A Reconstruction of Subtropical Western North Pacific SST Variability Back to 1578, Based on a Porites Coral Sr/Ca Record from the Northern Ryukyus, Japan

Abstract

We present a seasonal reconstruction of sea surface temperature (SST) from 1578 to 2008, based on a Porites coral Sr/Ca record from the northern Ryukyus, within the Kuroshio southern recirculation gyre. Interannual SST anomalies are generally ~0.5°C, making Sr/Ca‐derived SST reconstructions a challenging task. Replicate measurements along adjacent coral growth axes, enabled by the laser ablation inductively coupled plasma mass spectrometry technique used here, give evidence of rather large uncertainties. Nonetheless, derived winter SST anomalies are significantly correlated with the Western Pacific atmospheric pattern which has a dominant influence on winter temperature in East Asia. Annual mean SSTs show interdecadal variations, notably cold intervals between 1670 and 1700 during the Maunder Minimum (MM) and between 1766 and 1788 characterized by a negative phase of the North Atlantic Oscillation. Cold summers in 1783 and 1784 coincide with the long‐lasting Laki eruption that had a profound impact on the Northern Hemisphere climate, including the severe “Tenmei” famine in Japan. The decades between 1855 and 1900 are significantly cooler than the first half of the twentieth century, while those between 1700 and 1765, following the MM, are warmer than average. SST variability in the Ryukyus is only marginally influenced by the Pacific Decadal Oscillation, so that external forcing remains the main driver of low‐frequency temperature changes. However, the close connection between the Kuroshio extension (KE) and its recirculation gyre suggests that decadal SST anomalies associated with the KE front also impact the Ryukyus, and there is a possible additional role for feedback of the Kuroshio‐Oyashio variability to the large‐scale atmosphere at decadal timescale.

Empirical Evidence Linking the Pacific Decadal Precession to Kuroshio Extension Variability

“…Our empirical results indicate that the meridional dipole generates wind stress and wind stress curl anomalies (Figure 3d) that are conducive to initiating SSH changes south of the SPFZ (Figure 4d). These results are consistent with previous findings showing that the meridional dipole, which is characteristic of the NPO, energizes SSH height anomalies that subsequently propagate across the North Pacific as a first-baroclinic-mode Rossby wave (RW) and initiate variations in KE dynamics (Ceballos et al, 2009;Kawakubo et al, 2017;Qiu et al, 2014;Sasaki et al, 2014).…”

“…In particular, prior to large-scale adjustments of the KE structure, the northsouth (N-S) phase of the PDP's characteristic atmospheric pressure dipole establishes zonal wind stress anomalies on either side of the subpolar frontal zone (SPFZ) that drive substantial vertical variations in thermocline depths along the SPFZ. In accord with previous analyses, these vertical variations induce large-scale changes in the ocean heat content, reflected by changes in sea surface heights (SSH), that can propagate across the North Pacific as a first-baroclinic-mode Rossby wave (RW) and initiate variations in KE dynamics (Ceballos et al, 2009;Kawakubo et al, 2017;Qiu et al, 2014;Sasaki et al, 2014).…”

“…In this paper, we analyzed extratropical oceanic signatures that accompany the evolution of the Pacific Decadal Precession (PDP). This analysis was predicated on the fact that the quasi-decadal time scales associated with the PDP's evolution mirror a well-known quasi-decadal signal in the Kuroshio Current System and in particular in the structure of the Kuroshio Extension (KE-e.g., Qiu & Chen, 2005;Pierini & Dijkstra, 2009;Qui and Chen;Ceballos et al, 2009;Yi et al, 2015;Qiu et al, 2014;Pierini, 2014Pierini, , 2015Kawakubo et al, 2017), suggesting possible thermodynamic and dynamic links between the large-scale atmospheric circulations associated with the PDP and mesoscale KE variations. Here these links are analyzed empirically using self-consistent historical state estimates of the ocean and atmosphere over the North Pacific, derived from the 20th Century Reanalysis Version 2c (20CRv2c) and Simple Ocean Data Assimilationsparse input version 3 (SODAsi.3) data sets.…”

Calibration of Sr/Ca, Li/Mg and Sr‐U Paleothermometry in Branching and Foliose Corals

“…To date, Sr/Ca has been the most widely used coral paleothermometer (Figure 6b and supporting information Table S1; Bagnato et al, 2004;Calvo et al, 2007;Corrège et al, 2000;Fallon et al, 1999Fallon et al, , 2003Flannery et al, 2018;Gagan et al, 1998;Heiss et al, 1997;Hennekam et al, 2018;Jimenez et al, 2018;Kawakubo et al, 2017;Linsley et al, 2000;Marshall & McCulloch, 2001;McCulloch, 1999;Mitsuguchi et al, 1996;Nurhati et al, 2009;Ramos et al, 2017;von Reumont et al, 2018;Shen et al, 1996;Sinclair et al, 1998;Watanabe et al, 2017;Wu et al, 2013Wu et al, , 2014Zinke et al, 2004). However, separating the effects of temperature from the influence of vital effects on Sr/Ca has long proven difficult (Alibert & McCulloch, 1997;Corrège, 2006;de Villiers et al, 1995).…”

Last glacial temperature reconstructions using coupled isotopic analyses of fossil snails and stalagmites from archaeological caves in Okinawa, Japan

“…However, there are few of these from oceanic areas. Given the coral-based evidence of interannual and decadal climate variations at the sea surface around the Ryukyu Islands and western tropical Pacific associated with the EAM, El Niño/Southern Oscillation, and Pacific Decadal Oscillation 10 , 54 , 55 , the snapshots of air temperature variations for selected time windows from this study do not necessarily show the representative mean values during the LGM and the B–A periods. To reduce the uncertainties on the δ 18 O snail -based paleo-temperatures, further investigations should be needed.…”