Spring net community production and its coupling with the CO2 dynamics in the surface water of the northern Gulf of Mexico
Spring net community production and its coupling with the CO2 dynamics in the surface water of the northern Gulf of Mexico
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DOI：
10.5194/bg-16-3507-2019
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发表时间：
2019-09-17
期刊：
影响因子：
4.9
通讯作者：
Xu, Yuanyuan
中科院分区：
文献类型：
--
作者：
Jiang, Zong-Pei;Cai, Wei-Jun;Xu, Yuanyuan
在春季丰产季节，对墨西哥湾北部地表水（nGOM）的净群落生产（NCP）及其与二氧化碳系统的耦合进行了检查。 NCP 使用多种方法进行估计：(1) 正在进行的 O-2 和 Ar 比率，(2) 明/暗瓶氧气孵育期间的氧气变化，以及 (3) 溶解的无机碳或营养物的非保守变化。这些方法都显示出 NCP 的高空间变异性，并沿着河流-海洋混合梯度显示出类似的模式，显示羽流区域的高生产率。根据正在进行的高分辨率 O-2 和 Ar 测量估算出的 NCPO2Ar 表明，由于陆地碳输入和光合作用的光限制的影响，高营养和高浊度密西西比河末端的异养条件（当盐度 < 2 时为-51.3 +/- 11.9 mmol C m(-2) d(-1)）。在密西西比和阿查法拉亚羽流中观察到高 NCPO2Ar 速率（105.0 +/- 59.2 mmol C m(-2) d(-1)，高达 235.4 mmol C m(-2) d(-1)），中间盐度在 15 至 30 之间，其中光和营养物质都有利于浮游植物的产生。由于营养限制，在高盐度、贫营养近海水域（盐度 > 35.5）中观察到的 NCPO2Ar 率接近于零。海气CO2通量普遍表现出相应的变化，从河道中的CO2强源(55.5+/-7.6mmolCm(-2)d(-1))，到羽流中的CO2汇(-13.4+/-5.5mmolCm(-2)d(-1))，再到近海水域与大气接近平衡。总体而言，2017年春季nGOM的地表水呈净自养状态，面积加权平均NCPO2Ar为21.2 mmol C m(-2) d(-1)，CO2汇为-6.7 mmol C m(-2) d(-1)。通过盒模型显示原位生物生产与 O-2 和 CO2 气体交换之间的时间不匹配，导致 NCPO2Ar 和 CO2 通量之间的脱钩（例如，自养水作为密西西比河口外的 CO2 源，异位水作为 Atchafalaya 沿海水域的 CO2 汇）。这种解耦是由于缓慢的海气CO2交换率和碳酸盐系统的缓冲作用，原位生物生产叠加在来自源水的挥之不去的背景pCO(2)上的结果。
Net community production (NCP) in the surface water of the northern Gulf of Mexico (nGOM) and its coupling with the CO2 system were examined during the productive spring season. NCP was estimated using multiple approaches: (1) underway O-2 and Ar ratio, (2) oxygen changes during light/dark bottle oxygen incubations, and (3) non-conservative changes in dissolved inorganic carbon or nutrients. These methods all showed high spatial variability of NCP and displayed similar patterns along the river-ocean mixing gradient, showing high production rates in plume regions. NCPO2Ar estimated from high-resolution O-2 and Ar underway measurement indicated heterotrophic conditions at the high-nutrient and high-turbidity Mississippi River end (-51.3 +/- 11.9 mmol C m(-2) d(-1) when salinity < 2) resulting from the influence of terrestrial carbon input and light limitation on photosynthesis. High NCPO2Ar rates (105.0 +/- 59.2 mmol C m(-2) d(-1), up to 235.4 mmol C m(-2) d(-1)) were observed in the Mississippi and Atchafalaya plumes at intermediate salinities between 15 and 30 where light and nutrients were both favorable for phytoplankton production. NCPO2Ar rates observed in the high-salinity, oligotrophic offshore waters (salinity > 35.5) were close to zero due to nutrient limitation. Air-sea CO2 fluxes generally showed corresponding changes, from being a strong CO2 source in the river channel (55.5 +/- 7.6 mmol C m(-2) d(-1)), to a CO2 sink in the plume (-13.4 +/- 5.5 mmol C m(-2) d(-1)), and to being nearly in equilibrium with the atmosphere in offshore waters. Overall, the surface water of the nGOM was net autotrophic during spring 2017, with an area-weighted mean NCPO2Ar of 21.2 mmol C m(-2) d(-1), and was a CO2 sink of -6.7 mmol C m(-2) d(-1). A temporal mismatch between in situ biological production and gas exchange of O-2 and CO2 was shown through a box model to result in decoupling between NCPO2Ar and CO2 flux (e.g., autotrophic water as a CO2 source outside the Mississippi River mouth and heterotopic water as a CO2 sink in the Atchafalaya coastal water). This decoupling was a result of in situ biological production superimposed on the lingering background pCO(2) from the source water because of the slow air-sea CO2 exchange rate and the buffering effect of the carbonate system.