Climatic and oceanographic variations on the California continental margin during the last 160 kyr

Organic Geochemistry 31 (2000) 829±846

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Climatic and oceanographic variations on the California continental margin during the last 160 kyr Kai Mangelsdorf *, Ute GuÈntner, JuÈrgen RullkoÈtter 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 continental margin during the last 160 kyr. Alkenone-derived paleosea surface temperatures (SST) are 3 to 6 C colder in glacial stages and reveal a clear relationship with global climate changes; the di€erences are greater in the north. Latitudinal SST comparison exhibits water mixing of the colder California Current with warmer waters from the south, particularly in the southern central California borderland area. Organic matter accumulation on the California continental margin indicates an interplay between climatic and atmospheric glacial±interglacial variations and spatially and temporally 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 this suggests, due to the close connection of the California Current to the local wind patterns, that the California Current was 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 is strongly in¯uenced by the California Current system, which is formed by a complex structure of di€erent currents (Hickey, 1979). The California Current itself, one of the important eastern boundary currents of the world, ¯ows southward along the coast of North America (Fig. 1). Seasonal variations of strength and orientation of individual currents within the California Current system and changes of the local wind patterns are largely driven by the seasonal migration (28 N in

* Corresponding author. Tel.: +49-441-798-3415; fax: +49441-798-3404. E-mail address: [email protected] (K. Mangelsdorf).

January to 38 N in July; Fig. 1) of the North Paci®c High pressure system (Huyer, 1983). These shifts and the resulting di€erences in wind intensity and direction, and therefore of the California Current, cause intraannual variations of upwelling patterns along the California and Oregon coastline (Nelson, 1977; Huyer, 1983), with strongest upwelling during spring and summer. North of about 40 N, coastal upwelling is episodic and mostly occurs in summer and early fall (Huyer, 1983). The structure of the California Current system and the closely associated coastal upwelling are sensitive not only 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 to higher 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 reduced coastal upwelling for the last glacial interval (Sancetta et al., 1992; Dean et al., 1997; Ortiz et al., 1997).

0146-6380/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0146-6380(00)00066-8

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

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.

Evidence of an increase in marine productivity since the last glacial [oxygen isotope stage 2, (OIS 2)] to the present indicate signi®cant changes in atmospheric and oceanographic conditions along the California continental margin (Lyle et al., 1992). Longer studies up to 60 kyr similarly indicate higher productivity during the last interstadial (OIS 3) (Hemphill-Haley, 1995; Dean et al., 1997; Gardner et al., 1997). Modern seasonal high marine productivity along the California continental margin leads to oxygen depletion in the North Paci®c Intermediate Water (NPIW) from organic matter remineralisation in the water column (Dean et al., 1997). Oxygen concentrations of <0.5 ml/l de®ne an Oxygen Minimum Zone (OMZ) between 600 and 1200 m water depth in the northeastern Paci®c Ocean o€ California. Nevertheless, modern surface sediments in most areas are well bioturbated, indicating that oxygen depletion today is not strong enough to prevent a diverse benthic fauna from thriving on the ocean ¯oor. In contrast, laminated intervals in several cores along the northern and central California margin indicate anoxic sediment surface conditions in some areas during OIS 3 (Dean et al., 1994, 1997). Laminated intervals were also found in some basins of the Southern Californian Bight, e.g. in the Santa Barbara basin

(Kennett, 1995). However, the sediments of this study from Ocean Drilling Program (ODP) Holes 1017B and 1019C, which were drilled within the modern OMZ depth range, are mostly bioturbated with the exception of some thin laminated layers. A high-resolution sediment sequence recovered during ODP Leg 146 in the Santa Barbara basin (Site 893) in 1992 provides information on climatic variations in this area over the past 160 kyr (Kennett et al., 1995; Hinrichs et al., 1997). The alkenone-derived SST data of Hinrichs et al. (1997) re¯ect global climatic changes except for strong temperature ¯uctuations during the last glacial period and strongly elevated SST values in the Eemian (OIS 5e, 125 ka) in comparison to the Holocene. These unexpectedly high alkenone-derived temperatures during the last glacial and the Eemian were also reported by Herbert et al. (1995), but they di€er from 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 extended range and to obtain more information about the evolution of the California Current as well as the history of

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

coastal upwelling and marine productivity during the last 160 kyr using organic geochemical methods. The results are compared to those available from ODP Site 893 (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 oceanographic history of marine environments and the evolution of climate on Earth. Over the last two decades a 0 molecular organic geochemical proxy, the UK 37 -Index, has been established to estimate paleosea surface temperatures (Prahl and Wakeham, 1987). Long-chain polyunsaturated methyl and ethyl alkenones with 37±39 carbon atoms are constituents of phytoplankton genera of the class Haptophyceae, such as the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica (Volkman et al., 1980, 1995). The unsaturation ratio of the C37 methyl ketones with 2±4 double bonds (UK 37 =[C37:2ÿC37:4]/ [C37:2+C37:3+C37:4]) was recognized as a temperaturesensitive parameter re¯ecting environmental growth temperatures (Brassell et al., 1986). With rising temperature, the concentration of the C37:2 ketone increases relative to that of the more unsaturated congeners. In laboratory cultures of an Emiliania huxleyi strain collected in the North Paci®c, Prahl and Wakeham (1987) 0 found a linear relationship between the simpli®ed UK 37 0 Index (UK 37 =[C37:2]/[C37:2+C37:3]) and growth temperature over the range of 8±25 C. They established a calibration equation for SST assessment, which was subsequently 0 slightly modi®ed by Prahl et al. (1988) to UK 37 = 0.034SST+0.039. This equation allows SST estimates with remarkable accuracy throughout much of the world ocean (MuÈller et al., 1998).

831

west of Crescent City in the Eel River basin at a water depth of 977 m (northern California margin, NCal). Hole 893A (34 17.250 N, 120 02.20 W) was drilled earlier during ODP Leg 146 at a water depth of 576.5 m (Fig. 1) in the center of the semi-enclosed Santa Barbara basin, where occasionally suboxic to anoxic bottomwater conditions prevail (Kennett et al., 1995). 2.2. Chronostratigraphy

2. Materials and Methods

Sediment ages for Site 1017 are available from Hole 1017E (drilled parallel to Hole 1017B) based on the oxygen isotope record (d18O) of benthic foraminifera down to the onset of OIS 5 (129.8 ka) and, for the last 32 kyr, also on 14C measurements (Kennett et al., 2000). For sediments older than 130 ka, chronostratigraphy was estimated by comparing the alkenone-derived SST pro®le of Hole 1017B, which we determined down to about 900 kyr, with the standard oxygen isotope record of Martinson et al. (1987). We corrected a miscorrelation of the initial shipboard splice (Lyle et al., 1997) for the transition from Core 2H to Core 3H and from Core 3H to Core 4H of Hole 1017B (Table 2). Chronostratigraphy of Hole 1018A is based on correlations of dated CaCO3 and Corg events, observable in several cores along the northern and central California margin, con®rmed by the oxygen isotope compositions (d18O) of benthic foraminifera (Lyle et al., 2000). The late Holocene section (presumably the ®rst 8 kyr) is missing from Hole 1018A probably due to recovery problems (Lyle et al., 2000), which complicates the age assignment for the residual Holocene section (8 to 13.59 kyr) and consequently required rough extrapolation. Age assignments for Hole 1019C are from 14C measurements on planktonic and benthic foraminifera and from the oxygen isotope composition of benthic foraminifera (Mix et al., 2000). Gaps in sediment recovery in Holes 1017B and 1018A were bridged by samples from nearby Holes 1017C and 1018D, respectively.

