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SERUMs NATURGEOGRAFI <7* v
Lake sediments around the
Antarctic Peninsula
archives of climatic and environmental changes
Lake sediments aroundthe
Antarctic Peninsula
archives of climatic and environmental changes
Rolf Zale
Lake sediments around the Antarctic Peninsulaarchives of climatic and environmental changes
Rolf Zale
Akademisk avhandlingSom för avläggande av filosofie doktorsexamen vid Umeå
Universitet kommer att offentligt försvaras i hörsal 1, Skogshögskolan, SLU, torsdagen den 27 maj, kl. 10.00.
AbstractLakes and lake sediments from four areas around the Antarctic Peninsula are described.The concentrations of trace metals in sediment are found to
be a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environment.A tephrochronology based on Deception Island tephra is developed, and used to cross date sediments from different lakes in order to overcome the radiocarbon dating problem of the area.The fluctuating concentrations of copper and phosphorus from penguin guano in the sediment of Lake Boeckella are used as a proxy for the penguin inpact on the sediment, and the size of the penguin rookery on the shores of the lake. Anthropogenic activities in the area, as well as climatic changes are discussed in relation to the rookery size.A radiocarbon dating model developed for the sediment of
Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. The model is used to achieve more accurate radiocarbon dates of the Lake Boeckella sediment. This model, or a modified version, may contribute to a higher dating accuracy and a better understanding of the dating problems in Antarctica.Deglaciation dates, as well as data on the climatic and environmental history of Byers Peninsula on Livingston Island, South Shetland Islands, of Hope Bay, Antarctic Peninsula and of Hidden Lake area, James Ross Island are given.Key words: Lake sediments, Antarctic Peninsula, radiocarbon dating, climatic and environmental changes, sediment chemistry.Zale, Rolf 1993: Lake sediments around the Antarctic peninsula - archives of climatic and environmental changes. GERUM Naturgeografi nr 17, Department of Physical Geography, University of Umeå, 901 87 Umeå, Sweden. 104 pp.
ISBN 91-7174-790-7 ISSN 0282-5597
Lake sediments around the
Antarctic Peninsula
archives of climatic and environmental changes
Rolf Zale
Doctoral dissertation at Umeå University ISBN 91-7174-790-7
AbstractLakes and lake sediments from four areas around the Antarctic Peninsula are described.The concentrations of trace metals in sediment are found to
be a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environment.A tephrochronology based on Deception Island tephra is developed, and used to cross date sediments from different lakes in order to overcome the radiocarbon dating problem of the area.The fluctuating concentrations of copper and phosphorus from penguin guano in the sediment of Lake Eoeckella are used as a proxy for the penguin inpact on the sediment, and the size of the penguin rookery on the shores of the lake. Anthropogenic activities in the area, as well as climatic changes are discussed in relation to the rookery size.A radiocarbon dating model developed for the sediment of
Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. The model is used to achieve more accurate radiocarbon dates of the Lake Boeckella sediment. This model, or a modified version, may contribute to a higher dating accuracy and a better understanding of the dating problems in Antarctica.Deglaciation dates, as well as data on the climatic and
environmental history of Byers Peninsula on Livingston Island, South Shetland Islands, of Hope Bay, Antarctic Peninsula and of Hidden Lake area, James Ross Island are given.
This research was conducted under the the Swedish Antarctic Research Programme, SWEDARP.It was financed by grants from the Swedish Natural Research Council, Svenska Sällskapet för Antropologi och Geografi, the Kempe Foundations, Gyllenstiernska Krapperupsstiftelsen, Hierta-Retzius Fonder and Stiftelsen Lars Hiertas Minne.
Rolf ZaleDepartment of Physical Geography University of Umeå 901 87 Umeå Sweden.
