Proxy-to-proxy calibration: Increasing the temporal resolution of quantitative climate reconstructions

High-resolution paleoclimate reconstructions are often restricted by the difficulties of sampling geologic archives in great detail and the analytical costs of processing large numbers of samples. Using sediments from Lake Braya Sø, Greenland, we introduce a new method that provides a quantitative high-resolution paleoclimate record by combining measurements of the alkenone unsaturation index ([Image: see text]) with non-destructive scanning reflectance spectroscopic measurements in the visible range (VIS-RS). The proxy-to-proxy (PTP) method exploits two distinct calibrations: the in situ calibration of [Image: see text] to lake water temperature and the calibration of scanning VIS-RS data to down core [Image: see text] data. Using this approach, we produced a quantitative temperature record that is longer and has 5 times higher sampling resolution than the original [Image: see text] time series, thereby allowing detection of temperature variability in frequency bands characteristic of the AMO over the past 7,000 years

Abrupt climatic events during the last glacial-interglacial transition in Alaska

Evidence is mounting that abrupt climatic shifts occurred during the last glacial-interglacial transition (LGIT) in the North Atlantic and other regions. However, few high-resolution climatic records of the LGIT exist from the high latitudes of the North Pacific rim. We analyzed lake sediments from southwestern Alaska for biogenic silica, organic carbon, organic nitrogen, diatom assemblages, and compound-specific hydrogen isotopes. Results reveal climatic changes coincident with the Younger Dryas, Intra-Allerod Cold Period, and Pre-Boreal Oscillation. However, major discrepancies exist in the paleoclimate patterns of the Bolling-Allerod interstadial between our data and the GISP2 18O record from Greenland, and causes are uncertain. These data suggest that the North Pacific and North Atlantic experienced similar reversals during climatic warming of the LGIT but that the Bolling-Allerod cooling trend in the GISP2 18O record is probably not a hemispheric or global pattern

Crystal Structure of TDRD3 and Methyl-Arginine Binding Characterization of TDRD3, SMN and SPF30

SMN (Survival motor neuron protein) was characterized as a dimethyl-arginine binding protein over ten years ago. TDRD3 (Tudor domain-containing protein 3) and SPF30 (Splicing factor 30 kDa) were found to bind to various methyl-arginine proteins including Sm proteins as well later on. Recently, TDRD3 was shown to be a transcriptional coactivator, and its transcriptional activity is dependent on its ability to bind arginine-methylated histone marks. In this study, we systematically characterized the binding specificity and affinity of the Tudor domains of these three proteins quantitatively. Our results show that TDRD3 preferentially recognizes asymmetrical dimethylated arginine mark, and SMN is a very promiscuous effector molecule, which recognizes different arginine containing sequence motifs and preferentially binds symmetrical dimethylated arginine. SPF30 is the weakest methyl-arginine binder, which only binds the GAR motif sequences in our library. In addition, we also reported high-resolution crystal structures of the Tudor domain of TDRD3 in complex with two small molecules, which occupy the aromatic cage of TDRD3

蓮華寺池と西湖 : 石野雲嶺の風景

The potential for increased drought frequency and severity linked to anthropogenic climate change in the semi-arid regions of the southwestern United States (US) is a serious concern1. Multi-year droughts during the instrumental period2 and decadal-length droughts of the past two millennia1, 3 were shorter and climatically different from the future permanent, ‘dust-bowl-like’ megadrought conditions, lasting decades to a century, that are predicted as a consequence of warming4. So far, it has been unclear whether or not such megadroughts occurred in the southwestern US, and, if so, with what regularity and intensity. Here we show that periods of aridity lasting centuries to millennia occurred in the southwestern US during mid-Pleistocene interglacials. Using molecular palaeotemperature proxies5 to reconstruct the mean annual temperature (MAT) in mid-Pleistocene lacustrine sediment from the Valles Caldera, New Mexico, we found that the driest conditions occurred during the warmest phases of interglacials, when the MAT was comparable to or higher than the modern MAT. A collapse of drought-tolerant C4 plant communities during these warm, dry intervals indicates a significant reduction in summer precipitation, possibly in response to a poleward migration of the subtropical dry zone. Three MAT cycles ~2 °C in amplitude occurred within Marine Isotope Stage (MIS) 11 and seem to correspond to the muted precessional cycles within this interglacial. In comparison with MIS 11, MIS 13 experienced higher precessional-cycle amplitudes, larger variations in MAT (4–6 °C) and a longer period of extended warmth, suggesting that local insolation variations were important to interglacial climatic variability in the southwestern US. Comparison of the early MIS 11 climate record with the Holocene record shows many similarities and implies that, in the absence of anthropogenic forcing, the region should be entering a cooler and wetter phase

Climate exceeded human management as the dominant control of fire at the regional scale in California’s Sierra Nevada

