Luther, G.W., et al, Mar Chem 40
Holmkvist, L, et al, Geochim Cosmochim Acta 75
Hansel, C.M., et al, ISME J 9
Nielsen, L.P., et al., Nature 463
 Prabu, V., et al., Rev. Sci. Inst
J. Synchrotron Radiat 12
 We thank I. Adaktylou, F. Zeitvogel and G. Schmid for discussion and help during preliminary experiments. We thank J. Wang, Y. Lu, J. Geilhufe and J. Dynes (CLS) for their valuable help. Research was performed at CLS, which is supported by the Canada Foundation for Innovation. We also acknowledge DFG funding through the Heisenberg program (DFG grant OB 362/4-1).