DOCSLIB.ORG

Climate Controlled Sedimentary Processes in the Riiser Larsen Sea

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Climate Controlled Sedimentary Processes in the Riiser Larsen Sea Faculty of Science and Technology Department of Geosciences Climate controlled sedimentary processes in the Riiser Larsen Sea offshore Queen Maud Land, Antarctica Rita Brekken GEO-3900 Master’s thesis in geology November 2018 (adapted from AZAMARA (2018)) Abstract Multi-proxy analysis of gravity core PS56/029-1 have been performed in order to describe sedimentary processes and dynamics under pelagic, turbiditic and contouritic influences. The purpose is to reconstruct climate-controlled environmental change in the Riiser Larsen Sea, Antarctica, through past glacial/interglacial cycles. The gravity core was retrieved during expedition ANTARKTIS XVII/2 of R/V Polarstern in 2000. Data analysis was carried out in a collaboration between the Alfred Wegner Institute, Helmholtz centre for polar and marine research in Germany and the Department of Geosciences at UiT The Artic University of Tromsø. The core was retrieved from a levee in the central part of a large channel system in the Riiser Larsen Sea, at c. 4000 m water depth and c. 200 km offshore Princess Ragnhild Coast, Queen Maud Land, Antarctica. A multi-proxy analysis was conducted in order to determine depositional environments through past glacial/interglacial cycles. The analysis included physical properties, e.g. magnetic susceptibility, p-wave velocity and wet-bulk density, interpretation of line-scan images and X-radiographs, qualitative element geochemical analysis using an Avaatech XRF Core Scanner and high resolution grain-size distribution analysis using a CILAS 1180 laser granulometer. Core PS56/029-1 reveals alternating repetitive intervals of poorly sorted and fine-grained sediment accumulated in lighter brownish and greyish coloured intervals. The deposits have a polymodal signature which is interpreted to reflect a mixed pelagic, turbiditic, and contouritic influence, and the more occasional influence of icebergs. Four lithofacies are defined: Laminated Grey Layer (LGL), Grey Layer Thin (GLT), Massive Lighter Layer (MML) and Red Brown Layer (RBL). The greyish coloured intervals LGL and GLT are interpreted to be deposited during glacial periods, including fine sediments attributed to the advancing ice-sheet, along with a more extensive sea-ice, and smaller coastal polynyas. More frequent turbidity currents are suggested to be the explaining factor. The lighter brownish coloured layers MLL and RBL are interpreted to be deposited during interglacial periods, including slightly coarser sediments attributed to a stable or retreating ice sheet, along with less extensive sea-ice cover, and stronger coastal polynyas. Increased bottom-water velocities and denser water masses created in coastal polynyas are suggested to be the explaining factors. Acknowledgements The Master’s thesis is ready to be submitted, but I couldn’t have done it alone. I want especially give huge thanks to my supervisors Dr. Matthias Forwick and Dr. Christian Hass for excellent supervision and guidance through this past year. I have been privileged to be able to learn from you guys! Thank you Dr. Matthias Forrwick for always replaying my emails quickly and for always make time for me in your busy schedule. This is very much appreciated. I also want to thank you for the kindness you showed during my sick leaf. For giving me the time I needed in order to complete this thesis, thank you! Thank you Dr. Christian Hass for helping me through my stay at the Alfred Wegner Institute in Bremen and on Sylt, Germany, and for letting me participate on your cruises, this have truly been an interesting journey for me! Additionally I want to thank: All the kind people at the Alfred Wegner Institute on Sylt, which made my stay there so much better. Ingrid for helping me with the Avaatech XRF Core Scanner. Karina for helping me at the Geoscience Laboratory. My geology friends for five amazing years together! Especially thanks to, Sindre for solving my computer problems and Rebekka for helping me with the final correlations on this thesis. My boyfriend Chris Brynjulfsen for supporting me through this thesis. I will always be grateful and could not have done this without you! My family for supporting me through these five years. Rita Brekken Tromsø 12.11.2018 Contents Abstract ...................................................................................................................................... 2 Acknowledgements .................................................................................................................... 4 1 Introduction ........................................................................................................................ 2 1.1 Objectives .................................................................................................................... 2 1.2 Motivation ................................................................................................................... 2 1.3 Glacial history of Antarctica ........................................................................................ 7 1.3.1 Weddell Sea .......................................................................................................... 9 1.3.2 East Antarctica ................................................................................................... 15 2 Study area ......................................................................................................................... 19 2.1 Physiographic settings ............................................................................................... 