Climatic and oceanographic variations on the California ...directory.umm.ac.id/Data...

Climatic and oceanographic variations on the Californiacontinental margin during the last 160 kyr

Kai Mangelsdorf *, Ute GuÈ ntner, JuÈ rgen RullkoÈ tter

Institute of Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, PO Box 2503,

D-26111 Oldenburg, Germany

Received 24 May 1999; accepted 23 May 2000

(returned to author for revision 18 August 1999)

Abstract

Organic matter in sediment samples from three ODP sites (Ocean Drilling Program Leg 167) that form a south-north

transect was investigated to reconstruct the paleoclimatic and oceanographic conditions on the California continentalmargin during the last 160 kyr. Alkenone-derived paleosea surface temperatures (SST) are 3 to 6�C colder in glacialstages and reveal a clear relationship with global climate changes; the di�erences are greater in the north. LatitudinalSST comparison exhibits water mixing of the colder California Current with warmer waters from the south, particu-

larly in the southern central California borderland area. Organic matter accumulation on the California continentalmargin indicates an interplay between climatic and atmospheric glacial±interglacial variations and spatially and tem-porally changing nutrient availability along the California coastline. Climatic and atmospheric dependent circulations

apparently caused variations in the intensity of coastal upwelling along the southern central California margin and thissuggests, due to the close connection of the California Current to the local wind patterns, that the California Currentwas weaker during glacial and stronger during interglacial periods. # 2000 Elsevier Science Ltd. All rights reserved.

Keywords: n-Alkanes; California Current; Coastal upwelling; Dinosterol; SST; Stable carbon isotopes

1. Introduction

1.1. Study area

Sedimentation on the California continental margin isstrongly in¯uenced by the California Current system,

which is formed by a complex structure of di�erentcurrents (Hickey, 1979). The California Current itself,one of the important eastern boundary currents of the

world, ¯ows southward along the coast of NorthAmerica (Fig. 1). Seasonal variations of strength andorientation of individual currents within the California

Current system and changes of the local wind patternsare largely driven by the seasonal migration (28�N in

January to 38�N in July; Fig. 1) of the North Paci®cHigh pressure system (Huyer, 1983). These shifts andthe resulting di�erences in wind intensity and direction,

and therefore of the California Current, cause intra-annual variations of upwelling patterns along the Cali-fornia and Oregon coastline (Nelson, 1977; Huyer, 1983),

with strongest upwelling during spring and summer.North of about 40�N, coastal upwelling is episodic andmostly occurs in summer and early fall (Huyer, 1983).

The structure of the California Current system andthe closely associated coastal upwelling are sensitive notonly to seasonal changes but also to long-range climatic

changes. Reconstructions of sea surface temperatures(SST) over the last 30 kyr have revealed a change tohigher temperatures since the Last Glacial Maximum(LGM) (Prahl et al., 1995; Mortyn et al., 1996; Doose et

al., 1997; Ortiz et al., 1997). Other studies suggest reducedcoastal upwelling for the last glacial interval (Sancetta etal., 1992; Dean et al., 1997; Ortiz et al., 1997).

0146-6380/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.

PI I : S0146-6380(00 )00066-8

Organic Geochemistry 31 (2000) 829±846

www.elsevier.nl/locate/orggeochem

* Corresponding author. Tel.: +49-441-798-3415; fax: +49-

441-798-3404.

E-mail address: [email protected] (K. Mangelsdorf).

Evidence of an increase in marine productivity sincethe last glacial [oxygen isotope stage 2, (OIS 2)] to the

present indicate signi®cant changes in atmospheric andoceanographic conditions along the California con-tinental margin (Lyle et al., 1992). Longer studies up to

60 kyr similarly indicate higher productivity during thelast interstadial (OIS 3) (Hemphill-Haley, 1995; Dean etal., 1997; Gardner et al., 1997).Modern seasonal high marine productivity along the

California continental margin leads to oxygen depletionin the North Paci®c Intermediate Water (NPIW) fromorganic matter remineralisation in the water column

(Dean et al., 1997). Oxygen concentrations of <0.5 ml/lde®ne an Oxygen Minimum Zone (OMZ) between 600and 1200 m water depth in the northeastern Paci®c

Ocean o� California. Nevertheless, modern surfacesediments in most areas are well bioturbated, indicatingthat oxygen depletion today is not strong enough to

prevent a diverse benthic fauna from thriving on theocean ¯oor. In contrast, laminated intervals in severalcores along the northern and central California marginindicate anoxic sediment surface conditions in some

areas during OIS 3 (Dean et al., 1994, 1997). Laminatedintervals were also found in some basins of the SouthernCalifornian Bight, e.g. in the Santa Barbara basin

(Kennett, 1995). However, the sediments of this studyfrom Ocean Drilling Program (ODP) Holes 1017B and

1019C, which were drilled within the modern OMZdepth range, are mostly bioturbated with the exceptionof some thin laminated layers.

A high-resolution sediment sequence recovered dur-ing ODP Leg 146 in the Santa Barbara basin (Site 893)in 1992 provides information on climatic variations inthis area over the past 160 kyr (Kennett et al., 1995;

Hinrichs et al., 1997). The alkenone-derived SST data ofHinrichs et al. (1997) re¯ect global climatic changesexcept for strong temperature ¯uctuations during the

last glacial period and strongly elevated SST values inthe Eemian (OIS 5e, 125 ka) in comparison to theHolocene. These unexpectedly high alkenone-derived

temperatures during the last glacial and the Eemianwere also reported by Herbert et al. (1995), but they di�erfrom those derived from the oxygen isotope record of

benthic and planktonic foraminifera (Kennett, 1995;Kennett and Ingram, 1995a; Hendy and Kennett, 1999).The main objectives of the present study were to

investigate the climatic development on the California

continental margin in a latitudinally more extendedrange and to obtain more information about the evolu-tion of the California Current as well as the history of

Fig. 1. The major surface currents (adapted from Hickey, 1979) and the summer positions of the atmospheric pressure systems of the

northeast Paci®c Ocean. The inset shows the study area on the western North American continental margin with the drilling locations

1017, 1018 and 1019 (ODP Leg 167) as well as Site 893 in the Santa Barbara basin (ODP Leg 146). SCal, CCal, NCal=southern,

central and northern California continental margin;. SCB=Southern Californian Bight.

830 K. Mangelsdorf et al. / Organic Geochemistry 31 (2000) 829±846

coastal upwelling and marine productivity during thelast 160 kyr using organic geochemical methods. Theresults are compared to those available from ODP Site893 (Santa Barbara basin) south of the present study

area (Fig. 1).

