ALBERT

Description: We tested the applicability of the BIT (branched and isoprenoid tetraether) index as a proxy for palaeoflood events in the river-dominated continental margin of the Gulf of Lions (NW Mediterranean). We compared the concentrations of branched glycerol dialkyl glycerol tetraethers (br GDGTs) and crenarchaeol in suspended particulate matter (SPM) collected downstream in the Rhône River, as well as in surface sediments and a ca. 8m piston core from the Rhône prodelta. The core covered the last 400 yr, with four distinct intervals recording the river influence under natural and man-induced shifts in four main channels of the river mouth (Bras de Fer, Grand Rhône, Pégoulier and Roustan). The results indicate that there are mixed sources of br GDGTs and crenarchaeol in the prodelta, complicating application of the BIT index as an indicator of continental organic carbon input and thus as a palaeoflood proxy. However, the sedimentary BIT record for the period when ontinental material was delivered by the river more directly to the core site (Roustan phase; 1892 to the present) mimics the historical paleoflood record. This shows the potential of the BIT index as a palaeoflood proxy, provided that the delivery route of the continental material by rivers to the core sites remains constant over time. The study also highlights the idea that shifts in river channels should be taken into account for the use of the BIT index as a palaeoflood proxy.

Description: The Demerara Plateau, belonging to the passive transform margin of French Guiana, was investigated during the IGUANES cruise in 2013. The objectives of the cruise were to explore the poorly-known surficial sedimentary column overlying thick mass transport deposits as well as to understand the factors controlling recent sedimentation. The presence of numerous bedforms at the seafloor was observed thanks to newly acquired IGUANES bathymetric, high resolution seismic and chirp data, while sediment cores allowed the characterization of the deposits covering the mass transport deposits. Modern oceanographic conditions were determined in situ, using mooring monitoring over a 10-month period. Our data indicate the presence of a Contourite Depositional System along the Demerara Plateau, most likely related to bottom current activity of the North Atlantic Deep Water (NADW). However, at the regional scale, large longitudinal waves parallel the NADW flow. Their shape and orientation seem to be inherited from interactions between bottom currents and paleomorphologies expressed at the top of mass transport deposits. Their evolution is possibly driven by the intensity of bottom current activity that might have changed over time. Overall, this work presents an integrated approach combining seismic and sedimentological evidence to study the processes at the origin of contourite formation in the Demerara Plateau. Other regional factors, such as local slope values and slope instability, also control sedimentation.

Description: The Sea of Japan is a marginal sea, semi-enclosed by the Eurasian Continent, Korean Peninsula, Japanese archipelago, and connected to the Pacific Ocean and adjacent seas by three shallow straits (water depths 〈 130 m). Marginal seas are ideal natural laboratories to study biotic responses to large-scale environmental changes as they are typically sensitive to glacial-interglacial and stadial-interstadial climatic cycles. However, only limited number of studies covers time periods beyond 1 to 2 glacial-interglacial cycles. Here we present a 700,000-year record of benthic biotic response to past oceanographic changes in the southern Sea of Japan, covering the past seven glacial-interglacial cycles, based on ostracode assemblages at the IODP Site U1427. The results indicate that the long-term oxygen variability has been a major control of deep marginal sea biota. Five local extirpation events were recognized as barren zones during glacial maxima (i.e., sea-level minima) immediately before terminations I, II, IV, V, and VII in MISs 2, 6, 10, 12, and 16, which are probably caused by bottom-water oxygen depletion. The results of multivariate analyses indicated clear faunal cyclicity influenced by glacial-interglacial scale oxygen variability with the succession from opportunistic species dominance through tolerant infauna dominance to barren zone during the deoxygenation processes and the opposite succession during the recovery processes. The Sea of Japan ostracode abundance and faunal composition showed distinct difference between the post- and pre-MBE (Mid-Brunhes Event at around 400-350 ka) periods, indicating the MBE as a major disturbance event of deep-sea, especially marginal-sea ecosystems. The MBE shortened the duration of the extirpation events, fostered dominance of warmer-water species, and amplified the glacial-interglacial faunal cyclicity. Our long-term biotic response study clearly indicates that deep marginal sea ecosystems are dynamic and vulnerable to climate changes.

