Inter-annual variability of the California Current System and associated biochemical characteristics from prolonged data series

Abstract

This research investigates the California Current System (CCS) utilizing Synoptic Monthly Gridded World Ocean database (SMG-WOD) for temperature and salinity profiles, MODIS-A for surface chlorophyll-a (Chl-a) concentration, and climatological indices El Nino Modoki Index (EMI) and Multivariate El Nino Southern Oscillation Index (MEI), to compare inter-annual variations. The SMG- WOD produces 3D gridded fields with 1¡_1¡ horizontal resolution and 28 vertical layers. The area of interest was 0oÐ54¡N, 165¡WÐ105¡W from January 1945ÐDecember 2014. Because processes within 50 km of the coast are not well resolved by SMG-WOD, Chl-a data from MODIS-A with a 4.6 km resolution was used from July 2002ÐDecember 2014. Acceleration potential at the isopycnal surface of _= 26.9 kg/ m3 relative to the 1000 dbar was calculated from the SMG-WOD. Composite and Empirical Orthogonal Function (EOF) analysis was conducted to identify patterns of maximum variance. Correlation coefficients were calculated to determine connections between inter-annual variability and EMI/MEI. Acceleration potential had small seasonal variability, while Chl-a concentration demonstrated large seasonal variability. When Principal Component (PC) 1 is positive, EMI index will be negative, resulting in an increased geostrophic flow in the CCS. For positive PC2, MEI is negative resulting in an offshore flow and thus enhanced coastal upwelling in the CCS. Positive PC1 correspond to negative EMI/MEI and elevated surface Chl-a concentration in the CCS.