Ocean plants called phytoplankton produce half of the oxygen we breathe and help regulate Earth's climate by absorbing carbon dioxide from the atmosphere. Scientists use satellites to monitor these tiny organisms, but satellites can only see what's happening at the ocean surface.

In this study, we investigated phytoplankton living deeper in the Atlantic Ocean that satellites cannot detect. We used data collected on a research cruise from the Arctic to Antarctica to understand how surface and deep phytoplankton communities differ and contribute to ocean productivity.

We found that surface and deep phytoplankton have different survival strategies. Surface communities are adapted to bright sunlight, while deep communities are better at capturing dim light. Surprisingly, although deep communities make up 61% of the ocean's total plant biomass, surface communities are much more productive, contributing 78% of ocean productivity and 68% of carbon-related measurements.

These findings are important because climate change is affecting ocean conditions. To better predict future changes in ocean productivity and its impact on global climate, we need to monitor both surface and deep phytoplankton communities. Currently, satellites miss the deep communities that represent over half of ocean plant life.