Submarine Landforms in the Fjords of Southern Chile: Implications for Glacimarine Processes and Sedimentation in a Mild Glacier-Inﬂuenced Environment

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Quaternary Science Reviews 64 (2013) 1e19

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Invited review Submarine landforms in the fjords of southern Chile: implications for glacimarine processes and sedimentation in a mild glacier-inﬂuenced environment

J.A. Dowdeswell a,*, M. Vásquez b a Scott Polar Research Institute, University of Cambridge, Cambridge CB2 1ER, UK b Hydrographic and Oceanographic Service of the Chilean Navy (SHOA), Errázuriz 254 Playa Ancha, P.O. Box 324, Valparaiso 236-0167, Chile article info abstract

Article history: Chilean fjords are the lowest latitude at which glaciers reach the sea today. High accumulation and mass Received 2 October 2012 throughput sustain tidewater glacier margins in this relatively mild climatic and oceanographic setting. Received in revised form 27,000 km2 of swath bathymetry allow mapping of sea-floor landforms and inferences on glacimarine 6 December 2012 sediments and sedimentation. Tidewater glaciers are present in several fjords. Beyond retreating Tem- Accepted 10 December 2012 pano glacier, a terminal moraine marks the limit of probable Little Ice Age advance with smaller Available online 19 January 2013 transverse ridges closer to the glacier. Beyond advancing Pio XI Glacier there are few signs of organised submarine landforms. Older moraine ridges along several fjords formed at still-stands during deglaci- Keywords: Fjords ation. Elsewhere, meltwater-fed braided rivers connect the glacial and marine sedimentary systems. fl fl Chile Swath imagery shows glaci uvial and uvial deltas with small channels and chutes that develop into Glacimarine sediments long and sinuous turbidity-current channels. Few iceberg ploughmarks and submarine slope failures Glacimarine sedimentation were observed, but several fields of pockmarks were present. The fjords of Chile are dominated by Submarine landforms sediment delivery from turbid meltwater which distributes fine-grained debris widely, producing sorted Turbidity-current channels and laminated fine-grained ice-proximal wedges and draping ice-distal seismic architecture to give Retreat moraines a predominantly smooth sea floor. Turbidity currents also transfer sediments to some ice-distal envi- Landform-assemblage model ronments. The Chilean fjordlands represent the mildest climatic and oceanographic end-member of a continuum of glacier-influenced marine settings; similar to south-east Alaska in the northern hemisphere. Components of a landform-assemblage model for climatically mild meltwater-dominated fjords include ice-contact moraine ridges, glacifluvial and fluvial deltas, and turbidity-current channels. Full- glacial and deglacial streamlined subglacial landforms are likely to have been buried in many areas by subsequent glacimarine sedimentation. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction iceberg production are both important mechanisms of mass loss, with their relative significance varying widely between individual The fjordlands of Chile, at 42e55S, are one of the lowest glaciers (e.g. Rignot et al., 1996; Warren and Aniya, 1999). The most latitudes in either hemisphere where glaciers either reach the sea northerly tidewater glaciers are Jorge Montt and Tempano glaciers, today or deliver sediments via proglacial rivers. The Chilean glaciers at 48150S and 48430S respectively. In a number of other Chilean are fed by ice draining west from basins of up to 1300 km2 in the fjords, where glaciers no longer extend to the sea, glacifluvial Northern and Southern Patagonian ice caps (total areas 4197 km2 systems deliver meltwater to adjacent fjord heads. The Chilean and 13,000 km2, respectively; Rivera et al., 2007; Lopez et al., 2010). fjordlands were inundated by ice during the Last Glacial Maximum The ice caps are typical of many mountain ice masses, with glaciers (LGM) about 20,000 years ago (Hollin and Schilling, 1981; Hulton having a large altitudinal range (3300e4000 m) with very high et al., 2002); therefore, the sedimentary record in the fjord accumulation (several thousand mm yr 1) and throughput of mass systems includes a Late Quaternary full-glacial and deglacial record (Warren and Aniya, 1999; Lopez et al., 2010). Meltwater runoff and in addition to the imprint of modern glacimarine processes (DaSilva et al., 1997; Araya-Vergara, 1999a,b; Boyd et al., 2008). Few detailed studies of the sedimentary products or the glacial fl * Corresponding author. and marine processes that in uence sedimentation in the fjord- E-mail address: [email protected] (J.A. Dowdeswell). lands of Chile have taken place (e.g. DaSilva et al., 1997; Araya-

