基于CESM1.2.2模拟的浪致混合对末次冰盛期和工业革命前气候的影响

海洋上层垂向混合在模式中发挥重要的作用,以往的研究表明垂向混合的不足使得模拟的海洋温度和混合层深度与观测存在显著偏差。前人提出一种修正方案,考虑波浪产生的垂向混合,将由表面风作用下产生的波浪这样一个实际物理过程的湍混合进行参数化,其结果被证实能够显著提高模式模拟和预报的准确性。本文首次将浪致混合引入海气耦合的古气候模式,基于末次冰盛期和工业革命前2种不同的气候条件,探究浪致混合在海气耦合模式中的作用。在不同气候背景下,由于风场强度的不同,导致末次冰盛期浪致混合的强度小于工业革命前,但2个气候时期都体现出中纬度混合强度最大的特点。将浪致混合加入到气候模式中,模拟结果表明：中纬度海域2个时期都出现海表面降温而次表层升温的现象,但末次冰盛期的表面降温强度弱于工业革命前状态;不同月份下的模拟结果显示,在南北半球的夏季,海洋表层温度的降温最为显著。中纬度海域海洋上混合层深度在年平均条件下2个气候背景时期都出现加深现象,但末次冰盛期的加深程度弱于工业革命前;不同月份下的模拟结果显示,在南北半球的冬季,混合层加深的变化达到极值。另一方面,在高纬度海域,末次冰盛期的海表面温度出现了显著升高,这是由于浪...     

浪致混合对亚热带冬季海洋混合强度的影响

上层海洋在全球气候系统中起着至关重要的作用。对上层海洋层结及混合的模拟偏差一直是海洋和气候数值模式发展中悬而未决的问题。本文首先评估了CMIP5中45个模式对上层海洋层结模拟的偏差,确认了冬季亚热带地区海洋模式垂向混合偏强。随后,基于自然资源部第一海洋研究所地球系统模式(FIO-ESM v1.0),分别开展了1986-2005年期间包含和关闭海浪垂向混合情况下的数值实验,分析浪致混合对亚热带冬季海洋混合强度模拟的影响及机制。发现浪致混合使得气候模式中亚热带海域冬季的海洋层结增强,增强的层结使上层海洋更加稳定。首次揭示了增加浪致混合反而降低了海洋总体的垂向混合率:浪致混合使北半球冬季亚热带海域混合率从无浪实验的227 cm²/s降低到有浪实验的178 cm²/s,降低了21.6%;南半球冬季亚热带海域混合率从无浪实验的189 cm²/s降低到有浪实验的165 cm²/s,降低了12.7%。进一步分析发现,浪致混合主要是通过增加冬季亚热带海域上层海洋的热含量从而强化了海洋的层结,最终改善了气候模式对上层...     

Possible Density Change of the Origin of North Pacific Intermediate Water Due to Double Diffusion in the Mixed Water Region

In this study we test Talley's hypothesis that Oyashio winter mixed-layer water (26.5–26.6σ _θ) increases its density to produce the North Pacific Intermediate Water (NPIW) salinity minimum (26.7– 26.8σ_θ) in the Mixed Water Region, assuming a combination of cabbeling and double diffusion. The possible density change of Oyashio winter mixed-layer water is discussed using an instantaneous ratio of the change of temperature and salinity along any particular intrusion (R _l ). We estimate the range of R _l ^DD required to convert Oyashio winter mixed-layer water to the NPIW salinity minimum due to double diffusion, and then assume double-diffusive intrusions as this conversion mechanism. A double-diffusive intrusion model is used to estimate R _l ^DD in a situation where salt fingering dominates vertical mixing, as well as to determine whether Oyashio winter mixed-layer water can become the NPIW salinity minimum. Possible density changes are estimated from the model R _l ^DD by assuming the amount of density change due to cabbeling. From these results, we conclude that Oyashio winter mixed-layer water contributes to a freshening of the lighter layer of the NPIW salinity minimum (around 26.70σ_θ) in the MWR.     

