Description: The ice cover of the Arctic Ocean has been changing dramatically in the last decades and the consequences for the sea-ice associated ecosystem remain difficult to assess. Algal aggregates underneath sea ice have been described sporadically but the frequency and distribution of their occurrence is not well quantified. We used upward looking images obtained by a remotely operated vehicle (ROV) to derive estimates of ice algal aggregate biomass and to investigate their spatial distribution. During the IceArc expedition (ARK-XXVII/3) of RV Polarstern in late summer 2012, different types of algal aggregates were observed floating underneath various ice types in the Central Arctic basins. Our results show that the floe scale distribution of algal aggregates in late summer is very patchy and determined by the topography of the ice underside, with aggregates collecting in dome shaped structures and at the edges of pressure ridges. The buoyancy of the aggregates was also evident from analysis of the aggregate size distribution. Different approaches used to estimate aggregate biomass yield a wide range of results. This highlights that special care must be taken when upscaling observations and comparing results from surveys conducted using different methods or on different spatial scales.

Description: The ice-covered Central Arctic Ocean is characterized by low primary productivity due to light and nutrient limitations. It has been speculated that the recent reduction in ice cover could lead to a substantial increase in primary production, but still little is known as to the fate of the ice-associated primary production, and of nutrient supply with increasing warming. This study presents results from the Central Arctic Ocean collected during summer 2012, when sea-ice reached a minimum extent since the onset of satellite observations. Net primary productivity (NPP) was measured in water column, sea ice and melt ponds by 14CO2 uptake at different irradiances. Photosynthesis vs. irradiance (PI) curves were established in laboratory experiments and used to upscale measured NPP to the deep Eurasian Basin (north of 78°N) using the irradiance-based Central Arctic Ocean Primary Productivity model (CAOPP). In addition, new annual production was calculated from the seasonal nutrient drawdown in the mixed layer since last winter. Results show that ice algae can contribute up to 60% to primary production in the Central Arctic at the end of the season. The ice-covered water column had lower NPP rates than open water probably due to light limitation. According to the nutrient ratios in the euphotic zone, nitrate limitation was detected in the Siberian Seas (Laptev Sea area), while silicate was the main limiting nutrient at the ice margin influenced by Atlantic waters. Although sea-ice cover was substantially reduced in 2012, total annual new production in the Eurasian Basin was 17 ± 7 Tg C/yr, which is similar to previous estimates. However, when including the contribution by sub-ice algal filaments, the annual production for the deep Eurasian Basin (north of 78°N) is 16 Tg C/yr higher than estimated before. Our data suggest that sub-ice algae might be responsible for potential local increases in NPP due to higher light availability under the ice, and their ability to benefit from a wider area of nutrients as they drift with the ice.

Description: In the Arctic, under-ice primary production is limited to summer months and is not only restricted by ice thickness and snow cover but also by the stratification of the water column, which constrains nutrient supply for algal growth. RV Polarstern visited the ice-covered Eastern Central basins between 82 to 89°N and 30 to 130°E in summer 2012 when Arctic sea ice declined to a record minimum. During this cruise, we observed a widespread deposition of ice algal biomass of on average 9 g C per m**2 to the deep-sea floor of the Central Arctic basins. Data from this cruise will contribute to assessing the impact of current climate change on Arctic productivity, biodiversity, and ecological function.

Description: Size fractionated primary productivity rate measurements through 14C radioisotope incorporation rates from a KOSMOS mesocosm experiment carried out in the frame work of the Ocean Artificial Upwelling project. The experiment was performed in the North-East Atlantic Ocean off the coast of Gran Canaria in autumn 2018 and lasted for 39 days. In this study we investigated the effect of different intensities of artificial upwelling combined with two upwelling modes (recurring additions versus one singular addition) on the phytoplankton community. Data shown includes production rates of dissolved organic carbon, particulate organic carbon in 3 size fractions (0.2-2 µm, 2-20 µm, 〉20 µm) and total organic carbon.

