TWO-LAYER EXCHANGE IN AN ESTUARY BASIN WITH SPECIAL REFERENCE TO THE BALTIC SEA.

Abstract

STATIONARY AND TRANSIENT STATES OF A TWO-LAYER FJORD-TYPE ESTUARY ARE DISCUSSED ANALYTICALLY.THE FORCING FUNCTIONS ARE THE OUTER SALINITY S/SUB O/, THE FRESH-WATER SUPPLY Q/SUB F/, AND A METEOROLOGICALLY FORCED BAROTROPIC TRANSPORT Q/SUB M/.FORCED NONLINEAR, TIME-DEPENDENT CASES HAVE BEEN STUDIED NUMERICALLY.SOME ASSOCIATED LABORATORY EXPERIMENTS ARE DESCRIBED.THE MAIN RESULTS OBTAINED ARE AS FOLLOWS: (I) A SINGLE STEADY STATE EXISTS; THIS IS APPROACHED IN AN EXPONENTIAL-LIKE WAY.(II) THE TOTAL MIXING THROUGH THE INTERFACE MUST VARY WITH DEPTH (DECREASE FOR INCREASING INTERFACE DEPTH) TO ALLOW A STABLE STEADY STATE.(III) THE STATIC STABILITY INCREASES WITH INCREASING FRESH-WATER SUPPLY, UP TO A CRITICAL VALUE WHERE THE TWO-LAYER MODEL BREAKS DOWN.(IV) AN ADDED OSCILLATORY COMPONENT IN S/SUB O/ INCREASES AND IN Q/SUB F/ DECREASES THE ESTUARY SALINITY AND THE STATIC STABILITY.THE EFFECT OF AN OSCILLATORY Q/SUB M/ MAY GO IN EITHER DIRECTION.(V) THE STATISTICAL STEADY STATE IS SENSITIVE TO CERTAIN HIGH-ORDER STATISTICAL FEATURES OF THE FORCING FUNCTIONS.IT IS SUGGESTED THAT CHANGES IN SUCH STATISTICAL FEATURES, RATHER THAN CHANGES IN MEAN FORCING CONDITIONS, MAY EXPLAIN OBSERVED PHYSICAL-CHEMICAL SECULAR VARIATIONS IN THE BALTIC, IN PARTICULAR THE DROP OF OXYGEN CONCENTRATIONS OF THE DEEP-WATER.(A.)