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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. Eddies in the Southern Ocean

    NASA Image and Video Library

    2015-04-08

    The cloud cover over the Southern Ocean occasionally parts as it did on January 1, 2015 just west of the Drake Passage where the VIIRS instrument on the Suomi NPP satellite glimpsed the above collection of ocean-color delineated eddies which have diameters ranging from a couple of kilometers to a couple of hundred kilometers. Recent studies indicate that eddy activity has been increasing in the Southern Ocean with possible implications for climate change. Credit: NASA's OceanColor/Suomi NPP/VIIRS

  5. 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

  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. Eddies in the Southern Ocean

    NASA Image and Video Library

    2017-09-28

    The cloud cover over the Southern Ocean occasionally parts as it did on January 1, 2015 just west of the Drake Passage where the VIIRS instrument on the Suomi NPP satellite glimpsed the above collection of ocean-color delineated eddies which have diameters ranging from a couple of kilometers to a couple of hundred kilometers. Recent studies indicate that eddy activity has been increasing in the Southern Ocean with possible implications for climate change. Credit: NASA's OceanColor/Suomi NPP/VIIRS NASA image use policy. NASA Goddard Space Flight Center enables NASA’s mission through four scientific endeavors: Earth Science, Heliophysics, Solar System Exploration, and Astrophysics. Goddard plays a leading role in NASA’s accomplishments by contributing compelling scientific knowledge to advance the Agency’s mission. Follow us on Twitter Like us on Facebook Find us on Instagram

  8. Southern Ocean natural iron fertilization

    NASA Astrophysics Data System (ADS)

    Charette, Matt; Sanders, Richard; Zhou, Meng

    2011-08-01

    Modeling and Synthesis of Southern Ocean Natural Iron Fertilization; Woods Hole, Massachusetts, 27-29 June 2011; For many years a major paradox in ocean science was the existence of regions where the major nutrients are present in nonlimiting concentrations yet phytoplankton biomass is low. Pioneering experiments in the 1990s firmly established that the likely cause of this high-nutrient, low-chlorophyll condition is a deficit of iron relative to other nutrients. Iron is required for numerous processes within the cell, including photosynthesis, respiration, and nutrient uptake, yet because of its chemical properties, in seawater it is present at vanishingly small concentration levels. Elucidating the role of iron in governing ecosystem functioning and carbon sequestration is in its infancy; however, one promising approach is to make observations in regions where landmasses act as point sources of iron. In 2004-2006, three separate expeditions targeted the southern Indian Ocean around the Crozet and Kerguelen Islands and in the southern Scotia Sea around the southern Drake Passage. Representatives from all three programs met recently to compare findings and identify critical gaps in existing knowledge.

  9. Pteropods in Southern Ocean ecosystems

    NASA Astrophysics Data System (ADS)

    Hunt, B. P. V.; Pakhomov, E. A.; Hosie, G. W.; Siegel, V.; Ward, P.; Bernard, K.

    2008-09-01

    To date, little research has been carried out on pelagic gastropod molluscs (pteropods) in Southern Ocean ecosystems. However, recent predictions are that, due to acidification resulting from a business as usual approach to CO 2 emissions (IS92a), Southern Ocean surface waters may begin to become uninhabitable for aragonite shelled thecosome pteropods by 2050. To gain insight into the potential impact that this would have on Southern Ocean ecosystems, we have here synthesized available data on pteropod distributions and densities, assessed current knowledge of pteropod ecology, and highlighted knowledge gaps and directions for future research on this zooplankton group. Six species of pteropod are typical of the Southern Ocean south of the Sub-Tropical Convergence, including the four Thecosomes Limacina helicina antarctica, Limacina retroversa australis, Clio pyramidata, and Clio piatkowskii, and two Gymnosomes Clione limacina antarctica and Spongiobranchaea australis. Limacina retroversa australis dominated pteropod densities north of the Polar Front (PF), averaging 60 ind m -3 (max = 800 ind m -3) and 11% of total zooplankton at the Prince Edward Islands. South of the PF L. helicina antarctica predominated, averaging 165 ind m -3 (max = 2681 ind m -3) and up to >35% of total zooplankton at South Georgia, and up to 1397 ind m -3 and 63% of total zooplankton in the Ross Sea. Combined pteropods contributed <5% to total zooplankton in the Lazarev Sea, but 15% (max = 93%) to macrozooplankton in the East Antarctic. In addition to regional density distributions we have synthesized data on vertical distributions, seasonal cycles, and inter-annual density variation. Trophically, gymnosome are specialist predators on thecosomes, while thecosomes are considered predominantly herbivorous, capturing food with a mucous web. The ingestion rates of L. retroversa australis are in the upper range for sub-Antarctic mesozooplankton (31.2-4196.9 ng pig ind -1 d -1), while those of L

  10. Microplastics in the Southern Ocean.

    PubMed

    Isobe, Atsuhiko; Uchiyama-Matsumoto, Kaori; Uchida, Keiichi; Tokai, Tadashi

    2017-01-15

    A field survey to collect microplastics with sizes <5mm was conducted in the Southern Ocean in 2016. We performed five net-tows and collected 44 pieces of plastic. Total particle counts of the entire water column, which is free of vertical mixing, were computed using the surface concentration (particle count per unit seawater volume) of microplastics, wind speed, and significant wave height during the observation period. Total particle counts at two stations near Antarctica were estimated to be in the order of 100,000pieceskm(-2).

  11. Extratropical Cyclone in the Southern Ocean

    NASA Image and Video Library

    2001-11-07

    These images acquired on October 11, 2001 by NASA Terra satellite portray an occluded extratropical cyclone situated in the Southern Ocean, about 650 kilometers south of the Eyre Peninsula, South Australia.

  12. Southern Ocean: Its involvement in global change

    SciTech Connect

    Gordon, A.L.

    1992-03-01

    Southern Ocean is the site of considerable water mass formation which cools and ventilates the modern world ocean. At the polar front zone, formation of cool, low salinity water sinks and spreads northward at intermediate depths limiting the downward penetration of the thermocline. Within the seasonal sea ice zone and along the margins of Antarctica, convection injects very cold oxygenated water into the deep and bottom ocean. These conditions developed as Antarctica shifted into its present configuration and grew a persistent glacial ice sheet, about 14 million years ago. The potential of the Southern Ocean to ventilate the deep and bottom ocean layers is related to occurrence of polynyas that form within the winter sea ice cover. Global climate changes would be expected to alter the polynya size and frequency. Under greenhouse-induced warming offshore polynyas may become less common as the static stability of the Southern Ocean mixed layer increases. This would diminish the Southern Ocean's cooling influence on the deep layers of the world ocean, resulting in a warmer deep ocean. The fate of coastal polynyas is less clear.

  13. 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.

  14. Eddy impact on the Southern Ocean ventilation

    NASA Astrophysics Data System (ADS)

    Pennel, R. L.; Kamenkovich, I. V.; Fine, R. A.

    2012-12-01

    This study examines the specific role of mesoscale eddies and coherent structures in the ventilation of the Southern Ocean through the analysis of Lagrangian particle trajectories in a suite of idealized numerical simulations. Being the biggest potential reservoir for heat and atmospheric gases, the Southern Ocean is of great importance in the Earth's climate system. Therefore, the understanding of ventilation, the process establishing communication between the surface mixed layer and the ocean interior, is crucial to quantify the storage of CO2 by the ocean and to improve climate change projections. Idealized numerical simulations of the Southern Ocean at 1/8o resolution are carried out using the NEMO Ocean General Circulation Model. Twin simulations with and without eddies having the same stratification and mean circulation, are considered using several definitions of eddies. The analysis of the differences between such simulations allows examination of the direct effect of eddies on ventilation of the Southern Ocean. The role played by coherent structures is also discussed by looking at the trajectories of particles specifically injected inside individual vortices.

  15. Southern Ocean vertical iron fluxes; the ocean model effect

    NASA Astrophysics Data System (ADS)

    Schourup-Kristensen, V.; Haucke, J.; Losch, M. J.; Wolf-Gladrow, D.; Voelker, C. D.

    2016-02-01

    The Southern Ocean plays a key role in the climate system, but commonly used large-scale ocean general circulation biogeochemical models give different estimates of current and future Southern Ocean net primary and export production. The representation of the Southern Ocean iron sources plays an important role for the modeled biogeochemistry. Studies of the iron supply to the surface mixed layer have traditionally focused on the aeolian and sediment contributions, but recent work has highlighted the importance of the vertical supply from below. We have performed a model study in which the biogeochemical model REcoM2 was coupled to two different ocean models, the Finite Element Sea-ice Ocean Model (FESOM) and the MIT general circulation model (MITgcm) and analyzed the magnitude of the iron sources to the surface mixed layer from below in the two models. Our results revealed a remarkable difference in terms of mechanism and magnitude of transport. The mean iron supply from below in the Southern Ocean was on average four times higher in MITgcm than in FESOM and the dominant pathway was entrainment in MITgcm, whereas diffusion dominated in FESOM. Differences in the depth and seasonal amplitude of the mixed layer between the models affect on the vertical iron profile, the relative position of the base of the mixed layer and ferricline and thereby also on the iron fluxes. These differences contribute to differences in the phytoplankton composition in the two models, as well as in the timing of the onset of the spring bloom. The study shows that the choice of ocean model has a significant impact on the iron supply to the Southern Ocean mixed layer and thus on the modeled carbon cycle, with possible implications for model runs predicting the future carbon uptake in the region.

  16. Trends in Southern Ocean Eddy Kinetic Energy

    NASA Astrophysics Data System (ADS)

    Chambers, Don

    2016-04-01

    A recent study by Hogg et al. (JGR, 2015) has demonstrated a 20-year trend in eddy kinetic energy (EKE) computed from satellite altimetry data. However, this estimate is based on an averaging over large spatial areas. In this study, we use the same methods to examine regional EKE trends throughout the Southern Ocean, from 1993-2015. We do find significant positive trends in several areas of the Southern Ocean, mainly in regions with high mean EKE associated with interactions between jets and bathymetry. At the same time, however, there are also regions with significant negative trends. Overall, EKE in the majority of the Southern Ocean has not changed. These results suggest that the estimates of Hogg et al. may have been biased by these regional extremes, and that more work is needed to quantify climatic changes in EKE.

  17. 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.

  18. Deglacial Atlantic Radiocarbon: A Southern Ocean Perspective

    NASA Astrophysics Data System (ADS)

    Robinson, L. F.; Burke, A.; Adkins, J. F.; Chen, T.; Spooner, P.

    2014-12-01

    It is widely accepted that the Southern Ocean is an important component of the climate system, acting as a key site for carbon and heat exchange between the atmosphere and oceans. The deglaciation with its associated millenial climate changes is a key time period for testing the mechanisms behind these exchanges. Ascertaining the precise timing of these events is a challenge given complications from variable and largely unconstrained reservoir ages, dissolution of carbonate hard parts and sediment redistribution by strong currents. Nevertheless improvements to our understanding of Southern Ocean dynamics in the past requires accurately-dated proxy records that can be embedded in GCM models. Radiocarbon measured in deep-sea corals offers just such an archive and proxy. Using the skeletons of deep-sea corals we are now able to reconstruct aspects of the history of three distinct water masses in the Drake Passage on a precise timescale, allowing direct comparison to U-series dated speleothem terrestrial records and polar ice cores. We present here a new deglacial radiocarbon record from the Drake Passage which more than doubles the resolution of published records. We focus on the deglacial, as well as providing insights from the contrasting period leading up to the LGM. Together with new data from far-field sites we interpret our results as evidence for a Southern Ocean control on atmospheric carbon dioxide and radiocarbon evolution during the deglaciation, and a northern hemisphere control during the run up to the LGM.

  19. 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

  20. 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

  1. 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

  2. Ammonia gas concentrations over the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ayers, G. P.; Gras, J. L.

    1980-04-01

    Measurements of the concentration of ammonia in the atmosphere over the Southern Ocean in the vicinity of Tasmania are reported. Air samples were collected over a period of three or more hours on oxalic acid-impregnated filters using a PTFE prefilter, and ammonia was determined colorimetrically. For air apparently free of influence by land areas for several thousand km, as indicated by low levels of Aitken nuclei and ammonia, a mean ammonia gas concentration of 0.06 microgram/cu m is obtained, which is significantly lower than those determined elsewhere. The value is used to estimate a dissolved ammonia concentration in the ocean of 0.3 micromole/l, assuming equilibrium between the surface water and the air, is in agreement with measurements by other investigators and direct ocean water ammonia determinations.

  3. 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.

  4. 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.

  5. Transient tracer applications in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Stöven, T.; Tanhua, T.; Hoppema, M.

    2014-10-01

    Transient tracers can be used to constrain the Inverse-Gaussian transit time distribution (IG-TTD) and thus provide information about ocean ventilation. Individual transient tracers have different time and application ranges which are defined by their atmospheric history (chronological transient tracers) or their decay rate (radioactive transient tracers). The classification ranges from tracers for highly ventilated water masses, e.g. sulfur hexafluoride (SF6), the decay of Tritium (δ3H) and to some extent also dichlorodifluoromethane (CFC-12) to tracers for less ventilated deep ocean basins, e.g. CFC-12, Argon-39 (39Ar) and radiocarbon (14C). The IG-TTD can be empirically constrained by using transient tracer couples with sufficiently different input functions. Each tracer couple has specific characteristics which influence the application limit of the IG-TTD. Here we provide an overview of commonly used transient tracer couples and their validity areas within the IG-TTD by using the concept of tracer age differences (TAD). New measured CFC-12 and SF6 data from a section along 10° E in the Southern Ocean in 2012 are presented. These are combined with a similar data set of 1998 along 6° E in the Southern Ocean as well as with 39Ar data from the early 1980s in the western Atlantic Ocean and the Weddell Sea for investigating the application limit of the IG-TTD and to analyze changes in ventilation in the Southern Ocean. We found that the IG-TTD can be constrained south to 46° S which corresponds to the Subantarctic Front (SAF) denoting the application limit. The constrained IG-TTD north of the SAF shows a slight increase in mean ages between 1998 and 2012 in the upper 1200 m between 42-46° S. The absence of SF6 inhibits ventilation analyses below this depth. The time lag analysis between the 1998 and 2012 data shows an increase in ventilation down to 1000 m and a steady ventilation between 2000 m-bottom south of the SAF between 51-55° S.

  6. Nutrient Dynamics in the Glacial Southern Ocean

    NASA Astrophysics Data System (ADS)

    Latimer, J. C.; Filippelli, G. M.

    2004-12-01

    The Southern Ocean (SO) was likely a key contributor to glacial/interglacial climate change resulting from variability either in biogeochemical cycles or ocean stratification and CO2 degassing. Many of the hypotheses to explain the interglacial to glacial difference in atmospheric CO2 suggest that higher glacial dust fluxes led to Fe fertilization of surface waters and increased export production in the SO because the modern-day Southern Ocean is co-limited by both Fe and light availability. Documented Fe sources include upwelled Upper Circumpolar Deep Water, eolian deposition, and melting sea-ice. However, the influence of these sources is variable with latitude and position relative to major frontal zones. Presumably these same Fe sources were important during glacial times albeit at potentially different rates and magnitudes. To examine this effect, we have compared sedimentary Fe fluxes with records of dust deposition. We have found that Fe fluxes are higher than can be explained by eolian deposition, supporting an additional hemipelagic source of Fe to the deep ocean during glacial intervals. Furthermore, different proxies used to evaluate export production and nutrient utilization during glacial intervals yield different and seemingly contradictory results-for example, different studies have concluded that net productivity increased, decreased, and/or remained constant in the SO. Results from phosphorus geochemistry suggest that maxima in export production actually occur at terminations rather than either full glacial or interglacial conditions adding yet another possibility. The focus here will be to try to reconcile the nutrient, export production, and Fe data into a coherent view of nutrient utilization and export production in the glacial SO.

  7. 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.

  8. New Perspectives on Southern Ocean Frontal Variability

    NASA Astrophysics Data System (ADS)

    Chapman, Christopher

    2017-04-01

    The frontal structure of the Southern Ocean is investigated using a the Wavelet/Higher Order Statistics Enhancement (WHOSE) frontal detection method, introduced in Chapman (2014). This methodology is applied to 21 years of daily gridded sea-surface height (SSH) data to obtain daily maps of the locations of the fronts. By forming frontal occurrence frequency maps and then approximating these occurrence-maps by a superposition of simple functions, the time-mean locations of the fronts, as well as a measure of their capacity to meander, are obtained and related to the frontal locations found by previous studies. The spatial and temporal variability of the frontal structure is then considered. The number of fronts is found to be highly variable throughout the Southern Ocean, increasing (`splitting') downstream of large bathymetric features and decreasing (`merging') in regions where the fronts are tightly controlled by the underlying topography. In contrast, frontal meandering remains relatively constant. Contrary to many previous studies, little no southward migration of the fronts over the 1993-2014 time period is found, and there is only weak sensitivity to atmospheric forcing related to SAM or ENSO. Finally, the implications of splitting and merging for the flux of tracers will be discussed.

  9. Ecology of southern ocean pack ice.

    PubMed

    Brierley, Andrew S; Thomas, David N

    2002-01-01

    Around Antarctica the annual five-fold growth and decay of sea ice is the most prominent physical process and has a profound impact on marine life there. In winter the pack ice canopy extends to cover almost 20 million square kilometres--some 8% of the southern hemisphere and an area larger than the Antarctic continent itself (13.2 million square kilometres)--and is one of the largest, most dynamic ecosystems on earth. Biological activity is associated with all physical components of the sea-ice system: the sea-ice surface; the internal sea-ice matrix and brine channel system; the underside of sea ice and the waters in the vicinity of sea ice that are modified by the presence of sea ice. Microbial and microalgal communities proliferate on and within sea ice and are grazed by a wide range of proto- and macrozooplankton that inhabit the sea ice in large concentrations. Grazing organisms also exploit biogenic material released from the sea ice at ice break-up or melt. Although rates of primary production in the underlying water column are often low because of shading by sea-ice cover, sea ice itself forms a substratum that provides standing stocks of bacteria, algae and grazers significantly higher than those in ice-free areas. Decay of sea ice in summer releases particulate and dissolved organic matter to the water column, playing a major role in biogeochemical cycling as well as seeding water column phytoplankton blooms. Numerous zooplankton species graze sea-ice algae, benefiting additionally because the overlying sea-ice ceiling provides a refuge from surface predators. Sea ice is an important nursery habitat for Antarctic krill, the pivotal species in the Southern Ocean marine ecosystem. Some deep-water fish migrate to shallow depths beneath sea ice to exploit the elevated concentrations of some zooplankton there. The increased secondary production associated with pack ice and the sea-ice edge is exploited by many higher predators, with seals, seabirds and whales

  10. Eddy stirring in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Naveira Garabato, A. C.; Ferrari, R.; Polzin, K. L.

    2011-09-01

    There is an ongoing debate concerning the distribution of eddy stirring across the Antarctic Circumpolar Current (ACC) and the nature of its controlling processes. The problem is addressed here by estimating the isentropic eddy diffusivity κ from a collection of hydrographic and altimetric observations, analyzed in a mixing length theoretical framework. It is shown that, typically, κ is suppressed by an order of magnitude in the upper kilometer of the ACC frontal jets relative to their surroundings, primarily as a result of a local reduction of the mixing length. This observation is reproduced by a quasi-geostrophic theory of eddy stirring across a broad barotropic jet based on the scaling law derived by Ferrari and Nikurashin (2010). The theory interprets the observed widespread suppression of the mixing length and κ in the upper layers of frontal jets as the kinematic consequence of eddy propagation relative to the mean flow within jet cores. Deviations from the prevalent regime of mixing suppression in the core of upper-ocean jets are encountered in a few special sites. Such `leaky jet' segments appear to be associated with sharp stationary meanders of the mean flow that are generated by the interaction of the ACC with major topographic features. It is contended that the characteristic thermohaline structure of the Southern Ocean, consisting of multiple upper-ocean thermohaline fronts separated and underlaid by regions of homogenized properties, is largely a result of the widespread suppression of eddy stirring by parallel jets.

  11. 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.

  12. 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. Copyright © 2015, American Association for the Advancement of Science.

  13. 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

  14. Examining several Southern Ocean data sets

    NASA Technical Reports Server (NTRS)

    Mcclain, Charles R.; Koblinsky, Chester J.; Firestone, James; Darzi, Michael; Yeh, Eueng-Nan; Beckley, Brian D.

    1991-01-01

    Several datasets regarding the ocean in the Southern Hemisphere are combined into a coregistered format to analyze the use of the data in multidisciplinary research. The datasets are described detailing bathymetric climatological data on surface pigment concentration, eddy-kinetic-energy measurements, surface wind-stress magnitudes, sea-surface temperatures, surface densities, and nitrate concentrations. The data are combined in a common projection which facilitates the comparison of the fields, and the combined data yield insights regarding such phenomena as bottom topography, surface heat and moisture fluxes, and divergences in flow. The number of available datasets is shown to be good, and the data can be used to develop working hypotheses on the relationships between physical and biogeochemical processes.

  15. Processes controlling Southern Ocean cloud-climate feedbacks (Invited)

    NASA Astrophysics Data System (ADS)

    Kay, J. E.; Medeiros, B.; Hwang, Y.; Gettelman, A.

    2013-12-01

    We use a fully coupled climate model (CESM) to identify processes controlling intriguingly diverse Southern Ocean cloud feedbacks in response to increased greenhouse gas forcing. Modeled Southern Ocean cloud-climate feedbacks range from the most positive (enhancing greenhouse warming at ~40 degrees South) to the most negative (damping greenhouse warming at ~60 degrees South) on the planet. As greenhouse gas concentrations increase, Antarctic sea ice loss, warming, and a poleward stormtrack shift/sub-tropical expansion all modify Southern Ocean clouds. Our analysis shows that Southern Ocean clouds are controlled both by thermodynamics (cloud changes for a given subsidence rate) and by dynamics (changes in subsidence rates). Hinting at the importance of thermodynamics, absorbed shortwave radiation over the Southern Ocean is substantially more affected by increased greenhouse gas forcing than by a poleward stormtrack shift in the absence of greenhouse forcing. While we find CESM a useful tool, CESM has substantial Southern Ocean biases (e.g., excessive Antarctic sea ice, excessive absorbed shortwave radiation). Thus, we also assess the impact that these biases have on the realism of CESM Southern Ocean cloud-climate greenhouse feedbacks.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Plio-Pleistocene Biogenic Opal Deposition in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Kuhn, G.; Gersonde, R.

    2002-12-01

    About 2/3 of the annual supply of silicic acid to the World Ocean is buried in the Southern Ocean as biogenic silica (BSi), formed by diatoms and radiolaria in surface waters and exported to the seafloor. Main BSi accumulation occurs in an area between the sea ice edge and the Polar Front Zone and seems to be steered by a complex interaction of biological and physical parameters governing the modern Southern Ocean ecosystem. Sediment cores recovered during Ocean Drilling Program Leg 177 and expeditions with RV POLARSTERN reveal the history of the opal deposition in the Atlantic and Pacific sector of the Southern Ocean during the Pliocene and the Pleistocene. This period is characterized by distinct changes and variability in global climate and ocean circulation that can be related to the spatial-temporal distribution of BSi deposition on long and short time scales. Changes in ocean circulation, water mass structure, sea ice and climatic variability that impact the distribution of silicic acid and the development of coarsly silicified diatoms (e.g. Actinocyclus ingens, Thalassiosira antarctica, Fragilariopsis kerguelensis), presenting the major carriers of biogenic opal, control past BSi deposition in the Southern Ocean. Major deposition in the area of the modern Southern Ocean opal belt starts at the Plio/Pleistocene transition. Such strong export of BSi and related organic carbon might have reinforced the trend of global cooling observed since the Mid-Pliocene climate optimum.

  1. 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

  2. Superoxide decay kinetics in the southern ocean.

    PubMed

    Heller, Maija I; Croot, Peter L

    2010-01-01

    Measurements of superoxide (O(2)(-)) reaction kinetics were made during a transect with the research icebreaker Polarstern (ANT24-3) in the Antarctic through the Drake Passage in austral autumn 2008. Our sampling strategy was designed to investigate the sinks of superoxide in Polar waters; principally through reactions with dissolved organic matter (DOM) or metals (copper and iron). We modified an existing chemiluminescence flow injection system using methyl Cypridina luciferin analog (MCLA) for the detection of O(2)(-) and added O(2)(-) using KO(2) as the source. Our results indicate that O(2)(-) in ambient seawater had a half-life ranging from 9.3 to 194 s. DTPA additions to seawater, to remove the effects of reactions with metals, revealed O(2)(-) decay rates consistent with a second order reaction, indicating that the dismutation reaction dominated and that reactions with DOM were not significant. Titrations of seawater by the addition of nanomolar amounts of iron or copper revealed the importance of organic chelation of Fe and/or Cu in controlling the reactivity with O(2)(-). Throughout the water column reactions with Cu appeared to be the major sink for superoxide in the Southern Ocean. This new strategy suggests an alternative approach for speciation measurements of Fe and Cu in seawater.

  3. 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. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  4. The Southern Ocean Silica Cycle: Knowns and Unknowns

    NASA Astrophysics Data System (ADS)

    Treguer, P. J.; André, L.; Wadham, J.; Hawkings, J.; Maldonado, M.

    2016-02-01

    On the one hand, the Southern Ocean surface waters receive considerable amounts of silicic acid (dissolved silica - DSi) from the rest of the world's oceans 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 Subantarctic Mode Water, of the Antarctic Intermediate Water, and of the Antarctic Bottom Water; thus the Southern Ocean is a considerable source of DSi for other ocean basins. In a preliminary article Tréguer (2014) addressed the question of whether the Southern Ocean is a net importer or exporter of DSi. To further address this question, new estimates of the external silica inputs to the Southern Ocean (subglacial discharge, ice shelf melt and icebergs, aeolian and hydrothermal inputs), the long-term burial rate of opal in sediments, and the accumulation of silica by siliceous sponges are presented.

  5. Sources and Sinks of bioavailable iron in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Blain, S.

    2003-04-01

    During the glacial/interglacial transitions, the concentration of CO_2 in the atmosphere varied greatly. The responsible mechanisms are not yet completely elucidated, but there is evidence that the ocean was a corner stone of the story. The intensification of the biological pump for this period has been pointed out as a very likely scenario. The iron hypothesis: the increase of the input of iron to the ocean during the glacial period is one of the possible explanations. Such an increase of the iron flux to the ocean may also occur in the future due to global climate change or due to large scale iron fertilisation of the ocean. Despite the significant progress made using various experimental or modelling approaches, many questions related to sources and sinks of bioavailable iron in the Southern Ocean are still open and debated. These issues will be reviewed and discussed in the light of recent findings gathered in the Southern Ocean and other oceans as well.

  6. 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.

  7. Atmospheric Transport and Input of Iron to the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Tindale, N. W.

    2002-12-01

    While Australia is not generally considered to be a major source of mineral dust to the atmosphere, at least compared to Asian and African desert regions, it does appear to be the main source of mineral material to the Southern Ocean region south of Australia and New Zealand. In common with most of the greater Southern Ocean, this region contains high nitrate, low chlorophyll (HNLC) waters. Recent open ocean iron enrichment experiments in this region have demonstrated that phytoplankton growth and biomass are limited by iron availability. However the flux of atmospheric iron to this open ocean region is poorly known with very few direct measurements of mineral aerosol levels and input. Using mineral aerosol samples collected on Macquarie Island and at Cape Grim, together with other chemical data, air mass trajectories and satellite data, the spatial and temporal variability of aerosol iron transport and input to the Southern Ocean region south of Australia is estimated.

  8. Antarctic Ice Sheet fertilises the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Wadham, J. L.; Death, R.; Monteiro, F. M.; Le Brocq, A. M.; Tranter, M.; Ridgwell, A. J.; Raiswell, R.; Hawkings, J.

    2012-12-01

    Southern Ocean (SO) marine primary productivity (PP) is limited by the availability of iron in surface waters, such that variations in iron supply to the SO are thought to exert a major control upon atmospheric CO2 concentrations on glacial/interglacial timescales. The zone bordering the Antarctic Ice Sheet exhibits high PP, exhibiting seasonal plankton blooms in response to elevated dissolved iron concentrations. The source of iron stimulating these PP increases is in debate, traditionally ascribed contributors being aeolian dust, coastal sediments/upwelling and sea ice. More recently, icebergs and glacial meltwater have been suggested as sources. Data from glacial meltwaters worldwide indicate that sub-Antarctic meltwaters are likely to be anoxic, as a result of long flow paths and little surface input of oxygenated meltwaters. Hence, it is probable that they are rich in dissolved iron (as Fe(II)), acquired via the oxidation of sulphide minerals in sediments. In contrast, iron in iceberg rafted debris is dominated by iron oxyhydroxides, generated in oxic sectors of the ice sheet bed by regelation processes or entrained in icebergs as they pass over shelf sediments. The potential for iron from both these ice sheet sources to impact PP has not yet been quantified. Here we apply the MIT marine ecosystem model to determine the potential impact of ice sheet iron export on SO PP. Fluxes of iceberg and meltwater-derived iron are focused along major ice stream corridors, and enhance iron concentrations in surface ocean waters. The impact on SO PP is greatest in coastal regions, including the Ross Sea, Weddell Sea and Amundsen Sea, all of which are areas of high observed marine PP. Inclusion of ice sheet iron sources in modelled scenarios raises SO PP by 10-30%, and provides a plausible explanation for very high seasonally observed PP around the coastal zone. These results highlight Antarctic runoff and icebergs as previously neglected sources of bioavailable iron to the

  9. 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.

  10. 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.

  11. 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.

  12. Trace metal evidence for a poorly ventilated glacial Southern Ocean

    NASA Astrophysics Data System (ADS)

    Wagner, Meghan; Hendy, Ingrid L.

    2017-08-01

    Glacial benthic δ13C and Δ14C measurements from the Atlantic Ocean have been interpreted to indicate the existence of a poorly ventilated Southern Ocean with greater CO2 and nutrient contents compared to present. Enhanced storage of CO2 in the deep ocean predicts that oxygen concentrations should have declined at the same time-a prediction increasingly supported by evidence for oxygen depletion in the glacial Southern Ocean. Here we take a novel approach by using a suite of redox-sensitive trace metals (Ag, Cd, Re and Mo) to show that Southern Ocean sediments from two cores in the Atlantic sector were suboxic during and prior to deglaciation, implying changes to ocean circulation and/or elevated export production that significantly altered deep water chemistry. In the Cape Basin, enrichments of the authigenically deposited trace metal Re are comparable to those found in oxygen minimum zones, pointing to substantial decreases in oxygenation. Furthermore, trace metal results suggest potential spatial heterogeneity in the glacial Southern Ocean, and a more complicated oceanographic and oxygenation history than has previously been assumed.

  13. 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

  14. 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.

  15. Reduced calcification in modern Southern Ocean planktonic foraminifera

    NASA Astrophysics Data System (ADS)

    Moy, Andrew D.; Howard, William R.; Bray, Stephen G.; Trull, Thomas W.

    2009-04-01

    Anthropogenic carbon dioxide has been accumulating in the oceans, lowering both the concentration of carbonate ions and the pH (ref. 1), resulting in the acidification of sea water. Previous laboratory experiments have shown that decreased carbonate ion concentrations cause many marine calcareous organisms to show reduced calcification rates. If these results are widely applicable to ocean settings, ocean acidification could lead to ecosystem shifts. Planktonic foraminifera are single-celled calcite-secreting organisms that represent between 25 and 50% of the total open-ocean marine carbonate flux and influence the transport of organic carbon to the ocean interior. Here we compare the shell weights of the modern foraminifer Globigerina bulloides collected from sediment traps in the Southern Ocean with the weights of shells preserved in the underlying Holocene-aged sediments. We find that modern shell weights are 30-35% lower than those from the sediments, consistent with reduced calcification today induced by ocean acidification. We also find a link between higher atmospheric carbon dioxide and low shell weights in a 50,000-year-long record obtained from a Southern Ocean marine sediment core. It is unclear whether reduced calcification will affect the survival of this and other species, but a decline in the abundance of foraminifera caused by acidification could affect both marine ecosystems and the oceanic uptake of atmospheric carbon dioxide.

  16. Southern Ocean bottom water characteristics in CMIP5 models

    NASA Astrophysics Data System (ADS)

    Heuzé, CéLine; Heywood, Karen J.; Stevens, David P.; Ridley, Jeff K.

    2013-04-01

    Southern Ocean deep water properties and formation processes in climate models are indicative of their capability to simulate future climate, heat and carbon uptake, and sea level rise. Southern Ocean temperature and density averaged over 1986-2005 from 15 CMIP5 (Coupled Model Intercomparison Project Phase 5) climate models are compared with an observed climatology, focusing on bottom water. Bottom properties are reasonably accurate for half the models. Ten models create dense water on the Antarctic shelf, but it mixes with lighter water and is not exported as bottom water as in reality. Instead, most models create deep water by open ocean deep convection, a process occurring rarely in reality. Models with extensive deep convection are those with strong seasonality in sea ice. Optimum bottom properties occur in models with deep convection in the Weddell and Ross Gyres. Bottom Water formation processes are poorly represented in ocean models and are a key challenge for improving climate predictions.

  17. Nonmethane hydrocarbons in Southern Ocean boundary layer air

    NASA Astrophysics Data System (ADS)

    Lewis, Alastair C.; Carpenter, Lucy J.; Pilling, Michael J.

    2001-03-01

    Measurements at the remote marine boundary layer station of Cape Grim, Northwest Tasmania, allow study of the unperturbed background atmosphere. Here we present a continuous data series of nonmethane hydrocarbons (NMHCs), measured in situ and with high sensitivity during the Second Southern Ocean Photochemistry Experiment (SOAPEX 2) during austral summer 1999. Air masses arriving at Cape Grim originate from the Australian continent, Tasmania, and Southern Ocean and Antarctic regions. In Southern Ocean marine boundary layer (MBL) air, C2 and C3 alkanes show a highly uniform abundance (ethane 142±11.9 parts per trillion by volume (pptv), propane 8.9±1.7 pptv) at around 4 times lower concentrations than encountered in unpolluted Northern Hemisphere MBL air. The presence of shorter-lived NMHCs in marine air indicates sources of both C4-C6 alkanes and several alkenes in the Southern Ocean. The alkane isomer distributions and abundances are in broad agreement with literature sea-air flux rates. In dynamically stable maritime air, midday maxima in ethene, propene, and isoprene concentrations of a few pptv indicate photochemically driven sources very near to the sea surface. Despite their high reactivity, the impact of these oceanic alkenes on local OH concentrations in remote MBL air is not significant. However, the abundance of isoprene in marine air may significantly elevate formaldehyde above that generated by methane oxidation.

  18. The Semiannual Oscillation of Southern Ocean Sea Level

    NASA Astrophysics Data System (ADS)

    Hibbert, A.

    2012-04-01

    The atmospheric Semiannual Oscillation (SAO) is a half-yearly wave in mean sea level air pressure, which exhibits equinoctial maxima between 45°S and 50°S and solstitial maxima between 55°S and 65°s, with a phase reversal occurring at around 60°S. Its existence has been attributed to a phase difference in the annual temperature cycle between mid- and high-latitudes which sets up meridional temperature and pressure gradients that are largest during September and March, enhancing atmospheric baroclinicity and inducing equinoctial maxima in the Southern Hemisphere Westerlies. In this study, we use harmonic analysis of atmospheric and oceanic Southern Ocean datasets to show that this atmospheric SAO induces oceanic counterparts in sea level and circumpolar transport. This aspect of atmosphere-ocean interaction is particularly important, given the capacity of the Antarctic Circumpolar Current (ACC) to influence regional climate through the exchange of heat, fresh water and nutrients to each of the major ocean basins. We examine the relative contributions of local and regional semiannual atmospheric fluctuations in explaining the observed sea level response at 20 Southern Ocean and South Atlantic tide gauge stations and find that the oceanic SAO is associated with a modulation of zonal surface wind strength at key latitudes between ~55°S and 65°S. We also explore whether a seasonal inequality in SAO amplitude might facilitate the deduction of the timescales upon which Southern Ocean 'eddy saturation' theory might operate. However, though we find evidence of biannual fluctuations in eddy kinetic energy, regional variations in the phases and amplitudes of these emergent harmonics prevent us from elucidating the possible timescales upon which an eddy response to the atmospheric SAO might arise.

  19. 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

  20. Influence of the Southern Ocean on the Global deep ocean stratification

    NASA Astrophysics Data System (ADS)

    Sun, S.; Eisenman, I.; Stewart, A.

    2015-12-01

    The stratification of the deep ocean plays a key role in the climate system by influencing the ocean circulation and regulating the outgassing of CO2. Previous studies have suggested that Southern Ocean processes control the global ocean stratification below the main thermocline (i.e., below ~500m). In this study, three ocean-only simulations are carried out with the Community Earth System Model (CESM1): one control simulation forced with Pre-industrial (PI) surface conditions, a second control simulation forced with Last Glacial Maximum (LGM) surface conditions, and a test simulation forced with LGM surface conditions in southern high latitudes and PI surface conditions elsewhere. We find that the test simulation does broadly reproduce the LGM density stratification of the global ocean below 2000m, but not at intermediate depths between 500m and 1500m. We propose a mechanism whereby the stratification of the intermediate-depth waters is influenced by the differing effects on the surface buoyancy distribution of fixed versus restoring aspects of the surface buoyancy forcing. This implies the Southern Ocean exerts less influence over the global deep ocean stratification than has been previously suggested, at least when considering the difference between LGM and PI climates in CESM1.

  1. 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.

  2. Increased exposure of Southern Ocean phytoplankton to ultraviolet radiation

    NASA Astrophysics Data System (ADS)

    Lubin, Dan; Arrigo, Kevin R.; van Dijken, Gert L.

    2004-05-01

    Satellite remote sensing of both surface solar ultraviolet radiation (UVR) and chlorophyll over two decades shows that biologically significant ultraviolet radiation increases began to occur over the Southern Ocean three years before the ozone ``hole'' was discovered. Beginning in October 1983, the most frequent occurrences of enhanced UVR over phytoplankton-rich waters occurred in the Weddell Sea and Indian Ocean sectors of the Southern Ocean, impacting 60% of the surface biomass by the late 1990s. These results suggest two reasons why more serious impacts to the base of the marine food web may not have been detected by field experiments: (1) the onset of UVR increases several years before dedicated field work began may have impacted the most sensitive organisms long before such damage could be detected, and (2) most biological field work has so far not taken place in Antarctic waters most extensively subjected to enhanced UVR.

  3. 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.

  4. Silicon and zinc biogeochemical cycles coupled through the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Vance, Derek; Little, Susan H.; de Souza, Gregory F.; Khatiwala, Samar; Lohan, Maeve C.; Middag, Rob

    2017-02-01

    Zinc is vital for the physiology of oceanic phytoplankton. The striking similarity of the depth profiles of zinc to those of silicate suggests that the uptake of both elements into the opaline frustules of diatoms, and their regeneration from these frustules, should be coupled. However, the zinc content of diatom opal is negligible, and zinc is taken up into and regenerated from the organic parts of diatom cells. Thus, since opaline frustules dissolve deep in the water column while organic material is regenerated in the shallow subsurface ocean, there is little reason to expect the observed close similarity between zinc and silicate, and the dissimilarity between zinc and phosphate. Here we combine observations with simulations using a three-dimensional model of ocean circulation and biogeochemistry to show that the coupled distribution of zinc and silicate, as well as the decoupling of zinc and phosphate, can arise in the absence of mechanistic links between the uptake of zinc and silicate, and despite contrasting regeneration length scales. Our simulations indicate that the oceanic zinc distribution is, in fact, a natural result of the interaction between ocean biogeochemistry and the physical circulation through the Southern Ocean hub. Our analysis demonstrates the importance of uptake stoichiometry in controlling ocean biogeochemistry, and the utility of global-scale elemental covariation in the ocean in understanding these controls.

  5. 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.

  6. 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.

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

    PubMed

    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

    2012-04-24

    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.

