Application of bacterial glycerol dialkyl glycerol tetraethers (GDGTs) to develop modern and past temperature estimates from New Zealand lakes

Organic Geochemistry 41 (2010) 1060–1066

Contents lists available at ScienceDirect

Organic Geochemistry journal homepage: www.elsevier.com/locate/orggeochem

Application of bacterial glycerol dialkyl glycerol tetraethers (GDGTs) to develop modern and past temperature estimates from New Zealand lakes Klaus-G. Zink a,*, Marcus J. Vandergoes a, Kai Mangelsdorf b, Ann C. Dieffenbacher-Krall c, Lorenz Schwark d a

GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand GFZ Potsdam German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany c Climate Change Institute, University of Maine, Orono, ME 04469, USA d University of Kiel, Ludewig-Meyn Str. 10, 24118 Kiel, Germany b

a r t i c l e

i n f o

Article history: Received 30 September 2009 Received in revised form 9 March 2010 Accepted 10 March 2010 Available online 15 March 2010

a b s t r a c t Branched isoalkyl glycerol dialkyl glycerol tetraethers (GDGTs) of bacterial origin have been found in high abundance in both modern and glacial sediments of New Zealand South Island freshwater lakes covering a wide range of altitude (101–2000 m). Like isoprenoid GDGTs of archaeal origin, they provide excellent potential for temperature assessment. For this study, their distribution patterns (MBT, methylation ratio and CBT, cyclisation ratio of branched GDGTs) have been successfully used to develop an initial temperature calibration for the study area and to provide preliminary (palaeo)environmental interpretations. MBT data from modern lake sediments correlate well with measured annual air temperature (R2 0.74), enabling a regional calibration for reconstructing palaeotemperatures for fossil samples. MBT-derived palaeotemperatures for Alpine Lake, calibrated against mean annual temperature, were determined for the Last Glacial during an early cold phase (between 29,000 and 26,000 years BP) and for later less cold phases (between 23,000 and 18,000 years BP). Compared with the modern temperature regime, the MBT data indicate a decrease of ca. 5.6 and 2.8 °C respectively, during this time. Modern and past MBT-derived temperatures correlate with chironomid-based temperature reconstructions in the area. Archaeal GDGTs, commonly used for the TEX86 index, are abundant in fossil sediments (Alpine Lake) but scarce in modern sediments, hindering a new local calibration for this palaeotemperature proxy. Ó 2010 Elsevier Ltd. All rights reserved.

1. Introduction Detailed palaeoclimate reconstructions for the late Pleistocene and early Holocene in the Southern Hemisphere, in particular terrestrial records, are relatively rare (Andres et al., 2003; Lüer et al., 2009; Turney et al., 2006). Studies of New Zealand lakes and peat bogs, for instance, have provided insights into the local palaeoclimate and palaeoenvironmental evolution (Dieffenbacher-Krall et al., 2007; Vandergoes et al., 2005). However, the determination of palaeotemperature data using biomarker proxies would help improve and confirm palaeoclimate reconstructions, opening up the possibility of better comparing detailed climate records between the Northern Hemisphere and the Southern Hemisphere. Accurate reconstructions of past temperature change are needed as essential components of climate models for predicting future rates of climate change and impact. Bacterial and archaeal glycerol dialkyl glycerol tetraethers (GDGTs) have been proven to occur ubiquitously in sediments. They occur in marine and lacustrine systems, soil, peat and coal * Corresponding author. Tel./fax: +49 5141 9809285. E-mail address: [email protected] (Klaus-G. Zink). 0146-6380/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.orggeochem.2010.03.004

(Blaga et al., 2009; Fry et al., 2009; Hopmans et al., 2004; Schouten et al., 2002; Weijers et al., 2007a,b). The two main groups comprise isoprenoid compounds from archaea (DeLong et al., 1998; Sinninghe Damsté et al., 2002) and branched components derived from bacteria (Sinninghe Damsté et al., 2000; Weijers et al., 2009). Although it has been suggested that acidobacteria may comprise a likely source for branched GDGTs in peat, unequivocal evidence for the bacterial phyla producing branched GDGTs is pending (Weijers et al., 2006a). The compounds were originally thought to stem exclusively from soil microorganisms. However, recent studies suggest an autochthonous contribution (Sinninghe Damsté et al., 2009; Tierney and Russell, 2009) in limnic systems. Ratios of GDGTs such as the TEX86 index derived from archaeal lipids and the indices inferred from bacterial lipids, such as the MBT (methylation index of branched tetraethers) and, to a minor degree, the CBT (cyclisation index of branched tetraethers), reflect temperature-dependent membrane changes and are used to develop (palaeo)temperature records from marine sediments and soils (Schouten et al., 2002; Weijers et al., 2006b, 2007a,b). The relationship of the MBT and CBT ratios with temperature and pH observed in soils has been used to develop a calibration for soil temperature reconstruction (Weijers et al., 2007b). GDGT lipids have also been

