Description: The trace metal iron (Fe) is an essential micronutrient for phytoplankton growth and limits, or co-limits primary production across much of the world's surface ocean. Iron is a redox sensitive element, with Fe(II) and Fe(III) co-existing in natural waters. Whilst Fe(II) is the most soluble form, it is also transient with rapid oxidation rates in oxic seawater. Measurements of Fe(II) are therefore preferably undertaken in situ. For this purpose an autonomous wet chemical analyzer based on lab-on-chip technology was developed for the in situ determination of the concentration of dissolved (〈0.45 μm) Fe species (Fe(II) and labile Fe) suitable for deployments in a wide range of aquatic environments. The spectrophotometric approach utilizes a buffered ferrozine solution and a ferrozine/ascorbic acid mixture for Fe(II) and labile Fe(III) analyses, respectively. Diffusive mixing, color development and spectrophotometric detection take place in three separate flow cells with different lengths such that the analyzer can measure a broad concentration range from low nM to several μM of Fe, depending on the desired application. A detection limit of 1.9 nM Fe was found. The microfluidic analyzer was tested in situ for nine days in shallow waters in the Kiel Fjord (Germany) along with other sensors as a part of the SenseOCEAN EU-project. The analyzer's performance under natural conditions was assessed with discrete samples collected and processed according to GEOTRACES protocol [acidified to pH 〈 2 and analyzed via inductively coupled plasma mass spectrometry (ICP-MS)]. The mechanical performance of the analyzer over the nine day period was good (consistent high precision of Fe(II) and Fe(III) standards with a standard deviation of 2.7% (n = 214) and 1.9% (n = 217), respectively, and successful completion of every programmed data point). However, total dissolved Fe was consistently low compared to ICP-MS data. Recoveries between 16 and 75% were observed, indicating that the analyzer does not measure a significant fraction of natural dissolved Fe species in coastal seawater. It is suggested that an acidification step would be necessary in order to ensure that the analyzer derived total dissolved Fe concentration is reproducible and consistent with discrete values.

Description: The coastal and open oceans represent a major, but yet unconstrained, sink for plastics. It is likely that plastic-biota interactions are a key driver for the fragmentation, aggregation, and vertical transport of plastic litter from surface waters to sedimentary sinks. Cruise SO279 conducted sampling to address core questions of microplastic distribution in the open ocean water column, biota, and sediments. Seven stations were sampled between the outer Bay of Biscay and the primary working area south of the Azores. Additional samples were collected from surface waters along the cruise track to link European coastal and shelf waters with the open ocean gyre. Microplastic samples coupled with geochemical tracer analyses will build a mechanistic understanding of MP transport and its biological impact reaching from coastal seas to the central gyre water column and sinks at the seabed. Furthermore, floating plastics were sampled for microbial community and genetic analyses to investigate potential enzymatic degradation pathways. Cruise SO279 served as the third cruise of a number of connected research cruises to build an understanding of the transport pathways of plastic and microplastic debris in the North Atlantic from the input through rivers and air across coastal seas into the accumulation spots in the North Atlantic gyre and the vertical export to its sink at the seabed. The cruise was an international effort as part of the JPI Oceans project HOTMIC (“HOrizontal and vertical oceanic distribution, Transport, and impact of MICroplastics”) and the BMBF funded project PLASTISEA (‘Harvesting the marine Plastisphere for novel cleaning concepts’), and formed a joint effort of HOTMIC and PLASTISEA researchers from a range of countries and institutes.

Description: Herein, we present a small and versatile optode system with integrated battery and logger for monitoring of O-2, pH, and pCO(2) in seawater. Three sensing materials designed for seawater measurements are optimized with respect to dynamic measurement range and long-term stability. The spectral properties of the sensing materials were tailored to be compatible with a commercially available laboratory oxygen logger that was fitted into a pressure housing. Interchangeable sensor caps with appropriate "sensing chemistry" are conveniently attached to the end of the optical fiber. This approach allows using the same instrument for multiple analytes, which offers great flexibility and minimizes hardware costs. Applications of the new optode system were demonstrated by recording depth profiles for the three parameters during a research cruise in the Baltic Sea and by measuring surface water transects of pH. The optode was furthermore used to monitor the concentration of dissolved oxygen in a seagrass meadow in the Limfjord, Denmark, and sensor packages consisting of pO(2), pH, and pCO(2) were deployed in the harbors of Kiel, Germany, and Southampton, England, for 6 d. The measurements revealed that the system can resolve typical patterns in seawater chemistry related to spatial heterogeneities as well as temporal changes caused by biological and tidal activity.

