influence of a glacier melting cycle on the seasonal...

Estuaries and Coasts (2015) 38:24–34DOI 10.1007/s12237-014-9825-2

Influence of a Glacier Melting Cycle on the SeasonalHydrographic Conditions and Sediment Fluxin a Subantarctic Glacial Fjord

Julio Salcedo-Castro · Américo Montiel · Bibiana Jara ·Osvaldo Vásquez

Received: 2 September 2013 / Revised: 24 April 2014 / Accepted: 24 April 2014 / Published online: 17 May 2014© Coastal and Estuarine Research Federation 2014

Abstract Four hydrographic surveys were carried out inGallegos Sound (54◦ 28′58′′S–69◦ 50′55′′ W), a subantarc-tic glacial fjord. This is the first comprehensive seasonalstudy for the extreme isolated areas in the Cordillera Dar-win Ice Field, Chile. The fjord exhibits a strong seasonalpattern in its oceanographic characteristics. The highest val-ues of total suspended solid concentrations were observedin summer (>15 mg L−1), with the lowest concentrations inwinter (

Estuaries and Coasts (2015) 38:24–34 25

forcings (McClimans 1978). However, unlike river-fedfjords, glacial fjords are more responsive to changes inair temperature (Chu et al. 2009). This type of fjords isnot uncommon, Syvitski (1989) estimated that 25 % ofthe world’s fjords are under the influence of tidewaterglaciers or floating glaciers. One of the main characteris-tics of glacial fjords is its high sediment load. This largeamount of sediment has a strong influence on importantprocesses, such as heat exchange with the atmosphere,flocculation and aggregation of particles (Zaja̧czkowskiand Włodarska-Kowalczuk 2007), physical-chemical andgeotechnical properties of the sea floor, and the extent of thephotic zone (Svendsen et al. 2002). Moreover, the high sus-pended sediment concentration in glacial fjords impacts onthe structure and distribution of planktonic and benthic com-munities (Görlich et al. 1987; Wȩsławski and Legezyńska1998; Zaja̧czkowski and Legezyńska 2001; Hop et al. 2002;Fetzer et al. 2002; Etherington et al. 2007).

Transport and resuspension of sediments in estuaries area result of processes that involve the influence of bathymetryand tides, as described by Blanton et al. (2003). In glacialfjord, tides are especially relevant. By studying a smallglacier-fed inlet in Spitsbergen, Dowdeswell and Cromack(1991) found that the suspended sediment plume dynam-ics is mostly governed by tides behavior, with only a weakinfluence of overlaying wind field. The plume extensionwas higher with high tide and lower during ebb tide. Thisperiodicity associated to tidal cycles was also observed byCowan et al. (1999) in the laminated structure of sedimentcores taken in Muir Inlet. The sediment also got spatial vari-ability caused by the competing influence of the meltingdischarge and fjord oceanography on the overflow plume.Moreover, a fortnightly cycle could be distinguished in thesediment cores, as well as seasonal signals associated withspring productivity.

In glacial fjords, meltwater is the main driving mecha-nism influencing the sediment transport, as was concludedby Ó Cofaigh et al. (2001) based on the study of a com-plex glacimarine system in East Greenland. On the otherhand, due to the proximity of the glacier in one end,glacial fjords present strong horizontal gradients in the dis-tribution of oceanographic variables and, especially, totalsuspended sediment (TSS). According to Zaja̧czkowski andWłodarska-Kowalczuk (2007), three zones can be clearlyidentified along a glacial fjord: proximal, prodelta, and dis-tal zones. In the proximal zone, sediment flux is mostlydriven by highly seasonal terrigenous material supply anddominated by the plume energy, while turbid plumes andlarge vertical flux of suspended sediment are common fea-tures in the proximal and prodelta zones (Zaja̧czkowski andWłodarska-Kowalczuk 2007). In this sense, the importanceof suspended sediments in glacial fjords was mentioned bySyvitski and Shaw (1995), who asserted that these fjords

show the highest sediment accumulation rate. Therefore,many processes occurring in glacial fjords can be reflectedthrough the spatial and temporal variability of the oceano-graphic characteristics and suspended sediments. In turn,the characteristics of the surface layer are very dependenton climatic conditions, as asserted by Pickard (1971).

