Full-glacial Interval Research Articles

Skjoldryggen terminal moraine on the mid-Norwegian shelf

Terminal moraines are relatively large ridges of diamictic glacial debris produced at the outermost margins of past glaciers and ice sheets. Their identification on land is important in mapping the maximum extent of Quaternary ice sheets (e.g. Svendsen et al. 2004; Benn & Evans 2010). In marine environments where fast-flowing ice streams reach the shelf edge during full-glacial intervals, moraine ridges are not usually present and the seafloor is characterized by parallel-to-flow streamlined sediments (Ottesen & Dowdeswell 2009). Submarine terminal moraine ridges, by contrast, appear more typical of slower-flowing marine ice margins (Dahlgren et al. 2002; Dowdeswell & Elverhoi 2002; Dowdeswell et al. 2016). A very large ridge, about 150 km long and up to approximately 200 m high relative to the adjacent shelf, is located on the outermost part of the mid-Norwegian continental shelf edge between about 65° and 66° N (Fig. 1a). It is known as Skjoldryggen (‘skjold’ means ‘shield’ and ‘ryggen’ means ‘the ridge’ in Norwegian). Along most of its length, the ridge has a steeper offshore slope relative to …

Suborbital-scale surface and deep water records in the subtropical North Atlantic: implications on thermohaline overturn

We reconstruct millennial-scale variations in sea surface hydrography and deep water flow in the northwestern subtropical Atlantic (Ocean Drilling Program Leg 172 Sites 1056 and 1063) with a focus on Marine Isotope Stage (MIS) 9. Together with published records from this region, the new data also afford a longer-term perspective on millennial-scale changes in meridional overturning circulation spanning two full interglacial intervals (MIS 9 and 11) as well as two full glacial intervals (MIS 10 and 12). Planktic foraminiferal δ 18O values indicate relatively stable conditions during the peak warmth of MIS 9, but three large cold excursions disrupt the otherwise smooth transition toward glacial MIS 8. There is no unique response in the Site 1063 benthic foraminiferal δ 13C values that would suggest a concomitant decrease in the relative flux of NADW during these events. Similarly, there is no persistent correlation between millennial-scale variations in surface and deep water hydrography over the entire MIS 8–13 interval. While millennial-scale variations at the sea surface are most pronounced during glacial intervals (and the transitions toward glacial intervals), millennial-scale variations in the deep water hydrography tend to be largest during the warm periods. This observation supports that rapid changes in thermohaline circulation are sensitive to driving forces other than those directly related to ice sheet size. Time series analysis shows that spectral power in the benthic foraminiferal δ 13C record contains periodicities related to the second (∼10 kyr) and fourth harmonics (∼5 kyr) of precession in this record (∼20 kyr) pointing to the importance of tropical processes.

Limnological and Climatic Environments at Upper Klamath Lake, Oregon during the past 45 000 years

Upper Klamath Lake, in south-central Oregon, contains long sediment records with well-preserved diatoms and lithological variations that reflect climate-induced limnological changes. These sediment archives complement and extend high resolution terrestrial records along a north–south transect that includes areas influenced by the Aleutian Low and Subtropical High, which control both marine and continental climates in the western United States. The longest and oldest core collected in this study came from the southwest margin of the lake at Caledonia Marsh, and was dated by radiocarbon and tephrochronology to an age of about 45 ka. Paleolimnological interpretations of this core, based upon geochemical and diatom analyses, have been augmented by data from a short core collected from open water environments at nearby Howards Bay and from a 9-m core extending to 15 ka raised from the center of the northwestern part of Upper Klamath Lake. Pre- and full-glacial intervals of the Caledonia Marsh core are characterized and dominated by lithic detrital material. Planktic diatom taxa characteristic of cold-water habitats (Aulacoseira subarctica and A. islandica) alternate with warm-water planktic diatoms (A. ambigua) between 45 and 23 ka, documenting climate changes at millennial scales during oxygen isotope stage (OIS) 3. The full-glacial interval contains mostly cold-water planktic, benthic, and reworked Pliocene lacustrine diatoms (from the surrounding Yonna Formation) that document shallow water conditions in a cold, windy environment. After 15 ka, diatom productivity increased. Organic carbon and biogenic silica became significant sediment components and diatoms that live in the lake today, indicative of warm, eutrophic water, became prominent. Lake levels fell during the mid-Holocene and marsh environments extended over the core site. This interval is characterized by high levels of organic carbon from emergent aquatic vegetation (Scirpus) and by the Mazama ash (7.55 ka), generated by the eruption that created nearby Crater Lake. For a brief time the ash increased the salinity of Upper Klamath Lake. High concentrations of molybdenum, arsenic, and vanadium indicate that Caledonia Marsh was anoxic from about 7 to 5 ka. After the mid-Holocene, shallow, but open-water environments returned to the core site. The sediments became dominated (>80%) by biogenic silica. The open-water cores show analogous but less extreme limnological and climatic changes more typical of mid-lake environments. Millennial-scale lake and climate changes during OIS 3 at Upper Klamath Lake contrast with a similar record of variation at Owens Lake, about 750 km south. When Upper Klamath Lake experienced cold-climate episodes during OIS 3, Owens Lake had warm but wet episodes; the reverse occurred during warmer intervals at Upper Klamath Lake. Such climatic alternations apparently reflect the variable position and strength of the Aleutian Low during the mid-Wisconsin.

