Establishing Baseline Measurements of Sedimentary Chlorophyll-a and Pheophytin Pigments in NORI-D, Clarion Clipperton Zone

Abstract

Polymetallic nodule fields in the Clarion Clipperton Zone (CCZ) of the central Pacific have been identified as a viable source of metals to aid in the global transition to renewable energy usage. In order to gauge the potential impact harvesting these nodules would have on the benthic ecosystem of the CCZ, it is essential to provide baseline values of phyto-pigment concentrations. These values demonstrate the availability of organic matter as a food source for benthic organisms and potential energy transfer up trophic levels. This study focuses on the southeasternmost exploration area of the CCZ contracted to Nauru Ocean Resources Inc., NORI-D. Multicores were collected aboard the Maersk Launcher in October-November 2020 and again in May-June 2021 from three primary areas in the exploration zone; areas for test mining, affected areas, and preservation sites. Sediment cores from 0-5 centimeters in depth were collected and separated into 1 centimeter increment subsamples. Acetone extracts were taken from each subsample for spectrofluorometric analysis. These measurements reveal the presence of sedimentary particulate organic matter indicated by labile chlorophyll-a and refractory phaeophytin pigment concentrations. These values provide quantitative comparisons between each sampling site within the NORI-D area. Results thus far have included an average chlorophyll-a concentration of 26.6 (SE ± 2.8) µg/g in test mining sites, in comparison to the preservation site average of 36.9 (SE ± 7.3) µg/g. These findings are in support of, and will be incorporated into, a larger research effort to establish pre-test mining values for environmental factors in the CCZ. They will ultimately contribute to a greater understanding of deep sea productivity and factors that change this.