A high-resolution record of Mid- to Late-Holocene environmental changes from a land-locked lake in Schirmacher Oasis,East Antarctica

Abstract

We present a high-resolution record of environmental changes during the Mid-Late Holocene obtained from a lake sediment core covering the past 4.87 cal kyr BP in the Schirmacher Oasis, East Antarctica. The magnetic signal of Lake L6 was found to be primarily controlled by catchment-derived ferrimagnetic minerals. The period between 4.87 and 3.35 cal kyr BP is marked by several episodes of cold and warm conditions. Warm and wet conditions prevailed in the region from 3.35 to 2.43 cal kyr BP. Magnetic susceptibility values remained generally low indicating the pedogenic formation of fine magnetic grains. The high values of the chemical weathering indices reflected the warm and wet conditions conducive to chemical weathering. A transition to cold and dry conditions was observed at around 2.43 cal kyr BP, representing the Neoglacial cooling, with high values of magnetic concentration-dependent parameters. Following the Neoglacial period, a return to warm and wet conditions was observed at 1.63 cal kyr BP, coeval with the Medieval Climate Anomaly. Our record shows a Late-Holocene cooling marked by a sudden increase in magnetic susceptibility values, which could represent the Little Ice Age, followed by a shift to warmer conditions near the core top.

Keywords

chemical weathering East Antarctica high resolution lake sediments magnetic susceptibility Mid-Late Holocene

Introduction

There are different systems that record information related to past climate, viz., ice cores, marine, and lacustrine systems. The lakes can be considered “sentinels of change” (Williamson et al., 2009) or “early warning systems” (Hodgson and Smol, 2008), as they respond instantly to the variations in climate and record them in their sedimentary archives. The Holocene climate of Antarctica is marked by several prominent climate events, and such fluctuations are well documented in the sedimentary archives. The climate optimum during the Mid-Holocene, known as the Mid-Holocene Hypsithermal (MHH), was an episode of optimal climate conditions marked by high sedimentation rates and increased organic productivity (Hodgson et al., 2004). This event has been particularly well documented in the Antarctic Peninsula (AP) and coastal Antarctica (e.g. Bentley et al., 2009; Verleyen et al., 2004). This Antarctic-wide warming event was also reflected in ice-core data (Ciais et al., 1994; Masson-Delmotte et al., 2011) and marine sedimentary data (Domack et al., 1991). However, the timing of this event varies across different regions of Antarctica. MHH was observed between 4.5to 2.8 cal kyr BP in the AP (Bentley et al., 2009), at ~3.2 cal kyr BP in the Livingston Island (Björck et al., 1991) and between 4.2 and2 cal kyr BP in East Antarctica (Phartiyal, 2014; Verleyen et al., 2004, 2011; Warrier et al., 2014). Following the MHH, the onset of Neoglacial conditions was recorded around 2.05 cal kyr BP in the north-eastern AP (Čejka et al., 2020), while the Palmer Deep record places it around 3.36 cal kyr BP (Domack et al., 2001). Verleyen et al. (2011) reported the existence of Neoglacial cooling in the Larsemann Hills at ~2 cal kyr BP while in the Schirmacher Oasis, cold and dry climate at ~2.1 cal kyr BP was reported by Warrier et al. (2014). Records of climate events such as the “Medieval Climate Anomaly (MCA)” and the “Little Ice Age (LIA)” has also been observed in West Antarctica and AP (Bentley et al., 2009; Bertler et al., 2011; Lüning et al., 2019), but they are not very well reflected in records from East Antarctica and in particular, sedimentary archives. Tavernier et al. (2014) reported that Late-Holocene events such as the MCA and LIA are either absent or not well recorded in sedimentary records from East Antarctica. Further, there are no well-constrained records from the Schirmacher Oasis representing the Late-Holocene climate events due to lower age resolution. High-resolution paleoclimate records are a prerequisite to obtaining a clear representation of the Mid-Late Holocene environmental variations occurring in the region. In a previous study from Lake L6 in Schirmacher Oasis, East Antarctica, the particle size, and elemental analysis data indicated that the cold and dry conditions prevailed in the Oasis during the early to Mid-Holocene and warming conditions were reported from ~3.1 cal kyr BP continuing up to the present (Govil et al., 2016). The authors could not find evidence of any Late-Holocene climate episodes such as the Neoglacial cooling or Medieval Climate Anomaly, which may be attributed to the coarser temporal resolution. In the present study, we have carried out higher resolution studies on a sediment core from Lake L6 using multiple proxies such as environmental magnetism, inorganic geochemistry and organic carbon to gain a clear record of the response of the lake to mid to Late- Holocene climate events.

Study area

Schirmacher Oasis (SO) is a 35 km² deglaciated landmass situated in East Antarctica’s Queen Maud Land (Figure 1). It lies between Nivlisen Ice Shelf in the North and Queen Maud Land in the South. The oasis has a width of ~3.5 km and a length of around 20 km (Bhattacharya, 1987). There are 118 lakes in SO, which can be classified as epishelf, proglacial, and landlocked (Ravindra, 2001). The lakes are generally ice-free during summer and covered with ice of approximately 2 m through the winter months. SO is enclosed by the ice shelf toward the north and the East Antarctic Ice Sheet toward the southern margin. The mean annual air temperature is ~−10 ± 0.8°C (Soni et al., 2017). Mean wind speed is ~9.3 m/s during the winter months and about 6.3–7.2 m/s during the summer months (Soni et al., 2017). Precambrian crystalline terrain forms the basement of the SO, which is a fragment of the East Antarctic craton (Sengupta, 1986). The geology of SO is dominantly metamorphosed quartz of eldspathic gneisses alternating with mafic granulites, garnet-bearing leucogranite and veins of leucogneiss (Rao et al., 1997; Sengupta, 1986). Lake L6 (Lat: 70°45’21.4" S and Long: 11°35’52.6" E) (Figure 1) is landlocked located in the Schirmacher Oasis. The lake has an elevation of 70 m above the mean sea level and a water depth of ~8 m. The micro- to macro-scale landforms around the lake consist of roche moutonees, erratic boulders, glacial striations, trough-like glacial-erosives, a cirque, and a nivation niche (Richter, 1980).

Figure 1.

Geological map of Schirmacher Oasis in East Antarctica showing the location of Lake L6 (modified after Gerrish et al. (2020)).

