Distribution of phosphorus in the Middle and Upper Ordovician Baltoscandian carbonate palaeobasin

Baltoscandian Middle and Upper Ordovician carbonate rocks are relatively poor in phosphorus, with the P2O5 content of 0.05–0.5%, rarely exceeding 1%. Phosphorus distribution in the Ordovician carbonate succession shows spatial and temporal variations. In the Estonian Shelf P content is the highest in the Middle Ordovician, close to the Tremadocian P-rich siliciclastic sediments, decreasing towards younger carbonate rocks. In the basinal, i.e. deep shelf, sections two intervals of elevated P contents occur: the first is similar to the shallow shelf in the lowermost Darriwilian, the second is a moderate P increase in the upper Darriwilian–Sandbian interval. The Darriwilian–Sandbian interval of elevated P content in the deep shelf sections roughly corresponds to algal kukersite accumulations in the shallow shelf. Multiple processes determined phosphorus distribution in the studied sediments. Regional processes influencing P distribution include seawater circulation, e.g. P influx by coastal upwellings, and sedimentation rate. Global oceanic variation in bioproduction (δ13C trends) had no positive effect on P accumulation in the Baltoscandian epeiric sea

Stratigraphy and facies differences of the middle darriwilian isotopic carbon excursion (Mdice) in baltoscandia

© 2020 Authors. The Middle Darriwilian Isotopic Carbon Excursion (MDICE) is a global isotopic event described in sections from different palaeocontinents. Here we present new stable carbon isotopic data from carbonates of ten sections in different parts of the Baltoscandian Palaeobasin (Estonia, Latvia, Lithuania, Sweden, NW Russia). The definition of the MDICE as a chemostratigraphic unit is discussed, as well as the subdivision of its peak into two distinct peaks. The MDICE is one of the longest carbon isotopic events in the Palaeozoic. It was preceded by the L­chondritic cosmic dust flow event, which may have been responsible for cooling through the Darriwilian and the initiation of the Great Ordovician Biodiversification Event. High­resolution chemostratigraphic analyses show that the time interval between these environmental events and the base of the MDICE is up to one million years. Due to the long duration of the MDICE the modelling of this excursion should address more complex scenarios than a simple response of the carbon cycle to rapid climatic perturbations

Fluxes of nutrients and trace metals across the sediment-water interface controlled by sediment-capping agents: bentonite and sand

The effect of bentonite and sand, as natural capping agents, on the fluxes of nutrients and trace metals across the sediment-water interface was studied through sediment incubation, and the ecotoxicological impact was assessed by using Daphnia magna. Bentonite and sand were layered on the sediment at 15, 75, and 225 mg cm(-2), and the concentration of cations, nutrients, and trace metals was measured. Sediment incubation showed that bentonite reduced the N flux but increased the P flux as a result of dissolution of non-crystalline P from bentonite, while sand slightly decreased the N fluxes but not the P flux. The concentration of Na increased in the overlying water with increasing application rates of bentonite, while that of Ca decreased. However, regardless of the rate of sand application, concentrations of all cation species remained unchanged. The concentration of As and Cr increased with bentonite application rate but decreased with sand. Both capping materials suppressed fluxes of Cd, Cu, Ni, and Zn compared to control, and the extent of suppression was different depending on the trace metal species and capping agents used. During sediment incubation, the survival rate of D. magna significantly decreased in bentonite suspension but began to decrease at the end in sand suspension. Sediment capping of mildly polluted sediments by using bentonite and sand lowered the level of nutrients and trace metals. However, unexpected or undesirable side effects, such as influxes of P and As from bentonite to the overlying water and a possibility of toxic impacts to aquatic ecosystems, were observed, suggesting that capping agents with an adequate assessment of their side effects and toxicity should be predetermined for site-specific sediment management strategies.clos