An 11-year record of tropospheric aerosol methanesulfonate (MSA) in the Canadian high Arctic at Alert, Northwest Territories, from 1980 to 1991 shows marked seasonal and long-term variations. By using spectral-analysis techniques, the seasonal cycles and long-term variations have been quantified. There are two distinctly different seasonal peaks with levels of 12--23 ng m-3 in early May and 6--18 ng m-3 in July-August. Over the 11.3 years, the amplitudes of the MSA seasonal cycles and therefore the annual means of MSA concentrations decreased significantly by 33% (3% annually). So far there is no evidence of experimental artifact in this trend, but such a possibility will be further examined. Analysis of MSA monthly anomalies suggests that in spring they are weakly but significantly related to sea surface temperature anomalies (SSTA) in the North Atlantic west of the coast of continental Europe. In summer, MSA monthly anomalies are significantly correlated with SSTA in oceanic regions further north in the North Atlantic off the coast of Norway and in the northeast North Pacific. ¿ American Geophysical Union 1993