Why aren't the oceans covered in floating seaweed?

[Moontanman]

19 hours ago, CharonY said:

Even if we can manipulate current flow economically, there is a big issue in terms of the ecological effects. Say, if we were able to circulate from the ocean floor by magic means, then we would also move carbon back into the cycle. We could have more biological activity, but that also entails higher release of CO2. One of the reason why iron seeding was deemed attractive is that it would (in theory) target specific nutrient limitations, while leaving sunk carbon alone. In fact, the basic idea was that the newly produced biomass would sink before it can be oxidized. But it is still not clear whether that happens quantitatively. The other challenges of course is the interplay with existing currents. The deposition of carbon does not really happen locally. For example huge conveyor belts that move across the globe are instrumental in burying carbon, e.g. by downward movement of biomass rich warmer water once it moves to the colder region. In other words, effects are not only hard to impossible to contain, but sometimes it actually requires these long-distance transports to actually act as sinks. There are much more details to it but it would be way beyond my expertise. I admit that my eyes somewhat glaze over when they go full-bore on their research, but my takeaway from those seminars is always: "it's complicated" and "it is very global". 

The latter I suspect to justify all that travel for field work (and tans).

Agreed... but changing the environment to suit us and introducing exotic species is kind like what we (humans) do and have been doing for tens of thousands of years. My suggestion was bit tongue in cheek and maybe I should have made that clearer. But it is what we, as a species do... 
 

I have given this idea of why the oceans is not more widely covered by seaweed, this conundrum does have a logical solution. Mangroves are an example that can be compared. Mangroves surround the coast in vast areas of the tropics but they do not cover every coast, the reason is similar to why sargassum doesn't cover the entire or most oceans. Mangroves are temperature dependant, they cannot live where it freezes or the temps go below a certain tolerance, I'm not sure what that is, also mangroves grow best where they can catch and hold onto mud or sediment as it flows off the land, nutrients, also wind and waves also limit mangroves, on shores with high wave action is a regular thing mangroves tend not to grow. 
 

I can imagine in the future mangroves evolving to float out on the ocean and form huge islands of interlocking roots with the leaves and trunks above the water in warm ocean gyres but this is just fantasy... 

Sargassum is, as far as I know, kind of unique, it occurs only in one small area of one ocean. While currents do confine it to this area it does escape and is found all long the east coast washed up on shore after storms. I've seen it a couple feet deep in some areas on the beach, it has been used and mulch and fertilizer in past times. It does escape the "sargasso sea" but it either is immediately washed up on share by wave action or taken into cool or cold water where it cannot grow. 

A very similar if not identical "seaweed" I use that term because seaweeds are not vascular plants and are in fact members of the protist group if I am not mistaken. Be that as it may, a very similar but sessel version of this seaweed grows on rocky shores in the are as well and it is quite possible that the sargasso sea is the result of pieces being torn off that float away and are corralled by ocean currents in the area. 

I think the question of why it does cover more ocean, and it does get quite thick and widespread in some large areas on the sea surface, is significant. I think it's a unique to the area it's found in and if introduced to other gyres in other warm oceans it might take hold and one has to wonder why something similar hasn't evolved in other oceans and the answer might be that sargasso has evolved relatively recently from a brown seaweed that is normally attached to rocks in the immediate area and is often torn off by storms and some populations of this "plant" has managed to survive in the open ocean when contained in warm water by oceanic currents. The suspect does indeed grow in the surrounding area attached to rocks and has already evolved gas sacks to make it buoyant where it grows on rocks. I'm not sure if the oceanic version is genetically different from the form that grows on rocks but I suspect from personal observations that it is not... 

Edited October 3, 2019 by Moontanman

[CharonY]

6 hours ago, mistermack said:

Not really a problem, if you are producing high photosynthetic activity. The CO2 just becomes a useful source for the green algae. 

If CO2 capture was your motive, you would arrange your project in places where sinking matter falls into a low-oxygen zone, rather than the random way that nature does it.

