Introduction to the JoPL special issue, “Holocene paleoenvironmental records from Arctic lake sediment”     

Darrell S. Kaufman 《Journal of Paleolimnology》2012,48(1):1-7

The 18 papers in this Special Issue of the Journal of Paleolimnology report new records of Holocene environmental and climate change from Arctic lake sediment. At least 15 distinct physical, chemical, and biological properties were analyzed at lakes located across the North American Arctic and subarctic, and northwestern Europe. The studies are notable for their multi-proxy approach (eight present data for at least five different proxies), and for the high quality of their geochronological control. Three of the studies analyzed sediment from more than one lake to test the influence of contrasting physiographic settings on the response of proxies to the same climate forcing. The sedimentary sequences analyzed in seven studies extend beyond 11.5?cal?ka, providing evidence for pronounced climate shifts that took place during the late-glacial period. Two-thirds extend beyond 8?cal?ka; many of these records were interpreted in terms of the shift in temperature and moisture that occurred during the transition from the warm early to middle Holocene to the cooler late Holocene. These records contribute to the growing network of sites that is needed to reconstruct the spatial pattern of this pronounced paleoclimate transition, and to address how ocean-atmospheric circulation changed with the mean?state of climate.  相似文献   

Middle Pleistocene age of the Nome River glaciation, northwestern Alaska     

Darrell S. Kaufman  Robert C. Walter  Julie Brigham-Grette  David M. Hopkins   《Quaternary Research》1991,36(3)

During the middle Pleistocene Nome River glaciation of northwestern Alaska, glaciers covered an area an order of magnitude more extensive than during any subsequent glacial intervals. The age of the Nome River glaciation is constrained by laser-fusion ⁴⁰Ar/³⁹Ar analyses of basaltic lava that overlies Nome River drift at Minnie Creek, central Seward Peninsula, that average 470,000 ± 190,000 yr (±1σ). Milligram-size subsamples of the lava were dated to identify and eliminate extraneous ⁴⁰Ar enrichments that rendered the mean of conventional K---Ar dates on larger bulk samples of the same flow too old (700,000 ± 570,000 yr). While the ⁴⁰Ar/³⁹Ar analyses provide a minimum limiting age for the Nome River glaciation, maximum ages are provided by a provisional K---Ar date on a basaltic lava flow that underlies the Nome River drift at nearby Lave Creek, by paleomagnetic determinations of the drift itself at and near the type locality, and by amino acid epimerization analysis of molluscan fossils from nearshore sediments of the Anvilian marine transgression that underlie Nome River drift on the coastal plain at Nome. Taken together, the new age data indicate that the glaciation took place between 580,000 and 280,000 yr ago. The altitude of the Anvilian deposits suggests that eustatic sea level during the Anvilian transgression rose at least as high as and probably higher than during the last interglacial transgression; by correlation with the marine oxygen-isotope record, the transgression probably dates to stage 11 at 410,000 yr, and the Nome River glaciation is younger still. Analyses of floor altitudes of presumed Nome River cirques indicate that the Nome River regional snowline depression was at least twice that of the maximum late Wisconsin. The cause of the enhanced snowline lowering appears to be related to greater availability of moisture in northwestern Alaska during the middle Pleistocene.  相似文献   

Corrigendum to “Temperature and precipitation history of the Arctic” [Quat. Sci. Rev. 29 (2010) 1679–1715]     

G.H. Miller  J. Brigham-Grette  R.B. Alley  L. Anderson  H.A. Bauch  M.S.V. Douglas  M.E. Edwards  S.A. Elias  B.P. Finney  J.J. Fitzpatrick  S.V. Funder  T.D. Herbert  L.D. Hinzman  D.S. Kaufman  G.M. MacDonald  L. Polyak  A. Robock  M.C. Serreze  J.P. Smol  R. Spielhagen  E.W. Wolff 《Quaternary Science Reviews》2011,30(19-20):2841-2843

