Planktonic Foraminiferal and Alkenone Records of the Last Deglaciation from the Eastern Arabian Sea     

Olivia Cayre  Edouard Bard 《Quaternary Research》1999,52(3):337

The oxygen isotope record of planktonic foraminifera from tropical core MD77194 (Eastern Arabian Sea) exhibits a clear two-step deglaciation with a brief δ¹⁸O transient event. In the tropics, this δ¹⁸O maximum could correspond to a cooling or to a change in the δ¹⁸O content of sea water. In this study, past sea-surface temperature (SST) and primary production (PP) are reconstructed from foraminiferal transfer functions and compared to values estimated from alkenone measurements. SST and PP records from both proxies indicate a 1.5–2.5°C deglacial warming, coupled with a PP decrease, and a 0.5–1°C cooling during the Younger Dryas (YD). A detailed comparison between independent micropaleontological and geochemical proxies helps us identify potential biases and thus strengthen the paleo-reconstructions.  相似文献   

Middle and Late Holocene Sea-Level Changes in Eastern Maine Reconstructed from Foraminiferal Saltmarsh Stratigraphy and AMS C Dates on Basal Peat     

W. Roland Gehrels 《Quaternary Research》1999,52(3):350

A relative sea-level history is reconstructed for Machiasport, Maine, spanning the past 6000 calendar years and combining two different methods. The first method establishes the long-term (10³ yr) trend of sea-level rise by dating the base of the Holocene saltmarsh peat overlying a Pleistocene substrate. The second method uses detailed analyses of the foraminiferal stratigraphy of two saltmarsh peat cores to quantify fluctuations superimposed on the long-term trend. The indicative meaning of the peat (the height at which the peat was deposited relative to mean tide level) is calculated by a transfer function based on vertical distributions of modern foraminiferal assemblages. The chronology is determined from AMS ¹⁴C dates on saltmarsh plant fragments embedded in the peat. The combination of the two different approaches produces a high-resolution, replicable sea-level record, which takes into account the autocompaction of the peat sequence. Long-term mean rates of sea-level rise, corrected for changes in tidal range, are 0.75 mm/yr between 6000 and 1500 cal yr B.P. and 0.43 mm/yr during the past 1500 years. The foraminiferal stratigraphy reveals several low-amplitude fluctuations during a relatively stable period between 1100 and 400 cal yr B.P., and a sea-level rise of 0.5 m during the past 300 years.  相似文献   

Seasonal Response of Planktonic Foraminifera to Surface Ocean Condition: Sediment Trap Results from the Central North Pacific Ocean     

Nobuhisa O. Eguchi  Hodaka Kawahata  Asahiko Taira 《Journal of Oceanography》1999,55(6):681-691

The fluxes of planktonic foraminifera (calcareous shell producing zooplankton) were examined in order to clarify temporal and regional variations in production in the upper ocean in relation to hydrographic conditions. Three time-series sediment traps were deployed in the central North Pacific along 175°E for about one year, beginning in June 1993. Trap sites were located in the subarctic, the transition, and the subtropical water masses, from north to south. The southernmost site was under the influence of the transition zone in January to May. Both temporal and regional fluxes of planktonic foraminifera showed large variations during the experiment. In the subarctic water mass, high total foraminiferal fluxes (TFFs) and high organic matter fluxes (OMFs) were observed during summer to fall, suggesting that food availability is the most important factor for the production of planktonic foraminifera. Furthermore, low TFFs during winter were ascribed to low food availability and low temperatures. The OMFs and TFFs correlated well and increased rapidly after the disruption of the seasonal thermocline during winter, peaking in late February to early March in the transition zone. In the subtropical water mass, both OMFs and TFFs remained low due to lower productivity under oligotrophic conditions. In general, TFFs show a positive correlation with OMFs during the trap experiment, suggesting that food availability is one of the factors controlling the production of planktonic foraminifera in the central North Pacific. Relatively low TFFs during summer to fall in the subtropical water mass may be caused by the thermal structure of the upper ocean. Low SST possibly reduces the production of foraminifera during winter in the subarctic region.  相似文献   

