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10 February 2017

Antarctic Meltwater Outflow & the Resulting Impact on Climate

For years, the presence of meltwater from the ice caps of Antarctica at unexpected depths of several hundred metres has baffled scientists. Being less dense than the nutrient-rich seawater, it should rise and gather at the surface. Why then, when it seemingly goes against known scientific principles, does said meltwater gather in the deep?

Well according to new research published last month in the journal Nature, we may now have the answer – the rotation of the Earth itself.

The research, carried out by a team comprised of scientists from the University of Southampton, National Oceanography Centre, Southampton, University of East Anglia (UEA), British Antarctic Survey (BAS) and Stockholm University, seeks to provide an understanding into how the way in which meltwater circulates affects the climate of the region and beyond, as Professor Alberto Naveira Garabato, of Ocean and Earth Science at the University of Southampton and lead author of the study, explains:

“We believe our study is an important step in understanding how the meltwater mixes in the ocean and will help with the design of climate models, which largely assume meltwater is only present on the surface of oceans. Our research emphasises its detection at greater depths and explains why it is found there.”

The answer finally came during an expedition to the Southern Ocean in 2014. Undertaken as part of the NERC-funded iSTAR programme and led by Professor Karen Heywood of UEA, the expedition team measured turbulence experienced by meltwater as it flowed out of a cave beneath the Pine Island Glacier, making use of a Vertical Microstructure Profiler (VMP) to detect subtle fluctuations in the water.

What they found is that while the meltwater does try to rise above the seawater as expected, it is stopped along the way due to forces exerted as a result of the Earth’s rotation. The rotational force causes it to spin quickly around its vertical axis, which causes the ejection of meltwater filaments in a sideways motion into the surrounding sea, in turn preventing the meltwater from reaching the surface.

Scientists are particularly interested in the way in which meltwater behaves because of the knock-on effect this has on global ocean circulation and climate. According to BAS, surface meltwater makes the upper layers of the Southern Ocean lighter, which is thought to further slow the sinking of such waters in the region and favour the expansion of Antarctic sea ice. The ejection of meltwater at depth is believed to have the opposite effect, leading to a reduction in sea ice.

Co-author of the study and glaciologist for BAS, Dr Adrian Jenkins, says of the recent study:

“These new data show for the first time the complexity of the processes that mix meltwater from the Antarctic ice shelves into the interior of the ocean.  Although the rotation of the Earth affects the large-scale currents that transport the mixture of meltwater and seawater away from the continent, we had assumed up to now that planetary rotation played no role in the small-scale mixing processes themselves.  Now we see that we were wrong on that point.  The next challenge is to see how we can represent the impacts in ocean and climate models.”

Sam Bonson

Sam is an aspiring novelist with a passion for fantasy and crime thrillers. He is currently working as a content writer, journalist & editor in an attempt to expand his horizons.