Warm tropical ocean surface and global anoxia during the mid-Cretaceous period

Abstract

The middle of the Cretaceous period (about 120 to 80 Myr ago) was a time of unusually warm polar temperatures, repeated reef-drowning in the tropics and a series of oceanic anoxic events (OAEs) that promoted both the widespread deposition of organic-carbon-rich marine sediments and high biological turnover. The cause of the warm temperatures is unproven but widely attributed to high levels of atmospheric greenhouse gases such as carbon dioxide. In contrast, there is no consensus on the climatic causes and effects of the OAEs, with both high biological productivity and ocean 'stagnation' being invoked as the cause of ocean anoxia. Here we show, using stable isotope records from multiple species of well-preserved foraminifera, that the thermal structure of surface waters in the western tropical Atlantic Ocean underwent pronounced variability about 100 Myr ago, with maximum sea surface temperatures 3-5 degrees C warmer than today. This variability culminated in a collapse of upper-ocean stratification during OAE-1d (the 'Breistroffer' event), a globally significant period of organic-carbon burial that we show to have fundamental, stratigraphically valuable, geochemical similarities to the main OAEs of the Mesozoic era. Our records are consistent with greenhouse forcing being responsible for the warm temperatures, but are inconsistent both with explanations for OAEs based on ocean stagnation, and with the traditional view (reviewed in ref. 12) that past warm periods were more stable than today's climate.

The importance of diazotrophic cyanobacteria as primary producers during Cretaceous Oceanic Anoxic Event 2

“…Around the Cenomanian-Turonian boundary, the sea surface temperature was estimated to be substantially higher than that of the present (e.g., Wilson and Norris, 2001). Even in the high latitudes of both Northern and Southern Hemispheres, it has been estimated to be as high as 20 • C or more (Huber, 1998;Jenkyns et al, 2004).…”

Global patterns of diversification in the history of modern amphibians

“…The end-Permian mass extinction, estimated to be the most profound loss of vertebrate life on record (4-7), has been associated with a massive release of carbon gases in the atmosphere, causing a global greenhouse effect and abrupt climate warming (6,7). Similar environmental perturbations have been postulated for subsequent periods and have been associated with fossil evidence for extinctions and subsequent radiations in several amniote groups (8)(9)(10). However, there is no correlated pattern for amphibian fossils.…”

Depth-habitat reorganization of planktonic foraminifera across the Albian/Cenomanian boundary

“…Traditionally, the strategy for depthecology ranking of planktonic taxa was twofold: (1) comparison with modern morphological counterparts (small, simple, globular, Globigerina-like groups are attributed to the shallow-dwelling assemblage, whereas large, ornamented, flattened, Globorotalia-like groups are attributed to the deep-dwelling assemblage [Hart 1980[Hart , 1999Caron and Homewood 1983;Premoli Silva and Sliter 1999]); and (2) biogeographic distributions (taxa common in epicontinental shelf settings are attributed to the shallow-dwelling assemblage, whereas taxa that dominated in pelagic settings are attributed to the deep-dwelling assemblage [Hart and Bailey 1979;Leckie 1987]). Although these approaches have long been considered appropriate and were generally supported by available stable isotope data, a growing number of exceptions have been documented by recent measurements of glassy foraminifera (Norris and Wilson 1998;Wilson and Norris 2001;Bornemann and Norris 2007;Petrizzo et al 2008). For example, the Albian genus Planomalina, which by its single-keeled morphology would be identified as a thermocline dweller, exhibits isotopic features of an upper-ocean habitat.…”

“…Subsequent data generated from clayhosted foraminifera exhibiting exceptional ''glassy'' preservation (sensu Sexton et al 2006) have yielded significant insights into mid-Cretaceous paleoceanography. The major achievements include reconciliation of the so-called cool tropics paradox (Norris and Wilson 1998;Wilson and Norris 2001), establishment of the Turonian hyperthermal period (Huber et al 2002;Norris et al 2002;Wilson et al 2002;Bice et al 2003; see also Bornemann et al 2008), and recognition of short-term intensification (Erbacher et al 2001) or destabilization (Wilson and Norris 2001;Petrizzo et al 2008) of vertical stratification.…”