Working with the Carbon Group at NOAA’s Pacific Marine Environmental Lab, we propose to continue the now 4-year time series of real-time, high-frequency measurements of critical core OA parameters on the northern Washington shelf, including regular collection of validation samples. Specifically APL-UW will continue to maintain a heavily-instrumented surface mooring (Cha’ba) providing core OA and support parameters 13 miles WNW of La Push, WA, within the Olympic Coast National Marine Sanctuary, just shoreward and south of the Juan de Fuca Eddy—a known harmful algae bloom (HAB) source (Trainer et al., 2009; Hickey et al., 2013). Cha’ba currently houses a MAPCO2 system and many auxiliary sensors including two pH sensors, several CTDs, two oxygen sensors, an ADCP, and a fluorometer/turbidity sensor. Because of budget limitations, lack of ship time, and possessing only one surface mooring, we are only able to deploy the Cha’ba system for 6-8 mo/yr, typically from March-April through September-October. A LOI is attached to this workplan that would allow for continuous 12 mo/yr deployments in order to bring this to the full requirements of NOAA OAP. Cha’ba’s location, in an upwelling zone and near the source waters to Puget Sound via the Strait of Juan de Fuca, offers key insights. While Cha'ba records surface air and seawater conditions with some depth resolution, NANOOS also supports a subsurface profiling mooring 400m away from Cha''ba, measuring full water-column properties below 20m, soon to be instrumented (US IOOS funding) with a real-time HAB detection system, pH sensor and profiling CTD offering broader context and insights on biological responses. Synergies between OA and HAB toxicity have been suggested (Sun et al., 2011). Continuation of the MAPCO2 effort on Cha''ba with these ancillary data will facilitate analysis to further develop our understanding of shelf processes important to OA variability, prediction, and biological responses.