The impact of sampling depths on quantification of soil organic carbon stock in mangrove environments

• Mangrove soils can be peat, muck, organic-rich sediments or mineral sediments. • Shallow depth of sampling makes soil organic carbon (SOC) stock data unreliable. • Most studies (∼69 %) underestimate SOC stock in mangrove environments. • Mangroves store > 49 % of their SOC stock in deeper (>1 m) horizons. • Sampling at least to 2 m will result in robust SOC stock estimates. Mangroves are among the most productive blue carbon ecosystems, storing large quantities of organic carbon particularly in soils for millennia amidst of the global sea-level change. Despite the many attempts during the last decade to quantify soil organic carbon (SOC) stock of mangroves worldwide, most data remain highly ambiguous because of shallow depth of sampling (<1 m). Using the data extracted from previous studies, here we discuss the importance of sampling deep (>1 m) soil layers for SOC stock estimations. Carbon storage in deeper sediment layers varies notably among mangroves that occur in carbonate and terrigenous sedimentary landscapes. The organic soil material (OSM) layer of mangroves in terrigenous landscapes is often restricted to a depth < 1 m. The mineral soil material (MSM) layer that dominates these profiles may extend beyond 3 m in depth. As deep mangrove sediment layers (>1 m) can harbour SOC stocks ranging from 542.60 ± 43.92 to 1885.72 ± 64.5 Mg OC ha −1 , sampling only the first metre of the profile can greatly underestimate their C storage potential and ecosystem services. We also find that soil depth distribution functions as a useful tool in predicting deep SOC stock in mangrove environments, particularly when many studies do not sample the entire MSM layer.