Behavior of Mn in the western north pacific

The determination of dissolved Mn in sea water was carried out using a Chelex 100 resin and graphite furnace atomic absorption spectrophotometer. The nearshore surface layer waters off the Straits of Kii had the highest Mn concentration of 6.40 n mol kg⁻¹ at these stations. Mn concentration of intermediate and deep water off the Straits of Kii ranged between 0.18 and 1.42 n mol kg⁻¹. Mn concentration in deep and bottom waters at the Mariana Trough were between 0.71 and 2.48 n mol kg⁻¹. Sharp increases of Mn concentration near the bottoms were observed at two stations near the hydrothermal vents of the central ridge of the Mariana Trough.     

The characteristics of signal versus noise sst variability in the north pacific and the tropical pacific ocean

Total sea surface temperature (SST) in a coupled GCM is diagnosed by separating the variability into signal variance and noise variance. The signal and the noise is calculated from multi-decadal simulations from the COLA anomaly coupled GCM and the interactive ensemble model by assuming both simulations have a similar signal variance. The interactive ensemble model is a new coupling strategy that is designed to increase signal to noise ratio by using an ensemble of atmospheric realizations coupled to a single ocean model. The procedure for separating the signal and the noise variability presented here does not rely on any ad hoc temporal or spatial filter. Based on these simulations, we find that the signal versus the noise of SST variability in the North Pacific is significantly different from that in the equatorial Pacific. The noise SST variability explains the majority of the total variability in the North Pacific, whereas the signal dominates in the deep tropics. It is also found that the spatial characteristics of the signal and the noise are also distinct in the North Pacific and equatorial Pacific.     

Interannual correlations between sea level difference at the south coast of Japan and wind stress over the north pacific

Relationships of the sea level differences between Naze and Nishinoomote and between Kushimoto and Uragami with wind stress over the North Pacific are examined for interannual variability. These sea level differences are considered to be indications of Kuroshio transport in Tokara Strait and Kuroshio path south of Enshu-nada, respectively. In the sea level difference between Kushimoto and Uragami, dominant variations are found to have periods of about seven years and 3–4 years. The variation of about 7-year period, which corresponds to that in the Kuroshio path between the large meander and non-large meander, is coherent with the variation of the wind stress curl in a region about 2,400 km east of the Kii Peninsula, where negative stress curl weakens about two years before the sea level difference drops (i.e. the large meander path in the Kuroshio generates). The variation of the 3–4 year period is coherent with that of the wind stress in a large area covering the eastern equatorial Pacific, which suggests that it links with global-scale atmospheric variations. Interannual variation in sea level difference between Naze and Nishinoomote is not coherent with that between Kushimoto and Uragami, which suggests that it is not related to the variation of the Kuroshio path south of Enshu-nada, but is coherent with that of the zonally-integrated Sverdrup transport in the latitudinal zone along 30°N. It is suggested that the interannual variation of the Kuroshio transport in Tokara Strait can be explained by the barotropic response to the wind stress.     

Interannual SST variability in the Japan/East Sea and relationship with environmental variables

Interannual variability of the Japan/East Sea (JES) sea surface temperature (SST) is investigated from the reconstructed NOAA/AVHRR Oceans Pathfinder best SST data (1985–2002) using the complex empirical function (CEOF) analysis. The iterative empirical function analysis is used for the SST data reconstruction. The first two leading CEOFs account for 86.0% of total variance with 66.4% for the first mode and 19.6% for the second mode. The first CEOF mode represents a standing oscillation and a maximum belt in the central JES. There are two near-7-year events and one 2–3-year event during the period of 1985–2002. The first mode oscillates by adjacent atmospheric systems such as the Aleutian Low, the North Pacific High, the Siberian High, and the East Asian jet stream. Positive correlation in a zonal belt between the first mode JES SST anomaly and the background surface air temperature/SST anomaly reveals intensive ocean-atmosphere interaction near the Polar Front in the North Pacific. The second CEOF mode represents two features: standing oscillation and propagating signal. The standing oscillation occurs in the northern (north of 44°N) and southern (south of 39°N and west of 136°E) JES with around 180° phase difference. A weak southwestward propagating signal is detected between the two regions. The eastward propagating signal is detected from the East Korean Bay to near 135°E. The second mode contains 4–5-year periodicity before 1998 and 2–3-year periodicity thereafter. It is associated with the Arctic Oscillation, which leads it by 1–5-year. Furthermore, a strong correlation with the background surface air temperature/SST anomaly is detected in the tropical to subtropical western Pacific.     

