Interaction of the North Atlantic Current with the Deep Charlie Gibbs Fracture Zone Throughflow

Abstract

The Charlie Gibbs Fracture Zone (CGFZ), a passage of 3600 m sill depth through the Mid‐Atlantic Ridge near 52°N, is a known gateway for the passage of deep waters from the Northeast Atlantic into the western basin. During a shipboard survey of August 1997 deep current profiling yielded eastward deep flow through the passage while geostrophy calculated against an intermediate reference level resulted in westward relative deep transport. The reason was an unusual and deep‐reaching northward excursion of the North Atlantic Current (NAC). Inspection of historical data showed that such interference of the NAC with the CGFZ regime occured occasionally in the past. Relocation of surface circulation patterns by decadal ocean‐climate anomalies may thus be of significance also for the deep circulation.