Reconstructing atmospheric circulation and sea-ice extent in the West Antarctic over the past 200 years using data assimilation

Abstract

The West Antarctic climate has witnessed large changes during the second half of the 20 th century including a strong and widespread continental warming, important regional changes in sea-ice extent and snow accumulation, as well as a major mass loss from the melting of some ice shelves. However, the potential links between those observed changes are still unclear and instrumental data do not allow determination of whether they are part of a long-term evolution or specific to the recent decades. In this study, we analyze the climate variability of the past two centuries in the West Antarctic sector by reconstructing the key atmospheric variables (atmospheric circulation, near-surface air temperature and snow accumulation) as well as the sea-ice extent at the annual timescale using a data assimilation approach. To this end, information from Antarctic ice core records (snow accumulation and δ 18 O) and tree-ring width records situated in the mid-latitudes of the Southern Hemisphere are combined with the physics of climate models using a data

Using a process-based dendroclimatic proxy system model in a data assimilation framework: a test case in the Southern Hemisphere over the past centuries

“…The ice core data selected here are the same as in Dalaiden et al (2021), a study focusing on the mechanisms behind the West Antarctic climate changes. This includes the 48 annually resolved ice core snow accumulation records in Antarctica…”

“…The B40 ice core snow accumulation record of Medley et al (2018) has also been added as this record has been published after the publication of the Thomas et al (2017)'s database. Finally, as in Dalaiden et al (2021), we use the 29 annually resolved δ 18 O records in Antarctica from Stenni et al (2017). Fig.…”

“…MAIDEN was calibrated at the 12 SH sites from PAGES2k2017 in Rezsöhazy et al (2021) driven by the daily maximum and minimum temperature and precipitation from the Global Meteorological Forcing Dataset for land surface modelling (v2) (http://hydrology.princeton.edu/data.php, last access: 5 May 2021; Sheffield et al, 2006) at 0.5 • resolution (hereafter GMF), over 1950-2000 CE. The model was validated using the same dataset over the 1901-1949 CE time period.…”

“…MAIDEN includes the atmospheric CO 2 concentration among other inputs, which represents a major advantage for taking into account the potential effect of the recent exponential increase of CO 2 on tree growth (Myhre et al, 2013;Boucher et al, 2014). In Rezsöhazy et al (2021), the MAIDEN model has been successfully applied to the PAGES2k TRW database using the calibration protocol developed in Rezsöhazy et al (2020), highlighting the potential of MAIDEN to be used as a PSM for DA-based reconstruction of past climate variability.…”

“…The goal is to evaluate if and how a complex process-based model of tree growth like MAIDEN can contribute to the improvement of large-scale DA-based reconstructions of past climate variability compared to the regression model classically used so far. Because MAIDEN has shown to be skillful in different regions of the Southern Hemisphere (SH; Rezsöhazy et al, 2021), we focus on that region and provide climate reconstruction of near-surface air temperature, precipitation and winds in the mid-to-high latitudes of the SH over the past 400 years. The Southern Hemisphere also constitutes an interesting study case, as few reconstructions have been performed in this region so far (Neukom et al, 2011(Neukom et al, , 2014.…”