Introduction
Environmentalmagnetismemergedinthe1970sandisamarginalsubjectbetweenearthscience,environmentalscienceandmagnetism.Theprincipleistomeasurethemagneticresponseofnaturalmaterialssuchassoil,rocksandsedimentsandmaterialsproducedbyhumanactivitiesintheman-mademagneticfield,andextracttheinformationofthegeographicalenvironment.Duetotheadvantagesofsystemmagneticmeasurementtechnology,high-sensitivitytestinginstruments,andcomputerprocessingofmagneticmeasurementdata,environmentalmagnetismiswidelyusedinlakesandwatershedpaleogeographyresearch,soilformationandclassification,loess-paleosoilresearchandenvironmentalpollutionresearchAndmanyotherresearchfields.Therearesomenewdevelopmenttrendsinenvironmentalmagnetisminthefuture.
BasicPrinciples
Theprincipleofenvironmentalmagnetismisthroughtheuseofenvironmentalmaterials,suchassoil,rocks,lakeandoceansediments,volcanicash,atmosphericdustandothernaturalmaterials,aswellashumanactivities.Themagneticmeasurementoftheproducedsubstances,suchastheparticlesreleasedaftertheburningoffossilfuels,isreflectedbythecomparisonofsimulationexperimentsandrelatedresearch,tounderstandthecontent,typeandmovementofmagneticmineralsinenvironmentalsubstances,andthenreversetheevolutionofthegeographicalenvironmentProcess,extractinformationaboutchangesinthegeographicenvironment,understandtheimpactofnaturalprocessesandhumanactivitiesonthegeographicenvironment,predictthelong-termtrendofchangesinthegeographicenvironment,andprovideanewbasisforcreatingnewenvironmentalmonitoringmethodsandformulatingenvironmentalcontrolstrategies.
Researchobject
Anysubstancehasmagnetism.Themagneticpropertiesofparticlesinnaturearemainlyproducedbyminerals.Themagneticbehaviorofmineralsisusuallydividedintoparamagnetism,diamagnetism,andferrimagnetism.Severalbasictypessuchasincompleteantiferromagnetism.Diamagneticminerals,suchasquartzandcalcite,canobtainmagnetismoppositetothedirectionoftheappliedmagneticfieldinanexternalmagneticfield,whichisveryweakandhasnoremanence.Itistheweakestofseveralmagneticbehaviors,soinmostcasesitismaskedbyothermagneticbehaviors.Paramagneticmineralscanobtainthesamemagnetismintheappliedmagneticfieldasthedirectionoftheappliedmagneticfield.Thisweakco-directionalmagnetismdisappearsimmediatelyafterremovingtheappliedmagneticfield,sothereisnoremanence.Thestrongermagneticbehaviorusuallymasksparamagnetism.Themagneticpropertiesofseveralnaturalmineralsmainlystudiedinenvironmentalmagnetismarespecialvariantsofferromagnetism,includingferrimagnetismandincompleteantiferromagnetism.Ferrimagneticminerals,suchasmagnetite(Fe3O4)andmaghemite(XFe2O3),notonlycanobtainstrongmagnetisminanexternalmagneticfield,butthisstrongmagnetismispartiallyretainedaftertheexternalmagneticfieldisremoved.Itistheresidualmagnetization(referredtoasresidualmagnetization).Generally,thelowconcentrationofferrimagneticcrystalsinthesampledominateitsmagneticcharacteristics;incompleteantiferromagneticminerals,suchashematite(ΑFe2O3)andgoethite(ΑFeOOH),canobtainrelativelyweakisotropicmagnetisminanexternalmagneticfield,Andcanretainremanencejustlikeferrimagneticminerals.Infact,thetotalmagneticmomentobtainedfromthemagneticmeasurementofenvironmentalmaterialssuchasrocks,atmosphericparticles,soilandsedimentsisthesumofthemagneticmomentsofthesample'sdiamagnetic,paramagnetic,antiferromagneticandferrimagneticminerals.
