A multiple proxy and model study of Cretaceous upper ocean temperatures and atmospheric CO2 concentrations

摘要: foraminiferal d 18 O and Mg/Ca suggests that the ratio of magnesium to calcium in Turonian-Coniacian ocean may have been lower than Albian-Cenomanian ocean, perhaps coincident with an 87 Sr/ 86 Sr minimum. The carbon isotopic compositions distinct marine algal biomarkers were measured same sediment samples. 13 C values phytane, combined inferred temperatures, used estimate atmospheric dioxide concentrations through this interval. Estimates CO2 range between 600 2400 ppmv. Within uncertainty various proxies, there is only a weak overall correspondence higher (lower) tropical temperatures more (less) CO2. GENESIS climate model underpredicts Atlantic from ODP Leg 207 when we specify approximate estimated biomarker isotopes Possible errors temperature estimates possible deficiencies are discussed. potential for effects substantially methane during Cretaceous anoxic events, derived high fluxes oxygen minimum zone, considered light recent work shows quadratic relation increased flux CH4 concentrations. With 50 ppm CH4, sea surface upper proxy data specified near those using phytane proxy. However, 3500 or still required order reproduce maximum temperatures.