By Joshua Kiesel and Franz Schroeter | We have successfully finished the transit from the 30 to 60 degrees of longitude and are now on the Gakkel Ridge, the doorstep of the North Pole.
The Gakkel Ridge was named, in the 1960s, for a Soviet scientist. In 2001 the research vessels Polarstern and the US-American Healy observed the area closer and found out, that the submarine mountain chain is, in fact, a mid-ocean ridge: an area where the continental plates are pulled apart, and where hot magma rises to the surface, forming new crust. There are therefore hydrothermal vents and undersea volcanos in the area! One of them is of particular interest to Polarstern scientists: Karasik Mountain. This undersea mountain is the literal highpoint of this expedition: it rises from depths of 5000 m (~15,000 feet) to roughly 500 m (~1,500 feet) below the vast icy desert of the sea surface. Because of the remote character of the area, the region is still little-known. As of 2016, however, this fire mountain is going to be better-described. During this expedition the two young scientists of the benthos group have been carrying out an ambitious sediment-sampling program.
So far, they have worked with a tool called the multicorer (MUC) – a sediment sampler which is dropped to the sea floor, where tubes dig into the sediment, extracting sediment cores; watertight lids top and bottom prevent the sediment from leaking out when the MUC is hoisted back aboard Polarstern. However, this approach is not without risk at Karasik Mountain, since the rocky sea floor may damage the corer. They therefore need a more robust tool: the box corer, which looks and works like a clamshell digger.
As the name indicates, it’s a metal box which digs out a defined amount of sediment. The box, initially open at the bottom, sinks into the sediment; the sixth side, the shovel slices in from the side, closing the lower side of the box and thereby securing the sample. If everything has worked well, you have sampled some undisturbed sea floor sediment, with a thin layer of deep sea water on top. Success is, however, not certain, since it is impossible to determine exactly where the box corer will hit the bottom of the sea: steep slopes and big rocks can cause the box corer to tip over, with no sediment being sampled. It was therefore in an atmosphere of some suspense that the benthos group lowered the box corer to the giant seamount. They waited anxiously for any drop in tension on the line, which could tell them that their device had hit the sea floor. Then, to their great relief, the needle on the tension gauge moved, telling them that they had just hit the volcano’s summit. But did the box corer work as expected and gather a sample? Aboard Polarstern they had to keep waiting: when would they finally see the giant metal corer, rising from the dark waters of the deep sea? After waiting for what felt like ages, the heavily-laden box corer was hoisted onto the ship’s deck, ready for processing.
The contents of the box corer might bore many, since it brought up nothing more than slimy mud. But to benthologists, boxcoring is a marvelous way to study various aspects of the sea floor. Many previous Arctic expeditions have extended their knowledge of benthic ecosystem function. However, there are still many questions as to how these processes vary over time and space, especially with respect to changing environmental conditions. The quantification of these dynamics and spatial variations is one of the most challenging aspects of the benthos group’s research. They are also trying to find the factors which make for an especially productive and active sea floor. Is it faunal diversity, or the abundance of a certain species? Or are the ecosystem’s dynamics controlled by external factors, such as sinking algae from upper layers? These are questions of great importance, especially in the context of decreasing sea-ice extent and ocean warming. The major goal of their work is therefore to improve and extend knowledge of sea floor processes, which contributes to our general understanding of polar change. The sample of Karasik Mountain may represent one jigsaw piece we will use to build the big picture of answers to these questions.
We also deployed a mooring at Karasik Mountain. A rope is moored to a weight on the sea floor, and a series of scientific tools (such as a water sampler and sediment traps) and floats are attached to the rope. Between the anchoring weight (three railcar wheels, 300 kg each) and the rope is a releaser, which cuts the instruments loose on a signal from a collecting ship. The mooring instruments will gather data until Polarstern returns next year to recover them. Oceanographers and biologists then want to find out more about the interesting area around this Arctic deep-sea volcano.