南海北部陆坡ZSQD196PC柱状样末次间冰期以来的古海洋学记录：氧同位素、有孔虫和硅藻

为了解南海北部陆坡末次间冰期以来的古海洋沉积环境演化特征,对研究区ZSQD196PC柱状样有孔虫、硅藻及有孔虫氧同位素资料开展了分析。依据沉积有孔虫、硅藻主要属种的百分含量、丰度及组合特征,将有孔虫划分为3个组合,分别对应于氧同位素MIS1、2、3~4期;将硅藻划分为4个组合,大致对应于MIS1~4期。MIS1期有孔虫以暖水种占优势,Pulleniatina obliquiloculata百分含量显著升高;硅藻丰度低且以热性种占优势,其中冷期出现大量沿岸种,反映相对温暖的气候条件。MIS2~4期有孔虫以冷水种占优势,温跃层种含量相对较高;硅藻丰度高且以广布种占优势,出现沿岸种含量的升高,反映较冷的气候条件。通过对比浮游有孔虫氧同位素,分析讨论了末次盛冰期、Blling—Allerd暖期和新仙女木事件在ZSQD196PC柱状样的沉积响应,揭示了末次冰期中的气候波动。     

Ecophenotypic responses of benthic foraminifera to oxygen availability along an oxygen gradient in the California Borderland

Spatial variation in environmental conditions can elicit predictable size and morphological responses in marine organisms through influences on physiology. Thus, spatial and temporal variation in marine organism size and shape are often used to infer paleoenvironmental conditions, such as dissolved oxygen concentrations. Benthic foraminifera commonly serve as a tool for reconstructing past ocean oxygen levels. For example, benthic foraminiferal species assemblages, within‐ and among‐species patterns of test morphology, and geochemical analyses of carbonate tests are often employed to reconstruct past marine conditions. In this study, we measured the sizes and shapes of modern foraminifera representing four species that inhabit a steep oxygen gradient in the Santa Monica Basin on the Southern California Borderland with the aim of quantifying the influence of oxygen availability on foraminiferal morphology, both within and among species. Most foraminifera rely on aerobic respiration, but the four benthic foraminifera from the Santa Monica Basin do not show the predicted size and morphological responses to variations in dissolved oxygen concentrations based on first principles of cell physiology: Bolivina spissa shows no volume or volume‐to‐surface area response, Uvigerina peregrina increases in both test volume and volume‐to‐surface area ratio with decreasing dissolved oxygen concentrations, and both Bolivina argentea and Loxostomum pseudobeyrichi decrease in test volume, but only L. pseudobeyrichi shows a decrease in test volume‐to‐surface area ratio with decreasing oxygen concentrations as expected from physiological predictions. These findings imply that the morphological responses of individual foraminiferal species are not necessarily representative of the responses of other foraminiferal species within the community. Our findings further suggest that these species use physiological strategies such as depressed metabolic rates and alternative energy metabolisms to persist in low oxygen environments and, therefore, cannot be used in any simple way as paleo‐oxygen indicators. Should Proterozoic (1,000–542 million years ago) protists have possessed metabolic strategies similar to foraminifera, the sizes and shapes of protists in the fossil record may not usefully constrain ambient oxygen conditions during the appearance and initial taxonomic radiation of heterotrophic eukaryotes.     

Vertical distribution of living mangrove foraminifera from KwaZulu-Natal,South Africa

