A revised core-seismic integration in the Molloy Basin (ODP Site 909): Implications for the history of ice rafting and ocean circulation in the Atlantic-Arctic gateway

Today's cryosphere reflects an extreme climate state that developed through stepwise global Cenozoic cooling. In this context the opening of the Fram Strait, the Atlantic-Arctic Gateway (AAG), enabled deep-water exchange between the northern North Atlantic and the Arctic Ocean and thereby influenced global ocean circulation and climate. Here we present a new age model for Ocean Drilling Program Site 909 located in the Molloy Basin, a key site to investigate the late opening phase of the central Fram Strait and the early history of oceanic circulation in the AAG. Our results are based on a revised magnetostratigraphy calibrated by new palynomorph bioevents, which shifts previously used stratigraphies for Site 909 to significantly younger ages in the time interval from c. 15 Ma to 3 Ma. The revised late Miocene to present chronology combined with an improved core-log-seismic integration leads to a new high-resolution seismic stratigraphy for the central Fram Strait that allows a more comprehensive correlation with seismic markers from the western Barents Sea margin and also the adjacent Yermak Plateau. The new stratigraphy implies that prominent maxima in coarse sand particles and kaolinite, often interpreted as evidence for ice rafting in the Fram Strait occur at c. 10.8 Ma, c. 3 Myr later as previously inferred and thus well after the Middle Miocene Climate Transition (c. 15–13 Ma). In the late Tortonian (<7.5 Ma), sediment transport became current controlled, mainly through a western, recirculating branch of the West Spitsbergen Current. This transport was strongly enhanced between c. 6.4 and 4.6 Ma and likely linked to the subsiding Hovgaard (Hovgård) Ridge and the widening of the AAG. Late Pliocene to Pleistocene seismic reflectors correlate with episodes of elevated ice-rafted detritus input related to major steps in Northern Hemisphere ice sheet growth such as the prominent glacial inception MIS M2 that predates the mid-Piacenzian Warm Period and the intensification of Northern Hemisphere glaciation starting at c. 2.7 Ma. At the beginning of the Mid Pleistocene Transition (c. 1.2–0.8 Ma), sediment accumulation in the Fram Strait significantly decreased

The turbidity maximum zone of the Yenisei River (Siberia) and its impact on organic and inorganic proxies

A general overview of the processes taking place in the summer mixing zone of the fresh Yenisei River water with the marine waters of the Kara Sea is given in this study, with special emphasis on the interaction between bulk (total suspended matter), inorganic (Fe, Mn) and organic (suspended organic carbon, suspended nitrogen) proxies. Within the mixing zone, a zone of enhanced turbidity (maximum turbidity zone) was observed comparable to studies in other rivers. Flocculation of particles due to changes in salinity and hydrography cause this maximum turbidity zone, and resuspension additionally enhances the turbidity in the near-bottom layers. Organic matter behaves conservatively in the mixing zone in terms of its percentage of suspended matter. It, however, undergoes degradation as revealed by amino acid data. Inorganic, redox- and salinity-sensitive, proxies (Mn, Fe) behave non-conservatively. Dissolved iron is removed at low salinities (<2) due to precipitation of iron oxyhydroxides and adsorption of manganese on suspended particles, enhancing the Mn/Al ratio of the suspended matter in the same zone. At higher salinities within the mixing zone, Fe/Al and Mn/Al ratios of the suspended particles are depleted due to resuspension of sediment with lower Fe/Al and Mn/Al ratios. Dissolved manganese concentrations are significantly higher in the near-bottom layers of the mixing zone due to release from the anoxic sediment. All things considered, the Yenisei River mixing zone shows patterns similar to other world's rivers

