(Table 1) 10 Beryllium and CaCO3 at DSDP Holes 86-576B, 86-576, and 86-578

Extension of the 10Be geochronology for deep-sea sediments beyond the limit of late Pliocene age found in published works has been attempted. The results obtained on sediments from Deep Sea Drilling Project (DSDP) Sites 576 and 578 of Leg 86 suggest the feasibility of dating sediments as old as 12 to 15 m.y. At both sites, there have been large changes in sedimentation rate, with the Pleistocene sediments accumulating several times faster than those of the Pliocene, which in turn were deposited several times more rapidly than the late Miocene sediments. The Pleistocene-Pliocene section is considerably thicker in Hole 578 than in Hole 576B: the respective depths for the 7 m.y. time boundary in the two holes are about 125 and about 25 m. These 10Be-based age estimates are in agreement with the paleomagnetic stratigraphies established for the two sites. The suggested enhancement in the oceanic deposition of 10Be before 7 to 9 m.y. ago, as noticed in manganese crusts, has found tentative support from the present sedimentary records. A preliminary search for 10Be production variation during a geomagnetic field reversal has been conducted. In Hole 578, an enhanced 10Be concentration is found in a sample close to the Brunhes/Matuyama reversal boundary. More detailed and systematic measurements are required to confirm this observation, which bears on the detailed behavior of the geomagnetic field during the reversal.

Paleomagnetic record of Site 177-1089

We report geomagnetic directional paleosecular variation, relative paleointensity proxies and oxygen isotope data from the upper 88 m composite depth (mcd) at South Atlantic Ocean Drilling Program (ODP) Site 1089 (40°56.2?S, 9°53.64?E, 4620 m water depth). The age model is provided by high-resolution oxygen isotope stratigraphy, augmented by radiocarbon dates from the upper 8 mcd of nearby piston core RC11-83. Mean sedimentation rates at Site 1089 are in the range of 15 to 20 cm/kyr. Two intervals during the Brunhes Chron, at ?29.6 mcd (?190 ka) and at ?48 mcd (?335 ka), have component magnetization directions with positive (reverse polarity) inclination; however, the excursional directions are heavily overprinted by the postexcursional field. Magnetite is the dominant carrier of magnetic remanence, and occurs in the pseudosingle-domain (PSD) grain size. An additional higher-coercivity magnetic carrier, characterized by low unblocking temperatures (<350°C), is assumed to be authigenic pyrrhotite. A decrease in magnetization intensity down core is mirrored by a reduction in pore water sulfate, indicating diagenetic reduction of magnetite. Despite down-core changes in magnetic mineralogy, normalized intensity records from Site 1089 are comparable with high-resolution paleointensity records from the North Atlantic (e.g., ODP Sites 983 and 984). Sediment properties and sedimentation patterns within the Cape (Site 1089) and Iceland (Sites 983 and 984) Basins are distinctly different at both millennial and orbital timescales and therefore preclude lithologic variability from being the source of this correlation. Variations in normalized intensity from Site 1089 therefore appear to reflect changes in global-scale geomagnetic field intensity.

Eolian mass-accumulation rates and grain size at DSDP Sites 86-576 and 86-578

The mass-accumulation rate and grain size of the total eolian component of North Pacific pelagic clays at Deep Sea Drilling Project Sites 576 and 578 have been used to evaluate changes in eolian sedimentation and the intensity of atmospheric circulation that have occurred during the past 70 m.y. Eolian deposition, an indicator of source area aridity, was low in the Paleocene, Eocene, and Oligocene, apparently reflecting the humid environments of that time as well as the lack of glacial erosion products. A general increase in eoiian accumulation in the Miocene apparently reflects the relative increase in global aridity during the latter part of the Cenozoic. A dramatic increase in eolian accumulation rates in the Pliocene reflects the increased aridity and availability of glacial erosion products associated with Northern Hemisphere glaciation 2.5 m.y. ago. Eolian grain size, an indicator of wind intensity, suggests that Late Cretaceous wind strength was comparable to present-day wind strength. A sharp decrease in eolian grain size across the Paleocene/Eocene boundary is not readily interpreted, but may indicate a significant reduction in the intensity of atmospheric circulation at that time. Fine eolian grain size and low accumulation rates in the Eocene and early Oligocene are in agreement with low early Tertiary thermal gradients and less vigorous atmospheric circulation. Large increases in grain size during the Oligocene, mid-to-late Miocene, and Pliocene appear to be a response to steepening thermal gradients resulting from increasing polar isolation.

Pacific Neogene carbonate accumulation rates

I have compiled CaCO3 mass accumulation rates (MARs) for the period 0-25 Ma for 144 Deep Sea Drilling Project and Ocean Drilling Program drill sites in the Pacific in order to investigate the history of CaCO3 burial in the world's largest ocean basin. This is the first synthesis of data since the beginning of the Ocean Drilling Program. Sedimentation rates, CaCO3 contents, and bulk density were estimated for 0.5 Myr time intervals from 0 to 14 Ma and for 1 Myr time intervals from 14 to 25 Ma using mostly data from Initial Reports volumes. There is surprisingly little coherence between CaCO3 MAR time series from different Pacific regions, although regional patterns exist. A transition from high to low CaCO3 MAR from 23-20 Ma is the only event common to the entire Pacific Ocean. This event is found worldwide. The most likely cause of lowered pelagic carbonate burial is a rising sea-level trend in the early Miocene. The central and eastern equatorial Pacific is the only region with adequate drill site coverage to study carbonate compensation depth (CCD) changes in detail for the entire Neogene. The latitude-dependent decrease in CaCO3 production away from the equator is an important defining factor of the regional CCD, which shallows away from the equatorial region. Examination of latitudinal transects across the equatorial region is a useful way to separate the effects of changes in carbonate production ('productivity') from changes in bottom water chemistry ('dissolution') upon carbonate burial.