A method for reconstructing the origin and circulation of ancient deep ocean water based on radioactive lead-neodymium isotopes

Abstract

The present invention discloses a method for reconstructing the source and circulation of ancient ocean deep water based on radioactive lead-neodymium isotopes, including: obtaining a target deep-sea sediment gravity column, sampling the target deep-sea sediment gravity column according to unit intervals, extracting the iron-manganese oxide phase and the debris phase for each sample; and determining the age corresponding to each sample; separating and purifying the lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin, and determining the lead-neodymium isotope value; according to the lead-neodymium isotope value in the iron-manganese oxide phase and the debris phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, judging the source and circulation changes of deep seawater of different ages and the source area changes of the sediment debris source. The method of the present invention is suitable for isotope research of sediments and reconstruction of ancient ocean environments through the whole process from sample selection, isotope separation to data processing and result analysis.

Description

Technical Field

[0001] The present invention belongs to the technical field of ancient ocean deep water source and circulation reconstruction, and in particular relates to an ancient ocean deep water source and circulation reconstruction method based on radioactive lead neodymium isotopes in deep-sea sediments. Background Art

[0002] As the study of global climate change deepens, the reconstruction of the ancient ocean environment has become one of the key means to understand the historical evolution of the Earth's climate system. The reconstruction of the ancient ocean environment can reveal the temperature, salinity, depth, flow pattern and material source of the ocean in the past, providing an important basis for analyzing the driving mechanism of climate change.

[0003] In previous paleoceanographic studies, stable isotope geochemistry and microbial paleoecology have made outstanding contributions, such as the use of benthic foraminifera carbon and oxygen isotopes to trace deep water evolution. Radioactive isotopes of lead (Pb) and neodymium (Nd) in seawater are not affected by biological and thermodynamic processes. The residence time of Nd in seawater is 200 to 1000 years, while the residence time of Pb in seawater is 50 to 200 years, which is similar to or even shorter than the global ocean mixing time (about 1500 years). Therefore, they are widely used water mass tracers in recent years. The landmasses around the ocean have specific lithology and Pb and Nd isotope characteristics. The Pb and Nd isotopes of seawater mainly come from the input of terrestrial weathering products. Therefore, water masses from different sources have characteristic Pb and Nd isotope values. Common carriers of Nd and Pb isotopes in seawater include oceanic ferromanganese crusts, authigenic ferromanganese oxide phases in sediments, corals, foraminifera and fish tooth fossils.

[0004] Tessier et al. believed that the initial aggregation mechanism of elements in sediments is different, so the existence forms of elements in water sediments can be divided into five types: exchangeable phase, carbonate phase, iron-manganese oxide phase, organic and sulfide combined phase, and detrital phase. Self-generated iron-manganese oxides in marine sediments can be directly precipitated from the surrounding seawater and are rich in Pb and Nd in the surrounding seawater during deposition. Their isotopic composition can provide accurate information on the source of deep water masses and reveal the ocean current circulation related to environmental changes. At the same time, the detrital phase of marine sediments is mainly composed of terrigenous weathering materials and submarine volcanic weathering materials. They are brought to the sedimentation site and settled by multiple factors such as rivers, wind transportation, sea level currents and tectonic activities. By studying Pb and Nd in the detrital phase, the source and transportation mechanism of sediments can be revealed. The detrital materials that settle to the seabed usually include two major categories: biogenic components and abiotic components. The abiotic components are mainly composed of terrigenous and self-generated materials. The biogenic components in marine sediments include siliceous organisms and calcareous organism remains. The carbonates in the open sea sediments are mainly formed by the deposition of calcareous marine remains. Biogenic silica, also known as biogenic opal, is a type of amorphous silica composed of the remains of diatoms, radiolarians, sponge spicules and siliceous flagellates. The shells of siliceous organisms dissolve very slowly, and most of them sink directly to the seabed and eventually transform into biogenic silica. If biogenic biogenic silica exists in the detrital phase, it will act as a diluent for key metals such as Pb and Nd. When extracting the detrital phase in the sediment for Pb and Nd isotope analysis, it is necessary to remove the biogenic silica in advance. Therefore, accurately separating and extracting different chemical phases of sediments, especially the iron-manganese oxide phase and the detrital phase, and determining their elemental and isotopic compositions, are the key to reconstructing the deep-water cycle and provenance changes of the ancient ocean.

[0005] Due to the low sedimentation rate in the deep sea, in order to obtain the long-term record of the source and circulation of the deep water in the ancient ocean, hundreds of meters of sediment cores are required, which can only be obtained through ocean drilling. Therefore, there are few studies on the long-scale evolution of ancient ocean currents and changes in provenance in deep-sea basins. The carbonate content of deep-sea sediments usually varies with ocean depth, geographical location and local environmental conditions. The carbonate content in different oceans is different. For example, the carbonate content of sediments in the Atlantic Ocean is high, while the carbonate content in the deep-sea sediments of the Bering Sea is low. Therefore, it is difficult to select a sufficient number of foraminifera in the Bering deep-sea sediment samples for isotope analysis. Compared with foraminifera, the radioactive isotopes of sediment iron-manganese oxides or clastic phases are not affected by environmental factors such as the high and low carbonate content, and are more suitable for the long-scale evolution of ancient ocean currents and changes in provenance in multiple deep-sea areas around the world.

