Resource Ratios and Primary Productivity in the Ocean - George I. Hagstrom, Simon Levin, Adam Martiny
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Resource Ratios and Primary Productivity in the Ocean - George I. Hagstrom, Simon Levin, Adam Martiny
- 1. Resource Ratios and Primary Productivity in the Ocean George I. Hagstrom, Simon Levin, Adam Martiny Princeton University Department of Ecology and Evolutionary Biology
- 2. Stoichiometry Couples Nutrient Cycles Photosyntheis in surface ocean pumps carbon to the deep. Phytoplankton require nitrogen, phosphorus, iron, and sometimes other nutrients (sillicon) Depletion of these nutrients in surface ocean slows biological pump, couples Carbon cycle to nutrient cycles. Strength of coupling is elemental stoichiometry of phytoplankton. C OO C OO C OO
- 3. Nutrient Timescales Each major nutrient has different chemistry in the ocean: Inorganic Phosphorus: Residence time of 105 years. Inorganic Nitrogen: N-Fixation and denitrification. N2 + 8H+ + 8e− + 16ATP → 2NH3 + 16ADP + H2 Iron residence time 100 years.
- 4. Redfield-Tyrrell Paradigm Biologists: N is ULN Geochemists: P is ULN dBp dt = Bp γp − m , dBd dt = Bd (γd − m) dNS dt = (ND − NS ) τS + fN DS + (rS − DN )m(Bp + Bd ) − γpBp dPS dt = (PD − PS ) τS + fP DS + (rS m − γp)Bp (N:P)org + (rS m − γd )Bd (N:P)org dND dt = τ −1 D (NS − ND ) + mrD (Bp + Bd ) DS DD dPD dt = τ −1 D (PS − PD ) + mrD Bp + Bd (N:P)org DS DD − kP PD P is ultimate limiting nutrient (TPP) = m Bd + Bp = fP (N:P)p kP DD (1−rS ) Homeostasis (N:P)deep ∼ (N:P)p 1 − DN 1−rS (N:P)p
- 5. Challenges to Tyrrell/Redfield: Iron Limitation and Stoichiometry Widespread iron limitation, HNLC regions and diazotrophs. High (N:P)org in subtropical gyres, low (N:P)org in subpolar gyres.
- 6. Simple Biogeochemical Model Three nutrients: N, P, Fe Three phytoplankton types: diazotrophs, prokaryotes, eukaryotes Three ocean regions: High latitude, low-latitude, deep ocean.
- 7. Ultimate Limiting Nutrient Controlled by Supply and Demand Resource Supply: JP,L = 1 τL (PD − PL) + fP,L dL , JFe,L = 1 τL (FeD − FeL) + fFe,L dL , JN,L = 1 τL (ND − NL) + fN,L dL JP,U = 1 τU (PD − PU ) + fP,U dL , JFe,U = 1 τL (FeD − FeU ) + fFe,U dU , JN,U = 1 τU (ND − NU ) + fN,U dU Normalize by resource demand: φP,L = (N:P)pJP,L. φFe,L = (N:Fe)pJFe,L, φN,L = JN,L φP,U = (N:P)uJP,U , φFe,U = (N:Fe)uJFe,U , φN,U = JN,U Limiting nutrients set by lowest supply to demand ratio: WL =P,Fe (φP,L, φFe,L), WU =N,P,Fe (φP,U, φFe,U, φN,U) TPP = α1 ALφWL (1 − rS ) + α2fN,L + AUφWU (1 − rS ) α1 = 1, α2 = 0 when (N:P)p = (N:P)d or (N:Fe)p = (N:Fe)d .
- 8. Iron Supply Shifts Nutrient Limitation Scenarios
- 9. Deep Ocean N Regulated by Limiting Nutrient Supply to LL Fe Limited: ND JFe,LτL = (N:Fe)p − DN 1−rS (N:Fe)p + JFe,U JFe,L (N:Fe)u P Limited: (N:P)deep = (N:P)p + DN 1−rS −(N:P)p − kU kL (N:P)u Reconciliation: Iron limitation, high kU kL , lateral transport of P depleted waters (Weber and Deutsch).
- 10. Response to Nutrient Flux Changes How would ocean respond to increases in nutrient fluxes? Redfield picture: Rapid transition to P limitation, no change in TPP. John Martin and others: Iron/nitrate fertilization may be important. Perform experiments: biogeography and stoichiometry give new mechanisms.
- 11. Future Directions: Evolution of Phytoplankton Stoichiometry Many Directions to Go Stoichiometry more plastic than indicated here. Frugality? Growth Rate Hypothesis? Temperature, Phylogeny, Luxury Storage? Incorporate eco-evolutionary feedbacks. Could the ocean evolve to colimitation?
- 12. Thanks!