Interannual variability and predictability of summertime significant wave heights in the western north pacific

We propose and validate a linear regression model which enables us to predict the summer (June–August) mean of the monthly 90th percentile of significant wave heights (H₉₀) in the western North Pacific (WNP). The most prevailing interannual variability of H⁹⁰ is identified by applying an Empirical Orthogonal Function analysis to H⁹⁰ obtained from the ERA-40 wave reanalysis as well as from the optimally interpolated TOPEX/Poseidon (OITP) wave data. It is found that the increase of H⁹⁰ is correlated with cyclonic circulation in the WNP which links with warm SST anomalies in the Niño-3.4 region. We adopt zonal wind anomaly averaged over the region 5°N–15°N, 130°E–160°E (U^10N) as a predictor of the first principal component (PC1) of H⁹⁰, since U^10N is closely correlated with the PC1 of H⁹⁰. It is revealed that regression models obtained from two different wave datasets are nearly identical. The predictability of the regression model is assessed in terms of the reduction of the root-mean-square (rms) errors between H⁹⁰ and the reconstructed data. The predictor is found to be successful in reducing the rms errors by up to 40% for the ERA-40 wave reanalysis and by up to 70% for the OITP wave data within the latitudinal band 10°N–25°N, though rms errors exceeding 0.3 m still remain, particularly in the East China Sea.     

Spatial variations of rare earth elements in north pacific surface water

The concentration of dissolved rare earth elements (REE) were determined at 47 stations in the North Pacific surface waters. Combining with other previous data, we present the surface REE distribution in the North Pacific and discuss the controlling factors. The surface concentrations increase toward the high latitude and continental margin (e.g. [Nd] > 10 pmol kg⁻¹) from the central North Pacific (e.g. [Nd] < 5 pmol kg⁻¹). The North Pacific Deep Water-normalized REE patterns are varied, indicating that two or more factors contribute to the REE distribution. We examined four factors making the regional variation of surface REE concentrations mainly; a) particle scavenging, b) atmospheric dust input, c) vertical mixing and d) lateral transport from the coastal region. Flux calculations for Nd showed that the influence of atmospheric dust was less significant than the vertical input even in the western upwelling zone. Moreover, the longitudinal and latitudinal transitions of surface REE seem to reflect the lateral supply from the coastal areas. We constructed the diagram of surface Er/Lu and Er/Yb molar ratios in order to assess the origin and the input processes of the surface REE. Both molar ratios showed increasing trend toward PEW (Er/Lu (>10.5) and Er/Yb (>1.4)) from PSUW (Er/Lu (>7) and Er/Yb (>1.2)). The high Er/Lu and Er/Yb ratios in PEW indicate that the lateral supply of terrestrial materials from the coastal area is possibly the important factor in PEW, because only weathering and dissolution of rocks can explain such high Er/Lu and Er/Yb ratios to our knowledge.     

近百年西北太洋热带气旋频数变化特征与ENSO的关系

本文根据西北太平洋近106年(1899～2004年)热带气旋系列资料,分析了热带气旋年频数多年变化的统计特征.结果表明:西北太平洋台风频数既存在明显的短周期的年际变化也存在明显长周期的年代际变化,是一种短周期与长周期相互作用的多时间尺度的变化.年际变化与ENSO有明显关系,ENSO事件的当年9月到次年8月冷事件年相对与暖事件年会有更多的台风生成和登陆.在年代际尺度上,106年的台风活动可以分为几个明显的活跃期和不活跃期,这种年代际的变化可能与海气耦合的经向模态调制有关系.     

