Mesoscale variability of Sea-viewing Wide Field-of-view Sensor(SeaWiFS) satellite ocean color: Global patterns and spatial scales

[1] Using the semivariogram approach from geostatistics, we characterize for the first time the global patterns of mesoscale (approximately 10-200 km and days to a few weeks) ocean biological variability. The magnitude of the variability and spatial length scale fields are reported for a full year of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) ocean color data. The analysis shows a number of coherent geographical patterns across a wide range of biological and physical environments. Submonthly, small spatial scale variance dominates ocean color variability in oligotrophic regimes and is about a third of the total variance even in regions with strong seasonality. When normalized to the mean chlorophyll as a coefficient of variation, the resolved mesoscale variance (relative sill) is approximately uniform in the open-ocean tropics and subtropics (0.1-0.2), increasing to 0.3-1.0 in western boundary current, upwelling (Equatorial Pacific, coastal) and subpolar/polar regions, approximately scaling with the mean chlorophyll concentration. The unresolved variance (nugget), which includes submesoscale geophysical variability as well as instrument/algorithm noise, is inversely correlated with mean chlorophyll concentration in the oligotrophic subtropical gyres, reducing to a low background value (0.1) elsewhere. The high fraction of unresolved variance in the subtropics is consistent with other studies showing substantial speckling due to noise in the atmospheric correction methods. The mesoscale spatial scale (range) is approximately zonal, with values of 200-350km near the Equator to less than 50 km close to the poles similar to the physical scales estimated from altimeter sea surface height variability data and the first baroclinic Rossby deformation radius. Our results demonstrate the global generality of previous local and regional findings that small-scale variability in ocean biology and physics occurs on comparable spatial length scales. Regional deviations from these large-scale variance and spatial length scales trends, for example, lower range and higher resolved variance in coastal upwelling regimes, are explicable by the characteristics of the biological-physical interaction in those environments.