Assessing Deep and Abyssal Ocean Heat Content Changes With a Dynamically Consistent Ocean State Estimate
Date
2025-03-20
Journal Title
Journal ISSN
Volume Title
Publisher
Journal of Geophysical Research: Oceans
Abstract
Because of the sparseness of existing observations, our understanding of deep (2,000–4,000 m) and abyssal (>4,000 m) ocean heat content (OHC) changes remains limited. Previous studies utilizing repeated hydrographic section measurements identified a global warming trend in these layers. However, studies based on a widely used ocean state estimate ECCO v4 (Estimating the Circulation and Climate of the Ocean, version 4) show a contradictory cooling trend in the deep and abyssal Pacific and Indian Oceans. To examine if the sparseness of hydrographic measurements results in this contrasting conclusion, we conducted a sampling experiment with ECCO v4. Our results show that the signs of the OHC trends in the deep and abyssal oceans from the full spatial-temporal data and the sampled data are generally consistent. The largest uncertainties mainly occur in regions where the deep ocean is dominated by newly formed deep-water masses or where hydrographic sections are extremely sparse, such as the Northwest Atlantic Ocean and the Southern Ocean. Our findings also indicate that the discrepancies between ECCO v4 and observations in deep and abyssal OHC changes are not likely a sampling issue, and further studies are needed to determine the reasons.
Key Points
- A sampling experiment was conducted to assess possible biases of deep and abyssal ocean heat content changes due to under-sampling
- Deep and abyssal ocean heat content trends from sampled data are generally consistent with those from full spatial-temporal data
- Under-sampling does not explain the differences between ECCO and observations in the deep and abyssal ocean heat content changes
Plain Language Summary
Deep and abyssal oceans are key heat reservoirs in the Earth System. However, the limited number of available observations constrains our understanding of changes in deep and abyssal ocean heat content (OHC). In addition, studies based on limited observations and a widely used ocean state estimate display contrasting trends in deep and abyssal OHC changes in the Pacific and Indian Oceans. Here, we conduct a sampling experiment with a state-of-the-art ocean synthesis product to explore if under-sampling is the reason for the contrasting results. We found that the OHC changes estimated from the repeated hydrographic sections are generally reliable, suggesting that the current sampling framework is not likely the cause of the opposite OHC trends in studies based on observational data and the ocean state estimate. Significant uncertainties do exist and primarily appear in regions such as the Northwest Atlantic and Southern Ocean. Our findings provide a valuable reference for understanding deep and abyssal ocean changes as well as for designing and implementing future global ocean observational systems.
Description
This article was originally published in Journal of Geophysical Research: Oceans. The version of record is available at: https://doi.org/10.1029/2024JC020925.
© 2025 The Author(s).
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Keywords
Citation
Zhang, Y., Liang, X., Chambers, D. P., & Huang, M. (2025). Assessing deep and abyssal ocean heat content changes with a dynamically consistent ocean state estimate. Journal of Geophysical Research: Oceans, 130, e2024JC020925. https://doi.org/10.1029/2024JC020925