Coastal and Marine Environment PDF

Coastal and Marine Environment Prof. P. Shanmugam Professor / National Geospatial Chair Professor Department of Ocean Engineering...

Coastal and Marine Environment Prof. P. Shanmugam Professor / National Geospatial Chair Professor Department of Ocean Engineering Indian Institute of Technology Madras Note: Materials used in this PPT are taken from the various literature, books and open resources and should only be used for learning purposes. View and characteristics of the World ocean  Oceanography Earth is misnamed. The ocean of water dominates its, and white in some places with clouds surface and ice, sometimes swirling with storms. The ocean affects and moderates temperature and dramatically influences weather. Its creatures provide at least 2% of humanity’s food. Nearly one-third of oil ad gas is pumped from beneath its floor. It borders most of the planet’s largest cities. It is primary shipping and transportation route and a major recreational resource It contains immense mineral and biological resources It supports for development and growth of organisms and life Representations of the Earth A geoid is the equipotential surface of the earth’s gravity field, which best fits the mean sea level in the world. Therefore it is a measured surface – not a mathematical surface like ellipsoid. Sea surface Ellipsoid Isaac Newton (1670) suggested the earth would be flattened at the poles, due to centrifugal force by the earth’s rotation. Earth surface Geoid Mean Sea Level is a surface of constant gravitational potential called the Geoid Geoidal surface Geoidal surface  Oceanography Sediment Erosion Deposition Water Depth Basin Geometry Water Depth Particle Production Mixing Salinity Salinity Nutrients Contaminants Weathering Light attenuation / Bottom Topography Precipitation/Dissolution Circulation pattern Mixed layer depth Importance of Oceanography Oceanography is the general name given to the scientific study of the oceans. It is historically divided in terms of the basic sciences into physical, biological, chemical, geological, optical and acoustical oceanography. Physical Oceanography Physical oceanography is the study of the physical properties of seawater, dynamics properties of water masses on all time and space scales, and the processes that control these properties. This involves a balance of theory, field observation, experiments, and modelling. Eco sounders measure the depth of water beneath a vessel by measuring the time a sound pulse takes to travel from the vessel to the seafloor and back. Since sound travels in seawater at about 1,500 ms-1, a sound pulse takes 2 seconds to return to the research vessel when the water depth is 1,500m. The sound pulses spread out over a narrow angle as they travel downward from the vessel. Thus, particularly where the depth is great, they are reflected off a large area of seafloor. Physical Oceanography Salinity and temperature in the coastal ocean. Changes in coastal salinity (top row) can be caused by the input of fresh water (a), by dry offshore winds causing a high rate of evaporation (b), or by both (c). Changes in coastal temperature (bottom row) depend on latitude. In high latitudes (d), the temperature of coastal water remains uniformly near freezing. In low latitudes (e), coastal water may become uniformly warm. In the mid latitudes, coastal surface water is significantly warmed during summer (f) and cooled during the winter (g) Geological Oceanography Geological Oceanography is the study of morphology, composition, evolution of the seafloor and its sediments with regard to physical and chemical conditions in the water column. Production, transport, and burial of sedimentary materials are common topics of study. Chemical Oceanography Chemical oceanography is the study of the origin and composition of seawater, relationships between chemical compounds, and how the chemistry of the ocean affects, or is affected by, biological, geological and physical factors. A typical submersible consists of a glass or plastic sphere inside a hull. The scientists descend within the sphere, which is provided with air and heat. Motors, articulated arms and many different designs of samplers are mounted outside the sphere. These are used to provide propulsion and collect samples. Biological Oceanography Biological Oceanography is the study of pelagic and benthic communities of the ocean, specifically, how the distribution, abundance and life history of organisms are affected by physical, chemical, and geological processes. Biological oceanographers must