Surface Environmental Changes Research Articles

Quantifying the contribution of climate change and human activities to biophysical parameters in an arid region

Quantifying the variation of biophysical parameters and their driving mechanisms is essential for monitoring land surface environmental changes and for understanding the land–atmosphere interaction in the arid region. Due to the complexity of human activities, most researches are limited to climate change, whereas the response analysis of human activities to changes in biophysical parameters are still lacking or not comprehensively considered. Therefore, large biases and uncertainties still exist in the estimates of regional responses to global change. Firstly, we specifically quantified the main human activities related to land use/land cover change (LULCC) in the northern Tianshan Mountains (NTM), and identified the spatiotemporal changes of primary biophysical parameters, including Albedo, leaf area index (LAI), land surface temperature (LST), and Normalized Difference Vegetation Index (NDVI). Then, we tested the performance of the five models used, including multiple linear regression (MLR), random forest (RF), support vector regression (SVR), multi-layer perceptron (MLP), and K-nearest neighbor (KNN). RF outperformed others and was used to quantify and disaggregate the contribution of climate change and human activities to land surface parameters in the NTM. We found a strong spatial heterogeneity in the spatial variation of all biophysical parameters. Except for LST, the annual maximum Albedo, LAI, and NDVI showed a significant increasing trend in the NTM from 2000 to 2019 (p < 0.05). Generally, climate change contributed more to the biophysical parameters than human activities. However, the contribution of human activities to NDVI was 0.51, which was greater than that of climate change during 2000–2015. This study provides new insight on the impact of climate change and human activities on biophysical parameters and a scientific basis for model parameterization in the arid region.

Stable isotope studies of the water cycle and terrestrial environments: introduction

AbstractThe volume is devoted to Earth Surface environmental reconstructions and environmental changes, which may be deciphered and modeled using stable isotopes along with mineralogical/chemical, sedimentological, palaeontological/biological and climatological methodologies. The book is divided into two sections, both of them using stable isotopes analysis (δD, δ18O, δ13C, δ15N, δ34S, clumped isotopes D47) in various samples and phases as main research tools. The first section is devoted to studies focusing on the distribution of isotopes in precipitations, groundwaters, lakes, rivers, springs, mine waters and their relationship with terrestrial environments at regional to continental scale. In connection, the second section includes case studies from a range of continental settings, investigating cave deposits (stalagmites, bat guano), animal skeletons (dinosaurs, alligators, turtles, bivalves), present and past soils (palaeosols), limestones. The sections focus on the interaction between the surficial water cycle and underground water storage with deposits acting as archives of short- to long-term climatic and environmental changes. Examples from the Early Cretaceous to present time come from Europe, Asia, Africa and America.

About this title - Stable Isotope Studies of the Water Cycle and Terrestrial Environments

This volume is devoted to Earth surface environmental reconstructions and environmental changes that may be deciphered and modelled using stable isotopes along with mineralogical/chemical, sedimentological, palaeontological/biological and climatological methodologies. The book is divided into two sections, both using stable isotopes (δD, δ 18 O, δ 13 C, d 15 N, δ 34 S, clumped isotopes Δ 47 ) in various samples and phases as the main research tool. The first section is devoted to studies focusing on the distribution of isotopes in precipitation, groundwater, lakes, rivers, springs, tap water, mine water and their relationship with terrestrial environments at regional to continental scale. In relation to this, the second section includes case studies from a range of continental settings, investigating cave deposits (stalagmites, bat guano), animal skeletons (dinosaurs, alligators, turtles, bivalves), present and past soils (palaeosols) and limestones. The sections focus on the interaction between the surficial water cycle and underground water storage with deposits acting as archives of short- to long-term climatic and environmental changes. Examples from the Early Cretaceous to present time come from Europe, Asia, Africa, North and South America.

