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Molecular and elemental composition of dissolved organic matter in anoxic basins (Mariager Fjord, Denmark; Gotland Basin, Baltic Sea; Black Sea)

The sampling campaigns were conducted in the Black Sea (POS539), Baltic Sea/Gotland Basin (EMB324), and on a boat in Denmark/Mariager Fjord. All three study sites are differently influenced by ocean deoxygenation and anoxia. While Mariager Fjord waters are seasonally anoxic, the deep waters of Gotland Basin and Black Sea can remain anoxic for decades and millennia, respectively. Furthermore, to target potential abiotic reactions, we incubated filtered Gotland Basin waters at low (<1.5µM O2) and high (>200µM O2) oxygen concentrations. All samples were filtered to 0.2 µm pore size and acidified with hydrochloric acid to pH2. DOM was extracted and desalted prior to molecular analysis with ultrahigh resolution mass spectrometry (FT-ICR-MS) following an established method using cartridges filled with a styrene-divinylbenzene copolymer (Agilent Bond Elut PPL, 1 g). This data set contains two files: (1) environmental data, including oxygen concentrations, salinity, temperature, dissolved and solid-phase extractable dissolved carbon (DOC, SPE-DOC), nitrogen (TDN, SPE-DON), sulfur (SPE-DOS), and phosphorus (SPE-DOP), and (2) processed FT-ICR-MS data for all samples.

Dissolved organic matter (DOM) dynamics obtained through ultra-high resolution mass spectrometry (FT-ICR-MS) in the anoxic basin Mariager Fjord, Gotland Basin, and Black Sea

We studied dissolved organic matter (DOM) dynamics in the anoxic basin Mariager Fjord, Gotland Basin, and Black Sea. Therefore, we performed a mass spectrometric analysis of DOM extracts via FT-ICR MS on a 15 Tesla solariX XR Fourier-transform ion cyclotron resonance mass spectrometer (Bruker Daltonik GmbH, Bremen, Germany). The system was equipped with an electrospray ionization source (ESI, Bruker Apollo II) applied in negative ionization mode. Methanol extracts were mixed with ultrapure water (50:50 v/v) for FT-ICR MS analysis and diluted to a final DOC concentration of 2.5 mg C/L. 200 single scans with an ion accumulation time of 0.1 s were recorded over a mass range of m/z 100 to 1,000 Da and added to one spectrum. Data processing, molecular formula assignments, and compound category classifications were done with the software pipeline ICBM-OCEAN. All sample data was normalized to the intensity sum of 1. FT-ICR-MS data from Mariager Fjord (Denmark), Gotland Basin (Baltic Sea), Black Sea, and an abiotic (de)oxygenation experiment are provided. The data consists of the molecular formula with corresponding m/z measured at an FT-ICR-MS and relative intensities for each sample of these molecular formulas. Additionally, we included common molecular parameters, including H/C, O/C and S/C ratios for each molecular formula.

Environmental data from anoxic basins in the Mariager Fjord in Denmark, the Gotland Basin in the Baltic Sea, and the Black Sea

We studied dissolved organic matter (DOM) dynamics in the anoxic basin Mariager Fjord, Gotland Basin, and Black Sea. In this data set we provide environmental data (oxygen, salinity, temperature), dissolved and solid-phase extracted carbon (DOC, SPE-DOC), nitrogen (TDN, SPE-DON), sulfur (SPE-DOS), and phosphorus (SPE-DOP) concentrations. Elemental analysis of carbon and nitrogen were carried out with a High-temperature catalytic combustion, Shimadzu, Shimadzu TOC-VCPH equipped with TDN unit, analysis of extractable sulfur and phosphorus with Inductively coupled plasma optical emission spectroscopy, Thermo Fisher Scientific GmbH, iCAP PRO.

Physiological data of Pacific oyster Crassostrea (Magallana) gigas after exposure to intermittent hypoxia and the combination with (fluctuating) elevated temperature

Organisms in intertidal zones experience fluctuations in environmental stressors such as hypoxia and temperature. These stressors and their fluctuations often appear in combination. Combination of stressors can have different effects compared to single stressors. In this study, we investigate the physiological effects of intermittent hypoxia in combination with different temperature regimes on the Pacific Oyster Crassostrea (Magallana) gigas. The oysters were exposed to hypoxic cycles (12h hypoxia by emersion/12h submersion) at normal (15°C), elevated (30°C) or fluctuating (15°C submersion/30°C emersion) temperature for 10 days. After the last submersion phase, the gills and digestive gland were sampled. We measured markers for bioenergetics and redox-balance in the gills and digestive gland using colorimetric methods as well as a set of metabolites (predominantly amino acids, osmolytes, anaerobic end products and energetic metabolites) in the gills using LC-MS/MS. Oysters kept submerged for up to 10 days were used as controls.

Kiel Indoor Benthocosms: applied temperature profiles (Figure 3)

Kiel Indoor Benthocosms

Climate change will shift mean environmental conditions and also increase the frequency and intensity of extreme events, exerting additional stress on ecosystems. While field observations on extremes are emerging, experimental evidence of their biological consequences is rare. Here, we introduce a mesocosm system that was developed to study the effects of environmental variability of multiple drivers (temperature, salinity, pH, light) on single species and communities at various temporal scales (diurnal - seasonal): the Kiel Indoor Benthocosms (KIBs). Both, real- time offsets from field measurements or various dynamic regimes of environmental scenarios, can be implemented, including sinusoidal curve functions at any chosen amplitude or frequency, stochastic regimes matching in situ dynamics of previous years and modelled extreme events. With temperature as the driver in focus, we highlight the strengths and discuss limitations of the system. In addition, we examined the effects of different sinusoidal temperature fluctuation frequencies on mytilid mussel performance. High-frequency fluctuations around a warming mean (+2°C warming, ±2°C fluctuations, wavelength=1.5 days) increased mussel growth as did a constant warming of 2°C. Fluctuations at a lower frequency (+2 and ±2°C, wavelength=4.5 days), however, reduced the mussels' growth. This shows that environmental fluctuations, and importantly their associated characteristics (such as frequency), can mediate the strength of global change impacts on a key marine species. The here presented mesocosm system can help to overcome a major short-coming of marine experimental ecology and will provide more robust data for the prediction of shifts in ecosystem structure and services in a changing and fluctuating world.

Kiel Outdoor Benthoscosm experiment 2018 on ocean warming and upwelling: hourly means of temperature and oxygen

Hourly means of temperature and oxygen as logged in the tanks.

Kiel Outdoor Benthoscosm experiment 2018 on ocean warming and upwelling: abundances of major grazer species

Abundances (numbers) of major grazer species in the tanks as assessed by subsamples taken at three time points (before upwelling 2 and 3 and between the two upwelling events).

Kiel Outdoor Benthoscosm experiment 2018 on ocean warming and upwelling: tank abiotics

Temperature, pH, salinity and oxygen logged and measured in the tanks.

Kiel Outdoor Benthoscosm experiment 2018 on ocean warming and upwelling: tank abiotics control measures

Control measures of temperature, pH, salinity and oxygen as taken by WTW multimeter daily 3h after sunrise.

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