Modelling the Speciation and Biogeochemistry of Iron in Oceanic

3,46

MB

Surface Waters at the Bermuda Atlantic Time-series Study site

161

stron

5504

ID

University of Southampton

2007

rok

Contents

Abstract 2

List of tables 9

List of figures 13

Author’s declaration 14

Acknowledgements 15

List of abbreviations 17

1 Introduction and objectives 20

1.1 Background 20

1.2 Iron speciation 23

1.2.1 Redox states and the photochemistry of iron 25

1.2.2 Organically complexed iron . 28

1.2.3 Colloidal iron . 30

1.3 Iron in models . 32

1.4 Rationale for the performed research 33

1.4.1 Annotation 36

2 Model description 37

2.1 Study area . 37

2.1.1 Dust- and iron deposition at the BATS-site . 39

2.1.2 Dissolved iron at the BATS-site . 40

2.2 The zero-dimensional model . 41

2.2.1 Ecosystem model . 42

2.2.2 Chemical model 44

2.2.3 Forcing . 47

2.2.4 Model equations . 48

2.3 The one-dimensional model . 52

3 The zero-dimensional model approach: Results, disscussion and sensitivity studies 58

3.1 Results and discussion 58

3.1.1 Ecosystem model . 58

3.1.2 Particulate material 61

3.1.3 Reactive oxygen species . 62

3.1.4 Diurnal variability of iron speciation 64

3.1.5 Annual cycle and interannual variability of dissolved iron 68

3.2 Sensitivity studies . 72

3.2.1 Solubility of atmospheric iron 73

3.2.2 Fe:N and Fe:C ratio of the phytoplankton uptake . 75

3.2.3 The form of bioavailable and atmospheric iron . 78

3.2.4 Aggregation of colloids 80

3.2.5 Influence of Cu on the concentration of reactive oxygen species and Fe(II) . 82

3.2.6 The role of excess ligands 85

3.3 Summary and conclusions of Chapter 3 . 86

4 The one-dimensional model approach: results, disscussion and sensitivity studies 93

4.1 Results of the physical model (GOTM) . 93

4.2 Results of the ecosystem model . 96

4.3 Iron fluxes below the mixed layer 98

4.3.1 Initial state 98

4.3.2 Reconciling slow iron loss processes at depth with short timescales in the mixed layer . 101

4.3.3 Is the parameter modification justified in terms of observations? 104

4.4 Temporal dynamics in the mixed layer . 105

4.4.1 Diurnal variability of iron speciation 105

4.4.2 Annual cycle and interannual variability of dissolved iron111

4.4.3 Residence time of iron 113

4.5 Parameter sensitivity . 114

4.5.1 Comparison of parameter sensitivity between the 0d and the 1d model . 116

4.5.2 Atmospheric iron . 118

4.5.3 Iron uptake 119

4.5.4 Colloids and ligands . 120

4.5.5 Photochemical processes . 121

4.6 Introducing redissolution of particulate and colloidal iron . 123

4.7 Summary and conclusions of Chapter 4 . 126

5 Outlook 128

5.1 Contribution to laboratory and field experiments . 128

5.2 Contribution to 3d global modelling . 131

6 Summary 135

List of references 142