TRACING ORIGIN AND COLLAPSE OF HOLOCENE BENTHIC BASELINE COMMUNITIES IN THE NORTHERN ADRIATIC SEA

The shallow northern Adriatic Sea has a long history of anthropogenic impacts that reaches back many centuries. While the effects of eutrophication, overfishing, pollution, and trawling over recent decades have been extensively studied, the major ecological turnovers during the Holocene as a whole remain poorly explored. In this study, we reconstruct ecological baselines defining benthic ecosystem composition prior to major anthropogenic changes at four stations characterized by low sedimentation and millennial-scale time averaging of molluscan assemblages. We discriminate between natural and anthropogenic drivers based on (1) stratigraphic changes in the composition of molluscan communities observed in sediment cores and (2) changes in concentrations of heavy metals, pollutants, and organic enrichment. The four 1.5-m long sediment cores reach back to the Pleistocene–Holocene boundary, allowing for a stratigraphic distinction of the major sea-level phases of the Holocene. During the transgressive phase and maximum flooding, sea-level and establishment of the modern circulation pattern determined the development of benthic communities in shallow-water, vegetated habitats with epifaunal biostromes and, in deeper waters, with bryozoan meadows. After sea-level stabilization, the composition of these baseline communities remained relatively uniform and started to change markedly only with the intensification of human impacts in the late highstand, leading to a dominance of infauna and a decline of epifauna at all sites. This profound ecological change reduced species richness, increased the abundance of infaunal suspension feeders, and led to a decline of grazers and deposit feeders. We suggest that modern soft-bottom benthic communities in the northern Adriatic Sea today do not show the high geographic heterogeneity in composition characteristic of benthos prior to anthropogenic influences

Ocean acidification during the early Toarcian extinction event : evidence from boron isotopes in brachiopods

This project was funded by the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement and project BASE-LiNE Earth (643084) and by the Slovak Research and Development Agency (APVV17-0555) and the Slovak Scientific Grant Agency (VEGA 0169/19).The loss of carbonate production during the Toarcian Oceanic Anoxic Event (T-OAE, ca.183 Ma) is hypothesized to have been at least partly triggered by ocean acidification linkedto magmatism from the Karoo-Ferrar large igneous province (southern Africa and Antarctica).However, the dynamics of acidification have never been directly quantified across theT-OAE. Here, we present the first record of temporal evolution of seawater pH spanning thelate Pliensbachian and early Toarcian from the Lusitanian Basin (Portugal) reconstructedon the basis of boron isotopic composition (δ11B) of brachiopod shells. δ11B declines by ~1‰across the Pliensbachian-Toarcian boundary (Pl-To) and attains the lowest values (~12.5‰)just prior to and within the T-OAE, followed by fluctuations and a moderately increasingtrend afterwards. The decline in δ11B coincides with decreasing bulk CaCO3 content, inparallel with the two-phase decline in carbonate production observed at global scales andwith changes in pCO2 derived from stomatal indices. Seawater pH had declined significantlyalready prior to the T-OAE, probably due to the repeated emissions of volcanogenicCO2. During the earliest phase of the T-OAE, pH increased for a short period, likely dueto intensified continental weathering and organic carbon burial, resulting in atmosphericCO2 drawdown. Subsequently, pH dropped again, reaching the minimum in the middle ofthe T-OAE. The early Toarcian marine extinction and carbonate collapse were thus driven,in part, by ocean acidification, similar to other Phanerozoic events caused by major CO2 emissions and warming.Publisher PDFPeer reviewe

The Phanerozoic δ88/86Sr Record of Seawater: New Constraints on Past Changes in Oceanic Carbonate Fluxes

The isotopic composition of Phanerozoic marine sediments provides important information about changes in seawater chemistry. In particular, the radiogenic strontium isotope (87Sr/86Sr) system is a powerful tool for constraining plate tectonic processes and their influence on atmospheric CO2 concentrations. However, the 87Sr/86Sr isotope ratio of seawater is not sensitive to temporal changes in the marine strontium (Sr) output flux, which is primarily controlled by the burial of calcium carbonate (CaCO3) at the ocean floor. The Sr budget of the Phanerozoic ocean, including the associated changes in the amount of CaCO3 burial, is therefore only poorly constrained. Here, we present the first stable isotope record of Sr for Phanerozoic skeletal carbonates, and by inference for Phanerozoic seawater (δ88/86Srsw), which we find to be sensitive to imbalances in the Sr input and output fluxes. This δ88/86Srsw record varies from ∼0.25‰ to ∼0.60‰ (vs. SRM987) with a mean of ∼0.37‰. The fractionation factor between modern seawater and skeletal calcite Δ88/86Srcc-sw, based on the analysis of 13 modern brachiopods (mean δ88/86Sr of 0.176±0.016‰, 2 standard deviations (s.d.)), is -0.21‰ and was found to be independent of species, water temperature, and habitat location. Overall, the Phanerozoic δ88/86Srsw record is positively correlated with the Ca isotope record (δ44/40Casw), but not with the radiogenic Sr isotope record ((87Sr/86Sr)sw). A new numerical modeling approach, which considers both δ88/86Srsw and (87Sr/86Sr)sw, yields improved estimates for Phanerozoic fluxes and concentrations for seawater Sr. The oceanic net carbonate flux of Sr (F(Sr)carb) varied between an output of -4.7x1010mol/Myr and an input of +2.3x1010mol/Myr with a mean of -1.6x1010mol/Myr. On time scales in excess of 100Myrs the F(Sr)carb is proposed to have been controlled by the relative importance of calcium carbonate precipitates during the “aragonite” and “calcite” sea episodes. On time scales less than 20Myrs the F(Sr)carb seems to be controlled by variable combinations of carbonate burial rate, shelf carbonate weathering and recrystallization, ocean acidification, and ocean anoxia. In particular, the Permian/Triassic transition is marked by a prominent positive δ88/86Srsw-peak that reflects a significantly enhanced burial flux of Sr and carbonate, likely driven by bacterial sulfate reduction (BSR) and the related alkalinity production in deeper anoxic waters. We also argue that the residence time of Sr in the Phanerozoic ocean ranged from ∼1Myrs to ∼20Myrs

