Sarah L. Jacobson, a senior from Chicago who began working on the project as a National Science Foundation Summer Scholar and continued through the academic year, described the U-M team's analysis of sediment samples from a site on the Maud Rise in the Weddell Sea. Because Antarctica is covered with ice, scientists can not study its history with usual surface geology techniques, such as inspecting layers in rock outcrops. Instead, they study it indirectly by examining materials that have eroded from the continent in the past and settled into the surrounding oceans. In warmer, wetter times, soil and rock erode into rivers, which carry sediment into the sea. If ice sheets are present and mobile, the masses of moving ice drag sediment along, and the meltwaters from receding ice sheets help transport sediment from the continent to the sea.
Grain size hints at where sedimentary material came from and how it was deposited.
Very fine dust grains were most likely swept off from dry, desert-like areas by the wind and slowly settled at random on the sea floor, uninfluenced by ocean currents. Medium-sized grains represent mud that flowed out in plumes from rivers or mud that was piled into drifts by currents that flow along the bottom of the ocean floor. Large grains probably were deposited by very fast currents, possibly those that quickly bring material down to the ocean bottom from the continental shelf. Magnetic fabric analysis rounds out the picture by determining the orientation of grains in a sample, which is related to the velocity of ocean currents at the time and place they were deposited, Joseph explains. The faster the current, the more the grains are aligned with one another.