be knowledgeable of ocean physics, chemistry, geology, and atmospheric processes. Many different types of nets are used to sample pelagic and benthic organisms. Optical Oceanography Optical oceanography is concerned with the propagation and interaction of radiation in the water column, typically at wavelengths between approximately 350 and 750 nm Color observed from space representing various properties of the waters in Europe. Acoustical Oceanography Acoustical Oceanography also encourages a new generation of scientists, engineers, and entrepreneurs to apply the modern methods of acoustical physics to probe the unknown sea. Fundamentals of Acoustical Oceanography explains principles of underwater sound propagation, and describes how both actively probing sonars and passively listening hydrophones can reveal what the eye cannot see over vast ranges of the turbid ocean Ocean Engineering Ocean Engineering is the design and implementation of oceanic structures, instrumentation, and ships, as well as the application of physics, chemistry and mathematics to study the ocean and / or mitigate problems. Ocean Technology Ocean Technology is relevant to a wide range of multidisciplinary activities that broadly seek to develop, transfer, or apply instrumentation and technologies that will benefit research programs and implementation of marine Groins designed to stop beach erosion modify the longshore sand transport and projects. consequently, the beach. (a) sand accumulates on the upcurrent (longshore drift current) side of the groin and is eroded from the downcurrent side. (b) Often a line of groins are constructed along the length of a beach creating a saw-toothed beach shoreline Technologies for ocean observing Remote Sensing/Satellite Imagery: Geostationary Server - http://www.goes.noaa.gov Satellite significant events: http://www.osei.noaa.gov National Geophysical Data Center: http://www.ngdc.noaa.gov/ngdc.html Floating devices in the ocean: Argo Floats - http://www.argo.ucsd.edu Drifter Programs: http://www.aoml.noaa.gov/phod/graphics/pacifictraj.gif Remotely Operated Vehicles (ROVs) : Many discoveries… http://oceanexplorer.noaa.gov/technology/subs/rov/rov.html Automated Underwater Vehicles (AUVs) :  Physical and Chemical Properties of Sea Water Major components of Water Dissolved salts – 99% of all the salt ions in the sea are sodium (Na+), chlorine (Cl-), sulfate (SO4-2), Magnesium (Mg+2), calcium (Ca+2) and potassium (K+). – Sodium and chlorine alone comprise about 86% of the salt in the sea. – The major constituents of salinity display little variation over time and are a conservative property of sea water. Dissolved gases - nitrogen, oxygen, carbon dioxide (The surface layer is usually saturated in atmospheric gases because of direct exchange with the atmosphere) Organic and inorganic matter - dissolved organic materials, suspended particulate matter Major components of Water  Sources of salt and other components On average, concentration of dissolved salts, i.e., the salinity, in seawater is 3.5% or 35‰. The relative abundances of the ions listed above does not change, even though salinity does; are said to be conservative. Relative abundances of minor and trace constituents do vary Dissolved gases Three main ocean carbon pumps govern the regulation of atmospheric CO2 changes by the ocean (Helnze et al., 1991) Sources and sinks of gases Oxygen tends to be abundant in the surface layer and deep layer bottom, but lowest in the pycnocline. Surface layer is rich in oxygen because of photosynthesis and contact with the atmosphere. Oxygen minimum layer occurs at about 150 to 1500m below the surface and coincides with the pycnocline. Sinking food particles settle into this layer and become suspended in place because of the greater density of the water below. The food draws large numbers of organisms which respire, consuming oxygen. CO2 is important because it is needed by plants so they can photosynthesize. O2 is important because animals need it for respiration. Sources and sinks of gases The deep layer is rich in oxygen because its water is derived from the cold surface waters which sank (convect) to the bottom. Consumption is low because there are fewer organisms and less decay consuming oxygen. Anoxic waters contain no oxygen and are inhabited by anaerobic organisms (bacteria).  