Glacial/interglacial changes in the East Australian current     

H. C. Bostock  B. N. Opdyke  M. K. Gagan  A. E. Kiss  L. K. Fifield 《Climate Dynamics》2006,26(6):645-659

The East Australian Current (EAC) is the western boundary current of the south Pacific gyre transporting warm tropical waters to higher southern latitudes. Recent modelling shows that the partial separation of the EAC (~32°S) and the coupled formation of the Tasman Front (~34°S) are caused by a steep gradient in the zonally integrated wind stress curl. Analysis of oxygen isotope ratios (δ¹⁸O) in the planktonic foraminifer, Globigerinoides ruber, from sediment cores from the Coral Sea and Tasman Sea indicates that the EAC separation shifted northward to between 23 and 26°S during the last glacial. We suggest these results indicate a significant change in the Pacific wind stress curl during the glacial. Given recent evidence for El Niño-like conditions in the Pacific during the last glacial, with a reduction in the east–west sea surface temperature (SST) gradient, we suggest that weaker trade winds combined with more northerly, stronger westerlies were associated with a change to the wind stress curl, which repositioned the EAC separation and Tasman Front. In contrast, by ~11 ka BP, the EAC separation was forced south of 26°S. This southward shift was synchronous with a rapid warming of tropical SSTs, and the onset of a La Niña-like SST configuration across the tropical Pacific. It appears that the south Pacific trade winds strengthened accordingly, causing the EAC to readjust its flow. This readjustment of the EAC marks the onset of modern surface-ocean circulation in the southwest Pacific, but the present EAC transport was only achieved in the late Holocene, after 5 ka BP.  相似文献   

Deccan traps mantle degassing in the terminal Cretaceous marine extinctions     

Dewey M. McLean 《Cretaceous Research》1985,6(3):235-259

Mantle degassing continually releases gases onto the earth's surface. Over geologically long time intervals, a general equilibrium probably exists between mantle CO₂ release and uptake by surficial sinks. However, during periods of rapid plate movement, or continental flood basalt volcanism, the increased rate of mantle CO₂ release may exceed that of uptake, leading to CO₂ accumulation in the atmosphere and the marine mixed layer (top 50–100 m). This in turn triggers chemical changes in the mixed layer, climatic warming, and bioevolutionary turnover. The Cretaceous/Tertiary ($\text{K}\text{T}$) transition at 65 Ma seems to have been a time of major mantle degassing which induced a perturbation of the carbon cycle. During the $\text{K}\text{T}$ transition, Deccan Traps volcanism, perhaps the greatest episode of continental flood basalt volcanism in the Phanerozoic, flooded an estimated 2.6 × 10⁶ km² of India with basaltic lavas, releasing 5 × 10¹⁷ moles of CO₂ into the earth's atmosphere over a duration 0.53–1.36 Ma at the rate of 3.9 × 10¹¹ to 9.6 × 10¹¹ moles CO₂ per year. The modern mean annual rate of mantle CO₂ release from all sources is 4.1 × 10¹² moles CO₂ per year; assuming a comparable rate of release prior to the Deccan Traps volcanism, the Deccan Traps addition would have elevated the rate of mantle CO₂ release by 10–25%. Sluggish marine circulation and warm, deep, oceans (14–15°C) would have exacerbated CO₂ buildup in the atmosphere, accounting for the Cretaceous to Tertiary drop in oxygen-18 via climatic warming, and, in the marine mixed layer (top 50–100 m), explaining the selective nature of the terminal Cretaceous marine extinctions via a pH change. The extinctions were most severe amongst the calcareous microplankton of the mixed layer; calcareous microplankton (planktonic foraminifera and coccolithophorids) begin to have pH problems at 7.8 and 7.5, respectively. Failure of the coccolithophorids would have disrupted the Williams-Riley pump (algal productivity-gravity pump of CO₂ from the atmosphere and mixed layer into the deep oceans) producing dead ocean conditions (severely reduced photosynthesis and CaCO₃ production). Failure of the Williams-Riley pump is reflected in the extinctions themselves, and in the loss of biogenic CaCO₃ to the sea floor, causing the $\text{K}\text{T}$ boundary hiatus and (or) the $\text{K}\text{T}$ boundary clay. Failure of the pump today would elevate atmospheric pCO₂ severalfold; the $\text{K}\text{T}$ failure would have responded comparably. Dead ocean conditions would, in themselves, have produced a major CO₂ buildup. Early Tertiary “Strangelove” conditions in the mixed layer, characterized by a dominance of the thoracosphaerids, braarudosphaerids and small planktonic foraminifera, were coeval with the main pulse of Deccan Traps volcanism. Overall, the record is one of gradual $\text{K}\text{T}$ bioevolutionary turnover during a period of disequilibrium between the rate of mantle CO₂ degassing and uptake by sinks. Mantle degassing during the Deccan Traps volcanism unifies the $\text{K}\text{T}$ biological and physicochemical records.  相似文献   

