Abstract
Abstract. From 10 to 8 ka BP (thousand years before present), paleoclimate records show an atmospheric and oceanic cooling in the high latitudes of the Southern Hemisphere. During this interval, temperatures estimated from proxy data decrease by 0.8 °C over Antarctica and 1.2 °C over the Southern Ocean. In order to study the causes of this cooling, simulations covering the early Holocene have been performed with the climate model of intermediate complexity LOVECLIM constrained to follow the signal recorded in climate proxies using a data assimilation method based on a particle filtering approach. The selected proxies represent oceanic and atmospheric surface temperature in the Southern Hemisphere derived from terrestrial, marine and glaciological records. Two mechanisms previously suggested to explain the 10–8 ka BP cooling pattern are investigated using the data assimilation approach in our model. The first hypothesis is a change in atmospheric circulation, and the second one is a cooling of the sea surface temperature in the Southern Ocean, driven in our experimental setup by the impact of an increased West Antarctic melting rate on ocean circulation. For the atmosphere hypothesis, the climate state obtained by data assimilation produces a modification of the meridional atmospheric circulation leading to a 0.5 °C Antarctic cooling from 10 to 8 ka BP compared to the simulation without data assimilation, without congruent cooling of the atmospheric and sea surface temperature in the Southern Ocean. For the ocean hypothesis, the increased West Antarctic freshwater flux constrainted by data assimilation (+100 mSv from 10 to 8 ka BP) leads to an oceanic cooling of 0.7 °C and a strengthening of Southern Hemisphere westerlies (+6%). Thus, according to our experiments, the observed cooling in Antarctic and the Southern Ocean proxy records can only be reconciled with the reconstructions by the combination of a modified atmospheric circulation and an enhanced freshwater flux.
Highlights
Over Antarctica, water stable isotope records from deep ice cores show a temperature optimum around 12–10 ka BP (Masson-Delmotte et al, 2000, 2011; Stenni et al, 2011), followed by a large cooling of about 1 ◦C from 10 to 8 ka (Fig. 1), which is the strongest millennial Antarctic temperature fluctuation of the last 10 ka
Running LOVECLIM without data assimilation (STD8 and STD10) does not reproduce the cooling observed at high southern latitudes between 10 to 8 ka in both atmospheric and sea surface temperature
The comparison with proxy reconstruction available for these periods shows a relative high mean absolute error (MAE) of 1.01 ◦C (Antarctica) and 1.26 ◦C (Southern Ocean) (Table 3). This warming is caused by an inflow of warmer North Atlantic deep water (NADW) in the Southern Ocean at 8 ka compared to 10 ka
Summary
Over Antarctica, water stable isotope records from deep ice cores show a temperature optimum around 12–10 ka BP (thousand years before present, the notation ka is used hereafter) (Masson-Delmotte et al, 2000, 2011; Stenni et al, 2011), followed by a large cooling of about 1 ◦C from 10 to 8 ka (Fig. 1), which is the strongest millennial Antarctic temperature fluctuation of the last 10 ka. The mechanisms responsible for this variation have not yet been explored and could be related to changes in atmospheric and/or oceanic circulation, in relationship with changes in orbital forcing and deglacial meltwater fluxes. P. Mathiot et al.: Southern Hemisphere high latitude cooling from 10 to 8 ka BP oW o E 90oW 90oE.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
