North Pacific Area Research Articles

The role of sea ice in the distribution, habitat use, and phenology of eastern North Pacific gray whales

A strong negative relationship has been observed between calf production of eastern North Pacific gray whales Eschrichtius robustus and Pacific Arctic sea ice area with the exception of 2 potentially anomalous periods: 2013-2014 and 2017-2019. Sea ice may play a role in reproductive variability by blocking gray whale access to foraging hotspot habitats. We tested this ‘sea ice exclusion’ hypothesis using complementary aerial survey and moored hydrophone data sets that together provide broad spatial and temporal coverage. A negative relationship (generalized additive model, p < 0.001) was found between gray whale aerial counts and ice concentration in the northeast Chukchi Sea (2008-2019), with a nonlinear increase in negative slope above 45-55% concentration. A comparison of distribution patterns between years further indicated the absence of sightings within northern Bering and northeastern Chukchi foraging hotspots during years with delayed ice break-up versus years with an early-to-average ice retreat. Passive acoustic recordings likewise showed the near-absence of detections during periods of dense ice cover and indicated a strongly positive relationship between ice break-up dates and the timing of acoustic detection onset. Together, these analyses point to the important role of sea ice in gray whale distribution, habitat use, and phenology. However, a relatively consistent 10-15 d lag observed between ice break-up and acoustic onset dates suggested that the mechanism(s) underpinning gray whale interactions with sea ice may be more complex than simply ‘sea ice exclusion.’ Here, we propose ‘prey quality timing’ as a potential alternative hypothesis that warrants further investigation.

Break Events of the Western North Pacific Summer Monsoon during 1979–2018

Abstract The monsoon break is a typical phenomenon representing the monsoon’s subseasonal variability, but our understanding of it is still limited for the western North Pacific (WNP) area. This study identifies all break events of the WNP summer monsoon (WNPSM) from 1979 to 2018. The statistical analysis suggests that break events occur from late June to late October and peak at the end of August. The occurrence frequency of break events decreases as the duration increases, with 74% of events persisting for 3–7 days and merely 26% lasting longer (8–15 days). During the break period, which is characterized by significant suppression of convection, there is an extensive anticyclonic anomaly in the lower troposphere, corresponding to a notable westward retreat of the monsoon trough and a southwestward shift of the subtropical high. Meanwhile, an anomalous cyclone and convergence in the upper troposphere are also conducive to inhibiting convection. The composite results indicate that both 10–25- and 30–60-day oscillations contribute to the break, with their dry phases explaining 49.6% and 37.5% of the original suppression of convection, respectively. Around the break, the phase alternation of the 10–25-day oscillation causes convection fluctuation, while the 30–60-day oscillation maintains a stable dry phase that favors the establishment and maintenance of the break. A further case-by-case diagnosis suggests that 46 (51) out of the 61 break events occur in dry phases of the 10–25-day (30–60-day) oscillation, whereas only 10 (4) events occur in wet phases, indicating that the phase of the two oscillations significantly modulates the occurrence of the monsoon break.

Effects of the Assimilation of Relative Humidity Reproduced From T‐PARCII and Himawari‐8 Satellite Imagery Using Dynamical Initialization and Ocean‐Coupled Model: A Case Study of Typhoon Lan (2017)

AbstractEffects of the assimilation of relative humidity (RH) reproduced from dropsonde data from the Tropical cyclones‐Pacific Asian Research Campaign for Improvement of Intensity estimations/forecasts (T‐PARCII) campaign and Himawari‐8 satellite data on the simulation of Typhoon Lan (2017) were investigated herein using a weather research and forecasting model. The lateral boundary and initial conditions were obtained from Global Forecast System (GFS) forecast data. Four experiments varying from the initial vortex, assimilation of the reproduced RH (ARH), and ocean model (OCEAN, three‐dimensional Price‐Weller‐Pinkel upper‐ocean circulation model) activation were conducted for 42 h to evaluate tropical cyclone (TC) forecast performance: the GFS experiment and dynamical initialization (DI) experiments such as DI, DI‐OCEAN, and DI‐ARH‐OCEAN, respectively. All track forecast errors were less than 100 km until landfall, that is, up to 36 h. TC intensity forecasts such as the minimum sea‐level pressure and maximum surface wind speed were slightly improved in DI‐related experiments compared to the GFS experiment. The DI‐ARH‐OCEAN experiment, in particular, demonstrated improvements in both TC forecasts and convective areas. The ocean‐coupled experiments yielded significant sea surface temperature cooling in the rear‐right quadrant of TC, forming a stable boundary layer that could suppress the convective activity, particularly in the lower troposphere. These findings support that compared to the original DI method, ARH could improve initial conditions, resulting in more accurate TC forecasts. Furthermore, it may argue the necessity and urgency of regular aircraft surveillance of TCs in the western North Pacific area.

