Collisional shifts in optical-lattice atom clocks

We theoretically study the effects of elastic collisions on the determination of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom clocks. Interparticle interactions of bosonic atoms in multiply-occupied lattice sites can cause a linear frequency shift, as well as generate asymmetric Ramsey fringe patterns and reduce fringe visibility due to interparticle entanglement. We propose a method of reducing these collisional effects in an optical lattice by introducing a phase difference of $\pi$ between the Ramsey driving fields in adjacent sites. This configuration suppresses site to site hopping due to interference of two tunneling pathways, without degrading fringe visibility. Consequently, the probability of double occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure

Glacial-interglacial records of the reflectance of sediments from the Norwegian-Greenland-Iceland Sea (Nordic seas)

 The reflectance of sediments (gray level) were measured on 11 sediment cores from the Norwegian–Greenland–Iceland Sea (Nordic seas). The analyzed time interval covers the past five glacial–interglacial cycles. Although the results demonstrate that the gray-level method has a potential for stratigraphic purposes, it is indicated that gray-level changes in the Nordic seas are not necessarily driven by variations in the content of biogenic calcite. A detailed comparison of gray-level values with contents of total CaCO3 (carbonate) and total organic carbon (TOC) reveals no overall causal link between these proxies. However, specific glacial core sections with layers containing organic-rich sediment clasts as a consequence of iceberg-rafting seem to correlate well with law gray-level values. Of those cores which show relatively high and comparable carbonate values in the last three main interglacial intervals (stages 11, 5.5, and 1), stage 11 is always marked by the highest gray-level values. A close inspection of the surface structure of the foraminiferal tests as well as the conduction of reflectance measurements on these tests leads to the conclusion that enhanced carbonate corrosion occurred during stage 11. The test corrosion not only affected the reflectance of the tests by making them appear whiter, it also seems responsible for the comparatively high gray-level values of the total sediment in stage 11. In contrast, the relatively low gray-level values found in stages 5.5, and 1 are not associated with enhanced test corrosion. This observation implies that variable degrees of carbonate corrosion can have a profound effect on total sediment reflectance

Comparison of glacial and interglacial conditions between the polar and the subpolar North Atlantic Region over the past five climate cycles

A multiparameter-based interpretation of sediment records from the northeast Atlantic and the western Nordic seas suggests that during the last 500,000 years only in marine isotopes stage (MIS) 11, 5e, and 1 were there somewhat comparable interglacial boundary conditions in both regions, i.e., strongly reduced occurrence of iceberg-rafted debris (IRD) and high carbonate bioproductivity. Although the northeast Atlantic experienced such conditions during all peak interglaciations, with the exception of MIS 7, planktic foraminiferal δ18O from this region would still indicate that significantly colder sea surface temperatures (SST) prevailed during MIS 11 than during MIS 9, 5e, and 1. This assumption is corroborated by a continuous input of IRD into the western Nordic seas during MIS 11, implying a much steeper SST gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes. The iceberg proxy also reveals that maximum IRD discharge always happened during the final phase of glaciation and into early deglaciation (terminations). As these IRD records from the two regions are characterized by a high time coherency, it is concluded that short-term variability is a persistent feature of the glacial climate system

Late Pleistocene-Holocene productivity record of benthic foraminifera from the Iceland Plateau (Core PS1246-2)

Benthic foraminiferal assemblage patterns in Core PS 1246-2 from the Iceland Plateau are examined as they relate to annual productivity and seasonal productivity changes during the Late Pleistocene glacial (23,000-11,000 yrs B.P.), Younger Dryas cool period (11,000-10,000 yrs B.P.) and Holocene (10,000-2,900 yrs B.P.). Abundance fluctuations of Cibicidoides wuellerstorji, a suspension-feeder, are used as the proxy for annual productivity, while fluctuations of the phytodetritus-exploiting species Epistoininclln r ~ i p r a E, ponides tlinzid~illisa nd GloDocossidlrliiia strbglobosa are used as the indicators of seasonal productivity. These records show seasonal productivity began to increase around 22,500 yrs B.P. and experienced three subsequent peaks in the glacial, while annual productivity increased around 16,000 yrs B.P. and shows only one peak in the glacial. The Younger Dryas shows a decrease in both seasonal and annual productivity records. Seasonal productivity in the early Holocene is much higher than during the glacial, yet appears more extreme. The Holocene record of annualproductivity continues to show a strong general increase in intensity

Contrasting ocean changes between the subpolar and polar North Atlantic during the past 135 ka

