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Aluminum (Al), manganese (Mn), cobalt (Co), and lead (Pb) are key trace elements in seawater and thus significant in chemical oceanography research. However, although all of these elements are highly scavenged in the ocean, only a few studies focus on the intercomparison of their distributions. Here, we report the basin-scale and full-depth sectional distributions of these elements observed during three GEOTRACES Japan cruises in the North Pacific. We confirmed that a surface maximum of the dissolved (d) species is not a common feature for the four elements and that the d species have the lowest concentrations in the Pacific Deep Water (PDW) as compared to other oceans. The elements showed different speciations and distributions. The fraction of labile particulate (lp) species was calculated as the difference between the total dissolvable (td) species and d species. The lpM/tdM ratio, where M refers to an element, is highest for Al, at 0.66 ± 0.31 (average ± sd, n = 489), and lowest for Pb, at 0.02 ± 0.08 (n = 575). Further, the distribution of each element is uniquely related to ocean circulation. The tdAl concentration is high in the Equatorial Under Current (EUC), the North Equatorial Current (NEC), and the Lower Circumpolar Deep Water (LCDW). Manganese is supplied from reductive sources such as sediments on the continental shelves around the northern boundary. Cobalt is concentrated in the North Pacific Intermediate Water (NPIW) and in the Equatorial Pacific Intermediate Water (EqPIW) owing to the combined effects of supply from the continental shelves, biogeochemical cycling, and scavenging. Lead shows a subsurface maximum centered at ∼35°N and ∼200 m depth, implying an association with the formation of the Subtropical Mode Water (SMW) and the Central Mode Water (CMW). Although the subsurface Pb maximum in the Atlantic has diminished over the last three decades owing to the ban on leaded gasoline use, it has been sustained in the North Pacific through the growth of other anthropogenic sources in Asia and Russia. We propose that the enrichment factor of dM, defined as EF(dM) = (dM/dAl)seawater/(M/Al)upper crust, where (M/Al)upper crust is the molar ratio in upper crustal abundance, can be a good parameter for the sources. The median is 1.3 × 102 (n = 436) for EF(dMn), 3.2 × 102 (n = 430) for EF(dCo), and 1.2 × 103 (n = 413) for EF(dPb). The EF(dPb) found in this study is on the same order of magnitude as the EF values for aerosols found in the literature, suggesting that the deposition of aerosols is a major source for dPb. Because EF(dMn) and EF(dCo) are ten to hundred times higher than the EF for aerosols, sources other than the aerosol deposition are more significant contributors to the concentrations of Mn and Co.

Recent studies suggest that transport and water mass mixing may play a dominant role in controlling the distribution of dissolved rare earth element concentrations ([REE]) at least in parts of the North and South Atlantic and the Pacific Southern Ocean. Here we report vertically and spatially high-resolution profiles of dissolved REE concentrations ([REE]) along a NW–SE transect in the West Pacific and examine the processes affecting the [REE] distributions in this area. Surface water REE patterns reveal sources of trace element (TE) input near South Korea and in the tropical equatorial West Pacific. Positive europium anomalies and middle REE enrichments in surface and subsurface waters are indicative of TE input from volcanic islands and fingerprint in detail small-scale equatorial zonal eastward transport of TEs to the iron-limited tropical East Pacific. The low [REE] of North and South Pacific Tropical Waters and Antarctic Intermediate Water are a long-range (i.e., preformed) laterally advected signal, whereas increasing [REE] with depth within North Pacific Intermediate Water result from release from particles. Optimum multiparameter analysis of deep to bottom waters indicates a dominant control of lateral transport and mixing on [REE] at the depth of Lower Circumpolar Deep Water (≥3000 m water depth; ∼75–100% explained by water mass mixing), allowing the northward tracing of LCDW to ∼28°N in the Northwest Pacific. In contrast, scavenging in the hydrothermal plumes of the Lau Basin and Tonga-Fiji area at 1500–2000 m water depth leads to [REE] deficits (∼40–60% removal) and marked REE fractionation in the tropical West Pacific. Overall, our data provide evidence for active trace element input both near South Korea and Papua New Guinea, and for a strong lateral transport component in the distribution of dissolved REEs in large parts of the West Pacific.

The strong relationship between benthic foraminifera’s habitat and morphological characteristics to their surrounding environment are dominant component in marine community. This study attempts to understand the significance of benthic foraminifera in ecological importance and paleoceanographic reconstructions at Cascadia Margin, NE Pacific Ocean during the Pleistocene. The quantitative analyses of deep sea benthic foraminifera, particularly Bulimina exilis, Cibicides kullenbergi, Elphidium batialis, Epistominella exigua and Uvigerina proboscidea generally show higher abundances in the studied interval. The Gas Hydrate Stability Zone in the Cascadia Margin at ∼ 1200 ka to 162 ka (GHSZ; ∼ 240–70 mbsf) is related to low temperature and high-pressure conditions which are responsible for lower abundances of benthic foraminifera across that interval. The Alaska Current, North Pacific Current and California Current, also known as Eastern Boundary Currents (EBC), play a major role in the transportation of suspended sediments and coastal upwelling throughout the coast across the ∼ 650 to 450 ka and ∼ 35 to 2 ka intervals. The relative abundance rate of benthic foraminiferal community decreases with increasing core depth, indicating the influence of less ventilated and nutrient-enriched North Pacific Intermediate Water (NPIW). The present study also signifies the disappearance of benthic faunas throughout the Early–Middle Pleistocene Transition (EMPT, 1250–700 ka, Clark et al., 2006) period due to increased cyclic seasonality and decreased food supply, with few species (Bolivina alata, Bolivina spathulata, Cibicides wuellerstorfi, Epistominella exigua, Gavelinopsis lobatulus and Uvigerina peregrina) being exceptions.

Changes in water column conditions in the northwestern Pacific during the last 23 ka were reconstructed using geochemical and isotope proxies and redox elemental compositions along with published data (alkenone sea surface temperature (SST) and benthic foraminiferal fauna) at core GH02-1030. Surface water primary productivity in terms of biogenic opal and TOC contents, which mainly represented export production of diatom, was closely related to alkenone (spring-summer) SST and the development of spring-summer mixed layer depth. The different variation patterns of nitrate and silicic acid utilization, estimated by bulk δ 15 N and δ 30 Si diatom values, respectively, are most likely due to the water column denitrification influence on bulk δ 15 N. Dysoxic bottom water conditions occurred during the Bolling-Allerod (BA) and the Pre-Boreal (PB), which was evident by laminated sediments, abundant dysoxic benthic foraminifers, and increased redox elemental compositions. Although surface water productivity increased during the BA and PB, dysoxic bottom water conditions were caused by a combination of enhanced surface water productivity and reduced ventilation of North Pacific Intermediate Water (NPIW) in response to meltwater input from the high latitude areas. Based on records of core GH02-1030 and other cores in the northwestern Pacific, the Okhotsk Sea, and the Bering Sea, which are all proximal to the modern NPIW source region, dissolved oxygen concentrations of bottom water were more depleted during the BA than PB. Such difference was attributed to more sluggish NPIW ventilation due to more meltwater input during the BA than the PB. The opening or closure of the Bering Strait is critical to the direction of meltwater transport to the northwestern Pacific.

The Bering Sea is a potential location for the formation of the North Pacific Intermediate Water (NPIW), which drives the global ocean circulation as a counterpart to the North Atlantic Deep Water (NADW). To evaluate the NPIW-NADW seesaw hypothesis, we reconstructed the long-term variation of the bottom water Nd isotopic composition at site U1345 on the Bering Slope by extracting authigenic Fe-Mn oxyhydroxide from bulk sediments. We examined six different extractions in order to ensure that authentic seawater composition is recovered. For Bering Slope sediments whose typical carbonate content is less than 5% (average 2%), the most reliable results are obtained if the decarbonation step is omitted and a low reagent-to-sediment ratio is adopted. The reconstructed authigenic eNd record for the last 520 kyr exhibits large temporal variations depending on whether the NPIW formation or the boundary exchange process is dominant. Periods of radiogenic eNd can be attributed to NPIW formation triggered by brine rejection, as evidenced by the difference in δ18O of benthic foraminifera between sites (Δδ18Obf), high % sea-ice related diatoms, and low abundance of Bulimina aff. Exilis (low-oxygen deep fauna). Diminished supply of unradiogenic Nd from boundary exchange seems to intensify these radiogenic peaks. On the other hand, the unradiogenic eNd intervals can be attributed to stagnant bottom water conditions, as can be deduced from the Δδ18Obf values, low % sea-ice related diatoms, abundant B. aff. Exilis, and laminations. When there is no NPIW formation, the continental margin sediments are exposed to boundary exchange for a longer period of time, leading to release of unradiogenic Nd. The mid-MIS 6 and mid-MIS 5 are exceptions in that NPIW formation occurred yet the eNd compositions are unradiogenic. NPIW formation and cold climate (closed Bering Strait) are not always correlated. Comparison against eNd records of the South Atlantic suggests only an ambiguous NPIW-NADW seesaw for the last 200 kyr.

