scholarly journals Oxygen depletion recorded in upper waters of the glacial Southern Ocean

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Zunli Lu ◽  
Babette A. A. Hoogakker ◽  
Claus-Dieter Hillenbrand ◽  
Xiaoli Zhou ◽  
Ellen Thomas ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Planktonic Foraminifera ◽  
Critical Role ◽  
Oxygen Depletion ◽  
Polar Front ◽  
Ice Age ◽  
Upper Ocean ◽  
Antarctic Polar Front ◽  
Near Surface ◽  
Poor Ventilation

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

scholarly journals Winter Biogeochemical Cycling of Dissolved and Particulate Cadmium in the Indian Sector of the Southern Ocean (GEOTRACES GIpr07 Transect)

2021 ◽  
Vol 8 ◽  
Author(s):  
Ryan Cloete ◽  
Jean C. Loock ◽  
Natasha R. van Horsten ◽  
Susanne Fietz ◽  
Thato N. Mtshali ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Biogeochemical Cycling ◽  
Polar Front ◽  
Water Masses ◽  
Antarctic Polar Front ◽  
Intermediate Water ◽  
Subtropical Zone ◽  
Near Surface ◽  
The Antarctic ◽  
Indian Sector

Winter distributions of dissolved cadmium (dCd) and particulate cadmium (pCd) were measured for the first time in the Indian sector of the Southern Ocean thereby contributing a unique spatial and seasonal dataset. Seven depth profiles, between 41°S and 58°S, were collected along the 30°E longitude during the 2017 austral winter to investigate the biogeochemical cycling of cadmium during a period characterized by contrasting upper water column dynamics compared to summer. Our results support an important role for biological uptake during winter months albeit weaker compared to summer. Distinct, biologically driven changes in cadmium cycling across the transect were observed. For example, surface ratios of pCd to phosphorus (P; pCd:P) increased from 0.37 to 1.07 mmol mol–1 between the subtropical zone (STZ) and the Antarctic zone (AAZ) reflecting increased Cd requirements for diatoms at higher latitudes which, in turn, was driven by a complex relationship between the availability of dCd and dissolved iron (dFe), zinc (dZn) and manganese (dMn). Vertical profiles of pCd:P displayed near-surface maxima consistent with (1) P occurring in two phases with different labilities and the lability of Cd being somewhere in-between and (2) increasing dCd to phosphate (PO4; dCd:PO4) ratios with depth at each station. North of the Antarctic Polar Front (APF), a secondary, deeper pCd:P maximum may reflect an advective signal associated with northward subducting Antarctic Intermediate Water (AAIW). The strong southward increase in surface dCd and dCd:PO4, from approximately 10–700 pmol kg–1 and 40–400 μmol mol–1, respectively, reflected the net effect of preferential uptake and regeneration of diatoms with high Cd content and the upwelling of Cd enriched water masses in the AAZ. Furthermore, distinct dCd versus PO4 relationships were observed in each of the intermediate and deep water masses suggesting that dCd and PO4 distributions at depth are largely the result of physical water mass mixing.

scholarly journals Sea-ice extent in the Southern Ocean during the Last Glacial Maximum: another approach to the problem

1998 ◽  
Vol 27 ◽  
pp. 302-304 ◽  
Author(s):  
Lloyd H. Burckle ◽  
Richard Mortlock
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Surface Sediments ◽  
Open Water ◽  
Ice Cover ◽  
Polar Front ◽  
Age Dating ◽  
Antarctic Polar Front ◽  
Sea Ice Extent ◽  
Biogenic Opal

Determining past sea-ice distribution is an important goal of paleocean-ographers. Here, we present a possible approach to determining past sea-ice distribution in the Southern Ocean during the Last Glaciol Maximum (LGM). Diatoms are the prin-cipal opal-forming organisms south of the Antarctic Polar Front; their productivity is partly mediated by the presence/absence of sea ice. We reasoned that there should be good coherence between percentage biogenic opal in surface sediments and percentage annual sea-ice cover. This hypothesis was tested by comparing percentage biogenic opal in surface sediments against modern-day sea-ice cover in surface waters directly above each core site. The chronology for each core was determined by various means (biostratigraphy, 14C age dating, and carbonate and opal stratigraphy). With the resulting curve we estimate that yearly concentration of sea ice can be determined to within 30%. Using these data, we estimated percentage sea-ice cover during the LGM for a number of sediment sites (50-66°S) from the Southern Ocean. Core sites now beneath 100% open water witnessed some 25-60% sea ice during the LGM, while core sites presently beneath sea ice during half of the year witnessed more than 75% sea-ice cover during the LGM.

