Extensive surveys of the fluorescence and absorption of chromophore‐containing dissolved organic matter (CDOM), dissolved organic C (DOC) concentration, chlorophyll fluorescence, and salinity were performed during August and November 1993 and March and April 1994 along a cruise line extending from the mouth of Delaware Bay southeast to the Sargasso Sea. With shallow stratification in August, photobleaching dramatically altered the optical properties of the surface waters, with ∼70% of the CDOM absorption and fluorescence lost through photooxidation in the waters at the outer shelf. S, the slope of the log‐linearized absorption spectrum of CDOM, increased offshore and seemed to increase with photodegradation. The increase in S combined with the seasonal variation in the relationship between Chl and CDOM underscores the difficulty in developing algorithms to predict Chl concentrations in turbid coastal waters with ocean color data. Despite the photooxidation of CDOM, the seasonal variation in the CDOM fluorescence‐absorption relationship and fluorescence quantum yields was <15%. When using appropriate methods, the airborne lidar approach for remote determination of CDOM absorption coefficients seems to be a very robust technique. The photooxidation of CDOM in August also affected the relationship between CDOM and DOC concentration in the surface waters, although for the rest of the year the relationship was reasonably linear. The results of a simple model suggest ∼10% of the DOC in the mixed layer was directly converted photochemically to dissolved inorganic C (DIC).

Coastal upwelling zones may be at enhanced risk from ocean acidification as upwelling brings low aragonite saturation state (Ω_Ar) waters to the surface that are further suppressed by anthropogenic CO₂. Ω_Ar was calculated with pH, pCO₂, and salinity‐derived alkalinity time series data from autonomous pH and pCO₂ instruments moored on the Oregon shelf and shelf break during different seasons from 2007 to 2011. Surface Ω_Ar values ranged between 0.66 ± 0.04 and 3.9 ± 0.04 compared to an estimated pre‐industrial range of 1.0 ± 0.1 to 4.7 ± 0.1. Upwelling of high‐CO₂ water and subsequent removal of CO₂ by phytoplankton imparts a dynamic range to Ω_Ar from ~1.0 to ~4.0 between spring and autumn. Freshwater input also suppresses saturation states during the spring. Winter Ω_Ar is less variable than during other seasons and is controlled primarily by mixing of the water column.

A new instrument for studying seawater pCO2 dynamics is described. The Submersible Autonomous Moored Instrument for CO2 (SAMI-CO2) operates by equilibration of ambient seawater pCO2 with a colorimetr...