Regulation of seasonal primary production in eastern boundary upwelling systems Monique Messié & Francisco Chavez Monterey Bay Aquarium Research Institute

Regulation of seasonal primary production in eastern boundary upwelling systems Monique Messié & Francisco Chavez Monterey Bay Aquarium Research Institute 150 km surface regenerated primary production regeneration (NH4+)‏ new nitrate supply (NO3-)‏ mixed layer depth coast nitrate supply (N flux) ↔ potential new production (C flux)

Average primary production vs Average primary production vs. potential new production (nitrate supply)

1. The N-ratio concept = X wind primary production primary production Comparing primary production and nitrate supply satellite-derived primary production (Behrenfeld & Falkowski, 1997) from satellite winds and in-situ nitrate (Messié et al., 2009) wind coastal transport Ekman pumping 150 km surface regenerated primary production regeneration (NH4+)‏ new nitrate supply (NO3-)‏ mixed layer depth X Nitrate supply = nitrate at depth (60m) coast

1. The N-ratio concept = X wind primary production Comparing primary production and potential new production satellite-derived primary production (Behrenfeld & Falkowski, 1997) carbon-equivalent of nitrate supply assuming C:N = 106:16 (Messié et al., 2006) wind Potential new production = new production that would be achieved if all nitrate supplied was consumed 150 km surface regenerated primary production regeneration (NH4+)‏ new nitrate supply (NO3-)‏ mixed layer depth Ekman pumping Nitrate supply = X nitrate at depth (60m) coast coastal transport

Seasonal primary production 1. N-ratio concept Seasonal primary production PP latitude time

Seasonal primary production vs. potential new production 1. N-ratio concept Seasonal primary production vs. potential new production NPpot PP latitude time

N-ratio = f-ratio + 𝐍−𝐫𝐞𝐦𝐚𝐢𝐧 𝐏𝐏 1. N-ratio concept RP = regenerated production NP = new production f-ratio = 𝑁𝑃 𝑃𝑃 (Eppley & Peterson, 1979) N-ratio = NP pot PP N-ratio = f-ratio if all nitrate supplied is consumed N-ratio = f-ratio + 𝐍−𝐫𝐞𝐦𝐚𝐢𝐧 𝐏𝐏 RP 150 km nitrate supply (NO3-)‏ regeneration (NH4+)‏ potential RP potential NP coast surface mixed layer depth available N primary production N-ratio * PP f-ratio * PP N-remain non-used nitrate accumulation subduction offshore export RP NP photo- synthesis

N-ratio = f-ratio + 𝐍−𝐫𝐞𝐦𝐚𝐢𝐧 𝐏𝐏 1. N-ratio concept f-ratio = 𝑁𝑃 𝑃𝑃 (Eppley & Peterson, 1979)  f-ratio ~ 0.5, constant N-ratio = NP pot PP N-ratio = f-ratio + 𝐍−𝐫𝐞𝐦𝐚𝐢𝐧 𝐏𝐏 f-ratios (Laws et al. 2000; Dunne et al., 2005) N-ratios (Eppley & Peterson, 1979)

other factors regulating 1. N-ratio concept f-ratio ~ 0.5, constant f-ratios N-ratios N-ratio = f-ratio all nitrate supplied is consumed nitrate regulating N-ratio > f-ratio remaining nitrate other factors regulating N-ratio ≤ 0.5 N-ratio = f-ratio + 𝐍𝐫𝐞𝐦𝐚𝐢𝐧 𝐏𝐏 N-ratio ≥ 0.8 N-ratio Black contours = surface nitrate

2. The N-ratio analysis: nitrate vs. other factors Nitrate regulation ? PP lower than expected from N-supply  WHY?  N-ratio ≤ 0.5  nitrate regulates PP (N-remain ~ 0) N-ratio ≥ 0.8  other factors regulate PP (N-remain > 0) N-ratio ≤ 0.5  nitrate regulates PP (N-remain ~ 0)

back to the definition of primary production… 2. N-ratio analysis back to the definition of primary production… growth rate 𝜇 𝑚𝑎𝑥 max growth rate 0 ≤ 𝛾 ≤ 1 limitation term 𝑷𝑷=𝑏𝑖𝑜𝑚𝑎𝑠𝑠 ∗ 𝜇 𝑚𝑎𝑥 ∗ 𝛾 PP, physical export, mortality, sinking, grazing PP, physical export, mortality, sinking, grazing Temperature, species Temperature, species Light, nutrients Light, nutrients (nitrate, iron) (nitrate) shelf width Wshelf Iron supply dust deposition, river runoff (Johnson et al., 1999) (Chase et al., 2007) 150 km surface Light Temperature Physical export residence time Tbox wind-driven downwelling EKE biomass * growth Nitrate supply (Messié et al., 2006) mixed layer depth coast Data sources: QuikSCAT winds, ETOPO2 bathymetry, modeled dust from Mahowald et al. (2003), SST Reynolds, SeaWiFS PAR, AVISO sea level anomalies

only observed when computing Tbox up to Dupwell A few words about physical export… only observed when computing Tbox up to Dupwell Needs:  Tbox ≤ 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, Lathuilière et al., 2010; Gruber et al., 2011) and/or Ekman downwelling Ekman pumping Dupwell (Ekman downwelling) downwelling wind 150 km surface upwelling mixed layer depth Ekman pumping coastal transport coast

only observed when computing Tbox up to Dupwell A few words about physical export… Needs:  Tbox ≤ 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 Tbox up to Dupwell + isopycnal advection, mixing & frontal convergence possible (Washburn et al., 1991; Bograd & Mantyla, 2005)

What explains the high N-ratios? 2. N-ratio analysis What explains the high N-ratios? Iron regulation off NW Africa? No iron regulation off Peru? What about Benguela? Physical export Light Iron Tbox EKE Ekneg PAR MLD Imean Wshelf dust California X NW Africa Peru Benguela Physical export Light Iron Tbox EKE Ekneg PAR MLD Imean Wshelf dust California NW Africa Peru Benguela Based on correlations w/ N-ratio, mean value in high N-ratios situations, difference in high vs. low N-ratio situations

3. Correlation analysis and PP regulation Example: California Spatial correlations with PP Seasonal cycles PP N-supply Wshelf / dust light temperature Tbox From N-ratio analysis: high N-ratios = physical export 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)

3. Correlation analysis and PP regulation Spatial correlations with PP NW Africa From N-ratio analysis: high N-ratios = iron High N-ratio narrow shelf Seasonal cycles Benguela From N-ratio analysis: high N-ratios = light / export / iron

3. PP regulation high N-ratios Nitrate supply Iron supply Physical export Light

Conclusions 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) California Peru NW Africa Benguela averaged N-ratio 0.73 0.82 0.52 0.63 Nitrate supply Iron supply Physical export Light