Historical ecology in Beringia: The south land bridge coast at St. Paul Island

QUATERNARY

RESEARCH

Historical

16, 18-36 (1981)

Ecology

in Beringia: The South at St. Paul Island

Land Bridge

Coast

PAUL COLINVAUX Institute of Polar Studies und Depurtment of Zoology, The Ohio Stute University, 484 West 12th Avenue, Columbus, Ohio 43210 Received May 5, 1980 A 14-m core of lake sediments from St. Paul Island yields a long environmental history of the south coast of the Bering land bridge. Tritium assay demonstrates that sands in the bottom 8 m of deposit are injected with modern water, suggesting that a radiocarbon anomaly is the result of modern carbon introduced in groundwater. The remaining radiocarbon chronology, coupled with a time-stratigraphic pollen-zone boundary suggests that the record penetrates to the mid-Wisconsin interstadial. Pollen percentage data, Piceu pollen influx, and pollen species lists allow reconstruction of the land bridge vegetation, which was tundra, without shrubs or trees, with bare ground, and comparable to Bering land bridge tundras found further north. There was no coastal mild or wet strip. Plant associations comparable to those of the modem Aleutians or Pribilofs probably did not exist along the land bridge coast and the region was probably not suitable for breeding by fur seals and other marine mammals. A cold, dry, continental air-mass system reached to the coast itself. The south land bridge coast did not offer an environment to aboriginal human populations that was significantly milder than that of the land bridge plains to the north. At about 11,000 yr B.P. the Wisconsin dry climate was replaced by a regimen comparable to that at the modem tree line of the interior, and this climate in turn was replaced with the modem system at about 9500 yr B.P. Climatic change was independent of fluctuating sea level.

INTRODUCTION

tundra on upland sites and local sedge-grass meadows on lowlands.” Other published pollen data from sites in the land bridge interior are comparable with those of Colinvaux and of Cwynar and Ritchie (op. cit.), though different interpretations have sometimes been offered (Colinvaux, 1967a, 1973, 1977; Matthews, 1974, 1976; Rampton, 1971). Except for the partial analysis of Colinvaux (1967b), however, there are no published data describing the vegetation of the south land bridge coast. This paper reports pollen and paleolimnological data describing the vegetation and environment from a coastal site on what is now St. Paul Island of the Pribilof group (Fig. 1).

In reviewing the first pollen data from the Siberia-Alaska conjunction of glacial, and hence Bering land bridge age, Colinvaux (1964a) concluded that the vegetation “ . . . was reduced to the most frigid form of arctic tundra, a tussockless, grassy expanse, spotted with frost scars and loess deposits and devoid of all trees and shrubs except willows.” Pollen data on which this conclusion was based all came from latitudes near Bering Strait (Imuruk Lake, St. Lawrence Island, and Kotzebue Sound, Fig. l), but later studies revealed similar pollen spectra of land bridge age from the north land bridge coast (Colinvaux, 1964b, 1965). The most recent pollen work on lake sediments of land bridge age by Cwynar and Ritchie (1980) describes vegetation of the land bridge hinterland in language close to that used by Colinvaux (1964a) as follows, “The Beringian herb zone represents a sparse, discontinuous vegetation of herbaceous

ST. PAUL ISLAND: GEOGRAPHY, CLIMATE, LIMNOLOGY, AND VEGETATION

St. Paul is a volcanic island, roughly 18 x 12 km, in the southern Bering Sea about 80 km from the edge of the continental shelf. 18

0033-5894/81/040018-19$02.00/O Copyright All rights

@ 1981 by the University of Washington. of reproduction in any form reserved.

HISTORICAL

ECOLOGY

IN

BERINGIA

19

FIG. 1. Sketch map of the Siberia-Alaska conjunction. Light shading is the probable coastline of the Bering land bridge at the last glacial maximum. The dot by St. Matthew Island is the site of old lake sediments under the modern sea floor.

The main mass of the island is a series of nearly horizontal lava flows rising to about 60 m above modern sea level, but with scattered cinder cones standing up to 200 m above the lava shield (Figs. 2 and 3) (Stanley-Brown, 1892; Dawson, 1894; Barth, 1956). Remanent magnetism and WAr dating show that all the rocks of St. Paul were formed in the last few hundred thousand years (Cox er al., 1966). The youngest flows appear to be only a few thousand years old. There is no evidence that St. Paul has ever held glacial ice (Hopkins and Einarsson, 1966). Much of the modern shoreline of St. Paul has been shaped by sand bars worked from blackish, volcanic sand. Sand dunes line the northeast shore and a system of fossil sand dunes has been identified inland (Hopkins and Einarsson, 1966). Water between St. Paul and the edge of the Bering platform is mostly between 70 and 90 m deep. Intensive studies of old shorelines around the Bering Sea show that

there has been little movement of coasts through isostasy in the later Pleistocene (Hopkins, 1973). Submerged shorelines along the south edge of the platform, however, indicate a eustatic fall in sea level of 90-100 m in Wisconsin time, giving direct evidence that the platform was exposed (Knebel, 1972). Throughout much of Wisconsin time, therefore, St. Paul appeared as a hill between 150 and 300 m, standing in the classic shape of a shield volcano out of an immense plainsland. The plain lay close to sea level, much of it being only 10 m above the contemporary ocean. Submarine canyons suggest that the Yukon River flowed close by St. Paul to the east in glacial times to enter the North Pacific Ocean (Scholl and Hopkins, 1969; Nelson et al., 1974). The island, therefore, is nicely sited to provide a record of the south land bridge coast near the great river system which might have provided a favorable place for human and animal populations.

20

PAUL

COLINVAUX

FIG. 2. Top: St. Paul Island from the summit of Rush Hill (220 m) at the west end of the island looking east. Bottom: Cagaloq Lake. The axis is the same as in Fig. 3. The fence is a reindeer corral.

The climate of St. Paul is cool and moist with a mean annual temperature of about 1°C and an annual range between - 15” and +12”C. Precipitation is less than 53 cm (21 in.) per year but humidity is always high, from 68 to 99% (U.S. Local Climatological Data, 1978). Very often the island is fogbound, even though winds may be strong. There is a little precipitation, with least in the fall months. Puddles collect in summer wherever there are depressions, particularly on the higher hills. No peat bogs of significant thickness were found on St. Paul Island, though on the other main island of the Pribilof group, St. George (Fig. l), bogs up to several meters thick are prominent. There are a number of freshwater lagoons along the coasts of St. Paul, one, Big Lake, being about 4 km long. But these are dammed behind sand bars or dunes and cannot be of great age. Three maars hold small lakes in closed basins, though two of them probably dry up in the fall in most years as seepage through porous plugs ex-

ceeds precipitation. Only the lake on Lake Hill, Cagaloq Lake,’ is permanent and yielded long sediment cores. All the St. Paul lakes, lagoons as well as maars, are essentially closed, and have systems of abandoned shorelines up to 1 m

Cagoioq

Lake

Bo,m

irertic.l

exoggermon

3 II

3. Cross section of the Cagaloq Lake basin based on two borings (A, B) and observations of the shoreline. Compare with the panorama of Fig. 2 which is viewed from the same direction. FIG.

