Holocene Paleoclimatic Variation in the Schirmacher Oasis, East Antarctica: a Mineral Magnetic Approach

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Polar Science 8 (2014) 357e369 http://ees.elsevier.com/polar/

Holocene paleoclimatic variation in the Schirmacher Oasis, East Antarctica: A mineral magnetic approach

Binita Phartiyal

Birbal Sahni Institute of Palaeobotany, 53-University Road, Lucknow 226007, UP, India

Received 17 July 2013; revised 27 May 2014; accepted 9 June 2014 Available online 14 June 2014

Abstract

An analysis of remanent magnetism and radiocarbon ages in the dry lacustrine/sediment fills of the Schirmacher Oasis (SO) in East Antarctica was conducted to reconstruct past climatic condition. The statistically run mineral magnetic data on paleontological statistics software package (multivariate cluster analysis) placed on accelerator mass spectrometer radiocarbon chronology of the three sediment sections, trace 6 phases of climatic fluctuation between 13 and 3 ka, (Phases 1, 3 and 5 represent cold periods while Phases 2, 4, and 6 represent warm periods). One short warm period (Phase 2, ca. 12.5 ka) occurred in the late Pleistocene, and two marked warm periods (Phase 4, 11e8.7 ka; Phase 6, 4.4e3 ka) occurred in the Holocene. High magnetic susceptibility (c), saturation isothermal remanent magnetism (SIRM), and soft isothermal remanent magnetism (soft IRM) values correspond to colder periods and low values reflect comparatively warmer lacustrine phases. Holocene Optima (Phase 4) and Mid Holocene Hypsithermal (Phase 6) are distinguished by decreased values of concentrations dependent parameters. Remanence is preserved in the low-coercive minerals. Heavy metals in the sediments include, Fe, Rb, Zn, Mo, Co, Pb, Mn, Cu, and As in order of decreasing abundance. © 2014 Elsevier B.V. and NIPR. All rights reserved.

Keywords: Holocene; Schirmacher Oasis; Lacustrine sediments; Mineral remanent magnetism; Paleoclimate

1. Introduction wide range of geographic locations and depositional environments (Thompson and Oldﬁeld, 1986; Maher Reconstructions of past environment changes yield and Thompson, 1999; Evan and Heller, 2003). Mag- insights into the natural variability of the Earth's netic parameters provide rapid, robust, and economic climate system and provide a context for understanding measures of qualitative, and in some cases quantitative, present and future global changes. The universal compositions of magnetic minerals and their relative presence of magnetic minerals in sediments and their associations under different climate conditions and sensitivity to climatic conditions allows for in- depositional environments (Thompson and Oldﬁeld, vestigations of mineral magnetism (also known as 1986; Maher and Thompson, 1999; Evan and Heller, environmental magnetism or rock magnetism) in a 2003; Peters and Dekkers, 2003; Phartiyal et al., 2003; Warrier et al., 2011). The proxies used in this E-mail addresses: study include concentration-dependent parameters [email protected], binitaphartiyal@ c bsip.res.in. (magnetic susceptibility ( ) and saturation isothermal