CONTENTS
INTRODUCTIONpage
1METHODS 2
CONCLUSIONS 5PERSPECTIVE FOR FUTURE RESEARCH 6SUMMARY OF PAPERS 7REFERENCES 19
Papers included in the thesis:1 Zale, R. & Karle'n, W. 1989: Lake sediment
cores from the Antarctic Peninsula and surrounding islands. Geografiska Annaler 71 A (3-4):221-220.
2 Björck, S., Håkansson, H., Zale, R., Karle'n, W., Sc Liedberg Jönsson, B. 1991a: A late Holocene lake sediment sequence from Livingston Island, South Shetland Islands, with palaeoclimatic implications. Antarctic Science 3(1): 61- 7 2 .
3 Björck, S., Sandgren, P. Sc Zale, R. 1991b: Late Holocene tephrochronology of the northern Antarctic Peninsula. Quaternary Reseach 36:322-328.
4 Zale R., 1991a: Chemical changes in thesediment of "Skua Lake", Horseshoe Island, Antarctic Peninsula, r e l ated to a marine/limnic transition. Presented at the IGCP-274 symposium "Quaternary shorelines: evolution, processes and future changes" in La Plata, Argentina November 19-20, 1990.Submitted to Antarctic Science.
5 Zale, R. 1991b: The radiocarbon correction factor in the sediment of Lake Boeckella, Antarctic Peninsula. Submitted to Radiocarbon .
6 Zale. R. 1993: The changes in size of theHope Bay Adélie penguin rookery as inferred from the Lake Boeckella sediment. Submitted to Ecography.
INTRODUCTIONThis deals with Mid to Late Holocene lake sediments as archives of climatic and environmental changes around the Northern Antarctic Peninsula.The fieldwork was conducted during the ANT VI expedition
with R/V Polarstern in 1987-88 and during the SV7EDA.RP expedition with M/S Stena Arctica in 1988-89. All work was conducted under the Swedish Antarctic Research Programme, SWEDARP.The thesis is based on six papers;1 Zale, R. & Karle'n, W. 1989: Lake sediment cores from
the Antarctic Peninsula and surrounding islands. Geografiska Annaler 71 A (3-4):221-220.
2 Björck, S., Håkansson, H., Zale, R., Karle'n, W., St Liedberg Jönsson, B. 1991a: A late Holocene lake sediment sequence from Livingston Island, South Shetland Islands, with palaeoclimatic implications. Antarctic Science 3(l):61-72.
3 Björck, S., Sandgren, P. St Zale, R. 1991b: Late Holocene tephrochronology of the northern Antarctic Peninsula. Quaternary Reseach 36:322-328.
4 Zale R., 1991a: Chemical changes in the sediment of"Skua Lake", Horseshoe Island, Antarctic Peninsula, related to a marine/limnic transition. Presented at the IGCP-274 symposium "Quaternary shorelines: evolution, processes and future changes" in La Plata, Argentina November 19-20, 1990. Submitted to Antarctic Science.
5 Zale, R. 1991b: The radiocarbon correction factor in the sediment of Lake Boeckella, Antarctic Peninsula. Submitted to Radiocarbon.
6 Zale. R. 1993: The changes in size of the Hope BayAdêlie penguin rookery as inferred from the Lake Boeckella sediment. Submitted to Ecography.
These papers are referred to by the arabic numerals used aboveBACKGROUNDAntarctica's role in the global climate is recognised as very important, but only the broadest outlines are known. If the past climate of Antarctica was better known it would be possible to correlate Antarctica's climatic history to that of the rest of the world, which would increase our understanding of Antarctica's role in climatic changes.One of the research fields included in the Swedish Antarctic Research Programme, SWEDARP, was therefore the Holocene climatic- and environmental history of the Antarctic Peninsula .
