Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now

# Tag Info

42

There are two ways this problem needs to be looked at. The first is more astronomy than Earth science. The Earth as an entire system is largely contained. Its gravity and magnetic field retains nearly all of its elements. Earth does lose hydrogen and helium and cosmic rays will split water molecules leading to a loss of an impressive amount of ...

40

"Sea" versus "lake" versus "just part of the ocean" is a bit fuzzy, but there are two things that are universal about seas: They are saline. They are either endorheic or have a sea-level (tidally-influenced) connection to the ocean. Now, let's see how the Great Lakes look under these criteria. Saline? No, salinity is 0, give or take measurement error. ...

34

When dissolved in water, salt breaks up into sodium and chlorine ions, which combine with water molecules so they cannot easily sink. However, there is a tendency for streams of fresh water to float on salt water and rise to the top. This caused problems for British submarines in the Dardanelles Straits during WW1. Moving from almost fresh water to the ...

33

The area is experiencing post-glacial isostatic rebound. Much of Canada was covered in an extensive ice sheet in the last glacial period (the 'Ice Age'), from about 110 ka until 12 ka. The ice in the Hudson Bay area was among the last to melt: A thick ice sheet depresses the crust (the lithosphere), making a small dent in the uppermost mantle (the ...

32

There are many "uncharted waters". Nautical charts have information about water depths, dangers to navigation, aids to navigation, anchorages, and other features. You can see here what might be included in a nautical chart: U.S. Chart No. 1 The area in question is a shallow sea... so boats of different sizes may or may not be able to take certain routes ...

28

Your assumption that there is not a lot of water elsewhere in the solar system is incorrect. According the this article on NASA's website; Missions in recent years have overturned our view of a dry solar system, returning mounting evidence of ample water from a vast array of locations. Comets from the remote corners of our solar system are made of ...

27

In the case of Río de la Plata, part of it is history and politics, and part of it is oceanography. Most of Argentina and Uruguay considers Río de la Plata as a river (thus, the name, río) and as such it is the widest river in the world (maximum width >200km). Río de la Plata is formed as the confluence of the Paraná and Uruguay rivers and results in a ...

26

There are lots of controls on sea level, not just the volume of water in the world ocean. These controls operate on different time and spatial scales, and interact in nonlinear ways. As a result, both global ('absolute') sea level and local ('relative') sea level can rise in some places and fall in others. For example, absolute sea-level is currently rising,...

24

Sea level has a strong seasonal signal. The annual variability is less than the daily changes associated with tidal forcing in most locations, but still can be on the order of 5-10 cm (maximum values about 15 cm). The causes of the seasonal fluctuations are mostly associated with seasonal changes in wind intensity and patterns, changes in temperature that ...

23

In a nutshell: The instrument measures microwave radiances (after calibration) If we know the sea surface temperature, we can use radiances to calculate emissivity. The emissivity at 1.4 GHz is itself a function of near-surface ocean salinity. However, in reality, it's more complicated, because there are other factors that come into the equation, such as ...

23

The water was already present when the Earth assembled itself out of the accretionary disk. Continued outgassing of volcanoes transferred the water into the atmosphere which was saturated with water. And rain transferred the water onto the surface. Compared to other planets and smaller solar system object Earth has a big advantage. It is large enough to ...

22

Why does the salt in the oceans not sink to the bottom? Because there isn't any "salt", per se, in the ocean. Salt, as the compound sodium chloride (NaCl) does not exist as a solid in the ocean. It is dissolved into sodium and chloride ions (charged atoms) that exist within the ocean as a homogenous phase (that is, a "thing"). That said, water with sodium ...

21

Yes, there are lots of other factors. Factors affecting sea levels are no different from other natural processes: there is a large number of coupled, non-linear effects, operating on every time scale, and at every length scale, and across many orders of magnitude. The Wikipedia page Current sea level rise lists many of the known processes. And I wrote a ...

21

Why doesn't 71% water of the earth dry or evaporate? The simple answer: Because it rains. The not so simple answer: By some estimates, the Earth has already lost about a quarter of its water, and it is predicted to lose almost all of its water in a billion or so years from now. It rains because temperature decreases with altitude. This lapse rate means ...

19

For very quick visual comparison I would use Cube Browser or ncview together with a command line tool like the Climate Data Operators. For quick production of nice looking graphics (and animations) Panoply really makes good job. For further analysis or special graphics keep following your approach and script with things like MATLAB, Python (e.g. with Iris), ...

