Search for: All records

Information theory can be used to describe the gain of evolutionary fitness that an organism obtains from sensing, processing, and acting on environmental information. This paper considers the fitness value of subjective information, i.e., the context-dependent value of different kinds of information. A simplified model is given in which the organism requires two essential nutrients, and can prioritize sensing for one or the other. It is shown that a subjective strategy, in which the organism prioritizes a less abundant nutrient for sensing, leads to higher fitness than a balanced strategy, in which total information is maximized and the meaning of the acquired information is disregarded. Using this model, the fitness advantage of subjective information admits an analytical solution, and it is shown that subjective information is more advantageous when the organism's knowledge of the environment is less precise. 

Abstract Kelvin‐Helmholtz Instabilities (KHI) are known to be significant drivers of atmospheric turbulence. Recent observations show KHI forming with misaligned or angled billow segments that develop connecting vortex tubes and knots (T&K); these features promote distinctive, event‐defining instability and mixing characteristics that were not accounted for in prior idealized studies. Though T&K have been shown to increase mixing in KHI events with low Richardson numbers (Ri), their influence in weakly KH‐unstable, less‐idealized environments is unknown. Here we present modeling results of KHI in the stratosphere to assess the impact of T&K dynamics in weakly KH‐unstable environments. Radiosonde wind and temperature profiles from 22 February 2006 near Lamont, Oklahoma, measured vertically offset shear and stability peaks near 16.2 km with a minimum Ri = 0.11. Direct numerical simulations (DNS) of this event reveal decreasing shear and increasing stratification, where Ri increases to 0.2 as the shear and stratification peaks move to a common altitude. The resulting KHI exhibit T&K features forming adjacent to, and in superposition with, secondary convective instabilities (CI) rather than superseding them as in prior T&K studies with Ri = 0.05. Newly discovered “crankshaft” instabilities distort the billows and give rise to secondary KHI with delayed, elevated dissipation. KHI that exhibit T&K dynamics are found to accumulate % greater mixing than axially uniform KHI with equal or lower mixing efficiency. The substantial increase in mixing suggests significant contributions of T&K dynamics to KHI events throughout the atmosphere that remain unaddressed in general circulation models' turbulence parameterizations. 

Abstract Despite increased Atlantic hurricane risk, projected trends in hurricane frequency in the warming climate are still highly uncertain, mainly due to short instrumental record that limits our understanding of hurricane activity and its relationship to climate. Here we extend the record to the last millennium using two independent estimates: a reconstruction from sedimentary paleohurricane records and a statistical model of hurricane activity using sea surface temperatures (SSTs). We find statistically significant agreement between the two estimates and the late 20th century hurricane frequency is within the range seen over the past millennium. Numerical simulations using a hurricane-permitting climate model suggest that hurricane activity was likely driven by endogenous climate variability and linked to anomalous SSTs of warm Atlantic and cold Pacific. Volcanic eruptions can induce peaks in hurricane activity, but such peaks would likely be too weak to be detected in the proxy record due to large endogenous variability. 

Information theory has been successfully applied to biology with interesting results and applications, ranging from scientific discovery, to system modeling, and engineering. Novel concepts such as semantic and useful information have been proposed to address the peculiarity of biological systems in contrast to Shannon’s classical theory. In this paper, the concept of subjective information, previously observed as an emergent property in a simulated biological system with determinate char- acteristics, is further explored through the proposal of a novel metric for its quantification. This measure is based on a biological system’s ability to dynamically sense and react to environmental signals to achieve a goal. The novel metric is validated through the simulation of a computational model that enables its correlation with different strategies for information acquisition from the environment and processing. The obtained results indicate that the proposed measure of subjective information is reliable in quantifying the effectiveness of a biological system’s strategy in using information from the environment for its growth and survival. 

Sinkholes develop on carbonate landscapes when caves collapse and can subsequently become lake-like environments if they are flooded by local groundwater. Sediment cores retrieved from sinkholes have yielded high-resolution reconstructions of past environmental change, hydroclimate, and hurricane activity. However, our understanding of the internal sedimentary processes of these systems remains incomplete. Here, we use a multiproxy approach including sedimentology (stratigraphy, coarse-grained particle density, bulk organic matter content), micropaleontology (ostracods), and geochemistry (δ13C and δ2H on n-alkanoic acids) to reconstruct evidence for paleolimnology and regional hydroclimate from a continuous stratigraphic record (Emerald Pond sinkhole) in the northern Bahamas that spans the middle to late Holocene. Basal peat at 8.9 m below modern sea level documents the maximum sea-level position at ~ 8200 cal. yr BP. Subsequent upward vertical migration of the local aquifer caused by regional sea-level rise promoted carbonate-marl deposition from ~ 8300 to 1700 cal. yr BP. A shift in coarse particle deposition and ostracods at 5500 cal. yr BP suggests some environmental change, which may be related to one or multiple internal or external drivers. Sapropel deposition from ~ 1700 to 1300 cal. yr BP indicates a fundamental change in limnology to promote increased organic matter preservation, perhaps related to the regional cooling during the Dark Ages Cold Period. We find δ2H28 values are largely invariant from 7700 to 6150 cal. yr BP suggesting a generally stable hydroclimate (mean − 133‰, 1σ = 5‰). The shift to more depleted values (− 156‰, 1σ = 19‰) at ~ 6000–4800 cal. yr BP may be linked to a weakened (eastern displaced) North Atlantic Subtropical High. Nevertheless, additional local hydroclimate records are needed to better disentangle uncertainties from either internal or external influences on the resultant measurements.