’ The lake has no official name, being referred to as the lake on Lake Hill by visitors to the island. Dr. Richard S. Petersen noted that the older Aleuts named the lake on Lake Hill “Cagaloq,” possibly meaning “place of thanks.”

HISTORICAL

ECOLOGY

above the water level of July to August 1963, suggesting episodes of greater, or more prolonged, precipitation in the past. Lake waters in both lagoons and maars are low in dissolved nutrients and soft water, and have a pH of 6-6.5. The flora of both Pribilof islands together (St. Paul and St. George) numbers only about 190 species of vascular plants (Hulten, 1968; Macoun, 1898). Pribilof vegetation is herb-tundra, effectively without shrubs. Bet&a and Alnus, as well as Picea, are completely absent from the archipelago. One ericaceous shrub, Vaccinium vitis-idea has been recorded, but we did not collect it and it is certainly rare. Five species of Salk are common, but all are extremely procumbent forms, the tallest parts of which typically are the catkins as they arise from stems pressed flat to the ground. Very rarely is Salk even ankle-high, let alone forming thickets. Herbs physically dominate the Pribilof tundra, therefore, and all the larger plants are herbs. There is no permanently frozen ground, and there are none of the tussock fields that are common in the tundras of the Alaskan mainland. The plant communities on sand dunes along the coast and on the bare soil, or scree-covered slopes, near crater rims, are comparable to communities on similar sites elsewhere in Alaska, but the vegetation of most of the other parts of both Pribilof islands is different from all other Alaskan tundras and has not been formally described. Although very variable, there are large areas ,where much of the total cover is made of Umbelliferae (three genera but Angelica lucida the most prominent), Artemisia arctica or A. tilesii, grasses, lupines (Lupinus nootakensis), Pedicularis, Aconitum, and others. Mats of these plants are nearly knee-deep, dark green, and almost constantly wet from drizzle and fog-drip. In late autumn tall stems bearing the umbels of Angelica and Conioselinum are spread over the tundra. Earlier, the same expanse may be blue with lupines or pink with Pedicularis. Although both grasses (Gramineae) and sedges

IN

BERINGIA

21

(Cyperaceae) are always important components of the vegetation mat and there are large areas which may be likened to very rough grassland with mounds, grass and sedge presence is elsewhere subdued so that the plant cover looks to be an overgrown garden of broad-leaved flowering plants. Through this run the stems of Empetrum and Lycopodium, abundant threads in the vegetation quilt. The strangeness of this vegetation is particularly apparent in the association of species of Umbelliferae with Artemisia in a lush, lank and wet vegetation. This peculiar relationship of umbellifer genera with particular species of Artemisia is reflected in the modern pollen rain of the islands and is important to an understanding of the pollen history. Methods Two sediment cores were raised from Cagaloq Lake with a modified Livingstone piston sampler from a raft of rubber boats. The sampler was driven by a IO-lb sliding hammer which made it possible to penetrate a thick body of sand in the sediments. Core A penetrated to a stratum sufficiently hard to deform the mild-steel cutting shoe of the sampler suggesting that underlying rock was reached. Cores were returned to Yale University in their original dural sample tubes in l-m sections and later extruded. Sections of sandy sediment were cut open. Ten surface samples for modem pollen were taken by diving or wading in St. Paul lakes. A plant collection of 270 specimens was collected from both St. Paul and St. George Islands and later identified by E. Hulten. Pollen preparations from this field collection, and the reference collections maintained by E. S. Deevey provided pollen for all the vascular plant species known to occur in the Pribilofs. In addition a reference collection of spores of about 20 species of Pribilof mosses was prepared though they were not found as fossils. Allowing for the presence of pollen brought to St. Paul by long-distance transport, it was

22

PAUL COLINVAUX TABLE

1. PRIBILOF POLLEN TAXA

Pollen zone Surf. Salix (5) Umbelliferae (3) Cyperaceae (20) Gramineae (30) Elymus (1) Empetrum (1) Ericaceae (2) Artemisiu (3) Senecio sim (6) Petasifes (1) Arnicu (1) Tumxacum (5)

+ +

Caryophyllaceae (12) Coptis (1) Culthu (1) Aconitum (1) Rununcu/us (4) R. trichophyllus R. pullusii R. hyperboreus R. sulphureus Cumpunulu (2)

Cruciferae (11) Primula (1) Androsuce (1) Trienrulis (1) Pupuver (2) Corydulis (1) Gentiunu (3) Mimulus (1) Lupinus (1) Luthyrus (1) Mertensiu (1) Erifrichium (1) Cluytoniu (1) Montiu (1) Polygonum (1) Koenigiu (1) Oxyriu (1) Gerunium (1) Armeriu (1) Vuleriunu (1)

Seluginellu

A

+

+ + + + +

Piceu Betulu Alnus sibiricu

Chenopodiaceae

4

3

2

1

+ + + + + + + + + +

+ + + + + +

+ + + +

+ + + + + + + + + +

+ + +

+ + +

+

+

Pollen zone

+ + +

+ + + + + + + + +

+

+

+

+ + + + +

+ + + + + +

+ + +

+ + +

+

+ + +

+ + +

+

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +

+ +

f +

+ + +

+

+

+ + + +

+ + + +

+

Surf. Chrysosplenium (2) Suxifiugu (6) s. punctutu S. hierucifoliu S. hirculus S. bructeutu S. unuluschkensis S. oppositifoliu Pumussiu (I) Geum (1) Potentillu sim (6) Rubus chumuemorus Rubus (2) Violu (2) V. epipsilu V. lungsdorffii Cornus (1) Veronicu (2) Cuslilleju (1) Lugotis (1) Pediculuris (4) Polemonium (2) P. boreule P. ucuiiforum Gullium ( 1) Epilobium (1) Hippuris (2) Fritilluriu (1) Streptopus (1) Lloydiu (1) Luzulu (4) Potumogeton (1) Ruppiu (1) Zsoetes (1) Equisetum (1) Lycopodium (3) L. selugo L. unnotinum Botrichium (1) Polypodium (1)

t Other ferns (6) +

+ Sphagnum

(1)

4

3

2

+

+

+

+ f + + + + + + + +

+

+

+

+

+

+ + + +

+ + + + +

1

+ + +

+ +

+ + +

+ +

+

+ +

+

+

+

+ + + +

+ +

+ +

+ +

+

+ +

+ +

+ +

+

+ +

+ +

+ +

+ + + + + +

+ +

+ + + + +

+

4

+ + +

+ + +

+ + + + + +

Woody elements not in modern flora + + + + + + + + + + + + Other pollen found fossil + Polygonurn (persicuriu +

type) Spurgunium

+ +

Note. The list of taxa represents those recognizable from reference material comprising all known Pribilof species. Numbers in parentheses are numbers of known Pribilof species assigned to each taxon. Other columns represent pollen zones in which the taxa were found. Notice that between 10 and 20% of total pollen is of minorelement taxa (Fig. 5). These minor elements are listed by zone in this table.