Vergara, 1999a,b, 2008, 2011; Boyd et al., 2008; Rodrigo, 2008; sea floor close to the margins of both a retreating and an advancing Fernandez et al., 2012). Given their relatively low-latitude position tidewater glacier. at the equatorward limit of modern glacimarine environments, sedimentation would be expected to be dominated by meltwater- 3.1. Retreating tidewater glacier: Tempano Glacier, Iceberg Fjord related processes (Dowdeswell et al., 1998); a setting similar to that of south-east Alaska in the northern hemisphere (e.g. Powell The innermost 4 km of Iceberg Fjord, and the crevassed margin and Molnia, 1989; Cai et al., 1997). of Tempano Glacier, are shown in Fig. 2. The sedimentary Fjord floor In this paper, we examine an extensive dataset of swath- is marked by several sets of features: a series of transverse ridges of bathymetric imagery covering almost 27,000 km2 of the Chilean varying height distributed across the fjord; a number of sub-parallel fjordlands, from Golfo de Penas at 47350S to Europa Fjord at ridges orientated in the likely direction of past ice flow; and areas of 50170S; a latitudinal range of almost 400 km (Fig. 1). The spatial flat, smooth sea floor. The outermost and largest transverse ridge is coverage of the data allows us to investigate areas ranging from ice- about 100 m high and is clearly asymmetrical, with a steeper ice- proximal settings within a kilometre or two of present tidewater distal face (labelled LIA Mor in Fig. 2). A second large ridge has glacier margins (e.g. Eyre and Iceberg fjords), to locations over a similar long profile and is about 50 m high. The remaining ten or 100 km distal from fjord heads which are little influenced by so transverse ridges are smaller, at about 10 m high (labelled TR in modern glacimarine processes. Ice has, however, retreated through Fig. 2). Closer to the modern ice front, and extending northwards the fjord system since the LGM leaving a record of Late Quaternary into a relatively shallow enclosed basin, is a series of lineations of up subglacial and ice-contact landforms. We discuss, therefore, the to about 0.5 km in length that trend first just north of west and then sea-floor landforms of the fjordlands of Chile in terms of both to the north (labelled L in Fig. 2). Where the lineations are slightly modern processes and those relict features that record elements of more irregular in appearance, this may indicate that they are partly the Late Quaternary deglacial behaviour of the Patagonian Ice Cap. composed of bedrock as well as streamlined sediments. The The range of submarine landforms observed in the fjords of Chile is remainder of the floor of the inner fjord, between the transverse described and interpreted in the context of glacial, oceanographic ridges and lineations, is mainly smooth and flat (Fig. 2). and sub-aqueous mass-wasting processes before the spatial pattern The outermost transverse ridge (LIA Mor in Fig. 2) is interpreted of glacial and glacimarine landforms is described and discussed. as the terminal moraine of an ice advance that filled the inner fjord Finally, the Chilean fjords are set within the continuum of glacier- basin, probably at the time of the Little Ice Age advance that has influenced marine environments that ranges from the lowest lati- been observed widely in southern South American glaciers tudes at which glaciers reach the sea to the very cold glacimarine (Harrison et al., 2007; Masiokos et al., 2009) and in higher-latitude system of East Antarctica (Dowdeswell et al., 1998). regions (e.g. Dowdeswell, 1995). Its asymmetrical long profile and steeper distal face are typical of moraines marking the maximum 2. Data sources and methods recent advance of many northern hemisphere tidewater glaciers (e.g. Ottesen and Dowdeswell, 2009). Similarly, the sets of smaller Swath bathymetry of the sea floor in the fjordlands of southern transverse ridges closer to the glacier front (TR in Fig. 2) are typical Chile was acquired over an area of 26,838 km2 between 2003 and of those deposited during still-stands or minor readvances super- 2008 by the Hydrographic and Oceanographic Service of the Chil- imposed on more general glacier retreat (e.g. Boulton, 1986; ean Navy (SHOA). Two sets of equipment were used for data Ottesen and Dowdeswell, 2006). These smaller ridges are unlikely acquisition. For water depths up to 200 m, an Atlas Fansweep to have been deposited annually, however, given that retreat from system operating at 200 kHz was deployed. For deeper water, the terminal moraine to the present ice margin has probably taken a medium-depth Hydrosweep system (MD2) with a frequency of on the order of 100 years and only about ten ridges are observed 50 kHz was used. In each case, the ship speed for swath data (Fig. 2). acquisition was 8 knots, and tracks were acquired with a nominal The lineations that trend first west and then north in the 100% overlap. No sub-bottom profiler data are available from these innermost part of the fjord (L in Fig. 2) are interpreted as stream- cruises to provide information on shallow acoustic stratigraphy, lined landforms produced beneath actively flowing glacier ice although 3.5 kHz records from other cruises has been acquired from (Clark, 1993; Ottesen and Dowdeswell, 2009). This interpretation some fjords by, for example, Araya-Vergara (1999a,b, 2008). confirms that the tidewater glacier was grounded in the deepest Sea-floor data acquired using these swath-bathymetry systems parts of the inner fjord, where water depths reach about 200 m. It were processed through the removal of anomalous pings and were also suggests that ice flow included a northward component, either normally gridded at a horizontal resolution of 20 m using CARIS due to Little Ice Age advance into the northern enclosed bay as well HIPS and SIPS software, which was also used for image manipula- as westward to the terminal moraines described above, or when tion and display. The swath-bathymetric data have a vertical the ice had retreated from the area of transverse ridges to fill only resolution of better than 2 m. the innermost fjord. Finally, the smooth and flat areas of the sea-floor in Fig. 2, best 3. Tidewater glacier sedimentary systems developed between the transverse moraine ridges, but also present in the deep innermost fjord, are interpreted as sedimentary infill Tidewater glaciers draining westwards from the Southern from the rainout of fine-grained debris transported from the tide- Patagonian Ice Cap are present in several Chilean fjords. Swath- water glacier as a turbid plume of suspended sediment (e.g. bathymetric imagery is available from two areas, Iceberg and Eyre Syvitski, 1989; Powell, 1990). Such turbid plumes are observed on fjords, to within a kilometre or so of the grounded margins of modern satellite imagery of the tidewater glacier margin, and are Tempano and Pio XI glaciers (Figs. 2 and 3). A period of relatively typical of tidewater glaciers in regions where surface melting is widespread glacier advance between the 17th and 19th centuries in a significant component of glacier mass loss (e.g. Pfirman and much of Patagonia has been replaced typically by shrinkage since Solheim, 1989; Dowdeswell et al., 1998). Water penetrates to the that time (Masiokas et al., 2009). Pio XI Glacier is an exception, glacier bed through crevasses, which are illustrated near the however; it has been advancing through most of the 20th century terminus of Tempano Glacier in Fig. 2, and debris entrained in basal and may experience periodic surges (Rivera et al., 1997a,b). Our conduits forms a buoyant plume when the subglacial streams exit swath coverage provides, therefore, imagery of the well-preserved from portals at the base of tidewater ice cliffs (e.g. Powell, 1990; J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 3

Fig. 1. (A) Map of the Chilean fjordlands and the Patagonian ice ﬁelds showing the extent of swath-bathymetric data coverage (colour shaded). Inset is the location of the Chilean fjords within South America. CB is Canal Baker, ARG is Argentina. The locations of subsequent ﬁgures are show in panels B, C and D.

Mugford and Dowdeswell, 2011). The plume then spreads out at the et al., 1980; Ottesen and Dowdeswell, 2009). Beyond the terminal fjord surface under the influence of wind, tide and stream discharge moraine, about 5 km further down Iceberg Fjord, the sea-floor is (e.g. Syvitski, 1989; Dowdeswell and Cromack, 1991; Cowan, 1992). largely smooth, with sediment appearing to drape minor topo- Fine-grained sediments rain-out from the plume to form a smooth graphic features (Fig. 4A). This suggests that fine-grained sus- drape over the fjord floor, deposited at a rate that decreases with pended sediments continue to be deposited more distally, although distance from the plume source at the ice margin (e.g. Elverhøi probably at a slower rate than in the inner fjord. 4 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

Fig. 2. The innermost 4 km of Iceberg Fjord and the tidewater margin of Tempano Glacier (located in Fig. 1B). Swath-bathymetric data show the morphology of the sea ﬂoor and an aerial photograph shows the adjacent glacier and ice-free land. LIA Mor is a large ridge interpreted as having formed at the Little Ice Age maximum, TR are smaller transverse ridges, and L are sedimentary lineations. Cross-sections of the inner fjord and its moraine ridges are shown in proﬁles AeA0 and BeB0.

3.2. Advancing tidewater glacier: Pio XI Glacier, Eyre Fjord observed proximal to the present ice front is likely to be a product of deposition of fine-grained material from turbid meltwater The sea-floor of inner Eyre Fjord, beyond about a kilometre from plumes (e.g. Syvitski, 1989; Powell, 1990). Isolated hummocks and the modern ice front of Pio XI Glacier, shows few signs of an ridges are probably produced by a previous surge of the glacier, organised set of submarine landforms (Fig. 3). The largely flat given that deformed medial moraines on the modern glacier surface is broken by a number of irregular hummocks up to 14 m surface imply episodic surge activity (Meier and Post, 1969; Rivera high. In addition, there are several local areas where short ridges et al., 1997a; Rignot et al., 2003). It should be noted, however, that running both across- and along-fjord intersect in a rudimentary the characteristic assemblage of superimposed submarine land- rhombohedral pattern. These rather chaotic positive-relief features forms, including streamlined lineations, terminal moraines, give way to a smooth sea-floor down fjord (Fig. 3). rhombohedral moraines and small transverse ridges, observed at The observed 5 km advances of Pio XI Glacier during the 20th the margins of many Svalbard surge-type glaciers (Solheim and century (Rivera et al., 1997a,b) may have covered and reworked Pfirman, 1985; Ottesen and Dowdeswell, 2006; Ottesen et al., geomorphic evidence of earlier retreat linked to regional Little Ice 2008), is not observed in Eyre Fjord. In fact, the fjord floor is Age cooling (Masiokos et al., 2009). The overall rather flat sea-floor largely smooth through the inner fjord, with streamlined lineations J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 5

