Compiled records of carbon isotopes in atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; for historical simulations in CMIP6

Graven, Heather; Allison, C. E.; Etheridge, D. M.; Hammer, Samuel; Keeling, Ralph F.; Levin, Ingeborg; Meijer, H. A. J.; Rubino, Mauro; Tans, Pieter P.; Trudinger, Cathy M.; Vaughn, Bruce H.; White, James W. C.

doi:10.5194/gmd-10-4405-2017

Cited by 185 publications

(221 citation statements)

References 84 publications

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“…The δ 13 C a was obtained from Graven et al. (). Second, the iWUE, that is the ratio between photosynthesis ( A ) and stomatal conductance rates ( g ), was computed following Farquhar et al.…”

Section: Methodsmentioning

confidence: 99%

Recent decadal drought reverts warming‐triggered growth enhancement in contrasting climates in the southern Andes tree line

Fajardo

Gazol

Mayr

et al. 2019

Journal of Biogeography

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Aims Rising temperature and declining summer precipitation due to the 1970s‐climate shift in southern South America have reduced forest productivity at dry sites. Here, we worked with the most widespread Southern Hemisphere tree line species, Nothofagus pumilio, across contrasting climatic conditions and determined whether rising atmospheric CO2 concentrations as well as warmer and drier climatic conditions provoked by the 70s‐climatic shift have been causing systematic changes in tree line growth rates and intrinsic water‐use efficiency (iWUE). Location 36–54°S, southern Andes. Time period 1950–2010. Major taxa studied Nothofagus pumilio. Methods We worked at five disparate climatic tree line locations, spanning 18 degrees of latitude; at each location, we sampled trees at four different elevations, including tree line elevation. We quantified the variation in annual tree‐ring width (TRW) as a function of climate, elevation, tree age, size, annual CO2 concentrations and location, using linear mixed‐effects models and interpreted TRW trends in relation to iWUE and isotope (δ13C and δ18O) signalling. Results Across locations, the patterns of tree line growth occurring in the 1980–2010 period exhibited a clear and significant negative trend, in contrast to the previous 1950–1980 period. We found an increase in iWUE and δ18O across time and locations. Given that an increase in δ18O indicates a decrease in stomatal conductance, we assert that drought‐induced stomatal closure appears to be causing the reduction in growth. Main conclusions We show unequivocal evidence that warmer and drier summer conditions translated into a decrease in growth rates along the elevational tree line of the southern Andes, reverting previous growth improvements linked to climate warming. An improvement in iWUE at all locations is most likely explained by decreased stomatal conductance given the rising δ18O signal. An iWUE–growth decoupling may act as an ecological strategy to respond to drought.

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Section: Methodsmentioning

confidence: 99%

Recent decadal drought reverts warming‐triggered growth enhancement in contrasting climates in the southern Andes tree line

Fajardo

Gazol

Mayr

et al. 2019

Journal of Biogeography

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“…The Δ 14 C of biogenic CH 4 emissions, Δ b , for recently assimilated organic material that is the substrate for CH 4 from livestock, rice paddies, and landfills will be similar to atmospheric Δ 14 CO 2 , approximately 20‰ in 2014 (Graven et al, ). For CH 4 produced from older organic material Δ b may be higher or lower, depending on the age of the organic material (Chanton et al, ; Garnett et al, ; Nakagawa et al, ).…”

Section: Approach For Estimating Biogenic and Fossil Ch4 From δ14ch4mentioning

confidence: 99%

Detection of Fossil and Biogenic Methane at Regional Scales Using Atmospheric Radiocarbon

2019

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Regional emissions of methane and their attribution to a variety of sources presently have large uncertainties. Measurements of radiocarbon ( 14 C) in methane (CH 4 ) may provide a method for identifying regional CH 4 emissions from fossil versus biogenic sources because adding 14 C‐free fossil carbon reduces the 14 C/C ratio (Δ 14 CH 4 ) in atmospheric CH 4 much more than biogenic carbon does. We describe an approach for estimating fossil and biogenic CH 4 at regional scales using atmospheric Δ 14 CH 4 observations. As a case study to demonstrate expected Δ 14 CH 4 and Δ 14 CH 4 ‐CH 4 relationships, we simulate and compare Δ 14 CH 4 at a network of sites in California using two gridded CH 4 emissions estimates (Emissions Database for Global Atmospheric Research, EDGAR, and Gridded Environmental Protection Agency, GEPA) and the CarbonTracker‐Lagrange model for 2014, and for 2030 under business‐as‐usual and mitigation scenarios. The fossil fraction of CH 4 (F) is closely linked with the simulated Δ 14 CH 4 ‐CH 4 slope and differences of 2–21% in median F are found for EDGAR versus GEPA in 2014, and 7–10% for business‐as‐usual and mitigation scenarios in 2030. Differences of 10% in F for >200 ppb of added CH 4 produce differences of >10‰ in Δ 14 CH 4 , which are likely detectable from regular observations. Nuclear power plant 14 CH 4 emissions generally have small simulated median influences on Δ 14 CH 4 (0–7‰), but under certain atmospheric conditions they can be much stronger (>30‰) suggesting they must be considered in applications of Δ 14 CH 4 in California. This study suggests that atmospheric Δ 14 CH 4 measurements could provide powerful constraints on regional CH 4 emissions, complementary to other monitoring techniques.

