209 A testimony of detachment of an inland lake from marine influence during the mid-Holocene... Limnological Review (2013) 13, 4: 209-214 DOI 10.2478/limre-2013-0023 Introduction Diatoms are one othe ew biological compo- nents which thrive across a large spectrum oenvi- ronments, rom terrestrial environments, viz.rivers, lakes, wetlands, to coastal lagoons, estuaries, and in near-shore to open ocean environments. Teir valves are made osilica, and are preserved in depositional environments and ossilised. For these diatoms be- come a potential tool or characterising the palaeo- depositional environments and hence palaeoclimate. Tereore, diatoms are well used to decipher the pal- aeoenvironments and palaeoclimates (Stoermer and Smol 1999). Proper interpretation odiatom assem- blages depends on their individual ecological incli- nation. From surace sediment samples the modern diatom distribution al pattern and interaction with the environment can be determined. Understanding the distribution and abundance odiatoms in subsurace samples, and their interaction with the past environ- ment, and thereore, the inerence drawn to decipher the palaeoclimatic condition are the primary objec- tives othe present study. Te instrumental record ochange in climatic components is unable to show the trend how the cli- mate system operated on time scales in terms othou- sands oyears (Overpeck 1995). As An tarctica plays a pivotal role in the global cli mate system, we need to ac- cess reliable records onatural climate change patterns rom this region, on different time scales, to determine whether present climate changes are natural or a result oanthropogenic orcing. Palaeolimnological records are one othe best sources to determine the natural climatic change in Antarctica. Previously, palaeolim- nological records rom continental and marine parts oEast Antarctica were used several times to address the issue onatural changes in the Antarctic climate (e.g., Vestold Hills: Roberts and McMinn 1999a,b; Roberts et al. 1999, 2001a; Larsemann Hills: Hodgson et al. 2001a; V erleyen et a l. 2004; Bunger Hills: Melles et al.1997; Verkulich et al. 2002; Rauer Islands: Hodgson et al. 2001b; and Maritime and subantarctic islands: A testimony odetachment oan inl and lake rom marine influence during the mid-Holocene in the Vest old Hills region, East Antarctica Abhijit Mazumder 1 , Pawan Govil 1 , Shalini Sharma 2 , Rasik Ravindra 3 , Neloy Khare 3 , Subodh Kumar Chaturvedi 4 1 Birbal Sahni Institute oPalaeobotany, 53 University Road, Lucknow – 226 007, India, e-mail: [email protected](corresponding author) 2 Geology Department, Banaras Hindu University, Varanasi – 221 005, U.P., India 3 Ministry oEarth Sciences, Block 12, CGO Complex, Lodhi Road, New Delhi – 110 003, India 4 Department oDisaster Management & CARISM, SASRA University, hanjavur – 613 402, amil Nadu, India Abstract:A 47 cm long sediment core collected rom an inland lake othe Vestold Hills, East Antarctica has been examined to reconstruct the palaeolacustrine environmental changes. Te core shows dates at two core intervals o18-19 cm and 28-29 cm as 5050±98 yrs BP and 5560±96 yrs BP , respectively . Te core exhibits a good amount odiatom population throughout the length. Prior to 5560±96 yrs BP , the core shows high abundance odiatom population (>10×10 7 g –1 ) along with sufficient salt crystal, which indicates the connection othis lake w ith the marine environment. Fr om 5560±96 yrs BP to 5050±98 yrs BP the total number diatoms decreased substantially along with the decrease in salt crystal, which indicates the withdrawal othe marine influence rom the lake during that period. From 5050±98 yrs BP to Recent, the low number odiatoms and the rare occurrence osalt crystal suggest that the lake remained mostly detached rom the sea during the last 5000 yrs. Key words:Vestold Hills, lake sediment core, diatom, salt crystal, connection with sea Unauthenticated | 125 22 55 2 Download Date | 3/8/14 3:34 PM
209A testimony of detachment of an inland lake from marine influence during the mid-Holocene...Limnological Review (2013) 13, 4: 209-214DOI 10.2478/limre-2013-0023
Introduction
Diatoms are one o the ew biological compo-nents which thrive across a large spectrum o envi-ronments, rom terrestrial environments, viz. rivers,lakes, wetlands, to coastal lagoons, estuaries, and innear-shore to open ocean environments. Teir valvesare made o silica, and are preserved in depositionalenvironments and ossilised. For these diatoms be-come a potential tool or characterising the palaeo-
depositional environments and hence palaeoclimate.Tereore, diatoms are well used to decipher the pal-aeoenvironments and palaeoclimates (Stoermer andSmol 1999). Proper interpretation o diatom assem-blages depends on their individual ecological incli-nation. From surace sediment samples the moderndiatom distributional pattern and interaction with theenvironment can be determined. Understanding thedistribution and abundance o diatoms in subsuracesamples, and their interaction with the past environ-ment, and thereore, the inerence drawn to decipher
the palaeoclimatic condition are the primary objec-tives o the present study.
