Seasonal spillover and varve formation in the Santa Barbara Basin, California

Abstract

A temporal record of oxygen and NO3- concentrations in the bottom water of the Santa Barbara Basin indicates that outside waters spill over into the basin seasonally. It is proposed that an annual bottom-water cycle leads ultimately to varve production. As evidence in support of a benthic mechanism for varve formation, we present results of surface sediment and pore-water analyses, from box-core collections during three seasons in 1988. The greater degree of bottom-water oxygen depletion that occurs regularly in late summer and fall was coincident with a smaller pool of pore-water Fe, penetration of ΣH2S up to the sediment-water interface, maximal numbers of benthic Foraminifera, and bacterial mat growth. The latter was indicated by increases in concentrations of extractable ATP, organic C, and total N in sediments from the depth intervals 0–0.25 and 0.25–0.5 cm. The greatest numbers of siliceous phytoplankton skeletons were found on the sea floor soon after the late spring, surface-water, Chl a maximum. This event coincides with additions of new and more-oxygenated seawater to the deep basin