Geochemical and mineralogical evidence for Sahara and ... · islands bedrock. Kaolinite in the...

Quaternary Landscape Response to Climate Change

Geochemical and mineralogical evidence for Sahara and Saheldust additions to Quaternary soils on Lanzarote, eastern CanaryIslands, Spain

Daniel R. Muhs,1 James Budahn,1 Gary Skipp,1 Joseph M. Prospero,2 DeAnna Patterson3 andE. Arthur Bettis III41U.S. Geological Survey, MS 980, Box 25046, Federal Center, Denver, CO 80225, USA; 2Rosenstiel School of Marine and Atmospheric

Sciences, University of Miami, 4600 Rickenbacker Causeway, Miami, FL 33149, USA; 3ATA Services, Inc., 165 South Union Blvd., Suite 350,

Lakewood, CO 80228, USA; 4Department of Geoscience, 121 Trowbridge Hall, University of Iowa, Iowa City, IA 52242, USA

Introduction

Africa hosts the most importantsources of dust in the world today inthe Sahara and Sahel regions (Pros-pero et al., 2002; Goudie and Middle-ton, 2006; Mahowald et al., 2006;Kohfeld and Tegen, 2007). Becauseof the proximity of the Canary Islandsto Africa, dust storms are commonthere (Torres-Padron et al., 2002; Cri-ado and Dorta, 2003; Alastuey et al.,2005). Previous workers have recog-nized that eastern Canary Islands�soils contain quartz and mica, miner-als that do not occur in the localbasaltic rocks. Early investigatorsattributed quartz (Tejedor Salgueroet al., 1985) and mica (Jahn et al.,1987) to pedogenic processes. Morerecent investigators explain quartzand mica in the soils by African dust

ABSTRACT

Africa is the most important source of dust in the world today,and dust storms are frequent on the nearby Canary Islands.Previous workers have inferred that the Sahara is the mostimportant source of dust to Canary Islands soils, with littlecontribution from the Sahel region. Soils overlying a lateQuaternary basalt flow on Lanzarote, Canary Islands, contain, inaddition to volcanic minerals, quartz and mica, exotic to theisland�s bedrock. Kaolinite in the soils also likely has an exotic

origin. Trace-element geochemistry shows that the soils arederived from varying proportions of locally derived basalt andAfrican dust. Major-element geochemistry, clay mineralogy andinterpretation of satellite imagery suggest that dust additionsto the Canary Islands come not only from the Sahara Desert, butalso from the Sahel region.

Terra Nova, 22, 399–410, 2010

Canary Islands

Cape VerdeIslands

30°

40°

20°

10°

Atlantic

Ocean

EUROPE

AFRICA

S A H A R A

S A H E L

0 1000

Kilometres

Lanzarote

0°30° 15°

Algeria

Morocco

Libya

Mauritania

Mali

Niger

Nigeria

Wes

tern

Sahar

a

Senegal

IvoryCoast

BurkinaFaso

Guinea

Cameroon

Ghana

Tuni

sia

Cha

dSAHARANAIR LAYER(summer)

TRADEWINDS

(year-round)

HARMATTAN(winter)

TRADE WINDS(winter only)

Fig. 1 Map showing north-western Africa, the Canary Islands study area, localitiesreferred to in the text and the main dust-transporting winds and their seasons oftransport. Dust-bearing wind paths generalized from Dubief (1979), Kalu (1979),Sarnthein et al. (1981), McTainsh and Walker (1982), Stein and Sarnthein (1984),Tetzlaff and Peters (1986), Pye (1987), Stuut et al. (2005), and Schwanghart andSchutt (2008). Also shown (grey stippled areas) are major active sand seas,generalized from �Global Soil Regions� map, from US Department of Agriculture,Natural Resources Conservation Service (http://www.soils.usda.gov/use/worldsoils/mapindex/order.html), in turn derived from the FAO-UNESCO Soil Map of theWorld (Food and Agriculture Organization of the United Nations, UNESCO, 1974).

Correspondence: Dr Daniel R. Muhs, U.S.

Geological Survey, MS 980, Box 25046,

Federal Center, Denver, CO 80225, USA.

Tel.: +1 303 236 7919; fax: +1 303 236

5349; e-mail: [email protected]

This article forms part of a thematic set of

articles guest-edited by Professor Vincenzo

Pascucci on the topic of Quaternary land-

scape response to climate change and

presented at the 2009 IAS Alghero confer-

ence.

� Published 2010. This article is a US Government work and is in the public domain in the USA 399

doi: 10.1111/j.1365-3121.2010.00949.x

inputs (Mizota and Matsuhisa, 1995;Zoller et al., 2003, 2004; Meco et al.,2006; Von Suchodoletz et al., 2008,2009a,b; Stuut et al., 2009).There is less of a consensus on the

source of African dust and the trajec-tories by which it arrives to theCanary Islands. One important dustpathway is the north-easterly trade-wind belt (Fig. 1), which occurs at lowaltitudes year-round (Sarnthein et al.,1981; Stein and Sarnthein, 1984; Pye,1987; Stuut et al., 2005). A number ofworkers have emphasized the impor-tance of this dust pathway for theorigin of soils and sediments on theCanary Islands (Coude-Gaussenet al., 1987; Grousset et al., 1992,1998; Rognon et al., 1996).In contrast, Bergametti et al.

(1989) point out that more southerlysources, such as the Sahel, also play arole in delivering dust to the CanaryIslands. Stuut et al. (2009) even pro-pose that Canary Islands� sediments

and soils are derived largely from theSahel region. Dust from the Saheland southern Sahara is transportedto the Atlantic Ocean via the SaharanAir Layer, or SAL (Fig. 1), whichoccurs predominantly in summer(Prospero et al., 1970; Carlson andProspero, 1972; Prospero and Carl-son, 1972; Prospero and Lamb,2003). Near Africa, the SAL reachesaltitudes as high as 5–7 km, abovethe trade-wind zone. Sarnthein et al.(1981), Stein and Sarnthein (1984),Tetzlaff and Peters (1986) and Pye(1987) point out that, although themain direction of dust transport inthe SAL is to the west at latitudesbetween �15� and �21�N, south ofthe Canary Islands, a south-to-northcomponent of flow can occur in thelee of an easterly wave. Thus, a�hook-like� trajectory of dust move-ment from the Sahel to the CanaryIslands via the SAL is observed(Figs 1 and 2). Evidence presented

by both Sarnthein et al. (1981) andGrousset et al. (1998) indicates thatboth the trade winds and the SALwere situated approximately wherethey are now during the last glacialmaximum, c. 20 000 yr BP, but dustfluxes may have been greater.We test hypotheses of Sahara vs.

Sahel dust origins on the CanaryIslands by studying late Quaternarysoils on a well-dated basalt flow onLanzarote (Fig. 3). Geochemistry andmineralogy are used to evaluatewhether young soils are derived fromlocal basalt, Saharan dust, Sahel dustor some combination of these materi-als.

Study area

An extensive basalt flow from theCorona Volcano is found on the north-ern part of Lanzarote (Fig. 3) and isdated to 21 000 ± 6500 yr BP by the40Ar ⁄ 39Ar method (Carracedo et al.,

25 July 2004(a) (b) 9 May 2007

Fig. 2 Examples of summer dust storms over the Canary Islands that have sources in broad areas in western Africa and are derivedfrom the SAL (Saharan Air Layer); note northward �hook-like� form of dust masses west of the African coast, with trajectoriestowards the Canary Islands: (a) 25 July 2004, MODIS image from the Aqua satellite (courtesy of Jesse Allen, NASA EarthObservatory, using data from MODIS Land Rapid Response System); (b) 9 May 2007, MODIS image from the Terra satellite(courtesy of Jeff Schmaltz, MODIS Rapid Response Team, NASA Goddard Space Flight Center).