Predicting of land surface uplift caused by the flooding of underground coal mines – A case study

The liquidation of underground mines as in flooding of mining excavations and goafs often leads to movements of the rock mass and land surface as a result of pressure changes in the flooded zones. The changes resulting from the rising water table caused by the changes in the stress and strain state as well as the physical and mechanical properties of rock layers can lead to damage to surface construction objects and environmental changes, such as chemical pollution of the surface water. This is why the ability to predict the movements of rock masses generated as a result of mine closure by flooding serves a key function in relation to the protection of the land surface and buildings present thereon. Currently, the world literature presenting methods of forecasting ground surface uplift during mine flooding is very modest and is limited to three analytical methods: Pöttgens', Fenk's and Sroka's method. However, the numerical methods used in this subject area are limited only to modeling the phenomenon using the back analysis method and are not used for forecasting. The author's methodology based on the finite element method presented in the article allows on, after calibrating the 3D numerical model using surface subsidence measurements, as well as geological and mining data, to simulate the flooding process by changing the density of the medium according to classical soil and rock mechanics principles and then obtain prognostic values for ground surface uplift. This methodology has been used in the example of a German underground coal mine, which has been flooded in 1999. The authors have built a 3D numerical model and then performed simulations. The results of calculations were compared with the results of measurements obtaining compliance at the level of 5%.

Local land subsidence exacerbates inundation hazard to the Kujukuri Plain, Japan

Abstract. Flood-inundation hazard maps are generally made based on the anticipated flood patterns under the configurations such as current topography and land use/land cover situations. These maps have not taken into account the possible significance of land subsidence and surface environmental changes. The Kujukuri Plain, Japan, the site of this research, has experienced severe land subsidence due to 2011 Tohoku earthquake. This paper aims to quantify the effects of local land subsidence on flood hazards under heavy rainfalls in the Kujukuri Plain. The high-resolution LiDAR data at two different periods (before and after the Tohoku earthquake) were obtained and used as the input data for the physically-based hydrological model. Through the comparison of simulated inundation areas of the scenarios with the same precipitation pattern but different topographies, the effect of land subsidence was discussed. The maps estimating the inundation areas by only considering rainfalls, i.e., without taking into account the effect of land subsidence, underestimated the inundation areas by around 10 % compared with the ones that accounted for the local land subsidence. The results of this study highlight the importance of taking into account the temporal changes of elevations and other parameters in flood hazard assessments.

Cold region Quaternary science for earth surface processes and environmental changes

Cold region Quaternary science for earth surface processes and environmental changes

Seasonal and annual changes in soil/cave air pCO2 and the δ13CDIC of cave drip water in response to changes in temperature and rainfall

This study analyzes cave pCO2 and the δ13CDIC of drip water in response to surface environmental changes in the Furong Cave, Chongqing, southwestern China, between 2009 and 2016. Several indices were continuously monitored, including air temperature, rainfall, soil pCO2 outside the Furong Cave, as well as cave air pCO2 and δ13CDIC of drip water inside the Furong Cave. The results revealed that (1) the overlying soil pCO2 at the Furong Cave is directly controlled by the surface temperature and rainfall. Soil pCO2 is higher in summer and autumn and lower in winter and spring. On an interannual time scale, soil pCO2 shows a trend similar to annual rainfall. (2) Cave pCO2 and soil pCO2 both show characteristics of significant seasonal variation, which is similar to the seasonal variation in rainfall in Chongqing. Rainfall significantly affects cave pCO2. (3) The δ13CDIC values of the drip water at Furong Cave are generally lower in summer and autumn and higher in winter and spring. They are mainly affected by seasonal variation in rainfall and the consequent soil CO2 yield, which is also related to the increase in CO2 degassing of the drip water caused by cave pCO2 decreases in winter and spring. (4) The annual rainfall decreased in 2010–2011, and the δ13CDIC of the drip water was generally high. The annual rainfall gradually increased from 2012 to 2016, and the δ13CDIC of the cave drip water showed a consistent reduction. The δ13CDIC of the drip water at the Furong Cave may be used as an index of changes in surface rainfall which can reflect drought and flood events.

Late Quaternary palaeoenvironmental changes in the Aegean Sea: interrelations and interactions between North and South Aegean Sea.

