Thursday, July 16, 2015
A new study lead by Ph.D. student Melissa Hansen published in Paleoceanography sheds light on the behavior of the East Antarctic Ice Sheet in a warming world. The Antarctic Ice Sheet is the largest in the world and it has some vulnerable areas where the ice lies below sea level. Today, under the current warming climate, Antarctica is gaining mass at the top due to an increase in snow accumulation, but it is melting from below where warmer ocean water melts the ice. In East Antarctica, snow accumulation exceeds the melt from below, but recent studies have suggested that the future may be different. Ms. Hansen and her co-authors show that when ocean temperatures around Antarctica rose to more than 3 degrees C during past warm periods, the ice mass changed from one purging icebergs into the ocean following glacial rhythms to one with a very different dynamic. These results confirm earlier studies that the East Antarctic Ice Sheet might not be as stable under warmer conditions with consequences for predictions of future sea level rise.
Posted by Sandra Passchier at 1:06 PM
Thursday, February 13, 2014
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):
Posted by Sandra Passchier at 8:45 AM
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.
Posted by Sandra Passchier at 2:22 AM
Wednesday, February 5, 2014
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....
Posted by Sandra Passchier at 12:49 PM
Wednesday, January 29, 2014
We are in Bremen, Germany, at the Onshore Science Party of Expedition 347. We will be processing more than 1600 m of marine sediment core over a period of 4-5 weeks. The cores were retrieved from the Baltic Sea in Sept.-Nov. 2013, which is a brackish sea enclosed by Denmark, Sweden and Finland. Some spectacular core has come up with very distinct changes in sediment color and composition. The Baltic Sea has changed multiple times from a freshwater to a brackish basin due to changes in connections to the open ocean and local sea level changes. In addition, the Scandinavian ice sheet has reached these latitudes during the last Ice Age. We see evidence of these changes in environmental conditions recorded in the cores. Some glacial clays display very nice probable seasonal laminations (varves), as you can see in the image below. We also see very sharp changes in color and sediment composition, which indicate abrupt changes in the paleoenvironment of the Baltic Sea. As sedimentologists we get to spend some time examining the cut surfaces of the cores and we record all the features we see on log sheets. More later...
Posted by Sandra Passchier at 2:11 AM
Tuesday, November 19, 2013
Posted by Sandra Passchier at 7:04 AM