Don J. Easterbrook

Paleodeviations of radiocarbon marine reservoir values for the northeast Pacific

Differences in the radiocarbon ages of coeval marine shells and wood from emergent glaciomarine sediments in the Fraser Lowland of southwestern British Columbia and northwest Washington indicate that a total marine radiocarbon reservoir value of ∼-1.1 1 k.y. is applicable in the region. This is 40% greater (300 yr) than the -800 yr value currently used to correct the ages of both modern and late Pleistocene marine shells from this area. The glaciomarine sediments were deposited rapidly between ca. 12.5 and 11.5 1 4 C k.y. B.P. Paleodeviations of the marine reservoir value may illustrate that rapid environmental changes occurred during the last glacial to interglacial transition. These variations are thought to have been caused by changes in both deep and surface ocean circulation and by variations in the production of atmospheric radiocarbon (Δ 1 4 C). These findings may indicate a rapid reordering of oceanic-atmospheric circulation in the region.

Pleistocene Chronology of the Puget Lowland and San Juan Islands, Washington

The Puget Lowland and San Juan Islands, lying in the Puget Trough between the Cascade Range and the Olympic Mountains, were in the path of Pleistocene ice sheets which flowed southward from Canada. Floodplain, silt, sand, and peat of the Whidbey Formation were deposited prior to 40,000 years ago, during an interglaciation believed to be equivalent to the Puyallup and Sangamon Interglaciations. Possession Drift, which overlies sediments of the Whidbey Formation, is radiocarbon dated at 34,000 years B.P. in its upper part and is limited by a radiocarbon age of >39,900 in its lower part. The Possession is correlated with late phases of the Zyriansk Glaciation in Russia and the early Wurm in Europe. Peat lying on Possession Drift yielded radio-carbon dates between 27,200 and 22,700 ± 550, representing the Olympia Interglaciation which is correlated with the Karginsk Interglaciation of Russia, the Paudorf Interval of Europe and the Farmdalian of the midwestern United States. Esperance Sand, deposited by meltwater streams in front of advancing ice during the Fraser Glaciation and subsequently overridden during the Vashon Stade, was radiocarbon dated at 18,000 ± 400 years. During deglaciation, the ice sheet thinned until it floated in marine water and poorly sorted, fossiliferous glaciomarine drift was deposited in the Everson Interstade. Shell-bearing sediment at altitudes up to 400 feet above present sea level and unfossiliferous glaciomarine drift up to 600 feet indicate that relative sea level at that time was 500 to 700 feet higher. Eighteen radio-carbon dates from marine shells in Everson glaciomarine drift vary from 10,370 ± 300 to 13,010 ± 170 years. The Everson Interstade ended with lowering of relative sea level to approximately its present position and the disappearance of floating ice. The following Sumas Stade ended shortly before 9,920 ± 760 years ago.

Stratigraphy and chronology of quaternary deposits of the Puget Lowland and Olympic Mountains of Washington and the Cascade Mountains of Washington and Oregon

in the southern Puget Lowland probably are correlative with Salmon Springs Drift, but farther north, drift directly beneath Vashon till is most likely correlative with much younger drifts, such as the Double Bluff or Possession Drifts. Thus, virtually all previouslymapped Salmon Springs Drift needs to be re-examined to determine if it is indeed correlative with Salmon Springs Drift or is younger.

Stratigraphy and Palynology of Late Quaternary Sediments in the Puget Lowland, Washington

Paleoclimatic fluctuations from 50,000 yr BP to the present are recorded in pollen assemblages from buried Pleistocene peat and in postglacial bogs in the Puget Lowland of Washington. Two peat beds in Possession Drift, radiocarbon-dated at 47,600 + 3.300/− 1,800 and 34,900 + 3,000/− 2,000 yr B.P., contain high percentages of pine with minor spruce, fir, and western red cedar. Significant representation of total NAP suggests an open landscape dominated by herbs, with intermittent patches of lodgepole pine, characteristic of a cool climate and unstable physiographic conditions. The nonglacial interval immediately preceding the last glacial advance was originally defined as the Olympia Interglaciation, but new radiocarbon and palynological evidence now suggest that it should be considered to be a nonglacial interval of less than interglacial rank. Olympia peat beds yielded radiocarbon dates of 22,700 ± 550, 22,700 ± 600, 24,800 ± 600, 26,850 ± 1,700, 27,200 ± 1,000, and 27,600 ± 1,000 yr B.P. Pine maintains a dominant role throughout the units, although spruce, mountain hemlock, and total NAP increase in the younger units, suggesting a trend toward a cooler climate. Pollen from sediments of the Everson Interstade of the Fraser Glaciation is dominated by lodgepole pine, suggesting that the environment was characterized by extreme edaphic disturbance and severe climatic conditions. Postglacial bogs show a lower pine–Douglas fir zone and an upper western red cedar–western hemlock zone, separated by an ash younger than 7,140 ± 600 yr B.P. The Hypsithermal is marked by high pollen values for Douglas fir about 7,000 yr ago, followed by increased western red cedar and western hemlock, implying a moister, cooler climate.

