Introduction

Global-scale averages of observations of surface temperature in the atmosphere over both land and ocean exhibit a warming trend over the last century (Hansen et al., 1996; 2010) . However, detecting changes in coastal water temperatures at the scale of estuaries has frequently been confounded by the absence of sufficiently long data records and the presence of high amplitude variations at short time (days to years) and space (meters) scales. Separating the consequences of this global change from the local impacts of development and resource exploitation is critical to wise environmental management at the scale of estuaries and embayments and it is, therefore, important to make the most effective use of all available observations.

Over the last three decades, the high population density and long history of exploitation of fisheries in the estuaries of southern New England have led to the development and implementation of management regulations to improve water quality and restore fisheries populations. The harvest of American Lobster in Long Island Sound, for example, has declined substantially since 1991 (Howell et al., 2005) and it has been proposed by Camacho et al. (2006) that this is partially a consequence of physiological temperature stress that has been enhanced by warming bottom waters. Clearly, separating the effect of environmental change from that of fishing and other predation is critical to the regulation of the fishery.Temperature clearly affects other species as well (e.g., Atlantic Croaker (Hare and Able, 2007); brown algae (Keser et al., 2003); non-native species such as Sea Squirts (Stachowicz et al., 2002)).

Recently, Howell and Auster (2012) reported an analysis of the character of fish species distributions in Long Island Sound based on a long time series of trawl surveys. They showed that there has been an increase in the number of species that are more commonly observed to the south of the Sound (warm water adapted) and a coincident reduction in the number of species characteristic of communities to the north (cold water adapted). This shift correlated with temperature change. Understanding whether this is a shift, or part of a long term cycle is a critically important question for the choice and effectiveness of management approach.

Temperature is the best observed characteristic of coastal environments. Available observations were assembled to examine the characteristic of their variability in order to discern magnitude of the local consequences of global changes. 

Previous Studies

Previous studies have shown that temperature in LIS is mainly dominated by seasonal variation with the minimum temperature occurring in February and the maximum in September. The annual range of the minimum and maximum temperature is higher in the western Sound (~0.7^o to 22.6 ^oC) than in the eastern part (1.0^o–20.5^oC). The depth-averaged temperature contains larger inter-annual variability in winter than in summer. The magnitude and the timing of the inter-annual variations of temperature in eastern LIS do not appear to be correlated with those in the western LIS. For example, negative anomalies from the summer of 1992 to early 1994 seen at station F3 are larger than at station M3, and strong negative anomalies at station M3 in the winter of 1996 are hardly noticeable at station F3.

Long-term changes in surface temperature in LIS differ markedly between winter and summer. While winter temperatures have been shown to increase, the change for summer has been almost negligible (Lee and Lwiza, 2008). Wilson et al. (2008) reported that the increase in thermal stratification in the western LIS during summer months (July and August) from ~0.5^o to 2 ^oC between 1946 and 2006 was mainly due to the decrease in bottom.

In this study, previously unpublished archived temperature data are aggregated with more accessible observations and statistically derived temperature correlates to more completely describe the long term trends and variability in coastal water temperatures so that significance of the more recent, and well documented, changes can be placed in a broader climate context.

Data Sources

Noank Marine Laboratory Milford Laboratory Millstone Nuclear Power Plant Riley Observations New York City DEP Woods Hole water temps NOAA COOPS Bridgeport & New Haven air temps	11/1967 - 9/1987 since 1945 since 1970 1952 - 1960 since 1909 ~1885 - 2004 1996 - 2016 1780 - 2015	a) An example of the Bristol temperature recorder data storage media. b) and c) are examples of the data logs from 1957. These record the location, time, temperature and salinity
Excerpt from the water table temperature log from the University of Connecticut's Laboratory in Noank, CT, created by Prof. S. Feng and Ms. L. Haddad.

Summary and Conclusions

We have assembled and quality checked a large and diverse array of observations of temperature in Long Island Sound. We have included the data from the both the eastern and western extremities of the estuary. Our analysis of the seasonal cycle at the Millstone Power Plant record showed that the rate of change of temperature was smallest in January-March and July to September, so we chose these times to examine longer term trends since they would be less prone to bias by irregular sampling.

Means  cycle of water temperature at Millstone Point is shown by the blue line. The red lines show the standard deviation of weekly averages over the 40 year record. The dashed lines identify the interval when the temperature is not significantly different from the mean.

Four records were assembled for the winter and five for the summer. An index of the summer and winter temperatures was created by computing the mean difference between contemporaneous segments of the observation records. Three empirical constants were used in the summer and four in the winter. The data were then bin averaged in three year intervals to create records that span 1930 to 2012 in the winter and 1915 to 2012 in the summer.

The aggregated data series, a LIS temperature index, showed that water temperatures in the interval 1960-2010 were anomalously cool in both the winter and the summer, whereas the winters between 1945 and 1955 were anomalously warm. Since 1965 temperatures in both the summer and the winter have been rising. The summer and winter of 2012 were both anomalously warm.

The summer a) and winter b) bin averaged LIS temperature index (black) series with the Woods Hole water (green) and Bridgeport air (blue) temperatures averaged in the same manner

 
The winter temperature index was then shown to be very highly correlated with the water temperatures series created at Woods Hole Harbor by Nixon et al. (2004), and the air temperature record assembled by Rohde et al, (2013) for a coastal station in Bridgeport, CT. The correlation with the Bridgeport record was also significant in the summer. Accepting the assumption that the correlation has not changed, the LIS temperature index can be extrapolated backwards in time to assess whether recent changes in temperature are unusual.

