Climate variability in the North Pacific thermocline diagnosed from oxygen measurements:: An update based on the US CLIVAR/CO2 Repeat Hydrography cruises

New observations of oxygen variability in the North Pacific Ocean are reported on the basis of comparison of the U. S. Climate Variability and Predictability and Carbon (CLIVAR/CO2) Repeat Hydrography sections conducted along 30 degrees N (2004) and 152 degrees W (2006) with the earlier World Ocean Circulation Experiment (WOCE) data and other cruises along these sections. The largest changes in apparent oxygen utilization (AOU) continue to occur, as found in earlier North Pacific repeat section analyses, within the thermocline on sigma(theta) = 26.6 kg m(-3), which is the densest isopycnal to outcrop in the open North Pacific in climatological data. In the northeastern North Pacific along 152 degrees W, where a total of five cruises (1980, 1984, 1991, 1997, and 2006) spanning a period of 26 years are available, the AOU changes correspond to an overall increase in AOU on sigma(theta) = 26.6 kg m(-3) from the 1980s/early 1990s to 2006. However, from 1997 to 2006 a decrease in AOU is observed within the boundary region between the subtropical and subpolar gyres at 40 degrees-45 degrees N. Along the center axis of the subtropical gyre at 30 degrees N, where two cruises are available (1994 and 2004), AOU has also substantially increased on sigma(theta) = 26.6 kg m(-3) from 1994 to 2004 in the eastern part of the section. The repeat section data along 152 degrees W and 30 degrees N are consistent with a pattern of decadal-scale ventilation anomalies that originate in the northwestern Pacific, possibly through variability (including cessation) of the sigma(theta)= 26.6 kg m(-3) outcrop, travel eastward along the subtropical-subpolar gyre boundary, and enter the northern portion of the subtropical gyre along the way. For the 152 degrees W AOU data within the gyre boundary region (40 degrees-45 degrees N), good agreement exists with the close-by time series data from Ocean Station P (50 degrees N, 145 degrees W) where a bidecadal cycle in AOU has been observed. In contrast, a sensible correlation with the Pacific Decadal Oscillation could not be found.