Mesozooplankton in the Arctic Ocean in summer

The biomass, species and chemical composition of the mesozooplankton and their impact on lower food levels were estimated along a transect across the Arctic Ocean. Mesozooplankton biomass in the upper 200 m of the water column was significantly higher (19–42 mg DW m^-3) than has previously been reported for the Arctic Ocean, and it reached a maximum at ca. 87°N in the Amundsen Basin. The lowest values were recorded in the Chukchi Sea and Nansen Basin, where ice cover was lower (50–80%) than in the central Arctic Ocean. In the deeper strata (200–500 m) of the Canadian and Eurasian Basins, the biomass was always much lower (4.35–16.44 mg DW m^-3). The C/N (g/g) ratio for the mesozooplankton population was high (6.5–8.5) but within the documented range. These high values (when compared to 4.5 at lower latitudes) may be explained by the high lipid content. Mesozooplankton accounted for approximately 40% of the total particulate organic carbon in the upper 100 m of the water column. Mesozooplankton species composition was homogeneous along the transect, consisting mainly of copepods (70–90% of the total number). It was dominated by four large copepod species (Calanus hyperboreus, C. glacialis, C. finmarchicus and Metridia longa), which together accounted for more than 80% of the total biomass. According to measurements of gut pigment and gut turnover rates, the mesozooplankton on average ingested between 6 and 30% of their body carbon per day as phytoplankton. Microzooplankton may have provided an additional source of energy for the mesozooplankton community. These data emphasize the importance of mesozooplankton in the arctic food web and reinforce the idea that the Arctic Ocean should no longer be considered to be a “biological desert”.     

The Arctic Ocean halocline and its interannual variability from 1997 to 2008

As a key structure to understand the role of the ocean on the sea ice mass balance, the Arctic Ocean halocline and its spatiotemporal variability require serious attention. In this paper, we are proposing a new definition of the halocline, which is based on the salinity gradient structure, taking into account both the salinity amplitude and the thickness of the halocline. The Brunt Vaisala frequency is used as the halocline stratification index. CTD data collected from 1997 to 2008 and coming from various sources (icebreaker cruises, drifting buoys, etc.) are used to determine the halocline, and its time and space variability during three time periods, with a special focus on three main regions of the Arctic Ocean: the Canada basin, the Makarov basin and the Amundsen basin. Observations reveal that the halocline in the Amundsen basin was always present and rather stable over the three time periods. In contrast, the Canada and Makarov basins' halocline became more stratified during the IPY than before, mainly because of surface water freshening. In addition, observations also confirmed the importance of the halocline thickness for controlling the stratification variability. Observations suggest that both large scale and small scale processes affect the halocline. Changes in surface salinity observed in the Makarov basin are more likely due to atmospheric variability (AO, Dipole Anomaly), as previously observed. More locally, some observations point out that salt/heat diffusion from the Atlantic water underneath and brine rejection during sea ice formation from above could be responsible for salt content variability within the halocline and, as a consequence, being influential for the variability of the halocline. In spite of the existence of interannual variability, the Arctic Ocean main stratification, characterized by a stable and robust halocline until now, suggested that the deep ocean had a limited impact on the mixed layer and on sea ice in actual conditions. The drastic changes observed in Arctic sea ice during this period (1997-2008) cannot be attributed to a weakening of the halocline that could trigger an enhanced vertical heat flux from the deep ocean.     

Northward transport of pacific summer water along the Northwind Ridge in the Western Arctic Ocean

The recent sea-ice reduction in the Arctic Ocean is not spatially uniform, but is disproportionally large around the Northwind Ridge and Chukchi Plateau compared to elsewhere in the Canada Basin. In the Northwind Ridge region, Pacific Summer Water (PSW) delivered from the Bering Sea occupies the subsurface layer. The spatial distribution of warm PSW shows a quite similar pattern to the recent ice retreat, suggesting the influence of PSW on the sea-ice reduction. To understand the regionality of the recent ice retreat, we examine the dynamics and timing of the delivery of the PSW into this region. Here, we adopt a two-layer linearized potential vorticity equation to investigate the behavior of Rossby waves in the presence of a topographic discontinuity in the high latitude ocean. The analytical results show a quite different structure from those of mid-latitude basins due to the small value of β. Incident barotropic waves excited by the sea-ice motion with large annual variation can be scattered into both barotropic and baroclinic modes at the discontinuity. Since the scattered baroclinic Rossby wave with annual frequency cannot propagate freely, a strong baroclinic current near the topographic discontinuity is established. The seasonal variation of current near the topographic discontinuity would cause a kind of selective switching system for shelf water transport into the basin. In our simple analytical model, the enhanced northward transport of summer water and reduced northward transport of winter water are well demonstrated. The present study indicates that these basic dynamics imply that a strengthening of the surface forcing during winter in the Canada Basin could cause sea-ice reduction in the Western Arctic through the changes of underlying Pacific Summer Water.     

