The Indian-Atlantic Ocean gateway during the Pliocene: current dynamics and changing sediment provenance

The Pliocene epoch represents a discrete interval which reversed a long-term trend of late Neogene cooling and is also the most recent geological interval in which global temperatures were several degrees warmer than today. It is therefore often considered as the best analogue for a future anthropogenic greenhouse world. However, there is growing evidence that the Pliocene was not a stable period but can rather be subdivided in several distinct climate phases. Our understanding of Pliocene climate variability in the Southern Hemisphere, and especially in the Atlantic-Indian ocean gateway, is limited by scarce marine records and poor age control on existing terrestrial climate archives. At five from six drilling locations of IODP Exp. 361 (Jan. – March 2016) high resolution complete Plio-/Pleistocene sections have been recovered (see IODP Expedition 361 – Southern African Climates and Agulhas LGM Density Profile by Gruetzner et al., this Volume). Our new research proposal focuses on three of these sites forming a latitudinal transect in the Atlantic-/Indian Ocean gateway and combines chemical, physical property and seismic methods. Primary site for our investigations is Site U1475 with the focus on the interplay between northern and southern sourced deep water masses at the Agulhas Plateau. This will be augmented by investigations at Sites U1479 (Cape Basin) and U1474 (Natal Valley), both located in the pathway of modern NADW. Our research is driven by three main working hypotheses: Seismic stratigraphies for the last 6 Ma and sediment drift growth in the Atlantic-Indian gateway are mainly controlled by bottom water flow changes Using the new sediment archives and physical property records from IODP Exp. 361 (Hall et al., 2016) we aim to construct detailed seismic stratigraphies for the Agulhas Plateau, the Natal valley and the Cape basin for the last 6 Ma. At all Exp. 361 sites P-wave velocity and density records are of sufficient quality to enable detailed correlations of drilling results and site survey data through the calculation of synthetic seismograms. Our working hypothesis implies that seismic reflection patterns and sediment accumulation during the Pliocene are closely linked to deep water circulation changes associated with climate Pliocene phases. Furthermore four distinct high latitude Pliocene glaciation events have been identified. We speculate that these phases and events have led to deep water circulation changes in Agulhas region, have altered the sediment physical properties and thus may be recognized as reflectors in the seismic profiles. How did the sediment input of terrigenous vs. biogenic sediment components in the gateway change during these events? Are these changes driven by dilution, dissolution, or productivity? We strive to answer these questions by interpreting the physical and chemical (XRF) core scanning records. Trajectories and intensities of deep water masses in the Agulhas region during the Pliocene were influenced by Antarctic ice volume rather than by the closure of the Central American Seaway. The Exp. 361 drill sites offer the possibility to inter-correlate different flow speed proxies and to derive a detailed picture of flow changes during the Pliocene. By comparing core-measurements of sortable silt (S̅S̅), physical properties and XRF-core scanning data with seismic features we will tie the major flow speed changes to our seismic grid covering the Agulhas Plateau such that changing current intensities and pathways can be mapped together. Here we hypothesize that these changes are mainly driven by climate (Antarctic ice volume). What were the main changes associated with the Pliocene instability of Antarctic ice sheets and was the production of Antartic Bottom Water (AABW) reduced or enhanced during these intervals? How have the sedimentation patterns changed under the growing influence of North Atlantic Deep Water (NADW)? Was there also a potential influence of tectonic processes on the flow changes in the Agulhas region? Especially the closure of the Centarl American Seaway CAS between ~14 and ~2.7 Ma is thought to have had a profound impact on climate. The Pliocene variability in sediment provenance on millennial timescales is subdued when compared to the Pleistocene. Understanding the mechanisms and causes of abrupt climate change is one of the major challenges in global climate change research today and there is growing evidence that millennial scale climate variability was enhanced during times when a critical threshold in continental ice volume was surpassed. Dramatic millennial scale climate shifts are well documented for the “glacial world” of the late Pleistocene but are examined to a much lesser extent for earlier time periods. We suggest testing the potential threshold behaviour for the Atlantic-Indian gateway by comparing short term fluctuations in sediment composition and siliciclastic provenance in the Agulhas region before and after the onset of the Northern Hemisphere glaciation (NHG) at ~2.7 Ma. Time series of sediment provenance dated by “orbital tuning” will be analysed in the time and frequency domain to investigate at what times during the interval 2 – 6 Ma millennial scale climate variability was enhanced or subdued

