Nao and Sea-Surface Temperature Signatures in Tree-Ring Records from the North-Atlantic Sector

Temperature-sensitive tree-ring chronologies from Scandinavia and Labrador are, respectively, analyzed for their response to two major features of North Atlantic climate variability: (1) the North Atlantic Oscillation (NAO), and (2) Coastal and near-coastal surface air and sea surface temperatures (SSTs). (1) NAO: Using superposed epoch analysis (SEA), below (above) average ring-width departures from Scandinavian scots pine (Pinus sylvestris L.) were found to follow positive (negative) anomalies in winter (December-February) sea level pressure (SLP) related to the Icelandic low pressure cell, a key element of the NAO. In addition to a documented summer temperature relationship, these trees show a positive correlation with winter temperatures for Oslo, Norway. Oslo data are used to define the northwest European end of the winter temperature seesaw, another major feature of the NAO. Below (above) average tree-growth departures tend to follow Greenland Above, GA or (Greenland Below, GB) seesaw winters, which are associated with high (low) pressure and cold (warm) conditions over Scandinavia. (2) SSTs: Growing season (April-September) land/sea temperatures were reconstructed for three 5-degrees x 5-degrees gridcells (50-55-degrees-N, 50-65-degrees-W) near the coast of Labrador for the period from 1813 to 1988. The tree-ring data used in this case were four maximum latewood density chronologies of white spruce (Picea glauca [Moench] Voss) from sites in southern and central Labrador. An alternative model, based on only two chronologies, allows extension of these reconstructions back to 1713. The reconstructions explain about 45% of the temperature variance from 1915-1988 and pass several tests for model validation with high levels of statistical significance. They primarily provide information on short-period (< 10 years) temperature variability for the Labrador region.