Australia: The Land Where Time Began |
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PETM – Rapid,
Sustained Acidification of the Ocean Surface The PETM has been associated with the release of
carbon as methane and/or carbon dioxide in amounts of up to several
thousand petagrams of carbon (PgC) into the ocean-atmosphere system
within about 10,000 years, on the basis of a co-occurrence of a carbon
isotope excursion (CIE), widespread dissolution of deep sea carbonates,
and global warming. This rapid release of carbon should have, in theory,
severely acidified the surface water of the ocean, though there is no
geochemical evidence that has been previously presented. In this paper
Penman et
al. present the
first observational evidence of a lowering of the pH of surface and
thermohaline seawater during the PETM, their study being based on
boron-based proxies for carbonate chemistry in surface waters. A drill
site in the North Pacific Ocean (Ocean Drilling Program Site 1209)
produced planktonic foraminifers that show a decrease of about 0.8‰ at
the onset of the event in the boron isotope composition (δ11B),
as well as a 30-40% reduction in shell B/Ca. Similar trends of δ11B
were found in 2 records of lower resolution from the South Atlantic and
Equatorial Pacific. Penman et
al.
suggest these observations are consistent with signification
acidification on a global scale of the surface of the ocean that lasted
at least 70,000 years which required sustained carbon release. They also
say the anomalies in the boron records are consistent with an initial
drop of surface pH of about 0.3 units, at the upper range of model-based
estimates of acidification.
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Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |