Stable isotope composition of Neogene planktonic foraminifera from ODP Leg 130 sites

We produced a preliminary record for shallow-dwelling planktonic foraminifer d18O at Site 807 for the late Pleistocene, early Pliocene, and early Miocene. Site 807 d18O values between 4 and 5 Ma average 0.75 per mil more than Holocene values and show an average variation of 0.5 per mil. For the early Pliocene, peak maximum d18O at Site 807 attain values equivalent with the last glacial maximum whereas peak minimum d18O were never less than Holocene d18O. Shallow-dwelling planktonic d18O at Site 807 between 16 and 24 Ma average more than 1.0 per mil more positive than Holocene d18O and exhibit 0.5 per mil average amplitude. Assuming that the global ice budget for the early Pliocene and early Miocene was restricted to Antarctica, it is difficult to attribute the very positive Site 807 d18O for these intervals to ice on Antarctica. Site 807 d18O for these intervals more likely reflect sea-surface temperatures cooler than at present, sea-surface salinity greater than at present, increased dissolution, or some combination of these changes.

(Table 1) Calcium carbonate at DSDP Hole 81-552A

DSDP Hole 552A, cored with the HPC on Hatton Drift, represents an almost complete and undisturbed sediment section spanning the late Neogene and Quaternary. Lithologic, faunal, isotopic, and paleomagnetic analyses indicate that the section represents the most complete deep sea record of climatic evolution hitherto recovered at high latitudes in the northern hemisphere. A glacial record of remarkable resolution for the late Pliocene and Pleistocene is provided by oxygen and carbon isotope ratios in benthic foraminifers. In the upper part of the section, the whole of the standard oxygen isotope record of the past million years is well preserved. The onset of ice-rafting and glacial-interglacial alternations occurs at about 2.4 m.y. ago.

(Table 1) Diatom abundance and preservation in ODP Hole 130-806B samples

We report on diatom abundance and preservation stratigraphy in the uppermost four cores of Ocean Drilling Program Hole 806B, which span the Quaternary period. Changes in diatom abundance and preservation show a rather complicated pattern, with much noise at high frequencies. However, in the cycles corresponding to eccentricity and obliquity variations, the picture is quite clear. Abundance and preservation follow glacial-interglacial cycles, with lowest abundances and poorest preservation observed in sediments that correspond to glacial stages. Seventy taxa compose the diatom assemblage of Hole 806B (from Samples 130-806B-1H-1, 8-9 cm, to -4H-7, 73-74 cm) with Azpeitia nodulifera as the dominant member. This species exhibits significant size variations related to glacial and interglacial stages during the Pleistocene. The distribution of power in the Fourier spectrum of the diatom signal (in the time domain) displays the expected Milankovitch frequencies (at 100,41, and 24-18 k.y.). It also shows concentration at various "odd" frequencies, especially at 62 k.y., suggesting a complicated response of productivity (and silicate chemistry) to climatic forcing.