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The hydrogen isotopic compositions of leaf‐wax n‐alkanes (δDalk) and n‐alkanoic acids (δDacid) reflect ambient climatic conditions (including precipitation δD values, δDprecip). However, the understanding of climatic conditions of exactly which period (i.e., early or entire period of the leaf's lifespan) these biomarkers preserve is still evolving. Previous studies on the δDalk and δDacid values, done only in extra‐tropical regions, mostly indicate that δDalk values are biased toward the early growing season whereas δDacid values are not biased toward any season. To decipher the seasonal bias in δDalk and δDacid records from tropics, we conducted a long‐duration experiment wherein deciduous and evergreen species were grown using normal water (δD = −2‰) during early stages of the leaf growth and later using isotopically labeled water (δD = 1,000‰). Our experiment revealed (a) in deciduous and evergreen species, δDalk and δDacid values reflect δDprecip during early stages of the leaf growth, (b) synchronous synthesis of n‐alkanes and n‐alkanoic acids, and (c) in deciduous species, minor incorporation of the previous year's photosynthates in leaf wax pool of the current year's mature leaves. Our study suggests that δDalk and δDacid records in the tropics are biased toward the climatic conditions prevailing during early stages of leaf growth. This bias should be considered while comparing the δDprecip values generated from leaf wax proxy records and isotope‐enabled atmospheric circulation models. Plain Language Summary: The hydrogen isotopic composition of leaf wax n‐alkanes and n‐alkanoic acids preserved in sediments have been used extensively for reconstructing past climate variability. However, whether these records reflect a climate of a specific season or an entire year is not known. In our experiment, we grew various tropical plants using normal water during early growing season and heavy water during later growing season. Lack of isotopic signal associated with the heavy water in leaf wax compounds suggested that the bulk of leaf wax production occurred during the early growing season of the leaves. As the hydrogen isotopic composition of the leaf wax compounds reflects ambient climatic conditions, our results suggested that the hydrogen isotope record of tropical leaf wax compounds reflects the climatic conditions prevailing during the early stages of leaf growth. Key Points: Hydrogen isotope records of leaf wax n‐alkane and n‐alkanoic acid from the tropics reflect climatic conditions during the early leaf growthBoth deciduous and evergreen leaf wax hydrogen isotope records are biased toward the early stages of the leaf growthThis bias should be considered while comparing the hydrogen isotope of precipitation generated from climate models and leaf wax records [ABSTRACT FROM AUTHOR]

Paleoclimate investigations of the peat deposits in the Nilgiri Plateau, an important paleoclimate archive of India, are mainly restricted to the carbon isotope composition ((δ13C) of plant-derived materials and pollen studies. However, it is unclear whether these proxies reflect past variability in temperature or hydrology. Here, we report the hydrogen and carbon isotopic variability of n -alkanoic acid of chain length 28 (δDC28 and δ13CC28, respectively) and demonstrate that the peatland leaf wax hydrogen isotopes provide a sensitive record of past hydrology. The decoupling of δ13CC28 and δD of vegetation-corrected rain during the Holocene indicate that δD of the leaf wax compounds mainly respond to past hydrological variability whereas δ13C variations might reflect the temperature-controlled variability of C3 and C4 vegetation. Conforming with the other paleoclimate records from the region, the δDC28 variations showed a reducing precipitation trend since the early Holocene. However, a large amplitude of reconstructed δD of rain (~44‰) during the Holocene indicated changes in the moisture source and trajectory could be an additional factor contributing to the orbital-scale δD variability of proxies from the Indian region. [ABSTRACT FROM AUTHOR]

Although stable hydrogen (δ2H) and carbon (δ13C) isotopic compositions of bird feathers have been increasingly used to understand the migration of birds through assignment of individuals to established isoscapes, far less is known about the structure of feather isoscapes based on stable sulphur isotope (δ34S) assays. While δ2H isoscapes have been used to investigate the migratory origins of the Globe Skimmer (Pantala flavescens) dragonfly in India, no isotope studies have been applied to avian migration patterns in that region. Here, based on museum collections, we report the feather δ34S values of 13 avian species that included marine birds with expected 34S enriched feathers, resident birds throughout India and a single migratory species, Bar-headed Goose (Anser indicus). Feathers from the marine birds were the most enriched (20.6 ± 1.2 ‰, n = 10; range = 4.4 ‰) in 34S but terrestrial resident species also showed unexpectedly high δ34S values (11.7 ± 4.8 ‰, n = 74; range = 19.9 ‰) throughout most of India but the Himalayan region and Gangetic plain typically showed δ34S values less than 6.4 ‰. Our results show the utility of feather δ34S studies to decipher avian and other animal migration between these two regions. [ABSTRACT FROM AUTHOR]

Reconstructions of global hydroclimate during the Common Era (CE; the past ~ 2000 years) are important for providing context for current and future global environmental change. Stable isotope ratios in water are quantitative indicators of hydroclimate on regional to global scales, and these signals are encoded in a wide range of natural geologic archives. Here we present the Iso2k database, a global compilation of previously published datasets from a variety of natural archives that record the stable oxygen (δ18O) or hydrogen (δ²H) isotopic composition of environmental waters, which reflect hydroclimate changes over the CE. The Iso2k database contains 756 isotope records from the terrestrial and marine realms, including: glacier and ground ice (205); speleothems (68); corals, sclerosponges, and mollusks (145); wood (81); lake sediments and other terrestrial sediments (e.g., loess) (158); and marine sediments (99). Individual datasets have temporal resolutions ranging from sub-annual to centennial, and include chronological data where available. A fundamental feature of the database is its comprehensive metadata, which will assist both experts and non-experts in the interpretation of each record and in data synthesis. Key metadata fields have standardized vocabularies to facilitate comparisons across diverse archives and with climate model simulated fields. This is the first global-scale collection of water isotope proxy records from multiple types of geological and biological archives. It is suitable for evaluating hydroclimate processes through time and space using large-scale synthesis, model-data intercomparison and (paleo)data assimilation. The Iso2k database is available for download at: https://doi.org/10.6084/m9.figshare.11553162 (McKay and Konecky, 2020). [ABSTRACT FROM AUTHOR]