Late Neogene Ice Drainage Changes in Prydz Bay, East Antarctica and the Interaction of Antarctic Ice Sheet Evolution and Climate ⁎ P.E

Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 www.elsevier.com/locate/palaeo

Late Neogene ice drainage changes in Prydz Bay, East Antarctica and the interaction of Antarctic ice sheet evolution and climate ⁎ P.E. O'Brien a, , I. Goodwin b, C.-F. Forsberg c, A.K. Cooper d, J. Whitehead e

a Geoscience Australia, GPO Box 378, Canberra Australia 2904 b Environmental and Climate Change Group, School of Environmental and Life Sciences, University of Newcastle, Callaghan, NSW Australia 2308 c Norwegian Geotechnical Institute, P.O. Box 3930, Ulleval Hageby, N-0806 Oslo, Norway d Department of Geological and Environmental Sciences, Stanford University, Stanford California USA e Institute of Antarctic and Southern Ocean Studies, University of Tasmania, Australia

Received 18 January 2006; received in revised form 1 September 2006; accepted 5 September 2006

Abstract

During the late Neogene, the Lambert Glacier–Amery Ice Shelf drainage system flowed across Prydz Bay and showed several changes in flow pattern. In the Early Pliocene, the Lambert Glacier ice stream reached the shelf edge and built a trough mouth fan on the upper continental slope. This was associated with an increase in ice discharge from the Princess Elizabeth Land coast into Prydz Bay. The trough mouth fan consists mostly of debris flow deposits derived from the melting out of subglacial debris at the grounding line at the continental shelf edge. The composition of debris changes at around 1.1 Ma BP from material derived from erosion of the Lambert Graben and Prydz Bay Basin to mostly basement derived material. This probably results from a reduction in the depth of erosion and hence the volume of ice in the system. In the trough mouth fan, debris flow intervals are separated by thin mudstone horizons deposited when the ice had retreated from the shelf edge. Age control in an Ocean Drilling Program hole indicates that most of the trough mouth fan was deposited prior to the Brunhes–Matuyama Boundary (780 ka BP). This stratigraphy indicates that extreme ice advances in Prydz Bay were rare after the mid Pleistocene, and that ice discharge from Princess Elizabeth Land became more dominant than the Lambert Glacier ice in shelf grounding episodes, since the mid Pleistocene. Mechanisms that might have produced this change are extreme inner shelf erosion and/or decreasing ice accumulation in the interior of East Antarctica. We interpret this pattern as reflecting the increasing elevation of coastal ice through time and the increasing continentality of the interior of the East Antarctic Ice Sheet. The mid Pleistocene change to 100 ka climatic and sea level cycles may also have affected the critical relationship between ice dynamics and the symmetry or asymmetry of the interglacial/ glacial climate cycle duration. © 2006 Elsevier B.V. All rights reserved.

Keywords: East Antarctica; Extreme ice advances; Pliocene; Pleistocene; Trough mouth fan; Precipitation; Amery Ice Shelf

1. Introduction O'Brien et al., 2001). Since its inception, it has played a central role in global climate and in higher order sea The East Antarctic Ice Sheet is presently the largest level change. Although global ice volume/temperature and longest-lived ice mass on earth (Barron et al., 1991; changes can be estimated using low latitude δ18O records in ocean sediments, the distribution of ice on the ⁎ Corresponding author. Tel.: +61 2 62499409; fax: +61 2 62499920. continent and the detailed evolution of the Antarctic Ice E-mail address: [email protected] (P.E. O'Brien). Sheet require direct evidence from Antarctica (Barker

0031-0182/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.palaeo.2006.09.002 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 391 et al., 1998). The understanding of regional changes ice shelf grounding zone well inland (484 km) from Prydz in ice distribution and behaviour may provide evidence Bay (Fricker et al., 2002). On the eastern side of the bay, for the processes that have contributed to major climate the sea floor shoals to depths of 100–200 m on Four changes. Ladies Bank which is separated from the Ingrid Obtaining records of glacial history from the Antarc- Christensen Coast by a series of connected troughs and tic continental margin is complicated by the extensive saddles known as the Svenner Channel. The Amery erosion of the shelf by Cenozoic ice advances (Barron Depression is linked to the shelf edge by Prydz Channel et al., 1991). While subglacial and interglacial sediments which occupies the western part of the bay and has depths are preserved in places, erosion has removed large from 700 m below sea level at its inshore end to about amounts of sedimentary section (Solheim et al., 1991; 500 m below sea level at the shelf edge. Forsberg et al., 2001). However, erosion features can Prydz Bay lies at the seaward end of the Lambert-rift indicate palaeoflow directions and erosion surfaces can Graben that extends about 500 km south of Prydz Bay. be traced into their correlative conformities on the con- The adjacent rift-flank mountains (Prince Charles tinental slope, where the debris carried by the grounded Mountains) are mostly ice-covered and have a visible ice has been deposited (Cooper et al., 1991; Kuvaas and relief of up to 3500 m. Most of the basement rocks of the Leitchenkov, 1992; Bart et al., 2000). More complete region are high-grade Precambrian metamorphic and sedimentary records are possible in trough mouth fans intrusive rocks (Mikhalsky et al., 2001) with isolated formed where fast flowing ice streams reach the shelf exposures of Paleozoic granite, mafic dykes, Permian edge during episodes of extreme ice extent. These fans sediments, Paleogene volcanics, and Oligocene and consist of mass flow deposits formed from debris re- younger glacial sediments (Tingey, 1991; Hambrey and leased from the basal ice at the shelf break, interbedded McKelvey, 2000). The offshore area is underlain by the with thin hemipelagic and pelagic intervals deposited Prydz Bay sedimentary basin, with up to 12 km of when the ice was shoreward of the shelf edge (Boulton, sediment (Cooper et al., 1991), which is part of the an 1990; Vorren and Laberg, 1997). The East Antarctic extensive rift system that also includes the Lambert margin in Prydz Bay provides an important opportunity Graben. The rifting history extends back to at least to understand the behaviour of the East Antarctic Ice Cretaceous (Truswell, 1991) and probably back to the Sheet. Seismic data collected since 1982 and cores holes Permo-carboniferous (Arne, 1994). drilled on ODP Legs 119 and 188 drilled in Prydz Bay, provide a record of the Lambert Glacier–Amery Ice 2.1. Glaciology Shelf drainage system that flows from deep in the interior of the East Antarctic Ice Sheet. Neogene sediments are Prydz Bay and the shelf offshore receives ice from also represented in outcrops in the Prince Charles three regions; the Lambert Glacier–Amery Ice Shelf Mountains (PCMs) south of Prydz Bay (Hambrey and system, Princess Elizabeth Land and Mac.Robertson McKelvey, 2000; Whitehead and Boharty, 2003) Land, with four discrete ice drainage catchments (Fig. 2). providing samples of depositional conditions extending The main drainage into the Amery Ice Shelf is fed by nearly 700 km into the interior of East Antarctica. glaciers that break through the barrier of the PCMs along its length. At the southern end, the major glaciers are the 2. Regional setting Lambert, Mellor and Fisher Glaciers that flow into the graben through the southern group of nunataks and form Prydz Bay forms the terminus of the Lambert Glacier– the main axial ice drainage. They drain a catchment area Amery Ice Shelf ice drainage system, which drains about of 1,481,000 km2 (excluding the floating Amery Ice 16% of the grounded East Antarctic Ice Sheet (Allison, Shelf, Allison, 1979; Fricker et al., 2000). Examination 1979; Fricker et al., 2000). Most of the ice in the Lambert of a digital terrain model derived from satellite altimetry Glacier–Amery Ice Shelf system accumulates in the (Liu et al., 2001) indicates that four other ice drainage interior of East Antarctica (Allison, 1979; Fricker et al., basins discharge to the Amery Ice Shelf and Prydz Bay. 2000) so it responds to interior mass balance fluctuations. Ice flowing from Mount Creswell to the Northern Prince The dynamical response is recorded in the sediments of Charles Mountains along the western side of the Amery Prydz Bay and the adjacent slope and rise (Figs. 1 and 2). Ice Shelf drains about 303,710 km2. The largest glaciers Prydz Bay is typical of the Antarctic shelf with the deepest in this area are the Charybdis and Scylla Glaciers. Other areas (∼1200 m) inshore, near the front of the Amery Ice smaller ice streams feed into the Amery Ice shelf from Shelf in the Amery Depression (Fig. 1). Greater depths Mac.Robertson Land via re-entrants in the grounding (N2200 m, Fricker et al., 2001) are found near the present line, draining only about 113,200 km2. 392 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

Fig. 1. Location of Prydz Bay with named bathymetric features and Ocean Drilling Program sites.

