mechanisms remain poorly understood and our ability to detect these changes remains incomplete. Four main (interrelated) types of ocean change in particular are associated in the literature with greenhouse-gas forcing. These are: a slowing of MOC overturning rate; changes in northern seas which might effect a change in Atlantic overturning, including changes in the freshwater flux from the Arctic, and changes in the transport and/or hydrographic character of the northern overflows which ventilate the deep Atlantic; a change in the trans-ocean gradients of steric height (both zonal and meridional) which might accompany a change in the MOC; and an intensification of the global water cycle. Though as yet we have no direct measure of the freshwater flux passing from the Arctic to the Atlantic either via the Canadian Arctic Archipelago or along the East Greenland Shelf, and no direct measure yet of the Atlantic overturning rate, we examine a wide range of time-series from the existing hydrographic record for oceanic evidence of the other anticipated responses. Large amplitude and sustained changes are found (or indicated by proxy) over the past three to four decades in the southward transport of fresh waters along the Labrador shelf and slope, in the hydrography of the deep dense overflows from Nordic seas, in the transport of the eastern overflow through Faroe Bank Channel, and in the global hydrologic cycle. Though the type and scale of changes in ocean salinity are consistent with an amplification of the water cycle, we find no convincing evidence of any significant, concerted slowdown in the Atlantic overturning circulation.
SPURS: Salinity Processes in the Upper-Ocean Regional Study: THE NORTH ATLANTIC EXPERIMENT

NASA Technical Reports Server (NTRS)

Lindstrom, Eric; Bryan, Frank; Schmitt, Ray

2015-01-01

In this special issue of Oceanography, we explore the results of SPURS-1, the first part of the ocean process study Salinity Processes in the Upper-ocean Regional Study (SPURS). The experiment was conducted between August 2012 and October 2013 in the subtropical North Atlantic and was the first of two experiments (SPURS come in pairs!). SPURS-2 is planned for 20162017 in the tropical eastern Pacific Ocean.
Mesoscale Eddy Activity and Transport in the Atlantic Water Inflow Region North of Svalbard

NASA Astrophysics Data System (ADS)

Crews, L.; Sundfjord, A.; Albretsen, J.; Hattermann, T.

2018-01-01

Mesoscale eddies are known to transport heat and biogeochemical properties from Arctic Ocean boundary currents to basin interiors. Previous hydrographic surveys and model results suggest that eddy formation may be common in the Atlantic Water (AW) inflow area north of Svalbard, but no quantitative eddy survey has yet been done for the region. Here vorticity and water property signatures are used to identify and track AW eddies in an eddy-resolving sea ice-ocean model. The boundary current sheds AW eddies along most of the length of the continental slope considered, from the western Yermak Plateau to 40°E, though eddies forming east of 20°E are likely more important for slope-to-basin transport. Eddy formation seasonality reflects seasonal stability properties of the boundary current in the eastern portion of the study domain, but on and immediately east of the Yermak Plateau enhanced eddy formation during summer merits further investigation. AW eddies tend to be anticyclonic, have radii close to the local deformation radius, and be centered in the halocline. They transport roughly 0.16 Sv of AW and, due to their warm cores, 1.0 TW away from the boundary current. These findings suggest eddies may be important for halocline ventilation in the Eurasian Basin, as has been shown for Pacific Water eddies in the Canadian Basin.
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.
Early 21st-Century Mass loss of the North-Atlantic Glaciers and Ice Caps (Arne Richter Award for Outstanding Young Scientists Lecture)

NASA Astrophysics Data System (ADS)

Wouters, Bert; Ligtenberg, Stefan; Moholdt, Geir; Gardner, Alex S.; Noel, Brice; Kuipers Munneke, Peter; van den Broeke, Michiel; Bamber, Jonathan L.

2016-04-01

Historically, ice loss from mountain glaciers and ice caps has been one of the largest contributors to sea level rise over the last century. Of particular interest are the glaciers and ice caps in the North-Atlantic region of the Arctic. Despite the cold climate in this area, considerable melting and runoff occurs in summer. A small increase in temperature will have an immediate effect on these processes, so that a large change in the Arctic ice volume can be expected in response to the anticipated climate change in the coming century. Unfortunately, direct observations of glaciers are sparse and are biased toward glaciers systems in accessible, mostly maritime, climate conditions. Remote sensing is therefore essential to monitor the state of the the North-Atlantic glaciers and ice caps. In this presentation, we will discuss the progress that has been made in estimating the ice mass balance of these regions, with a particular focus on measurements made by ESA's Cryosat-2 radar altimeter mission (2010-present). Compared to earlier altimeter mission, Cryosat-2 provides unprecedented coverage of the cryosphere, with a resolution down to 1 km or better and sampling at monthly intervals. Combining the Cryosat-2 measurements with the laser altimetry data from ICESat (2003-2009) gives us a 12 yr time series of glacial mass loss in the North Atlantic. We find excellent agreement between the altimetry measurements and independent observations by the GRACE mission, which directly 'weighs' the ice caps, albeit at a much lower resolution. Mass loss in the region has increased from 120 Gigatonnes per year in 2003-2009 to roughly 140 Gt/yr in 2010-2014, with an important contribution from Greenland's peripheral glaciers and ice caps. Importantly, the mass loss is not stationary, but shows large regional interannual variability, with mass loss shifting between eastern and western regions from year to year. Comparison with regional climate models shows that these shifts can be
Contributions of Tropical Cyclones to the North Atlantic Climatological Rainfall as Observed from Satellites

NASA Technical Reports Server (NTRS)

Rodgers, Edward B.; Adler, Robert F.; Pierce, Harold F.; Einaudi, Franco (Technical Monitor)

2000-01-01

The tropical cyclone rainfall climatology study that was performed for the North Pacific was extended to the North Atlantic. Similar to the North Pacific tropical cyclone study, mean monthly rainfall within 444 km of the center of the North Atlantic tropical cyclones (i.e., that reached storm stage and greater) was estimated from passive microwave satellite observations during, an eleven year period. These satellite-observed rainfall estimates were used to assess the impact of tropical cyclone rainfall in altering the geographical, seasonal, and inter-annual distribution of the North Atlantic total rainfall during, June-November when tropical cyclones were most abundant. The main results from this study indicate: 1) that tropical cyclones contribute, respectively, 4%, 3%, and 4% to the western, eastern, and entire North Atlantic; 2) similar to that observed in the North Pacific, the maximum in North Atlantic tropical cyclone rainfall is approximately 5 - 10 deg poleward (depending on longitude) of the maximum non-tropical cyclone rainfall; 3) tropical cyclones contribute regionally a maximum of 30% of the total rainfall 'northeast of Puerto Rico, within a region near 15 deg N 55 deg W, and off the west coast of Africa; 4) there is no lag between the months with maximum tropical cyclone rainfall and non-tropical cyclone rainfall in the western North Atlantic, while in the eastern North Atlantic, maximum tropical cyclone rainfall precedes maximum non-tropical cyclone rainfall; 5) like the North Pacific, North Atlantic tropical cyclones Of hurricane intensity generate the greatest amount of rainfall in the higher latitudes; and 6) warm ENSO events inhibit tropical cyclone rainfall.
Emerging European winter precipitation pattern linked to atmospheric circulation changes over the North Atlantic region in recent decades

NASA Astrophysics Data System (ADS)

Ummenhofer, Caroline C.; Seo, Hyodae; Kwon, Young-Oh; Parfitt, Rhys; Brands, Swen; Joyce, Terrence M.

2017-08-01

Dominant European winter precipitation patterns over the past century, along with their associated extratropical North Atlantic circulation changes, are evaluated using cluster analysis. Contrary to the four regimes traditionally identified based on daily wintertime atmospheric circulation patterns, five distinct seasonal precipitation regimes are detected here. Recurrent precipitation patterns in each regime are linked to changes in atmospheric blocking, storm track, and sea surface temperatures across the North Atlantic region. Multidecadal variability in the frequency of the precipitation patterns reveals more (fewer) winters with wet conditions in northern (southern) Europe in recent decades and an emerging distinct pattern of enhanced wintertime precipitation over the northern British Isles. This pattern has become unusually common since the 1980s and is associated with changes in moisture transport and more frequent atmospheric river events. The observed precipitation changes post-1950 coincide with changes in storm track activity over the central/eastern North Atlantic toward the northern British Isles.
Soil Carbon in North American, Arctic, and Boreal Regions

NASA Astrophysics Data System (ADS)

Lajtha, K.; Bailey, V. L.; Schuur, E.; McGuire, D.; Romanovsky, V. E.

2017-12-01

Globally, soils contain more than 3 times as much as C as the atmosphere and >4 times more C than the world's biota, therefore even small changes in soil C stocks could lead to large changes in the atmospheric concentration of CO2. Since SOCCR-1, improvements have been made in quantifying stocks and uncertainties in stocks of soil C to a depth of 1 m across North America. Estimates for soil carbon stocks in the US (CONUS + Alaska) range from 151 - 162 Pg C, based on extensive sampling and analysis. Estimates for Canada average about 262 Pg C, but sampling is not as extensive. Soil C for Mexico is calculated as 18 Pg C, but there is a great deal of uncertainty surrounding this value. These soil carbon stocks are sensitive to agricultural management, land use and land cover change, and development and loss of C-rich soils such as wetlands. Climate change is a significant threat although may be partially mitigated by increased plant production. Carbon stored in permafrost zone circumpolar soils is equal to 1330-1580 Pg C, almost twice that contained in the atmosphere and about order of magnitude greater than carbon contained in plant biomass, woody debris, and litter in the boreal and tundra biomes combined. Surface air temperature change is amplified in high latitude regions such that Arctic temperature rise is about 2.5 times faster than for the globe as a whole, and thus 5 - 15% of this carbon is considered vulnerable to release to the atmosphere by the year 2100 following the current trajectory of global and Arctic warming. This amount is likely to be up to an order of magnitude larger loss than the increase in carbon stored in plant biomass under the same changing conditions. Models of soil organic matter dynamics have been greatly improved in the last decade by including greater process-level understanding of factors that affect soil C stabilization and destabilization, yet structural features of many models are still limited in representing Arctic and boreal
North Atlantic near-surface salinity contrasts and intra-basin water vapor transfer

NASA Astrophysics Data System (ADS)

Reagan, J. R.; Seidov, D.; Boyer, T.

2017-12-01

The geographic distribution of near-surface salinity (NSS) in the North Atlantic is characterized by a very salty (>37) subtropical region contrasting with a much fresher (<35) subpolar area. Multiple studies have shown that preserving this salinity contrast is important for maintaining the Atlantic Meridional Overturning Circulation (AMOC), and that changes to this salinity balance may reduce the strength of the AMOC. High subtropical salinity is primarily due to evaporation (E) dominating precipitation (P), whereas low subpolar salinity is at least partly due to precipitation dominating evaporation. Present-day understanding of the fate of water vapor in the atmosphere over the extratropical North Atlantic is that the precipitation which falls in the subpolar region primarily originates from the water vapor produced through evaporation in the subtropical North Atlantic. With this knowledge and in conjunction with a basic understanding of North Atlantic storm tracks—the main meridional transport conduits in mid and high latitudes— a preliminary time and spatial correlation analysis was completed to relate the North Atlantic decadal climatological salinity between 1985 and 2012 to the evaporation and precipitation climatologies for the same period. Preliminary results indicate that there is a clear connection between subtropical E-P and subpolar NSS. Additional results and potential implications will be presented and discussed.
Evaluation of the Atlantic Multidecadal Oscillation Impact on Large-Scale Atmospheric Circulation in the Atlantic Region in Summer

NASA Astrophysics Data System (ADS)

Semenov, V. A.; Cherenkova, E. A.

2018-02-01

The influence of the Atlantic Multidecadal Oscillation (AMO) on large-scale atmospheric circulation in the Atlantic region in summer for the period of 1950-2015 is investigated. It is shown that the intensification of the summer North Atlantic Oscillation (NAO) with significant changes in sea level pressure anomalies in the main centers of action (over Greenland and the British Isles) occurred while the North Atlantic was cooler. Sea surface temperature anomalies, which are linked to the AMO in the summer season, affect both the NAO index and fluctuations of the Eastern Atlantic/Western Russia (EAWR) centers of action. The positive (negative) phase of the AMO is characterized by a combination of negative (positive) values of the NAO and EAWR indices. The dominance of the opposite phases of the teleconnection indices in summer during the warm North Atlantic and in its colder period resulted in differences in the regional climate in Europe.

US regional tornado outbreaks and their links to spring ENSO phases and North Atlantic SST variability

NASA Astrophysics Data System (ADS)

Lee, Sang-Ki; Wittenberg, Andrew T.; Enfield, David B.; Weaver, Scott J.; Wang, Chunzai; Atlas, Robert

2016-04-01

Recent violent and widespread tornado outbreaks in the US, such as occurred in the spring of 2011, have caused devastating societal impact with significant loss of life and property. At present, our capacity to predict US tornado and other severe weather risk does not extend beyond seven days. In an effort to advance our capability for developing a skillful long-range outlook for US tornado outbreaks, here we investigate the spring probability patterns of US regional tornado outbreaks during 1950-2014. We show that the four dominant springtime El Niño-Southern Oscillation (ENSO) phases (persistent versus early-terminating El Niño and resurgent versus transitioning La Niña) and the North Atlantic sea surface temperature tripole variability are linked to distinct and significant US regional patterns of outbreak probability. These changes in the probability of outbreaks are shown to be largely consistent with remotely forced regional changes in the large-scale atmospheric processes conducive to tornado outbreaks. An implication of these findings is that the springtime ENSO phases and the North Atlantic SST tripole variability may provide seasonal predictability of US regional tornado outbreaks.
The last interglacial in eastern Canada and the northwest North Atlantic : further evidence for warmer climate and ocean conditions than during the Holocene

NASA Astrophysics Data System (ADS)

de Vernal, A.; Fréchette, B.; Hillaire-Marcel, C.; van Nieuwenhove, N.; Retailleau, S.

2012-04-01

The climate conditions of the last interglacial (LI) in northeastern and southeastern Canada are documented from pollen data of Baffin Island and Cape Breton Island respectively. The LI pollen assemblages indicate very different vegetation than at present and a northern limit of the deciduous forest biome as far as 500 km north of its modern position. The application of the modern analogue technique also reveal warmer climate during the LI than at present, 4-5°C warmer on Baffin Island at ~67-70°N in the Canadian Arctic, and up to 7°C warmer on Cape Breton Island at ~45°N in the southeastern Canada. The contrast between LI and Holocene climates is also shown from marine data (dinocysts, foraminifers, oxygen and carbon isotopes) that document warmer than Holocene conditions in surface waters (up to 5.5°C in summer, notably off southwest Greenland) and very distinct distribution of intermediate to deep waters in northern and southern part of the Labrador Sea. An important zonal atmospheric circulation component at mid-latitudes of the North Atlantic is also evidenced from the pollen content of marine cores collected in central North Atlantic (IODP Site 1304), which strongly suggests an origin from southeastern Canada. Altogether the data demonstrate much warmer conditions along the eastern Canadian margins, from North to South. The mild conditions along the coastlines and the relatively warm waters off eastern Canada and southern Greenland suggest reduced Arctic outflow components through the East Greenland Current and Labrador Current. Comparisons with records from eastern North Atlantic lead us to conclude in a more zonal climate during the LI than the Holocene, especially the early Holocene that was marked by a particularly pronounced west to east gradient of temperatures. Hence, the thermal optimum of the LI and that of the Holocene provide two examples of very different climate and ocean circulation regimes in the circum-Atlantic region during the "warm
Climate sensitivity to Arctic seaway restriction during the early Paleogene

NASA Astrophysics Data System (ADS)

Roberts, Christopher D.; LeGrande, Allegra N.; Tripati, Aradhna K.

2009-09-01

The opening and closing of ocean gateways affects the global distribution of heat, salt, and moisture, potentially driving climatic change on regional to global scales. Between 65 and 45 million years ago (Ma), during the early Paleogene, exchange between the Arctic and global oceans occurred through two narrow and shallow seaways, the Greenland-Norway seaway and the Turgai Strait. Sediments from the Arctic Ocean suggest that, during this interval, the surface ocean was warm, brackish, and episodically enabled the freshwater fern Azolla to bloom. The precise mechanisms responsible for the development of these conditions in the Paleogene Arctic remain uncertain. Here we show results from an isotope-enabled, atmosphere-ocean general circulation model, which indicate that Northern Hemisphere climate would have been very sensitive to the degree of oceanic exchange through the Arctic seaways. We also present modelled estimates of seawater and calcite δ18O for the Paleogene. By restricting these seaways, we simulate freshening of the surface Arctic Ocean to ~ 6 psu and warming of sea-surface temperatures by 2 °C in the North Atlantic and 5-10 °C in the Labrador Sea. Our results may help explain the occurrence of low-salinity tolerant taxa in the Arctic Ocean during the Eocene and provide a mechanism for enhanced warmth in the north western Atlantic. We propose that the formation of a volcanic land-bridge between Greenland and Europe could have caused increased ocean convection and warming of intermediate waters in the Atlantic. If true, this result is consistent with the theory that bathymetry changes may have caused thermal destabilisation of methane clathrates and supports a tectonic trigger hypothesis for the Paleocene Eocene Thermal Maximum (PETM).
Linking the Modern Distribution of Biogenic Proxies in High Arctic Greenland Shelf Sediments to Sea Ice, Primary Production, and Arctic-Atlantic Inflow

NASA Astrophysics Data System (ADS)

Limoges, Audrey; Ribeiro, Sofia; Weckström, Kaarina; Heikkilä, Maija; Zamelczyk, Katarzyna; Andersen, Thorbjørn J.; Tallberg, Petra; Massé, Guillaume; Rysgaard, Søren; Nørgaard-Pedersen, Niels; Seidenkrantz, Marit-Solveig

2018-03-01

The eastern north coast of Greenland is considered to be highly sensitive to the ongoing Arctic warming, but there is a general lack of data on modern conditions and in particular on the modern distribution of climate and environmental proxies to provide a baseline and context for studies on past variability. Here we present a detailed investigation of 11 biogenic proxies preserved in surface sediments from the remote High Arctic Wandel Sea shelf, the entrance to the Independence, Hagen, and Danmark fjords. The composition of organic matter (organic carbon, C:N ratios, δ13C, δ15N, biogenic silica, and IP25) and microfossil assemblages revealed an overall low primary production dominated by benthic diatoms, especially at the shallow sites. While the benthic and planktic foraminiferal assemblages underline the intrusion of chilled Atlantic waters into the deeper parts of the study area, the distribution of organic-walled dinoflagellate cysts is controlled by the local bathymetry and sea ice conditions. The distribution of the dinoflagellate cyst Polarella glacialis matches that of seasonal sea ice and the specific biomarker IP25, highlighting the potential of this species for paleo sea ice studies. The information inferred from our multiproxy study has important implications for the interpretation of the biogenic-proxy signal preserved in sediments from circum-Arctic fjords and shelf regions and can serve as a baseline for future studies. This is the first study of its kind in this area.
Digital elevations and extents of regional hydrogeologic units in the Northern Atlantic Coastal Plain aquifer system from Long Island, New York, to North Carolina

USGS Publications Warehouse

Pope, Jason P.; Andreasen, David C.; Mcfarland, E. Randolph; Watt, Martha K.

2016-08-31

Digital geospatial datasets of the extents and top elevations of the regional hydrogeologic units of the Northern Atlantic Coastal Plain aquifer system from Long Island, New York, to northeastern North Carolina were developed to provide an updated hydrogeologic framework to support analysis of groundwater resources. The 19 regional hydrogeologic units were delineated by elevation grids and extent polygons for 20 layers: the land and bathymetric surface at the top of the unconfined surficial aquifer, the upper surfaces of 9 confined aquifers and 9 confining units, and the bedrock surface that defines the base of all Northern Atlantic Coastal Plain sediments. The delineation of the regional hydrogeologic units relied on the interpretive work from source reports for New York, New Jersey, Delaware and Maryland, Virginia, and North Carolina rather than from re-analysis of fundamental hydrogeologic data. This model of regional hydrogeologic unit geometries represents interpolation, extrapolation, and generalization of the earlier interpretive work. Regional units were constructed from available digital data layers from the source studies in order to extend units consistently across political boundaries and approximate units in offshore areas.Though many of the Northern Atlantic Coastal Plain hydrogeologic units may extend eastward as far as the edge of the Atlantic Continental Shelf, the modeled boundaries of all regional hydrogeologic units in this study were clipped to an area approximately defined by the furthest offshore extent of fresh to brackish water in any part of the aquifer system, as indicated by chloride concentrations of 10,000 milligrams per liter. Elevations and extents of units that do not exist onshore in Long Island, New York, were not included north of New Jersey. Hydrogeologic units in North Carolina were included primarily to provide continuity across the Virginia-North Carolina State boundary, which was important for defining the southern edge of
A quantitative micropaleontologic method for shallow marine peleoclimatology: Application to Pliocene deposits of the western North Atlantic Ocean

USGS Publications Warehouse

Cronin, T. M.; Dowsett, H.J.

1990-01-01

A transfer function was developed to estimate summer and winter paleotemperatures for arctic to tropical regions of the western North Atlantic Ocean using fossil ostracode assemblages. Q-mode factor analysis was run on ostracode assemblages from 100 modern bottom sediment samples from continental shelves of North America, Greenland and the Caribbean using 59 ostracode taxa. Seven factors accounting for 80% of the variance define assemblages that correspond to frigid, subfrigid, cold temperate, mild temperate, warm temperate, subtropical and tropical climatic zones. Multiple regression of the factor matrix against observed February and August bottom temperatures yielded an astracode transfer function with an accuracy of about ??2??C. The transfer function was used to reconstruct middle Pliocene (3.5-3.0 Ma) shallow marine climates of the western North Atlantic during the marine transgression that deposited the Yorktown Formation (Virginia and North Carolina), the Duplin Formation (South and North Carolina) and the Pinecrest beds (Florida). Middle Pliocene paleowater temperatures in Virginia averaged 19??C in August and 13.5??C in February, about 5??C to 8??C warmer than at comparable depths off Virginia today. August and February water temperatures in North Carolina were 23??C and 13.4??C, in South Carolina about 23??C and 13.5??C and in southern Florida about 24.6??C and 15.4??C. Marine climates north of 35??N were warmer than today; south of 35??N, they were about the same or slightly cooler. Thermal gradients along the coast were generally not as steep as they are today. The North Atlantic transfer function can be applied to other shallow marine Pliocene and Pleistocene deposits of eastern North America. ?? 1990 Elsevier Science Publishers B.V.
Influence of the North Atlantic dipole on climate changes over Eurasia

NASA Astrophysics Data System (ADS)

Serykh, I. V.

2016-11-01

In this paper, some hydrophysical and meteorological characteristics of negative (1948-1976 and 1999-2015) and positive (1977-1998) phases of the Pacific Decadal Oscillation (PDO) and Interdecadal Pacific Oscillation (IPO) in the North Atlantic and Eurasia are constructed and investigated. Specifically, the near-surface temperature, sea-level atmospheric pressure, wind speed, heat content of the upper 700 m ocean layer, water temperature and salinity at various depths, the latent and sensible heat fluxes from the ocean to the atmosphere are analyzed. The fields obtained are in good agreement and complement each other. This gives important information about the hydrometeorological conditions in the region under study. Analysis of these data has shown that in the upper 1000 m North Atlantic layer there is a thermal dipole which can be interpreted as an oceanic analog of the atmospheric North Atlantic Oscillation (NAO). An index of the North Atlantic Dipole (NAD) as the difference between the mean heat contents in the upper 700 m oceanic layer between the regions (50°-70° N; 60°-10° W) and (20°-40° N; 80°-30° W) is proposed. A possible physical mechanism of the internal oscillations with a quasi-60-year period in the North Atlantics- Eurasia system of ocean-atmosphere interactions is discussed.
Interglacial climates and the Atlantic meridional overturning circulation: is there an Arctic controversy?

NASA Astrophysics Data System (ADS)

Bauch, Henning A.

2013-03-01

Arctic palaeorecords are important to understand the "natural range" of forcing and feedback mechanisms within the context of past and present climate change in this temperature-sensitive region. A wide array of methods and archives now provide a robust understanding of the Holocene climate evolution. By comparison rather little is still known about older interglacials, and in particular, on the effects of the northward propagation of heat transfer via the Atlantic meridional ocean circulation (AMOC) into the Arctic. Terrestrial records from this area often indicate a warmer and moister climate during past interglacials than in the Holocene implying a more vigorous AMOC activity. This is in conflict with marine data. Although recognized as very prominent interglacials in Antarctic ice cores, cross-latitudinal surface ocean temperature reconstructions show that little of the surface ocean warmth still identified in the Northeast Atlantic during older interglacial peaks (e.g., MIS5e, 9, 11) was further conveyed into the polar latitudes, and that each interglacial developed its own specific palaeoclimate features. Interactive processes between water mass overturning and the hydrological system of the Arctic, and how both developed together out of a glacial period with its particular ice sheet configuration and relative sea-level history, determined the efficiency of an evolving interglacial AMOC. Because of that glacial terminations developed some very specific water mass characteristics, which also affected the climate evolution of the ensuing interglacial periods. Moreover, the observed contrasts in the Arctic-directed meridional ocean heat flux between past interglacials have implications for the palaeoclimatic evaluation of this polar region. Crucial environmental factors of the Arctic climate system, such as the highly dynamical interactions between deep water mass flow, surface ocean temperature/salinity, sea ice, and atmosphere, exert strong feedbacks on
Projected climate changes threaten ancient refugia of kelp forests in the North Atlantic.

PubMed

Assis, Jorge; Araújo, Miguel B; Serrão, Ester A

2018-01-01

Intraspecific genetic variability is critical for species adaptation and evolution and yet it is generally overlooked in projections of the biological consequences of climate change. We ask whether ongoing climate changes can cause the loss of important gene pools from North Atlantic relict kelp forests that persisted over glacial-interglacial cycles. We use ecological niche modelling to predict genetic diversity hotspots for eight species of large brown algae with different thermal tolerances (Arctic to warm temperate), estimated as regions of persistence throughout the Last Glacial Maximum (20,000 YBP), the warmer Mid-Holocene (6,000 YBP), and the present. Changes in the genetic diversity within ancient refugia were projected for the future (year 2100) under two contrasting climate change scenarios (RCP2.6 and RCP8.5). Models predicted distributions that matched empirical distributions in cross-validation, and identified distinct refugia at the low latitude ranges, which largely coincide among species with similar ecological niches. Transferred models into the future projected polewards expansions and substantial range losses in lower latitudes, where richer gene pools are expected (in Nova Scotia and Iberia for cold affinity species and Gibraltar, Alboran, and Morocco for warm-temperate species). These effects were projected for both scenarios but were intensified under the extreme RCP8.5 scenario, with the complete borealization (circum-Arctic colonization) of kelp forests, the redistribution of the biogeographical transitional zones of the North Atlantic, and the erosion of global gene pools across all species. As the geographic distribution of genetic variability is unknown for most marine species, our results represent a baseline for identification of locations potentially rich in unique phylogeographic lineages that are also climatic relics in threat of disappearing. © 2017 John Wiley & Sons Ltd.
Regional nitrogen budgets and riverine N & P fluxes for the drainages to the North Atlantic Ocean: Natural and human influences

USGS Publications Warehouse

Howarth, R.W.; Billen, G.; Swaney, D.; Townsend, A.; Jaworski, N.; Lajtha, K.; Downing, J.A.; Elmgren, Ragnar; Caraco, N.; Jordan, T.; Berendse, F.; Freney, J.; Kudeyarov, V.; Murdoch, P.; Zhu, Z.-L.

1996-01-01

We present estimates of total nitrogen and total phosphorus fluxes in rivers to the North Atlantic Ocean from 14 regions in North America, South America, Europe, and Africa which collectively comprise the drainage basins to the North Atlantic. The Amazon basin dominates the overall phosphorus flux and has the highest phosphorus flux per area. The total nitrogen flux from the Amazon is also large, contributing 3.3 Tg yr-1 out of a total for the entire North Atlantic region of 13.1 Tg yr-1. On a per area basis, however, the largest nitrogen fluxes are found in the highly disturbed watersheds around the North Sea, in northwestern Europe, and in the northeastern U.S., all of which have riverine nitrogen fluxes greater than 1,000 kg N km-2 yr-1. Non-point sources of nitrogen dominate riverine fluxes to the coast in all regions. River fluxes of total nitrogen from the temperate regions of the North Atlantic basin are correlated with population density, as has been observed previously for fluxes of nitrate in the world's major rivers. However, more striking is a strong linear correlation between river fluxes of total nitrogen and the sum of anthropogenically-derived nitrogen inputs to the temperate regions (fertilizer application, human-induced increases in atmospheric deposition of oxidized forms of nitrogen, fixation by leguminous crops, and the import/export of nitrogen in agricultural products). On average, regional nitrogen fluxes in rivers are only 25% of these anthropogenically derived nitrogen inputs. Denitrification in wetlands and aquatic ecosystems is probably the dominant sink, with storage in forests perhaps also of importance. Storage of nitrogen in groundwater, although of importance in some localities, is a very small sink for nitrogen inputs in all regions. Agricultural sources of nitrogen dominate inputs in many regions, particularly the Mississippi basin and the North Sea drainages. Deposition of oxidized nitrogen, primarily of industrial origin, is the
Extreme storm activity in North Atlantic and European region

NASA Astrophysics Data System (ADS)

Vyazilova, N.

2010-09-01

The extreme storm activity study over North Atlantic and Europe includes the analyses of extreme cyclone (track number, integral cyclonic intensity) and extreme storm (track number) during winter and summer seasons in the regions: 1) 55°N-80N, 50°W-70°E; 2) 30°N-55°N, 50°W-70°E. Extreme cyclones were selected based on cyclone centre pressure (P<=970 mbar). Extreme storms were selected from extreme cyclones based on wind velocity on 925 mbar. The Bofort scala was used for this goal. Integral cyclonic intensity (for region) includes the calculation cyclone centers number and sum of MSLP anomalies in cyclone centers. The analyses based on automated cyclone tracking algorithm, 6-hourly MSLP and wind data (u and v on 925 gPa) from the NCEP/NCAR reanalyses from January 1948 to March 2010. The comparision of mean, calculated for every ten years, had shown, that in polar region extreme cyclone and storm track number, and integral cyclonic intensity gradually increases and have maximum during last years (as for summer, as for winter season). Every ten years means for summer season are more then for winter season, as for polar, as for tropical region. Means (ten years) for tropical region are significance less then for polar region.
Tracking of Arctic terns Sterna paradisaea reveals longest animal migration.

PubMed

Egevang, Carsten; Stenhouse, Iain J; Phillips, Richard A; Petersen, Aevar; Fox, James W; Silk, Janet R D

2010-02-02

The study of long-distance migration provides insights into the habits and performance of organisms at the limit of their physical abilities. The Arctic tern Sterna paradisaea is the epitome of such behavior; despite its small size (<125 g), banding recoveries and at-sea surveys suggest that its annual migration from boreal and high Arctic breeding grounds to the Southern Ocean may be the longest seasonal movement of any animal. Our tracking of 11 Arctic terns fitted with miniature (1.4-g) geolocators revealed that these birds do indeed travel huge distances (more than 80,000 km annually for some individuals). As well as confirming the location of the main wintering region, we also identified a previously unknown oceanic stopover area in the North Atlantic used by birds from at least two breeding populations (from Greenland and Iceland). Although birds from the same colony took one of two alternative southbound migration routes following the African or South American coast, all returned on a broadly similar, sigmoidal trajectory, crossing from east to west in the Atlantic in the region of the equatorial Intertropical Convergence Zone. Arctic terns clearly target regions of high marine productivity both as stopover and wintering areas, and exploit prevailing global wind systems to reduce flight costs on long-distance commutes.
Tracking of Arctic terns Sterna paradisaea reveals longest animal migration

PubMed Central

Egevang, Carsten; Stenhouse, Iain J.; Phillips, Richard A.; Petersen, Aevar; Fox, James W.; Silk, Janet R. D.

2010-01-01

The study of long-distance migration provides insights into the habits and performance of organisms at the limit of their physical abilities. The Arctic tern Sterna paradisaea is the epitome of such behavior; despite its small size (<125 g), banding recoveries and at-sea surveys suggest that its annual migration from boreal and high Arctic breeding grounds to the Southern Ocean may be the longest seasonal movement of any animal. Our tracking of 11 Arctic terns fitted with miniature (1.4-g) geolocators revealed that these birds do indeed travel huge distances (more than 80,000 km annually for some individuals). As well as confirming the location of the main wintering region, we also identified a previously unknown oceanic stopover area in the North Atlantic used by birds from at least two breeding populations (from Greenland and Iceland). Although birds from the same colony took one of two alternative southbound migration routes following the African or South American coast, all returned on a broadly similar, sigmoidal trajectory, crossing from east to west in the Atlantic in the region of the equatorial Intertropical Convergence Zone. Arctic terns clearly target regions of high marine productivity both as stopover and wintering areas, and exploit prevailing global wind systems to reduce flight costs on long-distance commutes. PMID:20080662
Regional Scale Variability in Background and Source δ13C of Methane in the Atlantic, Europe and the Arctic: Cautionary Tales for Isotopic Modeling

NASA Astrophysics Data System (ADS)

Lowry, D.; Fisher, R. E.; France, J. L.; Lanoiselle, M.; Zazzeri, G.; Nisbet, E. G.

2013-12-01

Modeling studies of methane δ13C, both of modern atmosphere and glacial palaeoclimates have used a global isotopic signature for each of the main source categories, whereas detailed studies of source fluxes, such as boreal wetlands, suggest that on the centimeter to meter scale there is very great variability. In recent years we have been reassessing the usefulness of using a generic source value from source up to regional scale through sampling campaigns in the European Arctic, the UK and onboard ships sailing the Atlantic up to the Arctic Ocean. Currently the boreal wetland source of methane dominates above 60°N. Within Finland this source varies at the wetland scale from -74 to -66‰ depending on wetland type and seasonal variability in temperature and water table. Lapland road trips and ship sampling suggest that these emissions are homogenized to -70 to -67‰ in the well-mixed regional atmosphere. An infrequent boreal forest fire emission adds a -30 to -26‰ component into the mix, and such inputs have been observed in the Mace Head (Ireland) isotopic record of 2002. The story is much more complex once the latitudes of heavily urbanized and agricultural areas of Northern Europe are reached. Isotopic signatures applied to UK and EC inventories suggest that national emissions can vary from -42 to -60‰ depending on source mix, but even this is too simplified. Fugitive emissions from gas distribution systems vary based on the source of the gas, with biogenic-dominated supplies from west Siberia at -50‰ to thermogenic gas of the Southern North Sea fields at -32‰. Coal emissions are also source-dependent and have a similar range to gas, but unlike pipeline-homogenized gas can vary from one mine to the next. Emissions from ruminants vary due to C3 and C4 plant diets, with C4 closer to -50‰ while C3 emissions are in the low -60's. A recent whole barn experiment in the UK recorded -66‰. Landfill signatures also vary. Sites engineered in the last decade
ASSOCIATIONS BETWEEN NAO VARIBILITY AND U.S. MID-ATLANTIC REGION HYDROCLIMATOLOGY

EPA Science Inventory

Variability in the climate of the US Mid-Atlantic Region is associated with larger scale variability in the El Nino-Southern Oscillation (ENSO), the Pacific North American (PNA) teleconnection pattern, and the North Atlantic Oscillation (NAO). Collectively, these three large-scal...
Modelling the impacts of a dipole-like climatic state over the Arctic

NASA Astrophysics Data System (ADS)

Pasha Karami, Mehdi; de Vernal, Anne; Hu, Xianmin; Myers, Paul G.

2015-04-01

The Arctic dipole anomaly (ADA) features a pattern with opposite sea-level pressure anomalies over the Canadian Archipelago and the Barents Sea. Changes in the predominance of Arctic atmospheric circulation modes and the shift towards a dipole mode in the past decade played a role in the summer sea ice loss and sea ice-freshwater export from the Arctic to the North Atlantic. Reconstruction of sea ice cover variations during Holocene also suggests opposite anomalies in the Barents Sea versus either the western Arctic or the Fram Strait area similar to the ADA pattern. It is vital to study such physical processes that cause dramatic changes in the Arctic sea ice recalling the link between the ADA and the current climate change. Here we focus on the question of how a persistent ADA-like state affects the Arctic sea ice distribution and its outflow to the Atlantic Ocean. For this purpose, an eddy-permitting regional configuration of the NEMO coupled ocean/sea-ice model is used. The regional domain covers the Arctic Ocean and the Northern-Hemisphere Atlantic, with a horizontal resolution of 1/4 degree at the equator (ANHA4). For the present-day simulations, boundary conditions are obtained by taking the average over the years with a positive ADA and those with a negative ADA. In the Holocene scenario, global climate model data are used to force our regional model. To exclude the role of Bering Strait and the heat flux from the Pacific Ocean, we repeat the experiments with a closed Bering Strait since a nearly closed Bering configuration was possible for the Early Holocene. The model results are compared with the paleoclimate data from Arctic and subarctic seas.
Advancing decadal-scale climate prediction in the North Atlantic sector.

PubMed

Keenlyside, N S; Latif, M; Jungclaus, J; Kornblueh, L; Roeckner, E

2008-05-01

The climate of the North Atlantic region exhibits fluctuations on decadal timescales that have large societal consequences. Prominent examples include hurricane activity in the Atlantic, and surface-temperature and rainfall variations over North America, Europe and northern Africa. Although these multidecadal variations are potentially predictable if the current state of the ocean is known, the lack of subsurface ocean observations that constrain this state has been a limiting factor for realizing the full skill potential of such predictions. Here we apply a simple approach-that uses only sea surface temperature (SST) observations-to partly overcome this difficulty and perform retrospective decadal predictions with a climate model. Skill is improved significantly relative to predictions made with incomplete knowledge of the ocean state, particularly in the North Atlantic and tropical Pacific oceans. Thus these results point towards the possibility of routine decadal climate predictions. Using this method, and by considering both internal natural climate variations and projected future anthropogenic forcing, we make the following forecast: over the next decade, the current Atlantic meridional overturning circulation will weaken to its long-term mean; moreover, North Atlantic SST and European and North American surface temperatures will cool slightly, whereas tropical Pacific SST will remain almost unchanged. Our results suggest that global surface temperature may not increase over the next decade, as natural climate variations in the North Atlantic and tropical Pacific temporarily offset the projected anthropogenic warming.
Short commentary on marine productivity at Arctic shelf breaks: upwelling, advection and vertical mixing

NASA Astrophysics Data System (ADS)

Randelhoff, Achim; Sundfjord, Arild

2018-04-01

The future of Arctic marine ecosystems has received increasing attention in recent years as the extent of the sea ice cover is dwindling. Although the Pacific and Atlantic inflows both import huge quantities of nutrients and plankton, they feed into the Arctic Ocean in quite diverse regions. The strongly stratified Pacific sector has a historically heavy ice cover, a shallow shelf and dominant upwelling-favourable winds, while the Atlantic sector is weakly stratified, with a dynamic ice edge and a complex bathymetry. We argue that shelf break upwelling is likely not a universal but rather a regional, albeit recurring, feature of the new Arctic. It is the regional oceanography that decides its importance through a range of diverse factors such as stratification, bathymetry and wind forcing. Teasing apart their individual contributions in different regions can only be achieved by spatially resolved time series and dedicated modelling efforts. The Northern Barents Sea shelf is an example of a region where shelf break upwelling likely does not play a dominant role, in contrast to the shallower shelves north of Alaska where ample evidence for its importance has already accumulated. Still, other factors can contribute to marked future increases in biological productivity along the Arctic shelf break. A warming inflow of nutrient-rich Atlantic Water feeds plankton at the same time as it melts the sea ice, permitting increased photosynthesis. Concurrent changes in sea ice cover and zooplankton communities advected with the boundary currents make for a complex mosaic of regulating factors that do not allow for Arctic-wide generalizations.
The North Atlantic-Eurasian teleconnection in summer and its effects on Eurasian climates

NASA Astrophysics Data System (ADS)

Li, Jianping; Ruan, Chengqing

2018-02-01

A teleconnection between the North Atlantic Ocean and the Eurasian continent is suggested by statistical and dynamical analysis of the northern summer 500 hPa geopotential height field. This teleconnection, termed the Atlantic-Eurasian (AEA) teleconnection, has five centers of action, in the subtropical North Atlantic Ocean, northeastern North Atlantic Ocean, Eastern Europe, the Kara Sea, and north China. The AEA index (AEAI) shows that the AEA undergoes a high degree of variability from year to year, and the AEAI has an increasing trend over the last 30 years. Our results suggest that this phenomenon is a large-scale Rossby wave train that originates in the subtropical North Atlantic Ocean. We support this conclusion by the methods of stationary wave ray tracing in non-uniform horizontal basic flow, wave activity flux calculations, and numerical models. The AEA and midlatitude circumglobal teleconnection pattern manifest distinct features at the hemispheric scale, despite the anomalies associated with them bear some similarities in the northeastern North Atlantic and Eastern Europe. Regional climate variations are strongly linked to this AEA along its path through northern Eurasia.
On the evolution of Atlantic Meridional Overturning Circulation Fingerprint and implications for decadal predictability in the North Atlantic

NASA Astrophysics Data System (ADS)

Zhang, Jinting; Zhang, Rong

2015-07-01

It has been suggested previously that the Atlantic Meridional Overturning Circulation (AMOC) anomaly associated with changes in the North Atlantic Deep Water formation propagates southward with an advection speed north of 34°N. In this study, using Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL CM2.1), we show that this slow southward propagation of the AMOC anomaly is crucial for the evolution and the enhanced decadal predictability of the AMOC fingerprint—the leading mode of upper ocean heat content (UOHC) in the extratropical North Atlantic. A positive AMOC anomaly in northern high latitudes leads to a convergence/divergence of the Atlantic meridional heat transport (MHT) anomaly in the subpolar/Gulf Stream region, thus warming in the subpolar gyre (SPG) and cooling in the Gulf Stream region after several years. Recent decadal prediction studies successfully predicted the observed warm shift in the SPG in the mid-1990s. Our results here provide the physical mechanism for the enhanced decadal prediction skills in the SPG UOHC.

Characterization of Chromophoric Dissolved Organic Matter across the Eastern and the Central Arctic Regions using PARAFAC Modelling

NASA Astrophysics Data System (ADS)

Molodtsova, T.; Amon, R. M. W.

2016-12-01

In this study the optical properties (absorption and fluorescence intensity) of chromophoric dissolved organic matter (CDOM) were investigated in water samples collected during the cruise conducted in August and September 2007 across the Eastern and Central Arctic regions. The fluorescence spectroscopy analysis was complimented with the parallel factor analysis (PARAFAC) and the identified six components were compared to other water properties including salinity, in situ fluorescence, dissolved organic carbon, and specific ultraviolet absorbance at 254 nm. The principal component analysis was conducted to distinguish between the water masses and identify the features such as the Trans Polar Drift and the North Atlantic Current. The preliminary results indicate that investigation of the optical properties of CDOM are able to provide better understanding of Arctic Ocean circulation and environmental changes such as the loss of the perennial sea ice and more light penetrating the water column.
Graduate training in Earth science across borders and disciplines: ArcTrain -"Processes and impacts of climate change in the North Atlantic Ocean and the Canadian Arctic"

NASA Astrophysics Data System (ADS)

Stein, Rüdiger; Kucera, Michal; Walter, Maren; de Vernal, Anne

2015-04-01

Due to a complex set of feedback processes collectively known as "polar amplification", the Arctic realm is expected to experience a greater-than-average response to global climate forcing. The cascades of feedback processes that connect the Arctic cryosphere, ocean and atmosphere remain incompletely constrained by observations and theory and are difficult to simulate in climate models. Our capacity to predict the future of the region and assess the impacts of Arctic change processes on global and regional environments hinges on the availability of interdisciplinary experts with strong international experience and understanding of the science/society interface. This is the basis of the International Research Training Group "Processes and impacts of climate change in the North Atlantic Ocean and the Canadian Arctic - ArcTrain", which was initiated in 2013. ArcTrain aims to educate PhD students in an interdisciplinary environment that combines paleoclimatology, physical oceanography, remote sensing and glaciology with comprehensive Earth system modelling, including sea-ice and ice-sheet components. The qualification program for the PhD students includes joint supervision, mandatory research residences at partner institutions, field courses on land and on sea (Floating University), annual meetings and training workshops and a challenging structured training in expert skills and transferrable skills. Its aim is to enhance the career prospects and employability of the graduates in a challenging international job market across academic and applied sectors. ArcTrain is a collaborative project at the University of Bremen and the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven. The German part of the project is designed to continue for nine years and educate three cohorts of twelve PhD students each. The Canadian partners comprise a consortium of eight universities led by the GEOTOP cluster at the Université du Québec à Montréal and including
Are changes in the phytoplankton community structure altering the flux of CO2 in regions of the North Atlantic?

NASA Astrophysics Data System (ADS)

Ostle, C.; Landschutzer, P.; Johnson, M.; Schuster, U.; Watson, A. J.; Edwards, M.; Robinson, C.

2016-02-01

The North Atlantic Ocean is a globally important sink of carbon dioxide (CO2). However, the strength of the sink varies temporally and regionally. This study uses a neural network method to map the surface ocean pCO2 (partial pressure of CO2) and flux of CO2from the atmosphere to the ocean alongside measurements of plankton abundance collected from the Continuous Plankton Recorder (CPR) survey to determine the relationship between regional changes in phytoplankton community structure and regional differences in carbon flux. Despite increasing sea surface temperatures, the Grand Banks of Newfoundland show a decrease in sea surface pCO2 of -2 µatm yr-1 from 1993 to 2011. The carbon flux in the North Sea is variable over the same period. This is in contrast to most of the open ocean within the North Atlantic, where increases in sea surface pCO2 follow the trend of increasing CO2 in the atmosphere, i.e. the flux or sink remains constant. The increasing CO2 sink in the Grand Banks of Newfoundland and the variable sink in the North Sea correlate with changes in phytoplankton community composition. This study investigates the biogeochemical and oceanographic mechanisms potentially linking increasing sea surface temperature, changes in phytoplankton community structure and the changing carbon sink in these two important regions of the Atlantic Ocean. The use of volunteer ships to concurrently collect these datasets demonstrates the potential to investigate relationships between plankton community structure and carbon flux in a cost-effective way. These results not only have implications for plankton-dynamic biogeochemical models, but also likely influence carbon export, as different phytoplankton communities have different carbon export efficiencies. Extending and maintaining such datasets is critical to improving our understanding of and monitoring carbon cycling in the surface ocean and improving climate model accuracy.
Digital depth horizon compilations of the Alaskan North Slope and adjacent Arctic regions

USGS Publications Warehouse

Saltus, Richard W.; Bird, Kenneth J.

2003-01-01

Data have been digitized and combined to create four detailed depth horizon grids spanning the Alaskan North Slope and adjacent offshore areas. These map horizon compilations were created to aid in petroleum system modeling and related studies. Topography/bathymetry is extracted from a recent Arctic compilation of global onshore DEM and satellite altimetry and ship soundings offshore. The Lower Cretaceous Unconformity (LCU), the top of the Triassic Shublik Formation, and the pre-Carboniferous acoustic basement horizon grids are created from numerous seismic studies, drill hole information, and interpolation. These horizons were selected because they mark critical times in the geologic evolution of the region as it relates to petroleum. The various horizons clearly show the major tectonic elements of this region including the Brooks Range, Colville Trough, Barrow Arch, Hanna Trough, Chukchi Platform, Nuwuk Basin, Kaktovik Basin, and Canada Basin. The gridded data are available in a variety of data formats for use in regional studies.
Adaptive strategies and life history characteristics in a warming climate: salmon in the Arctic?

USGS Publications Warehouse

Nielsen, Jennifer L.; Ruggerone, Gregory T.; Zimmerman, Christian E.

2013-01-01

In the warming Arctic, aquatic habitats are in flux and salmon are exploring their options. Adult Pacific salmon, including sockeye (Oncorhynchus nerka), coho (O. kisutch), Chinook (O. tshawytscha), pink (O. gorbuscha) and chum (O. keta) have been captured throughout the Arctic. Pink and chum salmon are the most common species found in the Arctic today. These species are less dependent on freshwater habitats as juveniles and grow quickly in marine habitats. Putative spawning populations are rare in the North American Arctic and limited to pink salmon in drainages north of Point Hope, Alaska, chum salmon spawning rivers draining to the northwestern Beaufort Sea, and small populations of chum and pink salmon in Canada’s Mackenzie River. Pacific salmon have colonized several large river basins draining to the Kara, Laptev and East Siberian seas in the Russian Arctic. These populations probably developed from hatchery supplementation efforts in the 1960’s. Hundreds of populations of Arctic Atlantic salmon (Salmo salar) are found in Russia, Norway and Finland. Atlantic salmon have extended their range eastward as far as the Kara Sea in central Russian. A small native population of Atlantic salmon is found in Canada’s Ungava Bay. The northern tip of Quebec seems to be an Atlantic salmon migration barrier for other North American stocks. Compatibility between life history requirements and ecological conditions are prerequisite for salmon colonizing Arctic habitats. Broad-scale predictive models of climate change in the Arctic give little information about feedback processes contributing to local conditions, especially in freshwater systems. This paper reviews the recent history of salmon in the Arctic and explores various patterns of climate change that may influence range expansions and future sustainability of salmon in Arctic habitats. A summary of the research needs that will allow informed expectation of further Arctic colonization by salmon is given.
North Atlantic climate model bias influence on multiyear predictability

NASA Astrophysics Data System (ADS)

Wu, Y.; Park, T.; Park, W.; Latif, M.

2018-01-01

The influences of North Atlantic biases on multiyear predictability of unforced surface air temperature (SAT) variability are examined in the Kiel Climate Model (KCM). By employing a freshwater flux correction over the North Atlantic to the model, which strongly alleviates both North Atlantic sea surface salinity (SSS) and sea surface temperature (SST) biases, the freshwater flux-corrected integration depicts significantly enhanced multiyear SAT predictability in the North Atlantic sector in comparison to the uncorrected one. The enhanced SAT predictability in the corrected integration is due to a stronger and more variable Atlantic Meridional Overturning Circulation (AMOC) and its enhanced influence on North Atlantic SST. Results obtained from preindustrial control integrations of models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) support the findings obtained from the KCM: models with large North Atlantic biases tend to have a weak AMOC influence on SAT and exhibit a smaller SAT predictability over the North Atlantic sector.
Economic Evaluation of the Information Security Levels Achieved by Electric Energy Providers in North Arctic Region

NASA Astrophysics Data System (ADS)

Sushko, O. P.; Kaznin, A. A.; Babkin, A. V.; Bogdanov, D. A.

2017-10-01

The study we are conducting involves the analysis of information security levels achieved by energy providers operating in the North Arctic Region. We look into whether the energy providers’ current information security levels meet reliability standards and determine what further actions may be needed for upgrading information security in the context of the digital transformation that the world community is undergoing. When developing the information security systems for electric energy providers or selecting the protection means for them, we are governed by the fact that the assets to be protected are process technologies. While information security risk can be assessed using different methods, the evaluation of the economic damage from these risks appears to be a difficult task. The most probable and harmful risks we have identified when evaluating the electric energy providers’ information security will be used by us as variables. To provide the evaluation, it is necessary to calculate the costs relating to elimination of the risks identified. The final stage of the study will involve the development of an operation algorithm for the North Arctic Region’s energy provider’s business information protection security system - a set of information security services, and security software and hardware.
Tropical Dominance of N2 Fixation in the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Marconi, Dario; Sigman, Daniel M.; Casciotti, Karen L.; Campbell, Ethan C.; Alexandra Weigand, M.; Fawcett, Sarah E.; Knapp, Angela N.; Rafter, Patrick A.; Ward, Bess B.; Haug, Gerald H.

2017-10-01

To investigate the controls on N2 fixation and the role of the Atlantic in the global ocean's fixed nitrogen (N) budget, Atlantic N2 fixation is calculated by combining meridional nitrate fluxes across World Ocean Circulation Experiment sections with observed nitrate 15N/14N differences between northward and southward transported nitrate. N2 fixation inputs of 27.1 ± 4.3 Tg N/yr and 3.0 ± 0.5 Tg N/yr are estimated north of 11°S and 24°N, respectively. That is, 90% of the N2 fixation in the Atlantic north of 11°S occurs south of 24°N in a region with upwelling that imports phosphorus (P) in excess of N relative to phytoplankton requirements. This suggests that, under the modern iron-rich conditions of the equatorial and North Atlantic, N2 fixation occurs predominantly in response to P-bearing, N-poor conditions. We estimate a N2 fixation rate of 30.5 ± 4.9 Tg N/yr north of 30°S, implying only 3 Tg N/yr between 30° and 11°S, despite evidence of P-bearing, N-poor surface waters in this region as well; this is consistent with iron limitation of N2 fixation in the South Atlantic. Since the ocean flows through the Atlantic surface in <2,500 years, similar to the residence time of oceanic fixed N, Atlantic N2 fixation can stabilize the N-to-P ratio of the global ocean. However, the calculated rate of Atlantic N2 fixation is a small fraction of global ocean estimates for either N2 fixation or fixed N loss. This suggests that, in the modern ocean, an approximate balance between N loss and N2 fixation is achieved within the combined Indian and Pacific basins.
22 CFR 120.31 - North Atlantic Treaty Organization.

Code of Federal Regulations, 2010 CFR

2010-04-01

... 22 Foreign Relations 1 2010-04-01 2010-04-01 false North Atlantic Treaty Organization. 120.31 Section 120.31 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.31 North Atlantic Treaty Organization. North Atlantic Treaty Organization (NATO) is...
22 CFR 120.31 - North Atlantic Treaty Organization.

Code of Federal Regulations, 2011 CFR

2011-04-01

... 22 Foreign Relations 1 2011-04-01 2011-04-01 false North Atlantic Treaty Organization. 120.31 Section 120.31 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.31 North Atlantic Treaty Organization. North Atlantic Treaty Organization (NATO) is...
22 CFR 120.31 - North Atlantic Treaty Organization.

Code of Federal Regulations, 2012 CFR

2012-04-01

... 22 Foreign Relations 1 2012-04-01 2012-04-01 false North Atlantic Treaty Organization. 120.31 Section 120.31 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.31 North Atlantic Treaty Organization. North Atlantic Treaty Organization (NATO) is...
22 CFR 120.31 - North Atlantic Treaty Organization.

Code of Federal Regulations, 2013 CFR

2013-04-01

... 22 Foreign Relations 1 2013-04-01 2013-04-01 false North Atlantic Treaty Organization. 120.31 Section 120.31 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.31 North Atlantic Treaty Organization. North Atlantic Treaty Organization (NATO) is...
22 CFR 120.31 - North Atlantic Treaty Organization.

Code of Federal Regulations, 2014 CFR

2014-04-01

... 22 Foreign Relations 1 2014-04-01 2014-04-01 false North Atlantic Treaty Organization. 120.31 Section 120.31 Foreign Relations DEPARTMENT OF STATE INTERNATIONAL TRAFFIC IN ARMS REGULATIONS PURPOSE AND DEFINITIONS § 120.31 North Atlantic Treaty Organization. North Atlantic Treaty Organization (NATO) is...
Greater role for Atlantic inflows on sea-ice loss in the Eurasian Basin of the Arctic Ocean

NASA Astrophysics Data System (ADS)

Polyakov, Igor V.; Pnyushkov, Andrey V.; Alkire, Matthew B.; Ashik, Igor M.; Baumann, Till M.; Carmack, Eddy C.; Goszczko, Ilona; Guthrie, John; Ivanov, Vladimir V.; Kanzow, Torsten; Krishfield, Richard; Kwok, Ronald; Sundfjord, Arild; Morison, James; Rember, Robert; Yulin, Alexander

2017-04-01

Arctic sea-ice loss is a leading indicator of climate change and can be attributed, in large part, to atmospheric forcing. Here, we show that recent ice reductions, weakening of the halocline, and shoaling of the intermediate-depth Atlantic Water layer in the eastern Eurasian Basin have increased winter ventilation in the ocean interior, making this region structurally similar to that of the western Eurasian Basin. The associated enhanced release of oceanic heat has reduced winter sea-ice formation at a rate now comparable to losses from atmospheric thermodynamic forcing, thus explaining the recent reduction in sea-ice cover in the eastern Eurasian Basin. This encroaching “atlantification” of the Eurasian Basin represents an essential step toward a new Arctic climate state, with a substantially greater role for Atlantic inflows.
Dissolved Organic Carbon in the North Atlantic Meridional Overturning Circulation.

PubMed

Fontela, Marcos; García-Ibáñez, Maribel I; Hansell, Dennis A; Mercier, Herlé; Pérez, Fiz F

2016-05-31

The quantitative role of the Atlantic Meridional Overturning Circulation (AMOC) in dissolved organic carbon (DOC) export is evaluated by combining DOC measurements with observed water mass transports. In the eastern subpolar North Atlantic, both upper and lower limbs of the AMOC transport high-DOC waters. Deep water formation that connects the two limbs of the AMOC results in a high downward export of non-refractory DOC (197 Tg-C·yr(-1)). Subsequent remineralization in the lower limb of the AMOC, between subpolar and subtropical latitudes, consumes 72% of the DOC exported by the whole Atlantic Ocean. The contribution of DOC to the carbon sequestration in the North Atlantic Ocean (62 Tg-C·yr(-1)) is considerable and represents almost a third of the atmospheric CO2 uptake in the region.
Dissolved Organic Carbon in the North Atlantic Meridional Overturning Circulation

PubMed Central

Fontela, Marcos; García-Ibáñez, Maribel I.; Hansell, Dennis A.; Mercier, Herlé; Pérez, Fiz F.

2016-01-01

The quantitative role of the Atlantic Meridional Overturning Circulation (AMOC) in dissolved organic carbon (DOC) export is evaluated by combining DOC measurements with observed water mass transports. In the eastern subpolar North Atlantic, both upper and lower limbs of the AMOC transport high-DOC waters. Deep water formation that connects the two limbs of the AMOC results in a high downward export of non-refractory DOC (197 Tg-C·yr−1). Subsequent remineralization in the lower limb of the AMOC, between subpolar and subtropical latitudes, consumes 72% of the DOC exported by the whole Atlantic Ocean. The contribution of DOC to the carbon sequestration in the North Atlantic Ocean (62 Tg-C·yr−1) is considerable and represents almost a third of the atmospheric CO2 uptake in the region. PMID:27240625
Deep and shallow structures in the Arctic region imaged by satellite magnetic and gravity data

NASA Astrophysics Data System (ADS)

Gaina, Carmen; Panet, Isabelle; Shephard, Grace

2016-07-01

The last decade has seen an increase in geoscientific data collection, which, together with available and older classified data made publicly available, is contributing to increasing our knowledge about Earth's structure and evolution. Despite this development, there are many gaps in data coverage in remote, hard-to-access regions. Satellite data have the advantage of acquiring measurements steadily and covering the entire globe. From a tectonics point of view, the specific heights of various satellites allow for the identification of moderate to large tectonic features, and can shed light on Earth's lower crust and lithosphere structure. In this contribution I discuss the use of magnetic and gravity models based on satellite data in deciphering the tectonic structure of remote areas. The present day Circum-Arctic region comprises a variety of tectonic settings: from active seafloor spreading in the North Atlantic and Eurasian Basin, and subduction in the North Pacific, to long-lived stable continental platforms in North America and Asia. A series of rifted margins, abandoned rifted areas and presumably extinct oceanic basins fringe these regions. Moreover, rifting- and seafloor spreading-related processes formed many continental splinters and terranes that were transported and docked at higher latitudes. Volcanic provinces of different ages have also been identified, from the Permian-Triassic Siberian traps at ca. 251 Ma to the (presumably) Cretaceous HALIP and smaller Cenozoic provinces in northern Greenland and the Barents Sea. We inspect global lithospheric magnetic data in order to identify the signature of the main volcanic provinces in the High Arctic. One of the most striking features in the Arctic domain is the strong magnetic anomaly close to the North Pole that correlates with a large, igneous oceanic plateau called the Alpha Mendeleev Ridge. The intensity and extent of the magnetic anomalies recorded by aircraft or satellites point towards a very thick
Arctic-midlatitude weather linkages in North America

NASA Astrophysics Data System (ADS)

Overland, James E.; Wang, Muyin

2018-06-01

There is intense public interest in whether major Arctic changes can and will impact midlatitude weather such as cold air outbreaks on the central and east side of continents. Although there is progress in linkage research for eastern Asia, a clear gap is conformation for North America. We show two stationary temperature/geopotential height patterns where warmer Arctic temperatures have reinforced existing tropospheric jet stream wave amplitudes over North America: a Greenland/Baffin Block pattern during December 2010 and an Alaska Ridge pattern during December 2017. Even with continuing Arctic warming over the past decade, other recent eastern US winter months were less susceptible for an Arctic linkage: the jet stream was represented by either zonal flow, progressive weather systems, or unfavorable phasing of the long wave pattern. The present analysis lays the scientific controversy over the validity of linkages to the inherent intermittency of jet stream dynamics, which provides only an occasional bridge between Arctic thermodynamic forcing and extended midlatitude weather events.
Role of extratropical cyclones in the recently observed increase in poleward moisture transport into the Arctic Ocean

NASA Astrophysics Data System (ADS)

Villamil-Otero, Gian A.; Zhang, Jing; He, Juanxiong; Zhang, Xiangdong

2018-01-01

Poleward atmospheric moisture transport (AMT) into the Arctic Ocean can change atmospheric moisture or water vapor content and cause cloud formation and redistribution, which may change downward longwave radiation and, in turn, surface energy budgets, air temperatures, and sea-ice production and melt. In this study, we found a consistently enhanced poleward AMT across 60°N since 1959 based on the NCAR-NCEP reanalysis. Regional analysis demonstrates that the poleward AMT predominantly occurs over the North Atlantic and North Pacific regions, contributing about 57% and 32%, respectively, to the total transport. To improve our understanding of the driving force for this enhanced poleward AMT, we explored the role that extratropical cyclone activity may play. Climatologically, about 207 extratropical cyclones move across 60°N into the Arctic Ocean each year, among which about 66 (32% of the total) and 47 (23%) originate from the North Atlantic and North Pacific Ocean, respectively. When analyzing the linear trends of the time series constructed by using a 20-year running window, we found a positive correlation of 0.70 between poleward yearly AMT and the integrated cyclone activity index (measurement of cyclone intensity, number, and duration). This shows the consistent multidecadal changes between these two parameters and may suggest cyclone activity plays a driving role in the enhanced poleward AMT. Furthermore, a composite analysis indicates that intensification and poleward extension of the Icelandic low and accompanying strengthened cyclone activity play an important role in enhancing poleward AMT over the North Atlantic region.
Late Eocene to present isotopic (Sr-Nd-Pb) and geochemical evolution of sediments from the Lomonosov Ridge, Arctic Ocean: Implications for continental sources and linkage with the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Stevenson, Ross; Poirier, André; Véron, Alain; Carignan, Jean; Hillaire-Marcel, Claude

2015-09-01

New geochemical and isotopic (Sr, Nd, Pb) data are presented for a composite sedimentary record encompassing the past 50 Ma of history of sedimentation on the Lomonosov Ridge in the Arctic Ocean. The sampled sediments encompass the transition of the Arctic basin from an enclosed anoxic basin to an open and ventilated oxidized ocean basin. The transition from anoxic basin to open ventilated ocean is accompanied by at least three geochemical and isotopic shifts and an increase in elements (e.g., K/Al) controlled by detrital minerals highlighting significant changes in sediment types and sources. The isotopic compositions of the sediments prior to ventilation are more variable but indicate a predominance of older crustal contributions consistent with sources from the Canadian Shield. Following ventilation, the isotopic compositions are more stable and indicate an increased contribution from younger material consistent with Eurasian and Pan-African crustal sources. The waxing and waning of these sources in conjunction with the passage of water through Fram Strait underlines the importance of the exchange of water mass between the Arctic and North Atlantic Oceans.

The 2008 Circum-Arctic Resource Appraisal

USGS Publications Warehouse

Moore, Thomas E.; Gautier, Donald L.

2017-11-15

Professional Paper 1824 comprises 30 chapters by various U.S. Geological Survey authors, including introduction and methodology chapters, which together provide documentation of the geological basis and methodology of the 2008 Circum-Arctic Resource Appraisal, results of which were first released in August 2008. Twenty-eight chapters summarize the petroleum geology and resource potential of individual, geologically defined provinces north of the Arctic Circle, including those of northern Alaska, northern Canada, east and west Greenland, and most of Arctic Russia, as well as certain offshore areas of the north Atlantic Basin and the Polar Sea. Appendixes tabulate the input and output information used during the assessment.
Survey trends of North American shorebirds: Population declines or shifting distributions?