Fig. 3. Swath-bathymetry of the innermost 4 km of Erye Fjord (located in Fig. 1C). The Fjord coastline and tidewater margin of Pio XI Glacier are shown on the aerial photograph. that appear to be part-bedrock and part-sediment protruding sandurs fed by ice cap meltwater connect the glacial and marine through a fine-grained drape at about 15 km from the ice front sedimentary systems. Examples include Occidental Glacier (Fig. 4B). This interpretation is confirmed by the presence of (448 km2), which reaches outer Iceberg Fjord via an 11 km-long draping and ponded sediments in 3.5 kHz records reported by braided channel (Fig. 5), and Bernado Glacier (710 km2) where Araya-Vergara (1999a). In the absence of chronological control, it is a 2 km-long braid plain links it with Bernado Fjord (Fig. 6). In each assumed that the lineations illustrated in Fig. 4B are linked to case, braided channels reach the sea across the top of glacifluvial a significantly earlier, probably full-glacial phase of glacial activity deltas that are about 1.5 km wide in Iceberg Fjord (Fig. 5) and in the Chilean fjords. almost 2 km wide in Bernado Fjord (Fig. 6). DaSilva et al. (1997) reported, based largely on seismic- Swath bathymetry of the delta faces in the two fjords shows reflection data from Canal Baker (48S), that the inner fiords of series of small submarine channels and narrow chutes (Figs. 5 and central Chile contained 200e400 ms-thick acoustically laminated 6), whose modern activity is presumably dependent on shifting ice-proximal sediments that may relate to deglaciation from the spring and summer discharge from varying parts of the subaerial LGM. They also noted that this has been augmented by the braid plain. The dissected slopes of the delta fronts are about a kil- continuing input of fine-grained sediment from turbid meltwater ometre in length, beyond which the sets of submarine channels and where Holocene tidewater glaciers remain at fjord heads. Short chutes appear to organise into a single major submarine channel piston cores sampled interbedded sands and muds at the head of (Figs. 5 and 6). These fjord-floor submarine channels are sinuous Canal Baker beyond the terminus of Jorge Montt Glacier (DaSilva and extend for a number of kilometres along the relatively flat et al., 1997). These acoustic and sedimentary characteristics were floors of Iceberg and Bernado fjords (Figs. 5 and 6). The submarine suggested to be similar to those of tidewater glacier influenced channel in outer Iceberg Fjord is at least 15 km long, up to about Baffin Island fjords in the Northern Hemisphere (Stravers and 50 m-deep, and with an average width of 275 m (maximum 400 m, Syvitski, 1991; Gilbert, 1992). minimum 150 m). The channel in Bernado Fjord extends about 10 km, and has a width and depth of 100 m and about 50 m, 4. Glacifluvial sedimentary systems: deltas and turbidity- respectively. A profile along the thalweg of the submarine channel current channels in Bernado Fjord, with a slope of over 100:1, is shown in Fig. 6. The submarine channel systems in Iceberg and Bernado fjords In a number of locations where glaciers draining west from the are interpreted to be formed by dense underflows or turbidity Southern Patagonian Ice Cap do not reach the sea, braided rivers or currents that are likely to be produced intermittently by one or 6 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

Fig. 4. Swath-bathymetry of the sea floor in two Chilean fjords from positions which are relatively distal to modern tidewater glaciers. (A) Iceberg Fjord, about 10 km from the present margin of Tempano Glacier (located in Fig. 1B). FSf indicates areas of flat sea-floor. Small white arrows with dashed tails indicate examples of artefacts from swath-data acquisition and processing. Note that North is not at the top of this image. (B) Eyre Fjord, about 15 km from the present margin of Pio XI Glacier showing streamlined sea-floor features (located in Fig. 1C).

both of two processes (Syvitski et al., 1987). First, glacifluvial since our bathymetric data end about 13 km from the ice front. It is meltwater flow and the delivery of relatively coarse-grained sedi- not clear, therefore, whether this channel differs from those ment from the braid plain, which will vary both diurnally and observed in Iceberg and Bernado fjords in extending close to seasonally with glacier melt rate, may cause turbidity-currents to a tidewater glacier terminus rather than to a glacifluvial braided form. Secondly, slope failures that translate into turbidity currents river system. Similar turbidity-current channels been have noted may occur on glacifluvial delta fronts, which are areas of high and on recently acquired swath-bathymetry data from several very variable rates of sediment delivery where the deposited Greenland fjords where marine-terminating glaciers are present material is likely to be relatively unstable on the delta front slope. (J.A. Dowdeswell, unpublished data). The time-dependent variability of sediment delivery from glacifluvial braided river systems has been discussed thoroughly by, for 5. Glacial and deglacial landforms example, Church and Gilbert (1975). The dissected nature of meltwater-fed delta fronts has been reported from a number of 5.1. Retreat moraines northern hemisphere fjords in, for example, British Columbia, Baffin Island and Spitsbergen (e.g. Prior et al., 1981; Syvitski et al., In several Chilean fjords, large sedimentary ridges are present 1987). The presence of sinuous turbidity-current channels, similar across fjord axes (Figs. 2 and 7). In the 50 km-long Europa Fjord those imaged in Figs. 5 and 6, is also characteristic of many there is one ridge at the fjord mouth where it enters the 250 m- northern hemisphere fjords that are fed by highly variable deeper Canal Wide. Three other sedimentary ridges are spaced discharge from glacifluvial braided rivers (e.g. Prior et al., 1986; about 8 km apart in the inner half of the fjord; two are illustrated in Syvitski et al., 1987). Fig. 7. Elsewhere, prominent sedimentary ridges of similar dimen- An additional submarine channel is mapped in Penguin Fjord sions are located where relatively shallower tributary fjords enter (50S). Its most distal 4 km is observed on swath imagery, but its the deeper and 40-km long Farquahar-Bernado Fjord system and in extent towards the tidewater glaciers at the fjord head is unknown, Ringdove Fjord (49420S). J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 7

Fig. 5. Glaciﬂuvial braided river system, delta and submarine channel in Iceberg Fjord and Canal Messier (located in Fig. 1B). (A) Swath-bathymetry of the submarine delta front in Iceberg Fjord combined with an aerial photograph of the braided-river and subaerial-delta system fed by meltwater from Occidental Glacier. (B) Swath-bathymetric imagery of a submarine turbidity-current channel system (indicated by white arrows) in outer Iceberg Fjord and Canal Messier. Note that the sun-illumination direction varies between the two swath images to show morphological features most clearly.

These large transverse ridges are characteristically asymmet- this study to quantify their internal structure. Their steeper, outer- rical in long proﬁle, with a steeper down fjord slope. They often fjord slopes are sometimes dissected by small channels or chutes of extend the full width of the fjord and are more than a kilometre in up to a few hundred metres in length and a few metres wide. There along-fjord length (Figs. 2 and 7); no seismic data are available from are also some lobate features on the distal side of these ridges that 8 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

Fig. 6. Glacifluvial braided river system, delta and submarine channel in Bernado Fjord (located in Fig. 1B). (A) Aerial photograph of the 2 km-wide braid-plain connecting Bernado Glacier with the sea, with swath imagery of the submarine delta offshore superimposed. (B) Swath imagery of submarine turbidity-current channel system (dashed white line) in Bernado Fjord. (C) Long-profile of the submarine channel is inset as CeC0. grade into the relatively smooth fjord floor, whereas others appear The interpretation of these large transverse ridges as retreat to override fjord-floor sediments (Fig. 7). The latter may reflect moraines is supported by the location of several of them at the relatively recent slope failure, whereas the former may represent mouths of fjords; points where water deepens by tens to hundreds subsequent partial burial by rain-out of fine-grained debris. Araya- of metres immediately distal of the ridges. In addition, Araya- Vergara (1999a) also suggests that downslope remobilisation Vergara (1999a) shows interpreted 3.5 kHz profiles from Europa processes may be operating on the steeper sides of these ridges, Fjord, where he maps both morainal banks and other ridges where based on 3.5 kHz records. acoustic penetration is limited. The rate of mass loss from tidewater The large transverse ridges, found along and at the mouths of glaciers by iceberg production is known to increase with water several Chilean fjords, are similar in dimensions to the large ice- depth due to increasing buoyancy (e.g. Brown et al., 1982; Pelto and proximal terminal moraine in inner Iceberg Fjord (Fig. 2). These Warren, 1991; Venteris, 1999; Benn et al., 2007); thus, retreat into ridges are interpreted to be moraines that formed at the termini or shallower water would decrease iceberg production and lead to retreating margins of grounded tidewater glaciers that extended a still-stand at such so-called ‘pinning points’. The size of moraine further into the Chilean fjord system during the LGM and subse- ridge would be a function of the rate of sediment supply to the ice quent deglaciation. The ridges therefore mark former ice-front margin and the duration of a still-stand e probably on the order of positions, and formed at either maximum or, more likely, still- decades to centuries for sedimentary ridges that are likely to be stand positions during more general retreat; deglaciation in fjords tens of metres thick (DaSilva et al., 1997). The lobes on the steeper, where these retreat moraines are located was therefore episodic ice-distal sides of the moraines ridges, illustrated in Fig. 7,are rather than catastrophic (Dowdeswell et al., 2008). Glasser et al. interpreted to be the morphological expression of debris flows of (2009) described cross-valley moraines of similar dimensions in relatively rapidly delivered and unstable glacial debris (e.g. Ottesen subaerial locations around the Northern Patagonian Ice Cap. and Dowdeswell, 2006; Ottesen et al., 2008). J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 9

Fig. 7. Swath-bathymetry of asymmetrical submarine ridges on the floor of Europa Fjord (located in Fig. 1D). The ice-proximal side of the ridge is to the right in each case. (A) Cross- fjord ridge at about 24 km from Europa Glacier, with long-profile AeA0 inset. (B) Cross-fjord ridge at about 16 km from Europa Glacier, with long-profile BeB0 inset.

