Large scale hydrogeochemical and isotopic observations in the Baltic Sea system

Area of Science:

• Marine chemistry
• Geochemistry
• Environmental science

Background:

• The Baltic Sea is a semi-enclosed sea facing environmental pressures.
• Understanding its hydrogeochemistry is crucial for managing coastal ecosystems.
• Submarine groundwater discharge (SGD) is a significant but often underquantified input to coastal seas.

Purpose of the Study:

• To conduct extensive hydrogeochemical and isotopic sampling in the Baltic Sea.
• To characterize terrestrial endmembers influencing coastal water composition.
• To provide a comprehensive dataset for studying estuarine biogeochemistry and SGD.

Main Methods:

• Two research expeditions: a ~5000 km R/V Skagerak cruise (2023) and land-based sampling (2024).
• Continuous monitoring of hydrographic parameters, pH, and radon-222 (Rn) in surface waters.
• Collection and analysis of 542 discrete water column samples, 69 vertical profiles, and terrestrial endmember samples (groundwater, nearshore water, rivers).
• Analysis of short-lived radium isotopes, nutrients, dissolved organic and inorganic carbon, total dissolved nitrogen, total alkalinity, methane, and stable isotopes (δ18OH2O, δ2H2O, δ13CDIC, δ13CCO2, δ13CCH4).

Main Results:

• Detailed hydrogeochemical and isotopic profiles across the Baltic Sea.
• Characterization of various terrestrial inputs (groundwater, rivers) and their chemical signatures.
• A comprehensive dataset including continuous monitoring and discrete sample analyses.

Conclusions:

• The collected data provides a valuable resource for understanding Baltic Sea hydrogeochemistry.
• This dataset will facilitate future research on submarine groundwater discharge and estuarine biogeochemistry.
• The findings contribute to the broader knowledge of coastal marine environments and their processes.