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Author Topic: Carbon Cycle  (Read 117872 times)

Daniel B.

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Re: Carbon Cycle
« Reply #450 on: October 26, 2017, 12:42:12 AM »
For example, I am very concerned about ocean acidification impacting phytoplankton in the oceans and the long term impact on organic carbon deposition and the resultant levels of atmospheric CO2 and oxygen.

https://pubs.geoscienceworld.org/geology/article-abstract/24/10/867/206380/carbon-isotopes-and-the-rise-of-atmospheric-oxygen?redirectedFrom=fulltext

We know, for example, that seasonal variations in northern hemisphere terrestrial plant activity and the resultant carbon uptake causes the seasonal variation in atmospheric CO2.

http://onlinelibrary.wiley.com/doi/10.1029/JD090iD06p10529/full

Doesn't this suggest that any negative impacts on plant activity caused by increasing CO2 levels (ocean acidification) can impact O2 levels as well? More simply, reduced carbon uptake necessarily means reduced oxygen production and atmospheric oxygen levels, doesn't it?

Since I am not a scientist, I do not know if my fear is warranted.

(Would love to have my concerns set aside by contributions here from people better informed than me.)

Oxygen levels would be a concern, if the atmospheric levels were on the same order as carbon dioxide, as one molecule of oxygen is consumed for every molecule of carbon dioxide generated.  However, the atmosphere consists of 21% oxygen, but only 0.04% carbon dioxide.  Recent, the carbon dioxide levels increased ~0.01%, which would mean a resulting drop of oxygen by a comparable amount.  This is a 35% increase for carbon dioxide, but a  0.5% drop in atmospheric oxygen - not a notable difference.  The increased plant growth that would occur under such a scenario would have a negligible impact on animal growth.

AbruptSLR

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Re: Carbon Cycle
« Reply #451 on: November 05, 2017, 10:23:45 AM »
Understanding the impacts of recent biotic disturbances on US forest carbon cycling is critical for developing a better understanding of how these biotic disturbances will intensify under continued global warming, and the linked reference provides this legwork:

M. Kautz, P. Anthoni, A. J. H. Meddens, T. A. M. Pugh & A. Arneth (3 November 2017), "Simulating the recent impacts of multiple biotic disturbances on forest carbon cycling across the United States", Global Change Biology, DOI: 10.1111/gcb.13974 

http://onlinelibrary.wiley.com/doi/10.1111/gcb.13974/abstract?utm_content=buffer0b718&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Biotic disturbances (BDs, e.g., insects, pathogens and wildlife herbivory) substantially affect boreal and temperate forest ecosystems globally. However, accurate impact assessments comprising larger spatial scales are lacking to date, although these are critically needed given the expected disturbance intensification under a warming climate. Hence, our quantitative knowledge on current and future BD impacts, e.g., on forest carbon (C) cycling, is strongly limited. We extended a Dynamic Global Vegetation Model to simulate ecosystem response to prescribed tree mortality and defoliation due to multiple biotic agents across United States forests during the period 1997-2015, and quantified the BD-induced vegetation C loss, i.e., C fluxes from live vegetation to dead organic matter pools. Annual disturbance fractions separated by BD type (tree mortality and defoliation) and agent (bark beetles, defoliator insects, other insects, pathogens, and other biotic agents) were calculated at 0.5° resolution from aerial-surveyed data and applied within the model. Simulated BD-induced C fluxes totaled 251.6 Mt C (annual mean: 13.2 Mt C yr−1, SD ±7.3 Mt C yr−1 between years) across the study domain, to which tree mortality contributed 95% and defoliation 5%. Among BD agents, bark beetles caused most C fluxes (61%), and total insect-induced C fluxes were about five times larger compared to non-insect agents, e.g., pathogens and wildlife. Our findings further demonstrate that BD-induced C cycle impacts (i) displayed high spatio-temporal variability, (ii) were dominated by different agents across BD types and regions, and (iii) were comparable in magnitude to fire-induced impacts. This study provides the first ecosystem model-based assessment of BD-induced impacts on forest C cycling at the continental scale and going beyond single agent-host systems, thus allowing for comparisons across regions, BD types and agents. Ultimately, a perspective on the potential and limitations of a more process-based incorporation of multiple BDs in ecosystem models is offered."
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jai mitchell