2.1. Samples

2.3. Mass accumulation rates

We selected 79 sediment samples from Holes 1017B, 1018A and 1019C that were drilled during ODP Leg 167 and constitute a south-north transect along the central and northern California continental margin (Fig. 1). Hole 1017B (34 32.0910 N, 121 6.4150 W) is located about 50 km west of Point Arguello on the continental slope at 955 m water depth (southern central California margin, SCCal). It is situated near an important modern upwelling center o€ Point Conception (Jones et al., 1983). Hole 1018A (36 59.3000 N, 123 16.6530 W) was drilled 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 40.9720 N, 124 55.9750 W) is located about 60 km

Total organic carbon (TOC) patterns based on weight percentages of dry sediment can sometimes be misleading, because this parameter can be a€ected by dilution with variable amounts of biogenic or clastic mineral matter. Organic carbon mass accumulation rates (CorgMAR, mg cmÿ2 kyrÿ1) are calculated to eliminate this dilution e€ect by using the equation (van Andel et al., 1975; Lyle, 1988): Corg MAR ˆ TOC    SA ; where TOC=total organic carbon content (mg gSedÿ1), =dry bulk density (g cmÿ3, shipboard data from ODP

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

Leg 167; Lyle et al., 1997) and SA=average sedimentation rate (cm kyrÿ1). Chronostratigraphic data used for the calculation of sedimentation rates are given in Table 1. Due to the chronostratigraphic problems in the Holocene section of Hole 1018A, sedimentation rates for the early Holocene period were only tentatively calculated based on the approach that the youngest Holocene sediment is about 8 ka old. Average sedimentation rates are highest at Hole 1019C (28.5 cm kyrÿ1) and somewhat 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 and ground, organic carbon content (TOC) was determined using a Leco-SC-444 combustion instrument and a UIC CO2-coulometer. For lipid analysis, sample aliquots of about 10 g were extracted ultrasonically using a mixture of CH2Cl2 and MeOH (99/1, v/v). After addition of internal standards (squalane, eruic acid [n-C22:1], 5a-androstan-17-one), the extracts were dissolved in n-hexane to precipitate asphaltenes, which were removed from the soluble fraction by ®ltration on NaSO4. The n-hexane-soluble fraction was separated by medium-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 NSO fraction using a column ®lled with KOH-impregnated silica gel prepared by adding 0.5 g KOH in 10 ml isopropanol to 5 g silica gel 100 (63±200 mm). The nonacidic 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 injection system and a fused silica capillary column (J&W; 30 m 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 programmed 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 s hold time) to 300 C (60 s hold time) at 8 C/s. For compound identi®cation an identical gas chromatographic system was linked to a Finnigan SSQ 710 B mass spectrometer that was operated in the electron impact mode at a scan rate of 1 scan/s. Carbon isotopic measurements of total organic matter were done after dissolution of carbonates with 0.1 N HCl and subsequent drying of the samples at 50 C overnight. For isotopic analyzes, a CHN analyzer was attached to a Finnigan MAT 252 isotope mass spectrometer. Isotopic ratios are expressed as d13C values in permil relative to the V-PDB standard.

3. Results and discussion 3.1. Reconstruction of paleosea surface temperatures on the 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 oceanographic conditions during the last 160 kyr. The Holocene SST values of Holes 1017B and 1018A and the upper Holocene values of Hole 1019C correspond with the measured modern average annual sea surface temperatures (Hole 1017B: 14±15 C, Hole 1018A: 12±14 C, and Hole 1019C: 11±13 C [National Oceanic and Atmospheric Administration (NOAA)1; Huyer, 1983] and with alkenone-derived SST data of core top sediments 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, depending on location. The Eemian temperature maxima in Holes 1017B and 1018A are 3±4 C higher than the Holocene values, con®rming the exceptionally high alkenone-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 section of OIS 5 the temperatures decline to values similar to those in the modern ocean. The transition to OIS 4 is characterized by a sharp decline of SST values to 8± 11 C at all locations. The temperature rise in OIS 3 is small and is interrupted by distinct declines, especially near the transition to the last glacial (OIS 2). The temperatures in the last glacial are consistently low, ranging from 11.5 C (Hole 1017B) to 6.5 C (Hole 1019C). At the 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, where sampling resolution for this interval was highest. The temperature record of Hole 1017B is fairly uniform during the Holocene, but the more resolved data of Hole 1019C indicate ¯uctuation of Holocene temperatures by 1±2 C. The SST records re¯ect the global glacial±interglacial climate variations during the last 160 kyr. These alternations are also marked by variable percentages of the C37:4 alkenone relative to total C37 alkenone concentrations (Table 2). The relative concentration of the tetraunsaturated C37 ketone, as expected, is in general lower during interglacial stages and increases during glacial stages and in the last interstadial (OIS 3).

1

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

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Table 1 Chronostratigraphic data used for calculation of sedimentation rates Hole (ODP 167-)

Depth (cmcd)a

Age (ka)

Sedimentation rate (cm kyrÿ1)

Reference

1017B

205.5 274.5 288.5 337.5 395.5 469.5 607.5 744.5 1224.5 1354.9 1476.5 1649.5 2077.5 2294.5 2411.5 2831.3

9.41 12.19 14.36 16.87 18.97 21.43 28.55 32.96 58.96 73.91 79.25 90.95 110.79 123.82 129.84 160.0

21.67 24.80 6.45 19.55 27.64 30.03 19.40 31.04 18.46 8.72 22.77 14.78 21.57 16.65 19.43 13.92

Kennett et al. (2000)

0 161 424 609 844 944 1004 1133 1173 1313 1657 1900 2000 2029 2089 2189 2229 2289 2409 2449 2589 2818 2878 2941 3061 3177 3437

8b 13.59 20.16 25.53 32.92 36.57 39.15 44.21 45.91 52.97 67.22 75.36 79.53 81.18 85.94 94.72 97.8 101.77 108.65 111.18 121.74 136.97 140.36 143.45 148.48 152.39 160.18

± 28.80c 40.03 34.45 31.8 27.39 23.26 25.49 23.53 19.83 24.14 29.85 23.98 17.58 12.61 11.39 12.99 15.11 17.44 15.81 13.26 15.04 17.7 20.39 23.86 29.67 33.38

Lyle et al. (2000)

418 718 821 1171 1461 1581 1800 1895 2027

9.80 14.7 17.0 22.67 30.02 34.56 47.79 55.53 62.34

42.65 61.24 44.78 61.67 39.48 26.43 16.55 12.27 19.38

Mix et al. (2000)

1018A

1019C

00 00 00 00 00 00 00 00 00 00 00 00 00 00

SST comparison 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

00 00 00 00 00 00 00 00

(continued overpage)

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

Table 1 (continued) Hole (ODP 167-)

Depth (cmcd)a

Age (ka)

Sedimentation rate (cm kyrÿ1)

Reference

2181 2361 2462 2789 2840 2914 3140 3966 4031 4556

71.27 77.77 83.08 107.25 109.87 112.81 119.86 139.65 143.04 160.06

17.25 27.69 19.02 13.53 19.47 25.17 32.05 41.74 19.17 30.85

Mix et al. (2000) 00 00 00 00 00 00 00 00 00

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).

