Last modified: 2011-08-16
Abstract
In order to understand the predictive ability of global circulation models (GCMs), many palaeoclimate studies use GCMs to simulate past climates. Evaluating these simulations requires a comprehensive view of palaeoclimate from the geological record. Many present day and Quaternary studies of dinoflagellate cysts have shown that they can be used to reconstruct past sea surface parameters (SSPs). In recent decades, dinoflagellate cysts have also proved useful for palaeoenvironmental analysis and have become a key element in reconstructing palaeoceanographic change and climate dynamics. The palaeo sea surface temperatures, salinities, sea ice cover and nutrient availability are also able to be gleaned from the distribution of dinoflagellate cysts.
Dinoflagellate cyst palaeoecology is made more comprehensive for Quaternary assemblages due to the increased number of extant taxa. However, working within the constraints of the Tortonian (11.6 - 7.25 Ma), means that only a limited number of taxa are still alive today. Regardless of this, reconstructions have become more complex and representative of their time periods. The advantages of using dinoflagellate cysts as a proxy are numerous. Restrictions on data obtained from traditional micropalaeontology do not apply to dinoflagellate cysts. They are not only abundant in neritic settings and resistant to chemical dissolution, but are also extremely sensitive to small changes in nutrient availability. It is for this reason why they are excellent as a promising tool for palaeoproductivity.
In this case we present an almost complete overview of global Tortonian dinoflagellate cyst distributions. We have constructed a comprehensive ArcGIS - MS Access database for the Tortonian using over 80 published studies on dinoflagellate cysts. This technique allows the distribution of individual taxa to be studied and assessed for SSPs. The ratio of Protoperidinium:Gonyaulacoid cysts at each site allows a measure of palaeoproductivity to be assessed based on Harland (1973), linking directly to climate characteristics such as surface current patterns, upwelling systems, water mass mixing, surface winds and the global carbon cycle. While also allowing the comparison of today's extant taxa to be cross referenced and start to build up palaeoceanographic environments for the Tortonian. This database combined with ongoing modelling and terrestrial proxy work is furthering our understanding of the Tortonian climate and the ability of GCMs.
Harland, R. 1973. Dinoflagellate cysts and acritarchs from the Bearpaw Formation (upper Campanian) south of Alberta, Canada. Palaeontology, 16: 665 - 706