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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 17, issue 1
Atmos. Chem. Phys., 17, 47–76, 2017
https://doi.org/10.5194/acp-17-47-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 17, 47–76, 2017
https://doi.org/10.5194/acp-17-47-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 02 Jan 2017

Research article | 02 Jan 2017

Atmospheric CO2 observations and models suggest strong carbon uptake by forests in New Zealand

Kay Steinkamp1, Sara E. Mikaloff Fletcher1, Gordon Brailsford1, Dan Smale1, Stuart Moore1, Elizabeth D. Keller2, W. Troy Baisden2, Hitoshi Mukai3, and Britton B. Stephens4 Kay Steinkamp et al.
  • 1National Institute of Water and Atmospheric Research, Wellington, New Zealand
  • 2GNS Science, Lower Hutt, New Zealand
  • 3National Institute for Environmental Studies, Tsukuba, Ibaraki, Japan
  • 4National Center for Atmospheric Research, Boulder, Colorado, USA

Abstract. A regional atmospheric inversion method has been developed to determine the spatial and temporal distribution of CO2 sinks and sources across New Zealand for 2011–2013. This approach infers net air–sea and air–land CO2 fluxes from measurement records, using back-trajectory simulations from the Numerical Atmospheric dispersion Modelling Environment (NAME) Lagrangian dispersion model, driven by meteorology from the New Zealand Limited Area Model (NZLAM) weather prediction model. The inversion uses in situ measurements from two fixed sites, Baring Head on the southern tip of New Zealand's North Island (41.408° S, 174.871° E) and Lauder from the central South Island (45.038° S, 169.684° E), and ship board data from monthly cruises between Japan, New Zealand, and Australia. A range of scenarios is used to assess the sensitivity of the inversion method to underlying assumptions and to ensure robustness of the results. The results indicate a strong seasonal cycle in terrestrial land fluxes from the South Island of New Zealand, especially in western regions covered by indigenous forest, suggesting higher photosynthetic and respiratory activity than is evident in the current a priori land process model. On the annual scale, the terrestrial biosphere in New Zealand is estimated to be a net CO2 sink, removing 98 (±37) Tg CO2 yr−1 from the atmosphere on average during 2011–2013. This sink is much larger than the reported 27 Tg CO2 yr−1 from the national inventory for the same time period. The difference can be partially reconciled when factors related to forest and agricultural management and exports, fossil fuel emission estimates, hydrologic fluxes, and soil carbon change are considered, but some differences are likely to remain. Baseline uncertainty, model transport uncertainty, and limited sensitivity to the northern half of the North Island are the main contributors to flux uncertainty.

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The exchange of carbon dioxide between the land biosphere in New Zealand and the atmosphere is estimated by combining measurements of the concentration of the gas in the air with model simulations of atmospheric circulation. The results indicate that over the study period of 2011–2013, New Zealand is a larger net sink for CO2 than estimated in the National Inventory Report. Regions in the western South Island, especially those covered predominantly by forests, contribute the most to this signal.
The exchange of carbon dioxide between the land biosphere in New Zealand and the atmosphere is...
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