Dataset: Water column data from samples collected on R/V Hugh Sharp cruise HRS1803GL in the Chesapeake Bay during July-August 2018

In situ pump profiler cast refers to profiling with a pump profiler for O₂ and H₂S using solid state gold-amalgam electrodes for voltammetry (Luther et al, 2008; Analytical Instrument Systems DLK-60). Water was pumped aboard to make measurements on discrete samples for Mn and Fe speciation as well. See Hudson et al (2019).

Samples for Mn and Fe parameters were filtered through 0.20 um filters. Whatman track etched polycarbonate filters were soaked in 1M HCl for 1 week before rinsing and storage in DI.

C parameters performed by Dr. Wei-Jun Cai's group for:
TA - Open cell Gran titration with semi-automatic AS-ALK2 Apollo Scitech titrator;
pH - glass electrode, NBS buffers;
DIC - infrared CO₂ analyzer (AS-C3, Apollo Scitech).

Uses Dickson CRM for calibration. DIC/TA samples were filtered (0.45um) and fixed with 100 ul of saturated mercury bichloride. Uses the methods of Gran (1952) and Huang, et al. (2012).

Dissolved Mn parameters:
The porphyrin spectrophotometric method of Madison et al (2011, 2013) measures dissolved Mn(II), Mn(III) bound to weaker ligands and total Mn. Method includes calibration and intercomparison of totals with other instrumentation (ICP, AA). Detection limit is 0.050 micromolar. Detection limit (DL) is 50 micromolar with a 1 cm path length cell.

Modification of Madison et al for Mn(III) bound to strong ligands by adding a reducing agent to a separate subsample with the porphyrin to obtain total Mn (Oldham 2015, 2017; Thibault de Chanvalon and Luther, 2019). Mn(III) bound to strong ligand complexes is determined by difference. Typically, triplicate measurements performed. Detection limit can be extended to 3.0 nanomolar with a 1m path length cell.

Modification of Madison et al. for water column samples by adding higher Cd(II) so that cadmium-chloride complex formation would not inhibit cadmium-porphyrin formation and thus incorporation of Mn into the porphyrin by Cd replacement (Thibault de Chanvalon and Luther, 2019, this work). This modification enhanced the kinetics of the reaction progress for both Mn(II) and weak Mn(III)-L complexes.

MnOₓ on unfiltered samples
The leucoberbelein blue method is that of Jones et al (2019, this work) in 1 cm cells, but can be modified for longer path length cells.

H₂S
O₂ and H₂S by the voltammetry method of Luther et al (2008) and Hudson et al (2019) using a flow cell. O₂ also from CTD sensor.

Fe parameters
The method of Stookey (1972) is used to determine dissolved Fe(II) and on addition if hydroxylamine Fe total. Fe(III) is determined by difference. Modified and calibrated by many including Lewis et al (2007). Typically, triplicate measurements performed.

Nitrite
Nitrite as determined by the method of Grasshoff (1983).

Dissolved Mn speciation references:
Madison et al. (2011)
Madison et al. (2013)
Oldham et al. (2015)
Oldham et al. (2017) - Here, we modified the method of Madison et al. (2011) for water column samples to achieve a detection limit of 3.0 nM (3 times the standard deviation of a blank) by using a 100-cm liquid waveguide capillary cell and the addition of a heating step as well as a strong reducing agent for Mn. Speciation [Mn³⁺ = MnT – Mn²⁺]. As weak Mn(III)-L complexes could not be measured in our previous work (Oldham et al, 2015; paper above), this method was used throughout this cruise.
Thibault de Chanvalon & Luther (2019) - Here, we modified the method of Madison et al. (2011) for water column samples by adding higher Cd(II) so that cadmium-chloride complex formation would not inhibit cadmium-porphyrin formation and thus incorporation of Mn into the porphyrin by Cd replacement. This modification enhanced the kinetics of the reaction progress for both Mn(II) and weak Mn(III)-L complexes.

Dissolved Fe speciation references:
Stookey (1970)
Lewis et al. (2007)

H2S (in situ voltammetry)– water column:
Luther et al. (2008)

H2S (UV-Vis spectrophotometry) – sedimentary porewater samples:
Luther et al. (2011)

MnOₓ​ solids:
Jones et al. (2019)

pH and inorganic carbon parameters:
Gran (1952)
Huang et al. (2012)

Nitrite:
Determination of nitrite, nitrate, oxygen, thiosulphate in Grasshoff et al. (1983)