pCO2 time series ground truthing and internal consistency at the Gray’s Reef mooring (NDBC-41008) in the South Atlantic Bight

Janet Reimer1, Wei-Jun Cai1, Scott Noakes2, Xinping Hu3, Baoshan Chen4, Aleck Zhaohui Wang5, Liqing Jiang6, Joseph Salisbury II7, Richard H Wanninkhof8, Leticia Barbero8, Richard A Feely9, Adrienne J Sutton10, Jeremy T Mathis11 and Christopher L Sabine9, (1)University of Delaware, School of Marine Science and Policy, Newark, DE, United States, (2)The University of Georgia, Center for Applied Isotope Studies, Athens, GA, United States, (3)Texas A&M University - Corpus Christi, Physical and Environmental Sciences, Corpus Christi, TX, United States, (4)University of Georgia, Athens, GA, United States, (5)Woods Hole Oceanographic Institution, Marine Chemistry and Geochemistry, Woods Hole, MA, United States, (6)National Centers for Environmental Information, Silver Spring, MD, United States, (7)University of New Hampshire, Durham, NH, United States, (8)Atlantic Oceanographic and Meteorological Laboratory, Miami, FL, United States, (9)NOAA Pacific Marine Environmental Laboratory, Seattle, WA, United States, (10)University of Washington, Joint Institute for the Study of the Atmosphere and Ocean, Seattle, WA, United States, (11)NOAA Seattle, Seattle, WA, United States
Abstract:
Periodic cruises allow us to ground truth autonomous moored time series of pCO2 via underway system measurements and discrete bottle samples for carbonate parameters (DIC, TA, pH). These time series are essential for monitoring ocean acidification (OA), yet their performance with respect to internal consistency is not yet widely documented. During cruises we focus extra effort at the Gray’s Reef (GR) mooring to ground truth and perform inter-consistency checks on our instrumentation by collecting water samples for carbonate parameters as well as underway pCO2. We remain as close to the GR mooring as possible for an extended period, up to several hours. Cruises include seasonal 2005-2015 and the three major east coast efforts: GOMECC I (Aug. 2007), GOMECC II (Aug. 2012), and ECOA (July 2015). We compare mooring and underway observations, which for the three major cruises agreed within ±8 µatm, with differences likely due to spatial heterogeneity and known system uncertainty. With bottle data we also calculate pCO2 from the DIC-TA pair, for which we have the most observations, which agrees with the mooring within ±17 µatm, approximately ¼ of the mean daily variability of the GR mooring time series (2006-2014). One of the goals of autonomous moored time series is to use continuous salinity to estimate TA (using known regional linear models), then use TA and pCO2 to calculate the other parameters. An internal consistency check for the three major cruises between the various discrete measured parameters and calculated mooring parameters all result in Ωar values, the OA biological measure, within the best-practices uncertainty range of ±0.2 units. These preliminary results GOMECC’s I and II and ECOA show that the mooring time series can be used to calculate DIC, TA, pH, Ωar, however ongoing work seeks to incorporate smaller scale regional cruises. Finally, this work may be a guide in other regional intercomparisons across platforms.
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