Voyage Plans and Summaries

[back to voyage document index]

Franklin Voyage Plan No. FR04/2001

Title

Tasman-Coral Sea mass and heat transport / Regional Ocean Observing Network design — Part 1.

Itinerary

Depart Hobart 1000hrs, Friday 11 May, 2001
Arrive Wellington 1000hrs, Wednesday 23 May, 2001 

Principal Investigators

Ken Ridgway (Chief Scientist)
CSIRO Marine Research (CMR)
GPO Box 1538
Hobart TAS 7000
Tel 03 6232 5226
Fax 03 6232 5000
Email Ken.Ridgway@marine.csiro.au

Rick Bailey, CSIRO Marine Research

Ian Barton, CSIRO Marine Research

Richard Coleman, CSIRO Marine Research/University of Tasmania

Phil Sutton, New Zealand Institute of Water and Atmosphere (NIWA)

Scientific Objectives

This cruise is the first component of a multi-cruise experiment to enclose the Coral-Tasman Sea. The two following cruises (FR05/2001 & FR06/2001) and a section east of New Zealand to be performed by colleagues at NIWA will complete the box around the region. We note that FR04/2001 also involves a high degree of collaboration between CMR and colleagues from NIWA.

The following objectives relate to both the individual leg (FR04/2001) and the combined set of cruises:

• to measure the seasonal, interannual and decadal fluctuations in the transport of mass, heat and freshwater into the Tasman Basin,
• to survey the East Australian Current and associated eddies and fronts using in-situ and satellite data,
• to investigate the relationship between oceanic heat transport into the Tasman Sea, SST anomalies and regional climate fluctuation,
• to provide appropriate in-situ data for testing and validation of remote sensing techniques as well as ocean only and coupled ocean-atmosphere models,
• to develop and validate multidisciplinary elements of a Regional Ocean Observing Network (ROONet) in support of an Australian Ocean Observing System (AOOS),
• to contribute to the development of an operational marine monitoring and nowcast system for Australian waters which also forms part of the Australian Ocean Observing System (AOOS),
• to gain an understanding of the basin-scale ocean variability within the Tasman and Coral Seas as part of the GOALS objective of the international Climate Variability program (CLIVAR).

Cruise Objectives

To occupy the PX34 section (Sydney — Wellington) as part of the long-term monitoring of the mass and heat transport in the Tasman Sea.

To "value add" to the 10 years of high density XBT data (1991-2001) collected along this route from merchant vessels by achieving the following:

• assess the errors involved in obtaining dynamic height from XBT temperature profiles along the section,
• quantify the contributions to the baroclinic flow below 800m along the section,
• assess the validity of steric height and temperature extrapolation schemes along this section,
• determine a revised sampling strategy to enable the section to be maintained in the long term with a combination of satellite and in-situ data collection,
• assess the validity of inferred subsurface temperatures from surface satellite altimeter/SST observations and improve existing vertical projection schemes,
• assess the capabilities and utility of a real-time oceanographic analysis system under operational conditions,
• assess a range of data collection methods for application to ‘Ship of Opportunity ‘ programs,
• acoustically map and monitor at suitable and spatial scales the critical water column plankton/nekton and seabed habitats of the region,
• obtain validation data for sea surface temperature (SST) for MODIS, ATSR-2 and AVHRR satellite instruments,
• collect data to assist with the development of ocean colour algorithms using SeaWiFS, MODIS, and other ocean colour data,
• calibrate and evaluate XBT and XCTD instrumentation against the CTD.

This cruise combined with the following two cruises (FR05/2001 & FR06/2001) will enable the closure of the SW Pacific boundary region. This will allow inverse methods to be applied to the region to resolve the fluxes of mass, heat, freshwater and other biogeochemical quantities. These data will be used to ‘calibrate’ the more than 30 realizations of the Tasman Box closure from the XBT transects and to compare with results determined from the T/P data. The entire ‘Tasman Box’ is shown in Figure 2.

During the cruise we plan to obtain near real-time gridded altimetry and SST fields, derived surface currents and inferred sub-surface fields. These data will be compared with the in-situ observations and will be used as a guide to the management of the cruise.

