The best laid Antarctic plans are entirely at the mercy of Antarctic sea ice, which can change very rapidly. Early in the voyage I met with the ship’s bridge team, including Ice Pilot Evan Solly – a veteran of many of these voyages south – to look at the various satellite images of how the ice in the region was evolving.
It was clear that our initial target areas for sampling were going to be filled with sea ice for a week or more, and our best option was to reverse the planned voyage route. After a long night with the scheduling spreadsheet, we had a new plan. So now, upon saying goodbye to Mount Melbourne, instead of the initial route north, we set our compass to the southward.
But before we got going too far, we stopped engines to drop off NIWA’s Ocean Glider Manaia. An ocean glider is a two-meter-long tube stacked with batteries, electronics and a miniature CTD (to measure salinity and temperature). It doesn’t have a propellor though – instead it adjusts its buoyancy so that, with its little wings, it can silently glide through the upper few hundred metres of the ocean, surfacing occasionally to report back via satellite, and pick up any new instructions – essentially a robot. It does all this at a rather leisurely pace, covering perhaps 20 km in a day.
Dr Jasmin McInerney is aboard Tangaroa for the voyage and, among her many tasks, leads NIWA’s ocean glider facility. Jasmin is a veteran of many glider launches, in both Antarctic waters, and other challenging places and from all kinds of vessels. After our route change, Jasmin and I had to plan a whole new mission for the glider.
After the deck crew carefully deployed it into the water using the ship’s crane, Jasmin ran a long list of checks to make sure Manaia was set to go. Ocean gliders are hugely complex with any number of things that can trip up operations and result in a rescue mission for the ship.
Eventually, with the all-clear, Jasmin set the glider on its way. By this time, it was about 2am but she was able to head off to bed because Eleanor Haigh back at the NIWA offices in Wellington took over piloting the glider remotely for the start of its journey north. Eleanor was doing this at the same time as keeping an eye on NIWA’s other ocean glider Betty, which is currently working in the Taranaki Bight.
The region Manaia was launched into is called the Drygalski Trough. It’s a 500 km long groove in the seafloor, in places over a kilometere deep, that is one of the critical transport corridors for cold salty waters formed in Antarctic coastal regions in winter. This water moves north to the edge of the continental shelf and beyond. Some of the final tasks of the voyage will be to gather sensors measuring this outflow.
As Tangaroa resumed her southward journey, the target was Franklin Island – at around 76°SSout (140 km north of Ross Island), it looks at first glance a rather unassuming slab of ice and rock. This was the second target area for the benthic ecology group. As we sidled up, the island slowly revealed itself to be full of life with penguins and orca in great abundance. Of course, once we looked a little harder it was clear the orca were chasing the penguins
After an intense 36 hours for the seafloor sampling team, we again departed – this time heading due east. Our next task was to launch a couple more robots – but a different flavour. Much earlier in the voyage we’d deployed ten “Core” Argo profiling floats across the Southern Ocean. Argo are like an ocean glider but without wings, and with a lifetime of five or more years, measuring temperature and salinity.
NIWA vessels have deployed thousands of these floats over the last 20 years. Argo is one of the most significant advances in our evidence base for understanding the ocean since the major World Ocean Circulation Experiment surveys of the 1990s.
However, once on the continental shelf itself we have a new class of Argo to deploy – BGC Argo (BioGeoChemical). These are essentially gourmet Argo floats, with an enhanced range of sensors helping understand how the changing physics relates to biological parameters. I like to think of them as a multi-year “voyage in a can”. BGC Argo is expanding our evidence base for the changing ocean to include ecologically essential variables. In particular, ocean oxygen levels, one of the looming climate signals we need to keep an eye on.
My co-voyage lead, Dr Denise Fernandez has been working for five years to get resources to deploy these complex drifting sentinels. The Antarctic Science Platform acquired two of the floats for this voyage. Denise, with help from Australia’s Dr Christina Schallenberg (CSIRO) and the International Argo Programme including NIWA's Dr Phil Sutton, spent some time planning the mission for these two floats. It requires extra care when they are being deployed in shallow continental shelf waters. Even then, it was touch and go for delivery as timelines were really tight – but much to everyone’s relief the two floats arrived just in time to be tested and loaded onto the ship.
The BGC Argo are a step up in terms of cost, complexity and sensors from Core Argo - deployment for Core Argo is over in a flash as the crew are well-practised at getting them in the water. BGC Argo on the other hand are much heavier and delicate and require Denise follow a lengthy checklist before she gives the OK to the crew to deploy the float into the water.
None of these robots are replacing voyages like ours any time soon because of all the other sampling that goes on. However, they are providing a huge boost to the evidence-base for changes to the marine domain – especially in places and times that are hard to monitor like the ocean around Antarctica in winter.
With the overarching mission of the Antarctic Science Platform being to understand the impacts on Antarctica of greenhouse gas emissions, it is not lost on us that in doing so we too are burning fossil fuels. While we await the shift to low-carbon vessels, the main response we have as ocean scientists is the increased use of robotics and the better sharing of data.
On the ACTUATE voyage we expect to do around 50 CTD profiles. However, the combined number of profiles from our robotics will be in the order of 3,500 and so a massive reduction in costs and emissions per profile. All these data will be openly available in many forms.
After getting the last BGC Argo into the ocean, Denise did a happy dance in the freezing cold. And from there we turned south again - next stop the Ross Ice Shelf itself - and Tangaroa’s farthest south.
-Craig Stevens (co Voyage lead with Denise Fernandez).