3.1.1. Comparison with paleo-SST record of the Santa Barbara basin Two 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 Herbert et al. (1995) seem to be 1±2 C higher than the data of Hinrichs et al. (1997) in some sections, but the general patterns of both curves match well. A combined SST curve of both data sets (Fig. 3c) mirrors most variations of the d18O curve of benthic foraminifera from the Santa Barbara basin (Fig. 3d) much better than each SST curve separately, indicating that some of the apparent temperature di€erences maybe due to di€erent sampling horizons. A comparison of the SST pro®les of the California continental margin transect (Fig. 2) with the SST data from Site 893 in the Santa Barbara basin (Fig. 3c) shows only little coincidence for the last glacial section. During this period, the alkenone-derived temperature signal of the Santa Barbara basin is characterized by strong temperature ¯uctuations, which are not, however, re¯ected in the oxygen isotope record of Hole 893A of either the benthic (Fig. 3d; Kennett, 1995) or the planktonic foraminifera (Globigerina bulloides) (Kennett and Ingram, 1995b; Hendy and Kennett, 1999). Unless the d18O data depend also on salinity changes and the ``ice volume e€ect'' [about 1.2±1.3 % (Broecker, 1989; Ortiz et al., 1997)], the oxygen isotope values of the foraminifera obviously re¯ect the general low-temperature signal of the last glacial, while the alkenone-derived SST pattern reveals occasional short-term warming events in the surface waters. The di€erence in temperature signals may relate to the di€erent water depths at which coccolithophores and planktonic foraminifera live. By comparing seasonal 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. Neogloboquadrina pachyderma and Globigerina bulloides) live at greater depths (100 m) and ascend to near-surface water (upper 20 m) during upwelling events (Thunell and Sautter, 1992). Upwelling intensity, however, was less during 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) recently favored the view that G. bulloides preferentially live in near-surface water and do not respond to changes in upwelling intensity over the year in the Santa Barbara basin. During glacial times of lowered sea level, the Santa Barbara basin was closed in the south by a large island and 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 further o€shore, the California Current may have been diverted 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 sill presumably has shifted the main ¯ow of the warmer Southern California Counter Current south of the Santa Barbara basin (Gardner and Dartnell, 1995), the reduced in¯uence of the California Current may at least occasionally have allowed the in¯ow of warmer nearsurface waters from the southeast. These events may be re¯ected in the alkenone temperature signal of the sediments from the Santa Barbara basin. In contrast to the latitudinal di€erences in temperature ¯uctuations in the last glacial, the SST pro®les of Holes 1017B, 1018A, 1019C and 893A (Figs. 2 and 3) show relatively uniform paleosea surface temperature variations during OIS 3±6, and these variations generally covary with the oxygen isotope record of benthic

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

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Table 2 0 Sample numbers, corrected core depths, ages, UK 37 values, sea surface temperature estimates (SST), percentage of C37:4 methyl ketone 13 relative to total C37 alkenone amounts, d C of total organic matter and TOC contents of the investigated sediment samples from Holes 1017B (C), 1018A (D) and 1019Ca 0

Sample no.

Depth (cmcd)

Age (ka)

UK 37

SST ( C)

C37:4 (%)

d13CTOC (%)

TOC (%)

167-1017B-1H-1,90±92 cm 1H-2,120±122 cm 1H-3,15±17 cm 1H-3,69±71 cm 1H-3,76±78 cm 1H-3,90±92 cm 1H-3,121±123 cm 1H-4,20±22 cm 1H-4,37±39 cm 2H-1,20±22 cm 2H-1,90±92 cm 2H-3,90±92 cm 2H-5,92±94 cm 167-1017C-2H-5,120±122 cm 167-1017B-3H-1,90±92 cm 3H-3,90±92 cm 3H-5,90±92 cm 4H-1,90±92 cm 4H-3,90±92 cm 4H-5,90±92 cm

1.2 3.0 3.45 3.99 4.06 4.20 4.51 5.00 5.17 6.20 6.90 9.90 12.92 15.90 16.52b 19.52b 22.52b 22.86b 25.86b 28.92b

5.5 15.0 17.1 19.1 19.3 19.8 20.8 22.5 23.9 28.9 31.2 46.3 66.7 86.9 91.1 105.0 121.3 123.4 142.4 164.4

0.526 0.432 0.479 0.450 0.386 0.436 0.422 0.441 0.420 0.431 0.438 0.439 0.465 0.488 0.559 0.534 0.644 0.621 0.408 0.435

14.3 11.6 12.9 12.1 10.2 11.7 11.3 11.8 11.2 11.5 11.7 11.8 12.5 13.2 15.3 14.6 17.8 16.8 10.9 11.7

1.3 5.9 6.1 6.8 4.2 4.9 6.8 6.0 7.7 7.4 7.6 4.9 4.8 3.0 1.4 1.5 ± 1.1 3.4 6.4

ÿ21.4 ÿ22.5 ÿ22.4 ÿ22.3 ÿ22.2 ÿ22.2 ÿ22.2 ÿ22.4 ÿ22.4 ÿ22.5 ÿ22.1 ÿ22.1 ÿ22.3 ÿ21.7 ÿ21.2 ÿ21.5 ÿ21.3 ÿ21.5 ÿ22.4 ÿ22.5

2.39 2.22 1.49 0.27 1.78 1.41 1.33 0.78 1.31 0.67 0.93 1.41 0.99 1.82 1.90 1.82 3.13 2.19 1.17 0.97

167-1018A-1H-1,10±12 cm 1H-1,90±95 cm 1H-2,90±92 cm 1H-2,130±132 cm 1H-3,22±24 cm 1H-3,50±52 cm 1H-3,68±70 cm 1H-3,90±95 cm 2H-1,103±108 cm 2H-2,90±92 cm 2H-3,90±95 cm 2H-4,90±92 cm 2H-5,90±95 cm 2H-6,90±92 cm 3H-1,90±95 cm 3H-2,90±92 cm 3H-3,90±95 cm 3H-4,90±92 cm 3H-5,25±27 cm 3H-5,90±95 cm 3H-6,10±12 cm 3H-6,49±51 cm 3H-6,72±74 cm 3H-6,80±82 cm 3H-6,90±92 cm 3H-6,120±122 cm 3H-7,10±12 cm 3H-7,32±34 cm 167-1018D-3H-5,80±82 cm 3H-5,100±102 cm 3H-5,120±122 cm 167-1018A-4H-1,90±95 cm

0 0.78 2.28 2.68 3.10 3.38 3.56 3.78 6.97 8.34 9.84 11.34 12.84 14.84 18.35 19.85 21.35 22.85 23.70 24.35 25.05 25.45 25.68 25.76 25.85 26.15 26.55 26.77 27.11 27.31 27.51 29.21

