DOI: 10.26008/1912/bco-dmo.914901.1
title: CTD-associated variables, bottle salinity measurements, oxygen titrations, nutrient analyses, biogeochemical/biological variables, and DIC chemistry variables from R/V Thomas G. Thompson cruise TN376 from January to March 2020

description: These data are part of the NSF project &quot;Collaborative Research: Biogeochemical and Physical Conditioning of Sub-Antarctic Mode Water in the Southern Ocean.&quot; Specifically, these are the discrete bottle data from cruise TN376 aboard R/V Thomas G. Thompson, which sailed from Cape Town, South Africa (22 January 2020) to the Southern Ocean and returned to Mauritius (3 March 2020). The purpose of the project was to define the processes that condition SubAntarctic Mode Water formed at the SubAntarctic Front in the Southern Ocean. The cruise track took us southeast from Cape Town for our first shakedown station at 38°35'S x 024°E, a station which was ultimately canceled due to heavy weather conditions. Two days out of Cape Town, the coupler between the ship's number three main engine and generator broke. This meant the ship only had one main engine, with an associated generator, plus two smaller engines/generators for all power needs. With the loss in redundancy, this meant we had to cut our cruise plans short, in order to stay within several hundred miles of Durban, SA, such that the ship could go in for repair once a replacement coupler could be found. This also meant we had to abandon the planned meridional transect that was to be done on this trip, since the travel to the shipyard, the repair, and return to the next station took over a week of sampling out of the cruise, and our proximity to Durban (and long distance from the Crozet Islands) meant we couldn't possibly accomplish the meridional transect and make it to Mauritius within the UNOLS ship schedule. We added the meridional transect to the second cruise of this project, RR2004. 

Bottle data were collected from CTD casts with tripped Niskin bottles on the CTD Rosette. Trace-metal-clean casts were performed using Niskin-X bottles suspended on Kevlar line and a trace-metal-clean block. The data reported herein fall into several categories: A) CTD-associated variables [temperature, salinity, density, dissolved oxygen and oxygen solubility, potential temperature, chlorophyll fluorescence, beam transmissivity, light], B) bottle salinity measurements using a salinometer, C) oxygen titrations and nutrient analyses performed aboard ship, biogeochemical/biological variables, and D) DIC chemistry variables. Regarding the specific data, we first report CTD variables (conductivity, salinity, temperature, potential temperature, density, dissolved oxygen, sound velocity, pressure, depth, conductivity, SeaBird-probe-derived oxygen concentrations, chlorophyll fluorescence, beam transmittance (660nm; %), backscattering, CTD PAR, and  surface PAR reference). Next, results from bottle samples for salinity, lab oxygen titration, and nutrient concentrations (nitrate, phosphate, silicate, nitrite, and ammonium). The following biogeochemical and biological results are presented (analyzed post-cruise): particulate organic carbon concentration (POC), particulate organic nitrogen (PON), particulate inorganic carbon (PIC), biogenic silicate (BSi), concentration of detached coccoliths (given as birefringent singlets, doublets, triplets or quadruplets, when viewed in a compound microscope with polarization optics), total coccolith concentration (the sum of singlets, doublets, triplets or quadruplets), concentration of birefringent plated coccolithophore cells, coccospheres or coccolith aggregates, planar area subtended by detached coccoliths or plated cells, concentration of extracted chlorophyll, phaeopigment and their sum (done aboard ship). There are a suite of variables from FlowCAM measurements (done aboard ship), mostly done on particles &gt;5 micrometers (um) diameter: Particle size distribution function (PSDF) slope, standard error of that PSDF slope, Y-intercept of the PSDF, R^2 of the PDF slope, F statistic of PSDF slope, total cell concentration per mL, concentrations (in cells per mL) of small 0-4um diameter cells, 4-12um round cells, 4-12um diameter ovoid cells, dinoflagellates, ciliates, diatoms silicoflagellates, other unidentified cells, followed by percent of total cell concentrations, and carbon biomass (using equations of Menden Deuer and Lessard) for the same cell categories. Carbon fixation rates were performed aboard the ship and samples were analyzed aboard ship. The data are presented here for: ratio of calcification/photosynthesis, photosynthesis, calcification, standard deviation of photosynthesis and calcification measurements, chlorophyll concentration within incubation bottles, chlorophyll normalized photosynthesis and calcification. Corrected salinity (based on bottle salinity), corrected SeaBird oxygen values based on lab oxygen titrations, dissolved inorganic carbon (DIC) concentrations, and total alkalinity. Finally, photophysiological measurements were made aboard ship and the photophysiological coefficients are presented for (a) average bulk PAM (pulse amplitude modulation) fluorimetry results and (b) average PAM microscopy results made on individual coccolithophores, dinoflagellates, and diatoms.