We investigated the microhabitats of benthic foraminifera and stable oxygen and carbon isotope compositions of living (stained) Elphidium batialis Saidova off Hidaka (northern Japan) in the Northwestern Pacific continental margin. In the study area, six major species reside in three microhabitats that are vertically distributed within the sediment column. Bolivina spissa, Uvigerina akitaensis, and E. batialis tend to be shallow infauna, whereas Chilostomellina fimbriata and Globobulimina pacifica are deep infauna. Nonionellina labradorica is intermediate infauna. The δ18O values of E. batialis and U. akitaensis increased gradually with the water depth, but those of E. batialis contain a systematic offset by about −1.0 to −1.2‰ to U. akitaensis. This offset range is consistent with that observed in previous fossil studies in the Bering Sea. The δ13C values of U. akitaensis are approximately consistent (−1.1‰ to −0.8‰) with the water depth, whereas those of E. batialis increase with water depth from the shallower sites (−3.0 to −2.0‰) to the deeper sites (−2.0 to −1.6‰). Depending on the water depth, the δ13C values of E. batialis are lower than U. akitaensis by −1.4 to −0.7‰. Elphidium batialis may produce slightly 13C-poor calcite at the severely oxygen-poor water depths of the oxygen minimum zone (OMZ), suggesting that dissolved oxygen level may affect δ13C values of E. batialis during calcite precipitation. It is hypothesized that the δ13C values of E. batialis may contain signals arising from food digestion (or an internal respiration effect) and change the proportion of carbonate ions for calcite precipitation between the DIC values of the ambient pore water and food materials, depending on the dissolved oxygen level on the seafloor. Thus, the δ13C difference between E. batialis and Uvigerina spp. might be useful when inferring the past development of the OMZ and/or changes in the evolution of the North Pacific Intermediate Water in the subarctic North Pacific margin including adjacent marginal seas such as the Bering Sea.

Visible wavelength fluorescent dissolved organic matter (FDOM), usually defined as humic-like FDOM, plays important roles in marine carbon and iron cycles as biorefractory dissolved organic matter and organic ligands, respectively. The major fractions of FDOM in the open ocean have been considered to be of marine origin (autochthonous) according to linear relationships between FDOM and apparent oxygen utilization (AOU) in the mesopelagic (200–1000 m) and bathypelagic (>1000 m) layers. Recently, Yamashita et al. (2020) quantified allochthonous FDOM from the positive deviation of the general FDOM–AOU relationship in the bathypelagic layer and found that allochthonous FDOM derived from the Sea of Okhotsk was conservatively transported to the western North Pacific through the circulation of intermediate water, including North Pacific Intermediate Water (NPIW). However, the contribution of allochthonous FDOM from the Bering Sea, the other source region of NPIW, has not been evaluated. Here, we determined the distributions of allochthonous FDOM in the entire North Pacific, including the Sea of Okhotsk and the Bering Sea, and the spatial distribution of allochthonous FDOM in the density range of NPIW for the entire North Pacific. We found that the major source region of allochthonous FDOM in NPIW was the Sea of Okhotsk but not the Bering Sea, although the water mass contributing to the lower part of NPIW is known to be mainly derived from the Bering Sea. Such different contributions of allochthonous FDOM from the marginal seas are likely due to a lack of expansion of the dense shelf water, which forms at coastal polynya and interacts with shelf sediments with a strong tidal current, to the basin region of the Bering Sea. We also demonstrated that allochthonous FDOM derived from the shelf sediments of the Sea of Okhotsk was conservatively distributed to the wide area of the North Pacific through the circulation of intermediate water, particularly the upper part of NPIW. Furthermore, the negative deviations of the FDOM-AOU relationship in the bathypelagic layer were evident for other water masses, such as Antarctic Intermediate Water (AAIW), suggesting that FDOM can help determine the spatiotemporal distribution of NPIW and its mixing with other water masses, such as AAIW.

Dissolved neodymium isotopes (143Nd/144Nd, expressed as eNd) and rare earth elements (REEs) have the potential to trace the provenance of lithogenic material as well as water masses. The central North Pacific is poorly investigated with respect to its Nd isotope signature and REE cycling, and little is known about the contributions of volcanic islands, such as Hawaii, relative to dust input from Asian deserts to the surface water REE budgets. Here we present dissolved Nd isotope and REE data along with long-lived radium isotope activities from Hawaii Ocean Time-Series Station ALOHA and coastal waters from Oahu, sampled for a GEOTRACES process study in February 2011. The data are supplemented with seasonal samples from ALOHA. Our results show a clear influence of the Hawaiian Islands on the coastal ocean and surface waters at ALOHA during February, expressed by higher surface water Ra activities, radiogenic surface eNd (eNd = +1.4 to −1.0), and elevated Eu anomalies (Eu/Eu∗ ⩾ 1.3). Seasonal cycles of Asian dust deposition most likely contribute to the seasonal eNd variability of surface waters at ALOHA, as suggested by more negative eNd and the lack of Eu anomalies in summer. Neodymium isotopes in the intermediate and deep water column at ALOHA trace typical North Pacific water masses, such as North Pacific Intermediate Water and North Pacific Deep Water. We suggest that a radiogenic eNd excursion in 1000–2000 m water depth, observed in various North Pacific profiles, is controlled by advection of a modified Upper Circumpolar Deep Water or North Equatorial Pacific Intermediate Water. We further present an updated average eNd signature of −3.5 ± 0.5 for North Pacific Deep Water and show that REE patterns of deep waters at ALOHA are dominantly controlled by vertical processes.

Oceanic deoxygenation observed since the 1950s has drawn increasing concern as dissolved oxygen (DO) regulates marine biodiversity and biogeochemical cycles. Yet the DO time series from direct instrumental measurements is insufficiently long (several decades) to constrain the centennial to millennial variability. Here we present redox-sensitive metal (Re, U, and Mo) records from Santa Barbara Basin (SBB), California to reconstruct subsurface DO through the Holocene. Significantly higher authigenic metal fluxes and coherent benthic foraminifera faunal responses along a published depth transect reveal vertical expansion and intensification of the Southern California oxygen minimum zone (OMZ) prior to ∼6 ka. Comparison with post-Industrial trace metal records suggests low-oxygen conditions were more extreme during early to mid-Holocene (MH), highlighting the magnitude of OMZ variability in the absence of anthropogenic influences. Inconsistencies between authigenic metal fluxes and local oxygen control indicate a remote weakening of the North Pacific Intermediate Water (NPIW) formation prior to the MH. Reduced ventilation of the mid-depth North Pacific is supported by state-of-the-art Earth system model simulations with realistic MH (6 ka) forcing, highlighting the importance of brine rejection during sea ice formation in changing the buoyancy of NPIW and its basin-wide influences on North Pacific OMZ. Evidence from Holocene marine/lake records and model simulations further suggests a southward Intertropical Convergence Zone (ITCZ) migration and a consequent deepening of the Aleutian Low (AL) towards late Holocene, which favors more sea ice brine rejection. Thus, mid-depth ventilation in the North Pacific was closely associated with atmospheric circulation during the Holocene.

International audience; Rare Earth Element (REE) concentrations and Nd isotopic compositions (εNd) of 16 seawater profiles collected in the northern South China Sea (SCS) and the Philippine Sea were investigated (1) to establish the distribution of the Nd isotopic composition of water masses along the tropical Western Pacific and the SCS until now underexplored, (2) to constrain hydrological exchanges between the SCS and the Philippine Sea through the Luzon Strait, and (3) to test, in the context of the semi-closed marginal sea (SCS), the possible impact of the process of exchange of Nd between SCS water masses and unradiogenic sediments from its north-western margin.εNd values for mid- and deep-water masses of the Philippine Sea and the SCS range from −2.3 to −4.4 and generally increase slightly as water depth increases. In the Philippine Sea, εNd values for the North Pacific Intermediate Water (NPIW) reach −2.7±0.4 at mid-depths (500 to 1400 m). Below ~1800 m, the Pacific Deep Water (PDW) is characterised by less radiogenic Nd (−4.1±0.5) indicating the intrusion of southern-sourced water. For most of the stations in the Northern SCS, water masses below 1500 m (PDW) display homogenous εNd values (~−4.1) identical to those of the PDW in the Philippine Sea. εNd values for the South China Sea Intermediate Water (SCSIW, 500–1500 m) vary from −3.0 to −3.9 as a result of the vertical mixing of the NPIW with the PDW in the SCS. Seawater εNd values for the SCS display local modification (~−5.3 to −7.0) in areas where water passes above sediment drift deposit systems. This implies locally confined “boundary exchange’’ with unradiogenic sediments (around −11) insufficient to alter the Nd isotopic composition of the PDW in the Northern SCS. In addition, εNd values analysed for the first time in nepheloid layers collected along the north-western margin of the SCS do not exhibit any significant modification of the seawater εNd which remains into a narrow range between −3.7 and −4.3, similar to that of the PDW. A compilation of εNd from the sea surface water of the SCS indicates lower εNd values in the western and the central SCS (−3.3 to −9.5), induced by sediments riverine input which are characterised by unradiogenic εNd (around −11). Finally, as significant variations are observed in seawater εNd at mid-depth between the SCS and the Philippine Sea, εNd values could be used in the future to track intermediate water mass exchange in the Luzon Strait, a process which, at present, remains poorly understood.

