Coccolith carbonate production in the Santa Barbara Basin (California borderland), linked to interannual and interdecadal climate changes

Coccolithophore ecology and the transformation of living biocoenoses into coccolith carbonate at the ocean floor are fundamental for documenting climatic effects and for estimating the global budget of coccolith carbonate. This understanding is also needed to quantitatively assess the information preserved in the sediment record, and to use coccolithophores as biotic proxies of climate change. In the Santa Barbara Basin (SBB), the combination of high biogeochemical input and the lack of bioturbation at the bottom allow the deposition of varved sediments. These laminated sediments are used here to trace the response of primary productivity, in particular on coccolithophore, to El Niño (EN) events and their climatic forcing. We use a sediment trap anchored in the center of the basin (3414’N, 12002’W; ~590m water depth, about 50m off the bottom) to trace the seasonal trend during non-EN conditions. In addition, a laminated box-corer (SABA 9610) recovered from the center of SBB (34° 19.004’ N; 120° 02.003’W) was used to characterized the effect of EN events on coccolithophore during the last 60 years. The EN events were defined by the Southern Oscillation Index (SOI). The fine fraction (<32um) flux varied between 1.453 gr/m2/day and 0.370 gr/m2/day, with a maximum contribution to the total flux in the spring and summer (average 0.996 gr/m2/day) and minor in winter (average 0.624 gr/m2/day). During this year, in the SBB the coccolithophores are a minor contributor to total carbonate flux during the spring when the upwelling is present (being only 2-3% of the total carbonate), while they increment (5-7% of the total carbonate) during the fall when the coccolith bloom was recorded. The sinking coccolithophore assemblage was dominated by Emiliania huxleyi (varied between 142.51 107 m-2 day-1and 1.844 107 m-2 day-1). Follow by Florisphaera profunda, Helicosphaera carteri, Gephyrocapsa muellerae and Calcidiscus leptoporus. In the box-core samples we observe an increment of coccolithophore flux during the year following EN event (negative SOI). In contrast, during the year following La Nina conditions (positive SOI) the flux of coccolithophore was reduced.