4 years ago

Tidal dynamics and their influence on the climate system from the Cretaceous to present day

Global numerical ocean models used for paleo-climate reconstructions commonly only consider the ocean's general circulation but neglect tidal dynamics. However, tidal dynamics affect the ocean's mean general circulation, in particular by vertical mixing and tidal residual mean currents. Through feedback loops the whole climate system is affected. Plate tectonics modify geometric resonance conditions in ocean basins and thereby tidal dynamics. We study the influence of ocean tides on the ocean general circulation and atmospheric parameters by forcing the coupled atmosphere-ocean model ECHAM5/MPIOM with the complete lunisolar tidal potential. Simulations have been performed for five tectonically important time-slices: the Early Albian (ca. 110millionyears ago, Ma), the Cenomanian-Turonian Boundary (ca. 93Ma, CTB), the Early Eocene (ca. 55Ma), the Early Pliocene (ca. 3.5Ma), and a pre-industrial period (ca. 1850CE). The model results suggest that the global mean tidal potential energy in the Early Eocene is almost three times larger than in the CTB. The large potential energy input in the Early Eocene leads to a tripling of current velocities in 10% of the deep ocean. Although the effect of tides on the general ocean circulation is less pronounced in the other time-slices, horizontal velocities are modified by more than 20% in 55% of the deep ocean. The tidally induced shifts of ocean currents and vertical mixing also have an effect on the three-dimensional temperature distribution in the ocean. The impact of tidal dynamics on atmospheric temperatures is particularly strong in the Southern Ocean of the Early Pliocene and the pre-industrial period. By a feedback loop with the atmosphere, tidal forcing locally reduces sea-ice concentration by up to 30% and local atmospheric 2m temperatures by up to 4°C. Although uncertainties in bathymetry reconstructions limit the significance of quantitative analysis, the qualitative conclusions suggest that the impacts of ocean tides on climate reach an order of magnitude, which require its consideration as additional uncertainty in the interpretation of paleo-climate studies. However, the impact of ocean tides has specific characteristics in each time-slice hampering its simple parametrization.

Publisher URL: www.sciencedirect.com/science

DOI: S0921818116301552

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