Grounding-zone wedges (GZW) also mark pauses in glacier data from the fjords of Chile. A clear example of a set of streamlined retreat during deglaciation on many high-latitude shelves (e.g. lineations, probably formed of predominantly sedimentary mate- Mosola and Anderson, 2006; Dowdeswell et al., 2008). They form rial with some protruding bedrock, is from Eyre Fjord (Fig. 4B). We where still-stands during retreat allow sediment build-up at the have observed a number of other occurrences of similar sets of glacier grounding-zone by the continuing delivery of deforming features in, for example, Canal Wide (at about 49450S), Paso del basal debris, at time-scales ranging from decades to centuries (e.g. Indio (at about 49080S), and Canal Messier (at about 48500S and Powell and Domack, 1995; Dowdeswell and Fugelli, 2012). GZW, 48200S). Some of these sets of lineations appear as streamlined which can be up to tens of metres thick and several kilometres or bedrock protruding above the flat, sedimentary fjord floors. more in length (Dowdeswell and Fugelli, 2012), are most easily These streamlined features are interpreted as a product of active identified from sub-bottom profiler or seismic records, as their glacier flow, formed subglacially, sometimes in a deformable sedi- surface expression is often relatively subdued (e.g. Ó Cofaigh et al., mentary substrate (e.g. Clark, 1993; Dowdeswell et al., 2004; Ó 2013). We do not identify any GZW in the fjords of Chile, nor are Cofaigh et al., 2005a) or as glacially sculpted bedrock features such features reported from the seismic investigations of DaSilva (Ottesen and Dowdeswell, 2009; Benn and Evans, 2010). Their et al. (1997) or Boyd et al. (2008). It appears that relatively well- orientation is indicative of the direction of past glacier flow; defined moraine ridges, produced at the margins of grounded however, the sense of flow can only be obtained if landforms tidewater glaciers, provide the main record of still-stands during attenuated in the flow direction are present (e.g. drumlins, crag- deglaciation of the fjords of Chile. Floating ice shelves or glacier and-tails; Benn and Evans, 2010), and such attenuated forms tongues, where vertical accommodation space for sediment build- were not observed in Chilean fjords. Similar subglacially produced up is limited beyond the grounding-zone (Dowdeswell and streamlined landforms, both sedimentary and bedrock, are Fugelli, 2012), may thus have been limited or absent in the commonly observed in fjord systems in, for example, Spitsbergen fjords of Chile during deglaciation. Our lack of sub-bottom and in deep troughs that cross-cut many high-latitude continental stratigraphic data must be borne in mind, however, as a caviat shelves (e.g. Canals et al., 2000; Evans et al., 2006; Ottesen and to this conclusion. Dowdeswell, 2009). It is possible that, if produced beneath past glaciers prior to deglaciation of the fjords of Chile, many such 5.2. Streamlined lineations features have been largely buried by post-glacial sediments delivered relatively rapidly by turbid meltwater plumes from glaciers Streamlined sea-floor lineations, with their long axes orientated which undergo strong summer melting and high mass throughput along-fjord, are observed in several areas of our swath-bathymetric (Warren and Aniya, 1999; Lopez et al., 2010). 10 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

5.3. Iceberg ploughmarks mountainous hinterland of the Chilean fjordlands. Some of the delta-fronts appear from swath bathymetry to be dominated by The tidewater glaciers of the Chilean fjords lose mass by both down-slope sediment-transfer processes that are confined laterally surface-melting and runoff and through the production of icebergs in well-defined channels and chutes (Fig. 8A). Turbidity currents (e.g. Rignot et al., 1996; Warren and Aniya, 1999). In many fjord and are most likely the dominant form of down-slope transport on shelf systems where glaciers reach sea level and icebergs are these deltas. On other delta-fronts with more lobate relief, mass- calved, the keels of these icebergs make contact with and plough wasting processes in the form of sediment slumps and slides furrows in the sea floor (e.g. Woodworth-Lynas et al., 1991). We probably predominate (Fig. 8B). Evidence that these deltas are observed almost no iceberg-keel ploughmarks on the sedimentary active today, and continue to build outwards into the Chilean fjords, floors of the fjords of Chile. This is interpreted to be for two reasons; is indicated by the sharp contact between the depocentre and the first, the fjords are for the most part hundreds of metres deep; and, smooth fjord floor shown in Fig. 8B, where the delta front appears secondly, the closely spaced crevasses typical of the grounded to be overriding fjord-floor sediments. A small fan/delta, which margins of Chilean tidewater glaciers (illustrated on Tempano appears to be located at the marine margins of a fluvial drainage Glacier in Fig. 2) result in the production of large numbers of small basin, has also been reported from swath bathymetry of Ainsworth icebergs of irregular size (e.g. Warren and Aniya, 1999) e a similar Fjord, south of our study area at 54230S(Boyd et al., 2008). situation to that in many Alaskan and Spitsbergen fjords today (e.g. Ovenshine, 1970; Dowdeswell, 1989; Dowdeswell and Forsberg, 6.2. Slope failures 1992). This contrasts with the smaller numbers of very large tabular and deep-keeled icebergs produced from floating ice There appear to be rather few clear examples of submarine slope shelves and outlet-glacier termini in Greenland and Antarctica failures on the swath bathymetry of the Chilean fjords that we have (Dowdeswell et al., 1992; Dowdeswell and Bamber, 2007). Thus, examined, although our recognition of more subdued features is very few deep-keeled icebergs are available to plough and rework likely to be inhibited by the lack of any sub-bottom acoustic data. sea-floor sediments in the fjord systems of Chile. Poorly defined lobes close to the steep walls of, for example, Europa Fjord probably represent limited down-slope mass-wasting. Most 6. Other submarine landforms down-slope mass transfer, however, appears to be linked either to turbidity-current channels or to lobate slumps on glacifluvial and 6.1. Fluvial deltas fluvial deltas (Fig. 8) and on the front-face of large glacier-derived moraine ridges (Figs. 2 and 7). These locations are sites of present Along the sides of several Chilean fjords, rivers draining fluvial or past delivery of sediments at relatively high rates from fluvial, catchments have depocentres at their marine margins that have glacifluvial and glacial systems. Fjord walls beyond these areas of built out into relatively deep fjord waters. Two examples of these high sediment input do not appear to be locations for sustained fluvially fed depocentres in Eyre Fjord are shown in Fig. 8. mass-wasting due, presumably, to the lack of a sediment source. Submarine chutes and channels are sometimes observed on the Further south in Chile, swath-bathymetric data from Ainsworth and relatively steep seaward fronts of these depocentres (Fig. 8A); other Marinelli fjords also show evidence of only very restricted slumps depocentres have a more uniform lobate morphology (Fig. 8B). and slides along the fjord margins (Boyd et al., 2008). In Aysen These marine depocentres are interpreted as fluvial deltas, fed Fjord, north of our study area at about 45200S, submarine slope from rivers draining relatively high-relief catchments in the failures have been reported by Araya-Vergara (2011).

