Integrating and ground truthing the profiling float microrosette

University Of California-San Diego Scripps Inst Of Oceanography, La Jolla CA

Investigators

Abstract

The autonomous profiling float platform provides the potential for orders-of-magnitude improvement in ocean observing, relative to ships. This fact has already been realized by physical oceanographers studying the ocean heat budget and large-scale mixing processes and is now gaining momentum in the ocean biogeochemistry and ecological modeling communities. The development of new chemical sensors for measurement of CO2 dissolved in the ocean will improve our ability to quantify globally significant biogeochemical processes such as annual net community production in the ocean; and, in addition, the process of ocean acidification which is considered to be one of the most significant anthropogenic threats to the marine ecosystem. This research will develop a new technology known as the Micro-Rosette which will ultimately contribute a new tool to the short list of sensors available for integration into autonomous profiling floats. The Micro-Rosette is a device intended to operate specifically on board a profiling float. The system captures sub-milliliter volumes of seawater at pre-determined depths, stores the samples for a period of time, analyzes all of the discrete seawater samples ex situ (at the park depth), ejects them, and then repeats the cycle. When combined with a typical profiling float cycle, this approach adapts to the float's ascent/decent/park cycle, taking advantage of the multi-day park cycle to perform all of the chemical analyses. Determination of dissolved inorganic carbon is accomplished through acidification of the seawater sample, equilibration across a gas-permeable membrane, and quantification via a conductivity measurement. The Micro Rosette is purposefully built for profiling floats, and by taking advantage of the extended park cycle to carry out chemical analyses, this approach embraces the fact that many chemical analysis techniques require a time-dependent reaction or diffusion step leading to response times that make such analyses poorly suited for on-the-fly measurements. The application of this research is the measurement of total dissolved inorganic carbon, but the concept of a micro-rosette system is well-suited to several other types of analyses such as ammonia, organic carbon, and iron, and may potentially lead to a new family of profiling-float-ready wet chemical analyzers.