Southward migration of the Southern Hemisphere westerly winds corresponds with warming climate over centennial timescales

Abstract

Recent changes in the strength and location of the Southern Hemisphere westerly winds (SHW) have been linked to continental droughts and wildfires, changes in the Southern Ocean carbon sink, sea ice extent, ocean circulation, and ice shelf stability. Despite their critical role, our ability to predict their impacts under future climates is limited by a lack of data on SHW behaviour over centennial timescales. Here, we present a 700-year record of changes in SHW intensity from sub-Antarctic Marion Island using diatom and geochemical proxies and compare it with paleoclimate records and recent instrumental data. During cool periods, such as the Little Ice Age (c. 1400–1870 CE), the winds weakened and shifted towards the equator, and during warm periods they intensified and migrated poleward. These results imply that changes in the latitudinal temperature gradient drive century-scale SHW migrations, and that intensification of impacts can be anticipated in the coming century.

Evolution of the Cook Ice Cap (Kerguelen Islands) between the last centuries and 2100 ce based on cosmogenic dating and glacio-climatic modelling

“…Contrary to the present-day, for which the SAM index is positive, a negative SAM index has been proposed for the period from~1400 CE to~1600 CE (Abram et al , 2014;Perren et al , 2020). A negative phase is expected to imply larger precipitation amounts and colder temperatures than during the reference period CE 1961-1990in Abram et al (2014.…”

“…Similar to the findings of Reynhout et al (2019) for Patagonia, our results suggest that climate and subsequent glacier evolution on the Kerguelen Islands over the last millennium was highly influenced by fluctuations in the SAM. The period between~1400 and~1600 CE corresponds to the period during which the SAM index was the most negative over the last millennium (Abram et al , 2014;Perren et al , 2020). This also suggests that past CIC wastage and extents reflected this extreme state of the SAM, making the Kerguelen Islands one of the best laboratories to study this most important climate feature at high latitudes in the Southern Hemisphere (as the leading empirical orthogonal function of extratropical atmospheric mode of variability in the Southern Hemisphere).…”

“…If we want to understand and predict the effect of the ice cap wastage on the current and future (by the end of the 21st century) colonisation of the archipelago by invasive species, we first need to contextualise the ice cap evolution over a period in the past that was characterised by significant climate and glacier fluctuations. The last millennium is particularly suited for this experiment, due to the occurence of the so-called Little Ice Age (LIA) between around 1400 and 1870 CE (Perren et al , 2020). The LIA corresponds to a period of the Earth's history that was globally~0.5°C colder than the end of the 20th century (Solomina et al , 2015).…”

Physical properties of shallow ice cores from Antarctic and sub-Antarctic islands

“…Lake sediments are similarly useful for studying vegetation composition on the SAIs. These are related to a wide range of environmental parameters within and around the lake used to reconstruct past natural variability (Saunders et al, 2008). Diatom and geochemical proxies from Marion Island have been used to track the migration of westerly winds over the past 700 years (Perren et al, 2020).…”

“…These are related to a wide range of environmental parameters within and around the lake used to reconstruct past natural variability (Saunders et al, 2008). Diatom and geochemical proxies from Marion Island have been used to track the migration of westerly winds over the past 700 years (Perren et al, 2020). A novel proxy, based on sea salt aerosols in lake sediments on Macquarie Island, reconstructed past westerly wind strength over the past 12 300 years (Saunders et al, 2018).…”