10th November: Vema Ridge

Moin moin Vema!

After a 4-day transit which included a small bonfire festivity we arrived just this morning at our next sampling location: the Vema transform fault. This transform fault displaces the Mid-Atlantic Ridge (MAR) axis by about 300 km (i.e. more than Ireland’s W-E extension). The MAR is a volcanic spreading axis in the Atlantic Ocean, separating the African and South American plates. The entire fracture zone extends over >2000km from east to west with a full spreading rate of about ~27 mm/yr, i.e. the two plates move apart with a “speed” of 27 mm/year. The geological evolution in time and space was accompanied by the formation of a spectacular submarine V-shaped transform valley. The southern wall of this valley is the result of the uplift of a single block of mantle material starting about 50 million years ago and currently erecting up to >4 km from bottom to top being one of the highest and longest ridges in the entire MAR system – and it may even have reached the sea surface in the past! The northern wall consists of exposed (oceanic) crust of 2-3 km thickness being slightly less spectacular compared to its southern counterpart.

Besides spectacular geology the Vema frature zone is also very interesting from an oceanographic point of view. It acts as a channel for deep and bottom water masses between the western and the eastern Atlantic basins allowing northwards flowing bottom water masses from Antarctica to pass the MAR and enter the deep East Atlantic Ocean.

Hence, during the next few days we will run the full range of equipment we have onboard the James Cook in order to collect (hopefully) loads of precious samples: starting off with a deep CTD profile this morning we aim to deploy the ROV and to raise some sediment cores in order to shed some light on this spectacular key deep-sea location in the equatorial Atlantic Ocean!

Blog Written by: Torben Struve

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