Modern foraminiferal assemblage zones can be used to reconstruct palaeo sea levels when applied to fossil foraminifera down a sediment core. Previous intertidal foraminiferal studies have predominantly focused on assemblages in surface sediments (0–1 cm), with the rationale that surface assemblages reflect the modern-day environment. Foraminifera live infaunally and therefore there is a need to document the infaunal vertical distribution of living foraminifera to fully capture the modern environment. Infaunal foraminiferal populations may compositionally differ from or be similar to those in the uppermost 1 cm of a core sample, but abundance is variable vertically, making it very complex to reconstruct and interpret past sea levels. This can have implications for the choice of assemblages to use as modern analogues for past sea-level reconstructions. This study documents the vertical infaunal distribution of living foraminifera, to allow for more informed interpretations of palaeo-reconstructions in mangrove environments. The down-core vertical distribution and abundance of living foraminifera, along with grain size and organic content, were documented using sediment cores along an elevational transect. Nine taxa were recorded as living at the time of collection, six of which were restricted to the top 4 cm. The majority of these were calcareous and found in the cores situated closer to the intertidal channel. Therefore, we argue that the diversity of living calcareous and agglutinated foraminifera could be restricted by grain size, with coarser grain sizes associated with lower species diversity. The findings suggest that foraminiferal species inhabiting the top 4 cm represent deeper living foraminiferal populations. Therefore, the top 4-cm interval can be used to establish a modern training set upon which reconstructions can be based. The findings from this study will provide guidance on the use of South African mangrove environments for future sea-level reconstructions.     

Benthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out.The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth.Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough.From continental shelf edge to the bottom of Okinawa Trough,benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages:(1) Continental shelf break assemblage,dominated by Cibicides pseudoungerianus,corresponds to subsurface water mass of the Kuroshio Current;(2) upper continental slope assemblage,dominated by Cassidulina carinata,Globocassidulina subglobosa,corresponds to intermediate water mass of the Kuroshio Current;(3) intermediate continental slope assemblage,dominated by Uvigerina hispida,corresponds to the Okinawa Trough deep water mass above the carbonate lysocline.     

NotesBenthic foraminiferal distribution in surface sediments along continental slope of the southern Okinawa Trough: dependance on water masses and food supply

Benthic foraminiferal analysis of 29 samples in surface sediments from the southern Okinawa Trough is carried out. The results indicate that benthic foraminiferal abundance decreases rapidly with increasing water depth. Percentage frequencies of agglutinated foraminifera further confirm the modern shallow carbonate lysocline in the southern Okinawa Trough. From continental shelf edge to the bottom of Okinawa Trough, benthic foraminiferal fauna in the surface sediments can be divided into 5 assemblages: (1) Continental shelf break assemblage, dominated by Cibicides pseudoungerianus, corresponds to subsurface water mass of the Kuroshio Current; (2) upper continental slope assemblage, dominated by Cassidulina carinata , Globocassidulina subglobosa, corresponds to intermediate water mass of the Kuroshio Current; (3) intermediate continental slope assemblage, dominated by Uvigerina hispi-da, corresponds to the Okinawa Trough deep water mass above the carbonate lysocline; (4) lower continental slope- trough b     

Distribution of benthic foraminifera in Upper Quaternary sediments of the Deryugin Basin (Sea of Okhotsk)

Benthic foraminifera are investigated in sediment core LV28-34-2 (53°51.971′N, 146°47.499′E, sea depth 1431 m, core length 965 cm). The distribution of foraminifera is studied in coarse-grained (>0.125 mm) sediment fractions of 191 samples taken with a step of 5 cm. The core covers the interval from oxygen isotope stage (OIS) 6 up to the Holocene. The foraminiferal assemblages of the penultimate (OIS 6) and last (OIS 5d-2) glaciations are characterized by low abundances and prevalence of Uvigerina auberiana. The specific structure of the OIS 6 assemblages differs from the last glaciation ones by the mass presence of Cassidulina teretis, which characterizes low temperatures and a high influx of organic matter to the sea floor. The major factor responsible for the weak development of benthic foraminifers during the glacial time is the deficiency of food resources. The foraminiferal assemblage of the interglacial optimum (OIS 5e) is composed of both calcareous and agglutinated species (Martinottiella communis).The inflow of Pacific waters was probably more intensive, the bioproductivity was higher, and the critical carbonate compensation depth was shallower at that time than during the glaciations. During the deglaciation, the quantity and structure of the foraminiferal assemblages reflected two pulses of warming (terminations 1B and 1A) with an intervenient cooling event (Younger Dryassic). The assemblages of warm periods were characterized by exclusively high foraminiferal abundances, which sharply decreased during the Younger Dryassic cooling. The specific structure of the foraminiferal assemblage during deglaciation was relatively uniform, being composed of only calcareous taxa typical of highly productive areas of the ocean. The paleoenvironmental conditions were similar to the conditions of the interglacial optimum (OIS 5e), although the preservation of calcareous tests is better. In the Holocene sediments, the concentration of benthic foraminifera is substantially lower than during the deglaciation, which is explainable by their dilution in the sediments by diatoms; the composition of the foraminiferal assemblages is similar to that of their glacial counterparts.     

