Oceanographers have long relied on a simple rule of thumb: green waters are teeming with microscopic life, while ultramarine blue signals relative scarcity. However, a new analysis of two decades of satellite images suggests the dividing line between these hues is shifting.
Researchers at Duke University analyzed global data from 2003 to 2022 using NASA’s MODIS-Aqua instrument. The study found that open-ocean waters in high latitudes are greening, while tropical and subtropical regions are losing chlorophyll. This trend hints at a large-scale rearrangement of life at the base of marine food webs.
The shift is driven by changes in chlorophyll concentration, which tracks phytoplankton’s use for photosynthesis. Phytoplankton absorb carbon dioxide and convert it to organic matter, sequestering carbon when dead cells sink. A poleward migration of productivity could rearrange this natural pump, affecting how long stored carbon remains out of circulation.
The study has implications for food security, as many equatorial nations rely on rich fisheries sustained by plankton blooms. A steady drop in primary producers could disrupt the food web, reducing fish stocks vital to diets and economies. The authors emphasize that two decades are only an opening chapter, highlighting the need for longer records, deeper observations, and improved models of phytoplankton physiology to predict the full ecological impact.
The ocean’s color shift signals change – green in high latitudes, blue near the equator – as ecosystems quietly reorganize. This subtle yet significant re-ordering of marine life could reshape climate feedbacks and global fisheries alike.
Source: https://www.earth.com/news/shifting-ocean-color-is-pushing-marine-life-toward-the-poles