Communications Earth & Environment最新文献

Climate change and increases in the frequency and severity of climate-driven wildfires, particularly in the western United States, has serious ramifications for enhanced downwind reactive nitrogen (Nr) emissions, deposition, and critical load exceedances. Here we present a multi-decadal (2002 - 2021), harmonized model-data-driven study using the George Mason University North American Chemical Reanalysis (NACR) system and simulations including both "with-fire" and "without-fire" conditions to quantify the change in trends of fire activity and source contributions to total Nr emissions and deposition over the U.S. Our results show that fire activity has increased substantially in the western U.S., especially in the west-northwest U.S. for wildfires, and that this increase is associated with positive annual near-surface temperature and vapor pressure deficit anomalies compared to the period average. Major results and implications of this work are increasing trends in the contribution of climate-driven wildfires to higher Nr emissions, deposition, and critical load exceedances of up to 20-40% due to fires in the western U.S. There are also smaller increases (<5 %) in Nr deposition trends for the eastern U.S., which are related to greater occurrence and reporting of agricultural and prescribed burns.

Archean ocean marine primary productivity may have been limited by biologically available nitrogen. Due to low molybdenum abundances, early biological nitrogen fixation is thought to have relied on alternative nitrogenases that incorporate vanadium or iron instead of molybdenum. Here, we examine nitrogen fixation in a Cyanobacteria-dominated, ferruginous, low-sulfate, low-molybdenum lake, which replicates biological and chemical conditions relevant to early marine primary productivity. Nitrogen fixation occurs even when molybdenum is <1 nM, 100x less than the abundance in modern oceans. Molybdenum additions did not increase nitrogen fixation rates, indicating that diazotrophs were not molybdenum limited. Only the molybdenum-iron nitrogenase was detected in metagenomes and metatranscriptomes, indicating that the alternative nitrogenases were not required. We suggest that low sulfate (<1 μM) and/or efficient uptake mitigated molybdenum limitation. These results indicate that molybdenum bioavailability may be strongly controlled by sulfate and that alternative nitrogenases are not essential for nitrogen fixation at low molybdenum.

Little is known about the structure of tropical forests despite its critical role in the provisioning of ecosystem services. Here we assess the vertical structure of forests in the Brazilian Amazon with a large-scale airborne LiDAR dataset. We show that fire has greater impact in the lowest forest strata, differently from selective logging and windthrow. We also find that secondary forests quickly recover or even exceed reference areas at the 1-10 m height stratum but that full recovery for the 20-30 m height stratum has not been achieved even after 35 years. Our modeling results suggest that proximity to roads, elevation, precipitation, soil pH, and proportion of sand in the soil are the most important predictors of forest structure. Finally, we identify 5 forest structural types (FSTs) and use them to visualize the spatial distribution of forest structure. This study provides important information for forest monitoring, management, and conservation.

Coral tissue depth reflects organismal health and is influenced by environmental stressors. Reconstructing its past variability on inter- and intra-annual timescales, however, is not yet possible. Here we reconstructed seasonal tissue depth by measuring spatial offsets between growth cycles in corallite porosity and theca geochemistry (Lithium/Magnesium and Barium/Calcium ratios) of a single Siderastrea siderea core collected in Barbados. We show spatial offsets and thus tissue depth vary systematically over multiyear timescales, with decreasing values associated with thermal stress that impact extension rate and calcification in subsequent growth cycles. Large environmental disturbances such as the 2021 volcanic eruption of La Soufrière (St. Vincent) also impact tissue depth, in this case likely due to the release of bioactive metals upon ash deposition. This study investigates the robustness of the offset signal within a single colony and with further validation across multiple colonies could help reconstruct regional to global environmental and ecological stressors.

Changes in atmospheric carbon dioxide concentrations, climate, and land management influence the abundance and distribution of C₃ and C₄ plants, yet their impact on the global carbon cycle remains uncertain. Here, we use a parsimonious model of C₃ and C₄ plant distribution, based on optimality principles, combined with a simplified representation of the global carbon cycle, to assess how shifts in plant abundances driven by carbon dioxide and climate affect global gross primary production, land carbon isotope discrimination, and the isotopic composition of atmospheric carbon dioxide. We estimate that the proportion of C₄ plants in total biomass declined from about 16% to 12% between 1982 and 2016, despite an increase in the abundance of C₄ crops. This decline reflects the reduced competitive advantage of C₄ photosynthesis in a carbon dioxide-enriched atmosphere. As a result, global gross primary production rose by approximately 16.5 ± 1.8 petagrams of carbon, and land carbon isotope discrimination increased by 0.017 ± 0.001‰ per year. Accounting for changes in C₃ and C₄ abundances reduces the difference between observed and modeled trends in atmospheric carbon isotope composition, but does not fully explain the observed decrease, pointing to additional, unaccounted drivers.