Surface-Water Quality of the Gulf of Papagayo, North Pacific, Costa Rica

In recent years, the northwestern part of the North Pacific areas of Costa Rica has undergone rapid socioeconomic development. This situation, combined with the scarce available information about the water quality of the Gulf of Papagayo, became the starting point to carry out a study to investigate the spatiotemporal variations of physicochemical and biological parameters of surface waters. Seven samplings were collected during the dry season and the rainy season from October 2016 to February 2018. Water quality parameters such as: temperature, salinity, dissolved oxygen, and chlorophyll a of six analytes: nitrate, nitrite, ammonia, phosphate, silicate and biological oxygen demand were measured. The results showed that phosphate and ammonium levels were lower during the rainy season (<6 µg P-PO4−3 L−1–9.53 µg P-PO4−3 L−1 and <11 µg N-NH4+ L−1–9.57 µg N-NH4+ L−1) than during the dry season (<6 µg P-PO4−3 L−1–13.64 µg P-PO4−3 L−1 and <11 µg N-NH4+ L−1–14.43 µg N-NH4+ L−1), which may be related to low rainfall (0, 00–26, 16 mm) during the sampling period. The dry season showed enrichment of ammonium, phosphate, and chlorophyll a due to the influence of the coastal upwelling for the intensification of the Papagayo winds from December to March. The physical, chemical, and biological indicators demonstrated that the Gulf waters had adequate quality. Nonetheless, there are specific areas such as Culebra Bay with conditions that could show deterioration of water quality.

Impact of interannually varying background circulation on summertime wave patterns and tropical cyclone tracks in the western North Pacific

This study analyzed summertime wave patterns in the western North Pacific by separating them into those during El Nino (EN) and La Nina (LN) years for 1979–2015. The background flow revealed that in the EN years, the subtropical high was weaker and the East Asian summer monsoon trough was deeper and extended farther southeastward. The composite results indicated that in the EN years, tropical cyclone (TC) tracks were more solid and stably associated with wave pattern propagation routes because the circulation anomalies were significantly stronger. However, in the LN years, when the wave patterns were weak under the shorter and less organized monsoon trough due to the enhanced subtropical high, the TC tracks and cyclonic anomalies were irregular and sporadic. Further background flow analyses indicated that the EN circulation favored the development of the monsoon trough and east–west expansion and contraction of the subtropical ridge, whereas the stronger subtropical ridge dominated most western North Pacific areas in the LN years. Therefore, the monsoon trough was weaker in the LN years and induced recurving TCs to take more scattered routes near Taiwan and China’s east coast. Therefore, Taiwan experienced more rainfall during recurving TC periods in the LN years than in the EN years. For the straight-moving TCs passing through Taiwan, rainfall was concentrated over southern Taiwan in the EN years but more evenly distributed in the LN years. Thus, background flow changes strongly affect wave patterns and TCs.

Variation of Surface Radiocarbon in the North Pacific During Summer Season 2004–2016

ABSTRACTSurface radiocarbon (Δ14C) in the North Pacific has been monitored using a commercial volunteer observation ship since the early 2000s. Here we report the temporal and spatial variations in Δ14C in the summer surface water when the surface ocean is vertically stratified over a 13-yr period, 2004–2016. The long-term Δ14C decreasing trend after the late 1970s in the subtropical region has continued to the present and the rate of decrease of the Kuroshio and Kuroshio Extension, North Pacific and California current areas is calculated to be –3.3, –5.2 and –3.3 ‰/yr, respectively. After 2012 the Δ14C of the Kuroshio and Kuroshio Extension area, however, has remained at an approximately constant value of around 50‰. The result may indicate that subtropical surface Δ14C in the western North Pacific has reached an equilibrium with atmospheric Δ14CO2. The Δ14C in the subarctic region is markedly lower than values in the subtropical region and it seems that the decreasing tendency of surface Δ14C has changed to an increasing tendency after 2010. The results may indicate that bomb-produced 14C, which has accumulated below the mixed layer in the past few decades, has been entrained into the surface layer by deep convection.

