During the last decades, advances in the field of speleothem’s magnetism opened a new door to investigate high-resolution and short-lived features of the Earth’s magnetic field. Due to the rapid precipitation of calcite/aragonite, the lock-in time of the detrital remanent magnetization resulting from the physical alignment of the magnetic minerals parallel to the Earth’s magnetic field is acquired almost instantaneously. The magnetic particles trapped into the speleothem usually originate from the soils capping the cave and are transported into the cave by dripwaters. Authigenic magnetic particles may also precipitate under conditions likely to prevail during speleothem growth. Here we investigate the magnetic mineralogy of a stalagmite from the Gruta da Ceramica of Central Portugal. We also analyzed the host carbonate, the cave sediments and the soils capping the cave. We measured concentration- and grainsize-dependent magnetic proxies, including natural remanent magnetization, anhysteretic remanent magnetization, isothermal remanent magnetization, mass specific magnetic susceptibility, FORC and hysteresis curves.  Results show that magnetic and hematite are the main magnetic carriers in all samples. A gradual enrichment of hematite relative to magnetite is observed following the transportation path from the soils to the cave sediments up to the stalagmite. The higher contribution of hematite relative to magnetite in the speleothem may reflect precipitation of authentic hematite during speleothem growth or the selective transport of finer particles from the soil to the cave.  

Acknowledgments: This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (refs. PTDC/CTA-GEO/0125/2021), (PIDDAC) – UIDB/50019/2020, UIDP/50019/2020 and LA/P/0068/2020

How to cite: Font, E., Brás, A. R., Feinberg, J., Egli, R., Reboleira, A. S., Melo, R., and Fonseca, P.: Selective transport and deposition of magnetic particles during speleothem growth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20274, https://doi.org/10.5194/egusphere-egu24-20274, 2024.

Magnetic properties from marine sediment cores, combined with other proxies, make it possible to study climatic variations. The type, concentration and grain size of magnetic minerals can be used as proxies of precipitation and deep oceanic circulation changes.  

In this study, we focus on core MD01-2385 retrieved on the northwest margin of Papua-New Guinea, in the western equatorial Pacific Ocean. This area is located in the Indo-Pacific Warm Pool (IPWP), which is a major source of heat and moisture to the atmosphere and plays an important role on global climate. The western Indo-Pacific climate is complex, being affected by the El Nino-Southern Oscillation (ENSO) and the Australian-Indonesian monsoon.

Core MD01-2385 was dated using ¹⁴C. The studied interval covers the last 40 ka with an average sedimentation rate of 30 cm/ka. We took samples every 2 cm (time resolution ~ 70 years). Magnetic granulometry proxies (ARM/SIRM and Karm/K) show a gradual decrease in grain size from the last glacial-interglacial transition (~17 ka) before a stabilization with fine grains from 8 ka. The records show variations associated with Heinrich events and the Younger Dryas. In the ~40 to 13 ka interval, the ARM/SIRM ratio is correlated with the d18O curve from EPICA-EDML ice cores (Antartica), whereas over the last 13 ka the ARM/SIRM ratio appears correlated to d18O curve of the NGRIP ice cores (Greenland).This observation suggests a stronger climatic influence of the Southern Hemisphere than the Northern Hemisphere in this region from 40 to 13 ka, followed since 13 ka by a period in which remote climatic influences originate from northern high latitudes.

Our magnetic results were combined with geochemical analyses carried out by Yu et al. (2023) on the same core (Rb/Sr ratio, chemical index of alteration (CIA), and the smectite/(illite + chlorite) ratio). These data indicate that heinrichs events (HS) are associated, in this region, with lower precipitation (Yu et al., 2023) and also correspond to lower magnetic concentrations, suggesting a dominant physical weathering in northwest Papua-New Guinea.

An interval with coarse magnetic grains and glass shards was dated at ~ 25 ka, suggesting the recording of a volcanic eruption during HS2. It could be the Oruanui supereruption from Taupo volcano, in New Zealand, dated at ~25.5 ka.

How to cite: Dauchy-Tric, L., Carlut, J., Bassinot, F., Meynadier, L., and Valet, J.-P.: Magnetic response of marine sediments to climate variations over the last 40 ka in the western equatorial Pacific., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20050, https://doi.org/10.5194/egusphere-egu24-20050, 2024.