The Chilean Patagonia (42◦ S–56◦ S) is a region with84,000 km of coastline and ice fields surrounded by alarge number of glaciers and fjords (Pantoja et al. 2011).Much of the oceanographic research have been focusedon the fjords located in the northern part of the ChileanPatagonia (Pickard 1971; Silva et al. 2001; Dávila et al.2002; Guzmán and Silva 2002; Valle-Levinson et al. 2002;Valle-Levinson et al. 2007; Prado-Fiedler and Salcedo-Castro 2008; Sievers 2008; Calvete and Sobarzo 2011;Castillo et al. 2012), while the glacial fjords located in theSubantarctic region of the Chilean Patagonia have receivedless attention due to their more distant location and thegreater relevance of northern part of the Chilean Patago-nia for aquaculture (Quiroga et al. 2013). In the first study,in this area, Pickard (1971) distinguished glacial fjords(“iceberg inlets”) for having comparatively lower surfacetemperature and several subsurface maxima and minimain temperature vertical distribution with increasing depth,along with a lower visibility, due to suspended matter fromglaciers. A few studies have been done south of the Strait ofMagellan. Recent studies have shown that some ice massesin this region exhibit an accelerated melting rate (Williset al. 2012). Moreover, this region has been regarded as animportant “CO2 sink” where changes in freshwater dynam-ics can affect the biogeochemical processes and circulationat local and regional scales (Iriarte et al. 2010; Montero et al.2011).

A few studies have focused on the glacier-fjord inter-action in Chilean Patagonia (Torres et al. 2011). Someof these studies have examined the productivity of phyto-plankton. For instance, González et al. (2011) describeda low productivity planktonic as result of large inputs ofsilt-rich freshwater from San Rafael Glacier. This is con-sistent with the description given by Silva et al. (2001).Montecino and Pizarro (2008) described the effect of thelight attenuation and high inorganic suspended matter onthe phytoplankton concentration and composition. In thesame vein, several authors have asserted that light is alimiting factor for phytoplankton communities in Chileanglacier-influenced fjords (Pizarro et al. 2000; Pizarro et al.2005; Prado-Fiedler 2009). Among the few studies inChilean subantarctic fjords, Antezana (1999) describedthe influence of glaciers melting on the hydrography ofcoastal waters around the Magellan Strait. According tothe study, in Magellan Strait, the cold and brackish watersand the thermal inversion were significant oceanographicfeatures.

26 Estuaries and Coasts (2015) 38:24–34

The fjords in the Cordillera Darwin Ice Field (CDIF)have been described in a general context, as part of thestudy of fjords and channels of southern Chile (Pickard1971; Valdenegro and Silva 2003; Valle-Levinson et al.2006). However, there is a research gap from an oceano-graphic point of view in spite of accelerated melting rateof the glaciers documented in this area (López et al. 2010).Recently, Vásquez et al. (2012) compared chlorophyll-aconcentration with the hydrographic variables in GallegosSound during winter conditions. They found a good cor-relation between chlorophyll-a and the TSS, density, anddepth.

A description of the seasonal and interannual variabil-ity of the hydrographic conditions in glacial fjords ofSouth America can provide valuable information about theresponse of glacial fjords to glacier melting. Moreover, thisinformation can be compared with data from similar glacial

systems in the Northern Hemisphere. The purpose of thisstudy is to provide the first description of the seasonal vari-ability of the oceanographic variables in glacier-influencedregions of CDIF in southern Chilean Patagonia.

