Extensive studies in the 1980s–1990s led to the characterization of latitudinal variations in sea surface δ13C values of particulate organic carbon (δ13CPOC), and relationships were found with CO2 concentrations, temperature, growth rates, and cell geometries. Surprisingly, no large-scale efforts have been made to describe variations in δ13CPOC values over depth in the water column. Here we compile published examples demonstrating a widespread isotopic pattern in particulate organic carbon (POC) of the upper water column. In 51 vertical profiles, δ13CPOC values in the lower euphotic zone on average are 1.4‰ lower than δ13CPOC values in the upper euphotic zone of open ocean settings. In a majority of locations this vertical decrease in δ13CPOC values is >2‰ and up to 5‰, larger than the commonly recognized vertical δ13C variation in dissolved inorganic carbon over the same depths. We briefly review hypotheses and supporting evidence offered by previous studies of individual water columns: The observed patterns could result from vertical differences in photosynthetic growth rates or community composition, biochemical composition of organic matter due to degradation, isotopic disequilibrium within the dissolved inorganic carbon pool, particle dynamics, or seasonal vertical mixing. Coordinated isotopic, biological, and seawater chemistry data are sparse, and consistent drivers of this widespread isotopic pattern are currently elusive. Further work is needed to adequately characterize the environmental conditions coinciding with this pattern, to test its origins, and to determine if the magnitude of upper water column δ13CPOC variations could be a useful marker of upper ocean carbon cycle dynamics.

中文翻译：

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低透光区颗粒有机碳δ13C值的开阔洋最小值

1980 年代至 1990 年代的广泛研究导致了对海面颗粒有机碳 (δ13CPOC) δ13C 值纬度变化的表征，并发现了与 CO2 浓度、温度、生长速率和细胞几何形状的关系。令人惊讶的是，没有进行大规模的努力来描述 δ13CPOC 值随水体深度的变化。在这里，我们汇编了已发表的例子，展示了上部水柱的颗粒有机碳 (POC) 中广泛的同位素模式。在51个垂直剖面中，下透光带的δ13CPOC值平均比公海环境下上透光带的δ13CPOC值低1.4‰。在大多数位置，δ13CPOC 值的垂直下降 >2‰ 并高达 5‰，大于相同深度的溶解无机碳中公认的垂直 δ13C 变化。我们简要回顾了先前对单个水柱的研究提供的假设和支持证据：观察到的模式可能是由于光合增长率或群落组成的垂直差异、降解导致的有机物质的生化组成、溶解的无机碳库内的同位素不平衡、粒子动力学，或季节性垂直混合。协调的同位素、生物和海水化学数据很少，这种广泛同位素模式的一致驱动因素目前难以捉摸。需要进一步的工作来充分表征与这种模式一致的环境条件，以测试其起源，