Ross Sea Voyage Update #10: Sea ice, sunsets and science

Collecting biophysical baseline data

One of the New Zealand objectives for the voyage is around biophysical baselines and change that are important for the Ross Sea region Marine Protected Area (MPA). This vast swath of the Ross Sea is subject to some quite stringent controls on fishing and the required science to understand the biophysical setting.

NIWA’s Dr Alina Madita Wieczorek collected a dedicated transect with the high resolution EK80 fisheries acoustic sounder, looking for tell-tale signs of a range of fish species. The transect ran most of the length of Hallett Ridge – a nearly 100 km long feature that extends out from the continental shelf. It has historically been a region worked by a number of fishing interests, and we could see why when we arrived. There was a lot more marine life than we were used to, with several species of whales passing by (though never when I was looking), plus a lot more zooplankton in the water (and in nets of Svenja Halfter and Georgia Pollard). Alina balanced the “remote” acoustic data with water samples, which were filtered down for later sampling of eDNA to determine the different species present.

Oceanography on the Ross continental shelf

Often in observational ocean science, we find ourselves looking at quite detailed components far removed from the big picture. However, these questions, and the changes they are aimed at understanding, are central to some of the many ways greenhouse gas emissions are changing the planet – often in ways, and at rates, we didn’t expect. New observational data are vital in order to get a better idea of what changes are coming, and when.

We spent several days working off the Cape Adare corner of the Ross continental shelf, primarily around Italian sampling stations and a hydrographic mooring. Much of this work complements Associate Professor Melissa Bowen’s (University of Auckland) work as part of ASP Project Two: Ocean Mechanics, in a longstanding collaboration with my on-board Italian colleagues, Professor Pierpaolo Falco and Dr Pasquale Castago. They’ve been quantifying the transport of water off this corner of the continental shelf for a decade or more.

The location turns out to be a critical gateway, but nuances in how water drains off the shelf means that one sample point in space or time won’t be enough. We need to develop a network of measurements to capture the various streams of salty, cold water. In particular, this collaboration has shown how the tides influence this drainage, especially around equinoxes. This is another example of how the relatively high frequency tides connect to climate problems, creating a unique challenge for projection modelling.

It's not only heat and salt that flows through the Cape Adare gateway though - oxygen also passes by. Melissa was involved in a recent study that included some of the data from this area collected by the RV Tangaroa (work started by the Deep South National Science Challenge), that is helping quantify changes in this oxygen flux. The Antarctic Science Platform is looking to build on this research, building on the major update on the processes in this region that Melissa, Pierpaolo, Pasquale and Dr. Denise Fernandez, published last year. Denise plans to get more Argo floats into the region with oxygen sensors on board, via the 2025 RV Tangaroa voyage to the Ross Sea.

This ship is currently working its way south, a little into the Joides Trough. Like the parallel pathway of the Drygalski Trough to the west, the Joides Trough is a conduit for water heading north to the global thermohaline system. We’re looking to cross the trough with some CTDs. Our aim is to nail down the spatial variability in transport (due to the Earth’s rotation, seabed shape, friction as well as other factors), so we can calibrate the flow quantified in our Antarctic Science Platform moorings that lie a little further south.

We’re closing in on the home stretch now. The team are a mix of tired, energised by the amazing voyage and data, and keeping a weather eye on the long-term forecast for the transit home.

This update was sent from the ship by Prof. Craig Stevens, New Zealand voyage leader and revised by the New Zealand-based communications team.