Seasonal and long-term sea level variability in the marginal seas of the Arctic Ocean

One of the parameters useful for monitoring large-scale climate variability in the Arctic Ocean is sea level. It integrates virtually all static and dynamic processes in the hydrosphere and atmosphere of the Arctic. Previously unavailable mean monthly sea level data at 44 coastal and island stations in the Kara, Laptev, East Siberian and Chukchi seas covering years from 1950 to 1990 were used to analyse seasonal and inter-annual variability. Sea level has a significant annual cycle with an average seasonal amplitude (from peak to peak) in the coastal zone of the Arctic seas on the order of 20 - 30 cm. The analysis of inter-annual and inter-decadal changes has shown that at nearly all stations in the Kara, Laptev, East Siberian and Chukchi seas from the beginning of the 1950s through the end of 1980s there is a positive trend in sea level variability. The main contribution to the sea level rise was in the 1980s; on average for the coastal zone of Siberian shelf the sea level in the 1980s was 5-6 cm higher than in the previous decades. A reasonable agreement between observed decadal mean sea level values and the results of diagnostic model simulations suggests that this rise in the Arctic seas is connected with the reorganization of large-scale circulation of the Arctic Ocean, rather than the regional lowering of the coasts, as has been suggested previously.     

Circulation in the Arctic Ocean

Much information on processes and circulation within the Arctic Ocean has emerged from measurements made on icebreaker expeditions during the past decade. This article offers a perspective based on these measurements, summarizing new ideas regarding how water masses are formed and how they circulate. Best understood at present is the circulation of the Atlantic Layer and mid-depth waters, to depths of about 1700 m, which move in cyclonic gyres in the four major basins of the Arctic Ocean. New ideas on halocline formation and circulation are directly relevant to concerns regarding changes in ice thickness. The circulation of the halocline water in part mimics that of the underlying Atlantic Layer. A number of large eddies contributing to water mass transport have been observed. The circulation of freshwater from the Pacific Ocean and from river runoff has been better delineated. Circulation within the surface layer resembles the circulation of ice, but is different in several respects. Least understood is the circulation of the deepest waters, though some information is available. Recent observed changes in the surface waters and warm Atlantic Layer have been correlated with the North Atlantic Oscillation. While these changes are dramatic, the qualitative circulation pattern may not have been altered significantly.     

Acoustic thermometry in the Arctic Ocean

Large increases in the temperature of the Atlantic Layer in the Arctic Ocean have been observed since the early to mid-1990s and have continued through to the present. These changes were detected in 1994 and in 1999 with acoustic "sections" using acoustic thermometry. Both icebreaker and submarine CTD sections have confirmed these observations. Calculations of the travel time of acoustic mode 2 for the submarine CTD sections show a linear correlation with the mean temperature of the Atlantic Layer of the section. A cabled-to-shore undersea mooring system of Arctic Ocean observatories is needed to provide real-time year-round observations using conventional as well as acoustic remote sensing techniques.     

Numerical simulation of the propagation of P waves in fractured media

We study the propagation of P waves through media containing open fractures by performing numerical simulations. The important parameter in such problems is the ratio between crack length and incident wavelength. When the wavelength of the incident wavefield is close to or shorter than the crack length, the scattered waves are efficiently excited and the attenuation of the primary waves can be observed on synthetic seismograms. On the other hand, when the incident wavelength is greater than the crack length, we can simulate the anisotropic behaviour of fractured media resulting from the scattering of seismic waves by the cracks through the time delay of the arrival of the transmitted wave. The method of calculation used is a boundary element method in which the Green's functions are computed by the discrete wavenumber method. For simplicity, the 2-D elastodynamic diffraction problem is considered. The rock matrix is supposed to be elastic, isotropic and homogeneous, while the cracks are all empty and have the same length and strike direction. An iterative method of calculation of the diffracted wavefield is developed in the case where a large number of cracks are present in order to reduce the computation time. The attenuation factor Q ⁻¹ of the direct waves passing through a fractured zone is measured in several frequency bands. We observe that the attenuation factor Q ⁻¹ of the direct P wave peaks around kd = 2, where k is the incident wavenumber and d the crack length, and decreases proportionally to ( kd ) ⁻¹ in the high-wavenumber range. In the long-wavelength domain, the velocity of the direct P wave measured for two different crack realizations is very close to the value predicted by Hudson's theory on the overall elastic properties of fractured materials.     

