Science.gov

Sample records for southern ocean supplementary

  1. Southern Ocean cephalopods.

    PubMed

    Collins, Martin A; Rodhouse, Paul G K

    2006-01-01

    The Southern Ocean cephalopod fauna is distinctive, with high levels of endemism in the squid and particularly in the octopodids. Loliginid squid, sepiids and sepiolids are absent from the Southern Ocean, and all the squid are oceanic pelagic species. The octopodids dominate the neritic cephalopod fauna, with high levels of diversity, probably associated with niche separation. In common with temperate cephalopods, Southern Ocean species appear to be semelparous, but growth rates are probably lower and longevity greater than temperate counterparts. Compared with equivalent temperate species, eggs are generally large and fecundity low, with putative long development times. Reproduction may be seasonal in the squid but is extended in the octopodids. Cephalopods play an important role in the ecology of the Southern Ocean, linking the abundant mesopelagic fish and crustaceans with higher predators such as albatross, seals and whales. To date Southern Ocean cephalopods have not been commercially exploited, but there is potential for exploitation of muscular species of the Family Ommastrephidae.

  2. The Southern Ocean silica cycle

    NASA Astrophysics Data System (ADS)

    Tréguer, Paul J.

    2014-11-01

    The Southern Ocean is a major opal sink and plays a key role in the silica cycle of the world ocean. So far however, a complete cycle of silicon in the Southern Ocean has not been published. On one hand, Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica, DSi) from the rest of the world ocean through the upwelling of the Circumpolar Deep Water, fed by contributions of deep waters of the Atlantic, Indian, and Pacific Oceans. On the other hand, the Southern Ocean exports a considerable flux of the silicic acid that is not used by diatoms in surface waters through the northward pathways of the Sub-Antarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water. Thus the Southern Ocean is a source of DSi for the rest of the world ocean. Here we show that the Southern Ocean is a net importer of DSi: because there is no significant external input of DSi, the flux of DSi imported through the Circumpolar Deep Water pathway compensates the sink flux of biogenic silica in sediments.

  3. Southern Ocean eddy phenomenology

    NASA Astrophysics Data System (ADS)

    Frenger, I.; Münnich, M.; Gruber, N.; Knutti, R.

    2015-11-01

    Mesoscale eddies are ubiquitous features in the Southern Ocean, yet their phenomenology is not well quantified. To tackle this task, we use satellite observations of sea level anomalies and sea surface temperature (SST) as well as in situ temperature and salinity measurements from profiling floats. Over the period 1997-2010, we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more. The Antarctic Circumpolar Current (ACC), the boundary current systems, and the regions where they interact are hot spots of eddy presence, representing also the birth places and graveyards of most eddies. These hot spots contrast strongly to areas shallower than about 2000 m, where mesoscale eddies are essentially absent, likely due to topographical steering. Anticyclones tend to dominate the southern subtropical gyres, and cyclones the northern flank of the ACC. Major causes of regional polarity dominance are larger formation numbers and lifespans, with a contribution of differential propagation pathways of long-lived eddies. Areas of dominance of one polarity are generally congruent with the same polarity being longer-lived, bigger, of larger amplitude, and more intense. Eddies extend down to at least 2000 m. In the ACC, eddies show near surface temperature and salinity maxima, whereas eddies in the subtropical areas generally have deeper anomaly maxima, presumably inherited from their origin in the boundary currents. The temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring.

  4. Southern Ocean Iron Experiment (SOFex)

    SciTech Connect

    Coale, Kenneth H.

    2005-07-28

    The Southern Ocean Iron Experiment (SOFeX) was an experiment decades in the planning. It's implementation was among the most complex ship operations that SIO has been involved in. The SOFeX field expedition was successful in creating and tracking two experimentally enriched areas of the Southern Ocean, one characterized by low silicic acid, one characterized by high silicic acid. Both experimental sites were replete with abundant nitrate. About 100 scientists were involved overall. The major findings of this study were significant in several ways: (1) The productivity of the southern ocean is limited by iron availability. (2) Carbon uptake and flux is therefore controlled by iron availability (3) In spite of low silicic acid, iron promotes non-silicious phytoplankton growth and the uptake of carbon dioxide. (4) The transport of fixed carbon from the surface layers proceeds with a C:N ratio that would indicate differential remineralization of nitrogen at shallow depths. (5) These finding have major implications for modeling of carbon export based on nitrate utilization. (6) The general results of the experiment indicate that, beyond other southern ocean enrichment experiments, iron inputs have a much wider impact of productivity and carbon cycling than previously demonstrated. Scientific presentations: Coale, K., Johnson, K, Buesseler, K., 2002. The SOFeX Group. Eos. Trans. AGU 83(47) OS11A-0199. Coale, K., Johnson, K. Buesseler, K., 2002. SOFeX: Southern Ocean Iron Experiments. Overview and Experimental Design. Eos. Trans. AGU 83 (47) OS22D-01. Buesseler, K.,et al. 2002. Does Iron Fertilization Enhance Carbon Sequestration? Particle flux results from the Southern Ocean Iron Experiment. Eos. Trans. AGU 83 (47), OS22D-09. Johnson, K. et al. 2002. Open Ocean Iron Fertilization Experiments From IronEx-I through SOFeX: What We Know and What We Still Need to Understand. Eos. Trans. AGU 83 (47), OS22D-12. Coale, K. H., 2003. Carbon and Nutrient Cycling During the Southern

  5. The Southern Ocean biogeochemical divide

    NASA Astrophysics Data System (ADS)

    Marinov, I.; Gnanadesikan, A.; Toggweiler, J. R.; Sarmiento, J. L.

    2006-06-01

    Modelling studies have demonstrated that the nutrient and carbon cycles in the Southern Ocean play a central role in setting the air-sea balance of CO2 and global biological production. Box model studies first pointed out that an increase in nutrient utilization in the high latitudes results in a strong decrease in the atmospheric carbon dioxide partial pressure (pCO2). This early research led to two important ideas: high latitude regions are more important in determining atmospheric pCO2 than low latitudes, despite their much smaller area, and nutrient utilization and atmospheric pCO2 are tightly linked. Subsequent general circulation model simulations show that the Southern Ocean is the most important high latitude region in controlling pre-industrial atmospheric CO2 because it serves as a lid to a larger volume of the deep ocean. Other studies point out the crucial role of the Southern Ocean in the uptake and storage of anthropogenic carbon dioxide and in controlling global biological production. Here we probe the system to determine whether certain regions of the Southern Ocean are more critical than others for air-sea CO2 balance and the biological export production, by increasing surface nutrient drawdown in an ocean general circulation model. We demonstrate that atmospheric CO2 and global biological export production are controlled by different regions of the Southern Ocean. The air-sea balance of carbon dioxide is controlled mainly by the biological pump and circulation in the Antarctic deep-water formation region, whereas global export production is controlled mainly by the biological pump and circulation in the Subantarctic intermediate and mode water formation region. The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human intervention to modify one of these without greatly altering the other.

  6. The Southern Ocean biogeochemical divide.

    PubMed

    Marinov, I; Gnanadesikan, A; Toggweiler, J R; Sarmiento, J L

    2006-06-22

    Modelling studies have demonstrated that the nutrient and carbon cycles in the Southern Ocean play a central role in setting the air-sea balance of CO(2) and global biological production. Box model studies first pointed out that an increase in nutrient utilization in the high latitudes results in a strong decrease in the atmospheric carbon dioxide partial pressure (pCO2). This early research led to two important ideas: high latitude regions are more important in determining atmospheric pCO2 than low latitudes, despite their much smaller area, and nutrient utilization and atmospheric pCO2 are tightly linked. Subsequent general circulation model simulations show that the Southern Ocean is the most important high latitude region in controlling pre-industrial atmospheric CO(2) because it serves as a lid to a larger volume of the deep ocean. Other studies point out the crucial role of the Southern Ocean in the uptake and storage of anthropogenic carbon dioxide and in controlling global biological production. Here we probe the system to determine whether certain regions of the Southern Ocean are more critical than others for air-sea CO(2) balance and the biological export production, by increasing surface nutrient drawdown in an ocean general circulation model. We demonstrate that atmospheric CO(2) and global biological export production are controlled by different regions of the Southern Ocean. The air-sea balance of carbon dioxide is controlled mainly by the biological pump and circulation in the Antarctic deep-water formation region, whereas global export production is controlled mainly by the biological pump and circulation in the Subantarctic intermediate and mode water formation region. The existence of this biogeochemical divide separating the Antarctic from the Subantarctic suggests that it may be possible for climate change or human intervention to modify one of these without greatly altering the other.

  7. The Southern Ocean: Source and sink?

    NASA Astrophysics Data System (ADS)

    Strugnell, J. M.; Cherel, Y.; Cooke, I. R.; Gleadall, I. G.; Hochberg, F. G.; Ibáñez, C. M.; Jorgensen, E.; Laptikhovsky, V. V.; Linse, K.; Norman, M.; Vecchione, M.; Voight, J. R.; Allcock, A. L.

    2011-03-01

    Many members of the benthic fauna of the Antarctic continental shelf share close phylogenetic relationships to the deep-sea fauna adjacent to Antarctica and in other ocean basins. It has been suggested that connections between the Southern Ocean and the deep sea have been facilitated by the presence of a deep Antarctic continental shelf coupled with submerging Antarctic bottom water and emerging circumpolar deep water. These conditions may have allowed 'polar submergence', whereby shallow Southern Ocean fauna have colonised the deep sea and 'polar emergence', whereby deep-sea fauna colonised the shallow Southern Ocean. A recent molecular study showed that a lineage of deep-sea and Southern Ocean octopuses with a uniserial sucker arrangement on their arms appear to have arisen via polar submergence. A distantly related clade of octopuses with a biserial sucker arrangement on their arms (historically placed in the genus Benthoctopus) is also present in the deep-sea basins of the world and the Southern Ocean. To date their evolutionary history has not been examined. The present study investigated the origins of this group using 3133 base pairs (bp) of nucleotide data from five mitochondrial genes (12S rRNA, 16S rRNA, cytochrome c oxidase subunit I, cytochrome c oxidase subunit III, cytochrome b) and the nuclear gene rhodopsin from at least 18 species (and 7 outgroup taxa). Bayesian relaxed clock analyses showed that Benthoctopus species with a high-latitude distribution in the Southern Hemisphere represent a paraphyletic group comprised of three independent clades. The results suggest that the Benthoctopus clade originated in relatively shallow Northern Hemisphere waters. Benthoctopus species distributed in the Southern Ocean are representative of polar emergence and occur at shallower depths than non-polar Benthoctopus species.

  8. Southern Ocean biological impacts on global ocean oxygen

    NASA Astrophysics Data System (ADS)

    Keller, David P.; Kriest, Iris; Koeve, Wolfgang; Oschlies, Andreas

    2016-06-01

    Southern Ocean (SO) physical and biological processes are known to have a large impact on global biogeochemistry. However, the role that SO biology plays in determining ocean oxygen concentrations is not completely understood. These dynamics are investigated here by shutting off SO biology in two marine biogeochemical models. The results suggest that SO biological processes reduce the ocean's oxygen content, mainly in the deep ocean, by 14 to 19%. However, since these processes also trap nutrients that would otherwise be transported northward to fuel productivity and subsequent organic matter export, consumption, and the accompanying oxygen consumption in midlatitude to low-latitude waters, SO biology helps to maintain higher oxygen concentrations in these subsurface waters. Thereby, SO biology can influence the size of the tropical oxygen minimum zones. As a result of ocean circulation the link between SO biological processes and remote oxygen changes operates on decadal to centennial time scales.

  9. Primary production in Southern Ocean waters

    NASA Astrophysics Data System (ADS)

    Arrigo, Kevin R.; Worthen, Denise; Schnell, Anthony; Lizotte, Michael P.

    1998-07-01

    The Southern Ocean forms a link between major ocean basins, is the site of deep and intermediate water ventilation, and is one of the few areas where macronutrients are underutilized by phytoplankton. Paradoxically, prior estimates of annual primary production are insufficient to support the Antarctic food web. Here we present results from a primary production algorithm based upon monthly climatological phytoplankton pigment concentrations from the coastal zone color scanner (CZCS). Phytoplankton production was forced using monthly temperature profiles and a radiative transfer model that computed changes in photosynthetically usable radiation at each CZCS pixel location. Average daily productivity (g C m-2 d-1) and total monthly production (Tg C month-1) were calculated for each of five geographic sectors (defined by longitude) and three ecological provinces (defined by sea ice coverage and bathymetry as the pelagic province, the marginal ice zone, and the shelf). Annual primary production in the Southern Ocean (south of 50°S) was calculated to be 4414 Tg C yr-1, 4-5 times higher than previous estimates made from in situ data. Primary production was greatest in the month of December (816 Tg C month-1) and in the pelagic province (contributing 88.6% of the annual primary production). Because of their small size the marginal ice zone (MIZ) and the shelf contributed only 9.5% and 1.8%, respectively, despite exhibiting higher daily production rates. The Ross Sea was the most productive region, accounting for 28% of annual production. The fourfold increase in the estimate of primary production for the Southern Ocean likely makes the notion of an "Antarctic paradox" (primary production insufficient to support the populations of Southern Ocean grazers, including krill, copepods, microzooplankton, etc.) obsolete.

  10. The Future of Southern Ocean Observing Systems

    NASA Astrophysics Data System (ADS)

    Talley, L. D.

    2015-12-01

    Knowledge of the Southern Ocean's role in global climate from seasonal to millennial timescales is evolving, with rapidly increasing recognition of the centrality of the Southern Ocean to Earth's heat, carbon, nutrient, and freshwater budgets, and of the impact of interactions between the ocean and the major ice shelves and grounded ice sheets of Antarctica, which have been decreasing in mass. Observations in this data-sparse and logistically remote region have never been so important, and many nations are rising to the challenge of supporting both experiments and long-term sustained observations. As illustrated in the figure from Meredith et al. (Current Op. Env. Sustain. 2013), autonomous in situ technologies are at the fore because of the difficulty and expense of sending ships year-round and because the crucial satellite remote sensing must be accompanied by in situ observations, including beneath sea ice and ice shelves. The Southern Ocean Observing System (SOOS) has grown out of this recognized need for coordinated observations from the Antarctic coastline northward to the subtropics, from the bottom water production regions in coastal polynyas over the continental shelves, to the regions of interaction of warm ocean waters with Antarctic ice shelves, beneath the vast seasonal sea ice region, and in the hot spots of air-sea fluxes and cross-Antarctic Circumpolar Current (ACC) mixing where the ACC interacts with topography and continental boundaries. The future includes international coordination and collaboration and strengthening of new and existing technologies, which include satellite observing, ice-enabled profiling floats, profiling from marine mammals, moored measurements in many strategic locations, glider and other autonomous operations in all regions, and drilling through floating ice shelves to measure the ocean waters below. Improved and consistent weather observations around the Antarctic coastlines will improve forecasting and reanalysis. Ice

  11. Cadmium isotope variations in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Xue, Zichen; Rehkämper, Mark; Horner, Tristan J.; Abouchami, Wafa; Middag, Rob; van de Flierd, Tina; de Baar, Hein J. W.

    2013-11-01

    Cadmium concentrations and isotope compositions were determined for 47 seawater samples from the high nutrient low chlorophyll (HNLC) zone of the Atlantic sector of the Southern Ocean. The samples include 13 surface waters from a transect of the Weddell Gyre and 3 depth profiles from the Weddell Sea and Drake Passage. The Southern Ocean mixed layer samples from this study and Abouchami et al. (2011) define a clear but broad ‘HNLC trend’ in a plot of εCd114/110 versus [Cd], which is primarily a consequence of isotopic fractionation associated with biological uptake (εCd114/110 is the deviation of the 114Cd/110Cd ratio of a sample from NIST SRM 3108 Cd in parts per 10,000). The trend is especially apparent in comparison to the large range of values shown by a global set of seawater Cd data for shallow depths. The Southern Ocean samples are also distinguished by their relatively high Cd concentrations (typically 0.2 to 0.6 nmol/kg) and moderately fractionated εCd114/110 (generally between +4 and +8) that reflect the limited biological productivity of this region. Detailed assessment reveals fine structure within the ‘HNLC trend’, which may record differences in the biological fractionation factor, different scenarios of closed and open system isotope fractionation, and/or distinct source water compositions. Southern Ocean seawater from depths ⩾1000 m has an average εCd114/110 of +2.5±0.2 (2se, n=16), and together with previous results this establishes a relatively constant εCd114/110 value of +3.0±0.3 (2se, n=27) for global deep waters. Significant isotopic variability was observed at intermediate depths in the Southern Ocean. Seawater from 200 m to 400 m in Weddell Sea has high Cd concentrations and εCd114/110 as low as +1, presumably due to remineralization of Cd from biomass that records incomplete nutrient utilization. Antarctic Intermediate Water, which was sampled at 150 to 750 m depth in the Drake Passage, features a distinct Cd isotope

  12. Southern Ocean Response to NADW Changes

    NASA Technical Reports Server (NTRS)

    Rind, David; Schmidt, G.; Russell, G.; deMenocal, P.; Hansen, James E. (Technical Monitor)

    2000-01-01

    The possibility of North Atlantic Deep Water (NADW) changes in both past and future climates has raised the issue of how the Southern Ocean would respond. Recent experiments with the GISS coupled atmosphere-ocean model have shown that a "bipolar see-saw" between NADW production and Antarctic Bottom Water (AABW) production in the Weddell Sea can occur in conjunction with freshening of the North Atlantic. However, this effect operates not through a slow ocean response but via a rapid atmospheric mechanism. As NADW reduces, colder temperatures in the North Atlantic, and Northern Hemisphere in general, are associated with higher surface pressure (increased atmospheric mass). Reduced mass in the Southern Hemisphere occurs in response, with lower pressure over the South Pole (an EOF #1 effect, the "high phase" of the Antarctic Oscillation).The lower pressure is associated with stronger west winds that generate an intensified Antarctic Circumpolar Current (ACC), which leads to longitudinal heat divergence in the South Atlantic (and heat convergence in the Southern Indian Ocean). Colder temperatures in the Weddell Sea region lead to sea ice growth, increased salinity and surface water density, and greater Weddell Sea Bottom Water production. Increased poleward transport of heat occurs in the South Atlantic in conjunction with increased bottom water production, but its convergence at high latitudes is not sufficient to offset the longitudinal heat divergence due to the intensified ACC. The colder temperatures at high latitudes in the South Atlantic increase the latitudinal temperature gradient, baroclinic instability, eddy energy and eddy poleward transport of momentum, helping to maintain the lower pressure over the pole in an interactive manner. The heat flux convergence in the Indian Ocean provides a warming tendency in that region, and overall global production of AABW remains unchanged. These results have implications for the interpretation of the ice core records of

  13. Low frequency variability of Southern Ocean jets

    NASA Astrophysics Data System (ADS)

    Thompson, A. F.; Richards, K. J.

    2011-12-01

    Both observations and high resolution numerical models show that the Southern Ocean circumpolar flow is concentrated in a large number (approximately 8 to 12) of narrow filamentary jets. It is shown here that coherent jets exhibit a range of low frequency variability, on time scales of months to years, that can lead to displacement and to intermittent formation and dissipation of jets. Using output from an eddy-resolving ocean general circulation model in local regions near topographic features, the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined. A novel approach that uses a time-dependent definition of the mean flow provides a clearer picture of eddy-mean flow interactions in regions with spatially and temporally varying flow structure. The dynamics are largely consistent with those in idealized quasi-geostrophic models, including topographically-organized and surface-enhanced Reynolds stress forcing of the mean flow. Jets form during periods of enhanced eddy activity, but may persist long after the eddy activity has decayed. Similarly, jets may evolve in a downstream sense, with jet formation localized near topography and undergoing modification in response to changing bathymetry. The evolution of both temperature and potential vorticity is used to show that the low-frequency variability of the jets impacts water mass structure and tracer transport. This study highlights various examples of Southern Ocean dynamics that will prove difficult to capture through existing parameterizations in coarser climate models.

  14. Low frequency variability of Southern Ocean jets

    NASA Astrophysics Data System (ADS)

    Thompson, Andrew F.; Richards, Kelvin J.

    2011-09-01

    Both observations and high resolution numerical models show that the Southern Ocean circumpolar flow is concentrated in a large number (approximately 8 to 12) of narrow filamentary jets. It is shown here that coherent jets exhibit a range of low frequency variability, on timescales of months to years, that can lead to displacement and to intermittent formation and dissipation of jets. Using output from an eddy-resolving ocean general circulation model in local regions near topographic features, the impact of energy exchange between eddy and mean flow components on jet persistence and variability is examined. A novel approach that uses a time-dependent definition of the mean flow provides a clearer picture of eddy-mean flow interactions in regions with spatially and temporally varying flow structure. The dynamics are largely consistent with those in idealized quasi-geostrophic models, including topographically-organized and surface-enhanced Reynolds stress forcing of the mean flow. Jets form during periods of enhanced eddy activity, but may persist long after the eddy activity has decayed. Similarly, jets may evolve in a downstream sense, with jet formation localized near topography and undergoing modification in response to changing bathymetry. The evolution of both temperature and potential vorticity is used to show that the low-frequency variability of the jets impacts water mass structure and tracer transport. This study highlights various examples of Southern Ocean dynamics that will prove difficult to capture through parameterizations in coarser climate models.

  15. Thickness diffusivity in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Eden, Carsten

    2006-06-01

    Thickness diffusivity ($\\kappa$) according to the Gent and McWilliams parameterisation which accounts for eddy-driven advection in the ocean, is estimated using output from an eddy-resolving model of the Southern Ocean. A physically meaningful definition of rotational eddy fluxes leads almost everywhere to positive $\\kappa$. Zonally averaged near surface values of $\\kappa$ remain smaller than 200 m2/s poleward of the polar front, increases between 60-45°S to about 600 m2/s and peak between 45-35° S at almost 3000 m2/s. $\\kappa$ stays high in the upper 500 m but decreases with depth and is essentially zero below 2500 m. In addition to the thickness diffusion ($\\kappa$) there is eddy-induced eastward (westward) advection of isopycnal thickness at the poleward (equatorward) flank of the ACC pointing toward strong anisotropic lateral mixing.

  16. Phytoplankton and cloudiness in the Southern Ocean.

    PubMed

    Meskhidze, Nicholas; Nenes, Athanasios

    2006-12-01

    The effect of ocean biological productivity on marine clouds is explored over a large phytoplankton bloom in the Southern Ocean with the use of remotely sensed data. Cloud droplet number concentration over the bloom was twice what it was away from the bloom, and cloud effective radius was reduced by 30%. The resulting change in the short-wave radiative flux at the top of the atmosphere was -15 watts per square meter, comparable to the aerosol indirect effect over highly polluted regions. This observed impact of phytoplankton on clouds is attributed to changes in the size distribution and chemical composition of cloud condensation nuclei. We propose that secondary organic aerosol, formed from the oxidation of phytoplankton-produced isoprene, can affect chemical composition of marine cloud condensation nuclei and influence cloud droplet number. Model simulations support this hypothesis, indicating that 100% of the observed changes in cloud properties can be attributed to the isoprene secondary organic aerosol.

  17. Ceilometer measurements in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    McDonald, Adrian; Alexander, Simon; French, John; Harvey, Mike; Ichoja, Andrew; Klekociuk, Andrew; Plank, Graeme; Katurji, Marwan

    2016-04-01

    Current climate models display a consistent deficit of reflected shortwave radiation over the Southern Ocean which is mainly due to the poor representation of clouds. Recent work has also shown that reanalysis also perform poorly relative to satellite observations in terms of cloud fraction. In particular, satellite observations have shown that low-level clouds (with tops below 3 km) are ubiquitous over the Southern Ocean. But, most satellite instruments, even the current generation of active satellite instruments, have difficulties in sampling low level clouds. As part of the New Zealand Deep South challenge project focussed on improving the representation of clouds in the Southern Ocean, we have begun to deploy autonomous instruments on 'ships of opportunity'. This study discusses measurements from a Väisälä CL51 laser ceilometer and ancillary instruments on the first two research voyages in the Southern Ocean and initial results. The route of the first voyage covers a return trip from Wellington (New Zealand) to Terra Nova Bay (Antarctica) onboard the R/V Tangaroa and occurred in January to mid-February 2015. The second deployment is onboard the Aurora Australis Australian Antarctic Division supply ship and began in October 2015 and is planned to finish at Macquarie Island in March 2016. The sampling provided by the ships route allows the ceilometer measurements of the height of the cloud base in a region where limited data apart from, potentially biased, satellite measurements of low-level cloud exist. Analysis of the boundary layer height derived from the ceilometer is also presented. The climatological structure derived from the ceilometer measurements is first detailed. We then compare these measurements with satellite and ground-based observations. We then examine variations in these measurements relative to their meteorological context. Details of plans for future voyages are also detailed. We will also present a preliminary analysis of a case study of

  18. Observations of change in the Southern Ocean.

    PubMed

    Jacobs, Stan

    2006-07-15

    The Southern Ocean has been in a state of disequilibrium with its atmosphere and cryosphere during recent decades. Ocean station and drifting float observations have revealed rising temperatures in the upper 3000m. Salinity has declined in intermediate waters and more rapidly in the sparsely sampled high latitudes. Dissolved oxygen levels may also have decreased, but measurement accuracy is inconsistent. Sea ice area increased from 1979 to 1998, particularly in the Ross Sea, while a decline in ice extent since the early 1970s has been led by the Amundsen-Bellingshausen sector. Fresher waters with lower oxygen isotope content on the Pacific-Antarctic continental shelf are consistent with increased melting of continental ice. Newly forming bottom water has become colder and less salty downstream from that region, but generally warmer in the Weddell Sea. Many ice shelves have retreated or thinned, but others have grown and no trend is apparent in the large iceberg calving rate. Warming and isotherm shoaling within the polar gyres may result in part from changes in the Southern Annular Mode, which could facilitate deep-water access to the continental shelves. Sea-level rise over the past half century has a strong eustatic component and has recently accelerated. Observations over longer periods and with better spatial coverage are needed to better understand the processes causing these changes and their links to the Antarctic ice sheet. PMID:16782605

  19. A Southern Ocean mode of multidecadal variability

    NASA Astrophysics Data System (ADS)

    Le Bars, D.; Viebahn, J. P.; Dijkstra, H. A.

    2016-03-01

    A 250 year simulation of a strongly eddying global version of the Parallel Ocean Program (POP) model reveals a new mode of intrinsic multidecadal variability, the Southern Ocean Mode (SOM), with a period of 40-50 year. The peak-to-peak difference in the global ocean heat content within a multidecadal cycle is up to 60 ZJ. This change results from surface heat flux variations in the South Atlantic and propagation of temperature anomalies along the Antarctic Circumpolar Current and into the Weddell gyre around 30°E. The temperature anomalies propagate as deep as 5000 m along the isopycnals between 50°S and 30°S and induce multidecadal changes in the Atlantic Meridional Overturning Circulation. A positive feedback loop between the generation of eddies through baroclinic instability and the dynamics of the mean circulation is essential for the existence of the SOM. The dominant physics appears similar to that responsible for variability found in a three-layer quasi-geostrophic eddy-resolving model. This combined with the fact that the SOM is not found in a noneddying version of the same global POP model further suggests that eddy processes are crucial for its existence and/or excitation.

  20. The reinvigoration of the Southern Ocean carbon sink.

    PubMed

    Landschützer, Peter; Gruber, Nicolas; Haumann, F Alexander; Rödenbeck, Christian; Bakker, Dorothee C E; van Heuven, Steven; Hoppema, Mario; Metzl, Nicolas; Sweeney, Colm; Takahashi, Taro; Tilbrook, Bronte; Wanninkhof, Rik

    2015-09-11

    Several studies have suggested that the carbon sink in the Southern Ocean-the ocean's strongest region for the uptake of anthropogenic CO2 -has weakened in recent decades. We demonstrated, on the basis of multidecadal analyses of surface ocean CO2 observations, that this weakening trend stopped around 2002, and by 2012, the Southern Ocean had regained its expected strength based on the growth of atmospheric CO2. All three Southern Ocean sectors have contributed to this reinvigoration of the carbon sink, yet differences in the processes between sectors exist, related to a tendency toward a zonally more asymmetric atmospheric circulation. The large decadal variations in the Southern Ocean carbon sink suggest a rather dynamic ocean carbon cycle that varies more in time than previously recognized.

  1. Atmosphere-ocean interactions in the Pacific Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lamy, F.; Gersonde, R.; Purcell, C.; Winckler, G.; Tiedemann, R.; Knorr, G.

    2014-12-01

    Atmosphere-ocean interactions play an important role for understanding processes and feedbacks in the Southern Ocean (SO) that play a key role for explaining the variability in atmospheric CO2 concentrations. The most important atmospheric forcing at high and mid-latitudes of the Southern Hemisphere is the westerly wind belt which strongly impacts the strength and extension of the Antarctic Circumpolar Current (ACC), upwelling of deep-water masses, and also controls the back-flow of intermediate waters to the tropics. We combine sea surface temperature, current strength, and mineral dust proxy data from the Pacific SO including Drake Passage with climate model results. Our data show that Drake Passage throughflow was reduced and the ACC generally weakened during the last glacial. The reduced Drake Passage throughflow was accompanied by a pronounced northward extension of the Antarctic cold-water sphere in the Southeast Pacific sector and stronger export of surface and intermediate water into the South Pacific gyre. These oceanographic changes are consistent with reduced westerly winds within the modern maximum wind strength zone over the subantarctic ACC and reduced wind forcing due to extended sea-ice further south. Despite of reduced winds in the core of the westerlies, we observe 3-fold higher dust deposition during glacial periods in the Pacific SO. This observation may be explained by a combination of factors including more expanded arid dust source areas in Australia and a northward extent or enhancement of the westerlies over Southeast Australia during glacials that would plausibly increase the dust uptake and export into the Pacific SO. Such scenario would imply stronger westerlies at the present northernmost margin of the wind belt coeval with weaker core westerlies and reduced ACC strength including Drake Passage throughflow during glacials. These results have strong implications for the global meridional overturning circulation and the interbasin

  2. Extratropical Cyclone in the Southern Ocean

    NASA Technical Reports Server (NTRS)

    2001-01-01

    These images from the Multi-angle Imaging SpectroRadiometer portray an occluded extratropical cyclone situated in the Southern Ocean, about 650 kilometers south of the Eyre Peninsula, South Australia.

    Parts of the Yorke Peninsula and a portion of the Murray-Darling River basin are visible between the clouds near the top of the left-hand image, a true-color view from MISR's nadir(vertical-viewing) camera. Retrieved cloud-tracked wind velocities are indicated by the superimposed arrows. The image on the right displays cloud-top heights. Areas where cloud heights could not be retrieved are shown in black. Both the wind vectors and the cloud heights were derived using data from multiple MISR cameras within automated computer processing algorithms. The stereoscopic algorithms used to generate these results are still being refined, and future versions of these products may show modest changes.

    Extratropical cyclones are the dominant weather system at midlatitudes, and the term is used generically for region allow-pressure systems in the mid- to high-latitudes. In the southern hemisphere, cyclonic rotation is clockwise. These storms obtain their energy from temperature differences between air masses on either side of warm and cold fronts, and their characteristic pattern is of warm and cold fronts radiating out from a migrating low pressure center which forms, deepens, and dissipates as the fronts fold and collapse on each other. The center of this cyclone has started to decay, with the band of cloud to the south most likely representing the main front that was originally connected with the cyclonic circulation.

    These views were acquired on October 11, 2001 during Terra orbit 9650, and represent an area of about 380 kilometers x 1900 kilometers.

  3. Extratropical Cyclone in the Southern Ocean

    NASA Technical Reports Server (NTRS)

    2002-01-01

    These images from the Multi-angle Imaging SpectroRadiometer (MISR) portray an occluded extratropical cyclone situated in the Southern Ocean, about 650 kilometers south of the Eyre Peninsula, South Australia. The left-hand image, a true-color view from MISR's nadir (vertical-viewing) camera, shows clouds just south of the Yorke Peninsula and the Murray-Darling river basin in Australia. Retrieved cloud-tracked wind velocities are indicated by the superimposed arrows. The image on the right displays cloud-top heights. Areas where cloud heights could not be retrieved are shown in black. Both the wind vectors and the cloud heights were derived using data from multiple MISR cameras within automated computer processing algorithms. The stereoscopic algorithms used to generate these results are still being refined, and future versions of these products may show modest changes. Extratropical cyclones are the dominant weather system at midlatitudes, and the term is used generically for regional low-pressure systems in the mid- to high-latitudes. In the southern hemisphere, cyclonic rotation is clockwise. These storms obtain their energy from temperature differences between air masses on either side of warm and cold fronts, and their characteristic pattern is of warm and cold fronts radiating out from a migrating low pressure center which forms, deepens, and dissipates as the fronts fold and collapse on each other. The center of this cyclone has started to decay, with the band of cloud to the south most likely representing the main front that was originally connected with the cyclonic circulation. These views were acquired on October 11, 2001, and the large view represents an area of about 380 kilometers x 1900 kilometers. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team.

  4. Exploring the southern ocean response to climate change

    NASA Technical Reports Server (NTRS)

    Martinson, Douglas G.; Rind, David; Parkinson, Claire

    1993-01-01

    The purpose of this project was to couple a regional (Southern Ocean) ocean/sea ice model to the existing Goddard Institute for Space Science (GISS) atmospheric general circulation model (GCM). This modification recognizes: the relative isolation of the Southern Ocean; the need to account, prognostically, for the significant air/sea/ice interaction through all involved components; and the advantage of translating the atmospheric lower boundary (typically the rapidly changing ocean surface) to a level that is consistent with the physical response times governing the system evolution (that is, to the base of the fast responding ocean surface layer). The deeper ocean beneath this layer varies on time scales several orders of magnitude slower than the atmosphere and surface ocean, and therefore the boundary between the upper and deep ocean represents a more reasonable fixed boundary condition.

  5. Sea Ice on the Southern Ocean

    NASA Technical Reports Server (NTRS)

    Jacobs, Stanley S.

    1998-01-01

    Year-round satellite records of sea ice distribution now extend over more than two decades, providing a valuable tool to investigate related characteristics and circulations in the Southern Ocean. We have studied a variety of features indicative of oceanic and atmospheric interactions with Antarctic sea ice. In the Amundsen & Bellingshausen Seas, sea ice extent was found to have decreased by approximately 20% from 1973 through the early 1990's. This change coincided with and probably contributed to recently warmer surface conditions on the west side of the Antarctic Peninsula, where air temperatures have increased by approximately 0.5 C/decade since the mid-1940's. The sea ice decline included multiyear cycles of several years in length superimposed on high interannual variability. The retreat was strongest in summer, and would have lowered the regional mean ice thickness, with attendant impacts upon vertical heat flux and the formation of snow ice and brine. The cause of the regional warming and loss of sea ice is believed to be linked to large-scale circulation changes in the atmosphere and ocean. At the eastern end of the Weddell Gyre, the Cosmonaut Polyna revealed greater activity since 1986, a recurrence pattern during recent winters and two possible modes of formation. Persistence in polynya location was noted off Cape Ann, where the coastal current can interact more strongly with the Antarctic Circumpolar Current. As a result of vorticity conservation, locally enhanced upwelling brings warmer deep water into the mixed layer, causing divergence and melting. In the Ross Sea, ice extent fluctuates over periods of several years, with summer minima and winter maxima roughly in phase. This leads to large interannual cycles of sea ice range, which correlate positively with meridinal winds, regional air temperatures and subsequent shelf water salinities. Deep shelf waters display considerable interannual variability, but have freshened by approximately 0.03/decade

  6. An observing system simulation for Southern Ocean carbon dioxide uptake.

    PubMed

    Majkut, Joseph D; Carter, Brendan R; Frölicher, Thomas L; Dufour, Carolina O; Rodgers, Keith B; Sarmiento, Jorge L

    2014-07-13

    The Southern Ocean is critically important to the oceanic uptake of anthropogenic CO2. Up to half of the excess CO2 currently in the ocean entered through the Southern Ocean. That uptake helps to maintain the global carbon balance and buffers transient climate change from fossil fuel emissions. However, the future evolution of the uptake is uncertain, because our understanding of the dynamics that govern the Southern Ocean CO2 uptake is incomplete. Sparse observations and incomplete model formulations limit our ability to constrain the monthly and annual uptake, interannual variability and long-term trends. Float-based sampling of ocean biogeochemistry provides an opportunity for transforming our understanding of the Southern Ocean CO2 flux. In this work, we review current estimates of the CO2 uptake in the Southern Ocean and projections of its response to climate change. We then show, via an observational system simulation experiment, that float-based sampling provides a significant opportunity for measuring the mean fluxes and monitoring the mean uptake over decadal scales.

  7. Decreased calcification in the Southern Ocean over the satellite record

    NASA Astrophysics Data System (ADS)

    Freeman, Natalie M.; Lovenduski, Nicole S.

    2015-03-01

    Widespread ocean acidification is occurring as the ocean absorbs anthropogenic carbon dioxide from the atmosphere, threatening marine ecosystems, particularly the calcifying plankton that provide the base of the marine food chain and play a key role within the global carbon cycle. We use satellite estimates of particulate inorganic carbon (PIC), surface chlorophyll, and sea surface temperature to provide a first estimate of changing calcification rates throughout the Southern Ocean. From 1998 to 2014 we observe a 4% basin-wide reduction in summer calcification, with ˜9% reductions in large regions (˜1 × 106 km2) of the Pacific and Indian sectors. Southern Ocean trends are spatially heterogeneous and primarily driven by changes in PIC concentration (suspended calcite), which has declined by ˜24% in these regions. The observed decline in Southern Ocean calcification and PIC is suggestive of large-scale changes in the carbon cycle and provides insight into organism vulnerability in a changing environment.

  8. Intrathermocline eddies in the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nauw, J. J.; van Aken, H. M.; Lutjeharms, J. R. E.; de Ruijter, W. P. M.

    2006-03-01

    In 2001, two relatively saline intrathermocline eddies (ITEs) were observed southeast of Madagascar at 200 m depth. They are characterized by a subsurface salinity maximum of over 35.8 at potential temperatures between 18° and 22°C. The oxygen concentrations within the high salinity cores are slightly elevated compared with those of the surrounding water. Their horizontal extent is about 180 km, several times the Rossby deformation radius, while their thickness is about 150 m. The observed circulation around the ITEs is anticyclonic and maximum velocities of 20 to 30 cm/s are observed at 200 m depth. In these cores the potential density anomaly (25.0 < γ < 25.9 kg/m3) has a relatively low vertical gradient and therefore a low planetary potential vorticity. The hydrographic properties of these ITEs are distinctly different from those of the surrounding thermocline water, and especially from the much fresher water mass in the East Madagascar Current. Strong evidence has been found that the distant formation area of the water mass in the ITEs is the subtropical Southern Indian Ocean east of 90°E and south of 25°S, where Subtropical Underwater (STUW) is formed with similar characteristics. Similar high-salinity cores as the ITEs are also found in the thermocline around 200 m depth along an almost zonal section between Madagascar and 100°E. Differences between the hydrographic properties of these cores and the ITEs near Madagascar may partly be explained by interannual variations in the temperature and salinity of the surface mixed layer water in the possible formation area.

  9. Climate science: Southern Ocean freshened by sea ice

    NASA Astrophysics Data System (ADS)

    Maksym, Ted

    2016-09-01

    The Southern Ocean has become less salty during the past few decades. An analysis of sea-ice transport in the ocean suggests that this phenomenon can be explained by coupled changes in sea-ice drift and thickness. See Letter p.89

  10. Southern Ocean warming delayed by circumpolar upwelling and equatorward transport

    NASA Astrophysics Data System (ADS)

    Armour, Kyle C.; Marshall, John; Scott, Jeffery R.; Donohoe, Aaron; Newsom, Emily R.

    2016-07-01

    The Southern Ocean has shown little warming over recent decades, in stark contrast to the rapid warming observed in the Arctic. Along the northern flank of the Antarctic Circumpolar Current, however, the upper ocean has warmed substantially. Here we present analyses of oceanographic observations and general circulation model simulations showing that these patterns--of delayed warming south of the Antarctic Circumpolar Current and enhanced warming to the north--are fundamentally shaped by the Southern Ocean's meridional overturning circulation: wind-driven upwelling of unmodified water from depth damps warming around Antarctica; greenhouse gas-induced surface heat uptake is largely balanced by anomalous northward heat transport associated with the equatorward flow of surface waters; and heat is preferentially stored where surface waters are subducted to the north. Further, these processes are primarily due to passive advection of the anomalous warming signal by climatological ocean currents; changes in ocean circulation are secondary. These findings suggest the Southern Ocean responds to greenhouse gas forcing on the centennial, or longer, timescale over which the deep ocean waters that are upwelled to the surface are warmed themselves. It is against this background of gradual warming that multidecadal Southern Ocean temperature trends must be understood.

  11. Microphysics and Southern Ocean Cloud Feedback

    NASA Astrophysics Data System (ADS)

    McCoy, Daniel T.

    Global climate models (GCMs) change their cloud properties in the Southern Ocean (SO) with warming in a qualitatively consistent fashion. Cloud albedo increases in the mid-latitudes and cloud fraction decreases in the subtropics. This creates a distinctive 'dipole' structure in the SW cloud feedback. However, the shape of the dipole varies from model to model. In this thesis we discuss the microphysical mechanisms underlying the SW cloud feedback over the mid-latitude SO. We will focus on the negative lobe of the dipole. The negative SW cloud feedback in the mid-latitudes is created by transitions from ice to liquid in models. If ice transitions to liquid in mixed-phase clouds the cloud albedo increases because ice crystals are larger than liquid droplets and therefore more reflective for a constant mass of water. Decreases in precipitation efficiency further enhance this effect by decreasing sinks of cloud water. This transition is dependent on the mixed-phase cloud parameterization. Parameterizations vary wildly between models and GCMs disagree by up to 35 K on the temperature where ice and liquid are equally prevalent. This results in a wide spread in the model predictions of the increase in liquid water path (LWP, where the path is the vertically integrated mass of water) with warming that drives the negative optical depth cloud feedback. It is found that this disagreement also results in a wide array of climate mean-states as models that create liquid at lower temperatures have a higher mean-state LWP, lower ice water path (IWP), and higher condensed (ice and liquid) water path (CWP). This presents a problem in climate models. GCMs need to have a reasonable planetary albedo in their climate mean-state. We show evidence that GCMs have tuned cloud fraction to compensate for the variation in mid-latitude cloud albedo driven by the mixed-phase cloud parameterization. This tuning results in mid-latitude clouds that are both too few and too bright as well as a

  12. Recent changes in the ventilation of the southern oceans.

    PubMed

    Waugh, Darryn W; Primeau, Francois; Devries, Tim; Holzer, Mark

    2013-02-01

    Surface westerly winds in the Southern Hemisphere have intensified over the past few decades, primarily in response to the formation of the Antarctic ozone hole, and there is intense debate on the impact of this on the ocean's circulation and uptake and redistribution of atmospheric gases. We used measurements of chlorofluorocarbon-12 (CFC-12) made in the southern oceans in the early 1990s and mid- to late 2000s to examine changes in ocean ventilation. Our analysis of the CFC-12 data reveals a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters, suggesting that the formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans. PMID:23372011

  13. Recent changes in the ventilation of the southern oceans.

    PubMed

    Waugh, Darryn W; Primeau, Francois; Devries, Tim; Holzer, Mark

    2013-02-01

    Surface westerly winds in the Southern Hemisphere have intensified over the past few decades, primarily in response to the formation of the Antarctic ozone hole, and there is intense debate on the impact of this on the ocean's circulation and uptake and redistribution of atmospheric gases. We used measurements of chlorofluorocarbon-12 (CFC-12) made in the southern oceans in the early 1990s and mid- to late 2000s to examine changes in ocean ventilation. Our analysis of the CFC-12 data reveals a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters, suggesting that the formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans.

  14. Recent Changes in the Ventilation of the Southern Oceans

    NASA Astrophysics Data System (ADS)

    Waugh, Darryn W.; Primeau, Francois; DeVries, Tim; Holzer, Mark

    2013-02-01

    Surface westerly winds in the Southern Hemisphere have intensified over the past few decades, primarily in response to the formation of the Antarctic ozone hole, and there is intense debate on the impact of this on the ocean's circulation and uptake and redistribution of atmospheric gases. We used measurements of chlorofluorocarbon-12 (CFC-12) made in the southern oceans in the early 1990s and mid- to late 2000s to examine changes in ocean ventilation. Our analysis of the CFC-12 data reveals a decrease in the age of subtropical subantarctic mode waters and an increase in the age of circumpolar deep waters, suggesting that the formation of the Antarctic ozone hole has caused large-scale coherent changes in the ventilation of the southern oceans.

  15. Controls on biogenic silica burial in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Chase, Zanna; Kohfeld, Karen E.; Matsumoto, Katsumi

    2015-10-01

    Understanding the controls on opal export in the Southern Ocean can inform both the prediction of how the leakage of silicic acid from the Southern Ocean responds to climate and the interpretation of paleo-proxies. We have compiled a database of 185 230Thorium-normalized opal burial rates and 493 opal concentration measurements in Southern Ocean sediments and matched these with environmental climatologies. By subdividing the Southern Ocean on the basis of oceanographic regions and interpolating the opal burial rates, we estimate a total biogenic Si burial south of 40°S of 2.3 ± 1.0 Tmol Si yr-1. In both the seasonally ice-covered and permanently ice-free regions we can explain 73% of opal burial variability from surface ocean properties. Where sea ice is present for at least part of the year, the length of the ice-free season determines the upper limit of opal burial in the underlying sediments. In the ice-free regions of the Southern Ocean, the supply of silicic acid through winter mixing is the most important factor. Our results do not support a strong role of iron in controlling opal burial. We do however find that satellite-derived net primary production increases with increasing (modeled) dust delivery. These findings support the decoupling between carbon and opal fluxes in the Southern Ocean. When corrected for opal dissolution, the observed opal fluxes are in reasonable agreement with fluxes simulated using an ocean biogeochemical model. However, the results suggest current preservation algorithms for opal could be improved by incorporating the composition of particle flux, not only its magnitude.

  16. Southern rim of Pacific Ocean basin: southern Andes to southern Alps

    SciTech Connect

    Dalziel, I.W.D.; Garrett, S.W.; Grunow, A.M.; Pankhurst, R.J.; Storey, B.C.; Vennum, W.R.

    1986-07-01

    Between the southern Andes of Tierra del Fuego and the southern Alps of New Zealand lies the least accessible and geologically least explored part of the Pacific Ocean basin. A joint United Kingdom-United States project was initiated in 1983 to elucidate the geologic history and structure of the Pacific margin of Antarctica from the Antarctic Peninsula to Pine Island Bay at approximately lone. 105/sup 0/W. The first season (1983-1984) of this West Antarctic Tectonics Project was spent in the Ellsworth-Whitmore crustal block, and the second (1984-1985) in the Thurston Island crustal block. The project involves structural and general field geology, petrology, geochemistry, paleomagnetism, and airborne geophysics (magnetics and radar ice echo sounding). A final geologic season will be spent in the Pensacola Mountains of the Transantarctic Range in 1987-1988.

  17. Krill excretion boosts microbial activity in the Southern Ocean.

    PubMed

    Arístegui, Javier; Duarte, Carlos M; Reche, Isabel; Gómez-Pinchetti, Juan L

    2014-01-01

    Antarctic krill are known to release large amounts of inorganic and organic nutrients to the water column. Here we test the role of krill excretion of dissolved products in stimulating heterotrophic bacteria on the basis of three experiments where ammonium and organic excretory products released by krill were added to bacterial assemblages, free of grazers. Our results demonstrate that the addition of krill excretion products (but not of ammonium alone), at levels expected in krill swarms, greatly stimulates bacteria resulting in an order-of-magnitude increase in growth and production. Furthermore, they suggest that bacterial growth rate in the Southern Ocean is suppressed well below their potential by resource limitation. Enhanced bacterial activity in the presence of krill, which are major sources of DOC in the Southern Ocean, would further increase recycling processes associated with krill activity, resulting in highly efficient krill-bacterial recycling that should be conducive to stimulating periods of high primary productivity in the Southern Ocean.

  18. Thaumeledone and other deep water octopodids from the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Allcock, A. L.; Collins, M. A.; Piatkowski, U.; Vecchione, M.

    2004-07-01

    Recent trawling in the Southern Ocean has yielded an unusual and relatively large collection of deep-sea octopods, comprising four species in two genera. Several deep-sea genera, which are inadequately characterised, have been reported previously from the Southern Ocean. Within this paper, all the relevant historical type material has been examined and a full revision has been undertaken. Species previously considered to be representative of the genus Bentheledone have either been moved to Thaumeledone or are considered nomen dubium. A revised diagnosis of Thaumeledone is provided together with redescriptions of its Southern Ocean species as well as a description of a new species. A new genus has been erected to accommodate the remainder of the new specimens.

  19. Incorporating Phaeocystis into a Southern Ocean ecosystem model

    NASA Astrophysics Data System (ADS)

    Wang, Shanlin; Moore, J. Keith

    2011-01-01

    Phaeocystis antarctica is an important phytoplankton species in the Southern Ocean. We incorporated P. antarctica into the biogeochemical elemental cycling ocean model to study Southern Ocean ecosystem dynamics and biogeochemistry. The optimum values of ecological parameters for Phaeocystis were sought through synthesizing laboratory and field observations, and the model output was evaluated with observed chlorophyll a, carbon biomass, and nutrient distributions. Several factors have been proposed to control Southern Ocean ecosystem structure, including light adaptation, iron uptake capability, and loss processes. Optimum simulation results were obtained when P. antarctica had a relatively high α (P-I curve initial slope) value and a higher half-saturation constant for iron uptake than other phytoplankton. Simulation results suggested that P. antarctica had a competitive advantage under low irradiance levels, especially in the Ross Sea and Weddell Sea. However, the distributions of P. antarctica and diatoms were also strongly influenced by iron availability. Although grazing rates had an influence on total biomass, our simulations did not show a strong influence of grazing pressure in the competition between P. antarctica and diatoms. However, limited observations and the relative simplicity of zooplankton in our model suggest further research is needed. Overall, P. antarctica contributed ˜13% of annual primary production and ˜19% of sinking carbon export in the Southern Ocean (>40°S) in our best case simulation. At higher latitudes (>60°S) P. antarctica accounts for ˜23% of annual primary production and ˜30% of sinking carbon export.

  20. The Need for a Branch Campus of Ocean County College in Southern Ocean County.

    ERIC Educational Resources Information Center

    Parrish, Richard M.; Harris, David W.

    A study was conducted to determine the feasibility of establishing a branch campus of Ocean County College (OCC) in southern Ocean County, New Jersey. Specific variables examined during the study included demographic characteristics; transportation systems, in terms of both public access and roadway networks; land usage; the history of education…

  1. Ocean transport and variability studies of the South Pacific, Southern, and Indian Oceans

    NASA Technical Reports Server (NTRS)

    Church, John A.; Cresswell, G. R.; Nilsson, C. S.; Mcdougall, T. J.; Coleman, R.; Rizos, C.; Penrose, J.; Hunter, J. R.; Lynch, M. J.

    1991-01-01

    The objectives of this study are to analyze ocean dynamics in the western South Pacific and the adjacent Southern Ocean and the eastern Indian Ocean. Specifically, our objectives for these three regions are, for the South Pacific Ocean: (1) To estimate the volume transport of the east Australian Current (EAC) along the Australian coast and in the Tasman Front, and to estimate the time variability (on seasonal and interannual time scales) of this transport. (2) To contribute to estimating the meridional heat and freshwater fluxes (and their variability) at about 30 deg S. Good estimates of the transport in the western boundary current are essential for accurate estimates of these fluxes. (3) To determine how the EAC transport (and its extension, the Tasman Front and the East Auckland Current) closes the subtropical gyre of the South Pacific and to better determine the structure at the confluence of this current and the Antarctic Circumpolar Current. (4) To examine the structure and time variability of the circulation in the western South Pacific and the adjacent Southern Ocean, particularly at the Tasman Front. For the Indian Ocean: (5) To study the seasonal interannual variations in the strength of the Leeuwin Current. (6) To monitor the Pacific-Indian Ocean throughflow and the South Equatorial and the South Java Currents between northwest Australia and Indonesia. (7) To study the processes that form the water of the permanent oceanic thermocline and, in particular, the way in which new thermocline water enters the permanent thermocline in late winter and early spring as the mixed layer restratifies. For the Southern Ocean: (8) To study the mesoscale and meridional structure of the Southern Ocean between 150 deg E and 170 deg E; in particular, to describe the Antarctic frontal system south of Tasmania and determine its interannual variability; to estimate the exchanges of heat, salt, and other properties between the Indian and Pacific Oceans; and to investigate the

  2. Enhanced Weathering Strategies for Stabilizing Climate and Averting Ocean Acidification - Supplementary Information

    NASA Technical Reports Server (NTRS)

    Taylor, Lyla L.; Quirk, Joe; Thorley, Rachel M. S.; Kharecha, Pushker A.; Hansen, James; Ridgwell, Andy; Lomas, Mark R.; Banwart, Steve A.; Beerling, David J.

    2015-01-01

    Chemical breakdown of rocks, weathering, is an important but very slow part of the carbon cycle that ultimately leads to CO2 being locked up in carbonates on the ocean floor. Artificial acceleration of this carbon sink via distribution of pulverized silicate rocks across terrestrial landscapes may help offset anthropogenic CO2 emissions. We show that idealized enhanced weathering scenarios over less than a third of tropical land could cause significant drawdown of atmospheric CO2 and ameliorate ocean acidification by 2100. Global carbon cycle modelling driven by ensemble Representative Concentration Pathway (RCP) projections of twenty-first-century climate change (RCP8.5, business-as-usual; RCP4.5, medium-level mitigation) indicates that enhanced weathering could lower atmospheric CO2 by 30-300 ppm by 2100, depending mainly on silicate rock application rate (1 kg or 5 kg m(exp. -2) yr (exp -1)) and composition. At the higher application rate, end-of-century ocean acidification is reversed under RCP4.5 and reduced by about two-thirds under RCP8.5. Additionally, surface ocean aragonite saturation state, a key control on coral calcification rates, is maintained above 3.5 throughout the low latitudes, thereby helping maintain the viability of tropical coral reef ecosystems. However, we highlight major issues of cost, social acceptability, and potential unanticipated consequences that will limit utilization and emphasize the need for urgent efforts to phase down fossil fuel emissions.

  3. Will krill fare well under Southern Ocean acidification?

    PubMed

    Kawaguchi, So; Kurihara, Haruko; King, Robert; Hale, Lillian; Berli, Thomas; Robinson, James P; Ishida, Akio; Wakita, Masahide; Virtue, Patti; Nicol, Stephen; Ishimatsu, Atsushi

    2011-04-23

    Antarctic krill embryos and larvae were experimentally exposed to 380 (control), 1000 and 2000 µatm pCO₂ in order to assess the possible impact of ocean acidification on early development of krill. No significant effects were detected on embryonic development or larval behaviour at 1000 µatm pCO₂; however, at 2000 µatm pCO₂ development was disrupted before gastrulation in 90 per cent of embryos, and no larvae hatched successfully. Our model projections demonstrated that Southern Ocean sea water pCO₂ could rise up to 1400 µatm in krill's depth range under the IPCC IS92a scenario by the year 2100 (atmospheric pCO₂ 788 µatm). These results point out the urgent need for understanding the pCO₂-response relationship for krill developmental and later stages, in order to predict the possible fate of this key species in the Southern Ocean.

  4. Intense summer Si-recycling in the surface Southern Ocean

    NASA Astrophysics Data System (ADS)

    Beucher, Charlotte; Tréguer, Paul; Hapette, Ana-Maria; Corvaisier, Rudolph; Metzl, Nicolas; Pichon, Jean-Jacques

    2004-05-01

    Si-cycle in surface waters was investigated in summer 2003 during a transect conducted from south-Australia to Antarctica. Diatoms dominated the microphytoplankton. Silicic acid was depleted up to 60°S a subsurface maximum of biogenic silica (= biosilica) was observed in the Permanent Open Ocean Zone. In the 100-0.01% light zone, the ratio of depth-integrated biosilica dissolution rate (D) to depth-integrated biosilica production rate (P) ranged between 0 to 3.1, being >1 for 5 of our 6 stations. The biosilica dissolution was related to the percentage of dead diatoms but not to the temperature and might be, at least partially, under bacteria mediation. This study shows that during summer the Southern Ocean silicate pump can be much less efficient than usually expected. Existence of scenarios with intense surface Si-recycling in the Southern Ocean has major consequences both for modelers and paleoceanographers.

  5. Dimethylsulfide air/sea gas transfer in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    De Bruyn, W. J.; Bell, T. G.; Marandino, C.; Saltzman, E. S.; Miller, S. D.; Law, C. S.; Smith, M. J.

    2012-12-01

    Air/sea dimethylsulfide (DMS) fluxes were measured by eddy correlation over the Southern Ocean (Feb/March 2012) aboard the R/V Tangaroa during the Surface Ocean Aerosol Production (SOAP) study. Atmospheric and seawater DMS were measured by atmospheric pressure chemical ionization mass spectrometry (API-CIMS). Seawater DMS was measured continuously from the ship underway system using a porous membrane equilibrator. The study included measurements inside and outside a dinoflagellate bloom of large areal extent, with seawater DMS levels ranging up to 20 nM. Horizontal wind speeds of up to 20 m/sec were encountered. Gas transfer coefficients were calculated from eddy covariance DMS flux measurements and the air-sea concentration gradient. This study represents a significant addition to the limited database of direct gas transfer measurements in the Southern Ocean.

  6. Fisheries in the Southern Ocean: an ecosystem approach.

    PubMed

    Kock, Karl-Hermann; Reid, Keith; Croxall, John; Nicol, Stephen

    2007-12-29

    The Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) is bound by its Article II, 3 to follow an ecosystem approach to management. This approach has been extended to the application of a precautionary approach in the late 1980s. In our review, we deal primarily with the science-related aspects of CCAMLR and its development towards an ecosystem approach to the management of the living resources of the Southern Ocean. To assist the Commission in meeting its objectives, as set out in Article II, 3, the Scientific Committee established the CCAMLR Ecosystem Monitoring Programme to detect possible effects of krill fishing on the performance of top-level predators, such as albatrosses, penguins, petrels and fur seals. Fisheries in the Southern Ocean followed the fate of other fisheries worldwide in which target species were depleted to low level one after the other. Currently, two types of fisheries are open: the longline fisheries on Patagonian toothfish (Dissostichus eleginoides) and Antarctic toothfish (Dissostichus mawsoni) and the trawl fisheries on mackerel icefish (Champsocephalus gunnari). Both fisheries are managed in a single-species context, however, with conservation measures in place to protect by-catch species, such as rattails (Macrouridae) and skates and rays (Rajidae). Two major problems still exist in fisheries in the Southern Ocean: the by-catch of birds in longline fisheries primarily in the Indian Ocean and the high level of IUU fishing again in the Indian Ocean. Both, the by-catch of birds and high IUU catches undermine the credibility of CCAMLR to safeguard the marine living resources in the Southern Ocean.

  7. Antarctic and Southern Ocean influences on Late Pliocene global cooling

    PubMed Central

    McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D.

    2012-01-01

    The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ∼3.3 Ma, followed by a coastal sea surface temperature cooling of ∼2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world. PMID:22496594

  8. Antarctic and Southern Ocean influences on Late Pliocene global cooling

    USGS Publications Warehouse

    McKay, Robert; Naish, Tim; Carter, Lionel; Riesselman, Christina; Dunbar, Robert; Sjunneskog, Charlotte; Winter, Diane; Sangiorgi, Francesca; Warren, Courtney; Pagani, Mark; Schouten, Stefan; Willmott, Veronica; Levy, Richard; DeConto, Robert; Powell, Ross D.

    2012-01-01

    The influence of Antarctica and the Southern Ocean on Late Pliocene global climate reconstructions has remained ambiguous due to a lack of well-dated Antarctic-proximal, paleoenvironmental records. Here we present ice sheet, sea-surface temperature, and sea ice reconstructions from the ANDRILL AND-1B sediment core recovered from beneath the Ross Ice Shelf. We provide evidence for a major expansion of an ice sheet in the Ross Sea that began at ~3.3 Ma, followed by a coastal sea surface temperature cooling of ~2.5 °C, a stepwise expansion of sea ice, and polynya-style deep mixing in the Ross Sea between 3.3 and 2.5 Ma. The intensification of Antarctic cooling resulted in strengthened westerly winds and invigorated ocean circulation. The associated northward migration of Southern Ocean fronts has been linked with reduced Atlantic Meridional Overturning Circulation by restricting surface water connectivity between the ocean basins, with implications for heat transport to the high latitudes of the North Atlantic. While our results do not exclude low-latitude mechanisms as drivers for Pliocene cooling, they indicate an additional role played by southern high-latitude cooling during development of the bipolar world.

  9. Antarctic warming driven by internal Southern Ocean deep convection oscillations

    NASA Astrophysics Data System (ADS)

    Martin, Torge; Pedro, Joel B.; Steig, Eric J.; Jochum, Markus; Park, Wonsun; Rasmussen, Sune O.

    2016-04-01

    Simulations with the free-running, complex coupled Kiel Climate Model (KCM) show that heat release associated with recurring Southern Ocean deep convection can drive centennial-scale Antarctic temperature variations of 0.5-2.0 °C. We propose a mechanism connecting the intrinsic ocean variability with Antarctic warming that involves the following three steps: Preconditioning: heat supplied by the lower branch of the Atlantic Meridional Overturning Circulation (AMOC) accumulates at depth in the Southern Ocean, trapped by the Weddell Gyre circulation; Convection onset: wind and/or sea-ice changes tip the preconditioned, thermally unstable system into the convective state; Antarctic warming: fast sea-ice-albedo feedbacks (on annual to decadal timescales) and slower Southern Ocean frontal and sea-surface temperature adjustments to the convective heat release (on multi-decadal to centennial timescales), drive an increase in atmospheric heat and moisture transport towards Antarctica resulting in warming over the continent. Further, we discuss the potential role of this mechanism to explain climate variability observed in Antarctic ice-core records.

  10. A Hierarchical Classification of Benthic Biodiversity and Assessment of Protected Areas in the Southern Ocean

    PubMed Central

    Douglass, Lucinda L.; Turner, Joel; Grantham, Hedley S.; Kaiser, Stefanie; Constable, Andrew; Nicoll, Rob; Raymond, Ben; Post, Alexandra; Brandt, Angelika; Beaver, Daniel

    2014-01-01

    An international effort is underway to establish a representative system of marine protected areas (MPAs) in the Southern Ocean to help provide for the long-term conservation of marine biodiversity in the region. Important to this undertaking is knowledge of the distribution of benthic assemblages. Here, our aim is to identify the areas where benthic marine assemblages are likely to differ from each other in the Southern Ocean including near-shore Antarctica. We achieve this by using a hierarchical spatial classification of ecoregions, bathomes and environmental types. Ecoregions are defined according to available data on biogeographic patterns and environmental drivers on dispersal. Bathomes are identified according to depth strata defined by species distributions. Environmental types are uniquely classified according to the geomorphic features found within the bathomes in each ecoregion. We identified 23 ecoregions and nine bathomes. From a set of 28 types of geomorphic features of the seabed, 562 unique environmental types were classified for the Southern Ocean. We applied the environmental types as surrogates of different assemblages of biodiversity to assess the representativeness of existing MPAs. We found that 12 ecoregions are not represented in MPAs and that no ecoregion has their full range of environmental types represented in MPAs. Current MPA planning processes, if implemented, will substantially increase the representation of environmental types particularly within 8 ecoregions. To meet internationally agreed conservation goals, additional MPAs will be needed. To assist with this process, we identified 107 spatially restricted environmental types, which should be considered for inclusion in future MPAs. Detailed supplementary data including a spatial dataset are provided. PMID:25032993

  11. Risk maps for Antarctic krill under projected Southern Ocean acidification

    NASA Astrophysics Data System (ADS)

    Kawaguchi, S.; Ishida, A.; King, R.; Raymond, B.; Waller, N.; Constable, A.; Nicol, S.; Wakita, M.; Ishimatsu, A.

    2013-09-01

    Marine ecosystems of the Southern Ocean are particularly vulnerable to ocean acidification. Antarctic krill (Euphausia superba; hereafter krill) is the key pelagic species of the region and its largest fishery resource. There is therefore concern about the combined effects of climate change, ocean acidification and an expanding fishery on krill and ultimately, their dependent predators--whales, seals and penguins. However, little is known about the sensitivity of krill to ocean acidification. Juvenile and adult krill are already exposed to variable seawater carbonate chemistry because they occupy a range of habitats and migrate both vertically and horizontally on a daily and seasonal basis. Moreover, krill eggs sink from the surface to hatch at 700-1,000m (ref. ), where the carbon dioxide partial pressure (pCO2) in sea water is already greater than it is in the atmosphere. Krill eggs sink passively and so cannot avoid these conditions. Here we describe the sensitivity of krill egg hatch rates to increased CO2, and present a circumpolar risk map of krill hatching success under projected pCO2 levels. We find that important krill habitats of the Weddell Sea and the Haakon VII Sea to the east are likely to become high-risk areas for krill recruitment within a century. Furthermore, unless CO2 emissions are mitigated, the Southern Ocean krill population could collapse by 2300 with dire consequences for the entire ecosystem.

  12. Isotopic evidence for reduced productivity in the glacial Southern Ocean

    SciTech Connect

    Shemesh, A. ); Macko, S.A. ); Charles, C.D. ); Rau, G.H. )

    1993-10-15

    Records of carbon and nitrogen isotopes in biogenic silica and carbon isotopes in planktonic foraminifera from deep-sea sediment cores from the Southern Ocean reveal that the primary production during the last glacial maximum was lower than Holocene productivity. These observations conflict with the hypothesis that the low atmospheric carbon dioxide concentrations were introduced by an increase in the efficiency of the high-latitude biological pump. Instead, different oceanic sectors may have had high glacial productivity, or alternative mechanisms that do not involve the biological pump must be considered as the primary cause of the low glacial atmospheric carbon dioxide concentrations.

  13. Interannual variability of monthly Southern Ocean sea ice distributions

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    1992-01-01

    The interannual variability of the Southern-Ocean sea-ice distributions was mapped and analyzed using data from Nimbus-5 ESMR and Nimbus-7 SMMR, collected from 1973 to 1987. The set of 12 monthly maps obtained reveals many details on spatial variability that are unobtainable from time series of ice extents. These maps can be used as baseline maps for comparisons against future Southern Ocean sea ice distributions. The maps are supplemented by more detailed maps of the frequency of ice coverage, presented in this paper for one month within each of the four seasons, and by the breakdown of these results to the periods covered individually by each of the two passive-microwave imagers.

  14. Strong responses of Southern Ocean phytoplankton communities to volcanic ash

    NASA Astrophysics Data System (ADS)

    Browning, T. J.; Bouman, H. A.; Henderson, G. M.; Mather, T. A.; Pyle, D. M.; Schlosser, C.; Woodward, E. M. S.; Moore, C. M.

    2014-04-01

    Volcanic eruptions have been hypothesized as an iron supply mechanism for phytoplankton blooms; however, little direct evidence of stimulatory responses has been obtained in the field. Here we present the results of twenty-one 1-2 day bottle enrichment experiments from cruises in the South Atlantic and Southern Ocean which conclusively demonstrated a photophysiological and biomass stimulation of phytoplankton communities following supply of basaltic or rhyolitic volcanic ash. Furthermore, experiments in the Southern Ocean demonstrated significant phytoplankton community responses to volcanic ash supply in the absence of responses to addition of dissolved iron alone. At these sites, dissolved manganese concentrations were among the lowest ever measured in seawater, and we therefore suggest that the enhanced response to ash may have been a result of the relief of manganese (co)limitation. Our results imply that volcanic ash deposition events could trigger extensive phytoplankton blooms, potentially capable of significant impacts on regional carbon cycling.

  15. Changes in the ventilation of the southern oceans.

    PubMed

    Waugh, Darryn W

    2014-07-13

    Changes in the ventilation of the southern oceans over the past few decades are examined using ocean measurements of CFC-12 and model simulations. Analysis of CFC-12 measurements made between the late 1980s and late 2000s reveal large-scale coherent changes in the ventilation, with a decrease in the age of subtropical Subantarctic Mode Waters (SAMW) and an increase in the age of Circumpolar Deep Waters. The decrease in SAMW age is consistent with the observed increase in wind stress curl and strength of the subtropical gyres over the same period. A decrease in the age of SAMW is also found in Community Climate System Model version 4 perturbation experiments where the zonal wind stress is increased. This decrease is due to both more rapid transport along isopycnals and the movement of the isopycnals. These results indicate that the intensification of surface winds in the Southern Hemisphere has caused large-scale coherent changes in the ventilation of the southern oceans. PMID:24891397

  16. Topographic form stress in the Southern Ocean State Estimate

    NASA Astrophysics Data System (ADS)

    Masich, Jessica; Chereskin, Teresa K.; Mazloff, Matthew R.

    2015-12-01

    We diagnose the Southern Ocean momentum balance in a 6 year, eddy-permitting state estimate of the Southern Ocean. We find that 95% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain. While the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, time-mean topographic form stress concentrates at shallow ridges and across the continents that lie within the Antarctic Circumpolar Current (ACC) latitudes; nearly 40% of topographic form stress occurs across South America, while the remaining 60% occurs across the major submerged ridges that underlie the ACC. Topographic form stress can be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88% of the variance in the 6 year form stress time series can be explained by the wind stress signal, suggesting that changes in the integrated wind stress signal are communicated via rapid barotropic response down to the level of bottom topography.

  17. Sea ice trends and cyclone activity in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Coggins, Jack; McDonald, Adrian; Rack, Wolfgang; Dale, Ethan

    2015-04-01

    Significant trends in the extent of Southern Hemisphere sea ice have been noted over the course of the satellite record, with highly variable trends between different seasons and regions. In this presentation, we describe efforts to assess the impact of cyclones on these trends. Employing a maximum cross-correlation method, we derive Southern Ocean ice-motion vectors from daily gridded SSMI 85.5 GHz brightness temperatures. We then derive a sea ice budget from the NASA-Team 25 km square daily sea ice concentrations. The budget quantifies the total daily change in sea ice area, and includes terms representing the effects of ice advection and divergence. A residual term represents the processes of rafting, ridging, freezing and thawing. We employ a cyclone tracking algorithm developed at the University of Canterbury to determine the timing, location, size and strength of Southern Hemisphere cyclones from mean sea-level pressure fields of the ERA-Interim reanalysis. We then form composites of the of sea ice budget below the location of cyclones. Unsurprisingly, we find that clockwise atmospheric flow around Southern Hemisphere cyclones exerts a strong influence on the movement of sea ice, an effect which is visible in the advection and divergence terms. Further, we assess the climatological importance of cyclones by comparing seasons of sea ice advance for periods with varying numbers of cyclones. This analysis is performed independently for each sea ice concentration pixel, thus affording us insight into the geographical importance of storm systems. We find that Southern Hemisphere sea ice extent is highly sensitive to the presence of cyclones in the periphery of the pack in the advance season. Notably, the sensitivity is particularly high in the northern Ross Sea, an area with a marked positive trend in sea ice extent. We discuss whether trends in cyclone activity in the Southern Ocean may have contributed to sea ice extent trends in this region.

  18. Lagrangian pathways of upwelling in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Viglione, Giuliana A.; Thompson, Andrew F.

    2016-08-01

    The spatial and temporal variability of upwelling into the mixed layer in the Southern Ocean is studied using a 1/10/° ocean general circulation model. Virtual drifters are released in a regularly spaced pattern across the Southern Ocean at depths of 250, 500, and 1000 m during both summer and winter months. The drifters are advected along isopycnals for a period of 4 years, unless they outcrop into the mixed layer, where lateral advection and a parameterization of vertical mixing are applied. The focus of this study is on the discrete exchange between the model mixed layer and the interior. Localization of interior-mixed layer exchange occurs downstream of major topographic features across the Indian and Pacific basins, creating "hotspots" of outcropping. Minimal outcropping occurs in the Atlantic basin, while 59% of drifters outcrop in the Pacific sector and in Drake Passage (the region from 140/° W to 40/° W), a disproportionately large amount even when considering the relative basin sizes. Due to spatial and temporal variations in mixed layer depth, the Lagrangian trajectories provide a statistical measure of mixed layer residence times. For each exchange into the mixed layer, the residence time has a Rayleigh distribution with a mean of 30 days; the cumulative residence time of the drifters is 261 ± 194 days, over a period of 4 years. These results suggest that certain oceanic gas concentrations, such as CO2 and 14C, will likely not reach equilibrium with the atmosphere before being resubducted.

  19. Bathymetry estimates in the southern oceans from Seasat altimetry

    NASA Technical Reports Server (NTRS)

    Dixon, T. H.; Parke, M. E.

    1983-01-01

    A 70-day Seasat altimeter set, where altitude was determined by the delay of a radar signal before return, was high pass filtered to obtain bathymetric data on the southern ocean. Variations were estimated over cross-track passages over the same points, and longer wavelength effects were removed to reveal the shorter wavelength geoid features. Edge effects near land, subtle geoid structure features at continental margins, smaller boundary seas, and lakes were preserved by the high pass filter, which involved substracting a constant height from each 6 x 6 deg square region. A volcanic origin was indicated for the nearly continuous Louisville Ridge, which had a major elongate plateau or positive gravity anomaly located just eastward and running east-west. A large Conrad Ridge was found in the Indian Ocean, compared to previous charts. The Indian Ocean was also found to contain more rises and plateaus than previously mapped.

