Data_Sheet_1_Evidence of Deep DOC Enrichment via Particle Export Beneath Subarctic and Northern Subtropical Fronts in the North Pacific.PDF

Here we provide compelling evidence that deep particle export enhanced dissolved organic carbon (DOC) concentrations beneath the Pacific’s Subarctic Front (SA, ∼42°N) and Northern Subtropical Front (NST, ∼34°N). We report three main findings: First, deep export of subjectively small particles (128–512 μm) was apparent throughout the frontal zone in which the SA resides. However, export of large particles was specifically associated with the SA, rather than the entire frontal zone, and appeared to exclusively transfer DOC into the bathypelagic water column. Second, a similar DOC enrichment existed beneath the NST, though this signal was curiously not accompanied by observable particles (>128 μm). We conclude that export occurring previously in winter left this DOC behind as a residue, though the associated particles were no longer present by spring. Third, the presence of strong hydrographic fronts was not the only control on export that resulted in these unique DOC distributions. Deep export and DOC enrichment was also controlled by latitude-specific biogeochemical and hydrographic conditions, such as depth of the nutricline and seasonal mixed layer shoaling. Given these observations, the fronts within the transitional region of the North Pacific are clearly special locations for deep carbon sequestration and for providing uncommon DOC enrichment that ultimately supports the deep microbial community.

本研究提供了确凿证据，表明太平洋亚极地锋面（Subarctic Front, SA，约42°N）与北亚热带锋面（Northern Subtropical Front, NST，约34°N）下方的深层颗粒输出过程，提升了溶解有机碳（dissolved organic carbon, DOC）的浓度。本研究报告了三项核心发现：其一，在SA所在的整个锋面区内，粒径128–512 μm的小型颗粒的深层输出现象均显著存在。然而，大型颗粒的输出仅与SA相关，而非覆盖整个锋面区，且似乎仅将DOC输送至深层带水柱（bathypelagic water column）。其二，NST下方同样存在类似的DOC富集现象，但令人费解的是，该信号并未伴随可观测到的（>128 μm）颗粒。本研究推断，此前冬季发生的颗粒输出过程将该DOC作为残留物留存下来，而相关颗粒至春季时已不复存在。其三，强水文锋面（hydrographic front）的存在并非造就这类独特DOC分布的输出过程的唯一调控因素。深层颗粒输出与DOC富集还受纬度特异性生物地球化学与水文条件调控，例如营养跃层（nutricline）深度以及季节性混合层变浅。基于上述观测结果，北太平洋过渡带内的锋面显然是深层碳固存的特殊区位，同时也是形成罕见DOC富集现象的场所，而这类富集最终可为深层微生物群落提供支撑。