69 research outputs found
Regional climate variability in the western subtropical North Atlantic during the past two millennia
Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography 26 (2011): PA2206, doi:10.1029/2010PA002038.Western subtropical North Atlantic oceanic and atmospheric circulations connect tropical and subpolar climates. Variations in these circulations can generate regional climate anomalies that are not reflected in Northern Hemisphere averages. Assessing the significance of anthropogenic climate change at regional scales requires proxy records that allow recent trends to be interpreted in the context of long-term regional variability. We present reconstructions of Gulf Stream sea surface temperature (SST) and hydrographic variability during the past two millennia based on the magnesium/calcium ratio and oxygen isotopic composition of planktic foraminifera preserved in two western subtropical North Atlantic sediment cores. Reconstructed SST suggests low-frequency variability of âŒ1°C during an interval that includes the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). A warm interval near 1250 A.D. is distinct from regional and hemispheric temperature, possibly reflecting regional variations in ocean-atmosphere heat flux associated with changes in atmospheric circulation (e.g., the North Atlantic Oscillation) or the Atlantic Meridional Overturning Circulation. Seawater ÎŽ 18O, which is marked by a fresher MCA and a more saline LIA, covaries with meridional migrations of the Atlantic Intertropical Convergence Zone. The northward advection of tropical salinity anomalies by mean surface currents provides a plausible mechanism linking Carolina Slope and tropical Atlantic hydrology.This study was
supported by the Woods Hole Oceanographic Institutionâs Ocean and Climate
Change Institute (OCCI) and by the National Science Foundation
Routing of western Canadian Plains runoff during the 8.2 ka cold event
The collapse of the Laurentide Ice Sheet over Hudson Bay âŒ8.47 ka allowed the rapid drainage of glacial Lake Agassiz into the Labrador Sea, an event identified as causing a reduction in Atlantic meridional overturning circulation (AMOC) and the 8.2 ka cold event. Atmosphere-ocean models simulations based on this forcing, however, fail to reproduce several characteristics of this event, particularly its duration. Here we use planktonic foraminifera U/Ca records to document the routing of western Canadian Plains runoff that accompanied ice-sheet collapse. Geochemical modeling of the âŒ7 nmol/mol increase in U/Ca at the opening of Hudson Bay indicates an increase in freshwater discharge of 0.13 ± 0.03 Sverdrups (106 m3 sâ1) from routing, a sufficient magnitude to cause an AMOC reduction. We suggest that this routing event suppressed AMOC strength for several centuries after the drainage of Lake Agassiz, explaining multi-centennial climate anomalies associated with the 8.2 ka cold event
Analytical model for the calculation of lateral velocity distributions in potential cross-sections
[EN] The hydraulic modeling of water depth and flow velocities in open channel flows that were fitted by power-law cross-section stand out for their versatility, allowing their use in numerous practical applications, both in natural and artificial channels. The determination of the hydraulic variables of depth and average velocity has been widely studied in potential cross-sections; however, the variation seen in these variables along the cross-section was not found in the literature. Knowledge of this variation allows the development of studies (e.g. to know the approximate damage in different areas of the cross-section, to analyse sediment transport, or other applications in river hydraulics). This paper presents a methodology which allows calculation of the hydraulic variables in any area of a power-law cross-section. The methodology is applied to symmetrical cross-sections, comparing its generated results with the obtained values by different computational hydraulic codes, which are thoroughly accepted by scientific community, such as CES, HEC-RAS and IBER. The obtained predictions of hydraulic parameters (using the explicit formulation described in this research) present very low errors when compared with results of other models, with great computational cost. These errors reach a root mean square error (RMSE) of 0.13 and 0.05 in the determination of velocities' lateral distribution and the ratio between velocity and average velocity. These values indicate a very successful validation for the analysed symmetrical sections.[ES] La modelizaciĂłn hidrĂĄulica de calados y velocidades de flujo, en cauces con secciones que admiten