So this does not really work. The reason is that low oxygen zones are the middle zone in the ocean (200-2000 m or so) which are deoxygneated because of organisms feeding on the dropping nutrients. I.e. they do not have sufficient light to for photosynthesis, plus they are nutrient rich to begin with. Pumping more nutrients in would either decrease oxygen content further or have no effect if they are in surplus to the biological activity they can sustain. The layer beneath that deoxygenated zone has again more oxygen as it is delivered from oxygenated polar waters. The combination of cold and rather fast sinking reduces the amount of biological consumption oxygen (it still occurs, though).

 

6 hours ago, mistermack said:

Personally, I wouldn't be aiming at CO2 fixing with this sort of project, but food production by making near-sterile oceans productive. Any carbon capture would be a bonus. 

So low productivity zoned could be stimulated by nutrient addition. But as mentioned, if feeding includes sunk carbon, we would invariably release carbon. And as we established before, more CO2 does not mean that suddenly it would be also consumed at a higher rate by the Calvin cycle. Overall, factors increasing biological activity, such as warming ocean waters are likely to decrease carbon burying and hence, increase CO2 in the atmosphere, which is one of the feedback loops which folks are worried about.

2 hours ago, Moontanman said:

Agreed... but changing the environment to suit us and introducing exotic species is kind like what we (humans) do and have been doing for tens of thousands of years. My suggestion was bit tongue in cheek and maybe I should have made that clearer. But it is what we, as a species do... 

No, that is a fair point. The mean difference is really that what did and do has unintended consequences (such as global warming). These engineered systems would ideally have predictable outcomes. But it does seem to be really difficult.

Among your other points, I would agree that temperature is a major player, it often defines the rate of biological activities. But I really know nothing about the ecology of the mangroves (you know more than I do), so being told that it is really an unique ecosystem is about the extent I can speculate on it.

In the ocean to my knowledge most of the phytoplankton in the ocean are cyanobacteria and I suspect it must boil down to metabolic efficiencies over plants. 

[mistermack]

2 hours ago, CharonY said:

So this does not really work. The reason is that low oxygen zones are the middle zone in the ocean (200-2000 m or so) which are deoxygneated because of organisms feeding on the dropping nutrients.

Maybe, but organic matter IS being captured somewhere in the oceans. Presumably that's where the petroleum industries' raw materials originated. Today's "dead zones" are coastal, and are reckoned to be caused by human action, so they don't come into the equation, and wouldn't have been the source of all that oil. 

Anyway, what I'm talking about is producing vigorous biological activity at the surface through a small amount of enrichment from below.

Yes, you may bring up some carbon from below, but according to your own posts, "down below" is higher is oxygen, so the bacteria down there would have been gobbling it up anyway. You can't have it both ways. What's the difference between leaving it down below, in oxygen rich water, and bringing it to the surface?  The only difference is the sunlight up above.

As far as falling matter is concerned, If it's all getting hoovered up by bacteria as you describe, that's not the end of it's story. What happens to the bacteria? i would assume that they are in the food chain, so you have an eventual increase in productivity. 

In any case, as I said, I'm only interested in the potential for food production, not carbon storing. If that happened, it would just be an unintended bonus.

[CharonY]

52 minutes ago, mistermack said:

As far as falling matter is concerned, If it's all getting hoovered up by bacteria as you describe, that's not the end of it's story. What happens to the bacteria? i would assume that they are in the food chain, so you have an eventual increase in productivity. 

That is not what is happening. In short, biomass produced near the surface drops down with a given kinetic. During the descent of biomass they get degraded (and releasing CO2). However, the rate of that happening depends on amount of biomass relative to biological activity and the speed in which the biomass moves downwards. Once it is on the seafloor they still can be degraded, but due to low temperature the rate is vastly reduced. There, due to sedimentation and other mechanisms, carbon can be buried where only slow biological activities can occur. So carbon burial (as well as net O2 production) is the net effect of all these functions and depending on the actual system, they can act as sinks (in case low activity) or CO2 producers (in case of high activity).

57 minutes ago, mistermack said:

Today's "dead zones" are coastal, and are reckoned to be caused by human action, so they don't come into the equation, and wouldn't have been the source of all that oil. 