A data assimilation system has been developed to apply to a fully coupled climate model, CM2.1, in the Korea Institute of Ocean Science and Technology (KIOST). While the ocean observation data are assimilated into the ocean component model through the data assimilation system of the KIOST (DASK), the other component models are freely integrated. Here, we evaluated the variability of the ocean climate in the climate reanalysis by the DASK from 1947 to 2012. To assess oceanic processes and ocean climate variability as modeled by the DASK, we examined the North Pacific Intermediate Water, El Nino–Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), Indian Ocean Dipole (IOD), upper 300 m heat content (HC300), Sea Surface Height (SSH), meridional heat transport, mean global temperature and salinity, and temperature and zonal velocity in the tropical Pacific. Furthermore, we compared these modeled features with various in-situ observations and with various other global reanalyses, such as the Simple Ocean Data Assimilation (SODA) and the GFDL Ensemble Coupled Data Assimilation systems (ECDA). The DASK represents global temperature and salinity well, not only at the surface but also at intermediate depths in the ocean. In addition, the DASK closely models the features of North Pacific Intermediate Water, a typical water mass in the North Pacific characterized by the salinity minimum layer. The DASK’s ocean climate variability also matches well with observations of the ENSO, PDO and IOD. The HC300 of the DASK shows as good or better correlations with real-world observations compared to other reanalyses systems except in the tropics. In addition, the SSH variability of the DASK shows lower correlation in the tropics and north Atlantic rather than its HC300 correlation. It is suggested that the poor performance of the DASK in the tropics and north Atlantic is resulted from the bias of its low-resolution atmospheric model. Nevertheless, it is noteworthy that the DASK performs better or comparable particularly in the North Pacific and North Atlantic even though the DASK applies the Ensemble Optimal Interpolation, which is numerically more efficient than the ensemble Kalman filter applied by the ECDA, and a lower horizontal model resolution than that of the SODA. The validation suggests the high performance of the DASK in terms of ocean climate estimation and variability at a lower computational cost than the other two reanalyses systems we studied.

In this study, rare earth element (REE) was treated as a paleo-redox proxy to investigate the changes of depositional environment in the southern Okinawa Trough since the last glacial maximum. The acid-leachable fraction (leachate) of the sediments recovered from the ODP Site 1202B is dominated by biogenic and authigenic components while detrital contamination is minor. The significant enrichment of middle REE suggests a large contribution from authigenic Mn oxyhydroxides and cerium (Ce) anomaly can indicate deepwater redox change. The REE parameters including Ce anomaly in the leachate exhibit remarkable and abrupt changes in the early Holocene (∼9.5 ka) and during LGM (∼20 ka). An increase of Ce anomaly at 28–22 ka implies the suboxic deepwater condition probably caused by increased primary productivity. Weak positive Ce anomalies during the last glacial maximum and deglaciation suggest an oxic depositional environment responding to the enhanced deepwater ventilation with the advection of the North Pacific Intermediate Water and/or South China Sea Intermediate Water into the trough. A decrease of Ce anomaly in the early Holocene might be caused by the intrusion and strengthening of the Kuroshio Current in the trough that enhanced the water stratification and induced a gradual development of suboxic depositional condition. Furthermore, an abrupt change of chemical composition at ca. 4 ka probably indicates a decrease of dissolved oxygen in deepwater and a weakening of ventilation in the Okinawa Trough. This study suggests that REE proxy can provide new insights into the linkage among surface current, deepwater circulation and sediment record in the continental margin where terrigenous input dominates.

The discharge of nitrate and phosphate from Changjiang (Yangtze River) has increased in recent decades. Eutrophication off the mouth of Changjiang has subsequently become a serious problem, as evidenced by the hypoxia area reaching 12,000 km 2 . This study demonstrates that in the wide East China Sea (ECS) the nitrate and phosphate concentrations in the Kuroshio Intermediate Water (KIW) have also increased, but the dissolved oxygen (DO) concentration has decreased since as early as 1982, most likely owning to reduced ventilation in the North Pacific Intermediate Water (NPIW). Conversely, the Kuroshio Tropical Water (KTW) has decreased in the nitrate and phosphate concentrations yet increased in DO concentration. As KIW contributes substantially to the upwelling, the nitrate and phosphate concentrations in the bottom water on the outer shelf of the ECS appear to have increased as well, but the DO has decreased. Given that the nutrient inputs from both the land and the Kuroshio Current have increased, yet the input of DO from the Kuroshio has decreased, more severe eutrophication and hypoxia may occur in the entire ECS. Similar processes may also affect other shelves that come into contact with NPIW.

Past sea surface temperature (SST) and salinity (SSS) changes in the northeastern East Sea/Japan Sea since 19 cal ka BP have been reconstructed by using an alkenone unsaturation index and the oxygen isotope ratio of planktonic foraminifera Neogloboquadrina pachyderma(s) in Core MR0604-PC03B. Coretop alkenone temperature and calcification temperature correspond to the temperature of seawater in summer and spring at the depth of 10–30 m, respectively. Based on the records from this core and previous studies, spatio-temporal changes in alkenone temperature of the East Sea/Japan Sea have been reconstructed to investigate changes of surface circulations and the subpolar front (SPF) position. During the transitional period from the glacial to the Holocene, the SST was lower (about 2–3 °C) than that of today and the SSS dramatically increased at that time in the entire East Sea/Japan Sea but it was still lower than that of today. However, the northern SSS was higher than that of the southern part. The source of the cold and saline seawater could have been the Oyashio Current (OY, inflow from the north), not the Tsushima Warm Current (TWC, inflow from the south). Probably, sea level rose rapidly at that time. There might be no strong development of the SPF during the transitional period due to the restricted inflow of the TWC. During the early Holocene, the SST and SSS of the East Sea/Japan Sea increased compared to the transitional period due to increased seawater exchange through straits. The SPF was tilted orienting from southwest to northeast because the inflow of the TWC was not fully developed due to lower sea level. Subsequently, the surface condition of the East Sea/Japan Sea was similar to that of today at 6 cal ka BP. The Forerunner of Soya Warm Water (FSWW) that flowed out through the Soya Strait in early spring did not affect the formation of the Okhotsk Sea Intermediate Water and the North Pacific Intermediate Water during the glacial and interglacial periods.

Radiolarian assemblages were analyzed using samples from the IODP Site U1340 to reconstruct the paleoceanographic conditions in the Bering Sea Based on the characteristic faunal changes, the radiolarian evolution at Site U1340 was divided into four major intervals from Stages I to IV, with Stage IV divided into Substages IVa and IVb. The radiolarians in each stage recorded significant paleoenvironmental conditions. In general, the Bering Sea was governed by an ocean ecological environment with stable warm and saline surface water during Stage I (4.15 Myr to 3.91 Myr). The environment in the Bering Sea fluctuated strongly during Stage 11 (3.91 Myr to 2.75 Myr) and was controlled by the cold-water masses and sea ices during Stage III (2.75 Myr to 1.07 Myr) with the gradual development of cold and well-ventilated intermediate water. Stage IVa (1.07 Myr to 0.47 Myr) was a transitional period characterized by the enhanced formation of cold subsurface and intermediate water as well as of the oxygen-rich deep water. During Stage IVb (after 0.47 Myr), the Bering Sea was mainly characterized by enhanced warmth during interglacial episodes and well-developed water layers that were generally comparable to those of the modern Bering Sea. These conditions indicated that the vertical water-mass structure of the modern Bering Sea began to form since 0.47 Ma. Every Stage boundary in the studied core was marked by notable changes in the radiolarian assemblages. These changes corresponded to the climatic cooling event at similar to 3.91 Ma, the intensification of Northern Hemisphere glaciation at similar to 2.75 Ma, the beginning of the middle Pleistocene transition at similar to 1.07 Ma, and the low-latitude radiolarian ecology event at similar to 0.47 Ma. In addition, the relative abundance pattern of Cycladophora davisiana indicates that the Bering Sea was the main source of the past North Pacific Intermediate Water at ca. 0.85 Ma (MIS22), ca. 0.63 Ma (MIS16), and ca. 0.18 Ma (MIS6), just as it was during the last glacial maximum. (C) 2014 Elsevier B.V. All rights reserved.

A high-recovery technique of dissolved organic matter (DOM) isolation – reverse osmosis coupled with electrodialysis (RO/ED) – was used to isolate DOM from the North Atlantic Senegal-Mauritanian upwelling area surface water (5 m), North Atlantic oxygen minimum water (415 m) and deep water (3000 m), North Pacific subtropical gyre surface water (5 m), and North Pacific intermediate water (674 m) and deep water (3500 m). Samples were characterized by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry with electrospray ionization (ESI FTICR-MS). RO/ED isolated DOM samples share a significant number of common formulas accounting for 54–79% of formulas in each sample. Total dissolved carbohydrate (TCHO) concentrations in RO/ED isolated DOM were specifically measured using a colorimetric method, and were found to have higher contribution to DOC than estimated by FTICR-MS data. Percentages of TCHO-C in DOC are in the range of 3.7–19.6% in all samples, with the North Pacific deep (3500 m) water having the lowest % and the North Atlantic upwelling core surface water having the highest %. Principal component analysis (PCA) using the relative magnitudes of MS peaks facilitated identification of specific peaks that are enriched in different samples. Peaks enriched in surface samples have higher H/C values than peaks enriched in deep samples, in both the North Atlantic DOM and the North Pacific DOM. This enrichment pattern is likely due to the selective photo-degradation of aromatic compounds and the bio-production of aliphatic and carbohydrate-like compounds in surface waters, and the selective bio-degradation of aliphatic and carbohydrate-like compounds with increasing depth. In further support of a photo-degraded signature for DOM in surface waters, photo-resistant and photo-produced molecular formulas were present in the highest numbers in the surface North Pacific subtropical gyre DOM. Peaks enriched in the North Pacific intermediate and deep DOM have significantly higher O/C values than the North Atlantic oxygen minimum layer and deep DOM, for both CHO formula compounds and CHON formula compounds. This difference in O/C values observed for the deep Pacific vs. Atlantic suggests oxidation of DOM, possibly via microbial activity during the ageing of DOM or the preferential remineralization of DOM from sinking particles at depth in the Pacific.