HISTORICAL

ECOLOGY

23

IN BERINGIA Gmms psr cc (ihousonds) (-=<200 grains per

14 J

FIG. 4. Loss on ignition, water content, and approximate sediments.

possible to reduce the small Pribilof vascular flora into 80 recognizable pollen or spore taxa (Table 1). Pollen analysis was performed in 19631964, before the technique of measuring concentration with added exotic pollen became available. Pollen extracts were made from measured volumes of fresh wet sediment taken as microcores with small brass tubes. Treatment with 5% NaOH and acetolysis was sufficient for most samples in the gyttja, but a heavy-liquid separation (bromophorm -acetone adjusted to specific gravity 2.1) and HF digestion was necessary for the silts and sands. Some coarser sand samples were concentrated through a lOOmesh screen. Pollen and pteridophyte spores were counted to a sum of 150 and expressed as percentage total pollen and spores. Total counts of spruce (Picea) pollen in the extracts from known volumes of wet sediment were made to allow calculation of total spruce pollen influx. Subsequent work in our laboratory with added exotic pollen has convinced us that extractions using heavy liquids or several digestions invariably lose some pollen, no matter how careful the procedure, but that estimates of pollen con-

pollen concentration

in Cagaloq Lake

centrations measured in this way are reliable within a factor of about 2. Total pollen concentration was calculated from the number of traverses needed to reach the pollen sum (Fig. 4). History of the Cagaloq Basin over 25,000 yr

The Cagaloq sediments are up to 14.6 m thick. A body of greenish algal gyttja 5.5 m thick overlies a body of grey sand, clay, and silt (Table 2). The deepest sediments are sands which appear closely comparable to sands of the modern beaches of the lake. Between the bottom sands and algal gyttja lie 6 m of grey mud and sand which can be divided further into two units, the uppermiddle and lower-middle units (Table 2). The upper-middle unit is characterized by massive grey mud divided by two massive sand layers. Pollen was absent or scarce in the sand layers, both in this unit and lower in the core. No mechanical analyses have been done but the textural feel of the grey mud of the upper-middle unit suggests a clay-silt mixture. The lower-middle unit is a variously banded deposit of silt and fine

24

PAUL

TABLE

COLINVAUX

2. STRATIGRAPHY

OF CAGALOQ

LAKE,

CORE A

Depth Cm) Top

unit

Sediment

O-5.5

Greenish

Upper-middle

unit

5.5-5.8 5.8-6.7 6.7-7.0 7.0-7.2 7.2-7.9

Lower-middle

unit

7.9-8.0 8.0-11.32 11.32-11.34 11.34-11.6

Bottom

sands

algal gyttja

mud

Sand Banded mud with White tephra Banded mud with

sand sand

11.6-14.6

sand, with intervals of up to 0.5 m, where tine banding of alternating mud and sand is nicely preserved. This banding is consistent with recurrent episodes of ponding and inwash separated by episodes of desiccation. It is possible that blowing sand on Lake Hill might be associated with formation of fossil sand dunes elsewhere on the island. The blackish fine sand of the lowest stratum in both cores is comparable with the sand of the modem beach, suggesting that a continuous stratum of sand lines the crater from beach to beach as in Fig. 4. Radiocarbon dating leads to anomalous young dates in the deepest sediments (Table 3). We can exclude most forms of carbon contamination and we use tritium analysis to show that the anomaly can be TABLE

accounted for as reflecting modern carbon injected into the botton sediments in flowing ground water. Physical inversion of the sediments is excluded by comparing the stratigraphy of the two cores and because the basin is both closed and shallow (Fig. 3). 13C assay indicates similar carbon sources for all the samples (Table 3) and supports the inference made from water chemistry and rock structure of the basin that contamination of any sample with carbonates has not occurred. Contamination in handling can be excluded because the two anomalous samples were taken from different core sections following procedures designed to preclude contamination, and were dated by different laboratories at different times. For these

3. RADIOCARBON

Lab no.

Depth 0-N

Y-1388 Y-1389 Y-1990

1.4-1.6 3.2-3.4 4.6-4.9

2,620 3.520

5.4-5.6 7.4-7.8 10.5-10.8 13.0-13.2 13.65-13.95

9,570 10,600 17,800 7,630 5,760

Y-1390 I-303 I Y-1391 I-1848 I- 1846

Grey Sand Mud Sand Mud

type

Core A (yr B.P.)

AGES

Core B (yr B.P.)

WC

? 160 + 100 9,250 k 2 k ? k

160 470 700 270 180

k 150

-24.4

-23.4

Note. Upper part of table is of dates in the gyttja and the lower part is of dates in lower strata of mud and sand. The whole core (after taking pollen subsamples and cleaning) was used for dating. Lengths of core to be dated were estimated to yield 2 g of carbon on the basis of loss on ignition and water contents (Fig. 4).

HISTORICAL TABLE

4.

TRITIUM

ECOLOGY ASSAY

OF INTERSTITIAL

Depth

(m)

Lab no.

0

TC TC TC TC TC

2525 2524 2490 2526 2561

TC 2568

25

IN BERINGIA WATER

Core A (Tritium units)

Lake

Core B

920 c 25

4.15 -4.3 5.0-5.2 6.0-6.25 8.0-8.2 10.15-10.4 12.72-12.92 13.6614.0

188 e 10 331 t 13 235 + 13 222 ‘- 12 1130 -+ 40 1220 t 30 924 2 30

Note. Cores and water sample were collected in July 1963 and assayed for tritium from autumn 1967 to spring 1968. The laboratory control sample of water not enriched with tritium was counted as 31 t 11 TU.

reasons, Colinvaux (1967b) put forward the hypothesis that carbon was brought in by flowing groundwater moving in from the modem beaches, into the sand lenses low in the sediment column, and thence down to the island water table (Fig. 3). Following the suggestion of J. Gordon Ogden III, this hypothesis was tested by tritium assay. Tritium analyses were performed by Isotopes, Inc. (Teledyne Isotopes), the core samples being first freeze-dried and the tritium counted as gas. The data (Table 4) show that the bottom sands contained tritium in concentrations comparable to lake water collected at the same time, whereas samples of gyttja near the transition to silt and sand were low in tritium. Groundwater flow, therefore, is demonstrated and contamination of the bottom samples with modern carbon in flowing water becomes the parsimonious explanation of the dating anomaly. Recently tritium was used to demonstrate groundwater flow in a similar way elsewhere (Verhagen et al. 1974).

The enhanced tritium

counts of samples TU compared with 31 TU of a dead sample) could represent ionic exchange within the sediment column or intrusion of small amounts of modern water during the coring operation, something which cannot be completely ruled out because all core sections had their ends exposed to lake water as

4-8 m down the core (220-300

they were lifted. By 10 m, however, the sediments have tritium concentrations comparable to the modern lake (3 x that in mud of the upper 8 m) and all dates from 10 m down are likely to be too young. Included with the suspect dates is the oldest date determined for the core, 17,800 yr for 10.5-10.8 m (Table 3). This date is, therefore, a minimum age. The following history is suggested: (i) Banded sands before 11,000 yr B.P.