Wave hindcast in the North Pacific area considering the propagation of surface disturbances

Ocean surface waves in the North Pacific area are affected by storm winds. It is necessary to consider the movement of storms to predict waves. The impact of a time interpolation method for winds that considers the propagation of surface disturbances on ocean wave prediction from 2005 to 2006 in the North Pacific area is demonstrated. It is possible to interpolate surface winds, even when there are multiple cyclones and anticyclones moving in different directions at different distances. This method will be useful for wind fields with increasing amounts of spatial information. The predicted wave heights and periods from the linearly interpolated winds and the winds predicted using this new method are compared with in-situ observations from several moored buoys. The predicted wave heights are also compared with those from several drifting buoys in the northwestern Pacific. The improvement of the wave height and period prediction is evident in the case where the difference in the predicted wave parameters between the linear interpolation and the present method is large. The improvement of the wave height and period prediction is statistically significant at more than 95% in most cases. It is shown that the wave height and period prediction can be improved by improving the time interpolation method; however, the improvement of the wave direction prediction is not evident.

Fall-winter cyclogenesis over the Pacific Ocean and Far-Eastern Seas and its influence on development of the sea ice

Cyclonic activity patterns over the North Pacific in fall-winter have changed prominently in the last two decades (since the middle 1990s) due to a gradual westward shift of the Aleutian Low and Siberian High. The maximum of cyclonic activity was observed in the eastern Bering Sea in the 1990s, but strong winter cyclones moved mostly to the Okhotsk Sea and Kuril Islands in the late 2000s. These changes caused the ice regime change: the ice cover was relatively low in the Bering Sea in opposite to heavy ice conditions in the Okhotsk Sea until the mid-2000s, but the ice cover decreased in the Okhotsk Sea and increased in the Bering Sea when tracks of cyclones had changed. Some changes concern the moderate latitudes, too, because cyclones in the Bering Sea made a cooling effect on the North Pacific area southward from Aleutian Islands but those in the Okhotsk Sea cool the Japan Sea area.

Áreas de congregación de cetáceos en el Pacífico norte de Costa Rica: recomendaciones para la gestión del recurso

<p>La información disponible sobre la distribución de los cetáceos para el Pacífico Norte de Costa Rica actualmente carece de análisis que faciliten la toma de decisiones con el fin de tomar medidas políticas o de manejo para la conservación de los cetáceos costeros. El objetivo de este estudio es identificar áreas de importancia para los cetáceos en el Pacífico Norte, especialmente fuera de la de las áreas protegidas existentes. Se analizaron datos publicados anteriormente sobre avistamientos de cetáceos entre 2004 y 2008, y se complementó esta información con esfuerzo de muestreo durante la estación seca del 2012. Se utilizó un análisis geoestadístico de Kriging ordinario para predecir la continuidad espacial de avistamientos de cetáceos dentro de cuatro áreas de estudio. Con base en este análisis, las áreas de congregación más importantes para los delfines son: Bahía Santa Elena, Parque Nacional Marino Las Baulas and Reserva Natural Cabo Blanco, debido a las altas densidades de grupos de delfines en actividades de alimentación. Las áreas de congregación relevantes para las ballenas jorobadas son: Bahía Santa Elena, Playa Tambor, Golfo de Papagayo and Reserva Natural Cabo Blanco. El estudio identifica las áreas de altas concentraciones de cetáceos en el Pacífico Norte, tanto dentro como fuera de las zonas protegidas. Nuestros resultados indican que algunas de las áreas no protegidas deben ser priorizadas con respecto a la priorización de estrategias de conservación, tales como: Península de Santa Elena, Bahía Culebra, Santa Rosa-Islas Murciélagos, y los alrededores de Punta Pargos y Cabo Blanco. Con base en una primera identificación de las amenazas marinas, se proponen medidas de gestión y políticas para garantizar la conservación de estos sitios de congregación de cetáceos.</p>

Sensitivity of simulated regional Arctic climate to the choice of coupled model domain

