Towards a comprehensive C-budgeting approach of a
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Transcript Towards a comprehensive C-budgeting approach of a
Coccolithophore blooms in the northern
Bay of Biscay: results from PEACE
project
Jérôme Harlay
Unité d’océanographie Chimique
Université de Liège
Co-authorship
•
•
•
•
Alberto Borges, Bruno Delille, Kim Suykens (ULg, Belgium)
Lei Chou, Caroline De Bodt (ULB, Belgium)
Koen Sabbe, Nicolas Van Oostende (UGent, Belgium)
Anja Engel, Judith Piontek, Corinna Borchard (AWI, Germany)
ROLE OF PELAGIC CALCIFICATION AND
EXPORT OF CARBONATE PRODUCTION
IN CLIMATE CHANGE
(2005-2009)
Belgian Federal Science Policy Office
Outline
• Introduction
– Pelagic Calcification
– Coccolithophores
– Problematic
– Objectives
• Material and Methods
– Study site
– Pelagic processes
– Benthic processes
• Results
• Synthesis
• Conclusions
Pelagic Calcification
Estimates of global calcification rates
Coccolithophores (Balch et al., 2007)
~1600 1012 g C yr-1
Foraminifera (Langer et al., 1997)
~162 1012 g C yr-1
Pteropods (Honjo, 1981)
~160 1012 g C yr-1
Coral Reefs (Vescei, 2004) ~90 1012 g C yr-1
Benthic Molluscs, Echinoderms… ?
They are the main contributors to
contemporary biogenic CaCO3
precipitation
Balch et al., 2007 – DSR II
Coccolithophores
Coccolithophores play a key role in the biogeochemical cycle of the
world Ocean:
- Primary producers:
106CO2 16NO3 H 2 PO4 17H 122H 2O CH 2O106 NH 3 16 H 3 PO4 138O2
- Key role in total alkalinity (TA) distribution:
2HCO3 Ca 2 CaCO3 CO2 H 2O
- CaCO3 ballasts particulate organic carbon (POC) and participates to
the biological pump that removes CO2 from the surface ocean to the
ocean interior.
Problematic
How important are pelagic calcifiers in the biogeochemical C cycle?
• “Carbonate rocks” is the most important reservoir of C on Earth
Berner, 1998
• CaCO3 production is a biotic process
• Ocean acidification and Global
Warming will affect the distribution
and the abundance of the pelagic
calcifiers.
(The Royal Society Report, 2005, IPCC, 2007)
Objectives
Objectives: ecosystem dynamics and
bentho-pelagic coupling during
coccolithophore blooms
• PEACE project: 3 cruises in the Bay of Biscay (May-June
2006; 2007 and 2008) :
ROLE OF PELAGIC CALCIFICATION AND
EXPORT OF CARBONATE PRODUCTION
IN CLIMATE CHANGE
(2005-2009)
Belgian Federal Science Policy Office
Understanding the functioning and characteristics of
coccolithophore blooms is of crucial importance to
describe the efficiency of the biological pumps.
Outline
• Introduction
– Pelagic Calcification
– Coccolithophores
– Problematic
– Objectives
• Material and Methods
– Study site
– Pelagic processes
– Benthic processes
• Results
• Synthesis
• Conclusions
Material and Methods
Study site: Northern Bay of Biscay
NE Altantic Ocean
52 °N
IR
U.K.
50 °N
200
100
200 0
0
48 °N
8
FR
7
5
400
0
6
12 °W
10 °W
8 °W
4
1
2
3
6 °W
4 °W
Pelagic Processes
We applied an original approach based on the Margalef’s Mandala.
“A shift towards oligotrophy is accompanied by
a change in the relative dominance of
phytoplankton species.”
