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Climate of the Past An interactive open-access journal of the European Geosciences Union
Clim. Past, 13, 1007-1022, 2017
https://doi.org/10.5194/cp-13-1007-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
16 Aug 2017
Experiments based on blue intensity for reconstructing North Pacific temperatures along the Gulf of Alaska
Rob Wilson1,2, Rosanne D'Arrigo2, Laia Andreu-Hayles2, Rose Oelkers2, Greg Wiles2,3, Kevin Anchukaitis4,2, and Nicole Davi2,5 1School of Earth and Environmental Sciences, University of St. Andrews, St. Andrews, UK
2Tree-Ring Laboratory, Lamont–Doherty Earth Observatory, Palisades, NY, USA
3Department of Geology, The College of Wooster, Wooster, Ohio, USA
4School of Geography and Development & Laboratory of Tree Ring Research, University of Arizona, Tucson, AZ, USA
5Department of Environmental Science, William Paterson University, New Jersey, USA
Abstract. Ring-width (RW) records from the Gulf of Alaska (GOA) have yielded a valuable long-term perspective for North Pacific changes on decadal to longer timescales in prior studies but contain a broad winter to late summer seasonal climate response. Similar to the highly climate-sensitive maximum latewood density (MXD) proxy, the blue intensity (BI) parameter has recently been shown to correlate well with year-to-year warm-season temperatures for a number of sites at northern latitudes. Since BI records are much less labour intensive and expensive to generate than MXD, such data hold great potential value for future tree-ring studies in the GOA and other regions in mid- to high latitudes. Here we explore the potential for improving tree-ring-based reconstructions using combinations of RW- and BI-related parameters (latewood BI and delta BI) from an experimental subset of samples at eight mountain hemlock (Tsuga mertensiana) sites along the GOA. This is the first study for the hemlock genus using BI data. We find that using either inverted latewood BI (LWBinv) or delta BI (DB) can improve the amount of explained temperature variance by > 10 % compared to RW alone, although the optimal target season shrinks to June–September, which may have implications for studying ocean–atmosphere variability in the region. One challenge in building these BI records is that resin extraction did not remove colour differences between the heartwood and sapwood; thus, long term trend biases, expressed as relatively warm temperatures in the 18th century, were noted when using the LWBinv data. Using DB appeared to overcome these trend biases, resulting in a reconstruction expressing 18th–19th century temperatures ca. 0.5 °C cooler than the 20th–21st centuries. This cool period agrees well with previous dendroclimatic studies and the glacial advance record in the region. Continuing BI measurement in the GOA region must focus on sampling and measuring more trees per site (> 20) and compiling more sites to overcome site-specific factors affecting climate response and using subfossil material to extend the record. Although LWBinv captures the inter-annual climate signal more strongly than DB, DB appears to better capture long-term secular trends that agree with other proxy archives in the region. Great care is needed, however, when implementing different detrending options and more experimentation is necessary to assess the utility of DB for different conifer species around the Northern Hemisphere.

Citation: Wilson, R., D'Arrigo, R., Andreu-Hayles, L., Oelkers, R., Wiles, G., Anchukaitis, K., and Davi, N.: Experiments based on blue intensity for reconstructing North Pacific temperatures along the Gulf of Alaska, Clim. Past, 13, 1007-1022, https://doi.org/10.5194/cp-13-1007-2017, 2017.
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Short summary
Blue intensity shows great potential for reconstructing past summer temperatures from conifer trees growing at high latitude or the treeline. However, conifer species that express a strong colour difference between the heartwood and sapwood can impart a long-term trend bias in the resultant reconstructions. Herein, we highlight this issue using eight mountain hemlock sites across the Gulf of Alaska and explore how a non-biased reconstruction of past temperature could be derived using such data.
Blue intensity shows great potential for reconstructing past summer temperatures from conifer...
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