Climate change, society, and pandemic disease in Roman Italy between 200 BCE and 600 CE

Records of past societies confronted with natural climate change can illuminate social responses to environmental stress and environment-disease connections, especially when locally constrained high-temporal resolution paleoclimate reconstructions are available. We present a temperature and precipitation reconstruction for ~200 BCE to ~600 CE, from a southern Italian marine sedimentary archive-the first high-resolution (~3 years) climate record from the heartland of the Roman Empire, stretching from the so-called Roman Climate Optimum to the Late Antique Little Ice Age. We document phases of instability and cooling from ~100 CE onward but more notably after ~130 CE. Pronounced cold phases between ~160 to 180 CE, ~245 to 275 CE, and after ~530 CE associate with pandemic disease, suggesting that climate stress interacted with social and biological variables. The importance of environment-disease dynamics in past civilizations underscores the need to incorporate health in risk assessments of climate change

Species-specific sensitivity of dinoflagellate cysts to aerobic degradation: A five-year natural exposure experiment

Post-depositional sedimentary dinoflagellate cyst associations undergo species-selective degradation under oxic conditions. However, there is little known about the temporal relationship between oxygen concentration and bulk dinocyst degradation rate over the time scale of several years, and if this degradation is mainly microbial or chemical. Whilst the overall sensitivity of heterotrophic dinoflagellate cysts is well documented, sensitivity differences within this group have not been studied. Here we examine the rates of cyst degradation of heterotrophic species over short temporal scales across an anoxic–oxic gradient. Sediment with a known dinoflagellate cyst association largely dominated by heterotrophic dinoflagellates, were connected to trap arrays at two different locations, Cap Blanc (NW Africa) and Gotland Basin (central Baltic Sea) and exposed to four different ambient oxygen concentrations representing a complete oxic gradient from 5.1 mL/L to sulphate bearing anoxic waters. Two treatments of either gauze or dialyse membrane in triplicate were established to investigate the effects of chemical or bacterial degradation. Cyst loss was significant at oxic settings, rapidly occurring within the first year of exposure (32%) whereas no significant degradation was observed for suboxic and anoxic exposures. Compiling the degradation rates of individual species under the different exposure settings reveals an overall species sensitivity ranking amongst cysts of heterotrophic species. Species of average resistance: Bitectatodinium spongium, Brigantedinium spp., Echinidinium spp., Echinidinium aculeatum, and Gymnodinium trapeziforme. Species more resistant than average: Stelladinium robustum and Trinovantedinium applanatum. We observe that oxic degradation of cysts of heterotrophic dinoflagellates is fast and selective with maximal cyst association changes during the first year of oxic exposure. These aspects have to be taken into account in palaeoenvironmental and palaeoceanographic reconstructions where bottom/pore water conditions of the upper sediments are oxygenated

Aerobic degradation of organic carbon inferred from dinoflagellate cyst decomposition in Southern Ocean sediments

Organic carbon (OC) burial is an important process influencing atmospheric CO2 concentration and global climate change; therefore it is essential to obtain information on the factors determining its preservation. The Southern Ocean (SO) is believed to play an important role in sequestering CO2 from the atmosphere via burial of OC. Here we investigate the degradation of organic-walled dinoflagellate cysts (dinocysts) in two short cores from the SO to obtain information on the factors influencing OC preservation. On the basis of the calculated degradation index kt, we conclude that both cores are affected by species-selective aerobic degradation of dinocysts. Further, we calculate a degradation constant k using oxygen exposure time derived from the ages of our cores. The constant k displays a strong relationship with pore-water O2, suggesting that decomposition of OC is dependent on both the bottom- and pore-water O2 concentrations

Postdepositional aerobic and anaerobic particulate organic matter degradation succession reflected by dinoflagellate cysts: The Madeira Abyssal Plain revisited