African dust to the Canary Islands • D. R. Muhs et al. Terra Nova, Vol 22, No. 6, 399–410

.............................................................................................................................................................

400 � Published 2010. This article is a US Government work and is in the public domain in the USA

2003). Soils on the flow are relativelythin (�5 to �15 cm thick) silt-loamswith yellowish-brown colours (10YR4 ⁄4, 5 ⁄4, 5 ⁄6, 6 ⁄6, dry). In places, silthas penetrated (to �50 cm or more)into joints and fractures in the basalt(Fig. 4a). Elsewhere, soils cover theflow more evenly, and a sparse stonepavement has formed (Fig. 4b). Soilparticles also fill voids and vesicles onthe undersides of basalt fragments(Fig. 4c). Elsewhere on Lanzarote,thicker soils, but with similar coloursand textures, can be observed overlyingPleistocene aeolian sands (Fig. 4d).

Analytical methods

Geochemical analyses (Tables 1–3)were conducted on splits of bulk soil,the soil fraction<20 lm (clay and finesilt), basalt samples and African dustsamples collected on Barbados (withsome data previously reported byMuhs et al., 2007a). African dust col-lected on Barbados includes both Sah-aran and Sahel sources (Prosperoet al., 1970; Prospero and Nees, 1977,

1986; Glaccum and Prospero, 1980).Major- and trace-element geochemis-try was conducted by instrumentalneutron activation analysis (INAA) inlaboratories of the US Geological Sur-vey, Denver (Budahn and Wandless,2002). INAA is a preferredmethod as ityields very precise concentrations ofimmobile trace elements that are usefulfor provenance studies (Muhs et al.,2007a,b, 2008a). Mineralogy wasdetermined by X-ray diffractometry(XRD). Whole-soil mineralogy wasconducted on bulk, pulverized samplesX-rayed as random mounts. Clay(<2 lm) separates were X-rayed asoriented mounts on glass slides threetimes: air-dry, glycolated and heattreated (550 �C). Clay mineralogy ofthe African dust samples is reported byGlaccum and Prospero (1980). Parti-cle-size analyses were conducted in theDepartment of Geoscience, Universityof Iowa, using wet sieving (sand) andpipette (silt and clay) after pretreat-ments including destruction of organicmatter with hydrogen peroxide,destruction of carbonates with hydro-

chloric acid, and dispersion withsodium hexametaphosphate.

Mineralogy

The Canary Islands, including theCorona Volcano, are composed lar-gely of basalt. The Corona flow con-tains plagioclase, pyroxene, olivineand magnetite. Major-element con-centrations (from Table 1, convertedhere to oxides) support the mineralidentifications: CaO is 9.9–11.4%;Na2O is 2.5–3.2%; K2O is 0.7–1.2%;and total Fe as Fe2O3 is 12.2–13.0%,in agreement with Carracedo et al.(2003).Soils on the flow have abundant

(44–59%) silt-sized particles (53–2lm) with the exception of soils(SP-494, SP-495, SP-502) downwindof small dune fields or modern bea-ches (Fig. 5). Lanzarote soils, unlikeNorth American loess, have more finesilt than coarse silt. Soils on Lanzarote(other than the three sand-dominatedsamples) also have significant (17–30%) amounts of clay (<2 lm).

SP-500

SP-504 SP-499

SP-502

SP-503

SP-494

SP-495

SP-496

SP-497

SP-498

SP-490

SP-492

SP-501

SP-491

SP-493

13°30’ 13°27’ 13°24’

29°09’

29°12’

La Quemada

LA GRACIOSA

Los Helechos

Corona

Atlantic

Ocean

Atlantic

Ocean

LANZAROTE

0 2

Kilometres

Atlantic

Ocean

Soil sample

Basalt sample

Basalt, ~21 ka

Basalt, ~90 ka

Basalt, olderPleistocene

Volcano

Lava flowpaths

Explanation

SP-496

Basalt, Tertiary

Smalldunefields

Fig. 3 Geological map of northernmost Lanzarote island, showing late Quaternary volcanic flows (Carracedo and Day, 2002;Carracedo et al., 2003) and basalt and soil-sample localities from the present study.

Terra Nova, Vol 22, No. 6, 399–410 D. R. Muhs et al. • African dust to the Canary Islands

.............................................................................................................................................................


Soils have a bulk mineralogy thatdiffers from the underlying bedrock,although the sand-sized particles areall composed of basalt. Thus,although soils contain the volcanicminerals pyroxene, plagioclase andolivine, the silt and clay fractions ofthe soils also contain quartz, mica,kaolinite and hematite. No calcite wasdetected in any bulk-soil sample. Foursoils spanning the geographical extentof the Corona lava flow were selectedfor clay mineralogy and differ littlefrom one another; all contain mica,kaolinite and quartz (Fig. 6).

Trace-element geochemistry

We use relatively immobile trace ele-ments as �fingerprints� for sourcematerials, following an approach used

elsewhere (Muhs et al., 2007a,b,2008a; Muhs and Budahn, 2009).Suites of certain trace elements showdistinct compositional fields for oce-anic crust and upper continental crust(Taylor and McLennan, 1985). BulkLanzarote soils have a Sc–Th–Tacomposition that spans the rangedefined by the two end-member parentmaterials, basalt and African dust. Incontrast, the <20 lm fractions ofLanzarote soils, although outside therange of African dust, fall closer to it.On both Co–Hf–Th and Cr–Hf–Thplots, bulk-soil samples also fall be-tween the two parent materials(Fig. 7). As with Sc–Th–Ta, the<20 lm fractions of Lanzarote soilsfall much closer to the range ofAfrican dust for both Co–Hf–Th andCr–Hf–Th.

Rare earth elements (REE) are alsoemployed as provenance indicators,particularly when reduced to key ele-ment ratios (chondrite-normalized)that define the nature of the wholeREE suite. LaN ⁄YbN vs. Eu ⁄Eu* andGdN ⁄YbN vs. Eu ⁄Eu* show gooddiscrimination between basalt andAfrican dust (Fig. 8). Both bulk soilsand the soil <20 lm fractions fallbetween the fields defined by the twoparent materials, similar to the Sc–Th–Ta, Co–Hf–Th and Cr–Hf–Thplots. Note that all of the <20 lmfractions of the soils have Eu ⁄Eu*within the range of African dust.

Major-element geochemistry

Chiapello et al. (1997) show thatFe ⁄Ca and K ⁄Ca are distinctive for

(a) (b)

(c) (d)

Fig. 4 Soils on northern Lanzarote island: (a) road cut exposure of silt-rich soil material penetrating c. 21 ka basalt flow nearSP-493 (Fig. 3), with metre stick for scale; (b) basaltic stone pavement (clasts are �2 to �10 cm) with underlying silt-rich soil nearSP-500 and SP-501; (c) underside of hand specimen of c. 21 ka basalt cobble, showing soil-impregnated voids and vesicles;(d) barranco exposure of thick, silt-rich soil overlying aeolian sand, in turn overlying mid-Pleistocene basalt flow near Famara;cliffs in background are composed of Miocene–Pliocene basalt. Locality coordinates: N29�04.548¢; W13�34.495¢.


.............................................................................................................................................................


