Transient floral change and rapid global warming at the Paleocene-Eocene boundary

Rapid global warming of 5 degrees to 10 degrees C during the Paleocene-Eocene Thermal Maximum (PETM) coincided with major turnover in vertebrate faunas, but previous studies have found little floral change. Plant fossils discovered in Wyoming, United States, show that PETM floras were a mixture of native and migrant lineages and that plant range shifts were large and rapid (occurring within 10,000 years). Floral composition and leaf shape and size suggest that climate warmed by approximately 5 degrees C during the PETM and that precipitation was low early in the event and increased later. Floral response to warming and/or increased atmospheric CO2 during the PETM was comparable in rate and magnitude to that seen in postglacial floras and to the predicted effects of anthropogenic carbon release and climate change on future vegetation.     

A transient rise in tropical sea surface temperature during the Paleocene-Eocene thermal maximum

The Paleocene-Eocene Thermal Maximum (PETM) has been attributed to a rapid rise in greenhouse gas levels. If so, warming should have occurred at all latitudes, although amplified toward the poles. Existing records reveal an increase in high-latitude sea surface temperatures (SSTs) (8 degrees to 10 degrees C) and in bottom water temperatures (4 degrees to 5 degrees C). To date, however, the character of the tropical SST response during this event remains unconstrained. Here we address this deficiency by using paired oxygen isotope and minor element (magnesium/calcium) ratios of planktonic foraminifera from a tropical Pacific core to estimate changes in SST. Using mixed-layer foraminifera, we found that the combined proxies imply a 4 degrees to 5 degrees C rise in Pacific SST during the PETM. These results would necessitate a rise in atmospheric pCO2 to levels three to four times as high as those estimated for the late Paleocene.     

Southern Hemisphere and deep-sea warming led deglacial atmospheric CO2 rise and tropical warming

Establishing what caused Earth's largest climatic changes in the past requires a precise knowledge of both the forcing and the regional responses. We determined the chronology of high- and low-latitude climate change at the last glacial termination by radiocarbon dating benthic and planktonic foraminiferal stable isotope and magnesium/calcium records from a marine core collected in the western tropical Pacific. Deep-sea temperatures warmed by approximately 2 degrees C between 19 and 17 thousand years before the present (ky B.P.), leading the rise in atmospheric CO2 and tropical-surface-ocean warming by approximately 1000 years. The cause of this deglacial deep-water warming does not lie within the tropics, nor can its early onset between 19 and 17 ky B.P. be attributed to CO2 forcing. Increasing austral-spring insolation combined with sea-ice albedo feedbacks appear to be the key factors responsible for this warming.     

Evolution of the earliest horses driven by climate change in the Paleocene-Eocene Thermal Maximum

Body size plays a critical role in mammalian ecology and physiology. Previous research has shown that many mammals became smaller during the Paleocene-Eocene Thermal Maximum (PETM), but the timing and magnitude of that change relative to climate change have been unclear. A high-resolution record of continental climate and equid body size change shows a directional size decrease of ~30% over the first ~130,000 years of the PETM, followed by a ~76% increase in the recovery phase of the PETM. These size changes are negatively correlated with temperature inferred from oxygen isotopes in mammal teeth and were probably driven by shifts in temperature and possibly high atmospheric CO(2) concentrations. These findings could be important for understanding mammalian evolutionary responses to future global warming.     

Nannoplankton extinction and origination across the Paleocene-Eocene Thermal Maximum

The Paleocene-Eocene Thermal Maximum (PETM, approximately 55 million years ago) was an interval of global warming and ocean acidification attributed to rapid release and oxidation of buried carbon. We show that the onset of the PETM coincided with a prominent increase in the origination and extinction of calcareous phytoplankton. Yet major perturbation of the surface-water saturation state across the PETM was not detrimental to the survival of most calcareous nannoplankton taxa and did not impart a calcification or ecological bias to the pattern of evolutionary turnover. Instead, the rate of environmental change appears to have driven turnover, preferentially affecting rare taxa living close to their viable limits.     

Absence of cooling in New Zealand and the adjacent ocean during the Younger Dryas chronozone

As the climate warmed at the end of the last glacial period, a rapid reversal in temperature, the Younger Dryas (YD) event, briefly returned much of the North Atlantic region to near full-glacial conditions. The event was associated with climate reversals in many other areas of the Northern Hemisphere and also with warming over and near Antarctica. However, the expression of the YD in the mid- to low latitudes of the Southern Hemisphere (and the southwest Pacific region in particular) is much more controversial. Here we show that the Waiho Loop advance of the Franz Josef Glacier in New Zealand was not a YD event, as previously thought, and that the adjacent ocean warmed throughout the YD.     

