GEOCHEMISTRY

We collected interstitial waters from Hole 1222A from one sample from every core for the first six cores at depths ranging from 2.95 to 47.85 mbsf (Table T10; Fig. F13).

Chlorinity, as measured by titration, increases with depth from 553 mM at 2.95 mbsf to 557 mM at 47.85 mbsf (Fig. F13). Sodium concentrations (determined by charge balance) are, on average, 1.6% higher than those measured by ion chromatograph. Sodium concentrations generally remain steady at values similar to that of average seawater. Salinity, as measured by a handheld refractometer, increases with depth from 34.5 at 2.95 mbsf to 35.0 at 47.85 mbsf.

Alkalinity increases with depth from 2.51 mM at 2.95 mbsf to 3.00 mM at 47.85 mbsf. The pH varies between 6.98 and 7.13. Like all other Leg 199 sites, average sulfate concentrations are high (30.0 mM) and ammonium concentrations are low (6 µM), indicating little oxidation of organic matter.

Dissolved silica concentrations increase slightly with depth, from 474 µM at 2.95 mbsf to ~628 µM at 47.85 mbsf. These interstitial water silica values are consistent with dissolution of biogenic silica.

Calcium and magnesium show little evidence of basement alteration. Calcium and magnesium concentrations are relatively constant downcore (9 and 55 mM, respectively), except for one sample at 19.35 mbsf, which has relatively high Ca (14 mM) and low magnesium (50.1 mM) concentrations. Potassium concentrations decrease slightly downsection from ~12 to 11 mM. Lithium concentrations increase slightly downsection, from ~27 to 29 µM.

Strontium concentrations remain at values similar to seawater throughout the record, consistent with the low levels of carbonate in these sediments. Dissolved manganese increases from ~0 µM at 2.95 mbsf to ~40 µM at the level of the calcium maxima and the magnesium minima (19.35 mbsf) and subsequently decreases to negligible values at 47.85 mbsf. Barium is low throughout the profile (1 µM). Levels of dissolved boron are slightly higher than average seawater (416 µM). Boron concentrations increase from ~472 µM at 2.95 mbsf to ~552 µM at 28.85 mbsf and subsequently decrease to ~487 µM at 47.85 mbsf (Table T10).

In summary, the pore water profiles from Site 1220 primarily reflect minor organic matter degradation and the dissolution of biogenic silica. Most of the dissolved chemical constituents show a lack of gradient with depth and values similar to or slightly higher than seawater.

We collected bulk-sediment samples in every other section, adjacent to the interval sampled for physical properties (see "Physical Properties") at Site 1222, resulting in a sampling resolution of approximately three samples per core. The bulk inductively coupled plasma-atomic emission spectroscopy data from Site 1222 is suspect because of excessively high levels of drift during the run. This resulted in very poor precision for most elements (e.g., Ba = 26%, Ca = 34%, Fe = 79%, Mn = 32%, Si = 22%, and Sr = 85%). For this reason, we do not report the data. The poor precision for Site 1222 data probably results from excessive ship motion during sample weighing and analyses (see "Geochemistry" in the "Explanatory Notes" chapter for more discussion).

Calcium carbonate (CaCO₃) (in weight percent) was determined by coulometric methods for two to three samples per core from 2.24 to 64.63 mbsf for Site 1222 (Table T11; Fig. F14). CaCO₃ is low (<1 wt%) in Unit I and is moderate in the nannofossil ooze of Unit II (40-67 wt%). Organic carbon (in weight percent) determined for one sample per core is uniformly low (<0.15 wt%).