Wednesday, February 08, 2012

Belshaw's World - no wonder it’s cold here

There are many mysteries in the history of the broader New England.

One that I have written about before is the apparent absence of Pleistocene Aboriginal occupation across New England. Now we may have a possible answer.

I need to set the scene first.

From around 36,000 years ago, the Australian climate became cooler and drier. The cooler temperatures offset the lower rainfall by reduced evaporation; the streams, lakes and wetlands of inland New England therefore retained their water, providing a continued base for Aboriginal occupation.

From perhaps 25,000 years ago, the local environment deteriorated significantly.

Sahul, the name given to the continent that then included Australia and New Guinea, became very dry, both intensely hot and intensely cold. This climatic regime peaked during what is called the Last Glacial Maximum, 21,000 to 15,000 years ago.

The sea retreated to perhaps 120 metres below current levels. The sea became colder, 2-4 degrees C below current levels. On land, mean monthly temperatures probably fell by 6-10 degrees C. Extensive inland dune building suggests that the climate become much windier.

According to Mulvaney and Kamminga, severe cold, drought, and strong winds over central and southern Sahul, would have discouraged tree growth , although some species common today must have survived in sheltered or better-watered refuges.

The retreating sea would have progressively increased the size of New England’s coastal strip. The impact here would have varied along the coast, depending upon water depth. In broad terms, the immediately adjacent shallow water to the east of the present coast is quite narrow, with the continental shelf then falling away sharply.

In South East Queensland to the north, the falling waters probably extended the coastal strip to between twelve and twenty kilometres east from what is now Stradbroke Island. Further south the lower water zone narrows, before widening a little after what is now Nambucca. In the case of what is now the Macleay Valley, the coast line probably extended ten to sixteen kilometres to the east.

The sclerophyll woodland and deciduous forests would have progressively colonised the new land, with the coastal dunes and associated wetlands following the shifting coast east.

The Tablelands would have been a very different story. Here average temperatures fell by perhaps 8 degrees C. The New England Tablelands marked the start of a region of cold steppe and scattered sub-alpine woodland sweeping down through the southern Snowy Mountains into Tasmania.

In the southern Snowy Mountains, the fall in temperature was sufficient to allow glaciers to form despite the lower precipitation. In New England, the higher portions of the Tablelands in the centre and south where average heights are around 1,300 metres must have been very cold, dry and windswept. Along New England’s Snowy Mountains where the highest peak (Round Mountain) is almost 1,600 metres, there were probably blizzards and semi-permanent snow despite the much lower precipitation.

To the west, Mulvaney and Kamminga suggest that much of the south-eastern interior of Sahul experienced cold arid conditions similar to modern Patagonia.

So far so good. However, of itself, this does not explain the apparent absence of Aboriginal sites, for there would have been areas where occupation could have continued.

But what might happen if the broader New England and especially the Tablelands were colder than we now realise?

Here Rod H, a geologist and one of my fellow bloggers, has put up a post pointing to evidence of cold climate even glacial features on the Tablelands. Now that’s fascinating, for it may explain the absence of Aboriginal occupation. It was just too darn cold!

If you would like to learn more, the link to Bob’s post is

Note to readers: This post appeared as a column in the Armidale Express on 1 February 2012. I am repeating the columns here with a lag because the Express columns are not on line. You can see all the columns by clicking here for 2009, here for 2010, here for 2011, here for 2012.

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