  20. An investigation of Bjerknes Compensation in the Southern Ocean in the CCSM4

    SciTech Connect

    Weijer, Wilbert; Kinstle, Caroline M.

    2012-08-28

    This project aims to understand the relationship between poleward oceanic and atmospheric heat transport in the Southern Ocean by analyzing output from the community Climate System Model Version 4 (CCSM4). In particular, time series of meridional heat transport in both the atmosphere and the ocean are used to study whether variability in ocean heat transport is balanced by opposing changes in atmospheric heat transport, called Bjerknes Compensation. It is shown that the heat storage term in the Southern Ocean has a significant impact on the oceanic heat budget; as a result, no robust coherences between oceanic and atmospheric heat transports could be found at these southern latitudes.

  1. Rethinking the Ocean's Role in the Southern Oscillation

    NASA Astrophysics Data System (ADS)

    Clement, A. C.; di Nezio, P. N.; Deser, C.

    2010-12-01

    The usual explanation for variability in the Southern Oscillation (SO), a shift of atmospheric mass between the Indo-Pacific warm pool region and the eastern Pacific reflected in opposite sign changes in sea level pressure, involves dynamical coupling between the atmosphere and ocean via the ‘Bjerknes feedback’ mechanism. Here we revisit this explanation using a collection of simulations with atmospheric general circulation models that have varying degrees of coupling to the ocean. The main finding is that the SO emerges as a dominant mode of tropical Pacific variability without dynamical coupling to the ocean. Atmospheric models coupled to a mixed layer ocean (i.e. with no coupled ocean dynamics) simulate what is refered to here as an ‘Atmospheric Walker Mode’ (AWM). This mode of variability has patterns in sea level pressure, sea surface temperature, and precipitation which strongly resemble observed patterns associated with the SO. The spectrum of the AWM is red out to about a decadal timescale, consistent with a stochastically forced, weakly damped process, and our analysis suggests that variability in the AWM is related to variability in the NE and SE trade winds and associated surface wind divergence in the warm pool. The main influence of ocean dynamics on the SO in fully coupled climate models is the addition power primarily at interannual timescales, as expected from the positive Bjerknes feedback. On decadal and longer timescales, ocean dynamics enhance the damping of (or act as a negative feedback on) SO variability. However, interactive ocean dynamics do not appear to be required to set the first-order spatial structure of the SO or associated patterns in SST, precipitation, or atmospheric circulation. Implications for Pacific climate variability on interannual, decadal, and century timescales are discussed.

  2. Mapping phytoplankton iron utilization: Insights into Southern Ocean supply mechanisms

    NASA Astrophysics Data System (ADS)

    Boyd, P. W.; Arrigo, K. R.; Strzepek, R.; van Dijken, G. L.

    2012-06-01

    The emerging field of ocean iron biogeochemistry has prompted interest in the identification and quantification of Fe supply mechanisms. However, less attention has been given to estimating biological Fe utilization, and using the magnitude of Fe utilization to enhance our understanding of modes of supply. Here, we combine regionally validated data sets (1997-2007) on remotely sensed net primary production (NPP) with the iron:carbon (Fe:C) molar ratios for resident phytoplankton to produce Southern Ocean maps of Fe utilization. This approach exploits the resolution of remotely sensed data to investigate the spatial patterns, areal extent and interannual variability of Fe utilization, and relates it to published temporal and spatial trends for Fe supply mechanisms. We estimate that Southern Ocean Fe utilization averaged ˜3.3 ± 0.3 × 108 mol Fe a-1. This utilization varied little between years (7.8-9.6 μmol Fe m-2 a-1), was greatest for subpolar waters, particularly in the Atlantic (up to 53.0 μmol Fe m-2 a-1), and was lowest for the polar waters of the Indian sector. Application of maps corresponding to the location and areal extent of Fe supply regions (e.g., dust deposition) revealed that Fe utilization was highest in waters supplied by Patagonian dust, and to a lesser extent, where sediment resuspension (i.e. <500 m depth) probably supplies the majority of the Fe. The Atlantic sector has regions where multiple supply mechanisms are evident, resulting in perennially high productivity. This approach provides a better assessment of the relative importance, realm of influence, and areal extent of different Fe supply mechanisms to Southern Ocean waters.

  3. Small iceberg bursts: melting breakwaters in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ardhuin, F.; Tournadre, J.; Queffeulou, P.; Girard-Ardhuin, F.

    2010-12-01

    The variability of small-size iceberg distributions is revealed from a novel analysis of satellite altimeter data. The yearly cycle is modulated by pulse-like events confined to single ocean basins. A strong iceberg population is found in the South Atlantic in 2003-2005, and in the South Pacific in 2008. Anomalies of the order of 1°C in sea surface temperatures may be related to the iceberg distribution. Icebergs are very strongly associated with anomalies in the heights of ocean waves, with far-reaching consequences for the global wave climate. A preliminary numerical modelling of wave blocking by icebergs, including partial wave reflection, reduces model errors on the significant wave height by 26% in the region south of 45° South. Observed changes in small iceberg populations thus have profound impacts on Southern ocean dynamics and beyond. Latitude-time Hovmöller diagrams of the small iceberg ice volume cumulated over each 2° band of latitude for (a) the South Atlantic 50°W to 30°E, (b) the Indian Ocean 50°E to 130°, (c) the South Pacific 130°E to 100°, for each 2° band of latitude. (d), (e), and (f) significant wave heigth model bias against satellite altimeters for the same three sectors of the Southern Ocean, for a model without iceberg effects. In the left panels (a,b,c) the black line marks the maximum extend of the sea ice, and in the right panels (c,d,e) the white areas give the minimum extent of the 80% sea ice coverage, used as a mask in the model.

  4. Inventory of ocean monitoring in the Southern California Bight.

    PubMed

    Schiff, Kenneth C; Weisberg, Stephen B; Raco-Rands, Valerie

    2002-06-01

    Monitoring of the ocean environment in southern California, USA, has been conducted by a diverse array of public and private organizations with different motivations, working on a variety of spatial and temporal scales. To create a basis from which to integrate information from these diverse programs, we conducted an inventory of ocean monitoring activities in the Southern California Bight to address the following questions: (1) How much money is being expended annually on marine monitoring programs? (2) Which organizations are conducting the most monitoring? (3) How are resources allocated among the different types of monitoring programs? This inventory focused on programs existing, or those expected to be in existence, for at least 10 years and that were active at any time between 1994 and 1997. For each program identified for inclusion in this study, information was collected on the number of sites, sampling intensity, parameters measured, and methods used. Levels of effort were translated into cost estimates based upon a market survey of local consulting firms. One hundred fourteen marine monitoring programs, conducted by 65 organizations and costing US $31 million annually, were identified. Most of the effort (81 programs, 65% of samples, 70% of costs) was expended by ocean dischargers as part of their compliance with National Pollutant Discharge Elimination System (NPDES) permit requirements. Federal programs (11 programs, 25% of samples, 10% of total expenditures) expended more than state or local government programs. More than one quarter of monitoring expenditures were conducted to measure concentrations and mass of effluent inputs to the ocean. The largest effort expended on receiving water monitoring was for measuring bacteria, followed by sediments, fish/shellfish, water quality, and intertidal habitats. The large level of expenditures by individual agencies has presented opportunities for integrating small, site-specific ocean monitoring programs into

  5. The SOOS Data Portal, providing access to Southern Oceans data

    NASA Astrophysics Data System (ADS)

    Proctor, Roger; Finney, Kim; Blain, Peter; Taylor, Fiona; Newman, Louise; Meredith, Mike; Schofield, Oscar

    2013-04-01

    The Southern Ocean Observing System (SOOS) is an international initiative to enhance, coordinate and expand the strategic observations of the Southern Oceans that are required to address key scientific and societal challenges. A key component of SOOS will be the creation and maintenance of a Southern Ocean Data Portal to provide improved access to historical and ongoing data (Schofield et al., 2012, Eos, Vol. 93, No. 26, pp 241-243). The scale of this effort will require strong leveraging of existing data centres, new cyberinfrastructure development efforts, and defined data collection, quality control, and archiving procedures across the international community. The task of assembling the SOOS data portal is assigned to the SOOS Data Management Sub-Committee. The information infrastructure chosen for the SOOS data portal is based on the Australian Ocean Data Network (AODN, http://portal.aodn.org.au). The AODN infrastructure is built on open-source tools and the use of international standards ensures efficiency of data exchange and interoperability between contributing systems. OGC standard web services protocols are used for serving of data via the internet. These include Web Map Service (WMS) for visualisation, Web Feature Service (WFS) for data download, and Catalogue Service for Web (CSW) for catalogue exchange. The portal offers a number of tools to access and visualize data: - a Search link to the metadata catalogue enables search and discovery by simple text search, by geographic area, temporal extent, keyword, parameter, organisation, or by any combination of these, allowing users to gain access to further information and/or the data for download. Also, searches can be restricted to items which have either data to download, or attached map layers, or both - a Map interface for discovery and display of data, with the ability to change the style and opacity of layers, add additional data layers via OGC Web Map Services, view animated timeseries datastreams

  6. Low-frequency sound level in the Southern Indian Ocean.

    PubMed

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Leroy, Emmanuelle C

    2015-12-01

    This study presents long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected on six widely distributed autonomous hydrophones from 47°S to 4°S and 53°E to 83°E. Daily mean power spectra (10-100 Hz) were analyzed in order to identify the main sound sources and their space and time variability. Periodic signals are principally associated with the seasonal presence of three types of blue whales and fin whales whose signatures are easily identified at specific frequencies. In the low frequencies, occurrence of winter lows and summer highs in the ambient noise levels are well correlated with iceberg volume variations at the southern latitudes, suggesting that icebergs are a major sound source, seasonally contributing to the ambient noise, even at tropical latitudes (26°S). The anthropogenic contribution to the noise spectrum is limited. Shipping sounds are only present north and west of the study area in the vicinity of major traffic lanes. Acoustic recordings from the southern sites may thus be representative of the pristine ambient noise in the Indian Ocean. PMID:26723301

  7. Low-frequency sound level in the Southern Indian Ocean.

    PubMed

    Tsang-Hin-Sun, Eve; Royer, Jean-Yves; Leroy, Emmanuelle C

    2015-12-01

    This study presents long-term statistics on the ambient sound in the Southern Indian Ocean basin based on 2 years of data collected on six widely distributed autonomous hydrophones from 47°S to 4°S and 53°E to 83°E. Daily mean power spectra (10-100 Hz) were analyzed in order to identify the main sound sources and their space and time variability. Periodic signals are principally associated with the seasonal presence of three types of blue whales and fin whales whose signatures are easily identified at specific frequencies. In the low frequencies, occurrence of winter lows and summer highs in the ambient noise levels are well correlated with iceberg volume variations at the southern latitudes, suggesting that icebergs are a major sound source, seasonally contributing to the ambient noise, even at tropical latitudes (26°S). The anthropogenic contribution to the noise spectrum is limited. Shipping sounds are only present north and west of the study area in the vicinity of major traffic lanes. Acoustic recordings from the southern sites may thus be representative of the pristine ambient noise in the Indian Ocean.

  8. Analysis of Low-Frequency Geostrophic Transport in the Southern Ocean Measurable with Ocean Bottom Pressure

    NASA Astrophysics Data System (ADS)

    Meyer, J.; Chambers, D. P.

    2015-12-01

    We sought to understand the relative importance of barotropic transport as measured from bottom pressure to total transport in the Southern Ocean. We used ocean bottom pressure and velocity data from the Estimating the Circulation and Climate of the Ocean (ECCO) state estimate run at Jet Propulsion Laboratory to quantify the percentage of total transport in various areas of the Southern Ocean that can be explained by ocean bottom pressure measurements. Only low-frequency (> 1-year) transport variations from 1993 to 2011 were considered. We examined the standard deviations, correlation, and percent variance for low-pass filtered transport integrated from 65°S - 40°S for each 1° longitude from 50°E to 150°E by vertically integrating the zonal velocity, the zonal component of the bottom current, and geostrophic current from bottom pressure gradients. We found that the transport computed from bottom pressure explained more of the full transport variability than that calculated from the bottom current.

  9. Deep Ocean Heat Uptake and the Influence of Sea Ice in the Southern Ocean

    SciTech Connect

    Cecilia M. Bitz

    2011-11-22

    Climate sensitivity defines the equilibrium response to climate forcing, but ocean heat uptake is equally important at controlling the transient, response. Heat stored beneath the mixed layer is not in close thermal contact with the atmosphere, and therefore warming below the mixed layer sequesters heat that would otherwise be available to warm the surface, slowing the rate of surface warming. In this study, we investigate mechanisms that control heat uptake, primarily in the Southern Ocean, where roughly 40% of the global heat uptake occurs.

  10. The Southern Ocean's biological pump during the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Anderson, Robert F.; Chase, Zanna; Fleisher, Martin Q.; Sachs, Julian

    Ice core records from Antarctica show large (˜80 ppm) and regular climate-related changes in atmospheric CO 2, with minimum values during glacial periods and maximum values during peak interglacials. The suggested role of the Southern Ocean in driving these changes is based on either the potential for increased utilization of surface nutrients or the potential for decreased ventilation of deep waters during glacial times. Several recent studies have invoked increased stratification of the Southern Ocean to explain lower glacial atmospheric CO 2 levels in terms of reduced exchange of CO 2 between the deep sea and the atmosphere. A northward displacement and/or substantial weakening of the westerly winds during glacial periods are implicit in the scenarios that invoke enhanced stratification. However, both circulation models and proxy results argue against a weakening of the westerlies. In fact, the mean flow of the Antarctic Circumpolar Current and wind-driven upwelling during the Last Glacial Maximum (LGM) are thought to be at least as vigorous as those which exist today. Given these boundary conditions, we offer two (competing) scenarios for ecosystem structure and export production of the glacial Southern Ocean. The first scenario satisfies all proxy records for nutrient utilization and phytoplankton growth rate, and requires increased (relative to today) nitrate utilization south of the Antarctic Polar Front (APF) by phytoplankton other than diatoms, together with a shift in the zone of maximum diatom growth from south (interglacials) to north (glacials) of the APF. The second scenario has reduced growth of all phytoplankton species south of the APF during glacials, and a shift in the zone of maximum export production to the north of the Polar Front. The principal weakness of the first scenario is that there is little sedimentary evidence to support the increased export of particulate organic carbon required by the inferred increase in nitrate utilization south

  11. Seabird guano enhances phytoplankton production in the Southern Ocean.

    NASA Astrophysics Data System (ADS)

    Shatova, Olga; Wing, Stephen; Hoffmann, Linn; Jack, Lucy; Gault-Ringold, Melanie

    2015-04-01

    Great congregations of seabirds in sub-Antarctic and Antarctic coastal areas result in delivery of nutrient-rich guano to marine ecosystems that potentially enhances productivity and supports biodiversity in the region. Guano-derived bio-available micronutrients and macronutrients might be utilized by marine phytoplankton for photosynthetic production, however, mechanisms and significance of guano fertilization in the Southern Ocean are largely understudied. Over austral summers of 2012 and 2013 we performed a series of guano-enrichment phytoplankton incubation experiments with water samples collected from three different water masses in the Southern Ocean: Antarctic waters of the Ross sea and sub-Antarctic waters offshore the Otago Peninsula, both showing iron limitation of phytoplankton productivity in summer, and in the subtropical frontal zone offshore from the Snares Islands, which is generally micronutrient-repleted. Samples were enriched with known concentrations of guano-derived nutrients. Phytoplankton biomass increased significantly in guano-treated samples during all three incubation experiments (7-10 fold increase), while remained low in control samples. This response indicates that seabird guano provides nutrients that limit primary production in the Southern Ocean and that these nutrients are readily taken up by phytoplankton. Guano additions were compared to Fe and Macronutrient treatments (both added in quantities similar to those in the guano treatment). Phytoplankton biomass increased significantly in response to the Macronutrient treatment in the subtropical frontal zone, however, the response had a smaller magnitude compared to the guano treatment (2.8 µgL-1 vs 5.2 µgL-1) ; there was no significant effect of Fe on phytoplankton growth. This suggests the potential importance of synergistic effects of nutrients in guano. Incubation with sub-Antarctic waters showed that Fe and Macronutrients might be equally important for enhancement of

  12. Southern Ocean isopycnal mixing and ventilation changes driven by winds

    NASA Astrophysics Data System (ADS)

    Abernathey, Ryan; Ferreira, David

    2015-12-01

    Observed and predicted changes in the strength of the westerly winds blowing over the Southern Ocean have motivated a number of studies on the response of the Antarctic Circumpolar Current and Southern Ocean meridional overturning circulation (MOC) to wind perturbations and led to the hypothesis of the "eddy compensation" regime, wherein the MOC becomes insensitive to wind changes. In addition to the MOC, tracer transport also depends on mixing processes. Here we show, in a high-resolution process model, that isopycnal mixing by mesoscale eddies is strongly dependent on the wind strength. This dependence can be explained by mixing length theory and is driven by increases in eddy kinetic energy; the mixing length does not change strongly in our simulation. Simulation of a passive ventilation tracer (analogous to CFCs or anthropogenic CO2) demonstrates that variations in tracer uptake across experiments are dominated by changes in isopycnal mixing, rather than changes in the MOC. We argue that to properly understand tracer uptake under different wind-forcing scenarios, the sensitivity of isopycnal mixing to winds must be accounted for.

  13. Recent Precipitation Trends Over the Southern Ocean in Relation to Oceanic Freshening Near Antarctica

    NASA Astrophysics Data System (ADS)

    Cullather, R. I.; Jacobs, S. S.; Giulivi, C. F.; Leonard, K. C.; Stammerjohn, S. E.

    2008-12-01

    Quantitative assessments of large-scale precipitation over the world's oceanic regions are problematic, particularly for significant regions of the data-sparse Southern Hemisphere. Available data sets are based on the assimilation of land-based measurements, satellite radiance values, numerical weather forecast models, or some combination of the three. In this study we examine several products that cover most or all of the satellite era 1979-2007 over the Southern Ocean and surrounding mid-latitudes to 45°S. These include CMAP, the NCEP Reanalysis II, ERA-40, GPCP version 2, and the Japanese Re-analysis. Averaged fields from these data show large discrepancies in the mean spatial depiction and the annual cycle. Comparisons with unique in situ snowfall measurements and satellite-derived accumulation on sea ice are presented. The available record of oceanographic measurements in the Ross Sea indicates that salinity below 200 m in the Ross Sea has decreased by 0.03 per decade since 1958, with the highest (lowest) values in 1967 (2000). The fields examined here suggest that precipitation is likely not directly influencing the oceanic freshening observed in the Ross Sea, or in other coastal seas adjacent to Antarctica. The salinity anomaly is consistent with increasing attrition of continental ice, but places a heavy demand on the melt rate. Potential contributions to oceanic freshening from changes in sea ice extent, transport, and thickness are discussed.

  14. Effects of Southern Hemisphere Wind Changes on the Meridional Overturning Circulation in Ocean Models.

    PubMed

    Gent, Peter R

    2016-01-01

    Observations show that the Southern Hemisphere zonal wind stress maximum has increased significantly over the past 30 years. Eddy-resolving ocean models show that the resulting increase in the Southern Ocean mean flow meridional overturning circulation (MOC) is partially compensated by an increase in the eddy MOC. This effect can be reproduced in the non-eddy-resolving ocean component of a climate model, providing the eddy parameterization coefficient is variable and not a constant. If the coefficient is a constant, then the Southern Ocean mean MOC change is balanced by an unrealistically large change in the Atlantic Ocean MOC. Southern Ocean eddy compensation means that Southern Hemisphere winds cannot be the dominant mechanism driving midlatitude North Atlantic MOC variability.

  15. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature.

    PubMed

    Yin, Qiuzhen

    2013-02-14

    Glacial-interglacial cycles characterized by long cold periods interrupted by short periods of warmth are the dominant feature of Pleistocene climate, with the relative intensity and duration of past and future interglacials being of particular interest for civilization. The interglacials after 430,000 years ago were characterized by warmer climates and higher atmospheric concentrations of carbon dioxide than the interglacials before, but the cause of this climatic transition (the so-called mid-Brunhes event (MBE)) is unknown. Here I show, on the basis of model simulations, that in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic bottom water formation and Southern Ocean ventilation. My results also show that strong westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and by changes in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward systematic difference in the astronomical parameters between the interglacials before and after 430,000 years ago. Rather than being a real 'event', the apparent MBE seems to have resulted from a series of individual interglacial responses--including notable exceptions to the general pattern--to various combinations of insolation conditions. Consequently, assuming no anthropogenic interference, future interglacials may have pre- or post-MBE characteristics without there being a systematic change in forcings. These findings are a first step towards understanding the magnitude change of the interglacial carbon dioxide concentration around 430

  16. Insolation-induced mid-Brunhes transition in Southern Ocean ventilation and deep-ocean temperature.

    PubMed

    Yin, Qiuzhen

    2013-02-14

    Glacial-interglacial cycles characterized by long cold periods interrupted by short periods of warmth are the dominant feature of Pleistocene climate, with the relative intensity and duration of past and future interglacials being of particular interest for civilization. The interglacials after 430,000 years ago were characterized by warmer climates and higher atmospheric concentrations of carbon dioxide than the interglacials before, but the cause of this climatic transition (the so-called mid-Brunhes event (MBE)) is unknown. Here I show, on the basis of model simulations, that in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic bottom water formation and Southern Ocean ventilation. My results also show that strong westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and by changes in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward systematic difference in the astronomical parameters between the interglacials before and after 430,000 years ago. Rather than being a real 'event', the apparent MBE seems to have resulted from a series of individual interglacial responses--including notable exceptions to the general pattern--to various combinations of insolation conditions. Consequently, assuming no anthropogenic interference, future interglacials may have pre- or post-MBE characteristics without there being a systematic change in forcings. These findings are a first step towards understanding the magnitude change of the interglacial carbon dioxide concentration around 430

  17. The Southern Ocean's role in carbon exchange during the last deglaciation.

    PubMed

    Burke, Andrea; Robinson, Laura F

    2012-02-01

    Changes in the upwelling and degassing of carbon from the Southern Ocean form one of the leading hypotheses for the cause of glacial-interglacial changes in atmospheric carbon dioxide. We present a 25,000-year-long Southern Ocean radiocarbon record reconstructed from deep-sea corals, which shows radiocarbon-depleted waters during the glacial period and through the early deglaciation. This depletion and associated deep stratification disappeared by ~14.6 ka (thousand years ago), consistent with the transfer of carbon from the deep ocean to the surface ocean and atmosphere via a Southern Ocean ventilation event. Given this evidence for carbon exchange in the Southern Ocean, we show that existing deep-ocean radiocarbon records from the glacial period are sufficiently depleted to explain the ~190 per mil drop in atmospheric radiocarbon between ~17 and 14.5 ka.

  18. Observed and Modeled Trends in Southern Ocean Sea Ice

    NASA Technical Reports Server (NTRS)

    Parkinson, Claire L.

    2003-01-01

    Conceptual models and global climate model (GCM) simulations have both indicated the likelihood of an enhanced sensitivity to climate change in the polar regions, derived from the positive feedbacks brought about by the polar abundance of snow and ice surfaces. Some models further indicate that the changes in the polar regions can have a significant impact globally. For instance, 37% of the temperature sensitivity to a doubling of atmospheric CO2 in simulations with the GCM of the Goddard Institute for Space Studies (GISS) is attributable exclusively to inclusion of sea ice variations in the model calculations. Both sea ice thickness and sea ice extent decrease markedly in the doubled CO, case, thereby allowing the ice feedbacks to occur. Stand-alone sea ice models have shown Southern Ocean hemispherically averaged winter ice-edge retreats of 1.4 deg latitude for each 1 K increase in atmospheric temperatures. Observations, however, show a much more varied Southern Ocean ice cover, both spatially and temporally, than many of the modeled expectations. In fact, the satellite passive-microwave record of Southern Ocean sea ice since late 1978 has revealed overall increases rather than decreases in ice extents, with ice extent trends on the order of 11,000 sq km/year. When broken down spatially, the positive trends are strongest in the Ross Sea, while the trends are negative in the Bellingshausen/Amundsen Seas. Greater spatial detail can be obtained by examining trends in the length of the sea ice season, and those trends show a coherent picture of shortening sea ice seasons throughout almost the entire Bellingshausen and Amundsen Seas to the west of the Antarctic Peninsula and in the far western Weddell Sea immediately to the east of the Peninsula, with lengthening sea ice seasons around much of the rest of the continent. This pattern corresponds well with the spatial pattern of temperature trends, as the Peninsula region is the one region in the Antarctic with a strong

  19. The Southern Ocean as a constraint to reduce uncertainty in future ocean carbon sinks

    NASA Astrophysics Data System (ADS)

    Kessler, A.; Tjiputra, J.

    2016-04-01

    Earth system model (ESM) simulations exhibit large biases compares to observation-based estimates of the present ocean CO2 sink. The inter-model spread in projections increases nearly 2-fold by the end of the 21st century and therefore contributes significantly to the uncertainty of future climate projections. In this study, the Southern Ocean (SO) is shown to be one of the hot-spot regions for future uptake of anthropogenic CO2, characterized by both the solubility pump and biologically mediated carbon drawdown in the spring and summer. We show, by analyzing a suite of fully interactive ESMs simulations from the Coupled Model Intercomparison Project phase 5 (CMIP5) over the 21st century under the high-CO2 Representative Concentration Pathway (RCP) 8.5 scenario, that the SO is the only region where the atmospheric CO2 uptake rate continues to increase toward the end of the 21st century. Furthermore, our study discovers a strong inter-model link between the contemporary CO2 uptake in the Southern Ocean and the projected global cumulated uptake over the 21st century. This strong correlation suggests that models with low (high) carbon uptake rate in the contemporary SO tend to simulate low (high) uptake rate in the future. Nevertheless, our analysis also shows that none of the models fully capture the observed biophysical mechanisms governing the CO2 fluxes in the SO. The inter-model spread for the contemporary CO2 uptake in the Southern Ocean is attributed to the variations in the simulated seasonal cycle of surface pCO2. Two groups of model behavior have been identified. The first one simulates anomalously strong SO carbon uptake, generally due to both too strong a net primary production and too low a surface pCO2 in December-January. The second group simulates an opposite CO2 flux seasonal phase, which is driven mainly by the bias in the sea surface temperature variability. We show that these biases are persistent throughout the 21st century, which highlights the

  20. Coastal ocean transport patterns in the central Southern California Bight

    USGS Publications Warehouse

    Noble, M.A.; Rosenberger, K.J.; Hamilton, P.; Xu, J. P.

    2009-01-01

    In the past decade, several large programs that monitor currents and transport patterns for periods from a few months to a few years were conducted by a consortium of university, federal, state, and municipal agencies in the central Southern California Bight, a heavily urbanized section of the coastal ocean off the west coast of the United States encompassing Santa Monica Bay, San Pedro Bay, and the Palos Verdes shelf. These programs were designed in part to determine how alongshelf and cross-shelf currents move sediments, pollutants, and suspended material through the region. Analysis of the data sets showed that the current patterns in this portion of the Bight have distinct changes in frequency and amplitude with location, in part because the topography of the shelf and upper slope varies rapidly over small spatial scales. However, because the mean, subtidal, and tidal-current patterns in any particular location were reasonably stable with time, one could determine a regional pattern for these current fields in the central Southern California Bight even though measurements at the various locations were obtained at different times. In particular, because the mean near-surface flows over the San Pedro and Palos Verdes shelves are divergent, near-surface waters from the upper slope tend to carry suspended material onto the shelf in the northwestern portion of San Pedro Bay. Water and suspended material are also carried off the shelf by the mean and subtidal flow fields in places where the orientation of the shelf break changes abruptly. The barotropic tidal currents in the central Southern California Bight flow primarily alongshore, but they have pronounced amplitude variations over relatively small changes in alongshelf location that are not totally predicted by numerical tidal models. Nonlinear internal tides and internal bores at tidal frequencies are oriented more across the shelf. They do not have a uniform transport direction, since they move fine sediment

  1. Distribution of perfluoroalkyl compounds in seawater from northern Europe, Atlantic Ocean, and Southern Ocean.

    PubMed

    Ahrens, Lutz; Xie, Zhiyong; Ebinghaus, Ralf

    2010-02-01

    The global distribution of perfluoroalkyl compounds (PFCs) were investigated in surface water samples collected onboard the Polarstern in Northern Europe, Atlantic and Southern Ocean (52 degrees N-69 degrees S) in 2008. The water samples were solid-phase extracted with Oasis WAX cartridges and analysed using the high-performance liquid chromatography interfaced to tandem mass spectrometry. Concentrations of various PFCs, including C(4), C(6), C(8) perfluoroalkyl sulfonates (PFSAs), perfluorooctane sulfinate (PFOSi), C(5)-C(12) perfluoroalkyl carboxylic acids (PFCA) and perfluorooctane sulfonamide (FOSA) were quantified. Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were the predominant compounds with a maximum concentration of 232 and 223pgL(-1), respectively. Results indicate that industrial areas like the European Continent act as source of PFCs, while ocean water is an important as a sink as well as the transport medium of these compounds. Interestingly, in the equator area the summation operatorPFC concentration increased, which indicates that there exists an atmospheric or other unknown input source of PFCs. In the Southern Ocean only PFOS was detected which could be caused by atmospheric transport of its precursors.

  2. Extraordinarily high biomass benthic community on Southern Ocean seamounts.

    PubMed

    Thresher, R E; Adkins, J; Fallon, S J; Gowlett-Holmes, K; Althaus, F; Williams, A

    2011-01-01

    We describe a previously unknown assemblage of seamount-associated megabenthos that has by far the highest peak biomass reported in the deep-sea outside of vent communities. The assemblage was found at depths of 2-2.5 km on rocky geomorphic features off the southeast coast of Australia, in an area near the Sub-Antarctic Zone characterised by high rates of surface productivity and carbon export to the deep-ocean. These conditions, and the taxa in the assemblage, are widely distributed around the Southern mid-latitudes, suggesting the high-biomass assemblage is also likely to be widespread. The role of this assemblage in regional ecosystem and carbon dynamics and its sensitivities to anthropogenic impacts are unknown. The discovery highlights the lack of information on deep-sea biota worldwide and the potential for unanticipated impacts of deep-sea exploitation. PMID:22355636

  3. Extraordinarily high biomass benthic community on Southern Ocean seamounts.

    PubMed

    Thresher, R E; Adkins, J; Fallon, S J; Gowlett-Holmes, K; Althaus, F; Williams, A

    2011-01-01

    We describe a previously unknown assemblage of seamount-associated megabenthos that has by far the highest peak biomass reported in the deep-sea outside of vent communities. The assemblage was found at depths of 2-2.5 km on rocky geomorphic features off the southeast coast of Australia, in an area near the Sub-Antarctic Zone characterised by high rates of surface productivity and carbon export to the deep-ocean. These conditions, and the taxa in the assemblage, are widely distributed around the Southern mid-latitudes, suggesting the high-biomass assemblage is also likely to be widespread. The role of this assemblage in regional ecosystem and carbon dynamics and its sensitivities to anthropogenic impacts are unknown. The discovery highlights the lack of information on deep-sea biota worldwide and the potential for unanticipated impacts of deep-sea exploitation.

  4. Benthic myodocopid Ostracoda (Philomedidae) from the Southern Ocean.

    PubMed

    Chavtur, Vladimir G; Keyser, Dietmar

    2016-01-01

    This study is based on the material of myodocopid ostracodes of the family Philomedidae collected by the Russian Antarctic Polar Expeditions (1963-2007) and the Germany Expeditions on R/V "Polarstern" (1990-2002) from the continental shelf and upper slope near the Mawson and Davis stations, the Weddell Seas, the region of the South Shetland Islands near the Russian Polar station "Molodezhnaya" and adjacent waters. Eight philomedid species belonging to two genera were identified in these collections. Scleroconcha tuberculata sp. nov. is described and figured as a new species. Additional descriptions and figures for the species S. gallardoi Kornicker, 1971, Philomedes assimilis Brady, 1907, P. charcoti Daday, 1908, P. heptatrix Kornicker, 1975, P. rotunda Skogsberg, 1920, P. orbicularis Brady, 1907 and P. tetrathrix Kornicker, 1975 are given. Keys for all species of the mentioned genera known from the Southern Ocean are presented. A list of sampling stations and species collected is provided in the Appendix 1. PMID:27470832

  5. The influence of Southern Ocean winds on the North Atlantic carbon sink

    NASA Astrophysics Data System (ADS)

    Bronselaer, Ben; Zanna, Laure; Munday, David R.; Lowe, Jason

    2016-06-01

    Observed and predicted increases in Southern Ocean winds are thought to upwell deep ocean carbon and increase atmospheric CO2. However, Southern Ocean dynamics affect biogeochemistry and circulation pathways on a global scale. Using idealized Massachusetts Institute of Technology General Circulation Model (MITgcm) simulations, we demonstrate that an increase in Southern Ocean winds reduces the carbon sink in the North Atlantic subpolar gyre. The increase in atmospheric CO2 due to the reduction of the North Atlantic carbon sink is shown to be of the same magnitude as the increase in atmospheric CO2 due to Southern Ocean outgassing. The mechanism can be described as follows: The increase in Southern Ocean winds leads to an increase in upper ocean northward nutrient transport. Biological productivity is therefore enhanced in the tropics, which alters the chemistry of the subthermocline waters that are ultimately upwelled in the subpolar gyre. The results demonstrate the influence of Southern Ocean winds on the North Atlantic carbon sink and show that the effect of Southern Ocean winds on atmospheric CO2 is likely twice as large as previously thought in past, present, and future climates.

  6. Magnetic Anomalies in the Enderby Basin, the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nogi, Y.; Sato, T.; Hanyu, T.

    2013-12-01

    Magnetic anomalies in the Southern indian Ocean are vital to understanding initial breakup process of Gondwana. However, seafloor age estimated from magnetic anomalies still remain less well-defined because of the sparse observations in this area. To understand the seafloor spreading history related to the initial breakup process of Gondwana, vector magnetic anomaly data as well as total intensity magnetic anomaly data obtained by the R/V Hakuho-maru and the icebreaker Shirase in the Enderby Basin, Southern Indian Ocean, are used. The strikes of magnetic structures are deduced from the vector magnetic anomalies. Magnetic anomaly signals, most likely indicating Mesozoic magnetic anomaly sequence, are obtained almost parallel to the west of WNW-ESE trending lineaments just to the south of Conrad Rise inferred from satellite gravity anomalies. Most of the strikes of magnetic structures indicate NNE-SSW trends, and are almost perpendicular to the WNW-ESE trending lineaments. Mesozoic sequence magnetic anomalies with mostly WNW-ESE strikes are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and Gunnerus Ridge. Magnetic anomalies originated from Cretaceous normal polarity superchron are found in these profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. However Mesozoic sequence magnetic anomalies are only observed in the west side of the WNW-ESE trending lineaments just to the south of Conrad Rise and not detected to the east of Cretaceous normal superchron signals. These results show that counter part of Mesozoic sequence magnetic anomalies in the south of Conrad Rise would be found in the East Enderby Basin, off East Antarctica. NNE-SSW trending magnetic structures, which are similar to those obtained just to the south of Conrad Rise, are found off East Antarctica in the East Enderby Basin. However, some of the strikes show almost E-W orientations. These suggest complicated ridge

  7. Iron defecation by sperm whales stimulates carbon export in the Southern Ocean.

    PubMed

    Lavery, Trish J; Roudnew, Ben; Gill, Peter; Seymour, Justin; Seuront, Laurent; Johnson, Genevieve; Mitchell, James G; Smetacek, Victor

    2010-11-22

    The iron-limited Southern Ocean plays an important role in regulating atmospheric CO(2) levels. Marine mammal respiration has been proposed to decrease the efficiency of the Southern Ocean biological pump by returning photosynthetically fixed carbon to the atmosphere. Here, we show that by consuming prey at depth and defecating iron-rich liquid faeces into the photic zone, sperm whales (Physeter macrocephalus) instead stimulate new primary production and carbon export to the deep ocean. We estimate that Southern Ocean sperm whales defecate 50 tonnes of iron into the photic zone each year. Molar ratios of C(export):Fe(added) determined during natural ocean fertilization events are used to estimate the amount of carbon exported to the deep ocean in response to the iron defecated by sperm whales. We find that Southern Ocean sperm whales stimulate the export of 4 × 10(5) tonnes of carbon per year to the deep ocean and respire only 2 × 10(5) tonnes of carbon per year. By enhancing new primary production, the populations of 12 000 sperm whales in the Southern Ocean act as a carbon sink, removing 2 × 10(5) tonnes more carbon from the atmosphere than they add during respiration. The ability of the Southern Ocean to act as a carbon sink may have been diminished by large-scale removal of sperm whales during industrial whaling.

  8. Variability and trends in Southern Ocean eddy activity in 1/12° ocean model simulations

    NASA Astrophysics Data System (ADS)

    Patara, Lavinia; Böning, Claus W.; Biastoch, Arne

    2016-05-01

    The response of eddy kinetic energy (EKE) to the strengthening of Southern Hemisphere winds occurring since the 1950s is investigated with a global ocean model having a resolution of 1/12° in the Antarctic Circumpolar Current domain. The simulations expose regional differences in the relative importance of stochastic and wind-related contributions to interannual EKE changes. In the Pacific and Indian sectors the model captures the EKE variability observed since 1993 and confirms previous hypotheses of a lagged response to regional wind stress anomalies. Here the multidecadal trend in wind stress is reflected in an increase in EKE typically exceeding 5 cm2 s-2 decade-1. In the western Atlantic, EKE variability is mostly stochastic, is weakly correlated with wind fluctuations, and its multidecadal trends are close to zero. The nonuniform distribution of wind-related changes in the eddy activity could affect the regional patterns of ocean circulation and biogeochemical responses to future climate change.

  9. Southern Ocean Seasonal Net Production from Satellite, Atmosphere, and Ocean Data Sets

    NASA Technical Reports Server (NTRS)

    Keeling, Ralph F.; Campbell, J. (Technical Monitor)

    2002-01-01

    A new climatology of monthly air-sea O2 flux was developed using the net air-sea heat flux as a template for spatial and temporal interpolation of sparse hydrographic data. The climatology improves upon the previous climatology of Najjar and Keeling in the Southern Hemisphere, where the heat-based approach helps to overcome limitations due to sparse data coverage. The climatology is used to make comparisons with productivity derived from CZCS images. The climatology is also used in support of an investigation of the plausible impact of recent global warming an oceanic O2 inventories.

  10. DNA Analyses of Phytoplankton in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Guo, K.; Bench, S.; Saltzman, J.

    2013-12-01

    Microbes and phytoplankton are extremely important for marine life because they produce much of Earth's oxygen and are the foundation for ocean ecosystems, such as the Southern Ocean around Antarctica. As it is undergoing some of the most extreme warming on Earth, the Western Antarctic Peninsula (WAP) is experiencing drastic changes in the ecosystem, which motivates researchers to study its population of microbes and phytoplankton. However, little research has been done on the genetic changes that the microbes and phytoplankton have undergone. The research project I worked on studies the genetic changes of the WAP organisms through three steps: sampling, which is done at the Palmer station in the WAP, sequencing, and microarrays. Throughout the course of the summer, I contributed to the sequencing aspect of the project by conducting DNA extractions and determining the quality and quantity of DNA in the samples. DNA extractions and quality checking are necessary for my project in order to prepare the DNA for sequencing and to use in microarray experiments. Additionally, I performed microscopy and looked at high-performance liquid chromatography (HPLC) pigment ratios to identify which organisms are in the collected samples. The data from the microscopy and the HPLC pigment ratios provide support for the results yielded from the DNA sequences and microarrays.

  11. How deep is deep enough? Ocean iron fertilization and carbon sequestration in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Robinson, J.; Popova, E. E.; Yool, A.; Srokosz, M.; Lampitt, R. S.; Blundell, J. R.

    2014-04-01

    Artificial ocean iron fertilization (OIF) enhances phytoplankton productivity and is being explored as a means of sequestering anthropogenic carbon within the deep ocean. To be considered successful, carbon should be exported from the surface ocean and isolated from the atmosphere for an extended period (e.g., the Intergovernmental Panel on Climate Change's standard 100 year time horizon). This study assesses the impact of deep circulation on carbon sequestered by OIF in the Southern Ocean, a high-nutrient low-chlorophyll region known to be iron stressed. A Lagrangian particle-tracking approach is employed to analyze water mass trajectories over a 100 year simulation. By the end of the experiment, for a sequestration depth of 1000 m, 66% of the carbon had been reexposed to the atmosphere, taking an average of 37.8 years. Upwelling occurs predominately within the Antarctic Circumpolar Current due to Ekman suction and topography. These results emphasize that successful OIF is dependent on the physical circulation, as well as the biogeochemistry.

  12. Mechanisms of the meridional heat transport in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Volkov, Denis L.; Fu, Lee-Lueng; Lee, Tong

    2010-08-01

    The Southern Ocean (SO) transports heat towards Antarctica and plays an important role in determining the heat budget of the Antarctic climate system. A global ocean data synthesis product at eddy-permitting resolution from the Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2) project is used to estimate the meridional heat transport (MHT) in the SO and to analyze its mechanisms. Despite the intense eddy activity, we demonstrate that most of the poleward MHT in the SO is due to the time-mean fields of the meridional velocity, V, and potential temperature, θ. This is because the mean circulation in the SO is not strictly zonal. The Antarctic Circumpolar Current carries warm waters from the region south of the Agulhas Retroflection to the lower latitudes of the Drake Passage and the Malvinas Current carries cold waters northward along the Argentinian shelf. Correlations between the time-varying fields of V and θ (defined as transient processes) significantly contribute to the horizontal-gyre heat transport, but not the overturning heat transport. In the highly energetic regions of the Agulhas Retroflection and the Brazil-Malvinas Confluence the contribution of the horizontal transient processes to the total MHT exceeds the contribution of the mean horizontal flow. We show that the southward total MHT is mainly maintained by the meridional excursion of the mean geostrophic horizontal shear flow (i.e., deviation from the zonal average) associated with the Antarctic Circumpolar Current that balances the equatorward MHT due to the Ekman transport and provides a net poleward MHT in the SO. The Indian sector of the SO serves as the main pathway for the poleward MHT.

  13. State of the Antarctic and Southern Ocean climate system

    NASA Astrophysics Data System (ADS)

    Mayewski, P. A.; Meredith, M. P.; Summerhayes, C. P.; Turner, J.; Worby, A.; Barrett, P. J.; Casassa, G.; Bertler, N. A. N.; Bracegirdle, T.; Naveira Garabato, A. C.; Bromwich, D.; Campbell, H.; Hamilton, G. S.; Lyons, W. B.; Maasch, K. A.; Aoki, S.; Xiao, C.; van Ommen, Tas

    2009-03-01

    This paper reviews developments in our understanding of the state of the Antarctic and Southern Ocean climate and its relation to the global climate system over the last few millennia. Climate over this and earlier periods has not been stable, as evidenced by the occurrence of abrupt changes in atmospheric circulation and temperature recorded in Antarctic ice core proxies for past climate. Two of the most prominent abrupt climate change events are characterized by intensification of the circumpolar westerlies (also known as the Southern Annular Mode) between ˜6000 and 5000 years ago and since 1200-1000 years ago. Following the last of these is a period of major trans-Antarctic reorganization of atmospheric circulation and temperature between A.D. 1700 and 1850. The two earlier Antarctic abrupt climate change events appear linked to but predate by several centuries even more abrupt climate change in the North Atlantic, and the end of the more recent event is coincident with reorganization of atmospheric circulation in the North Pacific. Improved understanding of such events and of the associations between abrupt climate change events recorded in both hemispheres is critical to predicting the impact and timing of future abrupt climate change events potentially forced by anthropogenic changes in greenhouse gases and aerosols. Special attention is given to the climate of the past 200 years, which was recorded by a network of recently available shallow firn cores, and to that of the past 50 years, which was monitored by the continuous instrumental record. Significant regional climate changes have taken place in the Antarctic during the past 50 years. Atmospheric temperatures have increased markedly over the Antarctic Peninsula, linked to nearby ocean warming and intensification of the circumpolar westerlies. Glaciers are retreating on the peninsula, in Patagonia, on the sub-Antarctic islands, and in West Antarctica adjacent to the peninsula. The penetration of marine

  14. The effects of iron fertilization on carbon sequestration in the Southern Ocean.

    PubMed

    Buesseler, Ken O; Andrews, John E; Pike, Steven M; Charette, Matthew A

    2004-04-16

    An unresolved issue in ocean and climate sciences is whether changes to the surface ocean input of the micronutrient iron can alter the flux of carbon to the deep ocean. During the Southern Ocean Iron Experiment, we measured an increase in the flux of particulate carbon from the surface mixed layer, as well as changes in particle cycling below the iron-fertilized patch. The flux of carbon was similar in magnitude to that of natural blooms in the Southern Ocean and thus small relative to global carbon budgets and proposed geoengineering plans to sequester atmospheric carbon dioxide in the deep sea.

  15. Dissolved organic carbon in the deep Southern Ocean: Local versus distant controls

    NASA Astrophysics Data System (ADS)

    Bercovici, Sarah K.; Hansell, Dennis A.

    2016-02-01

    The global ocean contains a massive reservoir (662 ± 32 Pg C) of dissolved organic carbon (DOC), and its dynamics, particularly in the deepest zones, are only slowly being understood. DOC in the deep ocean is ubiquitously low in concentration (~35 to 48 µmol kg-1) and aged (4000 to 6000 years), persisting for multiple meridional overturning circulations. Deep waters relatively enriched in DOC form in the North Atlantic, migrate to the Southern Ocean to mix with waters from Antarctic shelves and the deep Pacific and Indian Oceans, in turn forming the voluminous waters of the Circumpolar Deep Water. Here we seek evidence for local (autochthonous) versus distant (allochthonous) processes in determining the distribution of DOC in the deep Southern Ocean. Prior analyses on DOC in the deep Southern Ocean have conflicted, describing both conservative and nonconservative traits: the deep DOC field has been reported as uniform in distribution, yet local inputs have been suggested as quantitatively important. We use multiple approaches (multiple linear regression, mass transport, and mass balance calculations) with data from Climate Variability and Predictability Repeat Hydrography sections to evaluate the system. We find that DOC concentrations in the deep Southern Ocean largely reflect the conservative mixing of the several deep waters entering the system from the north. Mass balance suggests that the relatively depleted DOC radiocarbon content in the deep Southern Ocean is a conserved property as well. These analyses advance our understanding of the controls on the DOC reservoir of the Southern Ocean.

  16. The Need for a Southern Branch Campus of Ocean County College.

    ERIC Educational Resources Information Center

    Ocean County Coll., Toms River, NJ. Office of Institutional Research.

    In 1989, a study was conducted at Ocean County College (OCC) to determine the feasibility of establishing a branch campus in southern Ocean County, New Jersey. Specific factors examined in the study included Ocean County's demographic characteristics (e.g., land area and dispersion, population trends, public transportation, and economic trends);…

  17. Southern Ocean heat and carbon uptake: mechanisms, recent trends, and future changes

    NASA Astrophysics Data System (ADS)

    Froelicher, T. L.

    2015-12-01

    The Southern Ocean's dominant influence on the global heat balance and nutrient and carbon cycles stems from the fact that it is the primary gateway through which Earth's cold, centuries old and nutrient rich deep and bottom waters interact with the atmosphere. The westerly winds in the Southern Hemisphere drive a strongly divergent surface flow that draws up water from below in a wide ring circling the Antarctic continent. In the first part of the talk, we assess the uptake, transport, and storage of oceanic anthropogenic carbon and heat in the Southern Ocean over the period 1861-2005 in a new set of carbon-climate Earth System Models. Simulations show that the Southern Ocean south of 30°S, covering only 30% of the global surface ocean area, accounts for more than 40% of global anthropogenic carbon uptake. Furthermore, the Southern Ocean takes up three quarters of the total excess heat generated by the increasing levels of greenhouse gases in the atmosphere. Anthropogenic carbon and heat storage show a common broad-scale pattern of change, but ocean heat storage is more structured than ocean carbon storage suggesting that different mechanisms are important. The Southern Ocean, however, remains the region where models differ the most in the representation of anthropogenic carbon and, in particular, heat uptake. While the Southern Ocean carbon uptake has increased considerably in recent decades, as expected based on the substantial increase in atmospheric CO2, there is considerable concern that this sink will saturate or even reverse in response to warming, changing ocean circulation and chemistry. In the second part of the talk, novel multi-millennial global warming simulations with a comprehensive Earth System Model under a 1% yr-1 atmospheric CO2 increase to 2xCO2 and constant forcing thereafter scenario will be used to explore future long-term changes in the Southern Ocean carbon uptake. We show that after full equilibration of the model with doubling of

  18. Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long-term global warming

    NASA Astrophysics Data System (ADS)

    Yamamoto, A.; Abe-Ouchi, A.; Shigemitsu, M.; Oka, A.; Takahashi, K.; Ohgaito, R.; Yamanaka, Y.

    2015-10-01

    Global warming is expected to decrease ocean oxygen concentrations by less solubility of surface ocean and change in ocean circulation. The associated expansion of the oxygen minimum zone would have adverse impacts on marine organisms and ocean biogeochemical cycles. Oxygen reduction is expected to persist for a thousand years or more, even after atmospheric carbon dioxide stops rising. However, long-term changes in ocean oxygen and circulation are still unclear. Here we simulate multimillennium changes in ocean circulation and oxygen under doubling and quadrupling of atmospheric carbon dioxide, using a fully coupled atmosphere-ocean general circulation model and an offline biogeochemical model. In the first 500 years, global oxygen concentration decreases, consistent with previous studies. Thereafter, however, the oxygen concentration in the deep ocean globally recovers and overshoots at the end of the simulations, despite surface oxygen decrease and weaker Atlantic meridional overturning circulation. This is because, after the initial cessation, the recovery and overshooting of deep ocean convection in the Weddell Sea enhance ventilation and supply oxygen-rich surface waters to deep ocean. Another contributor to deep ocean oxygenation is seawater warming, which reduces the export production and shifts the organic matter remineralization to the upper water column. Our results indicate that the change in ocean circulation in the Southern Ocean potentially drives millennial-scale oxygenation in deep ocean, which is opposite to the centennial-scale global oxygen reduction and general expectation.

  19. High Biomass Low Export Regimes in the Southern Ocean

    SciTech Connect

    Lam, Phoebe J.; Bishop, James K.B.

    2006-01-27

    This paper investigates ballasting and remineralization controls of carbon sedimentation in the twilight zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 {micro}m, 1-51 {micro}m, >51 {micro}m) suspended particulate matter was collected by large volume in-situ filtration from the upper 1000 m in the Subantarctic (55 S, 172 W) and Antarctic (66 S, 172 W) zones of the Southern Ocean during the Southern Ocean Iron Experiment (SOFeX) in January-February 2002. Particles were analyzed for major chemical constituents (POC, P, biogenic Si, CaCO3), and digital and SEM image analyses of particles were used to aid in the interpretation of the chemical profiles. Twilight zone waters at 66 S in the Antarctic had a steeper decrease in POC with depth than at 55 S in the Subantarctic, with lower POC concentrations in all size fractions at 66 S than at 55 S, despite up to an order of magnitude higher POC in surface waters at 66 S. The decay length scale of >51 {micro}m POC was significantly shorter in the upper twilight zone at 66 S ({delta}{sub e}=26 m) compared to 55 S ({delta}{sub e}=81 m). Particles in the carbonate-producing 55 S did not have higher excess densities than particles from the diatom-dominated 66 S, indicating that there was no direct ballast effect that accounted for deeper POC penetration at 55 S. An indirect ballast effect due to differences in particle packaging and porosities cannot be ruled out, however, as aggregate porosities were high ({approx}97%) and variable. Image analyses point to the importance of particle loss rates from zooplankton grazing and remineralization as determining factors for the difference in twilight zone POC concentrations at 55 S and 66 S, with stronger and more focused shallow remineralization at 66 S. At 66 S, an abundance of large (several mm long) fecal pellets from the surface to 150 m, and almost total removal of large aggregates by 200 m, reflected the actions of a single or few zooplankton species capable of

  20. Satellite-Derived Dynamics of Southern Ocean Sea Ice

    NASA Technical Reports Server (NTRS)

    Drinkwater, Mark R.; Liu, Xiang

    2000-01-01

    Antarctic ERS-2, RADARSAT Synthetic Aperture Radar and ERS-1/2 Scatterometer images were analyzed with SMMI radiometer image time-series data to investigate seasonal variability in satellite-tracked sea-ice dynamics in the Southern Ocean during 1992. Supporting field data were acquired during 'in-situ' experiments including the winter 1992 Ice Station Weddell and Winter Weddell Gyre studies. A variety of surface measurements were made during these experiments including Argos-buoy deployment and GPS drift measurements. These are used in conjunction with International Program for Antarctic Buoys drift trajectories for ice-motion tracking validation. Comparisons between gridded Special Sensor Microwave Imager (SSMI) ice-motion vectors and European Center for Medium Range Weather Forecasts/National Centers for Environmental Prediction (ECMWF/NCEP) analyses indicate that large-scale drift is forced predominantly by the long-term mean, large-scale synoptic pressure field. Only sub-daily SAR sea-ice tracking can capture high-frequency fluctuations, driven by polar lows or tidal forcing. In these cases, sea-ice drift can respond rapidly to changes in forcing on semi-diurnal time scales depending on the location with respect to the coastline. Seasonality of ice drift, particularly in the Weddell and Ross Seas, is linked to ice extent and compactness, and internal ice stresses transmitted through the pack ice from the coast. Three-monthly seasonal climatologies are presented of austral winter of ice drift in the Southern Ocean. The large Weddell and Ross Sea gyres are clearly resolved along with key seasonal and spatial attributes of their cyclonic circulation. Regional time series of ice dynamics parameters are used to illustrate correlations with meteorological forcing. Persistent divergence such as that occurring in the Ronne-Filchner polynya system results in large fractions of new ice. Similarly, convergence zones produce large fractions of deformed ice and characterize

  1. The biodiversity of the deep Southern Ocean benthos

    PubMed Central

    Brandt, A; De Broyer, C; De Mesel, I; Ellingsen, K.E; Gooday, A.J; Hilbig, B; Linse, K; Thomson, M.R.A; Tyler, P.A

    2006-01-01

    Our knowledge of the biodiversity of the Southern Ocean (SO) deep benthos is scarce. In this review, we describe the general biodiversity patterns of meio-, macro- and megafaunal taxa, based on historical and recent expeditions, and against the background of the geological events and phylogenetic relationships that have influenced the biodiversity and evolution of the investigated taxa. The relationship of the fauna to environmental parameters, such as water depth, sediment type, food availability and carbonate solubility, as well as species interrelationships, probably have shaped present-day biodiversity patterns as much as evolution. However, different taxa exhibit different large-scale biodiversity and biogeographic patterns. Moreover, there is rarely any clear relationship of biodiversity pattern with depth, latitude or environmental parameters, such as sediment composition or grain size. Similarities and differences between the SO biodiversity and biodiversity of global oceans are outlined. The high percentage (often more than 90%) of new species in almost all taxa, as well as the high degree of endemism of many groups, may reflect undersampling of the area, and it is likely to decrease as more information is gathered about SO deep-sea biodiversity by future expeditions. Indeed, among certain taxa such as the Foraminifera, close links at the species level are already apparent between deep Weddell Sea faunas and those from similar depths in the North Atlantic and Arctic. With regard to the vertical zonation from the shelf edge into deep water, biodiversity patterns among some taxa in the SO might differ from those in other deep-sea areas, due to the deep Antarctic shelf and the evolution of eurybathy in many species, as well as to deep-water production that can fuel the SO deep sea with freshly produced organic matter derived not only from phytoplankton, but also from ice algae. PMID:17405207

  2. Meltwater input to the southern ocean during the last glacial maximum

    SciTech Connect

    Shemesh, A.; Burckle, L.H.; Hays, J.D.

    1994-12-02

    Three records of oxygen isotopes in biogenic silica from deep-sea sediment cores from the Atlantic and Indian sectors of the Southern Ocean reveal the presence of isotopically depleted diatomaceous opal in sediment from the last glacial maximum. This depletion is attributed to the presence of lids of meltwater that mixed with surface water along certain trajectories in the Southern Ocean. An increase in the drainage from Antarctica or extensive northward transport of icebergs are among the main mechanisms that could have produced the increase in meltwater input to the glacial Southern Ocean. Similar isotopic trends were observed in older climatic cycles at the same cores.

  3. Development of the Southern Ocean Climate Model Atlas

    NASA Astrophysics Data System (ADS)

    Rudd, J.; Russell, J. L.; Goodman, P. J.

    2014-12-01

    The development of consistent, observationally-based metrics, by which to assess the fidelity of a model simulation is being undertaken by many modelers and modeling groups. A "Southern Ocean Climate Model Atlas" is under construction that will house the results of these various analyses and will provide access for fellow scientists, stakeholders, resource managers and the public to the latest projections of climate and climate change from all of the available climate models. This Atlas will allow a visual comparison of simulated fields, differences and errors and will include quantification of the errors where the observations permit. It will also include the scripts required for anyone to create a comparable map with their own data/output. We will discuss the creation of observationally-based metrics and some of the challenges associated with the consistent quantification of simulations errors and inter-model differences. We will also present some of the commonly assessed variables (e.g. temperature, winds, ice, pH) useful to climate scientists, ecosystem scientists and the general public.

  4. Algal pigments in Southern Ocean abyssal foraminiferans indicate pelagobenthic coupling

    NASA Astrophysics Data System (ADS)

    Cedhagen, Tomas; Cheah, Wee; Bracher, Astrid; Lejzerowicz, Franck

    2014-10-01

    The cytoplasm of four species of abyssal benthic foraminiferans from the Southern Ocean (around 51°S; 12°W and 50°S; 39°W) was analysed by High Performance Liquid Chromatography (HPLC) and found to contain large concentrations of algal pigments and their degradation products. The composition of the algal pigments in the foraminiferan cytoplasm reflected the plankton community at the surface. Some foraminiferans contained high ratios of chlorophyll a/degraded pigments because they were feeding on fresher phytodetritus. Other foraminiferans contained only degraded pigments which shows that they utilized degraded phytodetritus. The concentration of algal pigment and corresponding degradation products in the foraminiferan cytoplasm is much higher than in the surrounding sediment. It shows that the foraminiferans collect a diluted and sparse food resource and concentrate it as they build up their cytoplasm. This ability contributes to the understanding of the great quantitative success of foraminiferans in the deep sea. Benthic foraminiferans are a food source for many abyssal metazoans. They form a link between the degraded food resources, phytodetritus, back to the active metazoan food chains.

  5. Response of the Southern Ocean to the Southern Annular Mode: interannual variability and multidecadal trend

    NASA Astrophysics Data System (ADS)

    Treguier, Anne Marie; Le Sommer, Julien; Molines, Jean-Marc; de Cuevas, Beverly

    2010-05-01

    We evaluate the response of the Southern Ocean to the variability and multi-decadal trend of the Southern Annular mode (SAM) from 1972 to 2001, in a global eddy-permitting model of the DRAKKAR project. The transport of the Antarctic Circumpolar Current (ACC) is correlated with the SAM at interannual time scales but exhibits a drift due to the thermodynamic adjustment of the model (the ACC transport decreases due to a low renewal rate of dense waters around Antarctica). The interannual variability of the eddy kinetic energy (EKE) and the ACC transport are uncorrelated, and meridional eddy fluxes of heat and buoyancy remain stable. The contribution of oceanic eddies to meridional transports is an important issue because a growth of the poleward eddy transport could, in theory, oppose the increase of the mean overturning circulation forced by the SAM. In our model, the total meridional circulation at 50S is well correlated with the SAM index (and the Ekman transport) at interannual time scales, and both increase over three decades between 1972 and 2001. However, given the long-term drift, no SAM-linked trend in the eddy contribution to the meridional overturning circulation is detectable. The increase of the meridional overturning is due to the time-mean component, and is compensated by an increased buoyancy gain at the surface. We emphasize that the meridional circulation does not vary in a simple relationship with the the zonal circulation. Our model solution points out that the zonal circulation and the eddy kinetic energy are governed by different mechanisms according to the time scale considered (interannual or decadal).

  6. Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation.

    PubMed

    Knorr, Gregor; Lohmann, Gerrit

    2003-07-31

    During the two most recent deglaciations, the Southern Hemisphere warmed before Greenland. At the same time, the northern Atlantic Ocean was exposed to meltwater discharge, which is generally assumed to reduce the formation of North Atlantic Deep Water. Yet during deglaciation, the Atlantic thermohaline circulation became more vigorous, in the transition from a weak glacial to a strong interglacial mode. Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation. We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation, triggered by increased mass transport into the Atlantic Ocean via the warm (Indian Ocean) and cold (Pacific Ocean) water route. This effect prevails over the influence of meltwater discharge, which would oppose a strengthening of the thermohaline circulation. A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation, in agreement with the available proxy records.

  7. Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles

    NASA Astrophysics Data System (ADS)

    Le Quéré, C.; Buitenhuis, E. T.; Moriarty, R.; Alvain, S.; Aumont, O.; Bopp, L.; Chollet, S.; Enright, C.; Franklin, D. J.; Geider, R. J.; Harrison, S. P.; Hirst, A.; Larsen, S.; Legendre, L.; Platt, T.; Prentice, I. C.; Rivkin, R. B.; Sathyendranath, S.; Stephens, N.; Vogt, M.; Sailley, S.; Vallina, S. M.

    2015-07-01

    Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs); six types of phytoplankton, three types of zooplankton, and heterotrophic bacteria. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing zooplankton, and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean High Nutrient Low Chlorophyll (HNLC) region during summer. When model simulations do not represent crustacean macrozooplankton grazing, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there was no iron deposition from dust. When model simulations included the developments of the zooplankton component, the simulation of phytoplankton biomass improved and the high chlorophyll summer bias in the Southern Ocean HNLC region largely disappeared. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community rather than iron limitation. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.

  8. Southern Ocean origin for the resumption of Atlantic thermohaline circulation during deglaciation.

    PubMed

    Knorr, Gregor; Lohmann, Gerrit

    2003-07-31

    During the two most recent deglaciations, the Southern Hemisphere warmed before Greenland. At the same time, the northern Atlantic Ocean was exposed to meltwater discharge, which is generally assumed to reduce the formation of North Atlantic Deep Water. Yet during deglaciation, the Atlantic thermohaline circulation became more vigorous, in the transition from a weak glacial to a strong interglacial mode. Here we use a three-dimensional ocean circulation model to investigate the impact of Southern Ocean warming and the associated sea-ice retreat on the Atlantic thermohaline circulation. We find that a gradual warming in the Southern Ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation, triggered by increased mass transport into the Atlantic Ocean via the warm (Indian Ocean) and cold (Pacific Ocean) water route. This effect prevails over the influence of meltwater discharge, which would oppose a strengthening of the thermohaline circulation. A Southern Ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of Southern and Northern hemispheric climate change at times of deglaciation, in agreement with the available proxy records. PMID:12891352

  9. Ocean Response to Possible Southern Meltwater Pulses During Eocene-Oligocene Cooling Climate Trend: A Sensitivity Ocean Modeling Study

    NASA Astrophysics Data System (ADS)

    Haupt, B. J.; Seidov, D.

    2003-12-01

    Understanding ocean circulation and sea level change in the past (and foreseeable future) is one of the focal points of paleoceanography. Sea level may change due to several primary causes, including the meltdown of the major ice sheets, sea ice melting, and changes in the thermohaline structure of the oceans. The sensitivity of the past ocean circulation to meltwater impacts may have been different from the present-day. We still have only a vague understanding of how ocean basin geography may influence the freshwater impacts in different oceans; the role of geography is important for reconstructing variability of past climates with substantially different land-sea distributions. As freshwater impacts in past geologic eras having different basins configurations may have been different from the present-day pattern, the sensitivity of the ocean circulation to sea surface density impacts and climate change could have been different as well. We use the Eocene-Oligocene geometry and climate to address the past ocean and sea level long-term internal variability because this time slice provides a substantially different geometry and for a strong sea ice impact that can be seen in the geologic record. The Eocene epoch is crucial as a transition from the warm Cretaceous ocean to cooler oceans that may have been subject to bi-polar millennial-scale oscillations of the deep ocean circulation caused by freshwater pulses of the developing southern cryosphere. In a series of numerical experiments, sea ice melting and sea water freezing around Antarctica were simulated by superimposing freshwater layers over zonally-averaged sea surface salinity. Eocene sea surface temperature and sea surface salinity are specified based on the paleoclimatic record and modeling. In our simulations, the Eocene ocean circulation is indeed sensitive to freshwater impacts in the Southern Hemisphere. There are noticeable sea level changes caused by the restructuring of the deep ocean thermal and

  10. Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age.

    PubMed

    Jaccard, Samuel L; Galbraith, Eric D; Martínez-García, Alfredo; Anderson, Robert F

    2016-02-11

    No single mechanism can account for the full amplitude of past atmospheric carbon dioxide (CO2) concentration variability over glacial-interglacial cycles. A build-up of carbon in the deep ocean has been shown to have occurred during the Last Glacial Maximum. However, the mechanisms responsible for the release of the deeply sequestered carbon to the atmosphere at deglaciation, and the relative importance of deep ocean sequestration in regulating millennial-timescale variations in atmospheric CO2 concentration before the Last Glacial Maximum, have remained unclear. Here we present sedimentary redox-sensitive trace-metal records from the Antarctic Zone of the Southern Ocean that provide a reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our data suggest that respired carbon was removed from the abyssal Southern Ocean during the Northern Hemisphere cold phases of the deglaciation, when atmospheric CO2 concentration increased rapidly, reflecting--at least in part--a combination of dwindling iron fertilization by dust and enhanced deep ocean ventilation. Furthermore, our records show that the observed covariation between atmospheric CO2 concentration and abyssal Southern Ocean oxygenation was maintained throughout most of the past 80,000 years. This suggests that on millennial timescales deep ocean circulation and iron fertilization in the Southern Ocean played a consistent role in modifying atmospheric CO2 concentration.

  11. Covariation of deep Southern Ocean oxygenation and atmospheric CO2 through the last ice age.

    PubMed

    Jaccard, Samuel L; Galbraith, Eric D; Martínez-García, Alfredo; Anderson, Robert F

    2016-02-11

    No single mechanism can account for the full amplitude of past atmospheric carbon dioxide (CO2) concentration variability over glacial-interglacial cycles. A build-up of carbon in the deep ocean has been shown to have occurred during the Last Glacial Maximum. However, the mechanisms responsible for the release of the deeply sequestered carbon to the atmosphere at deglaciation, and the relative importance of deep ocean sequestration in regulating millennial-timescale variations in atmospheric CO2 concentration before the Last Glacial Maximum, have remained unclear. Here we present sedimentary redox-sensitive trace-metal records from the Antarctic Zone of the Southern Ocean that provide a reconstruction of transient changes in deep ocean oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our data suggest that respired carbon was removed from the abyssal Southern Ocean during the Northern Hemisphere cold phases of the deglaciation, when atmospheric CO2 concentration increased rapidly, reflecting--at least in part--a combination of dwindling iron fertilization by dust and enhanced deep ocean ventilation. Furthermore, our records show that the observed covariation between atmospheric CO2 concentration and abyssal Southern Ocean oxygenation was maintained throughout most of the past 80,000 years. This suggests that on millennial timescales deep ocean circulation and iron fertilization in the Southern Ocean played a consistent role in modifying atmospheric CO2 concentration. PMID:26840491

  12. Iron Limitation Modulates Ocean Acidification Effects on Southern Ocean Phytoplankton Communities

    PubMed Central

    Hoppe, Clara J. M.; Hassler, Christel S.; Payne, Christopher D.; Tortell, Philippe D.; Rost, Björn; Trimborn, Scarlett

    2013-01-01

    The potential interactive effects of iron (Fe) limitation and Ocean Acidification in the Southern Ocean (SO) are largely unknown. Here we present results of a long-term incubation experiment investigating the combined effects of CO2 and Fe availability on natural phytoplankton assemblages from the Weddell Sea, Antarctica. Active Chl a fluorescence measurements revealed that we successfully cultured phytoplankton under both Fe-depleted and Fe-enriched conditions. Fe treatments had significant effects on photosynthetic efficiency (Fv/Fm; 0.3 for Fe-depleted and 0.5 for Fe-enriched conditions), non-photochemical quenching (NPQ), and relative electron transport rates (rETR). pCO2 treatments significantly affected NPQ and rETR, but had no effect on Fv/Fm. Under Fe limitation, increased pCO2 had no influence on C fixation whereas under Fe enrichment, primary production increased with increasing pCO2 levels. These CO2-dependent changes in productivity under Fe-enriched conditions were accompanied by a pronounced taxonomic shift from weakly to heavily silicified diatoms (i.e. from Pseudo-nitzschia sp. to Fragilariopsis sp.). Under Fe-depleted conditions, this functional shift was absent and thinly silicified species dominated all pCO2 treatments (Pseudo-nitzschia sp. and Synedropsis sp. for low and high pCO2, respectively). Our results suggest that Ocean Acidification could increase primary productivity and the abundance of heavily silicified, fast sinking diatoms in Fe-enriched areas, both potentially leading to a stimulation of the biological pump. Over much of the SO, however, Fe limitation could restrict this possible CO2 fertilization effect. PMID:24278207

  13. Developing priority variables ("ecosystem Essential Ocean Variables" - eEOVs) for observing dynamics and change in Southern Ocean ecosystems

    NASA Astrophysics Data System (ADS)

    Constable, Andrew J.; Costa, Daniel P.; Schofield, Oscar; Newman, Louise; Urban, Edward R.; Fulton, Elizabeth A.; Melbourne-Thomas, Jessica; Ballerini, Tosca; Boyd, Philip W.; Brandt, Angelika; de la Mare, Willaim K.; Edwards, Martin; Eléaume, Marc; Emmerson, Louise; Fennel, Katja; Fielding, Sophie; Griffiths, Huw; Gutt, Julian; Hindell, Mark A.; Hofmann, Eileen E.; Jennings, Simon; La, Hyoung Sul; McCurdy, Andrea; Mitchell, B. Greg; Moltmann, Tim; Muelbert, Monica; Murphy, Eugene; Press, Anthony J.; Raymond, Ben; Reid, Keith; Reiss, Christian; Rice, Jake; Salter, Ian; Smith, David C.; Song, Sun; Southwell, Colin; Swadling, Kerrie M.; Van de Putte, Anton; Willis, Zdenka

    2016-09-01

    Reliable statements about variability and change in marine ecosystems and their underlying causes are needed to report on their status and to guide management. Here we use the Framework on Ocean Observing (FOO) to begin developing ecosystem Essential Ocean Variables (eEOVs) for the Southern Ocean Observing System (SOOS). An eEOV is a defined biological or ecological quantity, which is derived from field observations, and which contributes significantly to assessments of Southern Ocean ecosystems. Here, assessments are concerned with estimating status and trends in ecosystem properties, attribution of trends to causes, and predicting future trajectories. eEOVs should be feasible to collect at appropriate spatial and temporal scales and are useful to the extent that they contribute to direct estimation of trends and/or attribution, and/or development of ecological (statistical or simulation) models to support assessments. In this paper we outline the rationale, including establishing a set of criteria, for selecting eEOVs for the SOOS and develop a list of candidate eEOVs for further evaluation. Other than habitat variables, nine types of eEOVs for Southern Ocean taxa are identified within three classes: state (magnitude, genetic/species, size spectrum), predator-prey (diet, foraging range), and autecology (phenology, reproductive rate, individual growth rate, detritus). Most candidates for the suite of Southern Ocean taxa relate to state or diet. Candidate autecological eEOVs have not been developed other than for marine mammals and birds. We consider some of the spatial and temporal issues that will influence the adoption and use of eEOVs in an observing system in the Southern Ocean, noting that existing operations and platforms potentially provide coverage of the four main sectors of the region - the East and West Pacific, Atlantic and Indian. Lastly, we discuss the importance of simulation modelling in helping with the design of the observing system in the long

  14. Life cycle strategies of epipelagic copepods in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Atkinson, Angus

    1998-06-01

    Twelve epipelagic copepod species were reviewed to compare their adaptations to the short primary production season and low temperatures which characterise the Southern Ocean. The species show a spectrum of adaptations, but three broad life cycle strategies were defined: (1) herbivorous in summer, a short reproductive period and winter diapause at depth ( Calanoides acutus and possibly Ctenocalanus citer); (2) predominantly omnivorous/detritivorous diet, an extended period of feeding, growth and reproduction and less reliance on diapause at depth ( Metridia gerlachei, Calanus propinquus, Calanus simillimus, Oithona similis, Microcalanus pygmaeus, and possibly Oncaea curvata and Oithona frigida); (3) overwintering and feeding within sea ice as early nauplii or copepodids ( Stephos longipes and Paralabidocera antarctica). The large species Rhincalanus gigas appears to be intermediate between strategies (1) and (2). Contrasting species from groups (1) and (2), namely C. acutus and O. similis, were selected for more detailed comparison. For C. acutus, maximum (probably food saturated) feeding and egg production rates are well below equivalent values for Calanus spp. at lower latitudes. Likewise, summer growth and moulting rates are slower, and the growth season of this herbivore is only 2-4 months. Therefore, both the low summer temperatures and short primary production season seem to dictate a long (˜1 year) life cycle for C. acutus. A collation of data on O. similis revealed that its abundance increases about tenfold from the Antarctic shelf northwards to the Polar Frontal Zone, where abundances are similar to those in temperate and tropical shelf seas. In contrast to C. acutus, O. similis appears to remain in the epipelagic and reproduce there year-round, although the food sources which sustain this are still uncertain.