Distribution of the turbulent kinetic energy dissipation rate e across the Bussol’ Strait was re-evaluated by applying an improved method using density inversions to tide-resolving density observations. The improved estimates without excessive rejection of density inversions provide about three-times higher mean values of e (1.45 × 10−7 W/kg), vertical diffusivity Kρ (153 × 10−4 m2/s) and depth-integrated e (187 mW/m2) in comparison with previous estimates. One-day mean vertical profiles of e in the potential density co-ordinate allows us to estimate diapycnal velocity at 3 × 10−5 m/s downwards through the 26.85σθ isopycnal surface, and was almost zero through 26.7σθ, suggesting the thinning of Okhotsk Sea Mode Water or of the core of North Pacific Intermediate Water as the water flows through the Bussol’ Strait from the Sea of Okhotsk to the North Pacific. The re-evaluated turbulence and current distributions confirmed following previous knowledge but with quantitative improvements and/or expansion of coverage: (1) All-averaged e and Kρ show distinctive mid-depth maxima at 800–1600 m, 26.9–27.6σθ and at a height of 300–400 m above the bottom, and enhanced e within 500 m of the bottom corresponding to the enhanced shear and low-Richardson number at vertical scales of less than 50 m. (2) A significant amount of the e variance (14%) is explained by the 50 m-scale vertical shear composed of mean and diurnal tidal currents. (3) The diurnal tidal currents are well approximated by six low-mode topographically trapped waves.

As a source region of North Pacific Intermediate Water, the Okhotsk Sea plays an important role in the ventilation of the North Pacific. To understand the detailed oceanographic changes in this marginal sea since the last glaciation, we studied decadal to centennial scale proxy records from new sediment cores from the southwestern Okhotsk Sea. Glacial to Holocene Δ14C records of benthic foraminiferal shells suggested enhanced ventilation in the Okhotsk Sea during the early deglacial period between 18 and 15 ka, corresponding to Heinrich Event 1. Although the Δ14C reconstruction has considerable uncertainties, the Okhotsk Sea may have acted as a source for vigorous ventilation of the subarctic Pacific during this period. CaCO3 preservation events appear to be better explained by the ventilation history of the Okhotsk Sea than by coccolithophores and foraminifera production. CaCO3 preservation started to improve during 18 to 15 ka, and pronounced peaks in the CaCO3 content corresponded to the Bolling–Allerod (15 to 13 ka) and Preboreal (11.5 to 10 ka) warm periods. Diatom and coccolithophore productivity remained low in the Okhotsk Sea throughout the glacial to deglacial periods, different from the situation in the open subarctic Pacific, where high productivity was observed during the Bolling–Allerod period. After the Preboreal period, biogenic opal gradually increased and δ15N decreased in the southern Okhotsk Sea, suggesting that productivity was enhanced by a relaxation of the nitrate limitation.

The distribution of dissolved manganese (dMn) in the northeast Pacific across the Line-P transect was evaluated to investigate the mechanisms responsible for the spatial and temporal variability of dMn. A total of 299 filtered seawater samples ( coastal sediments or eolian dust , as well as photo-reduction. At the onshore stations, the absolute concentration of dMn at the surface was annually variable, depending on the strength of the Ekman transport . Within the subsurface layer, dMn decreased rapidly with depth down to 150 m due to particle scavenging. Within the Oxygen Minimum Zone (OMZ), near the continental margin , we observed elevated and annually variable dMn. The high dMn concentration is likely due to mixing of remobilized Mn from the continental margin, which varies year-to-year depending on the intensity of sedimentary Mn reduction process. At the offshore stations, dMn showed subsurface maxima, within the Winter Mixing Layer (WML) rather than surface maxima. We attribute this to the combined effect of biological drawdown of dMn in the surface during the spring and summer, where iron (Fe) is depleted in this High Nutrient and Low Chlorophyll (HNLC) region, and remnant dMn deeper in the WML, from earlier in the year. Using a simple one-dimensional advection and diffusion model, we identified that dMn found in North Pacific Intermediate Water (NPIW) at the western end of the transect can be advected as far as the outermost of the onshore stations in 2011 and 2013, while dMn in the central area of the transect is likely diluted by low dMn water from the south in 2010 and 2012. Within the OMZ, dMn showed elevated and annually variable concentrations, yet the enhancement of dMn of this study area was found to be less intense than in other regions. Lastly, an eddy found in 2010 enhanced dMn concentrations within the surface mixing layers.

A basin-wide ocean general circulation model of the Pacific Ocean is employed to study how the air–sea exchange coefficient affects the distribution and storage of bomb 14 C in the ocean. Two numerical experiments are designed, including a constant exchange coefficient (RUN1) and a wind-dependent exchange coefficient (RUN2). RUN1 greatly overestimates the observed surface bomb 14 C concentration in 1973, while RUN2 reduces this overestimate due to a decreased flux in the tropical region. The difference of column bomb 14 C inventories between the two simulations in the North Pacific in 1973 is mainly controlled by the distribution of bomb 14 C in the upper ocean, because the simulated penetration is shallower than the observations. This indicates that the simulated transport of the North Pacific Intermediate water (NPIW) is not strong enough. The surface bomb 14 C concentration in 1994 from the two simulations is obviously decreased relative to that in 1973. The inventory distribution characteristic with high-west and low-east in the subtropical Pacific is more distinct in 1994 than in 1973, and the simulated results in 1994 are closer to the observations than those in 1973, especially in RUN2. Regardless of the surface or section distributions of bomb 14 C concentrations, the results from RUN2 are closer to the observations than those from RUN1. Therefore, it can be concluded that the wind-dependent exchange scheme provides a more accurate bomb 14 C concentration estimate. In addition, a comparison of these two simulations indicates that the simulation of NPIW transport can affect the accurate parameterization comparison used in the simulation of passive tracers in the North Pacific.

New benthic and planktic foraminiferal assemblage census data and Benthic Foraminiferal Oxygen Index (BFOI) values, previously published marine climate proxy data (stable isotopes and Ca/Cd), and unpublished results of total carbon, organic carbon, and calcium carbonate analyses of sediments recovered off central California on the Farallon Escarpment (1605 m water depth; 37°13.4′N, 123°14.6′W; core F-8-90-G21) document paleoceanographic changes during the latest Quaternary which reflect the intensity and source of North Pacific Intermediate Water (NPIW) and surface productivity. Accelerator mass spectrometry radiocarbon dates of both benthic and planktic species provide an excellent age-depth model for the last 16,000 years, covering the latest glacial, Bolling–Allerod, Younger Dryas, and early, middle, and late Holocene intervals. A Q-mode cluster analysis separated the benthic fauna into three clusters, one Pleistocene and two Holocene, whereas the planktic fauna was divided only into Pleistocene and Holocene clusters. Stable oxygen isotope values show an increase in water temperature of ∼1 °C from the late glacial to late Holocene and a change in faunal composition of the planktic assemblage implies surface waters warmed as well. A general trend of decreasing dissolved oxygen concentration from the Pleistocene (high oxic; 3.0–6.0+ ml/l O2) to the Holocene (low oxic; 1.5–3.0 ml/l O2) suggested by the BFOI and Cd/Ca data reflect decreased ventilation as the source of the NPIW shifted from the Sea of Okhotsk to the tropical east Pacific at ∼11,000 cal BP. The middle Holocene cooling reported in other central and northern California margin studies is not apparent in F-8-90-G21, which compares more favorably with studies from southern California and British Columbia. Total carbon and organic carbon values are highest in the Bolling–Allerod, early Holocene, and late Holocene. Similarly, calcium carbonate values are high in the Bolling–Allerod and peak in the early Holocene, but decrease significantly in the latest middle and late Holocene which coincides with a depauparate planktic foraminiferal fauna in the upper 60 cm (∼70000–0 cal BP) of the core and poor preservation of the benthic foraminiferal fauna at 40 cm (∼3000 cal BP). Decoupling is evident between the planktic and benthic faunal response to changing climatic conditions, with the surface-dwelling assemblage often leading the bottom-dwelling assemblage by several millennia.

Evidence from geochemical tracers (salinity, oxygen, silicate, nutrients, alkalinity, dissolved inorganic carbon (DIC), carbon isotopes (δ13CDIC) and radiocarbon (Δ14C)) collected during the Pacific Ocean World Ocean Circulation Experiment (WOCE) voyages (P10, P15, P17 and P19) indicate there are three main water types at intermediate depths in the Pacific Ocean; North Pacific Intermediate Water (NPIW), Antarctic Intermediate Water (AAIW) and Equatorial Pacific Intermediate Waters (EqPIW). We support previous suggestions of EqPIW as a separate equatorial intermediate depth water as it displays a distinct geochemical signature characterised by low salinity, low oxygen, high nutrients and low Δ14C (older radiocarbon). Using the geochemical properties of the different intermediate depth waters, we have mapped out their distribution in the main Pacific Basin. From the calculated pre-formed δ13Cair–sea conservative tracer, it is evident that EqPIW is a combination of AAIW parental waters, while quasi-conservative geochemical tracers, such as radiocarbon, also indicate mixing with old upwelling Pacific Deep Waters (PDW). The EqPIW also displays a latitudinal asymmetry in non-conservative geochemical tracers and can be further split into North (NEqPIW) and South (SEqPIW) separated at ∼2°N. The reason for this asymmetry is caused by higher surface diatom production in the north driven by higher silicate concentrations. The δ13C signature measured in benthic foraminifera, Cibicidoides spp. (δ13CCib), from four core tops bathed in AAIW, SEqPIW and NPIW, reflects that of the overlying intermediate depth waters. The δ13CCib from these cores show similarities and variations down-core that highlight changes in mixing over the last 30,000 yr BP. The reduced offset between the δ13CCib of AAIW and SEqPIW during the last glacial indicates that AAIW might have had an increased influence in the eastern equatorial Pacific (EEP) region at this time. Additional intermediate depth cores and other paleo-geochemical proxies such as Cd/Ca and radiocarbon are required from the broader Pacific Ocean to further understand changes in intermediate depth water formation, circulation and mixing over glacial/interglacial cycles.

