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 CO2?

2. How large is the impact on atmospheric chemistry and aerosols at different spatial scales?

e.g. N2O,CH4,DMS

3. Role of coastal salt marsh and mangrove swamps?

4. Role of river discharge?

The global carbon budget 1980-1999

(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 CO2 to the atmosphere.

• Recent studies suggest a global net sink for atmospheric CO2 (0.36 Gt C yr-1; values range from of 0.2 to 1 Gt C yr-1).

The global ocean carbon budget 1980-1999

(Sabine et al., SCOPE 2004)

Units: Reservoirs in Gt C, Fluxes in Gt C yr-1

The global ocean carbon budget 1980-1999

(Sabine et al., SCOPE 2004)

?

?

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

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)

Sea-air CO2 flux: Annual mean

Global net CO2 flux : 1.5 GtC yr-1

~106 measurements, 4ox5o grid

Satellite Chlorophyll: Annual mean

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 notresolve coastal zones (Takahashi et al., 2002).

• Large temporal and spatial (incl. meso- and submesoscale eddies) variability in the coastal ocean

Large variability of pCO2 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 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 notresolve 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

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. CO2 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 CO2 balance of the oceans

Proposed outline: Key questions / areas

1. How much do coastal zones matter for global atmospheric CO2?

2. 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?• …

The end

The global carbon budget 1980-1999

(Sabine et al., SCOPE 2003)

Modern annual carbon budgetfor continental margins

(Chen, SCOPE 2004)

Preindustrial organic carbon cyclefor coastal oceans

(Chen, SCOPE 2004; after Rabouille et al., 2001)