Method Of Partial Bleaching Research Articles

Testing the applicability of a partial bleach method for post-IR IRSL dating of Holocene-aged K-feldspar samples

Abstract In this article we test the potential use of a partial bleach method, which was traditionally used in thermoluminescence dating, for the post-infrared infrared stimulated luminescence (pIRIR) dating of K-feldspar, with an aim to correct for the impact of remnant dose on the dating of Holocene-aged K-feldspar samples. We show that the solar bleaching decay of the pIRIR signal can be described using several components with different sensitivities upon exposure to sunlight. An improved partial bleach pIRIR (PB-pIRIR) method based on a multi-aliquot regenerative (MAR) protocol is proposed, which can isolate the rapidly bleached components from the pIRIR signal for the dating purpose. Natural and experimental factors that can affect the PB-pIRIR De are investigated by numeric simulation and dose recovery experiments. A plateau test is proposed to assess a proper laboratory bleaching time in the PB-pIRIR measurement. Dating known-age samples indicates that for well-bleached samples the PB-pIRIR method can yield reliable ages; whereas for poorly-bleached samples this technique can produce pIRIR ages consistent with expected ages or improve the pIRIR dating results. We deduce that for insufficiently bleached samples, the efficacy of the PB-pIRIR approach is related to the significance of the remnant dose relative to the burial dose, as well as the degree of heterogeneity of the grains' signal resetting. Our results suggest the partial bleach method has the potential to reduce or even eliminate the impact of insufficient bleaching on K-feldspar pIRIR dating. This method is more suitable for insufficiently bleached samples for which all or most of the K-feldspar grains have been exposed shortly to sunlight before the last burial.

Thermoluminescence Dating of Late Pleistocene Sediments, St. Lawrence Lowland, Québec

This paper presents the results of a thermoluminescence (TL) dating program applied to waterlaid sediments of Late Pleistocene age, collected in the central St. Lawrence Lowland, in eastern Canada. The apparent TL ages were obtained using a partial bleach method (R-Gamma) in which the TL from light-sensitive traps is separated from the total TL. Fluvial (modern), marine (late-glacial) lacustrine (interstadial) and glacio-lacustrine (stadial) sediments yielded apparent ages ranging from 4 to 135 ka, and in general, these ages agreed with available stratigraphic evidence. Whilst testing the zeroing assumption, apparent TL ages obtained from modern fluvial and late glacial sediments suggest that laboratory overbleaching or insufficient natural bleaching may result in over-estimation of the apparent TL ages by 4-5 ka. All samples display anomalous fading, a problem that can be overcome by introducing a three month delay between artificial irradiation and glowing. Future research should focus on sediments for which the age as well as the sedimentology are well documented, such as the late glacial Champlain Sea sediments.

Study of non-linear luminescence-dose growth curves for the estimation of paleodose in luminescence dating: Results of Monte Carlo simulations

In luminescence dating applications, non-linear luminescence versus dose growth curves are often observed. An experimental data scatter of 5–15% is commonplace and this causes difficulties in estimating the equivalent dose D c and the error on the equivalent dose δ D e . Two aspects need consideration: (a) What configuration of experimental parameters (such as maximum radiation dose and radiation dose intervals) should be chosen so as to minimize δ D e ? and (b) How accurate are the estimates D e and δ D e given by the non-linear parameter estimation procedure? To address these aspects, Monte Carlo simulations of a large number of saturating exponential growth curves were carried out for the three principal experimental methods commonly used for the estimation of equivalent dose, i.e. additive dose method, the regeneration or slide method and the partial bleach method. Additionally, third-order polynomial growth curves (as seen in some quartz) were also examined. In these studies, the influence of various experimental parameters such as the maximum irradiation dose D max, the number of data points N dat and the spacing of dose on D e and δ D e were studied. Based on a synthesis of the simulation results, optimal values for the experimental parameters for the different methods are suggested.

