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Link to original content: https://pubmed.ncbi.nlm.nih.gov/24248344/
Arctic sea-ice decline archived by multicentury annual-resolution record from crustose coralline algal proxy - PubMed Skip to main page content
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. 2013 Dec 3;110(49):19737-41.
doi: 10.1073/pnas.1313775110. Epub 2013 Nov 18.

Arctic sea-ice decline archived by multicentury annual-resolution record from crustose coralline algal proxy

Jochen Halfar  1 , Walter H Adey, Andreas Kronz, Steffen Hetzinger, Evan Edinger, William W Fitzhugh
Affiliations

Arctic sea-ice decline archived by multicentury annual-resolution record from crustose coralline algal proxy

Jochen Halfar et al. Proc Natl Acad Sci U S A. .

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.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1.
Fig. 1.
(A) Locations of crustose coralline algal sea-ice proxy records (asterisks) near margins of summer and winter sea-ice extent (1979–2000 average; from NSIDC) (17). In addition, regions used for proxy verification (Fig. 2) are indicated on the map (Methods). Black circle indicates location of Devon Island ice core record within close proximity to Arctic Bay algal time series (18). GOL, Gulf of Saint Lawrence. (B) Polished slab of live-collected Clathromorphum compactum specimen. Specimen lifespan, 240 y. (C) Backscattered electron image showing annual growth increments. White dots are individual electron microprobe elemental ratio spot measurements.
Fig. 2.
Fig. 2.
Relation between sea-ice area coverage observations and crustose coralline algal proxy time series. (A) Algal proxy time series for two individual specimens [Arctic Bay (AB1) and Kingitok Island (Ki1)] compared with satellite (NSIDC) and sea-ice chart (CIS) data. Individual time series were calculated by averaging equally weighted normalized annual growth and Mg/Ca ratios of each specimen (see Methods for details). NSIDC data shown as July–August average from 1980 to 2007 (Arctic) and 1980–2010 (Labrador) as percent area covered by sea ice in selected region (Fig. 1). CIS data were computed for calendar week 30 and span from 1971 to 2007 in the Arctic and from 1980 to 2010 in Labrador. (B) Comparison of algal proxy time series compiled from multiple samples and locations (see Methods for details) to observational record of Newfoundland winter sea-ice extent (19) (r = −0.72, n = 144, padj <0.001, 5-y average) and instrumental winter NAO data (20) (r = −0.5, n = 144, padj = 0.006, 5-y average); gray lines represent annual data, thick lines 5-y averages.
Fig. 3.
Fig. 3.
Algal proxy record (red) compared with observational (blue) and proxy (green) data (see Methods for detail on records). Gray lines represent 5-y moving average and colored lines, 15-y low-pass filtered (Savitzky–Goley) annual data. Algal proxy time series plotted on inverted scale to indicate declining ice cover. Light gray bars show periods of positive algal anomalies, reflected by negative ice anomalies in observational records, and positive δ18O ice core excursions. Linear trends for all time series are plotted from 1850 onwards. All individual algal specimens yield similar trends (Fig. S3). RC indicates position of radiocarbon analyses. Values are 2σ calibrated results (Table S1); all values fall well within age model derived from growth increment counting.
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