Transformation of the Indonesian Throughflow Water by Vertical Mixing and Its Relation to Tidally Generated Internal Waves

Numerical experiments with two-dimensional nonhydrostatic model have been performed to investigate tidally generated internal waves at the Dewakang sill at the southern Makassar Strait where two large-amplitude “bumps” of relatively shallow water exist. We investigate the effect of these features on vertical mixing, with emphasis on the transformation of the Indonesian throughflow (ITF) water properties. The result shows that large-amplitude internal waves are generated at both bumps by the predominant M₂ tidal flow, even though the condition of the critical Froude number and the critical slope are not satisfied. The internal waves induce such vigorous vertical mixing in the sill region that the vertical diffusivity attains a maximum value of 6 × 10⁻³ m²s⁻¹ and the salinity maximum and minimum core layers characterizing the ITF thermocline water are considerably weakened. Close examination reveals that bottom-intensified currents produced mainly by the joint effect of barotropic M₂ flow and internal tides generated in the concave region surrounding both bumps can excite unsteady lee waves (Nakamura et al., 2000) on the inside slopes of the bumps, which tend to be trapped at the generation region and grow into large-amplitude waves. Such generation of unsteady lee waves does not occur in case of one bump alone. Trapping and amplification of the waves in the sill region induce large vertical displacements (∼60 m) of water parcels during one tidal period, leading to strong vertical mixing there. Since the K₁ tidal currents are relatively weak, large-amplitude internal waves causing intense vertical mixing are not generated. This revised version was published online in July 2006 with corrections to the Cover Date.     

刘公岛海洋牧场底层海水溶解氧浓度的变化特征

由于缺乏长期观测资料,前人对山东半岛邻近海域海水溶解氧的时间变化和空间分布特征的研究较少。本文基于威海刘公岛海洋牧场于2016年7月20日至2017年3月14日期间,利用生态环境实时在线观测系统获得的底层海水的温度、盐度、水深、溶解氧数据,分析了该牧场海水溶解氧浓度的时间变化特征及其影响因素,并探讨了低氧灾害发生的可能性。结果表明在观测期间,该牧场海水溶解氧浓度以季节变化为主,冬季最大、夏季最小,其中2月份平均值最高,约为10.86mg/L,8月份平均值最低,约为5.91mg/L。同时海水溶解氧浓度也存在显著的小时变化和日变化,且变化幅度于8月份最大、3月份最小。影响海水溶解氧浓度变化的主要因素是海水温度,溶解氧浓度随着温度的季节性变化而变化。夏季,水体分层会使溶解氧浓度发生大幅度的降低,大风过程对于溶解氧浓度也有一定的影响,通过打破夏季的季节性温跃层使水体发生垂向混合从而为海底提供氧气,但大风过程之后的几天会出现溶解氧浓度降低的现象。本次研究发现刘公岛海洋牧场在观测期间不存在低氧现象。     

浪致混合对2016年北太平洋海表温度季节性预测的影响

上层海洋通过海气交换影响大气-海洋耦合系统,海浪引起的垂向混合影响上层海洋结构,从而在气候预测过程中发挥着重要的作用。本文基于国家海洋局第一海洋研究所地球系统模式（FIO-ESM）,以2016年为例,分别开展了耦合和关闭海浪模式情况下的短期气候预测实验,分析浪致混合对北太平洋海表温度（SST）季节性预测的影响。通过对模式预测的SST异常（SSTA）进行定量评估发现,浪致混合能够显著降低北太平洋高纬度海区预测误差,在（45°N,150°E）附近海区SSTA改善可达1℃,气候模式能够更好地预测SSTA的经向分布特征,特别是能够准确地反映25°~45°N海区SSTA分布特征。通过分析有浪和无浪两个实验的热收支贡献发现,垂向混合是导致上层海洋温度差异的主导影响因子。海浪通过改变垂向混合,使2016年北太平洋SST在高纬度海区大幅降低,在低纬度海区略有升高,最终提升了模式对北太平洋SST的季节性预测能力。     

Sensitivity studies with the three-dimensional multi-level model for tidal motion

