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Planktic foraminiferal sedimentation and the marine calcite budget
Full text linkThe vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal CaCO3 budget is presented. Test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples. Modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget, highlighting the importance of ecological, autecological (e.g., reproduction), and biogeochemical conditions that determine the presence or absence of species. To complete the open-marine, particulate CaCO3 inventory, the contribution of coccolithophores, pteropods, and calcareous dinophytes is discussed. Based on the studied regions, the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1.3–3.2 Gt yr?1, equivalent to 23–56% of the total open marine CaCO3 flux. The preservation of tests varies on a regional and temporal scale, and is affected by local hydrography and dissolution. During most of the year (off-peak periods), many tests dissolve above 700-m water depth while settling through the water column, with on average only 1–3% of the initially exported CaCO3 reaching the deep-seafloor. Pulsed flux events, mass dumps of fast settling particles, yield a major contribution of tests to the formation of deep-sea sediments. On average, ?25% of the initially produced planktic foraminiferal test CaCO3 settles on the seafloor. The total planktic foraminiferal contribution of CaCO3 to global surface sediments amounts to 0.36–0.88 Gt yr?1, ?32–80% of the total deep-marine calcite budget
Interannual variability of planktic foraminiferal populations and test flux in the eastern North Atlantic Ocean
Full text linkPlanktic foraminiferal assemblages vary in response to seasonal fluctuations of hydrographic properties, between water masses, and after periodical changes and episodic events (e.g. reproduction, storms). Distinct annual variability of the planktic foraminiferal flux is also known from sediment trap data. In this paper we discuss the short-term impacts on interannual flux rates based on data from opening–closing net hauls obtained between the ocean surface and 500 m water depth. Data were recorded during April, May, June, and August at around 47°N, 20°W (BIOTRANS) in 1988, 1989, 1990, 1992, 1993, and during May 1989 and 1992 at 57°N, 20–22°W. Species assemblages closely resemble each other when comparing the mixed layer fauna with the fauna of the upper 100 m and the upper 500 m of the water column. In addition, species assemblages >100 ?m are almost indistinguishable from assemblages that are >125 ?m in test size. The standing stock of planktic foraminifers at BIOTRANS can vary by more than one order of magnitude over different years; however, species assemblages may be similar when comparing corresponding seasons. Early summer assemblages (June) are distinctly different from late summer assemblages (August). Significant variations in the species composition during spring (April/May) are independent of the mixed layer depth. Spring assemblages are characterized by high numbers of Globigerinita glutinata. In particular, day-to-day variations of the number of specimens and in species composition may have the same order of magnitude as interannual variations. This appears to be independent of the reproduction cycle. Species assemblages at 47°N and 57°N are similar during spring, although surface water temperatures and salinities differ by up to 10°C and 0.7 (PSU). We suggest that the main factors controlling the planktic foraminiferal fauna are the trophic properties in the upper ocean productive layer.Planktic foraminiferal carbonate flux as calculated from assemblages reveals large seasonal variations, a quasi-annual periodicity in flux levels, and substantial differences in timing and magnitude of peak fluxes. At the BIOTRANS station, the average annual planktic foraminiferal CaCO3 fluxes at 100 and 500 m depth are estimated to be 22.4 and 10.0 gm?2 yr?1, respectively
Planktic foraminifers and hydrography of the eastern and northern Caribbean Sea
Full text linkThe distribution of living planktic foraminifers and their relation to the hydrography of the Caribbean Sea was investigated in plankton net tows and surface sediment samples taken along the Antilles island arc during April/May 1996. The planktic foraminiferal community was strongly influenced by spatial variations in salinity that were largely due to the influx of Orinoco River water into the southeastern Caribbean Sea and inflowing Sargasso Sea water in the north. Along the Antilles island arc, Globigerinoides ruber was the dominant species in the surface waters throughout. In the southeastern Caribbean Sea, where Orinoco River outflow influences the planktic community, standing stocks of planktic foraminifers (>100 ?m) between 4 and 50 specimens m?3 were medium to low. The southeastern faunas between Tobago and Guadeloupe were characterized by increased proportions of Neogloboquadrina dutertrei. Highest standing stocks of 159 specimens m?3 in the upper 20 m of the water column were recorded in the northeastern Caribbean Sea and the assemblages were characterized by high proportions of Globigerinita glutinata, associated with cyclonic eddies. In the Anegada Passage, where Sargasso Sea water flows into the Caribbean Sea, low standing stocks of 18 specimens m?3 indicate oligotrophic conditions. Together with the oligotrophic surface waters, the Subtropical Underwater enters the Caribbean Sea through the Anegada Passage in water depths between 100 and 300 m. These waters are characterized by higher concentrations of Globorotalia truncatulinoides relative to the adjacent water masses. Comparison of the living planktic foraminiferal fauna with empty test assemblages from the water column and from surface sediments shows that differences in the faunal composition mostly correspond to the distribution of water masses and to the differential dissolution of species. In the vicinity of islands Globigerinoides ruber reaches higher relative frequencies than in the open ocean, pointing towards a higher tolerance of this species towards neritic conditions than in other species
