Analyzing the continent-ocean relationship in the centennial-scale Antarctic temperature variability over the past 2000 years

Reconstructions of Antarctic surface air temperature (SAT) covering the past two millennia include some large centennial variabilities that are still not well understood because of the model-data discrepancies. Paleoenvironmental and instrumental observations have highlighted strong interconnections in the Antarctic climate system as illustrated by close relationships between atmosphere and ocean (including sea ice) at all time scales. For instance, over past decades, the Amundsen Sea Low pressure (ASL) is associated with opposite regional sea ice changes in the Bellingshausen-Amundsen and Ross sea sector as well as with variations in snow accumulation over West Antarctica. This inspires us to explore the potentiality of better reconstructing and understanding the drivers of the centennial-scale variability of Antarctic SAT during the Common Era by taking advantage of those links between the Antarctic continental and the Southern Ocean data. To this end, we have compiled proxy-based sea surface temperature reconstructions for the Southern Ocean and qualitative sea-ice reconstructions around Antarctica, together with those having published ice-core based water isotopic and snow accumulation records. We first analyze the continent-ocean relationships by constraining the climate model with continental records through a data assimilation procedure. Results show that we are able to generally reproduce reconstructed variations in the Southern Ocean at centennial scale, particularly for sea surface temperature (SST) along the south Chilean coast and sea ice along the Antarctic Peninsula. In a second step, experiments with data assimilation combining both oceanic and continental records help us to determine how the inclusion of oceanic records improves the reconstruction of the SAT, atmospheric circulation, and sea ice (and SST) over the past two millennia in the high latitudes.