The Ross Sea Dipole – Temperature, Snow Accumulation and Sea Ice Variability in the Ross Sea Region, Antarctica, over the Past 2,700 Years

Abstract

Abstract. High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of climate patterns relevant for future projections. Here, we present data from a new, annually-dated ice core record from the eastern Ross Sea. Comparison of the Roosevelt Island Climate Evolution (RICE) ice core records with climate reanalysis data for the 1979–2012 calibration period shows that RICE records reliably capture temperature and snow precipitation variability of the region. RICE is compared with data from West Antarctica (West Antarctic Ice Sheet Divide Ice Core) and the western (Talos Dome) and eastern (Siple Dome) Ross Sea. For most of the past 2,700 years, the eastern Ross Sea was warming with perhaps increased snow accumulation and decreased sea ice extent. However, West Antarctica cooled whereas the western Ross Sea showed no significant temperature trend. From the 17th Century onwards, this relationship changes. All three regions now show signs of warming, with snow accumulation declining in West Antarctica and the eastern Ross Sea, but increasing in the western Ross Sea. Analysis of decadal to centennial-scale climate variability superimposed on the longer term trend reveal that periods characterised by opposing temperature trends between the Eastern and Western Ross Sea have occurred since the 3rd Century but are masked by longer-term trends. This pattern here is referred to as the Ross Sea Dipole, caused by a sensitive response of the region to dynamic interactions of the Southern Annual Mode and tropical forcings.

Regional Antarctic snow accumulation over the past 1000 years

“…In particular, blocking (ridging) events with a position and frequency determined by the intensity and position of the ASL (Renwick, 2005) have been identified as a major driver of snow precipitation in the eastern Ross Sea region, enhancing meridional flow across the eastern Ross Sea . The principal tropical teleconnection associated with the Rossby wave propagation from the western tropical Pacific exerts its influence on the entire Ross Sea region, with opposing influence between the east and west Bertler et al, 2017), which explains some of the differences observed in these two regions.…”

A novel approach to process brittle ice for continuous flow analysis of stable water isotopes

“…during two austral summer field seasons, 2011–2012 and 2012–2013. Roosevelt Island is a high snow accumulation site (Bertler and others, 2018) with the potential for a highly resolved record. The RICE BIZ occurs from 500 m depth to bedrock, which was reached at 764 m. This part of the core contained a higher number of fractures, representing a potentially significant loss of ice for CFA.…”

“…To ensure the integrity of planned measurements, particularly gases, ice cores need to be kept frozen at −18°C or colder (Ikeda-Fukazawa and others, 2005). Due to the relatively warm summertime temperatures at Roosevelt Island (Bertler and others, 2018), core curation in the field was an important challenge. Once the cores were drilled, they were kept in core rest buffer shelving (SF) to relax for up to 2 weeks.…”

Authors' answers to referees and short comments

“…The RICE δ 18 O record, situated on Roosevelt Island on the Ross Ice Shelf, is more influenced by air masses from the eastern Ross Sea sector than the rest of the West Antarctic Ice Sheet region, which is influenced predominantly by air masses from the Amundsen Sea (Neff et al, 2015;. Moreover, borehole temperature and δ 15 N thermal fractionation records at RICE highlight some notable differences in the isotope temperature reconstruction, which suggest that sea ice extent exerts an important control, perhaps masking aspects of the longer-term temperature trends in the region (Bertler et al, 2017). Over the period from 0 to 1900 CE the ECHAM temperature scaling suggests that the mean cooling trends are −0.38 • C 1000 yr −1 for the East Antarctic Plateau, −0.47 • C 1000 yr −1 for the West Antarctic Ice Sheet, −0.52 • C 1000 yr −1 for the Antarctic Peninsula and −0.34 • C 1000 yr −1 for Victoria Land.…”