The dataset was collected on the research voyage (IN2018_V05 on RV Investigator) and from satellite observations. The dataset includes in-situ data and satellite data collected at the Polar Front (PF) south of Tasmania in a region where the Antarctic Circumpolar Current (ACC) has a permanent meander upstream of the Macquarie Ridge. This study characterises the upwelling of Circumpolar Deep Water (CDW) in a standing meander of the ACC in the PF south of Tasmania and investigates the submesoscale processes associated with upwelling.
Maintenance and Update Frequency: notPlanned
Statement: 1. Satellite data
Sea surface height (SSH) gridded data were obtained from the DUACS (Data unification and Altimeter combination system) products over the Southern Ocean region [146° E, 158° E], [52.5° S, 57.5° S] during the Southern Hemisphere spring from October 16 to November 16, 2018. The satellite dataset has daily SSH data, in a 0.25° × 0.25° spatial grid, encompassing the 16° longitude × 5° latitude region. The absolute dynamic topography (adt) that is the SSH above geoid was used to identify the core of the PF meander. The adt is obtained from the calculation: adt=sla+mdt, where sla is sea level anomaly and mdt is mean dynamic topography.
2.In situ observations: voyage data
a. Triaxus data
The Triaxus instrument was towed behind the ship and equipped with the Seabird SBE911 CTD 25 sensor to record pressures, conductivity and temperature data. Other sensors were also installed to collect other hydrologic data like dissolved oxygen. Pressure, conductivity and temperature data were calculated using calibration factors provided by Sea-Bird and calibrations provided by CSIRO. The data were processed by automated QC to remove spikes and out-of-range values. Triaxus profiles were limited to 300 m depth with a vertical resolution of 1 dbar and an approximate 0.9-1.5 km lateral spacing between vertical Triaxus casts (averaged every 5 minutes). The oxygen data was directly measured from the dissolved oxygen sensors. The salinity was the absolute salinity. The temperature was converted to the conservative temperature at each depth. The potential density was derived from absolute salinity and conservative temperature. The Gibbs-SeaWater (GSW) Oceanographic Toolbox in MATLAB was applied for evaluating these thermodynamic properties (absolute salinity, conservative temperature, potential density and in situ density) of seawater.
b. Shipboard ADCP data
Shipboard Acoustic Doppler Current Profiler (SADCP) mounted on the ship hull was used to determine absolute currents in 8-m-depth bins and approximately at a 1 km lateral scale (averaged every 5 minutes) in the upper ocean in coordination with accurate heading and navigation data. Narrowband data collection was used both for the RDI Ocean Surveyor 150 kHz ADCP and the RDI Ocean Surveyor 75 kHz ADCP. The drop keel was at 6 m below the waterline during the voyage. In this study, the 150 kHz RDI ADCP measured velocities from 18 m to 500 m depth, and the data output was averaged every 5 minutes. The horizontal velocity has two components, with u being defined as the West-East (zonal) velocity component and v being defined as the North-South (meridional) velocity component. There was a spatial offset between the SADCP on the ship and the Triaxus that is towed behind the ship, which was adjusted by shifting the timestep of the SADCP back by 5 minutes.
c. CTD data
The voyage obtained 77 full-depth CTD casts with full hydrochemistry along 9 cross-front transects. The CTD was fitted with various sensors to collect the temperature, conductivity, pressure, dissolved oxygen and fluorescence data in a high vertical resolution. The CTD frame held 36 Niskin bottles that allowed water samples to be collected from different depths during the CTD deployments. The various parameters in the water samples, including salinity, dissolved oxygen, phosphate, silicate, nitrate plus nitrite and ammonium, were processed and analysed to calibrate the data directly on the ship.
IMAS Honours Student Program 2019-2020