Rhodolith beds as long-term carbon reservoirs: evidence from the Menorca Channel, Silvia de Juan

Rhodolith beds as long-term carbon reservoirs: evidence from the Menorca Channel Silvia de Juan Mohan 30/10/2026 Rhodolith and maërl beds form extensive biogenic carbonate deposits that can persist over millennial timescales, yet their role in long-term carbon storage remains poorly quantified. While most blue carbon research has focused on vegetated coastal ecosystems, calcifying algal habitats such as rhodolith beds may represent an overlooked component of marine carbon reservoirs. This study evaluates organic carbon storage in a well-preserved rhodolith bed located in the Menorca Channel (western Mediterranean), one of the largest rhodolith deposits in the region. Sediment cores (1.4–2.8 m length, 9 cm diameter) were collected at 60–80 m depth and analyzed for sediment composition, organic carbon content, and depositional history. Organic carbon was measured every 10 cm within the upper 50 cm of sediment and averaged 0.57% (±0.22), remaining relatively uniform with depth. Estimated carbon stocks reach ~32 Mg C ha⁻¹ within the upper 50 cm of sediment. Although sediment accretion is extremely slow (median 8.54 cm kyr⁻¹), these deposits allow the gradual accumulation and preservation of organic carbon over millennial timescales. Our results highlight Mediterranean rhodolith beds as persistent carbon reservoirs and emphasize the importance of protecting these slow-forming habitats to maintain long-term marine carbon storage.