19 2.1.1 Riiser Larsen Sea (RLS) ..................................................................................... 20 2.2 Oceanography ............................................................................................................ 26 2.2.1 The Southern Ocean ........................................................................................... 26 2.2.2 The Antarctic Circumpolar Current (ACC) ....................................................... 30 2.3 Geomorphology of glaciated continental shelves ...................................................... 31 2.3.1 Sea-ice ................................................................................................................ 32 2.3.2 Polynyas ............................................................................................................. 33 2.3.3 Icebergs .............................................................................................................. 34 2.4 Sedimentary processes and deposition ...................................................................... 35 2.4.1 Turbidites ........................................................................................................... 36 2.4.2 Contourites ......................................................................................................... 38 2.4.3 Pelagic settling ................................................................................................... 39 2.5 Channel-levee complexes .......................................................................................... 40 2.6 Sedimentation through a glacial/interglacial cycle .................................................... 40 3 Materials and methods ..................................................................................................... 43 3.1 Sediment cores ........................................................................................................... 43 3.2 Laboratory work ........................................................................................................ 44 3.2.1 Visual core description ....................................................................................... 44 3.2.2 X-radiographs ..................................................................................................... 45 3.2.3 Line-scan image ................................................................................................. 46 3.2.4 XRF core scanning data ..................................................................................... 47 3.2.5 Multi-Sensor Core Logger (MSCL) ................................................................... 49 3.2.6 Granulometry ..................................................................................................... 52 4 Lithostratigraphy .............................................................................................................. 59 4.1 Introduction ............................................................................................................... 59 4.1.1 Lithological logs / visual core description ......................................................... 60 4.1.2 Grain-size analysis ............................................................................................. 62 4.1.3 Physical properties ............................................................................................. 71 4.1.4 Element geochemical properties ........................................................................ 71 4.1.5 Presence/absence of foraminifera ....................................................................... 75 4.1.6 Lamination ......................................................................................................... 78 4.1.7 Ice-rafted debris (IRD) ....................................................................................... 79 4.1.8 Massive mud .....................................................................................................
Load more

Recommended publications
  • Introduction Itinerary
    ANTARCTICA - AKADEMIK SHOKALSKY TRIP CODE ACHEIWM DEPARTURE 10/02/2022 DURATION 25 Days LOCATIONS East Antarctica INTRODUCTION This is a 25 day expedition voyage to East Antarctica starting and ending in Invercargill, New Zealand. The journey will explore the rugged landscape and wildlife-rich Subantarctic Islands and cross the Antarctic circle into Mawsonâs Antarctica. Conditions depending, it will hope to visit Cape Denison, the location of Mawsonâs Hut. East Antarctica is one of the most remote and least frequented stretches of coast in the world and was the fascination of Australian Antarctic explorer, Sir Douglas Mawson. A true Australian hero, Douglas Mawson's initial interest in Antarctica was scientific. Whilst others were racing for polar records, Mawson was studying Antarctica and leading the charge on claiming a large chunk of the continent for Australia. On his quest Mawson, along with Xavier Mertz and Belgrave Ninnis, set out to explore and study east of the Mawson's Hut. On what began as a journey of discovery and science ended in Mertz and Ninnis perishing and Mawson surviving extreme conditions against all odds, with next to no food or supplies in the bitter cold of Antarctica. This expedition allows you to embrace your inner explorer to the backdrop of incredible scenery such as glaciers, icebergs and rare fauna while looking out for myriad whale, seal and penguin species. A truly unique journey not to be missed. ITINERARY DAY 1: Invercargill Arrive at Invercargill, New Zealand’s southernmost city. Established by Scottish settlers, the area’s wealth of rich farmland is well suited to the sheep and dairy farms that dot the landscape.
