References

Biogeosciences

1726-4189

Copernicus Publications

Göttingen, Germany

10.5194/bg-10-6639-2013

Calcification intensity in planktonic Foraminifera reflects ambient conditions irrespective of environmental stress

Weinkauf

M. F. G.

https://orcid.org/0000-0002-4640-9659

¹ ² Moller

¹ Koch

M. C.

³ Kučera

https://orcid.org/0000-0002-7817-9018

Eberhard Karls Universität, Mathematisch–Naturwissenschaftliche Fakultät, Fachbereich Geowissenschaften, Hölderlinstraße 12, 72074 Tübingen, Germany

MARUM, Leobener Straße, 28359 Bremen, Germany

Johann Wolfgang Goethe-Universität, Institut für Geowissenschaften, Facheinheit Paläontologie, Altenhöferallee 1, 60438 Frankfurt am Main, Germany

23 10 2013

10 10 6639 6655

2013

This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/

This article is available from https://bg.copernicus.org/articles/10/6639/2013/bg-10-6639-2013.html

The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/6639/2013/bg-10-6639-2013.pdf

Planktonic Foraminifera are important marine calcifiers, and the ongoing change in the oceanic carbon system makes it essential to understand the influence of environmental factors on the biomineralization of their shells. The amount of calcite deposited by planktonic Foraminifera during calcification has been hypothesized to reflect a range of environmental factors. However, it has never been assessed whether their calcification only passively responds to the conditions of the ambient seawater or whether it reflects changes in resource allocation due to physiological stress. To disentangle these two end-member scenarios, an experiment is required where the two processes are separated. A natural analogue to such an experiment occurred during the deposition of the Mediterranean sapropels, where large changes in surface water composition and stratification at the onset of the sapropel deposition were decoupled from local extinctions of planktonic Foraminifera species. We took advantage of this natural experiment and investigated the reaction of calcification intensity, expressed as mean area density (MAD), of four species of planktonic Foraminifera to changing conditions during the onset of Sapropel S5 (126–121 ka) in a sediment core from the Levantine Basin. We observed a significant relationship between MAD and surface water properties, as reflected by stable isotopes in the calcite of Foraminifera shells, but we failed to observe any reaction of calcification intensity on ecological stress during times of decreasing abundance culminating in local extinction. The reaction of calcification intensity to surface water perturbation at the onset of the sapropel was observed only in surface-dwelling species, but all species calcified more strongly prior to the sapropel deposition and less strongly within the sapropel than at similar conditions during the present-day. These results indicate that the high-salinity environment of the glacial Mediterranean Sea prior to sapropel deposition induced a~more intense calcification, whereas the freshwater injection to the surface waters associated with sapropel deposition inhibited calcification. The results are robust to changes in carbonate preservation and collectively imply that changes in normalized shell weight in planktonic Foraminifera should reflect mainly abiotic forcing.

References 1

Aldridge, D., Beer, C. J., and Purdie, D. A.: Calcfication in the planktonic Foraminifera Globigerina bulloides linked to phosphate concentrations in surface waters of the North Atlantic Ocean, Biogeosciences, 9, 1725–1739, <a href="http://dx.doi.org/10.5194/bg-9-1725-2012">https://doi.org/10.5194/bg-9-1725-2012</a>, 2012.

Aurahs, R., Treis, Y., Darling, K., and Kučera, M.: A revised taxonomic and phylogenetic concept for the planktonic foraminifer species Globigerinoides ruber based on molecular and morphometric evidence, Mar. Micropaleontol., 79, 1–14, <a href="http://dx.doi.org/10.1016/j.marmicro.2010.12.001">https://doi.org/10.1016/j.marmicro.2010.12.001</a>, 2011.

Barker, S. and Elderfield, H.: Foraminiferal calcification response to glacial–interglacial changes in atmospheric CO2, Science, 297, 833–836, <a href="http://dx.doi.org/10.1126/science.1072815">https://doi.org/10.1126/science.1072815</a>, 2002.

Beer, C. J., Schiebel, R., and Wilson, P. A.: Technical note: On methodologies for determining the size-normalised weight of planktic Foraminifera, Biogeosciences, 7, 2193–2198, <a href="http://dx.doi.org/10.5194/bg-7-2193-2010">https://doi.org/10.5194/bg-7-2193-2010</a>, 2010a.

