Tree-ring blue intensity and climate sensitivity: exploring site and method-specific variations in southern Yukon, Canada

Tree-ring blue intensity (BI), a substitute for tree-ring density, has gained increasing attention in recent years as a robust tree-ring proxy for climate reconstruction. However, it still presents considerable uncertainty due to its status as a relatively new tree-ring parameter with limitations related to sample discolouration issues and image resolution. This study aims to identify the climate information embedded in different tree-ring parameters measured from white spruce samples and examine whether the relationship between tree-ring parameters and climate is impacted by altitude, image resolution, and BI data collection method. By measuring ring width (RW), earlywood blue intensity (EWBI), latewood blue intensity (LWBI), and delta blue intensity (DBI) at higher (1065 m a.s.l.) and lower (965 m a.s.l.) sites in southern Yukon, we found that LWBI and DBI show a significantly stronger climate signal over RW, especially at high frequencies, aligning with previous climate studies. The upper site performed better than the lower site, agreeing with the expectation that the climate response will increase for sites closer to tree-line. While higher-resolution methods like the Advanced Tree-Ring Image Capturing System (ATRICS) did not outperform the scanner method, further testing is needed. Additionally, both the mean of sorted pixels (Pix) method and the mean of slices (Slc) method have their strength in DBI chronologies, but further testing is recommended to optimize data selection methods.