Paleogeographic and paleoclimatic significance of diatoms from middle Pleistocene marine and glaciomarine deposits on Baldwin Peninsula, northwestern Alaska

A newly revised diatom biostratigraphic scheme for the North Pacific Ocean based on studies of the diatom flora of the Cape Blossom and Hotham Inlet Formations of Baldwin Peninsula, northwestern Alaska provides new information on the paleoceanography of Kotzebue Sound, Alaska, during middle Pleistocene time. Sediments exposed along coastal bluffs of Baldwin Peninsula contain subarctic North Pacific zonal-index species, including extinct Proboscia barboi, Pr. curvirostris, Actinocyclus ochotensis var. fossilis, Thalassiosira nidulus var. nidulus, Th. jouseae, Th. gravida var. fossilis, and Stephanopyxis dimorpha, which are correlated with the middle part of the Proboscia barboi Zone (0.43–0.36 Ma). Based on the distribution of the zonal diatom species and on changes in the paleoecological structure of the diatom assemblages (e.g., warm- vs. cold-water assemblages), we conclude that the marine deposits of the Cape Blossom Formation and lower Baldwin Silt member of the Hotham Inlet Formation formed under relatively warm, high sea-level conditions associated with the marine oxygen isotope stage (OIS) 11 transgression. Glaciomarine sedimentation (middle and upper Baldwin Silt and Selawik Gravel members of the Hotham Inlet Formation) initiated during relatively warm conditions at the end of the stage 11 transgression and continued into stage 10. High-latitude glacier growth during a global `interglacial' period was likely facilitated by warm surface waters on flooded continental shelves and limited regional sea ice cover. The biostratigraphic record at Baldwin Peninsula provides further evidence that high-latitude ice growth is favored by increased moisture supply during warm climatic intervals and inhibited by arid conditions during full glacial intervals.

The properties of cold environment for Thujopsis dolabrata var. hondai and Criptomeria japonica in the northeastern Japan

Cryptomeria japonica and Thujopsis dolabrata var. hondai have similar life-form and make the cooltemperate coniferous forest in Japan. It was thought that these two species had different process of spread of distribution in the postglacial time. During the postglacial period in northeast Japan, C. japonica migrated from south to northeast and Th. dolabrata var. hondai developed from ice age refugia scattered there.The purpose of the present paper is to explain the difference of behavior between the two, based on the relation between the present distribution of habitat and climatic condition. The results are follows.(1) C. Japonica is restricted in Honshu under the climate of Japan Sea type and Th. dolabrata var. hondai reaches to southern Hokkaido under climate of Japan Sea and Pacific-Japan Sea transitional type; annual water surplus by Thornthwaite's method is over 800mm for C. Japonica and under 1, 400mm for Th. dolabrata var. hondai; minimum and maximum value of total winter (December, January and February) precipitation is 300mm and 900mm for C. japonica and 150mm and 600mm for Th. dolabrata var. hondai, respectively.(2) The lower limit of thermal condition for Th. dolabrata var. hondai is closely related with the condition of hydro-climate. It can reach to coldest condition about 25°C Month of warmth index under 700mm of the annual water surplus or 200mm-300mm of total winter precipitation. Th. dolabrata var. hondai grows in the mountain and subalpine zone with Tuga diversifolia, Abies mariesii and others and even in alpine zone where it is stunted conspicuously and flourishes in the shrub and herb layers. For C. Japonica, however, the properties as seen for Th. dolabrata var. hondai can not be recognized.(3) If the lowering mean annual temperature was 7°C at the maximum of the last glaciation, the altitude of 25°C Month warmth index is estimated about 500m above the sea level in Tohoku and about 200m a. s. l. in the Oshima peninsula, southern Hokkaido. Considering the present behavior of Th. dolabrata var. hondai and C. japonica, it is able to interpret that the Th. dolabrata var. hondai contracted into scattered refuges in Tohoku and southern Hokkaido under the condition of less winter precipitation, although C. japonica had not been able to grow in southern Hokkaido during the full glacial interval.

