Further correcting pressure effects on SBE911 CTD-conductivity data from hadal depths

TL;DR

This paper develops an improved pressure correction algorithm for deep-sea CTD conductivity data, addressing artificial salinity increases at hadal depths and enabling better analysis of deep ocean turbulence.

Contribution

It introduces a new algorithm for correcting pressure effects on conductivity data at extreme depths, improving data accuracy for hadal ocean research.

Findings

Artificial salinity increase with depth is corrected using the new algorithm.

Corrected data reveal potential influx of dense Antarctic bottom water.

Enhanced turbulence calculations based on corrected density profiles.

Abstract

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.