Nature Geoscience最新文献

Autotrophic nitrifiers, by catalysing the oxidation of ammonia to nitrate, play a vital role in the global nitrogen cycle. They convert carbon dioxide (CO₂) into biomass and, therefore, are expected to respond positively to increasing atmospheric CO₂ concentrations. However, in a long-term free-air CO₂ enrichment experiment, we demonstrated that elevated atmospheric CO₂ inhibited the growth of autotrophic nitrifiers, resulting in a reduction in nitrification in a rice ecosystem. By coupling stable-isotope probing with metagenomics, we found that the CO₂ inhibition of nitrifiers was mainly a consequence of CO₂-induced functional loss (genomes not recovered from metagenomes) of dominant but previously uncharacterized autotrophic nitrifying species. These species belonged mainly to ammonia-oxidizing archaea and nitrite-oxidizing bacteria and comprised 63% of total dominant members identified from the active nitrifying communities. We further showed that the functional loss of these novel nitrifying species under elevated CO₂ was due largely to the CO₂-induced aggravation of anoxic stress in the paddy soil. Our results provide insight into the fate of inorganic nitrogen pools in global lowland soil and water systems under climate change.

The prevailing view of the formation of porphyry copper deposits along convergent plate boundaries involves deep crustal differentiation of metal-bearing juvenile magmas derived from the mantle wedge above a subduction zone. However, many major porphyry districts formed during periods of flat-slab subduction when the mantle wedge would have been reduced or absent, leaving the source of the ore-forming magmas unclear. Here we use geochronology and thermobarometry to investigate deep crustal processes during the genesis of the Late Cretaceous–Palaeocene Laramide Porphyry Province in Arizona, which formed during flat-slab subduction of the Farallon Plate beneath North America. We show that the isotopic signatures of Laramide granitic rocks are consistent with a Proterozoic crustal source that was potentially pre-enriched in copper. This source underwent water-fluxed melting between 73 and 60 Ma, coincident with the peak of granitic magmatism (78–50 Ma), porphyry genesis (73–56 Ma) and flat-slab subduction (70–40 Ma). To explain the formation of the Laramide Porphyry Province, we propose that volatiles derived from the leading edge of the Farallon flat slab promoted melting of both mafic and felsic pre-enriched lower crust, without requiring extensive magmatic or metallogenic input from the mantle wedge. Other convergent plate boundaries with flat-slab regimes may undergo a similar mechanism of volatile-mediated lower-crustal melting.

The Atlantic meridional overturning circulation (AMOC) and the Amazon forest are viewed as connected tipping elements in a warming climate system. If global warming exceeds a critical threshold, the AMOC may slow down substantially, changing atmospheric circulation and leading to Amazonia becoming drier in the north and wetter in the south. Yet, the impact of an AMOC slowdown on Amazon vegetation is still not well constrained. Here we use pollen and microcharcoal data from a marine sediment core to assess changes in Amazon vegetation from 25,000 to 12,500 years ago. Additionally, we model vegetation responses to an AMOC slowdown under both glacial and pre-industrial conditions. During a past AMOC slowdown (Heinrich Stadial 1–18,000 to 14,800 years ago), pollen data evidence a decline in cold- and moist-affinity elements, coupled with a rise in seasonal tropical vegetation. This pattern is consistent with the decline in suitability of northern Amazon moist forests in a model with an imposed 50% AMOC weakening under glacial conditions. Our modelling results suggest similar changes for a comparable AMOC slowdown under pre-industrial conditions. Combined with current disturbances such as deforestation and wildfires elsewhere in the basin, an AMOC slowdown may exert a systemic impact on the Amazon forest.