Helmuth Thomas 1 ,
description
Transcript of Helmuth Thomas 1 ,
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
Temporal variability of the CO2 system in the North Atlantic Ocean
Observations in the North Atlanticduring 1995-2002/4
BATS, BermudaΔpCO2 constantBates, 2001/7
North SeaΔpCO2 declining
VOS line UK –CaribbeanΔpCO2 decliningSchuster and Watson2007Sub Polar North AtlanticΔpCO2 decliningOmar and Olsen, 2006
South of GreenlandΔpCO2 decliningCorbiere et al., 2007
North Atlantic Drift RegionΔpCO2 decliningLefèvre et al., 2004
NW AtlanticΔpCO2 increasingLueger et al., 2006
Thomas et al., 2008, GBC
•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
Simulations for the North Atlantic Ocean
What is the driver for the observed CO2 flux variability in the North Atlantic Ocean?
situin
situinnorm Sal
DICDIC
35*
.Thomas et al., 2008, GBC
Simulations vs. Observations for the North Atlantic Ocean
Corbière et al.
Model
water +2.5
ppm yr-1
+3.0
ppm yr-1
Atmos. +1.6
ppm yr-1
+1.6
ppm yr-1
temp.-
pCO2
+ +1.2
ppm yr-1
DIC +0.6
μmol (kg yr)-1
AT -0.3
μmol (kg yr)-1 Thomas et al., 2008, GBC
Period 1993-2003 2001-2008
Atm 1.9 µatm/yr 2.1 µatm/yr
Ocean 3.6 µatm/yr 5-7 µatm/yr
Why ? Warming +DIC/-TA
Full story presented by
Corbière et al. (Poster, CT1)
Ocean CO2 trends in the North Atlantic Subpolar Gyre :
winter 1993-2003/2001-2008 (based on DIC/TA Suratlant data)
Skògafoss
Nuka Arctica
1994-1995
2002-2005Schuster and Watson, 2007
JGR
mean
CO2 uptake in 1994/5 and 2002/4
[mo
l C
O2
m-2 y
r-1]
0
1.4
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?
UK-Caribbean route
Simulations vs. Observations for the North Atlantic Ocean
One conclusion:We need to maintain an observing system.
Tool:Trend regression analysisinstead of differences.
Simulations vs. Observations for the North Atlantic Ocean
Tool:Trend regression analysisinstead ofdifferences
Simulations vs. Observations for the North Atlantic Ocean
neutr./neg. NAO
Most of the observationscover the 95-04 period
ΔpCO2 trends
long term
pos. NAO
Note changein scale!
Thomas et al.2008, GBC
Outline
1: Fundamentalcontrol
2: Adjustments
3: Overlayingperturbance
Real World Ocean
Building the house
You move in
Your in-laws move in
NAO & the subpolar and subtropical gyres
Positive NAO:Strong westerliesStrong 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/
↑
1: Fundamental control
North Atlantic Oscillation during the past two decades
15
20
MO
C[S
v]
-5
0
5
Win
ter
NA
O
1,980 1,985 1,990 1,995 2,000 2,005
1: Fundamental control
Thomas et al., 2008, GBC
15
20
MO
C[S
v]
-5
0
5
Win
terN
AO
1,980 1,985 1,990 1,995 2,000 2,005
positive NAO(1989-1995 average)
Response of surface ocean to NAO forcing
Surface velocity
(each 2nd grid point shown)
x
x
1: Fundamental control
Subpolar gyre
Subtropical gyre
Labrador Current
Thomas et al., 2008, GBC
Neutral - positive NAO(1996/2004av.) - (1989/1995av.)
Response of surface ocean to NAO forcing
Surface velocity difference
Subpolar gyre
(each 2nd grid point shown)
Subtropical gyre
1: Fundamental control
Labrador Current
Thomas et al., 2008, GBC
Response of surface ocean to NAO forcing
1: Fundamental control
Thomas et al., 2008, GBC
Annual salinity anomalies:
1: Fundamental control (one more detail)
Expansion of subtropical gyre during positive NAO
Relevance western subpolar gyre:
Labrador Current cannot move south, it is diverted into the subpolar gyre
Thomas et al., 2008, GBC
Response of surface ocean to NAO forcing
Pos. NAO
Neutr./neg. NAO
1: Fundamental control
DICnorm and Salinity in the North Atlantic1: Fundamental control
Pos. NAONeutr./neg. NAO
North Atlantic Current is fed by low DICnorm / high salinity water:Northward transport of aCO2 deficiency
Thomas et al., 2008, GBC
Main driver of variability:DICnorm
(AT,norm exerts minor control)
Example:2 stations atthe easternand westernsubpolar gyre
WE
ST
1: Fundamental control
EA
ST
Note the phase lag between west and east
Thomas et al., 2008, GBC
Large scale control:NAC and its low DICnorm
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
Corrected for anthropogenic CO2!!
NAO+
NAO-/
1: Fundamental control
Longterm
Thomas et al., 2008, GBC
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
1: Fundamental control
however:
2: Adjustments
Effects of atmospheric temperature
Pos. NAO
neutr./neg. NAO
Long termAtm. Temperature effects:•Fast response•Spatially not uniform across the basin•Particularly dominant in the NW Atlantic
Note changein scale!
Thomas et al., 2008, GBC
Perturbing process:Great Salinity anomalies
Annual salinity anomalies:
Annual DICnorm anomalies:
3. Overlaying perturbance
Recall:1. Fundamental control:Pos. NAO = enhanced northward flow of low DICnorm Thomas et al., 2008, GBC
Do we still expect correlations?(??)
-1.0
-0.5
0.0
0.5
1.0
R
-2 0 2 4
Lag [yr]
Northern North Atlantic
Western Subpolar Gyre
CorrelationCO2 air-sea flux vs. NAO
>60ºN
15
20
MO
C[S
v]
-5
0
5W
inte
rN
AO
1,980 1,985 1,990 1,995 2,000 2,005
Annual SST anomalies:
+ NAO
neutr./neg. NAO
p<0.05
Thomas et al., 2008, GBC
Outline
1: Fundamentalcontrol
2: Adjustments
3: Overlayingperturbance
Real World Ocean
Building the house
Response of surface
circulation to NAO
You move in Atmospheric Temperature
Your in-laws move in
Great Salinity Anomaly
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 timevariant across the basinbecause of water masstravel time.
High correlations unlikely.
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.