8.0c 10.7c 15.3 16.3 17.3 18.0 18.5 19.0 28.3 32.6 38.3 44.3 51.5 60.1 73.2 78.9 90.0 101.5 106.4 110.3 115.4 118.4 120.2 120.8 121.4 123.5 126.1 127.6 129.9 131.2 132.5 142.5

0.480 0.481 0.339 0.302 0.302 0.322 0.314 0.325 0.313 0.339 0.390 0.396 0.412 ± 0.369 0.353 0.460 0.457 0.458 0.516 0.440 0.519 0.557 0.531 0.561 0.471 0.451 0.396 0.435 0.430 0.408 0.411

13.0 13.0 8.8 7.7 7.7 8.3 8.1 8.4 8.1 8.8 10.3 10.5 11.0 ± 9.7 9.3 12.4 12.3 12.3 14.0 11.8 14.1 15.2 14.5 15.2 12.7 12.1 10.5 11.7 11.5 10.9 10.9

2.1 1.7 8.1 10.7 8.1 8.5 9.2 9.1 9.0 7.5 7.8 5.5 6.1 ± 8.7 9.6 5.2 3.1 ± 2.4 4.9 ± 3.2 2.6 1.4 4.4 5 5.2 4.0 4.6 4.6 4.6

ÿ21.3 ÿ21.5 ÿ22.6 ÿ22.3 ÿ22.0 ÿ22.0 ÿ21.8 ÿ21.9 ÿ22.3 ÿ22.1 ÿ22.1 ÿ22.3 ÿ21.9 ÿ22.1 ÿ22.4 ÿ21.9 ÿ21.6 ÿ21.6 ÿ22.0 ÿ21.8 ÿ22.2 ± ± ± ÿ21.7 ÿ22.2 ÿ22.4 ÿ22.5 ÿ22.4 ÿ22.4 ÿ22.2 ÿ22.5

3.24 2.41 1.31 1.09 1.09 1.07 1.06 1.09 1.01 1.33 1.39 1.67 1.64 1.42 1.12 1.47 1.61 2.22 1.42 1.68 1.97 1.98 1.53 1.60 1.30 1.31 1.21 1.17 1.11 1.15 1.13 0.72 (continued overpage)

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Table 2 (continued) Sample no. 4H-2,90±92 cm 4H-3,90±92 cm 4H-4,90±92 cm 167-1019C-1H-1,80±85 cm 1H-3,80±85 cm 1H-5,80±85 cm 2H-1,32±34 cm 2H-1,80±85 cm 2H-2,37±39 cm 2H-2,112±114 cm 2H-3,80±85 cm 2H-4,106±108 cm 2H-5,80±85 cm 3H-1,80±85 cm 3H-3,80±85 cm 4H-1,80±85 cm 4H-2,62±64 cm 4H-2,148±150 cm 4H-3,52±54 cm 4H-3,80±85 cm 4H-4,92±94 cm 4H-5,80±85 cm 4H-5,142±144 cm 4H-6,52±54 cm 4H-7,21±23 cm 5H-1,80±85 cm 5H-3,80±85 cm a b c

0

Depth (cmcd)

Age (ka)

UK 37

SST ( C)

C37:4 (%)

d13CTOC (%)

TOC (%)

30.71 32.21 33.71

148.8 153.7 158.2

0.354 ± 0.305

9.3 ± 7.8

4.9 ± 9.6

ÿ22.1 ÿ22.6 ÿ22.3

1.21 1.17 0.88

0.80 3.80 6.80 8.63 9.11 10.18 10.93 12.11 13.87 15.12 18.72 21.72 30.22 31.54 32.4 32.94 33.22 34.84 36.22 36.84 37.44 38.63 40.69 43.69

1.9 8.9 14.1 17.7 18.5 20.2 21.4 23.7 28.1 31.9 53.7 70.7 116.2 120.2 122.3 123.5 124.2 128.1 131.4 132.9 134.3 137.2 144.3 154.0

0.457 0.442 0.457 0.261 0.298 0.297 0.260 0.338 0.324 0.295 0.394 0.316 0.349 0.426 0.467 0.455 0.484 0.488 0.461 0.404 ± 0.273 0.331 0.337

12.3 11.9 12.3 6.5 7.6 7.6 6.5 8.8 8.4 7.5 10.4 8.1 9.1 11.4 12.6 12.2 13.1 13.2 12.4 10.7 ± 6.9 8.6 8.8

2.8 4.2 4.8 12.3 7.6 8.7 14.6 11.3 11.9 12.1 9.6 10.4 6.1 3.7 4.0 3.7 3.7 4.5 3.7 4.2 ± 7.0 8.8 8.7

ÿ21.2 ÿ22.4 ÿ21.6 ÿ23.1 ÿ23.1 ÿ22.9 ÿ23.3 ÿ22.4 ÿ22.6 ÿ22.4 ÿ22.5 ÿ22.9 ÿ23.1 ± ± ± ÿ22.7 ÿ22.1 ÿ23.0 ± ± ± ÿ23.2 ÿ23.4

2.06 1.41 1.64 1.17 0.75 1.21 0.64 1.27 1.47 1.13 1.16 1.00 0.84 1.32 1.15 1.06 1.07 1.42 1.51 1.21 0.93 0.56 0.83 0.79

Shipboard data (Figs. 2, 6 and 7) are from ODP Leg 167 (Lyle et al., 1997). Revised cmcd (see text). 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 sections 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.

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

foraminifera in the Santa Barbara basin (Fig. 3d). These similarities suggest regionally uniform paleoclimate conditions. However, the alkenone-derived SST pro®les of Holes 893A, 1017B and 1018A do not show the same abrupt increase at the OIS 6/5 transition as the oxygen isotope record of Hole 893A. This again indicates that the two temperature assessments, at least during certain periods, record di€erent temperature signals.

837

3.1.2. Latitudinal paleosea surface temperature trends In order to visualize latitudinal trends along the California continental margin, we calculated average paleosea surface temperatures for each oxygen isotope stage, for the Eemian period (116±127 kyr) and the Last Glacial Maximum (17±22 kyr). For Hole 893A we used the 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) combined 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.