[0006] At present, the reconstruction method of ancient ocean deep water circulation and source changes is carried out by using radioactive isotopes of different chemical phases of sediments, which includes the following steps: (1) determining the extraction process of iron-manganese oxide phase and debris phase according to the geographical location and sedimentary characteristics of the sediments; (2) using ion exchange resin to separate and purify the isotopes in the iron-manganese oxide phase and the debris phase respectively; (3) measuring the isotopes on the computer and calculating the isotope values ​​based on the measurement results; (4) using the calculated isotope results to draw a map, and combining the isotope characteristic range of the possible source area to judge the source area changes and circulation process of deep seawater and sediment debris sources of different depths (ages).

[0007] The extraction process of the Fe-Mn oxide phase and the detrital phase is determined according to the geographical location and sedimentary characteristics of the sediments. The existing sequential extraction methods in the literature include: for the sediments in the central trough affected by hydrothermal fluids: remove the exchangeable phase → remove the carbonate phase → collect the Fe-Mn oxide phase → remove the organic binding phase → collect the detrital phase (Yu Zenghui, Gao Yuhua, Zhai Shikui, et al. Study on the sequential leaching extraction of hydrothermal source components in the sediments of the central Okinawa Trough [J]. Chinese Science: Earth Sciences, 2012, 55(4): 665−674.). For the deep-sea zeolite clay in the Central Indian Ocean Basin, the semi-deep-sea sediments in the Arctic, and the offshore sediments in the Andaman Sea: remove the exchangeable phase → remove the carbonate phase → collect the Fe-Mn oxide phase → collect the detrital phase.

[0008] However, the existing methods of reconstructing ancient ocean deep water circulation and provenance changes through sediment radioactive lead neodymium isotopes have the following technical problems:

[0009] (1) When determining the extraction process of the iron-manganese oxide phase and the clastic phase of the sediment, the location and genetic type of the sediment core (such as deep sea and offshore, zeolite clay and sediment) are different. Volcanic sediments, terrestrial weathering materials and deep-sea autogenous materials have different physical and chemical properties, resulting in different reaction rates and reaction degrees during extraction, and different requirements for the order of extraction of different phases, the concentration and dosage of extraction reagents, and the extraction time. In deep-sea areas with complex sediment sources such as the Bering Sea, the genetic types of sediments (such as shelf sediments, volcanic sediments and deep-sea sediments) vary significantly. Therefore, it is difficult to develop a general process suitable for all samples during the extraction process, and the extraction parameters must be adjusted according to the specific characteristics of the sample.

[0010] (2) Self-generated iron-manganese oxides are mainly adsorbed on the surface of sediment particles. It is easy to extract incompletely or over-extract in the extraction process, which will affect the isotope results of both the Fe-Mn oxide phase and the detrital phase. Therefore, it is very important to determine the appropriate extraction reagent concentration and extraction time. At present, there is still a lack of ideal extraction methods for the iron-manganese oxide phase in deep-sea sediments. At the same time, the existing methods do not remove the organic phase and the biogenic silica phase before extracting the detrital phase, or only remove the organic phase, which may affect the isotope determination of the detrital phase.

[0011] (3) When using ion exchange resin to separate and purify isotopes in the iron-manganese oxide phase and the detrital phase, the reconstruction process of the deep water cycle and source change of the ancient ocean is currently mostly determined by extracting different chemical phases of sediments to determine the Nd and strontium (Sr) isotopes of the iron-manganese oxide or detrital phase. Most researchers use multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) to determine Nd isotopes, and thermal ionization mass spectrometry (TIMS) or MC-ICP-MS to measure Sr isotopes. For Bering Sea samples with low Sr content and high precision requirements, thermal ionization mass spectrometry (TIMS) is the first choice for determination. However, the process of using TIMS to determine Sr isotopes is relatively cumbersome, and the measurement efficiency is lower than that of MC-ICP-MS.

[0012] In summary, the existing technology lacks a set of processes for accurately extracting iron-manganese oxide phases and debris phases from different deep-sea sediments, which can simplify the extraction process to the greatest extent without introducing reagent pollution and ensuring the extraction amount, ensuring that iron-manganese oxides are not excessively leached and that there is no biogenic silicon contamination in the debris phase. At the same time, Sr isotope determination is cumbersome compared to Nd isotope determination, and requires the use of two different instruments, which greatly reduces the measurement efficiency. It is urgent to propose a simpler, more efficient and scientific method for reconstructing the ancient ocean deep water cycle and material source changes based on radioactive isotopes in deep-sea sediments to solve this problem. Summary of the invention

[0013] In view of the shortcomings of the existing technology, the present invention provides a method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes.

[0014] The embodiment of the present invention provides a method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes, the method comprising:

[0015] Obtain the target deep-sea sediment gravity column, sample the target deep-sea sediment gravity column according to unit intervals, extract the iron-manganese oxide phase and the clastic phase from each sample; and determine the age corresponding to each sample;

[0016] The lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase were separated and purified by ion exchange resin, and the lead-neodymium isotope values ​​were determined;

[0017] Based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, the sources and circulation changes of deep seawater of different ages and the source area changes of sediment debris sources are determined.

[0018] Furthermore, the process of extracting the iron-manganese oxide phase and the detrital phase from each sample includes:

[0019] The target deep-sea sediment is treated with an ammonium sulfate solution, and the supernatant is discarded by centrifugation to remove the exchangeable phase;

[0020] The target deep-sea sediments for removing the exchangeable phase are treated with hydroxylamine hydrochloride acetic acid solution, centrifuged, and the supernatant is extracted to obtain the iron-manganese oxide phase;

[0021] The target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with a sodium carbonate solution, and the supernatant is discarded by centrifugation to remove the biogenic silicon phase;

[0022] The target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with hydrogen peroxide, and the supernatant is discarded by centrifugation to remove the organic phase;

[0023] The target deep-sea sediment after the removal of the biogenic silicon phase and the organic matter phase is digested with a solution obtained by mixing at least two of nitric acid, hydrofluoric acid and hydrochloric acid in any proportion, and the supernatant is extracted to obtain the debris phase.