Materials and methods

Sediment coring

During the 28th “Indian Scientific Expedition to Antarctica” (2008–09), a 94-cm-long sediment core was obtained using the percussion method from Lake L6. As the center of the lake was not accessible, the core was taken from a few meters (~50 m) from the lake’s periphery. A PVC pipe enclosed in a metallic tube was gently hammered onto the lakebed and the sediment core was retrieved. After retrieving the sediment core, it was stored at +4°C and then transported to the land-based laboratory at “National Centre for Polar and Ocean Research,” India. Prior to the measurements, the sediment core was subsampled at an interval of 1 cm and freeze dried using a FreeZone freeze-dryer.

Chronology of L6 sediments

Six radiocarbon dates were obtained for the sediment core by “Accelerated Mass Spectrometry” (AMS) on bulk sedimentary organic matter at the “Poznań Radiocarbon Laboratory,” Poland. The ¹⁴C dates (Supplemental Table S1) are calibrated to calendar years BP (cal. kyr BP) using the code Bacon (version 3.0.0; Blaauw and Christen, 2011) running on “R” (version 4.2.3), utilizing the SHCal20 calibration curve (Hogg et al., 2020). An age-depth model was created from the calibrated dates with a 95% confidence interval. The sedimentation rates between the dated samples were also calculated.

Environmental magnetism

Environmental magnetic analysis of 94 samples was performed at the “CSIR-National Institute of Oceanography,” Goa and the “National Centre for Polar and Ocean Research,” Goa as per standard protocols (Evans and Heller, 2003; Thompson and Oldfield, 1986; Walden et al., 1999). Low frequency (χ_lf = 0.47 kHz) and high frequency (χ_hf = 4.7 kHz) magnetic measurements were made on a Bartington MS2B dual frequency magnetic susceptibility meter. The magnetic parameters were converted into mass-specific values using sample density utilizing the known mass and volume. The percentage frequency-dependent magnetic susceptibility (χ_fd%) was calculated from the low and high frequency magnetic susceptibilities (Joju et al., 2023; Liu et al., 2012; Thompson and Oldfield, 1986). Anhysteretic Remanent Magnetization (ARM) was applied to the samples with a peak alternating field of 100mT superimposed with a fixed DC field of 50μT. The ARM susceptibility was determined by dividing the ARM by the strength of the DC field (Liu et al., 2012). Isothermal remanent magnetization (IRM) was applied by means of an MMPM10 pulse magnetizer. IRM was induced in steps of incrementing field intensities of 20, 100, 300, 500, and 1000mT. The remanence induced at a maximum field of 1 T was taken as the “Saturation Isothermal Remanent Magnetization” (SIRM). The remanence induced was determined on an AGICO JR-6A spinner magnetometer having a sensitivity of 2.4 × 10⁻⁶ A/m. L ratio for the samples was calculated using the equation “L ratio = (SIRM + IRM_−300mT)/(SIRM + IRM_−100mT)” (Liu et al., 2007, 2012). The inter-parametric ratios such as χ_ARM/SIRM, χ_ARM /χ_lf, SIRM/ χ_lf, IRM_20 mT/SIRM, and IRM_20 mT/ARM were calculated and plotted to interpret the magnetic properties of the studied samples (Dearing et al., 1997; Liu et al., 2012).

Geochemical analysis of sediment samples

For the inorganic geochemical studies, 47 sediment samples from the core were digested (United States Environmental Protection Agency [USEPA], 1996). Approximately 0.2 g of finely ground samples were taken for acid digestion. Five milliliter of concentrated HNO₃, 3 ml of 35% HCl, and 2 ml of 48% HF acid were added to the sediment and digested on a hotplate. After drying, the samples were made up to 25 ml with 0.2 N HNO₃ and filtered on Whatman filter paper (No. 1) to eliminate any remaining residue. The element concentrations were analyzed on an inductively coupled plasma atomic emission spectroscopy (ICP-OES; “Thermo Scientific iCAP 7000 Series”) instrument at the “Environmental Research Laboratory, Manipal Institute of Technology.” Accuracy of the analysis (RSD < 5%) was scrutinized with certified reference material BCR^®–667. Duplicate samples and check standards were placed at regular intervals to enforce the QA/QC checks.

Chemical weathering indices such as the “chemical index of alteration” (CIA; Nesbitt and Young, 1982) and “plagioclase index of alteration” (PIA; Fedo et al., 1995) were calculated for the sediment core from the element concentrations (Liu et al., 2013; Tsai et al., 2014; Wei et al., 2021). The formula for CIA is given as:

" C I A = [A l_{2} O_{3} / (A l_{2} O_{3} + C a O + N a_{2} O + K_{2} O)] * 100 "

(1)

CIA values below 50 indicate fresh rock, while values close to 100 indicate completely weathered rocks. PIA is indicative of the degree of alteration of feldspars in the samples.

" P I A = [(A l_{2} O_{3} - K_{2} O) / (\begin{array}{l} A l_{2} O_{3} + C a O + \\ N a_{2} O + K_{2} O \end{array})] * 100 "

(2)

PIA values below 50 indicate fresh rocks, while values near 100 indicate clay minerals.

The “index of compositional variation” (ICV; Cox et al., 1995) was also calculated to delineate the compositional maturity of the sediments. ICV is given as:

" I C V = (\begin{array}{l} F e_{2} O_{3} + K_{2} O + N a_{2} O + C a O + \\ M g O + M n O + T i O_{2} \end{array}) / A l_{2} O_{3} "

(3)

ICV values <1 signify compositionally mature sediments, whereas values >1 indicate compositionally immature sediments.

Loss on ignition

Approximately 1 g of the samples were taken in pre-weighed silica crucibles. The samples were oven dried at 105°C and weighed. Following this step, the crucibles were kept in a muffle furnace at 550°C for 4 h to estimate the loss-on-ignition. The samples were placed in a desiccator and weighed after cooling down to room temperature. The weight loss at 550°C (LOI₅₅₀) is proportional to the amount of organic carbon in the samples (Heiri et al., 2001).

Statistical analysis

The principal component analysis (PCA) of the multi-proxy dataset was carried out on the “paleontological statistics software package (PAST)” (Version 4.03; Hammer et al., 2001). The varimax rotation was used for the analysis. A loading factor of greater than 0.6 was kept as the cut-off to identify the significantly loaded parameters. Broken stick model (Frontier, 1976) was utilized to check for the significance of the extracted components. Broken Stick model is a useful technique to evaluate which principal components are statistically significant. The eigenvalues of the principal components are significant if they surpass the eigenvalues produced by this model (Jackson, 1993).

