THE MEJILLONES PENINSULA (23°S) IS A STRUCTURAL ZONE EXTENDING MORE THAN 40 KM OFF THE NORTH COAST OF CHILE GIVING SHAPE TO THE BAYS OF MEJILLONES AND MORENO WHICH ARE ORIENTED TO THE NORTH AND SOUTH OF THE PENINSULA, RESPECTIVELY. THE MESOSCALE OCEANOGRAPHIC VARIABILITY ASSOCIATED WITH THE PENINSULA WAS ANALYZED UTILIZING SATELLITE INFORMATION ON SEA SURFACE TEMPERATURE, CHLOROPHYLL-A CONCENTRATION, GEOSTROPHIC CURRENTS AND EKMAN TRANSPORT. THE ROLE OF THE SHAPE OF MEJILLONES PENINSULA IN THE ANNUAL AND INTERANNUAL OCEANOGRAPHIC VARIABILITY OF THE PARAMETERS IS REVEALED BY MEANS OF HOVMÖLLER DIAGRAMS AND EMPIRICAL ORTHOGONAL FUNCTIONS. THE LATITUDINAL DECREASE OF TEMPERATURE AND CHLOROPHYLL IS ABRUPTLY INTERRUPTED BY THE PENINSULA. THE FORM AND ORIENTATION OF THE MEJILLONES AND MORENO BAYS FAVOR THE RETENTION OF UPWELLED WATERS AND THE BIOLOGICAL PRODUCTION REFLECTED IN THE HIGH CHLOROPHYLL CONCENTRATION. THIS OCCURS INDEPENDENTLY OF THE PREDOMINANT TEMPERATURE AND EKMAN TRANSPORT IN THE HEAD AND SOUTH OF THE PENINSULA. THE PENINSULA INTERRUPTED AND DEVIATES TO THE WEST THE TRAJECTORY OF THE JET STREAM, WHICH VARIES SEASONALLY IN INTENSITY AND COULD GO MORE THAN 100 KM FROM THE COAST. IN ADDITION, THE RESULTS SHOW THE EXISTENCE OF CRITICAL LATITUDE (~ 22.8°S) OR TRANSITION IN WHICH THERE IS A MARKED CHANGE IN THE LATITUDINAL DISTRIBUTION OF EKMAN TRANSPORT.