  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. On the relationship between Southern Ocean eddies and phytoplankton

    NASA Astrophysics Data System (ADS)

    Frenger, Ivy; Münnich, Matthias; Gruber, Nicolas

    2017-04-01

    Effects on phytoplankton in the Southern Ocean are crucial for the global ocean nutrient and carbon cycles. Such effects potentially arise from mesoscale eddies which are omnipresent in the region. Eddies are known to affect phytoplankton through either advection and mixing, or the stimulation/suppression of growth. Yet, the climatological relationship between Southern Ocean eddies and phytoplankton has not been quantified in detail. To provide an estimate of this relationship, we identified more than100,000 eddies in the Southern Ocean and determined associated phytoplankton anomalies using satellite-based chlorophyll-a (chl) measurements. The eddies have a very substantial impact on the chl levels, with eddy associated chl differing by more than 10% from the background over wide areas. The structure of these anomalies is largely zonal, with positive anomalies north of the Antarctic Circumpolar Current (ACC) and negative anomalies within the circumpolar belt of the ACC for cyclonic eddies. The pattern is similar but of opposite sign for anticyclonic eddies. The seasonality of this signal is weak north to the ACC, but pronounced in the vicinity of the ACC. The spatial structure and seasonality of the signal can be explained largely by advection, i.e., the eddy-circulation driven lateral transport of anomalies across large-scale gradients. We conclude this based on the shape of local chl anomalies of eddies and ambient chl gradients. In contrast, ACC winter anomalies are consistent with an effect of eddies on the light exposure of phytoplankton. The clear impact of eddies on chl implies a downstream effect on Southern Ocean biogeochemical properties.

  11. 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

  12. High resolution dynamic ocean topography in the Southern Ocean from GOCE

    NASA Astrophysics Data System (ADS)

    Albertella, A.; Savcenko, R.; Janjić, T.; Rummel, R.; Bosch, W.; Schröter, J.

    2012-08-01

    A mean dynamic ocean topography (MDT) has been computed using a high resolution GOCE (Gravity field and steady-state Ocean Circulation Explorer) gravity model and a new mean sea surface obtained from a combination of satellite altimetry covering the period 1992 October till 2010 April. The considered gravity model is GO-CONS-GCF-2-TIM-R3, which computes geoid using 12 months of GOCE gravity field data. The GOCE gravity data allow for more detailed and accurate estimates of MDT. This is illustrated in the Southern Ocean where the commission error is reduced from 20 to 5 cm compared to the MDT computed using the GRACE gravity field model ITG-Grace2010. As a result of the more detailed and accurate MDT, the calculation of geostrophic velocities from the MDT is now possible with higher accuracy and spatial resolution, and the error estimate is about 7 cm s-1 for the Southern Ocean.

  13. Estimate chlorophyll a and POC concentrations in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Haëntjens, N.; Boss, E.; Talley, L. D.

    2016-02-01

    The Southern Ocean Carbon and Climate Observations and Modeling project (SOCCOM) is deploying hundreds of profiling floats with (NASA-funded) bio-optical sensors in the Southern Ocean. The optical sensor measure chlorophyll fluorescence (Ex/Em 470/685nm) and the backscattering coefficient at 700nm, which are routinely as proxies for chlorophyll a (chl-a) and particulate organic carbon (POC) concentrations. To assess the quality of the chl-a and POC derived from the float's measurements we compare them with chl-a and POC samples collected near the times the floats were deployed. Through the life of a float, we also compare its measurements to estimates of chl-a and the backscattering coefficient derived from remotely sensed ocean color. In addition, on most cruises where floats are deployed, a `golden' sensor is deployed on the CTD rosette for cross-calibration between floats. For fluorescence measurements done when there is significant irradiance in the upper ocean we correct for non-photochemical quenching of fluorescence with an average of Xing et al. (2012) and Sackmann et al.'s (2008) methods. To date we have found the backscattering measurement to be consistent with previous studies while chl-a estimated with fluorescence is significantly over estimated when using the manufacturer calibration (factor of 7 relative to HPLC, 3.5 relative to local ocean color algorithms). We hope that our work will provide for an unprecedented, quality-controlled, dataset of chl-a and POC for the Southern Ocean to be used in biogeochemical studies.

  14. Southern Ocean control of silicon stable isotope distribution in the deep Atlantic Ocean

    NASA Astrophysics Data System (ADS)

    de Souza, Gregory F.; Reynolds, Ben C.; Rickli, Jörg; Frank, Martin; Saito, Mak A.; Gerringa, Loes J. A.; Bourdon, Bernard

    2012-06-01

    The fractionation of silicon (Si) stable isotopes by biological activity in the surface ocean makes the stable isotope composition of silicon (δ30Si) dissolved in seawater a sensitive tracer of the oceanic biogeochemical Si cycle. We present a high-precision dataset that characterizes the δ30Si distribution in the deep Atlantic Ocean from Denmark Strait to Drake Passage, documenting strong meridional and smaller, but resolvable, vertical δ30Si gradients. We show that these gradients are related to the two sources of deep and bottom waters in the Atlantic Ocean: waters of North Atlantic and Nordic origin carry a high δ30Si signature of ≥+1.7‰ into the deep Atlantic, while Antarctic Bottom Water transports Si with a low δ30Si value of around +1.2‰. The deep Atlantic δ30Si distribution is thus governed by the quasi-conservative mixing of Si from these two isotopically distinct sources. This disparity in Si isotope composition between the North Atlantic and Southern Ocean is in marked contrast to the homogeneity of the stable nitrogen isotope composition of deep ocean nitrate (δ15N-NO3). We infer that the meridional δ30Si gradient derives from the transport of the high δ30Si signature of Southern Ocean intermediate/mode waters into the North Atlantic by the upper return path of the meridional overturning circulation (MOC). The basin-scale deep Atlantic δ30Si gradient thus owes its existence to the interaction of the physical circulation with biological nutrient uptake at high southern latitudes, which fractionates Si isotopes between the abyssal and intermediate/mode waters formed in the Southern Ocean.

  15. 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.

  16. Space and Time Variability of the Southern Ocean Carbon Budget

    NASA Astrophysics Data System (ADS)

    Rosso, I.; Mazloff, M. R.; Verdy, A.; Talley, L. D.

    2016-12-01

    The upper ocean dissolved inorganic carbon (DIC) concentration is regulated by advective and diffusive transport divergence, biological processes, and CO2 and fresh water fluxes. The relative importance of these mechanisms in the Southern Ocean are uncertain, as observations in this area have been limited. A biogeochemical-sea ice-ocean model of the Southern Ocean, run at 1/3 degree resolution, is used to investigate the drivers of the change in DIC concentration between January 2006 and December 2014.We find that advective transport governs the local upper ocean (down to 650 m) DIC budget on all time scales. Other components are influential, however, in setting the interannual variability: in particular, biological production in western boundary currents, at large topographic features (such as the Kerguelen Plateau) and in the Weddell and Ross gyres, or sea ice processes in Antarctic regions. For regional budgets, advection is less influential: in subpolar gyres biology and dilution shape the seasonal cycle, whereas air-sea exchanges are a primary driver of DIC changes in the subtropics. Meanwhile, all processes have a significant impact on the DIC budget in the ACC, with topographic features influencing the relative importance of advection, biological mechanisms and air-sea flux.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Horizontal mixing in the Southern Ocean from Argo float trajectories

    NASA Astrophysics Data System (ADS)

    Roach, Christopher J.; Balwada, Dhruv; Speer, Kevin

    2016-08-01

    We provide the first observational estimate of the circumpolar distribution of cross-stream eddy diffusivity at 1000 m in the Southern Ocean using Argo float trajectories. We show that Argo float trajectories, from the float surfacing positions, can be used to estimate lateral eddy diffusivities in the ocean and that these estimates are comparable to those obtained from RAFOS floats, where they overlap. Using the Southern Ocean State Estimate (SOSE) velocity fields to advect synthetic particles with imposed behavior that is "Argo-like" and "RAFOS-like" diffusivity estimates from both sets of synthetic particles agreed closely at the three dynamically very different test sites, the Kerguelen Island region, the Southeast Pacific Ocean, and the Scotia Sea, and support our approach. Observed cross-stream diffusivities at 1000 m, calculated from Argo float trajectories, ranged between 300 and 2500 m2 s-1, with peaks corresponding to topographic features associated with the Scotia Sea, the Kerguelen Plateau, the Campbell Plateau, and the Southeast Pacific Ridge. These observational estimates agree with previous regional estimates from the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) near the Drake Passage, and other estimates from natural tracers (helium), inverse modeling studies, and current meter measurements. These estimates are also compared to the suppressed eddy diffusivity in the presence of mean flows. The comparison suggests that away from regions of strong topographic steering suppression explains both the structure and magnitude of eddy diffusivity but that eddy diffusivities in the regions of topographic steering are greater than what would be theoretically expected and the ACC experiences localized enhanced cross-stream mixing in these regions.

  2. How ocean lateral mixing changes Southern Ocean variability in coupled climate models

    NASA Astrophysics Data System (ADS)

    Pradal, M. A. S.; Gnanadesikan, A.; Thomas, J. L.

    2016-02-01

    The lateral mixing of tracers represents a major uncertainty in the formulation of coupled climate models. The mixing of tracers along density surfaces in the interior and horizontally within the mixed layer is often parameterized using a mixing coefficient ARedi. The models used in the Coupled Model Intercomparison Project 5 exhibit more than an order of magnitude range in the values of this coefficient used within the Southern Ocean. The impacts of such uncertainty on Southern Ocean variability have remained unclear, even as recent work has shown that this variability differs between different models. In this poster, we change the lateral mixing coefficient within GFDL ESM2Mc, a coarse-resolution Earth System model that nonetheless has a reasonable circulation within the Southern Ocean. As the coefficient varies from 400 to 2400 m2/s the amplitude of the variability varies significantly. The low-mixing case shows strong decadal variability with an annual mean RMS temperature variability exceeding 1C in the Circumpolar Current. The highest-mixing case shows a very similar spatial pattern of variability, but with amplitudes only about 60% as large. The suppression of mixing is larger in the Atlantic Sector of the Southern Ocean relatively to the Pacific sector. We examine the salinity budgets of convective regions, paying particular attention to the extent to which high mixing prevents the buildup of low-saline waters that are capable of shutting off deep convection entirely.

  3. 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.

  4. Atlantic Southern Ocean productivity: Fertilization from above or below?

    NASA Astrophysics Data System (ADS)

    Meskhidze, Nicholas; Nenes, Athanasios; Chameides, William L.; Luo, Chao; Mahowald, Natalie

    2007-06-01

    Primary productivity and the associated uptake of atmospheric carbon dioxide in the Southern Ocean (SO) is thought to be generally limited by bioavailable iron (Fe). Two sources of Fe for the surface waters of the SO have been proposed: (1) oceanic input of nutrient-rich (i.e., Fe) waters from upwelling and lateral flows from continental margins; and (2) atmospheric input from the deposition of mineral dust emanating from the arid regions of South America and Australia. In this work, analysis of weekly remotely sensed sea surface temperature (SST), ocean chlorophyll a content [Chl a] and model-derived atmospheric dust-Fe fluxes are used to identify the predominant source of Fe during phytoplankton blooms in the surface waters of the south Atlantic Ocean between 40°S and 60°S. The results of our study suggest that oceanic source through upwelling of nutrient-rich waters due to mesoscale frontal dynamics is the major source of bioavailable Fe controlling biological activity in this region. This result is consistent with the idea that acidification of aeolian dust prior to its deposition to the ocean may be required to solubilize the large fraction of mineral-iron and make it bioavailable.

  5. 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.

  6. Deep Meridional Circulation in the Southern Ocean is Topographically Controlled

    NASA Astrophysics Data System (ADS)

    Chapman, Christopher; Sallée, Jean-Baptiste

    2016-04-01

    The Southern Ocean fundamentally influences the Earth's climate through it's strong control over the deep meridional circulation. This circulation moves vast amounts of mass, heat and tracers, acting to redistribute them throughout the global ocean. However, due to its complex dynamics and a lack of observations, the Southern Ocean's deep circulation is poorly understood. We present a new interpretation of the deep circulation by using a network of Lagrangian autonomous floats to derive the first observation-based maps of the deep meridional flow. Contrary to most existing studies that employ a quasi 2-dimensional framework, we find fluxes are strongly localised near large topographic features, with alternating northward and southward fluxes effectively cancelling each other, leaving a small residual that contributes to the total flux. A simple force-balance indicates that the dynamics that give rise to these fluxes occur due to steering of the large-scale Antarctic Circumpolar Current by the bottom topography. Finally, we discuss the implications of this work, noting that strongly localised fluxes which yield a small yet important net meridional flux, will influence the redistribution of heat and tracers within and between ocean basins, water mass transformation and the deep storage of CO2.

  7. 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.

  8. Using transient tracers to estimate decadal changes in Southern Ocean ventilation in an eddying ocean model

    NASA Astrophysics Data System (ADS)

    Patara, Lavinia; Schmidt, Christina; Tanhua, Toste; Böning, Claus

    2017-04-01

    Decadal changes in ocean ventilation of Southern Ocean water masses is estimated by performing a set of ocean simulations with the ocean model NEMO-LIM2 at 1/4° horizontal resolution ( 15 km grid spacing at 50°S). The model simulates the uptake and spreading of CFC-12 and SF6, which are atmospheric trace gases that both increased in past decades due to human activities, with CFC-12 leveling off in the mid-90s and SF6 steadily increasing. Two simulations are performed: a hindcast simulation from 1948 to 2010 and a climatological experiment performed under repeated-annual-cycle forcing. The latter is used to correct the hindcast experiment from model spurious trends unrelated to the atmospheric forcing. Simulated CFC-12 and SF6 are here used 1) to assess the simulated water mass ventilation in comparison with observations and 2) to estimate decadal changes in ocean ventilation. Owing to the similar atmospheric increase rates of CFC-12 and SF6, but with a time lag of 14-15 years, a change between historical CFC-12 and modern SF6 tracer ages implies a decadal change in ventilation. Using this approach it was possible to estimate whether changes in upper ocean ventilation occurred in the period between the 1980s and 2000s in different sectors of the Southern Ocean. Preliminary results show that ventilation of Antarctic Intermediate Water and - partially - of Subantarctic Mode Water increased between the 1980s and the 2000s in several sectors of the Southern Ocean. Despite this general pattern, conspicuous regional variability is also found and will here be discussed.

  9. The ocean mixed layer under Southern Ocean sea-ice: Seasonal cycle and forcing

    NASA Astrophysics Data System (ADS)

    Pellichero, Violaine; Sallée, Jean-Baptiste; Schmidtko, Sunke; Roquet, Fabien; Charrassin, Jean-Benoît

    2017-02-01

    The oceanic mixed layer is the gateway for the exchanges between the atmosphere and the ocean; in this layer, all hydrographic ocean properties are set for months to millennia. A vast area of the Southern Ocean is seasonally capped by sea-ice, which alters the characteristics of the ocean mixed layer. The interaction between the ocean mixed layer and sea-ice plays a key role for water mass transformation, the carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the under-ice mixed layer are poorly understood due to the sparseness of in situ observations and measurements. In this study, we combine distinct sources of observations to overcome this lack in our understanding of the polar regions. Working with elephant seal-derived, ship-based, and Argo float observations, we describe the seasonal cycle of the ocean mixed-layer characteristics and stability of the ocean mixed layer over the Southern Ocean and specifically under sea-ice. Mixed-layer heat and freshwater budgets are used to investigate the main forcing mechanisms of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity, and vertical entrainment play only secondary roles. Our results suggest that changes in regional sea-ice distribution and annual duration, as currently observed, widely affect the buoyancy budget of the underlying mixed layer, and impact large-scale water mass formation and transformation with far reaching consequences for ocean ventilation.

  10. Topographic enhancement of vertical turbulent mixing in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Mashayek, A.; Ferrari, R.; Merrifield, S.; Ledwell, J. R.; St Laurent, L.; Garabato, A. Naveira

    2017-03-01

    It is an open question whether turbulent mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. The diapycnal and isopycnal mixing experiment in the Southern Ocean found the turbulent diffusivity inferred from the vertical spreading of a tracer to be an order of magnitude larger than that inferred from the microstructure profiles at the mean tracer depth of 1,500 m in the Drake Passage. Using a high-resolution ocean model, it is shown that the fast vertical spreading of tracer occurs when it comes in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows. The increased tracer residence time may explain the large vertical fluxes of heat and salt required to close the abyssal circulation.

  11. Topographic enhancement of vertical turbulent mixing in the Southern Ocean

    PubMed Central

    Mashayek, A.; Ferrari, R.; Merrifield, S.; Ledwell, J. R.; St Laurent, L.; Garabato, A. Naveira

    2017-01-01

    It is an open question whether turbulent mixing across density surfaces is sufficiently large to play a dominant role in closing the deep branch of the ocean meridional overturning circulation. The diapycnal and isopycnal mixing experiment in the Southern Ocean found the turbulent diffusivity inferred from the vertical spreading of a tracer to be an order of magnitude larger than that inferred from the microstructure profiles at the mean tracer depth of 1,500 m in the Drake Passage. Using a high-resolution ocean model, it is shown that the fast vertical spreading of tracer occurs when it comes in contact with mixing hotspots over rough topography. The sparsity of such hotspots is made up for by enhanced tracer residence time in their vicinity due to diffusion toward weak bottom flows. The increased tracer residence time may explain the large vertical fluxes of heat and salt required to close the abyssal circulation. PMID:28262808

  12. 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.

  13. Southern Ocean buoyancy forcing of ocean ventilation and glacial atmospheric CO2

    NASA Astrophysics Data System (ADS)

    Watson, Andrew J.; Vallis, Geoffrey K.; Nikurashin, Maxim

    2015-11-01

    Atmospheric CO2 concentrations over glacial-interglacial cycles closely correspond to Antarctic temperature patterns. These are distinct from temperature variations in the mid to northern latitudes, so this suggests that the Southern Ocean is pivotal in controlling natural CO2 concentrations. Here we assess the sensitivity of atmospheric CO2 concentrations to glacial-interglacial changes in the ocean's meridional overturning circulation using a circulation model for upwelling and eddy transport in the Southern Ocean coupled with a simple biogeochemical description. Under glacial conditions, a broader region of surface buoyancy loss results in upwelling farther to the north, relative to interglacials. The northern location of upwelling results in reduced CO2 outgassing and stronger carbon sequestration in the deep ocean: we calculate that the shift to this glacial-style circulation can draw down 30 to 60 ppm of atmospheric CO2. We therefore suggest that the direct effect of temperatures on Southern Ocean buoyancy forcing, and hence the residual overturning circulation, explains much of the strong correlation between Antarctic temperature variations and atmospheric CO2 concentrations over glacial-interglacial cycles.

  14. 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.

  15. Iron supply to the Southern Ocean mixed layer from below; the ocean model effect

    NASA Astrophysics Data System (ADS)

    Schourup-Kristensen, Vibe; Hauck, Judith; Losch, Martin; Wolf-Gladrow, Dieter A.; Völker, Christoph

    2015-04-01

    In the iron limited Southern Ocean, the biogeochemical results of commonly used ocean general circulation biogeochemical models differ greatly dependent on the ocean model used. This is largely due to the difficulties in reproducing a realistic mixed layer depth (MLD), which leads to different degrees of light limitation and nutrient supply from below. Regarding the iron sources to the Southern Ocean, research has traditionally focused on the input from dust and the sediment, but recent studies have highlighted the importance of the vertical supply to the mixed layer from the nutrient rich deeper water. This latter supply mechanism may also be affected by the large inter-model differences in the MLD and thereby influence the total net primary production and export production in the models. We have performed a model study in which the biogeochemical model REcoM2 was coupled to two different ocean models, the Finite Element Sea-ice Ocean Model (FESOM) and the MIT general circulation model (MITgcm). The effect of the ocean mixed layer on the magnitude of the iron sources from below in the two models was analyzed, as was the effect on the export and net primary production. Our results revealed a remarkable difference in terms of mode and magnitude of transport dependent on the mixed layer depth in the two models; the mean iron supply from below in the Southern Ocean was on average four times higher in MITgcm than in FESOM. The dominant pathway was entrainment in MITgcm, whereas diffusion dominated in FESOM. We discuss how the difference in the depth and seasonal amplitude of the mixed layer between the models has a major effect on the vertical iron profile and thereby also on the iron fluxes. A further effect of the difference in supply is that the fraction of exported net primary production is higher in MITgcm than in FESOM, showing that the choice of ocean model has a significant impact on the modeled carbon cycle in the Southern Ocean, with possible implications for

  16. Southern ocean nitrogen and silicon dynamics during the last deglaciation

    NASA Astrophysics Data System (ADS)

    Horn, Matthew G.; Beucher, Charlotte P.; Robinson, Rebecca S.; Brzezinski, Mark A.

    2011-10-01

    The reinvigoration of overturning in the Southern Ocean is hypothesized to have returned CO 2 from the deep ocean to the atmosphere at the end of the last ice age. Large peaks in opal accumulation have been put forward as evidence for an increase in wind driven upwelling between 10 and 15 ka. Here, we use coupled nitrogen and silicon isotope records alongside opal accumulation rates to provide quasi-quantitative estimates of Southern Ocean nutrient supply, by upwelling, and nutrient utilization across this interval. Significant changes in the consumption of N and Si across the two opal accumulation peaks indicate major changes in both upwelling and nutrient demand. We find N and Si consumption to be relatively incomplete during peak opal accumulation at the onset of the deglaciation. This indicates that nutrient supply was significantly enhanced. The second deglacial peak in opal accumulation is associated with more complete Si consumption and variable N consumption. We suggest that this peak represents strong upwelling and more complete utilization of the available silicic acid pool. Differences between the Si and N responses during opal peaks may stem from decreasing iron availability across the glacial termination. The nutrient isotope evidence for excess nutrients during the deglaciation indicates that the high export productivity was insufficient to overcome the evasion of CO 2 to the atmosphere as a result of physical circulation changes. Previous work has demonstrated that the reinvigoration of overturning circulation during the deglaciation causes a transient peak in nutrient supply to the low latitudes. This is supported by our data, which indicate that relatively high macronutrient concentrations were maintained in the Southern Ocean surface waters that are incorporated into mode waters despite high demand.

  17. Increasing anti-Aβ-induced neurotoxicity ability of Antrodia camphorata-fermented product with deep ocean water supplementary.

    PubMed

    Shi, Yeuching; Yang, Shuyuan; Lee, David Yuewei; Lee, Chunlin

    2016-11-01

    Antrodia camphorata is proven to probably inhibit the neurotoxicity of amyloid β-peptide (Aβ), known as a risk factor toward the development of Alzheimer's disease. Deep ocean water (DOW), drawn from an ocean depth of more than 200 m, has proven to stimulate the growth and metabolite biosynthesis of fungi owing to its rich minerals and trace elements. Based on these advantages of DOW, this study used statistical response surface methodology (RSM) to investigate the effects of DOW on the growth and anti-Aβ-induced neurocytotoxicity ability of A. camphorata. The results showed that DOW was useful for increasing the biomass of A. camphorata and enhancing its neuroprotective capability. The anti-Aβ40-induced neurocytotoxicity ability of filtrate was increased via raising the mycelium-secreted components. Furthermore, the anti-Aβ40-induced neurocytotoxicity ability of mycelium was also increased by the DOW-stimulated intracellular antioxidants. Using 80% DOW concentration, initial pH 3.3 and 20% inoculum size as the optimal culture conditions of A. camphorata significantly stimulated the biomass and mycelium-mediated Aβ40-induced cell viability from 302 ± 14 mg per 100 mL and 49.2 ± 2.2% to 452 ± 33 mg per 100 mL and 65.0 ± 7.4% respectively. This study indicated that DOW could be used as a promising supplementary for the production of A. camphorata secondary metabolites with strong antioxidant activity to protect neuron cells from damage based on Aβ stimulation cytotoxicity. © 2016 Society of Chemical Industry. © 2016 Society of Chemical Industry.

  18. Surface boundary layer turbulence in the Southern ocean

    NASA Astrophysics Data System (ADS)

    Merrifield, Sophia; St. Laurent, Louis; Owens, Breck; Naveira Garabato, Alberto

    2015-04-01

    Due to the remote location and harsh conditions, few direct measurements of turbulence have been collected in the Southern Ocean. This region experiences some of the strongest wind forcing of the global ocean, leading to large inertial energy input. While mixed layers are known to have a strong seasonality and reach 500m depth, the depth structure of near-surface turbulent dissipation and diffusivity have not been examined using direct measurements. We present data collected during the Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) field program. In a range of wind conditions, the wave affected surface layer (WASL), where surface wave physics are actively forcing turbulence, is contained to the upper 15-20m. The lag-correlation between wind stress and turbulence shows a strong relationship up to 6 hours (˜1/2 inertial period), with the winds leading the oceanic turbulent response, in the depth range between 20-50m. We find the following characterize the data: i) Profiles that have a well-defined hydrographic mixed layer show that dissipation decays in the mixed layer inversely with depth, ii) WASLs are typically 15 meters deep and 30% of mixed layer depth, iii) Subject to strong winds, the value of dissipation as a function of depth is significantly lower than predicted by theory. Many dynamical processes are known to be missing from upper-ocean parameterizations of mixing in global models. These include surface-wave driven processes such as Langmuir turbulence, submesocale frontal processes, and nonlocal representations of mixing. Using velocity, hydrographic, and turbulence measurements, the existence of coherent structures in the boundary layer are investigated.

  19. Recent Ship, Satellite and Autonomous Observations of Southern Ocean Eddies

    NASA Astrophysics Data System (ADS)

    Strutton, P. G.; Moreau, S.; Llort, J.; Phillips, H. E.; Patel, R.; Della Penna, A.; Langlais, C.; Lenton, A.; Matear, R.; Dawson, H.; Boyd, P. W.

    2016-12-01

    The Southern Ocean is the area of greatest uncertainty regarding the exchange of CO2 between the ocean and atmosphere. It is also a region of abundant energetic eddies that significantly impact circulation and biogeochemistry. In the Indian sector of the Southern Ocean, cyclonic eddies are unusual in that they are upwelling favorable, as for cyclonic eddies elsewhere, but during summer they are low in silicate and phytoplankton biomass. The reverse is true for anticyclonic eddies in that they have counter-intuitive positive chlorophyll anomalies in summer. Similar but less obvious patterns occur in the Pacific and Atlantic sectors. Using ship, satellite and autonomous observations in the region south of Australia, the physical and biogeochemical signatures of both types of eddies were documented in 2016. A cyclonic eddy that lived for seven weeks exhibited doming isopycnals indicative of upwelling. However, low surface silicate and chlorophyll concentrations appeared to be characteristic of surface waters to the south where the eddy formed. Higher chlorophyll was confined to filaments at the eddy edge. Surface nitrate and phosphate concentrations were more than sufficient for a bloom of non-siliceous phytoplankton to occur. Acoustic observations from a high resolution TRIAXUS transect through the eddy documented high zooplankton biomass in the upper 150m. It is hypothesized that a non-diatom bloom was prevented by grazing pressure, but light may have also been an important limiting resource in late summer (April). Two SOCCOM floats that were deployed in the eddy field continued to monitor the physics, nitrate and bio-optics through the transition to winter. These observations across complementary platforms have identified and then explained the reason for these unexpected biological anomalies in an energetic and globally important region of the global ocean. Understanding the role of eddies in this region will be critical to the representation of mesoscale

  20. 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

  1. Phytoplankton composition and biomass across the southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Schlüter, Louise; Henriksen, Peter; Nielsen, Torkel Gissel; Jakobsen, Hans H.

    2011-05-01

    Phytoplankton composition and biomass was investigated across the southern Indian Ocean. Phytoplankton composition was determined from pigment analysis with subsequent calculations of group contributions to total chlorophyll a (Chl a) using CHEMTAX and, in addition, by examination in the microscope. The different plankton communities detected reflected the different water masses along a transect from Cape Town, South Africa, to Broome, Australia. The first station was influenced by the Agulhas Current with a very deep mixed surface layer. Based on pigment analysis this station was dominated by haptophytes, pelagophytes, cyanobacteria, and prasinophytes. Sub-Antarctic waters of the Southern Ocean were encountered at the next station, where new nutrients were intruded to the surface layer and the total Chl a concentration reached high concentrations of 1.7 μg Chl a L -1 with increased proportions of diatoms and dinoflagellates. The third station was also influenced by Southern Ocean waters, but located in a transition area on the boundary to subtropical water. Prochlorophytes appeared in the samples and Chl a was low, i.e., 0.3 μg L -1 in the surface with prevalence of haptophytes, pelagophytes, and cyanobacteria. The next two stations were located in the subtropical gyre with little mixing and general oligotrophic conditions where prochlorophytes, haptophytes and pelagophytes dominated. The last two stations were located in tropical waters influenced by down-welling of the Leeuwin Current and particularly prochlorophytes dominated at these two stations, but also pelagophytes, haptophytes and cyanobacteria were abundant. Haptophytes Type 6 ( sensuZapata et al., 2004), most likely Emiliania huxleyi, and pelagophytes were the dominating eucaryotes in the southern Indian Ocean. Prochlorophytes dominated in the subtrophic and oligotrophic eastern Indian Ocean where Chl a was low, i.e., 0.043-0.086 μg total Chl a L -1 in the surface, and up to 0.4 μg Chl a L -1 at

  2. 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.

  3. Eddy response to variable atmospheric forcing in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ward, M. L.; McC. Hogg, A.

    2009-04-01

    Satellite altimeter data of the Southern Ocean (SO) reveal an anomalous peak in eddy kinetic energy (EKE) in the Antarctic Circumpolar Current (ACC) in 2000-2002. This peak has been attributed to a delayed response to an earlier peak in the Southern Annular Mode (SAM) and its associated circumpolar eastward winds that occurred around 1998, where the delay is due to the formation and adjustment of the eddy field associated with the increased winds (Meredith & Hogg, 2006). A more recent analysis reveals that the EKE response varies regionally, with the strongest response in the Pacific, and it has been suggested that this variability is due to the additional influence of ENSO. The 2000-2002 peak in EKE is therefore attributed to the coincident peak in SAM and ENSO 2-3 years earlier, and that the EKE response was weaker in past years when modes were out of phase (Morrow & Pasquet, 2008). We investigate this issue by applying SAM-like and ENSO-like wind forcings to Q-GCM, the eddy-resolving model used in Meredith & Hogg and configured for the Southern Ocean. We analyze the EKE response to each individual forcing as well as a simultaneous forcing of the two, both in and out of phase. From these results, we are able to quantify both the global and regional response to each forcing, and the degree to which each mode is responsible for the EKE strength and distribution across the ACC.

  4. Storm tracks in the Southern Hemisphere subtropical oceans

    NASA Astrophysics Data System (ADS)

    O'Kane, T. J.; Matear, R. J.; Chamberlain, M. A.; Oliver, E. C. J.; Holbrook, N. J.

    2014-09-01

    Ocean storm tracks have previously been associated with the midlatitude western boundary currents (WBCs) and the Antarctic Circumpolar Current (ACC). Here we identify and examine large-scale baroclinically unstable waves occurring within waveguides associated with potential density gradients in the subtropical regions of the Southern Hemisphere (SH) oceans where the trade winds and westerlies meet and at depths associated with mode water formation. In contrast to the Northern Hemisphere subtropics, the SH pathways are more extensive allowing large-scale coherent disturbances to communicate information westward from the midlatitudes to the subtropics (South Pacific Ocean) and from the subtropics to the tropics (Indian Ocean). Particular consideration is given to the subtropical South Pacific Ocean as this is a region where resonant interactions between large-scale Rossby waves and significant topographic features have been reported to occur. Using an ocean general circulation model and a simple potential energy transfer diagnostic, we identify the relevant nonlinearly modified structures comparing their propagation characteristics to planetary Rossby waves calculated using a shallow water model. Although at first appearance baroclinic disturbances resemble planetary Rossby waves, we show they are inherently nonlinear, multiscale and are amplified where topography occurs. The location of the disturbances coincides with regions of high variability in sea surface height observed in satellite altimetry and their speeds closely match the large-scale coherent westward propagating structures described in the observational literature. Our study provides evidence that, in addition to the midlatitude WBCs and the ACC, significant ocean storm tracks are also manifest in the SH subtropics.

  5. Atmospheric Concentrations of Persistent Organic Pollutants in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Vlahos, P.; Edson, J.; Cifuentes, A.; McGillis, W. R.; Zappa, C.

    2008-12-01

    Long-range transport of persistent organic pollutant (POPs) is a global concern. Remote regions such as the Southern Ocean are greatly under-sampled though critical components in understanding POPs cycling. Over 20 high-volume air samples were collected in the Southern Ocean aboard the RV Brown during the GASEX III experiment between Mar 05 to April 9 2008. The relatively stationary platform (51S,38W) enabled the collection of a unique atmospheric time series at this open ocean station. Air sampling was also conducted across transects from Punto Arenas, Chile and to Montevideo, Uruguay. Samples were collected using glass sleeves packed with poly-urethane foam plugs and C-18 resin in order to collect target organic pollutants (per-fluorinated compounds, currently and historically used pesticides) in this under-sampled region. Here we present POPs concentrations and trends over the sampled period and compare variations with air parcel back trajectories to establish potential origins of their long-range transport.

  6. Shipborne observations of the radiative effect of Southern Ocean clouds

    NASA Astrophysics Data System (ADS)

    Protat, Alain; Schulz, Eric; Rikus, Lawrence; Sun, Zhian; Xiao, Yi; Keywood, Melita

    2017-01-01

    This study uses shipborne cloud radar and surface radiation measurements collected over the Southern Ocean to characterize the cloud frequency, cloud fraction, and cloud radiative effects on the ocean surface. These cloud and radiative properties are also used to evaluate a regional forecast model. Low-level clouds, either alone or cooccurring with cloud layers aloft, are present 77% of the time in this data set. These clouds either had a very low or a very high cloud fraction at 12 km horizontal resolution, with about half of the clouds characterized by a cloud fraction higher than 80%. Overall, shortwave surface cooling effect dominates longwave heating, with an estimate net radiative cooling of -22 W m-2, resulting from a -71 W m-2 shortwave cooling and a +49 W m-2 longwave heating. A strong relationship between daily surface cloud radiative effect and daily low-level cloud fraction is found, which, if confirmed with a larger data set, could be exploited in satellite retrievals or model parameterizations for the Southern Ocean. The regional model underestimates the frequency of low-level clouds but largely overestimates the frequency of multilayer situations. The associated radiative errors are large and complex, including reduced surface radiative cooling due to low-level clouds compensated by enhanced surface cooling in multilayer situations.

  7. 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.

  8. Hydrocarbon gas in sediment of the Southern Pacific Ocean

    USGS Publications Warehouse

    Kvenvolden, K.A.

    1988-01-01

    Methane, ethane, ethene, propane, and propene are common hydrocarbon gases in near-surface sediment from offshore areas in the southern Pacific Ocean near Papua New Guinea, the Solomon Islands, Vanuatu, Tonga, New Zealand, and Antarctica. Sea floor sites for sampling of sediment were selected on the basis of anomalies in marine seismic records, and the samples were intentionally biased toward finding possible thermogenic hydrocarbon gases. In none of the areas, however, were thermogenic hydrocarbons clearly identified. The hydrocarbon gases that were found appear to be mainly the products of in situ microbial processes. ?? 1988 Springer-Verlag New York Inc.

  9. 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

  10. The ocean mixed layer under Southern Ocean sea-ice: seasonal cycle and forcing.

    NASA Astrophysics Data System (ADS)

    Violaine, P.; Sallee, J. B.; Schmidtko, S.; Roquet, F.; Charrassin, J. B.

    2016-02-01

    The mixed-layer at the surface of the ocean is the gateway for all exchanges between air and sea. A vast area of the Southern Ocean is however seasonally capped by sea-ice, which alters this gateway and the characteristic the ocean mixed-layer. The interaction between the ocean mixed-layer and sea-ice plays a key role for water-mass formation and circulation, carbon cycle, sea-ice dynamics, and ultimately for the climate as a whole. However, the structure and characteristics of the mixed layer, as well as the processes responsible for its evolution, are poorly understood due to the lack of in-situ observations and measurements. We urgently need to better understand the forcing and the characteristics of the ocean mixed-layer under sea-ice if we are to understand and predict the world's climate. In this study, we combine a range of distinct sources of observation to overcome this lack in our understanding of the Polar Regions. Working on Elephant Seal-derived data as well as ship-based observations and Argo float data, we describe the seasonal cycle of the characteristics and stability of the ocean mixed layer over the entire Southern Ocean (South of 40°S), and specifically under sea-ice. Mixed-layer budgets of heat and freshwater are used to investigate the main forcings of the mixed-layer seasonal cycle. The seasonal variability of sea surface salinity and temperature are primarily driven by surface processes, dominated by sea-ice freshwater flux for the salt budget, and by air-sea flux for the heat budget. Ekman advection, vertical diffusivity and vertical entrainment play only secondary role.Our results suggest that changes in regional sea-ice distribution or sea-ice seasonal cycle duration, as currently observed, would widely affect the buoyancy budget of the underlying mixed-layer, and impacts large-scale water-mass formation and transformation.

  11. Rapid ocean-atmosphere response to Southern Ocean freshening during the last glacial period

    NASA Astrophysics Data System (ADS)

    Turney, Christian; Jones, Richard; Phipps, Steven; Thomas, Zoë; Hogg, Alan; Kershaw, Peter; Fogwill, Christopher; Palmer, Jonathan; Bronk Ramsey, Christopher; Adolphi, Florian; Muscheler, Raimund; Hughen, Konrad; Staff, Richard; Grosvenor, Mark; Golledge, Nicholas; Rasmussen, Sune; Hutchinson, David; Haberle, Simon; Lorrey, Andrew; Boswijk, Gretel

    2017-04-01

    Contrasting Greenland and Antarctic temperature trends during the late last glacial period (60,000 to 11,703 years ago) are thought to be driven by imbalances in the rate of formation of North Atlantic and Antarctic Deep Water (the 'bipolar seesaw'), with cooling in the north leading the onset of warming in the south. Some events, however, appear to have occurred independently of changes in deep water formation but still have a southern expression, implying that an alternative mechanism may have driven some global climatic changes during the glacial. Testing these competing hypotheses is challenging given the relatively large uncertainties associated with correlating terrestrial, marine and ice core records of abrupt change. Here we exploit a bidecadally-resolved 14C calibration dataset obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate datasets spanning 28,400 to 30,400 years ago. We observe no divergence between terrestrial and marine 14C datasets implying limited impact of freshwater hosing on the Atlantic Meridional Overturning Circulation (AMOC). However, an ice-rafted debris event (SA2) in Southern Ocean waters appears to be associated with dramatic synchronous warming over the North Atlantic and contrasting precipitation patterns across the low latitudes. Using a fully coupled climate system model we undertook an ensemble of transient meltwater simulations and find that a southern salinity anomaly can trigger low-latitude temperature changes through barotropic and baroclinic oceanic waves that are atmospherically propagated globally via a Rossby wave train, consistent with contemporary modelling studies. Our results suggest the Antarctic ice sheets and Southern Ocean dynamics may have contributed to some global climatic changes through rapid ocean-atmospheric teleconnections, with implications for past (and future) change.

  12. Seasonally different carbon flux changes in the Southern Ocean in response to the southern annular mode

    NASA Astrophysics Data System (ADS)

    Hauck, J.; Völker, C.; Wang, T.; Hoppema, M.; Losch, M.; Wolf-Gladrow, D. A.

