1. Iron Limitation and Biogeochemical Effects in Southern California Current Coastal Upwelling Filaments.
- Author
-
Forsch, K. O., Fulton, K. C., Weiss, M. M., Krause, J. W., Stukel, M. R., and Barbeau, K. A.
- Subjects
UPWELLING (Oceanography) ,FIBERS ,DIATOM frustules ,IRON ,DIATOMS ,EUPHOTIC zone ,WATER masses - Abstract
In the spring and summer, high rates of primary production occur in the California Current Ecosystem (CCE) when nutrients are supplied to the euphotic zone. During periods of intense coastal upwelling, a flux of the micronutrient iron comes from nearshore sedimentary sources. In this upwelling region, mesoscale filament features distribute iron laterally, leading to distinct iron‐influenced ecological zones. This study is the first to focus on the biogeochemical links between iron, the macronutrients, and particulates in coastal upwelling filaments. Broad spatial patterns of iron and biogenic silica concentrations, and proxies of iron‐stress of diatoms, support results from microcosm amendment studies conducted during CCE Long Term Ecological Research process cruises in the summers of 2017 and 2019. We found that the benthic boundary layer and shoreward filament endmember supply dissolved and total dissolvable iron to this feature, but rapid assimilation and sinking by biogenic particles (e.g., diatoms) depletes the surface concentrations. Subsequently, diatom blooms which form in recently upwelled water masses become iron limited over time, thereby affecting the ratios of surface macronutrient reservoirs and biogeochemical advective fluxes. The development of Fe‐limitation during lateral advection may lead to efficient carbon export downstream and offshore of the region with the highest phytoplankton growth rates and productivity. Plain Language Summary: Along the western continental margin of the United States, seasonal upwelling filaments appear as fast‐flowing waters with high concentrations of nutrients (e.g., nitrate, silicic acid, iron) and phytoplankton. Diatoms dominate the phytoplankton communities in filaments, and they accumulate particulate matter as organic carbon and dense biogenic silica. During transport offshore, diatoms quickly deplete the surface of the critical micronutrient iron (Fe) and become Fe‐limited. Using shipboard incubation experiments, we show that Fe‐stressed diatom communities become more heavily silicified, and thus denser. Iron‐stress indicators consistently correspond with these phytoplankton community biochemical reconfigurations in two separate studies of filaments, thereby demonstrating a mechanism for enhanced diatom community export out of the surface ocean in later stages of filaments. Key Points: Upwelling filaments become Fe‐limited features in the ocean, as sinking diatoms deplete surface dFe concentrations and are advected offshoreIron‐limitation of diatom blooms is evidenced by in situ geochemical proxies (e.g., negative Siex) and deckboard Fe amendment experimentsGreater biogenic silica‐to‐particulate organic carbon ratios among diatom communities make filaments hotspots of particulate matter export [ABSTRACT FROM AUTHOR]
- Published
- 2023
- Full Text
- View/download PDF