Additionally, most primary productivity occurs in the ocean by phytoplankton, which have a turnover time on the order of days. They are generally limited by light and/or nutrient availability rather than growth or reproductive rate, so it would be a matter of days before the marine system recovered.

Most VNs have a 'true' ending though. Other endings usually just give you more insight into a particular character. You're not going to be able to fully represent a branching VN as anime, but there are plenty of anime adaptations of branching VNs that still worked really well (e.g. Steins;Gate).

Doesn't this apply to novels too though? Sure there are behemoths like Umineko, but most VNs are comparable to novels (and novel series) in length.

Most of the ocean is between 32-36g/L (so quite a tight range!). You can get more extreme values in some marginal seas, and of course places like lagoons and estuaries.

Locally yes, and these plumes can be biologically and geochemically important. But if we're thinking about the large-scale overturning circulation of the ocean, these heat sources are negligibly small (not to mention the fact that there's no direct correlation between where these vents are and where upwelling of deep waters occurs).

Yes, but geothermal vents are highly localised and have a negligible contribution to the whole-ocean heat budget. Plumes associated with hydrothermal vents are important biologically and geochemically, but not for ocean physics as a whole.

It's a good question. The uppermost layer of the ocean is called the 'mixed layer'. As the name suggests, it's a well-mixed layer where the properties are set (over short timescales) by the atmospheric conditions above and, because of weaker stratification at higher latitudes, it tends to be shallow at low latitudes and deep at high latitudes, particularly in the winter. When we talk about a water mass being formed, this usually refers to water leaving the mixed layer, and thereby no longer having its properties directly forced by the atmosphere. This can either occur through a time-mean vertical velocity, or horizontal currents (if the mixed layer profile is sloped). Deep water formation specifically refers to the formation of a water mass that is deep (where "deep" usually means "below the thermocline").

Tidal forces are absolutely present at depth, and they're actually the source of much of the mechanical energy that drives mixing in the ocean interior.

> A storm can change the pressure and temperature of the water above it.

The difference between the highest and lowest atmospheric pressure ever recorded on earth is about 25kPa. That is over 1000 times smaller than the pressure at the bottom of the average ocean depth. Even a large wave would have a larger effect on pressure than that (but still negligibly small compared the pressure at a depth of >>1km).

> I don’t see how you could say with any certainty there’s no ice down there.

Because as I've already stated, it is physically impossible to naturally form ice at depth in the ocean. There is no way to cool the water below the freezing point below the surface. Pressures >> 0.1GPa do not exist in the ocean. There is no known source of freshwater in the deep ocean, nor is there any proposed mechanism for how such a source could exist, nor is there any evidence suggesting this exists.

Eddy velocities are by definition zero in the Eulerian time-mean, so that in itself isn't going to result in a time-mean vertical transport. Eddies in the Southern Ocean actually counteract Ekman suction but I'm not sure on what basis you're arguing that eddies are responsible for most upwelling in the Southern Ocean? Can you provide a study supporting this?

> The pressures in the deepest parts of the ocean are absolutely high enough to create different states of ice that would be denser than water.

Do you have any evidence for ice ever being observed forming in the deep ocean?

> It’s absolutely possible that the salinity changes at that depth

How? What source of freshwater are you proposing exists in the abyssal ocean?

> or the pressure of the water above changes

How?

> solid water has to be less dense than water

This is completely correct within the physical conditions that exist in the ocean. I have no idea what the density of ice is at 1GPa, but it's irrelevant, because these pressures do not exist in the ocean. The only way that you could physically generate ice in the deep ocean is by either (1) reducing the salinity, or (2) refrigeration, neither of which naturally occur in the deep ocean.