Modern planktic foraminifera
Full text linkPlanktic foraminifers are marine protozoans with calcareous Shells and chambered tests. They first appeared in the mid-Jurassic and spread since the mid-Cretaceous over all the world’s oceans. Modern planktic foraminifers evolved since the early Tertiary, when the first spinose species occurred. Most species live in the surface to sub-thermocline layer of the open ocean, and in marginal seas like the Mediterranean, Caribbean, South China Sea, and Red Sea. Planktic foraminifers are absent in shallow marginal seas, for example, the North Sea. Planktic foraminifers respond to food, temperature and chemistry of the ambient seawater. Species abundance varies according to seasons, water masses, and water depths. Symbiont-bearing species depend on light and are restricted to the euphotic zone. Planktic foraminifers constitute a minor portion of total Zooplankton, but are major producers of marine calcareous particles (shells) deposited on the ocean floor where they form the so-called foraminiferal ooze.Planktic foraminifers contribute substantially to the fossil record of marine Sediments and are of high ecologic, paleoceanographic, and stratigraphic significance since the mid-Cretaceous. Radiocarbon (14C) gives an absolute age of shell formation within late Pleistocene and Holocene Sediments. Factors that determine the modern faunal composition are applied to Interpretation of the fossil assemblages, for example, by multiple regression techniques (transfer functions) to yield an estimate on ancient environmental parameters. The chemical composition of the calcareous shell (stable isotopes and trace elements) holds clues to the chemical and physical State of the ambient seawater and is useful in the reconstruction of temperature, chemical State, and biological productivity of the ancient marine environment
Cd/Ca ratios of in situ sampled planktonic foraminifera (abstract of paper presented at: 17th Annual V. M. Goldschmidt Conference Cologne, Germany August 2007)
No full textCarbonate and carbon fluctuations in the eastern Arabian Sea over 140 ka: implications on productivity changes?
No full textBiological productivity in the western Arabian Sea was higher during interglacial than glacial times. In the eastern Arabian Sea productivity was higher during the glacials compared to interglacials, which is in sharp contrast to the southwest monsoon intensity variations. To examine temporal changes in productivity in the eastern Arabian Sea over the last 140 ka, oxygen isotopes, calcium carbonate and organic carbon on three cores (SL-1 & 4 and SK 129-CR05) were analyzed. Oxygen isotope records display distinct glacial and interglacial transitions. In the northeastern (Core SL-1) and eastern Arabian Sea (Core SL-4) both calcium carbonate and organic carbon variations show no significant systematic relationship with glacial and interglacials periods. In the southeastern Arabian Sea (Core SK-129-CR05) calcium carbonate shows high and low values during interglacial and glacials, respectively, and temporal changes in organic carbon concentration are significant only during MIS 5. Differential variation of calcium carbonate and organic carbon concentration at the northeastern and southeastern Arabian Sea, and between glacials and interglacials, are attributed to regional differences in sedimentation rates, dilution and preservation, which modify the signal of carbonate and carbon production
A new MC-ICPMS method for the determination of Cd/Ca ratios in foraminiferal tests (abstract of paper presented at 14th Annual Goldschmidt conference 5 to 11 June 2004 )
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Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tracking the Recent and late Pleistocene Azores front by the distribution of planktic foraminifers
Full text linkSouth of the Azores Islands, the population dynamics and sedimentation of planktic foraminifers are significantly influenced by the hydrography of the Azores Front Current System (AFCS). Planktic foraminifers collected from the water column during seasonal cruises across the Azores Front, record the temporal and spatial scale of hydrographic and faunal dynamics within this area. Surface sediment analysis reveals the presence of a large number of pteropod shells indicating preservation of aragonite and, therefore, little alteration of the calcitic foraminiferal tests. Consequently, most of the seasonal and spatial variability of the Azores Front is expected to be recorded by the planktic foraminiferal assemblages present within the surface sediment. In particular, Globorotalia scitula, a subsurface-dwelling species, decreases significantly in abundance to the south of the Azores Front, and shows fine-scale changes at the glacial/interglacial time scale. Enhanced faunal proportions of G. scitula in a sediment core that is located to the south of the modern Azores Current indicate a southward shift of the Azores Front Current System during the glacials and the presence of a transitional water mass at the Azores region. <br/
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