800-year ice-core record of nitrogen deposition in Svalbard linked to ocean productivity and biogenic emissions

Abstract. We present the records of the two nitrogen species nitrate (NO₃^-) and ammonium (NH₄⁺) analysed in a new ice core from Lomonosovfonna, Svalbard, in the Eurasian Arctic covering the period 1222–2009. Changes in melt at the Lomonosovfonna glacier are assumed to have a negligible effect on the decadal variations of the investigated compounds. Accordingly, we use decadal records to investigate the major emission sources of NO₃^- and NH₄⁺ precursors and find that during the twentieth century both records are influenced by anthropogenic pollution from Eurasia. In pre-industrial times NO₃^- is highly correlated with methane sulfonate (MSA), which we explain by a fertilising effect. We propose that enhanced atmospheric NO₃^- concentrations and the corresponding nitrogen input to the ocean trigger the growth of dimethyl-sulfide-(DMS)-producing phytoplankton. Increased DMS production results in elevated fluxes to the atmosphere where it is oxidised to MSA. Eurasia was presumably the main source area also of pre-industrial NO₃^-, but a more exact source apportionment could not be performed based on our data. This is different for NH₄⁺, where biogenic ammonia (NH₃) emissions from Siberian boreal forests were identified as the dominant source of pre-industrial NH₄⁺.