The results from shipboard flux fusions and those from shore-based flux fusions show strong correlations (r2 = ~0.95) for all elements, except for Mn, Ba, Sr, and Cr (Fig. F3). Most major elements reflect a systemic offset, whereby shipboard data are greater than shore-based data. This offset can be attributed to the fact that LOI was performed on the carbonate-rich shipboard samples and that the major elements were normalized with regard to Ca, such that the CaO concentrations were consistent with the amount required to balance the inorganic carbon (as CaCO3) determined by coulometry (Shipboard Scientific Party, 2003). Chromium is the only element with a significant difference between the analyses and is explained by the difficulty of precisely and accurately measuring trace elements in carbonates in the shipboard environment. Shore-based results also reflect Cr concentrations that are typical of biogenic-rich sediment, suggesting that the shore-based acid digestions are more accurate than shipboard results.
Microwave-assisted acid digestion results are listed in Table T5 and shipboard results are reported in the Leg 206 Initial Reports volume (Wilson, Teagle, Acton, et al., 2003). The depth profiles of shipboard flux fusions and high resolution shore-based microwave acid digestions exhibit strong correlation (r2 > 0.95) and display similar downhole trends for all elements, except for Mn and Cr (Table T6; Fig. F4). Systematic offsets however, as indicated by the regression slopes, highlight the differences between shipboard and shore-based analytical procedures and the corrections applied to shipboard data, in comparison to the more accurate shore-based data, as discussed above. The shore-based microwave acid digestions also reflect the higher resolution sampling. Nonetheless, both data sets exhibit the same lithological and chemical characteristics with depth.
More importantly, elemental ratios, such as Ba/Ti, Al/Ti, and Fe/Al, that were used in the Initial Reports (Wilson, Teagle, Acton, et al., 2003) for paleoceanographic interpretations are consistent with the shore-based acid digestions (Fig. F5). This consistency suggests that the shipboard first-order paleoceanographic interpretations are robust and that the acid digestion protocol successfully provides high-resolution chemical data.