The societal impacts of recent, severe fires in California highlight the need to understand the long-term effectiveness of human fire management. The relative influences of local management and climate at centennial timescales are controversial and poorly understood. This is the case in California’s Sierra Nevada, an actively managed area with a rich history of Native American fire use. We analyzed charcoal preserved in lake sediments from Yosemite National Park and spanning the last 1400 years to reconstruct local and regional area burned. Warm and dry climates promoted burning at both local and regional scales. However, at local scales fire management by Native Americans before 850 and between ca. 1350 and 1600 CE and, subsequently, Yosemite park managers from ca. 1900 to 1970 CE, decoupled fire extent dictated by regional climate scenarios. Climate acts as a top-down, broader scale control of fire, but human management serves a bottom-up, local control. Regional area burned peaked during the Medieval Climate Anomaly and declined during the last millennium, as climate became cooler and wetter and Native American burning declined. This trend was accentuated by 20th century fire suppression policies, which led to a minimum in burned area relative to the last 1400 years. In light of projected anthropogenic greenhouse gas emissions and predicted climate changes in California, our data indicate that although active management can mitigate local fire activity, broader regional burning may become more spatially extensive than has been observed in the last century

Comparison of black carbon chemical oxidation and macroscopic charcoal counts for quantification of fire by-products in sediments

Black carbon (BC) ranges in size from submicron to millimeter scales and represents incompletely combusted or pyrolysed organic fuels (e.g., coal, petroleum, biomass etc). The content of BC in sediments or in the atmosphere has been widely used to infer fossil fuel combustion from local to regional sources. However, the assessment of natural fires (biomass burning) in the past has been conventionally performed by counting charcoal particles in different size fractions (greater than ca. 10 and 100 µm for microscopic and macroscopic charcoal, respectively) using a microscope. Because similarly sized charcoal particles can have large differences in mass, counting using microscopes may induce significant error for quantifying fire-produced BC in sediments. A popular method oxidizes BC with nitric acid to produce benzene polycarboxyclic acids (BPCAs), which can be subsequently quantified using a gas chromatograph and mass spectrometer (GC-FID and GC–MS). In this paper, we provide the first parallel comparison of charcoal and BPCA analyses to assess their ability to quantitatively record BC content in experimental sediments. We find that while qualitatively comparable, the BPCA method more accurately quantifies changes in BC content than does charcoal microscopy. Additionally, we use metadata analyses of the Global Charcoal Database to contextualize our results. Further, we explore possible applications of these two methods in tandem which could provide novel insight into paleofire characteristics

The morphology of experimentally produced charcoal distinguishes fuel types in the Arctic tundra

Wildfires in the Arctic tundra have become increasingly frequent in recent years and have important implications for tundra ecosystems and for the global carbon cycle. Lake sediment–based records are the primary means of understanding the climatic influences on tundra fires. Sedimentary charcoal has been used to infer climate-driven changes in tundra fire frequency but thus far cannot differentiate characteristics of the vegetation burnt during fire events. In forested ecosystems, charcoal morphologies have been used to distinguish changes in fuel type consumed by wildfires of the past; however, no such approach has been developed for tundra ecosystems. We show experimentally that charcoal morphologies can be used to differentiate graminoid (mean = 6.77; standard deviation (SD) = 0.23) and shrub (mean = 2.42; SD = 1.86) biomass burnt in tundra fire records. This study is a first step needed to construct more nuanced tundra wildfire histories and to understand how wildfire will impact the region as vegetation and fire change in the future

Systematic chemotaxonomic profiling and novel paleotemperature indices based on alkenones and alkenoates: potential for disentangling mixed species input

The unsaturation indices (U(k/37),U(k/37)) of long chain alkenones are powerful paleotemperature proxies and have been widely applied for sea surface temperature (SST) reconstructions in the past three decades. However, these indices encounter major difficulties in systems harboring different alkenone-producing haptophyte species, such as saline lakes and marginal ocean environments. All haptophytes produce C37 alkenones, but different species often display large differences in temperature calibrations and may bloom in different seasons, hindering the use of U(k/37) and U(k/37) indices for reliable paleotemperature reconstructions in mixed systems. To overcome these problems, we have recently reported a new analytical method that allows comprehensive separation of up to 32 alkenones, alkenoates and their double bond positional isomers in culture and sediment samples. Here we report a systematic analysis of alkenones and alkenoates from six haptophyte cultures growing at a wide range of temperatures (4–25 °C). Together with a compilation of 230 previously published culture data sets, we present here systematic calibrations of temperature-sensitive indices based on all alkenone and alkenoate homologues (including isomers). Using this dataset, we extract systematic chemotaxonomic criteria for differentiating individual haptophyte species and demonstrate such chemotaxonomic features can be encoded into a machine learning model for reliable species identifications. Specifically, we show that temperature calibrations based on C38 methyl ketones and C39 ethyl ketones are potentially useful for disentangling mixed inputs in estuarine systems where Group III (E. huxleyi) and Group II alkenones mix, and that C36 ethyl alkenoate isomeric ratios display minimal species heterogeneity and are potentially more suited for reconstructing temperatures in mixed systems with different Group II haptophytes. Using the culture data as base profiles, we construct a mathematical model for estimating percentage inputs from alkenones of different Isochrysidales groups in mixed systems, with potential implications for inferring past salinity changes. Overall, the results from this study demonstrate important new applications of alkenone and alkenoate biomarkers in paleoclimate and paleoenvironmental research