• Picture courtesy NASDA/NASA This is an image of global sea surface temperatures taken from Japan National Space Development Agencys (NASDA) AMSR-E instrument aboard NASAs Aqua spacecraft on August 27, 2003. The colors in this false-color map represent temperatures of the oceans surface waters, ranging from a low of -2 C (28 F) in the darkest green areas to a high of 35 C (95 F) in the brightest yellow-white regions. Sea ice is shown as white and land is dark gray.
Temperature • Thermo-haline surface circulation: Thermohaline circulation simply refers to global density-driven circulation (convection) of the oceans.
Oceanic currents• Trade winds cause circles near equator• Westerly winds carry polar water towards equator• Labrador current –very cold• Equator currents slosh towards east after continetal heating• Gulf currents –very warm
• The flow of cold, saline surface water (blue) downward and toward the equator can only be clearly recognized in the Atlantic. Warm surface water (red) flows in the opposite direction,
Factors affecting: Oceanic currents• Another key factor that influences ocean currents is the density of seawater. Both temperature and salinity contribute to seawater density, thus local changes in temperature and the magnitude of freshwater inputs from rivers and streams can alter near shore ocean currents.
Marine upwelling• Winds near the peninsula push warm water away from the surface allowing deep, cool, nutrient-rich water to rise, bringing nourishment to plankton, the basis of the oceanic food web. This process of upwelling is essential to the ocean oasis.• Remains of dead, decomposing organisms sink to the ocean bottom making these deep, cold waters rich in nutrients. However, it is in the upper, sunlit layers of the ocean that phytoplankton (very small drifting plants) are able to utilize these nutrients.
Temp. Tolerance• Eurythermic species• Stenothermic species• There are many different ecosystems within the ocean depending on conditions such as the water temperature, the amount of sunlight that filters through the water, and the amount of nutrients.• Sunlight breaks through the top layer of ocean water. It can make its way as deep as 200 meters (656 feet).• Almost all marine life (about 90%) lives within this top, sunlit layer of the ocean.• The temperature of ocean water varies depending on its location. Water near the polar regions is colder than water near the equator. Water that is deep in the ocean is colder than water that is near the ocean surface.• Many animals and other organisms can only survive at certain temperatures.• Others are able to survive at wide range of temperatures and can live in more places in the ocean.
Temperature tolerance and Migration• Because cold-blooded fish live within a small temperature range (stenothermic).• Many fish try to stay within what is called their thermal optimum — not too warm, not too cold — just right. This thermal optimum varies for different species.• Water temperature is a key factor for fly fishermen who chase striped bass and other game fish along the Atlantic seaboard.• In spring, as the ocean starts to warm, the first arrivals from the south will be striped bass and bluefish, followed later by bonito and little tunny (false albacore).• This pattern reverses itself as the water starts to cool in the fall, when the albies and bonito generally head south first. Looking in more detail at the stripers, their spring migration may be more closely tied to the northward migration of prey, such as herring, which in turn are probably influenced by warming water and spawning urges.
Antarctic creatures• About 200 species have been discovered. These include midges, mites and tardigrades.• Krill are found in huge swarms which cover hundreds of kilometers in the waters around Antarctica.• Many of the fish that live in Antarctica have antifreeze in their bodies to stop their body fluids from freezing. Seaweeds, sponges, corals, worms, sea anemones and sea spiders are just some of the creatures to be found on the bottom of the Antarctic oceans.
Global warming affecting (changes in) oceanic temperature• Courtesy NOAA Three-dimensional view of projected surface air temperature and ocean warming due to greenhouse gases as calculated by a low-resolution GFDL coupled ocean-atmosphere climate model.