Arctic Ocean manganese contents and sediment colour cycles

Cyclical variations in colour and manganese content in sediments from the central Arctic Ocean have been interpreted to represent climatically controlled changes in the input of Mn from the Siberian hinterland, and/or variations in the intermediate and deep water ventilation of the Arctic basins, although a diagenetic origin has not been excluded. A reinvestigation of core 96/12-1pc using an Itrax X-ray fluoresence (XRF) core scanner confirms that these colour cycles are indeed controlled by variations in Mn content, although changes in the source region of the sediment may override the Mn colour signal in certain intervals. The prominent Mn cycles show no correspondence to any of the other measured elements. This decoupling of Mn and the bulk chemistry of the sediment is taken to indicate that the cycles observed are caused by variations in water column ventilation and riverine input, rather than variations in sediment source or diagenesis. We therefore conclude that the Mn maxima do represent warm phases with increased ventilation and/or riverine input, and that they therefore could be used for chronostratigraphic correlation between cores from the central Arctic Ocean, where traditional isotope stratigraphy is difficult or impossible to establish because of the lack of calcareous microfossils.     

Radiation of lamp and optimized experiment using artificial light in the Arctic Ocean

A winter optical experiment by an artificial lamp was conducted in the Amundsen Bay of Arctic Ocean from November of 2007 to January of 2008.The radiation field emitted from an artificial lamp was measured and is introduced in this paper ,and the optimized experiment project is discussed.It is demonstrated that the minimum size allowed of the lamp is determined by both the field of view(FOV) of optical instrument and the measuring distance from the lamp.Some problems that might influence on the experiment result often occur for a simple fluorescent lamp, such as instability,spatial nonuniformity,light divergence,effect of lamp temperature ,etc.By the analysis of the light radiation,three kind of measures are proposed to control the quality of the experiment,i.e.keeping consistency of lamp size with FOV of instrument,calibrating in situ downwind,and conducting measurement in effective range.Among them,the downwind calibration is the key step to overcome most problems arose by the lamp.The experiment indicated that the reliable results can be obtained only when the optical measurement is coordinated with the radiation field of artificial lamp.The measured radiation property of the lamp was used to advise the field experiment to minimize measuring error.As the experiment by artificial lamp was the first attempt in the Arctic Ocean,the experience given by this paper is a valuable reference to the correlative studies.     

国际北冰洋地质、地球物理大洋科考进展

受常年海冰限制, 北冰洋科学考察程度远低于其他大洋。系统的北冰洋科学调查始于20世纪90年代, 得益于科考破冰船、潜艇等新型调查设备和手段的使用, 科研人员可以主动选择研究目标和对象, 并成功开展了多次地质与地球物理科学考察, 包括海冰科学探索项目(SCICEX)、北极洋中脊考察航次(AMORE 2001)、加科尔洋中脊热液硫化物考察(AGAVE)、北极钻探航次(IODP 302)等。回顾了北冰洋地质与地球物理科学考察进展, 归纳了主要科学问题: 北冰洋主要地质单元大地构造属性及演化、超慢速扩张洋中脊构造与成矿特征、北冰洋新生代古海洋演化。北冰洋地质与地球物理科学考察进展表明: (1)调查手段是制约北冰洋科考水平的关键因素; (2)破冰船与常规探测手段结合是北冰洋科考的重要发展趋势; (3)近底探测手段有助于解决北冰洋主要地质科学问题。     

Upper layer circulation of the Nordic seas as inferred from the spatial distribution of heat and freshwater content and potential energy

The spatial distribution of heat and freshwater content and potential energy of a several hundred metre thick surface layer are computed for the Nordic seas and adjacent parts of the northern North Atlantic and the Arctic Ocean using a total of almost 100 000 hydrographic stations. The fields clearly show the major features of the area's circulation, with warm salty water in the eastern part and fresher, colder water in the western part. Comparisons with published estimates show that the potential energy field, representing the baroclinic part of the flow, accounts for about 30 % of the total flow but roughly 100 % of the flow of Polar Water in the northern part of the East Greenland Current, about 50 % of the total flow in the Norwegian Atlantic Current, and just a small fraction of the flow in the eastern part of Fram Strait. This suggests that the barotropic circulation is quite important in many parts of the Nordic seas. The barotropic circulation is also clearly seen by its effects on the integrated fields with isolines following deep bathymetric contours. We speculate that the barotropic circulation in combination with topographic obstacles, like the Greenland–Scotland Ridge and the ridge system in the Jan Mayen area, may have large impact on the spreading of freshwater and heat in the Nordic seas.     

西北太平洋边缘海区海面变化多尺度解析及空间分异

利用MODWT对西北太平洋边缘海区8站位1965~2005年验潮序列进行多尺度分解,讨论了该区域海面变化多尺度波动特征及空间分异。结果显示年周期组分振幅随纬度增大而逐渐增大,半年周期组分振幅以中国沿岸最大,其余站位相对较小。年际尺度的波动中ENSO信号与1~2年尺度的准周期波动存在模态混叠现象,表现为对序列构形和不同时段的相关关系的影响。利用ICA方法从小波分解的年际尺度和信号中分离出的ENSO信号,表明不同纬度海面对ENSO事件的响应整体上呈现向高纬衰减的变化特征。基于小波相似性的分析结果显示,低纬各站海面对ENSO在各尺度上均呈现出显著的负相关,而中高纬地区则呈现出正相关。1980年之前和之后中高纬地区的海面对ENSO的响应出现了显著的差异,这可能与ENSO自身频率的调整有关。     

