Southern Ocean sea ice and frontal changes during the Late Quaternary and their linkages to Asian summer monsoon

Nair, Abhilash; Mohan, Rahul; Crosta, Xavier; Manoj, M.C.; Thamban, Meloth; Marieu, Vincent

doi:10.1016/j.quascirev.2019.04.007

Cited by 32 publications

(26 citation statements)

References 80 publications

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“…Unfortunately, there are too-few proxy data available to robustly constrain the location of the austral summer sea-ice edge. We thus extrapolated the modern relationship between summer sea-ice extent and SST, whereby summer sea ice lies south of the 0 • C isotherm (Nicol et al, 2000) to the LGM. Caution is therefore needed when using the results, as this summer contour is not well constrained.…”

Section: Experimental Datamentioning

confidence: 99%

Impact of Southern Ocean surface conditions on deep ocean circulation during the LGM: a model analysis

et al. 2021

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Abstract. Changes in water mass distribution are considered to be a significant contributor to the atmospheric CO2 concentration drop to around 186 ppm recorded during the Last Glacial Maximum (LGM). Yet simulating a glacial Atlantic Meridional Overturning Circulation (AMOC) in agreement with paleotracer data remains a challenge, with most models from previous Paleoclimate Modelling Intercomparison Project (PMIP) phases showing a tendency to simulate a strong and deep North Atlantic Deep Water (NADW) instead of the shoaling inferred from proxy records of water mass distribution. Conversely, the simulated Antarctic Bottom Water (AABW) is often reduced compared to its pre-industrial volume, and the Atlantic Ocean stratification is underestimated with respect to paleoproxy data. Inadequate representation of surface conditions, driving deep convection around Antarctica, may explain inaccurately simulated bottom water properties in the Southern Ocean. We investigate here the impact of a range of surface conditions in the Southern Ocean in the iLOVECLIM model using nine simulations obtained with different LGM boundary conditions associated with the ice sheet reconstruction (e.g., changes of elevation, bathymetry, and land–sea mask) and/or modeling choices related to sea-ice export, formation of salty brines, and freshwater input. Based on model–data comparison of sea-surface temperatures and sea ice, we find that only simulations with a cold Southern Ocean and a quite extensive sea-ice cover show an improved agreement with proxy records of sea ice, despite systematic model biases in the seasonal and regional patterns. We then show that the only simulation which does not display a much deeper NADW is obtained by parameterizing the sinking of brines along Antarctica, a modeling choice reducing the open-ocean convection in the Southern Ocean. These results highlight the importance of the representation of convection processes, which have a large impact on the water mass properties, while the choice of boundary conditions appears secondary for the model resolution and variables considered in this study.

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Section: Experimental Datamentioning

confidence: 99%

Impact of Southern Ocean surface conditions on deep ocean circulation during the LGM: a model analysis

et al. 2021

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“…The numerical simulations are compared to a compilation of 149 proxy records covering the LGM (See Table S1 in the Supplement, Allen et al 2011;Benz et al 2016;Ferry et al 2015;Xiao et al 2016;Gersonde et al 2005;Ghadi et al 2020;Nair et al 2019). Of these, quantitative sea-surface temperature was reconstructed in 138 locations, proxy for winter sea-ice presence or concentration was available in 149 locations and proxy for summer sea-ice presence was available in 132 locations.…”

Section: Lgm Numerical Simulations and Proxy Datamentioning

confidence: 99%

“…However, the models exhibit large differences in austral summer sea-ice coverage with one model simulating a sea-ice edge at 55˚S (CCSM4), while two others (GISS-E2-R and CNRM) simulate an almost ice-free Southern Ocean. Our comparison with available summer sea-ice records is limited as there are only six sediment core locations that reflect the presence of summer sea ice (Allen et al, 2011;Benz et al, 2016;Ferry et al, 2015;Gersonde et al, 2005;Ghadi et al, 2020;Nair et al, 2019;Xiao et al, 2016). Additionally, these six locations are grouped within two small regions.…”

Section: Dynamic Control On Summer Sea-ice Extentmentioning

confidence: 99%

Evaluating seasonal sea-ice cover over the Southern Ocean from the Last Glacial Maximum

