General circulation and tidal wave propagation along the Beagle Channel

Abstract

The Beagle Channel (BC) is a subantarctic passage connecting the Pacific and Atlantic oceans at latitude ∼55°S. Along its tortuous path, the channel defines particular environments of prominent ecological value that are under study from a variety of scientific fields, while the main physical features that form the basis for these ecosystems are still critically understudied. In this work, historical data series of currents measured with surface drifters and moored current meters as well as sea-level data measured by gauge stations and pressure transducers, are analyzed. These are used to describe the propagation of the tidal wave and the general water motion along the BC. Astronomical amplitudes and phases of the main tidal components, computed from historical and recent sea-level data series obtained at the BC and gathered from global numerical models, are integrally analyzed to describe the propagation of a single, progressive tidal wave in the channel and in the surrounding ocean area, in contrast with previous assumptions that considered two tidal waves advancing in opposite directions. The relative narrowness of the channel, which is roughly oriented in a west-east direction, favors currents with a dominant zonal component. Such fact is exacerbated at and near topographic constrictions such as Mackinlay Strait, where a substantial acceleration of the flow is also observed. Superimposed on the mixed semidiurnal tidal regime, there is a remarkably persistent residual surface flow in an eastwards direction along the BC, likely contributing to the regional transport of water and properties from the Pacific Ocean to the Atlantic Patagonian Shelf. The existence of a semi-permanent sea-level tilt between the Pacific and Atlantic sides of the BC, is proposed as the main driver for that along-channel current. However, inversions of the residual current (i.e., westwards flow) do occur below the depths of major topographic constrictions, likely promoting recirculation and high residence times in the middle BC west of Mackinlay Strait.