What is Seawater: Definition and 33 Discussions

Seawater, or salt water, is water from a sea or ocean. On average, seawater in the world's oceans has a salinity of about 3.5% (35 g/l, 35 ppt, 600 mM). This means that every kilogram (roughly one liter by volume) of seawater has approximately 35 grams (1.2 oz) of dissolved salts (predominantly sodium (Na+) and chloride (Cl−) ions). Average density at the surface is 1.025 kg/l. Seawater is denser than both fresh water and pure water (density 1.0 kg/l at 4 °C (39 °F)) because the dissolved salts increase the mass by a larger proportion than the volume. The freezing point of seawater decreases as salt concentration increases. At typical salinity, it freezes at about −2 °C (28 °F). The coldest seawater still in the liquid state ever recorded was found in 2010, in a stream under an Antarctic glacier: the measured temperature was −2.6 °C (27.3 °F). Seawater pH is typically limited to a range between 7.5 and 8.4. However, there is no universally accepted reference pH-scale for seawater and the difference between measurements based on different reference scales may be up to 0.14 units.

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  1. xphrnzrjh

    Refractive index of seawater and a diver transmitting RF for 100 meters

    I thought I maybe need to find a way to calculate the refractive index (n) and using that calculating the velocity and then the time but I haven't managed to figure out how to get the refractive index? Would love your help.
  2. D

    Source of chloride in seawater

    Most of the salt in seawater is sodium chloride. From my understanding, the primary source of sodium is the errosion of magmatic rocks, which contain lots of feldspars, the most abundant mineral in Earth crust. On the other hand, I don't know any abundant magmatic mineral which contains...
  3. T

    Seawater sample temperature control – heat exchanger design

    I’m designing a system where a sea water sample must have its temperature controlled between near its freezing point (-2°C) and +30°C to simulate sea temperatures. To control it, the sample will be in contact with a block, which will be controlled by an external circulating water bath. The image...
  4. P

    When will mining seawater for elements be affordable?

    So, I was wondering when will mining seawater for minerals be affordable. The whole process seems very energy intensive to do. Will it ever be a reality one day where we see tritium and deuterium mined alongside lithium and other important elements? I've read somewhere that there are enough...
  5. T

    What could be causing unexpected voltage results in a seawater battery system?

    We created a 5x5 seawater battery system to test voltages across multiple pHs and concentrations of NaCl. Concentration ranges go from 0g/L to 32g/L (near saturation) and the pHs range from 3 to 11. We used copper and magnesium electrodes to test the voltages in each cell and got some results we...
  6. ReneVeerman

    Freshwater (industrial scale) from seawater, on sunlight

    i have this idea to produce fresh water for farming and all the other uses of fresh water, from seawater, on sunlight, using mostly/only off-the-shelf parts.. i am currently not able to pursue this idea myself due to financial constraints, so i thought i'd float the idea here looking for some...
  7. D

    Help Calculating Pressure of Seawater against a flat surface

    Hi, I'm trying to figure out the pressure that seawater would exert against a vertical surface (on average) over a large area but I am messing up somewhere. The height of the rectangle is 560 ft and the length is 20 miles, or 105,600 ft, giving an area of 2.12 mi². The weight of the water in...
  8. H Smith 94

    Electrical conductivity of seawater depends on salinity how?

    Hi! I am currently trying to determine how the salinity ##S## of a sample of seawater (or, objectively, a salt-water solution) changes its electrical conductivity ##\sigma##. It is clear that they are proportional since the mobility of the ##\text{Na}^{+}## and ##\text{Cl}^{-}## ions plays a...
  9. H Smith 94

    Understanding propagation loss: What does this output mean?

    Hi there! I am currently building a simulation to model the propagation of radio waves in seawater in terms of its propagation loss. I have previously discussed the models I've looked at but have settled on a model which depends primarily on the propagation distance ##r##, the carrier wave...
  10. H Smith 94

    How is radio wave propagation modelled in seawater?

    Before I start, I apologise for the information dump that is to follow. I don't expect all questions to be answered or all models to be addressed; I simply feel it is appropriate to provide the community with my current knowledge and stage of research so you may not have to search for it...
  11. L

    Low-energy air conditioning with seawater

    Over a decade back there was a company that sold air cooling devices for cruising sailboats. A sailboat at anchor is chronically short of electrical energy unless one runs a generator, which has its own trade-offs. The essence of operation of these devices was to pump seawater up from some small...
  12. berkeman

    Making gasoline from seawater (to store energy)

    This looks like it's mainstream work being done at the Naval Research Lab -- interesting stuff: U.S. Navy's new stealth destroyer http://www.cnn.com/2014/04/10/tech/innovation/navy-new-technology/index.html?hpt=hp_t2
  13. O

    What is the pressure inside the tube at 48 meters depth in seawater?

    Homework Statement The assignment is not in english but I'll try to translate it. I hope I've posted it in the right thread. You have a tube which is 48 meters long and one end is closed while the other end is open. You take the tube with the open end first into seawater (1025 kg/m3) and drop...
  14. R

    Seawater power plant efficiency

    1. Problem statement A power plant generates electricity from the difference in sea temperature. At the surface of the sea the temperature is 27°C. At the bottom of the sea the temperature is 6°C. a) What is the highest efficiency that this plant can have? b) If the power plant generates...
  15. xpell

    Why doesn't chlorine in seawater evaporate?