Researchbasis
Naturalsubstancesandsecondarysubstancesproducedbyhumanactivitiesoftenexhibitdifferentmagneticcharacteristics.Thesemagneticcharacteristicsarerelatedtothenumberandtypeofmagneticmineralstheycontain,thesizeofferromagneticcrystalgrainsandtheirratio.Thebasisofenvironmentalmagnetismresearchistorevealthetype,contentandgraincombinationcharacteristicsofmagneticmineralsinmatterthroughsystematicmagneticmeasurement,andextractinformationabouttheenvironmentanditsevolutionfromit.Themagneticmeasurementofalargenumberofsamplesshowsthatthelowcontentofferrimagneticmineralslargelydeterminesthemeasuredvalueofthemagneticsusceptibilityofthematerial.Forexample,aflyashsamplewithamagneticmineral(mainlyFe3O4)contentof48144Λg·ghasamassmagneticsusceptibility(X)of27177Λm3·kgandasaturatedisothermalremanence(SIRM)of571313ΛAm2·kg[1].Thesize(representedbymagneticdomains)offerromagneticcrystalgrainsofmagneticmineralsinenvironmentalmaterialsalsoshowsdifferencesinmagneticcharacteristics.Formagnetite,generally,themulti-domaingrainsare(MD)grainswithaparticlesizeof1～2Λmormore,0105～1Λmarepseudo-singledomain(PSD)grains,andthegrainsaboveandbelow0105Λmhavesingledomain(SSD)properties.Itischaracterizedbyfineviscous(FV)around0102Λm,andsuperparamagnetic(SP)grainsbelow01001～0101Λm.Throughthecomprehensivetestandcomparisoncalculationofmagneticparameters,thecompositionanddifferenceofferromagneticgrainscanbedistinguished.Forexample,thecombinationofnon-hysteresisremanenceARM?XandsoftisothermalremanenceIRMS?Xcandeterminetheexistenceandcontentofstablesingledomain(SSD)magnetite,whileIRMS?ARMcanunderstandthemulti-domain(MD)compositionofmagnetsinthesample.Ferromagneticminerals(suchasmagnetite,maghemite,pyrrhotite,etc.)andincompleteantiferromagneticminerals(suchashematite,goethite,etc.)Typesofminerals.Ferrimagneticmineralsgenerallycanobtainmorethan95%ofsaturatedisothermalremanenceafterbeingmagnetizedbyamagneticfieldlessthan011T,andtheircoercivityisalsolow,magnetiteisabout20mT;incompleteantiferromagneticmineralsneedtobe4~Aftermagnetizationinastrongmagneticfieldof7T,saturationremanencecanbeobtained.Softisothermalremanence.
Developmenthistory
Intheearly1970s,BritishenvironmentalecologistProfessorF1OldfieldandPhDR1Thompson,whilestudyingLoughNeaghLakeinNorthernIreland,discoveredalakesedimentsamplecoreThemagneticsusceptibilitycurvecoincideswiththetypeofspore-pollencombination,anditisrealizedthatitispossibletoextracthigh-resolutionenvironmentalchangeinformationthroughthemagneticmeasurementofnon-naturalremanenceoflakesediments,combinedwithbiochemicalindicators.Afterwards,thelong-termcooperativeresearchbetweenF1OldfieldandR1Thompsonandtheresearchofotherpioneerslaidthefoundationforthisnewdiscipline.Sincethe1980s,withthedevelopmentofelectronictechnologyandcomputerscience,theadventofhigh-sensitivitymagneticmeasuringinstrumentsusedinthefieldandlaboratoryhasgreatlyimprovedtheaccuracyandresolutionofmagneticmeasurement,formingacompletesetoffieldmagneticsurveysandsamples.Theworkingproceduresofcoremagneticscanning,laboratorywholesamplemagneticmeasurementandparticlesizecomponentmagneticmeasurement.Becausemagneticmeasurementhastheadvantagesofsimplicity,speed,economy,non-destructivenessandversatility,ithasattractedtheattentionofmanyscientistsintheworld.
Comprehensiveapplication
Comprehensiveapplicationofgeology,magnetism,geography,ecology,hydrology,meteorology,glaciology,archaeology,limnology,oceanographyandotherdisciplinesKnowledge,researchenvironmentalissues.Inshort,environmentalmagnetismstudiesthemagneticpropertiesofsubstancesintheenvironmentanditsrelationshipwithenvironmentalissues.
