Nathaniel W. Rutter

Late Holocene ,-..; 1500 yr climatic periodicities and their implications

Fourier and nonlinear regression analysis of a 4000+ yr paleoclimate proxy record in western Canada shows strong periodicities of ∼1500 yr and several weaker century- to millenial-scale periodicities. In conjunction with the 23 708 yr Milankovitch periodicity, these produce a model of climate fluctuation through the postglacial consistent with recognized paleoclimatic fluctuations of the past 15 000 yr in the northern mid-latitudes. These results suggest that postglacial climatic anomalies such as the Little Ice Age and the Younger Dryas were at least in part periodic phenomena rather than the result of unique, aperiodic events. Projecting these periodicities into the future suggests that even in the absence of anthropogenic climate forcing, a natural warming trend will continue until ca. a.d. 2400.

Age of the Crowfoot advance in the Canadian Rocky Mountains: A glacial event coeval with the Younger Dryas oscillation

A suite of sediment core samples was recovered from two lakes, Crowfoot and Bow lakes, that are adjacent to the Crowfoot moraine type locality, to identify and radiocarbon date sediments related to the Crowfoot advance. The Crowfoot moraine system, widely recognized throughout northwestern North America, represents a glacial advance that is post-Wisconsin and pre-Mazama tephra in age. An interval of inorganic sediments bracketed by accelerator mass spectrometry radiocarbon ages of ca. 11,330 and 10,100 [sup 14]C yr B.P. is associated with the Crowfoot moraine. The Crowfoot advance is therefore approximately synchronous with the European Younger Dryas cold event (ca. 11,000-10,000 [sup 14]C yr B.P.). Furthermore, the termination of the Crowfoot advance also appears to have been abrupt. These findings illustrate that the climatic change responsible for the European Younger Dryas event extended beyond the northern Atlantic basin and western Europe. Equilibrium-line altitude (ELA) depressions associated with the Crowfoot advance are similar to those determined for the Little Ice Age advance, whereas Younger Dryas ELA depressions in Europe significantly exceed Little Ice Age ELA depressions. 26 refs., 3 figs., 1 tab.

Late Quaternary Pollen Record from Big Meadow, Pend Oreille County, Washington

The pollen record at Big Meadow in northeastern Washington contains at least 5 pollen zones spanning ca. the last 12,500 yr. Initial vegetation after Pinedale deglaciation was nonarboreal. Estimates of the pollen influx and the dominance of Artemisia and Gramineae plus comparatively little pine pollen suggest a tundra—like landscape from the time of deglaciation until ca. 9,700 BP. Zone II probably lies disconformably atop this earliest zone and reveals a community dominated first by grasses plus diploxylon pines and later by diploxylon pines without prominent grasses (Zone III) between 9,700 and 3,300 BP. zone IV demarcates a short reversal of climatic conditions in which Picea and Abies are relatively prominent. Tsuga heterophylla, the present day climatic climax dominant of the area, rapidly emerged in the pollen record at ca. 2,400 BP. See full-text article at JSTOR

Reexamination of postglacial vegetation history in northern Idaho: Hager Pond, Bonner Co.

Abstract Hager Pond, a mire in northern Idaho, reveals at least five pollen zones since sediments formed after the last recession of continental ice (>9500 yr BP). Zone I (>9500-8300 yr BP) consists mainly of diploxylon pine, plus low percentages of Abies, Artemisia , and Picea . SEM examination of conifer pollen at selected levels in the zone reveals that Pinus albicaulis, P. monticola , and P. contorta are present in unknown proportions. The zone resembles modern pollen spectra from the Abies lasiocarpa-P. albicaulis association found locally today only at high elevation. Presence of whitebark pine indicates a cooler, moister climate than at present, but one which was rapidly replaced in Zone II (8300-7600 yr BP) by warmer, drier conditions as inferred by prominence of grass with diploxylon pine. Zone III (7600-3000 yr BP) was probably dominated by Pseudotsuga menziesii , plus diploxylon pine and prominent Artemisia and denotes a change in vegetation but continuation of the warmer drier conditions. Beginning at approximately 3000 yr BP Picea engelmannii, Abies lasiocarpa , and/or A. grandis and diploxylon pine were dominants and the inferred climate became cooler and moister concomitant with Neoglaciation. The modern climatic climax (Zone V), with Tsuga heterophylla as dominant, has emerged in approximately the last 1500 yr.

Clay minerals and their paleoenvironmental interpretation in the Baoji loess section, Southern Loess Plateau, China

Abstract Clay minerals from the loess-paleosol section at Baoji in north-central China were studied by X-ray Diffraction. Major components, calculated by comparing major peak heights, were estimated as follows: illite (55–75%), kaolinite (10–25%), mixed layer chlorite-vermiculite (10–20%), chlorite (