http://dx.doi.org/10.1016/j.polar.2014.06.001 1873-9652/© 2014 Elsevier B.V. and NIPR. All rights reserved. 358 B. Phartiyal / Polar Science 8 (2014) 357e369 remanent magnetism (SIRM)), grain-size-dependent 3. Materials and methods parameters (cARM,, SIRM/c, cfd%), and a mineralogy-dependent parameter (S-ratio). Magnetic The sedimentary sequences were mapped over the parameters are sensitive indicators of temporal varia- entire 35 km2 of the SO. Two cores, 30 and 75 cm in tions in the concentrations and grain sizes of magnetic length (DLL and PDL, respectively), were manually minerals deposited in lakes (Jelinowska et al., 1997). collected using 4.000 diameter plastic Polyvinyl Chlo- They can also provide information about the circum- ride pipes and sliced into 19 and 55 samples, respec- stances surrounding the deposition of sediments, as tively, using wooden knives to avoid contamination. In well as about post-depositional processes (Berner, addition, 23 samples were collected from the eastern 1981; Maher and Taylor, 1988; Mann et al., 1990). part of the SO (from the 30-cm-thick SWDL section) This study presents the mineral magnetic parame- by the pit-and-channel method. Standard techniques ters in sediments of Schirmacher Oasis (SO), were used for sample preparation (Walden, 1999a). Antarctica, as proxies to decipher the palaeoclimate of The samples were air dried in the laboratory under this region. The sediment records in the SO preserve normal temperature conditions (28e30 C), and gently the last period of late Pleistocene and nearly the entire crushed to powder; a 10-g sample was obtained by Holocene (~13e3 ka). coning and quartering, and was transferred to non- magnetic sample holders for analysis. 2. Geographic setting and geology of the study Several magnetic parameters were obtained. Mag- area netic susceptibility (c) was determined on susceptibility meter (Bartington Susceptibility meter; Model The study was conducted in the SO, an ice-free 35- MS2; with a dual sensor; Bartington Instruments Ltd, km2 area situated in Dronning Maud Land (East Oxford, England). The susceptibility used here are of Antarctica) at 112204000e115402000E, 704305000e low frequency (0.47 kHz; clf). Anhysteric Remanent 704604000S(Fig. 1). The region is located between the Magnetization (ARM) was induced in a constant margin of the ice sheet and areas of shelf ice. The SO biasing field of 0.1 mT superimposed on a decaying consists of low-lying hills up to 203 m in elevation, alternating field (a.f.) with a peak field strength of and with an average elevation of 100 m; it contains 100 mT at the decay rate of 0.001 mT per cycle (using 118 interspersed glacial lakes classified as pro-glacial, Molspin Alternating Field Demagnetizer with ARM landlocked, and epi-shelf lakes (Ravindra, 2001) attachment, Molspin Ltd., (presently owned by Bar- (Fig. 1). On the northern margin of the SO, towards tington Instruments Ltd., Oxford, England)). The sus- the ice shelf, steep cliffs with ~100 m of relief border ceptibility of ARM (cARM) was calculated by dividing the SO, whereas the southern margin is mostly the mass-specific ARM by the magnitude of the covered by the inland ice sheet. Extensive debris biasing field (0.1 mT ¼ 79.6 A m 1; Walden, 1999b). cover, moraine deposits, hillocky relief, and former Isothermal remanent magnetization (IRM) was lakes form a part of the present-day landscape. The induced in the samples at different field strengths (20, SO is a recent periglacial region that has been unaf- 50, 70, 100, 200, 300, and 1500 mT in 100-mT in- fected by anthropogenic activity (Krause et al., 1997). crements) and backfields of up to 300 mT using an The present lakes are mostly remnants of larger glacial impulse magnetizer (ASC Scientific IM 10e30, lakes that occupied the valleys in the past (Phartiyal Carlsbad, CA, USA). Remanence was measured using et al., 2011). The Precambrian crystalline basement the Minispin Fluxgate magnetometer [Molspin Ltd., of the SO, which forms a part of the East Antarctic (presently owned by Bartington Instruments Ltd., Ox- craton (Sengupta, 1991), is polymetamorphic. The ford, England)]. rocks have been strongly and repeatedly deformed Three interparametric ratios were used in the anal- under granulite- and amphibolite-facies conditions ysis: frequency-dependent susceptibility (cfd%), the S- (Hoch, 1999). The rock types consist of charnockites, ratio, and the SIRM/clf ratio. The cfd% value gives a enderbites, garnetesillimanite gneisses, gar- broad estimate of the average size of ferromagnetic netebiotite gneisses, quartzo-feldspathic augen grains (Dearing, 1999). The S-ratio is the negative of gneisses with minor amounts of foliated lamp- the ratio of the IRM induced at 300 mT to the SIRM rophyres, amphibolites, dolerites, metagabbros, and induced at 1500 mT (eIRMe300mT/SIRM1500mT). The metabasalts (Sengupta, 1991). The rock suites domi- SIRM/clf ratio gives a determination of grain size. nantly represent Grenvillean (1000 Ma) and Pan- For magnetic mineralogy measurements, the IRM African (550 Ma) events. acquisition was performed on all samples. Room B. Phartiyal / Polar Science 8 (2014) 357e369 359

Schirmacher Oasis 800 Kms Antarctic Peninsula DRONNING MAUD LAND

Larseman Hills

Vestfold Hills

Bunger Hills

QUEEN MARY LAND Windmill McMurdo Sound Islands WILKES LAND

11º25’ 11º30’ 11º35’ 11º40’ 11º45’ 11º50’ SWDL N Ice shelf DLL PDL 1 km Streaky gneiss 70º45’ Augen gneiss L Calc gneiss, khondalite P Alaskite G Garnet–biotite gneiss Continental ice sheet Banded gneiss Pro-glacial lakes Land-locked lakes Epi-shelf lakes L-Long Lake; P-Pridarshani (Zub) Lake; G- Globokoye Lake Core site Pit/trench site Extent of lakes during the Late Quaternary (Phartiyal et al., 2011) B

Fig. 1. A. Location map. B. Map of Schirmacher Oasis, showing geological and geomorphological details (modiﬁed after Sengupta, 1988 and Ravindra, 2001) and sampling sites.

