2 fluxes and spatial distribution of seawater pCO 2 in Yongle Atoll, northern-central South China Sea]]>

摘要

Yongle Atoll is a complex atoll composed of 13 separated small atolls/reefs in the Xisha Islands, northern-central South China Sea. Wide, deep channels connect the Yongle Atoll lagoon with the open ocean. The sea surface partial pressure of CO2(pCO2) and sea–air CO2flux was measured at different geomorphological locations on the atoll. AtmosphericpCO2generally showed small diurnal variations, while seawaterpCO2showed large diurnal variations. Lingyang Reef lagoon, an atoll within Yongle Atoll, was used to check the spatial difference in seawaterpCO2and air–sea CO2flux. The diurnal variation in seawaterpCO2was greater in the lagoon (258–748?μatm) than outside the lagoon area (354–476?μatm). Differences were also observed in the air–sea CO2fluxes depending on geomorphological zone. The mean seawaterpCO2at Yongle Atoll is in the order of Lingyang Reef lagoon >?inner reef slope of the Yongle Atoll >?Yongle Atoll channel slope?≈?outer reef slope of the Yongle Atoll. The degree mixing between the lagoon and open sea through channels may have a key role in the horizontal distribution of seawaterpCO2in the Yongle Atoll. Additional analyses indicated that the daily variations in surface seawaterpCO2are significantly influenced by biological metabolic processes. The mean air–sea CO2flux in the Yongle Atoll was ~?3.2?mmol CO2m?2d?1, indicating that the Yongle Atoll acts as a net source of CO2to the atmosphere.