## 3 Results and Discussion
### Database Characteristics
Figure 1: Top row: data distributions and counts (N) of relevant parameters and Chl (for context only) in Global Ocean Carbon Algorithm Database (GOCAD), NASA bio-Optical Marine Algorithm Dataset (NOMAD), and the synthetic ocean color dataset developed by the International Ocean Colour Coordinating Group (IOCCG). Bottom row: comparisons between the subset of GOCAD parameters used in optimization/tuning (Optim) and validation (Val) of algorithms (shown here with SeaWiFS match-ups, but also evaluated for MODIS Terra and Aqua with similar results). Populations of salinity and DOC share a common mean between optimization and validation datasets (ANOVA, \(p>0.01\)). Geographic locations of GOCAD field stations overlap with NOMAD stations (Figure 3). We can see that many of the NOMAD stations were ultimately excluded from GOCAD during the quality assurance analysis described in Section 2.2. Highlighted in the central panel of Figure 3 are those stations with high-quality in situ radiometry, which were set aside for tuning, training, and optimization of ocean color algorithms. The geographic distributions of both the training data and the validation data show a representational combination of stations from both offshore and nearshore waters, which theoretically improves the odds of being able to retrieve a broad dynamic range of bio-optical properties, although as pointed out above the optimization data appears to be slightly dominated by oceanic stations. It is clear from Figure 3 that while there is significant overlap in the CDOM and DOC datasets in certain regions such as northern Alaska and the mid-Atlantic Bight in the Northeastern U.S., globally they follow a somewhat different pattern, and many DOC field stations are not obviously represented in the CDOM dataset. The dense concentrations of field stations sampled in relatively smaller regions such as the Northeastern U.S. are difficult to resolve at the small scale in Figure 3. Figure 4 shows three-dimensional maps of select sub-regions with \(a_{S}\)(412), \(S_{S}\)(275-295), and \(S_{S}\)(412-555), including the Northeast US and coastal Alaska between the Chukchi Sea and the Beaufort Sea. These are set in broad continental shelves with numerous nearby river outflows. Not surprisingly, CDOM is high throughout the regions shown in Figure 4 with low spectral slope in the UV. CDOM and \(S_{S}\)(275-295) increase and decrease, respectively, in close relation to distance from shore, as expected given the considerations discussed in Section 1.2 and elsewhere. Variability is higher for spectral slope in the VIS (\(S_{S}\)(412-555)), but it generally follows the opposite pattern from that in the UV, i.e., decreasing with distance from new sources of CDOM. This is indicative of aging processes as the newly mobilized, near-shore CDOM mixes seaward and photo- and microbial degradation reduce absorption in the UVA relative to the UVB (thus increasing \(S_{S}\)(275-295) and relative to the VIS (thus decreasing \(S_{S}\)(412-555)). It may indicate marine sources of CDOM with chromophores that absorb in the UVA and blue rather than terrestrial sources that also absorb in the UVB. These patterns are perhaps clearest at the outflows of the Colville River (\(\sim\)135\({}^{\circ}\) W and 70\({}^{\circ}\) N) and the Chesapeake Bay (\(\sim\)77\({}^{\circ}\) W and 37\({}^{\circ}\) N). An interesting exception for \(S_{S}\)(412-555) can be found in the Gulf Stream transect (\(\sim\)70\({}^{\circ}\) W and 37\({}^{\circ}\)-40\({}^{\circ}\) N; GOMECC-2 experiment, Table 2), where slope increases upon entering the productive waters at the edge of the Gulf Stream  
Figure 2: Exponential slope of CDOM in NOMAD, IOCCG, and GOCAD. Median values for S\({}_{412}\)-600 are highlighted in red for comparison. NOMAD and IOCCG lack UV CDOM. despite a lack of CDOM increase, and then rapidly declines upon entering the oligotrophic waters south of the Gulf Stream. Figure 3: Global distribution of GOCAD and NOMAD field stations for CDOM (upper) and DOC (lower).