scholarly journals The influence of Southern Ocean surface buoyancy forcing on glacial-interglacial changes in the global deep ocean stratification

2016 ◽  
Vol 43 (15) ◽  
pp. 8124-8132 ◽  
Author(s):  
S. Sun ◽  
I. Eisenman ◽  
A. L. Stewart
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
Ocean Surface ◽  
Ocean Stratification ◽  
Buoyancy Forcing ◽  
Surface Buoyancy

scholarly journals Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks

2020 ◽  
Vol 117 (9) ◽  
pp. 4498-4504 ◽  
Author(s):  
Karl Stein ◽  
Axel Timmermann ◽  
Eun Young Kwon ◽  
Tobias Friedrich
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Sea Ice ◽  
General Circulation ◽  
Deep Ocean ◽  
General Circulation Models ◽  
Ice Dynamics ◽  
Carbon Cycle Model ◽  
Ocean Stratification ◽  
Ocean Ventilation

The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here, we use a transient run of an intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of 10. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared with the current climate. Sensitivity tests with a steady-state carbon cycle model indicate that the two mechanisms combined can reduce atmospheric carbon by 40 ppm, with ocean stratification acting early within a glacial cycle to amplify the carbon cycle response.

scholarly journals On the Importance of Surface Forcing in Conceptual Models of the Deep Ocean

2014 ◽  
Vol 44 (3) ◽  
pp. 891-899 ◽  
Author(s):  
Andrew L. Stewart ◽  
Raffaele Ferrari ◽  
Andrew F. Thompson
Keyword(s):  
Conceptual Models ◽  
Deep Ocean ◽  
Surface Fluxes ◽  
Meridional Overturning Circulation ◽  
Surface Boundary ◽  
Buoyancy Forcing ◽  
Surface Boundary Condition ◽  
Meridional Overturning ◽  
Surface Buoyancy ◽  
The Antarctic

Abstract In the major ocean basins, diapycnal mixing upwells dense Antarctic Bottom Water, which returns southward and closes the deepest cell of the meridional overturning circulation (MOC). This cell ventilates the deep ocean and regulates the partitioning of CO2 between the atmosphere and the ocean. The oceanographic community's conceptual understanding of the deep stratification and MOC has evolved from classic “abyssal recipes” arguments to a more recent appreciation of along-isopycnal upwelling in the Southern Ocean, consistent with a weakly mixed ocean interior. Both the deep stratification and the deep MOC are shown here to be sensitive to the form of the surface buoyancy forcing in a two-dimensional model that includes a circumpolar channel and northern basin. For a fixed surface buoyancy condition, the deep stratification is essentially prescribed, whereas for a fixed surface buoyancy flux, the deep stratification varies by orders of magnitude over the range of diapycnal diffusivity κ observed in the ocean. These cases also produce different scalings for the deep MOC with κ, in both weak and strong κ regimes. In addition, these scalings are shown to be sensitive not only to the type of surface boundary condition, but also to the latitudinal structure of the surface fluxes. This latter point is crucial as buoyancy budgets and dynamical features of the circulation are poorly constrained along the Antarctic margins. This study emphasizes the need for caution in the interpretation of simple conceptual models that, while useful, may not include all mechanisms that contribute to the MOC’s strength and structure.

Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks over the last eight glacial cycles

2020 ◽  
Author(s):  
Karl Stein ◽  
Axel Timmermann ◽  
Eun Young Kwon ◽  
Tobias Friedrich
Keyword(s):  
Carbon Sequestration ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Sea Ice ◽  
Deep Ocean ◽  
Glacial Cycles ◽  
Ice Dynamics ◽  
Ocean Stratification ◽  
Ocean Ventilation ◽  
The Impact

<p class="p1"><span class="s1">The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here we use a transient run of the LOVECLIM intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea-ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of ten. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared to the current climate. The impact of the two mechanisms on carbon sequestration was then tested within a steady-state carbon cycle. The two mechanisms combined can reduce atmospheric carbon by 40 ppm, of which approximately 30 ppm is due to ocean stratification. Moreover, ocean stratification from increased SO sea ice production acts early within glacial cycles to amplify the carbon cycle response.</span></p>

scholarly journals The Roles of Wind and Sea Ice in Driving the Deglacial Change in the Southern Ocean Upwelling: A Modeling Study