Results and discussion

Chronology and lithology

The L6 sediment core spans the past 4872 cal yr BP. As the reservoir correction data for Schirmacher Oasis was unavailable, it was not applied. From the obtained calibrated dates (Supplemental Table S1), an age-depth model was plotted, and the sedimentation rates were estimated (Figure 2b). The temporal resolution of the sediment core was found to be 51.83 years/cm. The sediment lithology comprises of silty clay with minor organic material between 73 and94 cm and 33 and 39 cm (Figure 2a). Sandy material with algal mats was observed between 39 and 73 cm and 33 cm to the core-top. The sedimentation rate varies between 8 and 38.46 cm/kyr, with a mean of 22.42 cm/kyr. Toward the core-bottom, between 73 and 94 cm, the sedimentation rate shows an average value of 24.27 cm/kyr. Further, between 39 and 73 cm, the average sedimentation rate is lower, around 19.86 cm/kyr. Between 33 and39 cm, the sedimentation rate remains the lowest with an average of 9.18 cm/kyr and from 33 cm to the core-top, higher sedimentation is observed with an average of 26.48 cm/kyr. Sedimentation rates were lowest between 42 and36 cm, while the highest value was recorded in the top 10 cm of the core.

Figure 2.

(a) Lithology of the sediment core; (b) Age-depth model for the Lake L6 sediment core reconstructed using BACON (version 3.0.0; Blaauw and Christeny, 2011). Based on six ¹⁴C ages, the middle best estimate for calibrated age is shown (red dotted line), and the upper and lower values are shown in the Gray band (95% confidence range; Gray dashed line). Sedimentation rate (yr/cm) is shown with probability distribution curves of calibrated ages.

Magnetic concentration

Figure 3 illustrates the down-core variations in the environmental magnetic parameters of the sediments of Lake L6. The parameter χ_lf represents the total concentration of the magnetic minerals in the sediment. The values for core L6 range from 20.44 to 390.11 × 10⁻⁸ m³ kg⁻¹ with an average (± SD) of 95.5 (±66.67) × 10⁻⁸ m³ kg⁻¹. The highest values of χ_lf are seen toward the core-bottom. Significant variations in the values of χ_lf can be seen through the core, which could be due to variations in the processes governing the supply of magnetic minerals to the lake. The parameter χ_fd reflects the intensity of pedogenic formation of magnetic minerals, while the “percentage frequency-dependent susceptibility,” χ_fd % is a semi-quantitative indicator of magnetic grains in the “superparamagnetic (SP)” size range (Dearing, 1999; Liu et al., 2012; Thompson and Oldfield, 1986). χ_fd % is responsive to the fine-grained particles around the SP/SD threshold (Worm, 1998) and can be used to identify the pedogenic SP magnetic grains, provided that the fine-grained particle assemblage consists of a wide grain size distribution spanning both SP and SD particles (Liu et al., 2012). χ_fd % values <2% indicate no SP grains; values between 2% and 10% indicate a mixed assemblage of SP and coarse grains; and values >10% signify the predominance of SP grains (Dearing et al., 1997). The values range from 0% to 12.5 %, with a mean (± SD) of 3.99 (±2.92) (Figure 3), indicating a mixed assemblage of fine and coarse grains. SP grains are fine magnetic grains that form in the catchment because of fire activity or pedogenesis (Dearing et al., 1997). Higher values of χ_fd % indicates larger concentrations of SP grains in the sediments. Since fire activity is improbable in the study area, the major mechanism behind the distribution of SP grains could be the pedogenic processes related to the chemical weathering of the soils and sediments. The formation of magnetic minerals during the process of pedogenesis have been previously reported from the soils and sediments of Schirmacher Oasis (Sedov et al., 2019; Warrier et al., 2021b, 2021c). The χ_fd % values show considerable variations throughout Lake L6 sediment core, suggesting some degree of pedogenesis occurring in the catchment. Higher values of χ_fd % signify a shift to warming conditions, providing a conducive environment for chemical weathering and the pedogenic development of SP grains. The parameter χ_ARM is reflective of the concentration of stable single domain (SSD) grains (Maher, 1988). χ_ARM values range from 4.6 to 284.1 × 10⁻⁸ m³ kg⁻¹ with a mean (± SD) of 22.54 (±35.34) × 10⁻⁸ m³ kg⁻¹ (Figure 3). χ_ARM shows a statistically significant correlation (r = 0.85, p < 0.05; n = 94) with χ_lf suggesting the control of SSD grains on the magnetic signal of core L6. The “saturation isothermal remanent magnetization” (SIRM) is representative of the concentration of the remanence-carrying magnetic minerals (Evans and Heller, 2003). The SIRM values of the studied samples lie between 7.25 and 509.76 × 10⁻⁵ A m² kg⁻¹ with a mean (± SD) 41.04 (±65.20) × 10⁻⁵ A m² kg⁻¹. SIRM also shows a significant correlation (r = 0.88, p < 0.05; n = 94; Supplemental Table S2) with χ_lf indicating the dominance of ferrimagnetic grains in core L6.

Figure 3.

Downcore variations in the environmental magnetic properties and loss-on-ignition at 550°C (LOI₅₅₀) of Lake L6 sediment core.

Magnetic mineralogy

The parameters S-ratio and HIRM reflect the magnetic mineralogy of the sediments (Liu et al., 2007, 2012). S-ratio and HIRM are semi-quantitative and further measurements such as high or low-temperature magnetic measurements, Mössbauer spectroscopy, could provide confirmation for the magnetic mineralogy. As such measurements are outside the scope of our study, we rely on the calculated ratios. S-ratio values close to one indicate that low-coercivity magnetic minerals predominate. S-ratio values for the samples are greater than 0.85, ranging between 0.86 and 1 (Figure 3), suggesting the control of magnetically soft ferrimagnets in the sediments. Hard IRM, or HIRM, signifies the proportion of high-coercivity magnetic minerals. The L-ratio values for the samples of lake L6 remain nearly constant showing only minor variations (1.0–1.21) (Supplemental Figure S2) indicating that the HIRM values are dominantly controlled by the varying concentrations of hematite (Chaparro et al., 2020; Liu et al., 2007). The HIRM values range from 7.05 to 502.85 × 10⁻⁵ A m² kg⁻¹, with an average (±sd) of 40.2 (±64.09) × 10⁻⁵ A m² kg⁻¹ (Figure 3). Comparatively higher values of HIRM are noticed for few samples that could indicate the presence of magnetically coarse minerals such as hematite. However, in the normalized IRM acquisition curves (Figure 4a), all the samples saturate at fields <300 mT, revealing the predominance of low coercivity magnetic minerals in the sediment of lake L6. IRM_20 mT or the soft component of IRM show statistically significant correlation (r = 0.94, p < 0.05; Supplemental Table S2) with χ_lf suggesting that low coercivity magnetic minerals are the primary remanence carriers. Furthermore, the biplot of SIRM versus χ_lf (Supplemental Figure S1) indicate a uniform magnetic mineralogy controlled by strongly magnetic minerals in the sediments of Lake L6. Previous studies from Schirmacher Oasis (Phartiyal, 2014; Warrier et al., 2014, 2021a) have documented the occurrence of magnetite/titanomagnetite in the lacustrine sediments of the area. These findings are consistent with our data suggesting that the magnetic signal of lake L6 is primarily generated by low-coercivity ferrimagnetic minerals with minor contributions from high-coercivity minerals.

