A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

Svante Björck; Jesper Sjolte; Karl Ljung; Florian Adolphi; Roger Flower; Rienk H. Smittenberg; Malin E. Kylander; Thomas F. Stocker; Sofia Holmgren; Hui Jiang; Raimund Muscheler; Yamoah K. K. Afrifa; Jayne E. Rattray; Nathalie Van der Putten

doi:10.5194/cp-15-1939-2019

A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

Svante Björck, Jesper Sjolte, Karl Ljung, Florian Adolphi, Roger Flower, Rienk H. Smittenberg, Malin E. Kylander, Thomas F. Stocker, Sofia Holmgren, Hui Jiang, Raimund Muscheler, Yamoah K. K. Afrifa, Jayne E. Rattray, Nathalie Van der Putten

Earth and Climate

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..

Original language	English
Pages (from-to)	1939-1958
Number of pages	20
Journal	Climate of the Past Discussions
Volume	15
Issue number	6
DOIs	https://doi.org/10.5194/cp-15-1939-2019
Publication status	Published - 15 Nov 2019

Funding

The co-members of the 2010 Tristan expedition (Martin Bjorck, Anders Anker Bjork, Anders Cronholm, James Haile, Matthieu Grignon) and Tristan islanders are gratefully acknowledged for hard work at sea and on Nightingale Island. The isotope-enabled climate model, ECHAM5-wiso/MPI-OM, was run at the Alfred-Wegener-Institut Computer and Data Center. We thank Martin Werner for helping to set up and run the model simulations; Stephen Barker, Francisco W. Cruz and Christian Millo for providing us with their data; Git Ahlberg for pollen sample preparations; and sa Wallin for magnetic susceptibility measurements. We are grateful for constructive reviews. We dedicate this paper to Charles T. Porter, our skipper on his ketch Ocean Tramp, who challenged all kinds of weather in the South Atlantic to retrieve our unique sediment cores. However, he sadly died suddenly in March 2014 while preparing for our next expedition: a great loss in many respects but mostly as an invaluable, memorable friend and colleague. This research has been supported by the Swedish Research Council (VR) (grants 621-2008-2894 and 621- 2012-3104), the Crafoord Foundation, the Royal Physiographic Society of Lund, the strategic research program of ModEling the Regional and Global Earth system (MERGE), the VR funded Linneus centres of LUCCI and Bolin Centre, at Lund and Stockholm University, respectively. Financial support. This research has been supported by the Swedish Research Council (VR) (grants 621-2008-2894 and 621-2012-3104), the Crafoord Foundation, the Royal Physiographic Society of Lund, the strategic research program of ModEling the Regional and Global Earth system (MERGE), the VR funded Linneus centres of LUCCI and Bolin Centre, at Lund and Stockholm University, respectively.

Funders	Funder number
Bolin Centre
Crafoord Foundation
LUCCI
Royal Physiographic Society of Lund
cores
Crafoordska Stiftelsen
Vetenskapsrådet	621-2008-2894, 621-2012-3104

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Björck, S., Sjolte, J., Ljung, K., Adolphi, F., Flower, R., Smittenberg, R. H., Kylander, M. E., Stocker, T. F., Holmgren, S., Jiang, H., Muscheler, R., Afrifa, Y. K. K., Rattray, J. E., & Van der Putten, N. (2019). A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial. Climate of the Past Discussions, 15(6), 1939-1958. https://doi.org/10.5194/cp-15-1939-2019

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title = "A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial",

abstract = "Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..",

author = "Svante Bj{\"o}rck and Jesper Sjolte and Karl Ljung and Florian Adolphi and Roger Flower and Smittenberg, {Rienk H.} and Kylander, {Malin E.} and Stocker, {Thomas F.} and Sofia Holmgren and Hui Jiang and Raimund Muscheler and Afrifa, {Yamoah K. K.} and Rattray, {Jayne E.} and {Van der Putten}, Nathalie",

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doi = "10.5194/cp-15-1939-2019",

language = "English",

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Björck, S, Sjolte, J, Ljung, K, Adolphi, F, Flower, R, Smittenberg, RH, Kylander, ME, Stocker, TF, Holmgren, S, Jiang, H, Muscheler, R, Afrifa, YKK, Rattray, JE & Van der Putten, N 2019, 'A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial', Climate of the Past Discussions, vol. 15, no. 6, pp. 1939-1958. https://doi.org/10.5194/cp-15-1939-2019

TY - JOUR

T1 - A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

AU - Björck, Svante

AU - Sjolte, Jesper

AU - Ljung, Karl

AU - Adolphi, Florian

AU - Flower, Roger

AU - Smittenberg, Rienk H.

AU - Kylander, Malin E.

AU - Stocker, Thomas F.

AU - Holmgren, Sofia

AU - Jiang, Hui

AU - Muscheler, Raimund

AU - Afrifa, Yamoah K. K.

AU - Rattray, Jayne E.

AU - Van der Putten, Nathalie

PY - 2019/11/15

Y1 - 2019/11/15

N2 - Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..

AB - Changes in the latitudinal position and strength of the Southern Hemisphere westerlies (SHW) are thought to be tightly coupled to important climate processes, such as cross-equatorial heat fluxes, Atlantic Meridional Overturning Circulation (AMOC), the bipolar seesaw, Southern Ocean ventilation and atmospheric CO2 levels. However, many uncertainties regarding magnitude, direction, and causes and effects of past SHW shifts still exist due to lack of suitable sites and scarcity of information on SHW dynamics, especially from the last glacial. Here we present a detailed hydroclimate multiproxy record from a 36.4-18.6 kyr old lake sediment sequence on Nightingale Island (NI). It is strategically located at 37ĝF S in the central South Atlantic (SA) within the SHW belt and situated just north of the marine Subtropical Front (SF). This has enabled us to assess hydroclimate changes and their link to the regional climate development as well as to large-scale climate events in polar ice cores. The NI record exhibits a continuous impact of the SHW, recording shifts in both position and strength, and between 36 and 31 ka the westerlies show high latitudinal and strength-wise variability possibly linked to the bipolar seesaw. This was followed by 4 kyr of slightly falling temperatures, decreasing humidity and fairly southerly westerlies. After 27 ka temperatures decreased 3-4 ĝC, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly-positioned SHW seem to be related to periods of increased CO2 outgassing from the ocean, while changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, our results show that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial. Finally we can conclude that multiproxy lake records from oceanic islands have the potential to record atmospheric variability coupled to large-scale climate shifts over vast oceanic areas..

UR - http://www.mendeley.com/research/south-atlantic-island-record-uncovers-shifts-westerlies-hydroclimate-during-last-glacial

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U2 - 10.5194/cp-15-1939-2019

DO - 10.5194/cp-15-1939-2019

M3 - Article

SN - 1814-9340

VL - 15

SP - 1939

EP - 1958

JO - Climate of the Past Discussions

JF - Climate of the Past Discussions

IS - 6

ER -

A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial

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