Characterising sea water temperature of Marsalforn Bay, Gozo

Abstract

This study set out to characterize the summer (August to September 2016) sea water temperatures of Marsalforn Bay, Gozo. Using temperature data loggers, seawater temperature was measured in situ at three different depths along the water column (sea surface, mid-depth and sea bottom) at nine monitoring stations distributed across the embayment. To provide a variation in depth, the monitoring locations were established along the length of the bay from shallow inshore waters, to mid-depth stations and deeper baymouth stations and across the bay, to overlie three different types of sea-bottom, namely sandy, rock and Posidonia oceanica meadow. The variation in sea bottom typology was chosen to analyse potential correlations with seawater temperature as a consequence of sea bottom albedo. Moreover the study sought to identify other variables that may influence sea water temperature such as depth and open sea water influx into the embayment. Generally, bayhead water temperatures were warmer than baymouth stations suggesting that bayhead waters experience less influx of cooler water from the outer sea. The surface waters at all stations experienced a diurnal variation, while the deep waters experienced little to no change. Seawater temperatures over sandy bottoms were identified as slightly cooler than those over rocky and seagrass sea bottoms. This suggests that sandy sea bottoms reflect more of the insolation received at the sea surface than other bottom types investigated; sea bottom types may therefore be considered as a variable influencing physical properties of ocean water. This is significant due to the ecology found in the bay that triggers these temperature variations. A comparison of the in situ SST records with various remotely sensed data sources identified a general tendency for the external sources to under estimate the temperatures of partially enclosed water bodies. The Enclosure Index calculated resulted in an index of less than one (1) which indicates that the embayment is exposed to outer waters.