Table 1 Details of AMS chronology after Phartiyal et al. (2011), based on dating of bulk sediment organic carbon. Silesian University of Technology, Gliwice, Poland No. Sample name Lab. No. Calibrated age range 68% Calibrated age range 95% Age 14C (BP) 1 A1 GdA-1236 11022BC (68.2%) 10881BC 11093BC (95.4%) 10812BC 12900 ± 70 2 A2 GdA-1237 10702BC (68.2%) 10561BC 10773BC (95.4%) 10492BC 12580 ± 70 3 A3 GdA-1238 6205BC (3.4%) 6192BC 6226BC (95.4%) 5894BC 7230 ± 80 6183BC (3.0%) 6171BC 6159BC (3.9%) 6143BC 6104BC (54.3%) 5982BC 5942BC (3.6%) 5928BC 4 B1 GdA-1239 6372BC (55.5%) 6207BC 6412BC (95.4%) 6071BC 7430 ± 80 6188BC (0.8%) 6185BC 6169BC (2.0%) 6161BC 6141BC (10.0%) 6106BC 5 C1 GdA-1240 5711BC (51.4%) 5606BC 5742BC (95.4%) 5484BC 6770 ± 80 5596BC (16.8%) 5560BC National Ocean Sciences AMS Facility (NOSAMS), Woods Hole Oceanographic Institute, USA No. Sample name Lab no. d13C F Modern Fm error Age 14C (BP) 6 AS01 OS-69329 24.46 0.3346 0.0019 8790 ± 45 7 AS02 OS-69330 13.26 0.6786 0.0023 3110 ± 25 360 B. Phartiyal / Polar Science 8 (2014) 357e369

) lf kg ) kg io % ARM ) X m Chronology fd X rat X SIRM SIRM/X(A m Lithology (AMS) yr BP (10 (10 m (10 A kg ) S-

0 C1- 8,790 ± 45

)

( 15

D 20

25 A S01- 6,770 ± 80 30 Base not exposed 87.5 92.5 97.5 04812 540 620 700 34 42 50 0.3 0.4 0.5 0.6 0.85 0.89 0.93

Clay Sand Silt Rock fragments

Fig. 2. Mineral magnetic parameters and inter-parametric ratios plotted against the SWDL section. AMS, accelerator mass spectrometry. temperature hysteresis loops for selected samples were methods were adapted to make graphite targets which measured on 20e25-mg samples using a maximum were analyzed by mass accelerator along with primary field strength of 500 mT, using a Princeton Measure- and secondary standard process (Piotrowska, 2013). ments alternating gradient force magnetometer (noise Details of chronologies are given in Table 1. level, 106 Am2 kg1 for a 20-mg sample). High- temperature susceptibility (ceT) was measured with 4. Results: litho-stratigraphy and mineral an Agico KLY 2 Kappabridge in combination with a magnetism CS-2 heating unit. The analyses were performed at the Wadia Institute of Himalayan Geology, Dehradun, Periglacial lakes in the SO include several each of India, and at the Institut fu¨r Geologie und epi-shelf, landlocked, and proglacial lakes, and several Pal€aontologie, Universitat Tu¨bingen, Germany. dry lake beds are also present. Sedimentation rates in To identify mineral magnetic zonation in the pro- the periglacial lakes are very low (Shen et al., 1998). files, the values of all parameters were entered into the Three sedimentary sections (SWDL, DLL, PDL) were paleontological statistics software package (PAST) selected for the present study. The SWDL section, statistical program, and analyzed using multivariate obtained from the western part of the SO (Fig. 2), is a cluster analysis, following Ward's method (Hammer 30-cm section composed of silty sand and clay, and et al., 2001) for choosing the most appropriate rock fragments in the basal 2 cm. An age inversion in parameter for assignment of magnetic zones. the AMS radiocarbon ages was detected in the sedi- Elemental abundances were measured using an X- ments between the depths of 28 cm below the sediment ray fluorescence spectrometer (Model a-S4000S, surface (6770 ± 80 yr BP) (Sample No-SO1; Lab. No.- Innov-X Systems) at the Directorate of Mining, GdA-1240) and 2 cm below the surface (8790 ± 45 yr Lucknow, India. The measurements were conducted in BP) (Sample No-C1; Lab. No.-OS-69329). This soil mode, with a precision of 10 ppm. inversion can be attributed to periglacial cryoturbation Organic carbon in the bulk sediments dated by e a processes related to freezeethaw cycles, that Phartiyal et al. (2011) were used in this paper. Seven mixes materials from various horizons in the sedi- accelerator mass spectrometer (AMS) dates were ob- mentary column. The mineral magnetic parameters and tained from Silesian University of Technology, Gli- inter-parametric ratios for the SWDL section are wice, Poland on total organic carbon from bulk plotted against lithology in Fig. 2. For the 23 levels of sediment samples. Standard sample preparation the studied section, the mean initial c, which is a

B. Phartiyal / Polar Science 8 (2014) 357e369 361

y y

s s

t t

N N

Mag (A m kg ) Mag (A m kg )

Cooling curve )