Figure 4.

(a) Isothermal remanent magnetization (IRM) acquisition curves of the samples of Lake L6 showing the presence of magnetically “soft” minerals like magnetite/titanomagnetite; biplots of (b) χ_ARM /SIRM versus χ_lf, and (C) χ_ARM versus χ_lf (King et al., 1982).

Magnetic grain size

The ratios χ_ARM /SIRM and χ_ARM /χ_lf are proxies for magnetic particle size. Higher (or lower) values for the ratios indicate finer (or coarser) magnetic grain sizes (Oldfield, 1991). χ_ARM /SIRM ranges between 26.97 and 109.29 × 10⁻⁵mA⁻¹ with an average (± SD) of 62.89 (± 17.3) × 10⁻⁵ mA⁻¹, whereas the χ_ARM /χ_lf values vary from a minimum of 0.10 to a maximum of 0.73 with an average (± SD) of 0.21 (±0.10) (Figure 3). Both ratios show low values for majority of the samples, reflecting coarse magnetic grain sizes. The biplot of χ_ARM versus χ_lf (Figure 4C; King et al., 1982), is a semi-quantitative indicator of the magnetic grain size distribution. Most of the grains lie above the SP/SSD boundary having relatively coarse grain sizes. From all the above results, it can be observed that the sediments from Lake L6 are mostly magnetically coarse-grained with low to moderate proportions of SP grains, and they are predominantly sourced from the catchment.

Sources of magnetic minerals

The iron oxide minerals in lacustrine sediments may be primarily lithogenic. Post-deposition, the magnetic minerals could be influenced by reductive dissolution (Roberts, 2015), the formation of bacterial magnetite (Evans and Heller, 2003; Paasche et al., 2004; Snowball, 1994), anthropogenic magnetite (Chaparro et al., 2005; Liu et al., 2012), and authigenic greigite (Roberts, 1995; Snowball, 1991). In the event of reductive dissolution, fine-grained magnetic minerals may be removed, giving rise to the coarsening of the suite of magnetic minerals (Warrier et al., 2014). This will result in a sharp drop in the ratios sensitive to the magnetic particle size, χ_{ARM /SIRM} and χ_ARM /χ_lf. Such a trend was absent in the studied core, and therefore reductive dissolution could be ruled out. The same parameters, χ_ARM /SIRM and χ_ARM /χ_lf can be utilized to delineate the presence of bacterial magnetite. χ_ARM /SIRM values >200 × 10^−5mA−1 or χ_ARM /χ_lf > 40 are indicative of their presence (Oldfield, 1994). The values from the present study are well below this threshold (Figure 3), suggesting the absence of any contribution from bacterial sources in core L6. The presence of anthropogenic magnetic minerals can be discounted due to the remote location of the study area and is generally limited to the surface sediments. Moreover, anthropogenic magnetic grains are generally coarse MD grains with large values of χ_lf (Yunginger et al., 2018). The occurrence of authigenic greigite is denoted by SIRM/χ_lf values >40 × 10³ Am⁻¹ (Snowball, 1991). The highest value of SIRM/χ_lf is 1.31 × 10³Am⁻¹ (Figure 3) suggesting the absence of greigite in the core. All the above data suggest that the magnetic minerals of Lake L6 are principally sourced from the catchment, with no reductive dissolution of magnetic minerals or any contributions from bacterial magnetite or authigenic greigite.

Elemental concentration and chemical weathering

The average elemental concentration in the sediments of Lake L6 varies in the following order:Al>Fe>K>Mg>Ca>Na>Cu>Ti>Rb>Ba>Mn>Zn>Cr>B>Sr>V>Pb>Ni>Co>Zr>Cd>As. Aluminum is the most abundant element, with its concentration in the core ranging from 1.12% to 4.53% with an average (± SD) of 2.54 (±0.79%).

The downcore variation in the metal/Al ratios of the major elements has been plotted for Lake L6 (Figure 5). The ratios K/Al, Ca/Al, Fe/Al, Na/Al, and Mg/Al exhibit a statistically significant correlation among themselves (Supplemental Table S3) suggesting a similar source or process affecting their distribution. The CIA for the studied core varies between a minimum of 57.2 to a maximum of 79.3, with an average (± SD) of 67 (±5.5), revealing a moderate grade of chemical weathering in the sediments of Lake L6 (Figure 6). PIA values range between 60.4 and 91.4, with an average (± SD) of 74.0 (±1.1) also suggesting moderate alteration taking place in the lower core (Figure 6). The downcore variations in CIA and PIA show a similar trend, with higher values observed during warm and wet periods. Increasingly warming conditions could have facilitated the interaction of lake sediments with the atmosphere, leading to a higher grade of chemical weathering in the region.

Figure 5.

Downcore variations in the metal/Al ratios and magnetic susceptibility data of the Lake L6 sediment core.

Figure 6.

Downcore variations in the geochemical ratios plotted alongside χ_lf.

