GOES-R3: Coastal CO2 fluxes

Pete Strutton, Burke Hales & Ricardo LetelierCollege of Oceanic and Atmospheric Sciences

Oregon State University

1. The coastal ocean as a CO2 sink (?)

2. Magnitude and variability of fluxes3. Measurements during field work phase

Coastal CO2 Fluxes

• pCO2 in upwelling systems (coastal & equatorial) is associated with characteristic chlorophyll and SST signatures.

• Using techniques such as multiple linear regression, we can determine sea surface pCO2 from space.

• Combining this with winds from either scatterometer(s) or coastal/buoy meteorological stations permits flux calculations.

• Important: In many areas we don’t even know the sign of the flux.

• Coastal ocean important for quantifying terrestrial fluxes.

NO3

NO3 gradient

Turbulent eddy-diffusion

NO3 flux

Coastal CO2: Relationship to temperature and chlorophyll

Productivity & CO2 uptake

N limitation offshore

Coastal CO2: Relationship to temperature and POC

Characteristics of the Oregon upwelling system

What makes this region a CO2 sink?• Strong (but episodic) upwelling throughout summer.• Extremely rapid depletion of NO3 and CO2.

– NO3 depleted from ~34 M to essentially zero over ~10km

– Corresponding drawdown of CO2 from ~600 to 200ppm– Low concentrations offshore persist, despite variability nearshore– Mean along-transect CO2 concentration typically ~300ppm

– Implies CO2 ~70ppm (as much as 150ppm on some transects)

• Minimal warming of the upwelled waters (cf California?)• Keep these properties in mind for field work

Characteristics of the California upwelling system

• In contrast to Oregon, not a strong source or sink.• Possible reasons (ie differences from Oregon)

– Limitation of CO2 drawdown by something other than NO3

– Greater warming (works against biological uptake)• Evidence for a significant change, towards a source, circa

1998• Illustrates the level of (lack of) understanding of the spatial

and temporal variability.

Coastal CO2 Fluxes: Satellite requirements

• Chlorophyll and SST will enable significant progress via multiple linear regression techniques.

• Temporal resolution ~3 hours will enable (primitive) budgets to be calculated: tracking of processes such as productivity and subduction. Higher temporal resolution of course better.

• This is a dynamic environment – any ability to ‘clear’ or alias clouds will enhance badly-needed coverage.

• Critical spatial scales ~1 to 10km.• Current and proposed observational programs will provide the

necessary in situ data for validation.

Field work: Underway measurements

• pCO2• Optics: ac9 (chl and POC), chl and CDOM fluorescence• Physics: SST, salinity, winds for flux calculations• Nutrients: Help interpret the drawdown story, particularly

important for the MB experiment (NO3 vs Fe limitation)• Include wind data from coastal stations, buoys and

scatterometer for comparison and estimates of spatial/temporal variability

• Consider the longer time scales: Frame our time window there within the year's upwelling dynamics

Field work: Sampling plan

• Repeated, long transects of all parameters• Sub-km spatial resolution from very near shore, then offshore

to where CO2 and NO3 stabilize• existing data suggest ~150km at most for Monterey Bay• Ideal: Uninterrupted transect work out (15+ hours) station

work on the way back in• Quantify spatial/temporal variability of the on-to-offshore

gradient• Do this ~5 times during the experiment, under different types

of upwelling conditions• Repeated aircraft overflights along the same track but at

higher repetition would fill in the blanks.

Data analysis and interpretation

• Correlation (and other tools) to determine the relationship between pCO2 and the measured optical/physical properties

• Quantification of the rates of warming and CO2 drawdown from on- to off-shore

• Quantification of the spatial and temporal variability using data from repeated transects

• Use higher spatial and temporal resolution overflights to quantify precision/accuracy as a function of sampling

• Use this to justify our goals for spatial/temporal sampling

Coastal CO2: Relationship to physics and biology

Productivity & CO2 uptake

N limitation offshore

What is the magnitude of the sink?

• Assume the conditions off Oregon are characteristic of upwelling regions along the entire west coast.

• Assume an upwelling season from May to August.• Carbon sink is ~0.02 Pg C, approx. 5% of the annual mean

North Pacific sink.• …or ½ of the North Pacific sink for the same time period (ie

May to August).