    [Show full text]
  • Concentrations, Particle-Size Distributions, and Dry Deposition fluxes of Aerosol Trace Elements Over the Antarctic Peninsula in Austral Summer
    Atmos. Chem. Phys., 21, 2105–2124, 2021 https://doi.org/10.5194/acp-21-2105-2021 © Author(s) 2021. This work is distributed under the Creative Commons Attribution 4.0 License. Concentrations, particle-size distributions, and dry deposition fluxes of aerosol trace elements over the Antarctic Peninsula in austral summer Songyun Fan1, Yuan Gao1, Robert M. Sherrell2, Shun Yu1, and Kaixuan Bu2 1Department of Earth and Environmental Sciences, Rutgers University, Newark, NJ 07102, USA 2Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, NJ 08901, USA Correspondence: Yuan Gao ([email protected]) Received: 1 July 2020 – Discussion started: 26 August 2020 Revised: 3 December 2020 – Accepted: 8 December 2020 – Published: 12 February 2021 Abstract. Size-segregated particulate air samples were col- sition processes may play a minor role in determining trace lected during the austral summer of 2016–2017 at Palmer element concentrations in surface seawater over the conti- Station on Anvers Island, western Antarctic Peninsula, to nental shelf of the western Antarctic Peninsula. characterize trace elements in aerosols. Trace elements in aerosol samples – including Al, P, Ca, Ti, V, Mn, Ni, Cu, Zn, Ce, and Pb – were determined by total digestion and a 1 Introduction sector field inductively coupled plasma mass spectrometer (SF-ICP-MS). The crustal enrichment factors (EFcrust) and Aerosols affect the climate through direct and indirect ra- k-means clustering results of particle-size distributions show diative forcing (Kaufman et al., 2002). The extent of such that these elements are derived primarily from three sources: forcing depends on both physical and chemical properties (1) regional crustal emissions, including possible resuspen- of aerosols, including particle size and chemical composi- sion of soils containing biogenic P, (2) long-range transport, tion (Pilinis et al., 1995).
    [Show full text]
  • Potential Regime Shift in Decreased Sea Ice Production After the Mertz Glacier Calving
    ARTICLE Received 27 Jan 2012 | Accepted 3 Apr 2012 | Published 8 May 2012 DOI: 10.1038/ncomms1820 Potential regime shift in decreased sea ice production after the Mertz Glacier calving T. Tamura1,2,*, G.D. Williams2,*, A.D. Fraser2 & K.I. Ohshima3 Variability in dense shelf water formation can potentially impact Antarctic Bottom Water (AABW) production, a vital component of the global climate system. In East Antarctica, the George V Land polynya system (142–150°E) is structured by the local ‘icescape’, promoting sea ice formation that is driven by the offshore wind regime. Here we present the first observations of this region after the repositioning of a large iceberg (B9B) precipitated the calving of the Mertz Glacier Tongue in 2010. Using satellite data, we find that the total sea ice production for the region in 2010 and 2011 was 144 and 134 km3, respectively, representing a 14–20% decrease from a value of 168 km3 averaged from 2000–2009. This abrupt change to the regional icescape could result in decreased polynya activity, sea ice production, and ultimately the dense shelf water export and AABW production from this region for the coming decades. 1 National Institute of Polar Research, Tachikawa, Japan. 2 Antarctic Climate & Ecosystem Cooperative Research Centre, University of Tasmania, Hobart, Australia. 3 Institute of Low Temperature of Science, Sapporo, Japan. *These authors contributed equally to this work. Correspondence and requests for materials should be addressed to T.T. (email: [email protected]) or to G.D.W. (email: [email protected]). NATURE COMMUNICATIONS | 3:826 | DOI: 10.1038/ncomms1820 | www.nature.com/naturecommunications © 2012 Macmillan Publishers Limited.
