Journal Article

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

Pratt, Larry J., Ma, Qiang, Wang, Jianing, Zhang, Hang, Wang, Fan, Lu, Youyu, Zhang, Zhixiang

2023

Overview

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. Plain Language Summary The North Pacific bottom water cannot be locally formed due to the shallow connection to the Arctic. It originates from the Antarctic and is transported northward by the lower deep branch of the Pacific Meridional Overturning Circulation (L‐PMOC). We deployed a six‐mooring array over 2019–2021 to measure the L‐PMOC from the Yap‐Mariana Junction (YMJ) to the Northern Philippine Basin (NPB). The new data extend our previous observations about the pathway and volume transport of L‐PMOC intruding into the western Pacific at the YMJ, and for the first time depicts the abyssal flow from the West Mariana Basin (WMB) into the NPB through the Kyushu‐Palau Ridge (KPR) Channel. Because the YMJ‐Northern and KPR Channels are effectively the only two channels allowing the Lower Circumpolar Water (LCPW) in/out of the WMB, the positive difference of transport through them is the net lateral flux of LCPW into the WMB over the 2.5 yr. A high‐resolution data assimilative ocean model is analyzed to link the variations of the transports through deep channels to the deep pressure gradient. Key Points A six‐mooring array captured hitherto unknown abyssal flow from Yap‐Mariana Junction to Northern Philippine Basin (NPB) during 2019–2021 A single mooring in a deep channel at Kyushu‐Palau Ridge provides an exploratory transport estimate of Lower Circumpolar Water into NPB Model data reveal that lower deep branch of the Pacific Meridional Overturning Circulation transport variations through channels correspond to deep pressure gradients mainly forced by upper ocean

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Abyssal circulation / Abyssal zone / Arrays / Bottom water / Channels / Kyushu‐Palau Ridge / Lower Circumpolar Water / Meridional overturning circulation / Mooring / Mooring systems / Northern Philippine Basin / Ocean models / Oceans / Pacific Meridional Overturning Circulation / Pressure gradients / Upper ocean / Volume transport / Yap‐Mariana Junction