1.2. Molecular paleotemperature indicator

Reconstructed paleosea surface temperatures (SST)are an important parameter for elucidating the oceano-

graphic history of marine environments and the evolu-tion of climate on Earth. Over the last two decades amolecular organic geochemical proxy, the UK0

37 -Index,

has been established to estimate paleosea surface tem-peratures (Prahl and Wakeham, 1987). Long-chainpolyunsaturated methyl and ethyl alkenones with 37±39carbon atoms are constituents of phytoplankton genera

of the class Haptophyceae, such as the coccolithophoresEmiliania huxleyi andGephyrocapsa oceanica (Volkman etal., 1980, 1995). The unsaturation ratio of the C37 methyl

ketones with 2±4 double bonds (UK37=[C37:2ÿC37:4]/

[C37:2+C37:3+C37:4]) was recognized as a temperature-sensitive parameter re¯ecting environmental growth

temperatures (Brassell et al., 1986). With rising tem-perature, the concentration of the C37:2 ketone increasesrelative to that of the more unsaturated congeners. In

laboratory cultures of an Emiliania huxleyi strain col-lected in the North Paci®c, Prahl and Wakeham (1987)found a linear relationship between the simpli®ed UK0

37 -Index (UK0

37=[C37:2]/[C37:2+C37:3]) and growth temperature

over the range of 8±25�C. They established a calibrationequation for SST assessment, which was subsequentlyslightly modi®ed by Prahl et al. (1988) to UK0

37=

0.034�SST+0.039. This equation allows SST estimateswith remarkable accuracy throughout much of theworld ocean (MuÈ ller et al., 1998).

2. Materials and Methods

2.1. Samples

We selected 79 sediment samples from Holes 1017B,

1018A and 1019C that were drilled during ODP Leg 167and constitute a south-north transect along the centraland northern California continental margin (Fig. 1).

Hole 1017B (34�32.0910N, 121�6.4150W) is locatedabout 50 km west of Point Arguello on the continentalslope at 955 m water depth (southern central California

margin, SCCal). It is situated near an important modernupwelling center o� Point Conception (Jones et al.,1983). Hole 1018A (36�59.3000N, 123�16.6530W) wasdrilled about 75 km west of Santa Cruz on a sediment

drift south of Guide Seamount at a water depth of 2477 m[central California margin, (CCal)]. Hole 1019C(41�40.9720N, 124�55.9750W) is located about 60 km

west of Crescent City in the Eel River basin at a waterdepth of 977 m (northern California margin, NCal).Hole 893A (34�17.250N, 120�02.20W) was drilled earlierduring ODP Leg 146 at a water depth of 576.5 m (Fig.

1) in the center of the semi-enclosed Santa Barbarabasin, where occasionally suboxic to anoxic bottom-water conditions prevail (Kennett et al., 1995).

2.2. Chronostratigraphy

Sediment ages for Site 1017 are available from Hole1017E (drilled parallel to Hole 1017B) based on theoxygen isotope record (d18O) of benthic foraminifera

down to the onset of OIS 5 (129.8 ka) and, for the last32 kyr, also on 14C measurements (Kennett et al., 2000).For sediments older than 130 ka, chronostratigraphywas estimated by comparing the alkenone-derived SST

pro®le of Hole 1017B, which we determined down toabout 900 kyr, with the standard oxygen isotope recordof Martinson et al. (1987). We corrected a miscorrela-

tion of the initial shipboard splice (Lyle et al., 1997) forthe transition from Core 2H to Core 3H and from Core3H to Core 4H of Hole 1017B (Table 2). Chronostrati-

graphy of Hole 1018A is based on correlations of datedCaCO3 and Corg events, observable in several coresalong the northern and central California margin, con-

®rmed by the oxygen isotope compositions (d18O) ofbenthic foraminifera (Lyle et al., 2000). The late Holo-cene section (presumably the ®rst 8 kyr) is missing fromHole 1018A probably due to recovery problems (Lyle et

al., 2000), which complicates the age assignment for theresidual Holocene section (�8 to 13.59 kyr) and conse-quently required rough extrapolation. Age assignments

for Hole 1019C are from 14C measurements on planktonicand benthic foraminifera and from the oxygen isotopecomposition of benthic foraminifera (Mix et al., 2000).

Gaps in sediment recovery in Holes 1017B and 1018Awere bridged by samples from nearby Holes 1017C and1018D, respectively.

2.3. Mass accumulation rates

Total organic carbon (TOC) patterns based on weight

percentages of dry sediment can sometimes be mislead-ing, because this parameter can be a�ected by dilutionwith variable amounts of biogenic or clastic mineral

matter. Organic carbon mass accumulation rates (Corg-

MAR, mg cmÿ2 kyrÿ1) are calculated to eliminate thisdilution e�ect by using the equation (van Andel et al.,

1975; Lyle, 1988):

CorgMAR � TOC� �� SA;

where TOC=total organic carbon content (mg gSedÿ1),�=dry bulk density (g cmÿ3, shipboard data from ODP

K. Mangelsdorf et al. / Organic Geochemistry 31 (2000) 829±846 831

Leg 167; Lyle et al., 1997) and SA=average sedimentationrate (cm kyrÿ1). Chronostratigraphic data used for thecalculation of sedimentation rates are given in Table 1.Due to the chronostratigraphic problems in the Holo-

cene section of Hole 1018A, sedimentation rates for theearly Holocene period were only tentatively calculatedbased on the approach that the youngest Holocene

sediment is about 8 ka old. Average sedimentation ratesare highest at Hole 1019C (28.5 cm kyrÿ1) and some-what lower at Hole 1018A (23.3 cm kyrÿ1) and Hole

1017B (19.1 cm kyrÿ1).

2.4. Analytical methods

After sediment samples had been freeze-dried andground, organic carbon content (TOC) was determinedusing a Leco-SC-444 combustion instrument and a UIC

CO2-coulometer. For lipid analysis, sample aliquotsof about 10 g were extracted ultrasonically using amixture of CH2Cl2 and MeOH (99/1, v/v). After addi-

tion of internal standards (squalane, eruic acid [n-C22:1],5a-androstan-17-one), the extracts were dissolved inn-hexane to precipitate asphaltenes, which were

removed from the soluble fraction by ®ltration onNaSO4. The n-hexane-soluble fraction was separated bymedium-pressure liquid chromatography (Radke et al.,

1980) into fractions of aliphatic/alicyclic hydrocarbons,aromatic hydrocarbons and polar heterocomponents(NSO). Carboxylic acids were separated from the NSOfraction using a column ®lled with KOH-impregnated

silica gel prepared by adding 0.5 g KOH in 10 ml iso-propanol to 5 g silica gel 100 (63±200 mm). The non-acidic compounds (neutral fraction) were eluted with

CH2Cl2.The compounds of interest were analyzed by gas

chromatography on a Hewlett-Packard 5890 Series II

instrument equipped with a Gerstel KAS 3 cold injec-tion system and a fused silica capillary column (J&W; 30m length, inner diameter=0.25 mm, coated with DB 5,®lm thickness=0.25 mm). Helium was used as carrier

gas, and the temperature of the GC oven was pro-grammed from 60�C (1 min) to 305�C at a rate of 3�C/min, followed by an isothermal phase of 50 min. The

injector temperature was programmed from 60�C (5 shold time) to 300�C (60 s hold time) at 8�C/s. For com-pound identi®cation an identical gas chromatographic

system was linked to a Finnigan SSQ 710 B mass spectro-meter that was operated in the electron impact mode ata scan rate of 1 scan/s.

