nnOcean biology: sensitivity to climate change and impacts on atmospheric CO2

Irina Marinov (Univ. of Pennsylvania)

UW PCC Summer School, WA, September 16th 2010

atmosphere

ocean

Solubility pump

Oceanic carbon pump = Solubility pump + Biological pump

warm

cold

Biological pump

Store CO2 and nutrients in the

deep

Store CO2 in the

deep

photosynthesis

Respiration (remineralization)

Ocean Carbon Storage

Solubility carbon pump

The natural ocean carbon: the solubility pump

warm

cold

Store CO2 in the

deep

Cold high latitude waters can hold more CO2 than warm low latitude waters.

This implies that most CO2 enters the ocean via high latitudes. Here NADW and AABW sink to the bottom of the ocean, taking CO2 with them. This is the solubility pump.

A warmer ocean will absorb less CO2 (a warm coke loses its CO2 and becomes flat quickly). A positive feedback on atmospheric CO2 !

CO2+PO4+NO3+ light organic matter + O2

Organic matter + O2 CO2+PO4+NO3

Biological carbon pump

Photosynthesis:

Remineralization: (Respiration)

PO4, CO2 consumed

PO4, CO2 added to the deep

CO2+PO4+NO3+ light organic matter + O2

Organic matter + O2 CO2+PO4+NO3

Biological carbon pump

Store PO4, CO2

Ocean Carbon Storage

(remineralized CO2)

Oceanic natural carbon pumps

Store CO2

Story 1: How will ocean carbon storage change with changes in ocean ventilation? How will that feedback to atmospheric pCO2?

Oceanic natural carbon pumps

Store CO2

Story2: How will phytoplankton biomass, production and size structure respond to climate change? How will

that feedback to atmospheric pCO2? (don’t know yet…)

Simplified 2D cartoon of oceanic thermohaline circulation

North Atlantic

NADW= North Atlantic Deep Water; AABW= Antarctic Bottom Water

AAIW = Antarctic Intermediate Water; CDW = Circumpolar Deep water

SAMW= Subantarctic Mode Water

Southern Ocean

AABW

NADW

North Atlantic

Low latitudes

AABW

NADW

Low latitudes

Increased Southern Ocean winds (future)

CO2

CO2

• Most CO2 is stored in the deep ocean. More upwelling (strong winds over Drake passage) results in more CO2 being released to the

atmosphere via the Southern Ocean, a decrease in the biological ocean storage and an increase in atmospheric pCO2.

• Positive feedback on atmospheric pCO2 !

PO4, CO2

present

What is the impact of an increase in S. Ocean winds on atmospheric pCO2?

North Atlantic

Increasing Southern Ocean winds results in:

- more loss of “natural” carbon stored in the deep via stronger CDW, a positive feedback.

- more anthropogenic CO2 uptake via stronger SAMW/AAIW, a negative feedback (Russell et al. ‘06)

Which one wins ?

Changes in the westerlies and atmospheric structure between interglacials and glacials, as proposed by

Toggweiler 2008

Glacials

Warm Interglacials

Strength of Westerlies over the Drake passage channel is lower during glacials.

Fig 4, Toggweiler et al 2006. Proposed positive feedback that propels transitions between warm and cold states of the climate system.

Fig 8, Toggweiler et al 2006. Modeled CO2 and T variation.

Toggweiler 2006 has a feasible theory to explain glacial-interglacial changes in CO2 and Temperature. Can we apply this

to the modern world?

(Marinov et al., 2008a,b)

Oceanic Carbon Storagesoft (PgC)

High windshigh Kv

control

Increasing Southern Ocean winds increases total ocean carbon storage (due to the biological pump), and decreases atmospheric

pCO2.

Increasing ventilation

pCO

2 at

m

(ppm

)

= Total Remineralized carbon in the ocean (PgC)

(Marinov et al., 2008a,b)

Oceanic biological Carbon Storage (PgC)

High windshigh Kv

control

Increasing ventilation

pCO

2 at

m

(ppm

)

Proposed simple theory fits model results well, but needs generalization!

€

pCO2a = c ⋅e−

OCSsoft

a1 + c 2 ⋅a2

a1

⋅e−

OCSsoft

a1 + ...Proposed analytic solution:

However, theory assumes fast gas exchange; no CaCO3 or solubility pumps.

