Variability and renewal of Labrador Sea Water in the Irminger Basin in 1991–2004

Abstract

Labrador Sea Water (LSW) property variations are analyzed using the data from six hydrographic sections occupied in 1991–2004 in the southern Irminger Basin between Cape Farewell and the Reykjanes Ridge. From 1991 to 1996, the LSW layer became steadily colder and fresher. The decrease in salinity of the LSW detected in 1994 was caused by the local convection, reaching into the weakly stratified layer of LSW advected from the Labrador Sea. Another indication of local deep convection is in the lateral distribution of dissolved oxygen concentrations in the LSW layer (∼1000–2000 m) obtained in 1997 from the section across the Labrador Sea and four sections running ∼100, 135 and 180° (true azimuth) from Cape Farewell. A separate lateral maximum of oxygen content in the LSW layer is revealed in the southern Irminger Sea: the concentrations increased from the Labrador Sea eastern edge toward the Irminger Sea rather than the reverse, as would be expected if there was no local modification of LSW via deep convection. Since 1996, the two‐modal structure of LSW has been observed in the Irminger Basin. The upper mode of LSW detected in 1996 was formed in situ; during the winter of 1996/1997, the upper mode was locally renewed. From 1997 to 2004, the temperature and salinity signatures of the deeper mode considerably eroded due to the lack of the renewal of the deeper LSW reservoir in the Labrador Sea, while the annually renewed upper mode, on the contrary, became more pronounced in the property patterns.