No, because:

• Any water capable of sinking into the deep ocean must be liquid (otherwise it wouldn't be dense enough to sink), so in other words, all deep water is above the freezing point (of seawater). So if all of your surrounding water is above freezing, and the sea-floor is above freezing (which is generally the case), how are you going to cool below the freezing point?
• If you look at the phase diagram of water, you'll see that, at 0C, you'd have to reach a pressure of ~1GPa to reach the freezing point, which is equivalent to a water depth of ~100km, ~10x deeper than the deepest part of the ocean. This phase diagram is for pure water, not seawater, but it's still not possible for water to naturally freeze in the ocean through pressure changes alone.

Yes, it will rise is a buoyant plume, until it has lost enough heat to surrounding water through mixing to reach a neutral density, e.g. see this acoustic image from a survey of a hydrothermal vent field.

> Ekman suction and tidal mixing are independent of deep water formation rates.

I think you're misunderstanding what I'm saying, because I'm not disagreeing with you - I'm not saying that Ekman suction and tidal mixing are a function of deep water formation rates. I'm saying that deep water formation rates are (to first-order) a function of Ekman suction and diapycnal mixing. As you say, at equilibrium, the rate of deep water formation is limited by the available return pathways. If upwelling ceases, it is not possible to maintain deep water formation.

The processes of deep water formation, and return pathways to the surface, are closely coupled because of conservation of volume. Unless you have an enormous expansion of abyssal water masses, Ekman suction + tidal mixing cannot be independent of deep water formation rates. The point is that, regardless of the buoyancy forcing taking place in locations of deep water formation, they're fundamentally limited by the amount of water that you're (mechanically) returning to the surface. You can create as much dense water in the North Atlantic as you want but, if there's no return pathway to the surface, you're not going to generate deep water at a significant rate.

> I can't speak for other ocean or climate models, bit geothermal heating is included in NASA's ECCO ocean models and state estimates.

That's good to know! I was not aware of this.

It depends on how thick the layers of fresh and salty water are, and whether there's anything mixing them together. The molecular diffusivity of salt in water is about 10^-9 m^(2)/s, which means that the distance salt can diffuse is roughly sqrt(10^(-9)t), where t is the time in seconds. So, for instance, if you had a 100m thick layer of freshwater lying on top of a 100m thick layer of saltwater, it would take well over 100,000 years for molecular diffusion to fully mix them.

In practice, in the ocean, there is mechanical forcing that causes mixing (e.g. the winds, tides, turbulence, etc). A typical value for the real, effective vertical diffusivity in the ocean (taking into account mechanical mixing) is 10^-5 m^(2)/s but, even then, it would take several decades to mix these layers together. And 100m is pretty small compared to the thickness of deep-ocean water masses.

Technically yes, but these heat sources are extremely small compared to the heating at the surface of the ocean, see this response.

This is a good point! Geothermal vents are too localised to be significant, but there is a geothermal heat flux everywhere on the ocean floor (due to heat escaping from the Earth's interior). However, this heat flux is on the order of 0.1W/m^2. By contrast, the heat flux at the ocean surface from the sun is of order 100W/m^2. So for the heat budget of the ocean as a whole, the geothermal heat flux is negligible. Locally, at the ocean floor, it has been argued that the geothermal heat flux could be non-negligible. However, this is not routinely incorporated into ocean or climate models (I will admit that I didn't even know this had been properly looked into before your comment made me look it up!) and, whilst it's possible that it could have some second-order effect, it's orders of magnitude too small to drive the kind of large-scale overturning we see in the modern Atlantic.

On the timescales over which ocean circulation processes occur (i.e. up to ~1000 years), there are no significant sources of water within the deep ocean. However, what you're describing (plumes of low-density water) does occur at one particular setting, namely deep-sea hydrothermal vents. Extremely hot water (which can be well above 100C because the boiling point of water increases with pressure) enters the ocean at these vents and, because the water is so hot, it has a lower density and therefore rises up in a plume (e.g. see this figure, from acoustic imagery of a hydrothermal vent). The plume continues to rise until the plume water has mixed and cooled sufficiently to reach a neutral density. Note that the water exiting from hydrothermal vents isn't "new" water, it's primarily water that has either been circulating through fissures in the seafloor and heated up due to the high geothermal gradient and through proximity with melt pockets.