Cagaloq lake was ephemeral or rapidly fluctuating through at least the last 10,000 yr of Wisconsin time. Permanent ponding ended this phase at about 11,000 yr B.P. There are no data to suggest that permanent ponding followed physical changes in the lake basin and the parsimonious explanation for lake permanence, therefore, is climatic change. The south Bering platform had been drowned, making St. Paul an island, though a large one, well before this, probably as early as 13,000 yr B.P. (Knebel, 1972; Knebel and Creager, 1973). The climatic change that made Cagaloq a permanent lake, therefore, was independent of land bridge flooding and was not merely a result of a change to maritime conditions. (ii) Silt and clay from 11,000 to 9500 yr B.P. Sediment changes in this interval

probably reflect, in part, lake ontogeny following primary climatic change. However, the pollen data also suggest a distinct

7

3

I5 + 144

+

+

13 5 10 16 12

+

+ +

139

4

4

180

+

+ +

4 16 + 17 6 8 27

+

Crater & Big Lakes %

5. SURFACE

141

40 4

I:7

23

+ +

71

52

f + +

+ + +

+

Village Marsh %

+

of Hill

St. Paul other

SPECTRA

Summit Hutchinson %

POLLEN

+

+

+

5 I5 75 +

+

+ +

Umnak %

4 3

4

+ 4 I5 65 4 + +

3

+

Adak %

Aleutians (surface peat)

3 153

8

10 6 18 24 25

t t +

St. George Bog (surface peat) %

lakes, dammed behind dunes on sand bars and surrounded by wet dune vegetation including Elymus. Cagaloq, Little Crater, for Big Lake and Crater Lake had low-pollen sums which were added together. Hutchinson Hill sample was mud from a rock rocks between which grow dense populations of Cruciferae which color the coast yellow. Village Marsh sample is from within Adak data are from Heuser (1973, 1978). St. George sample is surface peat from a bog beside the Garden Cove Trail.

4

4 5

4 + 14 14 12 31 8

4 + 26 6 8 27 4

+

+ +

+ +

+ +

Webster Lake %

Little Crater Lake %

Note. Webster Lake and Big Lake are coastal and Crater Lakes are inland maar lakes. Counts puddle 1 m across. The sample is close to coastal a stand of Hippuris in 10 cm water. Umnak and

Polypodiaceae 1

Koenigia Hippuris Lycopodium

Ericaceae Compositae Caryophyllaceae Rannunculaceae Saxifragaceae Cruciferae

Empetrum

Umbelliferae Cyperaceae Gramineae

Picea Betula AIWS Sa1i.x Artemisia

Cagaloq Lake %

St. Paul lakes

TABLE

HISTORICAL

ECOLOGY

climatic change roughly synchronous with this phase in lake history and ending 9500 yr B.P. (iii) Algal gyttja of the last 9500 yr. A lake comparable to the modern lake persists. Water level may fluctuate by ? l-2 m but an essentially unchanged maritime climatic regimen is maintained. The Modern

Pribilof

Pollen Rain

Pollen taxa present in the 10 surface samples from St. Paul are given in Table 5. Only a few hundred pollen grains were searched to produce this list of 48 taxa, showing the high diversity in the St. Paul pollen rain. Table 5 compares percent pollen of major elements in St. Paul surface samples with comparable data from St. George Island and from two Aleutian islands. Surface spectra from our four St. Paul lakes are comparable with surface spectra we obtained from St. George and with a St. Paul spectrum published by Moriya (1976), but are otherwise unlike any other known arctic spectra. They are peculiar in having high Artemisia associated with high Umbelliferae pollen percentages. Also striking is the regular appearance of Alnus at about 5% or more, since the nearest source of Alms is several hundred kilometers away. The significant influx of pollen from distant sources suggests that local pollen production is low. Even in face of the low pollen production and unusual pollen assemblages, however, the data suggest that the lakes are sampling the pollen rain of the island and not just local sources on the lake shorelines because the five lakes yielding the data have wide differences in shoreline, range from ephemeral to permanent, and come from all parts of the island. This conclusion is supported when the lake samples are compared with two other surface samples from different kinds of sites (Table 5). The sample from Hutchinson Hill was from mud in a small (< 1 m) puddle on a boulder at a site where crucifers grew prominently among rocks, as on most of the rocky shores. The influence of local overrepresentation is obvious. The village marsh

IN

BERINGIA

27

sample was from a swampy area, under a few centimeters of water but with a nearly closed canopy of emergent grasses and Hippuris; again the local overrepresentation is obvious. In both these point samples the island pollen spectra revealed elsewhere in the lakes seems to be overwhelmed by local Gramineae and the other locally prevalent taxa, Cruciferae in the one, Hippuris in the other. The St. Paul surface spectra, therefore, suggest the following: (i) Pollen production on the island is low: (ii) Lake sediments do sample the island pollen rain; (iii) The unusual Pribilof plant communities do yield characteristic pollen spectra. The apparent uniqueness of the St. Paul spectra can be tested by comparing them with spectra from the most similar vegetation types, tundras on the Aleutians. Spectra are available from Umnak and Adak (Table 5) (Heusser, 1973, 1978). though only from the surface peat of bogs. They are quite different from the St. Paul spectra, lacking the high Artemisia percentages and with very large percentages of Gramineae. They do, however, have Umbelliferae. plants notable in Aleutian tundras as on the Pribilofs. Since the Aleutian spectra are from bogs rather than lakes they might fail to reflect the local pollen rain. We have no peat bog samples from St. Paul to compare with lakes but we include in Table 5 a peat sample from St. George which should be comparable to Heusser’s Aleutian peats. The St. George peats collect pollen spectra remarkably similar to those in St. Paul lakes but not like those in Aleutian peats. It is reasonable to conclude, therefore, that differences between St. Paul Lake spectra and Aleutian spectra reflect true differences in the vegetation and that the cores from Cagaloq Lake contain a useful pollen history of the vegetation of the island. Cagaloq Lake Pollen Zones and Chronology

Figure 5 expresses the results of pollen analysis as percentage total pollen and

PAUL

28

COLINVAUX

Each divbicn is Wo to!4 pdbr She&d intends he kW pdbn

b

sldd

Each diviripl i-ltmd

k D% tota! pdlsn rxd rpora. how3 law pdbl cmmticns.

Cog&q Ldm, Pribilofr Elevation M)m

od WTS. COtXeMUtiiS.

CcgaLYq Elevation

tohe, 6Om

Pribibfr

FIG. 5. The upper and lower halves of a pollen percentage diagram from Cagaloq Lake core A. Pollen samples are at IO-cm intervals in gyttja (O-5.8 m) and at irregular intervals in banded sands and clays. 2 is 150 poilen and spores shown. Taxon “other” is the sum of all taxa appearing at 2% or less. Grains plotted as “other” are mostly entomophyllous taxa, were identified individually, and are listed in Table 1. Influx measurements show that the Picea present in zones 1, 2, and 4 are due to longdistance transport. Zones 1, 2, and 4, therefore, record herb tundras only. Picea influx into zone 3 suggests trees near the site. The high Alms and Betulu percentages of zone 3, together with the Picea data, suggest that a forest ecotone was close to St. Paul Island in zone 3 time.

