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To elucidate impacts of an Indian Ocean Dipole (IOD) event on surface seawater CO2 dynamics, we analyzed data collected along the World Ocean Circulation Experiment Hydrographic Program I08 N line (latitudes 20°S–6°N at 80°E) in December 2019, when a strong positive IOD (pIOD) event occurred. After removing the effects of anthropogenic CO2 accumulation, we examined anomalies of the surface seawater CO2 fugacity (fCO2) from the climatology in relation to other marine properties. At latitudes 11°S–6°S, where horizontal advection of upwelled water off Sumatra was observed, dissolved inorganic carbon and total alkalinity, both normalized to a salinity of 35 (nTCO2 and nTA) showed positive anomalies of +11.4 and +8.1 μmol kg−1, respectively. At latitudes 5°S–5°N, where distinct low‐salinity water was observed because of the pIOD, nTCO2 and nTA showed negative anomalies of −4.0 and ‒0.5 μmol kg−1, respectively. The combined effects of the nTCO2 and nTA anomalies on fCO2 made the observed fCO2 anomalies small, +3.2 and −6.6 μatm for 6°S–11°S and 5°S–5°N, respectively, because the direction of the Revelle factor for TCO2 is opposite to that for TA. We estimated that the pIOD modulated the air–sea CO2 flux by +0.45 and −0.55 mmol m−2 d−1 on average within11°S–6°S and 5°S–5°N, respectively. The impacts of the pIOD on the CO2 dynamics could be explained by the anomalous salinity conditions associated with upwelled water and the freshwater balance. Plain Language Summary: The Indian Ocean Dipole (IOD) is one of the dominant anomaly patterns in the Indian Ocean, and typically most prominently affects sea surface temperature. In 2019, the strongest IOD of the 21st century occurred. How did this extreme IOD affect the carbon cycle in the ocean? Answering this question was the purpose of this study. To this end, we analyzed data on marine biogeochemical properties observed along 80°E in December 2019. At latitudes 11°S–6°S, where the IOD led to a decrease in sea surface temperature, we detected positive anomalies of dissolved inorganic carbon and total alkalinity relative to their climatological values. In contrast, at latitudes 5°S–5°N, where the IOD led to a decrease in sea surface salinity, we detected small negative anomalies of dissolved inorganic carbon and total alkalinity. These chemical property anomalies individually caused large anomalies in surface seawater CO2 fugacity (fCO2), which determines the potential for air–sea CO2 exchange, but in combination they had only a small effect on fCO2. We found that anomalous salinity conditions due to upwelling and the freshwater balance, both related to the IOD, caused changes in the Indian Ocean CO2 dynamics. Key Points: Significant modulations of marine carbonate system properties during a positive Indian Ocean Dipole were detected along 80°EThe upwelled water advected from off Sumatra increased surface seawater fCO2 and the CO2 flux at latitudes 11°S–6°S at 80°EThe freshwater balance reduced surface seawater fCO2 and the CO2 flux at latitudes 5°S–5°N at 80°E [ABSTRACT FROM AUTHOR]

The spatiotemporal characteristics of the south Sri Lanka coastal current (SSLCC) during summer are examined in this study. Climatologically, the SSLCC flows eastward as a part of the southwest monsoon current during summer. However, westward SSLCC occurred lasting more than 20 days in the summer of 2013, 2016, 2017, and 2018 based on reanalysis data, implying significant interannual variability of the SSLCC. The analysis on the summer extreme westward SSLCC indicates that the intra‐seasonal wind associated with atmospheric boreal summer intra‐seasonal oscillation (BSISO) is the main factor leading to the westward SSLCC. Firstly, the northward propagation of the BSISO induces the westerly wind anomaly and positive wind stress curl anomaly along the south and east coast of Sri Lanka, which induces the westward SSLCC. Secondly, driven by equatorial Indian Ocean intra‐seasonal wind, the low sea level anomaly associated with upwelling Rossby wave reflected from the west coast of Sumatra Island propagates westward. This propagation significantly influences the cyclonic circulation off the south coast of Sri Lanka, thus facilitating the occurrence of the westward SSLCC. Plain Language Summary: Climatologically, the south Sri Lanka coastal current (SSLCC) transports high‐salinity water from the Arabian Sea to the Bay of Bengal as it flows eastward during summer. However, extreme westward SSLCC occurred in the summer of 2013, 2016, 2017, and 2018, lasting roughly 20 days and affecting the salinity balance of the Northern Indian Ocean. Our study aims at investigating the characteristics of the SSLCC and explores the mechanism of the summer westward SSLCC. The findings suggest that the westward SSLCC is primarily regulated by the intra‐seasonal component (30–105 days). The regulation of this intra‐seasonal signal involves a combination of factors, including a positive wind stress curl anomaly along the south and east coast of Sri Lanka and the presence of upwelling Rossby waves along the 5°N section. Key Points: The south Sri Lanka coastal current (SSLCC) exhibits significant intra‐seasonal, semi‐annual, and annual componentsIntra‐seasonal signal associated with boreal summer intra‐seasonal oscillation dominates the emergence of the summer westward SSLCCThe synergistic effect of the cyclonic wind stress curl anomaly on the southern Sri Lanka coast and upwelling Rossby waves reflected from Sumatra Island facilitates the summer westward SSLCC [ABSTRACT FROM AUTHOR]

