North Atlantic versus Southern Ocean contributions to a deglacial surge in deep ocean ventilation

Geology ◽  
2013 ◽  
Vol 41 (6) ◽  
pp. 667-670 ◽  
Author(s):  
L.C. Skinner ◽  
A.E. Scrivner ◽  
D. Vance ◽  
S. Barker ◽  
S. Fallon ◽  
...  
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Ocean ◽  
Ocean Ventilation

scholarly journals Deep ocean ventilation, carbon isotopes, marine sedimentation and the deglacial CO<sub>2</sub> rise

2011 ◽  
Vol 7 (3) ◽  
pp. 771-800 ◽  
Author(s):  
T. Tschumi ◽  
F. Joos ◽  
M. Gehlen ◽  
C. Heinze
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Isotope Composition ◽  
Deep Ocean ◽  
Atmospheric Co2 ◽  
Carbon Cycle Model ◽  
Ocean Ventilation ◽  
Marine Sedimentation ◽  
Sediment Formation ◽  
Ocean Carbon

Abstract. The link between the atmospheric CO2 level and the ventilation state of the deep ocean is an important building block of the key hypotheses put forth to explain glacial-interglacial CO2 fluctuations. In this study, we systematically examine the sensitivity of atmospheric CO2 and its carbon isotope composition to changes in deep ocean ventilation, the ocean carbon pumps, and sediment formation in a global 3-D ocean-sediment carbon cycle model. Our results provide support for the hypothesis that a break up of Southern Ocean stratification and invigorated deep ocean ventilation were the dominant drivers for the early deglacial CO2 rise of ~35 ppm between the Last Glacial Maximum and 14.6 ka BP. Another rise of 10 ppm until the end of the Holocene is attributed to carbonate compensation responding to the early deglacial change in ocean circulation. Our reasoning is based on a multi-proxy analysis which indicates that an acceleration of deep ocean ventilation during early deglaciation is not only consistent with recorded atmospheric CO2 but also with the reconstructed opal sedimentation peak in the Southern Ocean at around 16 ka BP, the record of atmospheric δ13CCO2, and the reconstructed changes in the Pacific CaCO3 saturation horizon.

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 Mid-depth South Atlantic Ocean circulation and chemical stratification during MIS-10 to 12: implications for atmospheric CO<sub>2</sub>

2008 ◽  
Vol 4 (4) ◽  
pp. 333-344 ◽  
Author(s):  
A. J. Dickson ◽  
M. J. Leng ◽  
M. A. Maslin
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Convective Cell ◽  
Ocean Ventilation ◽  
Cape Basin ◽  
Northern Atlantic ◽  
Glacial Periods ◽  
Atlantic Margin

Abstract. A detailed record of benthic foraminifera carbon isotopes from the intermediate-depth South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Northern Atlantic deepwaters consistently penetrated to at least 30° S. Millennial-scale increases in either the mass or flux of northern-sourced deepwaters over the core site occurred alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modelled CO2 drawdown of ~21–30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ~45 ppm drawdown.

scholarly journals Transient Overturning Compensation between Atlantic and Indo-Pacific Basins

2020 ◽  
Vol 50 (8) ◽  
pp. 2151-2172 ◽  
Author(s):  
Shantong Sun ◽  
Andrew F. Thompson ◽  
Ian Eisenman
Keyword(s):  
Southern Ocean ◽  
Time Scales ◽  
North Atlantic ◽  
Climate Models ◽  
Diffusion Processes ◽  
Formation Rate ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Overturning Circulation

AbstractClimate models consistently project (i) a decline in the formation of North Atlantic Deep Water (NADW) and (ii) a strengthening of the Southern Hemisphere westerly winds in response to anthropogenic greenhouse gas forcing. These two processes suggest potentially conflicting tendencies of the Atlantic meridional overturning circulation (AMOC): a weakening AMOC due to changes in the North Atlantic but a strengthening AMOC due to changes in the Southern Ocean. Here we focus on the transient evolution of the global ocean overturning circulation in response to a perturbation to the NADW formation rate. We propose that the adjustment of the Indo-Pacific overturning circulation is a critical component in mediating AMOC changes. Using a hierarchy of ocean and climate models, we show that the Indo-Pacific overturning circulation provides the first response to AMOC changes through wave processes, whereas the Southern Ocean overturning circulation responds on longer (centennial to millennial) time scales that are determined by eddy diffusion processes. Changes in the Indo-Pacific overturning circulation compensate AMOC changes, which allows the Southern Ocean overturning circulation to evolve independently of the AMOC, at least over time scales up to many decades. In a warming climate, the Indo-Pacific develops an overturning circulation anomaly associated with the weakening AMOC that is characterized by a northward transport close to the surface and a southward transport in the deep ocean, which could effectively redistribute heat between the basins. Our results highlight the importance of interbasin exchange in the response of the global ocean overturning circulation to a changing climate.

