Indian Ocean isotopic ratios

Marcantonio F, Turekian KK, Higgins S, Anderson RF, Stute M, Schlosser P (1999) The accretion rate of extraterrestrial He based on oceanic °Th flux and the relation to Os isotope variation over the past 200,000 years in an Indian Ocean core. Earth Planet Sci Lett 170 157-168 Marchal O, Francois R, Stocker TF, Joos F (2000) Ocean thermohaline circulation and sedimentary 23ipa/230Th ratio. Paleoceanography 15(6) 625-641... 

Gaye-Haake, B., Lahajnar, N., Emeis, K. C., Unger, D., Pdxen, T., Suthhof, A., Ramaswamy, V., Schulz, H., Paropkari, A. L., Guptha, M. V. S., and Ittekkot, V. (2005). Stable nitrogen isotopic ratios of sinking particles and sediments from the northern Indian Ocean. Mar. Chem. 96, 243-255. 

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.

Earth value (s d = —1.5 to —4.3). They concluded correctly that neodymium in the oceans is mainly derived from the continents, and incorrectly that neodymium-isotope ratios in the oceans are like strontium isotopes in the sense that they are globally well-mixed and display this restricted range. In order to reach this conclusion they ignored a sample from the Indian Ocean having high strontium-isotope ratios and a lower, even more continent-like neodymium-isotope ratio of 8n(J = —8.5. 

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). 

These observations, taken together, indicate that the neodymium-isotope ratios of intermediate and deep seawater are imprinted mainly in the Atlantic and Pacihc oceans. The circum-Antarctic is fed by both and its intermediate neodymium-isotope ratio reflects those of the Atlantic and Pacihc water sources. Indian Ocean intermediate and deep water is fed primarily by the circum-Antarctic and tends to retain a circum-Antarctic neodymium-isotope ratio. 

Passage values (Figure 7). This may indicate a source of neodymium with high isotope ratios in the South Atlantic. However, it is premature to conclude that deep South Atlantic neodymium-isotope ratios overstep the Southern Ocean values, for the following reasons. The maxima for all of the deep South Atlantic waters are between SNd = 7 to —9, more variable than presently available data from the Drake Passage but still quite similar. This range is also similar to circumpolar Fe-Mn sediments (Albare(c)de et al., 1997). Depth profiles from the western Indian Ocean near southern Africa are similar to the South Atlantic and Drake Passage, but like the South... 

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...

Figure 12. Sedimentary and geochemical records from oceans, showing dramatic transient shifts in most records in an interval from just before 8 Ma to 4 Ma (shaded), from Filippelli (1997b). Symbols in all records represent averages of 1 Myr intervals, except for normalized sediment flux curve, which represents 0.5 Myr averages. After interval averaging, all records were adjusted to time scale of Cande and Kent (1992) for consistency, (a) Normalized sediment flux in northern Indian Ocean (Rea 1992). (b) Ge/Si ratio in opaline silica from diatoms (Shemesh et al. 1989). (c) of bulk marine carbonates (Shackleton 1987). Although details of different carbon isotope records differ, general trends revealed in this low-resolution record are robust. PDB is Pee Dee belemnite. (d) Phosphorus accumulation rates in equatorial Pacific (Filippelli and Delaney 1994). Peak in accumulation rates is also observed in other parts of Pacific (Moody et al. 1988) and western Atlantic (Delaney and Anderson 1997). These peaks are linked with increased phosphorus input rates from continental weathering (e.g., Filippelli and Delaney 1994). (e) Sr/ Sr record from marine carbonates (Hodell et al. 1990, 1991). (f) of benthic foraminifera (Miller et al 1987).

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