The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles. Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8 degrees to 10 degrees C) and in bottom water temperatures (4 degrees to 5 degrees C). To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4 degrees to 5 degrees C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.

No abstract

It is only since the advent of the Deep Sea Drilling Project (DSDP) and the wider availability of older Cenozoic deep‐sea core material that large‐scale pre‐Quaternary paleoenvironmental studies using marine microplankton could be attempted. The present study is one of the first attempts at mapping the early Cenozoic (65–24 m.y. B.P.) spatial and temporal distributions of calcareous plankton of the Atlantic Ocean using the DSDP cores and reconstructing the paleoclimatic History of the region from the resultant patterns. The early Cenozoic biogeographic patterns of calcareous nannoplankton (coccoliths and discoasters) and planktonic foraminifera have been delineated on the basis of quantitatively defined assemblages. These patterns show (1) that latitudinal differentiation among the calcareous planktonic groups existed during most of the early Cenozoic, with the exception of the earliest Paleocene (65–64 m.y. B.P.) when planktonic foraminiferal assemblages were essentially homogeneous through all latitudes, showing little provinciality, and when the floral gradients exhibited by nannoplankton were more closely related to near‐shore and open ocean conditions and (2) that there have been major changes in the distributional patterns of both groups: those related to major latitudinal shifts with time and those due to evolution and disappearance of various forms. As is true in the present‐day ocean, the early Cenozoic patterns are considered to be controlled mainly by the latitudinal thermal gradient (climate). Thus the temporal oscillations in the assemblages are interpreted as being caused by major climatic fluctuations. Four marked cooling episodes are recorded within the early Cenozoic Atlantic Ocean: those during the middle Paleocene (60–58 m.y. B.P.), the middle Eocene (46–43 m.y. B.P.), the earliest Oligocene (37–35 m.y. B.P.), and the middle Oligocene (32–28 m.y. B.P.). A particularly marked warming episode occurred during the late Paleocene‐early Eocene (54–51 m.y. B.P.), and a second, less prominent warming trend began in the latest Oligocene (28 m.y. B.P.) and continued into the early Miocene.

No abstract

No abstract