Vertical mixing above Summit, Greenland: Insights into seasonal and high frequency variability from the radionuclide tracers 7Be and 210Pb

Authors

Jack E. Dibb, University of New HampshireFollow

Abstract

The activity of the natural radionuclide tracers ⁷Be and ²¹⁰Pb has been determined in bulk aerosol samples collected over 2-day intervals for nearly five full years at Summit, Greenland. Year-round sampling was conducted in three campaigns; summer 1997 to summer 1998, summer 2000 to summer 2002, and summer 2003 to present. As in previous summer campaigns at Summit, and a year-round investigation at Dye 3, variations in the activities of the tracers on short time scales were strongly correlated despite the upper troposphere/lower stratosphere source of ⁷Be and the continental surface source of ²²²Rn (precursor of ²¹⁰Pb). This behavior is attributed to boundary layer dynamics exerting the dominant control on activities in air just above the ice sheet. Aerosols and associated species are depleted from the boundary layer above the snow when a strong inversion limits exchange with the free troposphere. Episodic weakening of the inversion allows ventilation of the boundary layer. This cycle drives simultaneous decreases and increases in the radionuclide tracers. The correlation between ⁷Be and²¹⁰Pb on seasonal and annual bases was found to be stronger than at Dye 3, and the average activity of ⁷Be was lower at Summit despite the higher elevation (3.0 versus 2.5 km). These observations indicate that the boundary layer at Summit is more effectively isolated than at Dye 3. The activity of ⁷Be at Summit peaked in June or July all 5 years, closely following the seasonality of stratospheric injection of ⁷Be into the Arctic troposphere (based on seasonality of the ¹⁰Be/⁷Be ratio previously measured at Alert, NWT). This suggests that when the boundary layer at Summit is replenished by ventilation, it receives air reflecting the composition of the mid and upper troposphere.

Department

Earth Sciences

Publication Date

8-2007

Journal Title

Atmospheric Environment

Publisher

Elsevier

Digital Object Identifier (DOI)

10.1016/j.atmosenv.2006.12.005

Document Type

Article

Recommended Citation

Jack E. Dibb, Vertical mixing above Summit, Greenland: Insights into seasonal and high frequency variability from the radionuclide tracers 7Be and 210Pb, Atmospheric Environment, Volume 41, Issue 24, August 2007, Pages 5020-5030, ISSN 1352-2310, http://dx.doi.org/10.1016/j.atmosenv.2006.12.005.

Rights

Copyright © 2006 Elsevier Ltd. All rights reserved.