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

insolation. The steeper temperature gradient in the southern part of the transect between Holes 1017B and 1018A suggests an additional factor to be involved (Fig. 5a). Warmer surface water coming from the south (like the Southern California Counter Current today) probably has mixed with colder water of the California Current and has increased temperatures in the southern central California 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 has in¯uenced the northerly locations in a stronger way. This can also be seen from the di€erences between Holocene and LGM average temperatures for each location (Fig. 5b), which are about 2 C higher at Holes 1018A and 1019C than at Hole 1017B. This north-south trend 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 and 893A during the last glacial period is about 1.7 C (Fig. 5a and b). This di€erence over a short geographical distance is related to the strong ¯uctuations observed at Site 893, which have been ascribed above to occasional incursion of warmer surface waters from the south into the Santa Barbara basin. If only the lower last glacial temperatures in the Santa Barbara basin are used for comparison, the average values are approximately the same as those at Site 1017. During the Eemian (OIS 5e), the temperature di€erence (4±5 C) between the southerly locations and those on the central and northern California margin is greater than during any other period, with average temperatures at Holes 1018A and 1019C being in the range of the Holocene temperatures and those at Holes 1017B and 893A exceeding Holocene temperatures by 2.9±3.3 C (Fig. 5b). This points to an increased warming of the surface water at Holes 893A and 1017B and occasionally

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

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 Latitudes Average SST last 160 kyr Average SST Holocene (0±12 kyr) Average SST Last Glacial Maximum (17±22 kyr) Average SST Eemian (116±127 kyr)
SST LGM±Holocene
SST Eemian±Holocene Modern average annual SSTa a

893A 

1017B 0

34 17.25 N 13.3 C 14.7 C 13.3 C 18.0 C ÿ1.4 C 3.3 C 14±15 C



1018A 0

34 32.091 N 13.0 C 14.7 C 11.6 C 17.5 C ÿ3.1 C 2.8 C 14±15 C



1019C 0

36 59.300 N 10.6 C 13.0 C 8.1 C 14.0 C ÿ4.9 C 1.0 C 12±14 C

41 40.9720 N 10.4 C 12.5 C 7.1 C 12.5 C ÿ5.4 C 0 C 11±13 C

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

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

at Hole 1018A, as indicated by a temperature rise to 15.2 C (Fig. 2, middle). An incursion of water from a warmer source in the south is conceivable for the southern central California borderland area during the Eemian. Hinrichs et al. (1997) proposed that the high temperatures in the Eemian (OIS 5e) in the Santa Barbara basin could be related to a long-lasting ENSO (El NinÄoSouthern Oscillation) situation. However, this phenomenon seems not to have a€ected the northern part of the California continental margin. 3.2. Reconstruction of the paleoceanographic conditions on the California continental margin The California Current and coastal Californian upwelling are closely connected to each other by the local wind system. The coastal upwelling record should, therefore, provide information on the dynamics of the California Current over time. We measured TOC contents (Table 2), calculated organic carbon mass accumulation rates (CorgMAR), determined marine as well as terrestrial biomarkers in sediments from the last 160 kyr, 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 pronounced seasonal coastal upwelling. Large parts of the Holocene and the last interstadial (OIS 3) were probably characterized by similar conditions. Lyle et al. (1992) used Corg ¯ux studies in the multitracer 42 N east-west transect near Hole 1019C to conclude that marine organic carbon new productivity doubled from the LGM to the Holocene. Gardner et al. (1997) showed that marine productivity in the Holocene was relatively high and that strong coastal upwelling prevailed on the southern and the central California margin. Dean et al. (1997) inferred that productivity along the California coastline was highest during the Holocene and OIS 3 and lowest during the last glacial interval. These observations are supported by enrichment of other paleoproductivity proxies in Holocene and last interstadial (OIS 3) 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) during the Holocene and the last interstadial (OIS 3), suggesting that marine surface productivity was elevated at these sites during these periods. Lower CorgMAR in the early last glacial of Holes 1017B and 1018A then would be the result of weak or occasional lack of coastal upwelling, but enhanced organic carbon accumulation

839

starts at the beginning of the LGM (about 20 ka) at both sites. During OIS 4±6, a similar glacial±interglacial organic carbon accumulation contrast is evident in the sediments of the southern central California location (Hole 1017B). However, on the central California margin (Hole 1018A) the glacial±interglacial organic carbon accumulation alternation, although still recognizable in the TOC pro®le, is reduced to single Corg events during OIS 5 and 6 due to extremely variable sedimentation rates. In contrast to sediments at Sites 1017 and 1018, sediments of Hole 1019C display low CorgMAR during OIS 3 and in large parts of OIS 5, following a pronounced CorgMAR maximum in the Eemian after an early rise during the OIS 6/5 transition (Fig. 6). Last glacial sediments are characterized by a strongly ¯uctuating accumulation pattern with a distinct trend to higher CorgMAR. This seems to contradict observations of Sancetta et al. (1992), who inferred weakened summer upwelling in the last glacial from the absence of redwood pollen on the northern California/southern Oregon margin (upwelling causes coastal fog, which is an essential source of moisture required by redwoods). Lyle et al. (1992) in a nearshore location of a 42 N east±west transect adjacent to Hole 1019C also found that present and LGM CorgMAR data are in the same order of magnitude with a maximum during deglaciation, but they also found that the proportion of terrestrial organic matter during the LGM was twice as high as in the Holocene. Correction for the terrestrial organic matter fraction revealed that glacial marine CorgMAR was half of that of the Holocene. The total organic mass accumulation in the last glacial section at our northernmost location may also be a€ected by terrestrial organic matter supplied by the drainage of the Eel River, because this section shows a steep increase of sedimentation rates starting in late OIS 3 (Table 1). Lower organic carbon burial during OIS 3 and a large part of OIS 5 illustrates that the mechanisms a€ecting organic matter accumulation strongly varied between the northern and southern California continental margin. 3.2.2. Biomarker investigations To explore details of changes in delivery and accumulation of organic matter, we analyzed the concentrations of marine and terrestrial molecular organic biomarkers 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 as marine biomarkers and long-chain C25±C35 n±alkanes (maximum consistently at C29) as biomarkers representing a terrestrial source (Eglinton and Hamilton, 1967). Dinosterol appears to be restricted to the algae class of Dinophyceae (Volkman, 1986; Volkman et al., 1998), and the alkenones are constituents of phyto-

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

plankton belonging to the class of Haptophyceae (see Introduction). Both types of marine biomarkers were found in all sediments investigated in this study, indicating that source organisms of both biomarkers were common members of the phytoplanktonic community along the California coast over the last 160 kyr. Long chain n-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 this area may be eroded rocks of the Monterey Formation and 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.

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

The marine biomarkers indicate higher marine organic matter accumulation rates during the Holocene (OIS 1) and the last interglacial (OIS 5) on the southern central (Hole 1017B) California margin, which is, in general, accompanied by an elevated organic-carbonnormalized concentration of these compounds (Fig. 7). The concentrations of the terrigenous indicators are low during the Holocene and reveal the highest accumulation rates during OIS 2, OIS 3 and OIS 5, also obvious from TOC-normalized proportion of n-alkanes. On the central California margin (Hole 1018A), marine organic matter accumulation is higher during the Holocene and some parts of OIS 3, OIS 5 and notably during OIS 6. Terrigenous organic carbon accumulation is low during the 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 accumulation rate of marine biomarkers, but towards the end of the glacial period marine biomarker accumulation rates decrease. In contrast, the terrestrial biomarker concentrations remain relatively high in comparison to the Holocene, which suggests a higher terrestrial organic matter component in the late glacial sediments in these areas. At Site 1019, marine biomarker accumulation is elevated during the Holocene and the OIS 5/6 transition, which is in general consistent with the marine organic matter proportion of TOC. The C25±C35 n-alkanes show their highest accumulation rates during the last glacial and during the OIS 5/6 transition. This corroborates the results of Lyle et al. (1992), who suggest a higher terrigenous organic matter supply during the LGM in this area. 3.2.3. d13C values of organic matter along the California margin Organic matter d13C values in the California margin sediments range from ÿ21.2% to ÿ23.40.2% and thus indicate a predominantly marine origin of the organic matter (Table 2). Similar d13C data were reported in other studies of the California continental margin area (Dean et al., 1994, 1997; Ishiwatari et al., 2000). In general, the organic material is isotopically heavier at Sites 1017 and 1018 on the southern central and central California margin during the Holocene (OIS 1), the last interstadial (OIS 3) and the last interglacial (OIS 5) (Fig. 8). On the northern California margin (Site 1019) isotopically heavier organic matter occurs in the Holocene section and at the OIS 6/5 transition. This indicates a combination of higher primary productivity, a higher marine organic matter proportion, and warmer SSTs during those periods when organic carbon accumulation is also elevated (Fig. 6). During the glacial periods OIS 4 and 6, the organic material is isotopically relatively light, consistent with lower primary productivity, a smaller proportion of