Same as above but with a longer time range. The red lines show linear regression results for the Bridgeport air temperature series.

References

Bumpus, D. F. (1957). Surface water temperatures along Atlantic and Gulf Coasts of the United States. Special Scientific Report Fisheries No. 214. U.S. Department of the Interior, Fish and Wildlife, Washington, D.C.

Camacho, J., S. A. Qadri, H. Wang and M. K. Worden (2006), Temperature acclimation alters cardiac performance in the lobster Homarus americanus. J Comp Physiol A. DOI 10.1007/s00359-006-0162-1

Gay, P. S., J. O’Donnell, and C. A. Edwards (2004), Exchange between Long Island Sound and adjacent waters, J. Geophys. Res., 109, C06017, doi:10.1029/2004JC002319.

Hansen, J., R. Ruedy, Mki. Sato, and R. Reynolds (1996) Global surface air temperature in 1995: Return to pre-Pinatubo level. Geophys. Res. Lett., 23, 1665-1668, doi:10.1029/96GL01040.

Hansen, J., R. Ruedy. M. Sato and K.Lo (2010). Global surface temperature change. Reviews of Geophysics. Rev. Geophys., 48, RG4004, doi:10.1029/2010RG000345.

Hao, Y. (2008)  Tidal and residual circulation in Long Island Sound. Ph.D. Dissertation, Marine Sciences Research Center, Stony Brook University, Stony Brook, NY, 70  pp.

Hare, J. A. and Able, K. W. (2007) Mechanistic links between climate and fisheries along the east coast of the United States: explaining population outbursts of Atlantic croaker (Micropogonias undulatus). Fisheries Oceanography, 16: 31–45. doi: 10.1111/j.1365-2419.2006.00407.x

Howell, P., J. Benway, C. Giannini, K. McKown, 2005. Long-term population trends in American lobster (Homarus americanus) and their relation to temperature in Long Island Sound. Journal of Shellfish Research 24(3):849-857. doi: 10.2983/0730-8000(2005)24[849:LPTIAL]2.0.CO;2

Howell, P. and P.J. Auster (2012) Regime shift in the finfish community of a Northwest Atlantic estuary associated with changes in thermal regime. Coastal and Marine Fisheries: Dynamics, Management, and Ecosystem Science 4:481-495

Kaputa NP and Olsen CB (2000) State of Connecticut Department of Environmental Protection, Long Island Sound Ambient Water Quality Monitoring Program: Summer Hypoxia Monitoring Survey '91-'98 Data Review. CTDEEP, Water Management Bureau, 79 Elm St, Hartford, CT 06106. 45 pp.

Keser, M., J. T. Swenarton, J. M. Vozarick, and J . F. Foertch. (2003). Decline in eelgrass (Zostera marina L.) in Long Island Sound near Millstone Point, Connecticut (USA) unrelated to thermal input. Journal of Sea Research 49:11-26.

Lee, Y.J., (2009). Mechanisms Controlling Variability in Long Island Sound. Ph.D. thesis, School of Marine and Atmospheric Sciences, Stony Brook University, New York.

Lee, Y.J. and K.M.M. Lwiza. (2008). Characteristics of bottom dissolved oxygen in Long Island Sound, New York, Estuar.Coast. Shelf Sci., 76:187-200. doi:10.1016/j.ecss.2007.07.001

McCardell, G.M. and J. O’Donnell (2009) A novel method for estimating vertical eddy diffusivities using diurnal signals with application to Western Long Island Sound. J. Mar. Systems. 77 (2009) 397–408

Nixon S.W., S. Granger, B. A. Buckley, M. Lamont, and B. Rowell (2004). A one hundred and seventeen year coastal water temperature record from Woods Hole, Massachusetts. Estuaries 27: 397–404.

O'Donnell, J., R. E. Wilson, K. Lwiza, M. Whitney, W. F. Bohlen, D. Codiga, T. Fake, D. Fribance, M. Bowman, and J. Varekamp (2014) The Physical Oceanography of Long Island Sound. In Long Island Sound: Prospects for the Urban Sea. Latimer, J.S., Tedesco, M., Swanson, R.L., Yarish, C., Stacey, P., Garza, C. (Eds.), ISBN-13: 978-1461461258

Riley, G. A. (1952), Hydrography of the Long Island and Block Island Sounds, Bull. Bingham Oceanogr. Collect., 13, article 3.

Riley, G. A. (1956) Oceanography of Long Island Sound: 1952-1954. II. Physical Oceanography Bulletin of the Bingham Oceanographic Collection, V.15, Peabody Museum of Natural History,  Yale University, New Haven, Connecticut, USA

Rohde, R., R. A. Muller, R. Jacobsen, S. Perlmutter, A. Rosenfeld, J. Wurtele, J. Curry, C. Wickham, and S. Mosher, (2013) Berkeley Earth Temperature Averaging Process. Geoinfor Geostat: An Overview 1:2. doi:10.4172/gigs.1000103

Stachowicz, J. J., J. R. Terwin, R. B. Whitlatch, R. W. Osman (2002) Linking climate change and biological invasions: Ocean warming facilitates nonindigenous species invasions. Proc. Natl. Acad. Sci. U.S.A. 99, 15497

Wilson, R. E., R. L. Swanson, and H. A. Crowley (2008), Perspectives on long-term variations in hypoxic conditions in western Long Island Sound, J. Geophys. Res., 113, C12011, doi:10.1029/2007JC004693.

Back to top