Klaus-G. Zink et al. / Organic Geochemistry 41 (2010) 1060–1066

identified in limnic environments and their (palaeo)temperature dependence revealed (Blaga et al., 2009; Escala et al., 2007; Powers et al., 2004; Schouten et al., 2000; Sinninghe Damsté et al., 2009; Tierney and Russell, 2009). However, correlation of the indices with modern air or water temperature is still a critical task as other factors, such as the abundance and inventory of microbial communities, pH, Eh, alkalinity and substrate availability can strongly influence lipid composition and thereby hamper a reliable calibration for palaeotemperature determination (Sinninghe Damsté et al., 2009; Weijers et al., 2007b). In addition, it needs to be considered that a source dependence – soil or aquatic microorganisms – might exist for these indices (Tierney and Russell, 2009). Hence, the consistent applicability of these biomarker proxies for (palaeo)temperature estimation has to be confirmed. In an effort to validate new techniques for producing quantitative estimates of past temperature change, the current study explores whether MBT, CBT and also TEX86, can be used to produce terrestrial climate records from freshwater lake systems. We investigated recent sediment samples from lakes on the South Island of New Zealand (Fig. 1) to establish a calibration against local mean annual (or summer) air and water temperature. For a set of fossil sediment samples, validation of palaeotemperatures inferred from GDGT distribution using the new calibration was performed, based on variations in chironomid (midge fly) assemblages primarily driven by temperature (Dieffenbacher-Krall et al., 2007). Applying the approach for the first time to New Zealand lakes provides an opportunity to improve quantitative palaeotemperature reconstructions with the potential of being widely used in the terrestrial realm.

2. Material and methods Sediment samples were taken from 11 lakes in the westerncentral part of the South Island, New Zealand. Ten were from surface sediment (0–2 cm). Four were collected from an Alpine Lake core, covering sediment depths from 3–4 m below the lake bottom. The sediment stratigraphy at this depth is associated with the Last Glacial Cold Period (LGCP) in New Zealand and is confirmed by the close approximation to the Kawakawa Tephra (Table 1) deposited during the LGCP at 27,097 ± 957 years BP (cal. years BP; Lowe et al., 2008). All the lakes are relatively small (<0.6 km2), freshwater and range in altitude from 101 to 2000 m.a.s.l. (metres above sea level), with an observed mean annual air temperature (MAT)

1061

range of 9.9–1.5 °C and mean summer air temperature (MST) range of 14.4–6.8 °C (Table 1). GDGTs were extracted (2) from sediments with CH2Cl2/MeOH (1:1, v/v) using accelerated solvent extraction (DIONEX ASE 200) at 65 °C and 50 bar. Extracts were fractionated into non-polar and polar fraction using Al2O3-solid phase extraction (SPE) with n-hexane/ CH2Cl2 (9:1, v/v) employed as mobile phase. The polar fraction containing the GDGTs was dried, re-dissolved in n-hexane/propan-2-ol, centrifuged (20 min) at 3000 rpm, and the supernatant was filtered through 0.45 lm polytetrafluoroethylene (PTFE) filters. The cleaned fraction was analysed using liquid chromatography–atmospheric pressure chemical ionization-mass spectrometry (LC–APCI–MS) with a Prevail cyanopropyl (CN)-column (2.1  150 mm, 3 lm). The mobile phase consists of n-hexane (A) and propan-2-ol (B) (5 min 99% A, 1% B; linear gradient to 1.4% B within 22.5 min; in 1 min raised to 10% B; held 5 min to clean the column; return to initial conditions in 1 min; held 6 min for equilibration). The flow rate was 200 ll/min and injection was performed via an autosampler with a 5 ll loop. APCI source conditions were: corona current 5 lA, giving a voltage of around 4 kV; vaporiser temperature 350 °C; capillary temperature 200 °C; N2 as sheath gas. [M+H]+ ions were recorded in selected ion monitoring (SIM) mode using a Finnigan TSQ 7000 triple-quadrupole mass spectrometer. Multiplier voltage was 1500 V and the scan rate was 2 s. The methods have been described elsewhere (Hopmans et al., 2004; Leininger et al., 2006; Schouten et al., 2007). An external synthetic diether archaeol standard (Avanti Polar Lipids Inc., AL, USA) was used to test linearity and reproducibility (concentrations 0.1, 1, 10 lg/ml), with analysis in triplicate, and was used to calculate GDGT quantities assuming an identical response factor. Reproducibility of the authentic samples analysed in duplicate gave average errors < 6.3% for individual compounds relevant for the ratios applied. Integration included the peak areas of the [M+H]+ and [M+H]++1 (isotope peak) (Table 1). The indices were calculated as follows (Weijers et al., 2007b):

MBT ¼

ð½I þ ½Ib þ ½IcÞ ð½I þ ½Ib þ ½IcÞ þ ð½II þ ½IIb þ ½IIcÞ þ ð½III þ ½IIIb þ ½IIIcÞ ð1Þ

CBT ¼  log

  ð½Ib þ ½IIbÞ ð½I þ ½IIÞ

ð2Þ

Numbers in equations correspond to structures in Fig. 2.

