Quantifying seawater exchange rates in the Eocene Arctic Basin using osmium isotopes

The closure of seaways that connected the Arctic Ocean to the global ocean during the early Paleogene led to severe hydrographic restriction. We present new osmium isotope data from organic-rich sediments deposited in the central Arctic Ocean during the Early–Middle Eocene. The new data show that the long term isotopic composition of osmium in Arctic seawater began to diverge from that of the global ocean at ∼54 Ma, after the Eocene Thermal Maximum 2 hyperthermal event. This divergence was probably caused by the gradual closure of seaways connecting the Arctic Ocean to the global ocean. The Os data are used to calculate water exchange rates between the Arctic and surrounding oceans and to calculate Arctic Ocean salinity during the Early Eocene. The results show that the development of severe, long term Arctic Basin restriction after ∼54 Ma occurred as open ocean seawater input decreased below ∼0.01 Sv, resulting in a mean basin salinity between 8–16 PSU, depending on model assumptions

Upper limits on the extent of seafloor anoxia during the PETM from uranium isotopes.

The Paleocene Eocene Thermal Maximum (PETM) represents a major carbon cycle and climate perturbation that was associated with ocean de-oxygenation, in a qualitatively similar manner to the more extensive Mesozoic Oceanic Anoxic Events. Although indicators of ocean de-oxygenation are common for the PETM, and linked to biotic turnover, the global extent and temporal progression of de-oxygenation is poorly constrained. Here we present carbonate associated uranium isotope data for the PETM. A lack of resolvable perturbation to the U-cycle during the event suggests a limited expansion of seafloor anoxia on a global scale. We use this result, in conjunction with a biogeochemical model, to set an upper limit on the extent of global seafloor de-oxygenation. The model suggests that the new U isotope data, whilst also being consistent with plausible carbon emission scenarios and observations of carbon cycle recovery, permit a maximum ~10-fold expansion of anoxia, covering <2% of seafloor area

Aktywność zawodowa kobiet i dzietność w Polsce

The intention of the analysis is to indicate socioeconomic determinants of fertility for Poland. The analysis is made with respect to the labour market structures, living conditions, gender norms and appreciated values. Logistic regression models of first and second birth order were used, based on the 2006–2010 Polish Labour Force Survey data. Despite registered rebound in TFRs, there is no evidence to prove the Hypothesis of Fertility Positive Turn holds for Poland. Incompatibility of paid-work and childcare points the premises of the positive turn have not been fulfilled yet. Instead, the stability hypothesis seems to have some evidence as models show significant relation of marital status, household status and the labour market situation of the partner to fertility.Niniejsza analiza ma na celu wskazanie socjoekonomicznych determinant dzietności dla Polski. Analiza uwzględnia wpływ struktur rynku pracy, warunków życia, podziału ról ze względu na płeć i cenionych wartości. Zaprezentowano modele regresji logistycznej urodzeń pierwszego i drugiego dziecka, przygotowane na podstawie danych BAEL za lata 2006–2010. Pomimo zaobserwowanego odbicia w poziomie współczynnika dzietności, nie ma podstaw, by sądzić, że hipoteza o pozytywnym odbiciu współczynnika dzietności (the Hypothesis of Fertility Positive Turn) jest spełniona dla Polski. Trudności w łączeniu pracy zarobkowej i opieki nad dzieckiem wskazują, że przesłanki tej hipotezy nie zostały jeszcze spełnione. Wydaje się natomiast, że hipoteza o stabilizacji (the Stability Hypothesis) lepiej tłumaczy decyzję o urodzeniu i wychowaniu dziecka, jako że modele wskazują na istotną statystycznie relację między dzietnością a stanem cywilnym, faktem zamieszkania w domu rodziców i statusem męża/partnera na rynku pracy

Evaluating δ^238/235U records in mudrocks as a proxy for ocean oxygenation during the Early Eocene

It is generally established that Early Eocene climate was characterised by persistent warmth punctuated by abrupt global warming events that were associated with perturbations in the global carbon cycle. The distribution of O2 in the oceans would have been profoundly affected but the timing and extent of any fluctuations in global ocean oxygenation during these events are still poorly constrained. Records of seawater Mo isotope compositions derived from marine sediments from the Arctic Ocean suggest that euxinic areas were slightly more widespread in the Early Eocene ocean than they are at present [1,2]. Here, we present δ238/235U data from the same location. By comparing these new U isotope data with complementary δ98/95Mo data, we assess their capacity to provide additional constraints on the variations of global ocean oxygenation during this period. The residence times of Mo and U in the oceans differ from one another, and their isotope fractionations display different sensitivities to dissolved oxygen concentrations. By combining information from both isotope systems, we should therefore be able to better constrain the onset and the severity of the episodes of seawater anoxia during the Eocene, and to improve our understanding of the processes that control ocean oxygenation. Our analyses of Arctic Ocean mudrocks show that where δ98/95Mo likely records a global redox signal, δ238/235U has more complicated variations that appear to be related to changes in the nature and/or the flux of detrital material. Our observations highlight the importance of quantifying continental inputs and local sedimentation rates, as well as understanding the processes controlling U isotope fractionation, before δ238/235U data can be used reliably for paleo-environmental reconstructions. [1] Dickson, Cohen & Coe (2012), Geology 40-7, 639-642. [2] Dickson & Cohen (2012), Paleoceanography 27, PA3230

Seasonal variations of chemical composition of soil porewaters, streams and rivers in basaltic watersheds of central Siberia: the origin of river dissolved load in the permafrost zone

Rivers and streams draining basalts in Central Siberia allow thorough evaluation of the intensity of chemical weathering and its potential change induced by permafrost degradation. In order to get new insights to the origin of dissolved and suspended matter in this important subarctic region, we follow continuously over 4 years the chemical composition of dissolved load in two large rivers (N. Tunguska and Kochechumo), small experimental watershed (Kulingdakan) in the Yenissey River Basin and interstitial soils solutions from different landscape positions and soil horizons. The site (Tura, 64oN, 100oE) offers a unique opportunity for studying the processes occurring at high and low permafrost distribution watersheds. Indeed, at global scale we deal with two equivalent size rivers draining the northern and southern part of the Central Siberia (Kochechumo River and N. Tunguska River, respectively). At the local scale, there are north-facing and south-facing slopes of the watershed that receive equivalent precipitation but exhibit totally different heat input and consequently above-ground biomass and active layer thickness. There is a clear and strongly pronounced seasonal variability in trace and major elements concentration and organic carbon (OC) over the hydrological cycle with most of OC and trace element flux occurring during the spring flood. In summer time, the north-facing slope acts as a primary source of water and dissolved elements to the river as it exhibits the lowest thickness of the active layer. Indeed, the chemical composition of the suprapermafrost flow and that of the river water are very similar. In contrast, the south-facing slopes, although they exhibit twice higher concentrations of OC and TE in porewaters, do not deliver enough fluids to the river as these fluids are fully absorbed by thick active layer, mosses and vascular vegetation. Nevertheless, in early spring, the degradation products of plant litter from the S-facing slopes are abundant in stream waters. In winter time, when all soil fluid migration is stopped and the small rivers are fully frozen, the main source of solutes to the large rivers become groundwaters located in the thawed zone below the river channel. In collaboration with other researches, our results should allow quantitative modeling of the evolution of large boreal continental systems under global warming accompanied by the shift from the permafrost-dominating to permafrost-free environments

Origin of calcium isotope fractionation in river waters: evidence from the Strengbach catchment, France

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