1. 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

2. 1. Burrowing organisms in marine environments
OUTLINE
1. Burrowing organisms in marine environments
A fresh look at Darwin‘s last idea
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

3. 1. Burrowing organisms in marine environments
A fresh look at Darwin‘s last idea
Bioturbation refers to the biological reworking of soils and sediments, and its importance was first realized by Charles Darwin, who devoted his last scientific book to the subject. More than one hundred twenty-five years later, many studies within the biogeosciences (ecology, paleontology, biogeochemistry, sedimentology) now cite Darwin as the original reference.
Over 125 years ago he was the first to point out the importance of burrowing earthworms. In his last book The formation of vegetable mould, through the action of worms, with observations on their habits, published in 1881, Darwin described the role played by earthworms in soil formation and erosion, and their impact on the landscape. The book is largely based on experiments Darwin carried out in his garden, assisted by members of his family. Filip Meysman elaborates: “Darwin’s book gave the general public insight into the importance of soil organisms. Up until then, earthworms and their like were thought of as pests. Darwin himself found the topic interesting, but not very important. He had no idea of the critical role burrowing organisms played in evolution. What we now know about the influence of bioturbation on biodiversity and evolution would probably make him fall off his chair in astonishment.”

4. 1. A fresh look at Darwin’s last idea
Charles Darwin
*12 Feb 1809, †19 Apr 1882
Bioturbation refers to the biological reworking of soils and sediments, and its importance was first realized by Charles Darwin, who devoted his last scientific book to the subject. More than one hundred twenty-five years later, many studies within the biogeosciences (ecology, paleontology, biogeochemistry, sedimentology) now cite Darwin as the original reference.
Over 125 years ago he was the first to point out the importance of burrowing earthworms. In his last book The formation of vegetable mould, through the action of worms, with observations on their habits, published in 1881, Darwin described the role played by earthworms in soil formation and erosion, and their impact on the landscape. The book is largely based on experiments Darwin carried out in his garden, assisted by members of his family. Filip Meysman elaborates: “Darwin’s book gave the general public insight into the importance of soil organisms. Up until then, earthworms and their like were thought of as pests. Darwin himself found the topic interesting, but not very important. He had no idea of the critical role burrowing organisms played in evolution. What we now know about the influence of bioturbation on biodiversity and evolution would probably make him fall off his chair in astonishment.”

5. 1. A fresh look at Darwin’s last idea
Bioturbation refers to the biological reworking of soils and sediments, and its importance was first realized by Charles Darwin, who devoted his last scientific book to the subject. More than one hundred twenty-five years later, many studies within the biogeosciences (ecology, paleontology, biogeochemistry, sedimentology) now cite Darwin as the original reference.
Over 125 years ago he was the first to point out the importance of burrowing earthworms. In his last book The formation of vegetable mould, through the action of worms, with observations on their habits, published in 1881, Darwin described the role played by earthworms in soil formation and erosion, and their impact on the landscape. The book is largely based on experiments Darwin carried out in his garden, assisted by members of his family. Filip Meysman elaborates: “Darwin’s book gave the general public insight into the importance of soil organisms. Up until then, earthworms and their like were thought of as pests. Darwin himself found the topic interesting, but not very important. He had no idea of the critical role burrowing organisms played in evolution. What we now know about the influence of bioturbation on biodiversity and evolution would probably make him fall off his chair in astonishment.”

6. 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)

7. 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
Brittle star
Stahl & Glud, L&O (2006)

8. 1. A fresh look at Darwin’s last idea
Ocean floor without fauna O2
SO4
Anoxic sediment
5 mm
microbial mats
shallow O2 penetration
diffusive transport
10 cm
ventilated burrow systems
increased O2 supply
biol. mediated transport
Ocean floor with fauna
after Meysman, et al., Trends Ecol. Evol. (2006)

