Je Andrews

The stable isotope record of environmental and climatic signals in modern terrestrial microbial carbonates from Europe

Stable carbon and oxygen isotope data from over 80 samples of Recent freshwater microbial carbonates from western Europe, confirm that these deposits record environmental and climatic information. Our sample area tested whether recent microbial carbonates record environmental signals over large regions with differing δ18O compositions for rainfall (δw), particularly in the Alps where δw is influenced by lower condensation temperatures caused by the orographic effect. Microbial crusts in Alpine areas are clearly distinguished, i.e., have isotopically lower δ18O values by up to 4‰, from those forming in lowland areas on the east side of the mountains. Bavarian lakes and rivers which receive runoff from the Alps also have δ18O compositions that reflect the Alpine meteoric water input. Microbial crusts in the higher Alpine sites have δ13C values around −4‰, which are between 2 and 6‰ higher than values from lowland sites. This difference probably reflects a smaller soil-zone carbon component in the mountain sites where soils are thin, poorly vegetated, or absent. Oxygen and carbon isotope values do not vary significantly between different types of microbial precipitate (e.g., undifferentiated crusts, Rivularia colonies, moss tufa, etc.) at a site. The oxygen isotope compositions of freshwater lacustrine mussel shell aragonite and associated (sometimes shell encrusting) microbial carbonates differ by <1‰, and both are probably close to equilibrium isotopic values. However, δ13C values in mussel shell aragonite are consistently lower, typically by 5‰, than the associated microbial carbonate value. This suggests that the δ13C of the microbial carbonate is affected by the microenvironmental photosynthetic processes of the microbes. These microenvironmental effects are only evident at lake shore sites where water flushing rates are low. These data suggest that selected ancient microbial carbonates may contain clear records of palaeoclimate (particularly relative changes in temperature) and environmental change. Pools behind fluvial barrage tufas are probably the best targets for reasonably continuous, long, dateable records with isotopic conditions least affected by microenvironmental processes.

Does climate control the morphological fabric of freshwater carbonates? A comparative study of Holocene barrage tufas from Spain and Britain

Abstract Calcium carbonate production in most freshwater tufa systems is controlled by a combination of physico-chemical precipitation, and biomediation associated with procaryote-microphyte biofilms. Inorganic precipitation is dominant under turbulent flow regimes, whereas biomediation necessitates sluggish flow or static water. We show here that temperature is also likely to affect tufa formation rates and architecture, leading to the development of a clearly definable range of fabrics. Two contrasting models are proposed: Warm semi-arid tufas: well seen in the Ruidera Pools National Park, Albacete Province, Central Spain, where tufa barrages consist of vertical, narrow rimmed arcuate structures. Frequently these are bounded both upstream and downstream by deep lakes. Laterally accreting mammilate stromatolites dominate the upper two thirds of lake margin subaqueous overhangs, whereas conical growth-forms dominate shady basal parts of subaqueous overhangs. Dense reed stands grow in thin peats on top of the vertical lake margin walls. Resistivity survey and percussion augering show up to 20 m of earlier lake fill which is banded into dark and pale beds. The upper 10 m accumulated in 4600 years. There is little or no preservation of organic material within these deposits. Cool temperate tufas: typified by slowly accumulating barrage tufas at Caerwys (N. Wales) and Alport (N. Derbyshire, UK). Transverse barriers across valleys are dominated by arcuate buttress developments built up of downstream-facing tabular carbonate sheets. Pools upstream of the barriers are shallow, dominated by clotted lime mud and organic sapropels in their depocentres, and stromatolite-dominated (laminar to low domes, or oncoidal) facies in broad marginal zones. Marginal stands of semi-aquatic vegetation are rooted in thick peats but frequently are also encrusted around their exposed stems by oncoidal carbonate. Fabric preservation is good for the carbonate material, however, marginal peats rapidly oxidise and stem encrustations collapse to produce cylindrical oncoid beds. Depocentre sapropels are always preserved and contain important pollen records otherwise rare in carbonate regions. Carbonates in both models accumulate relatively rapidly. They have a moderate preservation potential within Late Cenozoic terrestrial successions. The distinctly different characteristics of their preserved fabrics should allow recognition of two contrasting “climatic” models for fluvial barrage tufas in ancient deposits.

Possible Microbial Effects on Stable Carbon Isotopes in Hot-spring Travertines

Recent and older (early Holocene to Pleistocene) hot-spring travertine carbonates from central Italy have two distinctive macrofabrics, crystalline crusts and shrubs. Crystalline crusts are laminated slope deposits that formed abiotically following CO 2 degassing from spring water. The formation of shrub travertine--irregular, dendritic precipitates from pool environments--is controversial and has been attributed to both abiotic and microbial processes. Oxygen isotope variation in our travertines can be explained by abiotic processes, mainly CO 2 degassing. In contrast, our carbon isotope data cannot be wholly explained by abiotic CO 2 degassing invoked in earlier studies. Because photosynthesis is known to preferentially remove 12 C, leaving ambient waters enriched in 13 C, this fractionation should be recorded in delta 13 C values of microbially influenced travertine. Our shrub carbon isotope values are between 0.5 per thousand and 6.0 per thousand larger than values for associated abiotic precipitates, and this difference is probably caused by microbial activity. These isotope data support previous visual evidence that some shrub fabrics are microbially influenced.