USGS Publications Warehouse

Bart, Jonathan; Brown, Stephen; Harrington, Brian A.; Morrison, R.I. Guy

2007-01-01

We analyzed data from two surveys of fall migrating shorebirds in central and eastern North America to estimate annual trends in means per survey and to determine whether trends indicate a change in population size or might have been caused by other factors. The analysis showed a broad decline in means per survey in Atlantic Canada and the northeastern United States (North Atlantic region). For example, 9 of 9 significant trends in this region were <1 (P=0.004), and the mean, annual rate of change among 30 species was 0.9783, a decline of −2.17% per year (P<0.001). Trends in the midwestern United States (Midwest region) showed no clear pattern. The mean among 29 species was 1.0090 (P=0.35). Only 4 of the trends were significant. Several hypotheses were evaluated to identify causes of the declining means per survey in the North Atlantic region. The most likely hypothesis appears to be a decline in the breeding populations that supply migrants to the North Atlantic region, but a change in movements, for example passing through the region more quickly in recent years, cannot be excluded as an explanation. Further surveys of arctic breeding areas coupled with analysis of long‐term survey data from western North America would be helpful in determining whether the declines found in this analysis are also occurring in other areas.
Atlantic Multidecadal Oscillation Modulates the Impacts of Arctic Sea Ice Decline

NASA Astrophysics Data System (ADS)

Li, Fei; Orsolini, Yvan J.; Wang, Huijun; Gao, Yongqi; He, Shengping

2018-03-01

The Arctic sea ice cover has been rapidly declining in the last two decades, concurrent with a shift in the Atlantic Multidecadal Oscillation (AMO) to its warm phase around 1996/1997. Here we use both observations and model simulations to investigate the modulation of the atmospheric impacts of the decreased sea ice cover in the Atlantic sector of the Arctic (AASIC) by the AMO. We find that the AASIC loss during a cold AMO phase induces increased Ural blocking activity, a southeastward-extended snowpack, and a cold continent anomaly over Eurasia in December through northerly cold air advection and moisture transport from the Arctic. The increased Ural blocking activity and more extended Eurasian snowpack strengthen the upward propagation of planetary waves over the Siberian-Pacific sector in the lower stratosphere and hence lead to a weakened stratospheric polar vortex and a negative Arctic Oscillation (AO) phase at the surface in February. However, corresponding to the AASIC loss during a warm AMO phase, one finds more widespread warming over the Arctic and a reduced snowpack over Northern Eurasia in December. The stratosphere-troposphere coupling is suppressed in early winter and no negative AO anomaly is found in February. We suggest that the cold AMO phase is important to regulate the atmospheric response to AASIC decline, and our study provides insight to the ongoing debate on the connection between the Arctic sea ice and the AO.
Western Arctic Temperature Sensitivity Varies under Different Mean States

NASA Astrophysics Data System (ADS)

Daniels, W.; Russell, J. M.; Morrill, C.; Longo, W. M.; Giblin, A. E.; Holland-Stergar, P.; Hu, A.; Huang, Y.

2017-12-01

The Arctic is warming faster than anywhere on earth. Predictions of future change, however, are hindered by uncertainty in the mechanisms that underpin Arctic amplification. Data from Beringia (Alaska and Eastern Siberia) are particularly inconclusive with regards to both glacial-interglacial climate change as well as the presence or absence of abrupt climate change events such as the Younger Dryas. Here we investigate temperature change in Beringia from the last glacial maximum (LGM) to present using a unique 30 kyr lacustrine record of leaf wax hydrogen isotope ratios (δDwax) from Northern Alaska. We evaluate our results in the context of PMIP3 climate simulations as well as sensitivity tests of the effects of sea level and Bering Strait closure on Arctic Alaskan climate. The amplitude of LGM cooling in Alaska (-3.2 °C relative to pre-industrial) is smaller than other parts of North America and areas proximal to LGM ice sheets, but similar to Arctic Asia and Europe. This suggests that the local feedbacks (vegetation, etc.) had limited impacts on regional temperatures during the last ice-age, and suggests most of the Arctic exhibited similar responses to global climate boundary conditions. Deglacial warming was superimposed by a series of rapid warming events that encompass most of the temperature increase. These events are largely synchronous with abrupt events in the North Atlantic, but are amplified, muted, or even reversed in comparison depending on the mean climate state. For example, we observe warming during Heinrich 1 and during the submergence of the Bering Land Bridge, which are associated with cooling in the North Atlantic. Climate modeling suggests that opening of the Bering Strait controlled the amplitude and sign of millennial-scale temperature changes across the glacial termination.
Comprehensive analysis of Curie-point depths and lithospheric effective elastic thickness at Arctic Region

NASA Astrophysics Data System (ADS)

Lu, Y.; Li, C. F.

2017-12-01

Arctic Ocean remains at the forefront of geological exploration. Here we investigate its deep geological structures and geodynamics on the basis of gravity, magnetic and bathymetric data. We estimate Curie-point depth and lithospheric effective elastic thickness to understand deep geothermal structures and Arctic lithospheric evolution. A fractal exponent of 3.0 for the 3D magnetization model is used in the Curie-point depth inversion. The result shows that Curie-point depths are between 5 and 50 km. Curie depths are mostly small near the active mid-ocean ridges, corresponding well to high heat flow and active shallow volcanism. Large curie depths are distributed mainly at continental marginal seas around the Arctic Ocean. We present a map of effective elastic thickness (Te) of the lithosphere using a multitaper coherence technique, and Te are between 5 and 110 km. Te primarily depends on geothermal gradient and composition, as well as structures in the lithosphere. We find that Te and Curie-point depths are often correlated. Large Te are distributed mainly at continental region and small Te are distributed at oceanic region. The Alpha-Mendeleyev Ridge (AMR) and The Svalbard Archipelago (SA) are symmetrical with the mid-ocean ridge. AMR and SA were formed before an early stage of Eurasian basin spreading, and they are considered as conjugate large igneous provinces, which show small Te and Curie-point depths. Novaya Zemlya region has large Curie-point depths and small Te. We consider that fault and fracture near the Novaya Zemlya orogenic belt cause small Te. A series of transform faults connect Arctic mid-ocean ridge with North Atlantic mid-ocean ridge. We can see large Te near transform faults, but small Curie-point depths. We consider that although temperature near transform faults is high, but mechanically the lithosphere near transform faults are strengthened.
North Atlantic variability and its links to European climate over the last 3000 years.

PubMed

Moffa-Sánchez, Paola; Hall, Ian R

2017-11-23

The subpolar North Atlantic is a key location for the Earth's climate system. In the Labrador Sea, intense winter air-sea heat exchange drives the formation of deep waters and the surface circulation of warm waters around the subpolar gyre. This process therefore has the ability to modulate the oceanic northward heat transport. Recent studies reveal decadal variability in the formation of Labrador Sea Water. Yet, crucially, its longer-term history and links with European climate remain limited. Here we present new decadally resolved marine proxy reconstructions, which suggest weakened Labrador Sea Water formation and gyre strength with similar timing to the centennial cold periods recorded in terrestrial climate archives and historical records over the last 3000 years. These new data support that subpolar North Atlantic circulation changes, likely forced by increased southward flow of Arctic waters, contributed to modulating the climate of Europe with important societal impacts as revealed in European history.
The Regional Influence of the Arctic Oscillation and Arctic Dipole on the Wintertime Arctic Surface Radiation Budget and Sea Ice Growth

NASA Technical Reports Server (NTRS)

Hegyi, Bradley M.; Taylor, Patrick C.

2017-01-01

An analysis of 2000-2015 monthly Clouds and the Earth's Radiant Energy System-Energy Balanced and Filled (CERES-EBAF) and Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA2) data reveals statistically significant fall and wintertime relationships between Arctic surface longwave (LW) radiative flux anomalies and the Arctic Oscillation (AO) and Arctic Dipole (AD). Signifying a substantial regional imprint, a negative AD index corresponds with positive downwelling clear-sky LW flux anomalies (greater than10W m(exp -2)) north of western Eurasia (0 deg E-120 deg E) and reduced sea ice growth in the Barents and Kara Seas in November-February. Conversely, a positive AO index coincides with negative clear-sky LW flux anomalies and minimal sea ice growth change in October-November across the Arctic. Increased (decreased) atmospheric temperature and water vapor coincide with the largest positive (negative) clear-sky flux anomalies. Positive surface LW cloud radiative effect anomalies also accompany the negative AD index in December-February. The results highlight a potential pathway by which Arctic atmospheric variability influences the regional surface radiation budget over areas of Arctic sea ice growth.
North Atlantic explosive cyclones and large scale atmospheric variability modes

NASA Astrophysics Data System (ADS)

Liberato, Margarida L. R.

2015-04-01

Extreme windstorms are one of the major natural catastrophes in the extratropics, one of the most costly natural hazards in Europe and are responsible for substantial economic damages and even fatalities. During the last decades Europe witnessed major damage from winter storms such as Lothar (December 1999), Kyrill (January 2007), Klaus (January 2009), Xynthia (February 2010), Gong (January 2013) and Stephanie (February 2014) which exhibited uncommon characteristics. In fact, most of these storms crossed the Atlantic in direction of Europe experiencing an explosive development at unusual lower latitudes along the edge of the dominant North Atlantic storm track and reaching Iberia with an uncommon intensity (Liberato et al., 2011; 2013; Liberato 2014). Results show that the explosive cyclogenesis process of most of these storms at such low latitudes is driven by: (i) the southerly displacement of a very strong polar jet stream; and (ii) the presence of an atmospheric river (AR), that is, by a (sub)tropical moisture export over the western and central (sub)tropical Atlantic which converges into the cyclogenesis region and then moves along with the storm towards Iberia. Previous studies have pointed to a link between the North Atlantic Oscillation (NAO) and intense European windstorms. On the other hand, the NAO exerts a decisive control on the average latitudinal location of the jet stream over the North Atlantic basin (Woollings et al. 2010). In this work the link between North Atlantic explosive cyclogenesis, atmospheric rivers and large scale atmospheric variability modes is reviewed and discussed. Liberato MLR (2014) The 19 January 2013 windstorm over the north Atlantic: Large-scale dynamics and impacts on Iberia. Weather and Climate Extremes, 5-6, 16-28. doi: 10.1016/j.wace.2014.06.002 Liberato MRL, Pinto JG, Trigo IF, Trigo RM. (2011) Klaus - an exceptional winter storm over Northern Iberia and Southern France. Weather 66:330-334. doi:10.1002/wea.755 Liberato
Sensitivity of the North Atlantic Basin to cyclic climatic forcing during the early Cretaceous

USGS Publications Warehouse

Dean, W.E.; Arthur, M.A.

1999-01-01

Striking cyclic interbeds of laminated dark-olive to black marlstone and bioturbated white to light-gray limestone of Neocomian (Early Cretaceous) age have been recovered at Deep Sea Drilling Project (DSDP) and Ocean Drilling Project (ODP) sites in the North Atlantic. These Neocomian sequences are equivalent to the Maiolica Formation that outcrops in the Tethyan regions of the Mediterranean and to thick limestone sequences of the Vocontian Trough of France. This lithologic unit marks the widespread deposition of biogenic carbonate over much of the North Atlantic and Tethyan seafloor during a time of overall low sealevel and a deep carbonate compensation depth. The dark clay-rich interbeds typically are rich in organic carbon (OC) with up to 5.5% OC in sequences in the eastern North Atlantic. These eastern North Atlantic sequences off northwest Africa, contain more abundant and better preserved hydrogen-rich, algal organic matter (type II kerogen) relative to the western North Atlantic, probably in response to coastal upwelling induced by an eastern boundary current in the young North Atlantic Ocean. The more abundant algal organic matter in sequences in the eastern North Atlantic is also expressed in the isotopic composition of the carbon in that organic matter. In contrast, organic matter in Neocomian sequences in the western North Atlantic along the continental margin of North America has geochemical and optical characteristics of herbaceous, woody, hydrogen-poor, humic, type III kerogen. The inorganic geochemical characteristics of the dark clay-rich (80% CaCO3) interbeds in both the eastern and western basins of the North Atlantic suggest that they contain minor amounts of relatively unweathered eolian dust derived from northwest Africa during dry intervals.
CARINA TCO2 data in the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Pierrot, D.; Brown, P.; van Heuven, S.; Tanhua, T.; Schuster, U.; Wanninkhof, R.; Key, R. M.

2010-01-01

Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 cruises in the Arctic, Atlantic and Southern Ocean have been retrieved and merged in a new data base: the CARINA (CARbon IN the Atlantic) Project. These data have gone through rigorous quality control (QC) procedures to assure the highest possible quality and consistency. Secondary quality control, which involved objective study of data in order to quantify systematic differences in the reported values, was performed for the pertinent parameters in the CARINA data base. Systematic biases in the data have been corrected in the data products. The products are three merged data files with measured, adjusted and interpolated data of all cruises for each of the three CARINA regions (Arctic, Atlantic and Southern Ocean). Ninety-eight cruises were conducted in the "Atlantic" defined as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we report the details of the secondary QC which was done on the total dissolved inorganic carbon (TCO2) data and the adjustments that were applied to yield the final data product in the Atlantic. Procedures of quality control - including crossover analysis between stations and inversion analysis of all crossover data - are briefly described. Adjustments were applied to TCO2 measurements for 17 of the cruises in the Atlantic Ocean region. With these adjustments, the CARINA data base is consistent both internally as well as with GLODAP data, an oceanographic data set based on the WOCE Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, regional oceanic carbon inventories, uptake rates and model validation.
Arctic-North Pacific Coupled Impacts on the Late Autumn Cold in North America

NASA Technical Reports Server (NTRS)

Sung, Mi-Kyung; Kim, Baek-Min; Baik, Eun-Hyuk; Lim, Young-Kwon; Kim, Seong-Joong

2016-01-01

The Pacific Decadal Oscillation (PDO) is known to bring an anomalously cold (warm) period to southeastern (northwestern) North America during the cold season of its positive phase through a Rossby wave linkage. This study provides evidence that the remote connection between the North Pacific and the downstream temperature over central North America is strengthened by the warm arctic conditions over the Chukchi and East Siberian Sea, especially in the late autumn season. The modulation effect of the Arctic manifests itself as an altered Rossby wave response to a transient vorticity forcing that results from an equatorward storm track shift, which is induced collaboratively by the PDO and the warm Arctic. This observational finding is supported by two independent modeling experiments: 1) an idealized coupled GCM experiment being nudged toward the warm arctic surface condition and 2) a simple stationary wave model (SWM) experiment forced by transient eddy forcing.
Provenance of ice rafted debris in the North Atlantic: biomarker approach

NASA Astrophysics Data System (ADS)

Kornilova, O.; Russell, M.; Rosell-Melé, A.

2003-04-01

During the last glacial period, there have been several episodes of quasi-periodic iceberg discharge from the ice sheets into the North Atlantic (Heinrich Events) (Heinrich, 1988). These episodes are recorded in Quaternary sediments as layers of ice rafted debris (IRD), whose properties differ from those of adjacent ambient sediments. Heinrich Events (HEs) are associated with changes in global climate. To determine the cause of HEs, work on provenance of IRD was undertaken. Previous studies included analysis of bulk properties of lithic &organic matter of IRD in Heinrich Layers (HLs) and an attempt to correlate them with possible continental sources (e.g. Grousset et al., 2001). We used biomarker approach to characterise the provenance of IRD in the North Atlantic, similar to oil-source rock correlation well established in petroleum industry. In this work, biomarker composition of Heinrich Layers from several North Atlantic cores was compared with that of possible source areas. As a proxy for source of IRD, we analysed glaciogenic debris flows from trough mouth fans (TMF) that formed as a result of iceberg discharge (Vorren &Laberg, 1997). Those include samples from the Nordic Seas, Labrador Sea, Baffin Bay and combined Arctic sources. Different classes of organic compounds (e.g. photosynthetic pigments and hydrocarbons) were characterised using UV-Vis, LC-MS and GC, GC-MS respectively. Variability within each class, relative abundances of different components and isotopic signatures were considered. Biomarker signatures of debris flows were compared with those of IRD in Heinrich Layers (HLs) from four North Atlantic cores containing HLs 1-6 (MD95-2024, ODP-609, BOSF-5K and SU90-09). Variability between different cores and between different HLs was considered as well as variability within each HL (1-5) for SU90-09. Cluster analysis was performed to correlate sources of IRD (TMFs) and sinks (HLs). Grousset et al. 2001. Zooming in on Heinrich layers. Paleoceanography
Arctic Ocean

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.; Zukor, Dorothy J. (Technical Monitor)

2000-01-01

The Arctic Ocean is the smallest of the Earth's four major oceans, covering 14x10(exp 6) sq km located entirely within the Arctic Circle (66 deg 33 min N). It is a major player in the climate of the north polar region and has a variable sea ice cover that tends to increase its sensitivity to climate change. Its temperature, salinity, and ice cover have all undergone changes in the past several decades, although it is uncertain whether these predominantly reflect long-term trends, oscillations within the system, or natural variability. Major changes include a warming and expansion of the Atlantic layer, at depths of 200-900 m, a warming of the upper ocean in the Beaufort Sea, a considerable thinning (perhaps as high as 40%) of the sea ice cover, a lesser and uneven retreat of the ice cover (averaging approximately 3% per decade), and a mixed pattern of salinity increases and decreases.
Influence of sea ice on Arctic precipitation

PubMed Central

Kopec, Ben G.; Feng, Xiahong; Michel, Fred A.; Posmentier, Eric S.

2016-01-01

Global climate is influenced by the Arctic hydrologic cycle, which is, in part, regulated by sea ice through its control on evaporation and precipitation. However, the quantitative link between precipitation and sea ice extent is poorly constrained. Here we present observational evidence for the response of precipitation to sea ice reduction and assess the sensitivity of the response. Changes in the proportion of moisture sourced from the Arctic with sea ice change in the Canadian Arctic and Greenland Sea regions over the past two decades are inferred from annually averaged deuterium excess (d-excess) measurements from six sites. Other influences on the Arctic hydrologic cycle, such as the strength of meridional transport, are assessed using the North Atlantic Oscillation index. We find that the independent, direct effect of sea ice on the increase of the percentage of Arctic sourced moisture (or Arctic moisture proportion, AMP) is 18.2 ± 4.6% and 10.8 ± 3.6%/100,000 km2 sea ice lost for each region, respectively, corresponding to increases of 10.9 ± 2.8% and 2.7 ± 1.1%/1 °C of warming in the vapor source regions. The moisture source changes likely result in increases of precipitation and changes in energy balance, creating significant uncertainty for climate predictions. PMID:26699509
Bomb Cyclones Of The Western North Atlantic

NASA Astrophysics Data System (ADS)

Adams, Ryan E.

"Bomb" cyclones represent a small subset of mid-latitude cyclones characterized by rapid intensification and frequently are associated with extreme weather conditions along the eastern coast of North America. Like other extreme phenomena, bomb cyclone predictions are prone to error leading to inadequate or untimely hazard warnings. The rare nature of bomb cyclones and the uniqueness of their evolutions has made it difficult for researchers to make meaningful generalizations on bomb cyclone events. This paper describes bomb cyclone climatology for the western North Atlantic, using data from the NCEP-NCAR Reanalysis for 1948-2016, and uses a synoptic climatological analysis to relate these bombs to their associated atmospheric environments. A self-organizing map (SOM) of 300-hPa geopotential height tendency is created to partition the regional atmospheric environment. Thermodynamic fields are contrasted by each 300-hPa geopotential height tendency pattern for both bomb and non-bomb events in composite difference maps. The SOM patterns most significantly associated with western North Atlantic bomb cyclogenesis are characterized by both strongly and weakly negative height tendencies along the eastern United States. In both cases, these patterns exhibit strong meridional flow, a distinction marked by the weakening and breaking down of the polar vortex in the boreal Winter. The composite maps for each pattern show the mean differences in low-mid level ascent and near surface thermodynamics for bomb environments contrasted with non-bomb environments, resulting in diverse spatiotemporal distributions of bombs in the western North Atlantic.
The Effect of Seasonal Variability of Atlantic Water on the Arctic Sea Ice Cover

NASA Astrophysics Data System (ADS)

Ivanov, V. V.; Repina, I. A.

2018-01-01

Under the influence of global warming, the sea ice in the Arctic Ocean (AO) is expected to reduce with a transition toward a seasonal ice cover by the end of this century. A comparison of climate-model predictions with measurements shows that the actual rate of ice cover decay in the AO is higher than the predicted one. This paper argues that the rapid shrinking of the Arctic summer ice cover is due to its increased seasonality, while seasonal oscillations of the Atlantic origin water temperature create favorable conditions for the formation of negative anomalies in the ice-cover area in winter. The basis for this hypothesis is the fundamental possibility of the activation of positive feedback provided by a specific feature of the seasonal cycle of the inflowing Atlantic origin water and the peaking of temperature in the Nansen Basin in midwinter. The recently accelerated reduction in the summer ice cover in the AO leads to an increased accumulation of heat in the upper ocean layer during the summer season. The extra heat content of the upper ocean layer favors prerequisite conditions for winter thermohaline convection and the transfer of heat from the Atlantic water (AW) layer to the ice cover. This, in turn, contributes to further ice thinning and a decrease in ice concentration, accelerated melting in summer, and a greater accumulation of heat in the ocean by the end of the following summer. An important role is played by the seasonal variability of the temperature of AW, which forms on the border between the North European and Arctic basins. The phase of seasonal oscillation changes while the AW is moving through the Nansen Basin. As a result, the timing of temperature peak shifts from summer to winter, additionally contributing to enhanced ice melting in winter. The formulated theoretical concept is substantiated by a simplified mathematical model and comparison with observations.
Using NWP to assess the influence of the Arctic atmosphere on midlatitude weather and climate

NASA Astrophysics Data System (ADS)

Semmler, Tido; Jung, Thomas; Kasper, Marta A.; Serrar, Soumia

2018-01-01

The influence of the Arctic atmosphere on Northern Hemisphere midlatitude tropospheric weather and climate is explored by comparing the skill of two sets of 14-day weather forecast experiments using the ECMWF model with and without relaxation of the Arctic atmosphere towards ERA-Interim reanalysis data during the integration. Two pathways are identified along which the Arctic influences midlatitude weather: a pronounced one over Asia and Eastern Europe, and a secondary one over North America. In general, linkages are found to be strongest (weakest) during boreal winter (summer) when the amplitude of stationary planetary waves over the Northern Hemisphere is strongest (weakest). No discernible Arctic impact is found over the North Atlantic and North Pacific region, which is consistent with predominantly southwesterly flow. An analysis of the flow-dependence of the linkages shows that anomalous northerly flow conditions increase the Arctic influence on midlatitude weather over the continents. Specifically, an anomalous northerly flow from the Kara Sea towards West Asia leads to cold surface temperature anomalies not only over West Asia but also over Eastern and Central Europe. Finally, the results of this study are discussed in the light of potential midlatitude benefits of improved Arctic prediction capabilities.
Monitoring the North Atlantic using ocean colour data

NASA Astrophysics Data System (ADS)

Fuentes-Yaco, C.; Caverhill, C.; Maass, H.; Porter, C.; White, GN, III

2016-04-01

The Remote Sensing Unit (RSU) at the Bedford Institute of Oceanography (BIO) has been monitoring the North Atlantic using ocean colour products for decades. Optical sensors used include CZCS, POLDER, SeaWiFS, MODIS/Aqua and MERIS. The monitoring area is defined by the Atlantic Zone Monitoring Program (AZMP) but certain products extend into Arctic waters, and all-Canadian waters which include the Pacific coast. RSU provides Level 3 images for various products in several formats and a range of temporal and spatial resolutions. Basic statistics for pre-defined areas of interest are compiled for each product. Climatologies and anomaly maps are also routinely produced, and custom products are delivered by request. RSU is involved in the generation of Level 4 products, such as characterizing the phenology of spring and fall phytoplankton blooms, computing primary production, using ocean colour to aid in EBSA (Ecologically and Biologically Significant Area) definition and developing habitat suitability maps. Upcoming operational products include maps of diatom distribution, biogeochemical province boundaries, and products from sensors such as VIIRS (Visible Infrared Imaging Radiometer Suite), OLCI (Ocean Land Colour Instrument), and PACE (Pre-Aerosol, Clouds and ocean Ecosystem) hyperspectral microsatellite mission.
Elemental ratios and enrichment factors in aerosols from the US-GEOTRACES North Atlantic transects

NASA Astrophysics Data System (ADS)

Shelley, Rachel U.; Morton, Peter L.; Landing, William M.

2015-06-01

The North Atlantic receives the highest aerosol (dust) input of all the oceanic basins. Dust deposition provides essential bioactive elements, as well as pollution-derived elements, to the surface ocean. The arid regions of North Africa are the predominant source of dust to the North Atlantic Ocean. In this study, we describe the elemental composition (Li, Na, Mg, Al, P, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Cd, Sn, Sb, Cs, Ba, La, Ce, Nd, Pb, Th, U) of the bulk aerosol from samples collected during the US-GEOTRACES North Atlantic Zonal Transect (2010/11) in order to highlight the differences between a Saharan dust end-member and the reported elemental composition of the upper continental crust (UCC), and the implications this has for identifying trace element enrichment in aerosols across the North Atlantic basin. As aerosol titanium (Ti) is less soluble than aerosol aluminum (Al), it is a more conservative tracer for lithogenic aerosols and trace element-to-Ti ratios. However, the presence of Ti-rich fine aerosols can confound the interpretation of elemental enrichments, making Al a more robust tracer of aerosol lithogenic material in this region.
A note on Bjerkne's hypothesis for North Atlantic variability

NASA Astrophysics Data System (ADS)

Bryan, Kirk; Stouffer, Ron

1991-01-01

On decadal time-scales the historical surface temperature record over land in the Northern Hemisphere is dominated by polar amplified variations. These variations are coherent with SST anomalies concentrated in the Northwest Atlantic, but extending with lesser amplitude into the North Pacific as well. Bierknes suggested that multi-year SST anomalies in the subpolar North Atlantic were due to irregular changes in the intensity of the thermohaline circulation. In support of the Bjerknes hypothesis there is evidence that winter overturning in the Labrador Sea was suppressed for a brief period from 1967-1969 by a cap of relative fresh water at the surface. Cause and effect are unclear, but this event was associated with a marked cooling of the entire Northern Hemisphere. The difference in SST averaged over the Northern Hemisphere oceans and SST averaged over the Southern Hemisphere oceans from the equator to 40°S is coherent with Sahel summer rainfall on decadal time scales. Empirical evidence is supported by numerical experiments with the British Meteorological Office atmospheric climate model which simulate augmented monsoonal rainfall in the Sahel region of Africa in response to realistic warm SST anomalies in the Northwest Atlantic. A coupled ocean-atmosphere global model exhibits two equilibrium climate states. One has an active thermohaline circulation in the North Atlantic and the other does not. The two climate states provide an extreme example which illustrates the type of large scale air sea interaction Bjerknes visualized as a mechanism for North Atlantic climate variability on decadal time-scales.

Identification and Quantification of Regional Aerosol Trends and Impact on Clouds Over the North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Jongeward, Andrew R.

Aerosols and clouds contribute to atmospheric variability and Earth's radiative balance across local, regional, and global scales. Originating from both natural and anthropogenic sources, aerosols can cause adverse health effects and can interact directly with solar radiation as well as indirectly through complex interactions with clouds. Aerosol optical depth (AOD) has been observed from satellite platforms for over 30 years. During this time, regional changes in emissions, arising from air quality policies and socioeconomic factors, have been suggested as causes for some observed AOD trends. In the United States, the Clean Air Act and amendments have produced improvements in air quality. In this work the impacts of improved air quality on the aerosol loading and aerosol direct and indirect effects over the North Atlantic Ocean are explored using satellite, ground, and model datasets on the monthly timescale during 2002 to 2012. It is established that two trends exist in the total AOD observed by MODIS over the North Atlantic. A decreasing AOD trend between ?0.02 and ?0.04 per decade is observed over the mid-latitude region. Using the GOCART aerosol model it is shown that this trend results from decreases in anthropogenic species. Ground based aerosol networks (AERONET and IMPROVE) support a decreasing trend in AOD and further strengthen links to anthropogenic aerosol species, particularly sulfate species. This anthropogenic decrease occurs primarily during spring and summer. During the same time period, MODIS also observes an increasing AOD trend of 0.02 per decade located in the sub-tropical region. This trend is shown to occur during summer and is the result of natural dust aerosol. Changes in the North African environment seen in the MERRA reanalysis suggest an accelerated warming over the Saharan Desert leads to changes in the African Easterly Jet, related Easterly Waves, and baroclinicity playing a role in an increase and northward shift in African dust
Combined Effects of the North Atlantic Oscillation and the Arctic Oscillation on Sea Surface Temperature in the Alborán Sea

PubMed Central

Báez, José C.; Gimeno, Luis; Gómez-Gesteira, Moncho; Ferri-Yáñez, Francisco; Real, Raimundo

2013-01-01

We explored the possible effects of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) on interannual sea surface temperature (SST) variations in the Alborán Sea, both separately and combined. The probability of observing mean annual SST values higher than average was related to NAO and AO values of the previous year. The effect of NAO on SST was negative, while that of AO was positive. The pure effects of NAO and AO on SST are obscuring each other, due to the positive correlation between them. When decomposing SST, NAO and AO in seasonal values, we found that variation in mean annual SST and mean winter SST was significantly related to the mean autumn NAO of the previous year, while mean summer SST was related to mean autumn AO of the previous year. The one year delay in the effect of the NAO and AO on the SST could be partially related to the amount of accumulated snow, as we found a significant correlation between the total snow in the North Alborán watershed for a year with the annual average SST of the subsequent year. A positive AO implies a colder atmosphere in the Polar Regions, which could favour occasional cold waves over the Iberian Peninsula which, when coupled with precipitations favoured by a negative NAO, may result in snow precipitation. This snow may be accumulated in the high peaks and melt down in spring-summer of the following year, which consequently increases the runoff of freshwater to the sea, which in turn causes a diminution of sea surface salinity and density, and blocks the local upwelling of colder water, resulting in a higher SST. PMID:23638005
Shifting Surface Currents in the Northern North Atlantic Ocean

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Rhines, Peter B.

2007-01-01

Analysis of surface drifter tracks in the North Atlantic Ocean from the time period 1990 to 2006 provides the first evidence that the Gulf Stream waters can have direct pathways to the Nordic Seas. Prior to 2000, the drifters entering the channels leading to the Nordic Seas originated in the western and central subpolar region. Since 2001 several paths from the western subtropics have been present in the drifter tracks leading to the Rockall Trough through which the most saline North Atlantic Waters pass to the Nordic Seas. Eddy kinetic energy from altimetry shows also the increased energy along the same paths as the drifters, These near surface changes have taken effect while the altimetry shows a continual weakening of the subpolar gyre. These findings highlight the changes in the vertical structure of the northern North Atlantic Ocean, its dynamics and exchanges with the higher latitudes, and show how pathways of the thermohaline circulation can open up and maintain or increase its intensity even as the basin-wide circulation spins down.
Recent Increase in North Atlantic Jet Variability Emerges from Three-Century Long Context

NASA Astrophysics Data System (ADS)

Trouet, V.; Babst, F.; Meko, M. D.

2017-12-01

stream patterns and QRA as potential dynamic pathways for Arctic warming to influence midlatitude weather. Moreover, the synchronization of variance increases between the North Atlantic and North Pacific basins in the late 20th century is unprecedented over the last 290 years and strongly suggests an impact of anthropogenic warming.
Abrupt transitions to a cold North Atlantic in the late Holocene

NASA Astrophysics Data System (ADS)

Geirsdóttir, Áslaug; Miller, Gifford; Larsen, Darren; Florian, Christopher; Pendleton, Simon

2015-04-01

after settlement during the warmer Medieval times, there was little or no soil erosion. During the transition into the Little Ice Age (LIA), between 1250 and 1300 AD, soil erosion and landscape instability returned. A more severe drop in summer temperatures followed this initial LIA summer cooling, culminating between 1500 and 1900 AD. The Icelandic lake records compare favorably to paleo-environmental records from the North Atlantic such as the sea-ice reconstruction North of Iceland and ice-cap expansion dates based on a composite of Arctic Canada calibrated 14C dates on tundra plants emerging from beneath receding ice caps. Global modeling experiments suggest that changes in sea ice extent and duration provides one of the strongest feedbacks that may explain both the magnitude of the change and the abrupt nature of summer-cold departures over this time. An expansion of Arctic Ocean sea ice and its export into the North Atlantic subpolar gyre could have been a major amplifier of abrupt summertime cooling and a mechanism to explain persistent cold summers during the LIA in the northern North Atlantic.
Data-adaptive harmonic analysis and prediction of sea level change in North Atlantic region

NASA Astrophysics Data System (ADS)

Kondrashov, D. A.; Chekroun, M.

2017-12-01

This study aims to characterize North Atlantic sea level variability across the temporal and spatial scales. We apply recently developed data-adaptive Harmonic Decomposition (DAH) and Multilayer Stuart-Landau Models (MSLM) stochastic modeling techniques [Chekroun and Kondrashov, 2017] to monthly 1993-2017 dataset of Combined TOPEX/Poseidon, Jason-1 and Jason-2/OSTM altimetry fields over North Atlantic region. The key numerical feature of the DAH relies on the eigendecomposition of a matrix constructed from time-lagged spatial cross-correlations. In particular, eigenmodes form an orthogonal set of oscillating data-adaptive harmonic modes (DAHMs) that come in pairs and in exact phase quadrature for a given temporal frequency. Furthermore, the pairs of data-adaptive harmonic coefficients (DAHCs), obtained by projecting the dataset onto associated DAHMs, can be very efficiently modeled by a universal parametric family of simple nonlinear stochastic models - coupled Stuart-Landau oscillators stacked per frequency, and synchronized across different frequencies by the stochastic forcing. Despite the short record of altimetry dataset, developed DAH-MSLM model provides for skillful prediction of key dynamical and statistical features of sea level variability. References M. D. Chekroun and D. Kondrashov, Data-adaptive harmonic spectra and multilayer Stuart-Landau models. HAL preprint, 2017, https://hal.archives-ouvertes.fr/hal-01537797
The North Atlantic Oscillation and the ITCZ in a climate simulation

NASA Astrophysics Data System (ADS)

Cavalcanti, I. F. A.; Souza, P.

2009-04-01

The North Atlantic Oscillation (NAO) and the Atlantic Intertropical Convergence Zone (ITCZ) features are analyzed in a climate simulation with the CPTEC/COLA AGCM. The CPTEC/COLA AGCM reproduces the ITCZ seasonal north-south displacement as well as the seasonal east-west intensity, but the model overestimates the convection. The two phases of NAO are well simulated in the four seasons and also the largest intensity in DJF. The main mode of atmospheric variability considering the North and South Atlantic region, which displays a shifting of the NAO centers and a center of action over South Atlantic to the south of Africa is also reproduced. This mode, in DJF, is associated with the north-south ITCZ displacement in April, in the observed data. The displacement of the NAO centers southwestward allows the increase of pressure over the tropical North Atlantic Ocean and the increase of trade winds and displacement of the confluence and convergence zone southwards. The opposite occurs when the centers are displaced northeastward. The model Atlantic ITCZ position in April is associated with the anomalous (observed) Atlantic SST and the southward displacement of the confluence zone, but the simulated atmospheric features in DJF does not display the main mode of variability, as in the observations. This occurs due to the lack of interaction between the atmosphere and ocean in the atmospheric model. While in the observations the physical mechanism that links the NAO centers of action to the ITCZ position is the ocean-atmosphere interaction, from DJF to April, the atmospheric model responds to the prescribed SST at the same month, in April.
The role of local sea surface temperature pattern changes in shaping climate change in the North Atlantic sector

NASA Astrophysics Data System (ADS)

Hand, Ralf; Keenlyside, Noel S.; Omrani, Nour-Eddine; Bader, Jürgen; Greatbatch, Richard J.

2018-03-01

Beside its global effects, climate change is manifested in many regionally pronounced features mainly resulting from changes in the oceanic and atmospheric circulation. Here we investigate the influence of the North Atlantic SST on shaping the winter-time response to global warming. Our results are based on a long-term climate projection with the Max Planck Institute Earth System Model (MPI-ESM) to investigate the influence of North Atlantic sea surface temperature pattern changes on shaping the atmospheric climate change signal. In sensitivity experiments with the model's atmospheric component we decompose the response into components controlled by the local SST structure and components controlled by global/remote changes. MPI-ESM simulates a global warming response in SST similar to other climate models: there is a warming minimum—or "warming hole"—in the subpolar North Atlantic, and the sharp SST gradients associated with the Gulf Stream and the North Atlantic Current shift northward by a few a degrees. Over the warming hole, global warming causes a relatively weak increase in rainfall. Beyond this, our experiments show more localized effects, likely resulting from future SST gradient changes in the North Atlantic. This includes a significant precipitation decrease to the south of the Gulf Stream despite increased underlying SSTs. Since this region is characterised by a strong band of precipitation in the current climate, this is contrary to the usual case that wet regions become wetter and dry regions become drier in a warmer climate. A moisture budget analysis identifies a complex interplay of various processes in the region of modified SST gradients: reduced surface winds cause a decrease in evaporation; and thermodynamic, modified atmospheric eddy transports, and coastal processes cause a change in the moisture convergence. The changes in the the North Atlantic storm track are mainly controlled by the non-regional changes in the forcing. The impact of
Rapid subtropical North Atlantic salinity oscillations across Dansgaard-Oeschger cycles.

PubMed

Schmidt, Matthew W; Vautravers, Maryline J; Spero, Howard J

2006-10-05

Geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age, the Dansgaard-Oeschger cycles, were coupled to fluctuations in North Atlantic meridional overturning circulation through its regulation of poleward heat flux. The balance between cold meltwater from the north and warm, salty subtropical gyre waters from the south influenced the strength and location of North Atlantic overturning circulation during this period of highly variable climate. Here we investigate how rapid reorganizations of the ocean-atmosphere system across these cycles are linked to salinity changes in the subtropical North Atlantic gyre. We combine Mg/Ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four Dansgaard-Oeschger cycles (spanning 45.9-59.2 kyr ago) to generate a seawater salinity proxy record from a subtropical gyre deep-sea sediment core. We show that North Atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials, covarying with inferred shifts in the Tropical Atlantic hydrologic cycle and North Atlantic overturning circulation. These salinity oscillations suggest a reduction in precipitation into the North Atlantic and/or reduced export of deep salty thermohaline waters during stadials. We hypothesize that increased stadial salinities preconditioned the North Atlantic Ocean for a rapid return to deep overturning circulation and high-latitude warming by contributing to increased North Atlantic surface-water density on interstadial transitions.
Arctic sea-ice variability and its implication to the path of pollutants under a changing climate

NASA Astrophysics Data System (ADS)

Castro-Morales, K.; Gerdes, R.; Riemann-Campe, K.; Köberle, C.; Losch, M.

2012-04-01

The increasing concentration of pollutants from anthropogenic origin in the Arctic atmosphere, water, sediments and biota has been evident during the last decade. The sea-ice is an important vehicle for pollutants in the Arctic Ocean. Pollutants are taken up by precipitation and dry atmospheric deposition over the snow and ice cover during winter and released to the ocean during melting. Recent changes in the sea-ice cover of the Arctic Ocean affect the fresh water balance and the oceanic circulation, and with it, the fate of pollutants in the system. The Arctic Ocean is characterized by complex dynamics and strong stratification. Thus, to evaluate the current and future changes in the Arctic circulation high-resolution models are needed. As part of the EU FP7 project ArcRisk (under the scope of the IPY), we use a high resolution regional sea-ice-ocean coupled model covering the Arctic Ocean and the subpolar North Atlantic based on the Massachusetts Institute of Technology - circulation model (MITgcm). Under realistic atmospheric forcing we obtain hindcast results of circulation patterns for the period 1990 - 2010 for validation of the model. We evaluate possible consequences on the pathways and transport of contaminants by downscaling future climate scenario runs available in the coupled model intercomparison project (CMIP3) for the following fifty years. Particular interest is set in the Barents Sea. In this shallow region strong river runoff, sea-ice delivered from the interior of the Arctic Ocean and warm waters from the North Atlantic current are main sources of contaminants. Under a changing climate, a higher input of contaminants delivered to surface waters is expected, remaining in the interior of the Arctic Ocean in a strongly stratified water column remaining.
A high-resolution Holocene speleothem record from NE Romania: the nexus of Arctic and North Atlantic atmospheric circulations

NASA Astrophysics Data System (ADS)

Constantin, S.; Pourmand, A.; Moldovan, O.; Sharifi, A.; Mehterian, S.; Swart, P. K.

2017-12-01

The Romanian Carpathians act as a geomorphological barrier between different atmospheric circulation systems over Central and Eastern Europe; the NW of Romania lies under the remote influence of the North Atlantic oscillation, while the NE is influenced by the Arctic climate. In NW Romania, previous stable isotope studies of speleothems have not yielded a clear account of abrupt climate oscillations during the Holocene. Here we present results from a stalagmite collected from the Tauşoare Cave, located in NE Carpathians. The chronology of stalagmite T141 is based on 15 high-precision Th/U dates ranging between 32 and 1.1 ka with a continuous growth between 13.3 and 1.1 ka. The portion of the record within the Holocene was analyzed for δ18O and δ13C at a resolution ranging between 15 to 200 years/sample. The resulting δ18O record captures the Younger Dryas (YD) event centered at 12.9 ka, with δ18O values about 4 ‰ more depleted than those corresponding to the Holocene Climatic Optimum. The 8.2 ka event appears to be also captured in the record, although less prominent. The T141 isotope record is significantly different when compared to coeval records measured in speleothems from NW Carpathians, which do not exhibit marked changes during the YD or 8.2 ka events. This is likely due to the contrasting effect of temperature and atmospheric transport on δ18O signal in NW Romania. Within a distance of 200 km to the east, on the eastern flank of the Carpathian range, the δ18O signal of the Arctic circulation appears to be more prominent and clearly exhibits a positive relationship with temperature changes.
Introduction to: Atlantic Meridional Overturning Circulation(AMOC)

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa; Carton, James A.

2011-01-01

A striking conclusion of the Intergovernmental Panel on Climate Change 2007 report is the crucial role that the Atlantic Meridional Overturning Circulation (AMOC) may play in anthropogenic climate change. However, these IPCC coupled climate simulations show a broad range of uncertainty in the magnitude and timing of AMOC transport change ranging from none to nearly complete collapse within the 21st century. The potential consequences of large changes in the characteristics of AMOC have motivated the creation in the United States of an interagency program and implementation plan to develop monitoring and prediction capabilities for the AMOC This program parallels the development of substantial monitoring efforts by European, South American and African countries -- notably the UK Rapid and Rapid-Watch programs. The papers contained in this volume are derived from presentations at the First U.S. Atlantic Meridional Overturning Circulation (AMOC) Meeting held 4 - 6 May, 2009 to review the US implementation plan and its coordination with other monitoring activities. The Atlantic Meridional Overturning Circulation consists of multiple components illustrated in an attached figure. Water enters the South Atlantic at upper and intermediate depths through both western and eastern routes (where eddy transport is especially important) and is transported northward across the equator, where it recirculates within the northern subtropical and subpolar gyres. The northern end is defined by the sinking regions of the Nordic Seas and the Labrador Sea where the waters that eventually form the upper and lower branches of North Atlantic Deep Water are conditioned. High surface salinities, the result of high net evaporation in the tropics and subtropics (including the Mediterranean Sea), and presence of regions of the Arctic Ocean that remain ice-free even in winter allow for the rapid cooling and thus densification of surface water. This dense surface water becomes the source of deep
The Arctic: Glacial Refugium or Area of Secondary Contact? Inference from the Population Genetic Structure of the Thick-Billed Murre (Uria lomvia), with Implications for Management.

PubMed

Tigano, Anna; Damus, Martin; Birt, Tim P; Morris-Pocock, Jamie A; Artukhin, Yuri B; Friesen, Vicki L

2015-01-01

Quaternary glaciations affected the distribution of many species. Here, we investigate whether the Arctic represented a glacial refugium during the Last Glacial Maximum or an area of secondary contact following the ice retreat, by analyzing the genetic population structure of the thick-billed murre (Uria lomvia), a seabird that breeds throughout the North Atlantic, North Pacific and Arctic Oceans. The thick-billed murre is a species of socio-economic importance and faces numerous threats including hunting, oil pollution, gill netting, and climate change. We compared variation in the mitochondrial DNA (mtDNA) control region (n = 424), supplemented by 4 microsatellite loci (n = 445), among thick-billed murres sampled throughout their range. MtDNA data indicated that colonies comprise 4 genetically differentiated groups (Φst = 0.11-0.81): 1) Atlantic Ocean plus New Siberian Islands region, 2) Cape Parry, 3) Chukchi Sea, and 4) Pacific Ocean. Microsatellite variation differed between Atlantic and Pacific populations. Otherwise, little substructure was found within either ocean. Atlantic and Pacific populations appear to have been genetically isolated since the last interglacial period and should be considered separate evolutionary significant units for management. The Chukchi Sea and Cape Parry appear to represent areas of secondary contact, rather than arctic refugial populations. © The American Genetic Association 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.
North Atlantic Oscillation modulates total ozone winter trends

NASA Astrophysics Data System (ADS)

Appenzeller, Christof; Weiss, Andrea K.; Staehelin, Johannes

2000-04-01

The North Atlantic Oscillation (NAO) is modulating the Earth's ozone shield such that the calculated anthropogenic total ozone decrease is enhanced over Europe whereas over the North Atlantic region it is reduced (for the last 30 years). Including the NAO in a statistical model suggests a more uniform chemical winter trend compared to the strong longitudinal variation reported earlier. At Arosa (Switzerland) the trend is reduced to -2.4% per decade compared to -3.2% and at Reykjavik (Iceland) it is enhanced to -3.8% compared to 0%. The revised trend is slightly below the predictions by 2D chemical models. Decadal ozone variability is linked to variations in the dynamical structure of the atmosphere, as reflected in the tropopause pressure. The latter varies in concert with the NAO index with a distinct geographical pattern.
Towards an Ice-Free Arctic Ocean in Summertime

NASA Astrophysics Data System (ADS)

Gascard, Jean Claude

2014-05-01

Dividing the Arctic Ocean in two parts, the so-called Atlantic versus the Pacific sector, two distinct modes of variability appear for characterizing the Arctic sea-ice extent from 70°N up to 80°N in both sectors. The Atlantic sector seasonal sea-ice extent is characterized by a longer time scale than the Pacific sector with a break up melting season starting in May and reaching a peak in June-July, one month earlier than the Pacific sector of the Arctic Ocean revealing a faster time evolution and a larger spatial amplitude than the Atlantic sector. During recent years like 2007, sea-ice extent with sea-ice concentration above 15% retreated from 4 millions km2 to about 1 million km2 in the Arctic Pacific sector between 70° and 80°N except for 2012 when most of sea-ice melted away in this region. That explained most of the differences between the two extreme years 2007 and 2012. In the Atlantic sector, Arctic sea-ice retreated from 2 millions km2 to nearly 0 during recent years including 2007 and 2012. The Atlantic inflow North of Svalbard and Franz Josef Land is more likely responsible for a northward retreat of the ice edge in that region. The important factor is not only that the Arctic summer sea-ice minimum extent decreased by 3 or 4 millions km2 over the past 10 years but also that the melting period was steadily increasing by one to two days every year during that period. An important factor concerns the strength of the freezing that can be quantified in terms of Freezing Degree Days FDD accumulated during the winter-spring season and the strength of the melting (MDD) that can be accumulated during the summer season. FDD and MDD have been calculated for the past 30 years all over the Arctic Ocean using ERA Interim Reanalysis surface temperature at 2m height in the atmosphere. It is clear that FDD decreased significantly by more than 2000 FDD between 1980 and 2012 which is equivalent to the sensible heat flux corresponding to more than a meter of sea
Role of the North Atlantic Oscillation in decadal temperature trends

NASA Astrophysics Data System (ADS)

Iles, Carley; Hegerl, Gabriele

2017-11-01

Global temperatures have undergone periods of enhanced warming and pauses over the last century, with greater variations at local scales due to internal variability of the climate system. Here we investigate the role of the North Atlantic Oscillation (NAO) in decadal temperature trends in the Northern Hemisphere for periods with large decadal NAO trends. Using a regression based technique we find a best estimate that trends in the NAO more than halved (reduced by 57%, 5%-95%: 47%-63%) the winter warming over the Northern Hemisphere extratropics (NH; 30N-90N) from 1920-1971 and account for 45% (±14%) of the warming there from 1963-1995, with larger impacts on regional scales. Over the period leading into the so-called warming hiatus, 1989-2013, the NAO reduced NH winter warming to around one quarter (24%; 19%-31%) of what it would have been, and caused large negative regional trends, for example, in Northern Eurasia. Warming is more spatially uniform across the Northern Hemisphere after removing the NAO influence in winter, and agreement with multi-model mean simulated trends improves. The impact of the summer NAO is much weaker, but still discernible over Europe, North America and Greenland, with the downward trend in the summer NAO from 1988-2012 reducing warming by about a third in Northern Europe and a half in North America. A composite analysis using CMIP5 control runs suggests that the ocean response to prolonged NAO trends may increase the influence of decadal NAO trends compared to estimates based on interannual regressions, particularly in the Arctic. Results imply that the long-term NAO trends over the 20th century alternately masked or enhanced anthropogenic warming, and will continue to temporarily offset or enhance its effects in the future.
Salinity of the Early and Middle Eocene Arctic Ocean From Oxygen Isotope Analysis of Fish Bone Carbonate

NASA Astrophysics Data System (ADS)

Waddell, L. M.; Moore, T. C.

2006-12-01

Plate tectonic reconstructions indicate that the Arctic was largely isolated from the world ocean during the early and middle Eocene, with exchange limited to shallow, and possibly intermittent, connections to the North Atlantic and Tethys (via the Turgay Strait). Relative isolation, combined with an intensification of the hydrologic cycle under an Eocene greenhouse climate, is suspected to have led to the development of a low- salinity surface water layer in the Arctic that could have affected deep and intermediate convection in the North Atlantic. Sediment cores recently recovered from the Lomonosov Ridge by the IODP 302 Arctic Coring Expedition (ACEX) allow for the first assessment of the salinity of the Arctic Ocean during the early and middle Eocene. Stable isotope analysis performed on the structural carbonate of fish bone apatite from ~30 samples between the ages of ~55 and ~44 myr yielded δ18O values between -6.84‰ and -2.96‰ VPDB, with a mean value of -4.89‰. From the δ18O values we calculate that the Arctic Ocean was probably brackish during most of the early and middle Eocene, with an average salinity of 19 to 24‰. Negative excursions in the δ18O record (<-6‰) indicate three events during which the salinity of the Arctic surface waters was severely lowered: the Paleocene Eocene Thermal Maximum (PETM), the Azolla event at ~49 Ma, and a third previously unidentified event at ~46 Ma. During the PETM, low salinities developed under conditions of increased regional precipitation and runoff associated with extreme high latitude warmth and possible tectonic uplift in the North Atlantic. During the other two low-salinity events, sea level was lowered by ~20-30 m, implying a possible severing of Arctic connections to the world ocean. The most positive δ18O value (-2.96‰) occurs at ~45 Ma, the age of the youngest dropstone discovered in the ACEX sediments, and may therefore correspond to a climatic cooling rather than a high salinity event.
Impact of the North Atlantic dipole on climate changes over Eurasia

NASA Astrophysics Data System (ADS)

Serykh, Ilya

2017-04-01

Hydrophysical and meteorological characteristics of negative (1948-1976, 1999-2015) and positive (1977-1998) phases of the Pacific Decadal Oscillation (PDO) / Interdecadal Pacific Oscillation (IPO) in the North Atlantic and Eurasia are constructed and investigated. Specifically, the near-surface temperature, sea-level atmospheric pressure, wind speed, heat content of the upper 700 m ocean layer, water temperature and salinity at various depths, the latent and sensible heat fluxes from the ocean to the atmosphere are analyzed. The fields obtained from different sources (20thC_ReanV2c, ERA-20C, JRA-55, NCEP/NCAR, HadCRUT4, HadSLP2, NODC, Ishii, SODA, OAFlux, HadSST3, COBE2, ERSSTv4) are in good agreement and complement each other. This gives important information about the hydrometeorological conditions in the region under study. Analysis of these data has shown that in the upper 1000 m North Atlantic layer there is a thermal dipole which can be interpreted as an oceanic analog of the atmospheric North Atlantic Oscillation (NAO). An index of the North Atlantic Dipole (NAD) as the difference between the mean heat contents in the upper 700 m oceanic layer between the regions (50°-70° N; 60°-10° W) and (20°-40° N; 80°-30° W) is proposed. A possible physical mechanism of the internal oscillations with a quasi-60-year period in the North Atlantics-Eurasia system of ocean-atmosphere interactions is discussed. Dipole spatial structure from observations datasets and re-analyses were compared with the results of the Historical Experiment from the climate models of the CMIP5 project. It is found that several climate models reproduce dipole spatial structure of the near-surface temperature and sea level pressure anomalies similarly to these fields in the re-analyses considered. However, the phase diagrams of the gradient of near-surface temperature and sea level pressure between the Azores High and Island Low from climate models do not separate on subsets as the
Pathways of Atlantic Waters in the Nordic seas: locally eddy-permitting ocean simulation in a global setup

NASA Astrophysics Data System (ADS)

Wekerle, C.; Wang, Q.; Danilov, S.; Jung, T.; Schourup-Kristensen, V.

2016-02-01

Atlantic Water (AW) passes through the Nordic Seas and enters the Arctic Ocean through the shallow Barents Sea and the deep Fram Strait. Since the 1990's, observations indicate a series of anomalously warm pulses of Atlantic Water that entered the Arctic Ocean. In fact, poleward oceanic heat transport may even increase in the future, which might have implications for the heat uptake in the Arctic Ocean as well as for the sea ice cover. The ability of models to faithfully simulate the pathway of the AW and accompanying dynamics is thus of high climate relevance. In this study, we explore the potential of a global multi-resolution sea ice-ocean model with a locally eddy-permitting resolution (around 4.5 km) in the Nordic seas region and Arctic Ocean in improving the representation of Atlantic Water inflow, and more broadly, the dynamics of the circulation in the Northern North Atlantic and Arctic. The simulation covers the time period 1969-2009. We find that locally increased resolution improves the localization and thickness of the Atlantic Water layer in the Nordic seas, compared with a 20 km resolution reference simulation. In particular, the inflow of Atlantic Waters through the Greenland Scotland Ridge and the narrow branches of the Norwegian Atlantic Current can be realistically represented. Lateral spreading due to simulated eddies essentially reduces the bias in the surface temperature. In addition, a qualitatively good agreement of the simulated eddy kinetic energy field with observations can be achieved. This study indicates that a substantial improvement in representing local ocean dynamics can be reached through the local refinement, which requires a rather moderate computational effort. The successful model assessment allows us to further investigate the variability and mechanisms behind Atlantic Water transport into the Arctic Ocean.
Replacement cost valuation of Northern Pintail (Anas acuta) subsistence harvest in Arctic and sub-Arctic North America

USGS Publications Warehouse

Goldstein, Joshua H.; Thogmartin, Wayne E.; Bagstad, Kenneth J.; Dubovsky, James A.; Mattsson, Brady J.; Semmens, Darius J.; López-Hoffman, Laura; Diffendorfer, James E.

2014-01-01

Migratory species provide economically beneficial ecosystem services to people throughout their range, yet often, information is lacking about the magnitude and spatial distribution of these benefits at regional scales. We conducted a case study for Northern Pintails (hereafter pintail) in which we quantified regional and sub-regional economic values of subsistence harvest to indigenous communities in Arctic and sub-Arctic North America. As a first step, we used the replacement cost method to quantify the cost of replacing pintail subsistence harvest with the most similar commercially available protein (chicken). For an estimated annual subsistence harvest of ˜15,000 pintail, our mean estimate of the total replacement cost was ˜$63,000 yr−1 ($2010 USD), with sub-regional values ranging from \\$263 yr−1 to \\$21,930 yr−1. Our results provide an order-of-magnitude, conservative estimate of one component of the regional ecosystem-service values of pintails, providing perspective on how spatially explicit values can inform migratory species conservation.

Southern Greenland water vapour isotopic composition at the crossroads of Atlantic and Arctic moisture

NASA Astrophysics Data System (ADS)

Bonne, J. L.; Steen-Larsen, H. C.; Risi, C. M.; Werner, M.; Sodemann, H.; Lacour, J. L.; Fettweis, X.; Cesana, G.; Delmotte, M.; Cattani, O.; Clerbaux, C.; Sveinbjörnsdottir, A. E.; Masson-Delmotte, V.

2014-12-01

Since September 2011, a continuous water vapour isotopic composition monitoring instrument has been remotely operated in Ivittuut (61.21°N, 48.17°W), southern Greenland. Meteorological parameters are monitored and precipitation has been sampled and analysed for isotopic composition, suggesting equilibrium between surface vapour and precipitation. The data depict small summer diurnal variations. δ18O and deuterium excess (d-excess) are generally anti-correlated and show important seasonal variations (with respective amplitudes of 10 and 20 ‰), and large synoptic variations associated to low-pressure systems (typically +5‰ on δ18O and -15‰ on d-excess). The moisture sources, estimated based on Lagrangian back-trajectories, are primarily influenced by the western North Atlantic, and north-eastern American continent. Notable are important seasonal and synoptic shifts of the moisture sources, and sporadic influences of the Arctic or the eastern North Atlantic. Moisture sources variations can be related to changes in water vapour isotopic composition, and the isotopic fingerprints can be attributed to the areas of moisture origins. Isotopic enabled AGCMs nudged to meteorology (LMDZiso, ECHAM5-wiso), despite biases, correctly capture the δ18O changes, but underestimate the d-excess changes. They allow to identify a high correlation between the southern Greenland d-excess and the simulated relative humidity and d-excess in the moisture source region south of Greenland. An extreme high temperature event in July 2012 affecting all Greenland, similar to ice sheet melt events during the medieval periods and one event in 1889 documented by Greenland ice core records, has been analysed regarding water vapour isotopic composition, using remote sensing (IASI) and in situ observations from Bermuda to northern Greenland (NEEM station). Our southern Greenland observations allow to track the water vapour evolution during this event along the moisture transport path
Rare earth element transport in the western North Atlantic inferred from Nd isotopic observations

NASA Technical Reports Server (NTRS)

Piepgras, D. J.; Wasserburg, G. J.

1987-01-01

The relationship between the Nd isotopic composition in the Atlantic waters and the origin and circulation of the water masses was investigated. Samples were collected in the western North Atlantic between 7 and 54 deg N. The isotopic composition (Nd-143/Nd-144 ratios) showed extensive vertical structure at all locations. In regions where a thermocline was well-developed, large isotopic shifts were observed across the base of the thermocline, while regions without a thermocline were characterized by much more gradual shifts in isotopic composition with depth. The data reveal an excellent correlation between the Nd isotopic distribution in the western North Atlantic water column and the distribution of water masses identified from temperature and salinity measurements.
Limits on determining the skill of North Atlantic Ocean decadal predictions.

PubMed

Menary, Matthew B; Hermanson, Leon

2018-04-27

The northern North Atlantic is important globally both through its impact on the Atlantic Meridional Overturning Circulation (AMOC) and through widespread atmospheric teleconnections. The region has been shown to be potentially predictable a decade ahead with the skill of decadal predictions assessed against reanalyses of the ocean state. Here, we show that the prediction skill in this region is strongly dependent on the choice of reanalysis used for validation, and describe the causes. Multiannual skill in key metrics such as Labrador Sea density and the AMOC depends on more than simply the choice of the prediction model. Instead, this skill is related to the similarity between the nature of interannual density variability in the underlying climate model and the chosen reanalysis. The climate models used in these decadal predictions are also used in climate projections, which raises questions about the sensitivity of these projections to the models' innate North Atlantic density variability.
Pliocene planktic foraminifer census data from the North Atlantic region

USGS Publications Warehouse

,

1996-01-01

INTRODUCTION: The U.S. Geological Survey is conducting a long-term study of the climatic and oceanographic conditions of the Pliocene known as PRISM (Pliocene Research, Interpretation, and Synoptic Mapping). One of the major elements of the study involves the use of quantitative composition of planktic foraminifer assemblages to estimate seasurface temperatures and identify major oceanographic boundaries and water masses (Dowsett, 1991; Dowsett and Poore, 1991; Dowsett et al., 1992; Dowsett et al., 1994). We have analyzed more than 900 samples from 19 core sites in the North Atlantic Basin (Fig. 1) resulting in a large volume of raw census data. These data are presented here together to facilitate comparison of North Atlantic faunal assemblages. Latitude, longitude, water depth, source of faunal data and source of data used to construct age model (or publication from which age model was taken) are provided for each locality in Table 1. All ages refer to the geomagnetic polarity time scale of Berggren et al. (1985). Counts of species tabulated in each sample are given in Tables 2-20. DSDP and ODP sample designations are abbreviated in Tables 2-20 as core-section, depth within section in centimeters (eg. 10-5, 34 = core 10, section 5, 34 cm below top of section 5).
Phase Variability of the Recent Climate in the North Atlantic Region

NASA Astrophysics Data System (ADS)

Serykh, Ilya; Anisimov, Mikhail; Byshev, Vladimir; Neiman, Victor; Romanov, Juri; Sidorova, Alexandra

2014-05-01

2000-2012. The results shown that during the 1980-2000 period the heat content in the region (50º-60ºN; 60º-30ºW) was lower than in the 1955-1970, but higher in (30º-40ºN; 60º-30ºW) region. The data on sea water temperature, obtained as a result of numerical calculations based on the Ocean General Circulation Model (INM RAS), were used for estimate of ocean specific heat. The model is based on a complete system of nonlinear (primitive) equations describing ocean hydro- and thermodynamics in the Boussinesq approximation and written in a spherical σ-coordinate system. Numerical calculations were carried out with horizontal resolution (0.25ºx0.25º) and time step 1 hour. Boundary conditions on surface were taken from data array of CORE. Anomalies of specific heat relative to the mean annual variation in the layer from ocean surface up to 700m depth in North Atlantic region, calculated on model data and averaged for each period of (1959-1974), (1975-1999), (2000-2006), are in very close accordance with the results based on the accepted Levitus' data.
Climate and ecosystem linkages explain widespread declines in North American Atlantic salmon populations.

PubMed

Mills, Katherine E; Pershing, Andrew J; Sheehan, Timothy F; Mountain, David

2013-10-01

North American Atlantic salmon (Salmo salar) populations experienced substantial declines in the early 1990s, and many populations have persisted at low abundances in recent years. Abundance and productivity declined in a coherent manner across major regions of North America, and this coherence points toward a potential shift in marine survivorship, rather than local, river-specific factors. The major declines in Atlantic salmon populations occurred against a backdrop of physical and biological shifts in Northwest Atlantic ecosystems. Analyses of changes in climate, physical, and lower trophic level biological factors provide substantial evidence that climate conditions directly and indirectly influence the abundance and productivity of North American Atlantic salmon populations. A major decline in salmon abundance after 1990 was preceded by a series of changes across multiple levels of the ecosystem, and a subsequent population change in 1997, primarily related to salmon productivity, followed an unusually low NAO event. Pairwise correlations further demonstrate that climate and physical conditions are associated with changes in plankton communities and prey availability, which are ultimately linked to Atlantic salmon populations. Results suggest that poor trophic conditions, likely due to climate-driven environmental factors, and warmer ocean temperatures throughout their marine habitat area are constraining the productivity and recovery of North American Atlantic salmon populations. © 2013 John Wiley & Sons Ltd.
Atmospheric moisture transport: the bridge between ocean evaporation and Arctic ice melting

NASA Astrophysics Data System (ADS)

Gimeno, L.; Vázquez, M.; Nieto, R.; Trigo, R. M.

2015-09-01

Changes in the atmospheric moisture transport have been proposed as a vehicle for interpreting some of the most significant changes in the Arctic region. The increasing moisture over the Arctic during the last decades is not strongly associated with the evaporation that takes place within the Arctic area itself, despite the fact that the sea ice cover is decreasing. Such an increment is consistent and is more dependent on the transport of moisture from the extratropical regions to the Arctic that has increased in recent decades and is expected to increase within a warming climate. This increase could be due either to changes in circulation patterns which have altered the moisture sources, or to changes in the intensity of the moisture sources because of enhanced evaporation, or a combination of these two mechanisms. In this short communication we focus on the more objective assessment of the strong link between ocean evaporation trends and Arctic Sea ice melting. We will critically analyse several recent results suggesting links between moisture transport and the extent of sea ice in the Arctic, this being one of the most distinct indicators of continuous climate change both in the Arctic and on a global scale. To do this we will use a sophisticated Lagrangian approach to develop a more robust framework on some of these previous disconnecting results, using new information and insights. Results reached in this study stress the connection between two climate change indicators, namely an increase in evaporation over source regions (mainly the Mediterranean Sea, the North Atlantic Ocean and the North Pacific Ocean in the paths of the global western boundary currents and their extensions) and Arctic ice melting precursors.
Toward Skillful Subseasonal Prediction of North Atlantic Hurricanes with regionally-refined GFDL HiRAM

NASA Astrophysics Data System (ADS)

Gao, K.; Harris, L.; Chen, J. H.; Lin, S. J.

