Regulation of seasonal primary productionin eastern boundary upwelling systems

Monique Messié & Francisco ChavezMonterey Bay Aquarium Research Institute

Regulation of seasonal primary productionin eastern boundary upwelling systems

Monique Messié & Francisco ChavezMonterey Bay Aquarium Research Institute

nitrate supply (N flux) ↔ potential new production (C flux)

nitrate supply(NO3

-)

regeneration (NH4

+)primary production

regenerated

new

coast

surface

mixed layer depth

150 km

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

XNitrate supply = nitrate at depth (60m)

1. The N-ratio concept

satellite-derived primary production (Behrenfeld & Falkowski, 1997)

nitrate supply(NO3

-)

regeneration (NH4

+)primary production

regenerated

new

coast

surface

mixed layer depth

wind

coastal transportEkman pumping

150 km

Comparing

primary production

and nitrate supply from satellite winds and in-situ nitrate (Messié et al., 2009)

1. The N-ratio concept

carbon-equivalent of nitrate supply assuming C:N = 106:16 (Messié et al., 2006)

satellite-derived primary production (Behrenfeld & Falkowski, 1997)

nitrate supply(NO3

-)

regeneration (NH4

+)primary production

regenerated

new

coast

surface

mixed layer depth

wind

Ekman pumpingcoastal 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

1. N-ratio concept

PP

Seasonal primary production

time

latit

ude

1. N-ratio concept

PP

Seasonal primary production vs. potential new production

time

latit

ude

NPpot

RP

150 km

nitrate supply(NO3

-)

regeneration (NH4

+)

potential RP

potential NP

coast

surface

mixed layer depth

avai

labl

e Nprimary

productionRP

NPphoto-

synthesis

N-remainnon-used nitrate

accumulation

subduction

offshore export

N-ratio

* PP

f-rati

o * P

P

N-ratio = 1. N-ratio concept

N-ratio = f-ratio if all nitrate supplied

is consumed

f-ratio = (Eppley & Peterson, 1979)

N-ratio = f-ratio +

RP = regenerated productionNP = new production

N-ratio = 1. N-ratio concept

f-ratios (Laws et al. 2000; Dunne et al., 2005)

N-ratios

(Eppley & Peterson, 1979)

f-ratio = (Eppley & Peterson, 1979)

f-ratio ~ 0.5, constant

N-ratio = f-ratio +

f-ratio ~ 0.5, constant1. N-ratio concept

N-ratio

Black contours = surface nitrate

N-ratio = f-ratioall nitrate supplied is consumed

nitrate regulating

N-ratio > f-ratioremaining nitrate

other factors regulatingN-ratio = f-ratio +

f-ratios

N-ratios

N-ratio ≤ 0.5 N-ratio ≥ 0.8

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?

?

2. N-ratio analysis

back to the definition of primary production…

PP, physical export, mortality, sinking, grazing

Temperature, species Light, nutrients

growth rate

max growth rate0 ≤ ≤ 1 limitation term𝑷𝑷=𝑏𝑖𝑜𝑚𝑎𝑠𝑠∗𝜇𝑚𝑎𝑥∗𝛾

coast

surface

mixed layer depth

biomass * growth

TemperatureLight

150 km

Physical export

residence time Tbox

wind-driven downwelling

EKE

shelf width Wshelf

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

(Messié et al., 2006)

PP, physical export, mortality, sinking, grazing

Light, nutrients(nitrate, iron)(nitrate)

Temperature, species

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 (increases offshore & vertical export of biomass & nutrients, Lathuilière et al., 2010; Gruber et al., 2011) and/or Ekman downwelling

only observed when computing Tbox up to Dupwell

coast

surface

mixed layer depth

wind

Ekman pumpingcoastal transport

150 km

upwelling

Ekman pumping

Dupwell

(Ekman downwelling)

downwelling

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)

2. N-ratio analysis

Physical export Light IronTbox EKE Ekneg PAR MLD Imean Wshelf dust

California X X XNW Africa X XPeru X X XBenguela X X X X X

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 export Light IronTbox EKE Ekneg PAR MLD Imean Wshelf dust

California

NW Africa

Peru

Benguela

3. Correlation analysis and PP regulation

Spatial correlations with PP Seasonal cycles

PPN-supplyWshelf / dustlighttemperatureTbox

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

3. Correlation analysis and PP regulationSpatial correlations with PP

Seasonal cycles

Benguela

From N-ratio analysis: high N-ratios = light / export / iron

NW AfricaFrom N-ratio analysis: high N-ratios = iron

High N-ratio narrow shelf

3. PP regulation

high N-ratios

Nitrate supplyIron supplyPhysical exportLight

• 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 supplyIron supplyPhysical exportLight

California Peru NW Africa Benguela

averaged N-ratio 0.73 0.82 0.52 0.63