SPARC Activity Workshop on CCl4 Zurich, Oct. 4th-6th, 2015

INVESTIGATING OCEANIC UPTAKE OF CCl4 USING GLOBAL DATA AND AN OCEAN BIOGEOCHEMISTRY

MODEL

P. Suntharalingam, L. J. Carpenter, O. Andrews, E. Buitenhuis, S.A. Andrews, S. C. Hackenberg,

J.H. Butler, S.A. Yvon-Lewis

ROLE OF THE OCEAN IN THE GLOBAL CCl4 BUDGET

TOTAL LIFETIME years

PARTIAL LIFETIME OCEAN UPTAKE

years WMO/UNEP/2014 Table 1.3

26 years 94 (82-191) Yvon Lewis and Butler 2002

SPARC 2013 24 years 81 (71-167) Butler et al. 2011

“The estimate of the total global lifetime (26 years) combined with the observed CCl4 trend in the atmosphere (−1.1 to −1.4 ppt yr-1 in 2011–2012) implies emissions of 57 (40–74) Gg yr-1 , which cannot be reconciled with estimated emissions from net reported production” WMO/UNEP 2014

AIMS and APPROACH Investigation of the Processes Governing Ocean CCl4 Uptake

• Discrepancy between current estimates of top-down vs. bottom-up estimates of CCl4 emissions

• Top-down approach is dependent on estimates of total and partial lifetimes of CCl4

• Re-examine the processes governing the ocean sink and τOCEAN using a global ocean biogeochemistry model

• Advantages : More detailed representation of ocean circulation and the

physical and biological processes influencing ocean CCl4 uptake

OUTLINE

• Introduction • Parameterizing CCl4 degradation using CCl4/AOU

Correlations

• Outline of Ocean Model CCl4 Simulations

SHORT-TERM AIM To investigate the role of biologically mediated degradation on

the ocean CCl4 distribution and air-sea flux

Data from 5 cruises spanning 83oN - 50oS

Measurements taken during 2011-2013

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2

4

6

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10

12

-50 -30 -10 10 30 50 70 90

CCl 4/

pM

ol

Latitude / deg N

AMT22TOREROACC-1AMT23ACC2

Wide variability in longitude and salinity

SLIDE : L. Carpenter

Systematic undersaturation of CCl4

Consistent with results of Butler and Yvon-Lewis SAs are NOT corrected for non-equilibrium/physical effects

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20

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60

80

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Satu

ratio

n an

omal

y, %

Latitude / deg N

AMT22 TORERO ACC-1

AMT23 ACC2

Calculated using Bullister salinity dependant kH

SLIDE : L. Carpenter

• Seen in both AMT22 and AMT23 • Causal link?

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100000

200000

300000

400000

500000

600000

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Satu

ratio

n an

omal

y, %

Latitude / deg N

SA AMT23

SA% AMT22

[Tot_Chl_a]AMT22

Surface undersaturation of CCl4 correlates with higher biological activity

SLIDE : L. Carpenter

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0 20 40 60 80 100 120

AOU

(um

ol/k

g)

% CCl4 saturation relative to surface water

• AMT22 data • Shallow depth profiles (to 150 m)

• SAs are not corrected for non-equilibrium/physical effects • Could be linked to mixing and/or biology. Which is dominant factor?

Variation of CCl4 saturation and AOU in AMT22 Depth Profiles

SLIDE : L. Carpenter

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-55 -35 -15 5 25 45 65 85

flux

/ nm

ol m

-2 d

ay-1

Latitude / deg N

AMT22 TORERO ACC1

ACC-2 AMT23

• Extrapolated global average loss rate is 3.72 x 105 mol d-1

• Leads to simple estimate of ocean partial lifetime of 102 yr

CCl4 fluxes and extrapolated ocean uptake

SLIDE : L. Carpenter

PROCESSES GOVERNING THE OCEAN CCl4 DISTRIBUTION AND AIR-SEA FLUX

1. Solubility and Gas-exchange 2. Hydrolysis 3. Degradation in sub-surface ocean (Biologically mediated ?)

GAS-EXCHANGE Flux = K . (Cocean – Catm)

Cocean

Catm

Hydrolysis

Degradation

CCl4 DEPLETION AT INTERMEDIATE DEPTHS

• Depth profiles of CCl4 indicate depletion in upper ocean

• This depletion not seen in profiles

of other halocarbons (e.g., CFC-11) • Suggestions that depletion due to

biologically mediated degradation of CCl4 in seawater

(e.g., Wallace et al. 1994, Krysell et al. 1994)

CCl4

CFC-11

West Pacific : Station 41, 39.0°N, 165°E Data from Bullister et al. 1992 reported in Lobert et al. 1995

(OAXTX92)

Table 1 : Min et al. 2010

Estimates of CCl4 Removal rates in Marine Environments

Higher rates in anoxic waters

Hydrolysis rate small

Depletion method not well understood. Hypothesis that it is biologically mediated

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0 20 40 60 80 100 120

AOU

(um

ol/k

g)

% CCl4 saturation relative to surface water

• AMT22 data • Shallow depth profiles (to 150 m)

• SAs are not corrected for non-equilibrium/physical effects • Could be linked to mixing and/or biology. Which is dominant factor?