Robust multivariate procedures applied to the interpretation of atypical individuals of a Cretaceous foraminifer     

N.A. Campbell  R.A. Reyment 《Cretaceous Research》1980,1(3):207-221

Robust multivariate statistical methods are applied to samples of the Cretaceous bolivinid foraminifer Afrobolivina afra, in which individuals from microspheric and megalospheric generations dominate, but which also contain some pseudo-megalospheric specimens. Pseudo-megalospheric tests may cause values which are atypical in the statistical sense but which are fully normal biologically. Other atypical values derive from crushed specimens, microspheric individuals and unusual normal megalospheres with exceptionally wide shells and pointed last chambers. A wrongly punched specimen was also found by the procedure. The method employed here consists of plotting the generalized statistical distances calculated from robust estimates of means and of covariances against the quantiles of a Gaussian distribution; the presence of an atypical observation(s) is readily exposed by its departure from the main trend of the plot.  相似文献   

Benthic foraminifera assemblages as elemental pollution bioindicator in marine sediments around fish farm (Vrgada Island,Central Adriatic,Croatia)     

Jelena Vidović  Matej Dolenec  Tadej Dolenec  Vatroslav Karamarko  Petra Žvab Rožič 《Marine pollution bulletin》2014

Effects on sediments of fish farming activity near Vrgada Island was analysed through living and total foraminiferal assemblages and concentration of major, minor and trace elements from three sediment cores. Elemental concentrations of sediments are in accordance with carbonate characteristics of the surrounding area and show mostly natural element variations between sampling locations and throughout the cores, with no significant increases due to fish farming activity. Only phosphorus concentration shows elevate values below the fish cage, assigned to fish pellets. Foraminiferal communities are dominated by epifaunal and stress tolerant species, while diversity indices point to normal marine conditions. The type of substrate and phosphorus content in sediments principally influence foraminiferal community composition, while other elemental concentrations have no perceptible effect on the assemblages. Some foraminiferal species Ammoniatepida, Ammoniabeccarii, Elphidiumcrispum, Elphidiummacellum and genus Haynesina are confirmed to be tolerant to elevated nutrient (phosphorus) content, while Ammonia parkinsoniana shows sensitivity to pollution. Postmortem processes cause decrease of foraminiferal density and species richness with core depth. All results point to negligible influence of fish farming and relatively stable environmental conditions at all sampling locations.  相似文献   

Impact of millennial mining activities on sediments and microfauna of the Tinto River estuary (SW Spain)   总被引：1，自引：0，他引：1  

Ruiz F  Borrego J  González-Regalado ML  López González N  Carro B  Abad M 《Marine pollution bulletin》2008,56(7):1258-1264

