Impact of Local Iron Enrichment on the Small Benthic Biota in the deep Arctic Ocean The study assesses the impact of local iron enrichment on the small benthic biota (bacteria, meiofauna) together with environmental parameters indicating the input of food at the deep seafloor. To evaluate the hypothesis that abundance, distribution, and diversity of the small benthic biota varies in relation to a local input of structural steel at the seabed, we analyzed sediment samples and the associated infauna along a short transect with increasing distance to an iron source, i.e., corroding steel weights of a free-falling observational platform (bottom-lander), lying on the seafloor for approximately seven years. Iron-enriched surface sediments in the vicinity of the bottom-weight left in summer 2008 after a short-term deployment of a bottom-lander in 2433 m water depth at the LTER (Long-Term Ecological Research) observation HAUSGARTEN in eastern parts of the Fram Strait were sampled on 28th July 2015 using push-corer (PC) handled by the Remotely Operated Vehicle (ROV) QUEST 4000 (MARUM Center for Marine Environmental Sciences, Germany) during Dive 369 from board RV Polarstern. The block-shaped steel bottom-weights (30 x 30 x 6 cm) were sitting about half of the height sunken into the seafloor and thus, almost not affecting near-bottom currents. During sampling in 2015, the plates were largely corroded. Surface sediments around the plates had an orange-red color with a gradient of decreasing color intensity with increasing distance from the source, i.e., the bottom weight. A total of eight push-corer samples (PC1-8) were taken at approx. regular distances (on average every 18 cm) along a short transect (about 1.5 m) crossing the iron gradient. Push-corers PC1-4 retrieved sediment from heavily impacted sediments, while samples taken from push-corers PC5-8 were visually indistinguishable from background sediments in the wider area. After recovery of the ROV, sediment cores (8 cm in diameter, and 20-25 cm in height) were sub-sampled using plastic syringes with cut-off anterior ends for meiofauna and nematode communities as well as for environmental parameters. The position specified in the data sets (longitude / latitude) refers to the position of the ROV.
