Geological, Physical & Biological Structure PDF

Geological, Physical & Biological Structure Subduction: when an ocean floor passes below another. 4km is the average depth of the ocean Coriolis effect: states that any object not attached to the Earth, when the...

Geological, Physical & Biological Structure Subduction: when an ocean floor passes below another. 4km is the average depth of the ocean Coriolis effect: states that any object not attached to the Earth, when the wind blows, will deviate to the right of the movement in the North hemisphere and to the left in the South hemisphere. Gulf Stream: a current that starts in the Gulf of Mexico, towards the British islands and Northwestern Europe. The warm water also brings a warm atmosphere. Warm water occupies a larger volume than cold water, one of the reasons the ocean rises as it heats The oceanic currents are created by the cold water in the surface water in the North and South poles continuously cooling and sinking, pushing down and creating this movement The Pacific Ocean is half of the ocean’s surface, all continents could fit in it and there would be additional room. The average depth is 4,000m and the deepest area is 11,000m (Marianas Trench or Challenger deep) The Atlantic Ocean is the second largest, covering about ¼ of the ocean surface and its average depth is also around 4,000m. The Indian Ocean is third in terms of size, covering ⅕ of the ocean with an average depth of 4,000m. It has an equatorial area, and two tropical areas but only one polar area. At some point in the year, a massive current brings warm water towards south-east Asia and this heat creates a lot of evaporation and rain bringing monsoons. This creates very dry and very wet seasons, impacting the development of the area. The Arctic Ocean surrounding the North Pole is the smallest and shallowest ocean only covering 3.5% of the ocean with an average depth of 1,000m. It is the least resilient ocean and is always cold and has constant upwelling. The Southern Ocean is composed of the southernmost waters of the World Ocean with an average depth of 1,000m. It encircles Antarctica and with no Geological, Physical & Biological Structure 1  physical boundaries around it, it continues circling around Antarctica making the ocean currents very important. The currents are called the circumpolar. 1-5% of the ocean is protected but with no management plans From 1950 to the beginning of the 90s we were able to adjust fish catch to demand. From the end of the 80s we’ve had to put more effort at sea with wild fisheries capture plateauing even with an increase of fishing efforts. Currently, approximately half of the fish we eat comes from aquaculture. There has been a 1° rise in sea surface temperature since pre-industrial times, most of it occurring in the last decades. We are expecting a +2° to 6° rise by the end of the century. The consequences have been observed since the end of the 90s. Most CO2 released into the atmosphere goes into plants and the ocean. This disbalancing equilibrium with CO2 going into the ocean causes ocean acidification. The more proportion of H+, or pH, placed into the water makes the ocean more acidic. There has been a -0.1 decrease in pH since preindustrial times, impacting all calcifying organisms and the food source for fish. Marine pollution is often a local source of issues. Eutrophication is when too many nutrients are released in the water, imbalances the equilibrium with plants overgrowing and dying before they are able to be eaten by fish, decaying and using all the oxygen leading to anoxia. Marine invasive species can be encouraged by climate change; rising climate makes the habitat welcoming for species that could previously not survive. It changes the potential area of distribution of a species. They are helped by cargo ships by being carried in the ballast water. Larvae from algae to fish are carried from one side of the world to the other. In their local environments, they are kept “under control” by predators, viruses and temperature but they have no predators and prey on local species. Geological, Physical and Biological Structure - Main patterns in the Ocean There is more biomass on the surface, but not biodiversity. About 1% of food from the surface reaches the depth. There is also light, therefore more productivity, and more oxygen on the surface. Two main division of the ocean: Geological, Physical & Biological Structure 2  1. Pelagos: the pelagic environment, the ocean water itself a. Light gradient - light is very quickly absorbed by water particles. From high light in the surface to total absence in the depths i. Euphotic layer - from surface to a depth where enough light still exists to support photosynthesis, rarely deeper than 100m ii. Disphotic layer - small but measurable amount of light that does not support photosynthesis. iii. Aphotic layer - below 1000m, total absence of light b. Nutrient gradient - Nutrients are chemicals, not living things, and are primary producers. Primary producers need light, so nutrients are more consumed in the euphotic layer, causing there to be more nutrients in the depths but not because there is more production in the depths. Phytoplankton uses more nutrients in the surface so nutrients are more abundant in the depths. 