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Holocene climate inferred from glacier extent,lake sediment and tree rings at Goat Lake,Kenai Mountains,Alaska, USA     

Thomas A. Daigle  Darrell S. Kaufman 《第四纪科学杂志》2009,24(1):33-45

Lake sediment, glacier extent and tree rings were used to reconstruct Holocene climate changes from Goat Lake at 550 m asl in the Kenai Mountains, south‐central Alaska. Radiocarbon‐dated sediment cores taken at 55 m water depth show glacial‐lacustrine conditions until about 9500 cal. yr BP, followed by organic‐rich sedimentation with an overall increasing trend in organic matter and biogenic silica content leading up to the Little Ice Age (LIA). Through most of the Holocene, the northern outlet of the Harding Icefield remained below the drainage divide that currently separates it from Goat Lake. A sharp transition from gyttja to inorganic mud about AD 1660 signifies the reappearance of glacier meltwater into Goat Lake during the LIA, marking the maximum Holocene (postglacial) extent. Meltwater continued to discharge into the lake until about AD 1900. A 207 yr tree‐ring series from 25 mountain hemlocks growing in the Goat Lake watershed correlates with other regional tree‐ring series that indicate an average summer temperature reduction of about 1°C during the 19th century compared with the early–mid 20th century. Cirque glaciers around Goat Lake reached their maximum LIA extent in the late 19th century. Assuming that glacier equilibrium‐line altitudes (ELA) are controlled solely by summer temperature, then the cooling of 1°C combined with the local environmental lapse rate would indicate an ELA lowering of 170 m. In contrast, reconstructed ELAs of 12 cirque glaciers near Goat Lake average only 34 ± 18 m lower during the LIA. The restricted ELA lowering can be explained by a reduction in accumulation‐season precipitation caused by a weakening of the Aleutian low‐pressure system during the late LIA. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Uptake of nitrogenous nutrients by phytoplankton in a barrier Island estuary: Great South Bay,New York     

Zena G. Kaufman  John S. Lively  Edward J. Carpenter 《Estuarine, Coastal and Shelf Science》1983,17(5):483-493

The uptake of urea, nitrate and ammonium by phytoplankton was measured using ¹⁵N isotopes over a one-year period in Great South Bay, a shallow coastal lagoon. The bay is a unique environment for the study of nutrient uptake since ambient concentrations of $\text{NO}{}_3{}^{\mathrm{?}}\text{NH}{}_4{}^{\mathrm{+}}$ and urea remain relatively high through the year, and phytoplankton are probably never nutrient limited. Urea nitrogen averaged 52% of the total assimilated, while ammonium represented 33% and nitrate 13%. High rates of ammonium uptake occurred only at low urea concentrations (ca< 1-μg-atom urea l^?1). Over the sampling period urea was present in relatively high concentrations, averaging 5·35 μg-atom N l^?1, while means for ammonium and nitrate averaged 1·94 and 0·65 μg-atom N l^?1, respectively. Total N uptake measured with ¹⁵N averaged about 3·3 times the calculated (from elemental ratios and ¹⁴C productivity measurements) N needs of the phytoplankton population. Highest nitrogen uptake occurred in the summer and coincided with the primary production maximum.  相似文献   

The residence time of thorium in surface sea water and its implications regarding the rate of reactive pollutants     

W.S. Broecker  A. Kaufman  R.M. Trier 《Earth and Planetary Science Letters》1973,20(1):35-44

The activity ratio of²²⁸Th/²²⁸Ra in the open surface ocean averages 0.21. This suggests that thorium is removed from surface water in about 0.7 yr. As plant matter is cycled within the surface sea on a similar time scale, the suggestion is made that highly reactive compounds are inadvertently removed by plants in their quest for the critical nutrients nitrate and phosphate. Combined with the coefficient for horizontal eddy diffusivity obtained from the distribution of²²⁸Ra in surface sea water this result provides a basis for the prediction of the distribution of “reactive” pollutants released to the surface sea from coastal areas.  相似文献   