[0024] Furthermore, the following steps are included between removing the exchangeable phase in the target deep-sea sediment and extracting the iron-manganese oxide phase in the target deep-sea sediment:

[0025] The target deep-sea sediment for removing the exchangeable phase is treated with acetic acid, and the supernatant is discarded by centrifugation to remove the carbonate phase.

[0026] Furthermore, the acetic acid solution of hydroxylamine hydrochloride is selected from a 25% acetic acid solution of 0.02M hydroxylamine hydrochloride.

[0027] Furthermore, the process of separating and purifying the lead and neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin comprises:

[0028] The iron-manganese oxide phase and the debris phase in the liquid phase are converted into hydrochloric acid medium respectively, and hydrochloric acid is added to the iron-manganese oxide phase converted into the hydrochloric acid medium and evaporated to dryness and the debris phase converted into the hydrochloric acid medium and evaporated to dryness respectively, and the supernatant is extracted by centrifugation to obtain an iron-manganese oxide phase extract and a debris phase extract;

[0029] The lead components in the iron-manganese oxide phase extract and the debris phase extract are separated and purified by the first ion exchange column;

[0030] The neodymium components in the iron-manganese oxide phase extract and the debris phase extract are separated and purified by the second ion exchange column.

[0031] Furthermore, the first ion exchange column is provided with Sr Spec resin, Ln Spec resin, and AG50W-X8 cation exchange resin in order from bottom to top; and the second ion exchange column is provided with Ln Spec resin.

[0032] Furthermore, the process of separating and purifying the lead and neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin also includes:

[0033] The Shin Etsu JNdi-1 standard was used to monitor the quality of Nd isotopes, and the NISTSRM 997 Tl standard was used to monitor the quality of Pb isotopes.

[0034] Furthermore, the process of determining the lead-neodymium isotope value includes:

[0035] The lead components in the iron-manganese oxide phase extract and the debris phase extract are measured respectively to obtain the lead isotope ratios in the iron-manganese oxide phase extract and the debris phase extract;

[0036] The neodymium components in the iron-manganese oxide phase extract and the debris phase extract are measured respectively to obtain the neodymium isotope ratios in the iron-manganese oxide phase extract and the debris phase extract;

[0037] According to the neodymium isotope ratio in the iron-manganese oxide phase extract and the debris phase extract, the neodymium isotope value in the iron-manganese oxide phase and the debris phase is calculated. The expression is as follows:

[0038] εNd = [( 143 Nd / 144 Nd) 样品 / ( 143 Nd / 144 Nd) 球粒陨石 −1]×10000

[0039] In the formula, ( 143 Nd / 144 Nd) 球粒陨石 Represents modern chondrites 143 Nd / 144 Nd, the value is 0.512638; ( 143 Nd / 144 Nd) 样品 Indicates the sample measured 143 Nd / 144 Nd.

[0040] Furthermore, based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, the process of judging the source and circulation changes of deep seawater of different ages and the source area changes of sediment detrital sources includes:

[0041] The εNd- 206 / 204 Pb and εNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the range of εNd- 206 / 204 Pb discrimination diagram and εNd- 208 / 204 The projected points on the Pb discrimination map are combined with the characteristic range of lead-neodymium isotopes in the candidate source areas to determine the sources and circulation changes of deep seawater of different ages;

[0042] Based on the εNd- 206 / 204 Pb and εNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the range of εNd- 206 / 204 Pb discrimination diagram and εNd- 208 / 204 The point on the Pb discrimination map is projected, combined with the characteristic range of lead-neodymium isotopes in the alternative source areas, to determine the source area changes of the sediment debris sources.

[0043] Furthermore, the method further comprises:

[0044] Compare the neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase to determine whether there is a correlation between the changes in the neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase;

[0045] When there is no correlation between the changes in the neodymium isotope values ​​in the iron-manganese oxide phase and the clastic phase, it is determined that the iron-manganese oxide phase and the clastic phase in the target deep-sea sediment are successfully separated. Compared with the prior art, the beneficial effects of the present invention are:

[0046] (1) The present invention obtains the target deep-sea sediment gravity column, samples the target deep-sea sediment gravity column according to unit intervals, and extracts the iron-manganese oxide phase and the debris phase from each sample; the lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase are separated and purified by ion exchange resin, and the lead Pb and neodymium Nd isotope values ​​are determined by MC-ICP-MS, which greatly saves time cost and measurement efficiency. The present invention ensures that sufficient iron-manganese oxide phase and debris phase are extracted for subsequent isotope determination, and also avoids the Pb and Nd element contamination caused by the extraction reagent, as well as the contamination of aquatic components (such as sediment exchangeable phases) and non-aquatic sediment components (such as continental debris and volcanic ash) introduced in the iron-manganese oxide phase extraction procedure. The method also achieves the removal of organic phases and biogenic siliceous phases in sediments under mild and simple experimental conditions, and restores the signals carried by Pb and Nd in the extracted authigenic iron-manganese oxide and debris phases as much as possible.

