Sensitivity of Ocean Heat Content to Various Instrumental Platforms in Global Ocean Observing Systems

Abstract

The global ocean observing system (GOOS) is an integrated system comprising various instrumental platforms distributed in different geographical locations and observing different climate regimes; this system is fundamental for monitoring ocean warming and climate change. This study investigated the impact of different instrument platforms on global and regional ocean heat content (OHC) estimates from 2005 to 2020 with a series of sensitivity tests, where data from one specific instrument were removed from GOOS in each test. Removing Argo, Conductivity-Temperature-Depth (CTD), eXpendable BathyThermographs (XBT), Autonomous Pinniped data (APB), Mooring and Drifting Buoys (MRB), and Glider (GLD) data led to a global 0- to 2,000-m OHC standard deviation of 18.3, 3.0, 2.8, 2.3, 1.2, and 1.2 ZJ, respectively, compared with the full-data estimate. We quantitatively verified that Argo was a central part of the GOOS since ~2005, although each system contributed substantially to climate monitoring. Argo, CTD, and XBT have near-global impacts, while the impacts of APB, MRB, and GLD are critical in specific regions, highlighting the importance of GOOS integration. The addition of the MRB to the GOOS leads to a marked positive OHC offset in the tropics, and the addition of the CTD to the GOOS leads to a systematically cold OHC offset in the boundary currents and Antarctic Circumpolar Current regions. Additionally, this study suggested the use of a better metric for effective data coverage than for determining the amount of data needed to indicate the capability of GOOS for climate monitoring. The implications for improving the current generation gap-filling method are also discussed, highlighting the importance of dealing with narrow current systems and eddy-rich regions.