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要旨

On early Earth increased rates of tidal energy dissipation are likely, but depend on the (unknown) distribution of continents. A stronger tidal heating could provide an additional energy source during times of substantially lower solar input. So far, the problem has been assessed in terms of the negligible contribution to Earth's global energy budget. Here we present a spatially resolved investigation of the impact of tidal heating, mixing, and geothermal heat on early Earth's climate. Using a random landmass distribution, tidal heating is calculated for three different rotation periods (12, 18, 24 hr) and fed into a climate model. For each rotation rate, three climate states with different atmospheric CO2 levels are simulated. We find that, depending on the climate state, tidal heating can affect regional ocean dynamics and sea-ice cover. The impact is strongest when tidal heating alters sea-ice dynamics and meridional heat transport close to the sea-ice edge, but its global impact remains negligible with only small global mean changes in ice cover (0.3%) and temperature (<0.05°C). Adding tidal mixing and geothermal heat, however, leads to significant reduction in sea-ice cover of ∼11% and ∼19%, respectively, and thus to larger global warming. As we do not consider the dynamical effects of a higher rotation rate or different landmass distributions, this is only a first glimpse at the importance of tides for the climate of early Earth. Nevertheless, our results suggest that tides and geothermal heat are important for understanding regional climates and could have contributed to warming early Earth.