Observations of large-scale fluid transport by laser-guided plankton aggregations

Diel vertical migration of plankton has been proposed to affect global ocean circulation to a degree comparable to winds and tides. This biomixing process has never been directly observed, however, due to the inability to predict its occurrence in situ or to reproduce it in a laboratory setting. Furthermore, it has been argued that the energy imparted to the ocean by plankton migrations occurs at the scale of individual organisms, which is too small to impact ocean mixing. We describe the development of a multi-laser guidance system that leverages the phototactic abilities of plankton to achieve controllable vertical migrations concurrently with laser velocimetry of the surrounding flow. Measurements in unstratified fluid show that the hydrodynamic interactions between neighboring swimmers establish an alternate energy transfer route from the small scales of individually migrating plankton to significantly larger scales. Observations of laser-induced vertical migrations of Artemia salina reveal the appearance of a downward jet, which triggers a Kelvin-Helmholtz instability that results in the generation of eddy-like structures with characteristic length scales much larger than the organisms. The measured energy spectrum is consistent with these findings and indicates energy input at large scales, despite the small individual size of the organisms. These results motivate the study of biomixing in the presence of stratification to assess the contribution of migrating zooplankton to local and global ocean dynamics. The laser control methodology developed here enables systematic study of the relevant processes

Asymmetry of motion: vortex rings crossing a density gradient

Vortex rings are critical for thrust production underwater. In the ocean, self-propelled mesozooplankton generate vortices while swimming within a weakly stratified fluid. While large-scale biogenic transport has been observed during vertical migration in the wild and lab experiments, little focus has been given to the evolution of induced vortex rings as a function of their propagation direction relative to the density gradient. In this study, the evolution of an isolated vortex ring crossing the interface of a stable two-layer system is examined as a function of its translation direction with respect to gravity. The vortex ring size and position are visualized using Planar Induced Fluorescence (PLIF) and the induced vorticity field derived from Particle Image Velocimetry (PIV) is examined. It is found that the production of baroclinic vorticity significantly affects the propagation of vortex rings crossing the density interface. As a result, any expected symmetry between vortex rings traveling from dense to light fluids and from light to dense fluids breaks down. In turn, the maximum penetration depth of the vortex ring occurs in the case in which the vortex propagates against the density gradient due to the misalignment of the pressure and density gradients. Our results have far-reaching implications for the characterization of local ecosystems in marine environments.Comment: 11 pages, 5 figure

RADIv1: a non-steady-state early diagenetic model for ocean sediments in Julia and MATLAB/GNU Octave

We introduce a time-dependent, one-dimensional model of early diagenesis that we term RADI, an acronym accounting for the main processes included in the model: chemical reactions, advection, molecular and bio-diffusion, and bio-irrigation. RADI is targeted for study of deep-sea sediments, in particular those containing calcium carbonates (CaCO3). RADI combines CaCO3 dissolution driven by organic matter degradation with a diffusive boundary layer and integrates state-of-the-art parameterizations of CaCO3 dissolution kinetics in seawater, thus serving as a link between mechanistic surface reaction modeling and global-scale biogeochemical models. RADI also includes CaCO3 precipitation, providing a continuum between CaCO3 dissolution and precipitation. RADI integrates components rather than individual chemical species for accessibility and is straightforward to compare against measurements. RADI is the first diagenetic model implemented in Julia, a high-performance programming language that is free and open source, and it is also available in MATLAB/GNU Octave. Here, we first describe the scientific background behind RADI and its implementations. Following this, we evaluate its performance in three selected locations and explore other potential applications, such as the influence of tides and seasonality on early diagenesis in the deep ocean. RADI is a powerful tool to study the time-transient and steady-state response of the sedimentary system to environmental perturbation, such as deep-sea mining, deoxygenation, or acidification events

Bridging Gaps in the Climate Observation Network: A Physics-based Nonlinear Dynamical Interpolation of Lagrangian Ice Floe Measurements via Data-Driven Stochastic Models

Modeling and understanding sea ice dynamics in marginal ice zones relies on acquiring Lagrangian ice floe measurements. However, optical satellite images are susceptible to atmospheric noise, leading to gaps in the retrieved time series of floe positions. This paper presents an efficient and statistically accurate nonlinear dynamical interpolation framework for recovering missing floe observations. It exploits a balanced physics-based and data-driven construction to address the challenges posed by the high-dimensional and nonlinear nature of the coupled atmosphere-ice-ocean system, where effective reduced-order stochastic models, nonlinear data assimilation, and simultaneous parameter estimation are systematically integrated. The new method succeeds in recovering the locations, curvatures, angular displacements, and the associated strong non-Gaussian distributions of the missing floes in the Beaufort Sea. It also accurately estimates floe thickness and recovers the unobserved underlying ocean field with an appropriate uncertainty quantification, advancing our understanding of Arctic climate

Pollock avoided hydrodynamic instabilities to paint with his dripping technique.

