Biogenic silica standing stock and export in the Santa Barbara Channel ecosystem

Abstract

[1] Time-series datasets of surface-water biogenic silica (bSiO 2) and deep-water bSiO2 export in the Santa Barbara Channel (SBC) allow for elucidation of the important scales of spatial and temporal variability and an evaluation of potential controlling mechanisms. Changes in local upwelling strength is the most important factor controlling seasonal variations for the surface bSiO2 dataset and accounts for ∼65% of the variance. bSiO2 export is also highly seasonal; however, the maximum export is generally offset from the bSiO2 standing stock maximum by 0.5-2 months, and export is enhanced for a longer period than is surface biomass. Strong cross-channel gradients in surface [bSiO2] occur during periods of elevated bSiO2 and account for ∼13% of the variability in standing stocks; these gradients appear to be sustained by a combination of both local (cyclonic flow in the western SBC) and nonlocal (advection of water into the SBC) processes. Since 2000, a significant linear decline in water-column-integrated bSiO2 has occurred concurrent with a significant increase in bSiO2 export. During this same period, phytoplankton biomass and net primary production increased in the general California Current. Coupling our results with previous studies supports the idea that a significant amount of the exported bSiO 2 caught in 540m sediment traps originates outside the SBC, and variability is driven by both local and the broader California Current Ecosystem effects. However, we cannot rule out a significant role for local episodic events in stimulating production of rapidly settling particles. © 2012 American Geophysical Union. All Rights Reserved.