Sea-surface bioproductivity changes in the Northwest Pacific over the last 25 kyr

The sea-surface bioproductivity changes over the last 25 kyr were inferred from published data on 30 sediment cores from the open Northwest Pacific (NWP), Sea of Okhotsk, Bering Sea and Sea of Japan accounting for the glacioeustatic sea-level changes. A novel method was developed to compare the variations of several independent productivity proxies relative to the present-day values. During the Last Glacial Maximum, the bioproductivity in the Sea of Okhotsk and the western Bering Sea (BS) was lower than at present, whereas the southern and southeastern Bering Sea and the open NWP are characterized by enhanced bioproductivity. During the early deglacial stage, an increase in bioproductivity was estimated only for the southeastern Bering Sea. High and fairly high bioproductivity was estimated for Heinrich 1 in the open NWP, above the Umnak Plateau and on the Shirshov and Bowers Ridges in the Bering Sea. The high productivity in the Bering Sea, Sea of Okhotsk and NWP during the Bølling/Allerød was caused by the global warming and enhanced nutrient supply by meltwater from the continent. During the Early Holocene, high productivity was estimated for almost the entire NWP. The Late Holocene sea-surface bioproductivity was generally lower than that of the Early Holocene. Proposed factors that have controlled the sea-surface bioproductivity during the last 25 kyr include: the location of the sea ice margin, the river runoff, gradual flooding of the Bering Sea and the Sea of Okhotsk shelf areas, the water mass exchange between the marginal seas and the open NWP, the eolian supply and the deep vertical mixing of the water column.     

Biomarker records from core GH02-1030 off Tokachi in the northwestern Pacific over the last 23,000 years: Environmental changes during the last deglaciation

We investigated marine and terrestrial environmental changes at the northern Japan margin in the northwestern Pacific during the last 23,000 years by analyzing biomarkers (alkenones, long-chain n-alkanes, long-chain n-fatty acids, and lignin-derived materials) in Core GH02-1030. The U ₃₇^K′-derived temperature in the last glacial maximum (LGM) centered at 21 ka was ∼10°C, which was 2°C lower than the core-top temperature (∼12°C). This small temperature drop does not agree with pollen evidence of a large air temperature drop (more than 4°C) in the Tokachi area. This disagreement might be attributed to a bias of U ₃₇^K′-derived temperature within 2.5°C by a seasonal shift in alkenone production. The U ₃₇^K′-derived temperature was significantly low during the last deglaciation. Because this cooling was significant in the Kuroshio-Oyashio transition zone, the temperature drops are attributable to the southward displacement of the Kuroshio-Oyashio boundary. Abundant lignin-derived materials, long-chain n-alkanes and long-chain n-fatty acids indicate a higher contribution of terrigenous organic matter from 17 to 12 ka. This phenomenon might have resulted from an enhanced coastal erosion of terrestrial soils due to marine transgression and/or an efficient inflow of higher plant debris to river waters from 17 to 12 ka.     

Probable limits of sea ice extent in the northwestern Subarctic Pacific during the last glacial maximum

The article summarizes and analyzes published data on the distribution of sea-ice and open-ocean diatoms in 42 cores of bottom sediments from the northwestern part of the Subarctic Pacific that accumulated during the last glacial maximum (LGM). Based on micropaleontological records, the extent of winter sea ice during the LGM could be limited to the Okhotsk and Bering seas. During the warm season, the surface water masses from the open Subarctic Pacific spread widely in the marginal seas.     