Description: In this study we investigated the effect of artificial upwelling with different Si:N ratios on a natural oligotrophic plankton community. Data on primary production, flow cytometry, photophysiology, internal nutrient storage, diatom size, diatom silicification and diatom carbon density from the mesocosms experiment conducted on the Canary Islands in autumn 2019. Values are depth-integrated averages in (mostly) 2-days intervals over the course of 33 days. The upwelling treatment started on day 6. All samples were depth integrated (0-2.5m). Oxygen production and respiration rates were measured through incubations and Winkler titrations. Flow cytometry and photophysiology samples were measured fresh. Parameters used for diatom per capita size, silicification and carbon density measurements were taken from the following published datasets on the same experiment: https://doi.org/10.1594/PANGAEA.954852 and https://doi.org/10.1594/PANGAEA.951417

Description: We aimed to explore the community composition and turnover of eukaryotic and bacterial microorganisms associated with ice-associated and sinking algal aggregates, as well as their similarity to potential source communities of sea ice, water and deep-sea sediments using Illumina tag sequencing. We sampled algae aggregates growing in melt ponds on sea ice, deposited algae aggregates at the seafloor in more than 4000 m water depth, sea ice, upper water column, sediment surface and the gut content of holothurians feeding on the deposits. For Illumina sequencing, the Amplicon libraries of the bacterial V4-V6 region of the 16S rRNA gene and the eukaryotic V4 region of the 18S rRNA gene were generated according to the protocol recommended by Illumina (16S Metagenomic Sequencing Library Preparation, Part # 15044223, Rev. B). For Bacteria we selected the S-D-Bact-0564-a-S-15 and S-*Univ-1100-a-A-15 primer pair based on a primer evaluation by Klindworth et al. (2013, doi:10.1093/nar/gks808) and for Eukaryota the TAReukFWD1 and TAReukREV3 primers (Stoeck et al., 2010; doi:10.1111/j.1365-294X.2009.04480.x). Libraries were sequenced on an Illumina MiSeq platform in 2x300 cycles paired end runs. For Sequence data cleaning & processin, we used cutadapt (v. 1.8.1; Martin, 2011; doi:10.14806/ej.17.1.200) for the removal of primer sequences and a custom awk script to ensure the correct orientation of reads prior to merging. For merging forward and reverse reads we used pear (v. 0.9.5; Zhang et al., 2014; doi:10.1093/bioinformatics/btt593) and trimmed and quality filtered all sequences using trimmomatic (v. 0.32; Bolger et al., 2014; doi:10.1093/bioinformatics/btu170). We reassured correct formatting of the fastq files with bbmap (v. 34.00; B. Bushnell - sourceforge.net/projects/bbmap) before clustering the reads into OTUs by applying a local clustering threshold of d=1 and the fastidious option in swarm (v. 2.1.1; Mahé et al., 2015; doi:10.7717/peerj.1420). Subsequently, we used the SINA aligner (v. 1.2.10; Pruesse et al., 2012; doi:10.1093/bioinformatics/bts252) to align and classify the seed sequence of each OTU with the SILVA SSU database release 123 (Quast et al., 2013; doi:10.1093/nar/gks1219). OTUs that were classified as chloroplasts, mitochondria, archaea, or those that could not be classified at domain level were removed from further analysis. OTUs that were classified as bacteria within the eukaryotic dataset and vice versa, were removed as well. Furthermore, we removed all absolute singletons, OTUs that were only represented by a single sequence across the complete dataset. Filtering and removal of absolute singletons resulted in a final number of 8,869 bacterial and 7,627 eukaryotic OTUs. All further analyses were performed on these processed OTU abundance tables.

