Continuous, Autonomous Measurement of the CO System in Waquoit , MA 2 Reagents and 1 1 2 3 TCO W.R. Martin , F.L. Sayles , D.C. McCorkle , and C. Weidman reference solutions 2 pH 1 Department of Marine Chemistry and Geochemistry, Oceanographic Institution 2 Department of Geology and Geophysics, Woods Hole Oceanographic Institution 3 Waquoit Bay National Estuarine Research Reserve RATS development was supported by awards from the National Science Foundation to FLS,, by a Woods Hole Oceanographic Institution Holger Jannasch Chair awarded to FLS, and by WHOI Coastal Ocean Institute awards to FLS, WRM, and DCM. The Waquoit Bay monthly time series was supported by a NOAA / Sea Grant award to DCM.

35 day RATS deployment in Waquoit Bay A clear diurnal signal in TCO2 and pH, whose intensity varies with incident radiation. Rain Shading shows water depth (tide) Precip. Photosynthesis and respiration cause pH increase

and TCO2 decrease during the day, and the reverse at night. The daily ranges were as much as 600 + µmol/kg in TCO2 and a factor of 10 in [H ].

Groundwater discharge – low salinity at low tide Less pronounced deviations from this signal, Controller & Syringe pump perhaps representing groundwater input, were batteries apparent at tidal frequencies.

The diurnal fluctuations of summertime TCO and The chemistry and biology of coastal systems are impacted by 2 pH were as large as the observed seasonal variations processes occurring on tidal, diurnal, and seasonal cycles, as well as in Waquoit Bay (see 3-year monthly time series). by unpredictable, discrete events. Continuous, autonomous measurements are essential for determining the impact of these processes on carbon cycling and seawater acidity. We deployed RATS, I. Cloudy, rainy II. Bright sun III. Rainy, then sunny Alkalinity (calc) 2200 the Robotic Analyzer for the Total CO2 System in Seawater, to make high-precision, in situ measurements of pH and TCO2, with a ( ) 2000 sampling frequency of 2.5 hours and including on-board calibration, for 35 days in June / July, 2013, in Waquoit Bay, MA. We combined

mol/kg 1800 these measurements with continuous salinity, temperature, water 

depth, and O2 measurements from a YSI sonde deployed by the Waquoit Bay National Estuarine Research Reserve, and with Alkalinity 1600

WBNERR light (PAR) and rainfall data. RATS 0.56 +/- 0.03 1400 Menauhant 1.00 +/- 0.05 0.98 +/- 0.08

1200 1400 1600 1800 2000 2200 RATS methods DIC mol/kg RATS – VINDTA comparison Alkalinity and TCO covary in both data sets; the pH is determined with the (n = 14) 2 lower slope of the RATS data suggests a stronger role spectro-photometric method of Shading shows PAR (daylight) for P / R cycles on diel timescales in the summer. Clayton and Byrne (1993) as TCO2 (RATS(meas)-VINDTA(meas)) implemented by Seidel et al. -0.8 +/- 4.7 µmol/kg (2008), with back-extrapolation of pH vs dye (mCP) concentration to pH (RATS(meas) – VINDTA(calc)) yield pH at 0 dye. 0.0056 +/- 0.0067 3-year monthly time series Linked [O2] & pH cycles

Precision: TAlk (RATS(calc) – VINDTA(meas)) Photosynthesis and respiration couple 1.9 +/- 4.5 µmol/kg pH precision ~ +/- 0.002 pH (and pCO2) and [O2] in Waquoit (in situ pH measurements of Bay on seasonal timescales (left) and Dickson CRMs.) in diel RATS data (below). RATS – SAMI pH comparison (19 day co-deployment) TCO2 is determined from the decrease in the conductivity of a NaOH solution resulting from pH (RATS(meas) – SAMI(meas)) acidification of a sea water sample 0.0048 +/- 0.0042 and passage of CO2 across a semi- permeable membrane into the base

(Sayles and Eck, 2009). Childs RATS River Mollusks use both calcite and aragonite to build their Precision: A three-year monthly time series of alkalinity shells. As CO increases, the concentration of carbonate TCO precision ~ +/- 4 µmol/kg and dissolved inorganic carbon (DIC)2 data from 2 ions in seawater decreases and can potentially affect the (in situ TCO2 measurements of two WBNERR SWMP stations revealed striking annual cyclesmollusks in (calculated) ability topCO produce, pH, a shell. Ocean acidification may Dickson CRMs.) 2 and Ω(Ar)), with strongalso summerinduce variousmaxima physiologicalin changes due to changing pCO and minima in pH and waterΩ(Ar). chemistry The times and associated stresses. Waquoit Bay, MA, showing 2 of highest pCO2 and lowest pH (summer) are the 2013 RATS and YSI not the times of highest DIC and alkalinity Continuous, two-parameter carbonate system measurements will make it deployment site (yellow star) possible to quantify the natural variability in the carbon cycle in coastal concentrations (winter). Instead, the pCO2, pH, and the four WBNERR and Ω(Ar) cycles reflect changes in the waters, to measure net community calcification and net community system-wide monitoring alkalinity:DIC ratio, driven by both CO and production and to quantify the effects of anthropogenic perturbations of the program (SWMP) stations (red 2 Menauhant alkalinity cycles. carbon cycle, including eutrophication and ocean acidification, on coastal pins). ecosystems.