HISTORICAL

ECOLOGY

spores on Cagaloq core A. The minor elements are listed in Table 1 and expressed as a sum of minor elements (other) in Fig. 5. The diagram may be divided conveniently into four pollen zones. Zone 4. Umbelliferae -Artemisia. Pollen spectra are closely comparable to surface spectra. Zone 4 spans the last 9500- 10,000 yr, and is essentially coincident with the upper sediment body (the algal gyttja). Zone 3. Picea-Alnus-Be&la. Spruce, alder, and birch pollen reach maxima of 21, 27, and 11% respectively at 6.9 m. With these three taxa removed from the pollen sum, the resulting spectra are comparable to those of zone 4, particularly showing the unique Pribilof association of Umbelliferae with Artemisia. Zone 3 spans 11 ,OOO-9500 yr B.P. and is essentially coincident with the stratum of silty gyttja and clay. Zone 2. Artemisia without Umbelliferae. Picea is present in conspicuous amounts but without the accompanying Alnus and Betula of zone 3. This zone is the only zone

in the diagram to be without Umbelliferae pollen. The zone spans the upper part of the body of banded sand, silt, and clay but there is no obvious stratigraphic horizon coincident with the start of the zone. It spans from 11,000 yr B.P., backward past the minimum radiocarbon age of 17,800 yr B.P. into sand strata contaminated by carbon in groundwater. Zone I. Umbelliferae -Artemisia. Pollen spectra are comparable to zone 4 and surface spectra, except for the notable inclusion of Picea pollen. Radiocarbon dating is not possible because all sediments of the zone are contaminated by groundwater. A tentative age for the zone l/zone 2 boundary can be given, however, on the basis of the pollen stratigraphy itself. Estimates of Picea influx (see below) suggest that spruce pollen arrived by long-distance transport as in modern times. Only the herbs, therefore, grew at the site and the zone is closely comparable to zone 1 and modern pollen spectra. This suggests that St. Paul was again an island in zone 1 time and the zone l/zone 2 boundary represents the close of

IN

BERINGIA

29

the mid-Wisconsin Interstadial Data from Siberia (Klein, 1971) suggest that the interstadial ended about 30,000 yr B.P. while recent work in my laboratory suggests 25,000 yr B.P. for Seward Peninsula (Shackleton, 1979). A tentative age of 25,000 yr B.P. may, therefore, be assigned to the zone l/zone 2 boundary (Table 6). Picea Influx Picea influx measurements are given in Table 6. The pollen analysis was completed before the exotic pollen technique of Maher (1972) became available. Picea pollen concentrations (Davis, 1963; Colinvaux, 1978) were measured by counting every Picea grain in extracts of pollen from measured volumes of wet sediment. Good radiocarbon control (Table 3) lets us calculate Picea influx with tolerable confidence for the top 5 m of sediment. Picea influx is uniformly low over this interval (zone 4), fluctuating around 0.002 grains cm-* yr-’ (Colinvaux, 1967b). This rough figure gives an orderof-magnitude estimate of Picea pollen reaching the island from forests growing more than 200 km away across the sea. Published (Colinvaux, 1967b) influx estimates for zone 3 were calculated without the benefit of all the radiocarbon determinations now available. It was known already that the date of 17,800 yr B.P. at 10.6 m might be suspect, so the most conservative sedimentation rate consistent with the whole radiocarbon sequence was considered. This was that the rate prevailing immediately above zone 2 sediments, and bounded by dates at 3.3 and 5.5 m, applied. This sedimentation rate (1 cm dry matter/ 231 yr) would require zone 3 to have a starting age of about 35,000 yr B.P. and yet the calculated Picea influx over the interval was still three to four orders of magnitude greater than in zone 1, reaching nearly 16 grains cm-” yr-’ (Colinvaux, 1967b). Additional radiocarbon dating suggests that this calculation truly is too conservative and that the real Picea influx was even larger than this in zone 3. An age of 10,600 yr B.P. was obtained in

-

Artemisiu

Umbelliferae -

without Umbelliferae

Artemisiu

Piceo pAlnus Beth

Artemisiu

Umbelliferae-

Pollen characteristics

Pribilof island >25,000

11,00&25,000

9500-11,000

Forest tundra ecotone

Beringian herb tundra

present -9500

Age (yr B.P.)

OFTHE

0.01

0.4-0.8

10.0-200.0

0.002

Pica2 influx (grains crne2 yr-I)

INTERPRETATION

Pribilof island tundra

Vegetation

CLIMATIC

MidWisconsin interstadial

Classical Wisconsin

Late glacial

Holocene

Glacial chronology

POLLEN-RECORD

Large island

Part of land bridge

Large island

Small island

Geography

Note. This is a summary of the conclusions. The zone l/zone 2 boundary is dated by using pollen zones as time-stratigraphic aries are dated by radiocarbon.

1

2

3

4

St. Paul pollen zones

TABLE6.

Possibly similar to modern

Dry, cold, windy

In path of summer storm tracks

Modern

Climate

indicators. Other bound-

<20

25-29

15-39

<20

Albedo (W

HISTORICAL

ECOLOGY

IN

BERINGIA

31

sediment from 7.6 m, the sample being cho- lated assuming the 25,000-yr date for the sen as nearly as practicable to date the start zone l/zone 2 boundary is correct (Table 6). of zone 3 time (Table 3). Zone 3 is thus The results suggest that rather more Piceu is reaching Cagaloq Lake in zone 2 time bounded by dates at 5.5 m (9600 yr B.P.) and 7.6 m (10,600 yr B.P.) suggesting rela- (land bridge) than in zone 1 (interstadial) or tively rapid sedimentation in the interval of zone 4 (Holocene). This result needs to be l-2 m per millenium. Since the average treated with great caution because most of water content over the interval is 49% we the deposits of zones 1 and 2 are coarse get dry sediment deposited at 0.5- lmm/yr, sands with very low concentrations of polwhich is a plausible rate for silty sediment len (Fig. 4). In zone 1, for instance, all the in a young lake basin being permanently samples were pooled to find sufficient sealed for the first time. But this deposition Piceu pollen to count so that Piceu influx of rate is 3 times the fastest rate used in the zone 1 is, in effect, based on a single sam1967 calculations, and 20 times the most ple. Furthermore, the sedimentation rate conservative rate used. If the radiocarbon used for zone 1 is pure extrapolation. But dates are even approximately correct, then the calculated Piceu influx of zone 2 may a real increase in Picea influx of several reflect reality. Even though samples were orders of magnitude in zone 3 time is estab- pooled to yield satisfactory counts, the lished. seven resulting aggregate samples held This large influx of Picea in zone 3 is ac- pollen concentrations which yielded influx curately reflected in a high percentage of rates in the range 0.4-0.8 grains crne2 yr-‘. This figure is two orders of magnitude more Piceu, and this high percentage is synchrothan the 0.002 grains crnm2 yr-’ of Holocene nous with high percentages of Alnus and zone 4. No reasonable assumptions about Beth. It appears inescapable that there was a high influx of Alnus and Bet& also. sedimentation rate can lead to recalculaThis suggests very strongly that Piceu, tions which eliminate this difference. The Alnus, and Betulu grew close to St. Paul alternative is systematic error or systematic Island in zone 3 time: the pollen was not enrichment of conifer grains in the sandy matrix through some unknown mechanism. brought in by long-distance transport. We have examined the suggestion by D. In spite of the need for caution, therefore, Hopkins that the Siberian pine Pinus the Piceu influx of zone 3 should yet be pumilu might be included in the zone 3 considered with an open mind, particularly Piceu pollen. A few of the original pollen comparing possible sources and transport preparations were still usable and have been distances with those that lead to the much reexamined by P.A.C. and W. Mode for the lower Piceu influx of Holocene times. presence of Pinus pollen. A trace of Pinus All the Picea grains reaching Cagaloq can be found in all seven preparations we Lake in modern times must come from examined, as would be expected. In prepcontinental sites 200 km or more across the arations from zones 2 and 4, Pinus might sea. The Alaskan Piceu trees grow in closed make up half of the total conifer flux, as in a forests where they produce pollen heavily preparation from one interval in zone 4 every year, and yet, the influx to Cagaloq where 1 Piceu and 1 Pinus grain were found Lake is only 0.002 grains crne2 yr-‘. for a total count of 2 conifer grains. But a But in zone 2 time the source forests of search of four preparations from zone 3 the present Piceu pollen influx did not exist (Piceu-Alnus-Betulu zone) confirms that (Colinvaux, 1963, 1965). There are two alternative possibilities for the source of zone the conifer pollen is almost entirely Piceu. A few Pinus grains, not necessarily P. 2 Piceu pollen: transport over extremely long distances from sites south of continenpumifu, suggest an input from distant sources tal ice sheets or from relict populations on comparable to the trace of Pinus reaching St. Paul in modern (zone 4) times. the land bridge itself. Nichols et al. (1978) have established that Piceu influx for zones 1 and 2 can be calcu-

