This shift in the accQPO4/accQCT relationship is explained by the complete

exhaustion of the previously deposited Fe-P supply and the confinement of PO4 release to organic matter mineralization. The Redfield-like composition of the organic matter contrasts with the C/P ratios of up to 400 that were observed during intense blooms of N2-fixing cyanobacteria (Larsson et al. 2001). Possibly this does not affect the accQPO4/accQCT ratio, because the excess carbon is mineralized before the corresponding particles have arrived in the deeper water layers. Crizotinib cost The opposite pattern for the relationship between accQPO4 and accQCT is observed in SL4 (Figure 4d). Because of the oxic conditions during the initial stagnation, PO4 generated by organic

matter mineralization is precipitated as Fe-P and the accQPO4 values are close to zero. Only at higher accQCT, when a shift to anoxic conditions develops in SL4, is a drastic increase of accQPO4 observed due to Fe-P dissolution. The situation is less clear in SL3 (Figure 4c), where no clear distinction between PO4 release by mineralization of organic matter MEK inhibitor drugs and Fe-P dissolution can be made. Based on accQPO4, we estimated the amount of Fe-P deposited at the sediment surface during the previous deep water renewal and redissolved during the subsequent stagnation period. Therefore, we used only the data from SL1 and SL2, because we

were unable to judge whether the Fe-P supply in SL3 and SL4 was entirely dissolved at the end of the stagnation period. Multiplication of accQPO4 in SL1 and CHIR-99021 in vitro SL2 at the end of the 26-month stagnation period (Table 4, last line) by the corresponding SL volumes (Table 1) gives the total accQPO4 inventory below 200 m. Relating this value to the underlying sediment area (Table 1) yields a total PO4 release of 100 mmol m−2, which includes contributions by Fe-P dissolution and organic phosphorus mineralization. To estimate the latter we first calculated the total CT release in SL1 and SL2 (Table 3) during the stagnation period following the same procedure as for the calculation of the total PO4 release. A value of 5.7 mol-C m−2 was obtained which, based on the Redfield C/P ratio of 106, corresponds to an organic P mineralization of 54 mmol m−2. Hence, the Fe-P dissolution and thus the Fe-P storage during the previous transition from anoxic to oxic conditions amounted to 46 mmol m−2. This is roughly 50% less than the value given by Gustafsson & Stigebrandt (2007) for the average release of PO4 by Fe-P dissolution at the sediment surface when the overlying waters are turning to anoxic conditions.