July 1, 2020
By Craig Stevens and Christina Hulbe
...There are indeed hidden ocean cavities around Antarctica, and our latest research explores how the ocean circulates underneath the continent's ice shelves - large floating extensions of the ice on land that rise and fall with the tides.
These ice shelves buttress the continent's massive land-based ice cap and play an important role in the assessment of future sea level rise. Our work sheds new light on how ocean currents contribute to melting in Antarctica, which is one of the largest uncertainties in climate model predictions.
The Ross Ice Shelf is the largest floating slab of ice on Earth, at 480,000 square kilometers. The ocean cavity it conceals extends 700km south from Antarctica's coast and remains largely unexplored.
We know ice shelves mainly melt from below, washed by a warming ocean. But we have very little data available about how the water mixes underneath the ice. This is often overlooked in climate models, but our new measurements will help redress this.
The only other expedition to the ocean cavity underneath the central Ross Ice Shelf goes back to the 1970s and came back with intriguing results. Despite the limited technology of the time, it showed the ocean cavity was not a static bathtub. Instead, it found fine layering of water masses, with subtly different temperatures and salinities between the layers....
I believe the science of 1983 was just as sound and if not more so compared to the facts of today. The formation of a methodology, even though different, does not mean it has a higher error or less important facts. In all honesty, the science of today is a validation of the past.
20 March 1983
By Theodore D. Foster
A series of temperature and salinity profiles (click here) was made in the ocean under the Ross Ice Shelf at 82°22.5′S, 168°37.5′W where the ice was 420 and the underlying seawater 240 m thick. The water structure consisted of a fairly well‐mixed, low salinity layer at the in situ freezing point of the ice‐water interface about 30 m thick, a transition layer characterized by intrusions about 85 m thick, a strongly stratified layer with increasing temperature and salinity about 50 m thick, another transition layer characterized by intrusions about 45 m thick, and an isohaline bottom layer with a nearly abiabatic temperature gradient about 30 m thick. The temperature fluctuations in the two transition layers can be attributed mainly to intrusive activity even though internal wave activity was highest in these regions. In the central stable layer, internal waves probably contribute to the temperature fluctuations equally with intrusions. The internal wave ‘dropped’ displacement spectrum seems to be very similar to those found in the open ocean. Some profiles showed intrusions in the top transition layer colder than the top boundary layer, and some showed intrusions in the bottom transition layer warmer than the bottom boundary layer, indicating that horizontal shear must be present. Internal waves of near inertial frequency excited by the semidiurnal tides combined with shear‐induced instabilities seem to be the likely causes of the observed fine structure.