冲绳海槽北部陆坡4.4万年以来古海洋环境演化的地质记录     

向荣  李铁刚  阎军 《海洋地质与第四纪地质》2005,25(1):71-78

利用AMS^14 C年代测试、氧同位素分析和浮游有孔虫分析重建了冲绳海槽北部陆坡DOC-42孔约44cal．kaBP以来的古海洋环境演化记录。DOC-42孔沉积速率整体较低，呈明显的阶段性变化：在氧同位素3期和LGM期间沉积速率相对较大，分别为7．3和14cm／ka；末次冰消期以来的沉积速率则显著降低，与冲绳海槽冰后期沉积速率高于末次冰期明显不同；自约6．4cal．kaBP以来，沉积物堆积作用基本可以忽略，表明了受黑潮入侵引起的中国东部陆架环流体系的改变，岩心所在区域的沉积格局发生了重大变化。浮游有孔虫氧碳同位素、转换函数古温度和低温、低盐特征种Globigerina quinqueloba等一致反映了冲绳海槽北部在氧同位素3期早期约37．5～44cal．kaBP期间存在明显的低温、低盐阶段，表明该期间冲绳海槽北部的沿岸冲淡水影响明显加强，而在氧同位素3期晚期该区可能受到了黑潮暖流的影响。此外，浮游有孔虫Pulleniatina obliquiloculata与氧同位素记录有很好的对应关系，表明它是冲绳海槽末次冰期以来的一个可靠的海洋环境指标。  相似文献   

New coring study in Augusta Bay expands understanding of offshore tsunami deposits (Eastern Sicily,Italy)     

Alessandra Smedile  Flavia Molisso  Catherine Chagué  Marina Iorio  Paolo Marco De Martini  Stefania Pinzi  Philip E. F. Collins  Leonardo Sagnotti  Daniela Pantosti 《Sedimentology》2020,67(3):1553-1576

Tsunami deposits present an important archive for understanding tsunami histories and dynamics. Most research in this field has focused on onshore preserved remains, while the offshore deposits have received less attention. In 2009, during a coring campaign with the Italian Navy Magnaghi, four 1 m long gravity cores (MG cores) were sampled from the northern part of Augusta Bay, along a transect in 60 to 110 m water depth. These cores were taken in the same area where a core (MS06) was collected in 2007 about 2·3 km offshore Augusta at a water depth of 72 m below sea level. Core MS06 consisted of a 6·7 m long sequence that included 12 anomalous intervals interpreted as the primary effect of tsunami backwash waves in the last 4500 years. In this study, tsunami deposits were identified, based on sedimentology and displaced benthic foraminifera (as for core MS06) reinforced by X-ray fluorescence data. Two erosional surfaces (L1 and L2) were recognized coupled with grain-size increase, abundant Posidonia oceanica seagrass remains and a significant amount of Nubecularia lucifuga, an epiphytic sessile benthic foraminifera considered to be transported from the inner shelf. The occurrence of Ti/Ca and Ti/Sr increments, coinciding with peaks in organic matter (Mo incoherent/coherent) suggests terrestrial run-off coupled with an input of organic matter. The L1 and L2 horizons were attributed to two distinct historical tsunamis (ad 1542 and ad 1693) by indirect age-estimation methods using ²¹⁰Pb profiles and the comparison of Volume Magnetic Susceptibility data between MG cores and MS06 cores. One most recent bioturbated horizon (Bh), despite not matching the above listed interpretative features, recorded an important palaeoenvironmental change that may correspond to the ad 1908 tsunami. These findings reinforce the value of offshore sediment records as an underutilized resource for the identification of past tsunamis.  相似文献   

Development of a foraminifera-based transfer function in the Basque marshes, N. Spain: Implications for sea-level studies in the Bay of Biscay     

Eduardo Leorri  Benjamin P. Horton  Alejandro Cearreta 《Marine Geology》2008,251(1-2):60-74

In order to reconstruct former sea level we have developed a foraminifera-based transfer function using three models based on a modern dataset of 59 samples and 23 species obtained from four Basque marshes in Northern Spain. The relationship between observed and foraminifera-predicted elevation illustrated the strong performance of the transfer function (r²_jack ranges from 0.74 to 0.81). These results indicated that precise reconstructions of former sea levels are possible (error ranges from 0.11 to 0.19 m). The transfer function was used to calibrate the foraminiferal assemblages collected from a 50 cm salt marsh core. We placed the foraminifera-based reconstructions into a temporal framework using ¹³⁷Cs, Pb concentrations, and ²¹⁰Pb-derived sediment accumulation rates. The resulting relative sea-level curve is in good agreement with regional tide-gauge data. Both instrumental data and microfossil records suggest a rate of relative sea-level rise of approximately 2 mm yr^− 1 for the 20th century.  相似文献   

The ecology of benthic foraminifera across the Frisian Front, southern North Sea   总被引：1，自引：0，他引：1  

L.J. de Nooijer  I.A.P. Duijnstee  M.J.N. Bergman  G.J. van der Zwaan   《Estuarine, Coastal and Shelf Science》2008,78(4):715-726

