New Tide and Estuary Exhibits at Alaska Island and Ocean Visitor Center in Homer
| Marilyn Sigman, Alaska SeaGrant/MAP
Tags: Communicating Science, Ocean and Climate Literacy
The Kachemak Bay National Research Reserve and Alaska Maritime National Wildlife Refuge collaborated on new permanent exhibits to illustrate Kachemak Bay's extreme tidal range and show how the tides influence a key ecosystem where the rivers and streams meet the bay. The tidal exhibit includes films that show tides in action, including a time lapse film of various locations in the Bay.
An article in the August 4 Homer News by Michael Armstrong reported on the new exhibits and corrected several misconceptions that many people hold about the extreme tidal range of the Bay upper Cook Inlet which is even more extreme. Turnagin Arm, with a mean range of 30.3 feet actually ranks fourth in the world behind the Bay of Fundy in Nova Scotia (38.4 feet), the Ungava Peninsula in Quebec (32 feet), and Bristol, England (31.5 feet). The difference between Kachemak's Bay highest recorded high tide of 26.09 feet in 1966 and its lowest tide of -6.47 feet in 2002 adds up to a whopping 32.56 feet. The mean tidal range calculation, however, averages the mean range between tides by taking all the high tides for a 13-year period and averaging them, taking all the low tides for that period and averaging them, and then calculating the difference. Looked at this way, the tidal range in Kachemak Bay is a mere 15.83 feet, not even in the top 10.
Kris Holderied, NOAA Director of the Kasitsna Bay Lab in Kachemak Bay, and Catie Bursch, marine educator with the Reserve, dispelled another myth - that distance from the equator has anything to do with extreme tides. Tides don't become more extreme closer to the Poles. Numerous factors affect tides. Distance does matter - but for the distance from neutral points in the ocean called amphidromic points where a place doesn't have a tide. The biggest effect on tides - and what causes them - is gravity.
"It basically really is all about gravity." Holderied said. "It's a tricky thing to understand. The tides are a great integrated measure of the gravitational effect of different cycles.
The Reserve held two Discovery Labs in early August to help people better understand the tides. Homer's Pratt Museum invited artists to attend the Labs to kick off a science-art collaboration that will culminate in a Driven by the Tides art exhibit in November and December.