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Vegetation and climate of the northwest coast of North America during the last 500 K.Y.: High-resolution pollen evidence from the northern California margin


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Pollen analyses of sediments from Holes 1019C, 1019E, 1020C, and 1020D as well as piston Core EW9504-17 provide continuous, chronostratigraphically controlled proxy vegetation and climate data for coastal northwest North America for the last ~500 k.y. Systematic changes in the representation of the diagnostic components of northern California plant assemblages clearly show orbital-scale variations. Interglacials are all marked by an abrupt increase in alder followed by expansion of lowland oak woodland and redwood forests. Glacials are dominated by montane forest and woodland assemblages. This sequence reflects large-scale climatic controls (e.g., orbital-scale variation in insolation and Northern Hemisphere ice sheets) in western North America over the last five glacial cycles. Regional climatic control (variations in sea-surface conditions) is implied by the differential development of xeric oak and mesic redwood communities.
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Lyle, M., Koizumi, I., Richter, C., and Moore, T.C., Jr. (Eds.), 2000
Proceedings of the Ocean Drilling Program, Scientific Results, Vol. 167
Lyle, M., Koizumi, I., Richter, C., and Moore, T.C., Jr. (Eds.), 2000. Proc. ODP,
Sci. Results, 167: College Station TX (Ocean Drilling Program).
Lamont-Doherty Geological Observatory, Columbia Univeristy, Palisades NY
10987, USA. (Present address: Heusser and Heusser, Inc., 100 Clinton Road, Tuxedo
NY 10987, USA.)
Center for Geophysical Investigation of the Shallow Subsurface, Boise State Uni-
versity, Boise ID 83725, USA.
College of Ocean and Atmospheric Science, Oregon State University, Corvallis
OR 97331, USA.
L.E. Heusser,
M. Lyle,
and A. Mix
Pollen analyses of sediments from Holes 1019C, 1019E, 1020C, and 1020D as well as piston Core EW9504-17 provide
continuous, chronostratigraphically controlled proxy vegetation and climate data for coastal northwest North America for the
last ~500 k.y. Systematic changes in the representation of the diagnostic components of northern California plant assemblages
clearly show orbital-scale variations. Interglacials are all marked by an abrupt increase in alder followed by expansion of low-
land oak woodland and redwood forests. Glacials are dominated by montane forest and woodland assemblages. This sequence
reflects large-scale climatic controls (e.g., orbital-scale variation in insolation and Northern Hemisphere ice sheets) in western
North America over the last five glacial cycles. Regional climatic control (variations in sea-surface conditions) is implied by
the differential development of xeric oak and mesic redwood communities.
It has been established that pollen deposited in marine sediments
on continental margins provides terrestrial vegetation and climate
records that are directly correlated with global chronostratigraphic
events (Dupont, 1992; Heusser and van de Geer, 1994; Van Campo et
al., 1982). Interpretations of past vegetation and climate of western
North America from pollen deposited offshore are based on compar-
isons of downcore pollen spectra with modern marine and terrestrial
pollen spectra (e.g., pollen assemblages from marine and terrestrial
sediment traps and surface samples), vegetation, and climate (Heusser
and Balsam, 1977; Heusser, 1988). Previous studies showed that Mi-
lankovitch-scale variations in vegetation of coastal Washington and
Southern California reconstructed from pollen deposited in the north-
east Pacific Ocean during the last glacial cycle were similar to those
inferred from onshore pollen data ascribed to the same time (Heusser
and Florer, 1973; Heusser, 1995). To extend these studies in space
and time, we present preliminary results from pollen analyses of sed-
iments deposited off Northern California during the last ~500 k.y.
Pollen from piston cores taken on the continental margin of west-
ern North America between 32°N and 43°N also showed systemati-
cally related short-term changes superposed on Milankovitch-scale
oscillations of the past 60 k.y. During oxygen isotope Stage 3, for ex-
ample, brief warming events in California and Oregon appear correl-
ative with interstadial events in waters offshore (Heusser, 1998).
Here we extend high-resolution pollen analyses of sediments depos-
ited on the northern California margin over the last ~140 k.y.
Natural coastal vegetation of California changes from xeric, open
oak woodland in the south to dense conifer rainforest in the north.
The complex mosaic of southern California scrub oak (Quercus), oak
woodland savanna, and oak-dominated foothill woodlands with iso-
lated groups of closed-cone pine and cypress (Pinus radiata and Cu-
pressus pygmaea) interfingers with chaparral and lowland sage
scrub. Conifer forests develop upslope in which open pine woodlands
with small, scattered stands of incense cedar (Libocedrus decurrens)
are succeeded at higher elevations by mid-montane parkland with
pine and incense cedar, upper montane juniper (Juniperus occidenta-
lis) woodland, and subalpine coniferous forests with lodgepole pine
(Pinus contorta) (Barbour and Billings, 1988; Barbour and Major,
1977; Franklin and Dyrness, 1973).
In Northern California, redwood (Sequoia sempervirens) distin-
quishes the southern extension of the Pacific Northwest evergreen
coniferous forests, which are unique in size and longevity among
temperate forest regions of the world (Waring and Franklin, 1979).
Associated with redwood are western hemlock (Tsuga heterophylla),
spruce (Picea sitchensis), Douglas fir (Pseudotsuga menziesii), and
western red cedar (Thuja plicata). Inland, xerophytic lowland decid-
uous oak communities (Quercus garryana, Quercus lobata, and
Quercus douglasii) and oak/pine/grassland mosaics develop. At
higher elevations in the Coastal Range, montane forest formations
develop with fir (Abies), hemlock, Douglas fir, pine, and evergreen
oaks (Barbour and Major, 1977). Just north of ~4°N in Oregon, west-
ern hemlock and Sitka spruce dominate along the Pacific Ocean, with
hemlock on the coast and spruce more prominent in the interior.
Common forest associates include Douglas fir, western red cedar (T.
plicata), and alder (Alnus) in moist habitats. Above the narrow band
of lowland forest are montane and subalpine forests of fir (Abies con-
color and Abies amabilis), pine (Pinus ponderosa and Pinus lamber-
tiana), and mountain hemlock (Tsuga mertensiana).
The two contrasting vegetation types of the California coast
(southern California oak woodland and Pacific Northwest conifer
forests) reflect significant differences in mean annual temperature
and precipitation (first-order controls of vegetation distribution).
South of ~40°Ν–42°N, mean annual temperatures and precipitation
average 19°C and 30 cm, and upper montane temperature and precip-
itation are ~8°C and ~57 cm. To the north in Oregon, mean annual
lowland temperature and precipitation are ~12°C and ~300 cm, and
subalpine temperatures and precipitation average ~10°C and ~140
cm (Elford, 1974; Sternes, 1974). The south–north transition from
excess evaporation to excess precipitation roughly coincides with the
frequency and intensity of frontal storms south and north of the atmo-
spheric and oceanic polar fronts.
