Planktonic foraminifer Globigerinoides ruber(white)and Trilobatus sacculifer are the most frequently used mixedlayer dwelling species for reconstructing past oceanic environments.Specifically,the Mg/Ca ratios of these...Planktonic foraminifer Globigerinoides ruber(white)and Trilobatus sacculifer are the most frequently used mixedlayer dwelling species for reconstructing past oceanic environments.Specifically,the Mg/Ca ratios of these two foraminiferal species have been used for reconstructing tropical/subtropical changes in sea surface temperature(SST).However,these two species have different morphotypes,of which the spatial and temporal differences in Mg/Ca ratios and their influencing factors are still unclear.Our objective is to investigate the potential differences between the Mg/Ca ratios of these different morphotypes of G.ruber(white)and T.sacculifer in the western Philippine Sea(WPS)and determine their implications for the reconstruction of SST and upper-ocean structure.Mg/Ca measurements are made on two basic morphotypes of G.ruber(white)[sensu stricto(s.s.)and sensu lato(s.l.)]and T.sacculifer[with(w)and without(w/o)a sac-like final chamber]on samples of Site MD06-3047B from the WPS.Our results reveal that Mg/Ca ratios of different G.ruber morphotypes show consistent differences;and those of T.sacculifer morphotypes show staged variations since MIS 3.It is suggested to select a single morphotype for reconstructing SST changes using the Mg/Ca ratios of G.ruber and T.sacculifer in the WPS.Furthermore,the Mg/Ca ratios between G.ruber s.s.and G.ruber s.l.[Δ(Mg/Ca)_(G.ruber s.s.-s.l.)]downcore MD06-3047B covaries with indexes of summer monsoon.Combining with the core-top results,showing regional variation of differences in theΔ(Mg/Ca)_(G.ruber s.s.-s.l.)over the western tropical Pacific,we propose thatΔ(Mg/Ca)_(G.ruber s.s.-s.l.)may tend to reflect summer mixed layer depth.展开更多
为了分析南海北部上陆坡东沙隆起西侧海域海底稳定性,对A和B两个岩芯进行了AMS14C测年、浮游有孔虫氧同位素分析、粉色红拟抱球虫Globigerinoides ruber鉴定、粒度分析等工作。综合研究表明,A、B岩芯分别发育了距今920 ka BP、960 ka B...为了分析南海北部上陆坡东沙隆起西侧海域海底稳定性,对A和B两个岩芯进行了AMS14C测年、浮游有孔虫氧同位素分析、粉色红拟抱球虫Globigerinoides ruber鉴定、粒度分析等工作。综合研究表明,A、B岩芯分别发育了距今920 ka BP、960 ka BP以来的更新世、全新世地层。A岩芯3.3~14.08 m层位地层发生了倒转,这与3.3m、6.12~6.18 m发育的两个浊积层有关。在71.5~71.63 m(冰期370 ka BP左右)也发育一浊积层。B岩芯在9.2 m、25.2~28.6 m等层位发育了浊积层。同样位于陆坡坡折,水深较大的A岩芯,由于滑坡导致的浊流活动略强一些。展开更多
Paired stable oxygen isotope and Mg/Ca analyses in calcite tests of the mixed-layer-dwelling planktic foraminifer Globigerinoides ruber has been used to reconstruct equatorial Indian Oceanδ18O of seawater （δ 18Osw ...Paired stable oxygen isotope and Mg/Ca analyses in calcite tests of the mixed-layer-dwelling planktic foraminifer Globigerinoides ruber has been used to reconstruct equatorial Indian Oceanδ18O of seawater （δ 18Osw ） over the last ~137 thousand years. On the basis of ice-volume-correctedδ18Osw （δ18Osw-ivc ）, relative changes in sea surface salinity （SSS） have been estimated. The SSS estimates suggest three episodes of higher SSS （131-113 thousand years before present （kyr BP）, 62-58 kyr BP, and 30-24 kyr BP） within the last glacial period as compared with the present. SSS comparison between interglacial episodes reveals that the surface seawater over the core site was significantly saltier during the penultimate interglacial than the Holocene. We suggest that the evolution of a seasonal insolation gradient between the Indian monsoon areas and the equator over the investigated time interval was instrumental in shaping the strength of the Indian winter and summer monsoons that left their imprints on the equatorial Indian Ocean SSS via freshwater input and wind-induced mixing. The study shows that the insolation difference between northern latitudes and the equator during winter affects monsoon strength in the Indian region, especially during cold intervals.展开更多