[0047] (2) The present invention determines the source and circulation changes of deep seawater of different ages and the source area changes of sediment debris sources based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, so as to more accurately determine the source of water masses or sediments on a long time scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0049] Figure 1 A schematic diagram of a process for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes provided in an embodiment of the present invention;

[0050] Figure 2 A schematic diagram of a process for extracting an iron-manganese oxide phase and a debris phase provided in an embodiment of the present invention;

[0051] Figure 3 Schematic diagram of the sources of iron, manganese, lead and neodymium isotopes in Bering Sea sediments provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0052] The present invention is further described below in conjunction with embodiments. The description of the following embodiments is only used to help understand the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principles of the present invention, several improvements and modifications may be made to the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0053] In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the fact that they can be implemented by ordinary technicians in this field. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0054] like Figure 1 As shown, an embodiment of the present invention provides a method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes in deep-sea sediments, the method comprising:

[0055] Step S1, obtaining a target deep-sea sediment gravity column, sampling the target deep-sea sediment gravity column according to unit intervals, and extracting the iron-manganese oxide phase and the debris phase from each sample; and 14 C determines the age corresponding to each sample.

[0056] Specifically, Figure 2 As shown, the process of extracting the iron-manganese oxide phase and the detrital phase for each sample includes:

[0057] Step S101: treating the target deep-sea sediment with ammonium sulfate (NH 4 ) 2 SO 4 For solution treatment, the mixture was placed in a shaker at room temperature and continuously shaken for 12 h. The supernatant was discarded by centrifugation to remove the exchangeable phase. The mixture was then washed three times with ultrapure water.

[0058] Step S102, treating the target deep-sea sediments for removing the exchangeable phase with acetic acid, centrifuging and discarding the supernatant, thereby removing the carbonate phase.

[0059] It should be noted that step S102 is an optional step, and whether the carbonate phase needs to be removed is determined based on the carbonate content of the deep-sea sediment.

[0060] Step S103, treating the target deep-sea sediment from which the exchangeable phase is removed with an acetic acid solution of hydroxylamine hydrochloride, centrifuging, and extracting the supernatant to obtain the iron-manganese oxide phase.

[0061] The target deep-sea sediments from which the exchangeable phase is removed are extracted several times with an acetic acid solution of hydroxylamine hydrochloride to obtain an iron-manganese oxide phase; the acetic acid solution of hydroxylamine hydrochloride is selected from a 25% acetic acid solution of 0.02M-1M hydroxylamine hydrochloride. It should be noted that in the process of extracting the same batch of samples several times, each extraction uses a 25% acetic acid solution of hydroxylamine hydrochloride of the same concentration; for sediment samples from different sea areas, 25% acetic acid solutions of hydroxylamine hydrochloride of different concentrations can be used for extraction. Exemplarily, the "three extractions of small amounts and multiple times" is adopted to avoid the contamination of the debris phase caused by excessive leaching of iron-manganese oxides, while ensuring sufficient leaching of iron-manganese oxides. First, add a 25% acetic acid solution of 1M hydroxylamine hydrochloride to the target deep-sea sediments from which the exchangeable phase is removed, put it in a shaker at room temperature for shaking, and then centrifuge it, and the supernatant is the iron-manganese oxide phase. Add a 25% acetic acid solution of 1M hydroxylamine hydrochloride to the target deep-sea sediments again, and repeat the above steps. Add 1M hydroxylamine hydrochloride 25% acetic acid solution again, repeat the above steps, the iron-manganese oxides extracted three times can be regarded as a single iron-manganese oxide phase, transfer the iron-manganese oxides obtained by three extractions to the same polytetrafluoroethylene centrifuge tube to obtain the final iron-manganese oxide phase, and wash with ultrapure water three times.

[0062] Step S104, the target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with sodium carbonate Na 2 CO 3 The solution was treated and shaken in a shaker at 60°C for 8 hours, and the supernatant was discarded by centrifugation to remove the bio-silica phase. The sample was washed three times with ultrapure water.

[0063] Step S105, the target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with hydrogen peroxide H 2 O 2 The mixture was shaken in a shaker at room temperature for 24 hours, and the supernatant was discarded by centrifugation to remove the organic phase. The mixture was washed three times with ultrapure water, and the residue was dried and weighed to obtain the debris phase.

[0064] It should be noted that the order of step S104 and step S105 can be swapped.

[0065] Step S106, the target deep-sea sediment (i.e., the solid debris phase) after the removal of the biosilicon phase and the organic phase is placed in a PTFE liner, and a solution obtained by mixing at least two of nitric acid, hydrofluoric acid, and hydrochloric acid in any proportion is placed on a heating plate and heated at 130° C. for 36 hours for digestion, and the supernatant is extracted to obtain the liquid debris phase.

[0066] It should be noted that in this example, experiments were conducted on each step in the process: removal of the exchangeable phase, removal of the carbonate phase, extraction of the iron-manganese oxide phase, and extraction of the debris phase. The reagent for removing the exchangeable phase was improved. Selective carbonate phase removal step. The reagent for extracting iron-manganese oxides is a mixed solution of hydroxylamine hydrochloride (HH) of different concentrations (0.02M-1M) and acetic acid (HAc) with a volume fraction of 25%, which will not introduce contamination of debris components. The leaching time is set to 1h-3h, and it is found that after the leaching time reaches a certain length, the leaching concentration of lead and neodymium tends to be stable. It is also found that the leaching time and temperature have little effect on the neodymium concentration, but a greater effect on the lead concentration. In order to effectively prevent the debris phase contamination caused by excessive leaching of iron-manganese oxides, the volume ratio of the extraction reagent and the sediment is about 1:1-5, that is, a low volume ratio, and the extraction is selected at room temperature. A "three-extraction method" with a small amount and multiple times is designed for iron-manganese oxides. Before extracting the debris phase, an organic phase and biosilica removal step was added, and the sample dissolving reagent of the debris phase was changed to a mixed solution of hydrochloric acid-nitric acid-hydrofluoric acid to ensure that the extracted debris phase could be completely dissolved.

