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Special Event

Radiocarbon signatures and size-age-composition relationships of major organic matter pools within a high-nutrient, low-chlorophyll California upwelling system (and beyond)

Monday, 29 June, 3:00 pm
Dr. Brett Walker, Associate Project Scientist
University of California, Irvine

Fairbanks—201 O'Neill • Seward— Rae Building • Juneau—101 Lena Point bldg.

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Coastal upwelling zones are among the most productive regions in the world and play a major role in the global carbon cycle. Radiocarbon (as D14C) is a powerful tool for tracing the source and cycling of marine suspended particulate and dissolved organic matter (POM, DOM), and has the potential to reconcile key carbon budgets within upwelling systems. However, the extent to which upwelling processes influence the D14C signature of surface dissolved inorganic carbon (DIC), or that of exported POM or DOM remains largely unknown. Here I present a geochemical time series of D14C data of major organic matter (OM) reservoirs within a unique high-nutrient, low-chlorophyll (HNLC) upwelling center on Central CA coast. The results demonstrate that DIC D14C is strongly correlated to coastal upwelling processes, and that this 14C-signal readily propagates up the food web and into both POM and DOM pools. While additional OM sources complicate the direct use of \"bulk\" OM D14C for tracing upwelling-derived carbon production/export, I discuss a few strategies for determining OM sources and biological reactivity. Despite high seasonal variability, quantitative relationships between OM physical size, composition (C:N ratio) and D14C are observed within this upwelling system. These size-age-composition relationships are also observed in the surface and deep ocean, suggesting OM transformation and degradation from large, chemically-fresh POM to small recalcitrant DOM molecules is a globally significant ocean process. The approaches described herein represent powerful new tools for modeling C and N fluxes in ocean biogeochemical cycles.