Warm ocean processes and carbon cycling in the Eocene

Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.533.7Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the bi...

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Bibliographic Details
Published in:Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences physical, and engineering sciences, 2013-10, Vol.371 (2001), p.1-20
Main Authors: John, Eleanor H., Pearson, Paul N., Coxall, Helen K., Birch, Heather, Wade, Bridget S., Foster, Gavin L.
Format: Article
Language:English
Subjects:
Biological Pump
Carbon cycle
carbon cycling
Carbon Cycling Temperature
Carbon isotopes
Climate models
Eocene
Isotopes
Metabolism
Ocean temperature
Oceans
Paleoclimatology
Planktonic Foraminifera
Sea water
Stable Isotopes
temperature
Water temperature
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Summary:Sea surface and subsurface temperatures over large parts of the ocean during the Eocene epoch (55.533.7Ma) exceeded modern values by several degrees, which must have affected a number of oceanic processes. Here, we focus on the effect of elevated water column temperatures on the efficiency of the biological pump, particularly in relation to carbon and nutrient cycling. We use stable isotope values from exceptionally well-preserved planktonic foraminiferal calcite from Tanzania and Mexico to reconstruct vertical carbon isotope gradients in the upper water column, exploiting the fact that individual species lived and calcified at different depths. The oxygen isotope ratios of different species' tests are used to estimate the temperature of calcification, which we converted to absolute depths using Eocene temperature profiles generated by general circulation models. This approach, along with potential pitfalls, is illustrated using data from modern core-top assemblages from the same area. Our results indicate that, during the Early and Middle Eocene, carbon isotope gradients were steeper (and larger) through the upper thermocline than in the modern ocean. This is consistent with a shallower average depth of organic matter remineralization and supports previously proposed hypotheses that invoke high metabolic rates in a warm Eocene ocean, leading to more efficient recycling of organic matter and reduced burial rates of organic carbon.
ISSN:1364-503X
1471-2962
1471-2962
DOI:10.1098/rsta.2013.0099