At some point, doesn’t all this ingestion of carbon lead to fossilization and removal of that carbon from the system?

Fossilization? Do you mean sequestration in geologic storage? If that is what you mean, then no, it does precisely the opposite. Oceanic DOC is a reasonably large pool of C (nearly as large as the atmospheric pool). When DOC is metabolized/remineralized CO2 gets released. Hence, the more DOC sponges (or any organisms) assimilate the more of it is oxidized to CO2. Most of the organic C the sponges take up is respired as CO2 (~80%, give or take a bit, for most organisms) while almost all of the other 20% is shed as choanocytes, which are then eaten or decomposed by some other organisms. This process is a source of CO2 and comes at the expense of the DOC sink.

If so, then since it is happening on a massive parallel scale, wouldn’t it have to be significant in the overall carbon budget?

And, if not, could you provide some other reference material to back yourself up?

Yes, if it did occur on a massive scale and if it were a significant pathway in the C cycle it would need to be considered separately in the planetary C budget. However, that is clearly not the case because 1) DOC conc. are elevated around coral reefs relative to much of the ocean, despite the presence of these sponges, 2) DOC conc. shows little variation throughout most of the ocean, 3) most DOC is old (mean ~5000 yrs+) and apparently quite refractory.

These sponges don’t keep up with DOC production on coral reefs, coral reefs contribute only a very small portion of the DOC present in the ocean (they’re still a net source though), and hence only a very small portion of oceanic DOC is remineralized through this pathway. For climatology, the pathway of the assimilation doesn’t particularly matter, only the quantity thereof (though you certainly want to understand the processes that contribute significantly to C fluxes). This process is simply a tiny, tiny drop in the ocean in terms of global C flux. Even major changes in the magnitude of this process aren’t going to mean much of anything to the global C cycle.

And, if not, could you provide some other reference material to back yourself up?

The first answer is evasive.

How do you figure??? Most DOC in the ocean comes form planktonic organisms. They derive the C from food. So, when you ask where plankton get C from, the answer is food. The answer is simple, not evasive.

The second, I know of reputable papers from the early 2000’s which hypothesize otherwise, but as they may be out of date, I’m not going to hang my hat on them.

Huh? You know of papers from the early 2000′s that suggest the reminieralization/respiration of organic material in the ocean does not result in the production of DIC? Please explain how that works.

Regardless, if the cycle leads to CO2 in the ocean, isn’t that relevant to the climate debate?

No, not really, because the effect is far to small to have global implications. The DOC concentration varies little in the most of the ocean. The few exceptions are places where you get a lot of DOC production, like around coral reefs. However, that excess production is coupled somewhere along the line with remineralization/utilization as we can tell by almost all of the ocean having a relatively invariant DOC concentration.

On coral reefs this sponge acts to funnel energy/material in DOC into POC, which is generally more accessible to most organisms. Whether the DOC goes through this pathway or is remineralized at some other stage, however, is completely immaterial to climatology. When trying to understand coral reef ecology/energetics, this is an important observation because it maters how and where material/energy moves. When creating a material budget for climatology it really doesn’t matter much if the DOC gets chewed up by sponges on a reef, or microbes far off in the water column. It gets chewed up and returned to DIC just the same.

All in all, I would have preferred it if you had stated, “while this could be an important link in the carbon cycle, it does not appear to provide a significant path for either long term storage (CO2 sink) or production (CO2 source). As such, it is not likely a significant finding as relates to the climate debate.”

Likely, nobody would have argued with you, people would have come away a little wiser, and you would have stood a better chance of attracting people to your side.

There’s no reason to think it is an important link in the global C cycle. It is an important link in coral reef ecology. If you didn’t like the way I phrased my comment, ummm, ok? What can I do about that? I gave as simple, straightforward an answer as I could.

Likely, nobody would have argued with you, people would have come away a little wiser, and you would have stood a better chance of attracting people to your side.

Regardless, if the cycle leads to CO2 in the ocean, isn’t that relevant to the climate debate?

“Most of it comes from planktonic organisms.”

Where do they get it?

Food.

After you answered that question, I was going to ask, what happens to the carbon when those creatures ingest “discarded choanocytes”?

The same thing that happens to all organic C: it is remineralized to DIC/CO2 (with a tiny, tiny portion slowly making its way into the geologic reservoir).

After you answered that question, I was going to ask, what happens to the carbon when those creatures ingest “discarded choanocytes”?

Where do they get it?

Inorganic carbon enters the biosphere via photosynthesis where it is incorporated into organic carbon. Thence, it proceeds to the ocean via rivers. It is part and parcel of the overall carbon cycle.

Only a small portion of the DOC in the ocean derived from terrestrial sources. Most of it comes from planktonic organisms. Regardless of the source, however, the research this article describes is about DOM/POM cycling on coral reefs. It has nothing whatsoever to do with sinking C (there are no sinks in the system in question, that’s the point!).

“They’re talking about Organic Carbon. CO2 is NOT included in Organic Carbon. So what’s the relevance to climate change?”

Inorganic carbon enters the biosphere via photosynthesis where it is incorporated into organic carbon. Thence, it proceeds to the ocean via rivers. It is part and parcel of the overall carbon cycle.

Chris (22:03:35)

You can’t convince me that posting this with a title like “Sea sponges soak up carbon …like a sponge” is not intended to imply they are a carbon sink.

Umm, yeah, I know…

The research relates to trophic dynamics on coral reefs and has nothing to do with climatology and/or providing a sink for CO2. The title of this post implies that the sponges are acting as a sink for CO2, as you suggest, which in fact has nothing whatsoever to do with what the research demonstrates.

This sponge takes up large amounts of DOM. It has very rapid turnover of choanocytes and sheds them into the environment. The result of these activities is to fuel material/energy from the DOM pool into the POM pool, which is more readily accessible to most reef organisms. None of that has a thing to do with climatology.

Agreed, the title was poorly and misleadingly worded.

You can’t convince me that posting this with a title like “Sea sponges soak up carbon …like a sponge” is not intended to imply they are a carbon sink.

There is (effectively) none. The study is important in understanding food web dynamics on coral reefs and adjacent ecosystems. It has no meaningful impact on climatology, ocean acidification, etc. These are wholly different topics (e.g., different somewhat like the price of Barbie dolls and apple pie recipes are wholly different, despite the fact that both Barbie dolls and apple pies contain C).