The present climate simulation and future projection of the Eastern Subtropical Mode Water （ESTMW） in the North Pacific are investigated based on the Geophysical Fluid Dynamics Laboratory Earth System Model （GFDL-E...The present climate simulation and future projection of the Eastern Subtropical Mode Water （ESTMW） in the North Pacific are investigated based on the Geophysical Fluid Dynamics Laboratory Earth System Model （GFDL-ESM2M）. Spatial patterns of the mixed layer depth （MLD） in the eastern subtropical North Pacific and the ESTMW are well simulated using this model. Compared with historical simulation, the ESTMW is produced at lighter isopycnal surfaces and its total volume is decreased in the RCP8.5 runs, because the subduction rate of the ESTMW decreases by 0.82×10？6 m/s during February–March. In addition, it is found that the lateral induction decreasing is approximately four times more than the Ekman pumping, and thus it plays a dominant role in the decreased subduction rate associated with global warming. Moreover, the MLD during February–March is banded shoaling in response to global warming, extending northeastward from the east of the Hawaii Islands （20°N, 155°W） to the west coast of North America （30°N, 125°W）, with a max-imum shoaling of 50 m, and then leads to the lateral induction reduction. Meanwhile, the increased north-eastward surface warm current to the east of Hawaii helps strengthen of the local upper ocean stratification and induces the banded shoaling MLD under warmer climate. This new finding indicates that the ocean surface currents play an important role in the response of the MLD and the ESTMW to global warming.展开更多
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’, 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
The annual subduction rate in the South Indian Ocean was calculated by analyzing Simple Ocean Data Assimilation （SODA） outputs in the period of 1950-2008. The subduction rate census for potential density classes sho...The annual subduction rate in the South Indian Ocean was calculated by analyzing Simple Ocean Data Assimilation （SODA） outputs in the period of 1950-2008. The subduction rate census for potential density classes showed a peak corresponding to Indian Ocean subtropical mode water （IOSTMW） in the southwestern part of the South Indian Ocean subtropical gyre. The deeper mixed layer depth, the sharper mixed-layer fronts and the associated relatively faster circulation in the present climatology resulted in a larger lateral induction, which primarily dominants the IOSTMW subduction rate, while with only minor contribution from vertical pumping. Without loss of generality, through careful analysis of the water characteristics in the layer of minimum vertical temperature gradient （LMVTG）, the authors suggest that the IOSTMW was identified as a thermostad, with a lateral minimum of low potential vorticity （PV, less than 200× 10^-12 m^-1·s^-1） and a low dT/dz （less than 1.5℃/（100 m））. The IOSTMW within the South Indian Ocean subtropical gyre distributed in the region approximately from 25° to 50° E and from 30° to 39°S. Additionally, the average characteristics （temperature, salinity, potential density） of the mode water were estimated about （16.38 ± 0.29）℃, （35.46 ±0.04）, （26.02 ±0.04） ae over the past 60 years.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
The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two po...The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two possible deviations in the method:one is an overestimation due to not considering that the amount of subducted water at the source location may be inadequate during the late winter of the first year when the mixed layer becomes shallow;the other one is an underestimation due to the neglect of the effective subduction caused by strong vertical pumping.Quantitative analysis shows that these two deviations mainly exist in the low-latitude subduction areas of the South Pacific and South Atlantic.The two deviations have very similar distribution areas and can partially off set each other.However,the overall deviation is still large,and the maximum relative deviation ratio can reach 50%;therefore,it cannot be ignored.展开更多
A synoptic snapshot in this study is made for the East Cape Eddy (ECE) based on the World Ocean Circulation Experiment (WOCE) P14C Hydrographic Section and Shipboard ADCP velocity vector data collected in September 19...A synoptic snapshot in this study is made for the East Cape Eddy (ECE) based on the World Ocean Circulation Experiment (WOCE) P14C Hydrographic Section and Shipboard ADCP velocity vector data collected in September 1992. The ECE is an anticyclonic eddy, barotropically structured and centered at 33.64"S and 176.2TE, with warm and salinous- cored subsurface water. The radius of the eddy is of the order O (110 km) and the maximum circumferential velocity is O (40cms-1); as a result, the relative vorticity is estimated to be O (7x 10-6s-1). Due to the existence of the ECE, the mixed layer north of New Zealand becomes deeper, reaching a depth of 300 m in the austral winter. The ECE plays an important role in the formation and distribution of the Subtropical Mode Water (STMW) over a considerable area in the South Pacific.展开更多
