4.6 Article

Spatial heterogeneity in the relationship between precipitation and carbon isotopic discrimination in C3 plants: Inferences from a global compilation

Journal

GLOBAL AND PLANETARY CHANGE
Volume 176, Issue -, Pages 123-131

Publisher

ELSEVIER
DOI: 10.1016/j.gloplacha.2019.02.002

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Funding

  1. Department of Science and Technology, New Delhi [SB/S4/ES-684/2013]

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Understanding the causes of large variations in carbon isotopic composition of C-3 plants (delta C-13(C3)) is a key challenge for paleoenvironmental reconstruction. Several investigations have attempted to study the global patterns in the delta C-13(C3) values and their correlation with the precipitation variability. Sparse representation of dataset from low-latitude and equatorial regions in the existing global compilation hinders to understand the precipitation-delta C-13(C3) gradient at different latitudinal bands. In the present study, available global compilation has been extended with the newly measured dataset, and the new compilation (ca. 15 times larger than previous dataset) comprises results from 720 sites across the world. All the delta C-13(C3) values have been converted to carbon isotopic discrimination between air and leaf (Delta(air-leaf)). Mann-Whitney analysis indicates distinct region-specific distribution of the Delta(air-leaf) values. The average average Delta(air-leaf) value in mid-latitude region of the Northern Hemisphere is ca. 2 parts per thousand lower than equatorial sites. Multiple linear models have been used to investigate relative influence of climatic (precipitation and temperature) and geographical factors (altitude and latitude) on the Delta(air-leaf) values. This analysis shows that precipitation controls the Delta(air-leaf) values in every latitudinal-bin though the effect of precipitation is negligible beyond 1500 mm. Furthermore, the Delta(air-leaf)-precipitation gradient has a large spatial variability and the most prominent changes in the Delta(air-leaf) values have been observed at arid regions in mid-latitudes of the Southern Hemisphere (maximum 1.3 parts per thousand 100 mm(-1)). Region-specific distribution of delta C-13 values of plant and Delta(air-leaf)-precipitation gradient prompt to recalculate the relative abundance of C-3-C-4 plants in the Siwalik sections of the Himalayan foreland basin. Our results show that earlier investigations in the Siwaliks for the Middle-Late Miocene have underestimated the abundance of C-4 plants by ca. 20%. The recalculation shows that C-4 plants existed in these regions earlier (ca. 17 Ma) than the previously proposed timings.

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