THE SOUTHERN OCEAN IS WARMING UP

 

A Report for BBC World Service “Calling the Falklands” by Dee Palmer (DP) 25/10/05

 

The waters of the Southern Ocean are warming up and the affect is being felt as far north as the Falklands, though the higher temperatures are most marked on the west of the Antarctic Peninsula.  That’s a conclusion of new research from the British Antarctic Survey (BAS).  We already knew that air temperatures over the Peninsula have risen markedly and that sea ice cover around it is shrinking.  But the study lead by John King (JK) is the first to show an increase in sea temperatures.

 

JK:  For summertime sea temperatures – it’s about 1C over 40 or so years, which doesn’t sound very large but, in fact, there is very little year to year variations in sea temperatures so that is actually quite a big change.

 

DP:  And, have you discovered anything else about the sea water?

 

JK:  We’ve also discovered that during the summertime the surface sea water is getting more salty.  Important to that is that it suggests that there have been big changes in the extent of winter sea ice to the west of the peninsula during the winter – that the seas west of the peninsula freeze up and there is a fairly extensive cover of sea ice in most winters.  During the summertime all that ice melts and dumps a load of fresh water into the surface waves of the ocean.  Now, if there is not as much sea ice forming during the winter, then you get less fresh water into the surface ocean during the summer and so the surface ocean appears to becoming saltier.

 

DP:  Now if I remember my basic physics, that also means that that surface water, which is a bit saltier, won’t freeze at 0C like pure water.  It’s actually going to freeze at a slightly lower temperature.

 

JK:  That’s right.  It makes it more difficult for sea ice to form in the next winter and we have what we call a positive feedback effect.  Once you’ve started this process it goes on happening more and more.

 

DP: How certain are you about these changes, John?

 

JK:  They are based on rather sparse measurements.  The oceans to the west of the peninsula aren’t well measured.  You have a number of ships visiting the area most summers and some of those make measurements of sea temperatures at various depths and the saltiness of the water as well.  The measurements are rather patchy but we have been basing our studies on an excellent new atlas that American colleagues of ours have put together all of the measurements that have been made by ships over the years in this region.  I think once you put all these things together you see a very clear pattern emerging and so you can be pretty certain  that this is a real trend.

 

DP:  Now I am looking at a segment of one of these maps and it shows that although it is the waters of the west of Antarctica that have warmed up most there also seems to have been a very slight warming of the water around the Falklands.  Is that the ase?

 

JK:  That’s right.  The biggest warming certainly has been to the west of the peninsula and fairly well south but we know that the way that the ocean works in this region is that if you effect what is going on in the west of the peninsula there will be a gradual drift northwards of those waters from that region and, indeed, they will be drifting towards the Falklands.  Maybe this isn’t the whole story of what’s going around the Falklands but it’s probably having some impact on it.

 

DP:  What could be the long-term affects on marine creatures if the waters around Antarctica start warming up?

 

JK:  Antarctic marine ecosystems are really very sensitive to changes in temperature and other aspects of the particular environment.  We know that the area to the west of the peninsula is a very important breeding ground for Antarctic Krill and, of course Krill is right at the heart of  the food web for many Antarctic ecosystems.  And, biologists believe sea ice covers the west of the peninsula is absolutely crucial to the breeding success of Krill.  So if we reduce that sea ice cover by warming up the atmosphere or ocean, then we are likely to have an impact on Krill populations and that will be seen right up through the food chain in the Antarctic.