Beer, C. J., Schiebel, R., and Wilson, P. A.: Testing planktic foraminiferal shell weight as a surface water [CO32-] proxy using plankton net samples, Geology, 38, 103–106, <a href="http://dx.doi.org/10.1130/G30150.1">https://doi.org/10.1130/G30150.1</a>, 2010b.

Bijma, J., Spero, H. J., and Lea, D. W.: Reassessing foraminiferal stable isotope geochemistry: Impact of the oceanic carbonate system (experimental results), in: Use of Proxies in Paleoceanography: Examples from the South Atlantic, edited by: Fischer, G. and Wefer, G., 489–512, Springer-Verlag, Berlin, Heidelberg, 1999.

Bleil, U., Brück, L., Frederichs, T., Haese, R., Hensen, C., Hilgenfeldt, C., Hoek, R., Hübscher, C., von Lom-Keil, H., Janke, A., Kreutz, R., Keenan, J., Little, M. L., Martens, H., Rosiak, U., Schmidt, W., Schneider, R., Segl, M., Spieß, V., Uenzelmann-Neben, G., Urbanek, H., and Zühlsdorff, L.: Geo Bremen South Atlantic 1996, \textscMeteor Berichte, Leitstelle \textscMeteor, Hamburg, 1997.

Broecker, W. and Clark, E.: An evaluation of Lohmann's Foraminifera weight dissolution index, Paleoceanography, 16, 531–534, <a href="http://dx.doi.org/10.1029/2000PA000600">https://doi.org/10.1029/2000PA000600</a>, 2001.

Cane, T., Rohling, E. J., Kemp, A. E. S., Cooke, S., and Pearce, R. B.: High-resolution stratigraphic framework for Mediterranean Sapropel S5: Defining temporal relationships between records of Eemian climate variability, Palaeogeogr. Palaeocl. Palaeoecol., 183, 87–101, <a href="http://dx.doi.org/10.1016/S0031-0182(01)00461-8">https://doi.org/10.1016/S0031-0182(01)00461-8</a>, 2002.

Chierici, M. and Fransson, A.: Calcium carbonate saturation in the surface water of the Arctic Ocean: Undersaturation in freshwater influenced shelves, Biogeosciences, 6, 2421–2432, <a href="http://dx.doi.org/10.5194/bg-6-2421-2009">https://doi.org/10.5194/bg-6-2421-2009</a>, 2009.

Conover, W. J.: Practical Nonparametric Statistics, Wiley Series in Probability and Mathematical Statistics, John Wiley & Sons, Ltd., New York, 1980.

Cramér, H.: Mathematical Methods of Statistics, vol. 9 of Princeton Mathematical Series, Princeton University Press, Princeton, 1946.

de Moel, H., Ganssen, G. M., Peeters, F. J. C., Jung, S. J. A., Kroon, D., Brummer, G. J. A., and Zeebe, R. E.: Planktic foraminiferal shell thinning in the Arabian Sea due to anthropogenic ocean acidification?, Biogeosciences, 6, 1917–1925, <a href="http://dx.doi.org/10.5194/bg-6-1917-2009">https://doi.org/10.5194/bg-6-1917-2009</a>, 2009.

de Vargas, C., Norris, R., Zaninetti, L., Gibb, S. W., and Pawlowski, J.: Molecular evidence of cryptic speciation in planktonic foraminifers and their relation to oceanic provinces, P. Natl. Acad. Sci. USA, 96, 2864–2868, <a href="http://dx.doi.org/10.1073/pnas.96.6.2864">https://doi.org/10.1073/pnas.96.6.2864</a>, 1999.

de Villiers, S.: Optimum growth conditions as opposed to calcite saturation as a control on the calcification rate and shell-weight of marine Foraminifera, Mar. Biol., 144, 45–49, <a href="http://dx.doi.org/10.1007/s00227-003-1183-8">https://doi.org/10.1007/s00227-003-1183-8</a>, 2004.

Gasse, F.: Hydrological changes in the African tropics since the last glacial maximum, Quaternary Sci. Rev., 19, 189–211, <a href="http://dx.doi.org/10.1016/S0277-3791(99)00061-X">https://doi.org/10.1016/S0277-3791(99)00061-X</a>, 2000.

Hartigan, J. A. and Hartigan, P. M.: The Dip Test of unimodality, Ann. Stat., 13, 70–84, <a href="http://dx.doi.org/10.1214/aos/1176346577">https://doi.org/10.1214/aos/1176346577</a>, 1985.