Benthic foraminifera for heavy metal pollution monitoring: A case study from the central Adriatic Sea coast of Italy

Benthic foraminifera are increasingly used as environmental bio-indicators of pollution in coastal and marginal marine settings. Their community structure provides information on the general characteristics of the environment and some species are sensitive to specific environmental parameters. Among various criteria, the occurrence of test abnormalities may represent a useful bioindicator for monitoring environmental impacts in coastal regions. A study of living benthic foraminifera was carried out in 42 sediment samples collected from the central Adriatic coast of Italy. Benthic foraminiferal assemblages from this area are rich, well preserved, and dominated by Ammonia parkinsoniana, and subordinately by Ammonia tepida, Aubignyna perlucida, Eggerella scabra, and Nonionella turgida. Heavy metal concentrations have been analysed which indicate low polluted environmental conditions. Foraminiferal species and heavy metal concentrations were investigated both with bivariate (correlation matrix) and multivariate techniques of principal component analysis (PCA) and cluster analysis. Statistical analysis shows a possible control of these pollutants both on the taxonomic composition of the benthic foraminiferal assemblages and the development of test malformations. Increasing heavy metal contents lead to an increase in relative abundance of A. tepida A. perlucida, N. turgida and E. scabra, and a relative concurrent decrease in relative abundance of A. parkinsoniana and higher percentages of deformed specimens (FAI) and species (FMI). Our results confirm that A. parkinsoniana prefers clean to low polluted environments and show that it is a very sensitive and un-tolerant species to heavy metal pollution being deeply affected by heavy metal content even at low concentrations. Our findings also confirm the capacity of the A. tepida to tolerate increasing heavy metal concentrations, and highlights that A. perlucida, N. turgida and E. scabra can be considered as tolerant species at least in low polluted environments. Following this, A. parkinsoniana and A. tepida can be reciprocally considered good bioindicator of heavy metal pollution over the surveyed area. The development of test abnormalities with a variety of malformations is a noticeable feature over the study area where the living deformed assemblages are largely dominated by a few species. The low percentages of deformed specimens (Foraminiferal Abnormality Index up to 4.7, with 2 on average) match well with the low concentrations of heavy metals that lead to low polluted environmental conditions. This study confirms and supports the suitability of studying benthic foraminifera as a technique for the in situ continuous bio-monitoring of heavy metal pollution of coastal marine sediments.     

Foraminiferal evidence for a pre‐middle eocene age of the chatham rise,New Zealand

Several sediment samples collected from the crest and slope of the Chatham Rise, and from the Chatham Islands, to the east of New Zealand, contain Globigerina linaperta‐Globorotalia increbescens foraminiferal faunas of upper Middle and middle Upper Eocene age. The foraminiferal faunas from the Chatham Islands, which include Rectuvigerina, Latibolivina, Dyocibicides, Discorbinella, Patellina, and Wadella, indicate shallow‐water palaeodepths, probably equivalent to the outer shelf (50–150 m). A faunal assemblage from near the crest of the rise is likewise indicative of shallow water, although distinct differences in the benthonic foraminiferal ifauna suggest slightly deeper‐water biofacies than the Eocene of the Chatham Islands. In contrast, a fauna of similar age from 1,100 m on the southern slope of the Chatham Rise contains a much deeper‐water benthonic foraminiferal assemblage including Osangularia, Vulvulina, Stilostomella, hispidocostate Uvigerina, and smooth‐shelled Bulimina, indicative of lower middle bathyal depths (1,500–2,500 m).