Al2O3-(CaO+Na₂O)-K₂O (A-CN-K) ternary plot has been plotted for the sediment samples of Lake L6 (Figure 7a). In the diagram, the samples plotted in the upper central region indicate dominant control of Al in the sediment distribution suggesting that the sediment influx is from the quartzofelspathic rocks found in the catchment. The samples can be seen plotting parallel to the smectite line, suggesting moderate grade of chemical weathering but incomplete alteration to clay minerals in the region. The intensity of chemical weathering was not high enough for the complete alteration of clay minerals. This observation is also supported by the values of CIA and PIA. All the samples display a similar weathering trend and plot parallel to the A-CN line. ICV values for all the studied samples remain >1 (Figure 7c), suggesting that the sediments of Lake L6 are compositionally immature and are undergoing progressive weathering. Srivastava et al. (2013) also reported high ICV values between 1.2 and 2.1 in the study area, indicating immature source rock. The ICV values have been plotted against CIA to give a better understanding of the weathering intensity. In the plot, most samples lie in the region of weak weathering; few samples show a higher degree of weathering. These samples correspond to the Mid-Holocene period. Higher degrees of chemical weathering observed during this interval point toward the existence of several episodes of warming conditions during the Mid-Holocene period. Warmer conditions recorded during this period could have provided a conducive environment for stronger chemical weathering in the region. In the biplot of TiO₂ versus Al₂O₃ (Figure 7b), the sediments of Lake L6 lie in a border region of intermediate and felsic rock fields, in agreement with the local geology indicating that the sediments are sourced from the catchment rocks. Even though mafic rocks are present toward the eastern side of the lake, their influence is not reflected in the sediments of Lake L6, which is evident from the TiO₂ versus Al₂O₃ plot. From the above results, the sediments of Lake L6 have a uniform provenance and that most of the sediments are derived from the weathering of the catchment rocks. The percentage of organic carbon (LOI₅₅₀) varies from a minimum of 3.4% to a maximum of 46.3% (Figure 3). Highest values of LOI₅₅₀ are recorded during warmer periods with warm and wet conditions favorable for higher organic productivity (open lake conditions). The ratio Mn/Fe can be used as an indicator to identify the paleoredox conditions, while V/(V + Ni) is a ratio of oxygenation (Davison, 1993; Hatch and Leventhal, 1992). Lower values of the Mn/Fe ratio indicate increasingly anoxic conditions (Naeher et al., 2013). V/(V + Ni) values between 0.46 and 0.60 represent a dysoxic water column, and values ranging between 0.54 and 0.82 represent anoxic conditions (Hatch and Leventhal, 1992). V/(V + Ni) show an average value of 0.59, while Mn/Fe show a mean value of 0.01 (Figure 6).

Figure 7.

(a) Ternary plot of Al₂O₃ - (CaO + Na₂O) - K₂O (in the text A-CN-K); biplots of (b) TiO₂ versus Al₂O₃ and (c) index of compositional variation (ICV) versus Chemical index of alteration (CIA).

Principal component analysis (PCA)

PCA for the multi-proxy dataset (environmental magnetic, inorganic geochemistry, and organic carbon) was carried out to identify the influence of paleoclimate on the environmental magnetic and elemental data of Lake L6. When the broken stick model (Frontier, 1976) was applied, four components (PC1 to PC4) were found to be significant. These components account for 70.29% of the total variance (Table 1). 35.14% of the total variance is accounted for by the first component, PC1. Ba/Al, Ca/Al, Cd/Al, Co/Al, Cr/Al, Fe/Al, K/Al, Mg/Al, Mn/Al, Ni/Al, Zr/Al, V/Al, and Ti/Al along with LOI₅₅₀ show high positive loadings (>0.6) in PC1. This component is controlled by the lithogenic elements and therefore could be termed as “terrigenous input.” The component PC2 explains 15.14% of the total variance. Only Mn/Al show significant positive loading in PC2. As manganese is sensitive to redox conditions (Sunda et al., 1983), PC2 could be termed as the “redox component.” PC3 accounts for 12.25% of the total variance. The parameters χ_lf, χ_ARM, HIRM, and χ_ARM /χ_lf show significant positive loadings in PC3. PC3 could represent the “aeolian-transported hematite grains.” The component PC4 accounts for 7.76% of the total variance. But none of the parameters show significant positive loadings in PC4. Therefore, PC4 is not considered for further interpretation.

Table 1.

Loading data along with variance for the significant principal components. Significant components have been highlighted in bold.

	PC 1	PC 2	PC 3	PC 4
χ_lf	−0.57	0.33	0.63	0.24
χ_fd	−0.01	0.29	0.42	−0.39
χ_fd %	0.47	−0.05	0.19	−0.54
χ_ARM	−0.45	0.15	0.73	0.41
χ_ARM /SIRM	0.19	−0.30	0.07	−0.02
χ_ARM /χ_lf	−0.21	−0.22	0.63	0.50
HIRM	−0.46	0.18	0.73	0.39
S-ratio	−0.03	0.32	0.09	−0.19
As/Al	0.23	−0.70	0.17	−0.35
B/Al	0.35	−0.58	0.02	0.44
Ba/Al	0.63	−0.59	0.04	0.30
Ca/Al	0.73	−0.27	0.18	0.23
Cd/Al	0.78	0.53	−0.01	0.04
Co/Al	0.91	0.29	0.15	-−0.05
Cr/Al	0.74	0.20	0.26	0.02
Cu/Al	0.26	−0.60	0.16	−0.13
Fe/Al	0.91	0.26	0.00	0.14
K/Al	0.88	0.28	0.09	0.05
Mg/Al	0.60	−0.52	−0.03	0.26
Mn/Al	0.69	0.65	0.08	−0.10
Ni/Al	0.90	−0.03	0.21	−0.14
Pb/Al	0.21	−0.14	−0.04	0.02
Sr/Al	0.36	0.54	0.26	0.03
Zn/Al	0.14	0.29	−0.70	0.51
Na/Al	0.53	−0.47	0.34	0.07
Zr/Al	0.71	0.15	−0.21	0.34
Rb/Al	−0.03	0.38	−0.70	0.47
V/Al	0.92	0.28	0.13	0.06
Ti/Al	0.94	0.13	0.21	0.05
LOI₅₅₀	0.63	−0.58	−0.26	−0.04
Eigenvalue	10.54	4.54	3.68	2.33
% variance	35.14	15.14	12.25	7.76

Paleoclimate reconstruction

The environmental magnetic and geochemical data exhibit warm and cold periods which is in coeval with major climate events recorded during the Mid-to-Late Holocene in Antarctica. During periods of cold and dry conditions, mechanical weathering is the prominent agent. Coarse grained magnetic minerals (high values of χ_lf, low values of χ_fd% and χ_ARM /SIRM) are released from the catchment rocks and accumulated in the lake basin. During warmer intervals, the predominant agent is the glacial meltwater resulting in reduced input of primary magnetic grains to the lake basin. The pedogenic formation of fine magnetic grains could also occur during warmer conditions (Čejka et al., 2020; Jordanova, 2017; Warrier et al., 2021b). This will result in lower values of χ_lf and higher values of χ_fd % and χ_ARM /SIRM during warm intervals (Wang et al., 2010). Therefore, higher values of χ_lf indicates colder periods, while lower values indicate the prevalence of warm and wet conditions (Phartiyal, 2014; Warrier et al., 2014, 2021a). Higher elemental concentrations are recorded during colder periods which could be resulting from the deposition of coarse grained particles probably due to transportation of aeolian materials by the katabatic winds (Doran et al., 2002; Mahesh et al., 2015, 2017). Based on these inferences and the downcore variations of magnetic parameters and geochemical elements, the paleoclimate of the region for the past ~ 4.87 kyr was reconstructed.

