Climate evolution at the last deglaciation: the role of the Southern Ocean

Abstract Northern and southern hemispheric influences—particularly changes in Southern Hemisphere westerly winds (SSW) and Southern Ocean ventilation—triggered the stepwise atmospheric CO2 increase that accompanied the last deglaciation. One approach for gaining potential insights into past changes in SWW/CO2 upwelling is to reconstruct the positions of the northern oceanic fronts associated with the Antarctic Circumpolar Current. Using two deep-sea cores located ~600 km apart off the southern coast of Australia, we detail oceanic changes from ~23 to 6 ka using foraminifer faunal and biomarker alkenone records. Our results indicate a tight coupling between hydrographic and related frontal displacements offshore South Australia (and by analogy, possibly the entire Southern Ocean) and Northern Hemisphere (NH) climate that may help confirm previous hypotheses that the westerlies play a critical role in modulating CO2 uptake and release from the Southern Ocean on millennial and potentially even centennial timescales. The intensity and extent of the northward displacements of the Subtropical Front following well-known NH cold events seem to decrease with progressing NH ice sheet deglaciation and parallel a weakening NH temperature response and amplitude of Intertropical Convergence Zone shifts. In addition, an exceptional poleward shift of Southern Hemisphere fronts occurs during the NH Heinrich Stadial 1. This event was likely facilitated by the NH ice maximum and acted as a coup-de-grâce for glacial ocean stratification and its high CO2 capacitance. Thus, through its influence on the global atmosphere and on ocean mixing, “excessive” NH glaciation could have triggered its own demise by facilitating the destratification of the glacial ocean CO2 state.

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The Driving Mechanisms on Southern Ocean Upwelling Change during the Last Deglaciation

Geosciences ◽

10.3390/geosciences11070266 ◽

2021 ◽

Vol 11 (7) ◽

pp. 266

Author(s):

Wei Liu ◽

Zhengyu Liu ◽

Shouwei Li

Keyword(s):

Southern Ocean ◽

Climate Model ◽

Model Simulation ◽

Early Stage ◽

Surface Wind ◽

Ekman Pumping ◽

Last Deglaciation ◽

Buoyancy Forcing ◽

Local Topography ◽

The Last Deglaciation

We explore the change in Southern Ocean upwelling during the last deglaciation, based on proxy records and a transient climate model simulation. Our analyses suggest that, beyond a conventional mechanism of the Southern Hemisphere westerlies shift, Southern Ocean upwelling is strongly influenced by surface buoyancy forcing and the local topography. Over the Antarctic Circumpolar Current region, the zonal mean and local upwelled flows exhibited distinct evolution patterns during the last deglaciation, since they are driven by different mechanisms. The zonal mean upwelling is primarily driven by surface wind stress via zonal mean Ekman pumping, whereas local upwelling is driven by both wind and buoyancy forcing, and is tightly coupled to local topography. During the early stage of the last deglaciation, the vertical extension of the upwelled flows increased downstream of submarine ridges but decreased upstream, which led to enhanced and diminished local upwelling, downstream and upstream of the submarine ridges, respectively.

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

Science Advances ◽

10.1126/sciadv.abb3807 ◽

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.

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Impact of ice sheet reconstructions on the deglacial climate in iLOVECLIM

10.5194/egusphere-egu21-8776 ◽

2021 ◽

Author(s):

Nathaelle Bouttes ◽

Didier Roche ◽

Fanny Lhardy ◽

Aurelien Quiquet ◽

Didier Paillard ◽

...

Keyword(s):