The nature and distribution of the assemblages, together with previous work by Norris (1964) and Cullen (1965), indicates that the Chatham Rise has been a significant structure since at least the Middle Eocene, with some uplift occurring since then.     

Holocene and Pleistocene dissolution cycles in deep-sea cores of Baffin Bay and Davis Strait: Palaeoceano-graphic implications

Calcium-carbonate dissolution has been studied in several grab samples and piston cores from Baffin Bay and Davis Strait ranging in water depth from 200 to 2300 m. The intensity of dissolution was determined from examining: (1) the ratio of arenaceous to calcareous benthonic foraminifera; (2) the ratio of benthonic to planktonic foraminifera; (3) the relationships between the dissolution-susceptible and dissolution-resistant foraminifera; (4) the degree of foraminiferal test fragmentation; and (5) the relationships between plankton tows and the fauna in the surface sediments. All core tops and grab samples from Baffin Bay surface sediments below 600–900 m water depth demonstrated intense dissolution of calcium carbonate. Sediments below 900 m were biogenic carbonate free, indicating 100% foraminiferal loss due to dissolution. Possible causes of substantial undersaturation in calcium carbonate of Baffin Bay Bottom Water are very low temperatures, and higher concentrations of carbon dioxide. All cores also demonstrated intense dissolution during interglacial or interstadial isotope stages 1, 3, 5, 7 and 9. Similarities in planktonic foraminiferal assemblages suggested the presence of similar bottom-water masses during these periods. The preservation state of biogenic carbonate debris in glacial isotope stages 2, 4, 6, 8 and 10 is similar to the assemblage found in the water at present.     

Beta diversity of tropical marine benthic assemblages in the Spermonde Archipelago, Indonesia

In order to preserve diversity it is essential to understand how assemblages change across space. Despite this fact, we still know very little about how marine diversity is spatially distributed, especially among lesser‐studied invertebrate taxa. In the present study beta‐diversity patterns of sea urchins, sponges, mushroom corals and larger foraminifera were assessed in the Spermonde Archipelago (Indonesia). Using ordinations we showed that the inshore zone (<5 km offshore), midshore zone (5 < x < 30 km offshore) and distance offshore zone (>30 km offshore) all contained distinct assemblages of sponges and corals, while only foraminifera assemblages from the inshore (<5 km offshore) zone were distinct. There was a significant spatial pattern of community similarity for all taxa surveyed, but this pattern proved to be wholly related to environmental variables for sponges and foraminifera, and primarily for mushroom corals and sea urchins. The lack of a pure spatial component suggests that these taxa may not be dispersal limited within the spatial scales of this study (c. 1600 km²). The analyses of the corals and foraminifera were additionally tested at two spatial scales of sampling. Both taxa were primarily associated with local‐scale environmental variables at the local scale and larger‐scale variables at the larger scale. Mean inter‐plot similarity was also higher and variation lower at the larger scale. The results suggest that substantial variation in similarity can be predicted using simple locally assessed environmental variables combined with remotely sensed parameters.     