Comparing modeled streamfunction,heat and freshwater content in the Arctic Ocean

Within the framework of the Arctic Ocean Model Intercomparison Project results from several coupled sea ice–ocean models are compared in order to investigate vertically integrated properties of the Arctic Ocean. Annual means and seasonal ranges of streamfunction, freshwater and heat content are shown. For streamfunction the entire water column is integrated. For heat and freshwater content integration is over the upper 1000 m. The study represents a step toward identifying differences among model approaches and will serve as a base for upcoming studies where all models will be executed with common forcing. In this first stage only readily available outputs are compared, while forcing as well as numerical parameterizations differ.The intercomparison shows streamfunctions differing in pattern and by several Sverdrups in magnitude. Differences occur as well for the seasonal range, where streamfunction is subject to large variability.Annual mean heat content, referenced to 0 °C, in the Canada Basin varies from −3.5 to +1.8 GJ m⁻² among the models, representing both colder and warmer solutions compared to the climatology. Seasonal range is highest in regions with seasonal or no ice cover.Corresponding freshwater content, referenced to 34.8 ppt, shows differences most obviously in the Beaufort Sea and Canada Basin where maximum values vary between 6 and 24 m for the individual models. Maxima in the seasonal range are related to river inflow.In the current stage of the project, applied windstress contributes significantly to the differences. However differences due to model resolutions and model parameterizations can already be detected.     

Distribution of Pacific-origin water in the region of the Chukchi Plateau in the Arctic Ocean in the summer of 2003

1Introduction Besidestheprecipitationandriverdischarges,the watersinthePacificOceanandtheAtlanticOceanare thesourcesoftheArcticOceanwater.TheAtlantic waterenterstheArcticOceanviatheFramStraitand theBarentsSea.Foritsdenserfeatureduetohigh salinity,mostofitsinkstothenorthofSvaldbardand circulatesinallthedeepbasinsintheArcticOcean, formingthedeepandbottomwatersoftheArcticO- cean(Aagaardetal.,1985;Rudelsetal.,1999).The BeringStraitistheonlychannelforthePacificwater toflowintotheArcticOce…     

2008年夏季西北冰洋表层水浮游植物群落结构的色素表征及其对不同水团的响应

本文依托2008年夏季中国第三次北极科学考察航次,对西北冰洋海盆区和楚科奇海陆架营养盐及光合色素进行了测定和分析。根据海水理化性质将研究海区分为5个区,并使用CHEMTAX软件（Mackery et al.,1996）讨论了西北冰洋不同海区浮游植物群落组成结构及其与环境因子之间的关系。结果显示在楚科奇海陆架区,太平洋入流显著影响浮游植物生物量和群落结构。高营养盐Anadyr水团以及白令陆架水控制海域,表现出高Chl a且浮游植物以硅藻为主,相反,低营养盐如阿拉斯加沿岸流控制海域,Chl a生物量低且以微型,微微型浮游植物为主。在外陆架海区,海冰覆盖情况影响着水团的物理特征及营养盐浓度水平,相应地显著影响浮游植物群落结构。在海冰覆盖区域,硅藻生物量站到总Chl a生物量的75%以上;在靠近门捷列夫深海平原海区,受相对高盐的冰融水影响（MW-HS）,营养盐浓度和Chl a浓度相对海冰覆盖区略高,浮游植物结构中微型、微微型藻类比重增加,硅藻比例则降至33%;南加拿大海盆无冰海区（IfB）,表层水盐度最淡,营养盐浓度最低,相应地显示出低Chl a生物量,表明海冰消退,开阔大洋持续时间延长,将导致低生物量及激发更小型浮游植物的生长,并不有利于有机碳向深海的有效输出。     

2007与2008年夏季北极海冰变化特征及原因的对比分析

2008年进行的中国第三次北极科学考察是我国响应国际极地年(IPY)计划的一个重要组成部分.通过本次考察我们在物理海洋、海洋化学、生物海洋学、地质及地球物理等领域取得丰富的数据.国家海洋环境预报中心承担航线保障及海冰观测任务,预报和观测的同时,积累了大量现场气象和海冰观测数据及卫星云图资料.本文利用这些数据,结合极地共享数据及历史观测资料和再分析数据,对2008年夏季北极地区大气、海冰的特征进行综合分析,同时,通过对2008年与2007年夏季北极大气环流的比较分析,研究在全球变暖的背景下,影响北极夏季海冰分布的主导因素.     

