Phytoplankton Biogeochemistry Logbooks from the Denman Marine Voyage of the RSV Nuyina, 2025

These data were collected on voyage 3 of the RSV Nuyina in the 2024/2025 season. The voyage was colloquially known as the "Denman Marine Voyage", as it operated in the vicinity of the Denman Glacier.During the Denman Marine Voyage, the aim of the Biology team was to study the parameters controlling phytoplankton growth near the Denman Glacier and within the Shackleton Polynya. Phytoplankton are microscopic single cell organisms playing key roles in the carbon cycle – through photosynthesis, and in supporting marine ecosystems, by being at the base of most oceanic food webs. In the Southern Ocean, phytoplankton is generally limited by iron, a trace metal present in very low concentrations. However, primary productivity tends to increase strongly near shelfs, where iron supply is much larger. Historical satellite recordings have repeatedly shown higher phytoplankton growth in the Shackleton polynya compared to the waters near the Denman Glacier. To study this, we sampled the CTD for multiple biological parameters (photophysiology, community composition, chlorophyll concentrations, particulate organic carbon, biogenic silica, carbon uptake and bacterial production), associated with trace metal measurements from nearby TMR deployments. We also performed bioassay incubations at two ‘process stations’, one near the Denman Glacier and one within the Shackleton polynya, where we incubated natural phytoplankton communities under modified conditions (e.g., different light or metal levels). Additional underway and opportunistic samples were performed when encountering features of interest (e.g., subsurface iceberg meltwater, aerosols).This dataset contains data of extracted chlorophyll-a (Chl-a) concentrations and photophysiology measured through Fast Repetition Rate Fluorometry (FRRF). Further sample analyses will provide data on particulate organic carbon (POC), biogenic silica (BSi), community composition (through flow cytometry, pigments measurements and microscopy for phytoplankton taxonomy), primary productivity (through use of 14C) and bacterial production (through 3H-leucine).