We report on the succession of selective degradation of dinoflagellate cyst species that can be considered representative for discrete particulate organic matter (POM) classes of different degradability. The effects of anaerobic and aerobic degradation as well as bioturbation in a natural setting are documented in high resolution by means of palynological and geochemical analyses on Madeira Abyssal Plain A- and F-turbidites. These turbidites are unique as their initial ungraded sediments are affected by a downward penetrating oxydation front. Geochemical analyses document the presence of an active downward penetrating oxidation front in the A turbidite, and a palaeo-oxidation front in the F-turbidite. In this latter turbidite, several zones can be distinguished from top to bottom: an oxidised bioturbated zone, an oxidised but not-bioturbated zone, a visible paleooxidation front, and a narrow nitrogenous zone overlying unoxidised sediments. We are the first to report that anaerobic degradation within the nitrogenous zones in both turbidites affects cysts of some heterotrophic dinoflagellates. The cyst species affected (Echinidinium aculeatum, Echinidinium spp., cysts of Protoperidinium monospinum and Brigantedinium spp.) exponentially decrease in this zone that is further characterised by a strong decrease in sulphur content due to sulphide oxidation. Degradation rates are different for each species. These cysts of heterotrophic dinoflagellates consist of a nitrogen-rich glycan in contrast to the cellulosic cysts walls of phototrophic dinoflagellates. Therefore, our observation supports the hypothesis that the quality of organic matter plays an important role in OM degradation in oxygen deficient environments with N-rich OM being more labile than other components in these environments. All heterotrophic species are strongly affected by aerobic degradation with their cyst concentrations exponentially decreasing with increasing oxygen exposure. Degradation rates vary between species and range von highly degradable to slightly degradable. Most strongly affected are cysts of Protoperidinium monospinum, Brigantedinium spp., and Echinidinium spp. Increasingly less affected are: Selenopemphix nephroides, Selenopemphix quanta, other Peridinioids and Echinidinium aculeatum. An effect of aerobic degradation on photosynthetic species could only be observed for Pentapharsodinium dalei. All Impagidinium species appeared to be resistant to aerobic degradation. Despite having analysed only a limited number of samples in the bioturbated zone of the F-turbidite, we have strong indications that the bioturbation can lead to the degradation of POM that is not affected by aerobic degradation alone. The cyst species Spiniferites ramosus, Impagidinium paradoxum, Lingulodinium machaerophorum, Nematosphaeropsis labyrinthus, Spiniferites spp., Impagidinium sphaericum, Spiniferites elongates and Spiniferites mirabilis do not show concentration changes in the non-bioturbated aerobic sediments but their concentrations are considerably decreased in the bioturbated part of the F-turbidite. This supports the hypothesis that bioturbation can increase the degradation of POM by e.g. increasing oxygen exposure time and/or by an alteration of aerobic and anaerobic conditions. We furthermore show that the degradation rates of POM components represented by individual cyst species differ between zones with different redox and biological conditions. This implies that POM degradation reaction rate coefficients are environment dependent. Our observation that dinoflagellate cyst species have different degradation rates ranging from extremely labile to extremely recalcitrant within the individual redox/bioturbation zones supports the hypothesis that cyst walls have a species specific molecular structure. Our results support continuum models of organic matter degradation that assume a continuous distribution of organic matter reactivity

Are the Kimmeridge Clay deposits affected by “burn-down” events? Palynological and geochemical studies on a 1 metre long section from the Upper Kimmeridge Clay Formation (Dorset, UK)

Two independent analytical approaches, palynology and inorganic geochemistry, were applied to identify potential oxygen “burn-down” events in the Late Jurassic Kimmeridge Clay Formation (KCF). The KCF interval of the rotunda ammonite zone, spanning 121.82–122.72 m depth was sampled from the Swanworth Quarry 1 borehole (Dorset, UK) at 2.5–5.0 cm resolution. Samples were analysed for total organic carbon (TOC), concentrations of elements that are known to be productivity- and/or nutrient-related (e.g. Cu, P), detrital (e.g. Al, Ti, Zr) and redox-sensitive/sulphide-forming (e.g. V, Mo, Fe, Mn, S), and palynofacies components including analysis of organic-walled dinoflagellate cysts (dinocysts) on a species level.The TOC contents generally exceed 2 wt.%, with a maximum of 8.8 wt.% at 122.37 cm depth and elevated values in the central part of the investigated interval. This interval of relatively higher TOC values correlates well with the maximum recovery of marine palynomorphs and low Al values, suggesting that the TOC is primarily of marine organic matter (OM).Changes in V/Al, Mo/Al, Fe/Al, Mn/Al and S patterns at 122.37 m depth mark a shift from anoxic conditions in the lower part of the studied interval to more oxic conditions in its upper part. Such a shift could explain the relatively high TOC and marine palynomorph concentrations in the lower part of the studied interval as a result of better preservation, and the subsequent decrease as an effect of a post-depositional “burn-down”, i.e. OM oxidation. As the amount of marine palynomorphs and TOC content diminishes from the middle part of the section upwards, species-specific changes in dinocyst assemblages can be observed. In particular, concentrations of Circulodinium spp., Cyclonephelium spp., Sirmiodinium grossi, Senoniasphaera jurassica and Systematophora spp. decrease rapidly in comparison to other species, such as Glossodinium dimorphum and Cribroperidinium sp. 1, which may suggest selective degradation of dinocysts due to oxidation.We suggest that post-depositional oxygenation of bottom and pore waters within the sediment was most probably the cause for decreasing TOC values and reduced recovery of marine palynomorphs towards the top of the studied interval in comparison to high TOC and marine palynomorph values in the central part of the studied interval due to anoxic conditions.<br/

