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Project details

Title: HEOBI Heard Earth-Ocean-Biosphere Interactions
Id: 2439
Acronym: HEOBI
Investigator(s): Mike Coffin
CSIRO Oceans & Atmosphere - Hobart [details]

Description: HEOBI Heard Earth-Ocean-Biosphere Interactions RV Investigator voyage IN2016_v01. Science Objectives: Iron supply limits oceanic primary production in the Southern Ocean as well as elsewhere in the global ocean. We aim to test the hypothesis that hydrothermal activity driven by active submarine magmatism fertilises surface waters with iron thereby enhancing biological productivity. Heard and McDonald Islands on the Kerguelen Plateau are among the world’s most active hotspot volcanoes, and are type examples sourced from a particular geochemical component in the Earth’s mantle (enriched mantle 1, or EM1). Existing data indicate that fields of submarine volcanoes extend for several hundred kilometres away from the islands. We will produce three-dimensional, high-resolution bathymetric, backscatter, and sub-seafloor maps of the seafloor surrounding the islands in near-real time. From this mapping and data from geotagged seals indicating locations of anomalously warm bottom water, together with deep tow camera imaging and TRIAXUS sensor data, we will identify candidate active submarine volcanoes and hydrothermal systems, and sample these volcanoes and their surrounding shallow sediments. In the water column over and downstream of these active volcanoes/hydrothermal systems, we will measure temperatures and obtain water samples for geochemical and biogeochemical analyses that will indicate the presence or absence of associated hydrothermalism and iron and other elemental enrichment. We will also sample the deep boundary current that impinges on the eastern flank of the Plateau, to investigate the generation of internal waves that enhance mixing of surface and subsurface waters, providing a mechanism to deliver iron enriched waters to the surface downstream of the volcanoes. If hydrothermally derived iron and other micro-nutrients are ascending to surface waters, we will compare our data to contemporaneous shipboard and satellitederived estimates of phytoplankton productivity and biomass to test for positive temporal and spatial correlations. Should it be proven that hydrothermally derived iron exerts controls on the dynamics of plankton blooms, this will be the first demonstration of linkages between dynamic solid Earth processes (magmatism) and major biological processes (oceanic primary production). Plankton blooms, in turn, affect the biogeochemical cycles of carbon, nitrogen, silicon, and sulphur, and ultimately influence the Earth’s climate system. Our results could therefore open significant new avenues of research in the solid Earth-Earth’s biosphere domain, including investigations of both past (e.g., oceanic anoxic events) and future (e.g., high atmospheric CO2) extreme Earth environments. This is an extract from the in2016_v01 Voyage plan.
Years: 2016


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List of surveys that this project was on.

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Survey InvestigatorDescription

M. Coffin (IMAS, UTAS) HEOBI Heard Earth-Ocean-Biosphere Interactions RV Investigator voyage IN2016_v01. Voyage objectives: [1] Seafloor and subseafloor mapping/geophysical characterisation. Continuous mapping will be carried out using the multibeam systems, multi-frequency split-beam echosounders, sub-bottom profiler, gravimeter, and (on long transits between ports and the study area) magnetometer to characterise bathymetric features and identify those most likely to include volcanic or hydrothermal activity. XBT or CTD data will be acquired at standard intervals for sound velocity corrections to the multibeam data. The data will be initially processed at sea to inform site selection for volcanic and hydrothermal sampling. [2] Nature of submarine volcanoes and hydrothermal systems. We will characterise the spatial distribution, morphology, and geology of active submarine volcanoes and hydrothermal systems. [Extract only] [3] Detecting hydrothermal inputs to the ocean, and vertical water movements that deliver them to surface waters. full-depth CTD/LADCP/TMR transects will be performed to capture cross-shore gradients in water. [Extract only] [4] Detecting impacts on surface phytoplankton production. During the underway mapping we will continuously operate sensors to measure biological activity (fluorescence for phytoplankton abundance, fast-repetition-rate fluorescence for phytoplankton photosynthetic competence, transmission for total carbon biomass, and O2/Ar ratio mass spectrometry for net community production). The sensors will be augmented by underway sampling for phytoplankton pigments, particulate organic and inorganic carbon, biogenic silica, heterotrophic bacterial responses, and microscopic phytoplankton identification to characterise community structures, and 15N measurements to identify the extent of nitrate versus ammonium metabolism - a key indicator of ecosystem Fe stimulation capable of additional carbon sequestration. Above and downstream of active hydrothermal systems, we will obtain samples for further analyses ashore. We also intend to carry out deckboard micro-nutrient enrichment incubation experiments to ascertain the biological response of hydrothermal iron to surface phytoplankton communities. Deployment of a bio-optical sensor package after each CTD deployment will provide measurements to link these communities to satellite images. [5] Ocean circulation around Heard Island and across the eastern Indian Ocean sector of the Southern Ocean. The shipboard ADCP and all available underway systems (thermosalinograph, meteorology, and biogeochemical systems) will be run at all times. We will seek contributions of autonomous instruments to deploy on the voyage to provide more detailed sampling of the circulation. We have contacted the Global Surface Drifter Program run by NOAA, and the Australian office of the International Argo Program. The lowered ADCP will be used at every CTD station to measure full water column velocity. New processing methods also allow the detection of internal waves and mixing using a shear-strain parameterisation, even in shallow waters. [Extract only] [6] Microbial response and bacterial processes What is the response of the microbial community to iron and organic carbon availability in different zones of the Southern Ocean, with focus on the possible impact of hydrothermal activity. More specific question: How does iron and carbon limitation affect heterotrophic bacterial respiration and growth efficiency, and its diversity? This text is an extract ONLY from the voyage plan. Please see in2016_v01 plan for full details.
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