The Western North Pacific Playing a Key Role in Global Biogeochemical Fluxes

The oceanic biogeochemical fluxes in the North Pacific, especially its northwestern part, are discussed to prove their importance on a global scale. First, the air-sea exchange processes of chemical substances are considered quantitatively. The topics discussed are sea salt particles transported to land, sporadic transport of soil dust to the ocean and its role in the marine ecosystem, the larger gas transfer velocity of CO₂ indicating the effect of bubbles, and DMS and greenhouse gases other than CO₂. Next, chemical tracers are utilized to reveal the water circulation systems in the region, which are the Pacific Deep Water including its vertical eddy diffusivity, the North Pacific Intermediate Water and the Japan Sea Deep Water. Thirdly, the particulate transport process of chemical substances through the water column is clarified by analyzing the distribution of insoluble radionuclides and the results obtained from sediment trap experiments. Fourthly, the northern North Pacific is characterized by stating the site decomposing organic matter and Si playing a key role in the marine ecosystem. Both are induced by the upwelled Pacific Deep Water. Fifthly, the oceanic CO₂ system related to global warming is presented by clarifying the distribution of anthropogenic CO₂ in the western North Pacific, and roles of the upwelled Pacific Deep Water and the continental shelf zone in the absorption of atmospheric CO₂. Finally, Mn and other chemical substances in sediments are discussed as recorders of the early diagenesis and indicators of low biological productivity during glacial ages in the northwestern North Pacific. It is concluded that the western North Pacific is characterized mainly by the Pacific Deep Water bringing nutrients to the northern North Pacific, located at the exit of the global deep water circulation and, therefore, the region plays a key role in the global biogeochemical fluxes. This revised version was published online in August 2006 with corrections to the Cover Date.     

Vertical Distributions of Phyllosoma Larvae of Palinurid and Scyllarid Lobsters in the Western North Pacific

Vertical distributions of phyllosoma larvae were examined in waters east of the Philippines or west of the Mariana Islands (18°56′ N to 19°04′ N; 129°10′ E to 129°35′ E) based on zooplankton samples collected with an Isaacs-Kidd Midwater Trawl on September 22–24, 1986. Phyllosoma larvae belonged to the two families Scyllaridae and Palinuridae comprising 4 genera and 9 species. Of the collected phyllosoma larvae, those of Scyllarus cultrifer and Panulirus longipes were most abundant and showed similar vertical distributions: (1) both species were collected from the mixed layer at night but not in the day, (2) their vertical distributions did not change with their stages, and (3) the upper limit of their vertical distributions during the day accorded with the base of mixed layer. Furthermore, their vertical distributions were similar to those of lepthocephalus larvae which were collected using the same sampling stations and gear in the present study. Vertical distributions of phyllosoma larvae were discussed in relation to their horizontal distributions. This revised version was published online in August 2006 with corrections to the Cover Date.     

Spatiotemporal Decreases of Nutrients and Chlorophyll-a in the Surface Mixed Layer of the Western North Pacific from 1971 to 2000

Using time series of hydrographic data in the wintertime and summertime obtained along 137°E from 1971 to 2000, we found that the average contents of nutrients in the surface mixed layer showed linear decreasing trends of 0.001∼0.004 μmol-PO₄ l⁻¹ yr⁻¹ and 0.01∼0.04 μmol-NO₃ l⁻¹ yr⁻¹ with the decrease of density. The water column Chl-a (CHL) and the net community production (NCP) had also declined by 0.27∼0.48 mg-Chl m⁻² yr⁻¹ and 0.08∼0.47 g-C-NCP m⁻² yr⁻¹ with a clear oscillation of 20.8±0.8 years. These changes showed a strong negative correlation with the Pacific Decadal Oscillation Index (PDO) with a time lag of 2 years (R = 0.89 ± 0.02). Considering the recent significant decrease of O₂ over the North Pacific subsurface water, these findings suggest that the long-term decreasing trend of surface-deep water mixing has caused the decrease of marine biological activity in the surface mixed layer with a bidecadal oscillation over the western North Pacific.     

