Paleo-ice flow directions of the Northern Antarctic Peninsula ice sheet

40 Pages·2014·4.18 MB·English

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Thisdiscussionpaperis/hasbeenunderreviewforthejournalTheCryosphere(TC). p
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directions of the
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Northern Antarctic
Paleo-ice flow directions of the Northern D
Peninsula ice sheet
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Antarctic Peninsula ice sheet based upon s C.Lavoieetal.
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a new synthesis of seabed imagery P
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C. Lavoie , E. W. Domack , E. C. Pettit , T. A. Scambos , R. D. Larter , | Abstract Introduction
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H.-W. Schenke , K. C. Yoo , J. Gutt , J. Wellner , M. Canals , J. B. Anderson ,
and D. Amblas10 Dis Conclusions References
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1IstitutoNazionalediOceanografiaediGeofisicaSperimentale(OGS), uss Tables Figures
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34010BorgoGrottaGigante,Sgonico,Italy n
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2CESAM/DepartmentofGeosciences,UniversityofAveiro,Aveiro,3810-193,Portugal Pa
3CollegeofMarineScience,UniversityofSouthFlorida,St.Petersburg,Florida,33701,USA pe J I
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4DepartmentofGeosciences,UniversityofAlaskaFairbanks,Fairbanks,Alaska,99775,USA
5NationalSnowandIceDataCenter,UniversityofColorado,Boulder,Colorado,80309,USA | Back Close
6BritishAntarcticSurvey,Cambridge,Cambridgeshire,CB30ET,UK D
7AlfredWegenerInstitute,HelmholtzCentreforPolarandMarineResearch, isc FullScreen/Esc
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Bremerhaven,27568,Germany s
8KoreanPolarResearchInstitute,Incheon,406-840,SouthKorea sio Printer-friendlyVersion
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9DepartmentofEarthandAtmosphericSciences,UniversityofHouston, P InteractiveDiscussion
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Houston,Texas,77204,USA p
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10Departamentd’Estratigrafia,PaleontologiaiGeociènciesMarines,UniversitatdeBarcelona, D
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Barcelona,08028,Spain c TCD
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11DepartmentofEarthScience,RiceUniversity,Houston,Texas,77251,USA ss
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Received:13September2014–Accepted:26September2014–Published:15October2014 P
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Correspondenceto:C.Lavoie([email protected])andE.W.Domack([email protected]) e Paleo-ice flow
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PublishedbyCopernicusPublicationsonbehalfoftheEuropeanGeosciencesUnion. directions of the
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Northern Antarctic
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Peninsula ice sheet
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Abstract D
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We present a new seafloor map for the northern Antarctic Peninsula (AP), including s
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swath multibeam data sets from five national programs. Our map allows for the exam- io 8,5321–5360,2014
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ination and interpretation of Last Glacial Maximum (LGM) paleo-ice sheet/stream flow P
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5 directionsdevelopedupontheseafloorfromthepreservationof:mega-scaleglaciallin- pe Paleo-ice flow
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eations,drumlinizedfeatures,andselectivelinearerosion.Wecombinethiswithterres- directions of the
trialobservationsofflowdirectiontoplaceconstraintsonicedividesandaccumulation | Northern Antarctic
centers(icedomes)ontheAPcontinentalshelf.Theresultsshowaflowbifurcationas D Peninsula ice sheet
ice exits the Larsen-B embayment. Flow emanating off the Seal Nunataks (including isc
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10 Robertson Island) is directed toward the southeast, then eastward as the flow transits ssio C.Lavoieetal.
