Depth profiles of pore water constituents from sediment cores collected on the Louisiana Shelf of the Northern Gulf of Mexico during November 2020 on R/V Savannah cruise SAV-20-07

Abstract

This data set reports depth profiles of pore water concentrations of dissolved inorganic carbon (DIC), orthophosphate (PO43-), ammonium (NH4+), total alkalinity (TA), carbon isotopic fractionation of DIC (13C-DIC), dissolved manganese (Mnd), dissolved calcium (Cad), reduced iron (Fe(II)), total dissolved Fe (Fed), and dissolved Fe(III) (Fe(III)d) by the difference of total dissolved Fe and Fe(II). These pore water data were obtained from sediment cores collected at five different stations on the Louisiana Shelf on the Northern Gulf of Mexico during the week of November 3-6, 2020 using an MC-800 multi-corer. These stations extend from the middle of the shelf offshore from Cocodrie, LA to the mouth of the Mississippi River North West Pass. All cores were processed within a few hours after collection. The field sampling was conducted during R/V Savannah cruise SAV-20-07.

The pore waters were first extracted by slicing sediment cores of < 25 centimeters (cm) long and centrifugation of the pore waters under N2 atmosphere to avoid air contamination. Pore waters were then immediately filtered through 0.22-micrometer (um) PSE syringe filters under N2 atmosphere and either analyzed immediately onboard (Fe speciation, orthophosphate, DIC), preserved acidified with hydrochloric acid at 4 degrees Celsius (Cad, Mnd), frozen (ammonium), or preserved at 4 degrees Celsius after addition of HgCl2 (TA) until analysis. In addition, samples for TA and carbon isotopic analyses were preserved in glass bottles, whereas other samples were preserved in polypropylene containers. DIC was analyzed by flow injection analysis (Hall and Aller, 1992), orthophosphate, ammonium, and Fe speciation by spectrophotometry (Murphy and Riley, 1962; Strickland and Parsons, 1972; Stookey, 1970), TA by Gran titration (Gran, 1952), the carbon isotopic signature by isotope ratio mass spectrometry (Wang et al, 2018), and Mnd and Cad by ICP-MS (Magette et al., 2023 In preparation). "nd" in the spreadsheet is provided when samples were not analyzed for these species ("nd" = not determined).

For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/904417