lawrence estuary
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2021 ◽  
Author(s):  
Elie Dumas-Lefebvre ◽  
Dany Dumont

Abstract. We provide the first in situ observations of floe size distributions (FSD) resulting from wave-induced sea ice break-up. In order to obtain such data, an unmanned aerial vehicle was deployed from the Canadian Coast Guard Ship Amundsen as it sailed in the vicinity of large ice floes in Baffin Bay and in the St. Lawrence Estuary, Canada. When represented as probability density functions weighted by the surface of ice floes, the FSDs exhibit a strong modal shape which confirms the preferential size hypothesis debated in the scientific community. Both FSDs are compared to a flexural rigidity length scale, which depends on ice properties, and with the wavelength scale. This comparison tends to show that the maximal distance between cracks is preferentially dictated by sea ice thickness and elasticity rather than by the wavelength. Temporal analysis of one fracture event is also done. Results show that the break-up advances almost as fast as the wave energy and that waves responsible for the break-up propagate following the mass loading dispersion relation. Moreover, our experiments show that thicker ice can attenuate wave less than thinner ice. This method thus provides key information on the wave-induced FSD, clarifies theoretical aspects from the construction of the FSD to its implementation in models and brings new knowledge regarding the temporal evolution of sea ice break-up.


2021 ◽  
Vol 173 ◽  
pp. 113096
Author(s):  
Rob Williams ◽  
Robert C. Lacy ◽  
Erin Ashe ◽  
Ailsa Hall ◽  
Stéphane Plourde ◽  
...  

Ocean Science ◽  
2021 ◽  
Vol 17 (5) ◽  
pp. 1509-1525
Author(s):  
Cynthia Evelyn Bluteau ◽  
Peter S. Galbraith ◽  
Daniel Bourgault ◽  
Vincent Villeneuve ◽  
Jean-Éric Tremblay

Abstract. The St. Lawrence Estuary connects the Great Lakes with the Atlantic Ocean. The accepted view, based on summer conditions, is that the estuary's surface layer receives its nutrient supply from vertical mixing processes. This mixing is caused by the estuarine circulation and tides interacting with the topography at the head of the Laurentian Channel. During winter when ice forms, historical process-based studies have been limited in scope. Winter monitoring has been typically confined to vertical profiles of salinity and temperature as well as near-surface water samples collected from a helicopter for nutrient analysis. In 2018, however, the Canadian Coast Guard approved a science team to sample in tandem with its ice-breaking and ship escorting operations. This opportunistic sampling provided the first winter turbulence observations, which covered the largest spatial extent ever measured during any season within the St. Lawrence Estuary and the Gulf of St. Lawrence. The nitrate enrichment from tidal mixing resulted in an upward nitrate flux of about 30 nmol m−2 s−1, comparable to summer values obtained at the same tidal phase. Further downstream, deep nutrient-rich water from the gulf was mixed into the subsurface nutrient-poor layer at a rate more than an order of magnitude smaller than at the head. These fluxes were compared to the nutrient load of the upstream St. Lawrence River. Contrary to previous assumptions, fluvial nitrate inputs are the most significant source of nitrate in the estuary. Nitrate loads from vertical mixing processes would only exceed those from fluvial sources at the end of summer when fluvial inputs reach their annual minimum.


2021 ◽  
Vol 8 ◽  
Author(s):  
Diane Lavoie ◽  
Nicolas Lambert ◽  
Michel Starr ◽  
Joël Chassé ◽  
Olivier Riche ◽  
...  

The goal of this paper is to give a detailed description of the coupled physical-biogeochemical model of the Gulf of St. Lawrence that includes dissolved oxygen and carbonate system components, as well as a detailed analysis of the riverine contribution for different nitrogen and carbonate system components. A particular attention was paid to the representation of the microbial loop in order to maintain the appropriate level of the different biogeochemical components within the system over long term simulations. The skill of the model is demonstrated using in situ data, satellite data and estimated fluxes from different studies based on observational data. The model reproduces the main features of the system such as the phytoplankton bloom, hypoxic areas, pH and calcium carbonate saturation states. The model also reproduces well the estimated transport of nitrate from one region to the other. We revisited previous estimates of the riverine nutrient contribution to surface nitrate in the Lower St. Lawrence Estuary using the model. We also explain the mechanisms that lead to high ammonium concentrations, low dissolved oxygen, and undersaturated calcium carbonate conditions on the Magdalen Shallows.