Description: This data is part of the BMBF projects CUSCO (Coastal Upwelling Systems in a Changing Ocean) and BioTip subproject Humboldt Tipping. Here we report water column nitrogen fixation, carbon fixation rates and particulate organic matter composition from the upper 300 m. Data was collected during cruise number MSM80 with research vessel Maria S. Merian from 23.12.2018 - 30.01.2019 (from Panama to Valparaiso) in the Humboldt Upwelling system off the Eastern Tropical south Pacific. Samples were taken by CTD- rosette sampler from different depths, injected with 15N labelled N2 gas based on the modified dissolution method (Großkopf et al., 2012 and Mohr et al., 2010) and additionally 13C labeled sodium bicarbonate. Samples were incubated for 24 hours at light intensities that resemble the in situ light conditions. After incubation a volume of the sample (20 - 1500 ml) was filtered onto a pre-combusted Whatman GF/75 filter. Filters were frozen, transported to the institute on dry ice and measured on a mass spectrometer for Delta15N and 13C (Delta V Advantage Isotope Ratio MS, ThermoFisher) with the ConFlo IV interface (ThermoFisher). Nitrogen fixation rates were calculated based on Montoya et al (1996) while carbon fixation rates were calculated based on the equation by Slawyk et al. (1977). Limits of detection (LOD) and minimum quantifiable rates (MQR) for Nitrogen fixation rates were calculated according to the criteria described by White et al. (2020) and standard error propagation methods described in Gradoville et al. (2017) respectively. POP and Biogenic silica concentrations were measured spectrophotometrically following Hansen and Koroleff (1999).

Description: This data is part of the BMBF projects CUSCO (Coastal Upwelling Systems in a Changing Ocean) and BioTip subproject Humboldt Tipping. Data was collected during cruise number MSM80 with research vessel Maria S. Merian from 23.12.2018 - 30.01.2019 (from Panama to Valparaiso) in the Humboldt Upwelling system off the Eastern Tropical south Pacific. Samples were taken by CTD- rosette sampler from different depths and analysed onboard for dissolved inorganic nutrients and total dissolved nutrients. Triplicate nutrient samples were analysed for concentrations with an autosampler (XY-2 autosampler, SEAL Analytical) and a continuous flow analyzer (QUAAtro Autoanalyzer, SEAL Analytical) using standard colorimetric and flourometric methods by Kastriot Qelaj. Dissolved organic nutrients were calculated as the difference of the two for respective nitrogen and phosphorous nutrients. Phosphate was measured according to Murphy and Riley (1962). Ammonium was measured fluorometrically based on Holmes et al. (1999). An empty cell means that corresponding nutrient samples were not taken for the respective depth.

Description: This data is part of the BMBF projects CUSCO (Coastal Upwelling Systems in a Changing Ocean) and BioTip subproject Humboldt Tipping. The file contains total dissolvable trace metal concentrations (Fe, Cd, Ni, Cu, Zn and Co) from various depths of sampled stations. Trace metal concentrations were determined via Inductively coupled plasma mass spectrometry (ICP-MS, Element XR, ThermoFisher Scientific) after pre-concentration as per Rapp et al. (2017).

Description: Microzooplankton (microZP, protists) and mesozooplankton (mesoZP, metazoans) abundances and biomass as well as presence of domoic acid (DA, phycotoxin) during the mesocosm experiment in the Canary Islands in autumn 2019. Depth-integrated (0-2.5m) water samples were taken over the course of 33 days, in 2-day intervals for microZP and mesoZP and 4-day intervals for DA. MicroZP was assessed by Utermöhl light microscopy and its biomass estimated using biovolume to carbon conversion factors from the literature. MesoZP samples were split into three size fractions (55-200, 200-500 and 〉500 µm), preserved with 70% ethanol and assessed under a stereo microscope. For biomass, mesoZP were measured in an element analyser. MesoZP data is provided for copepods only (dominant group) and all metazoan zooplankton combined (mainly copepods and appendicularians). For DA, particulate matter was filtered (〉0.7µm) and analysed via liquid chromatography and tandem mass spectrometry. The upwelling treatment started on day 6. Methodological details in Goldenberg et al. (doi:10.3389/fmars.2022.1015188) and Goldenberg et al. (under review).