The climate over the Arctic has undergone changes in recent decades. In order to evaluate the coupled response of the Arctic system to external and internal forcing, our study focuses on the estimation of regional climate variability and its dependence on large-scale atmospheric and regional ocean circulations. A global ocean–sea ice model with regionally high horizontal resolution is coupled to an atmospheric regional model and global terrestrial hydrology model. This way of coupling divides the global ocean model setup into two different domains: one coupled, where the ocean and the atmosphere are interacting, and one uncoupled, where the ocean model is driven by prescribed atmospheric forcing and runs in a so-called stand-alone mode. Therefore, selecting a specific area for the regional atmosphere implies that the ocean–atmosphere system can develop ‘freely’ in that area, whereas for the rest of the global ocean, the circulation is driven by prescribed atmospheric forcing without any feedbacks. Five different coupled setups are chosen for ensemble simulations. The choice of the coupled domains was done to estimate the influences of the Subtropical Atlantic, Eurasian and North Pacific regions on northern North Atlantic and Arctic climate. Our simulations show that the regional coupled ocean–atmosphere model is sensitive to the choice of the modelled area. The different model configurations reproduce differently both the mean climate and its variability. Only two out of five model setups were able to reproduce the Arctic climate as observed under recent climate conditions (ERA-40 Reanalysis). Evidence is found that the main source of uncertainty for Arctic climate variability and its predictability is the North Pacific. The prescription of North Pacific conditions in the regional model leads to significant correlation with observations, even if the whole North Atlantic is within the coupled model domain. However, the inclusion of the North Pacific area into the coupled system drastically changes the Arctic climate variability to a point where the Arctic Oscillation becomes an ‘internal mode’ of variability and correlations of year-to-year variability with observational data vanish. In line with previous studies, our simulations provide evidence that Arctic sea ice export is mainly due to ‘internal variability’ within the Arctic region. We conclude that the choice of model domains should be based on physical knowledge of the atmospheric and oceanic processes and not on ‘geographic’ reasons. This is particularly the case for areas like the Arctic, which has very complex feedbacks between components of the regional climate system.

Demographic histories of two deep-sea eelpouts, Lycodes japonicus and Lycodes ocellatus: paleoenvironmental implications of the western North Pacific deep waters

We compared the population histories of two deep-sea eelpouts, Lycodes japonicus and Lycodes ocellatus, to elucidate the impacts of the last glacial period on deep-sea species in the western North Pacific area. The results of phylogenetic analyses based on the nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I and cytochrome b genes revealed that the two species are closely related to each other. The results of mismatch distribution analyses, Bayesian skyline plots, and a Bayes factor test supported a constant population size of L. ocellatus in the western North Pacific during the last glacial period, but suggested a post-glacial population expansion of L. japonicus.

Low‐frequency ocean bottom pressure variations in the North Pacific in response to time‐variable surface winds

AbstractOne decade of time‐variable gravity field observations from the GRACE satellite mission reveals low‐frequency ocean bottom pressure (OBP) variability of up to 2.5 hPa centered at the northern flank of the subtropical gyre in the North Pacific. From a 145 year‐long simulation with a coupled chemistry climate model, OBP variability is found to be related to the prevailing atmospheric sea‐level pressure and surface wind conditions in the larger North Pacific area. The dominating atmospheric pressure patterns obtained from the climate model run allow in combination with ERA‐Interim sea‐level pressure and surface winds a reconstruction of the OBP variability in the North Pacific from atmospheric model data only, which correlates favorably (r=0.7) with GRACE ocean bottom pressure observations. The regression results indicate that GRACE‐based OBP observations are indeed sensitive to changes in the prevailing sea‐level pressure and thus surface wind conditions in the North Pacific, thereby opening opportunities to constrain atmospheric models from satellite gravity observations over the oceans.

Evaluation of the Effectiveness of Light Streamer Tori-Lines and Characteristics of Bait Attacks by Seabirds in the Western North Pacific

To improve the effectiveness of tori-lines it is necessary to evaluate the ability of tori-lines to mitigate seabird bycatch and determine what kind of seabird species gather during line settings, attack the bait and are incidentally caught. We conducted two experiments in the western North Pacific and examined the effectiveness for seabird mitigation of light streamer tori-lines which have no long streamers but many light (short) streamers and are mainly used in the North Pacific area. Firstly, the effectiveness of two different types of tori-line (light streamer (1 m) and long streamer (up to 7 m) tori-line) and of two different colors (yellow and red) of light streamers for seabird bycatch avoidance was evaluated using 567 sets based on data from 20 offshore surface commercial longliners. No significant difference in the bycatch number between the different tori-line types and streamer colors was found. Secondly, we investigated the characteristics of the seabird bycatch in the North Pacific and the effectiveness of three different types of streamers (light, hybrid and modified light types) by detailed observations of seabird attacks using a chartered longline vessel. Although the appearance rate of albatrosses and shearwaters were 40.9% and 27.7%, Laysan albatross was the main seabird species that followed the vessel but shearwaters seldom followed the vessel and did not aggregate during line setting. In all attacks on bait observed during line settings, 81% and 7% were by albatrosses and shearwaters, respectively. In the number of primary attacks by Laysan albatrosses which attacked most aggressively of all seabirds, there were no significant differences among the tori-line types. No individuals of shearwater were caught. The results of both experiments indicated that light streamer tori-lines were as effective as tori-lines with long streamers for mitigating seabird bycatch in the North Pacific.

