The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North ...The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North Pacific subtropical mode waters using a general circulation model (LICOM1.0) for the period of 1958-2001. The model experiments focused on interannual variations of ocean dynamical processes under daily wind forcings and seasonal heat fluxes. The mode water formation region was defined by a potential vorticity minimum at outcrop locations. The model results show that two subduction rate maxima (>100 m/a) were located in the Subtropical Mode Water (STMW) and the Central Mode Water (CMW) formation regions. These regions are consistent with a climatologically calculated value. The subduction rate in the Eastern Subtropical Mode Water (ESTMW) formation region was smaller at about 75 m/a. The subduction rate shows clear interannual and decadal variations associated with oceanic dynamic variabilities. The average subduction rate of the STMW was much smaller during the period of 1981-1990 compared with other periods, while that of the CMW had a negative anomaly before 1975 and a positive anomaly after 1978. The variability agreed with Ekman and geostrophic advections and mixed layer depths. The interannual variability of the subduction rate for the ESTMW was smallest during 1970-1990, as a result of a weak wind stress curl. This paper explores how interannual signals from the atmosphere are stored in different parts of the ocean, and thus may contribute to a better understanding of feedback mechanisms for the Pacific Decadal Oscillation (PDO) event.展开更多
The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing sim...The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing simulations with the Geo-physical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). The aerosol effect causes sea surface temperature (SST) to decrease in the mid-latitude North Pacific, especially in the Kuroshio Extension region, during the past five decades (1950-2005), and this cooling effect exceeds the warming effect by the GHG increase. The STCC response to the GHG and aerosol forcing are opposite. In the GHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased (increased) mode waters in the North Pacific, resulting from a weaker (stronger) front in the mixed layer depth and decreased (increased) subduction in the mode water formation region. The aerosol effect on the SST, mode waters and STCC more than offsets the GHG effect. The response of SST in a zonal band around 40?N and the STCC to the combined forcing in the historical simulation is similar to the response to the aerosol forcing.展开更多
Mode water is a distinct water mass characterized by a near vertical homogeneous layer or low potential vorticity, and is considered essential for understanding ocean climate variability. Based on the output of GFDL C...Mode water is a distinct water mass characterized by a near vertical homogeneous layer or low potential vorticity, and is considered essential for understanding ocean climate variability. Based on the output of GFDL CM3, this study investigates the response of eastern subtropical mode water （ESTMW） in the North Pacific to two different single forcings： greenhouse gases （GHGs） and aerosol. Under GHG forcing, ESTMW is produced on lighter isopycnal surfaces and is decreased in volume. Under aerosol forcing, in sharp contrast, it is produced on denser isopycnal surfaces and is increased in volume. The main reason for the opposite response is because surface ocean-to-atmosphere latent heat flux change over the ESTMW formation region shoals the mixed layer and thus weakens the lateral induction under GHG forcing, but deepens the mixed layer and thus strengthens the lateral induction under aerosol forcing. In addition, local wind changes are also favorable to the opposite response of ESTMW production to GHG versus aerosol.展开更多
Mode Water’, as a product of air-sea interaction, influences the thermal structure and circulation pattern in upper layer ocean and consequently affects the variations of climate. In this paper the recent research re...Mode Water’, as a product of air-sea interaction, influences the thermal structure and circulation pattern in upper layer ocean and consequently affects the variations of climate. In this paper the recent research results about the subtropi-cal Mode Water in the North Pacific are overiewed. A detailed description of the three kinds of Mode Water in the subtropical North Pacific and some comparisons of their similarities and differences are introduced. Some science problems that need further exploration have been raised.展开更多
Based on the in situ XBT and other data sets, by analyzing the seasonal cycle of the mixed layer depth (MLD)and using the conservative potential vorticity (PV) as a tool, a clear description of the formation process o...Based on the in situ XBT and other data sets, by analyzing the seasonal cycle of the mixed layer depth (MLD)and using the conservative potential vorticity (PV) as a tool, a clear description of the formation process of the North PacifNPSTMW reflects well the ventilation process of the isotherms of the permanent thermocline. The formation process can be the sea surface from October, the mixed layer deepens and correspondingly, the water mass with low PV emerges and sinks.After continual cooling from October to March, the mixed layer reaches its maximum value (＞300 m) in March. Then, in the second phase (April-June), the mixed layer shoals rapidly from April, a large part of the low PV water mass is sheltered from further air-sea interaction by the emerging seasonal thermocline, and thus forms new NPSTMW. Further analysis indicatesthat the formation region of warm NPSTMW (17-18℃) is limited between 140°-150°E, while the relatively cold NPSTMW (16-17℃) originates in a wider longitude range (140°-170°E).Climate features of NPSTMW are presented with the use of climatological Levitus (1994a, b) dataset. It is shown that NPSTMW lies in the region of(130°-170°E, 22°-34°N) with core temperature ranging from about 16-19℃ and potential density around 25-25.8σ0. NPSTMW has a three-dimensional structure lying below the seasonal thermocline (about 100 m deep) and reaches almost to 350 m depths.展开更多
