Impacts of Climate Change on Blue Carbon Stocks and Fluxes in Mangrove Forests

Mangroves store blue carbon (693 Mg C-ORG ha(-1)) disproportionate to their small area, mainly (74%) in deep soil horizons. Global stock estimates for mangroves (5.23-8.63 Pg C-ORG) are equivalent to 15-24% of those in the tropical coastal ocean. Carbon burial in mangrove soils averages 184 g C-ORG m(-2) a(-1) with global estimates (9.6-15.8 Tg C-ORG a(-1)) reflecting their importance in carbon sequestration. Extreme weather events result in carbon stock losses and declines in carbon cycling and export. Increased frequency and ferocity of storms result in increasingly negative responses with increasing strength. Increasing temperatures result in increases in carbon stocks and cycling up to a critical threshold, while positive/negative responses will likely result from increases/decreases in rainfall. Forest responses to sea-level rise (SLR) and rising CO2 are species- and site-specific and complex due to interactive effects with other drivers (e.g., temperature, salinity). The SLR critical threshold is approximate to 6 mm a(-1) indicating survival only under very low-low CO2 emissions scenarios. Under low coastal squeeze, landward migration could result in sequestration and CO2 losses of 1.5 and -1.1 Pg C with net stock gains and losses (-0.3 to +0.5 Pg C) and CO2 losses (-3.4 Pg) under high coastal squeeze.