LONG-TERM CHARACTERISTICS OF MARINE HEATWAVES (1982–2021) IN INDONESIAN WATERS AND THEIR IMPACT ON UPWELLING

• Main Author: Beliyana, Erlin
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/84909
• Institution: Institut Teknologi Bandung

Global warming due to human activities (anthropogenic) is characterized by an increasing air temperature of ±1.1 °C over the last century. Rising air temperature impacts rising sea surface temperature (SST) through the ocean-atmosphere interactions. One of the extreme phenomena due to rising of SST leads marine heatwaves (MHWs). Studies on the effects of global warming on the characteristics of MHWs in various parts of the world have been widely reported in recent years, while in Indonesian waters, the study of MHWs are still limited. As far as information is available in the previous study, the MHWs study did not consider the differences of warm and cold phases of Pacific Decadal Oscillation (PDO). Therefore, the aims of this dissertation research are to further investigate the characteristics of MHWs (i.e., frequency, maximum intensity, and duration of occurrence) in the Indonesian waters. The study utilizes primary data (i.e., SST) from the National Oceanic and Atmospheric Administration Optimum Interpolation Sea Surface Temperature. In addition, PDO, El Niño-Southern Oscillation (ENSO), and Indian Ocean Dipole (IOD) indices as global-scale climate variability are used to investigate their relationship with MHWs. Net surface heat flux component data (i.e., shortwave radiation, longwave radiation, sensible heat flux, and latent heat flux), current speed, mixed layer depth, density, chlorophyll-a, and wind speed were also used to further investigate dynamics of MHW events. The data covered a period within the last 40 years (1982– 2021) during the warm (1982–2007) and cold (2008–2021) phases of the PDO and were processed by statistical analysis methods and processed with MATLAB software. This study clearly reveals the highest average frequency (2–3 times/ year) and maximum intensity of MHWs (>1.5 °C) occurred during the warm phase of PDO (El Niño-like). Conversely, the longest durations of MHWs (7–15 days) in Indonesian waters were recorded during the cold phase of PDO (La Niñ-like). Through composite analysis, the highest maximum frequency (2.52 events/year) and he highest intensity of MHWs (1.54 °C) were found during El Niño and positive IOD occur simultaneously during warm phase PDO. In contrast, the longest durations (10.90 days) were closely linked to La Niña and negative IOD events during the cold PDO phase. Additionally, the study highlighted a stronger correlation between ENSO and MHW intensity in the Indonesian waters compared to the IOD. ENSO effect on the formation of MHWs with a time lag varying between 3–10 months for western and central Indonesian waters. Meanwhile, eastern Indonesian waters have a shorter time lag between 0–2 months. In addition, analysis of the heat budget in the surface mixing layer shows a significant role of advection associated with the Indonesian Throughflow on the formation of MHWs in southern Java with a correlation value between the rate of temperature change and horizontal advection of 0.55. Meanwhile, the other five study sites showed a dominant role of the net air-sea heat flux on the warming and occurrence of MHWs. On the other hand, the impact of MHWs on weakening the intensity of upwelling occurred during the JJA season from 1998 to 2021. Southern eastern Java experienced the strongest suppression of upwelling intensity due to SST warming associated with intense MHWs events, followed by the weakening of upwelling intensity in southern Central Java, and the lowest inhibition of upwelling intensity due to the impact of MHWs was found south of western Java. These findings highlight the complex interplay between climate phenomena and MHW characteristics. Therefore, a complete and in-depth understanding of MHWs and their formation mechanisms becomes an urgency to understand this matter as part of a mitigation effort to deal with the MHWs disasters in the Indonesian waters due to ongoing climate change.