Ocean meridional heat transport estimated from energy budget constraint

Abstract Oceanic meridional heat transport (MHT), a key component of Earth's energy flow, fundamentally shapes climate variability by redistributing heat between hemispheres and across latitudes, thereby regulating surface energy exchange, atmospheric circulation, and hydrological patterns. However, accurate quantification of the global MHT remains challenging. Here, we use the energy budget approach to derive MHT from 1985 to 2023 based on sea surface heat fluxes (Fs), ocean heat content tendency (OHCT), and heat changes related to sea ice melt/formation (Q ice ), with objective adjustment applied to these components under an ocean energy budget constraint. This approach enables an improved estimate of the MHT climatology, variability, and trend for the global, Indo-Pacific and Atlantic oceans. With good agreement with RAPID and OSNAP mooring array observation time series, our estimates indicate realistic northward MHT at all latitudes in the North Atlantic with a peak of 1.22 ± 0.07 PW at 24.5°N. In contrast, the Indo-Pacific MHT is poleward with a peak of −1.67 ± 0.06 PW at 13.5°S. Regional energy budgets reveal that Fs dominates the mean state of MHT, while OHCT controls its interannual variability. After 2000, when the data quality of both OHC and Fs improved a lot, the Indo-Pacific Ocean exhibited a statistically significant increase in MHT, whereas the Atlantic Ocean showed a basin-wide weakening of MHT, particularly between 25°S and 18°N. The derived ocean MHT data in this study provide a basis to evaluate model and reanalysis data, and support a better understanding of the Earth’s energy flow.