Interannual variations of heat and freshwater contents in the cold water dome of the Labrador Sea

Abstract

In this paper, we investigate the interannual variability of heat content and freshwater content in the Labrador Sea using ARMOR-3D data-set (1993–2016), which combines in situ and satellite observations. Significant trends of increasing the heat content and of decreasing the freshwater content in the upper 500th layer were detected. With the depth the slope coefficients of the trends decrease, which suggests the upper ocean origin of the processes, forming the observed tendencies. On interannual scales (after removal of the trends), negative correlation between these characteristics were obtained, which can be formed by the intensification of the ocean-atmosphere heat/freshwater exchange, as well as by intensification of oceanic advection of polar and/or subtropical water in the Labrador Sea. The interannual variability in the heat and freshwater content is dominated by 2–4 years and 5–8 years cycles. Significant correlation of the heat/freshwater content with the North Atlantic Oscillation Index (NAOI) is obtained. For the 2-year and 5–8 year cycles, the high coherence between the heat content and the NAOI is detected. For the 2-year it is found a delay of NAOI by a quarter of the period relative to the heat content, interpreted as the reverse effect of the Labrador Sea water temperature on the phase/intensity of NAOI. For 5–8-year cycles, the high coherence between the variations in the heat content and the Atlantic Multidecadal oscillation index (AMOI, characterizing the mean temperature of the North Atlantic) is detected with practically zero phase shift. After the beginning of 2000, the certain coherence with the AMOI was observed also for the 2–4-year cycles. At these time scales, AMOI leads the variations in the heat content in the sea.