We detected temperature (salinity) decreases on the neutral density surfaces above the salinity minimum and increases below throughout the western North Pacific subtropical gyre ( 25 ∘ N – 40 ∘ N , west of 170 ∘ W ) by comparing World Ocean Circulation Experiment (WOCE) hydrographic sections from the 1980s, 1990s, and 2000s. The temperature (salinity) changes around the salinity minimum were associated with an apparent oxygen utilization (AOU) increase, and could not be explained by an increase of the subpolar input. These property changes were due to a density decrease of the salinity minimum. Furthermore, similar changes in temperature (salinity) were detected along 165 ∘ E as a 12-year trend from 1996 to 2007. This suggests that the changes evident in the comparison of the WOCE sections are the representative of changes at the intermediate depths in the last decade. This pattern was not detected in the eastern subtropical gyre ( 25 ∘ N – 40 ∘ N , east of 170 ∘ W ) and along 47 ∘ N , where the AOU increase due to ventilation reduction has been reported. Along 47 ∘ N , changes in temperature, salinity and AOU from 1999 to 2007 were opposite to those from 1985 to 1999.

The formation of North Pacific Intermediate Water (NPIW) requires a densification of ∼0.2-0.3 σθ through interior transformation processes. Evidence of this density anomaly is discovered on neutral density surfaces in the subarctic-tropical frontal zone (SATFZ) showing an eastward tongue of positive density anomaly coincident with a cabbeling maximum tongue. The northward displacement of the SATFZ with depth east of dateline enables the transformed dense water from overlying thermocline to sink into the northeast subtropical NPIW domain. The further southward and southwestward spreading across the subtropical gyre yields the observed distribution of NPIW.

Hydrographic variability in the Mixed Water Region of the Northwest Pacific Ocean at latitudes 35°–40°N, between the Kuroshio Extension and Oyashio Front, causes complex upwelling, leading to large primary productivity and thus great fishery resources. We reconstructed the periodicity of the variability in North Pacific Intermediate Water upwelling and surface ocean hydrography based on the high-resolution analysis of diatom assemblages in seven cores, representing the last 150,000 years. We derived annual sea surface temperatures (SSTs) through a diatom-based proxy (Td′). The Td′-derived annual SSTs (°C) are controlled by orbital forcing, and show a reversed saw-tooth in southern cores, in contrast to a normal saw-tooth pattern in the northern cores. Oceanic diatom abundances along the northern margin of the Mixed Water Region are twice times as high as beneath the axis of the Kuroshio Extension, and fluctuated in a revised saw-tooth pattern with higher overall abundances interglacials. After the last deglaciation, annual SSTs declined markedly during Heinrich and Bond events in the northern North Atlantic, when ice-rafted detritus transported by icebergs was abundant. Wavelet analyses of the record of oceanic diatom abundances show significant variability at 2.0-kyr, 2 to 5.6-kyr and 3.2 to 9.6-kyr periods. Wavelet analyses of the annual SST records show significant periodicity at 1.4 to 2.6-kyr, 3.3 to 4.0-kyr, 7.2 to 12.8-kyr cycles.

Recent in situ observations of chromophoric dissolved organic material (CDOM) in the Pacific Ocean reveal the biogeochemical controls on CDOM and indicate predictive potential for open-ocean CDOM in diagnosing particulate organic matter (POM) remineralization rates within ocean basins. Relationships between CDOM and concentrations of dissolved oxygen, nutrients and inorganic carbon in the subthermocline waters of the Pacific reflect the relative influences of water mass ventilation and water-column oxidative remineralization. Apparent in situ oxygen utilization (AOU) accounts for 86% and 61% of variance in CDOM abundance, respectively, in Antarctic Intermediate Water and North Pacific Intermediate Water. In the deep waters of the Pacific below the zone of remineralization, AOU explains 26% of CDOM variability. The AOU–CDOM relationship results from competing biogeochemical and advective processes within the ocean interior. Dissolved organic carbon (DOC) is not statistically linked to the CDOM or AOU distributions, indicating that the majority of CDOM production occurs during the remineralization of sinking POM and thus potentially provides key information about carbon export. Once formed in the ocean interior, CDOM is relatively stable until it reaches the surface ocean where it is destroyed by solar bleaching. Susceptibility to bleaching confers an additional tracer-like quality for CDOM in water masses with active convection, such as mode waters that appear as subsurface CDOM minima. In the surface ocean, atypically low CDOM abundance highlights a region of unusually extreme oligotrophy: the subtropical South Pacific gyre. For these hyper-oligotrophic waters, the present CDOM observations are consistent with analysis of in situ radiometric observations of light attenuation and reflectance, demonstrating the accuracy of the CDOM spectrophotometric observations. Overall, we illustrate how CDOM abundance in the ocean interior can potentially diagnose rates of thermohaline overturning as they affect regional biogeochemistry and export. We further show how relative surface ocean CDOM abundances are driven in large part by processes occurring in the deep layers of the ocean. This is particularly significant for the interpretation of the global surface distribution of CDOM using satellite remote sensing.

Three vertical profiles of seawater concentration and isotopic composition of Nd were determined for the western to central North Pacific Ocean. In the subarctic oceanic region, at depths greater than 500 m, one vertical profile of Nd isotopic composition was indistinguishable from most previously reported profiles from here. The data indicate a rather homogeneous Nd isotopic composition in the subarctic oceanic region at middle to deep depths (>500 m). Two stations in the subtropical oceanic region exhibited similar Nd isotopic composition profiles to those previously reported. The maxima eNd values at depths of 800– 1000 m (eNd = � 3.4 to � 2.7), which correspond to the North Pacific Intermediate Water (NPIW), are found at both subtropical stations. This implies a ubiquitous distribution of NPIW showing a radiogenic eNd value in the North Pacific. The subsurface minimum at a depth of � 200 m, which indicates the penetration of the North Pacific Tropical Water (NPTW) with an unradiogenic Nd isotopic signal, was observed at one station in the western Pacific. This station had much lower eNd than the central station at depths around 5000 m, suggesting the greater prominence of Antarctic Bottom Water (AABW) in the western subtropical Pacific than in the central to eastern subtropical Pacific. Results of a model calculation assuming boundary exchange indicate that the Hawaiian Islands play an important role in supplying radiogenic Nd to the central Pacific, similar to some continental margins. We show that Nd isotopic composition is a versatile tracer for ocean circulation and the geochemical cycle of Nd in the North Pacific. Further studies on the distribution of Nd isotopic composition in the Pacific Ocean, including the Southern Pacific, will better elucidate the circulation and geochemical cycle of Nd in the Pacific.

To clarify the sources and transformation of NO3− on the Pacific coast of Japan, observations over the continental shelf were conducted during the summer in 2005 and 2006 when the Kuroshio flowed close to and away from the coastal area, respectively. Below the halocline, there are two prominent salinity peaks that originated in two different waters. In the subsurface layer, the salinity maximum (Smax) was indicative of the Kuroshio Water (KW), while the salinity minimum (Smin) in the middle layer at ∼400 m depth was indicative of the North Pacific Intermediate Water (NPIW). δ15NNO3 ranged from 4.1‰ to 5.1‰ with a mean of 4.8±0.4‰ in the deeper water around Smin. Below 50 m depth over the shelf break, δ15NNO3 values (3.1±0.8‰ in 2005 and 4.6±0.3‰ in 2006) clearly increased as contribution of NPIW increased in 2006. On the contrary, subsurface δ15N of NO3− values (−1.1±0.1‰) remained unchanged in both years, although the contribution of the KW to the subsurface water changed significantly. This suggests that the source of NO3− has little effect on the δ15N of NO3− in this layer. The negative δ15N values also coincided with the base of the chlorophyll maximum layer suggesting that these isotopic signals must be evidence of active nitrification in the upper layer.

