A Note on the Long-Term Sea Surface Temperature Records at Boothbay Harbor, Maine

Sea surface temperature (SST) records have been collected at Boothbay Harbor, Maine, since 1905. A dramatic change in the structure of the monthly mean SST anomalies occurred around 1950. Prior to 1950, when observations were made with a bucket thermometer, there was a large range in the monthly mean temperature anomalies with warmer summers and cooler winters. After 1950, when a fixed thermistor was used, the difference between winter and summer anomalies were much reduced. We show that the primary cause of the change in the monthly anomaly patterns is related to the difference in the depth of the measurements from near surface (pre-1950) to 1.7 m below mean low water (post-1950) combined with the thermal stratification of Boothbay Harbor waters. The non-homogeneous nature of the surface temperature time series at Boothbay Harbor means that they should not be used for retrospective analyses that cover the entire period. Since 2000, the annual mean Boothbay Harbor temperatures have been much warmer than nearby sites, however the cause of this phenomenon is as yet unclear.