Description: Dissolved organic matter (DOM) in the oceans constitutes a major carbon pool involved in global biogeochemical cycles. More than 96% of the marine DOM resists microbial degradation for thousands of years. The composition of this refractory DOM (RDOM) exhibits a molecular signature which is ubiquitously detected in the deep oceans. Surprisingly efficient microbial transformation of labile into RDOM was shown experimentally, implying that microorganisms produce far more RDOM than needed to sustain the global pool. By assessing the microbial formation and transformation of DOM in unprecedented molecular detail for 3 years, we show that most of the newly formed RDOM is molecularly different from deep sea RDOM. Only 〈0.4% of the net community production was channeled into RDOM molecularly undistinguishable from deep sea DOM. Our study provides novel experimentally derived molecular evidence and data for global models on the production, turnover and accumulation of marine DOM.

Description: Dissolved organic matter (DOM) is the main substrate and energy source for heterotrophic bacterioplankton. To understand the interactions between DOM and the bacterial community (BC), it is important to identify the key factors on both sides in detail, chemically distinct moieties in DOM and the various bacterial taxa. Next-generation sequencing facilitates the classification of millions of reads of environmental DNA and RNA amplicons and ultrahigh-resolution mass spectrometry yields up to 10,000 DOM molecular formulae in a marine water sample. Linking this detailed biological and chemical information is a crucial first step toward a mechanistic understanding of the role of microorganisms in the marine carbon cycle. In this study, we interpreted the complex microbiological and molecular information via a novel combination of multivariate statistics. We were able to reveal distinct relationships between the key factors of organic matter cycling along a latitudinal transect across the North Sea. Total BC and DOM composition were mainly driven by mixing of distinct water masses and presumably retain their respective terrigenous imprint on similar timescales on their way through the North Sea. The active microbial community, however, was rather influenced by local events and correlated with specific DOM molecular formulae indicative of compounds that are easily degradable. These trends were most pronounced on the highest resolved level, that is, operationally defined 'species', reflecting the functional diversity of microorganisms at high taxonomic resolution.

Description: Two bacterial species members of the Roseobacter group (P. inhibens and D. shibae) were cultivated using three different substrates as a sole carbon source. The molecular fingerprint of the medium was analyzed at three different time points corresponding to the lag, exponential and stationary growth phases. North equatorial pacific intermediate water was also measured in replicates. This water mass represents one of the oldest water masses in our oceans and it is therefore used as a representative for refractory dissolved organic matter. Data includes mass, molecular formula (if available) and relative intensity normalized to 100%

Description: Aerosol, seawater, and floodwater samples were taken during the 2017 California Thomas Fire and subsequent flash flood event. These samples were used to examine how fire-flood sequences affect metal and black carbon delivery to coastal waters, such as the Santa Barbara Basin (SBB). On day 11 of the Thomas Fire, aerosols sampled at sea level under a smoke plume over the SBB found high levels of PM2.5, levoglucosan, and black carbon (average: 49 μg/m^3, 1.05 μg/m^3, 14.93 μg/m^3, respectively) and both soluble and total aerosol metal concentrations were consistent with a forest fire signature. Metal, nutrient, and chlorophyll a concentrations in surface seawater (average: 2.42 nM Fe, 0.14 µM phosphate, and 0.44 µgChla/L) were similar to concentrations during non-fire conditions, thus we could not establish fire-related increases in the SBB surface waters. On days 37 to 40 of the fire, before, during, and after a flash flood in the Ventura River, dissolved organic carbon, dissolved black carbon, and dissolved metal concentrations were positively correlated with discharge. Our findings confirm that black carbon and metals were released by the Thomas Fire and transported by both atmospheric and fluvial pathways.