The Lambert–Amery System receives ice from a Ice Shelf Glacier. At the eastern edge of this region is catchment area of 635,500 km2 along its eastern side the West Ice Shelf (Fig. 2). There is a general between the Mawson Escarpment and edge of the asymmetry in the ice accumulation distribution across Amery Ice Shelf. North-east of the modern edge of the the Lambert–Amery System, with higher ice accumu- Amery Ice Shelf, Prydz Bay receives ice from the lation along the eastern side of the basin up to 2500 m Ingrid Christensen Coast (375,100 km2 in area). elevation. Ice accumulation rates along the Princess Several small glaciers drain through this margin and Elizabeth Land catchment are considerably less than include the Ranvick and Sørsdal Glaciers, together those measured for equivalent elevations further east in with some smaller glaciers flowing into the Publication Wilkes Land (Goodwin, 1995). P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 393

3. Sedimentation and ice drainage patterns During the Palaeogene, the Lambert Graben–Prydz Bay Basin would have trained the fluvial systems that formed 3.1. Pre Neogene the delta plain that deposited poorly sorted sands of Late Eocene age intersected by ODP Site 1166 (Macphail and The broad pattern of ice and sediment movement in Truswell, 2004; Cooper and O'Brien, 2004). The first the region has long been controlled by the Lambert signs of glaciation are ice-modified sand grains in these Graben. This feature has been a major influence on fluviodeltaic sediments (Strand et al., 2003) and ice- drainage since even the Carboniferous (Arne, 1994). rafted grains in overlying marine mudstone (Shipboard

Fig. 2. Major topographic features ice drainage basins in the Prydz Bay–Amery Ice Shelf region. N.PCMs – Northern Prince Charles Mountains, S.PCMs –Southern Prince Charles Mountains, Komso – Komsomolsky Peak, dark shading – outcrop, light shading – ice shelf. 394 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

Fig. 3. Seismic line (AGSO 149/0901) crossing the shelf edge and upper slope of Four Ladies Bank. A. Position of Early Pliocene surface pp-12 beneath upper slope and shelf and vertically aggrading palaeoshelf break. B. Detail of Line AGSO 149/1401 showing the interval of vertically aggraded topsets and palaeoshelf edge followed by rapid shelf progradation.

Scientific Party, 2001a). Major glacial ice advances onto was a huge fjord with tidewater glaciers flowing into the shelf then took place in the Early Oligocene the edges and a mixture of open water, sea ice and (Hambrey et al., 1991). The sediments produced by icebergs in the basin proper (Hambrey and McKel- this phase are mostly aggraded glaciomarine pebbly vey, 2000; McKelvey et al., 2001; Whitehead and mudstones and diamicts (Hambrey et al., 1991). McKelvey, 2001; Whitehead and Boharty, 2003). The cold, glacial maximum phase saw the confluence of 3.2. Miocene the glaciers into a major ice stream. Miocene sediments have not been intersected by drilling on Once glaciation was established, the Graben has the shelf, however, thin topsets that wedge out oscillated between two states. The warm phase state seaward of Site 739 and foresets below the shelf P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 395

Fig. 4. Seismic line across the shelf edge in the axis of Prydz Channel and the Prydz Channel Fan. (Line AGSO 149/0901). Topset deposition prior to pp-12 was aggradational whereas post pp-12, topsets were thin or eroded completely. Progradation of the shelf edge and slope was much faster than for Four Ladies Bank (Fig. 3). and slope are probably of Miocene age (Fig. 3A). of the Lambert Graben and crosses a basement ridge at an Reflection geometry indicates both aggradation of the angle of about 70° (Figs. 5 and 7). This suggests that the shelf and progradation of the shelf edge took place orientation of Prydz Channel is not controlled by basement with palaeoshelf edges preserved across Prydz structure. Faults that displace basement and extend into Bay (Figs. 3A and 4). These palaeoshelf edges Mesozoic units are oriented parallel to the ridge, also extend straight across Prydz Bay (Fig. 5, Cooper et making a steep angle with the Prydz Channel axis. al., 1991; Leitchenkov et al., 1994), suggesting that Unlike Prydz Channel, Svenner Channel, on the ice moved along the axis of the Lambert Graben and southeastern side of Prydz Bay, consists of a series of Prydz Bay Basin. This pattern indicates that there was deeps and saddles rather than a continuous trough. The no focused ice stream in the bay. Strike sections reveal saddles are offshore from coastal outcrops such as the large valleys cut in the shelf edge and then infilled, Vestfold and Larsemann Hills and the troughs are offshore suggesting significant periods where the ice did not from larger glaciers (Fig. 7). O'Brien and Harris (1996) reach the shelf edge. inferred from this morphology that Svenner Channel formed by enhanced erosion at the confluence of greatly 3.3. Early Pliocene reorganisation enlarged glaciers flowing from the Ingrid Christrensen Coast and the Lambert–Amery System. They concluded The Early Pliocene saw major changes in geomorphol- that the most likely cause of the orientation of Prydz ogy and sedimentation in the Prydz Bay region that Channel was deflection of the Lambert–Amery flow to produced Prydz and Svenner Channels on the shelf and the the west by the ice flowing from an expanded ice sheet Prydz Channel Trough Mouth fan on the upper slope margin along the Ingrid Christensen Coast (Fig. 7). (Fig. 1). These changes are marked initially by a wide- Stratal geometry changed across Prydz Bay after spread erosion surface on the shelf and slope designated surface pp-12 formed. Beneath Four Ladies Bank, flat Surface A by Mizukoshi et al. (1986) and pp-12 in O'Brien lying sediment up to about 300 m thick accumulated while et al. (2004). O'Brien and Harris (1996) suggested, on the the shelf edge prograded only about 1 km (Fig. 3B). This basis of a seismic tie to ODP Site 739, that surface pp-12 then changed to predominantly progradation in the early was Pliocene in age. Close examination of an expanded Pleistocene, producing seaward migration of the bank display of the seismic data indicates that pp-12 intersects shelf edge by about 8 km from the early Pleistocene till Site 739 within the Early Pliocene (3.9–3.6 Ma) interval now (Fig. 3B). Prydz Channel has a very thin post pp-12 between 105.9 m below sea floor (mbsf) – 130 mbsf section (Fig. 8). At the shelf edge of the newly-formed (Fig. 6, Barron et al., 1991). The surface marks the Prydz Channel, the shelf edge prograded strongly with development of Prydz Channel (O'Brien et al., 2004). The only very thin topsets (Fig. 4). Foresets making up the fan orientation of Prydz Channel is about 45° west of the axis downlap onto surface pp-12 at the foot of the upper slope. 396 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

Fig. 5. Miocene ice advance directions inferred from the geometry of palaeo shelf edges. Bathymetry has been modified to reflect the absence of the Prydz Channel Fan prior to the Early Pliocene. The axis of the basement ridge on the western side of Prydz Bay is shown.