Concentration of carbon dioxide in the Late Cretaceous atmosphere

Stable carbon isotope data from Late Cretaceous (Maastrichtian) palaeosols in India are used to estimate the concentration of carbon dioxide in the Late Cretaceous atmosphere. We show that the Maastrichtian atmosphere is unlikely to have contained more than about 1300 ppm by volume of CO2.This value agrees with an independently modeled value of CO2 in the Late Cretaceous atmosphere. A low concentration of the greenhouse gas carbon dioxide in the Maastrichtian atmosphere (relative to concentrations in the earlier Cretaceous) is consistent with palaeotemperature information from terrestrial plant and marine fossils, which suggest that the global climate cooled toward the end of the Cretaceous Period.

Palaeoenvironments of the dinosaur-bearing Lameta Beds (Maastrichtian), Narmada Valley, Central India

Abstract The Maastrichtian Lameta Beds of central India are intimately associated with the Deccan lavas and are critical to determining Upper Cretaceous palaeoenvironments and palaeogeography of the area. In the type Jabalpur sub-region, four mappable units of the Lameta Beds are recognised. The basal Green Sandstone is interpreted as a braided stream deposit. The Lower Limestone, characterised by brecciation and shrinkage cracks, is interpreted as a sub-aerially exposed palustrine flat with calcrete formation occurring on topographic highs of low relief plains. The overlying Mottled Nodular Beds exhibit a variable range of calcrete fabrics and morphologies including circum-granular and linear cracks, root casts and nodules. These are interpreted as pedogenically modified sheet wash deposits of a semiarid alluvial plain. The Upper Sandstone is a sheet flood deposit, again pedogenically modified before arrival of the basal lava flows. Overall the Lameta beds are considered to represent a regionally extensive Maastrichtian regolith. Carbon and oxygen isotope analyses of calcareous components are entirely consistent with soil-zone environments. The δ13C values are low, typically −8 to −9‰ PDB, demonstrating a strong input of carbon from the decay of terrestrial land plants. Calcrete δ18O values are variable, −5 to −10‰ PDB consistent with precipitation from meteoric water, some of which was evaporatively modified in pools on the alluvial/palustrine flat. The Lameta Beds are well known for sauropod nesting sites and sedimentological analyses of these sites suggest that the animals selected topographic highs, usually in marly or sandy, soft sediment. Multiple nests with similar egg types probably indicate colonial nesting. Isotopic analyses of eggshell carbonate agree with earlier work suggesting that the sauropods ate a “C3” plant food.

Nutrient fluxes through the Humber estuary - past, present and future

Abstract The geomorphology of the present day and Holocene (3000 years ago) Humber estuary, United Kingdom, are described. More than 90% of the intertidal area and sediment accumulation capacity of the estuary has been lost to reclamation over this period. A similar situation prevails in many other urbanized estuaries. Nutrient budgets for the modern estuary are presented demonstrating little trapping of nutrients, due to the loss of intertidal areas. A speculative budget for the Humber during the Holocene is constructed, which suggests that the estuary was then an efficient sink for nitrogen and phosphorus. A budget is presented describing how nutrient cycling might operate in the Humber with contemporary nutrient loadings, but with the pre-reclamation geography. This suggests that in this form the estuary would significantly attenuate nutrient fluxes to the North Sea. The results are discussed in terms of options for managed realignment of estuaries in response to predicted sea-level rise.

The Humber catchment and its coastal area: from UK to European perspectives

The present water quality of the Humber rivers and coastal zone depends on a complex interplay of factors, including physical ones, such as the underlying geology, which influences soil type, climatic ones, such as the rainfall, which influences runoff, socio-economic ones, which influence present-day human activities in the catchment, and the legacy of former activities, such as contaminated sediments from mining. All of these factors affect the fluxes of nutrients and other contaminants to the rivers and coastal zone. The Water Framework Directive (WFD) requires the production of a river basin management plan intended to lead to the achievement of good chemical and ecological status for all water bodies in the catchment over the next two decades. This paper provides an overview of the current environmental and socio-economic state of the Humber catchment and coastal zone, and broadly examines how socio-economic drivers affect the fluxes of nutrients and contaminants to the coastal zone, using the driver-pressure-state-impact-response (DPSIR) approach. This is followed by an overview of future research, describing the use of scenarios to simulate future fluxes and provide a consistent framework to evaluate potential policies to improve water quality in the estuary. The Humber catchment is one of eight case studies within a European research project, EUROCAT (EVK1-CT-2000-00044), which aims to achieve integrated catchment and coastal zone management by analysing the response of the coastal sea to changes in fluxes of nutrients and contaminants from the catchments. For the Humber case study, the research focuses on the fluxes of two nutrient elements, N and P, and four metal contaminants, As, Cu, Pb and Zn. The project requires the integration of scientific and socio-economic approaches, bringing together quantitative environmental data garnered for individual river catchments and coastal zones in previous research programmes, and local and regional socio-economic data, to aid decision-makers in their search for integrated and sustainable coastal zone management strategies.