Mid-Holocene period (~4.87 to 3.35 cal kyr BP)

The Mid-Holocene period is marked by several episodes of cold and warm conditions. The period from 4.87 to 4.4 cal kyr BP is marked by high values of the magnetic concentration-dependent parameters χ_lf, χ_ARM, and SIRM (Figure 3) suggesting the prevalence of cold and dry conditions. The magnetic grain granulometric ratio χ_ARM /SIRM show low values (Figure 3), indicating coarse magnetic grains. Decreasing values of magnetic concentration along with an increasing trend in χ_ARM /SIRM at 4.4 cal kyr BP suggest an influx of fine-grained magnetic minerals. This interval represents a transition to warmer conditions in the region (Phartiyal, 2014). The element concentrations in this phase remain low indicating low terrigenous input. The chemical weathering indices show increasing values during this period, indicating warmer conditions favorable for chemical alteration. Following this warm interval, at ~ 4.17 cal kyr BP, there is an observable increase in χ_lf, χ_ARM, and SIRM. Concurrently, the concentration of elements increases and the chemical weathering indices show a reducing trend. χ_ARM /SIRM also show a decreasing trend that indicated a shift to coarse magnetic grain size suggesting cold environmental conditions. This interval marks a return to cold and dry conditions in the study area. This cold interval is followed by a period of warm and wet conditions at ~3.88 cal kyr BP, extending up to ~3.6 cal kyr BP inferred from reducing values of χ_lf, χ_ARM, and SIRM. This interval of warm conditions is coeval with a period of intense glacial meltwater discharge in the Soya Coast, East Antarctica between 4.1 and 3.6 cal kyr BP (Sproson et al., 2021) (Figure 8e). The A-CN-K plot (Figure 7a) indicates that a cluster of few samples from the Mid-Holocene period plotted parallel to the smectite line, reflecting a higher degree of alteration. The same cluster shows intense weathering in the biplot of ICV versus CIA (Figure 7c) indicating the observed warm and wet intervals within the Mid-Holocene period. At ~3.6 cal kyr BP, a return to cold and dry conditions is observed, marked by increasing values of χ_lf, χ_ARM, and SIRM. Colder conditions during the Mid-Holocene in Lake L6 were also reported by Govil et al. (2016). Intervals of colder conditions during the Mid-Holocene were also reported in the Antarctic Peninsula, marked by minor glacier readvances (Heredia Barión et al., 2023).

Figure 8.

Comparison of (a) χ_lf data of Lake L6 with (b) magnetic susceptibility data of Lake Anonima, Antarctic Peninsula (Čejka et al., 2020); (c) δ₁₈O data of EDML ice core (EPICA Community Members, 2010); (d) dust flux data from EPICA Dome C Ice-core (Lambert et al., 2012); (e) ¹⁰Be/⁹Be data of Soya Coast (Sproson et al., 2021), and (f) summer, spring, and annual mean insolation at 65°S (Berger and Loutre, 1991; Etourneau et al., 2013). Light cyan bars represent colder periods and pale orange bars represents warmer periods.

Mid-Holocene Hypsithermal (MHH) (~3.35 to 2.43 cal kyr BP)

In the current study, a pronounced decrease in the magnetic susceptibility data can be observed from 3.35 cal kyr BP, indicating a shift to warmer conditions. The values of χ_ARM and SIRM can also be seen mirroring the trend of χ_lf (Figure 3). χ_ARM /SIRM shows higher values during this period, indicating finer magnetic grain sizes. χ_fd %, reflective of the pedogenic formation of magnetic minerals of the SP grain size, registers higher values (Figure 3), reflecting larger concentration of SP grains, pointing toward warmer conditions. Warm and wet conditions during this period could have provided conditions favorable for the pedogenic formation of fine-grained magnetic minerals. Similar conditions facilitating pedogenesis in the Schirmacher Oasis were also observed by Warrier et al. (2014). In the biplot of χ_ARM /SIRM versus χ_lf (Figure 4c), the samples from MHH can be observed to have finer magnetic grain sizes with consistently low values of χ_lf.

The chemical weathering indices CIA and PIA show relatively higher values during the MHH (Figure 6). In the biplot of ICV versus CIA (Figure 7c), most of the samples from MHH plot near the border region of weak and intense weathering, while in the A-CN-K plot (Figure 7a), the MHH samples can be seen trending toward the illite line, indicating a higher degree of alteration and providing further evidence for the higher intensity of chemical weathering at this interval with the existence of optimal climate conditions. Previous studies indicate that the soils of Schirmacher Oasis show chemical alteration of silicate minerals, particularly biotite (Sedov et al., 2019). Weathering processes lead to the formation of fine iron-clay particles, that adhere to the coarse fractions of the primary minerals (Sedov et al., 2019). In the present study, χ_fd % also shows a comparable trend to that of CIA during the MHH, indicative of warm and wet conditions favorable for chemical weathering. The values of Mn/Fe and V/(V + Ni) in this phase (Figure 6) indicate oxic conditions in the lake, which is consistent with the warming trend during the Mid-Holocene. Govil et al. (2016) reported the onset of deglaciation in Lake L6 at 3.1 cal kyr BP together with higher values of Mn/Fe in the lake indicating oxygenated conditions during the Mid-Holocene period. The Mid-Holocene Hypsithermal is associated with an increase in solar radiation, corroborated by climate models (Renssen et al., 2005). In the current study, the insolation values for annual, summer, and spring are higher during the MHH (Figure 8f).

Neoglacial cooling (~2.43 to 1.63 cal kyr BP)