Next steps: generalize this theory to include the above effects. Non trivial…

€

Sensitivity = −ΔpCO2a

ΔOCSsoft

=ΔpCO2a

ΔDICre min

low ventilation (LL)

high ventilation (high Kv)

• Atmospheric pCO2 is more sensitive (responds more) to changes in ocean biology if deep ocean ventilation is stronger (if Southern Ocean winds increase):

Oceanic biological Carbon Storage (PgC)

ocean carbon storage (biological pump)

atm

osph

eric

pCO

2

(present)

(future)High winds -> high ventilation

low ventilation

As Southern Ocean winds increase with global warming, the biological ocean carbon storage decreases, further increasing atmospheric pCO2.

the natural biological pump might therefore act as a positive feedback on the system ! Bad News !!!

• Part of the decline is attributed to up to a 30% decrease in the efficiency of the Southern Ocean sink over the last 20 years (Le Quere et al, 2007)

• This sink removes annually 0.7 Pg of anthropogenic carbon.

• The decline is attributed to the strengthening of the winds around Antarctica which enhances ventilation of natural carbon-rich deep waters.

• The strengthening of the winds is attributed to global warming and the ozone hole.

Le Quéré et al. 2007, Science

Cred

it: N

.Met

zl, A

ugus

t 200

0, o

cean

ogra

phic

crui

se O

ISO

-5

Le Quere et al (2007) notice a decline in the efficiency of the Southern Ocean carbon sink

Efficiency of Natural Sinks

Atmosphere(+ 0.23% y−1)

Land

Ocean

Canadell et al. 2007, PNAS; Raupach, Canadell, LeQuere 2008, Biogeosciences

LeQuere et al. 2007 (model)

difference

Obs.

Decline in the Efficiency of Natural CO2-Sinks

Oceanic natural carbon pumps

Store CO2

Story2: How will phytoplankton biomass, production and size structure respond to climate change? How will

that feedback to atmospheric pCO2? (don’t know yet…)

Marinov, Doney, Lima, Biogeosciences Discussions, Sept 2010

Phytoplankton Groups

Fixed C/N/P, Variable Fe/C, Chl/C, Si/C

Diatoms (C, Chl, Fe, Si)

Diazotrophs (C, Chl, Fe)

Picoplankton /Coccolithophores (C, Chl, Fe, CaCO3)

Zooplankton (C)

Nutrients

Ammonium

Nitrate

Phosphate

Silicate

Iron

Dissolved Organic Material (C, N, P, Fe)

Sinking Particulate Material (C, (N, P), Fe, Si, CaCO3, Dust)

CCSM3.1=Dynamic Green Ocean Model (DGOM)

Moore, Doney & Lindsay, Global Biogeochem. Cycles (2004)

1. Diatoms– Large photosynthetic phytoplankton, 50 mm

wide, with SiO2 shells– Best at exporting Carbon to the deep

ocean

2. Small phytoplankton (Nano-pico plankton)

- get recycled more at surface, less export

ex: Coccolithophores

– Photosynthetic phytoplankton with CaCO3 shell (nanoplankton, ~10mm wide).

– Respond to increased ocean acidity.

3. Diazotrophs

bacteria that fix atmospheric nitrogen gas into a more usable form such as ammonia.

Types of phytoplankton we model:

Biomass (1980-1999 NCAR model mean):

Small Phyto. Carbon Small Phyto. Carbon

Diatom Carbon

Diazotroph Carbon

Small phytoplankton: better at taking up nutrients in nutrient poor subtropical gyres. Strongly grazed.

Diatoms: require higher nutrients to reach their maximal growth rates. Grazed less. Dominant in turbulent conditions or under bloom conditions.

Diatom relative abundance

Atmospheric pCO2 (ppm)

CCSM-3 Carbon-Climate• control & prescribed CO2 emissions (SRES A2) simulations Increasing atmospheric CO2 =>• upper ocean warming & freshening (decr in salinity)• increased stratification

Upper ocean temperature (deg. C)

Upper ocean salinity (psu)

wind stress x

wind stress curl

vertical velocity vertical velocity

wind stress curl

wind stress x

present (1980-1999) (2080-2099)-(1980-1999)

- Increased Stratification with global warming over most of the ocean (due to enhanced temperature)

- Less change in Southern Ocean stratification, because of the counteracting impact of stronger winds.

Stratification (1980-1999)Stratification

Years (2080-2099) - (1980-1999)

Q: How will ocean ecology respond to these changes in stratification?

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Low mixing High mixing

Separate ecological biomes (based on physical principles)

Ice biome

Subpolar

Equatorial

Subtropical (permanent + seasonal)

LL Upwelling

* technique as in Sarmiento et al. 2004

Ecological BiomesEcological Biomes (Present)

Ecological Biome: control (1980-1999)

areas (1012 m2)

% change Climate driven trends

Marginal Sea Ice (Ice) N.Hem: 15.1

S.Hem: 25.0

-18.9%

-15.4%

Contraction

Contraction

Subpolar (SP) N Hem: 17.8

S Hem: 36.5

+ 8.9%

+ 3.5%

Expansion

Expansion

Subtropical gyres N Hem: 67.3

S Hem: 95.3

+ 4.5%

+ 1.6%

Expansion

Expansion

All biome changes are more pronounced in the Northern Hemisphere !

