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Regulation of seasonal primary production in eastern boundary upwelling systems Monique Messi & Francisco Chavez Monterey Bay Aquarium Research Institute Slide 2 Regulation of seasonal primary production in eastern boundary upwelling systems Monique Messi & Francisco Chavez Monterey Bay Aquarium Research Institute nitrate supply (N flux) potential new production (C flux) nitrate supply (NO 3 - ) regeneration (NH 4 + ) primary production regenerated new coast surface mixed layer depth 150 km Slide 3 Average primary production vs. potential new production (nitrate supply) Slide 4 X Nitrate supply = nitrate at depth (60m) 1. The N-ratio concept satellite-derived primary production (Behrenfeld & Falkowski, 1997) nitrate supply (NO 3 - ) regeneration (NH 4 + ) primary production regenerated new coast surface mixed layer depth wind coastal transport Ekman pumping 150 km Comparing primary production and nitrate supply from satellite winds and in-situ nitrate (Messi et al., 2009) Slide 5 1. The N-ratio concept carbon-equivalent of nitrate supply assuming C:N = 106:16 (Messi et al., 2006) satellite-derived primary production (Behrenfeld & Falkowski, 1997) nitrate supply (NO 3 - ) regeneration (NH 4 + ) primary production regenerated new coast surface mixed layer depth wind Ekman pumping coastal transport nitrate at depth (60m) X 150 km Nitrate supply = Potential new production = new production that would be achieved if all nitrate supplied was consumed Comparing primary production and potential new production Slide 6 1. N-ratio concept PP Seasonal primary production time latitude Slide 7 1. N-ratio concept PP Seasonal primary production vs. potential new production time latitude NP pot Slide 8 RP 150 km nitrate supply (NO 3 - ) regeneration (NH 4 + ) potential RP potential NP coast surface mixed layer depth available N primary production RP NP photo- synthesis N-remain non-used nitrate accumulation subduction offshore export N-ratio * PP f-ratio * PP 1. N-ratio concept N-ratio = f-ratio if all nitrate supplied is consumed (Eppley & Peterson, 1979) RP = regenerated production NP = new production Slide 9 1. N-ratio concept f-ratios (Laws et al. 2000; Dunne et al., 2005) N-ratios (Eppley & Peterson, 1979) f-ratio ~ 0.5, constant Slide 10 f-ratio ~ 0.5, constant 1. N-ratio concept N-ratio Black contours = surface nitrate N-ratio = f-ratio all nitrate supplied is consumed nitrate regulating N-ratio > f-ratio remaining nitrate other factors regulating f-ratios N-ratios N-ratio 0.5N-ratio 0.8 Slide 11 Nitrate regulation N-ratio 0.5 nitrate regulates PP (N-remain ~ 0) N-ratio 2. The N-ratio analysis: nitrate vs. other factors N-ratio 0.5 nitrate regulates PP (N-remain ~ 0) N-ratio 0.8 other factors regulate PP (N-remain > 0) ? ? ? ? PP lower than expected from N-supply WHY? ? Slide 12 2. N-ratio analysis back to the definition of primary production PP, physical export, mortality, sinking, grazing Temperature, species Light, nutrients growth rate coast surface mixed layer depth biomass * growth Temperature Light 150 km Physical export residence time T box wind-driven downwelling EKE shelf width W shelf Iron supply dust deposition, river runoff (Johnson et al., 1999) (Chase et al., 2007) Data sources: QuikSCAT winds, ETOPO2 bathymetry, modeled dust from Mahowald et al. (2003), SST Reynolds, SeaWiFS PAR, AVISO sea level anomalies Nitrate supply (Messi et al., 2006) PP, physical export, mortality, sinking, grazing Light, nutrients (nitrate, iron) (nitrate) Temperature, species Slide 13 A few words about physical export Needs: T box 8 days (Zimmerman et al., 1987; Wilkerson et al., 2006) a mechanism to subduct within the box: EKE ( increases offshore & vertical export of biomass & nutrients, Lathuilire et al., 2010; Gruber et al., 2011 ) and/or Ekman downwelling only observed when computing T box up to D upwell coast surface mixed layer depth wind Ekman pumping coastal transport 150 km upwelling Ekman pumping D upwell (Ekman downwelling) downwelling Slide 14 A few words about physical export Needs: T box 8 days (Zimmerman et al., 1987; Wilkerson et al., 2006) a mechanism to subduct within the box: EKE and/or Ekman downwelling only observed when computing T box up to D upwell + isopycnal advection, mixing & frontal convergence possible (Washburn et al., 1991; Bograd & Mantyla, 2005) Slide 15 2. N-ratio analysis Physical exportLightIron T box EKEEk neg PARMLDI mean W shelf dust CaliforniaXXX NW AfricaXX PeruXXX BenguelaXXXXX What explains the high N-ratios? Based on correlations w/ N-ratio, mean value in high N-ratios situations, difference in high vs. low N-ratio situations Iron regulation off NW Africa? No iron regulation off Peru? What about Benguela? Physical exportLightIron T box EKEEk neg PARMLDI mean W shelf dust California NW Africa Peru Benguela Slide 16 3. Correlation analysis and PP regulation Spatial correlations with PPSeasonal cycles PP N-supply W shelf / dust light temperature T box Example: California Winter: nitrate, light, temperature (Kudela and Dugdale, 2000) Spring: upwelling resumes, physical export (Bograd and Mantyla, 2005; Gruber et al., 2011) Late summer: iron regulation (Johnson et al., 2001; Elrod et al., 2008) From N-ratio analysis: high N-ratios = physical export Slide 17 3. Correlation analysis and PP regulation Spatial correlations with PP Seasonal cycles Benguela light From N-ratio analysis: high N-ratios = light / export / iron NW Africa From N-ratio analysis: high N-ratios = iron High N-ratio narrow shelf Slide 18 3. PP regulation high N-ratios Nitrate supply Iron supply Physical export Light Slide 19 N-ratio as a tool to monitor nitrate regulation but also ecosystem efficiency PP regulation highly variable in space and time, concept of co-limitations Need for validation of iron limitation (NW Africa / Benguela) Conclusions Nitrate supply Iron supply Physical export Light CaliforniaPeruNW AfricaBenguela averaged N-ratio 0.730.820.520.63