High
Margalef’s Mandala (1997)
DIATOMS
N, P, Chl-a
Succession
Pelagic Measurements (2006):
-
14C-Primary
production
-
14C-Calcification
- O2-based Dark Community Respiration
COCCOLITHOPHORES
- DSi, PO4
Succession
Low
- HPLC pigments (Chemtax re-analysis)
- POC, PIC
DINOFLAGELLATES
Low
Turbulence
High
-Total Alkalinity, pCO2
-3[H]-Thy Bacterial Production
Working hypothesis:
the thermal stratification favours the blooming of
Coccolithophores at the continental margin.
Ben
Benthic Processes
Incubations of sediment cores with overlying waters
- biogeochemical water-sediment fluxes (O2, TA, NO3-)
- FO2 : Benthic respiration rate
- FTA*:
corrected for:
- nitrification/denitrification :
- aerobic OM remineralisation:
- sediment characteristics (grain size, chlorophyll-a (Chla), POC and PIC content)
Water sampled above the bottom at depths between
208 and 4460 m)
Outline
• Introduction
– Pelagic Calcification
– Coccolithophores
– Problematic
– Objectives
• Material and Methods
– Study site
– Pelagic processes
– Benthic processes
• Results
• Synthesis
• Conclusions
Satellite images
14 W
a
12 W
10 W
8W
6W
2006/06/05
8
10 W
b
8W
5
3
1
51
50
50
8
49
7
4
48
Chl-a
47
0.2
mixing
Internal
waves
52
51
2
200 m
14 W
6W
2006/06/05
0.08
4000 m
12 W
49
4
SST
52
7
6
14 W
0.4
0.8
6
5
3
10 W
8W
6W
2006/06/05
8
7
4
1
48
6
2
47
2
c
12 W
5
Advection
5
1
2
Reflectance
3
Time series
1.50
1.25
4
Chl-a
22
Lwn (555)
SST
MLD
20
50
18
3
16
2
100
14
150
0.25
0.00
1
12
0
10
J
F
M
A
M
J
J
A
200
S
The onset of the coccolithophore bloom (Lwn(555)) coincides
with a warming (SST) and a shoaling of the mixed layer depth
after the first peak of Chl-a in early April
Data from:
GIOVANNI (Lwn (555), Chl-a)
GODIVA (Grid for Ocean Diagnostics, Interactive Visualisation and Analysis) (MLD)
Reynolds et al. (2002) (SST)
MLD [m]
0.50
Chl-a [µg L -1]
1.00
0.75
0
SST [°C]
Lwn (555) [mW cm -2 µm -1 sr -1]
5
Environmental Settings
T [°C]
10.5
0
20
11.5
12.5
13.5
2154
14.5
3 4b 1b 8 7 6
The vertical profiles of temperature
exhibit a warming over the shelf,
compared to the station located on
the shelf-break (in grey).
40
depth [m]
60
52 °N
IR
80
100
U.K.
50 °N
120
140
160
200
100
200 0
0
48 °N
8
FR
7
5
400
0
6
12 °W
10 °W
8 °W
4
1
2
3
6 °W
4 °W
Pelagic: Results
We used the density gradient to build a stratification index as an indicator for
the preferential niche of coccolithophores to characterize the status of the
different stations regarding the bloom development.
density
1026.8 1026.9
0
20
depth (m)
40
60
80
100
120
140
160
1027
1027.1 1027.2
Pelagic: Results
We used the density gradient to build a stratification index as an indicator for
the preferential niche of coccolithophores to characterize the status of the
different stations regarding the bloom development.
density
1026.8 1026.9
0
1027
1027.1 1027.2
20
depth (m)
40
60
80
100
120
140
Stratification
index
160
Higher index corresponds to
more stratified conditions
Pelagic: Results
We used the density gradient to build a stratification index as an indicator for
the preferential niche of coccolithophores to characterize the status of the
different stations regarding of bloom development.
density
1026.8 1026.9
0
1027
Example: Integrated Chl-a concentration
1027.1 1027.2
Slope-stations
Shelf-stations
Good mixing
160
Stratification
20
2
60
80
100
120
140
Stratification
index
Chl-a (mg m-2)
depth (m)
40
120
1
80
4b 7
5
40
4
1b
160
Higher index corresponds to
more stratified conditions
r²=0.62
0
0.0
0.2
0.4
0.6
8
0.8
Stratification
stratification
degreeindex
(kg m-3)
Pelagic: Results
0.16
PO4 [µmol L-1]
5
0.12
2
0.08
1
4
0.04
1b 7 8
The availability of PO4
decreased with increasing
stratification.
