ALBERT

Description: The Miocene Climatic Optimum (~17-14.7 Ma) represents one of several major interruptions in the long-term cooling trend of the past 50 million years. To date, the processes driving high-amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic. We present high-resolution benthic foraminiferal and bulk carbonate stable isotope records in an exceptional, continuous, carbonate-rich sedimentary archive (Integrated Ocean Drilling Program Site U1337, eastern equatorial Pacific Ocean), which offer a new view of climate evolution over the onset of the Climatic Optimum. A sharp decline in d18O and d13C at ~16.9 Ma, contemporaneous with a massive increase in carbonate dissolution, demonstrates that abrupt warming was coupled to an intense perturbation of the carbon cycle. The rapid recovery in d13C at ~16.7 Ma, ~200 k.y. after the beginning of the MCO, marks the onset of the first carbon isotope maximum within the long-lasting "Monterey Excursion". These results lend support to the notion that atmospheric pCO2 variations drove profound changes in the global carbon reservoir through the Climatic Optimum, implying a delicate balance between changing CO2 fluxes, rates of silicate weathering and global carbon sequestration. Comparison with a high-resolution d13C record spanning the onset of the Cretaceous Oceanic Anoxic Event 1a (~120 Ma ago) reveals common forcing factors and climatic responses, providing a long-term perspective to understand climate-carbon cycle feedbacks during warmer periods of Earth's climate with markedly different atmospheric CO2 concentrations.

Description: Delta18O and delta13C values for the calcareous dinoflagellate species Orthopithonella? globosa (Fütterer 1984) Lentin and Williams 1985 and Pirumella krasheninnikovii (Bolli 1974) Lentin and Williams 1993 from lates Campanian and earliest Maastrichtian of ODP Hole 690C (Weddell Sea, Antarctic Ocean) have been studied in order to evaluate the species' depth habitat in the water column and their applicability in paleoceanographic studies. The calcareous dinoflagellates show isotopic values comparable to probably shallow-dwelling planktic foraminifera from the same sample in delta18O, but have an offset of about -5 ‰ to -7‰ in delta13C. This suggests that calcareous dinoflagellate oxygen isotopes may provide information for paleoceanographic reconstructions of sea-surface water temperatures, whereas their extremely light carbon isotope values are probably due to photosynthetic processes.

Description: 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.

Description: The distribution of calcareous dinoflagellate cysts in surface sediments from the Mediterranean Sea was quantitatively analysed. The samples contain 11 cyst species and the vegetative coccoid Thoracosphaera heimii. Cyst abundance increases towards the deeper parts of the basins and is generally higher in the eastern Mediterranean Sea. Three major distribution characteristics exist: (1) different assemblages in oceanic and neritic regions, (2) little agreement with the associations of areas studied so far like the Atlantic Ocean, and (3) a unique oceanic assemblage in the eastern Mediterranean Sea. A gradual change in cyst assemblages from the western to the eastern Mediterranean Sea was observed and statistically compared with the main environmental gradients in the upper water column. Temperature, nitrate concentration and possibly salinity appear to be the most important factors controlling cyst production. Three groups containing cysts with similar environmental preferences can be distinguished: (1) an eastern Mediterranean group related to relatively high temperature and salinity but low nitrate concentration, (2) a group of more or less consistently abundant cosmopolitan species tolerating or even preferring relatively low temperature and salinity but high nitrate concentration, and (3) a group containing species that are possibly adapted to neritic environments and have probably been transported from coastal areas into the studied regions. In contrast to other calcareous plankton, calcareous dinoflagellate cysts correlate strongly with the main environmental gradients in the Mediterranean Sea, bearing a high potential for palaeoenvironmental reconstructions.