Determination of the height of deep-sea mooring lines above seafloor using turbulence measurements

Abstract. Height variations O(1) m of closely spaced moored oceanographic instrumentation are difficult to measure in the deep sea, requiring high-accuracy pressure sensors preferably on all instruments in a mooring-array. In this paper, an alternative method for relative height determination is presented using 2 m spaced high-resolution temperature sensors moored on multiple 9.5 m-spaced lines in the deep Western Mediterranean Sea. While it was anticipated that height variations between lines could be detected under near-homogeneous conditions via adiabatic lapse rate O(10−4 °C m−1) by the 3 × 10−5 °C-noise-level sensors, such was prevented by the impossibility of properly correcting for short-term bias due to electronic drift. Instead, a satisfactory height determination was achieved during a period of relatively strong stratification and large turbulence activity. By band-pass filtering data of the highest-resolved turbulent motions across the strongest temperature gradient, significant height variations were detectable to within ±0.2 m.