Microfossils and Climate Change

November 15th, 2006, 1pm
University College London, Medical Sciences A. V. Hill Lecture Theatre

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1. Tracking the Ordovician glaciation

Howard A. Armstrong, Department of Earth Sciences, Durham University, South Road, Durham DH1 3LE (h.a.armstrong@durham.ac.uk)Commonality of patterns and processes, identified from geological proxy data, occur in the sequence of events leading to Cenozoic and Ordovician glaciations. Both glaciations were set against a backdrop of long-term declining pCO2 likely initiated by changes in plate configuration that resulted in increased weathering and nutrient cycling into the oceans.  Rapid expansion of ice volume was triggered by the re-direction of warm, circum-equatorial currents into high latitudes to provide a source of warm moist air and high levels of snowfall.  Once ice sheets were large enough to survive successive precession and obliquity maxima, eccentricity pacing of ice margin processes embedded in obliquity and precession largely controlled their size.  Changes in family and generic diversity (dnorm and stage length corrected) in conodonts, ostracods and graptolites suggest glacial change affected biodiversity.  The rising diversity trajectory to the Llanvirn was terminated in the Caradoc. This was followed by a slight rise in diversity in all groups into the Ashgill as taxa adapted to the new environmental conditions.  A decline in diversity, of varying severity, into the Llandovery reflects the impact of mass extinction. Commonality in the sequence of events and pattern of environmental change leads to the rejection of the Ordovician glaciation being unique in Earth history.

2. Biotic change in relation to deglaciation and global warming in the Early PermianMike Stephenson, British Geological Survey, Keyworth, Nottingham, NG12 5GG (mhste@bgs.ac.uk)The Carboniferous-Permian ice age is the most widespread and well-represented ice age in geological history and has the benefit - for geologists at least - that it has truly ended, and therefore can be studied in its entirety. Deglaciation sequences of the Early Permian of Gondwana contain abundant fossils that record postglacial climate warming and are a potentially detailed record of the way that biota react to climate change over geological timescales. The sequences have until now been distinguished mainly on lithological criteria by reference to climate-sensitive lithologies such as diamictite, limestone, glacial shales (with dropstones and varves) and associated geochemistry, whereas identification on biotic criteria such as vegetational or faunal change has not been employed. The maximum rate of deglaciation probably occurred around the Granulatisporites confluens palynological Biozone, at least in Australia, Antarctica, East Africa, India and Arabia, in late Asselian – early Sakmarian times. Data from this biozone, which are admittedly widely-scattered geographically, and of different stratigraphic scales and resolutions, show diversity increase from glacial conditions to postglacial conditions. Amongst the marine fauna, a cold water fauna consisting of bivalves such as Eurydesma and Deltopecten, and brachiopods such as Lyonia and Trigonotreta, were established in the earliest post glacial marine transgressions that did not affect all of Gondwana. Above this is a more diverse, increasingly warmer, temperate fauna, including brachiopods, bryozoans, bivalves, cephalopods, gastropods, conularids, fusulinids, small foraminifers, asterozoans, blastoids and crinoids. The palynomorph succession shows some consistency across Gondwana in Asselian-Sakmarian rocks. Very broadly a change from monosaccate pollen assemblages, associated with fern spores to more diverse assemblages with common non-taeniate bisaccate pollen occurs through the deglaciation period. In Oman, where this has been studied in greatest detail, the upland saw changes from a glacial monosaccate pollen-producing flora to a warmer climate bisaccate pollen-producing flora; while in the terrestrial lowlands, a parallel change occurred from a glacial fern flora to a warmer climate colpate pollen-producing and lycopsid lowland flora. The sedimentary organic matter of the clastic rocks of the Oman sequence records a corresponding δ13Ctrend (from approximately -21 to -24‰) believed to reflect palaeo-atmospheric change due to postglacial global warming.However the trends are relatively ‘broad brush’. The chief difficulty in providing fine detail is that these mainly non-marine sequences are difficult to correlate precisely so we don’t know if the differences between them are due to differences in age or palaeogeography. In order to integrate the data and generalise we need to correlate very precisely using, if possible, non-biostratigraphic techniques, to avoid circularity of argument. The steep Early Permian curve for 87Sr / 86Sr, presents an opportunity, especially since brachiopods (the best preservers of original 87Sr / 86Sr), are common in Early Permian deglaciation sequences. However the 87Sr / 86Sr data that underlies the smoothed curve is capricious and difficult to use in high-resolution correlation. The best hope is to use high resolution radiometric dating of ash layers that are common in, for example, Brazil, Namibia, and Eastern Australia. A framework developed to sub-million year resolution would allow disparate biotic deglaciation successions to be correlated and integrated and data on local timing of increase and decrease of Gondwana glaciers to be derived.