Close to the ocean, California and Oregon temperatures and effec-
tive precipitation are moderated by fog associated with upwelling
(Barbour, 1988; Barbour et al., 1980) and by seasonal variations in
sea-surface temperatures (SSTs) of the southward-flowing California
Current and the poleward-flowing seasonal Davidson Current. South
of ~42°N, northerly winds drive near-coastal persistent seasonal up-
welling; to the north, upwelling intensity is more variable. Off Cali-
fornia and Oregon, waters north of 40°Ν42°N are subarctic in type
with mean SSTs of ~12° to ~13°C; off Southern California, mean
SSTs of ~14° to ~15°C reflect the presence of subtropical waters
(Gardner et al., 1997).
During the past glacial cycle, changes in the California Current
system and in California maritime vegetation and climate inferred
from pollen data appear to be related. Near-synchronous high-
frequency variations in the abundance of oak in Southern California
and SST in the Santa Barbara Basin characterize oxygen isotope
Stage (OIS) 5 (Heusser, 1995). Similar variations in redwoods in
Northern California correspond to temporal and geographic changes
in offshore upwelling and in movement of the Polar Front during
OISs 31 (Doose et al., 1997; Gardner et al., 1997; Heusser, 1998;
Lyle et al., 1992; Sabin and Pisias, 1996; Sancetta et al., 1992). Here
we use three pollen records from cores taken on the northeast Pacific
continental margin to document millennial-scale variability of coastal
North American ecosystems from OISs 1 through 13.
Pollen records are from cores taken at two Ocean Drilling Pro-
gram (ODP) drill sites (Site 1019: 41°40.696N, 124°55.981W, 989
meters below seafloor [mbsf]; Site 1020: 41°0.051′Ν, 126°26.065W,
3050 mbsf) and from piston Core EW9504-17PC (42°14.55N,
125°53.28W, 2671 mbsf; Fig. 1). The siliciclastic clays and silt from
the upper 60 m (meters composite depth [mcd]) of Holes 1020C,
1020D, 1019C, and 1019E were routinely sampled at 20-cm intervals
(Lyle, Koizumi, Richter, et al., 1997). Core EW9504-17PC, com-
posed predominantly of hemipelagic clay (Lund and Mix, 1998), was
sampled at 5-cm intervals. Standard processing procedures that in-
cluded the addition of known amounts of an exotic tracer to calculate
pollen concentration were preceded and succeeded by sieving
through 7-µm nylon screening. Taxonomic identification of pollen
was based on comparison with modern pollen reference collections
from western North America. Specific epithets are indicated for
grains that were clearly identified; otherwise, pollen and spores are
assigned to genera or higher rank. Other than the papillate grains of
Sequoia (redwood) and the large inaperturate grains assumed to rep-
resent P. menziesii, inaperturate pollen of other genera in the Taxodi-
aceae, Cupressaceae, and Taxaceae that cannot be satisfactorily sep-
arated using light microscopy (e.g., Juniperus, Torreya, Cupressus,
Libocedrus, Chamaecyparis, and Thuja) are here referred to as cedar
type. Other synthetic pollen groups include chaparral (sclerophylous
shrubs and other members of the Anacardiaceae, Rhamnaceae, and
Rosaceae) and herbs (Gramineae, Cyperaceae, and Compositae, in-
cluding Artemisia or sage). A mininum of 300 pollen grains were
identified in each sample from Core EW9504-17PC; the initial pollen
counts from Sites 1019 and 1020 presented here averaged ~110 and
~150 pollen grains, respectively. Pollen percentages were based on
the sum of terrestrial pollen (excluding fern spores), and pollen con-
centration was calculated on the number of pollen grains per gram dry
weight of sediment (gdws).
Age models were constructed by correlating the CaCO
and C
records to the best radiocarbon-dated sections and oxygen isotope
records. Methods are reported in detail in Lyle et al. (Chap. 32, this
volume). Age control for Core EW9504-17PC was achieved by (1)
correlating the CaCO
and C
records from Lyle et al. (Chap. 32, this
volume) with Core W870913PC (time scale of Lund and Mix, 1998)
for 050 ka, (2) correlating the oxygen isotope record from 50 to 140
ka in the core (Lund and Mix, 1998) with the Martinson et al. (1987)
age model, (3) allowing minor shifts in the record to minimize sedi-
mentation rate changes without losing significant correlation, and (4)
comparing the oxygen isotope record on the final age model to the
Martinson et al. (1987) age model to see if the two age models re-
mained consistent.
To construct an age model for Site 1020, we correlated the dated
carbonate and organic carbon records from Core EW9504-17PC with
the carbonate and organic carbon records of nearby Site 1020 and
hence were able to transfer the age model from Core EW9504-17PC
to Site 1020 (Lyle et al., Chap. 32, this volume). Below 140 ka, our
age model for Site 1020 is based upon reconnaissance-scale oxygen
isotope stratigraphy and biostratigraphic datums.
Development of an age model for Site 1019 was more problematic
(Lyle et al., Chap. 32, this volume). The preliminary age model used
here is based on reconnaissance-scale oxygen isotope stratigraphy
supplemented by radiocarbon age control from 6 to 24 ka. We note
that these preliminary age models will be modified when more age
control (radiocarbon and stable isotope data) is available. Using the
age models described above, the average sampling interval in Core
EW9504-17PC was ~500 yr, the average sampling interval in the up-
per 57 mcd of Holes 1020C and 1020D was ~1700 yr, and the average
sampling interval in the upper 40 m of Holes 1019C and 1019E was
~800 yr (Lyle, Koizumi, Richter, et al., 1997).
In the hemipelagic sediments from Core EW9504-17 and from
Sites 1019 and 1020, pollen concentration is high, with slightly more
pollen in sediments deposited closest to land (Fig. 2). Mean pollen
abundance in sediments deposited at Site 1019 (~59 km west of the
California coast) is 5500 grains/gdws compared with mean concen-
trations of 4000 grains/gdws in sediments deposited at Core
Figure 1. Map of the northeast Pacific continental margin showing core loca-
tions. Site 1019 is in the coastal upwelling system. Site 1020 and Core
W8709-17 are under the northern California Current, south of the North
Pacific Subpolar Front.