The present study describes the Late Quaternary palaeoenvironmental evolution and the main palaeoceanographic changes of the Aegean Sea reconstructed using planktonic foraminifera. This approach, including Q-mode and R-mode cluster analyses, gives an insight into the relationships between sea surface environmental changes between north and south Aegean, and furthermore serves as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern Mediterranean Sea.

The composition of mantle plumes and the deep Earth

Determining the composition and geochemical diversity of Earth's deep mantle and subsequent ascending mantle plumes is vital so that we can better understand how the Earth's primitive mantle reservoirs initially formed and how they have evolved over the last 4.6 billion years. Further data on the composition of mantle plumes, which generate voluminous eruptions on the planet's surface, are also essential to fully understand the evolution of the Earth's hydrosphere and atmosphere with links to surface environmental changes that may have led to mass extinction events. Here we present new major and trace element and Sr–Nd–Pb–Hf isotope data on basalts from Curacao, part of the Caribbean large igneous province. From these and literature data, we calculate combined major and trace element compositions for the mantle plumes that generated the Caribbean and Ontong Java large igneous provinces and use mass balance to determine the composition of the Earth's lower mantle. Incompatible element and isotope results indicate that mantle plumes have broadly distinctive depleted and enriched compositions that, in addition to the numerous mantle reservoirs already proposed in the literature, represent large planetary-scale geochemical heterogeneity in the Earth's deep mantle that are similar to non-chondritic Bulk Silicate Earth compositions.

Late Quaternary paleoenvironmental reconstruction and paleoclimatic implications of the Aegean Sea (eastern Mediterranean) based on paleoceanographic indexes and stable isotopes

The Late Quaternary palaeoenvironmental evolution and the main palaeoceanographic changes of the Aegean Sea was reconstructed using planktonic foraminifera obtained from the sediments of a northern (SK-1) and a southern (NS-14) core site. Multivariate statistical approach, including Q-mode cluster and Principal Component (PCA) Analyses, gives an insight into the relationships between sea surface environmental changes between the north and south Aegean, and furthermore serves as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern Mediterranean Sea. Stable isotope analyses coupled with additional paleoceanographic (sea surface temperature (SST), productivity (SSP), stratification (S-index), upwelling (U-index), seasonality (Sn-index)) proxies provide insights into the sedimentological, hydrographic and trophic evolution and ecosystem dynamics of the Aegean Sea, and furthermore serve as a baseline data set for palaeoclimatic and palaeoceanographic reconstructions of the eastern Mediterranean Sea. Concentrating on the last ∼19 ka, faunal and isotopic data concur, suggesting a series of climatic zones, corresponding to well-known climatic phases of the last glacial cycle. Cold and arid conditions during the late glacial period were followed by a warmer and wetter climate trend during deglacial time. A marked seasonality, characterized by homogenous water column favored by efficient upwelling during the winter and by warm stratified water column during the summer, has also been recognized during this period (Bølling–Allerød – B–A) in both basins. An abrupt switch to cool, arid climatic event (Younger Dryas – YD) suggests a strengthening of winter convection around 12.9 ka, which seems to be more evident in the north Aegean core. However, the more pronounced environmental changes between the north and south Aegean Sea were identified during the Holocene, and they coincide with the deposition of sapropel S1 and Sapropel-Mid-Holocene (SMH). The comparison between SK-1 and NS-14 records indicated significant changes in both the productivity and stratification patterns, with the former the main factor in north Aegean and the latter in south Aegean for S1 deposition. Regarding the localized deposition of SMH in the semi-enclosed shallow south Aegean site, the fully oxygenated and less productive water column conditions prevailing during that time (5.4–4.3 ka) in the north Aegean were the limiting factor for its deposition.