Carbon isotopic measurements of total organic mat-ter were done after dissolution of carbonates with 0.1 NHCl and subsequent drying of the samples at 50�Covernight. For isotopic analyzes, a CHN analyzer was

attached to a Finnigan MAT 252 isotope mass spectro-meter. Isotopic ratios are expressed as d13C values inpermil relative to the V-PDB standard.

3. Results and discussion

3.1. Reconstruction of paleosea surface temperatures onthe California continental margin

The alkenone-derived SST pro®les of the three holes(Table 2; Fig. 2), calculated by using the calibration of

Prahl et al. (1988), show strong ¯uctuations and, thus,point to a pronounced change in the climatic and oceano-graphic conditions during the last 160 kyr. The Holo-

cene SST values of Holes 1017B and 1018A and theupper Holocene values of Hole 1019C correspond withthe measured modern average annual sea surface tem-

peratures (Hole 1017B: 14±15�C, Hole 1018A: 12±14�C,and Hole 1019C: 11±13�C [National Oceanic andAtmospheric Administration (NOAA)1; Huyer, 1983]and with alkenone-derived SST data of core top sedi-

ments along the California margin (Herbert et al.,1998).At the transition from OIS 6 to OIS 5e (Eemian), SST

values steeply rise to temperatures of 13±18�C, depend-ing on location. The Eemian temperature maxima inHoles 1017B and 1018A are 3±4�C higher than the

Holocene values, con®rming the exceptionally highalkenone-based SST values calculated by Herbert et al.(1995) and Hinrichs et al. (1997) in the Santa Barbara

basin for the same time interval. In the younger sectionof OIS 5 the temperatures decline to values similar tothose in the modern ocean. The transition to OIS 4 ischaracterized by a sharp decline of SST values to 8±

11�C at all locations. The temperature rise in OIS 3 issmall and is interrupted by distinct declines, especiallynear the transition to the last glacial (OIS 2). The tem-

peratures in the last glacial are consistently low, rangingfrom 11.5�C (Hole 1017B) to 6.5�C (Hole 1019C). Atthe transition from the last glacial to the Holocene, the

sea surface temperature increases sharply by 4±6�C.This is particularly well expressed in Hole 1019C, wheresampling resolution for this interval was highest. Thetemperature record of Hole 1017B is fairly uniform

during the Holocene, but the more resolved data ofHole 1019C indicate ¯uctuation of Holocene tempera-tures by 1±2�C.The SST records re¯ect the global glacial±interglacial

climate variations during the last 160 kyr. These alter-nations are also marked by variable percentages of the

C37:4 alkenone relative to total C37 alkenone concentra-tions (Table 2). The relative concentration of the tetra-unsaturated C37 ketone, as expected, is in general lower

during interglacial stages and increases during glacialstages and in the last interstadial (OIS 3).

1 http://ferret.wrc.noaa.gov/fbin/climate_server


Table 1

Chronostratigraphic data used for calculation of sedimentation rates

Hole (ODP 167-) Depth

(cmcd)aAge

(ka)

Sedimentation rate

(cm kyrÿ1)Reference

1017B 205.5 9.41 21.67 Kennett et al. (2000)

274.5 12.19 24.80 0 0

288.5 14.36 6.45 0 0

337.5 16.87 19.55 0 0

395.5 18.97 27.64 0 0

469.5 21.43 30.03 0 0

607.5 28.55 19.40 0 0

744.5 32.96 31.04 0 0

1224.5 58.96 18.46 0 0

1354.9 73.91 8.72 0 0

1476.5 79.25 22.77 0 0

1649.5 90.95 14.78 0 0

2077.5 110.79 21.57 0 0

2294.5 123.82 16.65 0 0

2411.5 129.84 19.43 0 0

2831.3 160.0 13.92 SST comparison

1018A 0 8b ± Lyle et al. (2000)

161 13.59 28.80c 0 0

424 20.16 40.03 0 0

609 25.53 34.45 0 0

844 32.92 31.8 0 0

944 36.57 27.39 0 0

1004 39.15 23.26 0 0

1133 44.21 25.49 0 0

1173 45.91 23.53 0 0

1313 52.97 19.83 0 0

1657 67.22 24.14 0 0

1900 75.36 29.85 0 0

2000 79.53 23.98 0 0

2029 81.18 17.58 0 0

2089 85.94 12.61 0 0

2189 94.72 11.39 0 0

2229 97.8 12.99 0 0

2289 101.77 15.11 0 0

2409 108.65 17.44 0 0

2449 111.18 15.81 0 0

2589 121.74 13.26 0 0

2818 136.97 15.04 0 0

2878 140.36 17.7 0 0

2941 143.45 20.39 0 0

3061 148.48 23.86 0 0

3177 152.39 29.67 0 0

3437 160.18 33.38 0 0

1019C 418 9.80 42.65 Mix et al. (2000)

718 14.7 61.24 0 0

821 17.0 44.78 0 0

1171 22.67 61.67 0 0

1461 30.02 39.48 0 0

1581 34.56 26.43 0 0

1800 47.79 16.55 0 0

1895 55.53 12.27 0 0

2027 62.34 19.38 0 0

(continued overpage)


3.1.1. Comparison with paleo-SST record of the Santa

Barbara basinTwo alkenone-derived SST records are available for

the Santa Barbara basin (Fig. 3a: Hinrichs et al., 1997;

Fig. 3b: Herbert et al., 1995). The SST data of Herbertet al. (1995) seem to be 1±2�C higher than the data ofHinrichs et al. (1997) in some sections, but the general

patterns of both curves match well. A combined SSTcurve of both data sets (Fig. 3c) mirrors most variationsof the d18O curve of benthic foraminifera from theSanta Barbara basin (Fig. 3d) much better than each

SST curve separately, indicating that some of theapparent temperature di�erences maybe due to di�erentsampling horizons.

A comparison of the SST pro®les of the Californiacontinental margin transect (Fig. 2) with the SST datafrom Site 893 in the Santa Barbara basin (Fig. 3c) shows

only little coincidence for the last glacial section. Duringthis period, the alkenone-derived temperature signal ofthe Santa Barbara basin is characterized by strong tem-perature ¯uctuations, which are not, however, re¯ected

in the oxygen isotope record of Hole 893A of either thebenthic (Fig. 3d; Kennett, 1995) or the planktonic for-aminifera (Globigerina bulloides) (Kennett and Ingram,

1995b; Hendy and Kennett, 1999). Unless the d18O datadepend also on salinity changes and the ``ice volumee�ect'' [about 1.2±1.3 % (Broecker, 1989; Ortiz et al.,

1997)], the oxygen isotope values of the foraminiferaobviously re¯ect the general low-temperature signal ofthe last glacial, while the alkenone-derived SST pattern

reveals occasional short-term warming events in thesurface waters.The di�erence in temperature signals may relate to

the di�erent water depths at which coccolithophores

and planktonic foraminifera live. By comparing sea-sonal temperature variations at di�erent water depths,Herbert et al. (1998) concluded that coccolithophores

mainly live in the upper 30 m of the water column. In

contrast, planktonic foraminifera (i.e. Neogloboquadrinapachyderma and Globigerina bulloides) live at greaterdepths (�100 m) and ascend to near-surface water

