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Project details
| Title: | Constraining external iron inputs and cycling in the southern extension of the East Australian Current |
| Id: | 2466 |
| Investigator(s): | Michael Ellwood
Australian National University - Research School of Earth Sciences [details] April Abbott Macquarie University [details] |
| Description: | Scientific objectives The East Australian Current (EAC) is a major western boundary current that moves southward along the eastern margin of Australia. This current is climatically and biologically important as it exercises control over heat and nutrient distribution. The EAC is nutrient depleted to the north, but as it travels south, it entrains iron from a variety of sources – including riverine, sediment resuspension, eddies, lateral exchange of shelf waters, frontal jets and atmospheric dust inputs thereby elevating the concentration of dissolved iron. When the EAC reaches its southern extent, it breaks up to form eddy-like structures that become incorporated into the Subtropical Front (STF). The STF forms the boundary between warmer nutrient-depleted subtropical water and cool nutrient-rich Southern Ocean water. The waters southwest of Tasmania are nutrient-rich but depleted in dissolved iron, which is a typical characteristic of High Nutrient Low Chlorophyll (HNLC) regions within the Southern Ocean. In springtime, large phytoplankton blooms can be seen associated with a mingling of nutrient-depleted EAC waters with nutrient-rich, but iron depleted Southern Ocean waters in the vicinity of the STF east of Tasmania. Therefore, changes to the EAC caused by climatic shifts will have implications on elemental cycling, production, and local climate. We will assess the relationships between production and nutrient supply in the modern ocean while simultaneously improving our interpretations of past ocean records from the region. The aims of this voyage are to: • Assess the sources of external iron to the southern extension of the EAC • Compare and contrast the biogeochemistry of EAC waters with HNLC waters located southwest of Tasmania; • Determine the role of ‘new’ (externally sourced iron) versus ‘recycled’ iron in regulating springtime productivity across the STF; • Test the sensitivity of neodymium and thorium isotope sedimentary records to local sedimentary processes. |
| Years: | 2018 |
Publications
Dataset
- Latour, P., Strzepek, R., Ellwood, M., & Eggins, S. (2023). Seasonality of phytoplankton growth limitation by iron and manganese in subantarctic waters [Data set]. Institute for Marine and Antarctic Studies (IMAS), University of Tasmania (UTAS). 10.25959/BFF2-RC77
- data sourced from following voyages IN2020_V08 IN2019_V02 IN2018_V04
Journal Article
- Barrett, Pamela M.,Grun, Robin,Ellwood, Michael J. (2021) Tracing iron along the flowpath of East Australian Current using iron stable isotopes. Marine Chemistry 237 pp104039-. 10.1016/j.marchem.2021.104039
- data sourced from following voyages IN2018_V04
- Halfter, Svenja,Cavan, Emma L.,Butterworth, Philip,Swadling, Kerrie M.,Boyd, Philip W. (2022) “Sinking dead”—How zooplankton carcasses contribute to particulate organic carbon flux in the subantarctic Southern Ocean. Limnology and Oceanography 67 pp13-25. 10.1002/lno.11971
- data sourced from following voyages IN2018_V04
Scientific Highlight
- IN2018_V04 Voyage Scientific Highlights Download file
- data sourced from following voyages IN2018_V04
Voyage Summary
- IN2018_V04 Voyage Summary Download file
- data sourced from following voyages IN2018_V04
Metadata.
Use [details] link to view survey details (map, reports, metadata etc) including links to download data.
- RV Investigator Voyage IN2018_V04 Hydrology Data [link]
List of surveys that this project was on.
Use [details] link to view survey details (map, reports, metadata etc) including links to download data.
| Survey | Investigator | Description |
|---|---|---|
| IN2018_V04 [details] |
Michael Ellwood (ANU) | “RV Investigator research voyage in2016_v04, titled “Constraining external iron inputs and cycling in the southern extension of the East Australian Current.” The primary objective of the voyage is to characterise the sources and biogeochemical cycling of iron and associated nutrients and their impact on productivity southwest, southeast and northeast of Tasmania. This will require various deployments at a number of process and transit stations. Mesoscale and sub-mesoscale physics and biogeochemistry TRIAXUS: This will provide high-resolution real-time data acquisition on upper ocean (1-200 m) physics (mixed layer depth) and biology (chlorophyll fluorescence, transmissivity). We will survey each process station by conducting a transect across each station, ‘figure-eight’ type survey if possible for 10-12 hours, and tow the Triaxus between process stations 1, 2 and 3. These datasets will be complemented by those from underway sampling (including nutrient concentrations, biooptics, Fast Repetition Rate Fluorometry (FRRF, a measure of phytoplankton ‘health’), trace metal concentrations using a trace-metal clean tow-fish to sample at 5 m. SADCP/LADCP: Continuous measurements of velocity will be collected along the ships track using the 75 kHz and 150 kHz shipboard ADCPs. A lowered ADCP (LADCP) will collect horizontal velocity measurements at each station from the CTD package. Process and transit station deployments determine iron supply and cycling CTD rosette: Profiles of temperature, salinity, and oxygen through the upper ocean at transit stations and full ocean depth at process stations. Water samples collected with the 36-bottle rosette will be analysed on board for salinity, oxygen, nutrients. LADCP data will also be collected from the CTD deployments. TMR and ISP deployments: An autonomous 12 bottle trace metal-clean rosette (TMR) system and 6 in situ pumps (ISPs) will be used to collect trace element and isotope samples in dissolved and particulate phases. Clean sampling and analytical container laboratories will allow for shipboard processing, experiments and some near real-time analyses of iron at sea. The majority of the analyses will take place ashore after the voyage using sophisticated instrumentation not suited for shipboard use. In situ primary production: Primary production experiments will be conducted at each process station. The experiments will require radiolabeling samples with 55Fe and 14C in the Radiation van and then incubated in the deck-board incubators. Incubations: Some incubations may be conducted at each process station. The experiments will require the changes in light, nutrient and or trace metal conditions. Samples will then be incubated in the deck-board incubators or the ones in the dry lab. Multicorer deployment: Surface sediment cores (0 to 30 cm) will be collected on and off the Tasmanian shelf and at the three process stations. Cores will be evaluated for integrity upon recovery, sectioned inside a nitrogen-filled glove bag, and centrifuged to extract pore fluid for trace metal and rare-earth analysis. Kasten gravity corer: Longer sediment cores (0 to 4 m) will be collected at the three process stations. Cores will be evaluated for integrity upon recovery and subsampled for shore-based analyse. These will complement multicorer deployments. We hope to obtain one core at each of the process stations. Core barrels will 4 m in length. |