title: Arctic sea-ice decline archived by multicentury annual-resolution record from crustose coralline algal proxy.
abstract: Northern Hemisphere sea ice has been declining sharply over the past decades and 2012 exhibited the lowest Arctic summer sea-ice cover in historic times. Whereas ongoing changes are closely monitored through satellite observations, we have only limited data of past Arctic sea-ice cover derived from short historical records, indirect terrestrial proxies, and low-resolution marine sediment cores. A multicentury time series from extremely long-lived annual increment-forming crustose coralline algal buildups now provides the first high-resolution in situ marine proxy for sea-ice cover. Growth and Mg/Ca ratios of these Arctic-wide occurring calcified algae are sensitive to changes in both temperature and solar radiation. Growth sharply declines with increasing sea-ice blockage of light from the benthic algal habitat. The 646-y multisite record from the Canadian Arctic indicates that during the Little Ice Age, sea ice was extensive but highly variable on subdecadal time scales and coincided with an expansion of ice-dependent Thule/Labrador Inuit sea mammal hunters in the region. The past 150 y instead have been characterized by sea ice exhibiting multidecadal variability with a long-term decline distinctly steeper than at any time since the 14th century.
authors.affiliation: Department of Chemical and Physical Sciences, University of Toronto at Mississauga, Mississauga, ON, Canada L5L 1C6.
authors.forename: Jochen
authors.initials: J
authors.lastname: Halfar
authors.forename: Walter H
authors.initials: WH
authors.lastname: Adey
authors.forename: Andreas
authors.initials: A
authors.lastname: Kronz
authors.forename: Steffen
authors.initials: S
authors.lastname: Hetzinger
authors.forename: Evan
authors.initials: E
authors.lastname: Edinger
authors.forename: William W
authors.initials: WW
authors.lastname: Fitzhugh
mesh_terms: D001110:Arctic Regions; D002118:Calcium / Q000032:analysis; D057231:Climate Change / Q000266:history*; D005580:Fossils; D019015:Geologic Sediments / Q000382:microbiology*; D049668:History, 15th Century; D049669:History, 16th Century; D049670:History, 17th Century; D049671:History, 18th Century; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D049691:History, Medieval; D046448:Ice Cover / Q000737:chemistry*; D008274:Magnesium / Q000032:analysis; D008962:Models, Theoretical; D000461:Rhodophyta / Q000737:chemistry / Q000254:growth & development*
chemical_list: D008274:Magnesium; D002118:Calcium