Anthropogenic aerosol deposition reduces the

sensitivity of oceanic productivity to warming

Feng Zhou (Peking University, zhouf@pku.edu.cn)Rong Wang, Yves Balkanski, Laurent Bopp, Didier Hauglustaine, Philippe Ciais

INI2016 in Melbourne

Dec 4-8, 2016

McNutt, M. (2015), Science, 348, 841–841

25% CO2 is absorbed by the ocean,moderating climate warming

Ocean acidity increased by 30%,having negative impact on oceanicnet primary productivity (NPP)

30%

Ocean is a large sink of the Earth’s carbonemission, sustaining the habitability ofEarth

Motivation1

Behrenfeld et al. (2010) in Nature; Gregg and Rousseaux (2014), JGR

Multiple satellite data indicated that all North Hemisphere and EquatorialIndian basin experienced a significant decline of Chlorophyll-a (or NPP)

Motivation1

Increasing

Decreasing

Current: Such climate-driven decline is attributed mainly to the increasingthermal stratification of ocean water columns (reduced mixing, lower N supply,decreased phytoplankton).

From L Bopp in LSCE

ENSO - Observations

Motivation1

Future: The decline is simulated by ocean biogeochemical model and isexpected to continue further, reducing oceanic NPP and hence CO2 sink (-6% to-25% in 2050).

Bopp et al., 2013 in Biogeosciences

Motivation1

In contrast, anthropogenic aerosols provide nutrients to the surface oceans,

which stimulate the phytoplankton and promote the oceanic NPP.

Key question addressed -------

Can aerosol deposition partly offset the

decline of NPP caused by warming?

Motivation1

To understand the impact of aerosol deposition, we simulated the

change of Nr, phosphate (PO4), and sFe, deposition from 1850 to 2010

in a global atmospheric general circulation model (GCM) and input the

results into an ocean biogeochemical model with the varying climate.

Emission GCM Deposition Ocean model

NPP

Climate change

NPP Temperature

Data and methods2

Species Sector Source Period

NH3 + NOx + N2O Agriculture, CombustionACCMIP and MACCity

PKU-inventory1850-2010

NO + N2O + NH3 Natural soil, ocean PKU-inventory Constant

P + Fe Combustion, wildfire PKU-inventory 1960-2007

P + Fe Dust, biogenic aerosol, volcano Mahowald et al., 2008 Constant

P Bioavailability: 10% of P from dust, 100% of P from volcanoes, and 50% of P from others

Fe Bioavailability: 12± 9% for coal fly ash, 63.0 ± 17.0% for vehicle oil, 79.8 ± 8.5% for

heavy oil, 30± 14% for biomass, 2± 4% for dust

Data and methods2 Emission http://inventory.pku.edu.cn/

Historical emissions of Nr, PO4 and sFe

(0.5 0.5 grid cell)

• Increased by 1.8, 0.8, 0.4 times since

1850 globally

• Nr: increased until 1990s, then kept

stable

• PO4: persistently increased due to

biofuels and deforestation

• sFe: increased until 1990s and then

declined, due to dust abatment & use of

cleaner fuels

Data and methods2

Data and methods2An oceanic biogeochemical model NEMO-PISCES version 2 to simulate Nr, PO4, sFeas well as Chlorophyll and NPP

Aumont et al., 2015, Geosci. Model Dev., 8, 2465–2513

A global chemistry-aerosol-climate model LMDz-OR-INCA tosimulate aerosol deposition

Hauglustaine et al., 2014 in ACP

Models from LSCE

Data and methods2

The difference was considered as the response to aerosol deposition

Model performance3

Wang et al., ACP, 2015

Hauglustaine et al., 2014

NH4

NO3

PO4 Fe

Modeled v.s. observed deposition

Observed deposition: CASNET, EMEP, EANET

Model performance3

10-3 100 10110-110-3

B101

10-2

100

Mod

elle

d sF

e (μ

mol

m-3

)

Observed sFe (μmol m-3)

