The above scheme suggests that estimates of P budgets are needed that distinguish between reactive and non-reactive forms of P in the dissolved phase and then between exchangeable and acid-extractable P in the particulate phase. The notion that secondary carbonates sequester P during precipitation has not been supported by field data in Svalbard (Hodson et al., 2004) and so chemical weathering probably represents all P except the acid-extractable particulate P phase (after atmospheric inputs have been accounted for). With this provenance model, the data in Table 17.1 suggest that the liberation of P by dissolution is restricted in glacial settings. This probably reflects the fact that rock-water contact within the glacial system is limited by short residence times, especially where delayed flow pathways through the subglacial environment are absent. Thus the most significant impact of glacial erosion upon the P cycle probably involves the generation and redistribution of freshly comminuted apatite mineral surfaces which do not undergo significant dissolution until deglaciation has occurred. Significant lags might therefore characterize the changing impact of glaciation upon this global biogeochemical cycle.
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