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Makio C Honda - One of the best experts on this subject based on the ideXlab platform.

  • seasonal to interannual changes in planktonic Foraminiferal assemblages in the northwestern north pacific sediment trap results encompassing a warm period related to el nino
    Palaeogeography Palaeoclimatology Palaeoecology, 2008
    Co-Authors: Azumi Kuroyanagi, Hodaka Kawahata, Hiroshi Nishi, Makio C Honda
    Abstract:

    Abstract Planktonic Foraminifera provide a record of the upper ocean environment through their species assemblage and individual tests. To investigate the relationship between Foraminifera and oceanographic conditions and the impact of El Nino on Foraminifera, we analyzed Foraminiferal fluxes and relative abundances by using sediment trap samples collected biweekly at three sites in the northwestern North Pacific: Site 40N (39°60′N, 165°00′E), Site KNOT (43°58′N, 155°03′E), and Site 50N (50°01′N, 165°02′E) from 1998–2001, a period that included an El Nino event. Based on Foraminiferal production and assemblage composition, we divided the sampling duration into several periods during which certain characteristic oceanographic properties were observed. These sampling periods were classified into five types (I–V) based upon four factors: 1) the predominant Foraminiferal group, 2) total Foraminiferal fluxes (TFFs), 3) organic matter (OM) fluxes, and 4) hydrographic conditions, which included sea-surface temperature (SST) and thermal structure. Our results suggest that our observed seasonal changes in Foraminifera were closely related to water-mass properties in addition to SST. If species compositions were the same, then water-mass properties were the most important factors affecting the seasonal variation of Foraminiferal abundance in the northwestern North Pacific. Although one of the major controlling factors for Foraminiferal fluxes is food availability, the controlling factors for each type (Types I–V) are different because of specific oceanographic situations, such as phytoplankton blooms, which result in an excess food supply for Foraminifera. At Site KNOT, high surface temperatures and weak winds related to an El Nino period in 1998 would have caused a low nutrient supply and water-column stratification, and resulted in the relatively low fluxes of total Foraminifera, Neogloboquadrina pachyderma , and Globigerina bulloides and high fluxes of Neogloboquadrina dutertrei . The impact of El Nino on Foraminifera was variable depending on the strength of the El Nino event and site location. However, there were some instances of common annual Foraminiferal patterns; the patterns observed at Sites 40N and KNOT in 1998 were similar to those observed off Chile in 1997–1998 and in 1991–1992, respectively.

  • seasonal changes in planktonic Foraminifera in the northwestern north pacific ocean sediment trap experiments from subarctic and subtropical gyres
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2002
    Co-Authors: Azumi Kuroyanagi, Hodaka Kawahata, Hiroshi Nishi, Makio C Honda
    Abstract:

    Abstract Upper ocean environments such as seawater temperature, salinity, thermal structure in the water column, light intensity and food supply affect the assemblage of planktonic Foraminifera. Since detailed information on planktonic Foraminifera was not available for the northwestern North Pacific, we examined seasonal changes in fluxes and composition of planktonic Foraminifera there. Data were collected by sediment traps deployed at three sites (Site 50N (50°01′N, 165°02′E), Site KNOT (43°58′N, 155°03′E), and Site 40N (39°60′N, 165°00′E)) in this area in order to better understand the relationship between the Foraminiferal assemblage and surface-ocean environments. Although each planktonic Foraminiferal species showed specific seasonal variations in flux, some exhibited similar flux profiles. In order to define these more accurately, correlations among species were calculated and the Foraminiferal species classified into four groups: (1) Group A (subpolar species: Neogloboquadrina pachyderma , Globigerina quinqueloba , Globigerina bulloides , and Globigerinita glutinata ); (2) Group B (subtropical and tropical species: Globigerinoides ruber and Globigerinoides sacculifer ); (3) Group C (post-upwelling species: Neogloboquadrina dutertrei ); and (4) Group D (deep-water species: Globorotalia scitula and Globorotalia truncatulinoides ). The common environments for each period, based on Foraminiferal production and composition, were observed among the three sites. Based upon predominant Foraminiferal groups, total Foraminiferal fluxes (TFFs), organic matter (OM) fluxes and hydrographic conditions, including sea-surface temperatures (SST) and thermal structure, the surface-ocean environments in the northwestern North Pacific could be generalized into five types. Type I is characterized by a dominance of Group B, with low TFFs under high SST, and Type II is marked by a high flux of Group A. On the other hand, Type III shows low TFFs and low OM fluxes due to low insolation during winter. Type IV represents a high flux of Group A, and Group D at Site 40N, under a well-mixed surface ocean, and Type V is characterized by a prominent peak of Group C under a developed thermocline. A comparison of annual mean Foraminifera fluxes at 50°N between the northwestern (Site 50N) and the northeastern North Pacific (Station PAPA) during the normal “cold” mode demonstrated higher fluxes of Foraminifera at Site 50N due to higher nutrient concentrations. The results also showed that G. bulloides is not always a proxy for upwelling and that N. pachyderma is not solely controlled by seawater temperature in the northwestern Pacific, where the surface water is enriched in nutrients. The fluxes and composition of Foraminifera suggest that similar ocean environments are expected in large areas of the northern North Pacific, from Site KNOT to Station PAPA during the “warm” mode, which is affected by El Nino events.

