A research team led by Prof. WANG Jianjun from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, has produced a global map depicting the distribution and variation of dissolved organic matter (DOM) across Earth's oceans. The findings were recently published in Environmental Science & Technology.

In this study, the researchers analyzed more than 800 samples collected from 124 stations across the Atlantic, Pacific, and Southern Oceans. The sampling spanned surface waters down to depths of nearly 5,900 meters. Using ultrahigh-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry, they found that the molecular "communities" of DOM undergo predictable changes: DOM compositions grow more distinct as water masses are separated by greater horizontal or vertical distances. However, this rate of divergence slows significantly in the deep ocean and at high latitudes.

This pattern points to a process the researchers term "chemohomogenization"—a convergence toward a shared pool of long-lived molecules in the deep sea. The signal is consistent across both biochemically labile and recalcitrant compound classes, driven by a combination of deterministic forces (e.g., temperature, salinity, and carbon availability) and stochastic processes (e.g., physical transport).

The study further reveals that environmental factors shape DOM in the upper 200 meters of the ocean and at mid-latitudes. At broader scales, however, pure spatial effects, which consistent with dispersal limitation and unmeasured variables, account for the observed variance.

"Warming will likely expand horizontal homogenization but weaken vertical mixing, especially at high latitudes," said Prof. WANG. "This could enhance the deep ocean's role as a carbon sink by preserving more organic molecules over time."

The findings establish a new chemogeographical theoretical framework, offering a tool to predict how ocean carbon storage will respond to climate change, the researchers noted.