Late Pleistocene, post-Vashon, alpine glaciation of the Nooksack drainage, North Cascades, Washington

During the maximum late Wisconsin glaciation ca. 15 000 14C yr B.P., the Cordilleran Ice Sheet overwhelmed the Nooksack drainage of the northwestern Cascades, leaving only peaks higher than 2000 m above the ice surface. Ice-sheet flow over the Nooksack drainage and the adjacent Puget Lowland was essentially north-south. Rapid deglaciation between 14 500 and 12 500 14C yr B.P. resulted in dropping of the ice-sheet surface below ridge crests in the Nooksack drainage, and glacial activity thereafter became topographically controlled. Long valley glaciers in the upper Nooksack Valley were no longer connected to the Cordilleran Ice Sheet, and the source area changed from the main ice sheet to Mount Baker, Mount Shuksan, and the Twin Sisters Range. At that time, the margin of the remnants of the Cordilleran Ice Sheet was 30 km to the northwest, separated from the Nooksack Valley glaciers by several ridges 1200 m higher than the surface of the ice sheet. Moraines were built in all three forks of the Nooksack drainage, 25–45 km downvalley from their sources. The Middle Fork glacier stagnated 12 300 14C yr B.P. and deposited ice-contact drift that was later overridden when ice readvanced over ice-contact drift and deposited a prominent, 2-km-long, lateral moraine. Logs in a lateral moraine in the upper Middle Fork were dated at 10 680 ± 70 and 10 500 ± 70 14C yr B.P. The North Fork glacier, which originated at a large cirque on Mount Shuksan and was fed by glaciers from Mount Baker, extended to Kendall, where two moraines were deposited. Outwash from the younger moraine in the North Fork valley overlies glaciomarine drift, dated as 11 910 ± 80 14C yr B.P., and contains charcoal layers dated at 10 603 ± 69 and 10 788 ± 77 14C yr B.P. The South Fork glacier at its maximum was joined by ice from the Middle Fork and extended downvalley to Lake Whatcom and to Cranberry Lake. It retreated from its terminal position slightly before ca. 12 700 14C yr B.P.

Age of the Salmon Springs Glaciation in Washington

A tephra bed within the Salmon Springs Drift at its type locality near Sumner, Washington, has a zircon fission-track age of 0.84 ± 0.21 m.y., and the immediately overlying silts are reversely magnetized. The same distinctive tephra at Auburn, Washington, has a glass fission-track age of 0.66 ± 0.04 m.y. and a zircon age of 0.87 ± 0.27 m.y. The bracketing silts are likewise reversely magnetized. Therefore, the Salmon Springs Drift, as defined at its type section, is of middle Quaternary age and is much older than the currently accepted age of about 70,000 yr.

Lake Tapps tephra: An early Pleistocene stratigraphic marker in the Puget Lowland, Washington

Abstract The rhyolitic Lake Tapps tephra was deposited about 1.0 myr ago, shortly after culmination of the early phase of the Salmon Springs Glaciation in the Puget Lowland. It is contained within sediments that were deposited in ponds or lakes in front of the reteating glacier. An herb-dominated tundra existed in the southern Puget Lowland at that time. Lake Tapps tephra is most likely the product of an eruption that in part was phreatomagmatic. It forms an early Pleistocene stratigraphic marker across the southern sector of the Puget Lowland and provides a link between Puget lobe sediments of the Cordilleran Ice Sheet and sediments deposited by Olympic alpine glaciers.

Pre-Olympia Pleistocene Stratigraphy and Chronology in the Central Puget Lowland, Washington

Drifts of two pre-Olympia glaciations separated by nonglacial sediments are widespread in the central Puget Lowland of western Washington. The Double Bluff Drift (older) and Possession Drift represent advances of the Puget lobe of the Cordilleran ice sheet more than 40,000 years ago. The nonglacial Whidbey Formation between the drifts was formed in streams and lakes. During its deposition, climate was initially cool and moist, as inferred from pollen in peat beds, but subsequently it became much like that of the present in the lowland. The Possession Drift is tentatively correlated with glacial deposits of Salmon Springs age in the southern part of the lowland. The Whidbey Formation may correlate with nonglacial deposits between two Salmon Springs Drifts or with the Puyallup Formation.

VOID RATIOS AND BULK DENSITIES AS MEANS OF IDENTIFYING PLEISTOCENE TILLS

Distinguishing subglacial till from glaciomarine drift or similar till-like sediments is critical to understanding the late Pleistocene history of the Puget Lowland of Washington. Comparison of void ratios and bulk densities of glacial till and till-like sediments whose origin may be established by other criteria indicates that there are measureable differences related to degree of compaction. These differences may be used to determine whether or not a till-like sediment was deposited beneath glacial ice. Since both void ratio and bulk density depend on particle-size distribution as well as on degree of compaction, differences between till and other till-like sediments are significant only if the samples have similar particle-size distributions. Void ratios of till from the Puget Lowland are systematically lower than those of glaciomarine drift having similar lithologies, and bulk densities are higher. Although till-like sediments other than glaciomarine drift were not analyzed, the void ratio-bulk density methods should also apply to them.

Multidecadal Tendencies in ENSO and Global Temperatures Related to Multidecadal Oscillations

Perlwitz etal (2009) used computer model suites to contend that the 2008 North American cooling was naturally induced as a result of the continents sensitivity to widespread cooling of the tropical (La Nina) and northeastern Pacific sea surface temperatures. But they concluded from their models that warming is likely to resume in coming years and that climate is unlikely to embark upon a prolonged period of cooling. We here show how their models fail to recognize the multidecadal behavior of sea surface temperatures in the Pacific Basin, which determines the frequency of El Ninos and La Ninas and suggests that the cooling will likely continue for several decades. We show how this will be reinforced with multidecadal shift in the Atlantic.