Black Sea Suspended Particulate Matter Characterization

Sampling was performed during the Phoxy cruise (June–July 2013) aboard of the R/V Pelagia. The sampling station (PHOX2) was located at 42°53.8′N and 30°40.7′E in the western gyre of the Black Sea. SPM (water volume 148–796 L) was collected on pre‐ashed 142‐mm‐diameter 0.7‐μm pore size glass fiber GF/F filters (Pall Corporation, Washington) mounted on McLane WTS‐LV in situ pumps (McLane Laboratories Inc., Falmouth). In each cast, three pumps were deployed simultaneously at different depths. During a total of five pumping sessions, SPM from 15 different water depths was obtained. Upon the recovery of the in situ pumps on the deck of the ship, the filters were immediately stored at −80°C. Both IPL‐based characterization and DNA‐based characterization were performed on the same filters, allowing a direct comparison of results.
Physical parameters of the water column were recorded by a conductivity–temperature–density (CTD) unit (SBE 911 plus, Sea‐Bird Electronics). Dissolved oxygen (O₂) concentrations were measured by a SBE 43 electrochemical sensor mounted on the CTD rosette. The sensor has a detection limit of 1–2 μM, which has been recently proven to overestimate the oxygen level at the lowest concentrations (Tiano et al., 2014). Samples for inorganic nitrogen nutrients (i.e., NO3−, NO2−, and NH4+) and for hydrogen sulfide (HS^‐) were obtained with a GoFlow rosette sampler (General Oceanics, Miami) from the same water depths sampled for SPM. The water collected in the CTD bottles was immediately processed on‐board, and the concentrations were determined within 18 hr on a QuAAtro autoanalyzer. Specifically, ca. 5 ml samples were filtered over Acrodisc PF (pre‐filter) Syringe Filter with 0.8/0.2 μm Supor membrane (Pall Corporation) into separate pre‐rinsed pony vials. One vial already containing 40 μl 1N NaOH was used for HS⁻ analysis and one without any addition of NaOH for DIC. Another glass vial was used for NO3−, NO2−, and NH4+ analysis. The detection limits for NO3−, NO2−, and NH4+ were 0.008, 0.006, and 0.044 μM, respectively. The detection limit for HS⁻ was 0.263 μmol/L.