Hodaka Kawahata - One of the best experts on this subject based on the ideXlab platform.

  • Effect of dissolved oxygen concentration on planktonic Foraminifera through laboratory culture experiments and implications for oceanic anoxic events
    Marine Micropaleontology, 2013
    Co-Authors: Azumi Kuroyanagi, Régine Elisabeth Da Rocha, Jelle Bijma, Howard J. Spero, Ann D. Russell, Stephen Eggins, Hodaka Kawahata
    Abstract:

    Abstract Although substantial turnovers of planktonic Foraminiferal species occurred during Cretaceous oceanic anoxic events (OAEs), the direct effects of dissolved oxygen (DO) concentration on planktonic Foraminifera remain obscure. Culture experiments can quantify the relationship between planktonic Foraminiferal ecology and environmental parameters, but experiments controlling DO have yet to be conducted because it is difficult to maintain a stable oxygen concentration. In this study, we cultured two planktonic foraminifer species ( Orbulina universa and Globigerina bulloides ) at six different DO levels between 10% and 100% saturation. Both species showed a high tolerance to low DO, suggesting that “dysoxic” conditions (> 0.7 mg O 2  l − 1 ) were not a direct cause of planktonic Foraminiferal extinction at OAEs. The high tolerance of these species to extremely low DO might be attributable to their evolutionary descent from benthic Foraminifera. Final shell weight increased with increasing DO, suggesting that fossil Foraminiferal shell weight could vary with past DO conditions. Our results suggest that the extinction of many planktonic Foraminiferal species during OAEs may have been due to anoxic or euxinic conditions in the euphotic zone. The occurrence of these conditions can be explained either by the oxygen minimum layer model or by the stagnant ocean model combined with elevated riverine P input.

  • seasonal to interannual changes in planktonic Foraminiferal assemblages in the northwestern north pacific sediment trap results encompassing a warm period related to el nino
    Palaeogeography Palaeoclimatology Palaeoecology, 2008
    Co-Authors: Azumi Kuroyanagi, Hodaka Kawahata, Hiroshi Nishi, Makio C Honda
    Abstract:

    Abstract Planktonic Foraminifera provide a record of the upper ocean environment through their species assemblage and individual tests. To investigate the relationship between Foraminifera and oceanographic conditions and the impact of El Nino on Foraminifera, we analyzed Foraminiferal fluxes and relative abundances by using sediment trap samples collected biweekly at three sites in the northwestern North Pacific: Site 40N (39°60′N, 165°00′E), Site KNOT (43°58′N, 155°03′E), and Site 50N (50°01′N, 165°02′E) from 1998–2001, a period that included an El Nino event. Based on Foraminiferal production and assemblage composition, we divided the sampling duration into several periods during which certain characteristic oceanographic properties were observed. These sampling periods were classified into five types (I–V) based upon four factors: 1) the predominant Foraminiferal group, 2) total Foraminiferal fluxes (TFFs), 3) organic matter (OM) fluxes, and 4) hydrographic conditions, which included sea-surface temperature (SST) and thermal structure. Our results suggest that our observed seasonal changes in Foraminifera were closely related to water-mass properties in addition to SST. If species compositions were the same, then water-mass properties were the most important factors affecting the seasonal variation of Foraminiferal abundance in the northwestern North Pacific. Although one of the major controlling factors for Foraminiferal fluxes is food availability, the controlling factors for each type (Types I–V) are different because of specific oceanographic situations, such as phytoplankton blooms, which result in an excess food supply for Foraminifera. At Site KNOT, high surface temperatures and weak winds related to an El Nino period in 1998 would have caused a low nutrient supply and water-column stratification, and resulted in the relatively low fluxes of total Foraminifera, Neogloboquadrina pachyderma , and Globigerina bulloides and high fluxes of Neogloboquadrina dutertrei . The impact of El Nino on Foraminifera was variable depending on the strength of the El Nino event and site location. However, there were some instances of common annual Foraminiferal patterns; the patterns observed at Sites 40N and KNOT in 1998 were similar to those observed off Chile in 1997–1998 and in 1991–1992, respectively.

