In the Mi’kmaw calendar, December is Chief Moon Time (Kesikewiku’s).
This year, the Chief Moon Time will begin with the new moon on December 7, peak with a full moon on December 22, and then wane until about January 5.
The weekend before Christmas will be a time to celebrate, kicking off with the shortest day of the year on Friday, December 21. This is the winter solstice which has been celebrated as the “turning of the year” since ancient times. The term “solstice” derives from the Latin word “solstitium, “meaning “sun standing still.”
During the winter solstice, the northern hemisphere is the longest distance away from the sun during the year. It will now start to become a bit closer to the sun every day, and every day, the number of daylight hours will increase a bit.
If you are a beach goer, you may be anticipating a high tide during that December full moon. Although the Bras d’Or estuary is connected to the Atlantic Ocean and does experience tides, those tides are not as closely linked to the lunar cycle as are the tides on the ocean coast. The tides in the Bras d’Or estuary are more controlled by barometric pressure changes than the usual daily gravitational pull of the moon.
The Bras d’Or estuary is an area of limited tidal movement with small tidal currents and tide height in all but a few locations. Similar to the neck of a bottle, the narrow and shallow sections of the Great and Little Bras d’Or Channels that connect the estuary to the open ocean, limit the volume of tidal exchange that can occur on each cycle.
Within two kilometres of the Sydney Bight, along the Great Bras d’Or Channel, the tidal range is already reduced by almost 50% per cent. Further into the estuary, the tidal range is smaller, at 15 centimetres near Baddeck, and almost imperceptible in other areas. Barometric tidal ranges are about 10 times larger than those associated with the lunar tides and occur over days to weeks while lunar tides are occurring over approximately 12 hours.
Because this barometric influence is related to weather fluctuations, water levels within the estuary are unpredictable. You can test this during your next Sunday drive by comparing the tidal state on the Atlantic or Northumberland coast with that in the Bras d’Or Lake.
You might have noticed that the waters of the Bras d’Or estuary are not quite as salty as the waters on the oceanic coast. So, what controls the salinity of the Bras d’Or waters? There is a net outward flow of fresh surface waters and a net inward flow of the bottom marine layer to the estuary. This type of water circulation is typical of most estuaries.
During the summer swimming season, you may be able to see that boundary. You will have noticed blurriness as you looked towards the bottom when you were swimming. That blurriness is caused as the light bends a bit when it hits the boundary between the surface fresh layer and the bottom salty layer.
The separation of outward surface freshwater flows and inward salty sub-surface flows is mixed up in some areas of the estuary. For example, the tidal jets at Barra Strait may be of crucial importance to the ecology of the estuary since the associated turbulence seems to be responsible for a very large proportion of the mixing of surface and deeper waters.
The turbulence draws deeper, salty water up into the surface, and that salt maintains the salinity of the surface layer. It may be that the flow through this Strait will prove to be the primary engine driving the Bras d’Or ecosystem.
Ie wish you all the best on this moonlight-drenched solstice during Kesikewiku’s and during the Christmas season.
Dr. Annamarie Hatcher is a consulting ecologist and a board member of the Bras d’Or Lake Biosphere Reserve Association. For more information about the Bras d’Or Lake Biosphere Reserve Association, please visit http://blbra.ca/.