841

marine organic matter, and colder SSTs. In Holes 1017B and 1018A, a slight shift to isotopically heavier organic material occurs at the beginning of the LGM, followed by a reversal of the trend at about 19.3 ka, while CorgMAR increases. This is consistent with the biomarker pro®les during the last glacial period, which indicate a higher proportion of terrigenous (isotopically lighter) organic matter since about 19.3 ka. Ganeshram and Pedersen (1998) suggested, in general, wetter conditions and enhanced winter precipitation during the LGM for the southern California margin based on lake levels and pollen 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 especially isotopically light in view of the relatively high organic matter accumulation rates (Fig. 6). Based on the study of Lyle et al. (1992) we have inferred a higher terrigenous organic matter proportion during the last glacial in Hole 1019C, which is corroborated by the biomarker pro®les. The isotope data provide additional evidence that despite a similar organic matter accumulation rate during the last glacial at Site 1019 marine organic matter productivity was lower than during the Holocene and that instead there was a signi®cant proportion of terrigenous organic matter. 3.2.4. In¯uence of oxygen depletion in the North Paci®c Intermediate Water (NPIW) on the accumulation of organic matter The modern oxygen depletion in the NPIW is not sucient to prevent development of a benthic macrofaunal community on the open California continental margin, but conditions were de®nitely di€erent in the past as shown by some cores containing partly laminated OIS 3 sections (Dean et al., 1994, 1997). Restricted areas like the Santa Barbara basin in the southern Californian Bight are even more sensitive to oxygen variations in the NPIW than the open continental margin (Kennett and Ingram, 1995a; Behl and Kennett, 1996). Due to oxygen depletion, either caused by changes in the source of the NPIW as a result of global climatic variations (Behl and Kennett, 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 Holocene, 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 oxygen depletion of the NPIW had an additional e€ect on the organic carbon accumulation in the open continental margin sediments investigated in this study. Although our cores, despite being from the depth range of the present OMZ (Holes 1017B and 1019C), are mostly well bioturbated, we cannot exclude that reduced degradation

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

of organic matter in the water column together with a high organic carbon ¯ux due to enhanced primary productivity have contributed to the organic carbon accumulation pattern. However, the investigated sediments

do not reveal a particularly increased organic carbon accumulation rate during OIS 3, a period when laminated sediments were formed on the open continental margin 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 nalkanes) 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.

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

843

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.

3.2.5. Marine productivity Organic carbon accumulation along the California continental margin is in¯uenced by a complex interplay of di€erent factors like marine surface productivity, supply of terrigenous clastic and/or organic matter, and presumably preservation of organic matter. Nevertheless, the organic carbon accumulation patterns, the carbon isotope signal and the biomarker investigations point to an increased marine productivity due to elevated coastal upwelling on the southern central and central 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 at Hole 1018A. Marine productivity apparently was low during the early last glacial in the same area. For the late last glacial, biomarker investigations and the organic carbon isotope signal show that the increase of organic carbon accumulation is accompanied by a signi®cant proportion of terrigenous organic matter in comparison to the Holocene, indicating that marine productivity during that time was due to terrigenous nutrient supply rather than coastal upwelling. This is in agreement with other studies, which suggest less intense coastal 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. Elevated organic carbon accumulation during the last glacial is mainly attributed to terrigenous organic matter and nutrient supply from river discharge according to the shift to more negative d13C values. Low organic carbon accumulation rates during OIS 3 and the upper part of OIS 5 indicate that conditions on the southern Oregon/northern California margin were di€erent from those on the central and southern central California margin.

High sedimentation rate of mineral matter supports preservation of organic matter due to sorption of organic matter onto mineral surfaces in the water column and rapid burial on the sea ¯oor (Keil et al., 1994). During the last glacial high sedimentation rates can be observed in all investigated holes (Table 1). Hence, higher CorgMAR during the LGM may contain additionally an enhanced preservation signal. 3.2.6. Atmospheric and oceanographic implications The regional scenario for the California continental margin with enhanced marine productivity during the Holocene due to strong coastal upwelling and the opposite 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 this model, the LGM summer position of the North Paci®c High was located farther south (about 30 N) and closer to the North American coast (about 130 W) than today due to the glaciation of the North American continent. This displacement of the atmospheric pressure system leads to major changes in the intensity and direction of the local wind systems. The coast-parallel winds are replaced by weaker and variable winds coming more from the east than from the north. These winds are less favorable for inducing strong coastal upwelling on the northern and central California margin and should also reduce the intensity of the California Current. Kutzbach's (1987) model also describes the development of the modern atmospheric system with coast-parallel winds favorable for coastal upwelling becoming more and more important since the transition to the Holocene. Ganeshram and Pedersen (1998) could show a glacial±interglacial variability of coastal upwelling o€ NW Mexico during the last 140 kyr. An application of this variability to the pre-last glacial periods at our locations on the California margin is not straightforward. The

844

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

glacial±interglacial organic matter accumulation at Hole 1017B can probably be related to such variations in the atmospheric and oceanographic settings, but additional factors appear to be involved on the central (Hole 1018A; especially OIS 5 and 6) and northern California margin (Holes 1019C; especially OIS 3 and 5). We can only speculate, what these factors were. Occasional deviations of the northward migration of the atmospheric pressure system may have reduced coastal upwelling on the central and especially the northern California margin during these periods. It is also conceivable, that temporal and spatial di€erences of the nutrient supply from upwelling waters or terrigenous run-o€ may have in¯uenced the marine surface productivity. 4. Conclusions The organic geochemical investigation of sediment samples from a north-south transect of deep sea drilling holes on the California continental margin has revealed an in¯uence of global climate variations on the depositional history during the last 160 kyr. The study emphasizes 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 time reveals water mixing of the colder California Current with warmer waters from the south, particularly on the southern central California margin. Correlations between organic carbon accumulation rates and glacial±interglacial variability along the southern central California continental margin point to a link between marine productivity and climatic and atmospheric conditions prevailing in this area during the last 160 kyr. Di€erences between the organic carbon accumulation rates on the southern central and on the central and northern California margin during the last interstadial (OIS 3), the last interglacial (OIS 5) and OIS 6 re¯ect spatial atmospheric variations and/or temporal and 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 the glacials and a stronger current intensity during the interglacials. Acknowledgements We are grateful to D. Andreasen (University of California, Santa Cruz, USA), J.P. Kennett (University of California, Santa Barbara, USA), M. Lyle (Boise State

