Sea Experiments of the Underway Conductivity-Temperature-Depth Prototype Made in China

A new instrument for upper ocean survey, namely the UCTD （Underway Conductivity-Temperature- Depth）, which combines some of the advantages of other underway instruments, is introduced in this paper. The Introduction section presents a description of the construction and function of the UCTD, and the experiments conducted in the South China Sea on board the R/V Dong Fang Hong 2 in July 2007 and August 2008. The UCTD system, with pressure and temperature sensors in the probe, is con- veniently portable, cost-effective and environment-friendly. It is hopefully suitable for future cruises. An intercomparison based on regressing with the experiment temperature data from both SeaBird plus911 CTD and the UCTD showed that the standard deviation is 0.88~C and the correlation coefficient is 0.96, achieving the goals set for the current oceanography uses. In the hydrodynamic experiments, the descending velocities and depths were calculated for different ship speeds. A pulling test was designed with a tensiorneter to measure the magnitude of the pull. The maximal tension of the line was found to be 66.2 kg, which is far lower than the bearing limit of the Hollow Spectra line. Finally, some improvement suggestions are put forward for future experiments and production.

A unique subseafloor microbiosphere in the Mariana Trench driven by episodic sedimentation

Hadal trenches are characterized by enhanced and infrequent high-rate episodic sedimentation events that likely introduce not only labile organic carbon and key nutrients but also new microbes that significantly alter the subseafloor microbiosphere.Currently,the role of high-rate episodic sedimentation in controlling the composition of the hadal subseafloor microbiosphere is unknown.Here,analyses of carbon isotope composition in a~750 cm long sediment core from the Challenger Deep revealed noncontinuous deposition,with anomalous ^(14)C ages likely caused by seismically driven mass transport and the funneling effect of trench geomorphology.Microbial community composition and diverse enzyme activities in the upper~27 cm differed from those at lower depths,probably due to sudden sediment deposition and differences in redox condition and organic matter availability.At lower depths,microbial population numbers,and composition remained relatively constant,except at some discrete depths with altered enzyme activity and microbial phyla abundance,possibly due to additional sudden sedimentation events of different magnitude.Evidence is provided of a unique role for high-rate episodic sedimentation events in controlling the subsurface microbiosphere in Earth’s deepest ocean floor and highlight the need to perform thorough analysis over a large depth range to characterize hadal benthic populations.Such depositional processes are likely crucial in shaping deep-water geochemical environments and thereby the deep subseafloor biosphere.