This study investigates the contribution of mesoscale eddies to the subduction and transport of North Pacific Eastern Subtropical Mode Water(ESTMW)using the high-frequency output of an eddy-resolved ocean model spanni...This study investigates the contribution of mesoscale eddies to the subduction and transport of North Pacific Eastern Subtropical Mode Water(ESTMW)using the high-frequency output of an eddy-resolved ocean model spanning the period 1994–2010.Results show that the subduction induced by mesoscale eddies accounts for about 31%of the total subduction of ESTMW formation.The volume of ESTMW trapped by anticyclonic eddies is slightly larger than that trapped by cyclonic eddies.The ESTMW trapped by all eddies in May reaches up to about 2.8×1013m3,which is approximately 16%of the total ESTMW volume.The eddy-trapped ESTMW moves primarily westward,with its meridional integration at 18°–30°N reaching about 0.17Sv,which is approximately 18%of the total zonal ESTMW transport in this direction,at 140°W.This study highlights the important role of eddies in carrying ESTMW westward over the northeastern Pacific Ocean.展开更多
Oceanic uptake and storage of anthropogenic CO_(2)(CANT)are regulated by ocean circulation and ventilation.To decipher the storage and redistribution of CANT in the western North Pacific,where a major CANT sink develo...Oceanic uptake and storage of anthropogenic CO_(2)(CANT)are regulated by ocean circulation and ventilation.To decipher the storage and redistribution of CANT in the western North Pacific,where a major CANT sink develops,we investigated the water column carbonate system,dissolved inorganic radiocarbon and ancillary parameters in May and August 2018,spanning the Kuroshio Extension(KE,35-39°N),Kuroshio Recirculation(KR,27-35°N)and subtropical(21-27°N)zones.Water column CANT inventories were estimated to be 40.5±1.1 mol m^(-2) in the KR zone and 37.2±0.9 mol m^(-2) in the subtropical zone.In comparison with historical data obtained in 2005,relatively high rates of increase of the CANT inventory of 1.05±0.20 and 1.03±0.12 mol m^(-2) yr^(-1) in the recent decade were obtained in the KR and subtropical zones,respectively.Our water-mass-based analyses suggest that formation and transport of subtropical mode water dominate the deep penetration,storage,and redistribution of CANT in those two regions.In the KE zone,however,both the water column CANT inventory and the decadal CANT accumulation rate were small and uncertain owing to the dynamic hydrology,where the naturally uplifting isopycnal surfaces make CANT penetration relatively shallow.The findings of this study improve the understanding of the spatiotemporal variations of CANT distribution,storage,and transport in the western North Pacific.展开更多
A streamfunction projection method called gravest empirical mode(GEM) is applied to the hydrographic section at 137°E to filter out eddy noises in the western North Pacific and derive quantitative ensemble-averag...A streamfunction projection method called gravest empirical mode(GEM) is applied to the hydrographic section at 137°E to filter out eddy noises in the western North Pacific and derive quantitative ensemble-average water mass properties in the North Equatorial Current region. The GEM fields capture more than 80% of total property variances in the thermocline layer. The core layer structures of key water masses, including the North Pacific Tropical Water(NPTW) and the North Pacific Intermediate Water(NPIW), are examined with a definition of water mass boundary based on property gradient. It shows that a tongue of maximal root-mean-square(RMS) residual exists in the upper half of NPIW for all water properties. These subsurface RMS tongues appear to be close to sharp property gradients. It is the first time a GEM diagnosis is applied to nutrient data, which reveals a drastic difference of N/P reaction rate ratio above and below the maximal-nutrient core at 1250 m. Additionally, a GEM velocity reconstruction successfully produces the North Equatorial Undercurrent(NEUC), demonstrating the stable thermal-wind nature of this newly-discovered current.展开更多
基金Supported by the National Natural Science Foundation of China (Nos. 40906005, 40830106, 40730953, GYHY201106017)the National Basic Research Program of China (973 Program) (No. 2010CB428504)the National Key Technologies Research and Development Program of China (No. 2009BAC51B01)
文摘The climatology subduction rate for the entire Pacific is known, but the mechanism of interannual to decadal variation remains unclear. In this study, we calculated the annual subduction rates of three types of North Pacific subtropical mode waters using a general circulation model (LICOM1.0) for the period of 1958-2001. The model experiments focused on interannual variations of ocean dynamical processes under daily wind forcings and seasonal heat fluxes. The mode water formation region was defined by a potential vorticity minimum at outcrop locations. The model results show that two subduction rate maxima (>100 m/a) were located in the Subtropical Mode Water (STMW) and the Central Mode Water (CMW) formation regions. These regions are consistent with a climatologically calculated value. The subduction rate in the Eastern Subtropical Mode Water (ESTMW) formation region was smaller at about 75 m/a. The subduction rate shows clear interannual and decadal variations associated with oceanic dynamic variabilities. The average subduction rate of the STMW was much smaller during the period of 1981-1990 compared with other periods, while that of the CMW had a negative anomaly before 1975 and a positive anomaly after 1978. The variability agreed with Ekman and geostrophic advections and mixed layer depths. The interannual variability of the subduction rate for the ESTMW was smallest during 1970-1990, as a result of a weak wind stress curl. This paper explores how interannual signals from the atmosphere are stored in different parts of the ocean, and thus may contribute to a better understanding of feedback mechanisms for the Pacific Decadal Oscillation (PDO) event.