    [Show full text]
  • A NEWS BULLETIN Published Quarterly by the NEW ZEALAND ANTARCTIC SOCIETY (INC)
    A NEWS BULLETIN published quarterly by the NEW ZEALAND ANTARCTIC SOCIETY (INC) An English-born Post Office technician, Robin Hodgson, wearing a borrowed kilt, plays his pipes to huskies on the sea ice below Scott Base. So far he has had a cool response to his music from his New Zealand colleagues, and a noisy reception f r o m a l l 2 0 h u s k i e s . , „ _ . Antarctic Division photo Registered at Post Ollice Headquarters. Wellington. New Zealand, as a magazine. II '1.7 ^ I -!^I*"JTr -.*><\\>! »7^7 mm SOUTH GEORGIA, SOUTH SANDWICH Is- . C I R C L E / SOUTH ORKNEY Is x \ /o Orcadas arg Sanae s a Noydiazarevskaya ussr FALKLAND Is /6Signyl.uK , .60"W / SOUTH AMERICA tf Borga / S A A - S O U T H « A WEDDELL SHETLAND^fU / I s / Halley Bav3 MINING MAU0 LAN0 ENOERBY J /SEA uk'/COATS Ld / LAND T> ANTARCTIC ••?l\W Dr^hnaya^^General Belgrano arg / V ^ M a w s o n \ MAC ROBERTSON LAND\ '■ aust \ /PENINSULA' *\4- (see map betowi jrV^ Sobldl ARG 90-w {■ — Siple USA j. Amundsen-Scott / queen MARY LAND {Mirny ELLSWORTH" LAND 1, 1 1 °Vostok ussr MARIE BYRD L LAND WILKES LAND ouiiiv_. , ROSS|NZJ Y/lnda^Z / SEA I#V/VICTORIA .TERRE , **•»./ LAND \ /"AOELIE-V Leningradskaya .V USSR,-'' \ --- — -"'BALLENYIj ANTARCTIC PENINSULA 1 Tenitnte Matianzo arg 2 Esptrarua arg 3 Almirarrta Brown arc 4PttrtlAHG 5 Otcipcion arg 6 Vtcecomodoro Marambio arg * ANTARCTICA 7 Arturo Prat chile 8 Bernardo O'Higgins chile 1000 Miles 9 Prasid«fTtB Frei chile s 1000 Kilometres 10 Stonington I.
    [Show full text]
  • Ice Core Records As Sea Ice Proxies: an Evaluation from the Weddell Sea Region of Antarctica Nerilie J
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D15101, doi:10.1029/2006JD008139, 2007 Click Here for Full Article Ice core records as sea ice proxies: An evaluation from the Weddell Sea region of Antarctica Nerilie J. Abram,1 Robert Mulvaney,1 Eric W. Wolff,1 and Manfred Mudelsee2,3 Received 12 October 2006; revised 2 May 2007; accepted 5 June 2007; published 3 August 2007. [1] Ice core records of methanesulfonic acid (MSA) from three sites around the Weddell Sea are investigated for their potential as sea ice proxies. It is found that the amount of MSA reaching the ice core sites decreases following years of increased winter sea ice in the Weddell Sea; opposite to the expected relationship if MSA is to be used as a sea ice proxy. It is also shown that this negative MSA-sea ice relationship cannot be explained by the influence that the extensive summer ice pack in the Weddell Sea has on MSA production area and transport distance. A historical record of sea ice from the northern Weddell Sea shows that the negative relationship between MSA and winter sea ice exists over interannual (7-year period) and multidecadal (20-year period) timescales. National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data suggest that this negative relationship is most likely due to variations in the strength of cold offshore wind anomalies traveling across the Weddell Sea, which act to synergistically increase sea ice extent (SIE) while decreasing MSA delivery to the ice core sites. Hence our findings show that in some locations atmospheric transport strength, rather than sea ice conditions, is the dominant factor that determines the MSA signal preserved in near-coastal ice cores.