北太平洋海洋带状流的正压特性

海洋中包含着多种时空尺度的运动过程,海洋带状流是近年来发现的一种新的流动形式。这种流动现象介于地转湍流和准定常流之间。上层海洋中大尺度运动的强度远大于海洋带状流而将其遮盖,因而带状流需要借助滤波方法提取出来。本研究基于纬向速度数据,通过切比雪夫高通滤波提取了北太平洋海洋带状流的三维结构,定义了“流向稳定度”指数,量化分析了北太平洋海域带状流的正压特性,从而进一步加深了对北太平洋海洋带状流结构特征的认识。     

Anomalous Large Scavenging of 230Th and 231Pa Controlled by Particle Composition in the Northwestern North Pacific

We report the role of particle composition and lateral particle movement that influences the oceanic distribution of ²³¹Pa and ²³⁰Th. Settling particles were collected during sediment trap experiments. These and surface sediments were obtained from five stations along 38 to 44°N in the northwestern North Pacific. The high total mass flux and seasonal variations in the marginal area of the western North Pacific are controlled by the supply of lithogenic materials and primary productivity. The high content of the lithogenic material in the settling particles in this area contributes to ²³⁰Th_ex fluxes that exceed the local rate of supply. The lithogenic materials are important as a carrier of ²³⁰Th and contribute to the fractionation between ²³⁰Th and ²³¹Pa in the ocean, as the ²³¹Pa_ex/²³⁰Th_ex ratio in the settling particles decreases with increasing ²³²Th concentration. The ²³¹Pa_ex/²³⁰Th_ex ratio in the settling particles collected in the abyssal basin decreases with water depth, which indicates that lateral transport of the lithogenic particles from the marginal area and/or shallower depth plays an important role in determining the ²³¹Pa_ex/²³⁰Th_ex ratio in a population of settling particles and remineralization. This indicates that lateral redistribution of particles and sediment focusing influence the ²³¹Pa_ex/²³⁰Th_ex ratios in surface sediments. Thus, the observations reported here mean that the use of the sediment ²³¹Pa_ex/²³⁰Th_ex ratio as a paleoproductivity proxy will be problematic in the northwestern North Pacific. This revised version was published online in July 2006 with corrections to the Cover Date.     

边界条件对北太平洋海盆尺度环流模式的影响

采用Stevens开边界条件,将一个闭边界海盆尺度环流模式改造成开边界模式,对20°S以北太平洋大尺度环流进行了系统模拟。考察了开边界和不同等密面扩散系数对北太平洋环流和温盐结构的影响。模式较好地再现了太平洋大尺度环流特征,模拟出了表层赤道流系(包括北赤道流、黑潮和北太平流)以及对应的顺时针环流,同时还较好地反映了温盐场的基本分布特征。从年平均的纬向平均温度和盐度的断面分布可以看出,温跃层深度呈“W”型分布,在亚极地海区有一个梯度比较大的盐度锋区。南边界打开后使得模拟的北太平洋中层水温度和盐度更低,低盐水舌加深和向南延伸加强,更加接近观测值。增加沿等密面扩散系数后得到的中层水强度更大,尤其是34.6等盐线更接近观测资料。质量输运流函数分布表明,赤道两边各有一个翻转区,亚极地地区也存在一个浅的翻转区,打开南边界可以消除因为闭边界存在产生的假的下沉流,这些都为将来进行示踪物模拟打下基础。     

Decadal-Scale Climate and Ecosystem Interactions in the North Pacific Ocean

Decadal-scale climate variations in the Pacific Ocean wield a strong influence on the oceanic ecosystem. Two dominant patterns of large-scale SST variability and one dominant pattern of large-scale thermocline variability can be explained as a forced oceanic response to large-scale changes in the Aleutian Low. The physical mechanisms that generate this decadal variability are still unclear, but stochastic atmospheric forcing of the ocean combined with atmospheric teleconnections from the tropics to the midlatitudes and some weak ocean-atmosphere feedbacks processes are the most plausible explanation. These observed physical variations organize the oceanic ecosystem response through large-scale basin-wide forcings that exert distinct local influences through many different processes. The regional ecosystem impacts of these local processes are discussed for the Tropical Pacific, the Central North Pacific, the Kuroshio-Oyashio Extension, the Bering Sea, the Gulf of Alaska, and the California Current System regions in the context of the observed decadal climate variability. The physical ocean-atmosphere system and the oceanic ecosystem interact through many different processes. These include physical forcing of the ecosystem by changes in solar fluxes, ocean temperature, horizontal current advection, vertical mixing and upwelling, freshwater fluxes, and sea ice. These also include oceanic ecosystem forcing of the climate by attenuation of solar energy by phytoplankton absorption and atmospheric aerosol production by phytoplankton DMS fluxes. A more complete understanding of the complicated feedback processes controlling decadal variability, ocean ecosystems, and biogeochemical cycling requires a concerted and organized long-term observational and modeling effort. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of Time-Dependent Tracer Ages in the Western North Pacific: Oceanic Background Levels of (SF6, CFC-11, CFC-12 and CFC-113

