Directory UMM :Data Elmu:jurnal:O:Organic Geochemistry:Vol31.Issue9.2000:
Organic Geochemistry 31 (2000) 829±846
www.elsevier.nl/locate/orggeochem
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 dierences 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 dierent
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 dierences 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
830
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
www.elsevier.nl/locate/orggeochem
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 dierences 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 dierent
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 dierences 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
830
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