  • seasonal changes in planktonic Foraminifera in the northwestern north pacific ocean sediment trap experiments from subarctic and subtropical gyres
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2002
    Co-Authors: Azumi Kuroyanagi, Hodaka Kawahata, Hiroshi Nishi, Makio C Honda
    Abstract:

    Abstract Upper ocean environments such as seawater temperature, salinity, thermal structure in the water column, light intensity and food supply affect the assemblage of planktonic Foraminifera. Since detailed information on planktonic Foraminifera was not available for the northwestern North Pacific, we examined seasonal changes in fluxes and composition of planktonic Foraminifera there. Data were collected by sediment traps deployed at three sites (Site 50N (50°01′N, 165°02′E), Site KNOT (43°58′N, 155°03′E), and Site 40N (39°60′N, 165°00′E)) in this area in order to better understand the relationship between the Foraminiferal assemblage and surface-ocean environments. Although each planktonic Foraminiferal species showed specific seasonal variations in flux, some exhibited similar flux profiles. In order to define these more accurately, correlations among species were calculated and the Foraminiferal species classified into four groups: (1) Group A (subpolar species: Neogloboquadrina pachyderma , Globigerina quinqueloba , Globigerina bulloides , and Globigerinita glutinata ); (2) Group B (subtropical and tropical species: Globigerinoides ruber and Globigerinoides sacculifer ); (3) Group C (post-upwelling species: Neogloboquadrina dutertrei ); and (4) Group D (deep-water species: Globorotalia scitula and Globorotalia truncatulinoides ). The common environments for each period, based on Foraminiferal production and composition, were observed among the three sites. Based upon predominant Foraminiferal groups, total Foraminiferal fluxes (TFFs), organic matter (OM) fluxes and hydrographic conditions, including sea-surface temperatures (SST) and thermal structure, the surface-ocean environments in the northwestern North Pacific could be generalized into five types. Type I is characterized by a dominance of Group B, with low TFFs under high SST, and Type II is marked by a high flux of Group A. On the other hand, Type III shows low TFFs and low OM fluxes due to low insolation during winter. Type IV represents a high flux of Group A, and Group D at Site 40N, under a well-mixed surface ocean, and Type V is characterized by a prominent peak of Group C under a developed thermocline. A comparison of annual mean Foraminifera fluxes at 50°N between the northwestern (Site 50N) and the northeastern North Pacific (Station PAPA) during the normal “cold” mode demonstrated higher fluxes of Foraminifera at Site 50N due to higher nutrient concentrations. The results also showed that G. bulloides is not always a proxy for upwelling and that N. pachyderma is not solely controlled by seawater temperature in the northwestern Pacific, where the surface water is enriched in nutrients. The fluxes and composition of Foraminifera suggest that similar ocean environments are expected in large areas of the northern North Pacific, from Site KNOT to Station PAPA during the “warm” mode, which is affected by El Nino events.

Azumi Kuroyanagi - One of the best experts on this subject based on the ideXlab platform.

  • Effect of dissolved oxygen concentration on planktonic Foraminifera through laboratory culture experiments and implications for oceanic anoxic events
    Marine Micropaleontology, 2013
    Co-Authors: Azumi Kuroyanagi, Régine Elisabeth Da Rocha, Jelle Bijma, Howard J. Spero, Ann D. Russell, Stephen Eggins, Hodaka Kawahata
    Abstract:

    Abstract Although substantial turnovers of planktonic Foraminiferal species occurred during Cretaceous oceanic anoxic events (OAEs), the direct effects of dissolved oxygen (DO) concentration on planktonic Foraminifera remain obscure. Culture experiments can quantify the relationship between planktonic Foraminiferal ecology and environmental parameters, but experiments controlling DO have yet to be conducted because it is difficult to maintain a stable oxygen concentration. In this study, we cultured two planktonic foraminifer species ( Orbulina universa and Globigerina bulloides ) at six different DO levels between 10% and 100% saturation. Both species showed a high tolerance to low DO, suggesting that “dysoxic” conditions (> 0.7 mg O 2  l − 1 ) were not a direct cause of planktonic Foraminiferal extinction at OAEs. The high tolerance of these species to extremely low DO might be attributable to their evolutionary descent from benthic Foraminifera. Final shell weight increased with increasing DO, suggesting that fossil Foraminiferal shell weight could vary with past DO conditions. Our results suggest that the extinction of many planktonic Foraminiferal species during OAEs may have been due to anoxic or euxinic conditions in the euphotic zone. The occurrence of these conditions can be explained either by the oxygen minimum layer model or by the stagnant ocean model combined with elevated riverine P input.

  • seasonal to interannual changes in planktonic Foraminiferal assemblages in the northwestern north pacific sediment trap results encompassing a warm period related to el nino
    Palaeogeography Palaeoclimatology Palaeoecology, 2008
    Co-Authors: Azumi Kuroyanagi, Hodaka Kawahata, Hiroshi Nishi, Makio C Honda
    Abstract:

    Abstract Planktonic Foraminifera provide a record of the upper ocean environment through their species assemblage and individual tests. To investigate the relationship between Foraminifera and oceanographic conditions and the impact of El Nino on Foraminifera, we analyzed Foraminiferal fluxes and relative abundances by using sediment trap samples collected biweekly at three sites in the northwestern North Pacific: Site 40N (39°60′N, 165°00′E), Site KNOT (43°58′N, 155°03′E), and Site 50N (50°01′N, 165°02′E) from 1998–2001, a period that included an El Nino event. Based on Foraminiferal production and assemblage composition, we divided the sampling duration into several periods during which certain characteristic oceanographic properties were observed. These sampling periods were classified into five types (I–V) based upon four factors: 1) the predominant Foraminiferal group, 2) total Foraminiferal fluxes (TFFs), 3) organic matter (OM) fluxes, and 4) hydrographic conditions, which included sea-surface temperature (SST) and thermal structure. Our results suggest that our observed seasonal changes in Foraminifera were closely related to water-mass properties in addition to SST. If species compositions were the same, then water-mass properties were the most important factors affecting the seasonal variation of Foraminiferal abundance in the northwestern North Pacific. Although one of the major controlling factors for Foraminiferal fluxes is food availability, the controlling factors for each type (Types I–V) are different because of specific oceanographic situations, such as phytoplankton blooms, which result in an excess food supply for Foraminifera. At Site KNOT, high surface temperatures and weak winds related to an El Nino period in 1998 would have caused a low nutrient supply and water-column stratification, and resulted in the relatively low fluxes of total Foraminifera, Neogloboquadrina pachyderma , and Globigerina bulloides and high fluxes of Neogloboquadrina dutertrei . The impact of El Nino on Foraminifera was variable depending on the strength of the El Nino event and site location. However, there were some instances of common annual Foraminiferal patterns; the patterns observed at Sites 40N and KNOT in 1998 were similar to those observed off Chile in 1997–1998 and in 1991–1992, respectively.

  • seasonal changes in planktonic Foraminifera in the northwestern north pacific ocean sediment trap experiments from subarctic and subtropical gyres
    Deep-sea Research Part Ii-topical Studies in Oceanography, 2002
    Co-Authors: Azumi Kuroyanagi, Hodaka Kawahata, Hiroshi Nishi, Makio C Honda
    Abstract:

