Neodymium isotope evidence for coupled Southern Ocean circulation and Antarctic climate throughout the last 118,000 years

Williams, Thomas; Martin, E. E.; Sikes, Elisabeth L.; Starr, Aidan; Umling, Natalie; Glaubke, R.

doi:10.1016/j.quascirev.2021.106915

Cited by 15 publications

(11 citation statements)

References 80 publications

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“…In addition, the coupling of the Northern Hemisphere deep water formation and SH winds leads to an adjustment of the geostrophic balance upon reduced NADW production 54 . Therefore, our observations clearly support the leading hypothesis of old and poorly ventilated water masses of most likely Pacific origin intruding the CDW and glacial Atlantic Ocean between depths of 2.8 and 3.6 km, likely to a lesser extent even deeper 4,5,10,24,26 . Hence, our findings strongly support increased glacial carbon storage in the SO.…”

Section: Pdw Dominance and Persistence During Glacialssupporting

confidence: 84%

“…Neodymium isotopes (given as Nd) have proven useful to study deep ocean circulation thanks to basinscale isotope gradients between the Pacific and the North Atlantic [21][22][23] . Through the use of Nd isotopes, evidence was found for PDW intrusion into the SO during the Holocene and during periods of reduced AMOC 4,[24][25][26] . More recently, Nd isotope measurements in marine sediments of the SO point to a glacial absence of Weddell-Sea Antarctic Bottom Water export into the South Atlantic 10 .…”

Section: Introductionmentioning

confidence: 99%

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Large-scale Pacific-sourced intrusion into the glacial South Atlantic

Hallmaier

Rückert

Link

et al. 2022

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The deep Southern Ocean (SO) circulation plays a key role in the storage and release of CO2 in Earth’s climate system. Uptake and release of CO2 strongly depend on the redistribution of well and poorly ventilated water masses. Here, we present new neodymium isotope data (εNd) from three sediment cores from the Atlantic sector of the SO to assess the distribution of water masses during the past 150 ka. ODP 1094 (2807 m) reveals a tremendous Holocene εNd-variability (-0.25 to -6.07), which most likely reflects local influences. PS 1768-8 (3299 m) and ODP 1093 (3624 m), show far more unradiogenic interglacial εNd-signatures, which are similar to the present-day Antarctic Bottom Water (AABW) (εNd~-8). During peak glacial periods, radiogenic εNd-values of ~-2.5 to -3.5 are recorded. This confirms a predominance of glacial Pacific-sourced deep water at depths of 3.3-3.6 km in the South Atlantic, with proportions close to 100% and lacking AABW. We advocate for the presence of Pacific Deep Water even during interglacials and further hypothesize that a possible intrusion due to a warming climate could accelerate climate warming. The persistent occurrence of such a highly radiogenic water mass substantially changes the view regarding the selection of the Southern Hemisphere εNd-endmember for the Atlantic Ocean and reinforces the major importance of carbon storage in the Glacial SO.

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Section: Pdw Dominance and Persistence During Glacialssupporting

confidence: 84%

Section: Introductionmentioning

confidence: 99%

Large-scale Pacific-sourced intrusion into the glacial South Atlantic

Hallmaier

Rückert

Link

et al. 2022

Preprint

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“…Kohfeld & Chase (2017) benthic foraminifera and noted that the separation between δ 13 C values of abyssal and deep ocean waters were actually initiated between MIS 5d and MIS 5a (114 to 71 ka). Evidence for early changes in abyssal circulation have also been detected in Indian Ocean δ C records (Govin et al, 2009), and more recently in Indian Ocean eNd records (Williams et al, 2021),…”

Section: Other Potential Contributors To Early Glacial Co2 Variabilitymentioning

confidence: 74%

Sea Ice Changes in the Southwest Pacific Sector of the Southern Ocean During the Last 140,000 Years