To verify the actual usefulness of time-dependent tracer dating techniques in the ocean, we simultaneously obtained two cross sections of sulfur hexafluoride (SF₆) and chlrofluoromethanes (CFC-11, trichlorofluoromethane; CFC-12, dichloro-difluromethane; CFC-113, trichlorotrifluoroethane) in the western North Pacific in 1998. The vertical distribution patterns of SF₆ and CFC-113 were similar in shape to those of CFC-11 and CFC-12. Maximum penetration depths of SF₆ and CFC-113 remained around 800 m in the subpolar region and 400 m in the tropical region, while the maximum penetration depths of CFC-11 and CFC-12 were still found below 1000 m depth. We also found all maximum contents of these tracers around 26.6−26.8σ_θ with a gradual decrease southward. This suggested that a new subsurface water mass in the subpolar region spread out over the entire North Pacific, which agrees closely with previous studies based on the salinity minimum. Moreover, we compared the tracer ages (the elapsed period of a water mass from when the water mass left from the ocean surface) using ten time-dependent tracer dating techniques, CFC-11, CFC-12, CFC-113, SF₆, CFC-11/CFC-12, CFC-113/CFC-11, CFC-113/CFC-12, SF₆/CFC-11, SF₆/CFC-12 and SF₆/CFC-113. This quantitative evaluation of multiple tracer dating techniques in the ocean was the first confirmation of its usefulness based on the observational data on the ocean basin-wide scale. We conclude that SF₆/CFC-11, SF₆/CFC-12, SF₆/CFC-113 and SF₆ dating techniques would be the most promising tools for determining the age of water mass not only just for the past several decades but for the future, too. This revised version was published online in July 2006 with corrections to the Cover Date.     

北太平洋局地海洋-大气相互作用的主模态

本文分析美国国家大气研究中心(NCAR)的CCM3-ML耦合模式100 a积分模拟结果,依据对该模式结果中SSTA与海面风异常的最大协方差分析,证实的确存在北太平洋局地大气影响海洋和海洋"反馈"大气的主模态;指出通过局地海洋-大气的相互作用,冬季马蹄型海温异常可以持续到夏季,冬季大气对马蹄形暖海温异常可能的响应为高压异常,春夏季对马蹄形暖海温异常可能的响应为低压异常。     

西北太平洋累积气旋能量的年代际变化

利用1949—2011年CMA-STI热带气旋最佳路径数据集,分析了西北太平洋累积气旋能量(ACE)的年代际变化特征。结果表明,西北太平洋热带气旋(ACE)的年代际变化主要分为1957—1967高值期、1976—1986过渡期和1998—2008低值期。其中强热带风暴(STS)、台风(TY)和超强台风(SuperTY),特别超强台风是决定成分。副热带高压偏弱,垂直风切变偏小,低纬度低空正涡度异常偏东以及低纬度海表面温度(SST)正异常偏东等背景场的年代际特征,有利于形成ACE的年代高值期。     

Relationship between Composition of Settling Particles and Organic Carbon Flux in the Western North Pacific and the Japan Sea

Settling particles play an important role in transporting organic carbon from the surface to the deep ocean. It is known that major components of settling particles are biogenic silicates (opal), biogenic carbonate (CaCO₃), lithogenic clays and organic matter. Since each component aggregates and/or takes in organic carbon, all of these components have the ability to transport particulate organic carbon (POC) to the interior of the ocean. In this study, sediment trap experiments were carried out in four areas of the western North Pacific (including a marginal sea). Factors are proposed that correlate the composition of settling particles with POC flux. Annual mean organic carbon fluxes at 1 km depth in the western North Pacific Basin, Japan Sea, Hidaka Basin and northern Japan Trench were found to be 14.9, 18.1, 13.0 and 6.6 mg/m²/day, respectively. Organic carbon flux in the western North Pacific was greater than that in the Eastern North Pacific (7.4), the Equatorial Pacific (4.2), the Southern Ocean (5.8) and the Eastern North Atlantic (1.8). In the western North Pacific, it was calculated that 52% of POC was carried by opal particles. Opal is known to be a major component even in the Eastern North Pacific and the Southern Ocean, and the opal fluxes in these areas are similar to those in the western North Pacific. However, the organic carbon flux that was carried by opal particles (OC_opalflux) in the western North Pacific was greater than that in the Eastern North Pacific and the Southern Ocean. These results indicate that the ability of opal particles to transport POC to the deep ocean in the western North Pacific is greater than that in the other areas.     

