Isotopic ‘Altitude’ and ‘Continental’ Effects in Modern Precipitation across the Adriatic–Pannonian Region

It is generally observed that precipitation is gradually depleted in 18O and 2H isotopes as elevation increases (‘altitude’ effect) or when moving inland from seacoasts (‘continental’ effect); the regionally accurate estimation of these large-scale effects is important in isotope hydrological or paleoclimatological applications. Nevertheless, seasonal and spatial differences should be considered. Stable isotope composition of monthly precipitation fallen between January 2016 and December 2018 was studied for selected stations situated along an elevation transect and a continental transect in order to assess the isotopic ‘altitude’ and ‘continental’ effects in modern precipitation across the Adriatic–Pannonian region. Isotopic characteristics argue that the main driver of the apparent vertical depletion of precipitation in heavy stable isotopes is different in summer (raindrop evaporation) and winter (condensation), although, there is no significant difference in the resulting ‘altitude’ effect. Specifically, an ‘altitude’ effect of −1.2‰/km for δ18O and −7.9‰/km for δ2H can be used in modern precipitation across the Adriatic–Pannonian region. Isotopic characteristics of monthly precipitation showed seasonally different patterns and suggest different isotope hydrometeorological regimes along the continental transect. While no significant decrease was found in δ18O data moving inland from the Adriatic from May to August of the year, a clear decreasing trend was found in precipitation fallen during the colder season of the year (October to March) up to a break at ~400 km inland from the Adriatic coast. The estimated mean isotopic ‘continental’ effect for the colder season precipitation is −2.4‰/100 km in δ18O and −20‰/100 km in δ2H. A prevailing influence of the Mediterranean moisture in the colder season is detected up to this breakpoint, while the break in the δ18O data probably reflects the mixture of moisture sources with different isotopic characteristics. A sharp drop in the d-excess (>3‰) at the break in precipitation δ18O trend likely indicates a sudden switch from the Mediterranean moisture domain to additional (mainly Atlantic) influence, while a gradual change in the d-excess values might suggest a gradual increase of the non-Mediterranean moisture contribution along the transect.

Stable isotope constraints on hydrostratigraphy and aquifer connectivity in the Table Mountain Group

The Table Mountain Group is a folded, faulted, quartzite-dominated sedimentary sequence, metamorphosed to lower greenschist facies, that forms steep mountains dominating the topography of the Western Cape and causing orographic rainfall in an otherwise semi-arid region. These quartzites are highly fractured to depths of kilometres and act as a complex aquifer system that supplies groundwater directly and indirectly, through baseflow, essential for sustaining the natural environment and human activity in the region. Hydrogen and oxygen isotope data for rain, rivers and groundwater (boreholes and springs) in the region give typical altitude effects of -1.8‰ δD/100 m and -0.33‰ δ18O/100 m, and a very strong continental effect of -30‰ δD/100 km and -4.7‰ δ18O/100 km. This allows for application of stable isotopes as natural hydrological tracers. Groundwater at several locations had stable isotope compositions different from ambient rainfall, but similar to rainfall at high altitudes in adjacent mountains, indicating recharge at high altitude. The groundwater flow is through the Skurweberg Aquifer, here defined as all three formations of the Nardouw Subgroup. Observations on the Peninsula Aquifer suggest a very well mixed aquifer, due to extensive fracturing. Potential exists to delineate groundwater protection zones, detect overabstraction and understand aquifer connectivity better by applying stable isotope hydrology to the Table Mountain Group.

Determination of isotopic composition of rainwater to generate local meteoric water line in Thohoyandou, Limpopo Province, South Africa

Hydrogen (D) and oxygen (18O) isotopic compositions of precipitation are useful tools to delineate the nature of precipitation, groundwater recharge and climatological investigations. This study investigated the isotopic composition of 12 rainfall occurrences at Thohoyandou, with the objective of generating the local meteoric water line (LMWL) and determining the factors controlling the isotopic composition of the rain. The delta (δ) values for D and 18O of the samples were determined using a Thermo Delta V mass spectrometer connected to a Gasbench. Thohoyandou rainwater showed a wide range of stable isotope values; δD values of the rainwater varied from −76.3‰ to +22.7‰ (SMOW) with a weighted mean of −9.8‰ and δ18O values ranged from −10.78‰ to +3.07‰ (SMOW) with a weighted mean of −2.7‰. δ-values of rainwater were more enriched during winter and more depleted during summer, due to the amount of rainfall and seasonal effect. The LMWL in Thohoyandou is defined by δD = 7.56δ18O + 10.64, which shows a similar slope to the global meteoric water line (GMWL) but with a slightly higher intercept, of 10.64‰ instead of 10‰. This implies that the process of rain formation in Thohoyandou occurred under equilibrium conditions which are not significantly affected by evaporation. The slightly higher d-intercept value above the GMWL reflects an additional supply of recycled moisture across the regions. This implies that there is no continental effect but inland moisture from various water bodies and vegetation.

The specificities of the climate of Danilovgrad (Montenegro)

Danilovgrad and the Bjelopavlica Plain belong to the submediterranean zone of the Mediterranean climate region. The aim of this paper was to determine some specific characteristics of the Danilovgrad climate, such as the degree of continentality, aridity and bioclimatic characteristics. Data used in the research cover the period 1955-2011. The results of the study showed the dominance of the continental effect on temperature, while oceanicity was less pronounced. In hygric terms, during most of the year the climate of Danilovgrad is characterized as low humid to perhumid. Moreover, in the period October-March it is very humid, which points to the domination of oceanic influences. During the three summer months, it is dry to very dry. Based on the average monthly values of the equivalent temperature - an indicator of physiological (subjective) feeling of heat, the winter months in Danilovgrad are not assessed as very cold. It is cold in January, and in February and December it is cool. It is fresh in March and November, comfortable in April and October, and warm in May and September. In Danilovgrad, in summer it is overheated and a little muggy. All considered indicators point to quite pronounced oscillations during the year, especially in terms of humidity. Comparing the obtained results with Podgorica, it can be concluded that the climate of Danilovgrad is more continental, a bit colder and wetter.