EW9504-17 (~120 km offshore) and 3600 grains/gdws in sediments
deposited at Site 1020 (~167 km offshore). Rapid oscillations in pol-
len abundance that occur in pollen records from each of the three lo-
calities display high-amplitude peaks that show systematic variations
in Core EW9504-17 and Site 1019. Age plots (Fig. 2) show that al-
though the overall trends of pollen abundance in Core EW9504-17
broadly correspond to interglacialglacial climate change (e.g., max-
ima occur in warm intervals such as the Holocene and OIS 5, and
minima are associated with cold intervals such as OIS 2), correlation
between pollen concentration and climatic events is not consistent.
At Site 1019, maxima in total pollen abundance coincide with some
(OISs 5 and 7) but not all major warm intervals, whereas variations
in mass accumulation rates of redwood at Site 1020 (like that of ter-
rigenous minerals; see Hovan et al., Chap. 18, this volume) corre-
spond fairly closely to global δ
O variations. Pollen concentration
on the California continental margin reflects vegetation density, pol-
len sedimentation (including fluviomarine sedimentary processes),
and climatic processes (regional and global; Heusser and Balsam,
1977; Traverse, 1988; Fig. 2).
The pollen records from Sites 1019 and 1020 as well as Core
EW9504-17 are composed of taxa that presently grow in northwest
America. Paleoecologic interpretations of these pollen spectra are
based on several assumptions: (1) the diagnostic components of pol-
len assemblages from marine cores, like those from terrestrial cores,
reflect in varying degrees the composition of vegetation formations
from which they are derived (Heusser, 1983, 1988; Heusser and Bal-
sam, 1977); (2) modern climatic tolerances of vegetation with pollen
spectra similar to fossil pollen spectra provide a reliable foundation
for reconstructing past vegetation and climate (Heusser et al., 1980;
Whitlock and Bartlein, 1997); and (3) changes in the Quaternary veg-
etation of California and southern Oregon reflect regional and global
climatic change (Axelrod, 1977; Huntley and Webb, 1988).
At all three localities, pollen spectra of the uppermost samples are
marked by a succession of alder, oak, and redwood peaks accompa-
nied by ferns and lesser amounts of western hemlock, spruce, and ce-
dar (Figs. 35). These distinctive assemblages of pollen representative
of natural north coast forest and oak woodland communities occur re-
peatedly downcore: between ~13 and ~15 m in Core EW9504-17 (Fig.
3); also, between ~38 and ~32 mcd and between ~46 and ~66 mcd at
Site 1019 (Fig. 4). In the record from Site 1020, the alder-oak-
redwood-fern assemblage is repeated five times (Fig. 5). Although the
basic composition is essentially the same in the three records, differ-
ences exist in the sequence and relative abundance of taxa. In Holes
1019C and 1019E, the redwood maxima at 33.48 mcd precedes that of
oak (32.68 mcd). At Site 1020, redwood maxima vary in amplitude
from ~35% at 44 mcd to ~10% at 2628 mcd, and alder maxima range
from ~22% at ~55 mcd to ~7% at 14 mcd. Except for the peak at ~14
mcd, oak peaks display less variation.
The peaks of alder that initiate abrupt expansions of coastal low-
land forest types reflect the pioneer role of alder in aggressively colo-
nizing areas disturbed by catastrophic events (flooding and infrequent
wildfires) or by reorganization of plant communities related directly
EW9504-17PC 1020C/D
100 20
25 12
Depth (m)
Age (k.y.)
Figure 2. Depth plot of pollen concentration in number of pollen grains per gram dry weight of sediment at Sites 1019 and 1020 and piston Core EW9504-17
(left), and time series of pollen concentration at Site 1020 and in piston Core EW9504-17 (right). Depths of samples from Holes 1019C, 1019E, 1020C, and
1020D are meters composite depths (Lyle, Koizumi, Richter, et al., 1997). Age models are based on time scales developed by Lyle et al. (Chap. 32, this volume).
or indirectly to climate change. The apparent lack of systematic vari-
ation in charcoal fragments found in pollen samples suggests that
wildfires were probably not the primary cause of the high-amplitude
alder events. Alder habitats are wet, along streams and in marshy
places in redwood and mixed evergreen forests (Alnus oregona and A.
sinuata), and moist places in the north Coastal Range (A. tenuifolia;
Barbour and Billings, 1988; Munz, 1968). Increased alder in sedi-
ments deposited on the California margin thus may reflect expansion
and/or recolonization of alder habitats related to increased precipita-
tion and/or increased runoff from snowmelt during deglaciation
(Heusser and Shackleton, 1979). Alder expansion in areas of revege-
tation following disturbance is well documented in the Pacific North-
west (Barbour and Billings, 1988; Grigg and Whitlock, 1998; Heus-
ser, 1985).
Subsequent expansion of the two different north coast lowland
habitatsmesic redwood forests along the narrow band adjacent to
the Pacific Ocean and xeric oak woodland farther inlandmay be re-
lated to changes in temperature, precipitation, and other atmospheric
and oceanic processes. Higher temperatures and change in the
amount and seasonal distribution of rainfall that enhanced summer
drought (increased summer moisture stress related to decreased ef-
fective precipitation and increased summer temperatures, for exam-
ple) would favor development of lowland oak communities. Such
conditions would not be conducive to redwood expansion. Coastal
redwood requires much lower diurnal and annual temperature fluctu-
ations than oak and is now restricted to that part of the coast where
temperature extremes and summer moisture stress are modified by
prolonged cloudy periods and marine fog associated with offshore
upwelling (Zinke, 1977). We suggest that redwood expansion was
probably closely related to the development of maritime conditions
(changes in the distribution and intensity of upwelling in the Califor-
nia Current, for example), which moderated north coast climate. De-
tailed statistical analyses of radiolarian species and pollen taxa from
Core EW9504-17 show a very high degree of correlation between ra-
diolarians associated with coastal upwelling and redwood (N.G. Pi-
sias, pers. comm., 1998).
All the pollen records contain lengthy intervals dominated by
seemingly uniform assemblages composed of pine, herbs, and cedar,
along with spruce, hemlock, and mountain hemlock (T. mertensiana,
a subalpine species; Barbour and Billings, 1988). To some extent, the
apparent uniformity reflects limitations of pollen analysis; that is, the
presence of genera and families that cannot be discriminated into
more ecologically specific taxonomic taxa. The composition of these
conifer-dominated assemblages alternates between coastal forest
taxa like those now growing north of the present distribution of red-
wood (in northern Oregon, Washington, and British Columbia) and
forests or open pine woodlands not unlike those that now occur at
higher elevations (Barbour and Major, 1977). Oscillations in herbs
that occur throughout indicate variable development of vegetative
Similar sequences of temperate lowland conifer forest and oak
woodland assemblages alternating with those of montane forest/
woodland occur in upper Quaternary pollen records from sites in
Northern California, western Oregon, and Washington as well as in
Depth (m)
Figure 3. Depth plots of percentages of selected pollen types from piston Core EW9504-17. The relative abundance of sage (Artemisia) is shown as a solid black
line in the herbs plot; other herb percentages are shown by a dotted line. The percentage of cedar is a solid black line; pine percentages are plotted with a dotted
line. Note that scales vary for different taxa.