Variations in the poleward-directed Atlantic heat transfer was investigated over the past 135 ka with special emphasis on the last and present interglacial climate development (Eemian and Holocene). Both interglacials exhibited very similar climatic oscillations during each preceding glacial terminations (deglacial TI and TII). Like TI, also TII has pronounced cold–warm–cold changes akin to events such as H1, Bølling/Allerød, and the Younger Dryas. But unlike TI, the cold events in TII were associated with intermittent southerly invasions of an Atlantic faunal component which underscores quite a different water mass evolution in the Nordic Seas. Within the Eemian interglaciation proper, peak warming intervals were antiphased between the Nordic Seas and North Atlantic. Moreover, inferred temperatures for the Nordic Seas were generally colder in the Eemian than in the Holocene, and vice versa for the North Atlantic. A reduced intensity of Atlantic Ocean heat transfer to the Arctic therefore characterized the Eemian, requiring a reassessment of the actual role of the ocean–atmosphere system behind interglacial, but also, glacial climate changes. Key Points - Reduced AMOC during the Eemian - BA/YD-type warming/cooling in Termination 1 and 2 - Comparison of glacial inceptions reveals present climate statu

Temperature dependence of the nitrogen-vacancy magnetic resonance in diamond

The temperature dependence of the magnetic resonance spectra of nitrogen-vacancy (NV-) ensembles in the range of 280-330 K was studied. Four samples prepared under different conditions were studied with NV- concentrations ranging from 10 ppb to 15 ppm. For all of these samples, the axial zero-field splitting (ZFS) parameter, D, was found to vary significantly with temperature, T, as dD/dT = -74.2(7) kHz/K. The transverse ZFS parameter, E, was non-zero (between 4 and 11 MHz) in all samples, and exhibited a temperature dependence of dE/(EdT) = -1.4(3) x 10^(-4) K^(-1). The results might be accounted for by considering local thermal expansion. The observation of the temperature dependence of the ZFS parameters presents a significant challenge for room-temperature diamond magnetometers and may ultimately limit their bandwidth and sensitivity.Comment: 5 pages, 2 figures, 1 tabl

Modelling science trustworthiness under publish or perish pressure

Scientific publication is immensely important to the scientific endeavour. There is, however, concern that rewarding scientists chiefly on publication creates a perverse incentive, allowing careless and fraudulent conduct to thrive, compounded by the predisposition of top-tier journals towards novel, positive findings rather than investigations confirming null hypothesis. This potentially compounds a reproducibility crisis in several fields, and risks undermining science and public trust in scientific findings. To date, there has been comparatively little modelling on factors that influence science trustworthiness, despite the importance of quantifying the problem. We present a simple phenomenological model with cohorts of diligent, careless and unethical scientists, with funding allocated by published outputs. This analysis suggests that trustworthiness of published science in a given field is influenced by false positive rate, and pressures for positive results. We find decreasing available funding has negative consequences for resulting trustworthiness, and examine strategies to combat propagation of irreproducible science

A paleoclimatic evaluation of marine oxygen isotope stage 11 in the high-northern Atlantic (Nordic seas)

A sediment core from the high latitude of the Northern Atlantic (Nordic seas) was intensively studied by means of biogeochemical, sedimentological, and micropaleontological methods. The proxy records of interglacial marine oxygen isotope stage (MIS) 11 are directly compared with records from the Holocene (MIS 1), revealing that many features of MIS 11 are rather atypical for an interglaciation at these latitudes. Full-interglacial conditions without deposition of ice-rafted debris existed in MIS 11 for about 10 kyr (∼398–408 ka). This time is marked by the lightest d18O values in benthic foraminifera, indicating a small global ice volume, and by the appearance of subpolar planktic foraminifera, indicating a northward advection of Atlantic surface water. A comparison with MIS 1, using the same proxies, implies that surface temperatures were lower and global ice volume was larger during MIS 11. A comparative study of the ratio between planktic and benthic foraminifera also reveals strong differences among the two intervals. These data imply that the coupling between surface and bottom bioproductivity, i.e., the vertical transportation of the amount of fresh organic matter, was different in MIS 11. This is corroborated by a benthic fauna in MIS 11, which contains no epifaunally-living species. Despite comparable values in carbonate content (%), reflectance analyses of the total sediment (greylevel) show much higher values for MIS 11 than for MIS 1. These high values are attributed to increased corrosion of foraminiferal tests, directly affecting the sediment greylevel. The reason for this enhanced carbonate corrosion in MIS 11 remains speculative, but may be linked to the global carbon cycle

Russian-German collaboration in the arctic environmental research

The overview of the 20-years joint Russian-German multidisciplinary researches in the Arctic are represented in this article. Data were obtained during numerous marine and terrestrial expeditions, all-year-round measurements and observations. On the basis of modern research methods including satellite observation, radiocarbon (AMS 14C) dating of the Arctic sea sediments, isotope, biochemical and other methods, the new unique records were obtained. Special emphasis devoted to the latest data concerning modern sea-ice, ocean and sedimentation processes, evolution of the permafrost and paleoenvironments in the Laptev Sea System