Heating curve )

m m

r Heating curve

r o

Cooling curve o

(

M M

D 8-at 10.6-cm level D 35-at 43.1 cm level D E

Fig. 3. AeC. Isothermal remanent magnetism (IRM) acquisition curves of samples at different depths in the SWDL, DLL, and PDL proﬁles, respectively. D. Hysteresis loops of samples from the DLL section; E e c-temperature runs of selected samples in the DLL section. representation of the bulk ferromagnetic content (along top of the section, and values of nearly 10% in basal with the paramagnetic component), was layers (25e30 cm) are indicative of super para- 94.41 108 m3 kg1, with higher values being magnetic (SP) grains. The SP grains contribute to c but detected at depths of 0e9 and 16e24 cm. The SIRM not to the IRM; thus, their presence may be detected by values (1500 mT-SIRM values), which primarily lower SIRM/c values, which are observed at depths of represent the concentration of ferromagnetic materials 24e30 and 9e18 cm, indicating changes in the con- (and which, unlike c, are unaffected by diamagnetic tents of ferro- and ferri-magnetic grains. (Thompson and paramagnetic minerals) are high at depths of 0e10 and Oldﬁeld, 1986). The IRM acquisition curves and 16e24 cm. Values of cfd% decrease towards the show nearly 95% saturation at 300 mT (Fig. 3A),

SWDL Section

Lithology Fe Rb Fe Rb

0 C1- 8,790 ± 45

5 Co 5 Co

) Mo 10 m Mo c

)

( Zn

)

(

h 15 t 15

t Mo

D 20 Mo

25 25 A S01- Mo 6,770 ± 80 30 12000 22000 30 80 75 ppm ppm ppm ppm ppm ppm A B C Chronology (AMS) yr BP

Fig. 4. Relative abundances of elements plotted against the lithology of the SWDL (A), the DLL (B), and the PDL (C) sections. 362 B. Phartiyal / Polar Science 8 (2014) 357e369

Table 2 more than is currently present) can exist, even if the Distribution of heavy metals, as measured by a portable X-ray ﬂuo- IRM acquisition curve reaches 95%. rescence spectrometer, in the SWDL section (values in ppm; a hyphen The grain size indicator parameter, SIRM/c , sug- indicates values below the detection range). lf gests that grain sizes at depths of 0e10 and 16e25 cm SN Depth (cm) Co Fe Mo Rb are coarser than those at 23e30 and 10e16 cm. The S- S1 1.0 e 15888.58 e 34.64 ratio varies in the range of 0.55e0.9 throughout the e e S2 2.5 17679.13 53.17 section, which is indicative of a mixed mineralogy with S3 4.0 e 18291.04 e 36.63 S4 5.5 1101.11 17413.46 e 71.62 both soft and hard components (Bloemendal et al., S5 7.0 e 18570.2 e 46.96 1988). The most abundant metals in the proﬁle are S6 8.5 e 19624.91 e 52.56 Fe and Rb; Mo is present at depths of 11.5 and S7 10.0 e 17024.96 e 54.69 14.5e16 cm, and Co is present at a depth of 5.5 cm e S8 11.5 15220.07 47.39 39.51 (Fig. 4A and Table 2). S9 13.0 e 19877.32 e 64.28 S10 14.5 1145.31 18454.81 56.82 59.44 S11 16.0 e 19447.12 58.81 50.92 4.1. DLL Core S12 17.5 e 16641.8 e 49.90 S13 19.0 911.45 13892.15 e 32.31 The DLL section dates to 12,900 ± 70 yr BP at a S14 20.5 e 14683.13 e 43.50 e e depth of 65 cm (Sample No.-A1; Lab. No.-GdA-1236), S16 22.0 23795.-8 64.16 ± S17 23.5 e 22050.94 e 45.50 12,580 70 yr BP at a depth of 52 cm (Sample No.- S18 25.0 e 22766.64 e 40.23 A2; Lab No.-GdA-1237), and 7230 ± 90 yr BP in S19 26.5 e 18830.24 e 62.11 the upper 2 cm of the core (Sample No.-A3; Lab. No.- S20 28.0 e 21785.87 e 56.26 GdA-1238). The 75-cm-thick core consists of alter- e S21 29.5 1142.96 21935.26 83.04 nating silty clay and sand (Fig. 5). The surface and S22 31.0 e 17761.24 e 57.31 S23 32.5 1129.85 19704.76 e 47.70 basal layers are gravely, and the section sits on bedrock. The average susceptibility of the 52 studied which is indicative of ‘soft’ low-coercive minerals. levels is 53.59 10 8 m3 kg 1. High susceptibilities, However, the possibility that hematite is present cannot which indicate increased ferrimagnetic contents, occur be ruled out, as the c value of hematite is <102 that of at depths of 0e21, 42e49, and 58e73 cm. The SIRM magnetite and large amounts of hematite (10 times values are higher at depths of 0e21 and 60e75 cm.