Quaternary pollen data from other marine cores taken off Northern
California, Oregon, and Washington (Adam and West, 1983; Grigg
and Whitlock, 1998; Heusser, 1985, 1998; Heusser and Shackleton,
1979). Regional differences in vegetation are readily apparent in the
composition of the warm temperate pollen assemblages (i.e., the
prominence of redwood and/or oak in the south and of western hem-
lock and spruce in the north) and in the composition of the more ho-
mogeneous pollen assemblages in the intervening cooler intervals,
which are characterized by the greater prominence of juniper and ce-
dar types in cores from the south. The similarity between the system-
atic downcore variations in marine and continental records from the
same geographic area implies that marine pollen records, like those
on land, capture systematic variations in regional vegetation and cli-
When pollen data are plotted against age (Figs. 68), it is evident
that in Core EW9504-17, alder, oak, redwood, and fern maxima cor-
respond to benthic δ
O minima and that downcore variations in pol-
len stratigraphies of Sites 1019 and 1020 also reflect orbital-scale
global climate fluctuations. Small differences in the relative abun-
dance of the mesophytic, temperate taxa between OISs 1, 5, 7a, 7c,
and 9 suggest that the development and composition of interglacial
vegetation in Northern California was not always identical in each of
the last four interglacials. Because of the preliminary nature of age
models for Sites 1019 and 1020 (Lyle et al., Chap. 32, this volume),
we focus on the well-dated EW9504-17 time series.
The double beat of OIS 7 δ
O at Site 1020 (Fig. 8) is mirrored in
muted alder, oak, and redwood peaks that are more robust (as are
ferns) in the preceding interglacial (OIS 9). The OIS 6/5e transition
in Core EW9504-17 and at Site 1019 is marked by an abrupt rise in
alder that is rapidly succeeded in OIS 5e by oak and redwood peaks
in Core EW9504-17. At Site 1019, the redwood maximum precedes
that of oak. Multiple oscillations in these taxa occur in OIS 5c. These
large-scale patterns also occur in pollen assemblages in the upper
~130 k.y. of the lower resolution Site 1020 pollen record (Fig. 8). It
is worth noting that in all three records, pollen assemblages from OIS
5e are not exact replicates of those in OIS 1. During the last intergla-
cial, oak was more abundant than in the Holocene; the converse is
true for alder and redwood in Core EW9504-17 and at Site 1020.
Pine, dominant in OIS 5d and 5b, became increasingly important
during the last full glacial, as did sage and other herbs. In OIS 3, brief
pine events occurred at ~14, ~16, ~35, ~38, and ~42 k.y. in Core
EW9504-17 (Fig. 6). Two well-defined events coincide with major
episodes of North Atlantic ice rafting (Heinrich Events H1 and H4).
The low amplitude of redwood and oak oscillations during OIS 3,
which partly reflects overrepresentation of pine (a common feature of
pollen dispersal and sedimentation; Traverse, 1988), precludes corre-
lation with interstadial events elsewhere.
In Holes 1020C and 1020D, the rhythmic pattern of downcore
variation in the alder, oak, redwood, and fern maxima (Fig. 5) is evi-
dent through OIS 13 (M. Lyle, pers. comm., 1998). Between ~43 and
~45 mcd (OIS 11), the robust redwood acme is preceded by a sub-
stantial peak in alder and ferns. Oak percentages are comparable to
those of previous interglacials (excluding OIS 5). The high-ampli-
tude pulse of alder between ~51 and ~55 mcd (OIS 13) leads a lesser
0 100
Depth (m)
Figure 4. Depth plots of percentages of selected pollen types from the upper 66 m of Holes 1019C and 1019E. The relative abundance of sage (Artemisia) is
shown as a solid black line in the herbs plot; other herb percentages are shown by a dotted line. The percentage of cedar is a solid black line; pine percentages
are plotted with a dotted line. Note that scales vary for different taxa.
rise in redwood, oak, and ferns. As in the younger part of the pollen
record, interglacial assemblages display individualistic variations.
At glacialinterglacial transitions (OISs 8/7, 6/5e, 2/1, and most
probably 10/9), the abrupt changes in west coast vegetation (identi-
fied by the rapid expansion of the pioneer alder) and global warming
(higher benthic δ
O) are nearly synchronous (Figs. 6, 8). The initial
increase in alder and the shift in δ
O at glacial terminations occurs in
exactly the same sample depths in Core EW9504-17 and at Site 1020.
Directly correlative pollen and δ
O data from two other northeast Pa-
cific cores (Core Y7211-1 taken at 43°15N, 126°22W; Site 893
taken at 34°17.25N, 120°02.19W; Fig. 1) showed similar relation-
ships at the OIS 6/5e transition (Heusser, 1995; Heusser and Shackle-
ton, 1979). These data imply that glacialinterglacial variations in
northwest North American climate and vegetation over the last 350
k.y. were (within constraints of sample resolution) apparently nearly
synchronous with orbital-scale global ice-volume variations. Directly
correlative terrestrial/marine records from piston cores taken in the
northwest Pacific (Morley and Heusser, 1997) and from Site 594 in
the southwest Pacific (Heusser and van de Geer, 1994) showed that
large-scale variations in Japanese and New Zealand ecosystems over
the last ~350 k.y. could be attributed to orbital forcing of global cli-
mate mechanisms.
To display pollen data in a form less affected by overrepresenta-
tion of pine, we use pollen ratios (Fig. 9). The redwood and western
hemlock/spruce ratio can be regarded as a temperature indicator of
mesophytic lowland forests because average July temperatures in ar-
eas now dominated by redwood and/or western hemlock are ~1° to
2°C higher than in areas dominated by spruce (Heusser, 1985; Heus-
ser and Shackleton, 1979; Zinke, 1977). The oak/pine ratio serves as
an indicator of temperature trends in the more arid northern Califor-
nia interior since temperatures in the lowland oak woodlands are sev-
eral degrees higher than temperatures in montane pine forests (Adam
and West, 1983). At ~42°N, maximum mean monthly temperatures
at 332-m elevation in the nearby mountains are 6.2°C higher than on
the coast (Barbour and Major, 1977). Although we describe these cli-
mate proxies as temperature indicators, we recognize that effective
precipitation is a major factor in vegetative composition and cannot
be effectively separated from temperature in our paleoclimatic prox-
The close correspondence between pollen ratio, insolation, and
O curves implies that north coast environmental fluctuations were
broadly synchronous with changes in global climate over the last
~150 k.y. (Fig. 9). As suggested earlier, the lag in the response of red-
wood/western hemlock communities probably reflects the significant
role of sea-surface conditions in the development of north coast mar-
itime vegetation (Lyle et al., Chap. 32, this volume).