Satellite data suggests that ocean oligotrophic areas are getting larger

Increase in the Global area of extreme oligotrophic province in the ocean for SeaWIFS (black) and MODIS/Aqua (grey) Irwin, GRL 2009

Irwin et al. 2009 “Are ocean deserts getting larger?”

Polovina et al. 2008 “Ocean’s least productive waters are expanding”

Higher latitudes (light limited in winter)

Does this classical picture explain our model results?

-Subtropics: nutrient limited; Nutrient decrease will lower Chl and primary productivity

-High latitudes: light limitedMore light increases Chl and primary productivity in subpolar gyres

Tropics/mid-latitudes (nutrient limited)

Doney 2006; Sarmiento et al. 2004

Increased stratification decreases mixed layer depth: less nutrient supply, more light

- Subtropics: nutrient limited; Nutrient decrease will lower Chl and primary productivity

Tropics/mid-latitudes (nutrient limited)

Increased stratification decreases mixed layer depth: less nutrient supply, more light

The response to climate change in low/mid-latitudes:• Nutrients become more limiting: Diatoms decrease, partially replaced by small phytoplankton (less mixing and less vertical supply of NO3)• Overall total chlorophyll and primary production decrease• e-ratio decreases - increased surface recycling

Global phytoplankton decline over the past century (Boyce et al. Nature 2010)

Increases in Temp are associated with decreases in phytoplankton Chl. What is the underlying mechanism?

1899-2009

in situ Chl + transparency data

Effect of SST on Chl

€

SST

Total Primary Prod (PgC/yr)

Stratification (kg/m3)

Export Flux (PgC/yr) e-ratio

surface NO3 (mmol/m3)

N HemS Hem global

However … More increase in stratification in the N Hemisphere -> larger drop in nutrients, production and export ratio compared to

Southern Hemisphere. Very different responses in NH and SH !

Total Carbon (biomass)

Classical “expected” response to climate change in the Northern Hemisphere:

• Nutrients become more limiting. Diatoms decrease, partially replaced by small phytoplankton (less mixing and less vertical supply of NO3)• Overall total chlorophyll and primary production decrease• e-ratio decreases - increased surface recycling

“Unexpected” Southern hemisphere response to climate change:• Less increase in stratification due to stronger S Ocean winds!• Subtropical-subpolar S Ocean front shifts southward and upwelling/temperature increase locally• More upwelling means that diatoms do better relative to small phyto; slight increases in chlorophyll and production; e-ratio decrease minimal !

Biogeochemical Model Equations:

€

D(DiatC )

Dt= μ diat ⋅DiatC − mDiatDiatC − Diatgraze − Diatagg

€

D(SC )

Dt= μ sp ⋅SC − mS SC − Sgraze − Sagg

€

D(DiazC )

Dt= μ diaz ⋅DiazC − mDiazDiazC − Diazgraze

€

D(Nutrient)

Dt= Input − μ sp ⋅SC − μ diat ⋅DiatC − μ diaz ⋅DiazC

€

Sgraze = uS ⋅2(T−30) /10 ⋅SC

2

SC

2 + g2⋅ZC

€

D(ZC )

Dt= Diatgraze + Sgraze + Diazgraze − mZC − pZC

2

Grazing:

• Can we understand the response of this system to future changes in climate change by analyzing the underlying model equations ?

+ complicated equations for particulate organic carbon (POC), etc.

€

μx = μ ref ⋅Tf ⋅Vx ⋅Lx

Model Phytoplankton Growth Equations (biomass in mol C/m3)

€

Tf = 2

T−30o C

10o C

⎛

⎝ ⎜

⎞

⎠ ⎟

€

Vx = min(VxFe,Vx

N ,VxPO4 ,Vx

SiO3 )

Specific Growth Rate:

light availability

€

Lx =1− exp−α x ⋅θx

c ⋅ IPAR

μ ref VxTf

⎛

⎝ ⎜ ⎜

⎞

⎠ ⎟ ⎟

temperature function

nutrient functional response

€

VxFe =

Fe

Fe + KxFe

€

∂Px

∂t+∇ ⋅(

r u Px ) −∇ ⋅(K ⋅∇Px ) = μ x ⋅Px − Pgrazing − mx ⋅Px − Paggregation

IPAR(W/m2)= surf irradiance

€

VxN =

NO3

KxNO3

+NH4

KxNH 4

⎛

⎝ ⎜

⎞

⎠ ⎟ 1+

NO3

KxNO3

+NH4

KxNH 4

⎛

⎝ ⎜

⎞

⎠ ⎟

€

θxc = (Chl /C)x

α x = initial P − I slope

Assume that climate change results changes in light, nutrients and temperature. What is the impact on phytoplankton biomass S and L?