    [Show full text]
  • Data Structure
    Data structure – Water The aim of this document is to provide a short and clear description of parameters (data items) that are to be reported in the data collection forms of the Global Monitoring Plan (GMP) data collection campaigns 2013–2014. The data itself should be reported by means of MS Excel sheets as suggested in the document UNEP/POPS/COP.6/INF/31, chapter 2.3, p. 22. Aggregated data can also be reported via on-line forms available in the GMP data warehouse (GMP DWH). Structure of the database and associated code lists are based on following documents, recommendations and expert opinions as adopted by the Stockholm Convention COP6 in 2013: · Guidance on the Global Monitoring Plan for Persistent Organic Pollutants UNEP/POPS/COP.6/INF/31 (version January 2013) · Conclusions of the Meeting of the Global Coordination Group and Regional Organization Groups for the Global Monitoring Plan for POPs, held in Geneva, 10–12 October 2012 · Conclusions of the Meeting of the expert group on data handling under the global monitoring plan for persistent organic pollutants, held in Brno, Czech Republic, 13-15 June 2012 The individual reported data component is inserted as: · free text or number (e.g. Site name, Monitoring programme, Value) · a defined item selected from a particular code list (e.g., Country, Chemical – group, Sampling). All code lists (i.e., allowed values for individual parameters) are enclosed in this document, either in a particular section (e.g., Region, Method) or listed separately in the annexes below (Country, Chemical – group, Parameter) for your reference.
    [Show full text]
  • Species Status Assessment Emperor Penguin (Aptenodytes Fosteri)
    SPECIES STATUS ASSESSMENT EMPEROR PENGUIN (APTENODYTES FOSTERI) Emperor penguin chicks being socialized by male parents at Auster Rookery, 2008. Photo Credit: Gary Miller, Australian Antarctic Program. Version 1.0 December 2020 U.S. Fish and Wildlife Service, Ecological Services Program Branch of Delisting and Foreign Species Falls Church, Virginia Acknowledgements: EXECUTIVE SUMMARY Penguins are flightless birds that are highly adapted for the marine environment. The emperor penguin (Aptenodytes forsteri) is the tallest and heaviest of all living penguin species. Emperors are near the top of the Southern Ocean’s food chain and primarily consume Antarctic silverfish, Antarctic krill, and squid. They are excellent swimmers and can dive to great depths. The average life span of emperor penguin in the wild is 15 to 20 years. Emperor penguins currently breed at 61 colonies located around Antarctica, with the largest colonies in the Ross Sea and Weddell Sea. The total population size is estimated at approximately 270,000–280,000 breeding pairs or 625,000–650,000 total birds. Emperor penguin depends upon stable fast ice throughout their 8–9 month breeding season to complete the rearing of its single chick. They are the only warm-blooded Antarctic species that breeds during the austral winter and therefore uniquely adapted to its environment. Breeding colonies mainly occur on fast ice, close to the coast or closely offshore, and amongst closely packed grounded icebergs that prevent ice breaking out during the breeding season and provide shelter from the wind. Sea ice extent in the Southern Ocean has undergone considerable inter-annual variability over the last 40 years, although with much greater inter-annual variability in the five sectors than for the Southern Ocean as a whole.
