Investigating the potential of oxygen-isotope records from anthropogenic lakes as tracers of 20th century climate change

Historical climate change in southern England was investigated using ostracod oxygen-isotope (δ 18 O) records from two anthropogenic lakes in Hampshire, southern England. A strong relationship is observed between δ 18 O ostracod, δ 18 O precipitation and δ 18 O lakewater in the contemporary environment and therefore δ 18 O ostracod from the sedimentary record of these systems has the potential to reflect past climate variability. The possibility of these sites to act as archives of climate change through δ 18 O ostracod analysis is explored through the study of lake sediment cores that cover the period from the early 20th century onwards. Both lakes showed similar directionality of shifts in δ 18 O ostracod over this period, suggesting common driving mechanisms. Comparing δ 18 O ostracod timeseries to meteorological data is challenging in part because of the complexity with which climate parameters are recorded in the δ 18 O lakewater and consequently within lacustrine carbonates. Our findings highlight the potential of sediments from anthropogenic lakes to act as archives of past climate and indicate they may be an important resource for generating climatic reconstructions across the medieval to instrumental period, which the sediments of many anthropogenic lakes cover. Such climate reconstructions would greatly improve our spatial and temporal understanding of climate variability where instrumental data are unavailable and other natural archives are scarce.