  15. Export pathways of mode waters, intermediate waters, and carbon out of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Jones, D.; Meijers, A.; Haynes, P.; Karczewska, E.; Mazloff, M. R.; Sallee, J. B.; Shuckburgh, E.

    2014-12-01

    Recent observational evidence suggests that the water masses that ventilate the Southern Ocean thermocline (e.g. mode water, intermediate water) are formed and subducted via narrow, intense export windows [Sallée et al., 2010]. The idea that ventilation is localized is somewhat at odds with the more traditional picture of water mass formation as a broad circumpolar process. In this work, we aim to (i.) identify the primary mode and intermediate water export pathways out of the Southern Ocean and (ii.) to better understand the factors that control the location and intensity of these pathways. We examine the three-dimensional structure of the mode and intermediate water export routes on decadal to centennial timescales using both passive tracers and Lagrangian floats in an eddy-permitting Southern Ocean model. We find windows of strong mode water export in the Indian and Pacific sectors of the Southern Ocean and identify two potential tracks along which anthropogenic carbon dioxide and other tracers may be subducted. Our results suggest that the Pacific export pathway is especially intense, i.e. a large proportion of mode waters from both the Indian and Pacific sectors of the Southern Ocean enter subtropical latitudes via the Pacific pathway. Reference Sallée, J., K. Speer, S. Rintoul, and S. Wijffels (2010), Southern Ocean thermocline ventilation, Journal of Physical Oceanography, 40, 509-529.

  16. Impacts of Atmosphere-Ocean Coupling on Southern Hemisphere Climate Change

    NASA Technical Reports Server (NTRS)

    Li, Feng; Newman, Paul; Pawson, Steven

    2013-01-01

    Climate in the Southern Hemisphere (SH) has undergone significant changes in recent decades. These changes are closely linked to the shift of the Southern Annular Mode (SAM) towards its positive polarity, which is driven primarily by Antarctic ozone depletion. There is growing evidence that Antarctic ozone depletion has significant impacts on Southern Ocean circulation change. However, it is poorly understood whether and how ocean feedback might impact the SAM and climate change in the SH atmosphere. This outstanding science question is investigated using the Goddard Earth Observing System Coupled Atmosphere-Ocean-Chemistry Climate Model(GEOS-AOCCM).We perform ensemble simulations of the recent past (1960-2010) with and without the interactive ocean. For simulations without the interactive ocean, we use sea surface temperatures and sea ice concentrations produced by the interactive ocean simulations. The differences between these two ensemble simulations quantify the effects of atmosphere-ocean coupling. We will investigate the impacts of atmosphere-ocean coupling on stratospheric processes such as Antarctic ozone depletion and Antarctic polar vortex breakup. We will address whether ocean feedback affects Rossby wave generation in the troposphere and wave propagation into the stratosphere. Another focuson this study is to assess how ocean feedback might affect the tropospheric SAM response to Antarctic ozone depletion

  17. Atmospheric and Oceanic Response to Southern Ocean Deep Convection Oscillations on Decadal to Centennial Time Scales in Climate Models

    NASA Astrophysics Data System (ADS)

    Martin, T.; Reintges, A.; Park, W.; Latif, M.

    2014-12-01

    Many current coupled global climate models simulate open ocean deep convection in the Southern Ocean as a recurring event with time scales ranging from a few years to centennial (de Lavergne et al., 2014, Nat. Clim. Ch.). The only observation of such event, however, was the occurrence of the Weddell Polynya in the mid-1970s, an open water area of 350 000 km2 within the Antarctic sea ice in three consecutive winters. Both the wide range of modeled frequency of occurrence and the absence of deep convection in the Weddell Sea highlights the lack of understanding concerning the phenomenon. Nevertheless, simulations indicate that atmospheric and oceanic responses to the cessation of deep convection in the Southern Ocean include a strengthening of the low-level atmospheric circulation over the Southern Ocean (increasing SAM index) and a reduction in the export of Antarctic Bottom Water (AABW), potentially masking the regional effects of global warming (Latif et al., 2013, J. Clim.; Martin et al., 2014, Deep Sea Res. II). It is thus of great importance to enhance our understanding of Southern Ocean deep convection and clarify the associated time scales. In two multi-millennial simulations with the Kiel Climate Model (KCM, ECHAM5 T31 atmosphere & NEMO-LIM2 ~2˚ ocean) we showed that the deep convection is driven by strong oceanic warming at mid-depth periodically overriding the stabilizing effects of precipitation and ice melt (Martin et al., 2013, Clim. Dyn.). Sea ice thickness also affects location and duration of the deep convection. A new control simulation, in which, amongst others, the atmosphere grid resolution is changed to T42 (~2.8˚), yields a faster deep convection flip-flop with a period of 80-100 years and a weaker but still significant global climate response similar to CMIP5 simulations. While model physics seem to affect the time scale and intensity of the phenomenon, the driving mechanism is a rather robust feature. Finally, we compare the atmospheric and

  18. Dynamics of the Atlantic meridional overturning circulation and Southern Ocean in an ocean model of intermediate complexity

    NASA Astrophysics Data System (ADS)

    McCreary, Julian P.; Furue, Ryo; Schloesser, Fabian; Burkhardt, Theodore W.; Nonaka, Masami

    2016-04-01

    A steady-state, variable-density, 2-layer, ocean model (VLOM) is used to investigate basic dynamics of the Atlantic meridional overturning circulation and Southern Ocean. The domain consists of idealized (rectangular) representations of the Atlantic, Southern, and Pacific Oceans. The model equations represent the depth-averaged, layer-1 response (except for one solution in which they represent the depth-integrated flow over both layers). To allow for overturning, water can cross the bottom of layer 1 at the velocity we =wd +wm +wn , the three parts representing: interior diffusion wd that increases the layer-1 thickness h throughout the basin, mixed-layer entrainment wm that ensures h is never less than a minimum value hm , and diapycnal (cooling) processes external to the basin wn that adjust h to hn . For most solutions, horizontal mixing has the form of Rayleigh damping with coefficient ν , which we interpret to result from baroclinic instability through the closure, V∗ = - (ν /f2) ∇P , where ∇P = ∇(1/2 g‧h2) is the depth-integrated pressure gradient, g‧ is the reduced-gravity coefficient, and ν is a mixing coefficient; with this interpretation, the layer-1 flow corresponds to the sum of the Eulerian-mean and eddy-mean (V∗) transport/widths, that is, the "residual" circulation. Finally, layer-1 temperature cools polewards in response to a surface heat flux Q, and the cooling can be strong enough in the Southern Ocean for g‧ = 0 south of a latitude y0 , in which case layer 1 vanishes and the model reduces to a single layer 2. Solutions are obtained both numerically and analytically. The analytic approach splits fields into interior and boundary-layer parts, from which a coupled set of integral constraints can be derived. The set allows properties of the circulation (upwelling-driven transport out of the Southern Ocean M , downwelling transport in the North Atlantic, transport of the Antarctic Circumpolar Current) and stratification (Atlantic

  19. Southern Ocean dynamics and biogeochemistry in a changing climate: Introduction and overview

    NASA Astrophysics Data System (ADS)

    Downes, Stephanie M.; Weijer, Wilbert; Jeffery, Nicole; Mazloff, Matthew; Russell, Joellen

    2015-04-01

    The Southern Ocean has a unique place in our climate system. It is a region of extremes, where the world's strongest ocean currents, the strongest wind regime, the most extensive sea ice cover, and the largest ice sheets interact (for example, see the recent review by Rintoul and Naveira Garabato, 2013). In addition, it houses a very productive ecosystem that sequesters a significant fraction of the anthropogenic CO2 in the ocean (Sabine et al., 2004; Takahashi et al., 2012).

  20. Southern Ocean Climate and Sea Ice Anomalies Associated with the Southern Oscillation

    NASA Technical Reports Server (NTRS)

    Kwok, R.; Comiso, J. C.

    2001-01-01

    The anomalies in the climate and sea ice cover of the Southern Ocean and their relationships with the Southern Oscillation (SO) are investigated using a 17-year of data set from 1982 through 1998. We correlate the polar climate anomalies with the Southern Oscillation index (SOI) and examine the composites of these anomalies under the positive (SOI > 0), neutral (0 > SOI > -1), and negative (SOI < -1) phases of SOL The climate data set consists of sea-level pressure, wind, surface air temperature, and sea surface temperature fields, while the sea ice data set describes its extent, concentration, motion, and surface temperature. The analysis depicts, for the first time, the spatial variability in the relationship of the above variables and the SOL The strongest correlation between the SOI and the polar climate anomalies are found in the Bellingshausen, Amundsen and Ross sea sectors. The composite fields reveal anomalies that are organized in distinct large-scale spatial patterns with opposing polarities at the two extremes of SOI, and suggest oscillating climate anomalies that are closely linked to the SO. Within these sectors, positive (negative) phases of the SOI are generally associated with lower (higher) sea-level pressure, cooler (warmer) surface air temperature, and cooler (warmer) sea surface temperature in these sectors. Associations between these climate anomalies and the behavior of the Antarctic sea ice cover are clearly evident. Recent anomalies in the sea ice cover that are apparently associated with the SOI include: the record decrease in the sea ice extent in the Bellingshausen Sea from mid- 1988 through early 199 1; the relationship between Ross Sea SST and ENSO signal, and reduced sea ice concentration in the Ross Sea; and, the shortening of the ice season in the eastern Ross Sea, Amundsen Sea, far western Weddell Sea, and the lengthening of the ice season in the western Ross Sea, Bellingshausen Sea and central Weddell Sea gyre over the period 1988

  1. The evolutionary origins of the southern ocean Philobryid bivalves: hidden biodiversity, ancient persistence.

    PubMed

    Jackson, Jennifer A; Linse, Katrin; Whittle, Rowan; Griffiths, Huw J

    2015-01-01

    Philobryids (Bivalvia: Arcoida) are one of the most speciose marine bivalve families in the Southern Ocean and are common throughout the Southern Hemisphere. Considering this diversity and their brooding reproductive mode (limiting long-distance dispersal), this family may have been present in the Southern Ocean since its inception. However Philobrya and Adacnarca appear only in the Quaternary fossil record of the Antarctic, suggesting a much more recent incursion. Molecular dating provides an independent means of measuring the time of origin and radiation of this poorly known group. Here we present the first combined molecular and morphological investigation of the Philobryidae in the Southern Ocean. Two nuclear loci (18S and 28S) were amplified from 35 Southern Ocean Adacnarca and Philobrya specimens, with a combined sequence length of 2,282 base pairs (bp). Adacnarca specimens (A. nitens and A. limopsoides) were resolved as a strongly supported monophyletic group. Genus Philobrya fell into two strongly supported groups ('sublaevis' and 'magellanica/wandelensis'), paraphyletic with Adacnarca. The A. nitens species complex is identified as at least seven morpho-species through morphological and genetic analysis of taxon clustering. Phylogenetic analyses resolve Philobryidae as a strongly supported monophyletic clade and sister taxon to the Limopsidae, as anticipated by their classification into the superfamily Limopsoidea. Bayesian relaxed clock analyses of divergence times suggest that genus Adacnarca radiated in the Southern Ocean from the Early Paleogene, while P. sublaevis and P. wandelensis clades radiated in the late Miocene, following the formation of the Antarctic Circumpolar Current.

  2. A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?

    PubMed Central

    Rella, S. F.; Uchida, M.

    2014-01-01

    Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene. PMID:24509792

  3. A Southern Ocean trigger for Northwest Pacific ventilation during the Holocene?

    PubMed

    Rella, S F; Uchida, M

    2014-02-17

    Holocene ocean circulation is poorly understood due to sparsity of dateable marine archives with submillennial-scale resolution. Here we present a record of mid-depth water radiocarbon contents in the Northwest (NW) Pacific Ocean over the last 12.000 years, which shows remarkable millennial-scale variations relative to changes in atmospheric radiocarbon inventory. Apparent decoupling of these variations from regional ventilation and mixing processes leads us to the suggestion that the mid-depth NW Pacific may have responded to changes in Southern Ocean overturning forced by latitudinal displacements of the southern westerly winds. By inference, a tendency of in-phase related North Atlantic and Southern Ocean overturning would argue against the development of a steady bipolar seesaw regime during the Holocene.

  4. THE CD ISOTOPE SIGNATURE OF THE SOUTHERN OCEAN

    NASA Astrophysics Data System (ADS)

    Abouchami, W.; Galer, S. J.; Middag, R.; de Baar, H.; Andreae, M. O.; Feldmann, H.; Raczek, I.

    2009-12-01

    The availability of micronutrients can limit and control plankton ecosystems, notably in the Southern Ocean which plays a major role in regulating the CO2 biological pump. Cadmium has a nutrient-like distribution in seawater - it is directly incorporated into living plankton in the upper water column and re-mineralised at depth. The nutritional role of Cd (Price and Morel, 1990) makes it a potentially useful tracer of biological productivity. We report Cd concentration and Cd stable isotope data obtained using a double-spike TIMS method on seawater samples collected during the Zero and Drake Passage cruise (ANTXXIV-III, IPY-GEOTRACES 2008). Four vertical profiles were collected from 40 to 70°S across the Polar Front using the ultra-clean Titan frame (De Baar et al., 2008), providing a record of changes in biological productivity from the Subantarctic to the Antarctic region. Data from two profiles from the SE Atlantic (47.66°S, 4.28W) and Drake Passage (55.13°S, 65.53°W) obtained on 1 litre-sized samples are presented. Both profiles show a increase in Cd concentration with depth, with noticeably higher concentrations in the SE Atlantic. Cd and PO4 are positively correlated with distinct slopes for the two profiles. The Cd isotope data are expressed as ɛ112/110Cd relative to our JMC Mainz standard (± 8ppm, 2SD, N=17). ɛ112/110Cd values show a continuous decrease with increasing depth and a significant shift towards heavier values in the upper 400m at both stations resolvable outside analytical error (2SE ≤ 20ppm). The sense of Cd isotope fractionation confirms previous findings of uptake of “light” Cd by phytoplankton in the upper water column (Lacan et al., 2006; Ripperger et al., 2007; Schmidt et al., 2009). Most important is the evidence for a distinctive heavier Cd isotope signature in AASW relative to AAIW. This result demonstrates that different water masses carry distinct Cd isotopic compositions reflecting changes in Cd uptake by phytoplankton

  5. Organic-rich mud on the western margin of southern Africa: Nutrient source to the Southern Ocean?

    NASA Astrophysics Data System (ADS)

    Compton, John; Herbert, Caren; Schneider, Ralph

    2009-12-01

    The biological pump plays a major role in the transfer of CO2 from the atmosphere to the deep Southern Ocean, a transfer which is largely controlled by the supply of iron and which may partially explain glacial to interglacial variations in pCO2. Analogous to the well-documented, smaller-scale "island mass effect," we propose that the lateral advection of iron by south flowing intermediate waters along the southern African margin may sustain high-productivity blooms of the Subtropical Convergence Zone (SCZ) between 10 and 70°E. We assess the present-day interglacial (Holocene) reservoirs and fluxes of organic carbon (OC) and terrigenous mud on the western margin of southern Africa in order to estimate the potential supply of Fe to the Southern Ocean. The highly productive Benguela Upwelling System (BUS) appears to be a relatively inefficient coastal biological pump. Repeated sediment resuspension by wave and tidal energy dissipation limits OC burial to <0.2% of net primary production (NPP) in the southern BUS and to between 0.2 to 2.4% in the northern BUS. Productivity and OC-rich mud accumulation are focused on the inner portion of the 100-200 km wide shelf which, combined with south flowing bottom currents, limits the export of OC beyond the shelf break to 1.2-8.4% of NPP. However, winnowing of 1 million tons yr-1 of clay particles and the potential early diagenetic benthic (dissolved) Fe flux may supply 10 times more Fe than is transported by dust to the open ocean biological pump of the SCZ. Lowering sea level during glacial periods disperses interglacial mud deposits off the shelf and increases particulate Fe export by as much as a factor of 4. Glacial pulses of margin export may enhance the efficiency of the subantarctic Southern Ocean biological pump and contribute to the initial as well as glacial maximum drawdown in pCO2.

  6. Ocean export production and foraminiferal stable isotopes in the Antarctic Southern Ocean across the mid-Pleistocene transition

    NASA Astrophysics Data System (ADS)

    Hasenfratz, A. P.; Martinez-Garcia, A.; Jaccard, S.; Hodell, D. A.; Vance, D.; Bernasconi, S. M.; Greaves, M.; Haug, G. H.

    2014-12-01

    Changes in buoyancy forcing in the Antarctic Zone (AZ) of the Southern Ocean are believed to play an instrumental role in modulating atmospheric CO2 concentrations during glacial cycles by regulating the transfer of carbon between the ocean interior and the atmosphere. Indeed, a million-year-spanning high-resolution excess Barium record from the AZ of the South Atlantic (ODP 1094), which traces changes in export production, shows decreased export production during cold periods suggesting decreased overturning. Here, we extend this AZ export production record back to 1.6 Myr. In addition, we present new carbon and oxygen isotope records of benthic and planktic foraminifera from the same site, complemented by Mg/Ca measurements in some intervals. The interpretation of these new data in the context of other South Atlantic records contributes to a better understanding of Southern Ocean hydrography and its role in modulating glacial/interglacial cycles over the past 1.6 Myr.

  7. Determination of the Prebomb Southern (Antartic) Ocean Radiocarbon in Organic Matter

    SciTech Connect

    Guilderson, T P

    2001-02-26

    The Southern Hemisphere is an important and unique region of the world's oceans for water-mass formation and mixing, upwelling, nutrient utilization, and carbon export. In fact, one of the primary interests of the oceanographic community is to decipher the climatic record of these processes in the source or sink terms for Southern Ocean surface waters in the CO{sub 2} balance of the atmosphere. Current coupled ocean-atmosphere modeling efforts to trace the input of CO{sub 2} into the ocean imply a strong sink of anthropogenic CO{sub 2} in the southern ocean. However, because of its relative inaccessibility and the difficulty in directly measuring CO{sub 2} fluxes in the Southern Ocean, these results are controversial at best. An accepted diagnostic of the exchange of CO{sub 2} between the atmosphere and ocean is the prebomb distribution of radiocarbon in the ocean and its time-history since atmospheric nuclear testing. Such histories of {sup 14}C in the surface waters of the Southern Ocean do not currently exist, primarily because there are few continuous biological archives (e.g., in corals) such as those that have been used to monitor the {sup 14}C history of the tropics and subtropics. One of the possible long-term archives is the scallop Adamussium collbecki. Although not independently confirmed, relatively crude growth rate estimates of A. collbecki indicate that it has the potential to provide continuous 100 year time-series. We are exploring the suitability of this potential archive.

  8. Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

    PubMed

    Hogg, Andrew McC; Munday, David R

    2014-07-13

    The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change.

  9. Does the sensitivity of Southern Ocean circulation depend upon bathymetric details?

    PubMed

    Hogg, Andrew McC; Munday, David R

    2014-07-13

    The response of the major ocean currents to changes in wind stress forcing is investigated with a series of idealized, but eddy-permitting, model simulations. Previously, ostensibly similar models have shown considerable variation in the oceanic response to changing wind stress forcing. Here, it is shown that a major reason for these differences in model sensitivity is subtle modification of the idealized bathymetry. The key bathymetric parameter is the extent to which the strong eddy field generated in the circumpolar current can interact with the bottom water formation process. The addition of an embayment, which insulates bottom water formation from meridional eddy fluxes, acts to stabilize the deep ocean density and enhances the sensitivity of the circumpolar current. The degree of interaction between Southern Ocean eddies and Antarctic shelf processes may thereby control the sensitivity of the Southern Ocean to change. PMID:24891390

  10. The Impact of the Ozone Hole on the Salinity of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Solomon, A. L.; Polvani, L. M.; Abernathey, R. P.; Smith, K. L.

    2014-12-01

    Observations have revealed systematic changes in the temperature andsalinity of the Southern Ocean since 1960. These trends reflect theevolving exchange of heat and momentum between atmosphere and ocean andare, in part, driven by anthropogenic emissions. The key question is:which emissions are most important, greenhouse gases or ozone depletingsubstances? We answer this question using CESM-WACCM, a comprehensiveclimate model with interactive stratospheric chemistry, coupled tostate-of-the-art land, ocean and sea-ice components. We find that thechanges in Southern Ocean temperature South of 60S are primarily due tothe presence of a seasonal ozone hole, and between 60S and 40S thetrends are driven in equal measure by ozone depletion and all otherforcings combined. Furthermore, we demonstrate substantial changes inthe model's ocean salinity, and show that these are greatly enhanced byformation of the ozone hole, a fact that has not been previously reported.

  11. Atmospheric Teleconnections of Northern Hemisphere cooling to the Southern Hemisphere midlatitudes, and implications for Southern Ocean ventilation

    NASA Astrophysics Data System (ADS)

    Chiang, John; Lee, Shih-Yu; Matsumoto, Katsumi; Tokos, Kathy

    2010-05-01

    Recent marine proxy studies, most notably by Anderson et al. (2009), show intensification of wind-driven upwelling in the Southern Ocean during Heinrich events, and suggesting the possibility of robust atmospheric teleconnections from the Northern Hemisphere affecting the Southern Hemisphere midlatitude westerlies. We explore the latter hypothesis using simulations of an AGCM coupled to a reduced-gravity ocean, and with reference to current thinking regarding extratropical-tropical atmospheric dynamical linkages. When we simulate a Heinrich-like event in our model (by cooling the North Atlantic), we find a significant strengthening of the southern midlatitude westerlies, in particular during the austral winter (JJA), and in the South Pacific. The other pronounced climate change is a marked southward shift of the tropical rainbelt, indicating alteration of the Hadley circulation. Our analysis indicates that the teleconnection can be broken into two parts: first, the northern hemisphere cooling shifting the ITCZ southwards with a pronounced effect on the Hadley circulation (Lindzen and Hou 1988), and then the altered Hadley circulation in turn affecting the southern midlatitude westerlies through the former's control of the southern subtropical westerlies and subsequent effect on the eddy-driven midlatitude westerlies (Lee and Kim, 2003). The seasonal (JJA) and regional (South Pacific) preference of the teleconnection's effects can be explained in terms of the peculiarities of the regional atmospheric dynamics. As an aside, we also find that the growth or decay of the Laurentide ice sheet can also generate this type of north-south teleconnection, although the dynamics are somewhat different. With regards to possible implications for southern ocean ventilation and atmospheric CO2: we applied the wind changes we obtained in our AGCM 'Heinrich' simulation to a global biogeochemical model (the Minnesota Earth System Model for Ocean biogeochemistry), and found a ~20ppm

  12. The Influence of Sea Ice on Primary Production in the Southern Ocean: A Satellite Perspective

    NASA Technical Reports Server (NTRS)

    Smith, Walker O., Jr.; Comiso, Josefino C.

    2007-01-01

    Sea ice in the Southern Ocean is a major controlling factor on phytoplankton productivity and growth, but the relationship is modified by regional differences in atmospheric and oceanographic conditions. We used the phytoplankton biomass (binned at 7-day intervals), PAR and cloud cover data from SeaWiFS, ice concentrations data from SSM/I and AMSR-E, and sea-surface temperature data from AVHRR, in combination with a vertically integrated model to estimate primary productivity throughout the Southern Ocean (south of 60"s). We also selected six areas within the Southern Ocean and analyzed the variability of the primary productivity and trends through time, as well as the relationship of sea ice to productivity. We found substantial interannual variability in productivity from 1997 - 2005 in all regions of the Southern Ocean, and this variability appeared to be driven in large part by ice dynamics. The most productive regions of Antarctic waters were the continental shelves, which showed the earliest growth, the maximum biomass, and the greatest areal specific productivity. In contrast, no large, sustained blooms occurred in waters of greater depth (> 1,000 m). We suggest that this is due to the slightly greater mixed layer depths found in waters off the continental shelf, and that the interactive effects of iron and irradiance (that is, increased iron requirements in low irradiance environments) result in the limitation of phytoplankton biomass over large regions of the Southern Ocean.

  13. Southern Ocean Deep-Convection as a Driver of Centennial-to-Millennial-Scale Climate Variability at Southern High Latitudes

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S.

    2014-12-01

    Antarctic Isotope Maxima (AIM) are centennial-to-millennial scale warming events observed in Antarctic ice core records from the last glacial period and deglaciation. Mounting evidence links AIM events to parallel variations in atmospheric CO2, Southern Ocean (SO) sea surface temperatures and Antarctic Bottom Water production. According to the prevailing view, AIM events are forced from the North Atlantic by melt-water discharge from ice sheets suppressing the production of North Atlantic Deep Water and associated northward heat transport in the Atlantic. However observations and model studies increasingly suggest that melt-water fluxes have the wrong timing to be invoked as such a trigger. Here, drawing on results form the Kiel Climate Model, we present an alternative hypothesis in which AIM events are forced via internal oscillations in SO deep-convection. The quasi-periodic timescale of deep-convection events is set by heat (buoyancy) accumulation at SO intermediate depths and stochastic variability in sea ice conditions and freshening at the surface. Massive heat release from the SO convective zone drives Antarctic and large-scale southern hemisphere warming via a two-stage process involving changes in the location of Southern Ocean fronts, in the strength and intensity of the Westerlies and in meridional ocean and atmospheric heat flux anomalies. The potential for AIM events to be driven by internal Southern Ocean processes and the identification of time-lags internal to the southern high latitudes challenges conventional views on the North Atlantic as the pacemaker of millennial-scale climate variability.

  14. Southern Ocean Deep-Convection as a Driver of Centennial-to-Millennial-Scale Climate Variability at Southern High Latitudes

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S.

    2015-12-01

    Antarctic Isotope Maxima (AIM) are centennial-to-millennial scale warming events observed in Antarctic ice core records from the last glacial period and deglaciation. Mounting evidence links AIM events to parallel variations in atmospheric CO2, Southern Ocean (SO) sea surface temperatures and Antarctic Bottom Water production. According to the prevailing view, AIM events are forced from the North Atlantic by melt-water discharge from ice sheets suppressing the production of North Atlantic Deep Water and associated northward heat transport in the Atlantic. However observations and model studies increasingly suggest that melt-water fluxes have the wrong timing to be invoked as such a trigger. Here, drawing on results form the Kiel Climate Model, we present an alternative hypothesis in which AIM events are forced via internal oscillations in SO deep-convection. The quasi-periodic timescale of deep-convection events is set by heat (buoyancy) accumulation at SO intermediate depths and stochastic variability in sea ice conditions and freshening at the surface. Massive heat release from the SO convective zone drives Antarctic and large-scale southern hemisphere warming via a two-stage process involving changes in the location of Southern Ocean fronts, in the strength and intensity of the Westerlies and in meridional ocean and atmospheric heat flux anomalies. The potential for AIM events to be driven by internal Southern Ocean processes and the identification of time-lags internal to the southern high latitudes challenges conventional views on the North Atlantic as the pacemaker of millennial-scale climate variability.

  15. Osmium isotopic evidence for ancient subcontinental lithospheric mantle beneath the kerguelen islands, southern indian ocean

    PubMed

    Hassler; Shimizu

    1998-04-17

    Upper mantle xenoliths found in ocean island basalts are an important window through which the oceanic mantle lithosphere may be viewed directly. Osmium isotopic data on peridotite xenoliths from the Kerguelen Islands, an archipelago that is located on the northern Kerguelen Plateau in the southern Indian Ocean, demonstrate that pieces of mantle of diverse provenance are present beneath the Islands. In particular, peridotites with unradiogenic osmium and ancient rhenium-depletion ages (to 1.36 x 10(9) years old) may be pieces of the Gondwanaland subcontinental lithosphere that were incorporated into the Indian Ocean lithosphere as a result of the rifting process. PMID:9545216

  16. Osmium isotopic evidence for ancient subcontinental lithospheric mantle beneath the kerguelen islands, southern indian ocean

    PubMed

    Hassler; Shimizu

    1998-04-17

    Upper mantle xenoliths found in ocean island basalts are an important window through which the oceanic mantle lithosphere may be viewed directly. Osmium isotopic data on peridotite xenoliths from the Kerguelen Islands, an archipelago that is located on the northern Kerguelen Plateau in the southern Indian Ocean, demonstrate that pieces of mantle of diverse provenance are present beneath the Islands. In particular, peridotites with unradiogenic osmium and ancient rhenium-depletion ages (to 1.36 x 10(9) years old) may be pieces of the Gondwanaland subcontinental lithosphere that were incorporated into the Indian Ocean lithosphere as a result of the rifting process.

  17. Southern Ocean dust-climate coupling over the past four million years.

    PubMed

    Martínez-Garcia, Alfredo; Rosell-Melé, Antoni; Jaccard, Samuel L; Geibert, Walter; Sigman, Daniel M; Haug, Gerald H

    2011-08-18

    Dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean. Indeed, dust supply to the Southern Ocean increases during ice ages, and 'iron fertilization' of the subantarctic zone may have contributed up to 40 parts per million by volume (p.p.m.v.) of the decrease (80-100 p.p.m.v.) in atmospheric carbon dioxide observed during late Pleistocene glacial cycles. So far, however, the magnitude of Southern Ocean dust deposition in earlier times and its role in the development and evolution of Pleistocene glacial cycles have remained unclear. Here we report a high-resolution record of dust and iron supply to the Southern Ocean over the past four million years, derived from the analysis of marine sediments from ODP Site 1090, located in the Atlantic sector of the subantarctic zone. The close correspondence of our dust and iron deposition records with Antarctic ice core reconstructions of dust flux covering the past 800,000 years (refs 8, 9) indicates that both of these archives record large-scale deposition changes that should apply to most of the Southern Ocean, validating previous interpretations of the ice core data. The extension of the record beyond the interval covered by the Antarctic ice cores reveals that, in contrast to the relatively gradual intensification of glacial cycles over the past three million years, Southern Ocean dust and iron flux rose sharply at the Mid-Pleistocene climatic transition around 1.25 million years ago. This finding complements previous observations over late Pleistocene glacial cycles, providing new evidence of a tight connection between high dust input to the Southern Ocean and the emergence of the deep glaciations that characterize the past one million years of Earth history.

  18. The Southern Ocean Carbon and Climate Observations and Modeling Program (SOCCOM)

    NASA Astrophysics Data System (ADS)

    Russell, Joellen

    2016-04-01

    SOCCOM is a 6-year observational and modeling research program focused on the role of the Southern Ocean in the anthropogenic carbon budget, ocean biogeochemistry, and climate change. The operational goal of SOCCOM is to deploy nearly 200 Argo-compatible biogeochemically-sensored (BGC) profiling floats equipped with pH, oxygen, nitrate and bio-optical sensors throughout the Southern Ocean waters south of 30°S. These climate-ready BGC-floats are calibrated at the time of deployment by high accuracy biogeochemical measurements, and they operate year around, including in ice-covered waters. The data from the BGC-floats is being assimilated by a Southern Ocean State Estimate (SOSE) model that incorporates biogeochemical processes, and this gridded SOSE output is used to constrain high-resolution coupled atmosphere-ocean model simulations designed to both increase our understanding of Southern Ocean processes and to reduce the uncertainty of projections of the future trajectory of the Earth's carbon, climate and biogeochemistry. We will present an overview of the organization and recent results of SOCCOM as well as the exciting next steps being developed.

  19. Role of zooplankton dynamics for Southern Ocean phytoplankton biomass and global biogeochemical cycles

    NASA Astrophysics Data System (ADS)

    Le Quéré, Corinne; Buitenhuis, Erik T.; Moriarty, Róisín; Alvain, Séverine; Aumont, Olivier; Bopp, Laurent; Chollet, Sophie; Enright, Clare; Franklin, Daniel J.; Geider, Richard J.; Harrison, Sandy P.; Hirst, Andrew G.; Larsen, Stuart; Legendre, Louis; Platt, Trevor; Prentice, I. Colin; Rivkin, Richard B.; Sailley, Sévrine; Sathyendranath, Shubha; Stephens, Nick; Vogt, Meike; Vallina, Sergio M.

    2016-07-01

    Global ocean biogeochemistry models currently employed in climate change projections use highly simplified representations of pelagic food webs. These food webs do not necessarily include critical pathways by which ecosystems interact with ocean biogeochemistry and climate. Here we present a global biogeochemical model which incorporates ecosystem dynamics based on the representation of ten plankton functional types (PFTs): six types of phytoplankton, three types of zooplankton, and heterotrophic procaryotes. We improved the representation of zooplankton dynamics in our model through (a) the explicit inclusion of large, slow-growing macrozooplankton (e.g. krill), and (b) the introduction of trophic cascades among the three zooplankton types. We use the model to quantitatively assess the relative roles of iron vs. grazing in determining phytoplankton biomass in the Southern Ocean high-nutrient low-chlorophyll (HNLC) region during summer. When model simulations do not include macrozooplankton grazing explicitly, they systematically overestimate Southern Ocean chlorophyll biomass during the summer, even when there is no iron deposition from dust. When model simulations include a slow-growing macrozooplankton and trophic cascades among three zooplankton types, the high-chlorophyll summer bias in the Southern Ocean HNLC region largely disappears. Our model results suggest that the observed low phytoplankton biomass in the Southern Ocean during summer is primarily explained by the dynamics of the Southern Ocean zooplankton community, despite iron limitation of phytoplankton community growth rates. This result has implications for the representation of global biogeochemical cycles in models as zooplankton faecal pellets sink rapidly and partly control the carbon export to the intermediate and deep ocean.

  20. Shortwave feedbacks and El Nino-Southern Oscillation: Forced ocean coupled ocean-atmosphere experiments

    NASA Technical Reports Server (NTRS)

    Waliser, Duane E.; Blanke, Bruno; Neelin, J. David; Gautier, C.

    1994-01-01

    Changes in tropical sea surface temperature (SST) can produce changes in cloudiness that modify incoming solar shortwave (SW) radiation, which in turn affects SST. The effects of this negative feedback on Pacific interannual variability are examined in forced ocean model and hybrid coupled ocean-atmosphere model simulations. Two empirical schemes are used to model the large-scale, low-frequency response of surface SW to SST anomalies. The first scheme attempts to account for the nonlocal nature of the atmospheric response to SST based patterns of covariability analyzed through singular value decomposition. In the observations the primary coupled mode of variability is composed of a SW anomaly in the central Pacific that covaries with anomalous SST in the eastern Pacific. This is applied in the model as a nonlocal feedback. The second scheme examines the effects of a purely local feedback with a spatially varying coefficient of magnitude chosen similar to the first scheme. In almost all cases the second scheme behaved similarly to the first, presumably because the correlation scale of SST is large enough for El Nino-Southern Oscillation (ENSO) dynamics that there is little sensitivity to the local approximation in the SW feedback. In simulations forced by time series of observed wind stress the SW feedback induced very minor SST damping. Results for a simpified heat budget analysis showed that while the SW feedback increased the local heat flux damping on SST, it also induced a mean shallowing of the mixed layer. The resulting changes in both the local mean vertical temperature gradient and the zonal velocity response to the wind stress acted to oppose the local heat flux damping effects. When the observed SW anomalies were applied to forced simulations, the simulated SST anomalies were modified as expected, and agreement with observed SST improved. In coupled simulations the SW feedbacks had greater impact than in the case of specified stress. The main effects were

  1. Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals.

    PubMed

    Charrassin, J-B; Hindell, M; Rintoul, S R; Roquet, F; Sokolov, S; Biuw, M; Costa, D; Boehme, L; Lovell, P; Coleman, R; Timmermann, R; Meijers, A; Meredith, M; Park, Y-H; Bailleul, F; Goebel, M; Tremblay, Y; Bost, C-A; McMahon, C R; Field, I C; Fedak, M A; Guinet, C

    2008-08-19

    Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60 degrees S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April-May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean-sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a "blind spot" in our sampling coverage, enabling the establishment of a truly global ocean-observing system. PMID:18695241

  2. Phenotypic Plasticity of Southern Ocean Diatoms: Key to Success in the Sea Ice Habitat?

    PubMed Central

    Sackett, Olivia; Petrou, Katherina; Reedy, Brian; De Grazia, Adrian; Hill, Ross; Doblin, Martina; Beardall, John; Ralph, Peter; Heraud, Philip

    2013-01-01

    Diatoms are the primary source of nutrition and energy for the Southern Ocean ecosystem. Microalgae, including diatoms, synthesise biological macromolecules such as lipids, proteins and carbohydrates for growth, reproduction and acclimation to prevailing environmental conditions. Here we show that three key species of Southern Ocean diatom (Fragilariopsis cylindrus, Chaetoceros simplex and Pseudo-nitzschia subcurvata) exhibited phenotypic plasticity in response to salinity and temperature regimes experienced during the seasonal formation and decay of sea ice. The degree of phenotypic plasticity, in terms of changes in macromolecular composition, was highly species-specific and consistent with each species’ known distribution and abundance throughout sea ice, meltwater and pelagic habitats, suggesting that phenotypic plasticity may have been selected for by the extreme variability of the polar marine environment. We argue that changes in diatom macromolecular composition and shifts in species dominance in response to a changing climate have the potential to alter nutrient and energy fluxes throughout the Southern Ocean ecosystem. PMID:24363795

  3. Observationally-Based Data/Model Metrics from the Southern Ocean Climate Model Atlas

    NASA Astrophysics Data System (ADS)

    Abell, J.; Russell, J. L.; Goodman, P. J.

    2015-12-01

    The Southern Ocean Climate Model Atlas makes available observationally-based standardized data/model metrics of the latest simulations of climate and projections of climate change from available climate models. Global climate model simulations differ greatly in the Southern Ocean, so the development of consistent, observationally-based metrics, by which to assess the fidelity of model simulations is essential. We will present metrics showing and quantifying the results of the modern day climate simulations over the Southern Ocean from models submitted as part of the CMIP5/IPCC-AR5 process. Our analysis will focus on the simulations of the temperature, salinity and carbon at various depths and along significant hydrographic sections. The models exhibit different skill levels with various metrics between models and also within individual models.

  4. Southern Ocean deep convection as a driver of Antarctic warming events

    NASA Astrophysics Data System (ADS)

    Pedro, J. B.; Martin, T.; Steig, E. J.; Jochum, M.; Park, W.; Rasmussen, S. O.

    2016-03-01

    Simulations with a free-running coupled climate model show that heat release associated with Southern Ocean deep convection variability can drive centennial-scale Antarctic temperature variations of up to 2.0°C. The mechanism involves three steps: Preconditioning: heat accumulates at depth in the Southern Ocean; Convection onset: wind and/or sea ice changes tip the buoyantly unstable system into the convective state; and Antarctic warming: fast sea ice-albedo feedbacks (on annual-decadal time scales) and slow Southern Ocean frontal and sea surface temperature adjustments to convective heat release (on multidecadal-century time scales) drive an increase in atmospheric heat and moisture transport toward Antarctica. We discuss the potential of this mechanism to help drive and amplify climate variability as observed in Antarctic ice core records.

  5. Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Currie, J. C.; Lengaigne, M.; Vialard, J.; Kaplan, D. M.; Aumont, O.; Naqvi, S. W. A.; Maury, O.

    2013-03-01

    The Indian Ocean Dipole (IOD) and the El Niño-Southern Oscillation (ENSO) frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled bio-physical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely-sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997-1998 ENSO and IOD event. Results show that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. IOD depresses integrated chlorophyll in the 5° S-10° S thermocline ridge region, even though the signal is negligible in surface chlorophyll. A previously-unreported negative influence of IOD on chlorophyll concentrations is also shown in a region around the southern tip of India. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Lastly, we show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. ENSO and IOD cause significant and predictable regional re-organisation of phytoplankton productivity via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets.

  6. Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean

    NASA Astrophysics Data System (ADS)

    Currie, J. C.; Lengaigne, M.; Vialard, J.; Kaplan, D. M.; Aumont, O.; Naqvi, S. W. A.; Maury, O.

    2013-10-01

    The Indian Ocean Dipole (IOD) and the El Niño/Southern Oscillation (ENSO) are independent climate modes, which frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled biophysical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997/1998 ENSO and IOD event. Results suggest that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. A negative influence of IOD on chlorophyll concentrations is shown in a region around the southern tip of India in fall. IOD also depresses depth-integrated chlorophyll in the 5-10° S thermocline ridge region, yet the signal is negligible in surface chlorophyll. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Yet unlike most other regions examined, the combined explanatory power of IOD and ENSO in predicting depth-integrated chlorophyll anomalies is relatively low in this region, suggestive that other drivers are important there. We show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. Our results suggest that ENSO and IOD cause significant and predictable regional re-organisation of chlorophyll via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon

  7. Influence of sea ice on primary production in the Southern Ocean: A satellite perspective

    NASA Astrophysics Data System (ADS)

    Smith, Walker O.; Comiso, Josefino C.

    2008-05-01

    Sea ice in the Southern Ocean is a major controlling factor on phytoplankton productivity, but the relationship is modified by regional differences in atmospheric and oceanographic conditions. We used the phytoplankton biomass, photosynthetically active radiation (PAR), and cloud cover data from Sea-viewing Wide Field of View Sensor (SeaWiFS), ice concentrations data from Special Sensor Microwave Imager (SSM/I) and Advanced Microwave Scanning Radiometer-EOS (AMSR-E), sea-surface temperature data from advanced very high resolution radiometer (AVHRR), and a vertically integrated model to estimate primary productivity south of 60°S. We also selected six areas within the Southern Ocean and analyzed the variability of the primary productivity and trends through time. We found substantial interannual variability in productivity from 1997 to 2005 in all regions of the Southern Ocean, and this variability appeared to be driven in large part by ice dynamics. The most productive regions of Antarctic waters were the continental shelves, and no sustained blooms occurred in waters of greater depth (>1000 m). We suggest that this is due to the slightly greater mixed layer depths found in waters off the continental shelf, and that the interactive effects of iron and irradiance result in the limitation of phytoplankton biomass over large regions of the Southern Ocean. Annual productivity of the Southern Ocean averaged 23.65 g C m-2 a-1, but yearly means for the years between 1998 and 2004 ranged from 22.10 to 25.49 g C m-2 d-1, respectively. Annual primary productivity over the entire Southern Ocean appears to have increased significantly since 1998, and much of this increase was confined to the months of January and February. Causes for this trend are presently unclear.

  8. The influence of historical climate changes on Southern Ocean marine predator populations: a comparative analysis.

    PubMed

    Younger, Jane L; Emmerson, Louise M; Miller, Karen J

    2016-02-01

    The Southern Ocean ecosystem is undergoing rapid physical and biological changes that are likely to have profound implications for higher-order predators. Here, we compare the long-term, historical responses of Southern Ocean predators to climate change. We examine palaeoecological evidence for changes in the abundance and distribution of seabirds and marine mammals, and place these into context with palaeoclimate records in order to identify key environmental drivers associated with population changes. Our synthesis revealed two key factors underlying Southern Ocean predator population changes; (i) the availability of ice-free ground for breeding and (ii) access to productive foraging grounds. The processes of glaciation and sea ice fluctuation were key; the distributions and abundances of elephant seals, snow petrels, gentoo, chinstrap and Adélie penguins all responded strongly to the emergence of new breeding habitat coincident with deglaciation and reductions in sea ice. Access to productive foraging grounds was another limiting factor, with snow petrels, king and emperor penguins all affected by reduced prey availability in the past. Several species were isolated in glacial refugia and there is evidence that refuge populations were supported by polynyas. While the underlying drivers of population change were similar across most Southern Ocean predators, the individual responses of species to environmental change varied because of species specific factors such as dispersal ability and environmental sensitivity. Such interspecific differences are likely to affect the future climate change responses of Southern Ocean marine predators and should be considered in conservation plans. Comparative palaeoecological studies are a valuable source of long-term data on species' responses to environmental change that can provide important insights into future climate change responses. This synthesis highlights the importance of protecting productive foraging grounds

  9. The influence of historical climate changes on Southern Ocean marine predator populations: a comparative analysis.

    PubMed

    Younger, Jane L; Emmerson, Louise M; Miller, Karen J

    2016-02-01

    The Southern Ocean ecosystem is undergoing rapid physical and biological changes that are likely to have profound implications for higher-order predators. Here, we compare the long-term, historical responses of Southern Ocean predators to climate change. We examine palaeoecological evidence for changes in the abundance and distribution of seabirds and marine mammals, and place these into context with palaeoclimate records in order to identify key environmental drivers associated with population changes. Our synthesis revealed two key factors underlying Southern Ocean predator population changes; (i) the availability of ice-free ground for breeding and (ii) access to productive foraging grounds. The processes of glaciation and sea ice fluctuation were key; the distributions and abundances of elephant seals, snow petrels, gentoo, chinstrap and Adélie penguins all responded strongly to the emergence of new breeding habitat coincident with deglaciation and reductions in sea ice. Access to productive foraging grounds was another limiting factor, with snow petrels, king and emperor penguins all affected by reduced prey availability in the past. Several species were isolated in glacial refugia and there is evidence that refuge populations were supported by polynyas. While the underlying drivers of population change were similar across most Southern Ocean predators, the individual responses of species to environmental change varied because of species specific factors such as dispersal ability and environmental sensitivity. Such interspecific differences are likely to affect the future climate change responses of Southern Ocean marine predators and should be considered in conservation plans. Comparative palaeoecological studies are a valuable source of long-term data on species' responses to environmental change that can provide important insights into future climate change responses. This synthesis highlights the importance of protecting productive foraging grounds

  10. Southern Ocean Cooling in a Warming World: Reassessing the Role of Westerly Winds

    NASA Astrophysics Data System (ADS)

    Hausmann, U.; Kostov, Y. K.; Armour, K.; Marshall, J.

    2015-12-01

    In contrast to the global warming trend and the loss of Arctic sea ice, the Southern Ocean has exhibited a gradual decrease in sea surface temperatures (SSTs) and a net expansion of the sea ice cover over recent decades. Moreover, historical simulations with CMIP5 global climate models do not reproduce the observed cooling around Antarctica and, instead, predict slow but steady warming and sea ice loss. Here we identify enhanced Ekman transport as a possible mechanism allowing the Southern Ocean to cool. We further discuss the discrepancy between observations and CMIP5 historical simulations. The latter do not represent consistently the strengthening and the poleward shift of the Southern Hemisphere surface westerlies - due to internal variability or an inadequate representation of ozone forcing. We propose that under a realistic evolution of surface winds, CMIP5 models can produce cooling trends around Antarctica with magnitudes and spatial patterns similar to observations. To that end we consider the unforced preindustrial control runs of CMIP5 models and examine periods with multi-decadal trends in the speed and position of the Southern Hemisphere surface westerlies that are comparable to the 1979-2014 trends. Strengthening and southward displacement of surface winds produce an SST dipole around Antarctica: cooling south of 50S and warming in a zonal band along 30-50S, similar to observed patterns. The wind-induced cooling trends in the Southern Ocean are large enough to locally overwhelm the effect of greenhouse gas forcing. We reconcile our findings with those of modeling studies which suggest that poleward intensification of the westerlies leads to warming rather than cooling trends around Antarctica. We show that the Southern Ocean response to a wind perturbation is non-monotonic in time. An initial cooling regime can transition into a warming regime. Some of the inter-model diversity in these fast and slow responses is related to differences in the models

  11. On the interannual variability of ocean temperatures around South Georgia, Southern Ocean: Forcing by El Niño/Southern Oscillation and the Southern Annular Mode

    NASA Astrophysics Data System (ADS)

    Meredith, Michael P.; Murphy, Eugene J.; Hawker, Elizabeth J.; King, John C.; Wallace, Margaret I.

    2008-09-01

    The ocean around South Georgia, in the southwest Atlantic sector of the Southern Ocean, is highly productive, with large stocks of Antarctic krill supporting extensive colonies of marine- and land-based predators. The operation of this ecosystem is strongly influenced by physical forcings, and the role of the El Niño/Southern Oscillation (ENSO) phenomenon has been highlighted previously. Here we examine in detail the transmission of ENSO signals to South Georgia, and investigate other sources of interannual variability. ENSO variability generates anomalies in sea-surface temperature (SST) across the South Pacific via atmospheric teleconnections. These anomalies are advected toward South Georgia within the Antarctic Circumpolar Current (ACC), and previous studies have focussed on long-period advection (order of 2-3 years) from the southwest Pacific. We observe here, however, that the region close to the Antarctic Peninsula in the southeast Pacific is especially susceptible to ENSO forcing via anomalous meridional winds; this induces SST anomalies that are advected to South Georgia on a much more rapid timescale (order 5-6 months). The phasing of these teleconnections is such that anomalies that reach the southeast Pacific from farther west tend to be reinforced here by air-sea-ice interaction. We also find an important role for the Southern Annular Mode (SAM) in determining SST variability at South Georgia. This is a circumpolar mode of climate variability, and thus can readily influence local SST at South Georgia directly. The SAM is, however, not perfectly zonally symmetric, and (like ENSO) has a particular impact on meridional winds in the southeast Pacific. The average timescale for SAM influence on South Georgia SST is shorter than that of ENSO, since it includes a stronger component of direct local forcing. The South Georgia ecosystem is not self-sustaining, with import of krill from breeding and nursery grounds upstream in the ACC being important. We

  12. The Effects of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in an AOGCM

    NASA Technical Reports Server (NTRS)

    Li, Feng; Newman, Paul; Pawson, Steven; Waugh, Darryn

    2014-01-01

    Stratospheric ozone depletion has played a dominant role in driving Antarctic climate change in the last decades. In order to capture the stratospheric ozone forcing, many coupled atmosphere-ocean general circulation models (AOGCMs) prescribe the Antarctic ozone hole using monthly and zonally averaged ozone field. However, the prescribed ozone hole has a high ozone bias and lacks zonal asymmetry. The impacts of these biases on model simulations, particularly on Southern Ocean and the Antarctic sea ice, are not well understood. The purpose of this study is to determine the effects of using interactive stratospheric chemistry instead of prescribed ozone on Antarctic and Southern Ocean climate change in an AOGCM. We compare two sets of ensemble simulations for the 1960-2010 period using different versions of the Goddard Earth Observing System 5 - AOGCM: one with interactive stratospheric chemistry, and the other with prescribed monthly and zonally averaged ozone and 6 other stratospheric radiative species calculated from the interactive chemistry simulations. Consistent with previous studies using prescribed sea surface temperatures and sea ice concentrations, the interactive chemistry runs simulate a deeper Antarctic ozone hole and consistently larger changes in surface pressure and winds than the prescribed ozone runs. The use of a coupled atmosphere-ocean model in this study enables us to determine the impact of these surface changes on Southern Ocean circulation and Antarctic sea ice. The larger surface wind trends in the interactive chemistry case lead to larger Southern Ocean circulation trends with stronger changes in northerly and westerly surface flow near the Antarctica continent and stronger upwelling near 60S. Using interactive chemistry also simulates a larger decrease of sea ice concentrations. Our results highlight the importance of using interactive chemistry in order to correctly capture the influences of stratospheric ozone depletion on climate

  13. Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years

    NASA Astrophysics Data System (ADS)

    Crampton, James S.; Cody, Rosie D.; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R.

    2016-06-01

    It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate “baseline” variability on glacial–interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations.

  14. Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years.

    PubMed

    Crampton, James S; Cody, Rosie D; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R

    2016-06-21

    It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate "baseline" variability on glacial-interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations.

  15. Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years.

    PubMed

    Crampton, James S; Cody, Rosie D; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R

    2016-06-21

    It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate "baseline" variability on glacial-interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations. PMID:27274061

  16. Southern Ocean phytoplankton turnover in response to stepwise Antarctic cooling over the past 15 million years

    NASA Astrophysics Data System (ADS)

    Crampton, James S.; Cody, Rosie D.; Levy, Richard; Harwood, David; McKay, Robert; Naish, Tim R.

    2016-06-01

    It is not clear how Southern Ocean phytoplankton communities, which form the base of the marine food web and are a crucial element of the carbon cycle, respond to major environmental disturbance. Here, we use a new model ensemble reconstruction of diatom speciation and extinction rates to examine phytoplankton response to climate change in the southern high latitudes over the past 15 My. We identify five major episodes of species turnover (origination rate plus extinction rate) that were coincident with times of cooling in southern high-latitude climate, Antarctic ice sheet growth across the continental shelves, and associated seasonal sea-ice expansion across the Southern Ocean. We infer that past plankton turnover occurred when a warmer-than-present climate was terminated by a major period of glaciation that resulted in loss of open-ocean habitat south of the polar front, driving non-ice adapted diatoms to regional or global extinction. These findings suggest, therefore, that Southern Ocean phytoplankton communities tolerate “baseline” variability on glacial-interglacial timescales but are sensitive to large-scale changes in mean climate state driven by a combination of long-period variations in orbital forcing and atmospheric carbon dioxide perturbations.

  17. A review of the Southern Oscillation - Oceanic-atmospheric circulation changes and related rainfall anomalies

    NASA Technical Reports Server (NTRS)

    Kousky, V. E.; Kagano, M. T.; Cavalcanti, I. F. A.

    1984-01-01

    The region of South America is emphasized in the present consideration of the Southern Oscillation (SO) oceanic and atmospheric circulation changes. The persistence of climate anomalies associated with El Nino-SO events is due to strong atmosphere-ocean coupling. Once initiated, the SO follows a certain sequence of events with clearly defined effects on tropical and subtropical rainfall. Excessive rainfall related to the SO in the central and eastern Pacific, Peru, Ecuador, and southern Brazil, are complemented by drought in Australia, Indonesia, India, West Africa, and northeast Brazil. El Nino-SO events are also associated with dramatic changes in the tropospheric flow pattern over a broad area of both hemispheres.

  18. Estimates of late Quaternary mode and intermediate water silicic acid concentration in the Pacific Southern Ocean

    NASA Astrophysics Data System (ADS)

    Rousseau, Jonathon; Ellwood, Michael J.; Bostock, Helen; Neil, Helen

    2016-04-01

    The Southern Ocean plays a critical role in the exchange of carbon between the ocean and atmosphere over glacial-interglacial timescales. Hypotheses used to explain late Quaternary variations in atmospheric carbon dioxide (CO2) implicate changes in the nutrient dynamics and circulation of the Southern Ocean. Here we present silicon isotope (δ30Si) records of late Quaternary sponges and diatoms from the NZ-sector of the Southern Ocean. Analysis of our sponge δ30Si records strongly suggests that the silicic acid concentration at mode and intermediate depths was higher during the LGM and the deglacial period compared to the present day. Our diatom δ30Si record suggests biological productivity near of the Polar Front was greater during the deglacial period, but not significantly different during the LGM compared to the present day. Taking our dataset in context with other regional paleoceanographic records, we interpret the predicted elevation in LGM and deglacial silicic acid concentration to reflect a shoaling of water masses during the LGM and 'leakage' of excess Southern Ocean dissolved silicon during the deglacial period.

  19. Backarc Oceanic Core Complexes Formed During Initial Spreading in the Southern Shikoku Basin

    NASA Astrophysics Data System (ADS)

    Miura, R.; Coffin, M. F.; Nakamura, Y.; Nishizawa, A.; Koda, K.; Tokuyama, H.

    2007-12-01

    Seafloor spreading occurs in two distinct geodynamic environments, major ocean basins and backarc basins. Unusual magma-poor seafloor spreading has been identified at slow- and intermediate-rate spreading centers in major ocean basins, e.g., Mid-Atlantic Ridge, Southwest Indian Ridge, and Australia-Antarctica Discordance. Some of these spreading centers are characterized by corrugated bathymetry known as megamullions, and some by chaotic bathymetry. Serpentinized peridotite and altered gabbro have been sampled from megamullions, and the three-dimensional geological structures that form megamullions are known as oceanic core complexes. Oceanic core complexes have also been identified at extinct backarc spreading centers, e.g., Parece Vela Basin and Shikoku Basin. The Shikoku Basin formed in conjunction with subduction along the Izu- Bonin arc at the eastern edge of the Philippine Sea plate. Although the general spreading history of the basin is known from identification of magnetic lineations, the early tectonic history of Proto-Izu-Bonin arc breakup and subsequent initial backarc spreading is uncertain. We identify, describe, and interpret oceanic core complexes amid chaotic bathymetry of the southern Shikoku Basin just east of the Kyushu-Palau Ridge, the remnant arc of the Proto-Izu-Bonin arc, on the basis of marine geological and geophysical data including multichannel seismic reflection, seismic refraction, swath bathymetry, and gravity. Just west of the core complexes, the Kyushu-Palau Ridge has been dated as Oligocene in age (~25 Ma), and just to the east lies magnetic anomaly 6B (~23 Ma). Crustal structure derived from seismic and gravity data indicates that anomalously thin -less than 5 km thick- crust is located in the arc-ocean transition between the central Kyushu-Palau Ridge and southern Shikoku Basin, which suggests rift-related crustal thinning and low magma productivity during backarc spreading initiation. Near the core complexes, seamount fragments

  20. Southern Ocean frontal structure and sea-ice formation rates revealed by elephant seals

    PubMed Central

    Charrassin, J.-B.; Hindell, M.; Rintoul, S. R.; Roquet, F.; Sokolov, S.; Biuw, M.; Costa, D.; Boehme, L.; Lovell, P.; Coleman, R.; Timmermann, R.; Meijers, A.; Meredith, M.; Park, Y.-H.; Bailleul, F.; Goebel, M.; Tremblay, Y.; Bost, C.-A.; McMahon, C. R.; Field, I. C.; Fedak, M. A.; Guinet, C.

    2008-01-01

    Polar regions are particularly sensitive to climate change, with the potential for significant feedbacks between ocean circulation, sea ice, and the ocean carbon cycle. However, the difficulty in obtaining in situ data means that our ability to detect and interpret change is very limited, especially in the Southern Ocean, where the ocean beneath the sea ice remains almost entirely unobserved and the rate of sea-ice formation is poorly known. Here, we show that southern elephant seals (Mirounga leonina) equipped with oceanographic sensors can measure ocean structure and water mass changes in regions and seasons rarely observed with traditional oceanographic platforms. In particular, seals provided a 30-fold increase in hydrographic profiles from the sea-ice zone, allowing the major fronts to be mapped south of 60°S and sea-ice formation rates to be inferred from changes in upper ocean salinity. Sea-ice production rates peaked in early winter (April–May) during the rapid northward expansion of the pack ice and declined by a factor of 2 to 3 between May and August, in agreement with a three-dimensional coupled ocean–sea-ice model. By measuring the high-latitude ocean during winter, elephant seals fill a “blind spot” in our sampling coverage, enabling the establishment of a truly global ocean-observing system. PMID:18695241

  1. Front variability and surface ocean features of the presumed southern bluefin tuna spawning grounds in the tropical southeast Indian Ocean

    NASA Astrophysics Data System (ADS)

    Nieblas, Anne-Elise; Demarcq, Hervé; Drushka, Kyla; Sloyan, Bernadette; Bonhommeau, Sylvain

    2014-09-01

    The southern bluefin tuna (SBT, Thunnus maccoyii) is an ecologically and economically valuable fish. However, surprisingly little is known about its critical early life history, a period when mortality is several orders of magnitude higher than at any other life stage, and when larvae are highly sensitive to environmental conditions. Ocean fronts can be important in creating favourable spawning conditions, as they are a convergence of water masses with different properties that can concentrate planktonic particles and lead to enhanced productivity. In this study, we examine the front activity within the only region where SBT have been observed to spawn: the tropical southeast Indian Ocean between Indonesia and Australia (10°S-20°S, 105°E-125°E). We investigate front activity and its relationship to ocean dynamics and surface features of the region. Results are also presented for the entire Indian Ocean (30°N-45°S, 20°E-140°E) to provide a background context. We use an extension of the Cayula and Cornillon algorithm to detect ocean fronts from satellite images of sea surface temperature (SST) and chlorophyll-a concentration (chl-a). Front occurrence represents the probability of occurrence of a front at each pixel of an image. Front intensity represents the magnitude of the difference between the two water masses that make up a front. Relative to the rest of the Indian Ocean, both SST and chl-a fronts in the offshore spawning region are persistent in occurrence and weak in intensity. Front occurrence and intensity along the Australian coast are high, with persistent and intense fronts found along the northwest and west coasts. Fronts in the tropical southeast Indian Ocean are shown to have strong annual variability and some moderate interannual variability. SST front occurrence is found to lead the Southern Oscillation Index by one year, potentially linked to warming and wind anomalies in the Indian Ocean. The surface ocean characteristics of the offshore

  2. Forcing of anthropogenic aerosols on temperature trends of the sub-thermocline southern Indian Ocean.

    PubMed

    Cowan, Tim; Cai, Wenju; Purich, Ariaan; Rotstayn, Leon; England, Matthew H

    2013-01-01

    In the late twentieth century, the sub-thermocline waters of the southern tropical and subtropical Indian Ocean experienced a sharp cooling. This cooling has been previously attributed to an anthropogenic aerosol-induced strengthening of the global ocean conveyor, which transfers heat from the subtropical gyre latitudes toward the North Atlantic. From the mid-1990s the sub-thermocline southern Indian Ocean experienced a rapid temperature trend reversal. Here we show, using climate models from phase 5 of the Coupled Model Intercomparison Project, that the late twentieth century sub-thermocline cooling of the southern Indian Ocean was primarily driven by increasing anthropogenic aerosols and greenhouse gases. The models simulate a slow-down in the sub-thermocline cooling followed by a rapid warming towards the mid twenty-first century. The simulated evolution of the Indian Ocean temperature trend is linked with the peak in aerosols and their subsequent decline in the twenty-first century, reinforcing the hypothesis that aerosols influence ocean circulation trends.

  3. Forcing of anthropogenic aerosols on temperature trends of the sub-thermocline southern Indian Ocean

    PubMed Central

    Cowan, Tim; Cai, Wenju; Purich, Ariaan; Rotstayn, Leon; England, Matthew H.

    2013-01-01

    In the late twentieth century, the sub-thermocline waters of the southern tropical and subtropical Indian Ocean experienced a sharp cooling. This cooling has been previously attributed to an anthropogenic aerosol-induced strengthening of the global ocean conveyor, which transfers heat from the subtropical gyre latitudes toward the North Atlantic. From the mid-1990s the sub-thermocline southern Indian Ocean experienced a rapid temperature trend reversal. Here we show, using climate models from phase 5 of the Coupled Model Intercomparison Project, that the late twentieth century sub-thermocline cooling of the southern Indian Ocean was primarily driven by increasing anthropogenic aerosols and greenhouse gases. The models simulate a slow-down in the sub-thermocline cooling followed by a rapid warming towards the mid twenty-first century. The simulated evolution of the Indian Ocean temperature trend is linked with the peak in aerosols and their subsequent decline in the twenty-first century, reinforcing the hypothesis that aerosols influence ocean circulation trends. PMID:23873281

  4. Optical Measurements and Modeling to Estimate Concentrations and Fluxes of Organic Matter in the Southern Ocean

    NASA Technical Reports Server (NTRS)

    Stramski, Dariusz; Mitchell, B. Greg; Marra, John W. (Technical Monitor)

    2001-01-01

    This project was a collaboration between two Principal Investigators, Dr. Dariusz Stramski and Dr. Greg Mitchell of Scripps Institution of Oceanography, University of California San Diego. Our overall goal was to conduct optical measurements and modeling to estimate concentrations of organic matter in the Southern Ocean in support of the U.S. JGOFS Process Study in this region. Key variables and processes of high relevance to accomplish the JGOFS goals include time and space resolution of phytoplankton pigments, particulate organic carbon, and the formation and export of organic carbon. Our project focused on establishing the fundamental relationships for parameterization of these variables and processes in terms of the optical properties of seawater, and developing understanding of why the Southern Ocean differs from other low-latitude systems, or has differentiation within. Our approach builds upon historical observations that optical properties provide a useful proxy for key reservoirs of organic matter such as chlorophyll alpha (Chl) and particulate organic carbon (POC) concentrations, which are of relevance to the JGOFS objectives. We carried out detailed studies of in situ and water sample optical properties including spectral reflectance, absorption, beam attenuation, scattering, and backscattering coefficients. We evaluated the ability to estimate Chl from the spectral reflectance (ocean color) in the Southern Ocean. We examined relationships between the ocean optical properties and particulate organic carbon. We developed, for the first time, an algorithm for estimating particulate organic carbon concentration in the surface ocean from satellite imagery of ocean color. With this algorithm, we obtained maps of POC distribution in the Southern Ocean showing the seasonal progression of POC in the austral spring-summer season. We also developed a semianalytical reflectance model for the investigated polar waters based on our field measurements of absorption

  5. Concentration and toxic potential of polychlorinated biphenyl congeners in migratory oceanic birds from the North Pacific and the Southern Ocean.

    PubMed

    Guruge, K S; Tanaka, H; Tanabe, S

    2001-09-01

    Concentrations of PCBs and their toxic potential were examined in subcutaneous fat of eight albatross and one petrel species collected from the North Pacific and the Southern Oceans. Among all the species analyzed, high PCB levels were found in adult male blackfooted albatross from the North Pacific with the mean value of 92 microg/g wet weight. No significant gender difference in PCB accumulation was observed (P>0.1). The mean PCB levels in Southern Oceanic birds were 1 or 2 orders of magnitude lower than those from the North Pacific albatrosses. A regional-specific accumulation of non-ortho coplanar congeners were observed, most birds from the Southern Ocean had higher IUPAC 169 levels while IUPAC 126 concentrations were higher in those from the North Pacific. The estimated toxic equivalents for black-footed and Laysan albatrosses from the North Pacific were in the same range of some fish-eating birds, which were highly contaminated by PCBs. The correlation between ratio of IUPAC 169/126 concentration and total PCBs concentration indicated the possibility of induction in cytochrome P450 activities in North Pacific albatrosses (P<0.01). The calculated hazard indices indicated that black-footed and Laysan albatrosses inhabiting in the North Pacific had similar threshold levels which were known to cause toxic effects in some populations of fish-eating birds. PMID:11570807

  6. The Evolutionary Origins of the Southern Ocean Philobryid Bivalves: Hidden Biodiversity, Ancient Persistence

    PubMed Central

    Jackson, Jennifer A.; Linse, Katrin; Whittle, Rowan; Griffiths, Huw J.

    2015-01-01

    Philobryids (Bivalvia: Arcoida) are one of the most speciose marine bivalve families in the Southern Ocean and are common throughout the Southern Hemisphere. Considering this diversity and their brooding reproductive mode (limiting long-distance dispersal), this family may have been present in the Southern Ocean since its inception. However Philobrya and Adacnarca appear only in the Quaternary fossil record of the Antarctic, suggesting a much more recent incursion. Molecular dating provides an independent means of measuring the time of origin and radiation of this poorly known group. Here we present the first combined molecular and morphological investigation of the Philobryidae in the Southern Ocean. Two nuclear loci (18S and 28S) were amplified from 35 Southern Ocean Adacnarca and Philobrya specimens, with a combined sequence length of 2,282 base pairs (bp). Adacnarca specimens (A. nitens and A. limopsoides) were resolved as a strongly supported monophyletic group. Genus Philobrya fell into two strongly supported groups (‘sublaevis’ and ‘magellanica/wandelensis’), paraphyletic with Adacnarca. The A. nitens species complex is identified as at least seven morpho-species through morphological and genetic analysis of taxon clustering. Phylogenetic analyses resolve Philobryidae as a strongly supported monophyletic clade and sister taxon to the Limopsidae, as anticipated by their classification into the superfamily Limopsoidea. Bayesian relaxed clock analyses of divergence times suggest that genus Adacnarca radiated in the Southern Ocean from the Early Paleogene, while P. sublaevis and P. wandelensis clades radiated in the late Miocene, following the formation of the Antarctic Circumpolar Current. PMID:25853413

  7. Dissipation of the energy imparted by mid-latitude storms in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Jouanno, Julien; Capet, Xavier; Madec, Gurvan; Roullet, Guillaume; Klein, Patrice

    2016-06-01

    The aim of this study is to clarify the role of the Southern Ocean storms on interior mixing and meridional overturning circulation. A periodic and idealized numerical model has been designed to represent the key physical processes of a zonal portion of the Southern Ocean located between 70 and 40° S. It incorporates physical ingredients deemed essential for Southern Ocean functioning: rough topography, seasonally varying air-sea fluxes, and high-latitude storms with analytical form. The forcing strategy ensures that the time mean wind stress is the same between the different simulations, so the effect of the storms on the mean wind stress and resulting impacts on the Southern Ocean dynamics are not considered in this study. Level and distribution of mixing attributable to high-frequency winds are quantified and compared to those generated by eddy-topography interactions and dissipation of the balanced flow. Results suggest that (1) the synoptic atmospheric variability alone can generate the levels of mid-depth dissipation frequently observed in the Southern Ocean (10-10-10-9 W kg-1) and (2) the storms strengthen the overturning, primarily through enhanced mixing in the upper 300 m, whereas deeper mixing has a minor effect. The sensitivity of the results to horizontal resolution (20, 5, 2 and 1 km), vertical resolution and numerical choices is evaluated. Challenging issues concerning how numerical models are able to represent interior mixing forced by high-frequency winds are exposed and discussed, particularly in the context of the overturning circulation. Overall, submesoscale-permitting ocean modeling exhibits important delicacies owing to a lack of convergence of key components of its energetics even when reaching Δx = 1 km.

  8. The leading modes of decadal SST variability in the Southern Ocean in CMIP5 simulations

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Dommenget, Dietmar

    2016-09-01

    The leading modes of Sea Surface Temperature variability in the Southern Ocean on decadal and even larger time scales are analysed using Coupled Model Intercomparison Project 5 (CMIP5) model simulations and observations. The analysis is based on Empirical Orthogonal Function modes of the CMIP5 model super ensemble. We compare the modes from the CMIP5 super ensemble against several simple null hypotheses, such as isotropic diffusion (red noise) and a Slab Ocean model, to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes. The results show three main modes in the Southern Ocean: the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the Pacific, which is strongly related to atmospheric forcing by the Southern Annular Mode and El Nino Southern Oscillation. The second mode is an almost basin wide monopole pattern, which has pronounced multi-decadal and longer time scales variability. It is firstly inducted by the Wave-3 patterns in the atmosphere and further developed via ocean dynamics. The third mode is a dipole pattern in the southern Pacific that has a pronounced peak in the power spectrum at multi-decadal time scales. All three leading modes found in the CMIP5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis, thus all three leading modes are ocean-atmosphere coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes.

  9. Astronomically-induced Mid-Brunhes Transition in the Southern and Deep Oceans

    NASA Astrophysics Data System (ADS)

    Yin, Qiuzhen

    2013-04-01

    The interglacials after 430 ka (ka: 1000 years) ago were characterized by warmer climates and higher atmospheric CO2 concentrations than the interglacials before, but the cause of this climatic transition (the so-called Mid-Brunhes Event, MBE) is unknown. Based on model simulations, my results show that, in response to insolation changes only, feedbacks between sea ice, temperature, evaporation and salinity caused vigorous pre-MBE Antarctic Bottom Water formation and Southern Ocean ventilation. My results also show that strong Westerlies increased the pre-MBE overturning in the Southern Ocean via an increased latitudinal insolation gradient created by changes in eccentricity during austral winter and in obliquity during austral summer. The stronger bottom water formation led to a cooler deep ocean during the older interglacials. These insolation-induced differences in the deep-sea temperature and in the Southern Ocean ventilation between the more recent interglacials and the older ones were not expected, because there is no straightforward visible systematic difference in the astronomical parameters between the interglacials before and after 430 ka ago. Rather than being a real "event", the apparent MBE (i.e. the difference in the interglacial intensity before and after 430 ka BP) appears in my results to come from the complex response of the climate system to the astronomical and insolation forcings prevailing before and after 430 ka BP. This does not mean that nothing could have happened between MIS-13 and MIS-11 which might have amplified such difference. Given the important roles of the Southern and Deep Oceans on the carbon cycle, these findings are a first step towards understanding the magnitude change of the interglacial CO2 concentration around 430 ka. Reference: Yin Q.Z., 2013. Insolation-induced Mid-Brunhes Transition in the Southern and Deep Oceans. Nature, DOI 10.1038/nature11790. Acknowledgement: This work is supported by the European Research Council

  10. Isotopic composition of dissolved iron in the Equatorial Pacific and the Southern oceans

    NASA Astrophysics Data System (ADS)

    Radic, A.; Lacan, F.; Jeandel, C.; Poitrasson, F.; Sarthou, G.

    2009-12-01

    Iron is a fundamental element linking ocean biogeochemistry and climate. Iron isotopes are a very promising tool for the study of the iron oceanic cycle, notably for tracing its sources to the ocean and/or for studying its speciation. Several studies reports iron isotopic data in the marine environment: in plankton tows, pore waters, aerosols, seafloor or marginal seas (Bergquist and Boyle, 2006; Severmann et al., 2006; De Jong et al., 2007). To link these isotopic data together and to fully study the iron isotope marine cycle, we need to document the central reservoir in the marine environment : dissolved iron in seawater, espacially in High Nutrient Low Chlorophyll (NHLC) areas. So far there are very few comunicated data of dissolved iron isotopic composition in the open ocean (Rouxel, 2008; Lacan et al., 2008; John and Andkins, 2009;). Here, the first profiles in HNLC areas will be presented : 2 full-depth profiles in the Equatorial Pacific Ocean (EUCFe 2006), 2 full-depth profiles in the Atlantic sector of the Southern Ocean (Bonus-GoodHope 2008) and some data from the Kerguelen area (Southern Ocean, KEOPS 2005). δ56Fe values range from -0.7‰ to more than 1.0‰. All the samples from the Equatorial Pacific Ocean display positive values (heavy iron) whereas samples from the Sourthern Ocean display rather negative values (light iron), especially around 450 m deepth. These results will be discussed in terms of iron sources to ocean. Potential applications of this new tracer for studying internal oceanic processes, such as biological uptake, will be discussed.

