By Birgit Heim |
Seamounts are isolated submarine topographic elevations in the open ocean. They often originate from submarine volcanism, created over so-called hotspots in the upper mantle of the earth or along the mid-ocean spreading ridges. However, little is known about these seamounts and how they affect the physical, chemical, and biological environment. For example, it is likely that they have an effect on ocean currents, or modulate the upwelling of nutrient-rich waters. A particular characteristic is the development of a so-called Seamount Summit Water Layer, at the top, thereby creating rather untypical conditions in an otherwise open ocean setting.
On our south-bound journey, we passed by the Ampere Seamount which is located 600 km to the West of Gibraltar. It rises from a water depth of 4.7 km to 60 m below the surface (Oceanic Seamounts: An integrated Study OASIS). The Ampere Seamount has been the subject of previous cruises with RV Polarstern using echo-sounding techniques which resulted in a detailed topographic map. Ralf, the responsible person for the data management onboard RV Polarstern, explains the bathymetric data: “While the Eastern and Southern sides of the Ampere Seamount consist of steep flanks, it has rather low slopes toward the North and West”.
Catalina from the AWI Geophysics group explains: “Data from the Multibeam Echosounder reveals the submarine bottom topography. With the sediment Echosounder, we can even look into the uppermost sediment layers. While sailing over the Ampere Seamount, we could see that it is made of a hard material. In shallow water – like over the summit of the sea mount – the sediment Echosounder can also show the different water layers.” Sebastian, from FIELAX company, indicates the clearly separated seamount Summit Water Layer to us on his computer screen. Pauhla (SMART Ireland) from the oceanography team gets excited because it is so different.
Both the oceanography and biology groups carryout a first CTD depth profile for water samples at five km depth in the deep ocean. The next station ‘up the hill’ is on the slope of the Ampere Seamount in only 1.7 km water depth. At this location on the north-western slope of the Ampere Seamountwe sampled the same depth profile both during the day and during the night in order to investigate the daily, vertical migration of zooplankton and phytoplankton. The most shallow station measures a water depth of only 100 m (please remember we are in the middle of the open ocean). The next depth profile is again ‘down the hill’ at the steep south-eastern slope of the Ampere Seamount with a depth of 1.7 km.
The resulting pile of water samples is being processed in the labs by our students that work with great enthusiasm during day and nightshifts – with on-time meals becoming a rare luxury. Eventually one of the microscopes for phytoplankton analyses simply gave up- the power source exploding with a bang. Next day however it was back to normal functioning thanks to the expert skills of the Polarstern electrician, for which we were very grateful. The sea round the Ampere seamount seemed, in comparison to the desert around us, to be teeming with life, and birds and fish were all around us. We will get back to you with the findings of our data in the next blogs!