Data report: pore water nitrate and silicate concentrations for Expedition 320/321 Pacific Equatorial Age Transect

Abstract

Concentrations of dissolved nitrate and silicate were determined in pore water samples from all eight sites (U1331–U1338) of the Pacific Equatorial Age Transect, Integrated Ocean Drilling Program (IODP) Expedition 320/321. Nitrate measurements were not made shipboard, and they are useful in assessing the extent of suboxic diagenesis evident in these sites. Dissolved silicate concentrations were remeasured in this study because two different analytical techniques were used shipboard during Expeditions 320/321, and comparisons indicated issues with analytical consistency. Nitrate and silicate were measured simultaneously in pore water samples squeezed from whole rounds and obtained by Rhizon sampling using an automated colorimetric technique with flow injection analysis. Profiles of nitrate concentrations at Sites U1331–U1333 show the least variability with depth (~50–80 µM). Sites U1334–U1336 exhibit pronounced depletions (from ~300 to 0 µM at Site U1334, from ~150 to 1 µM at Site U1335, and from ~75 to 10 µM at Site U1336), whereas nitrate concentrations increase with depth at Sites U1337 and U1338 (to 64 and 198 µM, respectively). Silicate concentrations at Site U1331 reach ~1180 µM at ~8 meters below seafloor, whereas profiles at other sites generally increase with depth (from 550 to 1200 µM at Site U1332, from 700 to 1200 µM at Site U1333, from 800 to 1350 µM at Site U1334, from 870 to 1960 µM at Site U1337, and from 730 to 1560 µM at Site U1338). At Sites U1335 and U1336, silicate varies 800–1220 and 760–1100 µM, respectively.