Te instrumental record o change in climaticcomponents is unable to show the trend how the cli-mate system operated on time scales in terms o thou-sands o years (Overpeck 1995). As Antarctica plays apivotal role in the global climate system, we need to ac-cess reliable records o natural climate change patternsrom this region, on different time scales, to determinewhether present climate changes are natural or a result
o anthropogenic orcing. Palaeolimnological recordsare one o the best sources to determine the naturalclimatic change in Antarctica. Previously, palaeolim-nological records rom continental and marine partso East Antarctica were used several times to addressthe issue o natural changes in the Antarctic climate(e.g., Vestold Hills: Roberts and McMinn 1999a,b;Roberts et al. 1999, 2001a; Larsemann Hills: Hodgsonet al. 2001a; Verleyen et al. 2004; Bunger Hills: Melles etal. 1997; Verkulich et al. 2002; Rauer Islands: Hodgsonet al. 2001b; and Maritime and subantarctic islands:
A testimony o detachment o an inland lake rom marine influenceduring the mid-Holocene in the Vestold Hills region, East Antarctica
1Birbal Sahni Institute o Palaeobotany, 53 University Road, Lucknow – 226 007, India, e-mail: [email protected] (corresponding author)
2Geology Department, Banaras Hindu University, Varanasi – 221 005, U.P., India3Ministry o Earth Sciences, Block 12, CGO Complex, Lodhi Road, New Delhi – 110 003, India
4Department o Disaster Management & CARISM, SASRA University, hanjavur – 613 402, amil Nadu, India
Abstract: A 47 cm long sediment core collected rom an inland lake o the Vestold Hills, East Antarctica has been examined toreconstruct the palaeolacustrine environmental changes. Te core shows dates at two core intervals o 18-19 cm and 28-29 cm as5050±98 yrs BP and 5560±96 yrs BP, respectively. Te core exhibits a good amount o diatom population throughout the length. Priorto 5560±96 yrs BP, the core shows high abundance o diatom population (>10×107 g–1) along with sufficient salt crystal, which indicatesthe connection o this lake with the marine environment. From 5560±96 yrs BP to 5050±98 yrs BP the total number diatoms decreasedsubstantially along with the decrease in salt crystal, which indicates the withdrawal o the marine influence rom the lake during thatperiod. From 5050±98 yrs BP to Recent, the low number o diatoms and the rare occurrence o salt crystal suggest that the lake remainedmostly detached rom the sea during the last 5000 yrs.
Key words: Vestold Hills, lake sediment core, diatom, salt crystal, connection with sea
Jones et al. 2000). Te lack o sufficient palaeoclimatedata rom the Vestold Hills, East Antarctica needs tobe made up or here to bridge the gaps in the palaeo-climatic histories o the major limnological regions othe East Antarctica to establish the continuation o theHolocene climate over the East Antarctic region.
Physical, chemical and biological changes inlakes correspond to climatic changes and these signa-tures are recorded in lake sediments as different typeso proxy (Last and Smol 2001; Battarbee 2000). Tewater chemistry o an Antarctic lake is substantiallyrelated to local climate changes (Roberts et al. 2001).Variations in precipitation and evaporation balance ina catchment area change the concentration or dilutiono dissolved salts (Roberts et al. 2001). Tese changesare registered in different palaeolimnological proxies,
including diatom assemblage (Juggins et al. 1994), asdiatoms are one o the main biological components othe reshwater benthic algae in Antarctic standing lakewaters (Jones 1996). Moreover, diatoms in lake sedi-ments can be utilized to deal with ecological issuesand causes or environmental change on varying timescales (Jones 1996). Tus, the diatom rom subsuracesamples o Antarctic lakes exhibits the local climatichistory o the lake basin in any study area.
Study Area
Te Vestold Hills, Princess Elizabeth Land,orm one o a number o rocky, ice-ree ‘oases’ whichoccur at intervals along the margin o the East Antarc-tic ice-sheet. Following the retreat o the continentalice-sheet rom the region approximately 8000 yrs B.P.(Adamson and Pickard 1986), isostatic rebound ledto the gradual emergence o the land rom beneaththe encroaching ocean. As a result, seawater becametrapped in many o the depressions which occuracross the Hills (McLeod 1964; Burton 1981). oday,some o these trapped and now highly evaporated wa-
ter bodies orm hypersaline lakes, while flushing outo the relict seawater by glacial meltwaters in othercases has led to the ormation o lakes o very low sa-linity (Pickard et al. 1986).
