Pleistocen collapse of the West Antarctic ice sheet

Science

Volumn 281, Issue 5373, 1998, Pages 82-85

  Scherer, Reed P ^a   Aldahan, Ala ^a   Tulaczyk, Slawek ^b   Possnert, Göran ^c   Engelhardt, Hermann ^b   Kamb, Barclay ^b  

^a UPPSALA UNIVERSITY   (Sweden)

^b CALIFORNIA INSTITUTE OF TECHNOLOGY   (United States)

^c UPPSALA UNIVERSITY   (Sweden)

Author keywords

[No Author keywords available]

Indexed keywords

BERYLLIUM; ICE;

ICE SHEET; PLEISTOCENE;

ANTARCTICA; ARTICLE; CLIMATE; DIATOM; GEOLOGY; PRIORITY JOURNAL; SEA; SEDIMENT;

ANTARCTICA, WEST ANTARCTIC ICE SHEET;

BACILLARIOPHYTA;

EID: 0032479549     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.281.5373.82     Document Type: Article

References (49)

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24. We estimated the absolute abundance of diatoms using a modification of a recognized method [R. P. Scherer, J. Paleolimnol. 12, 171 (1994)]. Abundance is normally estimated on the basis of whole diatoms, with the use of standardized counting criteria, but whole diatoms are too rare in these sediments to allow statistically significant estimates. Instead, we counted diatom fragments in the size class from 2 to 5 μm (Table 1). The abundance of whole diatom valves is at Least three orders of magnitude lower. Extracting identifiable diatoms from these diamictons for biostratigraphic application requires specialized laboratory methods and extreme care to avoid sample contamination. All glassware and reusable supplies used in sample preparation are soaked in warm 15% NaOH for 4 hours and repeatedly rinsed with distilled and filtered water to remove any diatom residues that may be present. To test the reproducibility of abundance estimates and to test for potential laboratory contamination, we routinely prepare and analyze both sample duplicates and blanks. Duplicate preparations demonstrated consistent and reproducible results in diatom abundance (<10% error) and assemblage analyses. Thorough analysis of blanks revealed no evidence of sample contamination by identifiable diatom fragments.
25. 10Be (measured in atoms per gram) was normalized for the total sample dried at 110°C for 6 hours. The silt-clay fraction used is dominated by quartz, with lesser quantities of feldspar and clay minerals and negligible carbonate (8).
26. H.H. Engelhardt and B. Kamb, J. Glaciol. 43, 207 (1997).
27. Ice samples [M. Jackson and B. Kamb, J. Glaciol. 43, 415 (1998)] were washed under a stream of distilled deionized water to remove approximately 0.5 cm of the outer layers, then melted in new nylon beakers and filtered onto 25-mm microfitters. Additionally, two water blanks were filtered and analyzed (9). Filters were mounted on cover glass with Norland optical adhesive and analyzed in their entirety at X1200 magnification. The age of the ice samples is unknown but is likely to be early Holocene.
28. This sample was taken during field season 1988-1989 (borehole 2, sample 1, Winnower sample). Much of the clay and other fine-grained material was lost in recovery of this sample (3).
29. This percentage is an underestimate because it does not include the many extant antarctic diatoms that were also common in the Miocene ocean.
30. Although it is ubiquitous in modern antarctic continental shelf sediments, the age of the first stratigraphic occurrence of T. antarctica is not yet well documented because of a lack of continuous Quaternary near-shore reference sections. Its appearance can be reliably bracketed by its occurrence in MIS 5e interglacial deposits [B. L. Ward and P.-N. Webb, J. Foram. Res. 16, 176 (1986)] at Cape Barne, Ross Island [R. P. Scherer, unpublished data] and by its absence from well-dated (0.75 My) lower Quaternary diatomaceous deposits in the Southern Ocean [R. Gersonde and M. Barcena, Micropaleontology 44, 84 (1998)] and in McMurdo Sound (Fig. 1) (Cape Roberts Project core 1, unit 3.1, upper A. ingens zone) [Cape Roberts Science Team, Terra Antarctica 5, 1 (1998)]. J. Barron [U.S. Geol. Surv. Open File Report 96-173 (1996)] reports T. cf. antarctica in mid-Pliocene Antarctic sediments, but we believe that there are significant taxonomic differences between T. cf. antarctica sensu Barron and T. antarctica sensu stricto, which occurs in our samples.
