Data Trawler - Project details

This voyage will recover and re-deploy an array of six full-depth current meter and property (temperature, salinity and pressure) moorings from the continental slope to the abyssal waters off Brisbane (27oS). The observing system is designed to capture the mean and time-varying flow of the EAC. In order to resolve interannual and decadal signals we aim to maintain multi-year deployments of the array.

The data from the EAC mooring array and other oceanographic sampling are essential for understanding, at the regional to global scale, the role of boundary current in the climate system, and, at the local scale, simulating cross-shelf flows, upwelling, and frontal eddy formation. These local-scale processes have a fundamental impact on nutrient and phytoplankton concentrations and therefore far-reaching effects on annual fisheries productivity and coastal shark interactions along the eastern seaboard.

We will undertake CTD casts, sampling salinity and 02, and numerous Triaxus and ship ADCP sections across the EAC mooring line and at several locations during the transit from Hobart to the mooring sites. Additionally, we aim to complete two oceanographic surveys: one in the Fraser Island area between 28oS and 26oS; and the other on and over the continental shelf in the vicinity of the North Stradbroke Island National Reference Station. These surveys will include bongo net tows and Triaxus/SADCP sections and will occur in between the mooring operations and at the completion of the mooring operations, as well as opportunistic sampling of jellyfish and salps over the side of the vessel when it is stationary using the extendable “pool scoop”. We aim to sample small scale, ephemeral frontal eddies flowing down from Fraser Island and shelf – continental slope boundary exchanges.  These observations will enable us to characterise the spatial and temporal variability of shelf water and plankton around the Stradbroke Island National Reference Station (NRS) mooring, and their connection to the offshore regions. We will also deploy numerous eXpendable Bathymetric Thermographs (XBTs) during the transit from Hobart north.

We will also aim to perform Triaxus and bongo net tows during the northward transit at various locations, with top priority given to a location off the coast of Newcastle NSW (near 32.5oS) to supplement the IMOS mooring and HF radar installation at that location. We will also deploy a number of floats (core Argo and BCG-Argo) during the voyage.

We will collect salinity and oxygen samples for calibration of the CTD salinity and oxygen sensors. Limited dissolved inorganic carbon samples may be collected if we deploy BGC Argo floats).

The following specific objectives will be completed:

1. Moorings recovery and deployment at appropriate locations;
2. Full depth CTD/rosette stations at each mooring recovery location with only salt and O2 water samples;
3. Pre-deployment CTD casts for calibration of Seabird 37 and 39 mooring instruments to a depth of 2000 m;
4. Triaxus and Ship ADCP sections at various locations during the transit from Hobart to the mooring locations, across the mooring line, at the shelf-slope and Fraser Island survey regions;
5. Bongo net tows along the EAC mooring line, and as part of the shelf-slope and Fraser Island survey areas to study the significance of re-circulation features;
6. Bongo nets, CTD and bio-acoustic samplings at various locations during the transit from Hobart to the mooring sites; and surrounding the Stradbroke NRS site including opportunistic sampling of frontal eddies; and
7. Deploy Surface Velocity Program drifters, XBTs and Argo (core and BGC) floats during the voyage, with supporting CTDs in the case of BGC Argo floats.