Carbon sources in the North Sea evaluated by means of carbon isotope tracers

• Main Authors: Böttcher, Michael Ernst, Winde, Vera
• Format: Dataset
• Language: English
• Published: PANGAEA 2016
• Subjects: Alkalinity; total; BIOACID; Biological Impacts of Ocean Acidification; DATE/TIME; DEPTH; water; Event label; Inner and Outer Eider; Isotope ratio monitoring (IRM) mass spectrometry; LATITUDE; LONGITUDE; Potentiometric titration; Salinity; Tetra Con 325 salinity and temperature probe; Transect_Eider; Transect_Hoernumtief; Transect_Norderaue; Water sample; WS; δ13C; dissolved inorganic carbon; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.858134; https://doi.org/10.1594/PANGAEA.858134

A multitracer approach is applied to assess the impact of boundary fluxes (e.g., benthic input from sedi- ments or lateral inputs from the coastline) on the acid-base buffering capacity, and overall biogeochemistry, of the North Sea. Analyses of both basin-wide observations in the North Sea and transects through tidal basins at the North-Frisian coastline, reveal that surface distributions of the d13C signature of dissolved inorganic carbon (DIC) are predominantly controlled by a balance between biological production and respiration. In particular, variability in metabolic DIC throughout stations in the well-mixed southern North Sea indi- cates the presence of an external carbon source, which is traced to the European continental coastline using naturally occurring radium isotopes (224Ra and 228Ra). 228Ra is also shown to be a highly effective tracer of North Sea total alkalinity (AT) compared to the more conventional use of salinity. Coastal inputs of meta- bolic DIC and AT are calculated on a basin-wide scale, and ratios of these inputs suggest denitrification as a primary metabolic pathway for their formation. The AT input paralleling the metabolic DIC release prevents a significant decline in pH as compared to aerobic (i.e., unbuffered) release of metabolic DIC. Finally, long- term pH trends mimic those of riverine nitrate loading, highlighting the importance of coastal AT production via denitrification in regulating pH in the southern North Sea.