Paleohydrologic implications of some deep soilwater chloride profiles, Murray Basin, South Australia

A chloride mass-balance approach to estimating soilwater ages and paleorecharge rates was tested in an area where considerable paleoclimatic data were available for comparison. Application of the method to data from four cores of the unsaturated zone taken in the western Murray Basin showed that the soil water at the base of the chloride build-up or bulge associated with the root zone of the native mallee vegetation was emplaced during the last glacial interval (at least 20 000 years BP). Furthermore, recharge rates at this time were very low. These observations agree with independent paleoclimate evidence that suggest that this time was colder, windier and drier. Results are consistent with the notion that the root-zone chloride bulge, so typical of the Murray Mallee region, developed in response to aridity that peaked during the last full glacial interval in Australia. The chloride method is a useful tool in paleohydrology, especially when used in concert with other evidence.

Paleoecology of central Kentucky since the last glacial maximum

Pollen grains and spores, plant macrofossils, and sponge spicules from a 7.2-m sediment core from Jackson Pond dating back to 20,000 yr B.P. are the basis for new interpretations of vegetational, limnological, and climatic changes in central Kentucky. During the full-glacial interval (20,400 to 16,800 yr B.P.) upland vegetation was closed spruce forest with jack pine as a subdominant. Aquatic macrophyte and sponge assemblages indicate that the site was a relatively deep, open pond with low organic productivity. During late-glacial time (16,800 to 11,300 yr B.P.) spruce populations continued to dominate while jack pine declined and sedge increased as the vegetation became a more open, taiga-like boreal woodland. Between 11,300 and 10,000 yr B.P., abundances of spruce and oak pollen oscillated reciprocally, possibly reflecting the Younger Dryas oscillation as boreal taxa underwent a series of declines and increases at the southern limit of their ranges before becoming extirpated and replaced by deciduous forest. In the early Holocene (10,000 to 7300 yr B.P.) a mesic deciduous woodland developed; it was replaced by xeric oak-hickory forest during the middle Holocene between 7300 and 3900 yr B.P. Grass increased after 3900 yr B.P., indicating that the presettlement vegetation mosaic of mixed deciduous forest and prairie (the “Kentucky Barrens”) became established in central Kentucky after the Hypsithermal interval. Sponge spicules increased in number during the Holocene, reflecting reduced water depths in the pond. Sediment infilling, as well as climatic warming and the expansion of fringing shrub thickets, increased nutrient and habitat availability for freshwater sponges.

Altitudinal and latitudinal migration of Cryptomeria japonica for the past 20,000 years in Japan

Biostatistical analysis of modern pollen assemblages in 152 Japanese surface samples shows that Cryptomeria japonica can normally grow in areas with a mean January temperature of approximately −7° to 7°C, a mean August temperature of 19° to 27°C, and an effective precipitation (total precipitation during the growing season) of over 1000 mm. The full-glacial distribution of the species on both the Sea of Japan and the Pacific coasts (35–36°N lat) indicates that in these areas the maximum possible reduction of temperature was 8.7–10.2°C in January and 6.0–7.3°C in August, and that the effective precipitation was low, being 1000–1350 mm, or 40–55% below the modern level, provided that the species has not changed its physiological characteristics. Populations of C. japonica expanded northward and upslope from their full-glacial areas of distribution immediately after late-glacial climatic amelioration. This expansion appears to have been regulated mainly by the availability of effective precipitation which became high in northeastern Honshu about 4000 yr ago. After about 2500 yr B.P., C. japonica was planted extensively by humans in moist, temperate climatic regions (excluding Hokkaido), and now has its widest distribution since at least the last full-glacial interval.