Ocean Moorings CS

2021 Tangaroa Voyage: Climate monitoring at key Antarctic ocean gateways

14 January 2021

The following article is written by Project Two Co-PI Dr Craig Stevens

In early January the NIWA vessel RV Tangaroa headed off to the Southern Ross Sea to conduct a range of science including some Platform-supported hydrographic timeseries mooring work along the Ross Sea continental shelf break - near Cape Adare.

The work includes recovery and redeployment of hydrographic moorings close by Cape Adare designed to capture cold, salty water formed in polynya that is draining off the continental shelf and flowing north along the seabed.

If we weren’t changing how the planet’s climate system works, we wouldn’t see this water at the ocean surface for many centuries to come. However, with warming oceans and increased ice melting we are altering how the ocean around Antarctica operates and so there is an urgent need to monitor this evolution.

The Adare moorings were first occupied in the early 2000s by the Lamont-Dougherty Earth Observatory in the US. Following on from this pioneering work, Dr. Melissa Bowen from the University of Auckland (and an Objective Leader in ASP Project Two: Oceans), re-occupied these sampling stations with support from the Deep South National Science Challenge and dramatically extended the timeseries.

These early data were sufficient for her, along with colleague Dr. Denise Fernandez of NIWA, to recognise the importance of the time-perspective so the Platform will continue this monitoring. Unlike, irregular sampling from ships, the timeseries from moorings allow us to connect tidal timescales, where a good deal of the energy transfers take place, to climate mechanics where the impacts are being felt globally.

In addition to this continuation of data the team are deploying new oceanographic moorings further south across the head of a submarine trough. These stations complement an Italian mooring already in the water, so that we can now provide a reliable estimate of heat and salt fluxes. This international collaboration will dramatically improve estimates of warm water heading south towards the ice and also address questions about the connection between north and southward transport.

Compared to typical ocean moorings these are quite lean designs, built to cope with high risk, challenging environments. They comprise hundreds of kgs of weight on the seafloor connected via an acoustic release to a kevlar line held up by especially-designed submerged floats. The critical sensors are mounted on this line at key depths. Despite the challenges, we expect they will return very high precision data on temperature, salinity and ocean currents for years to come.

The plan is to next recover these instruments in a later voyage in 2023.