2008年夏季白令海和北冰洋异养浮游细菌丰度与分布特征

利用2008年夏季我国第3次北极科学考察资料,基于流式细胞技术,对白令海北部陆架区的微微型浮游植物丰度、细胞大小(碳含量)、色素浓度的分布特征进行了分析,并对该类群的环境适应性进行了研究。结果表明,微微型浮游植物中仅含聚球藻和真核藻,其丰度范围分别为0.14×106 2.69×106和0.23×106-12.49×106个/dm3。聚球藻的叶绿素a和藻红蛋白含量、微微型真核藻的叶绿素a含量与类群丰度以及微微型真核藻的类胡萝卜素含量与细胞大小间均存在同向变化趋势。两类藻偏向于喜温嗜淡型,更适合在寡营养环境中保持较高的丰度,但能在高营养盐浓度下形成相对较高的碳含量。越接近陆地,细胞越小,丰度越大,碳含量及FL2/FL3越低;所处层位越深、纬度越高,则细胞越大,碳含量及FL2/FL3越高。北极气温升高和径流量的增加有利于陆架区微微型浮游植物类群丰度的增加。     

融池热力学模式以及它在2010年夏季北极中央区的应用研究

A one-dimensional thermodynamic model of melt pond is established in this paper.The observation data measured in the summer of 2010 by the Chinese National Arctic Research Expedition(CHINARE-2010) are used to partially parameterize equations and to validate results of the model.About 85% of the incident solar radiation passed through the melt pond surface,and some of it was released in the form of sensible and latent heat.However,the released energy was very little(about 15%),compared to the incident solar radiation.More than 58.6% of the incident energy was absorbed by melt pond water,which caused pond-covered ice melting and variation of pond water temperature.The simulated temperature of melt pond had a diurnal variation and its value ranged between 0.0°C and 0.3°C.The melting rate of upper pond-covered ice is estimated to be around two times faster than snow-covered ice.At same time,the change of melting rate was relatively quick for pond depth less than 0.4 m,while the melting rate kept relatively constant(about 1.0 cm/d) for pond depth greater than 0.4 m.     

2016年夏季北冰洋浮冰站近地层辐射和湍流通量观测

2016年8月7－14日中国第七次北极科学考察期间,在83°N附近设立的长期浮冰站开展了辐射和湍流通量观测研究。结果表明,观测期间反照率变化范围为0.64~0.92,平均反照率为0.78;基于现场观测数据评估了PW79、HIRHAM、ARCSYM和CCSM3 4种不同复杂度的反照率参数化方案在天气尺度的表现,最为复杂的CCSM3结果优于其他参数化方案,但不能体现降雪条件下的反照率快速增长。浮冰区冰雪面平均净辐射为18.10 W/m2,平均感热通量为1.73 W/m2,平均潜热通量为5.55 W/m2,海冰表面消融率为（0.30±0.22） cm/d,表明此时北冰洋浮冰正处于快速消融期。冰面的平均动量通量为0.098（kg·m/s）/（m2·s）,动量通量与风速有很好的对应关系,相关系数达0.80。     

Exploring the Arctic Ocean under Arctic amplification

正Rate of surface air temperature increase in the Arctic is roughly twice that of the global average, and this phenomenon is referred to as "Arctic Amplification"(Serreze and Barry, 2011). The Arctic sea ice season (October to September) of 2017–2018 is the second warmest in Arctic since 1900 (Overland et al., 2018); 2014–2018 are the five warmest years in the Arctic since 1900 (Overland et al.,2018). Mean temperatures in Finland, Norway, and Svalbard in May 2018 are the highest in the instrumental record since the early1900s (NOAA, 2018), and the extensive warm spells over Scandinavia led to extensive forest fires (Overland et al., 2018).     

2003年夏季西北冰洋浮游动物群落结构和地理分布研究

根据西北冰洋43个调查站位的浮游动物种类组成和数量资料,分析了浮游动物的群落结构和地理分布特征,探讨了浮游动物群落与环境因子的关系.结果表明,在调查区域存在三种不同的浮游动物群落类型:楚科奇海台和加拿大海盆地区的高纬度深海群落;楚科奇海中部的陆架群落;阿拉斯加沿岸和楚科奇海北部的沿岸过渡群落.深海群落浮游动物数量较少,...     