University, Boise, USA), A. Mix (Oregon State University, Corvallis, USA), J. Pike (University of Wales Cardi€, Cardi€, UK), and R. Tada (University of Tokyo, Tokyo, Japan) for providing age data for the investigated holes. We also thank C. Ostertag-Henning (University of Erlangen-NuÈrnberg, Erlangen, Germany) for additional sediment samples from Hole 1018A. We are grateful to F. Prahl (Oregon State University, Corvallis), P.A. Meyers (University of Michigan, Ann Arbor, and Hanse Institute for Advanced Study, Delmenhorst, Germany), and an anonymous referee for critically reviewing the manuscript and for helpful advice. This study was ®nancially supported by the Deutsche Forschungsgemeinschaft (DFG), grant no. Ru 458/13. Associate EditorÐS.G. Wakeham

References Allen, B.D., Anderson, R.Y., 1993. Evidence from Western North America for rapid shifts in climate during the last glacial maximum. Science 260, 1920±1923. Behl, R.J., Kennett, J., 1996. Brief interstadial events in the Santa Barbara basin, NE Paci®c, during the past 60 kyr. Nature 379, 243±246. Brassell, S.C., Eglinton, G., Marlowe, I.T., P¯aumann, U., Sarnthein, M., 1986. Molecular stratigraphy: a new tool for climatic assessment. Nature 320, 129±133. Broecker, W.S., 1989. The salinity contrast between the Atlantic and Paci®c oceans during glacial time. Paleoceanography 4, 207±212. Curiale, J.A., Cameron, D., Davis, D.V., 1985. Biological marker distribution and signi®cance in oils and rocks of the Monterey Formation, California. Geochimica et Cosmochimica Acta 49, 271±288. Dean, W.E., Gardner, J.V., Anderson, R.Y., 1994. Geochemical evidence for enhanced preservation of organic matter in the oxygen minimum zone of the continental margin of northern California during the late Pleistocene. Paleoceanography 9, 47±61. Dean, W.E., Gardner, J.V., Piper, D.Z., 1997. Inorganic geochemical indicators of glacial±interglacial changes in productivity and anoxia on the California continental margin. Geochimica et Cosmochimica Acta 61, 4507±4518. Doose, H., Prahl, F.G., Lyle, M.W., 1997. Biomarker temperature estimates for modern and last glacial surface waters of the California Current system between 33 and 42 N. Paleoceanography 12, 615±622. Dymond, J., Suess, E., Lyle, M., 1992. Barium in deep-sea sediment: a geochemical proxy for paleoproductivity. Paleoceanography 7, 163±181. Eglinton, G., Hamilton, R.J., 1967. Leaf epicuticular waxes. Science 156, 1322±1335. Gagosian, R.B., Peltzer, E.T., Za®riou, O.C., 1981. Atmospheric transport of continentally derived lipids to the tropical North Paci®c. Nature 291, 313±314. Gagosian, R.B., Peltzer, E.T., Merrill, J.T., 1987. Long-range transport of terrestrially derived lipids in aerosols from the south Paci®c. Nature 325, 801±804.

K. Mangelsdorf et al. / Organic Geochemistry 31 (2000) 829±846 Ganeshram, R.S., Pedersen, T.F., 1998. Glacial±interglacial variability in upwelling and bioproductivity o€ NW Mexico: implications for Quarternary paleoclimate. Paleoceanography 13, 634±645. Gardner, J.V., Dartnell, P., 1995. Centennial-scale late Quarternary stratigraphies of carbonate and organic carbon from Santa Barbara basin, Hole 893A, and their paleoceanographic signi®cance. In: Kennett, J.P., Baldauf, J.G., Lyle, M. (Eds.), Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 146 (Pt. 2). Ocean Drilling Program, College Station, pp. 103±124. Gardner, J.V., Dean, W.E., Dartnell, P., 1997. Biogenic sedimentation beneath the California Current system for the past 30 kyr and its paleoceanographic signi®cance. Paleoceanography 12, 207±255. Hemphill-Haley, E., 1995. High productivity and upwelling in the California Current during oxygen isotope stage 3: diatom evidence. In: Isaac, C.M., Tharp, V.L. (Eds.), Proceedings of the Eleventh Annual Paci®c Climate (PACLIM) Workshop, 19±22 April 1994. California Department of Water Resources, Sacramento, CA, pp. 119±126. Hendy, I.L., Kennett, J.P., 1999. Latest Quarternary North Paci®c surface-water responses imply atmosphere-driven climate instability. Geology 27, 291±294. Herbert, T.D., Yasuda, M., Burnett, C., 1995. Glacial-interglacial sea-surface temperature record inferred from alkenone unsaturation indices, Site 893, Santa Barbara basin. In: Kennett, J.P., Baldauf, J.G., Lyle, M. (Eds.), Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 146 (Pt. 2). Ocean Drilling Program, College Station, pp. 257±264. Herbert, T.D., Schu€ert, J.D., Thomas, D., Lange, D., Weinheimer, A., Peleo-Alampay, A., Herguera, J.-C., 1998. Depth and seasonality of alkenone production along the California margin inferred from a core top transect. Paleoceanography 13, 263±271. Hickey, B.M., 1979. The California Current system Ð hypotheses and facts. Progress in Oceanography 8, 191±279. Hinrichs, K.U., RullkoÈtter, J., Stein, R., 1995. Preliminary assessment of organic geochemical signals in sediments from Hole 893A, Santa Barbara basin, o€shore California. In: Kennett, J.P., Baldauf, J.G., Lyle, M. (Eds.), In: Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 146 (Pt. 2). Ocean Drilling Programm, College Station, pp. 201± 211. Hinrichs, K.-U., Rinna, J., RullkoÈtter, J., Stein, R., 1997. A 160-kyr record of alkenone-derived sea-surface temperatures from Santa Barbara basin sediments. Naturwissenschaften 84, 126±128. Huyer, A., 1983. Coastal upwelling in the California Current system. Progress in Oceanography 12, 259±284. Ishiwatari, R., Matsumoto, K., Yamamoto, S., 2000. Variations in organic carbon isotopic composition in sediments at ODP Leg 167 Site 1017 during the last 26 kyr. In: Lyle, M., Koizumi, I., Richter, C. (Eds.), Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 167. Ocean Drilling Program, College Station, in press. Jones, B.H., Brink, K.H., Dugdale, R.C., Stuart, D.W., van Leer, J.C., Blasco, D., Kelley, J.C., 1983. Observations of a persistent upwelling center o€ Point Conception, California. In: Suess, E., Thiede, J. (Eds.), Coastal Upwelling: Its Sediment Record. Plenum Press, New York, pp. 37±60.

