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Here we explore two new tree-ring parameters, derived from measurements ofwood density and blue intensity (BI). The new proxies show an increase inthe interannual summer temperature signal compared to established proxies,and present the potential to improve long-term performance. At highlatitudes, where tree growth is mainly limited by low temperatures,radiodensitometric measurements of wood density, specifically maximumlatewood density (MXD), provides a temperature proxy that is superior tothat of tree-ring widths. The high cost of developing MXD has led toexperimentation with a less expensive method using optical flatbed scannersto produce a new proxy, herein referred to as maximum latewood blueabsorption intensity (abbreviated MXBI). MXBI is shown to be very similar toMXD on annual timescales but less accurate on centennial timescales. This isdue to the fact that extractives, such as resin, stain the wooddifferentially from tree to tree and from heartwood to sapwood. To overcomethis problem, and to address similar potential problems inradiodensitometric measurements, the new parameters Δblue intensity(ΔBI) and Δdensity are designed by subtracting the ambientBI/density in the earlywood, as a background value, from the latewoodmeasurements. As a case-study, based on Scots pine trees from NorthernSweden, we show that Δdensity can be used as a quality control ofMXD values and that the reconstructive performance of warm-season meantemperatures is more focused towards the summer months (JJA – June, July, August), with anincrease by roughly 20% when also utilising the interannual informationfrom the earlywood. However, even though the new parameter ΔBIexperiences an improvement as well, there are still puzzling dissimilaritiesbetween Δdensity and ΔBI on multicentennial timescales. Asa consequence, temperature reconstructions based on ΔBI willpresently only be able to resolve information on decadal-to-centennialtimescales. The possibility of trying to calibrate BI into a measure oflignin content or density, similarly to how radiographic measurements arecalibrated into density, could be a solution. If this works, only thencan ΔBI   be used as a reliable proxy in multicentennial-scaleclimate reconstructions

climate of the past

Blue intensity and density from northern Fennoscandian tree rings, exploring the potential to improve summer temperature reconstructions with earlywood information