(upper 20 m) during upwelling events (Thunell andSautter, 1992). Upwelling intensity, however, was lessduring the last glacial, as suggested for the northern part

of the California continental margin by Sancetta et al.(1992). In contrast, Hendy and Kennett (1999) recentlyfavored the view that G. bulloides preferentially live innear-surface water and do not respond to changes in

upwelling intensity over the year in the Santa Barbarabasin.During glacial times of lowered sea level, the Santa

Barbara basin was closed in the south by a large islandand to the west and east by shallow submarine sills (Fig.4). Due to the exposure of land masses covered today by

water and shallower depth of submarine elevations fur-ther o�shore, the California Current may have beendiverted westward, i.e. away from the coast, at this time.This then would have reduced the in¯uence of the cold

California Current on the Santa Barbara basin.Although during eustatic low sea level the eastern sillpresumably has shifted the main ¯ow of the warmer

Southern California Counter Current south of the SantaBarbara basin (Gardner and Dartnell, 1995), thereduced in¯uence of the California Current may at least

occasionally have allowed the in¯ow of warmer near-surface waters from the southeast. These events may bere¯ected in the alkenone temperature signal of the sedi-

ments from the Santa Barbara basin.In contrast to the latitudinal di�erences in tempera-

ture ¯uctuations in the last glacial, the SST pro®les ofHoles 1017B, 1018A, 1019C and 893A (Figs. 2 and 3)

show relatively uniform paleosea surface temperaturevariations during OIS 3±6, and these variations gen-erally covary with the oxygen isotope record of benthic

Table 1 (continued)

Hole (ODP 167-) Depth

(cmcd)aAge

(ka)

Sedimentation rate

(cm kyrÿ1)Reference

2181 71.27 17.25 Mix et al. (2000)

2361 77.77 27.69 0 0

2462 83.08 19.02 0 0

2789 107.25 13.53 0 0

2840 109.87 19.47 0 0

2914 112.81 25.17 0 0

3140 119.86 32.05 0 0

3966 139.65 41.74 0 0

4031 143.04 19.17 0 0

4556 160.06 30.85 0 0

a cmcd, depth in cm composite depth, which compensates for recovery gaps in separate boreholes by comparing physical properties

of multiple parallel cores at the same drilling location.b Estimated age of the youngest Holocene sediment of Hole 1018A (see text).c Tentatively estimated sedimentation rates (see text).


Table 2

Sample numbers, corrected core depths, ages, UK037 values, sea surface temperature estimates (SST), percentage of C37:4 methyl ketone

relative to total C37 alkenone amounts, d13C of total organic matter and TOC contents of the investigated sediment samples from

Holes 1017B (C), 1018A (D) and 1019Ca

Sample no. Depth (cmcd) Age (ka) UK037 SST (�C) C37:4 (%) d13CTOC (%) TOC (%)

