Robert E. Nelson

Anomalous radiocarbon ages from a Holocene detrital organic lens in Alaska and their implications for radiocarbon dating and paleoenvironmental reconstructions in the arctic

Abstract Eleven radiocarbon age determinations clearly show that a lens of Holocene fluvial organic debris on the Alaskan Arctic Coastal Plain contains mostly pre-Holocene organic material. Radio-carbon ages of identified plant macrofossils indicate the material was deposited about 9000 to 9500 yr B.P. Radiocarbon analyses of bulk samples from this deposit, however, range from 13,300 to 30,300 yr B.P. Most of the old organic matter seems to be in the smaller size fractions in the deposit, particularly in the fraction between 0.25 and 0.5 mm, but all size fractions are contaminated. Particular caution must be exercised in submitting bulk samples for radiocarbon dating from areas where conditions favor redeposition of isotopically “dead” carbon.

PALEOENVIRONMENTAL ANALYSIS OF INSECTS AND EXTRALIMITAL POPULUS FROM AN EARLY HOLOCENE SITE ON THE ARCTIC SLOPE OF ALASKA, U.S.A.

Analysis of pollen and plant and insect macrofossils from 9400-yr-old fluvial terrace deposits along the Ikpikpuk River on the Arctic Slope of Alaska permit reconstruction of the diversity of habitats present at that time, as well as an assessment of surface moisture conditions and summer temperatures relative to those of today. Consideration of the modern ecological requirements for the total fossil flora and fauna shows that the variety of habitats was similar to the total variety seen today. However, the beetle fauna is dominated by species indicative of dry, open grasslands, suggesting that dry, well-drained habitats were more widespread than now. Warmer summer temperatures are indicated by extralimital taxa including Populus balsamifera and seven beetle species that reach their present northern limits in the boreal forest zone of north-central Alaska and adjacent Canada. Consideration of the modern climatic tolerances of the beetle taxa suggests that early Holocene mean July temperatures at the fossil

Pollen analysis of a late pliocene and early pleistocene section from the Gubik Formation of Arctic Alaska

Abstract A 14-m-thick section of marine and nonmarine sediments of the Gubik Formation of northern Alaska, exposed in bluffs near Ocean Point on the Colville River, has been studied by means of pollen analysis. Pollen from the marine sediments, of probable late Pliocene age, records a boreal forest of spruce and birch with minor amounts of alder in the adjacent terrestrial vegetation. Pine and perhaps true fir were probably at or near their northern limit here, but hemlocks and hardwoods were absent. The suggested environment for the Arctic Slope during the time represented by the marine sediments is similar to that of present-day Anchorage. Pollen floras from the overlying fluvial strata, of early or middle Pleistocene age, record predominantly herbaceous taxa indicating tundra conditions probably more severe than those of the present day. These deposits were most likely contemporaneous with glacial conditions in the Brooks Range to the south. Pollen of woody taxa (spruce, alder, birch, heaths) is rare through most of the section, although birch and alder percentages similar to those found in modern river sediments indicate an interstadial or interglacial warming in midsection. Inland climates during glacial episodes may have been similar to those of the present Arctic coast.

Co-selection of mercury and antibiotic resistance in sphagnum core samples dating back 2000 years.

Metal exposure might induce multiple drug resistance (MDR) in bacteria in environments devoid of antibiotics via the process of co-selection, but the extent is poorly known. Core samples from two sphagnum peat bogs in central Maine, USA, were analyzed for total Hg content and were radiocarbon dated. Culturable bacteria isolated from various core depths were assayed for antibiotic- and Hg-resistance and the presence of merA (mercuric reductase). Our results show that sphagnum peat bogs represent natural ecosystems that contain ambient levels of Hg that select for indigenous bacterial strains that are not only Hg resistant, but also possess the MDR phenotype.

An Estuarine Assemblage from the Middle Devonian Trout Valley Formation of Northern Maine

Abstract The Middle Devonian (Emsian/Eifelian) Trout Valley Formation is exposed in the northeastern corner of Baxter State Park, Maine, and is noted for its abundant plant-fossil assemblages. However, to date no invertebrate macrofaunal assemblages have been reported in this fluvial-to-marine sequence; only isolated eurypterid parts have been reported. A previously undescribed outcrop of coarse- to medium-grained siltstone characterized by megaripples preserves a restricted, transported invertebrate assemblage. The macrofossils are randomly oriented and concentrated in the ripple crests. Similar sedimentological features in other parts of the stratigraphic section indicate an estuarine, tidally influenced depositional regime. The fossil assemblage is dominated by Phthonia sectifrons—an uncommon Devonian bivalve known previously from open-marine deposits. Few other fossil taxa occur. Typically associated with deep-shelf brachiopods, the presence of P. sectifrons in these estuarine deposits indicates that this taxon occupied a wider range of habitats, extending from the shallow silty shelf facies to more transitional settings. The facies associations in the Trout Valley Formation suggest that Devonian near-shore communities resembled modern bivalve-dominated near-shore communities.

Palynology of three bog cores shows complex European impact on the forests of Central Maine.

Abstract Short peat cores from three sphagnum bogs in central Maine were analyzed palynologically to determine whether recent reforestation approximates forest composition immediately prior to European colonization and deforestation. Radiocarbon dating and palynology show that the cores extend to 600–2000 years b.p., beginning well before 18th-century colonial forest disturbance. Cores from Round Pond bog (Franklin County) and Kanokolus Bog (Waldo County) show that Tsuga canadensis (Eastern Hemlock) was much more abundant on the local landscape at the time of European settlement than it is today; a core from Hamilton Pond bog (Kennebec County) records an abrupt local Eastern Hemlock decline, and accompanying Acer spp. (maple) rise, that preceded European contact by several centuries. All three bogs show increased heath (Ericales) abundance with deforestation, presumably a result of augmented nutrient flux into the bog basins due to increased erosion on surrounding slopes. Modern forest composition around all three sites is quite different from the forests immediately preceding European colonization and clearing. Pollen types indicative of agricultural activities (Ambrosia, other Asteraceae, Poaceae, Brassicaceae) that mark European deforestation and the onset of farming, have faded or disappeared as many farms have been allowed to revert to forest in the past half-century. Pine (mostly Pinus strobus [White Pine]) is more abundant in the modern pollen record than in subhistoric time, as are Abies spp. (fir) and Picea spp. (spruce); dominant hardwood taxa have responded differently to reforestation of the areas surrounding the study sites, in part determined by local edaphic conditions.