14C in the Deep Water of the East Atlantic

Abstract

The renewal of east Atlantic deep water and its large-scale circulation and mixing have been studied in observed distributions of temperature, silicate, Sigma-CO2, and 14C. 14C variations in northeast Atlantic deep water below 3500m depth are small. Delta-14C values range from -100 per mil to -125 per mil.14C bottom water concentrations decrease from &4C = -117 per mil in the Sierra Leone Basin to Delta-14C = -123 per mil in the Iberian Basin and are consistent with a mean northward bottom water flow. The characteristic of the water that flows from the west Atlantic through the Romanche Trench into the east Atlantic was determined by inspection of theta/Delta-14C and theta/Si02 diagrams. A mean potential temperature of theta = 1.50 +/- .05 degrees C was found for the inflowing water. A multi-box model including circulation, mixing, and chemical source terms in the deep water has been formulated. Linear programing and least-squares techniques have been used to obtain the transport and source parameters of the model from the observed tracer fields. Model calculations reveal an inflow through the Romanche Trench from the west Atlantic, which predominates over any other inflow, of (5 +/- 2) Sv (potential temperature 1.50 degrees C), a convective turnover of (150 +/- 50) years and a vertical apparent diffusivity of (4 +/- 1) cm2/s. Chemical source terms are in the expected ranges.