Lakes in the Desert

3 Oct 2012

At http://phys.org/print268301197.html ... an interesting story dating back to the Late Glacial Maximum - when the northern ice sheet reached down to the Great Lakes and beyond. At that time there were lakes in what is now the dry states of Utah and Nebraska, such as Bonneville, Lahontan and the Great Salt Lake, and they were really big lakes holding an enormous amount of water. It has always been thought they were formed as a result of the ice sheet forcing the jet stream to a more southerly position and they clearly represent a quite different climatic system in the region to what it is today. A quarter of what is now Utah and Nebraska was made up of these three giant bodies of water, captured in depressions. An analysis of ocean sediments, dry river valleys and former lake beds, and collated over a period of 30 years, has been put through the ringer to squeeze out some kind of explanation, namely a computer generated simulation created from the data, and published in the journal Science this month. They have ruled out the jet stream as the culprit - in spite of the amount of accummulated water. It is now thought tropical rainfall created the lakes. Rain bearing storms originating in the Pacific and the Caribbean basin are thought to have been responsible - but why didn't the Rockies create a rain shadow as they do now, creating dry weather - but of course a Caribbean origin may take that out of the equation, except the Carribbean was a different animal in the Ice Age, somewhat smaller in size as the islands were bigger, especially the Bahamas.

The idea of Pole Shift was not part of the simulation and is considered such a whacky idea that a lot of scientists get agitated if it is mentioned in their presence. Out of the equation - but is it? We know for example that Alaska and a great part of Siberia were largely ice free in the Late Glacial Maximum (probably not so at other times) and the Artctic Ocean was warmer (a paper a week or so ago) and now we have a desert that once had too much water. A Pole Shift does not just shift the Poles, and Peter Warlow suggested a few years ago that the North Pole was just off the coast of Greenland during the LGM, but it also means the equator was in a different location - and at a different angle as it circled the Earth. It would be skew-whiff to what it is today. For example, in the LGM mango forests grew on the coast of Asia near modern Hong Kong (Imrie) while in what is now a tropical rainforest on Borneo the vegetation was quite different (Imrie once more). Not a lot of work has been done on this subject, or on global sea levels in the LGM. The problem with models is the limitations on data - only so much can be input otherwise they become too complex. Hence, the data is specifically chosen with a view in mind beforehand - although in this instance they were simply testing the jet stream idea and found it wanting. Other scientists may well disagree with the results. We shall see. However, the findings are not contradictory to the idea of Pole Shift and the beast is best where it is used as an explanation for the topsy turvy sea level changes that occurred at the end of the LGM and in the early Holocene. The consensus view of sea level change, as enormous as it appears in some localities, is that it can be explained by a huge ice sheet covering a large portion of the northern hemisphere. Yet there is plenty of evidence to say the ice sheet was quite restricted in geographical terms, and if the recent discovery the Arctic Ocean was somewhat warmer in the LGM this may mean that region was also largely ice free. Not to say it was - but it might have been. If such an idea was part of the computer simulation the model may have come up with a completely different explanation for the actuality of the lakes in Utah and Nebraska. Worth thinking about.