Tab

le1

Majorandtrace

elem

entconcentrationsofLanzarote

soils,basaltsfrom

CoronavolcanoandAfricandust

collected14June1967.

Sam

ple

Fe (%)

Ca

(%)

Na

(%)

K (%)

Rb

(p.p

.m.)

Sr (p.p

.m.)

Cs

(p.p

.m.)

Ba

(p.p

.m.)

Th (p.p

.m.)

U (p.p

.m.)

Zr (p.p

.m.)

Hf

(p.p

.m.)

Ta (p.p

.m.)

W (p.p

.m.)

Sc (p.p

.m.)

Cr

(p.p

.m.)

Co

(p.p

.m.)

Ni

(p.p

.m.)

Zn (p.p

.m.)

As

(p.p

.m.)

Sb (p.p

.m.)

Who

leso

ilsSP

-490

7.12

2.91

0.87

1.74

8130

23.

1354

310

.62.

9132

48.

083.

581.

3120

.138

440

.315

798

6.79

0.54

SP-4

917.

762.

641.

231.

6769

303

2.60

432

9.62

2.69

281

7.23

3.64

0.64

20.6

397

43.9

215

975.

990.

52SP

-492

7.00

4.16

1.03

1.25

6241

62.

4841

48.

912.

3926

96.

623.

261.

2219

.236

239

.418

290

5.58

0.57

SP-4

937.

615.

631.

291.

4059

611

2.33

484

8.65

1.80

285

6.75

3.49

0.85

20.9

378

41.7

174

974.

350.

37SP

-494

7.98

5.39

1.67

1.24

4856

61.

7646

66.

951.

8425

16.

263.

620.

9121

.637

744

.921

110

13.

420.

32SP

-495

8.45

3.66

1.18

1.14

6842

72.

9554

710

.13.

2732

28.

073.

931.

7623

.141

947

.923

313

05.

310.

69SP

-496

6.07

1.02

1.00

2.04

102

262

3.87

487

11.2

2.94

308

7.78

3.00

0.48

17.1

254

29.5

115

828.

090.

66SP

-497

6.41

2.39

1.02

1.87

8435

23.

1451

510

.12.

5734

18.

043.

321.

5217

.630

731

.712

491

6.42

0.60

SP-4

986.

952.

011.

021.

5382

294

3.32

465

10.2

3.11

325

7.88

3.17

0.68

18.7

333

38.0

179

907.

050.

62SP

-499

6.78

2.71

1.10

1.91

9632

83.

9749

910

.63.

1633

27.

783.

151.

4118

.325

529

.211

110

07.

350.

52SP

-500

6.64

3.60

1.29

1.79

8543

73.

4456

210

.12.

8031

57.

853.

532.

1917

.628

431

.212

912

45.

550.

58SP

-501

6.49

2.35

1.07

2.40

104

353

4.44

540

10.9

3.16

324

8.36

3.20

1.79

16.7

250

26.7

9111

97.

470.

70SP

-502

7.81

6.25

1.57

1.66

4960

61.

6944

37.

141.

4227

15.

783.

320.

4821

.438

143

.318

310

72.

840.

25SP

-503

6.72

4.43

1.07

1.56

6846

12.

6849

68.

741.

8326

06.

533.

140.

6418

.730

036

.113

110

34.

540.

45SP

-504

7.04

2.27

1.00

1.57

8530

03.

5447

710

.53.

1734

48.

803.

330.

8617

.734

834

.113

599

7.12

0.66

Soils

,<

20l

mSP

-490

6.73

0.89

1.93

2.23

100

209

4.03

482

11.4

2.45

255

5.82

3.40

0.25

19.5

173

32.2

6812

87.

400.

74SP

-491

7.29

0.95

1.98

1.98

8619

23.

5940

411

.02.

4123

75.

853.

710.

3319

.814

030

.176

105

6.91

0.62

SP-4

926.

113.

142.

212.

2188

248

4.00

367

11.0

2.76

246

5.70

3.04

1.43

17.6

135

26.2

5699

9.08

0.85

SP-4

935.

762.

221.

922.

1698

301

4.25

344

11.3

1.84

207

5.00

3.42

1.51

14.1

110

26.0

6791

6.38

0.62

SP-4

945.

682.

513.

091.

6691

274

4.09

347

9.69

2.13

213

5.28

2.65

1.21

15.1

127

25.8

7413

47.

560.

73SP

-495

6.39

1.39

3.19

2.13

9022

24.

4544

711

.23.

5223

36.

082.

930.

3218

.811

523

.167

114

7.47

0.81

SP-4

966.

291.

541.

882.

5512

422

55.

0144

012

.02.

9921

65.

532.

851.

9017

.613

226

.663

819.

980.

76SP

-497

6.35

1.98

1.75

2.44

118

309

4.67

503

11.9

2.49

213

5.82

3.15

2.14

17.6

148

24.7

4310

09.

090.

78SP

-498

6.12

1.19

2.12

2.06

106

151

4.37

438

11.1

2.89

218

5.98

2.77

1.41

17.7

148

26.0

6210

18.

890.

72SP

-499

5.74

1.22

2.17

2.06

115

175

5.04

425

10.9

2.82

235

5.20

2.24

1.66

16.4

121

19.5

6799

9.26

0.82

SP-5

005.

871.

382.

182.

4011

121

94.

9850

410

.72.

6421

35.

352.

671.

7815

.711

920

.746

148

7.75

0.80

SP-5

016.

041.

561.

752.

4112

524

05.

4746

111

.12.

7021

15.

582.

711.

4815

.313

620

.641

118

9.52

0.79

SP-5

025.

243.

543.

192.

1391

239

3.83

323

8.91

1.60

213

4.87

2.56

1.04

13.3

100

25.0

9091

5.55

0.65

SP-5

035.

773.

302.

062.

2010

528

64.

4341

310

.91.

7619

95.

282.

971.

4014

.811

027

.977

178

6.40

0.66

SP-5

046.

761.

522.

161.

9310

720

04.

5541

611

.03.

2523

26.

452.

951.

7016

.714

726

.584

105

9.30

0.83

Bas

alts

SP-4

90A

9.22

7.50

2.05

0.66

1975

30.

3353

34.

450.

9221

54.

783.

110.

6524

.948

060

.029

213

10.

710.

12SP

-492

A9.

118.

052.

050.

6416

790

0.24

490

4.84

1.36

227

4.90

3.51

1.04

24.4

485

58.4

309

140

0.74

0.14

SP-4

93A

8.94

7.63

2.21

0.82

2290

90.

4166

95.

991.

6023

65.

544.

060.

9723

.847

757

.030

812

50.

770.

13SP

-494

A8.

947.

812.

410.

6123

661

0.38

382

4.43

1.08

214

5.11

3.46

0.73

23.8

427

55.7

261

119

0.91

0.12

SP-4

96A

9.11

7.08

2.12

0.58

2075

10.

2548

94.

591.

1323

35.

133.

540.

6624

.745

458

.228

411

40.

580.

09SP

-497

A9.

128.

121.

870.

9218

744

0.26

491

4.85

1.09

230

5.03

3.44

0.68

24.4

453

59.2

287

122

0.44

0.10

SP-4

98A

8.84

7.05

2.19

0.79

1660

10.

2055

33.

230.

8420

54.

212.

450.

5022

.939

354

.924

512

40.

600.

07SP

-502

A8.

667.

972.

260.

9720

825

0.28

453

5.91

1.34

229

4.83

3.26

0.88

23.3

445

54.9

280

120

0.58

0.14

Afr

ican

dust

14Ju

ne19

67<

2l

m5.

