Influence of basin-scale and mesoscale physical processes on biological productivity in the Bay of Bengal during the summer monsoon

Physical forcing plays a major role in determining biological processes in the ocean across the full spectrum of spatial and temporal scales. Variability of biological production in the Bay of Bengal (BoB) based on basin-scale and mesoscale physical processes is presented using hydrographic data collected during the peak summer monsoon in July–August, 2003. Three different and spatially varying physical processes were identified in the upper 300 m: (I) anticyclonic warm gyre offshore in the southern Bay; (II) a cyclonic eddy in the northern Bay; and (III) an upwelling region adjacent to the southern coast. In the warm gyre (>28.8 °C), the low salinity (33.5) surface waters contained low concentrations of nutrients. These warm surface waters extended below the euphotic zone, which resulted in an oligotrophic environment with low surface chlorophyll a (0.12 mg m⁻³), low surface primary production (2.55 mg C m⁻³ day⁻¹) and low zooplankton biovolume (0.14 ml m⁻³). In the cyclonic eddy, the elevated isopycnals raised the nutricline upto the surface (NO₃–N > 8.2 μM, PO₄–P > 0.8 μM, SiO₄–Si > 3.5 μM). Despite the system being highly eutrophic, response in the biological activity was low. In the upwelling zone, although the nutrient concentrations were lower compared to the cyclonic eddy, the surface phytoplankton biomass and production were high (Chl a – 0.25 mg m⁻³, PP – 9.23 mg C m⁻³ day⁻¹), and mesozooplankton biovolume (1.12 ml m⁻³) was rich. Normally in oligotrophic, open ocean ecosystems, primary production is based on ‘regenerated’ nutrients, but during episodic events like eddies the ‘production’ switches over to ‘new production’. The switching over from ‘regenerated production’ to ‘new production’ in the open ocean (cyclonic eddy) and establishment of a new phytoplankton community will take longer than in the coastal system (upwelling). Despite the functioning of a cyclonic eddy and upwelling being divergent (transporting of nutrients from deeper waters to surface), the utilization of nutrients leading to enhanced biological production and its transfer to upper trophic levels in the upwelling region imply that the energy transfer from primary production to secondary production (mesozooplankton) is more efficient than in the cyclonic eddy of the open ocean. The results suggest that basin-scale and mesoscale processes influence the abundance and spatial heterogeneity of plankton populations across a wide spatial scale in the BoB. The multifaceted effects of these physical processes on primary productivity thus play a prominent role in structuring of zooplankton communities and could consecutively affect the recruitment of pelagic fisheries.     