    [Show full text]
  • Zeszyt 10. Morza I Oceany
    Uwaga: Niniejsza publikacja została opracowana według stanu na 2008 rok i nie jest aktualizowana. Zamieszczony na stronie internetowej Komisji Standaryzacji Nazw Geograficznych poza Granica- mi Rzeczypospolitej Polskiej plik PDF jest jedynie zapisem cyfrowym wydrukowanej publikacji. Wykaz zalecanych przez Komisję polskich nazw geograficznych świata (Urzędowy wykaz polskich nazw geograficznych świata), wraz z aktualizowaną na bieżąco listą zmian w tym wykazie, zamieszczo- ny jest na stronie internetowej pod adresem: http://ksng.gugik.gov.pl/wpngs.php. KOMISJA STANDARYZACJI NAZW GEOGRAFICZNYCH POZA GRANICAMI RZECZYPOSPOLITEJ POLSKIEJ przy Głównym Geodecie Kraju NAZEWNICTWO GEOGRAFICZNE ŚWIATA Zeszyt 10 Morza i oceany GŁÓWNY URZĄD GEODEZJI I KARTOGRAFII Warszawa 2008 KOMISJA STANDARYZACJI NAZW GEOGRAFICZNYCH POZA GRANICAMI RZECZYPOSPOLITEJ POLSKIEJ przy Głównym Geodecie Kraju Waldemar Rudnicki (przewodniczący), Andrzej Markowski (zastępca przewodniczącego), Maciej Zych (zastępca przewodniczącego), Katarzyna Przyszewska (sekretarz); członkowie: Stanisław Alexandrowicz, Andrzej Czerny, Janusz Danecki, Janusz Gołaski, Romuald Huszcza, Sabina Kacieszczenko, Dariusz Kalisiewicz, Artur Karp, Zbigniew Obidowski, Jerzy Ostrowski, Jarosław Pietrow, Jerzy Pietruszka, Andrzej Pisowicz, Ewa Wolnicz-Pawłowska, Bogusław R. Zagórski Opracowanie Kazimierz Furmańczyk Recenzent Maciej Zych Komitet Redakcyjny Andrzej Czerny, Joanna Januszek, Sabina Kacieszczenko, Dariusz Kalisiewicz, Jerzy Ostrowski, Waldemar Rudnicki, Maciej Zych Redaktor prowadzący Maciej
    [Show full text]
  • Seasonal Dynamics of Totten Ice Shelf Controlled by Sea Ice Buttressing
    The Cryosphere, 12, 2869–2882, 2018 https://doi.org/10.5194/tc-12-2869-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. Seasonal dynamics of Totten Ice Shelf controlled by sea ice buttressing Chad A. Greene1, Duncan A. Young1, David E. Gwyther2, Benjamin K. Galton-Fenzi3,4, and Donald D. Blankenship1 1Institute for Geophysics, Jackson School of Geosciences, University of Texas at Austin, Austin, Texas, USA 2Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia 3Australian Antarctic Division, Kingston, Tasmania 7050, Australia 4Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania 7001, Australia Correspondence: Chad A. Greene ([email protected]) Received: 18 April 2018 – Discussion started: 4 May 2018 Revised: 15 August 2018 – Accepted: 23 August 2018 – Published: 6 September 2018 Abstract. Previous studies of Totten Ice Shelf have em- et al., 2015). Short-term observations have identified Totten ployed surface velocity measurements to estimate its mass Glacier and its ice shelf (TIS) as thinning rapidly (Pritchard balance and understand its sensitivities to interannual et al., 2009, 2012) and losing mass (Chen et al., 2009), changes in climate forcing. However, displacement measure- but longer-term observations paint a more complex picture ments acquired over timescales of days to weeks may not ac- of interannual variability marked by multiyear periods of curately characterize long-term flow rates wherein ice veloc- ice thickening, thinning, acceleration, and slowdown (Paolo ity fluctuates with the seasons. Quantifying annual mass bud- et al., 2015; Li et al., 2016; Roberts et al., 2017; Greene et al., gets or analyzing interannual changes in ice velocity requires 2017a).
    [Show full text]
  • 2.5.2. Alternative Construction Sites in Other Antarctic Areas
    Draft Comprehensive Environmental Evaluation 2.5.2. Alternative construction sites in other Antarctic areas Other BAS placement options in other Antarctic regions were further analised, taking into consideration scientific, environmental, logistic and other aspects. However, no alternative site for BAS placement was reported to meet all the criteria to a greater extent than that at Mount Vechernyaya location selected. 2.5.3. Zero alternative (no construction) As a zero alternative option, renovation and continuation of use of the Mount Vechernyaya field base infrastructure was subject to analysis. However, continued use of the residential premises and other RAE field base infrastructure turns out to become increasingly problematic due to their deterioration and incompliance to the Antarctic environmental protection requirements. Therefore, the zero alternative option seems to be only a temporary postponement of own station construction. Unavailability of existing facilities hampers substantially the development of scientific research, increasing the number of staff involved in BAE, making the field season longer and thus jeopardising the proper implementation of the National Program in its entirety. The up-to-date station construction would benefit to friendlier environment for living and working of polar explorers and contribute to reduced impact on the environment. Research Station at Mount Vechernyaya 39 Draft Comprehensive Environmental Evaluation 3. Initial Environmental Evaluation 3.1. General geographic description and relief The natural complex known as Mount Vechernyaya is located at the western part of Enderby Land, Tala Hills (eastern part), at the coastal area of the Alasheeva Gulf, Cosmonaut Sea. It incorporates a series of rocky ridges with a dominant mountain, the Mount Vecherniaya (272.0 m), and several lower ridges, breaking through the Antarctic ice sheet on the Cosmonauts Sea shore.