Pliocene and Pleistocene sedimentation concentrated number and timing of extreme advances of the in the Prydz Channel Fan. This can be seen in bathym- Lambert–Amery system (O'Brien et al., 2001). Models etric contours as a seaward bulge directly north of Prydz of trough mouth fans, derived mostly from fans sampled Channel, and in isopach contours as locally thick post- on North Atlantic margins, predicted that the fan would early Pliocene sediment (Fig. 8, O'Brien et al., 2001). consist of debris flow deposits formed by slumping of The fan extends to water depths of about 2400 m and has subglacial debris delivered to the shelf edge during a surface slope of ∼2°. Prydz Channel Fan is over extreme advances interbedded with fine grained facies 1000 m at its thickest and contains about 27,740 km3 of deposited during phases of reduced ice extent (Boulton, sediment based on seismic data and velocity information 1990; Vorren and Laberg, 1997). from ODD Site 1167 compared to 2058 km3 of similar Site 1167 intersected two units (Fig. 9, O'Brien et al., age sediment on the shelf to the east. The shelf edge at 2001; Passchier et al., 2003): Unit I extends from the sea the end of Prydz Channel prograded about 27 km from floor to 5.17 mbsf. It consists of olive to red brown clay the early Pliocene to the present (Fig. 4). and sandy clay with isolated beds of sand, some of which are normally graded. Lonestones are rare, and 3.4. Pleistocene changes diatoms and sponge spicules form up to 2% of the clay beds. Unit I formed mostly by hemipelagic deposition The later history of the Prydz Channel Fan can be with minor turbidites (Passchier et al., 2003). Unit II derived from ODP Site 1167, where the central part of extends from 5.17 mbsf to 447.5 mbsf and consists of the fan was drilled with the aim of investigating the diamicts and muddy, pebbly sands deposited by debris P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 397

Fig. 6. Age control on surface pp-12 from its intersection with ODP Site 739. Seismic line is AGSO 149/1201. ODP site 739 represented by the time- converted impedance log calculated by Cooper et al. (1991) and stratigraphy of Barron et al. (1991). Pp-12 intersects the well within the interval of Early Pliocene sediments. flows with interbedded thin hemipelagic muds and Strontium isotope dates on planktonic foraminifera sporadic sand beds deposited as turbidites (Passchier (Fig. 10). Although these data sources do not provide et al., 2003). This combination of lithofacies in Site tightly constrained ages, they provide estimates of a 1167 is consistent with the facies model for trough range of sedimentation rates, even though there are mouth fans (Boulton, 1990; Voren and Laberg, 1997; probably unresolved disconformities in the section. Passchier et al., 2003). Low recovery in the Hole 1167A Diatoms are restricted to the upper 5.25 mbsf. They made it impossible to estimate the number of debris flow include elements of the Thalassiosira lentiginosa Zone episodes from core alone. However, the LWD (Logging- that is less than 0.66 Ma old (O'Brien et al., 2001). While-Drilling) tools provided this information for the Theissen et al. (2003) report an Electron Spin upper 260 m of the hole (Fig. 10). LWD tools collect Resonance age of 36.9±3.3 ka BP for foraminifera geophysical measurements of the sediment using from 0.45 mbsf. The paleomagnetic record is marked by sensors in drill collars behind the bit (Ocean Drilling a reversal at 32 mbsf interpreted to be the Brunhes– Program, 2002) and are used where poor hole conditions Matuyama boundary (780 ka BP). Reverse polarity then prevent conventional logging. The LWD tools used in continues to the base of the hole. Nannoplankton of site 1167 gave shallow and deep resistivity and spectral Zone CN14a (200 ka–900 ka) are found at 37.4 mbsf, gamma readings (Fig. 10). These logs were compared to close to the interpreted Brunhes–Matuyama boundary. core lithologies and found to give good indications of We interpret the apparent absence of the Jaramillo sediment type. normal episode as the result of a disconformity or a The chronology of the hole is derived from paleo- break in core recovery. A Strontium isotope date on magnetic measurements on cores, diatoms in the upper- planktonic foraminifera from 218 mbsf gives 1.13 Ma most core, a few occurrences of nannoplankton and +0.25/−0.45 Ma BP and nannoplankton of Zone 398 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

Fig. 7. Post-early Pliocene pre-mid Pleistocene flow pattern for extreme ice advances. The relative increase in ice from the Ingrid Christensen Coast deflected ice flow to the west, forming Prydz Channel and the Prydz Channel Fan. Shallow water depths on Four Ladies Bank suggest that ice grounded on the bank.

CN13b between 218 and 228 mbsf giving an age range of the pre-Cenozoic sedimentary rocks of the Lambert of 900 ka to 2 Ma for the interval. Graben whereas illite, the product of erosion of the surrounding Precambrian basement rocks (Ehrmann 3.4.1. Early Pleistocene et al., 2003). Further evidence for a high proportion of Variations in sediment composition indicate signifi- recycled sedimentary detritus below 217 mbsf comes cant changes in sedimentation during fan accumulation from colour spectral analysis data by Damuth and (Fig. 9). The pebble assemblage changes markedly at Balsam (2004) and palaeomagnetic properties (Ship- 217 mbsf. Below this level, sandstone pebbles domi- board Scientific Party, 2001b). Damuth and Balsam's nate; above, basement lithologies such as granite and (2004) Factor 5 which correlates with finely-divided, metamorphic rocks outnumber sedimentary pebbles coaly organic matter is higher on average below (Fig. 9). Clay mineralogy also parallels this change 217 mbsf than above, suggesting higher amounts of (Fig. 9). The clay size fraction is dominated by illite, coal and dispersed organic matter reworked from Creta- quartz and feldspar above 217 mbsf, however, below ceous or Permian sediments in the Lambert Graben. 217 mbsf, smectites are more abundant, replacing some Magnetic susceptibility is significantly lower below illite, quartz and feldspar (Fig. 9). At 423 mbsf, this 217 mbsf than above, and magnetic properties indicate trend reverses with smectite reduced in the lowest part of finer-grained magnetic minerals below 217 mbsf (Ship- the hole. Smectites are likely to be the product of erosion board Scientific Party, 2001b). P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 399

Fig. 8. Isopach of post pp-12 sediments showing the Prydz Channel Fan, the thin to absent section in Prydz Channel and topsets on Four Ladies Bank.

3.4.2. Mid to Late Pleistocene as low as 0.041 mka−1 for the section above the Brunhes– The combination of resistivity and natural gamma logs Matuyama Boundary and the minimum sedimentation clearly shows 16 fine-grained interbeds within the 260 m rate obtained below the boundary is 0.31 mka−1,anorder logged (Fig. 10). Clay-rich interbeds appear as low of magnitude difference. resistivity spikes, associated with small gamma peaks. To verify that reduced late Pleistocene sedimentation Two resistivity peaks, at 40 mbsf and 60 mbsf correspond affected the entire fan, sediment volumes were calculated to gamma lows, and are therefore sand beds. The fine using intermediate resolution seismic data (O'Brien intervals represent interruptions to debris flow deposition, et al., 2004) and the average velocity of sediments drilled caused by retreat of the ice from the shelf edge. The in site 1167 (O'Brien et al., 2001). It was not possible to thickest interval of low resistivity is Unit I. It has a lower map a surface that corresponds exactly to the Brunhes– gamma response than other fine intervals, probably Matuyama Boundary but a surface (Surface pp-2) that because of a higher proportion of non-radioactive intersects Site 1167 at about 60 mbsf could be traced over biogenic material such as diatoms. The other fine intervals a large part of the fan (O'Brien et al., 2004). Post pp-2 are likely to be composed of hemipelagic muds. The thick sediments represent a volume of 1867 km3, about 11% of intervals of high resistivity are mostly debris flow units the total fan volume over the same area of 16,209 km3. (Fig. 10). Most debris flow deposition occurred prior to Given that surface pp-2 is older than the Brunhes– the Brunhes–Matuyama Boundary. There are only 3 Matuyama Boundary, this would indicate less than 10% debris flow intervals above this boundary and they are of the fan volume was deposited post-780 ka which much thinner than the units below (Fig. 10, O'Brien et al., represents 20% of the time interval over which the fan 2004). O'Brien et al. (2004) suggest sedimentation rates accumulated. This apparent reduction in sedimentation 400 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