scholarly journals Mid-depth South Atlantic ocean circulation and chemical stratification during MIS-10 to 12: implications for atmospheric CO<sub>2</sub>

2008 ◽  
Vol 4 (3) ◽  
pp. 667-695 ◽  
Author(s):  
A. J. Dickson ◽  
M. J. Leng ◽  
M. A. Maslin
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
North Atlantic ◽  
Sediment Cores ◽  
Convective Cell ◽  
Intermediate Water ◽  
Ocean Ventilation ◽  
Cape Basin ◽  
Glacial Periods ◽  
Atlantic Margin

Abstract. A detailed record of benthic foraminifera carbon isotopes from the South East Atlantic margin shows little glacial-interglacial variability between MIS-12 to MIS-10, suggesting that Glacial North Atlantic Intermediate Water (GNAIW) consistently penetrated to at least 30° S. Millennial-scale increases in either the mass or flux of GNAIW over the core site occur alongside reductions in Lower North Atlantic Deep Water recorded in North Atlantic sediment cores and show that the lower and intermediate limb of the Atlantic deepwater convective cell oscillated in anti-phase during previous glacial periods. In addition, a 500 yr resolution record of the Cape Basin intermediate-deep δ13C gradient shows that a reduction in deep Southern Ocean ventilation at the end of MIS-11 was consistent with a modelled CO2 drawdown of ~21–30 ppm. Further increases in the Southern Ocean chemical divide during the transition into MIS-10 were completed before minimum CO2 levels were reached, suggesting that other mechanisms such as alkalinity changes were responsible for the remaining ~45 ppm drawdown.

scholarly journals Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events

2020 ◽  
Vol 6 (42) ◽  
pp. eabb3807
Author(s):  
Tao Li ◽  
Laura F. Robinson ◽  
Tianyu Chen ◽  
Xingchen T. Wang ◽  
Andrea Burke ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Deep Sea ◽  
Deep Ocean ◽  
Biological Pump ◽  
Last Deglaciation ◽  
Proxy Data ◽  
Ocean Ventilation ◽  
Carbon Release ◽  
The Last Deglaciation

The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.

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

&lt;p class=&quot;p1&quot;&gt;&lt;span class=&quot;s1&quot;&gt;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.&lt;/span&gt;&lt;/p&gt;

scholarly journals Demons in the North Atlantic: Variability of Deep Ocean Ventilation

2021 ◽  
Vol 48 (9) ◽  
Author(s):  
G. A. MacGilchrist ◽  
H. L. Johnson ◽  
C. Lique ◽  
D. P. Marshall
Keyword(s):  
North Atlantic ◽  
Deep Ocean ◽  
The North ◽  
Ocean Ventilation ◽  
The North Atlantic ◽  
North Atlantic Variability

Was the onset of interhemispheric AMOC slightly prior to Antarctic glaciation at the Eocene-Oligocene transition?

2020 ◽  
Author(s):  
Meir Abelson ◽  
Jonathan Erez
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Atlantic Sector ◽  
The North ◽  
Global Cooling ◽  
Circulation Cell ◽  
Meridional Overturning ◽  
Circumpolar Current

&lt;p&gt;A compilation of benthic &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O from the whole Atlantic and the Southern Ocean (Atlantic sector), shows two major jumps in the interbasinal gradient of d&lt;sup&gt;18&lt;/sup&gt;O (&amp;#916;&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O) during the Eocene and the Oligocene: One at ~40 Ma and the second concomitant with the isotopic event of the Eocene-Oligocene transition (EOT), ~33.7 Ma ago. From previously published circulation models, we show that the first &amp;#916;&amp;#948;&lt;sup&gt;18&lt;/sup&gt;O jump reflects the thermal isolation of Antarctica associated with the proto-Antarctic circumpolar current (ACC). The second marks the onset of interhemispheric northern-sourced circulation cell, similar to the modern Atlantic meridional overturning circulation (AMOC). The onset of AMOC-like circulation probably slightly preceded (100-300 ky) the EOT, as we show by the high resolution profiles of &amp;#948;&lt;sup&gt;18&lt;/sup&gt;O and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C previously published from DSDP/ODP sites in the Southern Ocean and South Atlantic. We suggest that while the shallow proto-ACC supplied the energy for deep ocean convection in the Southern Hemisphere, the onset of the interhemispheric northern circulation cell was due to the significant EOT intensification of deepwater formation in the North Atlantic driven by the Nordic anti-estuarine circulation. This onset of the interhemispheric northern-sourced circulation cell could have prompted the EOT global cooling.&lt;/p&gt;

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