Gayan Pathirana

University of Ruhuna

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Jong‐Seong Kug

Seoul National University

Dongxiao Wang

Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)

Kyung Min Noh

Pohang University of Science and Technology

Dong-Geon Lee

Seoul National University

Hyo-Jin Park

Yonsei University

Donggeon Lee

Kyungpook National University

Ruijie Ye

Forschungszentrum Jülich

Pathmarasa Kajakokulan

University of Ruhuna

Lu Shou

Second Institute of Oceanography

Feng Zhou

Second Institute of Oceanography

Cooperative Institutions

Second Institute of Oceanography

Ministry of Natural Resources

Pohang University of Science and Technology

University of Ruhuna

Chinese Academy of Sciences

Yonsei University

Seoul National University

State Key Laboratory of Satellite Ocean Environment Dynamics

Zhejiang Marine Fisheries Research Institute

Institute of Oceanology

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Intensified Responses of Phytoplankton to the Indian Ocean Dipole Under Greenhouse Warming

Research Square (Research Square) (2024)

Gayan Pathirana Kyung Min Noh Donggeon Lee Hyo-Jin Park Dongxiao Wang

Abstract The Indian Ocean Dipole (IOD) has been proposed to be a key driver of biological processes in the Indian Ocean (IO) in the present climate. Given the expected influence of global warming on both the properties of the IOD and the biogeochemistry within the IO, a key question arises: How will the relationship between the IOD and chlorophyll evolve in a warming climate? Here, utilizing simulations from the Coupled Model Intercomparison Project (CMIP) Phase 6 Earth System models, our findings reveal a notable intensification in the IOD-chlorophyll relationship under greenhouse warming. This intensification is linked to an increase in phytoplankton biomass during the June to November period of positive IOD years in the southeastern IO (SEIO). Interestingly, our analysis indicates a substantial rise in IOD-induced chlorophyll levels in a warming climate, despite a marked decrease in IOD-induced upwelling in the SEIO. The shallower thermocline leads to an increase in the mean nutrient concentration in the subsurface layer, thereby facilitating an enhanced anomalous nutrient supply to the surface layer, which contributes to increased phytoplankton biomass. Our study highlights the consequential effects of IOD on chlorophyll dynamics and underscores the need for improvement of Earth System Models to resolve our understanding of biophysical interactions in the IO in response to global warming.

Greenhouse effect

10.21203/rs.3.rs-3935615/v1

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Strengthening of Sri Lanka summer monsoon rainfall with rapid Arabian Sea warming

International Journal of Climatology (2023)

Pathmarasa Kajakokulan A. R. P. Warnasooriya Gayan Pathirana

Abstract Several studies have shown that rapid sea surface temperature (SST) warming in the tropical Indian Ocean (IO) significantly modulates the summer monsoon rainfall (SMR) over India. However, it remains unclear how the IO SST warming affects the SMR in Sri Lanka (SL). Therefore, based on observations and reanalysis data, this study investigates the impact of IO warming on SMR variability in the wet‐zone of SL during 2001–2020. The results revealed that the SMR (May–September) in SL's wet zone is increasing and is associated with rapid SST warming in the Arabian Sea during the summer monsoon. Although it is reported that the SMR may decrease over India due to the weakening of land‐sea thermal gradient in summer associated with IO warming, the rapid warming of the AS appears to enhance the SMR in the wet zone of SL. The warming of the AS during summer strengthened the low‐level easterlies, favouring moisture convergence and convection over SL, which enhanced the SMR of the wet zone of SL.

Sri lanka

Convergence zone

10.1002/joc.8172

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An Energetic Mesoscale Anticyclonic Eddy in the Southern Bay of Bengal in June 2020: A Case Study

Journal of Geophysical Research Oceans (2023)

Ruijie Ye Feng Zhou Xiao Ma Lu Shou Qicheng Meng

Abstract The southern Bay of Bengal (BoB) is a region of rich mesoscale eddy activity that plays an important role in modulating water exchange between the BoB and the Arabian Sea. Although statistical surface characteristics of mesoscale eddies in the BoB have been sufficiently explored previously, most studies concentrated on the western and central BoB, but rarely in the southern BoB. In this study, an energetic mesoscale anticyclonic eddy (AE) was detected by long‐term mooring observations in the southern BoB during June 2020. The mooring observations revealed that the AE‐induced maximum temperature and salinity anomalies at 100 m were as large as 6.8°C and 0.3 psu, respectively. The available Argo profiles showed that the AE‐induced salinity anomalies had a three‐layer vertical structure, with a positive anomaly (maximum 0.28 psu) deeper than 100 m and (maximum 0.72 psu) shallower than 40 m, and a negative anomaly (maximum −0.86 psu) between 40 and 100 m, indicating that the AE could exert a significant effect on the redistribution of surface freshwater in the southern BoB. The AE formation was closely connected with remote forcing (equatorial Kelvin wave) and local processes (Rossby wave and local wind stress curl). Local energy conversion analysis demonstrated that baroclinic and barotropic instabilities, as well as wind stress work made comparable contributions to the generation of the AE. Given the frequent occurrence of the AEs to northwest of Sumatra, they could have significant effects on surface freshwater redistribution and regional ecosystem productivity in the southern BoB.

