Interannual variability in terrestrial dissolved organic matter advection to the eastern East Siberian Sea under contrasting Beaufort Gyre conditions

Abstract

Recent changes in Arctic Ocean circulation, particularly the weakening of the Beaufort Gyre (BG), have potentially significant implications for biogeochemical cycles. This study investigates how interannual BG variability influences the distribution of river water and terrestrial-derived dissolved organic matter (DOM) in the western Arctic Ocean by comparing observations from two contrasting years: 2019 (maximum BG strength: 0.48 x 10-6) and 2022 (minimum BG strength: 0.14 x 10-6). Under these contrasting BG conditions, we identified significant changes in both river water fraction (friver) and terrestrial-derived DOM (characterized by fluorescent DOM; FDOM) in the eastern East Siberian Sea surface waters. Specifically, the friver increased by 37%, while high-molecular-weight terrestrial humic-like FDOM increased by 29% from 2019 to 2022. These increases coincided with enhanced cyclonic circulation over the Eurasian Basin and a weakened anticyclonic BG in 2022, facilitating the eastward expansion of Lena River-influenced surface waters. Our findings demonstrate that BG conditions play a crucial role in controlling the distribution of river water and terrestrial-derived DOM from the Eurasian rivers in the western Arctic Ocean. Continued BG weakening could allow terrestrial DOM to penetrate further into the BG region, potentially altering its biogeochemical cycles and carbon dynamics.