Cj. Heusser et al., Humptulips revisited: a revised interpretation of Quaternary vegetation and climate of western Washington, USA, PALAEOGEO P, 150(3-4), 1999, pp. 191
New pollen data from a 770-cm core of a mire at Humptulips on the southwest
ern Olympic Peninsula (47 degrees 17'00"N, 123 degrees 54'40"W) and from a
nearby deposit regarded as interglacial in age on the West Fork of the Hump
tulips River provide evidence for a reinterpretation of previous accounts o
f the Quaternary vegetation and climate. Using a new age model, the highly
variable record at Humptulips is here correlated with marine oxygen-isotope
stages (OIS) 1-5a. Vegetation during OIS 5a was pine-dominated, mixed wood
land and tundra. In OIS 4, 3, and 2, oscillations in pollen assemblages imp
ly repeated intervals of mountain hemlock parkland and tundra. Pine, as an
indicator of openness, is also abundant in these stages. Interstadial fluct
uations in OIS 3 reflect episodes of lowland western hemlock communities. T
he earliest of the episodes is of infinite radiocarbon age and the latest d
ates to approximately 30,000 C-14 yr B.P Parkland in OIS 2, occurring after
24,600 until at least 18,440 C-14 yr B.P., was replaced by transitional pi
ne-alder in OIS 1 (Holocene), which, unlike any of the earlier stages, conv
eys the development of modem lowland forest dominated by western hemlock. P
ollen assemblages over the length of record imply that temperature and humi
dity at no time were as high as at present; only in OIS 3 do conditions app
roach those occurring in OIS 1. During OIS 2, 3, and 4, when tree line appa
rently stood at the location of the site, climate was colder and drier. Tem
peratures were depressed an estimated greater than or equal to 5 degrees C
with precipitation close to 1000 mm compared with 2000-3000 mm at present.
Atmospheric circulation during OIS 2 appears to have been much controlled b
y the location of the Laurentide ice sheet in the continental interior, whe
reas under the current climatic regime beginning in the early Holocene, wes
terly air flow has dominated, regulated by interplay between the North Paci
fic high in summer and the wintertime Aleutian low. (C) 1999 Elsevier Scien
ce B.V. All rights reserved.