黑潮延伸区系泊浮标海表pH的年际和季节变化

Decadal Trend and Seasonal Variation of Sea Surface pH of the Kuroshio Extension Observatory Moored Buoy

西北太平洋海表pH具有显著的长期酸化趋势和季节性变化。近十年来,位于黑潮延伸区的KEO浮标(144°36′E, 32°24′N)提供了丰富的观测数据。基于2008至2019年浮标海表实测盐度、温度、气压和CO_(2)分压数据,利用CO2SYS程序重建了近原位海表pH时间序列,并对其年际趋势和季节变化进行了分析讨论。结果表明,KEO站点2008年至2019年海表pH下降速率为(2.18±0.52)×10^(-3)/a,与日本周边海域pH下降速率趋势一致。气候态月平均pH在夏季最小,其季节变化与位于西北太平洋同一纬度的其他两个JMA(Japan Meteorological Agency)站点((137°E, 32°N)和(165°E, 32°N))相似。KEO站点的海表pH季节变化较邻近的近岸CL站点((140°22′E, 35°10′N),位于千叶县)更为显著。KEO站点海表pH最大下降速率发生在夏季(3.22±0.64)×10^(-3)/a,与秋季(2.55±0.44)×10^(-3)/a相当,其次发生在春季(1.89±0.42)×10^(-3)/a,最后在冬季(1.66±0.37)×10^(-3)/a,约为最大值的1/2。本研究所用时间序列较短(小于等于12年)且存在数据缺口,使得趋势计算具有较高不确定性,建议采用更长的时间序列进一步研究海洋酸化的年际和季节趋势差异。本研究有助于加深对黑潮延伸区海洋酸化的认识。

The sea surface pH in the Northwestern Pacific Ocean shows significant long-term and seasonal variation with an apparent acidification trend.In the past decade,the Kuroshio Extension Observatory(KEO)moored buoy in the Kuroshio extension(144°36′E,32°24′N)has provided a wealth of data.Based on the field measured salinity,temperature(°C),atmospheric pressure(hPa),and CO_(2) partial pressure(pCO_(2),μatm)from the sea surface,the near-situ seawater surface pH data was reconstructed from 2008 to 2019 using the CO2SYS program.Then,its decadal trend and seasonal variation were analyzed.At the KEO site,the rate of sea surface pH decline from 2008 to 2019 was(-2.18±0.52)×10^(-3)/a,consistent with the trend in the coastal sea around Japan.The climatological monthly average pH reached its minimum in summer,with seasonal variations similar to those observed at two other sites at the same latitude in the western North Pacific(137°E,32°N and 165°E,32°N).At the same time,the seasonal variation was more significant than the nearby coastal Central Laboratory site(located in Chiba Prefecture).The maximum rate of ocean acidification occurred in summer(-3.22±0.64)×10^(-3)/a,which was comparable to autumn(-2.55±0.44)×10^(-3)/a,followed by the spring(-1.89±0.42)×10^(-3)/a,and the lowest rate occurred in winter(-1.66±0.37)×10^(-3)/a,which was about twice less than the maximum.Considering the high uncertainties due to data gaps and the short length of the time series in this study(less than or equal to 12 years),more extended time series are suggested to be used to further investigate the decadal and seasonal trends in ocean acidification.This research could enrich our understanding of the accelerated ocean acidification rate in the Kuroshio extension area.