    2013-12-01

    Stratospheric ozone depletion and emission of greenhouse gases lead to a trend of the southern annular mode (SAM) toward its high-index polarity. The positive phase of the SAM is characterized by stronger than usual westerly winds that induce changes in the physical carbon transport. Changes in the natural carbon budget of the upper 100 m of the Southern Ocean in response to a positive SAM phase are explored with a coupled ecosystem-general circulation model and regression analysis. Previously overlooked processes that are important for the upper ocean carbon budget during a positive SAM period are identified, namely, export production and downward transport of carbon north of the polar front (PF) as large as the upwelling in the south. The limiting micronutrient iron is brought into the surface layer by upwelling and stimulates phytoplankton growth and export production but only in summer. This leads to a drawdown of carbon and less summertime outgassing (or more uptake) of natural CO2. In winter, biological mechanisms are inactive, and the surface ocean equilibrates with the atmosphere by releasing CO2. In the annual mean, the upper ocean region south of the PF loses more carbon by additional export production than by the release of CO2 into the atmosphere, highlighting the role of the biological carbon pump in response to a positive SAM event.

  13. The Southern Ocean's Grip on the Northward Meridional Flow

    NASA Astrophysics Data System (ADS)

    Nof, D.

    2002-12-01

    Recently, a "quasi-island" approach for examining the meridional flux of warm and intermediate water from the Southern Ocean into the South Atlantic, the South Pacific and the Indian Ocean was proposed. The method considers the continents to be "pseudo islands" in the sense that they are entirely surrounded by water but have no circulation around them. The method employs an integration of the linearized momentum equations along a closed contour containing the continents. This allows one to compute the meridional transport into these oceans without finding the detailed solution to the complete wind-thermohaline problem. The solution gives one expected and one unexpected result. It shows that, as expected, about 9 ñ 5 Sv of upper and intermediate water enter the South Atlantic from the Southern Ocean. It also shows, however, the unexpected result that the Pacific-Indian Ocean system should contain a "shallow" meridional overturning cell carrying 18 ñ 5 Sv. By "shallow" it is meant here that the cell does not extend all the way to the bottom (as it does in the Atlantic) but is terminated at mid-depth. (This reflects the fact that there is no bottom water formation in the Pacific.) Both of these calculations rely on the observation that there is almost no flow through the Bering Strait and on the assumption that there is a negligible pressure torque on the Bering Strait's sill. Here, we present a new and different approach which does not rely on the above two conditions regarding the Bering Strait and yet gives essentially the same result. The approach does not involve any quasi-island calculation but rather employs an integration of the linearized zonal momentum equation along a closed open-water latitudinal belt connecting the tips of South Africa and South America. The integration relies on the existence of a belt (corridor) where the linearized general circulation equations are valid. It allows for a net northward mass flux through either the Sverdrup interior or

  14. Development of a southern oceanic air standard reference material.

    PubMed

    Rhoderick, George C; Kelley, Michael E; Miller, Walter R; Brailsford, Gordon; Possolo, Antonio

    2016-02-01

    In 2009, the United States Congress charged the National Institute of Standards and Technology (NIST) with supporting climate change research. As part of this effort, the Gas Sensing Metrology Group at NIST began developing new gas standard mixtures for greenhouse gas mixtures relevant to atmospheric measurements. Suites of gravimetrically prepared primary standard mixtures (PSMs) were prepared at ambient concentration levels for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) in a dry-air balance. In parallel, 30 gas cylinders were filled, by the National Institute of Water and Atmospheric Research (NIWA) in Wellington, New Zealand, to high pressure from pristine southern oceanic air at Baring Head, New Zealand, and shipped to NIST. Using spectroscopic instrumentation, NIST analyzed the 30 cylinder samples for mole fractions of CO2, CH4, and N2O. Certified values were assigned to these mixtures by calibrating the instrumentation with the PSM suites that were recently developed at NIST. These mixtures became NIST Standard Reference Material (SRM) 1721 Southern Oceanic Air and are certified for ambient mole fraction, the first of their kind for NIST. The relative expanded uncertainties corresponding to coverage intervals with 95% probability are no larger than 0.06% of the certified values, representing the smallest uncertainties to date ever assigned to an NIST gas SRM.

  15. Characteristics of regional aerosols: Southern Arizona and eastern Pacific Ocean

    NASA Astrophysics Data System (ADS)

    Prabhakar, Gouri

    Atmospheric aerosols impact the quality of our life in many direct and indirect ways. Inhalation of aerosols can have harmful effects on human health. Aerosols also have climatic impacts by absorbing or scattering solar radiation, or more indirectly through their interactions with clouds. Despite a better understanding of several relevant aerosol properties and processes in the past years, they remain the largest uncertainty in the estimate of global radiative forcing. The uncertainties arise because although aerosols are ubiquitous in the Earth's atmosphere they are highly variable in space, time and their physicochemical properties. This makes in-situ measurements of aerosols vital in our effort towards reducing uncertainties in the estimate of global radiative forcing due to aerosols. This study is an effort to characterize atmospheric aerosols at a regional scale, in southern Arizona and eastern Pacific Ocean, based on ground and airborne observations of aerosols. Metals and metalloids in particles with aerodynamic diameter (Dp) smaller than 2.5 μm are found to be ubiquitous in southern Arizona. The major sources of the elements considered in the study are identified to be crustal dust, smelting/mining activities and fuel combustion. The spatial and temporal variability in the mass concentrations of these elements depend both on the source strength and meteorological conditions. Aircraft measurements of aerosol and cloud properties collected during various field campaigns over the eastern Pacific Ocean are used to study the sources of nitrate in stratocumulus cloud water and the relevant processes. The major sources of nitrate in cloud water in the region are emissions from ships and wildfires. Different pathways for nitrate to enter cloud water and the role of meteorology in these processes are examined. Observations of microphysical properties of ambient aerosols in ship plumes are examined. The study shows that there is an enhancement in the number

  16. 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.

  17. 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

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

    PubMed

    Burke, Andrea; Robinson, Laura F

    2012-02-03

    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.

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

    DOE PAGES

    Kessler, A.; Tjiputra, J.

    2016-04-07

    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. Here, we show, by analyzing a suite of fully interactive ESMs simulations from the Coupled Model Intercomparison Project phasemore » 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. None the less, 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. Furthermore, we show that these biases are persistent throughout the 21st

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

    SciTech Connect

    Kessler, A.; Tjiputra, J.

    2016-04-07

    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. Here, 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. None the less, 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

  1. 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

  2. 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

  3. 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

  4. Persistent organic pollutants in the Atlantic and southern oceans and oceanic atmosphere.

    PubMed

    Luek, Jenna L; Dickhut, Rebecca M; Cochran, Michele A; Falconer, Renee L; Kylin, Henrik

    2017-04-01

    Persistent organic pollutants (POPs) continue to cycle through the atmosphere and hydrosphere despite banned or severely restricted usages. Global scale analyses of POPs are challenging, but knowledge of the current distribution of these compounds is needed to understand the movement and long-term consequences of their global use. In the current study, air and seawater samples were collected Oct. 2007-Jan. 2008 aboard the Icebreaker Oden en route from Göteborg, Sweden to McMurdo Station, Antarctica. Both air and surface seawater samples consistently contained α-hexachlorocyclohexane (α-HCH), γ-HCH, hexachlorobenzene (HCB), α-Endosulfan, and polychlorinated biphenyls (PCBs). Sample concentrations for most POPs in air were higher in the northern hemisphere with the exception of HCB, which had high gas phase concentrations in the northern and southern latitudes and low concentrations near the equator. South Atlantic and Southern Ocean seawater had a high ratio of α-HCH to γ-HCH, indicating persisting levels from technical grade sources. The Atlantic and Southern Ocean continue to be net sinks for atmospheric α-, γ-HCH, and Endosulfan despite declining usage. Copyright © 2017 Elsevier B.V. All rights reserved.

  5. Paleoceanography and Paleoclimatology of the Southern Ocean: A Synthesis of Three Decades of Scientific Ocean Drilling

    NASA Astrophysics Data System (ADS)

    Warnke, D. A.; Filippelli, G.; Flores, J.; Marchitto, T. M.

    2004-12-01

    A Workshop on " Paleoceanography and Paleoclimatology of the Southern Ocean: A Synthesis of Three Decades of Scientific Ocean Drilling" Jan. 21-23, 2005 Boulder, CO Co-Convenors: D. Warnke, G. Filippelli, J.-A. Flores, T. Marchitto One of the greatest successes of the Ocean Drilling Program has been the concerted drilling efforts and exciting results recovered from the Southern Ocean (SO), which has been the focus of ten DSDP/ODP drilling legs. The SO is a critical component in the development and persistence of Antarctic glaciation, is a sensitive mixing pool of global water masses, a locus of high biological sedimentation, and contains high resolution records of climate forcing and response. As such, it is one of the most important oceanographic regions in the world. It is now an important time to mine the rich results from scientific ocean drilling over the past several decades and develop a scientific framework for future ocean drilling in this region. The focus of this Synthesis Workshop will be on the biogeochemical history of the SO, including: · Productivity proxies, rates, records, variations, and role of climate · Sedimentary records of organic carbon, calcium, silica, nutrients, and biogenic proxies: The role of the SO as a biogeochemical sink · Development and dynamics of the APFZ · Thermal structure and evolution of the SO · The role of limiting nutrients The overall goal to integrate the various proxies into a coherent paleoceanographic picture. Such a goal will help to synthesize several decades of scientific ocean drilling in the SO, and will likely bring to the forefront the as-yet-unanswered questions about the biogeochemical history of this important oceanic system. With this goal in mind, workshop participants will submit of a short (~250 word) abstract as the Workshop application, commit to presenting a poster at the workshop based on this abstract, and contribute to one or more manuscripts that will be published after the workshop, likely

  6. 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

  7. Sea ice and climate feedbacks in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Frew, Rebecca; Feltham, Daniel; Holland, Paul

    2017-04-01

    Arctic sea ice is melting rapidly under the effects of climate change, but at the same time Antarctic sea ice is actually expanding overall. Understanding the reasons for this difference could provide significant insight into the workings of polar climate change. The behaviour of sea ice is not simple to understand because it is an integral part of the wider climate system, with many feedbacks affecting its evolution. For example, snow-covered sea ice is much more reflective than seawater, so if some ice is lost, the ice-ocean system will absorb more heat in summer, leading to further ice loss. There are several other important feedbacks, including examples associated with the insulating properties of sea ice, and the mixing of ocean heat up towards the surface as the ice forms. For example, during sea ice growth, the thickness of ice controls the growth rate, with the rate of growth decreasing as the ice thickens due to poorer heat conduction through the thick ice. On the other hand, increased melting of sea ice decreases the salinity of the mixed layer, therefore raising the freezing temperature of the seawater, making it easier to grow more sea ice. It is important to understand these feedbacks in the Southern Ocean surrounding Antarctica for many reasons. The changes in Antarctic sea ice over the last thirty years have a strong seasonal dependence, and the way that these changes grow in spring and decay in autumn suggests that feedbacks are strongly involved. The changes might ultimately be caused by winds, atmospheric warming, snowfall changes, etc., but we cannot understand these forcings without first untangling the feedbacks. A highly simplified coupled sea ice-mixed layer model has been developed to investigate the impact of feedbacks on the behaviour of sea ice in the Southern Ocean. The latest generation of climate models are very poor at modelling Antarctic sea ice. Solving this problem is of crucial importance to predicting the response of Antarctic

  8. 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.

  9. 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.

  10. Extraordinarily high biomass benthic community on Southern Ocean seamounts

    PubMed Central

    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

  11. Distributions of phytoplankton blooms in the southern ocean

    SciTech Connect

    Sullivan, C.W. ); Arrigo, K.R.; McClain, C.R.; Comiso, J.C. ); Firestone, J. )

    1993-12-17

    A regional pigment retrieval algorithm for the Nimbus-7 Coastal Zone Color Scanner (CZCS) has been tested for the Southern Ocean. The pigment concentrations estimated with this algorithm agree to within 5 percent with in situ values and are more than twice as high as those previously reported. The CZCS data also revealed an asymmetric distribution of enhanced pigments in the waters surrounding Antarctica; in contrast, most surface geophysical properties are symmetrically distributed. The asymmetry is coherent with circumpolar current patterns and the availability of silicic acid in surface waters. Intense blooms (>1 milligram of pigment per cubic meter) that occur downcurrent from continental masses results from dissolved trace elements such as iron derived from shelf sediments and glacial melt.

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

    PubMed

    Chavtur, Vladimir G; Keyser, Dietmar

    2016-07-25

    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.

  13. 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

  14. 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.

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

    PubMed Central

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

    2010-01-01

    The iron-limited Southern Ocean plays an important role in regulating atmospheric CO2 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 Cexport ∶Feadded 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 × 105 tonnes of carbon per year to the deep ocean and respire only 2 × 105 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 × 105 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. PMID:20554546

  16. Tropical teleconnections via the ocean and atmosphere induced by Southern Ocean deep convective events

    NASA Astrophysics Data System (ADS)

    Marinov, I.; Cabre, A.; Gunn, A.; Gnanadesikan, A.

    2016-12-01

    The current generation (CMIP5) of Earth System Models (ESMs) shows a huge variability in their ability to represent Southern Ocean (SO) deep-ocean convection and Antarctic Bottom Water, with a preference for open-sea convection in the Weddell and Ross gyres. A long control simulation in a coarse 3o resolution ESM (the GFDL CM2Mc model) shows a highly regular multi-decadal oscillation between periods of SO open sea convection and non-convective periods. This process also happens naturally, with different frequencies and durations of convection across most CMIP5 models under preindustrial forcing (deLavergne et al, 2014). Here we assess the impact of SO deep convection and resulting sea surface temperature (SST) anomalies on the tropical atmosphere and ocean via teleconnections, with a focus on interannual to multi-decadal timescales. We combine analysis of our low-resolution coupled model with inter-model analysis across historical CMIP5 simulations. SST cooling south of 60S during non-convective decades triggers a stronger, northward shifted SH Hadley cell, which results in intensified northward cross-equatorial moist heat transport and a poleward shift in the ITCZ. Resulting correlations between the cross-equatorial atmospheric heat transport and ITCZ location are in good agreement with recent theories (e.g. Frierson et al. 2013; Donohoe et al. 2014). Lagged correlations between a SO convective index and cross-equatorial heat transports (in the atmosphere and ocean), as well as various tropical (and ENSO) climate indices are analyzed. In the ocean realm, we find that non-convective decades result in weaker AABW formation and weaker ACC but stronger Antarctic Intermediate Water (AAIW) formation, likely as a result of stronger SO westerlies (more positive SAM). The signals of AABW and AAIW are seen in the tropics on short timescales of years to decades in the temperature, heat storage and heat transport anomalies and also in deep and intermediate ocean oxygen. Most

  17. 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.

  18. SKS Splitting from Ocean Bottom Seismometer Data Offshore Southern California

    NASA Astrophysics Data System (ADS)

    Ramsay, J.; Kohler, M. D.; Davis, P. M.; Weeraratne, D. S.

    2014-12-01

    SKS arrivals from ocean bottom seismometer (OBS) data of the ALBACOREexperiment offshore Southern California are analyzed for shear wave splitting. The ALBACORE (Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment) project involved deployment of 34 OBSs for 12 months in a region extending up to 500 kilometers west onto the oceanic Pacific plate. Splitting fast directions are similar to on-land directions, WSW-ENE, and exhibit similar delays, 1.1-1.4 seconds. A numerical method to remove S-wave interference with SKKS arrivals by f-k velocity filtering is tested with synthetic and the observed OBS data. The fast directions are at 45 degrees to the direction of absolute plate motion (APM) of the Pacific plate suggesting that either frozen-in anisotropy from paleo-spreading dominates over APM effects in the asthenosphere or that deeper mantle shearing has occurred unrelated to APM. A toroidal flow around slab rollback would be consistent with the splitting results if the slab rollback resulted in large-scale secondary flow well into Pacific plate, or if the source of the splitting extended much deeper than 200 km.

  19. Saccharides enhance iron bioavailability to Southern Ocean phytoplankton

    PubMed Central

    Hassler, Christel S.; Nichols, Carol Mancuso; Butler, Edward C. V.; Boyd, Philip W.

    2011-01-01

    Iron limits primary productivity in vast regions of the ocean. Given that marine phytoplankton contribute up to 40% of global biological carbon fixation, it is important to understand what parameters control the availability of iron (iron bioavailability) to these organisms. Most studies on iron bioavailability have focused on the role of siderophores; however, eukaryotic phytoplankton do not produce or release siderophores. Here, we report on the pivotal role of saccharides—which may act like an organic ligand—in enhancing iron bioavailability to a Southern Ocean cultured diatom, a prymnesiophyte, as well as to natural populations of eukaryotic phytoplankton. Addition of a monosaccharide (>2 nM of glucuronic acid, GLU) to natural planktonic assemblages from both the polar front and subantarctic zones resulted in an increase in iron bioavailability for eukaryotic phytoplankton, relative to bacterioplankton. The enhanced iron bioavailability observed for several groups of eukaryotic phytoplankton (i.e., cultured and natural populations) using three saccharides, suggests it is a common phenomenon. Increased iron bioavailability resulted from the combination of saccharides forming highly bioavailable organic associations with iron and increasing iron solubility, mainly as colloidal iron. As saccharides are ubiquitous, present at nanomolar to micromolar concentrations, and produced by biota in surface waters, they also satisfy the prerequisites to be important constituents of the poorly defined “ligand soup,” known to weakly bind iron. Our findings point to an additional type of organic ligand, controlling iron bioavailability to eukaryotic phytoplankton—a key unknown in iron biogeochemistry. PMID:21169217

  20. 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.

  1. The 2010 Southern California Ocean Bottom Seismometer Deployment

    NASA Astrophysics Data System (ADS)

    Booth, C. M.; Kohler, M. D.; Weeraratne, D. S.

    2010-12-01

    Subduction, mid-ocean ridge spreading, and transpressional deformation are all processes that played important roles in the evolution of the diffuse Pacific-North America plate boundary offshore Southern California. Existing seismic data for the boundary typically end at the coastline due to the fact that onshore data collection is easier and more feasible. As a result, current models for plate boundary deformation and mantle flow lack data from nearly half the plate boundary offshore. In August 2010, twenty-four broadband and ten short period ocean bottom seismometers (OBS) were deployed on a research cruise as part of a year-long passive OBS experiment off the coast of Southern California. The Asthenospheric and Lithospheric Broadband Architecture from the California Offshore Region Experiment (ALBACORE) will study local seismicity, and crustal and upper mantle seismic structure. Studies using onshore data have shown a high velocity anomaly that exists in the region of convergence under the Transverse Ranges. The Transverse Ranges belong to a large crustal block that experienced clockwise rotation of at least ninety degrees. Geologic studies indicate that the entire Channel Islands on the western end belongs to the region of convergence and have been a part of this rotation. In anticipation of OBS data analysis, a hypothetical velocity model is being developed for the crust and uppermost mantle for the region under the Channel Islands. P-wave arrival times are predicted by propagating teleseismic waves through the model. Different possible P-wave arrival patterns are explored by varying the lithospheric thickness. The long-term goal for developing this model will be to compare it with the actual OBS travel-time residual data to assess the best-fitting model. In preparation for the ALBACORE cruise, existing gravity data near the Channel Island region were examined for correlations with geologic features. Gravity data collected during the ALBACORE cruise will help

  2. Simulated response of the Southern Ocean to wind changes: towards the role of mesoscale eddies

    NASA Astrophysics Data System (ADS)

    Patara, Lavinia; Böning, Claus; Biastoch, Arne

    2013-04-01

    The role of ocean mesoscale eddies in the Southern Ocean response to recent wind changes is explored with a suite of realistic global ocean simulations at increasing horizontal resolution. Southern Ocean mesoscale eddies are known to be critical in the meridional redistribution of tracers, and are suggested to affect how the Southern Ocean responds to wind changes, takes up heat, and exchanges CO2 with the atmosphere. By employing the ocean general circulation model NEMO-LIM, ocean simulations with horizontal resolutions of 1/2°, 1/4°, and 1/12°, i.e. ranging from non-eddying to eddy-resolving, are performed and compared. In particular, a "two-way" nesting technique is used to refine the ocean grid up to 1/12° in the Southern Ocean. The ocean models are forced with the CORE v.2 atmospheric reanalysis during the period 1948-2007, and companion experiments under a repeated-annual-cycle forcing are used to detect model spurious drifts. First, we assess the effect of explicitly simulated eddies on ocean mean properties. Mesoscale eddies are shown to modify the mixed layer depth and the upper-ocean density, with potential effects on the formation properties of Subantarctic Mode Waters. Second, we explore the role of mesoscale eddies in affecting the ocean circulation sensitivity to the sustained increase of Southern Hemisphere winds during the past decades. Whereas the non-eddying simulations exhibit large increases of the Antarctic Circumpolar Current transport, the 1/4° and 1/12° models are less sensitive to the wind increase, in better agreement with available observations. These results show a clear effect of model resolution on the Southern Ocean response to climate variability and change.

  3. Late Holocene diatom-based sea-surface temperature reconstruction from the Conrad Rise, Southern Ocean

    NASA Astrophysics Data System (ADS)

    Orme, Lisa; Mietinnen, Arto; Crosta, Xavier; Mohan, Rahul

    2017-04-01

    The Southern Ocean plays an important role in the global climate system. The temperature and sea ice extent alter the latitudinal temperature gradient of the Southern Ocean, which can be transferred to the atmosphere resulting in changes in the southern westerly winds. The temperature, sea ice and wind variations are also factors influencing Antarctic Bottom Water formation, which is a control on the strength of the Atlantic Meridional Overturning Circulation. Therefore conditions in the Southern Ocean may influence the climate in the northern and southern hemispheres. The Southern Ocean and North Atlantic were connected during the Last Glacial during Dansgaard-Oeschger events, when variations in ocean circulation caused a bipolar seesaw of temperatures. For the Holocene there is less evidence for a bipolar seesaw, although recent research shows concurrent, opposite trends in ocean circulation in the North Atlantic and in the Southern Ocean. Further reconstructions are required from the Southern Ocean in particular to enable greater understanding of how the temperature and sea ice varied during the Holocene. The OCTEL project (Ocean-sea-ice-atmosphere teleconnections between the Southern Ocean and North Atlantic during the Holocene) aims to investigate the ocean, atmosphere and sea-ice teleconnections for the Holocene using new, high resolution records from both the Southern Ocean and North Atlantic. We here present initial results from diatom analysis conducted on a sediment core from the Southern Ocean, sampled from the Conrad Rise (54˚ 16.04'S, 39˚ 45.98'W). The preliminary results highlight a dominance of diatom species Fragilariopsis kerguelensis and Thalassiosira lentiginosa, with lower abundances of Thalassiothrix antarctica and Thalassiosira gracilis among others, which suggests an open ocean setting close to the polar front. The diatom data will be converted to quantitative reconstructions of summer sea surface temperature and sea ice presence using the

  4. Rapid global ocean-atmosphere response to Southern Ocean freshening during the last glacial.

    PubMed

    Turney, Chris S M; Jones, Richard T; Phipps, Steven J; Thomas, Zoë; Hogg, Alan; Kershaw, A Peter; Fogwill, Christopher J; Palmer, Jonathan; Bronk Ramsey, Christopher; Adolphi, Florian; Muscheler, Raimund; Hughen, Konrad A; Staff, Richard A; Grosvenor, Mark; Golledge, Nicholas R; Rasmussen, Sune Olander; Hutchinson, David K; Haberle, Simon; Lorrey, Andrew; Boswijk, Gretel; Cooper, Alan

    2017-09-12

    Contrasting Greenland and Antarctic temperatures during the last glacial period (115,000 to 11,650 years ago) are thought to have been driven by imbalances in the rates of formation of North Atlantic and Antarctic Deep Water (the 'bipolar seesaw'). Here we exploit a bidecadally resolved (14)C data set obtained from New Zealand kauri (Agathis australis) to undertake high-precision alignment of key climate data sets spanning iceberg-rafted debris event Heinrich 3 and Greenland Interstadial (GI) 5.1 in the North Atlantic (~30,400 to 28,400 years ago). We observe no divergence between the kauri and Atlantic marine sediment (14)C data sets, implying limited changes in deep water formation. However, a Southern Ocean (Atlantic-sector) iceberg rafted debris event appears to have occurred synchronously with GI-5.1 warming and decreased precipitation over the western equatorial Pacific and Atlantic. An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can generate climate changes that are propagated globally via an atmospheric Rossby wave train.A challenge for testing mechanisms of past climate change is the precise correlation of palaeoclimate records. Here, through climate modelling and the alignment of terrestrial, ice and marine (14)C and (10)Be records, the authors show that Southern Ocean freshwater hosing can trigger global change.

  5. 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

  6. 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.

  7. Regional Variations in Low Frequency Transport Variability of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Makowski, Jessica; Chambers, Don

    2016-04-01

    Using ocean bottom pressure data from the Gravity Recovery and Climate Experiment (GRACE) and the ECCO2 state estimate, we estimate the variability of the low frequency zonal transport in the Southern Ocean. The interannual variations and trend estimates from calculated transport variability differ as the east-west averaging area and north-south boundaries change. We look at various study areas throughout the Southern Ocean, including west of the Drake Passage, in order to determine the regional variability and coherency within the Southern Ocean. We have observed a high coherency between the Southern Annular Mode (SAM) and interannual variability in the transport south of Australia, and further investigate how other regions respond to the SAM and zonally averaged Southern Hemisphere winds.

  8. Empirical ocean color algorithms for estimating particulate organic carbon in the Southern Ocean

    NASA Astrophysics Data System (ADS)

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

    2010-10-01

    We have examined empirical algorithms for estimating surface concentration of particulate organic carbon (POC) from remotely sensed ocean color in the Southern Ocean using field data of POC, spectral remote-sensing reflectance, Rrs(λ), and the inherent optical properties (IOPs) of seawater collected during a number of cruises. Several algorithm formulations have been considered, including direct relationships between POC and the blue-to-green band ratios of reflectance and a single-wavelength two-step algorithm that consists of relationships linking reflectance to the backscattering coefficient and POC to the particulate backscattering coefficient at 555 nm. The best error statistics among the algorithms tested were obtained for the power function fit POC (in mg m-3) = 189.29 [Rrs(443)/Rrs(555)]-0.87. This band ratio algorithm is based on 85 pairs of field data and shows a small mean bias of about 3%, the normalized root mean square error of 27%, and the determination coefficient of 0.93. These error statistics as well as the analysis of matchup comparisons of satellite-derived POC and in situ POC determinations support the prospect for reasonably good performance of this algorithm in the Southern Ocean. The two-step empirical algorithm operating at 555 nm shows inferior error statistics of the regression fits and matchup comparisons compared with the band ratio algorithm. The analysis of our data set also indicates that a general trend of variation in the blue-to-green reflectance band ratio over the examined range of POC values is driven primarily by the green-to-blue ratio of particulate absorption coefficient.

  9. The Southern Ocean FINEstructure project: Turbulent dissipation and mixing rates and mechanisms in a Southern Ocean mixing hotspot.

    NASA Astrophysics Data System (ADS)

    Waterman, S.; Naveira Garabato, A. C.; Polzin, K. L.

    2012-04-01

    The Southern Ocean FINE structure project is an observational field study designed to investigate various mechanisms of ocean mixing and the roles that they play in the larger-scale circulation in a standing meander of the Antarctic Circumpolar Current (ACC) north of the Kerguelen Plateau. The region is potentially of special significance to closing both the Southern Ocean overturning circulation and the momentum budget of ACC. By presenting both a large-scale topographic obstacle and small-scale topographic roughness in the path of multiple ACC jets, it is a likely site for both enhanced adiabatic and diabatic mixing processes. We present the first results of the project which relate to the rates and mechanisms of turbulent energy dissipation and turbulent mixing in the region. From the first-ever full-depth microstructure measurements in the Southern Ocean, we map the observed turbulent kinetic energy dissipation and diapycnal mixing rates in this mixing hotspot. We next explore some of the physical mechanisms that observations and theory suggest may underpin the observed distributions. This exploration leads us to a characterization of the internal wave field in the region, and a study of some of the processes related to its generation, evolution and eventual dissipation. Results show that the observed turbulent energy dissipation and mixing rates are highly spatially variable. Systematic structure with depth and proximity to rough topography suggest a link with the local internal wave field, which can be characterized as consisting of near-inertial waves propagating from the surface downwards and higher frequency internal waves potentially sourced at the bottom propagating upwards, both being modified by a background shear as they propagate. Turbulent dissipation is high in regions where internal wave energy is high, however, the rates of turbulent dissipation and mixing are, in key places, generally lower than anticipated from the observed internal wave energy

  10. High biomass, low export regimes in the Southern Ocean

    NASA Astrophysics Data System (ADS)

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

    2007-03-01

    This paper investigates ballasting and remineralization controls of carbon sedimentation in the Twilight Zone (100-1000 m) of the Southern Ocean. Size-fractionated (<1 μm, 1-51 μm, >51 μm) 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, CaCO 3), 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-μm POC was significantly shorter in the upper Twilight Zone at 66°S ( δe=26 m) compared to 55°S ( δe=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 (˜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 grazing diatoms in the

  11. 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

  12. Rationale for future Antarctic and Southern Ocean drilling

    NASA Astrophysics Data System (ADS)

    De Santis, Laura; Gohl, Karsten; Larter, Rob; Escutia, Carlota; Ikehara, Minoru; Hong, JongKuk; Naish, Tim; Barrett, Peter; Rack, Frank; Wellner, Julia

    2013-04-01

    .g. latitudinal and/or depth transects involving a combination of land/ice shelf, seabed, riser, and riserless drilling platforms) will likely make the most significant scientific advances. Fundamental hypothesis can be tested and accomplished by drilling depth transects from ice-proximal to ice-distal locations, that will enable researchers to link past perturbations in the ice sheet with Southern Ocean and global climate dynamics. The variable response of the ice sheet to ongoing climatic change mandates broad geographic drilling coverage, particularly in climatically sensitive regions, like those with large upstream drainage basins, whose marine terminus is presently melting, due to ocean, warming water impinging the continental shelf. Key transects were identified at community workshops (http://www.scar-ace.org) in the frame of the SCAR/ACE (Antarctic Climate Evolution) and PAIS (Past Antarctic Ice Sheet dynamics) programs. New proposals, also for MSP expeditions were then submitted to IODP, in addition to the existing ones, in the frame of a scientific concerted strategy and with a significant European participation. Main questions underpinning future scientific drilling tied IODP Science themes: 1) How did and will the Antarctic Ice Sheets respond to elevated temperatures and atmospheric pCO2? What is the contribution of Antarctic ice to past and future sea level changes? 2) What was the timing of rifting and subsidence controlling the opening of ocean gateways and the initiation of the circumpolar current system and the onset of glaciations?

  13. The biodiversity of the deep Southern Ocean benthos.

    PubMed

    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

    2007-01-29

    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.

  14. 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

  15. 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.

  16. Biogeographic partitioning of Southern Ocean microorganisms revealed by metagenomics.

    PubMed

    Wilkins, David; Lauro, Federico M; Williams, Timothy J; Demaere, Matthew Z; Brown, Mark V; Hoffman, Jeffrey M; Andrews-Pfannkoch, Cynthia; McQuaid, Jeffrey B; Riddle, Martin J; Rintoul, Stephen R; Cavicchioli, Ricardo

    2013-05-01

    We performed a metagenomic survey (6.6 Gbp of 454 sequence data) of Southern Ocean (SO) microorganisms during the austral summer of 2007-2008, examining the genomic signatures of communities across a latitudinal transect from Hobart (44°S) to the Mertz Glacier, Antarctica (67°S). Operational taxonomic units (OTUs) of the SAR11 and SAR116 clades and the cyanobacterial genera Prochlorococcus and Synechococcus were strongly overrepresented north of the Polar Front (PF). Conversely, OTUs of the Gammaproteobacterial Sulfur Oxidizer-EOSA-1 (GSO-EOSA-1) complex, the phyla Bacteroidetes and Verrucomicrobia and order Rhodobacterales were characteristic of waters south of the PF. Functions enriched south of the PF included a range of transporters, sulfur reduction and histidine degradation to glutamate, while branched-chain amino acid transport, nucleic acid biosynthesis and methionine salvage were overrepresented north of the PF. The taxonomic and functional characteristics suggested a shift of primary production from cyanobacteria in the north to eukaryotic phytoplankton in the south, and reflected the different trophic statuses of the two regions. The study provides a new level of understanding about SO microbial communities, describing the contrasting taxonomic and functional characteristics of microbial assemblages either side of the PF. © 2012 Society for Applied Microbiology and Blackwell Publishing Ltd.

  17. Uncertainty in projections of Southern Ocean carbon uptake and acidification

    NASA Astrophysics Data System (ADS)

    Lovenduski, Nicole; Hauri, Claudine

    2017-04-01

    We investigate projections of carbon uptake and the associated acidification of the Southern Ocean over 2006-2080 using output from two ensembles of the Community Earth System Model run under business as usual (RCP8.5) and mitigation (RCP4.5) emission scenarios. On basin-wide and regional scales we observe a rapid onset of aragonite undersaturation in surface waters by mid-century that may be detrimental to calcareous organisms. An analysis of variance reveals that the speed of transition from supersaturation to undersaturation is driven almost entirely by emission scenario, as internal variability in saturation depth across ensemble members is small. Regional differences are observed in the timing and magnitude of aragonite saturation state changes. In the Patagonian Shelf region, undersaturation of the top 200m of the water column is observed by 2080 regardless of emission scenario. Whereas, in the Weddell Sea, saturation state is significantly different between the two emission scenarios by 2080, and undersaturation of the surface waters is "avoidable" if we follow RCP4.5, rather than RCP8.5.

  18. The ocean tide in the southern Ross Sea

    NASA Astrophysics Data System (ADS)

    Williams, Richard T.; Robinson, Edwin S.

    1980-11-01

    A survey of the ocean tide in the southern Ross Sea was done by measuring tidal variations of gravity at nine locations on the floating Ross Ice Shelf. Tidal water level fluctuations were calculated from recordings between 29 days and 58 days long of the periodic variation in gravity on the ice shelf surface that is caused by tidal changes in elevation and water mass. Conventional tide gauge measurements from McMurdo Sound were included in the survey. The data indicate that the Ross Sea tide is principally diurnal. Along the northern margin of the Ross Ice Shelf the tropic (diurnal spring) tidal range is between 1 m and ?; m. The range increases to more than 2 m in the southernmost part of the Ross Sea. It is more than 3 times larger than the equatorial (diurnal neap) tidal range. Amplitudes of the principal diurnal constituents K1 P1 and O1 are apparently magnified by a condition of diurnal resonance in the Ross Sea. This would be expected because wavelengths of the diurnal harmonic constituents are approximately 4 times the length of the Ross Sea in the direction of propagation. The diurnal constituent amplitudes also appear to vary proportionally with the fourth root of the water depth as predicted from the theory of long wave propagation in a canal. Semidiurnal constituents M2, S2, and N2 have small amplitudes and appear to progress clockwise around amphidromes located beneath the northwestern part of the Ross Ice Shelf.

  19. Ocean color variability in the southern Atlantic and southeastern Pacific

    NASA Astrophysics Data System (ADS)

    Rudorff, Natalia M.; Frouin, Robert J.; Kampel, Milton

    2012-10-01

    The chlorophyll-a concentration (Chla) of surface waters is commonly retrieved from space using an empirical polynomial function of the maximum band ratio (MBR), i.e., the maximum ratio of remote sensing reflectance in selected spectral bands in the visible. Recent studies have revealed significant deviations in the relation between MBR and Chla across the oceans. The present work aims at accessing the main sources of MBR variability across the Southern Atlantic and South-east Pacific, using in situ data. The data was collected at 19 bio-optical CTD stations and 40 flowthrough stations during a cruise onboard the R/V Melville, from South Africa to Chile (February-March, 2011). The MBR was derived from modeled remote sensing reflectance using absorption and backscattering measurements. The second order MBR variations (MBR*) were obtained after subtraction of a global polynomial fit for CChla and Chla biases. Multivariate analyses were used to explain the variations with bio-optical properties and phytoplankton pigments. Chla overestimations were associated to high specific phytoplankton absorption (0.73), specific particle backscattering coefficient (0.42) and colored dissolved and particle organic matter (CDM) absorption normalized by non-water absorption (0.38), and vice-versa. The overestimations occurred at stations with dominance of small picoplankton, high concentration of bacteria, and high CDM, while underestimations were in microplankton dominated waters and low CDM. The results reveal important relations of the MBR* with the specific coefficient and associated phytoplankton community structure.

  20. Past and future wind changes over the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Chavaillaz, Y.; Codron, F.; Kageyama, M.

    2013-12-01

    Mid-latitude westerlies are a major component of the atmospheric circulation, and their response to climate change will determine changes in precipitation, storms, and ocean circulation and CO2 uptake. In this study, we analyse, mainly in terms of jet stream position, the behaviour of the southern westerlies for a future climate, obtained after stabilisation of the RCP4.5 scenario, as well as for the Last Glacial Maximum (LGM, 21 000 yr ago), which is the last past cold extreme with about opposite global temperature change from the future one. We use the models from the CMIP5-PMIP3 archive. The a priori guess would be that the behaviour of the westerly jet stream would be similar when examining its changes from LGM to pre-industrial (PI) con- ditions and from PI to RCP4.5, i.e. in both cases a poleward shift in response to global warming. While this is true for all models in the future case, the LGM shows instead little or inconsistent jet shifts, because of a strong cooling over Antarctica during the LGM. We show that the behavior of the jets in both cases can be quantitatively reproduced using two indices of temperature changes in the Tropics and the high latitudes.

  1. 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.

  2. Southern Ocean phytoplankton physiology in a changing climate.

    PubMed

    Petrou, Katherina; Kranz, Sven A; Trimborn, Scarlett; Hassler, Christel S; Ameijeiras, Sonia Blanco; Sackett, Olivia; Ralph, Peter J; Davidson, Andrew T

    2016-09-20

    The Southern Ocean (SO) is a major sink for anthropogenic atmospheric carbon dioxide (CO2), potentially harbouring even greater potential for additional sequestration of CO2 through enhanced phytoplankton productivity. In the SO, primary productivity is primarily driven by bottom up processes (physical and chemical conditions) which are spatially and temporally heterogeneous. Due to a paucity of trace metals (such as iron) and high variability in light, much of the SO is characterised by an ecological paradox of high macronutrient concentrations yet uncharacteristically low chlorophyll concentrations. It is expected that with increased anthropogenic CO2 emissions and the coincident warming, the major physical and chemical process that govern the SO will alter, influencing the biological capacity and functioning of the ecosystem. This review focuses on the SO primary producers and the bottom up processes that underpin their health and productivity. It looks at the major physico-chemical drivers of change in the SO, and based on current physiological knowledge, explores how these changes will likely manifest in phytoplankton, specifically, what are the physiological changes and floristic shifts that are likely to ensue and how this may translate into changes in the carbon sink capacity, net primary productivity and functionality of the SO. Copyright © 2016 Elsevier GmbH. All rights reserved.

  3. Carbon isotope records reveal precise timing of enhanced Southern Ocean upwelling during the last deglaciation.

    PubMed

    Siani, Giuseppe; Michel, Elisabeth; De Pol-Holz, Ricardo; Devries, Tim; Lamy, Frank; Carel, Mélanie; Isguder, Gulay; Dewilde, Fabien; Lourantou, Anna

    2013-01-01

    The Southern Ocean plays a prominent role in the Earth's climate and carbon cycle. Changes in the Southern Ocean circulation may have regulated the release of CO₂ to the atmosphere from a deep-ocean reservoir during the last deglaciation. However, the path and exact timing of this deglacial CO₂ release are still under debate. Here we present measurements of deglacial surface reservoir ¹⁴C age changes in the eastern Pacific sector of the Southern Ocean, obtained by ¹⁴C dating of tephra deposited over the marine and terrestrial regions. These results, along with records of foraminifera benthic-planktic ¹⁴C age and δ¹³C difference, provide evidence for three periods of enhanced upwelling in the Southern Ocean during the last deglaciation, supporting the hypothesis that Southern Ocean upwelling contributed to the deglacial rise in atmospheric CO₂. These independently dated marine records suggest synchronous changes in the Southern Ocean circulation and Antarctic climate during the last deglaciation.

  4. A Stratification Boomerang: Nonlinear Dependence of Deep Southern Ocean Ventilation on PCO2

    NASA Astrophysics Data System (ADS)

    Galbraith, E. D.; Merlis, T. M.