Temporal dynamics of groundwater-dissolved inorganic carbon beneath a drought-affected braided stream: Platte River case study

Impacts of environmental changes on groundwater carbon cycling are poorly understood despite their potentially high relevance to terrestrial carbon budgets. This study focuses on streambed groundwater chemistry during a period of drought-induced river drying and consequent disconnection between surface water and groundwater. Shallow groundwater underlying vegetated and bare portions of a braided streambed in the Platte River (Nebraska, USA) was monitored during drought conditions in summer 2012. Water temperature and dissolved inorganic carbon (dominated by HCO3−) in streambed groundwater were correlated over a 3 month period coinciding with a decline in river discharge from 35 to 0 m3 s−1. Physical, chemical, and isotopic parameters were monitored to investigate mechanisms affecting the HCO3− trend. Equilibrium thermodynamic modeling suggests that an increase of pCO2 near the water table, coupled with carbonate mineral weathering, can explain the trend. Stronger temporal trends in Ca2+ and Mg2+ compared to Cl− are consistent with carbonate mineral reequilibria rather than evaporative concentration as the primary mechanism of the increased HCO3−. Stable isotope trends are not apparent, providing further evidence of thermodynamic controls rather than evaporation from the water table. A combination of increased temperature and O2 in the dewatered portion of the streambed is the most likely driver of increased pCO2 near the water table. Results of this study highlight potential linkages between surface environmental changes and groundwater chemistry and underscore the need for high-resolution chemical monitoring of alluvial groundwater in order to identify environmental change impacts.

Solar-induced Thermal Activity and Stratification in Pond Water

Ponds are universally used to store water for a large number of uses. With the increasing demand for more fresh water, ponds, lakes and reservoirs are likely to be constructed on a larger scale. We must understand the effects of environmental changes on fresh water if we are to most efficiently utilize this resource. This study undertakes to increase our understanding of the rate of thermal response of ponds and other bodies of water to every-day environmental changes. The central research agenda is to investigate how the temperature of pond water from top to bottom responds to the day/night cycle, changes in air temperature just above the surface, cloud conditions, and other sudden environmental changes. Data collection for this study spanned October 2007 to June 2011 and had a continuous time resolution of 50 seconds.

In-situ analyses of phosphorus contents of carbonate minerals: Reconstruction of phosphorus contents of seawater from the Ediacaran to early Cambrian

The Ediacaran and Cambrian periods were one of the most important periods for the evolution of life. The biodiversity drastically expanded in the period. However, the origins are still ambiguous because surface environmental changes through the time have not been well understood yet. We conducted in-situ analyses of the phosphorus contents of carbonate minerals with a laser ablation-inductively coupled plasma-mass spectrometer (LA-ICP-MS) to estimate the phosphorus contents of seawater from the Ediacaran to the early Cambrian. Carbonate rocks contain not only the carbonate minerals but also detrital and authigenic materials such as silicate and phosphate minerals. Therefore, the whole rock compositions of carbonate rocks are not directly related with seawater composition. To avoid the influence of the involvement of the phosphate minerals, we performed the microscopic observation, elemental mapping of Si, Ca, Mg, Fe, and P contents with an electron probe microanalyzer (EPMA), and investigation of time profiles of signal intensities of Ca, Sr, Mn, P, La and Ba with the LA-ICP-MS. Especially, samples with low Mn/Sr ratios and primary textures such as oolites are suitable to estimate the primary phosphorus contents of the carbonates.The chemostratigraphy of the phosphorus contents of carbonates from the drill core and outcrop samples displays that the phosphorus contents decrease from ca. 400ppm in the Ediacaran through ca. 200ppm around the terminal Ediacaran and the beginning of the Cambrian to ca. 50ppm in the early Cambrian. Previous works on 87Sr/86Sr chemostratigraphy from the Ediacaran to the Cambrian sections suggested relatively high continental influx in the middle Ediacaran, and around the Precambrian–Cambrian (PC/C) boundary. The high phosphorus content in the Ediacaran was possibly due to the high continental flux. On the other hand, previous works on chemostratigraphy of carbon isotope values of carbonate carbon from the Ediacaran to the Cambrian sections showed some large negative anomalies in the Ediacaran and around the Precambrian–Cambrian (PC/C) boundary, and suggested that the negative anomalies were caused by remineralization and respiration of dissolved organic matter. The degradation of the organic matter also accounts for the high phosphorus contents in the Ediacaran. The high phosphorus content of seawater favors enhancement of primary productivity and formation of phosphorites. The high phosphorus contents in the seawater possibly led to the emergence of the large, and motile organism through the enhancement of primary productivity and the consequent increase of oxygen content of the seawater.