Materials and Methods

Study Area

The study area belongs to CDIF, located in the Tierra delFuego mountain range, which has several summits exceed-ing 2,000 masl (Holmlund and Fuenzalida 1995; Fernándezet al. 2011). Glaciers from CDIF descend from CordilleraDarwin towards the Pacific Ocean and Almirantazgo Sound(Fig. 1). In this zone, the winter season extends from Juneto September, with permanent winds from the southwest

Fig. 1 Study area, defined by Gallegos Sound and Garibaldi Glacier, in Tierra del Fuego. Black arrows represent glaciers influencing other fjordsnearby the study area


(Schneider et al. 2003). Although precipitation is even yearround (Pickard 1971), there is a strong asymmetry in theclimatic conditions between the north and south sides ofthe CDIF. This is associated with the topography, withdrier conditions and more rapid glacier retreat on the northside (Seno Almirantazgo) (Holmlund and Fuenzalida 1995).This asymmetry in the rain conditions due to orographiceffects was earlier described by Pickard (1971) and morerecently by Schneider et al. (2003) which states that themountain range of the Andes is a barrier that effectivelyblocks the westerly winds and produces a strong contrast inthe pluviosity on either side of this barrier.

Gallegos Sound is a glacial fjord that has the tidewaterterminus of Garibaldi Glacier at its head in CDIF (Fig. 1).The glacier terminus is divided into two arms separated bya small island. The southeast arm is permanently under sealevel and more advanced into the fjord whereas the north-west arm has retreated more rapidly and its grounding lineis already above the sea level.

This glacial fjord is 9-km long and 1.2- to 3.4-kmwide and discharges to Brooks Bay. Moreover, Brooks Bayreceives the sediment plume coming from glaciers dis-charging into Guerrero Bay. These fjords are connectedto Almirantazgo Sound, a larger multi-arm fjords systemopened to the Strait of Magellan (Fig. 1). Inside the Gal-legos Sound are two basins (maximum depth 100 and 170m) separated by a sill of 50 m deep; there is no sill at theentrance of the fjord (Fig. 2).

A shallow tidal flat with high concentration of suspendedparticles (identified as NI in Fig. 2) extends approximately1.2 km from the southeast arm and would correspond to the

proximal zone described by Zaja̧czkowski and Włodarska-Kowalczuk (2007). This zone was not surveyed during thisstudy due to its shallowness and the difficulty to accessby sea. The study area corresponds to the prodelta anddistal zones described by Zaja̧czkowski and Włodarska-Kowalczuk (2007). It is important to mention that thesezones are covered with fast ice in winter when ice meltingis almost negligible.

Sampling

This study was part of a project aimed at describing the ben-thic communities and hydrographic conditions in a glacialfjord of CDIF. Four hydrographic surveys were carried outin Gallegos Sound in May 2010, August 2010, November2010, and January 2011. As noted in the previous section,glacier front (GF) and fjord center (FC) sections correspondto the prodelta region, and fjord mouth (FM) represents thedistal region.

Twelve stations were occupied along the fjord axisgrouped in three longitudinal transects. Each transect wascomposed of four stations separated by about 200 m fromeach other, beginning ∼ 2.5 km from the glacier terminus(GF stations), in the center of the fjord (FC stations), and atthe fjord mouth (FM stations) (Fig. 2).

At each sampling station, a Seabird Electronics SBE19plus CTD was used to obtain vertical profiles of tempera-ture, salinity, and dissolved oxygen. Density was computedfrom pressure, salinity, and temperature data using the man-ufacturer’s software. Chlorophyll-a was measured with aWET labs fluorescence sensor. Water samples were taken at

Fig. 2 Bathymetry of Gallegossound (in m) and samplingsections. GF glacier front, FCfjord center, FM fjord mouth.Black diamond represents thesediment trap location. NI noinformation


0, 5, 10, 20, and 30 m depths with a Niskin bottle. Thesesamples were analyzed to determine the content of TSS byfiltering seawater onto a pre-weighed 0.45 μm nominal-pore polycarbonate filters and determining the weight dif-ference after drying the sample. Vertical sections of tem-perature, salinity, dissolved oxygen, and chlorophyll-a weredrawn by using Ocean Data View, Version 4 (Schlitzer2013).

