nn ocean biology: sensitivity to climate change and impacts on atmospheric co 2 irina marinov (univ....
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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?
€
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”
€
€
€
€
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)
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