Water Mass Measurements Around Benthic Communities: A Comparative Study Between Yo-Yo Conductivity-Temperature-Depth (CTD) Casts and High-Resolution Time Series Data Acquisition of Bottom Waters from the Pagès Escarpment in the Southern Bay of Biscay

Abstract

We performed a comparative test study applying conventional Conductivity-Temperature-Depth (CTD) casts and a self designed mini lander system, which was deployed on the Pages Escarpment on the Cantabrian Margin at 762 mbsl water depth for continuous bottom water measurements. Our lander data demonstrate that the mechanical movement of CTD gear disturbs the internal structure of the bottom water mass and extreme values are most likely to be missed. 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 benthic 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 only with the most obvious semi diurnal tidal dynamics but exhibit other tidal frequencies, mainly M4, which are not captured by yoyo-CTD analysis. High resolution CTD measurements in combination with ADCP data reveal a comprehensive picture of bottom water mass dynamics.