THE OCEAN CARBON CYCLE

Transcription

1 THE OCEAN CARBON CYCLE 21st February Box-model of the global ocean phosphorus, alkalinity, carbon 2 Pre-industrial model 3 Evolution during the industrial period 4 13C isotopic evolution

2 BOX-MODEL OF THE GLOBAL OCEAN Phosphorus, Alkalinity, Carbon

3 PHOSPHATE DISTRIBUTION IN THE OCEAN Ant Antarctic; A Atlantic; I Indian; P Pacific; N and S Northern and Southern parts of, resp.

4 THERMOHALINE CIRCULATION surface-todeep-sea gradient inter-basin gradient

5 MODEL STRUCTURE Water fluxes in Sverdrup (Sv): 1 Sv = 106 m3 s-1 Basin SNATL SEATL SANT SEI-P SNPAC TEATL TEI-P DATL DANT DI-P Input flux (m3/yr) E E E E E E E E E E+15 Output flux (m3/yr) E E E E E E E E E E+15 Reservoir budget (m3/yr) E E E E E E E E E E+00 Turnover Time (yr)

6 DIC DISTRIBUTION IN THE OCEAN Ant Antarctic; A Atlantic; I Indian; P Pacific; N and S Northern and Southern parts of, resp.

7 ALKALINITY DISTRIBUTION IN THE OCEAN Ant Antarctic; A Atlantic; I Indian; P Pacific; N and S Northern and Southern parts of, resp.

8 OXYGEN DISTRIBUTION IN THE OCEAN Ant Antarctic; A Atlantic; I Indian; P Pacific; N and S Northern and Southern parts of, resp.

9 PRE-INDUSTRIAL MODEL

10 PHOSPHORUS: PRODUCTIVITY CONTROL Surface boxes Surface Pbiol i New production Input Fluxes: Fin = wji cj (advection) with ci = Qi/Vi j Output Fluxes: Fout = ( wij) ci (advection) j Fin Fout Psed(d) Psed(d) = Pbiol = ut. Fin (new production) ut lower at high latitudes Thermocline and deep boxes Fin Fout Psed(s) Input Fluxes: Fin = wji cj (advection) j Roxy Thermocline or Deep Microbial Respiration i Psed(d) Roxy = koxy. Psed(s) (microbial respiration) Psed(d) = Psed(s) - Roxy Output Fluxes: Fout = ( wij) ci j (advection)

11 PRE-INDUSTRIAL STEADY-STATE SOLUTION (PHOSPHORUS) Integration: 4000 years Initial conditions: Homogeneous ocean (c = μmol P/litre)

12 COMPARISON WITH DATA: PHOSPHORUS Data: Geosecs ('70)

13 CARBON AND ALKALINITY Model linked to the phosphorus model through the usage elemental ratios At the surface: Corg and CaCO3 (aragonite/calcite) production Corg: C/P = 106/1 (Redfield) CaCO3: rcarb = CaCO3/Corg (adjustable parameter) In the thermocline: partial oxidation of Corg ( koxy) C/P = 106/1 (Redfield) At depth: oxidation of the remaining Corg ( 1-koxy) dissolution of CaCO3 In each box: ph calculation and carbonate speciation Exchange with the atmosphere in each surface reservoir i: Fao = kao. area(i). (pco2 - pco2(i))

14 PRE-INDUSTRIAL STEADY-STATE SOLUTION (ALKALINITY) integration: 4000 years initial conditions: homogeneous ocean (Alk = 2474 μeq/litre) rcarb = CaCO3/Corg = 0.15 (equator. box) 0.02 (polar boxes)

15 COMPARISON WITH DATA: ALKALINITY Data: Geosecs ('70)

16 PRE-INDUSTRIAL STEADY STATE (CARBON) Initial conditions: Homogeneous ocean (DIC = 2350 μmol/l), pco2(atm) = 280 ppmv

17 EVOLUTION DURING THE INDUSTRIAL PERIOD

18 FORCING OF THE MODEL FOR THE INDUSTRIAL PERIOD Initial conditions in 1800 provided by the previously calculated pre-industrial steady state Evolution of atmospheric CO2 prescribed from 1800 to 1990

19 EVOLUTION OF DISSOLVED INORGANIC CARBON

20 EVOLUTION OF ph IN THE SURFACE RESERVOIRS

21 COMPARISON WITH DATA: CARBON Data: Geosecs ('70)

22 FLUX BALANCE OF ATMOSPHERIC CO2 FOR THE INDUSTRIAL PERIOD Fossil fuel CO2 emissions Rate of change in the atmosphere (dpco2/dt) Transfer to the ocean (model) Transfer to the biosphere (by difference)

23 ATMOSPHERIC CO2 BALANCE ( ) (Gt C yr-1) SOURCES Fossil fuels & cements Land-use change This work IPCC Total Atmosphere Ocean (Model) Difference ( terrestrial biosphere) SINKS

24 C ISOTOPIC EVOLUTION 13

25 ISOTOPIC EVOLUTION EQUATION The equation describing the evolution of the isotopic composition of a reservoir i in time can be written (approximation): d i / dt = [ Fji ( ji - i) - Fij ( ij - i) ] / Ci j i where: j i Ci = carbon content of reservoir i Fji = flux entering reservoir i (from reservoir j) Fij = flux leaving reservoir i (for reservoir j) i = 13C of the carbon in reservoir i ji = 13C of flux Fji (into reservoir i) ij = 13C of flux Fij (out of reservoir i) Notice: output fluxes only have to be considered if they are subject to fractionation, i. e., if = ij- i 0

26 PRE-INDUSTRIAL STEADY-STATE SOLUTION ( 13C) integration: 3000 years initial conditions: homogeneous ocean ( 13C = )

27 EVOLUTION OF 13C DURING THE INDUSTRIAL PERIOD (coupled ocean-atmosphere-biosphere model) Biosphere