A three-dimensional multi-level hydrodynamic model has recently been developed and applied to tidal motion in Singapore’s coastal waters. This paper describes a series of numerical experiments to evaluate the sensitivity of the tidal currents and elevations to model parameters. The results show that the predicted tidal elevations are insensitive to three model parameters: horizontal eddy viscosity coefficient (Smagorinsky constant, c_h), bottom friction coefficient (c_b) and internal friction coefficient (c_v), whereas the effects of these parameters are quite different for tidal current velocities. The velocities are slightly reduced with an increase in c_h and c_b. The bottom friction effects on velocity profiles increase with water depth. The effect of c_v might be significant for the tidal velocities at all levels. The velocities at upper layers of the water column decrease with the increase in c_v, whereas the velocities at the bottom layer show the reverse trend. The effects of three model parameters on the magnitude and phase of the simulated currents are in the order (from strong to weak) of c_v, c_b and c_h.     

Additional flux arising from unresolved scales in eddying ocean models

An analysis is presented of snapshot data (eastward and northward velocity components: u and v; tracer such as potential temperature: τ) from an eddy-resolving (Rgrid: 1/12°) ocean model experiment, in order to explore a method for improving eddy-permitting model performance. Horizontal 3 × 3 R-grid averages give the eddy-permitting grid (P-grid: 1/4°) variables: 〈u〉, 〈v〉, and 〈τ〉, where 〈〉 denotes the spatial P-grid scale average. The difference between the horizontal tracer flux across the boundary face of a P-grid and that across the corresponding faces of R-grids is estimated as F_2E. It is found that the correlations among the gradients of u, v, and τ give a good approximation F_2C to the estimated flux F_2E. The approximated flux is a function of these gradients and the grid size. A method is presented for implementing the F_2C for density to an eddying ocean model as an additional advection. Practical experiments were conducted with a realistic configuration. It is shown that the zonal mean isotherms in the Kuroshio extension region are more flattened in the run using the proposed method than in another run using the conventional horizontal biharmonic operator, suggesting that the additional flux correction leads to an enhancement of sub-basin scale mixing.     

A refinement of the previous hypothesis of turbulent energy spectrum

To refine the previous hypothesis of turbulent energy spectrum (Nan-niti, 1970), further theoretical consideration and a simple experiment using electric fans was carried out. From the hypothesis ofq=δε/δk andεq=const., the following relations are derived for the spectrumF, and the autocorrelation functionR:F(k)∼k _{−(5−2α)/3} andR(t)∼1−(t/τ)_2(1−α)/3, whereq is the local energy supply,ε the energy dissipation rate, andk the wavenumber,t the time,τ the lifetime of the largest eddy. The following further relations are also obtained:ε∼l _−α,v∼l _β,v∼τ _γ andγ=(1−α)/(2+α)=β/(1−β), wherel is the length scale of the phenomenon,v turbulent velocity,α=1/2,β=1/6, andγ=1/5. The experimental results support these relations.     

北太平洋涡旋对基于细尺度参数化的海洋内部混合的影响

基于Vector Geometry方法对2016—2018年的高度计资料进行涡旋识别,并使用细尺度参数化方法和Argo数据计算了涡旋附近的海洋内部扩散率,分析了北太平洋的涡旋对海洋内部混合的影响。结果显示,研究区域在涡旋影响下的平均扩散率比无涡旋影响下的值大6%,并且气旋涡增强了600—1200m深度的混合,对600—900m深度的混合影响最大,可达18%;反气旋涡明显增强了300—900m深度的混合,但对900—1200m深度的混合没有明显影响。随着与涡旋中心距离的增大,涡旋外围混合扩散率缓慢减小,涡旋内部混合扩散率变化不明显,此结果与2014年3—10月在24°—36°N、132°—152°E区域的一个个例分析结果一致。此外,随着涡旋强度的增大,海洋内部混合明显增强。统计结果表明,在研究区域, 90%的扩散率值在10^-5.5—10^-4m²/s范围内。     

Spatial distribution of phytoplankton in the White Sea in the late summer period with regard to the water structure and dynamics