Variation of CCl4 saturation and AOU in AMT22 Depth Profiles

SLIDE : L. Carpenter

N2O FORMATION IN OXYGENATED WATERS

•Linear relationships observed between ∆N2O (‘excess N2O) and AOU (Apparent Oxygen Utilization, ‘oxygen deficit’) in oxic waters

•N2O model parameterizations estimate N2O production as a function of oxygen consumption

Measurements in the North Atlantic Walter et al. 2006

Apparent Oxygen Utilization

∆N2

O ‘E

xces

s N2O

’

Observed ∆ N2O vs. AOU

N2O FORMATION IN OXYGENATED WATERS

•Linear relationships observed between ∆N2O (‘excess N2O) and AOU (Apparent Oxygen Utilization, ‘oxygen deficit’) in oxic waters

•N2O model parameterizations estimate N2O production as a function of oxygen consumption

Represent CCl4 degradation by analogous model parameterizations ?

Measurements in the North Atlantic Walter et al. 2006

Apparent Oxygen Utilization

∆N2

O ‘E

xces

s N2O

’

Observed ∆ N2O vs. AOU

PARAMETERISATION OF MARINE N2O SOURCE

Empirical parameterisation : Based on ∆N2O and AOU data

2 2 2 2N O Production = [O Consumption] ( ) [O Consumption]f Oα β⋅ + ⋅ ⋅

Suntharalingam et al. 2000; 2012

∆N2

O

AOU

Can CCl4 degradation be represented by analogous model

parameterizations ?

PARAMETERISATION OF OCEANIC CCl4 DEGRADATION

CCl4 Degradation = (α + β f1(O2) + γ f2 (Temp) + …) [O2 Consumption]

Environmental factors reported to influence oceanic CCl4 degradation include : •AOU •Oxygen level (Hypoxia, Anoxia) •Temperature •Others ? Krysell et al. 1994, Wallace et al. 1994, Tanhua et al. 1996, Lee et al. 1999, Huhn et al. 2001, etc.

Potential form of model degradation parameterization :

PARAMETERISATION OF MARINE CCl4 DEGRADATION

CCl4 Degradation = (α + β f1(O2) + γ f2 (Temp) + …) [O2 Consumption]

Environmental factors reported to influence oceanic CCl4 degradation include : •AOU •Oxygen level (Hypoxia, Anoxia) •Temperature •Others ? Krysell et al. 1994, Wallace et al. 1994, Tanhua et al. 1996, Lee et al. 1999, Huhn et al. 2001, etc.

Potential form of model degradation parameterization :

INITIAL FOCUS

•Ocean Biogeochemistry and Ecosystem

. PISCES-PlankTOM10 Includes cycles of N,P,O2, Fe, organic and inorganic C, and a multi-component ecosystem model Aumont and Bopp, 2006; Le Quere et al. 2015

DMS : Vogt et al. 2010

N2O : Suntharalingam et al. 2012; Buitenhuis et al. in prep.

CCl4 : O. Andrews et al. (this study)

OCEAN AND BIOGEOCHEMISTRY MODEL

NEMO-PlankTOM • Physical Circulation

OPA8.1 ocean model. ORCA2 variable grid (2o x 1.5o with higher resolution (0.5o) at equator and poles, 31 levels)

Madec et al. 1998

Gas Exchange at Surface CCl4 solubility and Gas-exchange : Bullister and Wisegarver 1998; Wanninkhof 1992 Hydrolysis : Jeffers et al. 1996, 2006; Huhn et al., 2001

Biologically mediated degradation in sub-surface waters Based on analysis of oceanic CCl4/AOU correlations

NEMO-PlankTOM CCl4 SIMULATION

CCl4 Depth Profile Measurements CARINA-PACIFICA Data Synthesis

http://cdiac.ornl.gov/oceans/GLODAPv2/

Water column average (pmol/kg)

CCl4 Measurements from CARINA-PACIFICA Data Synthesis ZONAL MEAN

80N 80S EQ

0

2000m

4000m

(pmol/kg)

