Productivity and Export along an Upwelling Filament in the California Current Ecosystem using a Multi Method Approach

Located along the eastern margin of the north Pacific Ocean, the California Current Ecosystem (CCE) is vital to the economy of local coastal communities due to productive and abundant fisheries, valuable tourism and innumerable ecosystem services. Due to the ecological and economical importance of this ecosystem, it is imperative to characterize the spatial and temporal variability of marine productivity in order to predict food web interactions. In this presentation, we will describe marine productivity estimates based on multiple approaches during four Lagrangian experiments (“cycles”) conducted along an upwelling filament in the CCE. In addition to in situ incubations conducted to estimate net primary productivity (i.e. H¹⁴CO₃⁺ uptake and new production (¹⁵NO₃^- uptake)), we derived rates of net community productivity and gross primary productivity using a modified dO2/Ar Equilibration Inlet Mass spectrometer (EIMS) approach and chlorophyll fluorescence analysis using Fast Repetition Rate fluorometry (FRRf). We also quantified vertical carbon export using sediment traps and 238U-²³⁴Th disequilibrium. Rates of productivity showed a clear trend with higher rates in the coastal recently-upwelled waters and lower rates in the offshore region, although carbon export peaked in the offshore region. Intracycle productivity also varied widely due to changes in chlorophyll, mixed layer depth and nutrient availability. Net community productivity - as estimated using the EIMS approach - showed large discrepancies to new production estimates during all cycles. The gross productivity rates calculated from EIMS and FRRF showed better correlation over some diurnal cycles in the high productivity coastal regions compared to the offshore regions. This is most likely attributable to the limitations of both methods, which need to be evaluated further. Nonetheless, the high spatiotemporal productivity measurements (hourly, daily and/or station duration) provided by the EIMS and FRRF show rapid changes in productivity in the complex ecosystems of the CCE.