Accumulation of Carbonates Contributes to Coastal Vegetated Ecosystems Keeping Pace With Sea Level Rise in an Arid Region (Arabian Peninsula)

Anthropogenic sea level rise (SLR) presents one of the greatest risks to human lives and infrastructures. Coastal vegetated ecosystems, that is, tidal marshes, seagrass meadows, and mangrove forests, elevate the seabed through soil accretion, providing a natural coastline protection against SLR. The soil accretion of these ecosystems has never been assessed in hot desert climate regions, where water runoff is negligible. However, tropical marine ecosystems are areas of intense calcification that may constitute an important source of sediment supporting seabed elevation, compensating for the lack of terrestrial inputs. We estimated the long‐term (14C‐centennial) and short‐term (210Pb‐20th century) soil accretion rates (SARs) and inorganic carbon (Cinorg) burial in coastal vegetated ecosystems of the Saudi coasts of the central Red Sea and the Arabian Gulf. Short‐term SARs (±SE) in mangroves of the Red Sea (0.27 ± 0.22 cm/year) were twofold the SLR for that region since 1925 (0.13 cm/year). In the Arabian Gulf, only mangrove forest SAR is equivalent to local SLR estimates for the period 1979–2007 (0.21 ± 0.09 compared to 0.22 ± 0.05 cm/year, respectively). Long‐term SARs are comparable or higher than the global estimates of SLR for the late Holocene (0.01 cm/year). In all habitats of the Red Sea and Arabian Gulf, SARs are supported by high carbonate accretion rates, comprising 40% to 60% of the soil volume. Further studies on the role of carbonates in coastal vegetated ecosystems are required to understand their role in adaptation to SLR. Plain Language Summary Marine wetlands: mangroves, salt‐marshes, and seagrass beds protect the coast against the human‐induced sea level rise worldwide. They trap sediment, and this way elevated the seabeds, at paces equivalent to sea level rise. The amount of sediment trapped is generally linked to riverine inputs and surface runoff. However, in arid tropical regions, such as the Arabian peninsula, this source of sediment to the sea is almost unexistant. We studied the rate of seabed elevation in wetlands of the Red Sea and Arabian Gulf. We found that Mangrove and Seagrass (Red Sea only) seabed elevation rates are equivalent to sea level rise rates of the twentieth century, due to greenhouse gas emissions. This is possible because of accumulation of carbonate sediment coming from coral reefs weathering, replacing terrestrial inputs in the tropical arid area. Our study strengthens the relevance of wetlands to human societie