The atmosphere has no political frontiers. The global accumulation of anthropogenic and natural emissions of gases, contaminants, aerosols and particulate matter changes the atmosphere, which has global repercussions on the oceans through warming, deposition and gas exchange. The impacts are many and interactive, affecting water properties, circulation, the health and spatial distribution of marine organisms, the productivity of exploitable resources, biodiversity and fluxes of matter and energy in the ecosystem. The disrupted oceans act in turn on the atmosphere (feedback) by increasing or decreasing the quantities of heat and greenhouse gases that it captures or releases. Québec-Ocean teams are studying the causes and ecological consequences of 4 ocean responses to global change.

1.1. See ice melt
The decline in the extent, thickness and seasonal persistence of sea ice in arctic and subarctic zones threatens organisms that depend on it, allows the invasion of species from the south, facilitates navigation and the exploitation of natural resources, and weakens the "mirror effect" that reflects into space a large part of incoming solar radiations. The newly absorbed radiation heats the water and increases the light available for photosynthesis, which underpins ecosystem productivity. By exposing water to the air, the loss of ice facilitates the action of the wind on the water column and intensifies ocean-atmosphere interactions and wave activity, which further fragments the ice. Meltwater from sea ice, glaciers and icebergs combines with river discharge, resulting in the freshening of surface waters and increasing vertical stratification. This stratification interferes with the physical processes that allow the upward supply of nutrients on which all life depends, as well as the formation of deep water that drives global ocean circulation and buffers the climate.

The team is making in-situ and remote sensing measurements, carrying out laboratory experiments and developing coupled numerical models to quantify, understand and predict ice loss and its consequences on ocean circulation, deep water formation, ocean-atmosphere exchanges of heat and greenhouse gases, carbon storage and the diversity, productivity and function of living resources.

1.2. Oceanic acidification
A major portion of anthropogenic CO2 does not accumulate in the atmosphere but is captured by the oceans, where it reacts with the water to form carbonic acid, which is a weak acid whose dissociation releases hydrogen protons (H+) and lowers the pH of the water. The H+ concentration in seawater has increased globally by 26%. The acidification is accentuated in cold waters, where the solubility of gases is higher, and beneath the productive oceanic zones, where the decomposition of organic matter releases deepwater CO2. Acidification is likely to harm organisms (e.g., corals) that depend on a relatively high pH for shell synthesis, to promote the production of microalgae whose CO2 concentration mechanisms are relatively ineffective and to have an effect on some stages of the nitrogen cycle.

The team is quantifying and documenting acidification in the Arctic Ocean and the St. Lawrence Estuary and Gulf, where the input of fresh water and upwelling of deep water contributes to acidification. The team is documenting acidification and studying its impacts on organisms, community structures, gases affecting climate and biogeochemical fluxes of carbon, nitrogen and sulfur.
  © Chloť Martias

1.3. Oxygen loss
The ocean is loosing oxygen (O2) and the spatial extent of O2-poor areas is increasing. Lack of O2 (hypoxia) or its absence (anoxia) has harmful effects on marine animals. It also impedes the action of aerobic bacteria, which decompose organic matter and recycle essential nutrients, and promotes the development of anaerobic bacteria, which can release harmful substances (e.g., H2S and N2O) and deprive offshore waters of fixed nitrogen. Oxygen loss can also be caused by eutrophication and increasing runoff of terrestrial organic matter in coastal environments, the metabolism of migrating animals, the decline in solubility related to warming, ice melting, and the weakening of vertical motions that ventilate the deep ocean.

The team is studying physical, chemical and biological phenomena that affect O2 concentrations at the regional and global scales, as well as the consequences of O2 loss on biodiversity and the ocean’s biogeochemical functions.
  © Denis Gilbert

1.4. Ocean-climate feedbacks
The ocean acts on the atmosphere in several ways that either accentuate or attenuate climate change. The oceans regulate climate by absorbing and redistributing large quantities of heat and CO2 through the surface and deepwater circulation. They already absorbed over one third of anthropogenic CO2 emissions and 93% of the related heat gain on the planetary scale. Vast quantities of methane (CH4), which is a greenhouse gas more potent than CO2, are frozen in shallow Arctic sediments now exposed to warming. The activity of marine organisms also modifies sea-air gas exchange and ocean storage  by consuming or producing gases that exacerbate (CO2, CH4, N2O) or temper (DMS) warming.

The team is studying and modeling the processes responsible for the consumption, production and air-sea exchange of greenhouse gases with respect to the structure and function of food webs, ocean circulation and the formation of deep waters, acidification and the availability of the nutrients iron and nitrogen.
  © Martin Fortier