North Atlantic Oscillation controls on oxygen and hydrogen isotope gradients in winter precipitation across Europe; implications for palaeoclimate studies

Winter (October to March) precipitation δ18OP and δDP values in central Europe correlate with the winter North Atlantic Oscillation index (wNAOi), but the causal mechanisms remain poorly understood. Here we analyse the relationships between precipitation-weighted δ18OP and δDP datasets (δ18Opw and δDpw) from European GNIP and ANIP stations and the wNAOi, with a focus on isotope gradients. We demonstrate that longitudinal δ18Opw and δDpw gradients across Europe (“continental effect”) depend on the wNAOi state, with steeper gradients associated with more negative wNAOi states. Changing gradients reflect a combination of air temperature and variable amounts of precipitable water as a function of the wNAOi. The relationships between the wNAOi, δ18Opw and δDpw can provide additional information from palaeoclimate archives such as European speleothems that primarily record winter δ18Opw. Comparisons between present-day and past European longitudinal δ18O gradients inferred from Holocene speleothems suggest that atmospheric pressure configurations akin to negative wNAO modes dominated the early Holocene, whereas patterns resembling positive wNAO modes were more common in the late Holocene, possibly caused by persistent shifts in the relative locations of the Azores High and the Icelandic Low.

North Atlantic Oscillation controls on oxygen and hydrogen isotope gradients in winter precipitation across Europe; implications for palaeoclimate studies

Winter (October to March) precipitation δ18OP and δ18DP values in central Europe correlate with the winter NAO index (wNAOi), but the causal mechanisms remain poorly understood. Here we analyse the relationships between precipitation-weighted δ18OP and δ18DP datasets (δ18Opw and δ18Dpw) from European GNIP and ANIP stations and the wNAOi, with a focus on isotope gradients. We demonstrate that longitudinal δ18Opw and δ18Dpw gradients across Europe (continental effect) depend on the wNAOi state, with steeper gradients associated with more negative wNAOi states. Changing gradients reflect a combination of air temperature and variable amounts of precipitable water as a function of the wNAOi. The relationships between the wNAOi, δ18Opw and δ18Dpw can provide additional information from palaeoclimate archives such as European speleothems that primarily record winter δ18Opw. Comparisons between present-day and past European longitudinal δ18O gradients inferred from Holocene speleothems suggest that negative wNAO modes dominated the early Holocene, but positive wNAO modes were more common in the late Holocene.

French Alps and Alpine Forelands

The French Alps are the western part of the 1,200-km-long Alpine range extending eastward to the Vienna basin. They have the highest summits of the range, in the Mont-Blanc massif (4,807 m a.s.l.). In France, the chain has an arcuate form, convex to the north and west. It lies between Lake Geneva (46° 25′ N) and the Mediterranean coast (approximately 43° 35′ N). The Rhône valley forms a clear geological and morphological western limit. To the north (towards the Jura range) and the south-west (towards the ridges of Provence) the boundary is not so well defined. The French Alps and Alpine forelands have been thoroughly studied for over a century by many researchers from the Universities of Grenoble, Lyons, Aix-en-Provence, Nice, and Chambéry. First, it is necessary to outline the great diversity of landforms in relationship to the complex geological history, tectonics, and lithology. The importance of the Alpine karst landforms and caves must be emphasized; studies of these forms have been extended substantially in the last twenty years and they give many new insights into the Plio-Pleistocene tectonics and climates of this region. The past and present role of glaciers is another important topic in this chapter. From recent studies, we now have a much better knowledge of the transition from the last glacial period to the Holocene. It was impossible to write a chapter on the Alps and ignore the fact that the inhabitants of the Alps have to cope with many permanent natural hazards. The chapter ends with a short synthesis of the main morphogenic systems, which characterize the French Alps and forelands. In the north, the climate is oceanic and precipitation is evenly distributed throughout the year. A high relief, with landforms oriented transverse to the general western atmospheric circulation, results in a great variety of regional climates: from west to east, the continental effect is marked by a decreasing precipitation at the same altitude. Exposure and altitude combine to create contrasting local climates. Temperature inversion is frequent, especially when cold air is trapped in deep valleys.

Regional Variations of Snow Accumulation on Spitsbergen, Svalbard, 1997-99

End-of-winter snow accumulation has been measured over large areas on Spitsbergen, Svalbard, using Ground Penetrating Radar (GPR) in the years of 1997, 1998, and 1999. Measuring transects following different latitudes reveal west-to-east and south-to-north gradients of snow accumulation. Generally, the east coast receives over 40% more snow (in water equivalent) than the west coast. A continental effect with lower accumulation rates can be seen in central parts of Spitsbergen at middle and northern latitudes. In the southern part of Spitsbergen accumulation rates are approximately twice as high as in the north. Elevation gradients of snow accumulation vary considerably, from –9 mm per 100 metre increase of elevation in the north-east to 258 mm/100 m in the central south. In average, the accumulation increases with 97 mm/100 m. Finally, accumulation rates close to the summit of Austfonna ice cap range from about 200 mm to 800 mm, i.e., with a factor of 4, over a few tens of kilometres. The average snow accumulation for all glacier localities measured on Spitsbergen (i.e., Austfonna excluded) for all three years is 590 mm.