Millennium scale environment changes of the Okhotsk Sea during last 80 kyr and their phase relationship with global climate changes

The paper presents the records of several paleoproductivity proxies (PP) (biogenic opal and Ba (Si_bio, Ba_bio), organic carbon (C_org) and carbonate Ca_carb, chlorin and benthic foraminifera abundance (BFA)) in sediments of the Okhotsk Sea for the last 80 kyr with a resolution of ∼100–300 years. The sediment age model was based on the AMS ¹⁴C data, records of benthic foraminifera δ¹⁸O, paleointensity of the Earth’s geomagnetic field and magnetic susceptibility. PP values demonstrate series of severe prolonged productivity drops in the Okhotsk Sea followed by a sharp increase during the last glaciation. On the basis of quantitative estimations of the paleoproductivity in the Okhotsk Sea during the cold MIS 2 and warm Holocene (Gorbarenko and Goldberg, 2005), it is suggested that the millennium scale relationship in productivity-climate changes of this basin was similar: an increase in the sea’s productivity was related with regional climate warming and vice-versa. The PP records of productivity/climate oscillations in the Okhotsk Sea during MIS 2–4 occurred contemporaneously with the North Atlantic cold Heinrich events (HE) and Greenland Dansgaard-Oyeshger interstadial (DOI). Observed successions of prolonged climate cooling events followed by rapid, abrupt warming are similar to climate and environmental oscillations in the N. Atlantic and Greenland, that confirms the millennium-scale climate changes synchronicities in the Northern Hemisphere including the far NW Pacific, the hydrology and climate conditions of which are close to those of the Okhotsk Sea. Synchronism of the N. Hemisphere severe cooling (including the Okhotsk Sea) with the Antarctic warming suggests that mechanisms of the “seesaw” effect (Blunier and Brook, 2001) in the low latitude heat redistribution between high latitudes of both hemispheres were more complicated than direct NADW formation forcing and encompasses the global atmospheric reorganization. Within the PP used a closer connection in the Okhotsk Sea millennium oscillations was observed for the C_org, BFA and chlorin; Ba_bio increases more closely to DOI. Si_bio variability does not show any evident correlation with productivity changes.     

Sedimentary inorganic nitrogen and its isotope ratio in the western subarctic Pacific over the last 145 kyr

We have measured inorganic nitrogen (IN) content and the isotope ratio of IN (δ¹⁵N_IN) in a sediment core covering the last 145 kyr in the western subarctic Pacific (WSAP). IN content was generally high during glacial periods and shows positive correlations with both eolian dust content and the ratio of organic carbon (C) to organic nitrogen (ON) (C/ON) found in our previous studies. This means that IN was transported from continental areas to the WSAP together with eolian dust and that the IN was not contaminated by volcanic materials, because the eolian dust content was reconstructed using metal components to remove contaminating volcanic materials. Therefore, IN content in the WSAP sediments, the clay fraction of which is not greatly affected by drift deposits seen at the other sites in this region, may potentially be an effective proxy for eolian dust, without the need to consider contamination by volcanic materials. δ¹⁵N_IN was generally low during glacial periods and shows negative correlations with IN, eolian dust, and C/ON. The possible causes of the observed variations in δ¹⁵N_IN are as follows: (1) authigenic fixation of NH₄ ⁺ in water-column and pore water of sea-floor sediments to clay minerals; (2) contamination of measured IN by highly resistant organic matter; or (3) variations in the continental source region of the eolian dust supplied to the WSAP and climatically induced changes in δ¹⁵N of soil organic matter there. The last mechanism shows the potential for δ¹⁵N_IN to be used as a proxy for climate change on land, and is consistent with other published explanations of the spatial distribution of δ¹⁵N_IN in modern sea-floor sediments.     

Tritium in the northwestern North Pacific

Vertical profiles of tritium in seawater were determined for samples collected during the period from 1988 to 1990 at fourteen stations in the northwestern North Pacific (the Oyashio region) including the Okhotsk Sea and the Bering Sea. The profiles usually had a maximum in the surface layer and decreased gradually with depth down to 1,000 m. The water column inventory of tritium averaged 63% of the total atmospheric input in this region.The horizontal distribution of tritium showed a maximum in the region facing the Okhotsk Sea near 45°N for every isopycnal surface of ₀ ranging from 26.60 to 27.40. The ages of the intermediate water were calculated for the respective isopycnal surfaces in the maximum region. This calculation assumed that the intermediate water was formed by the isopycnal mixing of two water masses—the Okhotsk Sea and the Bering Sea Component Waters, which had been produced in wintertime by the diapycnal mixing of the surface and the deep waters in the respective marginal seas. The results show that the intermediate water in this region was formed in the late 1980's for the water which has ₀ of 26.60 to 26.80 and about 1970 for the water which has ₀ of 27.00 to 27.40. Although we have estimated the mean ages of the intermediate water, the horizontal profile of dissolved oxygen suggests that the Okhotsk Sea Component Water is younger than the mean age.     