  11. 50 CFR Figure 1 to Subpart G of... - Boundaries of the Statistical Reporting Area in the Southern Ocean

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ... 50 Wildlife and Fisheries 11 2013-10-01 2013-10-01 false Boundaries of the Statistical Reporting Area in the Southern Ocean 1 Figure 1 to Subpart G of Part 300 Wildlife and Fisheries INTERNATIONAL... in the Southern Ocean EC01JY91.072...

  12. 50 CFR Figure 1 to Subpart G of... - Boundaries of the Statistical Reporting Area in the Southern Ocean

    Code of Federal Regulations, 2010 CFR

    2010-10-01

    ... 50 Wildlife and Fisheries 7 2010-10-01 2010-10-01 false Boundaries of the Statistical Reporting Area in the Southern Ocean 1 Figure 1 to Subpart G of Part 300 Wildlife and Fisheries INTERNATIONAL... in the Southern Ocean EC01JY91.072...

  13. 50 CFR Figure 1 to Subpart G of... - Boundaries of the Statistical Reporting Area in the Southern Ocean

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ... 50 Wildlife and Fisheries 11 2014-10-01 2014-10-01 false Boundaries of the Statistical Reporting Area in the Southern Ocean 1 Figure 1 to Subpart G of Part 300 Wildlife and Fisheries INTERNATIONAL... in the Southern Ocean EC01JY91.072...

  14. 50 CFR Figure 1 to Subpart G of... - Boundaries of the Statistical Reporting Area in the Southern Ocean

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ... 50 Wildlife and Fisheries 9 2011-10-01 2011-10-01 false Boundaries of the Statistical Reporting Area in the Southern Ocean 1 Figure 1 to Subpart G of Part 300 Wildlife and Fisheries INTERNATIONAL... in the Southern Ocean EC01JY91.072...

  15. 50 CFR Figure 1 to Subpart G of... - Boundaries of the Statistical Reporting Area in the Southern Ocean

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ... 50 Wildlife and Fisheries 11 2012-10-01 2012-10-01 false Boundaries of the Statistical Reporting Area in the Southern Ocean 1 Figure 1 to Subpart G of Part 300 Wildlife and Fisheries INTERNATIONAL... in the Southern Ocean EC01JY91.072...

  16. Global climate impacts of fixing the Southern Ocean shortwave radiation bias in the Community Earth System Model (CESM)

    NASA Astrophysics Data System (ADS)

    Kay, J. E.; Medeiros, B.; Yettella, V. K. R.; Hannay, C.; Caldwell, P.; Wall, C.; Bitz, C. M.

    2015-12-01

    A large, long-standing, and pervasive climate model bias is excessive absorbed shortwave radiation (ASR) over the mid-latitude oceans, especially the Southern Ocean. We investigate both the underlying mechanisms for and climate impacts of this bias within the Community Earth System Model with the Community Atmosphere Model version 5 (CESM-CAM5). Excessive Southern Ocean ASR in CESM-CAM5 results in part because low-level clouds contain insufficient amounts of supercooled liquid. In a present-day atmosphere-only run, an observationally motivated modification to the shallow convection detrainment increases supercooled cloud liquid, brightens low-level clouds, and substantially reduces the Southern Ocean ASR bias. Tuning to maintain global energy balance enables reduction of a compensating tropical ASR bias. In the resulting pre-industrial fully coupled run with a brighter Southern Ocean and dimmer Tropics, the Southern Ocean cools and the Tropics warm. As a result of the enhanced meridional temperature gradient, poleward heat transport increases in both hemispheres (especially the Southern Hemisphere) and the Southern Hemisphere atmospheric jet strengthens. Cross-equatorial heat transport increases in the ocean, but not in the atmosphere. As a result, a proposed atmospheric teleconnection that links Southern Ocean ASR bias reduction and cooling with northward shifts in the Intertropical Convergence Zone is not found. All results discussed above are for the transient response. Ongoing work to assess the equilibrium response and the impact of the fix climate change experiments results will also be presented.

  17. Tropical ocean-atmosphere interaction, the Pacific cold tongue, and the El Nino-Southern Oscillation

    SciTech Connect

    Jin, F.F.

    1996-10-04

    The tropical Pacific basin allows strong feedbacks among the trade winds, equatorial zonal sea surface temperature contrast, and upper ocean heat content. Coupled atmosphere-ocean dynamics produce both the strong Pacific cold tongue climate state and the El Nino-Southern Oscillation phenomenon. A simple paradigm of the tropical climate system is presented, capturing the basic physics of these two important aspects of the tropic Pacific and basic features of the climate states of the Atlantic and Indian ocean basins. 21 refs., 3 figs.

  18. Southern Ocean frontal system changes precede Antarctic ice sheet growth during the middle Miocene

    NASA Astrophysics Data System (ADS)

    Kuhnert, Henning; Bickert, Torsten; Paulsen, Harald

    2009-07-01

    The middle Miocene climate approximately 14 Ma ago was characterized by the glaciation of Antarctica, deep-ocean cooling and variations in the global carbon cycle. Although the Southern Ocean underwent significant oceanographic changes, there is limited information on their spatial extent and timing. However, such knowledge is crucial for understanding the role of the Southern Ocean and the Antarctic Circumpolar Current (ACC) for Antarctic glaciation and the coupling between the ocean and continental climate. We have reconstructed surface temperatures and seawater oxygen isotopes at Ocean Drilling Program (ODP) Site 1092 in the Polar Frontal Zone of the Atlantic sector of the Southern Ocean from foraminiferal oxygen isotopes ( δ18O) and magnesium to calcium ratios (Mg/Ca). Sea surface cooling by ~ 4 °C and freshening indicated by the ~ 1‰ reduction of seawater δ18O ( δ18O sw) at 14.2 Ma precede the major step in Antarctic ice sheet growth at 13.8-13.9 Ma. This pattern qualitatively mirrors previous findings from the Pacific sector, and we interpret the surface hydrographic changes to reflect the circum-Antarctic northward shift of the Southern Ocean fronts and specifically at Site 1092 the passage of the Subantarctic Front. The magnitude of change in reconstructed δ18O sw requires a δ18O sw: salinity gradient significantly higher than the modern value (~ 0.52‰) and it possibly exceeded 1.1‰. This implies the Polar Frontal Zone was influenced by freshwater derived from Antarctica, which in turn confirms higher than modern continental precipitation. The latter has previously been suggested to have contributed to Antarctic glaciation.

  19. The Leading Modes of Decadal SST Variability in the Southern Ocean in CMIP5 Simulations

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Dommenget, Dietmar

    2016-04-01

    The leading modes of Sea Surface Temperature (SST) variability in the Southern Ocean on decadal and even larger time scales are analysed using Coupled Model Intercomparison Project 5 (CMIP5) model simulations and observations. We compare the modes from the CMIP5 super ensemble against several simple null hypotheses, such as isotropic diffusion (red noise) and a Slab Ocean model, to investigate the sources of decadal variability and the physical processes affecting the characteristics of the modes. The results show three main modes in the Southern Ocean: the first and most dominant mode on interannual to decadal time scales is an annular mode with largest amplitudes in the Pacific, which is strongly related to atmospheric forcing by the Southern Annular Mode (SAM) and El Nino Southern Oscillation (ENSO). The second mode is an almost basin wide monopole pattern, which has pronounced multi-decadal and longer time scales variability. It is firstly inducted by the Wave-3 patterns in the atmosphere and further developed via ocean dynamics. The third mode is a dipole pattern in the southern Pacific that has a pronounced peak in the power spectrum at multi-decadal time scales. All three leading modes found in the CMIP5 super model have distinct patterns and time scale behaviour that can not be explained by simple stochastic null hypothesis, thus all three leading modes are ocean-atmospheric coupled modes and are likely to be substantially influenced or driven by ocean dynamical processes. The mechanism of the basin-wide mode is further analysed based on a series of idealized experiments. The results show that the monopole mode has a two-step power spectrum, with a first spectral increase on interannual time scale and a second higher up level on the multi-decadal to centennial time scales. Ocean dynamics, especially the ocean advection, transport the anomalous signals, connect the entire ocean and lead to the homogeneous-like spatial pattern even under stochastic

  20. Pronounced warming in the Indian and Pacific sectors of the Southern Ocean during the 1970s

    NASA Astrophysics Data System (ADS)

    Turney, Chris; Fogwill, Chris; Palmer, Jonathan; van Sebille, Erik; Thomas, Zoë; McGlone, Matt; Richardson, Sarah; Wilmshurst, Janet; Fenwick, Pavla; Carter, Lionel; Jones, Richard; Harsch, Melanie; Wilson, Kerry-Jayne; Clark, Graeme; Marzinelli, Ezequiel; Rogers, Tracey; Rainsley, Eleanor; Ciasto, Laura; Waterman, Stephanie; Antarctic Expedition 2013-2014 Members, Australasian

    2015-04-01

    Occupying some 20% of the world's ocean surface, the Southern Ocean is home to a diverse and unique biota and plays a fundamental role in global oceanic circulation, climate variability, Antarctic ice sheet stability and carbon cycling. Significant warming has been observed over recent decades, most prominently in the Antarctic Circumpolar Current (ACC). The mechanism(s) behind this warming, however, remain uncertain. Here, we integrate historic ocean and atmospheric observations and climate-sensitive tree growth on subantarctic islands from the northern limit of the ACC to extend historic and satellite measurements to produce a unique proxy record of temperature across 4˚ of latitude in the southwest Pacific. We demonstrate a hitherto unobserved abrupt warming during the 1970s that is unprecedented over the past 130 years, coincident with a significant decline in marine vertebrate populations and wider warming across the Indian Ocean. Comparison between our reconstruction and high-resolution ocean modelling provides a possible mechanism, suggesting warmer waters resulted from a poleward migration of the subtropical and ACC fronts. Projected increases in the strength of westerly winds are likely to continue the fronts' migration, driving warming in the Southern Ocean (>50˚S), with significant impacts on biota.

  1. Interdisciplinary Coordinated Experiment of the Southern Ocean Carbon Cycle (ICESOCC) - A Field Campaign Scoping Project

    NASA Astrophysics Data System (ADS)

    Mitchell, B. G.

    2015-12-01

    Accurate estimates in time and space of organic carbon export to the ocean interior via plankton net community production (NCP) for the global oceans (the biological pump) are essential for understanding the feedback between NCP, atmospheric CO2 and climate. Since integrated, multi-sensor satellite and in situ observations of many ocean variables are required to estimate NCP from space, this is a complex, interdisciplinary challenge. Satellite ocean color sensors are a fundamental component in estimating spatial and temporal variations in NCP. Therefore, NASA's PACE mission (NASA-PACE 2012), a mission included in NASA's Climate Architecture Plan (NASA-CAP, 2010), specifies a need for field programs to improve satellite algorithms and models to reduce uncertainties in estimates of NCP. Diverse data from sediment and glacial cores, and climate models, indicate that the Southern Ocean plays a large role in the glacial-interglacial variations in the biological pump, with considerable implications for variations in atmospheric CO2. The "Interdisciplinary Coordinated Experiment of the Southern Ocean Carbon Cycle (ICESOCC)" project is a NASA-funded field campaign scoping (planning) effort. Over 18 months and many public meetings and workshops, the ICESOCC team of 13 interdisciplinary scientists has integrated the input from scientific experts in ocean, atmosphere, ice physics, biogeochemistry, advanced observational tools (ship, autonomous, atmospheric gases and dust, cryosphere dynamics, winds), and models, to create a draft recommendation to NASA for field observations required to constrain uncertainty of NCP for the Southern Ocean. The ICESOCC team requests and encourages careful review and comments of the draft to ensure the most robust final recommendations are submitted in early 2016 for NASA consideration.

  2. Can ocean acidification affect population dynamics of the barnacle Semibalanus balanoides at its southern range edge?

    PubMed

    Findlay, Helen S; Burrows, Michael T; Kendall, Michael A; Spicer, John I; Widdicombe, Stephen

    2010-10-01

    The global ocean and atmosphere are warming. There is increasing evidence suggesting that, in addition to other environmental factors, climate change is affecting species distributions and local population dynamics. Additionally, as a consequence of the growing levels of atmospheric carbon dioxide (CO2), the oceans are taking up increasing amounts of this CO2, causing ocean pH to decrease (ocean acidification). The relative impacts of ocean acidification on population dynamics have yet to be investigated, despite many studies indicating that there will be at least a sublethal impact on many marine organisms, particularly key calcifying organisms. Using empirical data, we forced a barnacle (Semibalanus balanoides) population model to investigate the relative influence of sea surface temperature (SST) and ocean acidification on a population nearing the southern limit of its geographic distribution. Hindcast models were compared to observational data from Cellar Beach (southwestern United Kingdom). Results indicate that a declining pH trend (-0.0017 unit/yr), indicative of ocean acidification over the past 50 years, does not cause an observable impact on the population abundance relative to changes caused by fluctuations in temperature. Below the critical temperature (here T(crit) = 13.1 degrees C), pH has a more significant affect on population dynamics at this southern range edge. However, above this value, SST has the overriding influence. At lower SST, a decrease in pH (according to the National Bureau of Standards, pHNBs) from 8.2 to 7.8 can significantly decrease the population abundance. The lethal impacts of ocean acidification observed in experiments on early life stages reduce cumulative survival by approximately 25%, which again will significantly alter the population level at this southern limit. Furthermore, forecast predictions from this model suggest that combined acidification and warming cause this local population to die out 10 years earlier than

  3. Shearwater Foraging in the Southern Ocean: The Roles of Prey Availability and Winds

    PubMed Central

    Raymond, Ben; Shaffer, Scott A.; Sokolov, Serguei; Woehler, Eric J.; Costa, Daniel P.; Einoder, Luke; Hindell, Mark; Hosie, Graham; Pinkerton, Matt; Sagar, Paul M.; Scott, Darren; Smith, Adam; Thompson, David R.; Vertigan, Caitlin; Weimerskirch, Henri

    2010-01-01

    Background Sooty (Puffinus griseus) and short-tailed (P. tenuirostris) shearwaters are abundant seabirds that range widely across global oceans. Understanding the foraging ecology of these species in the Southern Ocean is important for monitoring and ecosystem conservation and management. Methodology/Principal Findings Tracking data from sooty and short-tailed shearwaters from three regions of New Zealand and Australia were combined with at-sea observations of shearwaters in the Southern Ocean, physical oceanography, near-surface copepod distributions, pelagic trawl data, and synoptic near-surface winds. Shearwaters from all three regions foraged in the Polar Front zone, and showed particular overlap in the region around 140°E. Short-tailed shearwaters from South Australia also foraged in Antarctic waters south of the Polar Front. The spatial distribution of shearwater foraging effort in the Polar Front zone was matched by patterns in large-scale upwelling, primary production, and abundances of copepods and myctophid fish. Oceanic winds were found to be broad determinants of foraging distribution, and of the flight paths taken by the birds on long foraging trips to Antarctic waters. Conclusions/Significance The shearwaters displayed foraging site fidelity and overlap of foraging habitat between species and populations that may enhance their utility as indicators of Southern Ocean ecosystems. The results highlight the importance of upwellings due to interactions of the Antarctic Circumpolar Current with large-scale bottom topography, and the corresponding localised increases in the productivity of the Polar Front ecosystem. PMID:20532034

  4. Sea ice, winter convection, and the temperature minimum layer in the Southern Ocean

    SciTech Connect

    Toole, J.M.

    1981-09-20

    The structure of the near surface waters in the Southern Ocean, poleward of the Antarctic Polar Front but away from continental margins, is investigated with a three-dimensional time-dependent numerical model which resolves the annual sea ice cycle. The growth and decay of the ice field is predicted, using one of Semtner's (1976) thermodynamic ice models, in terms of specified atmospheric data and computed thermohaline characteristics of the ocean layers. The ice field is found to be sensitive to the lateral advection of heat by the oceanic circulation as well as vertical heat transports due to deep winter convection. The model treats the temperature minimum layer in the Southern Ocean as the remnant of a deep winter mixed layer which becomes capped by surface heating and precipitation in summer. The predicted thermohaline characteristics of the temperature minimum layer and the surface mixed layer are in good agreement with observations. Finally, the annual air-sea heat exchange predicted by the model is discussed. The model's predicted area averaged heat loss experienced by the ocean south of the Atlantic Polar Front is much smaller than was previously estimated. This is attributed to errors in the southern region of the model domain. It is suggested that models, which include the interactions between sea ice and surface, deep, and bottom waters along the continental margins, are needed to investigate this region.

  5. Abrupt onset and prolongation of aragonite undersaturation events in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Hauri, Claudine; Friedrich, Tobias; Timmermann, Axel

    2016-02-01

    Ocean acidification may lead to seasonal aragonite undersaturation in surface waters of the Southern Ocean as early as 2030 (ref. ). These conditions are harmful to key organisms such as pteropods, which contribute significantly to the pelagic foodweb and carbon export fluxes in this region. Although the severity of ocean acidification impacts is mainly determined by the duration, intensity and spatial extent of aragonite undersaturation events, little is known about the nature of these events, their evolving attributes and the timing of their onset in the Southern Ocean. Using an ensemble of ten Earth system models, we show that starting around 2030, aragonite undersaturation events will spread rapidly, affecting ~30% of Southern Ocean surface waters by 2060 and >70% by 2100, including the Patagonian Shelf. On their onset, the duration of these events will increase abruptly from 1 month to 6 months per year in less than 20 years in >75% of the area affected by end-of-century aragonite undersaturation. This is likely to decrease the ability of organisms to adapt to a quickly evolving environment. The rapid equatorward progression of surface aragonite undersaturation can be explained by the uptake of anthropogenic CO2, whereas climate-driven physical or biological changes will play a minor role.

  6. Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics

    NASA Astrophysics Data System (ADS)

    Phipps, Steven J.; Fogwill, Christopher J.; Turney, Christian S. M.

    2016-09-01

    Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water (AABW) formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 °C at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus, localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.

  7. Antarctic icebergs melt over the Southern Ocean : Climatology and impact on sea ice

    NASA Astrophysics Data System (ADS)

    Merino, Nacho; Le Sommer, Julien; Durand, Gael; Jourdain, Nicolas C.; Madec, Gurvan; Mathiot, Pierre; Tournadre, Jean

    2016-08-01

    Recent increase in Antarctic freshwater release to the Southern Ocean is suggested to contribute to change in water masses and sea ice. However, climate models differ in their representation of the freshwater sources. Recent improvements in altimetry-based detection of small icebergs and in estimates of the mass loss of Antarctica may help better constrain the values of Antarctic freshwater releases. We propose a model-based seasonal climatology of iceberg melt over the Southern Ocean using state-of-the-art observed glaciological estimates of the Antarctic mass loss. An improved version of a Lagrangian iceberg model is coupled with a global, eddy-permitting ocean/sea ice model and compared to small icebergs observations. Iceberg melt increases sea ice cover, about 10% in annual mean sea ice volume, and decreases sea surface temperature over most of the Southern Ocean, but with distinctive regional patterns. Our results underline the importance of improving the representation of Antarctic freshwater sources. This can be achieved by forcing ocean/sea ice models with a climatological iceberg fresh-water flux.

  8. Cosmic meteor dust: potentially the dominant source of bio-available iron in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Dyrud, L. P.; Marsh, D. R.; Del Castillo, C. E.; Fentzke, J.; Lopez-Rosado, R.; Behrenfeld, M.

    2012-12-01

    Johnson, 2001 [Johnson, Kenneth. S. (2001), Iron supply and demand in the upper ocean: Is extraterrestrial dust a significant source of bioavailable iron?, Global Biogeochem. Cycles, 15(1), 61-63, doi:10.1029/2000GB001295], first suggested that meteoric particulate flux could be a significant source of bio-available iron, particularly in regions with little or no eolean sources, such as the Southern Ocean. While these calculations raised intriguing questions, there were many large unknowns in the input calculations between meteor flux and bio-available ocean molecular densities. There has been significant research in the intervening decade on related topics, such as the magnitude (~200 ktons per year) and composition of the meteoric flux, its atmospheric evaporation, transport, mesospheric formation of potentially soluble meteoric smoke, and extraterrestrial iron isotope identification. Paramount of these findings are recent NCAR WACCM atmosphere model results demonstrating that the majority of meteoric constituents are transported towards the winter poles and the polar vortex. This may lead to a focusing of meteoritic iron deposition towards the Southern Ocean. We present a proposed research plan involving Southern Ocean sample collection and analysis and atmospheric and biological modeling to determine both the current relevance of meteoric iron, and examine the past and future consequences of cosmic dust under a changing climate.

  9. Lead isotopes in Southern Ocean marine sediments: implications for paleoclimatic provenance and seawater studies

    NASA Astrophysics Data System (ADS)

    Cook, C. P.; Martin, E. E.

    2014-12-01

    Lead (Pb) isotopes in detrital marine sediments and authigenic oxide coatings have proven useful in reconstructing past changes in continental weathering of glaciated continents and ocean circulation. This approach is under-utilised in the Southern Ocean, despite uncertainties about the evolution of Antarctica's ice sheets and oceanographic changes in this region throughout the Cenozoic. Lead isotopes in sediments are controlled by the mineralogy and age of their bedrock sources, making them an ideal tool to trace changes in Southern Ocean sediment provenance associated with onland erosion patterns (and ice sheet variability), and ocean circulation. However, core-top mapping of Pb isotope signatures of detrital marine sediments in this region is non-existent. We present new Pb isotope data for acid-digested <63µm and bulk Late Holocene sediments from 40 cores located in the East Antarctic sector of Southern Ocean. Results demonstrate that, similar to existing Nd and Sr core-top surveys, distinct provenance sectors can be seen in sediments proximal to the continent, due to the geological characteristics of bedrock sources along the margin. A striking N-S trend is also evident, with distal sediments characterised by less radiogenic isotopic signatures, likely associated with a decrease in radiogenic Pb-bearing minerals with increasing distance from the continental margin. This pattern suggests that Pb isotopes in marine sediments may be useful in reconstructing past provenance trends associated with ice sheet change, and migrations of Southern Ocean frontal positions. In addition, we will present new seawater Pb isotope data from reductive leaching of authigenic coatings of these same sediments, permitting for Late Holocene Pb isotope seawater mapping of the Southern Ocean. To ensure we measured the true seawater signal, we adapted established sequential leaching procedures to minimise detrital contamination, and monitored leachate compositions with Nd isotopes, and

  10. Marine gravity of the Southern Ocean and Antarctic margin from Geosat

    NASA Technical Reports Server (NTRS)

    Sandwell, David T.; Mcadoo, David C.

    1988-01-01

    Geosat altimeter data, collected from an orbit with a ground rack that repeated every 17 days and overlayed one of the 17-day Seasat ground tracks, were used to map the gravity field of the Southern Ocean and the continental margin of Antarctica. The combination of ascending an descending profiles produced a typical Geosat ground track spacing of 70 km at the equator, with the best coverage occurring between the latitudes of 60 and 72 deg in both the Northern and Southern hemispheres. The new data reveal many previously uncharted seamounts and fracture zones in the extreme Southern Ocean areas adjacent to Antarctica, showing the detailed gravity signatures of the passive and active continental margins of Antarctica. Seven large age-offset fracture zones apparent in the Geosat data record the early breakup of Gondwana.

  11. Two modes of change in Southern Ocean productivity over the past million years.

    PubMed

    Jaccard, S L; Hayes, C T; Martínez-García, A; Hodell, D A; Anderson, R F; Sigman, D M; Haug, G H

    2013-03-22

    Export of organic carbon from surface waters of the Antarctic Zone of the Southern Ocean decreased during the last ice age, coinciding with declining atmospheric carbon dioxide (CO(2)) concentrations, signaling reduced exchange of CO(2) between the ocean interior and the atmosphere. In contrast, in the Subantarctic Zone, export production increased into ice ages coinciding with rising dust fluxes, thus suggesting iron fertilization of subantarctic phytoplankton. Here, a new high-resolution productivity record from the Antarctic Zone is compiled with parallel subantarctic data over the past million years. Together, they fit the view that the combination of these two modes of Southern Ocean change determines the temporal structure of the glacial-interglacial atmospheric CO(2) record, including during the interval of "lukewarm" interglacials between 450 and 800 thousand years ago.

  12. What causes the inverse relationship between primary production and export efficiency in the Southern Ocean?

    NASA Astrophysics Data System (ADS)

    Le Moigne, Frédéric A. C.; Henson, Stephanie A.; Cavan, Emma; Georges, Clément; Pabortsava, Katsiaryna; Achterberg, Eric P.; Ceballos-Romero, Elena; Zubkov, Mike; Sanders, Richard J.

    2016-05-01

    The ocean contributes to regulating atmospheric CO2 levels, partly via variability in the fraction of primary production (PP) which is exported out of the surface layer (i.e., the e ratio). Southern Ocean studies have found that contrary to global-scale analyses, an inverse relationship exists between e ratio and PP. This relationship remains unexplained, with potential hypotheses being (i) large export of dissolved organic carbon (DOC) in high PP areas, (ii) strong surface microbial recycling in high PP regions, and/or (iii) grazing-mediated export that varies inversely with PP. We find that the export of DOC has a limited influence in setting the negative e ratio/PP relationship. However, we observed that at sites with low PP and high e ratios, zooplankton-mediated export is large and surface microbial abundance low suggesting that both are important drivers of the magnitude of the e ratio in the Southern Ocean.

  13. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-01

    Ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.

  14. Chemically and geographically distinct solid-phase iron pools in the Southern Ocean.

    PubMed

    von der Heyden, B P; Roychoudhury, A N; Mtshali, T N; Tyliszczak, T; Myneni, S C B

    2012-11-30

    Iron is a limiting nutrient in many parts of the oceans, including the unproductive regions of the Southern Ocean. Although the dominant fraction of the marine iron pool occurs in the form of solid-phase particles, its chemical speciation and mineralogy are challenging to characterize on a regional scale. We describe a diverse array of iron particles, ranging from 20 to 700 nanometers in diameter, in the waters of the Southern Ocean euphotic zone. Distinct variations in the oxidation state and composition of these iron particles exist between the coasts of South Africa and Antarctica, with different iron pools occurring in different frontal zones. These speciation variations can result in solubility differences that may affect the production of bioavailable dissolved iron.

  15. Evaluating the Silicic Acid Leakage Hypothesis in the Pacific Sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Wall, A.; Baldwin, M.; Burckle, L.; Anderson, R.

    2004-12-01

    The Silicic Acid Leakage Hypothesis (SALH; Matsumoto et al., 2002; Glob. Biogeochem. Cycles 16, 10.1029/2001GB001442) posits that lower atmospheric carbon dioxide concentrations during glacial times resulted from a net transfer of dissolved silicic acid from the Southern Ocean to the tropics, coupled with a corresponding shift in phytoplankton taxa in tropical waters toward a greater dominance by diatoms (relative to today). If valid, then the SALH requires that opal burial rates in the Southern Ocean were lower than today during the Last Glacial Maximum (LGM), while contemporary opal burial rates in tropical regions were greater than today. Previous studies in the Indian and Atlantic sectors of the Southern Ocean have shown little to no net change between the LGM and the Holocene when opal burial rates are integrated across Subantarctic and Antarctic zones. This study aims to test a sub-hypothesis suggested by Chase et al. (Deep-Sea Research-II, v.50, 2003, 799-832) that silicic acid was exported only out of the Pacific sector. Piston cores from the SW Pacific sector of the Southern Ocean were analyzed to determine opal burial fluxes. Magnetic susceptibility and Eucampia antarctica abundances were used to determine glacial cycles and identify cores containing both LGM and Holocene sediment. Fluxes of opal, calcium carbonate, and lithogenic material were evaluated by normalizing to 230Th to correct for sediment focusing. Our results show opal flux at, and to the south of, the Antarctic Polar Front (APF) to have been lower during the LGM compared to the Holocene, consistent with previous results from throughout the Southern Ocean. North of the APF, two cores show higher opal fluxes during the LGM. However, due to a possible hiatus in one of the cores, the degree to which opal flux during the LGM was greater than during the Holocene has a large uncertainty. Additional analyses are planned to help reduce this uncertainty.

  16. Variability and Change in Southern Ocean Ecosystems: Whither the Ice and What of Krill?

    NASA Astrophysics Data System (ADS)

    Murphy, E. J.

    2015-12-01

    Changes occurring in the Southern Ocean involve multiple physical, biogeochemical and ecological processes that have global connections. Developing a quantitative understanding of how biogeochemical cycles and ecosystems are affected by changes in these multiple processes is crucial for generating projections of the impacts of future change in the Southern Ocean. The changes occurring are not homogeneous, but instead show marked spatial and temporal variability, demonstrated most clearly by the regional nature of trends in sea-ice concentration over the last few decades. The impacts of these changes have also been observed at multiple trophic levels in Southern Ocean ecosystems, from primary producers to top predators, affecting the structure of the food webs in which they occur. Here, I consider briefly the changes occurring in the Southern Ocean and current views of expected future change, highlighting some of the complexity of the system interactions involved. I illustrate some of the major issues through a focus on sea-ice variability and change, noting the impacts on various ecosystem components, and particularly the effects on Antarctic krill. This perspective highlights that current knowledge of the detailed causes and consequences of change in Southern Ocean ecosystems, and hence future trajectories, are generally uncertain. It also shows the importance of understanding the intrinsic variability of the system and how interactions and feedbacks can influence the structure and functioning of ecosystems and associated biogeochemical cycles. Developing useful projections of the impacts of change requires integrated understanding of how physical, biogeochemical and ecological process interactions affect responses to change and provides a valuable focus for future research effort.

  17. Bathymetric distribution patterns of Southern Ocean macrofaunal taxa: Bivalvia, Gastropoda, Isopoda and Polychaeta

    NASA Astrophysics Data System (ADS)

    Brandt, Angelika; Linse, Katrin; Schüller, Myriam

    2009-11-01

    The aim of this study is to compare the depth distributions of four major Southern Ocean macrobenthic epi- and infaunal taxa, the Bivalvia, Gastropoda, Isopoda, and Polychaeta, from subtidal to abyssal depth. All literature data up to summer 2008, as well as the unpublished data from the most recent ANDEEP I-III (Antarctic benthic deep-sea biodiversity: colonisation history and recent community patterns) expeditions to the Southern Ocean deep sea are included in the analysis. Benthic invertebrates in the Southern Ocean are known for their wide bathymetric ranges. We analysed the distributions of four of the most abundant and species-rich taxa from intertidal to abyssal (5200 m) depths in depth zones of 100 m. The depth distributions of three macrofaunal classes (Bivalvia, Gastropoda, Polychaeta) and one order (Isopoda) showed distinct differences. In the case of bivalves, gastropods and polychaetes, the number of species per depth zone decreased from the shelf to the slope at around 1000 m depth and then showed stable low numbers. The isopods showed the opposite trend; they were less species rich in the upper 1000 m but increased in species numbers from the slope to bathyal and abyssal depths. Depth ranges of families of the studied taxa (Bivalvia: 31 families, Gastropoda: 60, Isopoda: 32, and Polychaeta: 46 families) were compiled and illustrated. At present vast areas of the deep sea in the Southern Ocean remain unexplored and species accumulation curves showed that only a fraction of the species have been discovered to date. We anticipate that further investigations will greatly increase the number of species known in the Southern Ocean deep sea.

  18. A unified history of the ocean around southern Africa

    NASA Astrophysics Data System (ADS)

    Reeves, Colin; Master, Sharad

    2010-05-01

    The movement with respect to Africa of the hotspot marked by present-day Bouvet island is extrapolated backward in time to a position in the Lower Limpopo Valley at the time of the Karoo-Ferrar basalt event (183 Ma). In a tight reconstruction of the Precambrian fragments of Gondwana at this time, the triangular gap that remains between South Africa's Precambrian, that of Dronning Maud Land, Antarctica, and the eastward-extrapolated front of the Cape Fold Belt we fill with the Precambrian fragments of South Patagonia and the Falkland Islands. We postulate that the 183 Ma mantle upwelling produced a triple junction-type fracture marked by the alignments of the Lebombo, the SE margin of the Zimbabwe craton and the giant Botswana dyke swarm (178 Ma) that was rather quickly followed by the expulsion of the South Patagonia terranes from the Gondwana assembly along the alignment of the Falklands-Agulhas Fault Zone (FAFZ) as a transform margin. The space created was filled with igneous material akin to the present day Afar triangle. The magma supply generated not only oceanic crust but also overlying igneous deposits, much probably erupted subaerially. These developed progressively into the Falklands Plateau, the Mozambique Plains, the Mozambique Rise and the Explora Wedge of Antarctica. Not until the early Cretaceous did the growth of normal ocean crust start to exceed the ability of the declining mantle plume to cover the new ocean crust in a confined space with subaerial deposits that substantially thickened otherwise ‘oceanic' crust. When Antarctica and Africa began to separate before about 167 Ma, the future Mozambique Rise moved with Antarctica until, at about 125 Ma, a modest ridge reorganization east of Africa left Madagascar and the Mozambique Rise as part of the Africa Plate. An increasing westerly component to the movement of Antarctica against Africa preceded the initial opening of the South Atlantic and the fusing of the South Patagonia terranes with the

  19. Insights into Ocean Acidification During the Middle Eocene Climatic Optimum from Boron Isotopes at Southern Ocean Site 738

    NASA Astrophysics Data System (ADS)

    Moebius, I.; Hoenisch, B.; Friedrich, O.

    2015-12-01

    The Middle Eocene Climatic Optimum (MECO) is a ~650-kyr interval of global warming, with a brief ~50 ky long peak warming interval, and an abrupt termination. Deep sea and surface ocean temperature evolution across this interval are fairly well constrained, but thus far we have little understanding of the mechanisms responsible for the gradual warming and rapid recovery. Carbonate mass accumulation rates suggest a shoaling of the carbonate compensation depth, and studies on alkenones indicate increasing atmospheric CO2 levels during the MECO. This suggests an increase in surface ocean CO2, and consequently ocean acidification. However, the severity and timing of the proposed ocean acidification with respect to the onset, peak warming and the termination are currently not well resolved. The boron isotopic composition (δ11B) recorded in planktic foraminifer shells offers an opportunity to infer oceanic pH across this interval. We are working on a boron isotope reconstruction from Southern Ocean IODP site 738 and South Atlantic IODP site 1263, covering 42.0 to 38.5 Ma. These sites are characterized by good carbonate preservation and well-defined age models have been established. Additionally, ecology, nutrient content and bottom-water oxygenation have been shown to change significantly across the event towards a more eutrophic, periodically oxygen-depleted environment supporting different biological communities. We selected the planktic foraminifera species Acarinina spinuloinflata for this study because it is symbiont-bearing, suggesting a near-surface habitat and little vertical migration in the water column, and because of its abundance in the samples. δ11B data will be translated to surface ocean pH and atmospheric pCO2 will be approximated to refine knowledge about the carbon cycle during this time. Parallel analysis of two core sites will help to evaluate the tenacity of the data.

  20. Coupled atmosphere-ocean model simulations of El Nino/Southern Oscillation with and without an active Indian Ocean

    SciTech Connect

    Nagai, T.; Kitamura, Y.; Endoh, M.; Tokioka, T.

    1995-01-01

    An atmospheric general circulation model (GCM) was coupled with an ocean GCM covering the Pacific. This coupled model (PAC) was integrated over a 30-year period. The PAC model stimulates well the mean seasonally varying atmospheric and ocean fields and reproduces interannual variations corresponding to ENSO (El Nino/Southern Oscillation). The same atmospheric GCM was coupled with an ocean GCM covering the Indian Ocean and the tropical Pacific. This coupled model (IPC) was integrated over a 35-year period. The model climate in IPC is fairly reasonable, and its Pacific part is very similar to the Pacific climate of the PAC model. ENSO is the major interannual variability in the IPC model. The dynamics of ENSO in IPC are essentially the same as that in PAC. In the Pacific, the subsurface ocean heat content anomalies are formed by wind anomalies and show westward propagation centered off the equator. After they reach the western Pacific, they show eastward propagation along the equator. They produce changes in the thermocline structure in the eastern equatorial Pacific resulting in anomalies in SSTs. The SST anomalies provide wind anomalies, the sign of which is opposite to that of the wind anomalies in the first stage, so that this chain will continue. ENSO in the PAC and IPC models can be regarded as the {open_quotes}delayed oscillator{close_quotes} operating in the Pacific. Although the major interannual variability in the Indian Ocean is linked to ENSO in the Pacific, the Indian Ocean does not play any active role in the ENSO cycle in the IPC model. Interannual variability of monsoon activity in the IPC model is more reasonable than that in the PAC model. However, any definite mechanism for the relationship between monsoon activity and ENSO does not emerge in the present study. 31 refs., 14 figs.

  1. Role of squid in the Southern Ocean pelagic ecosystem and the possible consequences of climate change

    NASA Astrophysics Data System (ADS)

    Rodhouse, Paul G. K.

    2013-10-01

    Southern Ocean squid are important predators and prey and are a potential fishery resource. Their future under climate change is analysed from predictions of change by 2100 and assessments of the effects on squid biology. There are ˜18 Antarctic species of squid. Young feed primarily on crustaceans and switch later to fishes. They are preyed on by odontocetes, seals and seabirds - which together consume ˜34×106tyr-1 - and fish. As predators, squid are second to fish as biomass producers but recent evidence suggests predator consumption of squid needs to be reassessed. Fatty acid composition and stable nitrogen isotope ratios indicate some predators consume less squid in their diet than gut contents data suggest. Southern Ocean oceanography is unique in having circumpolar circulation and frontal systems and at high latitudes it is heavily influenced by sea ice. The Antarctic Peninsula is among the fastest warming regions worldwide but elsewhere the Southern Ocean is warming more slowly and the Ross Sea is probably cooling. Sea ice is receding in the Peninsula region and increasing elsewhere. Modelled predictions for 2100 suggest although the Southern Ocean will warm less than other oceans and sea ice will reduce. The Antarctic Circumpolar Current may shift slightly southwards with intensification of westerly winds but resolution of the models is insufficient to predict mesoscale change. Globally, pH of seawater has decreased by 0.1 units since the mid-1900s and is predicted to decrease by another 0.5 units by 2100. Impact on calcifying organisms will be high in the cold Southern Ocean where solubility of calcium carbonate is high. Predicted temperature increases are unlikely to have major effects on squid other than changes in distribution near the limits of their range; acidification may have greater impact. Small changes in large scale circulation are unlikely to affect squid but changes in mesoscale oceanography may have high impact. Change in sea ice extent

  2. Bipolar Atlantic deepwater circulation in the middle-late Eocene: Effects of Southern Ocean gateway openings

    NASA Astrophysics Data System (ADS)

    Borrelli, Chiara; Cramer, Benjamin S.; Katz, Miriam E.

    2014-04-01

    We present evidence for Antarctic Circumpolar Current (ACC)-like effects on Atlantic deepwater circulation beginning in the late-middle Eocene. Modern ocean circulation is characterized by a thermal differentiation between Southern Ocean and North Atlantic deepwater formation regions. In order to better constrain the timing and nature of the initial thermal differentiation between Northern Component Water (NCW) and Southern Component Water (SCW), we analyze benthic foraminiferal stable isotope (δ18Obf and δ13Cbf) records from Ocean Drilling Program Site 1053 (upper deep water, western North Atlantic). Our data, compared with published records and interpreted in the context of ocean circulation models, indicate that progressive opening of Southern Ocean gateways and initiation of a circum-Antarctic current caused a transition to a modern-like deep ocean circulation characterized by thermal differentiation between SCW and NCW beginning ~38.5 Ma, in the initial stages of Drake Passage opening. In addition, the relatively low δ18Obf values recorded at Site 1053 show that the cooling trend of the middle-late Eocene was not global, because it was not recorded in the North Atlantic. The timing of thermal differentiation shows that NCW contributed to ocean circulation by the late-middle Eocene, ~1-4 Myr earlier than previously thought. We propose that early NCW originated in the Labrador Sea, based on tectonic reconstructions and changes in foraminiferal assemblages in this basin. Finally, we link further development of meridional isotopic gradients in the Atlantic and Pacific in the late Eocene with the Tasman Gateway deepening (~34 Ma) and the consequent development of a circumpolar proto-ACC.

  3. Southern Ocean biogeochemical control of glacial/interglacial carbon dioxide change

    NASA Astrophysics Data System (ADS)

    Sigman, D. M.

    2014-12-01

    In the effort to explain the lower atmospheric CO2 concentrations observed during ice ages, two of the first hypotheses involved redistributing dissolved inorganic carbon (DIC) within the ocean. Broecker (1982) proposed a strengthening of the ocean's biological pump during ice ages, which increased the dissolved inorganic carbon gradient between the dark, voluminous ocean interior and the surface ocean's sun-lit, wind-mixed layer. Boyle (1988) proposed a deepening in the ocean interior's pool of DIC associated with organic carbon regeneration, with its concentration maximum shifting from intermediate to abyssal depths. While not irrefutable, evidence has arisen that these mechanisms can explain much of the ice age CO2 reduction and that both were activated by changes in the Southern Ocean. In the Antarctic Zone, reduced exchange of water between the surface and the underlying ocean sequestered more DIC in the ocean interior (the biological pump mechanism). Dust-borne iron fertilization of the Subantarctic surface lowered CO2 partly by the biological pump mechanism and partly by Boyle's carbon deepening. Each mechanism owes a part of its CO2 effect to a transient increase in seafloor calcium carbonate dissolution, which raised the ice age ocean's alkalinity, causing it to absorb more CO2. However, calcium carbonate cycling also sets limits on these mechanisms and their CO2 effects, such that the combination of Antarctic and Subantarctic changes is needed to achieve the full (80-100 ppm) ice age CO2 decline. Data suggest that these changes began at different phases in the development of the last ice age, 110 and 70 ka, respectively, explaining a 40 ppm CO2 drop at each time. We lack a robust understanding of the potential causes for both the implied reduction in Antarctic surface/deep exchange and the increase in Subantarctic dust supply during ice ages. Thus, even if the evidence for these Southern Ocean changes were to become incontrovertible, conceptual gaps stand

  4. Wind increase over cooling Southern Ocean driven by tropical warming and polar ozone hole

    NASA Astrophysics Data System (ADS)

    Schneider, D. P.; Fan, T.; Deser, C.

    2014-12-01

    Changing winds over the Southern Ocean have had dramatic impacts on Antarctic sea ice extent, anthropogenic heat and carbon uptake by the ocean, and the contribution of the Antarctic ice sheet to global sea level rise. An overall intensification of the surface westerly winds has been attributed to several different forcings, including stratospheric ozone depletion, greenhouse gasses, and tropical sea surface temperatures (SSTs). However, the relative roles of these drivers have not been well quantified. Reconciling previous explanations, here we show that a combination of tropical SSTs and stratospheric ozone loss largely explains the magnitude, regional patterns, and seasonality of observed lower tropospheric zonal wind trends over the Southern Ocean. We evaluate multiple ensembles of atmospheric model simulations, with each ensemble forced by one or a combination of drivers. Considering all months of the year, tropical SSTs are the largest contributor to observed zonal wind trends over 40°S-80°S. In austral summer, tropical SSTs and stratospheric ozone loss have contributed approximately equally to near-surface wind trends. The tropical contribution in austral summer is associated with tropics-wide warming, which has been moderated in recent decades by a prevalence of La-Niña events. The relative phasing of natural variability with anthropogenic forcing is therefore essential for understanding and predicting Southern Ocean climate change.

  5. Southern Ocean Carbon Sink Constraints from Radiocarbon in Drake Passage Air

    NASA Astrophysics Data System (ADS)

    Lindsay, C. M.; Lehman, S.; Miller, J. B.

    2014-12-01

    The Southern Ocean is one of the earth's largest regional net carbon sinks due to strong westerly winds, which drive surface gas exchange, deep mixing and upwelling. The strength of the sink is set by complex interactions between the physical circulation, gas exchange and biological activity in surface waters. Recent work by others has predicted that global warming may weaken the sink by strengthening the regional winds, increasing upwelling and the flux of deep, naturally carbon-rich and radiocarbon-depleted water into the surface mixed layer. The resulting decrease in the air-sea pCO2 gradient is thought to overwhelm other compensating changes, causing a weakened net sink. Here we demonstrate the use of precise measurements of radiocarbon in Drake Passage air (14CO2) to detect short-term fluctuations in the Southern Ocean gross sea-to-air C flux, and by extension, possible changes in the net carbon sink and their underlying causes. Drake Passage boundary layer air has been sampled since 2006 at roughly fortnightly intervals as part of NOAA's Cooperative Air Sampling Network, resulting in a 5-year high-resolution 14CO2 time-series with accompanying same-flask CO2 concentration measurements. Atmospheric measurements at Drake Passage are representative of zonal average exchange fluxes due to strong mixing by the westerly winds. In preliminary results, anomalously low ∆14C values are correlated with positive states of the Southern Annular Mode, a hemispheric-scale indicator of stronger westerly winds in the high latitude Southern Ocean. Simulations from the TM5 atmospheric transport model with a detailed global radiocarbon budget are used to interpret the results. These results appear to support the hypothesized link between stronger westerly winds and a weaker Southern Ocean carbon sink.

  6. Sea Ice Induced Glacial/Deglacial Changes in Southern Ocean Surface Structure

    NASA Astrophysics Data System (ADS)

    Abelmann, A.; Gersonde, R.; Knorr, G.; Zhang, X.; Chapligin, B.; Maier, E.; Esper, O.; Lohmann, G.; Meyer, H.; Tiedemann, R.

    2014-12-01

    Glacial/deglacial sea ice variations in the Southern Ocean are suggested to be an important factor impacting ocean's surface structure and biological productivity and thus controlling glacial/interglacial changes in atmospheric CO2. However, the description of involved mechanisms and their implication on nutrient cycling and biological productivity remains incomplete. Isotope measurements on siliceous microorganisms (diatoms and radiolarians) provide a means of reconstructing past changes in nutrient utilization and surface water structure, thus provide information on past biological and physical properties crucial to better describe and model the mechanisms regulating glacial/interglacial variability in CO2 draw down in the Southern Ocean. As diatoms belong to the phytoplankton, they present a sea surface signal. Radiolarians, by contrast, are siliceous zooplankton distributed from surface to deep waters and their stable isotope signals can provide information about deeper water layers. Here, we specify Southern Ocean surface/subsurface contrasts using combined oxygen and silicon isotope measurements of diatom and radiolarian opal obtained from two cores gathered in the sea ice-free Antarctic Zone and northern Polar Front Zone of the Atlantic Southern Ocean. Our records point to a well established glacial spring/summer stratification induced by sea-ice melt. Numerical simulations corroborate this, but also suggest that seasonal stratification was variable with relatively deep mixing that occurred during fall/winter. We discuss various aspects of nutrient utilization in surface and subsurface waters with specific emphasis on the impact of sea ice variations on mixed layer depths and biological productivity during the last glacial and deglacial transition.

  7. Glacial-interglacial variability in diatom abundance and valve size: Implications for Southern Ocean paleoceanography

    NASA Astrophysics Data System (ADS)

    Nair, Abhilash; Mohan, Rahul; Manoj, M. C.; Thamban, Meloth

    2015-10-01

    Antarctic sea ice extent along with Southern Ocean biological productivity varied considerably during glacial-interglacial periods, and both are known to have played a considerable role in regulating atmospheric CO2 variations in the past. Here we present data on diatom absolute abundance (valves/g of sediment) and size over the past ~ 42 ka B.P. and how they link to glacial-interglacial changes in Antarctic sea ice extent, Southern Ocean frontal systems, and aeolian dust flux. Our records of sea ice and permanent open ocean zone diatom abundances suggest a shift in the Antarctic winter sea ice limit and Polar Front respectively up to the modern-day Polar Frontal Zone during marine isotopic stages (MIS) 2 and late MIS 3. In addition to glacial shifts in the Polar Front, diatom assemblages also recorded a plausible northward shifts in Polar Front during few intervals of MIS 1. Glacial periods north of the Polar Front in the Indian sector of the Southern Ocean were characterized by higher total diatom abundance, larger Fragilariopsis kerguelensis apical length, and Thalassiosira lentiginosa radius. This is probably a consequence of (1) a northward expansion of the opal belt, a region characterized by high production and export of biogenic silica; (2) an increase in terrigenous input, via erosion of Crozet Islands; and (3) the alleviation of iron deficit by high input of Fe-bearing dust. The larger and highly silicified diatoms such as F. kerguelensis and T. lentiginosa may have mainly contributed in transporting biogenic silica and organic carbon to the seabed for the last 42 ka, in the northern Polar Frontal Zone of the Indian sector of the Southern Ocean.

  8. The Deep South Clouds & Aerosols project: Improving the modelling of clouds in the Southern Ocean region

    NASA Astrophysics Data System (ADS)

    Morgenstern, Olaf; McDonald, Adrian; Harvey, Mike; Davies, Roger; Katurji, Marwan; Varma, Vidya; Williams, Jonny

    2016-04-01

    Southern-Hemisphere climate projections are subject to persistent climate model biases affecting the large majority of contemporary climate models, which degrade the reliability of these projections, particularly at the regional scale. Southern-Hemisphere specific problems include the fact that satellite-based observations comparisons with model output indicate that cloud occurrence above the Southern Ocean is substantially underestimated, with consequences for the radiation balance, sea surface temperatures, sea ice, and the position of storm tracks. The Southern-Ocean and Antarctic region is generally characterized by an acute paucity of surface-based and airborne observations, further complicating the situation. In recognition of this and other Southern-Hemisphere specific problems with climate modelling, the New Zealand Government has launched the Deep South National Science Challenge, whose purpose is to develop a new Earth System Model which reduces these very large radiative forcing problems associated with erroneous clouds. The plan is to conduct a campaign of targeted observations in the Southern Ocean region, leveraging off international measurement campaigns in this area, and using these and existing measurements of cloud and aerosol properties to improve the representation of clouds in the nascent New Zealand Earth System Model. Observations and model development will target aerosol physics and chemistry, particularly sulphate, sea salt, and non-sulphate organic aerosol, its interactions with clouds, and cloud microphysics. The hypothesis is that the cloud schemes in most GCMs are trained on Northern-Hemisphere data characterized by substantial anthropogenic or terrestrial aerosol-related influences which are almost completely absent in the Deep South.

  9. Last Glacial - Holocene climate variability in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Xiao, Wenshen; Esper, Oliver; Gersonde, Rainer

    2016-03-01

    The Southern Ocean plays a major role in the glacial/interglacial global carbon cycle. However, there is a substantial lack of information from its Antarctic Zone south of the Polar Front (PF) to understand key climate processes (e.g., sea ice variability, productivity changes, CO2 source region, shifts of the Southern Westerly Wind) active in this region during the glacial/interglacial transition, due to the limited high-resolution sediment records from this area. To close this gap, we investigated high resolution diatom records from a series of sediment cores from the Atlantic and Western Indian sectors of the Southern Ocean between the modern PF and the Winter Sea Ice (WSI) edge. Summer Sea Surface Temperature (SSST) and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators, which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation, as well as opal deposition. These complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes Southern Ocean. Our reconstructions show that the Last Glacial (LG) SSSTs south of the modern PF are 1-3 °C colder than modern conditions, WSI expanded to the modern PF. Our data suggests effective carbon export in the Antarctic Zone during the LG. Deglacial two steps of warming support the bipolar seesaw mechanism. Antarctic Zone is an important source region for the CO2 deglacial increase. The warming was more suppressed towards south, due to continuous ice discharge from Antarctica. The SSSTs exceeded modern values during the early Holocene optimum, when WSI extent probably retreated south of its modern position. The southern boundary of maximum opal deposition zone may have shifted to south of 55°S in the Bouvet Island area at this time. The mid-late Holocene cooling with WSI re-expanding to the

  10. Planktonic foraminiferal biogeography in the Indian sector of the Southern Ocean: Contribution from CPR data

    NASA Astrophysics Data System (ADS)

    Meilland, Julie; Fabri-Ruiz, Salomé; Koubbi, Philippe; Monaco, Claire Lo; Cotte, Cédric; Hosie, Graham W.; Sanchez, Sophie; Howa, Hélène

    2016-04-01

    Within the framework of the Scientific Committee on Antarctic Research (SCAR) Southern Ocean-Continuous Plankton Recorder (SO-CPR) Survey, the oceanic regions around Crozet and Kerguelen Islands were investigated in February-March 2013. Living planktonic Foraminifera (LPF) were collected in the upper mixed layer with a CPR along a 2160 nautical mile sea transect that crossed main hydrological fronts in the Indian sector of the Southern Ocean. In the SO-CPR database, mean total abundances of Foraminifera occurring during late austral summer are highly variable at an inter-annual scale, from 10 to 250 ind.m-3, representing 10-40% of the total zooplankton abundance, respectively. In the Southern Ocean, major inter-annual changes in zooplankton community structure were already reported. In this study, we describe the large scale distributional pattern of individual planktonic foraminiferal species living in near-surface waters of the Indian sector of the Southern Ocean, and we attempt to explain why major spatial variability in relative species abundances occurs during a late austral summer. In February-March 2013, LPF total abundances recorded between 42.86°S and 56.42°S ranged from 0 to a maximum of 258 ind.m-3. In the Open Ocean Zone, the LPF community was composed of four major species (Globigerinita uvula, Neogloboquadrina pachyderma, Neogloboquadrina incompta, Globigerina bulloides). Generally, LPF total abundances are supposed to mirror primary production induced by hydrological fronts or induced by topography near Crozet and Kerguelen Islands. However, during late austral summer 2013, high foraminiferal abundances in the upper mixed layer did not always match the pattern of near-surface primary production (high Chl-a concentration areas delineated from satellite imagery). Low LPF standing stocks in late austral summer in the Southern Ocean contrasted with the presence of high densities of heavily silicified diatoms. This suggests that the late bloom

  11. Links in CGCMs among biases in the Southern Ocean and in the Tropics

    NASA Astrophysics Data System (ADS)

    Mechoso, C. Roberto; Losada, Teresa; Koseki, Shunya; Rodriguez-Fonseca, Belen; Keenlyside, Noel; Mohino-Harris, Elsa; Castaño-Tierno, Antonio

    2016-04-01

    Coupled atmosphere-ocean models (CGCMs) tend to simulate too warm sea surface temperature (SST) over the southeastern equatorial Pacific and Atlantic oceans (SEP and SEA, respectively). Moreover, they tend to produce a too persistent double Inter-tropical Convergence Zone (ITCZ). CGCMs also show substantial errors in the extratropics, such as too warm SSTs in the Southern Ocean. The present study examines the possible links between CGCM biases in the tropics and in the Southern Ocean. These latter biases are interpreted as evidence of excessive energy absorbed by the southern hemisphere in comparison to the northern hemisphere. We use the CGCM of the University of California Los Angeles (UCLA CGCM), and the Earth System Model of the University of Norway (Nor-ESM). Our approach compares the climatology simulated by both models with experiments in which the energy input to the southern hemisphere is artificially decreased between 30S and 60S. The maximum decrease is ~ 30 W m-2 at approximately 45S. In the two models we find that less short wave incident results in a general cooling of the SST. In association with this cooling, the Hadley and Ferrel circulations intensify primarily in the southern hemisphere. The ITCZ moves northward and convection decreases south of the equator. In the southern hemisphere the core of the subtropical jet moves equator ward, while in the northern hemisphere upper level westerlies decrease in the tropics. Sea-level pressure increases in the southern tropical Atlantic and Pacific, and over the North Pacific. In the upper ocean, the gyres intensify in the south Pacific and Atlantic, and the northward heat transport decreases. In the Indian Ocean, changes are much smaller in general. Notable changes in the cloud and radiation fields accompany those in the large-scale circulation. Also in both models, there is a modest increase in low-level clouds around 30S-45S and a larger increase in the SEP and SEA. Upper level clouds decrease over the

  12. In situ measurement of the biogeochemical properties of Southern Ocean mesoscale eddies in the Southwest Indian Ocean, April 2014

    NASA Astrophysics Data System (ADS)

    de Villiers, S.; Siswana, K.; Vena, K.

    2015-10-01

    Several open-ocean mesoscale features, a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S, as well as an adjacent cold-core (cyclonic) eddy at 56° S, were surveyed during a M/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, that will be suitable for comparison and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards into the Southern Ocean. Results show that the older warm-core eddy at 57.5° S is, at its core, 2.7 °C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chl a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chl a and dissolved nutrient data (for NO3-, NO2-, PO43- and SiO2) have been processed, quality-controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875.

  13. Isotopic Composition of Cadmium across the Subtropical Convergence in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Gault-Ringold, M.; Stirling, C. H.; Frew, R.; Hunter, K. A.

    2010-12-01

    The almost linear relationship between cadmium (Cd) and phosphate (PO4) in the oceans has been used extensively as a paleoproxy to investigate historical nutrient cycling (Boyle, 1992, Annu. Rev. Earth Planet. Sci. 20, 245). However, our limited understanding of oceanic Cd cycling and the mechanism of the Cd/PO4 relationship limits the reliability of this paleoproxy (Elderfield and Rickaby, 2000, Nature. 405, 305), particularly in the surface waters of the Southern Ocean. Recent studies have shown that the biological uptake of Cd by phytoplankton can create significant (permil-level) isotopic shifts between the phytoplankton and surface ocean water (Ripperger and Rehkamper, 2007, Earth Planet. Sci. Lett. 261, 670) suggesting that Cd isotopes have the potential to provide more information about the marine cycling of Cd than concentration measurements alone. The subtropical convergence (STC) in the Southern Ocean has some of the world’s lowest Cd:PO4 ratios (Frew and Hunter, 1995, Mar. Chem. 51, 223) and provides an ideal location to study the biogeochemical cycling of Cd in the marine environment. Utilizing double-spiking protocols combined with multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS) (Ripperger and Rehkamper, 2007, Geochim. Cosmochim. Acta. 71, 631), we have determined the isotopic composition of Cd in seawater samples collected from the Otago transect off the southeast coast of New Zealand. This transect intersects the STC, passing through both subtropical (iron replete) and subantarctic (HNLC) water masses. Samples were collected seasonally from May 2008 through January 2010 to identify seasonal variability of isotopic composition and concentration due to changes in water mass chemistry and biological activity. This Cd isotope data will help determine the mechanisms controlling Cd uptake in the Southern Ocean and provide insight into the effectiveness of the current Cd/PO4 paleoproxy helping to improve its application.

  14. Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula.

    PubMed

    Shevenell, A E; Ingalls, A E; Domack, E W; Kelly, C

    2011-02-10

    The disintegration of ice shelves, reduced sea-ice and glacier extent, and shifting ecological zones observed around Antarctica highlight the impact of recent atmospheric and oceanic warming on the cryosphere. Observations and models suggest that oceanic and atmospheric temperature variations at Antarctica's margins affect global cryosphere stability, ocean circulation, sea levels and carbon cycling. In particular, recent climate changes on the Antarctic Peninsula have been dramatic, yet the Holocene climate variability of this region is largely unknown, limiting our ability to evaluate ongoing changes within the context of historical variability and underlying forcing mechanisms. Here we show that surface ocean temperatures at the continental margin of the western Antarctic Peninsula cooled by 3-4 °C over the past 12,000 years, tracking the Holocene decline of local (65° S) spring insolation. Our results, based on TEX(86) sea surface temperature (SST) proxy evidence from a marine sediment core, indicate the importance of regional summer duration as a driver of Antarctic seasonal sea-ice fluctuations. On millennial timescales, abrupt SST fluctuations of 2-4 °C coincide with globally recognized climate variability. Similarities between our SSTs, Southern Hemisphere westerly wind reconstructions and El Niño/Southern Oscillation variability indicate that present climate teleconnections between the tropical Pacific Ocean and the western Antarctic Peninsula strengthened late in the Holocene epoch. We conclude that during the Holocene, Southern Ocean temperatures at the western Antarctic Peninsula margin were tied to changes in the position of the westerlies, which have a critical role in global carbon cycling.

  15. Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Abernathey, Ryan P.; Cerovecki, Ivana; Holland, Paul R.; Newsom, Emily; Mazloff, Matt; Talley, Lynne D.

    2016-08-01

    Ocean overturning circulation requires a continuous thermodynamic transformation of the buoyancy of seawater. The steeply sloping isopycnals of the Southern Ocean provide a pathway for Circumpolar Deep Water to upwell from mid depth without strong diapycnal mixing, where it is transformed directly by surface fluxes of heat and freshwater and splits into an upper and lower branch. While brine rejection from sea ice is thought to contribute to the lower branch, the role of sea ice in the upper branch is less well understood, partly due to a paucity of observations of sea-ice thickness and transport. Here we quantify the sea-ice freshwater flux using the Southern Ocean State Estimate, a state-of-the-art data assimilation that incorporates millions of ocean and ice observations. We then use the water-mass transformation framework to compare the relative roles of atmospheric, sea-ice, and glacial freshwater fluxes, heat fluxes, and upper-ocean mixing in transforming buoyancy within the upper branch. We find that sea ice is a dominant term, with differential brine rejection and ice melt transforming upwelled Circumpolar Deep Water at a rate of ~22 × 106 m3 s-1. These results imply a prominent role for Antarctic sea ice in the upper branch and suggest that residual overturning and wind-driven sea-ice transport are tightly coupled.

  16. Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum

    PubMed Central

    Conway, T.M.; Wolff, E.W.; Röthlisberger, R.; Mulvaney, R.; Elderfield, H.E.

    2015-01-01

    Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial–interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial–interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1–42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01–0.84 mg m−2 per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply. PMID:26204562

  17. Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum.

    PubMed

    Conway, T M; Wolff, E W; Röthlisberger, R; Mulvaney, R; Elderfield, H E

    2015-01-01

    Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial-interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial-interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m(-2) per year) suggest that soluble Fe deposition to the Southern Ocean would have been ≥10 × modern deposition, rivalling upwelling supply.

  18. Constraints on soluble aerosol iron flux to the Southern Ocean at the Last Glacial Maximum

    NASA Astrophysics Data System (ADS)

    Conway, T. M.; Wolff, E. W.; Röthlisberger, R.; Mulvaney, R.; Elderfield, H. E.

    2015-07-01

    Relief of iron (Fe) limitation in the Southern Ocean during ice ages, with potentially increased carbon storage in the ocean, has been invoked as one driver of glacial-interglacial atmospheric CO2 cycles. Ice and marine sediment records demonstrate that atmospheric dust supply to the oceans increased by up to an order of magnitude during glacial intervals. However, poor constraints on soluble atmospheric Fe fluxes to the oceans limit assessment of the role of Fe in glacial-interglacial change. Here, using novel techniques, we present estimates of water- and seawater-soluble Fe solubility in Last Glacial Maximum (LGM) atmospheric dust from the European Project for Ice Coring in Antarctica (EPICA) Dome C and Berkner Island ice cores. Fe solubility was very variable (1-42%) during the interval, and frequently higher than typically assumed by models. Soluble aerosol Fe fluxes to Dome C at the LGM (0.01-0.84 mg m-2 per year) suggest that soluble Fe deposition to the Southern Ocean would have been >=10 × modern deposition, rivalling upwelling supply.

  19. King penguin population threatened by Southern Ocean warming

    PubMed Central

    Le Bohec, Céline; Durant, Joël M.; Gauthier-Clerc, Michel; Stenseth, Nils C.; Park, Young-Hyang; Pradel, Roger; Grémillet, David; Gendner, Jean-Paul; Le Maho, Yvon

    2008-01-01

    Seabirds are sensitive indicators of changes in marine ecosystems and might integrate and/or amplify the effects of climate forcing on lower levels in food chains. Current knowledge on the impact of climate changes on penguins is primarily based on Antarctic birds identified by using flipper bands. Although flipper bands have helped to answer many questions about penguin biology, they were shown in some penguin species to have a detrimental effect. Here, we present for a Subantarctic species, king penguin (Aptenodytes patagonicus), reliable results on the effect of climate on survival and breeding based on unbanded birds but instead marked by subcutaneous electronic tags. We show that warm events negatively affect both breeding success and adult survival of this seabird. However, the observed effect is complex because it affects penguins at several spatio/temporal levels. Breeding reveals an immediate response to forcing during warm phases of El Niño Southern Oscillation affecting food availability close to the colony. Conversely, adult survival decreases with a remote sea-surface temperature forcing (i.e., a 2-year lag warming taking place at the northern boundary of pack ice, their winter foraging place). We suggest that this time lag may be explained by the delay between the recruitment and abundance of their prey, adjusted to the particular 1-year breeding cycle of the king penguin. The derived population dynamic model suggests a 9% decline in adult survival for a 0.26°C warming. Our findings suggest that king penguin populations are at heavy extinction risk under the current global warming predictions. PMID:18268328

  20. King penguin population threatened by Southern Ocean warming.

    PubMed

    Le Bohec, Céline; Durant, Joël M; Gauthier-Clerc, Michel; Stenseth, Nils C; Park, Young-Hyang; Pradel, Roger; Grémillet, David; Gendner, Jean-Paul; Le Maho, Yvon

    2008-02-19

    Seabirds are sensitive indicators of changes in marine ecosystems and might integrate and/or amplify the effects of climate forcing on lower levels in food chains. Current knowledge on the impact of climate changes on penguins is primarily based on Antarctic birds identified by using flipper bands. Although flipper bands have helped to answer many questions about penguin biology, they were shown in some penguin species to have a detrimental effect. Here, we present for a Subantarctic species, king penguin (Aptenodytes patagonicus), reliable results on the effect of climate on survival and breeding based on unbanded birds but instead marked by subcutaneous electronic tags. We show that warm events negatively affect both breeding success and adult survival of this seabird. However, the observed effect is complex because it affects penguins at several spatio/temporal levels. Breeding reveals an immediate response to forcing during warm phases of El Niño Southern Oscillation affecting food availability close to the colony. Conversely, adult survival decreases with a remote sea-surface temperature forcing (i.e., a 2-year lag warming taking place at the northern boundary of pack ice, their winter foraging place). We suggest that this time lag may be explained by the delay between the recruitment and abundance of their prey, adjusted to the particular 1-year breeding cycle of the king penguin. The derived population dynamic model suggests a 9% decline in adult survival for a 0.26 degrees C warming. Our findings suggest that king penguin populations are at heavy extinction risk under the current global warming predictions. PMID:18268328

  1. King penguin population threatened by Southern Ocean warming.

    PubMed

    Le Bohec, Céline; Durant, Joël M; Gauthier-Clerc, Michel; Stenseth, Nils C; Park, Young-Hyang; Pradel, Roger; Grémillet, David; Gendner, Jean-Paul; Le Maho, Yvon

    2008-02-19

    Seabirds are sensitive indicators of changes in marine ecosystems and might integrate and/or amplify the effects of climate forcing on lower levels in food chains. Current knowledge on the impact of climate changes on penguins is primarily based on Antarctic birds identified by using flipper bands. Although flipper bands have helped to answer many questions about penguin biology, they were shown in some penguin species to have a detrimental effect. Here, we present for a Subantarctic species, king penguin (Aptenodytes patagonicus), reliable results on the effect of climate on survival and breeding based on unbanded birds but instead marked by subcutaneous electronic tags. We show that warm events negatively affect both breeding success and adult survival of this seabird. However, the observed effect is complex because it affects penguins at several spatio/temporal levels. Breeding reveals an immediate response to forcing during warm phases of El Niño Southern Oscillation affecting food availability close to the colony. Conversely, adult survival decreases with a remote sea-surface temperature forcing (i.e., a 2-year lag warming taking place at the northern boundary of pack ice, their winter foraging place). We suggest that this time lag may be explained by the delay between the recruitment and abundance of their prey, adjusted to the particular 1-year breeding cycle of the king penguin. The derived population dynamic model suggests a 9% decline in adult survival for a 0.26 degrees C warming. Our findings suggest that king penguin populations are at heavy extinction risk under the current global warming predictions.

  2. Biogeochemical cycling of zinc and its isotopes in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Zhao, Y.; Vance, D.; Abouchami, W.; de Baar, H. J. W.

    2014-01-01

    We report Zn concentration and isotope data for seawater samples from the Atlantic sector of the Southern Ocean, collected during the IPY/GEOTRACES ANT-XXIV/III cruise along the Greenwich Zero Meridian. Data are reported for the full depth range of the water column at three stations, as well as a transect of surface samples, using a new analytical approach that is presented in detail here. Zn concentrations increase with depth, though due to proximity to upwelling sites, surface concentrations are not as low as in some parts of the ocean such as further northward into the Sub-Antarctic Zone. For two depth profiles south of the Polar Front Zone, the physical stratification of the upper water column is reflected in sudden near-surface changes in Zn concentration with depth. In contrast, beneath 100-300 m Zn concentrations barely change with depth. Zn isotopic data beneath 1000 m, for the Southern Ocean data presented here as well as published data from the North Atlantic and North Pacific, are strikingly homogeneous, with an average δ66Zn = +0.53 ± 0.14‰ (2SD, 2SE = 0.03, n = 21). The surface Southern Ocean is more variable, with δ66Zn ranging from 0.07‰ to 0.80‰. Between the two is a thin horizon at 40-80 m which, in the Southern Ocean as well as the North Atlantic and North Pacific, is characterised by distinctly light isotopic signatures, with δ66Zn about 0.3‰ lower than surface waters. Strong correlations between Si and Zn concentrations seen here and elsewhere, coupled to the lack of any systematic relationship between Si and Zn isotopes in the Southern Ocean, suggest that the removal of Zn associated with diatom opal involves little or no isotopic fractionation. Regeneration of this Zn also explains the homogeneous Zn isotopic composition of the global deep ocean so far sampled. However, the low Zn content of opal requires that deep ocean Zn does not directly come from the opal phase itself, but rather from associated organic material external to

  3. The "white ocean" hypothesis: a late pleistocene southern ocean governed by coccolithophores and driven by phosphorus.

    PubMed

    Flores, José-Abel; Filippelli, Gabriel M; Sierro, Francisco J; Latimer, Jennifer

    2012-01-01

    Paleoproductivity is a critical component in past ocean biogeochemistry, but accurate reconstructions of productivity are often hindered by limited integration of proxies. Here, we integrate geochemical (phosphorus) and micropaleontological proxies at millennial timescales, revealing that the coccolithophore record in the Subantarctic zone of the South Atlantic Ocean is driven largely by variations in marine phosphorus availability. A quantitative micropaleontological and geochemical analysis carried out in sediments retrieved from Ocean Drilling Program Site 1089 (Subantarctic Zone) reveals that most of the export productivity in this region over the last 0.5 my was due to coccolithophores. Glacial periods were generally intervals of high productivity, with productivity reaching a peak at terminations. Particularly high productivity was observed at Termination V and Termination IV, events that are characterized by high abundance of coccolithophores and maxima in the phosphorus/titanium and strontium/titanium records. We link the increase in productivity both to regional oceanographic phenomena, i.e., the northward displacement of the upwelling cell of the Antarctic divergence when the ice-sheet expanded, and to the increase in the inventory of phosphorus in the ocean due to enhanced transfer of this nutrient from continental margins during glacial lowstands in sea level. The Mid-Brunhes interval stands out from the rest of the record, being dominated by the small and highly calcified species Gephyrocapsa caribbeanica that provides most of the carbonate in these sediments. This likely represents higher availability of phosphorus in the surface ocean, especially in mesotrophic and oligotrophic zones. Under these condition, some coccolithophore species developed an r-strategy (opportunistic species; growth rate maximized) resulting in the bloom of G. caribbeanica. These seasonal blooms of may have induced "white tides" similar to those observed today in Emiliania

  4. The "white ocean" hypothesis: a late pleistocene southern ocean governed by coccolithophores and driven by phosphorus.

    PubMed

    Flores, José-Abel; Filippelli, Gabriel M; Sierro, Francisco J; Latimer, Jennifer

    2012-01-01

    Paleoproductivity is a critical component in past ocean biogeochemistry, but accurate reconstructions of productivity are often hindered by limited integration of proxies. Here, we integrate geochemical (phosphorus) and micropaleontological proxies at millennial timescales, revealing that the coccolithophore record in the Subantarctic zone of the South Atlantic Ocean is driven largely by variations in marine phosphorus availability. A quantitative micropaleontological and geochemical analysis carried out in sediments retrieved from Ocean Drilling Program Site 1089 (Subantarctic Zone) reveals that most of the export productivity in this region over the last 0.5 my was due to coccolithophores. Glacial periods were generally intervals of high productivity, with productivity reaching a peak at terminations. Particularly high productivity was observed at Termination V and Termination IV, events that are characterized by high abundance of coccolithophores and maxima in the phosphorus/titanium and strontium/titanium records. We link the increase in productivity both to regional oceanographic phenomena, i.e., the northward displacement of the upwelling cell of the Antarctic divergence when the ice-sheet expanded, and to the increase in the inventory of phosphorus in the ocean due to enhanced transfer of this nutrient from continental margins during glacial lowstands in sea level. The Mid-Brunhes interval stands out from the rest of the record, being dominated by the small and highly calcified species Gephyrocapsa caribbeanica that provides most of the carbonate in these sediments. This likely represents higher availability of phosphorus in the surface ocean, especially in mesotrophic and oligotrophic zones. Under these condition, some coccolithophore species developed an r-strategy (opportunistic species; growth rate maximized) resulting in the bloom of G. caribbeanica. These seasonal blooms of may have induced "white tides" similar to those observed today in Emiliania

  5. The Biogeochemical Role of Antarctic Krill and Baleen Whales in Southern Ocean Nutrient Cycling.

    NASA Astrophysics Data System (ADS)

    Ratnarajah, L.

