Accumulation rates of bulk sediment and total organic carbon for Ontong Java Plateau sediments

Organic geochemical investigations were performed on sediments of Leg 130 to reconstruct the depositional environment of the Ontong Java Plateau. The Miocene to Quaternary sediments collected during the drilling campaign are characterized by extremely low organic carbon contents. As indicated by C/N ratios and Rock-Eval data, most of the organic matter is probably of marine origin. Based on mass-accumulation rates of organic carbon, the paleoproductivity for the Miocene-Pliocene and the late Pliocene-Pleistocene time intervals as well as the modern surface-water production were estimated. The productivity values of the surface sediments (25-59 gC/m2/yr) reflect the various influences of the equatorial upwelling cell on the different sites. The accumulation rates of organic carbon are generally low; however, they show a distinct increase at 8 Ma and a decrease at 2 Ma.

Paleoproductivity reconstruction for the eastern equatorial Pacific

Productivity at six core locations in the eastern equatorial Pacific (EEP) was reconstructed with a benthic foraminiferal transfer function. The core records show strong regionality, especially where affected by Peru margin upwelling of deeper Equatorial Undercurrent Water (EUC) (originally coming from the subantarctic). This "Peru margin" record differs from that seen along the equator where divergence leads to shallow upwelling, and it is generally inverse to that seen in cores outside the areas of equatorial upwelling. Principal components analysis shows that the main productivity pattern correlates well to the global oxygen isotope record and has lowest values during isotope stages 2 and 4. In addition to this, equatorial cores show a higher frequency pattern of variation which becomes much more pronounced during MIS 3 and 2. The reconstructions based on benthic foraminifera were tested against those from nonaccumulation rate based inorganic chemical proxies of export production. These were found to correlate well in the region influenced by Peru upwelling, and also to share common features for sites along the equator. All the nonaccumulation rate based paleotracers are consistent with one another and differ from accumulation rate derived proxies. The differences between the two classes of paleotracers may result from uncertainties in calculating actual biogenic fluxes since 230Th-normalized results conform more to those we obtained. Analysis of planktonic carbon isotope values for the EEP, and their comparison to the record of the Pacific subantarctic, indicates that the subantarctic contribution to the EUC was reduced during MIS 3 and 2.

CaCO3, density, sedimentation and accumulation rates at DSDP Hole 68-503B

Pelagic sediments from DSDP Hole 5O3B contain, in their carbonate abundance data, a clear record of glacial-interglacial cycles. The eolian component of those sediments was analyzed over the past four carbonate cycles, and the mass accumulation rate (MAR) and grain size of the eolian component was determined. Eolian MARs range from 24 to 169 mg/cm**2/10**3y. and commonly are higher by a factor of three to five during times of glacial retreat. Reduced contribution during periods of glaciation most likely reflects glacial-age humidity in the American source. Grain-size values (phi50) range from 8.25 to a minimum of 8.79phi-a variation in grain mass by a factor of 3.1. Larger grains reflect more vigorous atmospheric circulation, but sizes do not covary with the carbonate or eolian accumulation curves. These data suggest that the intensity of atmospheric circulation in the tropics may reflect the 42,000 y.-tilt cycle rather than the 100,000 y.-cycle of glacial advance.