1
Lake sediments are generally useful archives of the environmental and climatological changes in the surrounding area. The sediment consists of material washed down into the lake as well as detritus from primary production in the lake, and the sediment is thus an indication of both direct and indirect environmental changes. From analyses of sediment cores it is possible to get a fairly detailed picture of environmental and climatological changes in the area during thousands of years.The aim of this study was; to gain information about the
nature of the lake sediments in the area, to use standard analyses and methods the lake sediments to test these methods in an environment where they have hardly been used before, to obtain new data on the climatological and environmental history of the Antarctic Peninsula and to develops a method to overcome the generally recognized radiocarbon dating problem in this area.Three lakes were cored during the R/V Polarstern Expedition
ANT VI in late 1987 and eight were cored during the 1988/1989 SWEDARP expedition with M/S Stena Arctica (Fig. 1). A number of other geological samples were taken and other analyses were performed as well, all in order to make the available picture of the climatic and environmental changes as complete as possible.Most of the analyses and methods used in this study are standard procedures in this kind of sedimentology e.g., lithostratigraphical analysis, radiocarbon dating, magnetic analysis, sediment chemistry, microfossil analysis. In addition, a new radiocarbon dating model was developed to achieve higher accuracy of radiocarbon dating.PREVIOUS WORKTatur and del Valle (1986) described the sediment in three lakes on Fildes Peninsula, King George Island, one lake on Potter Peninsula also on King George Island and one lake in Hope Bay. They also presented radiocarbon dates from these lakes (Tatur and del Valle 1989). Mäusbacher et al. (1989) studied and dated sediments from three lakes on Fildes Peninsula, King George Island. Matthies et al. (1990) studied and dated eighteen ash-layers from five sediment cores from King George Island in order to establish a correlation between tephrostratigraphy and -chronology. Björck et al. (1991a) discuss the general radiocarbon dating problems of the Antarctic Peninsula, and the bulk of their examples are samples from the lakes cored under the SWEDARP program me. Apart from this, together with the papers in this thesis, little has been published on lake sediments from the Antarctic Peninsula area. However, numerous papers have been published on limnological aspects of the lakes in the area (Hansson 1989 and references therein).METHODSCORINGAll of the lake sediments analysed in this thesis were cored either with a Russian peat corer (diameter 5 or 10 cm) or with a Livingstone-type corer (diameter 9 cm) that were manouvered from the surface with wires. The Livingstone corer has some advantages over the Russian peat corer: it
2
6 Q*Elephant Island
King George Island
Livingston Island
d Deception Island
f e *Hope Bay
Snow Island James Ross Island
O 1OOkmi
Shelf iccHorseshoe Island #
Marguerite Bay
CSouth A m er ic a
South G eorg ia Q
Ale xande
Island
George V) Sound
7 0A n ta r c t ic a
Fig. 1. Map of the Antarctic Peninsula with surrounding islands. Sampled lakes are marked with dots.can be used at greater depths and yields a continuous core, with more material for each cm penetrated. The disadvantages are that it takes more skill to use and it is heavier than most Russian peat corers. Most of the lakes were cored from a small rubber boat, but some were cored from the ice.The surface of all of the cores was cleaned by scraping to
avoid contamination by sediment smeared onto the core surface.