961.

500.

151.

7511

522

36.

0161

115

.73.

3817

13.

891.

911.

8820

.412

026

.979

195

9.06

1.07

2–5

lm4.

402.

120.

412.

0411

122

65.

1475

213

.03.

1623

54.

872.

211.

3915

.294

18.8

6611

16.

801.

065–

10l

m3.

981.

020.

672.

1099

165

4.37

766

12.8

3.54

328

8.52

2.59

1.89

13.4

8914

.444

906.

230.

8910

–20

lm

3.80

1.62

0.82

1.94

8521

63.

6073

214

.64.

5861

514

.80

3.30

2.17

12.9

9713

.046

746

6.00

1.11

Typi

cal

coef

ficie

ntof

varia

tion

(as

perc

ent

ofre

port

edva

lue)

one-

sigm

a

13–

121–

44–

202–

72–

92–

101–

51–

23–

113–

71–

21–

211

–20

11–

21

2–10

2–3

3–17

4–13


.............................................................................................................................................................


three African dust-source areas(northern and western Sahara, south-ern and central Sahara, and Sahel) onthe basis of back-trajectory analysesof dust events. We recognize that,unlike the mostly immobile trace ele-ments discussed above, Fe, Ca and Kare potentially mobile in near-surface

soil zones. However, given that Lan-zarote has a mean annual precipita-tion of only 100–200 mm a)1 (GarcıaHerrera et al., 2001) and that thesubstrate is only c. 21 ka old, thesesoils have probably experienced min-imal chemical weathering. The reten-tion of easily weatherable minerals

in the soils, such as olivine and py-roxenes, supports this assumption.Thus, we use these elements cautiouslyin making interpretations of prove-nance.Both southern ⁄central Saharan dust

and northern ⁄western Saharan dusthave relatively low Fe ⁄Ca and K ⁄Ca,

Table 2 Rare earth element concentrations of Lanzarote soils, basalts from Corona volcano and African dust collected 14 June

1967.

Sample

La

(p.p.m.)

Ce

(p.p.m.)

Nd

(p.p.m.)

Sm

(p.p.m.)

Eu

(p.p.m.)

Gd

(p.p.m.)

Tb

(p.p.m.)

Ho

(p.p.m.)

Tm

(p.p.m.)

Yb

(p.p.m.)

Lu

(p.p.m.)

Whole soils

SP-490 51.4 111 50.7 9.80 2.27 7.93 1.16 1.33 0.47 2.91 0.433

SP-491 52.7 113 49.9 9.73 2.36 8.07 1.14 1.30 0.39 2.42 0.365

SP-492 46.9 102 46.5 9.05 2.23 8.11 1.06 1.24 0.41 2.34 0.342

SP-493 49.2 106 46.9 9.11 2.31 7.81 1.07 1.23 0.38 2.24 0.336

SP-494 43.6 93.8 44.9 8.90 2.39 7.48 1.09 1.17 0.40 2.13 0.300

SP-495 57.9 123 60.0 11.8 2.84 10.5 1.38 1.43 0.50 2.98 0.439

SP-496 46.4 98.4 42.8 8.86 1.85 6.99 1.05 1.31 0.47 2.93 0.446

SP-497 44.9 96.8 44.3 8.50 1.98 7.34 1.05 1.19 0.45 2.72 0.416

SP-498 48.0 102 49.5 9.34 2.10 7.97 1.11 1.29 0.47 2.76 0.422

SP-499 48.0 99.5 47.3 9.44 2.10 7.78 1.12 1.35 0.47 2.90 0.446

SP-500 48.0 101 47.3 9.29 2.13 7.68 1.03 1.32 0.44 2.68 0.405

SP-501 43.2 90.2 41.2 8.09 1.73 6.65 0.97 1.22 0.47 2.91 0.435

SP-502 46.3 96.8 44.8 9.12 2.42 7.57 1.02 1.02 0.34 2.05 0.300

SP-503 45.0 97.9 43.4 8.54 2.06 7.45 0.97 1.16 0.41 2.35 0.350

SP-504 44.1 95.8 42.4 8.44 1.87 6.90 1.02 1.18 0.44 2.83 0.417

Soils, <20 lm

SP-490 50.2 114 51.3 8.67 2.12 8.79 1.07 1.22 0.44 2.54 0.364

SP-491 54.3 127 50.6 9.93 2.39 8.72 1.10 1.06 0.39 2.30 0.314

SP-492 53.6 116 44.2 8.74 2.14 7.84 1.01 1.19 0.43 2.49 0.346

SP-493 46.8 112 40.3 6.93 1.60 6.94 0.84 0.95 0.36 2.07 0.292

SP-494 41.1 95.3 33.5 7.08 1.71 6.65 0.85 1.04 0.38 2.22 0.300

SP-495 56.8 118 66.6 10.4 2.52 9.12 1.25 1.36 0.52 2.96 0.422

SP-496 49.3 106 46.4 8.21 1.81 6.86 1.00 1.14 0.42 2.72 0.391

SP-497 48.3 103 39.6 8.07 1.79 6.93 0.99 1.12 0.43 2.64 0.370

SP-498 49.5 105 49.2 8.52 1.97 8.65 1.04 1.33 0.46 2.73 0.385

SP-499 44.1 90.0 38.8 7.44 1.64 6.48 0.93 1.07 0.43 2.51 0.370

SP-500 44.2 91.6 42.0 7.23 1.67 6.55 0.88 1.02 0.42 2.48 0.367

SP-501 39.6 82.1 37.5 6.35 1.34 5.32 0.79 1.02 0.40 2.54 0.360

SP-502 37.9 80.9 29.2 6.13 1.48 5.43 0.74 0.81 0.31 1.86 0.268

SP-503 44.9 99.2 42.3 7.10 1.65 6.72 0.90 1.14 0.40 2.22 0.328

SP-504 43.9 93.8 42.5 7.47 1.64 7.07 0.90 1.09 0.41 2.60 0.386

Basalts

SP-490A 40.4 80.2 39.2 7.92 2.58 7.57 1.05 0.99 0.32 1.78 0.243

SP-492A 50.3 95.7 45.9 8.82 2.85 8.61 1.11 1.09 0.33 1.81 0.252

SP-493A 58.4 107 50.0 9.33 2.94 8.34 1.17 1.13 0.33 1.87 0.254

SP-494A 40.2 78.3 38.5 7.73 2.52 7.96 1.01 1.06 0.31 1.73 0.244

SP-496A 43.5 83.7 40.1 8.11 2.67 7.95 1.06 1.01 0.30 1.74 0.238

SP-497A 46.9 88.5 43.7 8.38 2.73 7.39 1.07 0.97 0.30 1.75 0.242

SP-498A 28.9 58.7 29.5 6.40 2.25 6.27 0.92 0.97 0.29 1.65 0.219

SP-502A 57.6 107 49.9 9.18 2.95 8.75 1.15 1.18 0.33 1.92 0.261

African dust

<2 lm 61.0 133 57.1 11.5 2.31 11.4 1.35 1.62 3.69 0.543

2–5 lm 48.4 104 49.7 9.64 2.00 10.2 1.16 1.41 3.45 0.517

5–10 lm 44.2 90.2 42.9 8.43 1.64 9.19 1.19 1.58 4.33 0.617

10–20 lm 46.6 94.9 45.7 8.96 1.77 9.48 1.34 1.95 5.81 0.846

Typical coefficient of

variation (as percent

of reported value)

one-sigma

1 1 2–8 1 1–2 4–10 2–4 10–15 8–20 2–3 2–3


.............................................................................................................................................................


due to high carbonate contents in thesource areas (Chiapello et al., 1997).The geochemical fields for these twoSaharan regions do not form a rea-sonable mixing-line plot with basaltfor either whole Lanzarote soils or the<20 lm fraction of the soils (Fig. 9).In contrast, the Fe ⁄Ca–K ⁄Ca field forSahel dust (Fig. 9c) forms a goodmixing-line plot with basalt for Lan-zarote whole soils (Fig. 9c). A reason-able mixing-line plot is also seen forbasalt and fine-grained (<2 lm) Afri-can dust collected on Barbados, whichrepresents a mix of Saharan and Sahelsources (Fig. 9d).

