Higher climatological temperature sensitivity of soil carbon in cold than warm climates

Koven, Charles D.; Hugelius, Gustaf; Lawrence, David M.; Wieder, William R.

doi:10.1038/nclimate3421

Cited by 241 publications

(266 citation statements)

References 44 publications

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“…Overall this suggests that the DOC SR pool has higher activation energies and temperature dependence than the DOC L and DOC SL pools. A recent study demonstrated that in soils the Q 10 values scales inversely with temperature, with low temperature environments having a higher Q 10 than warmer ones (Koven et al, 2017). In a similar way we find that DOC SR , mostly present in the deep ocean with lower temperatures, has a higher Q 10 of ∼3-4, while DOC SL , with higher concentrations in warmer mesopelagic waters, has a lower Q 10 of ∼1.8-2.…”

Section: Discussionsupporting

confidence: 68%

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

et al. 2018

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More than 96% of organic carbon in the ocean is in the dissolved form, most of it with lifetimes of decades to millennia. Yet, we know very little about the temperature sensitivity of dissolved organic carbon (DOC) degradation in a warming ocean. Combining independent estimates from laboratory experiments, oceanographic cruises and a global ocean DOC cycling model, we assess the relationship between DOC decay constants and seawater temperatures. Our results show that the apparent activation energy of DOC decay (E a ) increases by three-fold from the labile (lifetime of days) and semi-labile (lifetime of months) to the semi-refractory (lifetime of decades) DOC pools, with only minor differences between the world's largest ocean basins. This translates into increasing temperature coefficients (Q 10 ) from 1.7-1.8 to 4-8, showing that the generalized assumption of a constant Q 10 of ∼2 for biological rates is not universally applicable for the microbial degradation of DOC in the ocean. Therefore, rising ocean temperatures will preferentially impact the microbial degradation of the more recalcitrant and larger of the three studied pools. Assuming a uniform 1 • C warming scenario throughout the ocean, our model predicts a global decrease of the DOC reservoir by 7 ± 1 Pg C. This represents a 15% reduction of the semi-labile + semi-refractory DOC pools.

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Section: Discussionsupporting

confidence: 68%

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

et al. 2018

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“…Reducing these biases would largely improve the accuracy of ESMs in the projection of future terrestrial C cycle and its feedback to climate change. Recent modelling activities aiming to 10 increase the soil heterogeneity, e.g., soil vertical profile (Koven et al, 2013(Koven et al, , 2017 and microbial dynamics (Allison et al, 2010, Wieder et al, 2013, are promising. Overall, this study shows the great spatial variation of τsoil in the natural ecosystems, and we recommend more research efforts to improve its representation by ESMs in the future.…”

Section: Resultsmentioning

confidence: 99%

“…This large uncertainty is difficult to be reduced or even diagnosed 5 because many processes collectively affect the time of C atoms transit the soil system (i.e., transit time; τsoil) (Sierra et al, 2016, Spohn and. Some recent attempts at evaluating and diagnosing the modeled SOC in ESMs have shown significant simulation uncertainties in the τsoil (Todd-Brown et al, 2013, Carvalhais et al, 2014, He et al, 2016, Koven et al, 2017. For example, there is a fourfold difference in the simulated τsoil among the ESMs from the 5 th phase of Coupled Model Intercomparison Project (CMIP5) (Todd-Brown et al, 2013).…”

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confidence: 99%

“…A recent data-driven 10 analysis has suggested that the current ESMs have substantially underestimated the τsoil by 16-17 times at the global scale (He et al, 2016). Therefore, identifying the locations of such underestimations is critical to improve the predictive ability of ESMs on terrestrial C cycle, and the construction of a benchmarking database based on available observations becomes urgently needed (Koven et al, 2017).…”

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confidence: 99%

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Evaluating the simulated mean soil carbon transit times by Earth system models using observations