Fig. 1. Map of lake locations in central part of South Island, New Zealand. Red star (no. 1) denotes Galway Tarn; blue star (no. 2) indicates Alpine Lake locations. (For interpretation of the references to colour in the legend, the reader is referred to the web version of this article.)

Lake (sediment depth):

T2-317 Alpine Lake (317 cm)

T2-329 Alpine Lake (328.5 cm)

Altitude (m.a.s.l.) Water depth (m) pH MAT, mean annual air temperature (°C) MST, mean summer air temperature (°C) MBT CBT MATcalc (MBT)a (°C) MATcalc (CBT)b (°C) MSTcalc (MBT)a (°C) MSTcalc (CBT)b (°C) MSTmod, modelled from chironomids (°C)

101 20.0 7.0c 9.9d 14.4d 0.235 0.860 6.9 6.6 11.9 11.6 12.1

101 20.0 7.0 9.9 14.4 0.244 0.804 7.3 7.0 12.3 12.0 11.9

c

e f g

101 20.0 7.0 9.9 14.4 0.185 0.972 4.1 5.8 9.4 11.0 9.7

303 Lake Lyndon

307 Duncan Stm 3

308 Royal Hut 1

306 Duncan Stm 2

317 Irishman Stm 3

305 Duncan Stm 1

316 Irishman Stm 2

315 Irishman Stm 1

589 14.5 7.9 9.1 14.1 0.267 0.648 8.7 8.0 13.5 12.9 14.2

671 11.2 8.0 8.7 13.5 0.234 0.805 6.8 6.9 11.8 12.0 14.3

841 16.9 7.8 7.9 12.7 0.256 0.648 8.0 8.0 12.9 12.9 12.7

1340 28.7 7.7 5.0 10.5 0.166 1.176 3.1 4.5 8.4 9.7 –

1400 12.8 7.8 4.5 9.4 0.208 1.012 5.4 5.6 10.5 10.7 9.8

1690 4.7 7.8 3.1 8.6 0.150 1.368 2.2 3.2 7.6 8.6 6.4

1790 3.8 7.8 2.5 7.9 0.195 (0.891)g 4.7 (6.4) 9.9 (11.4) 7.5

1840 4.5 8.0 2.3 7.7 0.157 1.204 2.6 4.3 8.0 9.6 9.0

1840 4.3 7.8 2.3 7.7 0.140 1.839 1.6 0.2 7.1 5.8 7.9

2000 4.6 7.8 1.5 6.8 0.180 1.302 3.8 3.7 9.1 9.0 7.8

MBT (MAT this study) MAT (MBT this study) MAT (MBT, CBT this study) TEX86 Reconstructed temperature brGDGT III brGDGT II brGDGT I

d

101 20.0 7.0 9.9 14.4 0.190 0.992 4.4 5.7 9.6 10.8 10.4

302 Lake Ida

MBT (MAT this study) MAT (MBT this study) MAT (MBT, CBT this study) TEX86 Reconstructed temperature brGDGT III brGDGT II brGDGT I

a

T2-344 Alpine Lake (344 cm)

301 Lake Letitia

Lake (sediment depth):

b

T2-339 Alpine Lake (339 cm)

T2-317 T2-329 Kawakawa T2-339 T2-344 Alpine Lake (317 cm) Alpine Lake (328.5 cm) Tephrae (333.5–334.5 cm) Alpine Lake (339 cm) Alpine Lake (344 cm) After Weijers et al. (2007b), MBT = 0.28 + 0.025  MAT – After Weijers et al. (2007b), MAT = (MBT-0.28)/0.025 (°C) 1.8 After Weijers et al. (2007b), MAT = (MBT-0.122-(0.187  CBT))/0.02 (°C) 2.4 0.488 13.2 After Powers et al. (2004) (TEX86) (°C) m/z 1046.1–1048.0, 1048.1–1050.0, 1050.1–1052.0 (%) 34.7 m/z 1032.1–1034.0, 1034.1–1036.0, 1036.1–1038.0 (%) 41.8 m/z 1018.1–1020.0, 1020.1–1022.0, 1022.1–1024.0 (%) 23.5

– 1.5 1.4 0.454 10.9 35.9 39.7 24.4

– 3.6 5.9 0.454 11.0 41.5 39.5 19.0

– 3.8 5.9 0.454 10.9 41.6 39.9 18.5

301 Lake Letitia

302 Lake Ida

303 Lake Lyndon

307 Duncan Stm 3

308 Royal Hut 1

306 Duncan Stm 2

317 Irishman Stm 3

305 Duncan Stm 1

316 Irishman Stm 2

315 Irishman Stm 1

0.507 0.5 1.2 0.383f 6.2 27.9 45.3 26.7

0.498 1.8 1.9 – – 29.7 46.4 23.9

0.478 1.0 0.6 0.416 8.4 28.5 45.7 25.7

0.405 4.6 8.8 – – 44.8 38.6 16.6

0.393 2.9 5.2 – – 37.5 41.7 20.8

0.356 5.2 11.4 – – 44.8 40.3 15.0

0.343 3.4 (4.7) 0.457 11.1 42.9 37.6 19.5

0.338 4.9 9.5 – – 42.8 41.4 15.7

0.337 5.6 16.3 – – 49.1 36.9 14.0

0.317 4.0 9.3 0.333 2.9 43.4 38.6 18.0

Calculated from MBT-MAT and MBT-MST correlations, respectively. Calculated from CBT-MAT and CBT-MST correlations, respectively. Modern pH for Alpine Lake. Estimated modern temperature from a nearby lake (Galway Tarn, see Fig. 1). Dated at 27,097 ± 957 years BP, Lowe et al. (2008). Cald/Cren ratio of 12 reflects dominance of archaea over crenarchaeota for this lake. In brackets: data excluded from temperature correlation.

