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| Titel |
Distributions of mesophilic archaeotal membrane lipids and TEX86 thermometry in the modern enclosed shallow coastal anoxic basin |
| VerfasserIn |
K. Moriya, M. Kuwae, M. Yamamoto, T. Kunihiro, H. Onishi, H. Hamaoka, M. Saito, T. Sagawa, J. Shibata, N. Fujii, N. Yoshie, K. Omori, H. Takeoka |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066482
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| Zusammenfassung |
| It is widely accepted that atmospheric carbon dioxide concentration is rapidly increasing over
the last 200 years. Global average surface temperature has been increased by 0.74 Ë C in the
last 100 years. While a large number of studies have also documented the annual sea surface
temperature (SST) and global mean sea level rising, global warming effect on enclosed
coastal seas, such as Seto Inland Sea or Chesapeake Bay, is less understood. Since
ecosystems of those shallow coastal basins would be severely altered in the near future, we
need to gather and understand archives of climate change and ecosystem responses
in these few hundred years. In this point of view, Beppu Bay in Seto Inland Sea
would provide one of archetypal records, because sediments in Beppu Bay yields
exquisitely preserved fish scales indicative of a historical record of macro faunal
abundance1).
On the other hand, since systematic and precise instrumental SST data for 200 years are very
scarce in Seto Inland Sea, we need to use a certain SST proxy for identifying the past SST
records. However, paleothermometry in the shallow coastal basin is quite difficult because
carbonate microfossils typically used for paleotemperature proxies are practically absent in
the shallow ocean. On the contrary, organic compound based paleo-temperature proxies, such
as TEX86, can be utilized even in the shallow coastal sea. However, since TEX86
thermometry has rarely been used for such shallow marine sediments, applicability of TEX86
in the coastal ocean is still uncertain.
Here we test potential ability of TEX86 paleothermometry in shallow coastal anoxic basin.
We collected particulate organic matters (POM) from the water column of Beppu Bay (~70m
deep) at every 10 m. We collected an additional sample at the depth showing chlorophyll
maximum. Then the vertical depth profile of glycerol dialkyl glycerol tetraethers (GTGTs)
distribution within the anoxic and oxygen-enriched water columns was determined. We also
calculated TEX86 values, which were compared with the in situ measurements of water
temperatures.
Total GDGTs abundance within the water column shows very unique distribution. Though
total GDGTs abundance in the oxygen-enriched surface and subsurface waters are almost
constant, it is significantly increased in the anoxic bottom water. Because Beppu Bay is an
archetypal restricted basin in Seto Inland Sea, cooler stagnant and anoxic water
masses have been developed at bottom of Beppu Bay. Because the depth showing
abrupt increase of total GDGTs is well correlated with the depth of oxic/anoxic
boundary within the water column, it is assumed that GDGTs production is enhanced
in the anoxic water mass. In fact, calculated TEX86 temperatures of the samples
collected in the cooler anoxic bottom water are cooler than those in the warmer
oxygen-enriched surface and subsurface waters. Moreover, those TEX86 derived
temperatures correlate with the in situ measurements of water temperatures. Therefore we
believe that TEX86 temperatures are representative of true water temperatures at Beppu
Bay.
1) Kuwae et al. (2008) International symposium ‘Effect of Climate Change on the World’s
Oceans’. |
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