18

Theoretically, I agree that there should be one instable equilibrium point between the two stable equilibrium points when we have a 2D current field. However, there are some additional components of the problem: Ocean currents are not 2D but 3D currents. Considering only the sea surface might lets field lines disappear. The wind has an additional forcing. ...

18

Yes, you're right, there should be (at least one) saddle point in the middle of the loop. And indeed, if you search for illustrations of Pacific ocean circulation, you can see the saddle point in some of them, like this one: Source: Introduction to Tropical Meteorology, 2nd ed., chapter 3.3.1, fig. 3.20. Now, in a lot of other maps, the saddle region is ...

17

The writers of netCDF, UNIDATA, maintain a pretty extensive list of visualisation software on the netCDF website. It even mentions an Excel add-in, for the masochistic, presumably. Over the years, I've found Ferret to be reliable with CF compliant files (and non-compliant ones, for that matter) and useful for interactive quick looks and simple ...

15

The easiest way this is measured is via Argo floats. They're probes which periodically dive into the sea, and measure the ocean heat content. This is done by calculating the formula. According to the European Environmental Agency, this formula is: Ocean heat content is defined as the integrated temperature change times the density of seawater, times ...

15

Here is an estimate from Beauchamp and Baud (2002), for parts of the ocean around Pangea, for the latter parts of it's existence (~300-250mya). It is based on various previous papers that looked at deposits of carbonates and phosphate deposits, and made a few assumptions, including a sufficient supply of silica and nutrient inputs, and environments suitable ...

15

Yes, there are many. According to the seafloor topographic data of ETOPO (1 arc second resolution), and the Exclusive Economic Zones (EEZ) database of marineregions.org. There are at least 157 seafloor features higher than -100 m (closer than 100 m to the sea surface). With that data, I made the following figure that shows: ETOPO topographic data All EEZ ...

14

I don't know about the size of land masses, but their distribution and the shape of ocean basins definitely play a big role. When considering the ideal case of an all-ocean globe, i.e. one with no land masses (equilibrium tidal theory), the combined effect of sun and moon give a theoretical tidal range of less than 1 m(1). As tidal ranges can be much larger ...

14

Because of post glacial rebound. The asthenosphere was pressed down under Laurentide ice sheet during last ice age and is now finding a new balance, without the weight of the ice. Note that around the ice sheet, the land is actually sinking today, like when ones partner gets up from a waterbed mattress.

13

I'm not familiar with land-based methods, but for global measurements, one method is to use satellite altimetry (I'm more familiar with the geodesy side, but many of the same satellites are used). I think many of the current methods interpolate global or regional currents from a sparse network of buoys. As more radar satellites are launched, however, ...

13

According to the Oxford Dictionary of Earth Sciences, seamount Isolated, submarine mountain rising more than 1000m above the ocean floor. The sharp, crested summits of seamounts are usually 1000-2000m below the ocean surface. Seamounts are of volcanic origin. To avoid classifying seamounts by arbitrary sea level (dependent on availability of surface ...

13

Some background. The idea of towing ice bergs to provide a source for fresh water in dry climate zones was first proposed in the 1970s by Weeks and Campbell (1973) and Hult and Ostrander (1973). This sparked interest that resulted in several studies published in conferences (Husseiny, 1980; IGS, 1980). The focus of the work was manly on the wastage of ice ...

13

To the best of our knowledge, sea-level is rising because the volume of water is increasing. There is substantial local variation in sea-level change; it's falling in some parts of Canada. But of the dozens of controls on local and global sea-level, the net effect is currently an average global rise of about 3 mm/y. It's not really 'a riddle'. The ...

13

In a 1983 Journal of Geology paper by Milliman and Meade, "World-Wide Delivery of River Sediment to the Oceans" (link) it is estimated that the world's rivers carry about $13.5\times 10^9$ tonnes of sediment per year. If we assume an average density of $2.5~\rm{g/cm^3}$, this corresponds to a volume of 8.8 cubic kilometers. The total surface area of the ...

13

Checking the Wikipedia page on underwater volcanoes and listing them by height, I think the best candidate is Vema Seamount. Vema Seamount is in international waters and its shallowest point is at 11 meters from the surface. It is so shallow that it represents a navigation hazard.

12

Almost all finite methods that use forward time models adhere to the Courant-Friedrichs-Lewy law which calculates a courant number and compares it to a $C_{max}$, which is what determines stability, so for 2-D: $$C = \frac {V_xdt}{dx} + \frac{V_ydt}{dy} \ge C_{max}$$ Where $C$ is the courant number, $V_i$ is the velocity in subscripted direction, $dx$ or \$...

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