Although the ability to undertake autonomous observations of biological and biogeochemical processes is continually improving, many crucial measurements require return of samples to the laboratory for in-depth characterization. However, marine science has been lacking technology to collect/preserve significant volume of discrete water and filtered suspended samples (in situ), in time and space. Ship-based sampling throughout the water column at open-ocean stations is impractical, and at best “snap shots” can be obtained using this approach. The combination of a time-series remote-access sampler (RAS) and water transfer system (WTS) (TS-RAS-WTS combined) fulfills this requirement . Discrete water samples, typically 500 ml, can be preserved with dissolved gas. The in situ pump can be configured to filter particulate matter from 10 liters of water with constant pressure, while maintaining preservative solution if necessary (Fig. 15). Discrete water samples can also be recovered using a modified RAS for microbial and DNA analysis (Automated Microbial Sampler; AMS; Fig. 17). We propose to deploy a mooring with time-series water and particle collectors in depth-series as a critical component of GBF-OOI program. (Mooring D).
This availability of water (dissolved) and particle samples (suspended particles) opens the door for the application of a broad range of geochemical and biogeochemical tracers and probes for characterization of the biological pump. New tracers have emerged that can provide constraints on both the proportion and provenance of materials supplied to intermediate or near-bottom depths, as well as to define overall contributions to the sinking flux. When coupled with the extensive hydrographic information available from adjacent OOI instrumented platforms, these tracers will yield a detailed picture of inputs and transport dynamics of biogenic and lithogenic materials, leading to refined estimates of carbon export at the study sites. For example, natural abundance radiocarbon measurements have proven to be a sensitive and effective means to quantitatively assess contributions of fresh and aged POC and DOC. Associated inorganic tracers (e.g., Al content, Nd isotopes) can provide complementary information on the abundance and provenance of lithogenic particles, and uranium-series radionuclides can place additional constraints on laterally- versus vertically-transported particles. Establishing the horizontal and vertical flux and character of carbon and other components is crucial for accurate parameterization of global models of the oceanic carbon cycle, as well as for paleoceanographic interpretation of underlying sedimentary records.
At a molecular level, specific organic compounds serve as effective tracers of biological source, and extent of organic matter transformation. The former, which primarily utilize lipids as marker molecules, span all three domains of life. Although less phylogenetically diagnostic than genomic markers (DNA), their structures retain a high degree of biological specificity, and have the benefit of persisting despite the overall attenuation in flux. As such, their signature can be traced from the precursor organism, through the water column, and into the underlying sedimentary. Moreover, the isotopic signatures carried by these molecules can provide a further layer of information, particularly regarding the environmental conditions experienced by the precursor organism during growth. The modified version of RAS, can also be used to collect and preserve discrete samples for DNA research (Automated Microbial Sampler, (Fig. 16, 17) enabling genomic studies on deep-ocean microbial populations.