Ocean Drilling Perspectives on Meteorite Impacts

Extraterrestrial impacts that reshape the surfaces of rocky bodies are ubiquitous in the solar system. On early Earth, impact structures may have nurtured the evolution of life. More recently, a large meteorite impact off the Yucatán Peninsula in Mexico at the end of the Cretaceous caused the disappearance of 75% of species known from the fossil record, including non-avian dinosaurs, and cleared the way for the dominance of mammals and the eventual evolution of humans. Understanding the fundamental processes associated with impact events is critical to understanding the history of life on Earth, and the potential for life in our solar system and beyond. Scientific ocean drilling has generated a large amount of unique data on impact pro- cesses. In particular, the Yucatán Chicxulub impact is the single largest and most sig- nificant impact event that can be studied by sampling in modern ocean basins, and marine sediment cores have been instrumental in quantifying its environmental, cli- matological, and biological effects. Drilling in the Chicxulub crater has significantly advanced our understanding of fundamental impact processes, notably the formation of peak rings in large impact craters, but these data have also raised new questions to be addressed with future drilling. Within the Chicxulub crater, the nature and thickness of the melt sheet in the central basin is unknown, and an expanded Paleocene hemipelagic section would provide insights to both the recovery of life and the climatic changes that followed the impact. Globally, new cores collected from today’s central Pacific could directly sample the downrange ejecta of this northeast-southwest trending impact. Extraterrestrial impacts have been controversially suggested as primary drivers for many important paleoclimatic and environmental events throughout Earth history. However, marine sediment archives collected via scientific ocean drilling and geo- chemical proxies (e.g., osmium isotopes) provide a long-term archive of major impact events in recent Earth history and show that, other than the end-Cretaceous, impacts do not appear to drive significant environmental changes

New details about the LGM extent and subsequent retreat of the West Antarctic Ice Sheet from the easternmost Amundsen Sea Embayment shelf

In recent years several previously undiscovered grounding-zone wedges (GZWs) have been described within the Abbot-Cosgrove palaeo-ice stream trough on the easternmost Amundsen Sea Embayment shelf. These GZWs document both the Last Glacial Maximum (LGM; 26.5-19 cal. ka BP) grounding-line extent and the subsequent episodic retreat within this trough that neighbors the larger Pine Island-Thwaites trough to the west. Here we combine bathymetric, seismic, and geologic data showing that 1) the grounding line in Abbot Trough did not reach the continental shelf break at any time during the last glacial period, and 2) a prominent stacked GZW constructed from six individual wedges lying upon another was deposited 100 km upstream from the LGM grounding-line position. The available data allow for calculating volumes for most of these individual GZWs and for the entire stack. Sediment cores were recovered seawards from the outermost GZW in the trough, and from the individual wedges of the stacked GZW in order to define the LGM grounding-line extent, and provide minimum grounding-line retreat ages for the respective positions on the stacked GZW. We present implications of a grounded-ice free outer shelf throughout the last glacial period. Furthermore, we assess the significance of the grounding-line stillstand period recorded by the stacked GZW in Abbot Trough for the timing of post-LGM retreat of the West Antarctic Ice Sheet from the Amundsen Sea Embayment shelf

First deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf: experiences from the MARUM-MeBo70 on Polarstern-Expedition PS104

The MARUM-MeBo (abbreviation for Meeresboden-Bohrgerät, the German expression for seafloor drill rig) is a robotic drilling system that is developed since 2004 at the MARUM Center for Marine Environmental Sciences at the University of Bremen in close cooperation with Bauer Maschinen GmbH and other industry partners. The MARUM-MeBo drill rigs can be deployed from multipurpose research vessel like, RV MARIA S. MERIAN, RV METEOR, RV SONNE and RV POLARSTERN and are used for getting long cores both in soft sediments as well as hard rocks in the deep sea. The first generation drill rig, the MARUM-MeBo70 is dedicated for drilling depths of more than 70 m (Freudenthal and Wefer, 2013). Between 2005 and 2017 it was deployed on 18 research expeditions and drilled more than. 3 km into different types of lithologies including carbonate and crystalline rocks, gas hydrates, sands and gravel, glacial till and hemipelagic mud with an average recovery rate of 67 %. In February and March 2017 the MeBo70 was used on the West Antarctic continental shelf in the Amundsen Sea Embayment for the first time. The goal of the deployment on RV Polarstern expedition PS104 was to recover a series of sediment cores from different ages that will provide material for investigating the glaciation history of this area known as the most dynamic drainage area of the West Antarctic Ice Sheet. In this presentation we will focus on the operational experiences of this first deployment of a multi-barrel sea floor drill rig on the Antarctic continental shelf. References: Freudenthal, T and Wefer, G (2013) Drilling cores on the sea floor with the remote-controlled sea floor drilling rig MeBo. Geoscientific Instrumentation, Methods and Data Systems, 2(2). 329-337. doi:10.5194/gi-2-329-201

Probing the hydrothermal system of the Chicxulub impact crater

The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years

First results of sedimentological investigations of MeBo drill cores recovered from the West Antarctic continental shelf in the Amundsen Sea

