scholarly journals Taxonomy, biogeography and ecology of quaternary Benthic Ostracoda (Crustacea) from circumpolar deep water of the Emerald Basin (Southern Ocean) and the S Tasman Rise (Tasman Sea)

2005 ◽  
Vol 35 (1) ◽  
pp. 1-119 ◽  
Author(s):  
Ilaria Mazzini
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Circumpolar Deep Water ◽  
Tasman Sea

Upper ocean salinity variabilities in the Southern Ocean responding to the recent surface salting in perspective of climate changes

2021 ◽  
Author(s):  
Ling Du ◽  
Xubin Ni
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Water Mass ◽  
Water Cycle ◽  
Upper Ocean ◽  
Tropical Ocean ◽  
Circumpolar Deep Water ◽  
Salinity Changes ◽  
Ocean Salinity ◽  
The Antarctic

<p>Water cycle have prevailed on upper ocean salinity acting as the climate change fingerprint in the numerous observation and simulation works. Water mass in the Southern Ocean accounted for the increasing importance associated with the heat and salt exchanges between Subantarctic basins and tropical oceans. The circumpolar deep water (CDW), the most extensive water mass in the Southern Ocean, plays an indispensable role in the formation of Antarctic Bottom Water. In our study, the observed CTDs and reanalysis datasets are examined to figure out the recent salinity changes in the three basins around the Antarctica. Significant surface salinity anomalies occurred in the South Indian/Pacific sectors south of 60ºS since 2008, which are connected with the enhanced CDW incursion onto the Antarctic continental shelf. Saltier shelf water was found to expand northward from the Antarctica coast. Meanwhile, the freshening of Upper Circumpolar Deep Water(UCDW), salting and submergence of Subantarctic Mode Water(SAMW) were also clearly observed. The modified vertical salinity structures contributed to the deepen mixed layer and enhanced intermediate stratification between SAMW and UCDW. Their transport of salinity flux attributed to the upper ocean processes responding to the recent atmospheric circulation anomalies, such as the Antarctic Oscillation and Indian Ocean Dipole. The phenomena of SAMW and UCDW salinity anomalies illustrated the contemporaneous changes of the subtropical and polar oceans, which reflected the meridional circulation fluctuation. Salinity changes in upper southern ocean (< 2000m) revealed the influence of global water cycle changes, from the Antarctic to the tropical ocean, by delivering anomalies from high- and middle-latitudes to low-latitudes oceans.</p>

scholarly journals Eddy-Resolving Model Estimate of the Cabbeling Effect on the Water Mass Transformation in the Southern Ocean

2012 ◽  
Vol 42 (8) ◽  
pp. 1288-1302 ◽  
Author(s):  
L. Shogo Urakawa ◽  
Hiroyasu Hasumi
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Water Mass ◽  
Formation Rate ◽  
Ocean Model ◽  
Intermediate Water ◽  
Mode Water ◽  
Model Estimate ◽  
Circumpolar Deep Water ◽  
Water Mass Transformation

Abstract Cabbeling effect on the water mass transformation in the Southern Ocean is investigated with the use of an eddy-resolving Southern Ocean model. A significant amount of water is densified by cabbeling: water mass transformation rates are about 4 Sv (1 Sv ≡ 106 m3 s−1) for transformation from surface/thermocline water to Subantarctic Mode Water (SAMW), about 7 Sv for transformation from SAMW to Antarctic Intermediate Water (AAIW), and about 5 Sv for transformation from AAIW to Upper Circumpolar Deep Water. These diapycnal volume transports occur around the Antarctic Circumpolar Current (ACC), where mesoscale eddies are active. The water mass transformation by cabbeling in this study is also characterized by a large amount of densification of Lower Circumpolar Deep Water (LCDW) into Antarctic Bottom Water (AABW) (about 9 Sv). Large diapycnal velocity is found not only along the ACC but also along the coast of Antarctica at the boundary between LCDW and AABW. It is found that about 3 Sv of LCDW is densified into AABW by cabbeling on the continental slopes of Antarctica in this study. This densification is not small compared with observational and numerical estimates on the AABW formation rate, which ranges from 10 to 20 Sv.

scholarly journals The Role of Southern Ocean Surface Forcings and Mixing in the Global Conveyor

2008 ◽  
Vol 38 (7) ◽  
pp. 1377-1400 ◽  
Author(s):  
Daniele Iudicone ◽  
Gurvan Madec ◽  
Bruno Blanke ◽  
Sabrina Speich
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
Thermohaline Circulation ◽  
North Atlantic Deep Water ◽  
Surface Fluxes ◽  
Weddell Sea ◽  
Mode Water ◽  
Circumpolar Deep Water ◽  
Subantarctic Mode Water