2021 ◽  
Vol 13 (1) ◽  
pp. 353
Author(s):  
Gagan Mandal ◽  
Shih-Yu Lee ◽  
Jia-Yuh Yu
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Southern Hemisphere ◽  
Wind Stress ◽  
Deep Ocean ◽  
Last Deglaciation ◽  
Buoyancy Forcing ◽  
Antarctic Sea Ice ◽  
Freshwater Fluxes ◽  
Deep Ocean Water

The Southern Ocean (SO) played a fundamental role in the deglacial climate system by exchanging carbon-rich deep ocean water with the surface. The contribution of the SO’s physical mechanisms toward improving our understanding of SO upwelling’s dynamical changes is developing. Here, we investigated the simulated transient SO atmosphere, ocean, and sea ice evolution during the last deglaciation in a fully coupled Earth system model. Our results showed that decreases in SO upwelling followed the weakening of the Southern Hemisphere surface westerlies, wind stress forcing, and Antarctic sea ice coverage from the Last Glacial Maximum to the Heinrich Stadial 1 and the Younger Dryas. Our results support the idea that the SO upwelling is primarily driven by wind stress forcing. However, during the onset of the Holocene, SO upwelling increased while the strength of the wind stress decreased. The Antarctic sea ice change controlled the salt and freshwater fluxes, ocean density, and buoyancy flux, thereby influencing the SO’s dynamics. Our study highlighted the dynamic linkage of the Southern Hemisphere westerlies, ocean, and sea ice in the SO’s latitudes. Furthermore, it emphasized that zonal wind stress forcing and buoyancy forcing control by sea ice together regulate the change in the SO upwelling.

Ocean stratification under oscillatory surface buoyancy forcing

2011 ◽  
Vol 69 (4) ◽  
pp. 523-543 ◽  
Author(s):  
Ross W. Griffiths ◽  
Nicola Maher ◽  
Graham O. Hughes
Keyword(s):  
Ocean Stratification ◽  
Buoyancy Forcing ◽  
Surface Buoyancy

scholarly journals Sensitivity of the Southern Ocean overturning circulation to surface buoyancy forcing

2011 ◽  
Vol 38 (14) ◽  
pp. n/a-n/a ◽  
Author(s):  
Adele K. Morrison ◽  
Andrew M. Hogg ◽  
Marshall L. Ward
Keyword(s):  
Southern Ocean ◽  
Overturning Circulation ◽  
Buoyancy Forcing ◽  
Surface Buoyancy

scholarly journals Response of Southern Ocean Convection and Abyssal Overturning to Surface Buoyancy Perturbations

2015 ◽  
Vol 28 (10) ◽  
pp. 4263-4278 ◽  
Author(s):  
Adele K. Morrison ◽  
Matthew H. England ◽  
Andrew McC. Hogg
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
Ocean Model ◽  
Surface Relaxation ◽  
Ocean Temperature ◽  
Surface Cooling ◽  
Overturning Circulation ◽  
Surface Warming ◽  
Freshwater Fluxes ◽  
Surface Buoyancy

Abstract This study explores how buoyancy-driven modulations in the abyssal overturning circulation affect Southern Ocean temperature and salinity in an eddy-permitting ocean model. Consistent with previous studies, the modeled surface ocean south of 50°S cools and freshens in response to enhanced surface freshwater fluxes. Paradoxically, upper-ocean cooling also occurs for small increases in the surface relaxation temperature. In both cases, the surface cooling and freshening trends are linked to reduced convection and a slowing of the abyssal overturning circulation, with associated changes in oceanic transport of heat and salt. For small perturbations, convective shutdown does not begin immediately, but instead develops via a slow feedback between the weakened overturning circulation and buoyancy anomalies. Two distinct phases of surface cooling are found: an initial smaller trend associated with the advective (overturning) adjustment of up to ~60 yr, followed by more rapid surface cooling during the convective shutdown period. The duration of the first advective phase decreases for larger forcing perturbations. As may be expected during the convective shutdown phase, the deep ocean warms and salinifies for both types of buoyancy perturbation. However, during the advective phase, the deep ocean freshens in response to freshwater perturbations but salinifies in the surface warming perturbations. The magnitudes of the modeled surface and abyssal trends during the advective phase are comparable to the recent observed multidecadal Southern Ocean temperature and salinity changes.

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