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As a part of the long-term program at Kitt Peak National Observatory (KPNO),the Mn I 539.4 nm line has been observed for nearly three solar cycles usingthe McMath telescope and the 13.5 m spectrograph in double-pass mode. Thesefull-disk spectrophotometric observations revealed an unusually strong changeof this line's parameters over the solar cycle. Optical pumping by the Mg II kline was originally proposed to explain these variations. More recent studieshave proposed that this is not required and that the magnetic variability mightexplain it. Magnetic variability is also the mechanism that drives the changesin total solar irradiance variations (TSI). With this work we investigate thisproposition quantitatively by using using the model SATIRE-S. We appliedexactly the same model atmospheres and value of the free parameter as were usedin previous solar irradiance reconstructions to now model the variation in theMn I 539.4 nm line profile and in neighboring Fe I lines. We compared theresults of the theoretical model with KPNO observations. Our result confirmsthat optical pumping of the Mn I 539.4 nm line by Mg II k is not the main causeof its solar cycle change. It also provides independent confirmation of solarirradiance models which are based on the assumption that irradiance variationsare caused by the evolution of the solar surface magnetic flux. The resultobtained here also supports the spectral irradiance variations computed bythese models.

Variation of the Mn I 539.4 nm line with the solar cycle