Chemical Composition of Sea Fog Water Along the South China Sea

The chemical and microphysical properties of sea fog were measured during a field experiment on Donghai Island, Zhanjiang of China from March 15 to April 18, 2010. The average pH and electrical conductivity (EC) value of the six sea fog cases during the experiment was 5.2 and 1,884 μS/cm. The observed total ion concentration of sea fog was four orders of magnitude higher than those in the North Pacific and other sea areas of China. The dominant anion and cation in all sea fog water samples were Cl− and Na+, respectively. From backward trajectory analysis and ion loading computation, it can be concluded that the ions in the samples were transported either from pollutants in distant industrial cities or from local ion deposition processes. The concentration of Ca2+ in the sea fog water samples in Case 2 suggested that a dust storm in the Inner Mongolia, a northern region of China several thousand kilometers away, could reach the South China Sea. The data also showed that the sea fog droplet spectrum over the South China Sea is unimodal. Through relationship analysis, it is illustrated that the evolution of microphysics (such as droplet concentration, diameter, and liquid water content) during fog process could affect the chemical properties of sea fog.

The 2011 recipient of the Brady Medal: Dr John A. Barron

![][1] Dr John Barron is an internationally renowned expert in marine diatom taxonomy, biostratigraphy, palaeoceanography and palaeoclimatology. He graduated from the University of California, Los Angeles (UCLA) in 1969 with a BS Geology degree and completed his doctoral research in Geology at UCLA, as a student of Helen N. Tappan, in 1974. John took up a position as a research geologist/micropalaeontologist for the United States Geological Survey (USGS) in Menlo Park, California in 1974 where he remains today as a Supervisory Research Geologist within the Volcano Science Center. Notably, he is the Survey’s internationally recognized expert on the climate of the past 15 000 years in the North Pacific area and on the climatic and glacial history of Antarctica during the past 65 million years. In 1984, John was elected a Fellow of the Geological Society of America and, in 1986, he was presented the Charles Schuchert Award by the Paleontological Society for excellence and promise in palaeontology. In 1994 he was awarded a US Department of Interior Meritorious Service Award by the USGS and, in 2005, was elected a Fellow of the California Academy of Sciences. John is the leading world authority on Cenozoic marine diatom biostratigraphy and evolution, having established and revised many biostratigraphic zonations during his 40+ year career, and described numerous new diatom species, such as Actinocyclus fryxellae , Thalassiosira gersondei and T. mahoodii (Baldauf & Barron, 1991). He has repeatedly demonstrated the value of marine diatoms for solving a range of important geological problems for the entire diatom fossil record (Cretaceous to Holocene), particularly in areas such as the Southern Ocean where other microfossil groups are rare. A creative thinker, from the time of his first publication on Neogene ocean palaeotemperatures (Barron, 1973) John was, in many respects, a leader in the field … [1]: /embed/graphic-1.gif

Structure and origin of Holocene cold events

The present interglacial, the Holocene, spans the period of the last 11,700 years. It has sustained the growth and development of modern society. The millennial-scale decreasing solar insolation in the Northern Hemisphere summer lead to Northern Hemisphere cooling, a southern shift of the Intertropical Convergence Zone (ITCZ) and a weakening of the Northern Hemisphere summer monsoon systems. On the multidecadal to multicentury-scale, periods of more stable and warmer climate were interrupted by several cold relapses, at least in the Northern Hemisphere extra-tropical area. Based on carefully selected 10,000-year-long time series of temperature and humidity/precipitation, as well as reconstructions of glacier advances, the spatiotemporal pattern of six cold relapses during the last 10,000 years was analysed and presented in form of a Holocene Climate Atlas (HOCLAT; see http://www.oeschger.unibe.ch/research/projects/holocene_atlas/). A clear cyclicity was not found, and the spatiotemporal variability of temperature and humidity/precipitation during the six specific cold events (8200, 6300, 4700, 2700, 1550 and 550 years BP) was very high. Different dynamical processes such as meltwater flux into the North Atlantic, low solar activity, explosive volcanic eruptions, and fluctuations of the thermohaline circulation likely played a major role. In addition, internal dynamics in the North Atlantic and Pacific area (including their complex interaction) were likely involved.