3
ORGANIC CONTENT AND WATER CONTENTEach cm of all the cores was analysed for organic content by loss on ignition (LOI) (one hour at 550 degrees centigrade). A few cores were analysed for water content for each cm of the core.X-RAY PHOTOSThe sediment of Lake Boeckella was x-rayed to reveal structures otherwise invisible. A number of troughs, 2*2*20 cm large, were pressed down into the core, parallel to the longitudinal axis of the core, and covering its length. The troughs were either pressed down edge to edge or with a 50 % overlap, depending on the core. The sediment was then x- rayed without being taken out of the plasic troughs. A tapered aluminum wedge was placed on the photographic film as an exposure reference. The samples were exposed for eight minutes using 35kV.RADIOCARBON DATINGMost of the radiocarbon datings have been performed with conventional techniques by Laboratoriet för Isotopgeologi, Stockholm or the Radiocarbon Dating laboratory in Lund. A few very small samples, mainly from Midge Lake, were dated by AMS technique by the Svedberg Laboratory in Uppsala.RADIOCARBON DATING MODELThe sediment of lake Boeckella receives/received carbon from 4 main sources, from the bedrock surrounding/ground, from the penguin guano, from dissolved CO2 in glacial meltwa-ter, and from CO2 in the air.A mathematical model that used the apparent age and amount of carbon from the different sources and calculated the "true" radiocarbon age was constructed.CHEMICAL ANALYSESSediment cores from most of the lakes were sampled for chemical analyses. In most cases, only one- or two-cm layers were analysed, but in Lake Boeckella, samples with the same thickness as the dated samples were used. This means that some samples span c. 20 cm of the core.The chemical analyses form the basis of Papers 4 and 5, and
to some extent Paper 6. For a more extensive description of the analyses, reference should be made to the papers in question.All of the chemical analyses were performed by Svensk Grundämnes Analys AB (SGAB), formerly Sveriges Geologiska AB, in Luleå.Samples from the Lake Boeckella sediment cores and from
sediment cores from the six other lakes were analysed with SGAB's routine "G-3" for Ag, Al, As, Ba, Be, Ca, Cd, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Nb, Ni, P, Pb, Sc, Si, Sn, Sr, Ti, Zn, Zr, V, W and Y. The samples were leached with a mixture of HNO3 and HC1 in a heated, ultrasonic bath and filtered prior to analysis of the filtrate by ICP-AES. The samples were kept in a freezer prior to analysis.
4
Eight samples from the Lake Boeckella sediment core were analysed by SGAB with their routine "M-l" for As, Ba, Co, Cr, Cu, Fe, La, Li, Mn, Mo, Ni, P, Pb, Sc, Sn, Sr, Zn, and V. The samples were leached with a 1:1 mixture of HNOg and water in sealed PTFE containers in a microwave oven prior to analysis by ICP-AES. The routine "M-l" corresponds to the discontinued routine "G-3" (SGAB pers. comm.)All of the sediment samples, except 11 from Lake Boeckella (the six dated samples and five other samples), were analysed by SGAB, using their routine "G-2n, for Al2Oo, CaO,
K20, MgO, MnO, Na20, ^2^5* S i O 2 , Ti02, Ba, Be, Co, Cr, Cu, La, Mo, Nb, Ni, Pb, Sc, Sn, Sr, V, W, Y, Yb, Zn and Zr. These samples were melted with LiB02 and then dissolved in HNO3 prior to analysis by ICP-AES.Water samples from the outflow and inflow of Lake Boeckella and the outflow of "Skua Lake" were collected in acid-rinsed glass containers and ultra pure HNO3 was added to preserve the samples. Analyses were performed by SGAB, using their routine "VI" for Al, As, B, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, La, Li, Mg, Mn, Mo, Na, Ni, P, Pb, S, Si, Sr, V and Zn. The water samples were filtered prior to analysis by ICP-AES.The penguin guano samples were kept in a freezer until
analysed by SGAB, using their "M3" routine for Al, As, Ba, C, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, Si, Sr, Ti, V and Zn. The samples were dried and then dissolved in HNO3 and HC1 in closed teflon vessels in a microwave oven prior to analysis by ICP-AES.Carbon was analysed in some samples where the organic
content expressed as LOI was not considered sufficiently accurate.Concentrations of all substances are expressed as per
