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Previous Projects: MassExtinct

Earth history has been punctuated by five mass extinction events, each of which resulted in major biodiversity loss and wholesale ecosystem reorganization. We are currently experiencing a sixth mass extinction due to anthropogenic causes. Projecting how future global change will influence ecosystem biodiversity is a major challenge.

The main objective of MassExtinct was to investigate the causes and consequences of the fourth greatest mass extinction event in Earth history, which occurred 200 million years ago at the Triassic–Jurassic boundary (Tr–J), and to use an understanding of past biodiversity responses to global climate change to inform contemporary conservation policy.

Marie Curie logoThese broad objectives were achieved by developing a novel and highly multidisciplinary research program, which strongly compliments existing research priorities in University College Dublin, Ireland. Fossil plant biodiversity (richness, evenness, heterogeneity) and ecology (rarity, dominance, persistence, reproductive strategy, disparity, fire history) were tracked in responses to Tr-J global warming, to enhance our understanding of how modern ecosystems respond to a doubling of carbon dioxide and 1–4ºC global warming by the end of this century. Palaeoecological studies of fossil plants from Kap Stewart Group strata in E. Greenland were coupled with long term ecophysiological experiments on model Tr-J plant communities in a new Marie Curie and UCD funded plant growth room facility called Péac (Program for Experimental Atmospheres and Climate).

MassExtinct Research Elements

Arrow Vegetation Dynamics
Luke Mander's research focused on investigating ecological interaction and biological evolution during episodes of major environmental change. To this end he studied the Triassic – Jurassic transition (c. 200 Ma), which witnessed one of the major extinction events of the Phanerozoic and was associated with net atmospheric and shallow-ocean carbon gain. Local studies of the plant macrofossil record from the Jamesonland region of East Greenland have provided evidence of ecosystem instability millions of years prior to, and following, peak extinction in the Late Triassic, demonstrating that terrestrial vegetation was profoundly disrupted by climatic changes at the Triassic – Jurassic transition. However, it is presently unclear exactly how these changes scale-up to the entire region. Outstanding questions include: Are plant community responses to environmental disturbance at this time recorded in the same way by all fossil groups? Are these responses consistent at all spatial and temporal scales? Do these responses vary according to the ecological and physiological properties of the plant taxa involved?

To explore these issues Luke reconstucted the vegetation history of the Jamesonland basin using fossil pollen. He employs Quaternary-style analytical techniques incorporating abundance data to samples that have been collected on centimeter scales. The results of this study are being directly compared with palaeoecological studies based on macrofossil leaves to build a more comprehensive picture of regional versus local vegetation dynamics at the Triassic – Jurassic transition. Analysis of the quality of the fossil record is an important component of his research, and taphonomic studies provide a means to rigorously assess the fidelity of fossil plant and pollen assemblages. He is particularly interested in the relationship between ‘time averaging’ of fossil assemblages and the adequacy of sampling of rare species in the geological record.

Arrow Palaeowildfire
Throughout Earth history fire has played the role of cause, consequence and catalyst to the development of terrestrial life on earth. Claire Belcher's research focused on developing a fire history using fossil charcoal across the Triassic-Jurassic Boundary (Tr-J) for the Jameson Landregion in E. Greenland.

Her research aims were two-fold:

  1. To test the limits of combustion under low oxygen (experimentally), using the state-of-the-art UCD Péac facility and link these findings to the palaeowildfire record for E. Greenland.  Few proxies have been developed for testing modelled past atmospheric O2 concentrations, particularly the low O2 predicted in the Triassic and Jurassic. Charcoal in the geological record offers a means to assess palaeoatmospheric oxygen levels and numerous studies have sought to test the limits of combustion under varying concentrations of oxygen however, none have been able to fully assess the limits of combustion within a fully controlled and realistic atmospheric environment. UCD Péac provides a unique opportunity to experimentally test fire behaviour under different atmospheric compositions, the results from which will be used to test the modelled Tr-J atmospheric oxygen concentrations using the fire record across the Tr-J boundary at Astartekløft in Greenland .
  2. The charcoal record will be used to study the potential role of fire in contributing to vegetation dynamics and biogeochemical cycling at the Tr-J boundary. As part of this work Claire aims to develop and assess semi-automated image analysis techniques for identifying and quantifying charred plant remains. Semi-automated methods have been used to quantify proportions of charcoal in Recent sediment samples but have not previously been used to identify and quantify different charred plant parts (e.g. charred wood, cuticle and flowers) within a fossil assemblage. Having the ability to quickly and easily identify and quantify fossil charred assemblages will allow ancient fire ecology to be better understood and links between the Earth’s fire and climate histories to be made.