€

S =∂S

∂N I par ,T constant

⋅ΔN +∂S

∂I parN,Tf constant

⋅ΔI par +∂S

∂T I par ,N constant

⋅ΔT

If the model is simple enough we can calculate analytically each of these terms at steady state !

€

S = ΔSnutr + ΔS light + ΔS temp

Q: Will a given change in nutrients change more S or L, i.e., will

€

S nut ≥ ΔLnut and∂S

∂N≥

∂L

∂N?

€

S ≥ ΔL

• In the 40oS-40oN region where background nutrients are below Ncritical (1.18 mmolNO3/m3), a change in nutrients will affect more small than

large phytoplankton:

• Outside 40oS-40oN, the opposite is the case.

For example, in the GFDL TOPAZ model we can show that:

€

D(L)

Dt= μL ⋅L − λ L

L

P*

⎛

⎝ ⎜

⎞

⎠ ⎟1/ b

L

D(S)

Dt= μS ⋅S − λ S

S

P*

⎛

⎝ ⎜

⎞

⎠ ⎟1/ a

S

At steady state, the equations translate to:

€

S =μS

λ S

⎛

⎝ ⎜

⎞

⎠ ⎟P

* L =μL

λ L

⎛

⎝ ⎜

⎞

⎠ ⎟

3

P*

€

μx = μ xref ⋅ekT ⋅Vx

nut ⋅(1− e−...Ipar )

€

λx = mx ⋅ekT

€

VxN =

N

N + KxN

,

diatoms respond more

Small phyto respond more

Small phyto respond more

€

S ≤ ΔL

high latitudes: high nutrient zone

40oS - 40oN: low nutrient regiona nutrient change will affect more small phytoplankton than diatoms.

a nutrient change will affect more diatoms than small phytoplankton

Critical Nutrient Hypothesis

diatoms respond more

• Critical nutrient hypothesis: In the 40S-40N biome, climate driven decreases in nutrients (due to increased stratification) have a larger impact on small phytoplankton than on diatom biomass. The opposite is the case in high nutrient high latitudes. (NCAR, GFDL)

• Similar analysis about temperature and light variations in the model …

€

S ≥ ΔL

New satellite backscattering method aims to separate size structure (shown are SeaWIFS

1997-2007 means)

Kostadinov et al. 2010

Pico (0.5-2um) particle number Nano (2-20um) particle number

Micro (20-50um)

Summary:Story 1:

• The sensitivity of atmospheric pCO2 to changes in ocean biology (and hence the feedback strength) depends on ocean ventilation. The stronger the ventilation, the more sensitive atmospheric pCO2 is to ocean biology.

• Increasing Southern Ocean winds act to decrease the biological storage in the Southern Ocean and increase atmospheric pCO2. Positive feedback.

Story 2:

• Increasing oceanic stratification in low and mid-latitudes results in a relative increase in small phytoplankton and a decrease in diatoms. Therefore, e-ratio decreases globally and ocean carbon storage is less efficient: positive feedback.

• This effect is less pronounced in the Southern Hemisphere, because of the counteracting effect of increasing S. Ocean winds (smaller positive feedback)

• On-going work to calculate the relative impacts of temperature, nutrients and light on different species, and the relative changes in the species with warming.

Thank you …

Friedlingstein et al. 2006

pCO2atm, coupled - uncoupled

Land Uptake, coupled (GtC/yr)

Land Uptake, coupled - uncoupled

Ocean Uptake, coupled - uncoupledOcean Uptake, coupled (GtC/yr)

pCO2atm (ppm), coupled

Hadley

CCSM-1

Hadley

UVic“Climate-C cycle feedback analysis: results from the CMIP-4 model intercomparison”

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CL = β LΔCA + γ LΔT

ΔCO = βOΔCA + γOΔTChange in land and ocean carbon (GtC):

Ocean C sensitivity to atmospheric CO2

Ocean C sensitivity to climate change

Carbon cycle gain, g, along with component sensitivities of climate to CO2 (α), land and ocean carbon storage to CO2 (βL, βO), and land and ocean carbon storage to climate (γL, γO). Calculations are done for year 2100. (Friedlingstein, 2006)