Marine paleo-environmental change
Dinocyst assemblage analyses, in combination with other environmental proxies have resulted in the development of a model that prescribes the ecological niche of specific dinocyst taxa on a generalized shelf. Many shelf taxa have very specialized niche requirements, likely related to physiological parameters in the surface waters, such as nutrient supply, temperature, salinity, and fresh-water input. Because of this high sensitivity, dinocyst assemblages are good tracers of changes in the physical properties of the surface waters.
Schematic representations of continental shelfs with the different environmental niches, a schematic dinocyst diversity profile along the shelf and the associated dinocyst assemblages along a hypothetical shelf. Figures courtesy of J. Pross, modified from Sluijs et al., Earth-Science reviews 68, p281, 2005
The Arctic Coring Expedition (ACEX) provided important information to determine characteristic marine dinocysts that were tolerant to low-salinity conditions of the surface waters. Palynological samples from ACEX cores dating back to the early-middle Eocene transition, contained high abundance of Azolla spores. Ample information suggest that the Azolla fresh-water ferns were growing in situ in the Arctic Ocean, which prescribes that the surface layer of the Arctic Ocean must have been fresh or slightly brackish. Basically, the only remaining dinocysts present in these samples were those of the genera Senegalinium and Phthanoperidinium. Outside of the Azolla strata, normal saline marine dinocysts were found. Also in characteristic near-shore environments with high riverine input we find abundance of Senegalinium spp. in the Eocene. This leads to the observation that these species can cope with high fresh-water input.
Dinocyst assemblages in the Azolla interval. The dinocyst genera that co-occur with the Azolla occurrences in the Arctic Ocean are Senegalinium and Phthanoperidinium. From Barke et al., Geology 39 no. 5, pp427-430, 2011.
A classic example of a good temperature indicator in Paleogene sediments is Svalbardella. This species is abundant in Eocene Northern high latitudes, and only crosses the equator to Southern high latitudes in the Oi-1b glaciation. Apectodinium spp. dominates strata from the Paleocene Eocene Thermal Maximum worldwide. Before the PETM, this genus is generally only found in high abundance in the Tethyan Ocean. The poleward migration of this genus suggests it is a clear indicator of the warmth that characterizes the PETM. Many sections studied from the K-Pg boundary revealed a distinct pattern of a short cold-water dinocyst species migration equator-ward directly post-impact, followed by a longer period of warm water species migrating equatorward, consistent with the inferred climatological evolution directly after a bolide impact of short cooling followed by longer warming.
Dinoflagellate migrations across the Cretaceous-Paleogene Boundary as a response to the rapid climatological response to the bolide impact in what is now Yucatan. From Brinkhuis et al., Palaeo3 141, p67, 1998
Dinocysts provide a sensitive tool to reconstruct paleoproductivity in the surface ocean. Dinocyst assemblages can be categorized in two morphological distinct groups: those with a Gonyaulacoid (g) tabulation pattern and those with Peridinioid (p) tabulation. In the present-day oceans, Peridinioid dinocysts are exclusively produced by heterotrophic dinoflagellates, while Gonyaulacoid dinocysts are derived from autotrophic dinoflagellates. The ratio of p over g cysts have proven a good tracer for paleo-productivity for instance in the Mediterranean Sea.
Paleoproductivity reconstructions in the Arabian Sea upwelling zone from multiple proxies, including dinoflagellate cysts. From Reichart and Brinkhuis, marine micropalaeontology 49, p 303, 2003
Sea level change
A good example of sea level change reconstructions from dinocysts comes from the Paleocene-Eocene Thermal Maximum (PETM), where dinocysts revealed in a multidisciplinary effort a global sea level rise starting at or slightly before the carbon isotope excursion of the PETM.
Sequence stratigraphic correlation of a set of late Paleocene-early Eocene sections scattered over the globe. From Sluijs et al., Paleoceanography 23, PA4216, 2008
Indices for stratification of the water column can be derived from dinocyst assemblage analyses. In the Arabian Sea, the presence of typical lagoonal dinocysts in an open marine setting, together with inorganic geochemical analyses suggest seasonal hyperstratification of the surface waters. The wind-induced stratification causes typical lagoonal surface water characteristics to be extended out into the open ocean.
