Organic Geochemical Analysis of Late-Glacial and Early-Holocene Ecosystem Changes: A Case Study from Northern New England Lakes

The lacustrine sedimentary archive of organic remains provides important evidence for the reconstruction of the environmental histories of lakes and their watersheds, recording the response of the Earth\u27s biota to changes on scales varying from the local to the global. The last Glacial-Interglacial transition presents an opportunity to investigate how, and at what rates, watershed and lake ecosystems were established on once glaciated, carbon and nutrient-poor landscapes. The small lakes of northern Vermont (USA) provide an appropriate setting in which to investigate such changes. As part of a multidisciplinary study of three Vermont lake sediment cores, samples ranging in age from approximately 5 to 11 ka were subjected to molecular organic geochemical analysis by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). Diagnostic compounds in the pyrolyzates (e.g., indole and guaiacol) permit discrimination between the principal organic matter sources (e.g., microbial and higher plant) and their shifting proportions over time as a function of environmental change. While the nature of this shift is similar, it does not occur at the same rate in all three lakes, indicating the profound influence of local conditions

Spatial Variability of the Dominant Climate Signal in Cassiope tetragona from Sites in Arctic Canada

Our study investigates the nature of the climate signal in three populations of the Arctic dwarf-shrub Cassiope tetragona using dendrochronological and stable isotope analysis techniques. We present 15 new C. tetragona chronologies from three sites (Axel Heiberg, Bathurst, and Devon islands) in the eastern Canadian Arctic, of which three are the first continuous stable carbon isotope ratio (δ¹³C) time series developed for Arctic shrubs. Correlation and multivariate regression analyses revealed that multiple and different climate factors influenced the chronologies within and between the three sites. At the Axel Heiberg Island site, the dominant climatic influences over annual stem elongation were previous year (t-1) and current year (t) summer precipitation, while annual production of flower buds was influenced by (t) winter precipitation and spring temperature. At Bathurst Island, annual production of flower buds responded to (t-1) growing season sunshine hours and winter precipitation and to (t) late growing season temperature and moisture availability. Our analysis of the Axel Heiberg and Bathurst Island models revealed the positive influence on δ13C values of (t-1) winter temperature—and on Bathurst Island only, of (t-1) spring sunshine hours. The combined influence of these parameters on spring moisture availability suggests that the δ13C ratios varied in response to stomatal conductance. At Devon Island, the δ13C values varied in response to (t) and (t-1) spring and summer temperature and spring and fall solar radiation, which in turn influence the rate of photosynthesis. Our study supports the emerging hypothesis that Arctic shrubs are sensitive to climate. However, strong spatial variation in plant-climate response characterized our sampling sites. This variation may be linked to site sensitivity, or regional climate variability due to geographic and topographic differences, or both. Notre étude prend la forme d’une enquête sur la nature du signal d’effet de serre au sein de trois populations arctiques d’arbustes nains Cassiope tetragona à l’aide de techniques d’analyse dendrochronologique et d’isotopes stables. Nous présentons 15 nouvelles chronologies de C. tetragona provenant de trois emplacements (îles Axel Heiberg, Bathurst et Devon) dans la partie est de l’Arctique canadien, dont trois de ces chronologies représentent la première série chronologique de rapport isotopique de carbone stable continu (δ¹³C) à avoir été établie pour des arbustes de l’Arctique. Des analyses de corrélation et de régression à plusieurs variables ont permis de révéler que des facteurs climatiques différents et variables ont exercé une influence sur les chronologies au sein des trois emplacements et entre ceux-ci. À l’emplacement de l’île Axel Heiberg, les influences climatiques dominantes par rapport à la montaison annuelle étaient les précipitations d’été de l’année précédente (t-1) et de l’année en cours (t), tandis que la production annuelle des boutons à fleur était influencée par les précipitations d’hiver (t) et les températures du printemps. À l’île Bathurst, la production annuelle de boutons à fleur réagissait à (t-1), soit le nombre d’heures d’ensoleillement pendant la saison de croissance et les précipitations d’hiver et à (t), soit les températures en fin de saison de croissance et l’humidité disponible. Notre analyse des modèles des îles Axel Heiberg and Bathurst a révélé l’influence positive des températures d’hiver (t-1) sur les valeurs de δ13C — et à l’île Bathurst seulement, des heures d’ensoleillement du printemps (t-1). L’influence conjointe de ces paramètres sur l’humidité disponible au printemps laisse entendre que les rapports de δ13C varient en fonction de la conductance stomatique. À l’île Devon, les valeurs de δ13C varient en fonction de (t) et de (t-1), soit les températures du printemps et de l’été ainsi que le rayonnement solaire du printemps et de l’automne, qui exercent, à leur tour, une influence sur le taux de photosynthèse. Notre étude vient appuyer la nouvelle hypothèse selon laquelle les arbustes de l’Arctique sont sensibles au climat. Cependant, nos lieux d’échantillonnage étaient caractérisés par une importante variation spatiale en matière de réponse climatique des végétaux. Cette variation pourrait se rattacher à la sensibilité de l’emplacement, ou à la variabilité climatique attribuable aux différences géographiques et topographiques, ou encore, à ces deux éléments.

