Description: The long-term dynamics of microbial communities across geographic, hydrographic, and biogeochemical gradients in the Arctic Ocean are largely unknown. To address this, we annually sampled polar, mixed, and Atlantic water masses of the Fram Strait (2015–2019; 5–100 m depth) to assess microbiome composition, substrate concentrations, and oceanographic parameters. Longitude and water depth were the major determinants (~30%) of microbial community variability. Bacterial alpha diversity was highest in lower-photic polar waters. Community composition shifted from west to east, with the prevalence of, for example, Dadabacteriales and Thiotrichales in Arctic- and Atlantic-influenced waters, respectively. Concentrations of dissolved organic carbon peaked in the western, compared to carbohydrates in the chlorophyll-maximum of eastern Fram Strait. Interannual differences due to the time of sampling, which varied between early (June 2016/2018) and late (September 2019) phytoplankton bloom stages, illustrated that phytoplankton composition and resulting availability of labile substrates influence bacterial dynamics. We identified 10 species clusters with stable environmental correlations, representing signature populations of distinct ecosystem states. In context with published metagenomic evidence, our microbial-biogeochemical inventory of a key Arctic region establishes a benchmark to assess ecosystem dynamics and the imprint of climate change.

Description: Submesoscale eddies and fronts are important components of oceanic mixing and energy fluxes. These phenomena occur in the surface ocean for a period of several days, on scales between a few hundred meters and few tens of kilometers. Remote sensing and modeling suggest that eddies and fronts may influence marine ecosystem dynamics, but their limited temporal and spatial scales make them challenging for observation and in situ sampling. Here, the study of a submesoscale filament in summerly Arctic waters (depth 0–400 m) revealed enhanced mixing of Polar and Atlantic water masses, resulting in a ca. 4 km wide and ca. 50 km long filament with distinct physical and biogeochemical characteristics. Compared to the surrounding waters, the filament was characterized by a distinct phytoplankton bloom, associated with depleted inorganic nutrients, elevated chlorophyll a concentrations, as well as twofold higher phyto- and bacterioplankton cell abundances. High-throughput 16S rRNA gene sequencing of bacterioplankton communities revealed enrichment of typical phytoplankton bloom-associated taxonomic groups (e.g., Flavobacteriales) inside the filament. Furthermore, linked to the strong water subduction, the vertical export of organic matter to 400 m depth inside the filament was twofold higher compared to the surrounding waters. Altogether, our results show that physical submesoscale mixing can shape distinct biogeochemical conditions and microbial communities within a few kilometers of the ocean. Hence, the role of submesoscale features in polar waters for surface ocean biodiversity and biogeochemical processes need further investigation, especially with regard to the fate of sea ice in the warming Arctic Ocean.

Description: Seasonal variations in day length and temperature, in combination with dynamic factors such as advection from the North Atlantic, influence primary production and the microbial loop in the Fram Strait. Here, we investigated the seasonal variability of biopolymers, microbial abundance, and microbial composition within the upper 100 m during summer and fall. Flow cytometry revealed a shift in the autotrophic community from picoeukaryotes dominating in summer to a 34-fold increase of Synechococcus by fall. Furthermore, a significant decline in biopolymers concentrations covaried with increasing microbial diversity based on 16S rRNA gene sequencing along with a community shift towards fewer polymer-degrading genera in fall. The seasonal succession in the biopolymer pool and microbes indicates distinct metabolic regimes, with a higher relative abundance of polysaccharide-degrading genera in summer and a higher relative abundance of common taxa in fall. The parallel analysis of DOM and microbial diversity provides an important baseline for microbe-substrate relationships over the seasonal cycle in the Arctic Ocean.

Description: Here we provide dissolved inorganic nutrient data generated via the analysis of samples collected by autonomous instruments, in particular Remote Access Samplers (RAS) and associated sensor data (CTD-O2, PAR, Fluorescence, pH, pCO2). Data was collected within the frame of the AWI Frontiers in Arctic Marine Monitoring (FRAM) Programme and HAUSGARTEN LTO. A report is also provided, which includes basic data about the data, which are associated with two Polarstern expeditions; PS99 (grant AWI_PS99_0) and PS107 (AWI_PS107_05).

Description: Time-series data of physical oceanography and carbon/particle export were obtained from mooring HG-N-FEVI-37 in the Fram Strait in July 2018 - August 2019 as part of the Helmholtz infrastructure program Frontiers in Arctic Marine Monitoring (FRAM) and the long-term monitoring program at AWI HAUSGARTEN. The mooring was deployed during RV POLARSTERN expedition PS114, and recovered during PS121. The attached archive contains raw data files of two Seabird SBE37 microcats (nominal depths: 48m, 2626m; sampling interval 1h), two AADI RCM11 current meters (nominal depths: 2448m, 2624m; sampling interval 1h) and one AADI Seaguard current meter (nominal depth: 210m; sampling interval 1h). The mooring also included two sediment traps (nominal depths: 203m, 2441m). Auxiliary information such as sensor calibration sheets, mooring diagrams and schedule files are also provided, if applicable.

