Plateau Ontong-Java

Rapid increases in the interstitial water concentrations of dissolved strontium with increasing burial depth of deep-sea carbonate sediments have been interpreted as evidence of the recrystallization reaction (Baker et al., 1982 Elderfield et al., 1982 Gieskes, 1983). Figure 8.17 shows an example of interstitial-water profiles of dissolved alkaline-earth species from a carbonate nanno-fossil ooze from the Ontong Java Plateau (DSDP site 288 5°58 S, 161°50 E). At this site calcium and magnesium concentrations are linearly correlated, and their gradients are governed by chemical reactions deep in the sediment column. 

Elderfield H., Gieskes J.M., Baker P.A., Oldfield R.K., Hawkesworth C.J. and Miller R. (1982) 87Sr/86Sr and 180/160 ratios, interstitial water chemistry and diagenesis in deep-sea carbonate sediments of the Ontong Java Plateau. Geochim. Cosmochim. Acta 46, 2259-2268. 

The Ontong Java plateau (OJP) in the western Pacific (Figure 1) has been tectonically uplifted and exposed along its south eastern margin, at the Solomon Islands arc, mostly on the Islands of Maliata and Santa Isabel. In contrast to the CCOP, which has numerous exposed sections, these are currently the only known subaerial exposures of the OJP. The rest of our knowledge of the OJP comes from a series of drill holes DSDP Site 289 and OOP Sites 803 and 807 (Mahoney et al. 

Babbs T. L. (1997) Geochemical and petrological investigations of the deeper portions of the Ontong Java Plateau Maliata, Solomon Islands. PhD Thesis, University of Leicester, UK, (unpublished). 

Gladczenko T. P., Coffin M. E., and Eldhohn O. (1997) Crustal structure of the Ontong Java Plateau modeling of new gravity and existing seismic data. J. Geophys. Res.-Solid Earth 102, 22711-22729. 

Klosko E. R., Russo R. M., Okal E. A., and Richardson W. P. (2001) Evidence for a rheologicaUy strong chemical mantle root beneath the Ontong-Java Plateau. Earth Planet. Sci. Lett. 186, 347-361. 

Neal C. R., Mahoney J. J., Kroenke L. W., Duncan R. A., and Petterson M. G. (1997) The Ontong Java Plateau. In Large Igneous Provinces Continental, Oceanic and Planetary Flood Volcanism, American Geophysical Union Monograph 100 (eds. J. J. Mahoney and M. Coffin), pp. 183-216. 

Higgins S. M., Anderson R. F., Marcantonio F., Schlosser P., and Stute M. (2002) Sediment focusing creates 100 ka cycles in Interplanetary Dust accumulation on the Ontong-Java Plateau. Earth Planet. Sci. Lett. 203, 383-397. 

Hales B. and Emerson S. (1996) Calcite dissolution in sediment of the Ontong-Java Plateau in situ measurements of pore water O2 and pH. Global Biogeochem. Cycles 10, 527-541. 

Figure 14 The " C-CaCOs age of the sediment bioturbated layer as a function of water depth on the Ontong-Java Plateau (X) in the western equatorial Pacific (Broecker et al., 1999) and the Sierra Leone Rise (O) in the eastern equatorial Atlantic (DuBois and Prell, 1988). The arrows indicate the depth of the first signs of CaC03 dissolution in the sediments as based on %CaC03 (for the Pacific) and %CaC03 fragments (for the Atlantic).

Broecker W. S., Clark E., McCorkle D. C., Hajdas I., and Bonani G. (1999) Core top C ages as a function of latitude and water depth on the Ontong-Java plateau. Paleoceano-graphy 14, 13-22. 

Herguera J. C., Jasen E., and Berger W. H. (1992) Evidence for a bathayal front at 2,000 m depth in the glacial Pacific, based on a depth transect on Ontong-Java Plateau. Paleoceano-graphy 7, 273-288. 

McCorkle D. C., Martin P. A., Lea D. W., and Klinkhammer G. P. (1995) Evidence of a dissolution effect on benthic foraminiferal shell chemistry delta C-13, Cd/Ca, Ba/Ca, and Sr/Ca results from the Ontong Java Plateau. Paleoceano-graphy 10(4), 699-714. 

Schwarz B., Mangini A., and Segl M. (1996) Geochemistry of a piston core from Ontong Java Plateau (western equatorial Pacific) evidence for sediment redistribution and changes in paleoproductivity. Geol. Rundsch. 85, 536—545. 

Figure 6 Microelectrode profiles of dissolved O2 and ApH obtained by Hales and Emerson (1996) at 2.3 km depth on the Ontong-Java Plateau in the western equatorial Pacific. On the right are model curves showing the pH trend expected if none of the CO2 released during the consumption of the O2 was neutralized by reaction with sediment CaCOs (dashed curve) and a best model fit to the measured ApH trend (solid curve). The latter requires that much of the respiration CO2 reacts with CaCOs before it escapes into the overlying bottom water.

Figure 8 Summary of the ratio of CaCOs dissolved and organic material oxidized for bottom chamber deployments in the northeastern Pacific, Ontong-Java Plateau, Ceara Rise, Cape Verde Plateau, northwestern Atlantic continental rise and California borderland basins (R. A. Jahnke and D. B. Jahnke, 2002). The absence of measurable alkalinity fluxes from high-CaCOs sites bathed in supersaturated bottom water appears to be inconsistent with observations...

Figure 9 The upper panel shows shell weight and CaC03 size fraction results from core top covering a range of water depth on the Ontong-Java Plateau. The lower panel shows shell weight results from Ceara Rise and CaC03...

Also shown is the slope of the shell-weight loss—carbonate ion concentration relationship for various water depths. The 0.7 xmol kg km increase in carbonate ion concentration in the Ontong—Java Plateau deep-water column is taken into account. 

Clear evidence for the compensation for an early Holocene preservation event is seen in shell weight results form a core from 4.04 km depth on the Ontong-Java Plateau in the western equatorial Pacific (see Figure 15). A drop in the weight of P. obliquiloculata shells of 11 p.g between about 7,500 yr ago and the core-top bioturbated zone (average age 4,000 yr) requires a decrease in carbonate ion concentration between 7,500 y ago and today (see Table 1). This Late Holocene... 

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