Description: This study of Antarctic sympagic meiofauna in pack ice during late winter compares communities between the perennially ice-covered western Weddell Sea and the seasonally ice-covered southern Indian Ocean. Sympagic meiofauna (proto- and metazoans 〉20 μm) and eggs 〉20 μm were studied in terms of diversity, abundance and carbon biomass, and with respect to vertical distribution. Metazoan meiofauna had significantly higher abundance and biomass in the western Weddell Sea (medians: 31.1×103 m−2 and 6.53mg m−2, respectively) than in the southern Indian Ocean (medians: 1.0×10 103 m−2and 0.06 mg m−2, respectively). Metazoan diversity was also significantly higher in the western Weddell Sea. Furthermore, the two regions differed significantly in terms of meiofauna community composition, as revealed through multivariate analyses. The overall diversity of sympagic meiofauna was high, and integrated abundance and biomass of total meiofauna were also high in both regions (0.6–178.6×103 m−2 and 0.02–89.70mg m−2, respectively), mostly exceeding values reported earlier from the western Weddell Sea in winter. We attribute the differences in meiofauna communities between the two regions to the older first-year ice and multi-year ice that is present in the western Weddell Sea, but not in the southern Indian Ocean. Our study indicates the significance of perennially ice-covered regions for the establishment of diverse and abundant meiofauna communities. Furthermore, it highlights the potential importance of sympagic meiofauna for the organic matter pool and trophic interactions in sea ice.

Description: Highlights: • Optode respirometry is an effective new method for copepod respiration measurements. • Respiration rates and Q10 values were established for tropical Atlantic key species. • Respiration was influenced by body mass, temperature and species-specific behavior. • Depth of occurrence did not have a significant effect on standardized respiration. • The oxygen minimum zone did not yet fundamentally impact copepod ecophysiology Abstract Zooplankton respiration plays an important role in the carbon cycling of pelagic ecosystems. The rate of oxygen consumption in zooplankton is affected by the physical environment, vertical distribution range and species-specific behavior. Especially in tropical oceans, oxygen minimum zones (OMZs) may influence zooplankton metabolic processes and vertical distribution and thus structure zooplankton communities. Here we present respiration rates of tropical Atlantic copepods in relation to environmental factors, especially O2 concentration, and species-specific characteristics. Copepods were sampled during two research stays on the Cape Verde Island São Vicente in March/April and May/June 2010. Minimum O2 concentrations of 51 μmol kg− 1 (pO2 of 4.25 kPa) at 400 m depth were recorded within the OMZ. Respiration rates of epi- and mesopelagic calanoid copepods were measured by optode respirometry at three different ambient temperatures (13, 18, and 23 °C) to establish the effect of temperature on metabolic rates. Mass-specific oxygen consumption ranged from 27 μmol O2 gDM− 1 h− 1 in copepodids C5 of Lophothrix sp. at 13 °C to 774 μmol O2 gDM− 1 h− 1 in Pleuromamma xiphias copepodids C5 at 18 °C and was mainly controlled by body mass and temperature. Mass-specific respiration rates were highest in surface-dwelling organisms and decreased with increasing depth. To allow for a comparison of shallow and deep-living copepods, respiration rates were standardized to a common temperature of 18 °C and a mean body dry mass of 0.5 mg, applying a Q10 of 2.0 and a body mass exponent of − 0.56. Temperature- and body mass-corrected respiration rates did not decrease with increasing depth indicating that neither depth of occurrence, nor current hypoxic conditions within the OMZ had a fundamental, persistent effect on zooplankton respiration.

Description: Vertical variations in physical and chemical conditions drive changes in marine zooplankton community composition. In turn, zooplankton communities play a critical role in regulating the transfer of organic matter produced in the surface ocean to deeper layers. Yet, the links between zooplankton community composition and the strength of vertical fluxes of particles remain elusive, especially on a global scale. Here, we provide a comprehensive analysis of variations in zooplankton community composition and vertical particle flux in the upper kilometer of the global ocean. Zooplankton samples were collected across five depth layers and vertical particle fluxes were assessed using continuous profiles of the Underwater Vision Profiler (UVP5) at 57 stations covering seven ocean basins. Zooplankton samples were analysed using a Zooscan and individual organisms were classified into 19 groups for the quantitative analyses. Zooplankton abundance, biomass and vertical particle flux decreased from the surface to 1000 m depth at all latitudes. The zooplankton abundance decrease rate was stronger at sites characterised by oxygen minima (〈5µmol O2.kg−1) where most zooplankton groups showed a marked decline in abundance, except the jellyfishes, molluscs, annelids, large protists and a few copepod families. The attenuation rate of vertical particle fluxes was weaker at such oxygen-depleted sites. Canonical redundancy analyses showed that the epipelagic zooplankton community composition depended on the temperature, on the phytoplankton size distribution and the surface large particulate organic matter while oxygen was an additional important factor for structuring zooplankton in the mesopelagic. Our results further suggest that future changes in surface phytoplankton size and taxa composition and mesopelagic oxygen loss might lead to profound shift in zooplankton abundance and community structure in both the euphotic and mesopelagic ocean. These changes may affect the vertical export and hereby the strength of the biological carbon pump.

Description: The Peruvian upwelling zone is one of the most productive marine ecosystems in the world with a spectacular, pronounced oxygen minimum zone (OMZ). Globally OMZs are increasing in size and intensity with far-reaching consequences for the marine biological carbon pump and carbon export; thus, these zones need to be carefully monitored to be able to understand future climate change impacts. The current study was carried out in 2013 and 2017 to quantify the vertical flux of organic matter exported out of the productive surface layer by measuring 234Thsingle bond238U disequilibria in the water column. Samples were collected in January 2013 and May 2017 along an identical transect located at 12°S off the Peruvian coast near Lima, Peru. Th-234 fluxes ranged from 0 to 2088 ± 95 dpm m−2 d−1 in 2013 and 698 ± 63 to 3648 ± 113 dpm m−2 d−1 in 2017. The corresponding POC fluxes varied between 0 and 164.2 ± 7.9 mg C m−2 d−1 in 2013 and 22.7 ± 2.7 to 133.1 ± 15.2 mg C m−2 d−1 in 2017, with POC fluxes gradually decreasing with distance from the coast. Despite higher POC fluxes, the export efficiencies were found to be extremely low due to high particle remineralization rates observed within the euphotic zone.

Description: This data is part of the BMBF projects CUSCO (Coastal Upwelling Systems in a Changing Ocean) and BioTip subproject Humboldt Tipping. Data was collected during cruise number MSM80 with research vessel Maria S. Merian from 23.12.2018 - 30.01.2019 (from Panama to Valparaiso) in the Humboldt Upwelling system off the Eastern Tropical south Pacific. Samples were taken by CTD- rosette sampler from different depths and analysed onboard for dissolved inorganic nutrients and total dissolved nutrients. Triplicate nutrient samples were analysed for concentrations with an autosampler (XY-2 autosampler, SEAL Analytical) and a continuous flow analyzer (QUAAtro Autoanalyzer, SEAL Analytical) using standard colorimetric and flourometric methods by Kastriot Qelaj. Dissolved organic nutrients were calculated as the difference of the two for respective nitrogen and phosphorous nutrients. Phosphate was measured according to Murphy and Riley (1962). Ammonium was measured fluorometrically based on Holmes et al. (1999). An empty cell means that corresponding nutrient samples were not taken for the respective depth.