HOLOCENE HYDROLOGICAL CHANGES INFERRED FROM DINOFLAGELLATE CYST AND POLLEN ASSEMBLAGES IN ESTUARINE DEPOSITS FROM CHARLOTTE HARBOR, FLORIDA

Past changes in hydrology played a major role in the environmental development in Florida, which can be linked to the onset of the El Niño-Southern Oscillation in the late Holocene. Here we present high-resolution dinoflagellate cyst and pollen assemblage analyses on a ~4 meter sediment core from Charlotte Harbor estuary, Florida, covering the last ~8 kyrs. Estuarine sediments offer the opportunity for coupling terrestrial and marine environmental changes and correlating them to long term hydrological variability.

The dinocyst assemblages show an overall shift in species dominance from Polysphaeridium zoharyi in the older sediments, to Lingulodinium macherophorum and to Spiniferites spp. in the younger part of the core. This indicates an overall environmental change from lagoonal, stratified euryhaline waters to a more marine setting and reflects the Holocene sea-level rise. Superimposed on this general trend, major changes in the species dominance are apparent on shorter timescales. Notably between 6 and 4 kyrs BP sudden peaks in Spiniferites spp., in the interval otherwise dominated by P. zoharyi, point to more vigorous water mixing with ingression of marine waters.

Pinus dominates the pollen assemblages throughout the core. These pollen, however, are commonly overrepresented in marine deposits. Quercus decreases significantly after 6 kyrs BP, consistent with palynological studies on inland lake deposits where this change is interpreted as a shift to wetter conditions, related to increased precipitation. Fluxes of both pollen and dinocysts show a strong increase between 6 - 3.5 kyrs BP, with a sudden 5-fold peak at ~5 kyrs BP. Amongst the possible explanations for such a major change are temporary increase in runoff due to wetter conditions at this time, increasing the input of terrestrial material as well as increasing productivity of dinoflagellates in the estuary due to higher nutrient input.

This study demonstrates the benefit of combined marine-terrestrial proxies in research leading to more robust data interpretation . As both terrestrial and marine environments are influenced by changes in hydrology, estuarine deposits have great potential for reconstructing Holocene precipitation in Florida.