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Author Topic: Carbon Cycle  (Read 182101 times)

Bruce Steele

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Re: Carbon Cycle
« Reply #550 on: January 29, 2020, 03:35:58 AM »
Kasy, Your question about the source of the waters upwelled in the other eastern boundary current systems and the time between formation and upwelling are important to understanding each of those currents . They will each be different, I am sure , and in general they will pull up water from <300 meters. I don’t know enough physical oceanography to give a description of each upwelling system and the formation processes of the waters upwelled.

 

kassy

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Re: Carbon Cycle
« Reply #551 on: January 29, 2020, 02:35:59 PM »
Thanks! I will see what i can dig up at a later date.
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gerontocrat

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Re: Carbon Cycle
« Reply #552 on: February 11, 2020, 09:03:45 PM »
Perhaps this post belongs in the "World of 2030" thread?

https://www.bbc.co.uk/news/science-environment-51464694
Amazon: Parts of rainforest 'emitting more CO2 than they absorb'
Quote
Results from a decade-long study of greenhouse gasses over the Amazon basin appear to show around 20% of the total area has become a net source of carbon dioxide in the atmosphere.

One of the main causes is deforestation. While trees are growing they absorb carbon dioxide from the atmosphere; dead trees release it again. Millions of trees have been lost to logging and fires in recent years.

They suggest that the Amazon rainforest - a vital carbon store, or "sink", that slows the pace of global warming - may be turning into a carbon source faster than previously thought.

Gatti's research suggests this south-eastern part of the forest, about 20% of the total area, has become a carbon source. "Each year is worse," she told Newsnight. "We observed that this area in the south-east is an important source of carbon. And it doesn't matter whether it is a wet year or a dry year. 2017-18 was a wet year, but it didn't make any difference."

For decades, scientists have warned of an "Amazon tipping-point": the point at which the forest loses its ability to renew itself and begins to emit more carbon than it absorbs.

"It [the Amazon] used to be, in the 1980s and '90s, a very strong carbon sink, perhaps extracting 2bn tons of carbon dioxide a year from the atmosphere," says Professor Nobre, who is also a researcher at the University of Sao Paulo's Institute for Advanced Studies and Brazil's leading expert on the Amazon.

"Today, that strength is reduced perhaps to 1-1.2bn tons of carbon dioxide a year."

To put that in context, a billion tonnes of carbon dioxide is almost three times what the UK said it officially emitted in 2018.

For decades, scientists have warned of an "Amazon tipping-point": the point at which the forest loses its ability to renew itself and begins to emit more carbon than it absorbs.

"Some people think that it won't be until three degrees warming - so towards the end of the century, whereas other people think that we could get [it with] deforestation up above 20% or so and that might happen in the next decade or two. So it's really really uncertain," explained Simon Lewis, professor of Global Change Science at UCL.
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TerryM

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Re: Carbon Cycle
« Reply #553 on: February 12, 2020, 02:49:37 AM »
^^
With the ESAS, permafrost melt, & now the possibility of the Amazon becoming a source not a sink, we soon won't need to turn down the AC or fire up the F-150 to produce enough GHG to fry us all!


Keep it Cool!
Terry

Bruce Steele

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Re: Carbon Cycle
« Reply #554 on: February 12, 2020, 05:22:33 PM »
“ We find that the largest contribution to the interior ocean pH gradient comes from organic matter remineralization, with CaCO3 cycling being the second most important process. The estimates of the impact of anthropogenic CO2 changes on pH reaffirm the large and well‐understood anthropogenic impact on pH in the surface ocean, and put it in the context of the natural pH gradient in the interior ocean. We also show that in the depth layer 500–1,500 m natural processes enhance ocean acidification by on average 28 ± 15%, but with large regional gradients.”

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GB006229

Open access,  Processes driving global interior ocean pH distribution

sidd

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Re: Carbon Cycle
« Reply #555 on: February 13, 2020, 08:46:55 AM »
Excluding herbivores increases sequestration in arid savanna in Kenya: doi: 10.1002/ecy.3008

Grasses continue to do more than trees, even after herbivores are gone.

" Large herbivore exclusion, which included a diverse community of grazers, browsers, and mixed‐feeding ungulates, resulted in significant increases in grass cover (~22%), woody basal area (~8 m2 ha‐1) and woody canopy cover (31%), translating to a ~8.5 t ha‐1 increase in aboveground carbon over two decades. Herbivore exclusion also led to a 54% increase (20.5 t ha‐1) in total soil carbon to 30 cm depth, with ~71% of this derived from C4 grasses (vs. ~76% with herbivores present) despite substantial increases in woody cover."

"study was conducted from 1999-2017 at the Mpala Research Centre (MRC) and Mpala Ranch which together encompass 190 km 2 of semiarid savanna within the Laikipia County in central Kenya (37°53’ E, O°17’ N)."

