Climate impact of late quaternary equatorial pacific sea surface temperature variations

Magnesium/calcium data from planktonic foraminifera in equatorial Pacific sediment cores demonstrate that tropical Pacific sea surface temperatures (SSTs) were 2.8 degrees +/- 0.7 degrees C colder than the present at the last glacial maximum. Glacial-interglacial temperature differences as great as 5 degrees C are observed over the last 450 thousand years. Changes in SST coincide with changes in Antarctic air temperature and precede changes in continental ice volume by about 3 thousand years, suggesting that tropical cooling played a major role in driving ice-age climate. Comparison of SST estimates from eastern and western sites indicates that the equatorial Pacific zonal SST gradient was similar or somewhat larger during glacial episodes. Extraction of a salinity proxy from the magnesium/calcium and oxygen isotope data indicates that transport of water vapor into the western Pacific was enhanced during glacial episodes.     

A mid-brunhes climatic event: long-term changes in global atmosphere and ocean circulation

A long-term climatic change 4.0 x 10(5) to 3.0 x 10(5) years ago is recorded in deep-sea sediments of the Angola and Canary basins in the eastern Atlantic Ocean. In the Angola Basin (Southern Hemisphere) the climatic signal shows a transition to more humid ("interglacial") conditions in equatorial Africa, and in the Canary Basin (Northern Hemisphere) to more "glacial" oceanic conditions. This trend is confirmed by comparison with all well-documented marine and continental records from various latitudes available; in the Northern Hemisphere, in the Atlantic north of 20 degrees N, climate merged into more "glacial" conditions and in equatorial regions and in the Southern Hemisphere to more "interglacial" conditions. The data point to a more northern position of early Brunhes oceanic fronts and to an intensified atmosphere and ocean surface circulation in the Southern Hemisphere during that time, probably accompanied by a more zonal circulation in the Northern Hemisphere. The mid-Brunhes climatic change may have been forced by the orbital eccentricity cycle of 4.13 x 10(5) years.     

Evolution of the eastern tropical Pacific through Plio-Pleistocene glaciation

A tropical Pacific climate state resembling that of a permanent El Ni?o is hypothesized to have ended as a result of a reorganization of the ocean heat budget approximately 3 million years ago, a time when large ice sheets appeared in the high latitudes of the Northern Hemisphere. We report a high-resolution alkenone reconstruction of conditions in the heart of the eastern equatorial Pacific (EEP) cold tongue that reflects the combined influences of changes in the equatorial thermocline, the properties of the thermocline's source waters, atmospheric greenhouse gas content, and orbital variations on sea surface temperature (SST) and biological productivity over the past 5 million years. Our data indicate that the intensification of Northern Hemisphere glaciation approximately 3 million years ago did not interrupt an almost monotonic cooling of the EEP during the Plio-Pleistocene. SST and productivity in the eastern tropical Pacific varied in phase with global ice volume changes at a dominant 41,000-year (obliquity) frequency throughout this time. Changes in the Southern Hemisphere most likely modulated most of the changes observed.     

Pacific pleistocene cores: faunal analyses and geochronology

Two cores from the eastern Pacific were analyzed faunally and dated by the ionium: thorium method. Comparison of the results of these and of similar studies of Atlantic cores indicate that faunal changes, representing changes between the glacial and interglacial stages of the Pleistocene, occurred in both oceans simultaneously.     

340,000-year centennial-scale marine record of Southern Hemisphere climatic oscillation

In order to investigate rapid climatic changes at mid-southern latitudes, we have developed centennial-scale paleoceanographic records from the southwest Pacific that enable detailed comparison with Antarctic ice core records. These records suggest close coupling of mid-southern latitudes with Antarctic climate during deglacial and interglacial periods. Glacial sections display higher variability than is seen in Antarctic ice cores, which implies climatic decoupling between mid- and high southern latitudes due to enhanced circum-Antarctic circulation. Structural and temporal similarity with the Greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations.     

Interglacial hydroclimate in the tropical West Pacific through the Late Pleistocene

Records of atmospheric carbon dioxide concentration (P(CO(2))) and Antarctic temperature have revealed an intriguing change in the magnitude of interglacial warmth and P(CO(2)) at around 430,000 years ago (430 ka), but the global climate repercussions of this change remain elusive. Here, we present a stalagmite-based reconstruction of tropical West Pacific hydroclimate from 570 to 210 ka. The results suggest similar regional precipitation amounts across the four interglacials contained in the record, implying that tropical hydroclimate was insensitive to interglacial differences in P(CO(2)) and high-latitude temperature. In contrast, during glacial terminations, drying in the tropical West Pacific accompanied cooling events in northern high latitudes. Therefore, the tropical convective heat engine can either stabilize or amplify global climate change, depending on the nature of the climate forcing.     