Green¹,

Menviel²,

Meißner³

et al. 2020

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Abstract. Sea-ice cover over the Southern Ocean responds to and impacts Southern Ocean dynamics and, thus, mid to high latitude climate in the Southern Hemisphere. In addition, sea-ice cover can significantly modulate the carbon exchange between the atmosphere and the ocean. As climate models are the only tool available to project future climate changes, it is important to assess their performance in simulating past changes. The Last Glacial Maximum (LGM, ∼21,000 years ago) represents an interesting target as it is a relatively well documented period with climatic conditions and a carbon cycle very different from pre-industrial conditions. Here, we study the changes in seasonal Antarctic sea-ice cover as simulated in numerical PMIP3 and LOVECLIM simulations of the LGM, and their relationship with windstress and ocean temperature. Simulations and paleo-proxy records suggest a fairly well constrained glacial winter sea-ice edge at 51.5° S (1 sigma range: 50°–55.5° S). Simulated glacial summer sea-ice cover however differs widely between models, ranging from almost no sea ice to a sea-ice edge reaching 55.5° S. The austral summer multi-model mean sea-ice edge lies at ∼60.5° S (1 sigma range: 57.5°–70.5° S). Given the lack of strong constraints on the summer sea-ice edge based on sea-ice proxy records, we extend our model-data comparison to summer sea-surface temperature. Our analysis suggests that the multi-model mean summer sea ice provides a reasonable, albeit upper end, estimate of the austral summer sea-ice edge allowing us to conclude that the multi-model mean of austral summer and winter sea-ice cover seem to provide good estimates of LGM conditions. Using these best estimates, we find that there was a larger sea-ice seasonality during the LGM compared to the present day.

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“…1). The incremental evolutions of this transfer function over the last 20 years have yielded robust SST and sea-ice reconstructions when compared alongside other proxies within the same cores (Civel-Mazens et al, 2021;Crosta et al, 2004;Ghadi et al, 2020;Nair et al, 2019;Shemesh et al, 2002).…”

Section: Modern Analogue Technique (Mat)mentioning

confidence: 99%

Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage 5e

et al. 2022

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Abstract. Environmental conditions during Marine Isotope Stage (MIS) 5e (130–116 ka) represent an important “process analogue” for understanding the climatic responses to present and future anthropogenic warming. The response of Antarctic sea ice to global warming is particularly uncertain due to the short length of the observational record. Reconstructing Antarctic winter sea-ice extent during MIS 5e therefore provides insights into the temporal and spatial patterns of sea-ice change under a warmer-than-present climate. This study presents new MIS 5e records from nine marine sediment cores located south of the Antarctic Polar Front between 55 and 70∘ S. Winter sea-ice extent and sea-surface temperatures are reconstructed using marine diatom assemblages and a modern analogue technique transfer function, and changes in these environmental variables between the three Southern Ocean sectors are investigated. The Atlantic and East Indian sector records show much more variable MIS 5e winter sea-ice extent and sea-surface temperatures than the Pacific sector records. High variability in the Atlantic sector winter sea-ice extent is attributed to high glacial meltwater flux in the Weddell Sea, indicated by increased abundances of the diatom species Eucampia antarctica and Fragilariopsis cylindrus. The high variability in the East Indian sector winter sea-ice extent is conversely believed to result from large latitudinal migrations of the flow bands of the Antarctic Circumpolar Current, inferred from latitudinal shifts in the sea-surface temperature isotherms. Overall, these findings suggest that Pacific sector winter sea ice displays a low sensitivity to warmer climates. The different variability and sensitivity of Antarctic winter sea-ice extent in the three Southern Ocean sectors during MIS 5e may have significant implications for the Southern Hemisphere climatic system under future warming.

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Southern Ocean sea ice and frontal changes during the Late Quaternary and their linkages to Asian summer monsoon

Cited by 32 publications

References 80 publications

Impact of Southern Ocean surface conditions on deep ocean circulation during the LGM: a model analysis

Impact of Southern Ocean surface conditions on deep ocean circulation during the LGM: a model analysis

Evaluating seasonal sea-ice cover over the Southern Ocean from the Last Glacial Maximum

Reconstructing Antarctic winter sea-ice extent during Marine Isotope Stage 5e

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