Study of continental material transported through the atmosphere to the oeean

I am deeply honored to have been selected as a recipient of the 1987 Okada Prize by the Oceanographical Society of Japan. The present paper reviews my work and recent studies of other investigators concerning mineral aerosol (dust) particles in the marine atmosphere over the Pacific Ocean. I would like to emphasize the importance of atmospheric deposition of continental substances to the ocean environment. From consecutive measurements of atmospheric dust concentrations and total deposition fluxes at 13 island stations in the Pacific Ocean, a strong seasonal transfort pattern of dust particles was found at most of the stations. High atmospheric dust concentrations occurred during the spring in both hemispheres. There was a latitudinal gradient in both the atmospheric dust concentration and flux, with the highest values observed at midlatitudes. When combined with observations of dust storms in Asia and isentropic trajectory analysis, it was clear that the dust over the central North Pacific was transported by the upper westerly winds from the arid desert regions in central and eastern Asia. Transport times were 1–2 weeks, and in some cases, atmospheric transport paths of over 10,000 km were observed. Infrequent short-term dust events contributed most of annual atmospheric dust flux to the open ocean. These sporadic inputs are major sources for both suspended mineral matter in the water column and the non-biogenic component of deep-sea sediments in the Pacific Ocean. The impact of atmospheric dust fluxes on chemical and biological processes in the water column remains to be determined.     

LONG-DISTANCE ATMOSPHERIC TRANSPORT OF DUST FROM CHINESE DESERT TO THE NORTH PACIFIC

The Chinese desert is one of the major sources of atmospheric mineral dust transported for a long distance to the North Pacific by the atmospheric circulation. The characteristic of the aerosol in the North Pacific is smilar to that of the aerosol in North China with a considerable concentration of mineral in spring due to the large-scale dust storm occurring in North China. The study of isotope tracer indicates that the concentration of Al is significantly related to 210Pb, suggesting that the mineral aerosol in the North Pacific may origir ate from the desert in Northwest China by using air mass trajectory analysis. About 6-12×106 tons of Chinese desert mineral dust per year would be transported to the North Pacific.     

Aluminum in the East China Sea and Okinawa Trough, marginal sea areas of the Western North Pacific

The distribution of aluminum (Al) in seawater has been investigated in the continental slope and the Okinawa Trough areas of the East China Sea, which is one of the marginal seas in the western North Pacific Ocean. Aluminum concentration in waters over the slope and the Trough ranged from 5.6 to 25 nmol/kg in the surface layer (0–100 m), and had a minima of 1.1 nmol/kg between 400 and 500 m depth and ranged from 1.3 to 9.7 nmol/kg in the deep or bottom waters. Aluminum values were higher than in the surface waters of the central North Pacific, while minimum values were similar to levels in the intermediate or deep waters of the central North Pacific, except for the bottom water over the slope. This suggests that the high Al concentration in the surface reflects the large atmospheric input of Asian dust around the western side of the North Pacific region. On the continental slope, Al concentrations in the upper 500 m depth decreased slopeward. This horizontal gradient of Al can be explained from the combination of dilution by upwelling of Al-poor water originated from the North Pacific Intermediate Water (NPIW) which intrudes into the mid-depth of the Okinawa Trough and the scavenging of Al by biogenic particles in the continental slope zone.     

Lead in the southern East China Sea

At present, in most oceans the lead (Pb) biogeochemical cycling has been disturbed by anthropogenic Pb through atmospheric input. The Pb concentrations in the upper water positively correlate with atmospheric input fluxes of Pb. The North Pacific is affected greatly by atmospheric substances via long-range transport from eastern Asia, especially from Mainland China. Mainland China may export considerable amounts of pollutants into the seas via rivers and the atmosphere owing to its recent fast growth in industry and economy. The East China Sea lies in an important geographical position--a transit between Mainland China and the western North Pacific. However, no data are available for seawater concentrations of Pb, a representative element with anthropogenic origin. In this work seawater samples from both 5 and 30-50 m water layers of 15 stations occupied over a cyclonic eddy in the southern East China Sea were analyzed for particulate Pb (PPb) and dissolved Pb (DPb). The Mean concentration of DPb (approximately 128 ng/l) in the southern East China Sea upper waters (< or = 50 m) is approximately several times higher than those in the Pacific; the high DPb concentrations in the southern East China Sea waters correspond to much higher atmospheric supplies of Pb to the East China Sea. Thus, this study partly fills the 'data gap' of the marginal seas. Also, it indicates that the East China Sea may be considerably contaminated by deposited polluted aerosols. Spatial distributions of DPb in the surface water show a tendency of increasing concentrations with distance offshore, that depends on the magnitudes of atmospheric Pb inputs and on particle scavenging processes. In contrast to DPb, spatial distributions of PPb basically display an 'omega'-like picture and a tendency of decreasing concentrations with distance offshore. These are related to riverine and scavenging sources and to the drive by the eddy. Additionally, the residence times of DPb in the surface water were estimated to be about 2 years, agreeing well with the reported data.     

