Lab-on-Chip for In Situ Analysis of Nutrients in the Deep Sea.

Microfluidic reagent-based nutrient sensors offer a promising technology to address the global undersampling of ocean chemistry but have so far not been shown to operate in the deep sea (>200 m). We report a new family of miniaturized lab-on-chip (LOC) colorimetric analyzers making in situ nitrate and phosphate measurements from the surface ocean to the deep sea (>4800 m). This new technology gives users a new low-cost, high-performance tool for measuring chemistry in hyperbaric environments. Using a combination of laboratory verification and field-based tests, we demonstrate that the analyzers are capable of in situ measurements during profiling that are comparable to laboratory-based analyses. The sensors feature a novel and efficient inertial-flow mixer that increases the mixing efficiency and reduces the back pressure and flushing time compared to a previously used serpentine mixing channel. Four separate replicate units of the nitrate and phosphate sensor were calibrated in the laboratory and showed an average limit of detection of 0.03 µM for nitrate and 0.016 µM for phosphate. Three on-chip optical absorption cell lengths provide a large linear range (to >750 µM (10.5 mg/L-N) for nitrate and >15 µM (0.47 mg/L-P) for phosphate), making the instruments suitable for typical concentrations in both ocean and freshwater aquatic environments. The LOC systems automatically collected a series of deep-sea nitrate and phosphate profiles in the northeast Atlantic while attached to a conductivity temperature depth (CTD) rosette, and the LOC nitrate sensor was attached to a PROVOR profiling float to conduct automated nitrate profiles in the Mediterranean Sea.

Technologies for retrieving sediment cores in Antarctic subglacial settings.

Accumulations of sediment beneath the Antarctic Ice Sheet contain a range of physical and chemical proxies with the potential to document changes in ice sheet history and to identify and characterize life in subglacial settings. Retrieving subglacial sediments and sediment cores presents several unique challenges to existing technologies. This paper briefly reviews the history of sediment sampling in subglacial environments. It then outlines some of the technological challenges and constraints in developing the corers being used in sub-ice shelf settings (e.g. George VI Ice Shelf and Larsen Ice Shelf), under ice streams (e.g. Rutford Ice Stream), at or close to the grounding line (e.g. Whillans Ice Stream) and in subglacial lakes deep under the ice sheet (e.g. Lake Ellsworth). The key features of the corers designed to operate in each of these subglacial settings are described and illustrated together with comments on their deployment procedures.

Probe technologies for clean sampling and measurement of subglacial lakes.

It is 4 years since the subglacial lake community published its plans for accessing, sampling, measuring and studying the pristine, and hitherto enigmatic and very different, Antarctic subglacial lakes, Vostok, Whillans and Ellsworth. This paper summarizes the contrasting probe technologies designed for each of these subglacial environments and briefly updates how these designs changed or were used differently when compared to previously published plans. A detailed update on the final engineering design and technical aspects of the probe for Subglacial Lake Ellsworth is presented. This probe is designed for clean access, is negatively buoyant (350 kg), 5.2 m long, 200 mm in diameter, approximately cylindrical and consists of five major units: (i) an upper power and communications unit attached to an optical and electrical conducting tether, (ii)-(iv) three water and particle samplers, and (v) a sensors, imaging and instrumentation pack tipped with a miniature sediment corer. To date, only in Subglacial Lake Whillans have instruments been successfully deployed. Probe technologies for Subglacial Lake Vostok (2014/15) and Lake Ellsworth (2012/13) were not deployed for technical reasons, in the case of Lake Ellsworth because hot-water drilling was unable to access the lake during the field season window. Lessons learned and opportunities for probe technologies in future subglacial access missions are discussed.

Reconciliation of the carbon budget in the ocean's twilight zone.

Photosynthesis in the surface ocean produces approximately 100 gigatonnes of organic carbon per year, of which 5 to 15 per cent is exported to the deep ocean. The rate at which the sinking carbon is converted into carbon dioxide by heterotrophic organisms at depth is important in controlling oceanic carbon storage. It remains uncertain, however, to what extent surface ocean carbon supply meets the demand of water-column biota; the discrepancy between known carbon sources and sinks is as much as two orders of magnitude. Here we present field measurements, respiration rate estimates and a steady-state model that allow us to balance carbon sources and sinks to within observational uncertainties at the Porcupine Abyssal Plain site in the eastern North Atlantic Ocean. We find that prokaryotes are responsible for 70 to 92 per cent of the estimated remineralization in the twilight zone (depths of 50 to 1,000 metres) despite the fact that much of the organic carbon is exported in the form of large, fast-sinking particles accessible to larger zooplankton. We suggest that this occurs because zooplankton fragment and ingest half of the fast-sinking particles, of which more than 30 per cent may be released as suspended and slowly sinking matter, stimulating the deep-ocean microbial loop. The synergy between microbes and zooplankton in the twilight zone is important to our understanding of the processes controlling the oceanic carbon sink.