Discussion

The particle-size distribution of Lan-zarote soils permits an inferenceof multiple parent materials. Localbasalt is the source of the sand frac-tion. Excluding the three soils withvery high sand contents, we interpretthe abundant (44–59%) quantities ofsilt to reflect aeolian inputs fromAfrica, in agreement with previousworkers. Silt-sized particles with diam-eters of �20–30 lm are expected forshort-to-intermediate range aeoliantransport from Africa. Long-range-transported particles from Africa aremore likely to be <20 lm, with most

Table 3 Major element concentrations in African dust collected on Barbados.

Date collected

Particle

size (lm)

Na

(%)

K

(%)

Ca

(%)

Fe

(%)

27 May 1967 0–2 0.32 2.35 1.90 5.32

2–5 0.50 2.4 2.16 4.19

5–10 0.64 2.05 2.47 4.01

10–20 0.62 2.1 1.17 3.20

7 June 1967 0–2 0.24 2.22 1.21 5.41

2–5 0.49 2.35 2.43 4.49

5–10 0.66 2.54 2.58 3.57

10–20 0.71 2.07 1.63 3.71

14 June 1967 0–2 0.154 1.75 1.50 5.96

2–5 0.411 2.04 2.12 4.40

5–10 0.673 2.1 1.02 3.98

10–20 0.821 1.94 1.62 3.80

3 July 1967 0–2 0.29 1.65 1.23 5.68

2–5 0.48 1.8 2.66 4.72

5–10 0.67 1.19 2.92 3.98

10–20 0.84 1.07 2.14 3.99

24 August 1967 0–2 0.24 2.53 1.24 5.33

2–5 0.53 2.23 3.09 4.40

5–10 0.80 2.63 3.38 4.01

10–20 0.92 2.05 2.65 3.85

27 September 1967 0–2 0.35 2.66 1.31 5.21

2–5 0.68 3.32 2.20 4.64

5–10 0.76 2.7 1.25 4.15

1 October 1968 0–2 0.28 1.67 2.20 5.45

2–5 0.52 1.69 3.65 4.45

5–10 0.74 3.26 3.35 4.15

3 July 1969 0–2 0.199 1.86 1.22 6.10

2–5 0.403 1.97 2.34 4.89

5–10 0.633 2.07 2.17 4.20

10–20 0.784 1.82 1.30 3.59

>20 0.770 1.34 1.66 3.53

6 July 1969 0–2 0.19 2.32 0.95 5.96

2–5 0.37 3.55 2.04 4.79

5–10 0.62 2.41 2.42 4.05

10–20 0.81 1.62 1.88 3.84

1

0.8

0.6

0.4

0.2

0 1 0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0 1 0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0

Coarse silt

Silt Fine silt

Cla

y

Sand

Cla

y

Iowaloess

Illinoisloess

Coloradoloess Iowa

loess

Illinoisloess

Coloradoloess

Lanzarotesoils

Lanzarotesoils

Fig. 5 Ternary diagrams showing amounts of sand (>53 lm), silt (53–2 lm) and clay(<2 lm) (left) and amounts of coarse silt (53–20 lm), fine silt (20–2 lm) and clay ona sand-free basis (right). Also shown for comparison are values for these particle-sizeclasses from North American loess sections of last-glacial age at Fort Morgan,Colorado, Sioux City, Iowa, and Greenbay Hollow, Illinois (North American loessdata from Muhs et al., 2008b).

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30

SP-492

SP-496

SP-499

SP-504

Sm

ectit

e

Mic

a Kao

linite

Qua

rtz

Qua

rtz

+m

ica

Mic

a

Kao

linite

Degrees 2-theta

Fig. 6 X-ray diffractograms for glyco-lated clay separates from four soils onLanzarote (see Fig. 3 for locations).


.............................................................................................................................................................


being <10 lm. A number of the dustsamples collected immediately offshoreAfrica by Stuut et al. (2005) haveprimary modes in the 20–30 lm sizerange, although many others havemodes that are <10 lm. The highamounts of fine (20–2 lm) silt and clay(<2 lm) in Lanzarote soils suggest thepossibility of long-range transportfrom distal African sources.The soil mineralogy, with quartz

and mica both in bulk samples and inthe clay fraction, indicates inputs fromsources external to the island. Thedominance of mica and quartz is con-

sistent with the most abundant miner-als found in modern dust collectedelsewhere on the Canary Islands (Alas-tuey et al., 2005). Kaolinite is moredifficult to explain in Lanzarote soils.Kaolinite could be an alteration prod-uct of plagioclase, which is well docu-mented (Birkeland, 1999) but is not aprocess expected on relatively younglava in an arid climate. Lanzarotecurrently receives only 100–200 mmof precipitation annually (Garcıa Her-rera et al., 2001) andwas probably aridduring the late glacial period as well(Hooghiemstra et al., 1992). Thus, we

interpret kaolinite in Lanzarote soils tohave an external, aeolian origin.Kaolinite is not abundant in the

Entisols and Aridisols that dominatethe soil geography of the SaharaDesert of northern and western Africa(Fig. 10). Paquet et al. (1984) studieda north–south soil ⁄ sediment transectacross Algeria, from �35� to �19�N.They report that mica and chlorite aredominant at higher latitudes, withgreater amounts of kaolinite at lowerlatitudes. On the basis of this study,we would not expect the largeamounts of kaolinite we observe in

0.8

0.6

0.4

0.2

0.6

0.4

0.2

0

0.8

0.6

0.4

0.2

1

0.8

0.6

0.4

0.2

0 1 0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0

Th

Ta

x 10

Sc

1

0.8

0.6

0.4

0.2

0 1 0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0

Th

Ta

x 10 Sc

Hf

Th

Cr/10

1

0.8

0.6

0.4

0.2

0

0.8

0.6

0.4

0.2

0

1

0.8

0.6

0.4

0.2

0

Hf

Th C

o

Africandust Corona

basalt

Africandust

Corona basalt

Africandust

Coronabasalt

Africandust

Corona basalt

Lanzarote soils:

Whole soil

< 20 µm fraction

< 20 µm

Whole soil

< 20 µm

Whole soil

< 20 µm

Whole soil < 20 µm

Whole soil

Fig. 7 Sc–Th–Ta x10 (full plot, plus blow-up of partial plot), Cr ⁄10–Hf–Th and Co–Hf–Th ternary plots of Lanzarote soils(circles) compared with c. 21 ka basalt samples and African dust collected on Barbados. Soil and basalt data are from the presentstudy; African dust data are from the present study and data in Muhs et al. (2007a).