Jones

Kohfeld

Bostock

et al. 2021

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Abstract. Sea ice expansion in the Southern Ocean is believed to have contributed to glacial-interglacial atmospheric CO2 variability by inhibiting air-sea gas exchange and influencing the ocean’s meridional overturning circulation. However, limited data on past sea ice coverage over the last 140 ka (a complete glacial cycle) have hindered our ability to link sea ice expansion to oceanic processes that affect atmospheric CO2 concentration. Assessments of past sea ice coverage using diatom assemblages have primarily focused on the Last Glacial Maximum (~21 ka) to Holocene, with few quantitative reconstructions extending to the onset of glacial Termination II (~135 ka). Here we provide new estimates of winter sea ice concentrations (wSIC) and summer sea surface temperatures (sSSTs) for a full glacial-interglacial cycle from the southwestern Pacific sector of the Southern Ocean using fossil diatom assemblages from deep-sea core TAN1302-96 (59.09° S, 157.05° E, water depth 3099 m). We find that winter sea ice was consolidated over the core site during the latter part of the penultimate glaciation, Marine Isotope Stage (MIS) 6 (from at least 140 to 134 ka), when sSSTs were between ~1 and 1.5 °C. The winter sea ice edge then retreated rapidly as sSSTs increased during the transition into the Last Interglacial Period (MIS 5e), reaching ~4.5 °C by 125 ka. As the Earth entered the early glacial stages, sSSTs began to decline around 112 ka, but winter sea ice largely remained absent until ~65 ka during MIS 4, when it was sporadically present but unconsolidated (< 40 % wSIC). WSIC and sSSTs reached their maximum concentration and coolest values by 24.5 ka, just prior to the Last Glacial Maximum. Winter sea ice remained absent throughout the Holocene, while SSSTs briefly exceeded modern values, reaching ~5 °C by 11.4 ka, before decreasing to ~4 °C and stabilizing. The absence of sea ice coverage over the core site during the early glacial period suggests that sea ice may not have been a major contributor to CO2 drawdown at this time. During MIS 5d, we observe a weakening of meridional SST gradients between 42° to 59° S throughout the region, which may have contributed to early reductions in atmospheric CO2 concentrations through its impact on air-sea gas exchange. Sea ice expansion during MIS 4, however, coincides with observed reductions in Antarctic Intermediate Water production and subduction, suggesting that sea ice may have influenced intermediate ocean circulation changes.

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“…Evidence for early changes in abyssal circulation and reductions in deep-ocean overturning have also been detected in Indian Ocean δ 13 C records (Govin et al, 2009). More recently, Indian Ocean εNd records (Williams et al, 2021) have suggested that the abyssal ocean may have responded to sea ice around the Antarctic continent early in the glacial cycle, with colder and more saline AABW forming as sea ice expanded near the continent. If indications of an early-glacial response in the global ocean circulation in the Indo-Pacific are correct, these data may also point to an elevated importance of sea ice near the Antarctic continent in triggering early, deep-ocean overturning changes.…”

Section: Other Potential Contributors To Early Glacial Co 2 Variabilitymentioning

confidence: 87%

Sea ice changes in the southwest Pacific sector of the Southern Ocean during the last 140 000 years

et al. 2022

View full text Add to dashboard Cite

Abstract. Sea ice expansion in the Southern Ocean is believed to have contributed to glacial–interglacial atmospheric CO2 variability by inhibiting air–sea gas exchange and influencing the ocean's meridional overturning circulation. However, limited data on past sea ice coverage over the last 140 ka (a complete glacial cycle) have hindered our ability to link sea ice expansion to oceanic processes that affect atmospheric CO2 concentration. Assessments of past sea ice coverage using diatom assemblages have primarily focused on the Last Glacial Maximum (∼21 ka) to Holocene, with few quantitative reconstructions extending to the onset of glacial Termination II (∼135 ka). Here we provide new estimates of winter sea ice concentrations (WSIC) and summer sea surface temperatures (SSST) for a full glacial–interglacial cycle from the southwestern Pacific sector of the Southern Ocean using the modern analog technique (MAT) on fossil diatom assemblages from deep-sea core TAN1302-96. We examine how the timing of changes in sea ice coverage relates to ocean circulation changes and previously proposed mechanisms of early glacial CO2 drawdown. We then place SSST estimates within the context of regional SSST records to better understand how these surface temperature changes may be influencing oceanic CO2 uptake. We find that winter sea ice was absent over the core site during the early glacial period until MIS 4 (∼65 ka), suggesting that sea ice may not have been a major contributor to early glacial CO2 drawdown. Sea ice expansion throughout the glacial–interglacial cycle, however, appears to coincide with observed regional reductions in Antarctic Intermediate Water production and subduction, suggesting that sea ice may have influenced intermediate ocean circulation changes. We observe an early glacial (MIS 5d) weakening of meridional SST gradients between 42 and 59∘ S throughout the region, which may have contributed to early reductions in atmospheric CO2 concentrations through its impact on air–sea gas exchange.

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Neodymium isotope evidence for coupled Southern Ocean circulation and Antarctic climate throughout the last 118,000 years

Cited by 15 publications

References 80 publications

Large-scale Pacific-sourced intrusion into the glacial South Atlantic

Large-scale Pacific-sourced intrusion into the glacial South Atlantic

Sea Ice Changes in the Southwest Pacific Sector of the Southern Ocean During the Last 140,000 Years

Sea ice changes in the southwest Pacific sector of the Southern Ocean during the last 140 000 years

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