Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Niño

Welp, L. R.; Keeling, Ralph F.; Meijer, H. A. J.; Bollenbacher, Alane F.; Piper, Stephen C.; Yoshimura, Kei; Francey, R. J.; Allison, C. E.; Wahlen, Mannheim Forschungsgruppe

doi:10.1038/nature10421

Cited by 237 publications

(279 citation statements)

References 26 publications

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“…The small fractional changes in global total GPP translate to a large influence on seasonal cycle metrics as the seasonal cycle is driven by a small difference between several large opposing fluxes. Our modeling framework allows us to make a clean evaluation of adding the daylength correction mechanism, despite large observational uncertainty in the magnitude of the gross fluxes (20,21).…”

Section: Resultsmentioning

confidence: 99%

Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling

Bauerle

Oren²,

Way³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

271

214

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Although temperature is an important driver of seasonal changes in photosynthetic physiology, photoperiod also regulates leaf activity. Climate change will extend growing seasons if temperature cues predominate, but photoperiod-controlled species will show limited responsiveness to warming. We show that photoperiod explains more seasonal variation in photosynthetic activity across 23 tree species than temperature. Although leaves remain green, photosynthetic capacity peaks just after summer solstice and declines with decreasing photoperiod, before air temperatures peak. In support of these findings, saplings grown at constant temperature but exposed to an extended photoperiod maintained high photosynthetic capacity, but photosynthetic activity declined in saplings experiencing a naturally shortening photoperiod; leaves remained equally green in both treatments. Incorporating a photoperiodic correction of photosynthetic physiology into a global-scale terrestrial carbon-cycle model significantly improves predictions of seasonal atmospheric CO 2 cycling, demonstrating the benefit of such a function in coupled climate system models. Accounting for photoperiod-induced seasonality in photosynthetic parameters reduces modeled global gross primary production 2.5% (∼4 PgC y −1 ), resulting in a >3% (∼2 PgC y −1 ) decrease of net primary production. Such a correction is also needed in models estimating current carbon uptake based on remotely sensed greenness. Photoperiod-associated declines in photosynthetic capacity could limit autumn carbon gain in forests, even if warming delays leaf senescence.day length | gross primary productivity | carbon sequestration | leaf area index | evapotranspiration W arming over the past 50 y has lengthened temperate growing seasons by 3.6 d per decade (1, 2). Longer growing seasons may increase net ecosystem productivity (2, 3), but increased spring carbon uptake has been accompanied by reduced autumn carbon uptake (2, 4). In extratropical ecosystems, where spring temperature is a major control on bud break, increased carbon sink strength has been linked to warmer April and May temperatures (3, 4), although drought can offset the increase in carbon uptake (5). The autumn switch from being a carbon sink to a carbon source in these ecosystems has been attributed to higher autumn temperatures, which are assumed to maintain high photosynthetic rates but even higher respiration rates (6). However, it is well known that leaf phenology responds to photoperiod, as well as temperature (7). Seasonal fluctuations in photosynthetic parameters are often modeled with temperature (8). However, photosynthetic physiology has also been shown to respond to photoperiod in controlled studies; instituting a short-day treatment in the fall, but maintaining high summer growth temperatures, inhibited the photosynthetic capacity of Pinus banksiana seedlings (9, 10). Seasonal measurements of photosynthetic capacity in trees under naturally changing photoperiod and air temperature signals are needed to ascertain whe...

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Section: Resultsmentioning

confidence: 99%

Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling

Bauerle

Oren²,

Way³

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

271

214

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“…For example, Welp et al (2011) provided a best guess of 150-175 PgC yr −1 and Koffi et al (2012) an estimate of 146 ± 19 PgC yr −1 . However, the estimate by Jung et al (2011) is based on the largest set of observations and also provides a spatial distribution of GPP.…”

Section: Evaluation Of the Present-day Carbon Cyclementioning

confidence: 99%

The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 2: Historical simulations