Yes exactly. As you completely correctly wrote, the parts of the ocean with the right conditions to create very dense water masses (e.g. the marginal seas of the North Atlantic and Southern Ocean) are the parts of the ocean where deep water formation occurs. You can't have an overturning circulation without deep water formation. But this isn't an energy source, because no energy input is required for dense waters to sink below lighter waters. The problem is that, in order to have vigorous overturning, these dense waters have to somehow be returned to the surface (and at a significant rate). There's no process in the deep-ocean that adds (non-negligible) freshwater or heat, so the deep waters can't rise buoyantly. As a result, the only way water can return to the surface is by being dragged up by wind-induced upwelling, or (probably to a lesser extent) mechanically mixed up, probably mainly due to tides. What exactly are the key processes that determine the strength of the AMOC is an active research question, and the freshening of the North Atlantic is absolutely capable of reducing the AMOC strength (because if you're generating deep water at a lower rate, you're also going to upwell less deep water), but the point is that deep water formation isn't a driver (or energy source) of the overturning.

In most of the ocean, the water is not saturated with respect to salt (even at 0C, the solubility of salt - or specifically NaCl - is over 350g/L, whereas the typical salinity of seawater is 35g/L). Perhaps this has some effect in hypersaline water bodies such as lagoons or the Dead Sea, but I don't think this would have any meaningful effect in most of the ocean. There are some other interesting interactions between temperature and salinity in the ocean though, such as double diffusive convection!

Because, as they explained, 'spicy' water is salty and warm. There is a correlation between salinity and temperature in the ocean, but they can be independently modified. In some situations, talking about spiciness might be useful, whereas in other situations (and more commonly) you'd discuss temperature and salinity independently.

As mentioned by /u/jellyfixh, most of the processes that modify the salinity of water (e.g. evaporation, precipitation, riverine inputs, and sea-ice formation) occur at the surface. As a result, to a reasonable approximation (ignoring the effects of mixing), you can assume the salinity of a water parcel is roughly constant once it leaves the surface of the ocean. In other words, understanding the salinity structure of the deep ocean is completely dependent on the three-dimensional circulation of the ocean interior, because the salinity of a deep water parcel is set by where that water parcel came from.

A good example of this is the Atlantic Meridional Overturning Circulation, or AMOC (which is sometimes misleadingly called the thermohaline circulation). Simply put, intense cooling and salinification in the subpolar North Atlantic results in water becoming fairly cold and very salty, which then sinks to a depth of around 2km (we call this resulting water North Atlantic Deep Water (NADW)). This water then travels south, mixing a little on the way, but mostly being dragged up towards the surface (upwelling) in the Southern Ocean, around Antarctica. There, some of the water gets pushed towards the north by the winds, freshening due to precipitation, but eventually being forced down as it sinks below the warmer, lighter waters to the north, settling at intermediate depths of around 1km (called the Antarctic Intermediate Water (AAIW)). However, some of the water upwelling around Antarctica instead moves south, freshening somewhat, but cooling intensely and forming an extremely dense water mass that sinks to the bottom of the ocean (called Antarctic Bottom Water (AABW)).

Have a look at this diagram, showing a cross-section of salinity in the Atlantic (North Atlantic on the right, South Atlantic on the left). Orange represents saltier water, blues represent fresher water. That big orange blob that goes from the surface to a depth of around 2km and moving southward is the NADW. The blue (fresh) tongue of water moving northwards and settling above the NADW is the AAIW. Finally, the blue(ish) (fresh(ish)) tongue of water sinking to the bottom of the ocean at the far left is AABW.

In the Pacific, by contrast, no deep-water formation occurs (contrary to the Atlantic). As a result, the depth-structure of salinity in the Pacific is more-or-less set by the depth-structure of salinity of deep waters entering the Pacific from other ocean basins so, whilst salinity does vary in the (subsurface) Pacific in depth, the lateral variations are fairly small compared to the Atlantic.