Huang Wei-Jen, Cai Wei-Jun, Wang Yongchen, Lohrenz Steven E, Murrell Michael C
School of Marine Science and Policy University of Delaware Newark Delaware USA; Department of Marine Sciences University of Georgia Athens Georgia USA.
School of Marine Science and Policy University of Delaware Newark Delaware USA.
J Geophys Res Oceans. 2015 Mar;120(3):1429-1445. doi: 10.1002/2014JC010498. Epub 2015 Mar 3.
River-dominated continental shelf environments are active sites of air-sea CO exchange. We conducted 13 cruises in the northern Gulf of Mexico, a region strongly influenced by fresh water and nutrients delivered from the Mississippi and Atchafalaya River system. The sea surface partial pressure of carbon dioxide (CO) was measured, and the air-sea CO flux was calculated. Results show that CO exchange exhibited a distinct seasonality: the study area was a net sink of atmospheric CO during spring and early summer, and it was neutral or a weak source of CO to the atmosphere during midsummer, fall, and winter. Along the salinity gradient, across the shelf, the sea surface shifted from a source of CO in low-salinity zones (0≤S<17) to a strong CO sink in the middle-to-high-salinity zones (17≤S<33), and finally was a near-neutral state in the high-salinity areas (33≤S<35) and in the open gulf (S≥35). High CO values were only observed in narrow regions near freshwater sources, and the distribution of undersaturated CO generally reflected the influence of freshwater inputs along the shelf. Systematic analyses of CO variation demonstrated the importance of riverine nitrogen export; that is, riverine nitrogen-enhanced biological removal, along with mixing processes, dominated CO variation along the salinity gradient. In addition, extreme or unusual weather events were observed to alter the alongshore CO distribution and to affect regional air-sea CO flux estimates. Overall, the study region acted as a net CO sink of 0.96 ± 3.7 mol m yr (1.15 ± 4.4 Tg C yr).
受河流主导的大陆架环境是海气二氧化碳交换的活跃区域。我们在墨西哥湾北部进行了13次巡航，该区域受到密西西比河和阿查法拉亚河水系输送的淡水和营养物质的强烈影响。测量了海表面二氧化碳分压（CO₂），并计算了海气二氧化碳通量。结果表明，二氧化碳交换呈现出明显的季节性：研究区域在春季和初夏是大气二氧化碳的净汇，而在仲夏、秋季和冬季则对大气呈中性或弱源。沿着盐度梯度，跨大陆架，海表面从低盐度区（0≤S<17）的二氧化碳源转变为中高盐度区（17≤S<33）的强二氧化碳汇，最终在高盐度区域（33≤S<35）和开阔海湾（S≥35）接近中性状态。高二氧化碳值仅在靠近淡水来源的狭窄区域观测到，不饱和二氧化碳的分布总体上反映了沿大陆架淡水输入的影响。对二氧化碳变化的系统分析表明了河流氮输出的重要性；也就是说，河流氮增强的生物去除作用，与混合过程一起，主导了沿盐度梯度的二氧化碳变化。此外，观测到极端或异常天气事件会改变沿岸二氧化碳分布并影响区域海气二氧化碳通量估计。总体而言，研究区域作为0.96±3.7 mol m⁻² yr⁻¹（1.15±4.4 Tg C yr⁻¹）的净二氧化碳汇。