Boundary Conditions ◽

Ice Sheets ◽

Ice Sheet ◽

Last Deglaciation ◽

Antarctic Ice Sheet ◽

Intermediate Complexity ◽

Climate Evolution ◽

The Last Deglaciation ◽

The Antarctic ◽

The Impact

The last deglaciation is a time of large climate transition from a cold Last Glacial Maximum at 21,000 years BP with extensive ice sheets, to the warmer Holocene 9,000 years BP onwards with reduced ice sheets. Despite more and more proxy data documenting this transition, the evolution of climate is not fully understood and difficult to simulate. The PMIP4 protocol (Ivanovic et al., 2016) has indicated which boundary conditions to use in model simulations during this transition. The common boundary conditions should enable consistent multi model and model-data comparisons. While the greenhouse gas concentration evolution and orbital forcing are well known and easy to prescribe, the evolution of ice sheets is less well constrained and several choices can be made by modelling groups. First, two ice sheet reconstructions are available: ICE-6G (Peltier et al., 2015) and GLAC-1D (Tarasov et al., 2014). On top of topographic changes, it is left to modelling groups to decide whether to account for the associated bathymetry and land-sea mask changes, which is technically more demanding. These choices could potentially lead to differences in the climate evolution, making model comparisons more complicated.We use the iLOVECLIM model of intermediate complexity (Goosse et al., 2010) to evaluate the impact of different ice sheet reconstructions and the effect of bathymetry changes on the global climate evolution during the Last deglaciation. We test the two ice sheet reconstructions (ICE-6G and GLAC-1D), and have implemented changes of bathymetry and land-sea mask. In addition, we also evaluate the impact of accounting for the Antarctic ice sheet evolution compared to the Northern ice sheets only.We show that despite showing the same long-term changes, the two reconstructions lead to different evolutions. The bathymetry plays a role, although only few changes take place before ~14ka. Finally, the impact of the Antarctic ice sheet is important during the deglaciation and should not be neglected.ReferencesGoosse, H., et al., Description of the Earth system model of intermediate complexity LOVECLIM version 1.2, Geosci. Model Dev., 3, 603&#8211;633, https://doi.org/10.5194/gmd-3-603-2010, 2010Ivanovic, R. F., et al., Transient climate simulations of the deglaciation 21&#8211;9&#160;thousand years before present (version&#160;1) &#8211; PMIP4 Core experiment design and boundary conditions, Geosci. Model Dev., 9, 2563&#8211;2587, https://doi.org/10.5194/gmd-9-2563-2016, 2016Peltier, W. R., Argus, D. F., and Drummond, R., Space geodesy constrains ice age terminal deglaciation: The global ICE-6G_C (VM5a) model, J. Geophys. Res.-Sol. Ea., 120, 450&#8211;487, doi:10.1002/2014JB011176, 2015Tarasov,L., &#160;et al., The global GLAC-1c deglaciation chronology, melwater pulse 1-a, and a question of missing ice, IGS Symposium on Contribution of Glaciers and Ice Sheets to Sea-Level Change, 2014

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Carbon isotope records reveal precise timing of enhanced Southern Ocean upwelling during the last deglaciation

Nature Communications ◽

10.1038/ncomms3758 ◽

2013 ◽

Vol 4 (1) ◽

Cited By ~ 81

Author(s):

Giuseppe Siani ◽

Elisabeth Michel ◽

Ricardo De Pol-Holz ◽

Tim DeVries ◽

Frank Lamy ◽

...

Keyword(s):

Southern Ocean ◽

Carbon Isotope ◽

Last Deglaciation ◽

Precise Timing ◽

The Last Deglaciation

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Southern Ocean source of 14C-depleted carbon in the North Pacific Ocean during the last deglaciation

Nature Geoscience ◽

10.1038/ngeo987 ◽

2010 ◽

Vol 3 (11) ◽

pp. 770-773 ◽

Cited By ~ 47

Author(s):

C. Basak ◽

E. E. Martin ◽

K. Horikawa ◽

T. M. Marchitto

Keyword(s):

Pacific Ocean ◽

Southern Ocean ◽

North Pacific ◽

North Pacific Ocean ◽

Last Deglaciation ◽

The North ◽

The Last Deglaciation ◽

The North Pacific

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Sequence of events during the last deglaciation in Southern Ocean sediments and Antarctic ice cores

Paleoceanography ◽

10.1029/2000pa000599 ◽

2002 ◽

Vol 17 (4) ◽

pp. 8-1-8-7 ◽

Cited By ~ 88

Author(s):

A. Shemesh ◽

D. Hodell ◽

X. Crosta ◽

S. Kanfoush ◽

C. Charles ◽

...