New chronological constraints for Cryogenian to Cambrian rocks in the Three Gorges, Weng'an and Chengjiang areas, South China

The Neoproterozoic and Cambrian were two of the most dramatic periods in the history of the Earth, because large multi-cellular animals first appeared then in the so-called “Cambrian Explosion”. To better understand this event, many paleontological and geochemical studies now focus on rocks in South China, because of the fossiliferous succession and good exposure. Since the recognition of the Yangtze Gorges and Chengjiang area as type localities of the Sinian (Ediacaran) and Meishucunian (Early Cambrian) Systems, both sections have been intensively investigated. In order to decipher the relationships between the evolution of life and surface environmental changes, it is necessary to understand their paleontological, geochemical and geo-chronological constraints.This study presents new chronological constraints for the Cryogenian to Cambrian rocks in the Three Gorges, Weng'an and Chengjiang areas, South China. We discovered two tuff layers, one at the base of the Shuijingtuo Fm at Three Gorges and the other at the bottom of the Dahai Member in Chengjiang. In addition, we collected sandstones from Neoproterozoic strata in the Three Gorges, Chengjiang and Weng'an areas for provenance analysis. Zircons, separated from the tuff layers, provide new Nano-SIMS U–Pb ages of 526.4±5.4Ma at the base of the Shuijingtuo Fm, and 523.9±6.7Ma at the bottom of the Dahai Member. The tuffaceous beds occur at an unconformity, and nodules are common in the Three Gorges, Meishucun and Taoying sections, indicating that major and relatively wide-scale volcanic and sedimentological events occurred at ca. 525Ma. Moreover, carbonate carbon isotope chemostratigraphies at Morocco, Siberia, Three Gorges and Meishucun display different characteristics during the Tommotian. One possibility is that the South China Ocean was separated from an outer ocean at that time. Detrital zircons in sandstones have age populations at ca. 2.7, 1.8, 1.6, 1.0 and from 0.9 to 0.75Ga. indicating that the paleo-hinterland of the Nanhua and Kangdian rift basins was geologically complex. Despite the lack of ca. 1.6Ga rocks in the Yangtze and Cathaysia Blocks, these data are nevertheless interpreted to indicate derivation of the zircons from basement rocks in the Yangtze craton.

The anomalous Ca cycle in the Ediacaran ocean: Evidence from Ca isotopes preserved in carbonates in the Three Gorges area, South China

The Ediacaran–Cambrian was one of the most important periods for the evolution of life. Recent studies have provided detailed chemostratigraphies that decipher the linkages between ambient surface environmental changes and biological evolution. The occurrence of skeletal fossils in Ediacaran rocks suggests that the possible onset of Ca-biomineralization started in the latest Neoproterozoic. Molecular clocks also predict the emergence of animals containing Ca-carbonate spicules in the Neoproterozoic. Therefore, it is important to estimate the transition of the Ca cycle in seawater. Ancient Ca cycles in the oceans are estimated from the calcium isotopic compositions of carbonate rocks. However, the lack of continuous Ca isotopic data in the Ediacaran leaves the Ca cycle unresolved.The almost continuously exposed, Ediacaran and Cambrian strata in South China mainly comprise carbonate rocks with subordinate black shales and sandstones, which contain many fossils, suitable for the study of environmental and biological changes. We conducted drilling from the Liantuo, via the Nantuo, Doushantuo, Dengying and Yanjiahe to the Shuijingtuo formation at four sites in the Three Gorges area in order to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed 44Ca/42Ca ratios in carbonate rocks with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) screened for diagenetic alteration.The resultant δ44/42Ca ratios exhibit a smooth curve. The values of δ44/42Ca are anomalously high relative to those in the Phanerozoic, and they gradually decrease towards the end of the Ediacaran. Our new Ca isotope chemostratigraphy suggests that a different Ca cycle had existed during the Ediacaran. The long-term, high δ44/42Ca is not simply explicable by changes in temperature, differences in carbonate mineralogy, or changes in the input/output fluxes of Ca to the ocean. We propose three possible explanations for the observed high δ44/42Ca ratios in the Ediacaran: high δ44/42Ca ratios of Ca inputs, potential undiscovered sinks of Ca with low δ44/42Ca values, and negligible isotope fractionation between carbonate and seawater; we consider that one or all of these contributed to the high δ44/42Ca ratios. Of these, we prefer the small isotope fractionation, which implies that the Ca concentration in seawater was initially low in the early Ediacaran and increased throughout that period.