centages or ppm of the dry weight, except water analyses which are expressed as mg/1 or ug/l.MAGNETIC ANALYSESMagnetic analyses were made every 2 cm along the cores from Midge Lake, "Chester Cone Lake", "Lake Åsa", Hidden Lake", Lake Boeckella Walker Point and on 10 bulk tephra samples from Deception Island. The magnetic remanence was measured on a spinner magnetometer, first after exposure of the sample to a high magnetic field of 0.7 T resulting in saturation magnetisation (SIRM), and subsequently after exposure to a low reversed field of 0.1 T. The S ratio ( S=0. l^,/0. 7t) and the mass specific high induced remanent magnetization (HIRM = (1-S)*SIRM/2) were calculated.CONCLUSIONSMETHODSThe concentration of trace metals in sediment is a useful tool in distinguishing between the different sedimentary phases during a transition from marine to limnic environments. In this case, i.e. "Skua Lake" on Horseshoe Island, cadmium, cobalt, chromium, strontium, zirconium, vanadium and to some extent arsenic were used.The tephrochronology developed, based on the Deception Island tephras, has been used to cross date lake sediments. Altogether 14 tephra horizons have been identified, from c. 5000 BP until recent times. The tephrochrono1ogy is
5
especially valuable in the Antarctic environment were it is often difficult to obtain accurate radiocarbon ages of all kinds of sediments.The radiocarbon dating model developed for the sediment of
Lake Boeckella showed that the radiocarbon correction factor in the sediment depends on the amount and apparent age of the penguin guano washed down into the lake, and the amount of particulate carbon from the watershed present in the sediment. Neither the supposedly "old" meltwater from the glaciers nor dissolved carbonates contributes significantly to the correction factor. This radiocarbon model, or a version modified for other sedimentary environments, may contribute to a higher dating accuracy and a better understanding of dating problems in Antarctica.CLIMATEHidden Lake on James Ross Island, that was deglaciated around 3900 BP or earlier, experienced a cold period that started c. 800 BP and still continues.Lake Boeckella, at the tip of the Antarctic Peninsula, was
deglaciated around 6300 BP and experienced a cold period that culminated around 4700 BP. The three moraines on Mount Flora dated by lichenometry might possibly be correlated with this period. A climatic deterioration that started around 800 BP can be detected in the Lake Boeckella sediment. The Adêlie penguin rookery on the shores of Lake Boeckella was established c. 5550 BP and penguins have been present ever since except for a short period around 5300 BP. The rookery started to grow rapidly between 1250 and 800 BP. This coincides with a period of cold climate in the whole region.Vega Island experienced a period with active glaciers a- round 10 2 35 BP.Byers Peninsula on Livingston Island became deglaciated in
c. 4800 BP. The area experienced a warm period between 3200 and 2700 BP when the summer climate, and possibly also the winter climate, were both significantly milder and more humid than today. The climate seems to have gradually changed since 2700 BP to today's conditions, with pulses of both warmer and colder conditions. The severest conditions for biological life seem to have been between 1500 and 500 BP. Since then, the conditions appear to have improved somewhat.The radiocarbon dating model suggests that the watermasses around the northern part of the Antarctic Peninsula have been stable since at least 5800 BP.The last millenium seems to be the only cold period to be
of regional importance as it can be traced all over the area; all other climatic fluctuations since deglaciation seem to be less widespread and only of local importance.
PERSPECTIVE FOR FUTURE RESEARCHLakes are scarce in Antarctica, and the possibility to get lake sediment cores are thus limited. It is therefore of prime importance to core and analyse lake sediments from as many areas as possible. This will provide us with data on the climatic and environmental history that otherwise would be very difficult to gather.The tephrochronology now established for the northern An
6
tarctic Peninsula will be useful both in the dating of, and in stratigraphical correlation between, lake sediments, marine sediments and glacial ice. It is important that the tephrochronology is extended both in areas covered and further back in time beyond its present limit of 5000 BP.By dating the bottommost sediment in a series of lakes
perpendicular to a glacier or inland ice margin, it will be possible to date glacier fluctuations and to establish their areal extent. This can only be done in a few areas like Byers Peninsula on Livingston Island where lakes are abundant .Radiocarbon dating in the Antarctic Peninsula area is very
difficult, as evident from the lack of correlation of, for example, deglaciation dates between different authors. A lot of time and effort will have to be spent on getting reliable radiocarbon dates and reliable correction factors. This is of utmost importance as most correlations between different areas depend on radiocarbon dates.