[0067] Step S2, separating and purifying the lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin, and determining the lead-neodymium isotope values.

[0068] Specifically, the step S2 includes the following sub-steps:

[0069] Step S201, converting the liquid iron-manganese oxide phase and the debris phase into hydrochloric acid medium respectively, adding 2N hydrochloric acid HCl to the iron-manganese oxide phase converted into the hydrochloric acid medium and evaporated, and the debris phase converted into the hydrochloric acid medium and evaporated, respectively, and extracting the supernatant by centrifugation to obtain the iron-manganese oxide phase extract and the debris phase extract for isotope analysis.

[0070] Step S202, separating and purifying the lead components in the iron-manganese oxide phase extract and the debris phase extract respectively through the first ion exchange column; wherein the first ion exchange column is provided with Sr Spec resin, LnSpec resin, and AG50W-X8 cation exchange resin in sequence from bottom to top.

[0071] Step S203, separating and purifying the neodymium components in the iron-manganese oxide phase extract and the debris phase extract respectively through a second ion exchange column; wherein the second ion exchange column is provided with Ln Spec resin.

[0072] Step S204, determining the lead-neodymium isotope value, includes:

[0073] The lead components in the iron-manganese oxide phase extract and the debris phase extract are measured respectively to obtain the lead isotope ratios in the iron-manganese oxide phase extract and the debris phase extract;

[0074] The neodymium components in the iron-manganese oxide phase extract and the debris phase extract are measured respectively to obtain the neodymium isotope ratios in the iron-manganese oxide phase extract and the debris phase extract;

[0075] Furthermore, in this example, the concentrations of Nd and Pb in the above samples were measured using Element XR ICP-MS. The total blank values ​​of Nd and Pb were below the detection limit. The Nd isotope standard Shin Etsu JNdi-1 was used to monitor the analytical quality, and the Pb isotope standard NIST SRM 997 Tl was used to monitor the analytical quality.

[0076] According to the neodymium isotope ratio in the iron-manganese oxide phase extract and the debris phase extract, the neodymium isotope value in the iron-manganese oxide phase and the debris phase is calculated. The expression is as follows:

[0077] εNd = [( 143 Nd / 144 Nd) 样品 / ( 143 Nd / 144 Nd) 球粒陨石 −1]×10000

[0078] In the formula, ( 143 Nd / 144 Nd) 球粒陨石 Represents modern chondrites 143 Nd / 144 Nd, the value is 0.512638; ( 143 Nd / 144 Nd) 样品 Indicates the sample measured 143 Nd / 144 Nd.

[0079] Among them, the Pb isotope ratio does not need to be calculated.

[0080] Step S3, based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, determine the source and circulation changes of deep seawater of different ages and the source area changes of sediment debris sources.

[0081] Specifically, the εNd- 206 / 204 Pb and εNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the range of εNd- 206 / 204 Pb discrimination diagram and εNd- 208 / 204The points on the Pb discrimination diagram are projected, combined with the characteristic range of lead-neodymium isotopes in the alternative source areas, to determine the sources and circulation changes of deep seawater of different ages.

[0082] Based on the εNd- 206 / 204 Pb and εNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the range of εNd- 206 / 204 Pb discrimination diagram and εNd- 208 / 204 The point on the Pb discrimination map is projected, combined with the lead-neodymium isotope characteristic range of the alternative source area, to determine the source area changes of the sediment debris.

[0083] Furthermore, the method further comprises:

[0084] Compare the neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase to determine whether there is a correlation between the changes in the neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase;

[0085] When there is no correlation between the changes in the neodymium isotope values ​​in the ferromanganese oxide phase and the clastic phase, it is determined that the ferromanganese oxide phase and the clastic phase in the target deep-sea sediments are successfully separated.

[0086] Example 1

[0087] Next, this example takes the Bering Sea deep-sea sediments as an example to illustrate the specific implementation process of the ancient ocean deep-water source and cycle reconstruction method based on the radioactive lead-neodymium isotopes of deep-sea sediments provided by the present invention. In order to solve the problem of low measurement efficiency caused by different instruments used for isotope measurement, this example chooses to measure the radioactive lead (Pb) and Nd isotopes of the iron-manganese oxide phase and the detrital phase of the Bering Sea sediments instead of Sr and Nd isotopes. Cycle and ancient ocean reconstruction, compared with Sr ( 87 Sr / 86 Sr) and Pb have more isotope ratios that can be used to assess the water mass or sediment source ( 206 Pb / 204 Pb, 207 Pb / 204 Pb and 208 Pb / 204 Pb), and the Nd isotope values ​​were 206 Pb / 204 Pb, 207 Pb / 204 Pb and 208 Pb / 204Pb mapping can further narrow the scope of deep water and sediment sources based on the location of sediment isotope values ​​on different isotope ratio diagrams, and obtain more accurate information on possible source areas of deep water and sediments, thereby more accurately judging the source area changes and circulation processes of seawater and sediment debris sources on a long time scale.

[0088] Specifically, the method comprises the following steps:

[0089] Step S1, obtaining a gravity column of deep-sea sediments in the Bering Sea, sampling the gravity column of deep-sea sediments in the Bering Sea according to unit intervals, and extracting an iron-manganese oxide phase and a clastic phase from each sample; and 14 C determines the age of each sample (in this example, the age of the Bering Sea deep-sea sediment gravity column spans 41 ka-8 ka).

[0090] Specifically, the process of extracting the iron-manganese oxide phase and the detrital phase for each sample includes:

[0091] Step S101, treating the Bering Sea deep-sea sediments with an ammonium sulfate solution, centrifuging and discarding the supernatant, thereby removing the exchangeable phase.