Hayes, A., Kučera, M., Kallel, N., Sbaffi, L., and Rohling, E. J.: Glacial Mediterranean sea surface temperatures based on planktonic foraminiferal assemblages, Quaternary Sci. Rev., 24, 999–1016, <a href="http://dx.doi.org/10.1016/j.quascirev.2004.02.018">https://doi.org/10.1016/j.quascirev.2004.02.018</a>, 2005.

Hayward, B. W., Sabaa, A. T., Kawagata, S., and Grenfell, H. R.: The Early Pliocene re-colonisation of the deep Mediterranean Sea by benthic Foraminifera and their pulsed Late Pliocene–Middle Pleistocene decline. Mar. Micropal., 71, 97–112, <a href="http://dx.doi.org/10.1016/j.marmicro.2009.01.008">https://doi.org/10.1016/j.marmicro.2009.01.008</a>, 2009.

Helsel, D. R. and Hirsch, R. M.: Statistical methods in water resources, in: Hydrologic Analysis and Interpretation, vol. 4 of Techniques of Water-Resources Investigations Reports, chap. A3, 1–510, US Geological Survey, 2002.

Hemleben, C., Becker, T., Bellas, S., Benningsen, G., Casford, J., Cagatay, N., Emeis, K.-C., Engelen, B., Ertan, T., Fontanier, C., Friedrich, O., Frydas, D., Giunta, S., Hoffelner, H., Jorissen, F., Kahl, G., Kaszemeik, K., Lykousis, V., Meier, S., Nickel, G., Overman, J., Pross, J., Reichel, T., Robert, C., Rohling, E., Ruschmeier, W., Sakinc, M., Schiebel, R., Schmiedl, G., Schubert, K., Schulz, H., Tischnak, J., and Truscheit, T.: Ostatlantik–Mittelmeer–Schwarzes Meer Part 3: Cruise No. 51, Leg 3, \textscMeteor Berichte, Leitstelle \textscMeteor, Hamburg, 2003.

Hoelzmann, P., Kruse, H.-J., and Rottinger, F.: Precipitation estimates for the eastern Saharan palaeomonsoon based on a water balance model of the West Nubian Palaeolake Basin, Global Planet. Change, 26, 105–120, <a href="http://dx.doi.org/10.1016/S0921-8181(00)00038-2">https://doi.org/10.1016/S0921-8181(00)00038-2</a>, 2000.

Hyndman, R. J. and Fan, Y.: Sample quantiles in statistical packages, Am. Stat., 50, 361–365, <a href="http://dx.doi.org/10.1080/00031305.1996.10473566">https://doi.org/10.1080/00031305.1996.10473566</a>, 1996.

Kendall, M. G.: A new measurement of rank correlation, Biometrika, 30, 81–93, <a href="http://dx.doi.org/10.1093/biomet/30.1-2.81">https://doi.org/10.1093/biomet/30.1-2.81</a>, 1938.

Kučera, M., Weinelt, M., Kiefer, T., Pflaumann, U., Hayes, A., Weinelt, M., Chen, M.-T., Mix, A. C., Barrows, T. T., Cortijo, E., Duprat, J., Juggins, S., and Waelbroeck, C.: Reconstruction of sea-surface temperatures from assemblages of planktonic Foraminifera: Multi-technique approach based on geographically constrained calibration data sets and its application to glacial Atlantic and Pacific Oceans, Quaternary Sci. Rev., 24, 951–998, <a href="http://dx.doi.org/10.1016/j.quascirev.2004.07.014">https://doi.org/10.1016/j.quascirev.2004.07.014</a>, 2005.

Lohmann, G. P.: A model for variation in the chemistry of planktonic Foraminifera due to secondary calcification selective dissolution, Paleoceanography, 10, 445–457, <a href="http://dx.doi.org/10.1029/95PA00059">https://doi.org/10.1029/95PA00059</a>, 1995.

Lombard, F., da Rocha, R. E., Bijma, J., and Gattuso, J.-P.: Effect of carbonate ion concentration and irradiance on calcfication in planktonic Foraminifera, Biogeosciences, 7, 247–255, <a href="http://dx.doi.org/10.5194/bg-7-247-2010">https://doi.org/10.5194/bg-7-247-2010</a>, 2010.

