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Working Group 3: What aspects of coastal ecosystems are significant globally?

Working Group 3: What aspects of coastal ecosystems are significant globally?. Contributed by G.-K. Plattner, J. Kleypas, C. Nevison, A. Subramaniam. Coastal Zone Impacts on Global Biogeochemistry NCAR, June 2004. Outline: Key questions / areas.

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Working Group 3: What aspects of coastal ecosystems are significant globally?

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  1. Working Group 3: What aspects of coastal ecosystems are significant globally? Contributed by G.-K. Plattner, J. Kleypas, C. Nevison, A. Subramaniam Coastal Zone Impacts on Global Biogeochemistry NCAR, June 2004

  2. Outline: Key questions / areas • How much do coastal zones matter for global atmospheric CO2? • How large is the impact on atmospheric chemistry and aerosols at different spatial scales? • e.g. N2O,CH4,DMS • Role of coastal salt marsh and mangrove swamps? • Role of river discharge?

  3. The global carbon budget 1980-1999 (Sabine et al., SCOPE 2004)

  4. Coastal Ocean and Global Carbon Cycle • Conventional wisdom suggests that due to large river inputs of organic and inorganic carbon and due to fast local remineralization, the coastal oceans act as a net source of CO2 to the atmosphere. • Recent studies suggest a global net sink for atmospheric CO2(0.36Gt C yr-1; valuesrange from of 0.2 to 1 Gt C yr-1).

  5. The global ocean carbon budget 1980-1999 • Units: Reservoirs in Gt C, Fluxes in Gt C yr-1 (Sabine et al., SCOPE 2004)

  6. The global ocean carbon budget 1980-1999 • Estim. coastal fluxes: • - River input • inorg. ~0.6 • org. ~0.5 • - Sedimentation • ~0.4 • - Net sea-air CO2 flux • ~0.36? (Chen, 2004) • - Export open ocean? • Units: Reservoirs in Gt C, Fluxes in Gt C yr-1 ? ? (Sabine et al., SCOPE 2004)

  7. Coastal Ocean and Global Carbon Cycle •  The coastal zone fluxes represent the largest unknown in the CO2 balance of the oceans • Why? • Net fluxes of CO2 are small compared to gross fluxes •  difficult to measure • Global analysis of net air-sea gas exchange does not resolve coastal zones (Takahashi et al., 2002)

  8. Sea-air CO2 flux: Annual mean ~106 measurements, 4ox5o grid Global net CO2 flux : 1.5 GtC yr-1

  9. Satellite Chlorophyll: Annual mean

  10. Coastal Ocean and Global Carbon Cycle •  The coastal zone fluxes represent the largest unknown in the CO2 balance of the oceans • Net fluxes of CO2 are small compared to gross fluxes •  difficult to measure • Global analysis of net air-sea gas exchange does not • resolve coastal zones (Takahashi et al., 2002). • Large temporal and spatial (incl. meso- and submesoscale eddies) variability in the coastal ocean

  11. Large variability of pCO2 in coastal systems: e.g. in an upwelling system (California) (Friederich et al., AGU 2002)

  12. Coastal Ocean and Global Carbon Cycle •  The coastal zone fluxes represent the largest unknown in the CO2 balance of the oceans • Net fluxes of CO2 are small compared to gross fluxes •  difficult to measure • Global analysis of net air-sea gas exchange does not • resolve coastal zones (Takahashi et al., 2002). • Large temporal and spatial (incl. meso- and submesoscale eddies) variability in the coastal ocean • Net sink or source of atmospheric CO2? • Models can’t help: coastal oceans not represented in current global ocean carbon cycle models •  see working group 4 outline

  13. Past, Present and Future Role? (Chen, SCOPE 2004; adapted from Ver et al. 1999)

  14. Summary • Significant river input of carbon (~0.6 Gt C yr-1 inorganic, ~0.5 Gt C yr-1organic) into coastal ocean • Sedimentation in the coastal zone is only ~0.4 Gt C yr-1 • Recent studies nevertheless suggest a sink for atm. CO2of 0.36Gt C yr-1(range of 0.2 to 1 Gt C yr-1) • Export to open ocean? •  The coastal zone fluxes represent the largest unknown in the CO2 balance of the oceans

  15. Proposed outline: Key questions / areas • How much do coastal zones matter for global atmospheric CO2? • How much do coastal zones matter for other atmospheric compounds? • e.g. N2O, CH4, DMS • Topics: • Which coastal ecosystems are of relevance? • What’s their relative importance? • Role of biology vs. physical processes (incl. river discharge)? • Natural flux vs. anthropogenic perturbation? • …

  16. The end

  17. The global carbon budget 1980-1999 (Sabine et al., SCOPE 2003)

  18. Modern annual carbon budgetfor continental margins (Chen, SCOPE 2004)

  19. Preindustrial organic carbon cyclefor coastal oceans (Chen, SCOPE 2004; after Rabouille et al., 2001)

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