[0092] Specifically, 1 g of ground and freeze-dried Bering Sea deep-sea sediment sample was placed in a 5 mL polytetrafluoroethylene centrifuge tube, and 3 mL of 1 M (NH 4 ) 2 SO 4 Solution (V 沉积物 :V 溶液 =1:3), and placed in a shaker at room temperature for 12 h at 150 rpm. Then centrifuge for 10 min (4000 r / min). Remove the supernatant from the centrifuge tube with a pipette and discard the supernatant. Wash with ultrapure water three times (10 min each time, 4000 r / min), and discard the supernatant.

[0093] Step S102, treating the target deep-sea sediment from which the exchangeable phase is removed with an acetic acid solution of hydroxylamine hydrochloride, centrifuging, and extracting the supernatant to obtain the iron-manganese oxide phase.

[0094] Specifically, in this example, the "three-extraction method of small amounts and multiple times" was adopted to avoid the contamination of the debris phase caused by excessive leaching of iron and manganese oxides, while ensuring sufficient leaching of iron and manganese oxides. First, 1 mL of 0.02M hydroxylamine hydrochloride and 25% acetic acid solution (V 沉积物 :V 溶液=1:1), placed in a shaker at room temperature for 1 h at 150 rpm, then centrifuged for 10 min (4000 r / min), the supernatant is the iron-manganese oxide phase. Then add 2 mL of 0.02M hydroxylamine hydrochloride 25% acetic acid solution (V 沉积物 :V 溶液 =1:2), repeat the above steps. Finally, add 1 mL of 0.02M hydroxylamine hydrochloride 25% acetic acid solution (V 沉积物 :V 溶液 =1:1), repeat the above steps, the iron-manganese oxides extracted three times can be regarded as a single iron-manganese oxide phase, transfer the iron-manganese oxides obtained by three extractions to the same polytetrafluoroethylene centrifuge tube to obtain the final iron-manganese oxide phase. Wash three times with ultrapure water, centrifuge for 10 min each time (4000 r / min).

[0095] Step S103, treating the target deep-sea sediment after the iron-manganese oxide phase is extracted with a sodium carbonate solution, centrifuging and discarding the supernatant, thereby removing the biogenic silicon phase.

[0096] Specifically, 3 mL of 20% sodium carbonate (Na 2 CO 3 ) solution (V 沉积物 :V 溶液 =1:3) and placed in a shaker at 60 °C for 8 h at 150 rpm to remove the bio-silicon phase. The supernatant was then centrifuged and washed three times with ultrapure water, each time by centrifugation for 10 min (4000 r / min).

[0097] In step S103, the target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with hydrogen peroxide, and the supernatant is discarded by centrifugation to remove the organic phase.

[0098] Specifically, 3 mL of 10% hydrogen peroxide (H2O2) was added to the sediment after the treatment in step S103. 2 O 2 )(V 沉积物 :V 溶液 =1:3), placed in a shaker at room temperature for 24 h, then centrifuged to discard the supernatant, washed three times with ultrapure water, each centrifuged for 10 min (4000 r / min). Finally, the residue was dried and weighed to obtain the debris phase.

[0099] Step S104, digesting the target deep-sea sediment after removing the biogenic silicon phase and the organic matter phase with a solution obtained by mixing at least two of nitric acid, hydrofluoric acid and hydrochloric acid in any proportion, and extracting the supernatant to obtain the debris phase.

[0100] Specifically, 50 mg of the debris phase sample was weighed into a PTFE liner, 0.5 mL of nitric acid and hydrofluoric acid, and 1.5 mL of hydrochloric acid (nitric acid: hydrofluoric acid: hydrochloric acid = 1:1:3) were added, and the liner was placed on a hot plate and heated at 130 °C for 36 h.

[0101] Step S2, separating and purifying the lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin, and determining the lead-neodymium isotope values.

[0102] Specifically, step S2 includes the following sub-steps:

[0103] Step S201, converting the liquid iron-manganese oxide phase and the debris phase into hydrochloric acid medium respectively, adding hydrochloric acid to the iron-manganese oxide phase converted into the hydrochloric acid medium and evaporated, and the debris phase converted into the hydrochloric acid medium and evaporated, respectively, and extracting the supernatant by centrifugation to obtain an iron-manganese oxide phase extract and a debris phase extract;

[0104] Step S202, the lead components in the iron-manganese oxide phase extract and the debris phase extract are separated and purified by the first ion exchange column; the first ion exchange column is filled with three layers of resin, namely, 0.5 mL Sr Spec resin at the bottom, 0.5 mL Ln Spec resin in the middle, and 0.8 mL cation exchange resin (AG50W-X8) at the top. The first mixed resin column is pre-washed (H 2 O, 3N HNO 3 , 8N HCl, 6N HCl) equilibrate (2N HCl), load, equilibrate again (2N HCl, 2.5N HNO 3 ) and then eluted the rare earth components (REE) (7N HNO 3 )、Sr (0.05N HNO 3 ) and Pb (8N HCl) components. The REE obtained from the first ion exchange column was evaporated to dryness at 130°C and the medium was switched to hydrochloric acid. The evaporated residue was then dissolved in 1 mL of 0.15N HCl.

[0105] Step S203, using a second ion exchange column to separate and purify the neodymium components in the iron-manganese oxide phase extract and the debris phase extract. The second ion exchange column is provided with 1 mL of Ln Spec resin. 2 O, 6N HCl), and equilibration (0.15N HCl). After loading the sample, the Nd component was eluted with 0.15N HCl.

[0106] Specifically, the process of separating and purifying Pb-Nd isotopes by two sets of ion exchange resin columns is shown in Table 1 below.

