Calcium isotope ratios of marine carbonates and sea water

Significant variations in the isotopic composition of marine calcium have occurred over the last 80 million years. These variations reflect deviations in the balance between inputs of calcium to the ocean from weathering and outputs due to carbonate sedimentation, processes that are important in controlling the concentration of carbon dioxide in the atmosphere and, hence, global climate. The calcium isotopic ratio of paleo-seawater is an indicator of past changes in atmospheric carbon dioxide when coupled with determinations of paleo-pH.

Valve concentration of Ethmodiscus sp. and carbon in sediment core GeoB3801-6

Within generally calcareous sediment sequences, layers of variable thickness of the giant diatom Ethmodiscus were found in five cores recovered in the Subtropical South Atlantic between 23° and 33°S from both sides of the Mid-Atlantic Ridge. Two types of oozes occur: (almost) monospecific layers of Ethmodiscus and layers dominated by Ethmodiscus, with several accompanying tropical/subtropical, oligotrophic-water diatoms. The two thickest Ethmodiscus layers occur in GeoB3801-6 around 29°S, and accumulated during late MIS 14 and MIS 12, respectively. Downcore concentrations of Ethmodiscus valves range between 3.4 10 4 and 2.3 10 7 valves g -1. We discuss the ooze formation in the context of migration of frontal systems and changes in the thermohaline circulation. The occurrence of Ethmodiscus oozes in sediments underlying the present-day pelagic, low-nutrient waters is associated with a terminal event of the Mid-Pleistocene Transition at around 530 ka, when the ocean circulation rearranged after a period of reduced NADW production.

(Table 3) Clay mineralogy and calcium carbonate and organic carbon contents of fabric samples of ODP Leg 117

Calcium carbonate and organic carbon concentrations are from measurements made on board the JOIDES Resolution during Leg 117 (Prell, Niitsuma, et al., 1989, doi:10.2973/odp.proc.ir.117.1989). Values are for samples immdiately adjacent to fabric samples, or for Site 723 within 25 cm of the fabric sample interval. Intervals for which carbon analyses were not performed are represented by values in parenthesis which are from the nearest interval of similar lithology. Organic carbon analyses were not performed for samples below 402 mbsf at Site 731. Analyses performed on similar sediments at Sites 722 and 731 indicate the organic carbon concentration is probably <0.20%.