With no dissolved oxygen to sustain animals or plants, ocean anoxic zones are areas where only microbes suited to the environment can live. These strange ecosystems are expanding, thanks to climate change — a development that is of concern for fisheries and anyone who relies on oxygen-rich oceans. But what piques Raven’s interest is the changing chemistry of the oceans — the Earth’s largest carbon sink — and how it could move carbon from the atmosphere to long-term reservoirs like rocks.