The cruise will also obtain ‘ground truth’ data to be used for the validation of remote sensing instruments. These include:

1. Sea Surface Temperature (SST) for MODIS, ATSR-2 and AVHRR satellite instruments. A highly accurate infrared radiometer will be deployed to measure the surface skin temperature and assist in the use of combined altimeter and SST measurements for determining ocean currents and sub-surface temperatures. Other radiometers will be used to assess the surface heat and radiation budget. The altimeter and SST validation tasks complement each other and allow a much more productive science return. Currently there is considerable effort being devoted to the development of an infrared radiometer system that can be operated on "ships-of-opportunity". This cruise will also offer the chance to further assess these developments.

2. Collection of data to assist with the development of ocean colour algorithms using SeaWiFS, MODIS, and other ocean colour data. This cruise will supply validation data for the MODIS instrument in both the visible (ocean colour) and infrared (SST) channels. Ship measurements will also assist in the use of the ocean surface as a dark target for instrument calibration.

We will also collect data along the sections to contribute to a map of acoustic seabed types around Australia. To contribute to this aim and assist with the ocean color validation, plankton samples will be collected during the cruise.

The methods of Hanawa et al. (1995) will be used to determine the depth, temperature, and salinity accuracies of several types of XBT and XCTD. These probes will be deployed simultaneously with the CTD (precision control instrument) as per previous Franklin voyages. This work contributes to the ongoing calibration requirements of the national and international Ship-of-Opportunity Programmes.

Throughout the cruise a suite of underway instruments will perform calibration experiments for the SST and ocean color satellites. Several types of XBT and XCTD probes will be deployed simultaneously with CTD stations.

Cruise track

The cruise track is shown in Fig. 1.

The major component of this cruise consists of following the typical route of merchant vessels which have conducted high-density XBT measurements between Sydney and Wellington (PX34). We depart from Hobart and steam directly to a location off the east coast of Tasmania where an ascending Topex/Poseidon altimeter track intersects the continental shelf (B on Figure 1). We then proceed northeastward along this altimeter track dropping XBTs at regular intervals and collecting the usual underway data. A CTD will be completed at point C (altimeter crossover point) and we turn northwestward and proceed along the descending altimeter track toward the NSW coast. A further deployment of XBTs will be made along this section. Upon reaching the shelf break (D) we will then steam directly to point E the start of the XBT section PX34. Full depth CTDs will be obtained along the whole of this section. These stations will be closely spaced (approximately 0.1^o-0.2^o) over the continental shelf and slope, and across the main flow of the EAC (out to ~156 ^o) and then 0.5 ^o spacing from then on. To improve spatial resolution XBTs will be deployed between the CTD stations. ADCP data will be collected with accurate ships heading derived from the 3D GPS.

Time Estimates

Piggy Back Project

Ian Helmond plans to conduct sea-going tests of the Aquashuttle. This is a small towed body which samples temperature, salinity and several biological properties in the top 50-m. The instrument will be deployed from the winch between CTD casts to test its stability (a new type of stabiliser has been installed) and hence refine the existing design. The tests will involve several deployments with Franklin proceeding at a range of speeds. 

ORV Facilities Required

CTD profiles

Standard CTD profiles are required with the 12 bottle rosette. We require ORV staff to measure oxygen, salinity, NO₃+NO₂, SiO₂ and PO₄. A total of 52 CTD profiles are proposed. The locations are given in Fig. 1.

Other

The ADCP and GPS (3D-Ashtech system) data are required at all times. We note that these data fulfill a crucial role in the satellite calibration aspects of the cruise.

Participants

Ken Ridgway, Chief Scientist, CMR
Phil Sutton, NIWA
TBA, CTD Technician, NIWA
TBA, ADCP Technician, NIWA
Lisa Cowen, JAFOOS/BRMC
Ken Suber, CMR
Ian Helmond, Ocean Engineering, CMR
Bernadette Heaney, Computing, CMR
Erik Madsen, Electronics, CMR
David Terhell, Hydrochemistry, CMR
Gary Critchley, Hydrochemistry, CMR
Neale Johnston, Hydrochemistry, CMR 

Data Distribution

Following a reasonable period for data processing and reporting of results, the data collected from this cruise will be made freely available to international scientific programs (e.g. CLIVAR) as well as national and international data archives, including those of New Zealand, Western Samoa, Fiji, Vanuatu and New Caledonia.

Ken Ridgway
Chief Scientist

Figure 1. Cruise track for FR04/2001

Figure 2. Combined cruise track for the 3 cruises FR04, FR05 & FR06/2001 which enclose the Tasman Sea.

Updated: 31/01/03