Paleoclimates, ocean depth, and the oxygen isotopic composition of seawater

Kasting, James F., Howard, M. Tazewell, Wallmann, Klaus, Veizer, Jan, Shields, Graham, and Jaffrés, Jasmine (2006) Paleoclimates, ocean depth, and the oxygen isotopic composition of seawater. Earth and Planetary Science Letters, 252 (1). pp. 82-93.

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A recurrent interpretation of ancient climate based on the oxygen isotopic composition of marine carbonates and cherts suggests that Earth's climate was substantially warmer in the distant past and remained so until as recently as 400 Myr ago. This interpretation is difficult to reconcile with the long-term glacial record, with evidence for modest weathering rates during most of Earth's history, with biomarker and fossil evidence for eukaryotes and even vertebrates at times of anomalously low δ18O values, and with the predicted faintness of the young Sun. We argue here, following earlier suggestions, that the low δ18O values in ancient rocks are a consequence of the low δ18O of ancient seawater. A modest increase in ocean depth with time, together with progressive increases in pelagic sedimentation on midocean ridge flanks since about 550 Ma, could account for the variation in seawater isotopic composition. The required change in ocean depth, coupled with thinning of the oceanic crust, is a natural consequence of the decline in heat flow over time. Contrary to previous assertions, such a model is not inconsistent with data from ophiolites. It seems likely that Earth's climate remained largely within Phanerozoic norms throughout the past 3.5 Ga.

Item ID: 3892
Item Type: Article (Research - C1)
ISSN: 1385-013X
Keywords: oxygen isotopes; paleoclimate; ocean depth; Archean; Precambrian
Date Deposited: 27 Nov 2009 00:24
FoR Codes: 04 EARTH SCIENCES > 0403 Geology > 040308 Palaeontology (incl Palynology) @ 33%
04 EARTH SCIENCES > 0404 Geophysics > 040499 Geophysics not elsewhere classified @ 34%
04 EARTH SCIENCES > 0402 Geochemistry > 040203 Isotope Geochemistry @ 33%
SEO Codes: 96 ENVIRONMENT > 9699 Other Environment > 969999 Environment not elsewhere classified @ 100%
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