167-1017B-1H-1,90±92 cm 1.2 5.5 0.526 14.3 1.3 ÿ21.4 2.39

1H-2,120±122 cm 3.0 15.0 0.432 11.6 5.9 ÿ22.5 2.22

1H-3,15±17 cm 3.45 17.1 0.479 12.9 6.1 ÿ22.4 1.49

1H-3,69±71 cm 3.99 19.1 0.450 12.1 6.8 ÿ22.3 0.27

1H-3,76±78 cm 4.06 19.3 0.386 10.2 4.2 ÿ22.2 1.78

1H-3,90±92 cm 4.20 19.8 0.436 11.7 4.9 ÿ22.2 1.41

1H-3,121±123 cm 4.51 20.8 0.422 11.3 6.8 ÿ22.2 1.33

1H-4,20±22 cm 5.00 22.5 0.441 11.8 6.0 ÿ22.4 0.78

1H-4,37±39 cm 5.17 23.9 0.420 11.2 7.7 ÿ22.4 1.31

2H-1,20±22 cm 6.20 28.9 0.431 11.5 7.4 ÿ22.5 0.67

2H-1,90±92 cm 6.90 31.2 0.438 11.7 7.6 ÿ22.1 0.93

2H-3,90±92 cm 9.90 46.3 0.439 11.8 4.9 ÿ22.1 1.41

2H-5,92±94 cm 12.92 66.7 0.465 12.5 4.8 ÿ22.3 0.99

167-1017C-2H-5,120±122 cm 15.90 86.9 0.488 13.2 3.0 ÿ21.7 1.82

167-1017B-3H-1,90±92 cm 16.52b 91.1 0.559 15.3 1.4 ÿ21.2 1.90

3H-3,90±92 cm 19.52b 105.0 0.534 14.6 1.5 ÿ21.5 1.82

3H-5,90±92 cm 22.52b 121.3 0.644 17.8 ± ÿ21.3 3.13

4H-1,90±92 cm 22.86b 123.4 0.621 16.8 1.1 ÿ21.5 2.19

4H-3,90±92 cm 25.86b 142.4 0.408 10.9 3.4 ÿ22.4 1.17

4H-5,90±92 cm 28.92b 164.4 0.435 11.7 6.4 ÿ22.5 0.97

167-1018A-1H-1,10±12 cm 0 8.0c 0.480 13.0 2.1 ÿ21.3 3.24

1H-1,90±95 cm 0.78 10.7c 0.481 13.0 1.7 ÿ21.5 2.41

1H-2,90±92 cm 2.28 15.3 0.339 8.8 8.1 ÿ22.6 1.31

1H-2,130±132 cm 2.68 16.3 0.302 7.7 10.7 ÿ22.3 1.09

1H-3,22±24 cm 3.10 17.3 0.302 7.7 8.1 ÿ22.0 1.09

1H-3,50±52 cm 3.38 18.0 0.322 8.3 8.5 ÿ22.0 1.07

1H-3,68±70 cm 3.56 18.5 0.314 8.1 9.2 ÿ21.8 1.06

1H-3,90±95 cm 3.78 19.0 0.325 8.4 9.1 ÿ21.9 1.09

2H-1,103±108 cm 6.97 28.3 0.313 8.1 9.0 ÿ22.3 1.01

2H-2,90±92 cm 8.34 32.6 0.339 8.8 7.5 ÿ22.1 1.33

2H-3,90±95 cm 9.84 38.3 0.390 10.3 7.8 ÿ22.1 1.39

2H-4,90±92 cm 11.34 44.3 0.396 10.5 5.5 ÿ22.3 1.67

2H-5,90±95 cm 12.84 51.5 0.412 11.0 6.1 ÿ21.9 1.64

2H-6,90±92 cm 14.84 60.1 ± ± ± ÿ22.1 1.42

3H-1,90±95 cm 18.35 73.2 0.369 9.7 8.7 ÿ22.4 1.12

3H-2,90±92 cm 19.85 78.9 0.353 9.3 9.6 ÿ21.9 1.47

3H-3,90±95 cm 21.35 90.0 0.460 12.4 5.2 ÿ21.6 1.61

3H-4,90±92 cm 22.85 101.5 0.457 12.3 3.1 ÿ21.6 2.22

3H-5,25±27 cm 23.70 106.4 0.458 12.3 ± ÿ22.0 1.42

3H-5,90±95 cm 24.35 110.3 0.516 14.0 2.4 ÿ21.8 1.68

3H-6,10±12 cm 25.05 115.4 0.440 11.8 4.9 ÿ22.2 1.97

3H-6,49±51 cm 25.45 118.4 0.519 14.1 ± ± 1.98

3H-6,72±74 cm 25.68 120.2 0.557 15.2 3.2 ± 1.53

3H-6,80±82 cm 25.76 120.8 0.531 14.5 2.6 ± 1.60

3H-6,90±92 cm 25.85 121.4 0.561 15.2 1.4 ÿ21.7 1.30

3H-6,120±122 cm 26.15 123.5 0.471 12.7 4.4 ÿ22.2 1.31

3H-7,10±12 cm 26.55 126.1 0.451 12.1 5 ÿ22.4 1.21

3H-7,32±34 cm 26.77 127.6 0.396 10.5 5.2 ÿ22.5 1.17

167-1018D-3H-5,80±82 cm 27.11 129.9 0.435 11.7 4.0 ÿ22.4 1.11

3H-5,100±102 cm 27.31 131.2 0.430 11.5 4.6 ÿ22.4 1.15

3H-5,120±122 cm 27.51 132.5 0.408 10.9 4.6 ÿ22.2 1.13

167-1018A-4H-1,90±95 cm 29.21 142.5 0.411 10.9 4.6 ÿ22.5 0.72

(continued overpage)


Table 2 (continued)

Sample no. Depth (cmcd) Age (ka) UK037 SST (�C) C37:4 (%) d13CTOC (%) TOC (%)

4H-2,90±92 cm 30.71 148.8 0.354 9.3 4.9 ÿ22.1 1.21

4H-3,90±92 cm 32.21 153.7 ± ± ± ÿ22.6 1.17

4H-4,90±92 cm 33.71 158.2 0.305 7.8 9.6 ÿ22.3 0.88

167-1019C-1H-1,80±85 cm 0.80 1.9 0.457 12.3 2.8 ÿ21.2 2.06

1H-3,80±85 cm 3.80 8.9 0.442 11.9 4.2 ÿ22.4 1.41

1H-5,80±85 cm 6.80 14.1 0.457 12.3 4.8 ÿ21.6 1.64

2H-1,32±34 cm 8.63 17.7 0.261 6.5 12.3 ÿ23.1 1.17

2H-1,80±85 cm 9.11 18.5 0.298 7.6 7.6 ÿ23.1 0.75

2H-2,37±39 cm 10.18 20.2 0.297 7.6 8.7 ÿ22.9 1.21

2H-2,112±114 cm 10.93 21.4 0.260 6.5 14.6 ÿ23.3 0.64

2H-3,80±85 cm 12.11 23.7 0.338 8.8 11.3 ÿ22.4 1.27

2H-4,106±108 cm 13.87 28.1 0.324 8.4 11.9 ÿ22.6 1.47

2H-5,80±85 cm 15.12 31.9 0.295 7.5 12.1 ÿ22.4 1.13

3H-1,80±85 cm 18.72 53.7 0.394 10.4 9.6 ÿ22.5 1.16

3H-3,80±85 cm 21.72 70.7 0.316 8.1 10.4 ÿ22.9 1.00

4H-1,80±85 cm 30.22 116.2 0.349 9.1 6.1 ÿ23.1 0.84

4H-2,62±64 cm 31.54 120.2 0.426 11.4 3.7 ± 1.32

4H-2,148±150 cm 32.4 122.3 0.467 12.6 4.0 ± 1.15

4H-3,52±54 cm 32.94 123.5 0.455 12.2 3.7 ± 1.06

4H-3,80±85 cm 33.22 124.2 0.484 13.1 3.7 ÿ22.7 1.07

4H-4,92±94 cm 34.84 128.1 0.488 13.2 4.5 ÿ22.1 1.42

4H-5,80±85 cm 36.22 131.4 0.461 12.4 3.7 ÿ23.0 1.51

4H-5,142±144 cm 36.84 132.9 0.404 10.7 4.2 ± 1.21

4H-6,52±54 cm 37.44 134.3 ± ± ± ± 0.93

4H-7,21±23 cm 38.63 137.2 0.273 6.9 7.0 ± 0.56

5H-1,80±85 cm 40.69 144.3 0.331 8.6 8.8 ÿ23.2 0.83

5H-3,80±85 cm 43.69 154.0 0.337 8.8 8.7 ÿ23.4 0.79

a Shipboard data (Figs. 2, 6 and 7) are from ODP Leg 167 (Lyle et al., 1997).b Revised cmcd (see text).c Tentatively extrapolated ages (see text).

Fig. 2. Alkenone-derived paleosea surface temperature (SST) pro®les for Holes 1017B, 1018A and 1019C (ODP Leg 167). The sec-

tions marked grey represent warmer periods. The dashed lines indicate average measured modern sea surface temperatures (NOAA).

Open circles represent shipboard data (Lyle et al., 1997). OIS=oxygen isotope stage; CCM=California continental margin.


foraminifera in the Santa Barbara basin (Fig. 3d). Thesesimilarities suggest regionally uniform paleoclimateconditions. However, the alkenone-derived SST pro®lesof Holes 893A, 1017B and 1018A do not show the same

abrupt increase at the OIS 6/5 transition as the oxygenisotope record of Hole 893A. This again indicates thatthe two temperature assessments, at least during certain

periods, record di�erent temperature signals.

3.1.2. Latitudinal paleosea surface temperature trendsIn order to visualize latitudinal trends along the

California continental margin, we calculated averagepaleosea surface temperatures for each oxygen isotope

stage, for the Eemian period (116±127 kyr) and the LastGlacial Maximum (17±22 kyr). For Hole 893A we usedthe combined SST curve (Fig. 3c). Temperatures clearly

decrease from south to north, certainly due to decreasing

Fig. 3. Alkenone-derived paleosea surface temperature (SST) pro®les of (a) Hinrichs et al. (1997), (b) Herbert et al. (1995), (c) com-

bined data sets (a) and (b), (d) d18O of benthic foraminifera (Kennett et al., 1995) for Hole 893A (Santa Barbara basin, ODP Leg 146).

The sections marked grey represent warmer periods. OIS=oxygen isotope stage.

Fig. 4. Geographical sketch visualizing di�erent currents probably in¯uencing sea surface temperatures in the Santa Barbara basin

and Site 1017 during the last glacial. The thin dotted line marks the modern coastline.


insolation. The steeper temperature gradient in thesouthern part of the transect between Holes 1017B and1018A suggests an additional factor to be involved (Fig.5a). Warmer surface water coming from the south (like

the Southern California Counter Current today) probablyhas mixed with colder water of the California Current andhas increased temperatures in the southern central Cali-

fornia borderland area.The temperature di�erence between Holes 1017B and

1018A is smaller during the Holocene (�2�C) than during

the LGM (�3.5�C), indicating that glacial cooling hasin¯uenced the northerly locations in a stronger way.This can also be seen from the di�erences between

Holocene and LGM average temperatures for eachlocation (Fig. 5b), which are about 2�C higher at Holes1018A and 1019C than at Hole 1017B. This north-southtrend is consistent with the alkenone-derived SST

assessments of Doose et al. (1997) and Prahl et al.(1995) for the last 30 kyr.