Carbon dioxide is of major importance in controlling acidity in the sea water. Major sources of carbon dioxide are respiration and decay. Major sinks are photosynthesis and construction of carbonate shells. Carbon dioxide controls the acidity of sea water. A solution is acid if it has excess H+ (hydrogen) ions and is a base if it has excess OH- (hydroxyl) ions. The pH Scale pH measures how acid or base water is. ̶ pH of 0 to 7 is acid. ̶ pH of 7 is neutral. ̶ pH of 7 to 14 is base. Phytoplankton Nutrients inorganic sources of N, P, S and other atoms required for phytoplankton growth. photosynthesis and respiration contributes in nutrient distribution. Especially important, because so much is needed, are N (nitrogen) and P (phosphorus). Si (silica) is also important for all the siliceous organisms: diatoms, radiolarians, and siliceous sponges. N is necessary to make proteins. P is necessary to make new cells (it's part of the cell wall), and also genetic material, DNA and RNA. Useful forms NO3- nitrate NO2- nitrite NH4+ ammonium PO43- phosphate Salinity Salinity is the total mass, expressed in grams, of all substances dissolved in one kilogram of sea water when all carbonate has been converted to oxide, all bromine and iodine has been replaced by chlorine and all organic compounds have been oxidized at a temperature of 480oC. Principle of constant proportion states that the absolute amount of salt in sea water varies, but the relative proportions of the ions is constant. Because of this principle, it is necessary to test for only one salt ion, usually chlorine, to determine the total amount of salt present. Salinity Chlorinity is the amount of halogens (chlorinity, bromine, iodine and fluorine) in the sea water and is expressed as grams/kilogram or %. Salinity is equal to 1.8065 times chlorinity. Salinometers determine salinity from the electrical conductivity produced by the dissolved salts. Salinity ppt = 1.80655 x Chlorinity in ppt If chlorinity is 19.2 ppt, what is the salinity of sea water? 34.6 ppt = 35 ppt Salt sources include weathering of rocks on land and the reaction of lava with sea water. Weathering mainly involves the chemical reaction between rock and acidic rainwater, produced by the interaction of carbon dioxide and rainwater forming carbonic acid. Salt sinks Salt sinks include the following: Evaporation removes only water molecules. ̶ Remaining water becomes increasingly saline, eventually producing a salty brine. ̶ If enough water evaporates, the brine becomes supersaturate and salt deposits begin to precipitate forming evaporite minerals. Wind-blown spray carries minute droplets of saltwater inland. Adsorption of ions onto clays and some authigenic minerals. Shell formation by organisms. Addition of salt modifies the properties of water Pure water freezes at 0oC. Adding salt increasingly lowers the freezing point because salt ions interfere with the formation of the hexagonal structure of ice. Density of water increases as salinity increases. Vapor pressure is the pressure exerted by the gaseous phase on the liquid phase of a material. It is proportional to the amount of material in the gaseous phase. Vapor pressure decreases as salinity increases because salt ions reduce the evaporation of water molecules. Salinity Annual mean of the sea surface salinity distribution (World Ocean Atlas, 2005) Salinity displays a latitudinal relationship related to precipitation and evaporation Highest ocean salinity is between 20-30o north and south or the equator. Low salinity at the equator and poleward of 30o results because evaporation decreases and precipitation increases. In some places surface water and deep water are separated by a halocline, a zone of rapid change in salinity. Water stratification (layering) within the ocean is more pronounced between 40oN and 40oS. Ocean surface temperature Ocean surface temperature strongly correlates with latitude because insolation, the amount of sunlight striking Earth’s surface, is directly related to latitude. Ocean isotherms, lines of equal temperature, generally trend east-west except where deflected by currents. Ocean currents carry warm water poleward on the western side of ocean basins and cooler water equatorward on the eastern side of the ocean. Insolation and ocean-surface water temperature vary with the season. Ocean temperature is highest in the tropics (25oC) and decreases poleward. Ocean temperature Tropical and subtropical oceans are permanently layered with warm, less dense surface water separated from the cold, dense deep water by a thermocline, a layer in which water temperature and density change rapidly. Temperate regions have a seasonal thermocline and polar regions have none. Annual mean of the sea surface temperature distribution (World Ocean Atlas, 2005) Sea surface temperature (regional