    2014-12-01

    Strong correlations between atmospheric CO2, Antarctic temperatures, and marine proxy records have hinted that ventilation of the deep Southern Ocean may have played a central role in the variations of CO2 over glacial-interglacial cycles. One proposition is that, in general, the Southern Ocean ventilates the deep more strongly under higher CO2, due to a change in winds and/or the dominance of thermal stratification in a warm ocean, which weakens ocean biological carbon storage. Here, we explore this idea with a suite of multi-millennial simulations using the GFDL CM2Mc global coupled model. The results are, indeed, consistent with increasing ventilation of the Southern Ocean as pCO2 increases above modern. However, they reveal a surprising twist under low pCO2: increased salinity of the Southern Ocean, due in part to weakening atmospheric moisture transport, actually increases ventilation rate of the deep ocean under low pCO2 as well. This implies that a nadir of Southern Ocean ventilation occurs at intermediate pCO2, which the model estimates as being close to that of the present-day. This is at odds with the interpretation that weak ventilation of the deep Southern Ocean was the unifying coupled mechanism for the glacial pCO2 cycles. Rather, it suggests that factors other than the ventilation rate of the deep Southern Ocean, such as iron fertilization, ecosystem changes, water mass distributions, and sea ice cover, were key players in the glacial-interglacial CO2 changes.

  5. 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.

  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. Control of ocean carbon storage and atmospheric pCO2 by Southern Ocean sea ice dynamics

    NASA Astrophysics Data System (ADS)

    Zakem, E.; Ferreira, D.; Follows, M. J.

    2012-12-01

    Change in annual sea ice in the Southern ocean has been proposed as a control on atmospheric pCO2 levels since Antarctic glacial inception around 34 Ma. Sea ice coverage slows or prevents the degassing of carbon-rich upwelled water, increasing ocean carbon storage, though the significance of this process has been doubted due to the coincidental decrease of the biological pump with ice cover. Here we explore the mechanism by which southern ocean sea ice coverage and dynamics drive atmospheric pCO2 levels in the Southern Ocean. To this end, we analyze the biogeochemical output of coupled ocean-atmosphere-sea ice GCM models with simplified geometry. Bottom water formation rates are controlled by manipulating ice dynamics. We show that the dominant difference in the ocean carbon content between model states is mainly driven by air-sea disequilibrium, rather than by solubility or biological productivity. As bottom water formation strengthens, the overturning cell underneath the sea ice is enriched in DIC at depth, but ice cover prevents outgassing to the atmosphere upon return to the surface. When bottom water is present, the ocean fills with carbon-rich water, driving down atmospheric pCO2. Our results suggest that it is the processes driving sea ice production on Antarctica continental margins such as atmospheric circulation and ice-shelf interaction that influence ocean carbon storage, rather than solely the existence of sea ice. This suggests the mechanism by which the onset of Antarctic Bottom Water formation after the opening of the Southern ocean gateways may have served as a positive feedback to decreasing pCO2 and a cooling climate.

  8. Pathways of upwelling deep waters to the surface of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Tamsitt, Veronica; Drake, Henri; Morrison, Adele; Talley, Lynne; Dufour, Carolina; Gray, Alison; Griffies, Stephen; Mazloff, Matthew; Sarmiento, Jorge; Wang, Jinbo; Weijer, Wilbert

    2017-04-01

    Upwelling of Atlantic, Indian and Pacific deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of anthropogenic carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. Here we go beyond the two-dimensional view of Southern Ocean upwelling, to show detailed Southern Ocean upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution ocean and climate models. The northern deep waters enter the Antarctic Circumpolar Current (ACC) via narrow southward currents along the boundaries of the three ocean basins, before spiraling southeastward and upward through the ACC. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the southern ACC boundary, with a spatially nonuniform distribution, regionalizing warm water supply to Antarctic ice shelves and the delivery of nutrient and carbon-rich water to the sea surface. The timescale for half of the deep water to upwell from 30°S to the mixed layer is on the order of 60-90 years, which has important implications for the timescale for signals to propagate through the deep ocean. In addition, we quantify the diabatic transformation along particle trajectories, to identify where diabatic processes are important along the upwelling pathways.

  9. 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.

  10. Sustained growth of the Southern Ocean carbon storage in a warming climate

    NASA Astrophysics Data System (ADS)

    Ito, Takamitsu; Bracco, Annalisa; Deutsch, Curtis; Frenzel, Hartmut; Long, Matthew; Takano, Yohei

    2015-06-01

    We investigate the mechanisms controlling the evolution of Southern Ocean carbon storage under a future climate warming scenario. A subset of Coupled Model Intercomparison Project Phase 5 models predicts that the inventory of biologically sequestered carbon south of 40°S increases about 18-34 Pg C by 2100 relative to the preindustrial condition. Sensitivity experiments with an ocean circulation and biogeochemistry model illustrates the impacts of the wind and buoyancy forcings under a warming climate. Intensified and poleward shifted westerly wind strengthens the upper overturning circulation, not only leading to an increased uptake of anthropogenic CO2 but also releasing biologically regenerated carbon to the atmosphere. Freshening of Antarctic Surface Water causes a slowdown of the lower overturning circulation, leading to an increased Southern Ocean biological carbon storage. The rectified effect of these processes operating together is the sustained growth of the carbon storage in the Southern Ocean, even under the warming climate with a weaker global ocean carbon uptake.

  11. Understanding Southern Ocean SST Trends in Historical Simulations and Observations

    NASA Astrophysics Data System (ADS)

    Kostov, Yavor; Ferreira, David; Marshall, John; Armour, Kyle

    2017-04-01

    Historical simulations with CMIP5 global climate models do not reproduce the observed 1979-2014 Southern Ocean (SO) cooling, and most ensemble members predict gradual warming around Antarctica. In order to understand this discrepancy and the mechanisms behind the SO cooling, we analyze output from 19 CMIP5 models. For each ensemble member we estimate the characteristic responses of SO SST to step changes in greenhouse gas (GHG) forcing and in the seasonal indices of the Southern Annular Mode (SAM). Using these step-response functions and linear convolution theory, we reconstruct the original CMIP5 simulations of 1979-2014 SO SST trends. We recover the CMIP5 ensemble mean trend, capture the intermodel spread, and reproduce very well the behavior of individual models. We thus suggest that GHG forcing and the SAM are major drivers of the simulated 1979-2014 SO SST trends. In consistence with the seasonal signature of the Antarctic ozone hole, our results imply that the summer (DJF) and fall (MAM) SAM exert a particularly important effect on the SO SST. In some CMIP5 models the SO SST response to SAM partially counteracts the warming due to GHG forcing, while in other ensemble members the SAM-induced SO SST trends complement the warming effect of GHG forcing. The compensation between GHG and SAM-induced SO SST anomalies is model-dependent and is determined by multiple factors. Firstly, CMIP5 models have different characteristic SST step response functions to SAM. Kostov et al. (2016) relate these differences to biases in the models' climatological SO temperature gradients. Secondly, many CMIP5 historical simulations underestimate the observed positive trends in the DJF and MAM seasonal SAM indices. We show that this affects the models' ability to reproduce the observed SO cooling. Last but not least, CMIP5 models differ in their SO SST step response functions to GHG forcing. Understanding the diverse behavior of CMIP5 models helps shed light on the physical processes

  12. 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

  13. Si Isotopic Signatures of Diatoms in the Spring Southern Ocean

    NASA Astrophysics Data System (ADS)

    Cardinal, D.; Alleman, L. Y.; Savoye, N.; Dehairs, F.; Trull, T. W.; André, L.

    2004-12-01

    Marine Si isotopic signatures have been shown to be of great relevance in quantifying the diatoms nutrient utilization efficiency, a key factor for many studies related to oceanic carbon sequestration (De La Rocha et al., 1998; Brzezinski et al., 2002). In order to better constrain and apply this new tool, spring diatoms and seawater have been sampled at five stations distributed in different biogeochemical provinces of the Southern Ocean's Australian sector: Polar Front Zone (PFZ), Antarctic Zone (AZ), Sea Ice Zone (SIZ). Total (>0.45um), medium-sized (20< <70um), and large diatoms (>70um) have been sampled at 2-4 depths in the upper 150m. Biogenic silica (BSi) was first digested in a hot diluted NaOH solution. After purification, silicon isotopic compositions of diatoms and seawater were then measured by MC-ICP-MS, in dry plasma mode using external Mg doping, with an overall repeatability of 0.08 p.mil (Cardinal et al., 2003). Results are expressed as \\delta29Si relatively to NBS28 standard. The isotopic composition of diatoms is generally homogeneous in the mixed layer and does not seem to exhibit an isotopic fractionation linked to a size effect. Diatoms \\delta29Si are systematically lighter than the ambient seawater signature, reflecting their preferential uptake of light isotopes (De La Rocha et al., 1997). We observe a trend of lighter isotopic signatures southward, both in diatoms and seawater samples, but the BSi isotopic gradient is much steeper with a diatoms \\delta29Si signature as low as -0.26 p.mil in the southernmost SIZ station, which strongly contrasts with the +0.65 p.mil signature measured on PFZ diatoms. Such latitudinal variation of diatom isotopic signature is well in accordance with the one observed in summer by Varela et al. (2004). In contrast, our spring samples display a difference between the ambient seawater and diatom isotopic signatures that strongly increases southward: it goes from 0.45 in the PFZ up to 1.08 p. mil in the SIZ

  14. Iron limitation modulates ocean acidification effects on southern ocean phytoplankton communities.

    PubMed

    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.

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

    NASA Astrophysics Data System (ADS)

    Kwok, R.; Comiso, J. C.

    2002-03-01

    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-yr dataset from 1982 to 1998. The polar climate anomalies are correlated with the Southern Oscillation index (SOI) and the composites of these anomalies are examined under the positive (SOI > 0), neutral (0 > SOI > 1), and negative (SOI < 1) phases of SOI. The climate dataset consists of sea level pressure, wind, surface air temperature, and sea surface temperature fields, while the sea ice dataset 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 with the SOI. The strongest correlation between the SOI and the polar climate anomalies are found in the Bellingshausen, Amundsen, and Ross Seas. 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 oscillations 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 evident. Recent anomalies in the sea ice cover that are clearly associated with the SOI include the following: the record decrease in the sea ice extent in the Bellingshausen Sea from mid-1988 to early 1991; the relationship between Ross Sea SST and the 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 lengthening of the ice season in the western Ross Sea, Bellinghausen Sea, and central Weddell Sea gyre during the period 1988-94. Four ENSO episodes over the

  16. Geographical variation in thermal tolerance within Southern Ocean marine ectotherms.

    PubMed

    Morley, Simon A; Hirse, Timo; Pörtner, Hans-Otto; Peck, Lloyd S

    2009-06-01

    Latitudinal comparisons of the Southern Ocean limpet, Nacella concinna, and clam, Laternula elliptica, acclimated to 0.0 degrees C, were used to assess differences in thermal response to two regimes, 0.0, 5.1 to 10.0 degrees C and 2.5, 7.5 to 12.5 degrees C, raised at 5.0 degrees C per week. At each temperature, tissue energy status was measured through a combination of O(2) consumption, intracellular pH, cCO(2), citrate synthase (CS) activity, organic acids (succinate, acetate, propionate), adenylates (ATP, ADP, AMP, ITP, PLA (phospho-L-arginine)) and heart rate. L. elliptica from Signy (60 degrees S) and Rothera (67 degrees S), which experience a similar thermal regime (-2 to +1 degrees C) had the same lethal (7.5-10.0 degrees C), critical (5.1-7.5 degrees C) and pejus (<5.1 degrees C;=getting worse) limits with only small differences in biochemical response. N. concinna, which experiences a wider thermal regime (-2 to +15.8 degrees C), had higher lethal limits (10.0-12.5 degrees C). However, at their Northern geographic limit N. concinna, which live in a warmer environment (South Georgia, 54 degrees S), had a lower critical limit (5.1-10.0 degrees C; O(2), PLA and organic acids) than Rothera and Signy N. concinna (10.0-12.5 degrees C). This lower limit indicates that South Georgia N. concinna have different biochemical responses to temperatures close to their thermal limit, which may make them more vulnerable to future warming trends.

  17. 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

  18. Understanding the recent changes in the Southern Ocean carbon cycle: A multidisciplinary approach

    NASA Astrophysics Data System (ADS)

    Manizza, M.; Kahru, M.; Menemenlis, D.; Nevison, C. D.; Mitchell, B. G.; Keeling, R. F.

    2016-12-01

    The Southern Ocean represents a key area of the global ocean for the uptake of the CO2 originating from fossil fuels emissions. In these waters, cold temperatures combined with high rates of biological production drive the carbon uptake that accounts for about one-third of the global ocean uptake.Recent studies showed that changes in the Southern Annular Mode (SAM) index, mainly a proxy of the intensity of westerly winds, had a significant impact on the temporal variability of the CO2 uptake in the Southern Ocean. In order to shed light on this problem we propose to use both satellite-derived estimates of ocean productivity and carbon export in combinations of ocean physical and biogeochemical state estimates focusing on the 2006-2013 period. While the estimates of carbon fixation and export based on remote sensing will provide key information on the spatial and temporal variations of the biological carbon pump, the ocean state estimates will provide additional information on physical and carbon cycle processes, including the air-sea CO2 fluxes of the Southern Ocean in the 2006-2013 period where model solutions have been optimized.These physical estimates will be used to force an ocean biogeochemical model (ECCO2-Darwin) that will compute the CO2 uptake for each year. The physical model, forced with optimized atmospheric forcing, aims to realistically simulate interannual ocean climate variability that drives changes in both physical and biogeochemical processes ultimately impacting the carbon uptake of the Southern Ocean, and potentially responding to the SAM index variations.Although in this study great emphasis is given to the role of physical climate variations at driving the CO2 uptake of these polar waters, we will integrate model results with estimates from remote sensing techniques to better understand role of the biological carbon pump and its variability potentially responding to the SAM index changes.

  19. The impact of Southern Ocean residual upwelling on atmospheric CO2 on centennial and millennial timescales

    NASA Astrophysics Data System (ADS)

    Lauderdale, Jonathan M.; Williams, Richard G.; Munday, David R.; Marshall, David P.

    2017-03-01

    The Southern Ocean plays a pivotal role in climate change by exchanging heat and carbon, and provides the primary window for the global deep ocean to communicate with the atmosphere. There has been a widespread focus on explaining atmospheric CO2 changes in terms of changes in wind forcing in the Southern Ocean. Here, we develop a dynamically-motivated metric, the residual upwelling, that measures the primary effect of Southern Ocean dynamics on atmospheric CO2 on centennial to millennial timescales by determining the communication with the deep ocean. The metric encapsulates the combined, net effect of winds and air-sea buoyancy forcing on both the upper and lower overturning cells, which have been invoked as explaining atmospheric CO2 changes for the present day and glacial-interglacial changes. The skill of the metric is assessed by employing suites of idealized ocean model experiments, including parameterized and explicitly simulated eddies, with online biogeochemistry and integrated for 10,000 years to equilibrium. Increased residual upwelling drives elevated atmospheric CO2 at a rate of typically 1-1.5 parts per million/106 m3 s-1 by enhancing the communication between the atmosphere and deep ocean. This metric can be used to interpret the long-term effect of Southern Ocean dynamics on the natural carbon cycle and atmospheric CO2, alongside other metrics, such as involving the proportion of preformed nutrients and the extent of sea ice cover.

  20. Air-sea Fluxes and Mode Waters in an Eddy Resolving Ocean Data Assimilating Southern Ocean State Estimate (SOSE) (Invited)

    NASA Astrophysics Data System (ADS)

    Cerovecki, I.; Talley, L. D.; Mazloff, M. R.

    2010-12-01

    An eddy-permitting data assimilating system, the Southern Ocean State Estimate (SOSE), has been developed by Mazloff et al. (2010) to estimate the Southern Ocean circulation in years 2005 and 2006. We assess the accuracy of SOSE air-sea heat and freshwater flux estimates by comparing them to widely used flux products (the National Center for Environmental Prediction-National Center for Atmospheric Reanalysis 1 (NCEP1), European Centre for Medium-Range Weather Forecasts operational model) and to a recently developed flux product constructed by Large and Yeager (2009). SOSE and Large and Yeager (2009) estimates show remarkable similarity in the large scale pattern of air-sea fluxes when compared to the NCEP1 fields that SOSE uses as an initial guess and constraint. Having verified that the accuracy of SOSE air-sea buoyancy flux estimate is satisfactory, we use SOSE fluxes and three-dimensional oceanic fields to investigate Subantarctic Mode Water (SAMW) formation and destruction by diapycnal buoyancy exchange at the ocean surface and in the ocean interior as well as identify and quantify SAMW transport pathways. Surface buoyancy fluxes produce on average 6.9 +/-1.6 Sv of Southeast Indian SAMW (SEISAMW) and 4.8 +/- 2.2 Sv of East Pacific SAMW, averaged over years 2005 and 2006. This transformation is largely compensated by diapycnal mixing in the ocean interior where SAMW gets mostly transformed into denser water, especially in the Pacific sector of the Southern Ocean. There is also a net conversion of lighter thermocline water into SAMW in the ocean interior (occurring mostly in the Indian Ocean), which is part of the shallow overturning. The zonally integrated export of SAMW across 30S is thus relatively small and on average equals approximately 3.5 Sv of (SEISAMW) and 2.0 Sv of East Pacific SAMW.

  1. Mean Upper-Ocean Circulation of the Southern Hemisphere Oceans Based on Goce Data

    NASA Astrophysics Data System (ADS)

    Menezes, V. V.; Bingham, R. J.; Vianna, M. L.; Phillips, H. E.

    2012-12-01

    One of the main goals of the Gravity and steady-state Ocean Circulation Explorer (GOCE) satellite mission launched in 2009 is to improve the previous estimates of the global ocean circulation structures determined from Mean Dynamic Topographies (MDTs). Recently published studies suggest that the GOCE-based MDTs and their respective mean geostrophic circulation fields (MGCs) are superior to those obtained from GRACE (Gravity Recovery and Climate Experiment)-only data. These studies focus mostly on the circulation of the North Atlantic and North Pacific oceans with emphasis on the strong western boundary current systems. In contrast, no detailed assessment has yet been made to determine the impact of the GOCE models in the southern hemisphere (SH) upper-ocean circulation especially in the subtropical region. It is generally recognized that the SH circulation is still not well established even at large scales, and the new GOCE and GRACE products can contribute to increase our understanding of the dominant currents in these regions, which may have even greater impact on the global climate than the NH counterparts. In the present work, we compute five global GOCE-derived MDTs with a 0.25 x 0.25 degree spatial grid based on three GOCE geoid models (TIM3, GOCO02S, GOCO3S) and three mean sea surfaces (CLS01, CLS11, DTU10) using the standard spectral approach (MSS minus Geoid). These MDTs do not have the well-known large-amplitude striation-type noise that plagued all of the GRACE-only MDTs with he same resolution, but still present commission errors which are filptered out with Singular Spectrum Analysis methods. Additionally, the MGCs were calculated by use of a Anderssen-Hegland averaging scheme for estimation of derivatives, which is able to filter out the well-known high amplitude noise caused by standard finite-difference methods. Comparisons with previous GRACE-only MGCs show that GOCE permits retrieval of currents with much higher intensities (e.g. the Agulhas

  2. Estimation of Fresh and Saltwater Fluxes and Transports in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Ferster, B. S.; Bulusu, S.

    2016-12-01

    Since the 20th century, the Antarctic climate has been changing and relatively unstable. The Southern Ocean plays a major role in global ocean circulation. Because the Southern Ocean around Antarctica is the only location where the ocean can circulate freely all the way around the globe without continental barriers, it's a huge part of the ocean cycle. The use of salinity remote sensing technology offers spatial and temporal salinity observations than insitu and other conventional observations to better represent the sea surface salinity (SSS) in the Southern Ocean (SO). Using data sets from NASA's Aquarius/SAC-D and ESA's Soil Moisture and Ocean Salinity (SMOS), and NASA's Soil Moisture Active and Passive (SMAP) we have estimated fresh and salt water fluxes. To address the issue of the satellites accuracy, this study validates Aquarius, SMOS and SMAP against Argo floats salinity data. Incorporating Ocean Surface Current Analyses Real-time (OSCAR) both zonal and meridional surface fresh and saltwater fluxes from the SO were calculated. We have compared Aquarius derived fluxes with SMOS, for the Aquarius time period, produced statistically similar zonal and meridional fresh and saltwater fluxes. This suggests the use of satellites within the SO can be used with confidence to monitor saline advection at higher frequencies and horizontal resolutions than the use of sparse in situ data of Argo in the SO. In addition to fluxes we have estimated integrated fresh and salt water transports using Simple Ocean Data Assimilation (SODA) reanalysis. The use of satellite derived fluxes may prove to be valuable sources in predicting sea ice and monitoring chemical and biological aspects within the SO. Our results indicate that recent changes in freshwater and salt transports are a major component of the deep-ocean warming in the SO. In particular, the role of changes in these fluxes in causing surface cooling and increasing deep oceanic storage of heat in the Southern Ocean is

  3. Evolution of Modern Deepwater Circulation: Evidence from the Late Miocene Southern Ocean

    NASA Astrophysics Data System (ADS)

    Wright, James D.; Miller, Kenneth G.; Fairbanks, Richard G.

    1991-04-01

    Deepwater circulation plays an important role in climate modulation through its redistribution of heat and salt and its control of atmospheric CO2. Oppo and Fairbanks (1987) showed that the Southern Ocean is an excellent monitor of deepwater circulation changes for two reasons: (1) the Southern Ocean is a mixing reservoir for incoming North Atlantic Deep Water and recirculated water from the Pacific and Indian oceans; and (2) the nutrient/δ13C tracers of deepwater are not significantly changed by surficial processes within the Southern Ocean. We can extend these principles to the late Miocene because tectonic changes in the Oligocene and early and middle Miocene developed near-modern basinal configurations. However, on these time scales, changes in the oceanic carbon reservoir and mean ocean nutrient levels also affect the δ13C differences between ocean basins. From 9.8 to 9.3 Ma, Southern Ocean δ13C values oscillated between high North Atlantic values and low Pacific values. The Southern Ocean recorded δ13C values similar to Pacific values from 9.2 to 8.9 Ma, reflecting a low contribution of Northern Component Water (NCW). The δ13C differences between the NCW and Pacific Outflow Water (POW) end-members were low from 8.9 to 8.0 Ma, making it difficult to discern circulation patterns. NCW production may have completely shutdown at 8.6 Ma, allowing Southern Component Water (SCW) to fill the North Atlantic and causing the δ13C values in the North Atlantic, Pacific, and Southern oceans to converge. Deepwater δ13C patterns resembling the modern distributions evolved by 7.0 Ma: δ13C values were near 1.0‰ in the North Atlantic; 0.0‰ in the Pacific; and 0.5‰ in the Southern Ocean. Development of near-modern δ13C distributions by 7.0 Ma resulted not only from an increase in NCW flux but also from an increase in deepwater nutrient levels. Both of these processes increased the δ13C difference between the North Atlantic and Pacific oceans. Deepwater circulation

  4. Perfluorooctanesulfonate and related fluorochemicals in albatrosses, elephant seals, penguins, and polar skuas from the Southern Ocean.

    PubMed

    Tao, Lin; Kannan, Kurunthachalam; Kajiwara, Natsuko; Costa, Monica M; Fillmann, Gilberto; Takahashi, Shin; Tanabe, Shinsuke

    2006-12-15

    Perfluorinated chemicals (PFCs) have been used as surfactants in industrial and commercial products for over 50 years. Earlier studies of the geographical distribution of PFCs focused primarily on the Northern Hemisphere, while little attention was paid to the Southern Hemisphere. In this study, livers from eight species of albatrosses, blood from elephant seal, and blood and eggs from penguins and polar skua collected from the Southern Ocean and the Antarctic during 1995-2005 were analyzed for 10 PFCs. In addition, for comparison with the Southern Ocean samples, we analyzed liver, sera, and eggs from two species of albatrosses from Midway Atoll in the North Pacific Ocean. Perfluorooctanesulfonate (PFOS) and perfluorooctanoic acid (PFOA) were found in livers of albatrosses from the Southern Ocean. PFOS was the major contaminant, although the concentrations were <5 ng/g, wet wt, in 92% of the albatross livers analyzed. PFOA was detected in 30% of the albatross livers, with a concentration range of <0.6-2.45 ng/g,wet wt. Other PFCs, including long-chain perfluorocarboxylates (PFCAs), were below the limits of quantitation in livers of albatrosses from the Southern Ocean. In liver, sera, and eggs of albatrosses from the North Pacific Ocean, long-chain PFCAs (perfluorononanoate, perfluorodecanoate, perfluoroundecanoate, and perfluorododecanoate) were found at concentrations similar to those of PFOS and PFOA. The mean concentration of PFOS in livers of Laysan albatrosses from the North Pacific Ocean (5.1 ng/g, wet wt) was higher than that in several species of albatrosses from the Southern Ocean (2.2 ng/g, wetwt). Species-specific differences in the concentrations of PFOS were noted among Southern Ocean albatrosses, whereas geographical differences in PFOS concentrations among the Indian Ocean, South Pacific Ocean, and South Atlantic Ocean were insignificant. Concentrations of PFOS and PFOA were, respectively, 2- and 17-fold higher in liver than in sera of Laysan

  5. 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.

  6. 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

  7. Zooplankton Atlas of the Southern Ocean: The SCAR SO-CPR Survey (1991-2008)

    NASA Astrophysics Data System (ADS)

    McLeod, David J.; Hosie, Graham W.; Kitchener, John A.; Takahashi, Kunio T.; Hunt, Brian P. V.

    2010-08-01

    The SCAR Southern Ocean Continuous Plankton Recorder (SO-CPR) Survey produces one of the largest and most accessed zooplankton data sets in the world. These data serve as a reference for other Southern Ocean monitoring programmes such as those run by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and the developing Southern Ocean Observing System (SOOS). It has been instrumental in providing baseline data on zooplankton composition, communities, and distribution patterns on the ocean basin scale. The SO-CPR Survey is publishing the first detailed geographical atlas of the near-surface Southern Ocean zooplankton. This atlas is based on 22,553 CPR samples collected from 1991 to 2008 from voyages operated by Australia, Japan, Germany, New Zealand, USA and Russia. The Atlas documents the distribution and abundance of the 50 most abundant zooplankton taxa amongst the 200+ taxa sampled. The maps are printed in alphabetical order of the genera within each taxon and nomenclature is based on the Register of Antarctic Marine Species (RAMS) developed by the SCAR Marine Biodiversity Information Network (SCAR-MarBIN). The SO-CPR Atlas will operate as a ready reference to researchers interested in the distribution of zooplankton in the Southern Ocean, for example knowing the distribution of grazers in relation to phytoplankton production or the availability of prey for higher predators.

  8. Satellite assessment of sea spray aerosol productivity: Southern Ocean case study

    NASA Astrophysics Data System (ADS)

    Witek, Marcin L.; Diner, David J.; Garay, Michael J.

    2016-01-01

    Despite many years of observations by multiple sensors, there is still substantial ambiguity regarding aerosol optical depths (AOD) over remote oceans, in particular, over the pristine Southern Ocean. Passive satellite retrievals (e.g., Multiangle Imaging Spectroradiometer (MISR) and Moderate Resolution Imaging Spectroradiometer (MODIS)) and global aerosol transport models show a distinct AOD maximum around the 60°S latitude band. Sun photometer measurements performed by the Maritime Aerosol Network (MAN), on the other hand, indicate no increased AODs over the Southern Ocean. In this study elevated Southern Ocean AODs are examined from the modeling perspective. The primary aerosol component over the Southern Ocean is sea spray aerosol (SSA). Multiple simulations of SSA concentrations and optical depths are carried out using a single modeling framework, the Navy Aerosol Analysis and Prediction System (NAAPS) model. Several SSA emission functions are examined, including recently proposed formulations with sea surface temperature corrections. The differences between NAAPS simulations are primarily due to different SSA emission formulations. The results are compared against satellite-derived AODs from the MISR and MODIS instruments. MISR and MODIS AOD retrievals are further filtered to eliminate retrievals potentially affected by cloud contamination and cloud adjacency effects. The results indicate a very large impact of SSA emission parameterization on the simulated AODs. For some scenarios, the Southern Ocean AOD maximum almost completely disappears. Further MISR and MODIS AOD quality screening substantially improves model/satellite agreement. Based on these comparisons, an optimal SSA emission function for global aerosol transport models is recommended.

  9. The role of internal variability for decadal carbon uptake anomalies in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Spring, Aaron; Hi, Hongmei; Ilyina, Tatiana

    2017-04-01

    The Southern Ocean is a major sink for anthropogenic CO2 emissions and hence it plays an essential role in modulating global carbon cycle and climate change. Previous studies based on observations (e.g., Landschützer et al. 2015) show pronounced decadal variations of carbon uptake in the Southern Ocean in recent decades and this variability is largely driven by internal climate variability. However, due to limited ensemble size of simulations, the variability of this important ocean sink is still poorly assessed by the state-of-the-art earth system models (ESMs). To assess the internal variability of carbon sink in the Southern Ocean, we use a large ensemble of 100 member simulations based on the Max Planck Institute-ESM (MPI-ESM). The large ensemble of simulations is generated via perturbed initial conditions in the ocean and atmosphere. Each ensemble member includes a historical simulation from 1850 to 2005 with an extension until 2100 under Representative Concentration Pathway (RCP) 4.5 future projections. Here we use model simulations from 1980-2015 to compare with available observation-based dataset. We found several ensemble members showing decadal decreasing trends in the carbon sink, which are similar to the trend shown in observations. This result suggests that MPI-ESM large ensemble simulations are able to reproduce decadal variation of carbon sink in the Southern Ocean. Moreover, the decreasing trends of Southern Ocean carbon sink in MPI-ESM are mainly contributed by region between 50-60°S. To understand the internal variability of the air-sea carbon fluxes in the Southern Ocean, we further investigate the variability of underlying processes, such as physical climate variability and ocean biological processes. Our results indicate two main drivers for the decadal decreasing trend of carbon sink: i) Intensified winds enhance upwelling of old carbon-rich waters, this leads to increase of the ocean surface pCO2; ii) Primary production is reduced in area

  10. 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

  11. 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.

  12. Polychaeta Orbiniidae from Antarctica, the Southern Ocean, the Abyssal Pacific Ocean, and off South America.

    PubMed

    Blake, James A

    2017-01-12

    The orbiniid polychaetes chiefly from Antarctic and subantarctic seas and off South America are described based on collections of the National Museum of Natural History and new material from surveys conducted by the United States Antarctic Program and other federal and privately funded sources as well as participation in international programs. A total of 44 species of Orbiniidae distributed in 10 genera are reported from the Pacific Ocean and waters off South America and Antarctica. Twenty-one species are new to science; one species is renamed. Berkeleyia heroae n. sp., B. abyssala n. sp., B. weddellia n. sp.; B. hadala n. sp., Leitoscoloplos simplex n. sp., L. plataensis n. sp., L. nasus n. sp., L. eltaninae n. sp., L. phyllobranchus n. sp., L. rankini n. sp., Scoloplos bathytatus n. sp., S. suroestense n. sp., Leodamas hyphalos n. sp., L. maciolekae n. sp., L. perissobranchiatus n. sp., Califia bilamellata n. sp., Orbinia orensanzi n. sp., Naineris antarctica n. sp., N. argentiniensis n. sp., Orbiniella spinosa n. sp., and O. landrumae n. sp. are new to science. A new name, Naineris furcillata, replaces N. chilensis Carrasco, 1977, a junior homonym of N. dendtritica chilensis Hartmann‑Schröder, 1965, which is raised to full species status. Leodamas cochleatus (Ehlers, 1900) is removed from synonymy and redescribed. A neotype is established for Leodamas verax Kinberg, 1966, the type species. A general overview of Leodamas species is provided. The Leitoscoloplos kerguelensis (McIntosh, 1885) complex is reviewed and partially revised. Definitions of the genera of the Orbiniidae are updated to conform to recently described taxa. Several new synonymies are proposed following a reexamination of previously described type specimens. The morphological characters used to identify and classify orbiniids are reviewed. The biogeographic and bathymetric distributions of the South American and Southern Ocean orbiniid fauna are reviewed.

  13. 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.

  14. Impact of the SH sea-ice cover and ocean surface on the Southern Ocean atmospheric variability

    NASA Astrophysics Data System (ADS)

    Merz, N.; Sedlacek, J.; Raible, C. C.

    2012-04-01

    Satellite observations of the last 30 years have shown a slight increase in the Antarctic sea-ice area (SIA). This increase seems to be counterintuitive regarding global warming and the strong decrease observed in Arctic SIA. Thus, dynamical processes rather than thermodynamical processes would be a more plausible cause for the Southern Hemisphere (SH) sea-ice increase. This raises interest in understanding the dynamics of the Southern Ocean climate system and its recent changes. Based on ERA-40 reanalysis data and satellite-borne HadISST1 observations for 1979-2008 we detect synchronous variability in the Southern Ocean mean sea-level pressure (SLP), sea surface temperatures (SST) and sea-ice concentration (SIC) fields. The strength of the Amundsen-Sea low (ASL) is strongly connected with the phase of a dipole-pattern in SICs and SSTs identified across the Western longitudes. With the aid of a comprehensive climate model, we further investigate the one-way impact of the lower boundaries on the Southern Ocean atmosphere. Therefore, a set of sensitivity atmosphere-land-only simulations is performed forced either with inter-annually variable (the HadISST1 observations) or climatological input data of SICs and SSTs. The sensitivity experiments exhibit a clear impact of both, the SSTs and the sea-ice cover on the Southern Ocean atmospheric inter-annual variability. For example, the variability of the ASL is drastically reduced in the experiment with climatological lower boundaries. The strongest decrease is due to the missing SST variability in the mid-latitudinal Pacific suppressing the generation of the so-called Pacific South America teleconnection, an ENSO-related wave pattern significantly influencing the state of the ASL. The wave generation is inhibited due to reduced variability of the latent heat flux. Further, variable sea ice impacts the SLP variability but to a lower degree. In summary, there is clear evidence that the Southern Ocean atmospheric variability

  15. Direct measurement of the cross-density overturning circulation in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Sallee, J. B.

    2015-12-01

    The global ocean overturning circulation plays a central role in climate by transporting heat, freshwater and carbon around the Earth. Cold water that sinks at high latitudes is upwelled along surfaces of constant density connecting the deep ocean to the sea surface in the Southern Hemisphere. Cross-density circulation can however shortcut the along-density circulation, thereby impacting large-scale water mass pathways, overturning time scales, and the abyssal ocean's ability to act as a carbon reservoir. Despite its crucial role for climate, the cross-density circulation is poorly known since our capacity to measure it has historically been lacking. In this study, we present the first measurements of the slow multi-year cross-density circulation in the Southern Ocean interior. We show that 10-25% of the Southern Ocean overturning circulation is redirected through cross-density shortcuts. We find strong regional variations in the intensity of cross-density circulation, with hotspots where cross-density velocities are enhanced by 5 to 14-fold. Our results suggest a disproportionate contribution of those regions to the Southern Ocean overturning circulation, and highlight the importance of reliably representing them in our conceptual and forecast models of the ocean's role in climate.

  16. Direct measurement of the cross-density overturning circulation in the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Sallee, J. B.; Ledwell, J. R.; Naveira Garabato, A.; Meredith, M. P.; Watson, A. J.; Messias, M. J.; Zika, J. D.; Mackay, N. S.

    2016-02-01

    The global ocean overturning circulation plays a central role in climate by transporting heat, freshwater and carbon around the Earth. Cold water that sinks at high latitudes is upwelled along surfaces of constant density connecting the deep ocean to the sea surface in the Southern Hemisphere. Cross-density circulation can however shortcut the along-density circulation, thereby impacting large-scale water mass pathways, overturning time scales, and the abyssal ocean's ability to act as a carbon reservoir. Despite its crucial role for climate, the cross-density circulation is poorly known since our capacity to measure it has historically been lacking. In this study, we present the first measurements of the slow multi-year cross-density circulation in the Southern Ocean interior. We show that 10-25% of the Southern Ocean overturning circulation is redirected through cross-density shortcuts. We find strong regional variations in the intensity of cross-density circulation, with hotspots where cross-density velocities are enhanced by 5 to 14-fold. Our results suggest a disproportionate contribution of those regions to the Southern Ocean overturning circulation, and highlight the importance of reliably representing them in our conceptual and forecast models of the ocean's role in climate.

  17. Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales

    NASA Astrophysics Data System (ADS)

    Sheen, K. L.; Naveira Garabato, A. C.; Brearley, J. A.; Meredith, M. P.; Polzin, K. L.; Smeed, D. A.; Forryan, A.; King, B. A.; Sallée, J.-B.; St. Laurent, L.; Thurnherr, A. M.; Toole, J. M.; Waterman, S. N.; Watson, A. J.

    2014-08-01

    The Southern Ocean plays a pivotal role in the global ocean circulation and climate. There, the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths, forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere. The sensitivity of the upper cell to climatic changes in forcing is relatively well established. However, little is known about how the lower cell responds, and in particular whether small-scale mixing in the abyssal Southern Ocean, an important controlling process of the lower cell, is influenced by atmospheric forcing. Here, we present observational evidence that relates changes in abyssal mixing to oceanic eddy variability on timescales of months to decades. Observational estimates of mixing rates, obtained along a repeat hydrographic transect across Drake Passage, are shown to be dependent on local oceanic eddy energy, derived from moored current meter and altimetric measurements. As the intensity of the regional eddy field is regulated by the Southern Hemisphere westerly winds, our findings suggest that Southern Ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing.

  18. Southern ocean: Its involvement in global change. (Reannouncement with new availability information)

    SciTech Connect

    Gordon, A.L.

    1990-06-15

    The Southern Ocean is the site of considerable water mass formation which cools and ventilates the modern world ocean. At the polar front zone, formation of cool, low salinity water sinks and spreads northward at intermediate depths limiting the downward penetration of the thermocline. Within the seasonal sea ice zone and along the margins of Antarctica, convection injects very cold oxygenated water into the deep and bottom ocean. These conditions developed as Antarctica shifted into its present configuration and grew a persistent glacial ice sheet, about 14 million years ago. The potential of the Southern Ocean to ventilate the deep and bottom ocean layers is related to occurrence of polynyas that form within the winter sea ice cover. Global climate changes would be expected to alter the polynya size and frequency. Under greenhouse-induced warming offshore polynyas may become less common as the static stability of the Southern Ocean mixed layer increases. This would diminish the Southern Ocean`s cooling influence on the deep layers of the world ocean, resulting in a warmer deep ocean. The fate of coastal polynyas is less clear. It is likely that they would continue at close to their present form providing a setting conducive to Antarctic Bottom Water formation. Within the polar front zone, global warming is expected to create lower salinity though slightly cooler surface water. A reduction in the salt input to the Antarctic Intermediate Water would inject it into a shallower horizon at the thermocline base, further limiting the thickness of the thermocline. Less heat storage in the thermocline would tend to counteract the proposed deep ocean warming.

  19. Importance of the Indian Ocean for simulating rainfall anomalies over eastern and southern Africa

    NASA Astrophysics Data System (ADS)

    Goddard, Lisa; Graham, Nicholas E.

    1999-08-01

    The relative contributions of the Indian Ocean and Pacific Ocean sea surface temperatures (SSTs) to the rainfall variability over eastern central, and southern Africa during the austral spring-summer are examined. The variability of African rainfall is statistically related to both oceans, but the variability in the two oceans is also related. To separate the effects of the Indian and Pacific Oceans, a suite of numerical model simulations is presented: GOGA, the atmosphere is forced by observed SSTs globally; IOGA, the atmosphere is forced by observed SSTs only in the Indian Ocean basin; and POGA, the atmosphere is forced by observed SSTs only in the tropical Pacific basin. While the SST variability of the tropical Pacific exerts some influence over the African region, it is the atmospheric response to the Indian Ocean variability that is essential for simulating the correct rainfall response over eastern, central, and southern Africa. Analyses of the dynamical response(s) seen in the numerical experiments and in the observations indicate that the Pacific and Indian Oceans have a competing influence over the Indian Ocean/African region. This competition is related to the influence of the two oceans on the Walker circulation and the consequences of that variability on low-level fluxes of moisture over central and southern Africa. Finally, given the high correlation found between SST variability in the Indian and Pacific Oceans with the Pacific leading by ˜3 months, we speculate on an approach to long-lead dynamical climate prediction over central-east and southern Africa.