scholarly journals Upper-ocean vertical mixing in the Antarctic Polar Front Zone

2005 ◽  
Vol 52 (9-10) ◽  
pp. 1087-1108 ◽  
Author(s):  
Boris Cisewski ◽  
Volker H. Strass ◽  
Hartmut Prandke
Keyword(s):  
Vertical Mixing ◽  
Polar Front ◽  
Upper Ocean ◽  
Antarctic Polar Front ◽  
The Antarctic ◽  
Front Zone

scholarly journals Application of sediment core modelling to interpreting the glacial-interglacial record of Southern Ocean silica cycling

2007 ◽  
Vol 3 (3) ◽  
pp. 387-396 ◽  
Author(s):  
A. Ridgwell
Keyword(s):  
Southern Ocean ◽  
Sediment Core ◽  
Polar Front ◽  
Antarctic Polar Front ◽  
Sea Ice Extent ◽  
Atlantic Sector ◽  
Silica Cycling ◽  
The North ◽  
Late Neogene ◽  
Primary Driver

Abstract. Sediments from the Southern Ocean reveal a meridional divide in biogeochemical cycling response to the glacial-interglacial cycles of the late Neogene. South of the present-day position of the Antarctic Polar Front in the Atlantic sector of the Southern Ocean, biogenic opal is generally much more abundant in sediments during interglacials compared to glacials. To the north, an anti-phased relationship is observed, with maximum opal abundance instead occurring during glacials. This antagonistic response of sedimentary properties provides an important model validation target for testing hypotheses of glacial-interglacial change against, particularly for understanding the causes of the concurrent variability in atmospheric CO2. Here, I illustrate a time-dependent modelling approach to helping understand climates of the past by means of the mechanistic simulation of marine sediment core records. I find that a close match between model-predicted and observed down-core changes in sedimentary opal content can be achieved when changes in seasonal sea-ice extent are imposed, whereas the predicted sedimentary response to iron fertilization on its own is not consistent with sedimentary observations. The results of this sediment record model-data comparison supports previous inferences that the changing cryosphere is the primary driver of the striking features exhibited by the paleoceanographic record of this region.

scholarly journals Distribution of short-finned squid Illex argentinus (Cephalopoda: Ommastrephidae) inferred from the diets of Southern Ocean albatrosses using stable isotope analyses

2015 ◽  
Vol 96 (6) ◽  
pp. 1211-1215 ◽  
Author(s):  
José Seco ◽  
Gustavo A. Daneri ◽  
Filipe R. Ceia ◽  
Rui Pedro Vieira ◽  
Simeon L. Hill ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Southern Ocean ◽  
Polar Front ◽  
Antarctic Polar Front ◽  
Stable Isotope Analyses ◽  
Patagonian Shelf ◽  
Illex Argentinus ◽  
Shelf Region ◽  
The Antarctic ◽  
Isotope Analyses

The diets of marine predators are a potential source of information about range shifts in their prey. For example, the short-finned squid Illex argentinus, a commercially fished species on the Patagonian Shelf in the South Atlantic, has been reported in the diet of grey-headed, Thalassarche chrysostoma; black-browed, T. melanophris; and wandering, Diomedea exulans, albatrosses breeding at Bird Island, South Georgia (54°S 28°W) in the Southern Ocean. Tracking data suggest that these birds may feed on I. argentinus while foraging in Southern Ocean waters during their breeding season. This led to the hypothesis that I. argentinus may occur south of the Antarctic Polar Front. To test this hypothesis, we used stable isotope analyses to assess the origin of I. argentinus. We compared I. argentinus beaks from the diets of the three albatross species with beaks of cephalopod species endemic to the Patagonian Shelf and others from the Southern Ocean. Our results show that I. argentinus from the diet of albatrosses at Bird Island have δ13C values in the range −18.77 to −15.28‰. This is consistent with δ13C values for Octopus tehuelchus, a typical species from the Patagonian Shelf. In contrast, Alluroteuthis antarcticus, a Southern Ocean squid, has typically Antarctic δ13C in the range −25.46 to −18.61‰. This suggests that I. argentinus originated from warmer waters of the Patagonian Shelf region. It is more likely that the albatross species obtained I. argentinus by foraging in the Patagonian Shelf region than that I. argentinus naturally occurs south of the Antarctic Polar Front.