    2015-12-01

    Iron limits primary productivity in large areas of the Southern Ocean. It has been suggested that baleen whales form a crucial part of biogeochemical cycling processes through the consumption of nutrient-rich krill and subsequent defecation, but evidence on their contribution is scarce. We analysed the concentration of iron in Antarctic krill and baleen whale faeces and muscle. Iron concentrations in Antarctic krill were over 1 million times higher, and whale faecal matter were almost 10 million times higher than typical Southern Ocean High Nutrient Low Chlorophyll seawater concentrations. This suggests that Antarctic krill act as a reservoir of in in Southern Ocean surface waters, and that baleen whales play an important role in converting this fixed iron into a liquid form in their faeces. We developed an exploratory model to examine potential contribution of blue, fin and humpback whales to the Southern Ocean iron cycle to explore the effect of the recovery of great whales to historical levels. Our results suggest that pre-exploitation populations of blue whales and, to a lesser extent fin and humpback whales, could have contributed to the more effective recycling of iron in surface waters, resulting in enhanced phytoplankton production. This enhanced primary productivity is estimated to be: 8.3 x 10-5 to 15 g C m-2 yr-1 (blue whales), 7 x 10-5 to 9 g C m-2 yr-1 (fin whales), and 10-5 to 1.7 g C m-2 yr-1 (humpback whales). To put these into perspective, current estimates of primary production in the Southern Ocean from remotely sensed ocean colour are in the order of 57 g C m-2 yr-1 (south of 50°). The high degree of uncertainty around the magnitude of these increases in primary productivity is mainly due to our limited quantitative understanding of key biogeochemical processes including iron content in krill, krill consumption rates by whales, persistence of iron in the photic zone, bioavailability of retained iron, and carbon-to-iron ratio of phytoplankton

  6. Environmental forcing and Southern Ocean marine predator populations: effects of climate change and variability.

    PubMed

    Trathan, P N; Forcada, J; Murphy, E J

    2007-12-29

    The Southern Ocean is a major component within the global ocean and climate system and potentially the location where the most rapid climate change is most likely to happen, particularly in the high-latitude polar regions. In these regions, even small temperature changes can potentially lead to major environmental perturbations. Climate change is likely to be regional and may be expressed in various ways, including alterations to climate and weather patterns across a variety of time-scales that include changes to the long interdecadal background signals such as the development of the El Niño-Southern Oscillation (ENSO). Oscillating climate signals such as ENSO potentially provide a unique opportunity to explore how biological communities respond to change. This approach is based on the premise that biological responses to shorter-term sub-decadal climate variability signals are potentially the best predictor of biological responses over longer time-scales. Around the Southern Ocean, marine predator populations show periodicity in breeding performance and productivity, with relationships with the environment driven by physical forcing from the ENSO region in the Pacific. Wherever examined, these relationships are congruent with mid-trophic-level processes that are also correlated with environmental variability. The short-term changes to ecosystem structure and function observed during ENSO events herald potential long-term changes that may ensue following regional climate change. For example, in the South Atlantic, failure of Antarctic krill recruitment will inevitably foreshadow recruitment failures in a range of higher trophic-level marine predators. Where predator species are not able to accommodate by switching to other prey species, population-level changes will follow. The Southern Ocean, though oceanographically interconnected, is not a single ecosystem and different areas are dominated by different food webs. Where species occupy different positions in

  7. Sources and fate of polycyclic aromatic hydrocarbons in the Antarctic and Southern Ocean atmosphere

    NASA Astrophysics Data System (ADS)

    Cabrerizo, Ana; Galbán-Malagón, Cristóbal; Del Vento, Sabino; Dachs, Jordi

    2014-12-01

    Polycyclic aromatic hydrocarbons (PAHs) are a geochemically relevant family of semivolatile compounds originating from fossil fuels, biomass burning, and their incomplete combustion, as well as biogenic sources. Even though PAHs are ubiquitous in the environment, there are no previous studies of their occurrence in the Southern Ocean and Antarctic atmosphere. Here we show the gas and aerosol phase PAHs concentrations obtained from three sampling cruises in the Southern Ocean (Weddell, Bellingshausen, and South Scotia Seas), and two sampling campaigns at Livingston Island (Southern Shetlands). This study shows an important variability of the atmospheric concentrations with higher concentrations in the South Scotia and northern Weddell Seas than in the Bellingshausen Sea. The assessment of the gas-particle partitioning of PAHs suggests that aerosol elemental carbon contribution is modest due to its low concentrations. Over the ocean, the atmospheric concentrations do not show a temperature dependence, which is consistent with an important role of long-range atmospheric transport of PAHs. Conversely, over land at Livingston Island, the PAHs gas phase concentrations increase when the temperature increases, consistently with the presence of local diffusive sources. The use of fugacity samplers allowed the determination of the air-soil and air-snow fugacity ratios of PAHs showing that there is a significant volatilization of lighter molecular weight PAHs from soil and snow during the austral summer. The higher volatilization, observed in correspondence of sites where the organic matter content in soil is higher, suggests that there may be a biogenic source of some PAHs. The volatilization of PAHs from soil and snow is sufficient to support the atmospheric occurrence of PAHs over land but may have a modest regional influence on the atmospheric occurrence of PAHs over the Southern Ocean.

  8. A Roadmap for Antarctic and Southern Ocean Science for the Next Two Decades and Beyond

    NASA Astrophysics Data System (ADS)

    Kennicutt, M. C., II

    2015-12-01

    Abstract: Antarctic and Southern Ocean science is vital to understanding natural variability, the processes that govern global change and the role of humans in the Earth and climate system. The potential for new knowledge to be gained from future Antarctic science is substantial. Therefore, the international Antarctic community came together to 'scan the horizon' to identify the highest priority scientific questions that researchers should aspire to answer in the next two decades and beyond. Wide consultation was a fundamental principle for the development of a collective, international view of the most important future directions in Antarctic science. From the many possibilities, the horizon scan identified 80 key scientific questions through structured debate, discussion, revision and voting. Questions were clustered into seven topics: i) Antarctic atmosphere and global connections, ii) Southern Ocean and sea ice in a warming world, iii) ice sheet and sea level, iv) the dynamic Earth, v) life on the precipice, vi) near-Earth space and beyond, and vii) human presence in Antarctica. Answering the questions identified by the horizon scan will require innovative experimental designs, novel applications of technology, invention of next-generation field and laboratory approaches, and expanded observing systems and networks. Unbiased, non-contaminating procedures will be required to retrieve the requisite air, biota, sediment, rock, ice and water samples. Sustained year-round access to Antarctica and the Southern Ocean will be essential to increase winter-time measurements. Improved models are needed that represent Antarctica and the Southern Ocean in the Earth System, and provide predictions at spatial and temporal resolutions useful for decision making. A co-ordinated portfolio of cross-disciplinary science, based on new models of international collaboration, will be essential as no scientist, programme or nation can realize these aspirations alone.

  9. Comment on "The Southern Ocean biological response to aeolian iron deposition".

    PubMed

    Boyd, Philip W; Mackie, Douglas

    2008-01-11

    Cassar et al. (Reports, 24 August 2007, p. 1067) proposed that aerosol-iron input enhances Southern Ocean export production. Their conclusion critically depends upon aerosol-iron modeling simulations not validated with iron-deposition data and dust dissolution rates based on Northern Hemisphere atmospheric chemical conditions (low pH). This diminishes the relevance of their findings and demonstrates that applying such models to this region is premature.

  10. Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics.

    PubMed

    Brum, Jennifer R; Hurwitz, Bonnie L; Schofield, Oscar; Ducklow, Hugh W; Sullivan, Matthew B

    2016-02-01

    Rapid warming in the highly productive western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels, yet viral influences on microbial processes and ecosystem function remain understudied in the Southern Ocean. Here we use cultivation-independent quantitative ecological and metagenomic assays, combined with new comparative bioinformatic techniques, to investigate double-stranded DNA viruses during the WAP spring-summer transition. This study demonstrates that (i) temperate viruses dominate this region, switching from lysogeny to lytic replication as bacterial production increases, and (ii) Southern Ocean viral assemblages are genetically distinct from lower-latitude assemblages, primarily driven by this temperate viral dominance. This new information suggests fundamentally different virus-host interactions in polar environments, where intense seasonal changes in bacterial production select for temperate viruses because of increased fitness imparted by the ability to switch replication strategies in response to resource availability. Further, temperate viral dominance may provide mechanisms (for example, bacterial mortality resulting from prophage induction) that help explain observed temporal delays between, and lower ratios of, bacterial and primary production in polar versus lower-latitude marine ecosystems. Together these results suggest that temperate virus-host interactions are critical to predicting changes in microbial dynamics brought on by warming in polar marine systems.

  11. The impact of multidecadal Atlantic meridional overturning circulation variations on the Southern Ocean

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The impact of multidecadal variations of the Atlantic meridional overturning circulation (AMOC) on the Southern Ocean (SO) is investigated using a coupled ocean-atmosphere model. We find that the AMOC can influence the SO via fast atmosphere teleconnections and subsequent ocean adjustments. A stronger than normal AMOC induces an anomalous warm SST over the North Atlantic, which favors an increased equator-to-pole temperature gradient in the Southern Hemisphere (SH) upper troposphere and lower stratosphere due to an amplified tropical upper tropospheric warming as a result of increased latent heat release. This eventually strengthens and pushes the Southern Hemisphere westerly jet poleward. The wind change over the SO then cools the SST by anomalous northward Ekman transports. The wind change also weakens the Antarctic bottom water (AABW) cell through changes in surface heat flux heating forcing. The poleward shifted westerly wind decreases the long term mean easterly winds over the Weddell Sea, thereby reducing the turbulent heat flux loss, decreasing surface density and therefore leading to a weakening of the AABW cell. The weakened AABW cell produces a temperature dipole in the SO, with a warm anomaly in the subsurface and a cold anomaly in the surface that corresponds to an increase of Antarctic sea ice. Opposite conditions occur for a weaker than normal AMOC. Our study here suggests that efforts to attribute the recent observed SO variability to various factors should take into consideration not only local process but also remote AMOC forcing.

  12. Observed chlorophyll trends in the Southern Ocean over 1997-2012 and associated mechanisms

    NASA Astrophysics Data System (ADS)

    Panassa, Essowe; Hauck, Judith; Völker, Christoph; Hoppema, Mario; Wolf-Gladrow, Dieter

    2016-04-01

    An up-to date 16-year time series of satellite chlorophyll from the ocean color climate change initiative (OC-CCI), was used together with its drivers (MLD and winds) to assess and explain recent trends in chlorophyll in the Southern Ocean. The evaluation of trends using linear regression analysis reveals a regionally varying chlorophyll increase. MLD deepens in a circumpolar band in the Subantarctic front regions and extends further to southeastwards in the Pacific sector. The regions of chlorophyll increase are located to the north of that, in the subtropical zone. These regions of MLD deepening have over the last two decades experienced intensification in zonal wind and a positive trend in northwards Ekman transport. We propose that increased northward Ekman transport of nutrient-rich (iron, silicate and nitrate) upwelled water is the main physical process that drives the change we observe in chlorophyll north to these regions. These findings suggest that Southern Ocean biology is changing in response to recent change in circulation in that region, partly induced by the positive trend in the Southern Annular Mode (SAM) index.

  13. Sea level trends in the Southern Ocean over the last century from historical data

    NASA Astrophysics Data System (ADS)

    Testut, Laurent; Martin-Miguez, Belén.; Watson, Christopher; Wöppelmann, Guy; Coleman, Richard; Creach, Ronan; Brolsma, Henk; Handsworth, Roger; Pouvreau, Nicolas; Legrésy, Benoit

    2010-05-01

    It is well known that the spatial distribution of sea level measurements throughout the Southern Ocean is sparse and mostly consists of datasets with short records. The PSMSL (Permanent Service for Mean Sea Level) has only a few sea level time series below 45° South and most of them are shorter than twenty years. The lack of observations constrains the ability to determine or reconstruct global estimates of mean sea level change over the past century. For this reason, any available historical information becomes invaluable for deriving long-term estimates of sea level change in this part of the world. The aim of this presentation is to describe the way we have recovered and analysed the available historic sea level observations made in few sites of the Southern Ocean and to propose new reliable long term sea level trend estimates in this region. The first site is Saint-Paul, a small island of the Southern Indian Ocean where historical measurements were done in 1874 and connected to the permanent GLOSS tide gauge. The two other historical observations were recorded by the Australasian Antarctic Expedition lead by Sir Douglas Mawson in 1912 at Maquarie Island and Cap Denison (Antarctica). The last site concerned by this presentation is the Dumont d'Urville (Antarctica) where historical information from the beginning of the 1950's were found and analysed.

  14. Seasonal time bombs: dominant temperate viruses affect Southern Ocean microbial dynamics

    PubMed Central

    Brum, Jennifer R; Hurwitz, Bonnie L; Schofield, Oscar; Ducklow, Hugh W; Sullivan, Matthew B

    2016-01-01

    Rapid warming in the highly productive western Antarctic Peninsula (WAP) region of the Southern Ocean has affected multiple trophic levels, yet viral influences on microbial processes and ecosystem function remain understudied in the Southern Ocean. Here we use cultivation-independent quantitative ecological and metagenomic assays, combined with new comparative bioinformatic techniques, to investigate double-stranded DNA viruses during the WAP spring–summer transition. This study demonstrates that (i) temperate viruses dominate this region, switching from lysogeny to lytic replication as bacterial production increases, and (ii) Southern Ocean viral assemblages are genetically distinct from lower-latitude assemblages, primarily driven by this temperate viral dominance. This new information suggests fundamentally different virus–host interactions in polar environments, where intense seasonal changes in bacterial production select for temperate viruses because of increased fitness imparted by the ability to switch replication strategies in response to resource availability. Further, temperate viral dominance may provide mechanisms (for example, bacterial mortality resulting from prophage induction) that help explain observed temporal delays between, and lower ratios of, bacterial and primary production in polar versus lower-latitude marine ecosystems. Together these results suggest that temperate virus–host interactions are critical to predicting changes in microbial dynamics brought on by warming in polar marine systems. PMID:26296067

  15. Empirical algorithms to estimate water column pH in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Williams, N. L.; Juranek, L. W.; Johnson, K. S.; Feely, R. A.; Riser, S. C.; Talley, L. D.; Russell, J. L.; Sarmiento, J. L.; Wanninkhof, R.

    2016-04-01

    Empirical algorithms are developed using high-quality GO-SHIP hydrographic measurements of commonly measured parameters (temperature, salinity, pressure, nitrate, and oxygen) that estimate pH in the Pacific sector of the Southern Ocean. The coefficients of determination, R2, are 0.98 for pH from nitrate (pHN) and 0.97 for pH from oxygen (pHOx) with RMS errors of 0.010 and 0.008, respectively. These algorithms are applied to Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) biogeochemical profiling floats, which include novel sensors (pH, nitrate, oxygen, fluorescence, and backscatter). These algorithms are used to estimate pH on floats with no pH sensors and to validate and adjust pH sensor data from floats with pH sensors. The adjusted float data provide, for the first time, seasonal cycles in surface pH on weekly resolution that range from 0.05 to 0.08 on weekly resolution for the Pacific sector of the Southern Ocean.

  16. Exploring the Link between Micronutrients and Phytoplankton in the Southern Ocean during the 2007 Austral Summer

    PubMed Central

    Hassler, Christel S.; Sinoir, Marie; Clementson, Lesley A.; Butler, Edward C. V.

    2012-01-01

    Bottle assays and large-scale fertilization experiments have demonstrated that, in the Southern Ocean, iron often controls the biomass and the biodiversity of primary producers. To grow, phytoplankton need numerous other trace metals (micronutrients) required for the activity of key enzymes and other intracellular functions. However, little is known of the potential these other trace elements have to limit the growth of phytoplankton in the Southern Ocean. This study, investigates whether micronutrients other than iron (Zn, Co, Cu, Cd, Ni) need to be considered as parameters for controlling the phytoplankton growth from the Australian Subantarctic to the Polar Frontal Zones during the austral summer 2007. Analysis of nutrient disappearance ratios, suggested differential zones in phytoplankton growth control in the study region with a most intense phytoplankton growth limitation between 49 and 50°S. Comparison of micronutrient disappearance ratios, metal distribution, and biomarker pigments used to identify dominating phytoplankton groups, demonstrated that a complex interaction between Fe, Zn, and Co might exist in the study region. Although iron remains the pivotal micronutrient for phytoplankton growth and community structure, Zn and Co are also important for the nutrition and the growth of most of the dominating phytoplankton groups in the Subantarctic Zone region. Understanding of the parameters controlling phytoplankton is paramount, as it affects the functioning of the Southern Ocean, its marine resources and ultimately the global carbon cycle. PMID:22787456

  17. Exploring the Link between Micronutrients and Phytoplankton in the Southern Ocean during the 2007 Austral Summer.

    PubMed

    Hassler, Christel S; Sinoir, Marie; Clementson, Lesley A; Butler, Edward C V

    2012-01-01

    Bottle assays and large-scale fertilization experiments have demonstrated that, in the Southern Ocean, iron often controls the biomass and the biodiversity of primary producers. To grow, phytoplankton need numerous other trace metals (micronutrients) required for the activity of key enzymes and other intracellular functions. However, little is known of the potential these other trace elements have to limit the growth of phytoplankton in the Southern Ocean. This study, investigates whether micronutrients other than iron (Zn, Co, Cu, Cd, Ni) need to be considered as parameters for controlling the phytoplankton growth from the Australian Subantarctic to the Polar Frontal Zones during the austral summer 2007. Analysis of nutrient disappearance ratios, suggested differential zones in phytoplankton growth control in the study region with a most intense phytoplankton growth limitation between 49 and 50°S. Comparison of micronutrient disappearance ratios, metal distribution, and biomarker pigments used to identify dominating phytoplankton groups, demonstrated that a complex interaction between Fe, Zn, and Co might exist in the study region. Although iron remains the pivotal micronutrient for phytoplankton growth and community structure, Zn and Co are also important for the nutrition and the growth of most of the dominating phytoplankton groups in the Subantarctic Zone region. Understanding of the parameters controlling phytoplankton is paramount, as it affects the functioning of the Southern Ocean, its marine resources and ultimately the global carbon cycle.

  18. Trends and variability of the atmosphere–ocean turbulent heat flux in the extratropical Southern Hemisphere

    PubMed Central

    Herman, Agnieszka

    2015-01-01

    Ocean–atmosphere interactions are complex and extend over a wide range of temporal and spatial scales. Among the key components of these interactions is the ocean–atmosphere (latent and sensible) turbulent heat flux (THF). Here, based on daily optimally-interpolated data from the extratropical Southern Hemisphere (south of 30°S) from a period 1985–2013, we analyze short-term variability and trends in THF and variables influencing it. It is shown that, in spite of climate-change-related positive trends in surface wind speeds over large parts of the Southern Ocean, the range of the THF variability has been decreasing due to decreasing air–water temperature and humidity differences. Occurrence frequency of very large heat flux events decreased accordingly. Remarkably, spectral analysis of the THF data reveals, in certain regions, robust periodicity at frequencies 0.03–0.04 day−1, corresponding exactly to frequencies of the baroclinic annular mode (BAM). Finally, it is shown that the THF is correlated with the position of the major fronts in sections of the Antarctic Circumpolar Current where the fronts are not constrained by the bottom topography and can adjust their position to the atmospheric and oceanic forcing, suggesting differential response of various sections of the Southern Ocean to the changing atmospheric forcing. PMID:26449323

  19. Air-Seawater Exchange of Organochlorine Pesticides in the Southern Ocean between Australia and Antarctica.

    PubMed

    Bigot, Marie; Muir, Derek C G; Hawker, Darryl W; Cropp, Roger; Dachs, Jordi; Teixeira, Camilla F; Bengtson Nash, Susan

    2016-08-01

    This study contributes new data on the spatial variability of persistent organic pollutants in the Indian-Pacific sector of the Southern Ocean and represents the first empirical data obtained from this region in 25 years. Paired high-volume atmospheric and seawater samples were collected along a transect between Australia and Antarctica to investigate the latitudinal dependence of the occurrence and distribution of legacy organochlorine pesticides (OCPs) and the current use pesticide chlorpyrifos in the Southern Ocean. Dissolved ΣHCH and dieldrin concentrations decreased linearly with increasing latitude from 7.7 to 3.0 and from 1.0 to 0.6 pg·L(-1), respectively. There was no consistent trend observed in the latitudinal profile of atmospheric samples; however, some compounds (such as dieldrin) showed reduced concentrations from 7.5-3.4 to 2.7-0.65 pg·m(-3) at the highest latitudes south of the Polar Front. Chlorpyrifos was found in samples from this area for the first time. Estimated air-seawater fugacity ratios and fluxes indicate a current net deposition between -3600 and -900, -6400 and -400, and -1400 and -200 (pg·m(-2)·d(-1)) for γ-HCH, dieldrin, and chlorpyrifos, respectively. These findings suggest that, under current climatic conditions, the Southern Ocean reservoir in the Indian-Pacific sector serves as an environmental sink rather than a source of OCPs to the atmosphere. PMID:27348023

  20. Polyfluorinated compounds in the atmosphere of the Atlantic and Southern Oceans: evidence for a global distribution.

    PubMed

    Dreyer, Annekatrin; Weinberg, Ingo; Temme, Christian; Ebinghaus, Ralf

    2009-09-01

    High volume air samples taken onboard several research vessels in the Atlantic Ocean, the Southern Ocean, and the Baltic Sea as well as at one land-based site close to Hamburg, Germany, in 2007 and 2008 were analyzed for per- and polyfluorinated organic compounds (PFCs). A set of neutral, volatile PFCs such as fluorotelomer alcohols (FTOH) or perfluoroalkyl sulfonamides and ionic nonvolatile PFCs like perfluorinated carboxylates (PFCA) and sulfonates (PFSA) were collected on PUF/XAD-2/PUF cartridges and glass fiber filters and determined using GC-MS and HPLC-MS/MS. PFCs were detected in all air samples, even in Antarctic regions, and occurred predominantly in the gas phase. Total gas-phase concentrations of ship-based samples ranged from 4.5 pg m(-3) in the Southern Ocean to 335 pg m(-3) in European source regions. Concentrations of 8:2 FTOH, the analyte that was usually observed in highest concentrations, were between 1.8 and 130 pg m(-3). PFC concentrations decreased from continental regions toward marine regions and from Central Europe toward the Arctic and Antarctica. Southern hemispheric concentrations of individual PFCs were significantly lower than those of the northern hemisphere. On the basis of this data set, marine background PFC concentrations and atmospheric residence times were calculated. This study gives further evidence that volatile PFCs undergo atmospheric long-range transportto remote regions and may contribute to their contamination with persistent PFCA and PFSA.

  1. The sensitivity of dimethyl sulfide production to simulated climate change in the Eastern Antarctic Southern Ocean

    NASA Astrophysics Data System (ADS)

    Gabric, Albert J.; Cropp, Roger; Hirst, Tony; Marchant, Harvey

    2003-11-01

    Dimethyl sulfide (DMS) is a radiatively active trace gas produced by enzymatic cleavage of its precursor compound, dimethyl sulfoniopropionate (DMSP), which is released by marine phytoplankton in the upper ocean. Once ventilated to the atmosphere, DMS is oxidised to form non-sea-salt sulfate and methane sulfonate (MSA) aerosols, which are a major source of cloud condensation nuclei (CCN) in remote marine air and may thus play a role in climate regulation. Here we simulate the change in DMS flux in the Eastern Antarctic ocean from 1960 2086, corresponding to equivalent CO2 tripling relative to pre-industrial levels. Calibration to contemporary climate conditions was carried out using a genetic algorithm to fit the model to surface chlorophyll from the 4-yr SeaWiFs satellite archive and surface DMS from an existing global database. Following the methodology used previously in the Subantarctic Southern Ocean, we then simulated DMS emissions under enhanced greenhouse conditions by forcing the DMS model with output from a coupled atmospheric ocean general circulation model (GCM). The GCM was run in transient mode under the IPCC/IS92a radiative forcing scenario. By 2086, the change simulated in annual integrated DMS flux is around 20% in ice-free waters, with a greater increase of 45% in the seasonal ice zone (SIZ). Interestingly, the large increase in flux in the SIZ is not due to higher in situ production but mainly because of a loss of ice cover during summer autumn and an increase in sea-to-air ventilation of DMS. These proportional changes in areal mean flux (25%) are much higher than previously estimated for the Subantarctic Southern Ocean (5%), and point to the possibility of a significant DMS climate feedback at high Southern latitudes. Due to the nexus between ice cover and food-web structure, the potential for ecological community shifts under enhanced greenhouse conditions is high, and the implications for DMS production are discussed.

  2. Constraining early to middle Eocene climate evolution of the southwest Pacific and Southern Ocean

    NASA Astrophysics Data System (ADS)

    Dallanave, Edoardo; Bachtadse, Valerian; Crouch, Erica M.; Tauxe, Lisa; Shepherd, Claire L.; Morgans, Hugh E. G.; Hollis, Christopher J.; Hines, Benjamin R.; Sugisaki, Saiko

    2016-01-01

    Studies of early Paleogene climate suffer from the scarcity of well-dated sedimentary records from the southern Pacific Ocean, the largest ocean basin during this time. We present a new magnetostratigraphic record from marine sediments that outcrop along the mid-Waipara River, South Island, New Zealand. Fully oriented samples for paleomagnetic analyses were collected along 45 m of stratigraphic section, which encompasses magnetic polarity Chrons from C23n to C21n (˜ 51.5- 47 Ma). These results are integrated with foraminiferal, calcareous nannofossil, and dinoflagellate cyst (dinocyst) biostratigraphy from samples collected in three different expeditions along a total of ˜80 m of section. Biostratigraphic data indicates relatively continuous sedimentation from the lower Waipawan to the upper Heretaungan New Zealand stages (i.e., lower Ypresian to lower Lutetian, 55.5 to 46 Ma). We provide the first magnetostratigraphically-calibrated age of 48.88 Ma for the base of the Heretaungan New Zealand stage (latest early Eocene). To improve the correlation of the climate record in this section with other Southern Ocean records, we reviewed the magnetostratigraphy of Ocean Drilling Program (ODP) Site 1172 (East Tasman Plateau) and Integrated Ocean Drilling Program (IODP) Site U1356 (Wilkes Land Margin, Antarctica). A paleomagnetic study of discrete samples could not confirm any reliable magnetic polarity reversals in the early Eocene at Site 1172. We use the robust magneto-biochronology of a succession of dinocyst bioevents that are common to mid-Waipara, Site 1172, and Site U1356 to assist correlation between the three records. A new integrated chronology offers new insights into the nature and completeness of the southern high-latitude climate histories derived from these sites.

  3. Antarctic lakes suggest millennial reorganizations of Southern Hemisphere atmospheric and oceanic circulation

    PubMed Central

    Hall, Brenda L.; Denton, George H.; Fountain, Andrew G.; Hendy, Chris H.; Henderson, Gideon M.

    2010-01-01

    The phasing of millennial-scale oscillations in Antarctica relative to those elsewhere in the world is important for discriminating among models for abrupt climate change, particularly those involving the Southern Ocean. However, records of millennial-scale variability from Antarctica dating to the last glacial maximum are rare and rely heavily on data from widely spaced ice cores, some of which show little variability through that time. Here, we present new data from closed-basin lakes in the Dry Valleys region of East Antarctica that show high-magnitude, high-frequency oscillations in surface level during the late Pleistocene synchronous with climate fluctuations elsewhere in the Southern Hemisphere. These data suggest a coherent Southern Hemisphere pattern of climate change on millennial time scales, at least in the Pacific sector, and indicate that any hypothesis concerning the origin of these events must account for synchronous changes in both high and temperate latitudes. PMID:21115838

  4. Revisiting atmospheric dust export to the Southern Hemisphere ocean: Biogeochemical implications

    NASA Astrophysics Data System (ADS)

    Wagener, Thibaut; Guieu, CéCile; Losno, RéMi; Bonnet, Sophie; Mahowald, Natalie

    2008-06-01

    Aerosol concentrations in the Southern Hemisphere are largely undersampled. This study presents a chemical and physical description of dust particles collected on board research vessels in the southeast Pacific (SEPS) and the Southern Ocean (SOKS). Concentrations of dust were 6.1 ± 2.4 ng m-3 for SEPS and 13.0 ± 6.3 ng m-3 for SOKS. Dust fluxes, derived from those concentrations, were 9.9 ± 3.7 μg m-2 d-1 for SEPS and 38 ± 14 μg m-2 d-1 for SOKS and are shown to be representative of actual fluxes in those areas. Dust and iron deposition are up to 2 orders of magnitude lower than former predictions. A map of dust deposition on the Southern Hemisphere is proposed by incorporating those in situ measurements into a dust model. This study confirms that dust deposition is not the dominant source of iron to the large high-nutrient low-chlorophyll Southern Ocean.

  5. Seasonal and interannual variability of particulate organic carbon within the Southern Ocean from satellite ocean color observations

    NASA Astrophysics Data System (ADS)

    Allison, David B.; Stramski, Dariusz; Mitchell, B. Greg

    2010-06-01

    We use field data of particulate organic carbon (POC) concentration and spectral remote-sensing reflectance, Rrs(λ), to develop an empirical algorithm for estimating POC from ocean color in the Southern Ocean. The algorithm based on the band ratio Rrs(443)/Rrs(555) is used in conjunction with Sea-viewing Wide Field-of-View Sensor satellite data to demonstrate seasonal and interannual variability in POC from 1997 to 2007. The surface POC concentrations generally range from 30 to 120 mg m-3. On a whole basin scale (south of 35°S), the monthly means are mostly 70-80 mg m-3. The seasonal signal is weakest at lower latitudes within the Sub-Antarctic Zone and most pronounced at higher latitudes (>55°S). The area-integrated stock of water column POC in the upper 100 m shows small interannual variations and no clear evidence for long-term trend during the examined 10 year period. The seasonal maximum of the POC stock occurs in December and reaches a value of about 0.6 Pg of carbon for the entire basin south of 35°S. The seasonal range of area-normalized POC is between about 5.5 and 6.6 g m-2. The region south of 55°S provides a dominant contribution to the accumulation of POC within the Southern Ocean during the productive period of the season. During the austral spring, the area-normalized POC accumulates in these high-latitude waters at rates from about 0.2 to 0.7 g m-2 month-1. The comparison of these rates with large-scale satellite-based estimates of net primary production indicates that only a small fraction (<10%) of production accumulates as POC.

  6. Reduced North Atlantic Deep Water flux to the glacial Southern Ocean inferred from neodymium isotope ratios

    PubMed

    Rutberg; Hemming; Goldstein

    2000-06-22

    The global circulation of the oceans and the atmosphere transports heat around the Earth. Broecker and Denton suggested that changes in the global ocean circulation might have triggered or enhanced the glacial-interglacial cycles. But proxy data for past circulation taken from sediment cores in the South Atlantic Ocean have yielded conflicting interpretations of ocean circulation in glacial times--delta13C variations in benthic foraminifera support the idea of a glacial weakening or shutdown of North Atlantic Deep Water production, whereas other proxies, such as Cd/Ca, Ba/Ca and 231Pa/230Th ratios, show little change from the Last Glacial Maximum to the Holocene epoch. Here we report neodymium isotope ratios from the dispersed Fe-Mn oxide component of two southeast Atlantic sediment cores. Both cores show variations that tend towards North Atlantic signatures during the warm marine isotope stages 1 and 3, whereas for the full glacial stages 2 and 4 they are closer to Pacific Ocean signatures. We conclude that the export of North Atlantic Deep Water to the Southern Ocean has resembled present-day conditions during the warm climate intervals, but was reduced during the cold stages. An increase in biological productivity may explain the various proxy data during the times of reduced North Atlantic Deep Water export. PMID:10879531

  7. Southern Ocean monthly wave fields for austral winters 1985-1988 by Geosat radar altimeter

    USGS Publications Warehouse

    Josberger, E.G.; Mognard, N.M.

    1996-01-01

    Four years of monthly averaged wave height fields for the austral winters 19851988 derived from the Geosat altimeter data show a spatial variability of the scale of 500-1000 km that varies monthly and annually. This variability is superimposed on the zonal patterns surrounding the Antarctic continent and characteristic of the climatology derived from the U.S. Navy [1992] Marine Climatic Atlas of the World. The location and the intensity of these large-scale features, which are not found in the climatological fields, exhibit strong monthly and yearly variations. A global underestimation of the climatological mean wave heights by more than l m is also found over large regions of the Southern Ocean. The largest monthly averaged significant wave heights are above 5 m and are found during August of every year in the Indian Ocean, south of 40??S. The monthly wave fields show more variability in the Atlantic and Pacific Oceans than in the Indian Ocean. The Seasat data from 1978 and the Geosat data from 1985 and 1988 show an eastward rotation of the largest wave heights. However, this rotation is absent in 1986 and 1987; the former was a year of unusually low sea states, and the latter was a year of unusually high sea states, which suggests a link to the El Nin??o-Southern Oscillation event of 1986. Copyright 1996 by the American Geophysical Union.

  8. The Southern Ocean in the Coupled Model Intercomparison Project phase 5

    PubMed Central

    Meijers, A. J. S.

    2014-01-01

    The Southern Ocean is an important part of the global climate system, but its complex coupled nature makes both its present state and its response to projected future climate forcing difficult to model. Clear trends in wind, sea-ice extent and ocean properties emerged from multi-model intercomparison in the Coupled Model Intercomparison Project phase 3 (CMIP3). Here, we review recent analyses of the historical and projected wind, sea ice, circulation and bulk properties of the Southern Ocean in the updated Coupled Model Intercomparison Project phase 5 (CMIP5) ensemble. Improvements to the models include higher resolutions, more complex and better-tuned parametrizations of ocean mixing, and improved biogeochemical cycles and atmospheric chemistry. CMIP5 largely reproduces the findings of CMIP3, but with smaller inter-model spreads and biases. By the end of the twenty-first century, mid-latitude wind stresses increase and shift polewards. All water masses warm, and intermediate waters freshen, while bottom waters increase in salinity. Surface mixed layers shallow, warm and freshen, whereas sea ice decreases. The upper overturning circulation intensifies, whereas bottom water formation is reduced. Significant disagreement exists between models for the response of the Antarctic Circumpolar Current strength, for reasons that are as yet unclear. PMID:24891395

  9. Low densities of drifting litter in the African sector of the Southern Ocean.

    PubMed

    Ryan, Peter G; Musker, Seth; Rink, Ariella

    2014-12-15

    Only 52 litter items (>1cm diameter) were observed in 10,467 km of at-sea transects in the African sector of the Southern Ocean. Litter density north of the Subtropical Front (0.58 items km(-2)) was less than in the adjacent South Atlantic Ocean (1-6 items km(-2)), but has increased compared to the mid-1980s. Litter density south of the Subtropical Front was an order of magnitude less than in temperate waters (0.032 items km(-2)). There was no difference in litter density between sub-Antarctic and Antarctic waters either side of the Antarctic Polar Front. Most litter was made of plastic (96%). Fishery-related debris comprised a greater proportion of litter south of the Subtropical Front (33%) than in temperate waters (13%), where packaging dominated litter items (68%). The results confirm that the Southern Ocean is the least polluted ocean in terms of drifting debris and suggest that most debris comes from local sources. PMID:25455366

  10. Low densities of drifting litter in the African sector of the Southern Ocean.

    PubMed

    Ryan, Peter G; Musker, Seth; Rink, Ariella

    2014-12-15

    Only 52 litter items (>1cm diameter) were observed in 10,467 km of at-sea transects in the African sector of the Southern Ocean. Litter density north of the Subtropical Front (0.58 items km(-2)) was less than in the adjacent South Atlantic Ocean (1-6 items km(-2)), but has increased compared to the mid-1980s. Litter density south of the Subtropical Front was an order of magnitude less than in temperate waters (0.032 items km(-2)). There was no difference in litter density between sub-Antarctic and Antarctic waters either side of the Antarctic Polar Front. Most litter was made of plastic (96%). Fishery-related debris comprised a greater proportion of litter south of the Subtropical Front (33%) than in temperate waters (13%), where packaging dominated litter items (68%). The results confirm that the Southern Ocean is the least polluted ocean in terms of drifting debris and suggest that most debris comes from local sources.

  11. The International Bathymetric Chart of the Southern Ocean - A new Map of Antarctica

    NASA Astrophysics Data System (ADS)

    Arndt, J.; Schenke, H. W.

    2012-12-01

    The International Bathymetric Chart of the Southern Ocean (IBCSO) is an expert group of the Scientific Committee on Antarctic Research (SCAR) since the XXVIII SCAR Conference held on 30th July 2004 in Bremen Germany and a regional Mapping project of the General Bathymetric Chart of the Ocean (GEBCO) operated under the joint auspices of the Intergovernmental Oceanographic Commission (IOC) (of UNESCO) and the International Hydrographic Organization (IHO). The objective of IBCSO was to produce a first seamless bathymetric grid for the area south of latitude 60° S covering the area of the Antarctic Treaty. The IBCSO is going to be a benefit for scientific purposes. These include (a) interpretation of seabed geology, (b) the building of habitat models and maps, and (c) mapping and tracing of deep ocean current pathways. In addition the IBCSO is going to serve as database for the development of new Electronic Nautical Charts (ENC) in the Southern Ocean to improve the safety of navigation in Antarctic waters. As the first version of the IBCSO grid is close to be released, so is the corresponding map. It is proposed to present the latest draft version, or even the final version, of the new IBCSO map. Besides the map itself, the process to achieve the first version of the IBCSO grid and map is going to be presented. This includes a description of the datasets used to create the map and a rough explanation of the working steps to generate the first grid version of the IBCSO.

  12. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

    PubMed Central

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-01-01

    Reduced surface–deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface–subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring–summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall–winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink. PMID:26382319

  13. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink.

    PubMed

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-01-01

    Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink. PMID:26382319

  14. The seasonal sea-ice zone in the glacial Southern Ocean as a carbon sink

    NASA Astrophysics Data System (ADS)

    Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf

    2015-09-01

    Reduced surface-deep ocean exchange and enhanced nutrient consumption by phytoplankton in the Southern Ocean have been linked to lower glacial atmospheric CO2. However, identification of the biological and physical conditions involved and the related processes remains incomplete. Here we specify Southern Ocean surface-subsurface contrasts using a new tool, the combined oxygen and silicon isotope measurement of diatom and radiolarian opal, in combination with numerical simulations. Our data do not indicate a permanent glacial halocline related to melt water from icebergs. Corroborated by numerical simulations, we find that glacial surface stratification was variable and linked to seasonal sea-ice changes. During glacial spring-summer, the mixed layer was relatively shallow, while deeper mixing occurred during fall-winter, allowing for surface-ocean refueling with nutrients from the deep reservoir, which was potentially richer in nutrients than today. This generated specific carbon and opal export regimes turning the glacial seasonal sea-ice zone into a carbon sink.

  15. Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lechtenfeld, Oliver J.; Kattner, Gerhard; Flerus, Ruth; McCallister, S. Leigh; Schmitt-Kopplin, Philippe; Koch, Boris P.

    2014-02-01

    More than 90% of the global ocean dissolved organic carbon (DOC) is refractory, has an average age of 4000-6000 years and a lifespan from months to millennia. The fraction of dissolved organic matter (DOM) that is resistant to degradation is a long-term buffer in the global carbon cycle but its chemical composition, structure, and biochemical formation and degradation mechanisms are still unresolved. We have compiled the most comprehensive molecular dataset of 197 Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analyses from solid-phase extracted marine DOM covering two major oceans, the Atlantic sector of the Southern Ocean and the East Atlantic Ocean (ranging from 50° N to 70° S). Molecular trends and radiocarbon dating of 34 DOM samples (comprising Δ14C values from -229‰ to -495‰) were combined to model an integrated degradation rate for bulk DOC resulting in a predicted age of >24 ka for the most persistent DOM fraction. First order kinetic degradation rates for 1557 mass peaks indicate that numerous DOM molecules cycle on timescales much longer than the turnover of the bulk DOC pool (estimated residence times of up to ~100 ka) and the range of validity of radiocarbon dating. Changes in elemental composition were determined by assigning molecular formulae to the detected mass peaks. The combination of residence times with molecular information enabled modelling of the average elemental composition of the slowest degrading fraction of the DOM pool. In our dataset, a group of 361 molecular formulae represented the most stable composition in the oceanic environment (“island of stability”). These most persistent compounds encompass only a narrow range of the molecular elemental ratios H/C (average of 1.17 ± 0.13), and O/C (average of 0.52 ± 0.10) and molecular masses (360 ± 28 and 497 ± 51 Da). In the Weddell Sea DOC concentrations in the surface waters were low (46.3 ± 3.3 μM) while the organic radiocarbon was significantly

  16. The Effects of Snow Depth Forcing on Southern Ocean Sea Ice Simulations

    NASA Technical Reports Server (NTRS)

    Powel, Dylan C.; Markus, Thorsten; Stoessel, Achim

    2003-01-01

    The spatial and temporal distribution of snow on sea ice is an important factor for sea ice and climate models. First, it acts as an efficient insulator between the ocean and the atmosphere, and second, snow is a source of fresh water for altering the already weak Southern Ocean stratification. For the Antarctic, where the ice thickness is relatively thin, snow can impact the ice thickness in two ways: a) As mentioned above snow on sea ice reduces the ocean-atmosphere heat flux and thus reduces freezing at the base of the ice flows; b) a heavy snow load can suppress the ice below sea level which causes flooding and, with subsequent freezing, a thickening of the sea ice (snow-to-ice conversion). In this paper, we compare different snow fall paramterizations (incl. the incorporation of satellite-derived snow depth) and study the effect on the sea ice using a sea ice model.

  17. Sea-ice transport driving Southern Ocean salinity and its recent trends.

    PubMed

    Haumann, F Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan

    2016-01-01

    Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of -0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters. PMID:27582222

  18. El Nino Southern Oscillation (ENSO) impact on tuna fisheries in Indian Ocean.

    PubMed

    Kumar, Palanisamy Satheesh; Pillai, Gopalakrishna N; Manjusha, Ushadevi

    2014-01-01

    El Nino Southern Oscillation (ENSO) is an important driver of interannual variations in climate and ecosystem productivity in tropical regions. However, detailed information about this important phenomenon of the Indian Ocean is scarce. Consequently, the objective of this study is to improve understanding of the impact of warm event El Nino and cool event La Nina on annual tuna landings from the Indian Ocean from 1980 to 2010. In this study, maximum tuna landings were recorded during a weak El Nino year (1456054 t in 2006) and during a weak La Nina year (1243562 t in 2000), although the lowest tuna catch was followed during the strong El Nino year (1204119 t in 2009) and during a strong La Nina year (706546 t in 1988). Validation of predicted tuna landings and SST were showing a significant positive correlation (p < 0.01) was observed all the major tuna species except Southern Bluefin Tuna. Whereas the other relationships such as sea level pressure, Wind actions; Zonal Wind (U), Meridonial Wind (V), and Scalar Wind (W) are less well-defined. In contrast with principal component analysis we find that Principal Components 1 explains 75.5% of the total variance and suggest that sea surface temperature plays a major role in determining tuna availability in the region especially during warm event El Nino years; landings in Indian Ocean tend to be optimum SST 25 to 26°C in ENSO event. Our results confirm the ENSO impact on climate, tuna abundance and production in the Indian Ocean. However, among the oceanic variables SST explained the highest deviance in generalized additive models and therefore considered the best habitat predictor in the Indian Ocean followed by sea level pressure and Winds (U, V, W).

  19. Contribution of glacial melt water to the recent Southern Ocean sea ice increase

    NASA Astrophysics Data System (ADS)

    Haid, Verena; Iovino, Dorotea

    2015-04-01

    In recent years climate change and global warming are topics that are discussed everywhere. Big concerns are the melting of land ice, the reduced summer sea ice cover in the Arctic Ocean, and the general decline of the cryosphere. In contrast to those scenarios, the response of Antarctic sea ice to a warming climate is elaborate and puzzling: sea ice extent has been slightly increasing on a circumpolar scale during the last decades. Atmospheric data analysis ascribed this expansion to changes in the wind dynamics; simulations with climate-scale ocean model suggest that accelerated basal melting of ice shelves plays a major role. We investigate the influence of the glacial melt water on the sea ice of the Southern Ocean on the circumpolar and regional scales employing the ocean/sea ice NEMO-LIM coupled system at eddy-permitting resolution. The forcing of the sea ice-ocean model is supplied from the ERA-Interim data set. After a 25-year spin-up period the reference run supplies a realistic simulation of the period 2004-2013. Different volumes and distributions of melt water are applied in individual model runs spanning the same period and results are compared with the reference run. The results of this study will increase our understanding of the effect of climate change on the Southern Ocean at present and thus also of the future development. Questions like how long the increasing trend in sea ice will last or how fast it will be reversed once the tipping point is reached will be able to be addressed with more accuracy.

  20. Sea-ice transport driving Southern Ocean salinity and its recent trends

    NASA Astrophysics Data System (ADS)

    Haumann, F. Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan

    2016-09-01

    Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of -0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters.

  1. Sea-ice transport driving Southern Ocean salinity and its recent trends.

    PubMed

    Haumann, F Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan

    2016-08-31

    Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of -0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters.

  2. Sea-ice transport driving Southern Ocean salinity and its recent trends

    NASA Astrophysics Data System (ADS)

    Haumann, F. Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan

    2016-09-01

    Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of ‑0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters.

  3. Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the Southern Ocean?

    NASA Astrophysics Data System (ADS)

    Bhattachan, Abinash; D'Odorico, Paolo

    2014-08-01

    The supply of soluble iron through atmospheric dust deposition limits the productivity of the Southern Ocean. In comparison to the Northern Hemisphere, the Southern Hemisphere exhibits low levels of dust activity. However, given their proximity to the Southern Ocean, dust emissions from continental sources in the Southern Hemisphere could have disproportionate impact on ocean productivity. Australia is the largest source of dust in the Southern Hemisphere and aeolian transport of dust has major ecological, economic and health implications. In the Mallee, agriculture is a major driver of dust emissions and dust storms that affect Southeastern Australia. In this study, we assess the dust generating potential of the sediment from the Mallee, analyze the sediment for soluble iron content and determine the likely depositional region of the emitted dust. Our results suggest that the Mallee sediments have comparable dust generating potential to other currently active dust sources in the Southern Hemisphere and the dust-sized fraction is rich in soluble iron. Forward trajectory analyses show that this dust will impact the Tasman Sea and the Australian section of the Southern Ocean. This iron-rich dust could stimulate ocean productivity in future as more areas are reactivated as a result of land-use and droughts.

  4. Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the Southern Ocean?

    PubMed

    Bhattachan, Abinash; D'Odorico, Paolo

    2014-01-01

    The supply of soluble iron through atmospheric dust deposition limits the productivity of the Southern Ocean. In comparison to the Northern Hemisphere, the Southern Hemisphere exhibits low levels of dust activity. However, given their proximity to the Southern Ocean, dust emissions from continental sources in the Southern Hemisphere could have disproportionate impact on ocean productivity. Australia is the largest source of dust in the Southern Hemisphere and aeolian transport of dust has major ecological, economic and health implications. In the Mallee, agriculture is a major driver of dust emissions and dust storms that affect Southeastern Australia. In this study, we assess the dust generating potential of the sediment from the Mallee, analyze the sediment for soluble iron content and determine the likely depositional region of the emitted dust. Our results suggest that the Mallee sediments have comparable dust generating potential to other currently active dust sources in the Southern Hemisphere and the dust-sized fraction is rich in soluble iron. Forward trajectory analyses show that this dust will impact the Tasman Sea and the Australian section of the Southern Ocean. This iron-rich dust could stimulate ocean productivity in future as more areas are reactivated as a result of land-use and droughts. PMID:25109703

  5. Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the Southern Ocean?

    PubMed

    Bhattachan, Abinash; D'Odorico, Paolo

    2014-08-11

    The supply of soluble iron through atmospheric dust deposition limits the productivity of the Southern Ocean. In comparison to the Northern Hemisphere, the Southern Hemisphere exhibits low levels of dust activity. However, given their proximity to the Southern Ocean, dust emissions from continental sources in the Southern Hemisphere could have disproportionate impact on ocean productivity. Australia is the largest source of dust in the Southern Hemisphere and aeolian transport of dust has major ecological, economic and health implications. In the Mallee, agriculture is a major driver of dust emissions and dust storms that affect Southeastern Australia. In this study, we assess the dust generating potential of the sediment from the Mallee, analyze the sediment for soluble iron content and determine the likely depositional region of the emitted dust. Our results suggest that the Mallee sediments have comparable dust generating potential to other currently active dust sources in the Southern Hemisphere and the dust-sized fraction is rich in soluble iron. Forward trajectory analyses show that this dust will impact the Tasman Sea and the Australian section of the Southern Ocean. This iron-rich dust could stimulate ocean productivity in future as more areas are reactivated as a result of land-use and droughts.

  6. Molecular phylogeny and historical biogeography of Nacella (Patellogastropoda: Nacellidae) in the Southern Ocean.

    PubMed

    González-Wevar, Claudio A; Nakano, Tomoyuki; Cañete, Juan I; Poulin, Elie

    2010-07-01

    The evolution and the historical biogeography of the Southern Ocean marine benthic fauna are closely related to major tectonic and climatic changes that occurred in this region during the last 55 million years (Ma). Several families, genera and even species of marine organisms are shared between distant biogeographic provinces in this region. This pattern of distribution in marine benthic invertebrates has been commonly explained by vicariant speciation due to plate tectonics. However, recent molecular studies have provided new evidence for long-distance dispersion as a plausible explanation of biogeographical patterns in the Southern Ocean. True limpets of the genus Nacella are currently distributed in different biogeographic regions of the Southern Ocean such as Antarctica, Kerguelen Province, southern New Zealand Antipodean Province, North-Central Chile and South American Magellanic Province. Here, we present phylogenetic reconstructions using two mitochondrial DNA markers (Cytochrome Oxidase I and Cytochrome b) to look into the relationships among Nacella species and to determine the origin and diversification of the genus. Phylogenies were reconstructed using two methods, Maximum Parsimony and Bayesian Inference, while divergence time among Nacella species was estimated following a relaxed Bayesian approach. For this purpose, we collected inter- and subtidal species belonging to four biogeographic regions in the Southern Ocean: Antarctica, Kerguelen Province, Central Chile, and Magellanic Province. Our molecular results agree with previous morphological and molecular studies supporting the monophyly of Nacella and its sister relationship with Cellana. Two rounds of diversification are recognized in the evolution of Nacella. The first one occurred at the end of the Miocene and gave rise to the main lineages, currently distributed in Antarctica, South America or Kerguelen Province. Large genetic divergence was detected among Nacella species from these distant

  7. Molecular phylogeny and historical biogeography of Nacella (Patellogastropoda: Nacellidae) in the Southern Ocean.

    PubMed

    González-Wevar, Claudio A; Nakano, Tomoyuki; Cañete, Juan I; Poulin, Elie

    2010-07-01

    The evolution and the historical biogeography of the Southern Ocean marine benthic fauna are closely related to major tectonic and climatic changes that occurred in this region during the last 55 million years (Ma). Several families, genera and even species of marine organisms are shared between distant biogeographic provinces in this region. This pattern of distribution in marine benthic invertebrates has been commonly explained by vicariant speciation due to plate tectonics. However, recent molecular studies have provided new evidence for long-distance dispersion as a plausible explanation of biogeographical patterns in the Southern Ocean. True limpets of the genus Nacella are currently distributed in different biogeographic regions of the Southern Ocean such as Antarctica, Kerguelen Province, southern New Zealand Antipodean Province, North-Central Chile and South American Magellanic Province. Here, we present phylogenetic reconstructions using two mitochondrial DNA markers (Cytochrome Oxidase I and Cytochrome b) to look into the relationships among Nacella species and to determine the origin and diversification of the genus. Phylogenies were reconstructed using two methods, Maximum Parsimony and Bayesian Inference, while divergence time among Nacella species was estimated following a relaxed Bayesian approach. For this purpose, we collected inter- and subtidal species belonging to four biogeographic regions in the Southern Ocean: Antarctica, Kerguelen Province, Central Chile, and Magellanic Province. Our molecular results agree with previous morphological and molecular studies supporting the monophyly of Nacella and its sister relationship with Cellana. Two rounds of diversification are recognized in the evolution of Nacella. The first one occurred at the end of the Miocene and gave rise to the main lineages, currently distributed in Antarctica, South America or Kerguelen Province. Large genetic divergence was detected among Nacella species from these distant

  8. The influence of marine monoterpene emissions on cloud condensation nuclei concentrations over the Southern Hemisphere oceans

    NASA Astrophysics Data System (ADS)

    Walker, Hannah; Arnold, Steve; Spracklen, Dominick; Rap, Alexandru; Scott, Catherine; Hackenberg, Sina; Carpenter, Lucy

    2016-04-01

    model simulates a strong response to monoterpene emissions over remote oceans south of 45° S, in particular during Southern Hemisphere summer (up to 388 % for 35 Tg a-1). We investigate the impact of co-located emissions of monoterpene and dimethyl sulphide in a small region of the Southern Ocean on CCN concentration. We use an offline radiative transfer model to calculate the radiative effects of the modelled CCN concentrations.

  9. Decadal Changes in Hydrography of the Southern Pacific Ocean and Ross Sea

    NASA Astrophysics Data System (ADS)

    Talley, L. D.; Carter, B.; Warner, M. J.; Swift, J. H.; Orsi, A. H.; Sloyan, B.

    2014-12-01

    Quasi-decadal hydrographic sections of the GO-SHIP program cross the world's oceans with the highest accuracy measurements, documenting temporal variability in physical and chemical properties. The central southern Pacific and Ross Sea have been surveyed regularly along GO-SHIP sections P16S (150W) and S4P (67S) since the first occupation in WOCE in 1992. Observed changes are consistent with anthropogenic forcing. The central Ross Sea gyre's bottom 1000 m is nearly adiabatic (well mixed), and well-ventilated based on chlorofluorocarbon (CFC) and sulfur hexafluoride observations (see Figure), and can be easily compared from one survey to the next. This Ross Sea bottom layer observed in March, 2014, on P16S continued to warm, with a monotonic increase over the 4 WOCE/GO-SHIP surveys thus far: 1992, 2005, 2011, and now 2014 (see Figure). Deep temperature has increased by 0.1°C since 1992, continuing the trend of enhanced global ocean deep warming in the Southern Ocean documented by Purkey/Johnson (2010) and IPCC AR5 WG1. The abyssal central Ross Sea waters also continued to freshen slightly. The upper ocean in the Ross Sea warmed, became more stratified, had higher nutrients and total carbon, and was less ventilated in terms of apparent oxygen utilization than in 2005. North of the Antarctic Circumpolar Current along 150W, the upper ocean's Subantarctic Mode Water became saltier, also continuing the subtropical trend of the past several decades (Durack/Wijffels 2010), with an apparently stronger incursion of saline subtropical waters that render it more salt and temperature stratified, ruling out a local deep mixed layer formation mechanism, with an increasing tendency towards double diffusive processes. The Antarctic Intermediate Water salinity minimum continued to freshen. The arrival in 2014 of CFC's at the ocean bottom between 32S and 40S indicates that the Antarctic Bottom Water there is about 40-50 years old. CFCs in the ocean's surface layer decreased, in

  10. Interannual Trends in Southern Ocean Sea Surface Temperatures and Sea Level from Remote Sensing Data

    NASA Astrophysics Data System (ADS)

    Lebedev, S. A.

    As is shown in last years researches climate changes in Antarctic result in interannual increase trend of surface air temperature and decrease of ice thickness These tendencies are must try in the Southern Ocean hydrological regime For that next remote sensing data AVHRR MCSST data and satellite altimetry data merged data of mission ERS TOPEX Poseidon Jason-1 ENVISAT GFO-1 are used to this task which give information about sea surface temperature SST and sea level anomaly SLA correspondingly According to obtained results SST has positive trend more 0 01 oC yr for 23-yr record 1982-2005 within 300-1000 km northward Antarctic coast However on average for the Southern Ocean SST have negative trend about -0 018 -0 035 oC yr In area of Pacific-Antarctic Ridge and of southern part of Mid Atlantic Ridge decrease rate is more than -0 075 oC yr SLA increases in all area of the Southern Ocean and has average rate about 0 024 -0 026 cm yr for 12-yr record 1993-2005 Around Antarctic SST rate good correspond with the trend analysis of surface air temperature of 8722 0 042 - 0 067oC yr inferred from the satellite 20-yr record Comiso 2000 Nevertheless the observed cooling is intriguing especially since it is compatible with the observed trend in the sea ice cover In the sea ice regions the northernmost positions of the ice edge are shown to be influenced by alternating warm and cold anomalies around the continent This work was partly supported by the Russian Fund of Basic Research Grant 06-05-65061

  11. Increased dust deposition in the Pacific Southern Ocean during glacial periods

    NASA Astrophysics Data System (ADS)

    Lamy, Frank; Gersonde, Rainer; Winckler, Gisela; Esper, Oliver; Jaeschke, Andrea; Kuhn, Gerhard; Ullermann, Johannes; Martinez-Garcia, Alfredo; Lambert, Fabrice; Kilian, Rolf

    2014-05-01

    Dust deposition across the Southern Ocean plays a critical role for marine biological production through iron fertilization and is supposed to control a significant fraction of glacial-interglacial atmospheric CO2 changes. However, in the Pacific, the largest Southern Ocean sector, reliable sediment records are sparse and climate models mostly indicate low dust deposition both for modern times and the last glacial maximum. Here, we present comprehensive data-sets of dust supply based on the analysis of sediment records recently retrieved across the Pacific Southern Ocean. The shape and glacial/interglacial pattern of lithogenic sediment input records in the western and central sector reveals strong similarities to dust records from Antarctica and the South Atlantic. Though our new data document substantial sediment redistribution, glacial dust mass accumulation rates corrected for sediment focusing exceed interglacial values by a factor of ~3. The first-order changes in Subantarctic biological productivity largely follow increased dust supply during glacials. Taken together our new sediment records document a substantial glacial dust supply from Australian and New Zealand sources to the Pacific SO sector eastward to at least 125°W. Such enhancement of dust supply is consistent with stronger aridity in Australia and a glacial dust source in New Zealand. Although the most likely dust source for the South Pacific is Australia/New Zealand, the glacial/interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from Antarctica and the South Atlantic dominated by Patagonian sources. These similarities imply large-scale common climate forcings such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia.

  12. Adaptations of phytoplankton in the Indian Ocean sector of the Southern Ocean during austral summer of 1998—2014

    NASA Astrophysics Data System (ADS)

    Mishra, R. K.; Naik, R. K.; Anil Kumar, N.

    2015-12-01

    This study investigates the effects of light and temperature on the surface water diatoms and chlorophytes, phytoplankton in the Indian Ocean sector of the Southern Ocean (SO) during the austral summer of 1998‒2014. Significant longitudinal variations in hydrographic and biological parameters were observed at the Sub tropical front (STF), Sub Antarctic front (SAF) and Polar front (PF) along 56°E‒58°E. The concentrations of total surface chlorophyll a ( Chl a), diatoms, and chlorophytes measured by the National Aeronautics Space Agency (NASA) estimated by the Sea-Viewing Wide Field-of-View Sensors (SeaWiFS), the Moderate Resolution Imaging Spectro Radiometer (MODIS), and the NASA Ocean Biological Model (NOBM) were used in the study. Variations in the concentration of total Chl a was remarkable amongst the fronts during the study period. The contribution of diatoms to the total concentration of surface Chl a increased towards south from the STF to the PF while it decreased in the case of chlorophytes. The maximum photosynthetically active radiation (PAR) was observed at the STF and it progressively decreased to the PF through the SAF. At the PF region the contribution of diatoms to the total Chl a biomass was ≥80%. On the other hand, the chlorophytes showed a contrary distribution pattern with ≥70% of the total Chl a biomass recorded at the STF which gradually decreased towards the PF, mainly attributed to the temperate adaptation. This clearly reveals that the trend of diatoms increased at the STF and decreased at the SAF and the PF. Further, the trend of chlorophytes was increased at the STF, SAF and PF with a shift in the community in the frontal system of the Indian Ocean sector of the SO.

  13. The effect of a northward shift in the southern hemisphere westerlies on the global ocean

    NASA Astrophysics Data System (ADS)

    Sijp, Willem P.; England, Matthew H.

    2008-10-01

    We examine the effect of a northward shift in the position of the southern hemisphere subpolar westerly winds (SWWs) on the vertical and horizontal distribution of temperature and salinity in the world ocean. A northward shift of the SWWs causes a latitudinal contraction of the subpolar gyres in the southern hemisphere (SH). In the Indian and Pacific, this leads to subsurface warming in the subtropical thermocline. As the southern margins of the gyres move into latitudes characterised by warmer surface air temperature (SAT), the layers at mid-depth below 400 m depth become ventilated by warmer water. We characterize the approximation of the ventilated thermocline in our coarse resolution model using a set of passive tracer experiments, and illustrate how the northward shift in the SWWs causes an equatorward shift in the latitude of origin of water ventilating layers deeper than 400 m in the Indian and Pacific, leaving the total surface ventilation of the upper 1200 m unchanged. In contrast, the latitudinal constraint on the Antarctic Circumpolar Current posed by the Drake Passage causes a cooling and freshening throughout the Atlantic thermocline; here, subsurface thermocline water originates from higher latitudes under the wind shift. On longer timescales Atlantic cooling and freshening is reinforced by a reduction in North Atlantic Deep Water (NADW) formation and surface salinification of the Indian and Pacific Oceans. In effect, the latitude of zero wind stress curl in the SWWs regulates the relative importance of the “cold water route” via the Drake Passage and the “warm water route” associated with thermocline water exchange via the Indian Ocean. Thus, a more northward location of the SWWs corresponds with a reduced salinity contrast between the Indian/ Pacific Oceans and the Atlantic. This results in reduced NADW formation. Also, a more northward location of the SWWs facilitates the injection of cool fresh Antarctic Intermediate Water into the South

  14. Observations of frozen skin of southern ocean from multifrequency scanning microwave radiometer (MSMR) onboard oceansat - 1

    NASA Astrophysics Data System (ADS)

    Vyas, N.; Bhandari, S.; Dash, M.; Pandey, P.; Khare, N.

    Encircling the Antarctic, Southern Ocean connects all the three oceans of the world with fastest current system found anywhere in the world. The region is thermally very stable and is covered with ice, which has a strong seasonal variability. The sea ice pulsates annually with seasonal migration varying from 4 million square kilometer to 20 million square kilometer during summer and winter respectively. This has strong influence on energy balance of the ocean-ice-atmosphere system, and hence on atmospheric general circulation affecting weather and climate. Sea ice also works as an insulator thus inhibiting the energy flux between ocean and atmosphere. It also influences the ecosystem of the southern ocean, which has rich fish resources with global economic values such as krill and tooth fish. During winter Krill survives on algae found at the under side of the sea ice. The southern ocean is known to have high nutrition but low concentration of chlorophyll-a, which is a proxy of the phytoplankton. It is now understood that iron is the limiting factor as has been shown by various iron fertilization experiments. Passive microwave radiometry from space has been extensively used for the study of sea ice types and concentration in the Arctic and the Antarctic regions. Since late 1970s, data from SMMR and SSM/I have been used to study trends in sea ice extent and area. We have further extended the above studies by using data from OCEANSAT - 1 MSMR. The data, acquired at 18 GHz (H) with 50 kilometer resolution and having a swath of 1360 kilometer and a repeat cycle of 2 days, was processed to generate the brightness temperature maps over the Antarctica for a period of 2 years and the results were analyzed in conjunction with those obtained earlier (since 1978) through the study of SMMR and SSM/I data. Besides strong seasonal variability, our analysis shows an increasing trend in the sea ice extent during the recent years and the rate appears to be accelerating contrary to

  15. AMOC Variability During the Last 400 ka from Nd Isotopes in a Southern Ocean Core

    NASA Astrophysics Data System (ADS)

    Lupien, R.; Pena, L.; Goldstein, S. L.

    2014-12-01

    Paleoceanographic studies have used Nd isotope ratios to characterize paleo-ocean deep-water mass distributions. The Southern Ocean has nearly homogeneous ɛNd that reflects the relative inputs from the north Atlantic and north Pacific, offering the possibility to quantify the AMOC strength through time. However, obtaining an ɛNd record from the Southern Ocean is a challenge because carbonates are poorly preserved there, hindering stratigraphic control and generally precluding use of this important substrate. Alternatively, studies of deep-sea corals and ferromanganese crusts provide snapshots or poor time resolution. Deep-sea core E33-22 (55°S, 120°W, 2743m) lies in the polar frontal zone of the Pacific sector, above the carbonate compensation depth, where foraminifera are preserved. It spans ~400,000 years (from the Holocene to MIS11) with a sedimentation rate of ~2.5 cm/kyr. We measured its ɛNd record with the purpose of determining the best estimate of the export of NADW out of the Atlantic system, which we suggest is our best measure of the vigor of the global thermohaline circulation system. The record shows expected ɛNd variability during orbital and sub-orbital time-scales, that is lower ɛNd during warm and higher ɛNd during cold climate intervals. Moreover, the record passes a critical test in that ɛNd-values are almost always between South Atlantic and Pacific values. The only exceptions are glacial periods when they coincide with South Atlantic values, indicating extension of Southern Ocean system into the South Atlantic. We conclude that these data represent a conservative record of AMOC variability through the late Pleistocene.

  16. Response of bacterioplankton to iron fertilization of the Southern Ocean, Antarctica

    PubMed Central

    Singh, Sanjay K.; Kotakonda, Arunasri; Kapardar, Raj K.; Kankipati, Hara Kishore; Sreenivasa Rao, Pasupuleti; Sankaranarayanan, Pratibha Mambatta; Vetaikorumagan, Sundareswaran R.; Gundlapally, Sathyanarayana Reddy; Nagappa, Ramaiah; Shivaji, Sisinthy

    2015-01-01

    Ocean iron fertilization is an approach to increase CO2 sequestration. The Indo-German iron fertilization experiment “LOHAFEX” was carried out in the Southern Ocean surrounding Antarctica in 2009 to monitor changes in bacterial community structure following iron fertilization-induced phytoplankton bloom of the seawater from different depths. 16S rRNA gene libraries were constructed using metagenomic DNA from seawater prior to and after iron fertilization and the clones were sequenced for identification of the major bacterial groups present and for phylogenetic analyses. A total of 4439 clones of 16S rRNA genes from ten 16S rRNA gene libraries were sequenced. More than 97.35% of the sequences represented four bacterial lineages i.e. Alphaproteobacteria, Gammaproteobacteria, Bacteroidetes, and Firmicutes and confirmed their role in scavenging of phytoplankton blooms induced following iron fertilization. The present study demonstrates the response of Firmicutes due to Iron fertilization which was not observed in previous southern ocean Iron fertilization studies. In addition, this study identifies three unique phylogenetic clusters LOHAFEX Cluster 1 (affiliated to Bacteroidetes), 2, and 3 (affiliated to Firmicutes) which were not detected in any of the earlier studies on iron fertilization. The relative abundance of these clusters in response to iron fertilization was different. The increase in abundance of LOHAFEX Cluster 2 and Papillibacter sp. another dominant Firmicutes may imply a role in phytoplankton degradation. Disappearance of LOHAFEX Cluster 3 and other bacterial genera after iron fertilization may imply conditions not conducive for their survival. It is hypothesized that heterotrophic bacterial abundance in the Southern Ocean would depend on their ability to utilize algal exudates, decaying algal biomass and other nutrients thus resulting in a dynamic bacterial succession of distinct genera. PMID:26379640

  17. Wind, mixed-layer depth and Chl-a variability in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Gille, S. T.; Carranza, M. M.; Franks, P. J. S.; Girton, J. B.; Johnson, K. S.

    2014-12-01

    The Southern Ocean, contains some of the ocean's deepest mixed layers and is under the constant influence of strong winds and buoyancy forcing. Phytoplankton growth is hypothesized to be co-limited by iron and light. Because deep mixed layers can transport phytoplankton below the depth of the euphotic zone, light levels depend on mixed-layer depth. We use satellite winds from multiple wind sensors, combined with Argo data, to show that deep mixed layers are generally correlated with strong winds over the Southern Ocean. These deep mixed layers correspond to cold sea surface temperatures. This might also be expected to lead to nutrient upwelling and high chlorophyll-a (Chl-a), as measured by satellite ocean color sensors. However, Chl-a is less strongly correlated with wind speed than SST is, particularly at the mesoscale, and in summer Chl-a is not well correlated with mixed-layer depth. Using new in situ observations of subsurface Chl-a from sensors on southern elephant seals, EM-APEX floats, and bio-optical Argo floats, we find that Chl-a typically has a subsurface maximum in spring, summer, and fall. As a result satellite-sensed Chl-a is an inadequate measure of total biomass within the mixed layer. Satellite Chl-a and integrated Chl-a over the euphotic zone are negatively correlated with MLD from fall through spring, and uncorrelated during the summer. However, integrated Chl-a within the mixed layer shows significant positive correlations with MLD in all seasons. The fact that the deep Chl-a maximum sits at the base of the MLD, closer to the nutrient (or iron) maximum than the light maximum, suggests nutrient limitation plays a greater role than light limitation in governing productivity, and that wind and buoyancy forcing likely govern the mixing processes at the base of the mixed layer that control phytoplankton growth.

  18. Comparisons of The Habitat Utilization Of Top Predators In The Southern Ocean And The North Pacific

    NASA Astrophysics Data System (ADS)

    Costa, D. P.; Robinson, P.; Huckstadt, L. E.; Crocker, D. E.; Goebel, M. E.

    2010-12-01

    Northern and Southern elephant seals (Mirounga angustirostris, M. leonina) separated some 4 MYA. While these congeners are physiologically very similar and thus have the potential to forage in similar ways they inhabit very different habitats. While southern elephant seals (SES) are distributed throughout the southern ocean, northern elephant seals (NES) are limited to the Northeast Pacific Ocean and range over lower latitudes than SES. In order to compare and contrast the physiological capability and response to different habitats we compared the foraging behavior of 167 adult female northern elephant seals (Año Nuevo and San Benitos Islands) and 55 southern elephant seals (Livingston Island, Antarctic Peninsula) using satellite telemetry and dive recorders. As expected both species carried out very similar dive depths (NES 509m ± 166 vs SES 345m±79) and dive durations (NES 23.0 min ± 6.7; SES 22.5 min ± 5.0). However, there were significant differences in their foraging pattern that we attribute to differences in the availability of continental shelf and suitable foraging habitat. While 85% of NES females foraged offshore, the dominant strategy for SES was benthic foraging on the continental shelf. Even with the differences in habitat, the fundamental components of their foraging patterns remained the same as when they foraged pelagically they both species relied on persistent large scale oceanographic features where mixing enhances productivity such as the North Pacific Transition zone (NES) and the Southern Antarctic Circumpolar Current Front (SES). Given the very different habitats and prey species consumed by these two species their overall foraging behavior is surprisingly similar suggesting that as a mesopelagic predator the elephant seal design is rather robust.

  19. Sediment transport and deposition processes near ocean outfalls in Southern California

    USGS Publications Warehouse

    Lee, H.J.; Noble, M.A.; Xu, Jie; ,

    2003-01-01

    An urbanized coastal ocean that has complex topography and large-scale atmospheric and oceanographic forcing can contain a variety of sediment and pollutant distribution patterns. For example, the central southern California Bight has two large embayments, Santa Monica and San Pedro Bays, that are connected by a short, very narrow shelf off the Palos Verdes peninsula. The complex topography causes quite different oceanographic and sediment distribution patterns in this fairly small region of the coastal ocean. In addition, three sewage outfalls discharge material over the outer shelf. A large suite of sediment cores was obtained and analyzed for contaminants, physical properties, accumulation rates, and grain sizes. Arrays of instrumented moorings that monitor currents, waves, water clarity, water density and collect resuspended materials were deployed. The data and models developed for the Palos Verdes margin suggest that a large reservoir of DDT and its byproducts exists in the coastal ocean sediment and will continue to be exhumed and transported along the shelf for a long time. On the Santa Monica shelf, very large internal waves, or bores, are generated at the shelf break. The near-bottom currents associated with these waves sweep sediment and the associated contaminants from the shelf onto the continental slope. On the San Pedro margin an initial examination of recent data collected in the coastal ocean does not suggest that bacterial contamination on local beaches is primarily caused by transport of material from the adjacent ocean outfall.

  20. Resource partitioning through oceanic segregation of foraging juvenile southern elephant seals ( Mirounga leonina).

    PubMed

    Field, Iain C; Bradshaw, Corey J A; Burton, Harry R; Sumner, Michael D; Hindell, Mark A

    2005-01-01

    In highly dynamic and unpredictable environments such as the Southern Ocean, species that have evolved behaviors that reduce the effects of intra-specific competition may have a selective advantage. This is particularly true when juveniles face disadvantages when foraging due to morphological or physiological limitation, which is the case for many marine mammals. We tracked the at-sea movements of 48 juvenile southern elephant seals ( Mirounga leonina) between the ages of 1 and 4 years from the population at Macquarie Island using locations derived from recorded light levels. There were significant differences in the total amount of the Southern Ocean covered by the different age-groups. The younger seals used a smaller area than the older seals. On average, the younger individuals also made more trips to sea than the older seals and did not travel as far on each trip. Females spent more time at sea than males and there were no significant differences between the total areas used by male and females. In summary, younger seals remained closer to the island at all times, and they spent more time in more northerly regions that older seals. These differences in behavior created temporal and spatial segregation between juveniles of different ages. Therefore, we suggest that these temporal and spatial separations help to avoid intra-specific competition for resources on land, space on beaches, and at-sea foraging areas. Such modifications of haul-out timing and behavior enable them to exploit a patchy and unpredictable environment.

