Seasonal and Interannual Variability of the Aragonite Saturation Horizon in the California Current System of Baja California

Abstract

Hydrographic data from cruises of the Investigaciones Mexicanas de la Corriente de California (IMECOCAL) program since 1998 were used to assess the chemical conditions associated with carbon variables in the water column in the transect “Line 100.” Seasonal climatologies along the IMECOCAL line highlight the upwelling season, during which water with different chemical characteristics is transported to the surface. Additionally, interannual events influenced the amplitude and timing of wind-driven coastal upwelling and the region's relative volumes of dominant water mass. Seasonal climatologies of pH, calcium carbonate saturation states, and dissolved inorganic carbon (DIC) concentration were estimated from hydrographic proxy variables. The strength of seasonal upwelling was reflected in the depth of the aragonite saturation horizon (ASH), which was variable nearshore: 90 m (±29 m) in spring and 133 m (±32 m) in winter. Offshore (>50 km), the effect of upwelling diminished, and the ASH was deeper and less variable (spring: 152 m ± 25 m; winter: 151 m ± 28 m). However, aragonite saturation values <1 were found at depths >250 m and were associated with Equatorial Subsurface Water (ESsW) dominance. At seasonal timescales, Subarctic Water (SAW) was found to modulate ASH depth. At interannual scales, ASH was found to be deeper (180 m) during periods of El Niño and shallower (120 m) during La Niña conditions. However, the impacts of El Niño and La Niña events give notable differences in the ASH depth.