The vertical flux of suspended particles was measuredat station GF near the glacier terminus (Fig. 2) usinga double cylindrical sediment trap with a recommendedlength/diameter ratio of 7:1 (Gardner 1980; Baker et al.1988; Zaja̧czkowski 2002). These traps were made of PVCand mounted on a metallic structure that kept them in avertical position.

During each survey, the sediment trap was moored at10 m depth for approximately 48 h. TSS and sediment trapsamples were vacuum-filtered from 400-mL seawater onpre-weighed Whatman GF/F filters with 0.45-μm pore size.Organisms visible to the naked eye (mostly copepods) wereremoved from the filters.

Laboratory Analysis

In the laboratory, the filtered samples for SPM from theNiskin bottles and sediment trap samples for vertical fluxmeasurements were dried at 60 ◦C for 24 h and weighedafter cooling down several times until a constant weight wasachieved. The suspended particulate matter concentration(mg L−1) was calculated according to Eaton et al. (2005).The total mass flux of particulate material, expressed as mil-ligrams per square meter per day, was calculated from the

total mass weight, the trap collecting area (m2), and thesampling interval (h).

In order to differentiate the characteristics fjord’s sur-face layer related to the seasonality of the glacier melting,we compared the variability of air temperature with theseasonal variation of the hydrographical characteristics inGallegos Sound. Air temperature data were obtained fromthe meteorological station (recording every 3 h) located inPunta Arenas (Fig. 1). For this comparison, we chose thefjord stations closest to the glacier terminus (GF stations).To obtain a representative value of the surface layer, weaveraged the values from 0 to 5 m along the four stations inthe GF section (see Fig. 2).

Results

The following paragraphs describe features and variabilitywe found in the prodelta and distal zones afterwards.

In fall (May 2010), no difference is observed along thefjord, where the prodelta and distal zones exhibit a thin sur-face layer with temperature < 6 ◦C and salinity < 28. Inwinter, besides no difference between the prodelta and dis-tal zones, the surface layer was colder (< 6 ◦C) and slightlysaltier (< 29) than the lower layer. During both seasons, thedissolved oxygen and chlorophyll-a showed no horizontalgradient along the prodelta and distal zones, with surfacevalues >8 and >2 mg L−1, respectively, although the lattershowed a subsurface maxima (Fig. 3).

In spring, a horizontal gradient begins to develop, witha thinner surface layer showing colder temperatures (


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Fig. 4 Daily mean air temperature in Punta Arenas during the sea-sonal surveys, along with the temporal variation of the fjord temper-ature, salinity, chlorophyll-a, and TSS observed in the GF zone (seeFig. 2). Mean values (black dots) calculated from the four stations andfrom 0 to 5 m. Box plots represent the median, quartiles, and extremevalues of the measurements. The TSS and TPOC fluxes at the sedimenttrap located in the GF zone are also shown

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Fig. 5 Linear regression between the air temperature and the meanwater temperature, salinity, chlorophyll-a, and total suspended solidsobserved in the GF zone surface layer (see Fig. 2). A scatter plot andregression between the air temperature and TSS flux at the sedimenttrap in the GF zone is also shown. Two cases are presented: daily meanair temperature (blue circles and continuous line) and 3-day averageair temperature (red crosses and dashed line)


the other hand, the concentration of dissolved oxygen andchlorophyll-a recorded during this period was very high,with values >11 and > 16 mg L−1, respectively. Thesemaxima were observed between 5 and 10 m in the prodeltazone (Fig. 3). In summer, a weak horizontal gradient wasobserved in the surface layer, with temperatures ∼ 8.5◦Cin the distal zone and > 9 ◦C in the prodelta. Salinity hadan opposite pattern, with values < 21 in the distal zone and>24 in the prodelta. This indicates that a colder water masswith lower salinity remained out of Gallegos Sound. Simi-larly, the distal zone exhibited higher subsurface dissolvedoxygen (>10 mg L−1) and chlorophyll-a concentrations(>10 mg L−1) when compared with the prodelta zone(Fig. 3).