Manno, C., Morata, N., and Bellerby, R.: Effect of ocean acidification and temperature increase on the planktonic foraminifer Neogloboquadrina pachyderma (sinistral), Polar Biol., 35, 1311–1319, <a href="http://dx.doi.org/10.1007/s00300-012-1174-7">https://doi.org/10.1007/s00300-012-1174-7</a>, 2012.

Marino, G., Rohling, E. J., Rijpstra, W. I. C., Sangiorgi, F., Schouten, S., and Damsté, J. S. S.: Aegean Sea as driver of hydrographic and ecological changes in the Eastern Mediterranean, Geology, 35, 675–678, <a href="http://dx.doi.org/10.1130/G23831A.1">https://doi.org/10.1130/G23831A.1</a>, 2007.

Marshall, B. J., Thunell, R. C., Henehan, M. H., Astor, Y., and Wejnert, K. R.: Planktonic foraminiferal area density as a proxy for carbonate ion concentration: A calibration study using the Cariaco Basin Ocean Time Series, Paleoceanography, 28, 1–14, <a href="http://dx.doi.org/10.1002/palo.20034">https://doi.org/10.1002/palo.20034</a>, 2013.

Media Cybernetics, Inc.: Image-Pro\textsuperscript\textregistered Plus Version 6.0 for Windows\textsuperscript\texttrademark Start-Up Guide, Silver-Spring, 2006.

Moller, T.: Formation and palaeoclimatic interpretation of a continuously laminated Sapropel S$_5$: A window to the climate variability during the Eemian interglacial in the Eastern Mediterranean, Ph.D. thesis, Eberhard–Karls-Universität Tübingen, Tübingen, <a href="http://nbn-resolving.de/urn:nbn:de:bsz:21-opus-63524">http://nbn-resolving.de/urn:nbn:de:bsz:21-opus-63524</a>, 2012.

Moller, T., Schulz, H., Hamann, Y., Dellwig, O., and Kučera, M.: Sedimentology and geochemistry of an exceptionally preserved last interglacial Sapropel S5 in the Levantine Basin (Mediterranean Sea), Mar. Geol., 291–294, 34–48, <a href="http://dx.doi.org/10.1016/j.margeo.2011.10.011">https://doi.org/10.1016/j.margeo.2011.10.011</a>, 2012.

Morard, R., Quillévéré, F., Douady, C. J., de Vargas, C., de Garidel-Thoron, T., and Escarguel, G.: Worldwide genotyping in the planktonic foraminifer Globoconella inflata: Implications for life history and paleoceanography, PLoS ONE, 6, e26665, <a href="http://dx.doi.org/10.1371/journal.pone.0026665">https://doi.org/10.1371/journal.pone.0026665</a>, 2011.

Moy, A. D., Howard, W. R., Bray, S. G., and Trull, T. W.: Reduced calcification in modern Southern Ocean planktonic Foraminifera, Nat. Geosci., 2, 276–280, <a href="http://dx.doi.org/10.1038/NGEO460">https://doi.org/10.1038/NGEO460</a>, 2009.

Myers, P. G., Haines, K., and Rohling, E. J.: Modeling the palecocirculation of the Mediterranean: The last glacial maximum and the Holocene with emphasis on the formation of Sapropel S$_1$, Paleoceanography, 13, 586–606, <a href="http://dx.doi.org/10.1029/98PA02736">https://doi.org/10.1029/98PA02736</a>, 1998.

Pearson, P. N., Ditchfield, P. W., Singano, J., Harcourt-Brown, K. G., Nicholas, C. J., Olsson, R. K., Shackleton, N. J., and Hall, M. A.: Warm tropical sea surface temperatures in the Late Cretaceous and Eocene epochs, Nature, 413, 481–487, <a href="http://dx.doi.org/10.1038/35097000">https://doi.org/10.1038/35097000</a>, 2001.

Pujol, C. and Vergnaud Grazzini, C.: Distribution patterns of live planktic foraminifers as related to regional hydrography and productive systems of the Mediterranean Sea, Mar. Micropaleontol., 25, 187–217, <a href="http://dx.doi.org/10.1016/0377-8398(95)00002-I">https://doi.org/10.1016/0377-8398(95)00002-I</a>, 1995.

R Development Core Team: R: A Language and Environment for Statistical Computing, R Foundation for Statistical Computing, Vienna, <a href="http://www.R-project.org/">http://www.R-project.org/</a>, 2011.