K.-G. Zink et al. / Organic Geochemistry 41 (2010) 1060–1066

Altitude Water depth pH MAT MST MBT CBT MATcalc (MBT)a MATcalc (CBT)b MSTcalc (MBT)a MSTcalc (CBT)b MSTmod

Kawakawa Tephrae (333.5–334.5 cm)

1062

Table 1 Lake identification, and limnological and molecular data for GDGTs from sediment samples, with data based on published equations for comparison.

Klaus-G. Zink et al. / Organic Geochemistry 41 (2010) 1060–1066

a

Modern Lake Lyndon (841 m.a.s.l., ID 303)

II

b

Last glacial maximum Alpine Lake (101 m.a.s.l.; ID T2-317)

II

I

III TIC

III

1063

III (1050)

TIC

I

IIIb (1048)

IIIc (1046)

m/z 1046 1048 1050

Relative abundance

III

m/z 1046 1048 1050

III

IIIb

IIb (1034)

II

m/z 1036 1034 1032

II

II (1036)

IIIc m/z 1036 1034 1032

IIc (1032)

IIb IIb I Ib

IIc

I

m/z 1022 1020 1018

Ib

Ic

I (1022)

m/z 1022 1020 1018

Ib (1020)

Ic Ic (1018)

26

28

30

32

34

36

38

40

42

26

28

30

32

34

36

38

40

42

Retention time (min) Fig. 2. TIC and selected ion chromatograms (HPLC–APCI–MS) of branched isoalkyl tetraether lipids from (a) modern and (b) fossil lake sediments (SIM mode); structures and molecular weight of branched GDGTs are shown.

3. Results and discussion 3.1. Temperature calibration for recent New Zealand South Island lake sediments 3.1.1. Bulk composition and GDGT distribution patterns Recent and fossil lake sediments afforded extract amounts of 349–6266 ppm, with nine samples in excess of 1500 ppm. GDGT lipids occurred in sufficient abundance to reliably determine differences in the distribution patterns (Fig. 2): concentrations for total branched GDGTs ranged between 24 and 768 ng/g sediment dry weight (Sed) in modern samples and 1048–3886 ng/g Sed in fossil samples. Low extraction yield and low concentrations of total branched GDGTs for sample ID 315 (Irishman Stm 1) render values for MBT and CBT less reliable. Nevertheless, the lake was included in the temperature calibrations (Fig. 3a–c) because triplicate analysis yielded low average errors for MBT (2.3%) and CBT (3.4%). Archaeal GDGTs ranged from 12–40 ng/g Sed in modern and 221–613 ng/g Sed in fossil samples. Distribution patterns of branched GDGTs clearly differed between recent and Last Glacial samples (Fig. 2), as shown by the proportions of branched GDGT groups I, II and III in Table 1. The relative abundance of GDGTs III, indicating cooler conditions, was more pronounced in fossil sediments, in particular in the two older samples, of Alpine Lake (101 m.a.s.l.) than in in recent lowland lakes. The higher lakes above 1340 m also revealed a dominance of GDGTs III, except for Royal Hut Lake (Table 1). There, the main controlling factor for the branched GDGT distribution is interpreted to be air temperature or altitude, respectively, because mean annual and summer air temperatures correlate almost exactly with lake altitude (Fig. 4a). We based all calibrations on air temperature instead of water temperature because the latter is less representative. Water temperatures could not be measured continuously and so, for the small-sized lakes, water temperature data scatter due to temporally rapid heating or cooling of the lake surface. Previous studies

by Dieffenbacher-Krall et al. (2007), based on a larger dataset, demonstrated that, on average, air temperature corresponds to surface water temperature. The TEX86 index could only be determined for four recent lakes because of a low abundance of the isoprenoid GDGTs. Consequently, a correlation with modern lake temperature was not obtained. One of these four samples, from Lake Letitia, showed a different caldarchaeol to crenarchaeol ratio of ca. 12 vs. the other sediments, which had average values of 0.8. This indicates that crenarchaeota were less dominant in the archaeal community of Lake Letitia. Therefore, the TEX86 value for this sample was excluded from further discussion. Overall, the lack of isoprenoid GDGTs in the recent sediments inhibited a robust temperature calibration for the New Zealand lakes studied. Hence, the transformation of TEX86 values from Alpine Lake fossil sediments to calibrated temperatures was not possible. 3.1.2. MBT and CBT correlations In contrast to TEX86, MBT values were determined for all the samples. Values for recent samples from the ten lakes, if plotted against mean annual as well as mean summer temperature, in both cases showed a positive linear correlation (Fig. 3a and c). The correlation of MBT with annual temperature gave a coefficient of determination (R2) of 0.74. The p-value for the regression was <0.01, indicating the statistical significance of this distribution. We used the equation inferred from this correlation to reconstruct temperatures (Fig. 3a):

