Organic carbon and nitrogen concentrations in surface waters of the North Atlantic along 20°E in July-August 1996

Redfield stoichiometry has proved a robust paradigm for the understanding of biological production and export in the ocean on a long-term and a large-scale basis. However, deviations of carbon and nitrogen uptake ratios from the Redfield ratio have been reported. A comprehensive data set including all carbon and nitrogen pools relevant to biological production in the surface ocean (DIC, DIN, DOC, DON, POC, PON) was used to calculate seasonal new production based on carbon and nitrogen uptake in summer along 20°W in the northeast Atlantic Ocean. The 20°W transect between 30 and 60°N covers different trophic states and seasonal stages of the productive surface layer, including early bloom, bloom, post-bloom and non-bloom situations. The spatial pattern has elements of a seasonal progression. We also calculated exported production, i.e., that part of seasonal new production not accumulated in particulate and dissolved pools, again separately for carbon and nitrogen. The pairs of estimates of 'seasonal new production' and 'exported production' allowed us to calculate the C : N ratios of these quantities. While suspended particulate matter in the mixed layer largely conforms to Redfield stoichiometry, marked deviations were observed in carbon and nitrogen uptake and export with progressing season or nutrient depletion. The spring system was characterized by nitrogen overconsumption and the oligotrophic summer system by a marked carbon overconsumption. The C : N ratios of seasonal new as well as exported production increase from early bloom values of 5-6 to values of 10-16 in the post-bloom/oligotrophic system. The summertime accumulation of nitrogen-poor dissolved organic matter can explain only part of this shift.

雷德菲尔德化学计量比（Redfield stoichiometry）长期以来都是理解海洋生物生产与输出的可靠范式。但已有研究报道了碳氮摄取比偏离雷德菲尔德比的现象。本研究采用涵盖表层海洋生物生产相关的全部碳、氮库（DIC、DIN、DOC、DON、POC、PON）的综合数据集，基于大西洋东北部20°W断面夏季的碳氮摄取情况，计算季节新生产量。该20°W断面覆盖北纬30°至60°海域，涵盖了生产力表层水层的不同营养盐状态与季节阶段，包括藻华初期、藻华期、藻华后期以及非藻华期场景，其空间分布格局呈现出季节演替的特征。本研究同时分别针对碳、氮计算了输出生产量——即未在颗粒态与溶解态库中留存的季节新生产部分。通过“季节新生产量”与“输出生产量”的两组估算值，可计算得到这两类过程的碳氮比。尽管混合层中的悬浮颗粒物大体符合雷德菲尔德化学计量比，但随着季节推进或营养盐耗竭，碳氮摄取与输出过程会出现显著偏离。春季海域系统表现为氮过度摄取，而寡营养夏季系统则表现为显著的碳过度摄取。季节新生产与输出生产的碳氮比从藻华初期的5~6上升至藻华后期/寡营养系统中的10~16。夏季贫氮溶解有机物的积累仅能部分解释这一变化趋势。