Novel gas-tight multi-sampler for discrete deep-sea water

Abstract

The issues of how to quickly collect seawater samples and of how to make sure that those samples truly reflect the in-situ information on gas composition and concentration have therefore become a hot but difficult topic in the field of ocean technology. Most conventional seawater samplers only focus on collecting seawater itself, but take little consideration on gas preservation. A set of new oceanographic tools are presented for ocean resource exploration such as hydrothermal sulfide and gas hydrate, and for investigations on the processes and mechanisms of marine physical, chemical and biological evolutions. A gas-tight deep-sea water sampling system (GTWSS) is designed for the collection of deep-sea geochemical samples. This set of tools mainly consists of a conductivity temperature depth profiler (CTD), release devices and gas-tight deep-sea water samplers (GTWS). The GTWS is able to hold the gases in deep-sea water samples tightly, providing in-situ information on gas contents in the seawater samples and can be deployed on a routine wire-deployed CTD sampler for multi-layer discrete sampling of gas-tight seawater. Sea trials are performed successfully in 2008 and 2009, on a research vessel named HaiYang Si Hao in South China Sea, with the deepest trial depth 3 930 m. GTWSS is capable of quickly sampling 12 discrete gas-tight seawater samples (8.3 L per sample) during its single deployment. The head space method is employed to separate the gases from the seawater samples immediately after recovery of the seawater samples on the vessel. Field geochemical analysis is carried out by gaseous hydrocarbon sensors and an infrared gas analyzer. Results show that the concentrations of CH4 and CO2 in the seawater sampled by GTWSS are higher than those sampled by general non-gas-tight water samplers, thus confirming the gas tightness of GTWSS. Seawater samples can be collected quickly by using GTWSS, and GTWSS can keep the samples’ integrity quite well.