Temporal variability of the CO
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Temporal variability of the CO 2 system in the North Atlantic Ocean. Helmuth Thomas 1 , Friederike Prowe 1,4 , Ivan D. Lima 2 , Scott C. Doney 2 , Rik Wanninkhof 3 , Richard Greatbach 1,4 , Antoine Corbière 5 & Ute Schuster 6.

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Helmuth thomas 1

Temporal variability of the CO2 system in the North Atlantic Ocean

Helmuth Thomas1,

Friederike Prowe1,4, Ivan D. Lima2, Scott C. Doney2, Rik Wanninkhof3, Richard Greatbach1,4,

Antoine Corbière5 & Ute Schuster6

1: Dalhousie University, Halifax, Canada. 2: Woods Hole Oceanographic Institution, Woods Hole MA, USA. 3: NOAA, Miami, USA. 4: now at IfM-Geomar, Kiel Germany. 6: Laboratoire d'Océanographie et du Climat: Expérimentations et Approches

Numériques, Pairs France. 6:University of East Anglia, Norwich, UK


Helmuth thomas 1

Observations in the North Atlanticduring 1995-2002/4

Thomas et al., 2008, GBC

North Sea

ΔpCO2declining

VOS line UK –

Caribbean

ΔpCO2 declining

Schuster and Watson

2007

Sub Polar North Atlantic

ΔpCO2 declining

Omar and Olsen, 2006

North Atlantic Drift Region

ΔpCO2 declining

Lefèvre et al., 2004

South of Greenland

ΔpCO2 declining

Corbiere et al., 2007

NW Atlantic

ΔpCO2 increasing

Lueger et al., 2006

BATS, Bermuda

ΔpCO2 constant

Bates, 2001/7


Helmuth thomas 1

What is the driver for the observed CO2 flux

variability in the North Atlantic Ocean?

Simulations for the North Atlantic Ocean

  • Simulations from 1958-2004

  • Community Climate System Model, POP coarse resolution

  • Ecosystem model coupled to modified OCMIP-II biogeochemistry

  • NCEP/NCAR reanalysis forcing

  • Further reading: Doney et al., 2004, Moore et al. 2004, Yeager et al., 2006

  • pCO2 decomposition (DICnorm, ATnorm, T, S)

  • Trend regression analysis

  • Anthropogenic and preindustrial runs

Thomas et al., 2008, GBC


Helmuth thomas 1

Simulations vs. Observations for the North Atlantic Ocean

Thomas et al., 2008, GBC


Helmuth thomas 1

Nuka Arctica

Skògafoss

Ocean CO2 trends in the North Atlantic Subpolar Gyre :

winter 1993-2003/2001-2008 (based on DIC/TA Suratlant data)

Full story presented by

Corbière et al. (Poster, CT1)


Uk caribbean route

1994-1995

2002-2005

0

[mol CO2 m-2 yr-1]

1.4

mean

UK-Caribbean route

Schuster and Watson, 2007

JGR

CO2 uptake in 1994/5 and 2002/4

The overall sink (14-65 degrees N):

1995: 0.40 PgC (Takahashi climatology)

2005: 0.24 Pg C for 2005

40% decline in CO2 uptake?


Helmuth thomas 1

Simulations vs. Observations for the North Atlantic Ocean

One conclusion:

We need to maintain an observing system.

Tool:

Trend regression analysis

instead of differences.


Helmuth thomas 1

Simulations vs. Observations for the North Atlantic Ocean

Tool:

Trend regression analysis

instead of

differences


Helmuth thomas 1

Thomas et al.

2008, GBC

Simulations vs. Observations for the North Atlantic Ocean

pos. NAO

Note change

in scale!

neutr./neg. NAO

Most of the observations

cover the 95-04 period

long term

ΔpCO2 trends


Helmuth thomas 1

Outline

1: Fundamental

control

2: Adjustments

3: Overlaying

perturbance


Nao the subpolar and subtropical gyres

1: Fundamental control

NAO & the subpolar and subtropical gyres

Positive NAO:

Strong westerlies

Strong NAC

Negative NAO:

weaker westerlies

weaker NAC

http://www.noc.soton.ac.uk

↑http://www.ldeo.columbia.edu/res/pi/NAO/

http://www.ldeo.columbia.edu/res/pi/NAO/ ↑


North atlantic oscillation during the past two decades

1: Fundamental control

North Atlantic Oscillation during the past two decades

Thomas et al., 2008, GBC


Helmuth thomas 1

1: Fundamental control

Labrador Current

Response of surface ocean to NAO forcing

Thomas et al., 2008, GBC

Surface velocity

positive NAO

(1989-1995 average)

x

Subpolar gyre

x

Subtropical gyre

(each 2nd grid point shown)


Helmuth thomas 1

1: Fundamental control

Response of surface ocean to NAO forcing

Surface velocity difference

Thomas et al., 2008, GBC

Neutral - positive NAO

(1996/2004av.) - (1989/1995av.)

