Glenn Havelock

<p>Saltmarshes play a key role in sequestering and storing carbon, as well as providing a wide range of other ecosystem services. Assessments of both total carbon stocks and rates of carbon accumulation are vital for quantifying saltmarsh contributions to climate-change mitigation and for guiding efforts to protect and restore coastal wetlands. Current assessments of the rates at which UK saltmarshes accumulate carbon are based on a small and spatially limited dataset. To address this knowledge gap, we estimate sedimentation rates and assess organic carbon density from 22 saltmarshes distributed around the UK. Bayesian modelling quantifies the relationship between depth and age from <sup>210</sup>Pb and <sup>137</sup>Cs activity data. We combine these sedimentation rates with centimetre-resolution organic carbon density measurements to quantify carbon accumulation rates through time. By upscaling these estimates to the total UK saltmarsh area and fully quantifying uncertainties, we conclude that UK saltmarsh carbon burial rates are lower than previously thought.</p>

Present models of Holocene estuary evolution are driven largely by changes in relative sea-level (RSL) with little reference to long-term changes in fluvial regime and regional climate. Recent US studies of estuarine sequences have shown that decadal-centennial scale fluctuations in river discharge and freshwater inflow can be inferred by changes in estuarine palaeosalinity and that the timing of these events reflect changes in regional precipitation. It is therefore becoming apparent that estuarine sequences may hold an archive of mid-late Holocene climate change information, as well as being recorders of