Responses of ocean circulation and carbon cycle to changes in the position of the Southern Hemisphere westerlies at Last Glacial Maximum

Völker, Christoph; Köhler, Peter

doi:10.1002/2013pa002556

Cited by 46 publications

(55 citation statements)

References 77 publications

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“…We, thus, propose that both of these oceanographic corridors are critical for the South Atlantic contribution to glacial meridional overturning circulation strength changes. Most oceanographic observations and models identify that variations in the position and strength of the southern westerly wind belt (SWW) impact changes in the strength of the ACC and DP throughflow (44). This conceptual picture is consistent with our reconstructed glacial reduction of sub-Antarctic DP throughflow being linked to a northward shift of the SWW as supported by the majority of the proxy-based SWW reconstructions (45).…”

Section: Discussionsupporting

confidence: 78%

Glacial reduction and millennial-scale variations in Drake Passage throughflow

Lamy

Arz

Kilian

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

114

111

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The Drake Passage (DP) is the major geographic constriction for the Antarctic Circumpolar Current (ACC) and exerts a strong control on the exchange of physical, chemical, and biological properties between the Atlantic, Pacific, and Indian Ocean basins. Resolving changes in the flow of circumpolar water masses through this gateway is, therefore, crucial for advancing our understanding of the Southern Ocean’s role in global ocean and climate variability. Here, we reconstruct changes in DP throughflow dynamics over the past 65,000 y based on grain size and geochemical properties of sediment records from the southernmost continental margin of South America. Combined with published sediment records from the Scotia Sea, we argue for a considerable total reduction of DP transport and reveal an up to ∼40% decrease in flow speed along the northernmost ACC pathway entering the DP during glacial times. Superimposed on this long-term decrease are high-amplitude, millennial-scale variations, which parallel Southern Ocean and Antarctic temperature patterns. The glacial intervals of strong weakening of the ACC entering the DP imply an enhanced export of northern ACC surface and intermediate waters into the South Pacific Gyre and reduced Pacific–Atlantic exchange through the DP (“cold water route”). We conclude that changes in DP throughflow play a critical role for the global meridional overturning circulation and interbasin exchange in the Southern Ocean, most likely regulated by variations in the westerly wind field and changes in Antarctic sea ice extent.

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Section: Discussionsupporting

confidence: 78%

Glacial reduction and millennial-scale variations in Drake Passage throughflow

Lamy

Arz

Kilian

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

114

111

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“…S8) and thus altered sea ice extent, leading to changes in upwelling of deep ocean carbon and nutrients, particularly in austral summer when, because of minimal sea ice and generally lower wind speeds, impacts on the carbon cycle were most pronounced (48). The net effect of these physical and biological pumps on the carbon cycle (16) likely started the release of CO 2 and initiated the rise in atmospheric CO 2 that followed the 17.7 ka Mount Takahe Event (Fig. 1) (14, 15).…”

Section: Plausible Linkages To Rapid Sh Deglaciationmentioning

confidence: 99%

“…1) (14, 15). As with modern increases in greenhouse gases (49), the atmospheric and oceanic circulation as well as hydroclimatic changes initiated by stratospheric ozone depletion were reinforced by rising CO 2 (15) and CH 4 (12,16).…”

Section: Plausible Linkages To Rapid Sh Deglaciationmentioning

confidence: 99%

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Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

McConnell

Burke

Dunbar

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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International audienceGlacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka

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“…Authors including Menviel et al (2008), Tschumi et al (2008), d 'Orgeville et al (2010), and Lee et al (2011) have investigated the effect that wind jet shifts have on ocean circulation during the Last Glacial Maximum (LGM) using numerical models. In one of the most complete recent studies, Völker and Köhler (2013) simulated the impact of jet shifts with a full ocean general circulation model (MITgcm), spun up to simulate LGM conditions, and used a dissolved inorganic carbon package (MITgcm Group, 2013) to simulate carbon changes. They found small net ef-L. C. Sime et al: Southern Ocean Winds at the LGM fects on atmospheric carbon, with a rise of only 3 to 9 ppm CO 2 under both a northward and a southward 10 • shift of the surface jet.…”

Section: Introductionmentioning

confidence: 99%

Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

et al. 2016

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Abstract. Latitudinal shifts in the Southern Ocean westerly wind jet could drive changes in the glacial to interglacial ocean CO 2 inventory. However, whilst CMIP5 model results feature consistent future-warming jet shifts, there is considerable disagreement in deglacial-warming jet shifts. We find here that the dependence of pre-industrial (PI) to Last Glacial Maximum (LGM) jet shifts on PI jet position, or state dependency, explains less of the shifts in jet simulated by the models for the LGM compared with future-warming scenarios. State dependence is also weaker for intensity changes, compared to latitudinal shifts in the jet. Winter sea ice was considerably more extensive during the LGM. Changes in surface heat fluxes, due to this sea ice change, probably had a large impact on the jet. Models that both simulate realistically large expansions in sea ice and feature PI jets which are south of 50 • S show an increase in wind speed around 55 • S and can show a poleward shift in the jet between the PI and the LGM. However, models with the PI jet positioned equatorwards of around 47 • S do not show this response: the sea ice edge is too far from the jet for it to respond. In models with accurately positioned PI jets, a +1 • difference in the latitude of the sea ice edge tends to be associated with a −0.85 • shift in the 850 hPa jet. However, it seems that around 5 • of expansion of LGM sea ice is necessary to hold the jet in its PI position. Since the Gersonde et al. (2005) data support an expansion of more than 5 • , this result suggests that a slight poleward shift and intensification was the most likely jet change between the PI and the LGM. Without the effect of sea ice, models simulate poleward-shifted westerlies in warming climates and equatorward-shifted westerlies in colder climates. However, the feedback of sea ice counters and reverses the equatorward trend in cooler climates so that the LGM winds were more likely to have also been shifted slightly poleward.

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Responses of ocean circulation and carbon cycle to changes in the position of the Southern Hemisphere westerlies at Last Glacial Maximum

Cited by 46 publications

References 77 publications

Glacial reduction and millennial-scale variations in Drake Passage throughflow

Glacial reduction and millennial-scale variations in Drake Passage throughflow

Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion

Sea ice led to poleward-shifted winds at the Last Glacial Maximum: the influence of state dependency on CMIP5 and PMIP3 models

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