Fig. 9. ODP Site 1167 lithological log with compositional information. Magnetic susceptibility increases above 217 mbsf in response to a greater contribution from basement rocks to the detritus. Sandstone pebbles are more common below 217 mbsf. Smectite increases in abundance at the expense of illite, quartz and feldspar below 217 mbsf apart from the lowermost 14 m, reflecting a sedimentary source. Spectral analysis that detects coaly material shows higher amounts of organic material below 217 mbsf. P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 401 rate and the lesser number of debris flows shallower than opment of a grounded ice dome during low sea level 32 mbsf implies a reduction in the frequency of debris periods. The present bathymetry over the Four Ladies flow episodes after the mid Pleistocene, around 780 ka bank is less than 200 m deep. During low sea level BP (Brunhes–Matuyama Boundary). This in turn stands, the ice from Princess Elizabeth Land coast north suggests that the Lambert Glacier advanced to the shelf of about 67°S would have grounded further seaward edge only a few times after 780 ka BP. The uncertainties towards the Four Ladies Bank, and the bank provided in the age dating make it difficult to nominate when the pinning points so that the area developed into an ice last advance took place. Theissen et al. (2003) used the shelf similar to or possibly combining with a grounded δ18O profile to suggest the last debris flows took place West Ice Shelf. Hence, when the main Lambert Glacier during Marine Isotope Stage 16 (∼614–698 ka, Lisiecki drainage extended onto the mid to outer shelf, its flow and Raymo, 2005). would have been deflected towards the north-west by The reduction in extreme ice advances in Prydz Bay the grounded ice (Fig. 14b). During low sea level interpreted from ODP Site 1167 extends the observations periods, the grounded ice would have further increased of maximum ice extents during the last glacial cycle by the climatic continentality of the Lambert basin interior, Domack et al. (1998) and O'Brien et al. (1999). In Prydz and further reduced ice accumulation rates feeding the Bay, the youngest grounding zone wedges around Prydz Amery system. Channel are more than 130 km from the continental shelf edge (Fig. 11, Domack et al., 1998; O'Brien et al., 1999). 4.2. Early Pleistocene Landward of the grounding zone wedges, subglacial flutes visible on sidescan images (Fig. 12) and core data The reduction in basin-derived detritus at about indicate grounded ice during the last glacial cycle. 1.1 Ma BP in ODP Site 1167 suggests either a change in Seaward of these wedges, flutes are not visible and cores the source of ice flowing into Prydz Bay or a reduction recovered diatom ooze and glacimarine muds indicating in the depth of erosion of the Lambert–Amery system. that the Lambert Glacier did not ground there during the Both reasons probably contributed to the change be- last glacial cycle. Thus, during the Late Pleistocene, ice cause it seems unlikely that all the ice and detritus would expansion was restricted to grounding ice sheet margins be derived from basement areas surrounding Prydz Bay on shallow banks (such as the Four Ladies Bank) on the rather than from the main trunk glacier. The composition eastern side of Prydz Bay towards the West Ice Shelf, and of detritus eroded and transported by the Lambert– on the western flank but not in Prydz Channel (Fig. 11). Amery system depends strongly on the depth of erosion A reconstruction of the extent of grounded ice on Four in the Lambert Graben (Fig. 13). Most sedimentary Ladies Bank is problematic because ice berg scours detritus in the region is likely to be derived from the cover most of the bank, and obscure other structures in Lambert Graben. In the current configuration of the water depths less than 700 m. Amery Ice Shelf and its bed topography, most detritus is derived from basement areas surrounding the Graben, 4. Interpretation both from main trunk glaciers and tributaries feeding from the sides of the graben (Fig. 13a). Increased ice 4.1. Early Pliocene volumes produce grounding of the ice and erosion of graben sediments (Fig. 13b). Maximum ice volumes The north-west orientation of Prydz Channel relative produce maximum depth of erosion and hence the to the underlying structural grain of Prydz Bay suggests largest component of recycled sedimentary basin detri- that the change in drainage in the early Pliocene results tus in the sediment load. Lower maximum ice volume from a change in the balance of ice discharge to Prydz will not erode so deeply so that a blanket of basement- Bay, as the relative ice volume discharged from the derived detritus may protect the basin fill from erosion, Ingrid Christensen Coast increased sufficiently to resulting in a reduced sedimentary signal in downstream deflect the main Lambert Glacier axial drainage. Both glacial deposits. This configuration of source rocks and geological and climatic processes are considered to have the Amery Ice Shelf bed implies that the change in contributed to this change in ice discharge. Erosion of sediment composition at about 1.1 Ma BP represents a the inner shelf is thought to have started in the mid to change to lower ice volumes during glacial maxima. The Late Miocene (La Macchia and De Santis, 2000; Cooper interval of predominantly basement-derived detritus and O'Brien, 2004). The excavation of the inner shelf in the deepest part of ODP Site 1167 (429–443 mbsf, left the Four Ladies Bank as a topographic barrier to ice Fig. 9) indicates that this is an ice volume effect and not flow from the interior and a potential locus for devel- just the passing of a threshold of over-deepening. 402 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

If over-deepening was the predominant process con- detritus that marked the maximum depth of erosion trolling sediment composition, the trend in detrital com- possible in the graben. The presence of an earlier phase position would be a single reduction in sedimentary of basement-dominated sedimentation implies P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 403

Fig. 11. Map of Prydz Bay showing ice configuration at the furthest extent of grounded ice during the last glacial cycle. Grounding zone wedges are shown after Domack et al. (1998). Flute direction from O'Brien et al. (1999). Arrows indicate ice flow directions (modified from O'Brien and Harris, 1996). fluctuations in erosion capacity in the Amery–Lambert rapid sliding and hence subglacial erosion would system. A further mechanism that might influence become progressively concentrated in the deep parts changes in sediment composition and fluctuations in ice of the system while the thinner tributary glaciers behavior is variations in thermal regime in the ice sheet. carrying basement derived detritus would become The trend to more polar conditions resulting in less colder and less active. Therefore the section would active ice has been suggested for some long term trends exhibit a trend to Lambert Graben sedimentary detritus in sedimentation on the Antarctic margin (e.g. Cooper as the climate cooled. This is not the pattern of sediment and O'Brien, 2004). However, recent work on subgla- composition seen in ODP Site 1167. cial lakes in Antarctica indicates that thick, interior parts of the East Antarctic Ice Sheet still have abundant melt 4.3. Mid- to Late Pleistocene water at the bed (Wingham et al., 2006). Thus, if changes to basal temperature and meltwater abundance The interpreted reduction in extreme ice advances in played a significant role in the Amery Ice Shelf system, Prydz Bay from Site 1167, extends the observations of

Fig. 10. Logging-While-Drilling (LWD) geophysical logs of ODP Site1167 with age information. High gamma and low resistivity peaks indicate fine grained interval deposited during periods of reduced ice volume. Fine grained intervals are separated by pebbly, muddy sands and diamicts deposited from the grounding zone at the shelf edge. Electron Spin Resonance age (U-Th) on foraminifera at 0.45 mbsf is 36.9±3.3 ka (Theissen et al., 2003). Magnetostratigraphy shows the 32 mbsf interpreted to be the Brunhes–Matuyama boundary (780 ka.) at 32 mbsf. This age is supported by nannoplankton of Zone CN14a (200 ka–900 ka) are found at 37.4 mbsf. Nannoplankton (Zone Cn13b) and a Strontium isotope age at 218 mbsf give an age of about 1.1 Ma. 404 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

of the inner shelf by a combination of erosion and isostatic loading (Boulton, 1990). With each successive advance, the inner shelf deep excavated by the Lambert Glacier became deeper, requiring greater ice volumes for subsequent advances to reach the shelf edge (ten Brink et al., 1995). The reduction in frequency of advances around the mid Pleistocene may reflect the passing of a threshold of over-deepening, after which only very large increases in ice volume in the Lambert–Amery system caused it to reach the shelf edge. This mechanism may apply only to systems like the Lambert–Amery or Western Ross Sea, which have had a very long erosion Fig. 12. Sidescan image of subglacial flutes formed by subglacial history. The Lambert–Amery system has eroded to at moulding inshore of the grounding zone wedges in Prydz Bay least 2200 m below sea level near its grounding zone identified by Domack et al. (1998). (Fricker et al., 2001). Taylor et al. (2004) conducted a maximum grounded ice extent by Domack et al. (1998) sensitivity analysis of the Lambert Glacier system and and O'Brien et al. (1999). In Prydz Bay, the Late Pleis- concluded that bed elevation was the most important tocene grounding zone wedges around Prydz Channel influence on the ability of the glacier to ground at the are more than 130 km from the continental shelf edge shelf edge. However, in testing the sensitivity of the (Figs. 11, 14, Domack et al., 1998; O'Brien et al., 1999). Seaward of these wedges, sea floor topography and stratigraphy indicate that the Lambert Glacier did not ground there during the last glacial cycle. The limit of grounded ice during the last glacial cycle is though to have been at the shelf edge on Antarctic Peninsula and in the eastern Ross Sea (Pudsey et al., 1994; Shipp et al., 1999; Domack et al., 1999) but in the western Ross Sea, the limit of grounding is back from the shelf edge (Shipp et al., 1999; Domack et al., 1999; Licht et al., 1999). This is similar to Prydz Bay but there has been no dating to indicate when the last extreme advances took place in the Ross Sea beyond assigning a Pleistocene, pre-LGM age (Domack et al., 1999; Bart et al., 2000).