Description: Time-series data of physical & biological oceanography, nutrient biogeochemistry and molecular biology were obtained from mooring HG-IV-S-3 in the Fram Strait in July 2018 - August 2019 as part of the Helmholtz infrastructure program Frontiers in Arctic Marine Monitoring (FRAM) and the long-term monitoring program at AWI HAUSGARTEN. The mooring was deployed during RV POLARSTERN expedition PS114, and recovered during PS121. The attached archive contains raw data files of two Seabird SBE37 microcats (nominal depths: 26m, 52m; sampling interval 1h) and one Wetlabs ECO Triplet fluorometer (nominal depth: 24m; sampling interval 2h). The Wetlabs ECO PAR sensor (nominal depth: 24m; sampling interval 1h) was flooded and all data was lost. The mooring also included a McLane RAS water sampler (nominal depth: 24m) and a McLane PPS phytoplankton sampler (nominal depth: 26m). Auxiliary information such as sensor calibration sheets, mooring diagrams and schedule files are also provided, if applicable. The processed data of all sensors will be made available in separate entries.

Description: Time-series data of physical oceanography and carbon/particle export were obtained from mooring HG-IV-FEVI-38 in the Fram Strait in July 2018 - August 2019 as part of the Helmholtz infrastructure program Frontiers in Arctic Marine Monitoring (FRAM) and the long-term monitoring program at AWI HAUSGARTEN. The mooring was deployed during RV POLARSTERN expedition PS114, and recovered during PS121. The attached archive contains raw data files of four Seabird SBE37 microcats (nominal depths: 52m, 253m, 1200m, 2526m; sampling interval 1h), two AADI RCM11 current meters (nominal depths: 203m, 1230m; sampling interval 1h), one Nortek Aquadopp current meter (nominal depth: 750m; sampling interval 20 min), one RDI Longranger ADCP (nominal depth: 409m; sampling interval 1h) and two AADI Seaguard current meters (nominal depths: 2348m, 2524m; sampling interval 1h). The mooring also included three sediment traps (nominal depths: 196m, 1223m, 2341m) and one BioOptical Platform (565m). Auxiliary information such as sensor calibration sheets, mooring diagrams and schedule files are also provided, if applicable.

Description: Time-series data of physical & biological oceanography, nutrient biogeochemistry and molecular biology were obtained from mooring HG-IV-S-4 in the Fram Strait in August 2019 - June 2021 as part of the Helmholtz infrastructure program Frontiers in Arctic Marine Monitoring (FRAM) and the long-term monitoring program at AWI HAUSGARTEN. The mooring was deployed during RV POLARSTERN expedition PS121, and recovered during PS126. The attached archive contains raw data files of three Seabird SBE37 microcats (nominal depths: 18m, 23m, 47m; sampling interval 1h), two Seabird SBE56 temperature loggers (nominal depths: 28m, 38m; sampling interval 30s), one Wetlabs ECO Triplet fluorometer (nominal depth: 23m; sampling interval 2h) and one Wetlabs ECO PAR sensor (nominal depth: 23m; sampling interval 2h). One ISUS nitrate sensor (nominal depth: 23m) was flooded and no data is available. The mooring also included a McLane RAS water sampler (nominal depth: 23m) and a McLane PPS phytoplankton sampler (nominal depth: 25m). Auxiliary information such as sensor calibration sheets, mooring diagrams and schedule files are also provided, if applicable.

Description: Time-series data of physical & biological oceanography, nutrient biogeochemistry and molecular biology were obtained from mooring F4-W-2 in the Fram Strait in August 2019 - June 2021 as part of the Helmholtz infrastructure program Frontiers in Arctic Marine Monitoring (FRAM) and the long-term monitoring program at AWI HAUSGARTEN. The mooring was deployed during RV POLARSTERN expedition PS121, and recovered during PS126. The attached archive contains raw data files of one Seabird SBE37 microcat (nominal depths: 249m; sampling interval 1h), one Satlantics SUNA nitrate sensor (nominal depth: 249m; sampling interval 6h), one Sunburst SAMI-pCO2 sensor (nominal depth: 249m; sampling interval 2h) and one Sunburst SAMI-pH sensor (nominal depth: 249m; sampling interval 3h). The mooring also included a McLane RAS water sampler (nominal depth: 249m). The profiling SBE19plus system that was operated on the NGK winch (nominal depth: 153m) was lost. Additionally, the available data could not be downloaded from the main controller due to a corrupt SD card. Auxiliary information such as sensor calibration sheets, mooring diagrams and schedule files are also provided, if applicable.

Description: Time-series data of physical oceanography, nutrient biogeochemistry, molecular biology and carbon/particle export were obtained from mooring F4-S-3 in the Fram Strait in July 2018 - August 2019 as part of the Helmholtz infrastructure program Frontiers in Arctic Marine Monitoring (FRAM) and the long-term monitoring program at AWI HAUSGARTEN. The mooring was deployed during RV POLARSTERN expedition PS121, and recovered during PS126. The attached archive contains raw data files of two Seabird SBE37 microcats (nominal depths: 16m, 21m, 47m; sampling interval 1h), one Seabird SBE56 temperature logger (nominal depth: 38m; sampling interval: 30s), one Wetlabs ECO PAR sensor (nominal depth: 21m; sampling interval 2h), one Wetlabs ECO Triplet fluorometer (nominal depth: 21m; sampling interval 2h), one Satlantics SUNA nitrate sensor (nominal depth: 21m; sampling interval 6h), one Sunburst SAMI-pCO2 sensor (nominal depth: 21m; sampling interval 2h) and one Sunburst SAMI-pH sensor (nominal depth: 21m; sampling interval 3h). The mooring also included a McLane RAS water sampler (nominal depth: 21m), a McLane PPS phytoplankton sampler (nominal depth: 23m) and two sediment traps (nominal depths: 204m, 613m). Auxiliary information such as sensor calibration sheets, mooring diagrams and schedule files are also provided, if applicable.