Premature rejection in science: The case of the Younger Dryas Impact Hypothesis

The progress of science has sometimes been unjustifiably delayed by the premature rejection of a hypothesis for which substantial evidence existed and which later achieved consensus. Continental drift, meteorite impact cratering, and anthropogenic global warming are examples from the first half of the twentieth century. This article presents evidence that the Younger Dryas Impact Hypothesis (YDIH) is a twenty-first century case. The hypothesis proposes that the airburst or impact of a comet ∼12,850 years ago caused the ensuing ∼1200-year-long Younger Dryas (YD) cool period and contributed to the extinction of the Pleistocene megafauna in the Western Hemisphere and the disappearance of the Clovis Paleo-Indian culture. Soon after publication, a few scientists reported that they were unable to replicate the critical evidence and the scientific community at large came to reject the hypothesis. By today, however, many independent studies have reproduced that evidence at dozens of YD sites. This article examines why scientists so readily accepted the early false claims of irreproducibility and what lessons the premature rejection of the YDIH holds for science.

Determination of swithgrass (Panicum virgatum L.) seeds quality

Purpose. Developing a method for determination of the laboratory seed germination that could reduce the biological dormancy period and, accordingly, increase the intensity of germination. Methods. Laboratory, measuring and weighing, mathematical and statistical. Results. Cooling switchgrass seeds at a temperature of 10°C for 7 days on average for three years did not lead to a decrease in germination energy and germination compared to cooling for 14 days. These indexes were almost the same and amounted to 74 and 76%, 73 and 75%, respectively. There were no significant deviations in germination energy and seed germination over the years of research as affected by duration of the cool period. The production test of the developed method, carried out in the accredited control and measuring laboratory, confirmed the obtained in the laboratory results. Conclusions. Seed germination by an improved method, when pre-cooling is carried out for 7 instead of 14 days and counting of germinated seeds on 15th day instead of 20th, has reduced the time to determine germination by 13 days without reducing the quality of analysis. It is advisable to determine the 1000-seed weight in one of three ways, but the most accurate is the third way, i.e. counting the seeds in 10 repetitions.

Twin Pregnancies in Dairy Cattle: Observations in a Large Herd of Holstein-Friesian Dairy Cows

Multiple pregnancies have devastating consequences on the herd economy of dairy cattle. This observational study examines incidence patterns based on data from the ultrasonographic examination of 1130 multiple pregnancies in cows in their third lactation or more carrying twins (98.8%), triplets (1.1%), or quadruplets (0.08%), and 3160 of their peers carrying singletons. Cows became pregnant following a spontaneous estrus with no previous hormone treatments. Irrespective of a significant decrease (p < 0.0001) in the conception rate (28–34 days post-insemination) during the warm period of the year, the multiple pregnancy rate was similar for both warm (26.5%) and cool (26.3%) periods. The incidence of unilateral multiple pregnancies (all embryos in the same uterine horn) was higher than that of bilateral pregnancies (at least one embryo in each uterine horn): 54.4% versus 45.6% (p < 0.0001). This difference rose to 17% during the warm season (p = 0.03). Pregnancy was monitored in unilateral multiple pregnancies until abortion or parturition (n = 615). In the warm period, the parturition rate was 43% compared to 61% recorded in the cool period (p < 0.0001). Thus, a warm climate is the main factor compromising the fate of multiple pregnancies. Some clinical suggestions are provided.

Multiproxy paleoceanographic study from the western Barents Sea reveals dramatic Younger Dryas onset followed by oscillatory warming trend

The Younger Dryas (YD) is recognized as a cool period that began and ended abruptly during a time of general warming at the end of the last glacial. New multi-proxy data from a sediment gravity core from Storfjordrenna (western Barents Sea, 253 m water depth) reveals that the onset of the YD occurred as a single short-lived dramatic environment deterioration, whereas the subsequent warming was oscillatory. The water masses in the western Barents Sea were likely strongly stratified at the onset of the YD, possibly due to runoff of meltwater combined with perennial sea-ice cover, the latter may last up to several decades without any brake-up. Consequently, anoxic conditions prevailed at the bottom of Storfjordrenna, leading to a sharp reduction of benthic biota and the appearance of vivianite microconcretions which formation is favoured by reducing conditions. While the anoxic conditions in Storfjordrenna were transient, the unfavorable conditions for benthic foraminifera lasted for c. 1300 years. We suggest that the Pre-Boreal Oscillation, just after the onset of the Holocene, may have been a continuation of the oscillatory warming trend during the YD.

