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

Outline: Key questions / areas 1.How much do coastal zones matter for global atmospheric CO 2 ? 2.How large is the impact on atmospheric chemistry and aerosols at different spatial scales? e.g. N 2 O,CH 4,DMS 3.Role of coastal salt marsh and mangrove swamps? 4.Role of river discharge?

The global carbon budget (Sabine et al., SCOPE 2004)

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 CO 2 to the atmosphere. Recent studies suggest a global net sink for atmospheric CO 2 (0.36 Gt C yr -1 ; values range from of 0.2 to 1 Gt C yr -1 ).

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

The global ocean carbon budget (Sabine et al., SCOPE 2004) ? ? Estim. coastal fluxes: - River input inorg. ~0.6 org. ~0.5 - Sedimentation ~0.4 - Net sea-air CO 2 flux ~0.36? (Chen, 2004) - Export open ocean? Units: Reservoirs in Gt C, Fluxes in Gt C yr -1

Coastal Ocean and Global Carbon Cycle  The coastal zone fluxes represent the largest unknown in the CO 2 balance of the oceans Why? Net fluxes of CO 2 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)

Sea-air CO 2 flux: Annual mean Global net CO 2 flux : 1.5 GtC yr -1 ~10 6 measurements, 4 o x5 o grid

Satellite Chlorophyll: Annual mean

Coastal Ocean and Global Carbon Cycle  The coastal zone fluxes represent the largest unknown in the CO 2 balance of the oceans Net fluxes of CO 2 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

Large variability of pCO 2 in coastal systems: e.g. in an upwelling system (California) (Friederich et al., AGU 2002)

Coastal Ocean and Global Carbon Cycle  The coastal zone fluxes represent the largest unknown in the CO 2 balance of the oceans Net fluxes of CO 2 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 CO 2 ? Models can’t help: coastal oceans not represented in current global ocean carbon cycle models  see working group 4 outline

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

Summary Significant river input of carbon (~0.6 Gt C yr -1 inorganic, ~0.5 Gt C yr -1 organic) into coastal ocean Sedimentation in the coastal zone is only ~0.4 Gt C yr -1 Recent studies nevertheless suggest a sink for atm. CO 2 of 0.36 Gt 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 CO 2 balance of the oceans

Proposed outline: Key questions / areas 1.How much do coastal zones matter for global atmospheric CO 2 ? 2.How much do coastal zones matter for other atmospheric compounds? e.g. N 2 O, CH 4, 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? …

The end

The global carbon budget (Sabine et al., SCOPE 2003)

Modern annual carbon budget for continental margins (Chen, SCOPE 2004)

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