It is well known that the intra‐seasonal component is critical for the occurrence of the westward south Sri Lanka coastal current (SSLCC) during summer. In this study, the relative contributions and physical processes that determine the westward SSLCC during summer on the intra‐seasonal timescale are quantified using the reanalysis data and a simple linear, continuously stratified (LCS) ocean model. A comprehensive analysis of the westward SSLCC events reveals that the wind forcing from south Sri Lanka coast, equatorial Indian Ocean, and southern Bay of Bengal (BoB) is responsible for the westward SSLCC (on the intra‐seasonal timescale), contributing 53%, 30%, and 17%, respectively. The local wind forcing along the southern Sri Lanka is linked to the boreal summer intra‐seasonal oscillation (BSISO). Specifically, the negative phase of the BSISO, characterized by active atmospheric convection, induces cyclonic wind stress curl along the south coast of Sri Lanka, and directly promoting the westward SSLCC. The equatorial forcing plays a secondary role in the westward SSLCC via mixing behavior of the first and second baroclinic modes upwelling Rossby waves (0.64 m s−1), propagating westward along the 5°N section as the cyclonic vortices. On the contrast, influenced by the modulation of the BSISO signal, the forcing from the southern BoB excites the rapid westward propagation of the first baroclinic mode upwelling Rossby waves (0.85 m s−1) near 90°E, contributing the westward SSLCC. Plain Language Summary: This study explores the crucial role of intra‐seasonal dynamics in driving the westward south Sri Lanka coastal current (SSLCC) during summer. Using reanalysis data and a simple linear, continuously stratified (LCS) ocean model, the research reveals the combined effects of wind forcing from three sources of southern Sri Lanka coast, equatorial Indian Ocean, and southern Bay of Bengal (BoB), contributing 53%, 30%, and 17%, respectively. These three forcings exhibit distinct physical processes: local wind forcing directly affects the westward SSLCC through the local cyclonic wind stress curl, while wind forcing from equatorial and southern BoB promotes the westward SSLCC through the first‐second baroclinic mode and first baroclinic mode of the upwelling Rossby waves, respectively. This study provides valuable insights into the mechanisms of the SSLCC variability and deepens our understanding of coastal circulation dynamics. Key Points: The wind forcing from southern Sri Lanka (53%), equatorial (30%), and Bay of Bengal (BoB, 17%) is responsible for the westward south Sri Lanka coastal current (SSLCC)The local wind forcing induces the cyclonic wind stress curl along the south coast of Sri Lanka, directly facilitating the westward SSLCCThe equatorial (BoB) forcing affects the westward SSLCC via the westward propagation of upwelling Rossby wave in the first‐second (first) baroclinic modes [ABSTRACT FROM AUTHOR]

This study investigates the impact of salinity stratification on the upper-ocean response to a category 5 tropical cyclone, Phailin, that crossed the northern Bay of Bengal (BOB) from 8 to 13 October 2013. A drastic increase of up to 5.0 psu in sea surface salinity (SSS) was observed after Phailin's passage, whereas a weak drop of below 0.5°C was observed in sea surface temperature (SST). Rightward biases were apparent in surface current and SSS but not evident in SST. Phailin-induced SST variations can be divided into the warming and cooling stages, corresponding to the existence of the thick barrier layer (BL) and temperature inversion before and erosion after Phailin's passage, respectively. During the warming stage, SST increased due to strong entrainment of warmer water from the BL, which overcame the cooling induced by surface heat fluxes and horizontal advection. During the cooling stage, the entrainment and upwelling dominated the SST decrease. The preexistence of the BL, which reduced entrainment cooling by ~1.09°Cday-1, significantly weakened the overall Phailin-induced SST cooling. The Hybrid Coordinate Ocean Model (HYCOM) experiments confirm the crucial roles of entrainment and upwelling in the Phailin-induced dramatic SSS increase and weak SST decrease. Analyses of upper-ocean stratification associated with 16 super TCs that occurred in the BOB during 1980-2015 show that intensifications of 13 TCs were associated with a thick isothermal layer, and 5 out of the 13 were associated with a thick BL. The calculation of TC intensity with and without considering subsurface temperature demonstrates the importance of large upper-ocean heat storage in TC growth. [ABSTRACT FROM AUTHOR]

The article focuses on a study related to a campaign ASIRI in Bay of Bengal (BoB) aimed at interaction and processes of lower- atmosphere and upper-ocean in the context of Indian Ocean monsoons (IOM). Topics discussed include ASIRI's objective the determination of freshwater distribution by submesoscale and mesoscale processes, principal investigators lead by ASIRI that focused on BoB modeling and turbulence process modeling.

The MV X-Press Pearl accident near Sri Lanka in May 2021 released several pollutants into the ocean, including 1843.3 t of urea, raising concerns about the impact on the region. This study uses a coupled ocean (NEMO)-biogeochemistry (ERSEM) model to simulate urea dispersion under various scenarios. While it doesn't directly reflect the real accident, it provides insights into the potential impact of similar chemical spills. By adjusting tracer release rates and timing, we assessed their impact on the distribution of the chemical plume. Findings show slower release rates prolong higher urea concentrations, potentially causing phytoplankton blooms, while monsoon conditions significantly affect dispersal patterns. Due to a lack of publicly available urea observations, we used particle tracking experiments validated with data on plastic nurdle beaching. This research shows how a simpler, affordable scenario approach could inform the management of chemical spills without a fully developed operational oceanographic system., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)