NOAA/WDS Paleoclimatology - Wilson - Faro - PCGL - ITRDB CANA597

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）表现为树轮宽度（tree ring width, RW）近数十年来温度信号的不稳定性。同一区域的晚木最大密度（maximum latewood density, MXD）几乎未显现DP迹象。尽管MXD是夏季温度的优质代用指标，但北美地区的长序列MXD记录极为匮乏。晚木蓝强度（latewood blue intensity, LWB）可测定与MXD相似的木材性质，呈现一致的气候响应特征，且测定成本大幅降低，因此有望显著拓展北美地区温度敏感型树轮年表（tree-ring, TR）的现存网络。本研究针对育空西南部17个白云杉（Picea glauca）样点开展LWB测定，以检验LWB是否不受RW中观测到的时间校准不稳定性影响。研究考察了多种去趋势方法，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，RW与LWB均可获得最优校准结果。RW与6-7月最高温（maximum temperatures, Tmax）的校准效果最佳，可解释最高28%的方差，但所有模型均未能通过验证及残差分析。相较而言，LWB的校准效果显著（可解释5-8月最高温43%~51%的方差）且验证表现良好。该温度重建序列可追溯至公元1337年，但由于17世纪早期之前的样本复现率较低，不确定性显著升高。来自阿拉斯加湾、兰格尔山脉及阿拉斯加北部基于RW、MXD和LWB的夏季温度重建序列在年代际及更高频率上展现出良好一致性，但育空地区的LWB重建序列在百年尺度变化的表达上似乎存在潜在局限。尽管LWB优化了树轮气候学校准流程，但未来研究需聚焦于保存完好的亚化石材料，以提升1650年之前的样本复现率。