A New Seismic Stratigraphy in the Indian-Atlantic Ocean Gateway Resembles Major Paleo-Oceanographic Changes of the Last 7 Ma

The exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long‐term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate‐rich stratigraphic section of the last ~7 Ma that provides an archive of climate‐induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (~5.3–4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (>10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water

A New Seismic Stratigraphy in the Indian-Atlantic Ocean Gateway Resembles Major Paleo-Oceanographic Changes of the Last 7 Ma

The exchange of water masses between the Indian Ocean and the Atlantic constitutes an integral interocean link in the global thermohaline circulation. Long‐term changes in deep water flow have been studied using seismic reflection profiles but the seismic stratigraphy was poorly constrained and not resolved for the time period from the late Miocene onward. Here we present results from International Ocean Discovery Program Site U1475 (Agulhas Plateau) located over a sediment drift proximal to the entrance of North Atlantic Deep Water into the Southern Ocean and South Indian Ocean. Site U1475 comprises a complete carbonate‐rich stratigraphic section of the last ~7 Ma that provides an archive of climate‐induced variations in ocean circulation. Six marker reflectors occurring in the upper 300 m of the drift are identified here for the first time. The formation of these reflectors is mainly due to density changes that are mostly caused by changes in biogenic versus terrigenous sediment deposition. Synthetic seismograms allow age assignments for the horizons based on biostratigraphy and magnetostratigraphy. Prominent reflectors are related to late Pleistocene glacial/interglacial variability, the middle and early Pleistocene transitions, and the onset of the northern hemisphere glaciation. A peculiar early Pliocene interval (~5.3–4.0 Ma) bounded by two reflectors is characterized by fourfold elevated sedimentation rates (>10 cm/kyr) and the occurrence of sediment waves. We argue that this enhanced sediment transport to the Agulhas Plateau was caused by a reorganization of the bottom current circulation pattern due to maximized inflow of North Atlantic Deep Water

GSH Attenuates Organ Injury and Improves Function after Transplantation of Fatty Livers

Ischemia-reperfusion injury (IRI) is increased after transplantation of steatotic livers. Since those livers are increasingly used for transplantation, protective strategies must be developed. Reactive oxygen species (ROS) play a key role in hepatic IRI. In lean organs, glutathione (GSH) is an efficient scavenger of ROS, diminishing IRI. The aim of this study was to evaluate whether GSH also protects steatotic allografts from IRI following transplantation. Fatty or lean livers were explanted from 10-week-old obese or lean Zucker rats and preserved (obese 4 h, lean 24 h) in hypothermic University of Wisconsin solution. Arterialized liver transplantation was then performed in lean syngeneic Zucker rats. Recipients of fatty livers were treated with GSH (200 mu mol/h/kg) or saline during reperfusion (2 h, n = 5). Parameters of hepatocellular damage and bile flow were measured. Transplantation of steatotic livers enhanced early reperfusion injury compared to lean organs as measured by increased aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase plasma levels. Bile flow was also reduced in steatotic grafts. Intravenous administration of GSH effectively decreased liver damage in fatty allografts and resulted in improved bile flow. Intravenous application of GSH effectively reduces early IRI in steatotic allografts and improves recovery of these marginal donor organs following transplantation. Copyright (C) 2010 S. Karger AG, Base

The Indian-Atlantic Ocean gateway during the Pliocene: current dynamics and changing sediment provenance

