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Anthropogenic CO 2 invasion

Anthropogenic CO 2 invasion. I. Anthropogenic CO 2 uptake. Tacoma, WA (1891). A. “Perturbed” carbon cycle (1990s). Pre-industrial Anthropogenic. Anthro Sources: Fossil fuels: 244 GtC Deforestation: ~140 GtC. Anthro Sinks: Ocean: 118 19 GtC (~30%) Reforestation: ~100 GtC (~25%)

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Anthropogenic CO 2 invasion

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  1. Anthropogenic CO2 invasion

  2. I. Anthropogenic CO2 uptake

  3. Tacoma, WA (1891)

  4. A. “Perturbed” carbon cycle (1990s) Pre-industrial Anthropogenic Anthro Sources: Fossil fuels: 244 GtC Deforestation: ~140 GtC Anthro Sinks: Ocean: 118 19 GtC (~30%) Reforestation: ~100 GtC (~25%) Atmosphere: 165 GtC (~45%)

  5. Pre-anthropogenic ocean:atmosphere DIC:CO2 >60:1 (98%) Anthropogenic ocean:atmosphere uptake ~0.7:1 (40%) What limits ocean uptake of CO2? How do we measure ocean uptake? What is the equilibrium capacity for uptake? What are the kinetic constraints?

  6. B. Measuring ocean uptake • 1. Direct measurement • measure increase of DIC over time • get expected rate of change from Revelle Factor • measureable but small compared to spatio-temporal variability

  7. 2. Isolating anthro component of DIC inventory • if pre-industrial preformed DIC were known, then it could be • subtracted from observed preformed DIC • pre-industrial preformed DIC estimated by additionally • considering ventilation age (complicated)

  8. Spatial pattern: Revelle Factor • higher values mean smaller DIC rise for a given pCO2 rise • higher DIC waters have higher Revelle Factor (high lats) • at constant Alk, adding DIC shifts equilibrium to left, towards • CO2(aq) • keeps equilibrium pCO2 high and limits uptake of CO2 Sabine et al. (2004) Science

  9. low latitude surface has more uptake due to lower Revelle Factor (lower DIC) • greater penetration into subtropical gyres and NADW Sabine et al. (2004) Science

  10. Water column inventory of anthropogenic CO2 Sabine et al. (2004) Science

  11. C. Ocean’s equilibrium uptake capacity • 1. DIC buffer • ocean’s uptake capacity is large due to reaction with DIC • calculate equilibrium uptake using Revelle Factor • for top 75 m in equilibrium: 8% in ocean (ignoring land) • for entire ocean volume: 81% in ocean • timescale depends on mixing (e-folding ~300 y) • since Revelle Factor rises as DIC rises, capacity will • decrease in future

  12. 2. CaCO3 buffer • dissolution of seafloor CaCO3raises Alk:DIC 2:1 • this drives DIC away from CO2(aq) and allows more uptake • total ocean uptake now ~90% • timescale depends on pore water diffusion and dissolution • kinetics (e-folding ~4000 y)

  13. 3. Weathering buffer • reaction with all CaCO3 on land still leaves 8% in atmosphere • silicate weathering ultimately removes rest of perturbation

  14. Remaining in atmosphere ~50% after 400 y ~20% after 2000 y ~8% after 40,000 y

  15. II. Ocean acidification • CO2 addition shifts DIC away from CO32- and OH- (lower pH) • surface pH has already dropped by 0.1 • at constant Alk, 2X pCO2 (560 ppm): CO32-↓30%, pH ↓0.3 IPCC4

  16. aragonite lysocline has shoaled by o(100 m) in Indo-Pacific • slight buffering due to reduced calcification (alkalinity gain) • greater buffering possible via sediment dissolution (longer) Feely et al. (2004) Science

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