Depth Distribution of the Subtropical Gyre in the North Pacific

Large-scale aspects of the North Pacific subtropical gyre have been investigated using a climatology of temperature and salinity (World Ocean Atlas 1998). In the central and eastern parts of the basin, the axis of the subtropical gyre, defined as the meridional maximum of dynamic height, tends to move poleward from about 25°N near the surface to about 40°N in the upper intermediate layers. In the western part of the basin, the axis is seen at about 30°N, remaining almost unchanged with depth. Striking features associated with this vertical distribution include a northward shift of the bifurcation latitude of the North Equatorial Current at increasing depth and a barotropic nature of the confluence point between the Kuroshio and Oyashio at their respective western boundaries. The former occurs at about 14°N near the surface and extends north of 20°N at depths around 800 m. The latter, situated at about 36.4°N off Japan, does not appear to have a strong signature of depth-dependence. While some of these results are already known from sporadic hydrographic observations, they have not hitherto been represented in a three-dimensional climatology. This revised version was published online in July 2006 with corrections to the Cover Date.     

An East-West Comparison of the Transition Zone Coastal Pelagic Nekton of the North Pacific Ocean

During the 1980s and 1990s, scientific research cruises were conducted in both the eastern and western boundary regions of the North Pacific Ocean. The main purpose of these cruises was to examine the abundance and distribution patterns of juvenile salmon in coastal waters. These studies created one of the most extensive databases ever collected on the species composition of coastal Transition Zone epipelagic nekton in the North Pacific Ocean. Catch data from two purse seine and two surface trawl surveys (one each from off northern Japan and eastern Russia and off the West Coast of the U.S.) were examined using multivariate techniques to analyze the community structure of nektonic cephalopods, elasmobranchs, and teleosts in the coastal zone during the summer and autumn months. Juvenile salmonids are generally among the most common species caught, but in terms of overall abundance, other potential competitors with juvenile salmon, such as small squids and clupeoid fishes predominated the catches. Species diversity and dominance varied among areas and gear types. Distinct assemblages were found in each area, but the two regions had closely related species occupying similar ecological positions in each habitat. This revised version was published online in August 2006 with corrections to the Cover Date.     

浪致混合对2016年北太平洋海表温度季节性预测的影响

上层海洋通过海气交换影响大气-海洋耦合系统,海浪引起的垂向混合影响上层海洋结构,从而在气候预测过程中发挥着重要的作用。本文基于国家海洋局第一海洋研究所地球系统模式（FIO-ESM）,以2016年为例,分别开展了耦合和关闭海浪模式情况下的短期气候预测实验,分析浪致混合对北太平洋海表温度（SST）季节性预测的影响。通过对模式预测的SST异常（SSTA）进行定量评估发现,浪致混合能够显著降低北太平洋高纬度海区预测误差,在（45°N,150°E）附近海区SSTA改善可达1℃,气候模式能够更好地预测SSTA的经向分布特征,特别是能够准确地反映25°~45°N海区SSTA分布特征。通过分析有浪和无浪两个实验的热收支贡献发现,垂向混合是导致上层海洋温度差异的主导影响因子。海浪通过改变垂向混合,使2016年北太平洋SST在高纬度海区大幅降低,在低纬度海区略有升高,最终提升了模式对北太平洋SST的季节性预测能力。     

Recent increase of DIC in the western North Pacific

The temporal variation of the total dissolved inorganic carbon (DIC) content in the western North Pacific is investigated by comparing the DIC distribution obtained from the data sets of three different periods, the GEOSECS data observed in 1973, the CO₂ dynamics Cruise data observed in 1982, and recent Japanese data sets observed during the early 1990s. The overall feature of the signal of temporal DIC change during 1973 and early 1990s agreed with that of former studies, and did not significantly change with the calculation scheme (the grid-selection method vs. the multiple regression method). The observed increase in DIC among the different time scales showed a good inner consistency, which also indicates the stability of the method used in the DIC change calculation. The apparent rate of increase of the DIC inventory in the upper 1000 m water column, however, differed significantly by the data set used for the calculation: It was 5.6±2.4 g C/m²/year, based on the data comparison between 1982 and the early 1990s, while it became 7.6±2.4 g C/m²/year when based on the data between 1973 and the early 1990s. This result provides us an information about the data-dependency on the former estimation of temporal DIC change.     

