BRANCHED GDGTS AND LOESS PALEOTEMPERATURE RECONSTRUCTION:OPPORTUNITIES AND CHALLENGES
Currently,our understanding of global paleotemperatures is primarily based on marine records.Due to the lack of reliable terrestrial paleotemperature indicators,our knowledge of terrestrial paleotemperatures,crucial for our survival,is limited.This constraint hampers our understanding of the patterns and mechanisms of terrestrial temperature changes under the background of global warming.Branched Glycerol Dialkyl Glycerol Tetraether compounds(brGDGTs),synthesized by bacterial membrane lipids,have emerged as popular terrestrial paleothermometers in the past two decades,playing a significant role in long-term scale reconstructions,particularly in loess paleotemperature reconstructions.The paper first reviews the developmental history of brGDGTs temperature proxies,summarizing recent innovations and advancements in bacterial culture experiments,modern process surveys,instrumental analysis methods,and data processing techniques.It then introduces the progress of branched GDGT-based reconstructions of paleotemperatures at various time scales in loess paleosols.Records of terrestrial temperatures from brGDGTs on the Chinese Loess Plateau exhibit distinct glacial-interglacial fluctuations,indicating significant driving roles of solar radiation and global ice volume in terrestrial temperature changes.However,the temperature increases during the glacial maximum to deglaciation in led to that of marine records,suggesting that dynamic evolution of land surfaces(vegetation,soil moisture,etc.)may play an important regulatory role in terrestrial temperature changes.Finally,the article provides a multi-faceted analysis of the opportunities and challenges facing brGDGT-based reconstructions of terrestrial paleotemperatures.As a scarce tool for reconstructing terrestrial paleotemperatures,brGDGTs offer valuable records for understanding patterns and mechanisms of terrestrial temperature changes.Yet,uncertainties remain regarding their exact biological sources and formation mechanisms,and significant challenges persist in explaining the global variations in trends,cycles,and magnitudes of brGDGT-based temperatures in loess.To tackle these challenges,it is crucial to enhance the foundational theoretical research of brGDGT proxies,clarifying their exact sources and formation mechanisms,and optimizing analytical methods and calibration models.Additionally,integrating modern observational and simulation studies can help explore the feedback mechanisms between land surface properties(such as vegetation and soil moisture)and temperature changes at different time scales.This approach will further enrich our understanding of the patterns and mechanisms of global temperature variability.
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