Here for the first time, we analyze the concentration of dissolved (DOC) and particulate organic carbon (POC), as well as its optical properties (absorbance and fluorescence) in proglacial streams of Iceland, location of Europe's largest nonpolar ice cap. DOC and POC concentrations range from 0.11 mg L^−1 to 0.94 mg L^−1 and from 0.67 mg L^−1 to 173.33 mg L^−1, respectively. We estimate an annual release of 0.008 Tg C yr^−1 (DOC) and 1.72 Tg C yr^−1 (POC) from Icelandic glaciers. Compared to the global release of 1.97 Tg C yr^−1 POC, these first calculations underline the necessity to include the Icelandic glaciers in global organic carbon budgets. Based on optical properties, we found that although glacial derived organic matter (OM) was dominated by proteinaceous florescence, organic matter composition was variable among glaciers, often exhibiting relatively higher aromatic content and increased humification closer to the glacier terminus, modulated by the presence of glacial lakes. While POC concentration decreased downstream, DOC concentration as well as the autochthonous fraction of OM increased suggesting the reworking of the OC by microbial communities, which has implications for downstream ecosystems as glaciers continue to melt.