A time series study of silica production and flux in an eastern boundary region: Santa Barbara Basin, California

A high-resolution data set describing the annual silica cycle between Janua ry 1994 and August 1999 in the Santa Barbara Basin (SBB) captures processes and events occurring in both surface and deep basin waters. Increases in b iogerric silica (bSi) concentrations in the surface waters indicated strong bloom events in the early spring of each year and sporadic blooms during t he summer and fall. Lithogenic silica (lSi) was present at elevated concent rations in surface waters in the winter and spring. At times, the siliceous biomass in the SBB is comparable to that in major global upwelling regions . However, anomalously low annual depth-integrated bSi concentrations were observed during the El Nino conditions of 1997-1998. A 1.5-year time series of biogenic silica production rate measurements was used to calculate the highest resolution estimate of annual silica production to date, an estimat ed 5.5 mol Si m(-2) yr(-1). This silica production rate approaches that est imated for the major global upwelling zones (8.3 mol Si m(-2) yr(-1)). East ern boundary regions outside of the major coastal upwelling zones would acc ount for 30-40% of global silica production if the Santa Barbara Basin is r epresentative of these coastal regions. Since the sediments of the SBB cont ain a high-resolution climate record, an understanding of the coupling betw een surface processes and deep basin sedimentation events is of value. Flux es of bSi and lSi to 470 m were not strongly coupled to the seasonal cycle of particulate concentrations or production rates in surface waters. Contin uous sediment trap collections of sedimenting particles indicate that both lSi and bSi tend to be exported at the highest rates during the spring and summer. As particles sink, lSi becomes enriched relative to bSi and consist ently dominates the mass flux of silica at 470 m. Brief increases in the pe rcent contribution of bSi to Si flux may create microlaminae within larger- scale laminations which are thought to be annual varves. A comparison of an nual bSi sedimentation rates with annual silica production estimates reveal that similar to 30% of the annual silica production is exported to a depth of 470 m. This export rate is the highest observed to date and suggests th e potential for large quantities of silica burial in coastal sediments.