Previously, a large platinum (Pt) anomaly was reported in the Greenland ice sheet at the Younger Dryas boundary (YDB) (12,800 Cal B.P.). In order to evaluate its geographic extent, fire-assay and inductively coupled plasma mass spectrometry (FA and ICP-MS) elemental analyses were performed on 11 widely separated archaeological bulk sedimentary sequences. We document discovery of a distinct Pt anomaly spread widely across North America and dating to the Younger Dryas (YD) onset. The apparent synchroneity of this widespread YDB Pt anomaly is consistent with Greenland Ice Sheet Project 2 (GISP2) data that indicated atmospheric input of platinum-rich dust. We expect the Pt anomaly to serve as a widely-distributed time marker horizon (datum) for identification and correlation of the onset of the YD climatic episode at 12,800 Cal B.P. This Pt datum will facilitate the dating and correlating of archaeological, paleontological, and paleoenvironmental data between sequences, especially those with limited age control.
Groundwater management in the USA is diverse and decentralized making generaliza- tions sometimes difficult. In many areas groundwater is managed well under permit systems that pre- vent wasteful overuse and allow planned development. In other areas individuals are free to pump water with few restrictions and sometimes with wasteful consequences. This chapter provides an overview of collective groundwater management systems used in the USA by summarizing the types of systems in place and the advantages and disadvantages of each system. It concludes with an exam- ination of what can be learned from the groundwater management experience in the USA and sug- gestions for the development of future groundwater management systems.
Human-driven increases in atmospheric CO2 (eCO2) are stimulating plant growth, thereby increasing the input of plant-derived carbon into soils. The fate of this additional carbon depends on the capacity of soil microbiomes to decompose and transform organic matter, a central process in regulating soil organic carbon (SOC) dynamics. However, how eCO2 affects this microbial capacity remains poorly understood. Because soil extracellular enzymes catalyse the degradation of various SOC pools, their activities (extracellular enzyme activities, EEAs) could offer mechanistic insights into microbially mediated SOC dynamics. We synthesized 272 observations on SOC and EEAs from eCO2 experiments across farmland, forest, grassland and shrubland, combining classical meta-analysis with random forest modelling. Our results showed that eCO2 significantly increased SOC by 4.2%. Among all variables tested, increased cellulase activity, which targets the breakdown of labile carbon sources, emerged as the strongest predictor of SOC accumulation. Specifically, eCO2 stimulated cellulase activity by 12.2% but had no effect on ligninase activity, which decomposes recalcitrant carbon. This enzymatic shift was likely driven by increased plant-derived labile carbon inputs under eCO2 and was associated with changes in the soil microbiome, including a higher fungi-to-bacteria ratio. These results underscore the potential of EEA as a predictive indicator of SOC accumulation under eCO2 and the importance of representing enzymatic processes in Earth system models.Read the free for this article on the Journal blog.
