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Deep Argo quantifies bottom water warming rates in the southwest Pacific Basin

Locations of Deep Argo float prof les in the Southwest Pacific Basin as of 20 November 2018
TitleDeep Argo quantifies bottom water warming rates in the southwest Pacific Basin
Publication TypeJournal Article
Year of Publication2019
AuthorsJohnson G.C, Purkey S.G, Zilberman N.V, Roemmich D.
JournalGeophysical Research Letters
Date Published2019/03
Type of ArticleArticle
ISBN Number0094-8276
Accession NumberWOS:000462612900037
Keywordsabyssal; abyssal warming; Antarctic Bottom Water; circulation; Deep Argo; Geology; global heat; land coast; ocean waters; sea-level rise; ventilation

Data reported from mid-2014 to late 2018 by a regional pilot array of Deep Argo floats in the Southwest Pacific Basin are used to estimate regional temperature anomalies from a long-term climatology as well as regional trends over the 4.4years of float data as a function of pressure. The data show warm anomalies that increase with increasing pressure from effectively 0 near 2,000 dbar to over 10 (+/- 1)m degrees C by 4,800 dbar, uncertainties estimated at 5-95%. The 4.4-year trend estimate shows warming at an average rate of 3 (+/- 1)m degrees C/year from 5,000 to 5,600dbar, in the near-homogeneous layer of cold, dense bottom water of Antarctic origin. These results suggest acceleration of previously reported long-term warming trends in the abyssal waters in this region. They also demonstrate the ability of Deep Argo to quantify changes in the deep ocean in near real-time over short periods with high accuracy. Plain Language Summary The coldest waters that fill much of the deep ocean worldwide originate near Antarctica. Temperature data collected from oceanographic cruises around the world at roughly 10-year intervals show that these near-bottom waters have been warming on average since the 1990s, absorbing a substantial amount of heat. Data from an array of robotic profiling Deep Argo floats deployed in the Southwest Pacific Ocean starting in mid-2014 reveal that near-bottom waters there have continued to warm over the past 4.4years. Furthermore, these new data suggest an acceleration of that warming rate. These data show that Deep Argo floats are capable of accurately measuring regional changes in the deep ocean. The ocean is the largest sink of heat on our warming planet. A global array of Deep Argo floats would provide data on how much Earth's climate system is warming and possibly improve predictions of future warming.


The time period over which these trends are calculated, 4.4 years, is rather short to infer much about long‐term changes. Nonetheless, this analysis does demonstrate that an array of Deep Argo floats maintained at near the 5° latitude × 5° longitude recommended density is able to resolve regional (basin‐scale) deep temperature changes with high statistical confidence over a relatively short (less than pentadal) time period. That ability is unprecedented on a regional scale in the deep and bottom waters. In addition, the 4.4‐year warming trend in the bottom waters suggests an accelerated bottom water warming relative to that observed in the region between the 1990s and the 2010s. The Deep Argo array, when global, will provide even more insights into the mean state and changing properties of deep and bottom waters and variations in their circulation.

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