917 research outputs found
Distribution of living benthic foraminifera in the northern Chukchi Sea
This is a post-peer-review, pre-copyedit version of an article published in Arktos. The final authenticated version is available online at: https://doi.org/10.1007/s41063-018-0062-y.Living (Rose Bengal stained) benthic foraminifera were studied in the topmost sediments of five multi- and box cores collected on the continental shelf, upper and lower slopes, of the Chukchi Sea to provide background information on modern benthic foraminiferal distribution, useful for future studies. Sediment cores were collected during August–September 2015, when the area is seasonally ice-free. Benthic foraminiferal contents in the 63–125 µm and > 125 µm size fractions are discussed in terms of water masses distribution, and sedimentological (grain size) and organic geochemical (total organic carbon, total nitrogen, C/N ratio and δ13Corg) characteristics of the surface sediments. Marine organic carbon-rich clay sediments characterize the faunal microhabitats. Despite relatively high organic carbon contents, standing stocks of living benthic foraminifera are generally low, especially for the 63–125 µm size fraction. This low living stock seems to reflect post-bloom conditions in August and September in the area. The reduced supply of fresh organic carbon also affects faunal microhabitats in the sediment with a concentration of living fauna in the upper 2 cm of the sediment. Over the Chukchi Sea shelf, a relatively mixed upper sediment layer likely due to bioturbation or bio-structures induces a disturbed vertical distribution in the sediment. Corrosive Pacific-derived bottom water over the shelf likely explains the relative importance of agglutinated vs. calcareous fauna in this shallow setting. Our results suggest that, in a post-bloom context, the main environmental control on benthic foraminiferal assemblages in the Chukchi Sea is the nature of the bottom water masses
Degree distributions under general node removal: Power-law or Poisson?
Perturbations made to networked systems may result in partial structural
loss, such as a blackout in a power-grid system. Investigating the resultant
disturbance in network properties is quintessential to understand real networks
in action. The removal of nodes is a representative disturbance, but previous
studies are seemingly contrasting about its effect on arguably the most
fundamental network statistic, the degree distribution. The key question is
about the functional form of the degree distributions that can be altered
during node removal or sampling, which is decisive in the remaining
subnetwork's static and dynamical properties. In this work, we clarify the
situation by utilizing the relative entropies with respect to the reference
distributions in the Poisson and power-law form. Introducing general sequential
node removal processes with continuously different levels of hub protection to
encompass a series of scenarios including random removal and preferred or
protective removal of the hub, we classify the altered degree distributions
starting from various power-law forms by comparing two relative entropy values.
From the extensive investigation in various scenarios based on direct
node-removal simulations and by solving the rate equation of degree
distributions, we discover in the parameter space two distinct regimes, one
where the degree distribution is closer to the power-law reference distribution
and the other closer to the Poisson distribution.Comment: 12 pages, 7 figure
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