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Morphological deviations in planktonic Foraminifera as a reaction to enhanced environmental stress: Opportunities and problems
WEINKAUF, Manuel, et al.
WEINKAUF, Manuel, et al . Morphological deviations in planktonic Foraminifera as a reaction to enhanced environmental stress: Opportunities and problems. In: Aberhan, M., Fröbisch, J., Hampe, O., Kiessling, W., Müller, J., Neumann, C., Voss, M. & Witzmann, F. Centenary Meeting of the Paläontologische Gesellschaft 2012 . Berlin : 2012. p. 193-194
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193 Abstracts
intervals exhibiting local extinctions or strong drops in abundance were selected to investigate responses of the calcification intensity of the tests. This offers the unique chance to assess the reactions of planktonic Foraminif- era to severe environmental stress.
Several specimens, taken from a narrow sieve fraction, were individually measured and weighed together using an ultrabalance (d = 0.1 μg); the mean weight of the tests was then normalised for the mean test size in each sample.
It could be shown that the shallow dwelling, symbiont- bearing species Orbulina universa shows a distinct drop in test weight at the onset of the sapropel, and that the weight is further continuously decreasing thereafter for about 4000 years, until a local extinction of the species.
The calcification intensity of that species is also well cor- related with stable oxygen isotope values retrieved from tests of Globigerinoides ruber, which are probably in- dicative of the intensity of freshwater influx. In the deep dwelling species Globorotalia scitula evidence for a con- tinuous decrease in calcification intensity could be found, that started as early as 3000 years before the onset of the sapropel. Globorotalia inflata, a species that mainly lives in intermediate water depths, shows some fluctuations in test weight, but those cannot be attributed to the avail- able information on the timing of environmental change.
Interestingly, this species shows much larger intra-sample variations of the test weight than any of the other species investigated. Globigerinoides ruber (pink), for which results are still pending, will serve as a second shallow- dwelling species to be investigated. The main influential parameters for the observed fluctuations in calcification intensity are as yet unknown, with changes in freshwater influx from Africa—possibly causing changes in the car- bon equilibrium system in the Eastern Mediterranean—or changes in sea water salinity being considered as possi- ble reasons. We show that the calcification intensity of planktonic Foraminifera is subject to fluctuations that can be attributed to environmental changes, and that both long-term (i.e. thousands of years) and short-term (i.e.
100–200 years) reactions can be observed.
S5 – Morphological deviations in planktonic Foraminifera as a reaction to enhanced environmental stress: opportunities and problems
Weinkauf M.1*, T. Moller2, M. Koch3 & M. Kučera1
*E-mail: manuel.weinkauf@uni-tuebingen.de
1Eberhard-Karls-Universität Tübingen, Mathematisch–
Naturwissenschaftliche Fakultät, Fachbereich Geowis- senschaften, Hölderlinstraße 12, 72074 Tübingen, Ger- many; current address: University Bremen, MARUM, Leobener Str., 28359 Bremen, Germany
2Eberhard-Karls-Universität Tübingen, Mathematisch–
Naturwissenschaftliche Fakultät, Fachbereich Geowis-
senschaften, Hölderlinstr. 12, 72074 Tübingen, Germany
3Eberhard-Karls-Universität Tübingen, Mathematisch–
Naturwissenschaftliche Fakultät, Fachbereich Geowissen- schaften, Hölderlinstraße 12, 72074 Tübingen, Germany;
current address: Johann Wolfgang Goethe-Universität, In- stitut für Geowissenschaften, Facheinheit Paläontologie, Altenhöferallee 1, 60438 Frankfurt am Main, Germany Foraminifera are amongst the best known groups of fos- sil protists, featuring a remarkably complete and continu- ous fossil record. This fossil record holds considerable potential to study how species phenotype (morphology) responds to environmental perturbation. In this respect, it is of particular interest to study such cases where the en- vironmental perturbation on the studied population led to extinction. Such cases are impossible to study at present, because extinctions under natural conditions cannot be predicted. This study investigates the morphological re- action of planktonic Foraminifera when exposed to vary- ing levels of environmental stress, ultimately resulting in extinction. To this end, a sediment section from the East- ern Mediterranean was chosen, that covers the onset of Sapropel S5 (c.125 ka). This event was associated with local extinctions of several species of planktonic Fo- raminifera, and thus offers the chance to investigate the reaction of those species to environmental stress during a natural experiment with known outcome.
In three selected species of planktonic Foraminifera a variety of morphological traits, such as size, roundness, growth pattern, outline, and incidence of abnormal mor- photypes, was investigated. In Orbulina universa, which shows two local extinctions in the studied time interval, an increase in size and the incidence of abnormal mor- photypes could be observed during both intervals imme- diately preceding the extinction levels. Furthermore, the species shows a significant shift in test roundness with the onset of the sapropel, with roundness values being generally stable in both intervals before and after sapro- pel onset, respectively. Globorotalia scitula shows a local extinction shortly before the onset of the sapropel. Beside a generally variable but otherwise stable morphology a distinct deviation in growth rate and variability of growth rate can be observed immediately before the species be- comes locally extinct. In Globorotalia inflata no morpho- logical reaction to the observed environmental forcing could be observed; the species became extinct immedi- ately after sapropel onset without an obvious reaction of its shell morphology. These results indicate that morpho- logical reactions on environmental stress in planktonic Foraminifera occur on different time scales and that the type and level of reaction is species-specific. On large time scales long-lasting, stable deviations in morphology can be observed, associated with large environmental shifts. Over short time periods, as a result of fatal stress leading to local extinction, other morphological reactions are obvious. These can most likely be attributed to a re- laxation of growth patterns and appear to operate over a time interval of decades or less. We speculate that severe
194 Abstracts
stress at times preceding extinction either hinders internal control mechanisms that would normally ensure a more regular growth pattern, or it induces the species to relax the morphogenetic constraints and manifest more phenotypic variation, which might increase the chances of survival.
