Abstract:
The Little Ice Age (LIA) (1400-1850 AD) represents one of the most significant climatic shifts over the past 5000 years. Previous studies from Antarctica indicate generally cooler and stormier conditions during this period, but this pattern shows distinct spatial and temporal variability. The Roosevelt Island Climate Evolution (RICE) ice core provides a new opportunity to study the drivers behind this variability at annual/seasonal resolution, in a relatively under-sampled and climatically sensitive region in the eastern Ross Sea. Contrary to previous studies, isotope measurements suggest warm conditions during the LIA at Roosevelt Island.
This study presents analysis of eight major ions (Na⁺, Mg²⁺, Ca²⁺, K⁺, MS⁻, Cl⁻, NO₃⁻, SO₄²⁻) using both Ion Chromatograph and ICP-MS data, in order to reconstruct the atmospheric circulation pattern, sea ice extent and marine primary productivity across this LIA to Modern Era (ME) at Roosevelt Island. The dataset is tied to a robust age model allowing annual dating and the opportunity to accurately reconstruct rates of change during this ME-LIA. Challenges revolving around the calibration of the Ion Chromatograph are also discussed. The major ion record determines whether the lack of cooling in the Roosevelt Island core implied by the stable isotopes represents a true temperature anomaly or whether the atmospheric circulation pattern caused an isotopic enrichment that masks an underlying cooling.
It was determined that Roosevelt Island experienced during the LIA (i) an increase in marine air mass intrusions along with weaker katabatic winds compared to the 200 years prior, (ii) decreased biological productivity and (iii) increased sea ice. From the 1850-1880s to 1992 AD, there is a shift to reduced marine winds, increased katabatics, increased biological productivity and decreased sea ice until 1992. In the wider Ross Sea context, this suggests an east-west divide in terms of the dominance of katabatics versus marine wind influence. This divide is attributed with the warming signal seen in the RICE record in the Eastern Ross Sea and the cooling in the Western Ross Sea records. It is also likely linked to the influence of climate indices on the depth/position of the Amundsen Sea Low.
