Texas A&M University, United States

North Pond is an isolated small sediment pond (8 km X 14 km) located on the western flank of the Mid-Atlantic Ridge (23 degrees N) that offers the opportunity to study microbial communities and their activities in deeply buried sediments and the underlying basement. North Pond has been previously studied by a series of Deep Sea Drilling Project and Ocean Drilling Program drill holes and seafloor observatories. However, the existing site survey data are not sufficient for the approved North Pond Integrated Ocean Drilling Program drilling expedition, scheduled to take place in 2011. Therefore, a site survey cruise on R/V Maria S. Merian (MSM 11/1) took place from 17 February through 12 March 2009 (Fort-de- France, Martinique, to Dakar, Senegal) with the goal of mapping in detail the sediment/basement interface and increasing the heat flow measurement coverage. A set of geophysical survey data was obtained comprising 14 lines (238 km) of multibeam data in combination with single-channel seismics and sediment echo-sounding, 61 successful heat flow measurements, and recovery of 68 m of cores. The survey confirms the existing results based on two seismic profiles from 1989, but the new data show the sediment/basement interface in much more detail. New heat flow measurements complement existing heat flow coverage and confirm the hydrothermal circulation pattern with inflow of cold seawater at the southern rim of the basin and upflow of warm water at the north-northwestern boundary. The new detailed geophysical data set will allow positioning the proposed drill holes and constrain hydrogeological modeling of the circulation in the upper crust.