Isotopic tracing (Sr, Nd, U and Hf) of continental and marine aerosols in an 18th century section of the Dye-3 ice core (Greenland)
Determining the sources and pathways of atmospheric mineral dust and marine aerosols remains a difficult problem. In order to address this problem, the radiogenic isotopic composition of the dust and soluble ice components of Greenland ice has been determined and used as a source tracer for mineral dust and marine aerosols. Sr and Nd isotopic composition was measured, with a yearly to seasonal resolution, on both the bulk dust and soluble fractions of a section of the Dye-3 (1988) ice core from Greenland in the age range of 1786-1793 A.D. Hf isotopic composition was also measured for three of the dust samples as a complementary tracer of dust origin, the first direct measurement of Hf in paleo-atmospheric dust. Measured Nd and Sr isotopic composition of the dust corrected for carbonate contributions are compared to literature potential source area (PSA) data (<5 μm size fraction) and shows variability of the potential source area on short time scales. Half of the samples show similar Sr and Nd compositions as previous work from Greenland ice cores, indicating Asia as one potential source to the Greenland dust load with contributions from the Taklimakan, Gobi desert and the Ordos Plateau. However, the remaining samples, with less radiogenic Sr compositions, suggest another dust source mixing with the Asian dust. Hf isotopic compositions exclude volcanic aerosols as the other main mixing source and we propose the Sahara as being this additional dust source to Greenland based on the limited data set from this region. The radiogenic isotopes within the soluble fraction are found to be of marine origin with 87Sr/86Sr values and 234U/238U activity ratios close to seawater. εNd variations are significant (>6 ε units) and are decoupled from dust composition, indicating that the Nd composition of seawater is preserved in the ice. The εNd of the ice suggests variable mixing of aerosols from Arctic sea salts with another, more radiogenic, source during transport.