Discharge and surface plume measurements during manganese nodule mining tests in the north equatorial pacific

Rates, concentrations, and composition of mining discharge and the size and structure of the ensuing surface plumes were examined during North Pacific tests of scaled manganese nodule mining systems. Discharge was composed principally of bottom water and pelagic silts and clays, although nodule fragments with diameters less than 1 mm were also discharged at widely varying rates. Average flow rates of the discharge varied from 95 to 160 litres/s, with the solid fraction varying from 550 to approximately 2000g/s. The plume, as determined by particulate concentrations in excess of ambient oceanic conditions, extended approximately 5 km from the mining ship and had a width of about 1 km. Fe and Mn signatures allowed detection of the plume nearly 35 km from the source. The plume provided evidence of settling more rapidly than expected of silt and clay-size particles: a mean settling velocity of 6 × 10^?2 cm/s for the particulates in the plume and a mixed layer vertical turbulent eddy diffusivity of 1 × 10^?2m²/s have been inferred from the data. Field and laboratory data together suggest that the rapid settling was due to flocculation of the discharge particulates.     

Variability of sea surface temperature in the Japan Sea and its relationship to the wind-curl field

The variability of sea surface temperature (SST) in the Japan Sea is investigated using the complex EOF analysis of daily data produced at Tohoku University, Japan (New Generation SST; 2002–2006). The relationship with the wind field is investigated from the daily NCEP/NCAR reanalysis data with a 1° spatial resolution. Anomalies in the SST (SSTAs) are calculated by subtracting the basin-average annual variation estimated as a leading mode of temperature. The leading mode of an SSTA represents a adjustment to the annual mean variation, most significant in December in the zone of subtropical waters entering the sea through the Korean Strait and in the northwestern sea, over which a cyclonic wind curl develops in the cold period. The semiannual variability mode is identified, which is characterized by the largest temperature increase (decrease) in the western branch of the subarctic front (in the Tatar Strait), which lags by two months behind the semiannual changes in wind curl over the sea. An episodic SSTA movement is detected in the northern part of the sea, which moves from east to west along the western branch of the Tsushima Warm Current with a speed corresponding in magnitude to an advective scale.     

Isotopic fractionation of dissolved nitrate during denitrification in the eastern tropical north pacific ocean

The isotopic composition (δ¹⁵N) of dissolved nitrate was measured at five stations within the oxygen-deficient region of the eastern tropical North Pacific Ocean (ETNP) and at one station 900 km northeast of Hawaii, which was considered to be representative of all major water masses of the Pacific. At this last station, the δ¹⁵N composition of dissolved nitrate decreased systematically from about +6‰ at 400 m to approximately +5‰ at 5,000 m; these results are consistent with other estimates from the western Pacific.In contrast, vertical profiles of δ¹⁵N of dissolved nitrate from the ETNP showed marked departure from the above observed trend and correlated with losses of nitrate arising from denitrification. Instantaneous fractionation factors (α) were estimated, using the one dimensional vertical diffusion-advection model. These results suggest that ¹⁴NO₃⁻ is consumed 3–4% faster than ¹⁵NO₃⁻, significantly larger than fractionations (2%) observed under laboratory conditions.Maximum rates of denitrification at 100 m were also evaluated and ranged from 0.6 to 8 μg-at 1⁻¹ yr⁻¹ for the stations investigated. The above upper limit is probably excessive, but the average maximum for the four stations analyzed is estimated to be 3.5 μg-at NO₃⁻ 1⁻¹ yr⁻¹. These results compare favorably with suitably corrected oxygen utilization rates derived from electron transport activity measurements.     