The temperature di�erence between Holes 1017B and893A during the last glacial period is about 1.7�C (Fig.5a and b). This di�erence over a short geographicaldistance is related to the strong ¯uctuations observed at

Site 893, which have been ascribed above to occasionalincursion of warmer surface waters from the south intothe Santa Barbara basin. If only the lower last glacial

temperatures in the Santa Barbara basin are used forcomparison, the average values are approximately thesame as those at Site 1017.

During the Eemian (OIS 5e), the temperature di�er-ence (4±5�C) between the southerly locations and thoseon the central and northern California margin is greater

than during any other period, with average temperaturesat Holes 1018A and 1019C being in the range of theHolocene temperatures and those at Holes 1017B and893A exceeding Holocene temperatures by 2.9±3.3�C(Fig. 5b). This points to an increased warming of thesurface water at Holes 893A and 1017B and occasionally

Table 3

Calculated average alkenone-derived SST data for the Holocene, the Last Glacial Maximum, the Eemian period and the last 160 kyr

and di�erences between Holocene and last glacial and Holocene and Eemian average SST values

Holes 893A 1017B 1018A 1019C

Latitudes 34�17.250N 34�32.0910N 36�59.3000N 41�40.9720NAverage SST last 160 kyr 13.3�C 13.0�C 10.6�C 10.4�CAverage SST Holocene (0±12 kyr) 14.7�C 14.7�C 13.0�C 12.5�CAverage SST Last Glacial Maximum (17±22 kyr) 13.3�C 11.6�C 8.1�C 7.1�CAverage SST Eemian (116±127 kyr) 18.0�C 17.5�C 14.0�C 12.5�C�SST LGM±Holocene ÿ1.4�C ÿ3.1�C ÿ4.9�C ÿ5.4�C�SST Eemian±Holocene 3.3�C 2.8�C 1.0�C 0�CModern average annual SSTa 14±15�C 14±15�C 12±14�C 11±13�C

a Modern physically determined average sea surface temperatures from National Oceanic and Atmospheric Administration.

Fig. 5. (a) Latitudinal trends of average alkenone-derived paleosea surface temperatures along the California coastline of the Holo-

cene, the Last Glacial Maximum (LGM), the Eemian (OIS 5e) and the last 160 kyr; (b) di�erences between Holocene and LGM and

between Holocene and Eemian SST data (Table 3).


at Hole 1018A, as indicated by a temperature rise to15.2�C (Fig. 2, middle). An incursion of water from awarmer source in the south is conceivable for the southerncentral California borderland area during the Eemian.

Hinrichs et al. (1997) proposed that the high tempera-tures in the Eemian (OIS 5e) in the Santa Barbara basincould be related to a long-lasting ENSO (El NinÄ o-

Southern Oscillation) situation. However, this phenom-enon seems not to have a�ected the northern part of theCalifornia continental margin.

3.2. Reconstruction of the paleoceanographic conditionson the California continental margin

The California Current and coastal Californianupwelling are closely connected to each other by thelocal wind system. The coastal upwelling record should,

therefore, provide information on the dynamics of theCalifornia Current over time. We measured TOC con-tents (Table 2), calculated organic carbon mass accu-

mulation rates (CorgMAR), determined marine as wellas terrestrial biomarkers in sediments from the last 160kyr, and analyzed d13C values of total organic matter as

organic geochemical proxies for upwelling dynamics.

3.2.1. Organic carbon accumulation

The modern California continental margin has a pro-nounced seasonal coastal upwelling. Large parts of theHolocene and the last interstadial (OIS 3) were probablycharacterized by similar conditions. Lyle et al. (1992)

used Corg ¯ux studies in the multitracer 42�N east-westtransect near Hole 1019C to conclude that marineorganic carbon new productivity doubled from the

LGM to the Holocene. Gardner et al. (1997) showedthat marine productivity in the Holocene was relativelyhigh and that strong coastal upwelling prevailed on the

southern and the central California margin. Dean et al.(1997) inferred that productivity along the Californiacoastline was highest during the Holocene and OIS 3and lowest during the last glacial interval. These obser-

vations are supported by enrichment of other paleopro-ductivity proxies in Holocene and last interstadial (OIS3) sediments, e.g. opal, biogenic Ba, as well as diatom

species (Thallasionoides nitzschioides) and pollen(Sequoia) that are restricted to upwelling regions(Dymond et al., 1992; Lyle et al., 1992; Hemphill-Haley,

1995; Dean et al., 1997; Gardner et al., 1997).Our TOC and CorgMAR measurements for the

southern central (Hole 1017B) and central (Hole 1018A)

California margin also reveal maxima (Fig. 6) duringthe Holocene and the last interstadial (OIS 3), suggest-ing that marine surface productivity was elevated atthese sites during these periods. Lower CorgMAR in the

early last glacial of Holes 1017B and 1018A then wouldbe the result of weak or occasional lack of coastalupwelling, but enhanced organic carbon accumulation

starts at the beginning of the LGM (about 20 ka) atboth sites.During OIS 4±6, a similar glacial±interglacial organic

carbon accumulation contrast is evident in the sedi-

ments of the southern central California location (Hole1017B). However, on the central California margin(Hole 1018A) the glacial±interglacial organic carbon

accumulation alternation, although still recognizable inthe TOC pro®le, is reduced to single Corg events duringOIS 5 and 6 due to extremely variable sedimentation

rates.In contrast to sediments at Sites 1017 and 1018, sedi-

ments of Hole 1019C display low CorgMAR during OIS 3

and in large parts of OIS 5, following a pronounced Corg-

MAR maximum in the Eemian after an early rise duringthe OIS 6/5 transition (Fig. 6). Last glacial sediments arecharacterized by a strongly ¯uctuating accumulation pat-

tern with a distinct trend to higher CorgMAR. Thisseems to contradict observations of Sancetta et al.(1992), who inferred weakened summer upwelling in the

last glacial from the absence of redwood pollen on thenorthern California/southern Oregon margin (upwellingcauses coastal fog, which is an essential source of

moisture required by redwoods). Lyle et al. (1992) in anearshore location of a 42�N east±west transect adjacentto Hole 1019C also found that present and LGM Corg-

MAR data are in the same order of magnitude with amaximum during deglaciation, but they also found thatthe proportion of terrestrial organic matter during theLGM was twice as high as in the Holocene. Correction

for the terrestrial organic matter fraction revealed thatglacial marine CorgMAR was half of that of the Holo-cene. The total organic mass accumulation in the last

glacial section at our northernmost location may also bea�ected by terrestrial organic matter supplied by thedrainage of the Eel River, because this section shows a

steep increase of sedimentation rates starting in late OIS3 (Table 1). Lower organic carbon burial during OIS 3and a large part of OIS 5 illustrates that the mechanismsa�ecting organic matter accumulation strongly varied

between the northern and southern California con-tinental margin.

