Daily Archives: August 13, 2019

Carbon dioxide and nitrogen drive greening of the earth

Michael O’Sullivan, Dominick V. Spracklen, Sarah A. Batterman, Steve R. Arnold, Manuel Gloor, Wolfgang Buermann. Have Synergies Between Nitrogen Deposition and Atmospheric CO2 Driven the Recent Enhancement of the Terrestrial Carbon Sink? Global Biogeochemical Cycles, Volume 33, Issue 2. https://doi.org/10.1029/2018GB005922

The terrestrial carbon sink has increased since the turn of this century at a time of increased fossil fuel burning, yet the mechanisms enhancing this sink are not fully understood. Here we assess the hypothesis that regional increases in nitrogen deposition since the early 2000s has alleviated nitrogen limitation and worked in tandem with enhanced CO2 fertilization to increase ecosystem productivity and carbon sequestration, providing a causal link between the parallel increases in emissions and the global land carbon sink. We use the Community Land Model (CLM4.5‐BGC) to estimate the influence of changes in atmospheric CO2, nitrogen deposition, climate, and their interactions to changes in net primary production and net biome production. We focus on two periods, 1901–2016 and 1990–2016, to estimate changes in land carbon fluxes relative to historical and contemporary baselines, respectively. We find that over the historical period, nitrogen deposition (14%) and carbon‐nitrogen synergy (14%) were significant contributors to the current terrestrial carbon sink, suggesting that long‐term increases in nitrogen deposition led to a substantial increase in CO2 fertilization. However, relative to the contemporary baseline, changes in nitrogen deposition and carbon‐nitrogen synergy had no substantial contribution to the 21st century increase in global carbon uptake. Nonetheless, we find that increased nitrogen deposition in East Asia since the early 1990s contributed 50% to the overall increase in net biome production over this region, highlighting the importance of carbon‐nitrogen interactions. Therefore, potential large‐scale changes in nitrogen deposition could have a significant impact on terrestrial carbon cycling and future climate.

Solar activity, atmospheric-oceanic variability drives temperatures

LIANG JIAO, SHENGJIE WANG, YUAN JIANG, XUERUI LIU. A 333-YEAR RECORD OF THE MEAN MINIMUM TEMPERATURE RECONSTRUCTION IN THE WESTERN TIANSHAN MOUNTAINS, CHINA. GEOCHRONOMETRIA 46 (2019): 37–48 DOI 10.1515/geochr-2015-0104

 

In this paper, a fragile ecological area in the Western Tianshan National Nature Reserve of China was selected as the research region, and Picea schrenkiana, which is sensitive to climate change, was selected as the research object. The mean minimum temperature in the growing season of the previous year (May to September) was the main limiting factor for tree radial growth based on an analysis of the relationship between chronological series and climatic factors during 1959–2012 (r = –0.792, p < 0.05). Moreover, the relationship was stable, which showed that tree rings can be used as alternative materials for climate reconstruction. Therefore, the mean minimum temperature of the previous year in 1680–2012 was reconstructed, and the explained variance of the reconstruction equation was 62.7% (R2adj = 62.0%, F = 85.8). The 31 dramatically altered years were found via char- acteristic year analyses, and extreme changes occurred most often under relatively warm conditions. The mean minimum temperature in the reconstruction shows a clear warming trend by the 11-year moving average of the reconstructive series since the 1950s (the temperature increase: 0.341°C/decade). The driving factors of the mean minimum temperature were influenced mainly by the interaction of solar activity and large-scale atmospheric–oceanic variability, especially the westerly circulations.