Changes in the Northern Limit of Spruce at Dubawnt Lake, Northwest Territories

Larsen described the treeline west of Hudson Bay and particularly at Ennadi, Yathkyed and Dubawnt Lakes, as clumps of spruce, relict from a former more northerly distribution. ... Evidence collected by us in 1966 on the Dubawnt River system on the Mackenzie-Keewatin border, indicates that the spruce trees are re-establishing themselves and have moved northward and closer to Dubawnt Lake during the past one hundred years. ... Larsen's view that spruce has not re-establsihed itself during the last half century does not apply at Dubawnt Lake, but may be true at the Ennadai and Yathkyed Lake regions. ... The known changes in the treeline in the Dubawnt Lake area can be summarized as follows: the south arm of the Keewatin Glacier left the lake area possibly from 7.5 to 7.9 thousands of years before the present or as late as 5.5 thousand years ago. By 4 thousand years ago, a closed canopy forest extended half way up the east shore of Lake Dubawnt, leaving fossil podzols. Individual clumps and trees probably extended further north. A southern retraction of treeline followed, but a re-extension took place c. A.D. 1100 at the "little climatic optimum". A southern retraction again occurred and by 1770 Hearne recorded dead stumps 20 miles north of the treeline. Around 1870, satisfactory growth conditions existed within 2 miles of the south end of Dubawnt Lake and a minor northward extension took place. Re-establishment of spruce by means other than layering occurred by 1931. Less favourable growth conditions may have begun again in 1960

Novel genetic loci associated with hippocampal volume

The hippocampal formation is a brain structure integrally involved in episodic memory, spatial navigation, cognition and stress responsiveness. Structural abnormalities in hippocampal volume and shape are found in several common neuropsychiatric disorders. To identify the genetic underpinnings of hippocampal structure here we perform a genome-wide association study (GWAS) of 33,536 individuals and discover six independent loci significantly associated with hippocampal volume, four of them novel. Of the novel loci, three lie within genes (ASTN2, DPP4 and MAST4) and one is found 200 kb upstream of SHH. A hippocampal subfield analysis shows that a locus within the MSRB3 gene shows evidence of a localized effect along the dentate gyrus, subiculum, CA1 and fissure. Further, we show that genetic variants associated with decreased hippocampal volume are also associated with increased risk for Alzheimer's disease (rg =-0.155). Our findings suggest novel biological pathways through which human genetic variation influences hippocampal volume and risk for neuropsychiatric illness

Reproducibility in the absence of selective reporting : An illustration from large-scale brain asymmetry research

Altres ajuts: Max Planck Society (Germany).The problem of poor reproducibility of scientific findings has received much attention over recent years, in a variety of fields including psychology and neuroscience. The problem has been partly attributed to publication bias and unwanted practices such as p-hacking. Low statistical power in individual studies is also understood to be an important factor. In a recent multisite collaborative study, we mapped brain anatomical left-right asymmetries for regional measures of surface area and cortical thickness, in 99 MRI datasets from around the world, for a total of over 17,000 participants. In the present study, we revisited these hemispheric effects from the perspective of reproducibility. Within each dataset, we considered that an effect had been reproduced when it matched the meta-analytic effect from the 98 other datasets, in terms of effect direction and significance threshold. In this sense, the results within each dataset were viewed as coming from separate studies in an "ideal publishing environment," that is, free from selective reporting and p hacking. We found an average reproducibility rate of 63.2% (SD = 22.9%, min = 22.2%, max = 97.0%). As expected, reproducibility was higher for larger effects and in larger datasets. Reproducibility was not obviously related to the age of participants, scanner field strength, FreeSurfer software version, cortical regional measurement reliability, or regional size. These findings constitute an empirical illustration of reproducibility in the absence of publication bias or p hacking, when assessing realistic biological effects in heterogeneous neuroscience data, and given typically-used sample sizes

An operational overview of the EXport processes in the ocean from RemoTe sensing (EXPORTS) northeast pacific field deployment