  20. 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

  1. 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.

  2. 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.

  3. 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. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  4. Southern Ocean abyssal heat uptake in fine and coarse resolution climate model simulations

    NASA Astrophysics Data System (ADS)

    Newsom, E. R.; Singh, H.; Bitz, C. M.

    2013-12-01

    The recently observed warming of Antarctic Bottom Water (AABW) represents an important component of accumulated sea level rise and global ocean heat uptake. Yet in simulations of greenhouse warming with coarse resolution climate models (which parameterize ocean eddies), Southern Ocean heat uptake dominantly occurs within near-surface waters, which are subsequently transported northward and subducted at mid-latitudes. Here, we examine the response of the abyssal Southern Ocean to greenhouse forcing within a global climate model run with a fine resolution (eddy-resolving) ocean component, which more faithfully simulates AABW formation than its coarse resolution counterparts. We argue that AABW warming may play a more important role in Southern Ocean heat uptake than is suggested by the CMIP5 ensemble of coarse resolution models. We examine the heat uptake in the Southern Ocean using the Community Climate System Model version 3.5 (CCSM 3.5). The model was run at two resolutions in the ocean and sea ice components: coarse (1 degree), which is a standard resolution of many CMIP5 models, and fine (.1 degree), in which sea ice and AABW is formed more realistically. The atmosphere and land components were fixed throughout at .5 degrees resolution. Each version was forced identically with a 1% ramping of CO2 for 150 years. The fine resolution simulation produces more dense water in the control climate, which sinks to a more realistic depth. We attribute this to the improved simulation of sea ice formation regions granted by increasing the ocean model resolution. The reduction of AABW formation as the climate warms leads to a larger response at depth at fine resolution; below 2000 meters, the fine resolution simulation takes up two orders of magnitude more heat than at coarse resolution. We further propose a framework to weigh the amount of heat taken up at depth in the Southern Ocean by the timescale at which it is sequestered, giving more value to heating of regions with

  5. 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

  6. How do the westerlies influence the Southern Ocean subduction of anthropogenic carbon?

    NASA Astrophysics Data System (ADS)

    Downes, Stephanie; Langlais, Clothilde; Brook, Jordan; Spence, Paul

    2017-04-01

    The Southern Ocean is responsible for roughly a third of the global oceanic anthropogenic carbon uptake, and this uptake occurs in the upper ocean Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW) layers. The process by which the anthropogenic carbon is transported into the ocean interior is commonly known as 'subduction'. Observationally-based and model studies have shown that the subduction of SAMW and AAIW occurs in hot spots primarily in the deep mixed layer depths in the Indian and Pacific sectors of the Southern Ocean. Two key atmospheric changes in recent decades in the Southern Ocean are increases in atmosphere to ocean buoyancy input, and the poleward intensification of the westerly wind stress band. Both buoyancy and winds are drivers of the Southern Ocean large scale circulation, and in this study we diagnose the impact of specifically the westerly winds on the upper ocean subduction. We evaluate the mean and eddy subduction components under three sensitivity experiments where the westerlies are increased, shifted poleward, and both shifted and increased. We use a 1/4-degree eddy-permitting ocean-ice model coupled to a reanalysis atmosphere. Our perturbation experiments reveal that intensified winds enhance the deep mixed layer depths locally, but a shift in the westerlies decreases (increases) the mixed layer depth in the Indian (southeast Pacific) sector. A poleward intensification of the westerlies combines the individual shift and intensified wind experiment change, as well as strongly enhancing Atlantic mixed layers. The mixed layer changes are associated with SAMW and AAIW subduction, and we find that the poleward intensification of the westerlies overall enhances both the eddy and large scale subduction rates. Using our subduction results and observations, we infer regional anthropogenic carbon inventory changes in a water mass framework under wind stress changes.

  7. The δ15N of nitrate in the Southern Ocean: Nitrogen cycling and circulation in the ocean interior

    NASA Astrophysics Data System (ADS)

    Sigman, D. M.; Altabet, M. A.; McCorkle, D. C.; Francois, R.; Fischer, G.

    2000-08-01

    We report analyses of the nitrogen isotopic composition of nitrate in the eastern Indian and Pacific sectors of the Southern Ocean. In this paper, we focus on the subsurface data as well as data from the deep waters of other ocean basins. Nitrate δ15N is relatively invariant in much of the abyssal ocean (i.e., below 2.5 km), with a value of 4.8±0.2‰ observed in Lower Circumpolar Deep Water, North Atlantic Deep Water, and central Pacific deep water. The isotopic invariance of deep ocean nitrate stems fundamentally from the completeness of nitrate utilization in most of the global surface ocean, the Southern Ocean surface being an important exception. In the Subantarctic Zone (north of the Polar Frontal Zone) the nitrate δ15N of Upper Circumpolar Deep Water is ˜0.7‰ greater than that of Lower Circumpolar Deep Water. This isotopic enrichment appears to result from denitrification in the low-latitude water masses with which Upper Circumpolar Deep Water communicates. The isotopic enrichment of Upper Circumpolar Deep Water is diminished in the Antarctic, probably because of the remineralization of sinking organic N, which has a low δ15N in the Antarctic. Relative to the other water masses of the Southern Ocean, the Subantarctic thermocline has a very low nitrate δ15N for its nitrate concentration because of exchange with the low-latitude thermocline, where this isotopic signature appears to originate. This signature of the low-latitude thermocline has two probable causes: (1) mixing with low-nitrate surface water and (2) the oxidation of newly fixed N.

  8. Long-term decline in krill stock and increase in salps within the Southern Ocean.

    PubMed

    Atkinson, Angus; Siegel, Volker; Pakhomov, Evgeny; Rothery, Peter

    2004-11-04

    Antarctic krill (Euphausia superba) and salps (mainly Salpa thompsoni) are major grazers in the Southern Ocean, and krill support commercial fisheries. Their density distributions have been described in the period 1926-51, while recent localized studies suggest short-term changes. To examine spatial and temporal changes over larger scales, we have combined all available scientific net sampling data from 1926 to 2003. This database shows that the productive southwest Atlantic sector contains >50% of Southern Ocean krill stocks, but here their density has declined since the 1970s. Spatially, within their habitat, summer krill density correlates positively with chlorophyll concentrations. Temporally, within the southwest Atlantic, summer krill densities correlate positively with sea-ice extent the previous winter. Summer food and the extent of winter sea ice are thus key factors in the high krill densities observed in the southwest Atlantic Ocean. Krill need the summer phytoplankton blooms of this sector, where winters of extensive sea ice mean plentiful winter food from ice algae, promoting larval recruitment and replenishing the stock. Salps, by contrast, occupy the extensive lower-productivity regions of the Southern Ocean and tolerate warmer water than krill. As krill densities decreased last century, salps appear to have increased in the southern part of their range. These changes have had profound effects within the Southern Ocean food web.

  9. 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.

  10. Lagrangian pathways of deep water upwelling in the Southern Ocean State Estimate

    NASA Astrophysics Data System (ADS)

    Tamsitt, V. M.; Talley, L. D.; Mazloff, M. R.; Wang, J.

    2016-02-01

    Pathways of upwelling of deep waters in the Southern Ocean are investigated using Lagrangian particle trajectories advected offline in the 1/6th°, data-assimilating Southern Ocean State Estimate (sose.ucsd.edu). A total of 18 million particles released at 1000 m - 3500 m at 30° S in each basin were tracked for 60 years by looping velocities from the latest 2005-2010 SOSE iteration. 5% of particles upwelled to 500 m or shallower by the end of the simulation with 37%, 42% and 21% from the Atlantic, Indian and Pacific basins, respectively. Trajectories indicate that particles in the neutral density range 26.7-28.1 from all basins enter the Antarctic Circumpolar Current (ACC), follow the fronts of the ACC, and tend to upwell to the surface ocean toward the southern edge of the ACC and south of the ACC. We analyze differences in upwelling pathways between North Atlantic Deep Water and Indian and Pacific deep waters and explore the role of topography in the upwelling of these deep water masses. These upwelling pathways are important to understanding the 3-dimensional structure of the Southern Ocean overturning circulation and the supply of carbon and nutrient-rich waters to the surface of the Southern Ocean.

  11. 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.

  12. 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

    2011-08-03

    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.

  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. Parameterization of eddy-induced subduction in the Southern Ocean surface-layer

    NASA Astrophysics Data System (ADS)

    Sallée, Jean-Baptiste; Rintoul, Stephen R.

    The divergence of the eddy mass flux in the surface layer of the Southern Ocean makes an important contribution to subduction of fluid through the base of the mixed layer. Therefore, accurate parameterization of this process is needed to correctly represent the Southern Ocean ventilation in coarse-resolution models. We test a common approach to the parameterization of eddy fluxes ( Gent and McWilliams, 1990) using output from the 1/6° eddy-permitting Southern Ocean State Estimate, which assimilates a variety of ocean observations using an adjoint method. When a constant diffusion coefficient of conventional magnitude O(1000 m 2 s -1) is used, the parameterized fluxes fail to reproduce the regional pattern and magnitude of eddy-driven subduction diagnosed from the model. However, when an appropriate choice is made for the diffusion coefficient, the parameterization does a good job of reproducing the distribution and strength of the eddy contribution to subduction. Using a spatially-varying coefficient is key to reproduce the regional pattern of the eddy-induced subduction. In addition, the magnitude of the subduction is correctly represented only with a diffusion coefficient that peaks at 10 4 m 2 s -1 in the most energetic areas of the Southern Ocean, a factor of ten larger than commonly used in coarse-resolution climate models. Using a diffusion coefficient that is too small will underestimate the contribution of eddies to the ocean sequestration of heat, salt and carbon.

  16. 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.

  17. 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.

  18. 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.

  19. Spiraling pathways of global deep waters to the surface of the Southern Ocean.

    PubMed

    Tamsitt, Veronica; Drake, Henri F; Morrison, Adele K; Talley, Lynne D; Dufour, Carolina O; Gray, Alison R; Griffies, Stephen M; Mazloff, Matthew R; Sarmiento, Jorge L; Wang, Jinbo; Weijer, Wilbert

    2017-08-02

    Upwelling of global deep waters to the sea surface in the Southern Ocean closes the global overturning circulation and is fundamentally important for oceanic uptake of carbon and heat, nutrient resupply for sustaining oceanic biological production, and the melt rate of ice shelves. However, the exact pathways and role of topography in Southern Ocean upwelling remain largely unknown. Here we show detailed upwelling pathways in three dimensions, using hydrographic observations and particle tracking in high-resolution models. The analysis reveals that the northern-sourced deep waters enter the Antarctic Circumpolar Current via southward flow along the boundaries of the three ocean basins, before spiraling southeastward and upward through the Antarctic Circumpolar Current. Upwelling is greatly enhanced at five major topographic features, associated with vigorous mesoscale eddy activity. Deep water reaches the upper ocean predominantly south of the Antarctic Circumpolar Current, with a spatially nonuniform distribution. The timescale for half of the deep water to upwell from 30° S to the mixed layer is ~60-90 years.Deep waters of the Atlantic, Pacific and Indian Oceans upwell in the Southern Oceanbut the exact pathways are not fully characterized. Here the authors present a three dimensional view showing a spiralling southward path, with enhanced upwelling by eddy-transport at topographic hotspots.

  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. Microsatellite loci from the endemic Southern Ocean octopus Adelieledone polymorpha (Robson, 1930).

    PubMed

    Strugnell, Jan M; Allcock, A Louise; Watts, Phillip C

    2009-05-01

    To determine the pattern of spatial genetic structure in the endemic Southern Ocean octopus Adelieledone polymorpha, microsatellite loci were isolated from partial genomic libraries enriched for repetitive DNA motifs. Seven dinucleotide and two trinucleotide microsatellite loci were isolated successfully and levels of polymorphism were quantified in 34 individuals sampled from the Southern Ocean near South Georgia. No pairs of microsatellite loci were linked significantly; however, one locus deviated (P < 0.05) from Hardy-Weinberg equilibrium. Overall, the nine loci produced between five and 16 alleles, with observed and expected heterozygosities varying between 0.22 and 0.86 and between 0.21 and 0.94 respectively. This is the first description of microsatellite loci from an octopus endemic to the Southern Ocean, and these genetic markers are being used to quantify spatial structure within A. polymorpha.

  2. Phenotypic plasticity of southern ocean diatoms: key to success in the sea ice habitat?

    PubMed

    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.

  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. 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

  5. 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.

  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. 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.

  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 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

  10. The post-2002 global surface warming slowdown caused by the subtropical Southern Ocean heating acceleration

    NASA Astrophysics Data System (ADS)

    Oka, A.; Watanabe, M.

    2017-04-01

    The warming rate of global mean surface temperature slowed down during 1998-2012. Previous studies pointed out role of increasing ocean heat uptake during this global warming slowdown, but its mechanism remains under discussion. Our numerical simulations, in which wind stress anomaly in the equatorial Pacific is imposed from reanalysis data, suggest that subsurface warming in the equatorial Pacific took place during initial phase of the global warming slowdown (1998-2002), as previously reported. It is newly clarified that the Ekman transport from tropics to subtropics is enhanced during the later phase of the slowdown (after 2002) and enhanced subtropical Ekman downwelling causes accelerated heat storage below depth of 700 m in the subtropical Southern Ocean, leading to the post-2002 global warming slowdown. Observational data of ocean temperature also support this scenario. This study provides clear evidence that deeper parts of the Southern Ocean play a critical role in the post-2002 warming slowdown.

  11. 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.

  12. 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.

  13. 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.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27274061

  15. 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.

  16. Southern Ocean acidification: A tipping point at 450-ppm atmospheric CO2

    PubMed Central

    McNeil, Ben I.; Matear, Richard J.

    2008-01-01

    Southern Ocean acidification via anthropogenic CO2 uptake is expected to be detrimental to multiple calcifying plankton species by lowering the concentration of carbonate ion (CO32−) to levels where calcium carbonate (both aragonite and calcite) shells begin to dissolve. Natural seasonal variations in carbonate ion concentrations could either hasten or dampen the future onset of this undersaturation of calcium carbonate. We present a large-scale Southern Ocean observational analysis that examines the seasonal magnitude and variability of CO32− and pH. Our analysis shows an intense wintertime minimum in CO32− south of the Antarctic Polar Front and when combined with anthropogenic CO2 uptake is likely to induce aragonite undersaturation when atmospheric CO2 levels reach ≈450 ppm. Under the IPCC IS92a scenario, Southern Ocean wintertime aragonite undersaturation is projected to occur by the year 2030 and no later than 2038. Some prominent calcifying plankton, in particular the Pteropod species Limacina helicina, have important veliger larval development during winter and will have to experience detrimental carbonate conditions much earlier than previously thought, with possible deleterious flow-on impacts for the wider Southern Ocean marine ecosystem. Our results highlight the critical importance of understanding seasonal carbon dynamics within all calcifying marine ecosystems such as continental shelves and coral reefs, because natural variability may potentially hasten the onset of future ocean acidification. PMID:19022908

  17. 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.

  18. Australian dust storms in 2002-2003 and their impact on Southern Ocean biogeochemistry

    NASA Astrophysics Data System (ADS)

    Gabric, A. J.; Cropp, R. A.; McTainsh, G. H.; Johnston, B. M.; Butler, H.; Tilbrook, B.; Keywood, M.

    2010-06-01

    During late 2002 and early 2003, southern Australia was in the grip of drought and experienced one of its most active dust storm seasons in the last 40 years with large dust plumes frequently advected over the adjacent Southern Ocean. We use meteorological records of dust activity, satellite ocean color, and aerosol optical depth data and dust transport modeling to investigate the transport and deposition of mineral dust from Australia over adjacent ocean regions and to correlate it with biological response in phytoplankton standing stock as measured by chlorophyll a concentration in 5 degree latitude bands from 40° to 60°S. Seasonal maxima in mean surface chlorophyll a of ˜0.5 mg m-3 were not achieved until late January 2003 or during February in the more southerly bands, which when compared with a 9 year satellite mean climatology suggests the phenology of the bloom in 2002-2003 was atypical. Contemporaneous field data on CO2 fugacity collected on transects between Tasmania and Antarctica show that significant atmospheric CO2 drawdown occurred as far south as 60°S during February 2003. Our results provide strong evidence for a large-scale natural dust fertilization event in the Australian sector of the Southern Ocean and highlight the importance of dust-derived nutrients in the marine carbon cycle of the Southern Ocean.

  19. Southern Ocean acidification: a tipping point at 450-ppm atmospheric CO2.

    PubMed

    McNeil, Ben I; Matear, Richard J

    2008-12-02

    Southern Ocean acidification via anthropogenic CO(2) uptake is expected to be detrimental to multiple calcifying plankton species by lowering the concentration of carbonate ion (CO(3)(2-)) to levels where calcium carbonate (both aragonite and calcite) shells begin to dissolve. Natural seasonal variations in carbonate ion concentrations could either hasten or dampen the future onset of this undersaturation of calcium carbonate. We present a large-scale Southern Ocean observational analysis that examines the seasonal magnitude and variability of CO(3)(2-) and pH. Our analysis shows an intense wintertime minimum in CO(3)(2-) south of the Antarctic Polar Front and when combined with anthropogenic CO(2) uptake is likely to induce aragonite undersaturation when atmospheric CO(2) levels reach approximately 450 ppm. Under the IPCC IS92a scenario, Southern Ocean wintertime aragonite undersaturation is projected to occur by the year 2030 and no later than 2038. Some prominent calcifying plankton, in particular the Pteropod species Limacina helicina, have important veliger larval development during winter and will have to experience detrimental carbonate conditions much earlier than previously thought, with possible deleterious flow-on impacts for the wider Southern Ocean marine ecosystem. Our results highlight the critical importance of understanding seasonal carbon dynamics within all calcifying marine ecosystems such as continental shelves and coral reefs, because natural variability may potentially hasten the onset of future ocean acidification.

  20. Bioavailable iron in the Southern Ocean: the significance of the iceberg conveyor belt.

    PubMed

    Raiswell, Rob; Benning, Liane G; Tranter, Martyn; Tulaczyk, Slawek

    2008-05-30

    Productivity in the Southern Oceans is iron-limited, and the supply of iron dissolved from aeolian dust is believed to be the main source from outside the marine reservoir. Glacial sediment sources of iron have rarely been considered, as the iron has been assumed to be inert and non-bioavailable. This study demonstrates the presence of potentially bioavailable Fe as ferrihydrite and goethite in nanoparticulate clusters, in sediments collected from icebergs in the Southern Ocean and glaciers on the Antarctic landmass. Nanoparticles in ice can be transported by icebergs away from coastal regions in the Southern Ocean, enabling melting to release bioavailable Fe to the open ocean. The abundance of nanoparticulate iron has been measured by an ascorbate extraction. This data indicates that the fluxes of bioavailable iron supplied to the Southern Ocean from aeolian dust (0.01-0.13 Tg yr(-1)) and icebergs (0.06-0.12 Tg yr(-1)) are comparable. Increases in iceberg production thus have the capacity to increase productivity and this newly identified negative feedback may help to mitigate fossil fuel emissions.

  1. Anthropogenic carbon dioxide transport in the Southern Ocean driven by Ekman flow.

    PubMed

    Ito, T; Woloszyn, M; Mazloff, M

    2010-01-07

    The Southern Ocean, with its large surface area and vigorous overturning circulation, is potentially a substantial sink of anthropogenic CO(2) (refs 1-4). Despite its importance, the mechanism and pathways of anthropogenic CO(2) uptake and transport are poorly understood. Regulation of the Southern Ocean carbon sink by the wind-driven Ekman flow, mesoscale eddies and their interaction is under debate. Here we use a high-resolution ocean circulation and carbon cycle model to address the mechanisms controlling the Southern Ocean sink of anthropogenic CO(2). The focus of our study is on the intra-annual variability in anthropogenic CO(2) over a two-year time period. We show that the pattern of carbon uptake is correlated with the oceanic vertical exchange. Zonally integrated carbon uptake peaks at the Antarctic polar front. The carbon is then advected away from the uptake regions by the circulation of the Southern Ocean, which is controlled by the interplay among Ekman flow, ocean eddies and subduction of water masses. Although lateral carbon fluxes are locally dominated by the imprint of mesoscale eddies, the Ekman transport is the primary mechanism for the zonally integrated, cross-frontal transport of anthropogenic CO(2). Intra-annual variability of the cross-frontal transport is dominated by the Ekman flow with little compensation from eddies. A budget analysis in the density coordinate highlights the importance of wind-driven transport across the polar front and subduction at the subtropical front. Our results suggest intimate connections between oceanic carbon uptake and climate variability through the temporal variability of Ekman transport.

  2. 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

  3. 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

  4. IMOS: How seals are changing the way we monitor the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Harcourt, R.; McMahon, C.; Jonsen, I.; Goldsworthy, S.; Hindell, M.; Hoenner, X.; Thums, M.

    2016-02-01

    IMOS (Integrated Marine Observing System) operates a wide range of ocean observing equipment throughout Australia's coastal waters and also the open oceans. This fully integrated, national system, covers physical, chemical and biological ocean sciences forming the basis for robust and informed study of the worlds oceans. Of particular interest in understanding global climate processes is the Southern Ocean (SO), but studying this remote region is difficult and most observations are collected during the short ice-free summer when the region is accessible. Through Winter and Spring it is extremely difficult to collect biophysical ocean information in the Southern Ocean. The importance of good observations from this region, the home of the Antarctic Circumpolar Current (ACC), the largest current system in the world, which connects water masses from the global ocean basins cannot be over emphasised. IMOS through the Australian Animal Tracking and Monitoring System (AATAMS) has made important inroads into collecting otherwise hard to obtain observations from the SO by using CTD bio-loggers to monitor coastal and oceanic movements of marine animals from the Australian mainland as far south as the Antarctic continent. In particular seals equipped with satellite-linked CTD tags have provided unique temporal and spatial coverage of the Southern Ocean. 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. Over 75,000 temperature and salinity profiles have been collected from 20-140 °E, between the Kerguelen archipelago and Prydz Bay Antarctica. These 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. Here we present an overview of the IMOS database of hydrographic (i

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. Seasonally different carbon flux changes in the Southern Ocean in response to the southern annular mode.

    PubMed

    Hauck, J; Völker, C; Wang, T; Hoppema, M; Losch, M; Wolf-Gladrow, D A

    2013-12-01

    Stratospheric ozone depletion and emission of greenhouse gases lead to a trend of the southern annular mode (SAM) toward its high-index polarity. The positive phase of the SAM is characterized by stronger than usual westerly winds that induce changes in the physical carbon transport. Changes in the natural carbon budget of the upper 100 m of the Southern Ocean in response to a positive SAM phase are explored with a coupled ecosystem-general circulation model and regression analysis. Previously overlooked processes that are important for the upper ocean carbon budget during a positive SAM period are identified, namely, export production and downward transport of carbon north of the polar front (PF) as large as the upwelling in the south. The limiting micronutrient iron is brought into the surface layer by upwelling and stimulates phytoplankton growth and export production but only in summer. This leads to a drawdown of carbon and less summertime outgassing (or more uptake) of natural CO2. In winter, biological mechanisms are inactive, and the surface ocean equilibrates with the atmosphere by releasing CO2. In the annual mean, the upper ocean region south of the PF loses more carbon by additional export production than by the release of CO2 into the atmosphere, highlighting the role of the biological carbon pump in response to a positive SAM event.

  10. Geochemical signatures of the oceanic complexes in southern Central America

    NASA Astrophysics Data System (ADS)

    Gazel, E.; Herzberg, C. T.; Carr, M. J.; Denyer, P.

    2006-12-01

    The Pacific coast of Costa Rica and western Panama is famous for wide occurrence of oceanic crust that represent fragmentary and disrupted Jurassic to Miocene sequences with a very complicated geological and geotectonic histories. In Northern Costa Rica, the Santa Elena Nappe of ultramafic and mafic associations overthrusts the Santa Rosa Accretionary Complex. The Nicoya Complex represents pre-Campanian Caribbean Large Igneous Province (CLIP) segments that crop out in the Nicoya Peninsula and the basement of the Herradura Block. The Tortugal Komatiitic-like Suite represents an accreted seamount section. The Tulin Formation (Maastrichtian to Lower Eocene) forms the main edifice of an accreted oceanic island of the Herradura Block. The Quepos Block was formed by the accretion of a late Cretaceous-Paleocene seamount. In the Osa and Burica peninsulas, Caño Island and Golfito area, a series of Upper Cretaceous to Eocene accreted CLIP and seamount blocks crop out. In western Panama, the oceanic rocks range from Upper Cretaceous to Miocene and their geochemistry show ocean island and CLIP signatures. These oceanic complexes are result of accretionary processes rather than tectonic erosion, even though this last process is currently active in the Middle American Trench. The mafic and ultramafic associations of Santa Elena Nappe and Murcielago Islands represent a supra-subduction complex with a subduction modified NMORB source. The Nicoya Complex, Herradura Basement, and CLIP rocks from Osa, Golfito, Burica and W Panamá were probably formed from high-degree melts of a NMORB source modified by the Galapagos hot-spot plume. The presence of rocks with an ocean island signature from Upper Cretaceous to Lower Miocene suggests the continuous arrivals of Galapagos hot-spot seamount tracks. Mantle reservoirs of the CLIP rocks and ocean islands trend to HIMU (high U/Pb), while Santa Elena rocks trend toward depleted reservoirs (DM). CLIP signature is characterized by high 206Pb

  11. 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

  12. Southern Ocean coccolithophore biogeography - controlling factors and implications for global biogeochemical cycles

    NASA Astrophysics Data System (ADS)

    Nissen, Cara; Vogt, Meike; Münnich, Matthias; Gruber, Nicolas

    2017-04-01

    Southern Ocean phytoplankton biogeography is important for the biogeochemical cycling of carbon, silicate, and the transport of macronutrients to lower latitudes. With the discovery of the "Great Calcite Belt" (GBC), revealing an unexpectedly high prevalence of calcifying phytoplankton in the subtropical frontal region between 40-55°S, the relative importance of Southern Ocean coccolithophores for phytoplankton biomass, net primary productivity and the carbon cycle need to be revisited. Using a regional high-resolution model with an embedded ecosystem module (ROMS-BEC) for the Southern Ocean (24-78°S) that has been extended to include an explicit representation of coccolithophores, we assess the environmental drivers of Southern Ocean coccolithophore biogeography over the course of the growing season. We thereby focus on biotic interactions and the relative importance of top-down (grazing) versus bottom-up factors (light, nutrient, temperature) controlling growth and abundance. In our simulation, coccolithophores are an important member of the Southern Ocean phytoplankton community, contributing 13% to annually integrated net primary productivity south of 30°S. We estimate the integrated annual calcification rate to account for 40% of the satellite derived global estimate. Modeled coccolithophore biomass is highest in February and March in a latitudinal band between 40-55°S, when diatoms become heavily silicate limited. This region is characterized by a number of divergent fronts with a low Si:Fe ratio of waters supplied to the mixed layer, supporting an increased growth of coccolithophores at the expense of diatoms. We find top down controls to be the major control on the relative abundance of diatoms and coccolithophores in the Southern Ocean. We perform iron and silicate fertilization experiments to assess the effects of changed nutrient availability on coccolithophore abundance in the GCB. We find that changes in nutrient stoichiometry significantly alter

  13. 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.

  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, 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 ...

  16. 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 ...

  17. 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 ...

  18. 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 ...

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

    NASA Astrophysics Data System (ADS)

    Wang, Gang; Dommenget, Dietmar

    2016-09-01

    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.

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. Antarctic climate, Southern Ocean circulation patterns, and deep water formation during the Eocene

    NASA Astrophysics Data System (ADS)

    Huck, Claire E.; van de Flierdt, Tina; Bohaty, Steven M.; Hammond, Samantha J.

    2017-07-01

    We assess early-to-middle Eocene seawater neodymium (Nd) isotope records from seven Southern Ocean deep-sea drill sites to evaluate the role of Southern Ocean circulation in long-term Cenozoic climate change. Our study sites are strategically located on either side of the Tasman Gateway and are positioned at a range of shallow (<500 m) to intermediate/deep ( 1000-2500 m) paleowater depths. Unradiogenic seawater Nd isotopic compositions, reconstructed from fish teeth at intermediate/deep Indian Ocean pelagic sites (Ocean Drilling Program (ODP) Sites 738 and 757 and Deep Sea Drilling Project (DSDP) Site 264), indicate a dominant Southern Ocean-sourced contribution to regional deep waters (ɛNd(t) = -9.3 ± 1.5). IODP Site U1356 off the coast of Adélie Land, a locus of modern-day Antarctic Bottom Water production, is identified as a site of persistent deep water formation from the early Eocene to the Oligocene. East of the Tasman Gateway an additional local source of intermediate/deep water formation is inferred at ODP Site 277 in the SW Pacific Ocean (ɛNd(t) = -8.7 ± 1.5). Antarctic-proximal shelf sites (ODP Site 1171 and Site U1356) reveal a pronounced erosional event between 49 and 48 Ma, manifested by 2 ɛNd unit negative excursions in seawater chemistry toward the composition of bulk sediments at these sites. This erosional event coincides with the termination of peak global warmth following the Early Eocene Climatic Optimum and is associated with documented cooling across the study region and increased export of Antarctic deep waters, highlighting the complexity and importance of Southern Ocean circulation in the greenhouse climate of the Eocene.

  5. 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.

  6. 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

  7. 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.

  8. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Fogwill, C. J.; Golledge, N. R.; Menviel, L.; Carter, L.; England, M. H.; Cortese, G.; Levy, R. H.

    2014-12-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise - `meltwater pulses' - took place. Although the timing and magnitude of these events have become better-constrained, a causal link between ocean stratification, the meltwater pulses, and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  9. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning

    NASA Astrophysics Data System (ADS)

    Golledge, N. R.; Menviel, L.; Carter, L.; Fogwill, C. J.; England, M. H.; Cortese, G.; Levy, R. H.

    2014-09-01

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise—meltwater pulses—took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  10. DNA barcoding highlights a cryptic species of grenadier Macrourus in the Southern Ocean.

    PubMed

    Smith, P J; Steinke, D; McMillan, P J; Stewart, A L; McVeagh, S M; Diaz de Astarloa, J M; Welsford, D; Ward, R D

    2011-01-01

    Although three species of the genus Macrourus are recognized in the Southern Ocean, DNA sequencing of the mitochondrial COI gene revealed four well-supported clades. These barcode data suggest the presence of an undescribed species, a conclusion supported by meristic and morphometric examination of specimens.

  11. Aurora Australis over the southern Indian ocean view taken by the Expedition 29 crew

    NASA Image and Video Library

    2011-09-17

    ISS029-E-005904 (17 Sept. 2011) --- This is one of a series of night time images photographed by one of the Expedition 29 crew members from the International Space Station. It features Aurora Australis over the southern Indian ocean. Nadir coordinates are 50.16 south latitude and 48.11 degrees east longitude.

  12. Southern Ocean deep-sea biodiversity—From patterns to processes

    NASA Astrophysics Data System (ADS)

    Brandt, Angelika; Ebbe, Brigitte

    2009-09-01

    The Southern Ocean is characterized by a narrow and deep shelf, an almost isothermal water column and a large area of deep sea surrounding Antarctica. However, knowledge of the deep-sea faunal composition, particularly in the Southern Ocean, is still scarce in comparison with shelf and upper slope environment. For that reason a deep-sea project was devoted to investigate this little-known area of the Southern Ocean. ANDEEP (ANtarctic benthic DEEP-sea biodiversity: colonisation history and recent community patterns) took place in 2002-2005 and provided first insights into the biodiversity and biogeography of Southern Ocean benthic animals from meio- to megafauna. The results with the very general patterns are outlined here. Based on the knowledge on biodiversity patterns gained through ANDEEP, a follow-up project, ANDEEP-SYSTCO (SYSTem COupling), was established in the international polar year in order to investigate the processes driving the biodiversity pattern observed. This expedition took place in 2007/2008 and only preliminary data can be presented at this stage given that the material was available for only a couple of months since the return of R.V. Polarstern. Some key results identified after the SYSTCO expedition are presented.

  13. The net effect of ultraviolet radiation on atmospheric dimethylsulphide over the Southern Indian Ocean.

    PubMed

    Kniveton, Dominic R; Todd, Martin C; Sciare, Jean; Mihalopoulos, Nikos

    2005-01-15

    Dimethylsulphide (DMS) in the atmosphere may play an important role in the climate system. This study shows an inverse relationship between ultraviolet extremes and atmospheric DMS, independent of changes in wind speed, sea-surface temperature and photosynthetically active radiation, as measured at Amsterdam Island in the Southern Indian Ocean.

  14. Accumulation status of persistent organochlorines in albatrosses from the North Pacific and the Southern Ocean.

    PubMed

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

    2001-01-01

    Current status of contamination by persistent organochlorines (OCs) such as polychlorinated biphenyles (PCBs), dichlorodiphenyl trichloroethane and its metabolites (DDTs), isomers of hexachlorocyclohexane (HCHs), hexachlorobenzene (HCB) and chlordane compounds (CHLs) were examined in 61 individuals belonging to eight albatross species collected from the North Pacific and the Southern Ocean. Generally high OC concentrations were found in albatrosses from the North Pacific than those from the Southern Oceans. Black-footed albatrosses had noticeably high PCBs and DDTs concentrations with mean values of 92 and 33 micrograms/g wet weight in subcutaneous fat, respectively. Among the other OCs, concentration of CHLs was higher than that of HCB in North Pacific albatrosses. HCHs accumulation was the lowest among all the OCs analyzed. Species-specific differences were observed for HCB, CHLs and DDTs in some species in the Southern Ocean. No significant difference of gender and age-related accumulation was observed in total OCs. However, PCB concentrations were higher in mature birds than those from immature ones in the Southern Ocean. Species-specific accumulation patterns of OCs in albatrosses were closely related with their feeding, migration, age and geographical ranges.

  15. Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning.

    PubMed

    Golledge, N R; Menviel, L; Carter, L; Fogwill, C J; England, M H; Cortese, G; Levy, R H

    2014-09-29

    During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise--meltwater pulses--took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.

  16. Southern Ocean Surface Temperature and Sea Ice Fields during the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Esper, O.; Gersonde, R.; Lohmann, G.

    2014-12-01

    Diatom assemblages preserved in 18 sediment cores recovered in the eastern Indian, Atlantic and Pacific sectors of the Southern Ocean are used for the reconstruction of the variability of summer sea surface temperature (SSST) and sea ice concentration during the Last Interglacial (LIG) or Marine Isotope Stage 5 (MIS 5). The large coverage of the core sites allows for reconstructions on latitudinal and longitudinal transects across the Southern Ocean and thus for the comparison of the environmental signal evolution in different sedimentary basins of the Southern Ocean. Such information is crucial for the understanding of climate signal propagation in the Southern Ocean and on inter-hemispheric scale. The quantitative temperature and sea ice records are derived with newly established diatom-based transfer functions at millennial to centennial resolution. Stratigraphic age assignment relies on a combination of oxygen isotope stratigraphy, biostratigraphy, core-core correlation using physical, geochemical and microfossil abundance pattern together with a tuning of sediment core signals with climate records in Antarctic ice cores. All records display a rapid transition from glacial (MIS 6) to MIS 5 conditions to reach maximum temperatures in the latest MIS 6/MIS 5 transition (Termination II) and the early LIG attributed to MIS 5.5. The amplitude of the SSST change is up to 5°C, with generally smaller values in the Pacific sector. During this period Southern Ocean temperature may exceed modern surface temperatures by up to 3°C and the winter sea ice edge is located south of the modern ice edge. Higher resolution cores display short-term temperature rebounds during the Termination II warming. Such cold rebounds are not discerned in the ice core records. The Southern Ocean warming could be triggered by precessional changes influencing high latitude summer insolation and potentially be accelerated by feedback mechanisms such as the reduction of surface albedo (sea ice

  17. Southern Ocean surface temperature and sea ice fields during the Last Interglacial

    NASA Astrophysics Data System (ADS)

    Esper, Oliver; Gersonde, Rainer

    2013-04-01

    Diatom assemblages preserved in 16 sediment cores recovered in the eastern Indian, Atlantic and Pacific sectors of the Southern Ocean are used for the reconstruction of the variability of summer sea surface temperature (SSST) and sea ice concentration during the Last Interglacial (LIG) or Marine Isotope Stage 5 (MIS 5). The large coverage of the core sites allows for reconstructions on latitudinal and longitudinal transects across the Southern Ocean and thus for the comparison of the environmental signal evolution in different sedimentary basins of the Southern Ocean. Such information is crucial for the understanding of climate signal propagation in the Southern Ocean and on inter-hemispheric scale. The quantitative temperature and sea ice records are derived with newly established diatom-based transfer functions at millennial to centennial resolution. Stratigraphic age assignment relies on a combination of oxygen isotope stratigraphy, biostratigraphy, core-core correlation using physical, geochemical and microfossil abundance pattern together with a tuning of sediment core signals with climate records in Antarctic ice cores. All records display a rapid transition from glacial (MIS 6) to MIS 5 conditions to reach maximum temperatures in the latest MIS 6/MIS 5 transition (Termination II) and the early LIG attributed to MIS 5.5. The amplitude of the SSST change is up to 5°C, with generally smaller values in the Pacific sector. During this period Southern Ocean temperature may exceed modern surface temperatures by up to 3°C and the winter sea ice edge is located south of the modern ice edge. Higher resolution cores display short-term temperature rebounds during the Termination II warming. Such cold rebounds are not discerned in the ice core records. The Southern Ocean warming could be triggered by precessional changes influencing high latitude summer insolation and potentially be accelerated by feedback mechanisms such as the reduction of surface albedo (sea ice

  18. 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

  19. 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.

  20. Temporal changes in ventilation and the carbonate system in the Atlantic sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Tanhua, Toste; Hoppema, Mario; Jones, Elizabeth M.; Stöven, Tim; Hauck, Judith; Dávila, Melchor González; Santana-Casiano, Magdalena; Álvarez, Marta; Strass, Volker H.

    2017-04-01

    The Southern Ocean is the most important area of anthropogenic carbon (Cant) uptake in the world ocean, only rivalled in importance by the North Atlantic Ocean. Significant variability on decadal time-scales in the uptake of Cant in the Southern Ocean has been observed and modelled, likely with consequences for the interior ocean storage of Cant in the region, and implications for the global carbon budget. Here we use eight cruises between 1973 and 2012 to assess decadal variability in Cant storage rates in the southeast Atlantic sector of the Southern Ocean. For this we employed the extended multiple linear regression (eMLR) method. We relate variability in DIC (dissolved inorganic carbon) storage, which is assumed to equal anthropogenic carbon storage, to changes in ventilation as observed from repeat measurements of transient tracers. Within the Antarctic Intermediate Water (AAIW) layer, which is the dominant transport conduit for Cant into the interior ocean, moderate Cant storage rates were found without any clear temporal trend. In Subantarctic Mode Water (SAMW), a less dense water mass found north of the Subantarctic Front and above AAIW, high storage rates of Cant were observed up to about 2005 but lower rates in more recent times. The transient tracer data suggest a significant speed-up of ventilation in the summer warmed upper part of AAIW between 1998 and 2012, which is consistent with the high storage rate of Cant. A shift of more northern Cant storage to more southern storage in near surface waters was detected in the early 2000s. Beneath the AAIW the eMLR method as applied here did not detect significant storage of Cant. However, the presence of the transient tracer CFC-12 all through the water column suggests that some Cant should be present, but at concentrations not reliably quantifiable. The observed temporal variability in the interior ocean seems at a first glance to be out of phase with observed surface ocean Cant fluxes, but this can be

  1. Accelerated warming of the Southern Ocean and its impacts on the hydrological cycle and sea ice.

    PubMed

    Liu, Jiping; Curry, Judith A

    2010-08-24

    The observed sea surface temperature in the Southern Ocean shows a substantial warming trend for the second half of the 20th century. Associated with the warming, there has been an enhanced atmospheric hydrological cycle in the Southern Ocean that results in an increase of the Antarctic sea ice for the past three decades through the reduced upward ocean heat transport and increased snowfall. The simulated sea surface temperature variability from two global coupled climate models for the second half of the 20th century is dominated by natural internal variability associated with the Antarctic Oscillation, suggesting that the models' internal variability is too strong, leading to a response to anthropogenic forcing that is too weak. With increased loading of greenhouse gases in the atmosphere through the 21st century, the models show an accelerated warming in the Southern Ocean, and indicate that anthropogenic forcing exceeds natural internal variability. The increased heating from below (ocean) and above (atmosphere) and increased liquid precipitation associated with the enhanced hydrological cycle results in a projected decline of the Antarctic sea ice.

