Wednesday, July 29, 2009

Arctic Sea Ice Predates Antarctic

Evidence for middle Eocene Arctic sea ice from diatoms and ice-rafted debris

Catherine E. Stickley (1,3)
Kristen St John(2)
Nalân Koç(1,3)
Richard W. Jordan(4)
Sandra Passchier(5)
Richard B. Pearce(6)
Lance E. Kearns(2)

1. Department of Geology, University of Tromsø, N-9037 Tromsø, Norway
2. Department of Geology and Environmental Science, James Madison University, Harrisonburg, Virginia 22807, USA
3. Norwegian Polar Institute, Polar Environmental Centre, N-9296 Tromsø, Norway
4. Department of Earth and Environmental Sciences, Yamagata University, Yamagata 990-8560, Japan
5. Department of Earth and Environmental Studies, Montclair State University, Montclair, New Jersey 07043, USA
6. National Oceanography Centre, Southampton, University of Southampton, Southampton SO14 3ZH, UK

Correspondence to: Catherine E. Stickley1,3 Correspondence and requests for materials should be addressed to C.E.S. (Email:


Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic1, contain ice-rafted debris (IRD) back to the middle Eocene epoch, prompting recent suggestions that ice appeared in the Arctic about 46 million years (Myr) ago2, 3. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice4, IRD records2, 3 are restricted to providing a history of general ice-rafting only. It is critical to differentiate sea ice from glacial (land-based) ice as climate feedback mechanisms vary and global impacts differ between these systems: sea ice directly affects ocean–atmosphere exchanges5, whereas land-based ice affects sea level and consequently ocean acidity6. An earlier report3 assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists2, these data are neither comprehensive nor quantified. Here we show the presence of middle Eocene Arctic sea ice from an extraordinary abundance of a group of sea-ice-dependent fossil diatoms (Synedropsis spp.). Analysis of quartz grain textural characteristics further supports sea ice as the dominant transporter of IRD at this time. Together with new information on cosmopolitan diatoms and existing IRD records2, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas approx47.5 Myr ago, followed approx0.5 Myr later by the onset of seasonally paced sea-ice formation in offshore areas of the central Arctic. Our data establish a 2-Myr record of sea ice, documenting the transition from a warm, ice-free3 environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase7.

Arctic sea ice before the Antarctic. (o.O)

Pop sci treatment here.

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