  Hadal, more than 6000 m deep shipborne Sea-Bird Electronics SBE 911plus
Conductivity Temperature Depth (CTD) data are obtained using two different
systems in the vicinity of the Earths deepest point, in the Challenger Deep,
Mariana Trench 14 years apart. Below 7000 m in very weakly density stratified
waters, the salinity data from both sets show an artificial increase with depth
of about 10-6 g kg-1 m-1 that is not covered by the SBE linear pressure
correction to the conductivity data. With the aid of independent water sample
data, salinity is corrected and an additional algorithm for the pressure
correction on conductivity data is formulated. The corrected salinity data
still weakly increase with depth, together with a decrease in temperature,
which may point at an influx of dense modified Antarctic bottom water. The
corrected density variations with depth are used in calculations of deep
turbulence values.