In Fig. 4, the daily mean air temperature in Punta Arenasis shown, along with the depth-averaged mean temperature,salinity, chlorophyll-a, and TSS at the GF section surfacelayer. It can be seen that there is a “synchronicity” betweenthe air temperature and the oceanographic variables. Airtemperature appears to correlate positively with the watersurface temperature, chlorophyll-a, and TSS, whereas therelationship is negative with salinity. Moreover, it can beobserved that the TSS concentration is lower in winter (10 and >15 mg L−1 in springand summer, respectively.

To obtain a clearer picture of the influence of the annualmelting cycle on the oceanographic characteristics in Gal-legos Sound, we plotted the oceanographic variables as afunction of daily mean air temperature. Moreover, we haveevaluated the cumulative effect of the air temperatures byplotting the ocean state variables as function of a 3-day aver-age air temperature (i.e., from 2 days before each survey).A good correlation is observed between the air temperaturesand all oceanographic variables, especially between temper-ature and total suspended solids. On the other hand, tem-perature and salinity are better correlated with daily meanair temperature; chlorophyll-a and total suspended solidsare better correlated with the 3-day average air temperature(Fig. 5).

Discussion

Seasonality of the oceanographic characteristics in Galle-gos Sound is mostly influenced by air temperature. In spiteof pluviosity being very high in this region, the CordilleraDarwin mountain range creates a drier condition that con-trasts with the maritime climate that influences glacial fjordsof Alaska (Cowan et al. 1988; Cowan and Powell 1990;Curran et al. 2004). During all seasons, a two-layered estu-arine structure was observed in Gallegos Sound. However,a colder surface water with a weak stratification, along withlittle difference in salinity between the surface and lower

layer, was seen during winter. The relatively high salin-ity observed in the surface layer during winter confirmsthat the influence of precipitacion on freshwater and TSSconcentration is negligible. In contrast, the stronger stratifi-cation observed during summer was associated with a largerfreshwater discharge from melting glacier owing to highertemperature. As Garibaldi Glacier is the most significantfreshwater source in the basin of Gallegos Sound, ice melt-ing represents the main forcing that influences the seasonalcharacteristics of the surface layer.

In terms of the mean TSS concentrations, the values fromGallegos Sound exhibit a higher range in comparison toother Chilean fjords (Table 1). For example, our values werehigher than those recorded for fjords adjacent to the SouthPatagonian Icefield (Siegel et al. 1981) and in the Strait of

Table 1 Comparison of TSS concentration found in Gallegos Soundwith typical values from other glacial fjords

Location Reference Concentration

range (mg L−1)

Gallegos Sound, Chile This study 1 − 35Chilean archipelago Siegel et al. (1981) 0.11 − −3.84

(winter)

Straits of Magellan, Chile Fabiano et al. (1999) 0.4 − 0.6Cierva, Brialmont, and Domack and 0.6 − 8

Lester Cove, Antarctica Williams (1990)

Arthur Harbor, Antarctica Ashley and Smith (2000) 3 − 35Martel Inlet, Antarctica Pichlmaier et al. (2004) 10 − 15Admiralty Bay, Antarctica Sicinski (2004) 2.8 − 100Kongsfjorden, Spitsbergen, Elverhøi et al. (1983) 20 − 500

Norway

Kongsfjorden, Spitsbergen, Svendsen et al. (2002) < 20 − 340Norway

Kongsfjorden, Spitsbergen, Zaja̧czkowski (2008) 350 − 460Norway

Hornsund Fjord, Görlich et al. (1987) 20 − 1, 000Spitsbergen, Norway

Nordaustlandet tidewater Pfirman and 1 − 28ice cap, Svalbard Solheim (1989)