2012年夏季西北冰洋浮游动物群落特征

北冰洋夏季海冰覆盖面积在2012年达到低值。为了了解海冰变化对浮游动物群落的影响, 利用夏季西北冰洋22个站位的网采样品, 通过种类组成和丰度研究了群落的类型、结构和地理分布, 探讨了其分布特征与环境因子的关系。根据记录到的54种(类)浮游动物, 21站位可以划分成在地理上基本隔离的三个浮游动物群落: 楚科奇海南部群落, 藤壶幼体数量占优, 站位丰度百分比在56.6%—79.8%之间, 桡足类次之(18.0%—42.2%), 同时还含有少量的白令海种类;楚科奇海中北部群落以广布性桡足类占绝对优势(62.3%—96.8%), 藤壶幼体次之(0—30.9%);深海群落浮游动物的丰度极低, 组成上以桡足类为主(71.6%—89.8%), 且多数是体型较大极地种。楚科奇海陆坡边缘的M06站丰度较高但是种类组成与深海站位相似, 没有归入任何群落。两个浅水群落优势种都是北极哲水蚤(Calanus glacialis)、伪哲水蚤类(Pseudocalanus sp.)、圆胃住囊虫(Oikopleur vanhoffeni)以及藤壶幼体(Barnacle larva), 但优势度各异。深海群落优势种较多, 北极哲水蚤(Calanus glacialis)、极北哲水蚤(Calanus hyperboreus)、细长长腹水蚤(Metridia longa)以及北极拟真刺水蚤(Paraeuchaeta glacialis)等体型较大的桡足类优势度较高, 体型较小的矮小微哲水蚤(Microcalanus pygmaeus)、长腹剑水蚤(Oithona similis)优势度相对较低。与群落类型按维度和深度的变化趋势一致, 统计分析显示表层温度和表层盐度是最重要的影响因子。与海冰覆盖面积较高的2003年相比, 群落类型和地理分布没有显著变化, 但是楚科奇海浮游动物丰度增加了1—2倍, 深海群落丰度降低而组成上大型种类比例升高。     

Anomalous sea-ice reduction in the Eurasian Basin of the Arctic Ocean during summer 2010

During the summer of 2010 ice concentration in the Eurasian Basin, Arctic Ocean was unusually low. This study examines the sea-ice reduction in the Eurasian Basin using ice-based autonomous buoy systems that collect temperature and salinity of seawater under the ice along the course of buoy drift. An array of GPS drifters was deployed with 10 miles radius around an ice-based profiler, enabling the quantitative discussion for mechanical ice divergence/convergence and its contribution to the sea-ice reduction. Oceanic heat fluxes to the ice estimated using buoy motion and mixed-layer (ML) temperature suggest significant spatial difference between fluxes under first-year and multi-year ice. In the former, the ML temperature reached 0.6 K above freezing temperature, providing >60–70 W m^?2 of heat flux to the overlying ice, equivalent to about 1.5 m of ice melt over three months. In contrast, the multiyear ice region indicates nearly 40 W m^?2 at most and cumulatively produced 0.8 m ice melt. The ice concentration was found to be reduced in association with an extensive low pressure system that persisted over the central Eurasian Basin. SSM/I indicates that ice concentration was reduced by 30–40% while the low pressure persisted. The low ice concentration persisted for 30 days even after the low dissipated. It appears that the wind-forced ice divergence led to enhanced absorption of incident solar energy in the expanded areas of open water and thus to increased ice melt.     

Outflow of Pacific water from the Chukchi Sea to the Arctic Ocean

Pacific water exits the Chukchi Sea shelf through Barrow Canyon in the east and Herald Canyon in the west,forming an eastward-directed shelfbreak boundary current that flows into the Beaufort Sea.Here we summarize the transformation that the Pacific water undergoes in the two canyons,and describe the characteristics and variability of the resulting sbelfbreak jet,using recently collected summertime hydrographic data and a year-long mooring data set.In both canyons the northward-flowing Pacific winter water switches from the western to the eastern flank of the canyon,interacting with the northward-flowing summer water.In Barrow canyon the vorticity structure of the current is altered,while in Herald canyon a new water mass mode is created.In both instances hydraulic effects are believed to be partly responsible for the observed changes.The shelfbreak jet that forms from the canyon outflows has distinct seasonal configurations,from a bottom-intensified flow carrying cold,dense Pacific water in spring,to a surface-intensified current advecting warm,buoyant water in summer.The current also varies significantly on short timescales,from less than a day to a week.In fall and winter much of this mesoscale variability is driven by storm events,whose easterly winds reverse the current and cause upwelling.Different types of eddies are spawned from the current,which are characterized here using hydrographic and satellite data.