Physical properties of the formation of water exchange between Atlantic and Arctic Ocean

Physical regularities of water exchange between the North Atlantic (NA) and Arctic Ocean (AO) in 1958–2009 are analyzed on the basis of numerical experiments with an eddy-permitting model of ocean circulation. Variations in the heat and salt fluxes in the Greenland Sea near the Fram Strait caused by atmospheric forcing generate baroclinic modes of ocean currents in the 0–300 m layer, which stabilize the response of the ocean to atmospheric forcing. This facilitates the conservation of water exchange between the NA and AO at a specific climatic level. A quick response of dense water outflow into the deep layers of the NA through the Denmark Strait to the variations in the North Atlantic Oscillation (NAO) index was revealed on the monthly scale. A response on a time scale of 39 months was also revealed. The quick response on the NAO index variation was interrupted in 1969–1978, which was related to the Great Salinity Anomaly. It was shown that transverse oscillations of the Norwegian Atlantic Current significantly influence the formation of intermediate dense waters in the Greenland and Norwegian seas (GNS). The dense water outflow by bottom current (BC) to the deep layers of the NA through the Faroe Channels with a time lag of 1 year correlates with the transversal oscillations of the Norwegian Current front. The mass transport of the BC outflow from the Faroe Channels to the NA can serve as an integral indicator of the formation and sink of new portions of dense waters formed as a result of mixing of warm saline Atlantic waters and cold freshened Arctic waters in the GNS.     

2010年西北冰洋浮游植物区域差异与环境关系

Global warming has caused Arctic sea ice to rapidly retreat,which is affecting phytoplankton,the primary producers at the base of the food chain,as well as the entire ecosystem.However,few studies with large spatial scales related to the Arctic Basin at high latitude have been conducted.This study aimed to investigate the relationship between changes in phytoplankton community structure and ice conditions.Fifty surface and 41 vertically stratified water samples from the western Arctic Ocean(67.0°–88°26′N,152°–178°54′W) were collected by the Chinese icebreaker R/V Xuelong from July 20 to August 30,2010 during China's fourth Arctic expedition.Using these samples,the species composition,spatial distribution,and regional disparities of phytoplankton during different stages of ice melt were assessed.A total of 157 phytoplankton taxa(5 μm) belonging to 69 genera were identified in the study area.The most abundant species were Navicula pelagica and Thalassiosira nordenskioeldii,accounting for 31.23% and 14.12% of the total phytoplankton abundance,respectively.The average abundance during the departure trip and the return trip were 797.07×10~2 cells/L and 84.94×10~2 cells/L,respectively.The highest abundance was observed at Sta.R09 in the north of Herald Shoal,where Navicula pelagica was the dominant species accounting for 59.42% of the abundance.The vertical distribution of phytoplankton abundance displayed regional differences,and the maximum abundances were confined to the lower layers of the euphotic zone near the layers of the halocline,thermocline,and nutricline.The species abundance of phytoplankton decreased from the low-latitude shelf to the high-latitude basin on both the departure and return trips.The phytoplankton community structure in the shallow continental shelf changed markedly during different stages of ice melt,and there was shift in dominant species from centric to pennate diatoms.Results of canonical correspondence analysis(CCA) showed that there were two distinct communities of phytoplankton in the western Arctic Ocean,and water temperature,ice coverage and silicate concentration were the most important environmental factors affecting phytoplankton distribution in the surveyed sea.These findings will help predict the responses of phytoplankton to the rapid melting of Arctic sea ice.     

Flow of Canadian basin deep water in the Western Eurasian Basin of the Arctic Ocean

The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data show that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross-slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.     

北冰洋加克利海岭(AMORE-2001)的考察

20 0 1年 1 0月 7日俄罗斯极地与海洋研究所使用的德国科学研究船队的主要船只“Po larstern”号破冰船回到了德国不来梅港 ,结束了为期 1 0个星期的北冰洋中部的加克利海岭AMORE -2 0 0 1考察。“Polarstern”号上有由俄罗斯极地与海洋研究所所长ЙОРНТиде领导的来自德国、俄罗斯和美国的 60位科学家。另一艘美国“Healy”号海岸保护破冰船上有以塔尔萨大学PMichael教授为首的 2 0位美国科学家。2 0 0 1年 7月 3 1日晚两条破冰船从挪威的特罗姆瑟港出发 ,驶向欧亚深水盆地中部 ,去研究实际上不为人知的全世界洋中脊体系最北的地…     

An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006-2008 period

Unprecedented summer-season sampling of the Arctic Ocean during the period 2006-2008 makes possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins. In comparison to observations from 1992 to 1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8400±2000 km³ in the Arctic Ocean (water depth greater than 500 m). This is close to the annual export of freshwater (liquid and solid) from the Arctic Ocean reported in the literature.Observations and a model simulation show regional variations in LFW were both due to changes in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a mean freshening of the water column above this depth, associated with an increased net sea ice melt and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a quarter of the salinity contribution, and non-linear effects due to both factors were negligible.     