2017-12-01

Skillful subseasonal prediction of hurricane activity (from two weeks to less than a season) is important for early preparedness and reducing the hurricane damage in coastal regions. In this study, we will present evaluations of the performance of GFDL HiRAM (High-Resolution Atmospheric Model) for the simulation and prediction of the North Atlantic hurricane activity on the sub-seasonal time scale. A series of sub-seasonal (30-day duration) retrospective predictions were performed over the years 2000-2014 using two configurations of HiRAM: a) global uniform 25km-resolution grid and b) two-way nested grid with a 8km-resolution nest over North Atlantic. The analysis of hurricane structure from the two sets of simulations indicates the two-way-nesting method is an efficient way to improve the representation of hurricanes in global models: the two-way nested configuration produces realistic hurricane inner-core size and structure, which leads to improved lifetime maximum intensity distribution. Both configurations show very promising performance in the subseasonal hurricane genesis prediction, but the two-way nested configuration shows better performance in the prediction of major hurricane (Categories 3-5) activity because of the improved intensity simulation. We will also present the analysis of how the phase and magnitude of MJO, as well as the initial SST anomaly affect the model's prediction skill.
The North Atlantic Ocean as habitat for Calanus finmarchicus: Environmental factors and life history traits

NASA Astrophysics Data System (ADS)

Melle, Webjørn; Runge, Jeffrey; Head, Erica; Plourde, Stéphane; Castellani, Claudia; Licandro, Priscilla; Pierson, James; Jonasdottir, Sigrun; Johnson, Catherine; Broms, Cecilie; Debes, Høgni; Falkenhaug, Tone; Gaard, Eilif; Gislason, Astthor; Heath, Michael; Niehoff, Barbara; Nielsen, Torkel Gissel; Pepin, Pierre; Stenevik, Erling Kaare; Chust, Guillem

2014-12-01

Here we present a new, pan-Atlantic compilation and analysis of data on Calanus finmarchicus abundance, demography, dormancy, egg production and mortality in relation to basin-scale patterns of temperature, phytoplankton biomass, circulation and other environmental characteristics in the context of understanding factors determining the distribution and abundance of C. finmarchicus across its North Atlantic habitat. A number of themes emerge: (1) the south-to-north transport of plankton in the northeast Atlantic contrasts with north-to-south transport in the western North Atlantic, which has implications for understanding population responses of C. finmarchicus to climate forcing, (2) recruitment to the youngest copepodite stages occurs during or just after the phytoplankton bloom in the east whereas it occurs after the bloom at many western sites, with up to 3.5 months difference in recruitment timing, (3) the deep basin and gyre of the southern Norwegian Sea is the centre of production and overwintering of C. finmarchicus, upon which the surrounding waters depend, whereas, in the Labrador/Irminger Seas production mainly occurs along the margins, such that the deep basins serve as collection areas and refugia for the overwintering populations, rather than as centres of production, (4) the western North Atlantic marginal seas have an important role in sustaining high C. finmarchicus abundance on the nearby coastal shelves, (5) differences in mean temperature and chlorophyll concentration between the western and eastern North Atlantic are reflected in regional differences in female body size and egg production, (6) regional differences in functional responses of egg production rate may reflect genetic differences between western and eastern populations, (7) dormancy duration is generally shorter in the deep waters adjacent to the lower latitude western North Atlantic shelves than in the east, (8) there are differences in stage-specific daily mortality rates between
Reduced North American terrestrial primary productivity linked to anomalous Arctic warming

DOE PAGES

Kim, Jin-Soo; Kug, Jong-Seong; Jeong, Su-Jong; ...

2017-07-10

Warming temperatures in the Northern Hemisphere have enhanced terrestrial productivity. Despite the warming trend, North America has experienced more frequent and more intense cold weather events during winters and springs. These events have been linked to anomalous Arctic warming since 1990, and may affect terrestrial processes. Here we analyse many observation data sets and numerical model simulations to evaluate links between Arctic temperatures and primary productivity in North America. We find that positive springtime temperature anomalies in the Arctic have led to negative anomalies in gross primary productivity over most of North America during the last three decades, which amountmore » to a net productivity decline of 0.31 PgC yr -1 across the continent. This decline is mainly explained by two factors: severe cold conditions in northern North America and lower precipitation in the South Central United States. In addition, United States crop-yield data reveal that during years experiencing anomalous warming in the Arctic, yields declined by approximately 1 to 4% on average, with individual states experiencing declines of up to 20%. We conclude that the strengthening of Arctic warming anomalies in the past decades has remotely reduced productivity over North America.« less
Reduced North American terrestrial primary productivity linked to anomalous Arctic warming

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

Kim, Jin-Soo; Kug, Jong-Seong; Jeong, Su-Jong

Warming temperatures in the Northern Hemisphere have enhanced terrestrial productivity. Despite the warming trend, North America has experienced more frequent and more intense cold weather events during winters and springs. These events have been linked to anomalous Arctic warming since 1990, and may affect terrestrial processes. Here we analyse many observation data sets and numerical model simulations to evaluate links between Arctic temperatures and primary productivity in North America. We find that positive springtime temperature anomalies in the Arctic have led to negative anomalies in gross primary productivity over most of North America during the last three decades, which amountmore » to a net productivity decline of 0.31 PgC yr -1 across the continent. This decline is mainly explained by two factors: severe cold conditions in northern North America and lower precipitation in the South Central United States. In addition, United States crop-yield data reveal that during years experiencing anomalous warming in the Arctic, yields declined by approximately 1 to 4% on average, with individual states experiencing declines of up to 20%. We conclude that the strengthening of Arctic warming anomalies in the past decades has remotely reduced productivity over North America.« less
Relation between extinction and assisted colonization of plants in the arctic-alpine and boreal regions.

PubMed

Pykälä, Juha

2017-06-01

Assisted colonization of vascular plants is considered by many ecologists an important tool to preserve biodiversity threatened by climate change. I argue that assisted colonization may have negative consequences in arctic-alpine and boreal regions. The observed slow movement of plants toward the north has been an argument for assisted colonization. However, these range shifts may be slow because for many plants microclimatic warming (ignored by advocates of assisted colonization) has been smaller than macroclimatic warming. Arctic-alpine and boreal plants may have limited possibilities to disperse farther north or to higher elevations. I suggest that arctic-alpine species are more likely to be driven to extinction because of competitive exclusion by southern species than by increasing temperatures. If so, the future existence of arctic-alpine and boreal flora may depend on delaying or preventing the migration of plants toward the north to allow northern species to evolve to survive in a warmer climate. In the arctic-alpine region, preventing the dispersal of trees and shrubs may be the most important method to mitigate the negative effects of climate change. The purported conservation benefits of assisted colonization should not be used to promote the migration of invasive species by forestry. © 2016 Society for Conservation Biology.
Domain-averaged, Shallow Precipitation Measurements During the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA)

NASA Astrophysics Data System (ADS)

Lamer, K.; Luke, E. P.; Kollias, P.; Oue, M.; Wang, J.

2017-12-01

The Atmospheric Radiation Measurement (ARM) Climate Research Facility operates a fixed observatory in the Eastern North Atlantic (ENA) on Graciosa Island in the Azores. Straddling the tropics and extratropics, the Azores receive air transported from North America, the Arctic and sometimes Europe. At the ARM ENA site, marine boundary layer clouds are frequently observed all year round. Estimates of drizzle mass flux from the surface to cloud base height are documented using a combination of high sensitivity profiling 35-GHz radar and ceilometer observations. Three years of drizzle mass flux retrievals reveal that statistically, directly over the ENA site, marine boundary layer cloud drizzle rates tend to be weak with few heavy drizzle events. In the summer of 2017, this site hosted the first phase of the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA) field campaign, which is motivated by the need for comprehensive in situ characterization of boundary layer structure, low clouds and aerosols. During this phase, the 35-GHz scanning ARM cloud radar was operated as a surveillance radar, providing regional context for the profiling observations. While less sensitive, the scanning radar measurements document a larger number of heavier drizzle events and provide domain-representative estimates of shallow precipitation. A best estimate, domain averaged, shallow precipitation rate for the region around the ARM ENA site is presented. The methodology optimally combines the ability of the profiling observations to detect the weak but frequently occurring drizzle events with the scanning cloud radar's ability to capture the less frequent heavier drizzle events. The technique is also evaluated using high resolution model output and a sophisticated forward radar operator.
Twentieth century bipolar seesaw of the Arctic and Antarctic surface air temperatures

NASA Astrophysics Data System (ADS)

Chylek, Petr; Folland, Chris K.; Lesins, Glen; Dubey, Manvendra K.

2010-04-01

Understanding the phase relationship between climate changes in the Arctic and Antarctic regions is essential for our understanding of the dynamics of the Earth's climate system. In this paper we show that the 20th century de-trended Arctic and Antarctic temperatures vary in anti-phase seesaw pattern - when the Arctic warms the Antarctica cools and visa versa. This is the first time that a bi-polar seesaw pattern has been identified in the 20th century Arctic and Antarctic temperature records. The Arctic (Antarctic) de-trended temperatures are highly correlated (anti-correlated) with the Atlantic Multi-decadal Oscillation (AMO) index suggesting the Atlantic Ocean as a possible link between the climate variability of the Arctic and Antarctic regions. Recent accelerated warming of the Arctic results from a positive reinforcement of the linear warming trend (due to an increasing concentration of greenhouse gases and other possible forcings) by the warming phase of the multidecadal climate variability (due to fluctuations of the Atlantic Ocean circulation).
Bidecadal North Atlantic ocean circulation variability controlled by timing of volcanic eruptions.

PubMed

Swingedouw, Didier; Ortega, Pablo; Mignot, Juliette; Guilyardi, Eric; Masson-Delmotte, Valérie; Butler, Paul G; Khodri, Myriam; Séférian, Roland

2015-03-30

While bidecadal climate variability has been evidenced in several North Atlantic paleoclimate records, its drivers remain poorly understood. Here we show that the subset of CMIP5 historical climate simulations that produce such bidecadal variability exhibits a robust synchronization, with a maximum in Atlantic Meridional Overturning Circulation (AMOC) 15 years after the 1963 Agung eruption. The mechanisms at play involve salinity advection from the Arctic and explain the timing of Great Salinity Anomalies observed in the 1970s and the 1990s. Simulations, as well as Greenland and Iceland paleoclimate records, indicate that coherent bidecadal cycles were excited following five Agung-like volcanic eruptions of the last millennium. Climate simulations and a conceptual model reveal that destructive interference caused by the Pinatubo 1991 eruption may have damped the observed decreasing trend of the AMOC in the 2000s. Our results imply a long-lasting climatic impact and predictability following the next Agung-like eruption.
Biological and climate controls on North Atlantic marine carbon dynamics over the last millennium: Insights from an absolutely-dated shell based record from the North Icelandic Shelf

NASA Astrophysics Data System (ADS)

Hall, I. R.; Reynolds, D.; Scourse, J. D.; Richardson, C.; Wanamaker, A. D.; Butler, P. G.

2017-12-01

Given the rapid increase in atmospheric carbon dioxide concentrations (pCO2) over the industrial era there is a pressing need to construct longterm records of natural carbon cycling prior to this perturbation and to develop a more robust understanding of the role the oceans play in the sequestration of atmospheric carbon. Here we reconstruct the historical biological and climatic controls on the carbon isotopic (δ13C-shell) composition of the North Icelandic shelf waters over the last millennium derived from the shells of the long-lived marine bivalve mollusc Arctica islandica. Variability in the annually resolved δ13C-shell record is dominated by multi-decadal variability with a negative trend (-0.003±0.002‰yr-1) over the industrial era (1800-2000). This trend is consistent with the marine Suess effect brought about by the sequestration of isotopically light carbon (δ13C of CO2) derived from the burning of fossil fuels. Comparison of the δ13C-shell record with contemporary proxy archives, over the last millennium, and instrumental data over the 20th century, suggests that primary productivity and climate conditions over the sub-polar North Atlantic region played a vital role in driving inter-annual to multi-decadal scale variability in the δ13C-shell record. Our results highlight that relative shifts in the proportion of sub-polar mode waters and Arctic intermediate waters entrained onto the North Icelandic shelf, coupled with atmospheric circulation patterns associated with the winter North Atlantic Oscillation (wNAO), are the likely physical mechanisms that drive natural variations in seawater δ13C variability on the North Icelandic shelf.
North Atlantic sub-decadal variability in climate models

NASA Astrophysics Data System (ADS)

Reintges, Annika; Martin, Thomas; Latif, Mojib; Park, Wonsun

2017-04-01

The North Atlantic Oscillation (NAO) is the dominant variability mode for the winter climate of the North Atlantic sector. During a positive (negative) NAO phase, the sea level pressure (SLP) difference between the subtropical Azores high and the subpolar Icelandic low is anomalously strong (weak). This affects, for example, temperature, precipitation, wind, and surface heat flux over the North Atlantic, and over large parts of Europe. In observations we find enhanced sub-decadal variability of the NAO index that goes along with a dipolar sea surface temperature (SST) pattern. The corresponding SLP and SST patterns are reproduced in a control experiment of the Kiel Climate Model (KCM). Large-scale air-sea interaction is suggested to be essential for the North Atlantic sub-decadal variability in the KCM. The Atlantic Meridional Overturning Circulation (AMOC) plays a key role, setting the timescale of the variability by providing a delayed negative feedback to the NAO. The interplay of the NAO and the AMOC on the sub-decadal timescale is further investigated in the CMIP5 model ensemble. For example, the average CMIP5 model AMOC pattern associated with sub-decadal variability is characterized by a deep-reaching dipolar structure, similar to the KCM's sub-decadal AMOC variability pattern. The results suggest that dynamical air-sea interactions are crucial to generate enhanced sub-decadal variability in the North Atlantic climate.
Analysis of North Atlantic Aircraft Data on Oxygenated Intermediate Species Using an Adapted Regional Chemistry-Transport Model

NASA Technical Reports Server (NTRS)

Chatfield, Robert; Mathur, Rohit; Alapaty, Kiran; Hanna, Adel; Binkowski, Frank; Guan, Hong; Esswein, Robert

2004-01-01

Our study is on the interaction of nitrogen oxides with organics as they are exported from their complex sources in Eastern North America. Both urban and specific industrial emissions contribute the nitrogen of the C-H-O-N compounds that affect the global atmosphere, helping determine both ozone and the self-cleaning radical chemistry of the troposphere mediated by the OH radical. Different industrial sources, urban, and natural emissions contribute the organic C. Peroxyacetyl nitrate, CH3C(double bonds O)OONO2 is the most interesting compound for which we can measure the outflow to the full depth of the Atlantic troposphere. As we adapt the 3-d chemical model to describe outflow for specific periods with sufficient accuracy, we are analyzing some valuable information in the NARE-97 complete airborne dataset. (NARE: North Atlantic Regional Experiment). Ames researchers find that there are substantial puzzles in the ratios of PAN/NO2. Peroxy acetyl nitrate provides one of the major long-distance export pathways for active nitrogen from Eastern North America. It should be closely linked with NO, (defined as the sum NO + NO2) by simple thermal association and decomposition reactions, at least when the ambient temperature is substantially above 5 C.
Mechanisms and detectability of oxygen depletion in the North Atlantic

NASA Astrophysics Data System (ADS)

Tjiputra, J. F.; Goris, N.; Lauvset, S. K.; Schwinger, J.

2016-12-01

Dissolved oxygen is a key tracer in models used to represent the tight interaction between ocean biogeochemical cycle and circulation. Future ocean warming and stratification are projected, leading to a reduced oxygen concentration. Reduction in export production, in contrast, is projected to increase subsurface concentration by lowering the oxygen consumption during organic matter remineralization. In this exercise, we use a suite of CMIP5 models to study the oxygen evolution under the RCP8.5 scenario focusing on the North Atlantic, a region of rapid and steady circulation change. Most models agree with a large reduction in the deep North Atlantic (north of 40N), whereas an increase is projected in the upper subtropical ocean region. We attribute the former to weakening of the net primary production due to stronger stratification and the latter to less air-sea oxygen flux owing to less ventilation. The models also show that interior oxygen could provide earlier indicator of climate change than surface tracers. Sustained observation of oxygen is therefore crucial to reaffirm the ongoing circulation change due to global warming.
Atlantic Ocean CARINA data: overview and salinity adjustments

NASA Astrophysics Data System (ADS)

Tanhua, T.; Steinfeldt, R.; Key, R. M.; Brown, P.; Gruber, N.; Wanninkhof, R.; Perez, F.; Körtzinger, A.; Velo, A.; Schuster, U.; van Heuven, S.; Bullister, J. L.; Stendardo, I.; Hoppema, M.; Olsen, A.; Kozyr, A.; Pierrot, D.; Schirnick, C.; Wallace, D. W. R.

2009-08-01

Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon IN the Atlantic). The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the data products, i.e. three merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. Arctic, Atlantic and Southern Ocean. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report details of the secondary QC for salinity for this data set. Procedures of quality control - including crossover analysis between stations and inversion analysis of all crossover data - are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal accuracy of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA database is consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s (Key et al., 2004), and is now suitable for accurate assessments of, for example, oceanic carbon inventories and uptake rates and for model validation.

Large-Scale Antecedent Conditions Associated with 2014-2015 Winter Onset over North America and mid-Winter Storminess Along the North Atlantic Coast

NASA Astrophysics Data System (ADS)

Bosart, L. F.; Papin, P. P.; Bentley, A. M.; Benjamin, M.; Winters, A. C.

2015-12-01

Winter 2014-2015 was marked by the coldest November weather in 35 years east of the Rockies and record-breaking snowstorms and cold from the eastern Great Lakes to Atlantic Canada in January and February 2015. Record-breaking warmth prevailed across the Intermountain West and Rockies beneath a persistent upper-level ridge. Winter began with a series of arctic air mass surges that culminated in an epic lake-effect snowstorm occurred over western New York before Thanksgiving and was followed by a series of snow and ice storms that disrupted Thanksgiving holiday travel widely. Winter briefly abated in part of December, but returned with a vengeance between mid-January and mid-February 2015 when multiple extreme weather events that featured record-breaking monthly and seasonal snowfalls and record-breaking daily minimum temperatures were observed. This presentation will show how: (1) the recurvature and extratropical transition (ET) of Supertyphoon (STY) Nuri in the western Pacific in early November 2014, and its subsequent explosive reintensification as an extratropical cyclone (EC), disrupted the North Pacific jet stream and downstream Northern Hemisphere (NH) circulation, produced high-latitude ridging and the formation of an omega block over western North America, triggered downstream baroclinic development and the formation of a deep trough over eastern North America, and ushered in winter 2014-2015, (2) the ET/EC of STY Nuri increased subsequent week two predictability over the North Pacific and North America in association with diabatically influenced high-latitude ridge building, and (3) the amplification of the large-scale NH flow pattern beginning in January 2015 resulted in the formation of persistent high-amplitude ridges over northeastern Russia, Alaska, western North America, and the North Atlantic while deep troughs formed over the eastern North Pacific and eastern North America. This persistent amplified flow pattern supported the occurrence of frequent
Impacts of large-scale atmospheric circulation changes in winter on black carbon transport and deposition to the Arctic

NASA Astrophysics Data System (ADS)

Pozzoli, Luca; Dobricic, Srdan; Russo, Simone; Vignati, Elisabetta

2017-10-01

Winter warming and sea-ice retreat observed in the Arctic in the last decades may be related to changes of large-scale atmospheric circulation pattern, which may impact the transport of black carbon (BC) to the Arctic and its deposition on the sea ice, with possible feedbacks on the regional and global climate forcing. In this study we developed and applied a statistical algorithm, based on the maximum likelihood estimate approach, to determine how the changes of three large-scale weather patterns associated with increasing temperatures in winter and sea-ice retreat in the Arctic impact the transport of BC to the Arctic and its deposition. We found that two atmospheric patterns together determine a decreasing winter deposition trend of BC between 1980 and 2015 in the eastern Arctic while they increase BC deposition in the western Arctic. The increasing BC trend is mainly due to a pattern characterized by a high-pressure anomaly near Scandinavia favouring the transport in the lower troposphere of BC from Europe and North Atlantic directly into to the Arctic. Another pattern with a high-pressure anomaly over the Arctic and low-pressure anomaly over the North Atlantic Ocean has a smaller impact on BC deposition but determines an increasing BC atmospheric load over the entire Arctic Ocean with increasing BC concentrations in the upper troposphere. The results show that changes in atmospheric circulation due to polar atmospheric warming and reduced winter sea ice significantly impacted BC transport and deposition. The anthropogenic emission reductions applied in the last decades were, therefore, crucial to counterbalance the most likely trend of increasing BC pollution in the Arctic.
North Tropical Atlantic Climate Variability and Model Biases

NASA Astrophysics Data System (ADS)

Yang, Y.

2017-12-01

Remote forcing from El Niño-Southern Oscillation (ENSO) and local ocean-atmosphere feedback are important for climate variability over the North Tropical Atlantic. These two factors are extracted by the ensemble mean and inter-member difference of a 10-member Pacific Ocean-Global Atmosphere (POGA) experiment, in which sea surface temperatures (SSTs) are restored to the observed anomalies over the tropical Pacific but fully coupled to the atmosphere elsewhere. POGA reasonably captures main features of observed North Tropical Atlantic variability. ENSO forced and local North Tropical Atlantic modes (NTAMs) develop with wind-evaporation-SST feedback, explaining one third and two thirds of total variance respectively. Notable biases, however, exist. The seasonality of the simulated NTAM is delayed by one month, due to the late development of the North Atlantic Oscillation (NAO) in the model. A spurious band of enhanced sea surface temperature (SST) variance (SBEV) is identified over the northern equatorial Atlantic in POGA and 14 out of 23 CMIP5 models. The SBEV is especially pronounced in boreal spring and due to the combined effect of both anomalous atmospheric thermal forcing and oceanic vertical upwelling. While the tropical North Atlantic variability is only weakly correlated with the Atlantic Zonal Mode (AZM) in observations, the SBEV in CMIP5 produces conditions that drive and intensify the AZM variability via triggering the Bjerknes feedback. This partially explains why AZM is strong in some CMIP5 models even though the equatorial cold tongue and easterly trades are biased low.
Surface Salinity Variability in the North Atlantic During Recent Decades

NASA Technical Reports Server (NTRS)

Haekkinen, Sirpa

2001-01-01

The sea surface salinity (SSS) variability in the North Atlantic is investigated using numerical model simulations for the last 50 years based on atmospheric forcing variability from Comprehensive Atmosphere Ocean Data Set (COADS) and National Center for Environmental Prediction / National Center for Atmospheric Research (NCEP/NCAR) Reanalysis. The largest interannual and longer term variability occurs in two regions: the Labrador Sea and the North Equatorial Countercurrent (NECC) region. In both regions the seasonality of the surface salinity variability is prominent with the maximum standard deviation occurring in the summer/fall period. In the Labrador Sea the summer SSS anomalies far exceed those of wintertime in amplitude. The interannual SSS variability in the subpolar gyre can be attributed to two factors: excess ice melt and heat flux (i.e. deep mixing) variations. On the other hand, heat flux variability can also lead to meridional overturning changes on decadal time scales such that weak overturning is manifested in fresh surface conditions in the subpolar gyre. The overturning changes also influence the NECC region SSS variability. Moreover, the subpolar freshening events are expected to occur during the negative phase of North Atlantic Oscillation which is associated with a weak wintertime surface heat loss in the subpolar gyre. No excess sea ice melt or precipitation is necessary for the formation of the fresh anomalies, because with the lack of wide-spread deep mixing, the fresh water that would be expected based on climatology, would accumulate at the surface. Thus, the fresh water 'conveyor' in the Atlantic operates via the overturning circulation such that deep mixing inserts fresh water while removing heat from the water column.
Current State and Recent Changes in the Arctic Ocean from the HYCOM-NCODA Global Ocean and Sea Ice Prediction System

NASA Astrophysics Data System (ADS)

Dukhovskoy, D. S.; Chassignet, E. P.; Hogan, P. J.; Metzger, E. J.; Posey, P.; Smedstad, O. M.; Stefanova, L. B.; Wallcraft, A. J.

2016-12-01

The great potential of numerical models to provide a high-resolution continuous picture of the environmental characteristics of the Arctic system is related to the problem of reliability and accuracy of the simulations. Recent Arctic Ocean model intercomparison projects have identified substantial disagreements in water mass distribution and circulation among the models over the last two decades. In situ and satellite observations cannot yield enough continuous in time and space information to interpret the observed changes in the Arctic system. Observations combined with Arctic Ocean models via data assimilation provide perhaps the most complete knowledge about the state of the Arctic system. We use outputs from the US Navy Global Ocean Forecast System (20-year reanalysis + analysis) to investigate several hypotheses that have been put forward regarding the current state and recent changes in the Arctic Ocean. The system is based on the 0.08-degree HYbrid Coordinate Ocean Model (HYCOM) and can be run with two-way coupling to the Los Alamos Community Ice CodE (CICE) or with an energy-loan ice model. Observations are assimilated by the Navy Coupled Ocean Data Assimilation (NCODA) algorithm. HYCOM temperature and salinity fields are shown to be in good agreement with observational data in the Arctic and North Atlantic. The model reproduces changes in the freshwater budget in the Arctic as reported in other studies. The modeled freshwater fluxes between the Arctic Ocean and the North Atlantic are analyzed to document and discuss the interaction between the two regions over the last two decades.
The subpolar North Atlantic - Response to North Atlantic oscillation like forcing and Influence on the Atlantic meridional overturning circulation

NASA Astrophysics Data System (ADS)

Lohmann, Katja; Drange, Helge; Jungclaus, Johann

2010-05-01

The extent and strength of the North Atlantic subpolar gyre (SPG) changed rapidly in the mid-1990s, going from large and strong in 1995 to substantially weakened in the following years. The abrupt change in the intensity of the SPG is commonly linked to the reversal of the North Atlantic Oscillation (NAO) index, changing from strong positive to negative values, in the winter 1995/96. In this study we investigate the impact of the initial SPG state on its subsequent behavior by means of an ocean general circulation model driven by NCEP-NCAR reanalysis fields. Our sensitivity integrations suggest that the weakening of the SPG cannot be explained by the change in the atmospheric forcing alone. Rather, for the time period around 1995, the SPG was about to weaken, irrespective of the actual atmospheric forcing, due to the ocean state governed by the persistently strong positive NAO during the preceding seven years (1989 to 1995). Our analysis indicates that it was this preconditioning of the ocean, in combination with the sudden drop in the NAO in 1995/96, that lead to the strong and rapid weakening of the SPG in the second half of the 1990s. In the second part, the sensitivity of the low-frequency variability of the Atlantic meridional overturning circulation to changes in the subpolar North Atlantic is investigated using a 2000 year long control integration as well as sensitivity experiments with the MPI-M Earth System Model. Two 1000 year long sensitivity experiments will be performed, in which the low-frequency variability in the overflow transports from the Nordic Seas and in the subpolar deep water formation rates is suppressed respectively. This is achieved by nudging temperature and salinity in the GIN Sea or in the subpolar North Atlantic (up to about 1500m depth) towards a monthly climatology obtained from the last 1000 years of the control integration.
Solar wind: A possible factor driving the interannual sea surface temperature tripolar mode over North Atlantic

NASA Astrophysics Data System (ADS)

Xiao, Ziniu; Li, Delin

2016-06-01

The effect of solar wind (SW) on the North Atlantic sea surface temperature (SST) in boreal winter is examined through an analysis of observational data during 1964-2013. The North Atlantic SSTs show a pronounced meridional tripolar pattern in response to solar wind speed (SWS) variations. This pattern is broadly similar to the leading empirical orthogonal function (EOF) mode of interannual variations in the wintertime SSTs over North Atlantic. The time series of this leading EOF mode of SST shows a significant interannual period, which is the same as that of wintertime SWS. This response also appears as a compact north-south seesaw of sea level pressure and a vertical tripolar structure of zonal wind, which simultaneously resembles the North Atlantic Oscillation (NAO) in the overlying atmosphere. As compared with the typical low SWS winters, during the typical high SWS winters, the stratospheric polar night jet (PNJ) is evidently enhanced and extends from the stratosphere to the troposphere, even down to the North Atlantic Ocean surface. Notably, the North Atlantic Ocean is an exclusive region in which the SW signal spreads downward from the stratosphere to the troposphere. Thus, it seems that the SW is a possible factor for this North Atlantic SST tripolar mode. The dynamical process of stratosphere-troposphere coupling, together with the global atmospheric electric circuit-cloud microphysical process, probably accounts for the particular downward propagation of the SW signal.
Branching of Atlantic Water within the Greenland-Spitsbergen Passage: An estimate of recirculation

NASA Astrophysics Data System (ADS)

Manley, T. O.

1995-10-01

Atlantic Water (AW) supplies the largest source of heat, mass, and salt to the Arctic Ocean via Fram Strait (Greenland-Spitsbergen Passage), yet it represents only a fraction of the Atlantic Water that resides in the Greenland, Iceland, Norwegian, and Barents Seas. This is a result of both the branching of the central core of AW along its northward flow and the modification of its T-S signature through air-sea-ice interactions and internal mixing. This paper addresses the quantitative analysis of the three dominant Atlantic Water cores within Fram Strait and north of 76°N using an 11-year (1977 to 1987) hydrographic database. Spatial variations of heat, volume, and salt along its flow path of some 600 km showed that the major core of Atlantic Water that directly enters the Arctic Ocean (Svalbard branch) did not extend past 20°E. Of the 9719 km3 of Atlantic Water existing within the region, one third resided within the Svalbard branch; the remainder, 22% and 45%, were held within the Return Atlantic Current and the Yermak branches, respectively. Restricting the analysis to a southern limit of 79°N effectively removed the Return Atlantic Current and showed a nearly equal split between the two remaining branches. Work completed by Bourke et al. (1988) indicated that the Yermak branch is largely recirculated to the south; if true, this analysis supports Rudels' (1987) model estimate of a 50% recirculation of AW within this region.
North Atlantic Surface Winds Examined as the Source of Warm Advection into Europe in Winter

NASA Technical Reports Server (NTRS)

Otterman, J.; Angell, J. K.; Ardizzone, J.; Atlas, Robert; Schubert, S.; Starr, D.; Wu, M.-L.

2002-01-01

When from the southwest, North Atlantic ocean surface winds are known to bring warm and moist airmasses into central Europe in winter. By tracing backward trajectories from western Europe, we establish that these airmasses originate in the southwestern North Atlantic, in the very warm regions of the Gulf Stream. Over the eastern North Atlantic, Lt the gateway to Europe, the ocean-surface winds changed directions in the second half of the XXth century, those from the northwest and from the southeast becoming so infrequent, that the direction from the southwest became even more dominant. For the January-to-March period, the strength of south-westerlies in this region, as well as in the source region, shows in the years 1948-1995 a significant increase, above 0.2 m/sec/ decade. Based on the sensitivity of the surface temperature in Europe, slightly more than 1 C for a 1m/sec increase in the southwesterly wind, found in the previous studies, the trend in the warm advection accounts for a large part of the warming in Europe established for this period in several reports. However, for the most recent years, 1996-2001, the positive trend in the southwesterly advection appears to be is broken, which is consistent with unseasonally cold events reported in Europe in those winters. This study had, some bearing on evaluating the respective roles of the North Atlantic Oscillation and the Greenhouse Gas Global warming, GGG, in the strong winter warming observed for about half a century over the northern-latitude continents. Changes in the ocean-surface temperatures induced by GGG may have produced the dominant southwesterly direction of the North Atlantic winds. However, this implies a monotonically (apart from inherent interannual variability) increasing advection, and if the break in the trend which we observe after 1995 persists, this mechanism is counter-indicated. The 1948-1995 trend in the south-westerlies could then be considered to a large degree attributable to the
A new high-resolution kinematic model for the southern North Atlantic region: the Iberian plate kinematics since the Late Cretaceous

NASA Astrophysics Data System (ADS)

Macchiavelli, Chiara; Vergés, Jaume; Schettino, Antonio; Fernández, Manel; Turco, Eugenio; Torné, Montserrat; Casciello, Emilio

2017-04-01

We present the first high-resolution kinematic model for the southern North Atlantic since the late Cretaceous, in order to constrain the Iberian kinematics during the last 83 Myr. Assessing the detailed movements of the Iberian plate is crucial to constrain the kinematics of the Western Mediterranean region and to better understand the Pyrenees and Betic - Rif orogenic systems evolution. The new plate motions model for the Iberia - North America plate pair is accompanied by a high-resolution isochron map for the southern North Atlantic region, resulting from a re-examination of 400 ship tracks and 3 aeromagnetic tracks in the NGDC data base for the area between the Azores triple junction and 46° N. We derive a well-constrained kinematic solution for the relative motion between an independent Iberia and North America from seafloor spreading data despite the short length of the magnetic lineations and the scarcity of large-offset transform faults and fracture zones. Accurate finite reconstruction poles for the Iberia - North America conjugate plate pair between the Late Cretaceous (Chron 34, 83.5 Ma) and the present day (Chron 2A, 2.58 Ma) are calculated on the basis of a set of 100 magnetic profiles through an iterative method. Euler poles and associated angles of rotation are computed as follow. An initial rotation pole is calculated using only magnetic anomaly crossings. The initial large uncertainty associated with the first determination is reduced by generating a set of synthetic fracture zones associated with the initial pole and using points sampled along these structures in conjunction with magnetic anomaly crossings to calculate a new Euler pole and associated confidence ellipse. This procedure is repeated n times, generating a sequence of improving approximate solutions and stopped when the solution become stable excluding solutions that were inconsistent with geological constraints. We used these results to build a comprehensive kinematic model for the
Combined influences of seasonal East Atlantic Pattern and North Atlantic Oscillation to excite Atlantic multidecadal variability in a climate model

NASA Astrophysics Data System (ADS)

Ruprich-Robert, Yohan; Cassou, Christophe

2015-01-01

additional atmospheric-forced experiments, both are interpreted as the local seasonal-dependent atmospheric response to warmer North Atlantic. Finally, advection of fresher water from the tropical basin created by local atmosphere/ocean anomalous circulation on one hand and from the Arctic on the other hand due to large-scale sea ice melting leads to decrease of density in the SPG and contributes terminating the model AMOC/AMV events. All together, the combined effects of NAO and EAP, their intertwined seasonal forcing/forced role upon/by the ocean and the primary role of salinity anomalies associated with oceanic dynamical changes acting as an integrator are responsible in CNRM-CM5 for an irregular and damped mode of variability for AMOC/AMV that takes about 35-40 (15-20) years to build up (dissipate).
North American Biome

USDA-ARS?s Scientific Manuscript database

The North America biome includes the major ecoregions that make up the land area of Canada, the United States, Mexico, and countries in Central America. The biome is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the west and south by the Pacific Ocean, and to the s...
A Skilful Marine Sclerochronological Network Based Reconstruction of North Atlantic Subpolar Gyre Dynamics

NASA Astrophysics Data System (ADS)

Reynolds, D.; Hall, I. R.; Slater, S. M.; Scourse, J. D.; Wanamaker, A. D.; Halloran, P. R.; Garry, F. K.

2017-12-01

Spatial network analyses of precisely dated, and annually resolved, tree-ring proxy records have facilitated robust reconstructions of past atmospheric climate variability and the associated mechanisms and forcings that drive it. In contrast, a lack of similarly dated marine archives has constrained the use of such techniques in the marine realm, despite the potential for developing a more robust understanding of the role basin scale ocean dynamics play in the global climate system. Here we show that a spatial network of marine molluscan sclerochronological oxygen isotope (δ18Oshell) series spanning the North Atlantic region provides a skilful reconstruction of basin scale North Atlantic sea surface temperatures (SSTs). Our analyses demonstrate that the composite marine series (referred to as δ18Oproxy_PC1) is significantly sensitive to inter-annual variability in North Atlantic SSTs (R=-0.61 P<0.01) and surface air temperatures (SATs; R=-0.67, P<0.01) over the 20th century. Subpolar gyre (SPG) SSTs dominates variability in the δ18Oproxy_PC1 series at sub-centennial frequencies (R=-0.51, P<0.01). Comparison of the δ18Oproxy_PC1 series against variability in the strength of the European Slope Current and maximum North Atlantic meridional overturning circulation derived from numeric climate models (CMIP5), indicates that variability in the SPG region, associated with the strength of the surface currents of the North Atlantic, are playing a significant role in shaping the multi-decadal scale SST variability over the industrial era. These analyses demonstrate that spatial networks developed from sclerochronological archives can provide powerful baseline archives of past ocean variability that can facilitate the development of a quantitative understanding for the role the oceans play in the global climate systems and constraining uncertainties in numeric climate models.
The complex Chukchi Borderland region as part of the Arctic Alaska extended margin

NASA Astrophysics Data System (ADS)

Saltus, R.; Hutchinson, D. R.; Miller, E. L.

2017-12-01

The Chukchi Borderland region (CBR; includes the Chukchi Plateau and its surrounding component elevations) is a physiographically complex and somewhat enigmatic seafloor high adjacent to the broad Chukchi Shelf in the Alaska/Chukotka quadrant of the Amerasian Basin beneath the Arctic Ocean. The CBR includes several physiographic sub-components including the relatively high-standing Northwind Ridge and Northwind Plain as well as a lower-standing northern region (here called the North Chukchi Component Elevation or NCCE) that consists of several un-named knolls, ramps, and benches. The CBR shows numerous N-S physiographic features including ridges and escarpments related to extension. The CBR adjoins the Chukchi Shelf to the south, abuts the Canada Basin to the east, and is separated on the west and north from the Mendeleev and Alpha Ridges by the Chukchi Plain, the Mendeleev Plain, and the Nautilus Basin. Available geophysical data, comparative physiography/geomorphology, and geologic analysis show that the CBR is continuous with Arctic Alaska and the adjoining Chukchi Shelf. CBR, Arctic Alaska, and the Chukchi Shelf share common early Paleozoic basement elements as well as Ellesmerian and younger cover sequences. The CBR owes its complex physiographic and structural character to its central location relative to the multiple extensional domains associated with the multi-stage rift formation of the Amerasian Basin, large igneous province-influenced volcanism associated with the Alpha and Mendeleev regions on the north and west, and hyper-extension of continental crust to the east in the deep Canada Basin. The CBR is often portrayed as an independent tectonic element within Arctic tectonic reconstructions, but we argue that models for the formation of the Amerasian Basin should include the CBR as an integral component of the Arctic Alaska microplate.
Predictability of North Atlantic Multidecadal Climate Variability

PubMed

Griffies; Bryan

1997-01-10

Atmospheric weather systems become unpredictable beyond a few weeks, but climate variations can be predictable over much longer periods because of the coupling of the ocean and atmosphere. With the use of a global coupled ocean-atmosphere model, it is shown that the North Atlantic may have climatic predictability on the order of a decade or longer. These results suggest that variations of the dominant multidecadal sea surface temperature patterns in the North Atlantic, which have been associated with changes in climate over Eurasia, can be predicted if an adequate and sustainable system for monitoring the Atlantic Ocean exists.
Effects of Climate Change on the Freshwaters of Arctic and Subarctic North America

NASA Astrophysics Data System (ADS)

Rouse, Wayne R.; Douglas, Marianne S. V.; Hecky, Robert E.; Hershey, Anne E.; Kling, George W.; Lesack, Lance; Marsh, Philip; McDonald, Michael; Nicholson, Barbara J.; Roulet, Nigel T.; Smol, John P.

1997-06-01

Region 2 comprises arctic and subarctic North America and is underlain by continuous or discontinuous permafrost. Its freshwater systems are dominated by a low energy environment and cold region processes. Central northern areas are almost totally influenced by arctic air masses while Pacific air becomes more prominent in the west, Atlantic air in the east and southern air masses at the lower latitudes. Air mass changes will play an important role in precipitation changes associated with climate warming. The snow season in the region is prolonged resulting in long-term storage of water so that the spring flood is often the major hydrological event of the year, even though, annual rainfall usually exceeds annual snowfall. The unique character of ponds and lakes is a result of the long frozen period, which affects nutrient status and gas exchange during the cold season and during thaw. GCM models are in close agreement for this region and predict temperature increases as large as 4°C in summer and 9°C in winter for a 2 × CO2 scenario. Palaeoclimate indicators support the probability that substantial temperature increases have occurred previously during the Holocene. The historical record indicates a temperature increase of > 1°C in parts of the region during the last century. GCM predictions of precipitation change indicate an increase, but there is little agreement amongst the various models on regional disposition or magnitude. Precipitation change is as important as temperature change in determining the water balance. The water balance is critical to every aspect of hydrology and limnology in the far north. Permafrost close to the surface plays a major role in freshwater systems because it often maintains lakes and wetlands above an impermeable frost table, which limits the water storage capabilities of the subsurface. Thawing associated with climate change would, particularly in areas of massive ice, stimulate landscape changes, which can affect every aspect
A new Calibrated Deglacial Drainage History for North America and Evidence for an Arctic Trigger for the Younger Dryas

NASA Astrophysics Data System (ADS)

Tarasov, L.; Peltier, W. R.

2004-05-01

We present a new deglacial drainage history for the North American ice complex using the 3D University of Toronto glacial systems model calibrated against a large set of RSL and geodetic data. During melt-water pulse 1a, large order 0.15 to 0.2 Sverdrup century-scale melt-water discharges into both the Gulf of Mexico and western Atlantic occur. During this period, it has generally been inferred that strong thermohaline overturning circulation (TOC) was maintained. As such, our results suggest that the TOC is relatively insensitive to injection of melt-water into the Western Atlantic. In contrast with past inferences, we find the periods of strongest combined melt-water and ice calving discharge (with peak flows of order 0.2 Sverdrups over a century) into the NW Arctic to be during both the onset of and within the Younger Dryas. Model results also show no significant freshwater flux into the Western Atlantic during the Younger Dryas onset period. Given that the Greenland-Iceland-Norwegian (GIN) seas basin was the only outlet route for Arctic waters at this time, we infer that some combination of reduced Canadian Basin sea surface salinities in combination with enhanced sea-ice export into the GIN seas basin played a critical role in triggering and sustaining the altered TOC that is believed to be responsible for the Younger Dryas cold interval. We also speculate that the prior lack of such large discharges into the Canadian Arctic Basin may explain the apparent uniqueness of the Younger Dryas interval.
Mesoscale eddies control meridional heat flux variability in the subpolar North Atlantic

NASA Astrophysics Data System (ADS)

Zhao, Jian; Bower, Amy; Yang, Jiayan; Lin, Xiaopei; Zhou, Chun

2017-04-01

The meridional heat flux in the subpolar North Atlantic is vital to the climate of the high-latitude North Atlantic. For the basinwide heat flux across a section between Greenland and Scotland, much of the variability occurs in the Iceland basin, where the North Atlantic Current (NAC) carries relatively warm and salty water northward. As a component of the Overturning in the Subpolar North Atlantic Program (OSNAP), WHOI and OUC are jointly operating gliders in the Iceland Basin to continuously monitor the circulation and corresponding heat flux in this eddy-rich region. Based on one year of observations, two circulation regimes in the Iceland basin have been identified: a mesoscale eddy like circulation pattern and northward NAC circulation pattern. When a mesoscale eddy is generated, the rotational currents associated with the eddy lead to both northward and southward flow in the Iceland basin. This is quite different from the broad northward flow associated with the NAC when there is no eddy. The transition between the two regimes coupled with the strong temperature front in the Iceland basin can modify the meridional heat flux on the order of 0.3PW, which is the dominant source for the heat flux change the Iceland Basin. According to high-resolution numerical model results, the Iceland Basin has the largest contribution to the meridional heat flux variability along the section between Greenland and Scotland. Therefore, mesoscale eddies in the Iceland Basin provide important dynamics to control the meridional heat flux variability in the subpolar North Atlantic.
Surface temperatures of the Mid-Pliocene North Atlantic Ocean: Implications for future climate

USGS Publications Warehouse

Dowsett, Harry J.; Chandler, Mark A.; Robinson, Marci M.

2009-01-01

The Mid-Pliocene is the most recent interval in the Earth's history to have experienced warming of the magnitude predicted for the second half of the twenty-first century and is, therefore, a possible analogue for future climate conditions. With continents basically in their current positions and atmospheric CO2 similar to early twenty-first century values, the cause of Mid-Pliocene warmth remains elusive. Understanding the behaviour of the North Atlantic Ocean during the Mid-Pliocene is integral to evaluating future climate scenarios owing to its role in deep water formation and its sensitivity to climate change. Under the framework of the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) sea surface reconstruction, we synthesize Mid-Pliocene North Atlantic studies by PRISM members and others, describing each region of the North Atlantic in terms of palaeoceanography. We then relate Mid-Pliocene sea surface conditions to expectations of future warming. The results of the data and climate model comparisons suggest that the North Atlantic is more sensitive to climate change than is suggested by climate model simulations, raising the concern that estimates of future climate change are conservative.
Solar forcing synchronizes decadal North Atlantic climate variability.

PubMed

Thiéblemont, Rémi; Matthes, Katja; Omrani, Nour-Eddine; Kodera, Kunihiko; Hansen, Felicitas

2015-09-15

Quasi-decadal variability in solar irradiance has been suggested to exert a substantial effect on Earth's regional climate. In the North Atlantic sector, the 11-year solar signal has been proposed to project onto a pattern resembling the North Atlantic Oscillation (NAO), with a lag of a few years due to ocean-atmosphere interactions. The solar/NAO relationship is, however, highly misrepresented in climate model simulations with realistic observed forcings. In addition, its detection is particularly complicated since NAO quasi-decadal fluctuations can be intrinsically generated by the coupled ocean-atmosphere system. Here we compare two multi-decadal ocean-atmosphere chemistry-climate simulations with and without solar forcing variability. While the experiment including solar variability simulates a 1-2-year lagged solar/NAO relationship, comparison of both experiments suggests that the 11-year solar cycle synchronizes quasi-decadal NAO variability intrinsic to the model. The synchronization is consistent with the downward propagation of the solar signal from the stratosphere to the surface.

Regime shifts in the northern North Atlantic during the past 6,000 years: A record of seabird population size and precipitation isotopes on Bjørnøya, Svalbard

NASA Astrophysics Data System (ADS)

D'Andrea, W. J.; Hormes, A.; Bakke, J.; Nicolaisen, L.

2015-12-01

The northeastern North Atlantic Ocean, and the Norwegian and Greenland Seas are subject to large hydrographic changes. These variations can influence oceanic heat transport to the Arctic, meridional overturning circulation, and atmospheric circulation patterns and thereby impact global climate patterns. Marine records suggest that numerous large-scale changes in the hydrography of the northern North Atlantic took place during the middle to late Holocene. Here, we report a record of nitrogen and hydrogen isotope measurements from a lake sediment core from Bjørnøya, Svalbard (74.38°N, 19.02°E) that documents major regime shifts in the climate of the northern North Atlantic during the past 6,000 years. Bjørnøya is the nesting ground for one of the largest seabird populations in the North Atlantic. As top predators in the marine ecosystem, seabirds (and their guano) are enriched in 15N; during spring and summer months they deliver this isotopically enriched nitrogen to their nesting area. We developed a record of seabird population changes on Bjørnøya based on the bulk nitrogen isotope composition of sediments in a core collected from lake Ellasjøen. The record reveals multiple multicentennial scale changes in δ15N values (varying between ~8-12‰) that track past changes in the size of seabird populations. From the same sediment core, we also developed a record of δD of precipitation, by measuring δD values of sedimentary n-alkanes. Past intervals with the largest inferred bird populations correspond with the most enriched δD of precipitation, which we interpret to represent a more Atlantic climate. Periods with reduced seabird populations correspond with intervals having more negative δD of precipitation and representing a more Arctic climate. Together, the nitrogen and hydrogen isotope records signify regime shifts in the oceanography, marine ecosystem, and atmospheric circulation of the northern North Atlantic that are related to variations in the
Composition and structure of the parasite faunas of cod, Gadus morhua L. (Teleostei: Gadidae), in the North East Atlantic.

PubMed

Perdiguero-Alonso, Diana; Montero, Francisco E; Raga, Juan Antonio; Kostadinova, Aneta

2008-07-18

Although numerous studies on parasites of the Atlantic cod, Gadus morhua L. have been conducted in the North Atlantic, comparative analyses on local cod parasite faunas are virtually lacking. The present study is based on examination of large samples of cod from six geographical areas of the North East Atlantic which yielded abundant baseline data on parasite distribution and abundance. A total of 826 fish was sampled in the Baltic, Celtic, Irish and North seas, Icelandic waters and Trondheimsfjord (Norway) in 2002 (spring and autumn) and 2003 (spring). The gills and internal organs (oesophagus, stomach, intestine, pyloric caeca, liver, heart, spleen, gall bladder and gonads) were examined for macroparasites following a standardised protocol. The taxonomic consistency of the identification was ensured thorough the entire study. We discuss some problems in parasite identification, outline the composition of the parasite faunas in cod in the six North East Atlantic regions, provide novel data on parasite prevalence and abundance and a comparative assessment of the structure of the regional parasite faunas with respect to the higher-level taxonomic groupings, host specificity and zoogeographical distribution of the parasites. Altogether 57 different parasite forms were found including seven new host records (Diclidophora merlangi, Rhipidocotyle sp., Fellodistomum sp., Steringotrema sp., Cucullanus sp., Spinitectus sp., and Chondracanthus ornatus). The predominant groups of cod parasites were trematodes (19 species) and nematodes (13 species) including larval anisakids which comprised 58.2% of the total number of individuals. Our study reveals relatively rich regional parasite faunas in cod from the North East Atlantic which are dominated by generalist parasites with Arcto-Boreal distribution. Further, it provides more detailed data on the distribution in the North East Atlantic of the majority of cod parasites which may serve as baselines for future studies on the
CHARACTERIZATION OF WESTERN NORTH ATLANTIC RIGHT WHALE SPRING FEEDING HABITAT

EPA Science Inventory

The Great South Channel region of the southwestern Gulf of Maine, between George's Bank and Cape Cod, is the primary spring feeding ground for the western North Atlantic population of the I northern right whale, E. glacialis .Since this whale is so endangered, it is critical to i...
Structural-tectonic zoning of the Arctic

NASA Astrophysics Data System (ADS)

Petrov, Oleg; Sobolev, Nikolay; Morozov, Andrey; Shokalsky, Sergey; Kashubin, Sergey; Grikurov, Garrik; Tolmacheva, Tatiana; Rekant, Pavel; Petrov, Evgeny

2017-04-01

Structural-tectonic zoning of the Arctic is based on the processing of geological and geophysical data and bottom sampling materials produced within the project "Atlas of Geological Maps of the Circumpolar Arctic." Zoning of the Arctic territories has been conducted taking into account the Earth's crust types, age of consolidated basement, and features of geological structure of the sedimentary cover. Developed legend for the zoning scheme incorporates five main groups of elements: continental and oceanic crust, folded platform covers, accretion-collision systems, and provinces of continental cover basalts. An important feature of the structural-tectonic zoning scheme is designation of continental crust in the central regions of the Arctic Ocean, the existence of which is assumed on the basis of numerous geological data. It has been found that most of the Arctic region has continental crust with the exception of the Eurasian Basin and the central part of the Canada Basin, which are characterized by oceanic crust type. Thickness of continental crust from seismic data varies widely: from 30-32 km on the Mendeleev Rise to 18-20 km on the Lomonosov Ridge, decreasing to 8-10 km in rift structures of the Podvodnikov-Makarov Basin at the expense of reduction of the upper granite layer. New data confirm similar basement structure on the western and eastern continental margins of the Eurasian oceanic basin. South to north, areas of Neoproterozoic (Baikalian) and Paleozoic (Ellesmerian) folding are successively distinguished. Neoproterozoic foldbelt is observed in Central Taimyr (Byrranga Mountains). Continuation of this belt in the eastern part of the Arctic is Novosibirsk-Chukchi fold system. Ellesmerian orogen incorporates the northernmost areas of Taimyr and Severnaya Zemlya, wherefrom it can be traced to the Geofizikov Spur of the Lomonosov Ridge and further across the De Long Archipelago and North Chukchi Basin to the north of Alaska Peninsula and in the Beaufort Sea
Nonmethane Hydrocarbon Measurements on the North Atlantic Flight Corridor During SONEX

NASA Technical Reports Server (NTRS)

Simpson, I. J.; Sive, B. C.; Blake, D. R.; Blake, N. J.; Chen, T.-Y.; Lopez, J. P.; Sachse, G. W.; Vay, S. A.; Fuelberg, H. E.; Kondo, Y.

1999-01-01

Mixing ratios of nonmethane hydrocarbons (NMHCS) were not enhanced in whole air samples collected within the North Atlantic Flight Corridor (NAFC) during the fall of 1997. The investigation was conducted aboard NASA's DC-8 research aircraft, as part of the Subsonic Assessment-Ozone and Nitrogen Experiment (SONEX). NMHC enhancements were not detected within the general Organized Tracking System (OTS) of the NAFC, nor during two tail-chases of the DC-8's own exhaust. Because positive evidence of aircraft emissions was demonstrated by enhancements in both nitrogen oxides and condensation nuclei during SONEX, the NMHC results suggest that the commercial air traffic fleet operating in the North Atlantic region does not contribute significantly to NMHCs in the NAFC.
Rapid Arctic Changes due to Infrastructure and Climate (RATIC) in the Russian North

NASA Astrophysics Data System (ADS)

Walker, D. A.; Kofinas, G.; Raynolds, M. K.; Kanevskiy, M. Z.; Shur, Y.; Ambrosius, K.; Matyshak, G. V.; Romanovsky, V. E.; Kumpula, T.; Forbes, B. C.; Khukmotov, A.; Leibman, M. O.; Khitun, O.; Lemay, M.; Allard, M.; Lamoureux, S. F.; Bell, T.; Forbes, D. L.; Vincent, W. F.; Kuznetsova, E.; Streletskiy, D. A.; Shiklomanov, N. I.; Fondahl, G.; Petrov, A.; Roy, L. P.; Schweitzer, P.; Buchhorn, M.

2015-12-01

The Rapid Arctic Transitions due to Infrastructure and Climate (RATIC) initiative is a forum developed by the International Arctic Science Committee (IASC) Terrestrial, Cryosphere, and Social & Human working groups for developing and sharing new ideas and methods to facilitate the best practices for assessing, responding to, and adaptively managing the cumulative effects of Arctic infrastructure and climate change. An IASC white paper summarizes the activities of two RATIC workshops at the Arctic Change 2014 Conference in Ottawa, Canada and the 2015 Third International Conference on Arctic Research Planning (ICARP III) meeting in Toyama, Japan (Walker & Pierce, ed. 2015). Here we present an overview of the recommendations from several key papers and posters presented at these conferences with a focus on oil and gas infrastructure in the Russian north and comparison with oil development infrastructure in Alaska. These analyses include: (1) the effects of gas- and oilfield activities on the landscapes and the Nenets indigenous reindeer herders of the Yamal Peninsula, Russia; (2) a study of urban infrastructure in the vicinity of Norilsk, Russia, (3) an analysis of the effects of pipeline-related soil warming on trace-gas fluxes in the vicinity of Nadym, Russia, (4) two Canadian initiatives that address multiple aspects of Arctic infrastructure called Arctic Development and Adaptation to Permafrost in Transition (ADAPT) and the ArcticNet Integrated Regional Impact Studies (IRIS), and (5) the effects of oilfield infrastructure on landscapes and permafrost in the Prudhoe Bay region, Alaska.
Nonlinear Response of the Stratosphere and the North Atlantic-European Climate to Global Warming

NASA Astrophysics Data System (ADS)

Manzini, E.; Karpechko, A. Yu.; Kornblueh, L.

2018-05-01

The response of the northern winter atmospheric circulation for two consecutive global warming periods of 2 K is examined in a grand ensemble (68 members) of idealized CO2 increase experiments performed with the same climate model. The comparison of the atmospheric responses for the two periods shows remarkable differences, indicating the nonlinearity of the response. The nonlinear signature of the atmospheric and surface responses is reminiscent of the positive phase of the annular mode of variability. The stratospheric vortex response shifts from an easterly wind change for the first 2 K to a westerly wind change for the second 2 K. The North Atlantic storm track shifts poleward only in the second period. A weaker November Arctic amplification during the second period suggests that differences in Arctic sea ice changes can act to trigger the atmospheric nonlinear response. Stratosphere-troposphere coupling thereafter can provide for the persistence of this nonlinearity throughout the winter.
North Atlantic storm track variability and its association to the North Atlantic oscillation and climate variability of northern Europe

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

Rogers, J.C.

The primary mode of North Atlantic track variability is identified using rotated principal component analysis (RPCA) on monthly fields of root-mean-squares of daily high-pass filtered (2-8-day periods) sea level pressures (SLP) for winters (December-February) 1900-92. It is examined in terms of its association with (1) monthly mean SLP fields, (2) regional low-frequency teleconnections, and (3) the seesaw in winter temperatures between Greenland and northern Europe. 32 refs., 9 figs.
Seabirds at risk around offshore oil platforms in the north-west Atlantic.

PubMed

Wiese, F K; Montevecchi, W A; Davoren, G K; Huettmann, F; Diamond, A W; Linke, J

2001-12-01

Seabirds aggregate around oil drilling platforms and rigs in above average numbers due to night lighting, flaring, food and other visual cues. Bird mortality has been documented due to impact on the structure, oiling and incineration by the flare. The environmental circumstances for offshore hydrocarbon development in North-west Atlantic are unique because of the harsh climate, cold waters and because enormous seabird concentrations inhabit and move through the Grand Banks in autumn (storm-petrels, Oceanodroma spp), winter (dovekies, Alle alle, murres, Uria spp), spring and summer (shearwaters, Puffinus spp). Many species are planktivorous and attracted to artificial light sources. Most of the seabirds in the region are long-distance migrants, and hydrocarbon development in the North-west Atlantic could affect both regional and global breeding populations. Regulators need to take responsibility for these circumstances. It is essential to implement comprehensive, independent arm's length monitoring of potential avian impacts of offshore hydrocarbon platforms in the North-west Atlantic. This should include quantifying and determining the nature, timing and extent of bird mortality caused by these structures. Based on existing evidence of potential impacts of offshore hydrocarbon platforms on seabirds, it is difficult to understand why this has not been, and is not being, systematically implemented.
Sheep grazing in the North Atlantic region: A long-term perspective on environmental sustainability.

PubMed

Ross, Louise C; Austrheim, Gunnar; Asheim, Leif-Jarle; Bjarnason, Gunnar; Feilberg, Jon; Fosaa, Anna Maria; Hester, Alison J; Holand, Øystein; Jónsdóttir, Ingibjörg S; Mortensen, Lis E; Mysterud, Atle; Olsen, Erla; Skonhoft, Anders; Speed, James D M; Steinheim, Geir; Thompson, Des B A; Thórhallsdóttir, Anna Gudrún

2016-09-01

Sheep grazing is an important part of agriculture in the North Atlantic region, defined here as the Faroe Islands, Greenland, Iceland, Norway and Scotland. This process has played a key role in shaping the landscape and biodiversity of the region, sometimes with major environmental consequences, and has also been instrumental in the development of its rural economy and culture. In this review, we present results of the first interdisciplinary study taking a long-term perspective on sheep management, resource economy and the ecological impacts of sheep grazing, showing that sustainability boundaries are most likely to be exceeded in fragile environments where financial support is linked to the number of sheep produced. The sustainability of sheep grazing can be enhanced by a management regime that promotes grazing densities appropriate to the site and supported by area-based subsidy systems, thus minimizing environmental degradation, encouraging biodiversity and preserving the integrity of ecosystem processes.
Lipid Content in Arctic Calanus: a Matter of Season and Size

NASA Astrophysics Data System (ADS)

Daase, M.; Søreide, J.; Freese, D.; Hatlebakk, M. K.; Jørgen, B.; Renaud, P.; Gabrielsen, T. M.; Vogedes, D.

2016-02-01

Copepods of the genus Calanus are considered key elements of the marine food chain of the Arctic and North Atlantic. They convert low-energy carbohydrates and proteins of their algae diet into high-energy wax ester lipids. These lipids are accumulated over the productive season and stored in a lipid sac which sustains the organism over long periods without algal food supply, and which makes Calanus spp. an important prey item. Here we investigated what determines the variability in lipid content of overwintering stages and adults of Arctic and North Atlantic Calanus species. Using image analysis of lipid sac area, we have estimated individual lipid content of Calanus species in the waters and fjords of Svalbard (78-81oN). Data were collected all year round, at surface and deep waters and in locations under the influence of either Atlantic or Arctic hydrographic conditions. Lipid content showed stage specific seasonal variability which can be related to life history strategies and the phenology of algae blooms. Depth specific differences in lipid content were only observed at the start of the overwintering period. Our data also demonstrate that species specific differences in lipid content were not as fundamentally different as previously assumed. Rather, based on molecular identification of the species, we show that the lipid content of the Arctic C. glacialis and the Atlantic C. finmarchicus is dependent on size alone, challenging the classical understanding of these two species yielding two distinctly different ecosystem services based upon a difference in lipid content.
Atlantic Meridional Overturning Circulation Influence on North Atlantic Sector Surface Air Temperature and its Predictability in the Kiel Climate Model

NASA Astrophysics Data System (ADS)

Latif, M.

2017-12-01

We investigate the influence of the Atlantic Meridional Overturning Circulation (AMOC) on the North Atlantic sector surface air temperature (SAT) in two multi-millennial control integrations of the Kiel Climate Model (KCM). One model version employs a freshwater flux correction over the North Atlantic, while the other does not. A clear influence of the AMOC on North Atlantic sector SAT only is simulated in the corrected model that depicts much reduced upper ocean salinity and temperature biases in comparison to the uncorrected model. Further, the model with much reduced biases depicts significantly enhanced multiyear SAT predictability in the North Atlantic sector relative to the uncorrected model. The enhanced SAT predictability in the corrected model is due to a stronger and more variable AMOC and its enhanced influence on North Atlantic sea surface temperature (SST). Results obtained from preindustrial control integrations of models participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) support the findings obtained from the KCM: models with large North Atlantic biases tend to have a weak AMOC influence on SST and exhibit a smaller SAT predictability over the North Atlantic sector.
Paleoceanography. Onset of Mediterranean outflow into the North Atlantic.

PubMed

Hernández-Molina, F Javier; Stow, Dorrik A V; Alvarez-Zarikian, Carlos A; Acton, Gary; Bahr, André; Balestra, Barbara; Ducassou, Emmanuelle; Flood, Roger; Flores, José-Abel; Furota, Satoshi; Grunert, Patrick; Hodell, David; Jimenez-Espejo, Francisco; Kim, Jin Kyoung; Krissek, Lawrence; Kuroda, Junichiro; Li, Baohua; Llave, Estefania; Lofi, Johanna; Lourens, Lucas; Miller, Madeline; Nanayama, Futoshi; Nishida, Naohisa; Richter, Carl; Roque, Cristina; Pereira, Hélder; Sanchez Goñi, Maria Fernanda; Sierro, Francisco J; Singh, Arun Deo; Sloss, Craig; Takashimizu, Yasuhiro; Tzanova, Alexandrina; Voelker, Antje; Williams, Trevor; Xuan, Chuang

2014-06-13

Sediments cored along the southwestern Iberian margin during Integrated Ocean Drilling Program Expedition 339 provide constraints on Mediterranean Outflow Water (MOW) circulation patterns from the Pliocene epoch to the present day. After the Strait of Gibraltar opened (5.33 million years ago), a limited volume of MOW entered the Atlantic. Depositional hiatuses indicate erosion by bottom currents related to higher volumes of MOW circulating into the North Atlantic, beginning in the late Pliocene. The hiatuses coincide with regional tectonic events and changes in global thermohaline circulation (THC). This suggests that MOW influenced Atlantic Meridional Overturning Circulation (AMOC), THC, and climatic shifts by contributing a component of warm, saline water to northern latitudes while in turn being influenced by plate tectonics. Copyright © 2014, American Association for the Advancement of Science.
Vicariance, long-distance dispersal, and regional extinction-recolonization dynamics explain the disjunct circumpolar distribution of the arctic-alpine plant Silene acaulis.

PubMed

Gussarova, Galina; Allen, Geraldine A; Mikhaylova, Yulia; McCormick, Laurie J; Mirré, Virginia; Marr, Kendrick L; Hebda, Richard J; Brochmann, Christian

2015-10-01

Many arctic-alpine species have vast geographic ranges, but these may encompass substantial gaps whose origins are poorly understood. Here we address the phylogeographic history of Silene acaulis, a perennial cushion plant with a circumpolar distribution except for a large gap in Siberia. We assessed genetic variation in a range-wide sample of 103 populations using plastid DNA (pDNA) sequences and AFLPs (amplified fragment length polymorphisms). We constructed a haplotype network and performed Bayesian phylogenetic analyses based on plastid sequences. We visualized AFLP patterns using principal coordinate analysis, identified genetic groups using the program structure, and estimated genetic diversity and rarity indices by geographic region. The history of the main pDNA lineages was estimated to span several glaciations. AFLP data revealed a distinct division between Beringia/North America and Europe/East Greenland. These two regions shared only one of 17 pDNA haplotypes. Populations on opposite sides of the Siberian range gap (Ural Mountains and Chukotka) were genetically distinct and appear to have resulted from postglacial leading-edge colonizations. We inferred two refugia in North America (Beringia and the southern Rocky Mountains) and two in Europe (central-southern Europe and northern Europe/East Greenland). Patterns in the East Atlantic region suggested transoceanic long-distance dispersal events. Silene acaulis has a highly dynamic history characterized by vicariance, regional extinction, and recolonization, with persistence in at least four refugia. Long-distance dispersal explains patterns across the Atlantic Ocean, but we found no evidence of dispersal across the Siberian range gap. © 2015 Botanical Society of America.
Variability of cyclones over the North Atlantic and Europe since 1871

NASA Astrophysics Data System (ADS)

Welker, C.; Martius, O.