Abstract Despite the renewed interest in the Southern Ocean, there are yet many unknowns because of the scarcity of measurements and the complexity of the thermohaline circulation. Hence the authors present here the analysis of the thermohaline circulation of the Southern Ocean of a steady-state simulation of a coupled ice–ocean model. The study aims to clarify the roles of surface fluxes and internal mixing, with focus on the mechanisms of the upper branch of the overturning. A quantitative dynamical analysis of the water-mass transformation has been performed using a new method. Surface fluxes, including the effect of the penetrative solar radiation, produce almost 40 Sv (1 Sv ≡ 106 m3 s−1) of Subantarctic Mode Water while about 5 Sv of the densest water masses (γ > 28.2) are formed by brine rejection on the shelves of Antarctica and in the Weddell Sea. Mixing transforms one-half of the Subantarctic Mode Water into intermediate water and Upper Circumpolar Deep Water while bottom water is produced by Lower Circumpolar Deep Water and North Atlantic Deep Water mixing with shelf water. The upwelling of part of the North Atlantic Deep Water inflow is due to internal processes, mainly downward propagation of the surface freshwater excess via vertical mixing at the base of the mixed layer. A complementary Lagrangian analysis of the thermohaline circulation will be presented in a companion paper.

scholarly journals Carbonate system in the water masses of the Southeast Atlantic sector of the Southern Ocean during February and March 2008

2011 ◽  
Vol 8 (5) ◽  
pp. 1401-1413 ◽  
Author(s):  
M. González-Dávila ◽  
J. M. Santana-Casiano ◽  
R. A. Fine ◽  
J. Happell ◽  
B. Delille ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Frontal Zone ◽  
Water Masses ◽  
Total Alkalinity ◽  
Carbonate System ◽  
Aragonite Saturation ◽  
Atlantic Sector ◽  
Circumpolar Deep Water ◽  
The Antarctic

Abstract. Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) from February to March 2008. Eddies detached from the retroflection of the Agulhas Current increased the gradients observed along the fronts. Minima in the fugacity of CO2, fCO2, and maxima in pH on either side of the frontal zone were observed, noting that within the frontal zone fCO2 reached maximum values and pH was at a minimum. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) offered pHT,25 values of 7.56 and 7.61, respectively. The UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1) as compared to deeper waters, revealing that UCDW was mixed with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentrations. The aragonite saturation horizon was observed at 1000 m in the subtropical area and north of the Subantarctic Front. At the position of the Polar Front, and under the influence of UCDW and LCDW, the aragonite saturation horizon deepened from 800 m to 1500 m at 50.37° S, and reached 700 m south of 57.5° S. High latitudes proved to be the most sensitive areas to predicted anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in dissolved inorganic carbon (CT) and total alkalinity (AT) offered minima values in the Antarctic Intermediate Water and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the status of pH and carbonate saturation. Here we present data that suggest that south of 55° S, surface water will be under-saturated with respect to aragonite within the next few decades.

Diapycnal and Isopycnal Transports in the Southern Ocean Estimated by a Box Inverse Model

2013 ◽  
Vol 43 (11) ◽  
pp. 2270-2287 ◽  
Author(s):  
K. Katsumata ◽  
B. M. Sloyan ◽  
S. Masuda
Keyword(s):  
Southern Ocean ◽  
Mixed Layer ◽  
Deep Water ◽  
General Circulation ◽  
General Circulation Models ◽  
Inverse Model ◽  
Ekman Transport ◽  
Surface Mixed Layer ◽  
Circumpolar Deep Water ◽  
Eddy Transport

Abstract Quantitative descriptions of Circumpolar Deep Water upwelling and evolution into a lighter mode and heavier bottom waters in the Southern Ocean are still not well constrained. Here, data from two occupations of eight hydrographic sections are combined and used in a box inverse model to estimate isopycnal and diapycnal transports in the Southern Ocean. A mixed layer box allows diapycnal transports in the surface mixed layer to be estimated separately. Current velocity at 1000 dbar was constrained by the mean velocity field estimated from subsurface float drift data. The estimated isopycnal transports are largely consistent with past estimates and with outputs of three ocean general circulation models. The estimated subduction and upwelling at the base of the Southern Ocean mixed layer show that Upper Circumpolar Deep Water upwells [16 ± 15 and 17 ± 21 Sv (where 1 Sv ≡ 106 m3 s−1) by different inversion methods] and evolves into heavier Lower Circumpolar Deep Water (5 ± 13 and 6 ± 18 Sv) and Bottom Water (8 ± 9 and 8 ± 13 Sv) or lighter Mode and Intermediate Waters (9 ± 18 and 13 ± 24 Sv). Meridional transport in the surface mixed layer is due to northward Ekman transport and mostly southward eddy transport. In seasonal ice-covered areas near Antarctica, a significant (14 ± 14 Sv) southward transport was found. The southward eddy transport is largest north of the Antarctic Circumpolar Current and decreases poleward because of the poleward decrease in the eddy diffusivity. The interior diapycnal transports, which can be either upward (gaining buoyancy) or downward (gaining density), are comparable in magnitude to the horizontal diapycnal transports within the surface mixed layer.