The Pliocene epoch represents a discrete interval which reversed a long-term trend of late Neogene cooling and is also the most recent geological interval in which global temperatures were several degrees warmer than today. It is therefore often considered as the best analogue for a future anthropogenic greenhouse world. However, there is growing evidence that the Pliocene was not a stable period but can rather be subdivided in several distinct climate phases. Our understanding of Pliocene climate variability in the Southern Hemisphere, and especially in the Atlantic-Indian ocean gateway, is limited by scarce marine records and poor age control on existing terrestrial climate archives. At five drilling locations IODP Exp. 361 recovered high resolution complete late Miocene to Pleistocene sections (Hall et al., 2017). Our research proposal is based on the Sites U1474 (Natal Valley), U1475 (Agulhas Plateau), and U1479 (Cape Basin) forming a latitudinal transect. The main focus is on the interplay between northern and southern sourced deep water masses in the Atlantic-/Indian Ocean gateway during the Pliocene and combines chemical, physical property and seismic methods. Our research is driven by three working hypotheses: Seismic stratigraphies for the last 6 Ma and sediment drift growth in the Atlantic-Indian gateway are mainly controlled by bottom water flow changes Using the sediment archives and physical property records from IODP Exp. 361 we aim to construct and compare detailed seismic stratigraphies for the Agulhas Plateau, the Natal valley and the Cape basin for the last 6 Ma. At all Exp. 361 sites P-wave velocity and density records enable detailed correlations of drilling results and site survey data through the calculation of synthetic seismograms. Our working hypothesis implies that seismic reflection patterns and sediment accumulation during the Pliocene are closely linked to deep water circulation changes associated with climate Pliocene phases. Furthermore four distinct high latitude Pliocene glaciation events have been identified. We speculate that these phases and events have led to deep water circulation changes in Agulhas region, have altered the sediment physical properties and thus may be recognized as reflectors in the seismic profiles. How did the sediment input of terrigenous vs. biogenic sediment components in the gateway change during these events? Are these changes driven by dilution, dissolution, or productivity? We strive to answer these questions by interpreting edited and in-situ corrected physical core scanning records in combination major element variabilty derived from post cruise XRF-scanning. Trajectories and intensities of deep water masses in the Agulhas region during the Pliocene were influenced by Antarctic ice volume rather then by the closure of the Central American Seaway. The Exp. 361 drill sites offer the possibility to inter-correlate different flow speed proxies and to derive a detailed picture of flow changes during the Pliocene. By comparing core-measurements of sortable silt (S̅S̅), physical properties and XRF-core scanning data with seismic features we will tie the major flow speed changes to our seismic grid covering the Agulhas Plateau such that changing current intensities and pathways can be mapped together. Here we hypothesize that these changes are mainly driven by climate (Antarctic ice volume). How have the sedimentation patterns changed under the growing influence of North Atlantic Deep Water (NADW) during the Pliocene? What were the main changes associated with the instability of Antarctic ice sheets and was the production of Antartic Bottom Water (AABW) reduced or enhanced during these intervals? Was there also a potential influence of tectonic processes on the flow changes in the Agulhas region? Especially the closure of the Centarl American Seaway (CAS) in various phases between ~14 and ~2.7 Ma is thought to have had a profound impact on climate. Changes in physical and chemical sediment properties in the Agulhas region are largely controlled by earth’s orbital variations and allow a significant improvement of age models by cyclostratigraphy. Another primary objective of our research is the detection and characterization of orbital and sub-orbital cycles in the Agulhas sedimentary environment in relation to paleoceanographic changes. The presence of orbital cycles in ocean sediments has widely been used to derive high resolution age models in Cenozoic sediments. Typically orbital chronologies are based on benthic oxygen isotope records (δ18O) that are correlated to astronomical forcing functions (“orbital tuning”). However, the generation of such records at high resolution over long time intervals is time consuming and will likely not be completed for the Exp. 361 sites over the next years. In the absence of δ18O records cyclic changes in high resolution measurements of physical (e.g. density, colour reflectance, magnetic susceptibility) and chemical (major elements from XRF core scanning) parameters have been successfully used for orbital tuning. At the Exp. 361 Sites very regular cyclic amplitude changes are evident in the Pliocene sections, but up to now have not been further investigated. Which orbital frequency do these cycles represent and how do the dominent frequencies change over time? What is the potential of the observed cycles for stratigraphic purposes? We will analyse those cyclicities in the depth and time domain and strive to generate orbitally tuned time series of sediment provenance

Disentangling the effects of particles and circulation on 231Pa/230Th during Heinrich Stadials