4b
r²=0.56
0.00
0.0
0.2
0.4
0.6
0.8
100m-3m [kg m-3]
2.0
DSi [µmol L-1]
2
1.5
8
1
1.0
0.5
4
1b
5
(Egge & Aksnes, 1992)
7
4b
0.0
0.0
0.2
0.4
0.6
100m-3m [kg m-3]
DSi remained at limiting
concentration for diatom’s
growth (< 2.0 µmol L-1)
0.8
Pelagic: Results
% Chl-a Diatoms
50
4b 7
40
30
20
2
1b
10
0
0.0
The relative proportion
of diatoms was unrelated
to stratification
1 4
8
0.2
0.4
0.6
0.8
-3
100m-3m [kg m ]
50
% Chl-a Cocco.
2
40
30
1b
20
1
8
4
4b
10
r²=0.30
0
0.0
0.2
7
0.4
0.6
0.8
-3
100m-3m [kg m ]
% Chl-a Dinofl.
25
20
8
15
10
2
4
5
7
1b
r²=0.28
0
0.0
0.2
1
0.4
4b
0.6
-3
100m-3m [kg m ]
0.8
Pelagic: Results
% Chl-a Diatoms
50
4b 7
40
30
20
2
1b
10
0
0.0
The relative proportion
of diatoms was unrelated
to stratification
1 4
8
0.2
0.4
0.6
0.8
-3
100m-3m [kg m ]
50
% Chl-a Cocco.
2
40
30
1b
20
1
8
4
4b
10
r²=0.30
0
0.0
0.2
7
0.4
0.6
0.8
-3
100m-3m [kg m ]
% Chl-a Dinofl.
25
20
8
15
Agreement with the
Mandala
10
2
4
5
7
1b
r²=0.28
0
0.0
0.2
1
0.4
4b
0.6
-3
100m-3m [kg m ]
The relative proportion
of coccolithophores
decreased while
dinoflagellates
increased with
stratification
0.8
Pelagic: Results
0.6
5
1b
1
7
4b
4
8
r²=0.22
60
8
0.4
2
0.2
4
7
1b
4b
5
r²=0.73 1
0.0
0.0
0.2
0.4
2
0.6
0.8
-3
100-10 [kg m ]
40
20
4
1b
4b
0.8
8
1 4
r²=0.32 1
4b
0.6
150
1b
100
8
4b
2
50
1
8
1b
0.2
7
0.4
0.6
100m-3m [kg m-3]
r²=0.45
0.2
2
0.4
r²=0.45
0.0
0.0
0.2
7
4
0
0.0
If one excludes the
stations located on
the shelf-break, the
CAL:PP ratio increases
with increasing
stratification over
the shelf
7
5
0
DCR (mmol C m -2 d-1)
CAL:PP
100
0
CAL (mmol C m -2 d-1)
Shelf-break/Shelf
2
PIC:POC
PP (mmol C m -2 d-1)
200
0.4
0.6
100m-3m [kg m-3]
0.8
0.8
An increase of the
process ratio
associated to a
decrease of the
standing-stock ratio
would indicate the
export of PIC to the
bottom over the shelf
Pelagic: Results
0.6
5
1b
1
7
4b
4
8
r²=0.22
60
8
0.4
2
0.2
4
7
1b
4b
5
r²=0.73 1
0.0
0.0
0.2
0.4
2
0.6
0.8
The CAL:PP ratio
increases with
increasing
stratification over
the shelf if one
excludes the stations
located on the slope
-3
100-10 [kg m ]
40
7
5
20
4
1b
4b
0
0.8
8
1 4
r²=0.32 1
4b
0.6
150