32

PAUL

COLINVAUX

large influxes of Picea pollen can be transported 1000 km or more across tundra from distant tree lines, though their data suggest that this long-distance transport is episodic at times of unusually strong winds. Following Nichols’ logic, the St. Paul Picea pollen of Wisconsin age may record persistent or recurrent strong atmospheric circulations in the spring, when Picea flowers, with winds blowing from Picea forests south of the ice sheets near the present state of Washington. The alternative explanation of relict Picea on the land bridge is also viable, although possible sites are very restricted. Published pollen studies (Colinvaux, 1967~) show that Picea was absent from all regions of comparable longitude in Beringia though the suspicion was long entertained that Picea populations persisted in the Yukon-Tanana basin. Colinvaux (1967b) postulated that the Picea -Alnus -Bet& invasion of zone 3 came from these Yukon-Tanana forests but subsequent unpublished pollen work in our laboratory (Ager, 1975) has demonstrated that Picea was absent from the Yukon as well. We have also shown by analysis of sediments from a land bridge lake now under the sea that Picea pollen concentrations and percentages were negligible near St. Matthew Island to the north of St. Paul (Colinvaux, unpublished). The only remaining site for a relict population of Picea is on the south land bridge coast, well removed from St. Paul Island, possibly in the old delta of the Yukon-Kuskokwim system to the East. This explanation has the advantage that it provides a source for the trees which invaded tundras near St. Paul in zone 3 time, but the St. Paul data are not, by themselves, good enough to let us distinguish between the hypotheses of transport over 1000 km or a relict coastal population within 100 km. Reconstructions of past sea levels (Hopkins, 1973; Knebel, 1972; Knebel and Creager, 1973) suggest that St. Paul was cut off by the rising sea perhaps as early as 13,000 yr B.P. and that the last causeway of the Bering land bridge was flooded about

12,000 yr B.P. These dates seem to bear no more relationship to the boundaries of pollen zones than they do to the stratigraphy of the sediments (Table 6). It is suggested that the zonal boundaries reflect times of rapid climatic change which are not directly tied to the progress of rising sea level. Summary of Vegetation and Climatic History Revealed by the Pollen Diagram During the mid-Wisconsin interstadial the vegetation around Cagaloq Lake was comparable to the modern St. Paul tundra. Umbelliferae and Artemisia were prominent as now, and there were no shrubs other than prostrate willows. Lake Hill, then a young volcanic cone, stood on an island comparable to modern St. Paul and the climate was cold and wet like that of the present day. In the land bridge episode of the later Wisconsin advance (25,000- 11,000 yr B.P.) a herb tundra without trees or shrubs of any kind occupied the site. The details of this vegetation, and its associated climate, are discussed more fully below. In late glacial time (11 ,OOO-9500 yr B.P.) a Picea -Alnus -Bet&a community advanced on the highland that is now St. Paul Island. The advance may have been gradual since the largest influx of Picea, and the highest percentages of Alnus and Bet&a, are at the top of zone 3. It is likely that this marginal forest community never reached the uplands that are the modern island because pollen spectra from modem Picea ecotones have still larger percentages of woody taxa (Short and Nichols, 1977; Ritchie, 1974), although the ecotone may have been drawing very near Cagaloq Lake at its final extinction. Unless the start of zone 3 at about 11,000 yr B.P. records the fortuitous arrival of propagules of Picea, Alnus, and Be&la synchronously, it must record a change of climate which let a vegetation with these elements develop. The extinction of these elements at 9500 yr B.P. at the top of zone 3 is most parsimoniously explained by a change from a climate suited to vegetation comparable to the forest

HISTORICAL

ECOLOGY

ecotones of modern Alaska to the modern maritime climate of the Bering Sea which denies both islands and continental coasts to the Picea community. The modern vegetation of St. Paul Island was established about 9500 yr B.P. and persisted with no change large enough to be revealed in the pollen record until the present day. A climatic regimen which fluctuated but little throughout the Holocene is implied. The Vegetation of the South Land Bridge Coast With the Picea of long-distance transport removed, the pollen spectra of land bridge zone 2, are closely comparable to the pollen spectra of the same radiocarbon age at Imuruk Lake on which the original description of the Beringian vegetation was based (Colinvaux, 1964a). Pollen spectra at Point Barrow for the same time interval are also closely comparable (Colinvaux, 1964b, 1965). These three sites, St. Paul Island, Imuruk Lake on Seward Peninsula, and Point Barrow, afford as yet the only published diagrams that span the whole of the last land bridge episode. Together their pollen spectra define the main characteristics of the Beringian vegetation, showing a remarkable homogeneity over the spread from north coast to south, a distance of some 1500 km. The characteristics that the St. Paul pollen spectra share with the other sites or which they show in extreme form, are as follows: (i) Picea in trace amounts consistent with the wind transport over continental distances; (ii) Alnus pollen is either absent from spectra or present in amounts consistent with wind transport over continental distances. Data from the Galapagos Islands show that Alnus pollen is regularly transported in significant amounts for distances of 1000-2000 km, and that after such longdistance transport Alnus pollen can make up 5% of the pollen rain of a well-vegetated island (Colinvaux and Schofield, 1976). In land bridge spectra at all three sites Alnus pollen, when it is present at all, fails to