MAT ¼ 55:01  MBT  6:055:

ð3Þ

Assuming that bacterial lipids in sediments most probably should reflect an averaged annual signal, we imply that the MBT ratio more likely represents mean annual temperature than summer temperature. However, in particular the alpine and high alpine lakes as well as soils in the watershed (above ca. 1000 m.a.s.l) are assumed to show a more intense bioproduction during the sum-

1064

K.-G. Zink et al. / Organic Geochemistry 41 (2010) 1060–1066

a

b

10

9

Mean annual air temperature MAT (°C)

Mean annual air temperature MAT (°C)

9 8 7 6

10

MAT = 55.010 × MBT - 6.055 R2 = 0.74 Data points = 10

5 4 3 2

Irishman Stm 1

1

8

MAT = -6.567 × CBT + 12.228 R2 = 0.72 Data points = 9

7 6 5 4 3 2

Irishman Stm 1

1 0.12

0.15

0.18

0.21

0.24

0.27

0.30

0.4

0.6

0.8

MBT methylation index

c

d

14

1.2

1.4

1.6

1.8

2.0

0.24

0.26

0.28

2.0

1.8

13

R2 = 0.82 Data points = 13

1.6

MST = 49.658 × MBT + 0.207 R2 = 0.70 Data points = 10

CBT cyclisation index

Mean summer air temperature MST (°C)

15

12

1.0

CBT cyclisation index

11 10 9

1.4

1.2

1.0

0.8

8

0.6

Irishman Stm 1

7 6 0.12

0.15

0.18

0.21

0.24

0.27

0.4 0.12

0.30

0.14

0.16

MBT methylation index

0.18

0.20

0.22

MBT methylation index

Fig. 3. Initial correlations for New Zealand freshwater lakes: (a) mean annual air temperature MAT with MBT index; (b) MAT with CBT index; (c) mean summer air temperature MST with MBT index for comparison; (d) correlation between MBT index plotted against CBT index (Lake Irishman Stm 1 is labelled as data are less reliable).

b

15 14

estimated modern temperature, Alpine Lake

12 11 10 9 8 7 6 5

MAT from MBT, R 2 = 0.74

4

Irishman Stm 1

MAT from CBT, R 2 = 0.73

3

MST based on chironomids, R2 = 0.89

2

MAT, measured, R 2 = 1

1

Mean annual air temperature MAT (°C)

10

13

Mean air temperature (°C)

11

9 8

sediment core

a

7 6 5 4

Irishman Stm 1

3

MAT from MBT, R 2 = 0.74 MAT from CBT,

2

R2

= 0.73

MAT, measured, R 2 = 1 MAT from MBT, Alpine Lake: Last Glacial Cold Period

1

MST, measured, R 2 = 0.99

0

0 400

800

1200

Altitude (m.a.s.l.)

1600

2000

0

400

800

1200

1600

2000

Altitude (m.a.s.l.)

Fig. 4. (a) Comparison of instrumental temperature and calibrated temperature based on MBT, CBT and chironomids plotted vs. altitude for New Zealand freshwater lakes: (b) lake altitude vs. mean annual air temperature (MAT) derived from MBT CBT and direct measurement; star symbols represent Last Glacial MBT palaeotemperatures for Alpine Lake. Assigned modern temperature level of Alpine Lake (101 m.a.s.l.) demonstrates the modelled warming since the Last Glacial (Lake Irishman Stm 1 is labelled as data are less reliable).

1065

Klaus-G. Zink et al. / Organic Geochemistry 41 (2010) 1060–1066

MST ¼ 49:658  MBT þ 0:207:

ð4Þ

Like MBT, a calibration equation for CBT values was derived from a cross plot against mean annual temperature (Fig. 3b). Here, a slightly lower coefficient of determination (R2 0.72) was obtained. Lake Irishman Stm 3 was excluded from the calibration using CBT because peak area counts of GDGTs Ib and IIb were near detection limit and produced erroneous values for CBT. Because of the narrow range of lake pH values (7.7–8.0), the pH dependence of CBT in soil as reported by Weijers et al. (2007b) could not be observed. The CBT and MBT indices revealed a strong correlation (R2 0.82; Fig. 3d), which suggests that the factors causing the slight scattering in Fig. 3a–c have an equal effect on both parameters. This is one argument against a primary origin of branched GDGTs from soil bacterial communities, as in such settings pH and temperature are decoupled, causing invariance in CBT vs. MBT values (Weijers et al., 2009). Consequently, within the current study, the CBT index seems to be mainly controlled by temperature and, with that, is suitable for estimating (palaeo)temperatures for lakes. A comparison of MBT- and CBT-derived mean annual temperature confirms the correspondence (Fig. 4 and Table 1). The preliminary temperature calibrations derived from MBT (Eqs. 3 and 4) and CBT (Fig. 3) were tested against instrumental and modelled chironomid-based temperature distributions (Dieffenbacher-Krall et al., 2007). The modelled temperatures showed, in general, a clear covariance with altitude (Fig. 4). It has to be considered that chironomid-based temperatures show the strongest correlation with mean summer temperature because the response of chironomid larvae to summer heat balance is expected to be more representative (Dieffenbacher-Krall et al., 2007). Therefore, chironomid-based temperatures are ca. 4.5–6 °C higher than mean annual MBT-based temperatures (Fig. 4a). This discrepancy reasonably corresponds to the difference between instrumental mean summer and annual temperatures (4.0–5.5 °C) obtained for the lakes. The shift of 0.5 °C is within the error margin. However, the current calibration of MBT with annual temperature might result in a slight underestimation of temperature because of higher microbial activity and autochthonous bioproduction in summer. Hence, lipid signatures, including those of organic matter-degrading bacteria, are suggested to reflect a higher proportion of microbial organic matter biosynthesized during the summer months. Therefore, the MBT values might represent a temperature signal in between MAT and MST (Table 1). Independently from using MST or MAT for calibration, the observed correspondence of MBT-based and chironomid-based temperatures could be further interpreted as an indication for a significant contribution of in situ branched GDGTs. As suggested by Sinninghe Damsté et al. (2009) for Lake Challa and by Tierney and Russell (2009) for Lake Towuti and its catchment area, the occurrence of GDGT-containing bacteria in aquatic lacustrine environments seems plausible. With regard to the New Zealand lakes, it is conceivable that the main bioproduction of branched GDGTs occurs in situ. However, their abundance could vary with lake altitude, length of ice cover, secchi depth (dissolved humic/fulvic acids), nutritional status, UV-radiation and other factors. Therefore, GDGT input could be derived to some extent from soil bacterial organic matter, which would explain some of the scatter in the correlation plot concerning the high altitude lakes (Fig. 4).

The equations calibrated for soil environments by Weijers et al. (2007b) using MBT or the combined MBT/CBT values to infer temperature cannot be directly applied to the New Zealand lakes. Without modification and adaptation to the lacustrine systems of the current study, both equations would result in a significant temperature underestimation (Fig. 5 and Table 1). For both calibrations established by Weijers et al. (2007b), the relative trend for modelled and instrumental temperatures prevails, though a clear offset towards lower temperature occurs and, for the combined MBT/CBT equation, a different slope is noted for the regression line (Fig. 5). The different slope in the MBT/CBT equation data is interpreted to be controlled by the difference in pH conditions between the soils used for the calibration and the lakes of the current study. For the freshwater lacustrine systems investigated, with the narrow pH range, the application of the MBT index is considered the appropriate temperature proxy. 3.2. Temperature reconstruction of fossil New Zealand South Island lake sediments In the next step, we applied Eq. 3 obtained from the MBT vs. MAT regression to reconstruct palaeotemperature estimates from core sediments of Alpine Lake (Table 1 and Fig. 1). The fossil sediments represent two phases of the Last Glacial Cold Period in New Zealand: an early cold phase, approximately between 29,000 and 26,000 years BP, and a later less cold phase that occurred periodically between 23,000 and 18,000 years BP (Vandergoes et al., 2005). MBT data indicated a temperature decline of ca. 2.8 °C for the less cold phases and ca. 5.6 °C lower mean annual air temperature for the early cold phase vs. the modern temperature level of 9.9 °C (Fig. 4b). These shifts correspond well with those of preliminary chironomid-based temperatures reconstructed from an adjacent lake (Galway Tarn; Vandergoes and Dieffenbacher-Krall unpublished; Table 1, Fig. 1) during the Last Glacial cold phase in New Zealand. Galway Tarn has a sediment stratigraphy and altitude almost identical to Alpine Lake. Although chironomid-based temperatures represent a ”summer signal”, the temperature depression of 2.4 °C and 4.4 °C for the different Last Glacial cold phases compared to the modern level of 14.4 °C (Table 1) is in the range of the temperature variability derived from MBT values based on annual temperatures. To some extent, observed discrepancies of 0.4 °C and 1.2 °C respectively, indicate remaining uncer-

Reconstructed mean annual air temperature MAT (°C)

mer. Higher microbial activity associated with enhanced biomass production during this time would then shift temperatures reflected by microbial GDGT lipids towards higher MBT values. In this context, we also tested the correlation of MBT and mean summer air temperature, resulting in the following equation with a coefficient of determination (R2) of 0.70 (Fig. 3c):

10 8 6 4 2 0 -2 -4 -6 -8

MAT from MBT, R2 = 0.74

-10

MAT from CBT, R2 = 0.73

-12

MAT from MBT (equation after Weijers et al. 2007b), R 2 = 0.74

-14

MAT from MBT/CBT (equation after Weijers et al. 2007b), R 2 = 0.78

-16 -16 -14 -12 -10 -8

-6

-4

-2

0

2

4

6

8

10

Measured mean annual air temperature MAT (°C) Fig. 5. Comparison of reconstructed temperature data from this study with data calculated using published equations by Weijers et al. (2007b). Different slopes of the regression lines and offset of determined temperatures between the different calibrations are reflected.