[0107] Table 1: Flow chart of two sets of ion exchange resin columns for separation and purification of Pb-Nd isotopes

[0108]

[0109] Step S204: After the Pb and Nd components are dried on a hot plate, they are converted into a nitric acid medium and then heated with 2 mL of 3% HNO 3 The concentrations of Nd and Pb in the Fe-Mn oxide and debris phases were measured by Element XR ICP-MS. The collected Pb and Nd components were concentrated in 3% HNO 3 80 μL 103 Rh (500 ppb) was diluted to 4 mL as an internal standard and then analyzed. The total blank values ​​for Nd and Pb were below the detection limit. Nd and Pb isotope ratios were measured using Neptune Plus MC-ICP-MS. The Nd isotope standard Shin Etsu JNdi-1 was used to monitor the analytical quality, and the measured Nd isotope ratios were normalized to 146 Nd / 144 Nd = 0.7219 to correct for mass fractionation. The concentration of the Nd sample solution was adjusted to 50 μg / L. During the analysis, 143 Nd / 144 The average value of Nd is 0.512108±0.000008 (2σ, n=11). Before measuring the Pb isotope, the concentration of the Pb sample solution was adjusted to 50 μg / L and 12.5 μg / L of NIST SRM 997 Tl was added. 205 Tl / 203 Tl = 2.3888 pairs 206 / 204 Pb, 207 / 204 Pb and 208 / 204 The mass fractionation ratio of Pb was corrected. The NIST SRM 981 standard was measured 11 times during the entire analysis. 206 / 204 Pb = 16.9363±0.0003 (2σ, n =11), 207 / 204 Pb =15.4901±0.0003 (2σ, n =11) and 208 / 204 Pb =36 .6958 ±0 .0008(2σ, n=11).

[0110] The Nd isotopic composition is expressed as εNd (εNd = [( 143 Nd / 144 Nd) 样品 / ( 143 Nd / 144 Nd) 球粒陨石 −1]×10000), among which modern chondrites 143 Nd / 144 The Nd value is 0.512 638. The Pb isotope ratio does not need to be calculated.

[0111] Step S4, based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, judge the source and circulation changes of deep seawater of different ages and the source area changes of sediment debris sources.

[0112] Specifically, the εNd- 206 / 204 Pb and εNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the range of εNd- 206 / 204 Pb discrimination diagram and εNd- 208 / 204 The points on the Pb discrimination diagram are projected, combined with the characteristic range of lead-neodymium isotopes in the alternative source areas, to determine the sources and circulation changes of deep seawater of different ages.

[0113] Based on the εNd- 206 / 204 Pb and εNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the range of εNd- 206 / 204 Pb discrimination diagram and εNd- 208 / 204 The point on the Pb discrimination map is projected, combined with the lead-neodymium isotope characteristic range of the alternative source area, to determine the source area changes of the sediment debris.

[0114] The Nd isotopes of the iron-manganese oxide phase and the detrital phase in the Bering Sea deep-sea sediments were compared. The results showed that there was no correlation between the Nd isotope changes of the iron-manganese oxide and the detrital phases (Pearson correlation coefficient = 0.2), indicating that the extraction method can well separate the iron-manganese oxide and detrital phases in the Bering Sea deep-sea sediments.

[0115] Figure 3 Demonstrating the use of eNd- 208 / 204 Pb discrimination diagram ( Figure 3 (A)) and eNd- 206 / 204 Pb discrimination diagram ( Figure 3 (B)) Projects the results of rock sample analysis to explain the reconstruction process of the origin of ancient ocean water masses based on radioactive lead and neodymium isotopes of deep-sea sediments in the Bering Sea.

[0116] As can be seen from the figure, the best explanation for the Pb and Nd isotope time series is a mixture of four end members, including: (a) eroded materials from the Yukon-Tenana Terrane transported by the Yukon River, (b) eroded materials from the Western and Central Aleutian Arc, (c) eroded materials from the Okhotsk-Chukchi Volcanic Belt (OCVB) transported by the Anadyr River, and (d) from the Pacific Deep Water. It can also be seen from the figure that the influence of the Kamchatka water mass on the Pb-Nd isotope values ​​of the Bering Sea sediment core is negligible.

[0117] In summary, the present invention obtains the target deep-sea sediment gravity column, samples the target deep-sea sediment gravity column according to unit intervals, extracts the iron-manganese oxide phase and the debris phase for each sample; separates and purifies the lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin, and determines the lead Pb and neodymium Nd isotope values ​​by MC-ICP-MS, which greatly saves time cost and measurement efficiency. The present invention ensures that sufficient iron-manganese oxide phase and debris phase are extracted for subsequent isotope determination, and also avoids the Pb and Nd element contamination caused by the extraction reagent, as well as the contamination of aquatic components (such as sediment exchangeable phases) and non-aquatic sediment components (such as continental debris and volcanic ash) introduced in the extraction procedure of the iron-manganese oxide phase. The method also achieves the removal of organic phases and biosilica phases in sediments under mild and simple experimental conditions, and restores the signals carried by Pb and Nd in the extracted authigenic iron-manganese oxide and debris phases as much as possible. The present invention determines the sources and circulation changes of deep seawater of different ages and the source area changes of sediment debris sources based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, so as to more accurately determine the source of water masses or sediments on a long time scale.

