Using non-combustible residual particles as a proxy for mineral dust deposition to estimate its contribution to light absorption in the 300-year Holtedahlfonna ice core

• The fractional light absorption by mineral dust exceeds 0.7 in the mid-20th century. • Reanalyzed regional wind suggests an important local source of mineral dust. • Excess red light absorption form basis for hypothesis on possible presence of algae. Whereas residual light-absorbing particles remaining after combustion are taken as proxy for mineral dust, light-absorbing particles removed by combustion in the thermal-optical analysis are attributed to carbonaceous material. The latter is assumed to mainly be composed of black carbon. The temporal evolution of residual particles observed in a Svalbard ice core (Holtedahlfonna), covering the period 1700 to 1998, shows strong relations with the reanalyzed local temperature and wind data. This indicates possible local sources for the mineral dust proxy. The relative contribution to light attenuation caused by residual particles prior to 1875 is in the range 0.2 to 0.5. After 1875 the contribution is generally above 0.4 with a maximum of about 0.7 in the middle of the 20th century. The increasing fraction in the beginning of the 20th century is attributed to enhanced emission of local mineral dust due to increased local summertime wind speeds. The decrease in the relative contribution follows a lowering in the wind speed and a concurrent increase in the deposition of BC from about the 1970′s. Enhanced light attenuation in the red wavelength not explained by the MD and BC proxies remains a conundrum but show clear covariations with positive monthly mean summer temperatures above zero and non-sea salt K + ions.