1066

K.-G. Zink et al. / Organic Geochemistry 41 (2010) 1060–1066

tainties between MAT and MST calibrations for palaeotemperature reconstruction. However, this independent validation of the initial lipid data with chironomid palaeothermometry data implies the consistency of the modern MBT-temperature relationship when applied to fossil records. MBT re-calibrated for limnic settings provides reasonable palaeotemperature approximation for Last Glacial sediments from Alpine Lake, South Island, New Zealand. The higher abundance of isoprenoidal GDGTs in the fossil sediments from Alpine Lake, in contrast to the recent lake sediments, enabled more reliable determination of TEX86 values, which are similarly expected to reliably reflect the palaeotemperature record. Because of a lack of a local temperature calibration, we tentatively applied the equation modified for lakes by Powers et al. (2004), as compared to the TEX86 equation established by Schouten et al. (2002) for marine environments. Blaga et al. (2009) recently re-calibrated the TEX86 palaeothermometer for a series of European lakes. The equations were calibrated to annual mean surface water temperature, whereas for the current study, reconstructed palaeotemperatures result in values between 10.9 °C and 13.2 °C, which are more close to mean summer temperatures derived from the chironomid-based model (Table 1). Although the temperature difference of about 2 °C between the early cold phase samples and the youngest sample is identical to that of the chironomid-based model, a new local calibration for TEX86 palaeotemperature reconstruction for New Zealand lakes seems necessary. 4. Conclusions The results of this study imply that the MBT index established for soils can be used as an accurate tool for the estimation of (palaeo)temperatures in New Zealand lakes, provided that a new temperature calibration is applied. The comparison with instrumental temperatures and chironomid-based temperature reconstructions with the preliminary molecular data, as well as the statistical significance of the inferred correlations, support the reliability of branched GDGT proxies, in particular the MBT index, as temperature indicators in the New Zealand lakes from the South Island. Although the current database is limited, it is concluded that the in situ production of branched GDGTs is generally higher than their contribution from soils in the watershed. Our multi-proxy application will be extended to recent and fossil sediments from more lacustrine environments, as well as soils around New Zealand, to confirm our preliminary calibration; this may provide a valuable new tool for understanding terrestrial palaeoclimate records. Acknowledgements We thank C. Karger (GFZ Postdam) and W. Ruebsam (University of Cologne) for laboratory assistance. We are thankful to O. Seki and J.P. Werne for constructive and helpful comments which improved the manuscript. Guest Associate Editor—K.U. Hinrichs References Andres, M.S., Bernasconi, S.M., McKenzie, J.A., Röhl, U., 2003. Southern Ocean deglacial record supports global Younger Dryas. Earth and Planetary Science Letters 216, 515–524. Blaga, C., Reichart, G.-J., Heiri, O., Sinninghe Damsté, J.S., 2009. Tetraether membrane lipid distributions in water-column particulate matter and sediments: a study of 47 European lakes along a north–south transect. Journal of Paleolimnology 41, 523–540. DeLong, E.F., King, L.L., Massana, R., Cittone, H., Murray, A., Schleper, C., Wakeham, S.G., 1998. Dibiphytanyl ether lipids in nonthermophilic crenarchaeotes. Applied and Environmental Microbiology 64, 1133–1138.