2. Benthos: the benthic environment, the ocean bottom a. The Continental shelf - part of the continent that is currently submerged, less than to 100m (the average depth for plants to survive) b. The abyss - the ocean bottom itself, generally around 4000m Density increases with salinity and decreasing temperature. In one liter of cold water there are more water molecules than in 1 liter of warm water, making it heavier and with higher density. The ocean is layered according to density. It is warmer in surface and colder in depths, with a thermocline in the middle (abrupt change of temperature). The thermocline is deep around the equator as the water on the surface is always warm. Upwelling is wind pushing the surface water away from the coast and deep, cold, nutrient-rich water is brought to the surface Global primary production Geological, Physical & Biological Structure 3  The yellow and red areas are the most nutrient rich. The med sea is oligotrophic, meaning it has low levels of nutrients. Meso-scale - flow with a medium length Eddy is a small whirlpool that turns around itself, it is the swirling of a fluid and the reverse current created. In this case, it moves warm water towards Europe. Eddies are also seen through satellite images. Because of the movement of the Earth and the lag between the wind blowing on the surface and the movement of the water in use by this wind, the water on the immediate surface will not move following the wind but will be deviated to the right by 45° compared to the wind. If the wind blows from the South to the North, the surface of the sea will move in the same direction but deviated to the right by 45°. This is known as the Ekman Spiral. Each time fluid creates a drag, Geological, Physical & Biological Structure 4  and with the additional time lag, each layer of density will be deviated. Eventually, you will reach a 180° difference compared to the wind and at a given depth there will be a current going into the opposite direction of the wind. Ekman spiral describes the speed and direction of seawater flow at different depths. Each successive layer moves increasingly to the right in the Northern Hemisphere. On average, the movement of water moved under the influence of the wind will be 90° to the right in the North Hemisphere and to the left in the South Hemisphere. Nutrients are brought over with the current, come up to the surface because of the continental shelf, and bloom once they reach the surface. Micro scale patterns When a water mass has a different density because of the temperature or salinity, these two water masses will not mix. Brackish water is when the salinity is between fresh and salty. They are full of nutrients but algae will not develop in the middle but towards the edge. Island Mass effect Nutrients coming from the depth hit against the island bottom, go upwards and follow the current causing nutrients to reach the surface. Chemicals in volcanoes also produce more nutrients. Langmuir Frontal zones Water is displaced by the wind to the right, it accumulates so it goes down and pulls water down from the left with it. It creates a surface convergence of i.e. algae, zooplankton, pollution etc. This only happens when wind is blowing strongly, constantly and homogeneously for hours. It is a local pattern, not something that can be seen Geological, Physical & Biological Structure 5  over an ocean Net Primary Productivity helps us understand the sustainability of fishing. Whatever g of carbon per m2 produced on the surface per year is spread for the ocean column. Geological, Physical & Biological Structure 6  The patterns of zoogeography are the same as the primary production patterns. Close to the shore where there are upwellings Food webs - not chain 1. Autotrophs - they produce their own food through light or chemicals i.e. seagrass, phytoplankton, symbiotic algae in coral a. Mixotrophs - can produce their own food but will feed on other nutrients if light is not available 2. Primary consumers - feed on plants to get their energy 3. Secondary consumers - feed on animals to get their energy 4. Top/ Apex predators - secondary consumers with no predators First: Taxonomy catch-up! Classification according to feeding behaviour Geological, Physical & Biological Structure 7  Autotrophs Able to use the sunlight to get energy = photosynthesis Use nutrients to create organic molecules with the energy of the Sun contains the primary producers (phytoplankton...) Heterotrophs Need to consume organic matter from other living (predators) or dead organisms (decomposers) Do they know how to swim? Nekton Active swimmers. Include fish, reptiles and marine mammals Plankton organism drifting with currents. Can swim but weaky and often only vertically. Cannot determine their horizontal displacement Do they use light? Phytoplankton Autotrophic plankton producing its own food by photosynthesis Zooplankton Heterotrophic plankton that eats food produces by other organisms Are they always part of plankton? Meroplankton Only spend only part of their life cycle as plankton. Larval and/or juvenile stage in the plankton, and the rest as nekton or benthos. Example: urchins, jellyfish… Phytoplankton Diatoms - unicellular organisms Dinoflagellates - single celled phytoplankton, use bioluminescence triggered by movement to dissipate energy Coccolithophores - single celled phytoplankton Geological, Physical & Biological Structure 8 Geological, Physical & Biological Structure 9