Joe, the simple answer to your question is yes there will most definately be a significant thermocline in the summer. But a detailed answer gets significantly more complicated from there. The depth and temperature profile of the top surface layer is dependent on many variables which include wind, currents, temperature difference between air-water, sunlight etc... Below that is the seasonal thermocline which varies throughout the year.
I suspect there have been measurements taken on this for your area of interest, but the data and conditions are quite variable. I would browse the website at the URI Graduate School of Physical Oceanography to see if any of it is available. You could also stop into the library at GSO and ask the librarian to point you to it.
Ed
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