How Heat and Freshwater Move Through the Ocean
The ocean warms up most at the equator. Ocean circulation then acts like a giant conveyor belt, moving this heat to higher latitudes where it's eventually released into the atmosphere.
Freshwater moves between the atmosphere and the ocean through evaporation, rain, river runoff, and ice melting. These patterns are different from how heat moves. A key result is that the Atlantic Ocean, which loses a lot of water to evaporation, ends up being saltier at the surface than other oceans. Changes in ocean circulation directly change the regional distribution of heat and freshwater.
The Ocean's Response to Climate Change
In our warming climate, the ocean has absorbed a huge amount of extra warmth, often called "excess heat." This is incredibly important because the ocean takes up more than 90% of the excess heat in the entire climate system, which moderates the warming we experience and its impacts on other parts of the Earth.
A warming climate speeds up the "hydrological cycle," meaning freshwater exchanges become more intense. This leads to a simple, dramatic pattern: the salty parts of the ocean get saltier, and the fresh parts get fresher.
The ocean's role is absolutely central to the climate system, controlling how heat and freshwater are absorbed and moved around the planet.
The regional distribution of heat and freshwater is what drives regional sea level and its variability. Warmer water also holds less dissolved oxygen, so a warming ocean is also a deoxygenating ocean. On a regional scale, these changing conditions (temperature, salinity, and oxygen) directly impact ocean ecosystems, with major consequences for ocean health and our global food systems.
Warming at the surface makes the top layer of the ocean less dense, which increases the density difference between the shallow and deep ocean. This gradient is called "stratification." Increased stratification makes it harder for the ocean to mix or exchange water between the layers. This reduction in vertical mixing can, in turn, impact the formation of deep water.
Research
In our National Capability project, AtlantiS, we are working to observe and model the way that the ocean takes up and redistributes heat and freshwater.
Our researchers have studied how global heat transport and Atlantic freshwater transports will change in the future (Mecking and Drijfhout, 2023; Mecking et al in preparation).
Recent work has been published on how heat transport convergence modifies ocean heat content in the North Atlantic (Moat et al 2024). We also have ongoing work examining how a combination of heat and freshwater transport causes feedback to the AMOC (Sinha et al 2025).
People
Our scientists, engineers, and researchers are driven by a mission to deepen understanding of ocean health amid a changing climate. Our heat and freshwater work shapes global policies and fosters industry collaboration to protect the ocean and tackle the pressing challenges of our time.
Impacts
Our researchers have studied how global heat transport and Atlantic freshwater transports will change in the future (Mecking and Drijfhout, 2023; Mecking et al in preparation).
Recent work has been published on how heat transport convergence modifies ocean heat content in the North Atlantic (Moat et al 2024). We also have ongoing work examining how a combination of heat and freshwater transport causes feedback to the AMOC (Sinha et al 2025).
Publications
One of the outputs of our science is publications. Publications show the impact and relevance of our science and technology.
The effect of model bias on Atlantic freshwater transport and implications for AMOC bi-stability
North Atlantic heat transport convergence derived from a regional energy budget using different ocean heat content estimates
Meyssignac, B.; Fourest, S.; Mayer, Michael; Johnson, G. C.; Calafat, F. M. 
ORCID: https://orcid.org/0000-0002-7474-135X; Ablain, M.; Boyer, T.; Cheng, L.; Desbruyères, D.; Forget, G.; Giglio, D.; Kuusela, M.; Locarnini, R.; Lyman, J. M.; Llovel, W.; Mishonov, A.; Reagan, J.; Rousseau, V.; Benveniste, J..
2024
North Atlantic heat transport convergence derived from a regional energy budget using different ocean heat content estimates.
Surveys in Geophysics.
10.1007/s10712-024-09865-5
2024
Article
Observation-based estimates of heat and freshwater exchanges from the subtropical North Atlantic to the Arctic
Li, Feili; Lozier, M. Susan; Holliday, N. Penny ORCID: https://orcid.org/0000-0002-9733-8002; Johns, William E.; Le Bras, Isabela A.; Moat, Ben I. ORCID: https://orcid.org/0000-0001-8676-7779; Cunningham, Stuart A.; de Jong, M. Femke.
2021
Observation-based estimates of heat and freshwater exchanges from the subtropical North Atlantic to the Arctic.
Progress in Oceanography, 197, 102640.
10.1016/j.pocean.2021.102640
2021
Article
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