基金supported by the National Basic Research Program of China(2012CB955602)National Key Program for Developing Basic Science(2010CB428904)Natural Science Foundation of China(41176006 and 40921004)
文摘The response of the North Pacific Subtropical Mode Water and Subtropical Countercurrent (STCC) to changes in greenhouse gas (GHG) and aerosol is investigated based on the 20th-century historical and single-forcing simulations with the Geo-physical Fluid Dynamics Laboratory Climate Model version 3 (GFDL CM3). The aerosol effect causes sea surface temperature (SST) to decrease in the mid-latitude North Pacific, especially in the Kuroshio Extension region, during the past five decades (1950-2005), and this cooling effect exceeds the warming effect by the GHG increase. The STCC response to the GHG and aerosol forcing are opposite. In the GHG (aerosol) forcing run, the STCC decelerates (accelerates) due to the decreased (increased) mode waters in the North Pacific, resulting from a weaker (stronger) front in the mixed layer depth and decreased (increased) subduction in the mode water formation region. The aerosol effect on the SST, mode waters and STCC more than offsets the GHG effect. The response of SST in a zonal band around 40?N and the STCC to the combined forcing in the historical simulation is similar to the response to the aerosol forcing.
基金supported by the National Basic Research Program of China (Grant No. 2012CB955600)National Natural Science Foundation of China (Grant Nos. 41376009 and 41176006)+1 种基金Strategic Priority Research Program of the Chinese Academy of Sciences (Grant Nos. XDA11010302 and XDA11010201)the Joint Program of Shandong Province and National Natural Science Foundation of China (Grant No.U1406401)
文摘Mode water is a distinct water mass characterized by a near vertical homogeneous layer or low potential vorticity, and is considered essential for understanding ocean climate variability. Based on the output of GFDL CM3, this study investigates the response of eastern subtropical mode water （ESTMW） in the North Pacific to two different single forcings： greenhouse gases （GHGs） and aerosol. Under GHG forcing, ESTMW is produced on lighter isopycnal surfaces and is decreased in volume. Under aerosol forcing, in sharp contrast, it is produced on denser isopycnal surfaces and is increased in volume. The main reason for the opposite response is because surface ocean-to-atmosphere latent heat flux change over the ESTMW formation region shoals the mixed layer and thus weakens the lateral induction under GHG forcing, but deepens the mixed layer and thus strengthens the lateral induction under aerosol forcing. In addition, local wind changes are also favorable to the opposite response of ESTMW production to GHG versus aerosol.
基金supported by the NSFC(No.49976004 and 40028605)National Key Program for Developing Basic Science(No.G1999043807).
文摘Mode Water’, as a product of air-sea interaction, influences the thermal structure and circulation pattern in upper layer ocean and consequently affects the variations of climate. In this paper the recent research results about the subtropi-cal Mode Water in the North Pacific are overiewed. A detailed description of the three kinds of Mode Water in the subtropical North Pacific and some comparisons of their similarities and differences are introduced. Some science problems that need further exploration have been raised.
基金supported by Free Application(No.40276009)NSFC Project for Oversea Young Scientist Found(No.40028605).
