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At least 19 recordsLinked to original sources

PubMed2006

Southern Ocean cephalopods.

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.

Animal Migration↗

PubMed2000

Resolving the 'opal paradox' in the Southern Ocean

In the Southern Ocean, high accumulation rates of opal--which forms by precipitation from silica-bearing solutions--have been found in the sediment in spite of low production rates of biogenic silica and carbon in the overlying surface waters. This so-called 'opal paradox' is generally attributed to a higher efficiency of opal preservation in the Southern Ocean than elsewhere. Here we report biogenic silica production rates, opal rain rates in the water column and opal sediment burial rates for the Indian Ocean sector of the Southern Ocean, which show that the assumed opal paradox is a result of underestimated opal production rates and overestimated opal accumulation rates. Our data thus demonstrate that the overall preservation efficiency of biogenic opal in this region is substantially lower than previously thought, and that it lies within a factor of two of the global mean. The comparison of our revised opal preservation efficiencies for the Southern Ocean with existing values from the equatorial Pacific Ocean and the North Atlantic Ocean shows that spatial differences in preservation efficiencies are not the primary reason for the differences in sedimentary opal accumulation. The reconciliation of surface production rates and sedimentary accumulation rates may enable the use of biogenic opal in the reconstruction of palaeo-productivity when the factors that affect the Si/C ratio are better understood.

Journal Article↗

PubMed2006

Observations of change in the Southern Ocean.

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.

Journal Article↗

PubMed2001

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

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.

Adipose Tissue↗

PubMed2000

Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean

During glacial periods, low atmospheric carbon dioxide concentration has been associated with increased oceanic carbon uptake, particularly in the southern oceans. The mechanism involved remains unclear. Because ocean productivity is strongly influenced by nutrient levels, palaeo-oceanographic proxies have been applied to investigate nutrient utilization in surface water across glacial transitions. Here we show that present-day cadmium and phosphorus concentrations in the global oceans can be explained by a chemical fractionation during particle formation, whereby uptake of cadmium occurs in preference to uptake of phosphorus. This allows the reconstruction of past surface water phosphate concentrations from the cadmium/calcium ratio of planktonic foraminifera. Results from the Last Glacial Maximum show similar phosphate utilization in the subantarctic to that of today, but much smaller utilization in the polar Southern Ocean, in a model that is consistent with the expansion of glacial sea ice and which can reconcile all proxy records of polar nutrient utilization. By restricting communication between the ocean and atmosphere, sea ice expansion also provides a mechanism for reduced CO2 release by the Southern Ocean and lower glacial atmospheric CO2.

Journal Article↗

PubMed2004

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

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

Biomass↗

PubMed2006

Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles.

Sea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial-interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago.

Calcium↗

PubMed1999

A possible 20th-century slowdown of southern ocean deep water formation

Chlorofluorocarbon-11 inventories for the deep Southern Ocean appear to confirm physical oceanographic and geochemical studies in the Southern Ocean, which suggest that no more than 5 x 10(6) cubic meters per second of ventilated deep water is currently being produced. This result conflicts with conclusions based on the distributions of the carbon-14/carbon ratio and a quasi-conservative property, PO(4)(*), in the deep sea, which seem to require an average of about 15 x 10(6) cubic meters per second of Southern Ocean deep ventilation over about the past 800 years. A major reduction in Southern Ocean deep water production during the 20th century (from high rates during the Little Ice Age) may explain this apparent discordance. If this is true, a seesawing of deep water production between the northern Atlantic and Southern oceans may lie at the heart of the 1500-year ice-rafting cycle.

Journal Article↗

PubMed2006

The Southern Ocean biogeochemical divide.

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.

Antarctic Regions↗

PubMed2000

The role of the southern ocean in uptake and storage of anthropogenic carbon dioxide

An ocean-climate model that shows high fluxes of anthropogenic carbon dioxide into the Southern Ocean, but very low storage of anthropogenic carbon there, agrees with observation-based estimates of ocean storage of anthropogenic carbon dioxide. This low simulated storage indicates a subordinate role for deep convection in the present-day Southern Ocean. The primary mechanism transporting anthropogenic carbon out of the Southern Ocean is isopycnal transport. These results imply that if global climate change reduces the density of surface waters in the Southern Ocean, isopycnal surfaces that now outcrop may become isolated from the atmosphere, tending to diminish Southern Ocean carbon uptake.

Journal Article↗

PubMed2000

Effect of iron supply on Southern Ocean CO2 uptake and implications for glacial atmospheric CO2.

Photosynthesis by marine phytoplankton in the Southern Ocean, and the associated uptake of carbon, is thought to be currently limited by the availability of iron. One implication of this limitation is that a larger iron supply to the region in glacial times could have stimulated algal photosynthesis, leading to lower concentrations of atmospheric CO2. Similarly, it has been proposed that artificial iron fertilization of the oceans might increase future carbon sequestration. Here we report data from a whole-ecosystem test of the iron-limitation hypothesis in the Southern Ocean, which show that surface uptake of atmospheric CO2 and uptake ratios of silica to carbon by phytoplankton were strongly influenced by nanomolar increases of iron concentration. We use these results to inform a model of global carbon and ocean nutrients, forced with atmospheric iron fluxes to the region derived from the Vostok ice-core dust record. During glacial periods, predicted magnitudes and timings of atmospheric CO2 changes match ice-core records well. At glacial terminations, the model suggests that forcing of Southern Ocean biota by iron caused the initial approximately 40 p.p.m. of glacial-interglacial CO2 change, but other mechanisms must have accounted for the remaining 40 p.p.m. increase. The experiment also confirms that modest sequestration of atmospheric CO2 by artificial additions of iron to the Southern Ocean is in principle possible, although the period and geographical extent over which sequestration would be effective remain poorly known.

