Outed by FOIA – EPA strategy memo reveals deep flaws in the integrity of the agency, and lack of integrity of the press
Nature Geoscience. doi:10.1038/ngeo2355
Author: Peter B. de Menocal
The Sahara was more humid and habitable thousands of years ago. Reconstructions of North African hydroclimate show that the onset of aridity started in the north, with the monsoon rains weakening progressively later at lower latitudes.
Nature Geoscience. doi:10.1038/ngeo2341
Authors: Rafael Marcé, Biel Obrador, Josep-Anton Morguí, Joan Lluís Riera, Pilar López & Joan Armengol
Most lakes and reservoirs have surface CO2 concentrations that are supersaturated relative to the atmosphere. The resulting CO2 emissions from lakes represent a substantial contribution to the continental carbon balance. Thus, the drivers of CO2 supersaturation in lakes need to be understood to constrain the sensitivity of the land carbon cycle to external perturbations. Carbon dioxide supersaturation has generally been attributed to the accumulation of inorganic carbon in lakes where respiration exceeds photosynthesis, but this interpretation has faced challenges. Here we report analyses of water chemistry data from a survey of Spanish reservoirs that represent a range of lithologies, using simple metabolic models. We find that, above an alkalinity threshold of 1 mequiv. l−1, CO2 supersaturation in lakes is directly related to carbonate weathering in the watershed. We then evaluate the global distribution of alkalinity in lakes and find that 57% of the surface area occupied by lakes and reservoirs—particularly in tropical and temperate latitudes—has alkalinity exceeding 1 mequiv. l−1. We conclude that lake inputs of dissolved inorganic carbon from carbonate weathering should be considered for the CO2 supersaturation of lakes at both regional and global scales.
Nature Geoscience. doi:10.1038/ngeo2349
Authors: Hanno Meyer, Thomas Opel, Thomas Laepple, Alexander Yu Dereviagin, Kirstin Hoffmann & Martin Werner
Relative to the past 2,000 years, the Arctic region has warmed significantly over the past few decades. However, the evolution of Arctic temperatures during the rest of the Holocene is less clear. Proxy reconstructions, suggest a long-term cooling trend throughout the mid- to late Holocene, whereas climate model simulations show only minor changes or even warming. Here we present a record of the oxygen isotope composition of permafrost ice wedges from the Lena River Delta in the Siberian Arctic. The isotope values, which reflect winter season temperatures, became progressively more enriched over the past 7,000 years, reaching unprecedented levels in the past five decades. This warming trend during the mid- to late Holocene is in opposition to the cooling seen in other proxy records. However, most of these existing proxy records are biased towards summer temperatures. We argue that the opposing trends are related to the seasonally different orbital forcing over this interval. Furthermore, our reconstructed trend as well as the recent maximum are consistent with the greenhouse gas forcing and climate model simulations, thus reconciling differing estimates of Arctic and northern high-latitude temperature evolution during the Holocene.
Nature Geoscience. doi:10.1038/ngeo2346
Authors: Gerard H. Roe, Nicole Feldl, Kyle C. Armour, Yen-Ting Hwang & Dargan M. W. Frierson
Nature Geoscience. doi:10.1038/ngeo2329
Authors: Timothy M. Shanahan, Nicholas P. McKay, Konrad A. Hughen, Jonathan T. Overpeck, Bette Otto-Bliesner, Clifford W. Heil, John King, Christopher A. Scholz & John Peck