But because of the continual formation of Fe-P, it increased steadily until February 2005, when a value of 124 was found ( Figure 2b). These observations are consistent with the fact that at the beginning of the stagnation period

the redoxcline propagated only slowly from the bottom water to the upper water layers and was located at depths between 225 m and 200 m in February 2005. Hence, most of the sediment surface below 150 m was still covered with oxic water, which facilitated Fe-P formation. The gradual increase in the CT, min/PO4 ratios also indicates that the formation of Fe-P is a slow process Selleckchem BTK inhibitor that takes place mainly at the sediment surface and is thus controlled by mixing. The possible spontaneous precipitation of Fe-P in the water column after the inflow of high-oxygen water masses is of minor importance. This conclusion can be drawn from the low Fe concentrations under anoxic conditions in the Gotland Sea deep water (1–2 μmol dm−3) and the low molar P/Fe ratios (0.17) of

P-containing FeO(OH) particles ( Turnewitsch & Pohl 2010). Also, significant PO4 removal by adsorption on manganese oxides, formed in the water column during the shift to oxic conditions, is unlikely. Indeed, the Mn concentrations are about one order of magnitude higher than those of Fe, however, this is approximately compensated for by the lower molar P/Mn ratios (0.03) of MnO2/PO4 associates ( Turnewitsch & Pohl 2010). After February learn more 2005 a strong increase in PO4 concentrations until the end of the stagnation period in July 2006 was observed,

which coincided with a substantial decrease in CT, min/PO4 ratios. During this phase the anoxic dissolution of previously deposited Fe-P prevailed over the oxic precipitation of Fe-P because the redoxcline moved further upwards and arrived at the 150 m depth level in February 2006. As a result, the system returned approximately to its state before the water renewal, with no net effect on the PO4 concentrations having occurred. For the period from May 2004 to July 2006 3-oxoacyl-(acyl-carrier-protein) reductase the temporal development of the salinity indicated almost ideally stagnant conditions below 150 m. The slight decrease in the salinity distribution during this period (Figure 3a) can be explained by vertical mixing. No indication was found either in the salinity or the temperature distribution for a lateral water inflow. The basin was therefore considered to be like a closed biogeochemical reaction vessel that was affected only by the input of organic matter produced in the euphotic zone, by mineralization of organic matter in the water column and in the sediments, and by vertical mixing. Accordingly, the continual mineralization of POC caused O2 depletion and after about two years resulted in fully anoxic conditions at depths below 150 m (Figure 3b).