#### Brief description

Data for the project -Investigating the source of the high nitrate, low oxygen layer in the Leeuwin Current- is including in the file. The data include CTD data, ADCP data and Triaxus data from RV Investigator (Voyage IN2019_V03). Also the Sea Surface Height satellite data and CSIRO Atlas of Regional Seas (CARS) data are included as the supporting data.
The MATLAB code including the code that calculate the rotated velocity and the transport of the EGC current in upper 300m including volume transport, salinity transport, heat transport and oxygen transport.
The nitrate data from Triaxus is uncompleted and will be upload later with the code for calculating the nitrate transport.

#### Lineage

Maintenance and Update Frequency: asNeeded
Statement: In this study, data was collected onboard the RV Investigator (Voyage IN2019_V03) between May 13 and June 14, 2019. This voyage explored the physical, biogeochemical and ecological processes in the Southeast Indian Ocean. Its objectives including quantifying physical, chemical and biological properties along the 110Β°E line and investigating the sources of nitrogen to the region.
A Conductivity-Temperature-Depth (CTD) profiler was deployed wat each station along 110Β°E line. Stations were 1.5 degrees apart in longitude and profiled from the surface to the seafloor. A lowered Acoustic Doppler Current Profiler (LADCP) was also attached to the CTD rosette to measure current speed and direction at each depth.
Triaxus data was collected along three transects through the EGC. Triaxus is an instrument that is towed behind a vessel to provide high resolution data of water properties. In this study it profiled from the surface to a depth of 300m.
Data from the voyage can be download from CSIRO website.(https://www.cmar.csiro.au/data/trawler/survey_details.cfm?survey=IN2019_V03).(https://www.marlin.csiro.au/geonetwork/srv/eng/search#!3bbb16fc-ecbe-4ad7-9f5d- 74e5e052714c).
CSIRO Atlas of Regional Seas (CARS) data can also download from website (http://www.marine.csiro.au/atlas/).
The sea surface height data is accessed from the Australian Ocean Data Network (AODN). In this study, we use the sea surface height data that has been delayed mode processed. It contains gridded (adjusted) sea level anomaly (GSLA), gridded sea level (GSL) and surface geostrophic velocity (eastward and northward velocity components) for the Australasian region. (https://portal.aodn.org.au/search).
Velocity data from the ADCP was transformed into a new coordinate system whose two axes are perpendicular to the Triaxus track (rotated x-axis) and along the Triaxus track (rotated y-axis) using the code comp2speed and speed2comp which need to calculate rotation of the velocity first.
Rotation was calculated using the equation: ππ = ο±tanβ1 (βπππ) β 180/π
Volume transport, temperature transport, salinity transport, oxygen transport as well as nitrate transport of EGC were calculated in each grid cell. The summed value in each grid cell is called the sum transport.
The volume transport in each grid-cell within the EGC is given by the product of the area of the cell times the cross-track velocity. Each cell is then summed over cells where the EGC is present (across-track velocity > 0.02ms-1). This gives the total transport of the EGC in each of the three transects.
Volume transport Q (t) is given by Equation(2): πΈ(π) = β βπ βπ π(π, π, π) (2)
Where, οx is the width of the grid cells (500m); οz is the height of the grid cells (1m) and v is cross-track velocity. The unit of Q(t) is m3/s which is equal to 1 x 10 -6 Sverdrups (Sv).
To calculate heat transport, we use Equation (3): πΈππππ(π)=βππͺπ(π»βπ»πππ)βπβππ (3)
Where, ο² is the density of sea water (which we treat as a constant of 1025 kg m-3). Cp is the specific heat capacity of seawater (the ratio of potential enthalpy to Conservative Temperature (J/ (kg K))). T is the conservative temperature and Tref is a reference temperature. In this study, the reference temperature is assumed to be 0 Β°C so that the heat transport is the total heat transport through the current. The unit of the heat transport is in Watts.
The salt transport, relative to a specified reference salinity Sref, is given by: ππ πππ‘(π‘)=βπ(πβππππ)βπ₯ ββπ§β π£ (4)
In equation (4), S is the absolute salinity (g kg-1) and the reference salinity Sref is 0. Then the absolute salinity transport can be estimated using equation (4) in units of kg s-1.
Oxygen and Nitrate transport are calculated using equation (5) and equation (6), respectively.
πππ₯π¦(π‘) = β π β π β βπ₯ β βπ§ β π£ (5) ππππ‘(π‘)=βπβπββπ₯ββπ§βπ£ (6)
Where, O and N are the concentration of oxygen and nitrate (micromol/L), respectively. The unit for the oxygen transport and nitrate transport is mcromol/s.

#### Notes

**Credit**

IMAS Honours Student Program 2019-2020