Te Vestold Hills, covering an area o 410 km2 (Pickard et al. 1986) are situated 157 m above sea leveland on the eastern edge o Prydz Bay on the coast oPrincess Elizabeth Land, East Antarctica (68°25’ to68°40’S; 77°50’ to 78°35’E). Tis area is flanked by theEast Antarctic Ice Sheet in the east and by the SørsdalGlacier, an outlet glacier o the ice sheet in the south.
Te region is the third largest ice-ree region in Ant-arctica. Tis region is characterized by long peninsu-las, ords and low hills. Tis area also truncated bymany raised beaches, saline and reshwater lakes.
Prydz Bay is typified by a coastal summer seasurace temperature rom –1.1 to –0.6°C (Kerry et al.1987), but the temperature increases as high as 1.39°Cnear the Vestold Hills (Gibson 1998). Te VestoldHills display a polar lowland periglacial climate witha mean annual temperature o -10.2°C (Schwerdteger1970), which is, on average, warmer than Antarctic sta-tions o similar latitude (Burton and Campbell 1980).Although no precipitation data are available, rainall isvery rare, and total precipitation is light (<250 mm peryear). Melting o snow and ice is restricted to the shortsummer (December to February). Te strong diurnal
component o the melt activity usually ceases between9 pm and 10 am, when air temperatures are below orclose to 0°C and the sun has a low angle o incidence.Because the time o melting is limited, both the rateso ice melt and sediment accumulation are slow. Meltwater rom ice and snow appears to be the primarycontrol on type and rate o depositional processes.
Materials and Method
A core with the length o 47 cm collected rom an
Antarctic lake (Lat. 68°37’26.7”S; Long. 77°58’14.6”E)in the Vestold Hills area during 24th Indian AntarcticExpedition, was selected or this study (Fig. 1). Coresediments were sub-sampled at intervals o 1 cm.
Te methodology or processing the samplesand making the diatom slides was ollowed as de-scribed by Setty (1966). Te sample was dried over-night at 120°C. Te ollowing day it was treated with15% hydrogen peroxide and boiled or 20 minutes ina hot water bath. Afer boiling, the sample was allowedto stand overnight afer adding distilled water. Tenext day the supernatant liquid was decanted and the
residue was boiled with 25% hydrochloric acid or 15minutes. Afer cooling down, the distilled water wasadded and it was kept overnight. Te next day, aferdecanting the supernatant, 25% nitric acid was addedto the residue and it was kept overnight afer addingdistilled water. Te ollowing day the supernatant wasdecanted and distilled water was added to the resi-due, which was kept overnight. Decanting and addingwater thereafer were repeated or three consecutivedays. On the last day, afer decanting the supernatant,the residue was ready to make slides. Te residue was
211A testimony of detachment of an inland lake from marine influence during the mid-Holocene...
stirred well and the suspension was deposited evenlyon the cover glass with the use o a pipette and thenthe cover glass was allowed to dry. A drop o Canadabalsam mounting medium was put on the sample overthe cover glass and the cover glass was warmed up to250°C, and covered cautiously with a standard glassslide. Afer cooling the slide was ready or examina-tion under the microscope.
Diatoms were enumerated until a minimum 300valves had been counted. Estimates o diatom con-
centration were calculated using the total number ovalves counted over a specific area o microscope sliderom a known aliquot o sample as ollows (modifiedrom Battarbee 1973):
otal valves = valves counted × area o coverslip/ area counted × sample volume / aliquot volume.
Concentrations are presented as the number odiatom valves per gram o sediment afer recalculatingwith the dry weight o the initial sample used. Teseprovide the relative concentrations between samplesin this study.
Results and Discussion
In the present core, the number o diatoms in1 gram o dry weight varies with a minimum valueo 18×106 g–1 at the core length o 21-22 cm intervaland a maximum value o 13×107 g–1 at 39-40 cm in-terval (Fig. 2). Te number o diatoms shows a drasticchange rom 18×106 g–1 to 13×107 g–1 with the inter-vals o 21-22 cm and 27-28 cm. Within the core inter-val 27-40 cm the total diatom number remains morethan 10×107 g–1, while the above and below intervals
Fig. 2. Plot o total number o diatoms (solid line) and qualitativeamount o the presence o salt crystal (dashed line) along the corelength
show a smaller number o diatoms. A total number o13 species o diatom were identified rom the entirecore; namely Achnanthes aff. Achnanthes groenlandica,
A. taylorensis, Amphora ovalis, Diploneis crabro, D.smithii, Fragilariopsis curta, F. ritscheri, Navicula direc-ta, Navicula sp., Paralia sulcata, Talassiosira anguste-lineata and rachyneis aspera.
