Search for: All records

Climate warming is increasing ocean stratification, which in turn should decrease the nutrient flux to the upper ocean. This may slow marine primary productivity, causing cascading effects throughout food webs. However, observing changes in upper ocean nutrients is challenging because surface concentrations are often below detection limits. We show that the nutricline depth, where nutrient concentrations reach well-detected levels, is tied to productivity and upper ocean nutrient availability. Next, we quantify nutricline depths from a global database of observed vertical nitrate and phosphate profiles to assess contemporary trends in global nutrient availability (1972–2022). We find strong evidence that the P-nutricline (phosphacline) is mostly deepening, especially throughout the southern hemisphere, but the N-nutricline (nitracline) remains mostly stable. Earth System Model (ESM) simulations support the hypothesis that reduced iron stress and increased nitrogen fixation buffer the nitracline, but not phosphacline, against increasing stratification. These contemporary trends are expected to continue in the coming decades, leading to increasing phosphorus but not nitrogen stress for marine phytoplankton, with important ramifications for ocean biogeochemistry and food web dynamics. 

Key Points Simulated Prochlorococcus , Synechococcus , and pico‐eukaryotes contribute ∼60% of marine net primary productivity (NPP) Pico‐phytoplankton cycling contributes half of the marine export production, approaching parity with their contribution to NPP Pico‐eukaryotes and diatoms with elevated C:P stoichiometry enhance carbon export at poleward flanks of western boundary currents 

Abstract Ambient vibration measurements can detect resonance frequency changes related to rock slope instability damage or boundary condition changes during progressive failure. However, the impact of slope kinematics on resonance changes and the expected form and sensitivity of frequency evolution during destabilization require clarification to improve the implementation of this technique across diverse settings. Since instrumented rock slope failures are rare, numerical modeling is needed to study the anticipated spectral response from in situ monitoring. We used 2D distinct‐element modeling to evaluate the sensitivity and evolution of rock slope resonance behavior for slab toppling, flexural toppling, and planar sliding instabilities during progressive failure. Model simulations revealed that fundamental resonance frequency decreases between 20% and 60% with changes correlated with increasing length of open joints. Changes to higher‐order frequencies associated with landslide sub‐volumes were also detectable for cases with multiple fracture networks. Resonance behavior was most pronounced for failures dominated by steeply dipping open tension cracks, that is, flexural and slab toppling. Additionally, amplification patterns across the slope varied for the flexural toppling and sliding cases, providing potential new information with which to characterize landslide failure mechanisms using ambient vibration array measurements. Our results demonstrate landslide characteristics well‐suited for in situ ambient resonance monitoring and provide new data describing the anticipated changes in resonance frequencies during progressive rock slope failure. 

Abstract Sulfate is a potential pollutant and important nutrient linked with the nitrogen, carbon, and phosphorus cycles. The importance of different anthropogenic sulfate sources in suburban streams (septic systems, fertilizer, road salt, and infrastructure) is uncertain, and the temporal dynamics of stream export sparsely documented. We study sources and export dynamics of sulfate in suburban and forested headwater catchments. Stream baseflow discharge and sulfate concentrations were strongly positively correlated in both watersheds with the highest values in spring. Suburban concentrations and fluxes (2.48–7.5 mg/L or 25.8–78.1 μM, 16.6 kg/ha/yr) were consistently higher than forested (0.56–2.78 mg/L or 5.8–28.9 μM, 5 kg/ha/yr). Following precipitation, sulfate concentrations in both forested and suburban streams increased to concentrations above pre‐storm values and remained high after peak discharge. These dynamics suggest that both catchments have a large pool of sulfate that can be mobilized under wet conditions. Ridge‐top forest soil samples contained 210 kg/ha stored, extractable sulfate. Current atmospheric sulfate deposition rates (5–7 kg/ha/yr) are approximately in balance with sulfate export in the forested stream. In the suburban watershed, we estimated septic fields contribute up to 11 kg/ha/yr (about half from surfactants) and lawn care up to 4.3 kg/ha/yr and are the most likely sources of elevated stream sulfate. Sulfate sulfur (4.9–5.8‰ forested; 6.1–7.0‰ suburban) and oxygen isotope values (0.7–2.0‰ forested; −0.1–4.1‰ suburban) are consistent with this interpretation, but do not provide strong corroboration due to large variation and overlap in estimated source values. 

Abstract Aim The microbial metabolic quotient (MMQ; mg CO 2 ‐C/mg MBC/h), defined as the amount of microbial CO 2 respired (MR; mg CO 2 ‐C/kg soil/h) per unit of microbial biomass C (MBC; mg C/kg soil), is a key parameter for understanding the microbial regulation of the carbon (C) cycle, including soil C sequestration. Here, we experimentally tested hypotheses about the individual and interactive effects of multiple nutrient addition (nitrogen + phosphorus + potassium + micronutrients) and herbivore exclusion on MR, MBC and MMQ across 23 sites (five continents). Our sites encompassed a wide range of edaphoclimatic conditions; thus, we assessed which edaphoclimatic variables affected MMQ the most and how they interacted with our treatments. Location Australia, Asia, Europe, North/South America. Time period 2015–2016. Major taxa Soil microbes. Methods Soils were collected from plots with established experimental treatments. MR was assessed in a 5‐week laboratory incubation without glucose addition, MBC via substrate‐induced respiration. MMQ was calculated as MR/MBC and corrected for soil temperatures (MMQsoil). Using linear mixed effects models (LMMs) and structural equation models (SEMs), we analysed how edaphoclimatic characteristics and treatments interactively affected MMQsoil. Results MMQsoil was higher in locations with higher mean annual temperature, lower water holding capacity and lower soil organic C concentration, but did not respond to our treatments across sites as neither MR nor MBC changed. We attributed this relative homeostasis to our treatments to the modulating influence of edaphoclimatic variables. For example, herbivore exclusion, regardless of fertilization, led to greater MMQsoil only at sites with lower soil organic C (< 1.7%). Main conclusions Our results pinpoint the main variables related to MMQsoil across grasslands and emphasize the importance of the local edaphoclimatic conditions in controlling the response of the C cycle to anthropogenic stressors. By testing hypotheses about MMQsoil across global edaphoclimatic gradients, this work also helps to align the conflicting results of prior studies. 

Efforts to cultivate scientific literacy in the public are often aimed at enabling people to make more informed decisions — both in their own lives (e.g., personal health, sustainable practices, &c.) and in the public sphere. Implicit in such efforts is the cultivation of some measure oftrustof science. To what extent does science reporting in mainstream newspapers contribute to these goals? Is what is reported likely to improve the public's understanding of science as a process for generating reliable knowledge? What are its likely effects on public trust of science? In this paper, we describe a content analysis of 163 instances of science reporting in three prominent newspapers from three years in the last decade. The dominant focus, we found, was on particular outcomes of cutting-edge science; it was comparatively rare for articles to attend to the methodology or the social–institutional processes by which particular results come about. At best, we argue that this represents a missed opportunity.