The marine carbonate system in the northwest European shelf seas: an internally consistent data product (NWESDAP)

Consistent and quality-controlled data products of marine carbonate system parameters, such as the Global Ocean Data Analysis Product (GLODAP), are needed to investigate the marine carbon cycle and its variability through space and time. However, GLODAP focuses on the open ocean, limiting its utility for understanding the marine carbonate system in shelf seas. While representing only  ̴7% of the global ocean area, these areas play an important role in the global carbon cycle. The northwest European shelf (NWES) seas are of particular interest because of their high heterogeneity and expected capacity to absorb, export and bury carbon. Here, we present a new internally consistent data product for this region, the Northwest European Shelf Data Analysis Product (NWESDAP). NWESDAP includes directly measured marine carbonate system parameters (total alkalinity, dissolved inorganic carbon and pH) as well as physical and nutrient variables focusing on the NWES above 1000 m and between 43°N and 70°N. NWESDAP gathers datasets of discrete measurements from research cruises and time-series stations from throughout the water column. Data from estuaries, deltas and fjords are also included. So far, NWESDAP consists of about 18,000 inorganic carbon data points (of which c. 5,000 were already in GLODAPv2.2023) from around 500 research cruise and station datasets, merged into a consistent format. Data quality flags corresponding to quantified systematic and random uncertainties have been assigned to each dataset depending on the measurement method used and other available metadata. As GLODAP-style quality control (QC) based on deep ocean cross-over analysis is not possible in this shallow region, a secondary QC based on parameter distributions and covariances has been conducted to identify suspected erroneous data points and systematic biases in specific datasets, aiming to ensure the internal consistency of the entire product so it can be used to investigate the highly variable marine carbon cycle in the NWES seas.