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Centennial-scale trends in the Southern Annular Mode revealed by hemisphere-wide fire and hydroclimatic trends over the past 2400 years

Fletcher, MS, Benson, A, Bowman, DMJS ORCID: 0000-0003-2215-7685, Gadd, PS, Heijnis, H, Mariani, M, Saunders, KM, Wolfe, BB and Zawadzki, A 2018 , 'Centennial-scale trends in the Southern Annular Mode revealed by hemisphere-wide fire and hydroclimatic trends over the past 2400 years' , Geology, vol. 46, no. 4 , pp. 363-366 , doi: 10.1130/G39661.1.

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Abstract

Millennial-scale latitudinal shifts in the southern westerly winds (SWW) drive changes in Southern Ocean upwelling, leading to changes in atmospheric CO2 levels, thereby affecting the global climate and carbon cycle. Our aim here is to understand whether century-scale shifts in the SWW also drive changes in atmospheric CO2 content. We report new multiproxy lake sediment data from southwest Tasmania, Australia, that show centennial-scale changes in vegetation and fire activity over the past 2400 yr. We compare our results with existing data from southern South America and reveal synchronous and in-phase centennial-scale trends in vegetation and fire activity between southwest Tasmania and southern South America over the past 2400 yr. Interannual to centennial-scale rainfall anomalies and fire activity in both these regions are significantly correlated with shifts in the SWW associated with the Southern Annular Mode (SAM; atmospheric variability of the Southern Hemisphere). Thus, we interpret the centennial-scale trends we have identified as reflecting century-scale SAM-like shifts in the SWW over the past 2400 yr. We identify covariance between our inferred century-scale shifts in the SWW and Antarctic ice core CO2 values, demonstrating that the SWW-CO2 relationship operating at a millennial scale also operates at a centennial scale through the past 2400 yr. Our results indicate a possible westerly-driven modulation of recent increases in global atmospheric CO2 content that could potentially exacerbate current greenhouse gas–related warming.

Item Type: Article
Authors/Creators:Fletcher, MS and Benson, A and Bowman, DMJS and Gadd, PS and Heijnis, H and Mariani, M and Saunders, KM and Wolfe, BB and Zawadzki, A
Keywords: atmospheric CO2, Southern Ocean, lake sediment, Tasmania
Journal or Publication Title: Geology
Publisher: Geological Soc America
ISSN: 0091-7613
DOI / ID Number: 10.1130/G39661.1
Copyright Information:

Copyright 2018 Geological Society of America

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