NOAA/WDS Paleoclimatology - Wilson - Mt. Mcintyre - PCGL - ITRDB CANA603

In north-western North America, the so-called divergence problem (DP) is expressed in tree ring width (RW) as an unstable temperature signal in recent decades. Maximum latewood density (MXD), from the same region, shows minimal evidence of DP. While MXD is a superior proxy for summer temperatures, there are very few long MXD records from North America. Latewood blue intensity (LWB) measures similar wood properties as MXD, expresses a similar climate response, is much cheaper to generate and thereby could provide the means to profoundly expand the extant network of temperature sensitive tree-ring (TR) chronologies in North America. In this study, LWB is measured from 17 white spruce sites (Picea glauca) in south-western Yukon to test whether LWB is immune to the temporal calibration instabilities observed in RW. A number of detrending methodologies are examined. The strongest calibration results for both RW and LWB are consistently returned using age-dependent spline (ADS) detrending within the signal-free (SF) framework. RW data calibrate best with June-July maximum temperatures (Tmax), explaining up to 28% variance, but all models fail validation and residual analysis. In comparison, LWB calibrates strongly (explaining 43-51% of May-August Tmax) and validates well. The reconstruction extends to 1337 CE, but uncertainties increase substantially before the early 17th century because of low replication. RW-, MXD- and LWB-based summer temperature reconstructions from the Gulf of Alaska, the Wrangell Mountains and Northern Alaska display good agreement at multi-decadal and higher frequencies, but the Yukon LWB reconstruction appears potentially limited in its expression of centennial-scale variation. While LWB improves dendroclimatic calibration, future work must focus on suitably preserved sub-fossil material to increase replication prior to 1650 CE.

在北美西北部，所谓的分歧问题（divergence problem, DP）在近几十年的树轮宽度（tree ring width, RW）记录中表现为不稳定的温度信号。同区域的晚材最大密度（maximum latewood density, MXD）几乎未表现出分歧问题。尽管晚材最大密度是夏季温度的优质代用指标，但北美地区的长序列晚材最大密度记录极少。晚材蓝度（latewood blue intensity, LWB）与晚材最大密度测量的木材性质相似，气候响应模式一致，且测量成本大幅降低，因此有望大幅拓展北美地区对温度敏感的树轮（tree-ring, TR）年表现存网络。本研究从育空西南部的17个白云杉（Picea glauca）采样点获取晚材蓝度数据，以检验晚材蓝度能否免受树轮宽度记录中出现的时间校准不稳定性影响。本研究对多种去趋势方法进行了检验。在无信号（signal-free, SF）框架下采用年龄依赖样条（age-dependent spline, ADS）去趋势时，树轮宽度与晚材蓝度均能获得最优的校准结果。树轮宽度数据与6-7月最高气温（maximum temperatures, Tmax）拟合效果最佳，可解释最高达28%的方差，但所有模型均未通过验证与残差分析。相较之下，晚材蓝度的校准效果优异（可解释5-8月最高气温43%~51%的方差），且通过了验证。本次温度重建序列可追溯至公元1337年，但由于17世纪早期之前的采样复本数较少，序列不确定性显著升高。基于树轮宽度、晚材最大密度与晚材蓝度的阿拉斯加湾、兰格尔山脉及阿拉斯加北部夏季温度重建序列，在年代际及更高频的变化上均表现出良好的一致性，但育空地区晚材蓝度重建序列在百年尺度变化的表达上存在潜在局限。尽管晚材蓝度提升了树轮气候校准效果，但未来研究需聚焦于保存完好的亚化石材料，以增加公元1650年之前的采样复本数。