Test of the partial bleach methodology as applied to the infra-red stimulated luminescence of an alluvial sediment from the Danube

A sample of fine-grained distal sediment deposited by the River Danube in Romania was selected for luminescence measurements using infra-red diodes for stimulation. To obtain the equivalent dose (ED) a partial bleach approach was applied using a restricted spectrum in an attempt to replicate bleaching conditions underwater. The results, and those of the thermoluminescence measurements, gave an age in agreement with the archaeological evidence, suggesting that this sample was well bleached at deposition. A more rigorous test was devised using a simulation experiment and the results suggested that the partial bleach method may not be able to date correctly sediments that have had only part of their infra-red stimulated luminescence (IRSL) signal removed at deposition. Additional types of measurement are required to detect incomplete resetting of the IRSL signal at deposition.

TL dating studies of tephra, loess and lacustrine sediments

A brief review is presented of my efforts to improve the accuracy of dating unheated sediments by TL and of the development of a new tephrochronometer. Specific applications to known-age deposits are outlined, as are studies of the depositional environment of subaqueous sediments. Removal of anomalous fading in loess by storage at 75°C for 8 days is demostrated. Throughout, for unheated sediments the preferential use of the partial bleach (R-gamma or R-beta) technique is emphasized, especially in situations where the growth curves are sublinear. Contrary to a widespread misconception, sublinearity does not invalidate the partial bleach method. Furthermore, examples are given of TL ‘sensitivity’ (or ‘efficiency’) changes occurring with the regeneration technique — changes that are variable and seemingly sample dependent.

Thermoluminescence properties and age estimates for Quaternary raised marine sediments, Hudson Bay Lowland, Canada

Thermoluminescence (TL) analyses of Quaternary nearshore marine sediments from the Hudson Bay Lowland revealed relatively high light emissions and linear growth curves to at least 400 Gy above the natural dose. Initial results indicate that anomalous fading may be circumvented by a preheating at 150 °C for 16 h without substantial thermal draining of stable TL components. Both the total bleach method with unfiltered sunlamp light and the partial bleach method with light blocked below 400 nm resulted in overbleaching and thus overestimates of age. A TL age estimate of 5.3 ± 0.8 ka on the Holocene control sample, similar to the radiocarbon age, was obtained using the partial bleach method with light blocked below 540 nm. This same method yielded an average TL age estimate of 73 ± 10 ka for a Pleistocene unit, which corresponds to the amino-acid-based age estimate of ca. 76 ka. The agreement of the two age estimates is encouraging, since both methods rely on separate assumptions that have not been independently verified.

The significance of spectral position in the rhodopsins of tropical marine fishes

Visual pigments were extracted from the retinae of a large and diverse sample (179 species, in 40 families) of tropical marinefishes. By the method of partial bleaching, most of these were found to be retinal-1 pigments, with their maxima tightly grouped between 489 and 502 nm; but a few have λ max at shorter wavelengths. The spectral position of these pigments does not correlate with diurnal or nocturnal activity patterns, nor do closely related species necessarily have similar pigments. In general, the deeper-living species have rhodopsins with λ max at shorter wavelengths, a correlation with the bluer quality of light in deeper water. The spectral distribution of light was measured in air and underwater at a coral atoll. During twilight the underwater spectrum narrows and shifts to shorter wavelengths, as a result of increased absorption of yellow-orange light by the atmosphere. This effect at twilight is unique among the general spectral events that constitute each day. The behavioral patterns of reef fishes make clear the relationships between underwater light and the visual pigments. During evening twilight, there is an orderly sequence, in which the diurnal fishes seek cover, and then, after a “Quiet Period”, the nocturnal species emerge. The “Quiet Period” is the most critical and visually difficult time because light intensities are transitional between the thresholds of photopic and scotopic vision. Predation reaches a maximum during the “Quiet Period”. The rhodopsins of all these fishes tend to match the background light available during evening and morning twilight. Photochemically, visual sensitivity is maximized and, as a result, predation is held in check. The relationships between light, behavior and visual physiology are discussed. Although their rhodopsins are spectrally similar to those of the prey, crepuscular predators obtain a visual advantage by having moderate numbers of very large cones, which provide adequate sensitivity and sufficient resolution for motion detection.

