We perform research on land-fast sea ice in McMurdo Sound (map), Ross Sea, Antarctica in cooperation with Dr. Tim Haskell of IRL and other collaborators. Our research base is usually Camp Haskell, a self contained camp of several wannigans on sea ice (see photos). We also use facilities and services provided by the New Zealand research station Scott Base of Antarctica New Zealand. Research facilities at the University of Otago include two walk-in freezers of adjustable air temperature (range 0°C to -30°C) with a 1500 litre seawater tank.
Tim Haskell, Industrial Research Limited, Lower Hutt, New Zealand
Joe Trodahl, Marc McGuinness, Victoria University, Wellington, New Zealand
Colin Fox, formerly Auckland University, Auckland, New Zealand (now at the University of Otago)
Sebastian Gerland, Norwegian Polar Institute, Tromsø, Norway
Dave Cole, CRREL, Hanover, NH, USA
John Dempsey, Civil and Environmental Engineering, Clarkson University, Potsdam, NY, USA
Jean-Louis Tison, Université Libre de Bruxelles, Belgium
Mike Williams, Craig Stevens, Andy Falconer, NIWA, Wellington, New Zealand
Manfred Lange, Institut für Geophysik der Westfälischen Wilhelms-Universität Münster, Germany
Ross Vennell, Department of Marine Science, University of Otago, Dunedin, New Zealand
Vernon Squire and group, Department of Mathematics, University of Otago, Dunedin, New Zealand
The Polar Environments Research Theme, University of Otago, Dunedin, New Zealand
- Winter sea ice growth process in McMurdo Sound, Antarctica. IPY proposal (field studies)
This research is a collaboration between two New Zealand universities (University of Otago and Victoria University of Wellington) and two CRIs (Industrial Research Ltd and National Institute of Water and Atmospheric Research). This team had already enjoyed fruitful interactions for over 4 years, with some of the team being involved in a successful winter sea ice experiment in 2003. Internationally the collaboration includes US scientists from the Universities of Alaska, Washington and Wyoming. Following a pilot study in September/October 2008, experiments were conducted on the winter sea ice of McMurdo Sound, Antarctica by a team who spent eight months at Scott Base, from February to October 2009. This research was part of the International Polar Year, IPY.
The thickness and growth of coastal sea ice during winter is a key unknown when considering polar influences on climate. Much of the coastline of Antarctica is ice shelf. Melting and/or freezing at the base of an ice shelf influences the heat content and salinity of the water in contact with it. In turn this strongly controls near-surface oceanography. The overall aim of this research was to observe the development of these processes and to measure their influence on sea ice growth during the winter season.
Sea ice thickness (or volume) is the critical parameter in determining the exchange of heat and moisture between atmosphere and ocean, and the reflection of incoming radiation by the sea ice. Ice strength and consequently break-up are also strongly dependent on thickness, as is the amount of thermal energy that is stored in the sea ice cover. Yet, at present, sea ice thickness cannot be measured by satellite. Thus while a great deal is known about the global sea ice extent, very little is known about its volume. This knowledge deficit is even greater when considered seasonally. Hence this research targeted winter, contributing to an understanding of the evolution of sea ice thickness. The project aims to provide an understanding that will underpin future modelling of coastal sea ice thickness. Further, it will contribute to the very sparse set of observational oceanographic and ice data collected in the polar winter.
- Sea ice and platelet ice formation in McMurdo Sound and their correlation with oceanographic conditions. (field and laboratory studies; Marsden Fund project)
(Greg Leonard, Craig Purdie, Inga Smith)
Sea ice in McMurdo Sound forms in close proximity to the McMurdo Ice Shelf. Under such circumstances, ice crystals may appear in the water column and can attach themselves to the ice-water interface, and grow. Termed platelet ice, similar crystals are observed at certain depths in the sea ice sheet, suggesting that their development is coupled to oceanographic conditions at the time of formation. This study correlates oceanographic conditions with the formation of platelet ice during the winter months in Antarctica. (Read more about the related Marsden Fund project.)
