SUBROUTINE PTS(T,S,P,PT)
C
C-----------------------------------------------------------------------
C     THIS SUBROUTINE CALCULATES THE POTENTIAL TEMPERATURE REFERRED TO
C     THE SURFACE. IT USES BRYDEN'S(1973) POLYNOMIAL FORMULA.
C     **UNITS**
C       IN-SITU TEMPERATURE(T): DEGREES CENTIGRADE
C       SALINITY(S): PERMIL
C       PRESSURE(P): DECIBARS
C       POTENTIAL TEMPERATURE(PT): DEGREES CENTIGRADE
C     ** REFERENCE**
C       H.L.BRYDEN(1973); NEW POLYNOMIALS FOR THERMAL EXPANSION, ADIA-
C       BATIC TEMPERATURE GRADIENT AND POTENTIAL TEMPERATURE OF SEA
C       WATER. DEEP-SEA RESEARCH, VOL.20, PP.401-408.
C-----------------------------------------------------------------------
C
      PT = T - (0.36504E-4+0.83198E-5*T-0.54065E-7*T**2+0.40274E-9*T**3)
     1        *P
     2       - (0.17439E-5-0.29778E-7*T)*P*(S-35.0)
     3       + 0.41057E-10*P**2*(S-35.0)
     4       - (0.89309E-8-0.31628E-9*T+0.21987E-11*T**2)*P**2
     5       - (-0.16056E-12+0.50484E-14*T)*P**3
C
      RETURN
      END