level) Gulf stream Gulf stream The Gulf Stream is the fastest ocean current in the world with peak velocities near 2m/s. Temperature differences between the surface and 1000m depth in the oceans Density Density of sea water is a function of temperature, salinity and pressure. Density increases as temperature decreases and salinity increases as pressure increases. Pressure increases regularly with depth, but temperature and salinity are more variable. Higher salinity water can rest above lower salinity water if the higher salinity water is sufficiently warm and the lower salinity water sufficiently cold. Pycnocline is a layer within the water column where water density changes rapidly with depth. Density The water column in the ocean can be divided into the surface layer, pycnocline and deep layer. The surface layer is about 100m thick, comprises about 2% of the ocean volume and is the most variable part of the ocean because it is in contact with the atmosphere. The surface layer is less dense because of lower salinity or higher temperature. The pycnocline is transitional between the surface and deep layers and comprises 18% of the ocean basin. In the low latitudes, the pycnocline coincides with the thermocline, but in the mid-latitudes it is the halocline. The deep layer represents 80% of the ocean volume. Water in the deep layer originates at the surface in high latitudes where it cools, becomes dense, sinks (convects) to the sea floor and flows outward (advects) across the ocean basin. Salinity CTD (conductivity, temperature, pressure) for measuring Autosalinometer for CTD Profiler with Niskin conductivity in a running salinity analyses Bottles profile (on the fly) relative to standard seawater Sound in the Ocean Convenient means for transmitting information over great distances in the ocean Only signal that can be used for the remotely sensing of the ocean below a depth of a few tens of meters. Used to measure the properties of the sea floor, the depth of the ocean, temperature and currents. Whales and other ocean animals use sound to navigate, communicate over great distances, and find food. Sound Speed, C = f (T, S, p) C = 1449 + 4.6T - 0.055T2 + 1.4(S-35) + 0.017D (m/s) Here T is temperature (°C), S is salinity and D is depth in meters. Typical sound speed in ocean: C = 1450 to 1550 m/s. Typical sound speed in ocean: C = 1450 to 1550 m/s. Light Transmission Transparent in visible part of spectrum Absorbed as it goes deeper in the water column strongly absorbs infrared (heat) and ultraviolet (prevents damage to DNA) light energy at the oceanic surface is attenuated by absorption also converted to other forms of energy (e.g., heat energy) light intensity decreases with depth – Absorption and scattering by water molecules – Absorption and scattering by particulates suspended in the water transmittance spectrum also changes with water depth short wavelengths and long wavelengths are rapidly absorbed only blue-green (visible) wavelengths penetrate to any significant depth – only ~1% of surface light remains at depths of ~100 meters – no sunlight penetrates below ~1,000 meters Spatial gradients, depth and layers in the marine environment The ocean covers ~70% of the surface of Earth, and is intimately tied to the atmosphere and land. Light, Salinity, Nutrients, Temperature, Pressure Ocean layers Depending on how deep the sea is, there can be up to five vertical layers in the ocean. From the top down, they are: Epipelagic (sunlit) – This zone is also known as the surface zone – The illuminated surface zone where there is enough light for photosynthesis. – Due to this, plants and animals are largely concentrated in this zone. – Nearly all primary production in the ocean occurs here. – This layer is the domain of fish such as tuna, many sharks, dolphin fish, and jellyfish. Mesopelagic (twilight) – Although some light penetrates this deep, it is insufficient for photosynthesis. – At about 500 m the water becomes depleted of oxygen. – Still, an abundance of life copes with more efficient gills or minimal movement. Ocean layers Bathypelagic (dark) By this depth the ocean is almost entirely dark. There are no living plants, and most animals survive by consuming the snow of detritus falling from the zones above Squids & octopodes live at this depth Abyssopelagic No light whatsoever penetrates to this depth. Hadopelagic This zone is mostly unknown, and very few species are known to live here. However, many organisms live in hydrothermal vents in this and other zones. Some define the hadopelagic as waters below 6,000 m (19,685 ft).