Researchers have identified chemical signatures in the South Atlantic Ocean that could allow scientists to track the movement of major deep-water masses using dissolved organic matter.
A recent study published in Deep Sea Research Part I: Oceanographic Research Papers, led by Celine Guéguen of the Université de Sherbrooke, demonstrates that the optical properties of
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The research team deployed
Five fluorescent DOM components were identified in the data set—one humic-like, two microbial humic-like, and two protein-like. Of these, the humic-like and microbial humic-like components produced measurably distinct optical signatures for three major water masses. These major water masses are Antarctic Intermediate Water (AAIW), North Atlantic Deep Water (NADW), and Lower Circumpolar Deep Water (LCDW).1
One aspect to this study that researchers had to account for was making sure the biogeochemical transformation of DOM did not mix with physical mixing. To make sure this did not happen, the researchers applied an optimum multiparameter (OMP) analysis using hydrological and DOM parameters.1 The analysis revealed that physical mixing was the dominant control on the distribution of most optical properties across the three water masses.1 However, the authors noted that one microbial humic-like component and one absorbance parameter exhibited non-conservative behavior at the boundary between AAIW and NADW.1 This observation suggests localized biogeochemical processing at that frontal interface.
In the upper mesopelagic layer, which is roughly 25 to 100 meters depth, DOM optical properties shifted markedly between seasons. During winter sampling, humic-like components allowed for clear differentiation of the Subtropical Front and the Subantarctic Front, with measurable optical gradients recorded across both boundaries.1 Those gradients were absent in spring profiles, which the authors attribute to elevated biological production at the surface diluting or transforming the DOM signal.1
The finding indicates that DOM optical properties may function as indirect indicators of frontal position and seasonal productivity cycles.
The South Atlantic plays a central role in global thermohaline circulation, serving as a conduit between water masses originating in the North Atlantic and the Southern Ocean.2 Tracking how these water masses mix and evolve has historically relied on temperature, salinity, and dissolved inorganic tracers.1,2 The identification of DOM optical parameters as complementary proxies adds a biochemical dimension to that toolkit.
The research is also relevant to ocean carbon accounting. DOM constitutes one of the largest reservoirs of organic carbon on Earth, and understanding its origin, transport, and transformation in the deep ocean is a prerequisite for accurately modeling the biological carbon pump.
