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

Ideas and perspectives: Human impacts alter the marine fossil record

The youngest fossil record is a crucial source of data documenting the recent history of marine ecosystems and their long-term alteration by humans. However, human activities that reshape communities and habitats also alter sedimentary and biological processes that control the formation of the sedimentary archives recording those impacts. These diverse physical, geochemical, and biological disturbances include changes in sediment fluxes due to the alteration of alluvial and coastal landscapes, seabed disturbance by bottom trawling and ship traffic, ocean acidification and deoxygenation, removal of native species, and introduction of invasive ecosystem engineers. These novel processes modify sedimentation rates, the depth and intensity of sediment mixing, the pore-water saturation state, and the preservation potential of skeletal remains – the parameters controlling the completeness and spatiotemporal resolution of the fossil record. We argue that humans have become a major force transforming the nature of the marine fossil record in ways that can both impede and improve our ability to reconstruct past ecological and climate dynamics. A better understanding of the feedback between human impacts on ecosystem processes and their preservation in the marine fossil record offers new research opportunities and novel tools for interpreting geohistorical archives of the ongoing anthropogenic transformation of the coastal ocean.</p

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

Calcitization of aragonitic bryozoans in Cenozoic tropical carbonates from East Kalimantan, Indonesia

© The Author(s) 2016. Open Access. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The file attached is the published version of the article

The Impact of Global Warming and Anoxia on Marine Benthic Community Dynamics: an Example from the Toarcian (Early Jurassic)

The Pliensbachian-Toarcian (Early Jurassic) fossil record is an archive of natural data of benthic community response to global warming and marine long-term hypoxia and anoxia. In the early Toarcian mean temperatures increased by the same order of magnitude as that predicted for the near future; laminated, organic-rich, black shales were deposited in many shallow water epicontinental basins; and a biotic crisis occurred in the marine realm, with the extinction of approximately 5% of families and 26% of genera. High-resolution quantitative abundance data of benthic invertebrates were collected from the Cleveland Basin (North Yorkshire, UK), and analysed with multivariate statistical methods to detect how the fauna responded to environmental changes during the early Toarcian. Twelve biofacies were identified. Their changes through time closely resemble the pattern of faunal degradation and recovery observed in modern habitats affected by anoxia. All four successional stages of community structure recorded in modern studies are recognised in the fossil data (i.e. Stage III: climax; II: transitional; I: pioneer; 0: highly disturbed). Two main faunal turnover events occurred: (i) at the onset of anoxia, with the extinction of most benthic species and the survival of a few adapted to thrive in low-oxygen conditions (Stages I to 0) and (ii) in the recovery, when newly evolved species colonized the re-oxygenated soft sediments and the path of recovery did not retrace of pattern of ecological degradation (Stages I to II). The ordination of samples coupled with sedimentological and palaeotemperature proxy data indicate that the onset of anoxia and the extinction horizon coincide with both a rise in temperature and sea level. Our study of how faunal associations co-vary with long and short term sea level and temperature changes has implications for predicting the long-term effects of “dead zones” in modern oceans

How quick was marine recovery after the end-Triassic mass extinction and what role did anoxia play?

Oxygen restricted conditions were widespread in European shelf seas after the end-Triassic mass extinction event and they are reported to have hindered the recovery of marine benthos. Here we reconstruct the redox history of the Early Jurassic Blue Lias Formation of southwest Britain using pyrite framboid size analysis and compare this with the recovery of bivalves based on field and museum collections. Results suggest widespread dysoxia punctuated by periods of anoxia in the region, with the latter developing frequently in deeper water settings. Despite these harsh conditions, initial benthic recovery occurred rapidly in the British Jurassic, especially in shallowest settings, and shows no relationship with the intensity of dysoxia. A stable diversity was reached by the first recognised ammonite zone after the end-Triassic mass extinction. This contrasts with the deeper-water, more oxygen-poor sections where the diversity increase was still continuing in the earliest Sinemurian Stage, considerably longer than previously reported. Similar recovery rates are seen amongst other groups (brachiopods and ammonites). Oxygen-poor conditions have been suggested to delay recovery after the Permo-Triassic mass extinction, but this is not the case after the end-Triassic crisis. We suggest that this was because the European dysoxia was only a regional phenomenon and there were plenty of well-ventilated regions available to allow an untrammelled bounce back

Knitting patterns of biodiversity, range size and body size in aquatic beetle faunas : significant relationships but slightly divergent drivers

1. Ecogeographical rules refer to recurring patterns in nature, including the latitudinal diversity gradient (LDG), Rapoport's rule and Bergmann's rule, amongst others. In the present study, the existence of these rules was examined for diving beetles (Coleoptera: Dytiscidae), a family of aquatic predatory beetles. 2. Assemblage-level data were analysed for diving beetles, focusing on species richness, local contribution to beta diversity (LCBD), mean range size and mean body size across the biogeographical provinces of Northern Europe. First, each of these variables was correlated with latitude, and then variation in each variable was modelled using actual environmental variables in boosted regression tree analysis. 3. Species richness was found to decrease with latitude, LCBD increased with latitude, mean range size did not show a significant relationship with latitude, and mean body size decreased with latitude. The latter finding was in contrast to Bergmann's rule. The actual environmental variables best predicting variation in these four response variables varied among the models, although they generally included temperature-related and land use variables as the most influential ones. 4. The results obtained in the present study suggest that diving beetles conformed to the LDG, did not follow Rapoport's rule, and showed a reversed latitudinal gradient in the context of Bergmann's rule. In addition, species-poor provinces harboured ecologically most unique faunas, suggesting that species richness and LCBD are complementary measures of biodiversity. 5. Even though general support was not found for most of the ecogeographical rules examined, the findings of the present study are interesting because they suggest that aquatic ectothermic invertebrates may show patterns different from those originally described for terrestrial endothermic vertebrates

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