The oceanic cycle of cadmium is still poorly understood, despite its importance for phytoplankton growth and paleoceanographic applications. As for other elements that are biologically recycled, variations in isotopic composition may bring unique insights. This article presents (i) a protocol for the measurement of cadmium isotopic composition (Cd IC) in seawater and in phytoplankton cells; (ii) the first Cd IC data in seawater, from two full depth stations, in the northwest Pacific and the northwest Mediterranean Sea; (iii) the first Cd IC data in phytoplankton cells, cultured in vitro. The Cd IC variation range in seawater found at these stations is not greater than 1.5 eCd/amu units, only slightly larger than the mean uncertainty of measurement (0.8 eCd/amu). Nevertheless, systematic variations of the Cd IC and concentration in the upper 300 m of the northwest Pacific suggest the occurrence of Cd isotopic fractionation by phytoplankton uptake, with a fractionation factor of 1.6 ± 1.4 eCd/amu units. This result is supported by the culture experiment data suggesting that freshwater phytoplankton (Chlamydomonas reinhardtii and Chlorella sp.) preferentially take up light Cd isotopes, with a fractionation factor of 3.4 ± 1.4 eCd/amu units. Systematic variations of the Cd IC and hydrographic data between 300 and 700 m in the northwest Pacific have been tentatively attributed to the mixing of the mesothermal (temperature maximum) water (eCd/amu = −0.9 ± 0.8) with the North Pacific Intermediate Water (eCd/amu = 0.5 ± 0.8). In contrast, no significant Cd IC variation is found in the northwest Mediterranean Sea. This observation was attributed to the small surface Cd depletion by phytoplankton uptake and the similar Cd IC of the different water masses found at this site. Overall, these data suggest that (i) phytoplankton uptake fractionates Cd isotopic composition to a measurable degree (fractionation factors of 1.6 and 3.4 eCd/amu units, for the in situ and culture experiment data, respectively), (ii) an open ocean profile of Cd IC shows upper water column variations consistent with preferential uptake and regeneration of light Cd isotopes, and (iii) different water masses may have different Cd IC. This isotopic system could therefore provide information on phytoplankton Cd uptake and on water mass trajectories and mixing in some areas of the ocean. However, the very small Cd IC variations found in this study indicate that applications of Cd isotopic composition to reveal aspects of the present or past Cd oceanic cycle will be very challenging and may require further analytical improvements. Better precision could possibly be obtained with larger seawater samples, a better chemical separation of tin and a more accurate mass bias correction through the use of the double spiking technique.

The North Pacific Intermediate Water (NPIW), source water (Oyashio Intermediate Water; OYIW) of which originates east of the southern Kuril Islands, plays an important role in the carbon cycle of the Pacific Ocean. The spatio-temporal changes of NPIW, however, have yet to be clarified. Because of OYIW flowing in the Oyashio region, from east of the southern Kuril Islands through south of Hokkaido to east of Honshu, it is important to understand past bottom water changes at intermediate depths of this region for study of the past NPIW. Two sediment cores, GH02-1030 and MD01-2409, were collected from south of eastern and central Hokkaido. Lithology and physical properties of the cores recorded well the surface and bottom water conditions. Higher diatom productivity in the surface waters led to diatomaceous sediments with higher water contents and lower grain densities during the last deglaciation and late Holocene. These lithological changes occurred not only at the two studied cores but also at several other sites along the western margin of the NW Pacific. Benthic foraminiferal assemblages and occurrence of parallel lamination indicated such a dysoxic bottom water condition during the last deglaciation. Absence of lamination in the late Holocene horizon suggested a somewhat higher dissolved oxygen concentration in bottom water than that during the last deglaciation. On the basis of benthic foraminifer assemblages corresponding to strengthening of intermediate water circulation inferred from coarsening of sediment grain size and decreasing of sedimentation rate indicating stronger winnowing effects, it appears that the bottom water oxygen level increased during the Younger Dryas cold period.

Characterized by extended seasonal sea-ice cover, the Okhotsk Sea is widely considered one possible source of the North Pacific Intermediate Water (NPIW). Therefore, reconstructing the characteristics of the sediments that resulted from the ice-melting pulses of this northeastern Asian sea during glacial–interglacial cycles is crucial to understanding past climatic changes and NPIW formation in the northwest Pacific Ocean. Here, we produced the detailed mineralogy and geochemistry of the upper 20 m of the sediments of IMAGES Core MD012414, which was drilled in the central part of the Okhotsk Sea. This depth covers the last 500 kyrs. The mineralogical data show that in glacial periods, the sediments were predominantly composed of quartz and plagioclase with a volume of about 80%, indicating that they were mainly from the surrounding landmasses. During interglacial periods, however, biogenetic calcite and amorphous opal drastically increased from less than 5% to a remarkable 40–60%, while the element ratios Mg/Al, Ca/Al and Si/Al also had anomalous increases from 0.2 to 0.5, 0.12 to 1.2 and 3.5 to 10, respectively. These characteristics of the sediments in interglacial periods strongly suggest that the melting of permanent ice opened a gateway, thereby letting the northwest Pacific warmer water flow into the Okhotsk Sea, which subsequently increased biogenetic productivity during the deglacial periods. In addition, in early interglacial periods, the bottom water became anoxic, as evidenced by the presence of dolomite and the enrichment of the Mn/Al and P/Al ratios more than 25 to 200 times. The fact that these trends did not occur in stage 7 strongly suggests that stage 8 may have been a warmer glacial period.

The role played by tide-induced diapycnal mixing at the Kuril Straits in the formation of the Okhotsk Sea water is examined using an ocean general circulation model. The result shows that tidal mixing causes a freshening of intermediate water down to ∼ 27.6 σ θ . This implies an enhancement of ventilation by tidal mixing, since a freshening flux can come only from above in the Okhotsk Sea. In fact, when compared with the case without tidal mixing, the production rate of Dense Shelf Water (DSW) increases from 0.01 to 0.13 Sv ( 10 6 m 3 s - 1 ) with maximum DSW density increased from 26.6 to 26.8 σ θ . This enhanced production of DSW allows us to successfully reproduce a layer of local potential vorticity minimum in the Okhotsk Sea, which characterizes the Okhotsk Sea Mode Water. The analysis reveals that tidal mixing at the Kuril Straits has two roles in enhancing ventilation. First, it preconditions the water properties of the DSW because tidal mixing at the Kuril Straits induces an upward salt flux from the saltier lower layer. The subsequent transport of the saline water from the Straits to regions of sea-ice generation increases the density of subducting water, resulting in more realistic densities and production rates of DSW. Second, tidal mixing directly modifies water properties throughout the water column. The ventilation due to this mechanical mixing further enhances the intermediate layer ventilation, and is dominant in the Kuril Straits and in the layer denser than the DSW. Although the effect of double diffusion on ventilation in the Okhotsk Sea is also examined, it is much less effective than the tidal mixing. Since the Okhotsk Sea is a key location for the ventilation of the North Pacific intermediate layer, the important implication here is that tidal mixing at the Kuril Straits enhances the meridional overturning in the entire North Pacific Ocean.

Like most other deep basins in Southeast Asia, the deep Sulu Sea (SS) basin is isolated from the neighboring seas by surrounding topography. While the near-surface circulation is mainly governed by the seasonally reversing monsoon winds, below the warm and fresh surface layer, the core of the incoming Subtropical Lower Water from the West Philippine Sea (WPS), by way of the South China Sea (SCS), can be seen, at a depth of around 200 m, to have a distinct salinity maximum. It lies well above the sill depth (420 m) in the Mindoro Strait and thus, its spreading is not hampered by topography. The deep circulation is forced by an inflow of upper North Pacific Intermediate Water (NPIW) from the SCS through the Mindoro Str. Below 1000 m, the physico-chemical properties are remarkably homogeneous. The higher temperature, but lower salinity, oxygen and nutrients, of the deep SS waters, compared to those of the SCS, is indicative of the intrusion of NPIW above the sill depth. The excess, anthropogenic CO2 penetrates the entire water column, because of the over-spill of the excess CO2-laden water from the SCS. It has been reported that the bottom of the SS is CaCO3 rich, relative to the SCS. Previous investigators attribute this to the higher θ in the SS. Indeed, the aragonite does not become undersaturated in the SS until below 1400 m, compared to 600 m in both the WPS and SCS; and the calcite does not become undersaturated until below 3800 m in the SS, compared to 2500 m in the SCS and around 1600 m in the WPS. However, the temperature effect is relatively small. These large differences are, in fact, largely a result of higher CO32− concentrations in the SS, relative to the WPS and SCS. The higher CO32− concentration in the SS, in turn, is mainly caused by the smaller amounts of organic carbon decomposition.

Seven piston cores were obtained from the Bering Sea and the western subarctic Pacific during Cruise KH99-3 of R.V. Hakuho-maru in August 1999: Cores BOW-8A, BOW-9A, BOW-12A, AB, UMK-3A, GAT-3A in the Bering Sea, and Core ES in the western subarctic Pacific. The quantitative high-resolution analyses of radiolarians in the cores revealed significant variations in both their faunal assemblages and accumulation rates (AR). A trend of conspicuous turn-over of the surface dwellers and intermediate dwellers (increase of one at expense of the other) after the last glacial maximum (LGM) is clearly visible in the Bering Sea data set. However, this turn-over is not present at Site ES in the western subarctic Pacific core. These changes in radiolarian assemblages around the LGM suggest that the surface waters had extremely low temperature and low salinity and that the subsurface dichothermal layer (temperature minimum layer) was thickened all the way across the entire east–west span of the Bering Sea. Furthermore, sea-ice coverage extended to the central Aleutian Basin around the LGM. This suggests that the water-mass structure in the western subarctic Pacific around the LGM was basically the same as that of the eastern Bering Sea based on the species composition of the surface dwellers. However, the detailed development of intermediate water masses differed from that of the eastern Bering Sea. During Marine Isotope Stage (MIS) 5 to 3, such species turn-over events did not occur and species abundance stayed relatively uniform in the studied cores. Therefore, the present water-mass structure is interpreted to have been formed after the LGM. Based on the relative abundances of Cycladophora davisiana (the most dominant species dwelling in the intermediate water, and a useful tracer of cold and well-oxygenated intermediate-water in the North Pacific), the past North Pacific Intermediate Water (NPIW) had the following source regions during the last 100 kyr: (1) both the Okhotsk Sea and the Bering Sea during MIS 5 to 3; (2) the Bering Sea around the LGM; and (3) shifting from the Bering Sea to the Okhotsk Sea after the LGM. Relatively low radiolarian AR at Site BOW-8A, which is the shallowest site studied here (present water depth: 884 m), were observed during the glacial periods. This is due to decrease of radiolarian production in the thinned upper water layer above the dicothermal layer caused by sea-level drop. Cycladophora davisiana probably lived deeper during the glacials than today, as it was absent in the shallow piston core. r 2005 Elsevier Ltd. All rights reserved.

