John L. Bullister (NOAA-PMEL)Rolf E. Sonnerup (UW-JISAO) David P. Wisegarver (NOAA-PMEL)

Using Chlorofluorocarbons to Better Constrain Estimates of Anthropogenic CO2 Uptake in the Ocean

Outline

• CFCs and Sulfur Hexafluoride (SF6) as Transient Tracers

• Estimating Water Mass Formation Rates using CFCs

• CFC concentration-derived tracer ages

• Examples of CFC tracer ages to help estimate anthropogenic CO2

• Improved age information using Transit Time Distributions (TTDs)

• Advantages of multiple tracers (CFCs and SF6)

• Progress in more routinely including SF6 with CFC measurements in the CLIVAR Repeat Hydrography Program

CFC-12 (F12) CCl2F2

CFC-11 (F11) CCl3F

Sulfur Hexafluoride SF6

Other Tracers:Radiocarbon 14C

13CTritium 3H

3He

F-12

SF6

CFCs and SF6 as Time-dependent Tracers

• Anthropogenic

• Conservative in seawater

• Well characterized input histories

• Sensitive analytical techniques available

• Provide information on rates and pathways of ocean circulation and mixing processes

• Evaluation of Ocean General Circulation Models

• Useful in the estimation of the uptake of anthropogenic CO2 in the ocean

CFC Column Inventory (mole km-2)

Estimating Water Mass Formation Rates using CFC Inventories

• I = ∫R(t) C(q,S,t) dt

• I is measured CFC Inventory

• R(t) is water mass formation rate• C(q,S,t) is CFC concentration in newly formed water

Using CFC inventories, water mass formation rates have been determined for:

•Antarctic Bottom Water (AABW) •Greenland Sea Deep Water (GSDW) •Labrador Sea Deep Water (LSW) •North Atlantic Deep Water (NADW)

Data from repeat surveys have allowed estimates to be made of changes in the rate of formation of GSDW and LSW on decadal timescales.

Tracer Ages Determined by comparing the measured tracer concentration in a sub-surface

water sample with the atmospheric record:

Tracer Ages

Determined by comparing the measured tracer concentration in a sub-surface

water sample with the atmospheric record

Tracer Ages

Determined by comparing the measured tracer concentration in a sub-surface

water sample with the atmospheric record

Tracer Ages

Determined by comparing the measured tracer concentration in a sub-surface

water sample with the atmospheric record

Tracer Age = 27 years

Tracer Ages

Determined by comparing the measured tracer concentration in a sub-surface

water sample with the atmospheric record

In the presence of mixing, each water parcel is composed of multiple components, and the resultant tracer age of the mixture can be biased from the average or ‘ideal’ age of the constituents

Direct Use of CFC Tracer Ages to Estimate Anthropogenic CO2 uptake

McNeil et. al. 2003.(McNeil, Matear, Key, Bullister, Sarmiento, 2003. Science, 299, 235-219.)

Used WOCE global CFC-12 data set.

CFC-12 tracer ages used directly to estimate change in global anthropogenic CO2 inventory from 1980-1999.

Change in anthropogenic CO2:

Cant(t2) - Cant(t1) =

Direct Use of CFC Tracer Ages to Estimate Anthropogenic CO2 uptake

McNeil et. al. 2003.(McNeil, Matear, Key, Bullister, Sarmiento, 2003. Science, 299, 235-219.)

Used WOCE global CFC-12 data set.

CFC-12 tracer ages used directly to estimate change in global anthropogenic CO2 inventory from 1980-1999.

Change in anthropogenic CO2:

Cant(t2) - Cant(t1) = DICeq [S,T, ALK0,fCO2(t2-ta)] - DICeq [S,T, ALK0,fCO2(t1-ta)] t2 = 1999

t1 = 1980

ta = observed CFC12 tracer age

Direct Use of CFC Tracer Ages to Estimate Anthropogenic CO2 uptake

McNeil et. al. 2003.(McNeil, Matear, Key, Bullister, Sarmiento, 2003. Science, 299, 235-219.)

Used WOCE global CFC-12 data set.

CFC-12 tracer ages used directly to estimate change in global anthropogenic CO2 inventory from 1980-1999.

Change in anthropogenic CO2:

Cant(t2) - Cant(t1) = DICeq [S,T, ALK0,fCO2(t2-ta)] - DICeq [S,T, ALK0,fCO2(t1-ta)] t2 = 1999

t1 = 1980

ta = observed CFC12 tracer age

Anthropogenic CO2

Sabine et. al., 2004: 118±19 petagrams of carbon(Sabine, Feely, Gruber, Key, Lee, Bullister, Wanninkhof, Wong, Wallace, Tilbrook, Peng, Kozyr, Ono, Rios,

2004.Science, 305, 367-371.)

Transit Time Distributions (TTDs)

In the real ocean with mixing, each water parcel is actually the sum of many individual components, each component having its individual path and time scale.

TTDs can be characterized by a mean age (Γ) and width (Δ).

Transit Time Distributions (TTDs)

In the real ocean with mixing, each water parcel is actually the sum of many individual components, each component having its individual path and time scale.

TTDs can be characterized by a mean age (Γ) and width (Δ).The shape of TTDs can vary.In the simple case of a 1-D advection diffusion model, TTDs have an inverse

gaussian shape.

Waugh et al, 2006

(Waugh, Hall, McNeil, Key, Matear, 2006. Tellus, 58B, 376-389)

Use of CFC-12 TTDs to Estimate Anthropogenic CO2 uptake

Waugh et. al. (2006) used the WOCE global CFC-12 data set.

CFC-12 derived TTDs used estimate global anthropogenic CO2 inventory.

They assumed the form of the CFC-12 TTD where:

Δ/Γ = 1

Resulting anthropogenic CO2 inventory similar to Sabine et al., 2004, but with some significant differences in spatial patterns.

Using 2 or more tracers to constrain TTDs

Waugh et. al., GRL (2002)

(Waugh, Vollmer, Weiss, Haine, Hall, 2002. GRL 29, doi: 10.1029/2002GL016201)

Bullister, et al (2006)

(Bullister, Sonnerup, Wisegarver, 2006. GRL 33, DOI:10.1029/2006GL026514)

Summary: CFC uses

• To determine the rates and pathways of ocean circulation and mixing processes.

• To estimate water mass formation rates (and determine long-term changes in these rates).

• To improve estimates of the rates of uptake and storage of anthropogenic CO2 in the ocean.

• To estimate the rates of key biogeochemical processes in the ocean• To provide a unique way to test numerical ocean model simulations,

evaluate strengths and weaknesses in the models, and suggest ways to improve the models.

• To determine regions of the ocean where surface-derived changes can propagate into the interior on decadal time-scales.