2012-04-01

The scarce availability of long-term atmospheric data series has so far limited the analysis of low-frequency activity and intensity changes of cyclones over the North Atlantic and Europe. A novel reanalysis product, the Twentieth Century Reanalysis (20CR; Compo et al., 2011), spanning 1871 to present, offers potentially a very valuable resource for the analysis of the decadal-scale variability of cyclones over the North Atlantic sector and Europe. In the 20CR, only observations of synoptic surface pressure were assimilated. Monthly sea surface temperature and sea ice distributions served as boundary conditions. An Ensemble Kalman Filter assimilation technique was applied. "First guess" fields were obtained from an ensemble (with 56 members) of short-range numerical weather prediction forecasts. We apply the cyclone identification algorithm of Wernli and Schwierz (2006) to this data set, i.e. to each individual ensemble member. This enables us to give an uncertainty estimation of our findings. We find that 20CR shows a temporally relatively homogeneous representation of cyclone activity over Europe and great parts of the North Atlantic. Pronounced decadal-scale variability is found both in the frequency and intensity of cyclones over the North Atlantic and Europe. The low-frequency variability is consistently represented in all ensemble members. Our analyses indicate that in the past approximately 140 years the variability of cyclone activity and intensity over the North Atlantic and Europe can principally be associated with the North Atlantic Oscillation and secondary with a pattern similar to the East Atlantic pattern. Regionally however, the correlation between cyclone activity and these dominant modes of variability changes over time. Compo, G. P., J. S. Whitaker, P. D. Sardeshmukh, N. Matsui, R. J. Allan, X. Yin, B. E. Gleason, R. S. Vose, G. Rutledge, P. Bessemoulin, S. Brönnimann, M. Brunet, R. I. Crouthamel, A. N. Grant, P. Y. Groisman, P. D. Jones, M. C
North Atlantic SST Patterns and NAO Flavors

NASA Astrophysics Data System (ADS)

Rousi, E.; Rahmstorf, S.; Coumou, D.

2017-12-01

North Atlantic SST variability results from the interaction of atmospheric and oceanic processes. The North Atlantic Oscillation (NAO) drives changes in SST patterns but is also driven by them on certain time-scales. These interactions are not very well understood and might be affected by anthropogenic climate change. Paleo reconstructions indicate a slowdown of the Atlantic Meridional Overturning Circulation (AMOC) in recent decades leading to a pronounced cold anomaly ("cold blob") in the North Atlantic (Rahmstorf et al., 2015). The latter may favor NAO to be in its negative mode. In this work, sea surface temperature (SST) patterns are studied in relation to NAO variations, with the aim of discovering preferred states and understanding their interactions. SST patterns are analyzed with Self-Organizing Maps (SOM), a clustering technique that helps identify different spatial patterns and their temporal evolution. NAO flavors refer to different longitudinal positions and tilts of the NAO action centers, also defined with SOMs. This way the limitations of the basic, index-based, NAO-definition are overcome, and the method handles different spatially shapes associated with NAO. Preliminary results show the existence of preferred combinations of SSTs and NAO flavors, which in turn affect weather and climate of Europe and North America. The possible influence of the cold blob on European weather is discussed.
North Atlantic Oscillation Drives Regional Greenland Glacier Volume During the 20th Century

NASA Astrophysics Data System (ADS)

Bjork, A. A.; Aagaard, S.; Hallander, A. M.; Khan, S. A.; Box, J. E.; Kjeldsen, K. K.; Larsen, N. K.; Korsgaard, N. J.; Cappelen, J.; Colgan, W. T.; Machguth, H.; Andresen, C. S.; Kjaer, K. H.

2016-12-01

While most areas of the Greenland ice sheet have undergone rapid mass loss since c. 1990, the central eastern section of the ice sheet has advanced and gained mass. This contrasting regional trend has been attributed to positive surface mass balance (SMB) in the absence of significant dynamic mass loss. To constrain the atypical behavior in this region, we mapped glacier length fluctuations of nearly 200 peripheral glaciers and ice caps (PGICs) over a 103-year period, and compare the results with c. 150 new glacier length records from central west Greenland. We demonstrate that the regional response in ice volume is closely correlated to changes in precipitation, governed by circulation patterns associated with the North Atlantic Oscillation (NAO) and secondarily influenced by temperature forcing in certain periods. More broadly, we find that the NAO contributes to contrasting precipitation variability in East and West Greenland, where it appears to be responsible for at least 10% and more than 25%, respectively, of the variability in ice sheet accumulation rate. This east-west asymmetry, which influences both LGICs and the ice sheet, illustrates how substantial uncertainty in NAO projections directly contributes to uncertainty in mass balance projections.
Physically driven Patchy O2 Changes in the North Atlantic Ocean simulated by the CMIP5 Earth System Models

NASA Astrophysics Data System (ADS)

Tagklis, Filippos; Bracco, Annalisa; Ito, Takamitsu

2017-04-01

Centennial trends of oxygen in the upper 700 m of the North Atlantic Ocean are investigated in Earth System Models (ESMs) included in the Coupled Model Intercomparison Project Phase 5. The focus is on the subpolar region, which is key for the oceanic uptake of oxygen and carbon dioxide. Historical simulations covering the twentieth century and projections for the twenty-first century under the Representative Concentration Pathway 8.5 scenario are investigated. Although the representation of convective activity differs among the models in space and strength, and most models have a cold bias south of Greenland resulting from a poor representation of the pathway of the North Atlantic Current, the observed climatological distribution of dissolved O2 averaged for the recent past period (1975-2005) is generally well captured. By the end of the 21st century, all models predict an increase in depth-integrated temperature of 2-3oC, a consequent solubility decrease, a weakening of the vertical mass transport, a decrease in nutrient supply into the euphotic layer, and a spatially variable change in apparent oxygen utilization (AOU). Despite an overall tendency of the North Atlantic to lose oxygen by the end of twenty-first century, patchy regions of O2 increase are observed in a subset of models. This regional resistance to deoxygenation is explained by the weakening of the North Atlantic Current that causes a regional solubility increase exceeding the effect of increasing stratification. Our results imply that potential shifts in the North Atlantic Current play a crucial role in the future projection of the regional oxygen concentration in the warming climate.
Coal burning leaves toxic heavy metal legacy in the Arctic

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

McConnell, J.R.; Edwards, R.

2008-08-26

Toxic heavy metals emitted by industrial activities in the midlatitudes are transported through the atmosphere and deposited in the polar regions; bioconcentration and biomagnification in the food chain mean that even low levels of atmospheric deposition may threaten human health and Arctic ecosystems. Little is known about sources and long-term trends of most heavy metals before approximate to 1980, when modern measurements began, although heavy-metal pollution in the Arctic was widespread during recent decades. Lacking detailed, long-term measurements until now, ecologists, health researchers, and policy makers generally have assumed that contamination was highest during the 1960s and 1970s peak ofmore » industrial activity in North America and Europe. We present continuous 1772-2003 monthly and annually averaged deposition records for highly toxic thallium, cadmium, and lead from a Greenland ice core showing that atmospheric deposition was much higher than expected in the early 20th century, with tenfold increases from preindustrial levels by the early 1900s that were two to five times higher than during recent decades. Tracer measurements indicate that coal burning in North America and Europe was the likely source of these metals in the Arctic after 1860. Although these results show that heavy-metal pollution in the North Atlantic sector of the Arctic is substantially lower today than a century ago, contamination of other sectors may be increasing because of the rapid coal-driven growth of Asian economies.« less
North Atlantic Deep Water Formation

NASA Technical Reports Server (NTRS)

Bennett, T. (Editor); Broecker, W. S. (Editor); Hansen, J. (Editor)

1984-01-01

Various studies concerning differing aspects of the North Atlantic are presented. The three major topics under which the works are classified include: (1) oceanography; (2) paleoclimate; and (3) ocean, ice and climate modeling.

Interannual-to-decadal air-sea interactions in the tropical Atlantic region

NASA Astrophysics Data System (ADS)

Ruiz-Barradas, Alfredo

2001-09-01

The present research identifies modes of atmosphere-ocean interaction in the tropical Atlantic region and the mechanisms by which air-sea interactions influence the regional climate. Novelties of the present work are (1)the use of relevant ocean and atmosphere variables important to identity coupled variability in the system. (2)The use of new data sets, including realistic diabatic heating. (3)The study of interactions between ocean and atmosphere relevant at interannual-to-decadal time scales. Two tropical modes of variability are identified during the period 1958-1993, the Atlantic Niño mode and the Interhemispheric mode. Those modes have defined structures in both ocean and atmosphere. Anomalous sea surface temperatures and winds are associated to anomalous placement of the Intertropical Convergence Zone (ITCZ). They develop maximum amplitude during boreal summer and spring, respectively. The anomalous positioning of the ITCZ produces anomalous precipitation in some places like Nordeste, Brazil and the Caribbean region. Through the use of a diagnostic primitive equation model, it is found that the most important terms controlling local anomalous surface winds over the ocean are boundary layer temperature gradients and diabatic heating anomalies at low levels (below 780 mb). The latter is of particular importance in the deep tropics in producing the anomalous meridional response to the surface circulation. Simulated latent heat anomalies indicate that a thermodynamic feedback establishes positive feedbacks at both sides of the equator and west of 20°W in the deep tropics and a negative feedback in front of the north west coast of Africa for the Interhemispheric mode. This thermodynamic feedback only establishes negative feedbacks for the Atlantic Niño mode. Transients establish some connection between the tropical Atlantic and other basins. Interhemispheric gradients of surface temperature in the tropical Atlantic influence winds in the midlatitude North
Climate, fishery and society interactions: Observations from the North Atlantic

NASA Astrophysics Data System (ADS)

Hamilton, Lawrence C.

2007-11-01

Interdisciplinary studies comparing fisheries-dependent regions across the North Atlantic find a number of broad patterns. Large ecological shifts, disastrous to historical fisheries, have resulted when unfavorable climatic events occur atop overfishing. The "teleconnections" linking fisheries crises across long distances include human technology and markets, as well as climate or migratory fish species. Overfishing and climate-driven changes have led to a shift downwards in trophic levels of fisheries takes in some ecosystems, from dominance by bony fish to crustaceans. Fishing societies adapt to new ecological conditions through social reorganization that have benefited some people and places, while leaving others behind. Characteristic patterns of demographic change are among the symptoms of such reorganization. These general observations emerge from a review of recent case studies of individual fishing communities, such as those conducted for the North Atlantic Arc research project.
Atlantic Ocean CARINA data: overview and salinity adjustments

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

Tanhua, T.; Steinfeldt, R.; Key, Robert

2010-01-01

Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon dioxide IN the Atlantic Ocean). The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the threemore » data products: merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. the Arctic Mediterranean Seas, the Atlantic and the Southern Ocean. These products have been corrected to be internally consistent. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30 S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report the details of the secondary QC (Quality Control) for salinity for this data set. Procedures of quality control including crossover analysis between stations and inversion analysis of all crossover data are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal consistency of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA data products are consistent both internally was well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, oceanic carbon
Atlantic Ocean CARINA data: overview and salinity adjustments

NASA Astrophysics Data System (ADS)

Tanhua, T.; Steinfeldt, R.; Key, R. M.; Brown, P.; Gruber, N.; Wanninkhof, R.; Perez, F.; Körtzinger, A.; Velo, A.; Schuster, U.; van Heuven, S.; Bullister, J. L.; Stendardo, I.; Hoppema, M.; Olsen, A.; Kozyr, A.; Pierrot, D.; Schirnick, C.; Wallace, D. W. R.

2010-02-01

Water column data of carbon and carbon-relevant hydrographic and hydrochemical parameters from 188 previously non-publicly available cruise data sets in the Arctic Mediterranean Seas, Atlantic and Southern Ocean have been retrieved and merged into a new database: CARINA (CARbon dioxide IN the Atlantic Ocean). The data have gone through rigorous quality control procedures to assure the highest possible quality and consistency. The data for the pertinent parameters in the CARINA database were objectively examined in order to quantify systematic differences in the reported values, i.e. secondary quality control. Systematic biases found in the data have been corrected in the three data products: merged data files with measured, calculated and interpolated data for each of the three CARINA regions, i.e. the Arctic Mediterranean Seas, the Atlantic and the Southern Ocean. These products have been corrected to be internally consistent. Ninety-eight of the cruises in the CARINA database were conducted in the Atlantic Ocean, defined here as the region south of the Greenland-Iceland-Scotland Ridge and north of about 30° S. Here we present an overview of the Atlantic Ocean synthesis of the CARINA data and the adjustments that were applied to the data product. We also report the details of the secondary QC (Quality Control) for salinity for this data set. Procedures of quality control - including crossover analysis between stations and inversion analysis of all crossover data - are briefly described. Adjustments to salinity measurements were applied to the data from 10 cruises in the Atlantic Ocean region. Based on our analysis we estimate the internal consistency of the CARINA-ATL salinity data to be 4.1 ppm. With these adjustments the CARINA data products are consistent both internally as well as with GLODAP data, an oceanographic data set based on the World Hydrographic Program in the 1990s, and is now suitable for accurate assessments of, for example, oceanic carbon
North Atlantic Coastal Tidal Wetlands

EPA Science Inventory

The book chapter provides college instructors, researchers, graduate and advanced undergraduate students, and environmental consultants interested in wetlands with foundation information on the ecology and conservation concerns of North Atlantic coastal wetlands. The book c...
North Atlantic coast of Canada from Skylab

NASA Image and Video Library

1974-02-01

SL4-139-4072 (February 1974) --- A high oblique view of the North Atlantic coast of Canada as seen from the Skylab space station in Earth orbit. A Skylab 4 crewman used a hand-held 70mm Hasselblad camera to take this picture. The Strait of Belle Isle, near the center of the picture, separates the Island of Newfoundland from the Canadian mainland. The Strait also connects the Gulf of St. Lawrence with North Atlantic Ocean. The elongated land mass (lower center) is the northern-most peninsula of the Island of Newfoundland. The large land mass at left center is mainland Newfoundland and Quebec. Note the sea ice in the Atlantic. Snow and some ice intermittently cover the land masses, and ice plumes of brash ice or pancake ice can be seen in various shapes and formations. General terrain and ice conditions can be distinguished and evaluated up to at least 55 degrees north latitude in this north looking view. Dr. William Campbell, sea and ice expert with the U.S. Geological Survey, will use this photograph in the study of ice dynamics. Photo credit: NASA
The Variation of Tropical Cyclone Rainfall within the North Atlantic and Pacific as Observed from Satellites

NASA Technical Reports Server (NTRS)

Rodgers, Edward; Pierce, Harold; Adler, Robert

1999-01-01

Tropical cyclone monthly rainfall amounts are estimated from passive microwave satellite observations in the North Atlantic and in three equal geographical regions of the North Pacific (i.e., Western, Central, and Eastern North Pacific). These satellite-derived rainfall amounts are used to assess the impact of tropical cyclone rainfall in altering the geographical, seasonal, and inter-annual distribution of the 1987-1989, 1991-1998 North Atlantic and Pacific rainfall during June-November when tropical cyclones are most abundant. To estimate these tropical cyclone rainfall amounts, mean monthly rain rates are derived from the Defence Meteorological Satellite Program (DMSP) Special Sensor Microwave/ Radiometer (SSM/I) observations within 444 km radius of the center of those North Atlantic and Pacific tropical cyclones that reached storm stage and greater. These rain rate observations are then multiplied by the number of hours in a given month. Mean monthly rainfall amounts are also constructed for all the other North Atlantic and Pacific raining systems during this eleven year period for the purpose of estimating the geographical distribution and intensity of rainfall contributed by non-tropical cyclone systems. Further, the combination of the non-tropical cyclone and tropical cyclone (i.e., total) rainfall is constructed to delineate the fractional amount that tropical cyclones contributed to the total North Pacific rainfall.
Pb isotope signatures in the North Atlantic: initial results from the U.S. GEOTRACES North Atlantic Transect

NASA Astrophysics Data System (ADS)

Noble, A.; Echegoyen-Sanz, Y.; Boyle, E. A.

2012-12-01

This study presents Pb isotope data from the US GEOTRACES North Atlantic Transect (US-GT-NAT) sampled during two cruises that took place during Fall 2010 and 2011. Almost all of the Pb in the modern ocean is derived from anthropogenic sources, and the North Atlantic has received major Pb inputs from the United States and Europe due to emissions from leaded gasoline and high temperature industrial processes. During the past three decades, Pb fluxes to the North Atlantic have decreased following the phasing out of leaded gasoline in the United States and Europe. Following the concentrations and isotope ratios of Pb in this basin over time reveals the temporal evolution of Pb in this highly-affected basin. The Pb isotope signatures reflect the relative importance of changing inputs from the United States and Europe as leaded gasoline was phased out faster in the United States relative to Europe. In the western North Atlantic, a shallow (~100-200m) low Pb-206/Pb-207 ratio feature was observed near the Subtropical Underwater salinity peak at many stations across the transect, coincident with shallow subsurface maxima in Pb concentration. This water mass originates from high-salinity surface water near 25°N (Defant), which is in the belt of European-Pb-gas-contaminated African aerosols, which we confirmed by Pb-206/Pb-207 ~ 1.17 from upper ocean samples from US-GT-NAT station 18 (23.24degN,38.04degW). At the Mid-Atlantic Ridge station, Pb scavenging onto iron oxides and sulfide was observed by a decrease in Pb concentrations within the TAG hydrothermal plume, although the isotopic signature within the plume was slightly (~3 permil) lower than the surrounding waters possibly indicating a small contribution of hydrothermal Pb or preferential uptake of the lighter isotope. In the Mediteranean Outflow plume near Lisbon, Pb-206/Pb-207 (~1.178) is also strongly influenced by European Pb. Further results from the section will be presented as more data will be available by the
Climate Change in the North American Arctic: A One Health Perspective.

PubMed

Dudley, Joseph P; Hoberg, Eric P; Jenkins, Emily J; Parkinson, Alan J

2015-12-01

Climate change is expected to increase the prevalence of acute and chronic diseases among human and animal populations within the Arctic and subarctic latitudes of North America. Warmer temperatures are expected to increase disease risks from food-borne pathogens, water-borne diseases, and vector-borne zoonoses in human and animal populations of Arctic landscapes. Existing high levels of mercury and persistent organic pollutant chemicals circulating within terrestrial and aquatic ecosystems in Arctic latitudes are a major concern for the reproductive health of humans and other mammals, and climate warming will accelerate the mobilization and biological amplification of toxic environmental contaminants. The adverse health impacts of Arctic warming will be especially important for wildlife populations and indigenous peoples dependent upon subsistence food resources from wild plants and animals. Additional research is needed to identify and monitor changes in the prevalence of zoonotic pathogens in humans, domestic dogs, and wildlife species of critical subsistence, cultural, and economic importance to Arctic peoples. The long-term effects of climate warming in the Arctic cannot be adequately predicted or mitigated without a comprehensive understanding of the interactive and synergistic effects between environmental contaminants and pathogens in the health of wildlife and human communities in Arctic ecosystems. The complexity and magnitude of the documented impacts of climate change on Arctic ecosystems, and the intimacy of connections between their human and wildlife communities, makes this region an appropriate area for development of One Health approaches to identify and mitigate the effects of climate warming at the community, ecosystem, and landscape scales.
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.
Airborne CH 2O measurements over the North Atlantic during the 1997 NARE campaign: Instrument comparisons and distributions

DOE PAGES

Fried, Alan; Lee, Yin -Nan; Frost, Greg; ...

2002-02-27

Here, formaldehyde measurements from two independent instruments are compared with photochemical box model calculations. The measurements were made on the NOAA P-3 aircraft as part of the 1997 North Atlantic Regional Experiment (NARE 1997). After examining the possible reasons for the model-measurement discrepancy, we conclude that there are probably one or more additional unknown sources of CH 2O in the North Atlantic troposphere.
The Arctic sea ice cover of 2016: a year of record-low highs and higher-than-expected lows

NASA Astrophysics Data System (ADS)

Petty, Alek A.; Stroeve, Julienne C.; Holland, Paul R.; Boisvert, Linette N.; Bliss, Angela C.; Kimura, Noriaki; Meier, Walter N.

2018-02-01

The Arctic sea ice cover of 2016 was highly noteworthy, as it featured record low monthly sea ice extents at the start of the year but a summer (September) extent that was higher than expected by most seasonal forecasts. Here we explore the 2016 Arctic sea ice state in terms of its monthly sea ice cover, placing this in the context of the sea ice conditions observed since 2000. We demonstrate the sensitivity of monthly Arctic sea ice extent and area estimates, in terms of their magnitude and annual rankings, to the ice concentration input data (using two widely used datasets) and to the averaging methodology used to convert concentration to extent (daily or monthly extent calculations). We use estimates of sea ice area over sea ice extent to analyse the relative "compactness" of the Arctic sea ice cover, highlighting anomalously low compactness in the summer of 2016 which contributed to the higher-than-expected September ice extent. Two cyclones that entered the Arctic Ocean during August appear to have driven this low-concentration/compactness ice cover but were not sufficient to cause more widespread melt-out and a new record-low September ice extent. We use concentration budgets to explore the regions and processes (thermodynamics/dynamics) contributing to the monthly 2016 extent/area estimates highlighting, amongst other things, rapid ice intensification across the central eastern Arctic through September. Two different products show significant early melt onset across the Arctic Ocean in 2016, including record-early melt onset in the North Atlantic sector of the Arctic. Our results also show record-late 2016 freeze-up in the central Arctic, North Atlantic and the Alaskan Arctic sector in particular, associated with strong sea surface temperature anomalies that appeared shortly after the 2016 minimum (October onwards). We explore the implications of this low summer ice compactness for seasonal forecasting, suggesting that sea ice area could be a more reliable
The JGOFS North Atlantic Bloom Experiment: An overview

NASA Technical Reports Server (NTRS)

Ducklow, Hugh W.

1992-01-01

The North Atlantic Bloom Experiment (NABE) of JGOFS presents a unique opportunity and challenge to the data management community because of the diversity and large size of biogeochemical data sets collected. NABE was a pilot study for JGOFS and has also served as a pilot study within the U.S. NODC for management and archiving of the data sets. Here I present an overview to some of the scientific results of NABE, which will be published as an Introduction to a special volume of NABE results in Deep-Sea Research later this year. An overview of NABE data management is given elsewhere in the present report. This is the first collection of papers from the Joint Global Ocean Flux Study (JGOFS). Formed as an international program in 1987, JGOFS has four principal elements: modelling and data management, multidisciplinary regional process studies, a global survey of biogeochemical properties and long-term time series observatories. In 1989-1990 JGOFS conducted a pilot process study of the spring phytoplankton bloom, the North Atlantic Bloom Experiment (NABE). JGOFS decided to conduct a large scale, internationally-coordinated pilot study in the North Atlantic because of its proximity to the founding nations of the project, the size and predictability of the bloom and its fundamental impact on ocean bio-geochemistry (Billett et al., 1983; Watson and Whitfield, 1985; Pfannkuche, 1992). In 1989, six research vessels from Canada, Germany, The Netherlands, the United Kingdom and the USA and over 200 scientists and students from more than a dozen nations participated in NABE. Some of their initial results are reported in this volume.
The Energy Cascade Associated with the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Castanheira, J. M.; Marques, C. A. F.

2017-12-01

The North Atlantic Oscillation or Arctic Oscillation (NAO/AO), in a more hemispheric expression, is the dominant mode of variability of the extratropical atmospheric circulation. In the literature which analyses the association of low frequency variability of the NAO/AO with other climate variables, it is very common to find the idea of circulation and climate impacts of the NAO/AO. It is usually suggested that the NAO influences the position of North Atlantic storm tracks and the related transport of heat and moisture. However, in spite of the long time since the NAO variability mode was uncovered (Walker and Bliss, 1932), its underlying dynamical mechanisms are not well understood yet. In fact, it is not yet consensual that the NAO influences the position of the storm tracks, being possible that the relationship is in the opposite way with the storm track activity influencing de NAO. In this communication we will present an analysis of anomalies of the energy cascade associated with the NAO. A detailed version of the Lorenz energy cycle, which decomposes the energy flows into baroclinic and barotropic terms and into zonal mean and eddy components, was applied to the 6-hourly ERA-I reanalysis for the period of 1979 to 2016. The obtained results show that the positive NAO phase is preceded by an significant increase of synoptic baroclinic eddy activity. The eddy available potential energy is converted into kinetic energy and transferred to barotropic synoptic eddies. Then, the kinetic energy is transferred upscale into the barotropic planetary waves, which reproduce the NAO pattern. Therefore, we conclude that the synoptic baroclinic eddy activity forces the NAO variability. No clear signal was found for a modulating role of the NAO in the baroclinic eddy activity.
Forced and Internal Multi-Decadal Variability in the North Atlantic and their Climate Impacts

NASA Astrophysics Data System (ADS)

Ting, M.

2017-12-01

Atlantic Multidecadal Variability (AMV), a basin-wide North Atlantic sea surface temperature warming or cooling pattern varying on decadal and longer time scales, is one of the most important climate variations in the Atlantic basin. The AMV has shown to be associated with significant climate impacts regionally and globally, from Atlantic hurricane activities, frequency and severity of droughts across North America, as well as rainfall anomalies across the African Sahel and northeast Brazil. Despite the important impacts of the AMV, its mechanisms are not completely understood. In particular, it is not clear how much of the historical Atlantic SST fluctuations were forced by anthropogenic sources such as greenhouse warming and aerosol cooling, versus driven internally by changes in the coupled ocean-atmosphere processes in the Atlantic. Using climate models such as the NCAR large ensemble simulations, we were able to successfully separate the forced and internally generated North Atlantic sea surface temperature anomalies through a signal-to-noise maximizing Empirical Orthogonal Function (S/N EOF) analysis method. Two forced modes were identified with one representing a hemispherical symmetric mode and one asymmetric mode. The symmetric mode largely represents the greenhouse forced component while the asymmetric mode resembles the anthropogenic aerosol forcing. When statistically removing both of the forced modes, the residual multidecadal Atlantic SST variability shows a very similar structure as the AMV in the preindustrial simulation. The distinct climate impacts of each of these modes are also identified and the implications and challenges for decadal climate prediction will be discussed.
AROME-Arctic: New operational NWP model for the Arctic region

NASA Astrophysics Data System (ADS)

Süld, Jakob; Dale, Knut S.; Myrland, Espen; Batrak, Yurii; Homleid, Mariken; Valkonen, Teresa; Seierstad, Ivar A.; Randriamampianina, Roger

2016-04-01

In the frame of the EU-funded project ACCESS (Arctic Climate Change, Economy and Society), MET Norway aimed 1) to describe the present monitoring and forecasting capabilities in the Arctic; and 2) to identify the key factors limiting the forecasting capabilities and to give recommendations on key areas to improve the forecasting capabilities in the Arctic. We have observed that the NWP forecast quality is lower in the Arctic than in the regions further south. Earlier research indicated that one of the factors behind this is the composition of the observing system in the Arctic, in particular the scarceness of conventional observations. To further assess possible strategies for alleviating the situation and propose scenarios for a future Arctic observing system, we have performed a set of experiments to gain a more detailed insight in the contribution of the components of the present observing system in a regional state-of-the-art non-hydrostatic NWP model using the AROME physics (Seity et al, 2011) at 2.5 km horizontal resolution - AROME-Arctic. Our observing system experiment studies showed that conventional observations (Synop, Buoys) can play an important role in correcting the surface state of the model, but prove that the present upper-air conventional (Radiosondes, Aircraft) observations in the area are too scarce to have a significant effect on forecasts. We demonstrate that satellite sounding data play an important role in improving forecast quality. This is the case with satellite temperature sounding data (AMSU-A, IASI), as well as with the satellite moisture sounding data (AMSU-B/MHS, IASI). With these sets of observations, the AROME-Arctic clearly performs better in forecasting extreme events, like for example polar lows. For more details see presentation by Randriamampianina et al. in this session. The encouraging performance of AROME-Arctic lead us to implement it with more observations and improved settings into daily runs with the objective to
Biogeography of jellyfish in the North Atlantic, by traditional and genomic methods

NASA Astrophysics Data System (ADS)

Licandro, P.; Blackett, M.; Fischer, A.; Hosia, A.; Kennedy, J.; Kirby, R. R.; Raab, K.; Stern, R.; Tranter, P.

2014-11-01

Scientific debate on whether the recent increase in reports of jellyfish outbreaks is related to a true rise in their abundance, have outlined the lack of reliable records of Cnidaria and Ctenophora. Here we describe different data sets produced within the EU program EUROBASIN, which have been assembled with the aim of presenting an up to date overview of the diversity and standing stocks of jellyfish in the North Atlantic region. Using a net adapted to sample gelatinous zooplankton quantitatively, Cnidaria and Ctenophora were collected in the epipelagic layer during spring-summer 2010-2013, in inshore and offshore waters between 59-68° N Lat and 62° W-5° E Long. Jellyfish were also identified and counted in samples opportunistically collected by other sampling equipment in the same region and at two coastal stations in the Bay of Biscay and in the Gulf of Cadiz. Continuous Plankton Recorder (CPR) samples collected in 2009-2012 were re-analysed with the aim of identifying the time and location of Cnidarian blooms across the North Atlantic basin. Overall the data show high variability in jellyfish abundance and diversity, mainly in relation with different water masses and with the bathymetry. Higher densities were generally recorded on the shelves, where populations tend to be more diversified due to the presence of meropelagic medusae. Comparisons of net records from the G.O. Sars transatlantic cruise show that information on jellyfish diversity differs significantly depending on the sampling gear utilised. Indeed, the big trawls mostly collect relatively large scyphozoan and hydrozoan species, while small hydrozoans and early stages of ctenophora are only caught by smaller nets. Based on CPR data from 2009-2012, blooms of Cnidarians occurred in all seasons across the whole North Atlantic basin. Molecular analysis revealed that, in contrast with what was previously hypothesized, the CPR is able to detect blooms of meroplanktonic and holoplanktonic hydrozoans and
Biogeography of jellyfish in the North Atlantic, by traditional and genomic methods

NASA Astrophysics Data System (ADS)

Licandro, P.; Blackett, M.; Fischer, A.; Hosia, A.; Kennedy, J.; Kirby, R. R.; Raab, K.; Stern, R.; Tranter, P.

2015-07-01

Scientific debate on whether or not the recent increase in reports of jellyfish outbreaks represents a true rise in their abundance has outlined a lack of reliable records of Cnidaria and Ctenophora. Here we describe different jellyfish data sets produced within the EU programme EURO-BASIN. These data were assembled with the aim of creating an improved baseline and providing new data that can be used to evaluate the current diversity and standing stocks of jellyfish in the North Atlantic region. Using a net adapted to sample gelatinous zooplankton quantitatively, cnidarians and ctenophores were collected from the epipelagic layer during spring-summer 2010-2013, in inshore and offshore waters between lat 59 and 68° N and long 62° W and 5° E. Jellyfish were also identified and counted in samples opportunistically collected by other sampling equipment in the same region and at two coastal stations in the Bay of Biscay and in the Gulf of Cadiz. Continuous Plankton Recorder (CPR) samples collected in 2009-2012 were re-analysed with the aim of identifying the time and location of cnidarian blooms across the North Atlantic Basin. Overall the data show high variability in jellyfish abundance and diversity, mainly in relation to different water masses and bathymetry. Higher densities were generally recorded on the shelves, where the communities tend to be more diverse due to the presence of meropelagic medusae. Comparison of net records from the G.O. Sars transatlantic cruise shows that information on jellyfish diversity differs significantly depending on the sampling gear utilised. Indeed, the big trawls mostly collect relatively large scyphozoan and hydrozoan species, while small hydrozoans and early stages of Ctenophora are only caught by smaller nets. Based on CPR data from 2009 to 2012, blooms of cnidarians occurred in all seasons across the whole North Atlantic Basin. Molecular analysis revealed that, contrary to previous hypotheses, the CPR is able to detect
Remote Drying in the North Atlantic as a Common Response to Precessional Changes and CO 2 Increase Over Land

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

Kelly, Patrick; Kravitz, Ben; Lu, Jian

In this study, we demonstrate that changes of the North Atlantic subtropical high and its regional rainfall pattern during mid-Holocene precessional changes and idealized 4xCO 2 increase can both be understood as a remote response to increased land heating near North Africa. Despite different sources and patterns of radiative forcing (increase in CO 2 concentration versus changes in orbital parameters), we find that the pattern of energy, circulation, and rainfall responses in the Northern Hemisphere summer subtropics are remarkably similar in the two forcing scenarios because both are dominated by the same land-sea heating contrast in response to the forcing.more » An increase in energy input over arid land drives a westward displacement of the coupled North Atlantic subtropical high-monsoon circulation, consistent with increased precipitation in the Afro-Asia region and decreased precipitation in the America-Atlantic region. This study underscores the importance of land heating in dictating remote drying through zonal shifts of the subtropical circulation.« less
Remote Drying in the North Atlantic as a Common Response to Precessional Changes and CO 2 Increase Over Land

DOE PAGES

Kelly, Patrick; Kravitz, Ben; Lu, Jian; ...

2018-04-16

In this study, we demonstrate that changes of the North Atlantic subtropical high and its regional rainfall pattern during mid-Holocene precessional changes and idealized 4xCO 2 increase can both be understood as a remote response to increased land heating near North Africa. Despite different sources and patterns of radiative forcing (increase in CO 2 concentration versus changes in orbital parameters), we find that the pattern of energy, circulation, and rainfall responses in the Northern Hemisphere summer subtropics are remarkably similar in the two forcing scenarios because both are dominated by the same land-sea heating contrast in response to the forcing.more » An increase in energy input over arid land drives a westward displacement of the coupled North Atlantic subtropical high-monsoon circulation, consistent with increased precipitation in the Afro-Asia region and decreased precipitation in the America-Atlantic region. This study underscores the importance of land heating in dictating remote drying through zonal shifts of the subtropical circulation.« less

Volcanic forcing of the North Atlantic Oscillation over the last 2,000 years

NASA Astrophysics Data System (ADS)

Breitenbach, Sebastian F. M.; Ridley, Harriet E.; Lechleitner, Franziska A.; Asmerom, Yemane; Rehfeld, Kira; Prufer, Keith M.; Kennett, Douglas J.; Aquino, Valorie V.; Polyak, Victor; Goswami, Bedartha; Marwan, Norbert; Haug, Gerald H.; Baldini, James U. L.

2015-04-01

The North Atlantic Oscillation (NAO) is a principal mode of atmospheric circulation in the North Atlantic realm (Hurrell et al. 2003) and influences rainfall distribution over Europe, North Africa and North America. Although observational data inform us on multi-annual variability of the NAO, long and detailed paleoclimate datasets are required to understand the mechanisms and full range of its variability and the spatial extent of its influence. Chronologies of available proxy-based NAO reconstructions are often interdependent and cover only the last ~1,100 years, while longer records are characterized by low sampling resolution and chronological constraints. This complicates the reconstruction of regional responses to NAO changes. We present data from a 2,000 year long sub-annual carbon isotope record from speleothem YOK-I from Yok Balum Cave, Belize, Central America. YOK-I has been extensively dated using U-series (Kennett et al. 2012). Monitoring shows that stalagmite δ13C in Yok Balum cave is governed by infiltration changes associated with tropical wet season rainfall. Higher (lower) δ13C values reflect drier (wetter) conditions related to Intertropical Convergence Zone position and trade winds intensity. Comparison with NAO reconstructions (Proctor et al. 2000, Trouet et al. 2009, Wassenburg et al. 2013) reveals that YOK-I δ13C sensitively records NAO-related rainfall dynamics over Belize. The Median Absolute Deviation (MAD) of δ13C extends NAO reconstructions to the last 2,000 years and indicates that high latitude volcanic aerosols force negative NAO phases. We infer that volcanic aerosols modify inter-hemispheric temperature contrasts at multi-annual scale, resulting in meridional relocation of the ITCZ and the Bermuda-Azores High, altering NAO and tropical rainfall patterns. Decade-long dry periods in the 11th and the late 18th century relate to major high northern latitude eruptions and exemplify the climatic response to volcanic forcing by
The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

NASA Astrophysics Data System (ADS)

van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

2016-02-01

Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.
The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin.

PubMed

van Hengstum, Peter J; Donnelly, Jeffrey P; Fall, Patricia L; Toomey, Michael R; Albury, Nancy A; Kakuk, Brian

2016-02-24

Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.
The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

USGS Publications Warehouse

van Hengstrum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael; Albury, Nancy A.; Kakuk, Brian

2016-01-01

Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval.
Latitudinal variation in virus-induced mortality of phytoplankton across the North Atlantic Ocean

PubMed Central

Mojica, Kristina D A; Huisman, Jef; Wilhelm, Steven W; Brussaard, Corina P D

2016-01-01

Viral lysis of phytoplankton constrains marine primary production, food web dynamics and biogeochemical cycles in the ocean. Yet, little is known about the biogeographical distribution of viral lysis rates across the global ocean. To address this, we investigated phytoplankton group-specific viral lysis rates along a latitudinal gradient within the North Atlantic Ocean. The data show large-scale distribution patterns of different virus groups across the North Atlantic that are associated with the biogeographical distributions of their potential microbial hosts. Average virus-mediated lysis rates of the picocyanobacteria Prochlorococcus and Synechococcus were lower than those of the picoeukaryotic and nanoeukaryotic phytoplankton (that is, 0.14 per day compared with 0.19 and 0.23 per day, respectively). Total phytoplankton mortality (virus plus grazer-mediated) was comparable to the gross growth rate, demonstrating high turnover rates of phytoplankton populations. Virus-induced mortality was an important loss process at low and mid latitudes, whereas phytoplankton mortality was dominated by microzooplankton grazing at higher latitudes (>56°N). This shift from a viral-lysis-dominated to a grazing-dominated phytoplankton community was associated with a decrease in temperature and salinity, and the decrease in viral lysis rates was also associated with increased vertical mixing at higher latitudes. Ocean-climate models predict that surface warming will lead to an expansion of the stratified and oligotrophic regions of the world's oceans. Our findings suggest that these future shifts in the regional climate of the ocean surface layer are likely to increase the contribution of viral lysis to phytoplankton mortality in the higher-latitude waters of the North Atlantic, which may potentially reduce transfer of matter and energy up the food chain and thus affect the capacity of the northern North Atlantic to act as a long-term sink for CO2. PMID:26262815
Latitudinal variation in virus-induced mortality of phytoplankton across the North Atlantic Ocean.

PubMed

Mojica, Kristina D A; Huisman, Jef; Wilhelm, Steven W; Brussaard, Corina P D

2016-02-01

Viral lysis of phytoplankton constrains marine primary production, food web dynamics and biogeochemical cycles in the ocean. Yet, little is known about the biogeographical distribution of viral lysis rates across the global ocean. To address this, we investigated phytoplankton group-specific viral lysis rates along a latitudinal gradient within the North Atlantic Ocean. The data show large-scale distribution patterns of different virus groups across the North Atlantic that are associated with the biogeographical distributions of their potential microbial hosts. Average virus-mediated lysis rates of the picocyanobacteria Prochlorococcus and Synechococcus were lower than those of the picoeukaryotic and nanoeukaryotic phytoplankton (that is, 0.14 per day compared with 0.19 and 0.23 per day, respectively). Total phytoplankton mortality (virus plus grazer-mediated) was comparable to the gross growth rate, demonstrating high turnover rates of phytoplankton populations. Virus-induced mortality was an important loss process at low and mid latitudes, whereas phytoplankton mortality was dominated by microzooplankton grazing at higher latitudes (>56°N). This shift from a viral-lysis-dominated to a grazing-dominated phytoplankton community was associated with a decrease in temperature and salinity, and the decrease in viral lysis rates was also associated with increased vertical mixing at higher latitudes. Ocean-climate models predict that surface warming will lead to an expansion of the stratified and oligotrophic regions of the world's oceans. Our findings suggest that these future shifts in the regional climate of the ocean surface layer are likely to increase the contribution of viral lysis to phytoplankton mortality in the higher-latitude waters of the North Atlantic, which may potentially reduce transfer of matter and energy up the food chain and thus affect the capacity of the northern North Atlantic to act as a long-term sink for CO2.
Links between North Atlantic atmospheric blocking and recent trends in European winter precipitation

NASA Astrophysics Data System (ADS)

Ummenhofer, Caroline; Seo, Hyodae; Kwon, Young-Oh; Joyce, Terrence

2015-04-01

European precipitation has sustained robust trends during wintertime (January - March) over recent decades. Central, western, and northern Europe have become wetter by an average 0.1-0.3% per annum for the period 1901-2010, while southern Europe, including the Iberian Peninsula, much of Italy and the Balkan States, has sustained drying of -0.2% per annum or more over the same period. The overall pattern is consistent across different observational precipitation products, while the magnitude of the precipitation trends varies amongst data sets. Using cluster analysis, which identifies recurrent states (or regimes) of European winter precipitation by grouping them according to an objective similarity criterion, changes in the frequency of dominant winter precipitation patterns over the past century are evaluated. Considerable multi-decadal variability exists in the frequency of dominant winter precipitation patterns: more recent decades are characterised by significantly fewer winters with anomalous wet conditions over southern, western, and central Europe. In contrast, winters with dry conditions in western and southern Europe, but above-average rainfall in western Scandinavia and the northern British Isles, have been more common recently. We evaluate the associated multi-decadal large-scale circulation changes across the broader extratropical North Atlantic region, which accompany the observed wintertime precipitation variability using the 20th Century reanalysis product. Some influence of the North Atlantic Oscillation (NAO) is apparent in modulating the frequency of dominant precipitation patterns. However, recent trends in the characteristics of atmospheric blocking across the North Atlantic sector indicate a change in the dominant blocking centres (near Greenland, the British Isles, and west of the Iberian Peninsula). Associated changes in sea level pressure, storm track position and strength, and oceanic heat fluxes across the North Atlantic region are also
Acoustic detections of summer and winter whales at Arctic gateways in the Atlantic and Pacific Oceans

NASA Astrophysics Data System (ADS)

Stafford, K.; Laidre, K. L.; Moore, S. E.

2016-02-01

Changes in sea ice phenology have been profound in regions north of arctic gateways, where the seasonal open-water period has increased by 1.5-3 months over the past 30 years. This has resulted in changes to the Arctic ecosystem, including increased primary productivity, changing food web structure, and opening of new habitat. In the "new normal" Arctic, ice obligate species such as ice seals and polar bears may fare poorly under reduced sea ice while sub-arctic "summer" whales (fin and humpback) are poised to inhabit new seasonal ice-free habitats in the Arctic. We examined the spatial and seasonal occurrence of summer and "winter" (bowhead) whales from September through December by deploying hydrophones in three Arctic gateways: Bering, Davis and Fram Straits. Acoustic occurrence of the three species was compared with decadal-scale changes in seasonal sea ice. In all three Straits, fin whale acoustic detections extended from summer to late autumn. Humpback whales showed the same pattern in Bering and Davis Straits, singing into November and December, respectively. Bowhead whale detections generally began after the departure of the summer whales and continued through the winter. In all three straits, summer whales occurred in seasons and regions that used to be ice-covered. This is likely due to both increased available habitat from sea ice reductions and post-whaling population recoveries. At present, in the straits examined here, there is spatial, but not temporal, overlap between summer and winter whales. In a future with further seasonal sea ice reductions, however, increased competition for resources between sub-Arctic and Arctic species may arise to the detriment of winter whales.
Seasonal-to-decadal predictability in the Nordic Seas and Arctic with the Norwegian Climate Prediction Model

NASA Astrophysics Data System (ADS)

Counillon, Francois; Kimmritz, Madlen; Keenlyside, Noel; Wang, Yiguo; Bethke, Ingo

2017-04-01

The Norwegian Climate Prediction Model combines the Norwegian Earth System Model and the Ensemble Kalman Filter data assimilation method. The prediction skills of different versions of the system (with 30 members) are tested in the Nordic Seas and the Arctic region. Comparing the hindcasts branched from a SST-only assimilation run with a free ensemble run of 30 members, we are able to dissociate the predictability rooted in the external forcing from the predictability harvest from SST derived initial conditions. The latter adds predictability in the North Atlantic subpolar gyre and the Nordic Seas regions and overall there is very little degradation or forecast drift. Combined assimilation of SST and T-S profiles further improves the prediction skill in the Nordic Seas and into the Arctic. These lead to multi-year predictability in the high-latitudes. Ongoing developments of strongly coupled assimilation (ocean and sea ice) of ice concentration in idealized twin experiment will be shown, as way to further enhance prediction skill in the Arctic.
Basin-scale observations of isoprene and monoterpenes in the Arctic and Atlantic Oceans

NASA Astrophysics Data System (ADS)

Carpenter, L.; Hackenberg, S.; Andrews, S.; Minaeian, J.; Chance, R.; Arnold, S.; Spracklen, D. V.; Walker, H.; Brewin, R. J.; Tarran, G.; Tilstone, G.; Small, A.; Bouman, H. A.

2016-12-01

We report surface ocean concentrations, atmospheric mixing ratios and calculated sea-to-air fluxes of isoprene and six monoterpenes (α- and β-pinene, myrcene, Δ 3-carene, ocimene, and limonene) spanning approximately 130 degrees of latitude (80 °N- 50 °S) in the Arctic and Atlantic Oceans. Oceanic isoprene concentrations showed covariance with a number of concurrently monitored biological parameters, and these relationships were dependent on sea surface temperatures. Parameterisations of isoprene seawater concentrations based on linear regression analyses of these relationships perform well for Arctic and Atlantic data. Levels of all monoterpenes were generally low, with oceanic concentrations ranging from below the detection limit of <1 pmol L-1 to 5 pmol L-1 . In air, monoterpene mixing ratios varied from below the detection limit ( 1 pptv) to 5 pptv, after careful filtering for ship-related contamination. Unlike in previous studies, no clear trends or relationships of the monoterpenes with biological data were found. Limonene showed generally the highest levels in water (up to 84 pmol L-1 in the Atlantic Ocean) and air; however this was attributed mostly to shipborne contamination. We calculate global sea-air fluxes of isoprene and monoterpenes based on this data and compare to previous estimates.
Interdecadal Trichodesmium variability in cold North Atlantic waters

NASA Astrophysics Data System (ADS)

Rivero-Calle, Sara; Del Castillo, Carlos E.; Gnanadesikan, Anand; Dezfuli, Amin; Zaitchik, Benjamin; Johns, David G.

2016-11-01

Studies of the nitrogen cycle in the ocean generally assume that the distribution of the marine diazotroph, Trichodesmium, is restricted to warm, tropical, and subtropical oligotrophic waters. Here we show evidence that Trichodesmium are widely distributed in the North Atlantic. We report an approximately fivefold increase during the 1980s and 1990s in Trichodesmium presence near the British Isles with respect to the average over the last 50 years. A potential explanation is an increase in the Saharan dust source starting in the 1980s, coupled with changes in North Atlantic winds that opened a pathway for dust transport. Results from a coarse-resolution model in which winds vary but iron deposition is climatologically fixed suggest frequent nitrogen limitation in the region and reversals of the Portugal current, but it does not simulate the observed changes in Trichodesmium. Our results suggest that Trichodesmium may be capable of growth at temperatures below 20°C and challenge assumptions about their latitudinal distribution. Therefore, we need to reevaluate assumptions about the temperature limitations of Trichodesmium and the dinitrogen (N2) fixation capabilities of extratropical strains, which may have important implications for the global nitrogen budget.
Interdecadal Trichodesmium Variability in Cold North Atlantic Waters

NASA Technical Reports Server (NTRS)

Rivero-Calle, Sara; Del Castillo, Carlos E.; Dezfuli, Amin; Gnanadesikan, Anand; Zaitchik, Benjamin; Johns, David G.

2016-01-01

Studies of the nitrogen cycle in the ocean generally assume that the distribution of the marine diazotroph, Trichodesmium, is restricted to warm, tropical, and subtropical oligotrophic waters. Here we show evidence that Trichodesmium are widely distributed in the North Atlantic. We report an approximately vefold increase during the 1980s and 1990s in Trichodesmium presence near the British Isles with respect to the average over the last 50 years. A potential explanation is an increase in the Saharan dust source starting in the 1980s, coupled with changes in North Atlantic winds that opened a pathway for dust transport. Results from a coarse-resolution model in which winds vary but iron deposition is climatologically fixed suggest frequent nitrogen limitation in the region and reversals of the Portugal current, but it does not simulate the observed changes in Trichodesmium. Our results suggest that Trichodesmium may be capable of growth at temperatures below 20C and challenge assumptions about their latitudinal distribution. Therefore, we need to reevaluate assumptions about the temperature limitations of Trichodesmium and the dinitrogen (N2) xation capabilities of extratropical strains, which may have important implications for the global nitrogen budget.
Recent Trends in the Arctic Navigable Ice Season and Links to Atmospheric Circulation

NASA Astrophysics Data System (ADS)

Maslanik, J.; Drobot, S.

2002-12-01

One of the potential effects of Arctic climate warming is an increase in the navigable ice season, perhaps resulting in development of the Arctic as a major shipping route. The distance from western North American ports to Europe through the Northwest Passage (NWP) or the Northern Sea Route (NSR) is typically 20 to 60 percent shorter than travel through the Panama Canal, while travel between Europe and the Far East may be reduced by as much as three weeks compared to transport through the Suez Canal. An increase in the navigable ice season would also improve commercial opportunities within the Arctic region, such as mineral and oil exploration and tourism, which could potentially expand the economic base of Arctic residents and companies, but which would also have negative environmental impacts. Utilizing daily passive-microwave derived sea ice concentrations, trends and variability in the Arctic navigable ice season are examined from 1979 through 2001. Trend analyses suggest large increases in the length of the navigable ice season in the Kara and Barents seas, the Sea of Okhotsk, and the Beaufort Sea, with decreases in the length of the navigable ice season in the Bering Sea. Interannual variations in the navigable ice season largely are governed by fluctuations in low-frequency atmospheric circulation, although the specific annular modes affecting the length of the navigable ice season vary by region. In the Beaufort and East Siberian seas, variations in the North Atlantic Oscillation/Arctic Oscillation control the navigable ice season, while variations in the East Pacific anomaly play an important role in controlling the navigable ice season in the Kara and Barents seas. In Hudson Bay, the Canadian Arctic Archipelago, and Baffin Bay, interannual variations in the navigable ice season are strongly related to the Pacific Decadal Oscillation.
Impact of fluctuation of hydro-physical regime in the North Atlantic on the climate of Eurasia

NASA Astrophysics Data System (ADS)

Serykh, Ilya; Anisimov, Mikhail; Byshev, Vladimir; Neiman, Victor; Romanov, Juri

2015-04-01

In the mid-1970s a heat content in the North Atlantic Ocean has substantially changed. Because of its high energy value the event appears to have a significant impact on the regional environment. To verify this suggestion we analyzed the global ocean-atmosphere data related to the negative (1950-1970) and positive (1980-1999) phases of the North Atlantic Oscillation (NAO). The analysis of these data have shown the existence of a thermal dipole in the North Atlantic upper layer which can be interpreted in a sense as an oceanic counterpart of atmospheric NAO. To identify this North Atlantic Dipole (NAD) its index was considered as the ocean 0-100-m layer temperature difference between regions (20°-40°N; 80°-30°W) and (50°-70°N; 60°-10°W). Then the NAD index was suggested a possible physical mechanism factor of the regional ocean-atmosphere system variability which in turn could produce a draw effect on the recent climate of Eurasia. The study showed that the current phase (2000-2013) of the climate in the North Atlantic region becomes qualitatively similar to the situation, typical for period 1950-1970, when the index of continentality in the Eurasian region was a very high. There is a reason to believe that in the coming decades this index is likely to increase, that would be primarily manifested by relatively cold weather in winters and by hot-dry summer seasons. To assess the variability of ocean heat content it was used a General Ocean Circulation model developed at the Institute of numerical mathematics, Russian Academy of Sciences. This model belongs to the class of σ-models, and its distinguishing feature is the splitting of the physical processes and spatial coordinates. By using the model there were performed numerical experiments for the evolution of hydrophysical regime of the North Atlantic Ocean at the period of 1958-2006, with a spatial resolution of 0.25°x0.25° for 25 horizons with time window of 1 hour. As initial conditions for the
North Atlantic Bloom

NASA Technical Reports Server (NTRS)

2007-01-01

Reminiscent of the distinctive swirls in a Van Gogh painting, millions of microscopic plants color the waters of the North Atlantic with strokes of blue, turquoise, green, and brown. Fed by nutrients that have built up during the winter and the long, sunlit days of late spring and early summer, the cool waters of the North Atlantic come alive every year with a vivid display of color. The microscopic plants, called phytoplankton, that give the water this color are the base of the marine food chain. Some species of phytoplankton are coated with scales of calcium (chalk), which turn the water electric blue. Chlorophyll and other light-capturing pigments in others give the water a deep green hue. The proliferation of many different species in various stages of growth and decay provides many nuances of color in this concentrated bloom. The bloom stretches across hundreds of kilometers, well beyond the edges of this photo-like image, captured on June 23, 2007, by the Moderate Resolution Imaging Spectroradiometer (MODIS) flying aboard NASA's Aqua satellite. The upper left edge of the image is bounded by Greenland. Iceland is in the upper right. Plumes of dust are blowing off the island, probably adding nutrients to the surface waters to its south. NASA image courtesy Norman Kuring, Ocean Color Group at NASA Goddard Space Flight Center
Mid-Pliocene planktic foraminifer assemblage of the North Atlantic Ocean

USGS Publications Warehouse

Dowsett, H.J.; Robinson, M.M.

2007-01-01

The US Geological Survey Pliocene Research, Interpretation and Synoptic Mapping (PRISM) North Atlantic faunal data set provides a unique, temporally constrained perspective to document and evaluate the quantitative geographic distribution of key mid-Pliocene taxa. Planktic foraminifer census data from within the PRISM time slab (3.29 to 2.97 Ma) at thirteen sites in the North Atlantic Ocean have been analyzed. We have compiled Scanning Electron Micrographs for an atlas of mid-Pliocene assemblages from the North Atlantic with descriptions of each taxon to document the taxonomic concepts that accompany the PRISM data. In mid-Pliocene assemblages, the geographic distributions of extant taxa are similar to their present day distributions, although some are extended to the north. We use the distribution of extinct taxa to assess previous assumptions regarding environmental preferences.
What Drives the Variability of the Atlantic Water Circulation in the Arctic Ocean?

NASA Astrophysics Data System (ADS)

Lique, C.; Johnson, H. L.

2016-02-01

The Atlantic Water (AW) layer in the Arctic Basin is isolated from the atmosphere by the overlaying surface layer; yet observations of the AW pan-Arctic boundary current have revealed that the velocities in this layer exhibit significant variations on all timescales. Here, analysis of a global ocean/sea ice model hindcast, complemented by experiments performed with an idealized process model, are used to investigate what controls the variability of AW circulation, with a focus on the role of wind forcing. The AW circulation carries the imprint of wind variations, both remotely over the Nordic and Barents seas where they force variability on the AW inflow to the Arctic Basin, and locally over the Arctic Basin through the forcing of the wind-driven Beaufort gyre, which modulates and transfers the wind variability to the AW layer. Our results further suggest that understanding variability in the large amount of heat contained within the AW layer requires a better understanding of the circulation within both AW and surface layers.
Structure of the North American Atlantic Continental Margin.

ERIC Educational Resources Information Center

Klitgord, K. K.; Schlee, J. S.

1986-01-01

Offers explanations on the origin of the North American Atlantic continental margin. Provides an analysis and illustrations of structural and strategraphic elements of cross sections of the Atlantic continental margin. Also explains the operations and applications of seismic-relection profiles in studying ocean areas. (ML)
Climate change in the North American Arctic: A one health perspective

USDA-ARS?s Scientific Manuscript database

Climate change is expected to increase the prevalence of acute and chronic diseases among human and animal populations within the Arctic and sub-Arctic latitudes of North America. Warmer temperatures are expected to increase disease risks from food-borne pathogens, water-borne diseases, and vector-...
Variability of sea surface height and circulation in the North Atlantic: Forcing mechanisms and linkages

NASA Astrophysics Data System (ADS)

Wang, Zeliang; Lu, Youyu; Dupont, Frederic; W. Loder, John; Hannah, Charles; G. Wright, Daniel

2015-03-01

Simulations with a coarse-resolution global ocean model during 1958-2004 are analyzed to understand the inter-annual and decadal variability of the North Atlantic. Analyses of Empirical Orthogonal Functions (EOFs) suggest relationships among basin-scale variations of sea surface height (SSH) and depth-integrated circulation, and the winter North Atlantic Oscillation (NAO) or the East Atlantic Pattern (EAP) indices. The linkages between the atmospheric indices and ocean variables are shown to be related to the different roles played by surface momentum and heat fluxes in driving ocean variability. In the subpolar region, variations of the gyre strength, SSH in the central Labrador Sea and the NAO index are highly correlated. Surface heat flux is important in driving variations of SSH and circulation in the upper ocean and decadal variations of the Atlantic Meridional Overturning Circulation (AMOC). Surface momentum flux drives a significant barotropic component of flow and makes a noticeable contribution to the AMOC. In the subtropical region, momentum flux plays a dominant role in driving variations of the gyre circulation and AMOC; there is a strong correlation between gyre strength and SSH at Bermuda.

Linking North Atlantic Teleconnections to Latitudinal Variability of Wave Climate Along the North American Atlantic Coast

NASA Astrophysics Data System (ADS)

Provancha, C.; Adams, P. N.; Hegermiller, C.; Storlazzi, C. D.

2015-12-01

Shoreline change via coastal erosion and accretion is largely influenced by variations in ocean wave climate. Identifying the sources of these variations is challenging because the timing of wave energy delivery varies over multiple timescales within ocean basins. We present the results of an investigation of USACE Wave Information Studies hindcast hourly wave heights, periods, and directions along the North American Atlantic coast from 1980-2012, designed to explore links between wave climate and teleconnection patterns. Trends in median and extreme significant wave heights (SWHs) demonstrate that mean monthly SWHs increased from 1 to 5 cm/yr along the roughly 3000 km reach of study area, with changes in hurricane season waves appearing to be most influential in producing the overall trends. Distributions of SWHs categorized by North Atlantic Oscillation (NAO) phase, show that positive-period NAO SWHs are greater than negative-period NAO SWHs along the entire eastern seaboard (25°N to 45°N). The most prominent wave direction off Cape Cod, MA during positive-period NAO is approximately 105°, as compared to approximately 75° during negative-period NAO. Prominent wave directions between Cape Canaveral, FL, and Savannah, GA exhibit a similar shift but during opposite phases of the NAO. The results of this analysis suggest that the atmosphere-ocean interactions associated with contrasting NAO phases can significantly change the wave climate observed offshore along the North American Atlantic coast, altering alongshore wave energy fluxes and sediment transport patterns along the coast.
Hydrological change in Southern Europe responding to increasing North Atlantic overturning during Greenland Stadial 1

PubMed Central

Bartolomé, Miguel; Moreno, Ana; Sancho, Carlos; Stoll, Heather M.; Cacho, Isabel; Spötl, Christoph; Belmonte, Ánchel; Edwards, R. Lawrence; Cheng, Hai; Hellstrom, John C.

2015-01-01

Greenland Stadial 1 (GS-1) was the last of a long series of severe cooling episodes in the Northern Hemisphere during the last glacial period. Numerous North Atlantic and European records reveal the intense environmental impact of that stadial, whose origin is attributed to an intense weakening of the Atlantic Meridional Overturning Circulation in response to freshening of the North Atlantic. Recent high-resolution studies of European lakes revealed a mid–GS-1 transition in the climatic regimes. The geographical extension of such atmospheric changes and their potential coupling with ocean dynamics still remains unclear. Here we use a subdecadally resolved stalagmite record from the Northern Iberian Peninsula to further investigate the timing and forcing of this transition. A solid interpretation of the environmental changes detected in this new, accurately dated, stalagmite record is based on a parallel cave monitoring exercise. This record reveals a gradual transition from dry to wet conditions starting at 12,500 y before 2000 A.D. in parallel to a progressive warming of the subtropical Atlantic Ocean. The observed atmospheric changes are proposed to be led by a progressive resumption of the North Atlantic convection and highlight the complex regional signature of GS-1, very distinctive from previous stadial events. PMID:25964366
Hydrological change in Southern Europe responding to increasing North Atlantic overturning during Greenland Stadial 1.

PubMed

Bartolomé, Miguel; Moreno, Ana; Sancho, Carlos; Stoll, Heather M; Cacho, Isabel; Spötl, Christoph; Belmonte, Ánchel; Edwards, R Lawrence; Cheng, Hai; Hellstrom, John C

2015-05-26

Greenland Stadial 1 (GS-1) was the last of a long series of severe cooling episodes in the Northern Hemisphere during the last glacial period. Numerous North Atlantic and European records reveal the intense environmental impact of that stadial, whose origin is attributed to an intense weakening of the Atlantic Meridional Overturning Circulation in response to freshening of the North Atlantic. Recent high-resolution studies of European lakes revealed a mid-GS-1 transition in the climatic regimes. The geographical extension of such atmospheric changes and their potential coupling with ocean dynamics still remains unclear. Here we use a subdecadally resolved stalagmite record from the Northern Iberian Peninsula to further investigate the timing and forcing of this transition. A solid interpretation of the environmental changes detected in this new, accurately dated, stalagmite record is based on a parallel cave monitoring exercise. This record reveals a gradual transition from dry to wet conditions starting at 12,500 y before 2000 A.D. in parallel to a progressive warming of the subtropical Atlantic Ocean. The observed atmospheric changes are proposed to be led by a progressive resumption of the North Atlantic convection and highlight the complex regional signature of GS-1, very distinctive from previous stadial events.
Assessment of Arctic and Antarctic Sea Ice Predictability in CMIP5 Decadal Hindcasts

NASA Technical Reports Server (NTRS)

Yang, Chao-Yuan; Liu, Jiping (Inventor); Hu, Yongyun; Horton, Radley M.; Chen, Liqi; Cheng, Xiao

2016-01-01

This paper examines the ability of coupled global climate models to predict decadal variability of Arctic and Antarctic sea ice. We analyze decadal hindcasts/predictions of 11 Coupled Model Intercomparison Project Phase 5 (CMIP5) models. Decadal hindcasts exhibit a large multimodel spread in the simulated sea ice extent, with some models deviating significantly from the observations as the predicted ice extent quickly drifts away from the initial constraint. The anomaly correlation analysis between the decadal hindcast and observed sea ice suggests that in the Arctic, for most models, the areas showing significant predictive skill become broader associated with increasing lead times. This area expansion is largely because nearly all the models are capable of predicting the observed decreasing Arctic sea ice cover. Sea ice extent in the North Pacific has better predictive skill than that in the North Atlantic (particularly at a lead time of 3-7 years), but there is a reemerging predictive skill in the North Atlantic at a lead time of 6-8 years. In contrast to the Arctic, Antarctic sea ice decadal hindcasts do not show broad predictive skill at any timescales, and there is no obvious improvement linking the areal extent of significant predictive skill to lead time increase. This might be because nearly all the models predict a retreating Antarctic sea ice cover, opposite to the observations. For the Arctic, the predictive skill of the multi-model ensemble mean outperforms most models and the persistence prediction at longer timescales, which is not the case for the Antarctic. Overall, for the Arctic, initialized decadal hindcasts show improved predictive skill compared to uninitialized simulations, although this improvement is not present in the Antarctic.
Geographic variation of persistent organic pollutant levels in humpback whale (Megaptera novaeangliae) feeding areas of the North Pacific and North Atlantic.

