Ocean Acidification from Below in the Tropical Pacific

Type Article
Date 2020-08
Language English
Author(s) Ishii Masao1, Rodgers Keith B.2, 3, Inoue Hisayuki Y.4, Toyama Katsuya1, Sasano Daisuke1, 5, Kosugi Naohiro1, Ono Hisashi1, Enyo Kazutaka5, Nakano Toshiya5, Iudicone Daniele6, Blanke Bruno7, Aumont Olivier8, Feely Richard A.9
Affiliation(s) 1 : Meteorological Research Institute, Japan Meteorological Agency Tsukuba ,Japan
2 : Center for Climate Physics Institute for Basic Science Busan ,South Korea
3 : Pusan National University Busan ,South Korea
4 : Graduate School of Environmental Earth Sciences Hokkaido University Sapporo ,Japan
5 : Global Environment and Marine Department, Japan Meteorological Agency Tokyo, Japan
6 : Department of Integrated Marine Ecology, Stazione Zoologica Anton Dohrn Naples, Italy
7 : Laboratoire d’Océanographie Physique et Spatiale, UMR 6523 CNRS‐Ifremer‐IRD‐UBO, Institut Universitaire Européen de la Mer Brest, France
8 : Laboratoire d’Océanographie et du Climat: Expérimentations et Approches Numériques (LOCEAN), Centre IRD de Bretagne Plouzané ,France
9 : Pacific Marine Environmental Laboratory, National Oceanic and Atmospheric Administration, Seattle Washington ,USA
Source Global Biogeochemical Cycles (0886-6236) (American Geophysical Union (AGU)), 2020-08 , Vol. 34 , N. 8 , P. e2019GB006368 (15p.)
DOI 10.1029/2019GB006368
Abstract

Identifying ocean acidification and its controlling mechanisms is an important priority within the broader question of understanding how sustained anthropogenic CO2 emissions are harming the health of the ocean. Through extensive analysis of observational data products for ocean inorganic carbon, here we quantify the rate at which acidification is proceeding in the western tropical Pacific Warm Pool, revealing ‐0.0013 ±0.0001 yr‐1 for pH and ‐0.0083±0.0007 yr‐1 for the saturation index of aragonite for the years 1985‐2016. However, the mean rate of total dissolved inorganic carbon increase (+0.81 ±0.06 μmol kg‐1 yr‐1) sustaining acidification was ~20% slower than what would be expected if it were simply controlled by the rate of atmospheric CO2 increase and transmitted through local air‐sea CO2 equilibration. Joint Lagrangian and Eulerian model diagnostics indicate that the acidification of the Warm Pool occurs primarily through the anthropogenic CO2 that invades the ocean in the extra‐tropics, is transported to the tropics through the thermocline shallow overturning circulation, and then re‐emerges into surface waters within the tropics through the Equatorial Undercurrent from below. An interior residence time of several years to decades, acting in conjunction with the accelerating CO2 growth in the atmosphere, can be expected to contribute to modulating the rate of Warm Pool acidification.

Key Points

Progress of ocean acidification in the western tropical Pacific Warm Pool was identified using the data of oceanic CO2 measurements

The rate of oceanic CO2 increase here was ~20% lower than that expected from the growth rate of the mixing ratio of CO2 in the atmosphere

Inter‐gyre exchange of anthropogenic CO2 within the thermocline predominantly controls the rate of acidification in this region

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Ishii Masao, Rodgers Keith B., Inoue Hisayuki Y., Toyama Katsuya, Sasano Daisuke, Kosugi Naohiro, Ono Hisashi, Enyo Kazutaka, Nakano Toshiya, Iudicone Daniele, Blanke Bruno, Aumont Olivier, Feely Richard A. (2020). Ocean Acidification from Below in the Tropical Pacific. Global Biogeochemical Cycles, 34(8), e2019GB006368 (15p.). Publisher's official version : https://doi.org/10.1029/2019GB006368 , Open Access version : https://archimer.ifremer.fr/doc/00641/75337/