31. Although it is ubiquitous in modern antarctic continental shelf sediments, the age of the first stratigraphic occurrence of T. antarctica is not yet well documented because of a lack of continuous Quaternary near-shore reference sections. Its appearance can be reliably bracketed by its occurrence in MIS 5e interglacial deposits [B. L. Ward and P.-N. Webb, J. Foram. Res. 16, 176 (1986)] at Cape Barne, Ross Island [R. P. Scherer, unpublished data] and by its absence from well-dated (0.75 My) lower Quaternary diatomaceous deposits in the Southern Ocean [R. Gersonde and M. Barcena, Micropaleontology 44, 84 (1998)] and in McMurdo Sound (Fig. 1) (Cape Roberts Project core 1, unit 3.1, upper A. ingens zone) [Cape Roberts Science Team, Terra Antarctica 5, 1 (1998)]. J. Barron [U.S. Geol. Surv. Open File Report 96-173 (1996)] reports T. cf. antarctica in mid-Pliocene Antarctic sediments, but we believe that there are significant taxonomic differences between T. cf. antarctica sensu Barron and T. antarctica sensu stricto, which occurs in our samples.
32. Although it is ubiquitous in modern antarctic continental shelf sediments, the age of the first stratigraphic occurrence of T. antarctica is not yet well documented because of a lack of continuous Quaternary near-shore reference sections. Its appearance can be reliably bracketed by its occurrence in MIS 5e interglacial deposits [B. L. Ward and P.-N. Webb, J. Foram. Res. 16, 176 (1986)] at Cape Barne, Ross Island [R. P. Scherer, unpublished data] and by its absence from well-dated (0.75 My) lower Quaternary diatomaceous deposits in the Southern Ocean [R. Gersonde and M. Barcena, Micropaleontology 44, 84 (1998)] and in McMurdo Sound (Fig. 1) (Cape Roberts Project core 1, unit 3.1, upper A. ingens zone) [Cape Roberts Science Team, Terra Antarctica 5, 1 (1998)]. J. Barron [U.S. Geol. Surv. Open File Report 96-173 (1996)] reports T. cf. antarctica in mid-Pliocene Antarctic sediments, but we believe that there are significant taxonomic differences between T. cf. antarctica sensu Barron and T. antarctica sensu stricto, which occurs in our samples.
33. Although it is ubiquitous in modern antarctic continental shelf sediments, the age of the first stratigraphic occurrence of T. antarctica is not yet well documented because of a lack of continuous Quaternary near-shore reference sections. Its appearance can be reliably bracketed by its occurrence in MIS 5e interglacial deposits [B. L. Ward and P.-N. Webb, J. Foram. Res. 16, 176 (1986)] at Cape Barne, Ross Island [R. P. Scherer, unpublished data] and by its absence from well-dated (0.75 My) lower Quaternary diatomaceous deposits in the Southern Ocean [R. Gersonde and M. Barcena, Micropaleontology 44, 84 (1998)] and in McMurdo Sound (Fig. 1) (Cape Roberts Project core 1, unit 3.1, upper A. ingens zone) [Cape Roberts Science Team, Terra Antarctica 5, 1 (1998)]. J. Barron [U.S. Geol. Surv. Open File Report 96-173 (1996)] reports T. cf. antarctica in mid-Pliocene Antarctic sediments, but we believe that there are significant taxonomic differences between T. cf. antarctica sensu Barron and T. antarctica sensu stricto, which occurs in our samples.
34. Although it is ubiquitous in modern antarctic continental shelf sediments, the age of the first stratigraphic occurrence of T. antarctica is not yet well documented because of a lack of continuous Quaternary near-shore reference sections. Its appearance can be reliably bracketed by its occurrence in MIS 5e interglacial deposits [B. L. Ward and P.-N. Webb, J. Foram. Res. 16, 176 (1986)] at Cape Barne, Ross Island [R. P. Scherer, unpublished data] and by its absence from well-dated (0.75 My) lower Quaternary diatomaceous deposits in the Southern Ocean [R. Gersonde and M. Barcena, Micropaleontology 44, 84 (1998)] and in McMurdo Sound (Fig. 1) (Cape Roberts Project core 1, unit 3.1, upper A. ingens zone) [Cape Roberts Science Team, Terra Antarctica 5, 1 (1998)]. J. Barron [U.S. Geol. Surv. Open File Report 96-173 (1996)] reports T. cf. antarctica in mid-Pliocene Antarctic sediments, but we believe that there are significant taxonomic differences between T. cf. antarctica sensu Barron and T. antarctica sensu stricto, which occurs in our samples.
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42. A massive volume of Pliocene and Pleistocene sediment has been eroded and transported toward the continental shelf edge by glacial processes [A. K. Cooper et al., Mar. Geol. 102, 175 (1991); R. P. Scherer, Antarct. J. U.S. 29, 11 (1994)] (16).
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49. Support for this study came from Uppsala University, the Swedish Natural Sciences Research Council, and the Knut and Alice Wallenberg Foundation to R.P.S., A.A., and G.P., and from a U.S. NSF grant OPP9319018 to B.K. and H.E.