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.     

Unraveling the mystery of Indian monsoon failure during El Niño

The 132-year historical rainfall record reveals that severe droughts in India have always been accompanied by El Ni?o events. Yet El Ni?o events have not always produced severe droughts. We show that El Ni?o events with the warmest sea surface temperature (SST) anomalies in the central equatorial Pacific are more effective in focusing drought-producing subsidence over India than events with the warmest SSTs in the eastern equatorial Pacific. The physical basis for such different impacts is established using atmospheric general circulation model experiments forced with idealized tropical Pacific warmings. These findings have important implications for Indian monsoon forecasting.     

Equatorial undercurrent disappears during 1982-1983 el nino

The equatorial undercurrent at 159 degrees W decayed during August 1982, partially reversed during September, and rapidly reappeared in January 1983. The virtual disappearance is consistent with the basin-wide adjustment of sea surface slope to the strong westerly winds in the western and central Pacific that caused the 1982-1983 El Ni?o event.     

Ventilation of the glacial deep Pacific Ocean

Measurements of the age difference between coexisting benthic and planktic foraminifera from western equatorial Pacific deep-sea cores suggest that during peak glacial time the radiocarbon age of water at 2-kilometers depth was no greater than that of today. These results make unlikely suggestions that a slowdown in deep-ocean ventilation was responsible for a sizable fraction of the increase of the ratio of carbon-14 (14C) to carbon in the atmosphere and surface ocean during glacial time. Comparison of 14C ages for coexisting wood and planktic foraminifera from the same site suggests that the atmosphere to surface ocean 14C to C ratio difference was not substantially different from today's.     

155,000 years of West African monsoon and ocean thermal evolution

A detailed reconstruction of West African monsoon hydrology over the past 155,000 years suggests a close linkage to northern high-latitude climate oscillations. Ba/Ca ratio and oxygen isotope composition of planktonic foraminifera in a marine sediment core from the Gulf of Guinea, in the eastern equatorial Atlantic (EEA), reveal centennial-scale variations of riverine freshwater input that are synchronous with northern high-latitude stadials and interstadials of the penultimate interglacial and the last deglaciation. EEA Mg/Ca-based sea surface temperatures (SSTs) were decoupled from northern high-latitude millennial-scale fluctuation and primarily responded to changes in atmospheric greenhouse gases and low-latitude solar insolation. The onset of enhanced monsoon precipitation lags behind the changes in EEA SSTs by up to 7000 years during glacial-interglacial transitions. This study demonstrates that the stadial-interstadial and deglacial climate instability of the northern high latitudes exerts dominant control on the West African monsoon dynamics through an atmospheric linkage.     

A 23,000-year record of surface water pH and PCO2 in the western equatorial Pacific Ocean

The oceans play a major role in defining atmospheric carbon dioxide (CO2) levels, and although the geographical distribution of CO2 uptake and release in the modern ocean is understood, little is known about past distributions. Boron isotope studies of planktonic foraminifera from the western equatorial Pacific show that this area was a strong source of CO2 to the atmosphere between approximately 13,800 and 15,600 years ago. This observation is most compatible with increased frequency of La Ni?a conditions during this interval. Hence, increased upwelling in the eastern equatorial Pacific may have played an important role in the rise in atmospheric CO2 during the last deglaciation.     

Oceanographic observations of the 1982 warming of the tropical eastern pacific

Moored current meter, sea level, hydrographic, and surface drifter measurements show the large changes that took place in the eastern tropical Pacific during the onset of the warm episode of 1982. In August the near-surface flow at 0 degrees , 110 degrees W reversed direction to eastward. By October the sea surface temperature in the equatorial zone increased by 5 degrees Celsius above the long-term monthly mean value, sea level rose by 22 centimeters at the Galápagos Islands, and the thermocline was displaced downward by 50 to 70 meters along the equator and the South American coast.     