Pollen records from the northern California and southern Oregon
margin of the northeast Pacific Ocean (Sites 1019 and 1020 and pis-
0 100
Depth (m)
Figure 5. Depth plots of percentages of selected pollen types from the upper 60 m of Holes 1020C and 1020D. The relative abundance of sage (Artemisia) is
shown as a solid black line in the herbs plot; other herb percentages are shown by a dotted line. The percentage of cedar is a solid black line; pine is plotted with
a dotted line. Note that scales vary for different taxa.
ton Core EW9504-17) capture vegetational-environmental changes
on the North American northwest coast. Glacial vegetation is domi-
nated by montane conifer types accompanied by a significant amount
of herbs. Major climatic thresholds such as glacialinterglacial tran-
sitions are marked by high-amplitude peaks of the pioneer alder that
precede the expansion of interglacial lowland oak woodlands and
coastal redwood forests. The similarity in the structure of oak- and
redwood-based pollen ratios, insolation, and δ
O curves implies that
environmental fluctuations on the Pacific Northwest coast reflect
large-scale variations in global climate over the last ~150 k.y. Com-
parison of preliminary pollen and oxygen isotope data from Sites
1019 and 1020 indicates that similar relationships prevailed over the
last 500 k.y. We suggest that differences in the development of low-
land oak- and redwood-dominated vegetation on the northwest coast
of North America reflect fluctuations in large-scale climate controls
and fluctuations in regional maritime conditions offshore.
This research was supported by JOI/USSAC and by National Sci-
ence Foundation grants. We thank the Ocean Drilling Program and
the Leg 167 Scientific Party. Other individuals who have contributed
to the development of this manuscript include N. Pisias, C. Heusser,
and E. Stock. We thank L. Dupont and A. Mix for reviewing the
manuscript. Oregon State University curating facilities are supported
by NSF grant OCE94-02298.
Adam, D.P., and West, G.J., 1983. Temperature and precipitation estimates
through the last glacial cycle from Clear Lake, California, pollen data.
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Figure 6. Time series of selected pollen types and stable isotope data from Core EW9504-17 with benthic oxygen isotope Stages (OISs) 1 through 5 superim-
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Date of initial receipt: 30 September 1998
Date of acceptance: 18 June 1999
Ms 167SR-206
Alder/ferns Oak Redwood Cedar/pine
Age (k.y.)
Figure 7. Time series of selected pollen types from Hole 1019C/E and Core EW9504-17 with benthic OISs 1 through 5 superimposed. This preliminary time
series is based on the initial time scale developed by Lyle et al. (Chap. 32, this volume). Percentages of ferns, pine, and herbs (excluding sage, which is shown
as a solid line in the herbs plot) are shown as dotted lines. OIS = oxygen isotope stage.
Age (k.y.)
O Alder/ferns Oak Redwood Cedar/pine Herbs
Figure 8. Time series of selected pollen types and preliminary stable isotope data from Holes 1020C and 1020D with benthic OISs 1 through 9 superimposed.
Percentages of ferns, pine, and herbs (excluding sage, which is shown as a solid line in the herbs plot) are shown as dotted lines. OIS = oxygen isotope stage.
Age (k.y.)
Insolation (65°N) δ
O Oak/pine ratio
Conifer ratio
Figure 9. Comparison of July insolation with time series of δ
O and pollen ratios (oak/oak + pine and redwood + western hemlock/spruce) from piston Core
... The concentration of pollen in marine sediments reflects the abundance of vegetation present as determined by regional and global climate patterns (Heusser and Balsam, 1977;Traverse, 1988), as well as the sedimentary processes responsible for delivering it to the deposition site. Typically, higher pollen abundances occur in marine sediments lying closer to their continental source (Muller, 1959;Groot and Groot, 1966;Traverse and Ginsburg, 1966;Groot et al., 1967;Heusser and Balsam, 1977;Heusser, 1978b;Melia, 1984;Heusser et al., 2000) and opposite major stream drainage areas (Cross et al., 1966;Groot et al., 1967;Heusser and Balsam, 1977;Heusser, 1978a;Heusser et al., 2015). Pollen concentrations in core S3-15G obtained~135 km offshore range between 5162 and 14,473 grains/g dry weight sediment (gdws) with a mean of 8700 grains/gdws (Table 3). ...
... Pollen concentrations in core S3-15G obtained~135 km offshore range between 5162 and 14,473 grains/g dry weight sediment (gdws) with a mean of 8700 grains/gdws (Table 3). These pollen concentrations are higher than those found off northern California and Oregon by Heusser et al. (2000), in which the mean pollen abundances were 5500, 4000, and 3600 grains/gdws at distances of~59,~120, and~167 km offshore, respectively. The higher pollen concentrations in S3-15G may simply reflect more dense vegetation onshore opposite the deposition site (Cross et al., 1966). ...
... Instead, higher pollen abundances in the Holocene most likely reflect warming conditions compared to the Pleistocene. Heusser et al. (2000) also noted maxima in pollen abundance during the warm intervals (Oxygen Isotope Stage (OIS) 5 and the Holocene) and minima during the cold intervals (e.g., OIS 2) off the northern California margin. ...
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A pollen record obtained from a deep-sea core from the continental margin off central California contains evidence of the terrestrial floral adaptation to changing climatic conditions over the last ca. 20,000 cal. BP. The pollen record is divided into three pollen zones, two of which are late Pleistocene in age (Glacial and Transitional) and the third is Holocene (Interglacial).The Glacial Pollen Zone (ca 20,000-17,000 cal BP) is characterized by Pinus and Abies pollen, reflecting environmental conditions during the last glacial maximum. Overlying this (ca 17,000-11,600 cal BP) is the Transitional Pollen Zone containing a pollen assemblage indicative of a transitional climatic regime, with species that reflect more arid environmental conditions (Pinus and Artemisia) decreasing in abundance and those reflecting moister conditions (Sequoia and Alnus) rising in abundance. Pediastrum and dinoflagellates are common and are attributable to increased nutrient-rich coastal runoff. The Bølling-Allerød (295-256 cm; ca 14,600-12,900 BP) and Younger Dryas (256-243 cm; ca 12,900-11,600 BP) events occur within the Transitional Pollen Zone as well. The Interglacial Pollen Zone (ca 11,600 cal BP to present) is characterized by decreasing Pinus and increasing Sequoia, Quercus, and Asteraceae, reflecting changes in vegetation during the climatic warming of the Holocene. Two brief dry periods are represented in this pollen zone, one from 150 to 125 cm (ca 8000-6400 cal BP) and the other at 22-20 cm (ca 800-700 cal BP). They are correlated with the middle Holocene dry period and the Medieval Climate Anomaly, respectively.
