As you arrive at the site, you should be able to see the plaques. Take time to identify the East Arm of Bonne Bay and the Tickle.
The East Arm is a deep saltwater inlet. It is considered a fjord. Glaciers carved the valleys deeper than the sea bed. When the glaciers retreated, sea water flooded the valleys and they became fjords. A fjord is a valley shaped by glaciers and flooded by sea water.
A tickle, as a Newfoundland term, could be described as any point between two rocks that you can get a boat thru or a short narrow strait. What's more important here is that there is a sill associated with it. The sill is a rise in depth which may have been caused by the terminal moraine of a previous glacier (there is some debate about this). In this case the sill does not block all the way up and does let some water thru. No such sill exist at the South Arm of Bonne Bay, making the East Arm different from the other.
Fresh water arrives to the East Arm from rivers and floats on salt water that is denser. The freshwater mixes with the seawater from the gulf of St Lawrence because of wind and currents. However, this only occurs in the first 40 meters.
The result is that the sill prevents the water from the fjord and the water from the Gulf of St-Lawrence to mix completely. Only the top layers mix and the bottom layers of the deep fjord remain cold.
Question one: What is the approximate depth of the East Arm of Bonne Bay?
The above description of the mixing is not exactly correct since, in the winter, when ice forms, salt becomes concentrated in the water below the ice, that water is then denser and mixes with the water to the depths of the bay.
All this results in layered water depths where different species exist. Including some species that would not be expected at the bottom layer.
Question 2: Can you name the bottom layer and it's temperature. Would you expect this without the sill?
Entirely optional, but you can take a picture looking at the sill.
Sources:
- Panel information
- Wikipedia, www.wikipedia.org. Terms: sill (geology), terminal moraine, tickle, pages visited 17 August 2014.
-Parcs Canada, Gros Morne National Park, Water Wonders, http://www.pc.gc.ca/eng/pn-np/nl/grosmorne/natcul/natcul6.aspx Page visited 17 August 2014