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Campbell Plateau 2018 – Mooring Recovery

The R V Tangaroa headed to the Campbell Plateau in April 2018, to the southeast of the South Island, to recover moorings and undertake a CTD survey.

 

 

Key:

Southland current CTD transect Southland current CTD transect

Solander Trough CTD transect Solander Trough CTD transect

Subantarctic Front CTD transect Subantarctic Front CTD transect

CTD moorings to be recovered CTD moorings to be recovered

Auckland Islands as seen from the RV Tangaroa during the 2018 Campbell Plateau mooring recovery voyage. [Photo: Ben Cathie]

A typical CTD apparatus, which measures water column properties of conductivity (salinity), temperature, and depth (pressure). [Photo: David Bowden]

The Campbell Plateau is an interesting area which separates the Subantarctic Front which flows around its southern flank from the Subtropical Front to the west and north. These moorings will hopefully provide the first year-long timeseries of physical conditions to define the annual cycle over Campbell Plateau. The region is interesting in that surface waters get sufficiently cold in winter to mix all the way down to the bottom (~800m), forming a deep layer of uniform water that is called Subantarctic Mode Water. This mode water then gets 'capped' the following spring by warmer surface water, effectively sequestering Carbon Dioxide and heat. The mooring timeseries will allow this process to be quantified for the first time and will be used to estimate how much mode water is formed and whether it moves off the plateau - making it of global rather than local significance.

In addition, Campbell Plateau is an anomalous region in that sea level there is dominated by mass changes rather than thermal changes which are more generally the norm. The mass changes amount to water either piling up or draining off the plateau. The reasons for these mass changes are currently unknown, but will be informed by the moored data.

Two of the CTD transects repeats earlier work to provide measurements of change. The first is across the Southland Current east of Otago, the second is across the Subantarctic Front southeast of Campbell Plateau. A third transect runs parallel to the Solander Trough between Stewart and Auckland Islands.

 

The voyage departed Wellington on Wednesday 11 April 2018 and returned on Tuesday 24 April 2018.

Voyage update: 17 April 2018

Phil Sutton, Voyage Leader

The voyage so far has been hampered by bad weather. First of all, the sailing from Wellington was delayed because of the storm on the Wahine anniversary (perhaps an inauspicious choice for a sailing day). We did had a good run down the east coast of the South Island and managed to complete our CTD transect off Nugget Point. We then headed south for the first mooring recovery, but had to delay operations for a day waiting for the wind to ease.

The mooring was successfully recovered yesterday in trying conditions, but with more high winds forecast, we continued south to shelter in the lee of Auckland Island. We are now heading to the second mooring site to undertake a CTD and then recover the mooring if conditions allow - the weather forecast looks far less than great.

A petrel flying near the ship while we were near Auckland Island. [Photo: Louise Butler]

The CTD being recovered after one of the CTD casts along the transect across the Southland Current off south Otago. [Photo: Sarah Searson]

Grappling for Mooring 1 once it had been released and had floated to the surface. [Photo: Sarah Searson]

Recovering mooring 1. The large orange thing is the floatation around a 75kHZ acoustic Doppler current profiler (ADCP) which has measured the currents across a 500m depth range every 10 minutes for the year since the mooring was deployed. [Photo: Ben Cathie]

Phil Sutton and Mike Brewer looking at the weather map for today - 17 April 2018. [Photo: Sarah Searson]