Differentielle Auswirkungen von Umweltfaktoren auf die Ökologie von Brachiopoden und Muscheln während später Trias und Jura

The aim of this study was to assess distribution patterns of articulate brachiopods during the Mesozoic. Exploratory and confirmatory multivariate analyses in this study evaluate whether environmental preferences of brachiopods and bivalves are substantially distinct and whether structure of their communities significantly differ. Specifically, the hypothesis being tested is that differential abundances of Mesozoic brachiopods and bivalves are not related to varying substrate properties only, but also to varying food supply, turbidity and oxygen levels. This hypothesis was evaluated with quantitative data gathered in various field areas and time intervals. They include the Upper Triassic deposits of the West Carpathians and Eastern Alps, the Lower and Middle Jurassic deposits of Morocco, the Middle and Upper Jurassic deposits of the West Carpathians, the Upper Jurassic deposits of the Franconian and Swabian Alb, and the Upper Jurassic deposits of the Swiss Jura. The main conclusion is that brachiopod-dominated communities are characterized by a unique guild structure, with dominance of trophic groups with low metabolic requirements or adapted to nutrient-poor or oxygen-poor conditions. For example, brachiopod co-occured more commonly with epifaunal than with infaunal bivalves in soft-bottom environments. Abundances of brachiopods correlate mostly negatively with increasing proportions of terrigenous admixture (i.e., with increasing amount of land-derived nutrient supply and turbidity).Das Ziel dieses Projekt war es, das Verbreitungsmuster im Erdmittelalter von artikulaten Brachiopoden zu interpretieren. Es basiert hauptsächlich auf der Charakterisierung der Struktur von Benthos-Gemeinschaften mit Brachiopoden und Bivalven. Ausgegangen wird dabei von der Hypothese, dass die Häufigkeit des Auftretens von Brachiopoden und Muscheln nicht allein mit Substratgradienten erklärt werden kann, sondern auch ein Zusammenhang mit Nährstoff-, Sauerstoff- und Turbiditätgradienten besteht. Diese Hypothese war mit Geländedaten aus spezifischen Gebieten (Obertrias der Westkarpaten und Ostalpen, Unterjura und Mitteljura in Marokko, Mitteljura und Oberjura in den Westkarpaten, Oberjura der Fränkische und Schäbische Alb in Deutschland, und Oberjura in Schweiz). Das wichtigste Ergebnis ist dass Brachiopoden-dominierte Gemeinschaften spezifische ökologische Strukturen zeigen und durch die Dominanz von Benthosgruppen charakterisiert sind, welche sind an nährstoffarme oder sauerstoffarme Bedingungen angepasst sind (zum Beispiel durch ein effizientes Filtriersystem) oder niedrige metabolische Ansprüche haben. Zum Beispiel kommen epifaunale Bivalven mit Brachiopoden wesentlich häufiger vor als infaunale Bivalven. Dies kann nicht nur mit unterschiedlichen Substratpräferenzen der infaunalen und epifaunalen Bivalven erklärt werden, weil diese Vergesellschaftungen häufig in mikritischen Wackestones und Floatstones vorkommen.Außerdem korreliert die Häufigkeit der Brachiopoden positiv mit der Abnahme des siliziklastischen Anteil (d.h., mit der Abnahme nährstoffreicher Partikel und Wassertrübe)

R language source code.txt

The code in R language used in simulation

Counts of living individuals in subtidal habitats off San Juan Islands

Counts of mollusk individuals sampled alive by dredge in 2002 at several subtidal stations off San Juan Islands. The source of data and description of sampling and counting methods is in: Kowalewski M., Carroll M., Casazza L., Gupta N., Hannisdal B., Hendy A., Krause R. A. Jr., LaBarbera M., Lazo D.G., Messina C., Puchalski S., Rothfus T. A., Sälgeback J., Stempien J., Terry R.C., Tomašových A. 2003, Quantitative fidelity of brachiopod-mollusk assemblages from modern subtidal environments of San Juan Islands, USA. Journal of Taphonomy 1, 43-6

Counts of complete dead individuals in subtidal habitats off San Juan Islands

Counts of dead mollusk individuals sampled by dredge in 2002 at several subtidal stations off San Juan Islands. This is restrictive dataset - includes complete individuals and is corrected for disarticulated elements. The source of data and description of sampling and counting methods is in: Kowalewski M., Carroll M., Casazza L., Gupta N., Hannisdal B., Hendy A., Krause R. A. Jr., LaBarbera M., Lazo D.G., Messina C., Puchalski S., Rothfus T. A., Sälgeback J., Stempien J., Terry R.C., Tomašových A. 2003, Quantitative fidelity of brachiopod-mollusk assemblages from modern subtidal environments of San Juan Islands, USA. Journal of Taphonomy 1, 43-6