3.2.2. Biomarker investigationsTo explore details of changes in delivery and accu-

mulation of organic matter, we analyzed the concentra-

tions of marine and terrestrial molecular organicbiomarkers at Sites 1017±1019. We selected dinosterol(4a-23,24-trimethylcholest-22-en-3b-ol) and the sum of

C37 methylketones with two and three double bonds asmarine biomarkers and long-chain C25±C35 n±alkanes(maximum consistently at C29) as biomarkers repre-senting a terrestrial source (Eglinton and Hamilton,

1967). Dinosterol appears to be restricted to the algaeclass of Dinophyceae (Volkman, 1986; Volkman et al.,1998), and the alkenones are constituents of phyto-


plankton belonging to the class of Haptophyceae (seeIntroduction). Both types of marine biomarkers werefound in all sediments investigated in this study, indicat-ing that source organisms of both biomarkers were com-

mon members of the phytoplanktonic community alongthe California coast over the last 160 kyr. Long chainn-alkanes are constituents of the epicuticular waxes of

higher land plants. They are transported to the marine

environment by river discharge or wind (Gagosian et al.,1981, 1987). Another possible source of n-alkanes in thisarea may be eroded rocks of the Monterey Formationand related oil seeps (Curiale et al., 1985; Hinrichs et al.,

1995), but average Carbon Preference Index (C27±C33)values of 5.6 (Hole 1017B), 5.8 (Hole 1018A) and 3(Hole 1019C) indicate only a minor in¯uence of oil on

the distribution of the long chain n-alkanes.

Fig. 6. (a) TOC contents, (b) organic carbon mass accumulation rates (CorgMAR) of sediment samples from Holes 1017B, 1018A and

1019C. The sections marked grey represent warmer periods. OIS=oxygen isotope stage. Triangles and dashed line=early Holocene

TOC data of Hole 1018A based on (a) extrapolated ages and (b) CorgMARs therefore on tentatively calculated sedimentation rates.

Note di�erent scales of CorgMAR axes.


The marine biomarkers indicate higher marineorganic matter accumulation rates during the Holocene(OIS 1) and the last interglacial (OIS 5) on the southerncentral (Hole 1017B) California margin, which is, in

general, accompanied by an elevated organic-carbon-normalized concentration of these compounds (Fig. 7).The concentrations of the terrigenous indicators are low

during the Holocene and reveal the highest accumula-tion rates during OIS 2, OIS 3 and OIS 5, also obviousfrom TOC-normalized proportion of n-alkanes. On the

central California margin (Hole 1018A), marine organicmatter accumulation is higher during the Holocene andsome parts of OIS 3, OIS 5 and notably during OIS 6.

Terrigenous organic carbon accumulation is low duringthe Holocene and highest during OIS 6.The higher organic carbon accumulation rate in

Holes 1017B and 1018A since the onset of the LGM is

initially paralleled by a slightly elevated accumulationrate of marine biomarkers, but towards the end of theglacial period marine biomarker accumulation rates

decrease. In contrast, the terrestrial biomarker con-centrations remain relatively high in comparison to theHolocene, which suggests a higher terrestrial organic

matter component in the late glacial sediments in theseareas. At Site 1019, marine biomarker accumulation iselevated during the Holocene and the OIS 5/6 transition,

which is in general consistent with the marine organicmatter proportion of TOC. The C25±C35 n-alkanes showtheir highest accumulation rates during the last glacialand during the OIS 5/6 transition. This corroborates the

results of Lyle et al. (1992), who suggest a higher terri-genous organic matter supply during the LGM in thisarea.

3.2.3. d13C values of organic matter along the Californiamargin

Organic matter d13C values in the California marginsediments range from ÿ21.2% to ÿ23.4�0.2% andthus indicate a predominantly marine origin of theorganic matter (Table 2). Similar d13C data were repor-

ted in other studies of the California continental marginarea (Dean et al., 1994, 1997; Ishiwatari et al., 2000). Ingeneral, the organic material is isotopically heavier at

Sites 1017 and 1018 on the southern central and centralCalifornia margin during the Holocene (OIS 1), the lastinterstadial (OIS 3) and the last interglacial (OIS 5) (Fig.

8). On the northern California margin (Site 1019) iso-topically heavier organic matter occurs in the Holocenesection and at the OIS 6/5 transition. This indicates a

combination of higher primary productivity, a highermarine organic matter proportion, and warmer SSTsduring those periods when organic carbon accumulationis also elevated (Fig. 6).

During the glacial periods OIS 4 and 6, the organicmaterial is isotopically relatively light, consistent withlower primary productivity, a smaller proportion of

marine organic matter, and colder SSTs. In Holes 1017Band 1018A, a slight shift to isotopically heavier organicmaterial occurs at the beginning of the LGM, followedby a reversal of the trend at about 19.3 ka, while Corg-

MAR increases. This is consistent with the biomarkerpro®les during the last glacial period, which indicate ahigher proportion of terrigenous (isotopically lighter)

organic matter since about 19.3 ka. Ganeshram andPedersen (1998) suggested, in general, wetter conditionsand enhanced winter precipitation during the LGM for

the southern California margin based on lake levels andpollen from woodland plants (Allen and Anderson,1993; Thompson et al., 1993), which is consistent with a

higher terrigenous supply by rivers or continental runo�.In Hole 1019C, the isotopic signal of the organic

matter is lighter on average than in the other two holes.The organic matter in the last glacial sediments is espe-

cially isotopically light in view of the relatively highorganic matter accumulation rates (Fig. 6). Based on thestudy of Lyle et al. (1992) we have inferred a higher

terrigenous organic matter proportion during the lastglacial in Hole 1019C, which is corroborated by thebiomarker pro®les. The isotope data provide additional

evidence that despite a similar organic matter accumu-lation rate during the last glacial at Site 1019 marineorganic matter productivity was lower than during the

Holocene and that instead there was a signi®cant pro-portion of terrigenous organic matter.

3.2.4. In¯uence of oxygen depletion in the North Paci®c

Intermediate Water (NPIW) on the accumulation oforganic matterThe modern oxygen depletion in the NPIW is not

su�cient to prevent development of a benthic macro-faunal community on the open California continentalmargin, but conditions were de®nitely di�erent in the

past as shown by some cores containing partly laminatedOIS 3 sections (Dean et al., 1994, 1997). Restricted areaslike the Santa Barbara basin in the southern CalifornianBight are even more sensitive to oxygen variations in the

NPIW than the open continental margin (Kennett andIngram, 1995a; Behl and Kennett, 1996). Due to oxygendepletion, either caused by changes in the source of the

NPIW as a result of global climatic variations (Behl andKennett, 1996) and/or by changes of surface productivity(Dean et al., 1997), the sediments of the Santa Barbara

basin reveal extended laminated sections in the Holo-cene, the OIS 3, and at the onset of OIS 5 (substages 5e/5d). Sediments deposited during OIS 2 do not show any

laminations. We can only speculate whether oxygendepletion of the NPIW had an additional e�ect on theorganic carbon accumulation in the open continentalmargin sediments investigated in this study. Although

our cores, despite being from the depth range of thepresent OMZ (Holes 1017B and 1019C), are mostly wellbioturbated, we cannot exclude that reduced degradation


of organic matter in the water column together with ahigh organic carbon ¯ux due to enhanced primary pro-ductivity have contributed to the organic carbon accu-mulation pattern. However, the investigated sediments

do not reveal a particularly increased organic carbonaccumulation rate during OIS 3, a period when lami-nated sediments were formed on the open continentalmargin at other locations (Dean et al., 1994, 1997).

