Mark Dowell

Relationship between the optical properties of chromophoric dissolved organic matter and total concentration of dissolved organic carbon in the southern Baltic Sea region

Abstract Absorption and fluorescence of chromophoric dissolved organic matter (CDOM) and dissolved organic carbon (DOC) measurements were performed during three oceanographic surveys in 1994 in the southern Baltic Sea (Polish area of the Baltic Proper). DOC was measured both by high-temperature catalytic oxidation (HTCO) and low-temperature oxidation (LTO) conventional persulphate methods. CDOM fluorescence was shown to be highly correlated with absorption, with the same regression parameters, despite the seasonal change in different hydrographic conditions and the fluorescence quantum yield variations (1.23 ± 0.07 in April and 0.97 ± 0.12 in September). The results show a good correlation between the optical parameters and DOC although ~ 70% of the DOC does not display significant absorption in the UV-visible range (350–750 nm). The non-absorbing DOC measured with HTCO method appears unaffected by seasonal changes. Consequently, total DOC can be predicted by optical methods using remote sensing techniques. The non-absorbing DOC measured by LTO method varies from 62% (April) to 76% (September), which implies that there is requirement for estimates on a seasonal basis.

Generalized ocean color inversion model for retrieving marine inherent optical properties

Ocean color measured from satellites provides daily, global estimates of marine inherent optical properties (IOPs). Semi-analytical algorithms (SAAs) provide one mechanism for inverting the color of the water observed by the satellite into IOPs. While numerous SAAs exist, most are similarly constructed and few are appropriately parameterized for all water masses for all seasons. To initiate community-wide discussion of these limitations, NASA organized two workshops that deconstructed SAAs to identify similarities and uniqueness and to progress toward consensus on a unified SAA. This effort resulted in the development of the generalized IOP (GIOP) model software that allows for the construction of different SAAs at runtime by selection from an assortment of model parameterizations. As such, GIOP permits isolation and evaluation of specific modeling assumptions, construction of SAAs, development of regionally tuned SAAs, and execution of ensemble inversion modeling. Working groups associated with the workshops proposed a preliminary default configuration for GIOP (GIOP-DC), with alternative model parameterizations and features defined for subsequent evaluation. In this paper, we: (1) describe the theoretical basis of GIOP; (2) present GIOP-DC and verify its comparable performance to other popular SAAs using both in situ and synthetic data sets; and, (3) quantify the sensitivities of their output to their parameterization. We use the latter to develop a hierarchical sensitivity of SAAs to various model parameterizations, to identify components of SAAs that merit focus in future research, and to provide material for discussion on algorithm uncertainties and future emsemble applications.

Absorption modeling in case II waters: the need to distinguish colored dissolved organic matter from nonchlorophyllous particulates

The presented study examines, for substantial datasets in different Case II waters, the variability of the spectral absorption of Non-Chlorophyllous Particles (NCP) and Colored Dissolved Organic Matter (CDOM). The investigation has considered the validity of the currently proposed modeling of the absorption of these tow components as a single variable, in applications to Case II water environments. In order to encompass a broad range of environmental situations in the comparison of NCP and CDOM absorption spectra, two very different sites were selected. The locations investigated were the Southern Baltic Proper and a site in the Northern Adriatic close to the Italian coast. These two regions differ both in their basic oceanographic properties and int heir relative proportions of both space and time, combining a series of seasonal oceanographic campaigns in the Baltic with a complete annual time series of monthly measurements at a fixed point in the Adriatic. The analysis has shown that, in the selected European Case II waters, the observed variability of the spectral absorption of NCP and CDOM, both with respect to each other as well as to the total absorption, are independent. It is therefore suggested that, in the frame of Reflectance modeling in Case II waters, attention must be placed on accounting for NCP an CDOM individually when defining the absorption segment.