Seasonal cycles of surface layer salinity in the Pacific Ocean

Abstract. The seasonal variability of surface layer salinity (SLS) is examined in the Pacific Ocean between 40° S and 60° N using a variety of data sources. Significant seasonal cycles were found in 5 regions: 1) The western North Pacific, 2) The northeastern North Pacific and Alaska gyre, 3) the intertropical convergence zone (ITCZ), 4) an area of the central North Pacific north of the Hawaiian Islands, 5) the central South Pacific along 10–20° S. Amplitudes range from 0.1 to > 0.5. The largest amplitudes are in the tropical band and the western North Pacific. Maximum salinity is obtained in late (northern) winter in the western North Pacific, late winter and early spring in the northeastern North Pacific, early summer in the ITCZ area, late summer and early fall in the central North Pacific area and (austral) winter in the central South Pacific. Large areas of the Pacific have no significant seasonal variation in SLS. Seasonal variability of evaporation rate, precipitation rate and the difference between them (E-P) were calculated from the OAFlux and Global Precipitation Climatology Project datasets. Typical amplitudes of E-P are 0.1–1 × 10−4 kg m−2 s−1. The seasonal variability of E-P is largely dominated by variability in evaporation in the western North Pacific and precipitation elsewhere. The largest amplitudes are in areas along the edge of the western North Pacific and in the far eastern tropical Pacific around 10° N. Phases in these areas indicate maximum E-P in mid- to late winter in these areas of large amplitude. The closest correspondence between E-P and SLS is in the ITCZ. E-P was combined with seasonal variation of the mixed-layer depth to calculate the freshwater flux forcing term of the SLS balance equation. The term was found to be similar in magnitude and distribution to E-P. Some other terms of the SLS balance were calculated. Horizontal advection was found to have seasonal cycles in a region near the equator. Entrainment was found to be mostly not significant except for a small region along 2.5–7.5° N in the eastern Pacific. Averaged spatially over large areas in the western North Pacific, ITCZ, South Pacific and northern North Pacific, the seasonal cycle is mostly a balance between changes in SLS and E-P, with entrainment and advection playing relatively minor roles. This work highlights the potentially significant role of surface salinity in the hydrologic cycle and in subtropical mode water formation. It can also help to interpret measurements that will soon be available from the Aquarius and SMOS (Soil Moisture and Ocean Salinity) satellite missions.

