Di Donato, ValentinoSgarrella, FrancaSprovieri, RodolfoDi Stefano, Enrico...
18页
查看更多>>摘要：Here we present a high-resolution record of benthic foraminiferal assemblages for the last 74 kyr from the Sicily Channel Ocean Drilling Program Leg 160 Site 963. Benthic foraminiferal results are compared with geochemical (benthic and planktic delta O-18 and delta C-13) and calcareous plankton data, previously acquired on the same marine core sediments. Within the succession, three benthic foraminifera compositional zones were defined. Temporal changes in the assemblages are interpreted in the context of the modification of subtropical and temperate climate systems that affected the Mediterranean thermohaline circulation. A close connection between bottom conditions in the Sicily Channel and eastern Mediterranean Sea is evident in two intervals, characterized in the ODP Site 963 by reduced oxygen conditions. The first one, around 53-51 ka, is tentatively attributed to the 'missing' sapropel S2 while the second, between 35 and 29 ka, is marked by short and recurrent episodes of bottom-water oxygen decrease. Both are related to a weakening of the intermediate circulation in the Sicily Channel connected with relatively high northern hemisphere summer insolation and increase in Nile River discharge, which inhibited vertical mixing and intermediate water ventilation in Eastern Mediterranean Sea. Over the last deglaciation, the African humid period (AHP) and the sea level rise, also influenced the water mass structure in the Sicily Channel and a reduction of the bottom ventilation is suggested by a strong reduction of deep-water Miliolids. Decreased bottom oxygen levels, which testifies for a weakening of intermediate circulation in Sicily Strait, also characterized the interval corresponding to S1 deposition. Yet, the strong decrease of benthic foraminiferal abundance related to a low surface water trophic level, appears to be conditioned by the reduction of trophic levels in the western Mediterranean. The very high relative abundance of U. mediterranea recorded during this interval is explained by the availability of organic matter during a limited short year period and/or the availability of more degraded organic matter from river runoff. In general, compositional data analysis highlighted a quite complex response of benthic foraminifera to paleoclimatic changes. However, changes in the benthic foraminiferal assemblages recorded during the last glacial are coherent with surface paleoproductivity dynamics connected with D-O oscillation, and support oligotrophic, meso-eutrophic and oligomesotrophic conditions during the early interstadials, late interstadials and stadials, respectively.
查看更多>>摘要：Exploring the Mid-Late Holocene interactions between ecological and climate variations in semi-arid areas such as Songnen grasslands (northeastern China) provide insights into how future vegetation changes and hydrological variations may have an impact on semi-arid ecosystems, in general. In this study, we present a high resolution palaeoecological dataset covering the past 7300 years. For this purpose, a peat section has been sampled from the shore of Dabusu lake situated in the southwestern part of the Songnen grasslands. We use pollen analyses to reconstruct the regional and local vegetation dynamics, and measure TOC (total organic carbon) and the degree of peat humification to study changes in regional and local biomass. Diatom analysis, grain size analysis, and CaCO3 contents are used to assess the water-table fluctuations of the Dabusu peatlands. The results show that from 7300 to 6000 cal BP, Dabusu peatlands were characterized by grasslands, dominated by Poaceae plants and high-water level. From 6000 to 910 cal BP, forest-steppes and dry-steppes dominated in the region alternatively. The water level of Dabusu peatlands experienced relatively low levels following an earlier rapid decline around 6000-5100 cal BP. Then after a slight increase between 5100 and 4000 cal BP, it remained at a relatively low level until 910 cal BP. After 910 cal BP, steppe vegetation dominated in the region and the water level of Dabusu peatlands slightly rose. By comparing these features with regional climate change, we show that EASM circulations might be the main driving forces controlling the regional paleovegetation dynamics and hydrological variations. This outcome is critical for the understanding of the long-term interactions between vegetation, hydrology, and climate of mid-latitude semi-arid grasslands.
