Hydrodynamic disturbance and zooplankton swimming behaviour

EDITORIAL OFFICE, TAIPEI, TAIWAN, 11

How islands stir and fertilize the upper ocean

2000 FLORIDA AVE NW, WASHINGTON, USA, DC, 2000

Diel vertical migration promotes zooplankton horizontal patchiness

Spatial patchiness of plankton enhances fishery production and carbon export in the ocean. While diel vertical migration (DVM) has been identified as an important factor contributing to vertical patchiness, its effect on horizontal patchiness has never been investigated. We use a simple individual based zooplankton model to examine the effect of DVM on the horizontal patchiness of four zooplankton groups with differing DVM patterns in a two-dimensional ocean circulation model. We find that zooplankton horizontal patchiness can be induced by two mechanisms: 1) in stratified waters, DVM can synchronize zooplankton vertical positions with the horizontal current velocities that drive them, resulting in horizontal patchiness; and 2) migrating zooplankton tend to aggregate in deep waters when they encounter sea bottom. Due to these mechanisms, zooplankton horizontal patchiness may be ubiquitous in the ocean, enhancing secondary production and fisheries

Dynamics and energetics of trapped diurnal internal Kelvin waves around a midlatitude lsland

Author Posting. © American Meteorological Society, 2017. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 47 (2017): 2479-2498, doi:10.1175/JPO-D-16-0167.1.The generation of trapped and radiating internal tides around Izu‐Oshima Island located off Sagami Bay, Japan, is investigated using the three-dimensional Stanford Unstructured Nonhydrostatic Terrain-following Adaptive Navier–Stokes Simulator (SUNTANS) that is validated with observations of isotherm displacements in shallow water. The model is forced by barotropic tides, which generate strong baroclinic internal tides in the study region. Model results showed that when diurnal K1 barotropic tides dominate, resonance of a trapped internal Kelvin wave leads to large-amplitude internal tides in shallow waters on the coast. This resonance produces diurnal motions that are much stronger than the semidiurnal motions. The weaker, freely propagating, semidiurnal internal tides are generated on the western side of the island, where the M2 internal tide beam angle matches the topographic slope. The internal wave energy flux due to the diurnal internal tides is much higher than that of the semidiurnal tides in the study region. Although the diurnal internal tide energy is trapped, this study shows that steepening of the Kelvin waves produces high-frequency internal tides that radiate from the island, thus acting as a mechanism to extract energy from the diurnal motions.This study was supported by JST CREST Grant Number JPRMJCR12A6.2018-04-1

小型クロロフィル・濁度計の空間解像度について

アレック電子株式会社東京水産大学海洋環境学科東京水産大学海洋環境学

Early-winter mixing event associated with baroclinic motions in weakly stratified Lake Biwa

The annual overturn of lake water (termed holomixis) during winter is essential in maintaining the environment of warm monomictic lakes by transporting heat and organic and inorganic constituents; however, direct observation of wintertime mixing processes is limited. To better understand the detailed physical processes responsible for holomixis, this study investigated a cold low-oxygen water intrusion event on the northeastern slope of weakly stratified Lake Biwa (Japan), observed using mooring systems. The intrusion occurred concurrently with superinertial oscillations of near-bottom currents. The effective Wedderburn number suggests that basin-scale Kelvin waves were excited by north¬eastward winds (~4 m s−1) prior to the intrusion event. The results of a modal analysis suggest that the intrusion was caused by a combination of Kelvin and Poincaré waves that locally uplifted the cold deep water. The heat budget analyses revealed that a substantial part of the intruded cold water was mixed diapycnally, induced by wind stirring, nighttime convection, and bottom friction. The superinertial currents enhanced the dissipation due to bottom friction by ~30%. The cold water intrusion and subsequent mixing provided local heat flux of 98 W m−2 over 6 days, which was 1.4 times larger than the average surface heat flux over the same period. In addition to previously studied processes, such as surface cooling and gravity currents from the shore, this study indicates that wind-induced baroclinic motions and subsequent diapycnal mixing of a stratified water column contribute to holomixis