The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations of export flux pathways, plankton community composition, food web processes, and optical, physical, and biogeochemical (BGC) properties are needed over a range of ecosystem states. Here we introduce the first EXPORTS field deployment to Ocean Station Papa in the Northeast Pacific Ocean during summer of 2018, providing context for other papers in this special collection. The experiment was conducted with two ships: a Process Ship, focused on ecological rates, BGC fluxes, temporal changes in food web, and BGC and optical properties, that followed an instrumented Lagrangian float; and a Survey Ship that sampled BGC and optical properties in spatial patterns around the Process Ship. An array of autonomous underwater assets provided measurements over a range of spatial and temporal scales, and partnering programs and remote sensing observations provided additional observational context. The oceanographic setting was typical of late-summer conditions at Ocean Station Papa: a shallow mixed layer, strong vertical and weak horizontal gradients in hydrographic properties, sluggish sub-inertial currents, elevated macronutrient concentrations and low phytoplankton abundances. Although nutrient concentrations were consistent with previous observations, mixed layer chlorophyll was lower than typically observed, resulting in a deeper euphotic zone. Analyses of surface layer temperature and salinity found three distinct surface water types, allowing for diagnosis of whether observed changes were spatial or temporal. The 2018 EXPORTS field deployment is among the most comprehensive biological pump studies ever conducted. A second deployment to the North Atlantic Ocean occurred in spring 2021, which will be followed by focused work on data synthesis and modeling using the entire EXPORTS data set

Influence of stratification on marine dissolved organic carbon (DOC) dynamics: The Mediterranean Sea case

•Strong influence of stratification on the DOC dynamics in the Mediterranean Sea.•More DOC will accumulate in a warmer and well stratified ocean.•DOC may contribute to oceanic carbon export more than is currently recognized.•DOC should be included in models studying the carbon cycle in a warmer ocean.•The Mediterranean Sea is a model system for studying C cycle in a warmer ocean. Vertical distributions of dissolved organic carbon (DOC) were determined in different seasons in the southern Adriatic and Tyrrhenian Seas to study the role of stratification in DOC patterns. These two seas are located at similar latitude but differ in extents of vertical stratification. Stratification affects DOC dynamics in both basins, but with interesting differences. In the Tyrrhenian Sea, where the upper water column was stratified during all cruises, DOC showed high surface layer values without substantial seasonality. By contrast, in the southern Adriatic Sea, the seasonal cycle of stratification forced opposite trends in the 0–50m and 50–800m stocks, with DOC removal from the upper 50m associated with DOC increase below 50m. Regarding DOC export via deep water formation in the southern Adriatic Sea, we estimate that 0.19TgCyr−1 was exported to the 50–800m layer by convective overturn, while 0.85–1.19TgCyr−1 was sequestered below 1000m due to a continental shelf pump mechanism. We hypothesize that enhanced stratification associated with a warmer ocean could further increase DOC concentrations in the mixed layer, changing the role of DOC in the oceanic carbon cycle

Assessment of excess nitrate development in the subtropical North Atlantic

Geochemical estimates of N2 fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the assumptions and choices made in the analyses. Employing one of these previously described methods, modified here with improved estimates of excess N spatial gradients and ventilation rates of the main thermocline, we determine a total excess N accumulation rate of 7.8 ± 1.7 × 1011 mol N yr− 1. Contributions to excess N development include atmospheric deposition of high N:P nutrients (adding excess N at a rate of 3.0 ± 0.9 × 1011 mol N yr− 1 for ∼ 38% of the total), high N:P dissolved organic matter advected into and mineralized in the main thermocline (adding excess N at 2.2 ± 1.1 × 1011 mol N yr− 1 for ∼ 28% of the total), and, calculated by mass balance of the excess N field, N2 fixation (adding excess N at 2.6 ± 2.2 × 1011 mol N yr− 1 for ∼ 33% of the total). Assuming an N:P of 40 and this rate of excess N accumulation due to the process, N2 fixation in the North Atlantic subtropical gyre is estimated at ∼ 4 × 1011 mol N yr− 1. This relatively low rate of N2 fixation suggests that i) the rate of N2 fixation in the North Atlantic is greatly overestimated in some previous analyses, ii) the main thermocline is not the primary repository of N fixed by diazotrophs, and/or iii) the N:P ratio of exported diazotrophic organic matter is much lower than generally assumed. It is this last possibility, and our uncertainty in the N:P ratios of exported material supporting excess N development, that greatly lessens our confidence in geochemical measures of N2 fixation