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“…The ‘Suess Effect’, describing a dilution in the proportion of isotopes 14 C and 13 C relative to 12 C in atmospheric CO 2 by the addition of aged, plant‐derived carbon that is depleted in 13 C and 14 C (Graven et al, ), should contribute to a depletion in SOM δ 13 C over time in all ecosystems. In KKB, we capture a depletion from 0 to –10‰ in mean δ 13 C of primary producers and OM pools in 2018 relative to KKB sampled two decades ago (Figure a; Thimdee et al , , ).…”

Section: Discussionmentioning

confidence: 99%

“…In KKB, we capture a depletion from 0 to –10‰ in mean δ 13 C of primary producers and OM pools in 2018 relative to KKB sampled two decades ago (Figure a; Thimdee et al , , ). The Suess Effect process has accelerated over the past three decades and we estimate that from the initial KKB isotopic study in 1998 to our collection of materials in 2018 this resulted in an atmospheric depletion of δ 13 C by ~0.6‰ (Graven et al, ). Therefore, the Suess Effect accounts for some but not all the 13 C depletion in KKB.…”

Section: Discussionmentioning

confidence: 99%

Understanding the fate of shrimp aquaculture effluent in a mangrove ecosystem: Aiding management for coastal conservation

Hargan

Williams

Nuangsaeng

et al. 2020

Journal of Applied Ecology

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Areas dedicated to shrimp aquaculture have increased dramatically over the last 50 years. Resultant land‐use changes directly threaten the extent of mangroves and yield conflicts on the discharge location of aquaculture effluent. Khung Krabaen Bay (KBB), Thailand, is reforesting mangroves while increasing the efficiency of shrimp aquaculture for local farmers. In this coupled shrimp farm–mangrove system, effective management requires understanding the fate of aquaculture organic matter (OM) in the coastal environment. We examined carbon and nitrogen stable isotope ratios (δ13C, δ15N) in primary producers and pools of particulate and sediment OM (POM, SOM) from the KKB mangrove and marine ecosystem to determine how shrimp aquaculture OM contributes to the coastal environment. Here, soy‐based shrimp feed resulted in low shrimp δ15N, similar to marine POM, and thus we focus on the use of δ13C in tracking shrimp pond effluent in the environment. δ13C signatures of SOM varied significantly along a land‐to‐ocean gradient (–29.1‰ to –23.9‰). We found consistently depleted mangrove SOM δ13C signatures (–29.4‰ to –28.2‰) indicating that mangrove leaf litter is the primary source of OM to mangrove sediments, and there is little evidence that marine and shrimp pond OM contributes to the mangrove habitat. In contrast, relatively low δ13C values for marine SOM (–25.7‰ to –23.9‰) overlap with the δ13C of shrimp feed (–25.3‰) and Bayesian mixing models indicate that shrimp aquaculture feed and mangrove vegetation contribute the greatest OM to the marine ecosystem. Compared to 20 years ago, marine SOM δ13C signatures are depleted by ~10‰ and similar throughout KKB, indicating a homogenization of marine SOM carbon sources from 1998 to 2018. Synthesis and applications. The doubling of shrimp aquaculture in Khung Krabaen Bay (KKB) since 1998 led to increased discharge to the bay, swamping organic matter (OM) contributions from 13C‐enriched seagrasses and marine plankton. Because of this increase in effluent release to KKB, the chemical impact is likely to be greater for the marine ecosystem than the mangrove and should also be a focus of conservation efforts. Continued technological improvements (e.g. closed systems, better feed efficiency) and support to local aquaculture farmers will help reduce OM discharge to coastal ecosystems and promote sustainable farming practices.

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Compiled records of carbon isotopes in atmospheric CO<sub>2</sub> for historical simulations in CMIP6

Cited by 185 publications

References 84 publications

Recent decadal drought reverts warming‐triggered growth enhancement in contrasting climates in the southern Andes tree line

Recent decadal drought reverts warming‐triggered growth enhancement in contrasting climates in the southern Andes tree line

Detection of Fossil and Biogenic Methane at Regional Scales Using Atmospheric Radiocarbon

Understanding the fate of shrimp aquaculture effluent in a mangrove ecosystem: Aiding management for coastal conservation

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