NORTH ATLANTIC ∆CCl4 / AOU Correlations

R2 =0.54 R2 =0.68

R2 =0.75

0-150m 150-250m

Significant linear correlations in upper

ocean

Range -0.031 to -0.084 (pmol/µmol)

Slope= - 0.031 (pmol/umol) Slope= - 0.026 (pmol/umol)

Slope= - 0.084 (pmol/umol)

250-500m

“∆CCl4” is the CCl4 deficit in comparison

to atmospheric equilibrium

INDIAN OCEAN ∆CCl4 / AOU Correlations

R2 =0.94 R2 =0.65

R2 =0.01

Slope= - 0.061 (pmol/umol) Slope= - 0.031 (pmol/umol)

Slope= 0.001 (pmol/umol)

150-250m 0-150m

250-500m

NORTH ATLANTIC ∆CFC-12 / AOU Correlations

R2 =0.003 R2 =0.01

R2 =0.02

0-150m 150-250m

250-500m

No significant correlations

between CFC-12 and AOU

Apparent Oxygen Utilization (AOU) in Upper Ocean NEMO-PlankTOM10

Depth Average 150m-1000m

(µmol/L)

Highest values associated with tropical oxygen minimum zones

SUMMARY

• Surface measurements from the Atlantic, Pacific and Arctic Oceans

show persistent undersaturation of CCl4, and correlations with levels of higher biological activity. Flux data suggest revised τOCEAN of 102 years (L. Carpenter et al. data)

• Analysis of CCl4 deficit/ AOU correlations from upper ocean

measurements display significant linear correlations, and provide support for biological degradation of CCl4 in the water column.

• These correlations are a promising means of parameterizing ocean biogeochemical models. They will support ongoing NEMO-PlankTOM simulations to identify the processes governing ocean CCl4 uptake and improve quantification of τOCEAN.

Automated purge and trap set-up

Methods • (Auto)Purge &Trap - TD - GC-MS (Agilent 6850 GC - 5975C MS) - underway water and depth samples: [CCl4]seawater

• TD - GC-MS (also Agilent 6850 GC - 5975C MS) - atmospheric sampling: [CCl4]air

• Halocarbons, isoprene, DMS, monoterpenes, BTEX

Water

MFC box TD-GC-MS

Standard

Air/ Blank

tap

Zero N2

VOC scrubber

Water removal

Andrews et al., Ocean Sci., 2015

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ACC2 (Arctic summer)

Arctic waters – variability in SA linked to water type (temp, salinity)

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SA, %

Salinity PSU

ACC-1

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ACC1 (Arctic winter)

salinity SA% SST

• Lower SA% in colder, fresher water (linked to lower CCl4 under sea-ice?)

• Little biological activity in these waters

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flux

/ nm

ol m

-2 d

ay-1

Latitude / deg N

AMT22 TORERO ACC1

ACC-2 AMT23

• Extrapolated global average loss rate is 3.72 x 105 mol d-1

• Leads to simple estimate of ocean partial lifetime of 102 yr

CCl4 fluxes and extrapolated ocean uptake

N2O Cruise Measurements SAGA2, BLAST2, RITS89, AMT, MEMENTO

J. Butler, J. Elkins, H. Bange, G. Forster, A. Freing, C. Nevison,

Global Mean : Observations and Model

OBS

‘Nitrification’ High 2β

Standard Nevison

N2O Model Evaluation N2O Simulations vs. Compiled Cruise Measurements

Suntharalingam et al. 2012

AIR-SEA CCl4 FLUXES NEMO-PlankTOM10 : Solubility/Gas-Exchange of CCl4 ONLY

VERY PRELIMINARY RESULTS (3 year run)

Red= Ocean Uptake

2 2 2 2N O Production = [O Consumption] ( ) [O Consumption]f Oα β⋅ + ⋅ ⋅

‘Nitrification source’

Linear dependence on rate of organic matter remineralization

‘High Yield : Sub-oxic zones’

Non-linear dependence with higher N2O yield at low oxygen levels

PARAMETERISATION OF BIOLOGICAL CCl4 LOSS

Observations of ∆ N2O vs. AOU Lab measurements of enhanced N2O yield in low-O2 environments

∆N2

O

N 2O

Yield

O2 (mg/l) AOU

Goreau et al. 1980

SURFACE ONLY

DEPTH PROFILES OF N2O AND O2 : Oxygenated Ocean

N. Atlantic W. Pacific

W. Pacific

DATA SOURCES : Butler et al. 1989 (B89); Cohen and Gordon 1979 (CG79); Yoshinari 1979 (Y79); Yoshida et al. 1989 (Yo89)