ALBERT

Description: Carbon cycling by Antarctic microbial plankton is poorly understood but it plays a major role in CO2 sequestration in the Southern Ocean. We investigated the summer bacterioplankton community in the largely understudied Weddell Sea, applying Illumina amplicon sequencing, measurements of bacterial production and chemical analyses of organic matter. The results revealed that the patchy distribution of productive coastal polynyas and less productive, mostly ice-covered sites was the major driver of the spatial changes in the taxonomic composition and activity of bacterioplankton. Gradients in organic matter availability induced by phytoplankton blooms were reflected in the concentrations and composition of dissolved carbohydrates and proteins. Bacterial production at bloom stations was, on average, 2.7 times higher than at less productive sites. Abundant bloom-responsive lineages were predominately affiliated with ubiquitous marine taxa, including Polaribacter, Yoonia-Loktanella, Sulfitobacter, the SAR92 clade, and Ulvibacter, suggesting a widespread genetic potential for adaptation to sub-zero seawater temperatures. A co-occurrence network analysis showed that dominant taxa at stations with low phytoplankton productivity were highly connected, indicating beneficial interactions. Overall, our study demonstrates that heterotrophic bacterial communities along Weddell Sea ice shelves were primarily constrained by the availability of labile organic matter rather than low seawater temperature.

Description: The expedition AL570 with the RV Alkor was carried out within the framework of the interdisciplinary DAM MGF-OSTSEE Project “Potential effects of closure for bottom fishing in the marine protected areas (MPAs) of the western Baltic Sea – baseline observations” funded by the Ministry of Education and Research (BMBF). Within MGF-OSTSEE a consortium of scientists from various institutions investigates how benthic ecosystems in Natura 2000 areas within the German exclusive economic zone develop after the exclusion of bottom trawling. Major goals of the project are i. the initial assessment of the environmental state and its variability in- and outside the three Natura 2000 areas Fehmarnbelt, Oder- and Rönnebank under the ongoing pressure of bottom trawling and ii. the general assessment of the effect of bottom trawling on benthic communities and benthic biogeochemical functioning as well as their development after fishery exclusion. The cruise AL570 concludes a series of three previous expeditions EMB238 (2020) and EMB267/268 (2021) and aimed to survey all components of the benthic food web including prokaryotes, protozoans, meiofauna and macrofauna, as well as sediment properties and biogeochemical processes in selected working areas in- and outside of the MPA. The working program comprised 156 station activities of various gears for biological and biogeochemical sampling of sediments. Solute exchange between the sediment and the water column was investigated using Landers and a novel underwater vehicle the Deep-Sea Rover (DSR) Panta Rhei. Investigations in the water column, seafloor observation and deployments of a dredge supplemented the station work. Due to stormy weather in situ solute fluxe measurements were not performed at the Rönnebank.

Description: Global warming poses new threats to marine ecosystems since rising seawater temperature potentially induces cascading effects in biogeochemical cycles and food webs. Heterotrophic bacteria are the main producers of CO2 in the ocean, thereby counteracting the biological drawdown of CO2 by primary production. In Antarctic marine systems, low seawater temperature, and the low availability of labile organic matter are major environmental constraints on bacterial growth and degradation activity. However, temperature and the availability of resources for heterotrophic bacteria undergo considerable change induced by climate warming combined with subsequent ice melt and changes in primary productivity. This project aims to test single and combined effects of temperature and organic matter availability on Antarctic marine bacterioplankton. This data set includes biological and biogeochemical parameters measured alongside the CTD casts during the Polarstern cruise PS111 to the Weddell Sea. Samples were collected in the upper 100 m of the water column at the Eastern Weddell Sea Shelf and at the Filchner-Ronne ice shelf. Concentrations of different components of dissolved organic matter and inorganic nutrients as well as chlorophyll a concentrations and bacterial cell numbers are reported.

Description: Global warming poses new threats to marine ecosystems since rising seawater temperature potentially induces cascading effects in biogeochemical cycles and food webs. Heterotrophic bacteria are the main producers of CO2 in the ocean, thereby counteracting the biological drawdown of CO2 by primary production. In Antarctic marine systems, low seawater temperature, and the low availability of labile organic matter are major environmental constraints on bacterial growth and degradation activity. However, temperature and the availability of resources for heterotrophic bacteria undergo considerable change induced by climate warming combined with subsequent ice melt and changes in primary productivity. This project aims to test single and combined effects of temperature and organic matter availability on Antarctic marine bacterioplankton. This data set includes measurements on bacterial biomass production at 0°C and 3°C measured alongside the CTD casts during the Polarstern cruise PS111 to the Weddell Sea. Samples were collected in the upper 100 m of the water column at the Eastern Weddell Sea Shelf and at the Filchner-Ronne ice shelf.

