Climate variability over the circum-Caribbean region during the past 1200 years from oxygen-isotope analyses of lake sediments

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Variations in water availability, especially drought, on timescales of years to decades are a major concern for society. Changes in the frequency and magnitude of drought on such timescales are a likely outcome of future climate change, especially in subtropical regions. The area that encompasses the eastern part of Central America, the Gulf of Mexico and the Caribbean (hereafter the circum-Caribbean region) is likely to be especially sensitive to climate change in the future, especially in terms of the incidence and severity of drought: it is this region that is the subject of our proposed research. Meteorological records of rainfall are too short to encompass the full range of variations in past rainfall on timescales of years to decades or to indicate whether geographical patterns have changed through time and under different conditions. Natural 'archives' of past climate, including lake and marine sediments, speleothems (cave deposits) and tree rings, provide an opportunity to extend the meteorological records further back into the past and to shed light on the modes and causes of rainfall variability. In this research, we will investigate changes in rainfall over the past 1200 years using oxygen-isotope analyses of the calcite shells of ostracods preserved in lake sediments. We plan to analyse lake sediment cores that have already been collected from sites in the Yucatan Peninsula of eastern Mexico, Jamaica, Haiti and Barbuda. These sites are located on a west to east transect, along which changes in rainfall are known to have occurred over recent decades. Our reconstructions will be complemented by existing studies along a north to south transect within the circum-Caribbean region, thus allowing us to investigate changes in the geographical patterns of past rainfall. The past 1200 years is an important time period to study as it covers intervals of marked change in climate including the Medieval Climate Anomaly (MCA) of predominantly wet climate, the drier little ice age (LIA) and the terminal classic period of marked drought at the end of the MCA, which is thought to have contributed to major societal change in the Yucatan Peninsula. The broad variations in climate over this interval are quite well known, but changes in the geographical patterns in the region, despite being implied by existing data, are poorly constrained. Furthermore, links to potential causes, such as variations in ocean circulation and sea-surface temperatures, changes in solar activity and volcanic eruptions, are not well understood. By generating new reconstructions of variability in rainfall over the past 1200 years, we will provide further insights in to the nature and causes of change during this period. By extending the timespan of records beyond that of meteorological data, we will be able to show whether geographical patterns of rainfall variability have remained constant over the recent past or, as seems likely, have changed. In addition to providing important palaeoclimatic data for the circum-Caribbean region, our research will generate much-needed reconstructions of climate for archaeologists, especially those working on links between climate and society in Mexico and Barbuda.