查看更多>>摘要：The past 2000 years represent an important period of climate change. The Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA) have attracted much attention, but the start and end times and humidity characteristics of these climate stages are still controversial. Here, we present a lacustrine sediment record from the Erxianyan wetland in central China covering a timespan of 1900 years. The pollen, grain size, total organic carbon (TOC) content, total nitrogen (TN) and carbon-to-nitrogen ratio (C/N) analyses of the sediments derived from the Erxianyan wetland revealed the vegetation and climate changes that have occurred in central China over the past 1900 years. From 70 to 740 CE, the water level was high, the organic matter content of the lake reached a high level, and many plants surrounded the lake. The climate was warm and humid. From 740 to 1150 CE, the forest coverage increased, the fern coverage decreased, and the lake water volume decreased. The climate gradually changed from humid to dry. From 1150 to 1990 CE, the vegetation coverage around the lake decreased, the tree proportion declined, and the proportions of terrestrial herbs and ferns increased. The climate was cold and dry. The climate change characteristics reflected in the EXY profile roughly correspond to the Qin-Han Warm Period and Sui-Tang Warm Period. The MCA was warm and dry, while the LIA was cold and arid. Based on comparisons with other climate records and modern precipitation records, we found that the Erxianyan climate changes over the past 1900 years may have been affected by the combined effects of solar radiation, the El Nin & SIM;o-Southern Oscillation (ENSO) and the East Asian Summer Monsoon (EASM). These results also confirm the complexity of the climate in the middle and upper reaches of the Yangtze River during the MCA and the LIA.
查看更多>>摘要：The dark and confined conditions of submarine caves allow the development of cryptic bioconstructions. They have been named "biostalactites" due to their distinctive growth from the ceiling and walls. Biostalactites resemble small scale "build-up" and have received increasing attention in recent years since they allow geo-biological studies that could clarify the style of growth of the cryptic bioconstructions in the fossil record. The "lu Lampiune" cave in Apulia represents an example of these natural laboratories where the presence of bio-constructions locally enhances biodiversity. Micromorphological observations, UV-epifluorescence and micro-Raman spectroscopy analyses were applied to investigate the internal structures and growth pattern of the oblique meter-long biostalactite. Two types of building engineers were detected: sessile skeletonized organisms and microbialites. These contribute to the formation of three boundstone frameworks: 1) core, represented by a skeletal-supported boundstone of large Protula tubes; 2) autochthonous micrite (microbialite)/skeletal bound-stone on the downward-facing side; and 3) pure microbialite boundstone on the upward-facing side of the biostalactite.Complex taphonomic and early diagenetic processes suggest variability in seawater chemistry. Phases of carbonate deposition, indicated by skeletal/microbialite growth and early cement precipitation, alternate with phases of carbonate dissolution and the precipitation of ferromanganiferous coatings.The uniformity of the organisms, microstructures and biochemical signals, from the base to the growing tip of the biostalactite, suggests a uniform growth style from its inception to the present-day.
Fiorillo, Anthony R.Fanti, FedericoBaucon, AndreaChiarenza, Alfio Alessandro...
13页
查看更多>>摘要：Paleontological survey in the remote Yukon-Charley Rivers National Preserve in Alaska led to the discovery of lobed Zoophycos from the lower Tahkandit Limestone (informally named Sandstone unit), an interval characterized by grayish-green glauconitic sandstone and conglomerate of coastal origin. The studied Zoophycos consists of a lobate skirt-like spreite bounded by a marginal tube. Smaller tongue-shaped lobes branch off from larger parent lobes that share the same tongue-like shape. Sedimentological features, together with body fossils and associated trace fossils (Planolites, Chondrites), indicate a shoreface habitat for the Zoophycos producer. This shallow-marine environmental setting is in contrast with the deeper bathymetries in which lobed Zoophycos are recovered in post-Palaeozoic times. The producer of the lobed Zoophycos of the Yukon River is interpreted as a deposit-feeder that used sensory-driven, directed search for locating heterogeneously distributed trophic resources. The Zoophycos producer filled its burrow with Coprolus-like fecal pellets, possibly complementing deposit feeding with microbial gardening and/or food caching. Data presented here provide useful insight into the morphological evolution and bathymetric distribution of Zoophycos, suggesting two 'Golden Ages' for lobed Zoophycos: (1) Carboniferous-Permian and (2) Cretaceous-Neogene. This stratigraphic distribution supports the important ecological role of major terrestrialization events, that are, the Palaeozoic expansion of land plants and the Mesozoic expansion of angiosperms. The consequent increased input of nutrients to coastal areas was an important contributor to declining trends in porewater oxygen concentrations. This phenomenon favored adaptive traits to exploit nutrient-rich but oxygen-poor niches, among which the U-shaped marginal tube of lobed Zoophycos was an efficient adaptation to bring oxygenated water into low-oxygen substrates.