PubMed

Elfes, Cristiane T; Vanblaricom, Glenn R; Boyd, Daryle; Calambokidis, John; Clapham, Phillip J; Pearce, Ronald W; Robbins, Jooke; Salinas, Juan Carlos; Straley, Janice M; Wade, Paul R; Krahn, Margaret M

2010-04-01

Seasonal feeding behavior and high fidelity to feeding areas allow humpback whales (Megaptera novaeangliae) to be used as biological indicators of regional contamination. Biopsy blubber samples from male individuals (n = 67) were collected through SPLASH, a multinational research project, in eight North Pacific feeding grounds. Additional male samples (n = 20) were collected from one North Atlantic feeding ground. Persistent organic pollutants were measured in the samples and used to assess contaminant distribution in the study areas. North Atlantic (Gulf of Maine) whales were more contaminated than North Pacific whales, showing the highest levels of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and chlordanes. The highest dichlorodiphenyltrichloroethane (DDT) levels were detected in whales feeding off southern California, USA. High-latitude regions were characterized by elevated levels of hexachlorocyclohexanes (HCHs) but generally nondetectable concentrations of PBDEs. Age was shown to have a positive relationship with SigmaPCBs, SigmaDDTs, Sigmachlordanes, and total percent lipid. Contaminant levels in humpback whales were comparable to other mysticetes and lower than those found in odontocete cetaceans and pinnipeds. Although these concentrations likely do not represent a significant conservation threat, levels in the Gulf of Maine and southern California may warrant further study. (c) 2009 SETAC.
Springtime extreme moisture transport into the Arctic and its impact on sea ice concentration

NASA Astrophysics Data System (ADS)

Yang, Wenchang; Magnusdottir, Gudrun

2017-05-01

Recent studies suggest that springtime moisture transport into the Arctic can initiate sea ice melt that extends to a large area in the following summer and fall, which can help explain Arctic sea ice interannual variability. Yet the impact from an individual moisture transport event, especially the extreme ones, is unclear on synoptic to intraseasonal time scales and this is the focus of the current study. Springtime extreme moisture transport into the Arctic from a daily data set is found to be dominant over Atlantic longitudes. Lag composite analysis shows that these extreme events are accompanied by a substantial sea ice concentration reduction over the Greenland-Barents-Kara Seas that lasts around a week. Surface air temperature also becomes anomalously high over these seas and cold to the west of Greenland as well as over the interior Eurasian continent. The blocking weather regime over the North Atlantic is mainly responsible for the extreme moisture transport, occupying more than 60% of the total extreme days, while the negative North Atlantic Oscillation regime is hardly observed at all during the extreme transport days. These extreme moisture transport events appear to be preceded by eastward propagating large-scale tropical convective forcing by as long as 2 weeks but with great uncertainty due to lack of statistical significance.
North Atlantic Jet Variability in PMIP3 LGM Simulations

NASA Astrophysics Data System (ADS)

Hezel, P.; Li, C.

2017-12-01

North Atlantic jet variability in glacial climates has been shown inmodelling studies to be strongly influenced by upstream ice sheettopography. We analyze the results of 8 models from the PMIP3simulations, forced with a hybrid Laurentide Ice Sheet topography, andcompare them to the PMIP2 simulations which were forced with theICE-5G topography, to develop a general understanding of the NorthAtlantic jet and jet variability. The strengthening of the jet andreduced spatial variability is a robust feature of the last glacialmaximum (LGM) simulations compared to the pre-industrial state.However, the canonical picture of the LGM North Atlantic jet as beingmore zonal and elongated compared to pre-industrial climate states isnot a robust result across models, and may have arisen in theliterature as a function of multiple studies performed with the samemodel.
North Atlantic forcing of tropical Indian Ocean climate.

PubMed

Mohtadi, Mahyar; Prange, Matthias; Oppo, Delia W; De Pol-Holz, Ricardo; Merkel, Ute; Zhang, Xiao; Steinke, Stephan; Lückge, Andreas

2014-05-01

The response of the tropical climate in the Indian Ocean realm to abrupt climate change events in the North Atlantic Ocean is contentious. Repositioning of the intertropical convergence zone is thought to have been responsible for changes in tropical hydroclimate during North Atlantic cold spells, but the dearth of high-resolution records outside the monsoon realm in the Indian Ocean precludes a full understanding of this remote relationship and its underlying mechanisms. Here we show that slowdowns of the Atlantic meridional overturning circulation during Heinrich stadials and the Younger Dryas stadial affected the tropical Indian Ocean hydroclimate through changes to the Hadley circulation including a southward shift in the rising branch (the intertropical convergence zone) and an overall weakening over the southern Indian Ocean. Our results are based on new, high-resolution sea surface temperature and seawater oxygen isotope records of well-dated sedimentary archives from the tropical eastern Indian Ocean for the past 45,000 years, combined with climate model simulations of Atlantic circulation slowdown under Marine Isotope Stages 2 and 3 boundary conditions. Similar conditions in the east and west of the basin rule out a zonal dipole structure as the dominant forcing of the tropical Indian Ocean hydroclimate of millennial-scale events. Results from our simulations and proxy data suggest dry conditions in the northern Indian Ocean realm and wet and warm conditions in the southern realm during North Atlantic cold spells.
Carbon Isotopes of Methane in the Atlantic Realm: Links Between Background Station Data and Emission Source Regions

NASA Astrophysics Data System (ADS)

Lowry, D.; Fisher, R. E.; Lanoisellé, M.; Nisbet, E. G.

2011-12-01

from source studies and monthly emission maps from satellite products. North Atlantic sites have a seasonal cycle (up to 0.7 to 0.8%) that increases polewards, reaching -48% in Arctic summer. Emissions contributing to this seasonal cycle and inter-annual anomalies in the cycle are wetlands (-70 to -55%, but generally more 13C-depleted with increasing latitude) and biomass burning (-30 to -25%). Added to these, and mostly with isotopic signatures between those of the two main natural sources, are anthropogenic fossil fuel (gas, coal), landfill, ruminant and vehicle emissions. The δ13C of the source mix that dominated the North Atlantic from 8 to 53°N in late September 2010 was -56.5%. This is lower than expected if anthropogenic emissions were dominant (eg. London -52 to -49%), but corresponds to the period when maximum influence of high latitude wetland (around -68%) is expected. Methane in air leaving the Eastern seaboard of Canada (Sable Island) allows regional contributions to the Atlantic mix to be assessed. These samples indicate a δ13C source mix of -52 ±2% for air leaving the NE USA and -60 ±2% for air leaving Southern Canada during summer 2010. Further north a wetland emission signal (-70 to -66%) has predominated during recent summers.
Long-term passive acoustic recordings track the changing distribution of North Atlantic right whales (Eubalaena glacialis) from 2004 to 2014.

PubMed

Davis, Genevieve E; Baumgartner, Mark F; Bonnell, Julianne M; Bell, Joel; Berchok, Catherine; Bort Thornton, Jacqueline; Brault, Solange; Buchanan, Gary; Charif, Russell A; Cholewiak, Danielle; Clark, Christopher W; Corkeron, Peter; Delarue, Julien; Dudzinski, Kathleen; Hatch, Leila; Hildebrand, John; Hodge, Lynne; Klinck, Holger; Kraus, Scott; Martin, Bruce; Mellinger, David K; Moors-Murphy, Hilary; Nieukirk, Sharon; Nowacek, Douglas P; Parks, Susan; Read, Andrew J; Rice, Aaron N; Risch, Denise; Širović, Ana; Soldevilla, Melissa; Stafford, Kate; Stanistreet, Joy E; Summers, Erin; Todd, Sean; Warde, Ann; Van Parijs, Sofie M

2017-10-18

Given new distribution patterns of the endangered North Atlantic right whale (NARW; Eubalaena glacialis) population in recent years, an improved understanding of spatio-temporal movements are imperative for the conservation of this species. While so far visual data have provided most information on NARW movements, passive acoustic monitoring (PAM) was used in this study in order to better capture year-round NARW presence. This project used PAM data from 2004 to 2014 collected by 19 organizations throughout the western North Atlantic Ocean. Overall, data from 324 recorders (35,600 days) were processed and analyzed using a classification and detection system. Results highlight almost year-round habitat use of the western North Atlantic Ocean, with a decrease in detections in waters off Cape Hatteras, North Carolina in summer and fall. Data collected post 2010 showed an increased NARW presence in the mid-Atlantic region and a simultaneous decrease in the northern Gulf of Maine. In addition, NARWs were widely distributed across most regions throughout winter months. This study demonstrates that a large-scale analysis of PAM data provides significant value to understanding and tracking shifts in large whale movements over long time scales.
Semidirect Dynamical and Radiative Impact of North African Dust Transport on Lower Tropospheric Clouds over the Subtropical North Atlantic in CESM 1.0

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

DeFlorio, Mike; Ghan, Steven J.; Singh, Balwinder

This study uses a century length pre-industrial climate simulation by the Community Earth System Model (CESM 1.0) to explore statistical relationships between dust, clouds and atmospheric circulation, and to suggest a dynamical, rather than microphysical, mechanism linking subtropical North Atlantic lower tropospheric cloud cover with North African dust transport. The length of the run allows us to account for interannual variability of dust emissions and transport downstream of North Africa in the model. CESM’s mean climatology and probability distribution of aerosol optical depth in this region agrees well with available AERONET observations. In addition, CESM shows strong seasonal cycles ofmore » dust burden and lower tropospheric cloud fraction, with maximum values occurring during boreal summer, when a strong correlation between these two variables exists downstream of North Africa over the subtropical North Atlantic. Calculations of Estimated Inversion Strength (EIS) and composites of EIS on high and low downstream North Africa dust months during boreal summer reveal that dust is likely increasing inversion strength over this region due to both solar absorption and reflection. We find no evidence for a microphysical link between dust and lower tropospheric clouds in this region. These results yield new insight over an extensive period of time into the complex relationship between North African dust and lower tropospheric clouds over the open ocean, which has previously been hindered by spatiotemporal constraints of observations. Our findings lay a framework for future analyses using sub-monthly data over regions with different underlying dynamics.« less
Epidemiology of bacterial meningitis in the North American Arctic, 2000-2010.

PubMed

Gounder, Prabhu P; Zulz, Tammy; Desai, Shalini; Stenz, Flemming; Rudolph, Karen; Tsang, Raymond; Tyrrell, Gregory J; Bruce, Michael G

2015-08-01

To determine the incidence of meningitis caused by Haemophilus influenzae, Neisseria meningitidis, and Streptococcus pneumoniae in the North American Arctic during 2000-2010. Surveillance data were obtained from the International Circumpolar Surveillance network. We defined a case of bacterial meningitis caused by H. influenzae, N. meningitidis, or S. pneumoniae as a culture-positive isolate obtained from a normally sterile site in a resident with a meningitis diagnosis. The annual incidence/100,000 persons for meningitis caused by H. influenzae, N. meningitidis, and S. pneumoniae among all North American Arctic residents was: 0.6, 0.5, and 1.5, respectively; the meningitis incidence among indigenous persons in Alaska and Canada (indigenous status not recorded in Greenland) for those three bacteria was: 2.1, 0.8, and 2.4, respectively. The percentage of pneumococcal isolates belonging to a 7-valent pneumococcal conjugate vaccine serotype declined from 2000-2004 to 2005-2010 (31%-2%, p-value <0.01). During 2005-2010, serotype a caused 55% of H. influenzae meningitis and serogroup B caused 86% of meningococcal meningitis. Compared with all North American Arctic residents, indigenous people suffer disproportionately from bacterial meningitis. Arctic residents could benefit from the development of an H. influenzae serotype a vaccine and implementation of a meningococcal serogroup B vaccine. Published by Elsevier Ltd.
The intertropical convergence zone modulates intense hurricane strikes on the western North Atlantic margin

PubMed Central

van Hengstum, Peter J.; Donnelly, Jeffrey P.; Fall, Patricia L.; Toomey, Michael R.; Albury, Nancy A.; Kakuk, Brian

2016-01-01

Most Atlantic hurricanes form in the Main Development Region between 9°N to 20°N along the northern edge of the Intertropical Convergence Zone (ITCZ). Previous research has suggested that meridional shifts in the ITCZ position on geologic timescales can modulate hurricane activity, but continuous and long-term storm records are needed from multiple sites to assess this hypothesis. Here we present a 3000 year record of intense hurricane strikes in the northern Bahamas (Abaco Island) based on overwash deposits in a coastal sinkhole, which indicates that the ITCZ has likely helped modulate intense hurricane strikes on the western North Atlantic margin on millennial to centennial-scales. The new reconstruction closely matches a previous reconstruction from Puerto Rico, and documents a period of elevated intense hurricane activity on the western North Atlantic margin from 2500 to 1000 years ago when paleo precipitation proxies suggest that the ITCZ occupied a more northern position. Considering that anthropogenic warming is predicted to be focused in the northern hemisphere in the coming century, these results provide a prehistoric analog that an attendant northern ITCZ shift in the future may again return the western North Atlantic margin to an active hurricane interval. PMID:26906670
Cenozoic Circulation History of the North Atlantic Ocean From Seismic Stratigraphy of the Newfoundland Ridge Drift Complex

NASA Astrophysics Data System (ADS)

Boyle, P. R.; Romans, B.; Norris, R. D.; Tucholke, B. E.; Swift, S. A.; Sexton, P. F.

2014-12-01

In the North Atlantic Ocean, contour-following bottom currents have eroded regional unconformities and deposited contourite drifts that exceed two km in thickness and extend for 100s of km. The character of deep-water masses that are conveyed through ocean basins by such currents influence global heat transfer and ocean-atmosphere partitioning of CO2. The Newfoundland Ridge Drift Complex lies directly under the modern Deep Western Boundary Current southeast of Newfoundland, close to the site of overturning in the northwest Atlantic Ocean and at the intersection of the warm Gulf Stream and cool Labrador surface currents. To the south are regions of the western North Atlantic basin that are influenced by southern- as well as northern-sourced bottom waters. Here, we document the evolution of North Atlantic deep-water circulation by seismic-stratigraphic analysis of the long-lived and areally extensive Newfoundland Ridge Drift Complex. IODP Expedition 342 boreholes provide age control on seismic units, allowing sedimentation patterns to be placed in a temporal framework. We find three major phases of sedimentation: pre-contourite drift (~115-50 Ma), active contourite drift (~50-2.6 Ma), and late-contourite drift (~2.6-0 Ma). Bottom-current-controlled deposition of terrigenous-rich sediment began at ~50 Ma, which correlates to the onset of a long-term global cooling trend. A further change in deep circulation near the Eocene-Oligocene transition (~30 Ma) is indicated by more focused drift sedimentation with greatly increased accumulation rates and stratal architecture dominated by mud waves. At ~2.6 Ma to present the axis of drift accumulation shifted markedly towards shallower water depths, corresponding with the onset of Northern Hemisphere ice sheets. We discuss how these reorganizations of deep circulation correlate with results of other North Atlantic seismic stratigraphic studies to the north and south.
Anthropogenic iodine-129 in seawater along a transect from the Norwegian coastal current to the North Pole.

PubMed

Alfimov, V; Aldahan, A; Possnert, G; Winsor, P

2004-12-01

Variation in the concentrations of iodine-129 (129I, T1/2=15.7 Myr), a low-level radioactive component of nuclear fuel waste, is documented in surface waters and depth profiles collected during 2001 along a transect from the Norwegian Coastal Current to the North Pole. The surface waters near the Norwegian coast are found to have 20 times higher 129I concentration than the surface waters of the Arctic Ocean. The depth profiles of 129I taken in the Arctic Ocean reveal a sharp decline in the concentration to a depth of about 300-500 m followed by a weaker gradient extending down to the bottom. A twofold increase in the 129I concentration is observed in the upper 1000 m since 1996. Based on known estimates of marine transient time from the release sources (the nuclear reprocessing facilities at La Hague, France, and Sellafield, UK), a doubling in the 129I inventory of the top 1000 m of the Arctic Ocean is expected to occur between the years 2001 and 2006. As 129I of polar mixed layer and Atlantic layer of the Arctic Ocean is ventilated by the East Greenland Current into the Nordic Seas and North Atlantic Ocean, further dispersal and increase of the isotope concentration in these regions will be encountered in the near future.
The East Atlantic - West Russia Teleconnection in the North Atlantic: Climate Impact and Relation to Rossby Wave Propagation

NASA Technical Reports Server (NTRS)

Lim, Young-Kwon

2014-01-01

Large-scale winter teleconnection of the East Atlantic - West Russia (EA-WR) over the Atlantic and surrounding regions is examined in order to quantify its impacts on temperature and precipitation and identify the physical mechanisms responsible for its existence. A rotated empirical orthogonal function (REOF) analysis of the upper-tropospheric monthly height field captures successfully the EA-WR pattern and its interannual variation, with the North Atlantic Oscillation as the first mode. EA-WRs climate impact extends from eastern North America to Eurasia. The positive (negative) EA-WR produces positive (negative) temperature anomalies over the eastern US, western Europe and Russia east of Caspian Sea, with negative (positive) anomalies over eastern Canada, eastern Europe including Ural Mountains and the Middle East. These anomalies are largely explained by lower-tropospheric temperature advections. Positive (negative) precipitation anomalies are found over the mid-latitude Atlantic and central Russia around 60E, where lower-level cyclonic (anticyclonic) circulation anomaly is dominant. The eastern Canada and the western Europe are characterized by negative (positive) precipitation anomalies.The EA-WR is found to be closely associated with Rossby wave propagation. Wave activity fluxes show that it is strongly tied to large-scale stationary waves. Furthermore, a stationary wave model (SWM) forced with vorticity transients in the mid-latitude Atlantic (approximately 40N) or diabatic heat source over the subtropical Atlantic near the Caribbean Sea produces well-organized EA-WR-like wave patterns, respectively. Sensitivity tests with the SWM indicate improvement in the simulation of the EA-WR when the mean state is modified to have a positive NAO component that enhances upper-level westerlies between 40-60N.
Thermal ecotypes of amphi-Atlantic algae. I. Algae of Arctic to cold-temperate distribution ( Chaetomorpha melagonium, Devaleraea ramentacea and Phycodrys rubens)

NASA Astrophysics Data System (ADS)

Novaczek, I.; Lubbers, G. W.; Breeman, A. M.

1990-09-01

Three species of Arctic to cold-temperate amphi-Atlantic algae, all occurring also in the North Pacific, were tested for growth and/or survival at temperatures of -20 to 30°C. When isolates from both western and eastern Atlantic shores were tested side-by-side, it was found that thermal ecotypes may occur in such Arctic algae. Chaetomorpha melagonium was the most eurythermal of the 3 species. Isolates of this alga were alike in temperature tolerance and growth rate but Icelandic plants were more sensitive to the lethal temperature of 25°C than were more southerly isolates from both east and west. With regard to Devaleraea ramentacea, one Canadian isolate grew extraordinarily well at -2 and 0°C, and all tolerated temperatures 2 3°C higher than the lethal limit (18 20°C) of isolates from Europe. Concerning Phycodrys rubens, both eastern and western isolates died at 20°C but European plants tolerated the lethal high temperature longer, were more sensitive to freezing, and attained more rapid growth at optimal temperatures. The intertidal species, C. melagonium and D. ramentacea, both survived freezing at -5 and -20°C, at least for short time periods. C. melagonium was more susceptible than D. ramentacea to desiccation. Patterns of thermal tolerance may provide insight into the evolutionary history of seaweed species.
The Arctic Boreal Vulnerability Experiment: Observing, Understanding, and Predicting Social-Ecological Change in the Far North

NASA Astrophysics Data System (ADS)

Mack, M. C.; Goetz, S. J.; Kasischke, E. S.; Kimball, J. S.; Boelman, N.

2015-12-01

In the high northern latitudes, climate is warming more rapidly than anywhere else on Earth, transforming vulnerable arctic tundra and boreal forest landscapes. These changes are altering the structure and function of energy, water and carbon cycles, producing significant feedbacks to regional and global climate through changes in energy, water and carbon cycles. These changes are also challenging local and global society. At the local level, communities seek to adapt to new social-ecological regimes. At the global level, changing arctic and boreal systems are increasing becoming the focus of policy discussions at all levels of decision-making. National and international scientific efforts associated with a new NASA field campaign, the Arctic-Boreal Vulnerability Experiment (ABOVE) will advance our ability to observe, understand and predict the complex, multiscale and non-linear processes that are confronting the natural and social systems in this rapidly changing region. Over the next decade, the newly assembled ABOVE Science Team will pursue this overarching question: "How vulnerable or resilient are ecosystems and society to environmental change in the Arctic and boreal region of western North America?" Through integration of remote sensing and in situ observations with modeling of both ecological and social systems, the ABOVE Science Team will advance an interdisciplinary understanding of the Far North. In this presentation, we will discuss the conceptual basis for the ABOVE Field Campaign, describe Science Team composition and timeline, and update the community on activities. In addition, we will reflect on the visionary role of Dr. Diane Wickland, retired NASA Terrestrial Ecology Program Manager and lead of the Carbon Cycle & Ecosystems Focus Area, in the development and commencement of ABOVE.
Late Paleozoic to Cenozoic reconstruction of the Arctic

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

Smith, D.G.

1985-04-01

The plate tectonic evolution of the Arctic is reassessed in the context of the known histories of the North Atlantic and North Pacific Oceans, and of the tectono-stratigraphic development of the lands around the Arctic Ocean. Computer map-drawing facilities were used to provide geometrical constraints on the reconstructions, which are presented to in the form of eight palinispatic maps. Stratigraphic similarities among presently dispersed continental areas identify fragments of a former Barents plate. Collision of this plate with the Euramerican plate was the cause of the Late Devonian Ellesmerian orogeny. In later Paleozoic time, the Siberian continent also joined Pangeamore » by collision with the combined Barents and Euramerican plates along the Ural-Taymyr suture. The Mesozoic-Cenozoic history of the Arctic is concerned with the fragmentation and dispersal of the former Barents plate, as well as the accretion of new continental fragments from the Pacific.« less
How Rapid Change Affects Deltas in the Arctic Region

NASA Astrophysics Data System (ADS)

Overeem, I.; Bendixen, M.

2017-12-01

Deltas form where the river drains into the ocean. Consequently, delta depositional processes are impacted by either changes in the respective river drainage basin or by changes in the regional marine environment. In a warming Arctic region rapid change has occurred over the last few decades in both the terrestrial domain as well as in the marine domain. Important terrestrial controls include 1) change in permafrost possibly destabilizing river banks, 2) strong seasonality of river discharge due to a short melting season, 3) high sediment supply if basins are extensively glaciated, 4) lake outbursts and ice jams favoring river flooding. Whereas in the Arctic marine domain sea ice loss promotes wave and storm surge impact, and increased longshore transport. We here ask which of these factors dominate any morphological change in Arctic deltas. First, we analyze hydrological data to assess change in Arctic-wide river discharge characteristics and timing, and sea ice concentration data to map changes in sea ice regime. Based on this observational analysis we set up a number of scenarios of change. We then model hypothetical small-scale delta formation considering change in these primary controls by setting up a numerical delta model, and combining it dynamically with a permafrost model. We find that for typical Greenlandic deltas changes in river forcing due to ice sheet melt dominate the morphological change, which is corroborated by mapping of delta progradation from aerial photos and satellite imagery. Whereas in other areas, along the North Slope and the Canadian Arctic small deltas are more stable or experienced retreat. Our preliminary coupled model allows us to further disentangle the impact of major forcing factors on delta evolution in high-latitude systems.

The North Atlantic Ocean Is in a State of Reduced Overturning

NASA Astrophysics Data System (ADS)

Smeed, D. A.; Josey, S. A.; Beaulieu, C.; Johns, W. E.; Moat, B. I.; Frajka-Williams, E.; Rayner, D.; Meinen, C. S.; Baringer, M. O.; Bryden, H. L.; McCarthy, G. D.

2018-02-01

The Atlantic Meridional Overturning Circulation (AMOC) is responsible for a variable and climatically important northward transport of heat. Using data from an array of instruments that span the Atlantic at 26°N, we show that the AMOC has been in a state of reduced overturning since 2008 as compared to 2004-2008. This change of AMOC state is concurrent with other changes in the North Atlantic such as a northward shift and broadening of the Gulf Stream and altered patterns of heat content and sea surface temperature. These changes resemble the response to a declining AMOC predicted by coupled climate models. Concurrent changes in air-sea fluxes close to the western boundary reveal that the changes in ocean heat transport and sea surface temperature have altered the pattern of ocean-atmosphere heat exchange over the North Atlantic. These results provide strong observational evidence that the AMOC is a major factor in decadal-scale variability of North Atlantic climate.
North Atlantic (NAT) aided inertial navigation system simulation volume I. : technical results

DOT National Transportation Integrated Search

1973-07-01

Current air traffic operations over the North ATlantic (NAT) and the application of hybrid navigation systems to obtain more accurate performance on these NAT routes are reviewed. A digital computer simulation program (NATNAV - North ATlantic NAVigat...
A Decadal-scale Air-sea Interaction Theory for North Atlantic Multidecadal Variability: the NAT-NAO-AMOC-AMO Coupled Mode and Its Remote Influences

NASA Astrophysics Data System (ADS)

Li, Jianping; Sun, Cheng; Jin, Fei-Fei

2017-04-01

ABSTRACT North Atlantic region shows prominent multidecadal variability. Observational analysis shows that the North Atlantic Oscillation (NAO) leads the oceanic Atlantic Multidecadal Oscillation (AMO) by 15-20 years and the latter also leads the former by around 15 years. The mechanisms are investigated using simulations from a fully coupled model, and a NATNAO-AMOC-AMO Coupled Mode is proposed to explain the multidecadal variability in North Atlantic region. The NAT-NAO-AMO-AMOC coupled mode has important remote influences on regional climates. Observational analysis identifies a significant in-phase relationship between the AMV and Siberian warm season (May to October) precipitation. The physical mechanism for this relationship is investigated using both observations and numerical simulations. North Atlantic sea surface temperature (SST) warming associated with the positive AMV phase can excite an eastward propagating wave train response across the entire Eurasian continent, which includes an east-west dipole structure over Siberia. The dipole then leads to anomalous southerly winds bringing moisture northward to Siberia; the precipitation increases correspondingly. Furthermore, a prominent teleconnection pattern of multidecadal variability of cold season (November to April) upper-level atmospheric circulation over North Africa and Eurasia (NA-EA) is revealed by empirical orthogonal function analysis of the Twentieth Century Reanalysis data, and this teleconnection pattern is referred to as the Africa-Asia multidecadal teleconnection pattern (AAMT). A strong inphase relationship is observed between the AAMT and Atlantic multidecadal variability (AMV) and this connection is mainly due to Rossby wave dynamics. The AAMT acts as an atmospheric bridge conveying the influence of AMV onto the downstream multidecadal climate variability.
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.
Understanding Mesoscale Land-Atmosphere Interactions in Arctic Region

NASA Astrophysics Data System (ADS)

Hong, X.; Wang, S.; Nachamkin, J. E.

2017-12-01

Land-atmosphere interactions in Arctic region are examined using the U.S. Navy Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS©*) with the Noah Land Surface Model (LSM). Initial land surface variables in COAMPS are interpolated from the real-time NASA Land Information System (LIS). The model simulations are configured for three nest grids with 27-9-3 km horizontal resolutions. The simulation period is set for October 2015 with 12-h data assimilation update cycle and 24-h integration length. The results are compared with those simulated without using LSM and evaluated with observations from ONR Sea State R/V Sikuliaq cruise and the North Slope of Alaska (NSA). There are complex soil and vegetation types over the surface for simulation with LSM, compared to without LSM simulation. The results show substantial differences in surface heat fluxes between bulk surface scheme and LSM, which may have an important impact on the sea ice evolution over the Arctic region. Evaluations from station data show surface air temperature and relative humidity have smaller biases for simulation using LSM. Diurnal variation of land surface temperature, which is necessary for physical processes of land-atmosphere, is also better captured than without LSM.
Major cause of unprecedented Arctic warming in January 2016: Critical role of an Atlantic windstorm

PubMed Central

Kim, Baek-Min; Hong, Ja-Young; Jun, Sang-Yoon; Zhang, Xiangdong; Kwon, Hataek; Kim, Seong-Joong; Kim, Joo-Hong; Kim, Sang-Woo; Kim, Hyun-Kyung

2017-01-01

In January 2016, the Arctic experienced an extremely anomalous warming event after an extraordinary increase in air temperature at the end of 2015. During this event, a strong intrusion of warm and moist air and an increase in downward longwave radiation, as well as a loss of sea ice in the Barents and Kara seas, were observed. Observational analyses revealed that the abrupt warming was triggered by the entry of a strong Atlantic windstorm into the Arctic in late December 2015, which brought enormous moist and warm air masses to the Arctic. Although the storm terminated at the eastern coast of Greenland in late December, it was followed by a prolonged blocking period in early 2016 that sustained the extreme Arctic warming. Numerical experiments indicate that the warming effect of sea ice loss and associated upward turbulent heat fluxes are relatively minor in this event. This result suggests the importance of the synoptically driven warm and moist air intrusion into the Arctic as a primary contributing factor of this extreme Arctic warming event. PMID:28051170
Paleoenvironmental Reconstruction of the North Atlantic Current Variations from MIS 3 to Holocene Based on Multiproxy Record from the North-East Scotland Continental Margin.

NASA Astrophysics Data System (ADS)

Ovsepyan, Y.; Tikhonova, A.; Novichkova, E.; Gupta, R. M.; Korsun, S.; Matul, A.

2017-12-01

In order to reconstruct the history of water mass interaction between the North Atlantic and the Nordic Seas since MIS 3 to the present, the sediment core from the North-East Scotland continental slope was investigated. The site of core AI-3521 (59°30.009 N, 7°20.062 E) from the 1051 m water depth is located beneath the pathway of the North Atlantic current which transports warm and saline Atlantic surface water to the Norwegian Sea. The age model of the sequence is based on stable isotope record of benthic Cassidulina neoteretis and planktic Neogloboquadrina pachyderma sin. and Globigerina bulloides. The Holocene interval of the upper 1.5 m is characterized by high sedimentation rates and the high biodiversity of microfauna. The distribution of ice rafted debris and CaCO3 content; benthic and planktic foraminiferal assemblages; oxygen, carbon and boron isotopes, Mg/Ca ratio were used to reconstruct the regional paleoceanographic conditions (bioproductivity, temperature, salinity) and to compare with the paleoclimatic events in the subpolar North Atlantic in the frame of the global environmental changes during the Late Pleistocene and Holocene. The research was supported by Russian Science Foundation projects 16-47-02009 and 14-50-00095.
North Atlantic observations sharpen meridional overturning projections

NASA Astrophysics Data System (ADS)

Olson, R.; An, S.-I.; Fan, Y.; Evans, J. P.; Caesar, L.

2018-06-01

Atlantic Meridional Overturning Circulation (AMOC) projections are uncertain due to both model errors, as well as internal climate variability. An AMOC slowdown projected by many climate models is likely to have considerable effects on many aspects of global and North Atlantic climate. Previous studies to make probabilistic AMOC projections have broken new ground. However, they do not drift-correct or cross-validate the projections, and do not fully account for internal variability. Furthermore, they consider a limited subset of models, and ignore the skill of models at representing the temporal North Atlantic dynamics. We improve on previous work by applying Bayesian Model Averaging to weight 13 Coupled Model Intercomparison Project phase 5 models by their skill at modeling the AMOC strength, and its temporal dynamics, as approximated by the northern North-Atlantic temperature-based AMOC Index. We make drift-corrected projections accounting for structural model errors, and for the internal variability. Cross-validation experiments give approximately correct empirical coverage probabilities, which validates our method. Our results present more evidence that AMOC likely already started slowing down. While weighting considerably moderates and sharpens our projections, our results are at low end of previously published estimates. We project mean AMOC changes between periods 1960-1999 and 2060-2099 of -4.0 Sv and -6.8 Sv for RCP4.5 and RCP8.5 emissions scenarios respectively. The corresponding average 90% credible intervals for our weighted experiments are [-7.2, -1.2] and [-10.5, -3.7] Sv respectively for the two scenarios.
Two Distinct Roles of Atlantic SSTs in ENSO Variability: North Tropical Atlantic SST and Atlantic Nino

NASA Technical Reports Server (NTRS)

Ham, Yoo-Geun; Kug, Jong-Seong; Park, Jong-Yeon

2013-01-01

Two distinct roles of the Atlantic sea surface temperatures (SSTs), namely, the North Tropical Atlantic (NTA) SST and the Atlantic Nino, on the El Nino-Southern Oscillation (ENSO) variability are investigated using the observational data from 1980 to 2010 and coupled model experiments. It appears that the NTA SST and the Atlantic Nino can be used as two independent predictors for predicting the development of ENSO events in the following season. Furthermore, they are likely to be linked to different types of El Nino events. Specifically, the NTA SST cooling during February, March, and April contributes to the central Pacific warming at the subsequent winter season, while the negative Atlantic Nino event during June, July, and August contributes to enhancing the eastern Pacific warming. The coupled model experiments support these results. With the aid of a lagged inverse relationship, the statistical forecast using two Atlantic indices can successfully predict various ENSO indices.
A detailed gravimetric geoid of North America, the North Atlantic, Eurasia, and Australia

NASA Technical Reports Server (NTRS)

Marsh, J. G.

1973-01-01

A computer program was developed for the calculation of a goid based upon a combination of satellite and surface gravity data. A detailed gravimetric geoid of North America, the North Atlantic, Eurasia, and Australia was derived by using this program.
Holocene evolution of the North Atlantic subsurface transport

NASA Astrophysics Data System (ADS)

Repschläger, Janne; Garbe-Schönberg, Dieter; Weinelt, Mara; Schneider, Ralph

2017-04-01

Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ18O and Mg / Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.
Pliocene cooling enhanced by flow of low-salinity Bering Sea water to the Arctic Ocean.

PubMed

Horikawa, Keiji; Martin, Ellen E; Basak, Chandranath; Onodera, Jonaotaro; Seki, Osamu; Sakamoto, Tatsuhiko; Ikehara, Minoru; Sakai, Saburo; Kawamura, Kimitaka

2015-06-29

Warming of high northern latitudes in the Pliocene (5.33-2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling.
Pliocene cooling enhanced by flow of low-salinity Bering Sea water to the Arctic Ocean

PubMed Central

Horikawa, Keiji; Martin, Ellen E.; Basak, Chandranath; Onodera, Jonaotaro; Seki, Osamu; Sakamoto, Tatsuhiko; Ikehara, Minoru; Sakai, Saburo; Kawamura, Kimitaka

2015-01-01

Warming of high northern latitudes in the Pliocene (5.33–2.58 Myr ago) has been linked to the closure of the Central American Seaway and intensification of North Atlantic Deep Water. Subsequent cooling in the late Pliocene may be related to the effects of freshwater input from the Arctic Ocean via the Bering Strait, disrupting North Atlantic Deep Water formation and enhancing sea ice formation. However, the timing of Arctic freshening has not been defined. Here we present neodymium and lead isotope records of detrital sediment from the Bering Sea for the past 4.3 million years. Isotopic data suggest the presence of Alaskan glaciers as far back as 4.2 Myr ago, while diatom and C37:4 alkenone records show a long-term trend towards colder and fresher water in the Bering Sea beginning with the M2 glaciation (3.3 Myr ago). We argue that the introduction of low-salinity Bering Sea water to the Arctic Ocean by 3.3 Myr ago preconditioned the climate system for global cooling. PMID:26119338
Air-sea exchange fluxes of synthetic polycyclic musks in the North Sea and the Arctic.

PubMed

Xie, Zhiyong; Ebinghaus, Ralf; Temme, Christian; Heemken, Olaf; Ruck, Wolfgang

2007-08-15

Synthetic polycyclic musk fragrances Galaxolide (HHCB) and Tonalide (AHTN) were measured simultaneously in air and seawater in the Arctic and the North Sea and in the rural air of northern Germany. Median concentrations of gas-phase HHCB and AHTN were 4 and 18 pg m(-3) in the Arctic, 28 and 18 pg m(-3) in the North Sea, and 71 and 21 pg m(-3) in northern Germany, respectively. Various ratios of HHCB/AHTN implied that HHCB is quickly removed by atmospheric degradation, while AHTN is relatively persistent in the atmosphere. Dissolved concentrations ranged from 12 to 2030 pg L(-1) for HHCB and from below the method detection limit (3 pg L(-1)) to 965 pg L(-1) for AHTN with median values of 59 and 23 pg L(-1), respectively. The medians of volatilization fluxes for HHCB and AHTN were 27.2 and 14.2 ng m(-2) day(-1) and the depositional fluxes were 5.9 and 3.3 ng m(-2) day(-1), respectively, indicating water-to-air volatilization is a significant process to eliminate HHCB and AHTN from the North Sea. In the Arctic, deposition fluxes dominated the air-sea gas exchange of HHCB and AHTN, suggesting atmospheric input controls the levels of HHCB and AHTN in the polar region.
Maestrichtian benthic foraminifers from Ocean Point, North Slope, Alaska ( USA).

USGS Publications Warehouse

McDougall, K.

1987-01-01

Previous studies of fauna and flora from Ocean Point, Alaska, have suggested ages ranging from Campanian to early Eocene and that these assemblages are either highly endemic or commonplace. I demonstrate that the moderately abundant benthic foraminifers constitute early Maestrichtian boreal assemblages common to Canada and northern Europe. Paleoenvironmental analysis indicates that deposition took place in outer neritic settings (50 to 150m). The Ocean Point benthic foraminiferal assemblages contain species that migrated from the US Gulf Coast, North American Interior and Europe during the Campanian, and from Europe during the Maestrichtian. These faunal affinities suggest that seaways connected the Arctic to the North American Interior and Atlantic during the Campanian and that a shallow seaway connected the Arctic to the Atlantic during the early Maestrichtian. - from Author
Impacts of Changed Extratropical Storm Tracks on Arctic Sea Ice Export through Fram Strait

NASA Astrophysics Data System (ADS)

Wei, J.; Zhang, X.; Wang, Z.

2017-12-01

Studies have indicated a poleward shift of extratropical storm tracks and intensification of Arctic storm activities, in particular on the North Atlantic side of the Arctic Ocean. To improve understanding of dynamic effect on changes in Arctic sea ice mass balance, we examined the impacts of the changed storm tracks and activities on Arctic sea ice export through Fram Strait through ocean-sea ice model simulations. The model employed is the high-resolution Massachusetts Institute of Technology general circulation model (MITgcm), which was forced by the Japanese 25-year Reanalysis (JRA-25) dataset. The results show that storm-induced strong northerly wind stress can cause simultaneous response of daily sea ice export and, in turn, exert cumulative effects on interannual variability and long-term changes of sea ice export. Further analysis indicates that storm impact on sea ice export is spatially dependent. The storms occurring southeast of Fram Strait exhibit the largest impacts. The weakened intensity of winter storms in this region after 1994/95 could be responsible for the decrease of total winter sea ice export during the same time period.
The Role of the North Atlantic Oscillation (NAO) on Recent Greenland Surface Mass Loss and Mass Partitioning

NASA Astrophysics Data System (ADS)

Tedesco, M.; Alexander, P.; Porter, D. F.; Fettweis, X.; Luthcke, S. B.; Mote, T. L.; Rennermalm, A.; Hanna, E.

2017-12-01

Despite recent changes in Greenland surface mass losses and atmospheric circulation over the Arctic, little attention has been given to the potential role of large-scale atmospheric processes on the spatial and temporal variability of mass loss and partitioning of the GrIS mass loss. Using a combination of satellite gravimetry measurements, outputs of the MAR regional climate model and reanalysis data, we show that changes in atmospheric patterns since 2013 over the North Atlantic region of the Arctic (NAA) modulate total mass loss trends over Greenland together with the spatial and temporal distribution of mass loss partitioning. For example, during the 2002 - 2012 period, melting persistently increased, especially along the west coast, as a consequence of increased insulation and negative NAO conditions characterizing that period. Starting in 2013, runoff along the west coast decreased while snowfall increased substantially, when NAO turned to a more neutral/positive state. Modeled surface mass balance terms since 1950 indicate that part of the GRACE-period, specifically the period between 2002 and 2012, was exceptional in terms of snowfall over the east and northeast regions. During that period snowfall trend decreased to almost 0 Gt/yr from a long-term increasing trend, which presumed again in 2013. To identify the potential impact of atmospheric patterns on mass balance and its partitioning, we studied the spatial and temporal correlations between NAO and snowfall/runoff. Our results indicate that the correlation between summer snowfall and NAO is not stable during the 1950 - 2015 period. We further looked at changes in patterns of circulation using self organizing maps (SOMs) to identify the atmospheric patterns characterizing snowfall during different periods. We discuss potential implications for past changes and future GCM and RCM simulations.
A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

NASA Technical Reports Server (NTRS)

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While magnetic anomaly data represent the main focus of this study recently derived satellite gravity data are playing a major role in Arctic studies.
A Review of Magnetic Anomaly Field Data for the Arctic Region: Geological Implications

NASA Technical Reports Server (NTRS)

Taylor, Patrick T.; vonFrese, Ralph; Roman, Daniel; Frawley, James J.

1999-01-01

Due to its inaccessibility and hostile physical environment remote sensing data, both airborne and satellite measurements, has been the main source of geopotential data over the entire Arctic region. Ubiquitous and significant external fields, however, hinder crustal magnetic field studies. These potential field data have been used to derive tectonic models for the two major tectonic sectors of this region, the Amerasian and Eurasian Basins. The latter is dominated by the Nansen-Gakkel or Mid-Arctic Ocean Ridge and is relatively well known. The origin and nature of the Alpha and Mendeleev Ridges, Chukchi Borderland and Canada Basin of the former are less well known and a subject of controversy. The Lomonosov Ridge divides these large provinces. In this report we will present a summary of the Arctic geopotential anomaly data derived from various sources by various groups in North America and Europe and show how these data help us unravel the last remaining major puzzle of the global plate tectonic framework. While Magnetic anomaly data represent the main focus of this study recently derived satellite gravity data (Laxon and McAdoo, 1998) are playing a major role in Arctic studies.
Annually resolved North Atlantic marine climate over the last millennium

NASA Astrophysics Data System (ADS)

Reynolds, D. J.; Scourse, J. D.; Halloran, P. R.; Nederbragt, A. J.; Wanamaker, A. D.; Butler, P. G.; Richardson, C. A.; Heinemeier, J.; Eiríksson, J.; Knudsen, K. L.; Hall, I. R.

2016-12-01

Owing to the lack of absolutely dated oceanographic information before the modern instrumental period, there is currently significant debate as to the role played by North Atlantic Ocean dynamics in previous climate transitions (for example, Medieval Climate Anomaly-Little Ice Age, MCA-LIA). Here we present analyses of a millennial-length, annually resolved and absolutely dated marine δ18O archive. We interpret our record of oxygen isotope ratios from the shells of the long-lived marine bivalve Arctica islandica (δ18O-shell), from the North Icelandic shelf, in relation to seawater density variability and demonstrate that solar and volcanic forcing coupled with ocean circulation dynamics are key drivers of climate variability over the last millennium. During the pre-industrial period (AD 1000-1800) variability in the sub-polar North Atlantic leads changes in Northern Hemisphere surface air temperatures at multi-decadal timescales, indicating that North Atlantic Ocean dynamics played an active role in modulating the response of the atmosphere to solar and volcanic forcing.

The global warming in the North Atlantic Sector and the role of the ocean

NASA Astrophysics Data System (ADS)

Hand, R.; Keenlyside, N. S.; Greatbatch, R. J.; Omrani, N. E.

2014-12-01

This work presents an analysis of North Atlantic ocean-atmosphere interaction in a warming climate, based on a long-term earth system model experiment forced by the RCP 8.5 scenario, the strongest greenhouse gas forcing used in the climate projections for the 5th Assessement report of the Intergovernmental Panel on Climate Change). In addition to a global increase in SSTs as a direct response to the radiative forcing, the model shows a distinct change of the local sea surface temperature (SST hereafter) patterns in the Gulf Stream region: The SST front moves northward by several hundred kilometers, likely as a response of the wind-driven part of the oceanic surface circulation, and becomes more zonal. As a consequence of a massive slowdown of the Atlantic Meridional Overturning Circulation, the northeast North Atlantic only shows a moderate warming compared to the rest of the ocean. The feedback of these changes on the atmosphere was studied in a set of sensitivity experiments based on the SST climatology of the coupled runs. The set consists of a control run based on the historical run, a run using the full SST from the coupled RCP 8.5 run and two runs, where the SST signal was deconstructed into a homogenous mean warming part and a local pattern change. In the region of the precipitation maximum in the historical run the future scenario shows an increase of absolute SSTs, but a significant decrease in local precipitation, low-level convergence and upward motion. Since warmer SSTs usually cause the opposite, this indicates that the local response in that region is connected to the (with respect to the historical run) weakened SST gradients rather than to the absolute SST. Consistently, the model shows enhanced precipitation north of this region, where the SST gradients are enhanced. However, the signal restricts to the low and mid-troposphere and does not reach the higher model levels. There is little evidence for a large-scale response to the changes in the Gulf
Cost analysis of ground-water supplies in the North Atlantic region, 1970

USGS Publications Warehouse

Cederstrom, Dagfin John

1973-01-01

The cost of municipal and industrial ground water (or, more specifically, large supplies of ground water) at the wellhead in the North Atlantic Region in 1970 generally ranged from 1.5 to 5 cents per thousand gallons. Water from crystalline rocks and shale is relatively expensive. Water from sandstone is less so. Costs of water from sands and gravels in glaciated areas and from Coastal Plain sediments range from moderate to very low. In carbonate rocks costs range from low to fairly high. The cost of ground water at the wellhead is low in areas of productive aquifers, but owing to the cost of connecting pipe, costs increase significantly in multiple-well fields. In the North Atlantic Region, development of small to moderate supplies of ground water may offer favorable cost alternatives to planners, but large supplies of ground water for delivery to one point cannot generally be developed inexpensively. Well fields in the less productive aquifers may be limited by costs to 1 or 2 million gallons a day, but in the more favorable aquifers development of several tens of millions of gallons a day may be practicable and inexpensive. Cost evaluations presented cannot be applied to any one specific well or specific site because yields of wells in any one place will depend on the local geologic and hydrologic conditions; however, with such cost adjustments as may be necessary, the methodology presented should have wide applicability. Data given show the cost of water at the wellhead based on the average yield of several wells. The cost of water delivered by a well field includes costs of connecting pipe and of wells that have the yields and spacings specified. Cost of transport of water from the well field to point of consumption and possible cost of treatment are not evaluated. In the methodology employed, costs of drilling and testing, pumping equipment, engineering for the well field, amortization at 5% percent interest, maintenance, and cost of power are considered. The
Loss of sea ice in the Arctic.

PubMed

Perovich, Donald K; Richter-Menge, Jacqueline A

2009-01-01

The Arctic sea ice cover is in decline. The areal extent of the ice cover has been decreasing for the past few decades at an accelerating rate. Evidence also points to a decrease in sea ice thickness and a reduction in the amount of thicker perennial sea ice. A general global warming trend has made the ice cover more vulnerable to natural fluctuations in atmospheric and oceanic forcing. The observed reduction in Arctic sea ice is a consequence of both thermodynamic and dynamic processes, including such factors as preconditioning of the ice cover, overall warming trends, changes in cloud coverage, shifts in atmospheric circulation patterns, increased export of older ice out of the Arctic, advection of ocean heat from the Pacific and North Atlantic, enhanced solar heating of the ocean, and the ice-albedo feedback. The diminishing Arctic sea ice is creating social, political, economic, and ecological challenges.
Latest Quaternary palaeoceanographic change in the eastern North Atlantic based upon a dinoflagellate cyst event ecostratigraphy.

PubMed

Harland, Rex; Polovodova Asteman, Irina; Morley, Audrey; Morris, Angela; Harris, Anthony; Howe, John A

2016-05-01

The analyses of dinoflagellate cyst records, from the latest Quaternary sediments recovered from DSDP Core 610A taken on the Feni Ridge in the southern Rockall Trough, and part of core MD01-2461 on the continental margin of the Porcupine Seabight in the eastern North Atlantic Ocean, has provided evidence for significant oceanographic change encompassing the Last Glacial Maximum (LGM) and part of the Holocene. This together with other published records has led to a regional evaluation of oceanographic change in the eastern North Atlantic over the past 68 ka, based upon a distinctive dinoflagellate event ecostratigraphy. These changes reflect changes in the surface waters of the North Atlantic Current (NAC), and perhaps the deeper thermohaline Atlantic Meridional Overturning Circulation (AMOC), driving fundamental regime changes within the phytoplanktonic communities. Three distinctive dinoflagellate cyst associations based upon both factor and cluster analyses have been recognised. Associations characterised by Bitectatodinium tepikiense (between 61.1 ± 6.2 to 13.4 ± 1.1 ka BP), Nematosphaeropsis labyrinthus (between 10.5 ± 0.3 and 11.45 ± 0.8 ka. BP), and the cyst of Protoceratium reticulatum (between 8.5 ± 0.9 and 5.2 ± 1.3 ka. BP) indicate major change within the eastern North Atlantic oceanography. The transitions between these changes occur over a relatively short time span (c.1.5 ka), given our sampling resolution, and have the potential to be incorporated into an event stratigraphy through the latest Quaternary as recommended by the INTIMATE (INTegrating Ice core, MArine and TErrestrial records) group. The inclusion of a dinoflagellate cyst event stratigraphy would highlight changes within the phytoplankton of the North Atlantic Ocean as a fully glacial world changed to our present interglacial.
Influence of North Atlantic modes on European climate extremes

NASA Astrophysics Data System (ADS)

Proemmel, K.; Cubasch, U.

2017-12-01

It is well known that the North Atlantic strongly influences European climate. Only few studies exist that focus on its impact on climate extremes. We are interested in these extremes and the processes and mechanisms behind it. For the analysis of the North Atlantic Oscillation (NAO) we use simulations performed with the Max Planck Institute for Meteorology Earth System Model (MPI-ESM). The NAO has a strong impact especially on European winter and the changes in minimum temperature are even larger than in maximum temperature. The impact of the Atlantic Multi-decadal Variability (AMV) on climate extremes is analyzed in ECHAM6 simulations forced with AMV warm and AMV cold sea surface temperature patterns. We analyze different extreme indices and try to understand the processes.
Regionally and seasonally differentiated primary production in the North Atlantic

NASA Astrophysics Data System (ADS)

Sathyendranath, Shubha; Longhurst, Alan; Caverhill, Carla M.; Platt, Trevor

1995-10-01

A bio-geochemical classification of the N. Atlantic Basin is presented according to which the basin is first divided into four primary algal domains: Polar, West-Wind, Trades and Coastal. These are in turn sub-divided into smaller provinces. The classification is based on differences in the physical environment which are likely to influence regional algal dynamics. The seasonally-differentiated parameters of the photosynthesis-light curve ( P-I curve) and parameters that define the vertical structure in chlorophyll profile are then established for each province, based on an analysis of an archive of over 6000 chlorophyll profiles, and over 1800 P-I curves. These are then combined with satellite-derived chlorophyll data for the N. Atlantic, and information on cloud cover, to compute primary production at the annual scale. using a model that computes spectral transmission of light underwater, and spectral, photosynthetic response of phytoplankton to available light. The results are compared with earlier, satellite-derived, estimates of basin-scale primary production.
76 FR 36892 - Atlantic Highly Migratory Species; 2011 North and South Atlantic Swordfish Quotas

Federal Register 2010, 2011, 2012, 2013, 2014

2011-06-23

... Atlantic Tunas (ICCAT) recommendations 10-02 and 09-03 into the quota adjustments for the 2011 fishing year... adopted for North Atlantic Swordfish for one year. Recommendation 10-02 included a total TAC of 13,700 mt... year. Recommendation 10-02 maintains the U.S. previous years' quota allocation of 2,937.6 mt dw as well...
Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation

NASA Astrophysics Data System (ADS)

Yang, Qian; Dixon, Timothy H.; Myers, Paul G.; Bonin, Jennifer; Chambers, Don; van den Broeke, M. R.

2016-01-01

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening.
Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation

PubMed Central

Yang, Qian; Dixon, Timothy H.; Myers, Paul G.; Bonin, Jennifer; Chambers, Don; van den Broeke, M. R.; Ribergaard, Mads H.; Mortensen, John

2016-01-01

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening. PMID:26796579
Recent increases in Arctic freshwater flux affects Labrador Sea convection and Atlantic overturning circulation.

PubMed

Yang, Qian; Dixon, Timothy H; Myers, Paul G; Bonin, Jennifer; Chambers, Don; van den Broeke, M R

2016-01-22

The Atlantic Meridional Overturning Circulation (AMOC) is an important component of ocean thermohaline circulation. Melting of Greenland's ice sheet is freshening the North Atlantic; however, whether the augmented freshwater flux is disrupting the AMOC is unclear. Dense Labrador Sea Water (LSW), formed by winter cooling of saline North Atlantic water and subsequent convection, is a key component of the deep southward return flow of the AMOC. Although LSW formation recently decreased, it also reached historically high values in the mid-1990s, making the connection to the freshwater flux unclear. Here we derive a new estimate of the recent freshwater flux from Greenland using updated GRACE satellite data, present new flux estimates for heat and salt from the North Atlantic into the Labrador Sea and explain recent variations in LSW formation. We suggest that changes in LSW can be directly linked to recent freshening, and suggest a possible link to AMOC weakening.
Atmospheric transmission of North Atlantic Heinrich events

USGS Publications Warehouse

Hostetler, S.W.; Clark, P.U.; Bartlein, P.J.; Mix, A.C.; Pisias, N.J.

1999-01-01

We model the response of the climate system during Heinrich event 2 (H2) by employing an atmospheric general circulation model, using boundary conditions based on the concept of a "canonical" Heinrich event. The canonical event is initialized with a full-height Laurentide ice sheet (LIS) and CLIMAP sea surface temperatures (SSTs), followed by lowering of the LIS, then warming of North Atlantic SSTs. Our modeled temperature and wind fields exhibit spatially variable responses over the Northern Hemisphere at each stage of the H2 event. In some regions the climatic responses are additive, whereas in other regions they cancel or are of opposite sign, suggesting that Heinrich event climatic variations may have left complex signatures in geologic records. We find variations in the tropical water balance and the mass balance of ice sheets, and implications for variations in terrestrial methane production from the contraction of northern permafrost regions and the expansion of tropical wetlands. Copyright 1999 by the American Geophysical Union.
Reconstructing Late Holocene North Atlantic atmospheric circulation changes using functional paleoclimate networks

NASA Astrophysics Data System (ADS)

Franke, Jasper G.; Werner, Johannes P.; Donner, Reik V.

2017-11-01

Obtaining reliable reconstructions of long-term atmospheric circulation changes in the North Atlantic region presents a persistent challenge to contemporary paleoclimate research, which has been addressed by a multitude of recent studies. In order to contribute a novel methodological aspect to this active field, we apply here evolving functional network analysis, a recently developed tool for studying temporal changes of the spatial co-variability structure of the Earth's climate system, to a set of Late Holocene paleoclimate proxy records covering the last two millennia. The emerging patterns obtained by our analysis are related to long-term changes in the dominant mode of atmospheric circulation in the region, the North Atlantic Oscillation (NAO). By comparing the time-dependent inter-regional linkage structures of the obtained functional paleoclimate network representations to a recent multi-centennial NAO reconstruction, we identify co-variability between southern Greenland, Svalbard, and Fennoscandia as being indicative of a positive NAO phase, while connections from Greenland and Fennoscandia to central Europe are more pronounced during negative NAO phases. By drawing upon this correspondence, we use some key parameters of the evolving network structure to obtain a qualitative reconstruction of the NAO long-term variability over the entire Common Era (last 2000 years) using a linear regression model trained upon the existing shorter reconstruction.
Recent evolution of 129I levels in the Nordic Seas and the North Atlantic Ocean.

PubMed

Vivo-Vilches, Carlos; López-Gutiérrez, José María; Periáñez, Raúl; Marcinko, Charlotte; Le Moigne, Frédéric; McGinnity, Paul; Peruchena, Juan Ignacio; Villa-Alfageme, María

2018-04-15

Most of the anthropogenic radionuclide 129 I released to the marine environment from the nuclear fuel reprocessing plants (NFRP) at Sellafield (England) and La Hague (France) is transported to the Arctic Ocean via the North Atlantic Current and the Norwegian Coastal Current. 129 I concentrations in seawater provides a powerful and well-established radiotracer technique to provide information about the mechanisms which govern water mass transport in the Nordic Seas and the Arctic Ocean and is gaining importance when coupled with other tracers (e.g. CFC, 236 U). In this work, 129 I concentrations in surface and depth profiles from the Nordic Seas and the North Atlantic (NA) Ocean collected from four different cruises between 2011 and 2012 are presented. This work allowed us to i) update information on 129 I concentrations in these areas, required for the accurate use of 129 I as a tracer of water masses; and ii) investigate the formation of deep water currents in the eastern part of the Nordic Seas, by the analysis of 129 I concentrations and temperature-salinity (T-S) diagrams from locations within the Greenland Sea Gyre. In the Nordic Seas, 129 I concentrations in seawater are of the order of 10 9 at·kg -1 , one or two orders of magnitude higher than those measured at the NA Ocean, not so importantly affected by the releases from the NFRP. 129 I concentrations of the order of 10 8 atoms·kg -1 at the Ellet Line and the PAP suggest a direct contribution from the NFRP in the NA Ocean. An increase in the concentrations in the Nordic Seas between 2002 and 2012 has been detected, which agrees with the temporal evolution of the 129 I liquid discharges from the NFRPs in years prior to this. Finally, 129 I profile concentrations, 129 I inventories and T-S diagrams suggest that deep water formation occurred in the easternmost area of the Nordic Seas during 2012. Copyright © 2017 Elsevier B.V. All rights reserved.
Earthquakes at North Atlantic passive margins

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

Gregersen, S.; Basham, P.W.

1989-01-01

The main focus of this volume is the earthquakes that occur at and near the continental margins on both sides of the North Atlantic. The book, which contains the proceedings of the NATO workshop on Causes and Effects of Earthquakes at Passive Margins and in Areas of Postglacial Rebound on Both Sides of the North Atlantic, draws together the fields of geophysics, geology and geodesy to address the stress and strain in the Earth's crust. The resulting earthquakes produced on ancient geological fault zones and the associated seismic hazards these pose to man are also addressed. Postglacial rebound in Northmore » America and Fennoscandia is a minor source of earthquakes today, during the interglacial period, but evidence is presented to suggest that the ice sheets suppressed earthquake strain while they were in place, and released this strain as a pulse of significant earthquakes after the ice melted about 9000 years ago.« less
Stratigraphic potential of Bolboforma significantly increased by new finds in the North Atlantic and South Pacific

USGS Publications Warehouse

Poag, C. Wylie; Karowe, A. I.

1986-01-01

Until now, the genus Bolboforma, a problematic group of calcareous microfossils, has been recorded only in Oligocene to Pliocene marine sedimentary rocks, chiefly in the eastern North Atlantic region. We add to this eastern North Atlantic record six new sites and eleven undescribed species from the continental slopes of Ireland and Morocco. More significantly, we record, for the first time, abundant assemblages of Bolboforma on the western side of the North Atlantic and in the western South Pacific. Seven boreholes on the continental shelf and slope of New Jersey and Virginia contain ten species, three of which are new. Two species are present in two outcrops in eastern Mississippi and four are present in a borehole in the coastal plain of Virginia. On the Lord Howe Rise, west of New Zealand, a DSDP corehole has yielded a rich assemblage including four undescribed species. In addition to expanding the geographic distribution of Bolboforma, our work extends the known stratigraphic range downward into the upper Eocene on both sides of the North Atlantic and in the western South Pacific. Our findings firmly support the inference of a planktonic life style for Bolboforma, which implies a significant potential for biostratigraphic, paleobiogeographic, and paleoenvironmental studies, on both a local and global scale. We recommend a concerted effort to further document the nature and distribution of Bolboforma.
Molluscan sclerochronology on the Faroese Shelf and its potential to obtain closer insights into the climate variability of North Atlantic water masses

NASA Astrophysics Data System (ADS)

Bonitz, F. G. W.; Andersson Dahl, C.; Trofimova, T.

2016-12-01

In this study, we investigate the climate variability in the North Atlantic during the last 350 years by applying sclerochronological methods. The inflow of North Atlantic water masses into the Arctic and the Norwegian Sea is important for the climate in these regions. A better understanding of the climate variability on highly resolved time scales is needed to obtain a better fundament for climate predictions for these areas. However, highly resolved paleoclimate records are sparse in the North Atlantic and instrumental data cover only the last 50 - 150 years. Bivalve shells provide highly resolved climate archives, especially the shells of the long-lived bivalve species Arctica islandica. This widely occurring species forms annual growth increments, which can be analyzed similarly to tree rings. Climatic and oceanographic changes are recorded population-wide in the shell`s growth rate and in the isotopic composition of the shell. Hence, multi-centennial absolutely dated chronologies can be built by cross-matching live-collected and sub-fossil specimens. Our chronology building effort has led to the first multi-centennial absolutely dated chronology from the Faroese Shelf covering the time period from AD 1642 - 2013. The growth indices of the chronology anti-correlate with April - September sea surface temperatures (SST) for the last 100 years indicating favorable conditions for growth when temperatures are lower. This also suggests that the main growing season of A. islandica around the Faroe Islands occurs in this time period; a hypothesis supported by δ18O-based temperature reconstructions from growth increments representing the years 2001 - 2013. The RBAR, which is an indicator for the signal strength throughout the chronology shows an inverse relationship with Atlantic Multi-decadal Oscillation (AMO) data indicating that periods of higher AMO indexes result in a weakened signal strength in the chronology for the same time period. In conclusion, our results
Interpretation of time series (salinity and temperature) layers in North Atlantic from 1950 to 2011

NASA Astrophysics Data System (ADS)

Rubchenia, A.; Popov, A.; Fedorova, A.; Lebedev, N.

2012-04-01

On the basis of long period data series (1950-2011) form various sources (National Oceanographic Data Center (NOAD) (www.nodc.noaa.gov), WOD09 database and data from ARGO project) 10 boxes in North Atlantic were selected. Location of boxes was determined by circulation pattern in North Atlantic and Euro-Arctic Seas. For further analysis two "seasons" was selected: "cold season" (October-May) and "warm season" (June-September). Data verification was made. Analysis of data series clearly show the "Great Salinity Anomaly" (so-called GSA) in 1960-70th, 1980th and 1990th. Trends of salinity and temperature data series were calculated. Spectral analysis allow us to calculate periodicity from 2 to 22 years. Boxes situated in regions with Arctic waters have singularity showed through domination of high frequency oscillation during propagation to South. In Fram Strait salinity fluctuates with periods 9..11 and 20 years, the same period was calculated using temperature data series. In Denmark Strait there are oscillations of temperature with specific period from 4 to 7 years. Range of variability vary. For salinity it is 0.4..4.6 psu, for temperature it is 0.04..5.5C. In salinity data series from boxes with surface Arctic waters noticed clear minimums connected with GSAs. Trends in Denmark Strait and Fram strait in the end of 2000th are negative at different levels. Since 1975 to 2001 salinity near the southern part of Greenland was increased, since 2001 - decreased. But temperature was raised from 0.04 in 1989 to 5.59 in 2010. Thermohaline characteristics of water masses which has Atlantic origin oscillated with period near 20 years. Salinity near Newfoundland was decreased since 2005. In Farrero-Shetland straits salinity trend is positive since at 100m level, Salinity rising from 1970th to 2006 is about 0.3 psu were noticed. Oscillations with period 2..4 years is weak. But at 800m layer salinity oscillations are different, since 1990 there is not significant oscillations
Intensified impact of tropical Atlantic SST on the western North Pacific summer climate under a weakened Atlantic thermohaline circulation

NASA Astrophysics Data System (ADS)

Chen, Wei; Lee, June-Yi; Lu, Riyu; Dong, Buwen; Ha, Kyung-Ja

2015-10-01

The tropical North Atlantic (TNA) sea surface temperature (SST) has been identified as one of regulators on the boreal summer climate over the western North Pacific (WNP), in addition to SSTs in the tropical Pacific and Indian Oceans. The major physical process proposed is that the TNA warming induces a pair of cyclonic circulation anomaly over the eastern Pacific and negative precipitation anomalies over the eastern to central tropical Pacific, which in turn lead to an anticyclonic circulation anomaly over the western to central North Pacific. This study further demonstrates that the modulation of the TNA warming to the WNP summer climate anomaly tends to be intensified under background of the weakened Atlantic thermohaline circulation (THC) by using a water-hosing experiment. The results suggest that the weakened THC induces a decrease in thermocline depth over the TNA region, resulting in the enhanced sensitivity of SST variability to wind anomalies and thus intensification of the interannual variation of TNA SST. Under the weakened THC, the atmospheric responses to the TNA warming are westward shifted, enhancing the anticyclonic circulation and negative precipitation anomaly over the WNP. This study supports the recent finding that the negative phase of the Atlantic multidecadal oscillation after the late 1960s has been favourable for the strengthening of the connection between TNA SST variability and WNP summer climate and has important implications for seasonal prediction and future projection of the WNP summer climate.
The link between eddy-driven jet variability and weather regimes in the North Atlantic-European sector

NASA Astrophysics Data System (ADS)

Madonna, E.; Li, C.; Grams, C. M.; Woollings, T.