... [14] Samples were chosen at 5-cm intervals from the upper 7.10 m composite depth (mcd) of ODP Site 1019 after referring to Mix et al.'s [1999] age model, which suggests that the last 15,000 years were sampled. In the case of sediment and pollen studies, these samples were supplemented by samples previously studied by Lyle et al. [2000] and Heusser et al. [2000] in order to bring the record back to 16,000 years B.P. ...
... [59] On the other hand, an increasing contribution of redwood pollen after 5.2 ka (Figure 7) might be taken as evidence of increasing coastal upwelling at Site 1019 during the later part of the Holocene [Heusser, 1998;Heusser et al., 2000]. Forests of coastal redwood are best developed where fog associated with cold upwelling waters moderates summer temperatures (mean July temperature of 17°C) and ameliorates drought. ...
... [14] Samples were chosen at 5-cm intervals from the upper 7.10 m composite depth (mcd) of ODP Site 1019 after referring to Mix et al.'s [1999] age model, which suggests that the last 15,000 years were sampled. In the case of sediment and pollen studies, these samples were supplemented by samples previously studied by Lyle et al. [2000] and Heusser et al. [2000] in order to bring the record back to 16,000 years B.P. ...
... [59] On the other hand, an increasing contribution of redwood pollen after 5.2 ka (Figure 7) might be taken as evidence of increasing coastal upwelling at Site 1019 during the later part of the Holocene [Heusser, 1998;Heusser et al., 2000]. Forests of coastal redwood are best developed where fog associated with cold upwelling waters moderates summer temperatures (mean July temperature of 17°C) and ameliorates drought. ...
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Holocene and latest Pleistocene oceanographic conditions and the coastal climate of northern California have varied greatly, based upon high-resolution studies (ca. every 100 years) of diatoms, alkenones, pollen, CaCO3%, and total organic carbon at Ocean Drilling Program (ODP) Site 1019 (41.682°N, 124.930°W, 980 m water depth . Marine climate proxies (alkenone sea surface temperatures [SSTs] and CaCO3%) behaved remarkably like the Greenland Ice Sheet Project (GISP)-2 oxygen isotope record during the Bølling-Allerod, Younger Dryas (YD), and early part of the Holocene. During the YD, alkenone SSTs decreased by >3°C below mean Bølling-Allerod and Holocene SSTs. The early Holocene (ca. 11.6 to 8.2 ka) was a time of generally warm conditions and moderate CaCO3 content (generally >4%). The middle part of the Holocene (ca. 8.2 to 3.2 ka) was marked by alkenone SSTs that were consistently 1-2°C cooler than either the earlier or later parts of the Holocene, by greatly reduced numbers of the gyre-diatom Pseudoeunotia doliolus (<10%), and by a permanent drop in CaCO3% to <3%. Starting at ca. 5.2 ka, coastal redwood and alder began a steady rise, arguing for increasing effective moisture and the development of the north coast temperate rain forest. At ca. 3.2 ka, a permanent ca. 1°C increase in alkenone SST and a threefold increase in P. doliolus signaled a warming of fall and winter SSTs. Intensified (higher amplitude and more frequent) cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature (enhanced El Niño-Southern Oscillation [ENSO] cycles) have characterized the Site 1019 record since about 3.5 ka.
... This holds true for Holocene and Pleistocene laminated (T d ) silt units as well (6814 grains/g and 6328 grains/g, respectively), although the trend is not statistically significant (p ¼ 0.1362), possibly because so few silt units were sampled in the Holocene to adequately test the hypothesis. The increased abundance of pollen further up-core in both the muds and turbiditic deposits is thought to reflect warming conditions in the Holocene (e.g., Heusser et al., 2000) and explains why the sample at 46e48 cm is somewhat of an outlier compared to the other turbiditic silts and sands ( Fig. 7A) with its higher pollen abundance (10,525 grains/g). ...
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The pollen assemblage of a deep-sea core (15G) collected at lower bathyal depths (3491 m) on a levee of Monterey Canyon off central California was investigated to gain insights into the delivery processes of terrigenous material to submarine fans and the effect this transport has on the palynological record. Thirty-two samples were obtained down the length of the core, 19 from hemipelagic and mixed mud deposits considered to be the background record, and 13 others from displaced flow deposits. The pollen record obtained from the background samples documents variations in the terrestrial flora as it adapted to changing climatic conditions over the last 19,000 cal yrs BP. A Q-mode cluster analysis defined three pollen zones: a Glacial Pollen Zone (ca. 20,000–17,000 cal yr BP), an overlying Transitional Pollen Zone (ca. 17,000–11,500 cal yr BP), and an Interglacial Pollen Zone (ca. 11,500 cal yr BP to present). Another Q-mode cluster analysis, of both the background mud and flow deposits, also defined these three pollen zones, but four of the 13 turbiditic deposits were assigned to pollen zones older than expected by their stratigraphic position. This was due to these samples containing statistically significant fewer palynomorphs than the background muds as well as being enriched (∼10–35% in some cases) in hydraulically-efficient Pinus pollen. A selective bias in the pollen assemblage, such as demonstrated here, may result in incorrect interpretations (e.g., climatic shifts or environmental perturbations) based on the floral record, indicating turbiditic deposits should be avoided in marine palynological studies. Particularly in the case of fine-grained flow deposits that may not be visually distinct, granulometry and grain size frequency distribution curves may not be enough to identify these biased deposits. Determining the relative abundance and source of displaced shallow-water benthic foraminifera entrained in these sediments serves as an excellent additional tool to do so.
