GO-SHIP Easy Ocean: Gridded ship-based hydrographic section of temperature, salinity, and dissolved oxygen

Abstract

Despite technological advances over the last several decades, ship-based hydrography remains the only method for obtaining high-quality, high spatial and vertical resolution measurements of physical, chemical, and biological parameters over the full water column essential for physical, chemical, and biological oceanography and climate science. The Global Ocean Ship-based Hydrographic Investigations Program (GO-SHIP) coordinates a network of globally sustained hydrographic sections. These data provide a unique data set that spans four decades, comprised of more than 40 cross-ocean transects. The section data are, however, difficult to use owing to inhomogeneous format. The purpose of this new temperature, salinity, and dissolved oxygen data product is to combine, reformat and grid these data measured by Conductivity-Temperature-Depth-Oxygen (CTDO) profilers in order to facilitate their use by a wider audience. The product is machine readable and readily accessible by many existing visualisation and analysis software packages. The data processing can be repeated with modifications to suit various applications such as analysis of deep ocean, validation of numerical simulation, and calibration of autonomous platforms.

Fig. 1

Dissolved oxygen concentration along the Pacific hydrographic section P16, nominally along 150°W from the World Ocean Circulation Experiment (WOCE) that preceded and set the section locations and protocols continued in GO-SHIP. The distribution demonstrates the meridional overturning circulation in the Pacific; sinking of a newly-ventilated water mass with high oxygen concentration around Antarctica, followed by northward penetration along the bottom and gradual lightening, losing oxygen by biological activity, and a southward return path at mid-depth. A cell of near surface overturning circulation can also be discerned. While this particular figure was produced with rosette sampled oxygens (small dots), it can equally be created from the CTDO profiles at the same stations, available through GO-SHIP Easy Ocean. Reproduced from Talley (2007).

Fig. 2

(a) A map of hydrographic stations included in the section data used to produce the gridded GO-SHIP Easy Ocean data product. The colour shows the year of occupation. Note many stations overlap. All stations included in the raw data are shown, some of which are not included in the final gridded product (Fig. 2b). (b) Approximate locations of GO-SHIP Easy Ocean gridded sections with section names. The colour shows how many times (at least partially) the sections have been occupied as of September 2021.

Fig. 3

Errors introduced in the gridding procedure. The thin lines show the average of the errors (biases) and the thick lines show the standard deviation of the errors estimated at each depth. The errors for Conservative Temperature and Absolute Salinity are not distinguishable from those for temperature and salinity, respectively, and not plotted.

Fig. 4

Pacific Ocean density (${\sigma }_0$) along 170°W (P15 between 70°S-0°S, see Fig. 5) observed in May and June 2016 from the GO-SHIP Easy Ocean gridded data product (white contours) overlaid on density (${\sigma }_0$) from the CAFE60 reanalysis product averaged over the same period. Colormap is from ref. .

Fig. 5

The difference in the observed Pacific Ocean Conservative Temperature (°C) along 150°W (P16) between 1992 and 2015 using the GO-SHIP Easy Ocean gridded data product.