Description: Domoic acid, a neurotoxin to vertebrates predominantly produced by the diatom Pseudo-nitzschia has been suggested to serve as an organic ligand. By binding iron and copper, it could increase their solubility and bioavailability. Domoic acid has to be released by the cells to serve this function and thus occur dissolved in sea water. Samples were pre-concentrated and desalted using solid-phase extraction, a procedure commonly applied for dissolved organic matter. Dissolved domoic acid was quantified in the East Atlantic, where it occurred ubiquitously, especially in the ocean surface. The maximum domoic acid concentration measured was 173 pmol L-1 and the average domoic acid carbon yield was 7.7 ppm. Both, carbon yield and dissolved domoic acid concentration, decreased with increasing water depth. Samples were taken during the cruise PS73 (ANT-XXV) on RV Polarstern. The extraction efficiency of domoic acid was 91%. The detection limit for solid-phase extractable domoic acid (DA-SPE) was 10 pmol L-1 and limit of quantification was 26 pmol L-1. Domoic acid concentrations below the limit of detection are marked as 〈LOD and concentrations below limit of quantification are marked as 〈LOQ in the data set.

Description: Although sulfur is an essential element for marine primary production and critical for climate processes, little is known about the oceanic pool of non-volatile dissolved organic sulfur (DOS). We present a basin-scale distribution of solid phase extractable DOS in the East Atlantic Ocean and the Atlantic sector of the Southern Ocean. While molar DOS versus dissolved organic nitrogen (DON) ratios of 0.11 ± 0.024 in Atlantic surface water resembled phytoplankton stoichiometry (S/N ~ 0.08), increasing dissolved organic carbon (DOC) versus DOS ratios and decreasing methionine-S yield demonstrated selective DOS removal and active involvement in marine biogeochemical cycles. Based on stoichiometric estimates, the minimum global inventory of marine DOS is 6.7 Pg S, exceeding all other marine organic sulfur reservoirs by an order of magnitude.

Description: Arctic regions have experienced pronounced biological and biophysical transformations as a result of global change processes over the last several decades. Current hypotheses propose an elevated impact of those environmental changes on the biodiversity, community composition and metabolic processes of species. The effects on ecosystem function and services, particularly when invasive or toxigenic harmful species become dominant, can be expressed over a wide range of temporal and spatial scales in plankton communities. Our study focused on the comparison of molecular biodiversity of three size-fractions (micro-, nano-, picoplankton) in the coastal pelagic zone of West Greenland and their association with environmental parameters. Molecular diversity was assessed via parallel amplicon sequencing the 28S rRNA hypervariable D1/D2 region. We showed that biodiversity distribution within the area of Uummannaq Fjord, Vaigat Strait and Disko Bay differed markedly within and among size-fractions. In general, we observed a higher diversity within the picoplankton size fraction compared to the nano- and microplankton. In multidimensional scaling analysis, community composition of all three size fractions correlated with cell size, silicate and phosphate, chlorophyll a (chl a) and dinophysistoxin (DTX). Individually, each size fraction community composition also correlated with other different environmental parameters, i.e. temperature and nitrate. We observed a more homogeneous community of the picoplankton across all stations compared to the larger size classes, despite different prevailing environmental conditions of the sampling areas. This suggests that habitat niche occupation for larger-celled species may lead to higher functional trait plasticity expressed as an enhanced range of phenotypes, whereas smaller organisms may compensate for lower potential plasticity with higher diversity. The presence of recently identified toxigenic harmful algal bloom (HAB) species (such as Alexandrium fundyense and A. ostenfeldii) in the area points out the potential risk for this vulnerable ecosystem in a changing world.