Widely used to infer past climates, isotope measurements from stalactites and stalagmites in caves can mislead researchers.They are among the most useful storytellers of earth history: speleothems, or cave formations. Scientists collect samples from stalactites and stalagmites, take them to their labs, and measure the fractions of stable oxygen and carbon isotopes found in their inclusions of crystals of calcium carbonate or calcite. From these crystal balls, the scientists look far into the past, envisioning climate change and long ages. What could be more straightforward? The data prove it.A funny thing happens on the way to the lab. The isotopic fractionations become altered. Here’s what a team of speleologists (cave scientists) conclude from expeditions into a couple of caves in Hungary.Speleothem deposits are among the most valuable continental formations in paleoclimate research, as they can be dated using absolute dating methods, and they also provide valuable climate proxies. However, alteration processes such as post-depositional mineralogical transformations can significantly influence the paleoclimatic application of their geochemical data.Climate scientists know about some of the alteration processes, but this team points out new ones that have not been appreciated. The paper in Nature‘s open-access journal Scientific Reports concentrates on one alteration process—the transformation of amorphous calcium carbonate (ACC) to nanocrystalline calcite—but suggests there are other factors that, if not properly accounted for, can have “serious consequences” on the interpretation given the data.Here’s the basic problem with ACC: it depletes the fraction of stable oxygen-18 ions (δ18O) before transforming into crystalline calcite. This happens within a few hours or days, potentially giving wrong readings in the lab when the speleothems are measured. The scientists, therefore, might be measuring different values in their refrigerator samples than the crystal as it was forming in the cave long ago. If they expect their measurements to represent a “proxy” (a measurement standing in for something else, like climate), they could be fooling themselves.Detection of ACC is rather difficult in cave deposits, as ACC can undergo transformation to calcite in minutes in a hydrous environment, and even stabilizing compounds like Mg or organic matter are only capable of extending its stability to some weeks. Taking into consideration the general precipitation rate (0.1 to 1 mm per year), the collection of carbonate in appropriate amounts for mineralogical or geochemical analyses requires several months. Over the course of such a long collection time, however, the original ACC can be transformed into calcite. Although ACC preparation in the laboratory is a routine procedure, its synthesis requires conditions distinctly different from those to be found in natural cave environments, e.g. mixing of CaCl2 and NaCO3 or (NH4)2CO3 solutions. Hence, the preparation conditions and characteristics of synthetic ACC render it inappropriate to function as an analogue of its natural counterpart, thus it cannot provide the information sought.The scientists observed ACC forming onsite in the cave on special collection surfaces. The ACC can exist in open or closed systems, depending on whether the inclusions become embedded within the dripwater, reaching equilibrium. The researchers in the lab will not always be able to tell whether calcite from which they obtain δ18O measurements reflect actual conditions in the cave or altered conditions when the ACC lowered the value during crystallization. The conclusions on which they base dates or paleoclimates could be in error.If this were the only worry, perhaps scientists could learn to correct for it by identifying other proxies for the presence of ACC. Unfortunately, this is not the only concern. ACC formation is a function of temperature, conductivity, pH, CO2 concentration, degassing rate, evaporation rate, drip rate and other factors. Unless these factors are known and controlled, and unless researchers gather their data in actual cave environments, they could be misled.The team also notes that scientists get different equations whether they use theoretical analyses, experimental techniques or empirical observations.Uncertainties in the estimation of ACC amount is a major weakness in the fractionation calculation, hence the verification of calcite-ACC fractionation estimation requires independent information provided either by experimental studies or by natural analogues. The experimental determination of ACC-water oxygen isotope fractionation representative for speleothem formation is challenging because (i) ACC rapidly transforms to calcite during the preparation and (ii) laboratory ACC synthesis requires physical and chemical conditions distinctly different from those found in a cave environment. Available estimations of δ18O differences between crystalline and amorphous carbonates formed in natural environments suggest that the crystalline carbonate is several ‰ more enriched in 18O than its amorphous counterpart (dolomite, aragonite, Mg-calcite).What you actually get may not be what you believe you got. Different caves and different forms of calcium carbonate may give very different results. The paper sounds a warning call to