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Lecture 93

GGR202H5 Lecture 93: Chapter-12-ENV

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University of Toronto Mississauga
Nicole Laliberte

Chapter 12: Oceans o 70% of earths surface o mean depth – 3.8km (absolute darkness) o extremely poorly studied o NASA’s budget exceeds NOAA’s by 1,600X Ocean Water: not just H2O o 96.5% water o ions of dissolved salts; dissolved gases o oxygen (photosynthesis, bacterial metabolism, atmospheric diffusion) o major reservoir for CO2 o gases are vertically stratified Ocean water is Vertically Structured Vertical Variation in: o temperature (Thermocline – heat) o salinity (Halocline – salt) o density (Pycnocline) o cline = zone of rapid transition o Change in a spatial gradient o Gradual at first (surface) and then sharp change (deeper) o temperature declines with depth o surface water heated by solar energy; colder, saltier water is denser and sinks o surface = warmer; absorbs solar radiation (heat rises) o colder = saltier; denier (sinks) ▪ important in moving heat around the globe and drives nutrients o density increases with depth Temperature stratification varies with latitude Ocean layers: Water Surface: o warmed by sunlight and stirred by wind; water density ↓ ▪ friction of wind allows new water molecule to be exposed and release heat Deeper: o thermocline = temperature ↓ o halocline = salinity ↑ (generally) o pycnocline = density ↑ Deep Zone: o dense, cold, sluggish water o unaffected by winds, storms, sunlight Some ocean zones support more life than others: o Photic zone = top layer; supports primary productivity o algae; diatoms (few plants) o Pelagic zone = water, habitats, and ecosystems occurring between the ocean’s surface and floor o Benthic zone = habitats and ecosystems occurring on the ocean floor o Littoral zone = habitats and ecosystems occurring in coastal areas (intertidal zone – tide hits the sand) o Neritic zone = between littoral and continental shelf o intertidal organisms are adapted to being sometimes submerged and sometimes exposed Ocean Zones: Plankton = floaters – subject to ocean currents Nekton = swimmers Benthos = sitters – at bottom Deep Water Ecosystems: o No photon of light o Chemosynthetic bacteria o Common theme – fish have enormous mouths – chance of encountering a meal in low o Light Organs: symbiotic bacteria that produce artificial light o Live under extreme pressure ▪ When brought to surface bodies often explode The ocean floor has Mountain Ranges - Very dynamic = tectonic plate movements occur 2 The ocean interacts with the atmosphere in complex ways o Oceans: moderating influence on temperature o water has high specific heat (capacity for storing heat energy); takes a lot of energy to change water temp o oceans absorb heat in summer; release in winter o islands & coastal areas have moderate climates o e.g. Victoria BC vs. Winnipeg MB o Winnipeg = colder o Victoria = warmer = coastal area; not as cold in winter and not as warm in summer ▪ Closer to ocean Vertical and Horizontal Flows o Upwelling = upward flow of cold, deep water where winds blow away from, or parallel to, coastlines o Bring nutrients o Downwelling = oxygen-rich water sinks where surface currents come together Surface currents are driven by wind, through friction - Shape of currents is drive by wind and shape of ocean floor o e.g. Gulf Stream: warms the coast of Western Europe = comes up and moves northward Thermohaline circulation: deep circulation is driven by density differences La Nina: the upwelling of cold nutrient rich water at surface - feeds fishers El Nino: weather phenomenon that highlights the interaction between the ocean and atmosphere (drives climate on the globe) - failure of winds and the upwelling of cold nutrient rich water is not coming up - hot water sitting on top = marine organisms tend to die - few nutrients available Impacts on biota: El Niño event: o failure of fisheries (Peruvian anchovy fishery) o marine mammals & birds suffer o droughts in Australia Oceans are threatened: o loss of specific habitats o resource extraction o overfishing o pollution o climate change & acidification 3 Several important marine habitats are in trouble: o coral reefs o mangroves o salt marshes o estuaries 1. Coral Reefs o extremely bio diverse; shallow subtropical and tropical waters o ~25% of all marine species o economically important (tourism, ecosystem services, etc.) o corals = colonial organisms (related to sea anemones and jellyfish) = an animal o many secrete carbonate exoskeletons; form reefs o symbiotic algae called zooxanthallae (photosynthesize, provide food source for corals) In worldwide decline: o losses of at least 40% worldwide o many factors — especially climate change o nutrient pollution causes algal growth, smothers coral (
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