) ) lf o X kg kg ) M kg m % m A ) Chronology ARM R Lithology fd SI m -rati (AMS) yr BP (10 X X (10 (10 SIRM/X(A S 0 A3-7,230 ± 80

)

m 30

(

e 40

50 A2-12,580 ± 70

60 A1-12,900 ± 70

Bedrock 44 52 60 68 0 2 4 6 228 276 324 120 280 440 2 4 6 0.5 0.6 0.7 0.8 0.9

Clay Sand Silt Rock fragments

Fig. 5. Mineral magnetic parameters and inter-parametric ratios plotted against the DLL section. B. Phartiyal / Polar Science 8 (2014) 357e369 363

Table 3 Distribution of heavy metals, as measured by a portable X-ray ﬂuorescence spectrometer, in the DLL section (values in ppm; a hyphen indicates values below the detection range). SN Depth (cm) As Co Cu Fe Mn Mo Pb Rb Ti Zn D 1 1.5 ee e14507.29 eee39.19 ee D 2 2.8 e 613.84 e 9901.77 eee45.67 ee D 3 4.1 e 847.66 e 13717.23 eee50.69 ee D 4 5.4 ee e13473.00 e 42.86 e 49.47 ee D 5 6.7 ee e10994.24 eee70.76 ee D 6 8.0 ee e11599.32 eee39.04 ee D 7 9.3 ee e10717.08 eee41.30 ee D 8 10.6 ee e12254.25 eee41.91 ee D 9 11.9 ee e 9986.83 eee50.85 ee D 10 13.2 ee e11161.60 eee44.70 ee D 11 14.5 ee e15142.70 eee44.84 ee D 12 15.8 e 847.18 e 12649.10 eee45.82 ee D 13 17.1 ee e14127.02 e 45.05 e 42.37 ee D 16 18.4 e 785.73 e 13799.82 623.94 ee 49.26 ee D 17 19.7 ee e15964.79 eee63.05 ee D 18 21.0 ee e15159.72 eee74.12 ee D 19 22.3 ee e13341.18 eee49.9 ee D 20 23.6 ee e13410.40 eee46.51 ee D 21 24.9 ee e12772.03 eee43.19 ee D 22 26.2 ee e12261.12 eee47.9 ee D 23 27.5 ee e14502.49 eee55.35 e 116.24 D 24 28.8 ee e12147.33 e 44.92 e 44.34 ee D 25 30.1 ee e15102.96 eee56.62 ee D 26 31.4 ee e14031.44 eee55.5 ee D 27 32.7 ee e12717.37 eee51.48 ee D 28 34.0 ee e14743.05 eee58.76 ee D 29 35.3 e 733.91 e 13421.49 e 80.19 e 42.02 ee D 30 36.6 ee e 9347.32 eee31.88 ee D 31 37.9 ee e12657.91 eee37.57 ee D 32 39.2 ee e 9864.88 e 52.22 e 37.85 ee D 33 40.5 ee e11528.67 eee57.35 ee D 34 41.8 ee e26489.22 eee70.58 ee D 35 43.1 ee e24274.69 eee48.55 ee D 36 44.4 ee e22471.77 ee228.27 48.75 ee D 37 45.7 ee e29736.44 ee106.64 39.18 ee D 38 47.0 ee e32254.26 eee55.66 ee D 39 48.3 29.05 e 26.58 12332.44 120.95 14.93 385.62 16.60 1918.01 46.32 D 40 49.6 ee e11216.31 eee60.01 e 167.35 D 42 50.9 ee e 4108.31 eee27.08 e 158.28 D 43 52.2 ee e12664.73 eee49.63 e 121.78 D 44 53.5 ee e 7375.64 eee56.28 e 233.45 D 45 54.8 ee e 9406.03 eee38.92 e 164.26 D 46 56.1 ee e11597.31 eee44.30 e 155.99 D 47 57.4 ee e 9438.45 eee43.08 e 253.09 D 48 58.7 ee e29070.74 eee37.96 14720 e D 49 60.0 ee e28875.33 eee66.41 e 157.80 D 50 61.3 ee e12317.10 eee28.77 ee D 51 62.6 ee e11838.23 eee44.07 e 144.65 D 52 63.9 ee e14148.23 eee45.21 e 197.85 D 53 65.2 ee e13400.97 eee39.83 ee D 54 66.5 ee e12961.13 eee44.62 e 159.46 D 55 67.0 ee e 5888.52 eee47.8 e 192.32 364 B. Phartiyal / Polar Science 8 (2014) 357e369

) ) ) kg io lf t % m a X ARM IRM r Chronology fd m) - X S (10 A kg SIRM/X Lithology (AMS) yr BP (10 m kg X (10 (A S 0

AS02-3,110 ± 25 5

)

c ( 15

e D 20

B1-7,430 ± 80 30 Base not exposed 32 48 64 0.0 5.0 10.0 12 20 28 36 44 2.5 12.5 22.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

Clay Sand Silt Rock fragments

Fig. 6. Mineral magnetic parameters and inter-parametric ratios plotted against the PDL section.

