Pan-Arctic Molecular Fingerprints: Multi-Year FT-ICR MS Data from the Major Arctic Rivers Reveal Unique Seasonal- and River-Specific Molecular Formulae

Climate change has caused rapid warming in the Arctic, which in turn is leading to permafrost degradation, shifts in vegetation and hydrology, and changes in the quantity and composition of dissolved organic matter (DOM) in riverine ecosystems. Since the Arctic Ocean receives a disproportionately large amount of the world's riverine runoff, Arctic riverine DOM composition is important to Arctic Ocean ecosystem functioning. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) provides an ultrahigh resolution tool for fingerprinting DOM and elucidating its chemical nature. In this study we present an extensive time series of Arctic riverine FT-ICR MS data (2012-2018) from the Arctic Great Rivers Observatory. We demonstrate the molecular formulae that are common to DOM in the six largest Arctic rivers (the Yenisey, Lena, Ob', Mackenzie, Yukon, and Kolyma), along with the unique fingerprints of each river. We show how both common and unique Arctic river molecular formulae compare to previously identified DOM compositional regions such as the "Island of Stability," and relate FT-ICR MS data to watershed characteristics such as land cover. We further highlight seasonal trends in DOM chemistry, link optical properties of DOM to FT-ICR MS data, and demonstrate the unique seasonal fingerprints of DOM across the major Arctic rivers. This work highlights that while there is an assemblage of molecular formulae common to all large Arctic rivers and all seasons, each river and each season is prone to discharging molecular formulae with unique formulae, implying that the presence of such molecular formulae in the Arctic Ocean could be suggestive of riverine and temporal DOM source.