Sedimentary, geochemical and paleontological data, extracted from a sediment core taken from the central Okhotsk Sea, record climatic and sedimentary changes over the past 100 ky. Benthic foraminiferal oxygen isotope record and accelerator mass spectrometry (AMS) 14C data provide the basis for the core age chronology. Planktonic and benthic foraminiferal δ18O and δ13C measurements, magnetic susceptibility, ice rafted debris and coarse fraction content, carbonate and organic carbon content, and diatom and pollen spectra show major changes in regional climate, sea surface conditions, ice extent and sedimentary regime, which are correlated with the global glacial–interglacial changes of marine isotope stages (MIS) 1 through 5.3. Regional cooling and intensification of winter sea ice formation during the last glaciation increased the northern shelf surface water density and Sea of Okhotsk Intermediate Water (SOIW) formation. In addition to major Milankovitch-scale changes, lithological, geochemical and paleontological indices also show suborbital oscillations in Okhotsk Sea hydrology, sedimentation and regional climate. These shorter-term oscillations are characterized by coupled maxima in ice rafted debris and sediment coarse fraction (lithodynamic indices, LDI) values and most are associated with cold events involving enhanced winter ice formation and intensification of SOIW and North Pacific intermediate water (NPIW) formation. The terminations of LDI maxima were induced by climate warming and reductions in ice formation, and were accompanied by sharp decreases in planktonic foraminiferal δ18O. During the glacial terminations of MIS 2 and 4, however, the onset of suborbital-scale LDI maxima occurs close to sharp negative δ18O shifts in planktonic foraminifera (δ18Opf) associated with climate warming. In these special cases, the LDI maxima occurred under warm climate and rising sea levels and did not lead to increases in SOIW or NPIW ventilation.

Four vertical profiles of the concentration and isotopic composition of Nd in seawater were obtained in the western North Pacific. Two profiles from the Kuroshio Current regime showed congruently that although the Nd concentration increases gradually with depth, its isotopic composition varies significantly with depth depending upon the water mass occupying the water column. The high-salinity Kuroshio waters originating from the North Pacific Tropical Water (NPTW) carry the least radiogenic Nd (ϵ Nd = −7.4 to −8.7) to this region at ∼250 m from the western margin continental shelves, most likely from the East China Sea. The Nd isotopic compositions in the North Pacific Intermediate Water (NPIW) that occurs at 600 to 1000 m in the subtropical region are fairly uniform at ϵ Nd = −3.7. The profile data from the ∼38° to 40°N Kuroshio/Oyashio mixed water region off Sanriku of Honshu, Japan, also suggest that the newest NPIW with ϵ Nd = −3.2 is formed there by the mixing of various source waters, and the radiogenic component of Nd is derived mainly from the Oyashio waters. In the Pacific Deep Water (PDW) below ∼1000 m, the Nd isotopic composition is neither vertically nor horizontally homogeneous, suggesting that it serves as a useful tracer for sluggish deep water circulation as well. Two profiles from the Izu-Ogasawara Trench showed a minimum ϵ Nd value at ∼2000 m, suggesting that there exists a horizontal advective flow in the vicinity of Honshu, Japan. There is some evidence from other chemical properties to support this observation. The waters below 4000 m including those within the trench in the subtropical region have ϵ Nd values of around −5, suggesting that the deep waters are fed from the south along the western boundary, ultimately from the Antarctic Bottom Water (AABW) in the South Pacific. This extends up to ∼40°N along the Japanese Islands. In the subarctic region (>∼42°N), the waters have more radiogenic Nd with ϵ Nd > −4.0 throughout the water column, presumably due to the supply of Nd by weathering in such igneous provinces as the Kuril-Kamchatska-Aleutian Island chain. The lateral inhomogeneity of the Nd isotopic composition in PDW suggests that there may be different circulation and mixing regimes in the North Pacific Basin.

The modern North Pacific is the terminus for deep-water circulation. While no deep-water mass is formed today, the region is the source of North Pacific Intermediate Water (300–800 m) formed primarily in the Sea of Okhotsk. However, the source and strength of intermediate-water in the glacial North Pacific was likely different from the present intermediate-water. Here we present microfossil evidence of Late Quaternary ventilation changes associated with changes in intermediate-water. Intermediate-water ventilation decreased drastically at the glacial termination when it switched to the modern circulation system. The ventilation change appears to have been widespread and synchronous in the North Pacific. Glacial microfossil assemblages indicate that there was relatively strong ventilation of intermediate-water, which seems to have been cold and well-oxygenated as if produced by brine rejection during the formation of sea ice. On the basis of the glacial distribution of microfossils in the North Pacific, we suggest that intermediate-water was derived from the Bering Sea during the glacials, rather than the Sea of Okhotsk.

Evidence is presented demonstrating intermediate water (∼500 m) temperature variability at ODP Hole 893A in Santa Barbara Basin during submillennial climate change (11–60 ka). Benthic δ 18 O oscillations are considered to result primarily from shifts in intermediate water temperature at the site. Detailed comparison of both benthic and planktonic records from the basin provide crucial evidence for differing surface and intermediate water mass temporal responses to rapid climate change. Gradual warming of intermediate water compared to abrupt cooling suggests mechanistic differences between processes controlling North Pacific Intermediate Water expansion and contraction relative to ‘southern component’ intermediate waters. Comparisons suggest intermediate water warming preceded (by 60–200 years) the most rapid interval of surface warming inferred to be associated with North Pacific atmospheric reorganization. Tropical forcing of sea level anomalies in the eastern Pacific via trade wind strength may control California Undercurrent flow (300–500 m) and be the cause of early intermediate water warming in Santa Barbara Basin.

Lignin measurements were made on suspended particulate organic matter (POM), total dissolved organic matter (DOM), high-molecular-weight (HMW) DOM, and low-molecular-weight (LMW) DOM in the North Pacific at Station Aloha. Carbon-normalized yields of lignin and d 13 C measurements indicate that while terrigenous organic matter accounts only for B1% of DOM in seawater, submicron POM has a substantial terrigenous component. The apparent size distribution and terrigenous nature of the particles is consistent with an aerosol source, but these particles could also be delivered to the ocean via rivers. Ratios of syringyl to vanillyl phenols as well as the fraction of dissolved lignin in HMW DOM provide molecular evidence of photochemical oxidation. Several differences in lignin composition and concentrations were evident between water masses. In particular, concentrations in North Pacific Intermediate Water were a factor of two greater than at all other depths. This is likely a reflection of higher riverine input via the Sea of Okhotsk. These trends suggest that lignin could serve as a general circulation tracer in addition to tracing riverine input and diagenetic processing of terrigenous organic matter in the ocean. r 2002 Elsevier Science Ltd. All rights reserved.

Processes relating to the formation of dense shelf water and intermediate water in the Okhotsk Sea were studied by examining oxygen isotope ratios ( δ 18 O), salinity, and temperature. The salinity and δ 18 O of the cold dense shelf water on the northern continental shelf showed peculiar relationship. The relationship indicates that 3% of the mixed-layer water, having salinity of 32.6, froze and the remaining 97% became dense shelf water of salinities of more than 33.2 ( σ θ >26.7) during the sea ice formation. The salinity– δ 18 O relationship also shows that 20% of the Okhotsk Sea Intermediate Water at the σ θ =26.8 level was derived from the dense shelf water. The remaining 80% came from the Western Subarctic Pacific water modified by diapycnal mixing of water affected by the surface cooling and freshening within the Okhotsk Sea. The mixing with dense shelf water contributes to only 26% of the temperature difference or 8% of the salinity difference between the original Pacific water and the Okhotsk Sea Intermediate Water at σ θ =26.8. This result suggests that the cold and less saline properties of the Okhotsk Sea Intermediate Water are produced mainly by diapycnal mixing, rather than by mixing of the Pacific water with the dense shelf water.

We have estimated the volume transports of the subarctic and subtropical waters in the intermediate layer in the potential density range of 26.6–27.5 σ θ in the Kuroshio–Oyashio interfrontal zone, using hydrographic data and directly measured velocity data with a LADCP from the R/V Soyo-maru cruise performed in May–June 1998. The subarctic water flowing into this area along the Oyashio near Hokkaido (5.2 Sv) and from the subarctic front (2.0 Sv) merged with the subtropical water (13.5 Sv) along the Kuroshio near Japan and formed 20.7 Sv of North Pacific intermediate water (NPIW). NPIW mainly flowed eastward along the Kuroshio Extension, and the transport across 158°E was about 18.8 Sv (7.2 Sv of subarctic water and 11.6 Sv of subtropical water). Another 2.3 Sv of the subtropical water were transported farther northward across 39°N. These results support the hypothesis that NPIW is mainly formed along the Kuroshio Extension.