9. 2. Carbon cycling in the ocean The role of the seafloor
Slide 02/15

10. CO2 + H2O CH2O + O2 O2 CH2O Atmosphere Carbon fixation (~54 Pg yr-1)
2. Carbon cycling – The role of the seafloor
Atmosphere
Organic carbon sequestration
Oxygen accumulation
CO2
sequestration O2
CH2O
0.4% 5%
4.6%
CO2 + H2O CH2O + O2
Recycling
15%
80%
Carbon fixation (~54 Pg yr-1)
Export
Release
Burial
200 m
Upper ocean
Deep Ocean
Surface sediment
Deep
sediment
after Sarmiento and Gruber, 2006
Slide 02/15

11. The seafloor – An efficient „batch reactor“
2. Carbon cycling – The role of the seafloor
The seafloor – An efficient „batch reactor“
Total area: ~ 362 Mio km2 Reservoir size: 150*1015 gC Turnover time: 0.1 – 1000 yr
Return CO2 to
water column
Seafloor flux
92 %
The ocean floor provides the last chance of recycling before “permanent” burial
8 %
Sequestration in deeper sediments

12. Critical questions to be asked...
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 Continental
margins
Organic matter input
Organic carbon content
Macrofaunal activity
What controls Corg burial?
• OXYGEN EXPOSURE TIME
– High flux of Corg to seds
– Low oxygen in overlying water
– High sedimentation rates
redrawn from Seiter et al., DSRII (2004)

13. Is macrofaunal activity a key player at the global scale?
2. Carbon cycling – The role of the seafloor
reproduced from Burdige, Chem. Rev. (2007)
Is macrofaunal activity a key
player at the global scale?
2 things are apparent:
Quantitative estimates of organic matter burial in continental margin sediments are uncertain.
Large differences in Corg burial estimates (up to 2 orders of magnitude).
Most Corg burial occurs at continental margins (here defined as 1000m and above), although they comprise only about 10% of the total seafloor area. But compared to the deep ocean the much higher export production per unit area at the continental margins results in a much higher flux of organic matter reaching the seafloor.
Carbon cycling is most intense on the continental shelf, while ocean C cycle models biased towards open ocean! (Dunne et al. 2006)
Bioturbation / bioirrigation is most intense on the continental shelves

14. 3. Does macrofaunal activity affect organic matter processing on a global scale?
A data mining approach
In situ data on key variables related to organic matter processing are about to reach a critical size with trends becoming apparent from the deep sea toward coastal sediments. These data are synthesized in one database. The database is coupled to a GIS and explored statistically to secure sound parameterizations of key variables as a function of e.g. water depth or organic matter input flux. By developing a reactive transport model we then will use the improved parameterizations to (1) revise estimates of carbon burial and (2) assess effects of macrofauna activity on organic carbon cycling in the global ocean floor.
1) Improve estimates and budgets of carbon processing and burial
2) Quantifying the influence of macrofauna (bioturbation/bio-irrigation)
1) Development of a global database on process parameters that control organic carbon reminaralization and burial.
2) Description of relationships between process parameters and environmental variables to improve parameterization of diagenetic models.
3) Run biogeochemical simulations with improved parameterization to get better quantitative assessment of organic carbon processing.

15. Data-mining GIS Parameterization Modelling
3. A data mining approach
Data-mining
GIS
Parameterization
Modelling
In situ data on key variables related to organic matter processing are about to reach a critical size with trends becoming apparent from the deep sea toward coastal sediments. These data are synthesized in one database. The database is coupled to a GIS and explored statistically to secure sound parameterizations of key variables as a function of e.g. water depth or organic matter input flux. By developing a reactive transport model we then will use the improved parameterizations to (1) revise estimates of carbon burial and (2) assess effects of macrofauna activity on organic carbon cycling in the global ocean floor.
1) Improve estimates and budgets of carbon processing and burial
2) Quantifying the influence of macrofauna (bioturbation/bio-irrigation)
1) Development of a global database on process parameters that control organic carbon reminaralization and burial.
2) Description of relationships between process parameters and environmental variables to improve parameterization of diagenetic models.
3) Run biogeochemical simulations with improved parameterization to get better quantitative assessment of organic carbon processing.
Quantitative assessment of macrofauna affect on sedimentary carbon cycling at a global scale

16. The model parameters in focus
3. A data mining approach
The model parameters in focus
Bio-irrigation
O2-consumption
Bioturbation
Burial
Degradation
Differential equation
General balance statement for a chemical compound
The above diagenetic equation provides a simplified model of organic carbon processing in marine sediments. Db is the mixing coefficient, v is the burial velocity and k the decomposition constant. In a first stage, the data-mining targets these parameters (see Table 1 for a full list of all parameters focused upon).