scholarly journals Carbonate system buffering in the water masses of the Southwest Atlantic sector of the Southern Ocean during February–March 2008

2011 ◽  
Vol 8 (1) ◽  
pp. 435-462
Author(s):  
M. González-Dávila ◽  
J. M. Santana-Casiano ◽  
R. A. Fine ◽  
J. Happell ◽  
B. Delille ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Frontal Zone ◽  
Water Masses ◽  
Intermediate Water ◽  
Carbonate System ◽  
Atlantic Sector ◽  
Circumpolar Deep Water ◽  
The Antarctic

Abstract. Carbonate system variables were measured in the South Atlantic sector of the Southern Ocean along a transect from South Africa to the southern limit of the Antarctic Circumpolar Current (ACC) in February–March 2008. Eddies detach from retroflection of the Agulhas Current located north of the Subantarctic Front (SAF). The eddies increase the gradients observed at the fronts so that minima in fCO2 and maxima in pH in situ on either side of the frontal zone are observed, while within the frontal zone fCO2 reached maximum values and pH in situ was a minimum. Mixing at the frontal zones, in particular where cyclonic rings were located, brought up CO2-rich water (low pH and high nutrient) that spread out the fronts where recent biological production favored by the nutrient input increases the pH in situ and decreases the fCO2 levels. Vertical distributions of water masses were described by their carbonate system properties and their relationship to CFC concentrations. Upper Circumpolar Deep Water (UCDW) and Lower Circumpolar Deep Water (LCDW) had pHT,25 values of 7.56 and 7.61, respectively. UCDW also had higher concentrations of CFC-12 (>0.2 pmol kg−1) as compared to deeper waters, revealing the mixing with recently ventilated waters. Calcite and aragonite saturation states (Ω) were also affected by the presence of these two water masses with high carbonate concentration. Ωarag = 1 was observed at 1000 m in the subtropical area and north of the SAF. At the position of the Polar front and under the influence of UCDW and LCDW Ωarag = 1 deepen from 600 m to 1500 m at 50.37° S, and it reaches to 700 m south of 57.5° S. High latitudes are the most sensitive areas under future anthropogenic carbon increase. Buffer coefficients related to changes in [CO2], [H+] and Ω with changes in CT and AT showed the minimum values are found in the Antarctic Intermediate Water (AAIW), and UCDW layers. These coefficients suggest that a small increase in CT will sharply decrease the pH and the carbonate saturation states. Here we present data that are used to suggest that south of 55° S by the year 2045 surface water will be undersaturated in aragonite.

Circumpolar Deep Water Circulation and Variability in a Coupled Climate Model

2006 ◽  
Vol 36 (8) ◽  
pp. 1523-1552 ◽  
Author(s):  
Agus Santoso ◽  
Matthew H. England ◽  
Anthony C. Hirst
Keyword(s):  
Southern Ocean ◽  
Southern Hemisphere ◽  
Time Scales ◽  
North Atlantic ◽  
Deep Water ◽  
Climate Model ◽  
Coupled Climate Model ◽  
Circumpolar Deep Water ◽  
The North ◽  
The North Atlantic