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.     

Iron, manganese and aluminum in upper waters of the western South Pacific Ocean and its adjacent seas

Total dissolvable iron, manganese and aluminum distributions in upper waters were determined in the western South Pacific, Solomon Sea, Coral Sea, and Tasman Sea. In these oceanic regions, the surface aluminum distributions well reflect the atmospheric deposition pattern of mineral dust in the western South Pacific reported previously. Surface manganese distributions derive mainly from lateral transportation from the coastal sediments of western tropical islands. Compared to Mn and Al, the Fe distributions reflect the nutrient cycle in upper waters. Iron limitation over the vast South Pacific, as revealed by physiological features of phytoplankton, seems to be caused by low atmospheric dust deposition and low Fe:N ratios in deep waters. In the western South Pacific, with its unique geographic and oceanographic settings, the local sources of trace metals might considerably affect their biogeochemical cycles.     

Distributions of low molecular weight dicarboxylic acids in the North Pacific aerosol samples

Marine aerosol samples collected from the North Pacific atmosphere were studied for molecular distributions of dicarboxylic acids by using a capillary gas chromatography and mass spectrometery. A homologous series of dicarboxylic acids (C₂–C₁₀) was detected in the marine aerosol samples as dibutyl esters. All the samples showed that the smallest diacid (oxalic acid: C₂) was the most abundant and comprised 41–67% of the total diacids. The second most abundant species was malonic acid (C₃) or succinic acid (C₄). The diacids with more carbon numbers were generally less abundant. Total diacid concentration range was 17–1040 ng m^–3, which accounted for up to 1.6% of total aerosol mass. This indicates that low molecular weight dicarboxylic acids are important class of organic compounds in the marine atmosphere. The concentrations were generally higher in the western North Pacific and lower in the central North Pacific. The major portion of diacids is probably derived from the Asian Continent and East Asian countries by long-range atmospheric transport and partly fromin situ photochemical production in the marine atmosphere.     

北太平洋大气沉降的时空特征及其对副极区海洋生态系统的影响

北太平洋副极地海区作为全球海洋三个高营养盐低叶绿素(high nutrient and low chlorophyll, HNLC)海区之一, 其浮游植物生长受到微量元素铁的限制。对于开阔大洋, 大气沉降是海洋表层铁的一个重要来源, 铁元素沉降进入海洋后能够促进浮游植物生长, 进而引起海洋初级生产力和生物泵的响应。本文利用SPRINTARS(Spectral Radiation-Transport Model for Aerosol Species)模式的时长为20a的日均大气沉降数据, 对北太平洋海区大气沉降的时空特征进行了分析。结果表明, 进入北太平洋海区的大气沉降量为26.81Tg·a^-1, 并且存在显著的季节变化: 春季最高, 冬季最低, 5月份进入海洋的沉降量达到峰值。大气沉降主要来源于陆地区域, 在风场的驱动下向海洋传输, 因此大气沉降量的空间分布呈现出西高东低的特征。本文以2010年8月中旬卫星观测到的一次强沙尘(即高大气沉降量)事件为例, 研究了大气沙尘的传播路径。进一步结合2001年4月9—12日及2008年4月20—22日的沙尘事件, 分析了西北太平洋K2站位(47°N, 160°E)附近海域海洋初级生产力对大气沉降——沙尘事件的响应。结果表明, 三次沙尘事件后, K2站位的颗粒有机碳通量、叶绿素浓度均有明显增加, 即沙尘事件对北太平洋副极区海洋初级生产力存在促进作用。     

赤道太平洋上层水体颗粒态生物硅分布及与营养盐的关系

依托中国“大洋一号”第20和第21调查航次,分析测定了东、西赤道太平洋4个站位的颗粒态生物硅浓度及其粒级结构。结果显示赤道太平洋采样站各层位颗粒态生物硅(PBSi)总浓度分布范围为5~65 nmol/dm³,东赤道太平洋的调查站位颗粒态生物硅的总浓度平均值达46 nmol/dm³,是西赤道太平洋的近3倍。PBSi的粒径结果显示在东赤道太平洋调查站位0.8~20 μm粒径颗粒是PBSi的主要来源,其平均贡献率高达64%;而在西赤道太平洋2种粒径的生物硅贡献率相当。营养盐分布对PBSi的浓度及粒径分布有显著的影响,并在一定程度上控制了“硅质泵”的组成结构,是控制大洋生物泵运转的重要因素。     

