Calibration-in-time: Transforming biogeochemical lake sediment proxies into quantitative climate variables

PAGES news • Vol 17 • No 3 • October 2009 Sc ie nc e H ig hl ig ht s: P al eo lim no lo gy mg/L (Jeziorski et al., 2008a), suggesting that the threshold measured under natural conditions may actually be higher than the 1.5 mg/L threshold identified in laboratory studies. The number of lakes at or nearing this threshold is considerable and increasing; an examination of changes in Ca concentrations for a set of 770 lakes covering a broad geographical area in Ontario (Canada) found that 35% of lakes currently have <1.5 mg/L of Ca, while 62% are already below 2.0 mg/L, reflecting substantial increases in percentages since the 1980s (Jeziorski et al., 2008a).