Antarctic Polar Front migrations in the Kerguelen Plateau region, Southern Ocean, over the past 360 kyrs

2021 ◽  
pp. 103526
Author(s):  
M. Civel-Mazens ◽  
X. Crosta ◽  
G. Cortese ◽  
E. Michel ◽  
A. Mazaud ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Polar Front ◽  
Antarctic Polar Front ◽  
Kerguelen Plateau ◽  
Plateau Region ◽  
The Past

Reshuffling of Nutrients in the Southern Ocean

2020 ◽  
Author(s):  
Ivy Frenger ◽  
Ivana Cerovecki ◽  
Matthew Mazloff
Keyword(s):  
Southern Ocean ◽  
Water Mass ◽  
Driving Forces ◽  
Water Masses ◽  
Global Ocean ◽  
Upper Ocean ◽  
Physical Processes ◽  
Near Surface ◽  
Deep Waters ◽  
Ocean Productivity

<p>Deep waters upwell in the Southern Ocean, replete with nutrients. Some of these nutrients enter lighter mode and intermediate waters (MIW), fueling upper ocean productivity in the otherwise nutrient depleted (sub)tropical waters. However some of the upwelled nutrients are retained in the Southern Ocean or leak into denser bottom waters (AABW), making them unavailable for upper ocean productivity. Despite its fundamental importance for the global ocean productivity, this “reshuffling” of nutrients between Southern Ocean water masses, and its driving forces and temporal variability, have not been quantified to date.</p><p>We analyze the globally major limiting macronutrient, nitrate (NO<sub>3</sub>), using the results of a data-assimilating coupled ocean-sea-ice and biogeochemistry model, the Biogeochemical Southern Ocean State Estimate (B-SOSE), for the years 2008 – 2017. Using a water mass framework, applied to five day averaged SOSE output south of 30<sup>o</sup>S, we quantify the processes controlling NO<sub>3</sub> inventories and fluxes. The water mass framework enables us to assess the relative importance of physical processes (such as surface buoyancy fluxes and diapycnal mixing) and biogeochemical processes (such as productivity and remineralization) in driving the transfer of NO<sub>3</sub> from upwelling deep waters (CDW) to MIW and AABW, and its interannual variability.</p><p>Our results show that two thirds of the NO<sub>3</sub> supplied to MIW occurs through lightening, or transforming, of CDW waters during the course of the overturning circulation. The other third of the NO<sub>3</sub> supplied to MIW occurs through upward mixing of NO<sub>3</sub> from NO<sub>3</sub>-enriched CDW. This means that physical processes determine the mean MIW NO<sub>3</sub> content. Biology does not have a net effect on MIW NO<sub>3</sub>: while biological uptake draws down the MIW concentration of  NO<sub>3</sub> near the surface, remineralization of organic matter compensates for this MIW loss below the surface. Also, we find that the productivity in the subtropical waters south of 30<sup>o</sup>S is fed through both, the canonical upward mixing of NO<sub>3</sub> through the thermocline, and through the near surface supply from MIW. Thus, again, water mass transformation is playing a large role in nutrient distributions. </p><p>In ongoing work, we assess the drivers of variability of the reshuffling of NO<sub>3</sub> between water masses and their potential sensitivity to climate change.</p>

scholarly journals Large aggregations of pelagic squid near the ocean surface at the Antarctic Polar Front, and their capture by grey-headed albatrosses

2010 ◽  
Vol 67 (7) ◽  
pp. 1432-1435 ◽  
Author(s):  
Paul G. Rodhouse ◽  
Peter R. Boyle
Keyword(s):  
Ocean Surface ◽  
Polar Front ◽  
Antarctic Polar Front ◽  
Marine Science ◽  
Near Surface ◽  
Midwater Trawl ◽  
The Antarctic

Abstract Rodhouse, P. G., and Boyle, P. R. 2010. Large aggregations of pelagic squid near the ocean surface at the Antarctic Polar Front, and their capture by grey-headed albatrosses. – ICES Journal of Marine Science, 67: 1432–1435. Satellite-tracked squid predators and fish-finding acoustics were used to locate squid concentrations at the Antarctic Polar Front, then to sample them with a midwater trawl. Near-surface hauls were dominated by the squid Martialia hyadesi similar in size to those fed to grey-headed albatross chicks. The characteristics of the squid and their proximity to the surface suggest that the birds locate squid concentrations by olfaction and catch them by plunging.

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