Climate sensitivity estimated from temperature reconstructions of the Last Glacial Maximum

Assessing the impact of future anthropogenic carbon emissions is currently impeded by uncertainties in our knowledge of equilibrium climate sensitivity to atmospheric carbon dioxide doubling. Previous studies suggest 3 kelvin (K) as the best estimate, 2 to 4.5 K as the 66% probability range, and nonzero probabilities for much higher values, the latter implying a small chance of high-impact climate changes that would be difficult to avoid. Here, combining extensive sea and land surface temperature reconstructions from the Last Glacial Maximum with climate model simulations, we estimate a lower median (2.3 K) and reduced uncertainty (1.7 to 2.6 K as the 66% probability range, which can be widened using alternate assumptions or data subsets). Assuming that paleoclimatic constraints apply to the future, as predicted by our model, these results imply a lower probability of imminent extreme climatic change than previously thought.     

Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum

The timing of the last maximum extent of the Antarctic ice sheets relative to those in the Northern Hemisphere remains poorly understood. We develop a chronology for the Weddell Sea sector of the East Antarctic Ice Sheet that, combined with ages from other Antarctic ice-sheet sectors, indicates that the advance to and retreat from their maximum extent was within dating uncertainties synchronous with most sectors of Northern Hemisphere ice sheets. Surface climate forcing of Antarctic mass balance would probably cause an opposite response, whereby a warming climate would increase accumulation but not surface melting. Our new data support teleconnections involving sea-level forcing from Northern Hemisphere ice sheets and changes in North Atlantic deep-water formation and attendant heat flux to Antarctic grounding lines to synchronize the hemispheric ice sheets.     

Atlantic meridional overturning circulation during the Last Glacial Maximum

The circulation of the deep Atlantic Ocean during the height of the last ice age appears to have been quite different from today. We review observations implying that Atlantic meridional overturning circulation during the Last Glacial Maximum was neither extremely sluggish nor an enhanced version of present-day circulation. The distribution of the decay products of uranium in sediments is consistent with a residence time for deep waters in the Atlantic only slightly greater than today. However, evidence from multiple water-mass tracers supports a different distribution of deep-water properties, including density, which is dynamically linked to circulation.     

High-latitude forcing of the South American summer monsoon during the Last Glacial

The climate of the Last Glacial period (10,000 to 110,000 years ago) was characterized by rapid millennial-scale climate fluctuations termed Dansgaard/Oeschger (D/O) and Heinrich events. We present results from a speleothem-derived proxy of the South American summer monsoon (SASM) from 16,000 to 50,000 years ago that demonstrate the occurrence of D/O cycles and Heinrich events. This tropical Southern Hemisphere monsoon reconstruction illustrates an antiphase relationship to Northern Hemisphere monsoon intensity at the millennial scale. Our results also show an influence of Antarctic millennial-scale climate fluctuations on the SASM. This high-resolution, precisely dated, tropical precipitation record can be used to establish the timing of climate events in the high latitudes of the Northern and Southern Hemispheres.     

Giant larvacean houses: rapid carbon transport to the deep sea floor

An unresolved issue in ocean science is the discrepancy between the food requirements of the animals living on the deep sea floor and their food supply, as measured by sediment traps. A 10-year time-series study of the water column off Monterey Bay, California, revealed that the discarded mucus feeding structures of giant larvaceans carry a substantial portion of the upper ocean's productivity to the deep seabed. These abundant, rapidly sinking, carbon-rich vectors are not detected by conventional sampling methods and thus have not been included in calculations of vertical nutrient flux or in oceanic carbon budgets.     

Slaty cleavage: incipient occurrences in the deep sea

Highly deformed Pleistocene mudstones from the inner wall of the Aleutian Trench and from the continental rise of the Gulf of Mexico show incipient slaty cleavage defined by the orientation of platy and elongate detrital minerals parallel to the axial surfaces of folds.     

High-magnesian calcite: leaching of magnesium in the deep sea

The high-magnesian calcite fraction of a shallow-water carbonate sand was converted to low-magnesian calcite after transport to the deep sea; strontium was also leached from the carbonate. Oxygen isotopic ratios indicate that loss of magnesium and strontium took place during recrystallization of the carbonate in the deep sea; this process did not alter textures of skeletal fragments. Previously, high-magnesian, calcite was thought only to dissolve in the deep sea.     

