Organic carbon (OC) stored in the sediments of seagrass meadows has been considered a globally significant OC reservoir. However, the sparsity and regional bias of studies on long-term OC accumulation in coastal sediments have limited reliable estimation of the capacity of seagrass meadows as a global OC sink. We evaluated the amount and accumulation rate of OC in sediment of seagrass meadows and adjacent areas in East and Southeast Asia. In temperate sites, the average OC concentration in the top 30 cm of sediment was higher in seagrass meadows (780-1080 μmol g . Carbon isotope mass balancing suggested that the contribution of seagrass-derived carbon to OC stored in sediments was often relatively minor (temperate: 10-40%; subtropical: 35-82%; tropical: 4-34%) and correlated to the habitat type, being particularly low in estuarine habitats. Stock of OC in the top meter of sediment of all the studied meadows ranged from 38 to 120 Mg ha À1 . The sediment accumulation rates were estimated by radiocarbon dating of six selected cores (0.32-1.34 mm yr À1). The long-term OC accumulation rates calculated from the sediment accumulation rate and the top 30 cm average OC concentration for the seagrass meadows (24-101 kg ha À1 yr À1 ) were considerably lower than the OC accumulation rates previously reported for Mediterranean Posidonia oceanica meadows (580 kg ha À1 yr À1 on average). Current estimates for the global carbon sink capacity of seagrass meadows, which rely largely on Mediterranean studies, may be considerable overestimations.

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The handy and inexpensive drilling method using SCUBA tanks was developed specifically for submerged massive coral drilling, which is an effective technique for its annual bands research. All required equipment for 10 m drilling can be packed up into two suitcases, except for the SCUBA tank. This carries the advantage that researchers can bring full equipment in carry-on luggage and can obtain samples quickly at inconvenient or inaccessible locations. A field experiment was successfully operated to obtain 1 m coral cores within 1 hour at a depth of 17 m below sea level.