  2. 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

  3. 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.

  4. Trends and variability of the atmosphere-ocean turbulent heat flux in the extratropical Southern Hemisphere.

    PubMed

    Herman, Agnieszka

    2015-10-09

    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.

  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. 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.

  7. 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.

  8. 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.

  9. Air-sea carbon dioxide exchange in the Southern Ocean and Antarctic Sea ice zone

    NASA Astrophysics Data System (ADS)

    Butterworth, Brian J.

    The Southern Ocean is an important part of the global carbon cycle, responsible for roughly half of the carbon dioxide (CO2) absorbed by the global ocean. The air-sea CO2 flux (Fc) can be expressed as the product of the water-air CO2 partial pressure difference (DeltapCO2) and the gas transfer velocity ( k), an exchange coefficient which represents the efficiency of gas exchange. Generally, Fc is negative (a sink) throughout the Southern Ocean and Antarctic sea ice zone (SIZ), but uncertainty in k has made it difficult to develop an accurate regional carbon budget. Constraining the functional dependence of k on wind speed in open water environments, and quantifying the effect of sea ice on k, will reduce uncertainty in the estimated contribution of the Southern Ocean and Antarctic SIZ to the global carbon cycle. To investigate Fc in the Southern Ocean, a ruggedized, unattended, closed-path eddy covariance (EC) system was deployed on the Antarctic research vessel Nathaniel B. Palmer for nine cruises during 18 months from January 2013 to June 2014 in the Southern Ocean and coastal Antarctica. The methods are described and results are shown for two cruises chosen for their latitudinal range, inclusion of open water and sea ice cover, and large DeltapCO2. The results indicated that ship-based unattended EC measurements in high latitudes are feasible, and recommendations for deployments in such environments were provided. Measurements of Fc and DeltapCO2 were used to compute k. The open water data showed a quadratic relationship between k (cm hr-1) and the neutral 10-m wind speed (U10n, m s -1), k=0.245 U10n 2+1.3, in close agreement with tracer-based results and much lower than previous EC studies. In the SIZ, it was found that k decreased in proportion to sea ice cover. This contrasted findings of enhanced Fc in the SIZ by previous open-path EC campaigns. Using the NBP results a net annual Southern Ocean (ocean south of 30°S) carbon flux of -1.1 PgC yr-1 was

  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. 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.

  12. 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.

  13. 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.

  14. 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.

  15. Interhemispheric gradient of atmospheric radiocarbon reveals natural variability of Southern Ocean winds

    NASA Astrophysics Data System (ADS)

    Rodgers, K. B.; Fletcher, S. E. M.; Bianchi, D.; Beaulieu, C.; Galbraith, E. D.; Gnanadesikan, A.; Hogg, A. G.; Iudicone, D.; Lintner, B.; Naegler, T.; Reimer, P. J.; Sarmiento, J. L.; Slater, R. D.

    2011-01-01

    Tree ring Δ14C data (Reimer et al., 2004; McCormac et al., 2004) indicate that atmospheric Δ14C varied on multi-decadal to centennial timescales, in both hemispheres, over the pre-industrial period AD 950-1830. Although the Northern and Southern Hemispheric Δ14C records display similar variability, it is difficult from these data alone to distinguish between variations driven by 14CO2 production in the upper atmosphere (Stuiver, 1980) and exchanges between carbon reservoirs (Siegenthaler, 1980). Here we consider rather the Interhemispheric Gradient in atmospheric Δ14C as revealing of the background pre-bomb air-sea Disequilbrium Flux between 14CO2 and CO2. As the global maximum of the Disequilibrium Flux is squarely centered in the open ocean regions of the Southern Ocean, relatively modest perturbations to the winds over this region drive significant perturbations to the Interhemispheric Gradient. The analysis presented here implies that changes to Southern Ocean windspeeds are likely a main driver of the observed variability in the Interhemispheric Gradient over 950-1830, and further, that this variability may be larger than the Southern Ocean wind trends that have been reported for recent decades (notably 1980-2004). This interpretation also implies a significant weakening of the winds over the Southern Ocean within a few decades of AD 1375, associated with the transition between the Medieval Climate Anomaly and the Little Ice Age. The driving forces that could have produced such a shift in the winds remain unkown.

  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. Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing

    NASA Astrophysics Data System (ADS)

    Morrison, A.; Hogg, A.; Ward, M.

    2011-12-01

    The southern limb of the ocean's meridional overturning circulation plays a key role in the Earth's response to climate change. The rise in atmospheric CO2 during glacial-interglacial transitions has been attributed to outgassing of enhanced upwelling water masses in the Southern Ocean. However a dynamical understanding of the physical mechanisms driving the change in overturning is lacking. Previous modelling studies of the Southern Ocean have focused on the effect of wind stress forcing on the overturning, while largely neglecting the response of the upper overturning cell to changes in surface buoyancy forcing. Using a series of eddy-permitting, idealised simulations of the Southern Ocean, we show that surface buoyancy forcing in the mid-latitudes is likely to play a significant role in setting the strength of the overturning circulation. Air-sea fluxes of heat and precipitation over the Antarctic Circumpolar Current region act to convert dense upwelled water masses into lighter waters at the surface. Additional fluxes of heat or freshwater thereby facilitate the meridional overturning up to a theoretical limit derived from Ekman transport. The sensitivity of the overturning to surface buoyancy forcing is strongly dependent on the relative locations of the wind stress profile, buoyancy forcing and upwelling region. The idealised model results provide support for the hypothesis that changes in upwelling during deglaciations may have been driven by changes in heat and freshwater fluxes, instead of, or in addition to, changes in wind stress. Morrison, A. K., A. M. Hogg, and M. L. Ward (2011), Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing, Geophys. Res. Lett., 38, L14602, doi:10.1029/2011GL048031.

  18. Seasonal southern hemisphere multi-variable reflection of the southern annular mode in atmosphere and ocean reanalyses

    NASA Astrophysics Data System (ADS)

    Zhang, Zhaoru; Uotila, Petteri; Stössel, Achim; Vihma, Timo; Liu, Hailong; Zhong, Yisen

    2017-04-01

    Variations of southern hemisphere (SH) climate variables are often linked to the southern annular mode (SAM) variability. We examined such linkage by seasons using state-of-the-art atmosphere and ocean/sea-ice reanalyses. The associated SAM related anomaly (SRA) fields of the climate variables, denoting anomalies corresponding to the same variation in SAM, are overall consistent across the reanalyses. Among the atmospheric products, 20CRV2 differs from ERA-interim and CFSR in the sea-level pressure SRAs over the Amundsen Sea, resulting in less warming over the Antarctic Peninsula. Among the ocean reanalyses, ORAP5 and C-GLORS exhibit the largest consistency. The major difference between them and the lower-resolution CFSR and SODA reanalyses is deeper penetration of anomalous meridional currents. Compared to the other ocean reanalyses, CFSR exhibits stronger and spatially more coherent surface-current SRAs, resulting in greater SRAs of sea-ice motion and ice thickness along the ice edges. The SRAs of sensible and total surface heat fluxes are reduced in CFSR due to ocean-atmosphere coupling. Significant sea-ice concentration SRAs are present on the west side of peninsulas along the east Antarctica coast in spring and winter, most notably in ORAP5 and C-GLORS, implying changes in new-ice production and shelf-water formation. Most atmosphere and ocean variables manifest an annular SRA pattern in summer and a non-annular pattern in the other seasons, with a wavenumber-3 structure strongest in autumn and weakest in summer. The wavenumber-3 structure should be related to the zonal wave three pattern of the SH circulation, the relation of which to SAM needs further exploration.

  19. SOFeX: Southern Ocean Iron Experiments. An Overview of the Biological Responses.

    NASA Astrophysics Data System (ADS)

    Barber, R. T.; Sofex Group,.

    2002-12-01

    A major intellectual advance in biological and chemical oceanography in the second half of the 20th century was John Martin's Iron Hypothesis that, for a few large oceanic regions, particularly the Southern Ocean, a shortage in the supply of the micronutrient iron limits the uptake of atmospheric carbon dioxide by phytoplankton primary productivity in the surface ocean. While iron regulation of primary productivity provides the cornerstone of our understanding of the role of iron in open ocean food webs, it is now clear that iron availability also affects a wide variety of processes in bacteria, protozoa and microalgae. SOFeX provided a unique opportunity to determine the biological response to iron addition in two distinct Southern Ocean regions. This presentation reviews highlights of the biological results of the two iron enrichments and compares them with earlier equatorial Pacific and Southern Ocean iron enrichment experiments. It includes results of iron enrichment on size-fractionated quantum yield, primary productivity, bacterial processes, pigment composition and nutrient uptake. The SOFeX results show that the community response to iron enrichment in the Subantarctic Zone around 56 deg S was fundamentally different from the response of the community in the high silicon and cool (- 0.5 deg C) waters south of the Southern Boundary of the Antarctic Circumpolar Current, at 66 deg S. While the Subantarctic community response was qualitatively similar to that of the equatorial Pacific community in IronEx-2 in 1995, the response at 66 deg S was unlike that of any previous iron enrichment experiment.

  20. 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

  1. Recent Southern Ocean surface cooling induced by sea-ice freshwater flux changes

    NASA Astrophysics Data System (ADS)

    Haumann, F. Alexander; Münnich, Matthias; Gruber, Nicolas

    2017-04-01

    Despite global warming, large areas of the Southern Ocean surface waters between the sea-ice edge and the Subantarctic Front have been cooling over recent decades. Yet, most global climate models simulate a warming of this region over this period. Here, we investigate the potential sources of the surface cooling by forcing a newly developed regional configuration of the Regional Ocean Modeling System (ROMS) for the Southern Ocean with atmospheric reanalysis data and with recent observation-based estimates of surface fluxes from sea ice and land ice for the period 1982 to 2008. We perform factorial sensitivity experiments in which we perturb either the surface freshwater fluxes or the surface wind stress according to the observed changes. We find that most of the surface cooling could be explained by increased northward freshwater transport by sea ice that freshens the open-ocean around the sea-ice edge in the model. The freshening increases the surface density stratification between the sea-ice edge and the Subantarctic Front that reduces mixing of warmer deep waters into the surface layer in winter. As a result, the surface ocean cools and the subsurface ocean warms significantly, especially in the Pacific sector where the largest sea-ice changes occurred. The spatial pattern of these simulated temperature changes agrees well with the satellite-observed trends and trends derived from ocean in-situ data, suggesting that the observed surface cooling occurs primarily due to an increased sea-ice freshwater flux. In contrast, the surface temperature weakly increases in response to the increased surface wind stress over this period. Overall, we find opposing tendencies induced by the surface wind stress changes and freshwater flux changes in the ocean hydrography. We conclude that the upwelling of deep waters in the Southern Ocean is highly sensitive to the freshwater transport to the sea-ice edge and that this process is a major driver of the observed recent cooling in

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. Anthropogenic Carbon Uptake in the Southern Ocean: Investigating the Spread Across Climate Models

    NASA Astrophysics Data System (ADS)

    Dufour, C.; de Souza, G. F.; Frenger, I.; Morrison, A. K.; Sarmiento, J. L.

    2016-02-01

    Model- and data-based analyses indicate that up to 50% of the anthropogenic CO2 ab-sorbed by the ocean is taken up in the Southern Ocean south of 30 °S. Recent syntheses basedon CMIP5 models show that much of these models' spread in anthropogenic CO2 uptake isthe result of disagreement within the Southern Ocean. The reasons for this disagreementremain unclear. In this study, we hypothesize that the disagreement between CMIP5 modelsis mainly due to ocean circulation, and more speci cally to the upwelling of deep waters un-contaminated with anthropogenic CO2 at the Antarctic Divergence. To test this hypothesis,we divided the Southern Ocean into four provinces, determined by the underlying mechanismof anthropogenic CO2 uptake. The "upwelling" province is dominated by the upwelling ofdeep water uncontaminated with anthropogenic CO2; the "WBC" province is dominated bythe cooling of subtropical waters transported southward by Western Boundary Currents; the"mixed layer" province is dominated by a combination of the above two mechanisms andcoincides with winter deep mixed layers; finally the "convection" province is dominated byopen-ocean deep convection associated with polynyas. We explored the diff erent provincesacross a suite of climate models that consists of (1) a subset of CMIP5 models and (2) threeGFDL climate models which only diff er by the resolution of their ocean (1° , 0.25° and 0.1 °).The anthropogenic CO2 is calculated from the diff erence between an idealized climate changesimulation and a preindustrial control simulation. For each province, we compared the an-thropogenic CO2 sink across the models. We found that the upwelling province consistentlyshows the most intense sink across the models, and it is also where models tend to disagree themost. We also found that increasing resolution decreases the uptake of anthropogenic CO2 inthe upwelling province.

  7. Teleconnection between the North Indian Ocean high swell events and meteorological conditions over the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Remya, P. G.; Vishnu, S.; Praveen Kumar, B.; Balakrishnan Nair, T. M.; Rohith, B.

    2016-10-01

    The link between North Indian Ocean (NIO) high swell events and the meteorological conditions over the Southern Indian Ocean (SIO) is explored in this article, using a combination of in situ measurements and model simulations for the year 2005. High waves, without any sign in the local winds, sometimes cause severe flooding events along the south-west coast of India, locally known as the Kallakkadal events and cause major societal problems along the coasts. In situ observations report 10 high swell events in NIO during 2005. Our study confirms that these events are caused by the swells propagating from south of 30°S. In all cases, 3-5 days prior to the high swell events in NIO, we observed a severe low pressure system, called the Cut-Off Low (COL) in the Southern Ocean. These COLs are quasistationary in nature, providing strong (˜25 ms-1) and long duration (˜3 days) surface winds over a large fetch; essential conditions for the generation of long-period swells. The intense equator ward winds associated with COLs in the SIO trigger the generation of high waves, which propagate to NIO as swells. Furthermore, these swells cause high wave activity and sometimes Kallakkadal events along the NIO coastal regions, depending on the local topography, angle of incidence, and tidal conditions. Our study shows that such natural hazards along the NIO coasts can be forecasted at least 2 days in advance if the meteorological conditions of the SIO are properly monitored.

  8. Observed southern upper-ocean warming over 2005-2014 and associated mechanisms

    NASA Astrophysics Data System (ADS)

    Llovel, William; Terray, Laurent

    2016-12-01

    The climate system is gaining heat owing to increasing concentration of greenhouse gases due to human activities. As the world’s oceans are the dominant reservoir of heat in the climate system, an accurate estimation of the ocean heat content change is essential to quantify the Earth’s energy budget and global mean sea level rise. Based on the mean estimate of the three Argo gridded products considered, we provide a decadal ocean heat content estimate (over 2005-2014), down to 2000 m, of 0.76 ± 0.14 W m-2 and its spatial pattern since 2005 with unprecedented data coverage. We find that the southern hemisphere explains 90% of the net ocean heat uptake located around 40°S mainly for the Indian and Pacific oceans that corresponds to the center of their subtropical gyres. We find that this rapid upper ocean warming is linked to a poleward shift of mean wind stress curl enhancing Ekman pumping for the 45°S-60°S band. Therefore, the increase of Ekman pumping steepens the isopycnal surface and can enhance heat penetration into the deeper layers of the ocean. We also highlight a relative consistency between the year-to-year net top-of-the-atmosphere flux inferred by satellite measurements and the ocean heating rates (correlation coefficient of 0.53). We conclude that there is no strong evidence of missing energy in the climate system because of remaining large uncertainties in the observing system.

  9. 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

  10. Surface-water iron supplies in the Southern Ocean sustained by deep winter mixing

    NASA Astrophysics Data System (ADS)

    Tagliabue, Alessandro; Sallée, Jean-Baptiste; Bowie, Andrew R.; Lévy, Marina; Swart, Sebastiaan; Boyd, Philip W.

    2014-04-01

    Low levels of iron limit primary productivity across much of the Southern Ocean. At the basin scale, most dissolved iron is supplied to surface waters from subsurface reservoirs, because land inputs are spatially limited. Deep mixing in winter together with year-round diffusion across density surfaces, known as diapycnal diffusion, are the main physical processes that carry iron-laden subsurface waters to the surface. Here, we analyse data on dissolved iron concentrations in the top 1,000 m of the Southern Ocean, taken from all known and available cruises to date, together with hydrographic data to determine the relative importance of deep winter mixing and diapycnal diffusion to dissolved iron fluxes at the basin scale. Using information on the vertical distribution of iron we show that deep winter mixing supplies ten times more iron to the surface ocean each year, on average, than diapycnal diffusion. Biological observations from the sub-Antarctic sector suggest that following the depletion of this wintertime iron pulse, intense iron recycling sustains productivity over the subsequent spring and summer. We conclude that winter mixing and surface-water iron recycling are important drivers of temporal variations in Southern Ocean primary production.

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

    NASA Astrophysics Data System (ADS)

    Phipps, Steven; Fogwill, Christopher; Turney, Christian

    2017-04-01

    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 formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1oC at depth. This warming is accompanied by a Southern Oceanwide "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.

  12. The Seasonal Cycle of Carbon in the Southern Pacific Ocean Observed from Biogeochemical Profiling Floats

    NASA Astrophysics Data System (ADS)

    Sarmiento, J. L.; Gray, A. R.; Johnson, K. S.; Carter, B.; Riser, S.; Talley, L. D.; Williams, N. L.

    2016-02-01

    The Southern Ocean is thought to play an important role in the ocean-atmosphere exchange of carbon dioxide and the uptake of anthropogenic carbon dioxide. However, the total number of observations of the carbonate system in this region is small and heavily biased towards the summer. Here we present 1.5 years of biogeochemical measurements, including pH, oxygen, and nitrate, collected by 11 autonomous profiling floats deployed in the Pacific sector of the Southern Ocean in April 2014. These floats sampled a variety of oceanographic regimes ranging from the seasonally ice-covered zone to the subtropical gyre. Using an algorithm trained with bottle measurements, alkalinity is estimated from salinity, temperature, and oxygen and then used together with the measured pH to calculate total carbon dioxide and pCO2 in the upper 1500 dbar. The seasonal cycle in the biogeochemical quantities is examined, and the factors governing pCO2 in the surface waters are analyzed. The mechanisms driving the seasonal cycle of carbon are further investigated by computing budgets of heat, carbon, and nitrogen in the mixed layer. Comparing the different regimes sampled by the floats demonstrates the complex and variable nature of the carbon cycle in the Southern Ocean.

  13. Controls on air-sea CO2 flux in the Southern Ocean east of Australia

    NASA Astrophysics Data System (ADS)

    Ayers, J.; Strutton, P. G.

    2014-12-01

    The temperate latitudes of the world oceans (~30-50° north and south) are strong sinks for atmospheric CO2 on a mean annual basis. Due to sparse data, the Southern Ocean is the least understood of these CO2 sink regions, with estimates of the annual air-sea CO2 flux varying by as much as 100%, depending upon the calculation method. This work investigates processes regulating air-sea CO2 flux in the Southern Ocean, with a focus on the Pacific sector east of Australia. We quantify the effects of temperature, biological drawdown, and the large-scale general circulation on seawater pCO2 on seasonal and annual timescales, and discuss the balance of these forcings. We expressly consider the impact of the general circulation on the air-sea CO2 flux, which we showed in a previous study to determine the location of the North Pacific carbon sink region. Worldwide, the regions of strong atmospheric CO2 uptake are all located in deep western boundary currents and their extensions, suggesting a larger role for the general circulation in forcing these sinks than is currently acknowledged or understood. Understanding the processes regulating air-sea CO2 flux in the Southern Ocean is critical for predicting how this gas exchange will change in the future.

  14. Longitudinal distributions of dissolved barium, silica and alkalinity in the western and southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Jeandel, C.; Dupré, B.; Lebaron, G.; Monnin, C.; Minster, J.-F.

    1996-01-01

    Dissolved Ba, Si and alkalinity contents are reported for 11 vertical profiles along a longitudinal section in the western Indian and Southern Oceans, sampled during 1985, 1986 and 1987 in the French expedition INDIGO. Barium concentrations increase from 30 nmol/kg at the surface to 100 nmol/kg at depth in the Southern Ocean. North of the Polar Front, Ba values range from 40 nmol/kg at the surface to 120 nmol/kg in the bottom waters. These vertical variations result from mixing of water masses as well as biologically controlled uptake/regeneration processes. By means of a water-mass mixing model, the non-conservative Ba signal was determined and compared to that of silica. The Δ Ba/Δ Si uptake/regeneration molar ratio is 0.15 × 10 -3 in the south and 0.45 × 10 -3 in the north. In the south, curiously, no release of Ba is observed in Circumpolar Deep Waters, whereas Ba appears to be regenerated in the underlying Antarctic Bottom Waters. Thermodynamic calculations show that Ba is somewhat supersaturated with respect to barite in the upper 3000 m of the southern waters. Thus, whereas surface Ba uptake is probably governed by the biological activity, Ba regeneration in deep waters appears to be controlled by saturation. Barium is correlated linearly with alkalinity at each station, but the slopes of the regression line vary by a factor greater than 2 along the section. The variability of the Δ Ba/Δ Alk ratio between the Southern Ocean and the subtropical and tropical areas raises questions about the validity of applying Δ Ba/Δ Alk values established on a global scale to reconstruct paleo-alkalinity distributions in the Southern Ocean.

  15. 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.

  16. 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.

  17. 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.

  18. Atmospheric and upper ocean environments of Southern Ocean polar mesocyclones in the transition season months and associations with teleconnections

    NASA Astrophysics Data System (ADS)

    Claud, Chantal; Carleton, Andrew M.; Duchiron, Bertrand; Terray, Pascal

    2009-12-01

    Over middle and higher latitudes of the Southern Hemisphere, intense mesoscale cyclonic vortices that develop in cold-air outbreaks (cold-air mesocyclones) occur frequently during transition season months. In this study, previously published mesocyclone inventories for March-April and October-November are compared to atmospheric and upper ocean variables pertinent to mesocyclogenesis, as provided by reanalyses. This procedure allows the determination of the large-scale environments favorable for mesocyclone occurrence: low midtropospheric temperatures, greater sea ice extent, and large positive differences in the sea surface temperature minus low-altitude air temperature, the latter coinciding with enhanced low-level winds having a southerly component. We then evaluate the associations between polar mesocyclone formation and dominant patterns of low-frequency variability in the atmospheric circulation: the El Niño-Southern Oscillation (ENSO), the Southern Annular Mode (SAM), and the Trans-Polar Index (TPI). Our results suggest that in spring, the intrahemispheric variability in mesocyclogenesis is dominated by ENSO. In autumn, the influences of ENSO, SAM, and TPI on mesocyclone activity are about equal, although the response differs regionally. Moreover, teleconnections' effects on mesocyclone activity are somewhat reduced compared to that in spring. In both seasons, the phase of the semiannual oscillation modulates the associations with mesocyclones by influencing the latitude of the circumpolar trough and the amount of cyclonic activity over the Southern Ocean. These associations likely result from the displacement of the storm track between opposite phases of a given teleconnection and its position relative to the sea ice edge.

  19. 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

  20. 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

  1. Side effects and accounting aspects of hypothetical large-scale Southern Ocean iron fertilization

    NASA Astrophysics Data System (ADS)

    Oschlies, A.; Koeve, W.; Rickels, W.; Rehdanz, K.

    2010-04-01

    Recent suggestions to slow down the increase in atmospheric carbon dioxide have included ocean fertilization by addition of the micronutrient iron to Southern Ocean surface waters, where a number of natural and artificial iron fertilization experiments have shown that low ambient iron concentrations limit phytoplankton growth. Using a coupled carbon-climate model with the marine biology's response to iron addition calibrated against data from natural iron fertilization experiments, we examine biogeochemical side effects of a hypothetical large-scale Southern Ocean Iron Fertilization (OIF) that need to be considered when attempting to account for possible OIF-induced carbon offsets. In agreement with earlier studies our model simulates an OIF-induced increase in local air-sea CO2 fluxes by about 60 GtC over a 100-year period, which amounts to about 40% of the OIF-induced increase in organic carbon export. Offsetting CO2 return fluxes outside the region and after stopping the fertilization at 1, 7, 10, 50, and 100 years are quantified for a typical accounting period of 100 years. For continuous Southern Ocean iron fertilization, the return flux outside the fertilized area cancels about 8% of the fertilization-induced CO2 air-sea flux within the fertilized area on a 100-yr timescale. This "leakage" effect has a similar radiative impact as the simulated enhancement of marine N2O emissions. Other side effects not yet discussed in terms of accounting schemes include a decrease in Southern Ocean oxygen levels and a simultaneous shrinking of tropical suboxic areas, and accelerated ocean acidification in the entire water column in the Southern Ocean on the expense of reduced globally averaged surface water acidification. A prudent approach to account for the OIF-induced carbon sequestration would account for global air-sea CO2 fluxes rather than for local fluxes into the fertilized area only. However, according to our model, this would underestimate the potential for

  2. Side effects and accounting aspects of hypothetical large-scale Southern Ocean iron fertilization

    NASA Astrophysics Data System (ADS)

    Oschlies, A.; Koeve, W.; Rickels, W.; Rehdanz, K.

    2010-12-01

    Recent suggestions to slow down the increase in atmospheric carbon dioxide have included ocean fertilization by addition of the micronutrient iron to Southern Ocean surface waters, where a number of natural and artificial iron fertilization experiments have shown that low ambient iron concentrations limit phytoplankton growth. Using a coupled carbon-climate model with the marine biology's response to iron addition calibrated against data from natural iron fertilization experiments, we examine biogeochemical side effects of a hypothetical large-scale Southern Ocean Iron Fertilization (OIF) that need to be considered when attempting to account for possible OIF-induced carbon offsets. In agreement with earlier studies our model simulates an OIF-induced increase in local air-sea CO2 fluxes by about 73 GtC over a 100-year period, which amounts to about 48% of the OIF-induced increase in organic carbon export out of the fertilized area. Offsetting CO2 return fluxes outside the region and after stopping the fertilization at 1, 7, 10, 50, and 100 years are quantified for a typical accounting period of 100 years. For continuous Southern Ocean iron fertilization, the CO2 return flux outside the fertilized area cancels about 20% of the fertilization-induced CO2 air-sea flux within the fertilized area on a 100-yr timescale. This "leakage" effect has a radiative impact more than twice as large as the simulated enhancement of marine N2O emissions. Other side effects not yet discussed in terms of accounting schemes include a decrease in Southern Ocean oxygen levels and a simultaneous shrinking of tropical suboxic areas, and accelerated ocean acidification in the entire water column in the Southern Ocean at the expense of reduced globally-averaged surface-water acidification. A prudent approach to account for the OIF-induced carbon sequestration would account for global air-sea CO2 fluxes rather than for local fluxes into the fertilized area only. However, according to our model

  3. 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

  4. Spatial distributions of Southern Ocean mesozooplankton communities have been resilient to long-term surface warming.

    PubMed

    Tarling, Geraint A; Ward, Peter; Thorpe, Sally E

    2017-08-29

    The biogeographic response of oceanic planktonic communities to climatic change has a large influence on the future stability of marine food webs and the functioning of global biogeochemical cycles. Temperature plays a pivotal role in determining the distribution of these communities and ocean warming has the potential to cause major distributional shifts, particularly in polar regions where the thermal envelope is narrow. We considered the impact of long-term ocean warming on the spatial distribution of Southern Ocean mesozooplankton communities through examining plankton abundance in relation to sea surface temperature between two distinct periods, separated by around 60 years. Analyses considered 16 dominant mesozooplankton taxa (in terms of biomass and abundance) in the southwest Atlantic sector of the Southern Ocean, from net samples and in situ temperature records collected during the Discovery Investigations (1926-1938) and contemporary campaigns (1996-2013). Sea surface temperature was found to have increased significantly by 0.74°C between the two eras. The corresponding sea surface temperature at which community abundance peaked was also significantly higher in contemporary times, by 0.98°C. Spatial projections indicated that the geographical location of community peak abundance had remained the same between the two eras despite the poleward advance of sea surface isotherms. If the community had remained within the same thermal envelope as in the 1920s-1930s, community peak abundance would be 500 km further south in the contemporary era. Studies in the northern hemisphere have found that dominant taxa, such as calanoid copepods, have conserved their thermal niches and tracked surface isotherms polewards. The fact that this has not occurred in the Southern Ocean suggests that other selective pressures, particularly food availability and the properties of underlying water masses, place greater constraints on spatial distributions in this region. It

  5. First insights into the biodiversity and biogeography of the Southern Ocean deep sea.

    PubMed

    Brandt, Angelika; Gooday, Andrew J; Brandão, Simone N; Brix, Saskia; Brökeland, Wiebke; Cedhagen, Tomas; Choudhury, Madhumita; Cornelius, Nils; Danis, Bruno; De Mesel, Ilse; Diaz, Robert J; Gillan, David C; Ebbe, Brigitte; Howe, John A; Janussen, Dorte; Kaiser, Stefanie; Linse, Katrin; Malyutina, Marina; Pawlowski, Jan; Raupach, Michael; Vanreusel, Ann

    2007-05-17

    Shallow marine benthic communities around Antarctica show high levels of endemism, gigantism, slow growth, longevity and late maturity, as well as adaptive radiations that have generated considerable biodiversity in some taxa. The deeper parts of the Southern Ocean exhibit some unique environmental features, including a very deep continental shelf and a weakly stratified water column, and are the source for much of the deep water in the world ocean. These features suggest that deep-sea faunas around the Antarctic may be related both to adjacent shelf communities and to those in other oceans. Unlike shallow-water Antarctic benthic communities, however, little is known about life in this vast deep-sea region. Here, we report new data from recent sampling expeditions in the deep Weddell Sea and adjacent areas (748-6,348 m water depth) that reveal high levels of new biodiversity; for example, 674 isopods species, of which 585 were new to science. Bathymetric and biogeographic trends varied between taxa. In groups such as the isopods and polychaetes, slope assemblages included species that have invaded from the shelf. In other taxa, the shelf and slope assemblages were more distinct. Abyssal faunas tended to have stronger links to other oceans, particularly the Atlantic, but mainly in taxa with good dispersal capabilities, such as the Foraminifera. The isopods, ostracods and nematodes, which are poor dispersers, include many species currently known only from the Southern Ocean. Our findings challenge suggestions that deep-sea diversity is depressed in the Southern Ocean and provide a basis for exploring the evolutionary significance of the varied biogeographic patterns observed in this remote environment.

  6. 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.

  7. Evolution of surface and deep water conditions in the Antarctic Southern Ocean across the MPT

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

    The mid-Pleistocene transition (MPT; 1.25-0.7 Myr) marked a fundamental change in the periodicity of the climate cycles, shifting from a 41-kyr to a high-amplitude, asymmetric 100-kyr cycle without any noticeable change in orbital forcing. Hypotheses to explain the MPT involve non-linear responses to orbital forcing, changes in glacial dynamics and internal changes in the carbon cycle. Specifically, a decrease in pCO2 during peak ice age conditions and the associated global cooling has been proposed as one of the possible triggers for the MPT. Previous results have indicated that the Southern Ocean provides a coherent two-part mechanism for the timing and amplitude of the glacial/interglacial pCO2 variations. However, there is still much uncertainty and debate regarding the response of the Antarctic Southern Ocean biogeochemistry to changes invoked for the MPT, and its contribution to the proposed pCO2 variations. Here, we show 1.5 Myr-long records of export production, and planktonic (Neogloboquadrina pachyderma) and benthic (Melonis pompilioides) foraminiferal stable isotopes and trace metals from ODP Site 1094 retrieved from the Atlantic sector of the Antarctic Southern Ocean (53.2°S, 5.1°E, 2807m). While glacial planktonic δ18O increases across the MPT, glacial Mg/Ca-derived SST decrease later, around 700 ka, when glacial atmospheric pCO2 has already dropped. As glacial export production that is crucially related to micronutrients upwelled from the subsurface ocean remains unchanged across the past 1.5 Myr, it seems that cooling of the glacial surface ocean did not significantly alter the stability of the water column. Furthermore, paired measurements of benthic δ18O and Mg/Ca enables the determination of seawater δ18O of the deep ocean, which allows us to estimate changes in the density gradient and the salinity of the deep water.

  8. 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.

  9. 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

  10. 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

    2015-07-23

    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.

  11. 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.

  12. Solubility of iron and other trace elements over the Southern Indian Ocean

    NASA Astrophysics Data System (ADS)

    Heimburger, A.; Losno, R.; Triquet, S.

    2013-03-01

    The fraction of soluble aerosols that is deposited on the open ocean is vital for phytoplankton growth. It is believed that a large proportion of this dissolved fraction is bioavailable for marine biota and thus plays an important role in primary production, especially in HNLC oceanic areas where this production is limited by micronutrient supply. There is still much uncertainty surrounding the solubility of atmospheric particles in global biogeochemical cycles and it is not well understood. In this study, we present the solubilities of seven elements (Al, Ce, Fe, La, Mn, Nd, Ti) in rainwater on Kerguelen Islands, in the middle of the Southern Indian Ocean. The solubilities exhibit high values, generally greater than 70%, and Ti remains the least soluble element. Because the Southern Indian Ocean is remote from its dust sources, only the fraction of smaller aerosols reaches Kerguelen Islands after undergoing several cloud and chemical processes during their transport resulting in a drastic increase in solubility. Finally, we deduced an average soluble iron deposition flux of 23 μg m-2 d-1 (0.4 μmol m-2 d-1) for the studied oceanic area, taking into account a~median iron solubility of 82% ± 18%.

  13. An extensive region of off-ridge normal-faulting earthquakes in the southern Indian Ocean

    NASA Technical Reports Server (NTRS)

    Bergman, E. A.; Nabelek, J. L.; Solomon, S. C.

    1984-01-01

    A verified prediction of the theory of plate tectonics is that the focal mechanisms of earthquakes on the mid-ocean ridge system indicate either normal faulting on ridge segments or strike-slip faulting on transform faults. A broad region in the southern Indian Ocean which differs from typical ridge and intraplate regimes has been identified. In this region a number of large off-ridge earthquakes have occurred in the last 20 years. The mechanisms for these events, where known, all involve normal faulting. Nine of these earthquakes have been studied in detail using a formal inversion technique based on matching synthetic body waves to observed seismograms.

  14. An extensive region of off-ridge normal-faulting earthquakes in the southern Indian Ocean

    NASA Technical Reports Server (NTRS)

    Bergman, E. A.; Nabelek, J. L.; Solomon, S. C.

    1984-01-01

    A verified prediction of the theory of plate tectonics is that the focal mechanisms of earthquakes on the mid-ocean ridge system indicate either normal faulting on ridge segments or strike-slip faulting on transform faults. A broad region in the southern Indian Ocean which differs from typical ridge and intraplate regimes has been identified. In this region a number of large off-ridge earthquakes have occurred in the last 20 years. The mechanisms for these events, where known, all involve normal faulting. Nine of these earthquakes have been studied in detail using a formal inversion technique based on matching synthetic body waves to observed seismograms.

  15. Restricted regions of enhanced growth of Antarctic krill in the circumpolar Southern Ocean.

    PubMed

    Murphy, Eugene J; Thorpe, Sally E; Tarling, Geraint A; Watkins, Jonathan L; Fielding, Sophie; Underwood, Philip

    2017-07-31

    Food webs in high-latitude oceans are dominated by relatively few species. Future ocean and sea-ice changes affecting the distribution of such species will impact the structure and functioning of whole ecosystems. Antarctic krill (Euphausia superba) is a key species in Southern Ocean food webs, but there is little understanding of the factors influencing its success throughout much of the ocean. The capacity of a habitat to maintain growth will be crucial and here we use an empirical relationship of growth rate to assess seasonal spatial variability. Over much of the ocean, potential for growth is limited, with three restricted oceanic regions where seasonal conditions permit high growth rates, and only a few areas around the Scotia Sea and Antarctic Peninsula suitable for growth of the largest krill (>60 mm). Our study demonstrates that projections of impacts of future change need to account for spatial and seasonal variability of key ecological processes within ocean ecosystems.

  16. Iron isotopes reveal distinct dissolved iron sources and pathways in the intermediate versus deep Southern Ocean

    NASA Astrophysics Data System (ADS)

    Abadie, Cyril; Lacan, Francois; Radic, Amandine; Pradoux, Catherine; Poitrasson, Franck

    2017-01-01

    As an essential micronutrient, iron plays a key role in oceanic biogeochemistry. It is therefore linked to the global carbon cycle and climate. Here, we report a dissolved iron (DFe) isotope section in the South Atlantic and Southern Ocean. Throughout the section, a striking DFe isotope minimum (light iron) is observed at intermediate depths (200-1,300 m), contrasting with heavier isotopic composition in deep waters. This unambiguously demonstrates distinct DFe sources and processes dominating the iron cycle in the intermediate and deep layers, a feature impossible to see with only iron concentration data largely used thus far in chemical oceanography. At intermediate depths, the data suggest that the dominant DFe sources are linked to organic matter remineralization, either in the water column or at continental margins. In deeper layers, however, abiotic non-reductive release of Fe (desorption, dissolution) from particulate iron—notably lithogenic—likely dominates. These results go against the common but oversimplified view that remineralization of organic matter is the major pathway releasing DFe throughout the water column in the open ocean. They suggest that the oceanic iron cycle, and therefore oceanic primary production and climate, could be more sensitive than previously thought to continental erosion (providing lithogenic particles to the ocean), particle transport within the ocean, dissolved/particle interactions, and deep water upwelling. These processes could also impact the cycles of other elements, including nutrients.

  17. Iron isotopes reveal distinct dissolved iron sources and pathways in the intermediate versus deep Southern Ocean.

    PubMed

    Abadie, Cyril; Lacan, Francois; Radic, Amandine; Pradoux, Catherine; Poitrasson, Franck

    2017-01-31

    As an essential micronutrient, iron plays a key role in oceanic biogeochemistry. It is therefore linked to the global carbon cycle and climate. Here, we report a dissolved iron (DFe) isotope section in the South Atlantic and Southern Ocean. Throughout the section, a striking DFe isotope minimum (light iron) is observed at intermediate depths (200-1,300 m), contrasting with heavier isotopic composition in deep waters. This unambiguously demonstrates distinct DFe sources and processes dominating the iron cycle in the intermediate and deep layers, a feature impossible to see with only iron concentration data largely used thus far in chemical oceanography. At intermediate depths, the data suggest that the dominant DFe sources are linked to organic matter remineralization, either in the water column or at continental margins. In deeper layers, however, abiotic non-reductive release of Fe (desorption, dissolution) from particulate iron-notably lithogenic-likely dominates. These results go against the common but oversimplified view that remineralization of organic matter is the major pathway releasing DFe throughout the water column in the open ocean. They suggest that the oceanic iron cycle, and therefore oceanic primary production and climate, could be more sensitive than previously thought to continental erosion (providing lithogenic particles to the ocean), particle transport within the ocean, dissolved/particle interactions, and deep water upwelling. These processes could also impact the cycles of other elements, including nutrients.

