This is an excellent review of gross primary production (GPP) and net community production (NCP) measurements in the world's oceans using a new fleet of autonomous ocean-going instruments called biogeochemical-Argo (BGC-Argo) floats. The number of BGC-Argo floats has recently been surging with their users, so this review is timely and helpful for many oceanographers and biogeochemists to understand the advantages and challenges in the measurements of GPP and NCP in the oceans with the recently emerged technology.

Reaching the Paris Agreement targets to limit global warming to 1.5 or 2°C implies not only reducing emissions, but also active carbon dioxide removal from the atmosphere. While land-based carbon dioxide removal or negative emission technologies have received most attention, ocean solutions are increasingly being considered. Ocean alkalinity enhancement (OAE), or alkalinization, is one promising ocean-based carbon dioxide technology. However, any new carbon dioxide removal technique needs thorough investigations for its effectiveness, longevity, benefits and lack of disbenefits, financial viability, social acceptance and governability. The paper by Bach is a nice illustration of the type of research that must be done if we are to consider large scale application of OAE. It focuses on the additionality problem of ocean alkalinity enhancement, specifically it investigates how the addition of alkalinity modifies the natural alkalinity cycle and in that way the efficiency of carbon dioxide sequestration.