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Author Topic: Glacial meltwaters previously unrecognized sinks of atmospheric CO2  (Read 559 times)

JMP

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Proglacial freshwaters are significant and previously unrecognized sinks of atmospheric CO2


https://www.pnas.org/content/116/36/17690
"Significance

Glacier melt is one of the most dramatic consequences of climate change in high-latitude and high-altitude environments. As meltwaters move across poorly consolidated landscapes, they transport vast quantities of highly reactive comminuted sediments prone to chemical weathering reactions that may consume atmospheric CO2. Using a whole watershed approach in the Canadian High Arctic, combined with additional dissolved CO2 measurements in glacial rivers in Greenland and the Canadian Rockies, we show that certain glacier-fed freshwater ecosystems are significant and previously unrecognized annual CO2 sinks due to chemical weathering. As many of the world’s rivers originate from glacial headwaters, we highlight the potential importance of this process for contemporary regional carbon budgets in rapidly changing high-latitude and high-altitude watersheds.

Abstract

Carbon dioxide (CO2) emissions from freshwater ecosystems are almost universally predicted to increase with climate warming. Glacier-fed rivers and lakes, however, differ critically from those in nonglacierized catchments in that they receive little terrestrial input of organic matter for decomposition and CO2 production, and transport large quantities of easily mobilized comminuted sediments available for carbonate and silicate weathering reactions that can consume atmospheric CO2. We used a whole-watershed approach, integrating concepts from glaciology and limnology, to conclusively show that certain glacier-fed freshwater ecosystems are important and previously overlooked annual CO2 sinks due to the overwhelming influence of these weathering reactions. Using the glacierized Lake Hazen watershed (Nunavut, Canada, 82°N) as a model system, we found that weathering reactions in the glacial rivers actively consumed CO2 up to 42 km downstream of glaciers, and cumulatively transformed the High Arctic’s most voluminous lake into an important CO2 sink. In conjunction with data collected at other proglacial freshwater sites in Greenland and the Canadian Rockies, we suggest that CO2 consumption in proglacial freshwaters due to glacial melt-enhanced weathering is likely a globally relevant phenomenon, with potentially important implications for regional annual carbon budgets in glacierized watersheds."

{can't view entire paper linked in Guardian article below}
 
Glacial rivers absorb carbon faster than rainforests, scientists find
https://www.theguardian.com/environment/2019/oct/25/scientists-glacial-rivers-absorb-carbon-faster-rainforests

"‘Total surprise’ discovery overturns conventional understanding of rivers"

"This means that during high melt periods, glacial river water will absorb 40 times as much carbon as the Amazon rainforest.

“On a per-metre-squared basis, these rivers can consume a phenomenal amount of carbon dioxide,” said St Pierre. But their limited size means on a gross scale, they pull in far less than the sprawling Amazon. The team plan on sampling meltwaters in the Canadian Rockies, and expect to find similar results."

The Guardian seems to view this as good news - but of course we're rapidly losing glaciers. 

So... perhaps in the sort term we've got a bit of help in delaying the effects of the climate crisis but doesn't this further indicate some future tipping point?   





 



Tor Bejnar

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Re: Glacial meltwaters previously unrecognized sinks of atmospheric CO2
« Reply #1 on: October 25, 2019, 09:02:47 PM »
This, for sure, is a carbon sink, but it has changed little over the last 10,000 years, I suspect. It will change positively as the Earth heats up (which, of course, it has done these past 30+ years), then decline when mountain glaciers melt out. 

The 'weathering of minerals' associated with general erosion of mountainous terrains is the one long-term (albeit slow) carbon sink that will cool the Earth down, some day. [SkepticalScience]  The outwash plains carbon sink process is undoubtedly an enhanced aspect of the general principle.
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JMP

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Re: Glacial meltwaters previously unrecognized sinks of atmospheric CO2
« Reply #2 on: October 26, 2019, 04:32:13 PM »
Yes. Glaciers have evidently been reducing atmospheric carbon all along. And so, as we lose them we lose their carbon sink ability.  To me this means that the loss of the world's glaciers is even more critical than we knew before.

I was amazed at this new perspective and agree with the Guardian article's quotation of Dr Kyra St Pierre - that in retrospect it does intuitively make sense - but the article doesn't seem to adequately address the down-side.  And, at first it almost seemed it was announcing the discovery of a new tool to sequester carbon. Instead I think this shows that glaciers are even more important to mitigating climate change than was previously understood. 

PragmaticAntithesis

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Re: Glacial meltwaters previously unrecognized sinks of atmospheric CO2
« Reply #3 on: November 10, 2019, 06:59:19 PM »
It's not often we see negative feedback loops rearing their heads. I'll take that as good news!