Rinna, J., Warning, B., Meyers, P. A., Brumsack, H.-J., and Rullkötter, J.: Combined organic and inorganic geochemical reconstruction of paleodepositional conditions of a Pliocene sapropel from the Eastern Mediterranean Sea, Geochim. Cosmochim. Ac., 66, 1969–1986, <a href="http://dx.doi.org/10.1016/S0016-7037(02)00826-8">https://doi.org/10.1016/S0016-7037(02)00826-8</a>, 2002.

Rohling, E., Abu-Zied, R., Casford, J., Hayes, A., and Hoogakker, B.: The marine environment: Present and past, in: The Physical Geography of the Mediterranean, edited by: Woodward, J., The Oxford Regional Environments Series, chap. 2, 33–67, Oxford University Press, New York, 2009.

Rohling, E. J.: Environmental control on Mediterranean salinity and δ18O, Paleoceanography, 14, 706–715, <a href="http://dx.doi.org/10.1029/1999PA900042">https://doi.org/10.1029/1999PA900042</a>, 1999.

Rohling, E. J., de Rijk, S., Myers, P. G., and Haines, K.: Palaeoceanography and numerical modelling: The Mediterranean Sea at times of sapropel formation, in: Climates: Past and Present, edited by: Hart, M. B., vol. 181 of Special Publications of the Geological Society, 135–149, Geological Society, London, <a href="http://dx.doi.org/10.1144/GSL.SP.2000.181.01.13">https://doi.org/10.1144/GSL.SP.2000.181.01.13</a>, 2000.

Rohling, E. J., Cane, T. R., Cooke, S., Sprovieri, M., Bouloubassi, I., Emeis, K.-C., Schiebel, R., Kroon, D., Jorissen, F. J., Lorre, A., and Kemp, A. E. S.: African monsoon variability during the previous interglacial maximum, Earth Planet. Sc. Lett., 202, 61–75, <a href="http://dx.doi.org/10.1016/S0012-821X(02)00775-6">https://doi.org/10.1016/S0012-821X(02)00775-6</a>, 2002.

Rohling, E. J., Sprovieri, M., Cane, T., Casford, J. S. L., Cooke, S., Bouloubassi, I., Emeis, K.-C., Schiebel, R., Rogerson, M., Hayes, A., Jorissen, F. J., and Kroon, D.: Reconstructing past planktic foraminiferal habitats using stable isotope data: A case history for Mediterranean Sapropel S5, Mar. Micropaleontol., 50, 89–123, <a href="http://dx.doi.org/10.1016/S0377-8398(03)00068-9">https://doi.org/10.1016/S0377-8398(03)00068-9</a>, 2004.

Rossignol-Strick, M.: African monsoons, an immediate climate response to orbital insolation, Nature, 304, 46–49, <a href="http://dx.doi.org/10.1038/304046a0">https://doi.org/10.1038/304046a0</a>, 1983.

Rossignol-Strick, M., Nesteroff, W., Olive, P., and Vergnaud Grazzini, C.: After the deluge: Mediterranean stagnation and sapropel formation, Nature, 295, 105–110, <a href="http://dx.doi.org/10.1038/295105a0">https://doi.org/10.1038/295105a0</a>, 1982.

Schiebel, R., Waniek, J., Zeltner, A., and Alves, M.: Impact of the Azores Front on the distribution of planktic foraminifers, shelled gastropods, and coccolithophorids, Deep-Sea Res. Pt. II, 49, 4035–4050, <a href="http://dx.doi.org/10.1016/S0967-0645(02)00141-8">https://doi.org/10.1016/S0967-0645(02)00141-8</a>, 2002.

Schindelin, J., Arganda-Carreras, I., Frise, E., Kaynig, V., Longair, M., Pietzsch, T., Preibisch, S., Rueden, C., Saalfeld, S., Schmid, B., Tinevez, J.-Y., White, D. J., Hartenstein, V., Eliceiri, K., Tomancak, P., and Cardona, A.: Fiji: An open-source platform for biological-image analysis, Nat. Methods, 9, 676–682, <a href="http://dx.doi.org/10.1038/nmeth.2019">https://doi.org/10.1038/nmeth.2019</a>, 2012.

Schmidt, D. N., Renaud, S., Bollmann, J., Schiebel, R., and Thierstein, H. R.: Size distribution of Holocene planktic foraminifer assemblages: Biogeography, ecology and adaptation, Mar. Micropaleontol., 50, 319–338, <a href="http://dx.doi.org/10.1016/S0377-8398(03)00098-7">https://doi.org/10.1016/S0377-8398(03)00098-7</a>, 2004.

