Dataset abstract Seawater samples were collected from the ship's underway system or from the surface niskin bottle from the CTD rosette. Some incidental samples were collected from the surface using a bucket from the side of the ship or a zodiac. The samples were collected every 6 hours from the underway and from every CTD cast as part of the Antarctic Circumnavigation Expedition (ACE) which took place in the Austral summer of 2016/2017. Ammonium is representative of the recycled nitrogen pool in the upper mixed layer where inputs include marine production and terrestrial runoff. Seawater samples were collected and frozen during the expedition and analysed post-cruise and quality controlled to produce this dataset, which presents ammonium concentration in surface seawater from the Southern Ocean. Dataset contents ace_ammonium_concentration_surface_seawater.csv file, data file, comma-separated values ace_ammonium_concentration_surface_seawater_chnage_log.txt, metadata, text data_file_header.txt, metadata, text README.txt, metadata, text Change log v1.1 - Added detection limit to README.txt. Data points formatted to 2 decimal places. v1.0 - Initial release of dataset

{"references": ["Holmes, R.M., Aminot, A., Kerouel, R., Hooker, B.A., Peterson, B.J., 1999. A simple and precise method for measuring ammonium in marine and freshwater ecosystems. Canadian Journal of Fisheries and Aquatic Sciences 56, 1801\u20131808.", "David W H Walton, & Jenny Thomas. (2018, November 22). Cruise Report - Antarctic Circumnavigation Expedition (ACE) 20th December 2016 - 19th March 2017 (Version 1.0). Zenodo. http://doi.org/10.5281/zenodo.1443511"]}

The Antarctic Circumnavigation Expedition was made possible by funding from the Swiss Polar Institute and Ferring Pharmaceuticals and the University of Cape Town.