Description: The file contains dissolved and total dissolvable trace metal concentrations (Fe, Co, Mn, Ni, Cd, Cu, Pb, Zn and V), hydrogen peroxide (H2O2), Fe(II), and iodide and iodate concentrations of surface water samples and station depth profiles. Trace metal concentrations were measured by ICP-MS after preconcentration (Rapp et al. 2017, Anal. Chim. Acta). Fe(II) and H2O2 were analyzed on-board using chemiluminescence flow injection analysis (Hopwood et al. 2017, Sci. Rep.). Iodide concentrations were analyzed by cathodic stripping square wave voltammetry (Luther et al. 1988, Anal. Chem.) and Iodate concentrations were measured spectrophotometrically (Chapman and Liss 1977, Mar. Chem.).

Description: The file contains dissolved and total dissolvable trace metal concentrations (Fe, Co, Mn, Ni, Cd, Cu, Pb, Zn and V), hydrogen peroxide (H2O2), Fe(II), and iodide and iodate concentrations of surface water samples and station depth profiles. Trace metal concentrations were measured by ICP-MS after preconcentration (Rapp et al. 2017, Anal. Chim. Acta). Fe(II) and H2O2 were analyzed on-board using chemiluminescence flow injection analysis (Hopwood et al. 2017, Sci. Rep.). Iodide concentrations were analyzed by cathodic stripping square wave voltammetry (Luther et al. 1988, Anal. Chem.) and Iodate concentrations were measured spectrophotometrically (Chapman and Liss 1977, Mar. Chem.).

Description: The file contains dissolved and total dissolvable trace metal concentrations (Fe, Co, Mn, Ni, Cd, Cu, Pb, Zn and V), hydrogen peroxide (H2O2), Fe(II), and iodide and iodate concentrations of surface water samples and station depth profiles. Trace metal concentrations were measured by ICP-MS after preconcentration (Rapp et al. 2017, Anal. Chim. Acta). Fe(II) and H2O2 were analyzed on-board using chemiluminescence flow injection analysis (Hopwood et al. 2017, Sci. Rep.). Iodide concentrations were analyzed by cathodic stripping square wave voltammetry (Luther et al. 1988, Anal. Chem.) and Iodate concentrations were measured spectrophotometrically (Chapman and Liss 1977, Mar. Chem.).

Description: The file contains dissolved and total dissolvable trace metal concentrations (Fe, Co, Mn, Ni, Cd, Cu, Pb, Zn and V), hydrogen peroxide (H2O2), Fe(II), and iodide and iodate concentrations of surface water samples and station depth profiles. Trace metal concentrations were measured by ICP-MS after preconcentration (Rapp et al. 2017, Anal. Chim. Acta). Fe(II) and H2O2 were analyzed on-board using chemiluminescence flow injection analysis (Hopwood et al. 2017, Sci. Rep.). Iodide concentrations were analyzed by cathodic stripping square wave voltammetry (Luther et al. 1988, Anal. Chem.) and Iodate concentrations were measured spectrophotometrically (Chapman and Liss 1977, Mar. Chem.).

Description: The file contains dissolved race metal concentrations (Fe, Co, Mn, Ni, Cd, Cu, Pb and Zn), Fe(II), and macronutrients (phosphate, nitrate + nitrite and silicic acid) concentrations of surface water samples (from Tow-Fish system) and station depth profiles (from Titanium CTD rosette). Trace metal concentrations were measured by ICP-MS after preconcentration (Rapp et al. 2017, Anal. Chim. Acta). Fe(II) were analyzed on-board using chemiluminescence flow injection analysis (Hopwood et al. 2017, Sci. Rep.). Number of data flag is following GEOTRACES Quality Flag Policy