Variability of Sea Surface Circulation in the Japan Sea

Composite sea surface dynamic heights (CSSDH) are calculated from both sea surface dynamic heights that are derived from altimetric data of ERS-2 and mean sea surface that is calculated by a numerical model. The CSSDH are consistent with sea surface temperature obtained by satellite and observed water temperature. Assuming the geostrophic balance, sea surface current velocities are calculated. It is found that temporal and spatial variations of sea surface circulation are considerably strong. In order to examine the characteristics of temporal and spatial variation of current pattern, EOF analysis is carried out with use of the CSSDH for 3.5 years. The spatial and temporal variations of mode 1 indicate the strength or weakness of sea surface circulation over the entire Japan Sea associated with seasonal variation of volume transport through the Tsushima Strait. The spatial and temporal variations of mode 2 mostly indicate the temporal variation of the second branch of the Tsushima Warm Current and the East Korean Warm Current. It is suggested that this variation is possibly associated with the seasonal variation of volume transport through the west channel of the Tsushima Strait. Variations of mode 3 indicate the interannual variability in the Yamato Basin.     

Lead in the North Sea and the north east Atlantic Ocean

Lead has been determined in 105 water samples from the north east Atlantic and from the North Sea. Rigorous precautions were applied to avoid contamination during sampling and analysis.Two different analytical methods were used: ASV and AAS. Determinations with ASV were carried out on board, directly after sampling. After two months storage, acidified samples were analysed by AAS after freon dithiocarbamate extraction and nitric acid back extraction. Particulate lead was determined by AAS after an acid digestion.The profiles of lead concentration versus depth show around 160 pM at the surface and around 20 pM at the bottom, both in the Atlantic and in the Norwegian Sea. The shapes of the profiles are different, however, depending on the hydrography of the area sampled. The profiles from the north east Atlantic coincide with a recently published profile from the north west Atlantic. Moreover, these profiles have lead concentrations about a factor of three higher than those in the Pacific.Considering the high lead input to the North Sea, the lead concentrations found there are remarkably low, probably because of scavenging effects in estuaries leading to a short residence time in the water column. The dominant lead input in offshore regions is from the atmosphere. The highest lead levels are found in the northern North Sea, around 300 pM in surface water.In the Atlantic, particulate lead is a minor part of the total lead whereas in the North Sea the particulate fraction is larger, up to 40%.     

Lead-210 in the Japan Sea

This is the first detailed study on the distribution of lead-210 in the Japan Sea water. The content of lead-210 ranged from 9.3±2.1 dph/l in the surface water to 3.4+-0.8 dph/l in the deep water—a quite low content as compared to that in the deep water of the North Pacific. Vertical profiles show that the content of lead-210 abruptly decreases below the seasonal thermocline (10–20 m in depth) and nearly uniform in the deep water. It is suggested that a significant amount of air-borne lead-210 deposited over the Japan Sea is transported along with the Tsushima Current to the open ocean. The budget of lead-210 is calculated by using a simple box-model and the mean residence time of lead-210 in the Japan Sea is estimated to be 15 yr.     

Abyssal circulation in the Japan Sea

Journal of Oceanography - The water below a depth of 1,000 m in the Japan Sea was found to consist of two water masses, the upper layer (the Deep Water) and the lower layer (the Bottom Water). The...     

Radium-228 in the Japan Sea

The distribution of²²⁸Ra in surface and subsurface waters in the Japan Sea was studied. The concentrations of²²⁸Ra in surface waters were around 100 dpm/1000l which were much higher than those reported for Pacific surface waters. The concentrations of²²⁸Ra decreased with increasing depth to less than 10 dpm/1000l in the Japan Sea Proper Water. Based on the comparison between observed values of²²⁸Ra and calculated profile through the near-surface water mass and the underlying main water mass in the Japan Sea, the apparent vertical eddy diffusion coefficient was estimated to be about 2 cm² s^–1.     