toward the Robertson Trough. A second, stronger “streaming flow” is directed toward n
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thesoutheastthensouthward,asiceoverflowedthetipoftheJasonPeninsulatoreach a
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thesouthernperimeteroftheembayment.Ourreconstructionalsorefinestheextentof e TitlePage
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at least five other distinct paleo-ice stream systems which, in turn, serve to delineate
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sevenbroadregionswherecontemporaneousicedomesmusthavebeencenteredon
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the continental shelf during the LGM time interval. Our reconstruction is more detailed Dis Conclusions References
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than other recent compilations because we followed specific flow indicators and have us Tables Figures
kept tributary flow paths parallel. s
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1 Introduction e J I
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The reconstruction of paleo-ice sheets/stream flow directions depends first upon an | Back Close
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accurate assessment of accumulation centers, ice divides, and flow paths (outlets) D
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(Andrews, 1982). Studies of the configuration of the Antarctic Peninsula Ice Sheet c
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(APIS) during the Last Glacial Maximum (LGM; time interval ∼23–19kyrBP) sug- s
gestthatthegroundedicereachedthecontinentalshelfbreak(e.g.LarterandBarker, sion Printer-friendlyVersion
1989; Banfield and Anderson, 1995; Larter and Vanneste, 1995; Wellner et al., 2001; P InteractiveDiscussion
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Canals et al., 2002; Evans et al., 2005; Heroy and Anderson, 2005; Amblas et al., e
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2006;Wellneretal.,2006;Simmsetal.,2011).TheseaflooroftheAntarcticPeninsula D
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(AP) continental shelf is characterized by over-deepened troughs and basins where c TCD
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mega-scaleglaciallineations(MSGLs)(Clark,1993;Clarketal.,2003)andlarge-scale s
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flowlinedbedformssuchasglacialflutes,mega-flutes,grooves,drumlinsandcrag-and- n
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5 tails provide geomorphic evidence for former regional corridors of fast-flowing ice and a
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drainage directions of the APIS on the continental shelf. Also of importance is their e Paleo-ice flow
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synchroneity as the ice flows change during the ice sheet evolution, from ice sheet to directions of the
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ice stream to ice shelf (Gilbert et al., 2003; Dowdeswell et al., 2008). Northern Antarctic
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Our capability to image specific flow directions and styles on the Antarctic continen- Peninsula ice sheet
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10 tal shelf is critical to any glacial reconstruction in so much as they help us to under- u
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stand the present and future ice sheet’s behavior. Recently, Livingstone et al. (2012) s
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published an inventory of evidence for paleo-ice streams on the continental shelf of n
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Antarctica at LGM. Their reviews are in agreement with previous studies and highlight a
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that the West (Pacific) AP continental shelf is characterized by preferred regional ice r
15 flowpathwaysonthemiddleshelfthroughcross-shelftroughsconnectedtomajorflow | Abstract Introduction
paths on the outer shelf (e.g. Evans et al., 2004; Heroy and Anderson, 2005). On the
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otherside,theEast(WeddellSea)APcontinentalshelfislesswelldefinedbutcharac- is
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terized by multiple deep tributaries on the inner shelf that converge in shallow troughs us Tables Figures
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on the mid to outer shelf (e.g. Evans et al., 2005). Nevertheless, our knowledge on io
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the accumulation centers, ice divides and flow paths at the LGM time interval, such J I
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as in the Larsen-B embayment, is limited and particularly relevant to the APIS recon- p
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struction, where the broad continental shelf served as a platform for extension of the r
glacialsystemsthatspilledofftheDetroitandBrucePlateauicecaps.InfacttheAPis | Back Close
believed to have experienced the largest percentage change in areal extent of glacial
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coverofanysectoroftheAntarcticmarginthroughthelastglacialcycle(i.e.MISstage is FullScreen/Esc
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2 to 1). For instance our reconstruction shows that the current APIS covers ∼23% s
of the total area of grounded ice coverage at LGM. The APIS system in particular is sio Printer-friendlyVersion
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asignificantbellwethersystemintheevolutionoftheAntarcticIceSheetbecauseitis: P InteractiveDiscussion
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1. theonesystemtodaythatismostcloselytiedtosurfacedrivenablationandaccu- D
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mulationchanges,havingequilibriumlinesa.s.l.asaconsequenceofsignificantly c TCD
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warm summer temperatures; s
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2. exposed to a contrasting oceanographic regime of cold and warm water on the P
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eastern and western sides, respectively, and p
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3. the most northern of the ice sheet systems and it is exposed to southward excur- directions of the
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sions in westerly winds and the Antarctic Circumpolar Current. Northern Antarctic
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Peninsula ice sheet
In this paper, we enhance our knowledge on the paleo-ice sheet/stream flow drainage is
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directions of the APIS based upon a new synthesis of single and swath bathymetry s C.Lavoieetal.
