Depth profiles in the euphotic zone of nitrate, silicate, and phosphate concentrations and profiles of silicic acid uptake rates from EXPORTS cruise DY131 in the North Atlantic during May 2021

Abstract

This dataset includes depth profiles in the euphotic zone of nutrient (nitrate, silicate, phosphate) concentrations and profiles of silicic acid uptake rates from seawater samples collected on EXPORTS cruise DY131 during May 2021.

This research focuses on the vertical export of the carbon associated with a major group of phytoplankton, the diatoms in the North Atlantic near the Porcupine Abyssal Plain. The major objective is to understand how diatom community composition and the prevailing nutrient conditions create taxonomic differences in metabolic state that combine to direct diatom taxa to different carbon export pathways. The focus is on diatoms, given their large contribution to global marine primary productivity and carbon export which translates into a significant contribution to the biogeochemical cycling of carbon (C), nitrogen (N), phosphorus (P), iron (Fe) and silicon (Si). It is hypothesized that the type and degree of diatom physiological stress are vital aspects of ecosystem state that drive export. To test this hypothesis, combined investigator expertise in phytoplankton physiology, genomics, and trace element chemistry is used to assess the rates of nutrient use and the genetic composition and response of diatom communities, with measurements of silicon and iron stress to evaluate stress as a predictor of the path of diatom carbon export.

The EXPORTS field campaign in the North Atlantic sampled a retentive eddy over nearly a month. At the beginning of the cruise, nitrate was abundant while silicic acid was nearly undetectable. Such low dissolved Si concentrations significantly limit diatom silicification resulting in diatoms with reduced mineral ballast and low Si:C and Si:N ratios that would reduce sinking rates and competition for Si can alter diatom taxonomic composition. Both factors can the path cells follow through the food web ultimately altering diatom carbon export.

Within each ecosystem state examined in the EXPORTS program, nutrient biogeochemistry, diatom and phytoplankton community structure, and global diatom gene expression patterns (metatranscriptomics) are characterized in the ocean. Nutrient amendment experiments with tracer addition (14C, 32Si) are used to quantify the level of Si, N, and Fe stress being experienced by the phytoplankton and to contextualize taxa-specific metatranscriptome responses for resolving gene expression profiles in the in situ communities.

For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/893293