Biomass, Abundance, and Vertical Distribution of Micronekton and Large Gelatinous Zooplankton in the Subarctic Pacific and the Bering Sea during the Summer of 1997

The biomass, abundance, and vertical distribution of micronekton, including enidarians, mysids, euphausiids, decapods, thaliaceans, and fishes, were studied on the basis of samples collected with an 8-m² opening-closing rectangular midwater trawl (RMT-8, mesh size: 4.5 mm) at three stations in the subarctic Pacific (the western subarctic gyre, the central Subarctic, and the Gulf of Alaska) and one station in the oceanic Bering Sea. The total biomass in the 0–1000 m water column ranged from 2.9 to 5.1 gDW m^–2. Except for primary consumers that showed highly variable biomass (thaliaceans and euphausiids), biomass was highest in the oceanic Bering Sea followed by the central (boundary between eastern and western gyres), western gyre, and eastern Gulf of Alaska. The biomass compositions by higher taxa were basically similar between regions: fishes were most dominant, followed by enidarians at all stations, except for the marked predominance of thaliaceans in the Gulf of Alaska. High biomasses of gelatinous animals (31% of overall dry weight), occasionally comparable to those of fishes and crustaceans, suggest their potential importance in the subarctic Pacific. Characteristics in vertical patterns of micronekton biomass common in all stations were: (1) a mesopelagic peak around 500–600 m both day and night, (2) a layer of low biomass in the cold intermediate water and/or in the upper mesopelagic zone, (3) a nighttime shift of biomass to upper layers, and (4) an highly variable biomass of epipelagic/interzonal migrants (euphausiids and thaliaceans).     

Non-sea-salt sulfate in the marine boundary layer and its possible impact on chloride depletion

1Introduction Sulfurisoneofthemostimportantelements whosebiogeochemicalcyclesarepivotaltotheatmo- sphericenvironmentandtotheclimaticchanges.The predominant,stablechemicalspeciesofsulfurinthe atmosphereissulfuricacidorsulfatewhichunderor- dinaryconditionsexistsmainlyinsmallaerosolparti- cles(Chinetal.,1996;Kerminenetal.,2000;Restadet al.,1998).Sulfuricacidorsulfate-dominatedaerosols areubiquitousintheloweratmosphere.Inthemarine boundarylayer(MBL),non-sea-saltsulfuricacidorsulfate(nss-SO42-)…     

Mesopelagic fishes of the Bering Sea and adjacent northern North Pacific Ocean

Fourteen midwater trawl collections to depths of 450 m to 1,400 m were taken at eleven stations in the Bering Sea and adjoining regions of the northern North Pacific by the R/V Hakuho Maru during the summer of 1975. A total of 29 kinds of fishes were identified. Mesopelagic fishes of the families Myctophidae, Gonostomatidae and Bathylagidae predominated in the catches, contributing 14 species (94%) of the fishes caught.Seventeen species of fishes were caught in the Bering Sea, and all of these are known from nearby areas. The mesopelagic fish fauna of the Bering Sea is similar to that in adjoining regions of the northern North Pacific Ocean: endemic species are rare or absent. Stenobrachius nannochir was usually the most common mesopelagic fish in our catches.Stenobrachius leucopsarus is a diel vertical migrant that is usually the dominant mesopelagic fish in modified Subarctic waters of the northeastern Pacific. The change in dominance fromS. nannochir in the western Bering Sea toS. leucopsarus in the eastern Bering Sea is related to differences in oceanographic conditions.     

Diel Changes in Vertical Distribution and Feeding Conditions of the Chaetognath Parasagitta elegans (Verill) in the Subarctic Pacific in Summer

Diel changes in vertical distribution and feeding conditions of the chaetognath Parasagitta elegans (Verill) were observed in three regions of the subarctic North Pacific in the summer of 1997. Samples were collected by repeated vertical hauls with a Vertical Multiple Plankton Sampler (VMPS) for 15–45 hours by demarcating the 0–500 m water column into four sampling layers. Integrated abundance through the entire water column and the proportion of juveniles were higher in the Bering Sea than the western and eastern subarctic Pacific. Juveniles always inhabited the surface layer in the western subarctic Pacific and Bering Sea, but they inhabited the underlying layer in the eastern subarctic Pacific. Stages I–III concentrated into the upper 150 m in the western subarctic Pacific but were distributed widely from 20–300 m in the Bering Sea. Among them, Stages II and III migrated rather synchronously over a wide vertical range in the eastern subarctic Pacific. The feeding rate of P. elegans was calculated to be 0.18 prey/chaetognath/day in the western subarctic Pacific, 0.27 prey/chaetognath/day in the Bering Sea and 0.07 prey/chaetognath/day in the eastern subarctic Pacific.     

