Some Peculiarities of Foraminifera Species Distribution Associated with Concentrations of 226Ra, 238U, 232Th in the Deryugin Basin (the Sea of Okhotsk)

Размещено на http://allbest.ru

P.P. Shirshov Institute of Oceanology

Some Peculiarities of Foraminifera Species Distribution Associated with Concentrations of ²²⁶Ra, ²³⁸U ²³²Th in the Deryugin Basin (the Sea of Okhotsk)

Mikhail M. Domanov* and Tatyana A. Khusid

Moscow

Abstract

An analysis of composition and quantitative distribution offoraminifera in bottom sediments collected in the Deryugin Basin (the Sea of Okhotsk) has demonstrated that specific foraminiferal assemblages at the depths of 691 to 1786 m are associated with distribution of natural radionuclides. A comparison of the percentage of Saccorhiza ramosa (Brady) as a dominant species in the community of benthic foraminifera and the concentrations of radionuclides in the sediments showed that the quantity of S. ramosa correlates with the concentrations of²³⁸U, ²³²Th and ²²⁶Ra in the sediments. The correlation coefficients for concentrations of²³⁸U, ²³²Th and ²²⁶Ra are 0.75, 0.83 and 0.86, respectively. Calcareous foraminifera abundance decreases with radioactivity growth and correlates with common radioactivity with the negative coefficient of -0.82.

Keywords: foraminifera, community of foraminifera, biocoenosis, radionuclides, ²³⁸U, ²³²Th, ²²⁶Ra, sediment, abundance.

Аннотация

Особенности распределения бентосных видов фораминифер и ²²⁶ Ra, ²³⁸ U, ²³² Th в донных осадках впадины Дерюгина (Охотское море)

М.М. Доманов, Т.А. Хусид

Институт океанологии им. П.П. Ширшова, Москва

Анализ состава и количественного распределения фораминифер в донных осадках впадины Дерюгина (Охотское море) показал, что специфический комплекс фораминифер впадины Дерюгина на глубине от 691 до 1786 м связан с распределением природных радионуклидов. Сопоставление процентного содержания Saccorhiza ramosa (Brady), доминирующей в сообществе бентосных фораминифер, и концентрации радионуклидов в донных осадках показало, что количество фораминифер S. ramosa коррелирует с концентрацией в осадках ²³⁸U, ²³²Th и ²²⁶Ra. Коэффициенты корреляции с концентрацией ²³⁸U, ²³²Th и ²²⁶Ra равны 0,75, 0,83 и 0,86 соответственно. Обилие известковых фораминифер с ростом радиоактивности снижается и коррелирует с общей радиоактивностью с отрицательным коэффициентом -0,82.

Ключевые слова: фораминиферы, сообщество фораминифер, биоценоз, радионуклиды, ²³⁸U, ²³²Th, ²²⁶Ra, морские осадки.

Introduction

Zones of increased natural radioactivity are of interest for research into evolutionary transformations in the history of the Earth biosphere (Odum, 1959; Neruchev, 1982). Benthic organisms living directly in the bottom sediments or on the sediment surface are mostly exposed to the influence of radiation from radionuclides concentrated in bottom sediments.

Benthic organisms can accumulate radionuclides, which intensifies the effect of radiation. Xenophyophores, a group of protists of the benthic community, are able to concentrate naturally occurring radionuclides ²³⁸U, ²³²Th, ²¹⁰Po, ²²⁶Ra, ²¹⁰Pb in the cytoplasm and the shell (Levin et al., 1986; Swinbanks, Shirayama, 1986; Lecrog et al., 2009).

It was shown that concentrations of ²²⁶Ra and ²³²Th in these protists depend on the following: the species of the organism, the composition of the material utilized in agglutination, and the concentration of radionuclides in the environment (Domanov, 2015).

Swinbanks & Shirayama (1986) demonstrated that high levels of natural radiation occur in xenophyophores, as a result of presence of ²²⁶Ra in intracellular barite crystals, and suggested that this radiation would induce numerous genetic mutations.