Wang¹,

Xia²,

Zhou³

et al. 2018

Preprint

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Abstract.One known bias in current Earth system models (ESMs) is the underestimation of global mean soil carbon (C) transit time (τsoil), which quantifies the mean age of the C atoms at the time they leave the soil. However, it remains unclear where such underestimations are located globally. Here, we constructed a global database of measured τsoil across 187 sites to evaluated results from twelve ESMs. The observations showed that the estimated τsoi was 20 dramatically shorter from the soil incubations studies in the laboratory environment (median as 4 with the interquartile range of 1-25 years) than that derived from field in-situ measurements (31 with 5-84 years) with the shifts of stable isotopic C ( 13 C) or the stock-over-flux approach. In comparison with the field observations, the multi-model ensemble simulated a shorter median (19 years) and a smaller spatial variation (interquartile range of 6-28 years) of τsoil across the same site locations. We then found a significant and negative linear correlation between the in-situ measured τsoil 25 and mean annual air temperature, and the underestimations of modeled τsoil are mainly located in cold and dry biomes especially tundra and desert. Furthermore, we showed that one ESM (i.e., CESM) has improved its τsoil estimate by incorporation of the soil vertical profile. These findings indicate that the spatial variation of τsoil is a useful benchmark for ESMs, and we recommend more observation and modeling efforts on soil C dynamics in hydrothermal limited regions. 30

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“…For example, thaw and release of permafrost C is not represented in CARDAMOM, but the influence on vegetation dynamics, permafrost degradation and soil respiration 400 is critical in high latitudes (Koven et al, 2015b;Parazoo et al, 2018). Also, Koven et al (2017) shown that soil thermal regimes are key to getting the long-term vulnerability of soil C right. Moreover, we have not characterized snow dynamics and the insulating effect of snow affecting respiratory losses across wintertime periods either (Essery, 2015).…”

Section: Discussionmentioning

confidence: 99%

Evaluation of terrestrial pan-Arctic carbon cycling using a data-assimilation system

López‐Blanco

Exbrayat

Lund

et al. 2018

Preprint

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Abstract. There is a significant knowledge gap in the current state of the terrestrial carbon (C) budget. The Arctic accounts 15 for approximately 50% of the global soil organic C stock, emphasizing the important role of Arctic regions in the global C cycle. Recent studies have pointed to the poor understanding of C pools turnover, although remain unclear as to whether productivity or biomass dominate the biases. Here, we use an improved version of the CARDAMOM data-assimilation system, to produce pan-Arctic terrestrial C-related variables without using traditional plant functional type or steady-state assumptions.Our approach integrates a range of data (soil organic C, leaf area index, biomass, and climate) to determine the most likely 20 state of the high latitude C cycle at a 1° x 1° resolution for the first 15 years of the 21 st century, but also to provide general guidance about the controlling biases in the turnover dynamics. As average, CARDAMOM estimates 513 (456, 579), 245(208, 290) and 204 (109, 427) g C m -2 yr -1 (90% confidence interval) from photosynthesis, autotrophic and heterotrophic respiration respectively, suggesting that the pan-Arctic region acted as a likely sink -55 (-152, 157) g C m -2 yr -1 , weaker in tundra and stronger in taiga, but our confidence intervals remain large (and so the region could be a source of C). In general, 25we find a good agreement between CARDAMOM and different sources of assimilated and independent data at both pan-Arctic and local scale. Using CARDAMOM as a benchmarking tool for global vegetation models (GVM), we also conclude that turnover time of vegetation C is weakly simulated in vegetation models and is a major component of error in their forecasts.Our findings highlight that GVM modellers need to focus on the vegetation C stocks dynamics, but also their respiratory losses, to improve our process-based understanding of internal C cycle dynamics in the Arctic. 30Earth Syst. Dynam. Discuss., https://doi

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Higher climatological temperature sensitivity of soil carbon in cold than warm climates

Cited by 241 publications

References 44 publications

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

Large Stimulation of Recalcitrant Dissolved Organic Carbon Degradation by Increasing Ocean Temperatures

Evaluating the simulated mean soil carbon transit times by Earth system models using observations

Evaluation of terrestrial pan-Arctic carbon cycling using a data-assimilation system

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