Publication Date:
2009-07-17
Description:
Oceanic sediments from long cores drilled on the Lomonosov ridge, in the central Arctic, 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) ago. However, because IRD can be transported by icebergs (derived from land-based ice) and also by sea ice, IRD records 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 exchanges, whereas land-based ice affects sea level and consequently ocean acidity. An earlier report assumed that sea ice was prevalent in the middle Eocene Arctic on the basis of IRD, and although somewhat preliminary supportive evidence exists, 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 records, our data strongly suggest a two-phase establishment of sea ice: initial episodic formation in marginal shelf areas approximately 47.5 Myr ago, followed approximately 0.5 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-free environment to one dominated by winter sea ice at the start of the middle Eocene climatic cooling phase.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Stickley, Catherine E -- St John, Kristen -- Koc, Nalan -- Jordan, Richard W -- Passchier, Sandra -- Pearce, Richard B -- Kearns, Lance E -- England -- Nature. 2009 Jul 16;460(7253):376-9. doi: 10.1038/nature08163.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉[1] Department of Geology, University of Tromso, N-9037 Tromso, Norway [2] Norwegian Polar Institute, Polar Environmental Centre, N-9296 Tromso, Norway.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/19606146" target="_blank"〉PubMed〈/a〉
Keywords:
Arctic Regions
;
*Cold Climate
;
Diatoms/chemistry/*isolation & purification/ultrastructure
;
Fossils
;
Geologic Sediments/microbiology
;
History, Ancient
;
Hydrogen-Ion Concentration
;
Ice Cover/*chemistry/*microbiology
;
Microscopy, Electron, Scanning
;
Oceans and Seas
;
Principal Component Analysis
;
Salinity
;
Seawater/chemistry
;
Silicon Dioxide/analysis
Print ISSN:
0028-0836
Electronic ISSN:
1476-4687
Topics:
Biology
,
Chemistry and Pharmacology
,
Medicine
,
Natural Sciences in General
,
Physics
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