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 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 North Atlantic Deep Water export to the Southern Ocean over the past 14 Myr: Evidence from Nd and Pb isotopes in ferromanganese crusts

2002 ◽  
Vol 17 (2) ◽  
pp. 12-1-12-9 ◽  
Author(s):  
Martin Frank ◽  
Nicholas Whiteley ◽  
Sabine Kasten ◽  
James R. Hein ◽  
Keith O'Nions
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
North Atlantic Deep Water ◽  
Pb Isotopes ◽  
Ferromanganese Crusts ◽  
The Past

scholarly journals Thermohaline Fingerprints of the Greenland-Scotland Ridge and Fram Strait Subsidence Histories

2020 ◽  
Author(s):  
Akil Hossain ◽  
Gregor Knorr ◽  
Gerrit Lohmann ◽  
Michael Stärz ◽  
Wilfried Jokat
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
North Atlantic Deep Water ◽  
The Arctic ◽  
Fram Strait ◽  
High Latitudes ◽  
Nordic Seas ◽  
Basin Scale ◽  
Salinity Increase

<p> <span><span>Changes in ocean gateway configuration are known to induce basin-scale rearrangements in ocean characteristics throughout the Cenozoic. </span><span>However, there is large uncertainty in the relative timing of the </span><span>subsidence histories of ocean gateways in the northern high latitudes. By using a fully coupled General Circulation </span><span>Model we investigate the salinity and temperature changes in response to the subsidence of two key ocean gateways in the northern high latitudes during early to middle Miocene. </span><span>Deepening of the Greenland-Scotland Ridge </span><span>causes a salinity increase and warming in the Nordic Seas and the Arctic Ocean. </span><span>While warming this realm, deep water formation takes place at lower temperatures due to a shift of the convection sites to north off Iceland. </span><span>The associated deep ocean cooling and </span><span>upwelling of deep waters to the Southern Ocean surface causes a cooling in the southern high latitudes.</span> <span>These characteristic impacts in response to the </span><span>Greenland-Scotland Ridge</span><span> deepening are independent of the </span><span>Fram Strait</span><span> state.</span> <span>Subsidence of the Fram Strait for a deep Greenland-Scotland Ridge causes </span><span>less pronounced warming and salinity increase</span><span> in </span><span>the </span><span>Nordic Seas. </span><span>A stronger salinity increase is detected in the Arctic while temperatures remain unaltered, which further increases the density of the North Atlantic Deep Water. This causes an enhanced contribution of North Atlantic Deep Water </span><span>to the abyssal ocean and on the expense of the colder southern source water component. These relative changes largely counteract each other and cause little </span><span>warming in the upwelling regions of the Southern Ocean.</span></span></p>

Evidence from Southern Ocean sediments for the effect of North Atlantic deep-water flux on climate

Nature ◽  
1992 ◽  
Vol 355 (6359) ◽  
pp. 416-419 ◽  
Author(s):  
Christopher D. Charles ◽  
Richard G. Fairbanks
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
Water Flux ◽  
North Atlantic Deep Water

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.

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

Nature ◽  
2000 ◽  
Vol 405 (6789) ◽  
pp. 935-938 ◽  
Author(s):  
Randye L. Rutberg ◽  
Sidney R. Hemming ◽  
Steven L. Goldstein
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Water ◽  
Water Flux ◽  
Isotope Ratios ◽  
North Atlantic Deep Water

scholarly journals Tracking water masses using passive-tracer transport in NEMO v3.4 with NEMOTAM: application to North Atlantic Deep Water and North Atlantic Subtropical Mode Water

2019 ◽  
Author(s):  
Dafydd Stephenson ◽  
Simon Müller ◽  
Florian Sévellec
Keyword(s):  
North Atlantic ◽  
Deep Water ◽  
Water Mass ◽  
North Atlantic Deep Water ◽  
The Arctic ◽  
Global Ocean ◽  
Passive Tracer ◽  
Tracer Transport ◽  
Mode Water ◽  
Subtropical Mode Water

Abstract. Water mass ventilation provides an important link between the atmosphere and the global ocean circulation. In this study, we present a newly developed, probabilistic tool for offline water mass tracking. In particular, NEMOTAM, the tangent-linear and adjoint counterpart to the NEMO ocean general circulation model, is modified to allow passive-tracer transport. By terminating dynamic feedbacks in NEMOTAM, tagged water can be tracked forward and backwards in time as a passive dye, producing a probability distribution of pathways and origins, respectively. Upon contact with the surface, the tracer is removed from the system, and a record of ventilation is produced. Two test cases are detailed, examining the creation and fate of North Atlantic Subtropical Mode Water (NASMW) and North Atlantic Deep Water (NADW) in a 2&degree; configuration of NEMO run with repeated annual forcing for up to 400 years. NASMW is shown to have an expected age of 4.5 years, and is predominantly eradicated by internal processes. A bed of more persistent NASMW is detected below the mixed layer with an expected age of 8.7 years It is shown that while model NADW has two distinct outcrops (in the Arctic and North Atlantic), its formation primarily takes place in the subpolar Labrador and Irminger seas. Its expected age is 112 years.

Sign in / Sign up

Export Citation Format

Share Document