Seasonal Variation of CDOM and DOC in the Middle Atlantic Bight:
Anthony Vodacek* and Neil V. Blough*
Terrestrial Inputs and Photooxidation
Department of Chemistry and Biochemistry
University of Maryland
College Park, MD 20742
Michael D. DeGrandpre,¹ Edward T. Peltzer² and Robert K. Nelson
Department of Marine Chemistry and Geochemistry
Woods Hole Oceanographic Institutiton
Woods Hole, MA 02543
Limnology and Oceanography (1997) 42: 674-686.
Submitted: 8 April 1996.
Accepted: 4 November 1996.
*: Corresponding authors.
¹: Present address: Department of Chemistry
University of Montana Missoula, Montana 59812.
²: Present address: Monterey Bay Aquarium Research Institute
PO Box 628, Moss Landing, CA 95039-0628, USA.
Extensive surveys of the fluorescence and absorption of chromophore-containing dissolved
organic matter (CDOM), dissolved organic carbon (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 adsorption 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 photooxidation. 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).
We thank the captain and the crew of the R/V Cape Henlopen, Steve Andrews, Liz Bruce,
Sigi Caron, Mike Giancola, Nancy Hayward, Sarah Herbelin, Frank Hoge, Joyce Irvine and Tim
Pfeiffer for their contributions to this work.
Support was provided by the Office of Naval Research (NVB), the NASA EOS Interdisciplinary
Program (NVB and ETP), and an NRC-NASA resident research associateship (AV).
This page was last updated on 19 April 1999.