Description: During expedition EMB201 in the Baltic Sea we investigated the local producers of glycerol dialkyl glycerol tetraethers (GDGT) and their thriving depth by a combined 16S rRNA gene amplicon sequencing/ CARD-FISH and lipidomic approach. Water samples were taken in December 2018 by a pump-CTD, a giant water sampler and with Niskin bottles at the surface, suboxic and sulfidic zones of the Landsort Deep, Fårö Basin and East Gotland Basin. This data set contains the CARD-FISH and lipidomics data, while the 16S rRNA gene sequencing data is available on ENA. Cell abundance was analysed in an aliquot of 40 ml filtered (pore size 0.22 micro m) sea water fixed with particle-free formaldehyde. Archaeal cells on the filters were specifically hybridized via catalysed reporter deposition-fluorescence in situ hybridization (CARD-FISH) using the Cren537 probe. Cells on the hybridized filter were counter-stained with 40,6-diamidin-2-phenylindol (DAPI). For lipid analysis, 150–600 L sea water were filtered with a flow rate of 1.5 L min-1 on pre-ashed, 142-mm-diameter, 0.7µm pore size glass fibre GF/F filters, and frozen at –20 °C. The filters were lyophilized before different extraction methods were used to obtain intact and core GDGTs by ultra-sonification in different solvent mixtures. The combined supernatants were phase separated before analysis by high performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS2) for intact polar lipids and by high performance liquid chromatography coupled to atmospheric pressure chemical ionization mass spectrometry (HPLC APCI-MS; ThermoScientific) for core GDGTs.

Description: Upwelling systems are significant sources of atmospheric nitrous oxide (N₂O). The Benguela Upwelling System is one of the most productive regions worldwide and a temporally variable source of N₂O. Strong O₂ depletions above the shelf are favoring periodically OMZ formations. We aimed to assess underlying N₂O production and consumption processes on different temporal and spatial scales during austral winter in the Benguela Upwelling System, when O₂⁻deficiency in the water column is relatively low. The fieldwork took place during the cruise M157 (August 4ᵗʰ – September 16ᵗʰ 2019) onboard the R/V METEOR. This expedition included four close-coastal regions around Walvis Bay at 23°S, which presented the lowest O₂ concentrations near the seafloor and thus may provide hotspots of N₂O production. Seawater was collected in 10 L free-flow bottles by using a rosette system equipped with conductivity-temperature-depth (CTD) sensors (SBE 911plus, Seabird-electronics, USA).Seawater samples were collected from 10 L free-flow bottles bubble-free, filled into 200 mL serum bottles and immediately fixed with saturated mercury chloride (HgCl₂). Concentrations of dissolved N₂O were measured by a purge and trap system using a dynamic headspace (Sabbaghzadeh et al., 2021). The N₂O gas saturation (N₂Oₛₐₜ in %) was calculated from the concentration ratio between the seawater sample and seawater equilibrated with the atmosphere. ∆N₂O (N₂O saturation disequilibrium in nmol L⁻¹) was calculated as the difference between the measured N₂O concentration and the atmospheric equilibrium N₂O concentration using Bunsen solubility coefficient (Weiss and Price, 1980). AOU (apparent oxygen utilization in µmol L⁻¹) expresses the O₂ consumption by microbial respiration and was calculated as the difference between the equilibrated O₂ and observed O₂ concentration with the same physico-chemical properties (Weiss and Price, 1980).

Description: Upwelling systems are significant sources of atmospheric nitrous oxide (N₂O). The Benguela Upwelling System is one of the most productive regions worldwide and a temporally variable source of N₂O. Strong O₂ depletions above the shelf are favoring periodically OMZ formations. We aimed to assess underlying N₂O production and consumption processes on different temporal and spatial scales during austral winter in the Benguela Upwelling System, when O₂-deficiency in the water column is relatively low. The fieldwork took place during the cruise M157 (August 4ᵗʰ – September 16ᵗʰ 2019) onboard the R/V METEOR. This expedition included four close-coastal regions around Walvis Bay at 23°S, which presented the lowest O₂ concentrations near the seafloor and thus may provide hotspots of N₂O production. Seawater was collected in 10 L free-flow bottles by using a rosette system equipped with conductivity-temperature-depth (CTD) sensors (SBE 911plus, Seabird-electronics, USA). Concentrations of inorganic nutrients (PO₄³⁻, NH₄⁺, NO₃⁻, NO₂⁻, and SiO₂) were measured colorimetrically according to Grasshoff et al. (1999) by means of a continuous segmented flow analyzer (SEAL Analytical, QuAAtro39). To determine the water mass fractions along the sampling transects, vertical profiles were collected using a free-falling microstructure profiler (MSS90L, Sea & Sun Technology). Temperature, dissolved oxygen, and salinity were measured with a CTD system consisting of a SeaBird 911+ probe, mounted on a sampling rosette.

