Sridevi B, Sabira Sk, Sarma V V S S
CSIR-National Institute of Oceanography, 176 Lawsons Bay Colony, Visakhapatnam, 530 017, India.
Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India.
Environ Sci Pollut Res Int. 2023 Apr;30(18):53616-53634. doi: 10.1007/s11356-023-26001-9. Epub 2023 Mar 2.
Warming due to climate change stratifies the upper ocean and reduces nutrient input to the photic zone resulting in a decline in net primary production (NPP). On the other hand, climate change increases both anthropogenic aerosol input into the atmosphere and the river discharge due to the melting of glaciers on land resulting in enhanced nutrient inputs to the surface ocean and NPP. To examine the balance between these two processes, spatial and temporal variations in the rate of warming, NPP, aerosol optical depth (AOD), and sea surface salinity (SSS) were studied between 2001 and 2020 in the northern Indian Ocean. Strong heterogeneity in the warming of the sea surface was observed in the northern Indian Ocean with significant warming in the south of 12°N. Insignificant trends in warming were observed in the northern Arabian Sea (AS), north of 12°N, during winter and fall, and western Bay of Bengal (BoB) during winter, spring, and fall associated with higher levels of anthropogenic AOD (AAOD) due to a reduction in incoming solar radiation. The decline in NPP was observed in the south of 12°N in both AS and BoB and correlated inversely with SST suggesting that a weak supply of nutrients due to upper ocean stratification controlled NPP. Despite warming, the weak trends in NPP in the north of 12°N were associated with higher AAOD levels and their rate of increase suggesting that the deposition of nutrients from the aerosols seems to be compensating for declining trends due to warming. The decrease in sea surface salinity confirmed an increase in river discharge, and nutrient supply led to weak NPP trends in the northern BoB. This study suggests that the enhanced atmospheric aerosols and river discharge played a significant role in warming and changes in NPP in the northern Indian Ocean, and these parameters must be included in the ocean biogeochemical models for accurate prediction of possible changes in the upper ocean biogeochemistry in the future due to climate change.
气候变化导致的变暖使上层海洋分层，并减少了进入光合层的营养物质输入，导致净初级生产力（NPP）下降。另一方面，气候变化增加了大气中人为气溶胶的输入以及由于陆地冰川融化导致的河流流量，从而增加了表层海洋的营养物质输入和NPP。为了研究这两个过程之间的平衡，2001年至2020年期间对北印度洋的升温速率、NPP、气溶胶光学厚度（AOD）和海表盐度（SSS）的时空变化进行了研究。在北印度洋观测到海表变暖存在强烈的不均匀性，在北纬12°以南有显著变暖。在冬季和秋季，北纬12°以北的阿拉伯海北部（AS）以及冬季、春季和秋季的孟加拉湾西部（BoB）观测到变暖趋势不显著，这与由于太阳辐射入射减少导致的较高水平的人为AOD（AAOD）有关。在AS和BoB中，北纬12°以南观测到NPP下降，并且与海表温度呈负相关，这表明上层海洋分层导致的营养物质供应不足控制了NPP。尽管有变暖现象，但北纬12°以北NPP的微弱趋势与较高的AAOD水平及其增加速率有关，这表明气溶胶中的营养物质沉积似乎在补偿由于变暖导致的下降趋势。海表盐度的降低证实了河流流量的增加，营养物质供应导致了孟加拉湾北部NPP的微弱趋势。这项研究表明，大气气溶胶和河流流量的增加在北印度洋的变暖和NPP变化中发挥了重要作用，并且这些参数必须纳入海洋生物地球化学模型中，以便准确预测未来由于气候变化导致的上层海洋生物地球化学可能发生的变化。
