The Tides

Fundy Facts

1. The Bay of Fundy is 270 km long, straight sided and somewhat funnel shaped.

2. It is 80 km wide at its mouth. At its head it forms two basins, Chignecto Basin and Minas Basin. Alma and FreshAir Adventure are located on the Chignecto Basin. At this point, the basin is 15 km wide providing excellent views of the Nova Scotia coast line.

3. With every tide, 100 cubic kilometers of water enters or exits the Bay; equal to the daily discharge of all the world’s fresh water rivers.

4. The Bay of Fundy experiences two high tides a day. Because of the mutual gravitational attractions between the Earth and the Moon, a tidal bulge is created on the side of the Earth closest to the Moon as well as on the opposite side of the Earth.

As the Earth rotates on its axis, the Bay of Fundy enters one bulge and approximately twelve hours later the second one. 

moon tide

                     tide moon 2

 

 

5. Each day the tide comes in 50 minutes later than it did the day previous. As the Earth rotates on its axis causing our day and night, each point on Earth passes through the two tidal bulges. If the Moon were stationary, we would pass through the bulges at the same time each day. But the Moon slowly revolves around the Earth (once every month) causing its phases.

To catch up to the Moon’s new position, the Earth must rotate on its axis once and a bit more. This extra bit of rotation takes approximately 50 minutes causing the tide to come in 50 minutes later. This daily change in the arrival of tides can be seen from tide tables for Fundy National Park.

6. The tidal range varies over a month, from 13 m at one time and only 6 m at another. What causes this variation in the heights of tides? The two most important reasons are:

    • the changing positions of the moon in respect to the Sun. Spring tides occur twice a month when the Sun Moon and Earth are lined up – at new and full moon. Since the effects of their respective gravitational forces are working together, we get our highest tides. Neap tide occurs when the Moon is at quarter phase. Now the gravitational effects are not added together and the tidal range is less – perhaps only half as much.
    • the elliptical orbit of the Moon. On its closest approach to the Earth, (at perigee) tides are substantially higher.(As the distance between the Earth and Moon decreases, gravitational forces between them increase.) At apogee – when the moon is the greatest distance from the Earth – the tidal bulges are not as large and tides not as high. Therefore our highest tides occur at spring tide when the Moon is at perigee.

7. The discussion above explains the causes of tides the world over. So why are the Fundy tides so high – the highest in the world? The explanation involves two factors:

    • Seiche – The water in any enclosed basin rocks rhythmically back and forth from one end to the other. The period of this oscillation depends on the basin’s length and depth. This rocking movement (or seiche) for the Bay of Fundy coincides with the tides. Therefore as the seiche is driving water higher into the Bay, the lunar tide is reinforcing the effect – giving us the world’s highest tides.
    • Shape and bottom topography – A secondary factor is the shape and bottom topography of the Bay. As the Bay narrows and becomes shallower, the incoming water is “squeezed” and has no-where to go but up.

8. The tidal action results in the vertical mixing of the water. This creates high productivity because of the nutrients it spreads around, but also some cold water. Water temperatures in the Bay generally do not exceed 14 degrees Celsius (57 degrees Fahrenheit) – except in the upper Bay where mud-flats and exposed beaches heat up the incoming water.

9. The Bay of Fundy is one of the marine wonders of the world. Its salt marshes provide habitat to many animal species and contribute to the health of the Bay. They were dyked by the early Acadians who valued their rich soil. The mud flats of the Bay are the feeding station for tens of thousands of sandpipers and its waters, summer home to the right whale.

10. In 2007, New Brunswick’s upper Bay of Fundy stretching from the Tantramar Marshes to Saint Martins was recognized as an UNESCO Biosphere Reserve. This area includes Fundy National Park, Mary’s Point Shorebird Reserve, the Hopewell Rocks and the dramatic Fundy Trail Parkway – soon to stretch from Saint Martins to Fundy National Park.

Header 5 - Abandoned Kayaks at Lunchtime