2017-12-01

Understanding the variability of the North Atlantic eddy-driven jet is key to unravelling the dynamics, predictability and climate change response of extratropical weather in the region. This study aims to 1) reconcile two perspectives on wintertime variability in the North Atlantic-European sector and 2) clarify their link to atmospheric blocking. Two common views of wintertime variability in the North Atlantic are the zonal-mean framework comprising three preferred locations of the eddy-driven jet (southern, central, northern), and the weather regime framework comprising four classical North Atlantic-European regimes (Atlantic ridge AR, zonal ZO, European/Scandinavian blocking BL, Greenland anticyclone GA). We use a k-means clustering algorithm to characterize the two-dimensional variability of the eddy-driven jet stream, defined by the lower tropospheric zonal wind in the ERA-Interim reanalysis. The first three clusters capture the central jet and northern jet, along with a new mixed jet configuration; a fourth cluster is needed to recover the southern jet. The mixed cluster represents a split or strongly tilted jet, neither of which is well described in the zonal-mean framework, and has a persistence of about one week, similar to the other clusters. Connections between the preferred jet locations and weather regimes are corroborated - southern to GA, central to ZO, and northern to AR. In addition, the new mixed cluster is found to be linked to European/Scandinavian blocking, whose relation to the eddy-driven jet was previously unclear. The results highlight the necessity of bridging from weather to climate scales for a deeper understanding of atmospheric circulation variability.
Tracing Marine Cryptotephras in the North Atlantic during the Last Glacial Period

NASA Astrophysics Data System (ADS)

Abbott, Peter; Davies, Siwan; Griggs, Adam; Bourne, Anna

2017-04-01

Tephrochronology is a powerful technique that can be utilised for the independent correlation and synchronisation of disparate palaeoclimatic records from different depositional environments. There is a high potential to utilise this technique to integrate ice, marine and terrestrial records to study climatic phasing within the North Atlantic region due to the high eruptive frequency of Icelandic volcanic systems. However, until now North Atlantic marine records have been relatively understudied. Here we report on investigations to define a tephra framework integrating new studies of cryptotephra horizons within a wide network of North Atlantic marine cores with horizons identified in prior work. This framework has the potential to underpin the correlation of the marine records to the Greenland ice-core records and European terrestrial sequences. Tephrochronological investigations were conducted on 13 marine sequences from a range of locations and depositional settings using cryptotephra extraction techniques, including density and magnetic separation, to gain high resolution glass shard concentration profiles and rigorous single-shard major element geochemical analysis to characterise identified deposits. Cryptotephras with an Icelandic source were identified in many records and displayed diversity in shard concentration profiles and the geochemical homo/heterogeneity of shards within the deposits. These differences reflect spatial and temporal variability in the operation of a range of transport processes, e.g. airfall, sea-ice and iceberg rafting, and post-depositional processes, e.g. bioturbation and secondary redeposition. The operation of these processes within the marine environment can potentially impart a temporal delay on tephra deposition and hamper the placement of the isochron, therefore, it is crucial to assess their influence. To aid this assessment a range of deposit types with common transport and depositional histories have been defined. Spatial

Oceanic link between abrupt changes in the North Atlantic Ocean and the African monsoon

NASA Astrophysics Data System (ADS)

Chang, Ping; Zhang, Rong; Hazeleger, Wilco; Wen, Caihong; Wan, Xiuquan; Ji, Link; Haarsma, Reindert J.; Breugem, Wim-Paul; Seidel, Howard

2008-07-01

Abrupt changes in the African monsoon can have pronounced socioeconomic impacts on many West African countries. Evidence for both prolonged humid periods and monsoon failures have been identified throughout the late Pleistocene and early Holocene epochs. In particular, drought conditions in West Africa have occurred during periods of reduced North Atlantic thermohaline circulation, such as the Younger Dryas cold event. Here, we use an ocean-atmosphere general circulation model to examine the link between oceanographic changes in the North Atlantic Ocean and changes in the strength of the African monsoon. Our simulations show that when North Atlantic thermohaline circulation is substantially weakened, the flow of the subsurface North Brazil Current reverses. This leads to decreased upper tropical ocean stratification and warmer sea surface temperatures in the equatorial South Atlantic Ocean, and consequently reduces African summer monsoonal winds and rainfall over West Africa. This mechanism is in agreement with reconstructions of past climate. We therefore suggest that the interaction between thermohaline circulation in the North Atlantic Ocean and wind-driven currents in the tropical Atlantic Ocean contributes to the rapidity of African monsoon transitions during abrupt climate change events.
Tropical-Subpolar Linkages in the North Atlantic during the last Glacial Period

NASA Astrophysics Data System (ADS)

Vautravers, M. J.; Hodell, D. A.

2010-12-01

We studied millennial-scale changes in planktonic foraminifera assemblages from the last glacial period in a high-resolution core (KN166-14-JPC13) recovered from the southern part of the Gardar Drift in the subpolar North Atlantic. Similar to recent findings reported by Jonkers et al. (2010), we also found that the sub-polar North Atlantic Ocean experienced some seasonal warming during each of the Heinrich Events (HEs). In addition, increasing abundances of tropical species are found just prior to the IRD event marking the end of each Bond cycle, suggesting that summer warming may have been involved in triggering Heinrich events. We suggest that tropical-subtropical water transported via the Gulf Stream and North Atlantic Drift may have triggered the collapse of large NH ice-shelves. Sharp decreases in polar species are tied to abrupt warming following Heinrich Events as documented in Greenland Ice cores and other marine records in the North Atlantic. The record bears a strong resemblance to the tropical record of Cariaco basin (Peterson et al., 2000), suggesting strong tropical-subpolar linkages in the glacial North Atlantic. Enhanced spring productivity, possibly related to eddy activity along the Subpolar Front, is recorded by increased shell size, high δ13C in G. bulloides and other biological indices early during the transition from HE stadials to the following interstadial.
Seismic and Thermal Structure of the Arctic Lithosphere, From Waveform Tomography and Thermodynamic Modelling

NASA Astrophysics Data System (ADS)

Lebedev, S.; Schaeffer, A. J.; Fullea, J.; Pease, V.

2015-12-01

Thermal structure of the lithosphere is reflected in the values of seismic velocities within it. Our new tomographic models of the crust and upper mantle of the Arctic are constrained by an unprecedentedly large global waveform dataset and provide substantially improved resolution, compared to previous models. The new tomography reveals lateral variations in the temperature and thickness of the lithosphere and defines deep boundaries between tectonic blocks with different lithospheric properties and age. The shape and evolution of the geotherm beneath a tectonic unit depends on both crustal and mantle-lithosphere structure beneath it: the lithospheric thickness and its changes with time (these determine the supply of heat from the deep Earth), the crustal thickness and heat production (the supply of heat from within the crust), and the thickness and thermal conductivity of the sedimentary cover (the insulation). Detailed thermal structure of the basins can be modelled by combining seismic velocities from tomography with data on the crustal structure and heat production, in the framework of computational petrological modelling. The most prominent lateral contrasts across the Arctic are between the cold, thick lithospheres of the cratons (in North America, Greenland and Eurasia) and the warmer, non-cratonic blocks. The lithosphere of the Canada Basin is cold and thick, similar to old oceanic lithosphere elsewhere around the world; its thermal structure offers evidence on its lithospheric age and formation mechanism. At 150-250 km depth, the central Arctic region shows a moderate low-velocity anomaly, cooler than that beneath Iceland and N Atlantic. An extension of N Atlantic low-velocity anomaly into the Arctic through the Fram Strait may indicate an influx of N Atlantic asthenosphere under the currently opening Eurasia Basin.
Near-Inertial and Thermal Upper Ocean Response to Atmospheric Forcing in the North Atlantic Ocean

DTIC Science & Technology

2010-06-01

meridional transport of heat (Hoskins and Valdes, 1990). Formation of North Atlantic Subtropical Mode Water is thought to take place during the...North Atlantic Ocean MIT/WHOI Joint Program in Oceanography/ Applied Ocean Science and Engineering Massachusetts Institute of Technology Woods Hole...Oceanographic Institution MITIWHOI 2010-16 Near-inertial and Thermal Upper Ocean Response to Atmospheric Forcing in the North Atlantic Ocean by
Impacts of extratropical storm tracks on Arctic sea ice export through Fram Strait

NASA Astrophysics Data System (ADS)

Wei, Jianfen; Zhang, Xiangdong; Wang, Zhaomin

2018-05-01

Studies have indicated regime shifts in atmospheric circulation, and associated changes in extratropical storm tracks and Arctic storm activity, in particular on the North Atlantic side of the Arctic Ocean. To improve understanding of changes in Arctic sea ice mass balance, we examined the impacts of the changed storm tracks and cyclone activity on Arctic sea ice export through Fram Strait by using a high resolution global ocean-sea ice model, MITgcm-ECCO2. The model was forced by the Japanese 25-year Reanalysis (JRA-25) dataset. The results show that storm-induced strong northerly wind stress can cause simultaneous response of daily sea ice export and, in turn, exert cumulative effects on interannual variability and long-term changes of sea ice export. Further analysis indicates that storm impact on sea ice export is spatially dependent. The storms occurring southeast of Fram Strait exhibit the largest impacts. The weakened intensity of winter (in this study winter is defined as October-March and summer as April-September) storms in this region after 1994/95 could be responsible for the decrease of total winter sea ice export during the same time period.
Enhanced Arctic Amplification Began at the Mid-Brunhes Event ~400,000 years ago.

PubMed

Cronin, T M; Dwyer, G S; Caverly, E K; Farmer, J; DeNinno, L H; Rodriguez-Lazaro, J; Gemery, L

2017-11-03

Arctic Ocean temperatures influence ecosystems, sea ice, species diversity, biogeochemical cycling, seafloor methane stability, deep-sea circulation, and CO 2 cycling. Today's Arctic Ocean and surrounding regions are undergoing climatic changes often attributed to "Arctic amplification" - that is, amplified warming in Arctic regions due to sea-ice loss and other processes, relative to global mean temperature. However, the long-term evolution of Arctic amplification is poorly constrained due to lack of continuous sediment proxy records of Arctic Ocean temperature, sea ice cover and circulation. Here we present reconstructions of Arctic Ocean intermediate depth water (AIW) temperatures and sea-ice cover spanning the last ~ 1.5 million years (Ma) of orbitally-paced glacial/interglacial cycles (GIC). Using Mg/Ca paleothermometry of the ostracode Krithe and sea-ice planktic and benthic indicator species, we suggest that the Mid-Brunhes Event (MBE), a major climate transition ~ 400-350 ka, involved fundamental changes in AIW temperature and sea-ice variability. Enhanced Arctic amplification at the MBE suggests a major climate threshold was reached at ~ 400 ka involving Atlantic Meridional Overturning Circulation (AMOC), inflowing warm Atlantic Layer water, ice sheet, sea-ice and ice-shelf feedbacks, and sensitivity to higher post-MBE interglacial CO 2 concentrations.
Enhanced Arctic amplification began at the Mid-Brunhes Event 430,000 years ago

USGS Publications Warehouse

Cronin, Thomas M.; Dwyer, Gary S.; Caverly, Emma; Farmer, Jesse; DeNinno, Lauren H.; Rodriguez-Lazaro, Julio; Gemery, Laura

2017-01-01

Arctic Ocean temperatures influence ecosystems, sea ice, species diversity, biogeochemical cycling, seafloor methane stability, deep-sea circulation, and CO2 cycling. Today's Arctic Ocean and surrounding regions are undergoing climatic changes often attributed to "Arctic amplification" - that is, amplified warming in Arctic regions due to sea-ice loss and other processes, relative to global mean temperature. However, the long-term evolution of Arctic amplification is poorly constrained due to lack of continuous sediment proxy records of Arctic Ocean temperature, sea ice cover and circulation. Here we present reconstructions of Arctic Ocean intermediate depth water (AIW) temperatures and sea-ice cover spanning the last ~ 1.5 million years (Ma) of orbitally-paced glacial/interglacial cycles (GIC). Using Mg/Ca paleothermometry of the ostracode Krithe and sea-ice planktic and benthic indicator species, we suggest that the Mid-Brunhes Event (MBE), a major climate transition ~ 400-350 ka, involved fundamental changes in AIW temperature and sea-ice variability. Enhanced Arctic amplification at the MBE suggests a major climate threshold was reached at ~ 400 ka involving Atlantic Meridional Overturning Circulation (AMOC), inflowing warm Atlantic Layer water, ice sheet, sea-ice and ice-shelf feedbacks, and sensitivity to higher post-MBE interglacial CO2 concentrations.
Regional climate impacts of a possible future grand solar minimum.

PubMed

Ineson, Sarah; Maycock, Amanda C; Gray, Lesley J; Scaife, Adam A; Dunstone, Nick J; Harder, Jerald W; Knight, Jeff R; Lockwood, Mike; Manners, James C; Wood, Richard A

2015-06-23

Any reduction in global mean near-surface temperature due to a future decline in solar activity is likely to be a small fraction of projected anthropogenic warming. However, variability in ultraviolet solar irradiance is linked to modulation of the Arctic and North Atlantic Oscillations, suggesting the potential for larger regional surface climate effects. Here, we explore possible impacts through two experiments designed to bracket uncertainty in ultraviolet irradiance in a scenario in which future solar activity decreases to Maunder Minimum-like conditions by 2050. Both experiments show regional structure in the wintertime response, resembling the North Atlantic Oscillation, with enhanced relative cooling over northern Eurasia and the eastern United States. For a high-end decline in solar ultraviolet irradiance, the impact on winter northern European surface temperatures over the late twenty-first century could be a significant fraction of the difference in climate change between plausible AR5 scenarios of greenhouse gas concentrations.
Temporal patterns of phytoplankton abundance in the North Atlantic

NASA Technical Reports Server (NTRS)

Campbell, Janet W.

1989-01-01

A time series of CZCS images is being developed to study phytoplankton distribution patterns in the North Atlantic. The goal of this study is to observe temporal variability in phytoplankton pigments and other organic particulates, and to infer from these patterns the potential flux of biogenic materials from the euphotic layer to the deep ocean. Early results of this project are presented in this paper. Specifically, the satellite data used were 13 monthly composited images of CZCS data for the North Atlantic from January 1979 to January 1980. Results are presented for seasonal patterns along the 20 deg W meridian.
Marine 14C reservoir ages for 19th century whales and molluscs from the North Atlantic

NASA Astrophysics Data System (ADS)

Mangerud, Jan; Bondevik, Stein; Gulliksen, Steinar; Karin Hufthammer, Anne; Høisæter, Tore

2006-12-01

In order to compare radiocarbon dates on marine and terrestrial samples the former have to be corrected for a reservoir age. We present reservoir ages from dating 21 whales collected 1860-1901 and recalculating dates of 23 molluscs collected 1857-1926. Most of the whales were caught along the coast of Norway, but one is from France and one from Iceland. We assume the former mainly lived in the North and equatorial Atlantic and in the Norwegian Sea. Whales feed only on pelagic organisms and will provide the reservoir age for the open ocean surface water. However, they travel long distances and will integrate the reservoir ages of the different water masses along their way. Molluscs (dated from Norway, Spitsbergen and Arctic Canada) are stationary and monitor the sea water passing their dwelling site, but some also take up carbon from particulate food or sediment pore water. Coastal water also often contains some continental carbon. We present two different views on how to analyze and interpret the data. Mangerud recommends to use reservoir ages based on a combination of the whale and mollusc dates, i.e. 380±30 and 360±30 yr relative to Intcal04 and British oak, respectively, and a Δ R value of 20±30 for the surface water in the N-Atlantic and Norwegian Sea. Bondevik and Gulliksen maintain that the reservoir age—and Δ R—along the Norwegian coast is latitude dependant, with Δ R-values increasing from -3±22 in the South to 105±24 at Spitsbergen. Whales, reflecting North Atlantic open ocean surface water have lower Δ R (7±11) than most molluscs.
Identification of Holocene millennial-scale forcing in the North Atlantic area: Ocean/atmosphere contribution

NASA Astrophysics Data System (ADS)

Debret, M.; Masson-Delmotte, V.; Christophe, C.; de Vernal, A.; Massei, N.; Eynaud, F.; Nicolle, M.; Frank, N.; Mary, Y.; Magny, M.

2017-12-01

Millennial (1500-year) cycles were evidenced decades ago from the advance and retreat of glaciers but many subsequent studies failed to demonstrate the unequivocal character of such oscillation from paleoclimate time series. Hence, the identification of a persistent 1500 year periodicity remains controversial both for the last glacial episode and the Holocene. Applying wavelet analysis to Holocene climate records, we have identified synchronous millennial-scale oscillations which permit to establish a North Atlantic millennial variability index (NAV-Index), maximum at 5330 ± 245, 3560 ± 190, 1810 ± 160 cal years BP and minimum at 4430 ± 250, 2640 ± 225 and 970 ± 200 years before present. This NAV-index was compared with the millennial variability of cosmogenic 10Be isotope, a proxy of solar activity. Differences between the two sets of records suggest that an internal mechanism (Ocean/atmosphere) must be at the origin of the North Atlantic millennial scale variability. Our data document an increased coherence and magnitude of the North Atlantic millennial variability since 6000 cal. years BP, with a frequency of 1780 ± 240 years. During the early Holocene, deglacial meltwater fluxes had strong regional impact and the coupling between subpolar gyre migration and Atlantic meridional oceanic circulation observed since afterward seems to be related to the end of the Laurentide and Inuitian ice sheet meltwater discharge. Hence, we may conclude that the evolution of this millennial oscillation in the future will depend upon the Greenland stability or melting.
Linkages between atmospheric blocking, sea ice export through Fram Strait and the Atlantic Meridional Overturning Circulation

PubMed Central

Ionita, M.; Scholz, P.; Lohmann, G.; Dima, M.; Prange, M.

2016-01-01

As a key persistent component of the atmospheric dynamics, the North Atlantic blocking activity has been linked to extreme climatic phenomena in the European sector. It has also been linked to Atlantic multidecadal ocean variability, but its potential links to rapid oceanic changes have not been investigated. Using a global ocean-sea ice model forced with atmospheric reanalysis data, here it is shown that the 1962–1966 period of enhanced blocking activity over Greenland resulted in anomalous sea ice accumulation in the Arctic and ended with a sea ice flush from the Arctic into the North Atlantic Ocean through Fram Strait. This event induced a significant decrease of Labrador Sea water surface salinity and an abrupt weakening of the Atlantic Meridional Overturning Circulation (AMOC) during the 1970s. These results have implications for the prediction of rapid AMOC changes and indicate that an important part of the atmosphere-ocean dynamics at mid- and high latitudes requires a proper representation of the Fram Strait sea ice transport and of the synoptic scale variability such as atmospheric blocking, which is a challenge for current coupled climate models. PMID:27619955
Linkages between atmospheric blocking, sea ice export through Fram Strait and the Atlantic Meridional Overturning Circulation.

PubMed

Ionita, M; Scholz, P; Lohmann, G; Dima, M; Prange, M

2016-09-13

As a key persistent component of the atmospheric dynamics, the North Atlantic blocking activity has been linked to extreme climatic phenomena in the European sector. It has also been linked to Atlantic multidecadal ocean variability, but its potential links to rapid oceanic changes have not been investigated. Using a global ocean-sea ice model forced with atmospheric reanalysis data, here it is shown that the 1962-1966 period of enhanced blocking activity over Greenland resulted in anomalous sea ice accumulation in the Arctic and ended with a sea ice flush from the Arctic into the North Atlantic Ocean through Fram Strait. This event induced a significant decrease of Labrador Sea water surface salinity and an abrupt weakening of the Atlantic Meridional Overturning Circulation (AMOC) during the 1970s. These results have implications for the prediction of rapid AMOC changes and indicate that an important part of the atmosphere-ocean dynamics at mid- and high latitudes requires a proper representation of the Fram Strait sea ice transport and of the synoptic scale variability such as atmospheric blocking, which is a challenge for current coupled climate models.
Species Profiles. Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates, North Atlantic, Mid-Atlantic, South Atlantic, South Florida, Gulf of Mexico, Pacific Southwest and Pacific Northwest.

DTIC Science & Technology

1986-01-01

COASTAL FISHES AND INVERTEBRATES FWS/OBS-82111 Ln jJL*-TR EL-82-4 NORTH ATLANTC MID-ATLANTIC SOUTH ATLANTIC SOUTrH FwRIDA GULF OF MEXICO PACIFIC...REQUIREMENTS OF COASTAL FISHES AND INVERTEBRATES (NORTH ATLANTIC) Managed by National Coastal Ecosystems Team Division of Biological Services Fish and...environmental requirements of selected coastal fishes and invertebrates of commercial, rec- reational, or ecological significance. They were prepared
Correspondence between North Pacific Ocean ventilation, Cordilleran Ice Sheet variations, and North Atlantic Heinrich Events

NASA Astrophysics Data System (ADS)

Walczak, M. H.; Mix, A.; Fallon, S.; Praetorius, S. K.; Cowan, E. A.; Du, J.; Hobern, T.; Padman, J.; Fifield, L. K.; Stoner, J. S.; Haley, B. A.

2017-12-01

Much remains unresolved concerning the origin and global implications of the episodes of rapid glacial failure in the North Atlantic known as Heinrich Events. Thought to occur during or at the termination of the coldest of the abrupt stadial climate events known as Dansgaard-Oschger cycles, various trigger mechanisms have been theorized, including external forcing in the form of oceanic or atmospheric warming, internal dynamics of the large Laurentide ice sheet, or the episodic failure of another (presumably European) ice sheet. Heinrich events may also be associated with a decrease in North Atlantic deep-water formation. New results from Gulf of Alaska IODP Expedition 341 reveal events of Cordilleran Ice Sheet retreat (based on ice-rafted detritus and sedimentation rates) synchronous with reorganization of ocean circulation (based on benthic-planktic 14C pairs) spanning the past 45,000 years on an independent high-resolution radiocarbon-based chronology. We document the relationship between these Pacific records and the North Atlantic Heinrich events, and find the data show an early Pacific expression of ice sheet instability in the form of pulses of Cordilleran glacial discharge. The benthic radiocarbon anomalies in the Northeast Pacific contemporaneous with Cordilleran discharge events indicate a close coupling of ice-ocean dynamics throughout Marine Isotope Stage 2. These data are hard to reconcile with triggering in the North Atlantic or internal to the Laurentide ice sheet, requiring us to re-think both the mechanisms that generate Heinrich events and their far-field impacts.
Observations of particulates within the North Atlantic Flight Corridor: POLINAT 2, September-October 1997

NASA Astrophysics Data System (ADS)

Paladino, J. D.; Hagen, D. E.; Whitefield, P. D.; Hopkins, A. R.; Schmid, O.; Wilson, M. R.; Schlager, H.; Schulte, P.

2000-02-01

This paper discusses participate concentration and size distribution data gathered using the University of Missouri-Rolla Mobile Aerosol Sampling System (UMR-MASS), and used to investigate the southern extent of the eastern end of the North Atlantic Flight Corridor (NAFC) during project Pollution From Aircraft Emissions in the North Atlantic Flight Corridor/Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (POLINAT 2/SONEX) from September 19 to October 23, 1997. The analysis presented in this paper focuses on "the corridor effect," or enhancement of pollutants by jet aircraft combustion events. To investigate the phenomena, both vertical and horizontal profiles of the corridor, and regions immediately adjacent to the corridor, were performed. The profiles showed a time-dependent enhancement of particulates within the corridor, and a nonvolatile (with respect to thermal volatilization at 300°C) aerosol enhancement at corridor altitudes by a factor of 3.6. The southern extent of the North Atlantic Flight Corridor was established from a four flight average of the particulate data and yielded a boundary near 42.5°N during the study period. A size distribution analysis of the nonvolatile particulates revealed an enhancement in the <40 nm particulates for size distributions recorded within the flight corridor.
The impact of North Atlantic wind and cyclone trends on European precipitation and significant wave height in the Atlantic.

PubMed

Trigo, Ricardo M; Valente, Maria A; Trigo, Isabel F; Miranda, Pedro M A; Ramos, Alexandre M; Paredes, Daniel; García-Herrera, Ricardo

2008-12-01

An analysis of the frequency of cyclones and surface wind velocity for the Euro-Atlantic sector is performed by means of an objective methodology. Monthly and seasonal trends of cyclones and wind speed magnitude are computed and trends between 1960 and 2000 evaluated. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February, and March. Seasonal and monthly analysis of wind magnitude trends shows similar spatial patterns. We show that these changes in the frequency of low-pressure centers and the associated wind patterns are partially responsible for trends in the significant height of waves. Throughout the extended winter months (October-March), regions with positive (negative) wind magnitude trends, of up to 5 cm/s/year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for January-March are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of lat 50 degrees N up to -3 cm/year, and positive up to 5 cm/year just north of Scotland). Trends in European precipitation are assessed using the Climatic Research Unit data set. The results of the assessment emphasize the link with the corresponding tendencies of cyclone frequencies. Finally, it is shown that these changes are associated, to a large extent, with the preferred phases of major large-scale atmospheric circulation modes, particularly with the North Atlantic Oscillation, the eastern Atlantic pattern, and the Scandinavian pattern.
Reconstruction of the North Atlantic tropical cyclones in Azores for the last 800 years.

NASA Astrophysics Data System (ADS)

Rubio-Ingles, Maria Jesus; Sánchez, Guiomar; Trigo, Ricardo; Francus, Pierre; Gonçalves, Vitor; Raposeiro, Pedro; Freitas, Conceiçao; Borges, Paolo; Hernández, Armand; Bao, Roberto; Vázquez-Loureiro, David; Andrade, Cesar; Sáez, Alberto; Giralt, Santiago

2014-05-01

.5 m long core allowed us to recover the whole sedimentary infill of Azul Lake, which has been characterized using a multiproxy (geochemistry, diatoms and chironomid head capsules) approach. The last 800 cal years BP, dated by the use of 14C (plant remains) and 210Pb, have been recorded in the 1.5 m of sediment. The layers of flood events deposits are characterized by low Ti content, no diatoms, and both high organic content and terrestrial plants remains. 14C and 210Pb dates obtained in this core have been used to link the flood events recorded in the offshore zones of the lake with the historical storms hitting the archipelago. According to the results of the studied sediment core, the number of tropical storms hitting the island has increased for the last 50 years. This is in accordance with the findings done by other authors (Liu et al., 2001 and Besonen et al., 2008). Moreover, two other periods located around the 1450s and the 1650s also recorded high number of storms. An increase of typhoons in China and hurricanes reaching the north Atlantic coast of United States during the same periods suggests a global climate pattern that ruled these extreme phenomena. LITERATURE: Andrade, C., Trigo R.M., Freitas, M.C., Gallego M.C., Borges, P., Ramos, A.M. (2008) "Comparing Historic Records of Storm frequency and the North Atlantic Oscillation (NAO) chronology for the Azores region", The Holocene, 18, 745-754 Besonen M.R., Bradley S.B., Mudelsee M., Abbott M.B, Francus P. (2008) "A 1000-year, annually-resolved record of hurricane activity from Boston, Massachussets" Geophysical Research Letters. Vol.35, L14705. Liu, K.-b., Shen, C. and Louie, K.-s. (2001), A 1,000-Year History of Typhoon Landfalls in Guangdong, Southern China, Reconstructed from Chinese Historical Documentary Records. Annals of the Association of American Geographers, 91: 453-464. doi: 10.1111/0004-5608.00253
North Atlantic early 20th century warming and impact on European summer: Mechanisms and Predictability

NASA Astrophysics Data System (ADS)

Müller, Wolfgang

2017-04-01

During the last century, substantial climate variations in the North Atlantic have occurred, such as the warmings in the 1920s and 1990s. Such variations are considered to be part of the variability known as the Atlantic Multidecadal Variations (AMV) and have a strong impact on local climates such as European summers. Here a synthesis of previous works is presented which describe the occurrence of the warming in the 1920s in the North Atlantic and its impact on the European summer climate (Müller et al. 2014, 2015). For this the 20th century reanalysis (20CR) and 20CR forced ocean experiments are evaluated. It can be shown that the North Atlantic Current and Sub-Polar Gyre are strengthened as a result of an increased pressure gradient over the North Atlantic. Concurrently, Labrador Sea convection and Atlantic meridional overturning circulation (AMOC) increase. The intensified NAC, SPG, and AMOC redistribute sub-tropical water into the North Atlantic and Nordic Seas, thereby increasing observed and modelled temperature and salinity during the 1920s. Further a mechanism is proposed by which North Atlantic heat fluxes associated with the AMV modulate European decadal summer climate (Ghosh et al. 2016). By using 20CR, it can be shown that multi-decadal variations in the European summer temperature are associated to a linear baroclinic atmospheric response to the AMV-related surface heat flux. This response induce a sea level pressure structure modulating meridional temperature advection over north-western Europe and Blocking statistics over central Europe. This structure is shown to be the leading mode of variability and is independent of the summer North Atlantic Oscillation. Ghosh, R., W.A. Müller, J. Bader, and J. Baehr, 2016: Impact of observed North Atlantic multidecadal variations to European summer climate: A linear baroclinic response to surface heating. Clim. Dyn. doi:10.10007/s00382-016-3283-4 Müller W. A., D. Matei, M. Bersch, J. H. Jungclaus, H. Haak, K
Identification of Younger Dryas outburst flood path from Lake Agassiz to the Arctic Ocean.

PubMed

Murton, Julian B; Bateman, Mark D; Dallimore, Scott R; Teller, James T; Yang, Zhirong

2010-04-01

The melting Laurentide Ice Sheet discharged thousands of cubic kilometres of fresh water each year into surrounding oceans, at times suppressing the Atlantic meridional overturning circulation and triggering abrupt climate change. Understanding the physical mechanisms leading to events such as the Younger Dryas cold interval requires identification of the paths and timing of the freshwater discharges. Although Broecker et al. hypothesized in 1989 that an outburst from glacial Lake Agassiz triggered the Younger Dryas, specific evidence has so far proved elusive, leading Broecker to conclude in 2006 that "our inability to identify the path taken by the flood is disconcerting". Here we identify the missing flood path-evident from gravels and a regional erosion surface-running through the Mackenzie River system in the Canadian Arctic Coastal Plain. Our modelling of the isostatically adjusted surface in the upstream Fort McMurray region, and a slight revision of the ice margin at this time, allows Lake Agassiz to spill into the Mackenzie drainage basin. From optically stimulated luminescence dating we have determined the approximate age of this Mackenzie River flood into the Arctic Ocean to be shortly after 13,000 years ago, near the start of the Younger Dryas. We attribute to this flood a boulder terrace near Fort McMurray with calibrated radiocarbon dates of over 11,500 years ago. A large flood into the Arctic Ocean at the start of the Younger Dryas leads us to reject the widespread view that Agassiz overflow at this time was solely eastward into the North Atlantic Ocean.

The role of clouds in driving North Atlantic multi-decadal climate variability in observations and models

NASA Astrophysics Data System (ADS)

Clement, A. C.; Bellomo, K.; Murphy, L.

2013-12-01

Large scale warming and cooling periods of the North Atlantic is known as the Atlantic Multidecadal Oscillation (AMO). The pattern of warming and cooling in the North Atlantic Ocean over the 20th century that has a characteristic spatial structure with maximum warming in the mid-latitudes and subtropics. This has been most often attributed to changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC), which in turn affects poleward heat transport. A recent modeling study by Booth et al. (2012), however, suggested that aerosols can explain both the spatial pattern and temporal history of Atlantic SST through indirect effects of aerosols on cloud cover; although this idea is controversial (Zhang et al., 2013). We have found observational evidence that changes in cloud amount can drive SST changes on multi-decadal timescale. We hypothesize that a positive local feedback between SST and cloud radiative effect amplifies SST and gives rise to the observed pattern of SST change. During cool North Atlantic periods, a southward shift of the ITCZ strengthens the trade winds in the tropical North Atlantic and increases low-level cloud cover, which acts to amplify the SST cooling in the North Atlantic. During warm periods in the North Atlantic, the opposite response occurs. We are testing whether the amplitude of this feedback is realistically simulated in the CMIP5 models, and whether inter-model differences in the amplitude of the feedback can explain differences in model simulations of Atlantic multi-decadal variability.
Arctic Risk Management (ARMNet) Network: Linking Risk Management Practitioners and Researchers Across the Arctic Regions of Canada and Alaska To Improve Risk, Emergency and Disaster Preparedness and Mitigation Through Comparative Analysis and Applied Research

NASA Astrophysics Data System (ADS)

Garland, A.

2015-12-01

The Arctic Risk Management Network (ARMNet) was conceived as a trans-disciplinary hub to encourage and facilitate greater cooperation, communication and exchange among American and Canadian academics and practitioners actively engaged in the research, management and mitigation of risks, emergencies and disasters in the Arctic regions. Its aim is to assist regional decision-makers through the sharing of applied research and best practices and to support greater inter-operability and bilateral collaboration through improved networking, joint exercises, workshops, teleconferences, radio programs, and virtual communications (eg. webinars). Most importantly, ARMNet is a clearinghouse for all information related to the management of the frequent hazards of Arctic climate and geography in North America, including new and emerging challenges arising from climate change, increased maritime polar traffic and expanding economic development in the region. ARMNet is an outcome of the Arctic Observing Network (AON) for Long Term Observations, Governance, and Management Discussions, www.arcus.org/search-program. The AON goals continue with CRIOS (www.ariesnonprofit.com/ARIESprojects.php) and coastal erosion research (www.ariesnonprofit.com/webinarCoastalErosion.php) led by the North Slope Borough Risk Management Office with assistance from ARIES (Applied Research in Environmental Sciences Nonprofit, Inc.). The constituency for ARMNet will include all northern academics and researchers, Arctic-based corporations, First Responders (FRs), Emergency Management Offices (EMOs) and Risk Management Offices (RMOs), military, Coast Guard, northern police forces, Search and Rescue (SAR) associations, boroughs, territories and communities throughout the Arctic. This presentation will be of interest to all those engaged in Arctic affairs, describe the genesis of ARMNet and present the results of stakeholder meetings and webinars designed to guide the next stages of the Project.
Iron limitation of microbial phosphorus acquisition in the tropical North Atlantic

PubMed Central

Browning, T. J.; Achterberg, E. P.; Yong, J. C.; Rapp, I.; Utermann, C.; Engel, A.; Moore, C. M.

2017-01-01

In certain regions of the predominantly nitrogen limited ocean, microbes can become co-limited by phosphorus. Within such regions, a proportion of the dissolved organic phosphorus pool can be accessed by microbes employing a variety of alkaline phosphatase (APase) enzymes. In contrast to the PhoA family of APases that utilize zinc as a cofactor, the recent discovery of iron as a cofactor in the more widespread PhoX and PhoD implies the potential for a biochemically dependant interplay between oceanic zinc, iron and phosphorus cycles. Here we demonstrate enhanced natural community APase activity following iron amendment within the low zinc and moderately low iron Western North Atlantic. In contrast we find no evidence for trace metal limitation of APase activity beneath the Saharan dust plume in the Eastern Atlantic. Such intermittent iron limitation of microbial phosphorus acquisition provides an additional facet in the argument for iron controlling the coupling between oceanic nitrogen and phosphorus cycles. PMID:28524880
Trends and variability of cloud fraction cover in the Arctic, 1982-2009

NASA Astrophysics Data System (ADS)

Boccolari, Mauro; Parmiggiani, Flavio

2018-05-01

Climatology, trends and variability of cloud fraction cover (CFC) data over the Arctic (north of 70°N), were analysed over the 1982-2009 period. Data, available from the Climate Monitoring Satellite Application Facility (CM SAF), are derived from satellite measurements by AVHRR. Climatological means confirm permanent high CFC values over the Atlantic sector during all the year and during summer over the eastern Arctic Ocean. Lower values are found in the rest of the analysed area especially over Greenland and the Canadian Archipelago, nearly continuously during all the months. These results are confirmed by CFC trends and variability. Statistically significant trends were found during all the months over the Greenland Sea, particularly during the winter season (negative, less than -5 % dec -1) and over the Beaufort Sea in spring (positive, more than +5 % dec -1). CFC variability, investigated by the Empirical Orthogonal Functions, shows a substantial "non-variability" in the Northern Atlantic Ocean. Statistically significant correlations between CFC principal components elements and both the Pacific Decadal Oscillation index and Pacific North America patterns are found.
Turbidity distribution in the Atlantic Ocean

USGS Publications Warehouse

Eittreim, S.; Thorndike, E.M.; Sullivan, L.

1976-01-01

The regional coverage of Lamont nephelometer data in the North and South Atlantic can be used to map seawater turbidity at all depths. At the level of the clearest water, in the mid-depth regions, the turbidity distribution primarily reflects the pattern of productivity in the surface waters. This suggests that the 'background' turbidity level in the oceans is largely a function of biogenic fallout. The bottom waters of the western Atlantic generally exhibit large increases in turbidity. The most intense benthic nepheloid layers are in the southwestern Argentine basin and northern North American basin; the lowest bottom water turbidity in the western Atlantic is in the equatorial regions. Both the Argentine and North American basin bottom waters appear to derive their high turbidity largely from local resuspension of terrigenous input in these basins. In contrast to the west, the eastern Atlantic basins show very low turbidities with the exception of three regions: the Mediterranean outflow area, the Cape basin, and the West European basin. ?? 1976.
The role of sea ice for vascular plant dispersal in the Arctic

PubMed Central

Ehrich, Dorothee; Bennike, Ole; Geirsdottir, Aslaug

2016-01-01

Sea ice has been suggested to be an important factor for dispersal of vascular plants in the Arctic. To assess its role for postglacial colonization in the North Atlantic region, we compiled data on the first Late Glacial to Holocene occurrence of vascular plant species in East Greenland, Iceland, the Faroe Islands and Svalbard. For each record, we reconstructed likely past dispersal events using data on species distributions and genetics. We compared these data to sea-ice reconstructions to evaluate the potential role of sea ice in these past colonization events and finally evaluated these results using a compilation of driftwood records as an independent source of evidence that sea ice can disperse biological material. Our results show that sea ice was, in general, more prevalent along the most likely dispersal routes at times of assumed first colonization than along other possible routes. Also, driftwood is frequently dispersed in regions that have sea ice today. Thus, sea ice may act as an important dispersal agent. Melting sea ice may hamper future dispersal of Arctic plants and thereby cause more genetic differentiation. It may also limit the northwards expansion of competing boreal species, and hence favour the persistence of Arctic species. PMID:27651529
Novel biodiversity baselines outpace models of fish distribution in Arctic waters

NASA Astrophysics Data System (ADS)

Christiansen, Jørgen S.; Bonsdorff, Erik; Byrkjedal, Ingvar; Fevolden, Svein-Erik; Karamushko, Oleg V.; Lynghammar, Arve; Mecklenburg, Catherine W.; Møller, Peter D. R.; Nielsen, Julius; Nordström, Marie C.; Præbel, Kim; Wienerroither, Rupert M.

2016-02-01

During a recent marine biological expedition to the Northeast Greenland shelf break (latitudes 74-77 °N), we made the first discovery of Atlantic cod ( Gadus morhua), beaked redfish ( Sebastes mentella) and capelin ( Mallotus villosus). Our novel observations shift the distribution range of Atlantic cod >1000 km further north in East Greenland waters. In light of climate change, we discuss physical forcing and putative connections between the faunas of the Northeast Greenland shelf and the Barents Sea. We emphasise the importance of using real data in spread scenarios for understudied Arctic seas.
Novel biodiversity baselines outpace models of fish distribution in Arctic waters.

PubMed

Christiansen, Jørgen S; Bonsdorff, Erik; Byrkjedal, Ingvar; Fevolden, Svein-Erik; Karamushko, Oleg V; Lynghammar, Arve; Mecklenburg, Catherine W; Møller, Peter D R; Nielsen, Julius; Nordström, Marie C; Præbel, Kim; Wienerroither, Rupert M

2016-02-01

During a recent marine biological expedition to the Northeast Greenland shelf break (latitudes 74-77 °N), we made the first discovery of Atlantic cod (Gadus morhua), beaked redfish (Sebastes mentella) and capelin (Mallotus villosus). Our novel observations shift the distribution range of Atlantic cod >1000 km further north in East Greenland waters. In light of climate change, we discuss physical forcing and putative connections between the faunas of the Northeast Greenland shelf and the Barents Sea. We emphasise the importance of using real data in spread scenarios for understudied Arctic seas.
A 21-Year Record of Arctic Sea Ice Extents and Their Regional, Seasonal, and Monthly Variability and Trends

NASA Technical Reports Server (NTRS)

Parkinson, Claire L.; Cavalieri, Donald J.; Zukor, Dorothy J. (Technical Monitor)

2001-01-01

Satellite passive-microwave data have been used to calculate sea ice extents over the period 1979-1999 for the north polar sea ice cover as a whole and for each of nine regions. Over this 21-year time period, the trend in yearly average ice extents for the ice cover as a whole is -32,900 +/- 6,100 sq km/yr (-2.7 +/- 0.5 %/decade), indicating a reduction in sea ice coverage that has decelerated from the earlier reported value of -34,000 +/- 8,300 sq km/yr (-2.8 +/- 0.7 %/decade) for the period 1979-1996. Regionally, the reductions are greatest in the Arctic Ocean, the Kara and Barents Seas, and the Seas of Okhotsk and Japan, whereas seasonally, the reductions are greatest in summer, for which season the 1979-1999 trend in ice extents is -41,600 +/- 12,900 sq km/ yr (-4.9 +/- 1.5 %/decade). On a monthly basis, the reductions are greatest in July and September for the north polar ice cover as a whole, in September for the Arctic Ocean, in June and July for the Kara and Barents Seas, and in April for the Seas of Okhotsk and Japan. Only two of the nine regions show overall ice extent increases, those being the Bering Sea and the Gulf of St. Lawrence.For neither of these two regions is the increase statistically significant, whereas the 1079 - 1999 ice extent decreases are statistically significant at the 99% confidence level for the north polar region as a whole, the Arctic Ocean, the Seas of Okhotsk and Japan, and Hudson Bay.
Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic region.

PubMed

Jones, E P; Skirnisson, K; McGovern, T H; Gilbert, M T P; Willerslev, E; Searle, J B

2012-03-19

House mice (Mus musculus) are commensals of humans and therefore their phylogeography can reflect human colonization and settlement patterns. Previous studies have linked the distribution of house mouse mitochondrial (mt) DNA clades to areas formerly occupied by the Norwegian Vikings in Norway and the British Isles. Norwegian Viking activity also extended further westwards in the North Atlantic with the settlement of Iceland, short-lived colonies in Greenland and a fleeting colony in Newfoundland in 1000 AD. Here we investigate whether house mouse mtDNA sequences reflect human history in these other regions as well. House mice samples from Iceland, whether from archaeological Viking Age material or from modern-day specimens, had an identical mtDNA haplotype to the clade previously linked with Norwegian Vikings. From mtDNA and microsatellite data, the modern-day Icelandic mice also share the low genetic diversity shown by their human hosts on Iceland. Viking Age mice from Greenland had an mtDNA haplotype deriving from the Icelandic haplotype, but the modern-day Greenlandic mice belong to an entirely different mtDNA clade. We found no genetic association between modern Newfoundland mice and the Icelandic/ancient Greenlandic mice (no ancient Newfoundland mice were available). The modern day Icelandic and Newfoundland mice belong to the subspecies M. m. domesticus, the Greenlandic mice to M. m. musculus. In the North Atlantic region, human settlement history over a thousand years is reflected remarkably by the mtDNA phylogeny of house mice. In Iceland, the mtDNA data show the arrival and continuity of the house mouse population to the present day, while in Greenland the data suggest the arrival, subsequent extinction and recolonization of house mice--in both places mirroring the history of the European human host populations. If house mice arrived in Newfoundland with the Viking settlers at all, then, like the humans, their presence was also fleeting and left no
Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic region

PubMed Central

2012-01-01

Background House mice (Mus musculus) are commensals of humans and therefore their phylogeography can reflect human colonization and settlement patterns. Previous studies have linked the distribution of house mouse mitochondrial (mt) DNA clades to areas formerly occupied by the Norwegian Vikings in Norway and the British Isles. Norwegian Viking activity also extended further westwards in the North Atlantic with the settlement of Iceland, short-lived colonies in Greenland and a fleeting colony in Newfoundland in 1000 AD. Here we investigate whether house mouse mtDNA sequences reflect human history in these other regions as well. Results House mice samples from Iceland, whether from archaeological Viking Age material or from modern-day specimens, had an identical mtDNA haplotype to the clade previously linked with Norwegian Vikings. From mtDNA and microsatellite data, the modern-day Icelandic mice also share the low genetic diversity shown by their human hosts on Iceland. Viking Age mice from Greenland had an mtDNA haplotype deriving from the Icelandic haplotype, but the modern-day Greenlandic mice belong to an entirely different mtDNA clade. We found no genetic association between modern Newfoundland mice and the Icelandic/ancient Greenlandic mice (no ancient Newfoundland mice were available). The modern day Icelandic and Newfoundland mice belong to the subspecies M. m. domesticus, the Greenlandic mice to M. m. musculus. Conclusions In the North Atlantic region, human settlement history over a thousand years is reflected remarkably by the mtDNA phylogeny of house mice. In Iceland, the mtDNA data show the arrival and continuity of the house mouse population to the present day, while in Greenland the data suggest the arrival, subsequent extinction and recolonization of house mice - in both places mirroring the history of the European human host populations. If house mice arrived in Newfoundland with the Viking settlers at all, then, like the humans, their presence was
Response of North Atlantic Ocean Chlorophyll a to the Change of Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Zhang, Min; Zhang, Yuanling; Shu, Qi; Zhao, Chang; Wang, Gang; Wu, Zhaohua; Qiao, Fangli

2017-04-01

Changes in marine phytoplankton are a vital component in global carbon cycling. Despite this far-reaching importance, the variable trend in phytoplankton and its response to climate variability remain unclear. This work presents the spatiotemporal evolution of the chlorophyll a trend in the North Atlantic Ocean by using merged ocean color products for the period 1997-2016. We find a dipole pattern between the subpolar gyre and the Gulf Stream path,and chlorophyll a trend signal propagatedalong the opposite direction of the North Atlantic Current. Such a dipole pattern and opposite propagation of chlorophyll a signal are consistent with the recent distinctive signature of the slowdown of the Atlantic MeridionalOverturning Circulation (AMOC). It is suggested that the spatiotemporal evolution of chlorophyll a during the two most recent decades is a part of the multidecadal variation and regulated byAMOC, which could be used as an indicator of AMOC variations.
South American monsoon response to iceberg discharge in the North Atlantic

NASA Astrophysics Data System (ADS)

Stríkis, Nicolás M.; Cruz, Francisco W.; Barreto, Eline A. S.; Naughton, Filipa; Vuille, Mathias; Cheng, Hai; Voelker, Antje H. L.; Zhang, Haiwei; Karmann, Ivo; Edwards, R. Lawrence; Auler, Augusto S.; Ventura Santos, Roberto; Reis Sales, Hamilton

2018-04-01

Heinrich Stadials significantly affected tropical precipitation through changes in the interhemispheric temperature gradient as a result of abrupt cooling in the North Atlantic. Here, we focus on changes in South American monsoon precipitation during Heinrich Stadials using a suite of speleothem records covering the last 85 ky B.P. from eastern South America. We document the response of South American monsoon precipitation to episodes of extensive iceberg discharge, which is distinct from the response to the cooling episodes that precede the main phase of ice-rafted detritus deposition. Our results demonstrate that iceberg discharge in the western subtropical North Atlantic led to an abrupt increase in monsoon precipitation over eastern South America. Our findings of an enhanced Southern Hemisphere monsoon, coeval with the iceberg discharge into the North Atlantic, are consistent with the observed abrupt increase in atmospheric methane concentrations during Heinrich Stadials.
Relating Regional Arctic Sea Ice and climate extremes over Europe

NASA Astrophysics Data System (ADS)

Ionita-Scholz, Monica; Grosfeld, Klaus; Lohmann, Gerrit; Scholz, Patrick

2016-04-01

The potential increase of temperature extremes under climate change is a major threat to society, as temperature extremes have a deep impact on environment, hydrology, agriculture, society and economy. Hence, the analysis of the mechanisms underlying their occurrence, including their relationships with the large-scale atmospheric circulation and sea ice concentration, is of major importance. At the same time, the decline in Arctic sea ice cover during the last 30 years has been widely documented and it is clear that this change is having profound impacts at regional as well as planetary scale. As such, this study aims to investigate the relation between the autumn regional sea ice concentration variability and cold winters in Europe, as identified by the numbers of cold nights (TN10p), cold days (TX10p), ice days (ID) and consecutive frost days (CFD). We analyze the relationship between Arctic sea ice variation in autumn (September-October-November) averaged over eight different Arctic regions (Barents/Kara Seas, Beaufort Sea, Chukchi/Bering Seas, Central Arctic, Greenland Sea, Labrador Sea/Baffin Bay, Laptev/East Siberian Seas and Northern Hemisphere) and variations in atmospheric circulation and climate extreme indices in the following winter season over Europe using composite map analysis. Based on the composite map analysis it is shown that the response of the winter extreme temperatures over Europe is highly correlated/connected to changes in Arctic sea ice variability. However, this signal is not symmetrical for the case of high and low sea ice years. Moreover, the response of temperatures extreme over Europe to sea ice variability over the different Arctic regions differs substantially. The regions which have the strongest impact on the extreme winter temperature over Europe are: Barents/Kara Seas, Beaufort Sea, Central Arctic and the Northern Hemisphere. For the years of high sea ice concentration in the Barents/Kara Seas there is a reduction in the number
The contemporary North Pangea supercontinent and the geodynamic causes of its formation

NASA Astrophysics Data System (ADS)

Kovalenko, V. I.; Yarmolyuk, V. V.; Bogatikov, O. A.

2010-11-01

The supercontinental status of the contemporary aggregation of continents called North Pangea is substantiated. This supercontinent comprises all continents with the probable exception of Antarctica. In addition to the spatial contiguity of continents, the supercontinent is characterized by the prevalence of the continental crust that combines North America and Eurasia, Eurasia and Africa, and Eurasia and Australia. Over the course of the 300-250-Ma evolution from Wegener's Pangea to contemporary North Pangea, the aggregation of continents has not lost its supercontinental status, despite modification of the supercontinent shape and opening and closure of the newly formed Paleotethys, Tethys, Atlantic, and Indian oceans. Over the last 250-300 Ma, all movements of the lithospheric plates have most likely occurred within the Indo-Atlantic segment of the Earth, whereas the Pacific segment has remained oceanic. In short, the formation of the North Pangea supercontinent can be outlined in the following terms. The long and deep subduction of the lithospheric plates beneath Eurasia and North America gave rise to the stabilization of the continents and accumulation of huge bodies of the cold lithosphere commensurable in volume with the upper mantle at the deeper mantle levels. This brought about compensation ascent of hot mantle (mantle plumes) near the convergent plate boundaries and far from them. A special geodynamic setting develops beneath the supercontinent. Due to encircling subduction of the lithospheric plates and related squeezing of the hot mantle, an ascending flow, or plume (superplume) formed beneath the central part of the supercontinent. In our view, the African superplume broke up Wegener's Pangea in the Atlantic region, caused the opening of the Atlantic and Indian oceans, and migrated to the Arctic Region 53 Ma ago.
Arctic shorebirds in North America: A decade of monitoring

USGS Publications Warehouse

Bart, Jonathan R.; Johnston, Victoria H.

2012-01-01

Each year shorebirds from North and South America migrate thousands of miles to spend the summer in the Arctic. There they feed in shoreline marshes and estuaries along some of the most productive and pristine coasts anywhere. With so much available food they are able to reproduce almost explosively; and as winter approaches, they retreat south along with their offspring, to return to the Arctic the following spring. This remarkable pattern of movement and activity has been the object of intensive study by an international team of ornithologists who have spent a decade counting, surveying, and observing these shorebirds. In this important synthetic work, they address multiple questions about these migratory bird populations. How many birds occupy Arctic ecosystems each summer? How long do visiting shorebirds linger before heading south? How fecund are these birds? Where exactly do they migrate and where exactly do they return? Are their populations growing or shrinking? The results of this study are crucial for better understanding how environmental policies will influence Arctic habitats as well as the far-ranging winter habitats used by migratory shorebirds.
Seasonal re-emergence of North Atlantic subsurface ocean temperature anomalies and Northern hemisphere climate

NASA Astrophysics Data System (ADS)

Sinha, Bablu; Blaker, Adam; Duchez, Aurelie; Grist, Jeremy; Hewitt, Helene; Hirschi, Joel; Hyder, Patrick; Josey, Simon; Maclachlan, Craig; New, Adrian

2017-04-01

A high-resolution coupled ocean atmosphere model is used to study the effects of seasonal re-emergence of North Atlantic subsurface ocean temperature anomalies on northern hemisphere winter climate. A 50-member control simulation is integrated from September 1 to 28 February and compared with a similar ensemble with perturbed ocean initial conditions. The perturbation consists of a density-compensated subsurface (deeper than 180m) temperature anomaly corresponding to the observed subsurface temperature anomaly for September 2010, which is known to have re-emerged at the ocean surface in subsequent months. The perturbation is confined to the North Atlantic Ocean between the Equator and 65 degrees North. The model has 1/4 degree horizontal resolution in the ocean and the experiment is repeated for two atmosphere horizontal resolutions ( 60km and 25km) in order to determine whether the sensitivity of the atmosphere to re-emerging temperature anomalies is dependent on resolution. The ensembles display a wide range of reemergence behaviour, in some cases re-emergence occurs by November, in others it is delayed or does not occur at all. A wide range of amplitudes of the re-emergent temperature anomalies is observed. In cases where re-emergence occurs, there is a marked effect on both the regional (North Atlantic and Europe) and hemispheric surface pressure and temperature patterns. The results highlight a potentially important process whereby ocean memory of conditions up to a year earlier can significantly enhance seasonal forecast skill.
Environmental Composites for Bomb Cyclones of the Western North Atlantic in Reanalysis, 1948-2016.

NASA Astrophysics Data System (ADS)

Adams, R.; Sheridan, S. C.

2017-12-01

"Bomb" cyclones represent a small subset of mid-latitude cyclones characterized by rapid intensification and frequently are associated with extreme weather conditions along the eastern coast of North America. Like other extreme phenomena, bomb cyclone predictions are prone to error leading to inadequate or untimely hazard warnings. The rare nature of bomb cyclones and the uniqueness of their evolutions has made it difficult for researchers to make meaningful generalizations on bomb cyclone events. This paper describes bomb cyclone climatology for the western North Atlantic, using data from the NCEP-NCAR Reanalysis for 1948-2016, and uses a synoptic climatological analysis to relate these bombs to their associated atmospheric environments. A self-organizing map (SOM) of 300-hPa geopotential height tendency is created to partition the regional atmospheric environment. Thermodynamic fields are contrasted by each 300-hPa geopotential height tendency pattern for both bomb and non-bomb events in composite difference maps. The SOM patterns most significantly associated with western North Atlantic bomb cyclogenesis are characterized by both strongly and weakly negative height tendencies along the eastern United States. In both cases, these patterns exhibit strong meridional flow, a distinction marked by the weakening and breaking down of the polar vortex in the boreal Winter. The composite maps for each pattern show the mean differences in low-mid level ascent and near surface thermodynamics for bomb environments contrasted with non-bomb environments, resulting in diverse spatiotemporal distributions of bombs in the western North Atlantic.
Influence of the vertical mixing parameterization on the modeling results of the Arctic Ocean hydrology

NASA Astrophysics Data System (ADS)

Iakshina, D. F.; Golubeva, E. N.

2017-11-01

The vertical distribution of the hydrological characteristics in the upper ocean layer is mostly formed under the influence of turbulent and convective mixing, which are not resolved in the system of equations for large-scale ocean. Therefore it is necessary to include additional parameterizations of these processes into the numerical models. In this paper we carry out a comparative analysis of the different vertical mixing parameterizations in simulations of climatic variability of the Arctic water and sea ice circulation. The 3D regional numerical model for the Arctic and North Atlantic developed in the ICMMG SB RAS (Institute of Computational Mathematics and Mathematical Geophysics of the Siberian Branch of the Russian Academy of Science) and package GOTM (General Ocean Turbulence Model1,2, http://www.gotm.net/) were used as the numerical instruments . NCEP/NCAR reanalysis data were used for determination of the surface fluxes related to ice and ocean. The next turbulence closure schemes were used for the vertical mixing parameterizations: 1) Integration scheme based on the Richardson criteria (RI); 2) Second-order scheme TKE with coefficients Canuto-A3 (CANUTO); 3) First-order scheme TKE with coefficients Schumann and Gerz4 (TKE-1); 4) Scheme KPP5 (KPP). In addition we investigated some important characteristics of the Arctic Ocean state including the intensity of Atlantic water inflow, ice cover state and fresh water content in Beaufort Sea.
Cretaceous paleoceanography of the western North Atlantic Ocean

USGS Publications Warehouse

Arthur, Michael A.; Dean, Walter E.

1986-01-01

In this paper we summarize available information on the Cretaceous lithostratigraphy and paleoceanography of the western North Atlantic. The data and some of our interpretations draw in large part on papers published in the Deep Sea Drilling Project (DSDP) volumes. We have attempted to cite relevant references when possible, but space limitations make it difficult to give proper credit to all sources; we apologize for any omissions.Organic carbon (Corg) and carbonate (CaCO3) analyses were tabulated for each site from papers in the DSDP Initial Report volumes and other published works (e.g., Summerhayes,1981). Corg, CaCO3, and non-CaCO3 mass accumulation rates (MARS) were calculated using core by core averages of component percentages for the more continuously cored sites; core averages for wet bulk density and porosity (from DSDP data files); biostratigraphies of de Graciansky and others (1982), Roth and Bowdler (1981), and Cool (1982); and the time scales of the Decade of North American Geology (Palmer, 1983; Kent and Gradstein, this volume) or Harland and others (1982; see Plate 1).Backtracked paleodepths for western North Atlantic DSDP Sites from Tucholke and Vogt (1979) with the revised stratigraphy of de Graciansky and others (1982) were used in plotting Corg and CaCO3 in Figures 2, 3, 4 and 5 (see also Thierstein, 1979).Backtracking curves of seafloor paleodepth versus age (Sclater and others, 1977; Tucholke and Vogt, 1979) for selected western North Atlantic DSDP sites. Average CaCO3 concentrations per core are shown by code number

Expanded record of Quaternary oceanographic change: Amerasian Arctic Ocean

USGS Publications Warehouse

Ishman, S.E.; Polyak, L.V.; Poore, R.Z.

1996-01-01

Four sediment cores collected from the Northwind and Mendeleyev ridges, Arctic Ocean, from 1089 m to 1909 m water depth, provide an oceanographic record extending back into the Matuyama reversed polarity chron. Benthic foraminiferal analyses show four prominent assemblage zones: Bolivina arctica, Cassidulina teretis, Bulimina aculeata, and Oridorsalis tener from the upper Matuyama reversed polarity chronozone through the Brunhes normal polarity chronozone. These assemblage zones represent depth-dependent benthic foraminiferal biofacies changes associated with oceanographic events that occurred in the Amerasian basin at ??? 780 and 300 ka, and indicate oceanographic influence from the North Atlantic. Recognition of these benthic assemblage zones in Arctic cores from the Alpha Ridge indicates that the benthic foraminiferal zonations in intermediate to deep water (>1000 m) Arctic cores may be more useful than preexisting lithostratigraphic zonations and should provide important information pertaining to the Quaternary paleoceanographic evolution of the Arctic Ocean.
A51F-0123: Model Analysis of Tropospheric Aerosol Variability and Sources over the North Atlantic During NAAMES 2015-2016

NASA Technical Reports Server (NTRS)

Liu, Hongyu; Moore, Richard; Hostetler, Chris A.; Ferrare, Richard Anthony; Fairlie, Thomas Duncan; Hu, Youngxiang; Chen, Gao; Hair, Johnathan W.; Johnson, Matthew S.

2016-01-01

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) is a five-year Earth-Venture Suborbital-2 Mission to characterize the plankton ecosystems and their influences on remote marine aerosols, boundary layer clouds, and their implications for climate in the North Atlantic. While marine-sourced aerosols have been shown to make important contributions to surface aerosol loading, cloud condensation nuclei and ice nuclei concentrations over remote marine and coastal regions, it is still a challenge to differentiate the marine biogenic aerosol signal from the strong influence of continental pollution outflow. We examine here the spatiotemporal variability and quantify the sources of tropospheric aerosols over the North Atlantic during the first two phases (November 2015 and May-June 2016) of NAAMES using a state-of-the-art chemical transport model (GEOS-Chem). The model is driven by the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) from the NASA Global Modeling and Assimilation Office (GMAO). It includes sulfate-nitrate-ammonium aerosol thermodynamics coupled to ozone-NOx-hydrocarbon-aerosol chemistry, mineral dust, sea salt, elemental and organic carbon aerosols, and especially a recently implemented parameterization for the marine primary organic aerosol emission. The simulated aerosols over the North Atlantic are evaluated with available satellite (e.g., MODIS) observations of aerosol optical depths (AOD), and aircraft and ship aerosol measurements. We diagnose transport pathways for continental pollution outflow over the North Atlantic using carbon monoxide, an excellent tracer for anthropogenic pollution transport. We also conduct model perturbation experiments to quantify the relative contributions of terrestrial and oceanic sources to the aerosol loading, AOD, and their variability over the North Atlantic.
North Atlantic cyclones; trends, impacts and links to large-scale variability

NASA Astrophysics Data System (ADS)

Trigo, R. M.; Trigo, I. F.; Ramos, A. M.; Paredes, D.; Garcia-Herrera, R.; Liberato, M. L. R.; Valente, M. A.

2009-04-01

Based on the cyclone detection and tracking algorithm previously developed (Trigo, 2006) we have assessed the inter-annual variability and cyclone frequency trends between 1960 and 2000 for the Euro-Atlantic sector using the highest spatial resolution available (1.125° x 1.125°) from the ERA-40 Surface Level Pressure. Additionally, trends for the u and v wind speed components are also computed at the monthly and seasonal scales, using the same dataset. All cyclone and wind speed trend maps were computed with the corresponding statistical significance field. Results reveal a significant frequency decrease (increase) in the western Mediterranean (Greenland and Scandinavia), particularly in December, February and March. Seasonal and monthly analysis of wind speed trends shows similar spatial patterns. We show that these changes in the frequency of low pressure centers and the associated wind patterns are partially responsible for trends of the significant height of waves. Throughout the extended winter months (ONDJFM), regions with positive (negative) wind magnitude trends, of up to 5 cm/s per year, often correspond to regions of positive (negative) significant wave height trends. The cyclone and wind speed trends computed for the JFM months are well matched by the corresponding trends in significant wave height, with February being the month with the highest trends (negative south of 50°N up to -3 cm/year, and positive up to 5cm/year just north of Scotland). Using precipitation data from ECMWF reanalyses and a CRU high resolution dataset we show the impact of these trends in cyclone frequencies upon the corresponding precipitation trends in the influenced areas. It is also shown that these changes are partially linked to major shifts on the indices of large-scale patterns modes, namely the North Atlantic Oscillation (NAO), the Eastern Atlantic (EA) and the Scandinavian Patterns (SCAN). Trigo, I. F. 2006: Climatology and Interannual Variability of Storm-Tracks in
Aerosols implicated as a prime driver of twentieth-century North Atlantic climate variability.

PubMed

Booth, Ben B B; Dunstone, Nick J; Halloran, Paul R; Andrews, Timothy; Bellouin, Nicolas

2012-04-04

Systematic climate shifts have been linked to multidecadal variability in observed sea surface temperatures in the North Atlantic Ocean. These links are extensive, influencing a range of climate processes such as hurricane activity and African Sahel and Amazonian droughts. The variability is distinct from historical global-mean temperature changes and is commonly attributed to natural ocean oscillations. A number of studies have provided evidence that aerosols can influence long-term changes in sea surface temperatures, but climate models have so far failed to reproduce these interactions and the role of aerosols in decadal variability remains unclear. Here we use a state-of-the-art Earth system climate model to show that aerosol emissions and periods of volcanic activity explain 76 per cent of the simulated multidecadal variance in detrended 1860-2005 North Atlantic sea surface temperatures. After 1950, simulated variability is within observational estimates; our estimates for 1910-1940 capture twice the warming of previous generation models but do not explain the entire observed trend. Other processes, such as ocean circulation, may also have contributed to variability in the early twentieth century. Mechanistically, we find that inclusion of aerosol-cloud microphysical effects, which were included in few previous multimodel ensembles, dominates the magnitude (80 per cent) and the spatial pattern of the total surface aerosol forcing in the North Atlantic. Our findings suggest that anthropogenic aerosol emissions influenced a range of societally important historical climate events such as peaks in hurricane activity and Sahel drought. Decadal-scale model predictions of regional Atlantic climate will probably be improved by incorporating aerosol-cloud microphysical interactions and estimates of future concentrations of aerosols, emissions of which are directly addressable by policy actions.
The not-so-silent world: Measuring Arctic, Equatorial, and Antarctic soundscapes in the Atlantic Ocean

NASA Astrophysics Data System (ADS)

Haver, Samara M.; Klinck, Holger; Nieukirk, Sharon L.; Matsumoto, Haru; Dziak, Robert P.; Miksis-Olds, Jennifer L.

