Reduced Temperature Sensitivity of Maximum Latewood Density Formation in High-Elevation Corsican Pines under Recent Warming

Maximum latewood density (MXD) measurements from long-lived Black pines (Pinus nigra spp. laricio) growing at the upper treeline in Corsica are one of the few archives to reconstruct southern European summer temperatures at annual resolution back into medieval times. Here, we present a compilation of five MXD chronologies from Corsican pines that contain high-to-low frequency variability between 1168 and 2016 CE and correlate significantly (p < 0.01) with the instrumental April–July and September–October mean temperatures from 1901 to 1980 CE (r = 0.52−0.64). The growth–climate correlations, however, dropped to −0.13 to 0.02 afterward, and scaling the MXD data resulted in a divergence of >1.5 °C between the colder reconstructed and warmer measured temperatures in the early-21st century. Our findings suggest a warming-induced shift from initially temperature-controlled to drought-prone MXD formation, and therefore question the suitability of using Corsican pine MXD data for climate reconstruction.

Is temperature still the most limiting factor for growth in northern boreal forests?

Over the last few decades – at a range of northern sites – changes in tree-ring width and latewood density have not followed mean summertime temperature fluctuations. This discrepancy sharply contrasts an earlier correlation between those variables. As the origin of this inconsistency has not been fully deciphered, questions have emerged regarding the use of tree-ring width and latewood density as a proxy in dendrochronological climate reconstructions. I suggest that temperature is no longer the most limiting factor in certain boreal areas, which might explain the observed divergence.

Water Over the Bridge: Can We Connect Tree Rings and Overwash Deposits to Understand Regional Tropical Cyclone Variability?

&lt;p&gt;Despite significant advances in methods, reconstructions using multiple proxies are uncommon in paleotempestology. Studies employing multiproxy techniques often rely on homologous proxies (e.g., grain-size distribution and organic content, or total ring width and maximum latewood density) that complement one another as they often reflect similar processes occurring within tropical cyclones. Unifying seemingly diametric proxies (i.e., tree rings and overwash deposits) receives less attention as they typically record different aspects of a tropical cyclone over substantially different temporal resolutions. However, given the spatial characteristics of storm-related hazards, tree rings and overwash might be far more complementary than previously thought. Here, I present work reconstructing tropical cyclone rainfall using tree rings, from which I develop frequency curves based on the number of years receiving tropical cyclone rainfall amounts &amp;#8805;75th percentile. Using this new metric, I compare tree-ring-based reconstructions with near-annually- to decadally-resolved sediment records from Florida and The Bahamas. Through this comparison, I demonstrate both synchronous and asynchronous behavior between records, highlighting the possible presence of regional signatures and climate controls in storm activity. While there remain numerous discrepancies between these records, this comparison serves as an example that these proxies augment one another when viewed through the lens of regional shifts in the hurricane climate. Given that trees respond to the widespread footprint of tropical cyclone rainfall, independent of storm intensity, tree rings may better capture regional changes in storm activity. As such, turning to the shorter, yet higher-resolution tree-ring record can provide additional context to active and quiescent intervals observed in overwash records, especially at sites with a higher sensitivity threshold. Comparing these two proxies is still in its infancy; however, we can use techniques unique to a particular proxy to produce analogous records of tropical cyclone activity. In addition to developing analogous records, is important to explore nontraditional signals of tropical cyclones in these proxies. In particular, I will discuss two approaches that could be key for developing holistic records of storm activity in the Gulf of Mexico. The first uses growth suppressions and geochemical signals in coastal trees in response to saltwater intrusion, while the second examines the sedimentary and geochemical signature of inland flooding from tropical cyclones. The advancement of paleotempestology necessitates developing multiproxy reconstructions. All of these novel approaches and proxies complement records of overwash, which is one of the few proxies able to provide a quantitative estimate of storm magnitude. Moreover, using these proxies in conjunction with one another is critical for understanding changes in the regional hurricane climate and reducing the manifold risks associated with tropical cyclones.&lt;/p&gt;

Maximum latewood density records of Great Basin Bristlecone pine (Pinus Longaeva) from the White Mountains, California