A quantitative temperature reconstruction of the ‘Little Ice Age’ in southern China

We present a branched glycerol dialkyl glycerol tetraethers (brGDGTs)–based mean annual temperature reconstruction covering the last millennium from a subtropical lake in Guangxi Province, southern China (23°N). We demonstrate that the pattern and absolute values of mean annual temperatures reconstructed using the eastern African lake brGDGTs calibration based on the methylation of 5-methyl branched tetraethers index provided the most reliable and accurate temperature estimates from the site. The results resemble regional and Northern Hemisphere changes over this period. The pattern shows a general cool period between ca. AD 1450 and 1950, including cooling minima centred at ca. AD 1600, 1750 and 1900, coeval with the ‘Little Ice Age’ temperature fluctuations in the Northern Hemisphere, followed by a warming trend from the mid-20th century to the present. The results suggest that both solar forcing and high-latitude Northern Hemisphere climate fluctuations play a role in influencing the terrestrial temperatures in southern China, possibly on different timescales. In addition, our results support the hypothesis that changes of the East Asian summer monsoon are primarily driven by the land–sea thermal gradient change between terrestrial southern China and the Indo-Pacific Warm Pool regions during the last millennium, owing to external radiative and/or volcanic forcings.

The Effect of High Summer Temperatures on Reproduction in Holstein and Czech Fleckvieh

The aim of this study was to evaluate the effect of the hot summer season on the length of service period (number of days from calving to the next conception). For the analysis was created two databases of twins. Twins had the same sire and dam and the first and second lactations took place on the same farm. In the first database (105 pairs) one of the twins was calved (and had the following service period) during the summer months and the second of the twin was calved in the cooler months. To compare the difference in service period between twins in the hot and cool seasons, it was made also second group of twin pairs with reproduction only during the cool period of the year (cool vs. cool season; 58 pairs). The data were analysed using PROC GLM of Statistica®. In addition to season, the effect of breed (Holstein, Czech Fleckvieh), milk production at 1st lactation and calving year were also taken into consideration. The results showed a significantly longer service period in the summer (133.8 days) than in the cool months (114.7 days). In the case of twins with reproduction in the cool months of the year, the difference between length of service period was shorter and insignificant (113.6 vs. 119.4 days).

Vegetation changes in the Hotyn Upland over the last 2000 years (based on pollen data)

Pollen study of two soil sections, located in two different relief positions (the gully bottom at Sadgora 1 and the upper part of a slope at Ridkivtsi I) enables us to show vegetational and climatic changes in the Bukovyna area (the Chernivtsi region) during the last 2000 years (the end of the Early Subatlantic, the Middle and Late Subatlantic). The reconstructions of past vegetation are based on the analyses of pollen surface samples, taken from the soils of different ecotops in the sites’ vicinity. The reconstructed short-period phases of environmental change correspond well with those established in other areas. These are the end of the “Roman warm period” (before the 14C date of 1.74 ka BP), with the humid climate; the relatively dry “Dark Ages cool period” (before the 14C date of 1.19 ka BP); the wet “Medieval warm period”; the cool “Little Ice Age” (with its wetter beginning and drier ending) and the modern warm phase (the last 150 years).Centennial environmental changes − the cooling within the Medieval Warming (XI cent.) and the warming within the “Little Ice Age” (XV cent.) – have been detected. Human impact on the vegetation can be demonstrated – forest clearance (with the presence of particles of microscopic charcoal and pollen of pyrophitic plants), the introduction of thermophilous walnut during warm periods, and the appearance of pasture lands in the place of former fern patches and woods during the “Little Ice Age”, and the last warm phase (with the presence of pollen of pastoral synanthropic plants). In the last 2000 years, broad-leaved woodland, dominated by hornbeam, grew extensively near Sadgora and Ridkivtsi only during the “Medieval Warm Period”.