Fig. 8. Swath-bathymetry of two deltas fed from ﬂuvial catchments in Eyre Fjord (located in Fig. 1C). White arrows show the positions of streams on the present coastline of the fjord. (A) Submarine delta at 4919.50S. (B) Submarine delta at 49160S. J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 11

6.3. Crater-like pockmarks 1981; Solheim and Elverhøi, 1985). Chaotic reflectors in seismic records from Marinelli Fjord, further south at 54180S, have been Sets of crater-like structures, numbering tens of individual interpreted as potential indicators of shallow gas by Boyd et al. features sometimes orientated in linear strings, are observed in (2008). three areas in water depths of less than about 160 m within the sedimentary sea-floor of the Chilean fjords (Fig. 9); between 48570 6.4. Distribution of submarine landforms in the fjords of Chile and 49020S, and 49040 to 49050S in Angostura Inglesa and at about 49110S in Paso del Indio. The depths and widths of over 80 The distribution of sedimentary submarine landforms identified individual craters from two of these areas are plotted in Fig. 10. in the almost 27,000 km of swath-bathymetric imagery we have Median crater depth is between 3 and 5 m and median diameter is examined from the fjords of Chile is shown in Fig. 11. Three main between 40 and 60 m. A sharp cut-off in minimum observed types of landform predominate: ice-contact moraine ridges; gla- diameter at about 30 m probably reflects the resolution of the cifluvial and fluvial deltas; and turbidity-current channels. Asso- swath-bathymetry system (Fig. 10), implying that some smaller ciated with these landforms are debris-flow lobes on the ice-distal craters may have gone undetected. In addition, the craters show faces of moraine ridges, and channels, chutes and debris-flow lobes few signs of infilling, suggesting that they either formed relatively on the steep faces of glacifluvial and fluvial deltas. Much of the fjord recently or that sedimentation rates in this part of the fjord system system, especially with increasing distance from tidewater glacier are very low. margins, is devoid of major sedimentary landforms, with the These crater-like features are interpreted as pockmarks, prob- exception of occasional streamlined features and pockmarks. Here, ably produced from the escape of shallow gas from the sediments the sea floor is mainly relatively smooth where sediments underlying these areas of the Chilean fjords. Pockmarks are found predominate, with bedrock outcrops providing additional topog- in many shallow continental-shelf settings throughout the world, raphy which we do not plot in Fig. 11 except where they appear to including some observations from high-latitudes (e.g. Hovland, be glacially sculpted.

Fig. 9. Swath-bathymetric examples of crater-like pockmarks on the relatively ﬂat ﬂoor of two Chilean fjords. (A) Angostura Inglesa (located in Fig. 1B). (B) Paso del Indio. Note also the streamlined bedrock landforms on the left of the panel (located in Fig. 1C). 12 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

Fig. 10. Histograms of the size-frequency distribution of pockmark geometry in two Chilean fjords. (A) Angostura Inglesa (Fig. 1B). (B) Paso del Indio (located in Fig. 1C). The histograms are for pockmark width and depth in each area, measured from swath-bathymetric data, with n indicating the number of individual pockmarks measured for each histogram.

7. Discussion high. On the west side of the Northern Patagonian Ice Cap, for example, precipitation is 3700 mm yr 1, rising to 6700 mm yr 1 at 7.1. Climatic and oceanographic setting of Chilean fjords 700 m-elevation (Harrison et al., 2007). It is the high accumulation and mass throughput of Chilean glaciers that enables some to reach The tidewater glaciers of the Chilean fjordlands reach the sea at sea level at tidewater termini even in these relatively mild climatic a lower latitude than any other ice masses in the world today. The conditions. regional climate of the fjordlands is typiﬁed by relatively cool Although the fjords of southern Chile are adjacent to the Paciﬁc summers and mild winters, with January temperatures around Ocean, the bathymetry of the many channels that connect the inner 11 C and July means of 2 C(Miller, 1976). Mean annual air fjords to the ocean margin is crucial to fjord oceanography (Pickard, temperature is between about 6 and 8 C, varying with latitude 1971; Palma and Silva, 2004; Hromic et al., 2006; Sievers, 2008; across the study area (Hulton et al., 2002). Precipitation is also very Sievers and Silva, 2008). Coastal sills ranging from about 60 m to J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 13

Fig. 11. Maps summarizing the distribution of submarine landforms observed from swath-bathymetry in the fjordlands of Chile (Fig. 1A).

150 m prevent ocean waters deeper than this from entering the and glacial meltwater to form a surface layer of Modified Subant- inner fjord systems, even though the fjords themselves are up to arctic Water (MSAAW) some tens of metres in thickness that flows about 1300 m deep in Messier Fjord. The fjords are, therefore, outward from fjord heads in a classical fjord circulation (Syvitski dominated by the inflow of Subantarctic Water (SAAW), which has et al., 1987), with SAAW flowing inward at depth, and filling most a typical temperature of about 9 C and salinity of 33e34.2 ppt. The of the deep inner-fjord basins. SAAW is slightly colder north of the 50 m-deep Angostura Inglesa These relatively high water temperatures mean that the (English Narrows) than to the south (8.3e8.5 C and 8.8e9 C, predominantly small and irregular icebergs calved from tidewater respectively) (Palma and Silva, 2004). In the inner fjords, SAAW glacier margins will melt rapidly once they drift beyond the cold mixes with colder fresh water that comes from rivers, coastal runoff glacial meltwater close to the terminal ice cliffs and the cooler 14 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