The species composition and biomass of the phytoplankton, as well as the hydrophysical and hydrochemical characteristics of the water masses, were estimated for different areas of the White Sea at 24 stations for the period of August 26 to September 3, 2007. The micronutrient concentrations were lower compared to the average long-term values for the summer period. The total biomass of phytoplankton (B _t ) varied from 87 to 1914 mg C/m². For most of the studied sites, B _t was low; dinoflagellates were the most abundant species. Diatoms dominated in the areas of elevated hydrodynamic activity, i.e., in the Gorlo (vertical mixing of the water layers), in intrusions of the Gorlo water masses into the basin of the White Sea, and in the peripheral areas of the Dvina outflow current. The B _t was also the highest in the listed areas.     

A generalized coordinate ocean model and a comparison of the bottom boundary layer dynamics in terrain-following and in z-level grids

Sensitivity studies with a new generalized coordinate ocean model are performed in order to compare the behavior of bottom boundary layers (BBLs) when terrain-following (sigma or combined sigma and z-level) or z-level vertical grids are used, but most other numerical aspects remain unchanged. The model uses a second-order turbulence closure scheme that provides surface and BBL mixing and results in a quite realistic climatology and deep water masses after 100 year simulations with a coarse resolution (1° × 1°) basin-scale terrain-following grid. However, with the same turbulence scheme but using a z-level grid, the model was unable to produce dense water masses in the deep ocean. The latter is a known problem for coarse resolution z-level models, unless they include highly empirical BBL schemes.A set of dense water overflow experiments with high-resolution grids (10 and 2.5 km) are used to investigate the influence of model parameters such as horizontal diffusivity, vertical mixing, horizontal resolution, and vertical resolution on the simulation of bottom layers for the different coordinate systems. Increasing horizontal diffusivity causes a thinner BBL and a bottom plume that extends further downslope in a sigma grid, but causes a thicker BBL and limited downslope plume extension in a z-level grid. A major difference in the behavior of the BBL in the two grids is due to the larger vertical mixing generated by the turbulence scheme over the step-like topography in the z-level grid, compared to a smaller vertical mixing and a more stably stratified BBL in the sigma grid. Therefore, the dense plume is able to maintain its water mass better and penetrates farther downslope in the sigma grid than in the z-level grid. Increasing horizontal and vertical resolution in the z-level grid converges the results toward those obtained by a much coarser resolution sigma coordinate grid, but some differences remain due to the basic differences in the mixing process in the BBL.     

Zooplankton vertical migration and the active transport of dissolved organic and inorganic carbon in the Sargasso Sea

The least known component of the “biological pump” is the active transport of carbon and nutrients by diel vertical migration of zooplankton. We measured CO₂ respiration and dissolved organic carbon (DOC) excretion by individual species of common vertically migrating zooplankton at the US JGOFS Bermuda Atlantic Time-series Study (BATS) station. The inclusion of DOC excretion in this study builds on published research on active transport by respiration of inorganic carbon and allows a direct assessment of the role of zooplankton in the production of dissolved organic matter used in midwater microbial processes. On average, excretion of DOC makes up 24% (range=5–42%) of the total C metabolized (excreted+respired) and could represent a significant augmentation to the vertical flux that has already been documented for respiratory CO₂ flux by migrant zooplankton. Migratory fluxes were compared to other transport processes at BATS. Estimates of combined active transport of CO₂ and DOC by migrators at BATS averaged 7.8% and reached 38.6% of mean sinking POC flux at 150 m, and reached 71.4% of mean sinking POC flux at 300 m. DOC export by migrator excretion averaged 1.9% and reached 13.3% of annual DOC export by physical mixing at this site. During most of the year when deep mixing does not occur, diel migration by zooplankton could provide a supply of DOC to the deeper layers that is available for use by the microbial community. A carbon budget comparing migrant zooplankton transport to the balance of fluxes in the 300–600 m depth strata at BATS shows on average that the total migrant flux supplies 37% of the organic carbon remineralized in this layer, and that migrant DOC flux is more than 3 times the DOC flux gradient by diapycnal mixing. New estimates of active transport of both organic and inorganic carbon by migrants may help resolve observed imbalances in the C budget at BATS, but the magnitude is highly dependent on the biomass of the migrating community.     