²¹⁰Pb and²¹⁰Po during the destruction of stratification in the Dead Sea     

M. Stiller  A. Kaufman 《Earth and Planetary Science Letters》1984,71(2):390-404

The progressive weakening and final disappearance (in 1979) of the long-term meromictic structure of the Dead Sea are clearly reflected in the depth profiles of²¹⁰Pb and²¹⁰Po. In 1977/78, prior to overturn, dissolved²¹⁰Pb (35–50 dpm kg^?1) predominated over particulate²¹⁰Pb (1–2 dpm kg^?1) in the oxic upper waters, whereas the reverse was true in the anoxic deep waters (16–20 dpm kg^?1 particulate vs. 2–5 dpm kg^?1 dissolved). The exact extent of the disequilibrium between²¹⁰Pb and²²⁶Ra is hard to evaluate in the upper oxic layers, because the progressive deepenings resulted in mixing with deep waters. By contrast, one can estimate the residence time of dissolved²¹⁰Pb in the unperturbed anoxic deepest layers, because these remained isolated, at about 3 years. Following the overturn of 1979, dissolved²¹⁰Pb exceeded particulate²¹⁰Pb at all depths. The²¹⁰Po profiles of the stratified lake resembled in shape those of its grandparent²¹⁰Pb, but with distinct characteristics of their own in the oxic upper waters where particulate²¹⁰Po (8–12 dpm kg^?1) was greatly in excess over particulate²¹⁰Pb, while dissolved²¹⁰Po (25–40 dpm kg^?1) was slightly deficient. Immediately following the overturn, dissolved and particulate²¹⁰Po were similar (about 15 dpm kg^?1), at all depths. The destruction of the lake's meromictic structure was accompanied by a reduction of its²¹⁰Pb inventory, while that of²¹⁰Po was almost unaffected. Thus, at overturn a transient state was created with the inventory of²¹⁰Po exceeding that of²¹⁰Pb.  相似文献   

The rate of Pleistocene subsidence and sedimentation in the Hula Basin as compared with those of other time spans in other Israeli tectonic regions     

U. Kafri  A. Kaufman  M. Magaritz 《Earth and Planetary Science Letters》1983,65(1):126-132

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The temperature anisotropy and adiabatic cooling of the protons in the solar wind     

M. Eyni  A. S. Kaufman 《Planetary and Space Science》1971,19(12):1609-1614

A simple theoretical expression for the mean kinetic temperature of the protons in a steady state as a function of heliocentric distance is derived. The basic assumption is that the temperature anisotropy of the protons is invariant in space where binary encounters are rare. For an assumed base temperature of 5 × 10⁵K at a distance of 0.05 AU, the calculated temperature at a distance of 1 AU is in the range (2–4) × 10⁴K for an average anisotropy factor of 3: this range of temperatures is close to the observed average value under so-called ‘quiet’ conditions. Measurement of the anisotropy factor at different heliocentric distances is required to test the basis of the model.  相似文献   

Large dust absorption of infrared radiation over Afro-Asian regions: evidence for anthropogenic impact     

Satheesh  S.K. Deepshikha  S. Srinivasan  J. Kaufman  Y.J. 《Geoscience and Remote Sensing Letters, IEEE》2006,3(3):307-311

There is a large uncertainty in the estimation of dust radiative forcing due to the lack of adequate data about complex spatial and temporal pattern of the radiative properties of dust. Here, we examine the temporal and spatial variability of dust absorption in the thermal infrared over the Afro-Asian regions using satellite data. Large dust absorption (nearly double compared to that of pure dust) was observed in regions with large anthropogenic influence, possibly due to deposition of black carbon on dust particles. While most of the recent estimates of global mean dust radiative forcing predicted net cooling, our studies indicate that there could be large heating due to dust over vast Afro-Asian regions. It appears that large dust heating is due to its interaction with anthropogenic black carbon.  相似文献