IN

BERINGIA

33

reach 5%. At Cagaloq Lake, Alnus not only never rises above 3% but is actually present in highest percentages in Holocene zone 4. Since total pollen concentration is high in zone 4 (Fig. 4) it follows that Alnus influx must also be larger in zone 4 than in zone 2, showing that Afnus populations were even further from St. Paul in land bridge times than they are now. (iii) Betula pollen is present at Cagaloq Lake as a trace or as less than 3%. This is much less than is now found at Point Barrow, or at Imuruk Lake in Wisconsin time: 5- 10%. The data show, therefore, that not only tree birches but Betula nana populations also were probably completely absent from the south land bridge coast. (iv) The herb pollen taxa are predominantly Artemisia, Gramineae, and Cyperaceae. At Barrow Artemisia was 7% of the pollen rain, on Seward Peninsula from 10 to 30%, and at Cagaloq Lake 5 to 15%. These data allow conclusions to be made about the south land bridge vegetation with tolerable confidence. Alnus and tree Betula were absent from the vicinity of Cagaloq Lake. B. nana was at best a rare plant and may have been completely absent. The tussock communities with which B. nana is almost invariably associated in modern Alaska were also absent. The nearest Picru trees were far away, but possibly existing in very small remnant populations in the Yukon-Kuskokwim delta. Willows (S&ix) were present, but the general similarity of the spectra to surface spectra from lakes near Point Barrow (Livingstone, 1955) suggest that only recumbent dwarf species like S. pulchra or S. reticulata were present. The vegetation was tundra. The Artemisia suggests bare ground, perhaps loess fields or frost boils, a conclusion consistent with dry times that prevented a permanent lake in Lake Hill and which deposited sand. This is the same vegetation and land surface that was tentatively described as tundra-steppe (Colinvaux, 1967~) and which is more safely called herb-tqndra (Cwynar & Ritchie, 1980: Colinvaux 1964a, 1980). It probably had an albedo of between 25 and 29%, the albedo of the whole Bering land

34

PAUL COLINVAUX TABLE

7.

POLLEN PECULIARITIES LAND BRIDGE TIME

OF

Taxa found only in pollen zone 2 Seluginellu

sibirico

Chenopodiaceae Polygonurn Spurgunium Hippuris Trientalis Arnica

(persicariu

type)

Taxa absent from pollen zone 2 but present in other zones Etymus Rubus chamaemorus Rubus sp. Vi& Fritilloriu Lurhyrus Armeria

The dryness, barrenness, and shrubless qualities of the south land bridge vegetation is strongly supported by this record of S. sibirica. Little can be made of the Arnica record since too many species are possible. Trientalis (Primulaceae) pollen is unlikely to be dispersed far and the few grains found probably represent a population living on the crater floor. Both Arnica and Trientalis, as well as Chenopodiaceae, are consistent with the dry and barren tundra suggested by S. sibiricu . Polygonum persicaria (type), Sparganium, and Hippuris probably represent

semiaquatic communities in the ephemeral ponds of the crater floor. The only Polygonurn species with P. persicaria type pollen on both HultCn’s Alaskan list and Hedberg’s (1946) list of the pollen type, bridge (contra the report of CLIMAP, apart from introduced weeds and hot 1976). The vegetation was more tundra than springs species, is P. amphibium, a plant of steppe, and it spread to the south land semisubmerged habit now growing in Arcbridge coast. tic Siberia. Both Sparganium and Hippuris This description can be amplified by are taxa of shallow ponds known from using the detailed St. Paul record of minor high-arctic regions. The community is conelements. The lists of pollen taxa given in sistent with temporary ponds in the crater Table 1 were compiled by searching the en- during wetter years of the 10,000 yr for tire surface of the cover slips of every pol- which the dry land-bridge vegetation perlen preparation at a magnification of 100 di- sisted. ameters and examining all possibly unusual Perhaps more revealing are the taxa which disappeared from the record throughpollen grains at higher magnification. When the results of the sample surveys are out land bridge time (Table 7): the grass lumped by pollen zone as in Table 1 the of moist sands and dunes (Elymus); eleresult represents a thorough search of a ments of wetter, less polar tundras (Rubus, very large population of pollen grains that is Viola, Fritillaria); and the coastal taxa likely to have found all the taxa present in Lathyrus and Armeria. Missing too are other taxa which might have been expected the zone except for extremely rare types. persisted, These data reveal that the pollen rain of if a moist coastal vegetation zone 2 (land bridge) time differed from Shepherdia in particular which could not other zones in species composition and have been overlooked if present, Iris, and richness, as well as in percentages of the Dryas. These data suggest very strongly that there was no coastal strip of common taxa. “maritime” tundra on the land bridge. Table 7 lists the peculiarities of pollen zone 2. The most significant taxon found GENERAL CONCLUSIONS: only in zone 2 is Selaginella sibirica. This CHRONOLOGY OF CLIMATIC CHANGE plant is confined to tundras in dry and exAND LIVING CONDITIONS ON THE posed sites at the moment as, for instance, SOUTH LAND BRIDGE COAST the higher elevations of the Brooks Range (HultCn, 1968). S. sibirica spores are presThe data suggest that major climatic ent in nearly all samples from zone 2 but not changes affecting St. Paul Island were not the result of changing sea level and a single spore was found in other zones.

HISTORICAL

ECOLOGY

maritime influence. St. Paul was an island by 13,000 yr B.P. but experienced climatic change at 11,000 yr B.P. From 11,000 to 9500 yr B.P. the climate of a forest ecotone prevailed, suggesting the pattern of storm tracks which follows the tree line in inland Alaska today. This climate changed to the modern climate at 9500 yr B.P. We think of the present pattern of coastal climate and tundra along the Bering Sea as “maritime.” However, this climate was established long after the return of the sea to near its present limits and reflects fundamental climatic change rather than nearness of the oceans. The pollen evidence of the south land bridge coast is one of tundra, bare ground, and dryness. Vegetation types that include shrub elements like Berula, Alnus, and woody Ericaceae were absent. This almost certainly includes Populus also. Populus pollen is not preserved in lake sediments except in rare circumstances, so the absence of its pollen is meaningless, but some other shrub elements, Shepherdia or other associated herbs would be expected if Populus grew. All these likely associates of Populus are absent. The vegetation was one of dry continental, shrubless tundra, implying a dry continental climate. The coast was not comparable to modern Pribilof or Aleutian coasts; it did not have the wet, foggy climate of modem south Beringian coasts but something more comparable to Arctic Ocean coasts. Very possibly the fog zone, so necessary to marine mammals on their breeding grounds, was absent so that the south land bridge coast may have supported only low populations of marine mammals. It is likely that the south coast was fringed with pack ice for part of each year, like the modern arctic coast. Finally human cultures which evolved on the coast would have faced climates quite different to those known to modem Aleuts. An arctic and dry-continental airmass spread down to the sea bringing clear skies, but coupled with strong, cold catabatic winds from the glaciers to the East. The coastal waters themselves must have been influenced by this regimen, so that it is not safe to esti-