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data, and provide a comprehensive assessment of the flow paths, ice divides and ac- io
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cumulation centers pertaining to the glacial history of the northern APIS at the LGM P
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time interval. The spatial coverage of the bathymetric data is extensive (Fig. 1) and for pe TitlePage
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this and the above reasons we focus upon regional systems by dividing it into seven
sectors. These include the (1) Larsen-B embayment, (2) Larsen-A and James Ross | Abstract Introduction
15 Island, (3) Joinville Archipelago Platform, (4) Bransfield Strait, (5) Gerlache–Croker– Dis Conclusions References
Boyd Straits, (6) Palmer Deep and Hugo Island Trough, and (7) Biscoe Trough. We c
draw upon our compiled seabed map the geomorphic features that define the spe- uss Tables Figures
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cific flow paths at LGM and glacial tributaries across the inner to outer shelf to infer n
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the flow paths, ice divides and the accumulation centers that controlled the APIS flow a
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drainage and subsequent retreat history. Finally, we discuss the characteristics of the e J I
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reconstructed northern APIS and its regional significance for ice sheet modeling.
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2.1 Data sets sio Printer-friendlyVersion
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Extensivemultibeamswathbathymetrydatahavebeenacquiredfromregionsrecently ap
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uncovered by the collapse of the Larsen Ice Shelf system. Ice-flow directions within r
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the Larsen-B embayment are indicated by a series of interconnected (1) multibeam D
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surveys beginning with a United States Antarctic Program (USAP) program in 2000 c TCD
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including work by the British Antarctic Survey (2002), additional USAP surveys (2001 s
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and 2006), Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research n
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5 surveys(2009and2011)andKoreaPolarResearchInstitutesurvey(KOPRI,2013)un- a
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dertheLARISSAproject,and(2)singlebeamsonardatafromUSAPin2005.Detailed e Paleo-ice flow
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observations of the seafloor morphology in the Larsen-A embayment, the area sur- directions of the
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roundingJamesRossIslandandoffshorefromJoinvilleArchipelagowerecollectedby Northern Antarctic
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theUSAPprogrambetween2000–2002,2005–2007,in2010and2012includingwork Peninsula ice sheet
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10 by the British Antarctic Survey (2002) and UK Hydrographic Office (2006–2008). The cu
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Bransfield Strait has been covered by the Spanish Antarctic program between 1991 s
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and 1997, USAP program (1995–1997, 1999–2002, and 2005–2011) and UK Hydro- n
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graphic Office (2006–2008, 2010 and 2012). The multibeam swath bathymetry data a
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from the Gerlache–Croker–Boyd Strait, Palmer Deep and Hugo Island Trough, and r
15 Biscoe Trough are from the Spanish Antarctic program in 1996–1997 and 2001–2002, | Abstract Introduction
theUSAPprogram(1995–1997,1999–2002,and2005–2012)andKOPRI(2013).The
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data set was gridded at a cell size of 30m×30m and analyzed with illumination at is
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variable azimuths. Furthermore, single beam sonar data from NGDC Marine Trackline us Tables Figures
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Geophysical database (http://ngdc.noaa.gov/mgg/geodas/trackline.html) were used to io
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support the delimitation of the continental shelf ice domes. J I
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2.2 Bedform mapping r
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We assume that our flow lines reconstructions are contemporaneous to the LGM time
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intervalconsideringthatourobservedseafloorlineationsoverresistantsubstratewere is FullScreen/Esc
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carved last by the APIS at LGM, although their formation may derive from previous u
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25 over time-integrated glacial processes. From the observed seafloor lineations, central sio Printer-friendlyVersion
flow lines were established at the root of all major glacier tributaries adjacent to areas n
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ofreasonablecoverageinthemultibeamdata.Thesecentralflowlineswerepreserved a
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along the path by forcing tributary contributions to remain parallel and consistent with r
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observedseafloorlineations.Inthiswayconvergingflowcanbeevaluatedmoreeasily D
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than by using “idealized” single-line flow arrows (as has been done on previous re- c TCD
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constructions). The number of lines in a given flow path is defined by the number of s
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tributaries, and is only a visual approximation of the ice discharge for that flow path. n
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parallel within the larger confining troughs or fjords. Small-scale basal-flow divergence e Paleo-ice flow
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patterns such as these were not preserved in our reconstruction. directions of the