Arrow Palaeophysiology
Matthew Haworth worked in the plant growth rooms at the Péac facility (Programme for Experimental Atmospheres and Climate) running plant growth experiments to investigate the responses of living plants to atmospheric conditions thought to have occurred at the Triassic – Jurassic Boundary (TJB).  Plants were grown in atmospheres of elevated carbon dioxide, high sulphur dioxide and sub-ambient oxygen. As part of the research we studied gas exchange, thermal, physiological and morphological responses of plants to these gases in isolation and combination.  The plants chosen for the growth experiments were ecological and morphological equivalents of fossil plants collected from the TJB sediments of Astartekløft, East Greenland. These relict plants with ancient evolutionary origins include conifers such as Kauri Pine (Agathis australis) from New Zealand and Swamp Cypress (Taxodium distichum) from southern USA, cycads such as Hope’s Cycad (Lepidozamia hopei) and ferns such as the Royal fern (Osmunda regalis), that occurs widely in gardens of Ireland.

From the ecophysiological and morphological responses of the living plants used in the growth experiments, and through comparison to the fossil flora of Astartekløft, we studied the causes and mechanisms of plant stress that contributed to the mass extinction event at the TJB.  A crucial area of investigation is thermal stress, one of the leading hypothesised mechanisms of plant stress at the TJB.  To do this we assessed the effect of exposure to these gases on how effectively plants dissipate heat energy using thermal imaging techniques.

Arrow Palaeo Atmospheres
The objective of Margret Steinthorsdottir's research was to develop a high-resolution record of atmospheric CO2 concentrations across the Triassic-Jurassic boundary (TJB) using census collected fossil leaf cuticles from Astartekløft in East Greenland. Specimens are hosted at UCD and at the Field Museum of Natural History, Chicago. The CO2 record was used to investigate the role of a high CO2 induced global warming in the major turnover of terrestrial plants and extinction of fauna at the TJB. In this research, stomatal numbers - stomatal density (SD) and stomatal index (SI) - are applied as proxy, since these are reversely correlated to atmospheric CO2 concentrations. Furthermore, changes in cuticular micro-morphology are recorded for additional information on environmental conditions, such as the presence of air pollutants (mainly SO2), which aid in the interpretation of the causal mechanism for the TJB extinction event.

The fossil leaf cuticles are represented by both intact, untreated cuticles that are studied using epifluorescence microscopy and were collected at bed to bed resolution, and by macerated cuticles from bulk samples that were collected at a very high (10 cm) resolution. Many of the cuticles are remarkably well preserved and wherever possible were studied directly from the leaf surface, but others were only obtainable from bulk maceration. Stomatal numbers are highly variable between taxa and it was therefore important to accurately identify the cuticles and assign them to mono-taxonomic groups. Margret focused on the cuticles of genera that were selected due to their prevalence in the stratigraphic section and/or their relationship with extant groups, allowing for tests of our various hypotheses to be conducted in the growth chamber facility at Péac on living representatives. These genera include the Ginkgoales group (Ginkgo, Baiera, Spehenobaiera and Czekanowskia), the Pteridosperm Lepidopteris, the Benittitales Anomozamites and Pterophyllum and the Conifer form genus Elatocladus.


 

 

 

 

 



UCD Plant Palaeoecology and Palaeobiology Group Updated: July 2013
Professor J.C. McElwain