MSAAW in some glacier-influenced inner fjords. Iceberg and also contain over 100 m of Holocene infill that is derived largely marginal ice-cliff melt rates in excess of 0.5 m day 1 are predicted from fine-grained meltwater-plume sedimentation, although for marine water temperatures of about 9 C using the equations of deltas and submarine channels have not been observed here Weeks and Campbell (1973) and Russell-Head (1980). This relative (Milliken et al., 2009). The strong environmental gradient across rapid melting means that iceberg rafting of debris and ploughing of Bransfield Strait to the colder Antarctic Peninsula is reflected in the sea floor by iceberg submarine keels are restricted largely to much lower Holocene sediment thicknesses, typically of only a few ice-proximal locations in the fjords of Chile. metres, attributed to reduced meltwater discharge and fine- grained sediment delivery (Griffith and Anderson, 1989; 7.2. Seismic and sedimentary facies in Chilean fjords Anderson, 1999). Thus, differences between ‘temperate fjords’, such as those of Chile and south-east Alaska, and those of colder glacier- Although our marine-geophysical data from the Chilean fjord- influenced environments include reduced meltwater and fine- lands are restricted to swath-bathymetric observations, several grained sediment inputs (Griffith and Anderson, 1989; Anderson, studies have obtained seismic records and core material from the 1999), together with the absence of submarine deltas and chan- region. Marine-seismic investigations by DaSilva et al. (1997) in nels. The latter may reflect a lack of any direct fluvial influence and Canal Baker (48S), near the northern limit of our study area, show the increasingly limited delivery of sediment-laden meltwater from two principal acoustic facies. The first facies, present on the records the base of tidewater glaciers in progressively colder conditions. obtained closest to the tidewater margins of Jorge Montt Glacier and extending about 60 km down fjord, is an acoustically laminated 7.3. Meltwater- and iceberg-dominated fjord sedimentary systems facies that is wedge-shaped in architecture and thins away from the sediment source. Cores collected from this facies consist of inter- Having noted the similarities in seismic and sedimentary bedded sands and muds. The second acoustic facies, found further observations between the Chilean fjords and several relatively mild seaward in the fjord, is semi-transparent in seismic character and northern hemisphere locations at which glaciers reach the sea, it is draping in its form. It is composed of interbedded massive to useful to consider just where the fjordlands of Chile sit on the stratified muds with occasional pebbles; the sediments are often continuum of marine environments in which glaciers and ice- bioturbated. The first facies grades into, and is sometimes inter- sheets enter marine waters. It is notable that locations such as bedded with the second. south-east Alaska, the sub-Antarctic South Shetland Islands, These acoustic and sedimentary facies were interpreted as ice- Spitsbergen and Canadian Baffin Island are all relatively mild proximal and ice-distal glacimarine, respectively, by DaSilva et al. compared with, for example, fjord and shelf settings in North and (1997),reflecting fined-grained and slower sedimentation with Northeast Greenland and much of Antarctica (excluding the rela- increasing distance from debris sourced from the Patagonian ice tively warm western Antarctic Peninsula). In these much colder caps both today and during neoglaciation associated with Little Ice locations, water temperatures of less than zero degrees Celsius are Age and earlier glacier advances (Masiokas et al., 2009). Similar not uncommon, with mean annual air temperatures also consis- acoustic facies have been reported from 3.5 kHz records from several tently below freezing. Here, glacier and ice-sheet mass loss is Chilean fjords by Araya-Vergara (1999a), which he interpreted as mainly by iceberg production and, sometimes, basal ice-shelf ponded glacimarine sediment. The processes of glacimarine trans- melting (e.g. Jenkins and Doake, 1991), instead of meltwater port and delivery of sediments are likely to be mainly by turbid runoff (e.g. Dowdeswell et al., 1998; Siegert and Dowdeswell, meltwater plumes derived from tidewater glaciers and glacifluvial 2002). Terrigenous sedimentation in these much harsher glacial systems. The rarely observed pebbles are presumably derived by and glacimarine settings is therefore dominated by debris transfer iceberg-rafting of debris of all grain sizes. Relatively similar seismic- by icebergs, which transport and deliver sediment of all grain sizes and litho-facies have also been reported from Marinelli and Ains- to the glacimarine environment, in contrast to the fine-grained and worth fjords to the south of our study area (Boyd et al., 2008). Here, sorted debris derived from meltwater plumes. Fjord and shelf radiocarbon dates allowed the calculation of sedimentation rates of sediments in these colder, iceberg-dominated glacimarine settings tens of millimetres per year and about 0.5 mm yr 1 for ice-proximal are often diamictic (e.g. Dowdeswell et al., 1994a,b, 1998) and, in and ice-distal sediments, respectively (Boyd et al., 2008). Sedi- the coldest waters offshore of East Antarctica, icebergs may even mentation rates are likely to be much higher than this as tidewater traverse the inner shelf without melting to release diamictic glacier margins are approached (e.g. Powell and Molnia, 1989). material; in these areas sedimentation is by very slow rain-out of The acoustic and sedimentary characteristics of glacimarine predominantly biogenic debris (e.g. Domack, 1988). sediments reported from Canal Baker and the Marinelli Fjord area In addition, the rate of sediment delivery to many high-latitude of the Chilean fjordlands (DaSilva et al., 1997; Boyd et al., 2008)are fjord and, especially, more distal continental-shelf environments is similar to observations from northern hemisphere fjords in south- very slow once ice sheets have retreated, sometimes hundreds of east Alaska (Powell and Molnia, 1989; Cowan and Powell, 1990; Cai kilometres, to their interglacial position (e.g. Canals et al., 2000; et al., 1997), Spitsbergen (e.g. Elverhøi et al., 1980; Dowdeswell and Dowdeswell et al., 2004, 2010; Mosola and Anderson, 2006). This Dowdeswell, 1989; Sexton et al., 1992; Svendsen et al., 1992) and explains, in part at least, why landforms produced beneath active Canadian Baffin Island (e.g. Syvitski, 1989; Gilbert et al., 1990; full-glacial ice sheets are often well-preserved in many high- Stravers and Syvitski, 1991; Gilbert, 1992). In all these areas, glaci- latitude sea-floor settings, where they remain largely unburied marine sedimentation beyond sandy to gravelly ice-contact fans, and unmodified in areas of low Holocene sedimentation which are formed in the few hundred metres closest to the subglacial chan- below wave-base. An exception is where these landforms are nels emerging at tidewater glacier margins (e.g. Powell, 1990), is reworked by the ploughing action of deep-keeled icebergs (e.g. usually of sorted and sometimes laminated fine-grained debris Dowdeswell et al., 1993, 2010; Ó Cofaigh et al., 2005b; Evans et al., derived from turbid meltwater (e.g. Elverhøi et al., 1980; Gilbert, 2006). 