Distributions and air-sea fluxes of CO_2 in the summer Bering Sea

The 3rd Chinese National Arctic Research Expedition （CHINARE-Arctic III） was carried out from July to September in 2008. The partial pressure of CO2 （pCO2） in the atmosphere and in surface seawater were determined in the Bering Sea during luly 11-27, 2008, and a large number of seawater samples were taken for total alkalinity （TA） and total dissolved inorganic carbon （DIC） analysis. The distributions of CO2 parameters in the Bering Sea and their controlling factors were discussed. The pCO2 values in surface seawater presented a drastic variation from 148 to 563 laatm （1 μatm = 1.013 25× 10-1Pa）. The lowest pCOz values were observed near the Bering Sea shelf break while the highest pCO2 existed at the western Bering Strait. The Bering Sea generally acts as a net sink for atmospheric CO2 in summer. The air-sea CO2 fluxes in the Bering Sea shelf, slope, and basin were estimated at -9.4, -16.3, and -5.1 mmol/（m2.d）, respectively. The annual uptake of CO2 was about 34 Tg C in the Bering Sea.

Evaluation of the net CO_2 uptake in the Canada Basin in the summer of 2008

The third Chinese National Arctic Research Expedition （CHINARE） was conducted in the summer of 2008. During the survey, the surface seawater partial pressure of CO2 （pCO2） was measured, and sea water samples were collected for CO2 measurement in the Canada Basin. The distribution of pCO2 in the Canada Basin was determined, the influencing factors were addressed, and the air-sea CO2 flux in the Canada Basin was evaluated. The Canada Basin was divided into three regions： the ice-free zone （south of 77°N）, the partially ice-covered zone （77°-80°N）, and the heavily ice-covered zone （north of 80°N）. In the ice-free zone, pCO2 was high （320 to 368 patm, 1 patm=0.101 325 Pa）, primarily due to rapid equilibration with atmospheric CO2 over a short time. In the partially ice-covered zone, the surface pCOs was relatively low （250 to 270 patm） due to ice-edge blooms and icemelt water dilution. In the heavily ice-covered zone, the seawater pCO2 varied between 270 and 300 laatm due to biological COs removal, the transportation of low pCOs water northward, and heavy ice cover. The surface seawater pCO2 during the survey was undersaturated with respect to the atmosphere in the Canada Basin, and it was a net sink for atmospheric CO2. The summertime net CO2 uptake of the ice-free zone, the partially ice-covered zone and the heavily ice-covered zone was （4.14±1.08）, （1.79±0.19）, and （0.57±0.03） Tg/a （calculated by carbon, 1 Tg=10^12 g）, respectively. Overall, the net COs sink of the Canada Basin in the summer of 2008 was （6.5＋1.3） Tg/a, which accounted for 4%-10% of the Arctic Ocean COs sink.

Effect of CO_2 partial pressure on SCC behavior of welded X80 pipeline in simulated soil solution

The stress corrosion cracking （SCC） behavior of welded X80 pipeline steel in simulated Ku＇erle soil solution was studied by means of electrochemical impedance spectroscopy （EIS） and slow strain rate tests （SSRT）. The microstructure of the welded steel was observed by optical microscopy （OM）. It is demonstrated that the microstructure of the weld metal consists of acicular ferrite and grain boundary ferrite, while that of heat affected zone （HAZ） is a mixture of acicular ferrite and bainitic ferrite micro- constituents. The microstructure of the base steel is composed of ferrite and pearlite. The anodic dissolution of X80 pipeline steel in simulated Ku＇erle soil solution could be enhanced and the SCC sensitivity increased with the increase of CO2 partial pressure. The SCC mechanism of X80 pipeline is a mixing mechanism of hydrogen embrittlement combined with anodic dissolution, and the hydrogen embrittlement plays a leading role. The higher SCC sensitivity of the weld metal was attributed to the metallurgical transformation, local hardening and residual stress.