An “Apatite” for Mud
February 21st-25th, 2017
The Laurence M. Gould made its way from Vernadsky Station southward to Marguerite Bay slowly navigating through sea ice and larger icebergs. This vessel has a unique shape compared to other research vessels because it needs to be able to break through ice. The hull of the ship is reinforced with extra steel to handle the added force of ice impacts. In addition, it has a shallow sloping hull that acts to direct ice beneath the ship as well as to the sides. In thick sea ice, the bow of the ship rides up on top of the ice which then breaks under the weight of the ship. In thick sea ice conditions it may be necessary for repeated backing and ramming motions to eventually break and push the ice away. These operations reduce the speed of the vessel to as little as 0.5-1 knot (0.5-1 nautical mile per hour) whereas the typical clear steaming speed may be 10 knots or more.
After navigating through the ice in Neny Fjord, we arrived at the desired sampling location. Two scientists aboard, Anna Clinger (UC Berkeley) and Matthew Fox (UC Berkeley and University College London) are collecting seafloor sediments with the box core to look for a mineral called Apatite. This mineral has properties which allow the group to determine the temperature at which it was deposited which further informs them about the geologic landscape from which it came. In order to box core in this fjord, however, we needed to conduct a SONAR survey so we could find a soft sediment pool deposited by the glacier inside the fjord otherwise the box core could be damaged by hard rock and we would not retrieve a useful sample. The reflection of sound sent out by the ship tells us information about the seafloor including whether it is flat or sloped, and soft mud or rocky. After running several survey tracks we had located what seemed like a suitable, flat sediment pond. To confirm that the bottom was soft mud and not laced with dropstones (rocks that fall from melting icebergs), we used a camera towed from the ship to take a look at the seafloor. From the camera footage we could see a soft muddy bottom perfect for coring! We repositioned the ship over the location we had surveyed and deployed the box core (see archived posts about how a box core works). 30 minutes or so later, we retrieved a wonderful sediment sample. Back in the lab at UC Berkely, the group will search through the mud for very small grains of apatite and begin to piece together the fjords’ erosion and formation history.
The group collecting the mud also graciously offered the FjordEco team the top 5 or 10 cm of mud to be used for biology. We then sieved the mud through a 300μm sieve to collect animals considered “macrofauna”. A wide diversity of these animals, such as polychaete worms and crustaceans, live within the mud and can exist in very high abundances and represent a large biomass. The samples we collect from farther south along the peninsula will be an interesting comparison to Andvord Bay.
We have now left Neny Fjord and are heading back north along Adelaide Island to our next sampling location in Lallemond Fjord. Here we will once again survey the seafloor and use the box core to collect mud from another glacial fjord. We are spoiled in these fjords with glass calm seas, gorgeous scenery and a bounty of wildlife.