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This report details the quality control (QC) procedures applied to oxygen data collected from the Southern Ocean Time Series (SOTS) moorings between 2009 and 2021. These measurements help to quantify net community production (and thus carbon export). The quality controlled datasets are publicly available via the AODN Data Portal. This report should be consulted when using the data Published Refereed Current 14.a Oxygen Mature Organisational Multi-organisational National N/A N/A N/A N/A Method

The live version of this SOP is on the Ocean Gliders community in GITHUB. The home repository of this publication is in the Ocean Best Practices Repository. This standard operating procedure (SOP) document for dissolved oxygen (DO) aims to guide the user through the steps necessary to collect good quality dissolved oxygen data using ocean gliders for both real time and post deployment data streams.

The dissolved oxygen (DO) content in seawater is controlled by several unrelated processes including exchange with air, metabolism of plants and animals, microbial and chemical decomposition of organic matter, hydrodynamic features such as mixing, advection, convection, and up- or down-welling. The DO content is always the result of multifactorial influences and the reasons for changes may be difficult to assess. In stratified Baltic waters, DO depletion occurs regularly below the halocline. When only physical processes are involved, the DO concentration in water is governed by the laws of solubility, i.e., it is a function of atmospheric pressure, water temperature, and salinity. The corresponding equilibrium concentration is generally called solubility. It is an essential reference for the interpretation of DO data. Precise solubility data, tables, and mathematical functions have been established (Carpenter, 1966; Murray and Riley, 1969; Weiss, 1970) and adopted by the international community (UNESCO, 1973). However, Weiss (1981) drew attention to an error in the international tables in which the values are low by 0.10 % since they are based on ideal gas molar volume instead of actual dioxygen molar volume. Later, the Joint Panel on Oceanographic Tables and Standards (JPOTS) recommended that the oxygen solubility equation of Benson and Krause (1984), which incorporated improved solubility measurements, be adopted and the tables updated (UNESCO, 1986). However, the UNESCO paper only referred to the equation that gives concentrations in the unit μmol kg-1. 1.2 Purpose and aims Monitoring of dissolved oxygen and hydrogen sulphide can provide information of an indirect effect of eutrophication, but hydrogen sulphide and oxygen depletion is also a naturally occurring condition in some areas. The purpose of the monitoring is to map the spatial distribution of concentrations of dissolved oxygen and hydrogen sulphide, with the aim to be able to assess the status of the seafloor and the waters above and to ensure that the data is comparable for the HELCOM pre-core indicator ‘Shallow water oxygen’ and core indicator ‘Oxygen debt’. The indicator descriptions, including their monitoring requirements, are given in the HELCOM core indicator web site: http://www.helcom.fi/baltic-sea-trends/indicators/oxygen- Published Refereed Current 14.a Oxygen Mature Multi-organisational International Method Specification of criteria

This manual is to be used with the SBE 63 Digital Optical Dissolved Oxygen Sensor. It is organized to guide the user from installation through operation and data collection. We’ve included detailed specifications, command descriptions, maintenance and calibration information, and helpful notes throughout the manual. Published Current Oxygen Mature Multi-organisational International Dissolved oxygen sensor Method Specification of criteria