PALYNOLOGICAL VARIATION IN A BELIZEAN PEAT CORE: EVIDENCE OF CLIMATE CHANGE OVER THE PAST ~8000 YEARS

Pollen and stable isotope data are presented from a 780 cm core of mangrove peat taken from Twin Cays, Belize. Twin Cays is ~12 km off the mainland coast of Belize and the modern vegetation is dominated by Rhizophora mangle (Red mangrove). Accelerator Mass Spectrometry (AMS) radiocarbon dates measured on macrofossils from the core have determined that the base represents ~8,000 ¹⁴C years BP. Although pollen from R. mangle is the most abundant (20 to ~95%) type in the samples analyzed (present in 90% of the samples) other pollen types from mangrove species are also present, including Avicennia germinans (Black mangrove), Laguncularia racemosa (White mangrove) and Conocarpus erectus (Buttonwood). Pollen grains from Myrsinaceae, grass, and Pinus sp. are also present in the core. Pollen from Pinus sp. increased in abundance over the past ~3,300 ¹⁴C years BP (representing 8 to 47% of the total pollen), with the exception of ~1,300 14C years BP where it only reached 2% of the total pollen. Pollen from A. germinans (a low pollen producer) peaked (17%, 22%, and 17% of the total pollen) at a number of points during the top 250 cm of the core (0, 10, and 250 cm), representing the last ~4,500 ¹⁴C years. These peaks are taken to imply significantly higher salinity levels in the pore water and more elevated topography. Pollen from L. racemosa and C. erectus are also poor pollen producers and as a result, their pollen is sparse throughout most of this core. However, pollen from these species are present in a greater number of samples prior to ~5,000 ¹⁴C years BP. Myrsinaceae pollen is consistently present from ~5,500 to 1,000 ¹⁴C years BP, reaching up to ~30% of the total pollen. Grass pollen is also present at points throughout this core, but is not very abundant (up to 30%). Sub-fossil leaves from R. mangle were present throughout the core. Carbon and nitrogen stable isotope analyses were conducted on these leaves and demonstrated ?¹³C values between –27.7‰ to –22.2‰ and ?¹⁵N values between –3.5‰ and +2.4‰. Based on stable isotope measurements of modern R. mangle leaves and taphonomic data, the ?¹³C and ?¹⁵N data derived from the core are taken to imply that the stand structure and nutrient dynamics in the mangroves at the site has altered during the last ~8,000 years. The pollen and stable isotope data imply that environmental changes occurred during the Holocene that prompted eco-physiological changes in mangroves at the site.