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Total and phytoplankton group chlorophyll concentrations from underway spectrophotometry with water mass classification in the East Greenland Sea from Polarstern expeditions 2015-2024

We present a high spatially resolved (around 300 m) data set on the chlorophyll-a concentrations of all phytoplankton (total chlorophyll-a), diatoms, haptophytes and chlorophytes various phytoplankton pigments (unit: mg/m³) estimated from particulate absorption data derived from underway AC-S measurements operated on eight R/V POLARSTERN expeditions in the Greenland Sea (North of 66.3°N to 82°N within the Atlantic Ocean) between 2015 to 2024: PS93.2, PS99.2, PS107, PS121, PS126, PS131, PS136 and PS143-2. For each data point we further provide the percentage of Atlantic Water and Polar Water and the association into the three regions: East Greenland Sea, Central Fram Strait and West Spitsbergen Current. Mind that the classification of water masses and regions is only valid for the Hausgarten area (78°N to 80°N and 7°W to 15°E). The details of the instrument set-up, the data and the methods are described in Bracher et al. (2025).

A validation data set of phytoplankton pigment concentrations and phytoplankton groups measured on water samples collected from various expeditions

This data set composes quality controlled in situ measurements of eight major pigments based on HPLC collected from various expeditions from 2016 to 2023. There are two subsets: subset 1 is the test dataset (99 matchups) extracted from and takes up 30 % of a global in situ PFT matchup data set, while the other 70 % was used for the retuning of the PFT algorithm for Sentinel 3 OLCI sensors. Subset 1 spans from 2016 to 2021 and is part of the global data set described in Xi et al. (2023): https://doi.pangaea.de/10.1594/PANGAEA.954738. Subset 2 containing 134 matchups is a newly compiled dataset that composites in situ PFT data collected from four recent mostly polar expeditions with the research vessel Polarstern (Alfred-Wegener-Institut Helmholtz-Zentrum für Polar- und Meeresforschung, 2017), that are PS126 (May–June 2021), PS131/1 (June–Aug 2022) and PS136 (May–June 2023) in the north Atlantic to the Arctic Ocean, and PS133 (Oct–Nov 2022) in the Southern Ocean. The in situ PFT data were derived from quality-controlled HPLC pigment concentrations using diagnostic pigment analysis (DPA) with updated pigment-specific weighting coefficients following Xi et al. (2023). This published data set has been used to validate satellite PFT products generated for the EU funded Copernicus Marine Service (CMEMS, https://marine.copernicus.eu/), which are derived from multi-sensor ocean color reflectance data and sea surface temperature using an empirical orthogonal function based approach (Xi et al. 2020; 2021).

KOSMOS 2023 Helgoland mesocosm study on ocean alkalinity enhancement: dissolved inorganic nutrients, chlorophyll a and suspended particulate organic matter

We conducted a mesocosm study to investigate ecosystem responses to ocean alkalinity enhancement (OAE) in the temperate waters of the German North Sea on Helgoland in spring 2023. We simulated non-CO2-equilibrated OAE via calcium hydroxide through the addition of calcium chloride and sodium hydroxide. Twelve 6 m³ mesocosms were used to simulate two scenarios: in six mesocosms we established a gradient of added alkalinity from 0 to 1250 µmol/kg in increments of 250 µmol/kg, simulating immediate (imm) dilution of alkalised waters. For the second set of six mesocosms, alkalinity was added only to the top 1 m of each mesocosm, doubling the target added alkalinity. The top layer was mixed with the untreated bottom layer after 48 hours, simulating delayed dilution of alkalised waters (del) and ultimately leading to the same alkalinity gradient as the immediate dilution treatment. This data contains water column biogeochemical variables, including dissolved inorganic nutrient concentrations (µmol/L), chlorophyll a concentrations (µg/L) and suspended particulate matter (biogenic silica, particulate organic carbon, nitrogen and phosphate; µmol/L). Nutrients, particulate organic phosphate and biogenic silica were measured spectrophotometrically (Unicam UV 300, Thermo Spectronic, USA). High-performance liquid chromatography (Thermo Scientific HPLC Ultimate 3000) was performed for chlorophyll a determination and particulate organic carbon and nitrogen were measured using an elemental analyser (Flash EA, Thermo Fisher).

Weekly water quality measurements at the Moselle river (Koblenz, Germany)

This dataset is part of a study investigating the impact of high and low flow in the central European River Moselle on water quality and cyanobacterial dynamics. It includes weekly physico-chemical data (Conductivity, pH, Oxygen), nutrients (NH4, oPO4, Si, TN, TP), carbon (TOC, DOC), Microcystis cell numbers and chlorophyll-a measurements in Koblenz (Germany).

Continuous water temperature measurements at the Moselle river (Mehring, Germany)

This dataset is part of a study investigating the impact of high and low flow in the central European River Moselle on water quality and cyanobacterial dynamics. It includes continuous (near to surface) water temperature measurements from 2021 – 2022 at Mehring (River kilometre 173, Germany).

Water quality and cyanobacterial abundance under varying hydrological conditions in the River Moselle

In this study we analysed a regulated European Central river (Moselle) over a course of two years with contrasting hydrological conditions. The year 2021 was characterized by cooler water temperatures, higher discharge and flow velocity in comparison to the warmer, low flow year 2022. To study the impacts on water quality and cyanobacterial dynamics, we were using a multidisciplinary approach: weekly in situ biochemical data, longitudinal profiles, hydrological modelling and remote sensing of chlorophyll. This dataset consists of weekly physico-chemical, nutrient and chlorophyll-a measurements in Koblenz (Germany) as well as two longitudinal profiles over a gradient of 240 river kilometre in late summer in 2021 and 2022, respectively.

Longitudinal profile of the Moselle river (Germany)

This dataset is part of a study investigating the impact of high and low flow in the central European River Moselle on water quality and cyanobacterial dynamics. It includes 23 samplings point along 240 km of the German part of the River Moselle in the respective summers of 2021 and 2022. At each sampling point water samples were taken for physico-chemical data (Conductivity, pH, Oxygen), nutrients (NH4, oPO4, Si, TN, TP), carbon (TOC, DOC), Microcystis cell numbers and chlorophyll-a measurements.

Measurements of turbidity, chlorophyll-a, suspended particulate matter and suspended particulate inorganic matter in six different study areas (in Argentina, China, France and Belgium)

Absorption coefficient for non water and CDOM, non water attenuation coefficient and particulate scattering from different study areas (in Argentina, China, France and Belgium) measured with an AC9

The HYPERMAQ dataset

The HYPERMAQ dataset contributes to a better description of marine optics in optically complex water bodies by providing optical and biogeochemical parameters for 180 sampling stations with turbidity and chlorophyll-a concentration ranging between 1 to 700 FNU and between 0.9 to 180 mg m-3 respectively. The HYPERMAQ dataset is composed of biogeochemical parameters (i.e. turbidity, suspended particulate matter, chlorophyll-a and other phytoplankton pigments concentrations), apparent optical properties (i.e. water reflectance from above water measurements) and inherent optical properties (i.e. absorption and attenuation coefficients) from six different study areas. These study areas include large estuaries (i.e. the Rio de la Plata in Argentina, the Yangtze Estuary in China and the Gironde Estuary in France), inland waters (i.e. the Spuikom in Belgium and Chascomus Lake in Argentina) and coastal waters (Belgium). All data were collected between April and September 2018.

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