A document by Chaithanya B P. Click on the document to view its contents.

The hydrogen isotopic compositions of the leaf-wax n-alkanes (δDalk) and n-alkanoic acids (δDacid) are known to reflect ambient climatic conditions (including precipitation δD values, δDPrecip). However, the climatic conditions of exactly which period (i.e. early or entire period of the leaf’s lifespan) these biomarkers represent, i.e. the seasonality in δDalk and δDacid records, is still evolving. The seasonality studies on the δDalk and δDacid values, done only in extra-tropical regions, mostly indicate the δDalk values are biased towards the early growing season whereas δDacid values are not biased towards any season. To decipher the seasonality in the δDalk and δDacid records from the tropics, we conducted a long-duration experiment wherein deciduous and evergreen species were grown using normal water (δD = −2‰) during the early stages of the leaf's growth and later using isotopically-labeled water (δD = 1000‰). Our experiment revealed (i) in deciduous and evergreen species, δDalk and δDacid values reflect δDPrecip during the early stages of the leaf's growth, (ii) synchronous synthesis of n-alkanes and n-alkanoic acids, and (iii) in deciduous species, minor incorporation of the previous year’s photosynthates in the leaf wax pool of the current year’s mature leaves. Our study suggests that the δDalk and δDacid records in the tropics are biased towards the climatic conditions prevailing during the early stages of the leaf's growth. This bias should be considered while comparing the δDPrecip values generated from the leaf wax proxy records and isotope-enabled atmospheric circulation models.

The local temperarture cannot explain the inter-annual variation in δ18Oprecip in the coastal Antarctic in past few decades. To understand this enigmatic variation, we have used long-term modern δ18Oprecip value of three coastal Antarctic sites. Using the δ18O-d-excess relationship and modelled δ18O value of vapor at source, we have shown that δ18Oprecip inherits the signature of moisture source parameters (MSPs). Furthermore, the wavelet analysis suggests that the variation in the MSPs impacts the seasonal cycle of δ18Oprecip which lead to disparity in the seasonal isotope-temperature relationship. The Southern Ocean surface stratification, due to increase in the freshwater flux by glacier melting, led to alignment of MSPs in such a manner that altogether significantly lowered the isotopic composition of initially formed vapor, which is reflected in δ18Oprecip at inter-annual scale. Our observations suggest that the palaeothermometry will underestimate the Antarctic temperature change for the periods characterized by warming and high glacier-melt.