IN2023_V01 POC and biogenic silica from 2 CTD stations

Full description

The CANYONS voyage on RV Investigator aimed to investigate past and present processes governing the flow pathways, formation and geochemical signatures of Antarctic Bottom Water (AABW) off Cape Darnley, East Antarctica. The proposed survey area was focussed on the Wild and Daly canyons and the adjacent sediment drifts - the Daly and ‘Armand’ drifts. The survey aimed to collect systematic multibeam bathymetry and sub-bottom profiles across the region to support collection of long sediment cores (up to 24 m), Kasten cores and multicores, CTDs (conductivity- temperature-depth instruments) and deep towed camera transects.

This dataset reports analyses of particulate organic carbon and biogenic silica from two CTD casts conducted in the Cape Darnley region. The voyage was terminated after a medical evacuation so only two CTD stations were occupied. These data were generated by IMAS Honour student Veda Surapaneni, and were included in her honours thesis. The dataset also includes hydrochemistry, DIC, Alkalinity and pigment data generated by CSIRO, although these data are published in other national repositories and reproduced here for completeness and convenience only.

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Maintenance and Update Frequency: notPlanned

Statement: Samples were collected at both CTD stations within the Cape Darnley survey area to characterise the biogeochemistry. This sampling also provided sensor comparison data for the two BGC-Argo floats deployed in the area. Briefly, we collected samples for DIC and Alkalinity, which were preserved in HgCl2, samples for nutrients and oxygen from every depth (analysed by MNF Hydrochemistry team on board), and samples for Particulate Organic Carbon (POC) and Pigments. In addition, the IMAS group collected samples for biogenic Si (bSi) analysis. All particulate samples (POC, pigments and bSi) were collected using in-line filtration directly from the Niskin bottles. POC was collected on 13mm pre-combusted QMA filters, pigments on 25mm GFF filters and bSi on 25mm acrylic co-polymer filters (1.2𝜇m pore size). Blank samples for POC were collected at both stations by setting up to sample a deep bottle and briefly turning on the pump. POC and pigment samples were stored at -80°C while bSi samples were stored at -20°C. POC filters were placed into a fume hood overnight to be acidified with 2 molar Hydrochloric Acid (HCL 2M). Once acidified the samples were dried for 48 hours at 60°C. The samples were transferred from IMAS to the University of Tasmania Central Science Laboratory for elemental analysis. All metal tools were muffled at 450°C for 4.5h and a laminar flow hood was used. bSi was determined after leaching samples in 0.1M NaOH at 85C. The Si concentration in the leach was determined spctrophotometrically. See Strickland & Parsons, (1972). Strickland, J., & Parsons, T. (1972). A PRACTICAL HANDBOOK OF SEAWATER ANALYSIS Hydrochemistry analyses were conducted on board by the CSIRO hydrochemistry team. Samples were collected from Niskin bottles sampled at various depths during CTD deployments. The following parameters were analysed: salinity, dissolved oxygen, phosphate, silicate, nitrate, nitrite and ammonium. Quality-controlled data is accessible via the Marlin data portal: https://marlin.csiro.au/geonetwork/srv/eng/catalog.search#/metadata/b472359a-5720-4ff3-8c1f-9a34d79a149a

Notes

Credit
This research was supported by a grant of sea time on RV Investigator from the CSIRO Marine National Facility (https://ror.org/01mae9353), and by the the Australian Research Council Special Research Initiative, Australian Centre for Excellence in Antarctic Science (ACEAS) (Project Number SR200100008).