Description: Zooplankton samples were collected between 03/26/2018 and 04/27/2018 around the northern tip of the Antarctic Peninsula (63° 0' 1.843'' S, 60° 0' 16.901''W) onboard the RV Polarstern during the PS112 campaign in order to identify spatial distribution in response to environmental variables (CTD raw data files from POLARSTERN cruise PS112, https://doi.org/10.1594/PANGAEA.895969) and the abundance of krill (Euphausia superba) and salps (Salpa thompsoni). Samples were taken using a Bongo net with a mesh size of 150 µm. The net was equipped with a flowmeter (HydroBios) to measure the filtered volume. On board, the net sample was sieved over a 2000 µm mesh in order to separate organisms 〉2000 µm. The smaller fraction (150 – 2000 µm) was homogenized in 200 mL 0.2 µm filtered seawater and equally split into 4 x 50 mL by using a Hensen-Stempel pipette. The mesozooplankton size range of 150 – 2000 µm was defined according to Atkinson et al. (2012). Two parts were then filtered on 47 mm GF/C Whatman filters (precombusted, acidified and weighed) for analysis of dry weight (DW), bulk carbon (C), nitrogen (N) and phosphorus (P) content, while the third part was preserved in 4 % formalin for abundance, biovolume and size structure analysis. The C/N filters were sealed in tin capsules and analyzed using a CHN analyzer (Thermo, Flash EA 1112). Prior to the analysis, filters for particulate phosphorus were combusted at 450 °C for 5 hours. Particulate organic phosphorus (POP) was measured photometrically as orthophosphate (PO4) by molybdate reaction after sulfuric acid and heat digestion at 90 °C, modified after (Grasshoff et al., 2009). Another filter containing the 4th part served as a back-up. Mesozooplankton bulk stoichiometry data are shown in dataset one. The zooplankton subsamples for taxonomic analysis were scanned using the ZooScan digital imaging system (Model Biotom, Hydroptic Inc., France), a water-proof scanner with a resolution of 2400 dpi (Gorsky et al., 2010; doi:10.1093/plankt/fbp124). Prior to scanning, the formalin preserved samples were rinsed and five samples were further subdivided with a Motoda splitter to reduce the number of organisms per scan and avoid overlapping in the scanning frame. The splits were then placed on the scanner and overlapping organisms were separated manually. Subsequently, the obtained scanning image was processed with ZooProcess, a macro of the image processing software ImageJ (Rasband, 2012) to allow automated processing and measurement of images. These single object images and their metadata were uploaded to the web-based application EcoTaxa (https://ecotaxa.obs-vlfr.fr/prj/2529). Manual validation of the results was required to ensure correct classification. The images were identified to the lowest taxonomic level possible. Prior to quantitative analysis of the obtained data, the image categories containing no zooplankton organisms such as “detritus”, “fiber”, “bubbles” etc. were removed. Abundance of zooplankton taxa was calculated based on the number of images per taxonomic category. Zooplankton organisms were identified to the lowest possible taxonomical level. Whenever identification to species level was not possible, the sample was identified to the next identifiable taxonomical category and assigned a putative species name. The abundance and biovolume data are shown in dataset two and three. The metadata of each image also contain the estimates for body size (body length: major axis of the best fitting ellipse; body width: minor axis) that were used to calculate the biovolume of each object. For the biovolume per size class, the biovolume (mm³/m³) was sorted in octave-scale size class intervals given as individual biovolume (mm3). The lowest limit of the first size class corresponded to the smallest detected ellipsoidal biovolume of 0.00025 mm³. Each size class was then doubled with respect to the previous one. Consequently, the resulting intervals were narrow for small body sizes and became progressively wider with increasing body size. The largest size class was determined by the largest individuals in each sample. As a result, the lower boundary of each size class equaled the interval width. The biovolume (mm³/m³) was then summed for each size class interval. The size distribution (mm³) with total biovolume (mm³/m³) per size bin is given in dataset four.

Description: Shallow submarine hydrothermal systems are extreme environments with unique biogeochemical conditions, originating from the interaction of hot, reduced fluids and cold, oxygenated seawater. Hydrothermal fluids represent one of the marine sources of essential trace elements like iron, the flux of which is controlled by dissolved organic matter (DOM) in and between terrestrial and marine ecosystems. However, the selectivity of the DOM with iron in marine environments is not well understood. Here we characterized at a molecular level the marine hydrothermal iron?DOM interaction using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Our study site was a shallow-water hydrothermal system off Dominica Island (Lesser Antilles, Caribbean Sea), where reduced fluids were strongly enriched in dissolved Fe and Si as compared to surface seawater. The dissolved organic carbon (DOC) concentration was lower in the hydrothermal fluids, most likely due to low-DOC meteoric water influence, but also suggesting biotic or abiotic processes consuming or depleting DOC when seawater is re-circulated through the sediment. The formation of hydrous ferric oxides upon aeration of the hydrothermal fluids for 10 h leads to an 8% decrease in DOC, indicating co-precipitation of iron and DOM. Re-solubilization of iron precipitates revealed increased relative abundance of aromatic compounds in co-precipitated DOM, which is in accordance with iron-coagulation observed in terrestrial environments. In conclusion, we provide evidence of co-precipitation of DOM with iron at hydrothermal systems as a selective process, which characteristically alters the molecular composition of DOM released with hydrothermal fluids.