27 Projects, page 1 of 6
Many researchers in archaeology and the geosciences obtain timescales for their projects by radiocarbon dating plant or animal remains from the preserved deposits with which they work. Radiocarbon dates are not the same as calendar dates, however, and have to be corrected for variations in the radiocarbon content of the atmosphere at the time that the plant or animal lived. This conversion of radiocarbon dates to calendar ages, known as calibration, is not a straightforward correction. Calibration of radiocarbon dates can only be done by comparison to a suitable calibration curve. Such curves are based on measurements of radiocarbon in samples of known calendar age such as tree-rings, or in a less strict sense, on other types of samples where an independent method of dating can be used. For samples which grew in the ocean, such as shells and corals, a separate calibration curve is needed to account for changes in ocean water circulation which may bring up 'old' water from the ocean depths (the reservoir effect). The calibration curves have been refined periodically to provide better estimates of the calendar ages. In 2004, the IntCal Working Group constructed new calibration curves from radiocarbon dated tree-rings back to 12,400 years before present and from independently dated ocean samples, using an estimated correction for the reservoir effect, back to 26,000 years before present. Rather than simply averaging the data, these curves were constructed with statistical tools (models) that allowed for the uncertainty in the calendar ages of the samples used as well as the radiocarbon dates. At that time data beyond 26,000 years before present did not agree so no curve was provided but an estimate of how far the data sets differed from the underlying true curve was given. In the last few years a lot of research has gone into producing radiocarbon datasets from a variety of records. Many of these datasets are now in fairly good agreement so it should be possible to provide curves for estimating calendar ages back to 55,000 years before present. In addition new tree-ring records are becoming available which will improve the precision of the calibration curve. Statistical methods have also been rapidly advancing and so some of the simplifying assumptions that we made about the models in 2004 will no longer be necessary. Working in collaboration with the IntCal Working Group, this project will develop an easily maintainable database of calibration quality radiocarbon data to be used to produce updates to the calibration curves on a regular basis. Advances in statistics will allow us to improve on the previous models to further refine the calibration curves. Measurements of carefully selected coral will help determine what corrections are needed for ocean samples to be used in calibration curves. By improving radiocarbon calibration this project will improve the understanding of the sequence and timing of events in numerous studies in archaeology and in the reconstruction of past environments.
There is a general perception that corals (and coral reefs) are highly susceptible to riverine inputs of terrigenous sediment, and that high rates of such inputs will negatively impact reef health and vitality (usually evidenced by low coral cover and/or high partial mortality rates). In coral reef settings where such inputs have been limited in the past and where corals are not adapted to deal with frequent sediment loading and reduced light penetration, this perception is likely to have considerable validity and may lead, over time, to shifts in coral community structure. However, there is an increasing body of sedimentological, geomorphological and palaeoecological data demonstrating not only long-term (>1,000 year) persistence of coral communities under conditions of high terrigenous sediment input and high turbidity, but also clear evidence of active and rapid reef-accretion. Under these conditions corals seem to be sufficiently adapted to these environmental conditions that coral cover is often high and well-developed reef structures can form. This has been demonstrated at sites in Thailand, Indonesia, Mozambique and at a range of sites along the nearshore (innermost shelf) areas of the Great Barrier Reef (GBR), Australia. An apparent paradox thus exists between the perceived negative effects of high turbidity and terrigenous sediment inputs on coral communities (which are widely referred to in the scientific literature) and the increasing sedimentary and palaeoecological evidence for historical timescale persistence of corals and of reef-building in these settings. This raises an intriguing question about coral carbonate production in these environments and about the nature of skeletal carbonate deposition. Are these coral communities able to produce reef structures, despite high terrigenoclastic sediment input and high turbidity regimes, because of particularly high coral growth and calcification rates? Little data exists from nearshore reefs of this type and there has been no attempt to quantify and compare these processes over temporal and spatial scales. This project thus aims to quantify coral extension (growth) and calcification rates, and to quantify the microskeletal characteristics (i.e., the size and density of key skeletal elements in the coral skeleton) from two of the dominant coral species associated with reef-building within nearshore, turbid-zone settings along the central GBR coastline. The focus for the research will be the two best-studied turbid-zone reefs in the region; Paluma Shoals and Lugger Shoal. Extensive datasets are available on the sedimentary environments, hydrodynamic conditions and contemporary community structures in each locality. In addition, radiocarbon (14C) date-constrained growth models exist for each site that allow data to be placed in a reliable chronological framework. Specifically, we will gather data on a massive coral species (Porites lobata) that makes a major contribution to contemporary reef-flat coral communities in both settings, and a branching coral species (Acropora pulchra) which previous research has demonstrated to have been a major framework contributor throughout the growth history of these reefs. The research will utilise novel Computerised (Axial) Tomography (CT) scanning and established Scanning Electron Microscopy (SEM) approaches to quantify coral growth rates and styles of coral skeletal deposition in these samples. Between-site comparisons will be made against data collected from the same species of Porites and Acropora that were collected from clear water sites at Low Isles during the 1928-1929 Great Barrier Reef Expedition. This extensive and well-catalogued coral repository is stored at the NHM and CT methodologies will allow us to examine the skeletal structures of these corals using non-destructive techniques.