Sea Surface Temperature, Surface Wind Divergence, and Convection over Tropical Oceans

Large-scale convection over the warm tropical oceans provides an important portion of the driving energy for the general circulation of the atmosphere. Analysis of regional associations between ocean temperature, surface wind divergence, and convection produced two important results. First, over broad regions of the Indian and Pacific oceans, sea surface temperatures (SSTs) in excess of 27.5 degrees C are required for large-scale deep convection to occur. However, SSTs above that temperature are not a sufficient condition for convection and further increases in SST appear to have little effect on the intensity of convection. Second, when SSTs are above 27.5 degrees C, surface wind divergence is closely associated with the presence or absence of deep convection. Although this result could have been expected, it was also found that areas of persistent divergent surface flow coincide with regions where convection appears to be consistently suppressed even when SSTs are above 27.5 degrees C. Thus changes in atmospheric stability caused by remotely forced changes in subsidence aloft may play a major role in regulating convection over warm tropical oceans.     

Tropical pacific forcing of decadal SST variability in the western indian ocean over the past two centuries

A 194-year annual record of skeletal delta(18)O from a coral growing at Malindi, Kenya, preserves a history of sea surface temperature (SST) change that is coherent with instrumental and proxy records of tropical Pacific climate variability over interannual to decadal periods. This variability is superimposed on a warming of as much as 1.3 degrees C since the early 1800s. These results suggest that the tropical Pacific imparts substantial decadal climate variability to the western Indian Ocean and, by implication, may force decadal variability in other regions with strong El Nino-Southern Oscillation teleconnections.     

Climatic warming and the decline of zooplankton in the california current

Since 1951, the biomass of macrozooplankton in waters off southern California has decreased by 80 percent. During the same period, the surface layer warmed-by more than 1.5 degrees C in some places-and the temperature difference across the thermocline increased. Increased stratification resulted in less lifting of the thermocline by wind-driven upwelling. A shallower source of upwelled waters provided less inorganic nutrient for new biological production and hence supported a smaller zooplankton population. Continued warming could lead to further decline of zooplankton.     

Counterclockwise circulation in the pacific subantarctic sector of the southern ocean

The distribution of isohalines in the upper 500 meters of Pacific subantarctic waters can be interpreted as evidence for an endemic counterclockwise circulation, the westward component of which is at 40 to 45 degrees south latitude. The distributions of a number of lanternfish species (family Myctophidae) lend support to such an interpretation.     

Geological history of the Western north pacific

A considerable portion of the abyssal floor of the western North Pacific was already receiving pelagic sediment in late Jurassic time. Carbonate sediments were later replaced by abyssal clays as the basin deepened and bottom waters became more aggressive. The resulting facies boundary, which can be recognized on seismic profiles, is broadly transgressive; it ranges in age from mid-Cretaceous in the western Pacific to Oligocene in the central Pacific. Cherts are encountered at and below the major facies boundary and appear to have been formed by postdepositional processes.     

Expanding oxygen-minimum zones in the tropical oceans

Oxygen-poor waters occupy large volumes of the intermediate-depth eastern tropical oceans. Oxygen-poor conditions have far-reaching impacts on ecosystems because important mobile macroorganisms avoid or cannot survive in hypoxic zones. Climate models predict declines in oceanic dissolved oxygen produced by global warming. We constructed 50-year time series of dissolved-oxygen concentration for select tropical oceanic regions by augmenting a historical database with recent measurements. These time series reveal vertical expansion of the intermediate-depth low-oxygen zones in the eastern tropical Atlantic and the equatorial Pacific during the past 50 years. The oxygen decrease in the 300- to 700-m layer is 0.09 to 0.34 micromoles per kilogram per year. Reduced oxygen levels may have dramatic consequences for ecosystems and coastal economies.     

The spatial pattern and mechanisms of heat-content change in the North Atlantic

The total heat gained by the North Atlantic Ocean over the past 50 years is equivalent to a basinwide increase in the flux of heat across the ocean surface of 0.4 +/- 0.05 watts per square meter. We show, however, that this basin has not warmed uniformly: Although the tropics and subtropics have warmed, the subpolar ocean has cooled. These regional differences require local surface heat flux changes (+/-4 watts per square meter) much larger than the basinwide average. Model investigations show that these regional differences can be explained by large-scale, decadal variability in wind and buoyancy forcing as measured by the North Atlantic Oscillation index. Whether the overall heat gain is due to anthropogenic warming is difficult to confirm because strong natural variability in this ocean basin is potentially masking such input at the present time.     