  1. Stormwater plume detection by MODIS imagery in the southern California coastal ocean

    USGS Publications Warehouse

    Nezlin, N.P.; DiGiacomo, P.M.; Diehl, D.W.; Jones, B.H.; Johnson, S.C.; Mengel, M.J.; Reifel, K.M.; Warrick, J.A.; Wang, M.

    2008-01-01

    Stormwater plumes in the southern California coastal ocean were detected by MODIS-Aqua satellite imagery and compared to ship-based data on surface salinity and fecal indicator bacterial (FIB) counts collected during the Bight'03 Regional Water Quality Program surveys in February-March of 2004 and 2005. MODIS imagery was processed using a combined near-infrared/shortwave-infrared (NIR-SWIR) atmospheric correction method, which substantially improved normalized water-leaving radiation (nLw) optical spectra in coastal waters with high turbidity. Plumes were detected using a minimum-distance supervised classification method based on nLw spectra averaged within the training areas, defined as circular zones of 1.5-5.0-km radii around field stations with a surface salinity of S 33.0 ('ocean'). The plume optical signatures (i.e., the nLw differences between 'plume' and 'ocean') were most evident during the first 2 days after the rainstorms. To assess the accuracy of plume detection, stations were classified into 'plume' and 'ocean' using two criteria: (1) 'plume' included the stations with salinity below a certain threshold estimated from the maximum accuracy of plume detection; and (2) FIB counts in 'plume' exceeded the California State Water Board standards. The salinity threshold between 'plume' and 'ocean' was estimated as 32.2. The total accuracy of plume detection in terms of surface salinity was not high (68% on average), seemingly because of imperfect correlation between plume salinity and ocean color. The accuracy of plume detection in terms of FIB exceedances was even lower (64% on average), resulting from low correlation between ocean color and bacterial contamination. Nevertheless, satellite imagery was shown to be a useful tool for the estimation of the extent of potentially polluted plumes, which was hardly achievable by direct sampling methods (in particular, because the grids of ship-based stations covered only small parts of the plumes detected via

  2. Emissions of Trace Gases and Particles from Two Ships in the Southern Atlantic Ocean

    NASA Technical Reports Server (NTRS)

    Sinha, Parikhit; Hobbs, Peter V.; Yokelson, Robert J.; Christian, Ted J.; Kirchstetter, Thomas W.; Bruintjes, Roelof

    2003-01-01

    Measurements were made of the emissions of particles and gases from two diesel-powered ships in the southern Atlantic Ocean off the coast of Namibia. The measurements are used to derive emission factors from ships of three species not reported previously, namely, black carbon, accumulation-mode particles, and cloud condensation nuclei (CCN), as well as for carbon dioxide, carbon monoxide (CO), methane (CH4), non-methane hydrocarbons, sulfur dioxide (SO2), nitrogen oxides (NOx), and condensation nuclei. The effects of fuel grade and engine power on ship emissions are discussed. The emission factors are combined with fuel usage data to obtain estimates of global annual emissions of various particles and gases from ocean-going ships. Global emissions of black carbon, accumulation- mode particles, and CCN from ocean-going ships are estimated to be 19-26 Gg yr(sup -1), (4.4-6.1) x 10(exp 26) particles yr(sup -1), and (1.0-1.5) x l0(exp 26) particles yr(sup -1), respectively. Black carbon emissions from ocean-going ships are approximately 0.2% of total anthropogenic emissions. Emissions of NOx and SO2 from ocean-going ships are approximately 10-14% and approximately 3-4%, respectively, of the total emissions of these species from the burning of fossil fuels, and approximately 40% and approximately 70%, respectively, of the total emissions of these species from the burning of biomass. Global annual emissions of CO and CH4 from ocean-going ships are approximately 2% and approximately 2-5%, respectively, of natural oceanic emissions of these species.

  3. Boreal spring Southern Hemisphere Annular Mode, Indian Ocean sea surface temperature, and East Asian summer monsoon

    NASA Astrophysics Data System (ADS)

    Nan, Sulan; Li, Jianping; Yuan, Xiaojun; Zhao, Ping

    2009-01-01

    The relationships among the boreal spring Southern Hemisphere Annular Mode (SAM), the Indian Ocean (IO) sea surface temperature (SST), and East Asian summer monsoon (EASM) are examined statistically in this paper. The variability of boreal spring SAM is closely related to the IO SST. When the SAM is in its strong positive phase in boreal spring, with low-pressure anomalies over the south pole and high-pressure anomalies over middle latitudes, SST over the subtropics and middle latitudes of the South Indian Ocean (SIO) increases, which persists into the summer. Following the positive SST anomalies over the subtropics and midlatitudes of the SIO, SST in the equatorial Indian Ocean and Bay of Bengal increases in summer. Moreover, the variability of SST in the equatorial Indian Ocean and Bay of Bengal is closely related to EASM. When SST in the equatorial Indian Ocean and Bay of Bengal increases, EASM tends to be weak. Therefore the IO SST may play an important role bridging boreal spring SAM and EASM. The atmospheric circulations and surface heat exchanges contribute to the SST anomalies in the SIO. When the spring SAM is in its strong positive phases, the regional Ferrel Cell weakens, and the anomalous upward motions at 20°S-30°S cause an increase of low cloud cover and downward longwave radiation flux. The surface atmospheric circulations also transport more (less) warmer (cooler) air from middle latitudes north of 50°S (high latitudes south of 60°S) into 50°S-60°S and warm the air, which reduces the temperature difference between the ocean and atmosphere and consequently reduces sensible heat flux from the ocean to atmosphere. The increased downward longwave radiation and decreased sensible heat are responsible for the SST increase in the SIO. The atmospheric circulation and surface heat flux anomalies are of opposite signs following the strong negative phases of SAM.

  4. The Biogeochemical Role of Baleen Whales and Krill in Southern Ocean Nutrient Cycling

    PubMed Central

    Ratnarajah, Lavenia; Bowie, Andrew R.; Lannuzel, Delphine; Meiners, Klaus M.; Nicol, Stephen

    2014-01-01

    The availability of micronutrients is a key factor that affects primary productivity in High Nutrient Low Chlorophyll (HNLC) regions of the Southern Ocean. Nutrient supply is governed by a range of physical, chemical and biological processes, and there are significant feedbacks within the ecosystem. It has been suggested that baleen whales form a crucial part of biogeochemical cycling processes through the consumption of nutrient-rich krill and subsequent defecation, but data on their contribution are scarce. We analysed the concentration of iron, cadmium, manganese, cobalt, copper, zinc, phosphorus and carbon in baleen whale faeces and muscle, and krill tissue using inductively coupled plasma mass spectrometry. Metal concentrations in krill tissue were between 20 thousand and 4.8 million times higher than typical Southern Ocean HNLC seawater concentrations, while whale faecal matter was between 276 thousand and 10 million times higher. These findings suggest that krill act as a mechanism for concentrating and retaining elements in the surface layer, which are subsequently released back into the ocean, once eaten by whales, through defecation. Trace metal to carbon ratios were also higher in whale faeces compared to whale muscle indicating that whales are concentrating carbon and actively defecating trace elements. Consequently, recovery of the great whales may facilitate the recycling of nutrients via defecation, which may affect productivity in HNLC areas. PMID:25469984

  5. Air-sea exchange of carbon dioxide in the Southern Ocean and Antarctic marginal ice zone

    NASA Astrophysics Data System (ADS)

    Butterworth, Brian J.; Miller, Scott D.

    2016-07-01

    Direct carbon dioxide flux measurements using eddy covariance from an icebreaker in the high-latitude Southern Ocean and Antarctic marginal ice zone are reported. Fluxes were combined with the measured water-air carbon dioxide partial pressure difference (ΔpCO2) to compute the air-sea gas transfer velocity (k, normalized to Schmidt number 660). The open water data showed a quadratic relationship between k (cm h-1) and the neutral 10 m wind speed (U10n, m s-1), kopen = 0.245 U10n2 + 1.3, in close agreement with decades old tracer-based results and much lower than cubic relationships inferred from previous open ocean eddy covariance studies. In the marginal ice zone, the effective gas transfer velocity decreased in proportion to sea ice cover, in contrast with predictions of enhanced gas exchange in the presence of sea ice. The combined open water and marginal ice zone results affect the calculated magnitude and spatial distribution of Southern Ocean carbon flux.

  6. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    SciTech Connect

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-14

    In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along an extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.

  7. Evidence for long-lived subduction of an ancient tectonic plate beneath the southern Indian Ocean

    DOE PAGES

    Simmons, N. A.; Myers, S. C.; Johannesson, G.; Matzel, E.; Grand, S. P.

    2015-11-14

    In this study, ancient subducted tectonic plates have been observed in past seismic images of the mantle beneath North America and Eurasia, and it is likely that other ancient slab structures have remained largely hidden, particularly in the seismic-data-limited regions beneath the vast oceans in the Southern Hemisphere. Here we present a new global tomographic image, which shows a slab-like structure beneath the southern Indian Ocean with coherency from the upper mantle to the core-mantle boundary region—a feature that has never been identified. We postulate that the structure is an ancient tectonic plate that sank into the mantle along anmore » extensive intraoceanic subduction zone that migrated southwestward across the ancient Tethys Ocean in the Mesozoic Era. Slab material still trapped in the transition zone is positioned near the edge of East Gondwana at 140 Ma suggesting that subduction terminated near the margin of the ancient continent prior to breakup and subsequent dispersal of its subcontinents.« less

  8. Enhanced Southern Ocean marine productivity due to fertilization by giant icebergs

    NASA Astrophysics Data System (ADS)

    Duprat, Luis P. A. M.; Bigg, Grant R.; Wilton, David J.

    2016-03-01

    Primary productivity is enhanced within a few kilometres of icebergs in the Weddell Sea owing to the input of terrigeneous nutrients and trace elements during iceberg melting. However, the influence of giant icebergs, over 18 km in length, on marine primary production in the Southern Ocean is less well studied. Here we present an analysis of 175 satellite images of open ocean colour before and after the passage of 17 giant icebergs between 2003 and 2013. We detect substantially enhanced chlorophyll levels, typically over a radius of at least 4-10 times the iceberg's length, that can persist for more than a month following passage of a giant iceberg. This area of influence is more than an order of magnitude larger than that found for sub-kilometre scale icebergs or in ship-based surveys of giant icebergs. Assuming that carbon export increases by a factor of 5-10 over the area of influence, we estimate that up to a fifth of the Southern Ocean's downward carbon flux originates with giant iceberg fertilization. We suggest that, if giant iceberg calving increases this century as expected, this negative feedback on the carbon cycle may become more important.

  9. The biogeochemical role of baleen whales and krill in Southern Ocean nutrient cycling.

    PubMed

    Ratnarajah, Lavenia; Bowie, Andrew R; Lannuzel, Delphine; Meiners, Klaus M; Nicol, Stephen

    2014-01-01

    The availability of micronutrients is a key factor that affects primary productivity in High Nutrient Low Chlorophyll (HNLC) regions of the Southern Ocean. Nutrient supply is governed by a range of physical, chemical and biological processes, and there are significant feedbacks within the ecosystem. It has been suggested that baleen whales form a crucial part of biogeochemical cycling processes through the consumption of nutrient-rich krill and subsequent defecation, but data on their contribution are scarce. We analysed the concentration of iron, cadmium, manganese, cobalt, copper, zinc, phosphorus and carbon in baleen whale faeces and muscle, and krill tissue using inductively coupled plasma mass spectrometry. Metal concentrations in krill tissue were between 20 thousand and 4.8 million times higher than typical Southern Ocean HNLC seawater concentrations, while whale faecal matter was between 276 thousand and 10 million times higher. These findings suggest that krill act as a mechanism for concentrating and retaining elements in the surface layer, which are subsequently released back into the ocean, once eaten by whales, through defecation. Trace metal to carbon ratios were also higher in whale faeces compared to whale muscle indicating that whales are concentrating carbon and actively defecating trace elements. Consequently, recovery of the great whales may facilitate the recycling of nutrients via defecation, which may affect productivity in HNLC areas.

  10. A mesoscale phytoplankton bloom in the polar Southern Ocean stimulated by iron fertilization.

    PubMed

    Boyd, P W; Watson, A J; Law, C S; Abraham, E R; Trull, T; Murdoch, R; Bakker, D C; Bowie, A R; Buesseler, K O; Chang, H; Charette, M; Croot, P; Downing, K; Frew, R; Gall, M; Hadfield, M; Hall, J; Harvey, M; Jameson, G; LaRoche, J; Liddicoat, M; Ling, R; Maldonado, M T; McKay, R M; Nodder, S; Pickmere, S; Pridmore, R; Rintoul, S; Safi, K; Sutton, P; Strzepek, R; Tanneberger, K; Turner, S; Waite, A; Zeldis, J

    2000-10-12

    Changes in iron supply to oceanic plankton are thought to have a significant effect on concentrations of atmospheric carbon dioxide by altering rates of carbon sequestration, a theory known as the 'iron hypothesis'. For this reason, it is important to understand the response of pelagic biota to increased iron supply. Here we report the results of a mesoscale iron fertilization experiment in the polar Southern Ocean, where the potential to sequester iron-elevated algal carbon is probably greatest. Increased iron supply led to elevated phytoplankton biomass and rates of photosynthesis in surface waters, causing a large drawdown of carbon dioxide and macronutrients, and elevated dimethyl sulphide levels after 13 days. This drawdown was mostly due to the proliferation of diatom stocks. But downward export of biogenic carbon was not increased. Moreover, satellite observations of this massive bloom 30 days later, suggest that a sufficient proportion of the added iron was retained in surface waters. Our findings demonstrate that iron supply controls phytoplankton growth and community composition during summer in these polar Southern Ocean waters, but the fate of algal carbon remains unknown and depends on the interplay between the processes controlling export, remineralisation and timescales of water mass subduction.

  11. Multi-elemental concentrations in the tissues of the oceanic squid Todarodes filippovae from Tasmania and the southern Indian Ocean.

    PubMed

    Kojadinovic, Jessica; Jackson, Christine H; Cherel, Yves; Jackson, George D; Bustamante, Paco

    2011-07-01

    This study investigates 14 elements (Ag, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, V and Zn) in the tissues of the oceanic ommastrephid squid Todarodes filippovae from waters surrounding Île Amsterdam (southern Indian Ocean) and Tasmania (Australia). As for other cephalopod species, the digestive gland and branchial hearts showed the highest concentrations of many elements (Ag, Cd, Se, V and Zn, and Cr and Ni, respectively) highlighting their role in bioaccumulation and detoxification processes. With the exception of As and Hg, the muscles showed relatively low trace element concentrations. Squid size was positively correlated to Ag, As, Cd, Hg and Zn concentrations in Tasmanian squid and negatively correlated to all but Hg and Zn concentrations in Île Amsterdam squid. Furthermore, no differences in elemental concentrations were noted between sexes. There were, however, some differences between mated and non-mated females from Tasmania. Comparing elemental concentrations in squid from both islands, higher concentrations of Cd, Co, Cr, Ni, Pb and V in squid sampled in Île Amsterdam reflect different exposure conditions. When considering T. filippovae as a dietary resource for humans it should be noted that, given their Hg content, squids from Île Amsterdam are not recommended for consumption on a regular basis. Moreover, regardless of the squid's origin, digestive glands should be avoided as Cd and Hg concentrations were above the European Union authorized limits in these organs.

  12. Physiological responses of a Southern Ocean diatom to complex future ocean conditions

    NASA Astrophysics Data System (ADS)

    Boyd, P. W.; Dillingham, P. W.; McGraw, C. M.; Armstrong, E. A.; Cornwall, C. E.; Feng, Y.-Y.; Hurd, C. L.; Gault-Ringold, M.; Roleda, M. Y.; Timmins-Schiffman, E.; Nunn, B. L.

    2016-02-01

    A changing climate is altering many ocean properties that consequently will modify marine productivity. Previous phytoplankton manipulation studies have focused on individual or subsets of these properties. Here, we investigate the cumulative effects of multi-faceted change on a subantarctic diatom Pseudonitzschia multiseries by concurrently manipulating five stressors (light/nutrients/CO2/temperature/iron) that primarily control its physiology, and explore underlying reasons for altered physiological performance. Climate change enhances diatom growth mainly owing to warming and iron enrichment, and both properties decrease cellular nutrient quotas, partially offsetting any effects of decreased nutrient supply by 2100. Physiological diagnostics and comparative proteomics demonstrate the joint importance of individual and interactive effects of temperature and iron, and reveal biased future predictions from experimental outcomes when only a subset of multi-stressors is considered. Our findings for subantarctic waters illustrate how composite regional studies are needed to provide accurate global projections of future shifts in productivity and distinguish underlying species-specific physiological mechanisms.

  13. In situ measurement of the biogeochemical properties of Southern Ocean mesoscale eddies in the Southwest Indian Ocean, April 2014

    NASA Astrophysics Data System (ADS)

    de Villiers, S.; Siswana, K.; Vena, K.

    2015-12-01

    Several open-ocean mesoscale features - a "young" warm-core (anti-cyclonic) eddy at 52° S, an "older" warm-core eddy at 57.5° S and an adjacent cold-core (cyclonic) eddy at 56° S - were surveyed during a R/V S.A. Agulhas II cruise in April 2014. The main aim of the survey was to obtain hydrographical and biogeochemical profile data for contrasting open-ocean eddies in the Southern Ocean, which will be suitable for comparative study and modelling of their heat, salt and nutrient characteristics, and the changes that occur in these properties as warm-core eddies migrate from the polar front southwards. The major result is that the older warm-core eddy at 57.5° S is, at its core, 2.7 °C colder than a younger eddy at 52° S, while its dissolved silicate levels are almost 500 % higher and accompanied by chlorophyll a levels that are more than 200 % higher than that in the younger eddy. A total of 18 CTD stations were occupied in a sector south of the Southwest Indian Ridge, along three transects crossing several mesoscale features identified from satellite altimetry data prior to the cruise. The CTD data, as well as chlorophyll a and dissolved nutrient data (for NO3-, NO2-, PO43- and SiO2), have been processed, quality controlled and made available via the PANGAEA Data Archiving and Publication database at doi:10.1594/PANGAEA.848875.

  14. The Effects of Interactive Stratospheric Chemistry on Antarctic and Southern Ocean Climate Change in a Coupled Atmosphere-Ocean General Circulation Model

    NASA Astrophysics Data System (ADS)

    Li, F.; Newman, P. A.; Pawson, S.; Waugh, D. W.

    2014-12-01

    Stratospheric ozone depletion has played a dominant role in driving Antarctic climate change in the last decades. In order to capture the stratospheric ozone forcing, many coupled atmosphere-ocean general circulation models (AOGCMs) prescribe the Antarctic ozone hole using monthly and zonally averaged ozone field. However, the prescribed ozone hole has a high ozone bias and lacks zonal asymmetry. The impacts of these biases on model simulations, particularly on Southern Ocean and the Antarctic sea ice, are not well understood. The purpose of this study is to determine the effects of using interactive stratospheric chemistry instead of prescribed ozone on Antarctic and Southern Ocean climate change in an AOGCM. We compare two sets of ensemble simulations for the 1960-2010 period using different versions of the Goddard Earth Observing System 5 - AOGCM: one with interactive stratospheric chemistry, and the other with prescribed monthly and zonally averaged ozone and 6 other stratospheric radiative species calculated from the interactive chemistry simulations. Consistent with previous studies using prescribed sea surface temperatures and sea ice concentrations, the interactive chemistry runs simulate a deeper Antarctic ozone hole and consistently larger changes in surface pressure and surface winds than the prescribed ozone runs. The use of a coupled atmosphere-ocean model in this study enables us to determine the impact of these surface trend differences on Southern Ocean circulation and Antarctic sea ice. The larger surface wind trends in the interactive chemistry case lead to larger Southern Ocean circulation trends with stronger changes in northerly and westerly surface flow near the Antarctica continent and stronger upwelling near 60ºS. Using interactive chemistry also simulates a larger decrease of sea ice concentrations. Our results highlight the importance of using interactive chemistry in order to correctly capture the influences of stratospheric ozone

  15. Biological productivity regime and associated N cycling in the vicinity of Kerguelen Island area, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Cavagna, A. J.; Fripiat, F.; Elskens, M.; Dehairs, F.; Mangion, P.; Chirurgien, L.; Closset, I.; Lasbleiz, M.; Flores-Leiva, L.; Cardinal, D.; Leblanc, K.; Fernandez, C.; Lefèvre, D.; Oriol, L.; Blain, S.; Quéguiner, B.

    2014-12-01

    Although the Southern Ocean is considered a High Nutrient Low Chlorophyll area (HNLC), massive and recurrent blooms are observed over and downstream the Kerguelen Plateau. This mosaic of blooms is triggered by a higher iron supply resulting from the interaction between the Antarctic Circumpolar Current and the local bathymetry. Net primary production, N-uptake (NO3- and NH4+), and nitrification rates were measured at 8 stations in austral spring 2011 (October-November) during the KEOPS2 cruise in the Kerguelen area. Iron fertilization stimulates primary production, with integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m-2 d-1 and up to 0.31 d-1, respectively) compared to the HNLC reference site (12 mmol C m-2 d-1 and 0.06 d-1, respectively). Primary production is mainly sustained by nitrate uptake, with f ratio (corresponding to NO3- uptake/(NO3- uptake + NH4+ uptake)) lying in the upper end of the observations for the Southern Ocean (up to 0.9). Unexpectedly, we report unprecedented rates of nitrification (up to ~3 mmol C m-2 d-1, with ~90% of them <1 mmol C m-2 d-1). It appears that nitrate is assimilated in the upper part of the mixed layer (coinciding with the euphotic layer) and regenerated in the lower parts. We suggest that such high contribution of nitrification to nitrate assimilation is driven by (i) a deep mixed layer, extending well below the euphotic layer, allowing nitrifiers to compete with phytoplankton for the assimilation of ammonium, (ii) extremely high rates of primary production for the Southern Ocean, stimulating the release of dissolved organic matter, and (iii) an efficient food web, allowing the reprocessing of organic N and the retention of nitrogen into the dissolved phase through ammonium, the substrate for nitrification.

  16. Atmospheric occurrence and deposition of hexachlorobenzene and hexachlorocyclohexanes in the Southern Ocean and Antarctic Peninsula

    NASA Astrophysics Data System (ADS)

    Galbán-Malagón, Cristóbal; Cabrerizo, Ana; Caballero, Gemma; Dachs, Jordi

    2013-12-01

    Despite the distance of Antarctica and the Southern Ocean to primary source regions of organochlorine pesticides, such as hexachlorobenzene (HCB) and hexachlorocyclohexanes (HCHs), these organic pollutants are found in this remote region due to long range atmospheric transport and deposition. This study reports the gas- and aerosol-phase concentrations of α-HCH, γ-HCH, and HCB in the atmosphere from the Weddell, South Scotia and Bellingshausen Seas. The atmospheric samples were obtained in two sampling cruises in 2008 and 2009, and in a third sampling campaign at Livingston Island (2009) in order to quantify the potential secondary sources of HCHs and HCB due to volatilization from Antarctic soils and snow. The gas phase concentrations of HCHs and HCB are low, and in the order of very few pg m-3 α-HCH and γ-HCH concentrations were higher when the air mass back trajectory was coming from the Antarctic continent, consistent with net volatilization fluxes of γ-HCH measured at Livingston Island being a significant secondary source to the regional atmosphere. In addition, the Southern ocean is an important net sink of HCHs, and to minor extent of HCB, due to high diffusive air-to-water fluxes. These net absorption fluxes for HCHs are presumably due to the role of bacterial degradation, depleting the water column concentrations of HCHs in surface waters and driving an air-water disequilibrium. This is the first field study that has investigated the coupling between the atmospheric occurrence of HCHs and HCB, the simultaneous air-water exchange, soil/snow-air exchange, and long range transport of organic pollutants in Antarctica and the Southern Ocean.

  17. Diatom species abundance and morphologically-based dissolution proxies in coastal Southern Ocean assemblages

    NASA Astrophysics Data System (ADS)

    Warnock, Jonathan P.; Scherer, Reed P.

    2015-07-01

    Taphonomic processes alter diatom assemblages in sediments, thus potentially negatively impacting paleoclimate records at various rates across space, time, and taxa. However, quantitative taphonomic data is rarely included in diatom-based paleoenvironmental reconstructions and no objective standard exists for comparing diatom dissolution in sediments recovered from marine depositional settings, including the Southern Ocean's opal belt. Furthermore, identifying changes to diatom dissolution through time can provide insight into the efficiency of both upper water column nutrient recycling and the biological pump. This is significant in that reactive metal proxies (e.g. Al, Ti) in the sediments only account for post-depositional dissolution, not the water column where the majority of dissolution occurs. In order to assess the range of variability of responses to dissolution in a typical Southern Ocean diatom community and provide a quantitative guideline for assessing taphonomic variability in diatoms recovered from core material, a sediment trap sample was subjected to controlled, serial dissolution. By evaluating dissolution-induced changes to diatom species' relative abundance, three preservational categories of diatoms have been identified: gracile, intermediate, and robust. The relative abundances of these categories can be used to establish a preservation grade for diatom assemblages. However, changes to the relative abundances of diatom species in sediment samples may reflect taphonomic or ecological factors. In order to address this complication, relative abundance changes have been tied to dissolution-induced morphological change to the areolae of Fragilariopsis curta, a significant sea-ice indicator in Southern Ocean sediments. This correlation allows differentiation between gracile species loss to dissolution versus ecological factors or sediment winnowing. These results mirror a similar morphological dissolution index from a parallel study utilizing

  18. Cloud and solar radiation biases over the Southern Ocean in climate models (Invited)

    NASA Astrophysics Data System (ADS)

    Bodas-Salcedo, A.; Williams, K. D.; Hyder, P.; Edwards, J. M.; Copsey, D.

    2013-12-01

    Current climate models generally reflect too little solar radiation over the Southern Ocean, which may be the leading cause of the prevalent sea-surface temperature biases in climate models. We study the role of clouds on the solar radiation biases in atmosphere-only simulations of the Cloud Feedback Model Intercomparison Project phase 2 (CFMIP2), which is part of the Climate Model Intercomparison Project phase 5 (CMIP5). The CFMIP2 protocol requests additional diagnostics that are useful to investigate the causes of cloud and radiation biases in models, and their relation with cloud feedbacks. We composite AMIP daily data around cyclone centres in the latitude band between 40S and 70S during the summer. Most of the model biases occur in the cold air side of the cyclone composite, away from the cold front. We show that the cyclone composite accounts for most of the climatological error in that latitudinal band. We then use cloud property estimates from the International Cloud Climatology Project (ISCCP) to classify clouds into different regimes, following the clustering technique of Williams and Webb (2009). The cloud regime labelled as 'mid-level' is the main contributor to the Southern Ocean shortwave radiation biases. We use information from the CALIPSO lidar to investigate in more detail the properties of the 'mid-level' cloud regime. CALIPSO shows that the 'mid-level' cloud regime is dominated by two main cloud types; cloud with tops actually at mid-level, and low-level cloud. We will also present initial analyses of biases in air-sea fluxes over the Southern Ocean in the most recent configuration of the Met Office coupled model.

  19. Antarctic Marine Biodiversity – What Do We Know About the Distribution of Life in the Southern Ocean?

    PubMed Central

    Griffiths, Huw J.

    2010-01-01

    The remote and hostile Southern Ocean is home to a diverse and rich community of life that thrives in an environment dominated by glaciations and strong currents. Marine biological studies in the region date back to the nineteenth century, but despite this long history of research, relatively little is known about the complex interactions between the highly seasonal physical environment and the species that inhabit the Southern Ocean. Oceanographically, the Southern Ocean is a major driver of global ocean circulation and plays a vital role in interacting with the deep water circulation in each of the Pacific, Atlantic, and Indian oceans. The Census of Antarctic Marine Life and the Scientific Committee on Antarctic Research Marine Biodiversity Information Network (SCAR-MarBIN) have strived to coordinate and unify the available scientific expertise and biodiversity data to improve our understanding of Southern Ocean biodiversity. Taxonomic lists for all marine species have been compiled to form the Register of Antarctic Marine Species, which currently includes over 8,200 species. SCAR-MarBIN has brought together over 1 million distribution records for Southern Ocean species, forming a baseline against which future change can be judged. The sample locations and numbers of known species from different regions were mapped and the depth distributions of benthic samples plotted. Our knowledge of the biodiversity of the Southern Ocean is largely determined by the relative inaccessibility of the region. Benthic sampling is largely restricted to the shelf; little is known about the fauna of the deep sea. The location of scientific bases heavily influences the distribution pattern of sample and observation data, and the logistical supply routes are the focus of much of the at-sea and pelagic work. Taxa such as mollusks and echinoderms are well represented within existing datasets with high numbers of georeferenced records. Other taxa, including the species-rich nematodes, are

  20. Regional differences in plastic ingestion among Southern Ocean fur seals and albatrosses.

    PubMed

    Ryan, Peter G; de Bruyn, P J Nico; Bester, Marthán N

    2016-03-15

    We provide data on regional differences in plastic ingestion for two Southern Ocean top predators: Arctocephalus fur seals and albatrosses (Diomedeidae). Fur seals breeding on Macquarie Island in the 1990s excreted small (mainly 2-5 mm) plastic fragments, probably derived secondarily from myctophid fish. No plastic was found in the scats of these seals breeding on three islands in the southwest Indian and central South Atlantic Oceans, despite myctophids dominating their diets at these locations. Compared to recent reports of plastic ingestion by albatrosses off the east coast of South America, we confirm that plastic is seldom found in the stomachs of Thalassarche albatrosses off South Africa, but found no Diomedea albatrosses to contain plastic, compared to 26% off South America. The reasons for such regional differences are unclear, but emphasize the importance of reporting negative as well as positive records of plastic ingestion by marine biota.

  1. Regional differences in plastic ingestion among Southern Ocean fur seals and albatrosses.

    PubMed

    Ryan, Peter G; de Bruyn, P J Nico; Bester, Marthán N

    2016-03-15

    We provide data on regional differences in plastic ingestion for two Southern Ocean top predators: Arctocephalus fur seals and albatrosses (Diomedeidae). Fur seals breeding on Macquarie Island in the 1990s excreted small (mainly 2-5 mm) plastic fragments, probably derived secondarily from myctophid fish. No plastic was found in the scats of these seals breeding on three islands in the southwest Indian and central South Atlantic Oceans, despite myctophids dominating their diets at these locations. Compared to recent reports of plastic ingestion by albatrosses off the east coast of South America, we confirm that plastic is seldom found in the stomachs of Thalassarche albatrosses off South Africa, but found no Diomedea albatrosses to contain plastic, compared to 26% off South America. The reasons for such regional differences are unclear, but emphasize the importance of reporting negative as well as positive records of plastic ingestion by marine biota. PMID:26827096

  2. Observation and parameterization of small icebergs: Drifting breakwaters in the southern ocean

    NASA Astrophysics Data System (ADS)

    Ardhuin, Fabrice; Tournadre, Jean; Queffeulou, Pierre; Girard-Ardhuin, Fanny; Collard, Fabrice

    The variability of small-size iceberg distributions is revealed from a novel analysis of satellite altimeter data. A strong annual cycle is modulated by pulse-like events confined to single ocean basins, with dense iceberg populations in the South Atlantic in 2004-2005, and in the South Pacific in 2008. Anomalies in sea surface temperatures of the order of 1 °C may be related to the iceberg distribution. Icebergs also appear very strongly associated with anomalies in the heights of ocean waves. A preliminary parameterization of wave blocking by icebergs significantly reduces wave model errors in the region south of 45° South, and has a perceptible influence on all the west coasts of the Southern hemisphere.

  3. How many species in the Southern Ocean? Towards a dynamic inventory of the Antarctic marine species

    NASA Astrophysics Data System (ADS)

    De Broyer, Claude; Danis, Bruno; with 64 SCAR-MarBIN Taxonomic Editors

    2011-03-01

    The IPY sister-projects CAML and SCAR-MarBIN provided a timely opportunity, a strong collaborative framework and an appropriate momentum to attempt assessing the "Known, Unknown and Unknowable" of Antarctic marine biodiversity. To allow assessing the known biodiversity, SCAR-MarBIN "Register of Antarctic Marine Species (RAMS)" was compiled and published by a panel of 64 taxonomic experts. Thanks to this outstanding expertise mobilized for the first time, an accurate list of more than 8100 valid species was compiled and an up-to-date systematic classification comprising more than 16,800 taxon names was established. This taxonomic information is progressively and systematically completed by species occurrence data, provided by literature, taxonomic and biogeographic databases, new data from CAML and other cruises, and museum collections. RAMS primary role was to establish a benchmark of the present taxonomic knowledge of the Southern Ocean biodiversity, particularly important in the context of the growing realization of potential impacts of the global change on Antarctic ecosystems. This, in turn, allowed detecting gaps in knowledge, taxonomic treatment and coverage, and estimating the importance of the taxonomic impediment, as well as the needs for more complete and efficient taxonomic tools. A second, but not less important, role of RAMS was to contribute to the "taxonomic backbone" of the SCAR-MarBIN, OBIS and GBIF networks, to establish a dynamic information system on Antarctic marine biodiversity for the future. The unknown part of the Southern Ocean biodiversity was approached by pointing out what remains to be explored and described in terms of geographical locations and bathymetric zones, habitats, or size classes of organisms. The growing importance of cryptic species is stressed, as they are more and more often detected by molecular studies in several taxa. Relying on RAMS results and on some case studies of particular model groups, the question of the

  4. Sources and sinks of momentum in the Southern Ocean State Estimate

    NASA Astrophysics Data System (ADS)

    Masich, J.; Chereskin, T. K.; Mazloff, M. R.

    2015-12-01

    Strong, persistent winds over the Southern Ocean drive the Antarctic Circumpolar Current (ACC) on an unblocked eastward path around Antarctica. Observations and reanalyses have shown that Southern Ocean winds have increased over the past 60 years [Thompson, 2002; Swart and Fyfe, 2012]. ACC baroclinic transport appears to remain stable [Böning et al., 2008], however, suggesting that the interior mechanisms that output momentum from the Antarctic Circumpolar Current (ACC) system are counterbalancing changes in the input wind stress. Here we describe where and how momentum exits the ACC system in a six-year, eddy permitting state estimate of the Southern Ocean. We find that 95% of the zonal momentum input via wind stress at the surface is balanced by topographic form stress across ocean ridges, while the remaining 5% is balanced via bottom friction and momentum flux divergences at the northern and southern boundaries of the analysis domain. While the time-mean zonal wind stress field exhibits a relatively uniform spatial distribution, time-mean topographic form stress concentrates at shallow ridges and across the continents that lie within the ACC latitudes -- primarily Kerguelen Plateau, the Macquarie Ridge region, and South America and the Drake Passage fracture zones -- as well as across deep basins separated by basin-scale plains. Topographic form stress can be divided into shallow and deep regimes: the shallow regime contributes most of the westward form stress that serves as a momentum sink for the ACC system, while the deep regime consists of strong eastward and westward form stresses that largely cancel in the zonal integral. The time-varying form stress signal, integrated longitudinally and over the ACC latitudes, tracks closely with the wind stress signal integrated over the same domain; at zero lag, 88% of the variance in the six-year form stress time series can be explained by the wind stress signal, indicating that changes in the integrated wind stress

  5. Life at the front: history, ecology and change on southern ocean islands.

    PubMed

    Bergstrom; Chown

    1999-12-01

    Terrestrial ecosystems of southern ocean islands have enjoyed renewed attention recently owing to the discovery that their climates are changing dramatically. This has led to an enhanced understanding of the biogeography of this region, and an increased awareness that these ecosystems provide unrivalled opportunities for investigating the impacts of environmental change on interactions between invasive and indigenous species. Recent studies have revealed increases in the abundance of established alien species and in the strength of their negative impacts on local biota, especially through indirect interactions. Also, increases in island temperature and human visitor frequency are likely to result in increasing numbers of successful alien colonization events. PMID:10542453

  6. Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota.

    PubMed

    Constable, Andrew J; Melbourne-Thomas, Jessica; Corney, Stuart P; Arrigo, Kevin R; Barbraud, Christophe; Barnes, David K A; Bindoff, Nathaniel L; Boyd, Philip W; Brandt, Angelika; Costa, Daniel P; Davidson, Andrew T; Ducklow, Hugh W; Emmerson, Louise; Fukuchi, Mitsuo; Gutt, Julian; Hindell, Mark A; Hofmann, Eileen E; Hosie, Graham W; Iida, Takahiro; Jacob, Sarah; Johnston, Nadine M; Kawaguchi, So; Kokubun, Nobuo; Koubbi, Philippe; Lea, Mary-Anne; Makhado, Azwianewi; Massom, Rob A; Meiners, Klaus; Meredith, Michael P; Murphy, Eugene J; Nicol, Stephen; Reid, Keith; Richerson, Kate; Riddle, Martin J; Rintoul, Stephen R; Smith, Walker O; Southwell, Colin; Stark, Jonathon S; Sumner, Michael; Swadling, Kerrie M; Takahashi, Kunio T; Trathan, Phil N; Welsford, Dirk C; Weimerskirch, Henri; Westwood, Karen J; Wienecke, Barbara C; Wolf-Gladrow, Dieter; Wright, Simon W; Xavier, Jose C; Ziegler, Philippe

    2014-10-01

    Antarctic and Southern Ocean (ASO) marine ecosystems have been changing for at least the last 30 years, including in response to increasing ocean temperatures and changes in the extent and seasonality of sea ice; the magnitude and direction of these changes differ between regions around Antarctica that could see populations of the same species changing differently in different regions. This article reviews current and expected changes in ASO physical habitats in response to climate change. It then reviews how these changes may impact the autecology of marine biota of this polar region: microbes, zooplankton, salps, Antarctic krill, fish, cephalopods, marine mammals, seabirds, and benthos. The general prognosis for ASO marine habitats is for an overall warming and freshening, strengthening of westerly winds, with a potential pole-ward movement of those winds and the frontal systems, and an increase in ocean eddy activity. Many habitat parameters will have regionally specific changes, particularly relating to sea ice characteristics and seasonal dynamics. Lower trophic levels are expected to move south as the ocean conditions in which they are currently found move pole-ward. For Antarctic krill and finfish, the latitudinal breadth of their range will depend on their tolerance of warming oceans and changes to productivity. Ocean acidification is a concern not only for calcifying organisms but also for crustaceans such as Antarctic krill; it is also likely to be the most important change in benthic habitats over the coming century. For marine mammals and birds, the expected changes primarily relate to their flexibility in moving to alternative locations for food and the energetic cost of longer or more complex foraging trips for those that are bound to breeding colonies. Few species are sufficiently well studied to make comprehensive species-specific vulnerability assessments possible. Priorities for future work are discussed.

  7. Increasing vertical mixing to reduce Southern Ocean deep convection in NEMO3.4

    NASA Astrophysics Data System (ADS)

    Heuzé, C.; Ridley, J. K.; Calvert, D.; Stevens, D. P.; Heywood, K. J.

    2015-10-01

    Most CMIP5 (Coupled Model Intercomparison Project Phase 5) models unrealistically form Antarctic Bottom Water by open ocean deep convection in the Weddell and Ross seas. To identify the mechanisms triggering Southern Ocean deep convection in models, we perform sensitivity experiments on the ocean model NEMO3.4 forced by prescribed atmospheric fluxes. We vary the vertical velocity scale of the Langmuir turbulence, the fraction of turbulent kinetic energy transferred below the mixed layer, and the background diffusivity and run short simulations from 1980. All experiments exhibit deep convection in the Riiser-Larsen Sea in 1987; the origin is a positive sea ice anomaly in 1985, causing a shallow anomaly in mixed layer depth, hence anomalously warm surface waters and subsequent polynya opening. Modifying the vertical mixing impacts both the climatological state and the associated surface anomalies. The experiments with enhanced mixing exhibit colder surface waters and reduced deep convection. The experiments with decreased mixing give warmer surface waters, open larger polynyas causing more saline surface waters and have deep convection across the Weddell Sea until the simulations end. Extended experiments reveal an increase in the Drake Passage transport of 4 Sv each year deep convection occurs, leading to an unrealistically large transport at the end of the simulation. North Atlantic deep convection is not significantly affected by the changes in mixing parameters. As new climate model overflow parameterisations are developed to form Antarctic Bottom Water more realistically, we argue that models would benefit from stopping Southern Ocean deep convection, for example by increasing their vertical mixing.

  8. Oxygen depletion recorded in upper waters of the glacial Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lu, Zunli; Hoogakker, Babette A. A.; Hillenbrand, Claus-Dieter; Zhou, Xiaoli; Thomas, Ellen; Gutchess, Kristina M.; Lu, Wanyi; Jones, Luke; Rickaby, Rosalind E. M.

    2016-03-01

    Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ~2.5 μmol mol-1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg-1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline.

  9. Competition between ocean carbon pumps in simulations with varying Southern Hemisphere westerly wind forcing

    NASA Astrophysics Data System (ADS)

    Huiskamp, W. N.; Meissner, K. J.; d'Orgeville, M.

    2016-06-01

    We analyse the impact of migration and strength of Southern Hemisphere westerly winds on the ocean carbon cycle in a systematic sensitivity study with the University of Victoria Earth System Climate Model. We find that changes in the biological pump are mainly driven by changes in ocean residence times while changes in export production are negligible. Changes in the biological and physical pumps are always of opposite sign; with the physical pump being dominant for southward shifts and the biological pump being dominant for northward shifts. Furthermore, changes in the Pacific Ocean carbon budget dictate the overall changes in global marine and atmospheric carbon. Overall, atmospheric hbox {CO}_2 increases (and Δ ^{14}hbox {C} decreases) for northward shifts or a strengthening in wind forcing. The opposite is true for a southward shift or a weakening in wind forcing. Combining forcings (shift and intensity change) results in a combination of their impacts with the direction of the shift being the first order forcing. The terrestrial carbon reservoir absorbs (releases) 50-70 % of the net oceanic carbon loss (increase), counterbalancing the effect on atmospheric hbox {CO}_2.

  10. Oxygen depletion recorded in upper waters of the glacial Southern Ocean

    PubMed Central

    Lu, Zunli; Hoogakker, Babette A. A.; Hillenbrand, Claus-Dieter; Zhou, Xiaoli; Thomas, Ellen; Gutchess, Kristina M.; Lu, Wanyi; Jones, Luke; Rickaby, Rosalind E. M.

    2016-01-01

    Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ∼2.5 μmol mol−1 indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg−1 during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline. PMID:27029225

  11. Oxygen depletion recorded in upper waters of the glacial Southern Ocean.

    PubMed

    Lu, Zunli; Hoogakker, Babette A A; Hillenbrand, Claus-Dieter; Zhou, Xiaoli; Thomas, Ellen; Gutchess, Kristina M; Lu, Wanyi; Jones, Luke; Rickaby, Rosalind E M

    2016-01-01

    Oxygen depletion in the upper ocean is commonly associated with poor ventilation and storage of respired carbon, potentially linked to atmospheric CO2 levels. Iodine to calcium ratios (I/Ca) in recent planktonic foraminifera suggest that values less than ∼2.5 μmol mol(-1) indicate the presence of O2-depleted water. Here we apply this proxy to estimate past dissolved oxygen concentrations in the near surface waters of the currently well-oxygenated Southern Ocean, which played a critical role in carbon sequestration during glacial times. A down-core planktonic I/Ca record from south of the Antarctic Polar Front (APF) suggests that minimum O2 concentrations in the upper ocean fell below 70 μmol kg(-1) during the last two glacial periods, indicating persistent glacial O2 depletion at the heart of the carbon engine of the Earth's climate system. These new estimates of past ocean oxygenation variability may assist in resolving mechanisms responsible for the much-debated ice-age atmospheric CO2 decline. PMID:27029225

  12. El Nino-southern oscillation simulated in an MRI atmosphere-ocean coupled general circulation model

    SciTech Connect

    Nagai, T.; Tokioka, T.; Endoh, M.; Kitamura, Y. )

    1992-11-01

    A coupled atmosphere-ocean general circulation model (GCM) was time integrated for 30 years to study interannual variability in the tropics. The atmospheric component is a global GCM with 5 levels in the vertical and 4[degrees]latitude X 5[degrees] longitude grids in the horizontal including standard physical processes (e.g., interactive clouds). The oceanic component is a GCM for the Pacific with 19 levels in the vertical and 1[degrees]x 2.5[degrees] grids in the horizontal including seasonal varying solar radiation as forcing. The model succeeded in reproducing interannual variations that resemble the El Nino-Southern Oscillation (ENSO) with realistic seasonal variations in the atmospheric and oceanic fields. The model ENSO cycle has a time scale of approximately 5 years and the model El Nino (warm) events are locked roughly in phase to the seasonal cycle. The cold events, however, are less evident in comparison with the El Nino events. The time scale of the model ENSO cycle is determined by propagation time of signals from the central-eastern Pacific to the western Pacific and back to the eastern Pacific. Seasonal timing is also important in the ENSO time scale: wind anomalies in the central-eastern Pacific occur in summer and the atmosphere ocean coupling in the western Pacific operates efficiently in the first half of the year.

  13. Experiments on the Southern Oscillation with CAM3 coupled to a Mixed Layer Ocean

    NASA Astrophysics Data System (ADS)

    Monier, E.; Sokolov, A. P.

    2010-12-01

    Recent modeling studies suggest that the atmospheric component plays a dominant role in the El Nino/Southern Oscillation (ENSO) phenomenon. In particular, simulations in which an Atmospheric General Circulation Model (AGCM) is coupled to a mixed-layer ocean model can produce ‘ENSO-like’ variability with associated patterns in SST, precipitation, or atmospheric circulation similar to that of ENSO, and referred to as 'Atmospheric Walker Mode' (AWM). In the absence of Bjerknes feedback (no ocean dynamics), the AWM relies on ocean-to-atmosphere latent heat flux and cloud forcing feedback. To study the AWM, we perform a number of experiments using the Community Atmosphere Model (CAM) version 3 coupled to a mixed-layer ocean, including varying the model resolution and the depth of the mixed layer. We investigate the possible climate change impacts on the AWM by carrying out a number of equilibrium climate change simulations for a doubled CO2 with different values of the model's climate sensitivity. Results show that both the magnitude and the periodicity of the simulated AWM are rather different. This study provides further insight into the ENSO response to increasing greenhouse gas—induced radiative forcing.

  14. Calibration of fossil scleraxonian Southern Ocean deep-sea corals for U-series dating

    NASA Astrophysics Data System (ADS)

    Gutjahr, M.; Vance, D.; Hoffmann, D.; Hillenbrand, C.; Kuhn, G.

    2008-12-01

    The deep Southern Ocean has been pinpointed as candidate reservoir capable of storing the additional respired carbon that was drawn from the atmosphere during the Last Glacial Maximum compared with the present-day. In this context the determination of deep ocean ventilation ages is a commonly applied tool, potentially identifying radiocarbon depletion in glacial deep water and enhanced ocean stratification. In order to derive deep-sea ventilation ages most studies to date have used either radiocarbon age differences between paired planktic and benthic foraminifera samples or coupled U-Th and radiocarbon dates obtained from aragonitic deep-sea corals. Results from both these approaches are, however, as yet very scarce for the Southern Ocean. We present calendar ages for a set of deep-sea scleraxonian corals from the Marie Byrd Seamounts in the Amundsen Sea sector of the Southern Ocean (~123°W, ~69°S, 2500 m to 1430 m water depth) employing the 230Th/U-dating method. The aim of our study is to evaluate whether these calcitic octocorals can be used for ventilation age determinations. Our corals have significantly lower uranium concentrations than aragonitic deep-sea corals, ranging from 80 to 250 ng/g. Most corals of Holocene age reproduced the present-day seawater 234U/238U. Pre-Holocene corals, however, show a systematic enrichment of 234U, leading to slightly elevated deglacial initial 234U/238U and significantly higher 234U/238U for ~MIS5 sub-samples. These corals also appear to grow very slowly, on the order of only few μm/year, making it essential to sample as little coral material as possible for combined 230Th/U- and radiocarbon dating purposes. One coral, sampled at high-resolution in various sections returned ages that scatter around 10 ka BP and the early deglaciation, though several significantly older ages were obtained as well. The present-day (234U/238U) ACT in different sections of this coral is very homogenous (1.155 ± 0.003) and more or less

  15. CLOUDS, AEROSOLS, RADIATION AND THE AIR-SEA INTERFACE OF THE SOUTHERN OCEAN: ESTABLISHING DIRECTIONS FOR FUTURE RESEARCH

    SciTech Connect

    Wood, Robert; Bretherton, Chris; McFarquhar, Greg; Protat, Alain; Quinn, Patricia; Siems, Steven; Jakob, Christian; Alexander, Simon; Weller, Bob

    2014-09-29

    A workshop sponsored by the Department of Energy was convened at the University of Washington to discuss the state of knowledge of clouds, aerosols and air-sea interaction over the Southern Ocean and to identify strategies for reducing uncertainties in their representation in global and regional models. The Southern Ocean plays a critical role in the global climate system and is a unique pristine environment, yet other than from satellite, there have been sparse observations of clouds, aerosols, radiation and the air-sea interface in this region. Consequently, much is unknown about atmospheric and oceanographic processes and their linkage in this region. Approximately 60 scientists, including graduate students, postdoctoral fellows and senior researchers working in atmospheric and oceanic sciences at U.S. and foreign universities and government laboratories, attended the Southern Ocean Workshop. It began with a day of scientific talks, partly in plenary and partly in two parallel sessions, discussing the current state of the science for clouds, aerosols and air-sea interaction in the Southern Ocean. After the talks, attendees broke into two working groups; one focused on clouds and meteorology, and one focused on aerosols and their interactions with clouds. This was followed by more plenary discussion to synthesize the two working group discussions and to consider possible plans for organized activities to study clouds, aerosols and the air-sea interface in the Southern Ocean. The agenda and talk slides, including short summaries of the highlights of the parallel session talks developed by the session chars, are available at http://www.atmos.washington.edu/socrates/presentations/SouthernOceanPresentations/.

  16. Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2.

    PubMed

    Watson, A J; Bakker, D C; Ridgwell, A J; Boyd, P W; Law, C S

    2000-10-12

    Photosynthesis by marine phytoplankton in the Southern Ocean, and the associated uptake of carbon, is thought to be currently limited by the availability of iron. One implication of this limitation is that a larger iron supply to the region in glacial times could have stimulated algal photosynthesis, leading to lower concentrations of atmospheric CO2. Similarly, it has been proposed that artificial iron fertilization of the oceans might increase future carbon sequestration. Here we report data from a whole-ecosystem test of the iron-limitation hypothesis in the Southern Ocean, which show that surface uptake of atmospheric CO2 and uptake ratios of silica to carbon by phytoplankton were strongly influenced by nanomolar increases of iron concentration. We use these results to inform a model of global carbon and ocean nutrients, forced with atmospheric iron fluxes to the region derived from the Vostok ice-core dust record. During glacial periods, predicted magnitudes and timings of atmospheric CO2 changes match ice-core records well. At glacial terminations, the model suggests that forcing of Southern Ocean biota by iron caused the initial approximately 40 p.p.m. of glacial-interglacial CO2 change, but other mechanisms must have accounted for the remaining 40 p.p.m. increase. The experiment also confirms that modest sequestration of atmospheric CO2 by artificial additions of iron to the Southern Ocean is in principle possible, although the period and geographical extent over which sequestration would be effective remain poorly known.

  17. A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals.

    PubMed

    Roquet, Fabien; Williams, Guy; Hindell, Mark A; Harcourt, Rob; McMahon, Clive; Guinet, Christophe; Charrassin, Jean-Benoit; Reverdin, Gilles; Boehme, Lars; Lovell, Phil; Fedak, Mike

    2014-01-01

    The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20-140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate.

  18. Marine introductions in the Southern Ocean: an unrecognised hazard to biodiversity.

    PubMed

    Lewis, Patrick N; Hewitt, Chad L; Riddle, Martin; McMinn, Andrew

    2003-02-01

    This study investigated the potential for transport of organisms between Hobart, Macquarie Island and the Antarctic continent by ships used in support of Antarctic science and tourism. Northward transport of plankton in ballast water is more likely than southward transport because ballast is normally loaded in the Antarctic and unloaded at the home port. Culturing of ballast water samples revealed that high-latitude hitchhikers were able to reach greater diversities when cultured at temperate thermal conditions than at typical Southern Ocean temperatures, suggesting the potential for establishment in the Tasmanian coastal environment. Several known invasive species were identified among fouling communities on the hulls of vessels that travel between Hobart and the Southern Ocean. Southward transport of hull fouling species is more likely than northward transport due to the accumulation of assemblages during the winter period spent in the home port of Hobart. This study does not prove that non-indigenous marine species have, or will be, transported and established as a consequence of Antarctic shipping but illustrates that the potential exists. Awareness of the potential risk and simple changes to operating procedures may reduce the chance of introductions in the future.

  19. Macronutrient and trace-metal geochemistry of an in situ iron-induced Southern Ocean bloom

    NASA Astrophysics Data System (ADS)

    Frew, Russell; Bowie, Andrew; Croot, Peter; Pickmere, Stuart

    We have investigated the effect of iron supply and increased phytoplankton growth on the cycling of the macronutrients phosphate, nitrate and silicic acid as well as the micronutrients copper (Cu), nickel (Ni), zinc (Zn) and cadmium (Cd). Nutrient levels were measured in situ in an iron-induced phytoplankton bloom at 61°S 140°E in the Southern Ocean Iron Release experiment (SOIREE). Nutrient ratios upon arrival at the study site indicate that much of the seasonal phytoplankton productivity was by iron-limited diatoms growing at low mean light levels. The addition of iron (Fe) induced a bloom that led to a draw-down in the macronutrients in ratios consistent with the growth of diatoms under iron-replete conditions. None of the bioutilised trace metals Cu, Ni, Zn or Cd showed any indication of co-limitation, with Fe, of phytoplankton growth. Zn concentrations did not decrease by algal uptake as expected. Cd was partitioned to the particulate phase indicating consumption by the algae. Cd was preferentially utilised with respect to P with a αCd/P=5.8. Interpretation of the Cd/Ca data from the sedimentary record using this higher induced αCd/P value would imply even higher Southern Ocean surface water P during the last glacial maximum.

  20. A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals

    PubMed Central

    Roquet, Fabien; Williams, Guy; Hindell, Mark A.; Harcourt, Rob; McMahon, Clive; Guinet, Christophe; Charrassin, Jean-Benoit; Reverdin, Gilles; Boehme, Lars; Lovell, Phil; Fedak, Mike

    2014-01-01

    The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20–140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate. PMID:25977785

  1. Salp/krill interactions in the Southern Ocean: spatial segregation and implications for the carbon flux

    NASA Astrophysics Data System (ADS)

    Pakhomov, E. A.; Froneman, P. W.; Perissinotto, R.

    Available data on the spatial distribution and feeding ecophysiology of Antarctic krill, Euphausia superba, and the tunicate, Salpa thompsoni, in the Southern Ocean are summarized in this study. Antarctic krill and salps generally display pronounced spatial segregation at all spatial scales. This appears to be the result of a clear biotopical separation of these key species in the Antarctic pelagic food web. Krill and salps are found in different water masses or water mass modifications, which are separated by primary or secondary frontal features. On the small-scale (<100 km), Antarctic krill and salps are usually restricted to the specific water parcels, or are well segregated vertically. Krill and salp grazing rates estimated using the in situ gut fluorescence technique are among the highest recorded in the Antarctic pelagic food web. Although krill and salps at times may remove the entire daily primary production, generally their grazing impact is moderate (⩽50% of primary production). The regional ecological consequences of years of high salp densities may be dramatic. If the warming trend, which is observed around the Antarctic Peninsula and in the Southern Ocean, continues, salps may become a more prominent player in the trophic structure of the Antarctic marine ecosystem. This likely would be coupled with a dramatic decrease in krill productivity, because of a parallel decrease in the spatial extension of the krill biotope. The high Antarctic regions, particularly the Marginal Ice Zone, have, however, effective physiological mechanisms that may provide protection against the salp invasion.

  2. Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo

    PubMed Central

    McCoy, Daniel T.; Burrows, Susannah M.; Wood, Robert; Grosvenor, Daniel P.; Elliott, Scott M.; Ma, Po-Lun; Rasch, Phillip J.; Hartmann, Dennis L.

    2015-01-01

    Atmospheric aerosols, suspended solid and liquid particles, act as nucleation sites for cloud drop formation, affecting clouds and cloud properties—ultimately influencing the cloud dynamics, lifetime, water path, and areal extent that determine the reflectivity (albedo) of clouds. The concentration Nd of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations affect not only cloud properties themselves but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. It is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed Nd. Enhanced Nd is spatially correlated with regions of high chlorophyll a, and the spatiotemporal variability in Nd is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35o to 45oS) and by organic matter in sea spray aerosol at higher latitudes (45o to 55oS). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m–2 over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere. PMID:26601216

  3. Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo.

    PubMed

    McCoy, Daniel T; Burrows, Susannah M; Wood, Robert; Grosvenor, Daniel P; Elliott, Scott M; Ma, Po-Lun; Rasch, Phillip J; Hartmann, Dennis L

    2015-07-01

    Atmospheric aerosols, suspended solid and liquid particles, act as nucleation sites for cloud drop formation, affecting clouds and cloud properties-ultimately influencing the cloud dynamics, lifetime, water path, and areal extent that determine the reflectivity (albedo) of clouds. The concentration N d of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations affect not only cloud properties themselves but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. It is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed N d. Enhanced N d is spatially correlated with regions of high chlorophyll a, and the spatiotemporal variability in N d is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35(o) to 45(o)S) and by organic matter in sea spray aerosol at higher latitudes (45(o) to 55(o)S). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m(-2) over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere.

  4. Natural Aerosols Explain Seasonal and Spatial Patterns of Southern Ocean Cloud Albedo

    SciTech Connect

    McCoy, Daniel; Burrows, Susannah M.; Wood, R.; Grosvenor, Daniel P.; Elliott, Scott; Ma, Po-Lun; Rasch, Philip J.; Hartmann, Dennis L.

    2015-07-17

    Small particles called aerosols act as nucleation sites for cloud drop formation, affecting clouds and cloud properties – ultimately influencing the cloud dynamics, lifetime, water path and areal extent that determine the reflectivity (albedo) of clouds. The concentration Nd of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations not only affect cloud properties themselves, but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. Here, it is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed Nd. Enhanced Nd over regions of high biological activity is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35-45°S) and by organic matter in sea spray aerosol at higher latitudes (45-55°S). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m-2 over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere.

  5. Ecosystem services of the Southern Ocean: trade-offs in decision-making.

    PubMed

    Grant, Susie M; Hill, Simeon L; Trathan, Philip N; Murphy, Eugene J

    2013-10-01

    Ecosystem services are the benefits that mankind obtains from natural ecosystems. Here we identify the key services provided by the Southern Ocean. These include provisioning of fishery products, nutrient cycling, climate regulation and the maintenance of biodiversity, with associated cultural and aesthetic benefits. Potential catch limits for Antarctic krill (Euphausia superba Dana) alone are equivalent to 11% of current global marine fisheries landings. We also examine the extent to which decision-making within the Antarctic Treaty System (ATS) considers trade-offs between ecosystem services, using the management of the Antarctic krill fishery as a case study. Management of this fishery considers a three-way trade-off between fisheries performance, the status of the krill stock and that of predator populations. However, there is a paucity of information on how well these components represent other ecosystem services that might be degraded as a result of fishing. There is also a lack of information on how beneficiaries value these ecosystem services. A formal ecosystem assessment would help to address these knowledge gaps. It could also help to harmonize decision-making across the ATS and promote global recognition of Southern Ocean ecosystem services by providing a standard inventory of the relevant ecosystem services and their value to beneficiaries.

  6. Natural aerosols explain seasonal and spatial patterns of Southern Ocean cloud albedo.

    PubMed

    McCoy, Daniel T; Burrows, Susannah M; Wood, Robert; Grosvenor, Daniel P; Elliott, Scott M; Ma, Po-Lun; Rasch, Phillip J; Hartmann, Dennis L

    2015-07-01

    Atmospheric aerosols, suspended solid and liquid particles, act as nucleation sites for cloud drop formation, affecting clouds and cloud properties-ultimately influencing the cloud dynamics, lifetime, water path, and areal extent that determine the reflectivity (albedo) of clouds. The concentration N d of droplets in clouds that influences planetary albedo is sensitive to the availability of aerosol particles on which the droplets form. Natural aerosol concentrations affect not only cloud properties themselves but also modulate the sensitivity of clouds to changes in anthropogenic aerosols. It is shown that modeled natural aerosols, principally marine biogenic primary and secondary aerosol sources, explain more than half of the spatiotemporal variability in satellite-observed N d. Enhanced N d is spatially correlated with regions of high chlorophyll a, and the spatiotemporal variability in N d is found to be driven primarily by high concentrations of sulfate aerosol at lower Southern Ocean latitudes (35(o) to 45(o)S) and by organic matter in sea spray aerosol at higher latitudes (45(o) to 55(o)S). Biogenic sources are estimated to increase the summertime mean reflected solar radiation in excess of 10 W m(-2) over parts of the Southern Ocean, which is comparable to the annual mean increases expected from anthropogenic aerosols over heavily polluted regions of the Northern Hemisphere. PMID:26601216

  7. Biomass and energy transfer to baleen whales in the South Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Reilly, S.; Hedley, S.; Borberg, J.; Hewitt, R.; Thiele, D.; Watkins, J.; Naganobu, M.

    2004-06-01

    Baleen whales are an important group of predators on Antarctic krill in the Southern Ocean. During the CCAMLR 2000 Survey to estimate the biomass and distribution of Antarctic krill, International Whaling Commission observers carried out a visual line transect survey to estimate the number of baleen whales occurring in the survey area. This paper reviews techniques used to estimate krill consumption by baleen whales and in combination with estimates of whale abundance estimates of krill consumption are generated for the South Atlantic sector of the Southern Ocean. This survey estimates that the present populations of whales feeding in this region are likely to consume approximately 1.6 million tonnes, but possibly up to as much as 2.7 million tonnes of krill within the summer season. Although this only represents 4-6% of the estimated krill biomass in the region (and probably less than this percentage of the total annual krill production), the depleted numbers of baleen whales resulting from past or current whaling activities should be taken into account when setting quotas for the commercial exploitation of krill if there is to be a recovery to pre-exploitation biomass levels of baleen whales.

  8. Year-round observations of carbon biomass and flux variability in the Southern Ocean

    SciTech Connect

    Bishop, James K.B.; Wood, Todd

    2009-02-01

    Three Carbon Explorer (CE) floats profiling to kilometer depths in the Southern Ocean tracked dawn-dusk variations of mixing/stratification, particulate organic carbon (POC), and light scattering and sedimentation at 100, 250, and 800 m continuously from January 2002 to April 2003. Data were analyzed in conjunction with contemporaneous satellite winds and chlorophyll and derived subsurface light fields. The CE deployed at 66{sup o}S 172{sup o}W operated in the ice edge zone in absence of light. Two CEs deployed at 55{sup o}S 172{sup o}W recorded wintertime mixing to {approx}400 m, yet observed very different bloom dynamics and sedimentation the following spring. Four hypotheses are explored. The strongest is that shallow transient stratification of the deep winter mixed layer to shallower than photosynthetic critical depth occurred more frequently in the non-bloom/higher sedimentation case. The lower particle export to 800 m under the bloom was hypothesized to be due to higher interception of sinking carbon by a relatively starved over wintering zooplankton population. In the Southern Ocean surface phytoplankton biomass may counter indicate particle flux at kilometer depths.

  9. A Southern Indian Ocean database of hydrographic profiles obtained with instrumented elephant seals.

    PubMed

    Roquet, Fabien; Williams, Guy; Hindell, Mark A; Harcourt, Rob; McMahon, Clive; Guinet, Christophe; Charrassin, Jean-Benoit; Reverdin, Gilles; Boehme, Lars; Lovell, Phil; Fedak, Mike

    2014-01-01

    The instrumentation of southern elephant seals with satellite-linked CTD tags has offered unique temporal and spatial coverage of the Southern Indian Ocean since 2004. This includes extensive data from the Antarctic continental slope and shelf regions during the winter months, which is outside the conventional areas of Argo autonomous floats and ship-based studies. This landmark dataset of around 75,000 temperature and salinity profiles from 20-140 °E, concentrated on the sector between the Kerguelen Islands and Prydz Bay, continues to grow through the coordinated efforts of French and Australian marine research teams. The seal data are quality controlled and calibrated using delayed-mode techniques involving comparisons with other existing profiles as well as cross-comparisons similar to established protocols within the Argo community, with a resulting accuracy of ±0.03 °C in temperature and ±0.05 in salinity or better. The data offer invaluable new insights into the water masses, oceanographic processes and provides a vital tool for oceanographers seeking to advance our understanding of this key component of the global ocean climate. PMID:25977785

  10. Pairwise surface drifter separation in the western Pacific sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    van Sebille, Erik; Waterman, Stephanie; Barthel, Alice; Lumpkin, Rick; Keating, Shane R.; Fogwill, Chris; Turney, Chris

    2015-10-01

    The Southern Ocean plays a critical role in global climate, yet the mixing properties of the circulation in this part of the ocean remain poorly understood. Here dispersion in the vicinity of the Southern Antarctic Circumpolar Current Front, one of the branches of the Antarctic Circumpolar Current, is studied using 10 pairs of surface drifters deployed systematically across the frontal jet and its flanks. Drifter pairs were deployed with an initial separation of 13 m and report their position every hour. The separation of the pairs over 7 months, in terms of their Finite-Scale Lyapunov Exponents (FSLE), dispersion, and diffusivity, is characterized and related to expected behavior from Quasi-Geostrophic (QG) and Surface Quasi-Geostrophic (SQG) theories. The FSLE analysis reveals two submesoscale regimes, with SQG-like behavior at scales below 3.2 km and mixed QG/SQG behavior at scales between 3.2 and 73 km. The dispersion analysis, however, suggests QG-like behavior for the smallest scales. Both dispersion and diffusivity appear isotropic for scales up to 500 km. Finally, there is no clear indication of a cross-jet variation of drifter dispersion.

  11. Paleocene/Eocene boundary changes in atmospheric and oceanic circulation: A Southern Hemisphere record

    SciTech Connect

    Hovan, S.A.; Rea, D.K. )

    1992-01-01

    Deep Sea Drilling Project (DSDP) Site 215 provides an expanded section across the Paleocene/Eocene boundary, the most complete mid-latitude sequence from a Southern Hemisphere location in the Indo-Pacific area. The events of this transition occurred during a span of about 1.2 m.y. Oxygen isotope values derived from benthic foraminiferal calcite decrease by about 1.0{per thousand}, a decrease most likely related to warming of deep ocean waters. Turnovers of benthic foraminifera accompany {delta}{sup 18}O changes and culminate in the predominant extinction event at the end of the Paleocene Epoch. Carbon isotope ratios also shift dramatically toward lighter values near the end of the Paleocene, beginning about 0.45 m.y. after oxygen isotope values start to change. The intensity of Southern Hemisphere atmospheric circulation as recorded by grain sizes of eolian particles shows a large and rapid reduction beginning another 0.45 m.y. later. A significant reduction of zonal wind strength at the Paleocene/Eocene boundary, until now observed only at Northern Hemisphere locations, appears to have been a global phenomenon related to decreased latitudinal thermal gradients occasioned by more effective poleward heat transport via the deep ocean.

  12. Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean.

    PubMed

    Samaran, Flore; Stafford, Kathleen M; Branch, Trevor A; Gedamke, Jason; Royer, Jean-Yves; Dziak, Robert P; Guinet, Christophe

    2013-01-01

    Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four "acoustic populations" occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds. PMID:23967221

  13. Seasonal and geographic variation of southern blue whale subspecies in the Indian Ocean.

    PubMed

    Samaran, Flore; Stafford, Kathleen M; Branch, Trevor A; Gedamke, Jason; Royer, Jean-Yves; Dziak, Robert P; Guinet, Christophe

    2013-01-01

    Understanding the seasonal movements and distribution patterns of migratory species over ocean basin scales is vital for appropriate conservation and management measures. However, assessing populations over remote regions is challenging, particularly if they are rare. Blue whales (Balaenoptera musculus spp) are an endangered species found in the Southern and Indian Oceans. Here two recognized subspecies of blue whales and, based on passive acoustic monitoring, four "acoustic populations" occur. Three of these are pygmy blue whale (B.m. brevicauda) populations while the fourth is the Antarctic blue whale (B.m. intermedia). Past whaling catches have dramatically reduced their numbers but recent acoustic recordings show that these oceans are still important habitat for blue whales. Presently little is known about the seasonal movements and degree of overlap of these four populations, particularly in the central Indian Ocean. We examined the geographic and seasonal occurrence of different blue whale acoustic populations using one year of passive acoustic recording from three sites located at different latitudes in the Indian Ocean. The vocalizations of the different blue whale subspecies and acoustic populations were recorded seasonally in different regions. For some call types and locations, there was spatial and temporal overlap, particularly between Antarctic and different pygmy blue whale acoustic populations. Except on the southernmost hydrophone, all three pygmy blue whale acoustic populations were found at different sites or during different seasons, which further suggests that these populations are generally geographically distinct. This unusual blue whale diversity in sub-Antarctic and sub-tropical waters indicates the importance of the area for blue whales in these former whaling grounds.

  14. Inferring source regions and supply mechanisms of iron in the Southern Ocean from satellite data

    NASA Astrophysics Data System (ADS)

    Graham, Robert M.; de Boer, Agatha M.; van Sebille, Erik; kohfeld, Karen E.; Schlosser, Christian

    2016-04-01

    In many biogeochemical models a large shelf sediment iron flux is prescribed through the seafloor over all areas of bathymetry shallower than 1000 m. Here we infer the likely location of shelf sediment iron sources by identifying where mean annual satellite chlorophyll concentrations are enhanced over shallow bathymetry ( > 1000 m). We show that mean annual chlorophyll concentrations are not visibly enhanced over areas of shallow bathymetry located more than 500 km from a coastline. Chlorophyll concentrations > 2 mg m-3 are only found within 50 km of a continental or island coastline. These results suggest that large sedimentary iron fluxes only exist on continental or island shelves. Large sedimentary iron fluxes are unlikely to be found on isolated seamounts and submerged plateaus. We further compare satellite chlorophyll concentrations to the position of ocean fronts to assess the relative role of horizontal advection and upwelling for supplying iron to the ocean surface. Sharp gradients in chlorophyll concentrations are observed across western boundary currents. Large chlorophyll blooms develop where western boundary currents detach from the continental shelves and turn eastwards into the Southern Ocean. Chlorophyll concentrations are enhanced along contours of sea surface height extending off continental and island shelves. These observations support the hypothesis that bioavailable iron from continental shelves is entrained into western boundary currents and advected into the Sub-Antarctic Zone along the Dynamical Subtropical Front. Likewise, iron from island shelves is entrained into nearby fronts and advected downstream. Mean annual chlorophyll concentrations are very low in open ocean regions with large modelled upwelling velocities, where fronts cross over topographic ridges. These results suggests that open ocean upwelling is unlikely to deliver iron to the surface from deep sources such as hydrothermal vents.

  15. Modelling Southern Ocean iceberg drift and decay with FESOM-IB

    NASA Astrophysics Data System (ADS)

    Rackow, Thomas; Wesche, Christine; Timmermann, Ralph; Juricke, Stephan

    2013-04-01

    Icebergs are commonly ignored in current general circulation models despite their connections to ocean stratification, phytoplankton growth and redistribution of freshwater in the Southern Ocean. On the way to fully including icebergs in ocean circulation models, we present FESOM-IB, the high resolution Finite Element Sea Ice - Ocean Model (FESOM) enhanced by an IceBerg drift and decay module developed at AWI Bremerhaven. By solving the momentum equations for iceberg drift, the iceberg trajectory is computed from an evaluation of the FESOM ice/ocean velocity fields and sea surface height at every time step. Icebergs are assumed to be cubical-shaped and treated as Lagrangian point masses having properties such as length, width and height. Simple diagnostic equations for computing the melt rates of icebergs are applied and iceberg dimensions are adjusted accordingly. Therefore the numerical method's stability for the solution of the momentum equations has to be independent from iceberg size. Our numerical procedure proved to be stable across the full range of iceberg classes; small to giant icebergs may be modelled. We present a 3-year simulation of 308 artifical icebergs from 4 different size classes started at 77 circum-Antarctic locations. Melt rates as well as the components of iceberg momentum balance are quantified and the influence of iceberg size on the drift patterns is discussed. In our simulation giant icebergs tend to stay close to the Antarctic coast. They drift westwards in the coastal current and may only leave it at well-defined bifurcation points in the Weddell Sea, the Ross Sea and over the Kerguelen Plateau. In contrast, smaller icebergs show an off-shore drift component early in their lives. Independent of the iceberg size, the dominant iceberg velocity component is changed into eastward as soon as icebergs reach the ACC.

  16. Southern Ocean variability derived from GRACE retrievals, model simulations and in-situ measurements

    NASA Astrophysics Data System (ADS)

    Böning, C.; Timmermann, R.; Macrander, A.; Schröter, J.; Boebel, O.

