180 resultados para Equivalent temperatures
Resumo:
Während sich Mitteleuropa bereits seit 1920 in einer Phase sinkender Januartemperatur befindet, trat dieser Klima-Umschwung in höheren Breiten immer später ein, so waren in Königsberg die beiden Januar Lustren 1916-1920 und 1921-1925 gleich warm, und in Upsala und Haparanda waren die Jahrfünfte mildester Januartemperatur in beiden Fällen 1931-35 - eine Erscheinung von übrigens weltweitem Charakter, denn auch weiteste Teile der U.S.A. hatten in dieser Zeit die mildesten Januarmonate.
Resumo:
Abundance variations of six Pliocene species of discoasters have been analyzed over the time interval from 1.89 to 2.95 Ma at five contrasting sites in the North Atlantic: Deep Sea Drilling Project Sites 552 (56°N) and 607 (41°N) and Ocean Drilling Program 658 (20°N), 659 (18°N), and 662 (1°S). A sampling interval equivalent to approximately 3 k.y. was used. Total Discoaster abundance showed a reduction with increasing latitude and from the effects of upwelling. This phenomenon is most obvious in Discoaster brouweri, the only species that survived over the entire time interval studied. Prior to 2.38 Ma, Discoaster pentaradiatus and Discoaster surculus are important components of the Discoaster assemblage: Discoaster pentaradiatus increases slightly with latitude up to 41°N, and its abundance relative to D. brouweri increases up to 56°N; D. surculus increases in abundance with latitude and with upwelling conditions relative to both D. brouweri and D. pentaradiatus and is dominant to the latter species at upwelling Site 658 and at the highest latitude sites. Discoaster asymmetricus and Discoaster tamalis appear to increase in abundance with latitude relative to D. brouweri. Many of the abundance changes observed appear to be connected with the initiation of glaciation in the North Atlantic at 2.4 Ma. The long-term trend of decreasing Discoaster abundance probably reflects the fall of sea-surface temperatures. This trend of cooling is overprinted by short-term variations that are probably associated with orbital forcing. Evidence for the astronomical elements of eccentricity and obliquity periodicities were found at all sites; however, only at Sites 607, 659, and 662 were precessional periodicities detected. Furthermore, only at Site 659 was precession found to be dominant to obliquity. Abundance peaks of individual species were found to cross-correlate between sites. The distinct abundance fluctuations observed especially in the tropics suggest that temperature is not the only factor responsible for this variation. This study reveals for the first time the importance of productivity pressure on the suppression of Discoaster abundance.
Resumo:
Here we present a new, pan-North-Atlantic compilation of data on key mesozooplankton species, including the most important copepod, Calanus finmarchicus. Distributional data of eight representative zooplankton taxa, from recent (2000-2009) Continuous Plankton Recorder data, are presented, along with basin-scale data of the phytoplankton colour index. Then we present a compilation of data on C. finmarchicus, including observations of abundance, demography, egg production and female size, with accompanying data on temperature and chlorophyll. . This is a contribution by Canadian, European and US scientists and their institutions.
Resumo:
Ist die Tatsache ungewöhnlicher Temperaturzunahme im Nordpolarraum in den letzten Jahrzehnten durch zahlreiche Publikationen allgemein bekannt, so möchte ich hier auf einige sehr bemerkenswerte, in jüngster Zeit von mir aufgedeckte Erscheinungen und Beziehungen hinweisen. 1. Die Milderung der Wintertemperatur an der W-Küste Grönlands. Bildet man die Wintertemperaturdifferenzen: Godthab minus Jakobshavn, so zeigt sich für die untersuchte Reihe 1876-1939: 2. eine periodische Schwankung mit sehr gut ausgeprägten Maximis um die Mitte der Neunzigerjahre und um 1920, Minima um 1880, 1905 und Ende der 20er Jahre, das besonders abgeschwächt ist; seitdem ist diese Differenz wieder in Zunahme begriffen; es zeigt sich somit auch hier meine an zahlreichen Gebieten von der Äquatorial bis zur Polarzone aufgedeckte 24 jährige Witterungsperiode. 3. Die Abschwächung der Winter-Temperaturdifferenz von Godthaah bis Jakobshavn ist (trotz der relativ nur geringen Entfernung von kaum 600 km) als ungewöhnlich hoch zu betrachten. Um diese Verhältnisse eindrucksvoll darlegen zu können, ist die klare Darlegung durch Tabellen unerläßlich.
Resumo:
Wet sedge tundra communities in the High Arctic are valuable sources of forage for several resident and migratory herbivores; however, the effects of grazing on these systems have been rarely studied. We simulated grazing in two wet sedge meadows at a site on Ellesmere Island that has not been affected by grazing. Over two summers, we clipped plots at four different frequencies and removed litter to assess effects on aboveground net primary production, availability of soil nitrogen, shoot concentrations of carbon and nitrogen, and soil temperature and moisture regimes. Available soil nitrate and ammonium were highest in plots with intermediate clipping frequencies. Shoot nitrogen concentrations were also greater at intermediate clipping frequencies in two of the four species studied. Aboveground net primary production decreased after clipping, regardless of frequency. Litter removal resulted in slightly increased soil moisture, but had no effect on aboveground net primary production. Soil temperature was not affected by any of our treatments. These results suggest that nitrogen cycling is stimulated by intermediate frequencies of simulated grazing, but clipping decreased aboveground net primary production in ungrazed high arctic wet sedge tundra.
Resumo:
Alkali phosphatase activity and hydrochemical structure of waters in the Barents and Norwegian seas were investigated. In a sea with the seasonal bioproduction cycle alkali phosphatase activity is also seasonal, rising with trophic level of waters. At the end of hydrological and biological winter activity is practically zero. Alkali phosphatase activity is especially important in summer, when plankton has consumed winter supply of phosphate in the euphotic layer and nutrient limitation of primary production begins. In summer production and destruction cycle, apparent time for recycling of phosphorus by phosphatase in suspended matter in the euphotic layer of the Barents Sea and Norwegian Sea averages from 7 to 30 hours.
Resumo:
The carbonate shell of the bivalve Arctica islandica has been recognized, for more than a decade, as a potentially important marine geochemical biorecorder owing to this species' great longevity (200+ years) and wide geographic distribution throughout the northern North Atlantic Ocean, a region vital to global climate and ocean circulation. However, until now this potential has not been realized owing to the difficulty of precisely sampling the shell of this slow growing species. Using newly available automated microsampling techniques combined with micromass stable isotope mass spectrometry, a stable oxygen isotope record (1956-1957 and 1961-1970) has been obtained from a live-captured, 38-year-old A. islandica specimen collected near the former position of the Nantucket Shoals Lightship (41°N. 69°W). The shell's delta18O signal is compared with an expected signal derived from ambient bottom temperature and salinity data recorded at the lightship for the same period. The results show that A islandica's delta18O record (1) is in phase with its growth banding, confirming the annual periodicity of this species' growth bands, (2) is in oxygen isotopic equilibrium with the ambient seawater, (3) shows a consistent shell growth shutdown temperature of ~6°C. which translates into an ~8-month (May-December) shell growth period at this location, and (4) records the ambient bottom temperature with a precision of ~ +/-1.2°C. These results add important information on the life history of this commercially important shellfish species and demonstrate that A. islandica shells can be used to reconstruct inter- and intra-annual records of the continental shelf bottom temperature.