International Journal of Marine Science, 2024, Vol.14, No.3, 218-230 http://www.aquapublisher.com/index.php/ijms 220 and climate, particularly in the Indo-Pacific region. This figure underscores the complexity of the ITF and its integral role in global ocean currents and climate systems. Additionally, the Indo-Pacific Warm Pool, a region with some of the highest sea surface temperatures (SSTs) in the world, plays a significant role in global atmospheric circulation. The warm pool's properties, such as size, zonal and meridional centers, and SST, exhibit distinct seasonal and interannual variations, which are crucial for understanding the region's climate dynamics (Yin et al., 2020). 2.2 Seasonal and interannual variability The Indo-Pacific Ocean Basin exhibits pronounced seasonal and interannual variability, driven by various climate phenomena such as the El Niño-Southern Oscillation (ENSO), Indian Ocean Dipole (IOD), and Pacific Decadal Oscillation (PDO). The ITF, for instance, shows significant interannual variability, with its transport being modulated by ENSO and IOD events. During El Niño events, the ITF transport weakens, while it strengthens during La Niña events. The IOD can offset the ENSO influences on the ITF transport during the developing and mature phases of these events (Feng et al., 2018). The Indo-Pacific Warm Pool also demonstrates substantial seasonal and interannual variability. The Indian Ocean sector of the warm pool exhibits more vigorous seasonal oscillations in size and intensity compared to the Pacific sector. However, both sectors show comparable interannual variability, with the Indian Warm Pool having weak interannual variations and the Pacific Warm Pool exhibiting strong interdecadal variations (Yin et al., 2020). 2.3 Long-term trends Long-term trends in the Indo-Pacific Ocean Basin circulation are influenced by both natural variability and anthropogenic climate change. Over the past century, the Indian Ocean has experienced significant warming, which can be attributed to human-induced climate change. However, since the 1980s, multi-decadal variability associated with the Interdecadal Pacific Oscillation has also played a significant role in modulating the region's heat and freshwater balance (Ummenhofer et al., 2021). Climate models project a weakening trend of the ITF under global warming scenarios, primarily due to the reduction of deep upwelling in the Pacific basin rather than changes in trade winds. This weakening of the ITF could have significant implications for the Indo-Pacific Ocean circulation and global climate (Feng et al., 2018). Additionally, the Indo-Pacific Warm Pool is expected to continue warming, with the La Niña-like warming pattern dominating the tropical Pacific and a negative IOD warming pattern occurring in the Indian Ocean (Zhang et al., 2020a). In summary, the Indo-Pacific Ocean Basin circulation is characterized by complex interactions between various currents, climate phenomena, and long-term trends. Understanding these dynamics is crucial for predicting future climate changes and their potential impacts on regional and global scales. 3 Drivers of Circulation Variability 3.1 Atmospheric forcing Atmospheric forcing plays a crucial role in driving the variability of ocean circulation in the Indo-Pacific region. The Walker circulation, a significant atmospheric feature, has been shown to influence sea surface temperature (SST) and sea-level pressure trends, which in turn affect ocean circulation patterns. Observations indicate a strengthening of the Walker circulation, which has led to intensified warming in the Indo-Pacific Warm Pool and slight cooling in the eastern equatorial Pacific over recent decades (Wills et al., 2022). Additionally, the Indian Ocean Dipole (IOD) and the El Niño-Southern Oscillation (ENSO) are key atmospheric phenomena that modulate the geostrophic transport of the Indonesian Throughflow (ITF), with La Niña events strengthening and El Niño events weakening the ITF (Feng et al., 2018). These atmospheric forces are critical in understanding the variability of ocean circulation in the region.
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