Warming periods off Greenland during 1800-2005: their potential influence on the abundance of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus) in Greenlandic waters

Abstract

Greenland and its adjacent waters are located at the northern boundary of the Subpolar Gyre and thus subject to climatic variations within this gyre. It is suggested that periods characterized by regional shrinkage of warm water masses within the Gyre adversely affect the propagation of gadids from upstream Icelandic waters to Greenlandic waters, and periods of regional dilatation of warm water masses within the Gyre are favourable for developing gadid stocks in Greenlandic waters. Recent observations of the sea surface temperature anomalies in the North Atlantic Subpolar Gyre indicate cold conditions in the 1980s and warming from the mid-1990s onwards, with maximum temperatures observed during October 2003. This is consistent with air temperatures at Nuuk, Greenland, which document that 2003 was the warmest year since 1950. Ocean temperatures off West Greenland show a significant upward trend, which is considerably higher than that for the North Atlantic Basin. Ocean properties off West Greenland during recent times were more saline and up to 2°C warmer-than-normal. Sub-surface oceanographic observations of the advection of warm Irminger Mode water masses indicate that during the 20th century and the early-2000s pulses of this water arrived at depths of 400 m–800 m off West Greenland. Long-term climate “proxy” data, which cover the period 1800–1982, were used for comparison with instrumental records of atmospheric data (Nuuk mean annual air temperatures), and of annual mean sea surface temperature data for West Greenland area A1. These data were compared to historic reports on the existence of cod in Greenland waters during the pre-1920s, and during the times of the Greenland cod fishery of the 1930s–1960s. Similar to the data on biomass and abundance of cod (Gadus morhua) and haddock (Melanogrammus aeglefinus), as obtained during German bottom trawl surveys between 1982 and 2005, these data suggested coupling of warming periods with the abundance of gadids in Greenland waters. By means of sea surface temperature anomalies for the North Atlantic Ocean it is shown that the regional extent of warm water masses within the North Atlantic Subpolar Gyre varies significantly during the 1850s