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Optical properties of colored dissolved organic matter (CDOM) were investigated along a latitudinal transect (67°–77° N) in upper water (<80 m depth) of the western Arctic Ocean. The absorption coefficient at 280 nm was 0.48–1.25 m−1, with the average for the oligotrophic basin area (1.04 ± 0.08 m−1) being slightly higher than that of the productive shelf area (0.95 ± 0.16 m−1), implying a decoupling effect between CDOM concentration and biological productivity in the western Arctic Ocean. The spectral slope coefficient S270–350 was negatively correlated with salinity, indicating that DOM molecular weight increases with salinity, and may be affected by melt-water input. Four fluorescent components were identified by excitation emission matrices elaborated by parallel factor analysis, including three humic-like (C1, C3, and C4) components and one protein-like (C2) component. Significant increases in concentrations of terrestrially derived humic-like C3 and C4 components with salinity were observed in the basin, mainly controlled by the physical mixing of surface fresh water and subsurface inflowing Pacific Ocean water. Terrestrial material carried by Pacific inflow is thus an important factor affecting the distribution of CDOM fluorescence components. The C3 and C4 fluorescence components may be useful as tracers of Pacific water in the western Arctic Ocean. [ABSTRACT FROM AUTHOR]

Understanding fluctuations in atmospheric CO 2 during transitions from glacial to interglacial states is critical for deciphering climate dynamics. This study investigates the influence of Late Pleistocene Arctic ice sheets on organic carbon remobilization and its subsequent effects on atmospheric CO 2 concentrations. We demonstrate that the main source of organic carbon deposited in the Arctic Ocean and northern Nordic Seas was derived from glacially exhumed terrestrial and shelf sediments, rather than primary productivity. The degradation of remobilized organic carbon contributed significantly to an increase in dissolved inorganic carbon (DIC), accounting for about 15–26% of the current DIC stock. Such a considerable addition poses a challenge to the ocean's CO 2 absorption capacity, potentially converting the Arctic region into a net carbon source. Nevertheless, the uncertainties associated with the age framework, along with the complexity of organic carbon degradation, limit the accuracy of carbon release assessments. Our findings offer new insights into the Arctic Ocean and northern Nordic Seas' roles in global CO 2 dynamics, emphasizing the urgent need for more precise studies on the ice sheet-driven carbon release and its broader climatic implications. • Arctic ice sheet expansion triggers organic carbon remobilization. • Remobilized organic carbon degradation limits Arctic Ocean's carbon sink capacity. • Ice sheet-driven carbon release regulates atmospheric CO 2 levels. [ABSTRACT FROM AUTHOR]

Spatial variability of ammonium concentrations along repeat transects were examined on the Chukchi shelf during 2012–2018. Two distinct near-bottom high ammonium pools (>1 μmol/kg) near 67.5°N and 72.5°N of the transects were identified in all years. The accumulation of ammonium in the regions is driven primarily by a combination of biogeochemical processes (e.g., dynamic bacterial remineralization of organic matter) and physical controls (e.g., strong density-contrast barrier limits upward mixing of ammonium). The ammonium pool on the shelf may became larger in the expectation of the stronger bacterial remineralization following elevate primary production, and may have potential impact on the structure and productivity of ecosystem on the Chukchi shelf. • High ammonium concentrations were measured in near-bottom water of the Chukchi shelf during summer of 2012–2018. • The accumulation of ammonium may be caused by a combination of intense remineralization and inhibited vertical diffusion. • The ammonium pool on the shelf may became larger with elevated primary production and enhanced bacterial remineralization. [ABSTRACT FROM AUTHOR]