Dieffenbacher-Krall, A.C., Vandergoes, M.J., Denton, G.H., 2007. An inference model for mean summer air temperatures in the Southern Alps, New Zealand, using subfossil chironomids. Quaternary Science Reviews 26, 2487–2504. Escala, M., Rosell-Melé, A., Masqué, P., 2007. Rapid screening of glycerol dialkyl glycerol tetraethers in continental Eurasia samples using HPLC/APCI-ion trap mass spectrometry. Organic Geochemistry 38, 161–164. Fry, J.C., Horsfield, B., Sykes, R., Cragg, B.A., Heywood, C., Kim, G.T., Mangelsdorf, K., Mildenhall, D.C., Rinna, J., Vieth, A., Zink, K.-G., Sass, H., Weightman, A.J., Parkes, R.J., 2009. Prokaryotic populations and activities in an interbedded coal deposit, including a previously deeply buried section (1.6–2.3 km) above 150 Ma basement rock. Geomicrobiology Journal 26, 163–178. Hopmans, E.C., Weijers, J.W.H., Schefuß, E., Herfort, L., Sinninghe Damsté, J.S., Schouten, S., 2004. A novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids. Earth and Planetary Science Letters 224, 107–116. Leininger, S., Urich, T., Schloter, M., Schwark, L., Qi, J., Nicol, G.W., Prosser, J.I., Schuster, S.C., Schleper, C., 2006. Archaea predominate among ammoniaoxidizing prokaryotes in soils. Nature 442, 806–809. Lowe, D.J., Shane, P.A.R., Alloway, B.V., Newnham, R.M., 2008. Fingerprints and age models for widespread New Zealand tephra marker beds erupted since 30,000 years ago: a framework for NZ-INTIMATE. Quaternary Science Reviews 27, 95– 126. Lüer, V., Cortese, G., Neil, H.L., Hollis, C.J., Willems, H., 2009. Radiolarian-based sea surface temperatures and paleoceanographic changes during the Late Pleistocene-Holocene in the subantarctic southwest Pacific. Marine Micropaleontology 70, 151–165. Powers, L.A., Werne, J.P., Johnson, T.C., Hopmans, E.C., Sinninghe Damsté, J.S., Schouten, S., 2004. Crenarchaeotal membrane lipids in lake sediments: a new paleotemperature proxy for continental paleoclimate reconstruction? Geology 32, 613–616. Schouten, S., Hopmans, E.C., Pancost, R.D., Sinninghe Damsté, J.S., 2000. Widespread occurrence of structurally diverse tetraether membrane lipids: evidence for the ubiquitous presence of low-temperature relatives of hyperthermophiles. Proceedings of the National Academy of Science USA 97, 14421–14426. Schouten, S., Hopmans, E.C., Schefuß, E., Sinninghe Damsté, J.S., 2002. Distributional variations in marine crenarchaeotal membrane lipids: a new tool for reconstructing ancient sea water temperatures? Earth and Planetary Science Letters 204, 265–274. Schouten, S., Huguet, C., Hopmans, E.C., Kienhuis, M.V.M., Sinninghe Damsté, J.S., 2007. Analytical methodology for TEX86 paleothermometry by highperformance liquid chromatography/atmospheric pressure chemical ionization-mass spectrometry. Analytical Chemistry 79, 2940–2944. Sinninghe Damsté, J.S., Hopmans, E.C., Pancost, R.D., Schouten, S., Geenevasen, J.A.J., 2000. Newly discovered non-isoprenoid glycerol dialkyl glycerol tetraether lipids in sediments. Chemical Communications 17, 1683–1684. Sinninghe Damsté, J.S., Schouten, S., Hopmans, E.C., van Duin, A.C.T., Geenevasen, J.A.J., 2002. Crenarchaeol: the characteristic core glycerol dibiphytanyl glycerol tetraether membrane lipid of cosmopolitan pelagic crenarchaeota. Journal of Lipid Research 43, 1641–1651. Sinninghe Damsté, J.S., Ossebaar, J., Abbas, B., Schouten, S., Verschuren, D., 2009. Fluxes and distribution of tetraether lipids in an equatorial African lake: constraints on the application of the TEX86 palaeothermometer and BIT index in lacustrine settings. Geochimica et Cosmochimica Acta 73, 4232–4249. Tierney, J.E., Russell, J.M., 2009. Distributions of branched GDGTs in a tropical lake system: Implications for lacustrine application of the MBT/CBT paleoproxy. Organic Geochemistry 40, 1032–1036. Turney, C.S.M. et al., 2006. Climatic variability in the southwest Pacific during the last termination (20–10 kyr BP). Quaternary Science Reviews 25, 886–903. Vandergoes, M.J., Newnham, R.M., Preusser, F., Hendy, C.H., Lowell, T.V., Fitzsimons, S.J., Hogg, A.G., Kasper, H.U., Schluchter, C., 2005. Regional insolation forcing of late quaternary climate change in the Southern hemisphere. Nature 436, 242– 245. Weijers, J.W.H., Schouten, S., Hopmans, E.C., Geenevasen, J.A.J., David, O.R.P., Coleman, J.M., Pancost, R.D., Sinninghe Damsté, J.S., 2006a. Membrane lipids of mesophilic anaerobic bacteria thriving in peats have typical archaeal traits. Environmental Microbiology 8, 648–657. Weijers, J.W.H., Schouten, S., Spaargaren, O.C., Sinninghe Damsté, J.S., 2006b. Occurrence and distribution of tetraether membrane lipids in soils: Implications for the use of the TEX86 proxy and the BIT index. Organic Geochemistry 37, 1680–1693. Weijers, J.W.H., Schefuß, E., Schouten, S., Sinninghe Damsté, J.S., 2007a. Coupled thermal and hydrological evolution of tropical Africa over the last deglaciation. Science 315, 1701–1704. Weijers, J.W.H., Schouten, S., van den Donker, J.C., Hopmans, E.C., Sinninghe Damsté, J.S., 2007b. Environmental controls on bacterial tetraether membrane lipid distribution in soils. Geochimica et Cosmochimica Acta 71, 703–713. Weijers, J.W.H., Panoto, E., van Bleijswijk, J., Schouten, S., Rijpstra, W.I.C., Balk, M., Stams, A.J.M., Sinninghe Damsté, J.S., 2009. Constraints on the biological source(s) of the orphan branched tetraether membrane lipids. Geomicrobiology Journal 26, 402–414.