Fifty years of the 137°E repeat hydrographic section in the western North Pacific Ocean

Abstract

The 137°E repeat hydrographic section of the Japan Meteorological Agency across the western North Pacific was initiated in 1967 as part of the Cooperative Study of the Kuroshio and Adjacent Regions and has been continued biannually in winter and summer. The publicly available data from the section have been widely used to reveal seasonal to decadal variations and long-term changes of currents and water masses, biogeochemical and biological properties, and marine pollutants in relation to climate variability such as the El Niño-Southern Oscillation and the Pacific Decadal Oscillation. In commemoration of the 50th anniversary in 2016, this review summarizes the history and scientific achievements of the 137°E section during 1967-2016. Through the publication of more than 100 papers over this 50-year span, with the frequency and significance of the publication increasing in time, the 137°E section has demonstrated its importance for future investigations of physical-biogeochemical-biological interactions on various spatiotemporal scales, and thereby its utility in enhancing process understanding to aid projections of the impact of future climate change on ocean resources and ecosystems over the twentyfirst century.

Remotely Forced Decadal Physical and Biogeochemical Variability of North Pacific Subtropical Mode Water Over the Last 40 Years

“…The shipboard observations have been conducted annually in winter (latter half of January) during 1967-1971 and biannually in winter and summer (around July) since 1972 and also in spring and fall between 1992 and 2009 (Oka et al, 2018). The shipboard observations have been conducted annually in winter (latter half of January) during 1967-1971 and biannually in winter and summer (around July) since 1972 and also in spring and fall between 1992 and 2009 (Oka et al, 2018).…”

“…The Meteorological Research Institute of the JMA also measured these variables at 29.5°N, 135.3°E during 1998-2000 ( Figure S2). As carbon system parameters other than DIC have been measured only since 2003, we averaged total alkalinity normalized at S = 35 (nTA) that has been measured since 2010 (Oka et al, 2018) at each latitude band and depth and calculated pH and Ω arag since 1994 from the observed DIC and the averaged nTA. As carbon system parameters other than DIC have been measured only since 2003, we averaged total alkalinity normalized at S = 35 (nTA) that has been measured since 2010 (Oka et al, 2018) at each latitude band and depth and calculated pH and Ω arag since 1994 from the observed DIC and the averaged nTA.…”

“…By examining biogeochemical time series on the isopycnal of σ θ = 25.0 kg/m 3 (σ θ is potential density) at 25°N in the 137°E repeat hydrographic section during 2002-2013, Oka et al (2015) detected consistent changes that pH and aragonite saturation state (Ω arag ) increased and apparent oxygen utilization (AOU), nitrate (NO 3 ) concentration, and total dissolved inorganic carbon (DIC) concentration decreased during 2010-2013 in a stable-KE period, associated with increasing advection of STMW from the east. To clarify decadal physical and biogeochemical variability of the North Pacific STMW for a longer period, we here analyze all available observations at the 137°E repeat hydrographic section, which has been maintained by the Japan Meteorological Agency (JMA) for 50 years since 1967 (Oka et al, 2018). To clarify decadal physical and biogeochemical variability of the North Pacific STMW for a longer period, we here analyze all available observations at the 137°E repeat hydrographic section, which has been maintained by the Japan Meteorological Agency (JMA) for 50 years since 1967 (Oka et al, 2018).…”

Assessment of the JMA Serial Observation Lines in the Northwestern Pacific in OSSE Studies with the GFDL Ensemble Coupled Data Assimilation System

“…However, a high RMSE remained in areas of high latitudes area including Tsugaru Strait. The 137°E line and 165°E line selected from this study have been widely used to investigate the variation of the NPIW (Nakano et al, 2005;Oka et al, 2018;Qui & Joyce, 1992;Saito et al, 2007;Talley, 1997). This study also examined the variation of the NPIW core over the last 6 years (2036)(2037)(2038)(2039)(2040)(2041) to verify data assimilation performance for the North Pacific.…”

“…Therefore, the present study provides the OSSE results for the Northwestern Pacific using the assimilation system developed by the Geophysical Fluid Dynamics Laboratory (GFDL) (Chang et al, 2013;Zhang et al, 2007). Among the various observation networks provided by the Japan Meteorological Agency (JMA), the 137°E line and the 165°E line were selected to compare and validate the data assimilation effect (Figure 1), as the data obtained from these observation lines have been mostly used in a number of studies investigating the seasonal, decadal, and long-term change of thermohaline structures, subsurface currents, biogeochemical properties, and marine pollutants in the Northwestern Pacific (Kawabe & Taira, 1998;Kouketsu et al, 2013;Midorikawa et al, 2002;Oka et al, 2018;Oka & Suga, 2005;Sasano et al, 2015).…”