Spatial and temporal variability of absorption by dissolved material at a continental shelf

Optical properties of dissolved (colored dissolved organic material (CDOM)) and particulate matter and hydrographic measurements were obtained at the Mid-Atlantic Eight during the fall of 1996 and the spring of 1997 as part of the Coastal Mixing and Optics experiment. To assess the temporal and spatial variability, time series were obtained at one location and cross-shelf transects were carried out. On short timescales, variability in the vertical distribution of the dissolved fraction was mostly due to high-frequency internal waves. This variability was conservative, resulting in no changes on isopycnals. Over longer periods and episodically, CDOM variability was dominated by storms. The storms were associated with sediment resuspension events and were accompanied by an increase in the absorption by the dissolved materials. Data from spatial transects show that near the bottom, over the shelf, acid in both spring and fall, increased particulate absorption and increased CDOM absorption co-occur. These data support the hypothesis that bottom sediments can act as a source of dissolved organic carbon during sediment resuspension events.