Otherapplications
ApplicationofEnvironmentalMagnetisminGeographicalEnvironmentResearch
EnvironmentalMagnetismSinceitsRiseinthe1970sIthasbeenpaidattentiontointheenvironmentalresearchofmanycountriesandregionsinEurope,Australia,NorthAmerica,SouthAsiaandNorthAfrica,anditsapplicationfieldshaveexpandedrapidly.Thestudyofenvironmentalmagnetismhasspreadallovertheworld'smajorclimatezonesandgeologicalandlithologicalregions,involvingdifferenttypesoflakes,swamps,riversandmarineenvironmentalsystems.Theobjectsofmagneticmeasurementincludenotonlythesedimentcoresofoceansandlakes,thesuspensionorbedloadofrivers,butalsosoilprofiles,loessprofilesequences,atmosphericdust,moraines,rockcoresandicecoresindifferentregions.Applicationareasareextendedtoregionalandglobalchangeresearch,regionalenvironmentalpollutionmonitoringandpollutionhistoryresearch,watershederosionandsedimentationresearch,researchontheimpactofhumanactivitiesonthegeographicalenvironment,environmentalarchaeology,petroleumexploration,etc.
Studyonlakesedimentstorestorethepaleogeographicenvironmentofthebasin.Thesourcesoflakesedimentsarediverse.Becausematerialsfromvarioussourceshavedifferentmagneticcharacteristics,theyretaintheoriginalMagnetism,sothemagneticchangepatternofthelakesedimentarysequencecancomprehensivelyreflectthesourceandproportionofsedimentarymaterials.
Indicativestudiesofenvironmentaleventshaveshownthatinacontinuousnormallakesedimentationsequence,theremaybeoneormorelayersofextremelyabnormalmagneticsedimentarylayers,whichoftenindicatecertainenvironmentsinthewatershedoradjacentareas.event.Forexample,forestandgrasslandfireswillleadtoasignificantincreaseinthemagnetismofthetopsoillayer.Thesematerialsarebroughtintothelakebyrunoff,leavingthe"trace"ofthefireeventinthesedimentarysequence.F1Oldfieldetal.identifiedfourvolcaniceruptionsonthePapuaNewGuineaplateauthroughmagneticmeasurement.InthestudyoflakesedimentsinXinghua,northernJiangsu,YuLizhongrevealedhistoricalfloodeventsfromthemagneticanomaliesofthesediments,whichwereconfirmedbyrelatedstudies.
Analysisofwatershedenvironmentalchanges,usingthemagneticinformationoflakesediments,canrevealtheprocessandmechanismofwatershedenvironmentalchanges.StudiesonthemagneticpropertiesofthesedimentsinDianchiLake,Yunnan,Chinahaveshownthatinareaswithstableforestvegetationcoverage,climatechangescanstillbereflectedinthemagneticcharacteristicsoflakesediments.WuRuijinbelievesthatthemagneticsusceptibilityandfrequencymagneticsusceptibilityoflakesedimentscanbeusedassensitiveindirectindicatorstoreflectthepaleoclimateandpaleoenvironmentalchanges.HuShouyunandotherspointedoutthatthemagneticsusceptibilitycanbeusedasaproxyindicatortoreflectenvironmentalchanges.Thehigh(low)frequencymagneticsusceptibilitycorrespondinglyindicatesahumid(arid)climateandahigher(low)lakesurface.ZhangZhenkeandothersbelievethatthehighfrequencymagneticsusceptibilitysectionoftheinlandclosedlakesedimentsinthehistoricalperiodindicatesthehumidstageoftheclimate;thelowvaluesectionindicatestheclimaticdroughtstage;YuLizhong’sresearchontheenvironmentalmagnetismofthesedimentsinTaihuLakerevealsthattheclimatechangeTheriseandfalloftheTaihuLake'swaterlevelcausedbyrotation.J1Dearingetal.'senvironmentalmagneticstudyinPerisLakenotonlyfoundthelossoftopsoilduetoovergrazing,butalsoexplainedthehistoricalprocessoflandusechangeinthewatershed.YuLizhongproposedaquantitativeanalysismethodthatusesthemagneticinformationoflakesedimentstoidentifythesourceofmaterials,andhasbeensuccessfullyappliedtowatershedenvironmentalresearch.