    Abstract Upper ocean environments such as seawater temperature, salinity, thermal structure in the water column, light intensity and food supply affect the assemblage of planktonic Foraminifera. Since detailed information on planktonic Foraminifera was not available for the northwestern North Pacific, we examined seasonal changes in fluxes and composition of planktonic Foraminifera there. Data were collected by sediment traps deployed at three sites (Site 50N (50°01′N, 165°02′E), Site KNOT (43°58′N, 155°03′E), and Site 40N (39°60′N, 165°00′E)) in this area in order to better understand the relationship between the Foraminiferal assemblage and surface-ocean environments. Although each planktonic Foraminiferal species showed specific seasonal variations in flux, some exhibited similar flux profiles. In order to define these more accurately, correlations among species were calculated and the Foraminiferal species classified into four groups: (1) Group A (subpolar species: Neogloboquadrina pachyderma , Globigerina quinqueloba , Globigerina bulloides , and Globigerinita glutinata ); (2) Group B (subtropical and tropical species: Globigerinoides ruber and Globigerinoides sacculifer ); (3) Group C (post-upwelling species: Neogloboquadrina dutertrei ); and (4) Group D (deep-water species: Globorotalia scitula and Globorotalia truncatulinoides ). The common environments for each period, based on Foraminiferal production and composition, were observed among the three sites. Based upon predominant Foraminiferal groups, total Foraminiferal fluxes (TFFs), organic matter (OM) fluxes and hydrographic conditions, including sea-surface temperatures (SST) and thermal structure, the surface-ocean environments in the northwestern North Pacific could be generalized into five types. Type I is characterized by a dominance of Group B, with low TFFs under high SST, and Type II is marked by a high flux of Group A. On the other hand, Type III shows low TFFs and low OM fluxes due to low insolation during winter. Type IV represents a high flux of Group A, and Group D at Site 40N, under a well-mixed surface ocean, and Type V is characterized by a prominent peak of Group C under a developed thermocline. A comparison of annual mean Foraminifera fluxes at 50°N between the northwestern (Site 50N) and the northeastern North Pacific (Station PAPA) during the normal “cold” mode demonstrated higher fluxes of Foraminifera at Site 50N due to higher nutrient concentrations. The results also showed that G. bulloides is not always a proxy for upwelling and that N. pachyderma is not solely controlled by seawater temperature in the northwestern Pacific, where the surface water is enriched in nutrients. The fluxes and composition of Foraminifera suggest that similar ocean environments are expected in large areas of the northern North Pacific, from Site KNOT to Station PAPA during the “warm” mode, which is affected by El Nino events.

Kirsty M Edgar - One of the best experts on this subject based on the ideXlab platform.

  • temporal variability in Foraminiferal morphology and geochemistry at the west antarctic peninsula a sediment trap study
    Biogeosciences, 2019
    Co-Authors: Anna Mikis, Daniela N Schmidt, Kirsty M Edgar, Katharine R Hendry, Jennifer Pike, Victoria L Peck, Frank Peeters, Melanie J Leng
    Abstract:

    Abstract. The West Antarctic Peninsula (WAP) exhibits strong spatial and temporal oceanographic variability, resulting in highly heterogeneous biological productivity. Calcifying organisms that live in the waters off the WAP respond to temporal and spatial variations in ocean temperature and chemistry. These marine calcifiers are potentially threatened by regional climate change with waters already naturally close to carbonate undersaturation. Future projections of carbonate production in the Southern Ocean are challenging due to the lack of historical data collection and complex, decadal climate variability. Here we present a 6-year-long record of the shell fluxes, morphology and stable isotope variability of the polar planktic Foraminifera Neogloboquadrina pachyderma (sensu stricto) from near Palmer Station, Antarctica. This species is fundamental to Southern Ocean planktic carbonate production as it is one of the very few planktic foraminifer species adapted to the marine polar environments. We use these new data to obtain insights into its ecology and to derive a robust assessment of the response of this polar species to environmental change. Morphology and stable isotope composition reveal the presence of different growth stages within this tightly defined species. Inter- and intra-annual variability of Foraminiferal flux and size is evident and driven by a combination of environmental forcing parameters, most importantly food availability, temperature and sea ice duration and extent. Foraminiferal growth occurs throughout the austral year and is influenced by environmental change, a large portion of which is driven by the Southern Annular Mode and El Nino–Southern Oscillation. A distinct seasonal production is observed, with the highest shell fluxes during the warmest and most productive months of the year. The sensitivity of calcifying Foraminifera to environmental variability in this region, from weeks to decades, has implications both for their response to future climatic change and for their use as palaeoclimate indicators. A longer ice-free season could increase carbonate production in this region at least while carbonate saturation is still high enough to allow for thick tests to grow.

