Transcript O 2

Do burrowing organisms influence
carbon processing on a global scale?
A data mining approach.
Frank Bockelmann
Olivier Maire
Filip Meysman
Laboratory of Analytical and Environmental Chemistry
Vrije Universiteit Brussel (VUB)
Pleinlaan 2, 1050 Brussel
[email protected]
www.vub.ac.be/ANCH
OUTLINE
1. Burrowing organisms in marine
environments
A fresh look at Darwin‘s last idea
2. Carbon cycling in the ocean
The role of the seafloor
3. Does macrofaunal activity affect
organic matter processing on a
global scale?
A data mining approach
4. Preliminary results
1. Burrowing organisms in marine environments
A fresh look at Darwin‘s last idea
1. A fresh look at Darwin’s last idea
Charles Darwin
*12 Feb 1809, †19 Apr 1882
1. A fresh look at Darwin’s last idea
1. A fresh look at Darwin’s last idea
Bioturbation is the displacement and mixing of sediment
particles by benthic animals or rooting plants resulting in
disturbance of sediment layers.
Spidercrab (Hyas araneus)
Solan et al., MEPS (2004)
1. A fresh look at Darwin’s last idea
Bioirrigation is the process of benthic organisms flushing
their burrows with seawater thereby exchanging dissolved
substances between the porewater and overlying seawater.
Evolution O2 concentration at particular point
% air saturation
120
100
80
60
40
20
0
0
20
25
40
45
55
60
65
75
100 115 145 150 175 180 190 195 200 205 215 220
Time (sec)
Brittle star
Stahl & Glud, L&O (2006)
1. A fresh look at Darwin’s last idea
Ocean floor without fauna
Ocean floor with fauna
O2 SO4
5 mm
10 cm
Anoxic sediment
• microbial mats
• shallow O2 penetration
• diffusive transport
•ventilated burrow systems
•increased O2 supply
•biol. mediated transport
after Meysman, et al., Trends Ecol. Evol. (2006)
2. Carbon cycling in the ocean
The role of the seafloor
Slide 02/15
2. Carbon cycling – The role of the seafloor
Atmosphere
Upper
ocean
Deep
Ocean
CO2
sequestration
Oxygen
accumulation
Carbon fixation (~54 Pg yr-1)
CO2 + H2O
Release
CH2O + O2
80%
200 m
15%
Export
5%
Recycling
Surface
sediment
Deep
sediment
CO2 + H2O
CH 2O + O2
4.6%
Burial
0.4%
Organic carbon
sequestration
after Sarmiento and Gruber, 2006
Slide 02/15
2. Carbon cycling – The role of the seafloor
The seafloor – An efficient „batch reactor“
Total area:
Reservoir size:
Turnover time:
Seafloor flux
~ 362 Mio km2
150*1015 gC
0.1 – 1000 yr
Return CO2 to
water column
92 %
CH2O  O2 
CO2  H2O
8%
Sequestration in
deeper sediments
2. Carbon cycling – The role of the seafloor
Critical questions to be asked...
How much carbon goes, how much stays?
How does this efficiency vary between environments?
What controls the recycling efficiency?
Deep sea
Organic matter input
Organic carbon content
Macrofaunal activity
Continental
margins
redrawn from Seiter et al., DSRII (2004)
2. Carbon cycling – The role of the seafloor
Is macrofaunal activity a key
player at the global scale?
reproduced from Burdige, Chem. Rev. (2007)
3. Does macrofaunal activity affect organic
matter processing on a global scale?
A data mining approach
3. A data mining approach
Data-mining
GIS
Parameterization
Modelling
Quantitative assessment of macrofauna affect on
sedimentary carbon cycling at a global scale
3. A data mining approach
The model parameters in focus
CH2O  O2 
CO2  H2O
Bioturbation
Burial
Degradation
Bio-irrigation
O2-consumption
3. A data mining approach
The model parameters in focus
Independent variables
water depth
temperature, salinity
primary production
Sediment transport
bioturbation coefficient (Db)
bioirrigation coefficient (α)
burial velocity (v)
mixed layer depth
mass flux to seafloor
Sediment type
porosity
density
sand, silt, clay content
Organic matter
seafloor flux
surface sediment content
burial flux
decay rate constant (k)
remineralization flux (ΣCO2)
O2 consumption
diffusive O2 uptake (DOU)
total O2 uptake (TOU)
O2 penetration depth
bottom water O2 content
3. A data mining approach
Sediment O2 uptake
TOU
DOU
Bioturbation coefficient (Db)
210Pb
234Th
4. Preliminary results
4. Preliminary results
ETOPO 1 Min. Global Bathymetry (NGDC/NOAA, 2008)
~ 10% < 1000m
4. Preliminary results
Sediment O2 uptake as a measure of remineralization
Organic matter degradation
supported by physical
transport only (DOU)
Total organic matter
degradation (TOU)
Extra organic matter
degradation induced by
the presence of fauna
(TOU-DOU = FMOU)
Glud, Mar. Biol. Rev. (2008)
4. Preliminary results
• Globally, TOU accounts for remineralization of 2.74 PgC yr-1
of that 70% DOU and 30% FMOU.
• Continental margins (above 1000m) release 1.84 PgC yr-1
(67% of global Rox) of that 54% DOU and 46% FMOU.
• Shutting down macrofaunal activity at continental margins
would result in ~ 5fold increase in C-burial!
67 %
TOU
FMOU
30 %
Things to remember...
•Macrofauna enhances the sediment oxygen uptake
through bioturbation and bio-irrigation
•Benthic activity has large effect on local biogeochemistry
of the ocean floor (ecosystem engineering)
•Continental margin sediments play a crucial role in
organic matter processing at a global scale
•(Global) carbon balance estimates are extremely
sensitive to the representation of benthic activity
However,
•Ocean floor is a more variable environment than
anticipated
•Sampling with respect to basal model parameters tends
to exclude large areas (e.g., Db bias to Atlantic; k bias
to Pacific)
•A more systematic approach towards deposition of
data into repositories is desirable.
Funding through
FWO-Odysseus project to Filip Meysman
"Quantifying Darwin's last idea: the influence of
bioturbation on the biogeochemistry of marine
sediments, and its impact on the global carbon cycle"
[email protected]
www.vub.ac.be/ANCH