The visual pigment of a chimaeroid fish

The visual pigment of the North Pacific coast chimaeroid fish, Hydrolagus colliei was extracted and analyzed by the method of partial bleaching. The prosthetic group was identified from the difference spectrum of the product formed by bleaching in the presence of NH 2OH. The visual pigment in the extract was found to be P484 1, a deep-sea type of visual pigment. This is interesting because field studies have indicated that Hydrolagus colliei is not always a deep-water fish. The nature of the visual pigment does not accord with this. It is tentatively concluded, however, that the ecology of this holocephalus fish is insufficiently known to warrant its classification as a strictly surface water inhabitant. In fact, there are reasons to suggest that it is basically a deep-water fish, like other chimaeroids, and that it can migrate vertically, perhaps in response to temperature.

Visual pigments of the burbot, Lota lota, and seasonal changes in their reative proportions

The visual pigments of the freshwater gadid, Lota lota, and of three species of marine gadids have been analyzed by the method of partial bleaching. Lota lota has a pair of visual pigments, VP503 1 and VP527 2, based on retinene 1 and retinene 2 respectively. The relative proportion of the two pigments changes seasonally, the percentage of VP527 2 being lowest in spring and summer and highest in fall and winter. The possible relationship of these changes in relation to the light environment and thyroid gland is discussed. The three species of marine gadids have visual pigments based solely on retinene 1.

The visual pigments of several species of birds

Retinal preparations were made from the outer segments or whole retinas of 20 species of birds. The oil droplets were extracted with petroleum ether, and the visual pigments either with digitonin or with Triton X-100. The visual pigment samples were analyzed by the method of partial bleaching. Fourteen species each yielded but one visual pigment, ranging in absorbance maximum from 500 nm to 506 nm. Five other species each yielded a predominant visual pigment with λ max near 502 nm, and also a second photopigment with λ max ranging from ca. 480 nm to 490 nm. One species yielded no measurable photopigment. No evidence was obtained for the presence of any cone pigments. The oil droplets were analyzed spectrophotometrically and exhibited inter se similar absorbance spectra.

The visual pigments of freshwater fishes

Dark-adapted retinae from 59 species of freshwater fishes were extracted in digitonin and analyzed for visual pigment content using the method of partial bleaching. Results of this survey, combined with the investigations of others, show that the classic view of visual pigment distribution among vertebrates is erroneous. Visual pigments based on both retinene 1 and retinene 2 occur commonly among freshwater fishes, even in groups that are neither euryhaline nor migratory. Evidence suggests that the distribution of these visual pigments is probably correlated to photic environment.

A suggested hereditary mechanism for visual pigments of chars (Salvelinus spp.).

A RECENT investigation (Munz, F. W., unpublished results) has shown that salmonid fishes of the genus Salvelinus have several different visual pigments. The methods used have been fully described elsewhere1. Retinae of dark-adapted animals were extracted with aqueous digitonin solution and then tested for homogeneity of the photosensitive pigment by the method of partial bleaching with coloured light2. Brook char, Salvelinus fontinalis (Mitchill), and Dolly Varden, S. malma (Walbaum), have the same visual pigments as are characteristic of Pacific salmon and of trout1. These are a retinene1 pigment with λmax 503 ± 1 mµ and the corresponding retinene2 pigment (λmax 527 ± 1 mµ). The arctic char, S. alpinus (L.), has a retinene1 pigment with λmax 509 ± 2 mµ; the single extract which was examined contained no retinene2 pigment. The lake char, S. namaycush (Walbaum), has a retinene1 pigment with λmax 512 ± 1 mµ. Some individuals of this species also possess the corresponding retinene2 pigment (λmax about 545 mµ,). Thus, in species of this genus, retinene1 pigments having three distinct maxima have been characterized. These maxima represent specific differences in the nature of the ‘opsin’, as the protein moiety of a visual pigment is usually called2.