5. Discussion

These observations pose several questions: why should some major East Antarctic ice streams not ground at the shelf edge during the last glacial cycle, and why did extreme advances cease in the Late Pleistocene when global ice volumes were apparently higher than during the Early-mid Pleistocene? There is also the question as to what climatic conditions produced the combination of open water, relatively warm conditions existing in areas Fig. 13. The influence of depth of erosion on sediment composition in now occupied by the Amery Ice Shelf during warm the Amery Ice Shelf–Lambert Glacier system. During interglacial phases, alternating with advances to the continental shelf conditions, the ice floats over the graben sediments so detritus comes edge during Miocene and Pliocene cold phases. We mostly from basement rocks surrounding the graben, giving glacial suggest several possible mechanisms may have forced sediments with high illite, quartz, feldspar and high magnetic mineral the interpreted pattern of glaciation, either in isolation or content, and low recycled organic matter and sedimentary clasts. During periods of high ice volume, the ice erodes graben sediments, in combination. producing glacial sediments with higher proportions of smectite, The first is shelf over-deepening. Advances of an ice recycled organic matter and more sandstone clasts and lower magnetic sheet onto a continental margin produce over-deepening mineral content. P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 405

Fig. 14. Evolution of ice drainage into Prydz Bay during extreme advances during the Neogene. a. Late Miocene ice came mostly from the interior and flowed down the Lambert Graben axis, building straight shelf edges. b. Early Pliocene to mid Pleistocene saw an increase in the importance of ice derived from the Ingrid Christensen Coast that deflected the ice flow westward. c. Mid- to Late Pleistocene saw a reduction in ice advances across the shelf. 406 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 system to accumulation changes, they tested the present shelf was not significantly over-deepened during the mid accumulation regime and that of the Last Glacial Maxi- Pleistocene. Furthermore, in ODP Site 1167, the change mum. Taylor et al. (2004) concluded that a doubling of from basin-derived detritus to hinterland detritus takes current accumulation rates in the Lambert–Amery place at around 1.1 Ma BP, at 217 mbsf, prior to the mid drainage basin would be insufficient to produce advance Pleistocene change in advance frequency. Thus, depths of the grounding zone to the shelf edge. of erosion have been shallower since before the mid Though bed erosion is clearly a major cause of change Pleistocene, with detritus coming from the basement in the Lambert–Amery system (Taylor et al., 2004), the surrounding the Lambert Graben, rather than from basin geological evidence suggests some additional factors in and therefore the rate of over-deepening was reduced the observed mid Pleistocene changes. The failure of ice prior to the mid Pleistocene change in advance frequen- streams to reach the shelf edge in the western Ross Sea cy. This would suggest that a reduction in the amount of during the last glacial cycle (Shipp et al., 1999; Domack ice in the system was involved. et al., 1999) may mean that a mechanism that affected the The changes in glacial sedimentation patterns whole East Antarctic Ice Sheet is a possibility. Over- through the late Neogene and Quaternary suggest a deepening is apparent on maps of the western Ross Sea progressive reduction in snow accumulation in the East (ANTOSTRAT Project, 1995), however bedrock depths Antarctic interior relative to the coast and possibly a seem to reach a maximum of about 1500 m near Terra reduction in overall ice volumes discharged to the Prydz Nova Bay and only a small proportion of Ross Ice Shelf Bay shelf during glacial maxima (Fig. 14). This inter- flow crosses the areas of over-deepening. Seismic sec- pretation of ice volume changes is supported by cosmo- tions in the axis of Prydz Channel reveal topsets pre- genic dating of outcrops in the Northern Prince Charles served beneath the outer part of the shelf that is mostly Mountains by Fink et al. (2006) who found that higher Pleistocene deposits (Fig. 4). This suggests that the outer peaks in the region have been ice free for at least 1,

Fig. 15. Extreme ice advances in during 41 ka cycles. The Lambert–Amery system is so large, ice accumulated in the deep interior during warm phases arrived at the grounding zone close to the lowest sea level part of the cycle, amplifying the ability of the system to advance. P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 407 possible 2 Ma. These ice volume trends are most likely a over Antarctica would have resulted in the penetration function of the evolution of the East Antarctic ice sheet of cyclones further into the ice sheet interior and gener- morphology, and its relationship to the circumpolar ally ice accumulation would have been greater. Regional vortex of transient low pressure systems embedded in sea ice extent and concentration also has an important the westerly atmospheric circulation. At present, these control on the cyclone tracks and the ensuing ice accu- moist air masses cannot penetrate far inland because the mulation pattern. Bromwich et al. (1998) found that for steep edge of the ice sheet forms a topographic barrier a global climate model with sea ice and ice shelves (Bromwich, 1988). Hence the orographic precipitation removed, the circum-Antarctic lows were 3–5° further is limited to the coastal slopes below 2000 to 2500 m south than present. This would see them tracking elevation. This causes a distinct gradient in ice accumu- slightly north of the northern Prince Charles Mountains, lation rates, from high at the coast to extremely low increasing ice accumulation rates in the interior of the in the interior of the ice sheet (Bromwich, 1988; Lambert Glacier basin. Richardson-Näslund, 2004). This process is reflected in A further contribution to the continued redistribution the pattern of annual accumulation for the Antarctic of snow accumulation may have been cooling in the mid (Giovinetto and Bentley, 1985; Smith et al., 1998). Pleistocene (Broecker and Denton, 1990; Tziperman and Models of ice sheet fluctuations during the Cenozoic Gildor, 2003) combined with changes to meridional (Huybrechts, 1993; Pollard and DeConto, 2003; De energy flux gradients (Raymo and Nisancioglu, 2003). An Conto and Pollard, 2003) show ice margins significantly Early Pleistocene glacial temperature regime warmer than different to those of today during warmer episodes, the Late Pleistocene combined with penetration of snow- which implies considerable variation in the penetration bearing systems into the interior driven by steeper mois- of maritime air masses over the coastal regions of the ture flux gradients could have produced sufficient precipi- Antarctic ice sheet. Expansion and steepening of the tation in the interior to drive the interior ice to the shelf East Antarctic Ice Sheet margin through time would edge during glacial episodes. Mechanisms suggested move the areas of orographic precipitation seaward for the mid Pleistocene Transition involve deep ocean while reducing the amount of snow fall in the interior. In cooling and increased sea ice (Tziperman and Gildor, the Prydz Bay region, the northward movement of the 2003). Increased sea ice extent could have reduced the ice margin through Princess Elizabeth Land would distance inland cyclonic systems penetrated, reducing the account for the increase in importance of the Ingrid volume of ice flowing down the main Amery–Lambert Christensen Coast as a source for ice flowing into Prydz drainage system and curtailed advances to the shelf edge. Bay (Fig. 14). The circumpolar vortex of cyclones Alternatively, Raymo and Nisancioglu (2003) suggest oscillates between the mid-latitudes and the Antarctic that, in the obliquity-dominated (41 ka cycles) climatic coast on timescales of weeks to millennia (Kidson, regime, insolation gradients and hence moisture fluxes 1988). This is known as the Southern Annular Mode were steeper than after the mid Pleistocene transition to (SAM) of climate variability. In what is known as the the eccentricity-dominated (100 ka cycles) regime. Such high phase of the SAM, the westerlies are more intense steeper gradients might have favoured moisture transport and cyclones track over the Antarctic coastal slopes. In into the East Antarctic interior, since they are associated the low phase of the SAM, the Polar high intensifies and with the high phase of the SAM. Steeper climatic gradi- the westerlies weaken and the circumpolar vortex moves ents in East Antarctica may explain the combination of towards the mid-latitudes, causing a reduction in cy- evidence through the Neogene for extreme ice advances clones penetrating the East Antarctic coastal slopes in Prydz Bay and evidence for conditions warmer than (Goodwin et al., 2004). Generally, higher snow accu- present in and around Prydz Bay and the Prince Charles mulation rates are observed during the high phase of the Mountains (Quilty, 1993; Hambrey and McKelvey, 2000; SAM (Goodwin et al., 2003). During periods of de- McKelvey et al., 2001; Whitehead J.M., 2001; Whitehead creased solar irradiance, such as during the glacial and Boharty, 2003). A further process that may have periods, the polar annular oscillations tend towards the enhanced the ability of the Lambert–Amery system to low phase with higher atmospheric pressure over the reach the shelf edge prior to the mid Pleistocene is the Poles (Shindell et al., 2001). The expansion of the Polar length of climate and sea level cycles. Before the mid high and displacement and weakening of the westerlies Pleistocene, 41 ka cycles dominated climatic and sea level northwards from the Antarctic coast, would result in fluctuations (Berger and Jansen, 1994; Raymo and lower ice accumulation. Conversely, during periods of Nisancioglu, 2003). The ice dynamical response time of higher solar irradiance, such as during the Pliocene the Lambert–Amery Ice drainage basin is ∼11 ka for (Berger and Loutre, 1991) lower atmospheric pressure regions where the ice thickness is 1000 to 1200 m, and 408 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

