An integrative view of the biological carbon pump

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21 Φεβ 2014 (πριν από 3 χρόνια και 3 μήνες)

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An integrative view of the biological
carbon pump

from the surface ocean to the deep sediment

Sandra Arndt (s.arndt@bristol.ac.uk)

Sandra Arndt (s.arndt@bristol.ac.uk)

The biological C pump


Controls importance of global ocean & sediments as C sink (or source)



temporal sequestration of C in deep ocean (very fast response)


CH
2
O burial (fast response)


weathering
-
CaCO
3
burial (slow response)




Controls atmospheric O
2




Controls nutrient and O
2
distribution in the ocean



Controls size of hydrocarbon reservoirs



Sandra Arndt (s.arndt@bristol.ac.uk)

Efficiency of the biological C pump

Euphotic/

Epipelagic zone (0
-
200m)

F
export
=10
-
20% NPP

10
-
1

yrs

10
3

yrs

Deposition flux

Sediment

(0
-
10
3
-
10
4
m)

Mesopelagic zone

(200
-
1000m)

Bathypelagic zone

(1000
-
4000m)

Abyssopelagic zone

(4000
-
6000m)

0 yrs

10
8

yrs

0.28
-
30% F
export

<1
-
5% F
export

<0.3% F
export

CH
2
O

F
export
=100% NPP

Burial flux

70% F
export

50% F
export

13% F
export

CaCO
3

Export flux

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial variability

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial variability
-

Global scale

Henson et al., 2012

Henson et al., 2012

Henson et al., 2012

Seiter et al., 2004

Primary Production (gC m
-
2 yr
-
1)

Export Efficiency P
eff
=F
export
/PP

Transfer Efficiency T
eff
=F
2000m
/F
export

Sediment TOC (wt%)

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial variability
-

Global scale

Arndt et al., ESR,
in press

Regional patterns of organic matter quality in surface
sediments

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial variability
-

Global scale

Seiter et al., 2005

Hensen et al., 1998

PO
4
flux

(mmol m
-
2 yr
-
1)

NO
3
flux

(mmol m
-
2 yr
-
1)

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial variability
-

Continental Margin

Arndt et al., in press

Mollenhauer and Eglinton, 2007

Lateral transport

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial variability
-

Lateral Transport

Schmidt et al., 2007

Marine
-
dominated inner shelf

Terrestrial mud dominated mid
-
shelf

mudbelt

Starved outer shelf and

continental slope

Sandra Arndt (s.arndt@bristol.ac.uk)

Spatial Variability
-

Continental Margin

Zabel and Hensen, 2006
(modified from Jahnke, 1990)

Sediments are the ultimate sediment trap!

Sandra Arndt (s.arndt@bristol.ac.uk)

Continental Margins
-
Spatial Variability

unpublished data

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability
-
Seasonal variability

Lutz et al., 2007

Seasonal variability NPP:

Low: Equ. low productivity
regions


High: high latitudes, monsoonal
and temperate high productivity
regions


Balance between seasonality of
flux and production reverses
with latitude

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability
-
Seasonal variability

Soetaert et al., 1996

Seasonal variability in CH
2
O input results in a complex benthic response

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability
-
Lessons from the past

Example: 1. Pliocene
-
Pleistocene Transition


at Bowers Ridge (Beringsea)

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability
-
Lessons from the past

Wehrmann et al., 2013

Inverse diagenetic modeling of
sediment porwater profiles…


indicates

peak

in

CH
2
O

deposition

flux

&

quality

across

transition

and

thus

important

changes

in

the

functioning

of

the

BCP

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability
-
Lessons from the past

Example: 2. Cretaceous Oceanic Anoxic Event


Greenhouse climate, anoxic/sulfidic ocean

Sandra Arndt (s.arndt@bristol.ac.uk)

Temporal variability
-
Lessons from the past

Arndt et al., 2009

Inverse diagenetic modeling of sediment porwater profiles
indicates low reactivity (high preservation efficiency) and thus
rapid transfer from surface ocean to deep sediment

Sandra Arndt (s.arndt@bristol.ac.uk)

What causes the spatial
-
temporal variability?

The efficiency of the biological C pump is mainly driven by the
production, transport
and alteration of POC

Sandra Arndt (s.arndt@bristol.ac.uk)

What causes the spatial
-
temporal variability?

1.
Ballasting





Model that partitions sinking CH
2
O in
two fractions:


1)
ballast associated

2)
unassociated


Sarmiento and Gruber, 2006

Sandra Arndt (s.arndt@bristol.ac.uk)

What causes the spatial
-
temporal variability?

1.
Ballasting

Spatial variability of CaCO3 carrying coefficients

Wilson et al., 2012

Sandra Arndt (s.arndt@bristol.ac.uk)

What causes the spatial
-
temporal variability?

2. Ecosystem Structure


Effect on transport



Effect on quality

Micklasz and Denny, 2010

Mayor et al., 2012

Sandra Arndt (s.arndt@bristol.ac.uk)

What causes the spatial
-
temporal variability?

3. Organic matter source

and transport



High quality:

Young marine material



Low quality:

Old marine material

Mix pre
-
aged, terrestrial
material


Arndt et al., in press

Sandra Arndt (s.arndt@bristol.ac.uk)

Representation of the pump in Earth System Models

Arndt et al., in press

(adapted from lutz et al., 2002)


Flux:


Simple power
-
law expression with
constant scaling factor (Martin curve,
Martin, 1987):







Limit ability of models to predict
response of the BCP to environmental
perturbations and climate change



no sediments




Sandra Arndt (s.arndt@bristol.ac.uk)

Conclusions

Biological carbon pump is a complex set of interlinked processes that act along the
surface ocean
-

deep sediment continuum




Its functioning and efficiency is highly variable in time and space with important
implications for global climate and biogeochemical cycles




Existing Earth system models include empirical, highly simplified and decoupled
representations of the biological carbon pump that are not related to factors that
control the quantity and quality of the flux










Thank you!

Sandra Arndt (s.arndt@bristol.ac.uk)