We compiled pollen sequences from lake and offshore cores at least 6,000 years old (6 ka) for the Mediterranean and Marine ecoregions of the US West Coast. Principal Component Analysis highlighted vegetation differences in core-tops, the Holocene Thermal Maximum (6 ka) and Last Glacial Maximum (LGM, 19 ka). Core-top and HTM ordination produced clusters that reflected geographic clusters in the Sierra Nevada, and the Pacific Northwest coast. Little change in these clusters between 6-0 ka suggested that vegetation communities in coastal and alpine settings persisted, despite warmer global temperatures. PCA outliers reflect distinct pollen assemblages that often were isolated sites or bordered the Great Basin. During the LGM, greater shrub and herb presence in the Marine ecoregion interior indicated enhanced aridity, while conifer presence in coastal and Southern California indicated moist conditions. Qualitatively, tree taxa from the Last Interglacial (~130–120 ka) showed how vegetation shifted over 6–10 kyr from alder, to oak, then redwood, a successional pattern that began again at the Late Glacial (~15 ka). In future West Coast pollen studies, sampling and chronologic control at centennial resolution will enable further study of more time periods and rates of vegetation change in response to climate.
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Marine microfossil and pollen assemblages, benthic foraminifer δ18O, physical properties, and calcium carbonate content in sediments from Ocean Drilling Program (ODP) Sites 1018 and 1020 off central and northern California in the eastern North Pacific reveal strong links between the marine and terrestrial environments during marine isotope stage 5 (MIS 5) (~125,000 years ago). Our multiproxy record indicates that at the beginning of the last interglacial (MIS 5e), reduction in global ice volume, increase in sea-surface temperature, and warming of air temperature along the central and northern California coast were synchronous within the resolution of our sampling interval. The waters off the coast of northern California (near ODP Site 1020) were strongly influenced by warm central Pacific waters at the beginning of MIS 5e near the maximum interglacial. The strong influence of central Pacific waters resulted in less intense upwelling and more zonal atmospheric circulation than exist under modern conditions. Foraminifer assemblages from ODP Site 1018 are generally sparse and poorly preserved, but the assemblages that are present support interpretations based on assemblages from ODP Site 1020. Redwood became most abundant on the west coast of North America after the peak interglacial, presumably as coastal upwelling became more organized or persistent and temperature cooled slightly. Variations in pollen records are similar at ODP Sites 1020 and 1018, indicating that our pollen data reflect regional-scale changes. Variations in physical properties, calcium carbonate content, and diatom assemblages in sediments from ODP Site 1020 appear to be related to changes in the dominance of coastal versus open ocean upwelling. Evidence of upwelling-related cycles of about 8,000 and 5,000 years duration is present throughout much of the MIS 5 record from ODP Site 1020. Two abrupt climatic coolings are identified in MIS 5e, at ~ 126 ka and at ~ 119 ka.
This paper outlines one of the first attempts to analyse the detailed pollen content of the marine sediments from a fjord (sea loch) located on the west coast of Scotland. The site chosen was in the Bonawe Deep, part of the upper basin of Loch Etive, and 2.3 m depth of sediments were sampled. These sediments were examined for their fossil pollen content and a pollen diagram was constructed from the results. The interpretation of the pollen record was supported by seven radiocarbon dates which demonstrated that the sediments accumulated over the last 8-9 ka of the Holocene. The pollen diagram was divided into three pollen assemblage zones. The lowest zone ET1 (c. 9-7.3 ka BP) was dominated by pollen of Betula, Pinus and Corylus, zone ET2 (c. 7.3-1.2 ka BP) contained a wide range of woodland pollen taxa (mainly Betula, Pinus, Quercus, Alnus and Corylus) and the uppermost zone ET3 (1.2-0 ka BP) was distinguished by fewer tree pollen taxa and increased values of open habitat taxa, particularly Calluna. The pollen diagram showed the development of vegetation during the Holocene which correlated well with existing results from studies of peat or freshwater lake sediments sampled in the west of Scotland. The only significant differences were the higher concentrations of Pinus pollen found in the Loch Etive site. These differences can be explained by the large catchment area of the loch which includes high ground, where it is proposed that extensive Pinus forest grew during much of the Holocene. The study demonstrates the practicality of using Scottish fjord sediments for Holocene pollen studies and potentially provides a link between terrestrial vegetation records and marine-based fossil records.
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Sediments collected off northern California by Ocean Drilling Program Leg 167 contain time series that show strong, orbitally driven insolation forcing of surface oceanographic conditions. Orbital forcing caused a strong response in the distribution of major terrestrial vegetation but a less predictable response for primary productivity offshore. Terrestrial vegetation responded primarily to regional sea surface temperature (SST). Coastal ocean productivity appears highest when SST is moderately high, not during peak interglacial conditions nor during insolation maxima. When individual interglacial intervals are examined closely, each has a different signature. Two of six interglacials (MIS [marine isotope stage] 5 and MIS 11) have higher SST than modern conditions, but each elicits a different response from the terrestrial and marine communities. The type of vegetation and the strength of upwelling vary between interglacials, depending on the relative strength of factors that drive the warming, including insolation, ice-cap size, and level of greenhouse gases.
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This chapter focuses on high-resolution studies of sediment cores taken from lakes located within the western United States and on sediment-based records that illustrate evolving concepts of climate change (e.g., solar forcing). Sediment coring allows access to continuous records of climate change from the deepest parts of lake basins and major advances are made in terms of age control. The development of atmospheric, hydrologic, thermal, and isotopic climate models allows evaluation of the magnitudes and directions of climate variability and permits the numerical experimentation with lake–atmosphere feedbacks. Lakes are extremely useful in testing global, hemispheric, and regional models of climate forcing, given adequate age control and accurate and precise proxies of climate change. Age control for marine-, ice-, and lake-based records is presently inadequate when comparing decadal- to millennial-scale oscillations in climate records. Two magnetic excursions, the Laschamp excursion and Mono Lake excursion, are important markers that are found in both lake and marine sediments across the Northern Hemisphere.
Chronologically-controlled, high-resolution (∼200yr average sampling interval) pollen data from a core in the Santa Barbara Basin (SBB) provide evidence of millennial-scale climate variability on the southern California coast from ∼70 to 140ka B.P. The first climate event, inferred from a brief reversal in the glacial/interglacial shift from montane conifer to lowland oak assemblages, occurred during the oxygen isotope stage (OIS) 6/5 transition. In OIS 5e, oak-dominated assemblages imply conditions similar to or slightly warmer than present. Cooler conditions that gradually replaced the relatively stable warm Mediterranean climate that continued across the OIS 5e/5d transition ended abruptly just before the end of OIS 5d. Warming, inferred from oak expansion, continued in OIS 5c. This lengthy cyclic sequence of high amplitude warming events, which peaked below interglacial values, extended into the first part of OIS 5b. Similar oscillations occurred in OIS 5a. These pollen data, that are directly correlated with isotopic data from the same sediment samples from Hole 893A, support previous observations that the last interglacial (sensu stricto) on the west coast of North America was correlative with oxygen isotope substage 5e. In addition, pollen data show that significant warming events reflected in terrestrial vegetation also occurred in different background states of the climate system — during processes of ice growth as well as ice decay.