Under the complex influences including the monsoonal climates and tropical hydrological cycle,the features and forcing mechanisms of precipitation changes in the tropical monsoon regions remain controversial.The north...Under the complex influences including the monsoonal climates and tropical hydrological cycle,the features and forcing mechanisms of precipitation changes in the tropical monsoon regions remain controversial.The northern coast of the South China Sea(NCSCS),connecting the South China Sea(SCS)and the Pearl River Estuary(PRE),is a critical area providing reliable tropical precipitation records and probing the possible forcing mechanism of tropical precipitation,benefitted from its high deposition rate and hydroclimatic sensitivity.Here,δ^(18)O variations of planktonic(δ^(18)O_(G).ruber)and benthic foraminifera(δ^(18)O_(C).lobatulus)were investigated respectively to reconstruct a high-resolution low-latitude precipitation record from the core 17NH-NC3 in the NCSCS.The results show a distinctδ^(18)O difference betweenδ^(18)O_(G).ruber andδ^(18)O_(C).lobatulus,not only with respect to values,but also with respect to trends in some time intervals.The clear difference between the planktonic and benthic foraminifera(Δδ^(18)O_(b-p))illustrates the significant vertical salinity stratification.And the temporal trend ofΔδ^(18)O_(b-p) indicates the degree of salinity stratification variated since the mid-Holocene.We assume that the degree of stratification in the NCSCS was mainly controlled by tropical precipitation changes.Thus,the trend ofΔδ^(18)O_(b-p) values could indicate the temporal change of the tropical precipitation.The precipitation record of our research area is closely related to the tropical atmosphere–ocean dynamics stimulated by sea surface temperature(SST)changes of the tropical Pacific zone,analogous to the El Niño–Southern Oscillation(ENSO)events.During the mid-Holocene(from 8260 to 5180 cal yr B.P.),the sustainable higherΔδ^(18)O_(b-p) values(>1.23‰)suggested a large amount of precipitation,pointing to a sustained state of La Niña-like,which is associated with lasted higher difference between Western SST and Eastern SST(W-E SST gradient)in the equatorial Pacific.Since 5180 cal yr B.P.,the decreasingΔδ^(18)O_(b-p) indicates less low-latitude precipitation,which can be ascribed to an El Niño-like mean state arising from decreased W-E SST gradient.Our study provides a new continuous high-resolution archive of low-latitude precipitation in the tropical monsoon region since 8260 cal yr B.P.And this record highlights that the thermal state of the tropical Pacific most likely adjusted the low-latitude precipitation since the mid-Holocene.展开更多
基金The National Natural Science Foundation of China under contract Nos 41830539 and 41906063the Marine S&T Fund of Shandong Province for Pilot National Laboratory for Marine Science and Technology(Qingdao)under contract No.2022QNLM050203the Taishan Scholars Project Funding under contract No.ts20190963。
文摘Planktonic foraminifer Globigerinoides ruber(white)and Trilobatus sacculifer are the most frequently used mixedlayer dwelling species for reconstructing past oceanic environments.Specifically,the Mg/Ca ratios of these two foraminiferal species have been used for reconstructing tropical/subtropical changes in sea surface temperature(SST).However,these two species have different morphotypes,of which the spatial and temporal differences in Mg/Ca ratios and their influencing factors are still unclear.Our objective is to investigate the potential differences between the Mg/Ca ratios of these different morphotypes of G.ruber(white)and T.sacculifer in the western Philippine Sea(WPS)and determine their implications for the reconstruction of SST and upper-ocean structure.Mg/Ca measurements are made on two basic morphotypes of G.ruber(white)[sensu stricto(s.s.)and sensu lato(s.l.)]and T.sacculifer[with(w)and without(w/o)a sac-like final chamber]on samples of Site MD06-3047B from the WPS.Our results reveal that Mg/Ca ratios of different G.ruber morphotypes show consistent differences;and those of T.sacculifer morphotypes show staged variations since MIS 3.It is suggested to select a single morphotype for reconstructing SST changes using the Mg/Ca ratios of G.ruber and T.sacculifer in the WPS.Furthermore,the Mg/Ca ratios between G.ruber s.s.and G.ruber s.l.[Δ(Mg/Ca)_(G.ruber s.s.-s.l.)]downcore MD06-3047B covaries with indexes of summer monsoon.Combining with the core-top results,showing regional variation of differences in theΔ(Mg/Ca)_(G.ruber s.s.-s.l.)over the western tropical Pacific,we propose thatΔ(Mg/Ca)_(G.ruber s.s.-s.l.)may tend to reflect summer mixed layer depth.
