Combined genetic, morphological and ecological approaches to reduce uncertainty in palaeoclimate reconstructions using benthic foraminifers

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It is very important for us to find out how climate changed in the past. Without knowing, we cannot predict how the future climate might behave. Global, systematic measurements of climatic variables have only been collected over the last few decades but we need to know how it varied through longer periods of time. We particularly need to know about this in the North Atlantic shelf seas which are currently experiencing accelerating climate change. The layers of ocean sediments in these regions contain the skeletons of microscopic organisms which can provide information about past climate. Benthic foraminifers in particular live in these shallow ocean habitats and their microscopic calcite shells accumulate through time providing a high resolution record of past environments. Communities of specific species (assemblages) are associated with the regional habitats of the shelf seas and this relationship is applied to similar assemblages found in time slices in the sediments (transfer functions). Forams also incorporate into their shells the physical and chemical signatures of the seawater in which they grow. This can be used as a geochemical 'proxy' to reconstruct the past environment in which they lived. All these past climate reconstructions are based on the assumption that the shells of a single species were constructed in the same range of environmental conditions. Using a unique DNA marker in living forams, we know that this is not always true. Individual morphospecies sometimes represent several distinct genetic types (genotypes) which may be adapted to different environments within a morphospecies range. It is highly likely that these are different species. Scientists are unknowingly analysing a mixture of different species because they look very similar (cryptic species). This will introduce noise and possible error into the data of both transfer function methods and geochemical proxies. To overcome this, we propose to genotype all the important benthic morphospecies used for past climate reconstruction throughout the regional habitats (biogeographic provinces) of the mid to high latitudes of the northeast Atlantic. We will sample these with the help of our four project partners from Norway and Iceland. We also have to bear in mind that these regions experience a wide range of environmental conditions as the seasons change. To address this, we will take samples from regions where seasonal studies are being carried to find out whether different genotypes appear as the environmental conditions change. Central to this study will be an extensive morphological investigation of shell shape to find out whether we can find subtle differences to help recognise the new genotypes in the modern ocean and most importantly, in the fossil record. We hope to genetically and morphologically define all important benthic morphospecies used for past climate reconstruction in the North East Atlantic to produce a unified classification scheme. From our high resolution sampling, we will be able to produce a new bioprovince distribution map for the present day northeast Atlantic/Arctic. We will discover whether 'generalist' species really occupy different bioprovinces or represent a series of different cryptic species with different ecologies. Finding identifiable new species will improve our understanding of how bioprovinces have migrated North/South as the glacial cycles have come and gone. Do different cryptic species appear in the same place as the seasons change? Their recognition would allow the exploration of seasonality in the fossil record. Do foram shells of the same species have a different shape in different environments? Confirmation will provide evidence of specific environmental conditions in the present day and in the past. This link between present and past also provides important clues about how extreme changes in these dynamic marine environments affect the survival of species and drive their evolution through time.