Optical particle measurements are emerging as an important technique for understanding the ocean carbon cycle, including contributions to estimates of their downward flux, which sequesters carbon dioxide (CO 2) in the deep sea. Optical instruments can be used from ships or installed on autonomous platforms, delivering much greater spatial and temporal coverage of particles in the mesopelagic zone of the ocean than traditional techniques, such as sediment traps. Technologies to image particles have advanced greatly over the last two decades, but the quantitative translation of these immense datasets into biogeochemical properties remains a challenge. In particular, advances are needed to enable the optimal translation of imaged objects into carbon content and sinking velocities. In addition, different devices often measure different optical properties, leading to difficulties in comparing results. Here we provide a practical overview of the challenges and potential of using these instruments, as a step toward improvement and expansion of their applications. Keywords: sinking particle fluxes, sinking velocities, carbon content, size, image processing, automated classification, in situ optical particle measurements, biological carbon pump * Different magnifications available. Quoted details are for the magnification that is most suitable for marine snow.

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Dimethylsulfoniopropionate (DMSP) cleavage was investigated during culture studies of grazing by the microzooplankter Oxyrrhis marina and viral lysis by Emiliania huxleyi virus 86 (EhV-86) on two axenic strains of E. huxleyi. The cleavage products of DMSP, dimethyl sulfide (DMS) and acrylic acid (AA), accumulated during viral infection of both strains, confirming that viral lysis of algae can lead directly to DMSP cleavage. AA and DMS accumulated in parallel with compromised E. huxleyi cells, indicating that DMSP cleavage occurred during the physical disruption of the infected cells. This is in agreement with the hypothesis that DMSP and DMSP lyase ([DL] the enzyme responsible for cleaving DMSP) are segregated in healthy or undamaged cells. During grazing, the concentrations of DMS and AA produced per eaten cell were an order of magnitude higher than the concentrations resulting from cell death caused by viral infection, suggesting that grazing is the quantitatively more significant pathway of DMS production in E. huxleyi. Levels of DL activity decreased in infected cultures to a minimum of 0.00065 fmol cell 21 min 21 as compared with an average of 0.09 fmol cell 21 min 21 in the control cultures, indicating that reduced DL activity in virally infected cells was responsible for the lower levels of DMSP cleavage observed during viral lysis.

focus to leverage long term sustained funding. The next 10 years will be "make or break" for many ocean systems. The decadal challenge is to develop the governance and cooperative mechanisms to harness emerging information technology to deliver on the goal of generating the information and knowledge required to sustain oceans into the future.