Over the last two months there have been increasing reports of the current El Niño causing massive coral bleaching along Australia's Great Barrier Reef (GBR), with aerial surveys reporting that >90% of reefs are bleaching, and with more that 50% of corals on these reefs already dead. However, these surveys cannot assess what is happening on the nearshore turbid-zone reefs, firstly because turbidity levels inhibit aerial assessments, and secondly because there is little ecological data against which to compare change. The bleaching response of corals on these turbid-zone reefs is however of significant scientific interest. This interest relates specifically to the hypothesis that there may be particular marine environments that might act as important refugia sites from bleaching i.e., settings that are more effectively buffered from surface warming such that coral populations remain largely unaffected. Reefs forming in well-flushed, highly turbid settings are one such candidate location for these refugia. Increased bleaching resilience has been hypothesized because high particulate content in the water may limit UV stress, and because the corals may be more readily able to switch to predominantly heterotrophic feeding modes - reasons for enhanced protection from thermal stress events that were initially hypothesised in the early 2000's. However, recent modelling now provides a global-scale framework through which the spatial extent of such potential refugia can be defined. What is lacking however is any empirical field evidence definitively showing that these turbid-zone reefs are actually able to withstand major coral bleaching events. Without doubt the best studied of these turbid-zone reefs are those along the nearshore areas of the GBR, which have been the focus of intensive study by the PI and his group since 2006. This work has largely focused on assessing rates and styles of reef growth, but our most recent work has had as its central aim an assessment of the spatial extent and contemporary ecological structure of these reefs. Working at sites in the central GBR we have undertaken an unprecedented mapping and ecological surveying campaign, collecting >130 km of seafloor swath survey data and >4,500 video still quadrats. The resulting datasets have enabled us to develop high resolution maps of reef structure and ecological composition, which show that despite their narrow bathymetric extent, these reefs are characterised by a clear depth-controlled ecological zonation, and that they exhibit high live coral cover (mean: 38%, but up to ~80%). We are thus in a unique position to quantitatively assess the extent to which this major bleaching event has impacted these turbid-zone reefs, and to test the recently proposed hypothesis that such reefs may act as critical climate change refugia sites. In this project we will undertake a rapid assessment of the impacts of bleaching on the turbid-zone reefs in the vicinity of Paluma Shoals (central Halifax Bay). We will re-examine a suite of six proximal reefs using remotely-operated underwater video survey methods and collect ecological data along replicate transects across each reef. Video data will be used to determine species abundance and bleaching intensity. This will allow us to ascertain: 1) the total extent of bleaching-induced mortality; 2) the extent to which specific coral species have been impacted; and 3) any immediate impacts on the structural complexity and diversity of the reefs. We will also undertake comparable assessments at other turbid-zone reefs which have been the focus of our earlier studies e.g., further north around Dunk Island and to the south at Middle Reef- these reefs occupying similar geomorphic and sedimentary settings to the Paluma complex. The work would thus deliver not only data on the extent of turbid-zone reef bleaching, but also provide a robust test of the hypothesis that turbid-zone reefs may form critical climate change refugia sites.
Climate change creates risks to biodiversity, in particular by changing the climate in which species live, and making it unsuitable for them to continue to live there. In December 2014, under the United Nations Paris Agreement countries agreed to 'pursue efforts to ...limit the temperature increase to 1.5C above pre-industrial levels'. IMPALA seeks to understand these risks to biodiversity arising in a future world in which humans limit climate change to 1.5C warming compared to pre-industrial times, and to compare this with the situation when there is 2C warming (hereafter referred to as 1.5/2C). It seeks understand the relative risks both globally, and at the regional scale. Species also face a challenge in being able to track their preferred climate space across a landscape, both in terms of the speed of movement required and in dealing with natural and/or manmade obstacles to movement. Several previous studies have projected extensive range loss and increased extinction risks across large fractions of species globally or regionally due to climate change e.g. amongst 50,000 species studied, 57+/-5% of plants and 34+/-7% of animals are projected to lose over half their climatic range for a warming of approximately 3.6C above pre-industrial levels. But what difference does 0.5C make? Is there really much difference between 1.5C and 2C of warming when it comes to terrestrial biodiversity? Examination of the large-scale potential changes in climatic ranges of 80,000 species at 2C versus 2.5C suggests that there may be a large difference, at least in some parts of the world. These differences have the potential to put much of the past investment in conservation at risk. This study will look at the areas where it makes the most difference to constrain warming to 1.5 versus 2C, looking specifically at Global Protected Areas, and key conservation regions such as biodiversity hotspots. It will identify which Protected Areas are most, and least, at risk from biodiversity changes at 1.5 vs. 2C, and where corridors between protected areas would do the most good. IMPALA is designed to inform decision makers in the UK government and also within environmental NGOs, in particular World Wildlife Fund-UK. Environmental NGOs are interested in conservation planning, that is deciding which areas of the world need to be brought into the protected area network, or protected by other means such as working with local people to protect habitats for species. Since it is not possible to protect all natural ecosystems, NGOs and Governments need to prioritise, and climate change will affect that prioritisation by changing the places where species can live. IMPALA will inform WWF-UK, other NGOs, and Governments whether the existing protected area system is robust to warming of 1.5/2C, which areas are most at risk, and which areas act as refuges where species can still live after 1.5/2C global warming has occurred. IMPALA considers how species try to move to track climate change, and will also identify places that need to be protected to enable species to move and colonize new areas in response to climate change. Complicating the efforts to allow ecosystems (and biodiversity) to adapt naturally to climate change may be the efforts needed to hold climate change to 1.5C of warming. Many proposals to limit warming to 1.5 and 2C of warming require large areas to be converted to bioenergy crops. There is the risk that it may be necessary to convert large areas of primary/secondary forest and other ecosystems to bioenergy crops, so that agricultural land can continue to grow food. As habitat loss is a major factor in biodiversity loss, then it might potentially be worse for biodiversity at 1.5C warming than 2C warming. This study will look for win-win solutions for biodiversity and mitigation in order to promote Article 2 compliant mitigation - that is, mitigation that hinders neither ecosystems from adapting naturally and the production of food.