Nonlinear aspects of sea surface temperature in Monterey Bay

Nonlinear aspects of sea surface temperature (SST) in Monterey Bay are examined, based on an 85-year record of daily observations from Pacific Grove, California. Oceanic processes that affect the waters of Monterey Bay are described, processes that could contribute to nonlinearity in the record. Exploratory data analysis reveals that the record at Pacific Grove is non-Gaussian and, most likely, nonstationary. A more recent test for stationarity based on a power law approximation to the slope of the power spectrum indicates that the record is stationary for frequencies up to ∼8 cycles per year (∼45 days), but nonstationary at higher frequencies. To examine the record at Pacific Grove for nonlinear behavior, third-order statistics, including the skewness, statistical measures of asymmetry, the bicorrelation, and the bispectrum, were employed. The bicorrelation revealed maxima located approximately 365 days apart, reflecting a nonlinear contribution to the annual cycle. Based on a 365-day moving window, the running skewness is positive almost 80% of the time, reflecting the overall impact of warming influences. The asymmetry is positive approximately 75% of the time, consistent with the asymmetric shape of the mean annual cycle. Based on the skewness and asymmetry, nonlinearities in the record, when they occur, appear to be event-driven with time scales possibly as short as several days, to several years. In many cases, these events are related to warm water intrusions into the bay, and El Niño warming episodes.The power spectrum indicates that the annual cycle is a dominant source of variability in the record and that there is a relatively strong semiannual component as well. To determine whether or not the annual and semiannual cycles are harmonically related, the bispectrum and bicoherence were calculated. The bispectrum is nonzero, providing a strong indication of nonlinearity in the record. The bicoherence indicates that the annual cycle is a major source of nonlinearity and further implies that the annual and semiannual cycles are harmonically related. Based on the wavelet power spectrum (WPS), the appearance of the semiannual cycle is transitory; however, pathways between the annual and semiannual cycles appear at certain times when nonlinear interaction between them could occur. Comparisons between the WPS and the running skewness suggest that there is a tendency for periods when pathways exist, to coincide with increased positive skewness, and, often, with El Niño warming episodes. The Hilbert-Huang transform, a relatively new tool for nonstationary and nonlinear spectral analysis, was used to further examine the origin of the semiannual cycle. The time-dependent Hilbert spectrum reveals large and erratic variations in frequency associated with semiannual cycle but far greater stability associated with the annual cycle. As a result, the time-integrated Hilbert spectrum does not indicate the presence of a semiannual cycle. The method of surrogates from the field of nonlinear dynamics was also employed to test the Hopkins record for nonlinearity. Differences between the data and the surrogates were found that were statistically significant, implying the existence of nonlinearity in the record. Using the method of surrogates together with a one-year moving window, El Niño warming episodes appear to be a likely source of nonlinearity, consistent with the other analyses that were performed. Finally, the influence of stochastic variability due to serial correlation in the data was examined by comparing standardized statistics for the observations and for simulations based on an autoregressive model whose properties were obtained from the observations. The magnitude of the variability for the simulations was found to be far less than that associated with the original data, and thus stochastic variability does not appear to be a factor that significantly affects the interpretation of our results.     

池养黄河鲤鱼含肉率及其肌肉营养成份的分析

本文就池养黄河鲤鱼的含肉率及其肉肉营养成份进行了测定分析。结果表明：池养黄河鲤鱼的含肉率为７１、９８５％；其肌肉营养成份蛋白质含量为１７．５８％、脂肪含量为３．９７％、灰分含量为１．１２％、水分含量为７７．３３％；肌肉中含有丰富的体全部必需８种氨基酸和４种鲜味氨基酸；肌肉中还含有丰富的人体必需微量元素铜，锌、铁等及大量元素、磷。     

夏季对马暖流“东海段”的温－盐特征及1987年和1989年夏季的盐度差异

本文分析该海域约７０个测站的温、盐资料，获得以下结果：（１）夏季在对马暖流的源区，于１０～７５ｍ水层内，其流路成一明显的分界线，左（西）侧温、盐度较低，右（东）侧温、盐度较高。（２）夏季对马暖流源区存在着三种海水：高温、高盐水，高温、低盐水和高温、次高盐水。（３）夏季朝鲜海峡地区，东水道的温、盐度高于西水道温、盐度。（４）１９８７年，东海黑潮区、长江口、杭州湾外及东海酉南部海域，夏季的表层盖度，皆比１９８９年同季、同一海域的盐度偏高；而对马暖流“东海段”却出现相反的低盐现象。其原因之一，１９８７年冲淡水势力极强，几乎盘踞了对马暖流源区的大部分海域，使源区盐度下降，并随对马暖流北上输送的缘故。其中：（１）和（４）两点认识系首次提出。     

Late Holocene coastal sand movements in the Outer Hebrides, N.W. Scotland

Lithostratigraphical and biostratigraphical investigation of coastal marshes along the Atlantic coast of the Outer Hebrides from Lewis in the north to Barra in the south discloses inland-tapering sand units within marshland areas. The inland extent of each sand unit has been radiometrically dated and the units have been collectively interpreted as a proxy for past coastal storminess. The data appear to indicate that for the study sites investigated, the majority of the sand units were produced during episodes of climate deterioration both prior to and after the well-known period of Medieval warmth (MWP). Many were produced after ca. AD 1400. It is argued that the episodes of sand blow indicated by the deposits may reflect periods of increased cyclogenesis in the Atlantic associated with increased sea ice cover and an increase in the thermal gradient across the North Atlantic region.     

