Investigating Iron Variability Across Productivity Regimes in the California Current Ecosystem
Hasan, Noelle
Hasan, Noelle
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Abstract
The California Current Ecosystem (CCE) is an eastern boundary upwelling system characterized by cold nutrient-rich waters that support high rates of primary productivity. Although iron is considered a limiting nutrient in high nutrient low chlorophyll (HNLC) zones, such as the Southern Ocean, recent research has shown that iron limitation can also occur in regions of high productivity, like the CCE, where iron supplied to the euphotic zone by coastal upwelling is rapidly assimilated and depleted from surface waters. This research contributes to a long-term study investigating the distribution and potential bioavailability of iron across the CCE. Seawater samples were collected during CCE Long-Term Ecological Research process cruises in summer 2021 and spring 2024 from stations in the benthic boundary layer (BBL), the Santa Barbara Basin (SBB), and five quasi-Lagrangian experiments tracking water parcels and filament evolution, termed �cycles�. Total dissolvable iron (TdFe), representing the sum of dissolved iron (dFe) and labile particulate iron (LpFe), was analyzed using flow injection analysis with chemiluminescence. Fe concentrations widely varied across sites. Elevated TdFe in BBL samples indicates sedimentary and fluvial inputs as an important source of Fe to the southern CCE, while increasing Fe with depth in the SBB reflects release from anoxic sediments. Across quasi-Lagrangian cycles, nearshore regions showed higher Fe and chlorophyll-a, whereas offshore regions exhibited lower Fe concentrations and lower productivity, consistent with previous studies showing the development of Fe limitation as water masses move offshore. However, elevated Fe did not always correspond to increased chlorophyll-a, suggesting co-limitation by macronutrients, like nitrate. These results highlight the temporally and spatially dynamic nature of iron cycling in the southern CCE and contribute to a broader understanding of how iron availability influences productivity in coastal upwelling systems.
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Date
1/1/2026
Student Status
Senior (Graduating in 2026)
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Poster
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Environmental Science
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Rubenstein School of Environment and Natural Resources
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Physical Science