Possible earthquake trigger for 6th century mass wasting deposit at Lake Ohrid (Macedonia/Albania)

Lake Ohrid shared by the Republics of Albania and Macedonia is formed by a tectonically active graben within the south Balkans and suggested to be the oldest lake in Europe. Several studies have shown that the lake provides a valuable record of climatic and environmental changes and a distal tephrostratigraphic record of volcanic eruptions from Italy. Fault structures identified in seismic data demonstrate that sediments have also the potential to record tectonic activity in the region. Here, we provide an example of linking seismic and sedimentological information with tectonic activity and historical documents. Historical documents indicate that a major earthquake destroyed the city of Lychnidus (today: city of Ohrid) in the early 6th century AD. Multichannel seismic profiles, parametric sediment echosounder profiles, and a 10.08m long sediment record from the western part of the lake indicate a 2m thick mass wasting deposit, which is tentatively correlated with this earthquake. The mass wasting deposit is chronologically well constrained, as it directly overlays the AD472/AD 512 tephra. Moreover, radiocarbon dates and cross correlation with other sediment sequences with similar geochemical characteristics of the Holocene indicate that the mass wasting event took place prior to the onset of the Medieval Warm Period, and is attributed it to one of the known earthquakes in the region in the early 6th century AD

Selective preservation of organic matter in marine environments; processes and impact on the sedimentary record

© The Authors, 2010. This article is distributed under the terms of the Creative Commons Attribution 3.0 License. The definitive version was published in Biogeosciences 7 (2010): 483-511, doi: 10.5194/bg-7-483-2010The present paper is the result of a workshop sponsored by the DFG Research Center/Cluster of Excellence MARUM "The Ocean in the Earth System", the International Graduate College EUROPROX, and the Alfred Wegener Institute for Polar and Marine Research. The workshop brought together specialists on organic matter degradation and on proxy-based environmental reconstruction. The paper deals with the main theme of the workshop, understanding the impact of selective degradation/preservation of organic matter (OM) in marine sediments on the interpretation of the fossil record. Special attention is paid to (A) the influence of the molecular composition of OM in relation to the biological and physical depositional environment, including new methods for determining complex organic biomolecules, (B) the impact of selective OM preservation on the interpretation of proxies for marine palaeoceanographic and palaeoclimatic reconstruction, and (C) past marine productivity and selective preservation in sediments. It appears that most of the factors influencing OM preservation have been identified, but many of the mechanisms by which they operate are partly, or even fragmentarily, understood. Some factors have not even been taken carefully into consideration. This incomplete understanding of OM breakdown hampers proper assessment of the present and past carbon cycle as well as the interpretation of OM based proxies and proxies affected by OM breakdown. To arrive at better proxy-based reconstructions "deformation functions" are needed, taking into account the transport and diagenesis-related molecular and atomic modifications following proxy formation. Some emerging proxies for OM degradation may shed light on such deformation functions. The use of palynomorph concentrations and selective changes in assemblage composition as models for production and preservation of OM may correct for bias due to selective degradation. Such quantitative assessment of OM degradation may lead to more accurate reconstruction of past productivity and bottom water oxygenation. Given the cost and effort associated with programs to recover sediment cores for paleoclimatological studies, as well as with generating proxy records, it would seem wise to develop a detailed sedimentological and diagenetic context for interpretation of these records. With respect to the latter, parallel acquisition of data that inform on the fidelity of the proxy signatures and reveal potential diagenetic biases would be of clear value.We acknowledge generous financial support by the DFG Research Center/Cluster of Excellence MARUM “The Ocean in the Earth System”, the International Graduate College EUROPROX and the Alfred Wegener Institute for Polar and Marine Research enabling the realisation of the “Workshop on Selective Preservation of Organic Matter: Processes and Impact on the Fossil Record” which formed the basis of this paper. GJMV acknowledges support by the German Science Foundation (DFG grant VE486/2)

A Late Glacial to Holocene record of environmental change from Lake Dojran (Macedonia, Greece)

A Late Glacial to Holocene sediment sequence (Co1260, 717 cm) from Lake Dojran, located at the boarder of the F.Y.R. of Macedonia and Greece, has been investigated to provide information on climate variability in the Balkan region. A robust age-model was established from 13 radiocarbon ages, and indicates that the base of the sequence was deposited at ca. 12 500 cal yr BP, when the lake-level was low. Variations in sedimentological (H2O, TOC, CaCO3, TS, TOC/TN, TOC/TS, grain-size, XRF, δ18Ocarb, δ13Ccarb, δ13Corg) data were linked to hydro-acoustic data and indicate that warmer and more humid climate conditions characterised the remaining period of the Younger Dryas until the beginning of the Holocene. The Holocene exhibits significant environmental variations, including the 8.2 and 4.2 ka cooling events, the Medieval Warm Period and the Little Ice Age. Human induced erosion processes in the catchment of Lake Dojran intensified after 2800 cal yr BP

Paleoclimatic and palaeoceanographic changes coupled to the Panama Isthmus closing (13-4 Ma) using organic proxies

This study reconstructs the climatic and oceanographic changes from 13 to 4 Ma at Ocean Drilling Program (ODP) Sites 999 (Caribbean) and 1241 (East Pacific) during Panama Isthmus closure. We used lipid biomarkers as marine production indicators and organic proxies (U37K ' and TEX86H) to estimate ocean surface and thermocline temperatures. Enhanced terrestrial input during the first 3 Ma of the record, possibly coupled to tectonic pro-cesses, may have triggered higher surface productivity at both sides of the Isthmus. Even though marine pro-duction is generally higher in the tropical Pacific, a peak in alkenone production at 12.4-10.6 Ma indicates unrestricted inflow of nutrient-rich waters into the Caribbean. Higher production is observed during the global late Miocene biogenic bloom (LMBB 8-4.5 Ma) coupled to enhanced nutrients from terrestrial sources and/or upwelling. We find a good correspondence between U37K ' and modern sea surface temperature (SST). The TEX86H is a good tracer for thermocline values, however, the deeper Thaumarchaeota distribution in the Caribbean may result in an underestimation of absolute temperatures at ODP Site 999. None the less, temperature records at both Sites show similar trends coupled to global climate dynamics, therefore Isthmus build up did not signifi-cantly affect surface or thermocline temperatures at a regional level. Globally reported decreasing temperatures during the late Miocene and early Pliocene coupled to decreasing CO2 levels are registered at both Sites down to at least 200 m. The late Miocene warm period (LMWP 9.5-7 Ma), late Miocene cold period (LMC 7-5.4 Ma) and the Pliocene warm period (PWP 4-3.5 Ma) are reflected by our temperature records confirming global climate is the main driver of temperature evolution in the study area. The reconstructed temperatures are mainly coupled to atmospheric forcing in the Caribbean, with a deviation possibly due to inflow of colder Pacific intermediate waters. While at ODP Site 1241 temperatures are mainly controlled by global climate, the Site also reflects changes in the water column as it migrates interacting with the complex current structure of the tropical Pacific. Decoupled temperature patterns at both Sites are related with differential changes in water column structure partially masking the climatic signal. Therefore, we could establish that while tectonic processes and related terrestrial input increases as well as upwelling control production and water column structure, climate in the study area remained tuned to global patterns regardless of Isthmus closure stage