Observation of the Soya Warm Current using HF ocean radar

Three High Frequency (HF) ocean radar stations were installed around the Soya/La Perouse Strait in the Sea of Okhotsk in order to monitor the Soya Warm Current (SWC). The frequency of the HF radar is 13.9 MHz, and the range and azimuth resolutions are 3 km and 5 deg., respectively. The radar covers a range of approximately 70 km from the coast. The surface current velocity observed by the HF radars was compared with data from drifting buoys and shipboard Acoustic Doppler Current Profilers (ADCPs). The current velocity derived from the HF radars shows good agreement with that observed using the drifting buoys. The root-mean-square (rms) differences were found to be less than 20 cm s⁻¹ for the zonal and meridional components in the buoy comparison. The observed current velocity was also found to exhibit reasonable agreement with the shipboard ADCP data. It was shown that the HF radars clearly capture seasonal and short-term variations of the SWC. The velocity of the Soya Warm Current reaches its maximum, approximately 1 m s⁻¹, in summer and weakens in winter. The velocity core is located 20 to 30 km from the coast, and its width is approximately 40 km. The surface transport by the SWC shows a significant correlation with the sea level difference along the strait, as derived from coastal tide gauge records at Wakkanai and Abashiri. Deceased.     

长江口邻近海域夏、冬季水文特征分析

长江冲淡水和台湾流是我国陆架海上两个重要的海洋现象。二者在长江口邻近海域交汇并相互制约，其分布和变化控制着该地区的温盐、环流结构，也影响着长江径流所携带的泥沙、营养盐等物质向外海的扩散和输运，以及舟山渔场的形成和变化。 长江每年以巨量径流注入东海，在长江口外形成一股很强的冲淡水，以低盐、高营养盐、高悬浮体含量为特征。毛汉礼等(1963)首先对长江冲淡水的扩散与混合特征作了系统的描述，并指出，冬季长江冲淡水沿岸南下，其范围仅限于贴岸的一狭带内；夏则在径流入海后不久转向东北，直指济州岛方向，到达对马海峡。众多学者通过资料分析、理论研究和数值模拟等探讨了长江冲淡水转向的原因，认为主要影响因素有长江径流量、地形效应、海面风应力、斜压效应、台湾曖流的顶托，以及黄海冷水团的诱导作用等(乐肯堂，1984；崔茂常，1984；顾玉荷，1985；王从敏，1986；赵保仁，1991；朱建荣，1998)，但至今对其转向机制的认识尚不一致。 台湾暖流水起源于台湾海峡和黑潮，是具有高盐、低悬浮体含量特征的大洋水体。翁学传等(1983，1984)研究认为，具有高温和次高盐特征的台湾暖流表层水同时起源于台湾海峡水和黑潮表层水，而具有高盐特征的深层水只来源于由台湾东北部入侵陆架的黑潮次表层水；翁学传(1983)还根据历史资料分析指出，夏季台湾暖流表层水的前锋大体沿着123°E可以伸展到31°N，深层水进一步延伸至31°N以北；且深层水在28°N和30°N断面并不终年存在，仅存于夏半年。王凡等(2001)的分析结果则显示，台湾暖流表层水和深层水在夏季可以在次表层北侵至30°N以北海域，而以深层水特点为主的台湾暖流水在冬季和晚秋甚至可在整个深度上伸展至30°N以北。总之，对台湾暖流水在不同季节、不同层次的北侵程度方面还存在着不同看法。 为深入研究长江口邻近海域的物质通量、扩散、传输和输运规律，中国科学院知识创新工程重要方向项目“中国主要河口及邻近陆架海域陆海相互作用”于2001年7-8月和2002年1月在长江口外28°~32°N、124°E以西海域组织了两次多学科综合考察。作者首先根据这两次考察获得的温盐深观测仪(CTD)观测到的温盐资料和声学多普勒流速剖面仪(ADP、ADCP)流速资料,分析该年夏、冬季长江口邻近海域的水文特征。考虑到调查海域有较强的年际变动，从年际变化的角度来更深刻地认识夏、冬季长江口邻近海域的水文特征，以及长江冲淡水与台湾暖流水的关系是很有必要的。为此，作者收集了1987~2001年其他项目3个夏季航次和2个冬季航次的温盐资料，以及1958~1982年标准断面历史资料，与最近2次观测资料相结合，综合分析研究了长江口邻近海域夏、冬季水文特征和变化情况，为今后更进一步开展此项研究提供了科学依据。     

