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Large Ocean Heat Storage Efficiency During the Last Deglaciation
Context:
A recent study published in Science Advances by an international team of scientists from China and the U.S. has explored the mechanisms behind ocean heat uptake and storage.
More on News:
- The researchers combined advanced deglacial simulations with proxy-based reconstructions to analyse three-dimensional changes in ocean temperature during the last deglaciation.
- Their findings showed a significant increase in ocean heat storage efficiency during this period, reaching values of at least 1, largely attributed to substantial warming in intermediate-depth waters.
The global ocean plays a crucial role in the climate system, absorbing over 90% of excess energy from anthropogenic warming. Most of this warming occurs in the upper 500 metres of the ocean, while the deep ocean experiences relatively weak warming, resulting in an ocean heat storage efficiency of about 0.1. However, paleoceanographic studies indicate that over long time scales, deep ocean warming can be comparable to, or even exceed, surface warming. During the last deglaciation, this efficiency was approximately ten times greater than today’s levels.
Key Findings:
- The study found that the warming during the last deglaciation was highly nonuniform, with the most pronounced increases occurring at intermediate depths, contrasting sharply with current observations.
Mechanisms of Enhanced Warming:
- Surface Warming and Ventilation: The warming of intermediate waters is linked to surface warming at mid-to-subpolar latitudes, driven by increased greenhouse gases and ice sheet dynamics.
- This surface warming enhances ventilation, allowing more heat to penetrate deeper layers.
- Oceanic Circulation Changes: The changes in ocean circulation associated with meltwater forcing further amplify warming in intermediate depths.
- This unique warming pattern helps clarify a paradox in conventional understanding, where warming is typically expected at deep-water formation sites that are often covered by sea ice.
Implications for Climate Models:
- The research indicates that future climate models may need to account for complex interactions between surface conditions and deeper ocean dynamics.
- Enhanced heat storage could potentially slow the rate of atmospheric warming, especially under scenarios where surface and intermediate-depth warming coincide.
- These findings underscore the importance of understanding historical climate patterns to better predict future ocean behaviour in response to ongoing warming.