In chapter 2 the isotopic fractionation of water in some simple condensation-evaporation processes are considered quantitatively on the basis of the fractionation factors given in section 1.2. The condensation temperature is an important parameter, which has got some glaciological applications. The temperature effect (the δ's decreasing with temperature) together with varying evaporation and exchange appear in the “amount effect” as high δ's in sparse rain. The relative deuterium-oxygen-18 fractionation is not quite simple. If the relative deviations from the standard water (S.M.O.W.) are called δ D and δ 18 , the best linear approximation is δ D = 8 δ 18 . Chapter 3 gives some qualitative considerations on non-equilibrium (fast) processes. Kinetic effects have heavy bearings upon the effective fractionation factors. Such effects have only been demonstrated clearly in evaporation processes, but may also influence condensation processes. The quantity d = δ D −8 δ 18 is used as an index for non-equilibrium conditions. The stable isotope data from the world wide I.A.E.A.-W.M.O. precipitation survey are discussed in chapter 4. The unweighted mean annual composition of rain at tropical island stations fits the line δ D = 4.6 δ 18 indicating a first stage equilibrium condensation from vapour evaporated in a non-equilibrium process. Regional characteristics appear in the weighted means. The Northern hemisphere continental stations, except African and Near East, fit the line δ D = 8.0 δ 18 + 10 as far as the weighted means are concerned (δ D = 8.1 δ 18 + 11 for the unweighted) corresponding to an equilibrium Rayleigh condensation from vapour, evaporated in a non-equilibrium process from S.M.O.W. The departure from equilibrium vapour seems even higher in the rest of the investigated part of the world. At most stations the δ D and varies linearily with δ 18 with a slope close to 8, only at two stations higher than 8, at several lower than 8 (mainly connected with relatively dry climates). Considerable variations in the isotopic composition of monthly precipitation occur at most stations. At low latitudes the amount effect accounts for the variations, whereas seasonal variation at high latitudes is ascribed to the temperature effect. Tokyo is an example of a mid latitude station influenced by both effects. Some possible hydrological applications are outlined in chapter 5. DOI: 10.1111/j.2153-3490.1964.tb00181.x

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.2153-3490.1964.tb00181.x

Stable isotopes in precipitation

An oxygen and carbon isotopic history based on analyses of benthonic and planktonic foraminifera in three overlapping subantarctic sections is presented for the last 55 m.y. with a sampling interval ofless than 1 m.y. Surface temperature at Site 277, on the Campbell Plateau, was about 19°C in the early Eocene, about 13°C in the middle Eocene, about 11°C in the late Eocene, and about 7°C in the Oligocene. Declines in temperature appear to have been rather rapid and are separated by episodes of relative temperature stability. Bottom temperature at Site 277 was about 1°C below surface temperature in the Paleocene and about 2°C below surface temperature in the Oligocene. Site 279, on the Macquarie Ridge, records an early Miocene warming of over 2°C followed by a cooling and a second similar temperature rise in the middle Miocene. Bottom temperature at this somewhat deeper site was about 3°C below surface temperature and was probably as low as 4°C during part of the early Miocene. Comparisons between Sites 277 and 279 suggest that from the early Oligocene temperatures of deep water were low like the present day, implying that the mean annual temperature in high southern latitudes was near freezing by the beginning of the Oligocene (but certainly no earlier). From this time glaciers would have descended to sea level, and there would have been sea-ice production. If an ice sheet were present, it could not have been more than a small fraction of its present-day size. Site 281, on the South Tasman Rise, extends the record into the middle and late Miocene during which time the major East Antarctic ice sheet accumulated. A significant rise in surface temperature during the late Miocene did not cause the melting of this ice sheet, demonstrating that by this time it had already achieved its present invulnerability to climatic change. Since temperatures during much of the Miocene were significantly above any Pleistocene values, it is extremely unlikely that any climatic change in the geologically near future will significantly affect the stability of the East Antarctic ice sheet.

Paleotemperature history of the Cenozoic and the initiation of Antarctic glaciation : Oxygen and carbon isotope analyses in DSDP Sites 277,279, and 281

Geochronology of lake sediments

An empirical model of firn densification from the surface to the zone of pore close-off has been constructed. Fundamental rate equations have been derived for the first two stages of densification. In the first stage, for densities less than 0.55 Mg m−3, the densification rate is proportional to the mean annual accumulation times the term (ρ i − ρ), where ρ is the density of the snow and ρ i is the density of pure ice. The densification rate in the second stage, where 0.55 Mg m −3 < ρ < 0.8 Mg m−3, is proportional to the square root of the accumulation rate and to (ρi− ρ). Depth–density and depth–age calculations from this model are compared with observation. Model accumulation rates are within about 20% of values obtained by other techniques. It is suggested that depth intervals of constant density in some Antarctic cores may represent a synchronous event in the 1880 ’s when ten times the normal accumulation fell within a year or two.