2017-04-01

Anthropogenic noise in the ocean has been shown, under certain conditions, to influence the behavior and health of marine mammals. Noise from human activities may interfere with the low-frequency acoustic communication of many Mysticete species, including blue (Balaenoptera musculus) and fin whales (B. physalus). This study analyzed three soundscapes in the Atlantic Ocean, from the Arctic to the Antarctic, to document ambient sound. For 16 months beginning in August 2009, acoustic data (15-100 Hz) were collected in the Fram Strait (79°N, 5.5°E), near Ascension Island (8°S, 14.4°W) and in the Bransfield Strait (62°S, 55.5°W). Results indicate (1) the highest overall sound levels were measured in the equatorial Atlantic, in association with high levels of seismic oil and gas exploration, (2) compared to the tropics, ambient sound levels in polar regions are more seasonally variable, and (3) individual elements beget the seasonal and annual variability of ambient sound levels in high latitudes. Understanding how the variability of natural and man-made contributors to sound may elicit differences in ocean soundscapes is essential to developing strategies to manage and conserve marine ecosystems and animals.
Interior pathways of the North Atlantic meridional overturning circulation.

PubMed

Bower, Amy S; Lozier, M Susan; Gary, Stefan F; Böning, Claus W

2009-05-14

To understand how our global climate will change in response to natural and anthropogenic forcing, it is essential to determine how quickly and by what pathways climate change signals are transported throughout the global ocean, a vast reservoir for heat and carbon dioxide. Labrador Sea Water (LSW), formed by open ocean convection in the subpolar North Atlantic, is a particularly sensitive indicator of climate change on interannual to decadal timescales. Hydrographic observations made anywhere along the western boundary of the North Atlantic reveal a core of LSW at intermediate depths advected southward within the Deep Western Boundary Current (DWBC). These observations have led to the widely held view that the DWBC is the dominant pathway for the export of LSW from its formation site in the northern North Atlantic towards the Equator. Here we show that most of the recently ventilated LSW entering the subtropics follows interior, not DWBC, pathways. The interior pathways are revealed by trajectories of subsurface RAFOS floats released during the period 2003-2005 that recorded once-daily temperature, pressure and acoustically determined position for two years, and by model-simulated 'e-floats' released in the subpolar DWBC. The evidence points to a few specific locations around the Grand Banks where LSW is most often injected into the interior. These results have implications for deep ocean ventilation and suggest that the interior subtropical gyre should not be ignored when considering the Atlantic meridional overturning circulation.
Reconstruction of the North Atlantic end-member of the Atlantic Meridional Overturning Circulation over glacial-interglacial cycles

NASA Astrophysics Data System (ADS)

Kim, J.; Seguí, M. J.; Knudson, K. P.; Yehudai, M.; Goldstein, S. L.; Pena, L. D.; Basak, C.; Ferretti, P.

2017-12-01

North Atlantic Deep Water (NADW) represents the major water mass that drives the Atlantic Meridional Ocean Circulation (AMOC), which undergoes substantial reorganization with changing climate. In order to understand its impact on ocean circulation and climate through time, it is necessary to constrain its composition. We report Nd isotope ratios of Fe-Mn oxide encrusted foraminifera and fish debris from DSDP Site 607 (41.00N 32.96W, 3427m), in the present-day core of NADW, and ODP 1063 (33.68N 57.62W, 4585m), on the deep abyssal plain at the interface between NADW and Antarctic Bottom Water. We provide a new North Atlantic paleocirculation record covering 2 Ma. At Site 607 interglacial ɛNd-values are consistently similar to present-day NADW (ɛNd -13.5), with median ɛNd-values of -14.3 in the Early Pleistocene and -13.8 in the Late Pleistocene. Glacial ɛNd-values are higher by 1 ɛNd-unit in the Early Pleistocene, and 1.5-2 ɛNd-units in the Late Pleistocene. Site 1063 shows much greater variability, with ɛNd ranging from -10 to -26. We interpret the North Atlantic AMOC source as represented by the Site 607 interglacial ɛNd-values, which has remained nearly stable throughout the entire period. The higher glacial ɛNd-values reflect incursions of some southern-sourced waters to Site 607, which is supported by coeval shifts to lower benthic foraminiferal d13C. In contrast, the Site 1063 ɛNd-values do not appear to reflect the AMOC end-member, and likely reflects local effects from a bottom source. A period of greatly disrupted ocean circulation marks 950-850 Ma, which may have been triggered by enhanced ice growth in the Northern Hemisphere that began around 1.2 Ma, as suggested by possible input events of Nd from the surrounding cratons into the North Atlantic observed in Site 607. Interglacial AMOC only recovers to the previously observed vigor over 200 ka following the disruption, whereas further intensified SSW incursion into the deep North Atlantic come to
Plastic Accumulation in the North Atlantic Subtropical Gyre

NASA Astrophysics Data System (ADS)

Law, Kara Lavender; Morét-Ferguson, Skye; Maximenko, Nikolai A.; Proskurowski, Giora; Peacock, Emily E.; Hafner, Jan; Reddy, Christopher M.

2010-09-01

Plastic marine pollution is a major environmental concern, yet a quantitative description of the scope of this problem in the open ocean is lacking. Here, we present a time series of plastic content at the surface of the western North Atlantic Ocean and Caribbean Sea from 1986 to 2008. More than 60% of 6136 surface plankton net tows collected buoyant plastic pieces, typically millimeters in size. The highest concentration of plastic debris was observed in subtropical latitudes and associated with the observed large-scale convergence in surface currents predicted by Ekman dynamics. Despite a rapid increase in plastic production and disposal during this time period, no trend in plastic concentration was observed in the region of highest accumulation.
Does Arctic sea ice reduction foster shelf-basin exchange?

PubMed

Ivanov, Vladimir; Watanabe, Eiji

2013-12-01

The recent shift in Arctic ice conditions from prevailing multi-year ice to first-year ice will presumably intensify fall-winter sea ice freezing and the associated salt flux to the underlying water column. Here, we conduct a dual modeling study whose results suggest that the predicted catastrophic consequences for the global thermohaline circulation (THC), as a result of the disappearance of Arctic sea ice, may not necessarily occur. In a warmer climate, the substantial fraction of dense water feeding the Greenland-Scotland overflow may form on Arctic shelves and cascade to the deep basin, thus replenishing dense water, which currently forms through open ocean convection in the sub-Arctic seas. We have used a simplified model for estimating how increased ice production influences shelf-basin exchange associated with dense water cascading. We have carried out case studies in two regions of the Arctic Ocean where cascading was observed in the past. The baseline range of buoyancy-forcing derived from the columnar ice formation was calculated as part of a 30-year experiment of the pan-Arctic coupled ice-ocean general circulation model (GCM). The GCM results indicate that mechanical sea ice divergence associated with lateral advection accounts for a significant part of the interannual variations in sea ice thermal production in the coastal polynya regions. This forcing was then rectified by taking into account sub-grid processes and used in a regional model with analytically prescribed bottom topography and vertical stratification in order to examine specific cascading conditions in the Pacific and Atlantic sectors of the Arctic Ocean. Our results demonstrate that the consequences of enhanced ice formation depend on geographical location and shelf-basin bathymetry. In the Pacific sector, strong density stratification in slope waters impedes noticeable deepening of shelf-origin water, even for the strongest forcing applied. In the Atlantic sector, a 1.5x increase of
THE RESPONSE OF MARINE ECOSYSTEMS TO CLIMATE VARIABILITY ASSOCIATED WITH THE NORTH ATLANTIC OSCILLATION

EPA Science Inventory

A strong association is documented between variability of the North Atlantic Oscillation (NAO) and changes in various trophic levels of the marine ecosystems of the North Atlantic. Examples are presented for phytoplankton, zooplankton, benthos, fish, marine diseases, whales and s...
Impacts of radiation management techniques on the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Adakudlu, Muralidhar; Helge Otterå, Odd; Tjiputra, Jerry; Muri, Helene; Grini, Alf; Schulz, Michael

2017-04-01

The effectiveness of various climate engineering techniques in limiting the global warming signal to reasonable levels has been the topic of state-of-the-art research on climate change. Using an Earth system model, we show that these techniques have the potential to bring down the high CO2 concentration climate in RCP8.5 to a moderate climate similar to RCP4.5 in terms of global temperature. Nevertheless, their influence on the regional aspects of atmospheric circulation is not clear. The regional circulation patterns in the atmosphere are largely characterized by the natural variability modes, such as the North Atlantic Oscillation (NAO). In this study, we assess the impacts of three radiation managment techniques, namely, Stratospheric Aerosol Injection (SAI), Marine Sky Brightening (MSB) and Cirrus Cloud Thinning (CCT), on the structure and features of the NAO. The results indicate an east-northeastward shift as well as intensification of the NAO spatial pattern in the global warming scenarios of RCP4.5 and RCP8.5, with the signal being most intense in the latter. The climate engineering forcings when applied to the RCP8.5 case tend to reduce the strength of the NAO with little impact on its position. The CCT case appears to have the maximum effect on the NAO signal. The patterns of cloud radiative forcing, expressed as the difference between net radiative forcing at TOA under average conditions and clear sky conditions, reveal a northeastward shift of the radiative heating in the north Atlantic region. This implies a possible link between the changes in the NAO signal and the cloud radiative forcing.
North Atlantic salinity as a predictor of Sahel rainfall.

PubMed

Li, Laifang; Schmitt, Raymond W; Ummenhofer, Caroline C; Karnauskas, Kristopher B

2016-05-01

Water evaporating from the ocean sustains precipitation on land. This ocean-to-land moisture transport leaves an imprint on sea surface salinity (SSS). Thus, the question arises of whether variations in SSS can provide insight into terrestrial precipitation. This study provides evidence that springtime SSS in the subtropical North Atlantic ocean can be used as a predictor of terrestrial precipitation during the subsequent summer monsoon in Africa. Specifically, increased springtime SSS in the central to eastern subtropical North Atlantic tends to be followed by above-normal monsoon-season precipitation in the African Sahel. In the spring, high SSS is associated with enhanced moisture flux divergence from the subtropical oceans, which converges over the African Sahel and helps to elevate local soil moisture content. From spring to the summer monsoon season, the initial water cycling signal is preserved, amplified, and manifested in excessive precipitation. According to our analysis of currently available soil moisture data sets, this 3-month delay is attributable to a positive coupling between soil moisture, moisture flux convergence, and precipitation in the Sahel. Because of the physical connection between salinity, ocean-to-land moisture transport, and local soil moisture feedback, seasonal forecasts of Sahel precipitation can be improved by incorporating SSS into prediction models. Thus, expanded monitoring of ocean salinity should contribute to more skillful predictions of precipitation in vulnerable subtropical regions, such as the Sahel.
North Atlantic salinity as a predictor of Sahel rainfall

PubMed Central

Li, Laifang; Schmitt, Raymond W.; Ummenhofer, Caroline C.; Karnauskas, Kristopher B.

2016-01-01

Water evaporating from the ocean sustains precipitation on land. This ocean-to-land moisture transport leaves an imprint on sea surface salinity (SSS). Thus, the question arises of whether variations in SSS can provide insight into terrestrial precipitation. This study provides evidence that springtime SSS in the subtropical North Atlantic ocean can be used as a predictor of terrestrial precipitation during the subsequent summer monsoon in Africa. Specifically, increased springtime SSS in the central to eastern subtropical North Atlantic tends to be followed by above-normal monsoon-season precipitation in the African Sahel. In the spring, high SSS is associated with enhanced moisture flux divergence from the subtropical oceans, which converges over the African Sahel and helps to elevate local soil moisture content. From spring to the summer monsoon season, the initial water cycling signal is preserved, amplified, and manifested in excessive precipitation. According to our analysis of currently available soil moisture data sets, this 3-month delay is attributable to a positive coupling between soil moisture, moisture flux convergence, and precipitation in the Sahel. Because of the physical connection between salinity, ocean-to-land moisture transport, and local soil moisture feedback, seasonal forecasts of Sahel precipitation can be improved by incorporating SSS into prediction models. Thus, expanded monitoring of ocean salinity should contribute to more skillful predictions of precipitation in vulnerable subtropical regions, such as the Sahel. PMID:27386525
The impacts of oceanic deep temperature perturbations in the North Atlantic on decadal climate variability and predictability

NASA Astrophysics Data System (ADS)

Germe, Agathe; Sévellec, Florian; Mignot, Juliette; Fedorov, Alexey; Nguyen, Sébastien; Swingedouw, Didier

2017-12-01

Decadal climate predictability in the North Atlantic is largely related to ocean low frequency variability, whose sensitivity to initial conditions is not very well understood. Recently, three-dimensional oceanic temperature anomalies optimally perturbing the North Atlantic Mean Temperature (NAMT) have been computed via an optimization procedure using a linear adjoint to a realistic ocean general circulation model. The spatial pattern of the identified perturbations, localized in the North Atlantic, has the largest magnitude between 1000 and 4000 m depth. In the present study, the impacts of these perturbations on NAMT, on the Atlantic meridional overturning circulation (AMOC), and on climate in general are investigated in a global coupled model that uses the same ocean model as was used to compute the three-dimensional optimal perturbations. In the coupled model, these perturbations induce AMOC and NAMT anomalies peaking after 5 and 10 years, respectively, generally consistent with the ocean-only linear predictions. To further understand their impact, their magnitude was varied in a broad range. For initial perturbations with a magnitude comparable to the internal variability of the coupled model, the model response exhibits a strong signature in sea surface temperature and precipitation over North America and the Sahel region. The existence and impacts of these ocean perturbations have important implications for decadal prediction: they can be seen either as a source of predictability or uncertainty, depending on whether the current observing system can detect them or not. In fact, comparing the magnitude of the imposed perturbations with the uncertainty of available ocean observations such as Argo data or ocean state estimates suggests that only the largest perturbations used in this study could be detectable. This highlights the importance for decadal climate prediction of accurate ocean density initialisation in the North Atlantic at intermediate and greater
Causes of Upper-Ocean Temperature Anomalies in the Tropical North Atlantic

NASA Astrophysics Data System (ADS)

Rugg, A.; Foltz, G. R.; Perez, R. C.

2016-02-01

Hurricane activity and regional rainfall are strongly impacted by upper ocean conditions in the tropical North Atlantic, defined as the region between the equator and 20°N. A previous study analyzed a strong cold sea surface temperature (SST) anomaly that developed in this region during early 2009 and was recorded by the Pilot Research Array in the Tropical Atlantic (PIRATA) moored buoy at 4°N, 23°W (Foltz et al. 2012). The same mooring shows a similar cold anomaly in the spring of 2015 as well as a strong warm anomaly in 2010, offering the opportunity for a more comprehensive analysis of the causes of these events. In this study we examine the main causes of the observed temperature anomalies between 1998 and 2015. Basin-scale conditions during these events are analyzed using satellite SST, wind, and rain data, as well as temperature and salinity profiles from the NCEP Global Ocean Data Assimilation System. A more detailed analysis is conducted using ten years of direct measurements from the PIRATA mooring at 4°N, 23°W. Results show that the cooling and warming anomalies were caused primarily by wind-driven changes in surface evaporative cooling, mixed layer depth, and upper-ocean vertical velocity. Anomalies in surface solar radiation acted to damp the wind-driven SST anomalies in the latitude bands of the ITCZ (3°-8°N). Basin-scale analyses also suggest a strong connection between the observed SST anomalies and the Atlantic Meridional Mode, a well-known pattern of SST and surface wind anomalies spanning the tropical Atlantic.
Estimation of Aerosol Direct Radiative Effects Over the Mid-Latitude North Atlantic from Satellite and In Situ Measurements

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.; Russell, P. B.

2000-01-01

We estimate solar radiative flux changes due to aerosols over the mid-latitude North Atlantic by combining optical depths from AVHRR measurements with aerosol properties from the recent TARFOX program. Results show that, over the ocean the aerosol decreases the net radiative flux at the tropopause and therefore has a cooling effect. Cloud-free, 24-hour average flux changes range from -9 W/sq m near the eastern US coast in summer to -1 W/sq m in the mid-Atlantic during winter. Cloud-free North Atlantic regional averages range from -5.1 W/sq m in summer to -1.7 W/sq m in winter, with an annual average of -3.5 W/sq m. Cloud effects estimated from ISCCP data, reduce the regional annual average to -0.8 W/sq m. All values are for the moderately absorbing TARFOX aerosol (omega(0.55 microns) = 0.9); values for a nonabsorbing aerosol are approx. 30% more negative. We compare our results to a variety of other calculations of aerosol radiative effects.
Acoustic Behavior of North Atlantic Right Whale (Eubalaena glacialis) Mother-Calf Pairs

DTIC Science & Technology

2013-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Acoustic Behavior of North Atlantic Right Whale ...LONG-TERM GOALS The long-term goal of this project is to quantify the behavior of mother-calf pairs from the North Atlantic right whale ...The primary objectives of this project are to: 1) determine the visual detectability of right whale mother-calf pairs from surface observations
Acoustic Behavior of North Atlantic Right Whale (Eubalaena glacialis) Mother-Calf Pairs

DTIC Science & Technology

2014-09-30

1 DISTRIBUTION STATEMENT A. Approved for public release; distribution is unlimited. Acoustic Behavior of North Atlantic Right Whale ...LONG-TERM GOALS The long-term goal of this project is to quantify the behavior of mother-calf pairs from the North Atlantic right whale ...The primary objectives of this project are to: 1) determine the visual detectability of right whale mother-calf pairs from surface observations
Arctic Ocean Pathways in the 21st century

NASA Astrophysics Data System (ADS)

Aksenov, Yevgeny; van Gennip, Simon J.; Kelly, Stephen J.; Popova, Ekaterina E.; Yool, Andrew

2017-04-01

weakening of the current and an anti-cyclonic gyre spin-up in the Makarov Basin. This presents a shift of the Arctic circulation "dipole" and of the Transpolar Drift, with the consequence that the PW flow towards Fram Strait is significantly reduced by the end of the century, weakening the Pacific-Atlantic connection via the Arctic Ocean, and reducing the Arctic freshwater outflow into the North Atlantic. Examination of the simulations suggests that these circulation changes are primarily due to the shift in the wind.
Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation.

PubMed

Biastoch, A; Böning, C W; Lutjeharms, J R E

2008-11-27

Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC). Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic (RAPID, at latitude 26.5 degrees N, and MOVE, at latitude 16 degrees N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of +/-1.5-3 Sv (1 Sv = 10(6) m(3) s(-1)) on decadal timescales in the subtropics. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.

Seasonal and regional differentiation of bio-optical properties within the north polar Atlantic

NASA Astrophysics Data System (ADS)

Stramska, Malgorzata; Stramski, Dariusz; Kaczmarek, SłAwomir; Allison, David B.; Schwarz, Jill

2006-08-01

Using field data from the north polar Atlantic, we examined seasonal variability of the spectral absorption, a(λ), and backscattering, bb(λ), coefficients of surface waters in relation to phytoplankton pigments. For a given chlorophyll a concentration, the concentrations of accessory pigments were lower in spring than in summer. This effect contributed to lower chlorophyll-specific absorption of phytoplankton and total particulate matter in spring. The spring values of the green-to-blue band ratio of a(λ) were higher than the summer ratios. The blue-to-green ratios of bb(λ) were also higher in spring. The higher bb values and lower blue-to-green bb ratios in summer were likely associated with higher concentrations of detrital particles in summer compared to spring. Because the product of these band ratios of a and bb is a proxy for the blue-to-green ratio of remote-sensing reflectance, the performance of ocean color band-ratio algorithms for estimating pigments is significantly affected by seasonal shifts in the relationships between absorption, backscattering, and chlorophyll a. Our results suggest that the algorithm for the spring season would predict chlorophyll a that is higher by as much as a factor of 4-6 compared to that predicted from the summer algorithm. This indicates a need for a seasonal approach in the north polar Atlantic. However, we also found that a fairly good estimate of the particulate beam attenuation coefficient at 660 nm (a proxy for total particulate matter or particulate organic carbon concentration) can be obtained by applying a single blue-to-green band-ratio algorithm regardless of the season.
Seasonal And Regional Differentiation Of Bio-Optical Properties Within The North Polar Atlantic

NASA Technical Reports Server (NTRS)

Stramska, Malgorzata; Stramski, Dariusz; Kaczmarek, Slawomir; Allison, David B.; Schwarz, Jill

2005-01-01

Using data collected during spring and summer seasons in the north polar Atlantic we examined the variability of the spectral absorption, a(lambda), and backscattering, b(sub b)(lambda), coefficients of surface waters and its relation to phytoplankton pigment concentration and composition. For a given chlorophyll a concentration (TChla), the concentrations of photosynthetic carotenoids (PSC), photoprotective carotenoids (PPC), and total accessory pigments (AP) were consistently lower in spring than in summer. The chlorophyll-specific absorption coefficients of phytoplankton and total particulate matter were also lower in spring, which can be partly attributed to lower proportions of PPC, PSC, and AP in spring. The spring values of the green-to-blue band ratio of the absorption coefficient were higher than the summer ratios. The blue-to-green ratios of backscattering coefficient were also higher in spring. The higher b(sub b) values and lower blue-to-green b(sub b) ratios in summer were likely associated with higher concentrations of detrital particles in summer compared to spring. Because the product of the green-to-blue absorption ratio and the blue-to-green backscattering ratio is a proxy for the blue-to-green ratio of remote-sensing reflectance, we conclude that the performance of ocean color band-ratio algorithms for estimating pigments in the north polar Atlantic is significantly affected by seasonal shifts in the relationships between absorption and TChla as well as between backscattering and TChla. Intriguingly, however, fairly good estimate of the particulate beam attenuation coefficient at 660 nm (potential measure of total particulate matter or particulate organic carbon concentration) can be obtained by applying a single blue-to-green band-ratio algorithm for both spring and summer seasons.
Marine Corps Equities in the Arctic

DTIC Science & Technology

2013-04-18

reduces the shipping time from Yokohama, Japan, to Hamburg , Germany, by 11 days as compared to the Suez Canal. Ships average approximately a 20...areas within the Arctic Circle. 10 Warming ocean water is causing fisheries to shift north as well. Fish populations usually found in the...people live in the Arctic region. Commercial fishing fleets are following these populations. 29 Russia holds the majority of the Arctic population
Behavioral interactions of penned red and arctic foxes

USGS Publications Warehouse

Rudzinski, D.R.; Graves, H.B.; Sargeant, A.B.; Storm, G.L.

1982-01-01

Expansion of the geographical distribution of red foxes (Vulpes vulpes) into the far north tundra region may lead to competition between arctic (Alopex lagopus) and red foxes for space and resources. Behavioral interactions between red and arctic foxes were evaluated during 9 trials conducted in a 4.05-ha enclosure near Woodworth, North Dakota. Each trial consisted of introducing a male-female pair of arctic foxes into the enclosure and allowing them to acclimate for approximately a week before releasing a female red fox into the enclosure, followed by her mate a few days later. In 8 of 9 trials, red foxes were dominant over arctic foxes during encounters. Activity of the arctic foxes decreased upon addition of red foxes. Arctic foxes tried unsuccessfully to defend preferred den, resting, and feeding areas. Even though the outcome of competition between red and arctic foxes in the Arctic is uncertain, the more aggressive red fox can dominate arctic foxes in direct competition for den sites and other limited resources.
Multinational Experiment 7. Maritime Security Region: The Arctic

DTIC Science & Technology

2013-07-08

Russia. Marine Resources The Arctic Ocean is home to countless species from microscopic plankton to gigantic whales . Large-scale commercial...Arctic is a circumpolar region that encompasses both marine and land masses and includes the Arctic Ocean and its seas that cover more than 30...and does not rise on the day of the winter solstice. The Arctic Ocean is the world’s smallest and shallowest, with an average depth of roughly a
Sea Ice and Hydrographic Variability in the Northwest North Atlantic

NASA Astrophysics Data System (ADS)

Fenty, I. G.; Heimbach, P.; Wunsch, C. I.

2010-12-01

Sea ice anomalies in the Northwest North Atlantic's Labrador Sea are of climatic interest because of known and hypothesized feedbacks with hydrographic anomalies, deep convection/mode water formation, and Northern Hemisphere atmospheric patterns. As greenhouse gas concentrations increase, hydrographic anomalies formed in the Arctic Ocean associated with warming will propagate into the Labrador Sea via the Fram Strait/West Greenland Current and the Canadian Archipelago/Baffin Island Current. Therefore, understanding the dynamical response of sea ice in the basin to hydrographic anomalies is essential for the prediction and interpretation of future high-latitude climate change. Historically, efforts to quantify the link between the observed sea ice and hydrographic variability in the region has been limited due to in situ observation paucity and technical challenges associated with synthesizing ocean and sea ice observations with numerical models. To elaborate the relationship between sea ice and ocean variability, we create three one-year (1992-1993, 1996-1997, 2003-2004) three-dimensional time-varying reconstructions of the ocean and sea ice state in Labrador Sea and Baffin Bay. The reconstructions are syntheses of a regional coupled 32 km ocean-sea ice model with a suite of contemporary in situ and satellite hydrographic and ice data using the adjoint method. The model and data are made consistent, in a least-squares sense, by iteratively adjusting several model control variables (e.g., ocean initial and lateral boundary conditions and the atmospheric state) to minimize an uncertainty-weighted model-data misfit cost function. The reconstructions reveal that the ice pack attains a state of quasi-equilibrium in mid-March (the annual sea ice maximum) in which the total ice-covered area reaches a steady state -ice production and dynamical divergence along the coasts balances dynamical convergence and melt along the pack’s seaward edge. Sea ice advected to the
Respective roles of direct GHG radiative forcing and induced Arctic sea ice loss on the Northern Hemisphere atmospheric circulation

NASA Astrophysics Data System (ADS)

Oudar, Thomas; Sanchez-Gomez, Emilia; Chauvin, Fabrice; Cattiaux, Julien; Terray, Laurent; Cassou, Christophe

2017-12-01

The large-scale and synoptic-scale Northern Hemisphere atmospheric circulation responses to projected late twenty-first century Arctic sea ice decline induced by increasing Greenhouse Gases (GHGs) concentrations are investigated using the CNRM-CM5 coupled model. An original protocol, based on a flux correction technique, allows isolating the respective roles of GHG direct radiative effect and induced Arctic sea ice loss under RCP8.5 scenario. In winter, the surface atmospheric response clearly exhibits opposing effects between GHGs increase and Arctic sea ice loss, leading to no significant pattern in the total response (particularly in the North Atlantic region). An analysis based on Eady growth rate shows that Arctic sea ice loss drives the weakening in the low-level meridional temperature gradient, causing a general decrease of the baroclinicity in the mid and high latitudes, whereas the direct impact of GHGs increase is more located in the mid-to-high troposphere. Changes in the flow waviness, evaluated from sinuosity and blocking frequency metrics, are found to be small relative to inter-annual variability.
Canadian Unilateralism in the Arctic: Using Scenario Planning to Help Canada Achieve Its Strategic Goals in the North

DTIC Science & Technology

2013-05-23

IN THE NORTH, by Major Sonny T. Hatton, 78 pages. Climate change and global warming could open up the Arctic to unprecedented energy and resource...heating up, both literally and figuratively. Climate change and global warming are melting the Polar ice cap in the North at an unprecedented rate...grow for Arctic nations as access increases due to global warming .35 Increased access and development in the Arctic will continue to encourage the
Solar Geoengineering and the Modulation of North Atlantic Tropical Cyclone Frequency

NASA Astrophysics Data System (ADS)

Jones, A. C.; Haywood, J. M.; Hawcroft, M.; Jones, A.; Dunstone, N. J.; Hodges, K.

2017-12-01

Solar geoengineering (SG) refers to a wide range of proposed methods for counteracting global warming by artificially reducing solar insolation at Earth's surface. The most widely known SG proposal is stratospheric aerosol injection (SAI) which has impacts analogous to those from large-scale volcanic eruptions. Observations following major volcanic eruptions indicate that aerosol enhancements confined to a single hemisphere effectively modulate North Atlantic tropical cyclone (TC) activity in the following years. Here we investigate the effects of both single-hemisphere and global SAI scenarios on North Atlantic TC activity using the HadGEM2-ES general circulation model (GCM). We show that a 5 Tg y-1 injection of sulphur dioxide (SO2) into the northern hemisphere (NH) stratosphere would produce a global-mean cooling of 1 K and simultaneously reduce TC activity (to 8 TCs y-1), while the same injection in the southern hemisphere (SH) would enhance TC activity (to 14 TCs y-1), relative to a recent historical period (1950-2000, 10 TCs y-1). Our results reemphasize the risks of regional geoengineering and should motivate policymakers to regulate large-scale unilateral geoengineering deployments.
Exceptional Arctic warmth of early winter 2016 and attribution to global warming

NASA Astrophysics Data System (ADS)

van Oldenborgh, Geert Jan; Macias-Fauria, Marc; King, Andrew; Uhe, Peter; Philip, Sjoukje; Kew, Sarah; Karoly, David; Otto, Friederike; Allen, Myles; Cullen, Heidi

2017-04-01

The dark polar winters usually sport the coldest extremes on Earth, however this winter, the North Pole and the surrounding Arctic region have experienced record high temperatures in November and December, with daily means reaching 15 °C (27 °F) above normal and a November monthly mean that was 13 °C (23 °F) above normal on the pole. November also saw a brief retreat of sea-ice that was virtually unprecedented in nearly 40 years of satellite records, followed by a record low in November sea ice area since 1850. Unlike the Antarctic, Arctic lands are inhabited and their socio-economic systems are greatly affected by the impacts of extreme and unprecedented sea ice dynamics and temperatures, such as for example, the timing of marine mammal migrations, and refreezing rain on snow that prevents reindeer from feeding. Here we report on our multi-method rapid attribution analysis of North Pole November-December temperatures. To quantify the rarity of the event, we computed the November-December averaged temperature around the North Pole (80-90 °N) in the (short but North-pole covering) ERA-interim reanalysis. To put the event in context of natural variability, we use a longer and closely related time series based on the northern most meteorological observations on land (70-80 °N). This allows for a reconstruction of Arctic temperatures back to about 1900. We also perform a multi-method analysis of North Pole temperatures with two sets of climate models: the CMIP5 multi-model ensemble, and a large ensemble of model runs in the so-called Weather@Home project. Physical mechanisms that are responsible for temperature and sea ice variability in the North Pole region are also discussed. The observations and the bias-corrected CMIP5 ensemble point to a return period of about 50 to 200 years in the present climate, i.e., the probability of such an extreme is about 0.5% to 2% every year, with a large uncertainty. The observations show that November-December temperatures
Status and Impacts of Arctic Freshwater Export

NASA Astrophysics Data System (ADS)

Haine, T. W. N.

2017-12-01

Large freshwater anomalies clearly exist in the Arctic Ocean. For example, liquid freshwater has accumulated in the Beaufort Gyre in the decade of the 2000s compared to 1980-2000, with an extra ≈5000 km3—about 25%—being stored. The sources of freshwater to the Arctic from precipitation and runoff have increased between these periods (most of the evidence comes from models). Despite flux increases from 2001 to 2011, it is uncertain if the marine freshwater source through Bering Strait for the 2000s has changed, as observations in the 1980s and 1990s are incomplete. The marine freshwater fluxes draining the Arctic through Fram and Davis straits are also insignificantly different. In this way, the balance of sources and sinks of freshwater to the Arctic, Canadian Arctic Archipelago (CAA), and Baffin Bay shifted to about 1200±730 km3yr-1 freshening the region, on average, during the 2000s. The observed accumulation of liquid freshwater is consistent with this increased supply and the loss of freshwater from sea ice (Figure, right). Evidence exists that such discharges can impact the Atlantic meridional overturning circulation, and hence Atlantic sector climate. Nevertheless, it appears that the observed AMOC variability since 2004, when high quality measurements began, is not attributable to anthropogenic influence. This work is based on, and updated from, Haine et al. (2015), Carmack et al. (2016), and Haine (2016). Haine, T. W. N. Ocean science: Vagaries of Atlantic overturning. Nature Geoscience, 9, 479-480, 10.1038/ngeo2748, 2016. T. W. N. Haine et al., Arctic Freshwater Export: Status, Mechanisms, and Prospects, Global Planetary Change, 125, 13-35, 10.1016/j.glopacha.2014.11.013, 2015. E. Carmack et al., Fresh water and its role in the Arctic Marine System: sources, disposition, storage, export, and physical and biogeochemical consequences in the Arctic and global oceans. J. G. Res. Biogeosciences, 10.1002/2015JG003140, 2016.
Role of Tropical Atlantic SST Variability as a Modulator of El Nino Teleconnections

NASA Technical Reports Server (NTRS)

Ham, Yoo-Geun; Sung, Mi-Kyung; An, Soon-II; Schubert, Siegfried D.; Kug, Jong-Seong

2014-01-01

The present study suggests that the off-equatorial North Atlantic (NATL) SST warming plays a significant role in modulating El Niño teleconnection and its impact on the North Atlantic and European regions. The El Niño events accompanied by NATL SST warming exhibit south-north dipole pattern over the Western Europe to Atlantic, while the ENSO teleconnection pattern without NATL warming exhibits a Rossby wave-like pattern confined over the North Pacific and western Atlantic. Especially, the El Niño events with NATL warming show positive (negative) geopotential-height anomalies over the North Atlantic (Western Europe) which resemble the negative phase of the NAO. Consistently, it is shown using a simple statistical model that NATL SSTA in addition to the tropical Pacific SSTA leads to better prediction on regional climate variation over the North Atlantic and European regions. This role of NATL SST on ENSO teleconnection is also validated and discussed in a long term simulation of coupled global circulation model (CGCM).
Effects of Arctic geoengineering on precipitation in the tropical monsoon regions

NASA Astrophysics Data System (ADS)

Nalam, Aditya; Bala, Govindasamy; Modak, Angshuman

2017-07-01

Arctic geoengineering wherein sunlight absorption is reduced only in the Arctic has been suggested as a remedial measure to counteract the on-going rapid climate change in the Arctic. Several modeling studies have shown that Arctic geoengineering can minimize Arctic warming but will shift the Inter-tropical Convergence Zone (ITCZ) southward, unless offset by comparable geoengineering in the Southern Hemisphere. In this study, we investigate and quantify the implications of this ITCZ shift due to Arctic geoengineering for the global monsoon regions using the Community Atmosphere Model version 4 coupled to a slab ocean model. A doubling of CO2 from pre-industrial levels leads to a warming of 6 K in the Arctic region and precipitation in the monsoon regions increases by up to 15%. In our Arctic geoengineering simulation which illustrates a plausible latitudinal distribution of the reduction in sunlight, an addition of sulfate aerosols (11 Mt) in the Arctic stratosphere nearly offsets the Arctic warming due to CO2 doubling but this shifts the ITCZ southward by 1.5° relative to the pre-industrial climate. The combined effect from this shift and the residual CO2-induced climate change in the tropics is a decrease/increase in annual mean precipitation in the Northern Hemisphere/Southern Hemisphere monsoon regions by up to -12/+17%. Polar geoengineering where sulfate aerosols are prescribed in both the Arctic (10 Mt) and Antarctic (8 Mt) nearly offsets the ITCZ shift due to Arctic geoengineering, but there is still a residual precipitation increase (up to 7%) in most monsoon regions associated with the residual CO2 induced warming in the tropics. The ITCZ shift due to our Global geoengineering simulation, where aerosols (20 Mt) are prescribed uniformly around the globe, is much smaller and the precipitation changes in most monsoon regions are within ±2% as the residual CO2-induced warming in the tropics is also much less than in Arctic and Polar geoengineering. Further
High Arctic sea ice conditions influence marine birds wintering in Low Arctic regions

NASA Astrophysics Data System (ADS)

McFarlane Tranquilla, Laura; Hedd, April; Burke, Chantelle; Montevecchi, William A.; Regular, Paul M.; Robertson, Gregory J.; Stapleton, Leslie Ann; Wilhelm, Sabina I.; Fifield, David A.; Buren, Alejandro D.

2010-09-01

Ocean climate change is having profound biological effects in polar regions. Such change can also have far-reaching downstream effects in sub-polar regions. This study documents an environmental relationship between High Arctic sea ice changes and mortality events of marine birds in Low Arctic coastal regions. During April 2007 and March 2009, hundreds of beached seabird carcasses and moribund seabirds were found along the east and northeast coasts of Newfoundland, Canada. These seabird "wrecks" (i.e. dead birds on beaches) coincided with a period of strong, persistent onshore winds and heavily-accumulated sea ice that blocked bays and trapped seabirds near beaches. Ninety-two percent of wreck seabirds were Thick-billed Murres ( Uria lomvia). Body condition and demographic patterns of wreck murres were compared to Thick-billed Murres shot in the Newfoundland murre hunt. Average body and pectoral masses of wreck carcasses were 34% and 40% lighter (respectively) than shot murres, indicating that wreck birds had starved. The acute nature of each wreck suggested that starvation and associated hypothermia occurred within 2-3 days. In 2007, first-winter murres (77%) dominated the wreck. In 2009, there were more adults (78%), mostly females (66%). These results suggest that spatial and temporal segregation in ages and sexes can play a role in differential survival when stochastic weather conditions affect discrete areas where these groups aggregate. In wreck years, southward movement of Arctic sea ice to Low Arctic latitudes was later and blocked bays longer than in most other years. These inshore conditions corresponded with recent climate-driven changes in High Arctic ice break-up and ice extent; coupled with local weather conditions, these ice conditions appeared to be the key environmental features that precipitated the ice-associated seabird wrecks in the Low Arctic region.
The spatial distribution and evolution characteristics of North Atlantic cyclones

NASA Astrophysics Data System (ADS)

Dacre, H.; Gray, S.

2009-09-01

Mid-latitude cyclones play a large role in determining the day-to-day weather conditions in western Europe through their associated wind and precipitation patterns. Thus, their typical spatial and evolution characteristics are of great interest to meteorologists, insurance and risk management companies. In this study a feature tracking algorithm is applied to a cyclone database produced using the Hewson-method of cyclone identification, based on low-level gradients of wet-bulb potential temperature, to produce a climatology of mid-latitude cyclones. The aim of this work is to compare the cyclone track and density statistics found in this study with previous climatologies and to determine reasons for any differences. This method is found to compare well with other cyclone identification methods; the north Atlantic storm track is reproduced along with the major regions of genesis. Differences are attributed to cyclone lifetime and strength thresholds, dataset resolution and cyclone identification and tracking methods. Previous work on cyclone development has been largely limited to case studies as opposed to analysis of climatological data, and does not distinguish between the different stages of cyclone evolution. The cyclone database used in this study allows cyclone characteristics to be tracked throughout the cyclone lifecycle. This enables the evaluation of the characteristics of cyclone evolution for systems forming in different genesis regions and a calculation of the spatial distribution and evolution of these characteristics in composite cyclones. It was found that most of the cyclones that cross western Europe originate in the east Atlantic where the baroclinicity and sea surface temperature gradients are weak compared to the west Atlantic. East Atlantic cyclones also have higher low-level relative vorticity and lower mean sea level pressure at their genesis point than west Atlantic cyclones. This is consistent with the hypothesis that they are secondary
The spatial distribution and evolution characteristics of North Atlantic cyclones

NASA Astrophysics Data System (ADS)

Dacre, H.; Gray, S.

2009-04-01

Mid-latitude cyclones play a large role in determining the day-to-day weather conditions in western Europe through their associated wind and precipitation patterns. Thus, their typical spatial and evolution characteristics are of great interest to meteorologists, insurance and risk management companies. In this study a feature tracking algorithm is applied to a cyclone database produced using the Hewson-method of cyclone identification, based on low-level gradients of wet-bulb potential temperature, to produce a climatology of mid-latitude cyclones. The aim of this work is to compare the cyclone track and density statistics found in this study with previous climatologies. This method is found to compare well with other cyclone identification methods; the north Atlantic storm track is reproduced along with the major regions of genesis. Differences are attributed to cyclone lifetime and strength thresholds, dataset resolution and cyclone identification and tracking methods. Previous work on cyclone development has been largely limited to case studies as opposed to analysis of climatological data, and does not distinguish between the different stages of cyclone evolution. The cyclone database used in this study allows cyclone characteristics to be tracked throughout the cyclone lifecycle. This enables the evaluation of the characteristics of cyclone evolution for systems forming in different genesis regions and a calculation of the spatial distribution and evolution of these characteristics in composite cyclones. It was found that most of the cyclones that cross western Europe originate in the east Atlantic where the baroclinicity and sea surface temperature gradients are weak compared to the west Atlantic. East Atlantic cyclones also have higher low-level relative vorticity and lower mean sea level pressure at their genesis point than west Atlantic cyclones. This is consistent with the hypothesis that they are secondary cyclones developing on the trailing fronts of
Coherent Multidecadal Atmospheric and Oceanic Variability in the North Atlantic: Blocking Corresponds with Warm Subpolar Ocean

NASA Technical Reports Server (NTRS)

Hakkinen, Sirpa M.; Rhines, P. B.; Worthen, D. L.

2012-01-01

Winters with frequent atmospheric blocking, in a band of latitudes from Greenland to Western Europe, are found to persist over several decades and correspond to a warm North Atlantic Ocean. This is evident in atmospheric reanalysis data, both modern and for the full 20th century. Blocking is approximately in phase with Atlantic multidecadal ocean variability (AMV). Wintertime atmospheric blocking involves a highly distorted jetstream, isolating large regions of air from the westerly circulation. It influences the ocean through windstress-curl and associated air/sea heat flux. While blocking is a relatively high-frequency phenomenon, it is strongly modulated over decadal timescales. The blocked regime (weaker ocean gyres, weaker air-sea heat flux, paradoxically increased transport of warm subtropical waters poleward) contributes to the warm phase of AMV. Atmospheric blocking better describes the early 20thC warming and 1996-2010 warm period than does the NAO index. It has roots in the hemispheric circulation and jet stream dynamics. Subpolar Atlantic variability covaries with distant AMOC fields: both these connections may express the global influence of the subpolar North Atlantic ocean on the global climate system.
Meridional fluxes of dissolved organic matter in the North Atlantic Ocean

NASA Technical Reports Server (NTRS)

Walsh, John J.; Carder, Kendall L.; Mueller-Karger, Frank E.

1992-01-01

Biooptical estimates of gelbstoff and a few platinum measurements of dissolved organic carbon (DOCpt) are used to construct a budget of the meridional flux of DOC and dissolved organic nitrogen (DON) across 36 deg 25 min N in the North Atlantic from previous inverse models of water and element transport. Distinct southward subsurface fluxes of dissolved organic matter within subducted shelf water, cabelled slope water, and overturned basin water are inferred. Within two cases of a positive gradient of DOCpt between terrestrial/shelf and offshore stocks, the net equatorward exports of O2 and DOCpt from the northern North Atlantic yield molar ratios of 2.1 to 9.1, compared to the expected Redfield O2/C ratio of 1.3. It is concluded that some shelf export of DOC, with a positive gradient between coastal and oceanic stocks, as well as falling particles, are required to balance carbon, nitrogen, and oxygen budgets of the North Atlantic.
Dispersal and population connectivity in the deep North Atlantic estimated from physical transport processes

NASA Astrophysics Data System (ADS)

Etter, Ron J.; Bower, Amy S.

2015-10-01

Little is known about how larvae disperse in deep ocean currents despite how critical estimates of population connectivity are for ecology, evolution and conservation. Estimates of connectivity can provide important insights about the mechanisms that shape patterns of genetic variation. Strong population genetic divergence above and below about 3000 m has been documented for multiple protobranch bivalves in the western North Atlantic. One possible explanation for this congruent divergence is that the Deep Western Boundary Current (DWBC), which flows southwestward along the slope in this region, entrains larvae and impedes dispersal between the upper/middle slope and the lower slope or abyss. We used Lagrangian particle trajectories based on an eddy-resolving ocean general circulation model (specifically FLAME - Family of Linked Atlantic Model Experiments) to estimate the nature and scale of dispersal of passive larvae released near the sea floor at 4 depths across the continental slope (1500, 2000, 2500 and 3200 m) in the western North Atlantic and to test the potential role of the DWBC in explaining patterns of genetic variation on the continental margin. Passive particles released into the model DWBC followed highly complex trajectories that led to both onshore and offshore transport. Transport averaged about 1 km d-1 with dispersal kernels skewed strongly right indicating that some larvae dispersed much greater distances. Offshore transport was more likely than onshore and, despite a prevailing southwestward flow, some particles drifted north and east. Dispersal trajectories and estimates of population connectivity suggested that the DWBC is unlikely to prevent dispersal among depths, in part because of strong cross-slope forces induced by interactions between the DWBC and the deeper flows of the Gulf Stream. The strong genetic divergence we find in this region of the Northwest Atlantic is therefore likely driven by larval behaviors and/or mortality that limit
Variability of tropical cyclone rapid intensification in the North Atlantic and its relationship with climate variations

NASA Astrophysics Data System (ADS)

Wang, Chunzai; Wang, Xidong; Weisberg, Robert H.; Black, Michael L.

2017-12-01

The paper uses observational data from 1950 to 2014 to investigate rapid intensification (RI) variability of tropical cyclones (TCs) in the North Atlantic and its relationships with large-scale climate variations. RI is defined as a TC intensity increase of at least 15.4 m/s (30 knots) in 24 h. The seasonal RI distribution follows the seasonal TC distribution, with the highest number in September. Although an RI event can occur anywhere over the tropical North Atlantic (TNA), there are three regions of maximum RI occurrence: (1) the western TNA of 12°N-18°N and 60°W-45°W, (2) the Gulf of Mexico and the western Caribbean Sea, and (3) the open ocean southeast and east of Florida. RI events also show a minimum value in the eastern Caribbean Sea north of South America—a place called a hurricane graveyard due to atmospheric divergence and subsidence. On longer time scales, RI displays both interannual and multidecadal variability, but RI does not show a long-term trend due to global warming. The top three climate indices showing high correlations with RI are the June-November ENSO and Atlantic warm pool indices, and the January-March North Atlantic oscillation index. It is found that variabilities of vertical wind shear and TC heat potential are important for TC RI in the hurricane main development region, whereas relative humidity at 500 hPa is the main factor responsible for TC RI in the eastern TNA. However, the large-scale oceanic and atmospheric variables analyzed in this study do not show an important role in TC RI in the Gulf of Mexico and the open ocean southeast and east of Florida. This suggests that other factors such as small-scale changes of oceanic and atmospheric variables or TC internal processes may be responsible for TC RI in these two regions. Additionally, the analyses indicate that large-scale atmospheric and oceanic variables are not critical to TC genesis and formation; however, once a tropical depression forms, large-scale climate

Linking the North Atlantic Oscillation to Rainfall Over Northern Lake Malawi

NASA Astrophysics Data System (ADS)

Johnson, T. C.; Powers, L. A.; Werne, J. P.; Brown, E. T.; Castaneda, I.; Schouten, S.; Sinninghe-Damste, J.

2005-12-01

Piston and multi-cores recovered from the north basin of Lake Malawi in 1998 by the International Decade for the East African Lakes (IDEAL) have provided a rich history of climate variability spanning the past 25,000 years. As we now begin to analyze the cores recovered by the Malawi Drilling Project in early 2005, we are considering the relationships among sedimentary signals of temperature (TEX86), northerly winds associated with a southward excursion of the Inter-Tropical Convergence Zone (per cent biogenic silica), and rainfall (terrigenous mass accumulation rate) in the well dated 1998 cores. A high-resolution record of the past 800 years suggests that rainfall in this region (10 - 12° S, 30 - 35° E) was relatively low during the Little Ice Age, when northerly winds were more prevalent, attributed to a more southerly position of the ITCZ during austral summers. The TEX86 signal of lake (surface?) temperature ranged mostly between 24 and 26°C during this period, with the coldest temperature of about 22°C around AD1680 and the warmest temperature, exceeding 27°C, in the youngest sediment sample. The cooler water temperatures coincide with periods of highest diatom productivity, consistent with the latter being due to relatively intense upwelling associated with the northerly winds. Our observation of low rainfall during periods of more southerly migration of the ITCZ is consistent with the results of McHugh and Rogers (2001), who linked rainfall in southeastern Africa to the North Atlantic Oscillation (NAO). During years of weak NAO, equatorial westerly transport of Atlantic moisture across Africa during austral summer is relatively intense, causing high rainfall in the East African Rift between the equator and 16° S. Conversely, when the NAO is positive, rainfall is higher south of 15° S than north of this latitude, which is consistent with a southward migration of the ITCZ. McHugh, M. J. and J. C. Rogers (2001). "North Atlantic Oscillation influence on
Heterogeneity of the North Atlantic oceanic lithosphere based on integrated analysis of GOCE satellite gravity and geological data

NASA Astrophysics Data System (ADS)

Barantseva, Olga; Artemieva, Irina; Thybo, Hans; Herceg, Matija

2015-04-01

We present the results from modelling the gravity and density structure of the upper mantle for the off-shore area of the North Atlantic region. The crust and upper mantle of the region is expected to be anomalous: Part of the region affected by the Icelandic plume has an anomalously shallow bathymetry, whereas the northern part of the region is characterized by ultraslow spreading. In order to understand the links between deep geodynamical processes that control the spreading rate, on one hand, and their manifestations such as oceanic floor bathymetry and heat flow, on the other hand, we model the gravity and density structure of the upper mantle from satellite gravity data. The calculations are based on interpretation of GOCE gravity satellite data for the North Atlantics. To separate the gravity signal responsible for density anomalies within the crust and upper mantle, we subtract the lower harmonics caused by deep density structure of the Earth (the core and the lower mantle). The gravity effect of the upper mantle is calculated by subtracting the gravity effect of the crust for two crustal models. We use a recent regional seismic model for the crustal structure (Artemieva and Thybo, 2013) based om seismic data together with borehole data for sediments. For comparison, similar results are presented for the global CRUST 1.0 model as well (Laske, 2013). The conversion of seismic velocity data for the crustal structure to crustal density structure is crucial for the final results. We use a combination of Vp-to-density conversion based on published laboratory measurements for the crystalline basement (Ludwig, Nafe, Drake, 1970; Christensen and Mooney, 1995) and for oceanic sediments and oceanic crust based on laboratory measurements for serpentinites and gabbros from the Mid-Atlantic Ridge (Kelemen et al., 2004). Also, to overcome the high degree of uncertainty in Vp-to-density conversion, we account for regional tectonic variations in the Northern Atlantics as
The western North Atlantic bloom experiment

NASA Astrophysics Data System (ADS)

Harrison, W. G.; Head, E. J. H.; Horne, E. P. W.; Irwin, B.; Li, W. K. W.; Longhurst, A. R.; Paranjape, M. A.; Platt, T.

An investigation of the spring bloom was carried out in the western North Atlantic (40-50°W) as one component of the multi-nation Joint Global Ocean Flux Study (JGOFS) North Atlantic Bloom Experiment (NABE). The cruise track included an extended hydrographic section from 32 to 47°N and process studies at two week-long time-series stations at 40 and 45°N. Biological and chemical data collected along the transect indicated that the time-series stations were located in regions where the spring bloom was well developed; algal biomass was high and surface nutrient concentrations were reduced from maximum wintertime levels. Despite similarities in the vertical structure and magnitude of phytoplankton biomass and productivity, the two stations clearly differed in physical, chemical and other biological characteristics. Detailed depth profiles of the major autotrophic and heterotrophic microplankton groups (bacteria, phytoplankton, microzooplankton) revealed a strong vertical coherence in distribution at both sites, with maximum concentrations in the upper 50 m being typical of the spring bloom. Ultraplankton (< 10 μm) were an important component of the primary producers at 40°N, whereas larger netplankton (diatoms, dinoflagellates) were more important at 45°N. Silicate depletion was clearly evident in surface waters at 45°N, where diatoms were most abundant. Despite the relative importance of diatoms at 45°N, dinoflagellates dominated the biomass of the netplankton at both sites; however, much of this community may have been heterotrophic. Bacterial biomass and production were high at both stations relative to phytoplankton levels, particularly at 45°N, and may have contributed to the unexpectedly high residual ammonium concentrations observed below the chlorophyll maximum layer at both stations. Microzooplankton grazing dominated phytoplankton losses at both stations, with consumption as high as 88% of the daily primary production. Grazing losses to the
Further evidence for a link between Late Pleistocene North Atlantic surface temperatures and North Atlantic deep-water production

NASA Astrophysics Data System (ADS)

Boyle, Edward A.; Rosener, Paula

1990-10-01

Reduced surface temperatures, salinity and North Atlantic Deep-Water (NADW) formation rate may be mechanistically linked. Previous studies have demonstrated the co-occurrence of lowered high-latitude T and NADW during glacial maxima and the brief ( t 1000 yr) Younger Dryas cooling event 10,500 years ago. This behavior also appears as a feature of a recent coupled ocean/atmosphere general circulation model. Here, it is shown that rapid fluctuations in North Atlantic surface temperatures (as indicated by variations from 7 to 22% left-cooling N. pachyderma) during oxygen isotope stage 3 also may be linked to fluctuations in deep-water chemistry (as indicated by benthic Cd/Ca variations from 0.080 to 0.120 μmol. mol. -1). Two complete cycles in both properties are observed in 30 cm of sediment; bioturbation modeling suggests that the true extrema are muted and that the reproducibility of replicate analyses is primarily limited by the sampling statistics of bioturbated mixrure. The current evidence raises the question of whether NADW is regulated by a "switch" or by a "valve".
Changes in the Arctic: Background and Issues for Congress

DTIC Science & Technology

2012-02-27

that most of the global warming of the last three decades is very likely caused by human-related emissions of greenhouse gases (GHG, mostly carbon...such warming is projected by most models throughout the Arctic, some models project slight cooling localized in the North Atlantic Ocean just south of...found that period to be distinctly different from the recent multi-decadal warming , in part because the current warmth is global . Changes in the
Regional variability in sea ice melt in a changing Arctic

PubMed Central

Perovich, Donald K.; Richter-Menge, Jacqueline A.

2015-01-01

In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover. PMID:26032323
Regional variability in sea ice melt in a changing Arctic.

PubMed

Perovich, Donald K; Richter-Menge, Jacqueline A

2015-07-13

In recent years, the Arctic sea ice cover has undergone a precipitous decline in summer extent. The sea ice mass balance integrates heat and provides insight on atmospheric and oceanic forcing. The amount of surface melt and bottom melt that occurs during the summer melt season was measured at 41 sites over the time period 1957 to 2014. There are large regional and temporal variations in both surface and bottom melting. Combined surface and bottom melt ranged from 16 to 294 cm, with a mean of 101 cm. The mean ice equivalent surface melt was 48 cm and the mean bottom melt was 53 cm. On average, surface melting decreases moving northward from the Beaufort Sea towards the North Pole; however interannual differences in atmospheric forcing can overwhelm the influence of latitude. Substantial increases in bottom melting are a major contributor to ice losses in the Beaufort Sea, due to decreases in ice concentration. In the central Arctic, surface and bottom melting demonstrate interannual variability, but show no strong temporal trends from 2000 to 2014. This suggests that under current conditions, summer melting in the central Arctic is not large enough to completely remove the sea ice cover. © 2015 The Author(s) Published by the Royal Society. All rights reserved.
Evidence for production and lateral transport of dissolved organic phosphorus in the eastern subtropical North Atlantic

NASA Astrophysics Data System (ADS)

Reynolds, Sarah; Mahaffey, Claire; Roussenov, Vassil; Williams, Richard G.

2014-08-01

The concentration of phosphate and dissolved organic phosphorus (DOP) is chronically low and limits phytoplankton growth in the subtropical North Atlantic relative to other ocean basins. Transport of phosphate and DOP from the productive flanks of the gyre to its interior has been hypothesized as an important phosphorus supply pathway. During a cruise in the eastern Atlantic in spring 2011, the rates of phosphate uptake, alkaline phosphatase activity (APA), and DOP production were measured in the northwest African shelf region, subtropics, and tropics. Rates of DOP production were sixfold higher in the shelf region (43 ± 41 nM d-1) relative to the subtropics (6.9 ± 4.4 nM d-1). In contrast, APA was threefold higher in the subtropics (8.0 ± 7.3 nM d-1), indicative of enhanced DOP utilization, relative to the shelf region (2.6 ± 2.1 nM d-1). Hence, observations suggest net production of DOP in the shelf region and either net consumption of DOP or a near balance in DOP production and consumption in the gyre interior. Eddy-permitting model experiments demonstrate that (i) DOP accounts for over half the total phosphorus in surface waters, (ii) DOP is transported westward from the shelf region by a combination of gyre and eddy circulations, and (iii) advected DOP supports up to 70% of the particle export over much of the subtropical gyre. Our combined observational and modeling study supports the view that the horizontal transport of DOP from the shelf region is an important mechanism supplying phosphorus to the surface subtropical North Atlantic.
Gateways and Water Mass Mixing in the Late Cretaceous North Atlantic

NASA Astrophysics Data System (ADS)

Asgharian Rostami, M.; Martin, E. E.; MacLeod, K. G.; Poulsen, C. J.; Vande Guchte, A.; Haynes, S.

2017-12-01

Regions of intermediate/deep water formation and water-mass mixing in the North Atlantic are poorly defined for the Late Cretaceous, a time of gateway evolution and cooler conditions following the Mid Cretaceous greenhouse. Improved proxy data combined with modeling efforts are required to effectively evaluate the relationship between CO2, paleogeography, and circulation during this cooler interval. We analyzed and compiled latest Cretaceous (79 - 66 Ma) ɛNd and δ13C records from seven bathyal (paleodepths 0.2 - 2 km) and eight abyssal (paleodepths > 2 km) sites in the North Atlantic. Data suggest local downwelling of Northern Component Water (NCW; ɛNd -9.5 and δ13C 1.7 ‰) is the primary source of intermediate/deep water masses in the basin. As this water flows southward and ages, δ13C values decrease and ɛNd values increase; however, additional chemical changes at several sites require mixing with contributions from several additional water masses. Lower ɛNd ( -10) and higher δ13C ( 1.9 ‰) values in the deep NW part of the basin indicate proximal contributions from a region draining old continental crust, potentially representing deep convection following opening of the Labrador Sea. In the deep NE Iberian Basin, higher ɛNd ( -7) and lower δ13C ( 0.8 ‰) during the Campanian suggest mixing with a Tethyan source (ɛNd -7 and δ13C 0.1 ‰) whose importance decreased with restriction of that gateway in the Maastrichtian. Data from bathyal sites suggest additional mixing. In the SE Cape Verde region, observed ɛNd variations from -10 in the Campanian to -13 and -12 in the early and late Maastrichtian, respectively, may record variations in output rates of Tethyan and/or NCW sources and Demerara Bottom Water (ɛNd -16), a proposed warm saline intermediate water mass formed in shallow, equatorial seas. Pacific inflow through the Caribbean gateway impacts intermediate sites at Blake Nose (ɛNd values -8), particularly the shallowest site during the late
A multi-model assessment of pollution transport to the Arctic

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

Shindell, D T; Chin, M; Dentener, F

2008-03-13

We examine the response of Arctic gas and aerosol concentrations to perturbations in pollutant emissions from Europe, East and South Asia, and North America using results from a coordinated model intercomparison. These sensitivities to regional emissions (mixing ratio change per unit emission) vary widely across models and species. Intermodel differences are systematic, however, so that the relative importance of different regions is robust. North America contributes the most to Arctic ozone pollution. For aerosols and CO, European emissions dominate at the Arctic surface but East Asian emissions become progressively more important with altitude, and are dominant in the upper troposphere.more » Sensitivities show strong seasonality: surface sensitivities typically maximize during boreal winter for European and during spring for East Asian and North American emissions. Mid-tropospheric sensitivities, however, nearly always maximize during spring or summer for all regions. Deposition of black carbon (BC) onto Greenland is most sensitive to North American emissions. North America and Europe each contribute {approx}40% of total BC deposition to Greenland, with {approx}20% from East Asia. Elsewhere in the Arctic, both sensitivity and total BC deposition are dominated by European emissions. Model diversity for aerosols is especially large, resulting primarily from differences in aerosol physical and chemical processing (including removal). Comparison of modeled aerosol concentrations with observations indicates problems in the models, and perhaps, interpretation of the measurements. For gas phase pollutants such as CO and O{sub 3}, which are relatively well-simulated, the processes contributing most to uncertainties depend on the source region and altitude examined. Uncertainties in the Arctic surface CO response to emissions perturbations are dominated by emissions for East Asian sources, while uncertainties in transport, emissions, and oxidation are comparable for
Circumpolar measurements of speciated mercury, ozone and carbon monoxide in the boundary layer of the Arctic Ocean

NASA Astrophysics Data System (ADS)

Sommar, J.; Andersson, M. E.; Jacobi, H.-W.

2009-10-01

Using the Swedish icebreaker Oden as a platform, continuous measurements of airborne mercury (gaseous elemental mercury (Hg0), divalent mercury HgII(g) (acronym RGM) and mercury attached to particles (PHg)) and some long-lived trace gases (carbon monoxide CO and ozone O3) were performed over the North Atlantic and the Arctic Ocean. The measurements were performed for nearly three months (July-September, 2005) during the Beringia 2005 expedition (from Göteborg, Sweden via the proper Northwest Passage to the Beringia region Alaska - Chukchi Penninsula - Wrangel Island and in-turn via a north-polar transect to Longyearbyen, Spitsbergen). The Beringia 2005 expedition was the first time that these species have been measured during summer over the Arctic Ocean going from 60° to 90° N. During the North Atlantic transect, concentration levels of Hg0, CO and O3 were measured comparable to typical levels for the ambient mid-hemispheric average. However, a rapid increase of Hg0 in air and surface water was observed when entering the ice-covered waters of the Canadian Arctic archipelago. Large parts of the measured waters were supersaturated with respect to Hg0, reflecting a strong disequilibrium. Heading through the sea ice of the Arctic Ocean, a fraction of the strong Hg0} pulse in the water was spilled with some time-delay into the air samples collected 20 m a.s.l. Several episodes of elevated Hg0(g) were encountered along the sea ice route with higher mean concentration (1.81±0.43 ng m-3) compared to the marine boundary layer over ice-free oceanic waters (1.55±0.21 ng m-3). In addition, an overall majority of the variance in the temporal series of Hg0 concentrations was observed during July. Atmospheric boundary layer {O3} mixing ratios decreased when initially sailing northward. In the Arctic, an O3 minimum around 15-20 ppbv was observed during summer (July-August). Alongside the polar transect during the beginning of autumn, a steady trend of increasing O3 mixing
Late Neogene changes in North America and Antarctica absolute plate motions inferred from the Mid-Atlantic and Southwest Indian Ridges spreading histories

NASA Astrophysics Data System (ADS)

Iaffaldano, Giampiero; DeMets, Charles

2017-04-01

Reconstructions of absolute plate motions underpin our understanding of the plate torque balance, but are challenging due to difficulties in inferring well-dated rates and directions of plate movements from hot spot tracks. Useful information about plate dynamics can be inferred from rapid absolute plate motion changes, as these are linked only to the torque(s) that changed. Here we infer late Neogene changes in the absolute motions of North America and possibly Antarctica from changes in the easier-to-determine relative plate motions recorded along the Arctic, northern Mid-Atlantic and Southwest Indian Ridges. We show that Eurasia/North America and Nubia/North America motions changed by the same amount between 8 and 5 Ma, as may have Nubia/Antarctica and Somalia/Antarctica plate motions. By considering additional, independent constraints on Somalia/India plate motion, we argue that a scenario in which North America and Antarctica absolute motions changed is the simplest one that explains the observed changes in relative motions. We speculate that these changes are linked to the late Neogene dynamics of the Pacific plate.
Late Neogene changes in North America and Antarctica absolute plate motions inferred from the Mid-Atlantic and Southwest Indian Ridges spreading histories

NASA Astrophysics Data System (ADS)

Iaffaldano, G.; DeMets, C.

2016-08-01

Reconstructions of absolute plate motions underpin our understanding of the plate torque balance, but are challenging due to difficulties in inferring well-dated rates and directions of plate movements from hot spot tracks. Useful information about plate dynamics can be inferred from rapid absolute plate motion changes, as these are linked only to the torque(s) that changed. Here we infer late Neogene changes in the absolute motions of North America and possibly Antarctica from changes in the easier-to-determine relative plate motions recorded along the Arctic, northern Mid-Atlantic and Southwest Indian Ridges. We show that Eurasia/North America and Nubia/North America motions changed by the same amount between 8 and 5 Ma, as may have Nubia/Antarctica and Somalia/Antarctica plate motions. By considering additional, independent constraints on Somalia/India plate motion, we argue that a scenario in which North America and Antarctica absolute motions changed is the simplest one that explains the observed changes in relative motions. We speculate that these changes are linked to the late Neogene dynamics of the Pacific plate.
Is snow-ice now a major contributor to sea ice mass balance in the western Transpolar Drift region?

NASA Astrophysics Data System (ADS)

Graham, R. M.; Merkouriadi, I.; Cheng, B.; Rösel, A.; Granskog, M. A.

