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