경험적 직교함수를 이용한 북서태평양 열대저기압의 이동빈도 특성에 관한 연구

북서태평양에서 발생하는 열대 저기압의 이동경로에 대한 변화패턴을 1951-2007년의 열대 저기압 경로 자료에 경험적 직교함수(Empirical Orthogonal Function, EOF)법을 적용하여 분석하였다. 북서태평양을 <TEX>$5^{\circ}\times5^{\circ}$</TEX>의 격자간격으로 나뉘어 연별 열대 저기압의 이동빈도를 각 격자에서의 변수로 정의하였다. 첫번째 모드는 동서성분(동경125도 기준)을, 두번째 모드는 남북성분(필리핀 동쪽해상에서 남지나해를 가로지르는 축 중심)을, 그리고 세번째 모드는 대각성분(타이완 동쪽 해상을 중심으로 동북방향과 동남방향을 축으로 하는)으로 나누어짐을 알 수 있었다. 첫번째와 두번째 모드의 주성분 시계열에서 각각 1997년과 1991년 부근을 기점으로 해서 주성분들의 부호가 교차되는 데, 이는 1990년대 이전 약 20년 동안에 남중국해 부근지역에서의 열대 저기압 이동 빈도가 동아시아 중위도 지역에서는 최근 20년 동안에 더 높았던 것과 관련성이 있는 것으로 보였다. 열대 저기압 발생의 경우, 첫번째와 두번째 모드에서 고유벡터 값이 음이고 진로가 북서태평양으로 주로 이동했던 열대 저기압은 고유벡터가 양의 값을 보였던 열대 저기압보다 더 동쪽에서 발생했던 것으로 나타났다. 이동특성에 있어 첫번째 모드는 바이칼호 남쪽에서 형성되는 기압 패턴에, 두번째 모드는 <TEX>$30^{\circ}N$</TEX> 부근을 중심으로 남과 북 사이에 형성된 진동패턴에, 세번째 모드는 일본 부근에 위치한 기압패턴에 의해 열대 저기압의 이동경향이 많은 영향을 받는 것을 알 수 있었다. 또한, 해수면 온도 아노말리 값과 상관분석결과 첫번째 모드는 <TEX>$Ni\tilde{n}o$</TEX>-3.4 지수와 높은 음의 상관관계를 보여 ENSO의 영향을 받고 있음을 알 수 있었다. A pattern of tropical cyclone (TC) movement in the western North Pacific area was studied using the empirical orthogonal function (EOF) and the best track data from 1951 to 2007. The independent variable used in this study was defined as the frequency of tropical cyclone passage in 5 by 5 degree grid. The <TEX>$1^{st}$</TEX>, <TEX>$2^{nd}$</TEX> and <TEX>$3^{rd}$</TEX> modes were the east-west, north-south and diagonal variation patterns. Based on the time series of each component, the signs of first and second mode changed in 1997 and 1991, respectively, which seems to be related to the fact that the passage frequency was higher in the South China Sea for 20 years before 1990s, and recent 20 years in the East Asian area. When the eigen vectors were negative values in the first and second modes and TC moves into the western North Pacific, TC was formed mainly at the east side relatively compared to the case of the positive eigen vectors. The first mode seems to relate to the pressure pattern at the south of Lake Baikal, the second mode the variation pattern around <TEX>$30^{\circ}N$</TEX>, and the third mode the pressure pattern around Japan. The first mode was also closely related to the ENSO and negatively related to the <TEX>$Ni\tilde{n}o$</TEX>-3.4 index in the correlation analysis with SST anomalies.

2007년 여름 북서태평양 이산화탄소 분압의 공간 변동성

In order to study spatial variabilities and major controlling factors, we measured fugacity of CO₂ (fCO₂), temperature, salinity and nutrients in surface waters of the North Pacific (7˚30'~33˚15'N, 123˚56'E~164˚24'W) between September~October 2007. The North Pacific and the marginal sea were distinguished by fCO₂ distribution as well as unique characteristics of temperature and salinity. There was a distinct diurnal SST variation in the tropical North Pacific area, and surface fCO₂ coincidently showed diurnal variation. In the North Pacific area, surface fCO₂ was mainly controlled by temperature, while in the marginal sea area it was primarily dependent on alkalinity and dissolved inorganic carbon concentrations. Air-sea CO₂ flux showed a large spatial variation, with a range of -6.10~5.06 mmol m?² day?¹. The center of subtropical gyre of North Pacific acted as a source of CO₂ (3.09±0.95 mmol m?² day?¹). Tropical western North Pacific (i.e. the 'warm pool' area and the subtropical western North Pacific) acted as weak sources of CO₂ (1.07±1.20 mmol m?² day?¹ and 0.50±0.53 mmol m?² day?¹, respectively). In the marginal sea, however, the flux was estimated to be -0.68±1.17 mmol m?² day?¹, indicating that this area acted as a sink for CO₂.

Effect of seafloor depth on phytoplankton blooms in high‐nitrate, low‐chlorophyll (HNLC) regions

We calculated correlations between seafloor depth and phytoplankton blooms in all three main high‐nitrate, low‐chlorophyll (HNLC) regions, but with a particular focus on the subarctic North Pacific area. It has long been known that the central parts of the east and west subarctic North Pacific are HNLC regions. The deep western basin of the Bering Sea is also HNLC, whereas the wide continental shelf of the eastern Bering Sea is not. We carried out a statistical comparison of spatial maps of (1) seafloor depth and (2) chlorophyll a concentration from satellite data. This comparison reveals that shallow waters have, on average, higher peak chlorophyll a concentrations (more intense phytoplankton blooms) than deep waters (p ≪ 0.01). Possible artifacts of the satellite data are considered but it is concluded that the signal is genuine, in part because the same patterns are found in in situ data. There are several possible explanations for the observed correlation; the most probable, we suggest, is that iron diffusing out of the seafloor causes alleviation of iron limitation in shallow waters.