    2009-04-01

    The Gravity Recovery and Climate Experiment (GRACE) provides estimates of the Earth's static and time-variant gravity field. Solutions from various processing centres (GFZ, CSR, GRGS, JPL etc.) enable us to determine mass redistributions on the globe. Given that land signals are generally large compared to anomalies over the ocean, an assessment of the latter requires a particularly careful filtering of the data. We utilized the Finite Element Sea-Ice Ocean Model (FESOM) to develop a filtering algorithm which relies on the spatial coherency of ocean bottom pressure (OBP) anomalies. Taking large-scale circulation patterns into account, the new filter yields an improved representation of OBP (i.e. ocean mass) variability in the filtered GRACE data. In order to investigate the representation of Antarctic Circumpolar Current (ACC) variability in the pattern-filtered GRACE retrievals, an analysis of OBP anomalies in FESOM results and in-situ measurements has been performed. A bottom pressure recorder array in the ACC region south of Africa (36°S-58°S, 1°W-7°E) provides data from 2002-2008. Based on anomalies of OBP gradients between individual instruments, these in-situ measurements give an estimate of the overall transport variability as well as of the movement of ACC fronts and transport redistribution between different sectors of the ACC. The validation of simulated and satellite-derived OBP anomaly gradients against these data yields a measure for the representation of this variability in FESOM and GRACE. Furthermore, model simulations are used to assess the relation between transport variations in individual filaments of the Southern Ocean and total transport variability in this and other sectors of the ACC.

  17. Response of the Southern Ocean dynamics to the changes in the Antarctic glacial runoff and icebergs discharge

    NASA Astrophysics Data System (ADS)

    Aksenov, Yevgeny; Nurser, George; Bacon, Sheldon; Rye, Craig; Megann, Alex; Kjellsson, Joakim; Holland, Paul; Ridley, Jeff; Coward, Andrew; Marshall, Gareth; Marsh, Bob; Mathiot, Pierre

    2016-04-01

    This study examines how changes in the freshwater discharge from the Antarctic (liquid runoff and icebergs) affect stratification and ocean circulation in the Southern Ocean. The changes in the ocean circulation could potentially modify transports of the warm subsurface waters onto the continental shelves and increase ice sheet melting. We investigate impacts of the increased freshwater discharge in the 1990s-2000s on the subsurface waters in the Southern Ocean in the NEMO 1° global sea ice-ocean model. In the simulations the warming signal is largely circum-Antarctic, with "hot spots" in the Bellingshausen-Amundsen and Ross seas. The warming of the subsurface waters in the Bellingshausen-Amundsen Sea exceeds 0.5°C/decade. Differences in spreading of the liquid freshwater and icebergs in the Southern Ocean are investigated. Hindcasts and forward projections with the eddy-admitting global NEMO 1/4° model are diagnosed to examine regional trends in the ocean and sea ice states and to attribute these to the changes in the freshwater forcing and wind. The study contributes to the "Poles Apart" research project and is funded by the Natural Environment Research Council UK.

  18. Penguins as bioindicators of mercury contamination in the southern Indian Ocean: geographical and temporal trends.

    PubMed

    Carravieri, Alice; Cherel, Yves; Jaeger, Audrey; Churlaud, Carine; Bustamante, Paco

    2016-06-01

    Penguins have been recently identified as useful bioindicators of mercury (Hg) transfer to food webs in the Southern Ocean over different spatial and temporal scales. Here, feather Hg concentrations were measured in adults and chicks of all the seven penguin species breeding in the southern Indian Ocean, over a large latitudinal gradient spanning Antarctic, subantarctic and subtropical sites. Hg was also measured in feathers of museum specimens of penguins collected at the same sites in the 1950s and 1970s. Our aim was to evaluate geographical and historical variations in Hg transfer to penguins, while accounting for feeding habits by using the stable isotope technique (δ(13)C, habitat; δ(15)N, diet/trophic level). Adult feather Hg concentrations in contemporary individuals ranged from 0.7 ± 0.2 to 5.9 ± 1.9 μg g(-1) dw in Adélie and gentoo penguins, respectively. Inter-specific differences in Hg accumulation were strong among both adults and chicks, and mainly linked to feeding habits. Overall, penguin species that feed in Antarctic waters had lower feather Hg concentrations than those that feed in subantarctic and subtropical waters, irrespective of age class and dietary group, suggesting different Hg incorporation into food webs depending on the water mass. While accounting for feeding habits, we detected different temporal variations in feather Hg concentrations depending on species. Notably, the subantarctic gentoo and macaroni penguins had higher Hg burdens in the contemporary rather than in the historical sample, despite similar or lower trophic levels, respectively. Whereas increases in Hg deposition have been recently documented in the Southern Hemisphere, future monitoring is highly needed to confirm or not this temporal trend in penguins, especially in the context of actual changing Hg emission patterns and global warming.

  19. Penguins as bioindicators of mercury contamination in the southern Indian Ocean: geographical and temporal trends.

    PubMed

    Carravieri, Alice; Cherel, Yves; Jaeger, Audrey; Churlaud, Carine; Bustamante, Paco

    2016-06-01

    Penguins have been recently identified as useful bioindicators of mercury (Hg) transfer to food webs in the Southern Ocean over different spatial and temporal scales. Here, feather Hg concentrations were measured in adults and chicks of all the seven penguin species breeding in the southern Indian Ocean, over a large latitudinal gradient spanning Antarctic, subantarctic and subtropical sites. Hg was also measured in feathers of museum specimens of penguins collected at the same sites in the 1950s and 1970s. Our aim was to evaluate geographical and historical variations in Hg transfer to penguins, while accounting for feeding habits by using the stable isotope technique (δ(13)C, habitat; δ(15)N, diet/trophic level). Adult feather Hg concentrations in contemporary individuals ranged from 0.7 ± 0.2 to 5.9 ± 1.9 μg g(-1) dw in Adélie and gentoo penguins, respectively. Inter-specific differences in Hg accumulation were strong among both adults and chicks, and mainly linked to feeding habits. Overall, penguin species that feed in Antarctic waters had lower feather Hg concentrations than those that feed in subantarctic and subtropical waters, irrespective of age class and dietary group, suggesting different Hg incorporation into food webs depending on the water mass. While accounting for feeding habits, we detected different temporal variations in feather Hg concentrations depending on species. Notably, the subantarctic gentoo and macaroni penguins had higher Hg burdens in the contemporary rather than in the historical sample, despite similar or lower trophic levels, respectively. Whereas increases in Hg deposition have been recently documented in the Southern Hemisphere, future monitoring is highly needed to confirm or not this temporal trend in penguins, especially in the context of actual changing Hg emission patterns and global warming. PMID:26896669

  20. The past, present and future distribution of a deep-sea shrimp in the Southern Ocean

    PubMed Central

    Costello, Mark J.

    2016-01-01

    Shrimps have a widespread distribution across the shelf, slope and seamount regions of the Southern Ocean. Studies of Antarctic organisms have shown that individual species and higher taxa display different degrees of sensitivity and adaptability in response to environmental change. We use species distribution models to predict changes in the geographic range of the deep-sea Antarctic shrimp Nematocarcinus lanceopes under changing climatic conditions from the Last Glacial Maximum to the present and to the year 2100. The present distribution range indicates a pole-ward shift of the shrimp population since the last glaciation. This occurred by colonization of slopes from nearby refugia located around the northern part of Scotia Arc, southern tip of South America, South Georgia, Bouvet Island, southern tip of the Campbell plateau and Kerguelen plateau. By 2100, the shrimp are likely to expand their distribution in east Antarctica but have a continued pole-ward contraction in west Antarctica. The range extension and contraction process followed by the deep-sea shrimp provide a geographic context of how other deep-sea Antarctic species may have survived during the last glaciation and may endure with projected changing climatic conditions in the future. PMID:26925334

  1. Applying a New Event Detection Algorithm to an Ocean Bottom Seismometer Dataset Recorded Offshore Southern California

    NASA Astrophysics Data System (ADS)

    Bishop, J.; Kohler, M. D.; Bunn, J.; Chandy, K. M.

    2015-12-01

    A number of active southern California offshore faults are capable of M>6 earthquakes, and the only permanent Southern California Seismic Network stations that can contribute to ongoing, small-magnitude earthquake detection and location are those located on the coastline and islands. To obtain a more detailed picture of the seismicity of the region, an array of 34 ocean bottom seismometers (OBSs) was deployed to record continuous waveform data off the coast of Southern California for 12 months (2010-2011) as part of the ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) project. To obtain a local event catalog based on OBS data, we make use of a newly developed data processing platform based on Python. The data processing procedure comprises a multi-step analysis that starts with the identification of significant signals above the time-adjusted noise floor for each sensor. This is followed by a time-dependent statistical estimate of the likelihood of an earthquake based on the aggregated signals in the array. For periods with elevated event likelihood, an adaptive grid-fitting procedure is used that yields candidate earthquake hypocenters with confidence estimates that best match the observed sensor signals. The results are validated with synthetic travel times and manual picks. Using results from ALBACORE, we have created a more complete view of active faulting in the California Borderland.

  2. The impact of multidecadal Atlantic meridional overturning circulation variations on the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Zhang, Liping; Delworth, Thomas L.; Zeng, Fanrong

    2016-05-01

    The impact of multidecadal variations of the Atlantic meridional overturning circulation (AMOC) on the Southern Ocean (SO) is investigated in the current paper using a coupled ocean-atmosphere model. We find that the AMOC can influence the SO via fast atmosphere teleconnections and subsequent ocean adjustments. A stronger than normal AMOC induces an anomalous warm SST over the North Atlantic, which leads to a warming of the Northern Hemisphere troposphere extending into the tropics. This induces an increased equator-to-pole temperature gradient in the Southern Hemisphere (SH) upper troposphere and lower stratosphere due to an amplified tropical upper tropospheric warming as a result of increased latent heat release. This altered gradients leads to a poleward displacement of the SH westerly jet. The wind change over the SO then cools the SST at high latitudes by anomalous northward Ekman transports. The wind change also weakens the Antarctic bottom water (AABW) cell through changes in surface heat flux forcing. The poleward shifted westerly wind decreases the long term mean easterly winds over the Weddell Sea, thereby reducing the turbulent heat flux loss, decreasing surface density and therefore leading to a weakening of the AABW cell. The weakened AABW cell produces a temperature dipole in the SO, with a warm anomaly in the subsurface and a cold anomaly in the surface that corresponds to an increase of Antarctic sea ice. Opposite conditions occur for a weaker than normal AMOC. Our study here suggests that efforts to attribute the recent observed SO variability to various factors should take into consideration not only local process but also remote forcing from the North Atlantic.

  3. Oceanic crust of the Grenada Basin in the Southern Lesser Antilles Arc Platform

    NASA Astrophysics Data System (ADS)

    Speed, R. C.; Walker, J. A.

    1991-03-01

    Seismic refraction data permit the southern Lesser Antilles arc and surrounding regions to be divided by the velocity of their basement. We propose that high-velocity basement of the arc platform beneath the Grenadine islands and below a part of the Tobago Trough forearc basin is oceanic and continuous and was originally connected with oceanic crust of the Grenada Basin. Low-velocity basements of the Tobago terrane and the arc platform from St. Vincent north lie south and north, respectively, of the high-velocity basement of the arc platform. An oceanic origin of this high-velocity crust in the Grenadines is argued to be more plausible than an origin as unroofed lower arc crust. The segment of probable oceanic crust in the arc platform was greatly uplifted during development of the present island arc, mainly in late Neogene time, relative to the Grenada Basin and Tobago Trough. Accepting the proposition of shallow oceanic crust in the Grenadines, early middle Eocene and possibly older pillow basalts of Mayreau, the oldest rock unit of the southern Lesser Antilles arc platform, may be an exposure of such basement. Major and minor element compositions of Mayreau Basalt are indicative of a spreading rather than arc origin. The stratigraphy of the pillow basalts indicates extrusion in an open marine environment, distant or shielded from sources of arc or continental sediment, followed by a period of pelagic sedimentation above the carbonate compensation depth. The Eocene basalt and pelagic cover formed a relatively deep floor of a marine basin in which arc-derived turbidites and pelagic sediments accumulated over the succeeding 25-30 ma. Such basalts thus indicate a probable spreading origin of the Grenada Basin and an age of cessation of spreading in the region of Mayreau in Eocene time. The configuration of the Eocene basin and the direction of spreading, however, are unknowns. Regional structural relationships imply the spreading was probably backarc, an origin also

  4. MODIS imagery as a tool for synoptic water quality assessments in the southern California coastal ocean

    USGS Publications Warehouse

    Nezlin, N.P.; DiGiacomo, P.M.; Jones, B.H.; Reifel, K.M.; Warrick, J.A.; Johnson, S.C.; Mengel, M.J.

    2007-01-01

    The dynamics of rainstorm plumes in the coastal waters of southern California was studied during the Bight'03 Regional Water Quality Program surveys. Measurements of surface salinity and bacterial counts collected from research vessels were compared to MODIS-Aqua satellite imagery. The spectra of normalized water-leaving radiation (nLw) were different in plumes and ambient ocean waters, enabling plumes discrimination and plume area size assessments from remotely-sensed data. The plume/ocean nLw differences (i.e., plume optical signatures) were most evident during first days after the rainstorm over the San Pedro shelf and in the San Diego region and less evident in Santa Monica Bay, where suspended sediments concentration in discharged water was lower than in other regions. In the Ventura area, plumes contained more suspended sediments than in other regions, but the grid of ship-based stations covered only a small part of the freshwater plume and was insufficient to reveal the differences between the plume and ocean optical signatures. The accuracy of plume area assessments from satellite imagery was not high (77% on average), seemingly because of inexactitude in satellite data processing. Nevertheless, satellite imagery is a useful tool for the estimation of the extent of polluted plumes, which is hardly achievable by contact methods.

  5. New Sericosura (Pycnogonida:Ammotheidae) from deep-sea hydrothermal vents in the Southern Ocean.

    PubMed

    Arango, Claudia P; Linse, Katrin

    2015-08-05

    Three new species of Sericosura (Pycnogonida: Ammotheidae) are described from recently discovered hydrothermal vents in the East Scotia Ridge, Southern Ocean: Sericosura bamberi sp. nov., S. dimorpha sp. nov. and S. curva sp. nov. The eleven species known to date in the genus Sericosura are all inhabitants of chemosynthetic environments in different oceans around the world. Morphology and preliminary DNA data from the COI locus suggest the East Scotia Ridge pycnogonids have relatively close evolutionary affinities with species known from the East Pacific Rise and the Mid-Atlantic Ridge. This finding highlights the importance of Sericosura as a characteristic taxon of hydrothermal vents and the great potential of this genus for global scale ecological and evolutionary studies of hydrothermal vents fauna. The use of pycnogonid DNA data combined with recent models explaining biogeographic provinces along the mid-ocean ridge system should prove extremely useful to understanding the patterns of diversification of endemic fauna from chemosynthetic environments and from the deep-sea in general.

  6. New Sericosura (Pycnogonida:Ammotheidae) from deep-sea hydrothermal vents in the Southern Ocean.

    PubMed

    Arango, Claudia P; Linse, Katrin

    2015-01-01

    Three new species of Sericosura (Pycnogonida: Ammotheidae) are described from recently discovered hydrothermal vents in the East Scotia Ridge, Southern Ocean: Sericosura bamberi sp. nov., S. dimorpha sp. nov. and S. curva sp. nov. The eleven species known to date in the genus Sericosura are all inhabitants of chemosynthetic environments in different oceans around the world. Morphology and preliminary DNA data from the COI locus suggest the East Scotia Ridge pycnogonids have relatively close evolutionary affinities with species known from the East Pacific Rise and the Mid-Atlantic Ridge. This finding highlights the importance of Sericosura as a characteristic taxon of hydrothermal vents and the great potential of this genus for global scale ecological and evolutionary studies of hydrothermal vents fauna. The use of pycnogonid DNA data combined with recent models explaining biogeographic provinces along the mid-ocean ridge system should prove extremely useful to understanding the patterns of diversification of endemic fauna from chemosynthetic environments and from the deep-sea in general. PMID:26250301

  7. Effects of whaling on the structure of the Southern Ocean food web: insights on the "krill surplus" from ecosystem modelling.

    PubMed

    Surma, Szymon; Pakhomov, Evgeny A; Pitcher, Tony J

    2014-01-01

    The aim of this study was to examine the ecological plausibility of the "krill surplus" hypothesis and the effects of whaling on the Southern Ocean food web using mass-balance ecosystem modelling. The depletion trajectory and unexploited biomass of each rorqual population in the Antarctic was reconstructed using yearly catch records and a set of species-specific surplus production models. The resulting estimates of the unexploited biomass of Antarctic rorquals were used to construct an Ecopath model of the Southern Ocean food web existing in 1900. The rorqual depletion trajectory was then used in an Ecosim scenario to drive rorqual biomasses and examine the "krill surplus" phenomenon and whaling effects on the food web in the years 1900-2008. An additional suite of Ecosim scenarios reflecting several hypothetical trends in Southern Ocean primary productivity were employed to examine the effect of bottom-up forcing on the documented krill biomass trend. The output of the Ecosim scenarios indicated that while the "krill surplus" hypothesis is a plausible explanation of the biomass trends observed in some penguin and pinniped species in the mid-20th century, the excess krill biomass was most likely eliminated by a rapid decline in primary productivity in the years 1975-1995. Our findings suggest that changes in physical conditions in the Southern Ocean during this time period could have eliminated the ecological effects of rorqual depletion, although the mechanism responsible is currently unknown. Furthermore, a decline in iron bioavailability due to rorqual depletion may have contributed to the rapid decline in overall Southern Ocean productivity during the last quarter of the 20th century. The results of this study underscore the need for further research on historical changes in the roles of top-down and bottom-up forcing in structuring the Southern Ocean food web.

  8. Evaluating CMIP5 ocean biogeochemistry and Southern Ocean carbon uptake using atmospheric potential oxygen: Present-day performance and future projection

    NASA Astrophysics Data System (ADS)

    Nevison, C. D.; Manizza, M.; Keeling, R. F.; Stephens, B. B.; Bent, J. D.; Dunne, J.; Ilyina, T.; Long, M.; Resplandy, L.; Tjiputra, J.; Yukimoto, S.

    2016-03-01

    Observed seasonal cycles in atmospheric potential oxygen (APO ~ O2 + 1.1 CO2) were used to evaluate eight ocean biogeochemistry models from the Coupled Model Intercomparison Project (CMIP5). Model APO seasonal cycles were computed from the CMIP5 air-sea O2 and CO2 fluxes and compared to observations at three Southern Hemisphere monitoring sites. Four of the models captured either the observed APO seasonal amplitude or phasing relatively well, while the other four did not. Many models had an unrealistic seasonal phasing or amplitude of the CO2 flux, which in turn influenced APO. By 2100 under RCP8.5, the models projected little change in the O2 component of APO but large changes in the seasonality of the CO2 component associated with ocean acidification. The models with poorer performance on present-day APO tended to project larger net carbon uptake in the Southern Ocean, both today and in 2100.

  9. Marine biogeochemical influence on primary sea spray aerosol composition in the Southern Ocean: predictions from a mechanistic model

    NASA Astrophysics Data System (ADS)

    McCoy, D.; Burrows, S. M.; Elliott, S.; Frossard, A. A.; Russell, L. M.; Liu, X.; Ogunro, O. O.; Easter, R. C.; Rasch, P. J.

    2014-12-01

    Remote marine clouds, such as those over the Southern Ocean, are particularly sensitive to variations in the concentration and chemical composition of aerosols that serve as cloud condensation nuclei (CCN). Observational evidence indicates that the organic content of fine marine aerosol is greatly increased during the biologically active season near strong phytoplankton blooms in certain locations, while being nearly constant in other locations. We have recently developed a novel modeling framework that mechanistically links the organic fraction of submicron sea spray to ocean biogeochemistry (Burrows et al., in discussion, ACPD, 2014; Elliott et al., ERL, 2014). Because of its combination of large phytoplankton blooms and high wind speeds, the Southern Ocean is an ideal location for testing our understanding of the processes driving the enrichment of organics in sea spray aerosol. Comparison of the simulated OM fraction with satellite observations shows that OM fraction is a statistically significant predictor of cloud droplet number concentration over the Southern Ocean. This presentation will focus on predictions from our modeling framework for the Southern Ocean, specifically, the predicted geographic gradients and seasonal cycles in the aerosol organic matter and its functional group composition. The timing and location of a Southern Ocean field campaign will determine its utility in observing the effects of highly localized and seasonal phytoplankton blooms on aerosol composition and clouds. Reference cited: Burrows, S. M., Ogunro, O., Frossard, A. A., Russell, L. M., Rasch, P. J., and Elliott, S.: A physically-based framework for modelling the organic fractionation of sea spray aerosol from bubble film Langmuir equilibria, Atmos. Chem. Phys. Discuss., 14, 5375-5443, doi:10.5194/acpd-14-5375-2014, 2014. Elliott, S., Burrows, S. M., Deal, C., Liu, X., Long, M., Ogunro, O., Russell, L. M., and Wingenter O.. "Prospects for simulating macromolecular surfactant

  10. The impact of Southern Ocean gateways on the Cenozoic climate evolution

    NASA Astrophysics Data System (ADS)

    von der Heydt, Anna; Viebahn, Jan; Dijkstra, Henk

    2016-04-01

    During the Cenozoic period, which covers the last 65 Million (Ma) years, Earth's climate has undergone a major long-term transition from warm "greenhouse" to colder "icehouse" conditions with extensive ice sheets in the polar regions of both hemispheres. On the very long term the gradual cooling may be seen as response to the overall slowly decreasing atmospheric CO2-concentration due to weathering processes in the Earth System, however, continental geometry has changed considerably over this period and the long-term gradual trend was interrupted, by several rapid transitions as well as periods where temperature and greenhouse gas concentrations seem to be decoupled. The Eocene-Oligocene boundary (˜34 Ma, E/O) and mid-Miocene climatic transition (˜13 Ma, MCT) reflect major phases of Antarctic ice sheet build-up and global climate cooling, while Northern Hemisphere ice sheets developed much later, most likely at the Pliocene-Pleistocene transition (˜2.7Ma). Thresholds in atmospheric CO2-concentration together with feedback mechanisms related to land ice formation are now among the favoured mechanisms of these climatic transitions, while the long-proposed ocean circulation changes caused by opening of tectonic gateways seem to play a less direct role. The opening of the Southern Ocean gateways, notably the Drake Passage and the Tasman Gateway as well as the northward movement of Australia over this long time period, however, has eventually led to the development of today's strongest ocean current, the Antarctic Circumpolar Current (ACC), playing a major role in the transport properties of the global ocean circulation. The overall state of the global ocean circulation, therefore, preconditions the climate system to dramatic events such as major ice sheet formation. Here, we present results of a state-of-the art global climate model (CESM) under various continental configurations: (i) present day geometry, (ii) present day geometry with a closed Drake Passage and

  11. Ocean Colour Radiometry across the Southern Atlantic and South-Eastern Pacific

    NASA Astrophysics Data System (ADS)

    Rudorff, N. D.; Kampel, M.; Frouin, R. J.

    2011-12-01

    An oceanographic cruise across the Southern Atlantic and South-eastern Pacific was undertaken from February 20th to March 14th, 2011, on board the R/V Melville (MV1102). The research vessel crossed highly dynamic regions with important roles on regional and global biogeochemical cycles, such as: the Benguela Upwelling System, the Subtropical Convergence Zone, the Patagonian Shelf, the Magellan Strait, and the Chilean Eastern Boundary Upwelling Zone. The Southern Ocean has been focus of many ocean colour studies due to the high spatio-temporal variability of bio-optical constituents and its biogeochemical importance. Nevertheless, the high latitudes and rough seas of the Southern Ocean are a great challenge for the estimation of these properties from in situ and satellite sensors. The present work shows the first results of the MV1102 cruise with the aim to access the magnitude and possible sources of errors for the estimation of in situ above water remote sensing reflectance (Rrs). Simultaneous measurements were taken at 18 stations with two hyperspectral radiometers: the Fieldspec HandHeld ASD Inc. (350-1100nm) for above water measurements, and the HyperOCR II Satlantic Inc. (380-800 nm) for in-water profiles. Above water measurements were performed with a sensor viewing geometry of 45o zenith and 137o azimuth solar angles, and the downwelling solar irradiance (ED) was estimated using a white Spectralon plaque. The Rrs was estimated with an average of 10 casts per station, and different sky reflectance factors were used to adjust to environmental conditions. Two methods were used to retrieve the Rrs: M01, without the residual sky correction (RSC); and M02, with the RSC, subtracting the Rrs at 870 nm, as a white spectral offset. The M02 was applied for all stations except in the Magellan Strait (coastal waters). For the profiler, the above water Rrs was estimated using two methods: MP01, with the ED measured from the profiler; and MP02, with ED measured from the

  12. Intraplate magmatism related to opening of the southern Iapetus Ocean: Cambrian Wichita igneous province in the Southern Oklahoma rift zone

    NASA Astrophysics Data System (ADS)

    Hanson, Richard E.; Puckett, Robert E.; Keller, G. Randy; Brueseke, Matthew E.; Bulen, Casey L.; Mertzman, Stanley A.; Finegan, Shane A.; McCleery, David A.

    2013-08-01

    Southern Oklahoma and adjacent parts of Texas contain an extensive igneous province emplaced during Early Cambrian rifting within the Southern Oklahoma rift zone. The rift zone was initiated in association with the opening of the southern Iapetus Ocean during Rodinia supercontinent breakup and later became the site of a series of linked uplifts and basins as a result of late Paleozoic inversion. Igneous rocks within the rift are referred to as the Wichita province and are present mostly in the subsurface, although critical exposures occur in the Wichita and Arbuckle Mountains in southwestern and southern Oklahoma. Wells drilled into basement in the region provide a wealth of information on the distribution and relations of the major igneous units in the upper crust, and geophysical data provide important constraints on deeper levels of the rift zone. The upper parts of the igneous rift fill comprise the Carlton Rhyolite Group, which has an estimated subsurface areal extent of ~ 40,000 km2, and the related Wichita sheet granites, which intrude the lower parts of the rhyolite succession. These rocks have A-type characteristics and were emplaced after intrusion, tilting and uplift of a large tholeiitic layered mafic complex; smaller bodies of gabbro also intruded the layered complex after it was tilted. U-Pb zircon and 40Ar/39Ar geochronology indicates the felsic rocks and at least some of the mafic units were emplaced in a relatively narrow time frame at ~ 539-530 Ma. Basalts and intermediate lavas are present only in the subsurface. Our new work shows these lavas to have tholeiitic to mildly alkaline compositions and to be more extensive than previously realized, forming thick successions that both underlie and are intercalated with the rhyolites. Diabase dikes were intruded into older crust during initial opening of the rift, and a suite of late diabase intrusions also cuts the rhyolites and granites, indicating that mafic magma was supplied to the rift throughout

  13. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean.

    PubMed

    Blain, Stéphane; Quéguiner, Bernard; Armand, Leanne; Belviso, Sauveur; Bombled, Bruno; Bopp, Laurent; Bowie, Andrew; Brunet, Christian; Brussaard, Corina; Carlotti, François; Christaki, Urania; Corbière, Antoine; Durand, Isabelle; Ebersbach, Frederike; Fuda, Jean-Luc; Garcia, Nicole; Gerringa, Loes; Griffiths, Brian; Guigue, Catherine; Guillerm, Christophe; Jacquet, Stéphanie; Jeandel, Catherine; Laan, Patrick; Lefèvre, Dominique; Lo Monaco, Claire; Malits, Andrea; Mosseri, Julie; Obernosterer, Ingrid; Park, Young-Hyang; Picheral, Marc; Pondaven, Philippe; Remenyi, Thomas; Sandroni, Valérie; Sarthou, Géraldine; Savoye, Nicolas; Scouarnec, Lionel; Souhaut, Marc; Thuiller, Doris; Timmermans, Klaas; Trull, Thomas; Uitz, Julia; van Beek, Pieter; Veldhuis, Marcel; Vincent, Dorothée; Viollier, Eric; Vong, Lilita; Wagener, Thibaut

    2007-04-26

    The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization--an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below--as invoked in some palaeoclimatic and future climate change scenarios--may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.

  14. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Blain, Stéphane; Quéguiner, Bernard; Armand, Leanne; Belviso, Sauveur; Bombled, Bruno; Bopp, Laurent; Bowie, Andrew; Brunet, Christian; Brussaard, Corina; Carlotti, François; Christaki, Urania; Corbière, Antoine; Durand, Isabelle; Ebersbach, Frederike; Fuda, Jean-Luc; Garcia, Nicole; Gerringa, Loes; Griffiths, Brian; Guigue, Catherine; Guillerm, Christophe; Jacquet, Stéphanie; Jeandel, Catherine; Laan, Patrick; Lefèvre, Dominique; Lo Monaco, Claire; Malits, Andrea; Mosseri, Julie; Obernosterer, Ingrid; Park, Young-Hyang; Picheral, Marc; Pondaven, Philippe; Remenyi, Thomas; Sandroni, Valérie; Sarthou, Géraldine; Savoye, Nicolas; Scouarnec, Lionel; Souhaut, Marc; Thuiller, Doris; Timmermans, Klaas; Trull, Thomas; Uitz, Julia; van Beek, Pieter; Veldhuis, Marcel; Vincent, Dorothée; Viollier, Eric; Vong, Lilita; Wagener, Thibaut

    2007-04-01

    The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization-an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below-as invoked in some palaeoclimatic and future climate change scenarios-may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought.

  15. Effect of natural iron fertilization on carbon sequestration in the Southern Ocean.

    PubMed

    Blain, Stéphane; Quéguiner, Bernard; Armand, Leanne; Belviso, Sauveur; Bombled, Bruno; Bopp, Laurent; Bowie, Andrew; Brunet, Christian; Brussaard, Corina; Carlotti, François; Christaki, Urania; Corbière, Antoine; Durand, Isabelle; Ebersbach, Frederike; Fuda, Jean-Luc; Garcia, Nicole; Gerringa, Loes; Griffiths, Brian; Guigue, Catherine; Guillerm, Christophe; Jacquet, Stéphanie; Jeandel, Catherine; Laan, Patrick; Lefèvre, Dominique; Lo Monaco, Claire; Malits, Andrea; Mosseri, Julie; Obernosterer, Ingrid; Park, Young-Hyang; Picheral, Marc; Pondaven, Philippe; Remenyi, Thomas; Sandroni, Valérie; Sarthou, Géraldine; Savoye, Nicolas; Scouarnec, Lionel; Souhaut, Marc; Thuiller, Doris; Timmermans, Klaas; Trull, Thomas; Uitz, Julia; van Beek, Pieter; Veldhuis, Marcel; Vincent, Dorothée; Viollier, Eric; Vong, Lilita; Wagener, Thibaut

    2007-04-26

    The availability of iron limits primary productivity and the associated uptake of carbon over large areas of the ocean. Iron thus plays an important role in the carbon cycle, and changes in its supply to the surface ocean may have had a significant effect on atmospheric carbon dioxide concentrations over glacial-interglacial cycles. To date, the role of iron in carbon cycling has largely been assessed using short-term iron-addition experiments. It is difficult, however, to reliably assess the magnitude of carbon export to the ocean interior using such methods, and the short observational periods preclude extrapolation of the results to longer timescales. Here we report observations of a phytoplankton bloom induced by natural iron fertilization--an approach that offers the opportunity to overcome some of the limitations of short-term experiments. We found that a large phytoplankton bloom over the Kerguelen plateau in the Southern Ocean was sustained by the supply of iron and major nutrients to surface waters from iron-rich deep water below. The efficiency of fertilization, defined as the ratio of the carbon export to the amount of iron supplied, was at least ten times higher than previous estimates from short-term blooms induced by iron-addition experiments. This result sheds new light on the effect of long-term fertilization by iron and macronutrients on carbon sequestration, suggesting that changes in iron supply from below--as invoked in some palaeoclimatic and future climate change scenarios--may have a more significant effect on atmospheric carbon dioxide concentrations than previously thought. PMID:17460670

  16. Characterising cloud regimes associated with the Southern Ocean shortwave radiation bias

    NASA Astrophysics Data System (ADS)

    Mason, S.; Jakob, C.; Protat, A.

    2013-12-01

    The high-latitude Southern Ocean is the site of persistent cloud biases in GCMs. A deficit of shortwave cloud radiative effect especially between 50-65S causes an excess of absorbed shortwave radiation, which has been associated with other biases in the global circulation. Recent model evaluation studies have found that the shortwave radiation bias is potentially associated with low- and mid-level clouds in the cold-air part of extratropical cyclones and ahead of transient ridges. However a coherent description of the cloud properties and cloud processes most associated with the bias has not yet emerged. This study focuses on three cloud regimes that are most frequent in the area of the shortwave radiation bias during the austral summer. They are selected from the cloud regimes derived for the Southern Ocean from International Satellite Cloud Climatology Project (ISCCP) cloud observations. We characterise the selected cloud regimes in terms of their meteorological conditions using the ECMWF Interim reanalysis. We also study their vertical macrophysical structure and microphysical properties based on active satellite observations using the DARDAR (raDAR/liDAR) combined CloudSat and CALIPSO data product. We find that two cloud regimes identified as mid-topped in the ISCCP based data set are associated with distinct meteorological processes. An optically thin mid-level top cloud regime is related to cold mid-levels, cold-air advection and moderate subsidence, while an optically thicker cloud regime is associated with a broader range of conditions resembling weak to moderate frontal events, with warm and moist mid-levels, moderate ascent and warm-air advection. The vertical cloud structure derived from DARDAR profiles show that both these regimes contain mostly low clouds, but both also include frequent occurrences of mid-level cloud. We use a clustering method to quantify the differences in microphysical properties between the regimes. We find that the optically

  17. Reconstruction of Middle Eocene - Late Oligocene Southern Ocean paleoclimate through calcareous nannofossils and stable isotopes

    NASA Astrophysics Data System (ADS)

    Villa, Giuliana; Fioroni, Chiara; Persico, Davide; Pea, Laura; Bohaty, Steve

    2010-05-01

    The transition from the ice free early Paleogene world to the glaciated conditions of the early Oligocene has been matter of discussion in the last years. This transition has not been monotonic but punctuated by numerous transient cooling and warming events. Here we present a summary of recent studies based on Nannofossil response to climatic changes during the Eocene and Oligocene. Collected data issue from high latitudes ODP Sites 748, 738, 744, 689 and 690. Based on a detailed revision of the biostratigraphy carried out through quantitative analysis, we conducted paleoecological studies on calcareous nannofossils through the late middle Eocene to the - late Oligocene interval to identify abundance variations of selected taxa in response to changes in sea surface temperature (SST) and trophic conditions. The nannofossil-based interpretation has been compared with detailed oxygen and carbon stable isotope stratigraphy confirming the climate variability in the Southern Ocean for this time interval. We identify the Middle Eocene Climatic optimum (MECO) event, related with the regional exclusion of Paleogenic warm-water taxa from the Southern Ocean, followed by the progressive cooling trend particularly emphasized during the cooling events at about 39 Ma, 37 Ma and 35.5 Ma. In the earliest Oligocene, marked changes in calcareous nannofossil assemblages are strikingly associated with the Oi-1 event recorded in perfect accordance with the oxygen isotope records. For most of the Oligocene we recorded a cold phase, while a warming trend is detected in the late Oligocene. In addiction, a marked increase of taxa thriving in eutrophic conditions coupled with a decrease in oligotrophic taxa, suggests the presence of a time interval (from about 36 Ma to about 26 Ma) with prevailing eutrophic conditions that correspond to an increase of the carbon stable isotope curve. This interval well corresponds with the clay mineral concentration that shows at Site 738 a higher

  18. The interdisciplinary marine system of the Amundsen Sea, Southern Ocean: Recent advances and the need for sustained observations

    NASA Astrophysics Data System (ADS)

    Meredith, Michael P.; Ducklow, Hugh W.; Schofield, Oscar; Wåhlin, Anna; Newman, Louise; Lee, SangHoon

    2016-01-01

    The Southern Ocean exerts a profound influence on the functioning of the Earth System, in part because its location and unique bathymetric configuration enable direct linkages to the other major ocean basins (Ganachaud and Wunsch, 2000; Lumpkin and Speer, 2007). It is the site of the world's largest current system, the Antarctic Circumpolar Current (ACC), which transfers waters and climatically/ecologically-important tracers between the Atlantic, Indian and Pacific Oceans (Rintoul et al., 2001). In addition to the strong horizontal connectivity, the ACC is also characterized by a vigorous overturning circulation, which upwells warm, nutrient-rich waters from intermediate depth to the surface, where they are modified by interactions with the atmosphere and cryosphere to form new water masses, some of which are lighter and others more dense (Marshall and Speer, 2012). This overturning circulation structures the Southern Ocean both horizontally and vertically, dictates the levels of its communication with the rest of the global ocean, and is a fundamental control on the sequestration of carbon from the atmosphere into the ocean interior (Sallée et al., 2012). In some locations, the upwelled waters can intrude onto the Antarctic shelves, supplying heat and nutrients to the shallower regions. This is believed to be especially effective in west Antarctica, where the southern edge of the ACC moves close to the shelf break (Martinson, 2011; Orsi et al., 1995; Thoma et al., 2008).

  19. Orographic Gravity Waves above Small Islands in the Southern Ocean and Their Role in Climate

    NASA Astrophysics Data System (ADS)

    Alexander, M.; Grimsdell, A.

    2012-12-01

    Most of today's climate models struggle with systematic westerly biases in the stratospheric circulation that lead to a delayed breakdown of the stratospheric vortex in spring and associated effects on temperature and ozone loss. Ozone loss in recent decades and predicted ozone recovery in the 21st century has a first-order impact on surface winds and climate, highlighting the importance of these common model biases in stratospheric winds. The cause is long believed to be that the Southern Hemisphere lacks sources for orographic gravity waves and associated wave drag relative to the Northern Hemisphere. Some models include hemispherically asymmetric non-orographic gravity wave momentum fluxes in their parameterizations despite any clear observational or theoretical justification for such differences other than the need to obtain more realistic stratospheric simulations. Our work examines the role of orographic gravity waves above small islands in the Southern Ocean, which are too small to be resolved in most climate models. Orographic waves above these small islands have been observed as temperature anomalies in radiance observations of the Atmospheric Infrared Sounder (AIRS) instrument on the Aqua satellite. A previously analyzed case study with AIRS data concluded such waves above South Georgia Island in the South Atlantic can have a considerable impact on the stratospheric circulation, yet these effects are omitted in most climate models. In the present work, we use AIRS observations to examine occurrence frequencies and momentum fluxes above six island groups in the Southern Ocean. Further, detailed seasonal and interannual variations and areal maps of time-mean momentum fluxes are examined for two of these groups: South Georgia/Sandwich Islands and Heard/Kerguelen Islands. We examine the effects of winds at the surface and winds in the stratosphere to infer the relative roles of source intermittency, propagation effects, and observational filter effects on the

  20. Modulation of the Southern Africa precipitation response to the El Niño Southern Oscillation by the subtropical Indian Ocean Dipole

    NASA Astrophysics Data System (ADS)

    Hoell, Andrew; Funk, Chris; Zinke, Jens; Harrison, Laura

    2016-06-01

    The climate of Southern Africa, defined as the land area bound by the region 15°S-35°S; 12.5°E-42.5°E, during the December-March rainy season is driven by Indo-Pacific sea surface temperature (SST) anomalies associated with the El Niño Southern Oscillation (ENSO) and the Subtropical Indian Ocean Dipole (SIOD). The observed December-March 1979-2014 Southern Africa precipitation during the four ENSO and SIOD phase combinations suggests that the phase of the SIOD can disrupt or enhance the Southern Africa precipitation response to ENSO. Here, we use a large ensemble of model simulations driven by global SST and ENSO-only SST to test whether the SIOD modifies the relationship between Southern Africa precipitation and ENSO. Since ENSO-based precipitation forecasts are used extensively over Southern Africa, an improved understanding of how other modes of SST variability modulate the regional response to ENSO is important. ENSO, in the absence of the SIOD, forces an equivalent barotropic Rossby wave over Southern Africa that modifies the regional mid-tropospheric vertical motions and precipitation anomalies. El Niño (La Niña) is related with high (low) pressure over Southern Africa that produces anomalous mid-tropospheric descent (ascent) and decreases (increases) in precipitation relative to average. When the SIOD and ENSO are in opposite phases, the SIOD compliments the ENSO-related atmospheric response over Southern Africa by strengthening the regional equivalent barotropic Rossby wave, anomalous mid-tropospheric vertical motions and anomalous precipitation. By contrast, when the SIOD and ENSO are in the same phase, the SIOD disrupts the ENSO-related atmospheric response over Southern Africa by weakening the regional equivalent barotropic Rossby wave, anomalous mid-tropospheric vertical motions and anomalous precipitation.

  1. Measurements of carbon dioxide in the Southern Ocean along the WOCE S-4 section

    SciTech Connect

    Chipman, D.W.; Rubin, S.I.; Takahashi, T.

    1992-08-01

    During the fist year of this two-year grant, we have completed the data acquisition phase at sea along the WOCE-S4 section located along 67{degree}S between 73{degree}W and 172{degree}E in the Pacific sector of the Southern Ocean. The expedition was carried out aboard the Russian Research Ship Akademik IOFFE'' in the period February 14 through April 6, 1992. The total CO{sub 2} concentration and pCO{sub 2} in a total of about 1290 water samples were determined using a coulometer for total CO{sub 2} and an equilibrator/gas chromatograph system for pCO{sub 2}. Surface water samples were analyzed at all the 112 hydrographic stations occupied. Complete or partial profiles were obtained at 58 stations. In addition, a total of 172 determinations were made at sea for 62 bottles of the Standard Reference Solution.

  2. Eddies Enhance Biological Production in the Weddell-Scotia Confluence of the Southern Ocean

    NASA Technical Reports Server (NTRS)

    Kahru, M.; Mitchell, B. G.; Gille, S. T.; Hewes, C. D.; Holm,-Hansen, O.

    2007-01-01

    Satellite data show that oceanic eddies generated in the Southern Antarctic Circumpolar Current Front (SACCF) are associated with increased phytoplankton biomass. Cyclonic eddies with high chlorophyll a concentration (Chl-a) retain phytoplankton within the eddy cores and increase the light available for photosynthesis in the upper mixed layer by limiting vertical mixing and lifting of the isopycnal surfaces. Anticyclonic eddies have low Chl-a in the core but increased Chl-a in the periphery. Cross-frontal mixing mediated by eddies transports nutrients (e.g., Fe and Si) to the north and contributes to the increased Chl-a in the frontal zone. Interannual variations in the cyclonic eddy activity are positively correlated with variations in Chl-a during the spring bloom in regions of the Antarctic Circumpolar Current around South Georgia.

  3. Antarctic ice dynamics and southern ocean surface hydrology during the last glacial maximum

    SciTech Connect

    Labeyrie, L.D.; Burckle, L.; Labracherie, M.; Pichon, J.J.; Ippolito, P.; Grojean, M.C.; Duplessy, J.C.

    1985-01-01

    Eight high sedimentation rate cores located between 61/sup 0/S and 43/sup 0/S in the Atlantic and Indian sectors of the Southern Ocean have been studied in detail for foraminifera and diatom /sup 18/O//sup 16/O ratios, and changes in radiolarian and diatom specific abundance. Comparison of these different parameters permits a detailed description of the surface water hydrology during the last glacial maximum. The authors demonstrate that from 25 kyr BP to 15 kyr BP a large number of icebergs formed around the Antarctic continent. Melting along the Polar Front decreased surface salinity by approximately 1.5 per thousand between 43/sup 0/S and 50/sup 0/S. They propose that an increase of snow accumulation at the Antarctic periphery and downdraw during maximum ice extension are primary causes for this major discharge of icebergs.

  4. Assessing XCTD Fall Rate Errors using Concurrent XCTD and CTD Profiles in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Millar, J.; Gille, S. T.; Sprintall, J.; Frants, M.

    2010-12-01

    Refinements in the fall rate equation for XCTDs are not as well understood as those for XBTs, due in part to the paucity of concurrent and collocated XCTD and CTD profiles. During February and March 2010, the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) conducted 31 collocated 1000-meter XCTD and CTD casts in the Drake Passage. These XCTD/CTD profile pairs are closely matched in space and time, with a mean distance between casts of 1.19 km and a mean lag time of 39 minutes. The profile pairs are well suited to address the XCTD fall rate problem specifically in higher latitude waters, where existing fall rate corrections have rarely been assessed. Many of these XCTD/CTD profile pairs reveal an observable depth offset in measurements of both temperature and conductivity. Here, the nature and extent of this depth offset is evaluated.

  5. Crinoids of the stalked family Hyocrinidae (Echinodermata) collected by the USNS Eltanin in the Southern Ocean.

    PubMed

    Roux, Michel

    2015-07-27

    Rare species only known from one or a few specimens, mainly collected from abyssal and hadal zones in the Southern Ocean are represented in a collection of stalked crinoids attributed to the family Hyocrinidae (Crinoidea, Echinodermata). The species studied here include Belyaevicrinus latipinnulus Mironov & Sorokina, 1998, Feracrinus heinzelleri Bohn, 2012, Ptilocrinus brucei Vaney, 1908 and Thalassocrinus clausus Mironov & Sorokina, 1998. This collection, mainly collected during the 1960s USNS Eltanin cruises, is housed at the Smithsonian Institution National Museum of Natural History in Washington DC. A detailed study of this material using SEM observations of ossicle articular facets and pinnule architecture allows the emendation of species diagnoses, and a better description of intraspecific variation and of changes in characters through ontogeny. Geographical and depth range extension of species are reported. A gonad with submature ovocytes of 100-150 µm was exceptionally preserved at the base of a genital pinnule of P. brucei. This species likely has a lecithotrophic larval development.

  6. Coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features

    NASA Technical Reports Server (NTRS)

    Comiso, J. C.; Mcclain, C. R.; Sullivan, C. W.; Ryan, J. P.; Leonard, C. L.

    1993-01-01

    Climatological data on the distribution of surface pigment fields in the entire southern ocean over a seasonal cycle are examined. The occurrence of intense phytoplankton blooms during austral summer months and during other seasons in different regions is identified and analyzed. The highest pigment concentrations are observed at high latitudes and over regions with water depths usually less than 600 m. Basin-scale pigment distribution shows a slightly asymmetric pattern of enhanced pigment concentrations about Antarctica, with enhanced concentrations extending to lower latitudes in the Atlantic and Indian sectors than in the Pacific sector. A general increase in pigment concentrations is evident from the low latitudes toward the Antarctic circumpolar region. Spatial relationships between pigment and archived geophysical data reveal significant correlation between pigment distributions and both bathymetry and wind stress, while general hemispheric scale patterns of pigment distributions are most coherent with the geostrophic flow of the Antarctic Circumpolar Current.

  7. The distribution and speciation of iron along 6°E in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Croot, Peter L.; Andersson, Karen; Öztürk, Murat; Turner, David R.

    2004-11-01

    The distribution and speciation of iron was determined along a transect in the eastern Atlantic sector (6°E) of the Southern Ocean during a collaborative Scandinavian/South African Antarctic cruise conducted in late austral summer (December 1997/January 1998). Elevated concentrations of dissolved iron (>0.4 nM) were found at 60°S in the vicinity of the Spring Ice Edge (SIE) in tandem with a phytoplankton bloom, chiefly dominated by Phaeocystis sp. This bloom had developed rapidly after the loss of the seasonal sea ice cover. The iron that fuelled this bloom was mostly likely derived from sea ice melt. In the Winter Ice Edge (WIE), around 55°S, dissolved iron concentrations were low ( <0.2nM) and corresponded to lower biological productivity, biomass. In the Antarctic Polar Front, at approximately 50°S, a vertical profile of dissolved iron showed low concentrations ( <0.2nM); however, a surface survey showed higher concentrations (1-3 nM), and considerable patchiness in this dynamic frontal region. The chemical speciation of iron was dominated by organic complexation throughout the study region. Organic iron-complexing ligands ([ L]) ranged from 0.9 to 3.0 nM Fe equivalents, with complex stability logKFeL'=21.4-23.5. Estimated concentrations of inorganic iron (Fe') ranged from 0.03 to 0.79 pM, with the highest values found in the Phaeocystis bloom in the SIE. A vertical profile of iron-complexing ligands in the WIE showed a maximum consistent with a biological source for ligand production and near surface minimum possibly consistent with loss via photodecomposition. This work further confirms the role iron that has in the Southern Ocean in limiting primary productivity.

  8. Microdistribution of Faunal Assemblages at Deep-Sea Hydrothermal Vents in the Southern Ocean

    PubMed Central

    Marsh, Leigh; Copley, Jonathan T.; Huvenne, Veerle A. I.; Linse, Katrin; Reid, William D. K.; Rogers, Alex D.; Sweeting, Christopher J.; Tyler, Paul A.

    2012-01-01

    Chemosynthetic primary production by microbes supports abundant faunal assemblages at deep-sea hydrothermal vents, with zonation of invertebrate species typically occurring along physico-chemical gradients. Recently discovered vent fields on the East Scotia Ridge (ESR) in the Southern Ocean represent a new province of vent biogeography, but the spatial dynamics of their distinct fauna have yet to be elucidated. This study determines patterns of faunal zonation, species associations, and relationships between faunal microdistribution and hydrothermal activity in a vent field at a depth of 2,400 m on the ESR. Remotely operated vehicle (ROV) dives obtained high-definition imagery of three chimney structures with varying levels of hydrothermal activity, and a mosaic image of >250 m2 of seafloor co-registered with temperature measurements. Analysis of faunal microdistribution within the mosaiced seafloor reveals a consistent pattern of faunal zonation with increasing distance from vent sources and peak temperatures. Assemblages closest to vent sources are visibly dominated by a new species of anomuran crab, Kiwa n. sp. (abundance >700 individuals m−2), followed by a peltospiroid gastropod (>1,500 individuals m−2), eolepadid barnacle (>1,500 individuals m−2), and carnivorous actinostolid anemone (>30 individuals m−2). Peripheral fauna are not dominated by a single taxon, but include predatory and scavenger taxa such as stichasterid seastars, pycnogonids and octopus. Variation in faunal microdistribution on chimneys with differing levels of activity suggests a possible successional sequence for vent fauna in this new biogeographic province. An increase in δ34S values of primary consumers with distance from vent sources, and variation in their δ13C values also indicate possible zonation of nutritional modes of the vent fauna. By using ROV videography to obtain a high-resolution representation of a vent environment over a greater extent than previous studies

  9. Co-limitation by iron, silicate, and light of three Southern Ocean diatom species

    NASA Astrophysics Data System (ADS)

    Hoffmann, L. J.; Peeken, I.; Lochte, K.

    2007-01-01

    The effect of combined iron, silicate, and light co-limitation was investigated in two Southern Ocean diatom species, Chaetoceros dichaeta and Actinocyclus sp. and one cosmopolitan species, Chaetoceros debilis, all isolated in the Southern Ocean (SO). We found species specific differences in the level of nutrient limitation and its effect on physiological and morphological parameters. Growth of all species tested was clearly co-limited by iron and silicate, reflected in a 4 to 40 times higher increase in cell numbers in the high iron, high silicate treatments compared with the controls. However, the effect of iron and silicate availability on chain length and frustules structures was species specific. Most drastic frustule malformation was found under iron and silicate co-limitation in C. dichaeta while Si limitation caused a strong cell elongation in both Chaetoceros species. Additional a significant increase in chain length was observed in these species under high iron conditions. Therefore, species composition in the SO is likely also indirectly affected by these nutrients via different effects on diatom grazing protection. These morphological changes reflect a potential as biological markers in sediments for the growth history of chain forming species. High light conditions, comparable with light intensities found in the upper 28 m of the SO, showed a negative impact on growth of the endemic species C. dichaeta and Actinocyclus sp. This is in contrast to the assumed light limitation of SO diatoms and indicates an adaptation strategy to the deep mixing and resulting low light conditions in the SO. In contrast to that, the cosmopolitan species C. debilis was not negatively affected by increased light intensity, indicating adaptation to a broader light environment. These results suggest that light limitation of SO phytoplankton due to deep wind mixed layers may play a minor role than hitherto assumed.

  10. Unstructured-grid coastal ocean modelling in Southern Adriatic and Northern Ionian Seas

    NASA Astrophysics Data System (ADS)

    Federico, Ivan; Pinardi, Nadia; Coppini, Giovanni; Oddo, Paolo

    2016-04-01

    The Southern Adriatic Northern Ionian coastal Forecasting System (SANIFS) is a short-term forecasting system based on unstructured grid approach. The model component is built on SHYFEM finite element three-dimensional hydrodynamic model. The operational chain exploits a downscaling approach starting from the Mediterranean oceanographic-scale model MFS (Mediterranean Forecasting System, operated by INGV). The implementation set-up has been designed to provide accurate hydrodynamics and active tracer processes in the coastal waters of Southern Eastern Italy (Apulia, Basilicata and Calabria regions), where the model is characterized by a variable resolution in range of 50-500 m. The horizontal resolution is also high in open-sea areas, where the elements size is approximately 3 km. The model is forced: (i) at the lateral open boundaries through a full nesting strategy directly with the MFS (temperature, salinity, non-tidal sea surface height and currents) and OTPS (tidal forcing) fields; (ii) at surface through two alternative atmospheric forcing datasets (ECMWF and COSMOME) via MFS-bulk-formulae. Given that the coastal fields are driven by a combination of both local/coastal and deep ocean forcings propagating along the shelf, the performance of SANIFS was verified first (i) at the large and shelf-coastal scales by comparing with a large scale CTD survey and then (ii) at the coastal-harbour scale by comparison with CTD, ADCP and tide gauge data. Sensitivity tests were performed on initialization conditions (mainly focused on spin-up procedures) and on surface boundary conditions by assessing the reliability of two alternative datasets at different horizontal resolution (12.5 and 7 km). The present work highlights how downscaling could improve the simulation of the flow field going from typical open-ocean scales of the order of several km to the coastal (and harbour) scales of tens to hundreds of meters.

  11. Microdistribution of faunal assemblages at deep-sea hydrothermal vents in the Southern Ocean.

    PubMed

    Marsh, Leigh; Copley, Jonathan T; Huvenne, Veerle A I; Linse, Katrin; Reid, William D K; Rogers, Alex D; Sweeting, Christopher J; Tyler, Paul A

    2012-01-01

    Chemosynthetic primary production by microbes supports abundant faunal assemblages at deep-sea hydrothermal vents, with zonation of invertebrate species typically occurring along physico-chemical gradients. Recently discovered vent fields on the East Scotia Ridge (ESR) in the Southern Ocean represent a new province of vent biogeography, but the spatial dynamics of their distinct fauna have yet to be elucidated. This study determines patterns of faunal zonation, species associations, and relationships between faunal microdistribution and hydrothermal activity in a vent field at a depth of 2,400 m on the ESR. Remotely operated vehicle (ROV) dives obtained high-definition imagery of three chimney structures with varying levels of hydrothermal activity, and a mosaic image of >250 m(2) of seafloor co-registered with temperature measurements. Analysis of faunal microdistribution within the mosaiced seafloor reveals a consistent pattern of faunal zonation with increasing distance from vent sources and peak temperatures. Assemblages closest to vent sources are visibly dominated by a new species of anomuran crab, Kiwa n. sp. (abundance >700 individuals m(-2)), followed by a peltospiroid gastropod (>1,500 individuals m(-2)), eolepadid barnacle (>1,500 individuals m(-2)), and carnivorous actinostolid anemone (>30 individuals m(-2)). Peripheral fauna are not dominated by a single taxon, but include predatory and scavenger taxa such as stichasterid seastars, pycnogonids and octopus. Variation in faunal microdistribution on chimneys with differing levels of activity suggests a possible successional sequence for vent fauna in this new biogeographic province. An increase in δ(34)S values of primary consumers with distance from vent sources, and variation in their δ(13)C values also indicate possible zonation of nutritional modes of the vent fauna. By using ROV videography to obtain a high-resolution representation of a vent environment over a greater extent than previous studies

  12. Major Characteristics of Southern Ocean Cloud Regimes and Their Effects on the Energy Budget

    NASA Technical Reports Server (NTRS)

    Haynes, John M.; Jakob, Christian; Rossow, William B.; Tselioudis, George; Brown, Josephine

    2011-01-01

    Clouds over the Southern Ocean are often poorly represented by climate models, but they make a significant contribution to the top-of-atmosphere (TOA) radiation balance, particularly in the shortwave portion of the energy spectrum. This study seeks to better quantify the organization and structure of Southern Hemisphere midlatitude clouds by combining measurements from active and passive satellite-based datasets. Geostationary and polar-orbiter satellite data from the International Satellite Cloud Climatology Project (ISCCP) are used to quantify large-scale, recurring modes of cloudiness, and active observations from CloudSat and Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) are used to examine vertical structure, radiative heating rates, and precipitation associated with these clouds. It is found that cloud systems are organized into eight distinct regimes and that ISCCP overestimates the midlevel cloudiness of these regimes. All regimes contain a relatively high occurrence of low cloud, with 79%of all cloud layers observed having tops below 3 km, but multiple-layered clouds systems are present in approximately 34% of observed cloud profiles. The spatial distribution of regimes varies according to season, with cloud systems being geometrically thicker, on average, during the austral winter. Those regimes found to be most closely associated with midlatitude cyclones produce precipitation the most frequently, although drizzle is extremely common in low-cloud regimes. The regimes associated with cyclones have the highest in-regime shortwave cloud radiative effect at the TOA, but the low-cloud regimes, by virtue of their high frequency of occurrence over the oceans, dominate both TOA and surface shortwave effects in this region as a whole.

  13. Microdistribution of faunal assemblages at deep-sea hydrothermal vents in the Southern Ocean.

    PubMed

    Marsh, Leigh; Copley, Jonathan T; Huvenne, Veerle A I; Linse, Katrin; Reid, William D K; Rogers, Alex D; Sweeting, Christopher J; Tyler, Paul A

    2012-01-01

    Chemosynthetic primary production by microbes supports abundant faunal assemblages at deep-sea hydrothermal vents, with zonation of invertebrate species typically occurring along physico-chemical gradients. Recently discovered vent fields on the East Scotia Ridge (ESR) in the Southern Ocean represent a new province of vent biogeography, but the spatial dynamics of their distinct fauna have yet to be elucidated. This study determines patterns of faunal zonation, species associations, and relationships between faunal microdistribution and hydrothermal activity in a vent field at a depth of 2,400 m on the ESR. Remotely operated vehicle (ROV) dives obtained high-definition imagery of three chimney structures with varying levels of hydrothermal activity, and a mosaic image of >250 m(2) of seafloor co-registered with temperature measurements. Analysis of faunal microdistribution within the mosaiced seafloor reveals a consistent pattern of faunal zonation with increasing distance from vent sources and peak temperatures. Assemblages closest to vent sources are visibly dominated by a new species of anomuran crab, Kiwa n. sp. (abundance >700 individuals m(-2)), followed by a peltospiroid gastropod (>1,500 individuals m(-2)), eolepadid barnacle (>1,500 individuals m(-2)), and carnivorous actinostolid anemone (>30 individuals m(-2)). Peripheral fauna are not dominated by a single taxon, but include predatory and scavenger taxa such as stichasterid seastars, pycnogonids and octopus. Variation in faunal microdistribution on chimneys with differing levels of activity suggests a possible successional sequence for vent fauna in this new biogeographic province. An increase in δ(34)S values of primary consumers with distance from vent sources, and variation in their δ(13)C values also indicate possible zonation of nutritional modes of the vent fauna. By using ROV videography to obtain a high-resolution representation of a vent environment over a greater extent than previous studies

  14. Southern Ocean Asteroidea: a proposed update for the Register of Antarctic Marine Species

    PubMed Central

    Aguera, Antonio; Jossart, Quentin; Danis, Bruno

    2015-01-01

    Abstract Background The Register of Antarctic Marine Species (RAMS, De Broyer et al. 2015) is the regional component of the World Register of Marine Species (WoRMS Editorial Board 2015) in the Southern Ocean. It has been operating for the last ten years, with a special effort devoted towards its completion after the International Polar Year (IPY) in 2007-2008, in the framework of the Census of Antarctic Marine Life (CAML, 2005 - 2010). Its objective is to offer free and open access to a complete register of all known species living in the Southern Ocean, building a workbench of the present taxonomic knowledge for that region. The Antarctic zone defined by this dynamic and community-based tool has been investigated with a particular interest. The Sub-Antarctic zone was a secondary objective during the establishment of the RAMS and is still lacking the impulse of the scientific community for some taxa. New information In the present study, more than 13,000 occurrences records of Asteroidea (Echinodermata) have been compiled within the RAMS area of interest and checked against the RAMS species list of sea stars, using WoRMS Taxon Match tool. Few mismatches (basionym mistakes : i.e. original name misspelled or incorrect) were found within the existing list and 97 unregistered species are actually occurring within the RAMS boundaries. After this update, the number of Asteroidea species was increased by around 50%, now reaching 295 accepted species. PMID:26696769

  15. Coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features

    SciTech Connect

    Comiso, J.C.; McClain, C.R. ); Sullivan, C.W. ); Ryan, J.P. ); Leonard, C.L. )

    1993-02-15

    The spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set (from October 1978 through June 1986). Enhanced pigment concentrations are observed between 35[degrees]S and 55[degrees]S throughout the year, with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter. North and south of the polar front, phytoplankton blooms (>1 mg/m[sup 3]) are not uniformly distributed around the circumpolar region. Instead, blooms appear to be located in regions of ice retreat (or high melt areas) such as the Scotia Sea and the Ross Sea, in relatively shallow areas (e.g., the Patagonian and the New Zealand shelves), in some regions of Ekman upwelling like the Tasman Sea, and near areas of high eddy kinetic such as the Agulhas retroflection. Among all features examined by regression analysis, bathymetry appears to be the one most consistently correlated with pigments (correlation coefficient being about [minus]0.3 for the entire region). The cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the Antarctic region. It is also consistent with resuspension of phytoplankton cells by wind-induced mixing, especially in shallow waters. Nutrients (phosphate, nitrate, and silicate) are found to correlate significantly with pigments when the entire southern ocean is considered, but south of 55[degrees]S the correlation is poor, probably because the Antarctic waters are not nutrient limited. Large interannual variability (>30%) in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters. 66 refs., 13 figs., 6 tabs.

  16. Late Triassic paleogeographic reconstruction along the Neo-Tethyan Ocean margins, southern Tibet

    NASA Astrophysics Data System (ADS)

    Cai, Fulong; Ding, Lin; Laskowski, Andrew K.; Kapp, Paul; Wang, Houqi; Xu, Qiang; Zhang, Liyun

    2016-02-01

    Sandstone petrographic and U-Pb detrital zircon analyses of Upper Triassic sedimentary rocks from the northern margin of India (Tethyan Himalaya Sequence) and southern margin of Eurasia (Lhasa terrane) provide new constraints on the Mesozoic paleogeography of Neo-Tethyan Ocean basins. The Upper Triassic Nieru Formation of the Tethyan Himalaya Sequence (THS) near Lazi city (∼29°N, 87.5°E) is dominated by Indian-affinity, Precambrian detrital zircons, which are typical of the majority of the THS. However, the Upper Triassic Langjiexue Formation of the THS exposed to the east (at 90-93°E longitude) includes significant populations of Permian to Early Jurassic (291-184 Ma) detrital zircons for which there is no known Indian source. In addition, the Upper Triassic Nieru Formation near Kangma town (∼28.5°N, 90°E), located ∼200 km to the southeast of Lazi city, yielded detrital zircon age spectra that are similar to those of Langjiexue Formation. Based on detrital zircon age spectra comparisons, we propose that both the Langjiexue and Nieru formations were derived from continental crustal fragments that were adjacent to the northwestern margin of Australia. Furthermore, we suggest that these THS units, and age-equivalent strata in Northwest Australia, West Sulawesi, Timor and West Papua, comprised a Late Triassic submarine fan along the northern Australian shelf. The Upper Triassic Mailonggang Formation in the southern Lhasa terrane (35 km northeast of Lhasa city, ∼30°N, 91.5°E) is dominated by Permian detrital zircons, which were likely derived from proximal Lhasa terrane sources. The Mailonggang Formation differs from all age-equivalent strata in the Tethyan Himalaya; therefore we interpret that it was separated from Greater India by the Neo-Tethyan Ocean.

  17. Dynamics of the Oligocene Southern Ocean: dinocysts as surface paleoceanographic tracers

    NASA Astrophysics Data System (ADS)

    Bijl, Peter; Houben, Alexander; Brinkhuis, Henk; Sangiorgi, Francesca

    2015-04-01

    The Oligocene Epoch (33.9-23 Ma) is the time interval in the Cenozoic that saw the establishment of a continental-scale Antarctic ice-sheet. There remains a controversy about whether this early episode of a glaciated Antarctica was stable, or whether dynamic ice conditions prevailed. Most of this controversy persists due to the absence of chronostratigraphically well-dated sedimentary archives from close to the east Antarctic ice sheet, which has recorded a direct signal of glacial dynamics. Another major question is how the Oligocene Southern Ocean responded to the glaciation and subsequent evolution of the ice sheet, as the Southern ocean is a major player in global ocean circulation. Numerical modelling studies suggest that alongside the buildup of continental ice on Antarctica, first sea-ice conditions may have started along the East Antarctic Margin, but this conclusion lacks support from field evidence. Other numerical models predict that hysteresis effects within the ice sheet will make a continental-size Antarctic ice sheet rather insensitive to warming. In contrast, deep-water benthic foraminiferal oxygen isotope records across the Oligocene suggest dramatic waxing and waning of Antarctic ice sheets. This paradox is as yet not solved Integrated Ocean Drilling Expedition 318 drilled the Antarctic Margin in 2010, and recovered sediments from the early phase of Antarctic glaciation. With this record, we can now evaluate the robustness of the results of the numerical models and the oceanographic changes with field data. Sediments recovered from Site U1356 yield a thick and relatively complete (albeit compromised by core gaps) Oligocene succession both of which are chrono-stratigraphically well-calibrated with use of nannoplankton- dinocyst- and magnetostratigraphy. Notably, this record yields well-preserved dinoflagellate cysts (dinocysts), which we can use to investigate surface-water condition changes across the Eocene-Oligocene to provide answers to these

  18. Southern Ocean albedo, inter-hemispheric energy transports and the double ITCZ: global impacts of biases in a coupled model

    NASA Astrophysics Data System (ADS)

    Hawcroft, Matt; Haywood, Jim M.; Collins, Mat; Jones, Andy; Jones, Anthony C.; Stephens, Graeme

    2016-06-01

    A causal link has been invoked between inter-hemispheric albedo, cross-equatorial energy transport and the double-Intertropical Convergence Zone (ITCZ) bias in climate models. Southern Ocean cloud biases are a major determinant of inter-hemispheric albedo biases in many models, including HadGEM2-ES, a fully coupled model with a dynamical ocean. In this study, targeted albedo corrections are applied in the Southern Ocean to explore the dynamical response to artificially reducing these biases. The Southern Hemisphere jet increases in strength in response to the increased tropical-extratropical temperature gradient, with increased energy transport into the mid-latitudes in the atmosphere, but no improvement is observed in the double-ITCZ bias or atmospheric cross-equatorial energy transport, a finding which supports other recent work. The majority of the adjustment in energy transport in the tropics is achieved in the ocean, with the response further limited to the Pacific Ocean. As a result, the frequently argued teleconnection between the Southern Ocean and tropical precipitation biases is muted. Further experiments in which tropical longwave biases are also reduced do not yield improvement in the representation of the tropical atmosphere. These results suggest that the dramatic improvements in tropical precipitation that have been shown in previous studies may be a function of the lack of dynamical ocean and/or the simplified hemispheric albedo bias corrections applied in that work. It further suggests that efforts to correct the double ITCZ problem in coupled models that focus on large-scale energetic controls will prove fruitless without improvements in the representation of atmospheric processes.

  19. Seasonal in situ observations of glyoxal and methylglyoxal over the temperate oceans of the Southern Hemisphere

    NASA Astrophysics Data System (ADS)

    Lawson, S. J.; Selleck, P. W.; Galbally, I. E.; Keywood, M. D.; Harvey, M. J.; Lerot, C.; Helmig, D.; Ristovski, Z.

    2015-01-01

    The dicarbonyls glyoxal and methylglyoxal have been measured with 2,4-dinitrophenylhydrazine (2,4-DNPH) cartridges and high-performance liquid chromatography (HPLC), optimised for dicarbonyl detection, in clean marine air over the temperate Southern Hemisphere (SH) oceans. Measurements of a range of dicarbonyl precursors (volatile organic compounds, VOCs) were made in parallel. These are the first in situ measurements of glyoxal and methylglyoxal over the remote temperate oceans. Six 24 h samples were collected in summer (February-March) over the Chatham Rise in the south-west Pacific Ocean during the Surface Ocean Aerosol Production (SOAP) voyage in 2012, while 34 24 h samples were collected at Cape Grim Baseline Air Pollution Station in the late winter (August-September) of 2011. Average glyoxal mixing ratios in clean marine air were 7 ppt at Cape Grim and 23 ppt over Chatham Rise. Average methylglyoxal mixing ratios in clean marine air were 28 ppt at Cape Grim and 10 ppt over Chatham Rise. The mixing ratios of glyoxal at Cape Grim are the lowest observed over the remote oceans, while mixing ratios over Chatham Rise are in good agreement with other temperate and tropical observations, including concurrent Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations. Methylglyoxal mixing ratios at both sites are comparable to the only other marine methylglyoxal observations available over the tropical Northern Hemisphere (NH) ocean. Ratios of glyoxal : methylglyoxal > 1 over Chatham Rise but < 1 at Cape Grim suggest that a different formation and/or loss processes or rates dominate at each site. Dicarbonyl precursor VOCs, including isoprene and monoterpenes, are used to calculate an upper-estimate yield of glyoxal and methylglyoxal in the remote marine boundary layer and explain at most 1-3 ppt of dicarbonyls observed, corresponding to 10% and 17% of the observed glyoxal and 29 and 10% of the methylglyoxal at Chatham Rise and Cape Grim

  20. Seasonal in situ observations of glyoxal and methylglyoxal over the temperate oceans of the Southern Hemisphere

    NASA Astrophysics Data System (ADS)

    Lawson, S. J.; Selleck, P. W.; Galbally, I. E.; Keywood, M. D.; Harvey, M. J.; Lerot, C.; Helmig, D.; Ristovski, Z.

    2014-08-01

    Dicarbonyls glyoxal and methylglyoxal have been measured with 2,4-dinitrophenylhydrazine (2,4-DNPH) cartridges and high performance liquid chromatography (HPLC), optimised for dicarbonyl detection, in clean marine air over the temperate Southern Hemisphere (SH) oceans. Measurements of a range of dicarbonyl precursors (volatile organic compounds, VOCs) were made in parallel. These are the first in situ measurements of glyoxal and methylglyoxal over the remote temperate oceans. Six 24 h samples were collected in late summer (February-March) over the Chatham Rise in the South West Pacific Ocean during the Surface Ocean Aerosol Production (SOAP) voyage in 2012, while 34 24 h samples were collected at Cape Grim Baseline Air Pollution Station in late winter (August-September) 2011. Average glyoxal mixing ratios in clean marine air were 7 ppt at Cape Grim, and 24 ppt over Chatham Rise. Average methylglyoxal mixing ratios in clean marine air were 28 ppt at Cape Grim and 12 ppt over Chatham Rise. The mixing ratios of glyoxal at Cape Grim are the lowest observed over the remote oceans, while mixing ratios over Chatham Rise are in good agreement with other temperate and tropical observations, including concurrent MAX-DOAS observations. Methylglyoxal mixing ratios at both sites are comparable to the only other marine methylglyoxal observations available over the tropical Northern Hemisphere (NH) ocean. Ratios of glyoxal : methylglyoxal > 1 over Chatham Rise but < 1 at Cape Grim, suggesting different formation and/or loss processes or rates dominate at each site. Dicarbonyl precursor VOCs, including isoprene and monoterpenes, are used to calculate an upper estimate yield of glyoxal and methylglyoxal in the remote marine boundary layer and explain at most 1-3 ppt of dicarbonyls observed, corresponding to 11 and 17% of the observed glyoxal and 28 and 10% of the methylglyoxal at Chatham Rise and Cape Grim, respectively, highlighting a significant but as yet unknown production

  1. Atmospheric drying as the main driver of dramatic glacier wastage in the southern Indian Ocean

    PubMed Central

    Favier, V.; Verfaillie, D.; Berthier, E.; Menegoz, M.; Jomelli, V.; Kay, J. E.; Ducret, L.; Malbéteau, Y.; Brunstein, D.; Gallée, H.; Park, Y.-H.; Rinterknecht, V.

    2016-01-01

    The ongoing retreat of glaciers at southern sub-polar latitudes is particularly rapid and widespread. Akin to northern sub-polar latitudes, this retreat is generally assumed to be linked to warming. However, no long-term and well-constrained glacier modeling has ever been performed to confirm this hypothesis. Here, we model the Cook Ice Cap mass balance on the Kerguelen Islands (Southern Indian Ocean, 49°S) since the 1850s. We show that glacier wastage during the 2000s in the Kerguelen was among the most dramatic on Earth. We attribute 77% of the increasingly negative mass balance since the 1960s to atmospheric drying associated with a poleward shift of the mid-latitude storm track. Because precipitation modeling is very challenging for the current generation of climate models over the study area, models incorrectly simulate the climate drivers behind the recent glacier wastage in the Kerguelen. This suggests that future glacier wastage projections should be considered cautiously where changes in atmospheric circulation are expected. PMID:27580801

  2. Quantifying connectivity in the coastal ocean with application to the Southern California Bight

    NASA Astrophysics Data System (ADS)

    Mitarai, S.; Siegel, D. A.; Watson, J. R.; Dong, C.; McWilliams, J. C.

