Seasonal variations in dissolved organic matter (DOM) fluxes from land to sea have been well documented in the Arctic, yet remarkably little is known about how DOM varies seasonally within Arctic coastal waters. This is particularly true for shallow inshore environments. Here we document seasonality of DOM in lagoons along the eastern Alaska Beaufort Sea coast during the spring ice break-up (June), summer open-water (August), and late winter ice-covered (April) periods. We measured dissolved organic carbon (DOC) concentrations, C:N ratios, and chromophoric DOM (CDOM) characteristics (SUVA₂₅₄ and S_275–295). On average, lagoon DOC was highest during spring (~200 μM) and lowest during winter (~120 μM). C:N and SUVA₂₅₄ also differed markedly between spring (C:N ~ 28; SUVA₂₅₄ ~ 3.5 L mg C⁻¹ m⁻¹) and winter (C:N ~ 16; SUVA₂₅₄ ~ 2.2 L mg C⁻¹ m⁻¹). Average S_275–295 values (~14–17 × 10⁻³ nm⁻¹) were not significantly different among seasons, but variability in S_275–295 was much lower in spring. This was attributed to terrestrial runoff based on its relatively uniform composition during the spring freshet. Seasonal variations in lagoon DOM were broadly correlated with variations in salinity (i.e., lagoon water transitioned from largely fresh in spring to hypersaline in winter), but a mixing analysis revealed strong evidence of processing and net DOC generation in summer. We also found evidence of DOC processing and build-up under the ice over the winter. This baseline understanding of DOM seasonality in Arctic lagoons is essential for evaluating climate-linked impacts on Arctic coastal ecosystems and broader feedbacks associated with carbon cycling.

中文翻译：

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阿拉斯加波弗特海沿岸泻湖生态系统中溶解有机物的季节性

从陆地到海洋的溶解有机质 (DOM) 通量的季节性变化在北极已有详细记录，但对于 DOM 在北极沿海水域中的季节性变化知之甚少。对于浅海近海环境尤其如此。在这里，我们记录了在春季冰层破裂（6 月）、夏季开放水域（8 月）和晚冬冰盖期（4 月）期间阿拉斯加波弗特海东部沿岸泻湖中 DOM 的季节性。我们测量了溶解有机碳 (DOC) 浓度、C:N 比和发色 DOM (CDOM) 特性（SUVA ₂₅₄和 S _275-295）。平均而言，泻湖 DOC 在春季（~200  μ M）最高，在冬季（~120 μ M）最低 。C:N 和 SUVA ₂₅₄春季 (C:N ~ 28; SUVA ₂₅₄  ~ 3.5 L mg C ^-1  m ^-1 ) 和冬季 (C:N ~ 16; SUVA ₂₅₄  ~ 2.2 L mg C ^-1  m ^-1 )之间也存在显着差异。平均 S _275-295值（~14-17 × 10 ^-3  nm ^-1）在季节之间没有显着差异，但 S _{275-295 的}变异性春天要低得多。这归因于基于春季新鲜期间相对均匀的成分的陆地径流。泻湖 DOM 的季节性变化与盐度的变化广泛相关（即，泻湖水从春季的大量新鲜转变为冬季的高盐度），但混合分析揭示了夏季加工和净 DOC 生成的有力证据。我们还发现了冬天冰层下 DOC 处理和积聚的证据。这种对北极泻湖 DOM 季节性的基线理解对于评估与气候相关的对北极沿海生态系统的影响以及与碳循环相关的更广泛的反馈至关重要。