SIP - Sea Ice Proxies
Sea Ice Proxies (SIP) was a working group of PAGES from 2011 to 2014.
SIP examined the proxies of sea ice from sedimentary and ice archives with the overarching objective of reconstructions to document the sea ice cover variability in time and space, and serve in model-data intercomparison.
Sea ice is indeed an important component of the climate system as it plays a major role on polar amplification. However, the variability of sea ice and its linkages with the global climate still remain to be documented on time scales before to the satellite observations. Hence there is a need for sea ice reconstructions from indirect observations and proxies.
To address its objectives, SIP started with an evaluation of biogenic and geochemical tracers as qualitative or quantitative proxies of sea ice. This led to the publication of a special issue of Quaternary Science Reviews entitled "Sea ice in the paleoclimate system: the challenge of reconstructing sea ice from proxies" (vol. 79, November 2013).
In a second phase, SIP developed a strategy for combining different and complementary proxies for the reconstruction of sea ice cover in the past with the best possible coverage and accuracy. In particular, the group worked on Holocene data sets from the Northern Hemisphere to prepare a multiproxy compilation with millennial time window. This compilation should be published in 2016 and will serve for the model-data intercomparison. Similarly, a synthesis of sea ice reconstructions from the circum-Antarctic Ocean during the Last interglacial should be available soon.
While SIP contributed to establish the basis for reconstructing the sea ice variability and permitted to initiate multi-proxy compilations, more work is needed for data acquisition to test hypotheses regarding the sea ice dynamics in the climate system and its long term resilience or instability. Hence, although the PAGES activity of SIP ended officially in 2014, the members of the group have continued to interact and organize sessions at international meetings, notably at the AGU (December 2014), INQUA (July 2015) and EGU (April 2016).
Sea ice is a crucial component of the polar climate system, impacting albedo, heat and gas exchange, primary productivity and carbon export, atmospheric and ocean circulation, freshwater budget, ocean stratification and deep water mass formation. It is therefore critical that it should be correctly specified as a forcing or predicted as a feedback in model studies. However, full and reliable knowledge (through satellite observation) of even the areal extent and seasonal variability of sea ice extends only to 1978.
Some earlier observational data are available, but their coverage is patchy and their reliability uncertain. Proxy data are therefore vital for extending the sea ice record to the geological past, to improve understanding of the interplay between sea ice and the climate system over a broad range of conditions.
Sea Ice Proxies (SIP) became a PAGES Working Group in mid-2011. The overall objective of this working group was to critically assess and compare the different proxies for sea ice, in order to make recommendations about the reliability and applicability of each in the Arctic and the Antarctic setting.
An extended objective was to facilitate the production of new synthesis estimates of past sea ice extent based on the assessed proxies.