ALBERT

Description: 2-D seismic data from the top and the western slope of Mergui Ridge in water depths between 300 and 2200 m off the Thai west coast have been investigated in order to identify mass transport deposits (MTDs) and evaluate the tsunamigenic potential of submarine landslides in this outer shelf area. Based on our newly collected data, 17 mass transport deposits have been identified. Minimum volumes of individual MTDs range between 0.3 km3 and 14 km3. Landslide deposits have been identified in three different settings: (i) stacked MTDs within disturbed and faulted basin sediments at the transition of the East Andaman Basin to the Mergui Ridge; (ii) MTDs within a pile of drift sediments at the basin-ridge transition; and (iii) MTDs near the edge of/on top of Mergui Ridge in relatively shallow water depths (〈 1000 m). Our data indicate that the Mergui Ridge slope area seems to have been generally unstable with repeated occurrence of slide events. We find that the most likely causes for slope instabilities may be the presence of unstable drift sediments, excess pore pressure, and active tectonics. Most MTDs are located in large water depths (〉 1000 m) and/or comprise small volumes suggesting a small tsunami potential. Moreover, the recurrence rates of failure events seem to be low. Some MTDs with tsunami potential, however, have been identified on top of Mergui Ridge. Mass-wasting events that may occur in the future at similar locations may trigger tsunamis if they comprise sufficient volumes. Landslide tsunamis, emerging from slope failures in the working area and affecting western Thailand coastal areas therefore cannot be excluded, though the probability is very small compared to the probability of earthquake-triggered tsunamis, arising from the Sunda Trench.

Description: Ancient Lake Ohrid is a steep-sided, oligotrophic, karst lake that was tectonically formed most likely within the Pliocene and often referred to as a hotspot of endemic biodiversity. This study aims on tracing significant lake level fluctuations at Lake Ohrid using high-resolution acoustic data in combination with lithological, geochemical, and chronological information from two sediment cores recovered from sub-aquatic terrace levels at ca. 32 and 60m water depth. According to our data, significant lake level fluctuations with prominent lowstands of ca. 60 and 35m below the present water level occurred during Marine Isotope Stage (MIS) 6 and MIS 5, respectively. The effect of these lowstands on biodiversity in most coastal parts of the lake is negligible, due to only small changes in lake surface area, coastline, and habitat. In contrast, biodiversity in shallower areas was more severely affected due to disconnection of today sublacustrine springs from the main water body. Multichannel seismic data from deeper parts of the lake clearly image several clinoform structures stacked on top of each other. These stacked clinoforms indicate significantly lower lake levels prior to MIS 6 and a stepwise rise of water level with intermittent stillstands since its existence as water-filled body, which might have caused enhanced expansion of endemic species within Lake Ohrid.

Description: 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.

Description: An international, multidisciplinary research group is proposing the “NICA-BRIDGE” drilling project, within the framework of the International Continental Scientific Drilling Program (ICDP). The project goal is to conduct scientific drilling in Lake Nicaragua and Lake Managua (Nicaragua, Central America) to obtain long lacustrine sediment records to (a) extend the neotropical paleoclimate record back to the Pliocene, making it one of the longest continental tropical climate archives in the world, and to (b) provide geological data on the long-term complex interplay among tectonics, volcanism, sea-level dynamics, climate change, and biosphere. The lakes are the two largest in Central America, and they are located in a trench-parallel half graben that hosts the volcanic front, which developed during or prior to the Pliocene, as a consequence of subduction-related tectonic activity. The lakes are uniquely suited for multidisciplinary scientific investigation as their long, con- tinuous sediment records (several Myr) will facilitate the study of (1) terrestrial and marine basin development at the southern Central American margin, (2) alternating lacustrine and marine environments in response to tec- tonic and climatic changes, (3) the longest record of tropical climate proxies, (4) the evolution of (and transition between) the Miocene to Pliocene/Pleistocene and Pleistocene to present volcanic arcs, which were separated by slab rollback, (5) the significance of the lakes as hot spots for endemism, and (6) the Great American Biotic Interchange at this strategic location, i.e., the N–S and reverse migration of fauna after the land bridge between the Americas was established. The planned ICDP project offers an opportunity to explore these topics through continent-based seismolog- ical, volcanological, paleoclimatological, paleoecological, and paleoenvironmental studies, combined with an International Ocean Discovery Program (IODP) drill project to explore its oceanic continuation. In preparation of this drilling project, an ICDP workshop was held in Montelimar, Nicaragua, on 2–5 March 2020 to develop drilling strategies and refine scientific questions, objectives, and hypotheses. The workshop was organized and hosted by the principal investigators and the Instituto Nicaragüense de Estudios Territoriales (INETER), with funding from the ICDP. Forty-five researchers from 12 countries participated in the workshop, including representatives from ICDP. During the workshop, previous research data on the study lakes, including new recent surveys, were reviewed, and a three-phase strategy for the proposed research was developed. The aim of Phase 0 is to complement the pre-site surveys where we identified the need for further data. In Phase I, with ICDP support, we will obtain sediment cores ∼ 100 m long, which will allow us to investigate many of the scientific questions. Based on the data from those drill cores, coring locations will be identified for a future Phase II, which we envisage as a combined ICDP/IODP project to collect deep drill cores in the lakes and the offshore Sandino Basin in order to extend Phase I results to much deeper time. The Sandino Basin is the oceanic continuation of the depression in which the studied lakes are located, and complementary marine drilling will improve the understanding of the evolution of this complex margin.