Atmosphere↗

PubMed2004

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

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.

Animals↗

PubMed1997

Lipids and buoyancy in Southern ocean pteropods.

The lipids of Clione limacina, a Southern Ocean pteropod (order Gymnosomata), contain 28% diacylglyceryl ether (DAGE) (as percentage of total lipid) whereas the pteropod Limacina helicina (order Thecosomata) lacks DAGE. The alkyl glyceryl ether diols (1-O-alkyl glycerols, GE) of Clione DAGE are dominated by 16:0 (60%) and 15:0 (21%), in contrast with deep-sea shark liver DAGE, which is dominated by 18:1 GE. The fatty acid profiles of Clione and Limacina are similar (28-32% polyunsaturated, 26-34% monounsaturated) as are the sterols, which include 24-methylenecholesterol, transdehydrocholesterol, cholesterol, and desmosterol. This finding probably reflects the fact that Limacina is the major food source for Clione. Spongiobranchaea australis, another Southern Ocean pteropod (order Gymnosomata), has 0.9-1.7% DAGE, but has less lipid (3.3-4.8 mg/g lipid, wet weight) than Clione (50.8 mg/g lipid, wet weight). We propose a buoyancy role for DAGE in Clione since Limacina has bubbles for flotation which Clione lack; DAGE provides 23% more uplift than triacylglycerol at a concentration of 1.025 g/mL seawater.

Animals↗

PubMed1999

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

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

Journal Article↗

PubMed2005

Ecological and biogeographic relationships of class Flavobacteria in the Southern Ocean.

The abundance, spatial distribution and diversity of class Flavobacteria were investigated in the Southern Ocean euphotic zone across a latitudinal transect and in the ice pack off Eastern Antarctica. Surface seawater samples filter-fractionated into 0.8 mum particulate and 0.2 m planktonic fractions were investigated with different molecular techniques. The abundance of particle-associated Flavobacteria, ascertained with real-time PCR and DGGE band analysis using Flavobacteria-specific primers, was found to be significantly higher in Polar Front Zone (PFZ) and Antarctic Zone (AZ) water samples than in nutrient limited Temperate Zone (TZ) and Sub-Antarctic Zone (SAZ) waters. Abundance of particle-associated Flavobacteria correlated positively with seawater chlorophyll a and nutrient concentrations, suggesting that increased Flavobacteria abundance may relate to enhanced primary production in the PFZ and AZ. This is supported by comparison of DGGE profiles that demonstrated significant differences in the total Flavobacteria community structure and 16S rRNA gene diversity between samples from the PFZ and AZ and those from TZ and SAZ. Sequence analysis revealed a broad diversity amongst class Flavobacteria in the Southern Ocean with several Flavobacteria clades detected in PFZ and AZ waters not detected in TZ and SAZ waters that putatively represent psychrophilic taxa. Sequence data included a large, so far uncultivated, cosmopolitan phylogenetic clade ("DE cluster 2") that is distributed throughout the Southern Ocean.

Antarctic Regions↗

PubMed2005

Colonization and community dynamics of class Flavobacteria on diatom detritus in experimental mesocosms based on Southern Ocean seawater.

In order to better understand the ecology of microorganisms responsible for secondary production in the Southern Ocean the activity of Flavobacteria communities on diatom detritus in seawater mesocosms was investigated. Seawater was collected from different parts of the Southern Ocean including the Polar Front Zone (PFZ), ice-edge area of the Antarctic Zone (AZ), and a site in the AZ ice pack. Detritus from the cosmopolitan marine diatom Nitzschia closterium Ehrenberg was resuspended in mesocosms containing seawater filtered to remove particulate organic matter, including particle-associated bacteria and most eukaryotes, but retaining native planktonic bacterial assemblages. Mesocosms were incubated at 2 degrees C and samples analysed for changes in community composition using denaturing gradient gel electrophoresis (DGGE), real-time PCR and fluorescent in-situ hybridization (FISH). DGGE banding patterns and FISH images demonstrated rapid bacterial colonization of the detritus, dominated by members of class gamma-Proteobacteria, alpha-Proteobacteria and Flavobacteria. Real-time PCR data indicated members of class Flavobacteria were involved in initial colonization of detrital aggregate, however relative abundance stayed at similar levels found for the original native particle-associated populations. 16S rRNA gene DGGE banding patterns and sequence analysis demonstrated significant variation in Flavobacteria community structure occurred in the first 20 days of the experiment before community stabilization occurred. The community structures between the three mesocosms also markedly differed and major colonizers were primarily derived from detectable members of the initial particle-associated Flavobacteria community, however the abundant uncultured Flavobacteria agg58 clone-related and DE cluster 2 clades, previously identified in Southern Ocean seawater were not observed to colonize the detritus.

DNA, Bacterial↗

PubMed2002

Warming of the Southern Ocean since the 1950s.

Autonomous Lagrangian Circulation Explorer floats recorded temperatures in depths between 700 and 1100 meters in the Southern Ocean throughout the 1990s. These temperature records are systematically warmer than earlier hydrographic temperature measurements from the region, suggesting that mid-depth Southern Ocean temperatures have risen 0.17 degrees C between the 1950s and the 1980s. This warming is faster than that of the global ocean and is concentrated within the Antarctic Circumpolar Current, where temperature rates of change are comparable to Southern Ocean atmospheric temperature increases.

Journal Article↗

PubMed2001

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

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.

Age Factors↗