.............................................................................................................................................................


young Lanzarote soils to be derivedfrom the northern and central parts ofthe Sahara. A more likely source forkaolinite is the east–west-trending belt

of Alfisols and Inceptisols found in theSahel region (Figs 1 and 10). TheSahel is an important dust sourcewhen droughts occur in this region,

as they did in the 1970s (Prospero andNees, 1977, 1986; Prospero and Lamb,2003). Chester et al. (1972) and Stuutet al. (2005), in shipboard studies of

1.2

0.8

0.6

0.4

1.0

5 10 15 20 25

Eu/

Eu*

Coronabasalt

African dust

Lanzarote soils

(a)

Whole soil< 20 µm fraction

LaN/YbN

1.0

1.2

0.8

0.6

0.41.0 1.5 2.0 2.5 3.0 3.5 4.0

Eu/

Eu*

GdN/YbN

Coronabasalt

African dust

(b)

Lanzarote soils

Whole soil< 20 µm fraction

Fig. 8 (a) Eu ⁄Eu* vs. LaN ⁄YbN and (b) Eu ⁄Eu* vs. GdN ⁄YbN in Lanzarote soils compared with c. 21 ka basalt samples andAfrican dust collected on Barbados. Soil and basalt data are from the present study; African dust data are from the present studyand data in Muhs et al. (2007a).

3.0

2.5

2.0

1.5

1.0

0.5

0.00 1 2 3 4 5 6 7

K/C

a

Fe/Ca0 1 2 3 4 5 6 7

Fe/Ca

3.0

2.5

2.0

1.5

1.0

0.5

0.00 1 2 3 4 5 6 7

K/C

a

Fe/Ca0 1 2 3 4 5 6 7

Fe/Ca8

88

8

Northern and western Saharan

dust

Southern and central Saharan

dust

Sahelregiondust

Corona basalt

Corona basalt Corona basalt

Corona basalt

African dust at

Barbados: 2–20 µm African

dust atBarbados:

<2 µm

Lanzarote soils:

Whole soil

< 20 µm fraction

Lanzarote soils:

Whole soil

< 20 µm fraction

Lanzarote soils:

Whole soil

< 20 µm fraction

Lanzarote soils:

Whole soil

< 20 µm fraction

(a) (b)

(c) (d)

Fig. 9 Fe ⁄Ca vs. K ⁄Ca for Lanzarote soils (circles), Corona basalt on Lanzarote (black ellipse), African dust collected onBarbados (stipple) and Sal Island (Cape Verde Islands) dust identified as being from the Sahel, southern and central Sahara, andnorthern and western Sahara (stippled boxes). Sahel and Saharan dust data are from Chiapello et al. (1997) and boxes define themean ±2 standard deviations. All other data are from the present study.


.............................................................................................................................................................


African dust, report a decrease in themica ⁄kaolinite ratio from the CanaryIslands southward. The southwardincrease in the kaolinite content ofdust probably reflects the increasingkaolinite content of adjacent Africansoils, moving from the Sahara to theSahel. Soils on Lanzarote havemica ⁄kaolinite peak-area ratios of0.9–2.0, corresponding to the rangesof mica ⁄kaolinite values in dust re-ported by Chester et al. (1972) forlatitudes of �15� to �5�S (Fig. 10).The arid climate ofLanzarote should

also retain calcite, if delivered fromcalcite-rich sources in Morocco (Khiriet al., 2004), as suggested by previousworkers. Its absence in all the soils weexamined suggests that much of theAfrican dust delivered to these soils isfrom a calcite-poor source, such as theSahel. A Sahel contribution also ex-plains the relatively high Fe ⁄Ca values

that are observed in soils on Lanzarote.Soils in the Sahel region not only haverelatively high kaolinite contents butalso have low Ca contents and high Fecontents (e.g., Ambrost et al., 1986;Faure and Volkoff, 1998; Duclouxet al., 2002).Although the main direction of

dust transport in the SAL is to thewest, at latitudes between �15� and�21�N, the northward hook-like tra-jectory of air-mass movement candeliver dust to the Canary Islands.MODIS imagery from the Terra andAqua satellites shows this componentof dust movement from southerlysources in the summers of 2004 and2007 (Fig. 2).

Conclusions

Soils on a late Quaternary volcanicflow in the Canary Islands contain

abundant fine silt and clay, evidenceof long-range aeolian transport. Thesoils contain quartz and mica, notfound in the local basalt and likelyfrom Africa. Kaolinite may also bederived from western-African soils ofthe Sahel region that are rich in thismineral. Immobile trace-element geo-chemistry shows that the soils arederived from varying proportions oflocally derived basalt and Africandust. Major-element geochemistry,along with the presence of kaolinitesuggest that of the aeolian compo-nent, both Sahel and Saharan dustsources in western Africa play animportant role in soil genesis. Satel-lite imagery shows that dust fromSahel sources is transported north-ward, in a hook-like form, west ofthe African coast and toward theCanary Islands. Our results showthat even young soils in an aridclimate can have a complex origin,with dust inputs from both theSahara and Sahel.

Acknowledgements

This study was supported by the GlobalChange Program of the US GeologicalSurvey and is a contribution to the�Impacts of Climate Change on Coastaland Eolian Landscapes� project (http://esp.cr.usgs.gov/info/eolian/). We appreciatethe efforts of Zachary Muhs Rowland,who ably assisted with field work. Manythanks to Dr Joaquın Meco (Universidadde Las Palmas de Gran Canaria) and hisfamily members, who taught us the localQuaternary geology and were gracioushosts while we visited the islands. A sam-pling permit was kindly provided by DrMaria Aranzazu Gutierrez Avila, Directo-ra General de Cooperacion y PatrimonioCultural, Gobierno de Canarias. Sincerethanks also to Dr Ludwig Zoller and DrHans Von Suchodoletz who introduced usto the geology of Lanzarote. We thankMax Coleman, Vincenzo Pascucci, RandySchaetzl, Yehouda Enzel, Paul Carrara,Jeff Pigati, Gene Ellis and three anony-mous reviewers who read an earlier versionof the paper and made helpful commentsfor its improvement.

References

Alastuey, A., Querol, X., Castillo, S.,Escudero, M., Avila, A., Cuevas, E.,Torres, C., Romero, P.-M., Exposito, F.,Garcıa, O., Diaz, J.P., Van Dingenen, R.and Putaud, J.P., 2005. Characterisationof TSP and PM2.5 at Izana and Sta.Cruz de Tenerife (Canary Islands, Spain)

Lanazarotesoils:

Cape VerdeIslands

0°30°

30°

40°

20°

10°

Atlantic

Ocean

Atlantic

Ocean

AFRICA

EUROPE

Active aeolian sand

Aridisols and Entisols

Alfisols and Inceptisols

Ultisols

Oxisols

Explanation

15°

CanaryIslands

Mica/Kaolinite:2.17

Mica/Kaolinite:2.17

Mica/Kaolinite:1.55

Mica/Kaolinite:0.97

Mica/Kaolinite: 0.20

Mica/Kaolinite:0.9–1.6

AlgeriaMorocco

Libya

Mauritania

Mali

Niger

Nigeria

Wes

tern

Sahar

a

Senegal

IvoryCoast

BurkinaFaso

Guinea

Cameroon

Ghana

Tuni

sia

Cha

d

Fig. 10 Soil geography of western Africa, redrawn and generalized from USDepartment of Agriculture, Natural Resources Conservation Service �Global SoilRegions� map (http://www.soils.usda.gov/use/worldsoils/mapindex/order.html), inturn derived from the FAO–UNESCO Soil Map of the World (Food and AgricultureOrganization of the United Nations, UNESCO, 1974). Also shown are ship tracks(dashed lines) in the dust-collecting expedition of Chester et al. (1972); solid horizontallines mark boundaries of individual dust-collection traverses. Mica ⁄kaolinite ratiosgiven are clay-mineral peak-height ratios (<2 lm fraction) calculated from data foreach dust-collection traverse in Chester et al. (1972) and Lanzarote soils (Fig. 6).


