Particle transport and organic carbon fluxes off NW Africa: impact of dust and carbonate

transcript

Particle transport and organic carbon fluxes off NW Africa:

impact of dust and carbonate

G. Fischer (1), M. Iversen (3, 4), G. Karakas (3) , N. Nowald (1) , P. Helmke (2) , R. Davenport (1) , V. Ratmeyer (1) , G. Wefer (1)

(1) Geosciences Department and Research Center Ocean Margins, University of Bremen, Germany(2) School of Life Sciences, Arizona State University, Tempe, Arizona, USA

(3) Alfred-Wegener-Institute for Polar and Marine Research, Bremerhaven, Germany(4) Max Planck Institute for marine Microbiology, Bremen

http://www.rcom.marum.de/Project_B3

Outline

• Introduction

• Organic carbon fluxes vs dust and carbonate off NW Africa

• Sinking velocities of particles in the Atlantic and off Cape Blanc

• Advective transport off NW Africa

• Summary and outlook

http://www.rcom.marum.de/Project_B3

Primary Production in four Eastern Boundary Current Systems

(EBC‘s)

Carr, 2002

Canary Current 0.3 GT C yr-1

(carbonate production system with high dust supply)

Winter-spring maximum of particle flux in the eastern N‘Atlantic: highest values in the Cape Blanc area

1 0 °

2 0 °

3 0 °

- 3 0 ° - 2 0 ° - 1 0 °

1 0 0 0 m

4 0 0 0 m

A f ric a

C a p e

G h i r

C a p e

B la n c

C a p e

V erd e

E U M E L I-m e so

E U M E L I-o l ig o

N A B E 3 4 °N

E S T O C /CI

Su mm e r d us t plu me

t rade w

us t plu

G u in ea D o m e

N E C C

1-Jan 1-Apr 1-Ju l 1-O ct 1-Jan

w in ter spring sum m er fa ll

E BC 2-1

N ABE 34°N

E U M ELI-m eso

EU -oligo

C V 1-2

Atmospheric – ocean coupling off NW Africa ?

aerosol index vs lithogenic fluxes

Annual fluxes and composition

Cape Verde

Lithogenics=dust/carbonatevs organic carbon off NW Africa

0 10 20 30 40 50a n n u a l ca rb o n a te flu x (g m -2)

C org/C carb= 1.3r²=0.91

0 5 10 15 20 25a n n u a l lith o g e n ic flu x (g m -2)

C org/lith = 0.22r²=0.62

Organic carbon and dust fluxes

at four coastal sites 1-Jan 1-Apr 1-Ju l 1-O ct 1-Jan

C anary Is lands

)C ape B lanc

)EUM ELI-m eso 162

)C ape Verde

r²=0.91 r²=0.36 r²=0.74

r²=0.84r²=0.21 r²=0.98

r²=0.64 r²=0.07r²=0.21 (1992)r²=0.96 (1991) r²=0.13

r²=0.84 r²=0.99 r²=0.98 r²=0.90

w interspring

sum m erfa lldust deposition e

Kaufm an et a l. 2005

Seasonal dust deposition from MODIS

Composition and sinking rates in

the Atlanticestimated from sediment traps

-80 -60 -40 -20 0 20LATITU D E

EqPacAS

- 6 0 °

-4 5 °

-3 0 °

-1 5 °

-6 0 ° -4 5 ° -3 0 ° -1 5 ° 0 ° 15 °

E BCC IL P

N A BE

E U M EL I- m

C BE U M EL I- o

GB SWA 7

W S1 00 0 m

3 00 0 m

Study area: the Cape Blanc filament

CBmeso CBieu

MODIS sensor: daily chl-a in december

ROMS nested grid

1-Jan 1-Apr 1-Ju l 1-O ct

)C B_13 (m eso)

2003 2002

sinking velocities: seasonal variability

65 m d-1

250 m d-1

BSi-dominated winter/spring

carbonate-dominated summer

sedimentation

additional source

advection of chl-a (SeaWiFS) and deep carbon fluxes

120 m d-1

90 m d-1

~ 100 km/30 days

Helmke et al., 2005, GBC

CB9 (meso)

eu- vs mesotrophic fluxes at 1300m

1-Jan 1-A pr 1-Ju l 1-O ct 1-Jan

1000C Bi_1 (eu)

20032004

1-Jan 1-A pr 1-Ju l 1 -O ct 1-Jan

C B_14 (m eso)

20032004

E-W advective transport of particles of ~ 100 km / 30 days

no distinct winter/sprin

g bloom

~ 45 daysdelay

CBi_2(eutrophic site)

C Bi_2 upper (eu)

C Bi_2 low er (eu)

20042005

fluxes very low

730 m d-1

Flow velocimeter

Pellet sinking velocities (CBcoastal-2)

Larvacean pellets ?

s.v. = 730 m d-1

400 x 1000 µm (ellipsoidal-type)

1.3 g cm-3 (quartz, coccos, diatoms)

CBi_2 u #10 CBi_2 l #10

CBi_2 l #10

ROMS-simulated distributionof larger particles > 150µm of shelf origin:

s.v. = 5 m d-1

Karakas et al., JGR, 2006

‚Intermediate Nepheloid Layer (INL)‘

persistentfeature

particles> 150 µm

Cape Blanc transect (~21°N)

ROMS-simulated offshore advection of particles in 400 m

Particle cameraprofiles

sediment trap sites

Summary and outlook organic carbon is best coupled to carbonate ballast

(except Cape Verde site)

s.v. estimated from chlorophyll and flux patterns were between65 and 250 m d-1 (larvacean pellets 730 m d-1)

flux patterns and chlorophyll distributions indicate a large advective component

particles advected from the shelf and producing an INL have s.v. of only 5-10 m d-1, but are relatively large (> 150 µm)

CURRENT and FUTURE RESEARCH- define various classes of particles and their s.v. (camera, ROV sinking chamber)- in situ s.v. (ROV sinking chamber)- lab measurements of s.v. of produced aggregates (flow system)- model particle fluxes (transport–ecosystem model approach)

ROMS: Model Configuration- 3-D hydostatic ocean model

- Parent only (8 km grid)

- Initialisation with January WOA 2001 climatology (cold start)

- 3 years spin-up with monthly COADS forcing

- QuikSCAT satellite daily winds

Nested Grid Configuration

- Etopo2 bathymetry

- Child grid 2.7 km

- 32 vertical levels

Gruber et al., 2005

Coupled Ecosystem Model in ROMS

Particle distribution:observations and modelling (ROMS - ecosystem)

> 150µm

Karakas et al., JGR, in press

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 20030

L ithogenic flux - upper trap

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 20030

Lithogenic flux - lower trap

1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 20030

C B - aerosol

CB site: SeaWiFs chlorophyll

1997 1998 1999 2000 2001 2002 2003 2004 2005

CB site: SST

1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Sites CI and CB: dust (TOMS)

1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 20030

sinking velocities: regional variability

C B_14 (m eso)

20032004

C Bi_1 (eu)

20032004

50 m d-1 25 m d-

Al concentrationsand fluxes at Cape Verde

Particle transport and organic carbon fluxes off NW Africa: impact of dust and carbonate

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