the fateof carbon and nutrients exported out of …...jul 07, 2019 · mitgcm-recom2 (hauck et al.,...
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THE FATE OF CARBON AND NUTRIENTSEXPORTED OUT OF THE SOUTHERN OCEAN
Judith HauckAndrew Lenton, Clothilde Langlais, Richard Matear
„Southern Ocean nutrient supplyaccounts for about three-quarters ofbiological production north of 30°S“
(Sarmiento et al., 2004)
„Southern Ocean nutrient supply accounts for aboutthree-quarters of biological production north of 30°S“
„Furthermore, this region acts also as the keygatekeeper controlling the supply of nutrients to the lowlatitude oceans, and thus the magnitude of low latitudeproductivity in the past, present and future (Sarmientoet al. 2004; Matsumoto et al. 2002; Moore et al. 2018)."
„models suggest that vertical exchange within theSouthern Ocean is responsible for supplyingnutrients that fertilize three-quarters of the biologicalproduction in the global ocean north of 30°S (Sarmiento et al., 2004, Marinov et al., 2006)“
„… providing nutrients that support low- latitudeproductivity […] Sarmiento et al., 2004 […] „
Previous studies„Southern Ocean nutrient supply accounts for about three quarters of biological productionnorth of 30°S“
Nutrient supply
Carbon sequestration
Preindustrial results atequilibrium!
Marinov et al., 2006
Sarmiento et al., 2004
Southern Ocean –decoupling of anthropogenic CO2 uptake and storage
Khat
iwal
aet
al.
(200
9)
>50% of Southern Ocean Cant in SAMW and AAIW (Langlais et al., Sci. Rep., 2017)
Aims of this talk
Provide a similar concept for carbon fluxes
Spoiler: Southern Ocean nutrient supply to low-latitudes is overestimated
Transient response – large decadal variability / future change
Panassa et al (2018): Significantincrease in nitrate concentrationin AAIW based on Polarstern data
Large decadal variability of Southern Ocean CO2 uptakeLandschützer et al., 2015
Iida et al., 2013; Ayers & Strutton, 2013; Hoppema et al., 2015; Pardo et al., 2017
Transient response – large decadal variability / future change
Land
schü
tzer
et a
l., 2
015
Pana
ssa
et a
l (20
18)
Moore et al (2018): Increased SO nutrient trapping leads to declineof global primary production after 2100.
Regulated Ecosystem Model (REcoM2)
Based on Schartau et al., BG, 2007
Non-Redfield model
Explicit sinking
Hauck et al., 2013, 2016Hauck et al., GBC, 2013
Model Experiments
1. Control2. No bio in Southern Ocean
x
Hauck et al., GBC, 2018
Model Experiments
1. Control2. No bio in Southern Ocean3. No bio + no gas-ex in SOx xx
Hauck et al., GBC, 2018
Model Experiments
Southern Ocean south of 40°S
x xx1. Control2. No bio in Southern Ocean3. No bio + no gas-ex in SO
Hauck et al., GBC, 2018
Model ExperimentsControl
Atm
CO2
No bio + no gas-exNo bio
biological pump
physical pump
MITgcm-REcoM2 (Hauck et al., 2013; 2015; 2016)
JRA55 reanalysis 1958-2016
Spin-up: two cycles of JRA forcing, third cycle until 2005Experiment: keep atmospheric forcing and CO2 concentration constant at 2005 levels
Positive: Southern Ocean primary production increase in DINNegative: Southern Ocean primary production decrease in DIN
Negative DIN anomaly in SO surface and north of 40°S surface and to ~3500 m.Positive DIN anomaly in SO subsurface to bottom
Atlantic Pacific
Results – Perturbations of nutrient fields, year 196-200
Positive: Southern Ocean primary production increase in DINNegative: Southern Ocean primary production decrease in DIN
DIN anomaly spreads all over the Atlantic in 200 years
Atlantic Pacific
Results – Perturbations of nutrient fields, year 196-200
Pacific shadow zone
De Lavergne et al., 2017
Pacific shadow zone, little overturning
Vertically-Integrated Net Primary Production
No nutrient utilization in Southern Ocean:
7.0 PgC/y loss south of 40°S
3.0 PgC/y gain north of 40°S locally 10% increase
32.8 PgC/y
29.8 PgC/y
43% compensation on 200-year time-scale
39% for export
7.0 PgC/y
Vertically-Integrated Net Primary Production
4.5 PgC/y
+3.9 PgC/y
2.5 PgC/y -1.0 PgC/y
No nutrient utilizationin Southern Ocean:
Locally 32% increase ofdiatom NPP (87% compensation)
Reinforcement ofnano-NPP rather thancompensation
‚silicate leakage‘
Change in mean Southern Ocean surface nutrients
DIN: 15 mmol m-3 26 mmol m-3 (+75%)DSi: 14 mmol m-3 50 mmol m-3 (+255%)DFe: 0.15 µmol m-3 0.64 µmol m-3 (+340%)
100% change in DIN would leadto 13% in NPP north of 40°S
„Southern Ocean nutrient supply accounts for about threequarters of biological production north of 30°S“
Sarmiento et al., 2004
??