北极河流径流对北冰洋环流的影响

北极河流径流是北冰洋淡水的最大来源,其变化会对北冰洋中的诸多过程有重要影响。本文基于全球高分辨率海洋-海冰耦合模式的模拟结果,研究北冰洋温盐、海冰以及环流对北极河流径流的敏感性。通过对比有气候态北极河流径流输入的控制实验结果和径流完全关闭的敏感性实验结果,研究发现北极径流对北冰洋温度、盐度、海冰以及海洋环流等有显著的影响。关闭北极河流径流后,在河口附近的陆架上温度降低、盐度升高,且导致500 m深度处温度下降以及盐度升高;河口附近的陆架处,海冰密集度与海冰厚度增加。关闭北极河流径流也对北冰洋内的环流有影响:由于缺少来自欧亚大陆的北极径流的输入,穿极漂流与东格陵兰流流速减小且盐度增加;关闭北极径流导致近岸海表面高度降低,沿欧亚陆架的北冰洋边界流减弱,白令海入流增强。通过对比关闭北极径流实验与控制实验的温度和盐度剖面,发现关闭北极径流后大西洋层温度降低,各陆架海盐跃层的梯度减小,盐跃层厚度减小。     

Community respiration/production and bacterial activity in the upper water column of the central Arctic Ocean

Community metabolism (respiration and production) and bacterial activity were assessed in the upper water column of the central Arctic Ocean during the SHEBA/JOIS ice camp experiment, October 1997–September 1998. In the upper 50 m, decrease in integrated dissolved oxygen (DO) stocks over a period of 124 d in mid-winter suggested a respiration rate of ∼3.3 nM O₂ h⁻¹ and a carbon demand of ∼4.5 gC m⁻². Increase in 0–50 m integrated stocks of DO during summer implied a net community production of ∼20 gC m⁻². Community respiration rates were directly measured via rate of decrease in DO in whole seawater during 72-h dark incubation experiments. Incubation-based respiration rates were on average 3-fold lower during winter (11.0±10.6 nM O₂ h⁻¹) compared to summer (35.3±24.8 nM O₂ h⁻¹). Bacterial heterotrophic activity responded strongly, without noticeable lag, to phytoplankton growth. Rate of leucine incorporation by bacteria (a proxy for protein synthesis and cell growth) increased ∼10-fold, and the cell-specific rate of leucine incorporation ∼5-fold, from winter to summer. Rates of production of bacterial biomass in the upper 50 m were, however, low compared to other oceanic regions, averaging 0.52±0.47 ngC l⁻¹ h⁻¹ during winter and 5.1±3.1 ngC l⁻¹ h⁻¹ during summer. Total carbon demand based on respiration experiments averaged 2.4±2.3 mgC m⁻³ d⁻¹ in winter and 7.8±5.5 mgC m⁻³ d⁻¹ in summer. Estimated bacterial carbon demand based on bacterial productivity and an assumed 10% gross growth efficiency was much lower, averaging about 0.12±0.12 mgC m⁻³ d⁻¹ in winter and 1.3±0.7 mgC m⁻³ d⁻¹ in summer. Our estimates of bacterial activity during summer were an order of magnitude less than rates reported from a summer 1994 study in the central Arctic Ocean, implying significant inter-annual variability of microbial processes in this region.     

Numerical modeling of the Arctic Ocean ice system response to variations in the atmospheric circulation from 1948 to 2007

The results of model calculations aimed at reproducing climate changes in the Arctic Ocean due to variations in the atmospheric circulation are presented. The combined ocean-ice numerical model is based on NCAR/NCEP reanalysis data and its modified version of CIAF on the state of the lower atmosphere, radiative fluxes, and precipitation from 1948 to the present. The numerical experiments reveal the effect of the ice cover, water circulation, and thermohaline structure of the Arctic Ocean on variations in the state of the atmosphere. We found the heating and cooling periods in the Atlantic water layer, as well as the freshwater accumulation regimes in the Canadian Basin and freshwater flow through the Fram Strait and Canadian Archipelago straits. The numerical model reproduces a reconfiguration of the water circulation of the surface and intermediate layers of the ocean, a shift in the boundary between Atlantic and Pacific waters, and a significant reduction of the ice area.