Argo

Anticyclone

Barotropic fluid

Mooring

Sea-surface height

Eddy

Kelvin wave

Temperature salinity diagrams

10.1029/2022jc019188

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Increase in convective extreme El Niño events in a CO ₂ removal scenario

Science Advances (2023)

Gayan Pathirana Ji‐Hoon Oh Wenju Cai Soon‐Il An Seung‐Ki Min

Convective extreme El Niño (CEE) events, characterized by strong convective events in the eastern Pacific, are known to have a direct link to anomalous climate conditions worldwide, and it has been reported that CEE will occur more frequently under greenhouse warming. Here, using a set of CO2 ramp-up and ramp-down ensemble experiments, we show that frequency and maximum intensity of CEE events increase further in the ramp-down period from the ramp-up period. These changes in CEE are associated with the southward shift of the intertropical convergence zone and intensified nonlinear rainfall response to sea surface temperature change in the ramp-down period. The increasing frequency of CEE has substantial impacts on regional abnormal events and contributed considerably to regional mean climate changes to the CO2 forcings.

Intertropical Convergence Zone

Intensity

10.1126/sciadv.adh2412

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Citations (17)

Anomalous propagation pathway of the Sri Lanka Dome in summer 2014

Journal of the National Science Foundation of Sri Lanka (2022)

Gayan Pathirana Guannan Chen D Wang M K Abeyratne Tilak Priyadarshana

The Journal of the National Science Foundation of Sri Lanka publishes the results of research in all aspects of Science and Technology. The journal also has a website at http://www.nsf.gov.lk/. 2021 Impact Factor: 0.682The JNSF provides immediate open access to its content on the principle that making research freely available to the public supports a greater global exchange of knowledge.Cover :Leatherback (a), green (b - adult & f - hatchling), hawksbill (c) and olive ridley (d) turtles who nest in Sri Lankan beaches, green turtle crawl marks (e) and by-catch of sea turtles in fisheries (c & d)Photo credits: SJ Perera (a & c), WPN Perera (b & e), K Ekaratne (d & f)

Sri lanka

Hatchling

10.4038/jnsfsr.v50i4.10636

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Monsoonal impact on circulation pathways in the Indian Ocean

Acta Oceanologica Sinica (2020)

S. U. P. Jinadasa Gayan Pathirana P.N. Ranasinghe Luca Centurioni Verena Hormann

BENGAL

Eddy

Boundary current

10.1007/s13131-020-1557-5

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Tropical cyclones in the Arabian Sea and the Bay of Bengal: comparison of environmental factors

Journal of the National Science Foundation of Sri Lanka (2022)

Gayan Pathirana K. Priyadarshani

BENGAL

Sri lanka

Foundation (evidence)

10.4038/jnsfsr.v50i1.10424

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Intermodel relation between present-day warm pool intensity and future precipitation changes

Climate Dynamics (2023)

Gayan Pathirana Na-Yeon Shin Yi‐Kai Wu Minho Kwon Jong‐Seong Kug

Forcing (mathematics)

10.1007/s00382-023-06918-0

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Influence of Indian Ocean warming on rainfall of Sri Lanka

International Journal of Climatology (2023)

Pathmarasa Kajakokulan Gayan Pathirana Maheshi Dheerasinghe Indeewari Edirisooriya

Abstract Recent studies have pointed out an increased warming over the tropical Indian Ocean (IO) and how such warming could alter the convection and rainfall in the region. In this study, using observational/reanalysis datasets from 1981 to 2020, we show that the early Maha rainfall of Sri Lanka (SL) has been increasing, and it is considerably influenced by the North‐western IO sea surface temperature (SST) increase in the second inter‐monsoon (SIM). A significant warming in the North‐western IO alters the zonal SST gradient and strengthens the low‐level circulation, which induces large‐scale convergence over the western IO during SIM, contributing to the enhancement of rainfall over SL. However, despite the substantial impact of IO warming, the moderate correlation suggests the importance of examining other factors, which may influence the rainfall variability of SL.

Walker circulation

Sri lanka

10.1002/joc.8124

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Asymmetric effects of Indian Ocean dipole on surface chlorophyll variability in the Indian Ocean

Research Square (Research Square) (2024)

Thivin Abeywickrama Gayan Pathirana Kyung Min Noh Kushlani Dissanayake Dongxiao Wang

Abstract The Indian Ocean Dipole (IOD) is a dominant climate mode in the Indian Ocean, characterized by oscillating sea surface temperature anomalies between the western and southeastern equatorial regions. The IOD influences surface circulation, affecting coastal upwelling (downwelling), thereby increasing (decreasing) surface nutrients. These changes alter surface phytoplankton populations, measurable through their photosynthetic pigment, chlorophyll-a. The positive (pIOD) and negative (nIOD) phases of the IOD affect surface chlorophyll differently, particularly along the west of Sumatra (WS) and southwest of the Indian subcontinent (SWI). While changes in surface chlorophyll occur oppositely during each IOD phase, it is unclear how the intensity of surface chlorophyll changes during the positive and negative IOD phases. Given its importance, we investigate this question using observational data and historical simulations from a Coupled Model Intercomparison Project Phase 6 (CMIP6) model. Our findings reveal that although the chlorophyll response follows a dipole pattern, the pIOD phase exerts a dominant influence, with chlorophyll intensity during pIOD exceeding that during nIOD. Specifically, during pIOD, chlorophyll concentrations increase in the WS region and decrease in the SWI region, showing pronounced asymmetry in the intensity of IOD-induced chlorophyll changes. This disparity is driven by anomalous southeasterly winds during pIOD, which enhance nutrient upwelling in the WS and suppress it in the SWI, leading to variations in surface chlorophyll blooms. Thus, our results emphasize the asymmetric nature of IOD-induced changes in surface chlorophyll in the Indian Ocean, with important implications for marine food webs, fisheries, ocean biogeochemical cycles, and global climate systems.

Downwelling

Biogeochemical Cycle

Sea-surface height

10.21203/rs.3.rs-5719068/v1

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