RESULTS

Minor and trace element concentrations (Ba, Fe, Li, Mn, Sr, and Rb) determined in our laboratory are presented in Table 1.

Dissolved Sr²⁺ concentrations determined on board the JOIDES Resolution by atomic absorption spectrometry (AAS) with a N₂O/C₂H₂ flame were compared with shore-based ICP/OES data for IW samples from Sites 1005 and 1006. Differences between the data sets are generally well below 10% relative, except for a few samples. Because of the remarkable agreement between the two methods, IW samples from Site 1007 were not analyzed for Sr²⁺, and discussions are based on shipboard data. Discussions of other trace pore-water constituents are based on shore-based results.

Significant differences exist, however, between the shipboard and shore-based Li⁺ data (Fig. 3), and their cause is explored in the discussion section.

Shore-based determinations of Fe²⁺ also show considerable deviation from the shipboard data (Fig. 4). Concentrations of Fe²⁺ determined aboard the JOIDES Resolution by flame atomic absorption spectrometry (FAAS) are higher than those determined in our laboratory by ICP/OES. The differences reach up to an order of magnitude for some of the lower concentration samples. The greatest deviations between shipboard and shore-based Fe²⁺ determinations were observed in IW from Site 1007. The most noticeable differences occur in the shallower sections of the hole, where the marked concentration increase with depth observed in the shipboard analyses is not evident in the shore-based data. Additionally, none of the large dissolved Fe²⁺ spikes observed in shipboard data exist in the shore-based data.

Results of shore-based spectrometric determinations of dissolved Mn²⁺, Rb⁺, and Ba²⁺ are also given in Table 1. Dissolved Mn²⁺ data in Table 1 are primarily results from FIA determinations on 0.2-µm-filtered trace metal splits, except below 400 mbsf at Site 1005 and below 340 mbsf at Site 1006. FIA results are presented wherever available. Although reasonable agreement was generally observed between Mn²⁺ data obtained by ICP/OES and FIA when concentrations exceeded 150 nM, FIA results are more reliable because of the greater sensitivity and accuracy of the latter technique, which includes a matrix elimination step. Because trace metal splits were not available below 400 mbsf at Site 1005, however, results of ICP/OES analyses of alkalinity splits are presented. All Mn²⁺ data at Site 1006 are from trace metal splits, however, samples below 340 mbsf were only analyzed by ICP/OES. Thus the data presented in Table 1 and shown in Figure 5 represent a combination of FIA and ICP/OES analyses. Dissolved Rb⁺ was only determined in IW from Site 1106; the depth profile is presented in Figure 6. Dissolved Ba²⁺ profiles (Fig. 7) exhibit large fluctuations within each hole as well as between sites. The lowest Ba²⁺ concentrations occur at Site 1005, whereas the greatest Ba²⁺ enrichments are in IW from Site 1006.