Month: August 2023

Finally, our new starter was installed today, we lost no time and set off further along our route. The next port of call is the unofficial fishing capital of Quebec, the village Riviere-au-Renard.

The next day we did another CTD cast during high tide and the oxygen situation improved significantly – the oxygen saturation dropped to 85-95%, back to the level for the 7th August CTD cast. The Chlorophyll a concentration level also dropped to 7-14ug/L.
The change in the oxygen regime was reflected in the presence of a two-layer stratification with a thermocline at a depth of 1.5 m, apparently “fresh” water mass came with a flood and NW wind, pushing more water into the harbour from the Gulf of St.Lawrence. Yesterday we had SW wind, which blew from the land, preventing the renewal of water in the harbour.

I took advantage of a warm calm sunny evening in the Cloridorme Harbour to introduce our work-sea-horse – the CTD measuring system RBRconcerto , provided with a CTD cast demonstration. It was filmed with one shot (the sun was coming down!), so, I apologize for the imperfection of my acting skills, I will work on it:)

Here is a plot of oceanographic data from the performed CTD cast at high tide:

As it seen on the plot, the temperature distribution with depth is quite uniform (15-15.1) degC, with more significant practical salinity stratification (25.5-26.1) with a positive gradient, which determines the overall stable stratification of the seawater layers. The dissolved oxygen concentration is quite high (286-294)uMol/L, or (106-108)% on the DO saturation scale. Possibly, this is a result of increased autotrophic productivity of DO from phytoplankton and kelp during a sunny day. The transmissometer shows a very low attenuation coefficient (0.002-0.003)m-1, which indicates quite clear water (also seen by visual observations of the submersed CTD system). Measurements of concentration of Chla (16.5-19.5)ug/L showed almost twice the increase from the previous cast (9Aug), which indicates the increase of phytoplankton concentration (bloom). Also, the concentration of dissolved organic matter (fDOM) has been increased from 6.5ppb to 9ppb, which indicates more nutrients in the waters with increasing of dissolved organic carbon. These factors indicate that the harbour’s waters are at the stage of developing hyperoxia, which will be determined by the state of bloom of phytoplankton in warmer-than-usual waters. I will preform another CTD cast to monitor development of this event.