SUMMARY OF PAPERS
1 LAKE SEDIMENT CORES FROM THE ANTARCTIC PENINSULA AND SURROUNDING ISLANDS.
This paper was written in cooperation with Wibjörn Karle'n. The fieldwork, as well as the preparation of the paper, was shared by the authors.The aim of the work was to reconstruct the Holocene clima
tic fluctuation in the area.Sediment cores from Lake Boeckella near the tip of the An
tarctic Peninsula, and from Hidden Lake on James Ross Island (Fig. 1) were collected and the organic content was analysed and selected parts were radiocarbon dated (Fig. 2). Licheno- metry was used to separate and approximately date the moraines of the Mount Flora circue glacier in Hope Bay. Organic samples in association with moraines were radiocarbon dated. Hidden Lake was deglaciated 3900 years BP or earlier. The age vs. sediment depth curve indicates no significant reservoir effect, although a glacier is calving in the lake (Fig. 2). Rabassa (1983, 1987) dated the outer moraines of the Bahia Bonita drift on James Ross Island to between 4100 and 6375 BP (reservoir effect 1075 years, Barsch and Mäusbacher 1986), which is in line with the deglaciation date of 3900 BP of Hidden Lake.A sharp drop in organic content occurred c. 800 BP, indi
cating a climatic deterioration. This correlates both with the neoglacial, dated to 500 to 700 BP found on South Georgia by Sugden and Clapperton (1986) and the latest glacieradvance on James Ross Island, dated to 515 BP (reservoir effect 1075 years) by Rabassa (1983). A vertebrate bone, found in a large moraine on the northwestern shore of Hidden Lake gives a maximum age of 1215 BP (reservoir effect 1075 years) for the glacier advance, which agrees with the climatic deterioration around 800 BP.
7
10000-n
8000CLOD
St 11619
6000
4000
St 11621
St 117482000- St 11620
St 1 1746 ISt 11990
St 11747
100Sediment depth (cm )
200 300
Fig. 2. Age as a function of depth in the sediment. The dashed line represents the sediment from Hidden Lake and the solid line Lake Boeckella. The datings are marked with +/- one standard deviation in the middle of the bulk samples analysed. The accuracy of the "hump" on the Lake Boeckella curve may be discussed as it implies a very fast sedimentation rate between c. 150 and 210 cm (around 1600 BP). However, this is not out of the question as it coincides with a rise in loss on ignition from c. 20 % to C. 35 %, which implies a faster sedimentation rate. An alternative curve (dotted line) for this period is drawn for the possibility that the dating St 11620 is erroneous. This does not, however, alter the conclusion of this paper.
The age of the topmost sediment of Lake Boeckella is found to be c. 2100 radiocarbon years too old. This reservoir effect is due to the fact that the sediment contains penguin remains and guano from the nearby penguin rookery. The reservoir effect is discussed and it is probable that it has not been constant through time.Hope Bay was ice-free at least around 8680 BP (Fig. 2) and faced a climatic deterioration around 5000 BP. Since then the grew climate warmer until 1200 to 500 BP, after which a
8
slightly colder period started. The climatic deterioration around 5000 BP correlates well with the datings of the Bahia Bonita drift between 4100 and 6375 BP. (Rabassa 1983, 1987). The climatic deterioration c. 500 BP is consistent with the findings in Hidden Lake.Lichens on the outer three of the four moraines in front of
the circu+e glacier of Mount Flora have maximum diameters of 36 mm, 45 mm and 62 mm from the glacier and outwards. The lichenometry is based on the deglaciation date 8680 BP, the observations of Rabassa (1983, 1987) that lichens 13 mm in diameter are 515 years old and that a diameter of 19 mm corresponds to an age of 4100-4840 years. The maximum diameter found was 100 mm. The lichenometry suggests that the moraines were formed between 7500 and 6200 BP which corresponds to a period of increased minerogenic input to the lake.Sediment containing organic material was found between the
