Oct 15, 2013 - This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution ... those organizing sea ice field campaigns that ... University of Cambridge, UK; email: ew428@ cam.
Eos, Vol. 94, No. 42, 15 October 2013
MEETING Reconstructing Past Sea Ice Second Sea Ice Proxies (SIP) Working Group Workshop; Cambridge, United Kingdom, 22–24 July 2013 PAGE 376 One obvious manifestation of changing climate has been the recent rapid reduction in the extent and volume of Arctic sea ice. However, a dense observational data set spans only a few decades. To better understand sea ice dynamics and especially the context of the recent decline, scientists need to construct longer records. This relies on proxy data from marine sediments, ice cores, and coastal material, each providing evidence of past sea ice presence or absence. About 30 scientists met in Cambridge in July for the second meeting of the Past Global Changes (PAGES) Sea Ice Proxies (SIP) Working Group (for participants and agenda, see http://www.pages-igbp.org/workinggroups/sea -ice-proxies/meetings/1-pages/322-sea-ice). The first SIP workshop, held in Montreal in 2012, assessed the basis for each individual proxy. The second workshop, which was sponsored by PAGES (a core project of the International Geosphere-Biosphere Programme) and the British Antarctic Survey, took this as its
starting point. Most proxies rely on a complex series of processes that link ice extent to the measurement, and new work to understand those processes and calibrate the proxies is under way. From ice cores, the use of sea salt as a sea ice proxy has been hampered by the possibility that other factors, such as changing transport, dominate the variability. New modeling studies are beginning to address this. The meeting also heard preliminary work on possible new proxies involving bromine or iodine. In the marine realm, organic biomarkers such as IP25 pose complex analytical as well as interpretative challenges. The first phase of an analytical intercomparison showed that inconsistencies between laboratories arose especially from imprecise characterization of the analytical response factors. New recommendations for standardizing analytical methods will be prepared. Many existing studies rely on the presence in sediment of particular diatom species or dinoflagellate cysts. Study of the modern processes that link ice to such biological vectors that may be present
only seasonally and to their deposition in sediment is essential. The workshop participants would particularly like to hear from those organizing sea ice field campaigns that may offer opportunities to study processes that form the paleoproxy record. Perhaps the biggest challenge is to import data from all these proxies, often reporting different ice properties, into a single reconstruction. Few studies have compared different marine proxies in a single core, and the meeting participants agreed to set up such a study on some exemplar marine core sections. Reconstructions have been attempted, and the workshop saw the first draft of Holocene time slices for both the Arctic and Southern oceans and for the last interglacial in Antarctica. The Arctic reconstructions show the extent of Arctic sea ice cover through the Holocene and will give a context for the recent changes. Discussion centered on how to improve and enhance these efforts, and the meeting tasked a subgroup to consider how best to report the inferred ice conditions in a way that is compatible both with modern data sets and with the requirements of sea ice modelers. Completion of such work will be the main task for the third workshop, planned for Bremerhaven in 2014.
—E. W. WOLFF, Department of Earth Sciences, University of Cambridge, UK; email: ew428@cam .ac.uk; R. GERSONDE, Alfred-Wegener-Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany; and ANNE DE VERNAL, GEOTOP, Université du Québec à Montréal, Canada
© 2013 The Authors. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