"The most common native ungulates include impala (Aepyceros melampus, c. 20 km -2 ), Günther’s dik-dik (Madoqua guentheri c. 140 km -2 ) and elephant (Loxodonta africana c. 1.7 km -2 ), while giraffe (Giraffa camelopardalis), greater kudu (Tragelaphus strepsiceros), zebra (Equus burchellii), waterbuck (Kobus ellipsiprymnus), buffalo (Syncerus caffer) and eland (Taurotragus oryx) occur at lower densities"

"Two paired ~0.5 ha (70 x 70 m) plots were demarcated at three sites located on red sandy soils in central and southern MRC in 1999. For each pair of these plots, one was retained as a control while the other fenced to exclude herbivores. These were protected using a 3 m tall electrified fence, consisting of 11 wire strands with additional mesh and electrified wires from ground level to half a meter above ground level (Augustine and McNaughton 2004). The exclosures were designed to exclude all herbivores larger than 2 kg."

"herbivore exclusion increased soil carbon pools to at least 30 cm (~20 t ha -1 )"

"exclusion resulted in much higher woody canopy cover compared to where herbivores were present (~70% at the end of the experiment inside exclosures vs. 27% where herbivores were present)."

"we found herbivore exclusion to have no effect on soil carbon under bare soil patches. If the direct effects of herbivores (e.g., trampling, addition of carbon in dung) were strong, we would have expected these differences to be evident (i.e. higher soil C) in the bare patches where herbivores were present."

"grass cover significantly increased with herbivore exclusion, even below tree canopies, both soil carbon originating from grass litter as well as soil carbon inputs from grass roots likely increased with herbivore removal"

"Our results also suggest a facilitative role of trees on grasses in this fine-leaved semi-arid savanna"

"the fine-leaved woody species with ‘sparse open’ canopies (e.g. Acacia etbaica and A. mellifera) that dominate this semi-arid savanna did not suppress grass cover. Similar responses may not be expected in more dense, broad-leaved savannas where high woody canopy cover can result in canopy closure and the exclusion of grasses."

"While we see an overall decrease in soil and aboveground carbon with herbivory, this result may be specific to the combination of herbivore species, densities and soil nutrient status at our study site. We know from a range of other systems that herbivores can sometimes increase soil carbon because they stimulate grasses (and grass roots) to grow faster and therefore result in greater carbon sequestration (Frank et al. 1995, Derner et al. 2006). However, in this system, herbivore offtake of carbon appears to exceed any enhancement through increased herbaceous production (Sankaran & Augustine 2004; Augustine & McNaughton 2006). While our results suggest that herbivores reduce both above- and belowground carbon in this ecosystem, these carbon losses must be evaluated against the biodiversity and livelihood benefits"

sidd

kassy

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Re: Carbon Cycle
« Reply #556 on: February 15, 2020, 11:52:41 AM »
Forest soils release more carbon dioxide than expected in rainy season

Current carbon cycle models may underestimate the amount of carbon dioxide released from the soil during rainy seasons in temperate forests like those found in the northeast United States, according to Penn State researchers.

Tree roots and microbes use oxygen to convert organic carbon in the soil to carbon dioxide (CO2) for energy through a process called aerobic respiration. This release of CO2 from soils to the atmosphere represents the largest flux of carbon from terrestrial ecosystems, making it a key component of the global carbon budget. Aerobic respiration is the dominant process contributing to this flux, but the researchers found that under wet conditions, anaerobic respiration—or respiration without oxygen—also significantly contributes to the flux.

"In current models, amounts of carbon dioxide and oxygen are controlled by the consumption of oxygen and the production of carbon dioxide through aerobic respiration," said Caitlin Hodges, a doctoral candidate in the Department of Ecosystem Science and Management. "It's usually a one-to-one relationship of consumption and production. But we found that, especially in summer, there was a significant signal of anaerobic respiration caused by the roots having a higher demand for oxygen and outcompeting the microbes. The microbes then have to switch over to using anaerobic respiration."

...

The researchers also calculated the total amount of carbon dioxide—36 grams per meter squared—that leaves the soil system every year due to anaerobic respiration. They said the conservative estimate constitutes 10% of all respiration done by soil microbes at their research sites, which is a large number since scientists don't think of these humid temperate forests as posting much anaerobic respiration.

"It's expected that the northeastern United States will have increased rainfall with climate change," said Hodges. "We expect that this anaerobic respiration will become a more dominant process in these forest systems, and our soil carbon models don't yet take this into account."

https://phys.org/news/2020-02-forest-soils-carbon-dioxide-rainy.html

DOI: 10.2136/sssaj2019.02.0049
full article needs subsricption
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wili

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Re: Carbon Cycle
« Reply #557 on: February 15, 2020, 03:33:11 PM »
I'm confused--How could ANaerobic respiration (without access to oxygen) create more CO2 (which is, of course, 2 parts oxygen) than aerobic respiration, which has access to lots of oxygen.

Do they mean that, since the anaerobic process creates methane, the CO2equivalent is much higher in rainy season? If so, the headline (at least) is misleading.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

kassy

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Re: Carbon Cycle
« Reply #558 on: February 16, 2020, 12:54:12 AM »
The processes work together. Under certain conditions the soil microbes switch to anaerobic respiration so you get the normal aerobic version and extra CO2 from the other process.

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Florifulgurator

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Re: Carbon Cycle
« Reply #559 on: February 16, 2020, 02:35:41 AM »
Aerobic methanotrophs in upper soil can transform the methane from deeper soil into CO2. It all depends how fast the methane diffuses upward. E.g. thawing permafrost covered with soil emits less methane than thermokarst lakes where the methane bubbles out into the atmosphere. Soil microbiology is quite a tangled web.
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