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TheorientationofthebedrockstriationsatCapeFramnesandFoynPoint(Larsen-B Northern Antarctic
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embayment; Fig. 2) were measured with a Brunton Compass, corrected for regional Peninsula ice sheet
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during 2010 (USAP-ship based helicopters during LARISSA NBP10-01 cruise). s
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2.3 Ice volume estimation and assumptions a
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Weutilizetwodifferentalgorithmstoestimatevolumesoftheicesheet,dependingupon
| Abstract Introduction
the type of system, ice domes or streaming flow. For the domes in this reconstruction,
weuseasimple,radiallysymmetric,Bodvarsson–VialovmodelaspresentedinBueler D Conclusions References
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et al. (2005). This model assumes the shallow-ice approximation (no sliding bed) and c
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Glen-typeiceflowwithasoftnessthatdependsontheaveragetemperature.Themodel s
candirectlypredictthethicknessasafunctionofdistancefromthedomecenter(r =0) ion
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as: a
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H(r)=(cid:18)2(n−1)b˙(cid:19)1/(2n+2)(L1+1/n−r1−1/n)n/(2n+2) (1) r| Back Close
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Γ= (2) c
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whereH istheicethickness,b˙ istheaccumulationrate,Listhelateralextentoftheice n
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dome, assuming it is circular, and n=3 for typical Glen-type ice flow. Γ is a parameter a
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of ice, and gravity (g). We are assuming that the same strongly orographic precipita- D
tion occurred during LGM interval as today, and the ice temperature was around 0◦C isc TCD
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(mostlytemperate)fortheWestAPdomesandaveraging−10◦Cforthedomeslocated ss
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on the East side (see Sect. 4.3). We based the minimum and maximum on a low-end n
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5 and high-end approximation of the accumulation rates, respectively. In these accumu- a
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lations rate assumptions, we took into account that some domes are more exposed e Paleo-ice flow
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to the prevailing storm direction and some will be in the lee, resulting higher or lower directions of the
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accumulation rates. Northern Antarctic
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To estimate the ice volume of the convergent flow paths we use less established Peninsula ice sheet
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10 assumptions. The average depths along the flow paths are estimated from our swath u
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bathymetry map and the IBCSO map gridded at 500m (Arndt et al., 2013). For the s
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minimum volumes, we assume that the ice streams were lightly grounded until the n
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shelf break or to the end of the defined flow path (except for Larsen-B/Jason Trough) a
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where the ice thickness must be about 10% more than the average depth to prevent r
15 flotation (allowing to the deepest areas to be subglacial lakes, rather than full of ice). | Abstract Introduction
We assume a minimal surface slope (0.001) similar to the lowest sloping modern ice
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streams. For the maximum volumes, we assume that the ice was grounded until the is
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continental shelf break (except for Larsen-B/Jason Trough). We assume the surface us Tables Figures
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slope of the ice was steeper (0.005), but not too steep to exceed the nearby ice dome io
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elevations. In both estimations, it will depend on the geology. A softer more malleable J I
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bed would have a lower profile ice stream (but it still needs to be thick enough to be p
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grounded), a stiffer bed would require a slightly steeper profile. r
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3.1 Larsen-B embayment sio Printer-friendlyVersion
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ThemajorcollapseoftheLarsen-BIceShelfin2002(Scambosetal.,2003),unprece- P InteractiveDiscussion
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dented in the Holocene history of this glacial system (Domack et al., 2005; Curry and e
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Pudsey, 2007), has provided a unique opportunity for seafloor mapping. This work re- D
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veals a far more detailed flow pattern in Larsen-B embayment than that inferred by c TCD
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general orientation of bathymetric troughs derived from sparse swath or single line s
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bathymetric data. Such earlier approaches suggested that all Larsen-B ice flowed out n
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5 toward the Robertson Trough (e.g. Evans et al., 2005; Davies et al., 2012; Livingstone a
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et al., 2012). e Paleo-ice flow
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Byusingmoreamoredetailedanalysisofflowindiciesavailablefromtheswathdata directions of the
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we now recognize two distinct flow trajectories that split the Larsen-B embayment into Northern Antarctic
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twooutlets(Fig.2).Thefirstrelatestotheattenuateddrumlinizedbedformsandhighly Peninsula ice sheet
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10 attenuated MSGLs observed in the northern perimeter of the Larsen-B embayment. u
The ice flow emanating off the Seal Nunataks and Robertson Island directed flow to- ss C.Lavoieetal.
