Wednesday, April 17, 2013

Note to keep the Antarctic Undersea Waterfall Working

 We utterly depend on ocean currents to bring us moisture and warmth.

The kick start for the global ocean pattern  is thought to develop off the coast of Antarctica during the Southern Hemisphere winter.   As the cold sets in, the sea water surface freezes forming  fresh-water ice, releasing salt beneath it into the ocean. This heavy saltwater downdraft occurs at such a volume that an enormous undersea waterfall spills the saltwater down all the way to the seafloor.   For a graphic illustration see NOVA's Earth from Space.
Altogether, the Cape Darnley Bottom Water and three other Antarctic bottom water salt currents are thought to be the main drivers for nothing less than the earth's ocean circulation, or more specifically called, thermohaline circulation.

Meanwhile, snow on the Antarctic continent is melting at an unprecedented rate.  Under what conditions could that fresh water snow melt interfere with the saltwater waterfalls?
The saltwater waterfalls depend on freezing of seawater,  not fresh water, as it its the freezing of sea water which produces both sea ice above at the surface and the heavier salt water that sinks.
As the summer freshwater melt flows to the ocean,  it is likely to stay on top of the water column, at least at first,  but would it still be there come winter time?  How the melt water affects both temperature and salinity in the adjacent ocean would be useful to know. If the low-salt surface melt lingers in the ocean around Antarctica, it could freeze in winter without prompting production of heavier salt water beneath. And that would mean, less of an undersea water fall, less of a driver for ocean circulation.
It had been reported that a layer of Antarctic meltwater has affected the bottom water, slowing the thermohaline circulation.

We are alarmed by the atmospheric disruption from the melting Arctic, but oceanic disruption from a thawed Antarctic hasn’t been given much layperson attention. The implications for climate disruption from perturbed oceans are even more catastrophic than the extreme, but not totally unfamiliar, weather occurring in the Northern Hemisphere from deformation of the northern circumpolar jet stream.

What is the risk of a diminished Antarctic saltwater waterfall?

 Let's hope it keeps working.

(For more on the Arctic, see work by Jennifer Francis at Rutgers and by the team at the Potsdam Institute).

This is an edited revised post, as I didn't have all the bits to include for ocean current links between Antarctic bottom water and the Gulf Stream.

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