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- Title
Impact of Water Mass Mixing on the Composition and Mineralization of Dissolved Organic Matter in the Deep Labrador Sea.
- Authors
Djenad, S.‐A.; Guéguen, C.
- Abstract
The Labrador Sea is a region of the North Atlantic known for its strong ocean currents and deep water formation, which contribute to the transport and mixing of water masses throughout the region. The absorbing and fluorescing properties of dissolved organic matter (DOM) were assessed to track the water masses and the in situ production in the Labrador Sea (>200 m). No significant differences in DOM composition were found in the mesopelagic waters (200–1,000 m). In the bathypelagic waters (1,000–4,000 m), the estimated dissolved organic carbon (DOC) and dissolved lignin concentrations, as well as humic‐like fluorescence intensities, allowed the discrimination of North East Atlantic Deep Water versus Denmark Strait overflow water. The humic‐like intensities were significantly different between upper Labrador Sea water (uLSW) and deep LSW (dLSW) suggesting their applications as tracers of deep winter mixing. The significant correlations with apparent oxygen utilization support the in situ production of humic‐like fluorescence and the net microbial consumption of DOC and lignin in the dark Labrador Sea. We also demonstrated that microbial activities play a role in the production of humic‐like compounds in the dLSW that experiences deep convection mixing. Plain Language Summary: The Labrador Sea is a region in the North Atlantic Ocean that is characterized by cold temperatures, and strong winds. It is known for its strong ocean currents and deep water formation, which contribute to the transport and mixing of water masses throughout the region. Dissolved organic matter (DOM) is a complex mixture of organic molecules and their concentration and composition can vary depending on several factors, including the depth of the water and the source of the organic material. In this study, we aim to better understand the sources, composition, and fate of the DOM pool in the main Labrador Sea water masses. Significant differences in the DOM composition were found in the deep waters (>1,000 m), which can be used to study water mass transformations and pathways in the deep Labrador Sea waters. Microbial respiration was shown to affect significantly the DOM composition in the dark Labrador Sea. Together these results help us understand the vertical DOM composition and its implication for the cycling of deep ocean DOM. Key Points: Dissolved organic carbon, lignin phenols, and humic‐like levels differentiate the bathypelagic water massesDifferences in humic‐like fluorescence intensities are proposed as winter deep convection mixing tracersNet consumption of dissolved organic carbon and lignin phenols by bacteria was found in the dark Labrador Sea
- Subjects
WATER masses; DISSOLVED organic matter; OCEAN currents; WATER currents; SEAWATER; LIGNINS; MICROBIAL respiration; CARBON compounds
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 12, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2023JC019829