Current structure and volume transport of the Soya Warm Current in summer

ADCP, CTD and XBT observations were conducted to investigate the current structure and temperature, salinity and density distributions in the Soya Warm Current (SWC) in August, 1998 and July, 2000. The ADCP observations clearly revealed the SWC along the Hokkaido coast, with a width of 30–35 km and an axis of maximum speed of 1.0 to 1.3 ms⁻¹, located at 20–25 km from the coast. The current speed gradually increased from the coast to a maximum and steeply decreased in the offshore direction. The SWC consisted of both barotropic and baroclinic components, and the existence of the baroclinic component was confirmed by both the density front near the current axis and vertical shear of the alongshore current. The baroclinic component strengthened the barotropic component in the upper layer near the axis of the SWC. The volume transport of the SWC was 1.2–1.3 SV in August, 1998 and about 1.5 SV and July, 2000, respectively. Of the total transport, 13 to 15% was taken up by the baroclinic component. A weak southeastward current was found off the SWC. It had barotropic characteristics, and is surmised to be a part of the East Sakhalin Current.     

Volume transport of the Tsushima Warm Current, west of Tsugaru Strait bifurcation area

Northern and southern latitudinal transects were conducted west of Tsugaru Strait to estimate the volume transport in this area. It was found that the Tsushima Warm Current is the northward volume transport across the southern transect and the Northward Current is the northward volume transport across the northern transect. The current in Tsugaru Strait,viz. the Tsugaru Warm Current, is the flow remaining when the Northward Current is subtracted from the Tsushima Warm Current. Both CTD transects covered from near-shore to west of the subarctic front, and observed depths were from the surface to the bottom or to 1000-1500 m depth. Our estimations indicate that large interannual variations of volume transport occur, relative to the seasonal ones, with interannual variations sometimes exceeding seasonal variations in the Tsushima Warm Current and the Northward Current. The Tsugaru Warm Current has near-steady transport. Fluctuations in the Tsushima Warm Current are thus transmitted to the Northward Current. Further, our results revealed seasonal variations in the flow: the baloclinic structure became deeper in April and the current axis tended to shift in a near-shore direction in October. Therefore, previous studies, which had shallow reference levels and lacked nearshore stations, may have underestimated the transport and excessive seasonal variations.     

On the Taiwan Warm Current Water

Using our data from special observation in the source area of the Taiwan Warm Current from 19S2 to 1985) and historical data, the authors conducted studies to clarify the temperature and salinity characteristics, variability, and origin of the Taiwan Warm Current Water, and its influence on the expanding direction of the Changjiang Diluted Water.The main results of these studies are briefly given below. (1) The Taiwan Warm Current Water can be divided into two parts:the Surface Water of the Taiwan Warm Current and the Deep Water of the Taiwan Warm Current; the former is formed due to the mixing of the Kuroshio Surface Water flowing northward along the east coast of Taiwan with the Taiwan Strait Water; the latter completed originates from Kuroshio Subsurface Water to the east of Taiwan. It is characterized by lower temperature and higher salinity in summer and the characteristics of temperature and salinity are more stable. The maximum seasonal variational range and maximum secular variational range of t