ResearchonsoilformationandsoilclassificationSoilmagnetismisanewresearchfieldestablishedinthelate1970s.Thebasicprincipleisthatironinthesoilcanchangethevalencestateandformenvironmentally-relatedKindofoxidationphaseorwithothercomponentsinthesoiltoformcomplexes.Thestateofironcompoundsinthesoiloftenindicatesthesoilmoisturestatus,formationprocessandsoiltype.Themagneticmeasurementsofvarioussoilsshowthatthereisaclearrelationshipbetweensoilenvironmentaltypesandmagneticproperties.Thetaskofsoilmagnetismistoconductroutineexplorationanddescriptionofsoilprofiles;studytheformationprocessofsoil,classifyandlayersoil,andidentifydifferentsoilformationprocesses.Theapplicationofsoilmagnetisminthefutureincludesseveralaspects:basicsoilmagnetism,oxideandoccurrenceresearch,soilgeography,soilsurvey,soilmagneticimprovement,soilstructureresearch,soilerosionstatus,etc.
Studyonloess-paleosoilsequencetoexplorethelawsofpaleoclimatechange.Themagneticsusceptibilitycurvehasbeenusedtoestablishthecorrespondinglayerconnectionofloessprofilesindifferentregions,andcomparethepaleoclimateextractedfromdeep-seasedimentsandpolaricecores.Evolveinformationtorevealthelawsofglobalpaleo-climatechanges.Thereasonwhythemagneticsusceptibilityofloesscanwellreflectclimatechangeisthatinalargerange,itcanbeconsideredthatthesedimentaryenvironmentofloessdoesnotchangemuch,andthelevelofmagneticsusceptibilityismainlydeterminedbysoilformationandtheamountoffinemagneticmaterialsproduced.Throughthemeasurementofthemagneticsusceptibilityfrequencycoefficientandothermagneticparametersoftheloessprofile,aswellasthecomparativestudyofthemagneticcharacteristicsoftheloessandpaleosolofeachgrainsize,ithasbeenrecognizedthatthesizecompositionandcombinationofferromagneticcrystalgrainsintheloessandpaleosolexist.Theobviousdifferencereflectstheimportantinfluenceofthestrengthofsoilformationonthemagneticdifferenceofloessprofileunderdifferentclimaticconditions.FriedrichHelleretal.studiedtheLuochuanloessinShaanxiProvinceandpointedoutthattheintensitychangesofnaturalremanence(NRM)andmagneticsusceptibilityareindicativeofclimatechangeduringthedepositionofloess.Alargenumberofstudieshaveshownthattheclimateisdryandcoldduringtheaccumulationofloess,warmandwetduringtheformationofpaleosol,themagneticsusceptibilityofloessislow,andthemagneticsusceptibilityofpaleosolishigh.
EnvironmentalpollutionresearchEnvironmentalmagnetismmainlymonitorsmodernenvironmentalpollution,reconstructionofpollutionhistory,andpollutionintypicalareas.AccordingtodatafromJohnDearing,magneticmeasurementshavebeenusedtoidentifyparticulatematterreleasedfromfossilfuelcombustion,automobiles,surfacebuildingmaterials,steelmanufacturing,andothermetalsmelting.Basedonthemagneticanalysisoflakeandreservoirsediments,peatswamps,andevenorganiclitter,manystudieshavereconstructedthehistoryofairpollution.T1M1WilliamsusesthemagneticsusceptibilitycurvetocomparethechemicalanalysisofheavymetalsinthesedimentsandthedataofcoalcombustioninEuropesince1820,andconcludesthatthelow-frequencymagneticsusceptibility(xlf)ishighlycorrelatedwithPb,ZnandCu(correlationcoefficientisabout018),andisrelatedtohistoryTheconclusionthattheEuropeancoalconsumptionhasthesametrend.BeckwithP1R1,etc.completedthestudyoftherelationshipbetweenheavymetalsandmagnetisminsedimentsfromurbansources.F1Oldfieldetal.'sstudyontheFinnishpeatprofilepointedoutthattheatmosphericpollutionfalloutofmagneticparticlesacceleratedfrom1860(approximatelythebeginningoftheIndustrialRevolution)andreachedapeakaftertheSecondWorldWar.Thisworkprovidesausefulwayforthestudyofenvironmentalmagnetismofparticulatematterairpollution.ThestudyonthemagneticpropertiesoftidalflatsedimentsintheYangtzeEstuaryindicatedthatthemagneticparametervaluesofthesedimentsarerelatedtothecontentofheavymetalelementsandarerelatedtothegrainsizecomposition.Magneticmeasurementcanprovideeffectivemeansandimportantbasisforenvironmentalmonitoringoflargecitiesandtheirneighboringestuariesandcoasts.