Description: The Kuroshio Current flows northward along the east coast of Taiwan toward the Okinawa Through and the East China Sea, but its dynamics and trajectory were probably different during the Last Glacial Maximum (LGM) due to the globally lower sea level that could have caused a (debated) deflection of the current along the eastern edge of the Ryukyu Arc. Core MD18-3532 has been recovered in an intra-slope basin of the Ryukyu accretionary prism, currently disconnected from the Kuroshio Current, but which could have been under its trajectory in case of a NE deflection. Measurements of clay mineral assemblages and illite crystallinity revealed that Taiwan has been the main sediment source at this site over the last 26 kyr. The significantly higher sedimentation rate between the glacial period and the Bølling–Allerød compared to the Younger Dryas and Holocene, coupled with very low δ15Nsed during the LGM and Heinrich Stadial 1, provide evidence for a deflection of the main branch of the Kuroshio Current toward the eastern edge of the Ryukyu Arc during those periods. The deflected current carried surface sediment plumes and Trichodesmium spp. cyanobacteria to the coring site. δ13Corg, TOC, TN, and XRF analyses indeed revealed increased marine primary productivity during the LGM and Heinrich Stadial 1, likely due to intensified East Asian Winter monsoon winds leading to increased nutrient input from dust and the upwelling of nutrient-rich subsurface water from the deflected Kuroshio Current through the deepening of the mixed layer.

Description: The Mio-Pliocene basins around the Antalya gulf in SW Turkey developed above the Tauric Mesozoic platforms on which the Antalya nappes had been thrusted (in Late Cretaceous-Paleocene times). The closure of the initial Isparta Angle during these events (E-W compression) initiated the N-S orientation of the main structural lines, which persisted later and explains the orientation of the Aksu basin in contrast with the E-W orientation of the eastern Neo-gene Mediterranean basins. The area, and all southwestern Turkey, became emergent at the end of the Oligocene and were the site of shallow-marine carbonate deposits in the Chattian-Aquitanian, giving way to the wide Lycian basin in Burdigalian-Langhian times. The progressive emplacement of the Lycian nappes from the north over this basin provoked first its subsidence and then its emersion when the nappes attained their final position over the Bey Daglari platform in Langhian times. Coinciding, or in response to the Lycian nappes emplacement, the Aksu basin was initiated as an elongated N-S graben which was filled by thick accumulations of terrestrial and marine deposits(including coral reefs), which derived from the erosion of the Lycian allochton and its basement (Langhian?, Serravallian and Tortonian times). The syn-sedimentary tectonics : reactivation of the normal faults along the west margin of the basin, the continuous uplift of the neighbouring continental areas (beginning of the Aksu thrust), governed the geometry of the basin. As a result and due to the uplift of its northern margin, the Aksu basin migrated towards the south and in Messinian times it was reduced to a narrow gulf along the eastern margin of which the Gebiz limestones were deposited as fringing coral reefs. The age of these limestones has been debated. Our new data allow us to attribute them to the Messinian. The drastic retreat of the sea at the end of this period, provoked the erosion of large parts of the Messinian deposits and the formation of deep canyons on land and under the sea down to the Antalya abyssal plain, in which evaporites were deposited. During the Zanclean transgression, the Eskikoy-Kargi canyon was filled by coarse clastics of a Gilbert delta derived from the northern continental area following a model well known elsewhere in the Mediterranean basins. Southward, shallow-marine sands and marls unconformably cover the remnants of the Messinian deposits and the emergent areas of the southern Antalya gulf. After Zanclean times (end of Pliocene?), the Aksu basin was deformed, due to the west-directed Aksu compressional event (end of the Aksu thrust). Quaternary terraces of the Aksu river at various altitudes, as well as the terraces of the Antalya tufa can be related to sea level fluctuations.