Tracking Southern Ocean Sea Ice Extent With Winter Water: A New Method Based on the Oxygen Isotopic Signature of Foraminifera

Lund, David C; Chase, Zanna; Kohfeld, Karen E.; Wilson, Earle A.

doi:10.1029/2020pa004095

Cited by 7 publications

(11 citation statements)

References 124 publications

(256 reference statements)

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“…The Antarctic sea ice played a pivotal role in the MOC by modifying water masses globally [60]. The Antarctic sea ice-ocean feedback included wintertime sea ice formation (brine rejection), which left salt content, and included summertime melting, which returned liquid freshwater to the ocean.…”

Section: Discussionmentioning

confidence: 99%

“…Antarctic sea ice plays a vital part in the global Meridional Overturning Circulation (MOC). It modifies globally widespread water masses through surface buoyancy gain (the region with lighter surface ocean density) and loss (the region with denser surface ocean density) [60]. The formation and melting of Antarctic sea ice alter surface buoyancy fluxes and modulate deep ocean stratification and MOC in the SO [22,24,57,58,[61][62][63][64][65][66][67].…”

Section: Introductionmentioning

confidence: 99%

“…The formation and melting of Antarctic sea ice alter surface buoyancy fluxes and modulate deep ocean stratification and MOC in the SO [22,24,57,58,[61][62][63][64][65][66][67]. Studies have found that increased ocean stratification subsequently increases the deep-ocean carbon inventory and contributes to lower atmospheric carbon dioxide concentrations [60]. In addition, Antarctic sea ice coverage reduces the exposure time of surface waters with the atmosphere [22,61] and air-sea gas exchange, enhancing deep ocean carbon sequestration [68].…”

Section: Introductionmentioning

confidence: 99%

“…The freshwater export increases the buoyancy of the upwelled circumpolar deep water [71], contributing to the closure of the upper branch of the overturning circulation in the SO [57,72]. Buoyancy gain in the SO helps transform the deep returning flow into the intermediate and mode waters [60]. Conversely, wintertime formation of the Antarctic sea ice leads to buoyancy loss, which contributes to the lower branch of the MOC in the SO [12,73,74].…”

Section: Introductionmentioning

confidence: 99%

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The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

Mandal

Lee

2022

Sustainability

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The last deglacial climate evolution, from 19 to 9 thousand years before the present, represents the vital role of feedback in the Earth’s climate system. The Southern Ocean played a fundamental role by exchanging nutrients and carbon-rich deep ocean water with the surface during the last deglaciation. This study employs a fully coupled Earth system model to investigate the evolution of Southern Ocean dynamics and the roles of changes in orbital and meltwater forcings during the last deglaciation. The simulation supports that the Southern Ocean upwelling was primarily driven by windstress. The results show that the melting and formation of Antarctic sea ice feedback influenced Southern Ocean surface buoyancy flux. The increase in Antarctic sea ice melt-induced freshwater flux resulted in a steepened north-south surface salinity gradient in the Southern Ocean, which enhanced the upwelling. The single-forcing experiments indicate that the deglacial changes in orbital insolation influenced the Southern Ocean upwelling. The experiments also highlight the dominant role of Northern Hemisphere meltwater discharge in the upper and lower branch of the Meridional Overturning Circulation. Furthermore, orbital forcing shows lesser deglacial Antarctic sea ice retreat than the Northern Hemisphere meltwater forcing, which follows the bipolar seesaw mechanism.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

Mandal

Lee

2022

Sustainability

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“…A new approach using oxygen isotope ratios (δ 18 O) of planktonic and benthic foraminifera was recently proposed to reconstruct WSI extent (Lund et al, 2021). The method relies on the fact that winter seaice formation creates a cold, surface mixed layer that persists in sub-surface layers during the spring and summer months.…”

Section: Other Approaches: Foraminifera Radiolaria Dinoflagellatesmentioning

confidence: 99%

Antarctic sea ice over the past 130,000 years, Part 1: A review of what proxy records tell us