  18. Iron isotopes reveal distinct dissolved iron sources and pathways in the intermediate versus deep Southern Ocean

    PubMed Central

    Abadie, Cyril; Lacan, Francois; Radic, Amandine; Pradoux, Catherine; Poitrasson, Franck

    2017-01-01

    As an essential micronutrient, iron plays a key role in oceanic biogeochemistry. It is therefore linked to the global carbon cycle and climate. Here, we report a dissolved iron (DFe) isotope section in the South Atlantic and Southern Ocean. Throughout the section, a striking DFe isotope minimum (light iron) is observed at intermediate depths (200–1,300 m), contrasting with heavier isotopic composition in deep waters. This unambiguously demonstrates distinct DFe sources and processes dominating the iron cycle in the intermediate and deep layers, a feature impossible to see with only iron concentration data largely used thus far in chemical oceanography. At intermediate depths, the data suggest that the dominant DFe sources are linked to organic matter remineralization, either in the water column or at continental margins. In deeper layers, however, abiotic non-reductive release of Fe (desorption, dissolution) from particulate iron—notably lithogenic—likely dominates. These results go against the common but oversimplified view that remineralization of organic matter is the major pathway releasing DFe throughout the water column in the open ocean. They suggest that the oceanic iron cycle, and therefore oceanic primary production and climate, could be more sensitive than previously thought to continental erosion (providing lithogenic particles to the ocean), particle transport within the ocean, dissolved/particle interactions, and deep water upwelling. These processes could also impact the cycles of other elements, including nutrients. PMID:28096366

  19. Multi-Model Comparison of Southern Ocean and Sea Ice Trends in CORE-II and CMIP5 Model

    NASA Astrophysics Data System (ADS)

    Downes, S. M.; Griffies, S. M.; Farneti, R.; Marsland, S. J.; Uotila, P.; Hogg, A.

    2014-12-01

    The Southern Ocean circulation, influenced by buoyancy, momentum and sea ice processes, varies on seasonal to centennial timescales. Incomplete spatio-temporal observations of the full ocean water column, overlying ocean-ice-atmosphere fluxes, and adjacent polar dynamics challenge our ability to model the Southern Ocean. However, several studies have indicated this region is particularly important in the evolving climate, including the anthropogenic influences. Models coherently capture large-scale Southern Ocean patterns, however it is the magnitude and location of these patterns that varies widely. In particular, difficulties with modelling of small scale processes remains an outstanding issue. Here we review the representation of the Southern Ocean circulation, including fluxes at the ocean-ice and ocean-atmosphere interfaces, in numerous coupled climate models from two international modeling efforts, namely the Coordinated Ocean-ice Reference Experiments Phase II (CORE-II) and Coupled Model Intercomparison Project Phase 5 (CMIP5). We focus on the relationships between large scale and mesoscale overturning circulation, formation of key water masses and the associated deep winter mixed layers, buoyancy and wind fluxes, and sea ice. We identify major uncertainties in the modelling of past, present and projected large-scale ocean processes, and provide insights for future modelling directions.

  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.

  1. 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

  2. Accuracy assessment of the global ionospheric model over the Southern Ocean based on dynamic observation

    NASA Astrophysics Data System (ADS)

    Luo, Xiaowen; Xu, Huajun; Li, Zishen; Zhang, Tao; Gao, Jinyao; Shen, Zhongyan; Yang, Chunguo; Wu, Ziyin

    2017-02-01

    The global ionospheric model based on the reference stations of the Global Navigation Satellite System (GNSS) of the International GNSS Services is presently the most commonly used products of the global ionosphere. It is very important to comprehensively analyze and evaluate the accuracy and reliability of the model for the reasonable use of this kind of ionospheric product. In terms of receiver station deployment, this work is different from the traditional performance evaluation of the global ionosphere model based on observation data of ground-based static reference stations. The preliminary evaluation and analysis of the the global ionospheric model was conducted with the dynamic observation data across different latitudes over the southern oceans. The validation results showed that the accuracy of the global ionospheric model over the southern oceans is about 5 TECu, which deviates from the measured ionospheric TEC by about -0.6 TECu.

  3. Excitation of T waves in the Indian Ocean between Srilanka and southern India

    NASA Astrophysics Data System (ADS)

    Chadha, R. K.

    1994-06-01

    T phases of three earthquakes from the Indian Ocean region, recorded by a short-period vertical-component seismic station network located in the vicinity of Kanyakumari on the southernmost tip of India, are studied. Two of these earthquakes are located west of 90°E ridge and one in the Nicobar Island region. However, seven other earthquakes which occurred 150 200 km south of Kanyakumari in the ocean did not produce T phases. An analysis of T-waves (tertiary waves) travel time reveals the zone of P-wave to T-wave conversion (i.e., PT phase) region to coincide with the western continental slope of Srilanka. Further, it is observed that the disposition of the bathymetry between Srilanka and southern India strongly favours the downslope propagation mechanism of T-wave travel to the southern coast of India through SOFAR channel. These observations are reported for the first time from India.

  4. Marine atmospheric boundary layer over some Southern Ocean fronts during the IPY BGH 2008 cruise

    NASA Astrophysics Data System (ADS)

    Messager, C.; Speich, S.; Key, E.

    2012-11-01

    A set of meteorological instruments was added to an oceanographic cruise crossing the Southern Ocean from Cape Town to 57°33' S during the summer of 2008. The Cape Cauldron, the Subtropical, Subantarctic, Polar and southern Antarctic Circumpolar current fronts were successively crossed. The recorded data permitted to derive the exchange of momentum, heat and water vapour at the ocean-atmosphere interface. A set of 38 radiosonde releases complemented the dataset. The marine atmospheric boundary layer characteristics and air-sea interaction when the ship crossed the fronts and eddies are discussed. The specific role of the atmospheric synoptic systems advection on the air-sea interaction over these regions is highlighted. Additionally, the Subantarctic front mesoscale variability induced an anticyclonic eddy considered as part of the Subantarctic front. The specific influence of this Agulhas ring on the aloft atmosphere is also presented.

  5. Estimates of the Southern Ocean general circulation improved by animal-borne instruments

    NASA Astrophysics Data System (ADS)

    Roquet, Fabien; Wunsch, Carl; Forget, Gael; Heimbach, Patrick; Guinet, Christophe; Reverdin, Gilles; Charrassin, Jean-Benoit; Bailleul, Frederic; Costa, Daniel P.; Huckstadt, Luis A.; Goetz, Kimberly T.; Kovacs, Kit M.; Lydersen, Christian; Biuw, Martin; Nøst, Ole A.; Bornemann, Horst; Ploetz, Joachim; Bester, Marthan N.; McIntyre, Trevor; Muelbert, Monica C.; Hindell, Mark A.; McMahon, Clive R.; Williams, Guy; Harcourt, Robert; Field, Iain C.; Chafik, Leon; Nicholls, Keith W.; Boehme, Lars; Fedak, Mike A.

    2013-12-01

    the last decade, several hundred seals have been equipped with conductivity-temperature-depth sensors in the Southern Ocean for both biological and physical oceanographic studies. A calibrated collection of seal-derived hydrographic data is now available, consisting of more than 165,000 profiles. The value of these hydrographic data within the existing Southern Ocean observing system is demonstrated herein by conducting two state estimation experiments, differing only in the use or not of seal data to constrain the system. Including seal-derived data substantially modifies the estimated surface mixed-layer properties and circulation patterns within and south of the Antarctic Circumpolar Current. Agreement with independent satellite observations of sea ice concentration is improved, especially along the East Antarctic shelf. Instrumented animals efficiently reduce a critical observational gap, and their contribution to monitoring polar climate variability will continue to grow as data accuracy and spatial coverage increase.

  6. Poleward decrease in the isotope effect of nitrate assimilation across the Southern Ocean

    NASA Astrophysics Data System (ADS)

    DiFiore, Peter J.; Sigman, Daniel M.; Karsh, Kristen L.; Trull, Thomas W.; Dunbar, Robert B.; Robinson, Rebecca S.

    2010-09-01

    Recent studies provide seasonally and spatially resolved information on the isotopic characteristics of nitrate supply and N cycling in Southern Ocean surface waters. The new data improve our understanding of the nitrate supply to the Antarctic surface and its isotopic characteristics, especially with regard to the summertime subsurface minimum temperature (Tmin) layer in the Antarctic. We use these findings to update and compile estimates of the N isotope effect of nitrate assimilation, $\\varepsilon$, in the Southern Ocean near Australia. A poleward decrease in $\\varepsilon$ emerges, from 8-9‰ in the Subantarctic Zone (SAZ, 40-52°S) to ˜5‰ in the Polar Antarctic Zone (PAZ, ˜66°S). $\\varepsilon$ is strongly correlated with mixed layer depth at the time of sampling. We hypothesize that the correlation is driven by the physiological response of diatoms to light availability, with light limitation leading to higher cellular efflux of nitrate and thus higher $\\varepsilon$.

  7. Southern Ocean deep-water carbon export enhanced by natural iron fertilization.

    PubMed

    Pollard, Raymond T; Salter, Ian; Sanders, Richard J; Lucas, Mike I; Moore, C Mark; Mills, Rachel A; Statham, Peter J; Allen, John T; Baker, Alex R; Bakker, Dorothee C E; Charette, Matthew A; Fielding, Sophie; Fones, Gary R; French, Megan; Hickman, Anna E; Holland, Ross J; Hughes, J Alan; Jickells, Timothy D; Lampitt, Richard S; Morris, Paul J; Nédélec, Florence H; Nielsdóttir, Maria; Planquette, Hélène; Popova, Ekaterina E; Poulton, Alex J; Read, Jane F; Seeyave, Sophie; Smith, Tania; Stinchcombe, Mark; Taylor, Sarah; Thomalla, Sandy; Venables, Hugh J; Williamson, Robert; Zubkov, Mike V

    2009-01-29

    The addition of iron to high-nutrient, low-chlorophyll regions induces phytoplankton blooms that take up carbon. Carbon export from the surface layer and, in particular, the ability of the ocean and sediments to sequester carbon for many years remains, however, poorly quantified. Here we report data from the CROZEX experiment in the Southern Ocean, which was conducted to test the hypothesis that the observed north-south gradient in phytoplankton concentrations in the vicinity of the Crozet Islands is induced by natural iron fertilization that results in enhanced organic carbon flux to the deep ocean. We report annual particulate carbon fluxes out of the surface layer, at three kilometres below the ocean surface and to the ocean floor. We find that carbon fluxes from a highly productive, naturally iron-fertilized region of the sub-Antarctic Southern Ocean are two to three times larger than the carbon fluxes from an adjacent high-nutrient, low-chlorophyll area not fertilized by iron. Our findings support the hypothesis that increased iron supply to the glacial sub-Antarctic may have directly enhanced carbon export to the deep ocean. The CROZEX sequestration efficiency (the amount of carbon sequestered below the depth of winter mixing for a given iron supply) of 8,600 mol mol(-1) was 18 times greater than that of a phytoplankton bloom induced artificially by adding iron, but 77 times smaller than that of another bloom initiated, like CROZEX, by a natural supply of iron. Large losses of purposefully added iron can explain the lower efficiency of the induced bloom(6). The discrepancy between the blooms naturally supplied with iron may result in part from an underestimate of horizontal iron supply.

  8. 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

  9. Observations of high droplet number concentrations in Southern Ocean boundary layer clouds

    NASA Astrophysics Data System (ADS)

    Chubb, T.; Huang, Y.; Jensen, J.; Campos, T.; Siems, S.; Manton, M.

    2015-09-01

    Data from the standard cloud physics payload during the NSF/NCAR High-performance Instrumented Airborne Platform for Environmental Research (HIAPER) Pole-to-Pole Observations (HIPPO) campaigns provide a snapshot of unusual wintertime microphysical conditions in the boundary layer over the Southern Ocean. On 29 June 2011, the HIAPER sampled the boundary layer in a region of pre-frontal warm air advection between 58 and 48° S to the south of Tasmania. Cloud droplet number concentrations were consistent with climatological values in the northernmost profiles but were exceptionally high for wintertime in the Southern Ocean at 100-200 cm-3 in the southernmost profiles. Sub-micron (0.06southern profiles were up to 400 cm-3. Analysis of back trajectories and atmospheric chemistry observations revealed that while conditions in the troposphere were more typical of a clean remote ocean airmass, there was some evidence of continental or anthropogenic influence. However, the hypothesis of long range transport of continental aerosol fails to explain the magnitude of the aerosol and cloud droplet concentration in the boundary layer. Instead, the gale force surface winds in this case (wind speed at 167 m above sea level was >25 m s-1) were most likely responsible for production of sea spray aerosol which influenced the microphysical properties of the boundary layer clouds. The smaller size and higher number concentration of cloud droplets is inferred to increase the albedo of these clouds, and these conditions occur regularly, and are expected to increase in frequency, over windy parts of the Southern Ocean.

  10. 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.

  11. 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.

  12. 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

  13. Heat uptake in the Southern Ocean in a warmer, windier world: a process-based analysis using an AOGCM with an eddy-permitting ocean

    NASA Astrophysics Data System (ADS)

    Kuhlbrodt, T.; Gregory, J. M.

    2016-02-01

    About 90% of the anthropogenic increase in heat stored in the climate system is found the oceans. Therefore it is relevant to understand the details of ocean heat uptake. Here we present a detailed, process-based analysis of ocean heat uptake (OHU) processes in HiGEM1.2, an atmosphere-ocean general circulation model (AOGCM) with an eddy-permitting ocean component of 1/3° resolution. Similarly to various other models, HiGEM1.2 shows that the global heat budget is dominated by a downward advection of heat compensated by upward isopycnal diffusion. This upward isopycnal diffusion of heat is located mostly in the Southern Ocean (Fig. 1a).We compare the responses to a 4xCO2 forcing and an enhancement of the windstress forcing in the Southern Ocean. In line with the CMIP5 models, HiGEM1.2 shows a band of strong OHU in the mid-latitude Southern Ocean in the 4xCO2 run, which is mostly advective. By contrast, in the high-latitude Southern Ocean regions it is the suppression of convection that leads to OHU (Fig. 1b). In the enhanced windstress run, convection is strengthened at high Southern latitudes (Fig. 1c), leading to heat loss, while the magnitude of the OHU in the Southern mid-latitudes is very similar to the 4xCO2 results. Remarkably, there is only very small global OHU in the enhanced windstress run. The wind stress forcing just leads to a redistribution of heat. We relate the ocean changes at high southern latitudes to the effect of climate change on the Antarctic Circumpolar Current (ACC). It weakens in the 4xCO2 run and strengthens in the wind stress run. The weakening is due to a narrowing of the ACC, caused by an expansion of the Weddell Gyre, and a flattening of the isopycnals, which are explained by a combination of the wind stress forcing and increased precipitation. The presentation will also try to clarify the definitions of terms like "advective", "diffusive" and "eddy-induced" when used for observed and modelled (at various resolutions) ocean heat

  14. SOFeX: Southern Ocean Iron Experiments. Overview and Experimental Design

    NASA Astrophysics Data System (ADS)

    Coale, K. H.; Johnson, K. S.; Buesseler, K.; Sofex Group,.

    2002-12-01

    Current numerical models suggest that, over time scales of 102 - 105 years, atmospheric CO2 is controlled largely by conditions in the polar ocean. These polar regions act as the source for abyssal water in all the oceans, and under present conditions, are the main route by which the huge reservoir of dissolved carbon in the deep sea communicates with the atmosphere. As a consequence, the Southern Ocean in particular has a disproportionately large influence on atmospheric carbon dioxide. Although it represent only 10-20% of the ocean surface area, processes controlling production and export of carbon from these HNLC waters will relate directly to carbon cycling and climate change. To date several factors conspire to limit the uptake of carbon dioxide by phytoplankton in these waters. These factors include the availability of major nutrients (particularly silicate), light and iron. Iron enrichment experiments in the Southern Ocean are of particular utility in understanding carbon cycling at high latitudes. In a landmark experiment, three US ships (R/V Revelle, R/V Melville and RIB Polar Star) conducted progressive iron enrichment experiments in two distinct regions of the Southern Ocean: One north of the Antarctic Polar Fronts Zone in low silicate waters (<3 μM), and another to the south, below the APFZ in high silicate waters (~60 \\muM) along 170°W. At both locations iron sulfate, infused with sulfurhexafluoride, was spread over 225 square kilometers and to the depth of the mixed layer. These experiments were reinfused with iron and tracked by multiple vessels over a seven week period to observe the physiological response of plankton, bacteria, changes in plankton community structure, the drawdown of major nutrients, the partitioning of carbon into POC, DOC, TCO2 and pCO2, and the flux of carbon from the surface waters. At this writing, values are being refined. The drawdowns in nutrients in the South Patch (NO3, 2.1 \\muM; SiO2, 3.7 \\muM and PO4, 0.25 \\mu

  15. High storage rates of anthropogenic CO_{2} in the Indian sector of the Southern Ocean

    NASA Astrophysics Data System (ADS)

    Murata, Akihiko; Kumamoto, Yu-ichiro; Sasaki, Ken-ichi

    2017-04-01

    Using high-quality data for CO2-system and related properties collected 17 years apart through international observation programs, we examined decadal-scale increases of anthropogenic CO2 along a zonal section at nominal 62˚ S ranging from 30˚ E to 160˚ E in the Indian sector of the Southern Ocean. In contrast to previous studies, increases of anthropogenic CO2 were largest (> 9.0 μmol kg-1) in Antarctic Bottom Water, where little storage of anthropogenic CO2 has been reported. Significant increases of anthropogenic CO2 in bottom and/or deep waters were detected through the section, although they became reduced in magnitude and depth range west of 110˚ E. Vertical distributions of anthropogenic CO2 showed significant positive correlations with decadal-scale changes in CFC-12, a proxy of circulation and ventilation, meaning that the distributions were mainly controlled by physical processes. Comparison of increases of anthropogenic CO2 between calculation methods with and without total alkalinity presented differences of increases of anthropogenic CO2west of 50˚ E. This is probably because decreases in production of particulate inorganic carbons in the Southern Ocean. The highest storage rate of anthropogenic CO2 was estimated to be 1.1 ± 0.6 mol m-2 a-1 at longitudes 130˚ -160˚ E. The results highlight storage rates higher than ever reported in the Southern Ocean, where very low storage of anthropogenic CO2 has been evidenced.

  16. 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

  17. 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.

  18. 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.

  19. Implications of Sea Ice on Southern Ocean Microseisms Detected by a Seismic Array in West Antarctica

    NASA Astrophysics Data System (ADS)

    Pratt, Martin J.; Wiens, Douglas A.; Winberry, J. Paul; Anandakrishnan, Sridhar; Euler, Garrett G.

