Abundance of abyssal ferromanganese nodules and ferromanganese coated rocks from the Samoa Basin (2026-604-FA)

38 box core samples were collected between April 13 and April 28, 2026, during USGS field activity 2026-604-FA. USGS directed the location of box core deployment. Seafloor mapping (ship- and AUV-based) and AUV imagery collected by NOAA in February-April 2026 were used to inform box core sample locations. External personnel working for organizations contracted through NOAA were responsible for deployment and recovery of an Ocean Instruments BX-750 Box Corer at each sample location; an AML Oceanographic CTD (conductivity temperature depth) and Kongsberg MiniS 37 -40V Ti transponder were mounted to the frame of the box core to determine the depth and location of each seafloor sample. Personnel contracted through NOAA collected USBL location data. USGS was responsible for all sample processing after the box core was recovered.

Top water was removed from the box core using a peristaltic pump and tubing, then a photograph of the box core surface was captured. All box core sample photos are available online through NOAA at https://oceanexplorer.noaa.gov/mineral-samples/2026-nv5-american-samoa/.

Surface ferromanganese nodules and ferromanganese coated rocks were immediately removed from the box core after top water removal and box core surface photography, then transferred to a laboratory van. Ferromanganese nodules and ferromanganese coated rocks along the edges of the box core that appeared to have been pushed down by the spade were included in the surface mass. Excess sediment was removed by rinsing the nodules with filtered seawater. The wet mass of surface ferromanganese nodules and ferromanganese coated rocks was determined using a RoMech digital crane scale that was calibrated with NIST certified weights and had a lower detection limit of 0.5 kilograms.

Buried ferromanganese nodules were recovered from four box cores (BX03, BX32, BX33, BX36) during subcoring (collection of push cores), push core processing, or by hand-searching the remaining sediment after subcores were removed. The sediment depth in these four box core samples ranged from 34-40 centimeters. Excess sediment was removed from buried nodules by rinsing with freshwater or filtered seawater. The wet mass of buried nodules was determined using a RoMech digital crane scale that was calibrated with NIST certified weights and had a lower detection limit of 0.5 kilograms. The wet mass of buried nodules was added to the wet mass of surface nodules to calculate the whole box mass of ferromanganese nodules and coated rocks.

The surface abundance and whole box abundance were calculated by dividing the measured surface mass and whole box mass of each box core by the surface area of the box core sample (0.5625 square meters).

The location of the box core on the seafloor was determined from the USBL location on bottom where available (BX38), from the deepest USBL location (BX06 and BX28) or by calculating the midpoint latitude and longitude of the deepest measured USBL coordinates from the up and down cast of each box core. Only downcast USBL data was available for BX06 and only upcast USBL data was available for BX28. Samples BX 01-05, 17, and 25 did not have functioning USBL data, indicated by -9999 in the data table. The water depth of each box core sample was determined by extracting the deepest measured depth value from the box core CTD data and correcting this depth for the mounted height of the CTD (2 meters from the base of the box core).

Box core sample information (date and time on bottom, station name, sample location and depth) and surface and total abundance were combined into a comma-delimited text values document (2026-604-FA_NoduleAbundance.csv).