Temporal variations in atmospheric CO2 on Rishiri Island in 2006–2013: responses of the interannual variation in amplitude to climate and the terrestrial sink in East Asia
C. Zhu1,* and H. Yoshikawa-Inoue21Graduate School of Environmental Science, Hokkaido University, Sapporo, 060-0810, Japan 2Faculty of Environmental Earth Science, Hokkaido University, Sapporo, 060-0810, Japan *now at: Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan
Received: 30 May 2014 – Accepted for review: 19 Jun 2014 – Discussion started: 27 Jun 2014
Abstract. Surface observation of the atmospheric CO2 mixing ratio implies the combined influences of both natural fluctuations and anthropogenic activities on the carbon cycle. Atmospheric CO2 has been measured on Rishiri Island in the outflow region of Eurasia since May 2006. We report the first 7 year temporal atmospheric CO2 variations from diurnal to interannual scales. In the diurnal scale, an obvious cycle appeared as a minimum in the afternoon and maximum at midnight in the summer months. Seasonally, the maximum CO2 concentration appeared around the beginning of April, while the minimum appeared around the middle of August. A mean growing season length of ~126 days was estimated. In the period from 2007 to 2012, the peak-to-peak amplitude increased until 2009 and decreased thereafter, with a mean value of 19.7 ppm. In the long term, atmospheric CO2 is increasing by a mean growth rate of 2.1 ppm year−1. Investigations on the driving climatic factors on the interannual variation in amplitude indicated that temperature in East Asia (40–60° N, 90–150° E) affected the CO2 amplitude by affecting the seasonal maximum, with a time lag of 1–2 years. On the contrary, precipitation did not likely affect CO2 amplitudes. The amplitude also responded to a natural carbon source/sink variation in East Asia. We suggest that temperature in the first year would affect carbon sinks in the second year in the fetch regions, which further affect CO2 amplitude mainly through ecosystem respiration. Circulation changes also likely contributed to the decreasing amplitude since 2009, as indicated by the simultaneous decrease in the 222Rn concentration in spring and summer.
Zhu, C. and Yoshikawa-Inoue, H.: Temporal variations in atmospheric CO2 on Rishiri Island in 2006–2013: responses of the interannual variation in amplitude to climate and the terrestrial sink in East Asia, Earth Syst. Dynam. Discuss., 5, 809-848, doi:10.5194/esdd-5-809-2014, 2014.