outer two of three moraines on Vega Island and dated to 10 235 BP. No datings on glacier advances of similar age in this area have been published except by Clapperton and Sugden (1986), who date a glacier advance on South Georgia prior to 9700 BP.2 A LATE HOLOCENE LAKE SEDIMENT SEQUENCE FROM LIVINGSTON
ISLAND, SOUTH SHETLAND ISLANDS, WITH PALAEOCLIMATIC IMPLICATIONS
The field work of this paper was performed in cooperation with Svante Björck and Wibjörn Karle'n. The paper was prepared in cooperation with Svante Björck, Hannelore Håkansson, Wibjörn Karle'n and Bodil Liedberg Jönsson. The microfossil analyses were performed by Svante Björck, Hannelore Håkansson and Bodil Liedberg Jönsson.The aim of the study was to reconstruct the environmental and climatic history of Midge Lake and the surrounding area by combining high quality dating with traditional palaeolim- nological and palaeoecological methods.The 150 cm thick sediment sequence from Midge Lake, Livingston Island (Fig. 1) showed some characteristics typical of lake sediments in this region: it was rich in mosses, contained layers of tephra and was rich in minerogenic matter.Five AMS radiocarbon datings were performed on pure moss remains in order to minimize contamination from carbon derived from the bedrock. The depth/age curve indicated that the datings were accurate.The 1ithostratigraphy indicated that the bottom of the sediment was not reached and that the deglaciation of the area took place prior to 4000 BP.The sedimentation rate rose from c. 3800 BP and reached a
maximum c. 2900 BP. The highest sedimentation rates existed between c. 3200 and 2750 BP (Fig. 3), which probably was caused by a high primary productivity and a significantly higher surface runoff. The former might have been caused by milder summers and/or increased input and release of nutrients. The latter may be a result of increased precipitation with possibly more rapid and extensive snowmelting. From c. 1700 BP until recent times, the sedimentation conditions seem to have been rather stable.The accumulation rate of Pe^iastruni sp. was greatest bet
ween c. 3200 and 2700 BP. This indicates more favourable conditions for plant growth during that time probably due to
9
0- r
QlCD
O(U>*c 2000 — oJOi—OO.2X ) IoQC
3000 —
(mm/year)Fig. 3. Sedimentation rate as a function of time in Midge Lake. The accumulation rate was calculated for each of the 17 levels analysed for microfossils.
milder and possibly more humid summers. Nine of the 17 Noto fagus pollen grains found belonged to this interval, indicating that warmer air masses from South America could more easily reach this region. The climate seems to have gradually changed towards colder and possibly drier conditions during the next 1200 years, interrupted by a brief warmer period around 2000 BP. The period after c. 1500 BP is characterized by low pollen and Pediastrum sedimentation rates, indicating a relatively cold and arid climate.Barsch and Mäusbacher (1986) date a glacier advance to c. 3000 BP, which is in line with the higher sedimentation rate between c 3200 and 2750 BP. Other dates available, both for deglaciation, glacier advances and tephra layers, are inconsistent both with each other and with this study (cf. Clapperton and Sugden 1980, Tatur and del Valle, 1986, 1989,Mäusbacher et al. 1989); one of the main reasons for being the difficulty to obtain reliable radiocarbon datings (Matthies et al. 1990, Björck et al. 1991a).3 LATE HOLOCENE TEPHROCHRONOLOGY OF THE NORTHERN ANTARC
TIC PENINSULA.The fieldwork was performed in cooperation with Svante Björck, Christan Hjort and Wibjörn Karlen. The paper was
10
prepared in cooperation with Svante Björk and Per Sandgren. The magnetic measurements were mainly carried out by Per Sandgren.The aim of this study was to construct a tephrochronology
of the northern Antarctic Peninsula area.Twentythree visible tephra layers from three different lakes on Byers Peninsula, Livingston Island are reported. Another 20 layers detected by magnetic analysis (HIRM, SIRM and S-ratio) are located in the lake sediment cores from Hidden Lake, James Ross Island, and Lake Boeckella, Hope Bay, and in a moss bank core from Walker Point, Elephant Island (Fig. 1).