Ocean temperature responses to Typhoon Mstsa in the East China Sea

The MASNUM wave-tide-circulation coupled model, with 21 layers in the vertical and （1/8） °horizontal resolution, was employed to investigate the oceanic responses to Typhoon Mstsa which traversed the East China Sea （ECS） during the period of 4 - 6 August, 2005. Numerical experiment results are analyzed and compared with observation. The responses of the sea surface temperature （SST）, in a focused area of （27° -29°N, 121° - 124°E）, include heating and cooling stages. The heating is mainly due to warm Kuroshio water transportation and downwelling due to the water accumulation. In the cooling stage, the amplitude of the simulated cold wake （ -3℃ ）, located on the right side of this typhoon track, is compared quite well with that of the satellite observed SST data. The wave-induced mixing（Bv） plays a key role for the SST cooling. Bv still plays a leading role, which accounts for 36%, for the ocean temperature drop in the upper ocean of 0 - 40 m, while the upwelling is responsible for 84% of the cooling for the lower layer of 40 - 70 m. The mixed layer depth （MLD） increased quickly from 28 to 50 m in the typhoon period. However, the simulated MLD without the wave-induced vertical mixing, evolution from 13 to 32 m, was seriously underestimated. The surface wave is too important to be ignored for the ocean responses to a typhoon.     

A study of estuarine flow using the roving adcp data

A study of estuarine flows during a neap tide was performed using 13-hour roving acoustic Doppler current profiles (ADCP) and conductivity-temperature-depth (CTD) profiles in the Altamaha River estuary, Georgia, U.S.A. The least-squared harmonic analysis method was used to fit the tidal (M₂) component and separate the flow into two components: the tidal and residual (M₂-removed) flows. We applied this method to depth-averaged data. Results show that the M₂ component demonstrates over 95% of the variability of observation data. As the flow was dominated by the M2 tidal component in a narrow channel, the tidal ellipse distribution was essentially a back-and-forth motion. The amplitude of M2 velocity component increased slightly from the river mouth (0.45 m/sec) to land (0.6 m/sec) and the phase showed fairly constant values in the center of the channel and rapidly decreasing values near the northern and southern shoaling areas. The residual flow and transport calculated from depth-averaged flow shows temporal variability over the tidal time scale. Strong landward flows appeared during slack waters which may be attributed to increased baroclinic forcing when turbulent mixing decreases.     

Distribution and photo-physiological condition of phytoplankton in the tropical and subtropical North Pacific

To better understand the vertical distribution of phytoplankton in the tropical and subtropical North Pacific, we used fast repetition rate fluorometry to investigate the photo-physiological condition of the phytoplankton assemblage in this region between February and March 2007. Along 155°E, between the equator and 24°N, the peak of fluorescence (F _m), an indication of the deep chlorophyll maximum (DCM), was deeper than the top of the nitracline and occurred at the 2.4 ± 1.3 % (mean ± SD) light depth (relative to 0 m). The photochemical efficiency (F _v/F _m) and effective absorption cross-section of photosystem II (σ_PSII) were low at the surface but increased rapidly at depths between the top of the nitracline (40–138 m) and the DCM (70–158 m), an indication that the photo-physiological condition of the phytoplankton improved below the top of the nitracline. The depth of the maximal F _v/F _m [Z(F _v/F _{m max})] was 18–32 m deeper than the DCM and corresponded to the 0.8 ± 0.2 % light depth. The values of F _v/F _m at the Z(F _v/F _{m max}) were 20 % higher than those at the DCM and averaged 0.48 ± 0.01. These results suggest that the phytoplankton assemblage beneath the DCM had a high potential photosynthetic performance capacity and was growing by using the very low ambient light in this region.     

