|9 July 2021 photo of dead cockles from the intertidal off of Marrowstone Island|
By this point the intertidal ramifications of the late June Pacific Northwest heat wave have been well reported on, with some pretty dire accounts coming in from throughout the Salish Sea and Pacific coast region of Washington and British Columbia. I've been seeing the influence as I visit various shorelines, including dead cockles on Marrowstone Island (photo above), and the same off of the Dungeness River delta:
|7 July 2021 photo of more dead cockles, taken about here on the Dungeness River delta.|
Yesterday I also hunted around Kalaloch Beach on the coast of Washington and for the most part was impressed by how little mortality there seemed to be on the intertidal rocks, though some impacts were visible:
|11 July 2021, dead mussels still attached to the rock on the rocks in the lower intertidal at Kalaloch about here.|
|Measured water level along a west-to-east gradient - at La Push, Port Angeles, and Friday Harbor - on Monday June 28th 2021, illustrating the pace of propagation of the low tide from the coast into the Strait of Juan de Fuca.|
|Air temperature recorded at tide gauges in La Push, Port Angeles and Friday Harbor during the late June heat wave|
So I focused in on the three hottest days - Saturday the 27th, Sunday the 28th and Monday the 29th...and the air temperature recorded at three tide gauges are shown above. The first thing that pops out to me is that La Push was considerably cooler than Port Angeles and Friday Harbor, especially on Saturday and Sunday. Not a huge surprise. Generally temperatures were a bit warmer in Friday Harbor as compared to Port Angeles, though not by a lot. Interesting, on both Sunday and Monday Friday Harbor cooled an hour or so sooner than Port Angeles at the end of the day...something I tentatively attribute to shading of the stations as the sun drops (Friday Harbor's station would be blocked in the late afternoon by the mass of San Juan Island, whereas the Port Angeles tide gauge likely doesn't have that same later afternoon shading).
|Amount of time (in hours) that various intertidal elevations exceeded 25 degrees celsius between 27 and 29 June 2021 at three locations in coastal Washington|
Okay, but can we see an influence of tidal propagation in heating? Yes we do. In the bar plot above I averaged the number of hours over 25C experienced by the lowest parts of the intertidal (below MLLW) at each of the three location, and we see that west to east gradient. Again, that COULD just be due to it being a bit warmer in Friday Harbor than it was in Port Angeles and La Push, but the difference between Port Angeles and Friday Harbor is telling - the tide gauge in Port Angeles actually experienced more time above 25C (31.7 hours in Port Angeles over those three days, versus 30.7 hours in Friday Harbor)...but there were more hours at the Friday Harbor tide gauge that the lowest part of the intertidal (again below MLLW) experienced those elevated temperatures (4.8 hours in Friday Harbor versus 3.8 in Port Angeles). To pull that out a bit I've expressed it as a percentage of the total time exceeding 25C at those three locations (lower panel in the figure above)...and we still see that gradient...that is the tidal influence at work.