17. Independent variables
3. A data mining approach
The model parameters in focus
Independent variables
water depth
temperature, salinity
primary production
Organic matter
seafloor flux
surface sediment content
burial flux
decay rate constant (k)
remineralization flux (ΣCO2)
Sediment transport
bioturbation coefficient (Db)
bioirrigation coefficient (α)
burial velocity (v)
mixed layer depth
mass flux to seafloor
O2 consumption
diffusive O2 uptake (DOU)
total O2 uptake (TOU)
O2 penetration depth
bottom water O2 content
Sediment type
porosity
density
sand, silt, clay content

18. Bioturbation coefficient (Db)
3. A data mining approach
Sediment O2 uptake
TOU
DOU
Bioturbation coefficient (Db)
210Pb
234Th

19. 4. Preliminary results
The ocean floor (and especially the deep sea) seems a more variable environment than currently anticipated
Poor coverage of a large global ecosystem. Unequal geographical distribution of the data (Db bias to Atlantic; k bias to Pacific)
A more systematic approach towards deposition of data into data repositories upon publication would be great.
Inconsistency (burial velocity, accumulation rate, sedimentation rate, or what?)
Data quality (i.e., often no indication of measurement error, variance)
Data gaps (e.g., Indo-Pacific, Southern Ocean)
Skewed data (i.e., large variance and non-normal distribution)
Spatial heterogeneity (can we distinguish between sand, mud, deltaic sediments)
Model assumption (how appropriate is 1D-approach?)
Pristine conditions? (historical and chronical human and natural pressure/disturbace)

20. ETOPO 1 Min. Global Bathymetry (NGDC/NOAA, 2008)
4. Preliminary results
ETOPO 1 Min. Global Bathymetry (NGDC/NOAA, 2008)
~ 10% < 1000m

21. Sediment O2 uptake as a measure of remineralization
4. Preliminary results
Sediment O2 uptake as a measure of remineralization
Organic matter degradation supported by physical transport only (DOU)
Extra organic matter degradation induced by the presence of fauna
(TOU-DOU = FMOU)
Total organic matter degradation (TOU)
Question: How does bioturbation affect the carbon cycle of the global ocean floor? What if bioturbating organisms had never evolved?
Combined data-mining and modelling approach: Expansion and exploration of current databases on organic matter processing. Equipping global-scale biogeochemical models with improved parameterizations of bioturbation, irrigation (better grip on oxygen exposure time).
Glud, Mar. Biol. Rev. (2008)

22. 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 %

23. Ocean floor is a more variable environment than anticipated
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.
The ocean floor (and especially the deep sea) seems a more variable environment than currently anticipated
Poor coverage of a large global ecosystem. Unequal geographical distribution of the data (Db bias to Atlantic; k bias to Pacific)
A more systematic approach towards deposition of data into data repositories upon publication would be great.
Inconsistency (burial velocity, accumulation rate, sedimentation rate, or what?)
Data quality (i.e., often no indication of measurement error, variance)
Data gaps (e.g., Indo-Pacific, Southern Ocean)
Skewed data (i.e., large variance and non-normal distribution)
Spatial heterogeneity (can we distinguish between sand, mud, deltaic sediments)
Model assumption (how appropriate is 1D-approach?)
Pristine conditions? (historical and chronical human and natural pressure/disturbace)

24. fbockelm@vub.ac.be www.vub.ac.be/ANCH
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"