文摘Based on the in situ XBT and other data sets, by analyzing the seasonal cycle of the mixed layer depth (MLD)and using the conservative potential vorticity (PV) as a tool, a clear description of the formation process of the North PacifNPSTMW reflects well the ventilation process of the isotherms of the permanent thermocline. The formation process can be the sea surface from October, the mixed layer deepens and correspondingly, the water mass with low PV emerges and sinks.After continual cooling from October to March, the mixed layer reaches its maximum value (＞300 m) in March. Then, in the second phase (April-June), the mixed layer shoals rapidly from April, a large part of the low PV water mass is sheltered from further air-sea interaction by the emerging seasonal thermocline, and thus forms new NPSTMW. Further analysis indicatesthat the formation region of warm NPSTMW (17-18℃) is limited between 140°-150°E, while the relatively cold NPSTMW (16-17℃) originates in a wider longitude range (140°-170°E).Climate features of NPSTMW are presented with the use of climatological Levitus (1994a, b) dataset. It is shown that NPSTMW lies in the region of(130°-170°E, 22°-34°N) with core temperature ranging from about 16-19℃ and potential density around 25-25.8σ0. NPSTMW has a three-dimensional structure lying below the seasonal thermocline (about 100 m deep) and reaches almost to 350 m depths.
基金supported by the National Natural Science Foundation of China (No. 41676002)
文摘This study investigates the contribution of mesoscale eddies to the subduction and transport of North Pacific Eastern Subtropical Mode Water(ESTMW)using the high-frequency output of an eddy-resolved ocean model spanning the period 1994–2010.Results show that the subduction induced by mesoscale eddies accounts for about 31%of the total subduction of ESTMW formation.The volume of ESTMW trapped by anticyclonic eddies is slightly larger than that trapped by cyclonic eddies.The ESTMW trapped by all eddies in May reaches up to about 2.8×1013m3,which is approximately 16%of the total ESTMW volume.The eddy-trapped ESTMW moves primarily westward,with its meridional integration at 18°–30°N reaching about 0.17Sv,which is approximately 18%of the total zonal ESTMW transport in this direction,at 140°W.This study highlights the important role of eddies in carrying ESTMW westward over the northeastern Pacific Ocean.
基金The research was supported by the National Natural Science Foundation of China(42141001 and 91858210).
文摘Oceanic uptake and storage of anthropogenic CO_(2)(CANT)are regulated by ocean circulation and ventilation.To decipher the storage and redistribution of CANT in the western North Pacific,where a major CANT sink develops,we investigated the water column carbonate system,dissolved inorganic radiocarbon and ancillary parameters in May and August 2018,spanning the Kuroshio Extension(KE,35-39°N),Kuroshio Recirculation(KR,27-35°N)and subtropical(21-27°N)zones.Water column CANT inventories were estimated to be 40.5±1.1 mol m^(-2) in the KR zone and 37.2±0.9 mol m^(-2) in the subtropical zone.In comparison with historical data obtained in 2005,relatively high rates of increase of the CANT inventory of 1.05±0.20 and 1.03±0.12 mol m^(-2) yr^(-1) in the recent decade were obtained in the KR and subtropical zones,respectively.Our water-mass-based analyses suggest that formation and transport of subtropical mode water dominate the deep penetration,storage,and redistribution of CANT in those two regions.In the KE zone,however,both the water column CANT inventory and the decadal CANT accumulation rate were small and uncertain owing to the dynamic hydrology,where the naturally uplifting isopycnal surfaces make CANT penetration relatively shallow.The findings of this study improve the understanding of the spatiotemporal variations of CANT distribution,storage,and transport in the western North Pacific.
基金supported by the National Key Research and Development Program of China [grant number2016YFA0602703]the National Natural Science Foundation of China [grant numbers 41661144019,41690123,41690120,and91637208]+1 种基金the CMA Guangzhou Joint Research Center for Atmospheric Sciencesthe Jiangsu Collaborative Innovation Center for Climate Change
基金supported by the National Basic Research Program of China(Grant No.2012CB417400)the National Natural Science Foundation of China(Grant Nos.41421005,U1406401)
文摘A streamfunction projection method called gravest empirical mode(GEM) is applied to the hydrographic section at 137°E to filter out eddy noises in the western North Pacific and derive quantitative ensemble-average water mass properties in the North Equatorial Current region. The GEM fields capture more than 80% of total property variances in the thermocline layer. The core layer structures of key water masses, including the North Pacific Tropical Water(NPTW) and the North Pacific Intermediate Water(NPIW), are examined with a definition of water mass boundary based on property gradient. It shows that a tongue of maximal root-mean-square(RMS) residual exists in the upper half of NPIW for all water properties. These subsurface RMS tongues appear to be close to sharp property gradients. It is the first time a GEM diagnosis is applied to nutrient data, which reveals a drastic difference of N/P reaction rate ratio above and below the maximal-nutrient core at 1250 m. Additionally, a GEM velocity reconstruction successfully produces the North Equatorial Undercurrent(NEUC), demonstrating the stable thermal-wind nature of this newly-discovered current.
