Pulleniatina obliquiloculata shells from 16 core-top samples from the tropical Indo-Pacific Oceans are analyzed for the ratios of boron and cadmium to calcium(B/Ca and Cd/Ca). The B/Ca ratios show a very weak positive...Pulleniatina obliquiloculata shells from 16 core-top samples from the tropical Indo-Pacific Oceans are analyzed for the ratios of boron and cadmium to calcium(B/Ca and Cd/Ca). The B/Ca ratios show a very weak positive relationship with [B(OH)_4^-] and the dissolved carbonate species at the apparent calcification depth of P.obliquiloculata. The boron partition coefficients(K_D) between P. obliquiloculata B/Ca and seawater[B(OH)_4^-]/[HCO_3^-] distribute around 1.1×10^(-3)-1.3×10^(-3) with a mean value of(1.19±0.12)×10^(-3),and are significantly related to the nutrient concentration, especially phosphate. The lack of any clear correlation between the P. obliquiloculata B/Ca and seawater carbonate chemical parameters suggests that the physiochemical controls on boron incorporation are masked by the complexity of natural seawater condition. But the significant dependence of Ku on nutrient may likely be explained by a nutrient related growth-rate effect. Cd/Ca of P.obliquiloculata shows significant correlation with seawater phosphate concentration, and its partition coefficients(D_(cd)) are significantly related to temperature. A first-principle methodology of P. obliquiloculata B/Ca is applied;with the aid of Cd/Ca as a phosphate proxy and a constraint on K_D, to estimating sea water carbonate chemistry(e.g., pH). The results are fairly promising and allow us to propose the possibility to apply the combination of B/Ca and Cd/Ca proxies(and also Mg/Ca and δ^(18)O for estimating temperature and salinity) for the paleoreconstruction of seawater carbonate chemistry.展开更多
The B/Ca ratio of planktonic foraminifer shells has been used as a proxy for reconstructing past ocean carbonate chemistry. However, recent studies have revealed significant uncertainties associated with this proxy, s...The B/Ca ratio of planktonic foraminifer shells has been used as a proxy for reconstructing past ocean carbonate chemistry. However, recent studies have revealed significant uncertainties associated with this proxy, such as whether seawater temperature or [CO^2-3 ] is the dominant control on the partition coefficient (KD) of planktonic foraminiferal B/Ca. To address these uncertainties and thus improve our understanding of the planktonic foraminiferal B/Ca proxy, we analysed B/Ca ratios in the tests of Neogloboquadrina dutertrei (300- 355 μm) and Pulleniatina obliquiloculata (355- 400 μm) in surface sediment samples from the tropical western Pacific and South China Sea. The relationship between these B/Ca ratios and bottom water calcite saturation states (Δ[CO^2-3 ]) is weak, thus suggesting only a small dissolution effect on the B/Ca of the two species. The correlation coefficients (R2) between the B/Ca ratios of N. dutertrei and P. obliquiloculata and environmental parameters (e.g., temperature, salinity, phosphate, DIC and ALK) in the tropical western Pacific and South China Sea are not high enough to justify using B/Ca ratios as a palaeoenvironmental proxy in the study areas. The significant correlation between KD values of N. dutertrei and P. obliquiloculata and carbonate system parameters (e.g.,[CO^2-3 ], DIC, ALK, pH and [HCO^-3 ]) in the study area reflect chemical links between the KD denominator and these variables. Based on our surface sediment calibration, an empirical relationship between the KD of N. dutertrei and temperature is proposed in the tropical western Pacific. We also generated a record of B/Ca ratios in N. dutertrei (300 -355 μm) from Core MD06-3052 in the tropical western Pacific over the past 24 ka to evaluate the application of the revised B/Ca proxy method. Based on the reconstructed empirical relationship for B/Ca and subsurface seawater ALK, we estimated subsurface seawater carbonate system parameters in the tropical western Pacific since 24 ka. In general, the estimated subsurface seawater pH and [CO^2-3 ] show an increase with time, and the record of subsurface seawater pCO2 shows a decrease with time, in the tropical western Pacific over the past 24 ka. The consistent trends in subsurface seawater pCO2 and opal flux during deglaciation may imply that the reported increase in subsurface water pCO2 in the study area was promoted by enhanced upwelling in the Southern Ocean.展开更多
基金The National Natural Science Foundation of China(NSFC)and NSFC-Shandong Joint Fund for Marine Science Research Centers under contract Nos 41606049,U1606401 and 41376054the China Postdoctoral Science Foundation under contract No.2015M581658