近45年太平洋海浪特征分析

利用来自欧洲中期天气预报中心(European Centre for Medium-Range Weather Forecasts,ECMWF)将风浪、涌浪分离的具有较高时空分辨率的45年ERA-40海浪资料,对太平洋的海表风场、风浪、涌浪、混合浪的特征进行分析。研究发现太平洋大部分海域的涌浪波高、混合浪波高呈显著的逐年线性递增趋势,趋势分别为0.3—0.6cm.a 1、0.3—1.2cm.a 1;太平洋的涌浪在混合浪中四季皆起主导作用,涌浪指标的低值区主要集中在南北半球的西风带,太平洋赤道附近海域存在明显的涌浪池;北太平洋的风场与风浪场的相关系数好于南太平洋,风场与涌浪场的相关系数则是南太平洋好于北太平洋;研究还发现太平洋的浪场与Nino3指数有着密切的关系。     

Nutricline shoaling in the eastern Pacific warm pool during the last two glacial maxima

Isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and alkenones were analyzed in sediment samples retrieved from Ocean Drilling Program Site 1241 covering the last 150000 years to understand the hydrological evolution of the eastern Pacific warm pool (EPWP). GDGT and alkenone concentrations showed higher values in marine isotope stage (MIS)-2 and MIS-6, which suggests the enhancement of primary production at glacial maxima. $ {\text{TEX}}_{86}^{\text{H}} $ - and $ U_{ 3 7^\prime }^{\text{K}} $ -derived temperature depicted different temperature evolutions. $ U_{ 3 7^\prime }^{\text{K}} $ -derived temperature was marked by small variation during the glacial–interglacial cycles, whereas $ {\text{TEX}}_{86}^{\text{H}} $ -derived temperature showed pronounced glacial–interglacial variation that was similar to Mg/Ca-derived temperature records from nearby cores in the EPWP. Given that enhanced primary production during glacial maxima suggests nutricline shoaling, unchanged $ U_{ 3 7^\prime }^{\text{K}} $ over glacial–interglacial cycles can be interpreted as the shift of alkenone production depth. $ {\text{TEX}}_{86}^{\text{H}} $ seems not to be influenced by glacial–interglacial changes in nutricline depths, recording an integrated temperature in surface and thermocline water. The shallow nutricline in the EPWP during glacial maxima most likely reflected the intense formation of Antarctic intermediate water.     

Paleoenvironment changes in the NW Okhotsk Sea for the last 18 kyr determined with micropaleontological,geochemical, and lithological data

