The Dissolution of Olivine Added to Soil at 4°C: Implications for Enhanced Weathering in Cold Regions

Crushed olivine was added to a soil core to mimic enhanced weathering, and water was continually dripped through for ~6 months. Our experiments were conducted at 4°C, and are compared to previously run identical experiments at 19°C. Olivine dissolution rates in both experiments start out similar, likely due to fines and sharp crystal corners. However, after >100 days of reaction, the dissolution rate at 4°C was two orders of magnitude lower than at 19°C. The accumulation of heavy metals, such as Ni and Cd, was low in both experiments, but soil retention of these elements was proportionally higher at higher temperatures, likely due to enhanced sorption and formation of clays. Overall, this study suggests that olivine dissolution rates in experiments that mimic natural settings are orders of magnitude slower than in normal laboratory experiments, and that enhanced weathering may be a considerably less efficient method of carbon dioxide removal at low climatic temperatures. Both of these conclusions have implications for the application of enhanced weathering as a CO2 removal method

Seasonal variability in silicate weathering signatures recorded by Li isotopes in cave drip-waters

Silicate weathering is a critical process in Earth’s carbon cycle, but the fundamental controls on weathering are poorly understood and its response to future climate change is uncertain. In particular, the potential for changes in seasonality or extreme weather events to control silicate weathering rates or mechanisms has been little studied. Here, we use lithium (Li) isotope measurements in bimonthly sampled drip-waters from two caves in the Yorkshire Dales (U.K.) to assess the response of silicate weathering processes to changes in temperature and hydrology over seasonal timescales. While the caves are contained in limestone bedrock, the drip-water Li isotope signal predominantly reflects silicate weathering of the overlying soils that are dominated by glacial till

Simvastatin-dependent apoptosis in Hodgkin’s lymphoma cells and growth impairment of human Hodgkin’s tumors in vivo

Statins are used to treat hypercholesterolemia and seem to have a preventive effect against cancer through pleiotropic effects including prenylation-inhibition. So far nothing is known about the activity of statins or more specific prenylation-inhibitors in Hodgkin’s lymphoma (HL). We, therefore, evaluated the anti-HL activity of simvastatin and specific prenylation-inhibitors. Two μM Simvastatin induced caspase-related apoptosis via depletion of prenylation-substrates in several HL-cell lines. Furthermore, it effectively impaired tumor growth in a mouse model for HL. Since the prenylation-inhibitors FTI-277 and GGTI-298 were also effective against HL-cells, we conclude that statins and specific prenylation-inhibitors should be evaluated in HL patients

Dendritic Cells Release HLA-B-Associated Transcript-3 Positive Exosomes to Regulate Natural Killer Function

NKp30, a natural cytotoxicity receptor expressed on NK cells is critically involved in direct cytotoxicity against various tumor cells and directs both maturation and selective killing of dendritic cells. Recently the intracellular protein BAT3, which is involved in DNA damage induced apoptosis, was identified as a ligand for NKp30. However, the mechanisms underlying the exposure of the intracellular ligand BAT3 to surface NKp30 and its role in NK-DC cross talk remained elusive. Electron microscopy and flow cytometry demonstrate that exosomes released from 293T cells and iDCs express BAT3 on the surface and are recognized by NKp30-Ig. Overexpression and depletion of BAT3 in 293T cells directly correlates with the exosomal expression level and the activation of NK cell-mediated cytokine release. Furthermore, the NKp30-mediated NK/DC cross talk resulting either in iDC killing or maturation was BAT3-dependent. Taken together this puts forward a new model for the activation of NK cells through intracellular signals that are released via exosomes from accessory cells. The manipulation of the exosomal regulation may offer a novel strategy to induce tumor immunity or inhibit autoimmune diseases caused by NK cell-activation

Extreme magnesium isotope fractionation at outcrop scale records the mechanism and rate at which reaction fronts advance

Isotopic fractionation of cationic species during diffusive transport provides novel means of constraining the style and timing of metamorphic transformations. Here we document a major (~1‰) decrease in the Mg isotopic composition of the reaction front of an exhumed contact between rocks of subducted crust and serpentinite, in the Syros mélange zone. This isotopic perturbation extends over a notable length-scale (~1 m), implicating diffusion of Mg through an intergranular fluid network over a period of ~100 kyr. These novel observations confirm models of diffusion-controlled growth of reaction zones formed between rocks of contrasting compositions, such as found at the slab-mantle interface in subduction zones. The results also demonstrate that diffusive processes can result in exotic stable isotope compositions of major elements with implications for mantle xenoliths and complex intrusions

Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes

Increasing global temperatures are causing widespread changes in the Arctic, including permafrost thawing and altered freshwater inputs and trace metal and carbon fluxes into the ocean and atmosphere. Changes in the permafrost active layer thickness can affect subsurface water flow-paths and water-rock interaction times, and hence weathering processes. Riverine lithium isotope ratios (reported as δ7Li) are tracers of silicate weathering that are unaffected by biological uptake, redox, carbonate weathering and primary lithology. Here we use Li isotopes to examine silicate weathering processes in one of the largest Russian Arctic rivers: the Lena River in eastern Siberia. The Lena River watershed is a large multi-lithological catchment, underlain by continuous permafrost. An extensive dataset of dissolved Li isotopic compositions of waters from the Lena River main channel, two main tributaries (the Aldan and Viliui Rivers) and a range of smaller sub-tributaries are presented from the post-spring flood/early-summer period at the onset of active layer development and enhanced water-rock interactions. The Lena River main channel (average δ7Lidiss ∼ 19‰) has a slightly lower isotopic composition than the mean global average of 23‰ (Huh et al., 1998a). The greatest range of [Li] and δ7Lidiss are observed in catchments draining the south-facing slopes of the Verkhoyansk Mountain Range. South-facing slopes in high-latitude, permafrost-dominated regions are typically characterised by increased summer insolation and higher daytime temperatures relative to other slope aspects. The increased solar radiation on south-facing catchments promotes repeated freeze-thaw cycles, and contributes to more rapid melting of snow cover, warmer soils, and increased active layer thaw depths. The greater variability in δ7Li and [Li] in the south-facing rivers likely reflect the greater infiltration of melt water and enhanced water-rock interactions within the active layer. A similar magnitude of isotopic fractionation is observed between the low-lying regions of the Central Siberian Plateau (and catchments draining into the Viliui River), and catchments draining the Verkhoyansk Mountain Range into the Aldan River. This is in contrast to global rivers in non-permafrost terrains that drain high elevations or areas of rapid uplift, where high degrees of physical erosion promote dissolution of freshly exposed primary rock typically yielding low δ7Lidiss, and low-lying regions exhibit high riverine δ7Li values resulting from greater water-rock interaction and formation of secondary mineral that fractionates Li isotopes. Overall, the range of Li concentrations and δ7Lidiss observed within the Lena River catchment are comparable to global rivers located in temperate and tropical regions. This suggests that cryogenic weathering features specific to permafrost regions (such as the continual exposure of fresh primary minerals due to seasonal freeze-thaw cycles, frost shattering and salt weathering), and climate (temperature and runoff), are not a dominant control on δ7Li variations. Despite vastly different climatic and weathering regimes, the same range of riverine δ7Li values globally suggests that the same processes govern Li geochemistry – that is, the balance between primary silicate mineral dissolution and the formation (or exchange with) secondary minerals. This has implications for the use of δ7Li as a palaeo-weathering tracer for interpreting changes in past weathering regimes

Possible links between extreme oxygen perturbations and the Cambrian radiation of animals

The role of oxygen as a driver for early animal evolution is widely debated. During the Cambrian explosion, episodic radiations of major animal phyla occurred coincident with repeated carbon isotope fluctuations. However, the driver of these isotope fluctuations and potential links to environmental oxygenation are unclear. Here, we report high-resolution carbon and sulphur isotope data for marine carbonates from the south-eastern Siberian Platform, which documents the canonical explosive phase of the Cambrian radiation from ~524 to ~514 Myr ago. These analyses demonstrate a strong positive covariation between carbonate 13C and carbonate-associated sulphate 34S through five isotope cycles. Biogeochemical modelling suggests that this isotopic coupling reflects periodic oscillations in atmospheric O2 and the extent of shallow ocean oxygenation which, remarkably, directly coincides with episodic maxima in biodiversity of animal phyla. Conversely, the subsequent Botoman–Toyonian animal extinction events (~514 to ~512 Myr ago) coincided with decoupled isotope records that suggest a shrinking marine sulphate reservoir and expanded shallow marine anoxia. These observations demonstrate that fluctuations in oxygen availability in the shallow marine realm exerted a primary control on the timing and tempo of biodiversity radiations at a crucial phase in the early history of animal life

Tracing North Atlantic volcanism and seaway connectivity across the Paleocene–Eocene Thermal Maximum (PETM)

Abstract. There is a temporal correlation between the peak activity of the North Atlantic Igneous Province (NAIP) and the Paleocene–Eocene Thermal Maximum (PETM), suggesting that the NAIP may have initiated and/or prolonged this extreme warming event. However, corroborating a causal relationship is hampered by a scarcity of expanded sedimentary records that contain both climatic and volcanic proxies. One locality hosting such a record is the island of Fur in Denmark, where an expanded pre- to post-PETM succession containing hundreds of NAIP ash layers is exceptionally well preserved. We compiled a range of environmental proxies, including mercury (Hg) anomalies, paleotemperature proxies, and lithium (Li) and osmium (Os) isotopes, to trace NAIP activity, hydrological changes, weathering, and seawater connectivity across this interval. Volcanic proxies suggest that NAIP activity was elevated before the PETM and appears to have peaked during the body of the δ13C excursion but decreased considerably during the PETM recovery. This suggests that the acme in NAIP activity, dominated by flood basalt volcanism and thermogenic degassing from contact metamorphism, was likely confined to just ∼ 200 kyr (ca. 56.0–55.8 Ma). The hundreds of thick (> 1 cm) basaltic ashes in the post-PETM strata likely represent a change from effusive to explosive activity, rather than an increase in NAIP activity. Detrital δ7Li values and clay abundances suggest that volcanic ash production increased the basaltic reactive surface area, likely enhancing silicate weathering and atmospheric carbon sequestration in the early Eocene. Signals in lipid biomarkers and Os isotopes, traditionally used to trace paleotemperature and weathering changes, are used here to track seaway connectivity. These proxies indicate that the North Sea was rapidly cut off from the North Atlantic in under 12 kyr during the PETM recovery due to NAIP thermal uplift. Our findings reinforce the hypothesis that the emplacement of the NAIP had a profound and complex impact on Paleocene–Eocene climate, both directly through volcanic and thermogenic degassing and indirectly by driving regional uplift and changing seaway connectivity