Calibrating novel palaeotemperature proxies in laboratory aquaria cultured long-lived Arctica islandica mollusc shells
Lead Research Organisation:
Manchester Metropolitan University
Department Name: School of Science and the Environment
Abstract
For the last approximately 200 years since the Industrial Revolution, human activity, primarily by burning of fossil fuels, has added carbon dioxide to planet Earth's atmosphere. Carbon dioxide is an important greenhouse gas and increasing concentrations of this chemical compound in the atmosphere causes climate warming. Understanding the temporal and spatial response of Earth's climate system to changing atmospheric carbon dioxide concentrations is a pressing issue for all of human society across the planet. One way to make such an assessment is to look back into the past and to reconstruct past temperature changes and to relate such variability to records of past atmospheric composition.
Despite the significance of global warming, long instrumental records of changing seawater temperature in the past are not available for all of the geographical regions which interest climate scientists, or such instrumental records do not extend far enough back in time. Therefore, in order to place the most recent instrumental records of seawater temperature change in a longer temporal context, as well as to enable reconstruction of past seawater temperature where instrumental records do not exist, it is important to delve deeper into history by application of what is called a proxy-based temperature reconstruction approach. Elements and isotope ratios of some elements, when incorporated into calcium carbonate biominerals (including corals, mollusc shells and some plankton), have demonstrated potential to be used as the proxy means of reconstructing the magnitude and rates of change of seawater temperatures, for those time periods before the existence of instrumental records and for geographical regions where such instrumental records do not exist. Such an approach has long been applied to low latitude warm-water corals, since they form easily dated annual growth increments, but these organisms are restricted in distribution to the warm low latitudes.
Arctica islandica is a marine bivalve mollusc that inhabits those middle to high latitude shelf seas that border the North Atlantic Ocean and individuals of this species have been shown to live for up to ~400 years. Furthermore, this organism (like a warm-water coral) deposits easily identified and dated annual shell growth increments, the composition of which has the potential to enable reconstruction of proxy-based records of past seawater temperature, on a calendar timescale (by counting annual growth increments from a known date of death), for the last few centuries and even for the last millennium (when shells of individuals are cross-correlated using the same approach as is applied to tree rings). However, to be able to generate these proxy-based records of past seawater temperature it is critically important that robust calibrations are derived, which document the strength of the relationship between the proxy measurement and seawater temperature, as well as identifying any limitations with any proxy. This detailed and systematic study will be the first use of specimens of A. islandica, which have already been cultured at constant seawater temperatures in laboratory aquaria, under controlled conditions, to derive calibrations for three novel temperature proxies. Such laboratory experiments are fundamental to the development of proxies for reconstructing past seawater temperatures, because such experiments allow for shell growth under controlled conditions. Once these calibrations have been determined the next step, in a follow-up project, will be to generate long time-series records of past seawater temperature change in different parts of the North Atlantic Ocean. Such records then will further climate scientist's understanding of the past and future evolution of climate in a geographical region which is of direct relevance to the UK and western Europe.
Despite the significance of global warming, long instrumental records of changing seawater temperature in the past are not available for all of the geographical regions which interest climate scientists, or such instrumental records do not extend far enough back in time. Therefore, in order to place the most recent instrumental records of seawater temperature change in a longer temporal context, as well as to enable reconstruction of past seawater temperature where instrumental records do not exist, it is important to delve deeper into history by application of what is called a proxy-based temperature reconstruction approach. Elements and isotope ratios of some elements, when incorporated into calcium carbonate biominerals (including corals, mollusc shells and some plankton), have demonstrated potential to be used as the proxy means of reconstructing the magnitude and rates of change of seawater temperatures, for those time periods before the existence of instrumental records and for geographical regions where such instrumental records do not exist. Such an approach has long been applied to low latitude warm-water corals, since they form easily dated annual growth increments, but these organisms are restricted in distribution to the warm low latitudes.
Arctica islandica is a marine bivalve mollusc that inhabits those middle to high latitude shelf seas that border the North Atlantic Ocean and individuals of this species have been shown to live for up to ~400 years. Furthermore, this organism (like a warm-water coral) deposits easily identified and dated annual shell growth increments, the composition of which has the potential to enable reconstruction of proxy-based records of past seawater temperature, on a calendar timescale (by counting annual growth increments from a known date of death), for the last few centuries and even for the last millennium (when shells of individuals are cross-correlated using the same approach as is applied to tree rings). However, to be able to generate these proxy-based records of past seawater temperature it is critically important that robust calibrations are derived, which document the strength of the relationship between the proxy measurement and seawater temperature, as well as identifying any limitations with any proxy. This detailed and systematic study will be the first use of specimens of A. islandica, which have already been cultured at constant seawater temperatures in laboratory aquaria, under controlled conditions, to derive calibrations for three novel temperature proxies. Such laboratory experiments are fundamental to the development of proxies for reconstructing past seawater temperatures, because such experiments allow for shell growth under controlled conditions. Once these calibrations have been determined the next step, in a follow-up project, will be to generate long time-series records of past seawater temperature change in different parts of the North Atlantic Ocean. Such records then will further climate scientist's understanding of the past and future evolution of climate in a geographical region which is of direct relevance to the UK and western Europe.
Planned Impact
This proposal is a detailed and systematic study which will calibrate, for the first time, three novel temperature proxies for the important long-lived (individuals up to ~400 years) Arctica islandica marine mollusc shell past climate archive. Once these temperature calibrations have been developed it will then be possible to apply them to the generation of high temporal resolution inter-annual (and possibly also intra-annual) past temperature records for the North Atlantic Ocean, where this mollusc species lives. As such, obvious societal impact will likely follow only after a more significant follow-up project, which will apply the new temperature proxy calibrations to understanding past magnitudes and rates of change of climate (seawater temperature), for a geographical region of direct relevance to the UK and western Europe climate system. The potential of using A. islandica shells as past climate archives, in combination with development of novel temperature proxies (element/Ca, Li/Mg, clumped isotopes and stable Sr isotope ratios), will enable reconstruction of spatial and temporal variability in historical seawater temperatures, which will have significant implications for all individuals (scientists and policy makers) interested in global climate change, as related to anthropogenic carbon dioxide emissions. For example, development of novel high temporal resolution past temperature records, for application over recent centennial timescales, for middle to high latitudes in the North Atlantic Ocean, could result in the inclusion of such data within future Intergovernmental Panel on Climate Change (IPCC) assessments, with resultant implications for development of future societal mitigation and adaptation strategies. However, before such past climate records can be generated a fundamental prerequisite is that the proxies are calibrated and well understood; these latter objectives are the aims of this study.
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