Kangerlussuaq Fjord, Chu et al. (2009) < 5− > 80Greenland

Disko Fjord, Greenland Gilbert et al. (2002) 40 − 100Blue Fjord, Alaska Hoskin et al. (1978) 20 − 300MacBride Glacier, Alaska Cowan et al. (1988), 500 − 2, 000

Cowan and

Powell (1990)

Hubbard Glacier, Alaska Curran et al. (2004) 10 − 35Coronation Fjord, Syvitski (1989) 10− > 120

Baffin Island


Magellan (Fabiano et al. 1999). The observed range in Gal-legos Sound is more similar to the concentrations observedin the ice-proximal environment of an Antarctic fjords,with exception of Admiralty Bay (King George, Antarctica)(Sicinski 2004), where higher SST concentrations have beenobserved (Table 1).

In general, TSS concentrations in Gallegos Sound aremuch lower than those of glacial fjords of the NorthernHemisphere. For instance, in Alaskan fjords, the TSS con-centrations are normally >100 mg L−1 but can exceed5,000 mg L−1 during rainy events (Cowan et al. 1988;Cowan and Powell 1990). More likely, this difference isbecause fjords from Alaska receive a sizable contribution ofmeltwater because of their maritime climate. On the con-trary, the Gallegos Sound is located in the dry site of theCordillera Darwin and is an inner fjord opened to otherbasin (e.g., Brooks Bay and Almirantazgo Sound). On theother hand, the regional topography seems to provide alocal microclimate that prevents ice melting at the samerate than that observed in glacial fjords from the NorthernHemisphere.

The surface plume described in a Greenland fjord hasTSS values greater than 80 mg L−1 (Chu et al. 2009). Sim-ilarly, Disko Fjord, situated west of Greenland, reached amagnitude of 43.8 mg L−1 (Gilbert et al. 2002). TSS con-centrations in Adventfjord (Spitsbergen) are found to varybetween 73 and 13 mg L−1 during summer and winter,respectively.

In this discussion, we must keep in mind that most ofsediment is lost close to the glacier, and TSS concentrationdecays exponentially with distance from glacier. Therefore,it is likely that TSS concentration was much higher in theproximal zone, which was not surveyed in this study. Inthis sense, flocculation is another factor to consider andthat as been shown to affect sediment flux in the proximalzone of glacial fjords (Curran et al. 2004; Zaja̧czkowski andWłodarska-Kowalczuk 2007).

We did not observe TSS maxima at intermediate nor deeplayers that could show the presence of hyperpycnal plumeslike those described by Zaja̧czkowski and Włodarska-Kowalczuk (2007) in Adventfjorden, a glacier-fed riverestuary. As the maximum inclination of the prodelta slopeis 1.5◦, the occurrence of gravity and turbidiy currentsdoes no seem to be a common component in this fjordin contrast to fjords in the northern Hemisphere. (Cowanet al. 1988; Cowan and Powell 1990; Zaja̧czkowski andWłodarska-Kowalczuk 2007).

The TSS flux in the Gallegos Sound showed a consistentseasonal pattern, with the lowest values recorded in autumnand winter and the highest values recorded in spring andsummer. This pattern may be explained by the absence ofthe occurrence of melting during that period and the scarcityof rain during fall-winter. In Gallegos Sound, the mean

value of TSS flux was 413 mg m−2 day−1. Similar shortduration particle fluxes were detected in Disko Fjord duringthe summer period, with fluctuations between 430 and 10mg m−2 day−1 (Gilbert et al. 2002). However, in the mud-flat of Adventfjorden, the mean TSS flux values were threeorders of magnitude (up to 153 g m−2 day−1) greater thanthose reported here, showing that comparisons must takeinto account different processes in glaciated and outwashfjords (Zaja̧czkowski 2008). On the other hand, the TSS fluxis highly variable within the water column and the result isaffected by factors such as the mooring depth of the trap,time of deployment, and currents. Therefore, these aspectsmust also be taken into account when comparing differentareas. For example, Isla et al. (2006) found that inter-annualdifferences in Antarctic particle flows can be up to threetimes larger than reported in the same place a decade ago byBathmann et al. (1991).

