A Description and Quality Assessment of the Historical Hydrographic Data for the South Pacific Ocean

Abstract

Modern high-quality hydrographic data obtained during the World Ocean Circulation Experiment (WOCE) are used to assess the quality of a large collection of historical hydrographic data in the Pacific Ocean south of the equator. To validate the data, individual observations are compared against locally averaged neutral density–parameter relations. To refine the data, the validation procedure is applied three times, each time rejecting (flagging) individual observations at observed levels, whole profiles, and cruises. Analysis of the rejected observations shows large variations in the data quality. Parameter offsets for historical cruises are computed comparing with high-quality WOCE data. High percentages of rejected observations and significant systematic biases found for many historical cruises stress the necessity to reassess the quality of the global historical hydrographic dataset as the complete WOCE dataset becomes available. The validated profile data with account made for the parameter offsets were used to produce a new climatology of the South Pacific Ocean. A considerable improvement compared with the 1994 World Ocean Atlas (WOA-94) climatology was achieved through a more elaborated data quality control and by interpolating the data on neutral surfaces. Compared with the WOA-94 climatology, the authors’ property distributions generally exhibit less patchiness and are free from artificial water masses obviously present in the WOA-94 climatology due to the effects of averaging the data on isobaric surfaces. The gridded data also retain tight deep water parameter relationships, in agreement with high-quality observations.