Just to clarify, you have the term dead zone quite a bit, but it is unclear how you think what the relationship is. Just to be clear, a dead zone refers generally to low oxygenized areas, which are depleted of oxygen due to (previous) biological activity. I.e. algae bloom are often a cause of dead zones as the increase in biomass and the following biological activity on that biomass depletes the oxygen. These areas are also rich in nutrients. Whether in those areas carbon would be effectively buried would depend on how much is produced vs consumed and the sedimentation rate (also movement of the sea floor, I imagine).

 

1 hour ago, mistermack said:

In any case, as I said, I'm only interested in the potential for food production, not carbon storing. If that happened, it would just be an unintended bonus.

So that is an aspect people are also worried about. More phytoplankton due to seeding with iron could feed animals. But if it leads to toxic blooms, they would expand dead zones and make areas inhabitable for more complex animals.

[mistermack]

4 minutes ago, CharonY said:

So carbon burial (as well as net O2 production) is the net effect of all these functions and depending on the actual system, they can act as sinks

That's all I meant in my original post. If you want to bury carbon, you would calculate where to site your unit to take advantage of natural "sink" conditions.

[CharonY]

1 hour ago, mistermack said:

That's all I meant in my original post. If you want to bury carbon, you would calculate where to site your unit to take advantage of natural "sink" conditions.

a) the issue is that improving carbon sinks is vastly difficult due to a list of complicating factors, of which several have been listed

b) if you refer to the post where you suggest pumping up sediments, the issue is that you would feed the somewhat inert carbon into the active cycle again.

[mistermack]

The design that I envisaged involved a continuous plastic sheet, sunk to a depth of not more that a few tens of metres below the surface. 

Under those conditions, a runaway bloom could be prevented by carefully measuring the amount of pumped water from below. Also, the amount of pumped water would be low, as the nutrients wouldn't immediately start sinking. 

As far as carbon goes, yes, some would be coming up with the nutrient water, but you have to factor in how much would be dropping back down as waste, probably more than comes up. Also, how much carbon is released in the current methods of food production? 

One thing to bear in mind is that the waste that you are dropping into the depths might eventually break down into CO2, but how long will it take? The CO2 global warming scare will probably be long gone by the end of the century, as the use of renewables will have mushroomed still more, and fusion energy will be widely available, and much cheaper than fossil fuel. 

We might even be worrying about the new glaciation, creeping down from the poles. It's overdue. 

[dimreepr]

50 minutes ago, mistermack said:

The design that I envisaged involved a continuous plastic sheet, sunk to a depth of not more that a few tens of metres below the surface. 

Under those conditions, a runaway bloom could be prevented by carefully measuring the amount of pumped water from below. Also, the amount of pumped water would be low, as the nutrients wouldn't immediately start sinking. 

As far as carbon goes, yes, some would be coming up with the nutrient water, but you have to factor in how much would be dropping back down as waste, probably more than comes up. Also, how much carbon is released in the current methods of food production? 

One thing to bear in mind is that the waste that you are dropping into the depths might eventually break down into CO2, but how long will it take? The CO2 global warming scare will probably be long gone by the end of the century, as the use of renewables will have mushroomed still more, and fusion energy will be widely available, and much cheaper than fossil fuel. 

We might even be worrying about the new glaciation, creeping down from the poles. It's overdue. 

Your posts on this subject are generally oversimplified and allways without evidense...

"It's overdue" would have buggered my meter if I hadn't burried it...

50 minutes ago, mistermack said:

and fusion energy will be widely available

Why?

Edited October 4, 2019 by dimreepr

[mistermack]

I'm not going to hijack the thread to another topic. I'm just making the point that if carbon waste at the ocean floor takes decades to break down, then things might be looking very different over those kinds of time scales. And almost certainly will. Nothing stands still. 

Look at the difference between 1919 and 2000, and imagine that kind of change over the next 80 years. Only much more so, as technology is accelerating all the time.

[dimreepr]

24 minutes ago, mistermack said:

I'm just making the point that if carbon waste at the ocean floor takes decades to break down, then things might be looking very different over those kinds of time scales. And almost certainly will. Nothing stands still. 

Look at the difference between 1919 and 2000, and imagine that kind of change over the next 80 years. Only much more so, as technology is accelerating all the time.

What else don't you know?