Meteoric 10Be as a tracer of subglacial processes and interglacial surface exposure in Greenland

In order to test whether sediment emerging from presently glaciated areas of Greenland was exposed near or at Earth's surface during previous interglacial periods, we measured the rare isotope 10Be contained in grain coatings of sediment collected at five ice marginal sites. Such grain coatings contain meteoric 10Be (10Bemet), which forms in the atmosphere and is deposited onto Earth's surface. Samples include sediment entrained in ice, glaciofluvial sediment collected at the ice margin, and subglacial sediment extracted during hot water drilling in the ablation zone. Due to burial by ice, contemporary subglacial sediment could only have acquired substantial 10Bemet concentrations during periods in the past when the Greenland Ice Sheet was less extensive than present. The highest measured 10Bemet concentrations are comparable to those found in well-developed, long-exposed soils, suggesting subglacial preservation and glacial transport of sediment exposed during preglacial or interglacial periods. Ice-bound sediment has significantly higher 10Bemet concentrations than glaciofluvial sediment, suggesting that glaciofluvial processes are sufficiently erosive to remove tracers of previous interglacial exposures. Northern Greenland sites where ice and sediment are supplied from the ice sheet's central main dome have significantly higher 10Bemet concentrations than sites in southern Greenland, indicating greater preglacial or interglacial landscape preservation in central Greenland than in the south. Because southern Greenland has more frequent and spatially extensive periods of glacial retreat but nevertheless has less evidence of past subaerial exposure, we suggest that 10Bemet measurements in glacial sediment are primarily controlled by erosional efficiency rather than interglacial exposure length

Preservation of a Preglacial Landscape Under the Center of the Greenland Ice Sheet

Continental ice sheets typically sculpt landscapes via erosion; under certain conditions, ancient landscapes can be preserved beneath ice and can survive extensive and repeated glaciation. We used concentrations of atmospherically produced cosmogenic beryllium-10, carbon, and nitrogen to show that ancient soil has been preserved in basal ice for millions of years at the center of the ice sheet at Summit, Greenland. This finding suggests ice sheet stability through the Pleistocene (i.e., the past 2.7 million years). The preservation of this soil implies that the ice has been non-erosive and frozen to the bed for much of that time, that there was no substantial exposure of central Greenland once the ice sheet became fully established, and that preglacial landscapes can remain preserved for long periods under continental ice sheet

Carbon and Nitrogen Stable Isotope Values for Plants and Mammals in a Semi-Desert Region of Mongolia

Little information exists on the isotopic signatures of plants and animals in Mongolia, limiting the application of stable isotope analysis to wildlife biology studies. Here we present plant and mammal carbon (δ 13 C) and nitrogen (δ 15 N) isotope values from a desert-steppe region of southeastern Mongolia. We analyzed 11 samples from 11 plant species and 93 samples from 24 mammal species across Ikh Nart Nature Reserve, and compared these numbers to isotope values reported from other areas of Mongolia. Our plant and mammal 13 C and 15 N values were similar to those from a similar arid steppe region and more enriched than those from less arid habitats. Habitat variation within and between study sites has an important infl uence on δ 13 C and δ 15 N variation. Our results supplement current knowledge of isotopic variation in Mongolia and provide a reference for future stable isotope research in Mongolia and similar Asian steppe ecosystems

Biberovic et al., Diatom-based transfer functions for pH and total phosphorus in Vermont, USA lakes

Data and model code associated with Biberovic et al., "Diatom-based transfer functions for pH and total phosphorus in Vermont, USA lakes", under review, Journal of Paleolimnology. Preprint (current 2 February 2024): https://www.researchsquare.com/article/rs-3098032/latest ; DOI will be updated when published.</p

Tier II MRV of livestock emissions in China - Final report & Annexes

Countries are required to account for greenhouse gas (GHG) emissions and their mitigation under the UNFCCC’s Paris Agreement, yet most countries are still developing their systems for the measurement, reporting and verification (MRV) of emissions in agriculture. Guidance from the IPCC exists to estimate impacts, yet implementation of MRV also requires tailoring to country needs and conditions. In the livestock sector, accurate, comparable, consistent, complete and transparent MRV systems that can capture changes in emissions and sequestration from a range of practices and agroecological conditions are essential to guide the transformation to a low emissions future. Many countries with livestock emissions are seeking advanced GHG accounting to better reflect national circumstances and track mitigation due to productivity changes. To help countries improve accounting, CCAFS and experts across the globe are working together with countries to identify cost-effective technically sound MRV and the guidance, tools, and platforms that support them. As part of its national accounting, China is now seeking to improve their MRV of emissions from livestock. This project supports that effort. The purpose of this study is to develop methods and systems for Tier II MRV of livestock emissions at provincial level (Hebei Province) in China. - The objectives of this project are: (1) Produce practical guidance; (2) Build capacity for Tier II MRV among province-level authorities; (3) Develop methods and that can be used to support Tier II MRV elsewhere