Jackson Pollock's most celebrated abstract paintings were produced with the so-called dripping technique. By pouring liquid paint with the help of a stick or from a can, Pollock deposited viscous fluid filaments on a horizontal canvas, rhythmically moving around it. The intricate webs of lines, ubiquitous in his compositions, have fascinated art historians and scientists. Based on image analysis of historical video recordings, we experimentally reproduced the painting process. We conclude that Pollock avoided the appearance of the hydrodynamic instabilities, contrary to what was argued by previous studies. Pollock selected the physical properties of the paint to prevent filament fragmentation before deposition, and applied it while moving his hand sufficiently fast and at certain heights to avoid fluid filaments from coiling into themselves. An understanding of the physical conditions at which these patterns were created is important to further art research and it can be used as a tool in the authentication of paintings

Anatomy of phobanes. diastereoselective synthesis of the three isomers of n-butylphobane and a comparison of their donor properties.

Three methods for the large scale (50-100 g) separation of the secondary phobanes 9-phosphabicyclo[3.3.1]nonane (s-PhobPH) and 9-phosphabicyclo[4.2.1]nonane (a-PhobPH) are described in detail. Selective protonation of s-PhobPH with aqueous HCl in the presence of a-PhobPH is an efficient way to obtain large quantities of a-PhobPH. Selective oxidation of a-PhobPH in an acidified mixture of a-PhobPH and s-PhobPH is an efficient way to obtain large quantities of s-PhobPH. The crystalline, air-stable phosphonium salts [s-PhobP(CH(2)OH)(2)]Cl and [a-PhobP(CH(2)OH)(2)]Cl can be separated by a selective deformylation with aqueous NaOH. a-PhobPH is shown to be a(5)-PhobPH in which the H lies over the five-membered ring. The isomeric a(7)-PhobPH has been detected but isomerizes to a(5)-PhobPH rapidly in the presence of water. s-PhobPH is more basic than a-PhobPH by about 2 pK(a) units in MeOH. Treatment of s-PhobPH with BH(3).THF gives s-PhobPH(BH(3)) and similarly a-PhobPH gives a(5)-PhobPH(BH(3)). Isomerically pure s-PhobPCl and a(5)-PhobPCl are prepared by reaction of the corresponding PhobPH with C(2)Cl(6). The n-butyl phobane s-PhobPBu is prepared by nucleophilic (using s-PhobPH or s-PhobPLi) and electrophilic (using s-PhobPCl) routes. Isomerically pure a(5)-PhobPBu is prepared by treatment of a-PhobPLi with (n)BuBr and a(7)-PhobPBu is prepared by quaternization of a-PhobPH with (n)BuBr followed by deprotonation. From the rates of conversion of a(7)-PhobPBu to a(5)-PhobPBu, the DeltaG(double dagger) (403 K) for P-inversion is calculated to be 38.1 kcal mol(-1) (160 kJ mol(-1)). The donor properties of the individual isomers of PhobPBu were assessed from the following spectroscopic measurements: (i) (1)J(PSe) for PhobP(Se)Bu; (ii) nu(CO) for trans-[RhCl(CO)(PhobPBu)(2)], (iii) (1)J(PtP) for the PEt(3) in trans-[PtCl(2)(PEt(3))(PhobPBu)]. In each case, the data are consistent with the order of sigma-donation being a(7)-PhobPBu > s-PhobPBu > a(5)-PhobPBu. This same order was found when the affinity of the PhobPBu isomers for platinum(II) was investigated by determining the relative stabilities of [Pt(CH(3))(s-PhobPBu)(dppe)][BPh(4)], [Pt(CH(3))(a(5)-PhobPBu)(dppe)][BPh(4)], and [Pt(CH(3))(a(7)-PhobPBu)(dppe)][BPh(4)] from competition experiments. Calculations of the relative stabilities of the isomers of PhobPH, [PhobPH(2)](+), and PhobPH(BH(3)) support the conclusions drawn from the experimental results. Moreover, calculations on the frontier orbital energies of PhobPMe isomers and their binding energies to H(+), BH(3), PdCl(3)(-), and PtCl(3)(-) corroborate the experimental observation of the order of sigma-donation being a(7)-PhobPR > s-PhobPR > a(5)-PhobPR. The calculated He(8) steric parameter shows that the bulk of the isomers increases in the order a(7)-PhobPR < s-PhobPR < a(5)-PhobPR. The crystal structures of [a-PhobP(CH(2)OH)(2)][s-PhobP(CH(2)OH)(2)]Cl(2), cis-[PtCl(2)(a(5)-PhobPCH(2)OH)(2)], trans-[PtCl(2)(s-PhobPBu)(2)], and trans-[PtCl(2)(a(7)-PhobPBu)(2)] are reported