Global climatological relationships between satellite biological and physical observations and upper ocean properties

Abstract

We evaluate the relationships of monthly climatological satellite measurements of sea surface height, temperature and chlorophyll‐a to climatological subsurface parameters (mixed layer depth, thermocline depth, and Z2N, the 2 μmol NO3 isocline depth) on a global scale to determine the spatial variability and mechanisms underlying their relationships. The goal is to situate satellite surface data in the context of subsurface processes so that ultimately surface variability on longer timescales can be related to physical processes. There are well‐defined physical regimes in the tropics (20°S–20°N), where surface and subsurface physical parameters are predominantly positively correlated because of the dominance of baroclinic processes, and the extratropics (20°–60° latitude), where they are negatively correlated, and barotropic processes dominate. The biological regimes differ between these regions. Correlations between surface chlorophyll and subsurface parameters are variable in the tropics, positive at midlatitudes (20°–40° latitude) and negative at high latitudes. We interpret these changing relationships in the context of differing underlying biophysical processes: dynamic uplift causing nutrient entrainment into the euphotic zone in parts of the tropics, seasonal entrainment of nutrients into the euphotic zone at midlatitudes, and seasonal controls on light supply at high latitudes. Together with the physical regimes, these biophysical conceptual models explain the relatively complex, broad‐scale relationships between global satellite measurements of sea surface height, temperature, and chlorophyll‐a on a climatological seasonal basis.