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

• Published in: Geology
• Main Authors: Fletcher, M-S, Benson, A, Bowman, DMJS, Gadd, PS, Heijnis, H, Mariani, M, Saunders, KM, Wolfe, BB, Zawadzki, A
• Format: Article in Journal/Newspaper
• Language: English
• Published: Geological Soc America 2018
• Subjects: Earth Sciences; Physical geography and environmental geoscience; Palaeoclimatology; Antarctic; Southern Ocean; Antarc*; ice core
• Online Access: https://doi.org/10.1130/G39661.1; http://ecite.utas.edu.au/129086

Millennial-scale latitudinal shifts in the southern westerly winds (SWW) drive changes in Southern Ocean upwelling, leading to changes in atmospheric CO 2 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 CO 2 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 CO 2 values, demonstrating that the SWW-CO 2 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 CO 2 content that could potentially exacerbate current greenhouse gasrelated warming.