Variability of Arctic climate and sea ice over the past millennium: implications for ice cap mass balance

Sea salt species, especially Na⁺ and Cl^-, can be used as indicators of the efficiency of transport of sea salt aerosols onto the ice cap. This provides an indication of the proximity of open water to the core site and, hence, these species can provide a proxy measure of sea ice extent (e.g. Grumet et. al., 2001). However, other factors that affect sea salt transportation, such as wind speed and changes in atmospheric source region must also be taken into account (Fischer, 2001).

Photosynthesising algae in sea ice and phytoplankton in the ocean water release dimethylsulfide (DMS) during cell lysis which oxidies to methanesulfonate (MSA). MSA aerosol is not produced during the polar night, and so has a distinct seasonality (Li, Barrie and Sirois, 1993; Sirois & Barrie, 1999). Peak productivity is thought to be associated with melting sea ice margins where freshwater and nutrients are released, so MSA concentration in the core can indicate both sea ice extent and marine biological productivity. MSA has been shown to have both negative (northern hemisphere) and positive (southern hemisphere) correlations with sea ice extent (Curran, et. al., 2003; O'Dwyer, 2000), so the relationship between MSA and sea ice extent is not simple, but we hope to use our high resolution records to develop MSA as a reliable sea ice proxy. The decay of DMS also produces sulfate and we can use sulfur isotope analysis to partition the sources of SO₄^2- from the core into anthropogenic, sea-salt and biogenic contributions (Norman et. al., 1999), in order to cross-check the MSA data with biogenic SO₄^2-.

Sea ice proxies will be used in conjunction with analysis of atmospheric modes and circulation that are thought to influence observed sea ice variablility (Deser, Walsh and Timlin, 2000; Rigor, Wallace and Colony, 2002; Krahman and Visbeck, 2003; Stern and Heide-Jorgensen, 2003) to clarify the interaction of these systems and to provide a record of past sea ice variability in the context of changing climate and circulation patterns (Dyke et al, 1997).