Description: Upwelling systems are significant sources of atmospheric nitrous oxide (N₂O). The Benguela Upwelling System is one of the most productive regions worldwide and a temporally variable source of N₂O. Strong O₂ depletions above the shelf are favoring periodically OMZ formations. We aimed to assess underlying N₂O production and consumption processes on different temporal and spatial scales during austral winter in the Benguela Upwelling System, when O₂-deficiency in the water column is relatively low. The fieldwork took place during the cruise M157 (August 4th – September 16th 2019) onboard the R/V METEOR. This expedition included four close-coastal regions around Walvis Bay at 23°S, which presented the lowest O₂ concentrations near the seafloor and thus may provide hotspots of N₂O production. Seawater was collected in 10 L free-flow bottles by using a rosette system equipped with conductivity-temperature-depth (CTD) sensors (SBE 911plus, Seabird-electronics, USA). Incubation experiments were performed using stable isotope ¹⁵N-tracers. Seawater samples for ¹⁵N-tracer incubations and natural abundance N₂O analysis were collected from 10 L free-flow bottles and filled bubble-free into 125 mL serum bottles. The samples for natural abundance N₂O analysis were immediately fixed with saturated HgCl₂ and stored in the dark. To perform the incubation, we added ¹⁵N-labeled NO₂-, NO₃⁻ and NH₄⁺ to estimate the in-situ N₂O production rates and associated reactions. To determine a single rate, the bottles were sacrificed after tracer addition, and within the time interval of 12 h, 24 h and 48 h by adding HgCl₂. Rates were calculated based on a linear regression over time. Total N₂O and natural abundance isotopologues of N₂O were analyzed by using an isotope ratio mass spectrometer (IRMS, Delta V Plus, Thermo Scientific). NO₂- production was additionally analyzed by transforming ¹⁵NO₂- to ¹⁵N₂O following the azide method after McIlvin & Altabet (2005) and the nitrogen isotope ratio of N₂O was measured by an IRMS. N₂ production was determined via an IRMS (Flash-EA-ConfloIV-DELTA V Advanced, Thermo Scientific) by injecting headspace from exetainers. The N₂O yield per nitrite produced and the N₂O yield during denitrification was calculated. Samples for natural abundance N₂O was sampled and measured in triplicates and is shown as an average with standard deviation (SD). In order to estimate the contribution of different N₂O producing pathways by major biological processes and the extent of N₂O reduction to N₂, the dual-isotope mapping approach was applied to natural abundance isotopologues of N₂O, which uses the relative position of background-subtracted N₂O samples in a δ¹⁵Nˢᴾ-N₂O vs. δ¹⁸O-N₂O diagram (Yu et al., 2020; Lewicka-Szczebak et al., 2020).

Description: Upwelling systems are significant sources of atmospheric nitrous oxide (N₂O). The Benguela Upwelling System is one of the most productive regions worldwide and a temporally variable source of N₂O. Strong O₂ depletions above the shelf are favoring periodically OMZ formations. We aimed to assess underlying N₂O production and consumption processes on different temporal and spatial scales during austral winter in the Benguela Upwelling System, when O₂-deficiency in the water column is relatively low. The fieldwork took place during the cruise M157 (August 4th – September 16th 2019) onboard the R/V METEOR. This expedition included four close-coastal regions around Walvis Bay at 23°S, which presented the lowest O₂ concentrations near the seafloor and thus may provide hotspots of N₂O production. Seawater was collected in 10 L free-flow bottles by using a rosette system equipped with conductivity-temperature-depth (CTD) sensors (SBE 911plus, Seabird-electronics, USA). Incubation experiments were performed using stable isotope ¹⁵N-tracers. Seawater samples for ¹⁵N-tracer incubations and natural abundance N₂O analysis were collected from 10 L free-flow bottles and filled bubble-free into 125 mL serum bottles. The samples for natural abundance N₂O analysis were immediately fixed with saturated HgCl₂ and stored in the dark. To perform the incubation, we added ¹⁵N-labeled NO₂-, NO₃⁻ and NH₄⁺ to estimate the in-situ N₂O production rates and associated reactions. To determine a single rate, the bottles were sacrificed after tracer addition, and within the time interval of 12 h, 24 h and 48 h by adding HgCl₂. Rates were calculated based on a linear regression over time. Total N₂O and natural abundance isotopologues of N₂O were analyzed by using an isotope ratio mass spectrometer (IRMS, Delta V Plus, Thermo Scientific). NO₂- production was additionally analyzed by transforming ¹⁵NO₂- to ¹⁵N₂O following the azide method after McIlvin & Altabet (2005) and the nitrogen isotope ratio of N₂O was measured by an IRMS. N₂ production was determined via an IRMS (Flash-EA-ConfloIV-DELTA V Advanced, Thermo Scientific) by injecting headspace from exetainers. The N₂O yield per nitrite produced and the N₂O yield during denitrification was calculated. Samples for natural abundance N₂O was sampled and measured in triplicates and is shown as an average with standard deviation (SD). In order to estimate the contribution of different N₂O producing pathways by major biological processes and the extent of N₂O reduction to N₂, the dual-isotope mapping approach was applied to natural abundance isotopologues of N₂O, which uses the relative position of background-subtracted N₂O samples in a δ¹⁵Nˢᴾ-N₂O vs. δ¹⁸O-N₂O diagram (Yu et al., 2020; Lewicka-Szczebak et al., 2020).