Blue Intensity based experiments 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 Davi2,51School of Earth and Environmental Sciences, University of Saint Andrews, Saint Andrews, UK 2Tree-Ring Laboratory, Lamont-Doherty Earth Observatory, Palisades, NY, USA 3Department of Geology, The College of Wooster, OH, USA 4School of Geography and Development & Laboratory of Tree Ring Research, University of Arizona, Tucson, AZ USA 5William Paterson University, New Jersey, USA
Received: 26 Feb 2017 – Accepted for review: 02 Mar 2017 – Discussion started: 06 Mar 2017
Abstract. Climate in the Gulf of Alaska (GOA) reflects large-scale ocean-atmosphere variability of the North Pacific climate system. Ring-width (RW) records from the GOA have yielded a valuable long-term perspective for North Pacific changes on decadal to longer time scales in prior studies, but express a broad winter to late summer seasonal 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 expensive and labor intensive to generate than MXD, such data hold great potential value for future tree-ring studies in the GOA and other regions at mid-to-high latitudes. Here we highlight the potential for improving tree-ring based reconstructions using combinations of RW and BI-related parameters (latewood BI (LWB) and delta BI (DB)) from an experimental sub-set of samples from eight mountain hemlock (Tsuga mertensiana) sites along the GOA. This is the first such study for the hemlock genus using BI data. We find that using either LWB or DB can improve the amount of explained temperature variance by > 10 % compared to RW alone although the optimal target season changes to June–September, which may have implications for studying ocean-atmosphere variability in the region. However, one challenge in building these BI records is that resin extraction did not remove colour differences between the heartwood and sapwood, so long term trend biases, expressed as relatively warm temperatures in the 18th century, were noted when using the LWB 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 more trees per site (> 20) and more sites to overcome site specific factors effecting climate response while sub-fossil material will extend the reflectance records back over 1000 years. DB appears to capture long term secular trends that agree with other proxy archives in the region but great care is needed when implementing different detrending options. Finally, more experimentation is needed to assess the utility of DB for different conifer species around the Northern Hemisphere.
Wilson, R., D'Arrigo, R., Andreu-Hayles, L., Oelkers, R., Wiles, G., Anchukaitis, K., and Davi, N.: Blue Intensity based experiments for reconstructing North
Pacific temperatures along the Gulf of Alaska, Clim. Past Discuss., doi:10.5194/cp-2017-26, in review, 2017.