Distribution patterns of living benthic foraminifera from Cap Breton canyon,Bay of Biscay: Faunal response to sediment instability

Analysis of living (Rose Bengal-stained) benthic foraminifera in 13 multicorer samples taken along the Cap Breton canyon (Bay of Biscay) revealed that the combination of organic-rich material and sediment instability provides very specific benthic ecosystem conditions. The active canyon hosts different foraminiferal assemblages that appear to be determined by different types and frequencies of environmental disturbance at the sites. Most of them are strongly dominated by shallow-infaunal living taxa that combine a tolerance for low-quality organic matter with a high reproductive potential. Foraminiferal assemblages characterized by high densities, very superficially living taxa and strong dominance of bolivinids and buliminids, follow a poor pioneer fauna dominated by Technitella melo. These assemblages are observed in the narrow canyon axis, where frequent sediment resuspension occurs and affects habitat stability. Assemblages studied from sites outside the canyon axis are still dominated by shallow-infaunal species but show lower foraminiferal densities and higher diversities. Deep-infaunal taxa are only present in some inner meanders and more distal stations. These assemblages are typical for ecological niches that are relatively stable and unaffected by re-sedimentation processes. They have attained a more advanced stage of ecosystem stability. They are influenced by neither lateral sediment nor enriched organic matter input.     

Influence of the hydrothermal vents on the distribution of benthic foraminifera from the Guaymas Basin,Mexico

The distribution and composition of four benthic foraminifera assemblages from the Guaymas Basin are depicted through Q- and R-mode Factor Analysis. One of these assemblages is distributed near hydrothermal vents,* another developed away from the influence of the vents, and the other two assemblages are found in the subbottom sediments.Biostratigraphic analysis of five cores collected within the hydrothermal region suggest that the foraminiferal remains have been affected by aselective dissolution process. Only small species, such asBulimina spinosa andBolivina sp 2, have been preserved in the subbottom sediments which have been influenced by the hydrothermal activity.     

Foraminifera from the continental slope off Cape Hatteras, North Carolina

The recent benthic meiofaunal foraminiferal assemblage from the continental slope (590-2 003 m) off Cape Hatteras, North Carolina exhibits high species richness and evenness, moderate diversity values, and lacks numerically dominant species. The preserved planktic assemblage has relatively low species richness, high evenness, low diversity, and a few numerically dominant species. Approximately 9% of the benthic species are those that typically live within continental shelf depth ranges. The benthic assemblage abundances and diversities do not follow depth patterns or geophysical characteristics. No biogeographic boundary can be described within the study area for meiofaunal foraminifera. Oxygen limitation does not appear to be a factor affecting the benthos of the North Carolina continental slope based upon the community structure of the benthic foraminifera, if total assemblage is assumed to reflect the recently living community. The high carbonate content of sediments in the area may be explained by foraminiferal tests. Within the study area, the foraminiferal assemblages are uniform, and probably reflect relative consistency of primary environmental variables as well as dynamic downslope transport and high influx of material from the water column in the vicinity where the Gulf Stream and the Western Boundary Undercurrent cross.     

The response of benthic foraminifera and ostracoda to heavy metal pollution in Gulf of Izmir (Eastern Aegean Sea)

Benthic foraminifera can be used as environmental bioindicators, especially in polluted environments where their sensitivity to pollutants may be expressed by a modification in the assemblage. Nineteen sediment samples were collected in November 2002 from surficial sediments of the Gulf of Izmir (Turkey). The Gulf of Izmir is located in Western Turkey and surrounded by a densely populated community. The gulf has been contaminated by numerous heavy metals, but geochemical analyses have shown that metals are significant pollutants only in the inner part of the gulf. Outer and Middle Sections showed low levels of heavy metals, except the estuary of Gediz River. Eight heavy metals have been analyzed in all the sampling points. Sixty-seven foraminifer and 22 ostracod species were identified in 16 sediment samples. Statistical analysis shows that there is a significant correlation between foraminifera species and heavy metals. The most polluted Inner Sections are dominated by the tolerant species Ammonia tepida that may be used as pollution indicator. The gradient observed in heavy metal concentrations between the Outer and Inner Sections has a prevalent influence on the foraminiferal distribution. There is a gradient of the number of species, increasing from the Inner Section toward the Outer Section. The occurrence of test abnormalities among foraminifera may represent a useful biomarker for evaluating long-term environmental impacts in a coastal region.     

