Salt and Heat Balances in the Labrador Sea Using a Box Model

A four-layer box model is employed as a diagnostic tool to estimate water exchange rates between the Labrador Sea and adjacent areas. These exchange rates are constrained to be compatible with the annual cycles and interannual variabilities of temperature and salinity observed at Ocean Weather Station Bravo. Air-sea interactions are calculated from the weather data at Bravo. Using the air-sea heat flux formulae of Smith and Dobson (1984), the heat and freshwater transports through the Labrador Sea are estimated to be 2 x 10(13) W northward and 10(12) m(3) yr(-1) southward, respectively. An additional heat transport of 3.5 x 10(13) W from the south is carried by the atmosphere. The model suggests that the freshening in 1968-71, compared with that in the "normal" years 1964-67, was produced by an increase in the exchange with the fresher Labrador and West Greenland Currents, at least when it is based upon the observed weather data and the assumed air-sea interaction formulae. Deep (similar to 1500 m) convection events, observed in the 1966-67 and 1971-72 winters, are simulated and attributed to atmospheric anomalies (lower air temperature, stronger winds and lower humidity).