1:30pm - 1:45pm
Quantitative assessment of the terrain transformation in proglacial areas (the Djankuat River catchment case study, Caucuses)
1Faculty of Geography, Lomonosov Moscow State University, Moscow, Russian Federation; 2Institute of Geography, Russian Academy of Sciences, Moscow, Russian Federation
Proglacial areas are extremely unstable and characterized by highly intensive geomorphic processes. In this study, we consider a typical proglacial area on the Caucuses – Djankuat river catchment. This research presents the first results for the complex monitoring of exogenic geomorphic process rates within the selected catchment. A repeated UAV survey for selected sites conducted in September 2019 and in August 2020 was the primary method. Also, high-resolution DEMs derived from stereo satellite images and the existing data obtained in field observations were used. It was determined that about 4122 ± 179 t yr-1 enters the glacier’s surface from the located above rockwalls due to rockfalls and avalanches, which corresponds to the erosion rate – 1.29 mm yr-1. The surface level averagely decreased by 0.48 m between surveys in the river valley just downstream from the glacier. The maximum losses were determined for the glacier front and buried ice outcrops, where values were -1.59 m (buried ice on the left valley side), -2.72 m (buried ice on the right valley side), -3.17 m (glacier front). The highest geomorphic intensity in the proglacial areas apparently associated with the rapid buried ice melting and occurs with a slight delay after the glacier retreat. Specific attention in proglacial areas should be paid to the quantitative assessment of extreme event consequences, which lead to main terrain transformations, sediment yield peak values, and, eventually, to total erosion.
The study was supported by the Russian Science Foundation (project No. 19-17-00181).
1:45pm - 2:00pm
First evidence from Lake Melville, Canada: Subglacial lake sediments underneath the Laurentide Ice Sheet?
1University of Bremen, Germany; 2Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany
The fjord-type Lake Melville is located in Labrador, Eastern Canada, as part of the Hamilton Inlet System. It is mainly characterised by riverine freshwater influx into its western end and intrusion of saline water from the Labrador Sea through the shallow Rigolet Narrows.
Previous studies assumed that the retreating Laurentide Ice Sheet (LIS) caused the deposition of a typical glacial sediment sequence when its margin reached Lake Melville between 10,000 to 8,000 years ago (King, 1985; Syvitski and Lee, 1997). However, as suggested for other sites (e.g. Great Slave Lake; Christoffersen et al., 2008), the up to 400 m thick sediment package might contain pre-deglacial sediment because Lake Melville potentially persisted as a subglacial lake underneath the LIS.
Initial measurements and lithological investigations on two selected sediment cores (~14 m and 16 m) recovered during expedition MSM84 (2019) indicate a significant change in lithology and selected sediment-physical parameters within the lowermost two meters. First 14C-dates of gastropod and bivalve remains resulted in a preliminary age model with an extrapolated basal age of ~11.6 ka cal BP, but hence pre-dating the local deglaciation. In accordance with sediment echosounder data, microscopic investigations and first XRF analysis, we assume that these initial findings point at sediment deposition in a subglacial lake environment. In a next step, we aim at significantly improving the age model by considering more 14C-samples from various sediment cores as well as conducting further multi-proxy analyses to test our hypothesis.
2:00pm - 2:15pm
Biological productivity in the Southern Ocean across the Eocene-Oligocene transition
1Museum für Naturkunde, Germany; 2Department of Earth Sciences, Freie Universität, Germany
The Eocene-Oligocene transition (EOT, ~34Ma) marks a dramatic climate change and carbon cycle perturbation in the Cenozoic. Understanding the variations in export productivity associated with EOT provides important information about the feedback in regulating climate.
We use the new generated benthic and planktonic oxygen and carbon isotope records combined with paleoproductivity proxies - Biological Barium [bio-Ba MAR] and benthic foraminifera accumulation rates [BFAR] - to infer variations in productivity during the EOT period in relation to changes in climate and paleoceanography.
In addition, we present preliminary diatom diversity data. Marine diatoms have been known to be great contributors to the biological ocean carbon pump, so these data provide support for the understanding of these climatic events.
Samples are from the Atlantic (ODP 689 and 1090) and Indian (ODP 748) sectors of the Southern Ocean. Our multiproxy records show evidence of increased export productivity in different periods throughout the Southern Ocean across EOT. The increase in productivity revealed in the late Eocene (~37 Ma) corroborates with an increase in marine diatoms diversity, suggesting that it could have contributed to the decrease in atmospheric CO2 and consequently to the cooling state.
The timing of some observed changes differs in the sites of the Atlantic sector of the Southern Ocean. The increase in productivity in the early Oligocene in the farther to the south ODP 689 site may be related to the water mass changes and development of the Atlantic Circumpolar Current.
2:15pm - 2:30pm
Biogeographic patterns of benthic foraminifera in contourite drift systems of the Atlantic Ocean
1University of Cologne, Institute of Geology and Mineralogy, Germany; 2Heidelberg University, Institute of Earth Sciences, Germany
Benthic foraminifera inhabit diverse marine environments, including areas of persistent bottom currents and contourite drift deposition. Certain highly adapted epibenthic foraminifera colonize contourite deposits as opportunistic suspension feeders. A correlation between these assemblages and high bottom current velocities has been highlighted in previous studies from the Iberian Margin (e.g. Schönfeld, 2002), suggesting their applicability as reliable proxy for reconstructing bottom currents.
