Using SVD Analysis of Combined Altimetry and Ocean Color Satellite Data for Assessing Basin Scale Physical-Biological Coupling in the Mediterranean Sea

The ocean is a highly variable system affected by a large range of processes that spans the continuous spectra of spatial and temporal scales (Wunsch, 1996). The spatial scales of variation range from basin-wide gyres (thousands of kilometers) to turbulence (less than a meter), and the time scales from those that are climate related (decades) to short-term processes (seconds). Information on this whole range of processes is required for the comprehension of the marine system dynamics. Despite the continuous advances in technology, remote sensing is the only observing platform capable of providing continuous information on biological and physical properties over vast areas of the ocean. With some limitations, the regular and repeated coverage offered by satellites is still unachievable through in situ measurements. Because the ocean is largely opaque over much of the usable electromagnetic spectrum, the ability of satellites to capture ocean properties is generally confined to the surface. Nevertheless, satellite-borne sensors provide us with a relatively large range of measurements such as sea surface color, sea surface height, sea surface temperature, sea surface winds, sea surface salinity, waves, and to a lesser extent, current fields. The availability, for the first time, of time series expanding for several years or decades at regional and global ocean scales has changed our perception of the ocean (Barber & Hilting, 2000). A majority of these measurements is restricted to physical properties such as temperature, sea level or sea surface roughness and inferred variables (currents, winds, etc.). The only routinely acquired satellite measurement providing information on ocean biological processes is sea surface color. Since early measurements obtained by the Coastal Zone Color Scanner (CZCS), sea color sensors have provided quantitative information on the distribution of surface chlorophyll (CHL) concentration (an index of phytoplankton biomass) at regional to global scales and its variability in space and time (e.g., Abbott & Zion, 1987; Antoine et al., 2005; Behrenfeld et al., 2001). This information is relevant to estimate the ocean productivity, a key factor for understanding the dynamics of pelagic foodwebs and some aspects of climate change.