A correlation between Earth’s magnetic field and climate change has been debated for over forty years, despite significant ~100- and ~41-kyr periods in both the stacked relative paleointensity and inclination records. In this paper, we construct a master relative intensity curve (SPIS-150) over the past ~150 kyr by stacking the data from one new core (PC27) with published intensity curves for the northern South China Sea. Additionally, we calculate the Dole effect from the sea surface temperature (SST) and d¹⁸O of planktonic foraminifera based on two cores, PC83 and PC27, and use it as a precipitation proxy. The results of this study show that geomagnetic field intensity lows are related to rich rainfall. During the ~23 kyr period, the relative intensity shows in-phase variations with simulating 0-30°N terrestrial precipitation, which shows that the superimposed effect of insolation and geomagnetic fields influences low-latitude precipitation. The strong summer monsoon predominated by insolation carries rich water vapor, which forms low cloud cover under one cloud-formation physical process where the geomagnetic field modulates galactic cosmic rays (GCRs) and leads to aerosol-related cloud condensation nuclei (CCN) formation. Deeper cloud cover produces strong rainfall in low-latitude regions.

How to cite: Yang, X.: Are there any links between geomagnetic field variations and hydrological cycles in the South China Sea since the Late Pleistocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2855, https://doi.org/10.5194/egusphere-egu24-2855, 2024.

The Guadalupian-Lopingian boundary (GLB) interval is characterized by the Pangea breakup, dramatic sea-level change, Emeishan Basalt volcanism, and biotic turnover. We conducted magnetostratigraphic, mineralogical, and calcite U-Pb geochronological studies at the Penglaitan Global Stratotype Section and Point section in South China. Rock-magnetic results indicate that magnetite and rare hematite are the dominant remanence carriers. After removing the viscous remanent magnetization, three components were isolated from the limestone at the Penglaitan section. The high-temperature remanence components were isolated from the tuffaceous limestone and yielded a mean direction of D_s/I_s = 195.3°/+5.6° (α_95s = 5.3°, k_s = 22.8, n = 34) after tilt correction. It defined a reversed magnetozone from the top of conodont Jinogondolella granti Zone to the lower part of the Clarkina. dukouensis Zone, straddling the GLB. Additionally, intermediate-temperature components represent the Jurassic and Triassic remagnetization, also supported by the in-situ calcite U-Pb dating (~133-166 Ma and ~213-224 Ma), pyrite-to-magnetite alteration, or magnetite oxidization to maghemite and hematite. The new paleomagnetic results and calcite U-Pb dating provide new insights into Mesozoic multi-remagnetization in the South China Block and refine the GLB positioned in a reversed magnetozone.

How to cite: Zhang, M., Qin, H., Deng, C., Shen, S., and Pan, Y.: Paleomagnetism and calcite U-Pb geochronology from the Penglaitan GSSP section, South China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3158, https://doi.org/10.5194/egusphere-egu24-3158, 2024.

Time-series analysis of high-resolution rock magnetic data from deep-sea marine sediments (piston core GP03, Alboran Sea, Westernmost Mediterranean), spanning the last 40.000 years, has been performed to reveal paleoenvironmental cyclicities and climate variability in this region during the uppermost Pleistocene and Holocene. We have applied both the classical Fast Fourier Transform (FFT), after regularizing our data by linear interpolation, and the Lomb-Scargle periodogram, which is well suited to analyze non-regular time series, as is the case. In addition to the usual Lomb-Scargle periodogram, we have also tested a modification of the periodogram that takes into account the experimental errors of the analyzed parameters. Also, in addition to the power spectrum and its peak spectral frequencies/periods, we have computed the Achieved Confidence Level (or false positive rate) of the different spectral peaks by a Monte Carlo evaluation of the permutation test, restricting our further analysis to those spectral peaks with Achieved Confidence Levels greater than 95%. The obtained results through these different approaches show a high degree of coherency, proving the reliability not only of the methods, but also of the modifications introduced and of the obtained results. Our results highlight the presence of characteristic cyclicities with periods in the range of 1600-4500 years during the last glaciation, especially between 25 and 38 ka. The most intense spectral peak has a period around 2 ka, which is consistent with the characteristic periods of Dansgaard-Oeschger (D-O) climate fluctuations. This strong 2 ka signal is clearly arising from the observed match between high magnetic susceptibility and saturation remanent magnetization values with D-O warm phases (interstadials). These relative maxima in magnetic mineral abundance are correlated with high S-ratio values, pointing to an increase in magnetite vs. hematite abundance in the sediments. Conversely, cold D-O phases (stadials) seem to be related to low susceptibility, low saturation remanence and lower S-ratio, indicating a decrease in the contribution of low coercivity phases (like magnetite) and an increase in the relative importance of high coercivity phases like hematite. We suggest this is connected with variations in the relative importance of riverine vs. aeolian terrigenous input. In contrast, Holocene rock magnetic data do not show this 2 ka peak, but instead cyclicities with periods around 2800, 3800 and 5500 years are recognized. To our knowledge, this is the first report of such a remarkable relationship between marine sedimentary rock magnetic data and paleoclimatic cyclicities in the frequency range of the Dansgaard-Oeschger or stadial-interstadial events in the Western Mediterranean over the last glaciation, pointing to the interest of further rock magnetic studies.