Deep-sea reef fish assemblage patterns on the Blake Plateau(Western North Atlantic Ocean)

Deep‐water coral habitats are scattered throughout slope depths (360–800 m) off the Southeastern United States (SEUS, Cape Lookout, North Carolina, to Cape Canaveral, Florida), contributing substantial structure and diversity to bottom habitats. In some areas (e.g. off North Carolina) deep corals form nearly monotypic (Lophelia pertusa) high profile mounds, and in other areas (e.g. off Florida) many species may colonize hard substrata. Deep coral and hard substrata ecosystems off the SEUS support a unique fish assemblage. Using the Johnson‐Sea‐Link submersible (in 2000–2005, 65 dives), and a remotely operated vehicle (in 2003, five dives), fishes were surveyed in nine deep reef study areas along the SEUS slope. Forty‐two benthic reef fish species occurred in deep reef habitats in these study areas. Species richness was greatest on the two coral banks off Cape Lookout, North Carolina (n = 23 and 27 species) and lowest on the two sites off Cape Canaveral, Florida (n = 7 and 8 species). Fish assemblages exhibited significantly (ANOSIM, Global R = 0.69, P = 0.001) different patterns among sites. Stations sampled off North Carolina (three study areas) formed a distinct group that differed from all dives conducted to the south. Although several species defined the fish assemblages at the North Carolina sites, Laemonema barbatulum, Laemonema melanurum, and Helicolenus dactylopterus generally had the most influence on the definition of the North Carolina group. Fish assemblages at three sites within the central survey area on the Blake Plateau were also similar to each other, and were dominated by Nezumia sclerorhynchus and L. melanurum. Synaphobranchus spp. and Neaumia sclerorhynchus differentiated the two southern sites off Cape Canaveral, Florida, from the other station groups. Combinations of depth and habitat type had the most influence on these station groups; however, explicit mechanisms contributing to the organization of these assemblages remain unclear.     

Foraminifera in surface sediments of the Bering and Chukchi Seas and their sedimentary environment

Based on a quantitative analysis of foraminifera in 39 surface samples of the Bering andChukchi Seas, the nearly absence of planktonic foraminifera in the surface sediments can be related to the low surface primary productivity and strong carbonate dissolution in the study area. It has been revealed that the surface primary productivity, and carbonate dissolution and properties of water masses related to the water depth mainly control the distribution of benthic foraminifera. The shelf of the Chukchi Sea is dominated by the Elphidium spp. assemblage and Nonionella robusta assemblage with low foraminiferal abundance and diversity, which is controlled by the coastal water mass of the Arctic Ocean. The slope of the Bering Sea is dominated by the Uvigerina peregrina - Globobulimina affinis assemblage with abundant N. robusta, and relatively high foraminiferal abundance and diversity, which is controlled by the intermediate and deep water masses of the Pacific Ocean. However, the Bering Sea has relatively sha     

白令海和楚科奇海表层沉积中的有孔虫及其沉积环境

通过对白令海和北冰洋楚科奇海39个表层沉积样品中有孔虫的定量分析,发现表层沉积中浮游有孔虫稀少可能与该区表层生产力低、碳酸盐溶解作用较强有关,而底栖有孔虫的分布则主要受表层初级生产力以及与水深相关的碳酸盐溶解作用和水团性质所控制,其中北冰洋楚科奇海陆架区有孔虫以Elphidium spp.组合和Nonionella robusta组合为主,丰度和分异度低,受北冰洋沿岸水团控制;白令海陆坡区有孔虫以Uvigerina peregrina-Globobulimina affinis组合为主,含N.robusta较多,丰度和分异度相对高,受太平洋中层和深层水团控制,但该区碳酸盐溶跃层和补偿深度(CCD)相对浅,约分别位于2000和3800m处.此外,白令海陆坡上部表层沉积中含有北冰洋陆坡区典型深水底栖有孔虫种Stetsonia arctica,说明白令海峡两侧的海区曾有深部水交流.     

