Wednesday, 27 April 2011

The Baltic Waters - Pool, Lake, Ocean?

A sea day like from the catalogue - sunshine, sunshine, sunshine. Phew, a lot of free time ahead. What a happy problem to have. So, while the day passes with books and meals and music and lectures (being lured into the lecture hall by creative lecturers) and waffles and watching the world go by, let's use the occasion to learn a little about this big mass of water we are currently travelling. Let's go back in time:
Map: Ron Blakey
When the world was very much younger, the continents had a completely different shape, size, and especially location. During their errands across our planets surface, driven by the slow but inexorable forces of mantle convection, they sustained many collisions, one of them known as the Caledonian Orogeny, the one that pressed North America against the Baltic parts of Europe and formed a mountain range that encompassed parts of Scotland (Caledonia) but also the entire front of western Norway. This big and in many places highly deformed block was connected to what is today central and southern Europe by a big fault line (Tornquist-Tesseire fault) that scarred the baserock from NW to SE over a long distance and will gain importance later on. These European masses were subjected to another, younger collision, which did not affect the northern parts significantly. It is only important to know that the aforementioned fault worked as a hinge around which the whole   system spun. The hinge itself subsided and formed a depression which subsequently was filled with sediments and is the weakness zone that shall - a long time after - turn into the Baltic sea.
Let's give the continent a break: Let the huge mountain ranges that span from southern England through Belgium down to Bohemia be levelled and carried away by erosion over time, let the oceans rise and fall again, watch the dinosaurs and many other species getting extinct by large-scale climatic events and impacts, witness a strange kind of mammal appear on the stage that walks on its hind legs, look how the continents assume their final position. And then it is time for ice. Enormous sheets of snow piling up in the North, being compressed to solid ice and forced across the land by its own weight, travel down south, doing many things at the same time:
The ice crushes everything that is in the way, carrying the self-made debris over long distances, using it as grinding material when it cuts into higher areas to make fjords, or just  drop it somewhere else, where we find it today as moraine, sander or one of the impressive erratic blocks that are spread out over northern Europe.

When the ice finally retreated, enormous amounts of water were released and filled a shallow basin that had opened right on top of the weakness zone that once was the big fault line, scooped out by the passing ice - the Baltic sea. Please do not take "sea" in the same meaning as "ocean", for this basin contained nothing but meltwater, no salt whatsoever. Only very late, about 9000 years ago (which is practically today after lunch, in geological terms), a tiny connection opened up towards the North Atlantik, bringing in small amounts of salt water, flowing around Denmark.
So what we are crossing today is actually the worlds largest reservoir of brackish water, widely devoid of the abundance of life that is to be found in the depths of a "real" ocean. Speaking of depth: The Baltic "Sea" is very, very shallow, only 52 meters in average. But this won't surprise us anymore now, will it? Now that we have learnt about its origins.

Oh, yes, and then there was the fashion show at night...