1992). This is supplemented by the occasional delivery of coarser- These cold, iceberg-dominated glacimarine environments grained iceberg-rafted debris (e.g. Dowdeswell and Dowdeswell, contrast with the fjordlands of Chile, which are dominated by 1989; Gilbert, 1990). sediment delivery from meltwater that is produced mainly by Some bays in the South Shetland Islands, offshore of the western strong surface ablation in summer and routed via the glacier bed Antarctic Peninsula and about 1500 km south of the Chilean fjords, before entering marine waters as a rising plume of high suspended- J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 15 sediment content that distributes fine-grained debris widely over (A) Moraine ridges mark the locations of still-stands during ice the adjacent fjord system. This form of meltwater-dominated retreat down fjords (Fig. 7), including the limit of recent ice sedimentation is reflected in the ice-proximal wedges and advance during the Little Ice Age (Fig. 2). The ridges are draping ice-distal seismic architecture of the Chilean fjords, the orientated transverse to past ice-flow, are asymmetrical with sorted and often laminated fine-grained nature of the sediments steeper ice-distal sides, and sometimes have debris-flow lobes (DaSilva et al., 1997; Boyd et al., 2008), and the predominantly flat on their ice-distal flanks. Smaller moraines ridges, located and relatively smooth floor of most Chilean fjords. The latter are inside Little Ice Age moraines, mark ice retreat over the past broken mainly by isolated moraine ridges that record still-stands in century or so (Fig. 2). ice retreat; elsewhere continuing sedimentation of fine-grained (B) Glacifluvial and fluvial deltas are formed from sediment meltwater-derived debris during the Holocene has probably delivered by braided rivers from terrestrial glaciers or fluvial contributed to the burial of many of the streamlined landforms catchments (Figs. 5, 6 and 8). They have small channels and produced under full-glacial conditions at the glacier bed. The chutes, and sometimes debris-flow lobes, on their submarine draping of sea-floor topography by fine-grained sediments raining faces. out of fjord waters can be seen clearly in Fig. 4A. An important (C) Sinuous and relatively deep turbidity-current channels are set exception to this is the sea floor close to the margins of Chilean within the predominantly smooth fjord floor (Figs. 5 and 6). tidewater glaciers that have retreated only recently from Little Ice Age maxima; here a more diverse set of moraine ridges and It should be noted that both glacifluvial and fluvial deltas, streamlined bedforms remains visible on swath-bathymetric together with turbidity-current channels, remain active today in imagery close to the modern margin of Tempano Glacier in the fjords of Chile, whereas the glacial component of the landform- Iceberg Fjord (Fig. 2). assemblage model is often relict. Apart from these landforms, the We can, therefore, plot the position of the Chilean fjordlands on sedimentary sea floor of Chilean fjords is predominantly smooth. a continuum of climatic and oceanographic settings from the Bedrock ridges may break through to the surface but, where mildest to the coldest parts of the Earth at which glaciers and ice underlying topography is present, it is often draped by subsequent sheets reach the sea (Fig. 12)(Dowdeswell et al., 1998). In the fine-grained sedimentation from meltwater plumes that gradually southern hemisphere, the fjords of southern Chile represent one buries any pre-existing relict landforms and smoothes out end of this continuum; their northern hemisphere equivalents are irregularities. the fjords of south-east Alaska where mass-turnover and melt- When this landform-assemblage model for the fjords of Chile is water production from the adjacent glaciers are of a similar order of compared with the morphology of the sea floor in fjords and cross- magnitude. In addition, rainwater sometimes provides an incre- shelf troughs from other glacier-influenced marine environments, ment of runoff in these areas (Cowan et al., 1988). Slightly colder it is clear that subglacially produced landforms (e.g. drumlins, crag- environments, with lower glacier mass-turnover and, hence, and-tails, mega-scale glacial lineations) are largely absent in the meltwater production, are the fjords of Spitsbergen and Baffin Chilean case (Figs. 11 and 13). Only within a few kilometres of Island. The much colder East and North Greenland and northern modern tidewater glacier margins, between moraine ridges Ellesmere Island in Arctic Canada are the coldest glacimarine marking the limit of Little Ice Age advance and the modern tide- settings in the northern hemisphere (Fig. 12). In the southern water glacier terminus, are smaller transverse moraine ridges hemisphere, the coastal glaciers of the western Antarctic Peninsula found (Fig. 2). In Spitsbergen fjords and cross-shelf troughs, for experience limited summer melting, whereas the marine- example, mega-scale glacial lineations and other sedimentary terminating margins of the West and East Antarctic ice sheets are landforms produced by active subglacial processes are common largely devoid of surface meltwater production. These are areas where fast-flowing ice streams drained the interior ice sheet dominated by sediment delivery from icebergs (Fig. 12). (Ottesen et al., 2005, 2007). In inter ice-stream locations, where ice flux was lower, series of transverse moraine ridges of various sizes 7.4. Landform assemblage model for mild meltwater-dominated predominate (Ottesen and Dowdeswell, 2009). Only in a few fjords Spitsbergen fjords, such as Magdalenefjorden on the relatively mild west coast, do smooth sea-floor basins and sediment-draped The assemblage of glacial, glacifluvial and glacimarine land- submarine topography predominate (Ottesen and Dowdeswell, forms found in the fjords of Chile is summarised in the schematic 2009). In colder high-polar glacimarine environments, stream- model in Fig. 13. The three main component landforms of the lined sedimentary landforms, moraine ridges and grounding-zone landform-assemblage model for such climatically mild meltwater- wedges, formed in subglacial and ice-contact positions during the dominated fjords are given below. LGM and deglacial period between about 20,000 and 10,000 years ago, are characteristic submarine landforms on swath-bathymetric imagery of Greenland and Antarctic continental shelves (e.g. Canals et al., 2000; Dowdeswell et al., 2004, 2010 ; Ó Cofaigh et al., 2005b; Mosola and Anderson, 2006; Dowdeswell and Fugelli, 2012). Subglacial and ice-contact landforms, similar to those observed in higher-latitude fjords and shelves, are likely to have been formed at the base and margins of Chilean glaciers under full-glacial and deglacial conditions. High rates of snow-accumulation and ice- surface melting on glaciers draining the Andian mountains led, however, to rapid meltwater and fine-grained sediment delivery into the relatively low-latitude Chilean fjords from both tidewater glaciers and glacifluvial drainage systems after deglaciation. Most pre-existing glacial landforms on the fjord floor, with the exception Fig. 12. Schematic diagram of the environmental continuum of glacier-influenced of major retreat moraines (Figs. 2 and 7) and protruding stream- marine settings from warmest to coldest (modified from Dowdeswell et al., 1998). Note that the fjordlands of Chile are one of the mildest places where ice reaches the sea lined bedrock (Fig. 4B), are likely to have been buried and obscured today, with their northern hemisphere equivalent in south-east Alaska. by this subsequent glacimarine and glacifluvial sedimentation 16 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