Micro-Scale Variability Impacts the Outcome of Competition Between Different Modeled Size Classes of Phytoplankton

Previous modeling studies have shown that observed micro-scale (mm) variability of nutrients and phytoplankton biomass can strongly impact the large-scale mean growth response of phytoplankton in ways that cannot be represented by typical models based on the mean field approximation. Also, models accounting for the flexible eco-physiology of phytoplankton predict quite different responses to changing environmental conditions compared to most current (inflexible) models. Combining these two ideas for nutrient-phytoplankton systems we have developed a new “Flexible NP closure model” to represent competition among the three typically observed phytoplankton size classes: pico-, nano-, and micro-phytoplankton. Both micro-scale variability and flexible eco-physiology are expected to impact the competition among these size classes. With this work we begin to address how both these factors determine the size structure and size diversity of phytoplankton in the ocean. Under eutrophic conditions, variability does not impact the modeled growth rate of any size class. On the other hand, under oligotrophic conditions, variability preferentially enhances the biomass of the largest typically observed micro-size class, and reduces the biomass of the smallest nano- and intermediate pico-size classes

Buoyancy generated turbulence in stably stratified flow with shear

The energy evolution in buoyancy-generated turbulence subjected to shear depends on the gradient Richardson number Ri and the stratification number St, which is a ratio of the time scale of the initial buoyancy fluctuations to the time scale of the mean stratification. During an initial period, the flow state evolves as in the unsheared case. After this period, shear generates fluctuating velocity components for St=0.25, but it depletes the fluctuating vertical velocity component and temperature variance faster than in the unsheared case for St=4. Weak shear causes the kinetic and total energy to decrease faster than in the unsheared case, whereas strong shear adds more energy in comparison with the unsheared case. Energy increased with time in only one case considered (St=0.1 and Ri=0.04). When St\u3e1, the nonlinearity of the flow does not become significant even when Ri is small. Thus, results from rapid distortion theory and direct numerical simulation compare well. In particular, the theory reproduces trends in the energy evolution for St\u3e1

Hadron-Hadron Interactions from Imaginary-time Nambu-Bethe-Salpeter Wave Function on the Lattice

Imaginary-time Nambu-Bethe-Salpeter (NBS) wave function is introduced to extend our previous approach for hadron-hadron interactions on the lattice. Scattering states of hadrons with different energies encoded in the NBS wave-function are utilized to extract non-local hadron-hadron potential. "The ground state saturation", which is commonly used in lattice QCD but is hard to be achieved for multi-baryons, is not required. We demonstrate that the present method works efficiently for the nucleon-nucleon interaction (the potential and the phase shift) in the 1S_0 channel.Comment: 13 pages, 6 figure

Two-Baryon Potentials and H-Dibaryon from 3-flavor Lattice QCD Simulations

Baryon-baryon potentials are obtained from 3-flavor QCD simulations with the lattice volume L ~ 4 fm, the lattice spacing a ~ 0.12 fm, and the pseudo-scalar-meson mass M_ps =469 - 1171 MeV. The NN scattering phase shift and the mass of H-dibaryon in the flavor SU(3) limit are extracted from the resultant potentials by solving the Schrodinger equation. The NN phase shift in the SU(3) limit is shown to have qualitatively similar behavior as the experimental data. A bound H-dibaryon in the SU(3) limit is found to exist in the flavor-singlet J^P=0^+ channel with the binding energy of about 26 MeV for the lightest quark mass M_ps = 469 MeV. Effect of flavor SU(3) symmetry breaking on the H-dibaryon is estimated by solving the coupled-channel Schrodinger equation for Lambda Lambda - N Xi - Sigma Sigma with the physical baryon masses and the potential matrix obtained in the SU(3) limit: a resonant H-dibaryon is found between Lambda Lambda and N Xi thresholds in this treatment.Comment: 22 pages, 11 figures, Version accepted to publish on Nucl. Phys.