How to cite: Beltrán de Heredia García-Nieto, S., Villasante Marcos, V., Martínez Ruiz, F., Casanova Arenillas, S., and Rodríguez Tovar, F. J.: Time-series analysis of rock magnetic data from sediments spanning the last 40.000 years in the Western Mediterranean: strong paleoenvironmental cyclicities during the last glaciation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5451, https://doi.org/10.5194/egusphere-egu24-5451, 2024.

      In the study, we present the rock magnetic property from three sediment cores collected by the R/V Marion Dufresne (MD) during the cruise MD214 off SW Taiwan, and two of these cores, MD18-3542 and MS18-3543, have collected shallow hydrate samples. Core site MD18-3542 is on the South Yuan-An East Ridge, where an unconformity covered by fine-silt sediments lies at ~5.5 m below the seafloor, and the core site MD18-3543 is close to the Good-Weather Ridge with a gas-related pockmark and authigenic carbonates near shallow strata. The other core MD18-3548 was obtained at a basin with relatively stable deposition settings to get the background information. Rock magnetic measurements, including magnetic susceptibility (MS) and hysteresis parameters, are used to describe the downcore variations of the magnetic features, while the Day Plot and XRD analysis are applied to classify and identify the dominance of core magnetic components. Both cores MD18-3542 and MD18-3543 show the attractive anomaly with dramatic value-drop in the records of MS and hysteresis parameters, and the feature looks absent in the core MD18-3548. Such signature may link to the pyritization caused by the gas hydrate dissociation. The dissociated methane with hydrogen sulfide trapped under the structures (an unconformity at site MD18-3542 and authigenic carbonates at site MD18-3543) would form an anoxic setting and activate the pyritization at shallow layers. Detrital magnetite would be gradually turned into authigenic iron sulfides, and thus could cause the attractive anomaly in the MS and hysteresis records.

How to cite: Huang, Y.-S., Horng, C.-S., Su, C.-C., Hsu, S.-K., Doo, W.-B., and Lin, J.-Y.: Rock magnetic anomaly caused by the pyritization linking to the gas hydrate dissociation off SW Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5780, https://doi.org/10.5194/egusphere-egu24-5780, 2024.

In this research, we revealed the findings from rock magnetic analyses, including Isothermal Remanent Magnetization (IRM) and High-Temperature Susceptibility (HTS), conducted on various volcanic and sedimentary rocks from the Early Jurassic – Middle Eocene located in the Eastern Pontides. These magnetic studies offer valuable insights into the minerals causing magnetization, as well as the composition and changes in magnetic minerals within these rocks. The experiments were carried out at the Doç.Dr. Yılmaz İspir Paleomagnetism Laboratory, Istanbul University-Cerrahpaşa.

For the Isothermal Remanent Magnetization (IRM) studies, samples were collected from 57 sites in the Eastern Pontides, ensuring representation of each rock type. The analysis revealed that “Hematite”, “Magnetite”, and a combination of “Hematite + Magnetite” are the minerals responsible for magnetization in the selected samples. Moreover, it was discovered that in 41 out of the 57 sites, the samples reached saturation magnetization, indicating that "Magnetite" is the predominant mineral responsible for magnetization. The magnetic susceptibility of the rocks was examined during the heating and cooling stages in these high-temperature susceptibility measurements. High-temperature susceptibility measurements were used to assess whether the minerals responsible for magnetization in the rocks underwent any changes due to temperature, to determine the Curie temperatures, and to understand the domain structure. For this aspect of the study, 23 sites representing various ages and types of rocks were chosen for high-temperature susceptibility studies. It can be said that some rocks are rich in "Ti-Magnetite". It is observed that mineral phase transformation occurs in some rocks as a result of heating phases.

This study was supported by the project of the Scientific Research Projects Commission of Gümüşhane University with Project Number: 21.B0126.01.01.

How to cite: Algur, B. S., Kayın, S., Dokuz, A., Hisarlı, Z. M., and İşseven, T.: Rock Magnetic Studies of The Early Jurassic Middle Eocene Volcanic and Sedimentary Rocks of the Eastern Pontides, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15097, https://doi.org/10.5194/egusphere-egu24-15097, 2024.

Speleothem are excellent recorders of the Earth’s magnetic field and climate variation. The nature and origin of the magnetic minerals trapped into the calcite laminae are controlled by climate and environmental processes acting on the surface soils and inside the cave.