Regionalization of Ukraine based on the influence of extreme values of maximum air temperature during warm and cold periods of the year

Based on the data of maximum daily near-surface air temperature (MSAT) taken from 186 meteorological stations of Ukraine the parameters of extremality with relation to maximum air temperature for different time periods as well as deviations between them during cold and warm periods of the year were calculated. Regionalization of Ukraine was carried out in order to identify climate-vulnerable regions by means of comparison, overlapping and match of the areas with the highest values towards selected extremality thresholds. The conclusion about general increase in extremality over the last decade with relation to a climatic standard is made, the areas with the greatest vulnerability are outlined, and the areas with increase in extremality degree are identified. During both periods of the year certain areas in the southern, central and eastern parts of Ukraine are considered, based on maximum air temperature data, as the most vulnerable ones. During both periods of the year over 2001-2010, as compared to 1991-2000, increase of recurrence of extreme values of average maximum of air temperature was observed: in March and December during the cold period and also from May to July, and in case of EHMP event – in August. Distribution of maximum air temperature of the EHMP category, in comparison to the category of extreme values, specifies and localizes the regions with the greatest vulnerability. The areas of the highest vulnerability during the cool period comprise the extreme west, south-western and southern regions and during the warm period – southern, south-eastern regions and the extreme east of Ukraine. The spatial distribution of the extreme values of the MSAT for the warm period has a predominantly meridional orientation. During both periods of the year regions in the south (areas of Black Sea region, Crimea, boundary subregions in the south) areas in the east and center of Ukraine affected by extreme MSAT values are the most vulnerable; in 2010-2014 this influence intensified. Increase in the vulnerability based on the maximum air temperature occurs on the background of certain changes in the atmospheric circulation, under conditions of anticyclonic fields prevalence throughout the year along with increase of the temporal exposure to the elementary synoptic process. On the other hand, the aforementioned increase of recurrence of extreme hydrometeorological phenomena is a consequence of sharp changes of synoptic situation, which is especially the case after a period of settled weather. The conclusion that atmospheric circulation is a main agent responsible for extreme weather and that it is not studied completely so far was made.

Sesame Yield Response to Deficit Irrigation and Water Application Techniques in Irrigated Agriculture, Ethiopia

The study was conducted at Werer Agricultural Research Center, Addis Ababa, for two years, 2013 and 2015, during main seasons and for three years, 2012/13, 2013/14, and 2014/15, during the cool period cropping season (November to February) as in the local cropping calendar. The study was aimed at identifying optimum soil moisture stress for sesame and thereby determining appropriate water-saving irrigation methods and also productivity under limited water resource conditions. Nine treatments with three levels of irrigation water percentage based on evapotranspiration of the crop (ETc) (100% ETc, 75% ETc, and 50% ETc) and three types of furrow irrigation methods (alternate furrow, fixed furrow, and conventional furrow) were used. The study design was randomized complete block design (RCBD) with three replications. The yield of sesame had significant (p<0.05) variation among treatments due to deficit irrigation levels and application methods for sesame planted in main seasons. The highest mean yield of 937.50 kg/ha and 2797.6 kg/ha was obtained from the treatment of 50% ETc with alternate and conventional furrow application methods in 2013 and 2015, respectively. The combined mean yield of two years (2013–2015) showed different levels of deficit irrigation, and irrigation methods had a significant effect (p<0.05) on main season planted sesame. Hence, the highest mean yield of 1846.7 kg/ha was obtained from the application of 50% ETc with the conventional furrow application method. In the cool planting season, the highest mean yield of 528.55 kg/ha, 1432.3 kg/ha, and 1562.5 kg/ha was obtained from treatments of 50% ETc, 75% ETc, and 100% ETc with the conventional furrow application method in 2012/13, 2013/14, and 2014/15, respectively. Moreover, during the same period over years, combined analysis showed that the highest mean yield of 1053 kg/ha was obtained from application of 100% ETc with the conventional furrow application method. Thus, it is concluded that a deficit irrigation treatment of 50% ETc with the conventional furrow application method for main season and application of 100% ETc with the conventional furrow application method for cool planting season are best practices of water-saving strategies for irrigated agriculture system.