文摘Pulleniatina obliquiloculata shells from 16 core-top samples from the tropical Indo-Pacific Oceans are analyzed for the ratios of boron and cadmium to calcium(B/Ca and Cd/Ca). The B/Ca ratios show a very weak positive relationship with [B(OH)_4^-] and the dissolved carbonate species at the apparent calcification depth of P.obliquiloculata. The boron partition coefficients(K_D) between P. obliquiloculata B/Ca and seawater[B(OH)_4^-]/[HCO_3^-] distribute around 1.1×10^(-3)-1.3×10^(-3) with a mean value of(1.19±0.12)×10^(-3),and are significantly related to the nutrient concentration, especially phosphate. The lack of any clear correlation between the P. obliquiloculata B/Ca and seawater carbonate chemical parameters suggests that the physiochemical controls on boron incorporation are masked by the complexity of natural seawater condition. But the significant dependence of Ku on nutrient may likely be explained by a nutrient related growth-rate effect. Cd/Ca of P.obliquiloculata shows significant correlation with seawater phosphate concentration, and its partition coefficients(D_(cd)) are significantly related to temperature. A first-principle methodology of P. obliquiloculata B/Ca is applied;with the aid of Cd/Ca as a phosphate proxy and a constraint on K_D, to estimating sea water carbonate chemistry(e.g., pH). The results are fairly promising and allow us to propose the possibility to apply the combination of B/Ca and Cd/Ca proxies(and also Mg/Ca and δ^(18)O for estimating temperature and salinity) for the paleoreconstruction of seawater carbonate chemistry.
基金The Open Fund of Qingdao National Laboratory for Marine Science and Technology under contract No.QNLM2016ORP0205the Basic Scientific Fund for National Public Research Institutes of China under contract Nos 2017Y07 and 2019S04+3 种基金the National Natural Science Foundation of China under contract Nos 41230959,41830539,91858106 and 41576051the Taishan Scholars Project Fundingthe Shandong Provincial Natural Science Foundation under contract No.ZR2016DQ17the Scientific and Technological Innovation Project of Qingdao National Laboratory for Marine Science and Technology under contract No.2016ASKJ13
文摘The B/Ca ratio of planktonic foraminifer shells has been used as a proxy for reconstructing past ocean carbonate chemistry. However, recent studies have revealed significant uncertainties associated with this proxy, such as whether seawater temperature or [CO^2-3 ] is the dominant control on the partition coefficient (KD) of planktonic foraminiferal B/Ca. To address these uncertainties and thus improve our understanding of the planktonic foraminiferal B/Ca proxy, we analysed B/Ca ratios in the tests of Neogloboquadrina dutertrei (300- 355 μm) and Pulleniatina obliquiloculata (355- 400 μm) in surface sediment samples from the tropical western Pacific and South China Sea. The relationship between these B/Ca ratios and bottom water calcite saturation states (Δ[CO^2-3 ]) is weak, thus suggesting only a small dissolution effect on the B/Ca of the two species. The correlation coefficients (R2) between the B/Ca ratios of N. dutertrei and P. obliquiloculata and environmental parameters (e.g., temperature, salinity, phosphate, DIC and ALK) in the tropical western Pacific and South China Sea are not high enough to justify using B/Ca ratios as a palaeoenvironmental proxy in the study areas. The significant correlation between KD values of N. dutertrei and P. obliquiloculata and carbonate system parameters (e.g.,[CO^2-3 ], DIC, ALK, pH and [HCO^-3 ]) in the study area reflect chemical links between the KD denominator and these variables. Based on our surface sediment calibration, an empirical relationship between the KD of N. dutertrei and temperature is proposed in the tropical western Pacific. We also generated a record of B/Ca ratios in N. dutertrei (300 -355 μm) from Core MD06-3052 in the tropical western Pacific over the past 24 ka to evaluate the application of the revised B/Ca proxy method. Based on the reconstructed empirical relationship for B/Ca and subsurface seawater ALK, we estimated subsurface seawater carbonate system parameters in the tropical western Pacific since 24 ka. In general, the estimated subsurface seawater pH and [CO^2-3 ] show an increase with time, and the record of subsurface seawater pCO2 shows a decrease with time, in the tropical western Pacific over the past 24 ka. The consistent trends in subsurface seawater pCO2 and opal flux during deglaciation may imply that the reported increase in subsurface water pCO2 in the study area was promoted by enhanced upwelling in the Southern Ocean.