A critical analysis of the visual pigments of salmon and trout

Retinal extracts have been prepared from individuals of five species of Pacific salmon (Oncorhynchus) and four species of trout (Salmo). These extracts were analysed by the method of partial bleaching. Mixtures of two visual pigments, one a retinene1 pigment (λmax = 503 ± 1 mμ) and the other a retinene2 pigment (λmax = 527 ± 1 mμ), were present in all nine species. The proportions of these two components, which were not the same in all extracts, were determined with the same method that had been used previously with the rudd. The analytical precision of this method and possible sources of error are discussed.

Variation of visual pigment amongst individuals of an american minnow, Notemigonus crysoleucas boscii

Digitonin extracts prepared from the dark-adapted retinae of single specimens of the Southeastern Golden Shiner ( Notemigonus crysoleucas boscii) were analysed by the Method of Partial Bleaching. All specimens were found to possess two visual pigments, one based on vitamin A 2 with λ max at 529 mμ, the other based on vitamin A 1 with λ max at 502 mμ. Although all the specimens came from the same isolated body of water, it was found that the proportions of these two pigments varied from fish to fish in any group netted at the same time. In one extreme case, the proportions in two fish were found to differ by as much as 44 per cent. No significant difference between the two eyes of any particular fish could be detected. It is concluded that environment cannot be the overriding factor in determining the retinal pigment composition of a given fish. It is suggested that the variability observed is related to the persistent schooling behaviour of the Golden Shiner, and might serve to broaden the spectral sensitivity’ of the school.

THE PHOTOSENSITIVE RETINAL PIGMENT SYSTEM OF GEKKO GEKKO.

Retinal extracts of Gekko gekko were found to contain two retinene(1) photopigments, one with maximum absorption at about 521 mmicro, the second with a maximum in the region of 478 mmicro. These pigments were assayed by the method of partial bleaching and their spectral characteristics studied by examining their difference spectra. The 478 mmicro pigment was present in the extracts as 8 per cent of the total photopigment concentration. The two pigment systems were shown to be biochemically independent and to have different properties. Unlike the 521 mmicro pigment, for example, the 478 mmicro pigment was found to resist the action of NH(2)OH and, within the cells, to be unaffected by sucrose solutions. These solutions destroyed or altered the 521 system so that extracts of sucrose-treated retinae were found to contain significantly less 521 photopigment. In digitonin solution the 521 pigment was unaffected by sucrose treatment. Both pigments were extracted from separated, washed outer segments and so are considered to be visual pigments. This dual system accounts for the spectral sensitivity of this gecko as determined by Denton. A search was made, but no evidence was secured for the presence of a photopigment absorbing at longer wavelengths. Electoretinographic data suggest, however, that an elevated sensitivity at longer wavelengths occurs in some geckos so that a continued search is justified for a third photopigment.

Visual pigments of the pigeon (Columba livia)

Abstract Aqueous 4 % digitonin extracts have been prepared from photoreceptors isolated by the sucrose technique from the retinae of dark-adapted pigeons. These extracts have been analysed by the method of partial bleaching, and have been found to contain two photosensitive pigments. One of these pigments has extinction maximum at 502 mμ. The other, which accounts for 13 to 16 per cent of the total pigment present, has extinction maximum at 544±3 mμ. Both pigments are based on vitamin A1 and have been designated pigeon rhodopsin and visual pigment 544 respectively. Unlike the rhodopsin component, visual pigment 544 is rapidly destroyed at pH 8.8. It is quite stable at pH 6.3 to 6.6. A partial separation of the photoreceptors containing these two pigments has been achieved. Thus by gently stirring the excised retinae in 0.9 % saline it has been found that as much as 82 per cent of the total visual pigment 544 compared with only 52 per cent of the total rhodopsin is found in the tissues separated from the main bulk of the retina. By shaking dried pigeon retinae with petroleum ether and chromatographing the resulting extract, it has been possible to isolate two carotenoids. One of these is astaxanthin, whilst the other corresponds to a carotenoid previously isolated from the chicken retina, and is possibly sarcinin or sarcinaxanthin. The relationship between the pigeon's visual pigments and its visual sensitivity has been discussed.