S5 – Travelling through time: the past, present and future biogeographic range of Amphistegina spp.
Weinmann A. E.1*, M. R. Langer1, S. Lötters2, D. Rödder3
*E-mail: weinmann@uni-bonn.de
1Steinmann-Institut für Geologie, Mineralogie und Palä- ontologie, Universität Bonn, Bonn, Germany
2Zoologisches Forschungsmuseum Alexander Koenig, Bonn, Germany
3Institut für Biogeographie, Universität Trier, Trier, Germany The larger, symbiont-bearing foraminiferal genus Am- phistegina is known to occupy warm, oligotrophic waters, preferably within reef areas. Its current biogeographic range lies between 30° N and S, but it has expanded to- wards higher latitudes during times of extensive global warming (e.g. during the Eocene or the Miocene). Dur- ing the last century, sea surface temperatures have been rising significantly due to global warming. This trend is expected to continue and climate change scenarios for 2100 suggest a further increase by 3° C in average (IPCC Synthesis Report 2007, among others). There are multiple examples from regions where range shifting of Amphistegina spp. can be observed, which most certain- ly relates to ongoing ocean warming.
In our studies on the biogeography of Amphistegina spp., we applied Species Distribution Models (SDMs) in order to evaluate the potential distribution of the taxon under current climate and to predict geographic range changes within the next decades. Our models for the glo- bal distribution of Amphistegina spp. showed that even under current climate conditions, potentially suitable hab- itats are not fully utilized and a general range expansion towards higher latitudes can be expected in the future.
Furthermore, we generated SDMs for the Mediterranean and the coast of East Africa – two regions where Am- phistegina spp. has known to expand its biogeographic range for decades. Our results suggest a progress of this trend for the next 50 years. Since Amphistegina spp. is one of the most prolific carbonate producers within the world’s oceans, the biogeographic changes predicted by our SDMs have to be closely monitored in the future.
S5 – Understanding stable isotope signals from fossil foraminifera – a Turonian Fossillagerstätte from Tanzania
Wendler I.1*, J. E. Wendler1, B. T. Huber2 & K. G. MacLeod3
*E-mail: flatter@uni-bremen.de
1Department of Geological Sciences, University of Bremen, P.O. Box 330 440, 28334 Bremen, Germany
2Department of Paleobiology, Smithsonian Museum of Natural History, PO Box 37012, MRC 121, Washington, DC 20013-7012, USA
3Department of Geological Sciences, University of Mis- souri, Columbia, Missouri 65211, USA
Upper Cretaceous sediments recovered during the Tan- zania Drilling Project from 2007 to 2009 include long intervals with exceptionally well preserved microfossils, providing an excellent sample base for generating sta- ble carbon and oxygen isotopic records as well as other geochemical data. Our study examines inter-species vari- ation in stable isotopic values of benthic and planktic fo- raminifera and one species of calcareous dinoflagellate cyst species. Our goal is (1) to evaluate the contribution of species-specific vital and microhabitat effects relative to the environmental signals on the isotopic signatures re- flected in the foraminiferal tests and (2) to indentify spe- cies that are best suited for studies of stable isotopes and temperature reconstructions in the Cretaceous. We present results from a Turonian sequence with rela- tively stable environmental conditions as inferred from minimal variation in intra-specific δ13C and δ18O values across the section. The studied material contains abun- dant and diverse benthic foraminifer assemblages that indicate an outer shelf to upper slope paleodepth. We performed single species δ13C and δ18O measurements for 18 calcareous benthic and 11 planktic species.
Cross plots of δ13C and δ18O show distinct offsets be- tween clusters of data points for individual species, re- flecting a combination of differences in habitat and dis- equilibrium fractionation due to kinetic and metabolic effects. Offsets in δ18O between two groups of trochospi- ral planktic foraminifera apparently reflect water depth- related differences in temperature during their lifetime.
An expected offset is observed between benthic species with aragonitic versus calcitic tests, but systematic offsets among aragonitic species indicate that micro-habitat or vital effects also influence measured values. The lowest δ13C values among the calcitic benthic foraminifera were observed for species of the genus Lenticulina. Because we did not observe differences in their preservation rela- tive to other benthic species, the isotope results suggest a strong influence of combined kinetic and metabolic effects on isotopic fractionation for Lenticulina species that are thought to be related to an opportunistic life style and fast growth and calcification rates. Among the stud- ied calcitic benthic species we identify four trochospiral epifaunal to shallow infaunal species that appear to have close-to-equilibrium isotopic values and are preferred for paleoenvironmental reconstructions. Relatively sta- ble within-sample inter-specific offsets in δ13C and δ18O