Labrador Current

Subpolar gyre

Subtropical gyre

(each 2nd grid point shown)


Helmuth thomas 1

1: Fundamental control

Response of surface ocean to NAO forcing

Thomas et al., 2008, GBC


Helmuth thomas 1

1: Fundamental control (one more detail)

Thomas et al., 2008, GBC

Expansion of subtropical gyre during positive NAO

Annual salinity anomalies:

Relevance western subpolar gyre:

Labrador Current cannot move south, it is diverted into the subpolar gyre


Helmuth thomas 1

1: Fundamental control

Pos. NAO

Neutr./neg. NAO

Response of surface ocean to NAO forcing


Dic norm and salinity in the north atlantic

1: Fundamental control

Pos. NAO

Neutr./neg. NAO

DICnorm and Salinity in the North Atlantic

North Atlantic Current is fed by low DICnorm / high salinity water:

Northward transport of a

CO2 deficiency

Thomas et al., 2008, GBC


Helmuth thomas 1

Main driver of variability:

DICnorm

(AT,norm exerts minor control)

Example:

2 stations at

the eastern

and western

subpolar gyre

1: Fundamental control

Thomas et al., 2008, GBC

WEST

Note the phase lag between west and east

EAST


Helmuth thomas 1

1: Fundamental control

  • Pos. NAO:

  • Fast NAC

  • High supply of low DICnorm

  • High CO2 uptake

  • Neut. / Neg NAO:

  • Slow NAC

  • Low supply of low DICnorm

  • low CO2 uptake

  • Long term:

  • no significant trend

Large scale control:

NAC and its low DICnorm

NAO+

Long

term

NAO-/

Thomas et al., 2008, GBC

Corrected for anthropogenic CO2!!


Conclusions 1

1: Fundamental control

Conclusions 1

  • Key process:

    • NAC exports CO2 sink from the tropics northward

  • Pos. NAO:

    • Fast NAC

    • High supply of low DICnorm

    • Higher CO2 uptake

  • Neut. / Neg NAO:

    • Slow NAC

    • Low supply of low DICnorm

    • lower CO2 uptake

  • Long term:

    • no significant trend

  • Temporal aspect:

    • Observed response depends on distance to NAC source region

however:


Helmuth thomas 1

2: Adjustments

Effects of atmospheric temperature

Long term

  • Atm. Temperature effects:

  • Fast response

  • Spatially not uniform across the basin

  • Particularly dominant

  • in the NW Atlantic

Pos. NAO

neutr./neg. NAO

Note change

in scale!

Thomas et al., 2008, GBC


Perturbing process great salinity anomalies

3. Overlaying perturbance

Perturbing process:Great Salinity anomalies

Annual salinity anomalies:

Annual DICnorm anomalies:

Recall:1. Fundamental control:

Pos. NAO = enhanced northward flow of low DICnorm

Thomas et al., 2008, GBC


Do we still expect correlations

Annual SST anomalies:

+ NAO

neutr./neg. NAO

Do we still expect correlations?(??)

>60ºN

p<0.05

Thomas et al., 2008, GBC


Helmuth thomas 1

Outline

1: Fundamental

control

2: Adjustments

3: Overlaying

perturbance


Conclusions

Conclusions

  • Key process:

    • NAC exports CO2 sink from the tropics northward

  • Pos. NAO:

    • Fast NAC

    • High supply of low DICnorm

    • Higher CO2 uptake

    • Strong cooling in NW Atlantic

  • Neut. / Neg NAO:

    • Slow NAC

    • Low supply of low DICnorm

    • lower CO2 uptake

    • Strong warming in NW Atlantic

  • Alternative view:

    • Partial redistribution of North Atlantic CO2 sink between subpolar and subtropical gyres

  • Long term:

    • no significant trend other than (global) warming and rising atmos. CO2.

  • Perturbation:

    • Great Salinity Anomalies

Consequences are time

variant across the basin

because of water mass

travel time.

High correlations unlikely.


Reference

Reference:

  • Thomas, H., F. Prowe, I.D. Lima, S.C. Doney, R. Wanninkhof, R.J. Greatbatch, A. Corbière and U. Schuster (2008). Changes in the North Atlantic Oscillation influence CO2 uptake in the North Atlantic over the past two decades Global Biogeochemical Cycles, in press.


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