Iron in ice cores from Law Dome, East Antarctica: implications for past deposition of aerosol iron

Abstract

Total-dissolvable iron has been measured in sections of three ice cores from Law Dome, East Antarctica, and the results used to calculate atmospheric iron deposition over this region during the late Holocene and to provide a preliminary estimate of aerosol iron deposition during the Last Glacial Maximum (LGM). Ice-core sections dating from 56-2730 sp (late Holocene) and similar to 18 000 BP (LGM) were decontaminated using trace-metal clean techniques, and total-dissolvable iron was determined in the acidified meltwaters by flow-injection analysis. Our results suggest that the atmospheric iron flux onto the Law Dome region has varied significantly over time-scales ranging from seasonal to glacial-interglacial. The iron concentrations in ice-core sections from the past century suggest (1) a 2-4-fold variation in the atmospheric iron flux over a single annual cycle, with the highest flux occurring during the spring and summer, and (2) a nearly 7-fold variation in the annual maximum atmospheric iron flux over a 14 year period. The average estimated atmospheric iron flux calculated from our late-Holocene samples is 0.056-0.14 mg m(-2) a(-1), which agrees well with Holocene flux estimates derived from aluminium measurements in inland Antarctic ice cores and a recent order-of-magnitude estimate of present-day atmospheric iran deposition over the Southern Ocean. The iron concentration of an ice-core section dating from the LGM was more than 50 times higher than in the late-Holocene ice samples. Using a snow-accumulation rate estimate of 130 kg m(-2) a(-1) for this period, we calculate 0.87 mg m(-2) a(-1) as a preliminary estimate of atmospheric iron deposition during the LGM, which is 6-16 times greater than our average late-Holocene iron flux. Our data are consistent with the suggestion that there was a significantly greater flux of atmospheric iron onto the Southern Ocean during the LGM than during the Holocene.