Pacific Ocean isotopic ratios

Fig. 18-1 Benthic foraminiferal oxygen isotope record from 3477 m water depth in the eastern tropical Pacific ocean from Ocean Drilling Program site 677 (Shackleton et al, 1990). ratios are expressed in the S...

Consequently, under normal trade wind conditions there is a secondary maximum of atmospheric CO2 in the neighborhood of the equator in the eastern Tropical Pacific (Figure 8). That this is due to an influx of oceanic CO2 to the atmosphere and not to tropical deforestation is clearly shown by the isotopic ratio of carbon 13 to carbon 12, which increases continuously from high northern latitudes where fossil fuel CO2 which, like the CO2 of the land biota, is low in carbon 13, enters the atmosphere, to about 20 south latitude. 

Wyrtki, K. (1962). The oxygen minima in relation to ocean circulation. Deep-Sea Res. 9, 11—28. Yoshikawa, C., Nakatsuka, T., and Kawahata, H. (2005). Transition of low-salinity water in the Western Pacific Warm Pool recorded in the nitrogen isotopic ratios of settling particles. Geophys. Res. Lett. 32(14), doi 10.1029/2005GL023103. 

Figure 6 Wt.% Na20 versus other major-element oxides, in wt.%, plus molar Ca/(Ca+Na) versus ppm Ti/Zr, for primitive arc lavas (Mg > 60). Many of these plots clearly show distinct compositional fields for primitive basalts, primitive andesites, and boninites. While most of the primitive andesites are from continental arcs, they plot together with western Aleutian primitive andesites, which are from an intra-oceanic arc and have MORB-like Sr, Pb, and Nd isotope ratios. Thus, assimilation of older, continental material is not essential to producing the distinctive composition of primitive andesites. Large filled circles show values for average MORE glasses from the East Pacific Rise, Juan de Fuca Ridge, and Indian Ocean. Other symbols and data as for Figure 1.

The first neodymium-isotopic analyses aimed at characterizing the oceans closely followed the initial development of neodymium isotopes as a chronometer and tracer (Richard et al., 1976 DePaolo and Wasserburg, 1976a O Nions et al., 1977). O Nions et al. (1978) was the first to report neodymium (along with lead and strontium) isotopes in manganese nodules and hydrothermal sediments. They confirmed the distinction between continental and mantle provenances of lead in hydrogenous and hydrothermal manganese sediments, respectively. Consistent with the previous studies, they found that strontium in these deposits is derived from seawater. All of the neodymium-isotope ratios in their samples from the Pacific were similar and lower than the bulk... 

Figure 5 Representative depth profiles of Nd-isotope ratios from the North Atlantic and Pacific oceans and the Drake Passage. The Atlantic and Pacific profiles were chosen to encompass the range of values for deep water in those oceans. Symbols show the data. The diagram illustrates the differences between the oceans and the greater variability of Nd isotopes in shallow versus deep waters (sources Piepgras and Wasserburg, 1982, 1983, 1987 Spivack and Wasserburg, 1988 Piepgras and Jacobsen, 1988 Shimizu et al., 1994).

Neodymium-isotope ratios of intermediate and deep water in the Indian Ocean are intermediate to the Atlantic and Pacific. They generally fall between s d = 1 to —9, and are consistent with domination by northward flowing circumpolar water (Bertram and Elderfield, 1993 Jeandel et al., 1998). A depth profile east of southern Africa (Figure 7) displays the same zig-zag pattern as South Atlantic intermediate and deep water, reflecting advection of NADW into the western Indian Ocean (Bertram and Elderfield, 1993). 

The broadest characteristics can be concisely summarized. Neodymium-isotope ratios in seawater vary systematically with location throughout the oceans, high in the Pacific, low in... 

Figure 11 Nd-isotope ratios versus silicate in Pacific, Indian, and Southern Ocean deep waters. The positive correlation shows that Nd-isotope ratios trace mixing of deep waters from the circum-Antarctic and Pacific. Plotted data are from >2,500 mb si, except two Drake Passage data from 1,900 m and 2,000 m (Nd data sources Piepgras and Wasserburg, 1980, 1982 Piepgras and Jacobsen, 1988 Bertram and Elderfield, 1993 Shimizu et al., 1994 Jeandel et al., 1998). Where salinity or silicate were not available in the publication, they were estimated from Levitus...

Shimizu H., Tachikawa K., Masuda A., and Nozaki Y. (1994) Cerium and neodymium isotope ratios and ree patterns in seawater from the North Pacific Ocean. Geochim. Cosmochim. Acta 58(1), 323-333. 

The oceans contain about 4.5 billion tons of dissolved uranium, almost a thousandfold of the reasonably assured and estimated terrestrial uranium resources in the western world 101). The concentration of uranium in sea water appears to be remarkably constant at about 3.3 pg/liter 120-122). Very recent measurements of uranium concentrations in sea water samples taken in the Arctic and South Pacific Ocean down to depths of more than 5000 m confirm this mean value 123). However, with increasing salinity of sea water a slight increase of uranium concentration is observed 124). The molar concentration of uranium in sea water is nearly 8 orders of magnitude lower than the total concentration of the major ions 125). Marine uranium displays no detactable deviation from the normal terrestrial U-235/U-238 isotope ratio, 03>126). 

The relation between the 5 0 of molecular O2 and the O2 concentration in the Pacific Ocean. Numbers indicate water column depth in meters. As the oxygen concentration is consumed by respiration the stable isotope ratio becomes progressively heavier because of the kinetic fractionation that accompanies this process. Reproduced from Kroopnick and Craig (1976). 

The carbon isotope ratio of DIC in the surface of the Pacific Ocean. The data illustrate how the value has decreased between 1970 and 1993 owing to the addition of fossil fuel CO2 to the atmosphere. Oaces (1993) and Hudson (1970) refer to two different ocean cruises. From Quay et al. (2003). 

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