Little Ice Age effects on Southern Ocean thermohaline circulation

Abstract

The Little Ice Age (LIA) was one of the strongest climate perturbations in the last millennium, with widespread albeit asynchronous periods of cooling globally¹. Its effects on oceanic properties and thermohaline circulation have been questioned, however². We provide evidence of changes in the properties of Antarctic Intermediate Water (AAIW) over the last millennium that are synchronous with LIA cooling events and that appear to derive proximately from variations in the proportion of Upper Circumpolar Deep Water (UCDW) in the AAIW source mixture, and ultimately from changes in the strength and position of the zonal west winds over the Southern Ocean (SO). Export of AAIW from the SO influences climate and biogeochemical cycles globally by transporting heat, freshwater, nutrients and carbon to lower latitudes^3-5, implying widespread impacts of its LIA-correlated variability. AAIW tracking of the LIA ceased in the late 1800s, which we suggest marked the onset of over-riding impacts of anthropogenic climate change on SO circulation.