The cfd% value above 55 cm fluctuates around 6%, hysteresis loops are generally thin (Fig. 3D), which is which is indicative of contributions of higher concen- indicative of a mixture of magnetic constituents with trations of SP grains. The SIRM/c values are low at different coercivities (Tauxe et al., 1996). Susceptibil- depths of 20e60 cm, which is indicative of finer grain ity versus temperature curves show a large decrease in sizes. The S-ratio is 0.5e0.8, showing variable con- susceptibility at 575 C for the majority of the samples, tributions of magnetic minerals. The maximum satu- confirming magnetite as the primary remanence carrier ration was acquired at 300 mT (Fig. 3B). The (Fig. 3E). However, a sample at a depth of 43.1 cm shows a decrease in susceptibility at temperatures of 575e700 C, perhaps due to a contribution of some Table 4 Distribution of heavy metals, as measured by a portable X-ray fluo- hard magnetic mineral. Fig. 4B and Table 3 show the rescence spectrometer, in the PDL section (values in ppm; a hyphen distributions of elements in the section; Fe and Rb indicates values below the detection range). constitute the major metals. The Fe and c curves SN Depth (cm) Co Fe Mo Rb Zn coincide in the lower section (depths of 21e75 cm); P1 29.0 e 16900.37 e 46.77 e however, in the upper part of the section, Fe variations P2 27.5 e 17480.2 43.59 39.60 e are small, and c values are higher, perhaps due to the P3 26.0 e 15720.93 e 60.12 e contributions of remanence from dia- and para- P4 24.5 e 16315.48 e 58.60 e magnetic minerals instead of Fe minerals. The section P5 23.0 e 17248.21 e 89.78 e e e is enriched in As, Cu, Mn, Mo, Pb, Rb, T, and Zn at P6 21.5 14110.74 40.95 70.33 e P7 20.0 e 15659.02 e 74.75 e depths of 23 24 cm, and in Cu, Mn, and Mo at depths P8 18.5 e 17887.39 e 30.38 e of 58.5e61 cm; Mo is present at depths of 36.5 and P9 17.0 e 16305.28 e 69.62 e 46.5 cm, Zn is present at 49 cm, and Co is present at P10 15.5 e 17035.95 54.6- 47.16 125.54 75e77.5 cm (Table 3). P11 14.0 e 16646.92 e 40.46 e e e e P12 12.5 14393.54 80.82 4.2. PDL Core P13 11.0 e 14367.75 e 43.19 86.74 P14 9.5 e 16444.93 61.82 56.39 e P15 8.0 e 17452.81 53.17 80.85 e The PDL core, obtained towards the eastern side of P16 6.5 e 16809.1 e 79.71 e the SO, gives an AMS date at the base of the core e e P17 5.0 706.03 14905.15 94.10 (depth, 29 cm) of 7430 ± 80 yr BP (Sample No. B1; P18 3.5 e 13577.95 e 75.60 e P19 2.0 e 15254.42 e 76.52 e Lab. No. GdA-1239), while the topmost clays (depth, B. Phartiyal / Polar Science 8 (2014) 357e369 365

lf ) ) lf kg kg ) ARM % X m X fd SIRM/X(A X Lithology (10 m (10 m Magnetic Zones 3,110 ± 25

X 1e fd%

)

m SIRM/X c 1d

(

e 1c S-ratio

XARM

SIRM

Xlf 32 48 64 12 20 28 36 44 0.1 0.2 0.3 0.4 0.0 5.0 10.0 Coph. corr., 0.905

lf ARM kg ) M kg ) A % X m kg ) X R fd Lithology SI (10 X Magnetic (10 (10 m 0 Zones

7,230 ± 80 D6

D5 XARM 20

) SIRM

(

p D4 Xfd% e 40

D SIRM/X

D3 S-ratio 12,580 ± 70 60

D2 Coph. corr., 0.9901 Xlf 12,900 ± 70 D1 80 44 52 60 68 228 276 324 120 280 440 0 2 4 6 B

Fig. 7. Zonation of the PDL section (A) and the DLL section (B) into magnetozones, using best representatives of the mineral magnetic dataset, as calculated by multivariate cluster analysis using Ward's method.

