The Impact of Rain on the Ocean’s Carbon Sink

The ocean plays a crucial role in the global carbon cycle, absorbing a significant amount of carbon dioxide emitted by human activities each year. A recent study published in Nature Geoscience, co-authored by a University of Hawai’i at Mānoa oceanographer, shed light on the impact of rainfall on the ocean’s ability to sequester carbon dioxide.

While the role of rain in air-sea CO2 fluxes has not been extensively studied, the research highlighted in the study provides valuable insights. Rainfall affects the exchange of CO2 between the air and the sea in three key ways: by generating turbulence on the ocean surface, diluting seawater, and directly injecting CO2 absorbed during their fall through the atmosphere into the ocean.

The study led by Laetitia Parc, a doctoral student at Ecole Normale Supérieure (ENS; France), is the first to provide a global estimate of the impact of rain on the ocean’s carbon sink. Through an analysis of satellite observations and climate data from 2008 to 2018, the research team found that rain increases the oceanic carbon sink by 140 to 190 million tons of carbon per year, contributing to a 5% to 7% increase in the total carbon absorbed by the oceans annually.

The study also highlighted regional differences in the impact of rain on the ocean’s carbon sink. Turbulence and seawater dilution, influenced by heavy rainfall events and weak winds, play a significant role in enhancing the CO2 sink in tropical regions. In contrast, the direct injection of dissolved carbon in raindrops is more prevalent in regions with heavy precipitation, including the tropics, storm tracks, and the Southern Ocean.

The results of the study suggest that the effect of rain should be explicitly incorporated into estimates used to construct the global carbon budget. By accounting for the additional carbon absorbed by the ocean due to rainfall, scientists can better understand and predict changes in the ocean’s ability to sequester carbon dioxide, especially in the face of shifting climate patterns.

Rainfall plays a significant role in the ocean’s carbon cycle, impacting the exchange of CO2 between the air and the sea. Understanding the effects of rain on the ocean’s carbon sink is vital for accurately assessing the global carbon budget and predicting future changes in the Earth’s climate system. By recognizing the importance of rain in carbon sequestration, researchers can take steps towards more effective climate change mitigation strategies.