845

Keil, R.G., 1994. MontlucËon, D. B., Prahl, F.G., Hedges, J.I., Sorptive preservation of labile organic matter in marine sediments. Nature 370, 549±552. Kennett, J.P., 1995. Latest Quarternary benthic oxygen and carbon isotope stratigraphy: Hole 893A, Santa Barbara basin, California. In: Kennett, J.P., Baldauf, J.G., Lyle, M. (Eds.), Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 146 (Pt. 2). Ocean Drilling Program, College Station, TX, pp. 3±18. Kennett, J.P., Ingram, B.L., 1995a. A 20000-years record of ocean circulation and climate change from the Santa Barbara basin. Nature 377, 510±516. Kennett, J.P., Ingram, B.L., 1995b. Paleoclimatic evolution of Santa Barbara basin during the last 20 k.y.: Marine evidence from Hole 893A. In: Kennett, J.P., Baldauf, J.G., Lyle, M. (Eds.), Proceeding of the Ocean Drilling Program, Scienti®c Results, Vol. 146 (Pt. 2). Ocean Drilling Program, College Station, TX, pp. 309±324. Kennett, J.P., Baldauf, J.G., Lyle, M., 1995. Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 146 (Pt. 2). Ocean Drilling Program, College Station, TX. Kennett, J.P., Roark, E.B., Cannariato, K.G., Ingram, B.L., Tada, R., 2000. Latest Quarternary paleoclimatic and radiocarbon chronology, ODP Hole 1017E, southern California margin. In: Koizumi, I., Lyle, M., Richter, C. (Eds.), Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 167. Ocean Drilling Program, College Station, TX, in press. Kutzbach, J.E., 1987. Model simulations of the climatic patterns during the deglaciation of North America. In: Ruddiman, W.F., Wright, H.E. (Eds.), North America and Adjacent Ocean during the Last Deglaciation. The Geology of North America. Vol. K-3. Geological Society of America. Boulder, CO, pp. 425±446. Lyle, M., 1988. Climatically forced organic carbon burial in equatorial Atlantic and Paci®c Oceans. Nature 335, 529±532. Lyle, M., Zahn, R., Prahl, F., Dymond, J., Collier, R., Pisias, N., Suess, E., 1992. Paleoproductivity and carbon burial across the California Current: the multitracers transect, 42 N. Paleoceanography 7, 251±272. Lyle, M., Koizumi, I., Richter, C., 1997. Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 167. Ocean Drilling Program, College Station. Lyle, M., Mix, A., Ravelo, C., Andreasen, D., Heusser, L., Olivarez, A., 2000. Millennial scale CaCO3 and Corg events along the northern and central California margin: Stratigraphy and Origins. In: Koizumi, I., Lyle, M., Richter, C. (Eds.), Proceedings of the Ocean Drilling Program, Scienti®c Results, Vol. 167. Ocean Drilling Program, College Station, in press. Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore, T.C.J., Shackleton, N.J., 1987. Age dating and the orbital theory of the ice ages: development of a high-resolution 0 to 300,000-year chronostratigraphy. Quaternary Research 27, 1±29. Mix, A.C., Lund, D.C., Pisias, N.G., Boden, P., Bornmarlm, L., Lyle, M., Pike, J., 2000. Rapid climate oscillations in the northeast Paci®c during the last glaciation re¯ect northern and southern hemispheric sources. In: Webb, R.S., Clark, P.U., Keigwin, L. (Eds.), Mechanisms of Millennial-scale Global Climate Change, Vol. 112. American Geophysical Union Monograph, pp. 127±147.

846

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

Mortyn, P.G., Thunell, R.C., Anderson, D.M., Stott, L.D., Jianning, L., 1996. Sea surface temperature changes in the Southern California Borderlands during the last glacial± interglacial cycle. Paleoceanography 11, 415±430. MuÈller, P.J., Kirst, G., Ruhland, G., von Storch, I., RosellMeleÂ, A., 1998. Calibration of the alkenone paleo0 temperature index UK 37 based on core-tops from the Eastern South Atlantic and the global ocean (60 N±60 S). Geochimica et Cosmochimica Acta 62, 1757±1772. Nelson, C.S. (1977) Wind stress and wind stress curl over the California Current. National Oceanic and Atmospheric Administration Technical Report NMFS SSRF-714. US Department of Commerce. Ortiz, J., Mix, A., Hostetler, S., Kashgarian, M., 1997. The California Current of the last glacial maximum: reconstruction at 42 N based on multiple proxies. Paleoceanography 12, 191±205. Prahl, F.G., Wakeham, S.G., 1987. Calibration of unsaturation patterns in long-chain ketone compositions for palaeotemperature assessment. Nature 330, 367±369. Prahl, F.G., Muehlhausen, L.A., Zahnle, D.L., 1988. Further evaluation of long-chain alkenones as indicators of paleoceanographic conditions. Geochimica et Cosmochimica Acta 52, 2303±2310. Prahl, F.G., Pisias, N., Sparrow, M.A., Sabin, A., 1995. Assessment of sea-surface temperature at 42 N in the California Current over the last 30,000 years. Paleoceanography 10, 763±773. Radke, M., Willsch, H., Welte, D., 1980. Preparative hydrocarbon group type determination by automated medium pressure liquid chromatography. Analytical Chemistry 52, 406±411. Sancetta, C., Lyle, M., Heusser, L., Zahn, R., Bradbury, J.P., 1992. Late-Glacial to Holocene changes in winds, upwelling,

and seasonal production of Northern California Current system. Quarternary Research 38, 359±370. Thompson, R.S., Whitlock, C., Bartlein, P.J., Harrison, S.P., Spaulding, W.G., 1993. Climate changes in the western United States since 18,000 yr B.P. In: Wright, H.E., Kutzbach, J.E., Webb, T., Ruddiman, W.F., Street-Perrott, F.A., Bartlein, P.J. (Eds.), Global Climates Since the Last Glacial Maximum. University of Minnesota Press, Minneapolis, pp. 468±513. Thunell, R., Sautter, L.R., 1992. Planktonic foraminiferal faunal and stable isotopic indices of upwelling: a sediment trap study in the San Pedro basin, Southern California Bight. In: Summerhayes, C.P., Prell, W.L., Emeis, K.C. (Eds.), Upwelling Systems: Evolution Since the Early Miocene. Geological Society Special Publication, Vol. 64. Blackwell, Oxford, pp. 77±91. van Andel, T.H., Heath, G.R., Moore Jr, T.C., 1975. Cenozoic History and Paleoceanography of the Central Equatorial Paci®c Ocean. Geological Society of America Memoir 143. Volkman, J.K., 1986. A review of sterol markers for marine and terrigenous organic matter. Organic Geochemistry 9, 83±99. Volkman, J.K., Eglinton, G., Corner, E.D.S., Sargent, J., 1980. Novel unsaturated straight-chain C37±C39 methyl and ethyl ketones in marine sediments and a coccolithophore Emiliania huxleyi. In: Douglas, A.G., Maxwell, J.R. (Eds.), Advances in Organic Geochemistry 1979. Pergamon Press, Oxford, 1979, pp. 219±228. Volkman, J.K., Barrett, S.M., Blackburn, S.I., Sikes, E.L., 1995. Alkenones in Gephyrocapsa oceanica: implications for studies of paleoclimate. Geochimica et Cosmochimica Acta 59, 513±520. Volkman, J.K., Barrett, S.M., Blackburn, S.I., Mansour, M.P., Sikes, E.L., Gelin, F., 1998. Microalgal biomarkers: a review of recent research developments. Organic Geochemistry 29, 1163±1179.