Yapan, Batuhan Cagri; Janssen, Felix; Boetius, Antje; Molari, Massimiliano (2026): Pigments in sediments from cores collected during R/V SONNE cruise SO268/1 and SO268/2 in the Eastern North Pacific Ocean [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.992889 (DOI registration in progress)

The data set reports phytopigment concentrations in the upper horizons of deep-sea sediments. Chlorophyll a (Chl a) represents the most fresh and labile part of the phytodetritus while concentrations of phaeopigments (the Chl a degradation product) targets the older, less labile fraction. The sum of both is referred to as Chloroplastic Pigment Equivalents (CPE). Samples were taken with a Multiple Corer (MUC) and with Push Cores (PUC) that were recovered by Remotely Operated Vehicle (ROV; KIEL6000, GEOMAR, Kiel, Germany) during two subsequent expeditions with the German Research Vessel SONNE (SO268/1 and SO268/2). Samples originate from six different locations in polymetallic nodule ecosystems in the deep Eastern North Pacific Ocean. Four are situated in the exploration license area of the German Bundesanstalt für Geowissenschaften und Rohstoffe (Federal Institute for Geosciences and Natural Resources; abbreviated BGR) granted by the International Seabed Authority (ISA). These include the Reference Site (GER Reference Site), a site that is designated for a nodule collector prototype trial (GER Trial Site), a site near the Reference Site where a benthic impact experiment (BIE) was carried out (GER Dredge Site) and a site where no polymetallic nodules are found (GER No-Nodule Site). The other two sites were located in the exploration license area of the Belgian company Global Sea Mineral Resources NV (abbreviated GSR): again a Reference Site (BEL Reference Site) and a trial site (BEL Trial Site). The primary aim of the study was to address natural spatial variability in benthic food availability and characterize baseline conditions in preparation of trials of GSR's pre-prototype polymetallic nodule collector Patania II and for the smaller BIE carried out with a dredge during SO268/2 on 11. Apr. 2019. Further the dredge area was sampled after the BIE to assess the impacts.

Determination of Chlorophyll a and Phaeopigment concentrations is based on the principle described by Boetius and Damm (1998). Samples are collected on board from homogenized wet sediment slices of cores and frozen at -20°C until analysis in the shore lab. In case of PUCs, layers from 2 cores are pooled before homogenizing. 1 mL of thawed sediments is transferred to tubes with approx. 1 mm diameter glass beads added to facilitate extraction. 8 ml cold acetone are added and samples are vigorously shaken in a cell mill (Vibrogenzellmühle VI 6, Edmund Bühler GmbH, Germany) for 3 min. Samples are centrifuged at 188 g for 10 min at 0 °C. 2 ml of the supernatant are transferred into a separate tube while the remaining supernatant is discarded. Extractions are repeated twice by again adding 8 ml of cold acetone to sediment samples and repeating shaking in the cell mill, subsequent centrifugation, transferring of 2 ml supernatant, and discarding remaining supernatant. The combined 3 x 2 ml supernatant of the three extractions are centrifuged again, and 2 ml are transferred to round-bottom cuvettes. Fluorescence (RFUb) is measured with a fluorometer at 428 nm excitation and 671 nm emission (Trilogy Laboratory Fluorometer with Chlorophyll a Acidification fluorescence module, Turner Design, CA, USA). A drop (approx. 30µL) of 20% hydrochloric acid is added to the extracts and fluorescence is measured again (RFUa). A calibration series with at least n=4 concentrations [Chla (Std 1...n)] ranging from 0 to 0.1 µg/ml is prepared from a stock solution (1 mg Chlorophyll a dissolved in 100 ml acetone, concentration validated photometrically) and measured the same way as the samples, i.e., before (RFUb(Std 1...n)) and after acidification (RFUa(Std 1...n)). The slope m of RFUb(Std 1...n) vs. [Chla (Std 1...n)] is turned into the calibration factor (CF=1/m). Further, the Acid Ratio (AR) is calculated as the average ratio of RFUb(Std n)/RFUa(Std n) and turned into the Acid Factor (AF=AR/(AR-1)). Finally, the dilution factor f is determined as the sum of the volume of Acetone added (VAc) and porewater (Vpw) included in the wet sediment volume V(sed) calculated as Vpw=V(sed) x porosity. Concentrations (µg / ml) of Chlorophyll a [chla] and phaeopigment [phaeo] in the sediment samples are determined as [Chla]=(RFUb - RFUa) x CF x AF x f / V(sed) and [phaeao]=(RFUa x AR - RFUb) x CF x AF x f / V(sed), respectively.