Benthic foraminifera were collected across the Frisian Front, a biologically enriched transition-zone with high organic matter content below a tidal-mixing front in the southern North Sea. On four occasions between 2002 and 2005, box-cores from different hydrographic regimes (i.e. tidally mixed, frontal and stratified) at depths between 30- and 45-m deep were sampled. The results indicate that standing stocks and foraminiferal diversity are higher in the central zone of the Frisian Front than further away from the frontal zone. Most of the abundant species occupy a specific zone relative to the front's central position. Elphidium excavatum is abundant at the southern edge of the Frisian Front, where input of labile organic matter is high and physical disturbance (i.e. resuspension of fine-grained material) is relatively frequent. Ammonia tepida and Quinqueloculina spp. dominate at the front's center where organic carbon input is relatively high. Hopkinsina pacifica has its highest abundances at the deepest, northerly boundary of the front, and Eggerella scabra dominates the deeper, seasonally stratified Oyster Grounds north of the front. Differences in seasonal distribution patterns were minor compared to spatial patterns. Depth distributions varied between summer (more ‘epifaunal’ distribution) and winter (vertically more evenly distributed). The latter suggests that the vertical distribution of foraminifera is governed by the arrival of fresh organic matter at the seafloor in spring and summer. A comparison with foraminiferal abundances across the Frisian Front in 1988/1989 reveals that total abundances and distribution of the most abundant species were similar in both data sets, despite a macrobenthic regime shift at the Frisian Front in the early 1990s. The decoupled dynamics of foraminifera and macrofauna suggests that foraminifera reflect reliably the hydrodynamic environment (stratified, frontal, mixed), despite the changed macrofaunal community and its physical and geochemical consequences.  相似文献   

Chronology of the sedimentary processes during the postglacial sea level rise in two estuaries of the Algarve coast,Southern Portugal     

T. Boski  S. Camacho  D. Moura  W. Fletcher  A. Wilamowski  C. Veiga-Pires  V. Correia  C. Loureiro  P. Santana 《Estuarine, Coastal and Shelf Science》2008

Four profiles of estuarine sediments obtained from boreholes drilled in the Algarve, Southern Portugal were studied in order to reconstruct the process of sediment accumulation driven by the postglacial sea level rise. In addition to the sedimentological analysis, the Foraminifera Index of Marine Influence (FIMI) permitted assessment of the nature and organization of sedimentary facies in the Beliche–Guadiana and Gilão–Almargem estuaries. The Beliche–Guadiana CM5 and Almargem G2 profiles accumulated in a sheltered environment, with the former presenting an almost continuous record of the sea level rise since ca 13?000 cal yr BP. The G1 and G3 profiles from the Gilão–Almargem area represent a more discontinuous record of the last 8000 years, which accumulated in the more dynamic environment of an outer estuary. The integration of all radiocarbon ages of dated levels, led to an estimate of sediment accumulation rates. Assuming a constant position of the sediment surface with respect to the tidal range and a negligible compaction of sediment, the sea level rose at the rate of 7 mm yr⁻¹ in the period from 13?000 to 7500 cal yr BP. This process slowed down to ca 0.9 mm yr⁻¹ from 7500 cal yr BP until the present. The marked historical change in the rate of sediment accumulation in these estuaries also occurred with the accumulation of organic matter and is, therefore, important data for global biogeochemical models of carbon. The main obstacle to obtain higher temporal resolution of the sedimentary processes was the intense anaerobic respiration of organic matter via sulphate reduction, which did not allow any accumulation of peat and, furthermore, led to erasure of the palaeontological record by acid formed from the subsequent oxidation of sulphides.  相似文献   

微体古生物微型计算机辅助研究系统   总被引：1，自引：1，他引：0  

郝诒纯  万世基  雷新华 《现代地质》1989,3(4):369

微体古生物微型计算机辅助研究系统是一个包括古生物化石属种数据厍、图象库、图象处理和数据采集系统以及定量分析系统在内的综合性古生物数据处理系统。其中,数据库和图象库的主要作用在于辅助化石鉴定。目前数据库和图象库包括了新生代浮游有孔虫1036个种的文字和图象资料。数据库和定量分析系统之间的数据传送非常方便,实现了对大批量古生物数据的定量分析,包括聚类分析、因子分析、瓦格纳网络分析、个体发育分析以及各种统计方法,这些分析程序都配制了相应的绘图功能,使分析结果能以直观的形式输出。定量分析有助于我们对一些“同物异名”和“异物同名”问题的厘定,并由此产生对分类问题的一些新认识。同时,定量分析有助于从定量的角度考查新生代浮游有孔虫的整体变化。  相似文献   

Thermocline fluctuations in the western tropical Indian Ocean during the past 35 ka          下载免费PDF全文

NADINE RIPPERT  KARL‐HEINZ BAUMANN  JÜRGEN PÄTZOLD 《第四纪科学杂志》2015,30(3):201-210

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