Marine pollen records from different parts of the world signal a general deterioration of climate at the end of the last interglacial (Substage 5e). Literature concerning marine pollen records covering Stage 5 is summarized. In more detail, results from the NE tropical Atlantic are discussed. Pollen influx indicating NE-trade vigor shows a strong increase during interglacial-glacial transitions at the end of Stages 7, 11, 13, and 15 and a stepwise increase during Stages 5 and 9. The extent of the tropical rain forest in northwest equatorial Africa was reduced during periods of strong trade winds, when Sahara, Sahel, savannas, and open forests shifted southwards indicating arid conditions in NW-Africa. A large southward shift of the Saharan-Sahelian boundary, from ca. 23°N during Substage 5e to ca. 14°N during Substage 5d, occurred in less than 5000 years after monsoonal activity during the last interglacial decreased. Other continents show increased aridity after the last interglacial, too. Temperatures and precipitation dropped during the substage transition 5e-5d in Japan and summer temperatures declined in NW America, while in Artie Canada and Greenland ice-growth started.
Divides the woodlands into 7 regional or elevational classes and then into 20 communities. Eight taxa can define each class: Quercus douglasii for the blue oak woodland, Q. agrifolia for the southern oak woodland, Q. chrysolepis for the mixed evergreen forest, Pinus ponderosa and P. jeffreyi for the mid-montane and eastside conifer forests, P. contorta var. murrayana for the upper montane conifer forest, and P. albicaulis and P. flexilis for the subalpine woodland. Greater floristic detail and associated environmental factors are given for each class. -P.J.Jarvis
Pollen records from two sites in western Oregon provide information on late-glacial variations in vegetation and climate and on the extent and character of Younger Dryas cooling in the Pacific Northwest. A subalpine forest was present at Little Lake, central Coast Range, between 15,700 and 14,850 cal yr B.P. A warm period between 14,850 and 14,500 cal yr B.P. is suggested by an increase inPseudotsugapollen and charcoal. The recurrence of subalpine forest at 14,500 cal yr B.P. implies a return to cool conditions. Another warming trend is evidenced by the reestablishment ofPseudotsugaforest at 14,250 cal yr B.P. Increased haploxylonPinuspollen between 12,400 and 11,000 cal yr B.P. indicates cooler winters than before. After 11,000 cal yr B.P. warm dry conditions are implied by the expansion ofPseudotsuga.A subalpine parkland occupied Gordon Lake, western Cascade Range, until 14,500 cal yr B.P., when it was replaced during a warming trend by a montane forest. A rise inPinuspollen from 12,800 to 11,000 cal yr B.P. suggests increased summer aridity.Pseudotsugadominated the vegetation after 11,000 cal yr B.P. Other records from the Pacific Northwest show an expansion ofPinusfrom ca. 13,000 to 11,000 cal yr B.P. This expansion may be a response either to submillennial climate changes of Younger Dryas age or to millennial-scale climatic variations.
Vegetation records spanning the past 21kyr in western North America display spatial patterns of change that reflect the influence of variations in the large-scale controls of climate. Among these controls are millennial-scale variations in the seasonal cycle of insolation and the size of the ice sheet, which affect regional climates directly through changes in temperature and net radiation, and indirectly by shifting atmospheric circulation. Longer vegetation records provide an opportunity to examine the regional response to different combinations of these large-scale controls, and whether non-climatic controls are important. But most of the longer North American records are of insufficient quality to allow a robust test, and the long European records are in regions where the vegetation response to climate is often difficult to separate from the response to ecological and anthropogenic controls. Here we present a 125-kyr record of vegetation and climate change for the forest/steppe border of the eastern Cascade Range, northwest America. Pollen data disclose alternations of forest and steppe that are consistent with variations in summer insolation and global ice-volume, and vegetational transitions correlate well with the marine isotope-stage boundaries. The close relationship between vegetation and climate beyond the Last Glacial Maximum provides evidence that climate variations are the primary cause of regional vegetation change on millennial timescales, and that non-climatic controls are secondary.
A north-south transect of 17 cores was constructed along the eastern boundary of the California Current system from 33° to 42°N to investigate the changes in biogenic sedimentation over the past 30 kyr. Percentages and mass accumulation rates of CaCO3, Corg, and biogenic opal were assembled at 500 to 1000 years/sample to provide relatively high resolution. Time-space maps reveal a complex pattern of changes that do not follow a simple glacial-interglacial two-mode model. Biogenic sedimentation shows responses that are sometimes time-transgressive and sometimes coeval, and most of the responses show more consistency within a limited geographic area than any temporal consistency. Reconstructed conditions during late oxygen isotope stage 3 were more like early Holocene conditions than any other time during the last 30 kyr. Coastal upwelling and productivity during oxygen isotope stage 3 were relatively strong along the central California margin but were weak along the northern California margin. Precipitation increased during the last glacial interval in the central California region, and the waters of the southern California margin had relatively low productivity. Productivity on the southern Oregon margin was relatively low at the beginning of the last glacial interval, but by about 20 ka, productivity in this area significantly increased. This change suggests that the center of the divergence of the West Wind Drift shifted south at this time. The end of the last glacial interval was characterized by increased productivity in the southern California margin and increased upwelling along the central California margin but upwelling remained weak along the northern California margin. A sudden (
Proxy records of northeast Asian precipitation (marine pollen) and northwest Pacific sea surface temperatures (marine fauna) contain concentrations of variance (frequency peaks) coincident with those of orbital variations (eccentricity, obliquity, and precession). Time series of these monitors of various components of the east Asian monsoon system are coherent with changing solar insolation and climate boundary conditions (ice volume, snow cover, albedo) at 41- and 23-kyr frequencies. Winter sea surface temperature (WSST) maxima are in phase with global ice volume minima at all three Milankovitch frequencies (100-, 41-, and 23-kyr periods). WSST maxima are also linearly related to summer insolation at 30°N, lagging radiation maxima by ~55° (~3.5kyr) across the precessional frequency band (23-kyr period). Our east Asian monsoon rainfall indicator (% Cryptomeria) reaches highest values immediately following summer insolation maxima during periods of low ice volume (interglacials). Across the eccentricity frequency band (100-kyr period), % Cryptomeria maxima are in phase with ice volume minima. At the higher frequency of orbital precession, monsoon rainfall lags both summer radiation maxima (~125° ~8kyr) and ice volume minima (~60° ~3.8kyr). Whereas much of the variation in northwest Pacific WSST can be attributed to summer radiation forcing and changes in global climate, mechanisms driving east Asian monsoon precipitation are more complex, involving other (possibly internal) factors.