Atmospheric pCO2 and depositional environment from stable-isotope geochemistry of calcrete nodules (Barremian, Lower Cretaceous, Wealden Beds, England)

Abstract: Nodular soil carbonates (calcretes) are present in overbank facies of Lower Cretaceous, non-marine Wealden Beds (Wessex Formation) of southern England. Field evidence suggests that these calcretes formed mostly under semi-arid Mediterranean-type climatic conditions. Typical calcrete fabrics, identified petrographically, include floating detrital grains, corroded grain margins and circumgranular cracks defining peds. Localized alteration of primary micrites is mainly associated with large cracks where early non-ferroan diagenetic cementation and neomorphism was focused. Diagenetic ferroan calcites occur as void fills and yield relatively light carbon-isotope and oxygen-isotope compositions (δ13C= −15.0‰; δ18O= –6.3‰) compared to well-preserved micrite (δ13C= –10.2‰; δ18O= –4.0‰). Precise definition of δ13C values for well-preserved micrites allow estimation of partial pressure of atmospheric CO2 (pCO2) for the early Barremian of 560 ppmV using a published diffusion-reaction model. The data suggest that atmospheric CO2 was low during the mid-Early Cretaceous before rising to a previously defined mid-Cretaceous high. Data from calcretes in the Weald Clay highlight the need for selection of appropriate material and careful evaluation before pCO2 calculations are attempted. The Weald Clay samples come from marshy palaeoenvironments where ingress of atmospheric CO2 into the soil-zone was either reduced or prevented.

Normal faulting and crustal deformation, Alkyonides Gulf and Perachora peninsula, eastern Gulf of Corinth rift, Greece

Geophysical, structural, geochronological and geomorphological data indicate that the Psatha, East Alkyonides, Skinos and Pisia faults are Holocene-active structures whereas the status of the West Alkyonides, Strava, Perachora and Loutraki faults is less certain. We see no evidence for significant lateral surface fault growth. New data for late Pleistocene footwall uplift of the Psatha fault are comparable with previously estimated Holocene rates. Pre-Holocene stratigraphic sequences in the Alkyonides Gulf allow calculation of vertical displacement on the Skinos fault of 1.42–1.60 km over a period of >0.6 Ma. Previous palaeoseismological studies indicate comparable displacement rates extrapolated to 0.61–2.20 Ma, whereas extrapolation of previous geodetic data indicate a range of 0.17–0.46 Ma. The latter is too short given the evidence of the stratigraphic record, signifying either that these data may not be representative of longer-term rates, or that significant deformation has taken place elsewhere, for example, on offshore antithetic faults. A case is established for uniform late Quaternary (post-MIS 7) uplift of the Perachora peninsula at rates of c. 0.2–0.3 mm a−1. The lack of regional tilting over Perachora–Corinth–Isthmia is in marked contrast to the situation in the Alkyonides–Megara basins to the east.

Coastal zone ecosystem services : from science to values and decision making : a case study

This research is concerned with the following environmental research questions: socio-ecological system complexity, especially when valuing ecosystem services; ecosystems stock and services flow sustainability and valuation; the incorporation of scale issues when valuing ecosystem services; and the integration of knowledge from diverse disciplines for governance and decision making. In this case study, we focused on ecosystem services that can be jointly supplied but independently valued in economic terms: healthy climate (via carbon sequestration and storage), food (via fisheries production in nursery grounds), and nature recreation (nature watching and enjoyment). We also explored the issue of ecosystem stock and services flow, and we provide recommendations on how to value stock and flows of ecosystem services via accounting and economic values respectively. We considered broadly comparable estuarine systems located on the English North Sea coast: the Blackwater estuary and the Humber estuary. In the past, these two estuaries have undergone major land-claim. Managed realignment is a policy through which previously claimed intertidal habitats are recreated allowing the enhancement of the ecosystem services provided by saltmarshes. In this context, we investigated ecosystem service values, through biophysical estimates and welfare value estimates. Using an optimistic (extended conservation of coastal ecosystems) and a pessimistic (loss of coastal ecosystems because of, for example, European policy reversal) scenario, we find that context dependency, and hence value transfer possibilities, vary among ecosystem services and benefits. As a result, careful consideration in the use and application of value transfer, both in biophysical estimates and welfare value estimates, is advocated to supply reliable information for policy making.