800 year ice-core record of nitrogen deposition in Svalbard linked to ocean productivity and biogenic emissions
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. We investigate the emission sources and the influence of melt on the records. During the 20th century both records are influenced by anthropogenic pollution from Eurasia. In pre-industrial times NO3- is highly correlated with methane-sulfonate (MSA) on decadal time-scales, which we explain by a fertilising effect. 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 for 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+. Changes in melt at the Lomonosovfonna glacier are excluded as major driving force for the decadal variations of the investigated compounds.