Thickness Of Surface Mixed Layer Research Articles

Karakteristik Fisik Perairan Selatan Kabupaten Kepulauan Tanimbar pada Musim Transisi II

This study investigated the characteristics of stratification and vertical stability of southern waters of Tanimbar Islands Regency. CTD Data from World Ocean Database 2018 especially November 1995 to represent second transitional season were utilized in this study. The CTD data were processed using Ocean Data View. This study showed that vertically the temperature of the surface layer ranged between 29 to 30 oC and the thickness of surface mixed layer was found to be 44 m. The thermocline layer has temperature ranging between 12 to 28 oC and a maximum depth of 306 m. Below thermocline layer temperature reduced to reach less than 7 oC (depth > 500 m). On the halocline layer, a high saline water was found between 66 - 94 m depth and was located on the southern part between Barbar Islands and Tanimbar Islands. Water mass was found to be unstable in the mixing layer.

Enhanced turbulent mixing induced by strong wind on the South China Sea shelf

Integrated observations were made on the South China Sea shelf at 19°37’ N, 112°04’ E, under strong wind and heavy raining weather conditions in August 2005. Current data were obtained using a moored 150-kHz Acoustic Doppler Current Profiler, turbulent kinetic energy dissipation rate were measured with TurboMapII, and temperature was recorded by thermistor chains. Both the mixed layer thickness and the corresponding mean dissipation rate increased after the strong wind bursts. Average surface mixed layer thickness was 13.4 m pre-wind and 22.4 m post-wind, and the average turbulent dissipation rate in the mixed layer pre-wind and post-wind were 4.26 × 10−7 and 1.09 × 10−6 Wkg−1, respectively. The post-wind dissipation rate was 2.5 times larger than the pre-wind dissipation rate in the interior layer and four times larger in the intermediate water column. Spectra and vertical mode analysis revealed that near-inertial motion post-wind, especially with high modes, was strengthened and propagated downward toward the intermediate layer. The downward group velocity of near-inertial current was about 8.1 × 10−5 ms−1 during the strong wind bursts. The mean percentage of wind work transmitted into the intermediate layer is about 4.2 %. The ratio of post-wind high-mode energy to total horizontal kinetic energy increased below the surface mixed layer, which would have caused instabilities and result in turbulent mixing. Based on these data, we discuss a previous parameterization that relates dissipation rate, stratification, and shear variance calculated from baroclinic currents with high modes (higher than mode 1) which concentrate a large fraction of energy.

Comment on “Improved global maps and 54‐year history of wind‐work on ocean inertial motions” by Matthew H. Alford: Time aliasing in estimating the wind‐induced inertial energy

where t is time, Z = u + iv with u and v the eastward and northward components of horizontal velocity, X = (Tx + iTy)/r with Tx and Ty the eastward and northward components of wind stress and r water density, H is the thickness of surface mixed layer, and w = r + if with f the local inertial frequency and r the damping constant parameterizing the downward radiation of energy through the base of the surface mixed layer. Subtracting the Ekman transport component ZE = X/wH from equation (1), the inertial oscillation component ZI = Z ZE is given by

Dependence of the Arctic Ocean ice thickness distribution on the poleward energy flux in the atmosphere

The sensitivity of the Arctic Ocean ice cover on the atmospheric poleward energy flux, D, is studied using a coupled column model of the ocean, ice, and atmosphere. In the model, the ice cover is described by a thickness distribution and the atmosphere is a simple two‐stream gray body in radiative equilibrium. It is shown that the thickness distribution, in combination with the albedo function, gives a strong nonlinear response to positive perturbations of D. The response on D is sensitive to the albedo parameterization and the shape of the thickness distribution, controlled by ridging and divergence. An increase of about 9 W m−2 from a standard value of D = 103 W m−2 has a dramatic effect, reducing the ice thickness by more than 2 m, and generates a large open‐water fraction during summer. The reduction of ice thickness is characterized by a clear transition between two regimes, going from a regime where first‐year ice survives the next summer melt period to a seasonal ice regime where the first‐year ice melts completely. It is shown that the existence of seasonal ice regime is dependent on the surface mixed layer thickness. The model enters a completely ice‐free state if the thickness of the mixed layer is increased above a threshold value. The adjustment timescale for the ice cover is 6 years for small positive and negative perturbations in D. For larger positive perturbations of about 10 W m−2, the adjustment timescale is up to 20 years.

Primary production at 47°N and 20°W in the North Atlantic Ocean: a comparison between the 14C incubation method and the mixed layer carbon budget

Abstract Primary production in the oceanshas been estimated mainly on the basis of in vitro incubation measurements. An implicit assumption is that the growth rate of phytoplankton observed in vitro represents that occurring in the freely circulating water of the euphotic zone. We have tested this assumption at 47°N-20°W in the eastern North Atlantic Ocean during the initial stages of a spring phytoplankton bloom. The daily primary production was measured by means of the 14C assimilation method, in which the incubation bottles were suspended in the ocean from dawn to dusk daily (about 14 h). The mean daily carbon assimilation rate in the photic zone and in the mixed layer was 107 ± 23 and 84 ± 18 mmol C m −2 day ∗−1 (where day ∗ = 14 daylight hours), respectively, during the 12-day period between 26 April and 7 May 1989. The mixed layer carbon assimilation data are found to be consistent with the in situ CO2 utilization rate of 82 ± 17 mmol C m − day ∗−1 estimated on the basis of the thickness of surface mixed layer, the CO2 concentration in it, and the air-sea CO2 flux. We conclude that primary production in the open ocean appears to be well represented by the in vitro measurements, if the samples are incubated under the in situ light and temperature conditions. The mean daily reduction rate of the total CO2 concentration observed in the mixed layer over the 12-day period is 2.3 μmol kg−1 day−1, about 75% of the rate, 3.1 μmol kg−1 day∗−1, expected from the rate of primary production. About 8.5% of this difference is explained by the atmospheric CO2 flux, and the remaining 16.5% may be attributed to the respiration and the influx of CO2-rich waters from the mixed layer.

The effect of sediment mixing on Pb-210 accumulation rates for the Washington continental shelf

Nine cores from the Washington continental shelf were examined by radiochemical techniques in order to evaluate the effect of mixing on the calculation of sediment accumulation rates from Pb-210 profiles. Th-234 profiles indicate mixing coefficients of 140 cm 2 yr −1 for the seabed offshore from the Columbia River and 47 cm 2 yr −1 for the seabed of the Mid-Shelf Silt Deposit (75 km north of the Columbia River). These large mixing coefficients demonstrate that particles can penetrate to the base of the intensely mixed surface layer (∼ 10 cm) within one year after emplacement at the seabed surface. Observed depths of Cs-137 penetration within the seabed are compared with depths predicted from the surface mixed-layer thickness and the Pb-210 accumulation rate. The observed and predicted depths agree well at all but one station. At this station a combination of Th-234, Co-60, Pb-210 and Cs-137 profiles suggests that active mixing occurs below the intensely mixed surface layer. The agreement of Pb-210 and Cs-137 data at the other stations, however, indicates a general absence of deep mixing on the Washington shelf. Thus, the apparent accumulation rates calculated from Pb-210 profiles (below the intensely mixed surface layer) on the Washington shelf generally reflect the true rates of sediment accumulation.