THE OCEAN CARBON CYCLE

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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 13 C 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 = 10 6 m 3 s -1 Basin Input flux Output flux Reservoir budget Turnover Time (m3/yr) (m3/yr) (m3/yr) (yr) 1 SNATL E E E SEATL E E E SANT E E E SEI-P E E E SNPAC E E E TEATL E E E TEI-P E E E DATL E E E DANT E E E DI-P E E E

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 F in Surface boxes Surface P biol F out New production i P sed (d) Input Fluxes: F in = w ji c j (advection) with c i = Q i /V i j Output Fluxes: F out = ( w ij ) c i (advection) j P sed (d) = P biol =. F (new production) ut in lower at high latitudes ut F in Thermocline and deep boxes F out R oxy Thermocline or Deep Microbial Respiration P sed (s) i P sed (d) Input Fluxes: F in = w ji c j (advection) j R oxy = k oxy. P sed (s) (microbial respiration) P sed (d) = P sed (s) - R oxy Output Fluxes: F out = ( w ij ) c i (advection) j

11 PRE-INDUSTRIAL STEADY-STATE SOLUTION (PHOSPHORUS) Integration: 4000 years Initial conditions: Homogeneous ocean (c = mol 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: C org and CaCO 3 (aragonite/calcite) production C org : C/P = 106/1 (Redfield) CaCO 3 : r carb = CaCO 3 /C org (adjustable parameter) In the thermocline: partial oxidation of C org ( k oxy ) C/P = 106/1 (Redfield) At depth: oxidation of the remaining C org ( 1-k oxy ) dissolution of CaCO 3 In each box: ph calculation and carbonate speciation Exchange with the atmosphere in each surface reservoir i: F ao = k ao. area(i). (pco 2 - pco 2 (i))

14 PRE-INDUSTRIAL STEADY-STATE SOLUTION (ALKALINITY) integration: 4000 years initial conditions: homogeneous ocean (Alk = 2474 eq/litre) r carb = CaCO 3 /C org = 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 /l), pco 2 (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 CO 2 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 CO 2 FOR THE INDUSTRIAL PERIOD Fossil fuel CO 2 emissions Rate of change in the atmosphere (dpco 2 /dt) Transfer to the ocean (model) Transfer to the biosphere (by difference)

23 SOURCES SINKS ATMOSPHERIC CO 2 BALANCE ( ) (Gt C yr -1 ) This work IPCC 1995 Fossil fuels & cements Land-use change Total Atmosphere Ocean (Model) Difference ( terrestrial biosphere)

24 13 C ISOTOPIC EVOLUTION

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 = [ F ji ( ji - i ) - F ij ( ij - i ) ] / C i j i j i where: C i = carbon content of reservoir i F ji = flux entering reservoir i (from reservoir j) F ij = flux leaving reservoir i (for reservoir j) = 13 C of the carbon in reservoir i i = 13 C of flux F ji ji (into reservoir i) = 13 C of flux F ij ij (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 ( 13 C) integration: 3000 years initial conditions: homogeneous ocean ( 13 C = )

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

1 Carbon - Motivation

1 Carbon - Motivation Figure 1: Atmospheric pco 2 over the past 400 thousand years as recorded in the ice core from Vostok, Antarctica (Petit et al., 1999). Figure 2: Air-sea flux of CO 2 (mol m 2 yr 1