Lithological, geochemical, and micropaleontological data indicate that the Late Glacial of the northwestern Okhotsk Sea (OS) is characterised by severe climatic and environmental conditions with mainly perennial sea ice coverage and low productivity accompanied by weak deep-water ventilation and a temperate formation of the upper Sea of Okhotsk Intermediate Water (SOIW). The age model of the studied core sediments was constructed by AMS ¹⁴C dating. The most severe environmental conditions occurred during the period 15.8–14.8 kyr, synchronous with cold Heinrich event 1. Insignificant regional environmental amelioration accompanied by an increase of productivity and ice weakening during summer occurred almost simultaneously with the Bølling–Allerøed (BA) warming. The obtained results distinguished both the Bølling and Allerøed warmings as having different environmental conditions. Oxygen content in the surface sediment was low, as seen from the production of the benthic foraminifera (BF) species. During 12.6–11.1 kyr, synchronous with the Younger Dryas (YD) cold event, the regional environment conditions were cold, but not as severe as the glacial ones. Some climatic warming since the Preboreal has stimulated sea ice melting and surface amelioration during the summer season, which in turn led to a productivity rise and changes in the water column and bottom environment. Some increase in the surface water stratification and the intensified oceanic diatom and surface radiolarian production is parallel with the development of a mesopelagic regime of productivity. The surface sediment condition favours BF abundance and domination by BF species tolerant to oxygen deficiencies. During the Boreal period more stable surface conditions were accompanied by continuously high productivity and an intensifying of its mesopelagic regime.Significant regional climate warming since the Atlantic (9 kyr ago) strongly intensified the summer sea ice melting in the OS, and this created considerable surface environment amelioration with the preferential transport of bacteria and phytodetritus into the SOIW. Further considerable warming of the regional climate from 6 kyr ago contributed to slight sea ice changes, surface water warming, and the enhancement of its stratification; all typical for most of the OS. Along with a high nutrient supply from the Amur River, the NW OS experienced a strong diatom production increase with the maximum amount occurring during the last 3.6 kyr. This changed the productivity type and organic matter export into the water column while increasing the feeding of the “productive” Plagoniidae spp. group and decreasing the microbial biomass supply into the upper SOIW. Some sea surface water cooling or saltier conditions at the beginning of the Subatlantic (2.4–1.8 kyr) was followed by its warming or freshening 1.5–1.0 kyr ago, which likely correlated with the Medieval Warm Period. In turn, that probably led to strong surface water stratification, productivity deterioration and considerable changes in the overall NW OS environment. The established sequence of the northwestern OS environmental changes during the Late Glacial–Holocene is related to the Northern Hemispheric climate changes and was likely forced by atmospheric teleconnection in line with the polar circulation index variability.     

Meridional and seasonal footprints of the Pacific Decadal Oscillation on phytoplankton biomass in the northwestern Pacific Ocean

We used 16 years of multiplatform-derived biophysical data to reveal the footprint of the Pacific Decadal Oscillation (PDO) on the phytoplankton biomass of the northwestern Pacific Ocean in terms of chlorophyll a concentration (Chl), and to discern the probable factors causing the observed footprint. There were meridional differences in the response of phytoplankton to changes of environmental conditions associated with deepening of the mixed layer during the positive phase of the PDO. In general, deepening of the mixed layer increased phytoplankton biomass at low latitudes (increase of Chl due to increase of nutrient supply), but lowered phytoplankton at high latitudes (decrease of Chl due to reduction of average irradiance and temperature in the mixed layer). The areas where Chl increased or decreased changed meridionally and seasonally in accord with regulation of nutrient and light/temperature limitation by changes of mixed layer depth. The observed PDO footprint on Chl in the northwestern Pacific is likely superimposed on the high-frequency component of the PDO excited by El Niño/Southern Oscillation interannual variability. On a decadal time scale, however, Chl in the northwestern Pacific were more strongly associated with the recently discovered North Pacific Gyre Oscillation.     

西北太平洋热带气旋路径预报偏差分析

基于2005—2018年日本气象厅的6 h主观预报数据,分析西北太平洋热带气旋路径预报偏差的方位分布特征,探讨路径预报偏差与副热带高压的可能关系。统计结果表明,以东、南、西、北方位划分预报偏差空间分布,路径预报偏差以偏向东北向和西南向为主,24、48、72 h预报中东北 西南向偏差分别占61.62%、64.02%、66.94%。分析东北 西南偏差空间特征,发现西南向的预报偏差主要发生在热带气旋路径密集区的北部海域(24°N附近),而东北向的预报偏差主要发生在南部海域(16°N附近)。进一步分析这种东北 西南偏差和副热带高压的关系,发现大部分东北偏差出现在副热带高压的西南侧,且对应的偏副热带高压脊线位置更靠北、西脊点更靠西、面积更大;而西南偏差出现在副热带高压的西北侧,副热带高压脊线位置则更靠南、西脊点更靠东、面积更小。即副热带高压引导的西行台风,路径预报易偏东北;北折台风,路径预报倾向偏西南。     

