Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Annual Review of Marine Science 8 (2016): 185-215, doi:10.1146/annurev-marine-052915-100829. ; The ocean, a central component of Earth’s climate system, is changing. Given the global scope of these changes, highly accurate measurements of physical and biogeochemical properties need to be conducted over the full water column, spanning the ocean basins from coast to coast, and repeated every decade at a minimum, with a ship-based observing system. Since the late 1970s, when the Geochemical Ocean Sections Study (GEOSECS) conducted the first global survey of this kind, the World Ocean Circulation Experiment (WOCE) and Joint Global Ocean Flux Study (JGOFS), and now the Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) have collected these “reference standard” data that allow quantification of ocean heat and carbon uptake, and variations in salinity, oxygen, nutrients, and acidity on basin scales. The evolving GO-SHIP measurement suite also provides new global information about dissolved organic carbon, a large bioactive reservoir of carbon. ; Climate Observations Division of the U.S. NOAA Climate Program Office and NOAA Research; Joint Institute for the Study of the Atmosphere and Ocean (JISAO) under NOAA Cooperative Agreement NA10OAR4320148; U.S. National Science Foundation [OCE- 0223869; OCE-0752970; OCE-0825163; OCE-1434000; OCE 0752972; OCE-0752980; OCE-1232962; OCE-1155983; OCE-1436748]; U.S. CLIVAR Project Office; Global Environment and Marine Department, Japan Meteorological Agency; Australian Climate Change Science Program (Australian Department of Environment and CSIRO); U.K. Natural Environment Research Council; European Union’s FP7 grant agreement 264879 (CarboChange); Horizon 2020 grant agreement No 633211; ETH Zurich Switzerland.