Keyword(s):

Southern Ocean ◽

Ice Cores ◽

Last Deglaciation ◽

Sequence Of Events ◽

The Last Deglaciation

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Role of the tropical Atlantic for the interhemispheric heat transport during the last deglaciation

Paleoceanography and Paleoclimatology ◽

10.1029/2020pa004107 ◽

2021 ◽

Author(s):

Karl J. F. Meier ◽

André Bahr ◽

Cristiano M. Chiessi ◽

Ana Luiza Albuquerque ◽

Jacek Raddatz ◽

...

Keyword(s):

Heat Transport ◽

Tropical Atlantic ◽

Last Deglaciation ◽

The Last Deglaciation

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On new developments in accelerator mass spectrometry and how they promote our understanding of global carbon cycle dynamics during the last deglaciation

10.5194/egusphere-egu2020-12768 ◽

2020 ◽

Author(s):

Julia Gottschalk ◽

Robert F. Anderson ◽

David A. Hodell ◽

Alfredo Martinez-Garcia ◽

Alain Mazaud ◽

...

Keyword(s):

High Resolution ◽

Southern Ocean ◽

Bottom Water ◽

Deep Ocean ◽

Global Ocean ◽

Last Deglaciation ◽

Surface Ocean ◽

Ocean Atmosphere ◽

The Last Deglaciation ◽

Reservoir Age

Ocean-atmosphere 14C disequilibria of the surface and deep ocean reflect past changes in the efficiency of ocean-atmosphere CO2 exchange and ocean mixing, while it may also be related to variations in global-ocean respired carbon content. A full assessment of the oceanic mechanisms controlling deglacial changes in atmospheric CO2 is complicated by a lack of high-resolution 14C ventilation age estimates from the Southern Ocean and other key regions due to low foraminiferal abundances in marine sediments in those areas. Here we present high-resolution deglacial 14C ventilation age records from key sites in the Atlantic and Indian Sector of the Southern Ocean obtained by radiocarbon analyses of small benthic and planktic foraminiferal samples (<1 mg CaCO3) with the UniBe Mini-Carbon Dating System (MICADAS). Our analyses specifically circumvent foraminiferal sample size requirements related to &#8220;conventional&#8221; accelerator mass spectrometer analyses involving sample graphitization (>1 mg CaCO3 in most laboratories). Complementing multi-proxy analyses of sea surface temperature (SST) changes at these sites allow the construction of a radiocarbon-independent age model through a stratigraphic alignment of SST changes to Antarctic (ice core) temperature variations. We demonstrate the value of refining the age models of our study cores on the basis of high-resolution sedimentary U- and Th flux estimates, which allows an improved quantification of surface ocean reservoir age variations in the past. The resulting deep-ocean ventilation age changes are compared against qualitative and quantitative indicators of bottom water [O2] variations, in order to assess the role of Southern Ocean overturning dynamics in respired carbon changes at our study sites. We discuss the implications of our new radiocarbon- and bottom water [O2] data for the ocean&#8217;s role in atmospheric CO2 changes throughout the last deglaciation, and evaluate down-stream effects of southern high-latitude surface ocean reservoir age anomalies.

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Release of old carbon from the deep South Pacific during the last deglaciation

10.5194/egusphere-egu2020-4230 ◽

2020 ◽

Author(s):

Yuhao Dai ◽

Jimin Yu ◽

Patrick Rafter

Keyword(s):

Southern Ocean ◽

Deep Ocean ◽

South Pacific ◽

Deep South ◽

Last Deglaciation ◽

Age Model ◽

The Last Deglaciation ◽

The Antarctic ◽

First Time ◽

Underlying Processes

The release of old carbon via the Southern Ocean has been thought to contribute to the last deglacial atmospheric CO2 rise, but underlying processes are not fully understood, in part, due to insufficient high-fidelity radiocarbon (&#916;14C) reconstructions minimally complicated by age models and release of &#8220;dead carbon&#8221;. Here, we present a new deep-water &#916;14C record for a core located at 3.3 km water depth from the Southwest Pacific, based on a robust age model using planktonic Mg/Ca along with co-existing benthic 14C measurements. Our results confirm previous records that suggest enhanced ventilation in the Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. For the first time, our data show a large &#916;14C decline during the Antarctic Cold Reversal, indicating strengthened stratification in the deep South Pacific. Our results strongly support that the deep ocean supplied old carbon to the atmosphere during the last deglaciation.

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