Effects of rapid global warming at the Paleocene-Eocene boundary on neotropical vegetation

Temperatures in tropical regions are estimated to have increased by 3° to 5°C, compared with Late Paleocene values, during the Paleocene-Eocene Thermal Maximum (PETM, 56.3 million years ago) event. We investigated the tropical forest response to this rapid warming by evaluating the palynological record of three stratigraphic sections in eastern Colombia and western Venezuela. We observed a rapid and distinct increase in plant diversity and origination rates, with a set of new taxa, mostly angiosperms, added to the existing stock of low-diversity Paleocene flora. There is no evidence for enhanced aridity in the northern Neotropics. The tropical rainforest was able to persist under elevated temperatures and high levels of atmospheric carbon dioxide, in contrast to speculations that tropical ecosystems were severely compromised by heat stress.     

A terminal mesozoic "greenhouse": lessons from the past

The late Mesozoic rock and life records implicate short-term (up to 10(5) to 10(6) years) global warming resulting from carbon dioxide-induced "greenhouse" conditions in the late Maestrichtian extinctions that terminated the Mesozoic Era. Oxygen isotope data from marine microfossils suggest late Mesozoic climatic cooling into middle Maestrichtian, and warming thereafter into the Cenozoic. Animals adapting to climatic cooling could not adapt to sudden warming. Small calcareous marine organisms would have suffered solution effects of carbon dioxide-enriched waters; animals dependent upon them for food would also have been affected. The widespread terrestrial tropical floras would likely not have reflected effects of a slight climatic warming. In late Mesozoic, the deep oceanic waters may have been triggered into releasing vast amounts of carbon dioxide into the atmosphere in a chain reaction of climatic warming and carbon dioxide expulsion. These conditions may be duplicated by human combustion of the fossil fuels and by forest clearing.     

Simulated increase of hurricane intensities in a CO2-warmed climate

Hurricanes can inflict catastrophic property damage and loss of human life. Thus, it is important to determine how the character of these powerful storms could change in response to greenhouse gas-induced global warming. The impact of climate warming on hurricane intensities was investigated with a regional, high-resolution, hurricane prediction model. In a case study, 51 western Pacific storm cases under present-day climate conditions were compared with 51 storm cases under high-CO2 conditions. More idealized experiments were also performed. The large-scale initial conditions were derived from a global climate model. For a sea surface temperature warming of about 2.2 degrees C, the simulations yielded hurricanes that were more intense by 3 to 7 meters per second (5 to 12 percent) for wind speed and 7 to 20 millibars for central surface pressure.     

不同墙体日光温室保温性能研究

为了确定合理的日光温室后墙材料与结构,2012年分别在睢宁、赣榆建造了不同墙体(普通空心砖墙、复合异质墙体、夹芯板墙体)构型的日光温室,并研究了不同墙体日光温室的增温、保温性能。结果表明:普通空心砖墙蓄热能力强,夜间保温效果好,但白天增温慢;夹芯板墙体热阻值大,白天升温较快,利于提高温室的最高温度,但夜间放热能力较弱,不利于夜间保温;复合异质墙体具有较好的热阻和蓄热能力,增温、保温性最佳。为使日光温室冬季获得较好增温保温效果,从节约成本方面考虑,建议选择1 cm内粉+24 cm空心砖+24 cm空心砖+10 cm聚苯乙烯泡沫塑料板+1 cm外粉为墙体的温室。     

Seismic Tomogram of the Earth's Mantle: Geodynamic Implications

Recent seismic tomography of the Earth's mantle has revealed a large-scale pattern of mantle convection comprising upwelling columnar plumes in the Pacific and Africa and downwelling planar sheets along the Circum Pacific. Upwelling and downwelling occur most extensively under the south Pacific and west Pacific, respectively. High-resolution image of plate subduction has been obtained from the dense seismic networks around Japan. Japanese seismologists are in the best position to resolve the internal structure of downwelling current as an integral part of the whole convection system.     

Sea-air partitioning of mercury in the equatorial pacific ocean

The partitioning of gaseous mercury between the atmosphere and surface waters was determined in the equatorial Pacific Ocean. The highest concentrations of dissolved gaseous mercury occurred in cooler, nutrient-rich waters that characterize equatorial upwelling and increased biological productivity at the sea surface. The surface waters were supersaturated with respect to elemental mercury; a significant flux of elemental mercury to the atmosphere is predicted for the equatorial Pacific. When normalized to primary production on a global basis, the ocean effluxes of mercury may rival anthropogenic emissions of mercury to the atmosphere.     

East pacific rise: hot springs and geophysical experiments

Hydrothermal vents jetting out water at 380 degrees +/- 30 degrees C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galápagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation.