Physical Oceanography

What we see in the Weddell Sea

My name is Dr Katherine Hutchinson and I am a South African Physical Oceanographer. This is my 7th time at sea and my 2nd time in Antarctica. Although I have much experience aboard the SA Agulhas II, I have never seen her plough through the Antarctic Ice before – a mightily impressive sight to see!

My main mission on the Weddell Sea Expedition is to understand more about the coldest, densest and deepest water in the world’s ocean: Antarctic Bottom Water. This water forms adjacent to and underneath the floating ice shelves of Antarctica in very select locations, one being the Weddell Sea’s Larsen C ice shelf – just where we are headed on our Expedition!

We care about this bottom water because it helps power the conveyor-belt of ocean currents that move warm water from the equator to the poles and cold water from the poles to the tropics, thereby moderating our global climate.

How does it work? In Antarctica the prevailing winds blow northwards off the continent, thus pushing the sea ice away from the coast and creating gaps of open water that can be super-cooled by the icy winds. This water is also hyper saline as salt is injected into the surface of the ocean when sea ice forms. The combination of low temperature and high salt content make this water very heavy and cause it to sink all the way to the bottom of the ocean, like a waterfall inside the sea! As this water sinks, it traps with it carbon dioxide and nutrients from the surface and acts as a window between the deep ocean and the atmosphere. This water then spreads very slowly (1cm/s) northwards to the Atlantic, Indian and Pacific Ocean basins carrying with it the ancient climate signals from the Antarctic.

We use an instrument called a CTD to measure the temperature, salinity, oxygen, nutrients, nitrogen, chlorophyll and productivity of the water to understand the conditions for bottom water formation and its influence on the water’s biology and chemistry.

Dr Katherine Hutchinson recently finished her PhD at the University of Cape Town working together with the South African Environmental Observations Network, the University of Miami and the Laboratoire d’Oceanographie Physique et Spatiale. She is 28 years old and is passionate about understanding more about our oceans and how they are changing in an altering climate.