Existingproblems
Mainproblemsinenvironmentalmagnetism
EnvironmentalmagnetismreliesontheinternalorderofnaturalsystemstounderstandtheenvironmentThenewmethodhasreceivedwideattention.However,duetothevastdifferenceingeographicalenvironment,thesensitivityofmagneticmineralstoenvironmentalchanges,theambiguityintheinterpretationofmagneticparameters,etc.,therearestillsomeproblemsinenvironmentalmagnetism,suchasthecontributionofmagneticparameterstodifferentparticlesizesandtypesofmagneticminerals.Thereisstillalotofworktobedoneintermsofmigrationandtransformationintheenvironment,quantificationofmagneticinformationanddatabaseconstruction.Practicehasprovedthatenvironmentalmagnetismisasubjectfullofvitalityandbroadapplicationprospects.
Developmenttrend
Developmenttrendofenvironmentalmagnetism
Thereareseveralnewdevelopmenttrendsofenvironmentalmagnetism.First,moreattentionwaspaidtomechanismresearch.LuGaoetal.conductedmagneticmeasurementandX-raydiffractionanalysisonthesoildevelopedonbasaltinYunnanandZhejiang,andanalyzedthemechanismofsoilmagneticsusceptibilityfromtheperspectiveofferromagneticironoxidemineralogy.ZhuLijunandothersusedavarietyofadvancedanalysisandobservationmethodstostudytheformationmechanismofmagneticmineralsincarbonaterock-developedsoils.A1J1WheelerandF1Oldfieldetal.studiedtheprocessesthataffectthemagneticgenerationandmaintenanceofsedimentsonthenorthwestcoastofIreland,andpointedoutthatbiologicalprocessesanddiageneticprocesseshaveastronginfluenceonthemaintenanceofmagneticrecords.DongRuibinstudiedthemagneticstabilityofredsoilunderthereductioneffectfromthemechanism,andquantifiedtherelationshipbetweentheinfluencingfactors.Secondly,itisappliedtothedirectionofproductionpractice.ZhangWeiguo,YuLizhong[44]showedthatthemagneticmeasurementofthesurfacesedimentsoftheEastChinaSeashelfshowsthatmagneticmeasurementcanbeusedasanindirectmeansofoilandgasexploration.Heavymetalpollutionisalsoanimportantapplicationarea.H1Yangetal.'sresearchonWuhanEastLake,ZhangWeiguoandYuLizhong'sresearchontidalflatsedimentsonthesouthbankoftheYangtzeRiverEstuary,S1M1Hutchinson,andL1Yu'sresearchonheavymetalpollutionintheYangtzeRiverestuarytidalflat,indicatetheapplicationofenvironmentalmagnetismTheresearchonheavymetalpollutionisofgreatsignificance.Third,quantificationisasubjectrequirementofenvironmentalmagnetism,andithasbecomeoneoftheresearchtrends.YuLizhongdidalotofworkinthisarea,andDongRuibinalsoappliedquantitativemethodsinhiswork.WangJianetal.establishedaregressionequationbetweenthemagneticsusceptibilityandthepercentageofmagnetite.Fourth,lakeanddeep-seasedimentresearchisoneoftheeffectivemethodstoapplymagneticsurveytechnologytostudyregionalclimatechangesandevenglobalenvironmentalchanges.TheworkofSunZhimingandWangHuizhong[51]isrepresentative.Finally,thecombinationofenvironmentalmagnetismandmulti-disciplinaryanalysisandtestingtechnology.Inthisregard,A1J1Platerandothersusegeochemistryandradionuclides,combinedwithmagneticmeasurementtostudypollutionintheestuaryarea,whichisoftypicalsignificance.