gsw is an R package that provides a connection to software relating to TEOS, the Thermodynamic Equation Of Seawater (see http://www.teos-10.org). This connection involves R wrappers to C functions within the GSW-C library (https://github.com/TEOS-10/GSW-C, release v3.06-16-0, commit 657216dd4f5ea079b5f0e021a4163e2d26893371), along with a data file within the GSW-Matlab library (https://github.com/TEOS-10/GSW-Matlab/blob/master/Toolbox/library/gsw_data_v3_0.mat, commit 38c9635d6fd93e74c2648e4ee23cec49c1f58530).
The foundational algorithms upon which both GSW-C and GSW-R rest were devised by the Scientific Committee on Oceanic Research / International Association for the Physical Sciences of the Oceans, Working Group 127. These algorithms were recommended as a replacement for a previous system (called UNESCO-80) at the twenty-fifth assembly in the Intergovernmental Oceanographic Commission in 2009.
The gsw functions reproduce test values in the GSW-Fortran documentation to a tolerance of 1.5e-8, the default for numerical comparison in R working on a 64-bit machine. This offers some assurance that the coding process has not introduced errors.
The naming convention in gsw is patterned on the system described at http://www.teos-10.org/pubs/gsw/html/gsw_contents.html, as a way to reduce the effort users might face in switching to R.