Heat budget in the Japan Sea

The long-term mean (31-year mean) surface heat fluxes over the Japan Sea are estimated by the bulk method using the most of the available vessel data with the resolution of 1^o×1^o. The long-term annual mean net heat flux is about –53 W m^–2 (negative sign means upward heat flux) with the annual range from 133 W m^–2 in May to –296 W m^–2 in December. The small gain of heat in the area near Vladivostok seems to indicate the existence of cold water flowing from the north. In that area in winter, the mean loss of heat attains about 200 W m^–2, and the Bowen's ratio is over the unity. The largest insolation occurs in May in the Japan Sea, and the upward latent heat flux becomes the largest in November in this area. The heat flux of Haney type is also calculated, and the result, shows that the constantQ ₁ has the remarkable seasonal and spatial variation, while the coefficientQ ₂ has relatively small variation throughout all seasons. Under the assumption of constant volume transport of 1.35×10⁶ m³s^–1 through the Tsugaru Strait, the long-term averages of the volume transport through the Tsushima and Soya Straits are estimated to be about 2.20 and 0.85×10⁶ m³s^–1 from the result of the mean surface heat flux, respectively.     

日本海、鄂霍次克海和白令海的古海洋学研究进展

边缘海的存在使大陆和大洋之间的物质和能量交换变得相当复杂。在构造运动和海平面升降的控制下,边缘海和大洋之间时而连通时而隔绝,各种古气候变化信号都在一定程度上被放大。基于近期有关西北太平洋边缘海的古海洋学研究成果,简要概述了日本海、鄂霍次克海、白令海以及北太平洋地区自中新世以来的古气候和古海洋环境演化特征,并认为它们与全球其它地区一样也受控于因地球轨道参数变化引起的太阳辐射率的变化,大尺度的气候变化具有与地球轨道偏心率周期相对应的100ka周期,而41ka的小尺度周期则受地球自转轴斜率变化的控制。一些突发性的气候变化则是由气候不稳定性、海峡的关闭与开启和其它一些地球气候系统的非线性活动所驱动。但同时作为中高纬度边缘海,它们的古海平面、古海水温度、古洋流等古海洋环境因子的变化特征还受到冰盖扩张和退缩、构造运动、冰川性地壳均衡补偿、东亚季风等因素的影响,具有一定的区域特点。     

Seasonal variations of the upper ocean in the western north pacific observed by an argo float

A seasonal evolution of surface mixed layer in the western North Pacific around 24°N between 143°E and 150°E was observed by using an Argo float for more than 9 months, from December 2001 through August 2002. The result showed that the mixed layer deepened gradually in the first two months. It reached its maximum depth of about 130 m at the end of January, after which the mixed layer varied largely and sometimes the pycnocline below the mixed layer was much weakened until the summer mixed layer formed in late April. The thin surface mixed layer was maintained during the rest of the observation period. Heat budget analysis suggests that the vertical and horizontal temperature advections are the two most dominant terms in the heat balance in the upper layer on time scales from a few days to a month. The vertical motions that are possibly responsible for the vertical temperature advection are discussed.     

Long-term bottom water warming in the north Ross Sea

We measured potential temperature, salinity, and dissolved oxygen profiles from the surface to the bottom at two locations in the north Ross Sea (65.2°S, 174.2°E and 67.2°S, 172.7°W) in December 2004. Comparison of our data with previous results from the same region reveals an increase in potential temperature and decreases in salinity and dissolved oxygen concentration in the bottom layer (deeper than 3000 m) over the past four decades. The changes were significantly different from the analytical precisions. Detailed investigation of the temperature, salinity, dissolved oxygen and σ ₃ value distributions and the bottom water flow in the north Ross Sea suggests a long-term change in water mass mixing balance. That is to say, it is speculated that the influence of cool, saline, high-oxygen bottom water (high-salinity Ross Sea Bottom Water) formed in the southwestern Ross Sea has possibly been decreased, while the influences of relatively warmer and fresher bottom water (low-salinity Ross Sea Bottom Water) and the Adélie Land Bottom Water coming from the Australia-Antarctic Basin have increased. The possible impact of global warming on ocean circulation needs much more investigation.