2 cm) date to 3110 ± 25 yr BP (Sample No. AS02; the range of 0.6e0.9, which is indicative of mixed Lab. No. OS-69330). The 30-cm core is composed of mineralogical contributions. A saturation of nearly clay and sand, with clayey basal layers, while the top 90% at 300 mT (Fig. 3C) is indicative of ‘soft’ low- layers contain more sand and gravel (Fig. 6). The coercive minerals, as well as of hard magnetic min- average c value for the 19 studied levels is erals, which is similar to that observed in the other two 52.84 108 m3 kg1. The concentration-dependent profiles. Fig. 4 and Table 4 show the distribution of parameters (c and SIRM) show decreasing trends to- heavy metals in the section. As in the other sections, Fe wards the surface, with sharp fluctuations at depths of and Rb are the major elements present; Mo is present 10e15 cm. The cfd% value ranges between 0% and at depths of 8e9.5, 21.5, and 27.5 cm, and Co and Zn 5%, except at depths of 15e24 cm. The cARM also are present at depths of 5 and 11 cm. shows sharp fluctuations at depths of 5e15 cm, and higher values at depths of 21e30 cm. The SIRM/clf 5. Discussion and conclusions ratios indicate that grain sizes are finer towards the top of the section (depths, 0e10 cm) and coarser in the High-latitude regions have experienced unusually lower section. The S-ratios are high near the surface large climatic and ecological changes since the last (depths, 0e7 cm); however, overall, the S-ratio is in glaciation as compared with other regions on Earth, 366 B. Phartiyal / Polar Science 8 (2014) 357e369 and their susceptibility to the impacts of future during colder periods enhanced concentrations of warming are particularly high on account of cryo- magnetic minerals. During warm periods, on the other sphereealbedo feedbacks involving changing sea-ice hand, fine sediments were deposited, as organic ac- and glacial cover (CAPE Project Members, 2001; tivity in these glacial lakes is negligible, and the Moritz et al., 2002; Overpeck et al., 1997). Despite magnetic signals of concentration are therefore the relative stability of present-day climate-forcing reduced. Phartiyal et al. (2011) reported increased mechanisms, as compared with those during glacial magnetic susceptibilities in samples with negligible periods, the Holocene interval has experienced dra- organic carbon contents (<1%). Therefore, it is matic environmental changes. The lakes investigated in assumed that high c, SIRM, and soft IRM values this study are in low-lying areas, which were part of a correspond to cold intervals, and that low values of more extensive lake system in the past (Phartiyal et al., these parameters correspond to comparatively warmer 2011). In cold arid desserts, lakes are covered by ice climatic conditions. and snow for a major portion of each year. The Using the AMS chronology and the ageedepth geomorphic and landscape evolution of the SO in model of Phartiyal et al. (2011), the DLL and PDL eastern Antarctica is such that sedimentation rates in sections are estimated to represent the climatic history the lakes are low. Moreover, sediment introduced from of the SO during ca. 13e3 ka. Because of the reversed catchment areas by glacial ice and glacial meltwater chronology in the SWDL section, this section was not

Glacial and environmental changes in

Schirmacher Oasis s

Vestfold Bunger Windmill Larseman Hills Antarctic s

n a

Hills Hills Islands Peninsula o h

(ka) z P

Warmer c

t c

than i

n a

present e

a a

? l

Glacial Arid and cool climate a

C m Climate t

readvance i l

a 3 l

Climate e c

Optimum m

n g Optimum t

Climatic optimum-Increased e

s e

Open marine n

i m

(ka)

E c insolation controls climate r conditions m

r e

P2 o l

optimum and deglaciation a

h o Glacial t

P We

4 4 i H

readvance s

- p

P1e d

Brief cooling i

Down-wasting Brief cooling y H of dead ice P1d M 5 Northern islands Glacial P1c readvance deglaciate Climatic getting warmer-moss banks and lake sedimnts start to accumulate; penguines 6 P1b 6 colonize coasal rookeries

n i

Slow m r

a P1a

deglaciation a Wg 7 h

Melting of dead P ice; expanding D6 avian habitats

Onset of e

8 lake sedimentation t 8 a

m D5 i

Ice retreat on l c

land l o

Southern islands o Deglaciation of deglaciate; C 9 southern part of Cold, but warming climate

Shelf areas e

the oasis m

deglaciate e

t e a

D4 m

Phase 4 i

10 m

10 o i

l Shelf areas l

Deglaciation of c

deglaciate g

Inner shelf areas O

m r

Increased martinity as glaciers a 11 and ice shelves retreat from W D3 Phase 3 continentl shelf areas

Increased sea 12 D2 Phase 2 Cold Intermediate climatic conditions Warm marinty as ice shelfs D1 retreat Phase 1