Episodic hyperstratification of Arabian Sea surface waters allows lagoonal dinocyst species P. zoharii to migrate to distal oceanic settings. From Reichart et al., Paleoceanography 19, PA2013, 2004
The model for dinocyst distributions on the shelf can be amended with use of the terrestrial palynomorph abundance in the samples. The abundance of terrestrial palynomorphs relative to those with a marine origin is expected to decrease from distal sites to more proximal settings. This independent line of evidence may help reconstructing coastal proximity, and links terrestrial and marine paleoenvironmental change.
In the Paleogene Southern Ocean, dinocyst assemblage compositions are dictated by the prevailing ocean current regime: Endemic Antarctic dinocyst species dominate assemblages in regions where ocean circulation models predict Antarctic-derived surface currents. This is a good example of the sensitivity of dinoflagellate cyst assemblage compositions and physical parameters of the surface waters.
Middle Eocene biogeographic chart showing all outcrops and drill cores that contained dinocysts. Colors indicate the relative abundance of endemic dinocysts, with absence in red to 100% in blue. Overlain is the simplified output of ocean circulation models that predict ocean surface current configuration in the Eocene tectonic configuration. Note that those regions with high relative abundance of endemic dinocysts are restricted to regions with Antarctic-derived surface currents. From Bijl et al., Paleoceanography 26, PA1202, 2011
The last decades have seen the birth of many organic geochemical tools to reconstruct paleoenvironmental change with. The proxies for sea surface temperature (TEX86, UK’37) are particularly useful in paleoclimate change reconstructions, especially at high latitudes where conventional paleo-temperature proxies based on carbonate geochemistry can often not be applied. Novel biomarkers were recognized for bacteria that need both anoxic water conditions and light to photosynthesize. The presence of these biomarkers (isorenieratane) in the sediments thus requires paleo-environmental settings with anoxia reaching the photic zone at time of deposition.
An example of our multidisciplinary research. We were able to reconstruct paleo-CO2 and temperature reconstructions and biotic response from a single sediment core covering the Middle Eocene Climatic Optimum from the southwest Pacific Ocean using two organic paleo-temperature proxies, one inorganic paleo-temperature proxy, an organic geochemical proxy for atmospheric CO2 and dinoflagellate cyst assemblages. From Bijl et al., Science 330, p819, 2010
Terrestrial paleo-environmental change
The LPP has an expertise in terrestrial palynomorph analyses for paleo-environmental reconstructions, for large parts of the geologic record. From the Paleozoic to the Holocene, terrestrial palynomorphs provide good tools to reconstruct continental paleoenvironmental change, such as precipitation and temperature.
Pollen assemblages as indicator of paleoenvironmental change across the most dramatic global extinction event at the Permian-Triassic Boundary. Looy et al., PNAS 98, no. 14, pp7879-7883, 2001.
Macrofloral remains were studied intensively in the past at LPP. The “Earth Sciences” Building of Utrecht University features a nice museum where a selection of the macroflora collection is displayed. Besides leaves, we have gained the expertise to study wood fragments through years of research, from the entire geologic record.
Terrestrial organic geochemical proxies
The recent years have seen the birth of many organic geochemical proxies for terrestrial paleoenvironmental change with also a large coupling to the marine realm. The MBT-CBT proxy was developed where the molecular structure of the remains of soil bacterial membrane lipids change as a function of air temperature and pH. Another important biomarker proxy from organic geochemistry is the BIT index, which provides a measure for soil organic matter input relative to marine organic matter production in a marine sediment core. This provides tool that is independent of the pollen-spores over dinocysts to reconstruct coastal proximity. Another important group of terrestrial organic geochemical compounds are the leaf waxes: n-alkanes. Carbon isotopes of those compounds are directly coupled to the atmospheric carbon reservoir and hence provide a tool to qualitatively assess changes in the amount of atmospheric CO2. We have the expertise and the equipment to apply these tools on sediments.