During expedition PS104 with RV Polarstern in February and March 2017 the MARUM MeBo 70 seabed drilling system was deployed at nine sites on the continental shelf of the Amundsen Sea Embayment, West Antarctica. A total of 57 meters of sediment core were recovered from 11 boreholes located in Pine Island Bay, Pine Island Trough, Bear Ridge and Cosgrove-Abbot Trough with recovery rates ranging from 7 to 76%. The main scientific objective of the drilling was to reconstruct the Late Mesozoic to Quaternary environmental history in this part of the Antarctic continental margin, with a special focus on the past dynamics of the marine based West Antarctic Ice Sheet (WAIS) from its inception to the last glacial cycle. Another main goal of the expedition was to test the suitability of the MeBo drill system for operating on the Antarctic continental shelf and recovering pre-glacial and glacially influenced sedimentary sequences. Here we will present the first results of sedimentological investigations carried out on the drill cores. These comprise (i) visual lithological descriptions, (ii) CT-scanning records of core stratigraphy, sedimentary structures, and possible artefacts induced by the drilling process, (iii) measurements of physical properties performed with a multi-sensor core logger, and (iv) characterisation of the geochemical composition of the drilled sedimentary strata using X-ray fluorescence (XRF) scanner data. Preliminary biostratigraphic investigations conducted on board ship indicated that the recovered sedimentary strata were deposited during various time slices spanning from the Late Cretaceous–Palaeocene to the Late Quaternary. We will provide an update of these initial chronological findings. Keywords: Drill cores, shelf sediments, West Antarctic Ice Sheet

Indications for the Occurrence of Gas Hydrates in the Fram Strait from Heat Flow and Multichannel Seismic Reflection Data

The distribution of gas hydrates recently raised increased attention, especially along glaciated continental margins, due to its potential importance for slope stability and global climate. We present new heat flow data together with multichannel reflection seismic data fromthe central FramStrait in-between Northeast Greenland and Svalbard.This area is only accessible by icebreaking vessels, and, therefore, knowledge about this area is still sparse.The new heat flow data concur with previous measurements in the region.High temperature gradients of >200mK/mwere recorded along the active spreading zone in the FramStrait, and gradients of 75 mK/m along the western slope of Yermak Plateau. Along the Northeast Greenland slope, the measured gradients reach 54 mK/m at maximum. Seismic data image bottom-simulating reflections proofing that the known gas-hydrate province spreadsmuch further north along thewestern slope of the Yermak Plateau than previously known. Existing slide scars indicate that there might be a causal relationship between the occurrence of gas hydrates and slope instability in that area. Along the Northeast Greenland continental margin and in the adjacent abyssal plain, strong indications for the occurrence of gas within the sedimentary basins and for its migration along fault zones and chimney-like structures are found

Magnetostratigraphy and Environmental Magnetism of Laguna Potrok Aike: Preliminary Results from the ICDP Project PASADO

Laguna Potrok Aike (51° 58'S, 70° 23'W), is a ~770 ka maar lake in southern Patagonia (Province of Santa Cruz, Argentina). In the austral spring 2008, the PASADO international team of scientists cored Laguna Potrok Aike using the GLAD800 equipment in order to obtain a high-resolution geological archive for paleoenvironmental reconstructions. Two long sedimentary sequences of approximately 100 meters each were recovered close to the center of the lake at 100 m water depth. In the field, the magnetic susceptibility was measured using a Multi Sensor Core Logger at 2 cm intervals. At the Paleo and Environmental Magnetism Laboratory of ISMER in Rimouski (Québec, Canada), core catcher samples (core 5022 2A) were analyzed using an alternating gradient force magnetometer to determine the magnetic mineralogy and grain size. In the framework of the PASADO project, the aim of this paleomagnetic study is to 1) reconstruct the first full paleomagnetic vector (inclination, declination and relative paleointensity) recorded from southern South America and presumably back to Oxygen Isotope Stage 5, 2) use magnetostratigraphy as a chronostratigraphic tool in Laguna Potrok Aike in addition to radiocarbon and optical (OSL) dating as well as tephrochronology and 3) develop high-resolution magnetic proxies of paleoenvironmental changes in southern Patagonia. Here we present the paleomagnetic study outline, the magnetic susceptibility profiles obtained in the field and preliminary laboratory results as a first step to characterize the magnetic mineralogy and grain size