.............................................................................................................................................................


during a Saharan dust episode (July2002). Atmos. Environ., 39, 4715–4728.

Ambrost, J.P., Nahon, D. and Herbillon,A.J., 1986. The epigenetic replacement ofkaolinite by hematite in laterite; petro-graphic evidence and the mechanismsinvolved. Geoderma, 37, 283–294.

Bergametti, G., Gomes, L., Coude-Gaus-sen, C., Rognon, P. and Le Coutumer,M.-N., 1989. African dust observed overCanary Islands: Source-regions identifi-cation and transport pattern for somesummer situations. J. Geophys. Res., 94,14855–14864.

Birkeland, P.W., 1999. Soils and Geomor-phology. Oxford University Press, NewYork.

Budahn, J.R. and Wandless, G.A., 2002.Instrumental neutron activation by longcount. U.S. Geol. Surv. Open-File Rep.OF, 02-0223, Y1–Y9.

Carlson, T.N. and Prospero, J.M., 1972.The large-scale movement of Saharanair outbreaks over the Northern Equa-torial Atlantic. J. Appl. Meteorol., 11,283–297.

Carracedo, J.C. and Day, S., 2002. CanaryIslands. Terra Publishing, Harpenden,UK.

Carracedo, J.C., Singer, B., Jicha, B.,Guillo, H., Rodrıguez Badiola, E.,Meco, J., Perez Torrado, F.J., Gimeno,D., Socorro, S. and Lainez, A., 2003. Laerupcion y el tubo volcanico del volcanCorona (Lanzarote, Isla Canarias). Es-tud. Geol., 59, 277–302.

Chester, R., Elderfield, H., Griffin, J.J.,Johnson, L.R. and Padgham, R.C.,1972. Eolian dust along the easternmargins of the Atlantic Ocean. Mar.Geol., 13, 91–105.

Chiapello, I., Bergametti, G., Chatenet, B.,Bousquet, P., Dulac, F. and Santos So-ares, E.S., 1997. Origins of African dusttransported over the northeastern tropi-cal Atlantic. J. Geophys. Res., 102,13701–13709.

Coude-Gaussen, G., Rognon, P., Berga-metti, G., Gomes, L., Strauss, B., Gros,J.M. and Le Coustumer, M.N., 1987.Saharan dust on Fuerteventura Island(Canaries): chemical and mineralogicalcharacteristics, air mass trajectories, andprobable sources. J. Geophys. Res., 92,9753–9771.

Criado, C. and Dorta, P., 2003. An unu-sual �blood rain� over the Canary Islands(Spain). The storm of January 1999.J. Arid Environ., 55, 765–783.

Dubief, J., 1979. Review of the northAfrican climate with particular emphasison the production of eolian dust in theSahel zone and in the Sahara. In: Saha-ran Dust: Mobilization, Transport,Deposition (C. Morales, ed.), pp. 27–48.John Wiley & Sons, Chicester.

Ducloux, J., Guero, Y., Sardini, P. andDecarreau, A., 2002. Xerolysis: a hypo-

thetical process of clay particles weath-ering under Sahelian climate. Geoderma,105, 93–110.

Faure, P. and Volkoff, B., 1998. Somefactors affecting regional differentiationof the soils in the Republic of Benin(West Africa). Catena, 32, 281–306.

Food and Agriculture Organization of theUnited Nations, UNESCO, 1974. SoilMap of the World, 1: 5,000,000, v. 6,Africa. UNESCO, Paris.

Garcıa Herrera, R., Gallego Puyol, D.,Hernandez Martın, E., Gimeno Presa, L.and Ribera Rodrıguez, P., 2001. Influ-ence of the North Atlantic Oscillationon the Canary Islands precipitation.J. Climate, 14, 3889–3903.

Glaccum, R.A. and Prospero, J.M., 1980.Saharan aerosols over the tropical northAtlantic – Mineralogy. Mar. Geol., 37,295–321.

Goudie, A.S. and Middleton, N.J., 2006.Desert Dust in the Global System.Springer, Heidelberg.

Grousset, F.E., Rognon, P., Coude-Gaus-sen, G. and Pedemay, P., 1992. Originsof peri-Saharan dust deposits traced bytheir Nd and Sr isotopic composition.Palaeogeogr. Palaeoclimatol. Palaeo-ecol., 93, 203–212.

Grousset, F.E., Parra, M., Bory, A.,Martinez, P., Bertrand, P., Shimmield,G. and Ellam, R.M., 1998. Saharan windregimes traced by the Sr-Nd isotopiccomposition of subtropical Atlanticsediments: last glacial maximum vstoday. Quatern. Sci. Rev., 17, 395–409.

Hooghiemstra, H., Stalling, H., Agwu,C.O.C. and Dupont, L.M., 1992.Vegetational and climatic changes atthe northern fringe of the Sahara250,000-5000 years BP: evidence from 4marine pollen records located betweenPortugal and the Canary Islands. Pal-aeogeogr. Palaeoclimatol. Palaeoecol.,74, 1–53.

Jahn, R., Zarei, M. and Stahr, K., 1987.Formation of clay minerals in soilsdeveloped from basic volcanic rocksunder semiarid climatic conditions inLanzarote, Spain. Catena, 14, 359–368.

Kalu, A.E., 1979. The African dust plume:Its characteristics and propagationacross west Africa in winter. In: Saharandust: Mobilization, Transport, Deposition(C. Morales, ed.), pp. 95–118. JohnWiley & Sons, Chicester.

Khiri, F., Ezaidi, A. and Kabbachi, K.,2004. Dust deposits in Souss-Massabasin, South-West of Morocco:granulometrical, mineralogical andgeochemical characterization. J. Afr.Earth Sci., 39, 459–464.

Kohfeld, K.E. and Tegen, I., 2007. Recordof mineral aerosols and their role in theEarth system. In: Treatise on Geochem-istry (H.D. Holland and K.K. Turekian,eds), 26 pp. Elsevier. Available at: http://

www.sciencedirect.com/science/refer-enceworks/9780080437514.

Mahowald, N.M., Muhs, D.R., Levis, S.,Rasch, P.J., Yoshioka, M., Zender, C.S.and Luo, C., 2006. Change in atmo-spheric mineral aerosols in response toclimate: Last glacial period, preindustri-al, modern, and doubled carbon dioxideclimates. J. Geophys. Res., 111, D10202.doi:10.1029/2005JD006653.

McTainsh, G. and Walker, P.H., 1982.Nature and distribution of Harmattandust. Z. Geomorphol., 26, 417–435.

Meco, J., Ballester, J., Betancort, J.F.,Cilleros, A., Scaillet, S., Guillou, H.,Carracedo, J.C., Lomoschitz, A., Petit-Maire, N., Ramos, A.J.G., Perera, N.,Meco, J.M., 2006. Paleoclimatologıa delNeogeno en las Islas Canarias. Geliense,Pleistoceno y Holoceno. Ministerio deMedio Ambiente – Universidad de LasPalmas de Gran Canaria, Servicio dePublicaciones de la ULPGC, LasPalmas, Spain.

Mizota, C. and Matsuhisa, Y., 1995.Isotopic evidence for the eolian originof quartz and mica in soils developedon volcanic materials in the CanaryArchipelago. Geoderma, 66, 313–320.

