Dissolved nitric oxide concentrations and other parameters measured in the Lower Elbe Estuary and the Hamburg Port Area during the RV Ludwig Prandtl Cruise in July 2021

The Elbe River's high nutrient loads and phytoplankton biomass contribute to the complex nutrient turnover processes in the Elbe Estuary, especially within the Port of Hamburg. This campaign aims to investigate the nitrogen turnover processes and nitrous oxide and nitric oxide production in the Elbe Estuary and the Port of Hamburg from 26 to 29 July 2021. Surface water samples were collected on board the RV Ludwig Prandtl using a FerryBox flow-through system. The system, which draws water from approximately 2 meters below the surface through a membrane pump, continuously measured in situ biogeochemical parameters, including dissolved oxygen, pH, salinity, and water temperature. Discrete water samples were collected every 20 minutes for nutrient analysis, chlorophyll a, and dissolved nitric oxide (NO) following established collection, preservation, and storage protocols (Schulz et al., 2022; Norbisrath et al., 2022). Furthermore, nitrous oxide (N2O) concentrations were measured continuously using laser-based off-axis integrated cavity output spectroscopy (OA_ICOS) coupled with a water/gas equilibrator. Additionally, wind speeds at a height of 10 meters were recorded using a MaxiMet GMX600 weather station. Triplicate NO samples were analyzed within 20 minutes of collection, adhering to the method outlined by Lutterbeck and Bange (2015).