United States Geological Survey

About: United States Geological Survey is a government organization based out in Reston, Virginia, United States. It is known for research contribution in the topics: Population & Groundwater. The organization has 17899 authors who have published 51097 publications receiving 2479125 citations. The organization is also known as: USGS & US Geological Survey.

Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary

Abstract: Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate1,2, other than the 1–2.5 ‰ negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary3, is the rapid global positive excursion of ∼2 ‰ (13C enrichment) which took place between ∼91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of 13C-depleted organic carbon, which coincided with a major global rise in sea level5 during the so-called C/T oceanic anoxic event (OAE)6. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO2 and O2 concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies.

Change in atmospheric mineral aerosols in response to climate: Last glacial period, preindustrial, modern, and doubled carbon dioxide climates

Abstract: Desert dust simulations generated by the National Center for Atmospheric Research's Community Climate System Model for the current climate are shown to be consistent with present day satellite and deposition data. The response of the dust cycle to last glacial maximum, preindustrial, modern, and doubled-carbon dioxide climates is analyzed. Only natural (non-land use related) dust sources are included in this simulation. Similar to some previous studies, dust production mainly responds to changes in the source areas from vegetation changes, not from winds or soil moisture changes alone. This model simulates a +92%, +33%, and −60% change in dust loading for the last glacial maximum, preindustrial, and doubled-carbon dioxide climate, respectively, when impacts of carbon dioxide fertilization on vegetation are included in the model. Terrestrial sediment records from the last glacial maximum compiled here indicate a large underestimate of deposition in continental regions, probably due to the lack of simulation of glaciogenic dust sources. In order to include the glaciogenic dust sources as a first approximation, we designate the location of these sources, and infer the size of the sources using an inversion method that best matches the available data. The inclusion of these inferred glaciogenic dust sources increases our dust flux in the last glacial maximum from 2.1 to 3.3 times current deposition.

Larger trees suffer most during drought in forests worldwide

Abstract: The frequency of severe droughts is increasing in many regions around the world as a result of climate change(1-3). Droughts alter the structure and function of forests(4,5). Site- and region-specific studies suggest that large trees, which play keystone roles in forests(6) and can be disproportionately important to ecosystem carbon storage(7) and hydrology(8), exhibit greater sensitivity to drought than small trees(4,5,9,10). Here, we synthesize data on tree growth and mortality collected during 40 drought events in forests worldwide to see whether this size-dependent sensitivity to drought holds more widely. We find that droughts consistently had a more detrimental impact on the growth and mortality rates of larger trees. Moreover, drought-related mortality increased with tree size in 65% of the droughts examined, especially when community-wide mortality was high or when bark beetles were present. The more pronounced drought sensitivity of larger trees could be underpinned by greater inherent vulnerability to hydraulic stress(11-14), the higher radiation and evaporative demand experienced by exposed crowns(4,15), and the tendency for bark beetles to preferentially attack larger trees(16). We suggest that future droughts will have a more detrimental impact on the growth and mortality of larger trees, potentially exacerbating feedbacks to climate change.