Quantitative assessments of moisture sources and temperature governing rainfall δ18O from 20 years' monitoring records in SW-France: Importance for isotopic-based climate reconstructions

Abstract

The quantitative distribution of atmospheric vapor mixture, AVM, into three distinguished vapor endmembers is lacking in the literature. This work lls such a gap. The isotope ratio, d 18 O L , of rainwater in Winter, and arti cial condensates in Summer, gave the 18 O V contents of local AVMs at temperature-dependent equilibrium, downtown Cairo city, Nile Delta apex. We used our models, TIMAM, CLAW, and SIGNALS to process the d 18 O V and the commensurate speci c humidity, S, values in several AVM data sets for determining the percent and mass contributions of three moisture origins and their temporal waveforms. The proportions and masses revealed Marine vapor dominance, followed by evapotranspiration. By far, the free Troposphere source showed a slight input. The quota of each constituent manifests a delayed waveform vs. AVM d 18 O in ux, which shows a diurnal peak and a nocturnal tunnel. The moderate ET percent inputs in Winter, and by daytime, impose signi cant AVM 18 O enrichment. In contrast, the high Maritime vapor inputs in Summer, and by night, stand behind the depleted AVM 18 O content. The relationships between the mass input of each source and the AVM isotope ratio show signi cant dispersion for the negative trend of the diurnal-nocturnal Marine vapor in the two seasons. Such a high scattering is due to the mingling of northern wind-gust diurnal convection (marked by low Marine vapor input) and northern steady nocturnal advection (characterized by high Marine vapor input). Marine vapor waveform has a 12-hour time-lag by the intertwining of turbulent diurnal transmission, and steady nocturnal transport, through the long trajectory (180 km) from the Mediterranean coast to Cairo. In contrast, the relationships between ET mass input and AVM isotope ratio, on the one hand, and between the Troposphere vapor mass input and AVM isotope ratio, on the other hand, manifest low-dispersion positive and negative regressions, respectively. Such a low dispersion is due to the short transport pathway, the narrow range of the biological input (that increases only by daytime), and sharp Troposphere downdraft (moving northward in Winter but southward in Summer). Also, the ET waveform has a Zero-hour time-lag, like that of the Tropospheric vapor. Albeit the low S value of the Troposphere vapor pole, its impact on the AVM isotopic depletion is signi cant due to its extremely shallow 18 O content. The increase of the Tropospheric input at low AVM S values is related to regional drought, as expected. The high S values, of Marine and biotic origins, usually go with temperature apogees, especially in Summertime, as anticipated. The used models help in improving the time-series simulation of evaporation runs, since using seasonal d 18 O V and S markers is better than using a snapshot. The ternaryvapor-source allocation procedure is a breakthrough in isotope hydrology. This thoroughly useful procedure will prove its ultimate bene ts when the users get CRDS laser-controlled devices for the continuous measurements of the isotopic ra...

Hydro-chemical Time-Series for Cairo-Nile Water and Atmospheric Moisture

“…The main features of the weather conditions prevailing in Cairo City, at the Nile Delta apex, are well known and entirely reported by recording and analyzing the typical relevant meteorological parameters for long decades. However, hydrology research workers seldom publish the isotopic composition of precipitation (Zhang et al, 2020) and atmospheric vapor of the Mediterranean basin and for countries to the south in the region. This work is the first of its category for the 400 km2 Cairo city urban zone, 180 km south of the seashore.…”

On the Quantitative Tripartite Allocation of Atmospheric Vapor, Oqtav, by Oxygen 18

“…The main features of the weather conditions prevailing in Cairo City, at the Nile Delta apex, are well known and entirely reported by recording and analyzing its typical parameters for long decades. However, hydrology research workers seldom publish the isotopic composition of precipitation (e.g., Zhang et al, 2020) and atmospheric vapor of the Mediterranean basin and for countries to the south in the region. This work is the rst of its category for the 400 km 2 Cairo city urban zone, 180 km south of the seashore.…”

On the Quantitative Tripartite Allocation of the Atmospheric Vapor, Oqtav

“…The main features of the weather conditions prevailing in Cairo City, at the Nile Delta apex, are well known and entirely reported by recording and analyzing the typical relevant meteorological parameters for long decades. However, hydrology research workers seldom publish the isotopic composition of precipitation (e.g., Zhang et al, 2020) and atmospheric vapor of the Mediterranean basin and for countries to the south in the region. This work is the rst of its category for the 400 km 2 Cairo city urban zone, 180 km south of the seashore.…”

“…Moreover, the thorough isotopic information on the atmospheric vapor may later induce the incorporation of the isotopic signals of the AVMs into the regional, and international, micro-meteorological data sets, since the isotopic composition of the AVMs is as energetic as the other meteorological parameters. Jointly with the satellite-based isotopic predictions, introduced by Isoscape, Ref, and Hysplit (Zhang et al, 2020). Such integration will promote the development of micrometeorology and isotope hydrology since the current climate change is actively imposing additional shifts in different vapor sources contributing to the local and regional AVMs.…”