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Re: Carbon Cycle
« Reply #452 on: November 05, 2017, 06:44:15 PM »
This study appears to be limited to the United States.  Since the majority of the worlds forests are located in Canada and Siberia I wonder what the projection of total global forest impacts would be.
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sidd

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Re: Carbon Cycle
« Reply #453 on: November 07, 2017, 07:35:32 PM »
Comprehensive review of soil carbon stocks, taking into bedrock horizons, mineralization and food webs.

"The global SOC stock in the upper 2 m of soil is 2,273 Pg C, with the boreal forest biome containing 623 Pg, or 27% of the global total (Table 2). Peatlands contain 543 Pg SOC, most of it in boreal, temperate broadleaf and tropical, moist broadleaf forest biomes; permafrost regions contain 582 Pg SOC, or 26% of the global total (Table 2)."

They have limited data on the 2-3m carbon stock, but they attempt it:

"Thus, the global total soil carbon pool to a depth of 3 m is estimated as 2,800 Pg C. Deeper (>3 m) deposits include an additional ~300–500 Pg OC in the permafrost region (Schuur et al. 2015), ~30–50 Pg C in tropical peatlands, and an unknown quantity of OC in other environments with deep sediments such as deltas, floodplains, and loess deposits."

doi:10.1146/annurev-ecolsys-112414-054234

open access. Read all about it. I attach table 2.

sidd

sidd

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Re: Carbon Cycle
« Reply #454 on: November 28, 2017, 10:15:06 PM »
I wasn't sure where to put this article reference, but it has relevance to the carbon cycle. Chalk et al. have a paper out arguing that the reason for the transition from 40Kyr to 100Kyr cycle was due to changing dust fertilization of southern oceans, and  find an increase in temperature sensitivity to CO2 across the transition.

"We argue that neither ice sheet dynamics nor CO 2 change in isolation can explain the MPT. Instead, we infer that the MPT was initiated by a change in ice sheet dynamics and that longer and deeper post-MPT ice ages were sustained by carbon cycle feedbacks related to dust fertilization of the Southern Ocean as a consequence of larger ice sheets. "

"The observed changes in the SL to ΔR CO2 relationships contain elements of both end member scenarios shown in Fig. 2 A and B, in which a greater slope is possibly related to changes internal to the ice sheets (scenario 1) and amplified glacial to interglacial CO 2 climate forcing is linked (this study) to increased glacial dustiness that causes enhanced Southern Ocean iron fertilization (scenario 2). Therefore, we propose a hybrid scenario (Fig. 2C) that incorporates both heightened ice sheet sensitivity to CO 2 forcing and dust-driven ocean sequestration of CO 2 to represent the observed climate system change across the MPT."

doi:10.1073/pnas.1702143114

open access, read all about it.

I attach fig 3.

sidd

AbruptSLR

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Re: Carbon Cycle
« Reply #455 on: December 01, 2017, 05:43:12 PM »
The linked reference indicates that current models of methane emissions from peatlands need to be improved to account for hotspots in the peat/soil with varying conditions (including varying ground water elevation):

Yang et al. (2017), "Evaluating the Classical Versus an Emerging Conceptual Model of Peatland Methane Dynamics", Global Biogeochemical Cycles, doi: 10.1002/2017GB005622

http://onlinelibrary.wiley.com/doi/10.1002/2017GB005622/abstract;jsessionid=120CA9C25B38DF660F8C127A470C3997.f02t01?systemMessage=Wiley+Online+Library+will+be+unavailable+on+2nd+Dec+2017+starting+from+0800+EST+%2F+1300+GMT+%2F+21.00+SGT+for+2.5+hours+due+to+urgent+server+maintenance.+Apologies+for+the+inconvenience.