Fig. 7. Accumulation pro®les of marine (dinosterol and sum of di- and triunsaturated C37 methyl ketones) and terrestrial (C25±C35 n-

alkanes) biomarkers as well as their contents normalized to total organic carbon for Holes 1017B, 1018A and 1019C. The sections

marked grey represent warmer periods. OIS=oxygen isotope stage. Triangles and dashed line=early Holocene data of Hole 1018A

based on tentatively calculated sedimentation rates. Note di�erent concentration scales.


3.2.5. Marine productivity

Organic carbon accumulation along the Californiacontinental margin is in¯uenced by a complex interplayof di�erent factors like marine surface productivity,

supply of terrigenous clastic and/or organic matter, andpresumably preservation of organic matter. Never-theless, the organic carbon accumulation patterns, the

carbon isotope signal and the biomarker investigationspoint to an increased marine productivity due to ele-vated coastal upwelling on the southern central andcentral California margin during the Holocene (OIS 1),

the last interstadial (OIS 3), and the last interglacial(OIS 5), or at least some parts of the last interglacial atHole 1018A. Marine productivity apparently was low

during the early last glacial in the same area. For thelate last glacial, biomarker investigations and theorganic carbon isotope signal show that the increase of

organic carbon accumulation is accompanied by a sig-ni®cant proportion of terrigenous organic matter incomparison to the Holocene, indicating that marineproductivity during that time was due to terrigenous

nutrient supply rather than coastal upwelling. This is inagreement with other studies, which suggest less intensecoastal upwelling during the last glacial (Lyle et al.,

1992; Sancetta et al., 1992; Dean et al., 1997).On the northern California margin (Hole 1019C)

marine productivity was higher in the Holocene and at

the OIS 5/6 transition than in the other periods. Ele-vated organic carbon accumulation during the last gla-cial is mainly attributed to terrigenous organic matter

and nutrient supply from river discharge according tothe shift to more negative d13C values. Low organiccarbon accumulation rates during OIS 3 and the upperpart of OIS 5 indicate that conditions on the southern

Oregon/northern California margin were di�erent fromthose on the central and southern central Californiamargin.

High sedimentation rate of mineral matter supports

preservation of organic matter due to sorption oforganic matter onto mineral surfaces in the water col-umn and rapid burial on the sea ¯oor (Keil et al., 1994).

During the last glacial high sedimentation rates can beobserved in all investigated holes (Table 1). Hence,higher CorgMAR during the LGM may contain addi-

tionally an enhanced preservation signal.

3.2.6. Atmospheric and oceanographic implicationsThe regional scenario for the California continental

margin with enhanced marine productivity during theHolocene due to strong coastal upwelling and theopposite for the last glacial is consistent with a climatic

model proposed for the Holocene/last glacial transition(Kutzbach, 1987; see also Lyle et al., 1992). In thismodel, the LGM summer position of the North Paci®c

High was located farther south (about 30�N) and closerto the North American coast (about 130�W) than todaydue to the glaciation of the North American continent.This displacement of the atmospheric pressure system

leads to major changes in the intensity and direction ofthe local wind systems. The coast-parallel winds arereplaced by weaker and variable winds coming more

from the east than from the north. These winds are lessfavorable for inducing strong coastal upwelling on thenorthern and central California margin and should also

reduce the intensity of the California Current. Kutzba-ch's (1987) model also describes the development of themodern atmospheric system with coast-parallel winds

favorable for coastal upwelling becoming more andmore important since the transition to the Holocene.Ganeshram and Pedersen (1998) could show a gla-

cial±interglacial variability of coastal upwelling o� NW

Mexico during the last 140 kyr. An application of thisvariability to the pre-last glacial periods at our locationson the California margin is not straightforward. The

Fig. 8. Organic carbon isotopic (d13C) signals of total organic carbon of sediments from Holes 1017B, 1018A and 1019C. The sections

marked grey represent warmer periods. OIS=oxygen isotope stage.


glacial±interglacial organic matter accumulation at Hole1017B can probably be related to such variations in theatmospheric and oceanographic settings, but additionalfactors appear to be involved on the central (Hole

1018A; especially OIS 5 and 6) and northern Californiamargin (Holes 1019C; especially OIS 3 and 5). We canonly speculate, what these factors were. Occasional

deviations of the northward migration of the atmo-spheric pressure system may have reduced coastalupwelling on the central and especially the northern

California margin during these periods. It is also con-ceivable, that temporal and spatial di�erences of thenutrient supply from upwelling waters or terrigenous

run-o� may have in¯uenced the marine surface prod-uctivity.

4. Conclusions

The organic geochemical investigation of sediment

samples from a north-south transect of deep sea drillingholes on the California continental margin has revealedan in¯uence of global climate variations on the deposi-

tional history during the last 160 kyr. The studyemphasizes the sensitivity of the California Current,transporting the main temperature signal into this area,

to climatic changes.A comparison of the paleosea surface temperatures

along the California continental margin with timereveals water mixing of the colder California Current

with warmer waters from the south, particularly on thesouthern central California margin.Correlations between organic carbon accumulation

rates and glacial±interglacial variability along thesouthern central California continental margin point toa link between marine productivity and climatic and

atmospheric conditions prevailing in this area during thelast 160 kyr. Di�erences between the organic carbonaccumulation rates on the southern central and on thecentral and northern California margin during the last

interstadial (OIS 3), the last interglacial (OIS 5) and OIS6 re¯ect spatial atmospheric variations and/or temporaland spatial changes in nutrient supply to the photic

zone.Investigation of coastal upwelling and, therefore, the

local wind system on the southern central California

margin suggests a weaker California Current during theglacials and a stronger current intensity during theinterglacials.

Acknowledgements

We are grateful to D. Andreasen (University of Cali-fornia, Santa Cruz, USA), J.P. Kennett (University ofCalifornia, Santa Barbara, USA), M. Lyle (Boise State

University, Boise, USA), A. Mix (Oregon State Uni-versity, Corvallis, USA), J. Pike (University of WalesCardi�, Cardi�, UK), and R. Tada (University ofTokyo, Tokyo, Japan) for providing age data for the

investigated holes. We also thank C. Ostertag-Henning(University of Erlangen-NuÈ rnberg, Erlangen, Germany)for additional sediment samples fromHole 1018A.We are

grateful to F. Prahl (Oregon State University, Corvallis),P.A. Meyers (University of Michigan, Ann Arbor, andHanse Institute for Advanced Study, Delmenhorst,

Germany), and an anonymous referee for criticallyreviewing the manuscript and for helpful advice. Thisstudy was ®nancially supported by the Deutsche For-

schungsgemeinschaft (DFG), grant no. Ru 458/13.

Associate EditorÐS.G. Wakeham

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