Arreguin-Rodriguez, Gabriela J.Thomas, EllenAlegret, Laia
14页
查看更多>>摘要：Long-term climatic trends of the Paleogene were interrupted by global perturbations of the carbon cycle, commonly associated with warming of surface and bottom waters and ecosystem disturbance. Most of these perturbations occurred in the Paleocene - Eocene greenhouse climate, but others were superimposed on the transition of greenhouse-to- icehouse conditions during the middle to late Eocene. Here we analyze deep-sea benthic foraminifera to focus on the impact of Paleogene warming events on ocean bottom water ecosystems. We compare changes in assemblage diversity (Fisher-alpha index) across nine warming events at 16 locations (ocean drilling sites and land sections; 25 case studies) by applying the Epps-Singleton and Fligner-Killeen non-parametric statistical tests. Generally, diversity decreased whereas the coefficient of variation increased during warming events, but not all changes were statistically significant. The declines in diversity may have been due to adaptation to stressed conditions, whereas the higher coefficients of variation may have been caused by unstable environmental conditions. The most severe events, the Paleocene-Eocene Thermal Maximum (PETM, -56 Ma) and Eocene Thermal Maximum 2 (ETM2, -53.7 Ma), had a higher impact on bottom water ecosystems, as shown in major drops in diversity. Regression analysis of data for ODP Sites 1262 and 1263 (SE Atlantic) shows that only up to 62% of the variability of benthic foraminiferal diversity at these sites depends on delta 13C and delta 18O values, indicating that changes in diversity were not exclusively determined by the magnitude of the events as defined by the magnitude of changes in carbon isotope excursion and temperature. No major changes in diversity were identified during middle Eocene warming events, and post-event diversity became significantly more stable, suggesting that the overall cooler middle Eocene conditions supported higher faunal diversity and stability of benthic foraminiferal assemblages.
Su, TaoHuang, JianSpicer, Robert A.Li, Shu-Feng...
16页
查看更多>>摘要：The antiquity of the tropical Asian flora is being revealed by recent detailed work on a number of Cenozoic plant megafossil sites, some of which have been radiometrically dated for the first time, but our knowledge of how the highly diverse modern biota came into being remains poor due to a sparsity of records. In this paper, we describe fossil plant assemblages from the Oligocene Dong Ho Formation of the Ha Long region, northern Vietnam. The Oligocene Ha Long megafossil flora has so far yielded 38 species, including conifers and angiosperms mainly belonging to Fagaceae, Lauraceae and Dipterocarpaceae, all with significant tropical Asian kinship. The Ha Long flora is similar to other Paleogene floras from southern China, especially those from the Pan Gulf of Tonkin region. The Ha Long floral composition is typical of a tropical-subtropical ecotone and the vegetation is reconstructed as a lowland tropical evergreen forest mixed with calcicole (limestone-loving) taxa. These taxa and the vegetation type they comprise still exist in this area. Palaeoclimate reconstruction made using both the Coexistence Approach and the Climate Leaf Analysis Multivariate Program indicate a mean annual temperature of ~20 degrees C, a coldest month mean temperature around 10 degrees C, and yearly precipitation averaging almost 2000 mm. These results suggest a warm and humid peripheral tropical environment. Floristic and climatic comparison within the Ha Long and other southern China palaeofloras reveals a long-term environmental, floristic and vegetational stability in this region since the Paleogene. This long-maintained plant diversity also provided a source for populating the East Asian flora and vegetation after the late Paleogene East Asian arid belt retreat.
NSTL
Elsevier