IN

35

BERINGIA

mate seafood for land bridge people and animals from what we know of present coastal waters. REFERENCES Ager, T. (1975). “Late Quaternary Environmental History of the Tanana Valley, Alaska.” Ph.D. thesis, The Ohio State University, Columbus. Barth, T. F. W. (1956). Geology and petrology of the Pribilof Islands. Alaska. U.S. Geologicul Surly~ Bulletin 1028-F. IOI- 160. CLIMAP (1976). The surface of the ice-age earth. Science 191, No. 4232. 1131-l 137. Colinvaux, P. A. ( 1963). A pollen record from Arctic Alaska reaching glacial and Bering land bridge times. Nature 198, 609-610. Colinvaux, P. A. (1964a). The environment of the Bering land bridge. Ecologicul Monogruphs. 34. 297-325. Colinvaux, P. A. (1964b). Origin of ice ages: Pollen evidence from Arctic Alaska. Science 145, 707-708. Colinvaux. P. A. (1965). Pollen from Alaska and the origin of ice ages. Science 147, 633. Colinvaux. P. A. (1967a). A long pollen record from St. Lawrence Island. Bering Sea Alaska. Palrogeography. Puleoclimuto1og.v. Puleoecology 3, 29-48. Colinvaux, P. A. (1967b). Bering land bridge: Pollen evidence for spruce in late-Wisconsin times. Sciarrcr 156, 380-383. Colinvaux, P. A. (1967~). Quaternary vegetational history of Arctic Alaska. In “The Bering Land Bridge” (D. M. Hopkins, Ed.), pp. 207-231. Stanford Univ. Press, Stanford. Calif. Colinvaux. P. A. (1973) Vegetation of the Bering land bridge and the refugium problem: Pollen evidence from sediments in the Bering and Chukchi Seas. Theses of Reports of All-Union Symposium of USSR Acudem! of Sciences. KhuhurovJL, pp. 80-84. Colinvaux, P. A. (1977) History of the Beringian and Arctic Alaskan ecosystems. Ahstruct.c of 10th INQUA Congress, Birminghum. Colinvaux. P. A. (1978). On the use of the word “abin pollen statistics. Quuternury Reseurch solute” 9, 132, 133. Colinvaux, P. A. (1980). Vegetation of the Bering land bridge revisited. Quurier1.v Review of Archueolo~? 1, 2-15. Colinvaux, P. A., and Schofield, E. K. (1976). Historical Ecology in the Galapagos Islands. I. ‘A Holocene pollen record from El Junco Lake, I& San Cristobal. Journul ofEcology 64, 989% 1012. Cox, A., Hopkins. D. M.. and Dalrymple. G. B. (1966). Geomagnetic polarity epochs, Pribilof ISlands. Geological Society of America Bulletin 77. 883 -909. Cwynar, L. C., and Ritchie, J. C. (1980) Arctic steppe-tundra: A Yukon perspective. Science 208. 1375-1377.

PAUL

36

COLINVAUX

Davis, M. B. (1963). On the theory of pollen analysis. Americun Journal of Science, 261, 897-912. Dawson, G. M. (1894). Geological notes on some of the coasts and islands of Bering Sea and vicinity. Bulletin

of the

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117-146. Hedberg, 0. (1946). Pollen morphology in the genus Polygonum L. S. Lut. and its taxonomical significance. Svensk Botanisk Tidskrift, 40, 371-403. Heusser, C. J. (1973). Postglacial vegetation on Umnak Island, Aleutian Islands, Alaska. Review of Polueobotnny und Pulynology 15, 277-285. Heusser, C. J. (1978) Post-glacial vegetation on Adak Island. Aleutian Islands, Alaska. Bulletin of the Torrey Botunicul Club 105, 18-23. Hopkins, D. M. (1973) Sea level history in Beringia during the past 250,000 years. Quuternury Research 3, 520-540. Hopkins, D. M., and Einarsson, T. (1966). Pleistocene glaciation on St. George, Pribilof Islands. Science 152, 343-345. Hulten. E. (1968). “Flora of Alaska and Neighboring Territories.” Stanford Univ. Press, Stanford, Calif. Klein, R. G. (1971). The Pleistocene prehistory of Siberia. Quuternury Reseurch 1, 133-161. Knebel, H. J. (1972). “Holocene Sedimentary Framework of the East-Central Bering Sea Continental Shelf.” Ph.D. thesis, University of Washington. Seattle. Knebel. H. J., and Creager, J. S. (1973). Yukon River: Evidence for extensive migration during the Holocene transgression. Science 179, 1230-1231. Livingstone, D. A. (1955). Some pollen profiles from arctic Alaska. Ecology 36, 587-600. Macoun. J. M. (1898). A list of the plants of the Pribilof Islands, Bering Sea. With notes on their distribution. In “Fur Seals and Fur-Seal Islands” (D. S. Jordan, Ed.), Vol. 3. Washington, D.C. Maher. L. J., Jr. (1972). Absolute pollen diagram of Redrock Lake, Boulder County Colorado. Quuternury

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Matthews, J. V.. Jr. (1974). Quaternary environments

at Cape Deceit (Seward Peninsula. Alaska): Evolution of a tundra ecosystem. Geologicul Society of Americu Bulletin 85, 1353 - 1384. Matthews, J. V., Jr. (1976). Arctic steppe: An extinct biome. IVth Conference AMQUA. Tempe. Moriya, K. (1976). “Flora and Palynomorphs of Alaska.” Kodansha Co.. Tokyo. [in Japanese] Nelson, C. H., Hopkins, D. M.. and School, D. W. (1974). Cenozoic sedimentary and tectonic history of the Bering Sea. In “Oceanography of the Bering Sea” (D. W. Hood and E. J. Kelley, Eds.), pp. 485-516. Institute of Marine Science, University of Alaska, Fairbanks. Nichols, H., Kelly, P. M., and Andrews, J. T. (1978). Holocene palaeo-wind evidence from palynology in Bafhn Island. Nuture 273, 140-142. Rampton. V. (1971). Late quaternary vegetational and climatic history of the Snag-Klutlan area, Southwestern Yukon Territory. Canada. Geological Society of America

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Ritchie. J. C. (1974). Modern pollen assemblages near the arctic treeline, Mackenzie Delta Region, Northwest Territories. Cunudiun Journal of Botuny 52, 381-396. Scholl, D. W., and Hopkins, D. M. (1969). Newly discovered Cenozoic Basins, Bering Sea Shelf, Alaska. The Americun Associution Bulletin 53, 2067-2068.

of Petroleum

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Shackleton. J. (1979). “Paleoenvironmental Histories from Whitefish and Imuruk Lakes, Seward Peninsula, Alaska.” M.S. thesis, The Ohio State University, Columbus. Short, S. K., and Nichols, H. (1977). Holocene pollen diagrams from subarctic Labrador-Ungava: Vegetational history and climate change. Arctic und Alpine Reseurch

9, 265-290.

Stanley-Brown, J. (1892). Geology of the Pribilof Islands. Geologicul Society of Americu Bulletin. 3, 496-500. Verhagen. B. Th., Mazor. E., and Sellschop, J. P. F., (1974). Radiocarbon and tritium evidence for direct rain recharge to ground waters in the northern Kalahari. Nuture 249, 643, 644.