In this paper, we analyze two short cores collected in the Tinto estuary (SW Spain), and describe the palaeoenvironmental evolution of this area during the last two millennia, along with the influence of historical mining activities and recent industrial pollution on sediments and microfauna (foraminifera and ostracoda). Although there were no significant changes in the distribution of microorganisms, a first pollution period (0-150 AD) was recorded in high sediment pollution by Cu in the shallow palaeochannels of the middle estuary. During this period and the following 1700 years, tolerant pioneer species of both foraminifera and ostracoda were found predominantly in the inner, protected areas of the estuary, while the bottom sediments were subjected to high hydrodynamic gradients, and consequently showed lower density and diversity of organisms. In the last 150 years, acid mine drainage processes, introduction of a new mining period, and the polluted inputs derived from two industrial processes resulted in increased heavy metal contamination of the bottom sediments, and corresponding extirpation of ostracodes and restriction of foraminifers to the inner zones of the estuary.  相似文献   

Evidence for marine transgression between 7500–5400BC at the Luotuodun Site in Yixing, Jiangsu Province     

LI Lan  ZHU Cheng  LIN Liugen  ZHAO Quanhong  SHI Gongyue  ZHENG Chaogui  FAN Chao 《地理学报》2009,19(6):671-680

Based on archaeological excavations, 217 samples were collected from the Luotuodun Site. Of them 63 samples from the section plane of the site layer were used for identification analysis of foraminifera, plant debris and seed fossils, and four samples were used for 14C dating and relevant analysis. Through many kinds of experiments, we have drawn some conclusions. Firstly, benthic foraminifera, such as Ammonia compressiuscula and Ammonia cff. sobrina, are found in the 10th layer, indicating that between 7500 and 5400 BC, i.e. before the emergence of the Majiabang Culture, Luotuodun Site and its nearby regions had ever experienced a marine transgression event. Secondly, we have found 450 plant fossils in this site, such as Polygonum sp., Scripus sp., Najas sp., Physalis sp., which indicated lacustrine or swamp environment.  相似文献   

Impact of fish farming on foraminiferal community, Drvenik Veliki Island, Adriatic Sea, Croatia     

Jelena Vidovi&#x;  Vlasta &#x;osovi&#x;  Mladen Jura i&#x;  Donat Petricioli 《Marine pollution bulletin》2009,58(9):1297-1309

This study examined the impact of fish farming on foraminiferal communities in the Adriatic coastal zone. Samples were taken directly beneath the farm, near the edge of the farm, and at a reference station away from the farm. The foraminiferal community near the farm is characterized by Epistominella exigua, Globocassidulina subglobosa, Haynesina germanica and the genera Elphidium, Bulimina and Brizalina. These foraminiferal species are less abundant seaward. Asterigerinata mamilla, Neoconorbina terquemi and genus Cibicides are almost absent below the cages. Total phosphorus (TP) and total nitrogen (TN) in the sediments decrease with distance from the cages. The abundances of E. exigua, G. subglobosa, H. germanica and the genera Elphidium, Bulimina and Brizalina are correlated with TP and TN, indicating their dependence on nutrient input. The absence of A. mamilla, N. terquemi and the genus Cibicides below the cages is a due to a degraded Posidonia community. According to our study, foraminiferal community composition can be used as indicator of organic enrichment caused by fish farm activities.  相似文献   

Comparison of benthic foraminifera and macrofaunal indicators of the impact of oil-based drill mud disposal   总被引：1，自引：0，他引：1  

Mariéva Denoyelle  Frans J. Jorissen  Daniel Martin 《Marine pollution bulletin》2010,60(11):2007-2021

We compare foraminifera and macrofauna as bio-indicators of oil-based drill mud disposal site off Congo. The most polluted sites are characterized by poor faunas, dominated by some very tolerant taxa. Slightly further from the disposal site, there is an area with strongly increased densities, heavily dominated by opportunistic taxa. Still further, macrofauna appears to be similar to that at the reference area, but the foraminiferal meiofauna still suggests a slight environmental perturbation. The foraminiferal FIEI index, based on the species distribution in the study area, appears to be more discriminative than the macrofaunal ITI index, based on a priori definitions of the trophic guilds of the various taxa. Our comparative approach allows us to point out the benefits of (1) the use of macrofauna and foraminifera together and (2) the definition of the species groups used in biotic indices on the basis of observations made directly in the study area.  相似文献   

