Hundreds of sediment and pore water samples were analysed in the context of this study. The sediment samples contain a record of nutrient and carbon cycling through time, while the pore waters inform us about the current cycling of nutrients and carbon within the seafloor (driven by microbial communities living in the sediment) and the potential recycling of bioavailable nutrients back to the water column.
Analyses included bulk chemical analyses of the sediments as well as specific extraction methods to quantify different chemical species of the nutrients nitrogen, phosphorus and iron in the sediment (their different speciation being related to their input process into the ocean in the first place, but also changes that occurred after they were buried into the seafloor). Pore waters were analysed for dissolved nutrients, metals, and other elements that are involved in sedimentary carbon cycling.
From these data, the depositional environment of sediments back to and during the last interglacial was reconstructed (in terms of organic matter export to the seafloor, sea ice cover, and in particular the availability of different nutrient species), and modern-day fluxes of nutrients back to the water column were calculated.
The main findings from this project so far are the following:
Since the last interglacial, several periods were identified when substantial amounts of bioavailable iron (an important micronutrient) was delivered to the study site north of Svalbard, which is the first time that significant and sustained amounts of iron oxides were reported that far north of an Arctic landmass. This has important implications for the potential to deliver nutrients from land to the open Arctic Ocean during what we assume were meltwater events on Svalbard associated with globally recognised sub-millennial warming events. The exciting results are currently being written up for publication in a peer-reviewed international journal.
Regarding nutrient cycling at the modern seafloor, we recognise that the sediments at all sites are important sources of silicic acid and ammonium to the bottom waters, with shallower sites close to Svalbard being more active than both deep and shallow water sites on the more distal Yermak Plateau. Phosphate and iron, in contrast, are fairly efficiently retained in the sediment due to iron oxides precipitating at the oxic seafloor, and phosphate adsorption onto these newly forming iron oxides. These data are currently being written up for publication in a peer-reviewed international journal.
