Interdisciplinary Research Cruise to the Marginal Ice Zone of Antarctica

26 Jun 2017 - 13:15

Sea Ice team collecting frazil ice from a personnel platform

The Southern Ocean is one major buffer for anthropogenic heat and carbon. It is a major mediator of the exchange of heat and momentum between the atmosphere and the ocean and its large seasonal variation is determined by the interaction between these components in the marginal ice zone (MIZ). In March and April 2017 the extent of Antarctic sea ice reached the lowest minima in the existing records, raising concerns on the anticipated response to anthropogenic warming. The way sea ice would respond to atmospheric and oceanic changes and set the conditions for the exchange of heat, momentum and gases is largely related to its physical and mechanical properties and how they evolve with time. These properties are largely unknown in the Atlantic-Indian sectors of the Southern Ocean surrounding South Africa, and especially at the margin with the open ocean during winter and at the starting of the sea-ice retreat in spring.

This knowledge gap requires a an integrated approach that encompasses sea-ice sampling, ocean/sea-ice modelling as well as information on MIZ biogeochemistry and carbon fluxes. These properties are largely unknown in the Antarctic marginal ice zone (MIZ), thus limiting the predictive capability of climate models. Furthermore, current models still fail to accurately capture the sea ice behaviour due in part to computational costs in resolving the proper physical and biogeochemical features.

It is against this backdrop that a multi-disciplinary Sea Ice Research group from the UCT departments of Oceanography, led by Associate Professor Marcello Vichi, and Civil Engineering, led by Dr Keith MacHutchon and Dr Sebastian Skatulla, was formed at the beginning of 2016 to study sea ice dynamics and thermodynamics in the MIZ, with the aim to collect multi-disciplinary data and develop computational simulations of sea ice to be incorporated into global climate models.

In July 2016, a Sea Ice team embarked on a two-week long research cruise from Cape Town into the MIZ aboard the South African ice-breaking research vessel SA Agulhas II. The team was led by Dr Keith MacHutchon and comprised ice analyst Trond Robertsen of the Norwegian Ice Service, Oceanography postgraduate students Ehlke de Jong, Casey Lyttle and Chloe Blyth, civil engineering postgraduate students Emmanuel Omatuku Ngongo and Devin Dollery, and numerical engineer from ICEMASA, Emeline Cadier. The cruise was limited in scope, but afforded the team an opportunity to build an initial expertise in the MIZ. The cruise objectives were the study of sea ice structure and morphology in the MIZ by means of observation, and the collection and testing of frazil and pancake ice for the analysis of physical properties aboard the vessel and for testing of mechanical properties of pancake ice in the UCT civil engineering laboratory.

Measurement of the temperature distribution of pancake ice sample

Seven pancake ice samples were collected using lifting baskets. The latter were lowered into the water between pancakes, and the pancakes were then lifted to be unloaded on the vessel deck. Frazil ice was collected by the team operating on a personnel platform suspended from a vessel crane using sampling tubes (Figure 1). After the ice collection, the vessel returned to Cape Town, with the collected ice stored in the vessel cold room at -4°C. While crossing the Southern Antarctic ocean, the salinity of the frazil ice, as well as the temperature, salinity and density of about 80% of the collected pancakes, was measured (Figure 2). The remaining pancakes were then tested for compressive strength in the UCT laboratory (Figure 3).

This cruise was a success and the team gathered reasonable initial results and the expertise to conduct further research cruises in the MIZ. However, the need to develop sea ice computational models and better understand the Southern Ocean sea ice, sets off for a 16 day voyage on 27th June  2017. The interdisciplinary team will include biogeochemical measurements by Dr Sarah Fawcett and Dr Katye Altieri (Department of Oceanography), measurements of trace elemnts and dust (Prof Roychoudhury and Dr Fietz, Stellenbosch University), sea ice algae and plankton (Dr David Walker, CPUT) and with international participation of scientists from Melbourne University, New York University at Abu Dhabi and the German universities of Duisburg-Essen and TU Dortmund.