DCR (mmol C m -2 d-1)
CAL:PP
100
0
CAL (mmol C m -2 d-1)
Shelf-break/Shelf
2
PIC:POC
PP (mmol C m -2 d-1)
200
1b
100
8
4b
2
50
1
0.2
0.2
7
0.4
0.6
100m-3m [kg m-3]
r²=0.45
0
0.0
8
1b
r²=0.45
0.0
0.0
0.2
7
4
2
0.4
0.4
0.6
100m-3m [kg m-3]
0.8
0.8
An increase of the
process ratio
associated to a
decrease of the
standing-stock ratio
would indicate the
export of PIC to the
bottom over the shelf
Pelagic: Results
0.6
5
1b
1
7
4b
4
8
r²=0.22
60
8
0.4
2
0.2
4
7
1b
4b
5
r²=0.73 1
0.0
0.0
0.2
0.4
2
0.6
0.8
-3
100-10 [kg m ]
40
20
4
1b
4b
0.8
8
1 4
r²=0.32 1
4b
0.6
150
1b
100
8
4b
2
50
1
8
1b
0.2
7
0.4
0.6
100m-3m [kg m-3]
r²=0.45
0.2
2
0.4
r²=0.45
0.0
0.0
0.2
7
4
0
0.0
The CAL:PP ratio
increases with
increasing
stratification over
the shelf if one
excludes the stations
located on the shelfbreak
7
5
0
DCR (mmol C m -2 d-1)
CAL:PP
100
0
CAL (mmol C m -2 d-1)
Shelf-break/Shelf
2
PIC:POC
PP (mmol C m -2 d-1)
200
0.4
0.6
100m-3m [kg m-3]
0.8
0.8
An increase of the
process ratio
associated to a
decrease of the
standing-stock ratio
would indicate the
export
Pelagic: Results
Trophic status of the bloom
(2006)
140
Autotrophy
1.5
1.0
Heterotrophy
GPP:DCR
2.0
0.5
0.0
0
2
120
-1
2
r = 0.98
100
-2
If PP=GPP:
80
4
8
60
1
7
40
4bis
1bis
50
GPP:DCR
BP
100
150
-2
-1
GPP [mmol C m d ]
20
0
200
BP [mmol C m d ]
2.5
52 °N
IR
U.K.
50 °N
200
100
200 0
0
48 °N
8
FR
7
5
400
0
6
12 °W
10 °W
8 °W
4
1
2
3
6 °W
4 °W
Pelagic: Synthesis
Rate measurements (mmol C m-2 d-1)
CO2 fluxes (mmol CO2 m-2 d-1)
C fluxes (mmol C m-2 d-1)
Net CO2
flux based
on
measured
pCO2
NCP
Aphotic C
demand
Resp.
(DCR)
fPP
fCAL
fDCR
Net CO2
flux based
on
metabolic
rates
51.4
81.3
-180.0
30.9
81.3
-67.9
-11.4
98.7
89.0
79.3
7.5
73.7
-79.3
4.5
73.7
-1.0
-17.8
5.5
98.2
7(HR)
75.1
36.1
81.4
-75.1
21.7
81.4
28.0
-10.2
-6.4
35.1
4(HR)
54.0
12.9
78.9
-54.0
7.8
78.9
32.6
-13.4
-24.9
66.9
1bis
59.2
15.8
103.5
-59.2
9.5
103.5
53.8
-16.1
-44.4
159.0
4bis(HR)
54.6
12.5
101.2
-54.6
7.5
101.2
54.1
-10.7
-46.6
168.5
8(HR)
35.5
13.3
104.3
-35.5
8.0
104.3
76.8
-8.5
-68.8
72.3
Stations
C prim.
Prod. (PP)
2
180.0
1
14
CO2
0.7
CaCO3
14
C calcif.