Planktonic foraminiferal biostratigraphy of the Plio-Pleistcene Chikura Group, southernmost part of the Boso Peninsula, central Japan and inferred sea surface environmental changes

Planktonic foraminiferal biostratigraphy of the Plio-Pleistcene Chikura Group, southernmost part of the Boso Peninsula, central Japan and inferred sea surface environmental changes

A synopsis of recent conceptual models on supercontinent tectonics in relation to mantle dynamics, life evolution and surface environment

A synthesis of some of the recent conceptual models suggests that mantle dynamics exerted a significant control on the assembly and breakup of supercontinents through the history of the Earth. During the amalgamation of continental fragments, the subducted oceanic lithosphere of intervening oceans either moves down to the deep mantle or gets horizontally flattened as stagnant slabs in the mantle transition zone. Blobs of these stagnant slabs sink down into the deep mantle and accumulate as slab graveyards at the core–mantle boundary. The recycled oceanic lithosphere at the core–mantle boundary is thought to contribute potential fuel for generating superplumes which rise from the core–mantle interface to the uppermost mantle, penetrating the mantle transition zone and eventually giving rise to hot spots. Multiple subduction zones promote the rapid amalgamation of continental fragments into supercontinents and also act as major zones of material flux into the deep mantle transporting substantial volume of trench sediments and arc crust through sediment subduction and tectonic erosion. Due to buoyancy, the subducted TTG (tonalite-trondhjemite-granite) material is stacked in the mid mantle region and may not sink down to deeper levels. Thus, continents and supercontinents can be speculated to occur as three layers: on the surface of the globe, at the mid mantle region and on the core–mantle boundary, with material transfer on a whole earth scale controlled by plate, plume and ‘anti-plate’ tectonics. Whereas mantle tomography opens windows into the deep Earth, the imbricated remnants of ‘ocean plate stratigraphy’ preserved in accretionary orogens constitute useful geological tools to study subduction-accretion-collision history, particularly in relation to the assembly of older supercontinents on the surface of the globe. The dynamics of supercontinents also impact the origin and extinction of life as well as surface environmental changes. Large scale flow of material and energy through mantle downwelling and upwelling associated with supercontinent assembly and breakup is thought to affect the Earth's dynamo which would lead to catastrophic environmental changes, sometimes even triggering mass extinction. When a rising plume impinges the base of a supercontinent, the resultant continental rifting, formation of large igneous provinces and volcanic emissions might lead to the initiation of a plume winter, the aftermath of which would be mass extinction and long-term oceanic anoxia. Supercontinent tectonics in relation to mantle dynamics thus provides a key to evaluate the history of evolution and destruction of the continental crust, to understand the history of life, and to trace the major surface environmental changes of our planet.

Earth Surface Processes and Environmental Changes of Lake-Catchment Systems in East Asia

Earth Surface Processes and Environmental Changes of Lake-Catchment Systems in East Asia

The Ediacaran radiogenic Sr isotope excursion in the Doushantuo Formation in the Three Gorges area, South China