researchers:The present study provides direct evidence for relatively 18O-depleted ACC formation in caves at about 10 °C. Since the δ18O value of inclusion-hosted water may carry significant paleoclimatic/paleohydrological information, it is important to note that its use is limited by the cave environment.The authors add one more source of uncertainty: microbes. They toss out that potentially significant alteration right at the end of the paper, after summarizing reasons why you can’t trust the values in this “most valuable” method of inferring paleoclimates and dates. Oh, and don’t forget the unidentified organic compounds in the dripwater, which can vary significantly from cave to cave and also affect ACC formation.A number of experimental studies have shown that the formation and stability of ACC may be influenced by the physical parameters of the ambient environment and the chemical compositions of the parent solutions. In natural cave environments the most important factors might be the cave temperature, drip water pH, as well as concentrations of Mg, SO42− and organic compounds in the solution. A comprehensive study is suggested to cover several cave environments with different temperatures, ventilation degree, soil characteristics, drip water chemistry and carbonate growth rates in order to determine the exact factors governing ACC formation. The transition from ACC to calcite has been shown to take place in several steps with intermediate hydration states and mineral phases like vaterite. Investigations on the ACC-calcite transition and its governing factors require monitoring of mineralogical changes at high temporal resolution. Additionally to the inorganic factors, the role of microbial activity should also be investigated. Amorphous carbonates are ubiquitously secreted by living organisms in sedimentary environments, hence microbial mediated carbonate precipitation is also a potentially important process in ACC formation, whose exploration requires systematic biological/biochemical investigations.It appears that climatologists leaning on cave data know a lot less than they thought they knew. This final paragraph almost makes it seem like it’s time to toss out the equations and interpretations and start over. Isn’t that implied by “a comprehensive study is suggested” using “systematic biological/biochemical investigations” in multiple caves with varying conditions?Reference: “Formation of amorphous calcium carbonate in caves and its implications for speleothem research” by Attila Demény, Péter Németh, et al., Scientific Reports 6, Article number: 39602 (2016), doi:10.1038/srep39602, published 22 Dec 2016.Remember this paper the next time you are presented with scientific “facts” that prove a scientific “consensus” of one sort or another. The conclusions of any empirical study cannot be divorced from the assumptions that go into those conclusions. A consensus is most dangerous when the conclusion is decided in advance, and scientists within a preferred paradigm go out looking for evidence to confirm it. (Visited 56 times, 1 visits today)FacebookTwitterPinterestSave分享0
Lens whacking can elevate your shot in seemingly magical ways, from adding light leaks to creating a vintage look. Here’s everything you need to know about the technique.Top Image via UglyMcGregorLens whacking. It sounds like something that will cost you a night in jail. However, it is indeed a very creative use of the camera and lens which can help produce a gorgeous in-camera effect which can never be replicated as organic in post.What Is Lens Whacking?All images are captured after the light has passed through the lens and hit the sensor (or film). The light passes through many elements within the lens that have been engineered in a very specific way. A 20mm has different elements than an 85mm. Nonetheless, the light passes through in an orderly fashion.Lens whacking is where you remove the lens and physically hold it in front of the sensor. Light then passes through both the lens and the gap between the lens and the camera body. This essentially causes a light leak.As you are partially pushing one part of the lens forward to let in the light, it also will cause a section of the image to fall out of focus, and, to some extent, produce a slight tilt-shift effect. This is entirely done by hand, and as a result of this, no two takes are going to look remotely the same — it’s wildly unpredictable, and as a result, it’s great fun.How To Do ItThe lens choice is the first important step to undertake. Lens whacking a 200mm, well, it’s not going to happen. Not successfully, anyway. Lenses that have a short focal length are ideal for lens whacking, as you want the focus window to be as wide as possible. If you were to use a lens such as an 85mm, you might find yourself trying to find the subject in the viewfinder more than perfecting the light leak. Older lenses with manual aperture and focus are preferred, as it can be quite a pain to have to keep reconnecting your lens to the camera if you wish to change the aperture.You want to set your lens to have the smallest aperture available to you. Again, this is to stop the extremity of your subject falling too much out of focus.Set up your framing, start recording, and then remove the lens from the camera. You only want your lens to be detached from