As regards the presence o salt, the core interval0-23 cm shows the absence or very rare presence osalt crystal. From 23 cm up to the total core lengththe presence o sufficient salt crystals is shown in thesample.
Radiocarbon dating o the samples rom 18-19cm and 28-29 cm intervals shows the age o the depo-sition as 5050±98 yrs BP and 5560±96 yrs BP, respec-tively. Te higher abundance o diatoms (>10×107 g–1)
and the presence o sufficient salt crystals within thisinterval suggest a change in the environmental set upduring this period.
Antarctic lakes have long been known to besensitive recorders o climate change (e.g., Björck etal. 1991; Wasell and Håkansson 1992; Jones et al. 1993;Roberts and McMinn 1998, 1999b). In the absence oinstrumental records, these sediments provide well-preserved proxies or changes in climate on timescales rom thousands to tens o years. Climate changeaffects the physical, chemical and biological changes
in a lake environment, which leave their signature onlake sediments (Last and Smol 2001; Battarbee 2000).Tese changes are recorded in the orm o palaeoli-mnological proxies, including the diatom assemblages(Juggins et al. 1994). Previously it was reported thatlesser concentrations o diatoms and their assemblag-es strongly affected by dissolution were encounteredin the Weddell Basin (Zielinski and Gersonde 1997).In spite o changes in the diatom assemblages prior totheir incorporation into the sediment record, the bio-geographic distribution and the abundance pattern omost o the studied diatom species show a very close
relationship with the surace water temperature. Teserelationships can be used to decipher past surace wa-ter temperatures based on statistical analyses o thediatom assemblages or on simple relations o speciesoccurrences in the geological record. Another closelink occurs between the distribution o sea ice andsea ice related diatoms (Zielinski and Gersonde 1997).It was accounted that the subarctic North Pacific andmarginal seas had much higher values o diatom cellsthan the subtropical-temperate waters to the south(Marumo 1967; Aizawa et al. 2005). It was ound that
inshore waters off Vancouver Island have the poten-tial to support larger phytoplankton populations dueto higher nutrient values than offshore (Whitney andFreeland 1999). Changes in concentration o diatomscan also be used to record the changes in diatomproductivity and hence overall primary productiv-ity (Batterbee 1973, 1978; Bradbury and Waddington1973; Anderson 1989). emperature changes, varia-tion in sea ice duration, length o the growing seasonand light intensity may control the size o the diatompopulation (Crosta 2009).
In the present study area, the core showing asudden decrease in diatom population and salt con-tent during ~5,000-5,500 yrs BP indicates the detach-ment o the lake rom marine input around this time.In Ace Lake, the diatom species shows a considerable
decrease in number during 5,500 to 3,800 yrs BP timespan (Fulord-Smith and Sikes 1996). Bird et al. (1991)established the palaeomarine connection o threelakes, namely Highway Lake, Organic Lake and AceLake. According to them, the detachment o these nowinland lakes rom the sea happened within 2700 and5400 yrs B.P. (or Highway Lake it was 4600 yrs B.P.,or Organic Lake it was 2700 yrs B.P. and or Ace Lakeit was 5400 yrs B.P.).
Te early and early-mid-Holocene (~10,500 to~4000 yrs BP) is characterized by the Antarctic glacial
retreat (Goodwin 1998). In the southern Windmill Is-lands and Vestold Hills, the early and early-mid-Ho-locene show a stage o glacial retreat with relativelycool temperatures and low bioproductivity (Cremeret al. 2003; Cromer et al. 2005). With the decrease inthe marine influence, minimization o aunal assem-blages occurred as biota depending on the immigra-tion o larval stages into the basin could no longercontinue their populations. A similar type o decreasein biodiversity has been reported rom marine lakesormed by isostatic uplif in recent times (Ström andKlaveness 2003), and other seasonally isolated marine
basins in the Vestold Hills (Bayly 1986; Eslake et al.1991). Te lake rom the present study area shows thedetachment o the lake rom marine influence, whichis probably linked with the glacial retreat in this areaduring ~5,000-5,500 yrs BP.
Conclusion
Te presence o abundant diatoms (>10×107 g–1) along with sufficient salt crystal at the bottom othe core suggests the connection o the lake with the
213A testimony of detachment of an inland lake from marine influence during the mid-Holocene...
sea beore 5,500 yrs BP. During 5,500 to 5,000 yrs BP,the decrease in salt crystal and diatom population in-dicates the detachment o the lake rom a marine con-nection at that time. Aferwards the lake continued itsstatus o being disconnected rom continuous marineconnection.
Acknowledgements
Te authors would like to express their thanksto Director, National Centre or Antarctic and OceanResearch, Goa, India and Director, Birbal Sahni Insti-tute o Palaeobotany, Lucknow, India.
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