利用Argo资料研究2001-2004年期间西北太平洋海洋上层对热带气旋的响应

利用Argo剖面浮标观测资料,对2001-2004年11月期间西北太平洋热带气旋经过后海洋上层的响应作了分析研究.结果显示,热带气旋经过后,55.6%的观测剖面其混合层深度会加深,范围在0-60m,并且在气旋过后5d内更为明显;由于混合加剧,大约有77.8%的观测剖面其混合层温度会下降,最多达5℃;61.1%的混合层盐度会下降,平均降盐约0.12;表层流速增大的占54%,平均增大30cm·s,表层流速的变化与风速的大小呈正相关,相关系数仅为0.06;混合层内温度变化与热带气旋风速呈负相关,相关系数为-0.15;混合层温度下降有明显的右偏现象,在气旋路径右侧50-150km处,温度下降尤为明显,而混合层盐度在气旋路径两侧的变化基本呈对称状分布;混合层深度在气旋路径右侧加深更为明显,在右侧100 150km范围内达到最大;混合层深度的变化与气旋经过前混合层的初始深度呈明显的负相关,相关系数达-0.42.     

Projections of ocean climate for northwestern Pacific Ocean

The long-term adjustment processes of atmosphere and ocean in response to gradually increased atmospheric CO2 concentration have been analyzed in 70 and 140a integrations with NCAR fully-coupled climate system model (CSM). In these experiments the CO2 concentration has been increased to double and quadruples the initial concentration, respectively. After 70a, at the time of CO2 doubling, the model predicts surface air temperature rises by 1.2 and 1.5K for the globe and the northwestern Pacific Ocean, respectively. The behavior of the quadrupling run is similar: each global and regional mean surface air temperatures increase by 2.8 and 3.0K at the time of CO2 quadrupling. From the experiments, surface air temperature changes in the northwestern Pacific Ocean will be more distinctive compared with the global average, mainly due to exceptionally large warming and sea level change near the entrance of the Kuroshio extension.     

Relationship between transitional variation of summer sea surface temperature in the northwestern Pacific and ocean events during the 1960s

INTRODUCTIONIt has been pointed out in recent years by Yan et al. (1990 a, b) through analyses of timeand space variations in the different elements in the summer of the Northern Hemisphere during1951 ~ 1980 that climate jump generally occurred in the summer of the Northern Hemisphere during the 1960s, in which geopotential height on 500 hPa in the Northern Hemisphere, the nearsurface air temperature and the SST of the northwestern Pacific appeared in the early of the1960's (Fig. 1).T…     

Picocyanobacterial abundances and diversity in surface water of the northwestern Pacific Ocean

To understand picocyanobacterial distribution patterns in the northwestern Pacific Ocean, their abundances and genetic diversity were studied using flow cytometry and a barcoded amplicon pyrosequencing approach. At open ocean stations affected by the North Equatorial Current, Prochlorococcus was the predominant picocyanobacteria, and a high-light-adapted ecotype (HLII) made up most of the population. In contrast, at stations in shelf areas of the East China Sea (ECS) and South Sea, Synechococcus was the predominant picocyanobacteria and clade II was dominant. At other ECS stations affected by the Kuroshio Current, both Prochlorococcus and Synechococcus made up similar proportions of the picocyanobacterial community. These results indicate that picocyanobacterial diversity differs among oceanic regions, and that physicochemical properties related to dominant water masses, seem to be important in determining picocyanobacterial diversity.     

末次冰盛期山东半岛高分辨率气候环境变化

末次冰盛期是末次冰期以来地球表面最寒冷的时期。通过对山东半岛地下画廊溶洞石笋DXHL3进行高精度230Th定年和高分辨率氧-碳稳定同位素分析,重建了该地区23.2～18.8 ka时期高分辨率夏季风气候环境变化历史。结果发现,山东半岛末次冰盛期夏季风气候存在显著的千年尺度波动;REDFIT分析表明,氧、碳同位素值均存在显著的2.2 ka周期。末次冰盛期山东半岛总体处于冷干状态,具体又可细分为4个阶段,即冷干（23.2～22 ka）-相对暖湿（22～21 ka）-冷干（21～19 ka）-相对暖湿（19～18.8 ka）。石笋DXHL3的δ18O变化趋势总体上与亚洲季风区内其他石笋记录相似,也与西太平洋暖池婆罗洲的石笋记录类似。这反映了末次冰盛期西太平洋暖池气候环境变化可能对山东半岛的夏季风气候变化产生了重要影响,推测西太平洋暖池表层海水温度变化引起的大气环流和黑潮的变化,是将气候环境变化信号从低纬地区传递到中高纬地区的纽带。     

