Coupled sea ice and climate variability from modern observations and proxy reconstructions
Creators: name: Kinnard, Christophe
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2009
Subjects: subject: Physical Geography.
subject: Climate Change.
subject: Physical Oceanography.

description: Coupled climate and sea ice variability in the Arctic was investigated using a combination of modern, historical and proxy observations. In the Canadian Arctic, operational sea ice charts were homogenized into a spatially and temporally consistent gridded dataset. A complete climatic analysis of this dataset revealed the presence of dominant modes of sea ice variability related to driving climate patterns and atmospheric circulation indices such as the North Atlantic Oscillation (NAO) and El Nino Southern Oscillation (ENSO). On a hemispheric scale, the late-summer ice cover extent is decreasing at a much faster rate than the maximum winter ice cover. The disappearing perennial ice is partly replaced by seasonal ice, the areal extent of which has increased steadily over the last century. The enhanced seasonal sea ice freeze-thaw cycle is predicted to increase the salinity of surface waters over continental shelves, thereby enhancing haline convection and ventilation of the deeper Arctic Ocean. Coupled sea ice and climate proxies for the North Baffin Bay region were developed from an existing ice core from Devon Ice Cap and a new ice core from the Prince-of-Wales (POW) Icefield on Ellesmere Island. A sea-salt concentration record from the Devon ice core was found to relate with sea ice concentration in nearby Baffin Bay. The record was used to study past sea ice conditions in Baffin Bay over the last 200 years in relation with temperature proxies (melt %, delta18O). Sea ice extent variations in northern Baffin Bay appear to be mostly dynamically driven, with sea ice decreasing when Nares Strait becomes congested with ice from the Arctic Ocean, and northerly winds advect ice from Baffin Bay southward. A new high-resolution melt record was developed using digital image analysis of the POW ice core. The record was used to show that melting affects the solid conductivity signal of the core, which compromises dating by seasonal layer counting, and hinders the identification of acidic volcanic horizons. The POW melt record, a proxy for summer warmth, was shown to be site-specific, which may be explained by the close presence of the North Open Water polynya and the peculiar position of the ice cap which rests on the shifting boundary between the maritime climate of Baffin Bay and the drier, colder climate of the high Arctic. The long-term, natural variability of late-summer Arctic sea ice was reconstructed from a network of 68 climate proxies from the circum-Arctic region. The proxy network contains both a temperature and a sea ice signal. Past sea ice extent was reconstructed using multivariate statistical calibration of the network against historical sea ice observations over the last century. The record shows that the decline in sea ice extent of the last two decades is anomalous in the context of the last 900 years. Non-linear processes are responsible for much of the variability in ice extent over the past millennium, and the same processes may be enhancing the greenhouse gas-induced decrease in ice extent currently observed.