Chief moon and win­ter sol­stice

In the Bras d'or Lake Bio­sphere Re­serve

The Victoria Standard - - Environment - ANNAMARIE HATCHER

In the Mi’kmaw cal­en­dar, De­cem­ber is Chief Moon Time (Ke­sikewiku’s). This year, the Chief moon time be­gan with the new moon on Dec. 7, will peak with a full moon on Dec. 22, and then wane un­til about Jan. 5. The week­end be­fore Christ­mas will be a time to cel­e­brate, kick­ing off with the short­est day of the year on Fri­day, Dec. 21. This is the win­ter sol­stice that 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 2 km of the Syd­ney Bight along the Great Bras d’or Chan­nel, the tidal range is al­ready re­duced by al­most 50%. Fur­ther into the es­tu­ary, the tidal range is smaller, at 15 cm 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 twelve 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 tidal state on the At­lantic or Northum­ber­land coast with that in the Bras d’or.

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 Lakes. For ex­am­ple, the tidal jets at Barra Strait may be of cru­cial im­por­tance to the ecol­ogy of the Lakes 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!

We wish you all the best on this moon­light-drenched sol­stice dur­ing Ke­sikewiku’s and dur­ing the Christ­mas sea­son. Re­mem­ber, pe­jipuk (win­ter is com­ing) to the Bio­sphere.

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/.

Photo by Bruce Hatcher.

Sun­set on the beach in Iona, Barra Strait.

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