Holocene vegetational history of the Kootenai River Valley, Montana

Abstract Pollen records in the Kootenai and Fisher River drainages in western Montana reveal a fivezone sequence of Holocene vegetation change. Deposition of Glacier Peak Ash-Layer G (ca. 10,540 ± 660 yr B.P.) in the lowermost sediments (clay intermixed with pebbles) at Tepee Lake gives a minimum date for the initiation of sedimentation. Initial vegetation on the newly deglaciated terrain was dominated by Pinus (probably white bark pine) with small amounts of Gramineae, Picea and Abies, reflecting a relatively cool, moist macroclimate. Two vegetation units appear to contribute to Pollen Zone II (ca. 11,000–7100 yr B.P.): arboreal communities with pines, along with Pseudotsuga or Larix, or both, and treeless vegetation dominated by Artemisia. Pollen Zone II represents an overall warmer macroclimate than occurred upon ice withdrawal. After ca. 7100 yr B.P. (Pollen Zone III) diploxylon pines became a major pollen contributor near both Tepee Lake and McKillop Creek Pond, indicating an expansion of xerophytic forest (P. contorta and P. ponderosa) along with an increase in the prominence of Pseudotsuga menziesii or Larix occidentalis, or both. Artemisia briefly expanded coverage near Tepee Lake concomitant with the Mazama ashfall ca. 6700 yr B.P. A short-term climatic trend with more available water began after ca. 4000 yr B.P. as Abies (probably A. grandis) along with Picea engelmannii became a more regular component of the forest surrounding both sites. Emergence of the modern macroclimate is indicated primarily with the first regular appearance of Tsuga heterophylla in the pollen record by ca. 2700 yr B.P., synchronous with the development of western hemlock forest within the same latitudes in northern Idaho and northeastern Washington.

Preliminary magnetostratigraphy of the red clay underlying the loess sequence at Baoji, China

Magnetic remanence and bulk susceptibility measurements are reported from 93 samples spanning the uppermost 27m of the Red Clay underlying the loess sequence at Baoji, Shaanxi province, China. If a new, previously undetected, short (about 20ka) excursion or reversed interval near 3.3Ma be accepted, then a reasonable fit to the standard time scale emerges. A linear accumulation rate of 1.5cm/ka is implied and the correlation coefficient is 0.992. No significant hiatus occurs between the Red Clay and the overlying loess, so the 27m investigated reach back to about 4.3Ma. Fourier analysis of the bulk susceptibility data yields a strong peak near 400ka in agreement with astronomical calculations of the orbital parameters responsible for climatic forcing.

Late Quaternary Vegetation History at Waits Lake, Colville River Valley, Washington

A 10.6-m section of mostly calcareous sediments at Waits Lake, Washington, reveals a multizoned history of vegetation change since recession of Pinedale (P-2) glacial ice from the Colville River Valley. The oldest unit with high percentages of Artemisia, Gramineae, and Shepherdia canadensis-type pollen characterizes vegetation in which trees were not major components and the climate was cooler and moister than today. Pollen Zone II (ca. 10,000-6,700 yr before present [BP]) records a warmer period in which diploxylon pine was prominent. Concomitant with the Mazama ash fall (6,700 yr BP), Artemisia became particularly prominent (Pollen Zone II); but by about 5,000 yr BP, diploxylon pine was conspicuous. This comparatively short-term vegetation change probably indicates the advance of drought-tolerant Artemisia-dominated steppe northward in the Colville River Valley. The modern climax vegetation in the vicinity of Waits Lake (Pseudotsuga-dominated forest) appears to have emerged around 2,300 yr BP, although more detailed documentation of this event is hampered by the low pollen production of Pseudotsuga menziesii. The 14C dates from these calcareous sediments were corrected through use of the Mazama and Glacier Peak ash layers as time-stratigraphic marker horizons.

Magnetoclimatology: Teleconnection between the Siberian loess record and North Atlantic Heinrich events

New environmental magnetic data from loess and paleosol successions in outcrops in the upper reaches of the Ob River drainage, southern Siberia, track the major climatic variations over the last glacial-interglacial cycle. Profiles of magnetic susceptibility and alternating deposition of loess and soil-formation events correspond to oxygen isotope stages 1–5. The magnetic-susceptibility data, in association with the stratigraphic succession, confirm that the wind-vigor magnetoclimatological model is a viable alternative to the classic pedogenic model. Interpretation of magnetic-susceptibility data from loess- paleosol successions must therefore consider eolian dynamics, available source materials, and transport directions, in addition to pedogenic processes. Rapid magnetic fluctuations are also observed. These are identified—for the first time in Siberian records—as the signature of the abrupt cold pulses responsible for the Heinrich layers in North Atlantic marine sediments. The data thus form a component of climatic teleconnections across the Northern Hemisphere, allowing correlations to be made among (1) Siberian magnetic susceptibility stratigraphy, (2) data recorded from other loess-paleosol successions in China, European Russia, Europe, and North America, (3) North Atlantic ice-rafted detritus, and (4) sea-surface temperatures derived from molecular stratigraphy of marine sediments off the northwest coast of Africa.

Holocene vegetation history of the Okanogan Valley, Washington

Abstract Haploxylon pine(s) and Artemisia dominated the initial vegetation in front of the receding Okanogan Lobe until ca. 10,000 yr B.P., as revealed by two pollen records in north-central Washington. After 10,000 yr B.P. the macroclimate became warmer throughout the Okanogan drainage as diploxylon pines and Artemisia increased. The Mount Mazama eruption at ca. 6700 yr B.P. is recorded as two stratigraphically separate and petrographically distinct tephra units at Bonaparte Meadows. While there are apparent short-term changes in the vegetation coincident with the ashfall(s), Artemisia continues to dominate the Okanogan Valley until ca. 5000 yr B.P. By 4700 yr B.P. the modern vegetation, dominated by Pseudotsuga menziesii , had become established around Bonaparte Meadows.