    2017-01-01

    SUMMARYThe proximity of <span class="hlt">Southern</span> <span class="hlt">Ocean</span> storms coupled with seasonal variation in sea ice make Antarctica ideal for the study of microseism sources. We explore frequency-dependent beamforming results using a short-duration, 60 km aperture, broadband seismic array located on the Whillans Ice Stream, West Antarctica. Locations of single-frequency microseism (13-16 s period) generation are in regions where the continental shelf is ice-free, consistent with previous studies, and show Rayleigh wave sources remaining at consistent back azimuths throughout the duration of the array. Beamforming analysis of daily noise correlations shows that long-period double-frequency microseisms (9-11 s) consist predominantly of Rayleigh waves excited by storms in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. Modelling of source locations based on wave-wave interaction provides a good fit to our data at these periods. We show that short-period double-frequency microseisms (5-7 s) in Antarctica consist of crustal phase Lg and body waves. Lg arrivals propagate through regions of continental crust and our data show that the Lg energy is generated when storm systems interact with the sea ice-free continental shelf during austral summers. Ultra-short-period (0.3-2 s) microseismic body waves back project to regions that correlate with <span class="hlt">oceanic</span> storm systems in both the <span class="hlt">Southern</span> and Northern Hemispheres.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3392650','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3392650"><span>Exploring the Link between Micronutrients and Phytoplankton in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> during the 2007 Austral Summer</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hassler, Christel S.; Sinoir, Marie; Clementson, Lesley A.; Butler, Edward C. V.</p> <p>2012-01-01</p> <p>Bottle assays and large-scale fertilization experiments have demonstrated that, in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, its marine resources and ultimately the global carbon cycle. PMID:22787456</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.C51A0687Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.C51A0687Z"><span>The impact of multidecadal Atlantic meridional overturning circulation variations on the <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, L.; Delworth, T. L.; Zeng, F. J.</p> <p>2015-12-01</p> <p>The impact of multidecadal variations of the Atlantic meridional overturning circulation (AMOC) on the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> (SO) is investigated using a coupled <span class="hlt">ocean</span>-atmosphere model. We find that the AMOC can influence the SO via fast atmosphere teleconnections and subsequent <span class="hlt">ocean</span> 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 <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4598877','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4598877"><span>Trends and variability of the atmosphere–<span class="hlt">ocean</span> turbulent heat flux in the extratropical <span class="hlt">Southern</span> Hemisphere</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Herman, Agnieszka</p> <p>2015-01-01</p> <p>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 <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, 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 <span class="hlt">oceanic</span> forcing, suggesting differential response of various sections of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> to the changing atmospheric forcing. PMID:26449323</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017ClDy...48.1595K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017ClDy...48.1595K"><span>Fast and slow responses of <span class="hlt">Southern</span> <span class="hlt">Ocean</span> sea surface temperature to SAM in coupled climate models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kostov, Yavor; Marshall, John; Hausmann, Ute; Armour, Kyle C.; Ferreira, David; Holland, Marika M.</p> <p>2017-03-01</p> <p>We investigate how sea surface temperatures (SSTs) around Antarctica respond to the <span class="hlt">Southern</span> Annular Mode (SAM) on multiple timescales. To that end we examine the relationship between SAM and SST within unperturbed preindustrial control simulations of coupled general circulation models (GCMs) included in the Climate Modeling Intercomparison Project phase 5 (CMIP5). We develop a technique to extract the response of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> SST (55°S-70°S) to a hypothetical step increase in the SAM index. We demonstrate that in many GCMs, the expected SST step response function is nonmonotonic in time. Following a shift to a positive SAM anomaly, an initial cooling regime can transition into surface warming around Antarctica. However, there are large differences across the CMIP5 ensemble. In some models the step response function never changes sign and cooling persists, while in other GCMs the SST anomaly crosses over from negative to positive values only 3 years after a step increase in the SAM. This intermodel diversity can be related to differences in the models' climatological thermal <span class="hlt">ocean</span> stratification in the region of seasonal sea ice around Antarctica. Exploiting this relationship, we use observational data for the time-mean meridional and vertical temperature gradients to constrain the real <span class="hlt">Southern</span> <span class="hlt">Ocean</span> response to SAM on fast and slow timescales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.4330P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.4330P"><span>Observed chlorophyll trends in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> over 1997-2012 and associated mechanisms</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Panassa, Essowe; Hauck, Judith; Völker, Christoph; Hoppema, Mario; Wolf-Gladrow, Dieter</p> <p>2016-04-01</p> <p>An up-to date 16-year time series of satellite chlorophyll from the <span class="hlt">ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> biology is changing in response to recent change in circulation in that region, partly induced by the positive trend in the <span class="hlt">Southern</span> Annular Mode (SAM) index.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.433..380D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.433..380D"><span>Constraining early to middle Eocene climate evolution of the southwest Pacific and <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dallanave, Edoardo; Bachtadse, Valerian; Crouch, Erica M.; Tauxe, Lisa; Shepherd, Claire L.; Morgans, Hugh E. G.; Hollis, Christopher J.; Hines, Benjamin R.; Sugisaki, Saiko</p> <p>2016-01-01</p> <p>Studies of early Paleogene climate suffer from the scarcity of well-dated sedimentary records from the <span class="hlt">southern</span> Pacific <span class="hlt">Ocean</span>, the largest <span class="hlt">ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> records, we reviewed the magnetostratigraphy of <span class="hlt">Ocean</span> Drilling Program (ODP) Site 1172 (East Tasman Plateau) and Integrated <span class="hlt">Ocean</span> 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 <span class="hlt">southern</span> high-latitude climate histories derived from these sites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.6460N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.6460N"><span>Mesozoic Sequence Magnetic Anomalies in the South of Corad Rise, the <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nogi, Y.; Ikehara, M.; Nakamura, Y.; Kameo, K.; Katsuki, K.; Kawamura, S.; Kita, S.</p> <p>2009-04-01</p> <p>The <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span> is key area for understanding the fragmentation process of the Gondwana. However, tectonic history in the <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span> still remains less well-defined because of the sparse observations in this area. The R/V Hakuho-maru cruise KH-07-4 Leg3 were conducted to understand the tectonic history related to the Gondwana breakup in the <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span> between Cape Town, South Africa, and off Lutzow-Holm Bay, Antarctica. Total intensity and vector geomagnetic field measurements as well as swath bathymetry mapping were collected during the cruise. Magnetic anomaly data have been collected along WNW-ESE trending inferred from satellite gravity anomalies just to the south of Conrad Rise. We have also collected magnetic anomaly data along NNE-SSW trending lineaments from satellite gravity anomaly data between the south of the Conrad Rise and off Lutzow-Holm Bay. Magnetic anomalies with amplitude of about 500 nT, originating from normal and reversed magnetization of <span class="hlt">oceanic</span> crust are detected along the WNW-ESE trending structures just to the south of Conrad Rise. Those magnetic anomalies most likely indicate Mesozoic magnetic anomaly sequence, Mesozoic sequence magnetic anomalies with amplitude of about 300 nT are also observed along the NNE-SSW trending lineaments between the south of the Conrad Rise and off Lutzow-Holm Bay. <span class="hlt">Oceanic</span> crusts formed during Cretaceous normal polarity superchron are found in both profiles, although magnetic anomaly C34 has been identified just to the north of the Conrad Rise. These suggest the extinct spreading axes in the south of Conrad Rise and the two different seafloor spreading systems were active around Cretaceous normal polarity superchron between the south of the Conrad Rise and off Lutzow-Holm Bay. These provide new constraints for the fragmentation process of the Gondwana.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.1567R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.1567R"><span><span class="hlt">Southern</span> <span class="hlt">Ocean</span> ventilation and bottom water formation driven by Weddell Sea polynyas</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rheinlaender, Jonathan; Nisancioglu, Kerim; Smedsrud, Lars Henrik</p> <p>2017-04-01</p> <p>A distinct feature of the last glacial period, are the abrupt temperature fluctuations in Greenland associated with Dansgaard-Oeschger events and a similar but opposite response in Antarctica. The prevailing hypothesis behind this inter-hemispheric coupling, points to changes in deep water formation as the main driver, thus highlighting the pivotal role of the high latitude <span class="hlt">oceans</span> in global climate. Bottom water formation through open-<span class="hlt">ocean</span> deep convection in an Antarctic polynya, a large open water area inside the winter sea ice cover, provide a potential mechanism to trigger such changes in <span class="hlt">ocean</span> circulation. In this study, an <span class="hlt">ocean</span>-sea ice only version of the Norwegian Earth System Model (NorESM) is explored and shows strong open-<span class="hlt">ocean</span> deep convection associated with large polynyas in the Weddell Sea. This provides us with an opportunity to test (1) how internal <span class="hlt">ocean</span> dynamics can trigger abrupt changes in sea-ice cover and (2) how these polynyas affect the overturning circulation through changes in bottom water formation. During the 1,000 year long free-running simulation two polynyas are observed. We show, that the polynya is caused by subsurface warming leading to a gradual weakening of the surface stratification which destabilizes the whole water column and eventually triggers deep convective overturning. This mixes up relatively warm deep water causing extensive melt of sea ice in the Weddell Sea, while cold and fresh surface water sinks to the bottom. Consequently, the polynya leads to extensive bottom water formation and increase in the northward flow of Antarctic Bottom Water, while the southward flow of North Atlantic Deep Water is reduced. Finally, our results suggest that a decrease in the temperature of warm deep water in the Weddell Sea leads to cessation of open-<span class="hlt">ocean</span> deep convection. This raises the question if open-<span class="hlt">ocean</span> deep convection associated with polynyas in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> could be a realistic feature in a cold, glacial climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/21115838','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/21115838"><span>Antarctic lakes suggest millennial reorganizations of <span class="hlt">Southern</span> Hemisphere atmospheric and <span class="hlt">oceanic</span> circulation.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hall, Brenda L; Denton, George H; Fountain, Andrew G; Hendy, Chris H; Henderson, Gideon M</p> <p>2010-12-14</p> <p>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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. 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 <span class="hlt">Southern</span> Hemisphere. These data suggest a coherent <span class="hlt">Southern</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFMOS11A0202P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFMOS11A0202P"><span>Phytoplankton Photosynthetic Response During the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Iron Experiment Using Pulse Amplitude Modulated (PAM) Fluorescence</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peloquin, J. A.; Smith, W. O.</p> <p>2002-12-01</p> <p>Phytoplankton production in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> is controlled by complicated interactions of light, nutrients, and iron availability. In early 2002, the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Iron Experiment (SOFeX), was completed in the <span class="hlt">Southern</span> Pacific (along ~ 170° W). Two iron enriched patches were created North and South of the Polar Front with initially distinct silicic acid concentrations, ~1 μM and ~60 μM, respectively. PAM was employed for measuring phytoplankton whole water (bulk) and single-celled photochemical efficiency of Photosystem II (Fv}/F{m). Bulk measurements of photochemical efficiency for PAM show increases as phytoplankton from iron-enriched patches are relieved from iron stress for both the North and South Patch. For single-celled analysis with PAM, a time course from the South Patch will be presented along with late North Patch data. For the <span class="hlt">Southern</span> Patch, a distinct increase in Fv}/F{m with time was detected for all diatom genera analyzed and Fv}/F{m values continued to increase over the duration of analysis. For the late Northern Patch phytoplankton assemblage, bulk Fv}/F{m estimates were still elevated, ~0.5. However, the dominant species, Pseudonitzchia sp., exhibited lower photochemical efficiency (0.25-0.35), suggesting that it may have been experiencing iron or silica stress. In contrast, Fv}/F{m measurements of another dominant species, Phaeocystis antarctica, exhibited higher (0.5-0.6) values, suggesting that the colonial haptophyte was not significantly stressed at the time of measurement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.410..152T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.410..152T"><span>Disparities in glacial advection of <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Intermediate Water to the South Pacific Gyre</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tapia, R.; Nürnberg, D.; Ronge, T.; Tiedemann, R.</p> <p>2015-01-01</p> <p>The Intermediate Waters formed in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> are critical for ventilating the thermocline in the <span class="hlt">Southern</span> Hemisphere Gyres and transporting climatic signals from high to low latitudes on glacial-interglacial time-scales. Despite the importance of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Intermediate Waters (SOIWs), information on past changes in SOIWs formation is fragmentary, and its impact on the South Pacific Gyre (SPG)'s thermocline largely unknown. Here, we present a 200 kyr record of paired Mg/Ca ratios and stable oxygen isotope from surface and deep dwelling planktonic foraminifera, from the SPG. On average, the Globigerina bulloides Mg/Ca-derived sea surface temperatures show similar conditions during the LGM and Marine Isotope Stage (MIS) 6 (9.4 °C versus 9.8 °C). In contrast, the subsurface temperatures derived from the Mg/Ca values of Globorotalia inflata and Globorotalia truncatulinoides suggest that LGM is ∼3 to ∼2 °C colder than MIS 6. Furthermore, at subsurface depths the reconstructed δ18Osw-ivc record (proxy for relative local salinity changes) suggests opposite glacial conditions, with slightly saltier-than-Holocene waters during MIS 6, and fresher-than-Holocene waters during LGM. Contrasting glacial scenarios, plausibly due to changes in the presence of SOIWs at the study site, suggest variable formation and/or advection of SOIWs to the SPG during different glacial stages. The variability in SOIWs is probably driven by the changes in the intensity of the <span class="hlt">Southern</span> Westerly Winds.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GMDD....8.2949H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GMDD....8.2949H"><span>Increasing vertical mixing to reduce <span class="hlt">Southern</span> <span class="hlt">Ocean</span> deep convection in NEMO</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Heuzé, C.; Ridley, J. K.; Calvert, D.; Stevens, D. P.; Heywood, K. J.</p> <p>2015-03-01</p> <p>Most CMIP5 models unrealistically form Antarctic Bottom Water by open <span class="hlt">ocean</span> deep convection in the Weddell and Ross Seas. To identify the triggering mechanisms leading to <span class="hlt">Southern</span> <span class="hlt">Ocean</span> deep convection in models, we perform sensitivity experiments on the <span class="hlt">ocean</span> model NEMO 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 are warmer, open larger polynyas 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> deep convection, for example by increasing their vertical mixing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4595604','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4595604"><span>The seasonal sea-ice zone in the glacial <span class="hlt">Southern</span> <span class="hlt">Ocean</span> as a carbon sink</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf</p> <p>2015-01-01</p> <p>Reduced surface–deep <span class="hlt">ocean</span> exchange and enhanced nutrient consumption by phytoplankton in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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-<span class="hlt">ocean</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25455366','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25455366"><span>Low densities of drifting litter in the African sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ryan, Peter G; Musker, Seth; Rink, Ariella</p> <p>2014-12-15</p> <p>Only 52 litter items (>1cm diameter) were observed in 10,467 km of at-sea transects in the African sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. Litter density north of the Subtropical Front (0.58 items km(-2)) was less than in the adjacent South Atlantic <span class="hlt">Ocean</span> (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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> is the least polluted <span class="hlt">ocean</span> in terms of drifting debris and suggest that most debris comes from local sources.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMOS41D1757A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMOS41D1757A"><span>The International Bathymetric Chart of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> - A new Map of Antarctica</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arndt, J.; Schenke, H. W.</p> <p>2012-12-01</p> <p>The International Bathymetric Chart of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> (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 <span class="hlt">Ocean</span> (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 <span class="hlt">ocean</span> current pathways. In addition the IBCSO is going to serve as database for the development of new Electronic Nautical Charts (ENC) in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/24891395','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/24891395"><span>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> in the Coupled Model Intercomparison Project phase 5.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Meijers, A J S</p> <p>2014-07-13</p> <p>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">ocean</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFMOS31B..07J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFMOS31B..07J"><span>Net Community Production in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Monitored with Nitrate and Oxygen Sensors on Profiling Floats</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Johnson, K. S.; Riser, S.; Swift, D.; Coletti, L.; Jannasch, H. W.; Plant, J.; Sakamoto, C.</p> <p>2011-12-01</p> <p>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> is the least observed <span class="hlt">ocean</span> due to its remote location and severe weather. There are few areas visited regularly by ships and surface moorings are difficult to maintain. Profiling floats equipped with biogeochemical sensors provide one mechanism to sustain long term observations in this region. Here we present results obtained from two Apex profiling floats equipped with In Situ Ultraviolet Spectrophotometer (ISUS) nitrate sensors and Aanderaa Optode oxygen sensors. Float 5146 operated for over three years near 55° South in the Indian <span class="hlt">Ocean</span> sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. It made 230 vertical profiles at 5 day intervals from 1000 m to the surface with 60 nitrate and oxygen measurements on each profile before its batteries were exhausted near the Kerguelen Plateau. Nitrate reported by Float 5146 is shown in the figure. Float 5426 has operated over 2.5 years and made 190 vertical profiles to date. It was initially launched in the near 55° South, 80° West in the Pacific sector and then passed through the Drake Passage and is now near 45° South in the Atlantic sector. Each of these floats provides a unique perspective on changes in net community production along their trajectory. Data quality over the multi-year operating life of each float will first be assessed. Rates of biogeochemical processes that are diagnosed by combining sensor data with a 1-D mixed layer model will then be discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016RSPTA.37450292M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016RSPTA.37450292M"><span><span class="hlt">Southern</span> <span class="hlt">Ocean</span> biological iron cycling in the pre-whaling and present ecosystems</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maldonado, Maria T.; Surma, Szymon; Pakhomov, Evgeny A.</p> <p>2016-11-01</p> <p>This study aimed to create the first model of biological iron (Fe) cycling in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> food web. Two biomass mass-balanced Ecopath models were built to represent pre- and post-whaling ecosystem states (1900 and 2008). Functional group biomasses (tonnes wet weight km-2) were converted to biogenic Fe pools (kg Fe km-2) using published Fe content ranges. In both models, biogenic Fe pools and consumption in the pelagic <span class="hlt">Southern</span> <span class="hlt">Ocean</span> were highest for plankton and small nektonic groups. The production of plankton biomass, particularly unicellular groups, accounted for the highest annual Fe demand. Microzooplankton contributed most to biological Fe recycling, followed by carnivorous zooplankton and krill. Biological Fe recycling matched previous estimates, and, under most conditions, could entirely meet the Fe demand of bacterioplankton and phytoplankton. Iron recycling by large baleen whales was reduced 10-fold by whaling between 1900 and 2008. However, even under the 1900 scenario, the contribution of whales to biological Fe recycling was negligible compared with that of planktonic consumers. These models are a first step in examining <span class="hlt">oceanic</span>-scale biological Fe cycling, highlighting gaps in our present knowledge and key questions for future research on the role of marine food webs in the cycling of trace elements in the sea. This article is part of the themed issue 'Biological and climatic impacts of <span class="hlt">ocean</span> trace element chemistry'.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018602','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018602"><span><span class="hlt">Southern</span> <span class="hlt">Ocean</span> monthly wave fields for austral winters 1985-1988 by Geosat radar altimeter</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Josberger, E.G.; Mognard, N.M.</p> <p>1996-01-01</p> <p>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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. The largest monthly averaged significant wave heights are above 5 m and are found during August of every year in the Indian <span class="hlt">Ocean</span>, south of 40??S. The monthly wave fields show more variability in the Atlantic and Pacific <span class="hlt">Oceans</span> than in the Indian <span class="hlt">Ocean</span>. 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-<span class="hlt">Southern</span> Oscillation event of 1986. Copyright 1996 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.1140O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.1140O"><span>Decadal Variability in an OGCM <span class="hlt">Southern</span> <span class="hlt">Ocean</span>: intrinsic modes, forced modes and metastable states</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>O'Kane, Terence; Matear, Richard; Chamberlain, Matthew; Risbey, James; Horenko, Illia; Sloyan, Bernadette</p> <p>2014-05-01</p> <p>An <span class="hlt">Ocean</span> General Circulation Model (OGCM) is used to identify a <span class="hlt">Southern</span> <span class="hlt">Ocean</span> southeast Pacific intrinsic mode of low frequency variability. Using CORE data a comprehensive suite of experiments were carried out to elucidate excitation and amplification responses of this intrinsic mode to low frequency forcing (ENSO, SAM) and stochastic forcing due to high frequency winds. Subsurface anomalies were found to teleconnect the Pacific and Atlantic regions of the Antarctic Circumpolar Current (ACC) thermocline. The Pacific region of the ACC is characterised by intrinsic baroclinic disturbances that respond to both SAM and ENSO, while the Atlantic sector of the ACC is sensitive to higher frequency winds that act to amplify thermocline anomalies propagating downstream from the Pacific. Non-stationary cluster analysis was used to identify the system's dynamical regimes and characterise meta-stability, persistence and transitions between the respective states. This analysis reveals significant trends, indicating fundamental changes to the meta-stability of the <span class="hlt">ocean</span> dynamics in response to changes in atmospheric forcing. Intrinsic variability in sea-ice concentration was found to be coupled to thermocline processes. Sea-ice variability localised in the Atlantic was most closely associated with high frequency weather forcing. The SAM was associated with a circumpolar sea-ice response whereas ENSO was found to be a major driver of sea-ice variability only in the Pacific. This simulation study identifies plausible mechanisms that determine the predictability of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> climate on multi-decadal timescales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26382319','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26382319"><span>The seasonal sea-ice zone in the glacial <span class="hlt">Southern</span> <span class="hlt">Ocean</span> as a carbon sink.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf</p> <p>2015-09-18</p> <p>Reduced surface-deep <span class="hlt">ocean</span> exchange and enhanced nutrient consumption by phytoplankton in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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-<span class="hlt">ocean</span> 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.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996JGR...101.6689J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996JGR...101.6689J"><span><span class="hlt">Southern</span> <span class="hlt">Ocean</span> monthly wave fields for austral winters 1985-1988 by Geosat radar altimeter</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Josberger, Edward G.; Mognard, Nelly M.</p> <p>1996-03-01</p> <p>Four years of monthly averaged wave height fields for the austral winters 1985-1988 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 1 m is also found over large regions of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. The largest monthly averaged significant wave heights are above 5 m and are found during August of every year in the Indian <span class="hlt">Ocean</span>, south of 40°S. The monthly wave fields show more variability in the Atlantic and Pacific <span class="hlt">Oceans</span> than in the Indian <span class="hlt">Ocean</span>. 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 Niño-<span class="hlt">Southern</span> Oscillation event of 1986.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19830043081&hterms=doldrums&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Ddoldrums','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19830043081&hterms=doldrums&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Ddoldrums"><span><span class="hlt">Southern</span> <span class="hlt">ocean</span> mean monthly waves and surface winds for winter 1978 by Seasat radar altimeter</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mognard, N. M.; Campbell, W. J.; Cheney, R. E.; Marsh, J. G.</p> <p>1983-01-01</p> <p>Data acquired by the SEASAT radar altimeter during the 3 month satellite lifetime are analyzed in a study of the sea state of the <span class="hlt">southern</span> hemisphere <span class="hlt">oceans</span>. The lifetime of the SEASAT satellite, July 7 to October 10, 1978, corresponds to the Antarctic winter. Mean monthly maps of wind speed, significant wave height, and swell have been generated from the altimeter measurements along the satellite tracks. These maps delineate spatial and temporal differences of these parameters in the Atlantic, Indian, and Pacific <span class="hlt">oceans</span>. Several features of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> wind and wave fields agree with conventional descriptions. For example, the principle zonal wind regimes established by the Southeast Trades and Westerlies are clearly evident in the monthly averages. Significant wave height and swell also exhibit minima near the Doldrums at low latitudes with steady increases southward to the latitudes of the Westerlies. However, superimposed on these general patterns is significant variability with horizontal scales as small as 1000 km. The maps also document a gradual migration of the region of absolute maximum wind and wave from the Atlantic eastward to the Indian <span class="hlt">Ocean</span> and finally into the Pacific.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983JGR....88.1736M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983JGR....88.1736M"><span><span class="hlt">Southern</span> <span class="hlt">ocean</span> mean monthly waves and surface winds for winter 1978 by Seasat radar altimeter</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mognard, Nelly M.; Campbell, William J.; Cheney, Robert E.; Marsh, James G.</p> <p>1983-02-01</p> <p>Data acquired by the SEASAT radar altimeter during the 3 month satellite lifetime are analyzed in a study of the sea state of the <span class="hlt">southern</span> hemisphere <span class="hlt">oceans</span>. The lifetime of the SEASAT satellite, July 7 to October 10, 1978, corresponds to the Antarctic winter. Mean monthly maps of wind speed, significant wave height, and swell have been generated from the altimeter measurements along the satellite tracks. These maps delineate spatial and temporal differences of these parameters in the Atlantic, Indian, and Pacific <span class="hlt">oceans</span>. Several features of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> wind and wave fields agree with conventional descriptions. For example, the principle zonal wind regimes established by the Southeast Trades and Westerlies are clearly evident in the monthly averages. Significant wave height and swell also exhibit minima near the Doldrums at low latitudes with steady increases southward to the latitudes of the Westerlies. However, superimposed on these general patterns is significant variability with horizontal scales as small as 1000 km. The maps also document a gradual migration of the region of absolute maximum wind and wave from the Atlantic eastward to the Indian <span class="hlt">Ocean</span> and finally into the Pacific.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015NatCo...6E8136A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015NatCo...6E8136A"><span>The seasonal sea-ice zone in the glacial <span class="hlt">Southern</span> <span class="hlt">Ocean</span> as a carbon sink</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Abelmann, Andrea; Gersonde, Rainer; Knorr, Gregor; Zhang, Xu; Chapligin, Bernhard; Maier, Edith; Esper, Oliver; Friedrichsen, Hans; Lohmann, Gerrit; Meyer, Hanno; Tiedemann, Ralf</p> <p>2015-09-01</p> <p>Reduced surface-deep <span class="hlt">ocean</span> exchange and enhanced nutrient consumption by phytoplankton in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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-<span class="hlt">ocean</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014GeCoA.126..321L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014GeCoA.126..321L"><span>Molecular transformation and degradation of refractory dissolved organic matter in the Atlantic and <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lechtenfeld, Oliver J.; Kattner, Gerhard; Flerus, Ruth; McCallister, S. Leigh; Schmitt-Kopplin, Philippe; Koch, Boris P.</p> <p>2014-02-01</p> <p>More than 90% of the global <span class="hlt">ocean</span> 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 <span class="hlt">oceans</span>, the Atlantic sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> and the East Atlantic <span class="hlt">Ocean</span> (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 <span class="hlt">oceanic</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMOS43E1859C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMOS43E1859C"><span>Physical processes governing summer Chl-a in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carranza, M. M.; Gille, S. T.</p> <p>2012-12-01</p> <p>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> plays a crucial role in sequestering atmospheric CO2 by exporting fixed carbon into the deep <span class="hlt">ocean</span> through the biological pump. It is a High Nitrate Low Chlorophyll (HNLC) region where phytoplankton growth is primarily Fe-limited. Several sources of Fe have been identified in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, and phytoplankton blooms occur annually. Many of these blooms persist through the summer and even peak in the summer months. The mechanisms that explain spring blooms are well known, and the shoaling of the mixed-layer depth (MLD) plays a critical role in terms of light availability. A question that remains unanswered is what sustains blooms through the summer when presumably light conditions are optimal and nutrients in the mixed layer have been depleted. One source of Fe is the deep <span class="hlt">ocean</span>, and models and observations suggest blooms in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> are largely driven by <span class="hlt">ocean</span> dynamics. The evaluation of the input of Fe from subsurface waters into the euphotic zone depends in part on mixed-layer dynamics and Ekman-induced upwelling. The turbulent mixing caused by winds, along with the buoyancy forcing, prescribe the MLD and deepening of the MLD may facilitate the entrainment of Fe. The curl of the wind stress, by Ekman pumping, provides a mechanism of upwelling that can also contribute to the supply of Fe. Sea surface temperature (SST) responds to both of these processes, as well as to surface heat fluxes at the <span class="hlt">ocean</span>-air interphase. In this work we explore the potential influence of nutrient entrainment due to MLD deepening and Ekman-induced upwelling on summer phytoplankton blooms. Using weekly satellite estimates and <span class="hlt">ocean</span> reanalysis we correlate anomalies of Chlorophyll-a (Chl-a) with anomalies of physical variables such as wind speed intensity (W), Ekman pumping velocities (WEK), SST and surface heat fluxes (Qnet). Winds and SST can have strong feedbacks through Qnet and instabilities in the atmospheric boundary layer, and therefore in our</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040040106','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040040106"><span>The Effects of Snow Depth Forcing on <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Sea Ice Simulations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Powel, Dylan C.; Markus, Thorsten; Stoessel, Achim</p> <p>2003-01-01</p> <p>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 <span class="hlt">ocean</span> and the atmosphere, and second, snow is a source of fresh water for altering the already weak <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">ocean</span>-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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PolSc..12....1M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PolSc..12....1M"><span>Ecosystem studies in the Indian <span class="hlt">Ocean</span> sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> undertaken by the training vessel Umitaka-maru</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moteki, Masato; Odate, Tsuneo; Hosie, Graham W.; Takahashi, Kunio T.; Swadling, Kerrie M.; Tanimura, Atsushi</p> <p>2017-06-01</p> <p>This special issue provides an overview of the ten voyages undertaken by the Umitaka-maru from the austral summers of 2002/2003 to 2014/2015 to promote the next phase of study of the ecosystems in the Indian <span class="hlt">Ocean</span> sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. The voyages by the Umitaka-maru have mainly targeted three areas in the Indian <span class="hlt">Ocean</span> sector: off Dumont d'Urville Base (France, 140°E transect), off Casey Station (Australia, 110°E transect), and off Syowa Station (Japan, north of Lützow Holm Bay). The findings of Umitaka-maru's research on the krill-independent food web, animal assemblages, community structure and distribution patterns from the epipelagic to the deeper waters provide invaluable information for elucidating the material cycle and predicting future ecosystem changes. Further studies on assessing the influence of sea ice on food webs in the water column are required, which will provide crucial information for predicting ecosystem changes as a result of projected sea ice changes in the near future.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Natur.537...89H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Natur.537...89H"><span>Sea-ice transport driving <span class="hlt">Southern</span> <span class="hlt">Ocean</span> salinity and its recent trends</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Haumann, F. Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan</p> <p>2016-09-01</p> <p>Recent salinity changes in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> are among the most prominent signals of climate change in the global <span class="hlt">ocean</span>, 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 <span class="hlt">ocean</span>, 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the <span class="hlt">ocean</span>, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep <span class="hlt">ocean</span> and surface waters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26034673','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26034673"><span>El Nino <span class="hlt">Southern</span> Oscillation (ENSO) impact on tuna fisheries in Indian <span class="hlt">Ocean</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kumar, Palanisamy Satheesh; Pillai, Gopalakrishna N; Manjusha, Ushadevi</p> <p>2014-01-01</p> <p>El Nino <span class="hlt">Southern</span> 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 <span class="hlt">Ocean</span> 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 <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> 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 <span class="hlt">Ocean</span> 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 <span class="hlt">Ocean</span>. However, among the <span class="hlt">oceanic</span> variables SST explained the highest deviance in generalized additive models and therefore considered the best habitat predictor in the Indian <span class="hlt">Ocean</span> followed by sea level pressure and Winds (U, V, W).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/27582222','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/27582222"><span>Sea-ice transport driving <span class="hlt">Southern</span> <span class="hlt">Ocean</span> salinity and its recent trends.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Haumann, F Alexander; Gruber, Nicolas; Münnich, Matthias; Frenger, Ivy; Kern, Stefan</p> <p>2016-09-01</p> <p>Recent salinity changes in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> are among the most prominent signals of climate change in the global <span class="hlt">ocean</span>, 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 <span class="hlt">ocean</span>, 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the <span class="hlt">ocean</span>, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep <span class="hlt">ocean</span> and surface waters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5381401','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=5381401"><span>Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>?</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Bhattachan, Abinash; D'Odorico, Paolo</p> <p>2014-01-01</p> <p>The supply of soluble iron through atmospheric dust deposition limits the productivity of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. In comparison to the Northern Hemisphere, the <span class="hlt">Southern</span> Hemisphere exhibits low levels of dust activity. However, given their proximity to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, dust emissions from continental sources in the <span class="hlt">Southern</span> Hemisphere could have disproportionate impact on <span class="hlt">ocean</span> productivity. Australia is the largest source of dust in the <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. This iron-rich dust could stimulate <span class="hlt">ocean</span> productivity in future as more areas are reactivated as a result of land-use and droughts. PMID:25109703</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014NatSR...4E6009B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014NatSR...4E6009B"><span>Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bhattachan, Abinash; D'Odorico, Paolo</p> <p>2014-08-01</p> <p>The supply of soluble iron through atmospheric dust deposition limits the productivity of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. In comparison to the Northern Hemisphere, the <span class="hlt">Southern</span> Hemisphere exhibits low levels of dust activity. However, given their proximity to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, dust emissions from continental sources in the <span class="hlt">Southern</span> Hemisphere could have disproportionate impact on <span class="hlt">ocean</span> productivity. Australia is the largest source of dust in the <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. This iron-rich dust could stimulate <span class="hlt">ocean</span> productivity in future as more areas are reactivated as a result of land-use and droughts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25109703','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25109703"><span>Can land use intensification in the Mallee, Australia increase the supply of soluble iron to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>?</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Bhattachan, Abinash; D'Odorico, Paolo</p> <p>2014-08-11</p> <p>The supply of soluble iron through atmospheric dust deposition limits the productivity of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. In comparison to the Northern Hemisphere, the <span class="hlt">Southern</span> Hemisphere exhibits low levels of dust activity. However, given their proximity to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, dust emissions from continental sources in the <span class="hlt">Southern</span> Hemisphere could have disproportionate impact on <span class="hlt">ocean</span> productivity. Australia is the largest source of dust in the <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. This iron-rich dust could stimulate <span class="hlt">ocean</span> productivity in future as more areas are reactivated as a result of land-use and droughts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008DSRII..55..594B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008DSRII..55..594B"><span>Distribution of dissolved iron during the natural iron-fertilization experiment KEOPS (Kerguelen Plateau, <span class="hlt">Southern</span> <span class="hlt">Ocean</span>)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blain, Stéphane; Sarthou, Géraldine; Laan, Patrick</p> <p>2008-03-01</p> <p>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> is the largest high-nutrient low-chlorophyll (HNLC) region of the world <span class="hlt">ocean</span>. It is now well recognized that the low biological productivity in this region is mainly due to the limitation of phytoplankton growth by iron. However, in the core of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, a massive bloom occurs annually above the Kerguelen Plateau. In the context of KEOPS (Kerguelen Plateau and <span class="hlt">Ocean</span> compared Study) we investigated the three-dimensional distribution of dissolved iron (DFe) concentrations southeast of the island. We show that in surface waters, DFe was low and not significantly different above and outside the plateau (0.090±0.034 and 0.073±0.014 nM, respectively). By contrast, below 150 m major differences in vertical profiles of DFe were observed. The deep waters above the plateau were clearly enriched, with DFe concentrations up to 0.6 nM near the seafloor. The regeneration from sinking biogenic material and the input from the sediments are very likely the major processes delivering DFe to the deep water. The deep iron-rich reservoir existing above the plateau was responsible for the natural iron fertilization of the surface water by two different mechanisms: (i) winter mixing provided 5 times more DFe to the surface waters above the plateau than outside and (ii) enhanced vertical gradients of DFe and elevated vertical diffusivity resulted in an 8-fold higher diapycnal diffusive flux. The natural iron fertilization presented major differences from artificial iron-fertilization experiments carried out in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. The amount of DFe required to stimulate the biological activity is much less and the mode of addition is clearly different. The quantification of the excess of DFe supplied in the naturally fertilized area leads to the conclusion that the natural iron fertilization is 10-150 times more efficient to export carbon below 200 m than in artificial fertilization experiments. The bloom above the Kerguelen Plateau was contingent to iron</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/20139020','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/20139020"><span>Molecular phylogeny and historical biogeography of Nacella (Patellogastropoda: Nacellidae) in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>González-Wevar, Claudio A; Nakano, Tomoyuki; Cañete, Juan I; Poulin, Elie</p> <p>2010-07-01</p> <p>The evolution and the historical biogeography of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. True limpets of the genus Nacella are currently distributed in different biogeographic regions of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> such as Antarctica, Kerguelen Province, <span class="hlt">southern</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>: 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMGC13C0653T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMGC13C0653T"><span>Decadal Changes in Hydrography of the <span class="hlt">Southern</span> Pacific <span class="hlt">Ocean</span> and Ross Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Talley, L. D.; Carter, B.; Warner, M. J.; Swift, J. H.; Orsi, A. H.; Sloyan, B.</p> <p>2014-12-01</p> <p>Quasi-decadal hydrographic sections of the GO-SHIP program cross the world's <span class="hlt">oceans</span> with the highest accuracy measurements, documenting temporal variability in physical and chemical properties. The central <span class="hlt">southern</span> 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 <span class="hlt">ocean</span> deep warming in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> documented by Purkey/Johnson (2010) and IPCC AR5 WG1. The abyssal central Ross Sea waters also continued to freshen slightly. The upper <span class="hlt">ocean</span> 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 <span class="hlt">ocean</span>'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 <span class="hlt">ocean</span> bottom between 32S and 40S indicates that the Antarctic Bottom Water there is about 40-50 years old. CFCs in the <span class="hlt">ocean</span>'s surface layer decreased, in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813893W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813893W"><span>The influence of marine monoterpene emissions on cloud condensation nuclei concentrations over the <span class="hlt">Southern</span> Hemisphere <span class="hlt">oceans</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Walker, Hannah; Arnold, Steve; Spracklen, Dominick; Rap, Alexandru; Scott, Catherine; Hackenberg, Sina; Carpenter, Lucy</p> <p>2016-04-01</p> <p> model simulates a strong response to monoterpene emissions over remote <span class="hlt">oceans</span> south of 45° S, in particular during <span class="hlt">Southern</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> on CCN concentration. We use an offline radiative transfer model to calculate the radiative effects of the modelled CCN concentrations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006cosp...36.1415L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006cosp...36.1415L"><span>Interannual Trends in <span class="hlt">Southern</span> <span class="hlt">Ocean</span> Sea Surface Temperatures and Sea Level from Remote Sensing Data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lebedev, S. A.</p> <p></p> <p>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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> SST have negative trend about -0 018 -0 035 oC yr In area of Pacific-Antarctic Ridge and of <span class="hlt">southern</span> part of Mid Atlantic Ridge decrease rate is more than -0 075 oC yr SLA increases in all area of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.6945L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.6945L"><span>Increased dust deposition in the Pacific <span class="hlt">Southern</span> <span class="hlt">Ocean</span> during glacial periods</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lamy, Frank; Gersonde, Rainer; Winckler, Gisela; Esper, Oliver; Jaeschke, Andrea; Kuhn, Gerhard; Ullermann, Johannes; Martinez-Garcia, Alfredo; Lambert, Fabrice; Kilian, Rolf</p> <p>2014-05-01</p> <p>Dust deposition across the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. 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 <span class="hlt">southern</span> westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007DSRI...54.1129H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007DSRI...54.1129H"><span>Community structure across a large-scale <span class="hlt">ocean</span> productivity gradient: Marine bird assemblages of the <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hyrenbach, K. David; Veit, Richard R.; Weimerskirch, Henri; Metzl, Nicolas; Hunt, George L., Jr.</p> <p>2007-07-01</p> <p>Our objective was to understand how marine birds respond to oceanographic variability across the <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span> using data collected during an 16-day cruise (4-21 January 2003). We quantified concurrent water mass distributions, <span class="hlt">ocean</span> productivity patterns, and seabird distributions across a heterogeneous pelagic ecosystem from subtropical to sub-Antarctic waters. We surveyed 5155 km and sighted 15,606 birds from 51 species, and used these data to investigate how seabirds respond to spatial variability in the structure and productivity of the <span class="hlt">ocean</span>. We addressed two spatial scales: the structure of seabird communities across macro-mega scale (1000 s km) biogeographic domains, and their coarse-scale (10 s km) aggregation at hydrographic and bathymetric gradients. Both seabird density and species composition changed with latitudinal and onshore-offshore gradients in depth, water temperature, and chlorophyll-a concentration. The average seabird density increased across the subtropical convergence (STC) from 2.4 birds km -2 in subtropical waters to 23.8 birds km -2 in sub-Antarctic waters. The composition of the avifauna also differed across biogeographic domains. Prions ( Pachyptila spp.) accounted for 57% of all sub-Antarctic birds, wedge-tailed shearwaters ( Puffinus pacificus) accounted for 46% of all subtropical birds, and Indian <span class="hlt">Ocean</span> yellow-nosed albatross ( Thallasarche carteri) accounted for 32% of all birds in the STC. While surface feeders were the most abundant foraging guild across the study area, divers were disproportionately more numerous in the sub-Antarctic domain, and plungers were disproportionately more abundant in subtropical waters. Seabird densities were also higher within shallow shelf-slope regions, especially in sub-Antarctic waters, where large numbers of breeding seabirds concentrated. However, we did not find elevated seabird densities along the STC, suggesting that this broad frontal region is not a site of enhanced aggregation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3612620','PMC'); return false;" href="https://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3612620"><span>Link between the double-Intertropical Convergence Zone problem and cloud biases over the <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Hwang, Yen-Ting; Frierson, Dargan M. W.</p> <p>2013-01-01</p> <p>The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the <span class="hlt">Southern</span> Hemisphere tropics, which resembles a <span class="hlt">Southern</span> Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth’s energy budget. Our results show that models with more energy flux into the <span class="hlt">Southern</span> Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> explain most of the model-to-model differences in the amount of excessive precipitation in <span class="hlt">Southern</span> Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models. PMID:23493552</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/23493552','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/23493552"><span>Link between the double-Intertropical Convergence Zone problem and cloud biases over the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hwang, Yen-Ting; Frierson, Dargan M W</p> <p>2013-03-26</p> <p>The double-Intertropical Convergence Zone (ITCZ) problem, in which excessive precipitation is produced in the <span class="hlt">Southern</span> Hemisphere tropics, which resembles a <span class="hlt">Southern</span> Hemisphere counterpart to the strong Northern Hemisphere ITCZ, is perhaps the most significant and most persistent bias of global climate models. In this study, we look to the extratropics for possible causes of the double-ITCZ problem by performing a global energetic analysis with historical simulations from a suite of global climate models and comparing with satellite observations of the Earth's energy budget. Our results show that models with more energy flux into the <span class="hlt">Southern</span> Hemisphere atmosphere (at the top of the atmosphere and at the surface) tend to have a stronger double-ITCZ bias, consistent with recent theoretical studies that suggest that the ITCZ is drawn toward heating even outside the tropics. In particular, we find that cloud biases over the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> explain most of the model-to-model differences in the amount of excessive precipitation in <span class="hlt">Southern</span> Hemisphere tropics, and are suggested to be responsible for this aspect of the double-ITCZ problem in most global climate models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002cosp...34E1901V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002cosp...34E1901V"><span>Observations of frozen skin of <span class="hlt">southern</span> <span class="hlt">ocean</span> from multifrequency scanning microwave radiometer (MSMR) onboard oceansat - 1</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vyas, N.; Bhandari, S.; Dash, M.; Pandey, P.; Khare, N.</p> <p></p> <p>Encircling the Antarctic, <span class="hlt">Southern</span> <span class="hlt">Ocean</span> connects all the three <span class="hlt">oceans</span> 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 <span class="hlt">ocean</span>-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 <span class="hlt">ocean</span> and atmosphere. It also influences the ecosystem of the <span class="hlt">southern</span> <span class="hlt">ocean</span>, 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 <span class="hlt">southern</span> <span class="hlt">ocean</span> 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</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998JMS....17..275P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998JMS....17..275P"><span>Estimates of <span class="hlt">Southern</span> <span class="hlt">Ocean</span> primary production—constraints from predator carbon demand and nutrient drawdown</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Priddle, J.; Boyd, I. L.; Whitehouse, M. J.; Murphy, E. J.; Croxall, J. P.</p> <p>1998-11-01</p> <p>In view of the wide range of estimates for the total primary production for the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> south of the Subantarctic Front—current estimates range from 1.2 to 3.5 Gtonne C year -1—we have examined two indirect methods for assessing primary production. First, we have estimated the primary production needed to sustain the carbon requirements of the endotherm top predators in the ecosystem. Estimation of the carbon requirements for crabeater seals of about 7 Mtonne C year -1 is extrapolated to a value for all endotherm predators of 15-30 Mtonne C year -1. Current data indicate that 70-80% of the diet of this suite of predators is zooplankton (predominantly the euphausiid krill), making for highly efficient transfer from primary production to top predators. Our best estimate of <span class="hlt">Southern</span> <span class="hlt">Ocean</span> primary production by this method is of the order of 1.7 Gtonne C year -1, or an averaged areal primary production of about 30-40 g C m -2 year -1. Our second approach is to estimate primary production from the drawdown of inorganic nutrients, based on the limited suite of studies from which an annual nutrient deficit can be calculated. Again, this indicates annual primary production of the order of 1.5 Gtonne. Although both methods have inherent uncertainties, taken together they provide a relatively robust constraint on annual primary production. For both methods to underestimate primary production by the 1-1.5 Gtonne C implied by the higher current estimates, carbon export from the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> pelagic ecosystem would need to be much higher than is normally found in other <span class="hlt">oceans</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.V43F..07C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.V43F..07C"><span>Volcanism, Iron, and Phytoplankton in the Heard and McDonald Islands Region, <span class="hlt">Southern</span> Indian <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Coffin, M. F.; Arculus, R. J.; Bowie, A. R.; Chase, Z.; Robertson, R.; Trull, T. W.; Heobi in2016 v01 Shipboard Party, T.</p> <p>2016-12-01</p> <p>Phytoplankton supply approximately half of the oxygen in Earth's atmosphere, and iron supply limits the growth of phytoplankton in the anemic <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. Situated entirely within the Indian <span class="hlt">Ocean</span> sector of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> are Australia's only active subaerial volcanoes, Heard and McDonald islands (HIMI) on the central Kerguelen Plateau, a large igneous province. Widespread fields of submarine volcanoes, some of which may be active, extend for distances of up to several hundred kilometers from the islands. The predominantly eastward-flowing Antarctic Circumpolar Current sweeps across the central Kerguelen Plateau, and extensive blooms of phytoplankton are observed on the Plateau down-current of HIMI. The goal of RV Investigator voyage IN2016_V01, conducted in January/February 2016, is to test the hypothesis that hydrothermal fluids, which cool active submarine volcanoes in the HIMI region, ascend from the seafloor and fertilise surface waters with iron, thereby enhancing biological productivity beginning with phytoplankton. Significant initial shipboard results include: Documentation, for the first time, of the role of active HIMI and nearby submarine volcanoes in supplying iron to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. Nearshore waters had elevated dissolved iron levels. Although biomass was not correspondingly elevated, fluorescence induction data indicated highly productive resident phytoplankton. Discovery of >200 acoustic plumes emanating from the seafloor and ascending up to tens of meters into the water column near HIMI. Deep tow camera footage shows bubbles rising from the seafloor in an acoustic plume field north of Heard Island. Mapping 1,000 km2 of uncharted seafloor around HIMI. Submarine volcanic edifices punctuate the adjacent seafloor, and yielded iron-rich rocks similar to those found on HIMI, respectively. Acoustic plumes emanating from some of these features suggest active seafloor hydrothermal systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMPP23B2328S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMPP23B2328S"><span>Present and Past Impact of Glacially Sourced Dust on Iron Fertilization of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shoenfelt, E. M.; Winckler, G.; Kaplan, M. R.; Sambrotto, R.; Bostick, B. C.</p> <p>2016-12-01</p> <p>An increase in iron-containing dust flux and a more efficient biological pump in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> have been associated with the CO2 drawdown and global cooling of the Last Glacial Maximum (LGM). While iron (Fe) mineralogy is known to affect Fe bioavailability through its impact on Fe solubility, there are limited studies investigating the importance of Fe mineralogy in dust fluxes to the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, and no previous studies investigating interactions between eukaryotic phytoplankton and particulate-phase Fe in natural dusts applicable to <span class="hlt">Southern</span> <span class="hlt">Ocean</span> environments. Since physically weathered bedrock becomes less soluble as it becomes weathered and oxidized, we hypothesized that glacially sourced dusts would contain more Fe(II)-rich primary minerals and would be more bioavailable than dusts from areas not impacted by glaciers. We used a series of natural dusts from Patagonia as the sole Fe source in incubation experiments with the model diatom Phaeodactylum tricornutum, and evaluated Fe bioavailability using culture growth rates, cell density, and variable fluorescence. Monod curves were also used to evaluate the efficiency of the different particulates as sources of nutrient Fe. Using these Monod curves fit to growth rates plotted against particulate Fe concentrations, we observed that 1) Fe(II)-rich primary silicates were significantly more effective as an Fe source to diatoms than Fe(III)-rich oxides, that 2) Fe(II) content itself was responsible for the difference in Fe bioavailability/efficiency of the Fe nutrient source, and that 3) surface interactions with the particulates were important. In an effort to explore the possibility that Fe mineralogy impacted Fe bioavailability in past <span class="hlt">oceans</span>, we will present our hypotheses regarding productivity and Fe mineralogy/bioavailability through the last glacial cycle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/26379640','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/26379640"><span>Response of bacterioplankton to iron fertilization of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, Antarctica.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>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</p> <p>2015-01-01</p> <p><span class="hlt">Ocean</span> iron fertilization is an approach to increase CO2 sequestration. The Indo-German iron fertilization experiment "LOHAFEX" was carried out in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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 <span class="hlt">southern</span> <span class="hlt">ocean</span> 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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMOS53A1018G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMOS53A1018G"><span>Wind, mixed-layer depth and Chl-a variability in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gille, S. T.; Carranza, M. M.; Franks, P. J. S.; Girton, J. B.; Johnson, K. S.</p> <p>2014-12-01</p> <p>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span>, contains some of the <span class="hlt">ocean</span>'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 <span class="hlt">Southern</span> <span class="hlt">Ocean</span>. 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 <span class="hlt">ocean</span> 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 <span class="hlt">southern</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMPP43E..07J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMPP43E..07J"><span><span class="hlt">Southern</span> <span class="hlt">Ocean</span> abyssal oxygenation linked to the air-sea partitioning of carbon throughout the last glacial cycle</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jaccard, S.; Galbraith, E. D.; Martinez-Garcia, A.; Anderson, R. F.</p> <p>2015-12-01</p> <p>Although no single mechanism can account for the full amplitude of past atmospheric CO2 variability over glacial interglacial cycles, a build-up of biologically-stored carbon in the deep <span class="hlt">ocean</span> has emerged as a central mechanism for low CO2 during the Last Glacial Maximum (LGM). However, the mechanisms for which this deeply sequestered carbon was released, and the relative importance it played in the history of atmospheric CO2 prior to the LGM, remain subjects of debate. Here, we present new redox-sensitive trace metal records from the Antarctic Zone of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> that provide an unprecedented reconstruction of transient changes in deep <span class="hlt">ocean</span> oxygenation and, by inference, respired carbon storage throughout the last glacial cycle. Our results show that respired carbon was removed from the abyssal <span class="hlt">Southern</span> <span class="hlt">Ocean</span> during the northern hemisphere cold phases of the deglaciation, when atmospheric CO2 rose rapidly, due to a combination of dwindling iron fertilization by dust and enhanced deep <span class="hlt">ocean</span> ventilation. Furthermore, our new records show that the correlation between atmospheric CO2 and abyssal <span class="hlt">Southern</span> <span class="hlt">Ocean</span> oxygenation was maintained throughout most of the prior 80 kyrs, consistent with a unifying role of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> through a coupled control on deep <span class="hlt">ocean</span> circulation and iron fertilization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014QSRv...89...13H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014QSRv...89...13H"><span>Using silicon isotopes to understand the role of the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> in modern and ancient biogeochemistry and climate</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hendry, Katharine R.; Brzezinski, Mark A.</p> <p>2014-04-01</p> <p>The growth of siliceous phytoplankton, mainly diatoms, in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> influences the preformed nutrient inventory in the <span class="hlt">ocean</span> on a global scale. Silicic acid use by diatoms and deep circulation combine to trap dissolved Si in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> resulting in high levels of silica production and expansive diatom oozes in <span class="hlt">Southern</span> <span class="hlt">Ocean</span> sediments. The analysis of the silicon isotope composition of biogenic silica, or opal, and dissolved silicic acid provide insight into the operation of the global marine silicon cycle and the role played by the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> in nutrient supply and carbon drawdown, both in the modern and in the past. Silicon isotope studies of diatoms have provided insight into the history of silica production in surface waters, while the analysis of spicules from deep sea sponges has defined both the spatial and the temporal variability of silicic acid concentrations in the water column; together these - and other - proxies reveal variations in the northward flow of <span class="hlt">Southern</span> <span class="hlt">Ocean</span> intermediate and mode waters and how changes in <span class="hlt">Southern</span> <span class="hlt">Ocean</span> productivity altered their preformed nutrient content. We present a new hypothesis - the "Silicic Acid Ventilation Hypothesis" (SAVH) - to explain the geographical variation of opal-based proxy records, in particular the contrasting patterns of opal burial change found in the low and high latitudes. By understanding the silicon isotope systematics of opal and silicic acid in the modern, we will be able to use opal-based proxies to reconstruct past changes in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> and so investigate its role in global carbon cycling and climate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PhDT.......191C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PhDT.......191C"><span>On the role of atmospheric forcing on upper <span class="hlt">ocean</span> physics in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> and biological impacts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carranza, Magdalena M.</p> <p></p> <p>The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> (SO) plays a key role in regulating climate by absorbing nearly half of anthropogenic carbon dioxide (CO2). Both physical and biogeochemical processes contribute to the net CO2 sink. As a result of global warming and ozone depletion, westerly winds have increased, with consequences for upper <span class="hlt">ocean</span> physics but little is known on how primary producers are expected to respond to changes in atmospheric forcing. This thesis addresses the impact of atmospheric forcing on upper <span class="hlt">ocean</span> dynamics and phytoplankton bloom development in the SO on synoptic storm scales, combining a broad range of observations derived from satellites, reanalysis, profiling floats and <span class="hlt">Southern</span> elephant seals. On atmospheric synoptic timescales (2-10 days), relevant for phytoplankton growth and accumulation, wind speed has a larger impact on satellite Chl-a variability than surface heat fluxes or wind stress curl. In summer, strong winds are linked to deep mixed layers, cold sea surface temperatures and enhanced satellite chlorophyll-a (Chl-a), which suggest wind-driven entrainment plays a role in sustaining phytoplankton blooms at the surface. Subsurface bio-optical data from floats and seals reveal deep Chl-a fluorescence maxima (DFM) are ubiquitous in summer and tend to sit at the base of the mixed layer, but can occur in all seasons. The fact that wind speed and Chl-a correlations are maximal at zero lag time (from daily data) and incubation experiments indicate phytoplankton growth occurs 3-4 days after iron addition, suggests high winds in summer entrain Chl-a from a subsurface maximum. Vertical profiles also reveal Chl-a fluorescence unevenness within hydrographically defined mixed layers, suggesting the biological timescales of adaptation through the light gradient (i.e. growth and/or photoacclimation) are often faster than mixing timescales, and periods of quiescence between storms are long enough for biological gradients to form within the homogeneous layer in density</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFMOS13C1250C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFMOS13C1250C"><span>Comparisons of The Habitat Utilization Of Top Predators In The <span class="hlt">Southern</span> <span class="hlt">Ocean</span> And The North Pacific</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Costa, D. P.; Robinson, P.; Huckstadt, L. E.; Crocker, D. E.; Goebel, M. E.</p> <p>2010-12-01</p> <p>Northern and <span class="hlt">Southern</span> 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 <span class="hlt">southern</span> elephant seals (SES) are distributed throughout the <span class="hlt">southern</span> <span class="hlt">ocean</span>, northern elephant seals (NES) are limited to the Northeast Pacific <span class="hlt">Ocean</span> 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 <span class="hlt">southern</span> 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 <span class="hlt">Southern</span> 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.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70025455','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70025455"><span>Sediment transport and deposition processes near <span class="hlt">ocean</span> outfalls in <span class="hlt">Southern</span> California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lee, H.J.; Noble, M.A.; Xu, Jie; ,</p> <p>2003-01-01</p> <p>An urbanized coastal <span class="hlt">ocean</span> 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 <span class="hlt">southern</span> 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 <span class="hlt">ocean</span>. 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 <span class="hlt">ocean</span> 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 <span class="hlt">ocean</span> does not suggest that bacterial contamination on local beaches is primarily caused by transport of material from the adjacent <span class="hlt">ocean</span> outfall.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/6742211','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/6742211"><span>Plate kinematics and passive margin development in the <span class="hlt">southern</span> Indian <span class="hlt">Ocean</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Coffin, M.F.; Royer, J.Y.; Sclater, J.G. ); Cande, S.C. ); Schlich, R. ); Symonds, P.A. ); Kelts, K. ); Wise, S.W. )</p> <p>1990-05-01</p> <p>The development of the Indian <span class="hlt">Ocean</span> began in the Middle to Late Jurassic with the breakup of Gondwanaland. Marine magnetic anomalies and limited Deep Sea Drilling Project and <span class="hlt">Ocean</span> Drilling Program core samples have been used to date the crust. Fracture zone trends interpreted from satellite (Seasat and Geosat) altimetry and marine seismic, gravity, and magnetic data have been combined with crustal dates to product kinematic models of plate movements. Between Jurassic and Late Cretaceous time the plate tectonic evolution of the Indian <span class="hlt">Ocean</span> is poorly known. Mesozoic marine magnetic anomalies offshore eastern Africa Antarctica, and Western Australia document plate motions during the interval; however, extensive areas of <span class="hlt">oceanic</span> crust from which no anomalies have been identified and a dearth of fracture zones prevent detailed links with the much better defined plate kinematic synthesis of the past 80 m.y. The passive margins of the <span class="hlt">southern</span> Indian <span class="hlt">Ocean</span> flank eastern Africa, Madagascar, Antarctica, and Australia. Simple and pure shear models have been proposed to account for these margins' development but compelling evidence for a unique rifting mechanism has yet to be presented for any part of the margins. Each margin contains rifted and sheared sectors of markedly different structural style. Prerift sedimentary sections typically document a rift phase lasting several tens of millions of years before breakup occurred. Synrift sequences commonly contain evidence of volcanic activity. Variations in sediment supply and type, as well as variations in climate have resulted in widely differing postrift sedimentary sequences along the margins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRC..120..304C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRC..120..304C"><span><span class="hlt">Southern</span> <span class="hlt">Ocean</span> wind-driven entrainment enhances satellite chlorophyll-a through the summer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carranza, Magdalena M.; Gille, Sarah T.</p> <p>2015-01-01</p> <p>Despite being the largest High Nitrate Low Chlorophyll (HNLC) region, the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> sustains phytoplankton blooms through the summer, when presumably there is sufficient light, but nutrients in the euphotic zone have been depleted. Physical processes that can potentially supply nutrients from subsurface waters to the euphotic zone, and promote phytoplankton growth in the summer, have not been fully explored at the large scale. By means of a correlation analysis, this study combines high-resolution satellite observations of <span class="hlt">ocean</span> color, winds and sea surface temperature, surface heat fluxes from reanalysis and Argo mixed-layer depth (MLD) estimates to explore the role of the atmospheric forcing (i.e., winds and surface heat fluxes) on upper <span class="hlt">ocean</span> processes that may help sustain high satellite chlorophyll-a (Chl-a) through the summer. Two physical processes that can supply nutrients to the euphotic zone are: MLD deepening, caused by wind-mixing and/or surface cooling, and Ekman pumping driven by the wind stress curl. We find that high winds correlate with high Chl-a over broad open <span class="hlt">ocean</span> areas, suggesting that transient MLD deepening through wind-mixing (i.e., wind-driven entrainment) helps sustain high Chl-a. Wind-driven entrainment plays a dominant role on time scales associated with atmospheric synoptic storms (i.e., <10 days) and has a larger influence on surface Chl-a than storm scale local Ekman pumping. Based on our analysis of statistically significant correlation patterns, we identify regions in the <span class="hlt">Southern</span> <span class="hlt">Ocean</span> where wind-induced entrainment may play a role in sustaining summer phytoplankton blooms.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008ECSS...80..141N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008ECSS...80..141N"><span>Stormwater plume detection by MODIS imagery in the <span class="hlt">southern</span> California coastal <span class="hlt">ocean</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nezlin, Nikolay P.; DiGiacomo, Paul M.; Diehl, Dario W.; Jones, Burton H.; Johnson, Scott C.; Mengel, Michael J.; Reifel, Kristen M.; Warrick, Jonathan A.; Wang, Menghua</p> <p>2008-10-01</p> <p>Stormwater plumes in the <span class="hlt">southern</span> California coastal <span class="hlt">ocean</span> 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 < 32.0 ("plume") and S > 33.0 ("<span class="hlt">ocean</span>"). The plume optical signatures (i.e., the nLw differences between "plume" and "<span class="hlt">ocean</span>") were most evident during the first 2 days after the rainstorms. To assess the accuracy of plume detection, stations were classified into "plume" and "<span class="hlt">ocean</span>" 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 "<span class="hlt">ocean</span>" 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 <span class="hlt">ocean</span> color. The accuracy of plume detection in terms of FIB exceedances was even lower (64% on average), resulting from low correlation between <span class="hlt">ocean</span> color and bacterial c