Surface Temperature Variability in the Delaware Bay Estuary System

Temperature variability plays an important role in estuarine ecosystems but is understudied because it is not typically a primary driver of circulation. Here, temperature variability within the Delaware Estuary system (defined to include the tidal river, estuary, bay, and adjacent shelf) is characterized over tidal to interannual timescales using nearly 20-year records of surface temperature from eight NOAA monitoring sites. The seasonal cycle explains 93% of the temperature variability at all sites, with annual temperature ranges O(30C). A combination of spring-neap, weather-band, and river discharge variations generate 1-6C fluctuations, and semidiurnal tidal variability is 1-3C. The along-estuary surface temperature gradient reverses seasonally, with a summertime mid-estuary temperature maximum in most years. Satellite sea-surface temperature data and near-surface temperature data from eight along-estuary seasonal cruises in 2010 and 2011, which provide greater horizontal resolution than the NOAA sites, are used to further evaluate along-system patterns. Despite a significant warming trend on the shelf, long-term trends in water temperature are statistically insignificant within the estuary. There is interannual variability in the characteristics of the seasonal cycle at each site, including annual minimum/maximum surface temperatures (which vary up to 6C from year to year), the onset of the warming season (+/- 30 days), and the length of the warming season (+/- 40 days), but there are no long-term trends in these characteristics over the 20-year record. This system-wide characterization of surface temperature patterns, variability, and change provides a foundation for future studies of mechanisms controlling temperature variability.