Iron Uptake Experiments
Iron uptake rates were measured at most stations where incubations were started
and a few other select locations. Radioactive 55Fe was added in various concentrations
chelated to EDTA. Final Iron concentrations are listed below. Final EDTA concentrations
were 10uM in all experiments. These rates should be regarded as potential or proxy
uptake rates rather than values reflecting in situ rates. Iron in the natural environment is
bound to strong binding organic ligands, such that almost no iron is in an inorganic form.
However EDTA is a weaker binding ligand and it is the inorganic Fe in equilibrium with
FeEDTA that is available for uptake. The data is still very raw and needs to be corrected
for quenching as well as normalized to an appropriate measure of phytoplankton and/or
bacterial biomass or numbers such as cell counts, POC, or chlorophyll. When normalized
to chlorophyll no trends were immediately observed.
We were attempting to find half saturation constants for iron uptake in the Blue
and Green water and while the data is not final it seems that data as a function of added
Iron is linear rather than reaching saturation (see graph below).
Attempts were also made to measure uptake rates of iron bound to
Desferrioxamine, a strong iron binding ligand. However, no conclusive evidence for
active uptake was observed.
Fe-55 Uptake Experiments
Experiment
1
2
2
2
2
3
4
5
6
6
6
6
7
Station
16
27
27
27
27
48
57
55
64
64
64
64
75
Depth (m)
10
25
25
25
25
20
20
20
20
20
20
10
Ligand
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
EDTA
Fe (nM)
2
0.2
2
5
20
2
2
2
0.2
2
5
20
2
Uptake Rate (CPM/mL/hr)
0.2um
2.0um
1.20
0.47
0.59
0.38
2.03
1.64
3.01
3.57
15.11
17.17
1.85
1.53
1.60
1.41
3.27
0.55
1.13
0.97
4.87
4.12
11.71
13.21
44.02
47.16
6.43
6.02
Uptake (CPM/mL/hr)
Fe Uptake Rates St 64 20m
50
45
40
35
30
25
20
15
10
5
0
0
5
10
15
FeEDTA (nM)
20
25