  • assessing the impact of diagenesis on δ11b δ13c δ18o sr ca and b ca values in fossil planktic Foraminiferal calcite
    Geochimica et Cosmochimica Acta, 2015
    Co-Authors: Kirsty M Edgar, Eleni Anagnostou, Paul Nicholas Pearson, Gavin L. Foster
    Abstract:

    The geochemical composition of Foraminiferal tests is a valuable archive for the reconstruction of paleo-climatic, -oceanographic and -ecological changes. However, dissolution of biogenic calcite and precipitation of inorganic calcite (overgrowth and recrystallization) at the seafloor and in the sediment column can potentially alter the original geochemical composition of the Foraminiferal test, biasing any resulting paleoenvironmental reconstruction. The δ11B of planktic Foraminiferal calcite is a promising ocean pH-proxy but the effect of diagenesis is still poorly known. Here we present new δ11B, δ13C, δ18O, Sr/Ca and B/Ca data from multiple species of planktic Foraminifera from time-equivalent samples for two low latitude sites: clay-rich Tanzanian Drilling Project (TDP) Site 18 from the Indian Ocean containing well-preserved (‘glassy’) Foraminifera and carbonate-rich Ocean Drilling Program (ODP) Site 865 from the central Pacific Ocean hosting recrystallized (‘frosty’) Foraminifera. Our approach makes the assumption that environmental conditions were initially similar at both sites so most chemical differences are attributable to diagenesis. Planktic Foraminiferal δ18O and δ13C records show offsets in both relative and absolute values between the two sites consistent with earlier findings that these isotopic ratios are strongly influenced by diagenetic alteration. Sr/Ca and B/Ca ratios in planktic Foraminiferal calcite are also offset between the two sites but there is little change in the relative difference between surface and deep dwelling taxa. In contrast, δ11B values indicate no large differences between well-preserved and recrystallized Foraminifera suggesting that despite extensive diagenetic alteration the δ11B of biogenic calcite appears robust, potentially indicative of a lack of free exchange of boron between pore fluids and the recrystallizing CaCO3. Our finding may remove one potential source of uncertainty in δ11B based pH reconstructions and provide us with greater confidence in our ability to reconstruct pH in the ancient oceans from at least some recrystallized Foraminiferal calcite. However, further investigations should extend this approach to test the robustness of our findings across a range of taphonomies, ages and burial settings.

  • testing the impact of diagenesis on the δ18o and δ13c of benthic Foraminiferal calcite from a sediment burial depth transect in the equatorial pacific
    Paleoceanography, 2013
    Co-Authors: Kirsty M Edgar, Heiko Palike, Paul A Wilson
    Abstract:

    Stable oxygen and carbon isotope (δ18O and δ13C) values measured in Foraminiferal calcite are one of the primary tools used in paleoceanography. Diagenetic recrystallisation of Foraminiferal calcite can act to reset primary isotopic values but its effects are typically poorly quantified. Here we test the impact of early stage diagenesis on stable isotope records generated from a suite of drill sites in the equatorial Pacific Ocean recovered during Ocean Drilling Program (ODP) Leg 199 and Integrated Ocean Drilling Program (IODP) Expedition 320. Our selected sites form paleowater- and burial-depth transects, with excellent stratigraphic control allowing us to confidently correlate our records. We observe large inter-site differences in the preservation state of benthic Foraminiferal calcite, implying very different recrystallisation histories, but negligible inter-site offsets in benthic δ18O and δ13C values. We infer that diagenetic alteration of benthic Foraminiferal calcite (in sedimentary oozes) must predominantly occur at shallow burial depths (<100 m) where offsets in both the temperature and isotopic composition of waters in which the Foraminifera calcified and pore-waters in which diagenesis occurs are small. Our results suggest that even extensive recrystallisation of benthic Foraminiferal calcite results in minimal shifts from primary δ18O and δ13C values. This finding supports the long-held suspicion that diagenetic alteration of Foraminiferal calcite is less problematic in benthic than in planktic Foraminifera and that in deep–sea sediments routinely employed for palaeoceanographic studies benthic Foraminifera are robust recorders of stable isotope values in the fossil record.

Atike Nazik - One of the best experts on this subject based on the ideXlab platform.

  • the response of benthic Foraminifera and ostracoda to heavy metal pollution in gulf of izmir eastern aegean sea
    Estuarine Coastal and Shelf Science, 2006
    Co-Authors: Fulya Bergin, F Kucuksezgin, E Uluturhan, Ipek F Barut, Engin Meric, Niyazi Avsar, Atike Nazik
    Abstract:

    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.