Seasonal and regional dynamics of carbonate chemistry and buffering capacity in contrasting marine systems: The Northeastern Mediterranean and The Sea of Marmara

Date

2025-8

Author

Alemdar, Polen

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This thesis investigates seasonal and spatial variability in carbonate system dynamics and buffering capacity across two contrasting semi enclosed Turkish seas: the oligotrophic Northeastern Mediterranean and the eutrophic Sea of Marmara. Data were collected in winter and summer on research cruises conducted in 2022–2023. High quality multi-index measurements included total alkalinity (TA), nutrients, and spectrophotometric pH. Derived carbonate system parameters were calculated with PyCO2SYS, and a standardized, layer-based approach was applied to reflect regional hydrography and vertical structure. The Sea of Marmara showed high TA, often above 2700 μmol kg⁻¹, together with elevated dissolved inorganic carbon (DIC) below the halocline due to respiration and weak ventilation. Revelle factors were high, vertical gradients in pH and aragonite saturation state were strong, and hypoxia was present in sub halocline and deep waters. In the Northeastern Mediterranean, TA and DIC were lower and more stable. Revelle factors were lower, and buffering was stronger in surface and intermediate layers, with only modest sensitivity increases at depth. Advanced indices added diagnostic value beyond the Revelle factor. In the Sea of Marmara, βDIC and γDIC were highest below the halocline, identifying where small DIC additions most strongly raise the partial pressure of carbon dioxide (pCO₂) and lower pH. γAlk and ωAlk indicated greater benefit of marginal TA gains at depth. ωDIC isolated saturation state sensitivity to carbon loading in respiration dominated layers. In the Northeastern Mediterranean, the Revelle factor captured first order seasonal shifts in well mixed winter layers, while the advanced indices flagged narrow coastal and subsurface windows of rising sensitivity. These results provide the first multi seasonal, multi-index baseline for Turkish seas. They show that eutrophication, stratification, and ventilation control local acidification risk and that advanced buffer indices sharpen process attribution. The study supports monitoring that couples carbonate chemistry with oxygen and nutrients and guides management toward nutrient reduction and protection of sub halocline habitats where buffering is weakest.

Subject Keywords

Carbonate System, Buffering Capacity, Revelle Factor, Ocean Acidification, Sea of Marmara, Northeastern Mediterranean Sea, Advanced Buffer Indices

URI

https://hdl.handle.net/11511/118238

Collections

Graduate School of Marine Sciences, Thesis