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Lookup NU author(s): Bita Sabbaghzadeh, Dr Guenther Uher, Professor Robert Upstill-GoddardORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
Copyright © 2024 Sabbaghzadeh, Uher and Upstill-Goddard.We report on the spatial distributions and optical characteristics of chromophoric dissolved organic matter (CDOM) in the sea surface microlayer (SML), subsurface seawater (SSW), and water column profiles down to 500 m across a range of Atlantic Ocean biogeochemical provinces during two cruises of the UK Atlantic Meridional Transect program (AMT24 and AMT25). We measured the CDOM absorption coefficient at 300 nm, aCDOM(300), and determined CDOM spectral slopes across two UV wavelength ranges: S1 (275-295 nm) and S2 (350-400 nm). We used spectral slope ratios (SR: S1/S2) to infer CDOM source characteristics and transformation history. During both cruises, SML aCDOM(300) was highest in the Northern Hemisphere, particularly in the North Atlantic Drift Region (NADR). CDOM was always enriched in the SML, with enrichment factors (SML aCDOM(300) / SSW aCDOM(300)) ranging from 1.03 to 2.00, reflecting preferential accumulation of CDOM in the SML. We also found a significant inverse correlation between aCDOM(300) and S1 in both the SML (Spearman’s rank correlation coefficient, r2 = -0.75, p < 0.001, n = 114) and water column profiles (r2 = -0.74, p < 0.001, n = 845). Biogeochemical province-dependent variations in the relationships between CDOM and chlorophyll a were also observed. In high-latitude regions, elevated aCDOM(300) and low SR values indicated a dominance of terrestrially-derived CDOM, whereas oligotrophic subtropical areas showed lower aCDOM(300) and higher SR values, suggestive of aged, refractory, and photodegraded biologically-derived CDOM. Taken together, these findings reveal a complexity of drivers affecting CDOM distributions and spectral properties, which may limit the use of CDOM in predictive relationships in the oceans. However, the potential use of chlorophyll a as a CDOM proxy may prove most successful in open ocean regions devoid of terrestrial inputs, where biological production predominates.
Author(s): Sabbaghzadeh B, Uher G, Upstill-Goddard R
Publication type: Article
Publication status: Published
Journal: Frontiers in Marine Science
Year: 2024
Volume: 11
Online publication date: 23/07/2024
Acceptance date: 19/06/2024
Date deposited: 12/08/2024
ISSN (electronic): 2296-7745
Publisher: Frontiers Media SA
URL: https://doi.org/10.3389/fmars.2024.1432133
DOI: 10.3389/fmars.2024.1432133
Data Access Statement: The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found below: British Oceanographic Data center (BODC) (www.BODC.ac.uk).
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