Valdes James R.

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Valdes
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James R.
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Author: Fucile, Paul D. ×

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  • Preprint
    An autonomous, in situ light-dark bottle device for determining community respiration and net community production
    ( 2018-03) Collins, James R. ; Fucile, Paul D. ; McDonald, Glenn ; Ossolinski, Justin E. ; Keil, Richard G. ; Valdes, James R. ; Doney, Scott C. ; Van Mooy, Benjamin A. S.
    We describe a new, autonomous, incubation-based instrument that is deployed in situ to determine rates of gross community respiration and net community production in marine and aquatic ecosystems. During deployments at a coastal pier and in the open ocean, the PHORCYS (PHOtosynthesis and Respiration Comparison-Yielding System) captured dissolved oxygen fluxes over hourly timescales that were missed by traditional methods. The instrument uses fluorescence-quenching optodes fitted into separate light and dark chambers; these are opened and closed with piston-like actuators, allowing the instrument to make multiple, independent rate estimates in the course of each deployment. Consistent with other studies in which methods purporting to measure the same metabolic processes have yielded divergent results, respiration rate estimates from the PHORCYS were systematically higher than those calculated for the same waters using a traditional two-point Winkler titration technique. However, PHORCYS estimates of gross respiration agreed generally with separate incubations in bottles fitted with optode sensor spots. An Appendix describes a new method for estimating uncertainties in metabolic rates calculated from continuous dissolved oxygen data. Multiple successful, unattended deployments of the PHORCYS represent a small step toward fully autonomous observations of community metabolism. Yet the persistence of unexplained disagreements among aquatic metabolic rate estimates — such as those we observed between rates calculated with the PHORCYS and two existing, widely-accepted bottle-based methods — suggests that a new community intercalibration effort is warranted to address lingering sources of error in these critical measurements.
  • Technical Report
    An FSK telemetry module for vector measuring current meters
    (Woods Hole Oceanographic Institution, 1987-12) Fucile, Paul D. ; Valdes, James R.
    The EG&G Vector Measuring Current Meter (VMCM) used in mooring work provides a 20 ma Serial ASCII Instrumentation Loop (SAIL) communication system. A projected application of the VMCM is to have a surface mooring communicate with a series of VMCMs via a Frequency Shift Keying (FSK) link. While an FSK modem can communicate with the VMCM. a problem exists with the general operation of the VMCM. If the VMCM is addressed to dump data; it remains on until the unit is re-addressed. If a failure in the link occurs. then the VMCM stays on in . a higher power mode and the batteries will be depleted early. The insertion of a processing block between the modem the VMCM provides a way to look at incoming data. qualify it re-transmit it to the VMCM. The VMCM will reply and preprocessor can channel the data to the modem. In the event VMCM malfunction. the preprocessor has a timeout function will turn off the carrier keeping the line quiet.