    I'm having trouble to understand this. Let's see, as far as I've read, salt in seawater is not present as NaCl molecules but in the form of dissolved (solvated) ions Na+ and Cl-. Provided that chlorine is a gas at ambient temperature, why don't these Cl- ions just evaporate (alone or...
  16. U

    Buoyant force in seawater and freshwater

    Homework Statement I'm doing a problem that is likely a common one. It is comparing the buoyant force of an object in seawater to that of the same object in freshwater. which has more buoyant force acting on it? Homework Equations not sure of equations at this stage, and we are just...
  17. P

    Melting Ice in Seawater: Cooling Steel on Seabed with 30kg Ice Block at -20degC

    Using a 30kg cubic block Ice at -20degC, I want to cool down a piece of steel which is resting on the seabed. The mass of steel is 1kg and the ice block is place on top of the steel. The current sea temperature as well as the steel temp is estimated at 12degC Assuming that the piece of steel...
  18. N

    Current in Seawater (Purcell 7.12)

    Homework Statement This is Purcell 7.12. Seawater moves at 1 meter/second, there is a vertical B-field of .35 gauss, and the conductivity of water is .04 (1/ohm*cm). What is the current in Amps/meter/meter? If you moved water in a bottle at this speed, would there be a current induced...
  19. Z

    Extracting Uranium from seawater

    So, I recently came upon a SA article "How long will the world's uranium supplies last?" (http://www.scientificamerican.com/article.cfm?id=how-long-will-global-uranium-deposits-last), and one of the paragraphs talked about: "Two technologies could greatly extend the uranium supply itself...
  20. G

    Iron Bacteria in Seawater: What We Know

    Homework Statement Does anyone know whether Iron Bacteria can be found in seawater or not? Homework Equations The Attempt at a Solution
  21. T

    Sending strong electric currents through seawater

    Hi everyone, I'm writing a novel in which a character "electrifies" water. He sends electric currents through the water to fend off a monster. So obviously the current must be high in volts and amps. My question is, what would be the easiest way to do this? So far, the best thing I can come...
  22. M

    Soil Mechanics: Relationship between pH of seawater and sand

    Is there any relationship between the pH of seawater and any properties of the sand at the beach? If so, what/ why/ how? Context: I am writing a report for my Soil Mechanics course, for which we analysed some sand we collected at the beach, as well as some seawater. One of the key properties...
  23. D

    Stars with 6 legs in seawater aquarium

    Recently I visited a sea water aquarium with tropical fish anemona, corals. At the glas walls I observed little (about 1 cm diameter) white stars with 6 legs. Now starfish have 5 legs, as far as I know. Any idea what this could have been?
  24. morrobay

    Scripps Institute of Oceanography Re: Seawater Alkalinity

    I have recently contacted three pH D 's in the chemistry dept at Scripps Institute of Oceanography, U.C. San Diego on why seawater is alkaline. since like you all I want facts on a subject. So far I have one reply from Andrew Dickson, Professor of Marine Chemistry: The pH of the oceans is...
  25. L

    What is the specific heat of seawater?

    Homework Statement What is the specific heat of seawater? Homework Equations I'm confused about what units are used, and what the specific heat of seawater is defined at? The Attempt at a Solution I found a website quoting, 'specific heat is about 3850 J/(kg C)'
  26. L

    What is the specific heat of seawater?

    I'm confused about what units are used, and what the specific heat of seawater is defined at? I found a website quoting, 'specific heat is about 3850 J/(kg C)' Is this correct, with these units?
  27. V

    Analysis of current flow and EM fields in seawater?

    Hi, I have a few queries regarding the flow of electric current through (sea)water... In general, can the flow of electricity through seawater be treated the same as through a metal conductor? I am wondering whether the fact that it is ions rather than electrons that carry the charge has...
  28. J

    Electrolysis of Seawater under pressure

    I have perused a number of related posts, but have not found the answer I'm looking for. My problem is this: I need to electrolyze seawater and capture the gas at a given pressure (I'm mixing the O2 and H2). It seems to me that there should be a relationship of the form: dVolume...
  29. T

    Jet nozzles effect in seawater

    Is it possible to calculate a high-pressure nozzles effect/carrying length in seawater if the medium used in the high-pressure nozzle is seawater?
  30. J

    Accretion of specific minerals from seawater

    I understand the process of electro-accretion of limestone from seawater. I was wondering if anyone had any links to information regarding the accretion of specific minerals from seawater...such as gold or silicon. I remember reading something a long time ago that you could modify the...
  31. K

    What is the fraction of an iceberg's volume exposed in seawater?

    Homework Statement The density of ice is 920 kg/m3, and that of seawater is 1030 kg/m3. What fraction of the total volume of an iceburg is exposed? Homework Equations The Attempt at a Solution I know your supposed to do volume of the ice divided by the volume of the seawater, x...
  32. M

    Quick question: speed of sound in seawater

    Dolphins emit ultrasonic waves with a frequency as high as 5.5 x 10^5Hz. What is the wavelength of such a wave in seawater at 25°C? i know how to solve this one, all i need is the speed of sound waves in seawater at 25 degrees Celsius. My teacher gave us the speed in water at 20C which =...
  33. T

    Extracting Gold from Seawater: Is It Possible?

    Has anyone any idea how to extract gold from seawater? is it possible?