Spatial and temporal variability and size fractionation of chlorophyll a in the tropical and subtropical Pacific Ocean

The spatial and temporal variability and size fractionation of chlorophyll a(Chl a) were investigated in the tropical and subtropical Pacific Ocean during four survey cruises from 2005 to 2009.The surface Chl a(S-Chl a) concentration ranged from 0.002 to 0.497 mg/m 3 and was obviously higher in the eastern Pacific than in the western and central Pacific.The vertical distribution of Chl a displayed a single peak pattern,and the maximum Chl a layer(MCL) was observed at a shallower depth in the eastern Pacific than in the western Pacific.All three size fractions of Chl a measurements in the surface water showed a similar distribution to total Chl a and were found in higher concentrations in the eastern Pacific than in the western and central Pacific.Picoplankton dominated the phytoplankton in the surveyed tropical and subtropical Pacific Ocean.Furthermore,pico-Chl a(0.2-2 μm) accounted for a larger percentage of the total Chl a in the central Pacific than it did in the western Pacific and eastern Pacific.In the western Pacific,there seemed to be a latitudinal variability in the phytoplankton community composition where small-sized phytoplankton(<2 μm) were more dominant in the tropical than in the subtropical western Pacific.The spatial and temporal variability and size fractionation of Chl a were controlled by hydrological and chemical characteristics and climate events,such as El Nin o and La Nin a.     

How are large western hemisphere warm pools formed?

During the boreal summer the Western Hemisphere warm pool (WHWP) stretches from the eastern North Pacific to the tropical North Atlantic and is a key feature of the climate of the Americas and Africa. In the summers following nine El Niño events during 1950–2000, there have been five instances of extraordinarily large warm pools averaging about twice the climatological annual size. These large warm pools have induced a strengthened divergent circulation aloft and have been associated with rainfall anomalies throughout the western hemisphere tropics and subtropics and with more frequent hurricanes. However, following four other El Niño events large warm pools did not develop, such that the mere existence of El Niño during the boreal winter does not provide the basis for predicting an anomalously large warm pool the following summer.In this paper, we find consistency with the hypothesis that large warm pools result from an anomalous divergent circulation forced by sea surface temperature (SST) anomalies in the Pacific, the so-called atmospheric bridge. We also find significant explanations for why large warm pools do not always develop. If the El Niño event ends early in the eastern Pacific, the Pacific warm anomaly lacks the persistence needed to force the atmospheric bridge and the Atlantic portion of the warm pool remains normal. If SST anomalies in the eastern Pacific do not last much beyond February of the following year, then the eastern North Pacific portion of the warm pool remains normal. The overall strength of the Pacific El Niño does not appear to be a critical factor. We also find that when conditions favor a developing atmospheric bridge and the winter atmosphere over the North Atlantic conforms to a negative North Atlantic Oscillation (NAO) pattern (as in 1957–58 and 1968–69), the forcing is reinforced and the warm pool is stronger. On the other hand, if a positive NAO pattern develops the warm pool may remain normal even if other circumstances favor the atmospheric bridge, as in 1991–92. Finally, we could find little evidence that interactions internal to the tropical Atlantic are likely to mitigate for or against the formation of the largest warm pools, although they may affect smaller warm pool fluctuations or the warm pool persistence.     

The distribution of planktonic Ostracoda between the source of Kuroshio and west of Taiwan Strait

Little was studied on oceanography and ecology on the eastern sea waters off the Philippines,Bashi Channel and Balintang Channel in the past.In this paper are presented the results of an ecological study on Ostracoda in the above-stated sea waters in which the samples of Ostracoda were collected in the North Pacific nets from 90 stations by Surveyer I(May-July,1968) in accordance with CSK Program.The study took into consideration the in situ temperature-salinity data.In addition,a comparative dissection has been carried out on the samples of Ostracoda obtained in the normal nettings trawled from bottom to surface during an annual survey(see May,1984-May,1985)in the west from the central line of the Taiwan Strait(see Fig.1) by the Third Institute of Oceanography,State Oceanic Administration.The interaction of different current systems,especially the Kuroshio on Ostracoda,is described from the distribution of different ecological attributions.     