The Eocene/Oligocene boundary event in the deep sea

Analysis of middle Eocene to early, Oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the Eocene/Oligocene boundary. Biotic changes in the late Paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the Eocenel Oligocene boundary.     

近十年来中部地区农村义务教育供给主体变化的实证分析

按照公共物品有效供给理论,公共物品可由政府、私人和第三部门供给。根据对安徽省霍邱县农村义务教育1999年至2007年供给情况的调研分析,我国中部地区农村义务教育供给主体为政府、农民和第三部门,近十年来政府供给渐居主导地位,农民供给逐渐消失,第三部门供给持续薄弱。其中存在的问题表现在:政府供给增加完全取决于上级财政转移支付力度,县级财政缺失;农民供给强度变化直接影响农村义务教育供给质量;第三部门供给受自然灾害影响而起伏。     

Geophysics from triton to the deep blue sea: new quake forecast: north by northwest

Geophysics is closing out the 1980s with a bang. October's Loma Prieta earthquake grabbed the spotlight at this month's American Geophysical Union's annual fall meeting in, of all places, San Francisco; the quake also closed down one of the official hotels, depriving hundreds of the 4500 attendees of rooms. Other hot topics of the late 1980s-Voyager's tour of the outer solar system and the greenhouse effect-got their share of attention as well.     

Iron-rich Basal sediments from the eastern equatorial pacific: leg 16, deep sea drilling project

Iron-rich sediments chemically similar to those forming at present on the crest of the East Pacific Rise have been found just above basement at widely separated drill sites in the eastern equatorial Pacific, including three sites of Leg 16 of the Deep Sea Drilling Project. These sediments were probably formed when the basement was at the crest of this rise and have moved to their present location as a result of sea-floor spreading.     

Glacial and pluvial periods: their relationship revealed by pleistocene sediments of the red sea and gulf of aden

Oxygen isotope analyses of planktonic foraminifera from the Red Sea and Gulf of Aden indicate that during periods of maximum continental and polar glaciation in the late Pleistocene, the Red Sea was subject to strong evaporation. Between glacial maximums the salinity of the Red Sea was equal to or below that of the open ocean. This suggests that high-latitude glacial periods corresponded in time to interpluvial stages in the present-day desert belt of northern Africa, whereas high-latitude interglacial periods coincided with pluvial stages.     

Phaeodarian skeletons: their role in silica transport to the deep sea

The skeletons of phaeodarian Radiolaria transport and redistribute silica to the tropical deep oceans by dissolving in the water column and on the sea floor. The skeletons are initially solid but within a few days to months become progressively more porous while settling through the water column. Phaeodarian Radiolaria are rarely preserved in the bottom sediments; in contrast, polycystine Radiolaria are the dominant Radiolaria preserved in the fossil record. This preservational difference may be due to differences in skeletal constituents.     

Decomposition of calcium carbonate and organic carbon in the deep oceans

Simple mass-balance calculations indicate that in seawater the calcium variation (DeltaCa) correlates with the variation in the titration alkalinity (DeltaTA) and the variation in the total carbon dioxide (DeltasigmaCO(2)) or nitrate (DeltaNO(3)) according to the equations DeltaCa = 0.46288 DeltaTA + 0.074236 DeltasigmaCO(2) and DeltaCa = 0.5 DeltaTA + 0.53125 DeltaNO(3). The estimated values for DeltaCa from these equations, which agree with the values obtained from direct measurements, have been used to estimate the ratio of the in situ inorganic to organic carbon fluxes in the oceans. The precise vertical distribution of this ratio is shown for the first time.     

Evidence for sediment eruption on deep sea floor, gulf of Mexico

A large crater has been discovered on the sea floor, Gulf of Mexico, in a water depth of 2176 meters. Deep-tow high-resolution imagery shows that the crater is cut into a low hill surrounded by near-surface concentric faults. Approximately 2 million cubic meters of ejected sediment forms a peripheral debris field. The low hill and faults may be related to mud diapirism or intrusion of gas hydrates into near-surface sediments. A recent eruption evacuated sediments from the crater, apparently because of release of overpressured petrogenic gas.