Preprints
https://doi.org/10.5194/bg-2016-233
https://doi.org/10.5194/bg-2016-233
06 Jun 2016
 | 06 Jun 2016
Status: this preprint has been retracted.

Large uncertainty in ecosystem carbon dynamics resulting from ambiguous numerical coupling of carbon and nitrogen biogeochemistry: A demonstration with the ACME land model

Jinyun Tang and William J. Riley

Abstract. Most Earth System Models (ESMs) have incorporated, or are incorporating, coupled carbon and nutrient dynamics in their land modules. We show here that different numerical implementations of nutrient controls may imply different ecological mechanisms not recognized in the original model design and can have first order impacts on predicted terrestrial carbon cycling. Using ALM, the land module of the DOE ESM (ACME), we analysed land-atmosphere CO2 exchange with coupled carbon and nitrogen dynamics through three commonly-applied numerical implementations of nitrogen limitation: (1) Mineral Nitrogen based Limitation (MNL), (2) Net nitrogen Uptake based Limitation (NUL), and (3) Proportional Nitrogen flux based Limitation (PNL). By the last decade of the contemporary period (1850–2000), the three schemes resulted in very similar global terrestrial carbon and nitrogen distributions. However, under an RCP4.5 CO2 concentration forcing, the implementations resulted in wildly diverging 2001–2300 land-atmosphere CO2 exchanges. Quantitatively, the divergence is as large as that of the CMIP5 models by 2100 and is about 1900 Pg C (~ 890 ppmv) by 2300. Our analysis suggests that these differences result from: (1) the typically high predicted terrestrial ecosystem carbon to nitrogen ratios (i.e., nutrient constrained conditions) and (2) the schemes predict different levels of nitrogen limitation to the carbon cycle, so that the PNL scheme leads to larger nitrogen loss through aerobic and anaerobic denitrification and surface and subsurface hydrological transport. We also found significant sensitivity of model predictions to initial conditions and numerical time step size but insignificant sensitivity to the sequence of numerical oxygen and nitrogen limitation or the ordering of reaction and chemical transport. We conclude that inconsistencies in imposing nutrient limitations will very likely lead to large uncertainties in predicted carbon stocks and long-term carbon-climate feedbacks. Finally, we recommend approaches to systematically alleviate these uncertainties.

This preprint has been retracted.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Jinyun Tang and William J. Riley

Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement
Jinyun Tang and William J. Riley
Jinyun Tang and William J. Riley

Viewed

Total article views: 1,204 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
802 312 90 1,204 204 70 96
  • HTML: 802
  • PDF: 312
  • XML: 90
  • Total: 1,204
  • Supplement: 204
  • BibTeX: 70
  • EndNote: 96
Views and downloads (calculated since 06 Jun 2016)
Cumulative views and downloads (calculated since 06 Jun 2016)

Cited

Latest update: 11 Oct 2024
Download

This preprint has been retracted.

Altmetrics