Search

The interannual variability in fluorescent dissolved organic matter (FDOM) was assessed in the Pacific‐ and Atlantic‐derived halocline, and Atlantic waters (AWs) of the Canada Basin during late summer/early fall expeditions in 2007–2017. Fluorescence spectroscopy excitation‐emission matrices coupled with parallel factor analysis were used to validate a seven‐component model. During the 11 years, humic‐like intensities increased by 0.0002–0.0006 r.u. (Raman unit) (p < 0.05) with greater annual rates of change in shallower waters (i.e., Pacific summer water) than in deeper waters (i.e., AWs). No significant temporal trends were observed for protein‐like intensities in any water layer (p > 0.05) due to the labile nature of these components. The increases in humic‐like fluorescence intensities were likely the results of changes in Bering Strait inflow and its modification over the Chukchi Shelf and/or the accumulation of freshwater under anticyclonic wind forcing in the Beaufort gyre. This 11‐year late summer/early fall survey shows the first evidence of changes in FDOM composition in the halocline of the Arctic Ocean basin. Plain Language Summary: The highly stratified Arctic Ocean receives a disproportionate amount of freshwater and plays a large role in the regulation of the global climate. Over the last decade, the effects of sea ice decline, hydrological cycle intensification, and vertical stratification have strengthened. Dissolved organic matter (DOM) is a heterogeneous mixture of non‐living organic compounds and is central to the marine carbon cycle. This study, which is part of the Joint Ocean Ice Study/Arctic Observing Network—Beaufort Gyre Observing System program, aims to assess the level and composition of fluorescent dissolved organic matter (FDOM) in water samples collected in the dark Canada Basin waters of the Arctic Ocean in late summer/early autumn between 2007 and 2017. The results of the present study indicate that microbial activity constitutes a significant source of humic‐like FDOM in the Atlantic—derived halocline waters. During the 11 years, the humic‐like component levels increased in both the Pacific and Atlantic‐origin halocline waters, which were likely the results of changes in Bering Strait inflow, heat transfer over the Chukchi Sea shelves, and/or the accumulation of FDOM‐rich freshwater under clockwise wind forcing in the Beaufort gyre. Key Points: Statistically significant temporal increases were observed in humic‐like fluorescence intensities in the halocline watersIncreases in halocline humic‐like reflect changes in Pacific‐origin flow, organic input, and, Chukchi shelf and advection processesEvidence of in situ microbial production of humic‐like fluorescence was found in the Atlantic‐origin halocline [ABSTRACT FROM AUTHOR]