    [Show full text]
  • Observation of Ocean Tides Below the Filchner
    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 105, NO. C8, PAGES 19,615-19,630,AUGUST 15, 2000 Observation of ocean tides below the Filchher and Ronne Ice Shelves, Antarctica, using synthetic aperture radar interferometry' Comparison with tide model predictions E. Rignot,1 L. Padman,•' D. R. MacAyeal,3 and M. Schmeltz1 Abstract. Tides near and under floating glacial ice, such as ice shelvesand glacier termini in fjords, can influence heat transport into the subice cavity, mixing of the under-ice water column, and the calving and subsequentdrift of icebergs. Free- surface displacementpatterns associatedwith ocean variability below glacial ice can be observedby differencingtwo syntheticaperture radar (SAR) interferograms, each of which representsthe combination of the displacement patterns associated with the time-varying vertical motion and the time-independent lateral ice flow. We present the pattern of net free-surface displacement for the iceberg calving regions of the Ronne and Filchher Ice Shelves in the southern Weddell Sea. By comparing SAR-based displacementfields with ocean tidal models, the free-surface displacementvariability for these regions is found to be dominated by ocean tides. The inverse barometer effect, i.e., the ocean's isostatic responseto changing atmospheric pressure, also contributes to the observed vertical displacement. The principal value of using SAR interferometry in this manner lies in the very high lateral resolution(tens of meters) obtainedover the large regioncovered by each SAR image. Small features that are not well resolvedby the typical grid spacing of ocean tidal models may contribute to such processesas iceberg calving and cross-frontalventilation of the ocean cavity under the ice shelf.
    [Show full text]
  • Multidecadal Warming and Density Loss in the Deep Weddell Sea, Antarctica
    15 NOVEMBER 2020 S T R A S S E T A L . 9863 Multidecadal Warming and Density Loss in the Deep Weddell Sea, Antarctica VOLKER H. STRASS,GERD ROHARDT,TORSTEN KANZOW,MARIO HOPPEMA, AND OLAF BOEBEL Alfred-Wegener-Institut Helmholtz-Zentrum fur€ Polar- und Meeresforschung, Bremerhaven, Germany (Manuscript received 16 April 2020, in final form 10 August 2020) ABSTRACT: The World Ocean is estimated to store more than 90% of the excess energy resulting from man-made greenhouse gas–driven radiative forcing as heat. Uncertainties of this estimate are related to undersampling of the subpolar and polar regions and of the depths below 2000 m. Here we present measurements from the Weddell Sea that cover the whole water column down to the sea floor, taken by the same accurate method at locations revisited every few years since 1989. Our results show widespread warming with similar long-term temperature trends below 700-m depth at all sampling sites. The mean heating rate below 2000 m exceeds that of the global ocean by a factor of about 5. Salinity tends to increase—in contrast to other Southern Ocean regions—at most sites and depths below 700 m, but nowhere strongly enough to fully compensate for the warming effect on seawater density, which hence shows a general decrease. In the top 700 m neither temperature nor salinity shows clear trends. A closer look at the vertical distribution of changes along an ap- proximately zonal and a meridional section across the Weddell Gyre reveals that the strongest vertically coherent warming is observed at the flanks of the gyre over the deep continental slopes and at its northern edge where the gyre connects to the Antarctic Circumpolar Current (ACC).
    [Show full text]