The structure of Tuscarora fracture zone,northwestern Pacific

The Tuscarora fracture zone in the northwestern Pacific bounds parts of the Pacific plate that are characterized by linear (southwestern part) and non-linear (northeastern part) magnetic anomalies respectively. The fracture zone is traced from the oceanic plate across the Kuril-Kamchatka deep-sea trench into the shoreward trench slope. It therefore can not be considered as an ordinary transform fault.     

Time-series observation of dissolved inorganic carbon and nutrients in the northwestern North Pacific

Time-series measurements of dissolved inorganic carbon (DIC) and nutrient concentrations were conducted in the northwestern North Pacific from October 2002 to August 2004. Assuming that data obtained in different years represented time-series seasonal data for a single year, vertical distributions of DIC and nutrients showed large seasonal variabilities in the surface layer (∼100 m). Seasonal variabilities in normalized DIC (nDIC) and nitrate concentrations at the sea surface were estimated to be 81–113 μmol kg⁻¹ and 12.7–15.7 μmol kg⁻¹, respectively, in the Western Subarctic Gyre. The variability in nutrients between May and July was generally at least double that in other seasons. In the Western Subarctic Gyre, estimations based on statistical analyses revealed that seasonal new production was 39–61 gC m⁻² and tended to be higher in the southwestern regions or coastal regions. The seasonal new productions in the northwestern North Pacific were two or more times higher than in the North Pacific subtropical gyre and the northeastern North Pacific. It is likely that this difference is due to spatial variations in the concentrations of trace metals and the species of phytoplankton present. In addition, from estimations of surface pCO₂ it was verified that the Western Subarctic Gyre is a source of atmospheric CO₂ between February and May and a sink for CO₂ between July and October.     

Relationship between SSTA in the northwestern Pacific and winter climate anomaly in China

1IntroductionRelationshipbetweenseasurfacetemper-atureanomaly(SSTA)andclimateanomalyisattheheartofair-seainteractionstudy.ManyresearchershaveinvestigatedhowSSTAworksonclimate.Sincethe1960s,ithasbeenpointedoutthattheequatorialeastPacificwarming(ElNinoevent)resultsinclimateanomalyinthenorthernAmericaviaanoma-lousenergytransportationbyHadleycircula-tions(Bjerknes1966;1969).Afterthe1980s,owingtothedevelopmentofnumericalmodelanddynamicaltheory,itiswellacceptedthatatmospherecirculationwouldbei…     

Transport of copper from the Bering Sea to the northwestern North Pacific

Dissolved copper concentrations in surface waters of the Bering Sea ranged from 106 to 882 ngl^–1. Higher concentrations were found in continental shelf waters. In the northwestern North Pacific dissolved copper ranged from 54 to 140 ngl^–1. Particulate copper concentrations varied regionally and seasonally from 6 to 79 ngl^–1. Regionally averaged particulate copper concentrations decreased from 175 to 33g g^–1 against an increase in suspended materials because of the dilution effects of biological fractions. Apparent sporadic increases in copper concentrations were found in the mixing area of the Kuroshio and the Oyashio waters. The feature is attributed to the lateral distribution of different water types rather than to the upwelling of deeper waters by eddies. In the same area west of 160E, waters with high concentrations of dissolved copper (96±9 ngl^–1) were found. Their origin appears to be the continental shelf of the Bering Sea. In spite of intensive biological activity, a considerable fraction of copper added to shelf waters was transported to the area off Japan via the circulation in the Bering Sea and the Oyashio current.