Part 1: Sea ices' past, methods and uses

Interpreting recent changes and modelling future changes in sea ice cover requires a longer term perspective. From which we can better understand the Arctic’s natural variability and response to external forcing over time. The past distribution of sea ice is recorded in sediments preserved on the sea floor and in archived deposits along the coasts. Indirect sea ice extent can also be inferred from terrestrial sources such as coastal vegetation and ice cores.

Marine sedimentary records are the most complete and spatially extensive records of past sea ice conditions and area affected physically, chemically and biologically by sea ice (Polyak et al, 2010). Thus allowing ice characteristic reconstruction, however generally sea ice deposition is low (Polyak et al, 2010) making short term characteristic are hard to capture. For example the September 2007 record minimum. Cores are preferably taken from deep sites as they are far less eroded by temporal erosion. Ice rafted sediment is the most direct proxy, which is the sediment that melts and drops out of the sea ice which has been transported from the site of entrainment. Other Marine proxies include skeletons of microscopic organisms in bottom sediments such as diatoms which may indicate the conditions of ice cover above the study site thus the climatic conditions can be inferred.

Costal records such as coastal sediments and coastal forms (eg. Plains, marine terraces) evidence of the past can be found. Change in sea level has exposed formerly marine environments and present easy opportunity for study. However such landforms only present a limited indication due to their limited time span. Information on past sea-surface and air temperatures, circulation and sea ice conditions can be obtained. Driftwood distribution can be used to infer the presence or absence of land fast ice. Ice is essential for the transport of driftwood, as it would otherwise become saturated, loose buoyancy, and sink after a year (Polyack et al, 2010). Whalebone and other mammal bones can be used to derive sea ice extents as such mammals have an affinity for sea ice. Seasonal migrations of certain species are known to follow breaks in the ice-pack and thus can be combined to give an indication of paleo sea ice distribution.

Terrestrial records including vegetation can be used to provide information on past environments for example past tree lines. Ice cores are taken to view more recent characteristics and the value for past climates is limited. So the overall goal is to identify key indicating chemicals (such as sea salt) in the composition which can then be used when viewing the aforementioned paleo sea ice proxies.

Historical records such as noted shipping routes have been compiled since 1870 (Walsh, 1978).