Description: We present the first regional-scale records of biogenic Barium (xsBa) fluxes in the Panama basin of the eastern-equatorial margin of the Pacific Ocean in order to assess xsBa as a paleoproductivity proxy. Measurements of xsBa from thirteen cores that range in water depths from about 700 ¬¬to 3000 m show an increase in 230Th normalized xsBa mass accumulation rates (MARs) with increasing water depth during both Marine Oxygen Isotope Stages (MIS) 1 and 2. The correlation of xsBa MARs with depth are strong despite differences in bulk sediment mass accumulation rates and differing degrees of sediment redistribution. We interpret the increasing xsBa with water depth as likely due to the continued decomposition and remineralization of falling and/or resuspended biogenic particles. xsBa does not seem to be affected by diagenetic sulfate reduction in most of the cores. Calculated estimates of xsBa preservation in the sediment pile are high and fluctuate between 45% - 52% throughout the last 25 kyr. Although xsBa fluxes can be a robust indicator of paleoproductivity, caution is needed if a) there is evidence of sulfate reduction in sediments being analyzed, and b) one is trying to quantify differences in paleoproductivity among sites that are located at different depths in the water column.

Description: Cores, submarine photography and dredges described in this report were taken during the R/V Melville Cruise Vulcan-1 in September 1980 by the School of Oceanography, Oregon State University. This cruise was part of the International Decade of Ocean Exploration (IDOE) Manganese Nodule Program (MANOP). It surveyed MANOP Sites H and M in the Pacific Ocean.

Description: The samples analysed were dredged on Pleiades Leg II during a program of heat flow measurements, bottom photography and coring. They are located on topographic mounds in a band 20 km south of the Galapagos Rift on sediments ranging from 20 to 30 m in thickness. The dredge hauls were sampled to represent the diversity of dredged material either Mn encrusted altered basalt or relatively thick Mn coating deposited directly in contact with sediments. Each sample was analysed by atomic absorption spectrophotometry for major elemnts and instrumental neutron activation analysis for minor elements or rare earths.

Description: Using radiochemical methods, the authors have measured the distribution of uranium, thorium, radium, polonium and protactinium isotopes from the top and bottom sides of the a manganese nodule from Station 20 of the PLEIADES Mn7601 campaign. This "apple" shaped nodule (6.5x3.0 cm) was laying on a bed of siliceous ooze (see illustrations). Successive thin layers of the nodule were carefully scraped from the surface of the measured area with a sharp surgical blade. All samples reduced to powder were air-dried at 110°C for at least two hours before analysis. The relative gross alpha activities from each layer were assayed by Alpha spectrometry using a thick-source counting in a scintillation counter.

Description: We have generated approx. 300 Kyr records of biogenic opal, calcite, and organic carbon (Corg) for three cores in the eastern and central equatorial Pacific Ocean and have compared the records to determine whether common periods of biogenic sedimentation have occurred throughout the region. We find that Corg has been deposited in common pulses throughout the area, while opal has a much more local pattern of variation. Calcite varies regionally, but the record is shaped by superimposed dissolution and productivity processes. The most intense Corg peak occurs at 18 ka and can have greater than 2 times the Holocene Corg content. Other major Corg peaks occur 150 ka and perhaps at 280 ka. We have compared the Corg record in one of the cores, V19-28, to a model deepwater oxygen record developed from d13C data in the nearby V19-30 to test whether the Corg record has been mostly shaped by degradation or by the rain of organic matter from the euphotic zone. We found no coherence between the two records, implying that the Corg record is primarily a measure of productivity. By comparing the opal, calcite, and Corg records in V19-28, a core which is at or above the lysocline, we found that both increased calcite and opal deposition matches high Corg accumulation. We also found, however, that the calcite and opal records were uncorrelated, so that episodes of high opal deposition do not necessarily accumulate calcite rapidly. We hypothesize that at least two different plankton communities have been dominant in the waters above this site, one rich in opal-secreting plankton and one more dominated by calcite producers. The opal-rich plankton community was dominant during the intervals 10-15 ka and 35-60 ka.