LIGHT• The visible light spectrum is the section of the electromagnetic radiation spectrum that is visible to the human eye. It ranges in wavelength from approximately 400 nm to 700 nm and is also known as the optical spectrum of light. Electromagnetic spectrum
Fate of light in aquatic systems: • Reflection - prevented from entering water by air- water surface interface • Scattering - suspended particles reflect light at a massive array of angles • Absorption - diminution of light by transformation into heat energy
Visible light penetration • Visible light penetrates into the ocean, but once past the sea surface, light is rapidly weakened by scattering and absorption (coastal water). The more particles that are in the water, the more the light is scattered. This means that light travels farther in clear water (open ocean).
Light: Oceanic Zonation • 45% of red and 2% of blue light is absorbed for every meter of depth. • Euphotic zone (00 to 200 m) • Disphotic zone (200 to 1000 m) • Aphotic zone (1000 to 4000 m) • Abyssal zone more than 4000 m.
Photic zone animals • he dark backs and light undersides of • these near-surface fish help them match • their environment in the open ocean. To • a predator looking from above, their dark • backs seem to blend into the dark depths. • From the side, their lighter sides blend • with the sunlit water
Deep sea animals• Several organisms living in ocean depths have red coloration. Their red color effectively makes them “disappear” in the inky darkness, because no red wavelengths are present.• Many deep sea organisms are able to produce their own light, called bioluminescence. Some animals, like the viperfish, possess bioluminescent organs on their bellies. As they migrate upwards to find food in shallower depths, where some visible light does penetrate, the bioluminescent organs on their bellies brighten.
Many bristlemouth species, such as the "spark angle -mouth"above, are also bathypelagic ambush predators which canswallow prey larger than themselves.
Light: Vertical migration• Figure 1. Vertical distribution of the sardine (Sardina pilchardus) in the Thracian Sea. The dots show the observed average depths, and the solid line shows the predicted average depth of the distribution according to a cosine function model based on the time of day.
• Plankton at the sea surface is consumed by vertically migrating midwater fishes and squids. The daily migrations of these midwater species take them to the surface at night to feed, and to depths below 500 meters during the day. This helps them avoid predators by keeping them in constant darkness. However, these vertical migrators decend on the bottom during daytime (downward migrations), are available to bottom dweller wreckfish to consume them. This vertical migration completes a transfer of energy from sunlit surface layers to the dark depths where wreckfish dwell
• Marine zooplankton perform daily excursions (i.e., vertical migrations) up and down in the water column, with changing levels of light triggering these daily migrations. For example, the classic pattern consists of zooplankton residing deep in the water column during the day when light levels are high. They ascend at dusk to the surface waters where they graze on phytoplankton at night.
• Red flabby whale fish make nightly vertical migrations into the lower mesopelagic zone to feed on copepods.
Oxygen• Oxygen is a very important gas in the ocean because of its role in biological processes. Marine plants such as phytoplankton , seaweed, and other types of algae produce organic matter from carbon dioxide and nutrients through photosynthesis , the process that produces oxygen.• The upper 10 to 50 meters (33 to 164 feet) of the ocean can be highly supersaturated with oxygen owing to photosynthesis.
Factors governing DO• Atmospheric pressure, temperature and the rates of photosynthesis and decomposition.• Oxygen is produced during photosynthesis and consumed during respiration and decomposition (compensation depth). The latter processes occur throughout the day and night, while the former occurs only during the day. For this reason, dissolved oxygen levels are often lowest just before dawn before photosynthesis resumes.• Since the concentration of oxygen in our atmosphere is about 21%, and only a fraction of 1% in water, oxygen seeks equilibrium by dissolving into water. This diffusion is increased by any turbulent flow over riffles in the creek, or by wind-driven waves both of which increase the surface area through which the diffusion can occur.• The other major control of DO concentration is water temperature. Cold water can hold more dissolved gas than warm water.
Relationship betweentemperature and DO • Oxygen has limited solubility in water, usually ranging from 6 to 14 mg L -1 • Oxygen solubility varies inversely with salinity, water temperature and atmospheric and hydrostatic pressure.