&lt;p&gt;Great Basin Bristlecone pine (Pinus longaeva) is known for its longevity. The longest continuous tree-ring width chronology covers more than 9000 years. Tree-ring width of upper treeline bristlecone pine trees is influenced by summer temperature variability at decadal to centennial scales, but to infer a temperature signal on interannual scales, Maximum Latewood Density (MXD) is a better proxy. Here, we present a preliminary MXD chronology to investigate the temperature signal in upper treeline and lower elevation bristlecone pines. MXD was measured with an X-ray Computed Tomography toolchain in 24 dated cores, &amp;#160;with the oldest sample dating back to 776 CE. Ring and fibre angles were corrected and two MXD chronologies for different elevations were developed, which will be used to study climate-growth relationships and the effect of elevation on them. Future scanning will allow constructing a 5000+ year-long MXD chronology from upper treeline sites, which will provide an annual-resolution North American temperature record covering the mid-to-late Holocene.&lt;/p&gt;

Chemical destaining and the delta correction for blue intensity measurements of stained lake subfossil trees

The stain of wood samples from lake subfossil trees (LSTs) is challenging the wide application of the blue intensity (BI) technique for millennial dendroclimatic reconstructions. In this study, we used seven chemical destaining reagents to treat samples of subfossil black spruce (Picea mariana (Mill.) B.S.P.) trees from two lakes in the eastern Canadian boreal forest. We subsequently compared latewood BI (LBI) and delta BI (DBI) time series along with conventional maximum latewood density (MXD) measured from the stained and destained samples. Results showed that the stain of our samples is most likely caused by postsampling oxidation of dissolved ferrous iron in lake sediments that penetrated into wood. Three reagents (ascorbic acid, sodium ascorbate, and sodium dithionite all mixed with ethylenediaminetetraacetic acid) could remove >90 % of Fe. However, even for the best chemical protocol, a discrepancy of about +2 ∘C compared to MXD data remained in the LBI-based temperature reconstruction due to incomplete destaining. On the contrary, the simple mathematical delta correction, DBI, was unaffected by the Fe stain and showed very similar results compared to MXD data (r>0.82) from annual to centennial timescales over the past ∼360 years. This study underlines the difficulty of completely destaining lake subfossil samples while confirming the robustness of the DBI approach. DBI data measured from stained LSTs can be used to perform robust millennial temperature reconstructions.

Reconstructing Summer Precipitation with MXD Data from Pinus sylvestris Growing in the Stockholm Archipelago

Maximum latewood density (MXD) chronologies have been widely used to reconstruct summer temperature variations. Precipitation signals inferred from MXD data are, however, rather scarce. In this study, we assess the potential of using MXD data derived from Scots pine (Pinus sylvestris L.) growing in the Stockholm archipelago (Sweden) to reconstruct past precipitation variability. In this area, slow-growing pine trees emerge on flat plateaus of bedrock outcrops with thin or absent soil layers and are, therefore, sensitive to moisture variability. A 268-year-long MXD chronology was produced, and climate–growth relationships show a significant and robust correlation with May–July precipitation (PMJJr = 0.64, p < 0.01). The MXD based May–July precipitation reconstruction covers the period 1750–2018 CE and explains 41% of the variance (r2) of the observed precipitation (1985–2018). The reconstruction suggests that the region has experienced more pluvial phases than drought conditions since the 1750s. The latter half of the 18th century was the wettest and the first half of the 19th century the driest. Climate analysis of “light rings” (LR), latewood layers of extreme low-density cells, finds their occurrence often coincides with significantly dry (<41 mm precipitation) and warmer (1–2 °C above average temperature), May–July conditions. Our analysis suggests that these extremes may be triggered by the summer North Atlantic Oscillation (SNAO).

Pinus cembra L. tree-ring data as a proxy for summer mass-balance variability of the Careser Glacier (Italian Rhaetian Alps)

Glacial extent and mass balance are sensitive climate proxies providing solid information on past climatic conditions. However, series of annual mass-balance measurements of more than 60 years are scarce. To our knowledge, this is the first time the latewood density data (MXD) of the Swiss stone pine (Pinus cembra L.) have been used to reconstruct the summer mass balance (Bs) of an Alpine glacier. The MXD-based Bs well correlates with a Bs reconstruction based on the May to September temperature. Winter precipitation has been used as an independent proxy to infer the winter mass balance and to obtain an annual mass-balance (Bn) estimate dating back to the glaciological year 1811/12. The reconstructed MXD/precipitation-based Bn well correlates with the data both of the Careser and of other Alpine glaciers measured by the glaciological method. A number of critical issues should be considered in both proxies, including non-linear response of glacial mass balance to temperature, bedrock topography, ice thinning and fragmentation, MXD acquisition and standardization methods, and finally the ‘divergence problem’ responsible for the recently reduced sensitivity of the dendrochronological data. Nevertheless, our results highlight the possibility of performing MXD-based dendroglaciological reconstructions using this stable and reliable proxy.