基金The National Basic Research Program(973 Program)of China under contract No.2012CB955603the National Natural Science Foundation of China under contract Nos 41176006,41221063 and U1406401
文摘The present climate simulation and future projection of the Eastern Subtropical Mode Water （ESTMW） in the North Pacific are investigated based on the Geophysical Fluid Dynamics Laboratory Earth System Model （GFDL-ESM2M）. Spatial patterns of the mixed layer depth （MLD） in the eastern subtropical North Pacific and the ESTMW are well simulated using this model. Compared with historical simulation, the ESTMW is produced at lighter isopycnal surfaces and its total volume is decreased in the RCP8.5 runs, because the subduction rate of the ESTMW decreases by 0.82×10？6 m/s during February–March. In addition, it is found that the lateral induction decreasing is approximately four times more than the Ekman pumping, and thus it plays a dominant role in the decreased subduction rate associated with global warming. Moreover, the MLD during February–March is banded shoaling in response to global warming, extending northeastward from the east of the Hawaii Islands （20°N, 155°W） to the west coast of North America （30°N, 125°W）, with a max-imum shoaling of 50 m, and then leads to the lateral induction reduction. Meanwhile, the increased north-eastward surface warm current to the east of Hawaii helps strengthen of the local upper ocean stratification and induces the banded shoaling MLD under warmer climate. This new finding indicates that the ocean surface currents play an important role in the response of the MLD and the ESTMW to global warming.
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 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The National Natural Science Foundation of China under contract Nos 41276011 and 41221063the Research Project of Chinese Ministry of Education under contract No.113041Athe Global Change and Air-Sea Interaction under contract under contract No.GASI-03-01-01-05
文摘The annual subduction rate in the South Indian Ocean was calculated by analyzing Simple Ocean Data Assimilation （SODA） outputs in the period of 1950-2008. The subduction rate census for potential density classes showed a peak corresponding to Indian Ocean subtropical mode water （IOSTMW） in the southwestern part of the South Indian Ocean subtropical gyre. The deeper mixed layer depth, the sharper mixed-layer fronts and the associated relatively faster circulation in the present climatology resulted in a larger lateral induction, which primarily dominants the IOSTMW subduction rate, while with only minor contribution from vertical pumping. Without loss of generality, through careful analysis of the water characteristics in the layer of minimum vertical temperature gradient （LMVTG）, the authors suggest that the IOSTMW was identified as a thermostad, with a lateral minimum of low potential vorticity （PV, less than 200× 10^-12 m^-1·s^-1） and a low dT/dz （less than 1.5℃/（100 m））. The IOSTMW within the South Indian Ocean subtropical gyre distributed in the region approximately from 25° to 50° E and from 30° to 39°S. Additionally, the average characteristics （temperature, salinity, potential density） of the mode water were estimated about （16.38 ± 0.29）℃, （35.46 ±0.04）, （26.02 ±0.04） ae over the past 60 years.
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 Natural Science Foundation of China(No.41676009)the National Key R&D Program of China(No.2016YFC0301203)the State Key Program of National Natural Science of China(No.41730534)。
文摘The classical Lagrangian particle tracing method is widely used in the evaluation of the ocean annual subduction rate.However,our analysis indicates that in addition to neglecting the effect of mixing,there are two possible deviations in the method:one is an overestimation due to not considering that the amount of subducted water at the source location may be inadequate during the late winter of the first year when the mixed layer becomes shallow;the other one is an underestimation due to the neglect of the effective subduction caused by strong vertical pumping.Quantitative analysis shows that these two deviations mainly exist in the low-latitude subduction areas of the South Pacific and South Atlantic.The two deviations have very similar distribution areas and can partially off set each other.However,the overall deviation is still large,and the maximum relative deviation ratio can reach 50%;therefore,it cannot be ignored.
文摘A synoptic snapshot in this study is made for the East Cape Eddy (ECE) based on the World Ocean Circulation Experiment (WOCE) P14C Hydrographic Section and Shipboard ADCP velocity vector data collected in September 1992. The ECE is an anticyclonic eddy, barotropically structured and centered at 33.64"S and 176.2TE, with warm and salinous- cored subsurface water. The radius of the eddy is of the order O (110 km) and the maximum circumferential velocity is O (40cms-1); as a result, the relative vorticity is estimated to be O (7x 10-6s-1). Due to the existence of the ECE, the mixed layer north of New Zealand becomes deeper, reaching a depth of 300 m in the austral winter. The ECE plays an important role in the formation and distribution of the Subtropical Mode Water (STMW) over a considerable area in the South Pacific.