19 ka where the average ice thickness is 2500 m Ice Sheet moved the zone of orographic snowfall (Goodwin, 1995). These estimates are about half the seaward, reducing precipitation in the interior of East length of climatic and sea level cycles prior to the mid Antarctica. Strengthening and expansion of the Polar Pleistocene Transition (Berger and Jansen, 1994). The high pressure cell that displaced low pressure systems 41 ka cycles were characterised by symmetrical glacial seaward may have contributed in reducing the penetra- and deglacial periods, rather than the asymmetrical tion of precipitation-bearing low pressure systems into periods in the ensuing 100 ka cycles (Tziperman and the Antarctic interior. Continued reduction in precipita- Gildor, 2003). Thus, the extra snow delivered to the tion related to cooling and the change from 41 ka interior of the Amery drainage basin would be reaching climatic cycles to 100 ka cycles in the mid Pleistocene the grounding zone near the lowest part of the sea level curtailed advances to the shelf edge by the Lambert– cycle (Fig. 15). This correspondence of the pulse of extra Amery System in the mid to late Pleistocene. This ice with low sea level would enhance the advance of the combination of processes helps to explain the record of grounding zone. Once the 100 ka cycles in global climate both extreme ice advances and warm episodes during and sea level became established, the extra interior snow the Miocene to early Pleistocene in Prydz Bay. delivered in the interglacials would reach the grounding zone well before the sea level minimum of the cycle, Acknowledgments reducing the potential for advance. Thus, during the late Miocene, Pliocene and early Pleistocene, under the We thank all those who supported ODP Leg 188, obliquity-controlled cycles, Prydz Bay featured both ice especially the captain, crew and technical staff of the advances and warm episodes more extreme than during JOIDES Resolution. German Leitchenkov, Takemai the longer Late Pleistocene cycles. Ishihara and Manabu Tanahashi contributed data and advice on drill sites. Reviews by Alix Post, Mark Hemer, 6. Conclusions Damian Gore and an anonymous reviewer assisted in improving the paper. Philip O'Brien publishes with the The Lambert Glacier–Amery Ice Shelf system expe- permission of the Chief Executive Officer, Geoscience rienced several reorganisations of ice flow and sedi- Australia. mentation during the Neogene. In the late Miocene, ice advanced evenly across Prydz Bay. Then, in the Early References Pliocene (3.6–3.9 Ma.), an increase in the importance of ice discharged from coastal Princess Elizabeth Land Allison, I., 1979. The mass budget of the Lambert Glacier drainage relative to the interior drainage basin produced extra basin, Antarctica. J. Glaciol. 22, 223–235. outflow from the southeast of Prydz Bay. Combined ANTOSTRAT Project, 1995. Seismic stratigraphic atlas of the Ross with erosion of the inner shelf, this flow deflected the Sea, Antarctica. In: Cooper, A.K., Barker, P.F., Brancolini, G. main axial drainage towards the west, forming an ice (Eds.), Geology and Seismic Stratigraphy of the Antarctic Margin. AGU Antarctic Res. Series, vol. 68, pp. A271–A286. stream that cut Prydz Channel and deposited a trough Arne, D.C., 1994. Phanerozoic exhumation history of northern Prince mouth fan. From around 1.1 Ma BP, the Lambert– Charles Mountains (East Antarctica). Antarct. Sci. 6, 69–84. Amery system continued to reach the shelf edge and Barker, P.F., Barrett, P.J., Camerlenghi, A., Cooper, A.K., Davey, F.J., deposit the trough mouth fan but scarcity of sedimentary Domack, E.W., Escutia, C., Kristoffersen, Y., O'Brien, P.E., 1998. detritus in the fan indicates that the glacier was much Ice sheet history from Antarctic continental margin sediments: the ANTOSTRAT approach. Terra Antartica 5, 737–760. less effective at eroding the sedimentary rocks of the Barron, J., Larsen, B., Baldauf, J.G., 1991. Evidence for Late Eocene Lambert Graben. This suggests that subsequent ice to Early Oligocene Antarctic glaciation and observations on Late volumes were lower and the glaciers unable to erode as Neogene glacial history of Antarctica: results from Leg 119. In: deeply. Most of the Prydz Channel trough mouth fan Barron, J.A., Larsen, B., et al. (Eds.), Proc. OP Sci. Res., vol. 119, – was deposited prior to 780 ka BP. As few as 3 advances pp. 869 889. Bart, P.J., Anderson, J.B., Trincardi, F., Shipp, S.S., 2000. Seismic data to the shelf edge may have taken place since that time. from the Northern Basin Ross Sea record multiple expansions of Thus, the extreme ice advances in Prydz Channel ceased the East Antarctic Ice Sheet during the late Neogene. Mar. Geol. in the Mid to Late Pleistocene. These progressive 166, 31–50. changes in ice behavior can be explained by progressive Berger, W.H., Jansen, E., 1994. Mid-Pleisocene climate shift-the Nansen deepening of the inner shelf by glacial erosion, making connection. In: Johannessen, O.M., Muerch, R.D., Overland, J.E. (Eds.), The Polar Oceans and their Role in Shaping the Global it harder for major ice streams to reach the shelf edge, Environment. AGU Geophys. Mon., vol. 84, pp. 295–311. coupled with seaward migration of the zone of Berger, A., Loutre, M.F., 1991. Insolation values for the climate of the maximum accumulation. Growth of the East Antarctic last 10 million years. Quat. Sci. Rev. 10, 297–317. P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410 409