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ward the southeast then eastward as the flow transits toward the Robertson Trough, n
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a feature that connects Larsen-A and B (Evans et al., 2005). This flow pattern extends a
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across relatively shallow depths of less than 500m and was fed by indistinct tributary r
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In contrast, the southern perimeter is marked by stronger “streaming flow” indica-
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tors fed by large tributaries draining the APIS, including the Crane Glacier and most is
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likely the Evans, Green and Hektoria Glaciers. The well-defined drumlinized bedforms us Tables Figures
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with crescentric scour and MSGLs indicate that ice flow was funneled into the Cold io
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SeepBasin(Fig.3a)andmovedtowardthesoutheastfromtheinterior.Fromtheedge J I
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of the SCAR Inlet (Larsen-B Ice Shelf), the swath bathymetric map shows evidence p
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of a northeastward flow (Fig. 3b) that downstream shifted toward the southeast, thus r
convergent with the flow streaming from the Cold Seep Basin corridor. The SCAR In- | Back Close
let ice stream system was fed by the tributaries of the Starbuck, Flask, and Leppard
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Glaciers. Our flowlined bedform compilation suggests that the southeastward flow in is FullScreen/Esc
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thesouthernperimeteroftheLarsen-Bchangedtoasouthwarddirectionwithiceover- s
flowingthetipoftheJasonPeninsula,offshorethenorthernregionoftheLarsen-CIce sio Printer-friendlyVersion
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Shelf (Figs. 2 and 3c), to reach the Jason Trough. This southward flow orientation is P InteractiveDiscussion
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supported by bedrock striations and flute orientations SSW at Cape Framnes, Jason D
Peninsula (Fig. 4) that parallel marine flow indicies found directly offshore. isc TCD
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Finally,thesouthernmostswathbathymetrydataattheedgeofthenorthernLarsen- s
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C Ice Shelf indicates a southeastward ice flow orientation on a seafloor deeper than n
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5 400m. Recent seismic reflection soundings close to the northern ice shelf front and a
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inward the shipboard surveys show a uniform water cavity thickness beneath the ice e Paleo-ice flow
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shelf of around 220 to 240m (Brisbourne et al., 2014). directions of the
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3.2 Larsen-A and James Ross Island D Peninsula ice sheet
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Our mapped flow pattern of the Larsen-A and James Ross Island sector differs only in s C.Lavoieetal.
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fine detail to those of earlier reconstructions (e.g. Evans et al., 2005; Johnson et al., io
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2011; Davies et al., 2012). The evidence is the establishment of two major outlets: P
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the Robertson Trough system and the Erebus–Terror system (Fig. 5). The Robertson e TitlePage
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Trough system collected flow out of the Larsen-A, southern Prince Gustav Channel,
| Abstract Introduction
and portions of Admiralty Sound. The ice flowed from the Larsen-A, derived mainly
from the Detroit Plateau (AP), toward the south, then east. It then coalesced with the D Conclusions References
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southernPrinceGustavChannelflowacrosstheshelftowardthesoutheastandfinally c
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directlyeast(Pudseyetal.,2001;Gilbertetal.,2003;Evansetal.,2005).Ontheouter s
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shelf the ice flow coalesced with the northern perimeter of the Larsen-B flow to form n
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a major ice flow trend in the Robertson Trough. a
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TheErebus–TerrorsystemcapturedflowoutofthenorthernPrinceGustavChannel, e J I
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Antarctic Sound, and Admiralty Sound. The northern Prince Gustav Channel, shows
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evidence of a main eastern flow direction, fed by tributaries from ice caps on Trin-
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ity Peninsula and James Ross Island before coalescing with the Antarctic Sound and is FullScreen/Esc
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the Admiralty Sound flows into the Erebus and Terror Gulf to reach the shelf break. u
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tembyanicedivide,asaconsequenceofanicesaddle(divide)thatextendedfromthe n
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Detroit Plateau across the James Ross Island (Camerlenghi et al., 2001). Recent ob- a
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servationsandcosmogenicisotopeexposure-agedatingonerraticbouldersonJames r
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