Isotopic composition of foraminifera from sediments of DSDP Legs 3, 6-9, 17

Oxygen isotopic compositions of the tests of planktonic foraminifera from several Deep Sea Drilling Project sites provide a general picture of low-latitude marine temperatures from Maastrichtian time to the present. Bottom temperatures determined from the isotopic compositions of benthonic foraminifera are interpreted as being indicative of high-latitude surface temperatures. Prior to the beginning of middle Miocene time, high- and low-latitude temperatures changed in parallel fashion. Following an apparently small and short-lived drop in temperature near the Tertiary-Cretaceous boundary, temperatures remained warm and relatively constant through Paleocene and early and middle Eocene time; bottom temperatures then were on the order of 12°C. A sharp temperature drop in late Eocene time was followed by a more gradual lowering of temperature, culminating in a late Oligocene high-latitude temperature minimum of about 4°C. A temperature rise through early Miocene time was followed in middle Miocene time by a sudden divergence of high- and low-latitude temperatures: high-latitude temperatures dropped dramatically, perhaps corresponding to the onset of major glaciation in Antarctica, but low-latitude temperatures remained constant or perhaps increased. This uncoupling of high-and low-latitude temperatures is postulated to be related to the establishment of a circum-Antarctic circulation similar to that of today. A further drop in high-latitude temperatures in late Pliocene time probably signaled the onset of a major increase in polar glaciation, including extensive sea-ice formation. Early Miocene, small-amplitude (1 per mil) sympathetic fluctuations in isotopic compositions of planktonic and benthonic foraminifera have been identified. These have a period of several hundred thousand years. Superimposed upon these are much more rapid and smaller fluctuations (0.2 to 0.5 per mil) with a period of about 80000 to 90000 yr. This is similar to the period observed for Pleistocene isotopic temperature fluctuations. In low latitudes, much smaller vertical temperature gradients seem to have existed during Maastrichtian and Paleogene time than exist at present. The absence of a sharply defined thermocline during early Tertiary time is also suggested.

Maastrichtian planktic foraminifera of the South Atlantic Ocean

Stratigraphic, faunal and isotopic analyses of the Maastrichtian at DSDP sites 525A and 21 in the South Atlantic reveal a planktic foraminiferal fauna characterized by two major events, an early late Maastrichtian diversification and end-Maastrichtian mass extinction. Both events are accompanied by major changes in climate and productivity. The diversification event which occurred in two steps between 70.5 and 69.1 Ma increased species richness by a total of 43% and coincided with the onset of major cooling in surface and bottom waters and increased surface productivity. The onset of the terminal decline in Maastrichtian species richness began at 67.5 Ma and the first significant decline in surface productivity occurred at 66.2 Ma, coincident maximum cooling to 13°C in surface waters and the reduction of the surface-to-deep temperature gradient to less than 5°C. Major climatic and moderate productivity changes mark the mass extinction and the last 500 kyr of the Maastrichtian. Between 200 and 400 kyr before the K-T boundary surface and deep waters warmed rapidly by 3-4°C and cooled again during the last 100 kyr of the Maastrichtian. Surface productivity decreased only moderately across the K-T boundary. Species richness began to decline during the late Maastrichtian cooling and by K-T boundary time, the mass extinction had claimed 66% of the species. Viewed within the context of Maastrichtian climate and productivity changes, the K-T mass extinction could have resulted from extreme environmental stress even without the addition of an extraterrestrial impact.

Stable oxygen and carbon isotope ratios and paleotemperature reconstructions from Inoceramus in Cretaceous sediments of DSDP Sites

Inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths. A survey of all Cretaceous sediments from Deep Sea Drilling Project legs 1-69 and 75 revealed over 500 Inoceramus specimens at twenty sites. Of these, 47 well-preserved Late Cretaceous specimens from the South Atlantic, Pacific and Indian Oceans were analyzed for oxygen and carbon isotopes. The specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep-sea habitat. Paleotemperatures ranging from 5 to 16°C show that Late Cretaceous oceans were significantly warmer than the present oceans. The data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics.

Grain-size distributions and bulk chemistry of sediment core MD00-2361

The terrigenous fraction of sediments from a deep-sea sediment core recovered from the northwestern Western Australian continental slope offshore North West Cape, SE Indian Ocean, reveals a history of Western Australian climate throughout the last 550 ka. End-member modelling of a data set of grain-size distributions (n = 438) of the terrigenous sediment fraction allows to interpret the record in terms of aeolian and fluvial sediment deposition, both related to palaeo-environmental conditions in the North West Cape area. The data set can be best described by two aeolian end members and one fluvial one. Changes in the ratio of the two aeolian end members over the fluvial one are interpreted as aridity variations in northwestern Western Australia. These grain-size data are compared with bulk geochemical data obtained by XRF scans of the core. Log-ratios of the elements Zr/Fe and Ti/Ca, which indicate a terrigenous origin, corroborate the grain-size data. We postulate that the mid- to late Quaternary near North West Cape climate was relatively arid during the glacial and relatively humid during the interglacial stages, owing to meridional shifts in the atmospheric circulation system. Opposite to published palaeo-environmental records from the same latitude (20°S) offshore Chile and offshore Namibia, the Australian aridity record does not show the typical southern hemisphere climate variability of humid glacials and dry interglacials, which we interpret to be the result of the relatively large land mass of the Australian continent, which emphasises a strong monsoonal climatic system.