Mid-XIX Century Estuary SST Time Series Recorded in the Venice Lagoon

Abstract

Sea surface temperature (SST) is of paramount importance for comprehending oceandynamics and hence the Earth’s climate system. Accordingly, it is also the most measuredoceanographic parameter. However, until the end of the XIX century, no continuous time series ofSST seem to exist, with most of the available data deriving from measurements on ships. Here,we present a continuous record of surface water measurements retrieved thrice daily in the Venice lagoon,in the northeastern part of the Italian peninsula, from June to August 1851 and 1852. To the best of ourknowledge, these data represent the oldest SST time series of the entire world ocean. Themeasurements were performed by immersing a Réaumur thermometer a few meters deep in thelagoon water at 8 a.m., 12 p.m., and 8 p.m. Despite several limitations affecting these data (e.g.,lacking information regarding the exact water depth where measurements were performed andinstrumental metadata), they are of utmost significance, as they put many decades backward thedate of the development of a fundamental aspect of oceanographic observations. Moreover, thedata were collected close to the Punta della Salute site, where actual sea water temperaturemeasurements have been performed since 2002. Therefore, a unique comparison betweensurface water temperatures within the Lagoon of Venice across three centuries is possible.