Subtropical-tropical pathways of spiciness anomalies and their impact on equatorial Pacific temperature
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Subtropical‑tropical pathways of spiciness anomalies and their impact on equatorial Pacific temperature Mathias Zeller1,2 · Shayne McGregor1 · Erik van Sebille3 · Antonietta Capotondi4 · Paul Spence5 Received: 15 November 2019 / Accepted: 4 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Understanding mechanisms of tropical Pacific decadal variability (TPDV) is of high importance for differentiating between natural climate variability and human induced climate change as this region sustains strong global teleconnections. Here, we use an ocean general circulation model along with a Lagrangian tracer simulator to investigate the advection of density compensated temperature anomalies (“spiciness mechanism”) as a potential contributor to TPDV during the 1980–2016 period. Consistent with observations, we find the primary regions of spiciness generation in the eastern subtropics of each hemisphere. Our results indicate that 75% of the equatorial subsurface water originates in the subtropics, of which two thirds come from the Southern hemisphere. We further show two prominent cases where remotely generated spiciness anomalies are advected to the equatorial Pacific, impacting subsurface temperature. The relative contribution of Northern versus Southern Hemisphere prominence and/or interior versus western boundary pathways depends on the specific event. The anomalously warm case largely results from advection via the Southern hemisphere interior (65% ), while the anomalously cold case largely results from advection via the Northern hemisphere western boundary (48% ). The relatively slow travel times from the subtropics to the equator (> 4 years) suggests that these spiciness anomalies underpin a potentially predictable contribution to TPDV. However, not all decadal peaks in equatorial spiciness can be explained by remotely generated spiciness anomalies. In those cases, we propose that spiciness anomalies are generated in the equatorial zone through changes in the proportion of Northern/Southern hemisphere source waters due to their different mean spiciness distribution. Keywords Tropical Pacific · Decadal variability · Ocean spiciness
1 Introduction
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00382-020-05524-8) contains supplementary material, which is available to authorized users. * Mathias Zeller [email protected] 1
School of Earth, Atmosphere and Environment, Monash University, Melbourne, Australia
2
GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
3
Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, The Netherlands
4
Physical Sciences Division, NOAA Earth System Research Laboratory, Boulder, CO, USA
5
School of Geosciences, University of Sydney, Sydney, Australia
In recent decades, a lot of effort has been put into the understanding of the Pacific Decadal Oscillation (PDO) which has its dominant expression in the extratropical North Pacific. A summary of the
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