Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise
Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise
Glassy Turonian foraminifera preserved in clay-rich sediments from the western tropical Atlantic yield the warmest equivalent δ18O sea-surface temperatures (SSTs) yet reported for the entire Cretaceous-Cenozoic. We estimate Turonian SSTs that were at least as warm as (conservative mean ~30 °C) to significantly warmer (warm mean ~33 °C) than those in the region today. However, if independent evidence for high middle Cretaceous pCO2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea-surface pH, our conservative and warm SST estimates would be even higher (32 and 36 °C, respectively). Our new tropical SSTs help reconcile geologic data with the predictions of general circulation models that incorporate high Cretaceous pCO2 and lend support to the hypothesis of a Cretaceous greenhouse. Our data also strengthen the case for a Turonian age for the Cretaceous thermal maximum and highlight a 20–40 m.y. mismatch between peak Cretaceous-Cenozoic global warmth and peak inferred tectonic CO2 production. We infer that this mismatch is either an artifact of a hidden Turonian pulse in global ocean-crust cycling or real evidence of the influence of some other factor on atmospheric CO2 and/or SSTs. A hidden pulse in crust cycling would explain the timing of peak Cretaceous-Cenozoic sea level (also Turonian), but other factors are needed to explain high-frequency (~10–100 k.y.) instability in middle Cretaceous SSTs reported elsewhere.
cretaceous, carbon dioxide partial pressure, planktonic foraminifera, sea-surface temperatures, tropics, turonian, surface temperature, foraminifera, climactic changes, geology
607-610
Wilson, P.A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Norris, R.D.
81ac4a17-2a84-4c7c-9c02-c9f14bb2695e
Cooper, M.J.
54f7bff0-1f8c-4835-8358-71eef8529e7a
2002
Wilson, P.A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Norris, R.D.
81ac4a17-2a84-4c7c-9c02-c9f14bb2695e
Cooper, M.J.
54f7bff0-1f8c-4835-8358-71eef8529e7a
Wilson, P.A., Norris, R.D. and Cooper, M.J.
(2002)
Testing the Cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the Turonian tropics on Demerara Rise.
Geology, 30 (7), .
(doi:10.1130/0091-7613(2002)030<0607:TTCGHU>2.0.CO;2).
Abstract
Glassy Turonian foraminifera preserved in clay-rich sediments from the western tropical Atlantic yield the warmest equivalent δ18O sea-surface temperatures (SSTs) yet reported for the entire Cretaceous-Cenozoic. We estimate Turonian SSTs that were at least as warm as (conservative mean ~30 °C) to significantly warmer (warm mean ~33 °C) than those in the region today. However, if independent evidence for high middle Cretaceous pCO2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea-surface pH, our conservative and warm SST estimates would be even higher (32 and 36 °C, respectively). Our new tropical SSTs help reconcile geologic data with the predictions of general circulation models that incorporate high Cretaceous pCO2 and lend support to the hypothesis of a Cretaceous greenhouse. Our data also strengthen the case for a Turonian age for the Cretaceous thermal maximum and highlight a 20–40 m.y. mismatch between peak Cretaceous-Cenozoic global warmth and peak inferred tectonic CO2 production. We infer that this mismatch is either an artifact of a hidden Turonian pulse in global ocean-crust cycling or real evidence of the influence of some other factor on atmospheric CO2 and/or SSTs. A hidden pulse in crust cycling would explain the timing of peak Cretaceous-Cenozoic sea level (also Turonian), but other factors are needed to explain high-frequency (~10–100 k.y.) instability in middle Cretaceous SSTs reported elsewhere.
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Published date: 2002
Keywords:
cretaceous, carbon dioxide partial pressure, planktonic foraminifera, sea-surface temperatures, tropics, turonian, surface temperature, foraminifera, climactic changes, geology
Identifiers
Local EPrints ID: 6149
URI: http://eprints.soton.ac.uk/id/eprint/6149
ISSN: 0091-7613
PURE UUID: e5f965fb-68a4-4d36-b4ce-c54f540860ab
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Date deposited: 30 Jun 2004
Last modified: 16 Mar 2024 03:20
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Author:
R.D. Norris
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