DOI: 10.26008/1912/bco-dmo.959033.1
title: Benthic chamber geochemical data obtained with an in situ benthic lander from the R/V Savannah at sampling stations across the Louisiana shelf and slope in the Northern Gulf of Mexico during four cruise between July 2021 and July 2022

description: This data set reports benthic flux measurements of dissolved inorganic carbon (DIC), orthophosphate (SPO43-), ammonium (NH4+), total alkalinity (TA), carbon isotopic fractionation of DIC (13-C-DIC), dissolved manganese (Mnd), dissolved calcium (Cad), nitrate (NO3-), and excess bromide (Br-) injected in the chamber as chemical tracer. 
 
In summer 2021, benthic flux data were obtained from benthic chamber deployments at eleven different stations on the Louisiana Shelf and slope in the Northern Gulf of Mexico during July 15-27, 2021 using two different benthic landers. These stations span two transects, one from the middle of the shelf offshore from Cocodrie, LA to the mouth of the Mississippi River North West Pass, and another from North West Pass of the Mississippi River mouth to the south, across the slope. A single station (St. 15) was also sampled on the eastern side of the second transect in the transition from the shelf break to the mid-slope. All benthic chamber samples were processed within an hour after collection. 
 
In fall 2021, benthic flux data were obtained from benthic chamber deployments at ten different stations on the Louisiana Shelf and slope in the Northern Gulf of Mexico between October 25 and November 10, 2021 using two different benthic landers. These stations span two transects, one from the middle of the shelf offshore from Cocodrie, LA to the mouth of the Mississippi River South West Pass, and another from South West Pass of the Mississippi River mouth to the south, across the slope. Two stations (St. 15 and St. 12) were also sampled on a second transect from the shelf break to the slope southeast of the Bird’s Foot. 
 
In spring 2022, benthic flux data were obtained from benthic chamber deployments at ten different stations on the Louisiana Shelf and slope in the Northern Gulf of Mexico during April 9-20, 2021 using two different benthic landers. These stations span two transects, one from the middle of the shelf offshore from Cocodrie, LA to the mouth of the Mississippi River South West Pass, and another from South West Pass of the Mississippi River mouth to the south, across the slope. Two stations (St. 15 and St. 12) were also sampled on a second transect from the shelf break to the slope southeast of the Bird’s Foot. 
 
In summer 2022, benthic flux data were obtained from benthic chamber deployments at eleven different stations on the Louisiana Shelf and slope in the Northern Gulf of Mexico in July 9 -23, 2022 using two different benthic landers. These stations span two transects, one from the middle of the shelf offshore from Cocodrie, LA to the mouth of the Mississippi River South West Pass, and another from South West Pass of the Mississippi River mouth to the south, across the slope. Two stations (St. 15 and St. 12) were also sampled on a second transect from the shelf break to the slope southeast of the Bird’s Foot. 
 
Samples were immediately filtered through 0.22-micrometer (µm) PSE syringe filters and either analyzed immediately onboard (SPO43-), preserved acidified with hydrochloric acid at 4 degrees Celsius (Cad, Mnd), frozen (NH4+, NO3-, Br-), or preserved at 4 degrees Celsius after addition of HgCl2 (TA) until analysis.  In addition, samples for DIC, TA, and carbon isotopic analyses were preserved in glass bottles, whereas other samples were preserved in polypropylene containers.  DIC and TA were analyzed by Gran titration (Gran, 1952) using temperature-controlled closed cells (Dickson et al. 2007), orthophosphate and ammonium by spectrophotometry (Murphy and Riley, 1962; Strickland and Parsons, 1972), the carbon isotopic signature by isotope ratio mass spectrometry (Wang et al, 2018), Mnd and Cad by ICP-MS (Magette et al., 2025 In review), and NO3- and Br- by high performance liquid chromatography (HPLC) (Beckler et al., 2014). In summer 2022, benthic chamber and pore water DIC and TA samples were analyzed by cavity ring-down spectrometry (CRDS, Picarro G2131-i) with an automatic CO2 extraction system (Apollo SciTech AS-D1) and open-cell potentiometric titrations, respectively (Ferreira et al., 2025).