Fig. 8. Comparison chart of the circum-Antarctic climate records to that of Schirmacher Oasis. B. Phartiyal / Polar Science 8 (2014) 357e369 367 considered in the final interpretations of the region's during 7.9e7.1 and 6.4e5.6 ka. The trend from 5.3 ka climatic history. The calculated mean sedimentation onwards is indicative of increasingly warm conditions, rate for the PDL core is ~0.069 mm y1, and that for which continued until 3 ka, and which are comparable the DDL core is 0.132 mm y1 Shen et al. (1998) re- to conditions during the mid-Holocene Hypsithermal ported sedimentation rates of 0.004e1.1 mm y1 in (MHH), which have been recorded in most of the lacustrine environments in other areas of Antarctica. studied sections in Antarctica to date (Bentley et al., A multivariate cluster analysis divided the seven 2005). In the SO, the period of 4.6e4.4 ka was a parameters into four clusters. Because cfd%, SIRM/clf, time of intermediate climatic conditions. The recorded and the S-ratio fall within one cluster, cfd% was timing of the MHH varies in different regions of selected as a representative measure from this cluster. Antarctica: 4e2.7 ka (Bentley et al., 2005, 2009), Fig. 7A and B shows that the parameters cfd%, c, 4.5e2.8 ka on the Antarctic Peninsula, and 3.8e1.7 ka cARM, and SIRM explain most of the variation in the in maritime Antarctica (Hodgson and Convey, 2005; PDL and DLL sections. On the basis of variations Jones and Bowser, 1979), as compared with ca. observed in the above parameters, as well as the rela- 4.4e3 ka in the SO. tive abundances of elements (Fig. 4C), the PDL section Land-based geological evidence from the Antarctic was divided into two major magnetic zones, P1 and P2, shows two marked warm periods during the Holocene, with P1 consisting of five subzones. The sediments in at 11.5e9 ka and 4e2 ka. Some marine records also the SO are generally super paramagnetic and single show evidence of a climate optimum at ca. 7e3ka domain. A mixed magnetic mineralogy, with both soft (www.scar.org/treaty). These land-based and marine and hard components, is evident from the IRM records correlate with records from the SO, which acquisition curves, the thin shape of the hysteresis show a warmer period during 11 to ca. 8.7 ka and a loops, and ceT values. The sources of Fe, Rb, Mn, Co, gradual diminishment of harsh conditions from 5 to and Zn are gneisses of Pre-Cambrian crystalline 3 ka. basement in the SO, especially banded gneiss and The understanding of past climatic trends is of Alaskite. considerable interest, from both social and environ- The magnetic zones of the PDL (P1eP2) and DLL mental perspectives, as such an understanding will help (D1eD6) exhibit a suite of proxy results that can be predict possible effects of future climate change. As used to identify different climatic phases, specifically a only a few regions in East Antarctica are currently set that includes high values of concentration- deglaciated, the ice-free area of the SO represents a dependent parameters, representing cold climatic valuable repository of climatic data. Our ongoing work conditions, and a set that includes lower values of such on chemical and biotic proxies will further strengthen parameters, representing warmer climatic conditions the dataset of climate proxies from this region of the (Fig. 7). Fig. 8 shows the different climatic phases in icy continent. the SO and their correlation with the data thus far collected from Vestfold Hills, Bunger Hills, Windmill Acknowledgments Islands, Larseman Hills, and the Antarctic Peninsula (Wilson and Wellman, 1962, 1998; Kaup et al., 1993; I sincerely thank Directors, Birbal Sahni Institute of Smith and Friedman, 1993; Doran et al., 1994, 2004; Palaeobotany, Lucknow, India and National Centre for Verleyen et al., 2011; Govil et al., 2012). Phase 1 is Antarctic and Ocean Research (NCAOR), Goa, India a short-duration climatic phase occurring at ca. for their encouragement. I thank NCAOR, Goa, for 12.9 ka, which was a prelude to Phase 2 at 12.5 ka, selection to participate in the 25th Indian Antarctic both formed under comparatively warmer climates. Expedition (IAE), 2005e06. I am grateful to the field Phase 3, at ca. 11.8e11 ka, shows conditions similar to teams and all members of the 24th and 25th IAEs for those of Phase 1, while the Larseman Hills area shows help during fieldwork. I also thank Deutscher Akade- increased marine incursion and glacial retreat during mischer Austauschdienst (DAAD) for the Wieder- this time. A warmer and longer Phase 4, from 11 to ca. einladungen Programme Fellowship, and Professor 8.7 ka, recorded in the DLL sediments can be corre- Erwin Appel of Universitat Tu¨bingen for assistance. I lated with the worldwide Holocene Optimum, and also am grateful to Dr. Santosh K. Shah for assistance with an apparent signature of deglaciation of shelf areas in the statistical analyses. I also thank the anonymous the Antarctic (see Fig. 8). Phase 5, during 8.7e4.4 ka, reviewers for useful suggestions and comments, which was a period of an arid and cold climate, which helped to bring the manuscript into its present form. included shorter and comparatively warmer signals Laboratory facilities provided by the Wadia Institute of 368 B. Phartiyal / Polar Science 8 (2014) 357e369

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