(CAL)
(Frankignoulle et al., 1994)
Net CO2 flux = fPP+fCAL+fDCR
O2:C for Resp. = 1:1
NCP (net community production) = PP-DCR
Aphotic C demand = Respiration in the aphotic
zone
Our approach has some caveats:
- Steady state is assumed
- No dissolved C production nor Coverconsumption products are
included
Pelagic: Synthesis
CO2 fluxes
Station
Cruise 1
2006
Cruise 2
2007
Cruise 3
2008
date
PIC
export
GPP
rates
2
1/06/2006
1
31/05/2006
7
7/06/2006
4
2/06/2006
1bis
9/06/2006
4bis
8/06/2006
8
6/06/2006
5
2/06/2006
Average
2006
51
8
36
13
16
13
13
24
22
35
15
14
10
11
10
7
19
15
-180
-79
-75
-54
-59
-55
-36
-97
-79
36
5
25
9
11
9
9
17
15
93
81
89
89
121
117
116
1.9
1.0
0.8
0.6
0.5
0.5
0.3
-51
7
40
44
73
71
90
101
0.8
39
11
16/05/2007
9
14/05/2007
2bis
24/05/2007
8
13/05/2007
10
15/05/2007
4
23/05/2007
8bis
21/05/2007
2
10/05/2007
5bis
22/05/2007
5
12/05/2007
7
23/05/2007
Average
2007
65
44
24
82
118
47
59
140
42
10
36
61
-38
26
18
23
11
14
11
10
8
6
8
9
-198
-134
-96
-118
-56
-72
-58
-54
-42
-30
-41
-82
45
31
17
57
82
33
41
98
30
7
25
42
78
55
62
117
65
85
96
90
88
90
2.5
2.4
1.5
1.0
0.9
0.8
0.6
0.6
0.5
0.3
-74
-48
-17
57
91
46
79
134
76
67
83
1.1
41
1
9bis
12
6
8
5bis
11
13
10
5
9
2
4
26
67
15
14
21
17
5
24
10
6
31
2
10
30
14
8
7
11
14
7
11
9
5
8
3
9
-154
-75
-43
-36
-55
-72
-38
-57
-45
-26
-41
-16
-48
18
47
10
10
15
12
4
17
7
4
22
1
7
54
68
46
39
62
86
51
87
85
76
174
122
2.9
1.1
0.9
0.9
0.9
0.8
0.7
0.7
0.5
0.3
0.2
0.1
-82
39
13
13
22
27
17
46
47
54
155
107
7/05/2008
21/05/2008
18/05/2008
9/05/2008
11/05/2008
22/05/2008
14/05/2008
20/05/2008
13/05/2008
10/05/2008
12/05/2008
8/05/2008
23/05/2008
Average
3 year
2008
average
Average values
(2006-2008)
0.7*CAL
PCR
CO2 Flux
GPP:PCR
C fluxes
Pelagic
Calcification
NC flux based on
Air-sea metabolic NCP
Aphotic
Benthic demand
-12
-13
-8
-10
-13
-9
-7
-7
-10
87
-2
-14
-35
-62
-63
-80
-24
118
73
41
74
177
155
42
97
3.8
2.3
7.2
4.7
4.5
-15
-11
-6
-12
-14
-10
-14
-6
-14
-14
-15
-12
120
79
34
0.2
-9
-13
-38
-36
-46
-60
152
3
136
132
122
102
46
107
6.0
5.8
4.7
5.3
5.7
5.5
-6
-8
-8
-3
-8
-7
-9
-9
-9
-8
-10
-8
-6
87
90
88
106
100
8
-3
-3
-7
-15
-13
-30
-40
-50
-134
-106
118
77
81
84
51
73
52
142
63
61
60
158
19
10
-54
13
79
0.8
38
-8
-24
85
34 ± 32
11 ± 11
-70 ± 44
24 ± 22
86 ± 28
0.9 ± 0.7
39 ± 56
-10 ± 3
-15 ± 57
95 ± 39
6.2
8.4
6.8
4.7
4.1
4.1
5.4
6.5
3.7
7.3
6.6
5.8
5.5 ± 1.5
• GPP = 70 ± 44 mmolC/m²/d
• Cal = 34 ± 32 mmol/m²/d
• Pelagic respiration = 95 ± 39 mmolC/m²/d
Benthic results
Core incubations:
Characteristic of bottom waters:
•
•
•
•
•
•
•
•
•
Low temperature (10.5-11°C)
