Ross Sea Voyage Update #5: Traversing the Ross Ice Shelf
We have sailed beyond the katabatic weather system - it remained active for many days with winds reaching 100 knots - and worked our way eastward along the face of the largest ice shelf on the planet.
The Ross Ice Shelf is something most of us aboard spend a lot of time thinking about and, though many have been close by to it previously, we remain in awe every day. A good number of our research locations are within a few hundred meters of the ice front. Occasionally, we look out a porthole and see an incongruous ice wall stretching for as far as we can see - east and west.
Moorings
We’ve just finished deploying a sequence of hydrographic moorings along the western part of the Ross Ice Shelf front. Three moorings hold sensors near the seafloor and the fourth was a longer instrument array, designed to try and capture upper water column mixing processes driven when polynya operate. This latter mooring is high risk, with all the icebergs drifting around. For this very reason, these processes are very poorly observed.
This sampling approach was developed in ASP Project: Two Ocean Mechanics, which seeks to quantify the critical heat and oxygen transfer processes that take place in polynya.
There were some tricky design issues for the moorings – we want the instruments close to the ice shelf, but we need to account for the ice movement forward over the ocean - it creeps almost kilometre a year on average. At the same time, we want our instruments on the long mooring to be near the surface, which meant that the depth of water it is deployed in has to be very precise. If we drop it in too shallow, the floats would not be beneath the surface, and we’d have to try and recover and redeploy. If too deep, we’d miss out on the surface processes.
The mooring operations were designed and led by NIWA’s Jasmin McInerney with help from Craig Stewart and Liv Cornelissen. Liv is working on her PhD examining polynya mechanics with models and existing data so it’s a great benefit for her to see the work that goes on behind the scenes to get those data.
An oceanographer, Craig Stewart has spent a lot of his career measuring the ice shelf melt-rates just to south of where we have been travelling (his 2019 paper on the subject is a modern classic). It used ice-penetrating radar units mounted on the ice looking downwards – and this expanded network of sensors continues to monitor the ice front. The opportunity to work on the ocean side was sufficient to lure him aboard for the leg 2 voyage.
Dr Craig Stewart prepares the current meter. Photo: Craig Stevens.
Liv Cornelissen and Jasmin McInerney prepare acoustic release for mooring. Photo: Lana Young.
Gliders
Unfortunately, we had to put a halt to the glider mission designed to run up the Glomar Challenger Trough, as the weather conditions were borderline. We deployed the instrument but weren't happy with the glider stability - rough waves and icing affecting it during its start-up cycle. So the glider was retrieved by Jasmin in good but chilly condition. We will repair and rethink.
Preparing the glider for deployment. Photo: Lana Young.
Biological Sampling
Svenja Halfter (NIWA), Georgia Pollard (University of Waikato) and Alina Madita Wieczorek (NIWA) are combining water sampling and filtering with acoustics and CTD data to look at biological trophic levels. We’ll cover their activities later in the trip.
Matthias Dehling’s (Monash University) heroic seabird/seal counts continued. The ‘heroic’ is no joke – with wind-chill, we are in -26°C at present.
The Italians also deployed two ocean gliders (in calmer weather than us) as well as an array of CTD stations. Many of these are very close by the ice shelf front and provide excellent opportunities for new discoveries around how the ice shelf cavity ocean and the Ross Sea continental shelf connect both with and without active polynya.
Svenja ready for the first bongo tow for zooplankton. Photo: Lana Young.
So other worldly is this place, not only do we have to contend with the magnetic South Pole being way north of here (in fact one of James Clark Ross’s primary science goals was location of this pole), but we have also crossed the dateline. Unfortunately, as the ship stays in New Zealand's summer-time, we were not able to claim an extra meal.
Next stop: the Bay of Whales.
The Ross Ice Shelf, with a berg. Photo: Lana Young.
This update was sent from the ship by New Zealand voyage leader Prof Craig Stevens and revised by the New Zealand-based communications team.