The effect of hydrothermal vents on surface photosynthetic production rates above the Brothers and Rumble III volcanoes
Hydrothermal vent plumes emit dissolved micronutrients such as iron, methane sulfur, and hydrogen. These are known to provide energy and carbon sources for chemoautotrophic production for benthic organisms and other extremophiles in the plume’s immediate vicinity. However, it is unknown how the emitted micronutrients affect the local photic-zone photosynthetic production. Nutrients emitted from the plume, specifically iron and silicate, may promote phytoplankton production in two methods: 1) direct fertilization of the euphotic zone with nutrients from the vents by vertically circulating currents, and 2) chemoautotrophy, nutrient fixation and regeneration by organisms near the vents which then circulate to and fertilize the surface waters. This study will take quantitative measurements of total community photosynthesis rates using onboard incubations and changes in dissolved oxygen concentration. Samples will be taken from the euphotic zone above hydrothermally active Brothers and Rumble III volcanoes on the Southern Kermadec Arc (SKA) and a background station offsite. Phytoplankton nutrient limitation will be evaluated from the three sample locations via onboard enrichment–incubation experiments with iron, nitrate and silicate. Possible changes in phytoplankton community structure will be quantified using net tows and microscope identification. Micronutrient concentrations emitted from the plume will be analyzed, and plume water will be used in incubation experiments to evaluate effects of plume water on local phytoplankton production. This study will provide additional insight into the extent of vent ecosystems that can be used to refine models of oceanic and atmospheric carbon dioxide.