et al. 2017

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Abstract. Over the last decade many climate models have evolved into Earth system models (ESMs), which are able to simulate both physical and biogeochemical processes through the inclusion of additional components such as the carbon cycle. The Australian Community Climate and Earth System Simulator (ACCESS) has been recently extended to include land and ocean carbon cycle components in its ACCESS-ESM1 version. A detailed description of ACCESS-ESM1 components including results from pre-industrial simulations is provided in Part 1. Here, we focus on the evaluation of ACCESS-ESM1 over the historical period in terms of its capability to reproduce climate and carbon-related variables. Comparisons are performed with observations, if available, but also with other ESMs to highlight common weaknesses. We find that climate variables controlling the exchange of carbon are well reproduced. However, the aerosol forcing in ACCESS-ESM1 is somewhat larger than in other models, which leads to an overly strong cooling response in the land from about 1960 onwards. The land carbon cycle is evaluated for two scenarios: running with a prescribed leaf area index (LAI) and running with a prognostic LAI. We overestimate the seasonal mean (1.7 vs. 1.4) and peak amplitude (2.0 vs. 1.8) of the prognostic LAI at the global scale, which is common amongst CMIP5 ESMs. However, the prognostic LAI is our preferred choice, because it allows for the vegetation feedback through the coupling between LAI and the leaf carbon pool. Our globally integrated land-atmosphere flux over the historical period is 98 PgC for prescribed LAI and 137 PgC for prognostic LAI, which is in line with estimates of land use emissions (ACCESS-ESM1 does not include land use change).The integrated ocean-atmosphere flux is 83 PgC, which is in agreement with a recent estimate of 82 PgC from the Global Carbon Project for the period 1959-2005. The seasonal cycle of simulated atmospheric CO 2 is close to the observed seasonal cycle (up to 1 ppm difference for the station at Mace Head and up to 2 ppm for the station at Mauna Loa), but shows a larger amplitude (up to 6 ppm) in the high northern latitudes. Overall, ACCESS-ESM1 performs well over the historical period, making it a useful tool to explore the change in land and oceanic carbon uptake in the future.

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“…These tree-ring isotope studies show that ENSO affects interannual variation in plant δ 18 O over large areas in the tropics. As the tropics are also regions with very high net primary productivity, this pan-tropically coherent ENSO signal in plant water δ 18 O is passed on to oxygen isotope ratios in atmospheric CO 2 through biosphere-atmosphere gas exchange, and leads to higher δ 18 O in atmospheric CO 2 several months after El Niño's occurred (42). In all, our results confirm the potential of tree ring δ 18 O to elucidate historical influences of ENSO on precipitation in the tropics.…”

Section: Large-scale Drivers Of Interannual To Decadal Variation In Tmentioning

confidence: 99%

Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Niño-Southern Oscillation variability

Brienen

Helle

Pons

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

175

145

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We present a unique proxy for the reconstruction of variation in precipitation over the Amazon: oxygen isotope ratios in annual rings in tropical cedar (Cedrela odorata). A century-long record from northern Bolivia shows that tree rings preserve the signal of oxygen isotopes in precipitation during the wet season, with weaker influences of temperature and vapor pressure. Tree ring δ 18 O correlates strongly with δ 18 O in precipitation from distant stations in the center and west of the basin, and with Andean ice core δ 18 O showing that the signal is coherent over large areas. The signal correlates most strongly with basin-wide precipitation and Amazon river discharge. We attribute the strength of this (negative) correlation mainly to the cumulative rainout processes of oxygen isotopes (Rayleigh distillation) in air parcels during westward transport across the basin. We further find a clear signature of the El Niño-Southern Oscillation (ENSO) in the record, with strong ENSO influences over recent decades, but weaker influence from 1925 to 1975 indicating decadal scale variation in the controls on the hydrological cycle. The record exhibits a significant increase in δ 18 O over the 20th century consistent with increases in Andean δ 18 O ice core and lake records, which we tentatively attribute to increased water vapor transport into the basin. Taking these data together, our record reveals a fresh path to diagnose and improve our understanding of variation and trends of the hydrological cycle of the world's largest river catchment.climate change | dendrochronology | plant physiology T he Amazon basin is a major center of atmospheric convection and precipitation (1), and at the same time the world's largest drainage basin. The Amazon's river discharge accounts for ∼17% of the annual global discharge to the oceans (2); its hydrological cycle is tightly linked with the carbon cycle of the Amazon rainforest (3), which itself is one of the largest terrestrial biomass carbon pools. Changes in the hydrological cycle of the Amazon may therefore significantly affect atmospheric dynamics and global climate by changing atmospheric CO 2 concentration. Two particularly severe droughts occurred within the last decade (4), and long-term river records of the Amazon show a steady increase in discharge over the last century (5), indicating that the system may start to undergo some changes. It has been suggested that these changes are a result of anthropogenic warming, but they may also be part of longer-term, natural climatic variability. To clarify such a globally important issue, long-term, accurate records of the hydrological cycle of the Amazon basin are needed. However, meteorological data are only reliable for the last 50-60 y (6), and annually resolved long-term proxies for the hydrological cycle from within the Amazon basin itself are very scarce (7).A commonly used diagnostic for strength and functioning of the water cycle is the isotopic composition of precipitation. Although variation of oxygen isotope ratios in precip...

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Interannual variability in the oxygen isotopes of atmospheric CO2 driven by El Niño

Cited by 237 publications

References 26 publications

Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling

Photoperiodic regulation of the seasonal pattern of photosynthetic capacity and the implications for carbon cycling

The carbon cycle in the Australian Community Climate and Earth System Simulator (ACCESS-ESM1) – Part 2: Historical simulations

Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Niño-Southern Oscillation variability

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