Reprinted with permission from Dr. Charles Flagg of the Stony Brook University School of Marine and Atmospheric Sciences.  Follow more of Dr. Flagg’s research on the Old Inlet Breach here


October 29, 2018
Recent Changes in the Fire Island Breach
Charles Flagg, Claudia Hinrichs Roger Flood and Robert Wilson
School of Marine and Atmospheric Sciences
Stony Brook University

We are closing out the summer season and the sixth year of the existence of the Fire Island breach so this is a good time to assess its current status and the latest changes. As you all know, we have been conducting more or less monthly aerial surveys of the breach, assisted by other folks at times, while collecting water property and water level data from around the Great South Bay. Of particular interest is the latest salinity data from Bellport which suggested a closer look at the conditions of the breach was in order. The Bellport salinity record shows suggests that we have been getting fewer high salinities events than in the past leading to the question of whether this was because of recent rain events or was the breach getting smaller and thus reducing the amount of exchange with the more saline ocean.

So first, let us look at the salinity record from Bellport for the past 21 months, ie. since January 2017, as shown in Figure 1. During the first five months or so in 2017 there were numerous times with salinities greater than 30 psu. (The ocean’s salinity south of Long Island is between 32 and 33 psu and psu stands for “practical salinity units” which is numerically nearly equivalent to parts per million by weight.) By the middle of 2017 these high salinity events became less frequency. Since January 2018 there has only been a couple of instances greater than 30 psu while the average salinities since March 2018 have been around 28 psu as compared to about 29 psu for the first half of 2017. The red line in the figure is least squares fit to the salinity record and it clearly indicates an overall decrease in salinity within Bellport Bay of about 1.5 psu since January 2017. The precipitation record from McArthur Airport for the rain fall rate this year is nearly identical to that of 2017 so lower salinities are not due to extra rain or fresh water runoff from shore.

You may also notice in Figure 1 that the water temperatures in Bellport Bay during the summer of 2018 appear to be a little warmer than during the previous year. Warming of the waters of the Bay is primarily due to incoming solar radiation and it has not been noticeably less cloudy this year than last. So this is an additional indication of reduced exchange with the ocean which tends to be colder than the Bay during the summer. The ice boaters might be encouraged by this as it means that the Bay will get less relatively warm waters from the ocean this coming winter.

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