Abyssal Circulation From the Yap‐Mariana Junction to the Northern Philippine Basin

Abstract

The lower deep branch of the Pacific Meridional Overturning Circulation (L‐PMOC) is a crucial element of the ocean's climate and biogeochemical systems through carrying the Lower Circumpolar Water (LCPW). For the first time, the pathway and volume transport of L‐PMOC from the Yap‐Mariana Junction (YMJ) to the Northern Philippine Basin (NPB) are revealed by a six‐mooring array measurement over 2019–2021. The L‐PMOC seasonally intrudes into the western Pacific at the YMJ. Then, it is directed into the West Mariana Basin (WMB) through YMJ‐Northern Channel with 1.41 ± 1.43/0.26 (mean ± standard deviation/total rms error) Sv, and further into the NPB through Kyushu‐Palau Ridge (KPR) Channel with 0.75 ± 0.53/0.18 Sv. Their difference 0.65 ± 1.35/0.28 Sv is the net lateral flux of LCPW into the WMB over the 2.5 yr. Analyses of a data‐assimilative ocean model solution suggest that the L‐PMOC transports through the deep channels are consistent with deep pressure gradients forced mainly by upper ocean processes.

Diapycnal Upwelling Over the Kyushu‐Palau Ridge in the North Pacific Ocean

“…Due to the topographic constraint of the KPR, no LCDW is identified on the western half of the section. This is consistent with previous studies (Tian et al, 2021;Wang et al, 2023), which suggests that the LCDW penetrates through the gaps of the KPR to the north and constrain at the Northern Philippine Basin. Therefore, notable difference of water mass properties is manifested between the deep water to the east and west of the KPR, resulting in weaker stratification in the PB.…”

“…The deep water below 3,500 m undergoes a significant increase in temperature and a decrease in density and salinity as it transitions from the MT to the PVB (Figure 2b). Although there are several gaps, where deep water exchanged between the PB and PVB (Wang et al., 2023), at the KPR below 3,800 m, the deep water in the PB is distinctly warmer and lighter than that in the PVB. Additionally, it is worth noting that the deep water exhibits a remarkable warming and lightening trend from the PB eastward to the KPR and from the PVB westward to the KPR (Figures 2c and 2d).…”

“…However, part of the generated lower-mode internal tides in the Mariana Arc and Luzon Strait could propagate to the KPR and the refraction and interference effects of these internal tides could affect mixing near the KPR (Chen et al, 2021;Wang et al, 2021aWang et al, , 2021bXu et al, 2021;Zhao et al, 2016Zhao et al, , 2021. Besides, other energetic dynamic processes were revealed in the deep Philippine Sea, such as bottom current across the KPR (Wang et al, 2023) and deep eddies in the PB (Ma et al, 2023). The energy from these geostrophic flows into lee waves can break and sustain enhanced turbulent mixing (e.g., Nikurashin & Ferrari, 2011;Voet et al, 2020).…”

Tracing Organophosphate Ester Pollutants in Hadal Trenches─Distribution, Possible Origins, and Transport Mechanisms

“…This current potentially introduces a significant amount of OPEs, leading to an increase in pollution levels. The role of atmospheric deposition here is less pronounced compared to surface waters, as oceanic currents play a more dominant role in transporting pollutants; (3) Deep ocean depths (3000–4600 m and beyond 4000 m): The dynamics at these depths are influenced by topographic Rossby waves (TRWs) in the deep channel at the Pacific Yap-Mariana Junction (YMJ) and the transport of Lower Circumpolar Deep Water (LCDW) in the Mariana Trench and the YMJ. , These TRWs are known to be linked to a seasonal reversal of abyssal flow from the Philippine Sea to the Mariana Trench . While specific studies directly linking the TRWs to the transport of pollutants from industrialized regions are limited, the TRWs trajectory, stretching from the western Pacific toward the east, could intersect with OPEs originating from industrialized coastal regions or river outflows, thereby carrying these OPEs across vast oceanic distances.…”