    2009-10-01

    The quantification of coastal connectivity is important for a wide range of real-world applications ranging from assessment of pollutant risk to nearshore fisheries management. For these purposes, coastal connectivity can be defined as the probability that water parcels from one location have advected to another site over a given time interval. Here we demonstrate how to quantify connectivity using Lagrangian probability-density functions (PDFs) based on numerical solutions of the coastal circulation of the Southern California Bight (SCB). Ensemble mean dispersal patterns from a single release site show strong dependencies on particle-release location, season, and year, reflecting annual and interannual circulation patterns in the SCB. Mean connectivity patterns are heterogeneous for the advection time of 30 days or less, due to local circulation patterns, and they become more homogeneous for longer advection times. However, connectivity patterns for a single realization are highly variable because of intrinsic eddy-driven transport and synoptic wind-forcing variability. In the long term, mainland sites are good sources while both Northern and Southern Channel Islands are poor sources, although they receive substantial fluxes of water parcels from the mainland. The predicted connectivity gives useful information to ecological and other applications for the SCB (e.g., designing marine protected areas and predicting the impact of a pollution event) and demonstrates how high-resolution numerical solutions of coastal ocean circulations can be used to quantify nearshore connectivity.

  3. Atmospheric drying as the main driver of dramatic glacier wastage in the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Favier, V.; Verfaillie, D.; Berthier, E.; Menegoz, M.; Jomelli, V.; Kay, J. E.; Ducret, L.; Malbéteau, Y.; Brunstein, D.; Gallée, H.; Park, Y.-H.; Rinterknecht, V.

    2016-09-01

    The ongoing retreat of glaciers at southern sub-polar latitudes is particularly rapid and widespread. Akin to northern sub-polar latitudes, this retreat is generally assumed to be linked to warming. However, no long-term and well-constrained glacier modeling has ever been performed to confirm this hypothesis. Here, we model the Cook Ice Cap mass balance on the Kerguelen Islands (Southern Indian Ocean, 49°S) since the 1850s. We show that glacier wastage during the 2000s in the Kerguelen was among the most dramatic on Earth. We attribute 77% of the increasingly negative mass balance since the 1960s to atmospheric drying associated with a poleward shift of the mid-latitude storm track. Because precipitation modeling is very challenging for the current generation of climate models over the study area, models incorrectly simulate the climate drivers behind the recent glacier wastage in the Kerguelen. This suggests that future glacier wastage projections should be considered cautiously where changes in atmospheric circulation are expected.

  4. Carbohydrate Production and Consumption In Phytoplankton Subjected To Iron Fertilisation In The Southern Ocean

    NASA Astrophysics Data System (ADS)

    van Oijen, T.; Veldhuis, M. J. W.; van Leeuwe, M. A.; de Baar, H. J. W.

    Iron concentrations in the Southern Ocean are generally low. At these concentrations microalgal growth, in particular of large diatoms, is affected because iron plays a central role in photosynthesis and several metabolic processes. During the Polarstern 2000 iron release experiment, we studied the effect of in situ iron enrichment on the microalgal production and consumption of intracellular carbohydrates. The experi- ment was performed in the Southern Polar Frontal Zone and lasted three weeks. Dur- ing the course of the experiment, discrete samples were taken along vertical profiles (0-100m), both in the centre of the iron enriched patch and outside the patch. In the patch, the particulate carbohydrate concentration had doubled at the end of the exper- iment. An increasing part of the carbohydrates was produced by large diatom cells (>10 micrometer). Outside the patch, little changes were observed. On day 6, 10 and 19 after the release, seawater from inside and outside the patch was incubated on deck for 24h. In all three deck incubations, the diurnal production and nocturnal con- sumption of intracellular carbohydrates by phytoplankton were higher in iron-enriched bottles. Concluding, particulate carbohydrate concentration showed to be a sensitive parameter that clearly responded to iron fertilisation. This study contributes to a bet- ter understanding of factors governing phytoplankton growth in High Nitrogen Low Chlorophyll areas.

  5. Enhanced Carbohydrate Production by Phytoplankton of the Southern Ocean in Response to Iron Fertilization

    NASA Astrophysics Data System (ADS)

    van Oijen, T.; Veldhuis, M. J.; van Leeuwe, M. A.; de Baar, H. J.

    2002-12-01

    Iron concentrations in the Southern Ocean are generally low. At these concentrations microalgal growth, in particular of large diatoms, is affected because iron plays a central role in photosynthesis and several metabolic processes. During the Polarstern 2000 iron release experiment, we studied the effect of in situ iron enrichment on the microalgal production and consumption of water-extractable carbohydrates. The experiment was performed in the Southern Polar Frontal Zone and lasted three weeks. During the course of the experiment, discrete samples were taken along vertical profiles (0-100m), both in the center of the iron enriched patch and outside the patch. In the patch, the carbohydrate concentration in the particulate fraction had doubled at the end of the experiment. An increasing part of the carbohydrates was produced by large diatom cells. Outside the patch, little changes were observed. On day 6, 10 and 19 after the release, seawater from inside and outside the patch was incubated on deck for 24h. In all three deck incubations, the diurnal production and nocturnal consumption of carbohydrates by phytoplankton were higher in iron-enriched bottles. Concluding, carbohydrate production showed to be a sensitive parameter that clearly indicated enhanced phytoplankton growth in response to iron fertilization. This study contributes to a better understanding of factors governing phytoplankton growth in High Nitrogen Low Chlorophyll areas.

  6. Atmospheric drying as the main driver of dramatic glacier wastage in the southern Indian Ocean.

    PubMed

    Favier, V; Verfaillie, D; Berthier, E; Menegoz, M; Jomelli, V; Kay, J E; Ducret, L; Malbéteau, Y; Brunstein, D; Gallée, H; Park, Y-H; Rinterknecht, V

    2016-01-01

    The ongoing retreat of glaciers at southern sub-polar latitudes is particularly rapid and widespread. Akin to northern sub-polar latitudes, this retreat is generally assumed to be linked to warming. However, no long-term and well-constrained glacier modeling has ever been performed to confirm this hypothesis. Here, we model the Cook Ice Cap mass balance on the Kerguelen Islands (Southern Indian Ocean, 49°S) since the 1850s. We show that glacier wastage during the 2000s in the Kerguelen was among the most dramatic on Earth. We attribute 77% of the increasingly negative mass balance since the 1960s to atmospheric drying associated with a poleward shift of the mid-latitude storm track. Because precipitation modeling is very challenging for the current generation of climate models over the study area, models incorrectly simulate the climate drivers behind the recent glacier wastage in the Kerguelen. This suggests that future glacier wastage projections should be considered cautiously where changes in atmospheric circulation are expected. PMID:27580801

  7. Teleconnections of the Southern Oscillation in the tropical Atlantic sector in the OSU coupled upper ocean-atomosphere GCM

    SciTech Connect

    Hameed, S.; Meinster, A. ); Sperber, K.R. )

    1993-03-01

    The Oregon State University coupled upper ocean-atmosphere GCM has been shown to qualitatively simulate the Southern Oscillation. A composite analysis of the warm and cold events simulated in this 23-year integration has been performed. During the low phase of the Southern Oscillation, when warm anomalies occur in the eastern Pacific, the model simulates for the Atlantic region during March-May (1) a deficit of precipitation over the tropical South American continent, (2) Caribbean and Gulf of Mexico sea level pressure and sea surface temperature are in phase with the eastern Pacific anomalies, while those east of the Nordeste region are out of phase, and (3) northeast trade winds are anomalously weak and southwest trade winds are anomalously strong (as inferred from surface current anomalies). The anomalies in the oceanic processes are induced by perturbations in the atmospheric circulation over the Atlantic and are coupled to changes in the Walker circulation. During the high phase of the simulated Southern Oscillation, conditions in the atmosphere and ocean are essentially the reverse of the low phase. The model produces a response in the South American region during the opposing phases of the Southern Oscillation that is in general agreement with observations. The interannual variation of Nordeste rainfall is shown to be dominated by a few band-limited frequencies. These frequencies are found in the SST series of those regions of the Atlantic and Pacific oceans where strong correlations with Nordeste precipitation exist.

  8. The link between meiofauna and surface productivity in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Lins, L.; Guilini, K.; Veit-Köhler, G.; Hauquier, F.; Alves, R. M. S.; Esteves, A. M.; Vanreusel, A.

    2014-10-01

    Particulate organic carbon (POC) export fluxes generally reflect patterns of primary production in the upper ocean, sinking to the seabed and acting as a food source for benthic organisms. Data on meiobenthic communities from two SYSTem COupling cruises (SYSTCO) in the deep Southern Ocean (RV Polarstern ANT-XXIV/2, north-south transect along the prime meridian, and ANT-XXVIII/3, east-west transect along the Polar Front) were combined with surface and benthic environmental parameters, as well as POC flux estimates based on satellite measurements. It was tested to what extent meiofaunal communities were determined by prevailing conditions of an east-west increase in net primary productivity (NPP) and bottom Chlorophyll a (Chla) concentration, and a westwards, divergently decreasing estimated POC flux. Nematodes dominated the meiofauna (84.4-92.4%) and occurred with a westward increase in relative abundance and density for the ANT-XXVIII/3 stations, associated with a parallel increase in NPP and Chla. Nematode biomass was negatively correlated to the estimated POC flux. Along the north-south transect no significant correlation was found but higher estimated POC fluxes at stations south of the Polar Front were associated with higher meiofauna diversity and density at higher taxon level, while stations located at the Polar Front, which were associated with lower POC fluxes, contained communities with lower diversity and density.

  9. The Southern Ocean ecosystem under multiple climate change stresses--an integrated circumpolar assessment.

    PubMed

    Gutt, Julian; Bertler, Nancy; Bracegirdle, Thomas J; Buschmann, Alexander; Comiso, Josefino; Hosie, Graham; Isla, Enrique; Schloss, Irene R; Smith, Craig R; Tournadre, Jean; Xavier, José C

    2015-04-01

    A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem.

  10. Surface heat flow measurements from the East Siberian continental slope and southern Lomonosov Ridge, Arctic Ocean

    NASA Astrophysics Data System (ADS)

    O'Regan, Matt; Preto, Pedro; Stranne, Christian; Jakobsson, Martin; Koshurnikov, Andrey

    2016-05-01

    Surface heat flow data in the Arctic Ocean are needed to assess hydrocarbon and methane hydrate distributions, and provide constraints into the tectonic origins and nature of underlying crust. However, across broad areas of the Arctic, few published measurements exist. This is true for the outer continental shelf and slope of the East Siberian Sea, and the adjoining deep water ridges and basins. Here we present 21 new surface heat flow measurements from this region of the Arctic Ocean. On the Southern Lomonosov Ridge, the average measured heat flow, uncorrected for effects of sedimentation and topography, is 57 ± 4 mW/m2 (n = 4). On the outer continental shelf and slope of the East Siberian Sea (ESS), the average is 57 ± 10 mW/m2 (n = 16). An anomalously high heat flow of 203 ± 28 mW/m2 was measured at a single station in the Herald Canyon. With the exception of this high heat flow, the new data from the ESS are consistent with predictions for thermally equilibrated lithosphere of continental origin that was last affected by thermotectonic processes in the Cretaceous to early Cenozoic. Variability within the data likely arises from differences in radiogenic heat production within the continental crust and overlying sediments. This can be further explored by comparing the data with geophysical constraints on sediment and crustal thicknesses.

  11. Connectivity, small islands and large distances: the Cellana strigilis limpet complex in the Southern Ocean.

    PubMed

    Reisser, Céline M O; Wood, Ann R; Bell, James J; Gardner, Jonathan P A

    2011-08-01

    The Southern Ocean contains some of the most isolated islands on Earth, and fundamental questions remain regarding their colonization and the connectivity of their coastal biotas. Here, we conduct a genetic investigation into the Cellana strigilis (limpet) complex that was originally classified based on morphological characters into six subspecies, five of which are endemic to the New Zealand (NZ) subantarctic and Chatham islands (44-52°S). Previous genetic analyses of C. strigilis from six of the seven island groups revealed two lineages with little or no within-lineage variation. We analysed C. strigilis samples from all seven island groups using two mitochondrial (COI and 16S), one nuclear (ATPase β) and 58 loci from four randomly amplified polymorphic DNA markers (RAPDs) and confirmed the existence of two distinct lineages. The pronounced genetic structuring within each lineage and the presence of private haplotypes in individual islands are the result of little genetic connectivity and therefore very high self-recruitment. This study supports the significance of the subantarctic islands as refugia during the last glacial maximum and adds to the knowledge of contemporary population connectivity among coastal populations of remote islands in large oceans and the distance barrier to gene flow that exists in the sea (despite its continuous medium) for most taxa.

  12. Global cooperation among diverse organizations to reduce illegal fishing in the Southern Ocean.

    PubMed

    Osterblom, Henrik; Bodin, Orjan

    2012-08-01

    Illegal, unreported, and unregulated (IUU) fishing is prevalent globally and has detrimental effects on commercial fish stocks and nontarget species. Effective monitoring and enforcement aimed at reducing the level of IUU fishing in extensive, remote ocean fisheries requires international collaboration. Changes in trade and vessel activities further complicate enforcement. We used a web-based survey of governmental and nongovernmental organizations engaged in reducing IUU fishing in the Southern Ocean to collect information on interorganizational collaborations. We used social-network analyses to examine the nature of collaborations among the identified 117 organizations engaged in reducing IUU fishing. International collaboration improved the ability to control and manage harvest of commercially important toothfish (Dissostichus spp.) stocks and reduced bycatch of albatrosses (Diomedeidae) and petrels (Procellariidae) in longlines of IUU fishing vessels. The diverse group of surveyed organizations cooperated frequently, thereby making a wide range of resources available for improved detection of suspected IUU vessels and trade flows, cooperation aimed at prosecuting suspected offenders or developing new policy measures. Our results suggest the importance of a central agency for coordination and for maintaining commonly agreed-upon protocols for communication that facilities collaboration. Despite their differences, the surveyed organizations have developed common perceptions about key problems associated with IUU fishing. This has likely contributed to a sustained willingness to invest in collaborations. Our results show that successful international environmental governance can be accomplished through interorganizational collaborations. Such cooperation requires trust, continuous funding, and incentives for actors to participate.

  13. Case studies of nonorographic gravity waves over the Southern Ocean emphasize the role of moisture

    NASA Astrophysics Data System (ADS)

    Plougonven, Riwal; Hertzog, Albert; Alexander, M. Joan

    2015-02-01

    Two case studies of nonorographic gravity waves are carried out for wave events that occurred over the Southern Ocean in November 2005. Mesoscale simulations were carried out with the Weather and Research Forecast model. The simulated waves were compared to observations from superpressure balloons of the Vorcore campaign and from the High Resolution Dynamic Limb Sounder satellite. Satisfactory agreement is found, giving confidence in the estimations of wave parameters and amplitudes. For the amplitudes, both the model and observations provide a lower bound, for different reasons. Waves are found in the lower stratosphere with horizontal wavelengths of the order of 150-200 km in the horizontal, 5-8 km in the vertical, corresponding to intrinsic frequencies between 5 and 10 f, where f is the Coriolis parameter. Although the tropospheric flow is very different between the two cases, there are features which are common and appear significant for the gravity waves: these include intense localized updrafts associated with convection in the troposphere and a displaced polar vortex inducing strong winds in the stratosphere above the frontal region. Relative to theoretical expectations, the simulations emphasize the role of moisture. Intrinsic frequencies are significantly higher than those expected for waves produced by dry spontaneous generation from jets. To quantify the contribution of moisture, dry simulations were carried out, yielding momentum fluxes over oceanic regions that were 2.5 times weaker. Identification of the generation mechanisms in these complex flows calls for further study, and these should include moisture and a realistic stratospheric jet.

  14. Dimethylsulfide gas transfer coefficients from algal blooms in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Bell, T. G.; De Bruyn, W.; Marandino, C. A.; Miller, S. D.; Law, C. S.; Smith, M. J.; Saltzman, E. S.

    2015-02-01

    Air-sea dimethylsulfide (DMS) fluxes and bulk air-sea gradients were measured over the Southern Ocean in February-March 2012 during the Surface Ocean Aerosol Production (SOAP) study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (> 15 nM). Gas transfer coefficients were considerably scattered at wind speeds above 5 m s-1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind-speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data show no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.

  15. Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

    PubMed Central

    Prasanna, K.; Ghosh, Prosenjit; Bhattacharya, S. K.; Mohan, K.; Anilkumar, N.

    2016-01-01

    Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ18O and δ13C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75–200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ18O and δ13C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a ‘vital effect’ or a higher calcification rate. An interesting pattern of increase in the δ13C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ13C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude. PMID:26903274

  16. Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean

    NASA Astrophysics Data System (ADS)

    Prasanna, K.; Ghosh, Prosenjit; Bhattacharya, S. K.; Mohan, K.; Anilkumar, N.

    2016-02-01

    Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ18O and δ13C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75-200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ18O and δ13C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a ‘vital effect’ or a higher calcification rate. An interesting pattern of increase in the δ13C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ13C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude.

  17. DMS gas transfer coefficients from algal blooms in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Bell, T. G.; De Bruyn, W.; Marandino, C. A.; Miller, S. D.; Law, C. S.; Smith, M. J.; Saltzman, E. S.

    2014-11-01

    Air/sea dimethylsulfide (DMS) fluxes and bulk air/sea gradients were measured over the Southern Ocean in February/March 2012 during the Surface Ocean Aerosol Production (SOAP) study. The cruise encountered three distinct phytoplankton bloom regions, consisting of two blooms with moderate DMS levels, and a high biomass, dinoflagellate-dominated bloom with high seawater DMS levels (>15 nM). Gas transfer coefficients were considerably scattered at wind speeds above 5 m s-1. Bin averaging the data resulted in a linear relationship between wind speed and mean gas transfer velocity consistent with that previously observed. However, the wind speed-binned gas transfer data distribution at all wind speeds is positively skewed. The flux and seawater DMS distributions were also positively skewed, which suggests that eddy covariance-derived gas transfer velocities are consistently influenced by additional, log-normal noise. A~flux footprint analysis was conducted during a transect into the prevailing wind and through elevated DMS levels in the dinoflagellate bloom. Accounting for the temporal/spatial separation between flux and seawater concentration significantly reduces the scatter in computed transfer velocity. The SOAP gas transfer velocity data shows no obvious modification of the gas transfer-wind speed relationship by biological activity or waves. This study highlights the challenges associated with eddy covariance gas transfer measurements in biologically active and heterogeneous bloom environments.

  18. Upwelling in the Atlantic sector of the Southern Ocean inferred from helium isotope disequilibrium

    NASA Astrophysics Data System (ADS)

    Buß, A.; Huhn, O.; Sültenfuß, J.; Rhein, M.

    2012-04-01

    Upwelling plays an important role regarding the physical and biogeochemical characteristics of the mixed layer, and it may also counteract the uptake of atmospheric gases like CO2. However, estimates of upwelling velocities are rare, particularly in the Southern Ocean. Since upwelling velocities are too small to be measured directly - in the order of a few meters per day - an indirect method to infer upwelling velocities from the helium isotope disequilibrium in the mixed layer is applied here instead. The main source of 3He to the ocean is hydrothermal venting and thus a significant excess of 3He in the mixed layer can only be maintained by vertical motion. Helium isotope data - measured from 1986 to 2009 - in the Antarctic Circumpolar Current (ACC) and the Weddell Sea shows a significant excess of 3He in the mixed layer from which upwelling velocities will be inferred. Here, first results of upwelling estimates inferred from helium isotope disequilibria in the ACC and the Weddell Sea will be presented.

  19. Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

    NASA Astrophysics Data System (ADS)

    Rosengard, S. Z.; Lam, P. J.; Balch, W. M.; Auro, M. E.; Pike, S.; Drapeau, D.; Bowler, B.

    2015-07-01

    Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize, and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of > 51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition, and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-rich communities produce large and labile POC aggregates, which not only generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

  20. Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

    NASA Astrophysics Data System (ADS)

    Rosengard, S. Z.; Lam, P. J.; Balch, W. M.; Auro, M. E.; Pike, S.; Drapeau, D.; Bowler, B.

    2015-02-01

    Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of >51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-dominated communities produce large and labile POC aggregates, which generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

  1. Isotopic disequilibrium in Globigerina bulloides and carbon isotope response to productivity increase in Southern Ocean.

    PubMed

    Prasanna, K; Ghosh, Prosenjit; Bhattacharya, S K; Mohan, K; Anilkumar, N

    2016-01-01

    Oxygen and carbon isotope ratios in planktonic foraminifera Globigerina bulloides collected from tow samples along a transect from the equatorial Indian ocean to the Southern Ocean (45°E and 80°E and 10°N to 53°S) were analysed and compared with the equilibrium δ(18)O and δ(13)C values of calcite calculated using the temperature and isotopic composition of the water column. The results agree within ~0.25‰ for the region between 10°N and 40°S and 75-200 m water depth which is considered to be the habitat of Globigerina bulloides. Further south (from 40°S to 55°S), however, the measured δ(18)O and δ(13)C values are higher than the expected values by ~2‰ and ~1‰ respectively. These enrichments can be attributed to either a 'vital effect' or a higher calcification rate. An interesting pattern of increase in the δ(13)C(DIC) value of the surface water with latitude is observed between 35°S and~ 60°S, with a peak at~ 42°S. This can be caused by increased organic matter production and associated removal. A simple model accounting for the increase in the δ(13)C(DIC) values is proposed which fits well with the observed chlorophyll abundance as a function of latitude. PMID:26903274

  2. The Southern Ocean ecosystem under multiple climate change stresses--an integrated circumpolar assessment.

    PubMed

    Gutt, Julian; Bertler, Nancy; Bracegirdle, Thomas J; Buschmann, Alexander; Comiso, Josefino; Hosie, Graham; Isla, Enrique; Schloss, Irene R; Smith, Craig R; Tournadre, Jean; Xavier, José C

    2015-04-01

    A quantitative assessment of observed and projected environmental changes in the Southern Ocean (SO) with a potential impact on the marine ecosystem shows: (i) large proportions of the SO are and will be affected by one or more climate change processes; areas projected to be affected in the future are larger than areas that are already under environmental stress, (ii) areas affected by changes in sea-ice in the past and likely in the future are much larger than areas affected by ocean warming. The smallest areas (<1% area of the SO) are affected by glacier retreat and warming in the deeper euphotic layer. In the future, decrease in the sea-ice is expected to be widespread. Changes in iceberg impact resulting from further collapse of ice-shelves can potentially affect large parts of shelf and ephemerally in the off-shore regions. However, aragonite undersaturation (acidification) might become one of the biggest problems for the Antarctic marine ecosystem by affecting almost the entire SO. Direct and indirect impacts of various environmental changes to the three major habitats, sea-ice, pelagic and benthos and their biota are complex. The areas affected by environmental stressors range from 33% of the SO for a single stressor, 11% for two and 2% for three, to <1% for four and five overlapping factors. In the future, areas expected to be affected by 2 and 3 overlapping factors are equally large, including potential iceberg changes, and together cover almost 86% of the SO ecosystem. PMID:25369312

  3. MODIS imagery as a tool for water quality assessments in southern California coastal ocean

    NASA Astrophysics Data System (ADS)

    Nezlin, N. P.; Digiacomo, P. M.; Jones, B. H.; Reifel, K. M.; Warrick, J. A.; Johnson, S. C.; Mengel, M.

    2007-05-01

    Stormwater plumes are main source of coastal pollution in southern California coastal waters. The data on surface salinity, concentrations of total suspended solids (TSS), colored dissolved organic matter (CDOM) and bacterial counts collected during the Bight'03 Regional Water Quality Program surveys in February 2004 and February-March 2005 were compared to MODIS-Aqua satellite imagery. The spectra of normalized water-leaving radiation (nLw) were different in plumes and in ambient ocean waters, enabling plumes discrimination and plume area size assessments from remotely-sensed data. The plume/ocean nLw differences (i.e., plume optical signatures) were most evident during first days after the rainstorm and less evident in the area where TSS concentration in discharged water was lower than in other regions. The accuracy of plume area assessments from satellite imagery was not high (77% on average), seemingly because of inexactitude in satellite data processing. In particular, the expected correlation between remotely-sensed CDOM absorption estimated by Lee's quasi-analytical algorithm (QAA) and CDOM concentrations in water column was often obscured by external factors including wind-driven sea state and phytoplankton blooms. Nevertheless, satellite imagery is a useful tool for estimation of the extension of polluted plumes, which is hardly achievable by contact methods.

  4. Global cooperation among diverse organizations to reduce illegal fishing in the Southern Ocean.

    PubMed

    Osterblom, Henrik; Bodin, Orjan

    2012-08-01

    Illegal, unreported, and unregulated (IUU) fishing is prevalent globally and has detrimental effects on commercial fish stocks and nontarget species. Effective monitoring and enforcement aimed at reducing the level of IUU fishing in extensive, remote ocean fisheries requires international collaboration. Changes in trade and vessel activities further complicate enforcement. We used a web-based survey of governmental and nongovernmental organizations engaged in reducing IUU fishing in the Southern Ocean to collect information on interorganizational collaborations. We used social-network analyses to examine the nature of collaborations among the identified 117 organizations engaged in reducing IUU fishing. International collaboration improved the ability to control and manage harvest of commercially important toothfish (Dissostichus spp.) stocks and reduced bycatch of albatrosses (Diomedeidae) and petrels (Procellariidae) in longlines of IUU fishing vessels. The diverse group of surveyed organizations cooperated frequently, thereby making a wide range of resources available for improved detection of suspected IUU vessels and trade flows, cooperation aimed at prosecuting suspected offenders or developing new policy measures. Our results suggest the importance of a central agency for coordination and for maintaining commonly agreed-upon protocols for communication that facilities collaboration. Despite their differences, the surveyed organizations have developed common perceptions about key problems associated with IUU fishing. This has likely contributed to a sustained willingness to invest in collaborations. Our results show that successful international environmental governance can be accomplished through interorganizational collaborations. Such cooperation requires trust, continuous funding, and incentives for actors to participate. PMID:22624623

  5. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes.

    PubMed

    Gottschalk, Julia; Skinner, Luke C; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L; Waelbroeck, Claire

    2016-01-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and (14)C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes. PMID:27187527

  6. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes

    NASA Astrophysics Data System (ADS)

    Gottschalk, Julia; Skinner, Luke C.; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L.; Waelbroeck, Claire

    2016-05-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean-atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air-sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes.

  7. Coastal ocean climatology of temperature and salinity off the Southern California Bight: Seasonal variability, climate index correlation, and linear trend

    NASA Astrophysics Data System (ADS)

    Kim, Sung Yong; Cornuelle, Bruce D.

    2015-11-01

    A coastal ocean climatology of temperature and salinity in the Southern California Bight is estimated from conductivity-temperature-depth (CTD) and bottle sample profiles collected by historical California Cooperative Oceanic Fisheries Investigation (CalCOFI) cruises (1950-2009; quarterly after 1984) off southern California and quarterly/monthly nearshore CTD surveys (within 30 km from the coast except for the surfzone; 1999-2009) off San Diego and Los Angeles. As these fields are sampled regularly in space, but not in time, conventional Fourier analysis may not be possible. The time dependent temperature and salinity fields are modeled as linear combinations of an annual cycle and its five harmonics, as well as three standard climate indices (El Niňo-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO)), the Scripps Pier temperature time series, and a mean and linear trend without time lags. Since several of the predictor indices are correlated, the indices are successively orthogonalized to eliminate ambiguity in the identification of the contributed variance of each component. Regression coefficients are displayed in both vertical transects and horizontal maps to evaluate (1) whether the temporal and spatial scales of the two data sets of nearshore and offshore observations are consistent and (2) how oceanic variability at a regional scale is related to variability in the nearshore waters. The data-derived climatology can be used to identify anomalous events and atypical behaviors in regional-scale oceanic variability and to provide background ocean estimates for mapping or modeling.

  8. Wide Range of Mercury Contamination in Chicks of Southern Ocean Seabirds

    PubMed Central

    Blévin, Pierre; Carravieri, Alice; Jaeger, Audrey; Chastel, Olivier; Bustamante, Paco; Cherel, Yves

    2013-01-01

    Using top predators as sentinels of the marine environment, Hg contamination was investigated within the large subantarctic seabird community of Kerguelen Islands, a remote area from the poorly known Southern Indian Ocean. Chicks of 21 sympatric seabirds presented a wide range of Hg concentrations, with the highest contaminated species containing ∼102 times more feather Hg than the less contaminated species. Hence, Kerguelen seabirds encompass the whole range of chick feather Hg values that were previously collected worldwide in poorly industrialized localities. Using stable isotopes, the effects of foraging habitats (reflected by δ13C) and trophic positions (reflected by δ15N) on Hg concentrations were investigated. Species-related Hg variations were highly and positively linked to feather δ15N values, thus highlighting the occurrence of efficient Hg biomagnification processes within subantarctic marine trophic webs. By contrast, Hg contamination overall correlated poorly with feeding habitats, because of the pooling of species foraging within different isotopic gradients corresponding to distinct seabird habitats (benthic, pelagic, neritic and oceanic). However, when focusing on oceanic seabirds, Hg concentration was related to feather δ13C values, with species feeding in colder waters (lower δ13C values) south of Kerguelen Islands being less prone to be contaminated than species feeding in northern warmer waters (higher δ13C values). Within the context of continuous increase in global Hg emissions, Kerguelen Islands that are located far away from anthropogenic sources can be considered as an ideal study site to monitor the temporal trend of global Hg contamination. The present work helps selecting some seabird species as sentinels of environmental pollution according to their high Hg concentrations and their contrasted foraging ecology. PMID:23349912

  9. Airborne dust transport to the eastern Pacific Ocean off southern California: Evidence from San Clemente Island

    USGS Publications Warehouse

    Muhs, D.R.; Budahn, J.; Reheis, M.; Beann, J.; Skipp, G.; Fisher, E.

    2007-01-01

    Islands are natural dust traps, and San Clemente Island, California, is a good example. Soils on marine terraces cut into Miocene andesite on this island are clay-rich Vertisols or Alfisols with vertic properties. These soils are overlain by silt-rich mantles, 5-20 cm thick, that contrast sharply with the underlying clay-rich subsoils. The silt mantles have a mineralogy that is distinct from the island bedrock. Silt mantles are rich in quartz, which is rare in the island andesite. The clay fraction of the silt mantles is dominated by mica, also absent from local andesite, and contrasts with the subsoils, dominated by smectite. Ternary plots of immobile trace elements (Sc-Th-La and Ta-Nd-Cr) show that the island andesite has a composition intermediate between average upper continental crust and average oceanic crust. In contrast, the silt and, to a lesser extent, clay fractions of the silt mantles have compositions closer to average upper continental crust. The silt mantles have particle size distributions similar to loess and Mojave Desert dust, but are coarser than long-range-transported Asian dust. We infer from these observations that the silt mantles are derived from airborne dust from the North American mainland, probably river valleys in the coastal mountains of southern California and/or the Mojave Desert. Although average winds are from the northwest in coastal California, easterly winds occur numerous times of the year when "Santa Ana" conditions prevail, caused by a high-pressure cell centered over the Great Basin. Examination of satellite imagery shows that easterly Santa Ana winds carry abundant dust to the eastern Pacific Ocean and the California Channel Islands. Airborne dust from mainland North America may be an important component of the offshore sediment budget in the easternmost Pacific Ocean, a finding of potential biogeochemical and climatic significance.

  10. Seismic properties of the Nazca oceanic crust in southern Peruvian subduction system

    NASA Astrophysics Data System (ADS)

    Kim, Y.; Clayton, R. W.

    2015-12-01

    The horizontal Nazca slab, extending over a distance of ~800 km along the trench is one of enigmatic features in Peruvian subduction zone. Increased buoyancy of the oceanic lithosphere alone due to the subduction of Nazca Ridge is insufficient to fully explain such a lengthy segment. We use data from the recent seismic experiment in southern Peru to find that the subduction-related hydration plays a major role in controlling shear wave velocities within the upper part of the oceanic crust and overlying materials. We observe substantial velocity reductions of ~20-40% near the top plate interface along- and perpendicular-to the trench from ~40-120 km depths. In particular, significant shear wave velocity reductions and subsequently higher P-to-S velocity ratio (exceeding 2.0) at the flat slab region suggest that the seismically probed layer is fluid-rich and mechanically weak. The dominant source of fluid comes from metasediments and subducted crust (Nazca Ridge). Long-term supply of fluid from the southward migrating Nazca Ridge provides additional buoyancy of the subducting oceanic lithosphere and also lowers the viscosity of the overlying mantle wedge to drive and sustain the flat plate segment of ~800 km along the trench. Also, by comparing calculated seismic velocities with experimentally derived mineral physics data, we additionally provide mechanical constraints on the possible changes in frictional behavior across the subduction zone plate interface. Observed low seismic velocities in the seismogenic zone suggest a presence of low strength materials that may be explained by overpressured pore fluids (i.e., accreted sediment included in the subduction channel).

  11. Seismic properties of the Nazca oceanic crust in southern Peruvian subduction system

    NASA Astrophysics Data System (ADS)

    Kim, YoungHee; Clayton, Robert W.

    2015-11-01

    The horizontal Nazca slab, extending over a distance of ∼800 km along the trench is one of enigmatic features in Peruvian subduction zone. Increased buoyancy of the oceanic lithosphere alone due to the subduction of Nazca Ridge is insufficient to fully explain such a lengthy segment. We use data from the recent seismic experiment in southern Peru to find that the subduction-related hydration plays a major role in controlling shear wave velocities within the upper part of the oceanic crust and overlying materials. We observe substantial velocity reductions of ∼20-40% near the top plate interface along- and perpendicular-to the trench from ∼40-120 km depths. In particular, significant shear wave velocity reductions and subsequently higher P-to-S velocity ratio (exceeding 2.0) at the flat slab region suggest that the seismically probed layer is fluid-rich and mechanically weak. The dominant source of fluid comes from metasediments and subducted crust (Nazca Ridge). Long-term supply of fluid from the southward migrating Nazca Ridge provides additional buoyancy of the subducting oceanic lithosphere and also lowers the viscosity of the overlying mantle wedge to drive and sustain the flat plate segment of ∼800 km along the trench. Also, by comparing calculated seismic velocities with experimentally derived mineral physics data, we additionally provide mechanical constraints on the possible changes in frictional behavior across the subduction zone plate interface. Observed low seismic velocities in the seismogenic zone suggest a presence of low strength materials that may be explained by overpressured pore fluids (i.e., accreted sediment included in the subduction channel).

  12. Improving past sea surface temperature reconstructions from the Southern Hemisphere oceans using planktonic foraminiferal census data

    NASA Astrophysics Data System (ADS)

    Haddam, N. A.; Michel, E.; Siani, G.; Cortese, G.; Bostock, H. C.; Duprat, J. M.; Isguder, G.

    2016-06-01

    We present an improved database of planktonic foraminiferal census counts from the Southern Hemisphere oceans (SHO) from 15°S to 64°S. The SHO database combines three existing databases. Using this SHO database, we investigated dissolution biases that might affect faunal census counts. We suggest a depth/ΔCO32- threshold of ~3800 m/ΔCO32- = ~ -10 to -5 µmol/kg for the Pacific and Indian Oceans and ~4000 m/ΔCO32- = ~0 to 10 µmol/kg for the Atlantic Ocean, under which core-top assemblages can be affected by dissolution and are less reliable for paleo-sea surface temperature (SST) reconstructions. We removed all core tops beyond these thresholds from the SHO database. This database has 598 core tops and is able to reconstruct past SST variations from 2° to 25.5°C, with a root mean square error of 1.00°C, for annual temperatures. To inspect how dissolution affects SST reconstruction quality, we tested the data base with two "leave-one-out" tests, with and without the deep core tops. We used this database to reconstruct summer SST (SSST) over the last 20 ka, using the Modern Analog Technique method, on the Southeast Pacific core MD07-3100. This was compared to the SSST reconstructed using the three databases used to compile the SHO database, thus showing that the reconstruction using the SHO database is more reliable, as its dissimilarity values are the lowest. The most important aspect here is the importance of a bias-free, geographic-rich database. We leave this data set open-ended to future additions; the new core tops must be carefully selected, with their chronological frameworks, and evidence of dissolution assessed.

  13. Southern Ocean nutrient trapping and the efficiency of the biological pump

    NASA Astrophysics Data System (ADS)

    Primeau, FrançOis W.; Holzer, Mark; Devries, Timothy

    2013-05-01

    We present a data-assimilated model of the ocean's phosphorus cycle that is constrained by climatological phosphate, temperature, salinity, sea-surface height, surface heat and freshwater fluxes, as well as chlorofluorocarbon-11(CFC-11) and natural Δ14C. Export production is estimated to be 5.8±2.0×1012 mol P/yr of which (26±6)% originates in the Southern Ocean (SO) south of 40°S. The biological pump efficiency, defined as the proportion of the ocean's phosphate inventory that is regenerated, is (39±7)%. Dividing the SO south of 40°S into a sub-Antarctic zone (SANTZ) and an Antarctic zone (ANTZ) separated by the latitude of maximum Ekman divergence, we estimate that the SANTZ and ANTZ account, respectively, for (23±5)% and (3±1)% of global export production, (17±4)% and (3±1)% of the regenerated nutrient inventory, and (31±1)% and (43±5)% of the preformed nutrient inventory. Idealized SO nutrient depletion experiments reveal a large-scale transfer of nutrients into circumpolar and deep waters and from the preformed to the regenerated pool. In accord with the concept of the biogeochemical divide, we find that nutrient drawdown in the ANTZ is more effective than in the SANTZ for increasing the efficiency of the biological pump, while having a smaller impact on production in regions north of 40°S. Complete SO nutrient drawdown would allow the biological pump to operate at 94% efficiency by short circuiting the transport of nutrients in northward Ekman currents, leading to a trapping of nutrients in circumpolar and deep waters that would decrease production outside the SO by approximately 44% while increasing it in the SO by more than 725%.

  14. Wide range of mercury contamination in chicks of southern ocean seabirds.

    PubMed

    Blévin, Pierre; Carravieri, Alice; Jaeger, Audrey; Chastel, Olivier; Bustamante, Paco; Cherel, Yves

    2013-01-01

    Using top predators as sentinels of the marine environment, Hg contamination was investigated within the large subantarctic seabird community of Kerguelen Islands, a remote area from the poorly known Southern Indian Ocean. Chicks of 21 sympatric seabirds presented a wide range of Hg concentrations, with the highest contaminated species containing ~102 times more feather Hg than the less contaminated species. Hence, Kerguelen seabirds encompass the whole range of chick feather Hg values that were previously collected worldwide in poorly industrialized localities. Using stable isotopes, the effects of foraging habitats (reflected by δ(13)C) and trophic positions (reflected by δ(15)N) on Hg concentrations were investigated. Species-related Hg variations were highly and positively linked to feather δ(15)N values, thus highlighting the occurrence of efficient Hg biomagnification processes within subantarctic marine trophic webs. By contrast, Hg contamination overall correlated poorly with feeding habitats, because of the pooling of species foraging within different isotopic gradients corresponding to distinct seabird habitats (benthic, pelagic, neritic and oceanic). However, when focusing on oceanic seabirds, Hg concentration was related to feather δ(13)C values, with species feeding in colder waters (lower δ(13)C values) south of Kerguelen Islands being less prone to be contaminated than species feeding in northern warmer waters (higher δ(13)C values). Within the context of continuous increase in global Hg emissions, Kerguelen Islands that are located far away from anthropogenic sources can be considered as an ideal study site to monitor the temporal trend of global Hg contamination. The present work helps selecting some seabird species as sentinels of environmental pollution according to their high Hg concentrations and their contrasted foraging ecology. PMID:23349912

  15. Testing the Phosphorus Paleoproductivity Proxy Across a Productivity and Sedimentology Gradient in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Latimer, J. C.; Filippelli, G. M.

    2003-12-01

    Because of its role in biological productivity and its tendency to be preserved in sediments, records of phosphorus (P) burial (reactive P concentrations and accumulation, P/Ti ratios) have been used as proxies of export production. Unlike organic C, P is redistributed into different sedimentary pools during diagenesis and much of the sedimentary P flux to the seafloor may actually be retained in sediments in certain depositional environments. At three sites in the southeastern Atlantic Ocean and one site off the coast of Tasmania, we have systematically compared detailed P geochemistry with P/Ti ratios from bulk sediment geochemistry. We have verified that in these settings P/Ti ratios reflect the reactive P component, which is indicative of P that was once bioactive. However, based on quantification of opal intrinsic P, we have discovered that the commonly used SedEx reaction scheme does not liberate organic P found within opal. P/Ti ratios are a useful proxy because the ratios are resistant to the effects of dissolution and potentially sediment focusing, and they are not influenced by sediment type. Using downcore P/Ti ratios as a proxy for export production in the Southern Ocean is particularly useful because of the variability in sediment type and the paucity of carbonate at some sites. Surprisingly, maxima in P/Ti ratios over the last 1 Ma tend to occur at all sites at glacial terminations, regardless of position relative to important frontal zones. These findings are in contrast to other work suggesting that productivity north and south of the Antarctic Polar Front is opposite on glacial/interglacial time scales. We suggest that the increases in export production at terminations are related to changes in surface ocean circulation, nutrient delivery, and sea-ice interactions.

  16. A tale of three islands: Downstream natural iron fertilization in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Robinson, J.; Popova, E. E.; Srokosz, M. A.; Yool, A.

    2016-05-01

    Iron limitation of primary productivity prevails across much of the Southern Ocean but there are exceptions; in particular, the phytoplankton blooms associated with the Kerguelen Plateau, Crozet Islands, and South Georgia. These blooms occur annually, fertilized by iron and nutrient-rich shelf waters that are transported downstream from the islands. Here we use a high-resolution (1/12°) ocean general circulation model and Lagrangian particle tracking to investigate whether inter-annual variability in the potential lateral advection of iron could explain the inter-annual variability in the spatial extent of the blooms. Comparison with ocean color data, 1998-2007, suggests that iron fertilization via advection can explain the extent of each island's annual bloom, but only the inter-annual variability of the Crozet bloom. The area that could potentially be fertilized by iron from Kerguelen was much larger than the bloom, suggesting that there is another primary limiting factor, potentially silicate, that controls the inter-annual variability of bloom spatial extent. For South Georgia, there are differences in the year-to-year timing of advection and consequently fertilization, but no clear explanation of the inter-annual variability observed in the bloom's spatial extent has been identified. The model results suggest that the Kerguelen and Crozet blooms are terminated by nutrient exhaustion, probably iron and or silicate, whereas the deepening of the mixed layer in winter terminates the South Georgia bloom. Therefore, iron fertilization via lateral advection alone can explain the annual variability of the Crozet bloom, but not fully that of the Kerguelen and South Georgia blooms.

  17. Iron fertilization and the structure of planktonic communities in high nutrient regions of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Quéguiner, Bernard

    2013-06-01

    In this review article, plankton community structure observations are analyzed both for artificial iron fertilization experiments and also for experiments dedicated to the study of naturally iron-fertilized systems in the Atlantic, Indian and Pacific sectors of the Southern Ocean in the POOZ (Permanently Open Ocean Zone) and the PFZ (Polar Frontal Zone). Observations made in natural systems are combined with those from artificially perturbed systems, in order to evaluate the seasonal evolution of pelagic communities, taking into account controlling factors related to the life cycles and the ecophysiology of dominant organisms. The analysis considers several types of planktonic communities, including both autotrophs and heterotrophs. These communities are spatially segregated owing to different life strategies. A conceptual general scheme is proposed to account for these observations and their variability, regardless of experiment type. Diatoms can be separated into 2 groups: Group 1 has slightly silicified fast growing cells that are homogeneously distributed in the surface mixed layer, and Group 2 has strongly silicified slowly growing cells within discrete layers. During the growth season, Group 1 diatoms show a typical seasonal succession of dominant species, within time windows of development that are conditioned by physical factors (light and temperature) as well as endogenous specific rhythms (internal clock), and biomass accumulation is controlled by the availability of nutrients. Group 1 diatoms are not directly grazed by mesozooplankton which is fed by protozooplankton, linking the microbial food web to higher trophic levels. Instead, successive dominant species of Group 1 are degraded via bacterial activity at the end of their growth season. Organic detritus fragments feed protozooplankton and mesozooplankton. The effective silicon pump leads to the progressive disappearance of silicic acid in surface waters. In contrast, Group 2 is resistant to grazing

  18. Production regime and associated N cycling in the vicinity of Kerguelen Island, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Cavagna, A. J.; Fripiat, F.; Elskens, M.; Mangion, P.; Chirurgien, L.; Closset, I.; Lasbleiz, M.; Florez-Leiva, L.; Cardinal, D.; Leblanc, K.; Fernandez, C.; Lefèvre, D.; Oriol, L.; Blain, S.; Quéguiner, B.; Dehairs, F.

    2015-11-01

    Although the Southern Ocean is considered a high-nutrient, low-chlorophyll (HNLC) area, massive and recurrent blooms are observed over and downstream of the Kerguelen Plateau. This mosaic of blooms is triggered by a higher iron supply resulting from the interaction between the Antarctic Circumpolar Current and the local bathymetry. Net primary production, N uptake (NO3- and NH4+), and nitrification rates were measured at eight stations in austral spring 2011 (October-November) during the KEOPS 2 cruise in the Kerguelen Plateau area. Natural iron fertilization stimulated primary production, with mixed layer integrated net primary production and growth rates much higher in the fertilized areas (up to 315 mmol C m-2 d-1 and up to 0.31 d-1 respectively) compared to the HNLC reference site (12 mmol C m-2 d-1 and 0.06 d-1 respectively). Primary production was mainly sustained by nitrate uptake, with f ratios (corresponding to NO3--uptake / (NO3--uptake + NH4+-uptake)) lying at the upper end of the observations for the Southern Ocean (up to 0.9). We report high rates of nitrification (up to ~ 3 μmol N L-1 d-1, with ~ 90 % of them < 1 μmol N L-1 d-1) typically occurring below the euphotic zone, as classically observed in the global ocean. The specificity of the studied area is that at most of the stations, the euphotic layer was shallower than the mixed layer, implying that nitrifiers can efficiently compete with phytoplankton for the ammonium produced by remineralization at low-light intensities. Nitrate produced by nitrification in the mixed layer below the euphotic zone is easily supplied to the euphotic zone waters above, and nitrification sustained 70 ± 30 % of the nitrate uptake in the productive area above the Kerguelen Plateau. This complicates estimations of new production as potentially exportable production. We conclude that high productivity in deep mixing system stimulates the N cycle by increasing both assimilation and regeneration.

  19. Serving data from the SCAR Southern Ocean Observing System (SOOS) using the SeaDataNet infrastructure

    NASA Astrophysics Data System (ADS)

    de Bruin, T. F.

    2010-09-01

    The Scientific Committee on Antarctic Research (SCAR) and the Scientific Committee on Oceanic Research (SCOR) jointly intend to build a Southern Ocean Observing System (SOOS). This paper addresses the required data flow infrastructure. SOOS will use a system of systems approach, using existing observation programmes and projects. Data should be submitted to professional data centres. The problem arises how to link all these data centres and get a central overview of the SOOS data as well as direct access to the data. The Netherlands National Oceanographic Data Committee (NL-NODC) has successfully built a national distributed oceanographic data acccess infrastructure, adopting and implementing technology developed by the European SeaDataNet project. The Dutch system has been operational since early 2009. The conclusion is that the SeaDataNet technology can be used to build an operational, distributed data delivery infrastructure, featuring all elements required by the Southern Ocean Observing System (SOOS).

  20. Developing an enhanced tropical cyclone data portal for the Southern Hemisphere and the Western Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Kuleshov, Yuriy; de Wit, Roald; Atalifo, Terry; Prakash, Bipendra; Waqaicelua, Alipate; Kunitsugu, Masashi; Caroff, Philippe; Chane-Ming, Fabrice

    2013-04-01

    Tropical cyclones are the most extreme weather phenomena which severely impact coastal communities and island nations. There is an ongoing research (i) on accurate analysis of observed trends in tropical cyclone occurrences, and (ii) how tropical cyclone frequency and intensity may change in the future as a result of climate change. Reliable historical records of cyclone activity are vital for this research. The Pacific Australia Climate Change Science and Adaptation Planning (PACCSAP) program is dedicated to help Pacific Island countries and Timor Leste gain a better understanding of how climate change will impact their regions. One of the key PACCSAP projects is focused on developing a tropical cyclone archive, climatology and seasonal prediction for the regions. As part of the project, historical tropical cyclone best track data have been examined and prepared to be subsequently displayed through the enhanced tropical cyclone data portal for the Southern Hemisphere and the Western Pacific Ocean. Data from the Regional Specialised Meteorological Centre (RSMC) Nadi, Fiji and Tropical Cyclone Warning Centres (TCWCs) in Brisbane, Darwin and Wellington for 1969-1970 to 2010-2011 tropical cyclone seasons have been carefully examined. Errors and inconsistencies which have been found during the quality control procedure have been corrected. To produce a consolidated data set for the South Pacific Ocean, best track data from these four centres have been used. Specifically, for 1969-1970 to 1994-1995 tropical cyclone seasons, data from TCWCs in Brisbane, Darwin and Wellington have been used. In 1995, RSMC Nadi, Fiji has been established with responsibilities for issuing tropical cyclone warnings and preparing best track data for the area south of the equator to 25°S, 160°E to 120°W. Consequently, data from RSMC Nadi have been used as a primary source for this area, starting from the 1995-1996 tropical cyclone season. These data have been combined with the data from

  1. A History of Water Mass Circulation in the Paleogene Southern Ocean from Nd Isotopes

    NASA Astrophysics Data System (ADS)

    Scher, H. D.; Martin, E. E.

    2003-12-01

    Using fossil fish teeth from ODP site 689 (2080m, Maud Rise) we have generated a 28 Myr record of Nd isotope ratios and concentrations for the early middle Eocene to early Miocene at an average resolution of 250-300 kyr. ɛ Nd(T) values documented in this time series range from -9.5 to -7.35, and demonstrate a pattern of secular variations that is remarkably similar to benthic foraminiferal δ 13C records from this site. This correlation suggests that secular variations of ɛ Nd(T) values observed at site 689 are related to changes in ocean circulation and may provide insight into the history of water mass circulation in the Southern Ocean. Early middle Eocene ɛ Nd(T) values average -9.25 and display little variation compared to younger portions of the record, which illustrate long term oscillations beginning in the late middle Eocene. Starting at 40.8 Ma ɛ Nd(T) values increase over a 6 Myr interval from -9.4 to -7.35 in a stepwise fashion. Although ɛ Nd(T) values begin to rise during the late middle Eocene the period of most rapid change occurs in the late Eocene (after 37 Ma). ɛ Nd(T) values begin to fall in the earliest Oligocene reaching -8.75 at 30 Ma, then rise to -7.75 during the late Oligocene, but fall again to -8.75 by the end of the Oligocene. A hiatus occurs from the latest Oligocene to early Miocene. Following that interval, late early Miocene values average -8.5. Throughout the record the most radiogenic Nd isotopic compositions ( ˜ -7.5), are associated with high δ 13C values (1.2-1.4 ‰ ), while nonradiogenic Nd isotopic compositions are associated with lower δ 13C values (.2-.4 ‰ ). The subsidence curve constructed for site 689 indicates a middle Eocene paleodepth of 1200-1500 m. A mean ɛ Nd(T) value of -9.25 during the middle Eocene possibly reflects upward mixing of Warm Saline Deep Water (WSDW) from the Tethys Sea, which has been documented at a deeper site on the Maud Rise (690) on the basis of an oxygen isotopic inversion between

  2. Turnover, Diversity, and Productivity of Siliceous Plankton in the Pliocene Southern Ocean

    NASA Astrophysics Data System (ADS)

    Cody, R. D.; Naish, T.; Crampton, J. S.; Levy, R. H.

    2010-12-01

    The siliceous microfossil record of the Southern Ocean and Antarctic margin reveals much about the climatic and oceanographic evolution of the region during the late Cenozoic. We have constructed a composite record of the first and last appearances of 106 diatom taxa and 96 radiolarian taxa from 40 Neogene drillcores ranging from 40-80°S latitude. The composite biostratigraphic ranges, which correct for incomplete preservation and sampling in individual sections, are dated to within an average of ±33kyrs for the Pliocene, and allow us to discriminate local migration events from regional origination and extinction events. We examine the environmental history of the region in the context of the pace of evolution and extinction, regional diversity and productivity, and the biogeographic ranges of individual species through time. The Miocene-Pliocene transition was marked by a dramatic increase in nearshore biosiliceous production around the Antarctic margin, suggesting a longer growing season and enhanced nutrient supply in the warm Pliocene. The start of the Pliocene was also marked by rapid synchronous evolutionary turnover among both diatoms and radiolaria. However, whereas endemic diatom diversity increased throughout the Pliocene and underwent a subsequent major turnover pulse ~3.5Ma, rates of origination and extinction among radiolaria have been uniformly low since 4.7Ma. Episodes of rapid turnover among diatoms (5.0-4.7Ma, and 3.6-3.3Ma) coincide with intervals of elevated environmental instability, as measured by long-term benthic oxygen isotope variance. They may also reflect profound oceanographic transitions which altered the biogeographic isolation and nutrient supply patterns of the region. High endemic diversity and high nearshore productivity of fossil diatom assemblages from the Pliocene Southern Ocean indicates that these ecosystems evolved in response to unique environmental conditions that are without analog elsewhere in the Pliocene oceans, or

  3. Late Cretaceous Arc Initiation on the Edge of an Oceanic Plateau (Southern Central America)

    NASA Astrophysics Data System (ADS)

    Buchs, D. M.; Baumgartner, P. O.; Arculus, R.

    2007-12-01

    The Caribbean Plate comprises one or several late Cretaceous oceanic plateaus imbricated between the Northern and Southern Americas. Uplifted portions of plateau(s) along plate boundaries have been recognized in many sites, including that underlying the south Central American Volcanic Arc. We provide new constraints for the role of the plateau in the evolution of this arc obtained by mapping of the uplifted forearc area between southern Costa Rica and western Panama. An oceanic plateau, accreted seamounts and arc rocks were identified, and a new tectono-stratigraphy defined. The arc basement is composed of a Coniacian oceanic plateau. In the outer margin, late Cretaceous-Eocene accreted seamounts are in contact with the plateau along tectonic mélanges and active faults. Campanian-Maastrichtian primitive arc rocks are found 40-110 km to the trench on the top of -or as dykes within- the plateau. The location of these rocks correlates to previous observations and indicates that the arc front migrated away from the trench during the late Cretaceous, potentially in response to subduction erosion or slab flattening [Lissinna et al., EGU 2006]. The first island arc lavas were deposited under sea level, over a broad area. They were quickly followed by more evolved intrusives and lavas, which were emplaced along a volcanic front during the late Cretaceous-Paleocene. Detrital and volcanic records along the Central American isthmus indicate that a continuous volcanic arc extended between eastern Panama and northern Costa Rica in this time. In southern Costa Rica (Golfito complex) and western Panama (Sona-Azuero-Coiba complex), the oceanic plateau consists mainly of pillowed and massive low Fe (tholeiitic) basalts. These rocks have a highly consistent geochemistry characterized by flat, primitive upper mantle-normalized incompatible element patterns with low Pb and high Nb-Ti contents. Primitive arc igneous samples are low-medium Fe basalts to trachyandesites found as pillow

  4. A theoretical study of the effect of subsurface oceanic bubbles on the enhanced aerosol optical depth band over the southern oceans as detected from MODIS

    NASA Astrophysics Data System (ADS)

    Christensen, M.; Zhang, J.; Reid, J. S.; Zhang, X.; Hyer, E. J.; Smirnov, A.

    2014-12-01

    Submerged oceanic bubbles, which could have a much longer life span than whitecaps or bubble rafts, have been hypothesized to increase the water-leaving radiance and thus affect satellite based estimates of water-leaving radiance to non-trivial levels. This study explores this effect further to determine if such bubbles are of sufficient magnitude to impact satellite Aerosol Optical Depth (AOD) retrievals through perturbation of the lower boundary conditions. Indeed, there has been significant discussion in the community regarding the high positive biases in retrieved AODs in many remote ocean regions. In this study, for the first time, the effects of oceanic bubbles on satellite retrievals of AOD are studied by using a linked Second Simulation of a Satellite Signal in the Solar Spectrum (6S) atmospheric and HydroLight oceanic radiative transfer models. The results suggest an insignificant impact on AOD retrievals in regions with near-surface wind speeds of less than 12 m s-1. However, the impact of bubbles on aerosol retrievals could be on the order of 0.02-0.04 for higher wind conditions within the scope of our simulations (e.g., winds < 20 m s-1). This bias is propagated to global scales using one year of Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer - Earth (AMSR-E) data to investigate the possible impacts of oceanic bubbles on an enhanced AOD belt observed over the high latitude southern oceans (also called Enhanced Southern Oceans Anomaly, or ESOA) by some passive satellite sensors. Ultimately, this study is supportive of the null hypothesis: submerged bubbles are not the major contributor to the ESOA feature. This said, as retrievals progress to higher and higher resolutions, such as from airborne platforms, in clean marine conditions the uniform bubble correction should probably be separately accounted for against individual bright whitecaps and bubble rafts.

  5. A theoretical study of the effect of subsurface oceanic bubbles on the enhanced aerosol optical depth band over the southern oceans as detected from MODIS and MISR

    NASA Astrophysics Data System (ADS)

    Christensen, M.; Zhang, J.; Reid, J. S.; Zhang, X.; Hyer, E. J.; Smirnov, A.

    2015-05-01

    Submerged oceanic bubbles, which have a much longer life span than whitecaps or bubble rafts, have been hypothesized to increase the water-leaving radiance and thus affect satellite-based estimates of water-leaving radiance to non-trivial levels. This study explores this effect further to determine whether such bubbles are of sufficient magnitude to impact satellite aerosol optical depth (AOD) retrievals through perturbation of the lower boundary conditions. There has been significant discussion in the community regarding the high positive biases in retrieved AODs in many remote ocean regions. In this study, for the first time, the effects of oceanic bubbles on satellite retrievals of AOD are studied by using a linked Second Simulation of a Satellite Signal in the Solar Spectrum (6S) atmospheric and HydroLight oceanic radiative transfer models. The results suggest an insignificant impact on AOD retrievals in regions with near-surface wind speeds of less than 12 m s-1. However, the impact of bubbles on aerosol retrievals could be on the order of 0.02-0.04 for higher wind conditions within the scope of our simulations (e.g., winds < 20 m -1. This bias is propagated to global scales using 1 year of Moderate Resolution Imaging Spectroradiometer (MODIS) and Advanced Microwave Scanning Radiometer EOS (AMSR-E) data to investigate the possible impacts of oceanic bubbles on an enhanced AOD belt observed over the high-latitude southern oceans (also called the enhanced southern oceans anomaly, or ESOA) by some passive satellite sensors. Ultimately, this study is supportive of the null hypothesis: submerged bubbles are not the major contributor to the ESOA feature. This said, as retrievals progress to higher and higher resolutions, such as from airborne platforms, the uniform bubble correction in clean marine conditions should probably be separately accounted for against individual bright whitecaps and bubble rafts.

  6. Feather mercury concentrations in Southern Ocean seabirds: Variation by species, site and time.

    PubMed

    Becker, Peter H; Goutner, Vassilis; Ryan, Peter G; González-Solís, Jacob

    2016-09-01

    We studied mercury contamination in 25 seabird species breeding along a latitudinal gradient across the Southern Ocean, from Gough Island (40°S) through Marion Island (47°S) to Byers Peninsula (63°S). Total mercury concentrations in body feather samples of adults caught at breeding colonies from 2008 to 2011 were determined. Krill (Euphausia spp.) and other zooplankton consumers had low mercury concentrations (gentoo penguin Pygoscelis papua, chinstrap penguin Pseudomonas Antarctica, common diving petrel Pelecanoides urinatrix, broad-billed prion Pachyptila vittata; mean levels 308-753 ng g(-1)), whereas seabirds consuming squid or carrion had high mercury concentrations (ascending order: Kerguelen petrel Aphrodroma brevirostris, southern giant petrel Macronectes giganteus, soft-plumaged petrel Pterodroma mollis, sooty albatross Phoebetria fusca, Atlantic petrel Pterodroma incerta, northern giant petrel Macronectes halli, great-winged petrel Pterodroma macroptera; 10,720-28038 ng g(-1)). The two species with the highest mercury concentrations, northern giant petrels and great-winged petrels, bred at Marion Island. Among species investigated at multiple sites, southern giant petrels had higher mercury levels at Marion than at Gough Island and Byers Peninsula. Mercury levels among Byers Peninsula seabirds were low, in two species even lower than levels measured 10 years before at Bird Island, South Georgia. Replicate measurements after about 25 years at Gough Island showed much higher mercury levels in feathers of sooty albatrosses (by 187%), soft-plumaged petrels (53%) and Atlantic petrels (49%). Concentrations similar to the past were detected in southern giant petrels at Gough and Marion islands, and in northern giant petrels at Marion. There were no clear indications that timing of moult or migratory behavior affected mercury contamination patterns among species. Causes of inter-site or temporal differences in mercury contamination could not be verified

  7. Feather mercury concentrations in Southern Ocean seabirds: Variation by species, site and time.

    PubMed

    Becker, Peter H; Goutner, Vassilis; Ryan, Peter G; González-Solís, Jacob

    2016-09-01

    We studied mercury contamination in 25 seabird species breeding along a latitudinal gradient across the Southern Ocean, from Gough Island (40°S) through Marion Island (47°S) to Byers Peninsula (63°S). Total mercury concentrations in body feather samples of adults caught at breeding colonies from 2008 to 2011 were determined. Krill (Euphausia spp.) and other zooplankton consumers had low mercury concentrations (gentoo penguin Pygoscelis papua, chinstrap penguin Pseudomonas Antarctica, common diving petrel Pelecanoides urinatrix, broad-billed prion Pachyptila vittata; mean levels 308-753 ng g(-1)), whereas seabirds consuming squid or carrion had high mercury concentrations (ascending order: Kerguelen petrel Aphrodroma brevirostris, southern giant petrel Macronectes giganteus, soft-plumaged petrel Pterodroma mollis, sooty albatross Phoebetria fusca, Atlantic petrel Pterodroma incerta, northern giant petrel Macronectes halli, great-winged petrel Pterodroma macroptera; 10,720-28038 ng g(-1)). The two species with the highest mercury concentrations, northern giant petrels and great-winged petrels, bred at Marion Island. Among species investigated at multiple sites, southern giant petrels had higher mercury levels at Marion than at Gough Island and Byers Peninsula. Mercury levels among Byers Peninsula seabirds were low, in two species even lower than levels measured 10 years before at Bird Island, South Georgia. Replicate measurements after about 25 years at Gough Island showed much higher mercury levels in feathers of sooty albatrosses (by 187%), soft-plumaged petrels (53%) and Atlantic petrels (49%). Concentrations similar to the past were detected in southern giant petrels at Gough and Marion islands, and in northern giant petrels at Marion. There were no clear indications that timing of moult or migratory behavior affected mercury contamination patterns among species. Causes of inter-site or temporal differences in mercury contamination could not be verified

  8. The Discovery of New Deep-Sea Hydrothermal Vent Communities in the Southern Ocean and Implications for Biogeography

    PubMed Central

    Rogers, Alex D.; Tyler, Paul A.; Connelly, Douglas P.; Copley, Jon T.; James, Rachael; Larter, Robert D.; Linse, Katrin; Mills, Rachel A.; Garabato, Alfredo Naveira; Pancost, Richard D.; Pearce, David A.; Polunin, Nicholas V. C.; German, Christopher R.; Shank, Timothy; Boersch-Supan, Philipp H.; Alker, Belinda J.; Aquilina, Alfred; Bennett, Sarah A.; Clarke, Andrew; Dinley, Robert J. J.; Graham, Alastair G. C.; Green, Darryl R. H.; Hawkes, Jeffrey A.; Hepburn, Laura; Hilario, Ana; Huvenne, Veerle A. I.; Marsh, Leigh; Ramirez-Llodra, Eva; Reid, William D. K.; Roterman, Christopher N.; Sweeting, Christopher J.; Thatje, Sven; Zwirglmaier, Katrin

    2012-01-01

    Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than

  9. The discovery of new deep-sea hydrothermal vent communities in the southern ocean and implications for biogeography.

    PubMed

    Rogers, Alex D; Tyler, Paul A; Connelly, Douglas P; Copley, Jon T; James, Rachael; Larter, Robert D; Linse, Katrin; Mills, Rachel A; Garabato, Alfredo Naveira; Pancost, Richard D; Pearce, David A; Polunin, Nicholas V C; German, Christopher R; Shank, Timothy; Boersch-Supan, Philipp H; Alker, Belinda J; Aquilina, Alfred; Bennett, Sarah A; Clarke, Andrew; Dinley, Robert J J; Graham, Alastair G C; Green, Darryl R H; Hawkes, Jeffrey A; Hepburn, Laura; Hilario, Ana; Huvenne, Veerle A I; Marsh, Leigh; Ramirez-Llodra, Eva; Reid, William D K; Roterman, Christopher N; Sweeting, Christopher J; Thatje, Sven; Zwirglmaier, Katrin

    2012-01-01

    Since the first discovery of deep-sea hydrothermal vents along the Galápagos Rift in 1977, numerous vent sites and endemic faunal assemblages have been found along mid-ocean ridges and back-arc basins at low to mid latitudes. These discoveries have suggested the existence of separate biogeographic provinces in the Atlantic and the North West Pacific, the existence of a province including the South West Pacific and Indian Ocean, and a separation of the North East Pacific, North East Pacific Rise, and South East Pacific Rise. The Southern Ocean is known to be a region of high deep-sea species diversity and centre of origin for the global deep-sea fauna. It has also been proposed as a gateway connecting hydrothermal vents in different oceans but is little explored because of extreme conditions. Since 2009 we have explored two segments of the East Scotia Ridge (ESR) in the Southern Ocean using a remotely operated vehicle. In each segment we located deep-sea hydrothermal vents hosting high-temperature black smokers up to 382.8°C and diffuse venting. The chemosynthetic ecosystems hosted by these vents are dominated by a new yeti crab (Kiwa n. sp.), stalked barnacles, limpets, peltospiroid gastropods, anemones, and a predatory sea star. Taxa abundant in vent ecosystems in other oceans, including polychaete worms (Siboglinidae), bathymodiolid mussels, and alvinocaridid shrimps, are absent from the ESR vents. These groups, except the Siboglinidae, possess planktotrophic larvae, rare in Antarctic marine invertebrates, suggesting that the environmental conditions of the Southern Ocean may act as a dispersal filter for vent taxa. Evidence from the distinctive fauna, the unique community structure, and multivariate analyses suggest that the Antarctic vent ecosystems represent a new vent biogeographic province. However, multivariate analyses of species present at the ESR and at other deep-sea hydrothermal vents globally indicate that vent biogeography is more complex than

  10. The effects of natural iron fertilisation on deep-sea ecology: the Crozet Plateau, Southern Indian Ocean.

    PubMed

    Wolff, George A; Billett, David S M; Bett, Brian J; Holtvoeth, Jens; FitzGeorge-Balfour, Tania; Fisher, Elizabeth H; Cross, Ian; Shannon, Roger; Salter, Ian; Boorman, Ben; King, Nicola J; Jamieson, Alan; Chaillan, Frédéric

    2011-01-01

    The addition of iron to high-nutrient low-chlorophyll (HNLC) oceanic waters stimulates phytoplankton, leading to greater primary production. Large-scale artificial ocean iron fertilization (OIF) has been proposed as a means of mitigating anthropogenic atmospheric CO(2), but its impacts on ocean ecosystems below the photic zone are unknown. Natural OIF, through the addition of iron leached from volcanic islands, has been shown to enhance primary productivity and carbon export and so can be used to study the effects of OIF on life in the ocean. We compared two closely-located deep-sea sites (∼400 km apart and both at ∼4200 m water depth) to the East (naturally iron fertilized; +Fe) and South (HNLC) of the Crozet Islands in the southern Indian Ocean. Our results suggest that long-term geo-engineering of surface oceanic waters via artificial OIF would lead to significant changes in deep-sea ecosystems. We found that the +Fe area had greater supplies of organic matter inputs to the seafloor, including polyunsaturated fatty acid and carotenoid nutrients. The +Fe site also had greater densities and biomasses of large deep-sea animals with lower levels of evenness in community structuring. The species composition was also very different, with the +Fe site showing similarities to eutrophic sites in other ocean basins. Moreover, major differences occurred in the taxa at the +Fe and HNLC sites revealing the crucial role that surface oceanic conditions play in changing and structuring deep-sea benthic communities.

  11. Explanations for Temperature Increases in the Northern and Southern Atlantic Ocean are Proposed

    NASA Astrophysics Data System (ADS)

    Cimorelli, S. A.

    2012-04-01

    Primarily, consider some background hypotheses in the first paragraph: Three Types of mechanisms for Stellar Origin, Formation and Evolution are hypothesized. The first type (A) is well known; whereas, the other two (B&C) are new and proposed herein. The type A process, the presently universally accepted process, consists of the three phases of gravitation, followed by accretion, followed by fragmentation. In a Type B process, a star originates as an expanded, modified, category 3 Black Hole (BH) [1], with none or little help from gravitation/accretion, that begins to radiate, and continues to grow into a star. In a Type C process, a star would originate from a combination of the mechanisms described above for Type B and A. This mechanism, Type C, is perhaps the most common type. This type starts as an expanded, modified, category 3 BH inside of a gas and dust cloud. This then serves as the nucleus that starts the subsequent gravitation/accretion process; however, it greatly accelerates the accretion/formation process as in a standard Type A process. This mechanism could then explain how some super-cluster complexes, which have been estimated would take 40 to 60 billion years to form, can occur in a universe of a much younger age, i.e. 13.7 billion years. Also, consider that the ratio of the 'surface area to volume' is greater in a relatively smaller sphere; which would cause that smaller body of limited energy to cool off'/down, faster; however to continue to grow. A suggested sequence to explain why the Northern (South Greenland) and Southern Regions of the Atlantic Ocean are getting warmer is proposed: As the earth grows, two things occur, among others [1]. It is hypothesized the earth is expanding, circumferentially, about 3 cm per year at the equator (1 cm in the Atlantic, and 2 cm in the Pacific), rather than just 1 cm at the center of the Atlantic, as is commonly accepted. The earth may be expanding at an even greater rate, longitudinally (north and south

  12. High genetic diversity and connectivity in a common mesopelagic fish of the Southern Ocean: The myctophid Electrona antarctica

    NASA Astrophysics Data System (ADS)

    Van de Putte, A. P.; Van Houdt, J. K. J.; Maes, G. E.; Hellemans, B.; Collins, M. A.; Volckaert, F. A. M.

    2012-01-01

    Many marine pelagic fish species are characterized by subtle but complex genetic structures and dynamics, depending on the balance between current-mediated larval dispersal and adult active homing behavior. The circumantarctic continuous hydrodynamics of the Southern Ocean is a prime example of a system with a potentially great homogenizing effect among distant populations. We tested this hypothesis by analyzing the contemporary genetic relatedness among populations of a common and endemic mesopelagic fish of the Southern Ocean, Electrona antarctica. Seven newly developed species-specific microsatellite markers were used to investigate patterns of neutral genetic variation in 11 geographically widespread samples ( n=400) collected between 2006 and 2007. We detected a very high level of genetic diversity, but a striking lack of genetic differentiation on a circumantarctic scale, indicating large effective population sizes complemented with high levels of admixture. These findings underscore the large scale homogenizing effect of the Southern Coastal Current, leading to a high level of connectivity of our model species in the Southern Ocean, which is congruent with its huge biomass and central role in marine food webs. As an important Antarctic marine living resource this species may as such be managed on a circumantarctic level, although the demographic stability of this stock should be estimated urgently.

  13. Biological and physical controls in the Southern Ocean on past millennial-scale atmospheric CO2 changes

    PubMed Central

    Gottschalk, Julia; Skinner, Luke C.; Lippold, Jörg; Vogel, Hendrik; Frank, Norbert; Jaccard, Samuel L.; Waelbroeck, Claire

    2016-01-01

    Millennial-scale climate changes during the last glacial period and deglaciation were accompanied by rapid changes in atmospheric CO2 that remain unexplained. While the role of the Southern Ocean as a 'control valve' on ocean–atmosphere CO2 exchange has been emphasized, the exact nature of this role, in particular the relative contributions of physical (for example, ocean dynamics and air–sea gas exchange) versus biological processes (for example, export productivity), remains poorly constrained. Here we combine reconstructions of bottom-water [O2], export production and 14C ventilation ages in the sub-Antarctic Atlantic, and show that atmospheric CO2 pulses during the last glacial- and deglacial periods were consistently accompanied by decreases in the biological export of carbon and increases in deep-ocean ventilation via southern-sourced water masses. These findings demonstrate how the Southern Ocean's 'organic carbon pump' has exerted a tight control on atmospheric CO2, and thus global climate, specifically via a synergy of both physical and biological processes. PMID:27187527

  14. Snapshot prediction of carbon productivity, carbon and protein content in a Southern Ocean diatom using FTIR spectroscopy.

    PubMed

    Sackett, Olivia; Petrou, Katherina; Reedy, Brian; Hill, Ross; Doblin, Martina; Beardall, John; Ralph, Peter; Heraud, Philip

    2016-02-01