The Arctic Ocean's Dissolved Organic Carbon: A Land-Driven Phenomenon
The Arctic's frozen ground is melting at an alarming rate due to climate change, releasing ancient organic matter into the central Arctic Ocean. This matter, rich in organic carbon, originates from plants, microorganisms, and animals, and has been frozen in the soil for centuries. Rivers carry this material into the ocean, where it dissolves, forming 'dissolved organic matter (DOM).'
Dr. Xianyu Kong, a scientist at the Alfred Wegener Institute, highlights the significance of this process. DOM constitutes a vast reservoir of organic carbon in the ocean, rivaling the amount of atmospheric CO2. The Arctic Ocean receives an unusually large amount of freshwater and terrestrial organic matter from permafrost thaw, river discharge, and coastal erosion, making it distinct from other oceans.
In a groundbreaking study, Kong and colleagues quantified the accumulation of organic carbon in the central Arctic Ocean. They discovered that approximately 16% of dissolved organic carbon originates from land, even in deep waters, where terrestrial contributions were unexpectedly high. This finding suggests that land-derived organic matter is chemically stable enough to survive long-distance transport, connecting Arctic processes to the global carbon cycle.
The Transpolar Drift, a surface current, plays a crucial role in transporting terrestrial dissolved organic carbon across the Arctic Ocean towards the North Atlantic. Regions affected by this current had twice the amount of organic carbon as neighboring areas, leading to an estimated annual transport of 39 million tons of terrestrial carbon from the Arctic to the Atlantic.
The impact of DOM from terrestrial sources on the Arctic Ocean's organic carbon cycle is significant. It influences light attenuation, nutrient availability, and microbial processes. While previous studies show an increase in dissolved organic carbon concentration in freshwater environments due to climate change, the Arctic Ocean lacks similar data, partly due to the absence of appropriate methods.
The AWI researchers addressed this knowledge gap by developing a new analytical approach to analyze seawater samples from the central Arctic Ocean. They used ultrahigh-resolution Fourier-transform mass spectrometry to identify and quantify thousands of individual organic molecular formulas, distinguishing between ocean, sea ice, and terrestrial sources. This method allowed them to quantify terrestrial carbon concentration and estimate its degradation progress.
The study's findings have important implications for understanding carbon cycling and broader biogeochemical processes in the Arctic Ocean. As Arctic warming accelerates, inputs of terrestrial organic matter are expected to increase, potentially altering the region's carbon dynamics. Previous climate models do not yet reflect these findings, emphasizing the need for further research to predict the impact of land inputs on Arctic marine ecosystems and the Arctic carbon inventory in a warming climate.
