The 100th expedition

The aim of the “Greenland ice sheet/ocean interaction and Fram Strait fluxes” (GRIFF) expedition is to conduct investigations regarding the physical, biochemical and biological exchanges between the Arctic Ocean and the Nordic Seas through Fram Strait and to combine them with observations of the interaction between the Greenland ice sheet and the Nordic Seas.

While most participants of the expedition are interested in the seawater itself, the seismologist consider the ocean as an obstacle that obscures the sight of a magnificient submarine mountain range – the Knipovich ridge. Here, the continents of Eurasia and North America drift apart so slowly that magma hardly manages to fill the gap between the diverging plates.

As a result, giant volcanoes form at some places whereas the Earth’s mantle is brought to the surface at other places. This uneven distribution of magma makes the characteristics of the Arctic mid-ocean ridge system and the Southwest Indian Ridge between South Africa and Antarctica to be considerably different from those of all other spreading ridges.

To better understand how new ocean floor is created at these so-called ultraslow spreading ridges, we record the small earthquakes that accompany this process. During the cruise we will deploy 23 ocean bottom seismometers along 180 km of the ridge axis to study the earthquake activity of two volcanoes and the magma-starved region inbetween. The depths of the earthquake foci will allow us to estimate the thickness of the young ocean lithosphere and to determine its temperature.

The earthquake distribution will tell us where active deformation takes place and will delineate areas that deform without any earthquakes, for example if water circulates deeply through the mantle rocks and transforms them into a soft rock called serpentinite. We will use the waves emitted by the earthquakes for a tomographic investigation – just like in medicine – only that our patient is Logachev volcano whose magma interior we want to study.

Ten ocean bottom seismometers have already found their place on the seafloor during the last days. Thirteen more will follow towards the end of the expedition. In about 14 months’ time we will recover the instruments and hope that they will return exciting data from the bottom of the ocean.

Many greetings from board,

Vera Schlindwein, Henning Kirk, Torsten Kanzow AWI