Integrated biostratigraphy and palaeoenvironmental interpretation of the Upper Cretaceous to Paleocene succession in the northern Moldavidian Domain (Eastern Carpathians,Romania)     

《Cretaceous Research》2017

This study of the upper Maastrichtian to Danian sedimentary succession from the northern part of the Romanian Eastern Carpathians (Varniţa section) aims to establish an integrated biostratigraphy based on calcareous nannofossils, organic-walled dinoflagellate cysts (dinocysts) and foraminiferal assemblages, and to reconstruct the depositional environments of the interval. The stratigraphic record across the studied section is incomplete, considering that an approximately 16 m thick strata interval from the top of the Maastrichtian to lowermost Danian cannot be analyzed due to a landslide covering the outcrop. The upper Maastrichtian is marked by a succession of biostratigraphic events, such as the First Appearance Datum (FAD) of the nannoplankton taxon Nephrolithus frequens and FAD of the dinocyst species Deflandrea galeata and Disphaerogena carposphaeropsis, and the Last Appearance Datum (LAD) of Isabelidinium cooksoniae in the lower part of the section. These bioevents are followed by the LAD of the Dinogymnium spp. and Palynodinium grallator dinocyst markers in the top of the Maastrichtian deposits analyzed. In terms of foraminiferal biostratigraphy, the upper Maastrichtian Abathomphalus mayaroensis Zone is documented in the lower part of the studied section. Some bioevents, such as the bloom of the calcareous dinoflagellate genus Thoracosphaera and the FAD of the organic-walled dinocysts Damassadinium californicum, Senoniasphaera inornata, Xenicodinium lubricum and X. reticulatum suggest an early Danian age for the middle part of the section. From the Danian deposits in the Varniţa section, we describe a new organic-walled dinocyst species, Pentadinium darmirae sp. nov., which is until now the only species of the Pentadinium genus discovered in the Paleocene. The occurrence of the global Danian dinocyst marker Senoniasphaera inornata in the top of the section, suggests an age not younger than middle Danian (62.6 Ma) for the analyzed deposits.The palynofacies constituents, as well as the agglutinated foraminiferal morphogroups, used to reconstruct the depositional environments, show that the late Maastrichtian sediments were deposited in an outer shelf to distal (bathyal) environment, followed by a marine transgression during the Danian.  相似文献   

Paleoceanography and climate of the Badenian (Middle Miocene, 16.4–13.0 Ma) in the Central Paratethys based on foraminifera and stable isotope (δ18O and δ13C) evidence     

Katalin Báldi 《International Journal of Earth Sciences》2006,95(1):119-142

Benthic foraminifera and stable isotopes analyses revealed changes emerging in the paleoceanographic scenery in the Paratethys. The percentage of inbenthic, oxyphylic taxa and diversity in the benthic foraminiferal assemblage showed increasing food supply (organic matter), decreasing oxygen level and growing stress on the sea floor. Oxygen isotopes measured in planktonic and benthic foraminifera pointed to strengthening stratification during the Badenian period. The carbon isotopes indicated intensified accumulation of light marine organic matter. This increasing stratification trend is especially pronounced by Late Badenian (13.5–13 Ma) when surface water oxygen isotope values are rather negative. A simple two-layer circulation model was worked out for the Badenian Paratethys explaining these characteristic environmental changes. An antiestuarine (lagoonal) circulation is assumed for the Central Paratethys during the Early (16.4–15 Ma) and mid Badenian (15–13.5 Ma). The mid Badenian period of time comprises the short episode of evaporite formation in the Carpathian Foredeep and the Transylvanian Basin. Evidence presented here supported a reversal of circulation to estuarine type after the deposition of salts by Late Badenian (13.5–13 Ma). The Early Badenian antiestuarine circulation is suggested to associate with the high temperatures of the Mid-Miocene Climatic Optimum, and the Late Badenian estuarine circulation with the cooler period following it.  相似文献