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The hydrogen isotopic composition of lake water (δ2Hlw) contains hydrologic information and can be used as a recorder of lake water hydrology, including the extent of evaporation of the lake system. Initial studies indicate that the hydrogen isotopes of highly branched isoprenoids (δ2HHBI), synthesized by lake diatoms and preserved in lake sediments are a promising proxy for constraining past δ2Hlw values that are free from terrestrial in- fluences. However, there are many aspects of this proxy, including the seasonality of HBI production, that are unknown and need to be addressed more fully before the proxy can by widely applied. To determine when HBIs are produced throughout the year, and whether there are seasonal biases in δ2Hlw reconstructions, we deployed two sediment traps at Brown’s Lake, in northeastern Ohio. We present HBI concentrations, δ2HHBI values, HBI carbon isotopes and bulk sediment carbon isotopes from sediment traps collected monthly for 26 months to investigate seasonality of HBIs. We observed HBIs in each of the monthly sediment traps throughout the study interval with an increase in HBI concentration during September and October, suggesting that HBIs are made throughout the year with greater production during fall. We calculated the difference between δ2HHBI and δ2Hlw values (ε2HHBI/lw) and observe a range in ε2HHBI/lw values of up to 64‰, which we speculate is related to changes in the diatom communities that synthesize HBIs throughout the year and between different years. Different diatom communities may have different biosynthetic pathways or metabolisms that result in isotope effects. This study is the first that examines the seasonality of HBIs in lake sediments and provides framework for interpreting the seasonality of hydroclimate records generated from δ2HHBI values in temperate eutrophic lakes. 

Diatom-derived highly branched isoprenoid lipids (HBIs) are found extensively in marine sediments, but to date are only reported in a few lacustrine sediments. To expand on prior lake studies, we collected lake surface sediment samples, water samples, and filtered photic zone water from 50 lakes from the Great Plains to the northeastern United States. Samples were collected in May and June and a few sites were revisited in September and October. Studied lakes vary in climate, water chemistry (e.g., pH, salinity, alkalinity), size, and trophic states. They also vary in their diatom species compositions with 344 diatom taxa reported. We characterized HBI assemblages in each lake and found 11 different HBI compounds including one C20:0 HBI, five C20:1 HBI isomers, C21:0 HBI, C25:2 HBI, two C25:3 HBIs, and C25:4 HBI. C20:0 HBI was present in all but two lakes and was often the most abundant HBI present. HBIs were also detected in nearly all the water filter samples indicating they are produced in the photic zone. C20:0 HBI was present in all freshwater lakes, but not present or at very low con- centration in the highest salinity lakes, which were dominated by C21:0 HBI and C25 HBIs. Many of the lakes were dominated by diatom genera and species that are not known to be HBI-producing genera, suggesting there are unrecognized HBI-producing diatom taxa. This inventory, illustrating the widespread presence and diversity of HBIs from lakes across large differences in water chemistries and climate, further suggests that HBIs may be useful diatom biomarkers for paleoclimate applications. 

White oak, a keystone species of the broadleaf forests of the North American Midwest, has a significant role in providing ecosystems services in a region experiencing warming and increasingly pluvial conditions. A one- hundred-year-old white oak stand in an arboretum, along with two second growth (~200-year-old) stands from Northeast Ohio have consistently responded positively to summer (June-July) precipitation over the past century, whereas four nearby old growth sites (>300 years old) have lost their moisture sensitivity since about the mid 1970s. This “fading drought signal,” which has been previously reported, appears to be more a result of the legacy of land use at the individual sites rather than tree age. The younger oak stands and their relative sustained drought sensitivity is also related to their history of recently attaining the canopy and similar responses associated with intervals of selective logging. All sites are strongly, negatively correlated with summer (June- July) maximum monthly temperatures and in general the maximum temperatures are negatively correlated with precipitation in those months. Future warming in the Midwest is projected to see increases in spring precipitation and likely decreases in late summer precipitation linked to a northward migration of the North American Westerly Jet. This projected decrease in summer precipitation coupled with an increase in maximum and min- imum summer temperatures in the coming decades would increase the moisture stress on these trees. Our ex- amination of these varying climate responses with respect to site characteristics and forest age can help future assessments of tree health and the forest’s ability to sequester carbon, as well as facilitate efforts to reconstruct climate by using a range of tree sites for intervals when sensitivity in old growth sites is lost. 

Abstract How forests respond to accelerated climate change will affect the terrestrial carbon cycle. To better understand these responses, more examples are needed to assess how tree growth rates react to abrupt changes in growing‐season temperatures. Here we use a natural experiment in which a glacier's fluctuations exposed a temperate rainforest to changes in summer temperatures of similar magnitude to those predicted to occur by 2050. We hypothesized that the onset of glacier‐accentuated temperature trends would act to increase the variance in stand‐level tree growth rates, a proxy for forest net primary productivity. Instead, dendrochronological records reveal that the growth rates of five, co‐occurring conifer species became less synchronous, and this diversification of species responses acted to reduce the variance and to increase the stability of community‐wide growth rates. These results warrant further inquiry into how climate‐induced changes in tree‐growth diversity may help stabilize future ecosystem services like forest carbon storage. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 285 to -67 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 36 to -70 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 38 to -71 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Ohio, United States Of America. The time period coverage is from 150 to -70 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data. 

Abstract Reconstructing how biota have responded to fast‐paced warming events in the past can help predict their responses to rapid climate changes in the future. Here we suggest that natural communities located near glaciers are useful laboratories for this purpose as they experienced climate changes accentuated by past ice‐margin fluctuations. By reconstructing an Alaskan glacier's position over a 166‐year period and measuring the periglacial air temperatures over the last 3 years, we estimate that the adjacent temperate rainforest episodically cooled and warmed by 0.5–0.7°C/decade. These rates of change exceed most historical warming trends measured elsewhere on Earth and are comparable to the rates of climate warming predicted for the next century. The ring‐width responses of yellow‐cedar trees growing at varying distances from the ice edge illustrate the potential for using periglacial ecosystems to predict how forests may respond to rapid warming in the future. 

Abstract Two large volcanic eruptions contributed to extreme cold temperatures during the early 1800s, one of the coldest phases of the Little Ice Age. While impacts from the massive 1815 Tambora eruption in Indonesia are relatively well‐documented, much less is known regarding an unidentified volcanic event around 1809. Here, we describe the spatial extent, duration, and magnitude of cold conditions following this eruption in northwestern North America using a high‐resolution network of tree‐ring records that capture past warm‐season temperature variability. Extreme and persistent cold temperatures were centered around the Gulf of Alaska, the adjacent Wrangell‐St Elias Mountains, and the southern Yukon, while cold anomalies diminished with distance from this core region. This distinct spatial pattern of temperature anomalies suggests that a weak Aleutian Low and conditions similar to a negative phase of the Pacific Decadal Oscillation could have contributed to regional cold extremes after the 1809 eruption.