Figure 4- Seasonal high-flow events appear to coincide with decreased pCO2. From late fall through mid-spring the Kennebec Estuary appears to be a modest sink for atmospheric CO 2, while from late spring through mid-fall the estuary is apparently a moderate source of CO 2 to the atmosphere. Study Area and Data Collection The Kennebec Estuary in west-central Maine drains approximately 25,000 km^2, making it one of the largest contributors of fresh water to the Gulf of Maine system. Peak river flow generally occurs during spring snowmelt, and is a strong source of fresh water and terrestrial material to the Gulf of Maine (Oczkowski et al 2006). We have performed monthly surveys of the physical, chemical, and optical properties of the Kennebec Estuary and nearby coastal waters for three years (2005 and 2006 presented here), using both continuous-flow and discrete methods, as part of UNH’s Coastal Ocean Observing Center’s monthly Coastal Transect cruise. The data presented here were gathered from the following sources: Continuous along-track measurements of the surface partial pressure of carbon dioxide (pCO2), using a fast-rate equilibrator and IR gas analyzers, with on-board atmospheric pressure measurements. Intake depth= 0.7m. Along-track salinity and temperature. Discrete total alkalinity (TA, measured by Gran titration) and pH. River flow data from USGS gage # ( Kennebec River at North Sidney, Maine) Data processing performed: pCO2 measurements were matched with daily USGS discharge, and binned in 5-psu increments. A median value for these 5-psu bins was then computed. Conservative pCO2 was calculated over the salinity gradient using the following endpoints: River endpoints at zero salinity was derived from discharge and the presented curve. The lowest observed salinty, and pCO 2 at this salinity, were used to estimate TA and pH. The TA and pH at the oceanic endmember were estimated from salinity and pCO2. TA and pH were allowed to mix conservatively over the salinity gradient for each cruise, and conservative pCO 2 was calculated for each data point of corresponding salinity and temperature. All these data and much more are freely available at our group’s website: cooa.sr.unh.edu Objectives At present, a thorough understanding of the transfer of carbon across the land-ocean interface has not been developed. An important part of this transfer is the interaction of carbon dioxide (CO 2 ) - rich estuarine water with the atmosphere. This work represents part of an ongoing study addressing several key carbon transport issues: Does the Kennebec Estuary, a temperate Northeastern U.S. estuary, act as a source or sink of atmospheric CO 2 ? Does the interaction between the Kennebec Estuary and the atmosphere vary on a spatial or temporal basis? Do changing climatic conditions (in this case, discharge) act as a control upon carbon dioxide expression in this estuary? Can we estimate how future climate changes might affect estuaries of this type? Chris Hunt 1, Joe Salisbury 1, Doug Vandemark 1, Janet Campbell 1, Wade McGillis 2 1 Coastal Ocean Observing Center, University of New Hampshire 2 Lamont Doherty Earth Observatory, Columbia University How might Kennebec Estuary pCO 2 look in 100 years according to climate predictions? Kennebec Estuary Gulf of Maine Nova Scotia References Borges, A.V Do we have enough pieces of the jigsaw to integrate CO2 fluxes in the coastal ocean? Estuaries 28: The New England Regional Assessment of The Potential Consequences of Climate Variability and Change Oczkowski, A.J. Pellerin, B.A. Hunt, C.W. Wollheim, W.M. Vorosmarty, C.A. Loder, T.C The role of snowmelt and spring rainfall in inorganic nutrient fluxes from a large temperate watershed, the Androscoggin River basin (Maine and New Hampshire). Biogeochemistry. 80: Acknowledgments Thank the crew of the Gulf Challenger, and the rest of the COOA team who brave the seas every month. Thanks also to the workers in the lab who get our samples run with care and dedication. Observations Median, binned pCO2 shows general decreases with decreasing salinity (Figure 4) The Kennebec Estuary appears to be a net source of CO 2 to the atmosphere, which is not unusual among other estuary studies found in the literature (see Borges 2005). However, at certain time of the year pCO 2 levels drop below mean atmospheric levels, indicating CO 2 uptake by the estuary Support for this work was provided by the NOAA Coastal Services Center through an award to the UNH Coastal Ocean Observing Center, NOAA Award NA16OC2740. Figure 2- Discharge curve for the Kennebec River, with survey cruise dates indicated Figure 3- Relationship between endmember (zero salinity) TA and discharge Figure 1- Map of study area within the Gulf of Maine (left), with the Kennebec Estuary circled. our fast-rate CO 2 equilibrator (top left) was deployed aboard the UNH R/V Gulf Challenger for this work. Salinity Range Mean pCO2 pCO2 at current mean Q Estimated pCO2 with +10% discharge Estimated pCO2 with +30% discharge Atmospheric pCO2 in 100 years psu psu psu Salinity pCO2 (uatm) Observed pCO2 Conservative pCO2 pCO2 anomaly = (observed pCO2) – (conservative pCO2) Figure 5- The median pCO2 for each salinity bin decreases with increased river flow. Two models described in the New England Regional Assessment of The Potential Consequences of Climate Variability and Change predict regional precipitation increases of 10% and 30% in the next century. If we equate a precipitation increase with discharge, we predict decreased river-borne pCO2. Combined with an expected increase in atmospheric pCO 2 (data from Mauna Loa, Hawaii), estuarine pCO2 levels would become sub-atmospheric. Thus the Kennebec Estuary could shift from a CO 2 source to a CO 2 sink under some climate change scenarios. Figure 6- The monthly pCO2 anomaly for each estuary survey was calculated from the difference between observed and conservative pCO2. River and ocean endmember TA and pCO2 were used to determine pH, and pH and TA were mixed conservatively across the salinity gradient. Figure 7- The median pCO 2 anomaly for each salinity bin Decreases with increasing river Flow, indicating that greater river Discharge promotes greater autotrophy and primary production. This would also coincide with decreased pCO 2 levels in the estuary (Figure 5). Summary The Kennebec Estuary acts as a seasonal CO 2 source to the atmosphere in spring and summer, and as a small sink of atmospheric CO 2 in the late fall and winter. Increased river flow coincides with decreased CO 2 levels in estuarine water. We also see seasonal trends in Kennebec Estuary metabolism: inferred autotrophy during the spring and summer, changing to inferred heterotrophy for the fall and winter. Increased precipitation, predicted by several regional climate models, if translated into increased river runoff, would promote lower estuarine CO 2 levels. Coupled with a predicted increase in atmospheric CO 2, systems such as the Kennebec Estuary could change from overall sources of CO 2 to overall sinks of atmospheric CO 2.