uk geotraces 40 ° s atlantic ocean water column biogeochemistry

UK GEOTRACES 40° S Atlantic Ocean

Water column Biogeochemistry

Eric Achterberg and Mark Moore

Modelled dust deposition (Mahowald, 2006)

dFe/Dal Micha Rijkenberg&Simon UssherMoore et al., submitted

-40 -20 0 20 40L a titu d e

0

40

80

120

160

200

N2

fixa

tion

(m

ol m

-2 d

-1)

0

40

80

120

160

200

Trich

odesm

ium

(fil

am

en

ts l-1

)

0

1

2

3

4

5

Su

rfa

ce N

2 fi

xatio

n(n

mo

l l-1

d-1

)

- 8

- 6

- 4

- 2

0

2

4

N*

(M

)1

10

100

1000

DIN

or

DIP

(n

M)

-400

-200

0

200

400

Su

rfa

ce P

*, D

OP

*, T

DP

* (n

M)

0

0 .4

0.8

1.2

DF

e (

nM

)

0

10

20

30

40

50

DA

l (n

M)

a)

b)

c)

d)

e)

f)

g )

Total

<20 m

h)

DF

e (n

M)D

Al (nM

)

Surface water dissolved Fe and Al along AMT17

ID-ICP-MSIsotope dilution-inductively coupled plasma-mass

spectrometry

6 elements - not suitable for mono-isotopic elements Can be used for Ag, Cd, Cu, Fe, Ni, Pb, Zn

• Off-line preconconcentration• Single sample - 8 minutes extraction• Use of isotopic ratio

• E.g. Fe56 (natural) and Fe57 (spike)

Preconcentration

• 12 ml sample• Spiked with isotope mixture• Standard addition for mono-

isotopic elements (Al, Co, Mn)• Chelating resin 1 ml elution

- 100 µl isotope mix- Standard addition- Buffer

1.5 M HNO3

Accuracy

• Accuracy verified by intercalibration samples from SAFe project and Geotraces project

East and West edges

Cadmium

Cadmium

Cd vs. P

11

Hypothesis for 40°S consortium

• Bioactive trace elements control productivity along 40ºS in the Atlantic Ocean.

• The bioactive trace elements are intimately involved in various physical-biogeochemical feedback loops that influence our climate

12

Objectives

• Determine deep water TEI supply from diapycnal mixing and upwelling (incl. turbulence measurements)

• Identify sources of TEI to the region through tracer measurements (Al, Ti, Mn)

• Establish natural microbial community structure• Determine nitrogen fixation rates• Establish trace elements and nutrient streams

through modelling

Conclusions

• ID-ICP-MS - powerful technique for high accuracy multi-element detection in low volumes of seawater

• HNLC status of region results in preferential removal of Fe in surface waters relative to other elements

• Strong correlation observed between Cd and phosphate (in agreement with literature)

• Mn confirms sedimentary source of Fe for Kerguelen region