Subtidal dynamics and environmental conditions of the Río Deseado estuary, Santa Cruz

Abstract

The geometry of the Río Deseado estuary, the semiarid climatic conditions and the morphology of gorges carved into volcanic rocks contributed to the dominance of a macrotidal regime in this part of the Patagonian coast. In turn, the effects of tidal currents are increased due to the impoverishment of the Río Deseado discharge, whose valley used to drain the ice cover that occupied the Lago Buenos Aires basin. When the Río Backer valley became free of ice, the lake began to discharge to the Pacific Ocean. Since then, the Río Deseado has received only the supply of the Pinturas and Fénix Grande rivers. The decrease of the tidal action towards the headlands produces a grain-size segregation in the bottom sediments: gravel at Puerto Deseado, sand in Bahía Uruguay and mud in Bahía Concordia. Bedforms recognized in side-scan sonar records distinguished flood-oriented 2-D megaripples in the area of isla de los Pájaros, and ebb-oriented sand waves at a greater depth and some kilometres inland in the inlet of Bahía Uruguay. Sonographs and bottom samples confirmed flat beds composed of sands with gravel in Bahía Uruguay and furrows eroded in muds in Bahía Concordia. Water mixing (marine and freshwater) occurs in Puesto El Paso while turbidity maximum was measured in Bahía Concordia.