The Gulf Stream is part of the Atlantic Meridional Overturning Circulation (AMOC). The AMOC is a tipping element and may collapse under changing forcing. However, the role of the Gulf Stream in such a tipping event is unknown. Here, we investigate the link between the AMOC and Gulf Stream using a high-resolution (0. 1°) stand-alone ocean simulation, in which the AMOC collapses under a slowly-increasing freshwater forcing. AMOC weakening gradually shifts the Gulf Stream near Cape Hatteras northward, followed by an abrupt northward displacement of 219 km within 2 years. This rapid shift occurs a few decades before the simulated AMOC collapse. Satellite altimetry shows a significant (1993-2024, p < 0.05) northward Gulf Stream trend near Cape Hatteras, which is also confirmed in subsurface temperature observations (1965-2024, p < 0.01). These findings provide indirect evidence for present-day AMOC weakening and demonstrate that abrupt Gulf Stream shifts can serve as early warning indicator for AMOC tipping.

Outcrops and cores are primary sources of information about the Earth's past. Quantitative analyses rely on geochronologies that take into account highly variable sedimentation and erosion rates as well as gaps from missing strata. Using 23 geochronologies from the Holocene, Quaternary, Phanerozoic and Precambrian, we apply Haar fluctuation analysis to statistically characterize the number of measurements per unit time - the measurement densities. The analysis determines the densities' (multifractal) scaling regimes and exponents; collectively, the analyses span over nine orders of magnitude in time scale. The measurement density is a new paleoindicator that we show is typically correlated with the primary paleoindicator, biasing and complicating its statistical interpretation. We also analyze the distribution of gaps linking the latter's (probability) scaling with series incompleteness and the length Sadler effect. The density characteristics are needed to unbias spectra and other statistical characterizations.

Marine Protected Areas (MPAs) are important tools in marine conservation. However, MPAs have unforeseen consequences, including complex adverse outcomes for human coastal communities through impacts such as dispossession of people to resource access. Here we searched the literature for evidence of MPA effects across the Sustainable Development Goals (SDGs), collected information on these effects and the forms of evidence used to document these effects. Our analysis indicated that MPAs can have both positive and negative effects across each of the 17 SDGs, and that many papers rely on secondary data over primary data to assess those effects. For SDGs 1 (End Poverty), 2 (No Hunger), and 5 (Gender Equality) we found that papers highlighting benefits of MPAs were usually more reliant on secondary information than papers emphasizing adverse impacts. Given the importance of local contexts, MPAs are better used as precision interventions rather than broad policy tools for achieving large-scale marine sustainability.

Snow water is key to water supply in cold regions and beyond. Here we introduce Snow Water Availability that quantifies water stored in the snow-covered portion of an area. By integrating a plausible set of available gridded datasets for snow depth, density, and cover fraction, we form four estimates of Snow Water Availability at the 25 × 25 km² across Canada and Alaska. We show that annual long-term mean of Snow Water Availability over the domain was 996 ± 170 km³ during 2000-2019. While annual Snow Water Availability increased from 799 ± 121 km³ in 2000-2009 to 1208 ± 231 km³ in 2010-2019, significant losses (p-value ≤ 0.05) were observed in ~3% of the domain, mainly in North American Cordillera, headwaters to major rivers in western Canada. These losses alongside insignificant decreases across southern Canada can threaten water supply in a quarter of the country, where ~86% of its population reside.

The outbreak of Highly Pathogenic Avian Influenza H5N1 in U.S. dairy cattle poses substantial risks to public health, economic sustainability of farming, and global food systems. Using a Computable General Equilibrium model, we simulate its short- to medium-term impacts on Gross Domestic Product and other macro-economic outcomes for the US and its main trading partners. We simulate impacts under the current situation and realistic and reasonable worst-case scenarios. We estimate domestic economic losses ranging between 0.06% and 0.9% of US GDP, with losses to the dairy sector ranging between 3.4% and 20.6%. Trading partners increase dairy production to compensate for the loss. Current government subsidies are about 1.2% (95% HDI: 1% to 1.4%) of output losses, and likely insufficient to incentivise farmers to step up surveillance and biosecurity for mitigating the possible emergence of H5N1 strains with pandemic potential into human populations.