una representaciĂłn de tipo potencial, se destaca por su versatilidad, permitiendo su utilizaciĂłn en
numerosas aplicaciones prĂĄcticas tanto en canales naturales como artificiales. El cĂĄlculo de las
variables hidrĂĄulicas (calado y velocidad media) ha sido ampliamente estudiado para este tipo de
secciones. Sin embargo, en la literatura técnica no se han encontrado estudios que muestren la
variaciĂłn de estas magnitudes a lo largo de la secciĂłn transversal. El conocimiento de esta variaciĂłn
permite desarrollar estudios (ejemplo: conocer de manera aproximada los daños en diferentes zonas
de la secciĂłn, analizar el transporte de sedimentos, estudiar los procesos de erosiĂłn u otras aplicaciones en hidrĂĄulica fluvial). Presentamos una metodologĂa que permite el cĂĄlculo de las variables
hidrĂĄulicas en cualquier zona de una secciĂłn tipo potencial. La metodologĂa es aplicada a secciones
simétricas, comparando los resultados generados con los obtenidos por diferentes códigos
hidrĂĄulicos computacionales ampliamente aceptados por la comunidad cientĂfica (p-e- CES, HECRAS e IBER). Las predicciones de los parĂĄmetros hidrĂĄulicos obtenidas (usando la formulaciĂłn
explĂcita descrita en este artĂculo) presentan errores muy bajos, en comparaciĂłn con otros modelos
con mayor costo computacional. Estos errores alcanzan un valor promedio para la raĂz del error
cuadrĂĄtico medio (RMSE) en el cĂĄlculo de la distribuciĂłn lateral de velocidades de 0.13 y de 0.05, en el
cĂĄlculo de la relaciĂłn de velocidades respecto a la velocidad media. Estos valores indican una
validaciĂłn muy satisfactoria para las secciones simĂ©tricas analizadas.SĂĄnchez-Romero, F.; PĂ©rez-SĂĄnchez, M.; LĂłpez JimĂ©nez, PA. (2018). Modelo analĂtico para el cĂĄlculo de distribuciones de velocidad laterales en secciones tipo potencial-ley. RIBAGUA - Revista Iberoamericana del Agua. 5(1):29-47. doi:10.1080/23863781.2018.1442189S29475
Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era
Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high-and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.(TABLE)Since the pioneering work of D'Arrigo and Jacoby1-3, as well as Mann et al. 4,5, temperature reconstructions of the Common Era have become a key component of climate assessments6-9. Such reconstructions depend strongly on the composition of the underlying network of climate proxies10, and it is therefore critical for the climate community to have access to a community-vetted, quality-controlled database of temperature-sensitive records stored in a self-describing format. The Past Global Changes (PAGES) 2k consortium, a self-organized, international group of experts, recently assembled such a database, and used it to reconstruct surface temperature over continental-scale regions11 (hereafter, ` PAGES2k-2013').This data descriptor presents version 2.0.0 of the PAGES2k proxy temperature database (Data Citation 1). It augments the PAGES2k-2013 collection of terrestrial records with marine records assembled by the Ocean2k working group at centennial12 and annual13 time scales. In addition to these previously published data compilations, this version includes substantially more records, extensive new metadata, and validation. Furthermore, the selection criteria for records included in this version are applied more uniformly and transparently across regions, resulting in a more cohesive data product.This data descriptor describes the contents of the database, the criteria for inclusion, and quantifies the relation of each record with instrumental temperature. In addition, the paleotemperature time series are summarized as composites to highlight the most salient decadal-to centennial-scale behaviour of the dataset and check mutual consistency between paleoclimate archives. We provide extensive Matlab code to probe the database-processing, filtering and aggregating it in various ways to investigate temperature variability over the Common Era. The unique approach to data stewardship and code-sharing employed here is designed to enable an unprecedented scale of investigation of the temperature history of the Common Era, by the scientific community and citizen-scientists alike
Inhibition of spontaneous mammary carcinoma of mice by treatment with interferon and poly i.c.
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