Timescales and Mechanisms of Rapid Redox Change in the Mid-Cretaceous Ocean
Abstract
Understanding the timing, mechanisms and feedbacks capable of driving parts of the ocean from oxic to either anoxic or sulfidic (euxinic) conditions is critical to identify possible scenarios for the future ocean on a warmer Earth. The mid Cretaceous is well-known as a time of extreme greenhouse conditions, and linked to this were a series of major black shale deposition events associated with global perturbations of the carbon cycle (ocean anoxic events; OAEs). The internal structure of these black shale units potentially document a remarkable record of the driving factors and response of the Earth System to rapid climate change, and have therefore become a focal point for extreme climate research. Recent orbital and shorter time-scale stratigraphic records have demonstrated that the Cretaceous ocean was characterized by repeated rapid changes between oxic and anoxic depositional conditions, which were particularly extreme during black shale deposition and were linked to orbital-driven natural processes. Understanding these short-term redox cycles is essential to improve our understanding of how future predictions of rapid swings in climate may effect ocean chemistry and hence ecosystem stability and climate feedback mechanisms. We present millennial and shorter scale geochemical, isotopic, and molecular records from the low-latitude Atlantic that constrain the effects of orbital-driven fluctuations in continental climate on ocean productivity, chemistry and surface water temperature, and deep ocean carbon burial along the continental margin of the evolving Equatorial Atlantic Gateway and NW-Africa. These marine records cover different critical periods of Mid-Cretaceous extreme warmth (OAE's) and provide evidence on regional to global mechanisms determining tropical African climate, hydrological cycling and continental run-off, and at what time scales the shallow and deep ocean responded to these fluctuations in the atmosphere-land system. The data suggest that ocean redox changes occurred on centennial time scales. One key mechanism in perturbing ocean chemistry was increased supply of freshwater and continental nutrients further supporting the concept that hydrologic cycling and associated land-ocean interactions were vital to force large parts of the Cretaceous ocean into an anoxic mode. Coupling of geological records with global climate and coupled atmosphere-and-ocean modelling supports distinguishing the various successions of mechanisms and remote controls that caused rapid change in ocean chemistry.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFMPP32A..05W
- Keywords:
-
- 1630 Impacts of global change (1225);
- 1631 Land/atmosphere interactions (1218;
- 1843;
- 3322);
- 4901 Abrupt/rapid climate change (1605);
- 4912 Biogeochemical cycles;
- processes;
- and modeling (0412;
- 0414;
- 0793;
- 1615