2015: Year in review

In Brief

  • Graham Hughes is departing the GFD group for a Professorship at Imperial College, London, after 18 years of service. Graham’s GFD legacy is his major contributions to the development of our laboratory, and particularly a series of Horizontal Convection experiments that have redefined the oceanographic community’s understanding of the overturning circulation.
  • Adele Morrison awarded the Uwe Radok prize for the best Australian PhD thesis, awarded by the Australian Meteorological and Oceanographic Society (AMOS).
  • Sophie Lewis awarded a DECRA Fellowship to begin in 2016.
  • Andy Hogg received the Fofonoff award from the American Meteorological Society and the Priestley Medal from AMOS.
  • Kial Stewart and Callum Shakespeare joined the group as Postdoctoral Fellows.
  • Isa Rosso graduated from her PhD; Mainak Mondal and Angus Gibson joined the group as new PhD students. 
Figure 1: Snapshots of numerical simulation of convection. From the bottom: temperature distribution imposed on the boundary (red: hot, blue: cold), horizontal sections showing velocity component horizontal direction at mid-depth, and, at the top, 3D maps of vertical velocity.

Research Highlights

The GFD group conducts research into fluid processes relevant to the earth system. Current research priorities include oceanic convection, ice-ocean interactions and the large-scale circulation of the ocean.

The rate of melting of the polar ice sheets comprises the largest uncertainty in predicting future sea level rise. During 2015 we have continued our experimental and theoretical work into understanding the dynamics of convective meltwater plumes that form next to Antarctic and Greenland ice shelves – and  control the speed at which the ocean can melt the ice (Kerr & McConnochie, 2015). A theoretical model has been developed to describe the meltwater plume, while the effect of ocean stratification on ice-ocean interactions has been explored experimentally. Stratification significantly reduces the ice melt rates and the meltwater plume velocity. Direct numerical simulations have been used to show that a sloping ice face will alter the heat and salt transport to the ice, and hence the melt rate.

Circulation in the Southern Ocean remains poorly understood and undersampled by observations, yet is one of the fastest changing regions on the planet. A major obstacle to progress in Southern Ocean research has been the role of fine scale processes such as eddies and jets in controlling the large-scale circulation; these processes are difficult to model and observe. We now have strong observational evidence (using satellite altimetry; Hogg et al. 2015) that the intensity of these eddies has increased over the last two decades. Furthermore, we can unambiguously attribute these eddy increases to increases in the magnitude of westerly winds that drive the Southern Ocean.

In the far southern reaches of the Southern Ocean, dense water is formed on the Antarctic shelves through a combination of cooling and salinification. This water then cascades off the shallow shelves down to the abyssal ocean to form a water mass known as Antarctic Bottom Water. Recent observational evidence has indicated that Antarctic Bottom Water is becoming less saline and less cold; and therefore less dense. The reduction in deep ocean density has the potential to alter the global circulation and ocean carbon budget, but the processes controlling this change are unknown. We have shown that this water mass formation process is primarily sensitive the changes in the buoyancy forcing at the ocean surface, such as warming or freshening through the meltwater from Antarctica (Snow et al. 2015). Our studies have emphasised the importance of ocean circulation on the Antarctic shelf in controlling the abyssal ocean response to climate change, and this a future research priority for our group. 

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