Reconstructing past tidal currents: A numerical approach to the paleotides of northern Patagonia

This study presents a two-dimensional, depth-averaged hydrodynamic model designed to simulate paleotidal conditions in the northern Patagonian coastal region around 11.5 radiocarbon thousand years before present (11.5 ¹⁴C kyr BP), which corresponds approximately to 13 calibrated thousand years before present (cal kyr BP), representing a scenario prior to the flooding of San Matías Gulf. To reconstruct paleo-bathymetry, the mean sea level was lowered by 50 m relative to present conditions and the tidal-generating potential was maintained. The model is forced by present-day M₂ tidal constituent—the dominant component in the area—applied at the open boundaries. Results reveal that tidal currents during the late Holocene were considerably more intense than today, particularly in the central sector of the San Matías Gulf outlet. The simulated flow directions align with the orientation of the ancient coastline, and a convergence/divergence zone identified near 41.5°S, 61.5°W is interpreted as a coastal paleo-amphidromic point, where tidal wave rotation was restricted by shoreline geometry. The work also addresses a long-standing question regarding the origin of submerged gravel dunes at the southern entrance of the gulf. Simulation results indicate that present-day tidal currents are insufficient to mobilize such coarse sediment, suggesting that these features formed under different conditions—possibly during a transitional phase when the gulf was a dry basin being flooded by rising sea level. These findings provide new insight into the paleo-hydrodynamics of the region and contribute to the understanding of sedimentary processes linked to sea-level changes.