Airborne, In Situ and Laboratory Measurements of the Optical and Photochemical Properties of Surface Marine Waters [report]

Neil V. Blough
1999 unpublished
LONG TERM GOALS The principal long-term objectives of this work are 1) to uncover and quantify the primary factors controlling the spatial and temporal distributions of the light-absorbing (colored) constituents of dissolved organic matter (CDOM) in marine and estuarine waters, 2) to determine the impact of CDOM on the aquatic light field and remotely-sensed optical signals, 3) to examine the effects of photooxidation on the optical absorption and emission properties of this material, as well
more » ... material, as well as the relationship between the loss of absorption (and fluorescence) by photooxidation and the yield of photochemical intermediates and products, 4) to develop and apply new techniques for determining the photoproduction rates of transient intermediates in natural waters. A combination of field and laboratory measurements are being employed to estimate the wavelength dependence of the rates of the photobleaching response and its relationship to organic carbon photooxidation and the production of photochemical intermediates in order to better understand the impact of photooxidation on marine carbon and trace element cycles and the optical properties of seawater. OBJECTIVES Our near-term objectives have been 1) to complete two research cruises in July and September of 1998 devoted to examining the seasonal dependence of CDOM absorption and emission in the Middle Atlantic, the contribution of CDOM to the aquatic light field, and the effects of stratification on the photodegradation of CDOM and on the vertical structure of the optical properties, 2) to begin developing a photochemical model for photobleaching based on an extensive laboratory study of CDOM photobleaching kinetics that employed both monochromatic and broad band light sources, 3) to develop and apply new techniques for determining the photoproduction rates of the hydroxyl radical (OH) and the hydrated electron (e (aq) -), and 4) to begin construction of a web site for archiving data collected on our past cruises, so that other researchers can have access to these data. APPROACH One seven-day cruise in July and one five-day cruise in late September 1998 were performed to examine the optical and photochemical properties of waters in the Middle Atlantic Bight and in the Delaware and Chesapeake Bays. Data obtained from these cruises included: 1) optical absorption spectra of CDOM
doi:10.21236/ada630976 fatcat:jlzfs65sdvcwnhv4ev6wkfg7xe