2021 ◽  
Vol 40 ◽  
Author(s):  
Véronique Lesage

Until 2012, the St. Lawrence Estuary beluga population was considered stable with about 1100 individuals. An abnormally high number of calves reported dead that year triggered a population status reassessment. This review article summarizes the findings from this reassessment and various studies subsequent to it and provides an updated analysis of carcass recovery rates up to 2019. The 2013 review indicated a decreased incidence of cancer in adults, suggesting positive impacts from the regulation of toxic substances (e.g., PCBs and PAHs). However, the review also revealed that the population initiated a decline of ca. 1% per year in the early 2000s and had reached a size of ca. 900 individuals by 2012. This decline was accompanied by high inter-annual variability in calf survival and pregnancy rates and by more frequent peripartum complications among dead females. The change in population dynamics coincided with a shift in the St. Lawrence ecosystem structure and warmer environmental conditions, suggesting a link through effects on reproductive success and adult female body condition. This was supported by the continued high calf mortality after 2012 and a documented decline of fat reserves in beluga blubber from 1998 to 2016. Other factors, such as the exposure to chronic vessel noise, increasing whale-watching activities, high contaminant levels and episodic harmful algal blooms, may also be contributing to the long-term non-recovery and current decline of the population. The strong natal philopatry and complex social system of the beluga likely increase its vulnerability to extinction risk by limiting dispersal.


2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Cabrol Jory ◽  
Véronique Lesage ◽  
Alexandra Leclerc ◽  
Janie Giard ◽  
Sara Iverson ◽  
...  

AbstractThis study sought to estimate the effect of an anthropogenic and climate-driven change in prey availability on the degree of individual and population specialization of a large marine predator, the fin whale (Balaenoptera physalus). We examined skin biopsies from 99 fin whales sampled in the St. Lawrence Estuary (Canada) over a nine year period (1998–2006) during which environmental change was documented. We analyzed stable isotope ratios in skin and fatty acid signatures in blubber samples of whales, as well as in seven potential prey species, and diet was quantitatively assessed using Bayesian isotopic models. An abrupt change in fin whale dietary niche coincided with a decrease in biomass of their predominant prey, Arctic krill (Thysanoessa spp.). This dietary niche widening toward generalist diets occurred in nearly 60% of sampled individuals. The fin whale population, typically composed of specialists of either krill or lipid-rich pelagic fishes, shifted toward one composed either of krill specialists or true generalists feeding on various zooplankton and fish prey. This change likely reduced intraspecific competition. In the context of the current “Atlantification” of northern water masses, our findings emphasize the importance of considering individual-specific foraging tactics and not only population or group average responses when assessing population resilience or when implementing conservation measures.


2021 ◽  
Vol 40 ◽  
Author(s):  
Valeria Vergara ◽  
Jason Wood ◽  
Véronique Lesage ◽  
Audra Ames ◽  
Marie-Ana Mikus ◽  
...  

Noise and anthropogenic disturbances from vessel traffic are an important threat to the recovery of the endangered St. Lawrence Estuary (SLE) beluga population. The consequences of acoustic masking could be particularly adverse in the case of critical vocalizations that maintain contact between mothers and their dependent but mobile calves. This study models the communication range of adults, sub-adults and newborn beluga contact calls in the presence and absence of vessels in an important summering area for this population. Ambient noise measurements, a composite beluga audiogram and apparent source levels of adult/sub-adult and newborn calls, informed the model. Apparent source levels were estimated from received levels of contact calls produced by four individuals carrying digital acoustic tags in the SLE, Canada, and from received levels of calls recorded from two adults and a newborn calf at an aquarium, at known distances from a calibrated hydrophone. The median communication ranges were over 18 times larger for SLE adult and sub-adult calls than for newborn calls, with a 57 and 53% reduction in range in the presence of vessel noise, respectively. For newborn calls, this results in a median range of 170 m in vessel noise. These first estimates of the communication range of beluga vocalizations with a known function suggest that masking of the quiet calls of newborns by anthropogenic noise could impair mother–calf contact.


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