DO at different depths • Surface is richest due to surface diffusion and photosynthesis • Minimal zone where respiration exceeds the photosynthesis • The deeper zone retains oxygen due to less respiration and decomposition rate
Oxygen regime at depths • Compensation depth is the balance between the photosynthesis of phytoplankters and the oxygen cosumed in respiration of all organisms and decomposition.
Diurnal pattern of DO • Diurnal pattern of DO in sea shallows control the vertical migration of zooplankters and fish
Salinity• Definition: Total amount of solid materials in grams dissolved in one kilogram of sea water when all the carbonate has been converted to oxide, the bromine and iodine replaced by chlorine and all organic matter completely oxidized.• It is calculated by Knudsen’s formula• It is referred by ppt (part per thousand or % )• Salinity is an ecological factor of considerable importance, influencing the types of organisms that live in a body of water.
• Marine waters are those of the ocean, another term for which is euhaline seas. The salinity of euhaline seas is 30 to 35. Brackish seas or waters have salinity in the range of 0.5 to 29 and metahaline seas from 36 to 40• On average, seawater in the worlds oceans has a salinity of about 35 ppt.• Although the vast majority of seawater has a salinity of between 31 ppt and 38 ppt, seawater is not uniformly saline throughout the world.• Climate, weather, currents and seasons can all have an affect on salinity.
Extremes of salinity• Where mixing occurs with fresh water runoff from river mouths or near melting glaciers, seawater can be substantially less saline.• The most saline open sea is the Red Sea (41 ppt), where high rates of evaporation, low precipitation and river inflow, and confined circulation result in unusually salty water.• The salinity in isolated bodies of water like, the Dead Sea ranges between 300 and 400 ppt.
Conveyor belt• The degree of salinity in oceans is a driver of the worlds ocean circulation, where density changes due to both salinity changes and temperature
Salinity tolerance• Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the molly (Poecilia sp.) which can live in fresh, brackish, or salt water. The European shore crab (Carcinus maenas) is an example of a euryhaline invertebrate that can live in salt and brackish water. Euryhaline organisms are commonly found in habitats such as estuaries and tide pools where the salinity changes regularly. However, some organisms are euryhaline because their life cycle involves migration between freshwater and marine environments, as is the case with salmon and eels.• The opposite of euryhaline organisms are stenohaline ones, which can only survive within a narrow range of salinities.
• Salinity tolerance leads to zonation in estuarine plants and animals. Estuarine organisms have different tolerances and responses to salinity changes.• Many bottom-dwelling animals, like oysters and crabs, can tolerate some change in salinity, but salinities outside an acceptable range will negatively affect their growth and reproduction, and ultimately, their survival.• Some groups of animals, such as the echinoderms, which include animals such as sea stars, brittle stars and sea cucumbers, have very few species living in estuaries because of their low tolerance of reduced salinity.
pH• pH is generally understood to be an expression of acidity or the hydrogen ion (H+) concentration in water. The value is a negative (reciprocal) logarithm, which means that acidity increases as the value decreases and that each unit change reflects a 10- fold change(logarithmic).
• Normal pH values in sea water are about 8.1 at the surface and decrease to about 7.7 in deep water.• Many shellfish and algae are more sensitive than fish to large changes in pH, so they need the sea’s relatively stable pH environment to survive.
• pH balance is one of the biggest factors in affecting marine life. The ocean absorbs vast amounts of carbon dioxide from the atmosphere, which reacts with the water and produces carbonic acid. This causes the waters natural pH balance to lower to an increased acidic level. This damages marine life because it destroys the essential calcium in the water that is needed to build their internal and external skeletons.
• Shallow waters in subtropical regions that hold considerable organic matter often vary from pH 9.5 in the daytime to pH 7.3 at night. Organisms living in these waters are able to tolerate these extremes
• As the carbon dioxide is absorbed, it reacts with the ocean water to form carbonic acid. This process is called ocean acidification. Over time, this acid causes the pH of the oceans to decrease, making ocean water more acidic.