In terms of vertical fluxes of particulate organic carbon,our study showed that the values are nearly twice as high inspring as in winter (15.1 vs 6.4 mg C m−2 day−1) and washighest in fall, with a magnitude of 22.8 mg C m−2 day−1.Although one order of magnitude is lower, this pattern issimilar to that observed by González et al. (2011) in AysenFjord, where fluxes of 266 and 168 mg C m−2 day−1 weremeasured in spring and winter, respectively (Table 2). Thesevalues are lower than those observed in Norway and Arcticfjords (Table 2) and can be explained by the combinationof high concentration of TSS and the low concentrations ofnutrients (Vásquez 2011).

The effect of rotation on the plume circulation duringspring-summer can be estimated by the internal Rossbyradius of deformation (deYoung and Hay 1987):

r = (g′ h)1/2 /f (1)where g′ is the reduced gravity (g (ρ2 − ρ1)/ρ2), h is thethickness of the upper brackish layer, f the Coriolis param-eter (1.2×10−4 s−1 at the latitude of Gallegos Sound), g isthe gravitational acceleration (9.81 m s−2), ρ1 is the density

Table 2 Comparison of organic carbon flux found in Gallegos Soundwith other fjords from Chile and the northern hemisphere

Location Reference Flux

(mg m−2 day−1)

Gallegos Sound, Chile This study 3 − 22.8Reloncavi Fjord, Chile González et al. (2010) 334 − 725Aysen Fjord, Chile González et al. (2011) 168 − 266Baltic Sea Smetacek et al. (1978) 99

Bjonafiorden, Norway González et al. (1994) 58

Skagerrak Fjord, Maar et al. (2004) 168 − 708Spitsbergen


of the upper layer (1,022 and 1,020 kg m−3 during springand summer, respectively), and ρ2 is the density of the lowerlayer (1,029 kg m−3 during spring-summer). By using thedensity profiles from the CTD data, we obtained h = 5 mand a value of r ∼ 4.8 − 5.5 km, which is larger than thefjord width (between 1.2 and 3.4 km). Therefore, we assumethe rotational effects are negligible.

It is worth mentioning that other external forcing, likewind mixing and precipitation, has not been consideredin this analysis. The predominant winds in this region arewesterly year round, and precipitation has a low variability(Holmlund and Fuenzalida 1995). Therefore, we can expectthat their influence would be secondary in comparison withthe air temperature. However, the influence of tides is anaspect that should necessarily be included in future studies.It is probable that resuspension occurs in the tidal flat andthat should be part of future research. In this sense, this fjordmust be in the process from a glacial to non-glaciated oroutwash fjord, as asserted by Zaja̧czkowski (2008).

In summary, the water column of Gallegos Sound rep-resents an under-studied proglacial environment within theconspicuous and highly heterogeneous Chilean fjords andchannels ecosystem. The absence of previous data for thestudy area determines the scope of our research. Therefore,our data represents an important advance toward the under-standing of the temporal and spatial dynamics of brackishwater proglacial environment adjacent to the Cordillera Dar-win Ice Field. Finally, in the context of climate change,our data will be extremely useful as a baseline for futuremonitoring studies.

Acknowledgments This research was carried out through the “Pat-terns in benthic communities off the Marinelli glacier (Darwin IceField, South Chile: Response to glacier retreat?” National Fund forScience and Technology (FONDECYT 11090208)—Government ofChile. We appreciate the constructive comments and suggestions of Dr.Vera Novak and Dr. Prasanth Divakaran as they significantly helped toimprove this manuscript. We thank the anonymous reviewers for theirvaluable comments.

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Influence of a Glacier Melting Cycle on the Seasonal Hydrographic Conditions and Sediment Flux in a Subantarctic Glacial FjordAbstractIntroductionMaterials and MethodsStudy AreaSamplingLaboratory Analysis

ResultsDiscussionAcknowledgmentsReferences

influence of a glacier melting cycle on the seasonal...

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