Quantifying molecular oxygen isotope variations during a Heinrich stadial

Abstract

Abstract. δ 18 O of atmospheric oxygen (δ 18 O atm ) undergoes millennial-scale variations during the last glacial period, and systematically increases during Heinrich stadials (HSs). Changes in δ 18 O atm combine variations in biospheric and water cycle processes. The identification of the main driver of the millennial variability in δ 18 O atm is thus not straightforward. Here, we quantify the response of δ 18 O atm to such millennial events using a freshwater hosing simulation performed under glacial boundary conditions. Our global approach takes into account the latest estimates of isotope fractionation factor for respiratory and photosynthetic processes and make use of atmospheric water isotope and vegetation changes. Our modeling approach allows to reproduce the main observed features of a HS in terms of climatic conditions, vegetation distribution and δ 18 O of precipitation. We use it to decipher the relative importance of the different processes behind the observed changes in δ 18 O atm . The results highlight the dominant role of hydrology on δ 18 O atm and confirm that δ 18 O atm can be seen as a global integrator of hydrological changes over vegetated areas.

Does δ<sup>18</sup>O of O<sub>2</sub> record meridional shifts in tropical rainfall?

“…Many studies of Dole effect variability over the last glacial cycle (e.g., Bender et al, 1994;Severinghaus et al, 2009;Landais et al, 2010) have identified low-latitude precipitation as a key driver, based on coherence with orbital precession and atmospheric methane as well as high correlation with Chinese stalagmite δ 18 O. A recent quantitative, earth-system-model-based analysis of Dole effect variations over a simulated HS corroborates the hypothesized influence of low-latitude precipitation and finds that the increase in δ 18 O atm over a HS can be explained almost entirely by changes in terrestrial oxygen production-weighted δ 18 O precip (Reutenauer et al, 2015). Reutenauer et al (2015) find that oxygen production-weighted relative humidity stays effectively constant between HS and background glacial conditions.…”

“…Modeling results from a recent freshwater hosing experiment suggest that changes in δ 18 O atm over a HS are dominated by changes in δ 18 O precip over the terrestrial biosphere (Reutenauer et al, 2015). In terms of Eq.…”

“…Variability in the Dole effect throughout the past glacialinterglacial cycle has been hypothesized to be related to terrestrial hydrology based on coherence with atmospheric CH 4 measured in ice core bubbles (Bender et al, 1994), comparison with Chinese cave records (Severinghaus et al, 2009), and climate modeling experiments (Reutenauer et al, 2015). To investigate instantaneous changes in the isotopic fractionation of atmospheric O 2 , Severinghaus et al (2009) used a one-box model deconvolution to account for the smoothing effect of the ∼ 1000-year residence time of atmospheric O 2 .…”

“…Past changes in the Dole effect -the amount by which δ 18 O of atmospheric O 2 (δ 18 O atm ) exceeds that of seawater (Dole, 1935;Morita, 1935) -have been shown to be closely linked to terrestrial hydroclimate (Bender et al, 1994;Landais et al, 2010;Reutenauer et al, 2015;Severinghaus et al, 2009). We quantitatively explore a simple relationship between meridional shifts in terrestrial oxygen production and δ 18 O of oxygen production-weighted terrestrial rainfall (δ 18 O precip ) over the modern seasonal cycle using spatially gridded monthly observations.…”

Phase relationships between orbital forcing and the composition of air trapped in Antarctic ice cores

“…Again the δ 18 O atm signal over these two terminations parallels the calcite δ 18 O signals of Chinese speleothems. Following this finding, Reutenauer et al (2015) used outputs from coupled climate model and atmospheric general circulation model equipped with water isotopes to estimate the change of δ 18 O atm induced by a freshwater input. These calculations show that the increase of δ 18 O atm during a Heinrich event is induced by a southward shift of the ITCZ associated with the freshwater input leading to an increase of the δ 18 O of the low-latitude meteoric water in the Northern Hemisphere.…”