Abstract The natural variability of Circumpolar Deep Water (CDW) is analyzed using a long-term integration of a coupled climate model. The variability is decomposed using a standard EOF analysis into three separate modes accounting for 68% and 82% of the total variance in the upper and lower CDW layers, respectively. The first mode exhibits an interbasin-scale variability on multicentennial time scales, originating in the North Atlantic and flowing southward into the Southern Ocean via North Atlantic Deep Water (NADW). Salinity dipole anomalies appear to propagate around the Atlantic meridional overturning circulation on these time scales with the strengthening and weakening of NADW formation. The anomaly propagates northward from the midlatitude subsurface of the South Atlantic and sinks in the North Atlantic before flowing southward along the CDW isopycnal layers. This suggests an interhemispheric connection in the generation of the first CDW variability mode. The second mode shows a localized θ−S variability in the Brazil–Malvinas confluence zone on multidecadal to centennial time scales. Heat and salt budget analyses reveal that this variability is controlled by meridional advection driven by fluctuations in the strength of the Deep Western Boundary and the Malvinas Currents. The third mode suggests an Antarctic Intermediate Water source in the South Pacific contributing to variability in upper CDW. It is further found that NADW formation is mainly buoyancy driven on the time scales resolved, with only a weak connection with Southern Hemisphere winds. On the other hand, Southern Hemisphere winds have a more direct influence on the rate of NADW outflow into the Southern Ocean. The model’s spatial pattern of θ−S variability is consistent with the limited observational record in the Southern Hemisphere. However, some observations of decadal CDW θ−S changes are beyond that seen in the model in its unperturbed state.

Deep flow in the Madagascar–Mascarene Basin over the last 150000 years

2005 ◽  
Vol 363 (1826) ◽  
pp. 81-99 ◽  
Author(s):  
I. N. McCave ◽  
T. Kiefer ◽  
D. J. R. Thornalley ◽  
H. Elderfield
Keyword(s):  
Southern Ocean ◽  
Water Flow ◽  
Deep Water ◽  
Last Interglacial ◽  
Circumpolar Deep Water ◽  
The North ◽  
Bottom Waters ◽  
Lower Circumpolar Deep Water ◽  
Sw Indian Ocean ◽  
Fast Flow

The SW Indian Ocean contains at least four layers of water masses with different sources: deep Antarctic (Lower Circumpolar Deep Water) flow to the north, midwater North Indian Deep Water flow to the south and Upper Circumpolar Deep Water to the north, meridional convergence of intermediate waters at 500–1500 m, and the shallow South Equatorial Current flowing west. Sedimentation rates in the area are rather low, being less than 1 cm ka −1 on Madagascar Ridge, but up to 4 cm ka −1 at Amirante Passage. Bottom flow through the Madagascar–Mascarene Basin into Amirante Passage varies slightly on glacial–interglacial time–scales, with faster flow in the warm periods of the last interglacial and minima in cold periods. Far more important are the particularly high flow rates, inferred from silt grain size, which occur at warm–to–cold transitions rather than extrema. This suggests the cause is changing density gradient driving a transiently fast flow. Corroboration is found in the glacial–interglacial range of benthic d 18 O which is ca. 2%, suggesting water close to freezing and at least 1.2 more saline and thus more dense glacial bottom waters than present. Significant density steps are inferred in isotope stage 6, the 5e–5d, and 5a–4 transitions. Oxygen isotope data suggest little change by mixing in glacial bottom water on their northward path. Benthic carbon isotope ratios at Amirante Passage differ from glacial Southern Ocean values, due possibly to absence of a local productivity effect present in the Southern Ocean.

scholarly journals Warm Circumpolar Deep Water at the Western Getz Ice Shelf Front, Antarctica

2019 ◽  
Vol 46 (2) ◽  
pp. 870-878 ◽  
Author(s):  
K. M. Assmann ◽  
E. Darelius ◽  
A. K. Wåhlin ◽  
T. W. Kim ◽  
S. H. Lee
Keyword(s):  
Deep Water ◽  
Ice Shelf ◽  
Circumpolar Deep Water

The work of the Discovery Committee

1950 ◽  
Vol 202 (1068) ◽  
pp. 1-16 ◽  
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Deep Sea ◽  
Original Form ◽  
The Past ◽  
Scientific Staff ◽  
Form Part ◽  
Whaling Industry ◽  
Major Industry ◽  
Colonial Office

The geographical field in which most of the Discovery Committee’s work has been carried out during the past 25 years is the Southern Ocean. This zone of continuous deep water, very rich in marine fife, supports one major industry—the whaling industry—but is otherwise little developed as yet, and seldom visited. It is not easy to find a short descriptive label for the work itself, but nearly all of it comes under the headings of deep-sea oceanography, whales and whaling, or Antarctic geography, and much of it is concerned with the interrelations of these subjects. Since the beginning in 1924 the Discovery Committee has worked under the Colonial Office, but in 1949 the Committee’s functions, together with the scientific staff, the ships, and other assets, were taken over by the Admiralty, and now form part of the new National Institute of Oceanography. The Discovery Committee, in its original form, has been dissolved, but it is encouraging to know that the continuation of its work is assured.

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