Global meteoric water line

Craig observed that δ¹⁸O and δ²H isotopic composition of cold meteoric water from sea ice in the Arctic and Antarctica are much more negative than that in warm meteoric water from the tropic.^[2] A correlation between temperature (T) and δ¹⁸O was proposed later^[6] in the 1970s. Such correlation is then applied to study surface temperature change over time.^[7] The δ¹⁸O of ancient meteoric water, preserved in ice cores, can also be collected and applied to reconstruct paleoclimate.^[8][9]

A meteoric water line can be calculated for a given area, named as local meteoric water line (LMWL), and used as a baseline within that area. Local meteoric water line can differ from the global meteoric water line in slope and intercept. Such deviated slope and intercept is a result largely from humidity. In 1964, the concept of deuterium excess d (d = δ²H - 8δ¹⁸O)^[3] was proposed. Later, a parameter of deuterium excess as a function of humidity has been established, as such the isotopic composition in local meteoric water can be applied to trace local relative humidity,^[10] study local climate and used as a tracer of climate change.^[6]

In hydrogeology, the δ¹⁸O and δ²H of groundwater are often used to study the origin of groundwater^[11] and groundwater recharge.^[12]

It has been shown that, even taking into account the standard deviation related to instrumental errors and the natural variability of the amount-weighted precipitations, the LMWL calculated with the EIV (error in variable regression)^[13] method has no differences on the slope compared to classic OLSR (ordinary least square regression) or other regression methods.^[14] However, for certain purposes such as the evaluation of the shifts from the line of the geothermal waters, it would be more appropriate to calculate the so-called "prediction interval" or "error wings" related to LMWL.^[13]

• Isotope fractionation
• Meteoric water
• Water cycle