3. Nannofossils, carbonate production and atmospheric CO2, Cretaceous to RecentToby Tyrrell, National Oceanography Centre, Southampton University, European Way, Southampton, SO14 3ZH (tt@noc.soton.ac.uk)Some aspects of ocean chemistry have changed over the last 100 My (Mg/Ca ratio, carbonate ion concentration), whereas others have stayed more or less the same (CaCO3 saturation state). The interrelationship of these chemical changes with coccolithophores, and with overall CaCO3 production, will be discussed. Underlying much of our understanding is the carbonate compensation feedback, which must maintain (over timescales >10 ky or so) a balance between burial of CaCO3 and the river inputs of dissolved calcium and carbon. The geological record is a powerful resource for helping us understand the probable impacts of the current and upcoming ocean acidification. However, because of carbonate compensation, it is only appropriate to study high CO2 events of rather sudden onset (< ~10 ky) and short duration, such as the PETM, Cretaceous oceanic anoxic events and, possibly, the K/T impact event. Studying the Cretaceous as a whole is not relevant, because carbonate compensation would not have allowed the high atmospheric CO2 levels to be accompanied by a prolonged acidic ocean. Attempts to quantify nannofossil extinction (species turnover) during short acidification events such as the PETM are therefore of great interest.

4. A Palynological Record of the Late Paleocene Thermal Maximum (LPTM) in the UK Central North SeaNick Hogg, Shell UK Ltd, 1 Altens Farm Road, Nigg, Aberdeen, AB12 3FY (Nick.Hogg@Shell.com)The LPTM is well preserved in the North Sea Basin of North West Europe and has been documented across a broad range of facies tracts from the punctuated records of the UK onshore basin margin to the more continuous records of the epicontinental basin centre. In the past several years, the desire to understand the occurrence and development of petroliferous deepwater sand systems during this time period has enabled Shell UK to amass an unprecedented account of palynological events through this micropalaeontologically and nannopalaeontologically depauperate interval. Here, I present an account of the land and plankton record in a restricted epicontinental basin over the late Paleocene Thermal Maximum and discuss the influence of climate, catchment areas and potential feedback mechanisms through this time period.

5. Modelling Ancient Earth ClimateAlan M. Haywood.  Geological Sciences Division, British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET (ahay@bas.ac.uk)Models are of central importance in many scientific contexts. The centrality of models such as the Lorenz model of the atmosphere, the Lotka-Volterra model of predator-prey interaction, the double helix model of DNA are cases in point. Scientists spend a great deal of time building, testing, comparing and revising models. In short, models are one of the principle instruments of modern science, but they are by definition simplifications of reality and can be considered merely as tools to help us understand complex natural systems (e.g. the climate system).    Numerical models of climate, often referred to as General Circulation Models (GCMs), are being increasingly used to simulate how Earth’s climate and environments have changed over geological time. There are many reasons for this but arguably two of the most important reasons include (a) the evolution of Earth Sciences as a whole into a modelling as well as observationally based science and (b) the clear scientific and political requirement, in light of anthropogenic modification of climate, to evaluate the performance of GCMs over a diverse range of past climate scenarios.This talk will provide a brief summary of climate change during the Cenozoic and review the rationale for palaeoclimate modelling. Examples, of the types of data and how data can be synthesised and used to drive and/or evaluate palaeoclimate models will be presented by reference to the CLIMAP (Climate Long Range Investigation Mapping & Prediction) and PRISM (Pliocene Research Interpretation & Synoptic Mapping) Projects. Finally, three case studies are presented which 1) investigate the assertion that the Pliocene was characterised by a permanent El Niño-like state, 2) explore the role of polar ocean gateways in the initiation of the East Antarctic Ice Sheet and development of Antarctic Circumpolar Current at the Eocene/Oligocene boundary and 3) study the greenhouse climate states of the Eocene/Cretaceous and how well models reproduce such conditions. 

6. A Mutual Temperature Range method for European Quaternary nonmarine Ostracoda
David J. Horne, Department of Geography, Queen Mary, University of London, Mile End Road, London E1 4NS (d.j.horne@qmul.ac.uk)

The value of nonmarine ostracods in Quaternary palaeoclimate reconstruction has long been recognized, mainly in terms of the use of indicator species and, more recently, analyses of the trace element and stable isotope chemistry of their calcareous valves.  A new Mutual Temperature Range (MTR) method for European Quaternary nonmarine Ostracoda is presented, using the NODE (Nonmarine Ostracod Distribution in Europe) database and a modern climate dataset in conjunction with DIVA-GIS software. The MTR method is intended as a step towards the development of a sophisticated Mutual Climate Range (MCR) method; preliminary testing has yielded good matches with both modern temperatures (using living assemblages not already in NODE) and palaeotemperatures inferred by the coleopteran MCR method, but further testing and refinement are needed. Assumptions about the climatic tolerances of living and fossil ostracod species, as well as complicating factors (such as the relationship between water temperature and air temperature, habitat preferences and taxonomic errors) require careful examination; nevertheless, the ostracod MTR method shows considerable promise.

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