![]() |
||||||||||||||
Australia: The Land Where Time Began |
||||||||||||||
Glacial-Interglacial Bottom Water Oxygen Content
Changes on the Portuguese Margin Atmospheric CO2 concentrations were lower than at
present during the
last and penultimate glacial maxima, possibly partly because of the
increased storage of respired carbon in the deep oceans (Sigman & Boyle,
2000). It is possible to calculate the amount of respired carbon in a
water mass from its oxygen content through apparent oxygen utilisation,
and the oxygen content can in turn be calculated from the carbon isotope
gradient within the sediment column (McCorkle & Emerson, 1988). In the
study reported in this paper Hoogakker et
al. analysed the shells of
benthic foraminifera that are present at the surface of the sediment and
the oxic/anoxic interface on the Portuguese margin which they used to
reconstruct the carbon isotope gradient and therefore the oxygenation of
bottom water over the past 150,000 years. Their results suggested that
the oxygen concentrations of the bottom water are 45 and 65 μmol/kg
lower during the last and penultimate glacial maxima respectively than
they are at present. Hoogakker et
al. calculated that the concentration of remineralised organic
carbon was at least twice as high during the glacial maxima than they
are at the present. They attributed these changes to ventilation that
was decreased linked to a reorganisation of circulation of the ocean
(McManus et
al., 2004) and an
increased strength of the biological pump (Kohfeld et al., 2005). If the
pool of respired carbon remained of similar size throughout the entire
glacial deep
Atlantic basin, this sink could have accounted for 15-20 %
of the glacial
Pco2
drawdown during the last and penultimate glacial maxima. Hoogakker, B. A. A., H. Elderfield, G. Schmiedl, I.
N. McCave and R. E. M. Rickaby (2015). "Glacial-interglacial
changes in bottom-water oxygen content on the Portuguese margin."
Nature Geosci
8(1): 40-43.
|
|
|||||||||||||
|
||||||||||||||
Author: M.H.Monroe Email: admin@austhrutime.com Sources & Further reading |