Marine palynology and its use for studying nearshore environments

Abstract

Palynology is the study of microfossils composed of highly resistant organic matter called palynomorphs. In the sediments of neritic environments, palynomorphs may include cysts of dinoflagellates, phycoma of prasinophytes, organic linings of benthic foraminifers and thecamoebians, in addition to inputs from the terrestrial vegetation (pollen grains and spores) or the freshwater biota (chlorococcales). Marine palynology is thus used for characterizing the type of sedimentary environment, identifying the source of organic matter in the sediment, and weighting the relative importance of fluvial and pelagic inputs. Among marine palynomorphs, dinoflagellate cysts or dinocysts usually dominate the assemblages. Dinocysts comprise phototrophic and heterotrophic taxa and occur in almost all aquatic environments. Along the continental margins, assemblages are usually characterized by high species diversity and cyst concentrations reaching up to 105 cysts cm-3. The distribution of dinocyst assemblages in sediments shows latitudinal patterns in addition to onshore to offshore gradients. Multivariate analyses illustrate close relationships between dinocyst assemblages and sea-surface parameters such as sea-ice cover, salinity, temperature, seasonality and productivity. Transfer functions developed from dinocysts permit the reconstruction of sea- surface temperature and salinity and the evaluation of past productivity, with applications dealing with climate changes and eutrophication. Dinocysts are also used for the study of harmful algal blooms since a few taxa relate to toxic species.