Fig. 13. A schematic landform-assemblage model for meltwater-dominated fjords subject to relatively mild climatic and oceanographic conditions, such as the fjordlands of southern Chile. The inset shows the efﬂux of a subglacial meltwater channel at the tidewater glacier terminus and the plume of turbid sediment and ice-proximal fan produced beyond the channel mouth.

(Fig. 13); it is predominantly submarine landforms which remain in macrotidal, with a tidal range exceeding 4 m in its inner arms that an active process environment today, for example turbidity-current generates currents of about 2.5 m s 1 where fjords narrow (Hooge channels, which are observed on our swath-bathymetric imagery. and Hooge, 2002). This compares with tides of 1.66 m and 2.05 in South-east Alaska provides a likely northern-hemisphere Canal Messier and Canal Wide in our Chilean fjord study area equivalent to the fjordlands of Chile, with similarly high precipi- (Fierro, 2008). Strong currents, especially where fjords narrow, may tation and glacier melt rates. In Alaskan fjords, sedimentation also be a mechanism for sediment reworking and redistribution in derived predominantly from glacial meltwater reaches rates of Chilean fjords. more than a metre per year close to the margins of modern tidewater glaciers and is transported to more ice-distal locations by 8. Summary and conclusions plumes of suspended sediment (e.g. Powell and Molnia, 1989); this would be quite sufficient to bury most subglacial and ice-contact The Chilean fjords are at the lowest latitude in either hemi- landforms produced by LGM ice sheets or during subsequent sphere where glaciers reach the sea today. High accumulation and deglaciation beneath a relatively smooth cover of draping fine- mass throughput sustain tidewater glacier margins in what are grained glacimarine debris. It is noteworthy that the turbidity- relatively mild climatic and oceanographic conditions. Swath current channels that are observed in Alaskan and British Colum- bathymetry of almost 27,000 km2 of sea floor in the fjordlands of bian fjords remain active today (Syvitski et al., 1987), precluding southern Chile (42e55S) was acquired between 2003 and 2008, burial by rain-out of fine-grained glacifluvial and fluvial sediments. allowing mapping of sea-floor landforms and inferences to be made In addition to deposition from meltwater, sediment gravity flows on the nature of glacimarine sediments and sedimentation. that are sometimes sourced from steep fjord walls have also been Tidewater glaciers draining the Southern Patagonian Ice Cap are reported to infill the floors of Alaskan fjords (Cowan et al., 2010). present in several fjords. The sea floor beyond retreating Tempano Tides are a further mechanism for the redistribution of fine-grained Glacier has an outermost terminal moraine marking the limit of ice sediments in many Alaskan fjords (Cowan et al., 2010), through advance during the Little Ice Age (Fig. 2). Sets of smaller transverse both the generation of strong currents and their effects on the ridges closer to the glacier were deposited during still-stands or time-dependent behaviour of meltwater plumes. Glacier Bay is minor readvances in ice retreat. Streamlined lineations in the J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19 17 innermost fjord were produced beneath active ice. By contrast, The paper is published with permission of the Chilean Navy beyond advancing Pio XI Glacier there are few signs of organised (SHOA). Writing of the paper took place mainly while JAD was submarine landforms (Fig. 3). Isolated hummocks and ridges are Visiting Cambridge Fellow at Gateway Antarctica, University of probably the product of a previous glacier surge. Predominantly Canterbury, New Zealand, funded through the Erskine Bequest. smooth and flat areas of the sea-floor beyond the two tidewater glaciers are interpreted as sedimentary infill from rainout of fine- References grained debris from turbid meltwater (Fig. 4). Older ridges are also located along and at the outer mouths of Anderson, J.B., 1999. Antarctic Marine Geology. Cambridge University Press, 289 pp. fi fi several Chilean fjords (Fig. 7), and are interpreted to be moraines Araya-Vergara, J.F., 1999a. Per les longitudinales doe ordos de Patagonia Central. Ciencia y Tecnología del Mar 22, 3e29. formed at retreating margins of grounded tidewater glaciers during Araya-Vergara, J.F., 1999b. Secuencia de formas deposicionales submarinas en la still-stands in deglaciation; deglaciation is inferred to be episodic fractura del Canal Messier, Patagonia Central. Investigaciones Marinas Valpar- e rather than catastrophic (Dowdeswell et al., 2008). aiso 27, 39 52. Araya-Vergara, J., 2008. The submarine geomorphology of the Chilean Patagonian Where glaciers do not reach the sea, meltwater-fed braided fjords and piedmonts. In: Silva, N., Palma, S. (Eds.), Progress in the Oceano- rivers connect the glacial and marine sedimentary systems. Swath graphic Knowledge of Chilean Interior Waters, from Puerto Montt to Cape Horn. imagery shows glacifluvial and fluvial deltas with series of small Comite Oceanografico Nacional, Valparaiso, Chile, pp. 25e27. Araya-Vergara, J.F., 2011. Submarine failures in the bottom of the Aysen fjord, channels and narrow chutes (Figs. 5 and 6). Beyond the delta-fronts Northern Patagonia, Chile. Investigaciones Geographic Santiago, Chile 43, 17e34. are sinuous turbidity-current channels extending for kilometres Benn, D.I., Evans, D.J.A., 2010. Glaciers and Glaciation, second ed. Arnold, London. along flat fjord floors (Figs. 5 and 6). Benn, D.I., Warren, C.R., Mottram, R.H., 2007. Calving processes and the dynamics of calving glaciers. Earth-Science Reviews 82, 143e179. Relatively few other sedimentary landforms were imaged. Some Boulton, G.S., 1986. Push-moraines and glacier-contact fans in marine and terres- streamlined sea-floor lineations were observed (Fig. 4B), but are trial environments. Sedimentology 33, 667e698. largely buried by rapid post-glacial sediment delivery except where Boyd, B.L., Anderson, J.B., Wellner, J.S., Fernandez, R.A., 2008. The sedimentary record of glacial retreat, Marinelli Fjord, Patagonia: regional correlations and forming sculpted bedrock highs. Almost no iceberg-keel plough- climate ties. Marine Geology 255, 165e178. marks were observed, probably due to a combination of relatively Brown, C.S., Meier, M.F., Post, A., 1982. Calving Speed of Alaska Tidewater Glaciers deep water, the restricted keel-depth of most tidewater-glacier- with Applications to the Columbia Glacier, Southeast Alaska. U.S. Geological derived icebergs, and rapid melting in mild water. Examples of Survey, Professional Paper, 1258-C, 13 pp. Cai, J., Powell, R.D., Cowan, E.A., Carlson, P.R., 1997. Lithofacies and seismic-reflection submarine slope failures were restricted mainly to lobate slumps interpretation of temperate glacimarine sedimentation in Tarr Inlet, Glacier Bay, on delta fronts (Figs, 6 and 8). In addition, sets of crater-like Alaska. Marine Geology 143, 5e37. fl pockmarks provide potential indicators of shallow gas in a few Canals, M., Urgeles, R., Calafat, A.M., 2000. Deep sea oor evidence of past ice streams off the Antarctic Peninsula. Geology 28, 31e34. locations (Figs. 9 and 10). Church, M., Gilbert, R., 1975. Proglacial fluvial and lacustrine environments. In: The fjords of Chile are dominated by sediment delivery from Jopling, A.V., McDonald, B.C. (Eds.), Glaciofluvial and Glaciolacustrine Sedi- turbid meltwater produced by ice-surface ablation and snowmelt mentation. Society of Economic Paleontologists and Mineralogists, Special e fl Publication, vol. 23, pp. 22 100. that enters marine waters from tidewater glaciers and glaci uvial Clark, C.D., 1993. Mega-scale glacial lineations and cross-cutting ice-flow landforms. systems and distributes fine-grained debris widely over the adja- Earth Surface Processes and Landforms 18, 1e19. cent fjord systems. This meltwater-dominated sedimentation is Cowan, E.A., 1992. Meltwater and tidal currents: controls on circulation in a small e fl fi glacial fjord. Estuarine, Coastal and Shelf Science 34, 381 392. re ected in the sorted and often laminated ne-grained nature of Cowan, E.A., Powell, R.D., 1990. Suspended sediment transport and deposition of the sediments (DaSilva et al., 1997; Boyd et al., 2008), the ice- cyclically interlaminated sediment in a temperate glacial fjord, Alaska, USA. In: proximal wedges and draping ice-distal seismic architecture, and Dowdeswell, J.A., Scourse, J.D. (Eds.), Glacimarine Environments: Processes and fl fl Sediments. Geological Society, London, Special Publication, vol. 53, pp. 75e89. the predominantly at and relatively smooth oor of most Chilean Cowan, E.A., Powell, R.D., Smith, N.D., 1988. Rainstorm-induced event sedimenta- fjords. tion at the tidewater front of a temperate glacier. Geology 16, 409e412. The Chilean fjordlands represent the mildest climatic and Cowan, E.A., Seramur, K.C., Powell, R.D., Willems, B.A., Gulick, S.P.S., Jaeger, J.M., oceanographic end-member of a continuum of glacier-influenced 2010. Fjords as temporary sediment traps: History of glacial erosion and deposition in Muir Inlet, Glacier Bay National Park, southeastern Alaska. marine settings (Fig. 12). Their northern hemisphere equivalent is Geological Society of America Bulletin 122, 1067e1080. south-east Alaska. Slightly colder environments, with lower glacier DaSilva, J.L., Anderson, J.B., Stravers, J., 1997. Seismic facies changes along a nearly continuous 24 latitudinal transect: the fjords of Chile and the northern mass-turnover and, hence, meltwater production, are the fjords of e fi Antarctic Peninsula. Marine Geology 143, 103 123. Spitsbergen and Baf n Island. By contrast, the waters offshore of Domack, E.W., 1988. Biogenic facies in the Antarctic glacimarine environment: basis East Antarctica represent the most extreme glacimarine environ- for a polar glacimarine summary. Palaeogeography, Palaeoclimatology, Palae- ment, where even icebergs do not melt in the frigid waters (Fig. 12). oecology 63, 357e372. Dowdeswell, J.A., 1989. On the nature of Svalbard icebergs. Journal of Glaciology 35, A landform-assemblage model for climatically mild meltwater- 224e234. dominated fjords is given in Fig. 13. Three main types of landform Dowdeswell, J.A., 1995. Glaciers in the High Arctic and recent environmental predominate (Figs. 11 and 13): ice-contact moraine ridges; glaci- change. Philosophical Transactions of the Royal Society, Series A 352, 321e334. fl fl Dowdeswell, J.A., Dowdeswell, E.K., 1989. Debris in icebergs and rates of glaci- uvial and uvial deltas; and turbidity-current channels. Full- marine sedimentation: observations from Spitsbergen and a simple model. glacial and deglacial streamlined subglacial landforms are likely Journal of Geology 97, 221e231. to have been buried and obscured by subsequent glacimarine Dowdeswell, J.A., Cromack, M., 1991. Behavior of a glacier-derived suspended sediment plume in a small Arctic inlet. Journal of Geology 99, 111e123. sedimentation; it is predominantly submarine landforms where Dowdeswell, J.A., Forsberg, C.F., 1992. The size and frequency of icebergs and bergy sedimentary processes remain active today, such as turbidity- bits from tidewater glaciers in Kongsfjorden, north-west Spitsbergen. Polar current channels, that are observed on our swath-bathymetric Research 11, 81e91. imagery of otherwise relatively smooth sedimentary fjord floors. Dowdeswell, J.A., Bamber, J.L., 2007. Keel depths of modern Antarctic icebergs and implications for sea-floor scouring in the geological record. Marine Geology 243, 120e131. Acknowledgements Dowdeswell, J.A., Fugelli, E.M.G., 2012. The seismic architecture and geometry of grounding-zone wedges formed at the marine margins of past ice sheets. Geological Society of America, Bulletin 124, 1750e1761. We thank Alexis Muñoz and Pilar Ortiz (SHOA) for their Dowdeswell, J.A., Whittington, R.J., Hodgkins, R., 1992. The sizes, frequencies and considerable assistance with data processing, and Kelly Hogan and freeboards of East Greenland icebergs observed using ship radar and sextant. Daniel Price for producing the final figures. John Anderson and Journal of Geophysical Research 97, 3515e3528. Dowdeswell, J.A., Villinger, H., Whittington, R.J., Marienfeld, P., 1993. Iceberg Ellen Cowan provided helpful reviews and Prof. J.F. Araya-Vergara scouring in Scoresby Sund and on the East Greenland continental shelf. Marine kindly commented on an oral presentation of the work in Chile. Geology 111, 37e53. 18 J.A. Dowdeswell, M. Vásquez / Quaternary Science Reviews 64 (2013) 1e19

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