Numerical study of the meridional overturning circulation with “mixing hotspots” in the Pacific Ocean     

Takahiro Endoh  Toshiyuki Hibiya 《Journal of Oceanography》2006,62(3):259-266

Using an idealized ocean general circulation model, we examine the effect of “mixing hotspots” (localized regions of intense diapycnal mixing) predicted based on internal wave-wave interaction theory (Hibiya et al., 2006) on the meridional overturning circulation of the Pacific Ocean. Although the assumed diapycnal diffusivity in the mixing hotspots is a little larger than the predicted value, the upwelling in the mixing hotspots is not sufficient to balance the deep-water production; out of 17 Sv of the downwelled water along the southern boundary, only 9.2 Sv is found to upwell in the mixing hotspots. The imbalance as much as 7.8 Sv is compensated by entrainment into the surface mixed layer in the vicinity of the downwelling region. As a result, the northward transport of the deep water crossing the equator is limited to 5.5 Sv, much less than estimated from previous current meter moorings and hydrographic surveys. One plausible explanation for this is that the magnitude of the meridional overturning circulation of the Pacific Ocean has been overestimated by these observations. We raise doubts about the validity of the previous ocean general circulation models where diapycnal diffusivity is assigned ad hoc to attain the current magnitude suggested from current meter moorings and hydrographic surveys.  相似文献   

Mean flow and variability in the southwestern East Sea     

Kyung-Il Chang  Nelson G. Hogg  Moon-Sik Suk  Sang-Kyung Byun  Young-Gyu Kim  Kuh Kim 《Deep Sea Research Part I: Oceanographic Research Papers》2002,49(12)

The Ulleung Basin is one of three deep basins that are contained within the East/Japan Sea. Current meter moorings have been maintained in this basin beginning in 1996. The data from these moorings are used to investigate the mean circulation pattern, variability of deep flows, and volume transports of major water masses in the Ulleung Basin with supporting hydrographic data and help from a high-resolution numerical model. The bottom water within the Ulleung Basin, which must enter through a constricted passage from the north, is found to circulate cyclonically—a pattern that seems prevalent throughout the East Sea. A strong current of about 6 cms⁻¹ on average flows southward over the continental slope off the Korean coast underlying the northward East Korean Warm Current as part of the mean abyssal cyclonic circulation. Volume transports of the northward East Korean Warm Current, and southward flowing East Sea Intermediate Water and East Sea Proper Water are estimated to be 1.4 Sv (1 Sv=10⁻⁶ m³ s⁻¹), 0.8 Sv, and 3.0–4.0 Sv, respectively. Deep flow variability involves a wide range of time scales with no apparent seasonal variations, whereas the deep currents in the northern East Sea are known to be strongly seasonal.  相似文献   

辽东半岛南部地区滨海黄土的沉积特征   总被引：8，自引：2，他引：8  

李雪铭 《海洋科学》2001,25(1):32-35

分布在孙东半岛南端滨海地区的黄民庙岛群岛、胶辽半岛黄土一起构成了我国大陆黄土分布的最东界。通过对滨海马兰黄土粒度分布的因子对应分析、拟合度计算，结合滨海黄土的孢粉分析资料，初步认为：滨海黄土是风成的，是来自西北内陆的粉砂与冰期低海面海底砂混合堆积的产物，对应的样品因子载荷值及拟合度值计算表明，粒度分布中＞4φ粒级的细粒部分主要来自西北内陆，＜4φ粒级源于渤海湾西部。  相似文献   

Determining the age of water and long-term transport timescale of the Chesapeake Bay   总被引：5，自引：0，他引：5  

Jian Shen  Harry V. Wang 《Estuarine, Coastal and Shelf Science》2007,74(4):585-598

The concept of age of water (AW) is applied to the Chesapeake Bay to investigate the long-term transport properties for dissolved substances. A real-time calibrated hydrodynamic Chesapeake Bay model in 3 Dimensions (CH3D), employing a boundary-fitted curvilinear grid, is used for the study. The long-term transport properties, represented by AW, are investigated under the conditions of low river inflow of 1995 and high river inflow of 1996, as well as for constant mean inflows. The influences of freshwater, density-induced circulation, and wind-induced transport on age distribution have been investigated. Model results show that river inflows, wind stress, and density-induced circulation play important roles in controlling the long-term transport in the Bay. The model results shows that it requires 120–300 days for a marked change in the characteristics of the pollutant source discharged into the Bay from the Susquehanna River to affect significantly the conditions near the mouth under different hydrodynamic conditions. An increase of river discharge results in increases of downstream residual current and gravitational circulation, and thus reduces AW. The density-induced circulation contributes to the transport substantially. The dissolved substances discharged into the Bay are transported out of the Bay more rapidly when the estuary becomes more stratified. Southeasterly and southwesterly winds have strong impacts on the transport compared to the northeasterly and northwesterly winds. The former increases lateral and vertical mixing significantly. Consequently, the gravitational circulation is reduced and the transport time is increased by 50%. The model results provide useful information for understanding the long-term transport processes in the Bay.  相似文献   