天津市潮滩活体和埋藏有孔虫群的分布及地质环境意义

对天津市潮滩8条垂直于海岸线剖面的57个表层沉积物样品进行了活体和死体有孔虫分析鉴定、粒度分析、含盐量测定,利用全站仪对剖面进行了水准测量,同时测定了海水盐度。研究了天津市潮滩有孔虫群的组成、数量及分异度等特征;通过聚类分析将天津市潮滩活体有孔虫群分为7个带,埋藏有孔虫群(活体+死体)分为5个带,但除了埋藏群Ⅰ、Ⅳ与活体有孔虫群Ⅰ、Ⅳ组合特征一致外,其他各带的组合特征及分带界线均不一致。通过分析活体有孔虫群分带与沉积物含盐量、海水盐度、潮位、沉积物组成等生态环境参数的关系,探讨了活体有孔虫群的主要控制因素;通过分析埋藏有孔虫群分带与潮位、沉积物粒径、现代沉积速率等沉积环境参数的关系,探讨了埋藏有孔虫群的搬运及沉积作用。指出了天津市海岸带活体有孔虫群和埋藏有孔虫群的关系、环境特征及地质意义,为该区高精度的古沉积环境划分提供了重要指标。     

Late Quaternary variations in calcium carbonate preservation of deep-sea sediments in the northern Cape Basin: results from a multiproxy approach

In this study, we test various parameters in deep-sea sediments (bulk sediment parameters and changes in microfossil abundances and preservation character) which are generally accepted as indicators of calcium carbonate dissolution. We investigate sediment material from station GeoB 1710-3 in the northern Cape Basin (eastern South Atlantic), 280 km away from the Namibian coast, well outside today’s coastal upwelling. As northern Benguela upwelling cells were displaced westward and periodically preceded the core location during the past 245 kyr (Volbers et al., submitted), GeoB 1710-3 sediments reflect these changes in upwelling productivity. Results of the most commonly used calcium carbonate dissolution proxies do not only monitor dissolution within these calcareous sediments but also reflect changes in upwelling intensity. Accordingly, these conventional proxy parameters misrepresent, to some extent, the extent of calcium carbonate dissolution. These results were verified by an independent dissolution proxy, the Globigerina bulloides dissolution index (BDX′) (Volbers and Henrich, submitted). The BDX′ is based on scanning electronic microscope ultrastructural investigation of planktonic foraminiferal tests and indicates persistent good carbonate preservation throughout the past 245 kyr, with the exception of one pronounced dissolution event at early oxygen isotopic stage (OIS) 6.

The early OIS 6 is characterized by calcium carbonate contents, sand contents, and planktonic foraminiferal concentrations all at their lowest levels for the last 245 kyr. At the same time, the ratio of radiolarian to planktonic foraminiferal abundances and the ratio of benthic to planktonic foraminiferal tests are strongly increased, as are the rain ratio, the fragmentation index, and the BDX′. The sedimentary calcite lysocline rose above the core position and GeoB 1710-3 sediments were heavily altered, as attested to by the unusual accumulation of pellets, aggregates, sponge spicules, radiolaria, benthic foraminifera, and planktonic foraminiferal assemblages.

Solely the early OIS 6 dissolution event altered the coarse fraction intensely, and is therefore reflected by all conventional calcium carbonate preservation proxies and the BDX′. We attribute the more than 1000 m rise of the sedimentary calcite lysocline to the combination of two processes: (a) a prominent change in the deep-water mass distribution within the South Atlantic and (b) intense degradation of organic material within the sediment (preserved as maximum total organic carbon content) creating microenvironments favorable for calcium carbonate dissolution.     

台湾海峡西部海域底质柱状样中有孔虫特征及其环境意义

本文通过对台湾海峡西部海域7个柱状样计79块样品中的有孔虫分析,阐述了海峡柱样中有孔虫组合及其特征,并由此讨论台湾海峡西部海域晚更新世以来的沉积环境。