See also:

Thompson, E. (2017), A new model yields a better picture of methane fluxes, Eos, 98, https://doi.org/10.1029/2017EO086831

https://eos.org/research-spotlights/a-new-model-yields-a-better-picture-of-methane-fluxes?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz120117

Extract: "… generally speaking, methane is produced below the water table, where there is little to no oxygen, and it is destroyed above the water table, especially right at the boundary, where the most methane accumulates. When the water table is high, a greater proportion of the soil falls into methane-producing conditions. Likewise, when the water table drops, more soil is exposed to oxygen and thereby able to destroy methane. Current models commonly use this relationship to predict net methane production essentially on the basis of water table height.

Now Yang et al. suggest updating this classical conceptual model to include new information on methane dynamics gleaned from recent studies: For example, oxygen-poor pockets within the soil produce methane even above the water table, and methane can be destroyed below the water table in the absence of oxygen, depending on the presence of specific microbes and molecules in the soil that can play the role of oxygen to gain the electrons lost by methane."
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AbruptSLR

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Re: Carbon Cycle
« Reply #456 on: December 04, 2017, 08:47:24 PM »
The linked article documents how trees are the dominant source of methane emissions in the Amazon wetlands:

Title : "Trees are the dominant source of methane emissions in Amazon wetlands"

https://www.carbonbrief.org/guest-post-trees-are-the-dominant-source-of-methane-emissions-in-amazon-wetlands

Extract: " … trees needing to get oxygen down to their roots to keep them alive in an otherwise anaerobic soil. The methane produced in the soil is emitted in the opposite direction, out of the stems and into the atmosphere.

Scaling up our findings using maps of known floodplain extent, we estimate that wetland trees emit between 14m and 25m tonnes of methane each year.

This is similar in size to emissions from Arctic tundra, all the oceans combined or the total emission from wild animals and termites across the world combined.

Remarkably, we found that tree stems contributed around half of all methane emissions from the Amazon, which – when added to the emissions from other pathways – gave very close agreement with the top-down aircraft based emissions estimates."

See also:

Pangala, S. R. et al. (2017) Large emissions from floodplain trees close the Amazon methane budget, Nature, doi:10.1038/nature24639

http://www.nature.com/articles/nature24639
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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TerryM

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Re: Carbon Cycle
« Reply #457 on: December 04, 2017, 09:21:58 PM »
Ouch!
I thought the Amazon was a carbon sink.
Terry

AbruptSLR

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Re: Carbon Cycle
« Reply #458 on: December 04, 2017, 10:20:00 PM »
Ouch!
I thought the Amazon was a carbon sink.
Terry

On the bright side, the methane emissions from these wetland tropical trees have been relatively constant for millennia, and who knows where deforestation (thus reducing the number of trees as methane sources) vs potential increased methane from more decaying submerged deadwood (due to deforestation), will result in an increase trend, or a decreasing trend, in methane emissions from the Amazon wetland trees (which currently do absorb a lot of CO2).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Daniel B.

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Re: Carbon Cycle
« Reply #459 on: December 05, 2017, 03:48:49 AM »
Ouch!
I thought the Amazon was a carbon sink.
Terry

Fear not.  It still is.  "For the nations of the Amazon basin as a whole this means that since 1980 the carbon uptake has matched the entire combined emissions from deforestation and fossil fuels."

https://phys.org/news/2017-02-carbon-uptake-amazon-forests-region.html

gerontocrat

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Re: Carbon Cycle
« Reply #460 on: December 07, 2017, 04:25:21 PM »
Off topic but perhaps worth pointing out that atmospheric CO2 concentrations continue to rise at an unabated rate.
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