Thickness of the mixed bottom layer in the Northern Atlantic

The thickness of the mixed bottom boundary layer (BBL) has been analyzed based on the CTD data at transoceanic sections in abyssal waters of the Northern Atlantic. The measurements were carried out at two transoceanic sections approximately along 48° N (ASV-99) and 5° N (AI-2000) in 1999 and 2000. These data, and the WOCE data obtained at four zonal sections (AR7E and AR12 along 57° N, AR01 along 24.5° S, and A06 along 7.5° N), were used for the calculation of the statistical characteristics of the BBL??s thickness H _B . The probability distribution function F(H _B ) was close to lognormal. The mean value ??H _B ?? at different latitudes was in the range from 30 to 60 m. The averaged BBL thickness = 46.1 m. The BBL??s thickness was about 1% of the ocean??s depth D; the ratio H _B /D was the minimum (0.8%) near the equator and increased up to 1.6% in the polar latitudes.     

Water mass exchange and diapycnal mixing at Bussol’ Strait revealed by water mass properties

Intensive CTD observations that resolve the mean and tidal components were done with a total of 129 casts in summer of 2001 at Bussol’ Strait. Based on these data and all the available historical data, we have revealed the outflow from Bussol’ Strait to the Pacific and the significant diapycnal mixing in the strait. In the range 27.0−27.3σ _θ , the water property in Bussol’ Strait is almost identical to that of the Kuril Basin Water (KBW). The KBW out of Bussol’ Strait forms a water mass front with the East Kamchatka Current Water (EKCW). This front also corresponds to the front of the Oyashio Current. In the lower part of the intermediate layer (27.3−27.6σ _θ ), part of the water in the strait is characterized by lower temperature, lower salinity, and higher dissolved oxygen than that of KBW and EKCW, which can be explained only by the diapycnal mixing. The strong diapycnal mixing in the strait can also be shown by the density inversion, occurrence frequency of which corresponds well to the amplitude distribution of the diurnal current. In the density range 26.7−26.8σ _θ , the water in Bussol’ Strait has the lowest potential vorticity, suggesting that it is a source region of the low potential vorticity water. Seasonal change of the water can reach up to a density of 26.8σ _θ around Bussol’ Strait. This leads us to propose that the combination of winter convection and local tidal mixing leads to effective ventilation of the intermediate layer.     

吕宋海峡及周边海域湍流混合的时空分布特征研究

利用1992—2002年的温盐深数据与2012—2016年的Argo数据,基于细尺度参数化方法研究了吕宋海峡及周边海域(12°—30°N,115°—129°E)湍流混合的时空分布特征,并分析了地形粗糙度、内潮以及风输入的近惯性能通量对湍流混合的影响。结果表明,吕宋海峡和东海陆坡处具有强混合的特征,扩散率高达4×10~(-3) m~2/s,主要是由内潮产生导致的,其中吕宋海峡主要是M2、K1和O1内潮的贡献,而东海陆坡处主要是M_2内潮的贡献;南海北部也呈现较强的混合,且陆坡处的混合比海盆高1—2个量级;南海中央海盆和离岸的菲律宾海混合较弱,扩散率为O (10-5 m2/s)。此外,在研究区域内,湍流混合的年际变化和季节变化均不明显,且混合扩散率与风输入的近惯性能通量未表现出明显的季节相关。     

Saldanha Bay,South Africa I: the use of ocean colour remote sensing to assess phytoplankton biomass

The efficacy of ocean colour remote sensing in assessing the variability of phytoplankton biomass within Saldanha Bay is examined. Satellite estimates of chlorophyll a (Chl a) were obtained using the maximum peak-height (MPH) algorithm on full-resolution (300?m) data from the Medium Resolution Imaging Spectrometer (MERIS). Subsurface Chl a maxima often occur within Saldanha Bay below the mean detection depth of the satellite (1.5?m) during periods of thermal stratification. Consequently, the MPH product was poorly correlated to in situ data from 4?m depth (r² and average relative percentage difference [RPD] of 0.094 and 53% respectively); however, the coefficient of determination was much improved if limited to in situ data collected under conditions of mixing (r² and RPD of 0.869 and 89%, respectively). Composites of monthly MPH Chl a data reveal mean concentrations consistent with in situ seasonal trends of phytoplankton biomass, confirming the capability of the MPH algorithm to qualitatively resolve surface Chl a distribution within the bay.