Voyage Plans and Summaries

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Franklin Voyage Plan No. FR06/2001

Title

Tasman-Coral Sea mass and heat transport / Regional Ocean Observing Network design – Part 2.

Itinerary

Sail Apia 1000hrs, Sunday, 8 July, 2001 (Western Samoa local time)
Arrive Brisbane 1000hrs, Monday 23 July, 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 final component of a multi-cruise experiment to enclose the Coral-Tasman Sea. The two previous cruises FR04/2001, FR05/2001 and a section east of New Zealand to be performed by colleagues at NIWA complete the box around the region.

The following objectives relate to both the individual part (FR06/2001) 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,

• 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 PX30 section (Brisbane-Fiji) as part of the long-term monitoring of the mass and heat transport in the Tasman Sea and obtain closed volume observation around the SW Pacific boundary to compare direct transport closures with estimates derived from satellite observations.

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 preceding 2 cruises (FR04/2001 and FR05/2001) 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 40 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 1

In particular the FR06/2001 cruise begins at Apia (Western Samoa) and proceeds directly to Fiji. This component is required to complete the closed box and full-depth CTDs will be obtained at high spatial resolution. From Fiji to Brisbane (The PX30 XBT section) the sampling will follow the general pattern of the Sydney – Wellington section (FR04/2001) but in reverse (higher spatial sampling at the Brisbane end of the section where the EAC is crossed).

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.

Several methods will be used to determine the depth, temperature, and salinity accuracies of a range of XBT and XCTD types. The probes will be deployed both simultaneously and between the CTD stations (precision control instrument). 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 for the cruise is shown in Fig. 2.

The cruise consists of a track from Apia (Western Samoa) to Brisbane. A total of 80 full depth CTDs will be obtained along the whole of the section. We depart from Apia and steam directly towards Fiji. Along this portion of the cruise track the CTD stations will be occupied at approximately 0.5 ^o spacing. West of Fiji the cruise track follows the typical route of the XBT high-density merchant vessels between Fiji and Brisbane (PX30). A further series of CTDs will be completed at 0.5 ^o spacing over the eastern end of this segment apart from the region adjacent to Fiji and south of New Caledonia where the spacing will be increased to resolve boundary currents and internal wave activity.

When the eastern flank of the EAC flow is reached (~158^oE) the station spacing will be reduced to about 0.3^o and then upon reaching the continental shelf and slope the stations will be even more closely spaced (approximately 0.1 ^o – 0.2^o). To further 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. Where the cruise track is intersected by satellite tracks, meteorological radio-sondes will be released to obtain reference atmospheric data to be used for the improvement of altimeter processing algorithms. At locations to be determined along the length of the section, up to 6 Argo profiling floats will be deployed.

Time Estimates

Supplementary Project - Argo/SOLO Profiling Float Deployments

As part of the International Argo Float Program up to 6 floats will be deployed along the cruise track (subject to availability at the time of the cruise). The float deployments are part of the global Argo array of profiling floats (www-argo.ucsd.edu). The global array will collect temperature/salinity profiles and mid-depth velocity measurements in order to increase our understanding of the role of the ocean in the climate system. The floats will be used both to describe the evolving physical state of the ocean - its heat content and circulation - and in data assimilating models aimed at improving seasonal to interannual climate forecasts. Together with TOPEX satellite measurements of sea surface height, the floats will provide the subsurface information that is required for interpretation of sea level variability on long time-scales.

Franklin Facilities Required

CTD profiles

Standard CTD profiles are required with 12 bottle rosettes being sufficient. We require ORV staff to measure oxygen, salinity, NO₃+NO₂, SiO₂ and PO₄. A total of 80 CTD profiles are proposed. The locations are given in Fig. 2.

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
Richard Coleman, CMR/Tas Uni.
Ian Barton, CMR
Jeff Dunn, CMR
Lisa Cowen, JAFOOS/BMRC
Pamela Brodie, Computing, CSIRO ORV
Erik Madsen, Electronics, CSIRO ORV
Val Latham, Hydrochemistry, CSIRO ORV
Mark Rayner, Hydrochemistry, CSIRO ORV
Neale Johnston, Hydrochemistry, CSIRO ORV

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), national and international data archives, including those of New Zealand, Western Samoa, Fiji, Vanuatu and New Caledonia.

This cruise plan is in accordance with the directions of the National Facility Steering Committee for the Research Vessel Franklin.

Ken Ridgway
Chief Scientist

Figure 1 The combined cruise track for the 3 cruises FR04, FR05 & FR06/2001 which enclose the Tasman Sea.

Figure 2 Cruise track for FR06/2001: the Apia – Brisbane section.

Updated: 31/01/03