北太平洋海表温度及各贡献因子的变化

采用1958年1月至2007年12月SODA海洋上层温度的月平均资料,基于海温变化方程和统计分析方法,分析了北太平洋海表面温度(SST)异常特征及各局地因子贡献比例的变化。结果表明,伴随着1976/1977风场最强中心位置的南北移动,形成了两个北太平洋SST年际-年代际变化的异常中心:一个是位于30°N附近的副热带海盆内区,SST异常主要受风应力强度的主导;一个是位于40°N附近的副热带和副极地环流交汇区,SST异常主要受风应力旋度的位置即风场位置的影响。在副热带海盆内区,最强降温发生在1978-1982年,SST异常的主要局地贡献因子为海表热通量和经向平流,二者所占比例和约为50%~60%,均为同相增温或降温作用,余项所占比例约为20%~50%。在副热带和副极地环流交汇区,海盆内区和西部边界区的SST异常的跃变时间同为1975年,但是内区的垂直混合项的跃变时间早于西部5年左右。SST异常的主要贡献因子为海表热通量和经向平流,但在1983-1988年海温强降温期间,经向平流项贡献大于海表热通量项的贡献。两个区域的垂直混合项均为降温贡献,虽然量值小却显示出很强的年代际变化信号。平流项中经向平流最大,垂直平流最小。     

Long-Term Variability of North Pacific Subtropical Mode Water in Response to Spin-Up of the Subtropical Gyre

The Meteorological Research Institute's ocean general circulation model (MRI-OGCM) has been used to investigate the temperature variability of the North Pacific Subtropical Mode Water (NPSTMW) over a time series longer than 5 years via the spin-up of the subtropical gyre. Besides an interannual variation, the wintertime sea surface temperature in the area where the NPSTMW is formed, and the temperature of the NPSTMW itself, both change remarkably in a >5-year time scale. An analysis of heat budgets showed that the long-term changes in NPSTMW temperature are due mainly to a leading advection of heat by the Kuroshio Extension and compensating surface heat flux. As a result of a dynamical adjustment to the wind stress fields, the transports of the Kuroshio and the Kuroshio Extension increased in the mid 1970s with a lag of 3 years after the wind stress curl in the central North Pacific. The increased heat advection by the Kuroshio Extension induces a warming in the mixed layer in the NPSTMW formation area, followed by a warming of the NPSTMW itself. Both these warming actions increase the heat release to the atmosphere. These results imply that the surface heat flux over the Kuroshio Extension area varies in response to the change in the ocean circulation through the spin-up of the subtropical gyre. This revised version was published online in August 2006 with corrections to the Cover Date.     

A Comparison of the Seasonality and Interannual Variability of Phytoplankton Biomass and Production in the Western and Eastern Gyres of the Subarctic Pacific Using Multi-Sensor Satellite Data

This study documents the results of a multi-sensor satellite investigation aimed at comparing the seasonality and interannual variability of phytoplankton biomass and primary productivity (PP) in the western and eastern gyres of the subarctic Pacific. Satellite data helped discern several features, most importantly the existence of significant east-west gradients in the supply of nitrate in winter, in the consumption of nitrate by phytoplankton and in phytoplankton production and biomass accumulation over the growth season. In the western subarctic gyre many of these features appear to be regulated by the strength of sea surface winds through increased iron and nitrate inputs. Multiple regression analysis of data extracted from 12 boxes spanning different hydrographic regimes in the subarctic Pacific, showed that over 65% of the variations in PP in the subarctic Pacific could be explained solely on the basis of changes in the strength of sea surface winds and the intensity of incident irradiance (PAR). The dependence of PP on sea surface wind stress was far greater in the western subarctic Pacific Gyre (WSG), than in the Alaskan Gyre (ALG) due to diminishing impact of surface winds towards the east. Spring accumulation of phytoplankton biomass was greater in the WSG than in the ALG despite the higher rates of PP in the latter. This study assumes particular significance because it helps ascertain the existence of several sub-regions within the two broader domains of the WSG and the ALG. In addition, large interannual variations in phytoplankton biomass and PP were observed in the subarctic Pacific following the onset of the El-Niño event of 1997 and the transition to La-Niña conditions in 1999. These variations were largely the result of differences in meteorological and oceanographic conditions across the subarctic Pacific following the development of the El-Niño.     

北太平洋原子弹14C分布的模拟

利用一个开边界的北太平洋海盆尺度环流模式模拟了北太平洋原子弹14C的分布和吸收。为了考察开边界与闭边界模式的不同以及开边界模式中不同等密度面扩散系数对模拟结果的影响,相应地做了一个闭边界实验和开边界的两组不同等密度面扩散系数的实验。结果表明,打开南边界改善了赤道以南海区的模拟结果,增大等密度面扩散系数使得模拟的北太平洋中层水强度增大,相应地在165°E等断面模拟的含高浓度原子弹14C的海水向南、向下输送的强度和影响范围都有比较明显的加强,改善了模式的模拟结果,证明大的等密度面扩散系数可以改善模式的模拟结果,能较好地再现在副热带海区原子弹14C水柱总量的梯度由西向东的观测特征。