Stable carbon and oxygen isotope ratios of the calcareous dinoflagellate cyst Pirumella krasheninnikovii from the Campanian/Maastrichtian section of ODP Hole 113-690C in the Weddell Sea (Table 1)

In order to determine the possible usefulness of stable isotope measurements on calcareous dinoflagellate cysts for paleoceanographic and paleoclimatic studies, we have produced oxygen and carbon isotope records of the species Pirumella krasheninnikovii (Bolli, H.M., 1974. Jurassic and Cretaceous Calcisphaerulidae from DSDP Leg 27, eastern Indian Ocean. Initial Reports of the Deep Sea Drilling Project 27, 843-907, doi:10.2973/dsdp.proc.27.139.1974.) for the latest Campanian to earliest Maastrichtian (~73-68 Ma) of highlatitude Ocean Drilling Program Hole 690C in the southern South Atlantic (eastern Weddell Sea). Foraminiferal stable isotope values characterize this time interval as a phase of continuous cooling, superimposed by a short-term, strong cooling event between 71 and 70 Ma that was detected at various sites in the mid to high latitudes. This event is interpreted to reflect short-term surfacewater cooling, leading to changes in the mode and direction of deep-water formation and possibly the growth of continental ice sheets. Our delta18O values of calcareous cysts verify this event as well as the general cooling of surface waters during the latest Campanian and early Maastrichtian. Prior to this cooling event, between ~72 and 71 Ma, a negative excursion in accompanying delta13C records of planktic and benthic foraminifera was observed. This negative excursion and the subsequent positive one were proposed to reflect sea-level fluctuations, changes in productivity, and/or changes in the ratio of organic to inorganic carbon input to the ocean. The delta13C values of calcareous cysts show the positive excursion between 71 and 70 Ma, but don't show the expected negative excursion before. In addition, they yield extremely light carbon isotope values that probably resulted from photosynthetic processes. As the stable oxygen isotope data of the calcareous dinoflagellate species P. krasheninnikovii show isotopic shifts comparable to planktic foraminifera from the same locality and from various other sites in the Pacific and South Atlantic oceans, we suggest that calcareous cyst oxygen isotopes can provide information for paleoceanographic reconstructions of sea-surface water temperatures and paleoceanographic changes. However, the application of carbon isotope data from cysts of P. krasheninnikovii appears to be questionable, and investigations of different species are needed to further evaluate the reconstruction potential based on stable isotopes and to assess species-specific vital effects.