Multidirectional influence of radioactivity on biodiversity and abundance of meiobenthos (particularly in the community of foraminifera) was noted in the Kara Sea (Alexeev, Galtsova, 2012) Thus, to assess the impact of various factors on functioning of benthic foraminiferal communities, radionuclides are to be taken into account.

One of the areas with high natural radioactivity of bottom sediments is the Deryugin Basin in the Sea of Okhotsk. The concentrations of ²³⁸U, ²³²Th are 2-3 times higher and ²²⁶Ra concentration is 10-25 times higher in the central part of the Deryugin Basin than in the periphery (Domanov, 2009).

In this area, a particular community of benthos foraminifera with a small amount of species and a predominance of agglutinated foraminifera was discovered (Khusid et al., 2006,).

The research was aimed to study a correlation between distribution of benthic foraminifera and radionuclides ²³⁸U, ²³²Th, and ²²⁶Ra in the Deryugin Basin in order to identify a connection of dominant foraminifera species with the distribution of natural radionuclides in bottom sediments.

Materials and methods

The Deryugin Basin (Fig. 1) is bounded in the west by the northern Sakhalin continental slope and in the north by the Staretsky Trough and the Kashevarov Bank of the North Okhotsk margin.

The structure and composition of benthic foraminiferal communities from the Deryugin Basin were analyzed in 11 samples taken with the bottom grab ”Okean” at the depths of 691 to 1786 m from the surface 0-2 cm sediment layer. Samples were collected during the 50^th and 51^st cruises of the R/V Professor Khromov. The location of the stations, their depths, and sediment description are given in Table 1. The majority of samples were collected in the deepest part of the Deryugin Basin at a small range of depths (from 1420 to 1786 m) (Fig. 2) and only one sample (St. 51-23) was taken at the southern edge of the basin, from the depth of 691 m.

Table 1. Description of the bottom sediments and position of the stations in Deryugin Basin

Fig. 1. Location of the study area

Sediment samples (40-60 g) were washed and passed through a 0.05 mm mesh size sieve. Taxonomical identification of foraminifera was based on the accepted classification (Loeblich and Tappan, 1964, 1986, 1987). The planktonic and benthic foraminifers were studied under a Leica WILD M3C light microscope at x100 magnification.

The taxonomic composition, proportion of all foraminiferal species, and their total abundance (individuals per g dry sediment) were determined in each sample. The radioactivity analysis was performed in the Laboratory of Dosimetry and Environmental Radioactivity of the Chemistry Department of Moscow State University. The radioactivity of natural radionuclides (²³⁸U, ²³²Th and ²²⁶Ra) in bottom sediments was measured on a gamma- spectrometer with a super pure germanium GC- 3020 detector with a relative efficiency of 30% (Co-60 line - 1.332 Me) and a resolution of 1.8 Kev. The software GENIE-400 PC was used. The accuracy of measurements for Ra, Th and U was 5-7%, 10-15% and 15-20% respectively. benthic foraminifera saccorhiza deryugin

Fig. 2. Position of the stations in thedeepest partofthe DeryuginBasin

Results

Conclusion

A correlation analysis between the percentage of S. ramosa in the community of benthic foraminifera and the concentrations of radionuclides in sediments showed that domination of S. ramosa in the community increases with the increase of ²³⁸U, ²³²Th and ²²⁶Ra concentration and common radioactivity in sediments. The coefficients of correlation for ²³⁸U, ²³²Th and ²²⁶Ra equal 0.75, 0.83 and 0.86, respectively. It may be a result of the influence of raised radioactivity on a natural benthic foraminiferal community and is connected with the structural reorganization of community dominants in which S. ramosa is probably the most resistant species. The revealed changes in the structure of benthic foraminifera may also be caused by other factors. Thus, it is necessary to examine if the radioactivity is the dominating factor or these changes are the summative result of a number of causes. Such study is a part of a multi-stressor approach which helps to improve our understanding of the influence of the environment on the fauna.