The composition and diversity of dinosporin in species of the Apectodinium complex (Dinoflagellata)

Organic-walled dinoflagellate cysts, produced as a result of sexual reproduction, are important tools for studies on recent and past environments. Additionally, the organic-walled cysts can be used as proxies for understanding the composition and chemical transformations of marine kerogen, the largest global organic carbon pool. However, any usage of dinoflagellate cysts in this manner is predicated on an understanding of the composition and transformations of this potential proxy. Dinoflagellate cyst walls are composed of “dinosporin”, a refractory biomacromolecule that probably represents a suite of chemically distinct biopolymers. In order to investigate both the nature of dinosporin and the extent to which the composition of this biomacromolecule may differ between dinoflagellate cyst taxa, we analyzed cyst species from the genus Apectodinium. The species defined within this genus are visually similar with several seeming to represent end-members along a continuum of morphological variation. Micro-Fourier transform infrared (FTIR) analysis was performed on three of these morphospecies (identified visually as A. paniculatum, A. parvum and A. augustum) from two regionally distinct samples. The analyses showed consistent patterns with clear differences between the species. The dinosporin of A. paniculatum closely resembles cellulose and is rich in ether bonds (Csingle bondO), while the dinosporin of A. augustum contains more carboxyl (COOH) groups. A. parvum appears intermediate in many respects, despite representing an end-member in terms of morphology. These differences are consistent regardless of the regional setting or post-depositional conditions, and strongly suggest that the original cyst wall composition of the species differed when the cysts were formed. These data are the first to clearly show differences in cyst wall composition between species of the same genus and indicate that the chemical diversity of dinosporins is greater than previously thought

Differences in the chemical composition of organic-walled dinoflagellate resting cysts from phototrophic and heterotrophic dinoflagellates

Dinoflagellates constitute a large proportion of the planktonic biomass from marine to freshwater environments. Some species produce a preservable organic-walled resting cyst (dinocyst) during the sexual phase of their life cycle that is an important link between the organisms, the environment in which their parent motile theca grew, and the sedimentary record. Despite their abundance and widespread usage as proxy indicators for environmental conditions, there is a lack of knowledge regarding the dinocyst wall chemical composition. It is likely that numerous factors, including phylogeny and life strategy, determine the cyst wall chemistry. However, the extent to which this composition varies based on inherent (phylogenetic) or variable (ecological) factors has not been studied. To address this, we used micro-Fourier transform infrared (FTIR) spectroscopy to analyze nine cyst species produced by either phototrophic or heterotrophic dinoflagellates from the extant orders Gonyaulacales, Gymnodiniales and Peridiniales. Based on the presence of characteristic functional groups, two significantly different cyst wall compositions are observed that correspond to the dinoflagellate's nutritional strategy. The dinocyst wall compositions analyzed appeared carbohydrate-based, but the cyst wall produced by phototrophic dinoflagellates suggested a cellulose-like glucan, while heterotrophic forms produced a nitrogen-rich glycan. This constitutes the first empirical evidence nutritional strategy is related to different dinocyst wall chemistries. Our results indicated phylogeny was less important for predicting composition than the nutritional strategy of the dinoflagellate, suggesting potential for cyst wall chemistry to infer past nutritional strategies of extinct taxa preserved in the sedimentary record