热带太平洋深海微生物的若干生理生态特征     

骆祝华  裴耀文  黄翔玲  叶德赞 《海洋学报》2006,28(5):130-137

从2001年春、秋季于热带太平洋区采集到的深海样品中共分离到110株微生物,从中挑取31株进行形态特征和对环境理化因子适应特征的研究,同时利用Biolog微生物自动鉴定系统进行菌种鉴定和碳源代谢分析.结果表明:31株微生物中2株为酵母,21株为革兰氏阳性细菌,8株为革兰氏阴性细菌,来自底质的细菌菌株阳性菌占优势,而海水、蓝藻中阴性菌居多;温度、盐度、pH适应性试验表明,严格意义上的狭适性微生物不到总数的1/3,而具有较宽生态幅的广适性微生物占有相当大的比例.另一方面,耐冷菌、中度嗜盐菌和抗碱菌在这些微生物中的比例很高,同时,来自蓝藻的菌株大多数在4℃下不生长,而来自上覆水和底质的菌株可在4℃生长,这些都体现了微生物对生存环境的响应.31株微生物经Biolog鉴定12株得出鉴定结果.15株革兰氏阳性细菌对95种碳源的利用能力分析表明,不同菌株可利用碳源的数目从3种到46种不等,差异很大,体现了深海微生物营养类型的极大多样性;同时,发现有8种碳源可被一半以上的受试菌株所利用,这些碳源均是微生物各类代谢途径中的重要中间代谢物.  相似文献   

钦州湾内湾贝类养殖海区水环境特征及营养状况初探     

韦蔓新  童万平  赖廷和  何本茂 《海洋科学进展》2001,19(4):51-55

根据 1 998年 1 0月和 1 999年 5月的调查资料 ,阐述了钦州湾内湾水环境特征及 N/P的变化 ,以 DIN、DIP、COD和 Chl- a为富营养化指标 ,用营养状态质量指数 (NQI )分析探讨了该湾的营养状态 ,并从富营养角度讨论了该湾的污染程度  相似文献   

红树植物白骨壤叶片衰老过程中叶肉细胞Ca2+水平的变化     

杨盛昌  谢潮添  陈文列 《台湾海峡》2003,22(2):145-149,T001

用焦锑酸钙沉淀的电镜细胞化学方法，研究了白骨壤叶片衰老过程中叶肉细胞Ca^2 水平的变化．结果表明，在白骨壤幼叶和成熟叶叶肉细胞中，焦锑酸钙沉淀颗粒大量出现在液池和细胞间隙中，细胞壁中也可见少量沉淀，而细胞基质中则看不到焦锑酸钙沉淀．在衰老叶中，细胞基质和细胞膜上焦锑酸钙沉淀增加，而液泡和细胞间隙中的锑酸钙沉淀则显著减少，并且叶绿体外膜部分破损，结构破坏，核膜与液泡膜内部结构模糊，叶绿素含量、净光合速率、气扎手率和蒸腾速率显著下降．Ca^2 的区域性分布的变化与植物叶片衰老密切相关。  相似文献   

Ice Sheet-Thermohaline Circulation Interactions in a Climate Model of Intermediate Complexity   总被引：3，自引：0，他引：3  

Zhaomin Wang  Lawrence A. Mysak 《Journal of Oceanography》2001,57(4):481-494

A vertically integrated dynamic ice sheet model is coupled to the atmosphere-ocean-sea ice-land surface climate model recently developed by Wang and Mysak (2000). The background lateral (east-west) ice sheet discharge rate used by Gallee et al. (1992) is reduced and the planetary emissivity is increased (to parameterize the cooling effect of a decrease of the atmospheric CO₂ concentration), in order to build up substantial ice sheets during a glacial period and hence set the stage for ice sheet-thermohaline circulation (THC) interactions. The following iceberg calving scheme is then introduced: when the maximum model height of the North American ice sheet reaches a critical value (2400 m), a prescribed lateral discharged rate is imposed on top of the background discharge rate for a finite time. Per a small prescribed discharge rate, repeated small iceberg calving events occur, which lead to millennial-scale climate cycles with small amplitudes. These are a crude representation of Dansgaard-Oeschger oscillations. Over one such cycle, the zonally averaged January surface air temperature (SAT) drops about 1.5°C at 72.5°N. However, a large prescribed lateral discharge rate leads to the shut down of the THC. In this case, the January SAT drops about 5°C at 72.5°N, the sea ice extent advances equatorward from 57.5° to 47.5°N and the net ice accumulation rate at the grid of maximum ice sheet height is reduced from 0.24 to 0.15 m/y. Since data strongly suggest that a collapsed THC was not a steady state during the last glacial, we restore the THC by increasing the vertical diffusivity in the North Atlantic Ocean for a finite time. The resulting climate cycles associated with conveyor-on and conveyor-off phases have much larger amplitudes; furthermore, the strong iceberg calving events lead to a larger loss of ice sheet mass and hence the period of the oscillations is longer (several thousand years). This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

科氏力对河口分汊的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

金元欢  沈焕庭 《海洋科学》1993,17(4):52-56

以长江口、黄河口、珠江口、闽江口等几个分汊河口为例,分析了科氏力在河口分汊中的作用。结果表明,涨落潮流路分歧主要通过形成涨落潮冲刷槽和中央缓流区浅滩而逐渐使河口产生分汊;水面横比降则以横向环流和横向切滩两种形式,或堆积或冲刷,导致河口分汊。  相似文献   

广东红海湾、珠江口及电白—阳江近海第四纪沉积     

康长生  杨胜明  廖志良 《热带海洋学报》1997,(1)

根据物探和钻探资料，研究区内第四纪沉积物可分为两部分，下部地震反射结构复杂，斜层理发育，粒度较粗，为晚更新世产物；上部的地震反射结构简单，呈水平状或近水平状结构，粒度较细，为全新世沉积。  相似文献