Following the MHH, the values of χ_lf, χ_ARM, and SIRM (Figure 3), can be seen increasing, indicating a shift to colder conditions. This observed cooling trend is synchronous with the Neoglacial cooling, an interval of cold and dry conditions recorded during the Late-Holocene and has been reported from several Antarctic records (Čejka et al., 2020 and numerous references there in), including from the Schirmacher Oasis (Phartiyal, 2014; Warrier et al., 2014, 2021a). The magnetic granulometric parameter, χ_ARM /SIRM, shows a declining trend, indicating coarser magnetic grain sizes, while χ_fd % shows low values throughout the Neoglacial, indicating the absence of any significant concentration of SP grains (Figure 3). The metal/Al ratios of the major elements are found to have increased into the Neoglacial period (Figure 5). This could be due to detrital inputs supplied by glacial abrasion of the catchment rocks. The downcore variations in PC1 (Supplemental Figure S3), which represents terrigenous input also shows an increasing trend into the Neoglacial period. Downcore variations in PC3 (Supplementary Figure S3) can also be seen increasing into the Neoglacial period indicating higher influx of aeolian-transported magnetic grains during this period. The ratio 100Ti/Al acts as a proxy for the aeolian input (Chen et al., 2013; Noronha-D’Mello et al., 2021; Reichart et al., 1997) and shows an increasing trend following the MHH (Figure 5). Higher values of HIRM are also observed during this period in comparison with the MHH (Figure 3). Strengthened wind activity during the Neoglacial could have resulted in a higher influx of aeolian hematite grains into the catchment. The chemical weathering indices (CIA and PIA) exhibit a sharp drop immediately after the Mid-Holocene period (Figure 6), indicating a shift in the regional climate with conditions unsuitable for chemical weathering. This observation is also corroborated by the ICV versus CIA biplot (Fig. 7C), where the samples from the Neoglacial period show a high degree of immaturity. In the A-CN-K plot (Figure 7a), the Neoglacial samples display comparatively lower degree of alteration, reflecting cold and dry conditions in the region. Following the Mid-Holocene Hypsithermal, at ~2.43 cal kyr BP, higher values of V/(V + Ni) and low values of Mn/Fe are observed (Figure 6), implying major environmental changes in the region at this time with a shift to more anoxic conditions. This could be due to prolonged ice cover conditions over the lake limiting the lakes interaction with the atmosphere, thus leading to an oxygen-deficient environment in the region. LOI₅₅₀ values also show a reducing trend following the MHH indicating low levels of organic productivity due to cold and dry conditions during the Neoglacial (Figure 3).

The χ_lf data from Lake L6 (Fig. 8A) has been compared with the magnetic susceptibility data of Lake Anonima on the Antarctic Peninsula (Figure 8b) (Čejka et al., 2020). Lake Anonima record represents a robust, high-resolution data of the Neoglacial cooling in the Antarctic Peninsula. The data from the current study agree with the lake Anonima data, validating the occurrence of the observed Neoglacial cooling in our record. The timing of these events correlates with a slight offset which is most likely due to the difference in resolution. The percentage frequency-dependent susceptibility (χ_fd %) from Lake Anonima (Čejka et al., 2020) (Supplemental Figure S4) also shows a similar trend to the data of Lake L6. The mineral magnetic data of Lake L6 has also been compared with the δ¹⁸O data of EDM ice-core (EPICA Community Members, 2010) (Figure 8c) and dust flux data of EPICA Dome C ice core (Lambert et al., 2012) (Figure 8d) and is in good agreement with our record. The offset observed is due to the higher resolution of the ice-core data.

The changes in solar insolation due to orbital forcing could have driven the onset of Neoglacial cooling (Palacios et al., 2020; Solomina et al., 2015). The summer insolation can be seen increasing, but the spring and annual insolation can be observed to be attaining minimum values at 2 cal kyr BP (Figure 8f). Even though the summer insolation values were high, the intensity of the summer season was possibly the lowest (longer duration of ice-cover conditions) since the early Holocene during this period, and the colder winter and spring seasons could have given rise to longer sea ice seasons (Etourneau et al., 2013; Pike et al., 2009).

Medieval climate anomaly (~MCA: 1.63 to 0.53 cal kyr BP)

In the current study, the environmental magnetic parameters χ_lf, χ_ARM, and SIRM display a declining trend following the Neoglacial (Figure 3), indicating a shift to warmer conditions in the region. The magnetic granulometric ratios χ_ARM /SIRM and χ_ARM /χ_lf show an increasing trend (Figure 3) suggesting finer magnetic grain sizes. The shifting environmental conditions are also reflected by the χ_fd % values, which show a sharp increase following the Neoglacial. The warming conditions are coeval with the Medieval Climate Anomaly (MCA).

The metal/Al ratios are increasing into the this period. Downcore variations in PC1 scores also show an increasing trend (Supplemental Figure S3). This could be due to enhanced input of detrital material aided by increased meltwater input responding to warmer conditions. PC2 also shows increasing values during the MCA along with 100Ti/Al (Figure 5) suggesting that higher influx of aeolian material continued into this period. The chemical weathering indices show an increasing trend after the Neoglacial period (Figure 6). During this period, the CIA and PIA indices register mean values of 60.12 and 65.38, respectively. The sediments are compositionally immature with weak weathering conditions. This observation is reinforced by the A-CN-K diagram (Figure 7a), where the samples during this interval can be seen having a lower degree of alteration, possibly suggesting intermediate climate conditions in the region during this period. The concentration of the major elements can be seen increasing into this period. The chemical weathering indices CIA and PIA also show increasing values following the Neoglacial period. The ratio V/(V + Ni) can be seen decreasing during this interval, indicating the availability of more oxygen in the lake. Mn and Fe also show a shift to more oxic conditions, indicating longer periods of ice-free conditions in the lake during the summer season.

The Medieval Climate Anomaly (MCA) was a short interval of warm conditions recorded between 1150 and650 cal yr BP (Esper and Frank, 2009; Mann et al., 2009). MCA is well represented in many northern hemisphere records (e.g. Broecker, 2001; Mann et al., 2009; Trouet et al., 2009), and few records from Antarctica (Guglielmin et al., 2016; Lüning et al., 2019), but not very well represented in the East Antarctic records. The insolation is maximum during the MCA at 65°S (Figure 8f). During summer season, the insolation that Antarctica receives is higher than that of the tropics, but due to the high albedo, most of the radiation is reflected (Turner et al., 2009). When the land is exposed following the melting of snow cover, the solar radiation gets absorbed, resulting in the warming of the local environment (Verleyen et al., 2011).

Little Ice Age (LIA) (~0.53 to 0.35 cal kyr BP)

χ_lf, χ_ARM, and SIRM, show a sharp increasing trend (Figure 3), indicating a transition to colder conditions. PC3 can be seen increasing during the LIA (Supplemental Figure S3) along with 100Ti/Al (Figure 5) indicating higher influx of aeolian material reflecting windier conditions in the region. χ_ARM /SIRM and χ_ARM /χ_lf show a sharp decline in their values (Figure 3), reflecting coarser magnetic grain sizes. The Mn/Fe ratio is showing a higher value during a short interval in the LIA, while V/(V + Ni) can be seen reducing at the same time (Figure 6). This could be due to the oxygenated bottom sediments resulting from low biological productivity during this period (Davin, 2013; Noronha-D’Mello et al., 2021). The chemical indices of weathering (CIA and PIA) show slightly higher values in the LIA. One sample shows anomalously high values for CIA and PIA. The samples from the LIA are observed to be immature sediments with low degrees of alteration, as observed in the biplot of ICV versus CIA (Figure 7c). However, one sample shows a higher degree of weathering, which is also reflected in the A-CN-K plot. The sum overall observation suggests the prevalence of colder conditions which could possibly indicate the response of the lake ecosystem to LIA.

