Cenozoic climate change and the δ18Obf record: temperature vs ice volume, and comparison with other proxies
Abstract
The benthic foraminiferal δ18O record has served as a primary indicator of Cenozoic climate change for four decades. As a climate indicator, the δ18Obf record is encumbered by ambiguity as to whether specific variations result from changes in deep ocean temperature or continental ice volume, with a smaller potential contribution from deep ocean pH and hydrothermal cycling effects on seawater δ18O. Numerous other proxies have been developed that supplement δ18Obf records in investigations of climate change over Cenozoic timescales: Alkenone (UK') and tetraether (TEX86) indices for sea surface temperature; elemental ratios (Mg/Ca, Li/Ca, B/Ca) for marine temperatures and carbonate saturation; isotopic ratios (δ11B, δ13C) for ocean carbon chemistry, pH, and by extension atmospheric pCO2; sea level as a proxy for continental ice volume. Proxies applicable in terrestrial environments are also available. Cenozoic records for these other proxies are not as well constrained and less easily interpretable compared with the δ18Obf record. We have recently used a strategy of integrating δ18Obf, Mg/Cabf, and sea level records to place constraints on the separate variation in temperature and ice volume reflected in the δ18Obf record. This analysis highlights uncertainty regarding the degree of covariation between temperature and ice volume during the Cenozoic: overall temperature has decreased and ice volume increased since 50 Ma, but the contribution of each to the δ18Obf record at specific times is uncertain. Long-term trends in cooling and ice sheet growth since the early Eocene are at least partially decoupled: the bulk of the cooling occurred gradually in the middle-late Eocene and late Miocene-Pliocene while ice sheet growth occurred rapidly in the earliest Oligocene, middle Miocene, and Plio-Pleistocene. Here, we further investigate the constraints placed on temperature and ice volume variations using climate proxy records and a simple model for variability in atmospheric pCO2. We emphasize the importance of a conceptual separation of long-timescale (>2 Myr) and short-timescale (<2 Myr) climate variability.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP22A..02C
- Keywords:
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- 0473 BIOGEOSCIENCES / Paleoclimatology and paleoceanography;
- 1635 GLOBAL CHANGE / Oceans;
- 4900 PALEOCEANOGRAPHY;
- 4924 PALEOCEANOGRAPHY / Geochemical tracers