Crosta

Kohfeld

Bostock

et al. 2022

Preprint

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Abstract. Antarctic sea ice plays a critical role in the Earth system, influencing energy, heat, and freshwater fluxes, air-sea gas exchange, ice shelf dynamics, ocean circulation, nutrient cycling, marine productivity, and global carbon cycling. However, accurate simulation of recent sea-ice changes remains challenging, and therefore projecting future sea-ice changes and their influence on the global climate system is uncertain. Reconstructing past changes in sea-ice cover can provide additional insights into climate feedbacks within the Earth system at different timescales. This paper is the first of two review papers from the Cycles of Sea Ice Dynamics in the Earth system (C-SIDE) Working Group. In this first paper, we review marine- and ice core-based sea-ice proxies and reconstructions of sea-ice changes throughout the last glacial-interglacial cycle. Antarctic sea-ice reconstructions rely mainly on diatom fossil assemblages and highly branched isoprenoid (HBI) alkenes in marine sediments, supported by chemical proxies in Antarctic ice cores. Most reconstructions for the Last Glacial Maximum (LGM) suggest winter sea-ice expanded all around Antarctica and covered almost twice its modern surface extent. In contrast, LGM summer sea-ice expanded mainly in the regions off the Weddell and Ross seas. The difference between winter and summer sea ice during the LGM led to a larger seasonal cycle than today. More recent efforts have focused on reconstructing Antarctic sea-ice during warm periods, such as the Holocene and the Last Interglacial (LIG), which may serve as an analogue the future. Notwithstanding regional heterogeneities, existing reconstructions suggest sea-ice cover increased from the warm mid-Holocene to the colder Late Holocene, with pervasive decadal-to-millennial scale variability throughout the Holocene. Sparse marine and ice core data, supported by proxy modelling experiments, suggest that sea-ice cover was halved during the warmer LIG, when global average temperatures were ~2 °C above the pre-industrial (PI). There are limited marine (14) and ice core (4) sea-ice proxy records covering the complete 130,000 year (130 ka) last glacial cycle. The glacial-interglacial pattern of sea-ice advance and retreat appears relatively similar in each basin of the Southern Ocean. Rapid retreat of sea ice occurred during Terminations II and I, while the expansion of sea ice during the last glaciation appears more gradual, especially in cores data sets. Marine records suggest that the first prominent expansion occurred during Marine Isotope Stage (MIS) 4 and that sea ice reached maximum extent during MIS 2. We however note that additional sea-ice records and transient model simulations are required to better identify the underlying drivers and feedbacks of Antarctic sea-ice changes over the last 130 ka. This understanding is critical to improve future predictions.

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Proxy‐Based Preformed Phosphate Estimates Point to Increased Biological Pump Efficiency as Primary Cause of Last Glacial Maximum CO₂ Drawdown

Vollmer

Ito

Lynch‐Stieglitz

2022

Paleoceanog and Paleoclimatol

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Upwelling deep waters in the Southern Ocean release biologically sequestered carbon into the atmosphere, contributing to the relatively high atmospheric CO2 levels during interglacial climate periods. Paleoceanographic evidence suggests this “CO2 leak” was lessened during the last glacial maximum (LGM), potentially due to increased stratification, weaker and equatorward‐shifted winds, and/or enhanced biological carbon export. The collective influences of these mechanisms on the ocean's biological pump efficiency and amount of atmospheric CO2 can be quantified by determining preformed phosphate of deep waters. We quantify preformed PO4 (Ppre,AOU) and preformed δ13normalC ${\delta }^{13}\mathrm{C}$ (δ13Cnormalpnormalrnormale,normalAnormalOnormalU ${\delta }^{13}{\mathrm{C}}_{\mathrm{p}\mathrm{r}\mathrm{e},\mathrm{A}\mathrm{O}\mathrm{U}}$) of LGM bottom waters using a compilation of published paleo‐temperature, nutrient and oxygen estimates from benthic foraminifera. Our results show that preformed phosphate of the Pacific and Indian deep oceans was reduced by about −0.53 ± 0.13 μM and suggest that much (64 ± 28 ppmv) of the Glacial‐Interglacial CO2 drawdown resulted from changes in the ocean's biological pump efficiency. Once carbonate compensation is accounted for, this can explain the entire CO2 drawdown (87 ± 40 ppmv). Preformed δ13normalC ${\delta }^{13}\mathrm{C}$ shows similar results. The reconstructed LGM Ppre,AOU and oxygen are qualitatively consistent with the changes produced by a suite of numerical sensitivity experiments that roughly simulate three proposed mechanisms for an increase in LGM biological pump efficiency: an increase in biological activity, a decrease in wind‐driven upwelling, and an increase in stratification in the Southern Ocean.

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Tracking Southern Ocean Sea Ice Extent With Winter Water: A New Method Based on the Oxygen Isotopic Signature of Foraminifera

Cited by 7 publications

References 124 publications

The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

Antarctic sea ice over the past 130,000 years, Part 1: A review of what proxy records tell us

Proxy‐Based Preformed Phosphate Estimates Point to Increased Biological Pump Efficiency as Primary Cause of Last Glacial Maximum CO₂ Drawdown

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Tracking Southern Ocean Sea Ice Extent With Winter Water: A New Method Based on the Oxygen Isotopic Signature of Foraminifera

Cited by 7 publications

References 124 publications

The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

The Roles of Orbital and Meltwater Climate Forcings on the Southern Ocean Dynamics during the Last Deglaciation

Antarctic sea ice over the past 130,000 years, Part 1: A review of what proxy records tell us

Proxy‐Based Preformed Phosphate Estimates Point to Increased Biological Pump Efficiency as Primary Cause of Last Glacial Maximum CO2 Drawdown

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Product

Resources

About

Proxy‐Based Preformed Phosphate Estimates Point to Increased Biological Pump Efficiency as Primary Cause of Last Glacial Maximum CO₂ Drawdown