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Deep Argo Quantifies Bottom Water Warming Rates in the Southwest Pacific Basin

Johnson, G. C., S. G. Purkey, N. V. Zilberman, and D. Roemmich, 2019: Deep Argo Quantifies Bottom Water Warming Rates in the Southwest Pacific Basin. Geophysical Research Letters46, 2662-2669,

The first regional pilot array of Deep Argo floats profiling from the sea floor to the sea surface was deployed in the Southwest Pacific Basin, starting with a few floats in 2014, and commencing in earnest in 2016. An analysis of the data from these floats (Johnson et al., 2019) revealed that the circa 2017 float temperature anomalies relative to the World Ocean Atlas 2018 (WOA-18) long-term (1955–2017) climatology in the basin were statistically significantly and increasingly warm from 2800 dbar to the sea floor, reaching 11 (±1) m°C by 5500 dbar (Fig., top panel). Furthermore, the average warming rate estimated from Deep Argo temperature anomalies was about 3 (±1) m°C yr-1 from 5000 to 5600 dbar and from 2014 to 2018 (Fig., bottom panel). This warming trend in the bottom water, which spreads northward from its origins around Antarctica, has been documented using data from research cruises at about 1 m°C yr-1 from the 1990s to the 2000s, and about 2 m°C yr-1 from the 2000s to the 2010s (Purkey et al., 2019). The estimate of 3 m°C yr1 from 2018 to 2018 using Deep Argo data suggests a further acceleration of this signal. Building out this and similar Deep Argo pilot arrays into a global array would allow monitoring of abyssal and deep warming below the 2000 dbar sampling limit of standard core Argo floats. This deep ocean warming has been estimated to be approximate 10% of the warming in the climate system (Johnson et al., 2016).

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