References

1. Alam L., Mohamed C.A.R. (2011) A mini review on bioaccumulation of ²¹⁰Po by marine organisms. International Food Research Journal, 18: 1-10

2. Alexeev D.K., Galtsova V.V. (2012) Effect of radioactive pollution on the biodiversity of marine benthic ecosystems of the Russian Arctic shelf. Polar Science, 6: 183-195

3. Domanov M.M. (2009) Speciation of ²²⁶Ra in seabed sediments formed in hydrothermal cold fluid zones (Deryugin Deep, Sea of Okhotsk). Radiochemistry, 51(1): 85-90

4. Domanov M.M. (2015) Natural ²²⁶Ra and ²³²Th radionuclides in xenophyophores of the Pacific Ocean. Geochemistry International, 53(7): 664-669

5. Domanov M.M., Moskvina M.I., Ilinskiy V.V. (2015) Development of populations of marine heterotrophic bacteria irradiated with 226Ra contained in natural barite. Proceedings of the International Scientific Conference “Radiobiology: “Mayak”, Chernobyl, Fukushima” (Gomel, September 24-25, 2015). Gomel, Institute of Radiology, p. 76-80 (in Russian)

6. Galtsova V.V., Kulangieva L.V., Pogrebov V.B. (2004) Meiobenthos of the former nuclear test area and nuclear waste disposal grounds around the Novaya Zemlya Archipelago (Barents and Kara Seas). Russian Journal of Marine Biology, 30 (4): 231-240

7. Khusid T.A., Belyaeva N.V., Demina L.L., Domanov M.M., Chekhovskaya M.P. (2013) Changes of planktonic and benthic foraminiferal assemblages in upper quaternaru sediments of the Deryugin Basin, Sea of Okhotsk. Stratigraphy and Geological Correlation, 21(2): 237-248

8. Khusid T.A., Domanov M.M., Svininnikov A.M. (2006) Species composition and distribution of foraminifers in the Deryugin Basin (Sea of Okhotsk). Biology Bulletin, 33(2): 172-178

9. Kuzin A.M. (1991) Natural radioactive background and its significance for Earth's Biosphere. Moscow, Nauka, 116 p. (in Russian)

10. Levin L.A., DeMaster D.J., McCann L.D., Thomas C.L. (1986) Effects of giant protozoans (class: Xenophyophorea) on deep-seamount benthos. Marine Ecology Progress Series, 29: 99-104

11. Lecroq B., Gooday A.J., Tsuchiya M., Pawlowski J. (2009) A new genus of xenophyophores (Foraminifera) from Japan Trench: morphological description, molecular phylogeny and elemental analysis. Zoological Journal of the Linnean Society, 156: 455-464

12. Loeblich A.R., Tappan H. (1964) Sarcodina, chiefly “Thecamoebians” and Foraminiferida. Treatise on invertebrate paleontology. Part C. Protista 2 (2 volumes). Moore R.C. (ed.) University of Kansas Press, 900 p.

13. Loeblich A.R., Tappan H. (1986) Some new and revised genera and families of hyaline calcareous Foraminiferida (Protozoa). Transactions of the American Microscopical Society, 105: 239-265

14. Loeblich A.R., Tappan H. (1987) Foraminiferal genera and their classification. New York, Van Nostrand Rienhold Co., 970 p.

15. Neruchev S.G. (1982) Uranium and life in Earth's history. Leningrad, Nauka Press, 208 p. (in Russian)

16. Odum E.P. (1959) Fundamentals of Ecology. 2^ndEdition. Philadelphia, W.B. Saunders, 384 p.

17. Swinbanks D.D., Shirayama Y. (1986) High levels of natural radionuclides in a deep-sea infaunal xenophyophore. Nature, 320: 354-358

Размещено на Allbest.ru