It has been shown that during Heinrich stadials northern deep water production ceased leading to an enhanced inflow of southern sourced water. Although Heinrich events are not considered to represent the primary trigger of Heinrich stadials the reorganisation of Atlantic ocean dynamics during their occurrences is an active field of research. In particular, Heinrich stadial 2 (HS2) is of high interest, based on the observation that the interplay with the climate system was very different during HS2 compared to HS1, although the magnitude of iceberg and freshwater discharge was similar (Hemming, 2004). During HS2 sea-level was still decreasing while the atmospheric CO­2 content was relatively stable unlike the climatic evolution during Heinrich HS1.The notion of a reduced Atlantic Meridional Overturning Circulation (AMOC) during Heinrich Stadials is mainly strengthened by the 231Pa/230Th records from the Bermuda Rise. However, other influencing factors, capable of increasing the sedimentary 231Pa/230Th without according decreases in AMOC strength, need to be considered as well. Besides biogenic opal, high dust fluxes may also result in enhanced scavenging rate of both radionuclides and consequently higher sedimentary 231Pa/230Th signals, since another distinct feature that accompanies Heinrich Stadials is the high atmospheric concentration of dust in the northern hemisphere. Furthermore, high dust concentrations might be an indicator of a vigorous wind system and therefore strong ocean mixing, which can lead to the enhanced formation of nepheloid layers These layers are suspected to cause strong bottom scavenging and consequently high sedimentary 231Pa/230Th. Very high dust fluxes were observed e.g. during HS2 and MIS4. Here, we compare 231Pa/230Th with dust records in order to disentangle the effects of scavenging and circulation on the recorded sedimentary 231Pa/230Th from the northwestern Atlanti

Edgar Degas: Six Friends at Dieppe

The lives of the six men depicted in Edgar Degas\u27 Six Friends at Dieppe - as well as Degas himself - are explored. The history of the painting\u27s placement in the RISD Museum\u27s collection is traced back to Degas\u27 relationship with one of the men featured in the painting. The narrative is interspersed with paintings, photographs, and excerpts from various memoirs, autobiographies and correspondences.https://digitalcommons.risd.edu/risdmuseum_publications/1004/thumbnail.jp

Harmonic analysis on the boundary of hyperbolic groups

In this paper we show that a Möbius-structure $\mathcal{M}$ of dimension $Q$ has a minimal Ahlfors-David constant.This shows that a Möbius space is uniformly $Q$-Ahlfors-David regular.In summary, many classical theorems of harmonic analysis on $\mathbb{R}^n$ admit a Möbius-invariant formulation in the context of Möbius-geometry.We use this observation to show that the Knapp-Stein operator$$(I_d^\alpha u_d)(x) = \int \frac{u_d(y)}{d(x,y)^{Q - \alpha}} \, d\mu_d(y), \quad\quad (\, 0 < \alpha < \frac{Q}{2}\,)$$is a continuous operator on the weighted $L^2$-space $L^2((\frac{d'}{d})^{\alpha} d\mu_d)$, with a norm independent of $d$ and $d'$.From here we construct a Sobolev space $\mathcal{H}^{-\alpha}_d$ on $s$-densities for a given $s$ as a function of $\alpha$.We would like to say that the construction is topologically independent of the metric $d$.In this paper we prove that the norms on a large class of functions are comparable.The work is inspired by a paper by Astengo, Cowling, and Di Blasio, who construct uniformly bounded representations for simple Lie groups of rank $1$.We formulate the problem in a much more general framework of groups acting on Möbius structures.In particular, all hyperbolic groups

Slowdown of Circumpolar Deepwater flow during the Late Neogene: Evidence from a mudwave field at the Argentine continental slope

Geochemical evidence from boreholes suggests enhanced transport of Northern Component Water (NCW) to southern latitudes from about 6 Ma onwards. However, information on how this change in transport influenced the intensity and position of current systems is sparse. Here we use seismic reflection profiles interpreted together with bathymetric data to investigate current derived deposits at the central Argentine Margin. Upslope migrating mudwaves overlying a late Miocene erosional unconformity provide evidence that Circumpolar Deepwater (CDW) flow slowed down with the onset of NCW inflow. During the last ~3 Ma changes in dimensions and migration rates of the waves are small indicating continuous bottom current flow conditions similar to today with only minor variations in flow speed, suggesting that the Deep Western Boundary Current (DWBC) in the western south Atlantic as observed today, has been a pervasive feature of the global thermohaline circulation system during the Plio-/Pleistocene