/pdf/firn-densification-an-empirical-model-eec6no810n.pdf

Firn Densification: An Empirical Model

The Camp Century, Greenland, deep ice core reveals seasonal variations in the isotopic composition of the ice back to 8,300 years BP. This is not the case for the Byrd Station, Antarctica, deep ice core. Both cores show long-term perturbations in isotopic composition reflecting climatic changes from before the beginning of the last glaciation. But the complexity of the glaciological regime at Byrd Station precludes a rational choice of a time scale. Pole-to-pole correlations of the palaeoclimatic data therefore become speculative except for the more pronounced features and general trends.

Oxygen Isotope Profiles through the Antarctic and Greenland Ice Sheets

After a short discussion on the Pb210 dating method, the results of Pb210 measurements on snow and firn samples from four Antarctic stations are reported as well as the experimental procedure used. Pb210 was also measured in the air at ground level, at Base Roi Baudouin, the average Pb210 activity of aerosols in 1958 being 1.3 × 10−3 dpm/kg of air. In samples of surface snow accumulated during the last two to five years, the average Pb210 activity is of the order of 100 dph/kg of snow. This activity seems to be independent of the local rate of accumulation. The variations of Pb210 activity as a function of depth were studied on two vertical firn profiles spanning an interval of more than 200 years, at Base Roi Baudouin (70°S, 24°E) and at Amundsen Scott Station (South Pole). Within experimental errors, the Pb210 activity was found to decrease exponentially with depth at both stations. The most plausible interpretation is that the rate of water accumulation and the initial Pb210 concentration in the snow have remained constant at both places over the last 100 years. The annual rates of water accumulation calculated from the decay curves are 6±1 cm at the South Pole and 45±3 cm at Base Roi Baudouin, in good agreement (to better than 10 percent) with accumulation rates so far obtained by other methods.

/pdf/antarctic-snow-chronology-with-pb210-s014qlnbqp.pdf

Antarctic snow chronology with Pb210

Accumulation on the South Pole–Queen Maud Land Traverse, 1964–1968

/pdf/rate-of-accumulation-of-snow-at-the-south-pole-as-determined-5d2wj5ozn4.pdf

Rate of Accumulation of Snow at the South Pole as Determined by Radioactive Measurements

O18/O16 ratios have been measured along a firn profile extending from the surface to a depth of 16 meters in the shelf ice of King Baudouin station (East Antarctica, 70°26′S, 24°19′E). Periodical variations are found which are believed to reflect the seasonal variations in the O18/O10 ratio of precipitations. They allow the identification of annual layers following the method suggested by Epstein and Sharp. The oxygen isotope variations are compared with the stratigraphic features of the same profile. The notion ‘winter’ or ‘summer’ layers is shown to be meaningless when the layers are derived from stratigraphie criteria only. Very often the fine-grained unmetamorphosed layers (generally called ‘winter’ layers) are made up of snow with high O18 content which must represent summer precipitation. On the other hand, the coarse-grained recrystallized layers (‘summer’ layers) often display a minimum O18 content and are composed of snow that fell in the winter. Identification of annual layers involves a similar degree of uncertainty from personal interpretation in the stratigraphic method as well as in the isotope ratio method, but the two methods are complementary, being affected differently by natural circumstances. A good agreement is found between the average accumulation rates deduced from both methods.

/pdf/snow-stratigraphy-and-oxygen-isotope-variations-in-the-2r5gidgurm.pdf

Snow stratigraphy and oxygen isotope variations in the glaciological pit of King Baudouin station, Queen Maud Land, Antarctica

Sr90 and gross β activities were measured on firn sections collected around Base Roi Baudouin, Scott Base, and South Pole Station. The firn layers were dated by stratigraphy and by oxygen isotope variations. The depth distribution of Sr90 and gross β activities revealed three radioactive horizons of potential glaciological application. The deepest horizon occurred at the end of 1953 as a result of the fallout of fission products from the Ivy test series, the second and most important one was formed in early 1955 by the debris of the Castle test series, and a third horizon, defined by a sudden increase in the gross β activity but not in the Sr90 content, was formed at the end of 1962. The rate of Sr90 deposition over Antarctica has been nearly constant since 1956, amounting to 0.2 and 0.1 mc/km2 yr at Base Roi Baudouin and at the South Pole, respectively. The cumulative Sr90 deposition up to January 1963 in the 70–90°S latitude belt is found to lie between 1 and 3 mc/km2.

/pdf/strontium-90-fallout-in-antarctica-3sg7lrr1aw.pdf

W. De Breuck

Papers

Antarctic snow chronology with Pb210

Accumulation on the South Pole–Queen Maud Land Traverse, 1964–1968

Rate of Accumulation of Snow at the South Pole as Determined by Radioactive Measurements

Snow stratigraphy and oxygen isotope variations in the glaciological pit of King Baudouin station, Queen Maud Land, Antarctica

Strontium 90 fallout in Antarctica