O2% ~85% -> oxygenated waters
ΩCAL 3.5
NO3-: 3.9-11 µmol/L
DSi: 1.4-4.7 µmol/L
Chl-a: 0.03-0.58 µg/L
SPM: 0.2-1.5 mg/L
POC: 14-97 µgC/L
PIC: 5-72 µgC/L
Characteristics of surface
sediments:
•
•
•
•
•
Visual aspect: recent phytoplankton
deposition
Fine to coarse sandy sediments (median
grain size: 190-285 µm)
Chl-a content: 0.01-0.95 µgChl-a/g
Low %OM: 1.4-4.0%
%PIC: 1.5-9.5% (mainly bivalve debris)
Benthic: Results
Core incubations:
FTA*: -1.1 to +3.7 mmol/m²/d
negative values = noise
Average Dissolution rates:
• FTA*/2= 0.33 mmol CaCO3/m²/d)
Low CaCO3 dissolution rates compared to other studies
(e.g.) due to high saturation state ΩCAL 3.5 in the Bay of
Biscay
CaCO3 dissolution (mmol m -2 d-1)
FO2: -2.4 to -8.4 mmol/m²/d
9
this study
Jahnke et al. (1997)
Jahnke and Jahnke (2000)
Silverberg et al. (2000)
Berelson et al. (2007)
8
7
decreasing CAL
of bottom waters
6
From Suykens et al, 2011
5
4
3
2
1
0
-14
-12
-10
-8
-6
-4
-2
-2
0
-1
FO2 (mmol O2 m d )
Average CaCO3 dissolution to OC oxidation ratio:
• -FTA*/(2xFO2)= 0.06 ± 0.09
metabolic driven dissolution of CaCO3 in sediments underlying bottom waters
highly over-saturated with respect to CaCO3 (Jahnke and Jahnke, 2004)
FTA* (mmol m-2 d-1)
5
4
3
2
1
0
-10
From Suykens et al, 2011
-8
-6
-4
-2
-2
0
-1
FO2 (mmol O2 m d )
Outline
• Introduction
– Pelagic Calcification
– Coccolithophores
– Problematic
– Objectives
• Material and Methods
– Study site
– Pelagic processes
– Benthic processes
• Results
• Synthesis
• Conclusions
Synthesis
Average CaCO3 Dissolution rate = 0.33 ± 0.47 mmol/m²/d
~1% of the Pelagic Calcification (34 ± 32 mmol/m²/d)
Average Benthic respiration: -5.5 ± 1.5 mmol O2 /m2/ d
~8% of the Pelagic Primary production (70 ± 44 mmolC/m²/d)
~6% of the Pelagic respiration in the aphotic zone (95 ± 39 mmolC/m²/d)
Correlation between FTA and FO2 => metabolic driven CaCO3 dissolution in the
sediments
Conclusions
Bentho-pelagic coupling:
• CaCO3 dissolution:
• is a metabolic process that occurs in waters over-saturated with
respect to calcite and
• is driven by OM respiration in the sediment
(in contrast to biogenic silica dissolution that is a thermodynamic process)
• CaCO3 dissolution and benthic respiration are low compared to surface
productions
Evidence of a decoupling of calcification by coccolithophores and the
dissolution of CaCO3 in the sediments.
PIC produced by coccolithophores is either:
• stored in the sediments or
• exported out of the system (advection)
• but does not seem to be significantly dissolved in the sediments.
Thank you
for your
attention!
Jess & Glynn Gorick