Jean-Claude Duplessy

The last interglacial ocean

The final effort of the CLIMAP project was a study of the last interglaciation, a time of minimum ice volume some 122,000 yr ago coincident with the Substage 5e oxygen isotopic minimum. Based on detailed oxygen isotope analyses and biotic census counts in 52 cores across the world ocean, last interglacial sea-surface temperatures (SST) were compared with those today. There are small SST departures in the mid-latitude North Atlantic (warmer) and the Gulf of Mexico (cooler). The eastern boundary currents of the South Atlantic and Pacific oceans are marked by large SST anomalies in individual cores, but their interpretations are precluded by no-analog problems and by discordancies among estimates from different biotic groups. In general, the last interglacial ocean was not significantly different from the modern ocean. The relative sequencing of ice decay versus oceanic warming on the Stage 6/5 oxygen isotopic transition and of ice growth versus oceanic cooling on the Stage 5e/5d transition was also studied. In most of the Southern Hemisphere, the oceanic response marked by the biotic census counts preceded (led) the global ice-volume response marked by the oxygen-isotope signal by several thousand years. The reverse pattern is evident in the North Atlantic Ocean and the Gulf of Mexico, where the oceanic response lagged that of global ice volume by several thousand years. As a result, the very warm temperatures associated with the last interglaciation were regionally diachronous by several thousand years. These regional lead-lag relationships agree with those observed on other transitions and in long-term phase relationships; they cannot be explained simply as artifacts of bioturbational translations of the original signals.

Disappearance of pink-pigmented Globigerinoides ruber at 120, 000 yr BP in the Indian and Pacific Oceans

The planktonic foraminiferal species Globigerinoides ruber with pink-pigmented tests occupied a worldwide warm-water belt during much of the Pleistocene. This variety was exterminated from the Indian and Pacific Oceans at about 120,000 yr BP, based on the oxygen isotope stratigraphy in 11 Indo-Pacific deep-sea cores, but it continued to live on to the present in the North and South Atlantic Ocean and the Mediterranean Sea. The disparate Atlantic and Indo-Pacific records reflect faunal provincialism that has been developing in the two regions since the Pliocene.

Response of global deep-water circulation to Earth's climatic change 135,000-107,000 years ago

The response of deep ocean circulation to major climatic events of the past 135,000 years is inferred using carbon-13 analyses of benthic foraminifera from the major ocean basins. The results demonstrate that the circulation of the world ocean deep water is very sensitive to climate and that it changes drastically during climatic transitions.

Hydrological relationship between the North Atlantic Ocean and the Mediterranean Sea during the past 15‐75 kyr

The Mediterranean Sea hydrology at the time of the Heinrich formation in the North Atlantic Ocean was analyzed by comparing sea surface temperatures (SSTs) and oxygen isotope composition of seawater (δw) changes during the past 75 kyr in two marine cores. These were compared to the palynological variations derived in the Mediterranean Sea core. During the last glacial the two oceanic SST records show similar and synchronous patterns, with several long-term cooling periods, ending by abrupt SST increases. At the time of the Heinrich events, cold SSTs and low salinity prevailed in the Mediterranean Sea. The freshwater budget was similar to the modern one, permitting the presence of a mixed forest on the Mediterranean borderlands. The post-Heinrich periods are marked by a freshwater budget decrease, limiting oak and fir tree growth in the Mediterranean region. Increase of precipitation or reduction of evaporation is observed before the Heinrich episode, and is associated with a well-developed mixed Mediterranean forest.

Oceanic Radiocarbon Between Antarctica and South Africa Along Woce Section 16 at 30°E

Accelerator mass spectrometry (AMS) radiocarbon measurements were made on 120 samples collected between Antarctica and South Africa along 30 degrees E during the WOCE-France CIVA1 campaign in February 1993. Our principal objective was to complement the Southern Oceans sparse existing data set in order to improve the (super 14) C benchmark used for validating ocean carbon-cycle models, which disagree considerably in this region. Measured (super 14) C is consistent with the theta -S characteristics of CIVA1. Antarctic Intermediate Water (AAIW) forming north of the Polar Front (PF) is rich in (super 14) C, whereas surface waters south of the PF are depleted in (super 14) C. A distinct old (super 14) C signal was found for the contribution of the Pacific Deep Water (PDW) to the return flow of Circumpolar Deep Waters (CDW). Comparison to previous measurements shows a (super 14) C decrease in surface waters, consistent with northward displacement of surface waters, replacement by old deep waters upwelled at the Antarctic Divergence, and atmospheric decline in (super 14) C. Conversely, an increase was found in deeper layers, in the AAIW. Large uncertainties, associated with previous methods for separating natural and bomb (super 14) C when in the Southern Ocean south of 45 degrees S, motivated us to develop a new approach that relies on a simple mixing model and on chlorofluorocarbon (CFC) measurements also taken during CIVA1. This approach leads to inventories for CIVA1 that are equal to or higher than those calculated with previous methods. Differences between old and new methods are especially high south of approximately 55 degrees S, where bomb (super 14) C inventories are relatively modest.

correction: The timing of the last deglaciation in North Atlantic climate records

This corrects the article DOI: 35089060

Glacial-to-Interglacial Changes in Ocean Circulation

Only a few years after its discovery by Anderson and Libby (1947), radiocarbon has revolutionized our understanding of the climatic history of the upper Quaternary. Flint and Rubin (1955) demonstrated that the moraines deposited over the northern United States by the last great ice sheets contained organic material with measurable 14C activity. Numerous measurements performed on moraines and glacial sediments from northern America and northern Europe (see a review in Denton and Hughes (1981)) showed that continental ice sheets reached their maximum extension only 18,000 years ago, and retreated slowly to disappear about 6500 years ago.