Resource Ratios and Primary Productivity in the Ocean - George I. Hagstrom, Simon Levin, Adam Martiny
Resource Ratios and Primary Productivity in the
George I. Hagstrom, Simon Levin, Adam Martiny
Department of Ecology and Evolutionary Biology
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
Each major nutrient has diﬀerent chemistry in the ocean:
Inorganic Phosphorus: Residence time of 105 years.
Inorganic Nitrogen: N-Fixation and denitriﬁcation.
N2 + 8H+
+ 16ATP → 2NH3 + 16ADP + H2
Iron residence time 100 years.
Biologists: N is ULN
Geochemists: P is ULN
= Bp γp − m ,
= Bd (γd − m)
(ND − NS )
+ (rS − DN )m(Bp + Bd ) − γpBp
(PD − PS )
(rS m − γp)Bp
(rS m − γd )Bd
D (NS − ND ) + mrD (Bp + Bd )
D (PS − PD ) + mrD
Bp + Bd
− kP PD
P is ultimate limiting nutrient
(TPP) = m Bd + Bp =
kP DD (1−rS )
(N:P)deep ∼ (N:P)p 1 −
Challenges to Tyrrell/Redﬁeld: Iron Limitation and
Widespread iron limitation, HNLC regions and diazotrophs.
High (N:P)org in subtropical gyres, low (N:P)org in subpolar
Simple Biogeochemical Model
Three nutrients: N, P, Fe
Three phytoplankton types: diazotrophs, prokaryotes,
Three ocean regions: High latitude, low-latitude, deep ocean.
Iron Supply Shifts Nutrient Limitation Scenarios
Deep Ocean N Regulated by Limiting Nutrient Supply to
Fe Limited: ND
= (N:Fe)p − DN
P Limited: (N:P)deep = (N:P)p + DN
−(N:P)p − kU
Reconciliation: Iron limitation, high kU
, lateral transport of P depleted
waters (Weber and Deutsch).
Response to Nutrient Flux Changes
How would ocean respond to increases in nutrient ﬂuxes?
Redﬁeld picture: Rapid transition to P limitation, no change
John Martin and others: Iron/nitrate fertilization may be
Perform experiments: biogeography and stoichiometry give
Future Directions: Evolution of Phytoplankton
Many Directions to Go
Stoichiometry more plastic than indicated here.
Growth Rate Hypothesis?
Temperature, Phylogeny, Luxury Storage?
Incorporate eco-evolutionary feedbacks.
Could the ocean evolve to colimitation?