In this work, we analysed samples from a stalagmite from Cueva Mayor in the archaeological site of Atapuerca (Burgos, Spain). Cueva Mayor site hosts a very important record of Pleistocene human occupation. Finding speleothems that record signs of human activity is unusual. However, in the karst system of the Sierra de Atapuerca, different works on speleothems revealed a significant human fossil record. The stalagmite studied has a small size, the sampled section measures 10 cm from base to top and is not oriented. It shows a calcite laminae alternation with darker micritic and/or ash-rich laminae, composed of aggregates of soot/smoke in the last 2.7 cm to the top. These black soot laminae are interpreted as derived from anthropogenic fires. The remaining part the stalagmite is a sequence of whitish and brownish laminae. A high detrital fraction is inferred from the brown layers. Available U-Th age data on a nearby stalagmite indicate that they grew during the last 14 kyr approximately.

In order to characterize the magnetic properties in a stalagmite of special interest considering its record of human activity, we have carried out experiments on paleomagnetism, rock magnetism, and anisotropy of magnetic susceptibility. We obtained paleomagnetic directions for most samples of calcite laminae with high detrital content and laminae with soot by alternating field demagnetization. Isothermal remanent magnetization acquisition curves of and hysteresis cycles show the presence of low coercivity ferromagnetic minerals in the soot-bearing samples, while the magnetization intensity in the rest of the samples is too weak to show clear results. The thermomagnetic curves reveal magnetite in both brownish-white and soot-containing samples. Other very low Curie temperature magnetic phases also appear in the soot samples. Finally, AMS shows a triaxial magnetic fabric with magnetic foliation pseudo-parallel to the calcite lamellae and horizontal lineation.

Acknowledgments: This work was funded by the Agencia Estatal de Investigación (España) (PID2019-105796GB-100), the postdoctoral program María Zambrano 2021 (España), the Junta de Castilla y León (España) (project BU037P23) and the Fundação para a Ciência e a Tecnologia (Portugal) (PTDC/CTA-GEO/0125/2021).

How to cite: Sánchez-Moreno, E. M., Iriarte, E., Calvo-Rathert, M., Font, E., Bógalo, M.-F., and Carrancho, Á.: Preliminary results of paleomagnetism, rock magnetism and AMS in a soot-layered speleothem from Cueva Mayor (Atapuerca, Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19599, https://doi.org/10.5194/egusphere-egu24-19599, 2024.

The East Asian Winter Monsoon (EAWM) is driven by the dry and cold north-westerly winds blowing from central Asia towards the Western Pacific Ocean as atmospheric high-pressure cell develops over Siberia and Mongolia due to low continental temperatures during boreal winter. Today, the EAWM surface winds together with the prevailing mid-latitude upper troposphere westerly jet (WJ) winds transport hundreds of millions of tons of dust every year across East Asia and/or to the North Pacific and further. Various records of past EAWM and/or WJ variability are available but well-resolved records with (sub)orbital resolution to investigate the dynamics of and relationships between EAWM and WJ are rare. The Japan Sea, as the largest marginal sea located in mid-latitude East Asia, is significantly under the influence of the EAWM and WJ. Previous studies suggest that the composition, concentration, and size of magnetic particles in sediments are sensitive to changes in aeolian dust input. Here, we study the magnetic mineralogy and reconstruct high-resolution continuous environmental magnetic records spanning the last 500 kyrs using sediments cored during Integrated Ocean Drilling Program (IODP) Expedition 346 (Asian Monsoon) at Site U1424 in the Japan Sea. Our results suggest that magnetite is the dominant magnetic phase at Site U1424 and there is a significantly increased contribution of high-coercivity magnetic phase, presumably hematite transported through aeolian dust, in samples from glacial periods. Magnetic grain size proxy (k_ARM/k) of Site U1424 sediments appears to covary with the population of coarse particles (> ~14 μm) that are dominated by aeolian dust, and shows a striking similarity to published EAWM records, especially during the interglacials and glacial inceptions. During the glacial maxima, largely enhanced EAWM indicated by published records are, however, not shown in the Site U1424 k_ARM/k record. We suggest that Site U1424 k_ARM/k is a proxy for dust transportation to the Japan Sea modulated by EAWM intensity as well as interactions between EAWM and the WJ. During the interglacials and glacial inceptions when the main axis of WJ frequently reaches Northern China close to the dust source region of the EAWM, interactions between the EAWM and WJ during winter/spring at mid-level troposphere enable long-distance transportation of coarse dust particles (mainly modulated by EAWM) to the Japan Sea. During the glacial maxima, when the WJ main axis no longer frequently reaches the EAWM source regions, reduced interaction between WJ and EAWM prevented long-distance transportation of coarse dust particles. A conceptual model is also presented to summarise the consequences of changes in EAWM and WJ and their interactions over glacial and interglacial cycles at different locations along the Asian dust transportation pathway.

How to cite: Wang, J., Xuan, C., and Wilson, P.: East Asian winter monsoon variability during the last 500 thousand years recorded by environmental magnetism of sediments in the Japan Sea, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19484, https://doi.org/10.5194/egusphere-egu24-19484, 2024.