High-resolution water mass measurements around cold-water corals: a comparative test study between repeated Conductivity-Temperature-Depth (CTD) casts and continuous data acquisition of bottom waters from the West Florida Slope, Gulf of Mexico

Cold-water corals and their associated mounds and reefs attracted a growing number of marine geologists to study these biogenic structures in detail, since these mounds may represent modern analogs to the well-known mound structures from Paleozoic and Early Mesozoic times. A key to better understand the distribution and frame building potential of cold-water corals is to correctly monitor their physical and chemical boundary conditions with new techniques. We performed a comparative test study applying conventional Conductivity-Temperature-Depth (CTD) casts and a newly and self designed mini lander system, which was deployed on the West Florida slope at 531 m water depth for continuous bottom water measurements. Our lander data demonstrate that the mechanical movement of gear disturbs the internal structure of the bottom water mass which requires a certain time to reestablish. This questions the reliability of repeated CTD casts at the same site (yoyo-CTD) with respect to the detailed bottom water mass characteristics bathing the cold-water coral communities. Although, repeated CTD casts may provide information about the amplitude in temperature and salinity variability our data clearly exhibit that temperature and salinity maxima and minima respectively do not coincide with tidal dynamics but depend on bottom water dynamics which are current direction and intensity.