Impact of mesoscale eddies on particulate organic carbon flux in the western subarctic North Pacific

The mechanism that controls particulate organic carbon (POC) flux in the deep sea differs depending on the season and sea. The POC produced in the western subarctic North Pacific are known to be transported to the deep sea efficiently, but the direct relationship between the POC flux and physical processes is still unclear. In this study, we evaluated the effect of mesoscale eddies on POC flux in the western subarctic North Pacific. The seasonal and interannual variabilities of POC flux were investigated using data from a time-series sediment trap deployed at 4810 m at station K2 (47°N, 160°E) from 2005 to 2018. POC flux was high during May–November, appearing to reflect spring and fall blooms at the ocean surface. POC flux also showed interannual variability, with twelve peaks that were mostly affected by enhanced bloom just before the peak. Nine peaks of the twelve peaks were affected by mesoscale eddies, which enhanced bloom around K2 by extending the area with a high chlorophyll-a concentration along the coastal region into the offshore region, suggesting that mesoscale eddies strongly impact the interannual variability of POC flux at K2.

     

Concentration and behavior of detrital mineral grains suspended in the water column of the open sea in the western Pacific

The pattern of distribution of detrital mineral grains in the water column was investigated at three stations in the western Pacific during July through August of 1979. The sedimentation of detrital mineral grains was also studied using piston cores from two sites adjacent to the three stations. The concentration of suspended detrital mineral grains in the subsurface waters becomes lower with increasing distance from the land, and shows a prominent peak in the intermediate zone of the water column. The sharp increase in water density and viscosity in the pycnocline in the intermediate zone decreases the settling velocity of grains, and may result in the accumulation of falling grains in the intermediate layer. Proportion of detrital mineral grains to organic remains in the sediment was more than two orders of magnitude larger than in the overlying water column, and reasons for this are briefly discussed.     

热带中东太平洋海域10°N断面水团分析

本文基于实测温盐数据等资料,利用水团的浓度混合分析等方法,揭示了热带中东太平洋海域10°N断面的水团构成自上而下分别为东部赤道–热带水团、北太平洋中央水团、加利福尼亚流系水团、南太平洋中央水团、太平洋亚北极水团和太平洋深层水团。分析发现,受热带辐合带影响,9°～10°N海域常年持续的正风应力旋度诱发上升流出现,北太平洋中央水团、加利福尼亚流系水团、南太平洋中央水团和太平洋亚北极水团4个通风潜沉水团经向运动至该纬度带时被抽吸至次表层和中层,并散布在不同深度。以往研究仅指出上述4个水团在海表通风形成后将潜沉并向赤道方向运动,本研究进一步阐明了4个水团潜沉后向热带海域运动的动力机制及其在热带中东太平洋10°N断面的散布深度。研究成果揭示了热带中东太平洋水团与北太平洋副热带、亚极地和南太平洋副热带海区中上层水团间的循环过程,对认识北太平洋高–中–低纬度间物质和能量的交换和再分配具有重要科学价值。     

Has the 1998 regime shift also occurred in the oceanographic conditions and lower trophic ecosystem of the Oyashio region?

To examine whether the regime shift in 1998 that has been variously reported to have occurred in the oceanographic conditions of the central and eastern North Pacific also occurred in the Oyashio region, western North Pacific, we compared data over the period 1990–2003. Oceanographic conditions were compared before 1997 with those after 1998, using the A-line dataset (1990–2003) obtained by the oceanographic surveys of the Hokkaido National Fisheries Research Institute, Fisheries Research Agency (HNFRI/FRA). Seasonal changes of the monthly-mean SST (as temperature in the surface layer) show a significant increase in spring after 1998. After 1998, the mean concentration of chlorophyll a at the surface was higher in spring than that before 1997. This was more remarkable in the main current of the Oyashio. These changes suggest that the spring phytoplankton bloom in the Oyashio region after 1998 was larger in magnitude and initiated earlier. Consumption of nutrients during the spring bloom and standing stock of netplankton also shows a distinct difference between the time period before 1997 and after 1998. These results support the occurrence of the regime shift around 1998 in the Oyashio region. The changes of hydrographical conditions accompanying with the 1998 regime shift are discussed. The hydrographic mechanism of enhancement of primary productivity during the spring phytoplankton bloom was not fully clarified, though. Results in this study may support the usefulness of the A-line dataset for analysis of long-term variability in the western subarctic Pacific.