文摘为了分析南海北部上陆坡东沙隆起西侧海域海底稳定性,对A和B两个岩芯进行了AMS14C测年、浮游有孔虫氧同位素分析、粉色红拟抱球虫Globigerinoides ruber鉴定、粒度分析等工作。综合研究表明,A、B岩芯分别发育了距今920 ka BP、960 ka BP以来的更新世、全新世地层。A岩芯3.3~14.08 m层位地层发生了倒转,这与3.3m、6.12~6.18 m发育的两个浊积层有关。在71.5~71.63 m(冰期370 ka BP左右)也发育一浊积层。B岩芯在9.2 m、25.2~28.6 m等层位发育了浊积层。同样位于陆坡坡折,水深较大的A岩芯,由于滑坡导致的浊流活动略强一些。
基金the DAAD,Germany,Council of Scientific and Industrial Research,Indiathe the Department of Science and Technology, India forproviding financial support
文摘Paired stable oxygen isotope and Mg/Ca analyses in calcite tests of the mixed-layer-dwelling planktic foraminifer Globigerinoides ruber has been used to reconstruct equatorial Indian Oceanδ18O of seawater （δ 18Osw ） over the last ~137 thousand years. On the basis of ice-volume-correctedδ18Osw （δ18Osw-ivc ）, relative changes in sea surface salinity （SSS） have been estimated. The SSS estimates suggest three episodes of higher SSS （131-113 thousand years before present （kyr BP）, 62-58 kyr BP, and 30-24 kyr BP） within the last glacial period as compared with the present. SSS comparison between interglacial episodes reveals that the surface seawater over the core site was significantly saltier during the penultimate interglacial than the Holocene. We suggest that the evolution of a seasonal insolation gradient between the Indian monsoon areas and the equator over the investigated time interval was instrumental in shaping the strength of the Indian winter and summer monsoons that left their imprints on the equatorial Indian Ocean SSS via freshwater input and wind-induced mixing. The study shows that the insolation difference between northern latitudes and the equator during winter affects monsoon strength in the Indian region, especially during cold intervals.
基金supported by Guangdong Province Introduced Innovative R&D Team of Geological Processes and Natural Disasters around the South China Sea(Grant no.2106ZT06N331)the National Natural Science Foundation of China(Grant no.41872217)Innovation Group Project of Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(Grant no.311021004)。
文摘Under the complex influences including the monsoonal climates and tropical hydrological cycle,the features and forcing mechanisms of precipitation changes in the tropical monsoon regions remain controversial.The northern coast of the South China Sea(NCSCS),connecting the South China Sea(SCS)and the Pearl River Estuary(PRE),is a critical area providing reliable tropical precipitation records and probing the possible forcing mechanism of tropical precipitation,benefitted from its high deposition rate and hydroclimatic sensitivity.Here,δ^(18)O variations of planktonic(δ^(18)O_(G).ruber)and benthic foraminifera(δ^(18)O_(C).lobatulus)were investigated respectively to reconstruct a high-resolution low-latitude precipitation record from the core 17NH-NC3 in the NCSCS.The results show a distinctδ^(18)O difference betweenδ^(18)O_(G).ruber andδ^(18)O_(C).lobatulus,not only with respect to values,but also with respect to trends in some time intervals.The clear difference between the planktonic and benthic foraminifera(Δδ^(18)O_(b-p))illustrates the significant vertical salinity stratification.And the temporal trend ofΔδ^(18)O_(b-p) indicates the degree of salinity stratification variated since the mid-Holocene.We assume that the degree of stratification in the NCSCS was mainly controlled by tropical precipitation changes.Thus,the trend ofΔδ^(18)O_(b-p) values could indicate the temporal change of the tropical precipitation.The precipitation record of our research area is closely related to the tropical atmosphere–ocean dynamics stimulated by sea surface temperature(SST)changes of the tropical Pacific zone,analogous to the El Niño–Southern Oscillation(ENSO)events.During the mid-Holocene(from 8260 to 5180 cal yr B.P.),the sustainable higherΔδ^(18)O_(b-p) values(>1.23‰)suggested a large amount of precipitation,pointing to a sustained state of La Niña-like,which is associated with lasted higher difference between Western SST and Eastern SST(W-E SST gradient)in the equatorial Pacific.Since 5180 cal yr B.P.,the decreasingΔδ^(18)O_(b-p) indicates less low-latitude precipitation,which can be ascribed to an El Niño-like mean state arising from decreased W-E SST gradient.Our study provides a new continuous high-resolution archive of low-latitude precipitation in the tropical monsoon region since 8260 cal yr B.P.And this record highlights that the thermal state of the tropical Pacific most likely adjusted the low-latitude precipitation since the mid-Holocene.