Previous studies„Southern Ocean nutrient supplyaccounts for about three quarters ofbiological production north of 30°S“
Sarmiento et al., 2004
33 – 75% of low latitude productivityis sustained by nutrient export fromSAMW
Palter et al., 2010
27% of midlatitude and subpolar North Atlantic fuelled by nutrientslast utilized in the Southern Ocean, with even lower numberselsewhere Holzer and Primeau, 2013 Holzer and Primeau, 2013
Previous studies
Primeau et al., 2013
unperturbed
Increase in SO production Decrease
Signal dependson direction ofperturbation
Non-linear state-dependency
Previous studies
Primeau et al., 2013
unperturbed
Signal dependson direction ofperturbationNon-linear state-dependency
NPP frac sustained by SO nutrients
Sarmiento et al
This study
Increase in SO production Decrease
Carbon
Results – Perturbations of DIC fields, year 196-200Bi
ol. p
ump
Phys
. pum
p
Atlantic Pacific
The fate of carbon
-0.52 PgC/yr
Uptake low, as atm. CO2 is constant
-1.14 PgC/yr (uptake)
+0.62PgC/yr (outgassing)
0.2 PgC/yr(outgassing)
0.57 PgC/yr(tendency to outgas)
-0.55 PgC/yr(tendency to uptake)
The fate of carbon
Bio and physeffects nearlybalance, but
Changes in SO phys, incompletelycompensated by bioLeQuéré et et al. (2007), Hauck et al. (2013)
Changes in SO bio, uncompensated by SO physicsMoore et al. (2018)
The fate of carbon
Const. CO2
Atm
CO2
Atm CO2 increasing with rate of increase(2000-2010) = 1.98 ppm/year
388
773
The fate of carbon
Larger uptake due to higherand increasing atm CO2
SO turns fromoutgassing to uptakeafter ~50 years
Smaller uptake
Southern Ocean carbon pumpslead to outgassing of 0.47 PgC/yr
Implications for carbon uptake
Compensation = - CO2 flux north of 40°SCO2 flux south of 40°S
0: SO C-pumps do not lead to changenorth of 40°S
1: complete compensation
Implications for carbon uptake
0: SO C-pumps do not lead to changenorth of 40°S
1: complete compensation
Compensation = - CO2 flux north of 40°SCO2 flux south of 40°S
Biological pump: 50% compensation
Physical pump: 90% compensation
Implications for carbon uptake
Compensation = - CO2 flux north of 40°SCO2 flux south of 40°S
Biological pump stores CO2 for longerthan physical pump
Incomplete compensation of NPP Sinking of particles to deeper
depths
Feedbacks in the ocean carbon sink due to potential future changes in• physically-driven CO2 uptakeoccur faster and are nearly balancedafter 200 years• biological C-pumpoccur slower but last longer
Summary
Hauck et al., 2018, GBC
Physical pump: CO2 outgassing, 90% reventilated after 200 yearsBiological pump: CO2 uptake, 50% reventilated after 200 yearsNet Primary Production perturbation: 40% compensation on 200 year time-scale
% S
AMW
reac
hed
Equa
toria
lUnd
ercu
rren
t Tmin 28 years
50% ~ 100 years
70% ~ 200 years
Rodgers et al., GRL, 2003
Timescales of subduction and reventilation
Results – timescale of reventilation
5°S to5°N
Emergence of signal in equatorial
Atlantic: ~15 years
Pacific: ~30 years
Somewhat shorter time-scalethan Rodgers et al, because:• Rodgers neglect stochastic terms
in Lagrangian models to accountfor transport by eddies (Shah et al., 2017)
• Includes perturbation of surface• Rodgers stricter definition of eq.
Pac.
Si remineralizationdeeper than for DIN
Fe stark contrast deepAtl and Pac
SO NPP accumulation of Fe in surface Atl
Atlantic Pacific
Results – Perturbations of nutrient fields, year 196-200
The fate of carbonDIC CO2 flux
The fate of carbon
SO active biology negative NPP anomaly positive DIC anomalypositive CO2 flux anomaly (more outgassing or less uptake)
The fate of carbon
SO active biology negative NPP anomaly positive DIC anomalypositive CO2 flux anomaly (more outgassing or less uptake) SO active biology upwelling of DIC depleted water negative DIC anomaly negative CO2 flux anomaly (less outgassing or more uptake)
Previous studies
Holzer and Primeau, 2013
27% North Atlantic
Blue: fraction ofNPP sustained bySO nutrients
Previous studies„Southern Ocean nutrient supply accounts for about three quarters of biological productionnorth of 30°S“ Sarmiento et al., 2004
33 – 75% of low latitude productivity is sustained by nutrient export from SAMWPalter et al., 2010
27% of midlatitude and subpolar North Atlantic fuelled by nutrients last utilized in theSouthern Ocean, with even lower numbers elsewhere
Holzer and Primeau, 2013
Increasing nutrient utilization in the Southern Ocean resulted in a larger fraction of nutrientslast utilized in the Southern Ocean (up to 45%), but decreaded the overall productivity.
Holzer and Primeau, 2013Non-linear response of productivity outside the Southern Ocean to perturbations within theSouthern Ocean (increase/decrease of nutrient utilization) Primeau et al., 2013
Southern Ocean carbon cycle
Transport of Cant into the ocean interior through:Northward-Ekman transport, and formation of Subantartcic Mode Water (SAMW) andAntarctic Intermediate Water (AAIW)>50% of Southern Ocean Cant in SAMW and AAIW (Langlais et al., 2017)