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

2. 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)

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

4. 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

5. 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

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

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

8. 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

9. 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)

10. 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

11. 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)

12. 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

13. 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

14. 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)

15. 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

16. 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)

17. 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

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

19. 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