[0118] The above embodiments are only used to illustrate the design ideas and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. The protection scope of the present invention is not limited to the above embodiments. Therefore, any equivalent changes or modifications made based on the principles and design ideas disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes, characterized in that: The method comprises: Obtain the target deep-sea sediment gravity column, sample the target deep-sea sediment gravity column according to unit intervals, extract the iron-manganese oxide phase and the clastic phase from each sample; and determine the age corresponding to each sample; The lead-neodymium isotopes in the iron-manganese oxide phase and the debris phase were separated and purified by ion exchange resin, and the lead-neodymium isotope values ​​were determined; Based on the lead-neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase, combined with the lead-neodymium isotope characteristic range of the alternative source area, the source and circulation changes of deep seawater of different ages and the source area changes of sediment detrital sources are judged; including: eNd- 206 / 204 Pb and eNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the eNd- 206 / 204 Pb discrimination diagram and eNd- 208 / 204 The projected points on the Pb discrimination map are combined with the characteristic range of lead-neodymium isotopes in the candidate source areas to determine the sources and circulation changes of deep seawater of different ages; Based on the eNd- 206 / 204 Pb and eNd- 208 / 204 Pb were respectively drawn to discriminate the lead isotope ratios and neodymium isotope values ​​corresponding to samples of different ages in the eNd- 206 / 204 Pb discrimination diagram and eNd- 208 / 204 The point on the Pb discrimination map is projected, combined with the characteristic range of lead-neodymium isotopes in the candidate source areas, to determine the source area changes of the sediment debris sources; The process of extracting the iron-manganese oxide phase and the debris phase from each sample includes: The target deep-sea sediment is treated with an ammonium sulfate solution, and the supernatant is discarded by centrifugation to remove the exchangeable phase; The target deep-sea sediments for removing the exchangeable phase are treated with hydroxylamine hydrochloride acetic acid solution, centrifuged, and the supernatant is extracted to obtain the iron-manganese oxide phase; The target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with a sodium carbonate solution, and the supernatant is discarded by centrifugation to remove the biogenic silicon phase; The target deep-sea sediment after the iron-manganese oxide phase is extracted is treated with hydrogen peroxide, and the supernatant is discarded by centrifugation to remove the organic phase; The target deep-sea sediment after the removal of the biogenic silicon phase and the organic matter phase is digested with a solution obtained by mixing at least two of nitric acid, hydrofluoric acid and hydrochloric acid in any proportion, and the supernatant is extracted to obtain the debris phase; The method further comprises: Compare the neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase to determine whether there is a correlation between the changes in the neodymium isotope values ​​in the iron-manganese oxide phase and the detrital phase; When there is no correlation between the changes in the neodymium isotope values ​​in the ferromanganese oxide phase and the clastic phase, it is determined that the ferromanganese oxide phase and the clastic phase in the target deep-sea sediments are successfully separated.

2. The method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes according to claim 1, characterized in that: The following steps are also included between removing the exchangeable phase in the target deep-sea sediment and extracting the iron-manganese oxide phase in the target deep-sea sediment: The target deep-sea sediment for removing the exchangeable phase is treated with acetic acid, and the supernatant is discarded by centrifugation to remove the carbonate phase.

3. The method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes according to claim 1, characterized in that: The acetic acid solution of hydroxylamine hydrochloride is selected from 25% acetic acid solution of 0.02M hydroxylamine hydrochloride.

4. The method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes according to claim 1, characterized in that: The process of separating and purifying lead and neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resin includes: The iron-manganese oxide phase and the debris phase in the liquid phase are converted into hydrochloric acid medium respectively, and hydrochloric acid is added to the iron-manganese oxide phase converted into the hydrochloric acid medium and evaporated to dryness and the debris phase converted into the hydrochloric acid medium and evaporated to dryness respectively, and the supernatant is extracted by centrifugation to obtain an iron-manganese oxide phase extract and a debris phase extract; The lead components in the iron-manganese oxide phase extract and the debris phase extract are separated and purified by the first ion exchange column; The neodymium components in the iron-manganese oxide phase extract and the debris phase extract are separated and purified by the second ion exchange column.

5. The method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes according to claim 4, characterized in that: The first ion exchange column is provided with Sr Spec resin, Ln Spec resin, and AG50W-X8 cation exchange resin from bottom to top; the second ion exchange column is provided with Ln Spec resin.

6. A method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes according to claim 1 or 4, characterized in that: The process of separating and purifying the lead and neodymium isotopes in the iron-manganese oxide phase and the debris phase by ion exchange resins also includes: The quality of the analysis was monitored using the Shin Etsu JNdi-1 standard for neodymium isotopes and the quality of the analysis was monitored using the NIST SRM997 Tl standard for lead isotopes.

7. The method for reconstructing the origin and circulation of ancient ocean deep water based on radioactive lead neodymium isotopes according to claim 1, characterized in that: The process of determining the lead-neodymium isotope value includes: The lead components in the iron-manganese oxide phase extract and the debris phase extract are measured respectively to obtain the lead isotope ratios in the iron-manganese oxide phase extract and the debris phase extract; The neodymium components in the iron-manganese oxide phase extract and the debris phase extract are measured respectively to obtain the neodymium isotope ratios in the iron-manganese oxide phase extract and the debris phase extract; According to the neodymium isotope ratio in the iron-manganese oxide phase extract and the debris phase extract, the neodymium isotope value in the iron-manganese oxide phase and the debris phase is calculated. The expression is as follows: eNd = [( 143 Mr. / 144 (Yes) 样品 / ( 143 Mr. / 144 (Yes) 球粒陨石 -1]×10000 In the formula, ( 143 Nd / 144 Nd) 球粒陨石 Represents modern chondrites 143 Nd / 144 Nd, the value is 0.512638; ( 143 Nd / 144 Nd) 样品 Indicates the sample measured 143 Nd / 144 Nd.

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