the camera like the cover image above. If you open the gap too much, you’ll flood the sensor with light and wash out the image. (Although, that in itself can work very well for a creative transition.) The best method for lens whacking is not to keep the lens fully removed from the camera at all times, but to bring it in and out every so often. The shot can become very distracting if there’s a constant light-leak focus-loss throughout the entire shot.Image via SLR LoungeFor the best results, try removing your lens to the side where light is hitting the camera. You’ll have a much more powerful flare. Alternatively, if you find that the light leak is too strong, place a finger over the gap you’ve created. The light will still find its way to the sensor, but your finger will diffuse most of it, creating a softer light leak.Many lens whacking examples often have the camera free in the hands of the operator, which in most cases, causes shaky footage. I would recommend locking the camera down onto a tripod for a smoother shot. You can then delegate panning/tilting to another person while you take the sole focus of the lens whacking.If needed, you can also take lens whacking to the extreme, and cause mass blur and washout. Just remove both sides of the lens away from the body. I recently used this method to put emphasis on how dazed and confused a character was. He’s awoken after watching himself die, enough to cause confusion to anyone, I would imagine. The character is going to be in a state of confusion, and he’s not going to understand why he is alive. To emphasize this, I removed the lens quite far away to completely wash out the image at points to add to his hysteria while he was coming around.Video Playerhttps://s3.amazonaws.com/pbblogassets/uploads/2016/09/Sequence-05_1.mp400:0000:0000:04Use Up/Down Arrow keys to increase or decrease volume.Why Do It?The most important aspect of any filmmaking choice is asking, “Will this further the story?” Or, “Will this enhance the emotional impact?”If the answer is no, then at most times it’s probably best to ditch that idea. While lens whacking is extremely popular with music and fashion videos, it’s also ideal for many creative storytelling elements. Here’s a small list of scenarios where you can creatively implement the technique.The character has been poisoned.The character is under the influence of drugs.The character is disoriented.The character is dying.A dream sequence.A scene involving magic.A flashback.The list is almost endless; I’m sure there are many other creative applications to lens whacking that haven’t even crossed my mind. In the still below from Killing Them Softly by Andrew Dominik, the character is under the influence of drugs, and lens whacking (along with several other in-camera effects) has been applied to help portray his state.There are some considerations to take into account. This effect is, of course, in camera, and there’s no removing or “fixing” it if you change your mind later on. Test and practice the effect within your free time. If you have an important job coming up and think the lens whack effect may look great on a few shots, but you’re not 100% confident, have a look at a few digital elements you can use to help mimic the effect in post.Have you used lens whacking within your projects? Post your clips in the comment section below.
In a major bureaucratic reshuffle, the Rajasthan government has transferred 81 Indian Administrative Service (IAS) officers after the appointment of D.B. Gupta as the new Chief Secretary. The Collectors of 15 districts and three Divisional Commissioners were among those shifted in the orders issued late on Monday night.Mr. Gupta, a 1983-batch IAS officer, was appointed the Chief Secretary after the retirement of N.C. Goel, who had the shortest tenure of four months. Speculations were rife about Mr. Goel’s extension, but the Centre reportedly did not accept a proposal sent by the State government in this regard.Mr. Goel played a key role in the execution of the Vasundhara Raje government’s ambitious projects, including the inauguration of oil refinery in Barmer, during his tenure. Mr. Gupta, 58, was earlier Additional Chief Secretary (Finance, Excise and Taxation). The charge of these departments has been given to Mukesh Kumar Sharma.‘Political overtones’The reshuffle, which may have been the last before the State goes to Assembly polls in December this year, seemingly had political overtones with the ruling Bharatiya Janata Party keen on sending across a message of good governance to the electorate.Seven officers of the rank of Additional Chief Secretary were given new responsibilities in the reshuffle, while T. Ravikanth was posted as Divisional Commissioner in Jaipur, Lalit Kumar Gupta in Jodhpur and Kailash Chand Verma in Kota.Neeraj K. Pawan, who was reinstated in November last year after his arrest and suspension in connection with a graft case, was posted as Special Secretary, Administrative Reforms Department. The 2003-batch IAS officer spent eight months in jail on charges of corruption in the award of contracts in the National Rural Health Mission.The Collectors of Bikaner, Pratapgarh, Kota, Ajmer, Dholpur, Rajsamand, Bhilwara, Tonk, Sawai Madhopur, Bundi, Hanumangarh, Churu, Alwar, Jaisalmer and Bharatpur were transferred in the reshuffle.