The deep ocean during the last interglacial period.

Oxygen isotope analysis of benthic foraminifera in deep sea cores from the Atlantic and Southern Oceans shows that during the last interglacial period, North Atlantic Deep Water (NADW) was 0.4 degrees +/- 0.2 degrees C warmer than today, whereas Antarctic Bottom Water temperatures were unchanged. Model simulations show that this distribution of deep water temperatures can be explained as a response of the ocean to forcing by high-latitude insolation. The warming of NADW was transferred to the Circumpolar Deep Water, providing additional heat around Antarctica, which may have been responsible for partial melting of the West Antarctic Ice Sheet.

The timing of the last deglaciation in North Atlantic climate records.

To determine the mechanisms governing the last deglaciation and the sequence of events that lead to deglaciation, it is important to obtain a temporal framework that applies to both continental and marine climate records. Radiocarbon dating has been widely used to derive calendar dates for marine sediments, but it rests on the assumption that the 'apparent age' of surface water (the age of surface water relative to the atmosphere) has remained constant over time. Here we present new evidence for variation in the apparent age of surface water (or reservoir age) in the North Atlantic ocean north of 40 degrees N over the past 20,000 years. In two cores we found apparent surface-water ages to be larger than those of today by 1,230 +/- 600 and 1,940 +/- 750 years at the end of the Heinrich 1 surge event (15,000 years BP) and by 820 +/- 430 to 1,010 +/- 340 years at the end of the Younger Dryas cold episode. During the warm Bølling-Allerød period, between these two periods of large reservoir ages, apparent surface-water ages were comparable to present values. Our results allow us to reconcile the chronologies from ice cores and the North Atlantic marine records over the entire deglaciation period. Moreover, the data imply that marine carbon dates from the North Atlantic north of 40 degrees N will need to be corrected for these highly variable effects.

Variability of the earth's climate

climate of our planet has remained within a range compatible with life since several billion year. Theories of star evolution suggest that the amount of heat emitted be the sun increased be about 10

since 4 10º years, so that several factors or the climatic system, such as the chemical composition of the atmosphere, must have changed in orderto maintain the air temperature within a range permitting the occurrence of abundant liquid water at the earth's surface (AU)

The last climatic cycle and past ocean changes

During the last 150.000 years, the earth's climate alternated from warm conditions to cold conditions. The peak of the last glaciation occurred about 18.000 years ago and a deglaciation led to the present climatic pattern. In order to reconstruct past climatic and past oceanographic conditions, geologists must define proxy - data, which describe various climatic parameters in the past and dermine the time scaleof the records of these proxy - data. The age of the sediment is determined by absolute dating either by the carbon - 14 method (for the last 40.000 years) or by uranium series disequilibrium (for the last 300.000 years). A good stratigraphy for marine sediments can also be deribed from the oxygen isotope record of planktonic and benthic faraminifera, which partly reflects the variations of the volume of ice stored over the high - latitude continents. (AU)

Subtropical convergence fluctuations and quaternary climates in the middle latitudes of the Indian ocean.

Oxygen isotopic and microfaunal analyses and shell size variations of Orbulina universa in two Indian Ocean cores indicate that the position of the Subtropical Convergence has fluctuated between a northern limit north of 31 degrees S during glacial stages and its present, maximum southern limit. The northward displacement of the Subtropical Convergence to a position off Durban, South Africa, reflects the general weakness of the Agulhas Current during glacial stages and parts of interglacial stages, representing about 65 percent of the past 540,000 years.

Weyl's Theory of Glaciation Supported by Isotopic Study of Norwegian Core K 11.

Oxygen-18 analyses of pelagic and benthic foraminifera from core K 11 indicate that during the last glaciation Norwegian Sea bottom waters were warmer than in modern times and had the same physical parameters (temperature, oxygen isotope ratio, and salinity) as the North Atlantic deep water. This result indicates that the glacial Norwegian Sea was not a sink for dense surface water, as it is now, and that during glacial times North Atlantic deep water invaded the deep Norwegian basin.

Differential isotopic fractionation in benthic foraminifera and paleotemperatures reassessed.

Different species of benthic Foraminifera taken at the same level in an Atlantic core yielded different oxygen isotopic values. It was therefore impossible to deduce paleotemperature values. In addition, pelagic and benthic species showed the same isotopic variations, an indication that pelagic and benthic species reflect only the variation of oxygen-18 composition of the ocean.