Geochemical Characteristics of Carbonates in Coastal Sediments from the Mediterranean Sea: Implications for Paleoenvironmental Reconstruction and Anthropogenic Carbonate Input

Abstract:

This study investigates the geochemical characteristics of carbonates (mineralogy, major/trace element composition, stable isotopes) in surface sediments (0–15 cm) from 56 sampling sites across the Mediterranean Sea. Samples were collected between 2021–2023, covering the Western, Central, and Eastern Mediterranean sub-basins. Carbonate content ranges from 12.3% to 78.6% (average=45.8%), dominated by calcite (65–92%) and minor aragonite (5–25%) and dolomite (3–10%). Stable carbon (δ¹³C) and oxygen (δ¹⁸O) isotopes range from -2.8‰ to 1.5‰ (VPDB) and -4.2‰ to 0.8‰ (VPDB), respectively, reflecting mixed biogenic and detrital carbonate sources. Trace element ratios (Sr/Ca, Mg/Ca, Mn/Ca) indicate temperature-dependent fractionation in biogenic carbonates and detrital input from riverine and aeolian sources. Anthropogenic carbonate input (e.g., concrete particles, shell fragments from aquaculture) is identified in coastal areas, characterized by elevated Sr/Ca ratios (0.015) and anomalous δ¹³C values (1.0‰). Paleoenvironmental reconstruction suggests Holocene sea surface temperature variations of 2–4°C and salinity fluctuations of 1–2 psu. This study provides a baseline for carbonate geochemistry in the Mediterranean, supporting paleoenvironmental research and monitoring of anthropogenic impacts on coastal sediment systems.