Following the MCA, Lake L6 experienced a short interval of cold and dry episode coeval with the Little Ice Age (LIA). The LIA was a period of colder and drier conditions, greater wind velocities, and wide-ranging sea-ice cover (Bertler et al., 2011). The LIA cooling event was prominent in the northern hemisphere. The timing of the LIA is synchronous with Bond Event 0 and coincident with a series of solar minima (Wanner et al., 2011). The spring, summer, and annual insolation values at 65°S can be seen as showing very low values during the LIA period (Figure 8f). The imprints of LIA have also been recorded in several Antarctic datasets viz., (a) a Late-Holocene cooling event recorded in ice cores (Masson et al., 2000); (b) LIA conditions in Palmer Deep (Bentley et al., 2009); (c) cold conditions and glacial readvances in maritime Antarctica and the Antarctic Peninsula (Píšková et al., 2019; Simms et al., 2021; Wasiłowska et al., 2017; (d) cold and dry conditions in the Larsemann Hills (Noronha-D’Mello et al., 2021; Verleyen et al., 2004; (e) strong katabatic winds in the McMurdo Dry Valleys (Bertler et al., 2011); and East Antarctica (Mosley-Thompson et al., 1990; Rhodes et al., 2012). An intensification of the westerly winds coincident with the LIA has also been reported by Mayewski et al. (2009). Even though, the resolution of our sediment cores is much lesser than the ice-core records, and a one-to-one correlation is very unlikely, the present study does record imprints of LIA as observed in the overall proxy data.

Recent warming (~0.35 cal kyr BP to present)

Following the Little Ice Age, χ_lf, χ_ARM, and SIRM show a sudden drop in their values, while χ_fd % can be seen increasing (Figure 3), marking a transition in the regional climate from cold and dry to warm and wet conditions. χ_ARM/SIRM and χ_ARM /χ_lf are observed to increase (Figure 3), denoting finer magnetic particle sizes. The biplot of χ_ARM /SIRM versus χ_lf also indicate the predominance of finer magnetic grains with low magnetic susceptibilities during the recent warming period (Figure 4b).

The elemental concentrations show an increasing trend following the LIA. The metal/Al ratios of all the major elements are increasing (Figure 5). The weathering indices, CIA and PIA are also seen increasing indicating warm and wet conditions suitable for chemical weathering in the region (Figure 6). The proxies for oxic-anoxic conditions, Mn/Fe and V/(V + Ni), show increasing values, indicating a shift to more oxic conditions in the lake during this period (Figure 6). LOI₅₅₀ also shows a sharp peak during the recent warming period and remains comparatively high at the core-top (Figure 3), suggesting increased organic productivity within the lake and its catchment, resulting from warm and wet conditions in the region. In the A-CN-K plot (Figure 7a), the recent warming period samples display moderate degree of alteration, plotting just below the samples from the MHH. The ICV versus CIA plot indicates that the sediments from this period are immature like all other samples of Lake L6 (Figure 7c). The above data indicates that during the recent period, a warming trend can be observed in the Schirmacher Oasis which agrees with several other records from Antarctica (e.g. Bentley et al., 2009; Bertler et al., 2011)

Conclusions

In this study, we discuss a high-resolution record of Mid-Late-Holocene climate changes recorded from a land-locked lake in East Antarctica spanning the past 4872 years.

• The mineral magnetic signal of the lake is primarily generated by catchment-derived ferrimagnetic minerals, along with minor inputs from superparamagnetic (SP) grains.

• The sediments of lake L6 are immature with moderate degree of weathering.

• The Mid-Holocene Hypsithermal was associated with increasingly warming conditions in the lake. Higher values of magnetic susceptibility observed during this period could be influenced by the pedogenic formation of SP grains.

• The highest degree of chemical weathering is seen in the samples from the Mid-Holocene Hypsithermal, during which time optimal climate conditions were recorded in the region.

• At ~2.43 cal kyr BP, the lake experienced Neoglacial conditions marked by an abrupt increase in the magnetic concentration along with a decrease in the geochemical indices.

• Following the Neoglacial period, the region experienced warm and wet conditions at around 1.63 cal kyr BP, coincident with the Medieval Climate Anomaly. Warm and wet conditions in the Schirmacher Oasis were more prominent during the Mid-Holocene period as compared to the medieval climate anomaly (MCA).

• After the MCA, the lake returned to a short interval of cold and dry conditions, the Little Ice Age marked by higher concentrations of magnetic minerals and low productivity.

• Increasing values of chemical weathering can be seen toward the core-top, signifying a recent warming trend in the region.

Supplemental Material

sj-docx-1-hol-10.1177_09596836241236347 – Supplemental material for A high-resolution record of Mid- to Late-Holocene environmental changes from a land-locked lake in Schirmacher Oasis, East Antarctica

Supplemental material, sj-docx-1-hol-10.1177_09596836241236347 for A high-resolution record of Mid- to Late-Holocene environmental changes from a land-locked lake in Schirmacher Oasis, East Antarctica by GS Joju, Anish Kumar Warrier, BS Mahesh, AS Yamuna Sali, Cheryl A Noronha-D’Mello, K Balakrishna and Rahul Mohan in The Holocene

Footnotes

Acknowledgements

AKW thanks the Director, CSIR-NIO, Goa, and Dr Firoz Badesab, Scientist, CSIR-NIO, for providing the magnetic instrumental facility. MBS and RM are thankful to the Director, NCPOR for constant support and encouragement. We thank Ponzan Radiocarbon Laboratory, Poland for providing the AMS radiocarbon dates. JGS thanks Dr Lino Yovan, for his help with location map preparation and ICP-OES analysis. JGS also thanks Mr Gokul Valsan, research scholar, Manipal Institute of Technology, for his help with figure preparation. We are thankful to the Antarctic Logistics Division, NCPOR, and the leader and station commander, Maitri, and the members of the 28^th Indian Scientific Expedition to Antarctica for their assistance during the field work. We thank the editor and reviewers for their comments which helped in improving the quality of the manuscript. This is NCPOR contribution no. J-67/2023-24.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The financial support for this work was provided by the ESSO-National Centre for Polar and Ocean Research, Ministry of Earth Sciences, Government of India, in the form of a research project to AKW and KB (Sanction: NCPOR/2019/PACER-POP/ES-02 dated 05/07/2019) under the PACER Outreach Programme (POP) initiative.

ORCID iDs

GS Joju

Anish Kumar Warrier

Supplemental material

Supplemental material for this article is available online.

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