Effects of climate and landscape development on the terrestrial phosphoruscycle

Past variations in the terrestrial cycle of phosphorus (P), a biolimiting n utrient, are poorly understood. Detailed geochemical analysis of P in lake- sediment cores spanning the late Pleistocene to the present from the wester n Appalachian Plateau, the Coast Mountains of British Columbia, and the San Bernardino Mountains of southern California reveal large changes in terres trial P cycling. P is transformed from a mineralized form to more bioavaila ble forms with increased soil development and landscape stability in the ca tchments. This process occurs relatively rapidly (i.e., within 3000-5000 yr ) and can be reset quickly; the degree of transformation depends on local c limate and the starting point of the soil system. The release of solid-phas e P from these landscapes follows modeled patterns of high rates during the initial stages of soil development and low rates upon soil and landscape s tabilization. Changes in weathering style were confirmed for the southern C alifornia catchment by analysis of Ge/Si ratios of lake diatoms, which reve aled substantially higher values during an interval of high P release and l ow values at present, These records point to significant variability in the terrestrial P mass balance on glacial time scales, a feature that needs to be incorporated into models of nutrient and carbon cycling in the past.