KARAKTERISTIK JANGKA PANJANG MARINE HEATWAVES (1982–2021) DI PERAIRAN INDONESIA DAN DAMPAKNYA TERHADAP UPWELLING DISERTASI Karya tulis sebagai salah satu syarat untuk memperoleh gelar Doktor dari Institut Teknologi Bandung Oleh ERLIN BELIYANA NIM: 32420304 (Program Studi Doktor Sains Kebumian) INSTITUT TEKNOLOGI BANDUNG Juli 2024 i ABSTRAK KARAKTERISTIK JANGKA PANJANG MARINE HEATWAVES (1982–2021) DI PERAIRAN INDONESIA DAN DAMPAKNYA TERHADAP UPWELLING Oleh Erlin Beliyana NIM: 32420304 (Program Studi Doktor Sains Kebumian) Pemanasan global akibat aktivitas manusia (antropogenik) ditandai dengan adanya kenaikan suhu udara ±1,1 °C terjadi dalam satu abad terakhir. Kenaikan suhu udara berdampak terhadap kenaikan suhu permukaan laut (SPL) melalui interaksi laut- atmosfer. Salah satu fenomena ekstrem akibat dari kenaikan SPL, yaitu marine heatwaves (MHWs). Studi dampak pemanasan global terhadap karakteristik MHWs di berbagai belahan dunia sudah banyak dilaporkan dalam beberapa tahun terakhir, sedangkan di perairan Indonesia masih terbatas. Sejauh informasi yang didapatkan, penelitian tersebut dikaji tanpa meninjau perbedaan fase hangat dan dingin Pacific Decadal Oscillation (PDO). Oleh sebab itu, tujuan dalam penelitian disertasi ini adalah mengidentifikasi karakteristik (a.l. frekuensi, intensitas maksimum, dan durasi kejadian) dan mekanisme MHWs di perairan Indonesia. Data utama yang digunakan dalam penelitian adalah data Sea Surface Temperature dari National Oceanic and Atmospheric Administration Optimum Interpolation Sea Surface Temperature. Selain itu digunakan pula data indeks PDO, El Niño- Southern Oscillation (ENSO), dan Indian Ocean Dipole (IOD) sebagai variabilitas iklim skala global untuk menyelidiki hubungannya dengan MHWs. Digunakan pula data komponen net surface heat flux (a.l., shortwave radiation, longwave radiation, sensible heat flux, dan latent heat flux), kecepatan arus, mixed layer depth, densitas, klorofil-a, dan kecepatan angin untuk menginvestigasi lebih lanjut dinamika kejadian MHWs. Keseluruhan data selama 40 tahun (1982–2021) tersebut selanjutnya diidentifikasi berdasarkan fase hangat (1982–2007) dan dingin (2008– 2021) PDO menggunakan metode analisis statistik dan diolah dengan software MATLAB. Hasil penelitian menunjukkan rata-rata frekuensi tertinggi (2–3 kali/tahun) dan intensitas maksimum MHWs tertinggi (>1,5 °C) terjadi selama fase hangat PDO (El Niño-like). Sebaliknya, durasi terpanjang MHWs (7–15 hari) di perairan Indonesia tercatat selama fase dingin PDO (La Niña-like). Melalui analisis komposit, diperoleh frekuensi tertinggi (2,52 kali/tahun) dan intensitas maksimum MHWs tertinggi (1,54 °C) saat El Niño terjadi bersamaan dengan positif IOD selama fase hangat PDO. Sebaliknya, durasi terpanjang MHWs (10,90 hari) ditemukan saat La Niña terjadi bersamaan dengan negatif IOD selama fase dingin PDO. Selain itu, penelitian ini juga menyoroti korelasi yang lebih kuat antara ENSO ii dan intensitas MHWs di perairan Indonesia dibandingkan dengan IOD. ENSO berpengaruh terhadap pembentukan MHWs dengan jeda waktu bervariasi antara 3– 10 bulan untuk perairan barat dan tengah Indonesia, sedangkan di perairan timur Indonesia memiliki jeda waktu lebih pendek antara 0–2 bulan. Selain itu, analisis heat budget di lapisan percampuran permukaan menunjukkan peranan signifikan dari adveksi yang berasosiasi dengan Arus Lintas Indonesia terhadap pembentukan MHWs di selatan Jawa dengan nilai korelasi antara laju berubahan temperatur dan adveksi horizontal 0,55. Sementara itu, di lima lokasi kajian lainnya menunjukkan adanya peranan dominan dari net air-sea heat flux terhadap pemanasan dan kejadian MHWs. Di sisi lain, kejadian MHWs memberikan dampak signifikan terhadap pelemahan intensitas upwelling di selatan Jawa selama musim timur (Juni–Juli–Agustus) dari tahun 1998 hingga 2021. Selatan Jawa bagian timur mengalami penekanan intensitas upwelling yang paling kuat akibat pemanasan SST yang berkaitan dengan kejadian intens MHWs kuat di wilayah tersebut, disusul oleh pelemahan intensitas upwelling di selatan Jawa bagian Tengah, dan penghambatan intensitas upwelling yang paling rendah akibat dampak dari MHWs ditemukan di selatan Jawa bagian barat. Temuan ini menyoroti hubungan yang kompleks antara fenomena iklim dan karakteristik MHWs. Oleh sebab itu, pemahaman yang utuh dan mendalam mengenai MHWs dan mekanisme pembentukannya menjadi kebutuhan urgen untuk terus dikaji sebagai bagian dari upaya mitigasi bencana MHWs di perairan Indonesia akibat dampak pemanasan global yang masih terus berlangsung hingga saat ini. Kata kunci: pemanasan global, marine heatwaves, remote forcing, local forcing, upwelling, perairan Indonesia. iii ABSTRACT LONG-TERM CHARACTERISTICS OF MARINE HEATWAVES (1982–2021) IN INDONESIAN WATERS AND THEIR IMPACT ON UPWELLING By Erlin Beliyana NIM: 32420304 (Doctoral Program in Earth Sciences) 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 iv 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. Keywords: global warming, marine heatwaves, remote forcing, local forcing, upwelling, Indonesian waters. v KARAKTERISTIK JANGKA PANJANG MARINE HEATWAVES (1982–2021) DI PERAIRAN INDONESIA DAN DAMPAKNYA TERHADAP UPWELLING HALAMAN PENGESAHAN Oleh Erlin Beliyana NIM: 32420304 (Program Studi Doktor Sains Kebumian) Institut Teknologi Bandung Menyetujui Tim Pembimbing Tanggal 10 Juli 2024 Ketua ______________________ (Prof. Dr.