Antarctic sea-ice and palaeoproductivity variation over the last 156,000 years in the Indian sector of Southern Ocean

Ghadi, Pooja; Nair, Abhilash; Crosta, Xavier; Mohan, Rahul; Manoj, M.C.; Thamban, Meloth

doi:10.1016/j.marmicro.2020.101894

Cited by 26 publications

(36 citation statements)

References 91 publications

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“…The dearth of diatoms in glacial sediments from A005‐PC01 and C012‐PC05 indicates that permanent summer sea ice conditions extended past their modern limit during glaciations since the MPT. This agrees with previous studies based on modeling (Ferrari et al, 2014) and a circum‐Antarctic observations of diatom abundances and assemblages (Benz et al, 2016; Collins et al, 2012; Gersonde et al, 2005; Ghadi et al, 2020) and other proxy compilations (Fischer et al, 2010; Kohfeld & Chase, 2017), which suggests a northward advance of 10–12° latitude in the permanent summer sea ice edge during past glacial periods. During such glacial intervals, permanent sea ice cover impacts the spatial distribution and extent of primary productivity in the upper ocean, influencing the diatom record at the sea floor (Armand, 2000; Armand & Leventer, 2009).…”

Section: Discussionsupporting

confidence: 92%

“…The physical barrier formed by permanent sea ice restricts air-sea gas exchange and CO 2 outgassing, while also stratifying surface waters during summer melt and hence restricting the ventilation of deep water (Collins et al, 2012). Ghadi et al, 2020 reported a northward shift in the seasonal winter sea ice extent to 49°S in the Indian sector of the Southern Ocean during the last glacial period. This study adds further constraint to the permanent summer sea ice extent, which must have extended north of 64°S during glaciations since the MPT.…”

Section: Paleoceanography and Paleoclimatologymentioning

confidence: 99%

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Controls Since the mid‐Pleistocene Transition on Sedimentation and Primary Productivity Downslope of Totten Glacier, East Antarctica

Holder

Duffy

Opdyke

et al. 2020

Paleoceanog and Paleoclimatol

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The rapidly thinning Totten Glacier on the Sabrina Coast, East Antarctica, is the primary drainage outlet for ice within the Aurora Subglacial Basin, which could destabilize under the current atmospheric warming trend. There is growing need for direct geological evidence from the Sabrina Coast to frame late twentieth century Totten melting in the context of past warm climate analogs. Addressing this need, sediment archives were recovered from two sites on the Sabrina Coast slope and rise that record changes in terrigenous sedimentation and primary productivity in the region over glacial cycles since the mid‐Pleistocene transition (MPT). This research presents physical properties, grain size, diatom abundance and assemblages, and geochemical analysis from the two sites to determine how the processes that control sedimentation change between glacial and interglacial phases. The stratigraphic sequences in both cores record cyclic variations in physical properties and diatom abundances, which radiocarbon and biostratigraphic chronologies reveal as 100 Kyr glacial‐interglacial cyclicity. During glacials, terrigenous sediment deposition is enhanced by advanced grounded ice on the shelf, while primary productivity is restricted due to permanent summer sea ice extending past the continental slope. During interglacials, pelagic sedimentation suggests high surface productivity associated with contractions of regional sea ice cover. Comparison with post‐MPT slope records from Wilkes Land and the Amundsen Sea shows that this pattern is consistent in slope sediments around the margin. The higher‐amplitude variations in Antarctic ice volume and sea ice extent post‐MPT ensure that these signals are pervasive around the Antarctic margin.

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Section: Discussionsupporting

confidence: 92%

Section: Paleoceanography and Paleoclimatologymentioning

confidence: 99%

Controls Since the mid‐Pleistocene Transition on Sedimentation and Primary Productivity Downslope of Totten Glacier, East Antarctica

Holder

Duffy

Opdyke

et al. 2020

Paleoceanog and Paleoclimatol

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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

Preprint

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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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“…Secondly, to evaluate the glacial Antarctic sea-ice distribution we compiled sea-ice proxy data from Gersonde et al (2005), Allen et al (2011), Ferry et al (2015), Benz et al (2016), Xiao et al (2016), Nair et al (2019) and Ghadi et al (2020).…”

Section: Experimental Datamentioning

confidence: 99%

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

Lhardy¹,

Bouttes²,

Roche³

et al. 2020

Preprint

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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 data. 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 data. Inadequate representation of surface conditions, driving deep convection around Antarctica, may explain inaccurate simulated bottom water properties in the Southern Ocean. We investigate here the impact of a range of surface conditions in the Southern Ocean, using nine simulations obtained using different modelling choices and/or boundary conditions in the iLOVECLIM model. Based on data-model comparison of key parameters (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 data, 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 modelling 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 masses properties, while the choice of boundary conditions appears secondary for the model resolution and variables considered in this study.

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Antarctic sea-ice and palaeoproductivity variation over the last 156,000 years in the Indian sector of Southern Ocean

Cited by 26 publications

References 91 publications

Controls Since the mid‐Pleistocene Transition on Sedimentation and Primary Productivity Downslope of Totten Glacier, East Antarctica

Controls Since the mid‐Pleistocene Transition on Sedimentation and Primary Productivity Downslope of Totten Glacier, East Antarctica

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

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

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