Muhs, D.R. and Budahn, J.R., 2009.Geochemical evidence for African dustand volcanic ash inputs to terra rossasoils on carbonate reef terraces, northernJamaica, West Indies. Quatern. Int., 196,13–35.

Muhs, D.R., Budahn, J., Prospero, J.M.and Carey, S.N., 2007a. Geochemicalevidence for African dust inputs to soilsof western Atlantic islands: Barbados,the Bahamas and Florida. J. Geophys.Res., 112, F02009. doi:10.1029/2005JF000445.

Muhs, D.R., Budahn, J., Reheis, M., Be-ann, J., Skipp, G. and Fisher, E., 2007b.Airborne dust transport to the easternPacific Ocean off southern California:evidence from San Clemente Island.J. Geophys. Res., 112, D13203.doi:10.1029/2006JD007577.

Muhs, D.R., Budahn, J., Johnson, D.L.,Reheis, M., Beann, J., Skipp, G., Fisher,E. and Jones, J.A., 2008a. Geochemicalevidence for airborne dust additions tosoils in Channel Islands National Park,California. Geol. Soc. Am. Bull., 120,106–126.

Muhs, D.R., Bettis, E.A., III, Aleinikoff,J., McGeehin, J.P., Beann, J., Skipp, G.,Marshall, B.D., Roberts, H.M., John-son, W.C. and Benton, R., 2008b. Originand paleoclimatic significance of lateQuaternary loess in Nebraska: Evidencefrom stratigraphy, chronology, sedi-mentology, and geochemistry. Geol. Soc.Am. Bull., 120, 1378–1407.

Paquet, H., Coude-Gaussen, G. andRognon, P., 1984. Etude mineralogiquede poussieres sahariennes le long d�un


.............................................................................................................................................................


itineraire entre 19� et 35� de latitudenord. Rev. Geol. Dynam. Geog. Phys., 25,257–265.

Prospero, J.M. and Carlson, T.N., 1972.Vertical and areal distribution of Saha-ran dust over the western equatorialNorth Atlantic Ocean. J. Geophys. Res.,77, 5255–5265.

Prospero, J.M. and Lamb, P.J., 2003.African droughts and dust transport tothe Caribbean: climate change implica-tions. Science, 302, 1024–1027.

Prospero, J.M. and Nees, R.T., 1977. Dustconcentration in the atmosphere of theequatorial North Atlantic: possible rela-tionship to the Sahelian drought. Sci-ence, 196, 1196–1198.

Prospero, J.M. and Nees, R.T., 1986. Im-pact of the North African drought andEl Nino on mineral dust in the Barbadostrade winds. Nature, 320, 735–738.

Prospero, J.M., Bonatti, E., Schubert, C.and Carlson, T.N., 1970. Dust in theCaribbean atmosphere traced to anAfrican dust storm. Earth Planet. Sci.Lett., 9, 287–293.

Prospero, J.M., Ginoux, P., Torres, O.,Nicholson, S.E. and Gill, T.E., 2002.Environmental characterization of glo-bal sources of atmospheric soil dustidentified with the Nimbus 7 TotalOzone Mapping Spectrometer (TOMS)absorbing aerosol product. Rev. Geo-phys., 40, 1002. doi:10.1029/2000RG000095.

Pye, K., 1987. Aeolian Dust and DustDeposits. Academic Press, London.

Rognon, P., Coude-Gaussen, G., Revel,M., Grousset, F.E. and Pedemay, P.,1996. Holocene Saharan dust depositionon the Cape Verde Islands: sedimento-logical and Nd-Sr isotopic evidence.Sedimentology, 43, 359–366.

Sarnthein, M., Tetzlaff, G., Koopman, B.,Wolter, K. and Pflaumann, U., 1981.Glacial and interglacial wind regimesover the eastern subtropical Atlantic andNorth-West Africa. Nature, 293, 193–196.

Schwanghart, W. and Schutt, B., 2008.Meteorological causes of Harmattandust in West Africa. Geomorphology, 95,412–428.

Stein, R. and Sarnthein, M., 1984. LateNeogene events of atmospheric andoceanic circulation offshore northwestAfrica: High-resolution record fromdeep-sea sediments. Palaeoecol. Afr., 16,9–36.

Stuut, J.-B., Zabel, M., Ratmeyer, V.,Helmke, P., Schefuß, E., Lavik, G. andSchneider, R., 2005. Provenance ofpresent-day eolian dust collected off NWAfrica. J. Geophys. Res., 110, D04202.doi:10.1029/2004JD005161.

Stuut, J.-B., Smalley, I. and O�Hara-Dhand, K., 2009. Aeolian dust in Eur-ope: African sources and Europeandeposits. Quatern. Int., 198, 234–245.

Taylor, S.R. and McLennan, S.M., 1985.The Continental Crust: Its Compositionand Evolution. Blackwell Scientific Pub-lications, Oxford.

Tejedor Salguero, M.L., Jimenez Mendoza,C., Rodriguez, A. and Caldas, E.F.,1985. Polygenesis on deeply weatheredPliocene basalt, Gomera (Canary is-lands): from ferrallitization to saliniza-tion. Catena Suppl., 7, 131–151.

Tetzlaff, G. and Peters, M., 1986. Deep-seasediments in the eastern equatorialAtlantic off the African coast and mete-orological flow patterns over the Sahel.Geol. Rundsch., 75, 71–79.

Torres-Padron, M.E., Gelado-Caballero,M.D., Collado-Sanchez, C., Siruela-

Matos, V.F., Cardona-Castellano, P.J.and Hernandez-Brito, J.J., 2002. Vari-ability of dust inputs to the CANIGOzone. Deep-Sea Res. II, 49, 3455–3464.

Von Suchodoletz, H., Fuchs, M. and Zol-ler, L., 2008. Dating Saharan dustdeposits on Lanzarote (Canary Islands)by luminescence dating techniques andtheir implication for paleoclimate con-struction of NW Africa. Geochem. Geo-phys. Geosyst., 9, Q02Q07. doi:10.1029/2007GC001658.

Von Suchodoletz, H., Faust, D. andZoller, L., 2009a. Geomorphologicalinvestigations of sediment traps onLanzarote (Canary Islands) as a keyfor the interpretation of a paleoclimateoff NW Africa. Quatern. Int., 196, 44–56.

Von Suchodoletz, H., Kuhn, P., Hambach,U., Dietz, M., Zoller, L. and Faust, D.,2009b. Loess-like and palaeosol sedi-ments from Lanzarote (Canary Is-lands ⁄Spain) – indicators ofpalaeoenvironmental change during theLate Quaternary. Palaeogeogr. Palaeo-climatol. Palaeoecol., 278, 71–87.

Zoller, L., H. Von Suchodoletz, H. andKuster, N., 2003. Geoarchaeological andchronometrical evidence of early humanoccupation on Lanzarote (Canary Is-lands).Quatern. Sci. Rev., 22, 1299–1307.

Zoller, L., Von Suchodoletz, H., Blan-chard, H., Faust, D. and Hambach, U.,2004. Reply to the comment by J.C.Carracedo et al. on �Geoarchaaeologicaland chronometrical evidence of earlyhuman occupation on Lanzarote (Can-ary Islands)�. Quatern. Sci. Rev., 23,2049–2055.

Received 2 March 2010; revised versionaccepted 27 April 2010


.............................................................................................................................................................


Geochemical and mineralogical evidence for Sahara and ... · islands bedrock. Kaolinite in the...

Documents

Transcript of Geochemical and mineralogical evidence for Sahara and ... · islands bedrock. Kaolinite in the...