Long-Term Changes of Surface Total Alkalinity and Its Driving Mechanisms in the North Indian Ocean

IF 5.5 2区 地球科学 Q1 ENVIRONMENTAL SCIENCES
A. P. Joshi, Prasanna Kanti Ghoshal, Kunal Chakraborty, Rajdeep Roy, Chiranjivi Jayaram, B. Sridevi, V. V. S. S. Sarma
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Abstract

This study examines long-term changes in surface total alkalinity (TA) in the North Indian Ocean (NIO) by developing a machine learning-based data product (INCOIS_TA) using ship-based observations collected from different sources during the period 1978–2019 and a reanalysis data product. We identify three sub-regions within the NIO exhibiting significantly increasing TA trends, which are south of 7°N (0.81 ± $\pm $ 0.38 μ ${\upmu }$ mol kg 1 ${\text{kg}}^{-1}$ yr 1 ${\text{yr}}^{-1}$ ), southeastern coast of the Arabian Sea (AS) (1.16 ± $\pm $ 0.42 μ ${\upmu }$ mol kg 1 ${\text{kg}}^{-1}$ yr 1 ${\text{yr}}^{-1}$ ), and the southwestern region of the Bay of Bengal (BoB) (0.47 ± $\pm $ 0.26 μ ${\upmu }$ mol kg 1 ${\text{kg}}^{-1}$ yr 1 ${\text{yr}}^{-1}$ ). The increasing trend in surface salinity primarily drives the rise in TA in these three regions. In other regions, upper ocean warming that increases stratification and weakens vertical mixing results in a reduced vertical supply of nutrients and high sub-surface TA, which may, in turn, lead to a decline in surface TA. However, this expected decrease is found to be insignificant, likely due to substantial atmospheric deposition of nutrients. Analysis of the annual mean excess alkalinity spatial pattern, after normalizing TA, indicates that the AS may be favorable for calcification, while the BoB may not. At interannual time scales, both the climatic modes (El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD)) have significant and equal impact on the surface TA in the BoB, whereas in the AS, the changes in surface TA are dominated only by ENSO. Further, we find that strong El-Niño (La-Niña) and positive (negative) IOD years show a decrease (increase) in surface TA in the NIO.

Abstract Image

Abstract Image

北印度洋表层总碱度的长期变化及其驱动机制
本研究利用1978-2019年期间从不同来源收集的船舶观测数据和再分析数据产品,开发了基于机器学习的数据产品(INCOIS_TA),研究了北印度洋(NIO)表面总碱度(TA)的长期变化。我们在NIO内确定了三个显示TA显著增加趋势的子区域。7°N以南(0.81±$\pm $ 0.38 μ ${\upmu}$ mol kg−1 ${\text{kg}}^{-1}$${\text{Yr}}^{-1}$),阿拉伯海东南海岸(AS)(1.16±$\pm $ 0.42 μ ${\upmu}$ mol kg−1 ${\text{kg}}^{-1}$${\text{Yr}}^{-1}$),孟加拉湾西南部地区(BoB)为(0.47±$\pm $ 0.26 μ ${\upmu}$ mol kg−1 ${\text{kg}}^{-1}$Yr -1 ${\text{Yr}}^{-1}$)。表层盐度的升高是三个区域TA升高的主要驱动力。在其他地区,上层海洋变暖增加了分层和减弱了垂直混合,导致垂直供应的营养物质减少和高次表层热饱和度,这反过来又可能导致表面热饱和度下降。然而,这种预期的减少被发现是微不足道的,可能是由于大量的营养物在大气中沉积。对TA标准化后的年平均过量碱度空间格局分析表明,AS可能有利于钙化,而BoB可能不利于钙化。在年际时间尺度上,厄尔尼诺Niño-Southern涛动(ENSO)和印度洋偶极子(IOD)两种气候模式对赤道地区地表温度的影响均显著且相同,而在赤道地区,地表温度的变化仅受ENSO主导。此外,我们发现强El-Niño (La-Niña)和正(负)IOD年份显示NIO表面TA减少(增加)。
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来源期刊
Global Biogeochemical Cycles
Global Biogeochemical Cycles 环境科学-地球科学综合
CiteScore
8.90
自引率
7.70%
发文量
141
审稿时长
8-16 weeks
期刊介绍: Global Biogeochemical Cycles (GBC) features research on regional to global biogeochemical interactions, as well as more local studies that demonstrate fundamental implications for biogeochemical processing at regional or global scales. Published papers draw on a wide array of methods and knowledge and extend in time from the deep geologic past to recent historical and potential future interactions. This broad scope includes studies that elucidate human activities as interactive components of biogeochemical cycles and physical Earth Systems including climate. Authors are required to make their work accessible to a broad interdisciplinary range of scientists.
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