Our ongoing project aims to document biogeographic patterns of benthic foraminifera from extended contourite drift systems in the Atlantic Ocean. The results will provide a framework to evaluate the applicability of foraminifera-based proxy methods for reconstructing bottom currents in different Atlantic contourite deposits. Existing data from the mid-latitude Iberian Margin are complemented by new faunal data from surface samples at high (50-62°N; Björn and Gardar Drifts, Iceland Basin; Eirik Drift, southern Greenland Margin) and low latitudes (10°-22°S Campos Drift, Brazilian Margin).
Preliminary results show variations in faunal composition along gradients of current intensity. Low current velocities at Björn and Gardar Drifts (max. 10 cm/s) favor tubular agglutinated taxa such as Rhabdammina abyssorum and Saccorhiza ramosa. An association of hyaline attached species including Cibicides refulgens and Cibicidoides wuellerstorfi preferentially settle in intermediate flow speeds at the Eirik Drift (12-22 cm/s). Communities of Campos Drift dwell at higher current velocities (up to 80 m/s) and show increased abundances of Cibicides lobatulus, Globocassidulina subglobosa, and Planulina ariminensis.
Schönfeld, J., 2002. Recent benthic foraminiferal assemblages in deep high-energy environments from the Gulf of Cadiz (Spain). Mar. Micropaleontol. 44, 141–162. https://doi.org/10.1016/S0377-8398(01)00039-1
2:30pm - 2:45pm
The micropaleontological fingerprint on contourites and turbidites
1University of Cologne, Faculty of Mathematics and Natural Sciences, Institute of Geology and Mineralogy, Zülpicher Str. 49a, 50674 Cologne, Germany; 2Heidelberg University, Faculty of Chemistry and Earth Sciences, Institute of Earth Sciences, Im Neuenheimer Feld 234, 69120 Heidelberg, Germany
Bottom current-induced sediments such as contourites contain fundamental information for reconstructions of water mass properties and ocean circulation. The distinction between contourites and other deposits on continental slopes is particularly complex in areas where downslope and along-slope sedimentary processes co-occur. Clear and easily applicable diagnostic criteria for properly distinguishing between contourites and other coarse-grained and/or graded deep-water deposits such as turbidites are still limited (e.g., de Castro et al., 2020) and mainly focus on sedimentological data. The present study investigates Pleistocene contouritic (~0.5 Ma) and turbiditic (~0.9 Ma, ~1.1 Ma) sequences from the SW Iberian Margin in the Gulf of Cádiz (IODP Site U1389), where thick contourite drift bodies with extensively intercalated turbidites are preserved (Stow et al., 2013). The aim of the study is to define diagnostic criteria based on benthic foraminiferal assemblage composition in order to differentiate between normally graded contourites and turbidites as well as reworked turbidites. The revealed “foraminiferal fingerprint” will allow for improving paleoceanographic interpretations of sedimentary archives from complex depositional environments along continental margins.
De Castro, S., Hernández-Molina, F.J., de Weger, W., Jiménez-Espejo, F.J., Rodríguez-Tovar, F.J., Mena, A., Llave, E., Sierro, F.J., 2020. Contourite characterization and its discrimination from other deep‐water deposits in the Gulf of Cadiz contourite depositional system. Sedimentology.
Stow, D.A.V., Hernández-Molina, F.J., Llave, E., Bruno, M., García, M., Díaz del Rio, V., Somoza, L., Brackenridge, R.E., 2013. The Cadiz Contourite Channel: Sandy contourites, bedforms and dynamic current interaction. Mar. Geol. 343, 99–114.
2:45pm - 3:00pm
on GPS-IR technique for measuring shallow sediment compaction
Institute of Geodesy and Geoinformation, University of Bonn, Germany
The solid Earth aspects of relative sea-level change can dominate in low-lying coastal areas with potentially vulnerable to accelerating rates of sea-level rise. Global Positioning System (GPS) as companion tools to tide gauges allow long-term assessment of solid Earth deformation, thus essential for disclosing climate-forced mechanisms contributing to sea-level rise (SLR). So far, it has not been possible to measure shallow displacements that occur above the base of GPS monument because conventional positioning determines the vertical component of position changes resulting from displacements occurring beneath the foundation. We use an emerging technique, GPS interferometric reflectometry (GPS-IR), to estimate the rate of this process in two coastal regions with thick Holocene deposits, the Mississippi Delta and the eastern margin of the North Sea. We show that the rate of land motion from shallow compaction is comparable to or larger than the rate of SLR. Since many of the world's great coastal cities are built on river deltas with comparable Holocene sections, our results suggest that estimates of flood risk and land loss have been underestimated. We demonstrate environmental impact of parking lots and streets surrounding a monitoring site on GPS measurements. Such kinematic environments will perturb the amplitude of reflected signals to GPS sensors and thus leave time-variable imprints on GPS observations. Thus, obtaining desirable reflections for shallow subsidence monitoring could be challenging.