Cruise Report for Deepwater Sediment Sampling Cruise M/V IRISH: Leg 1, 29 May to 10 June 2014, to Assess Potential Benthic Impacts from the Deepwater Horizon (DWH) Oil Spill

To meet the objectives of the Deep Benthic Work Plan Addendum, a cruise was conducted to assess potential effects of the Deepwater Horizon (DWH) oil spill on deep-sea (>200 m) sediments and resident benthic fauna. Leg 1 of the cruise was conducted on the M/V IRISH, 29 May – 10 June 2014, under the auspices of the DWH/Natural Resource Damage Assessment (NRDA) Deepwater Benthic Communities Technical Working Group. A related deep-sea benthic sampling effort, M/V IRISH: Leg 2, was conducted June 14 – 28, 2014 and will be reported elsewhere. Only Leg 1 information is included in this document. A total of 2452 physical samples were collected from 56 deep-sea stations for the analysis of various biotic and abiotic environmental variables. Stations were included at near-field sites where DWH-related oil was measured at elevated levels during prior Response efforts, that were in paths of possible oil exposure based on subsurface trajectory-model predictions, and that serve as anticipated reference sites. At each station, a multi-corer (12 core system) was used to collect sediment samples for analysis of macrofauna, meiofauna, hydrocarbons, metals, and other basic sediment properties (total carbon, total organic carbon, total inorganic carbon, total nitrogen, grain size). Additional samples for sediment toxicity testing were collected at 12 of the 56 stations. A CTD with a dissolved-oxygen (DO) sensor also was deployed to obtain water-column profiles of salinity, temperature, DO, pH, and depth. The present cruise report provides a summary of sampling activities. Conclusions about the potential spatial extent of oil exposure, persistence of oil exposure over time, or resulting biological impacts based on these samples cannot be drawn until ongoing sample analyses are completed.