Quantifying organic carbon burial rates and stocks in seagrass meadow sediments influenced by sargassum-brown tides

Seagrass meadow sediments are efficient organic carbon (C-org) sinks and can store C-org for hundreds of years. The temporal variation of C-org burial rates and stocks over recent decades at nearshore seagrass meadows in the Puerto Morelos Reef Lagoon, Mexico, was evaluated in Pb-210-dated sediment cores from nearshore meadows dominated by Thalassia testudinum. The sediments were predominantly sandy (>52% sand) rich in carbonate grains (11.8-12.5% C-inorg) with minor C-org (0.24-1.12%) and N-org (0.02-0.13%) concentrations. The C:N ratio (9.4-13.0) indicated that marine-derived C-org was prevalent. C-org stocks in the upper 30 cm sediment were 15.9 +/- 3.0-24.8 +/- 4.6 Mg ha(-1). Sedimentary mass accumulation rates (MAR) (0.7-1.5 g cm(-2) yr(-1)) were higher than those previously recorded in seagrass sediments from the reef lagoon and other parts of the world. The highest MAR values, recorded in 2015 (+/- 0.13) and 2018 (+/- 0.03), coincided with the peak sargassum influx years. MAR and C-org burial rates (11.4-133 g m(-2) yr(-1)) were correlated (r(2) = 0.76), indicating that the massive influxes of sargassum have accelerated C-org burial rates in the region since 2015. This study marks the initial evaluation of the interaction between the massive influx of sargassum, MAR, and C-org burial rates in seagrass sediments, potentially laying the groundwork for future extended monitoring initiatives.