25th International Meeting on Organic Geochemistry IMOG 2011

O-02
Melting history of West Antarctic Ice Sheet since the last glacial
maximum revealed by compound-specific radiocarbon dating
Nao Ohkouchi 1 , Hisami Suga 1 , Yoshito Chikaraishi 1 , Yusuke Yokoyama 2 , Takahiro
Yamazaki 2 , Yosuke Miyairi 2 , Hiroyuki Matsuzaki 2 , John Anderson 3 , John Southon 4 ,
Timothy Eglinton 5
1 JAMSTEC, Yokosuka, Japan, 2 University of Tokyo, Kashiwa, Japan, 3 Rice University, Houston, United
States of America, 4 University of California, Irvine, Irvine, United States of America, 5 ETH, Zurich,
Switzerland (corresponding author:nohkouchi@jamstec.go.jp)
The stability of the marine-based West Antarctic
Ice Sheet (WAIS) is the subject of major scientific and
societal concern because of its potential susceptibility
to collapse as a consequence of global warming, with
resulting consequences for global sea level. On the
Antarctic margin, paleoclimatologic investigations of
the sediment record have been hindered seriously by
a paucity of calcareous fossils, which yield precise
chronology through their radiocarbon content. Recent
developments in molecular-level radiocarbon dating of
sediments provide tools for overcoming the problem
(Ohkouchi et al., 2003; Ohkouchi and Eglinton, 2008).
In this presentation, we report recent applications
of this method to the Ross Sea sediment cores. Fatty
acid ages from 7 sediment cores recovered in the
wide area of the Ross Sea (Fig. 1) indicated
substantially younger chronologies relative to bulk-
TOC based chronologies. Together with
atmospherically derived
10 Be concentration, we
estimated the precise timing when edge of Ross Ice
Shelf crossed over these core sites. It suggested that
the Ross Sea section of WAIS substantially retreated
during the Holocene. During the mid-Holocene, it
could have been located about 200-400 km north to
the modern shelf edge (Fig. 1).
Furthermore, hydrogen isotopic record of certain
marine biomarkers in a core from the NW Ross Sea is
punctuated by intervals of extremely D-depletions (�D
values as low as to -570‰) around 6.8, 5.7, 4.1, 2.5,
and 1.5 ka. We attribute these abrupt isotopic
excursions to freshwater discharge events,
suggesting the WAIS has experienced several
intermittent, rapid melting episodes during the
Holocene.
Our record suggested that the WAIS melting
episodes occurred after sea-level had returned to
within 4 m of the modern-day level, implying that the
WAIS at most supplied an equivalent to ~1.5 × 10 6
km 3 of water during the last 7 kyr. If these D-depletion
events were of the same magnitude, each event
would have produced up to ~3 × 10 5 km 3 of
meltwater, which is three orders of magnitude larger
than the contemporary annual meltwater flux from the
WAIS. Therefore, future sea-level rise associated with
the attrition of the WAIS could be rapid rather than
gradual given the intermittent, rather than continuous,
nature of prior melting events.
Ross Sea
WAIS
Fig. 1. Core sites (red dots) and estimated position of
WAIS edge in the Ross Sea (a blue broken line)
during the mid- Holocene (~5000 years ago).
References
Ohkouchi N, Eglinton TI, Hayes JM (2003)
Radiocarbon, 45, 17-24.
Ohkouchi N, Eglinton TI (2008) Quaternary
Geochronology, 3, 235-243.
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