Coastal El Niño triggers rapid marine silicate alteration on the seafloor.

Marine silicate alteration plays a key role in the global carbon and cation cycles, although the timeframe of this process in response to extreme weather events is poorly understood. Here we investigate surface sediments across the Peruvian margin before and after extreme rainfall and runoff (coastal El Niño) using Ge/Si ratios and laser-ablated solid and pore fluid Si isotopes (δ30Si). Pore fluids following the rainfall show elevated Ge/Si ratios (2.87 µmol mol-1) and δ30Si values (3.72‰), which we relate to rapid authigenic clay formation from reactive terrigenous minerals delivered by continental runoff. This study highlights the direct coupling of terrestrial erosion and associated marine sedimentary processes. We show that marine silicate alteration can be rapid and highly dynamic in response to local weather conditions, with a potential impact on marine alkalinity and CO2-cycling on short timescales of weeks to months, and thus element turnover on human time scales.

Serpentine alteration as source of high dissolved silicon and elevated δ30Si values to the marine Si cycle.

Serpentine alteration is recognized as an important process for element cycling, however, related silicon fluxes are unknown. Pore fluids from serpentinite seamounts sampled in the Mariana forearc region during IODP Expedition 366 were investigated for their Si, B, and Sr isotope signatures (δ30Si, δ11B, and 87Sr/86Sr, respectively) to study serpentinization in the mantle wedge and shallow serpentine alteration to authigenic clays by seawater. While serpentinization in the mantle wedge caused no significant Si isotope fractionation, implying closed system conditions, serpentine alteration by seawater led to the formation of authigenic phyllosilicates, causing the highest natural fluid δ30Si values measured to date (up to +5.2 ± 0.2‰). Here we show that seafloor alteration of serpentinites is a source of Si to the ocean with extremely high fluid δ30Si values, which can explain anomalies in the marine Si budget like in the Cascadia Basin and which has to be considered in future investigations of the global marine Si cycle.

Bat breath reveals metabolic substrate use in free-ranging vampires.

We analysed the stable carbon isotope ratio in exhaled CO(2) (delta(13)C(breath)) of free-ranging vampires to assess the type of metabolized substrate (endogenous or exogenous substrate) and its origin, i.e. whether the carbon atoms came from a C(4) food web (grass and cattle) or the C(3) food web in which they were captured (a rainforest remnant and its mammals). For an improved understanding of factors influencing the delta(13)C(breath) of vampires, we conducted feeding experiments with captive animals. The mean delta(13)C(breath) of starved bats was depleted in (13)C in relation to the diet by 4.6 per thousand (n = 10). Once fed with blood, delta(13)C(breath )levelled off within a short time approximately 2.2 per thousand above the stable carbon isotope signature of the diet. The median time required to exchange 50% of the carbon atoms in exhaled CO(2) with carbon atoms from the ingested blood was 18.6 min (mean 29.5 +/- 19.0 min, n = 5). The average delta(13)C of wing membrane and fur in free-ranging vampire bats suggested that bats almost exclusively foraged for cattle blood during the past weeks. The delta(13)C(breath) of the same bats averaged -19.1 per thousand. Given that all free-ranging vampires were starving and that the delta(13)C of cattle was more in enriched in (13)C by 5-6 per thousand than the delta(13)C(breath) of vampires, we conclude that the vampire bats of our study metabolised fat that was predominantly built from carbon atoms originating from cattle blood. Since delta(13)C of wing membrane and fur integrates over weeks and months respectively and delta(13)C(breath) over hours and days, we also conclude that vampire bats of the studied population consistently ignored rainforest mammals and chose cattle as their prey during and prior to our study.