Regional heat content change over the Atlantic Ocean with the space geodetic approach

Given the major role of the Atlantic Ocean in the climate system, it is essential to characterize the temporal and spatial variations of its heat content. The 4DATLANTIC-OHC project (2021-2023) aims at developing and testing space geodetic methods - from satellite altimetry and gravimetry - to estimate the regional ocean heat content (OHC) change over the Atlantic.

The space geodetic approach

The OHC change can be estimated directly from net ocean surface heat fluxes measured based on CERES space measurements, from in situ data observed by the ARGO floats or from ocean model reanalyses. Here we estimate the OHC change from an alternative method based on satellite altimetry and gravimetry observations which complements these other approaches and which is very promising to reduce uncertainty estimates. 

The OHC change is estimated from the measurement of the thermal expansion of the ocean based on differences between the total sea-level content derived from altimetry measurements and the mass content derived from gravimetry data. This space geodetic approach provides consistent spatial and temporal sampling of the ocean. It samples nearly the entire global ocean, except in polar regions where the sea is partially or completely covered with sea ice (i.e. essentially north of 80°N) and it provides estimates of the OHC variations over the ocean’s full depth.

Application to the Atlantic Ocean and objectives

The ESA-funded project MOHeaCAN acted as a proof-of-concept, describing the application of the space geodetic approach on a global scale (Marti et al., 2022). The objective of the 4DAtlantic-OHC project is focused on the Atlantic Ocean and provides the opportunity to extend MOHeaCAN’s work at regional scale where new challenges need to be taken up. Indeed, a series of processes and parameters (coastal area, mixed layer variability,...) that could be neglected at global scale cannot be neglected anymore at regional scale.

The strategy established at global scale has been extended and further developed at regional scale both for the data generation and the uncertainty estimate. In particular, halosteric sea level variations due to saline contraction which are not negligible at regional scale are estimated from in situ data and removed from the steric sea level variations from altimetry minus gravimetry. 

Thus we need to explore the capability of EO missions and EO-based products in terms of space and time resolution to monitor the regional OHC in the Atlantic Ocean. In addition, we need to develop a proper scheme to characterise and then propagate the uncertainty of the input measurements to derive reliable uncertainties of the final estimate of the regional OHC.

The 4DAtlantic-OHC project’s objectives are:

• to develop, test and validate a regional EO-based Atlantic OHC product to enable a realistic monitoring of the Atlantic Ocean Heat Uptake and to understand the role played by the Atlantic Ocean in the climate system.
• to use and analyse the product to better understand the complexity of the Earth and climate system. The investigation will be focused on the Meridional Heat Transport (MHT) in the North Atlantic with a regional heat budget.
• to promote and use the product to assess its strengths and limitations for the implementation of new solutions for society.

The 4DAtlantic-OHC product

Users will be mainly interested in:

• Monthly gridded Atlantic Ocean heat content change
• OHC trends and their uncertainties

Product Versions

Consult the table below for the different versions of the 4DAtlantic-OHC product.

DOI and metadata

This product is referenced with a DOI: 10.24400/527896/a01-2022.012

More metadata: https://commons.datacite.org/doi.org/10.24400/527896/a01-2022.012

Product access and condition of access

The product (NetCDF file) can be downloaded in open acces on the HTTPS server or via the non authenticated FTP download (if the FTP protocol is not supported by your browsers, see this note)

The product is available free of charge for any project or study, and delivered as stated in the licence agreement. 

Citation

If you use the data, please cite:
"The 4DAtlantic OHC product from space altimetry and space gravimetry was produced by Magellium/LEGOS and distributed by AVISO+ (https://aviso.altimetry.fr) with support from ESA (https://doi.org/10.24400/527896/a01-2022.012 version XX)"

Contacts

For any technical issues or additional information related to the 4D Atlantic OHC product, users are advised to contact Robin Fraudeau (technical coordinator) : robin.fraudeau(at)magellium.fr

Acknowledgment

This work is supported by the European Space Agency in the framework of the 4DAtlantic-Ocean heat content Project (ESA Contract number 4000134928/21/I-NB):  https://eo4society.esa.int/projects/4datlantic-ohc/

References

Ablain et al., OSTST 2022: Monitoring the regional heat content change over the Atlantic Ocean with the space geodetic approach: the 4DATLANTIC-OHC project

Blazquez, A., Meyssignac, B., Lemoine, J., Berthier, E., Ribes, A. and Cazenave, A. (2018) Exploring the uncertainty in GRACE estimates of the mass redistributions at the Earth surface: implications for the global water and sea level budgets, Geophys. J. Int., 215(1), 415–430, doi:10.1093/gji/ggy293, 2018.

Marti, F., Blazquez, A., Meyssignac, B., Ablain, M., Barnoud, A., Fraudeau, R., Jugier, R., Chenal, J., Larnicol, G., Pfeffer, J., Restano, M., and Benveniste, J.: Monitoring the ocean heat content change and the Earth energy imbalance from space altimetry and space gravimetry, Earth Syst. Sci. Data Discuss., 1–32, doi: 10.5194/essd-2021-220, 2021.

Meyssignac, B., Boyer, T., Zhao, Z., Hakuba, M. Z., Landerer, F. W., Stammer, D., Köhl, A., Kato, S., L’Ecuyer, T., Ablain, M., Abraham, J. P., Blazquez, A., Cazenave, A., Church, J. A., Cowley, R., Cheng, L., Domingues, C. M., Giglio, D., Gouretski, V., Ishii, M., Johnson, G. C., Killick, R. E., Legler, D., Llovel, W., Lyman, J., Palmer, M. D., Piotrowicz, S., Purkey, S. G., Roemmich, D., Roca, R., Savita, A., Schuckmann, K. von, Speich, S., Stephens, G., Wang, G., Wijffels, S. E., Zilberman, N. (2019) Measuring Global Ocean Heat Content to Estimate the Earth Energy Imbalance, Front. Mar. Sci., 6, doi:10.3389/fmars.2019.00432, 2019.

List of the product versions

Name	Version	Publication date	Product characteristics	Documentation			Product access
				Product user manual	Algorithm theoretical basis document	Associated publication	HTTPS	FTP
4DAtlantic-OHC	1.0	Oct 2022	Atlantic ocean 1*1 deg 04/2002-12/2020 Monthly	Experimental Dataset Description (EDD v1.1)	ATBD v1.2	-	open access	non authenticated ftp