Permanent El Niño-like conditions during the Pliocene warm period

During the warm early Pliocene (approximately 4.5 to 3.0 million years ago), the most recent interval with a climate warmer than today, the eastern Pacific thermocline was deep and the average west-to-east sea surface temperature difference across the equatorial Pacific was only 1.5 +/- 0.9 degrees C, much like it is during a modern El Ni?o event. Thus, the modern strong sea surface temperature gradient across the equatorial Pacific is not a stable and permanent feature. Sustained El Ni?o-like conditions, including relatively weak zonal atmospheric (Walker) circulation, could be a consequence of, and play an important role in determining, global warmth.     

2010年8月葫芦岛高频次暴雨的气候背景与环流形势分析

利用常规气象观测资料和国家气候中心的赤道中东太平洋海表温度、850 hPa纬向风距平和副热带高压脊线的数据,使用天气学分析方法,对2010年8月葫芦岛地区高频次暴雨的气候背景及环流形势进行分析。结果表明:2010年7月以来,赤道中东太平洋海表温度较常年同期偏低1.5～2.5℃,快速进入拉尼娜状态;热带地区低层850 hPa赤道中太平洋出现纬向风的强的负趋势,Walker环流有明显增强的正趋势;副高明显偏强,利于西太平洋暖湿的气流沿副高边缘向我国东北地区输送;3次暴雨过程均具有完整的高低空配置,低层辐合、高层辐散,水汽充沛,具有对流不稳定层结。     

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.     

Glacial/interglacial changes in subarctic north pacific stratification

Since the first evidence of low algal productivity during ice ages in the Antarctic Zone of the Southern Ocean was discovered, there has been debate as to whether it was associated with increased polar ocean stratification or with sea-ice cover, shortening the productive season. The sediment concentration of biogenic barium at Ocean Drilling Program site 882 indicates low algal productivity during ice ages in the Subarctic North Pacific as well. Site 882 is located southeast of the summer sea-ice extent even during glacial maxima, ruling out sea-ice-driven light limitation and supporting stratification as the explanation, with implications for the glacial cycles of atmospheric carbon dioxide concentration.     

Cosmogenic chlorine-36 chronology for glacial deposits at bloody canyon, eastern sierra nevada

Deposits from mountain glaciers provide an important record of Quaternary climatic fluctuations but have proved difficult to date directly. A chronology has been obtained for glacial deposits at Bloody Canyon, California, by measurement ofthe accumulation of chlorine-36 produced by cosmic rays in boulders exposed on moraine crests. The accumulation ofchlorine-36 indicates that episodes of glaciation occurred at about 21, 24, 65, 115, 145, and 200 ka (thousand years ago). Although the timing of the glaciations correlates well with peaks of global ice volume inferred from the marine oxygen isotope record, the relative magnitudes differ markedly. The lengths of the moraines dating from 115 ka and 65 ka show that the early glacial episodes were more extensive than those during the later Wisconsin and indicate that the transition from interglacial to full glacial conditions was rapid.     

Warmth of the subpolar north atlantic ocean during northern hemisphere ice-sheet growth

Two 10,000-year periods of Northern Hemisphere continental ice-sheet growth stand out prominently within the last full interglacial-to-glacial cycle. During the first half of each rapid ice-growth phase, the subpolar North Atlantic from 40 degrees N to 60 degrees N maintained warm sea-surface temperatures comparable to those of today's ocean. The juxtaposition at latitudes 50 degrees N to 60 degrees N of an "interglacial" ocean along-side a "glacial" land mass, particularly along eastern North America, is regarded as an optimal configuration for delivering moisture to the growing ice sheets.     

The history of South American tropical precipitation for the past 25,000 years

Long sediment cores recovered from the deep portions of Lake Titicaca are used to reconstruct the precipitation history of tropical South America for the past 25,000 years. Lake Titicaca was a deep, fresh, and continuously overflowing lake during the last glacial stage, from before 25,000 to 15,000 calibrated years before the present (cal yr B.P.), signifying that during the last glacial maximum (LGM), the Altiplano of Bolivia and Peru and much of the Amazon basin were wetter than today. The LGM in this part of the Andes is dated at 21,000 cal yr B.P., approximately coincident with the global LGM. Maximum aridity and lowest lake level occurred in the early and middle Holocene (8000 to 5500 cal yr B.P.) during a time of low summer insolation. Today, rising levels of Lake Titicaca and wet conditions in Amazonia are correlated with anomalously cold sea-surface temperatures in the northern equatorial Atlantic. Likewise, during the deglacial and Holocene periods, there were several millennial-scale wet phases on the Altiplano and in Amazonia that coincided with anomalously cold periods in the equatorial and high-latitude North Atlantic, such as the Younger Dryas.