Boulton, G.S., 1990. Sedimentary and sea level changes during glacial Fricker, H.A., Allison, I., Craven, M., Hyland, G., Ruddell, A., Young, cycles and their control on glacimarine facies architecture. In: N.,Coleman,R.,King,M.,Krebs,K.,Popov,S.,2002. Dowdeswell, J.A., Scourse, J.D. (Eds.), Glacimarine Environ- Redefinition of the Amery Ice Shelf, East Antarctica, grounding ments: Processes and Sediments. Geol. Soc. Spec. Pub., vol. 53, zone. J. Geophys. Res. 107, doi:10.1029/2001JB000383. pp. 15–52. Giovinetto, M.B., Bentley, C.R., 1985. Surface drainage systems of Broecker, W.S., Denton, G.H., 1990. The role of ocean-atmosphere Antarctica. Antarc. J. U. S. 20 (4), 6–13. reorganization in glacial cycles. Quat. Sci. Rev. 9, 305–341. Goodwin, I.D. 1995. On the Antarctic contribution to Holocene sea- Bromwich, D.H., 1988. Snowfall in high southern latitudes. Rev. level. PhD thesis, Institute for Antarctic and Southern Ocean Geophys. 26, 149–168. Studies (IASOS), University of Tasmania, Tasmania, Australia. Bromwich, D.H., Chen, Bioa, Hines, K.M., Cullather, R.I., 1998. Goodwin, I., de Angelis, M., Pook, M., Young, N.W., 2003. Snow Global atmospheric responses to Antarctic forcing. Ann. Glaciol. accumulation variability in Wilkes Land, East Antarctica and the 27, 521–527. relationship to atmospheric ridging in the 130° to 170° E region Cooper, A.K., O'Brien, P.E., 2004. Leg 188 synthesis: transitions in since 1930. J. Geophys. Res. 108 (D21), 4673, doi:10.1029/ the glacial history of the Prydz Bay region, East Antarctica, from 2002JD002995. ODP drilling. In: Cooper, A.K., O'Brien, P.E., Richter, C. (Eds.), Goodwin, I.D., van Ommen, T.D., Curran, M.A.J., Mayewski, P.A., Proc. ODP, Sci. Results, 188, 1–42 [CD-ROM]. Available from: 2004. Mid latitude winter climate variability in the south Indian Ocean Drilling Program, Texas A and M University, College and south-west Pacific regions since 1300 AD. Clim. Dyn. 22, Station TX 77845-9547, USA. 783–794, doi:10.1007/S00382-004-0403-3. Cooper, A., Stagg, H., Geist, E., 1991. Seismic stratigraphy and Hambrey, M.J., Ehrmann, W.U., Larsen, B., 1991. Cenozoic glacial structure of Prydz Bay, Antarctica: implications from Leg 119 record of the Prydz Bay continental shelf, East Antarctica. In: drilling. In: Barron, J., Larsen, B., et al. (Eds.), Proc. ODP Sci. Barron, J., Larson, B., et al. (Eds.), Proc. ODP Sci. Results, vol. 119. Res., vol. 119, pp. 5–26. College Station, TX (Ocean Drilling Program), pp. 77–132. Damuth, J.E., Balsam, W.L., 2004. Data report: Spectral data from Hambrey, M.J., McKelvey, B., 2000. Neogene sedimentation of the Sites 1165 and 1167 including the HiRISC section from Hole western margin of the Lambert Glacier. Sedimentology 47, 1165B. In: Cooper, A.K., O'Brien, P.E., and Richter, C. (Eds.), 577–607. Proc. ODP, Sci. Results, 188, 1–49 [CD-ROM]. Available from: Huybrechts, P., 1993. Glaciological modelling of the late Cenozoic Ocean Drilling Program, Texas A and M University, College East Antarctic Ice Sheet: stability or dynamism? Geogr. Ann. 75A, Station TX 77845-9547, USA. 221–238. De Conto, R.M., Pollard, D., 2003. A coupled climate-ice modelling Kidson, J.W., 1988. Interannual variations in Southern Hemisphere approach to the Early Cenozoic history of the Antarctic Ice Sheet. circulation. J. Climate 1, 1177–1198. Palaeogeogr. Palaeoclimatol. Palaeoecol. 198, 30–52. Kuvaas, B., Leitchenkov, G., 1992. Glaciomarine turbidite and current Domack, E., O'Brien, P.E., Harris, P.T., Taylor, F., Quilty, P.G., controlled deposits in Prydz Bay, Antarctica. Mar. Geol. 108, DeSantis, L., Raker, B., 1998. Late Quaternary sedimentary facies 365–381. in Prydz Bay, East Antarctica and their relationship to glacial La Macchia, C., De Santis, L., 2000. Seismostratigraphic sequence advance onto the continental shelf. Antarct. Sci. 10, 227–235. analysis in the Prydz Bay area, (East Antarctica). In: Brambati, A. Domack, E.W., Jacobson, E.A., Shipp, S., Anderson, J.A., 1999. Late (Ed.), Proceedings of the Meeting on Palaeoclimatic Reconstruc- Pleistocene–Holocene retreat of the West Antarctic Ice-Sheet tions from Antarctic Marine Sediments 2000. Terra Antartica Rep., system on the Ross Sea: Part 2-Sedimentological and stratigraphic vol. 4, p. 267. signature. Geol. Soc. Amer. Bull. 111, 1517–1536. Leitchenkov, G., Stagg, H.M.J., Gandjukhin, V., Cooper, A.K., Ehrmann, W., Bloemendal, J., Hambrey, M.J., McKelvey, B.C., Tanahashi, M., O'Brien, P., 1994. Cenozoic seismic stratigraphy Whitehead, J.M., 2003. Variations in the compositions of the clay of Prydz Bay (Antarctica). In: Cooper, A.K., Barker, P.F., Webb, fraction of the Cenozoic Pagodroma Group, East Antarctica: P.-N., Brancolini, G. (Eds.), The Antarctic Continental Margin: implications for determining provenance. Sediment. Geol. 161, Geophysical and Geological Stratigraphic Records of Cenozoic 131–152. Glaciation, Paleoenvironments and Sea-level Change. Terra Fink, D., McKelvey, B., Hambrey, M.J., Fabel, D., Brown, R., 2006. Antartica, vol. 1(2), pp. 395–398. Pleistocene deglaciation chronology of the Amery Oasis and Licht, K.J., Dunbar, N.W., Andrews, J.T., Jennings, A.E., 1999. Radok Lake, Norhtern Prince Charles Mountains, Antarctica. Distinguishing subglacial till and glacial marine diamictons in the Earth Planet. Sci. Lett. 243, 229–243. western Ross Sea, Antarctica: implications for a Last Glacial Forsberg, C.F., Solheim, A., Gruetzner, J., Taylor, B., Strand, K., 2001. Maximum grounding line. Geol. Soc. Amer. Bull. 111, 91–103. Glacial development in the Prydz Bay region as witnessed by Lisiecki, L.E., Raymo, M.E., 2005. A Pliocene–Pleistocene stack of geotechnical and mineralogical properties of Leg 188 Sites 1166 and 57 globally distributed benthic δ18O records. Palaeoceanography 1167. In: Florindo, F., Cooper, A.K. (Eds.), Extended Abstracts for 20, A1003, doi:10.1029/2004PA001071. the International ANTOSTRAT Symposium on the Geological Liu, H., Jezek, K., Li, B., Zhao, Z., 2001. Radarsat Antarctic Mapping Record of the Antarctic Ice Sheet from Drilling, Coring and Seismic Project digital elevation model version 2. Boulder, CO: National Studies. Quaderni di Geofisica, vol. 16, pp. 71–72. Snow and Ice Data Center. Digital Media. Fricker, H.A., Warner, R.C., Allison, I., 2000. Mass balance of the Macphail, M.K., Truswell, E.M., 2004. Palynology of Site 1166. In: Lambert Glacier–Amery Ice Shelf system, East Antarctica: a Cooper, A.K., O'Brien, P.E., Richter, C. (Eds.), Proc. ODP Sci. comparison of computed balance fluxes and measured fluxes. Results, 188. 1–43 [CD-ROM]. Available from: Ocean Drilling J. Glaciol. 46, 561–570. Program, Texas A and M University, College Station TX Fricker, H.A., Popov, S., Allison, I., Young, N., 2001. Distribution of 77845-9547, USA. marine ice beneath the Amery Ice Shelf. Geophys. Res. Lett. 28, McKelvey, B.C., Hambrey, M.J., Harwood, D.M., Mabin, M.C.G., 2241–2244. Webb, P.-N., Whitehead, J.M., 2001. The Pagodroma Group – 410 P.E. O'Brien et al. / Palaeogeography, Palaeoclimatology, Palaeoecology 245 (2007) 390–410

a Cenozoic record of the East Antarctic ice sheet in the northern Shipboard Scientific Party, 2001b. Site 1167. In: O'Brien, P.E., Prince Charles Mountains. Antarct. Sci. 13, 455–468. Cooper, A.K., Richter, C., et al., Proc. ODP., Init. Repts., 188, Mikhalsky, E.V., Sheraton, J.W., Laiba, A.A., Tingey, R.J., Thost, [CD-ROM]. Available from: Ocean Drilling Program, College D.E., Kamenev, E.N., Fedorov, L.V., 2001. Geology of the Prince Station TX, 1-97. Charles Mountains, Antarctica. AGSO–Geosci. Aust. Bull. 247, Shipp, S., Anderson, J.A., Domack, E.W., 1999. Late Pleistocene– 209. Holocene retreat of the West Antarctic Ice-Sheet system on the Mizukoshi, T., Sunouchi, H., Saki, T., Tanahshi, M., 1986. Preliminary Ross Sea: part 1–geophysical results. Geol. Soc. Amer. Bull. 111, report of the geological and geophysical surveys of Amery Ice 1486–1516. Shelf, East Antarctica. Mem. Nat. Inst. Polar Res. Jpn. 43, 48–62 Smith, I.N., Budd, W.F., Reid, P., 1998. Model estimates of Antarctic (Special Issue). accumulation rates and their relationship to temperature change. O'Brien, P.E., Harris, P.T., 1996. Patterns of glacial erosion and Ann. Glaciol. 27, 246–250. deposition in Prydz Bay and the past behaviour of the Lambert Solheim, A., Forsberg, C.F. Pittenger, A., 1991. Stepwise consolida- Glacier. Pap. Proc. R. Soc. Tasman. 130, 79–86. tion of glacigenic sediments related to the glacial history of Prydz O'Brien, P.E., De Santis, L., Harris, P.T., Domack, E., Quilty, P.G., Bay. In: Barron, J., Larson, B., et al., 1991. Proc.ODP Sci. Res., 1999. Ice shelf grounding zone features of western Prydz Bay, 119, 169–184, Ocean Drilling Program, Texas A and M University, Antarctica: sedimentary processes from seismic and sidescan College Station TX 77845-9547, USA. images. Antarct. Sci. 11, 78–91. Strand, K., Passchier, S., Näsi, J., 2003. Implications of quartz grain O'Brien, P.E., Cooper, A.K., Richter, C., et al., 2001. Initial Report, microtextures for onset of Eocene/Oligocene glaciation in Prydz Prydz Bay-Cooperation Sea, Antarctica: glacial history and Bay, ODP Site 1166, Antarctica. Palaeogeogr. Palaeoclimatol. paleoceanography: Proc. ODP Init. Repts. 188 (CD-ROM), Palaeoecol. 198, 101–112. Texas A and M University, College Station Texas. Taylor, J., Siegert, M.J., Payne, A.J., Hambrey, M.J., O'Brien, P.E., O'Brien, P.E., Cooper, A.K., Florindo, F., Handwereger, D.A., Lavelle, Cooper, A.K., Leitchenkov, G., 2004. Topographic controls on M., Passchier, S., Pospichal, J.J., Quilty, P.G., Richter, C., post-Oligocene changes in ice-sheet dynamics, Prydz Bay region, Theissen, K.M., Whitehead, J.M., 2004. Prydz Channel Fan and East Antarctica. Geology 32, 197–200. the history of extreme ice advances in Prydz Bay. In: Cooper, A.K., ten Brink, U.S., Schneider, C., Johnson, A.H., 1995. Morphology and O'Brien, P.E., Richter, C. (Eds.), Proc. ODP, Sci. Results 188, 1–32 stratal geometry of the Antarctic continental shelf: insights from [CDROM]. Available from: Ocean Drilling Program, Texas A and models. In: Cooper, A.K., Barker, P.F., Brancolini, G. (Eds.), M University, College Station TX 77845-9547, USA. Geology and Seismic Stratigraphy of the Antarctic Margin. AGU Ocean Drilling Program, 2002. Guide to Logging http://www.ldeo. Antarctic Research Series, vol. 68, pp. 1–24. columbia.edu/BRG/ODP/LOGGING/TOOLS/tools.html. Theissen, K.M., Dunbar, R.B., Cooper, A.K., Mucciarone, D.A., 2003. Passchier, S., O'Brien, P.E., Damuth, J.E., Janusczak, N., Handwerger, The Pleistocene evolution of the East Antarctic Ice Sheet in the D.A., Whitehead, J.M., 2003. Pliocene–Pleistocene glaciomarine Prydz Bay region. Glob. Planet. Change 39, 227–256. sedimentation in eastern Prydz Bay and development of the Prydz Tingey, R.J., 1991. Mesozoic tholeitic igneous rocks in Antarctica: The trough-mouth fan, ODP Sites 1166 and 1167, East Antarctica. Ferrar (Super) Group and related rocks. In: Tingey, R.J. (Ed.), The Mar. Geol. 199, 205–279. Geology of Antarctica. Clarendon Press, Oxford, pp. 153–174. Pollard, D., DeConto, R.M., 2003. Antarctic ice and sediment flux in Truswell, E.M., 1991. Data report: Palynology of sediments from Leg the Oligocene simulated by a climate-ice-sheet-sediment model. 119 drill sites in Prydz Bay, Antarctica. In: Barron, J., Larson, B., Palaeogeogr. Palaeoclimatol. Palaeoecol. 198, 53–68. et al., Proc. ODP Sci. Res., 119, 941–948. Ocean Drilling Program, Pudsey, C.J., Barker, P.F., Larter, R.D., 1994. Ice sheet retreat from the Texas A and M University, College Station TX 77845-9547, USA. Antarctic Peninsula shelf. Cont. Shelf Res. 14, 1647–1675. Tziperman, E., Gildor, H., 2003. On the mid-Pleistocene transition to Quilty, P.G., 1993. Coastal East Antarctic Neogene sections and their 100-kyr glacial cycles and the asymmetry between glaciation contribution to the ice sheet evolution debate. In: Kennett, J.P., and deglaciation times. Paleoceanography 18, doi:10.1029/ Warnke,D.A.(Eds.),TheAntarctic Paleoenvironment: A 2001PA000627. Perspective in Global Change. AGU Antarctic Research Series, Vorren, T.O., Laberg, J.S., 1997. Trough mouth fans-palaeoclimate vol. 60, pp. 251–264. and ice sheet monitors. Quat. Sci. Rev. 16, 865–881. Raymo, M.E., Nisancioglu, K., 2003. The 41 kyr world: Milanko- Whitehead, J.M., Boharty, S.M., 2003. Pliocene summer sea surface vitch's other unsolved mystery. Paleoceanography 18, doi:10.1029/ temperature reconstruction using silicoflagellates from Southern 2002PA00079. Ocean ODP Site 1165. Paleoceanography 18, 1075, doi:10.1029/ Richardson-Näslund, C., 2004. Spatial characteristics of snow 2002PA000829. accumulation in Dronning-Maud Land, Antarctica. Glob. Planet. Whitehead, J.M., McKelvey, B.C., 2001. The stratigraphy of the Change 42, 31–44. Pliocene–lower Pleistocene Bardin Bluffs Formation, Amery Shindell, D.T., Schmidt, G.A., Mann, M.E., Rind, D., Waple, A., 2001. Oasis, northern Prince Charles Mountains, Antarctica. Antarct. Solar forcing of regional climate change during the Maunder Sci. 13, 79–86. Minimum. Science 294, 2149–2152. Wingham, D.J., Seigert, M.J., Shepherd, A.P., Muir, A.S., 2006. Rapid Shipboard Scientific Party, 2001a. Site 1166. In: O' Brien, P.E.,Cooper, discharge connects Antarctic subglacial lakes. Scientific Commit- A.K., Richter, C., et al., Proc. ODP., Init. Repts., 188, [CD-ROM]. tee on Antarctic Research Second Open Science Conference. Ocean Drilling Program, College Station TX, 1-110. Abstract 310.