Thursday, February 13, 2014

Expedition 347 was on TV

The number one German newsprogram Die Tagesschau came to record an item about our operation this morning. You can find the newsitem as this link (in German, but the images are a good illustration of what we are doing):

Diamicton: keeping it close to the source

We are logging diamicton, one of my favorites considering its esthetic quality! These sediments were generated by glacial erosion, and probably originate from the Scandinavian Ice Sheet abrading ancient rock surfaces to the north. Baltica, which carried the Scandinavian craton used to be a separate continent before it collided with first Eurasia and then North America (Laurentia) some 400 million years ago. It is composed of the three rock groups: igneous, metamorphic, and sedimentary rocks. Igneous rocks, such as granite were formed through consolidation of magma, metamorphic rocks through a rise in pressure and temperature during  mountain building, and the sedimentary rocks accumulated in ancient basins. Much later, during the last Ice Age, when people were populating Europe, ice sheets plucked rock fragments out of the Baltic Shield and dumped them into the Baltic Sea Basin to form these diamictons. The diamictons are competely barren of macro and microfossils and are only composed of detrital components, meaning rock fragments derived from erosion of pre-existing rock. The rock fragments in the diamicton range from invisible to several centimeters across and are angular and not chemically weathered: we call this an immature sediment. The composition of the diamicton can tell us about the mode of deposition and source regions of the ice, a topic to be studied later in the lab at Montclair State University. For these post-expedition studies, samples are taken. The diamictons are very hard and consolidated and require the sampling team to use hammers as you can see in this picture.

Wednesday, February 5, 2014

Swedish varves

Examining Swedish varves is like eating Dutch Gouda cheese or Russian Kaviar: it is the real thing, not some cheap knock-off! The word varve (varv) has its origin in Sweden and in geology it is used to indicate an annual layer of sediment. In our cores we have been logging what appear to be many different types of varves, but the examples in this picture struck me as the textbook type. Our Swedish co-chief scientist Thomas Andren, a varve specialist, said that the hardcore varve scientists sit and wait for hours next to the core for the sediment to dry out, so that it brings out the contrasting seasonal layers.Varves are the result of seasonal changes in the discharge of meltwater into a lake from an ice sheet or glacier. As the Scandinavian ice sheet retreated it dammed the drainage of water and large proglacial lakes were formed in the Baltic Basin. You can see a picture of an ice-marginal lake here in this photo from a field work in Greenland years ago. Note the dark muddy water: this is the sediment that will slowly sink to the bottom of the lake and form these seasonal layers. In these ice lakes bottom life is very minimal and the sediments hence are preserved due to the absence of bioturbation (animal burrowing). The light-colored somewhat coarser layers are the "summer" layers deposited during peak meltwater discharge bringing sediment of many sizes into the basin. The darker layers are the "winter" layers of fine-grained clay, particles that sink much slower. In the photo to the right, again from Greenland, you can see the brown sediment-laden meltwater emerging from a tunnel in the ice during the summer. During the winter there is not much meltwater and only what is already in the water column of the lakes will slowly contribute sediment to the bottom and form the winter layer. During the winter, lakes are also frozen over, so the water is very quiet and is not stirred by wind-driven waves or currents. What a story, huh, for such a small piece of core! See if you can find the winter and summer layers in our core picture above....