TY - JOUR
T1 - The impact of taphonomic processes on interpreting paleoecologic changes in large lake ecosystems
T2 - Ostracodes in Lakes Tanganyika and Malawi
AU - Park, Lisa E.
AU - Cohen, Andrew S.
AU - Martens, Koen
AU - Bralek, Rebecca
N1 - Funding Information:
We wish to acknowledge and thank the following individuals for their assistance in this project: Simone Alin, Catherine O’Reilly and Melissa Hays for help with the field data acquisition of the experimental transects, Jean Jacques Tiercelin for access to BUR1 core from GEORIFT resources, Thomas Johnson for access to Malawi cores in Duluth, Doug Ricketts and Yvonne Chan for logistical support at the Large Lakes Observatory (Duluth, MN). We would also like to thank Susan Kidwell and Thomas Cronin for their helpful comments on this manuscript. A special thanks to Elizabeth Gierlowski-Kordesch and the editors of the Journal of Paleolimnology for compiling this issue. We would also like to thank the Governments of Tanzania, Burundi, Zambia and Malawi for their support of the different portions of data acquisition for this project. This work was supported by ATM 9619458 and EAR 9510033, as well as University of Akron Faculty Research Grant #1728 and the Stoller Research Fund, the University of Arizona Sulzer Research Fund, Sigma Xi, The Paleontological Society, The Geological Society of America, and Chevron. This paper is IDEAL publication no. 135 and is dedicated to the memory of Kerry Kelts, who inspired us all.
PY - 2003/8
Y1 - 2003/8
N2 - Nonmarine ostracodes are often used as proxy indicators for the biotic response to climate as well as anthropogenic changes in large lakes. Their large numbers, small size and sensitivities to environmental conditions make them ideal for assessing how organisms respond to environmental perturbations. However, little is known about the various taphonomic processes related to preserving these organisms in the lacustrine fossil record. Without understanding the amount of time averaging associated with these assemblages, any interpretation of their biodiversity and paleoecology may be problematic. To address these issues, we conducted actualistic experiments to determine transport, time-averaging, and the amount of taphonomic bias in ostracode sub-fossil assemblages. Sand transport experiments revealed significant mixing at all sites at shallower depths and significant mixing on rocky substrates but not sandy ones. Comparisons with ostracode material collected along the experimental transects support this model and demonstrate time averaging in both the sandy and rocky substrates. Preservational models were derived from the experimental data and applied to interpreting the paleobiologic record of ostracodes from piston cores in both Lake Tanganyika and Malawi. The core record reveals assemblages that have undergone significant time-averaging, and in the case of Lake Malawi, preservational degradation. In the core examined from Tanganyika, most assemblages resemble the time-averaged experimental model with respect to species richness, percentage of articulated shells and heavy bias towards adult dead individuals. In the Malawi cores, most of the valves were preserved only as internal molds. The taphonomic signature of these samples resemble the time-averaged assemblages of Tanganyika cores, even though carapaces are not often present. Both the experimental and live/dead valve data suggest significant time-averaging and transport, smearing seasonal-yearly data in some environments involved in using ostracodes to assess biotic changes as a result of climate and or anthropogenically-induced environmental change. Ostracode species richness estimates were impacted by time averaging because transport of dead valve material occurs at high percentages in the shallow depths and on the rocky substrates, suggesting that the ostracode death assemblages in these areas will not reflect living populations. In addition, ecologic models based only upon death assemblages will be less resolved than those based upon live assemblages. A time averaging index was derived using the % dead juveniles ratio, as well as sedimentation rate and information on the population dynamics, if known.
AB - Nonmarine ostracodes are often used as proxy indicators for the biotic response to climate as well as anthropogenic changes in large lakes. Their large numbers, small size and sensitivities to environmental conditions make them ideal for assessing how organisms respond to environmental perturbations. However, little is known about the various taphonomic processes related to preserving these organisms in the lacustrine fossil record. Without understanding the amount of time averaging associated with these assemblages, any interpretation of their biodiversity and paleoecology may be problematic. To address these issues, we conducted actualistic experiments to determine transport, time-averaging, and the amount of taphonomic bias in ostracode sub-fossil assemblages. Sand transport experiments revealed significant mixing at all sites at shallower depths and significant mixing on rocky substrates but not sandy ones. Comparisons with ostracode material collected along the experimental transects support this model and demonstrate time averaging in both the sandy and rocky substrates. Preservational models were derived from the experimental data and applied to interpreting the paleobiologic record of ostracodes from piston cores in both Lake Tanganyika and Malawi. The core record reveals assemblages that have undergone significant time-averaging, and in the case of Lake Malawi, preservational degradation. In the core examined from Tanganyika, most assemblages resemble the time-averaged experimental model with respect to species richness, percentage of articulated shells and heavy bias towards adult dead individuals. In the Malawi cores, most of the valves were preserved only as internal molds. The taphonomic signature of these samples resemble the time-averaged assemblages of Tanganyika cores, even though carapaces are not often present. Both the experimental and live/dead valve data suggest significant time-averaging and transport, smearing seasonal-yearly data in some environments involved in using ostracodes to assess biotic changes as a result of climate and or anthropogenically-induced environmental change. Ostracode species richness estimates were impacted by time averaging because transport of dead valve material occurs at high percentages in the shallow depths and on the rocky substrates, suggesting that the ostracode death assemblages in these areas will not reflect living populations. In addition, ecologic models based only upon death assemblages will be less resolved than those based upon live assemblages. A time averaging index was derived using the % dead juveniles ratio, as well as sedimentation rate and information on the population dynamics, if known.
KW - Lake Malawi
KW - Lake Tanganyika
KW - Ostracoda
KW - Taphonomy
KW - Time averaging
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U2 - 10.1023/A:1025570032179
DO - 10.1023/A:1025570032179
M3 - Article
AN - SCOPUS:0141563469
VL - 30
SP - 127
EP - 138
JO - Journal of Paleolimnology
JF - Journal of Paleolimnology
SN - 0921-2728
IS - 2
ER -