Invasion of the bomb radiocarbon was investigated in the northwestern North Pacific, including the subarctic (Oyashio region), the subtropical (Kuroshio region), and the subarctic/subtropical mixing (transition) areas. After the GEOSECS Pacific expedition in 1973, the bomb radiocarbon decreased in the Oyashio region and increased in the Kuroshio region. The former was caused by rapid ventilation of the Oyashio water. The latter was owing to accumulation of the bomb radiocarbon in the intermediate water of the Kuroshio region. The reverse trends in the temporal variation of radiocarbon between the Oyashio and the Kuroshio regions lead to virtually small temporal change of the bomb radiocarbon in the transition area where the two waters mix. The temporal changes of the bomb radiocarbon suggest that the North Pacific Intermediate Water is formed in the northwestern North Pacific.

In the transition area between the subarctic and subtropical regions in the western North Pacific, vertical distributions of radiocarbon at seven stations were clarified by AMS radiocarbon measurement in 1997. The radiocarbon in intermediate water at those stations indicate (1) direct ventilation of upper intermediate water above 26.6σθ surface and (2) no temporal increment of radiocarbon in the transition area during the last two decades. These results positively suggest that the North Pacific intermediate water is formed in the transition area in the western North Pacific.

New benthic foraminiferal stable isotopic records of northeast Pacific intermediate water (ODP Site 1014, 1177 m) and mid-depth water (ODP Site 1018, 2476 m) were compared to isotopic records of deep water in the tropical Pacific (ODP Site 849, 3851 m) for the reconstruction of vertical profiles of nutrient and physical properties from the Early Pliocene to the Early Pleistocene (approx. 5–1.4 Ma). Our data indicate that, for the entire interval, there was enhanced north Pacific intermediate water ventilation relative to today, and a similar to modern circulation pattern with northward flowing Pacific Bottom Water (PBW) beneath its southward flowing return flow. However, the core of maximally aged return flow resided as deep as ∼2500 m (as compared to ∼1500 m today), probably due to the strengthened intermediate water flow. Less apparent aging of deep water along its path before 2.7 Ma indicates that thermohaline overturning may have been more rapid in the warm period of the Early Pliocene. In addition, prior to 2.7 Ma, foraminiferal oxygen isotopic values at mid-depth sites are higher than at deep sites (a reversed vertical gradient relative to today) in both the Atlantic and Pacific Oceans. We suggest that NADW was warmer and more saline than today and that it influenced mid-depth waters throughout the Atlantic and Pacific Oceans. Enhanced Pliocene formation of warmer/saltier intermediate water in the north Pacific, and deep water in the north Atlantic, may have been a result of higher than modern high/mid-latitude sea surface temperatures, evaporation, and salinity.

The Okhotsk Sea is a locus of the North Pacific Intermediate Water formation today. The formation of the Okhotsk Intermediate Water is linked with seasonal sea-ice cover. Diatom records from the Okhotsk Sea show the following. (1) During the last glacial maximum (between 21,000 yr B.P. and 18,000 yr B.P.), sea ice covered the western side of the sea throughout the whole year, but the eastern part was open. This permitted more efficient heat exchange with the atmosphere than waters and hence ventilation of the glacial Okhotsk Sea waters which in turn caused a greater extent of Intermediate Water formation through the Bussol' Strait. (2) The perennial sea-ice cover extended northward, and sea ice was present throughout the whole year over a great part of the sea except for the eastern part between 18,000 yr B.P. and 17,000 yr B.P. (3) The ice-free area extended greatly to the south during the interval between 17,000 yr B.P. and 11,000 yr B.P. (4) There was no perennial ice cover over the whole sea, and the ice-free area that appeared as the seasonal ice area began to extend to the western part between 11,000 yr B.P. and 8,000 yr B.P. (5) After 8000 yr B.P. the ice-free waters contracted to the present extent.

The salinity minimum frequently occurring in the Mixed Water Region between the Oyashio and Kuroshio Fronts seems to originate from the salinity minimum at the density of 26.8σθ called the North Pacific Intermediate Water. We examined water exchange of this region with the Oyashio and the Kuroshio Extension using mixing ratio RK defined as (θ−θOY)/(θK−θOY)×100, where θOY,θK, and θ represent potential temperature of the Oyashio and Kuroshio Waters and their mixture on the isopycnal surfaces, respectively. CTD data were obtained by repeated observation from January 1990 to May 1991. RK increases southward from the Oyashio Front to the Kuroshio Front with the range of −20 to 120%. The gradient of RK on the isopycnal surfaces is large around the Oyashio Front above the 26.8σθ surface, while it is large around the Kuroshio Front below it. This agrees with the average RK in the Mixed Water Region decreasing greatly with the increase of density at densities less dense than 26.8σθ. We calculated thickness and volume transport of the Oyashio between the isopycnal surfaces near the coast of Hokkaido. They increase largely with density at densities less dense than 26.8σθ. It is supposed that the salinity minimum in the Mixed Water Region is the upper limit of the water largely influenced by the Oyashio Water. Its density could depend only on the density structure of the Oyashio.

The high biological productivity and an efficient biological pumping in the subarctic Pacific and adjacent seas make this region important to the modern carbon cycle and both modern and the past climate of the Earth. Knowledge of the northern marginal seas of the Pacific, however, is unsubstantial. The Bering Sea is located between the Pacific Ocean and the Arctic Sea and plays an important role in ocean circulation, involving balances of heat, salt and various chemical properties. Thus, it is necessary to unravel the geologic history of the Bering Sea as a gateway to the Pacific and the Arctic/Atlantic during the last 5 million years and beyond. The Okhotsk Sea is considered a locus of North Pacific intermediate water formation today. The intermediate water formation is linked with seasonal sea-ice cover. Diatom records from the Okhotsk Sea demonstrate that sea-ice cover was distributed on the western side of the sea and the eastern part was open water during the last glacial maximum. This configuration permitted a better ventilation of the glacial Okhotsk Sea through increased quantity of intermediate water, presumably formed there at that time.

The purpose of this study is to assess changes in the ocean biogeochemistry and oceanic partial pressure of CO 2 (pCO 2 ) due to CO 2 disposal and its effects, and to discuss the oceanographic parameters affecting the return of disposed CO 2 back to the atmosphere. The primary focus will be on CO 2 scenarios for North Pacific intermediate water (NPIW) and the deep water off the Japanese coast. CO 2 chemistry shows that pCO 2 values in the intermediate and deep North Pacific waters are already higher than the present atmospheric CO 2 level. The factors maintaining high pCO 2 in the waters of the North Pacific Ocean are (1) ocean diffusivity, (2) penetration and mixing into deeper water, (3) transport of NPIW, (4) deep Pacific circulation, and (5) the efficiency of the biological pump. Review of recent work on ventilation of deep Pacific waters suggests a mid-depth return flow to Antarctic circumpolar water, increasing the residence time of disposed CO 2 into the deep water. A review of CO 2 source and sink areas in the Pacific Ocean indicates potential escape routes of disposed CO 2 back to the atmosphere. Several strategies are available for disposing CO 2 into the ocean: (1) Disposal into the upper ocean can be combined with simultaneous fertilization to create a detritus flux, transporting CO 2 into deep waters. (2) Disposal into NPIW will buy 20 to 50 years of time depending on the maintaining of the ventilation rate of NPIW. (3) Disposal into the deep Pacific waters relies on the tightness of the thermocline lid and the continuous action of the biological pump to keep the upper ocean low in pCO 2 . Thus, certain crucial areas of research need to be looked at to remove uncertainties in knowledge such as: (a) the experimental assessment of vertical diffusivity ( K v ) in the upper, the intermediate and deep waters, (b) an assessment of the time-scale of Pacific ventilation, and (c) fertilization to enhance the biological pump. A Pacific SF 6 tracer and CO 2 storage experiment is a logical approach to tackle these important areas of research.

Changes of the Oyashio Water properties are examined along the Oyashio northeast of Honshu, Japan. CTD data from simultaneous observations made by multiple ships in September 1989 are used. The Oyashio Water is modified by layering and vertical mixing with warm, saline waters flowing out from the Okhotsk Sea and the Japan Sea at densities lower than 130 cl/ton (26.7 σ δ ). At densities greater than 130 cl/ton, the properties of Oyashio Water do not change significantly from the southeast of Iturup Island to the coast of Tohoku district at 39°20′N. The large and abrupt modification of Oyashio Water occurs within 400 km of the coast of Tohoku district, i.e. at the westernmost part of the Oyashio Front at about 39°N, by mixing with Kuroshio Water. By this modification, a salinity minimum is formed at densities around 26.8 6e corresponding to North Pacific Intermediate Water, which is the salinity minimum water broadly located in the subtropical region. The modified Oyashio Water flows northeastward along the Oyashio Front and joins the offshore flow of the Oyashio, which is separated from the main flow of the Oyashio southeast of the southern Kuril Islands carrying the typical western subarctic water.

A hydrographic section in the region east of Luzon was repeated 14 times during the period from 1986 to 1991. The data revealed the existence of a subsurface countercurrent located on the shoreward side of the Kuroshio with its upper boundary at about 500 m. The countercurrent, which should be called the Luzon Undercurrent (LUG), was only about 50 km wide, which is comparable to the baroclinic radius of deformation. Despite considerable variabilities both in velocity profile and intensity, the LUC appears to be a permanent feature. Over the period of observations, the maximum speed in the LUC calculated from the mean temperature and salinity by assuming geostrophy (relative to 2500 db) was 7 cm s(-1) at about 700 m and its mean geostrophic volume transport was 3.6 Sv (1 Sv = 10(6) m(3) s(-1)). About 28% of this transport was composed of the low-salinity North Pacific Intermediate Water (NPIW) advected to the south along the coast of Luzon. (C) 1997 Elsevier Science Ltd.