MIDDLE CRETACEOUS REEF COLLAPSE LINKED TO OCEAN HEAT-TRANSPORT

Biologically defined fluctuations in Cretaceous tropical reef boundari es of the Caribbean region record a dynamic rather than stable environ mental history, These fluctuations may be related to major thermal cha nges resulting from ocean heat transport, With simultaneous poleward m ovement of surface and subsurface waters on sea-level highstands, the superheated middle Cretaceous tropics cooled, the reef line contracted , diversity decreased, and reef ecosystems collapsed, leading to mass extinction, Geologic data qualitatively test and support the hypothesi s of enhanced Cretaceous ocean heat transport formulated from general circulation models, In these models, four times the present-day atmosp heric concentration of CO2 and twice the present-day model value of oc ean heat transport cooled the superheated tropics and provided the bes t match to the distribution of inferred middle Cretaceous temperature data, These dynamic changes suggest an important role for large-scale disturbance in the evolution of tropical ecosystems.