- Internal waves in McMurdo Sound. (field studies)
Vertical profiles of temperature and salinity under the sea ice cover of McMurdo Sound show that the temperature and salinity structure does not only depend on the time of the year but also on the depth. It has been suggested that the depth dependence may be due, in part, to internal waves. This study gathered evidence for or against the presence of internal waves in McMurdo Sound.
- Ocean density structure in McMurdo Sound. (numerical studies, field studies)
Vertical profiles of temperature and salinity under the sea ice cover of McMurdo Sound show that the density structure depends on the time of the year and on depth. This study investigates the influence of the sea ice cover and the adjacent ice shelf on the seasonal evolution of water temperature and salinity in McMurdo Sound and beyond.
- Crystal structure of lake ice and ice growing from water of low salinity. (laboratory studies)
Sea ice growing from brackish water exhibits a similar crystal structure to sea ice growing from more saline ocean water. However, the crystal orientations of lake ice, growing from freshwater, are often significantly different from the brackish orientations. This study attempted to eludicate the the dependence of the orientation of crystal axes in the ice on the salinity of the original water.
- Refreezing process, structure, and stability of refrozen cracks in sea ice. (field, laboratory, and numerical studies)
(Chris Petrich, Tim Divett)
The sea ice cover often fractures during the growth season in the presence of wind, waves, or rapid temperature changes. Many cracks eventually refreeze but have been found to remain weak spots in the ice cover. This study characterised the refreezing process of cracks and determines their physical properties, structure and mechanical strength.
- Freezing interface definition in sea ice. (field, laboratory, and numerical studies)
(Daisuke Yamagishi, Chris Petrich)
The bottom of a sea ice sheets is often characterised by a dense array of thin, vertically growing lamellae of fresh ice, interspered with brine. While temperature probes offer a convenient way to track the freezing progress of an ice sheet, the relationship between measured temperature and structure of the sea ice matrix is not obvious. This study will correlate the structure of the sea ice interface with the temperature signal.
- Formation of banding in sea ice. (laboratory studies)
Sea ice consists of a matrix of fresh ice, that contains air inclusions and inclusions of liquid brine. Horizontal bands of an increased density of inclusions are sometimes observed in natural sea ice sheets. The present hypothesis is that the formation of bands is the result of either changes in under-ice currents or of variations in air temperature. This study attempted to reproduce banding features in saltwater ice in a controlled environment.
- Brine pocket migration. (laboratory studies)
Liquid brine is present in sea ice either in isolated pockets or in channels. Driven by buoyancy gradients, the brine may convect, increasing the speed at which the pockets migrate through the ice. Migration of brine inclusions may have implications for the development of a connected network of pockets, and for the availability of nutrients to algal communities. This study attempts to quantify convection and migration of artificial brine pockets through blocks of freshwater ice.
- Strength and fatigue of sea ice. (field and laboratory studies)
The disintegration of the sea ice cover is accelerated by fatigue processes due to ocean waves. This study measured the response of natural sea ice sheets to cyclic loading under various conditions and artificial sheets of NaCl ice grown in the laboratory. The results were displayed in terms of the measured flexural strength of sea ice.
- Movement of the McMurdo Ice Shelf. (numerical studies)
This study measured the velocity of some areas of the McMurdo Ice Shelf from satellite images. A finite element model of the movement of the ice shelf in the vicinity of Minna Bluff was constructed.
- Two-dimensional fluid dynamics modelling of sea ice growth. (numerical studies; examples)
Sea ice changes its brine content during formation and during melting. This affects heat transfer, the amount of brine released to the ocean, transport of nutrients through the sea ice, and the inclusion structure. This study has developed a computational fluid dynamics model and used it to predict the salinity pattern in refrozen cracks.
- Percolation simulations. (numerical studies; examples)
Although experimental work concerning the size distribution of inclusions in sea ice has been performed in recent years, the theoretical description is still in its infancy. This study attempts to assess the applicability of statistical models to sea ice.
- Optical characteristics of saline ice. (field, laboratory, and numerical studies)
Light propagation through sea ice depends on the distribution of brine and air inclusions. This study investigated the dependence of surface reflection, and of light scattering and propagation on the structure of sea ice.