Search

Intraspecific coiling variations of the planktonic foraminifer Neogloboquadrina pachyderma (Ehrenberg) form an important micropalaeontological technique for the palaeoclimatic interpretation of late Cenozoic mid-latitude marine sediments. In all the modern oceans, this species preferentially coils dextrally in subtropical to temperate latitudes and sinistrally in subpolar to polar latitudes1,2. Plankton3–5 and surface sediment studies6–20 of the North Pacific clearly associate sinistral populations with subarctic water masses and dextral populations with temperate subtropical regions. Here we show that down-core ratios of sinistral to dextral coiling, when correlated with oxygen isotopes, indicate major late Quaternary southward advances of the subarctic boundary (polar front) and the Oyashio Current during oxygen isotope stages 2,4 and 6.

Faunal census data on zooplankton microfossils in surface sediment samples are treated by Q-mode factor analysis and are used to describe the global distributions of five faunal provinces: the polar, subpolar, transitional-subtropical, and eastern and western tropical provinces. The same assemblages (factors) are used to describe and to map equivalent faunal provinces in the ice-age ocean (18 000 B.P.; CLIMAP 1976 1981). Although based on individual studies in each ocean basin, the compilation of these data on different faunal groups allows a clear comparison of water mass distributions in the modern and ice-age oceans. This comparison shows an expansion of the polar province, an equatorward shift and compression of the subpolar and transitional-subtropical provinces, and an extension of the subpolar province equatorward in eastern boundary currents for the ice-age interval. The total area of dominance for the tropical and subpolar assemblages remained approximately constant. Comparison of census data between surface sediment and 18 000 B.P. samples shows that the greatest faunal change occurred near the subpolar regions (where water mass boundaries shifted equatorward) and in areas of expanded upwelling and divergence (primarily eastern boundary currents and eastern equatorial areas). In contrast, little faunal change occurred either in the polar regions or within the central subtropical gyres.

A 120 m thick section of the Cozy Dell Formation (middle Eocene), southem California, consists of a graylaminated mudstone and a tanungraded mudstone; sandstone beds are associated with the laminated mudstone. Sedimentary structures, stratification sequences, foraminiferal distributions, and composition indicate that the ungraded mudstone is an upper slope hemipelagic deposit, while the laminated mudstone is an overbank deposit associated with shallow channels or gullies in which the sandstone beds were deposited. This depositional setting may be analogous to that of the modern Mississippi River delta front.

International audience; 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.

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.

Neoacarinina blowi n. gen., n. sp., Globorotalia crozetensis n. sp. may be useful datum for Pleistocene/Holocene boundary