Search results for " Climate"
showing 10 items of 3933 documents
Facies variations in response to Holocene sea-level and climate change on Bora Bora, French Polynesia: Unravelling the role of synsedimentary siderit…
2017
International audience; Five mixed carbonate-siliciclastic sedimentary facies were identified in the barrier-reef lagoon of Bora Bora using microfacies and statistical analyses of 70 sediment samples taken at high resolution from two vibrocores. Fades and fades successions were interpreted with respect to Holocene sea-level and climate changes. The windward lagoon core is characterized by sideritic marly wackestones and foraminifera-sideritic wackestones, deposited around 7700 years BP (years before present) during the early-mid Holocene transgression. At that time, extensive weathering and erosion of iron-bearing minerals from the volcanic island, due to a wetter climate, were expressed in…
Continental late Pliocene paleoclimatic history recorded in the Bresse Basin (France)
1992
International audience; We present results to show that the Beaune P & C borehole, cored in the Bresse Basin (France), records late Pliocene climatic variations. Pollen analysis allows precise correlations with northern and southern European stratigraphies. Using Kukla et al.'s (1981) climate index, we show that cold climate phases occur during the Brunssumian, at around 3.2, 3.6 and 5.2 Myr B.P., respectively, in agreement with Atlantic core results. The onset of a general cooling trend is felt early in the Reuverian, at about 3 Myr B.P. which corresponds to the end of a warm event characterized by high percentages of oak. This is followed by minor climatic pulses of increasing magnitude s…
Growth-increment characteristics and isotopic (delta O-18) temperature record of sub- thermocline Aequipecten opercularis (Mollusca: Bivalvia): evide…
2021
Abstract The shell δ18O of young modern Aequipecten opercularis from the southern North Sea provides an essentially faithful record of seasonal variation in seafloor temperature. In this well-mixed setting, A. opercularis shell δ18O also serves as a proxy for seasonal variation in surface temperature. Individuals from less agitated (e.g. deeper) settings in a warm climate would not be expected to record the full seasonal range in surface temperature because of thermal stratification in summer. Such circumstances have been invoked to explain cool isotopic summer temperatures from early Pliocene A. opercularis of eastern England. Support for a sub-thermocline setting derives from high-amplitu…
Changing patterns of eastern Mediterranean shellfish exploitation in the Late Glacial and Early Holocene: Oxygen isotope evidence from gastropod in E…
2016
Abstract The seasonal pattern of shellfish foraging at the archaeological site of Haua Fteah in the Gebel Akhdar, Libya was investigated from the Epipaleolithic to the Neolithic via oxygen isotope (δ 18 O) analyses of the topshell Phorcus (Osilinus) turbinatus . To validate this species as faithful year-round palaeoenvironmental recorder, the intra-annual variability of δ 18 O in modern shells and sea water was analysed and compared with measured sea surface temperature (SST). The shells were found to be good candidates for seasonal shellfish forging studies as they preserve nearly the complete annual SST cycle in their shell δ 18 O with minimal slowing or stoppage of growth. During the ter…
The Last Deglaciation of the Southeastern Sector of Scandinavian Ice Sheet
2006
The Scandinavian Ice Sheet (SIS) was an important component of the global ice sheet system during the last glaciation, but the timing of its growth to or retreat from its maximum extent remains poorly known. We used 115 cosmogenic beryllium-10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice-margin fluctuations of the SIS between 25,000 and 12,000 years before the present. The age of initial deglaciation indicates that the SIS may have contributed to an abrupt rise in global sea level. Subsequent ice-margin fluctuations identify opposite mass-balance responses to North Atlantic climate change, indicating differing ice-sheet sensitivities to mean climate state.
Testing the hypothesis of post-volcanic missing rings in temperature sensitive dendrochronological data
2013
a b s t r a c t The precise, annual dating control, inherent to dendrochronology, has recently been questioned through a combined analysis of tree-growth and coupled climate models (Mann et al. (2012; hereafter MAN12)) suggesting single tree-rings in temperature limited environments are missing following large volcanic events. We test this hypothesis of missing, post-volcanic rings by using a compilation of maximum late- wood density (MXD) records that are typically used for reconstructing temperature and the detection of volcanic events, together with a unique set of long instrumental station data from Europe reaching back into the early 18th century. We investigate the temporal coherence …
Ion fractionation in young sea ice from Kongsfjorden, Svalbard
2011
AbstractThe fractionation of major sea-water ions, or deviation in their relative concentrations from Standard Mean Ocean Water ratios, has been frequently observed in sea ice. It is generally thought to be associated with precipitation of solid salts at certain eutectic temperatures. the variability found in bulk sea-ice samples indicates that the fractionation of ions depends on the often unknown thermal history of sea ice, which affects the structure of pore networks and fate of solid salts within them. Here we investigate the distribution of ions in Arctic sea ice that is a few weeks old with a reconstructible thermal history. We separate the centrifugable (interconnected) and entrapped…
Paleoclimatic evolution of the Uvs Nuur basin and adjacent areas (Western Mongolia)
2000
Abstract The investigations presented in this paper focus on the shifts in Pleistocene glaciations and the geomorphic changes in landforms, as well as lake level changes and aeolian deposits of the last glacial–interglacial cycle, including the Holocene. Geomorphic evidence and high lake levels show that the climate was more humid before the last glacial maximum (LGM); however, at least one arid phase also occurred. During the second half of the LGM the climate was dry and cold, turning to wet and cold during the Late Glacial of the last Ice Age. Fluctuations in humidity and temperature occurred during the Holocene. Since about 2000 yr BP the impact of human activity has increased.
Climatic ups and downs in a disturbed Jurassic world.
2011
4 pages; International audience; The tropical, warm, and equable climate of the Jurassic world is regularly challenged by geoscientists, especially since oxygen isotopes ( 18O) of fossil hardparts have been used to reconstruct the paleotemperature history of seawater. By applying the innovative “SiZer” (significant zero crossings of the derivatives) statistical approach to a newly compiled 18O database for the Jurassic, we demonstrate the occurrence of major and multiscale 18O changes mainly related to climate disturbances. For the first time, two long-term anomalies in 18O are identified during the Toarcian and the Late Jurassic, in conjunction with intensive volcanism in large igneous pro…
ISOTOPIC TEMPERATURES FROM THE EARLY AND MID-PLIOCENE OF THE US MIDDLE ATLANTIC COASTAL PLAIN, AND THEIR IMPLICATIONS FOR THE CAUSE OF REGIONAL MARIN…
2017
Mean seasonal extreme temperatures on the seafloor calculated from the shell d 18 Oofthescallop Placopecten clintonius from the basal part of the early Pliocene Sunken Meadow Member (Yorktown Formation) in Virginia are very similar to those from the same horizon at the latitude of Cape Hatteras in North Carolina ( ~ 210 km to the south). The lowest and highest temperatures calculated from each shell (using d 18 O seawater ¼þ 0.7 % )givemean values for winter and summer of 8.4 6 1.1 8 C( 6 1 r ) and 18.2 6 0.6 8 CinVirginia,and8.6 6 0.4 8 Cand16.5 6 1.1 8 C in North Carolina (respective median temperatures: 13.3 8 C and 12.6 8 C). Patterns of ontogenetic variation in d 18 O, d 13 C and micro…