RRS James Cook Cruise JC55, 13 Jan-22 Feb 2011. Bransfield Strait, the East Scotia Ridge and the Kemp Seamount Calderas, Cruise 3 of the NERC Consortium Grant ‘Chemosynthetically-driven ecosystems in the Southern Ocean: Ecology and Biogeography’ (ChEsSo).

Abstract

The whole programme of JC55 changed with the extensive damage to the ROV Isis on day 5 of the 42-day cruise. As a result Plan B, an over-the-side science programme was put in place and sampling with CTD/SAPs, Megacore, gravity cores and SHRIMP. This limited a number of aspects of the sampling and visual observation of the seabed but resulted in a programme that achieved a remarkably high proportion of the objectives of the cruise. In the Bransfield Strait some hydrothermal activity was observed at Hook Ridge, together with areas of reducing sediment but no areas of extensive hydrothermal activity. A Middle Sister a small anomaly in the Eh readings on the CTD suggested hydrothermal release but visual observation of the seabed showed only sedimented and old areas of pillow lava. At the Axe (aka Edifice A), despite extensive CTDs, there was no evidence of any modern hydrothermal activity. At the three sites we did obtain excellent samples for geochemical and water analysis, as well as samples for microbial analysis, macrofaunal and isotope analysis. Megafauna and mosaic analysis was not possible because of the loss of use of Isis. On moving to the East Scotia Ridge at E9 we were able to use SHRIMP to locate the Twin Peaks area (first sighted in 2009) and obtain a third annual set of images over a specified area. Additional exploration did not find any additional vents to those found on JC42. Water column sampling in the plume for chemistry and microbiology was successful. At the Kemp seamount crater there were successful stations for water chemistry and microbiology. A long SHRIMP transect over the venting area within the caldera was particularly successful and this together with fine scale mosaicking gave a clear map of this venting field. Planned fine scale sampling and ROV swath could not be completed. A SHRIMP transect at the nearby recently-mapped Adventure caldera discovered a small vent site on the southern side of the crater. Lastly, we returned to the putative cold seep site off the southwestern end of South Georgia. High CH4 levels in the water column and reduced sediment in cores suggested methane release but two SHRIMP surveys revealed no evidence of surface expression of a cold seep.

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