The Ediacaran period was one of the most important times for the evolution of life. However, the scarcity of well-preserved outcrops of Ediacaran rocks still leaves ambiguity in decoding ambient surface environmental changes and biological evolution. The Ediacaran strata in South China are almost continuously exposed, comprise mainly carbonate rocks with subordinate black shales and sandstones, and they contain many fossils, suitable for study of environmental and biological changes in the Ediacaran. We conducted drilling through the Doushantuo Fm at four sites in the Three Gorges area to obtain continuous, fresh samples without surface alteration and oxidation. We analyzed 87Sr/ 86Sr and 88Sr/ 86Sr ratios of the fresh carbonate rocks, selected on the basis of microscopic observations and the geochemical signatures of Sr contents, Mn/Sr and Rb/Sr ratios, and δ 18O values, with a multiple collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS). The chemostratigraphy of the 87Sr/ 86Sr ratios of the drilled samples displays a smooth curve and two large positive shifts during Ediacaran time. The combination of the detailed chemostratigraphies of δ 13C, δ 18O and 87Sr/ 86Sr values and Mn and Fe contents enables us to decode the surface environmental changes and their causes in the Ediacaran. The first large positive excursion of 87Sr/ 86Sr occurred together with negative δ 13C and positive δ 18O excursions. The higher 87Sr/ 86Sr values indicate an enhancement of continental weathering, whereas the positive δ 18O excursion suggests global cooling. Global regression due to global cooling enhanced the oxidative decay of exposed marine organic sediments and continental weathering. Accelerated influx of nutrients promoted primary productivity, resulting in oxidation of dissolved organic carbon (DOC), whereas active sulfate reduction due to a higher sulfate influx from the continents caused remineralization of the large DOC, both of which caused a negative δ 13C anomaly. The 580 Ma Gaskiers glaciation accounts for the close correlation among the positive 87Sr/ 86Sr, negative δ 13C and positive δ 18O excursions. The second large positive shift of 87Sr/ 86Sr firstly accompanied a positive δ 13C excursion, and continued through the Shuram δ 13C negative excursion. The positive correlation of δ 13C and 87Sr/ 86Sr values is consistent with an enhanced continental weathering rate due to continental collisions that built Trans-Gondwana mountain chains, and with a higher primary activity due to the enhancement of continental weathering and consequent higher nutrient contents in seawater. The accompanied increase in Mn and Fe contents implies a gradual decline of the seawater oxygen content due to more active aerobic respiration and oxidation of reductive materials flowing in the oceans. In the Shuram excursion, higher 87Sr/ 86Sr values and a transition from increase to decrease in Mn and Fe contents were accompanied by the large negative δ 13C excursion. The higher 87Sr/ 86Sr values are the first compelling evidence for enhanced continental weathering, which was responsible for the large δ 13C anomaly through the remineralization of the DOC by more active sulfate reduction due to a higher sulfate influx. Higher Mn and Fe contents in the early and middle stages of the excursion suggest a decline in the oxygen content of seawater due to oxidative decay of the DOC, whereas in the late stages the decrease in Mn and Fe contents is consistent with oceanic oxygenation. The emergence of Ediacara biota after the Gaskiers glaciation and the prosperity of the latest Ediacaran is concomitant with the formation of more radiogenic seawater with high 87Sr/ 86Sr values, suggesting that enhanced continental weathering, and the consequent higher influx of nutrients, played an important role in biological evolution.

Surface–bottom relationships in the Gulf of Salerno (Tyrrhenian Sea) over the last 34 kyr: Compositional data analysis of palaeontological proxies and geochemical evidence

The palaeontological, geochemical and mineralogical records of core GNS84-C106 were analysed in order to reconstruct palaeohydrological changes and palaeoproductivity patterns in the Gulf of Salerno for the last 34 kyr. This approach, including compositional analysis of planktonic and benthic assemblages, gave an insight into the relationships between continental, sea surface and bottom environmental changes. The main source of variability of planktonic and benthic assemblages is related respectively to sea surface temperature and palaeobathymetry. Interrelated changes in surface salinity, nutrients, density gradient in the water column and organic fluxes at the bottom act as a secondary factor controlling the composition of both planktonic and benthic assemblages. The highest palaeoproductivity rates were reached during an interval spanning from late glacial to Middle Holocene, in conditions of enhanced continental run-off. During the Early and Middle Holocene, reduced surface salinity and density stratification were also coupled with the development of a deep chlorophyll maximum and enhanced flux or organic matter at the bottom. From about 6.5 kyr B.P. onward, a sharp reduction in palaeoproductivity took place, coupled with an increase in surface salinities.