Ocean biology: sensitivity
to climate
nn
change and impacts on atmospheric CO2
Irina Marinov (Univ. of Pennsylvania)
UW PCC Summer School, WA, September 16th 2010
Oceanic carbon pump = Solubility pump + Biological pump
Solubility pump
Biological pump
atmosphere
photosynthesis
warm
ocean
Respiration
(remineralization)
cold
Store CO2 in the
deep
Ocean
Carbon
Storage
Store CO2 and
nutrients in the
deep
The natural ocean carbon: the solubility pump
Solubility carbon pump
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.
warm
cold
Store CO2 in the
deep
A warmer ocean will absorb less CO2
(a warm coke loses its CO2 and
becomes flat quickly). A positive
feedback on atmospheric CO2 !
Photosynthesis:
CO2+PO4+NO3+ light
Remineralization:
(Respiration)
Organic matter + O2
organic matter + O2
CO2+PO4+NO3
Biological
carbon pump
CO2+PO4+NO3+ light
organic matter + O2
Biological
carbon
pump
PO4, CO2
consumed
Store PO4, CO2
PO4, CO2
added to the
deep
Organic matter + O2
(remineralized CO2)
CO2+PO4+NO3
Ocean
Carbon
Storage
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…)
Oceanic natural
carbon pumps
Store CO2
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
present
Southern Ocean
North
Atlantic
CO2
Low
latitudes
Increased Southern Ocean winds
(future)
CO2
Low
latitudes
NADW
AABW
PO4,
CO2
NADW
AABW
• 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 pCO !
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
Warm
Interglacials
Strength of Westerlies over
the Drake passage channel is
lower during glacials.
Glacials
Toggweiler 2006 has a feasible theory to explain glacialinterglacial changes in CO2 and Temperature. Can we apply this
to the modern world?
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.
Increasing Southern Ocean winds increases total ocean carbon
storage (due to the biological pump), and decreases atmospheric
pCO2.
High winds
pCO2 atm (ppm)
high Kv
control
Increasing ventilation
Oceanic Carbon Storagesoft (PgC)
= Total Remineralized carbon in the ocean (PgC)
(Marinov et al., 2008a,b)
Proposed simple theory fits model results well, but
needs generalization!
High winds
pCO2 atm (ppm)
high Kv
However, theory assumes fast gas
exchange; no CaCO3 or solubility pumps.
control
Next steps: generalize this theory to
include the above effects. Non trivial…
Increasing ventilation
Oceanic biological Carbon Storage (PgC)
Proposed
analytic
solution:

pCO2a  c  e
OCS soft
a1

a2
c  e
a1
2
OCS soft
a1
 ...
(Marinov et al.,
2008a,b)
• Atmospheric pCO2 is more sensitive (responds more) to changes in
ocean biology if deep ocean ventilation is stronger (if Southern
Ocean winds increase):
high ventilation (high Kv)
low ventilation (LL)
Oceanic biological Carbon Storage
(PgC)
Sensitivity 
pCO2a
pCO2a

OCSsoft DICre min
atmospheric pCO2
High winds ->
high
ventilation
(future)
low
ventilation
(present)
ocean carbon storage
(biological pump)
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 !!!
Le Quere et al (2007) notice a decline in the
efficiency of the Southern Ocean carbon sink
• 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)
Credit: N.Metzl, August 2000, oceanographic cruise OISO-5
• 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
Efficiency of Natural Sinks
Atmosphere
(+ 0.23% y−1)
Land
Ocean
Obs.
difference
LeQuere et al.
2007 (model)
Canadell et al. 2007, PNAS; Raupach, Canadell, LeQuere 2008, Biogeosciences
Decline in the Efficiency of Natural CO2-Sinks
Story2: How will phytoplankton biomass, production and size
structure respond to climate change? How will that
feedback to atmospheric pCO2? (don’t know yet…)
Oceanic natural
carbon pumps
Marinov, Doney, Lima,
Biogeosciences Discussions,
Sept 2010
Store CO2
CCSM3.1=Dynamic Green Ocean Model
(DGOM)
Phytoplankton Groups
Diazotrophs
Zooplankton
Picoplankton /
Coccolithophores
(C, Chl, Fe, CaCO3)
(C, Chl, Fe)
Diatoms
(C, Chl, Fe, Si)
Fixed C/N/P, Variable Fe/C, Chl/C, Si/C
Dissolved Organic Material
(C, N, P, Fe)
Sinking Particulate Material
(C, (N, P), Fe, Si, CaCO3, Dust)
Moore, Doney & Lindsay, Global
Biogeochem. Cycles (2004)
(C)
Nutrients
Ammonium
Nitrate
Phosphate
Silicate
Iron
Types of phytoplankton we model:
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.
Biomass (1980-1999 NCAR model mean):
Diatom Carbon
Diatom relative abundance
Small Phyto. Carbon
Small Phyto. Carbon
Small phytoplankton: better at taking up
nutrients in nutrient poor subtropical gyres.
Strongly grazed.
Diazotroph Carbon
Diatoms: require higher nutrients to reach
their maximal growth rates. Grazed less.
Dominant in turbulent conditions or under
bloom conditions.
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)
present (1980-1999)
wind stress x
wind stress curl
vertical velocity
(2080-2099)-(1980-1999)
 wind stress x
 wind stress curl
 vertical velocity
- 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
Stratification (1980-1999)
Years (2080-2099) - (1980-1999)