10-1

10-2

N 214RMSD 0.64NMB -68%

CTL

10-3 100 10110-1

N 214RMSD 0.57NMB -63%

10-3

C101

10-2

100

Mod

elle

d sF

e (μ

mol

m-3

)

Observed sFe (μmol m-3)

10-1

10-2

DEP

10-4 100 10210-2

N 13 974RMSD 0.56NMB -46%

10-4

A102

10-2

100

Observed NO3 (mmol m-3)

Mod

elle

dN

O3

(mm

olm

-3)

12 2671

DEP

Mod

elle

dP

O4

(mm

olm

-3)

10-4

B102

Observed PO4 (mmol m-3)

10-2

10-4 100 102

100

10-2

N 75 656RMSD 0.46NMB -47%

91 6851

DEP

10-4 100 10210-210-4

B102

10-2

100

Observed NO3 (mmol m-3)

Mod

elle

dN

O3

(mm

olm

-3)

10 9791

N 12 439RMSD 0.61NMB -56%

CTL

Mod

elle

dP

O4

(mm

olm

-3)

10-4

D102

Observed PO4 (mmol m-3)

10-2

10-4 100 102

100

10-2

N 81 949RMSD 0.45NMB -45%

103 4601

CTL RMSD 0.18NMB -39%

Mod

eled

[Chl

](m

g m

-3)

10-2

101

Observed [Chl] (mg m-3)

10-1

10-2 100 101

100

10-1

N = 182552

196

836

B

RMSD 0.17NMB -38%

N = 182552Mod

eled

[Chl

](m

g m

-3)

10-2

101

Observed [Chl] (mg m-3)

10-1

10-2 100 101

100

10-1

198

187

D

182,552 data

214 data

438,240 data

170,588 data

https://www.nodc.noaa.gov/OC5/WOD13/; http://www.bodc.ac.uk/geotraces/

NO3

PO4

sFe

Chl-a

Model performance3

Pre-industrial, 1850 1997-2013

Nr (1850) Nr (1997-2013)

P (1850) P (1997-2013)

Impact to concentration4

DIN sFe

PO4

AD increases the concentrations ofDIN and sFe,but decreases PO4, due to theenhancing phytoplankton growth

226 v.s. 9 Gmol yr-1

Difference of 2 experiments

Impact to concentration4

Chl-a

NPP1.3 Pg yr-1

34%

Difference of 2 experiments

the ocean area with a relative differencelarger than 10% for DIN and Chl-a/NPPaccounts for 65% and 34%, respectively

65%

>10%

RD=Difference in 0.5

Mean in 0.5

Impact to NPP sensitivity5

Figure: Changes of the annual mean sea-surface temperature (SST) and oceanic NPP in thepermanently stratified oceans from 1948-1977 to 1978-2007 in the simulations (A) with, or (B)without aerosol deposition

Behrenfeld et al. [2006] found an inverse relationship. We observed a similar

relationship when comparing the period from 1948–1977 to 1978–2007

Impact to NPP sensitivity5

SST: Sea-surface temperature

However, aerosol depositiondecreases the sensitivity ofNPP to SST changes

NPP Temperature

15 to 13 Pg Cyr-1 C-1 or 12.5%

• North Pacific: 23% (2.56->1.96)

• North Atlantic: 40% (0.35 to 0.21)

• Indian: 25% (1.1 to 0.83)

Take-home messages6• Aerosol deposition offsets the oceanic NPP sensitivity to SST, which

is much important for calculating terrestrial carbon source/sink

(=Emission – atmosphere sink – ocean sink)

• Future observation-based techniques to detect the influence of

global warming on oceanic NPP have to take into account the role of

aerosol deposition esp. of Nr

• Fertilizing effects of aerosols (N, PO4, sFe) should be considered

along with the effects of climate change in driving NPP variations

Wang R., Zhou F., et al., GRL, 2016

Thanks so much for your attention

Feng Zhouzhouf@pku.edu.cn