2017-12-01

During the Norwegian young sea ICE (N-ICE2015) campaign, which took place in the first half of 2015 north of Svalbard, a deep winter snow pack (50 cm) on sea ice was observed, that was 50% thicker than earlier climatological studies suggested for this region. Moreover, a significant fraction of snow contributed to the total ice mass in second-year ice (SYI) (9% on average). Interestingly, very little snow (3% snow by mass) was present in first-year ice (FYI). The combination of sea ice thinning and increased precipitation north of Svalbard is expected to promote the formation of snow-ice. Here we use the 1-D snow/ice thermodynamic model HIGHTSI forced with reanalysis data, to show that for the case study of N-ICE2015, snow-ice would even form over SYI with an initial thickness of 2 m. In current conditions north of Svalbard, snow-ice is ubiquitous and contributes to the thickness growth up to 30%. This contribution is important, especially in the absence of any bottom thermodynamic growth due to the thick insulating snow cover. Growth of FYI north of Svalbard is mainly controlled by the timing of growth onset relative to snow precipitation events and cold spells. These usually short-lived conditions are largely determined by the frequency of storms entering the Arctic from the Atlantic Ocean. In our case, a later freeze onset was favorable for FYI growth due to less snow accumulation in early autumn. This limited snow-ice formation but promoted bottom thermodynamic growth. We surmise these findings are related to a regional phenomenon in the Atlantic sector of the Arctic, with frequent storm events which bring increasing amounts of precipitation in autumn and winter, and also affect the duration of cold temperatures required for ice growth in winter. We discuss the implications for the importance of snow-ice in the future Arctic, formerly believed to be non-existent in the central Arctic due to thick perennial ice.
Atmospheric teleconnections between the Arctic and the Baltic Sea regions

NASA Astrophysics Data System (ADS)

Jakobson, L.; Jakobson, E.

2017-12-01

The observed enhanced warming of the Arctic, referred to as the AA, is expected to be related to further changes that impact mid-latitudes and the rest of the world. Our aim is to clarify how the climatic parameters in the Baltic Sea and Arctic regions are associated. Knowledge of such connections helps to define regions in the Arctic that could be with higher extent associated with the Baltic Sea region climate change. We used monthly mean reanalysis data from NCEP-CFSR and ERA-Interim. The strongest teleconnections between the same parameter (temperature, SLP, specific humidity, wind speed) at the Baltic Sea region and the Arctic are found in winter, but they are clearly affected by the Arctic Oscillation (AO) index. After removal of the AO index variability, correlations in winter were everywhere below ±0.5, while in other seasons there remained regions with strong (|R|>0.5, p<0.002) correlations. Strong correlations are also present between different climate variables at the Baltic Sea region and different regions of the Arctic. Temperature from 1000 to 500 hPa level at the Baltic Sea region have a strong negative correlation with the Greenland sector (the region between 20 - 80W and 55 - 80N) during all seasons except summer. The positive temperature anomaly of mild winter at the Greenland sector shifts towards east during the next seasons, reaching to Scandinavia/Baltic Sea region in summer. The Greenland sector is the region which gives the most significant correlations with the climatic parameters (temperature, wind speed, specific humidity, SLP) of the Baltic Sea region. These relationships can be explained by the AO index variability only in winter. In other seasons there has to be other influencing factors. The results of this study are valuable for selecting regions in the Arctic that have statistically the largest effect on climate in the Baltic Sea region.
Carbon dioxide in Arctic and subarctic regions

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

Gosink, T. A.; Kelley, J. J.

1981-03-01

A three year research project was presented that would define the role of the Arctic ocean, sea ice, tundra, taiga, high latitude ponds and lakes and polar anthropogenic activity on the carbon dioxide content of the atmosphere. Due to the large physical and geographical differences between the two polar regions, a comparison of CO/sub 2/ source and sink strengths of the two areas was proposed. Research opportunities during the first year, particularly those aboard the Swedish icebreaker, YMER, provided additional confirmatory data about the natural source and sink strengths for carbon dioxide in the Arctic regions. As a result, themore » hypothesis that these natural sources and sinks are strong enough to significantly affect global atmospheric carbon dioxide levels is considerably strengthened. Based on the available data we calculate that the whole Arctic region is a net annual sink for about 1.1 x 10/sup 15/ g of CO/sub 2/, or the equivalent of about 5% of the annual anthropogenic input into the atmosphere. For the second year of this research effort, research on the seasonal sources and sinks of CO/sub 2/ in the Arctic will be continued. Particular attention will be paid to the seasonal sea ice zones during the freeze and thaw periods, and the tundra-taiga regions, also during the freeze and thaw periods.« less
A multi-decadal study of Polar and Atlantic Water changes on the North Iceland shelf during the last Millennium

NASA Astrophysics Data System (ADS)

Perner, Kerstin; Moros, Matthias; Simon, Margit; Berben, Sarah; Griem, Lisa; Dokken, Trond; Wacker, Lukas; Jansen, Eystein

2017-04-01

The region offshore North Iceland is known to be sensitive to broad scale climatic and oceanographic changes in the North Atlantic Ocean. Changes in surface and subsurface water conditions link to the varying influence of Polar-sourced East Icelandic Current (EIC) and Atlantic-sourced North Irminger Icelandic Current (NIIC). Cold/fresh Polar waters from the East Greenland Current feed the surface flowing EIC, while warm/saline Subpolar Mode Waters (SPMW) from the Irminger Current (IC) feed the subsurface flowing NIIC. Here, we present a new and well-dated multi-proxy record that allows high-resolution reconstruction of surface and subsurface water mass changes on the western North Iceland shelf. An age-depth model for the last Millennium has been developed based on the combined information from radionuclide measurements (137Cs, 210Pb) dating, 25 AMS 14C radiocarbon dates, and identified Tephra horizons. Our dating results provide further support to previous assumptions that North of Iceland a conventional reservoir age correction application of 400 years (ΔR=0) is inadequate (e.g., Eikíksson et al., 2000; Wanamaker Jr. et al., 2012). The combined evidence from radionuclide dating and the identified Tephra horizons point to a ΔR of c. 360 years during the last Millennium. Our benthic and planktic foraminiferal assemblage and stable oxygen isotope (18O) record of Neogloboquadrina pachyderma s. (NPS) resolve the last Millennium at a centennial to multi-decadal resolution. Comparison of abundance changes of the Atlantic Water related species Cassidulina neoteretis and NPS, as well as the 18O record agree well with the instrumental data time series from the monitoring station Hunafloi nearby. This provides further support that our data is representative of relative temperature and salinity changes in surface and subsurface waters. Hence, this new record allows a more detailed investigation on the timing of Polar (EIC) and Atlantic (NIIC, IC) Water contribution
Arctic Intermediate Water in the Nordic Seas, 1991-2009

NASA Astrophysics Data System (ADS)

Jeansson, Emil; Olsen, Are; Jutterström, Sara

2017-10-01

The evolution of the different types of Arctic Intermediate Water (AIW) in the Nordic Seas is evaluated and compared utilising hydro-chemical data from 1991 to 2009. It has been suggested that these waters are important components of the Norwegian Sea Arctic Intermediate Water (NSAIW), and of the dense overflows to the North Atlantic. Thus, it is important to understand how their properties and distribution vary with time. The AIWs from the Greenland and Iceland Seas, show different degrees of variability during the studied period; however, only the Greenland Sea Arctic Intermediate Water (GSAIW) shows an increasing temperature and salinity throughout the 2000s, which considerably changed the properties of this water mass. Optimum multiparameter (OMP) analysis was conducted to assess the sources of the NSAIW. The analysis shows that the Iceland Sea Arctic Intermediate Water (ISAIW) and the GSAIW both contribute to NSAIW, at different densities corresponding to their respective density range. This illustrates that they flow largely isopycnally from their source regions to the Norwegian Sea. The main source of the NSAIW, however, is the upper Polar Deep Water, which explains the lower concentrations of oxygen and chlorofluorocarbons, and higher salinity and nutrient concentrations of the NSAIW layer compared with the ISAIW and GSAIW. This shows how vital it is to include chemical tracers in any water mass analysis to correctly assess the sources of the water mass being studied.
Impact of Greenland orography on the Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Davini, P.; Hardenberg, J.; Filippi, L.; Provenzale, A.

2015-02-01

We show that the absence of the Greenland ice sheet would have important consequences on the North Atlantic Ocean circulation, even without taking into account the effect of the freshwater input to the ocean from ice melting. These effects are investigated in a 600year long coupled ocean-atmosphere simulation with the high-resolution global climate model EC-Earth 3.0.1. Once a new equilibrium is established, a cooling of Eurasia and of the North Atlantic and a poleward shift of the subtropical jet are observed. These hemispheric changes are ascribed to a weakening of the Atlantic Meridional Overturning Circulation (AMOC) by about 12%. We attribute this slowdown to a reduction in salinity of the Arctic basin and to the related change of the mass and salt transport through the Fram Strait—a consequence of the new surface wind pattern over the lower orography. This idealized experiment illustrates the sensitivity of the AMOC to local surface winds.
Impact of Greenland orography on the Atlantic Meridional Overturning Circulation

NASA Astrophysics Data System (ADS)

Davini, Paolo; von Hardenberg, Jost; Filippi, Luca; Provenzale, Antonello

2015-04-01

We show that the absence of the Greenland Ice Sheet would have important consequences on the North Atlantic Ocean circulation, even without taking into account the effect of the freshwater input from ice melting. These effects are investigated in a 200-year long coupled ocean-atmosphere simulation with the high-resolution global climate model EC-Earth 3.0.1. Once a new equilibrium is established, cooling of Eurasia and of the North Atlantic and poleward shift of the subtropical jet are observed. These hemispheric changes are ascribed to a weakening of the Atlantic Meridional Overturning Circulation (AMOC) by about 20%. Such slowdown is associated to the freshening of the Arctic basin and to the related reduction in the freshwater export through the Fram Strait, as a result of the new wind pattern generated by the lower orography. This idealized experiment reveals the possibility of decreasing the AMOC by locally changing the surface winds.

An Arctic Ocean freshwater event as the trigger of the Younger Dryas stadial? Answers from Arctic deep-sea sediment cores

NASA Astrophysics Data System (ADS)

Spielhagen, Robert F.

2017-04-01

At ca. 12.8-11.5 ka the northern hemisphere climate experienced a dramatic fall-back to quasi-glacial conditions. Since the late 1980s, a major meltwater ejection to the North Atlantic through the Gulf of St.Lawrence was considered the most likely trigger for this "Younger Dryas event". It may have caused a slowdown of the Atlantic meridional overturning circulation (AMOC) and a diminished heat transport to the northern latitudes. However, field evidence from the potential meltwater route in North America has been discussed controversially in the last years, and the detection of a freshwater signal in marine sediments off the St.Lawrence river rendered difficult. More recently, the idea of an "Arctic route" of meltwater originating from proglacial lake Agassiz was put forward (Tarasov & Peltier, Nature 2005) and has gained further attraction through evidence from radiogenic isotopes (Not and Hillaire-Marcel; Nature Comm., 2012) and through modelling results of Condron and Winsor (PNAS, 2012) which showed that only a freshwater outflow through Fram Strait was capable of triggering a climate perturbation like the Younger Dryas. Here I present a review of isotopic records from the Arctic Ocean, the Fram Strait, and the Greenland Sea in search of evidence for a strong freshwater event in the Arctic Ocean at the onset of the Younger Dryas, supporting an Arctic origin of the trigger. A number of Arctic cores show a light planktic oxygen isotope spike at 13 ka. For several of them the age model is detailed enough to exclude a confusion with other deglacial spikes. On the central Arctic Lomonosov Ridge there is even evidence for a diminshed intermediate/bottom water circulation immediately following the freshwater event. On the other hand, there are many records which do not show a meltwater spike in the critical time interval, most likely because of low temporal resolution, a thick ice cover and/or a habitat change of the planktic foraminifers. The largest uncertainty is
Can regional climate engineering save the summer Arctic sea ice?

NASA Astrophysics Data System (ADS)

Tilmes, S.; Jahn, Alexandra; Kay, Jennifer E.; Holland, Marika; Lamarque, Jean-Francois

2014-02-01

Rapid declines in summer Arctic sea ice extent are projected under high-forcing future climate scenarios. Regional Arctic climate engineering has been suggested as an emergency strategy to save the sea ice. Model simulations of idealized regional dimming experiments compared to a business-as-usual greenhouse gas emission simulation demonstrate the importance of both local and remote feedback mechanisms to the surface energy budget in high latitudes. With increasing artificial reduction in incoming shortwave radiation, the positive surface albedo feedback from Arctic sea ice loss is reduced. However, changes in Arctic clouds and the strongly increasing northward heat transport both counteract the direct dimming effects. A 4 times stronger local reduction in solar radiation compared to a global experiment is required to preserve summer Arctic sea ice area. Even with regional Arctic dimming, a reduction in the strength of the oceanic meridional overturning circulation and a shut down of Labrador Sea deep convection are possible.
Characteristics of tropical cyclones in the North Atlantic and East Pacific

NASA Astrophysics Data System (ADS)

Barrett, Bradford Scott

In this dissertation, I present a series of investigations to expand our understanding of TCs in the East Pacific and North Atlantic basins. First, I developed and applied a climatological tool that quickly and succinctly displays the spread of historical TC tracks for any point in the North Atlantic basin. This tool is useful in all parts of a basin because it is derived from prior storm motion trajectories and summarily captures the historical synoptic and mesoscale steering patterns. It displays the strength of the climatological signal and allow for rapid qualitative comparison between historical TC tracks and NWP models. Second, I have used a robust statistical technique to quantify the relationships between fifteen different metrics of TC activity in nine ocean basins and twelve climate indices of the leading modes of atmospheric and oceanic variability. In a thorough, encyclopedic manner, over 12,000 Spearman rank correlation coefficients were calculated and examined to identify relationships between TCs and their environment. This investigation was not limited to the East Pacific or North Atlantic, and new climatic associations were found between seasonal levels of TC activity and the major climate indices across the nine basins. This information is critical to forecasters, economists, actuaries, energy traders, and societal planners who apply knowledge of levels of TC activity on intraseasonal to interdecadal timescales. The statistics are also valuable to climatologists seeking to understand how regional TC frequency will change as the global climate warms. Third, I have examined the leading intraseasonal mode of atmospheric and oceanic variability, the Madden-Julian Oscillation (MJO), and discovered statistically significant relationships with the frequency of TC genesis, intensification, and landfall over the nine basins. Like the significance of the longer-period oscillations to the frequency of TC activity on intraseasonal and longer timescales, these
Baroclinic stabilization effect of the Atlantic-Arctic water exchange simulated by the eddy-permitting ocean model and global atmosphere-ocean model

NASA Astrophysics Data System (ADS)

Moshonkin, Sergey; Bagno, Alexey; Gritsun, Andrey; Gusev, Anatoly

2017-04-01

Numerical experiments were performed with the global atmosphere-ocean model INMCM5 (for version of the international project CMIP6, resolution for atmosphere is 2°x1.5°, 21 level) and with the three-dimensional, free surface, sigma coordinate eddy-permitting ocean circulation model for Atlantic (from 30°S) - Arctic and Bering sea domain (0.25 degrees resolution, Institute of Numerical Mathematics Ocean Model or INMOM). Spatial resolution of the INMCM5 oceanic component is 0.5°x0.25°. Both models have 40 s-levels in ocean. Previously, the simulations were carried out for INMCM5 to generate climatic system stable state. Then model was run for 180 years. In the experiment with INMOM, CORE-II data for 1948-2009 were used. As the goal for comparing results of two these numerical models, we selected evolution of the density and velocity anomalies in the 0-300m active ocean layer near Fram Strait in the Greenland Sea, where oceanic cyclonic circulation influences Atlantic-Arctic water exchange. Anomalies were count without climatic seasonal cycle for time scales smaller than 30 years. We use Singular Value Decomposition analysis (SVD) for density-velocity anomalies with time lag from minus one to six months. Both models perform identical stable physical result. They reveal that changes of heat and salt transports by West Spitsbergen and East Greenland currents, caused by atmospheric forcing, produce the baroclinic modes of velocity anomalies in 0-300m layer, thereby stabilizing ocean response on the atmospheric forcing, which stimulates keeping water exchange between the North Atlantic and Arctic Ocean at the certain climatological level. The first SVD-mode of density-velocity anomalies is responsible for the cyclonic circulation variability. The second and third SVD-modes stabilize existing ocean circulation by the anticyclonic vorticity generation. The second and third SVD-modes give 35% of the input to the total dispersion of density anomalies and 16-18% of the
A Glacial Perspective on the Impact of Heinrich Stadials on North Atlantic Climate

NASA Astrophysics Data System (ADS)

Bromley, G. R.; Putnam, A. E.; Rademaker, K. M.; Balter, A.; Hall, B. L.

2017-12-01

The British Isles contain a rich geologic record of Late Pleistocene ice sheet behaviour in the NE North Atlantic basin. We are using cosmogenic 10Be surface-exposure dating, in conjunction with detailed glacial-geomorphic mapping, to reconstruct the timing and nature of cryospheric change - and thus climate variability - in northern Scotland since the Last Glacial Maximum. Our specific focus is Heinrich Stadial 1 (18,300-14,700 years ago), arguably the most significant abrupt climate event of the last glacial cycle and a major feature in global palaeoclimate records. Such constraint is needed because of currently conflicting models of how these events impact terrestrial environments and a recent hypothesis attributing this disparity to enhanced seasonality in the North Atlantic basin. To date, we have measured 10Be in > 30 samples from glacial erratics located on moraines deposited by the British Ice Sheet as it retreated from the continental shelf to its highland source regions. Our preliminary results indicate that the stadial was characterised by widespread deglaciation driven by atmospheric warming, a pattern that is suggestive of pronounced seasonality. Additionally, we report new exposure ages from moraines deposited during a subsequent phase of alpine glaciation (known locally as the Loch Lomond Readvance) that has long been attributed to the Younger Dryas stadial. With the growing focus on the full expression of stadials, and the inherent vulnerability of Europe to shifts in North Atlantic climate, developing the extant record of terrestrial glaciation and comparing these data to marine records is a critical step towards understanding the drivers of abrupt climate change.
An anatomy of the projected North Atlantic warming hole in CMIP5 models

NASA Astrophysics Data System (ADS)

Menary, Matthew B.; Wood, Richard A.

2018-04-01

Global mean surface air temperature has increased over the past century and climate models project this trend to continue. However, the pattern of change is not homogeneous. Of particular interest is the subpolar North Atlantic, which has cooled in recent years and is projected to continue to warm less rapidly than the global mean. This is often termed the North Atlantic warming hole (WH). In climate model projections, the development of the WH is concomitant with a weakening of the Atlantic meridional overturning circulation (AMOC). Here, we further investigate the possible link between the AMOC and WH and the competing drivers of vertical mixing and surface heat fluxes. Across a large ensemble of 41 climate models we find that the spatial structure of the WH varies considerably from model to model but is generally upstream of the simulated deep water formation regions. A heat budget analysis suggests the formation of the WH is related to changes in ocean heat transport. Although the models display a plethora of AMOC mean states, they generally predict a weakening and shallowing of the AMOC also consistent with the evolving depth structure of the WH. A lagged regression analysis during the WH onset phase suggests that reductions in wintertime mixing lead a weakening of the AMOC by 5 years in turn leading initiation of the WH by 5 years. Inter-model differences in the evolution and structure of the WH are likely to lead to somewhat different projected climate impacts in nearby Europe and North America.
Intraseasonal interaction between the Madden-Julian Oscillation and the North Atlantic Oscillation.

PubMed

Cassou, Christophe

2008-09-25

Bridging the traditional gap between the spatio-temporal scales of weather and climate is a significant challenge facing the atmospheric community. In particular, progress in both medium-range and seasonal-to-interannual climate prediction relies on our understanding of recurrent weather patterns and the identification of specific causes responsible for their favoured occurrence, persistence or transition. Within this framework, I here present evidence that the main climate intra-seasonal oscillation in the tropics-the Madden-Julian Oscillation (MJO)-controls part of the distribution and sequences of the four daily weather regimes defined over the North Atlantic-European region in winter. North Atlantic Oscillation (NAO) regimes are the most affected, allowing for medium-range predictability of their phase far exceeding the limit of around one week that is usually quoted. The tropical-extratropical lagged relationship is asymmetrical. Positive NAO events mostly respond to a mid-latitude low-frequency wave train initiated by the MJO in the western-central tropical Pacific and propagating eastwards. Precursors for negative NAO events are found in the eastern tropical Pacific-western Atlantic, leading to changes along the North Atlantic storm track. Wave-breaking diagnostics tend to support the MJO preconditioning and the role of transient eddies in setting the phase of the NAO. I present a simple statistical model to quantitatively assess the potential predictability of the daily NAO index or the sign of the NAO regimes when they occur. Forecasts are successful in approximately 70 per cent of the cases based on the knowledge of the previous approximately 12-day MJO phase used as a predictor. This promising skill could be of importance considering the tight link between weather regimes and both mean conditions and the chances of extreme events occurring over Europe. These findings are useful for further stressing the need to better simulate and forecast the tropical
The North Atlantic Treaty Organization at 40.

ERIC Educational Resources Information Center

Baker, John A.

1989-01-01

Surveys the history of the North Atlantic Treaty Organization's (NATO) on the 40th anniversary of the signing of the Treaty. Highlights milestones in the Organization's history of dealing with the Soviet Union, from containment to the Intermediate-Range Nuclear Forces Treaty. Discusses needs, tasks, and challenges that NATO faces in the 1990s.…
Spin-Down of the North Atlantic Subpolar Circulation

NASA Technical Reports Server (NTRS)

Hakkinen, S.; Rhines, P. B.

2004-01-01

Dramatic changes have occurred in the mid-to-high-latitude North Atlantic Ocean as evidenced by TOPEX/Poseidon observations of sea surface height (SSH) in the subpolar gyre and the Gulf Stream. Analysis of altimeter data shows that subpolar SSH has increased during the 1990s and the geostrophic velocity derived from altimeter data shows a decline in the gyre circulation. Direct current-meter observations in the boundary current of the Labrador Sea support the trend in the 199Os, and, together with hydrographic data show that in the mid-late 1990s the trend extends deep in the water column. We find that buoyancy forcing over the northern North Atlantic has a dynamic effect consistent with the altimeter data and hydrographic observations: a weak thermohaline forcing and the subsequent decay of the domed structure of the subpolar isopycnals would give rise to the observed anticyclonic circulation trend.
Storm-driven Mixing and Potential Impact on the Arctic Ocean

NASA Technical Reports Server (NTRS)

Yang, Jiayan; Comiso, Josefino; Walsh, David; Krishfield, Richard; Honjo, Susumu; Koblinsky, Chester J. (Technical Monitor)

2001-01-01

Observations of the ocean, atmosphere, and ice made by Ice-Ocean Environmental Buoys (IOEBs) indicate that mixing events reaching the depth of the halocline have occurred in various regions in the Arctic Ocean. Our analysis suggests that these mixing events were mechanically forced by intense storms moving across the buoy sites. In this study, we analyzed these mixing events in the context of storm developments that occurred in the Beaufort Sea and in the general area just north of Fram Strait, two areas with quite different hydrographic structures. The Beaufort Sea is strongly influenced by inflow of Pacific water through Bering Strait, while the area north of Fram Strait is directly affected by the inflow of warm and salty North Atlantic water. Our analyses of the basin-wide evolution of the surface pressure and geostrophic wind fields indicate that the characteristics of the storms could be very different. The buoy-observed mixing occurred only in the spring and winter seasons when the stratification was relatively weak. This indicates the importance of stratification, although the mixing itself was mechanically driven. We also analyze the distribution of storms, both the long-term climatology as well as the patterns for each year in the last two decades. The frequency of storms is also shown to be correlated- (but not strongly) to Arctic Oscillation indices. This study indicates that the formation of new ice that leads to brine rejection is unlikely the mechanism that results in the type of mixing that could overturn the halocline. On the other hand, synoptic-scale storms can force mixing deep enough to the halocline and thermocline layer. Despite a very stable stratification associated with the Arctic halocline, the warm subsurface thermocline water is not always insulated from the mixed layer.
Tropical Indo-Pacific hydroclimate response to North Atlantic forcing during the last deglaciation as recorded by a speleothem from Sumatra, Indonesia

NASA Astrophysics Data System (ADS)

Wurtzel, Jennifer B.; Abram, Nerilie J.; Lewis, Sophie C.; Bajo, Petra; Hellstrom, John C.; Troitzsch, Ulrike; Heslop, David

2018-06-01

Abrupt changes in Atlantic Meridional Overturning Circulation are known to have affected the strength of the Indian and Asian Monsoons during glacial and deglacial climate states. However, there is still much uncertainty around the hydroclimate response of the Indo-Pacific Warm Pool (IPWP) region to abrupt climate changes in the North Atlantic. Many studies suggest a mean southward shift in the intertropical convergence zone (ITCZ) in the IPWP region during phases of reduced Atlantic meridional overturning, however, existing proxies have seasonal biases and conflicting responses, making it difficult to determine the true extent of North Atlantic forcing in this climatically important region. Here we present a precisely-dated, high-resolution record of eastern Indian Ocean hydroclimate variability spanning the last 16 ky (thousand years) from δ18O measurements in an aragonite-calcite speleothem from central Sumatra. This represents the western-most speleothem record from the IPWP region. Precipitation arrives year-round at this site, with the majority sourced from the local tropical eastern Indian Ocean and two additional long-range seasonal sources associated with the boreal and austral summer monsoons. The Sumatran speleothem demonstrates a clear deglacial structure that includes 18O enrichment during the Younger Dryas and 18O depletion during the Bølling-Allerød, similar to the pattern seen in speleothems of the Asian and Indian monsoon realms. The speleothem δ18O changes at this site are best explained by changes in rainfall amount and changes in the contributions from different moisture pathways. Reduced rainfall in Sumatra during the Younger Dryas is most likely driven by reductions in moisture transport along the northern or southern monsoon transport pathways to Sumatra. Considered with other regional proxies, the record from Sumatra suggests the response of the IPWP to North Atlantic freshwater forcing is not solely driven by southward shifts of the
Simulation of the modern arctic climate by the NCAR CCM1

NASA Technical Reports Server (NTRS)

Bromwich, David H.; Tzeng, Ren-Yow; Parish, Thomas, R.

1994-01-01

The National Center of Atmospheric Research (NCAR) Community Climate Model Version 1 (CCM1's) simulation of the modern arctic climate is evaluated by comparing a five-year seasonal cycle simulation with the European Center for Medium-Range Weather Forecasts (ECMWF) global analyses. The sea level pressure (SLP), storm tracks, vertical cross section of height, 500-hPa height, total energy budget, and moisture budget are analyzed to investigate the biases in the simulated arctic climate. The results show that the model simulates anomalously low SLP, too much storm activity, and anomalously strong baroclinicity to the west of Greenland and vice versa to the east of Greenland. This bias is mainly attributed to the model's topographic representation of Greenland. First, the broadened Greenland topography in the model distorts the path of cyclone waves over the North Atlantic Ocean. Second, the model oversimulates the ridge over Greenland, which intensifies its blocking effect and steers the cyclone waves clockwise around it and hence produces an artificial circum-Greenland trough. These biases are significantly alleviated when the horizontal resolution increases to T42. Over the Arctic basin, the model simulates large amounts of low-level (stratus) clouds in winter and almost no stratus in summer, which is opposite to the observations. This bias is mainly due to the location of the simulated SLP features and the negative anomaly of storm activity, which prevent the transport of moisture into this region during summer but favor this transport in winter. The moisture budget analysis shows that the model's net annual precipitation (P-E) between 70 deg N and the North Pole is 6.6 times larger than the observations and the model transports six times more moisture into this region. The bias in the advection term is attributed to the positive moisture fixer scheme and the distorted flow pattern. However, the excessive moisture transport into the Arctic basin does not solely
Dynamical downscaling with the fifth-generation Canadian regional climate model (CRCM5) over the CORDEX Arctic domain: effect of large-scale spectral nudging and of empirical correction of sea-surface temperature

NASA Astrophysics Data System (ADS)

Takhsha, Maryam; Nikiéma, Oumarou; Lucas-Picher, Philippe; Laprise, René; Hernández-Díaz, Leticia; Winger, Katja

2017-10-01

As part of the CORDEX project, the fifth-generation Canadian Regional Climate Model (CRCM5) is used over the Arctic for climate simulations driven by reanalyses and by the MPI-ESM-MR coupled global climate model (CGCM) under the RCP8.5 scenario. The CRCM5 shows adequate skills capturing general features of mean sea level pressure (MSLP) for all seasons. Evaluating 2-m temperature (T2m) and precipitation is more problematic, because of inconsistencies between observational reference datasets over the Arctic that suffer of a sparse distribution of weather stations. In our study, we additionally investigated the effect of large-scale spectral nudging (SN) on the hindcast simulation driven by reanalyses. The analysis shows that SN is effective in reducing the spring MSLP bias, but otherwise it has little impact. We have also conducted another experiment in which the CGCM-simulated sea-surface temperature (SST) is empirically corrected and used as lower boundary conditions over the ocean for an atmosphere-only global simulation (AGCM), which in turn provides the atmospheric lateral boundary conditions to drive the CRCM5 simulation. This approach, so-called 3-step approach of dynamical downscaling (CGCM-AGCM-RCM), which had considerably improved the CRCM5 historical simulations over Africa, exhibits reduced impact over the Arctic domain. The most notable positive effect over the Arctic is a reduction of the T2m bias over the North Pacific Ocean and the North Atlantic Ocean in all seasons. Future projections using this method are compared with the results obtained with the traditional 2-step dynamical downscaling (CGCM-RCM) to assess the impact of correcting systematic biases of SST upon future-climate projections. The future projections are mostly similar for the two methods, except for precipitation.
Subpolar Atlantic cooling and North American east coast warming linked to AMOC slowdown

NASA Astrophysics Data System (ADS)

Rahmstorf, Stefan; Caesar, Levke; Feulner, Georg; Saba, Vincent

2017-04-01

Reconstructing the history of the Atlantic Meridional Overturning Circulation (AMOC) is difficult due to the limited availability of data. One approach has been to use instrumental and proxy data for sea surface temperature (SST), taking multi-decadal and longer SST variations in the subpolar gyre region as indicator for AMOC changes [Rahmstorf et al., 2015]. Recent high-resolution global climate model results [Saba et al., 2016] as well as dynamical theory and conceptual modelling [Zhang and Vallis, 2007] suggest that an AMOC weakening will not only cool the subpolar Atlantic but simultaneously warm the Northwest Atlantic between Cape Hatteras and Nova Scotia, thus providing a characteristic SST pattern associated with AMOC variations. We analyse sea surface temperature (SST) observations from this region together with high-resolution climate model simulations to better understand the linkages of SST variations to AMOC variability and to provide further evidence for an ongoing AMOC slowdown. References Rahmstorf, S., J. E. Box, G. Feulner, M. E. Mann, A. Robinson, S. Rutherford, and E. J. Schaffernicht (2015), Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Climate Change, 5(5), 475-480, doi: 10.1038/nclimate2554. Saba, V. S., et al. (2016), Enhanced warming of the Northwest Atlantic Ocean under climate change, Journal of Geophysical Research-Oceans, 121(1), 118-132, doi: 10.1002/2015JC011346. Zhang, R., and G. K. Vallis (2007), The Role of Bottom Vortex Stretching on the Path of the North Atlantic Western Boundary Current and on the Northern Recirculation Gyre, Journal of Physical Oceanography, 37(8), 2053-2080, doi: 10.1175/jpo3102.1.
Satellite and Model Assessment of Regional Aerosol Trends and Potential Impacts on Clouds in the western North Atlantic Ocean

NASA Astrophysics Data System (ADS)

Jongeward, A.; Li, Z.

2014-12-01

Aerosols and clouds contribute to atmospheric variability and to Earth's radiative balance, and while aerosol-cloud interactions have been studied in the past, long-term assessments of their regional interactions are only beginning to be realized. Changes in emissions and air quality policies as well as socioeconomic factors ultimately lead to changes in AOD (aerosol optical depth) with cascading effects on clouds and ultimately on the combined radiative effects where agreement is yet to be seen. In this work, an assessment of any trends observed in the aerosol loading over the western North Atlantic Ocean during the period of 2000 to 2012 is presented. Monthly mean data from NASA's MODIS instruments onboard both Terra and Aqua satellites are employed. Two aerosol models (GOCART and MERRAero) with the capability to model five individual aerosol species are also used and can separate anthropogenic from natural contributions to the total aerosol load and the aerosol trend. Preliminary results show two distinct regions of opposite trend in the satellite AOD over the western North Atlantic. From analysis of the model trends, the trends in these two regions are also of different origin: the negative AOD trend (ranging from -0.020 to -0.040 per decade) seen just off the eastern coast of the U.S. is of anthropogenic origin while the positive AOD trend (ranging from 0.015 to 0.030 per decade) seen in the south of the domain is of natural origins. Compelling evidence from a ground-based aerosol record (AERONET) as well as EPA emissions records corroborates the anthropogenic origin of the negative trend off the eastern U.S. coast. Finally, any trends seen in the cloud effective radius are explored to examine the presence of the first indirect effect (Twomey effect). The analysis from Aqua appears stronger and more coherent, likely a testament to its calibration stability relative to Terra. Statistical significance tests are performed for the 90% and 95% levels using the
Sensitivity of two Iberian lakes to North Atlantic atmospheric circulation modes

NASA Astrophysics Data System (ADS)

Hernández, Armand; Trigo, Ricardo M.; Pla-Rabes, Sergi; Valero-Garcés, Blas L.; Jerez, Sonia; Rico-Herrero, Mayte; Vega, José C.; Jambrina-Enríquez, Margarita; Giralt, Santiago

2015-12-01

The North Atlantic Oscillation (NAO) exerts a major influence on the climate of the North Atlantic region. However, other atmospheric circulation modes (ACMs), such as the East Atlantic (EA) and Scandinavian (SCAND) patterns, also play significant roles. The dynamics of lakes on the Iberian Peninsula are greatly controlled by climatic parameters, but their relationship with these various ACMs has not been investigated in detail. In this paper, we analyze monthly meteorological and limnological long-term datasets (1950-2011 and 1992-2011, respectively) from two lakes on the northern and central Iberian Peninsula (Sanabria and Las Madres) to develop an understanding of the seasonal sensitivity of these freshwater systems to the NAO, EA and SCAND circulation modes. The limnological variability within Lake Sanabria is primarily controlled by fluctuations in the seasonal precipitation and wind, and the primary ACMs associated with the winter limnological processes are the NAO and the SCAND modes, whereas only the EA mode appears to weakly influence processes during the summer. However, Lake Las Madres is affected by precipitation, wind and, to a lesser extent, temperature, whereas the ACMs have less influence. Therefore, we aim to show that the lakes of the Iberian Peninsula are sensitive to these ACMs. The results presented here indicate that the lake dynamics, in some cases, have a higher sensitivity to variations in the ACMs than single local meteorological variables. However, certain local features, such as geography, lake morphology and anthropic influences, are crucial to properly record the signals of these ACMs.
Connectivity between surface and deep waters determines prokaryotic diversity in the North Atlantic Deep Water

PubMed Central

Frank, Alexander H.; Garcia, Juan A. L.; Herndl, Gerhard J.

2016-01-01

Summary To decipher the influence of depth stratification and surface provincialism on the dark ocean prokaryotic community composition, we sampled the major deep‐water masses in the eastern North Atlantic covering three biogeographic provinces. Their diversity was evaluated using ordination and canonical analysis of 454 pyrotag sequences. Variance partitioning suggested that 16% of the variation in the bacterial community composition was based on depth stratification while 9% of the variation was due to geographic location. General linear mixed effect models showed that the community of the subsurface waters was connected to the dark ocean prokaryotic communities in different biogeographic provinces. Cluster analysis indicated that some prokaryotic taxa are specific to distinct regions in bathypelagic water masses. Taken together, our data suggest that the dark ocean prokaryotic community composition of the eastern North Atlantic is primed by the formation and the horizontal transport of water masses. PMID:26914787
DOE Office of Scientific and Technical Information (OSTI.GOV)

Otto-Bliesner, Bette L.; Jahn, Alexandra; Feng, Ran

Under previous reconstructions of late Pliocene boundary conditions, climate models have failed to reproduce the warm sea surface temperatures reconstructed in the North Atlantic. Using a reconstruction of mid-Piacenzian paleogeography that has the Bering Strait and Canadian Arctic Archipelago Straits closed, however, improves the simulation of the proxy-indicated warm sea surface temperatures in the North Atlantic in the Community Climate System Model. We find that the closure of these small Arctic gateways strengthens the Atlantic Meridional Overturning Circulation, by inhibiting freshwater transport from the Pacific to the Arctic Ocean and from the Arctic Ocean to the Labrador Sea, leading tomore » warmer sea surface temperatures in the North Atlantic. In conclusion, this indicates that the state of the Arctic gateways may influence the sensitivity of the North Atlantic climate in complex ways, and better understanding of the state of these Arctic gateways for past time periods is needed.« less
Collaborative Research: Improving Decadal Prediction of Arctic Climate Variability and Change Using a Regional Arctic

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

Gutowski, William J.

This project developed and applied a regional Arctic System model for enhanced decadal predictions. It built on successful research by four of the current PIs with support from the DOE Climate Change Prediction Program, which has resulted in the development of a fully coupled Regional Arctic Climate Model (RACM) consisting of atmosphere, land-hydrology, ocean and sea ice components. An expanded RACM, a Regional Arctic System Model (RASM), has been set up to include ice sheets, ice caps, mountain glaciers, and dynamic vegetation to allow investigation of coupled physical processes responsible for decadal-scale climate change and variability in the Arctic. RASMmore » can have high spatial resolution (~4-20 times higher than currently practical in global models) to advance modeling of critical processes and determine the need for their explicit representation in Global Earth System Models (GESMs). The pan-Arctic region is a key indicator of the state of global climate through polar amplification. However, a system-level understanding of critical arctic processes and feedbacks needs further development. Rapid climate change has occurred in a number of Arctic System components during the past few decades, including retreat of the perennial sea ice cover, increased surface melting of the Greenland ice sheet, acceleration and thinning of outlet glaciers, reduced snow cover, thawing permafrost, and shifts in vegetation. Such changes could have significant ramifications for global sea level, the ocean thermohaline circulation and heat budget, ecosystems, native communities, natural resource exploration, and commercial transportation. The overarching goal of the RASM project has been to advance understanding of past and present states of arctic climate and to improve seasonal to decadal predictions. To do this the project has focused on variability and long-term change of energy and freshwater flows through the arctic climate system. The three foci of this research are
Breakup of Pangaea and plate kinematics of the central Atlantic and Atlas regions

NASA Astrophysics Data System (ADS)

Schettino, Antonio; Turco, Eugenio

2009-08-01

and the conjugate margin of Nova Scotia. The inversion of the Atlas rift and the subsequent formation of the Atlas mountain belt occurred during the Oligocene-early Miocene time interval. In the central Atlantic, this event was associated with higher spreading rates of the ridge segments north of the Atlantis FZ. An estimate of 170 km of dextral offset of Morocco relative to northwest Africa, in the central Atlantic, is required by an analysis of marine magnetic anomalies. Five plate tectonic reconstructions and a computer animation are proposed to illustrate the late Triassic and Jurassic process of breakup of Pangaea in the central Atlantic and Atlas regions.

Arctic Sea Ice Export Through Fram Strait and Atmospheric Planetary Waves

NASA Technical Reports Server (NTRS)

Cavalieri, Donald J.; Koblinsky, Chester (Technical Monitor)

2001-01-01

A link is found between the variability of Arctic sea ice export through Ram Strait and the phase of the longest atmospheric planetary wave (zonal wave 1) in SLP for the period 1958-1997. Previous studies have identified a link between From Strait ice export and the North Atlantic Oscillation (NAO), but this link has been described as unstable because of a lack of consistency over time scales longer than the last two decades. Inconsistent and low correlations are also found between From Strait ice export and the Arctic Oscillation (AD) index. This paper shows that the phase of zonal wave 1 explains 60% - 70% of the simulated From Strait ice export variance over the Goodyear period 1958 - 1997. Unlike the NAB and AD links, these high variances are consistent for both the first and second halves of the Goodyear period. This consistency is attributed to the sensitivity of the wave I phase at high latitudes to the presence of secondary low pressure systems in the Barents Sea that serve to drive sea ice southward through From Strait. These results provide further evidence that the phase of zonal wave 1 in SLP at high latitudes drives regional as well as hemispheric low frequency Arctic Ocean and sea ice variability.
Replicating annual North Atlantic hurricane activity 1878-2012 from environmental variables

NASA Astrophysics Data System (ADS)

Saunders, Mark A.; Klotzbach, Philip J.; Lea, Adam S. R.

2017-06-01

Statistical models can replicate annual North Atlantic hurricane activity from large-scale environmental field data for August and September, the months of peak hurricane activity. We assess how well the six environmental fields used most often in contemporary statistical modeling of seasonal hurricane activity replicate North Atlantic hurricane numbers and Accumulated Cyclone Energy (ACE) over the 135 year period from 1878 to 2012. We find that these fields replicate historical hurricane activity surprisingly well, showing that contemporary statistical models and their seasonal physical links have long-term robustness. We find that August-September zonal trade wind speed over the Caribbean Sea and the tropical North Atlantic is the environmental field which individually replicates long-term hurricane activity the best and that trade wind speed combined with the difference in sea surface temperature between the tropical Atlantic and the tropical mean is the best multi-predictor model. Comparing the performance of the best single-predictor and best multi-predictor models shows that they exhibit little difference in hindcast skill for predicting long-term ACE but that the best multipredictor model offers improved skill for predicting long-term hurricane numbers. We examine whether replicated real-time prediction skill 1983-2012 increases as the model training period lengthens and find evidence that this happens slowly. We identify a dropout in hurricane replication centered on the 1940s and show that this is likely due to a decrease in data quality which affects all data sets but Atlantic sea surface temperatures in particular. Finally, we offer insights on the implications of our findings for seasonal hurricane prediction.
Arctic Outflow West of Greenland: Mass and Freshwater Fluxes at Davis Strait

NASA Astrophysics Data System (ADS)

Lee, Craig; Curry, Beth; Petrie, Brian; Azetsu-Scott, Kumiko; Gobat, Jason

2014-05-01

Eberhard Fahrbach worked to understand the communication between the Arctic and subpolar oceans and its role in modulating Arctic change. This included long-standing leadership in the Arctic-Subarctic Ocean Flux program and the long-term quantification of fluxes east of Greenland, through Fram Strait, the primary pathway for Atlantic water passing into the Arctic and one of two gateways for freshwater flowing out. Freshwater also exits the Arctic west of Greenland, though the Canadian Arctic Archipelago and, to the south, Davis Strait. The strait provides a convenient choke point for monitoring temporal and spatial variability of Arctic outflow while also characterizing a critical upstream boundary condition for Labrador Sea convection. Fluxes through the Strait represent the net integrated Canadian Archipelago throughflow, over 50% of the Arctic's liquid freshwater discharge, modified by terrestrial inputs and oceanic processes during its southward transit through Baffin Bay. By the time they reach Davis Strait, Arctic waters already embody most of the transformations they undergo prior to exerting their influence on the deepwater formation sites in the Labrador Sea. An ongoing program has characterized Davis Strait volume, freshwater and heat flux since September 2004. Measurements include continuous velocity, temperature and salinity time series collected by a moored array, autumn ship-based hydrographic sections and high-resolution sections occupied by autonomous gliders. Moored instrumentation includes novel new instruments that provide temperature and salinity measurements in the critical region neat the ice-ocean interface and measurements over the shallow Baffin and West Greenland shelves, while gliders have captured the first high-resolution wintertime sections across the Strait. These data show large interannual variability in volume and freshwater transport, with no clear trends observed between 2004-2010. Average volume, liquid freshwater and sea ice
Comparison of the response of Atlantic cod ( Gadus morhua) in the high-latitude regions of the North Atlantic during the warm periods of the 1920s-1960s and the 1990s-2000s

NASA Astrophysics Data System (ADS)

Drinkwater, Ken

2009-10-01

Concern about future anthropogenic warming has lead to demands for information on what might happen to fish and fisheries under various climate-change scenarios. One suggestion has been to use past events as a proxy for what will happen in the future. In this paper a comparison between the responses of Atlantic cod ( Gadus morhua) to two major warm periods in the North Atlantic during the 20th century is carried out to determine how reliable the past might be as a predictor of the future. The first warm period began during the 1920s, remained relatively warm through the 1960s, and was limited primarily to the northern regions (>60°N). The second warm period, which again covered the northern regions but also extended farther south (30°N), began in the 1990s and has continued into the present century. During the earlier warm period, the most northern of the cod stocks (West Greenland, Icelandic, and Northeast Arctic cod in the Barents Sea) increased in abundance, individual growth was high, recruitment was strong, and their distribution spread northward. Available plankton data suggest that these cod responses were driven by bottom-up processes. Fishing pressure increased during this period of high cod abundance and the northern cod stocks began to decline, as early as the 1950s in the Barents Sea but during the 1960s elsewhere. Individual growth declined as temperatures cooled and the cod distributions retracted southward. During the warming in the 1990s, the spawning stock biomass of cod in the Barents Sea again increased, recruitment rose, and the stock spread northward, but the individual growth did not improve significantly. Cod off West Greenland also have shown signs of improving recruitment and increasing biomass, albeit they are still very low in comparison to the earlier warming period. The abundance of Icelandic cod, on the other hand, has remained low through the recent warm period and spawning stock biomass and total biomass are at levels near the
Nonmethane hydrocarbon measurements in the North Atlantic Flight Corridor during the Subsonic Assessment Ozone and Nitrogen Oxide Experiment

NASA Astrophysics Data System (ADS)

Simpson, I. J.; Sive, B. C.; Blake, D. R.; Blake, N. J.; Chen, T.-Y.; Lopez, J. P.; Anderson, B. E.; Sachse, G. W.; Vay, S. A.; Fuelberg, H. E.; Kondo, Y.; Thompson, A. M.; Rowland, F. S.

2000-02-01

Mixing ratios of nonmethane hydrocarbons (NMHCs) were not enhanced in whole air samples collected within the North Atlantic Flight Corridor (NAFC) during the fall of 1997. The investigation was conducted aboard NASA's DC-8 research aircraft, as part of the Subsonic Assessment (SASS) Ozone and Nitrogen Oxide Experiment (SONEX). NMHC enhancements were not detected within the general organized tracking system of the NAFC, nor during two tail chases of the DC-8's own exhaust. Because positive evidence of aircraft emissions was demonstrated by enhancements in both nitrogen oxides and condensation nuclei during SONEX, the NMHC results suggest that the commercial air traffic fleet operating in the North Atlantic region does not contribute at all or contributes negligibly to NMHCs in the NAFC.
Influence of SST anomalies in low latitudes on atmospheric heat transport to the Arctic

NASA Astrophysics Data System (ADS)

Alekseev, Genrikh; Kuzmina, Svetlana; Glok, Natalia

2017-04-01

The purpose of the study is to assess the influence of SST anomalies in the low latitudes of the Atlantic, Indian and Pacific oceans to climatic change of the winter atmospheric meridional heat transport (MAHT) to the Arctic and to propose the mechanisms of this influence. Estimates of sensible and latent heat transport to the Arctic through the "Atlantic Gate" at 70 ° N in winter (December-February) 1980-2015 fulfilled on base ERA / Interim and monthly SST from HadISST were used. Multi-dimensional cross-correlation analysis was applied. The area and month in each ocean were found with maximal correlations between SST and winter MAHT. Mean SST in selected areas for each month of 1980-2015 were calculated and its correlations with MAHT were estimated. The correlation coefficients equal from 0.57 to 0.42, and after removing the noise increased up to 0.75 with MAHT lag from 27 to 30 months. The SST and MAHT series include together with positive trend the 5-7 years fluctuations. The mechanism of SST anomalies influence on winter MAHT to the Arctic includes the interaction of atmospheric (Hadley and Ferrel circulations, jet streams, NAO) and oceanic (Gulf Stream, the North Atlantic, the Norwegian currents) circulation patterns. To justify the proposed scheme the evaluation of the links between SST anomalies, the NAO index, the Atlantic water inflow to the Barents Sea, are investigated. The study is supported with RFBR project 15-05-03512.
Developing an acoustic method for reducing North Atlantic right whale (Eubalaena glacialis) ship strike mortality along the United States eastern seaboard

NASA Astrophysics Data System (ADS)

Mullen, Kaitlyn Allen

North Atlantic right whales (Eubalaena glacialis ) are among the world's most endangered cetaceans. Although protected from commercial whaling since 1949, North Atlantic right whales exhibit little to no population growth. Ship strike mortality is the leading known cause of North Atlantic right whale mortality. North Atlantic right whales exhibit developed auditory systems, and vocalize in the frequency range that dominates ship acoustic signatures. With no behavioral audiogram published, current literature assumes these whales should be able to acoustically detect signals in the same frequencies they vocalize. Recorded ship acoustic signatures occur at intensities that are similar or higher to those recorded by vocalizing North Atlantic right whales. If North Atlantic right whales are capable of acoustically detecting oncoming ship, why are they susceptible to ship strike mortality? This thesis models potential acoustic impediments to North Atlantic right whale detection of oncoming ships, and concludes the presence of modeled and observed bow null effect acoustic shadow zones, located directly ahead of oncoming ships, are likely to impair the ability of North Atlantic right whales to detect and/or localize oncoming shipping traffic. This lack of detection and/or localization likely leads to a lack of ship strike avoidance, and thus contributes to the observed high rates of North Atlantic right whale ship strike mortality. I propose that North Atlantic right whale ship strike mortality reduction is possible via reducing and/or eliminating the presence of bow null effect acoustic shadow zones. This thesis develops and tests one method for bow null effect acoustic shadow zone reduction on five ships. Finally, I review current United States policy towards North Atlantic right whale ship strike mortality in an effort to determine if the bow null effect acoustic shadow zone reduction method developed is a viable method for reducing North Atlantic right whale ship
Aromatic acids in an Arctic ice core from Svalbard: a proxy record of biomass burning

NASA Astrophysics Data System (ADS)

Grieman, Mackenzie M.; Aydin, Murat; Isaksson, Elisabeth; Schwikowski, Margit; Saltzman, Eric S.

2018-05-01

This study presents vanillic acid and para-hydroxybenzoic acid levels in an Arctic ice core from Lomonosovfonna, Svalbard covering the past 800 years. These aromatic acids are likely derived from lignin combustion in wildfires and long-range aerosol transport. Vanillic and para-hydroxybenzoic acid are present throughout the ice core, confirming that these compounds are preserved on millennial timescales. Vanillic and para-hydroxybenzoic acid concentrations in the Lomonosovfonna ice core ranged from below the limits of detection to 0.2 and 0.07 ppb, respectively (1 ppb = 1000 ng L-1). Vanillic acid levels are high (maximum of 0.1 ppb) from 1200 to 1400 CE, then gradually decline into the twentieth century. The largest peak in the vanillic acid in the record occurs from 2000 to 2008 CE. In the para-hydrobenzoic acid record, there are three centennial-scale peaks around 1300, 1550, and 1650 CE superimposed on a long-term decline in the baseline levels throughout the record. Ten-day air mass back trajectories for a decade of fire seasons (March-November, 2006-2015) indicate that Siberia and Europe are the principle modern source regions for wildfire emissions reaching the Lomonosovfonna site. The Lomonosovfonna data are similar to those from the Eurasian Arctic Akademii Nauk ice core during the early part of the record (1220-1400 CE), but the two ice cores diverge markedly after 1400 CE. This coincides with a shift in North Atlantic climate marked by a change of the North Atlantic Oscillation from a positive to a more negative state.
Deglacial climate modulated by the storage and release of Arctic sea ice

NASA Astrophysics Data System (ADS)

Condron, A.; Coletti, A. J.; Bradley, R. S.

2017-12-01

Periods of abrupt climate cooling during the last deglaciation (20 - 8 kyr ago) are often attributed to glacial outburst floods slowing the Atlantic meridional overturning circulation (AMOC). Here, we present results from a series of climate model simulations showing that the episodic break-up and mobilization of thick, perennial, Arctic sea ice during this time would have released considerable volumes of freshwater directly to the Nordic Seas, where processes regulating large-scale climate occur. Massive sea ice export events to the North Atlantic are generated whenever the transport of sea ice is enhanced, either by changes in atmospheric circulation, rising sea level submerging the Bering land bridge, or glacial outburst floods draining into the Arctic Ocean from the Mackenzie River. We find that the volumes of freshwater released to the Nordic Seas are similar to, or larger than, those estimated to have come from terrestrial outburst floods, including the discharge at the onset of the Younger Dryas. Our results provide the first evidence that the storage and release of Arctic sea ice helped drive deglacial climate change by modulating the strength of the AMOC.
Aerosol, cloud, and precipitation interactions in Eastern North Atlantic

NASA Astrophysics Data System (ADS)

Wang, J.; Wood, R.; Dong, X.

2017-12-01

With their extensive coverage, marine low clouds greatly impact global climate. Presently, marine low clouds are poorly represented in global climate models, and the response of marine low clouds to changes in atmospheric greenhouse gases and aerosols remains the major source of uncertainty in climate simulations. The Eastern North Atlantic (ENA) is a region of persistent but diverse subtropical marine boundary layer clouds, whose albedo and precipitation are highly susceptible to perturbations in aerosol properties. In addition, ENA is periodically impacted by anthropogenic aerosol both from North American and from continental Europe, making it an excellent location to study the CCN budget in a remote marine region periodically perturbed by anthropogenic emissions, and to investigate the impacts of long-range transport of aerosols on remote marine clouds. Aerosol and Cloud Experiments in Eastern North Atlantic (ACE-ENA), funded by DOE Atmospheric Radiation Measurement (ARM) program, is designed to improve the understanding of marine boundary CCN budget, cloud and drizzle microphysics, and the impact of aerosol on marine low cloud and precipitation in the ENA by combining airborne observations and long term surface based measurements. The study has two airborne deployments. The first deployment took place from June 15 to July 25, 2017, and the second one will take place from January 10 to February 20, 2018. Flights during the first deployment were carried out in the Azores, near the ARM ENA site on Graciosa Island. The long term measurements at the ENA site provide important Climatological context for the airborne observations during the two deployments, and the cloud structures provided by the scanning radars at the ENA site put the detailed in-situ measurements into mesoscale and cloud lifecycle contexts. Another important aspect of this study is to provide high quality in-situ measurements for validating and improving ground-based retrieval algorithms at the ENA
Connecting Regional Modeling Communities Across the Atlantic: The Air Quality Model Evaluation International Initiative (AQMEII)

EPA Science Inventory

As any traveler crossing the Atlantic can attest, there certainly are differences between North America and Europe – differences in language, food, culture, and social attitudes, to name but a few. However, the “Old World” and “New World” have a lot in common as well; both region...
Connectivity between surface and deep waters determines prokaryotic diversity in the North Atlantic Deep Water.

PubMed

Frank, Alexander H; Garcia, Juan A L; Herndl, Gerhard J; Reinthaler, Thomas

2016-06-01

To decipher the influence of depth stratification and surface provincialism on the dark ocean prokaryotic community composition, we sampled the major deep-water masses in the eastern North Atlantic covering three biogeographic provinces. Their diversity was evaluated using ordination and canonical analysis of 454 pyrotag sequences. Variance partitioning suggested that 16% of the variation in the bacterial community composition was based on depth stratification while 9% of the variation was due to geographic location. General linear mixed effect models showed that the community of the subsurface waters was connected to the dark ocean prokaryotic communities in different biogeographic provinces. Cluster analysis indicated that some prokaryotic taxa are specific to distinct regions in bathypelagic water masses. Taken together, our data suggest that the dark ocean prokaryotic community composition of the eastern North Atlantic is primed by the formation and the horizontal transport of water masses. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.
On the Influence of North Pacific Sea Surface Temperature on the Arctic Winter Climate

NASA Technical Reports Server (NTRS)

Hurwitz, Margaret M.; Newman, P. A.; Garfinkel, C. I.

2012-01-01

Differences between two ensembles of Goddard Earth Observing System Chemistry-Climate Model simulations isolate the impact of North Pacific sea surface temperatures (SSTs) on the Arctic winter climate. One ensemble of extended winter season forecasts is forced by unusually high SSTs in the North Pacific, while in the second ensemble SSTs in the North Pacific are unusually low. High Low differences are consistent with a weakened Western Pacific atmospheric teleconnection pattern, and in particular, a weakening of the Aleutian low. This relative change in tropospheric circulation inhibits planetary wave propagation into the stratosphere, in turn reducing polar stratospheric temperature in mid- and late winter. The number of winters with sudden stratospheric warmings is approximately tripled in the Low ensemble as compared with the High ensemble. Enhanced North Pacific SSTs, and thus a more stable and persistent Arctic vortex, lead to a relative decrease in lower stratospheric ozone in late winter, affecting the April clear-sky UV index at Northern Hemisphere mid-latitudes.
Arctic sea ice variability in the context of recent atmospheric circulation trends

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

Deser, C.; Walsh, J.E.; Timlin, M.S.

Sea ice is a sensitive component of the climate system, influenced by conditions in both the atmosphere and ocean. Variations in sea ice may in turn modulate climate by altering the surface albedo; the exchange of heat, moisture, and momentum between the atmosphere and ocean; and the upper ocean stratification in areas of deep water formation. The surface albedo effect is considered to be one of the dominant factors in the poleward amplification of global warming due to increased greenhouse gas concentrations simulated in many climate models. Forty years (1958--97) of reanalysis products and corresponding sea ice concentration data aremore » used to document Arctic sea ice variability and its association with surface air temperature (SAT) and sea level pressure (SLP) throughout the Northern Hemisphere extratropics. The dominant mode of winter (January-March) sea ice variability exhibits out-of-phase fluctuations between the western and eastern North Atlantic, together with a weaker dipole in the North Pacific. The time series of this mode has a high winter-to-winter autocorrelation (0.69) and is dominated by decadal-scale variations and a longer-term trend of diminishing ice cover east of Greenland and increasing ice cover west of Greenland. Associated with the dominant pattern of winter sea ice variability are large-scale changes in SAT and SLP that closely resemble the North Atlantic oscillation. The associated SAT and surface sensible and latent heat flux anomalies are largest over the portions of the marginal sea ice zone in which the trends of ice coverage have been greatest, although the well-documented warming of the northern continental regions is also apparent. the temporal and spatial relationships between the SLP and ice anomaly fields are consistent with the notion that atmospheric circulation anomalies force the sea ice variations. However, there appears to be a local response of the atmospheric circulation to the changing sea ice variations. However
Marine radiocarbon reservoir corrections (∆R) for Chesapeake Bay and the Middle Atlantic Coast of North America

NASA Astrophysics Data System (ADS)

Rick, Torben C.; Henkes, Gregory A.; Lowery, Darrin L.; Colman, Steven M.; Culleton, Brendan J.

2012-01-01

Radiocarbon dates from known age, pre-bomb eastern oyster (Crassostrea virginica) shells provide local marine reservoir corrections (∆R) for Chesapeake Bay and the Middle Atlantic coastal area of eastern North America. These data suggest subregional variability in ∆R, ranging from 148 ± 46 14C yr on the Potomac River to - 109 ± 38 14C yr at Swan Point, Maryland. The ∆R weighted mean for the Chesapeake's Western Shore (129 ± 22 14C yr) is substantially higher than the Eastern Shore (- 88 ± 23 14C yr), with outer Atlantic Coast samples falling between these values (106 ± 46 and 2 ± 46 14C yr). These differences may result from a combination of factors, including 14C-depleted freshwater that enters the bay from some if its drainages, 14C-depleted seawater that enters the bay at its mouth, and/or biological carbon recycling. We advocate using different subregional ∆R corrections when calibrating 14C dates on aquatic specimens from the Chesapeake Bay and coastal Middle Atlantic region of North America.
Meltwater routing and the Younger Dryas.

PubMed

Condron, Alan; Winsor, Peter

2012-12-04

The Younger Dryas--the last major cold episode on Earth--is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989 Nature 341:318-321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC). More recently, Tarasov and Peltier [2005 Nature 435:662-665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenzie Valley ~4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ~3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling.
Meltwater routing and the Younger Dryas

DOE PAGES

Condron, Alan; Winsor, Peter

2012-12-04

The Younger Dryas -- the last major cold episode on Earth -- is generally considered to have been triggered by a meltwater flood into the North Atlantic. The prevailing hypothesis, proposed by Broecker et al. [1989 Nature 341:318–321] more than two decades ago, suggests that an abrupt rerouting of Lake Agassiz overflow through the Great Lakes and St. Lawrence Valley inhibited deep water formation in the subpolar North Atlantic and weakened the strength of the Atlantic Meridional Overturning Circulation (AMOC).More recently, Tarasov and Peltier [2005 Nature 435:662–665] showed that meltwater could have discharged into the Arctic Ocean via the Mackenziemore » Valley ~4,000 km northwest of the St. Lawrence outlet. Here we use a sophisticated, high-resolution, ocean sea-ice model to study the delivery of meltwater from the two drainage outlets to the deep water formation regions in the North Atlantic. Unlike the hypothesis of Broecker et al., freshwater from the St. Lawrence Valley advects into the subtropical gyre ~3,000 km south of the North Atlantic deep water formation regions and weakens the AMOC by <15%. In contrast, narrow coastal boundary currents efficiently deliver meltwater from the Mackenzie Valley to the deep water formation regions of the subpolar North Atlantic and weaken the AMOC by >30%. We conclude that meltwater discharge from the Arctic, rather than the St. Lawrence Valley, was more likely to have triggered the Younger Dryas cooling.« less
TRACEing Last Glacial Period (25-80 ka b2k) tephra horizons within North Atlantic marine cores and exploring links to the Greenland ice-cores

NASA Astrophysics Data System (ADS)

Abbott, P. M.; Davies, S. M.; Griggs, A. J.; Bourne, A. J.; Cook, E.; Pearce, N. J. G.; Austin, W. E. N.; Chapman, M.; Hall, I. R.; Purcell, C. S.; Scourse, J. D.; Rasmussen, T. L.

2015-12-01

Tephrochronology is a powerful technique for the correlation and synchronisation of disparate palaeoclimatic records from different depositional environments and has considerable potential for testing climatic phasing. For example, the relative timing of atmospheric and marine changes caused by the abrupt climatic events that punctuated the last glacial period within the North Atlantic region. Here we report on efforts to establish a framework of tephra horizons within North Atlantic marine sequences that can correlate these records and if traced in the Greenland ice-cores can act as isochronous tie-lines. Investigations have been conducted on a network of marine cores from a number of sites across the North Atlantic. Tephra horizons have been identified using cryptotephra extraction techniques more commonly applied to the study of terrestrial sequences. There are two main challenges with assessing cryptotephras in the glacial North Atlantic; i) determining the transportation processes and ii) assessing the influence of secondary reworking processes and the stratigraphic integrity of the isochrons. These processes and their influence are investigated for each cryptotephra using shard size variations, major element heterogeneity and co-variance of IRD input for some cores. Numerous Icelandic cryptophras have been successfully identified in the marine records and we will discuss the integration of a number of these with an isochronous nature into a marine tephra framework and how potential correlations to the Greenland ice-core tephra framework are determined. Spatial patterns in the nature of tephra records that are emerging from the core network will be highlighted to outline some of the key areas that could be explored in the future. In addition, the synchronisation of multiple North Atlantic records to the Greenland ice-cores using the North Atlantic Ash Zone II to test the synchroneity of an abrupt cooling in the North Atlantic will be discussed.
Modeling the influence of atmospheric leading modes on the variability of the Arctic freshwater cycle

NASA Astrophysics Data System (ADS)

Niederdrenk, L.; Sein, D.; Mikolajewicz, U.

2013-12-01

Global general circulation models show remarkable differences in modeling the Arctic freshwater cycle. While they agree on the general sinks and sources of the freshwater budget, they differ largely in the magnitude of the mean values as well as in the variability of the freshwater terms. Regional models can better resolve the complex topography and small scale processes, but they are often uncoupled, thus missing the air-sea interaction. Additionally, regional models mostly use some kind of salinity restoring or flux correction, thus disturbing the freshwater budget. Our approach to investigate the Arctic hydrologic cycle and its variability is a regional atmosphere-ocean model setup, consisting of the global ocean model MPIOM with high resolution in the Arctic coupled to the regional atmosphere model REMO. The domain of the atmosphere model covers all catchment areas of the rivers draining into the Arctic. To account for all sinks and sources of freshwater in the Arctic, we include a discharge model providing terrestrial lateral waterflows. We run the model without salinity restoring but with freshwater correction, which is set to zero in the Arctic. This allows for the analysis of a closed freshwater budget in the Artic region. We perform experiments for the second half of the 20th century and use data from the global model MPIOM/ECHAM5 performed with historical conditions, that was used within the 4th Assessment Report of the IPCC, as forcing for our regional model. With this setup, we investigate how the dominant modes of large-scale atmospheric variability impact the variability in the freshwater components. We focus on the two leading empirical orthogonal functions of winter mean sea level pressure, as well as on the North Atlantic Oscillation and the Siberian High. These modes have a large impact on the Arctic Ocean circulation as well as on the solid and liquid export through Fram Strait and through the Canadian archipelago. However, they cannot explain
78 FR 61844 - North Atlantic Coast Comprehensive Study

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-04

... Comprehensive Study AGENCY: Department of the Army, U.S. Army Corps of Engineers, DoD. ACTION: Notice. SUMMARY... in the preparation of the North Atlantic Coast Comprehensive Study (Hurricane Sandy). The USACE is... Comprehensive Study authorized under the Disaster Relief Appropriations Act, Public Law 113-2 are to (1) provide...

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