Low mixing
High mixing
Q: How will ocean ecology respond to these changes in
stratification?
Separate ecological biomes (based on
physical principles)
LL Upwelling
Equatorial
Subtropical
(permanent +
seasonal)
Subpolar
Ice biome
* technique as in Sarmiento et al. 2004
Ecological Biomes (Present)
 Ecological Biomes
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
Irwin et al. 2009 “Are ocean deserts getting
larger?”
Polovina et al. 2008 “Ocean’s least
productive waters are expanding”
Increase in the Global area of
extreme oligotrophic province in the
ocean for SeaWIFS (black) and
MODIS/Aqua (grey)
Irwin, GRL 2009
Increased stratification decreases mixed layer depth:
less nutrient supply, more light
Tropics/mid-latitudes (nutrient limited)
-Subtropics: nutrient limited;
Nutrient decrease will lower Chl
and primary productivity
Higher latitudes (light limited in winter)
-High latitudes: light limited
More light increases Chl and
primary productivity in subpolar
gyres
Doney 2006; Sarmiento et al. 2004
Does this classical picture explain our model results?
Increased stratification decreases mixed layer depth:
less nutrient supply, more light
Tropics/mid-latitudes (nutrient limited)
- Subtropics: nutrient limited;
Nutrient decrease will lower Chl
and primary productivity
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?
SST 1899-2009

Effect of SST on Chl
in situ Chl + transparency data
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 !
S Hem
N Hem
Stratification (kg/m3)
Total Primary Prod (PgC/yr)
global
surface NO3
(mmol/m3)
Export Flux (PgC/yr)
Total Carbon (biomass)
e-ratio
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 )
 diat  DiatC  mDiatDiatC  Diatgraze  Diatagg
Dt
D(SC )
 sp  SC  mS SC  Sgraze  Sagg
Dt
2
Grazing: Sgraze  u  2
S
(T30) /10
S
 2 C 2  ZC
SC  g
D(DiazC )
 diaz  DiazC  mDiazDiazC  Diazgraze
Dt

D(ZC )
2
 Diatgraze  Sgraze  Diazgraze  mZC  pZC
Dt
D(Nutrient)
 Input sp  SC  diat  DiatC  diaz  DiazC
Dt
+ complicated equations for particulate organic carbon (POC), etc.
•
Can we understand the response of this system to future
changes in climate change by analyzing the underlying
model equations ?
Model Phytoplankton Growth Equations (biomass in mol C/m3)
Px
r
   (uPx )    (K  Px )  x  Px  Pgrazing  mx  Px  Paggregation
t

Specific Growth Rate:
x  ref  Tf  Vx  Lx
light availability
temperature function
   c  I 
x
x
PAR
Lx  1 exp
  V T 

 ref x f 

T30o C 


o
 10 C 
Tf  2
IPAR(W/m2)= surf irradiance
nutrient functional
response

Vx  min(VxFe,VxN ,VxPO4 ,VxSiO3 )

Fe
x
V
Fe

Fe  K xFe
VxN
 NO NH 
  NO3  NH4 
Kx 3 Kx 4 

xc  (Chl/C) x
 x  initial P  I slope
 NO NH 
1 NO33  NH44 
Kx 
 Kx
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
 N 
par
,T constant
S
I par
 I par 
N,Tf constant
S
T I
 T
par
,N constant
S  S nutr  S light  S temp
If the model is simple enough we can calculate analytically
each of these terms at steady state !
Q: Will a given change in nutrients change more S or L, i.e., will
S nut  Lnut and
S L

?
N N
For example, in the GFDL TOPAZ model we
can show that:
• 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:
S  L
• Outside 40oS-40oN, the opposite is the case.

1/ b


D(L)
L
 L  L  L  *  L
P 
Dt
At steady state, the equations translate to:
S  *
S   P
S 
 S 1/ a
D(S)
 S  S  S  *  S
P 
Dt

L 3 *
L    P
L 
x  xref  e kT  Vxnut  (1 e...Ipar )
N
N
kT
V

,
x  mx  e
x
N
N  Kx
Critical Nutrient Hypothesis
• 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 …
40oS - 40oN: low nutrient region
a nutrient change will affect more
small phytoplankton than diatoms.
diatoms respond more
S  L
Small phyto
respond more
Small phyto
respond
more
diatoms respond more
high latitudes: high nutrient zone
a nutrient
change will affect more

diatoms than small phytoplankton
S  L
New satellite backscattering method aims to
separate size structure (shown are SeaWIFS
1997-2007 means)
Pico (0.5-2um) particle number
Nano (2-20um) particle number
Micro (20-50um)
Kostadinov et al. 2010
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 …
 pCO2atm, coupled - uncoupled
pCO2atm (ppm),
coupled

Land Uptake, coupled
(GtC/yr)
 Land Uptake, coupled -
uncoupled

Hadley
 Ocean Uptake, coupled - uncoupled
Ocean Uptake,
coupled (GtC/yr)
Hadley
Friedlingstein et al. 2006

CCSM-1
UVic
“Climate-C cycle feedback
analysis: results from the
CMIP-4 model
intercomparison”
Change in land and ocean carbon (GtC):
CL   L CA   L T
CO  OCA   OT
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)