Schneider, A., Wallace, D. W. R., and Körtzinger, A.: Alkalinity of the Mediterranean Sea, Geophys. Res. Lett., 34, L15608, <a href="http://dx.doi.org/10.1029/2006GL028842">https://doi.org/10.1029/2006GL028842</a>, 2007.

Schulz, H., Bayer, M., Denker, C., Hemleben, C., Martínez Botí, M., Numberger, L. D., Palamenghi, L., Storz, D., and van Raden, U.: Cruise Report – Cruise No.: 334, F. S. Poseidon Cruise Reports, Leibniz-Institut für Meereswissenschaften an der Universität Kiel, Kiel, 2006.

Seiter, K., Hensen, C., and Zabel, M.: Benthic carbon mineralization on a global scale. Global Biogeochem. Cy., 19, GB1010, <a href="http://dx.doi.org/10.1029/2004GB002225">https://doi.org/10.1029/2004GB002225</a>, 2005.

Sen, P. K.: Estimates of the regression coefficient based on Kendall's Tau, J. Am. Stat. Assoc., 63, 1379–1389, <a href="http://www.jstor.org/stable/2285891">http://www.jstor.org/stable/2285891</a>, 1968.

Shapiro, S. S. and Wilk, M. B.: An analysis of variance test for normality (complete samples), Biometrika, 52, 591–611, <a href="http://dx.doi.org/10.1093/biomet/52.3-4.591">https://doi.org/10.1093/biomet/52.3-4.591</a>, 1965.

Theil, H.: A rank-invariant method of linear and polynomial regression analysis, III, P. K. Ned. Akad. Wetensc., 53, 1397–1412, 1950.

Trask, P. D.: Relation of salinity to the calcium carbonate content of marine sediments, in: Shorter Contributions to General Geology, edited by: Ickes, H. I. and Mendenhall, W. C., vol. 186 of United States Geological Survey Professional Papers, 273–299, United States Government Printing Office, Washington, <a href="https://play.google.com/store/books/details?id=P0IRAAAAIAAJ&rdid=book-P0IRAAAAIAAJ&rdot=1">https://play.google.com/store/books/details?id=P0IRAAAAIAAJ&rdid=book-P0IRAAAAIAAJ&rdot=1</a>, 1937.

van der Meer, M. T. J., Baas, M., Rijpstra, W. I. C., Marino, G., Rohling, E. J., Damsté, J. S. S., and Schouten, S.: Hydrogen isotopic compositions of long-chain alkenones record freshwater flooding of the Eastern Mediterranean at the onset of sapropel deposition, Earth Planet. Sc. Lett., 262, 594–600, <a href="http://dx.doi.org/10.1016/j.epsl.2007.08.014">https://doi.org/10.1016/j.epsl.2007.08.014</a>, 2007.

van Raden, U. J., Groeneveld, J., Raitzsch, M., and Kučera, M.: Mg/Ca in the planktonic Foraminifera Globorotalia inflata and Globigerinoides bulloides from Western Mediterranean plankton tow and core top samples, Mar. Micropaleontol., 78, 101–112, <a href="http://dx.doi.org/10.1016/j.marmicro.2010.11.002">https://doi.org/10.1016/j.marmicro.2010.11.002</a>, 2011.

Vangel, M. G.: Confidence intervals for a normal coefficient of variation, Am. Stat., 50, 21–26, <a href="http://www.jstor.org/stable/2685039">http://www.jstor.org/stable/2685039</a>, 1996.

Williams, D. F., Thunell, R. C., and Kennett, J. P.: Periodic freshwater flooding and stagnation of the Eastern Mediterranean Sea during the late Quaternary, Science, 201, 252–254, <a href="http://dx.doi.org/10.1126/science.201.4352.252">https://doi.org/10.1126/science.201.4352.252</a>, 1978.

Wüst, G.: On the vertical circulation of the Mediterranean Sea, J. Geophys. Res., 66, 3261–3271, <a href="http://dx.doi.org/10.1029/JZ066i010p03261">https://doi.org/10.1029/JZ066i010p03261</a>, 1961.

Yates, F.: Contingency tables involving small numbers and the $\chi^2$ Test, J. Roy. Stat. Soc. Supp., 1, 217–235, <a href="http://www.jstor.org/stable/2983604">http://www.jstor.org/stable/2983604</a>, 1934.