A detailed 8^*0 and 8"C stratigraphy has been generated from analysis of well-preserved Albian-early Maastrichtian foraminifera from Deep Sea Drilling Project (DSDP) Sites 511 and 327 (Falldand Plateau;-58°S-62°S paleolatitude) in the southern South Atlantic, and Cenomanian and Coniacian-Santonian foraminifera from DSDP Site 258 (Naturaliste Plateau; «»58°S paleolatitude) in the southern Indian Ocean. These results, when combined with previously published Maastrichtian stable isotope data from Ocean Drilling Program (ODP) Site 690 (Weddell Sea, '»65°S paleolatitude), provide new insight into the climatic and oceanographic history of the southern high latitudes during middle-Late Cretaceous time. The planktonic foraminifer S^^O curves reveal a gradual warming of surface waters from the Albian through the Cenomanian followed by extremely warm surface waters from the Turonian through the early Campanian. Long-term cooling of surface waters began in the late early Campanian and continued through the end of the Maastrichtian. The benthic foraminifer 8^*0 record generally parallels changes in the oxygen isotopic curves defined by shallow-dwelling planktonic foraminifera. The vertical oxygen and carbon isotopic gradients were relatively low during the Albian-Cenomanian, high from the Turonian-early Campanian, and then low during the late Campanian and Maastrichtian. Foraminiferal oxygen isotopic data from published sources and this study are averaged for each site, corrected for latitudinal changes in salinity based on modern-day surface-water values, and plotted versus paleolatitude for the late Albian, Coniacian-Santonian, and late Maastrichtian. Differences between low-and highlatitude surface-water paleotemperatures are estimated at "^14 °C during the late Albian and late Maastrichtian, but the Coniacian-Santonian reconstruction reveals only a 0-4 °C latitudinal temperature gradient. Uncertainty regarding Cretaceous salinity gradients and possible diagenetic alteration of 8'*0 values introduce error into our estimates of paleolatitudinal thermal gradients; however, apparent low equator-to-pole temperature differences could indicate much higher poleward heat transport than at present.

Several species of planktonic foraminifera precipitate a final layer of calcite onto the shell surface immediately prior to gamete release at the end of the foraminifera life cycle. Here, we present the results of carbon-13, oxygen-18 and thermal labeling experiments conducted under high (HL) and low light (LL) regimes that vary symbiont photosynthetic activity. Mean experimental group data show that gametogenic (gam) calcite contributes between 4-17% and 14-20% to final shell mass for high and low light experiments respectively. These data indicate that past studies of gam calcite addition have overestimated the amount of gam calcite on foraminifera shells by~30-55%. Calculations indicate that the mass of gam calcite added to the O. universa shell, 4.2 ± 2.0 μg and 4.0 ± 2.4 μg, is constant in the HL and LL groups respectively. We propose that the production of gam calcite may be the result of the discharge of a relatively constant-volume cytoplasmic pool of either Ca 2+ or alkalinity (carbon pool) that increases the calcite saturation state in the microenvironment adjacent to the foraminifera shell just prior to gamete formation and release. Results from these experiments indicate that the geochemistry of thin-walled O. universa from deep sea sediments is composed of N 80% ontogenetic calcite that was precipitated in the primary, near surface habitat of this species. Published by Elsevier B.V.

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