o-q
500
1000
1500
2000
Tephrahorizons
Midge Chest ercone Lake Lake Lake Asa
HiddenLake
LakeBoeckella
WalkerPoint
O 2500
tu(3< 3000
3500 i API3
4000
4500
5000 J
AP 1
AP 2
AP 3
AP 4
AP 5
AP 6
AP 7 AP 8
AP 9
AP14
12 =
Fig. 4. The 14 detected tephra horizons from six different sites in the Antarctic Peninsula region related to radiocarbon years BP. At least two, AP3 and AP5, seem to consist of more than one tephra layer suggesting multiple eruption separated by short breaks. The vertical lines show the period analysed at each site.
Twenty radiocarbon datings were carried out on the tephra layers from Byers Peninsula. Unfortunately, analyses of most of the bulk sediment samples resulted in an overestimation of the radiocarbon age (cf. Björck et a.1» 1991a). However, the 5 AMS datings from Midge Lake and 4 conventional datings
11
from "Lake Åsa" and "Chester Cone Lake" of pure moss remains were reliable. With these samples it was possible to date all of the tephra horizons from Byers Peninsula. The 6 tephra horizons from Hidden Lake were dated using the interpolated sedimentation curve, based on 2 reliable dates (Zale and Karlen 1989). Seven tephra horizons from Lake Boeckella are dated using a special correction factor for the very problematic dating of this sediment (Zale 1991b). The 9 radiocarbon dates from the moss bank from Walker Point are considered reliable. These dates from different parts of the area make it possible to crossdate several of the horizons, and thus form a base for the tephrochronology of the area (Fig. 4).The ratio TiC^/^ versus SÌO2 indicates that Deception Island is the source of the tephra, a view also reached by Matthies et al. (1990) for the tephra on King George Island.4 CHEMICAL CHANGES IN THE SEDIMENT OF "SKUA LAKE", HORSE
SHOE ISLAND, ANTARCTIC PENINSULA, RELATED TO MARINE/ LIMNIC TRANSITION.
The 1ithostratigraphy as well as the diatom stratigraphy (Wasell 1990) of the sediment of "Skua Lake", Horseshoe Island (Fig. 1) show a transition from marine over brackish to limnic environments.The aim of this study was to compare the chemical contents
of the sediment with the different sedimentary environments during the shift from marine to limnic environments, and to see if the concentration of trace metals can be used as a tool to distinguish between the different phases of this transition.Sediment from five different levels was leached in acid and
the concentrations of 32 elements, mostly metals, were analysed by ICP-AES. The quartz-corrected concentrations (cf. Thomas 1969, Thomas et al. 1972) of cadmium, cobalt, chromium, strontium, vanadium, zirconium, and to some extent arsenic, were well correlated with the transition from marine to limnic environment in the lake (Fig. 5). It is suggested that these metals might be used as indicators of transitions from marine to fresh water in other lakes in the area.It is shown that the quartz-corrected concentrations did
not relate to a different composition of primary minerals, but is interpreted as due to changes in the chemical environment of the lake basin.The metals do not have significantly higher concentrations in the sediment of "Skua Lake" than other lake sediment in the area, with the exception of the concentration of arsenic and cadmium in the marine part of the sediment.
12
factor40Jj ♦J1
234
1Ï
Co Cr As Cd
cBA
5 10 IS
Pk :
\
Cr Sr V
Fig* 5A. Sediment log. Horizons 1 and 2 are interpreted as limnic sediments, 3 as transitional and 4, 5 and 6 as marine sediments.
B. Organic content of "Skua Lake", expressed as loss on ignition, vs. sediment depth.C and D. The quartz corrected concentration factor (con
centration at sample depth/concentration at 3 cm) vs. sediment depth of some trace metals analysed with different methods. Method "G-2" (sample melted in LiB02) is marked by dashed lines and method "G-3" (sample leached in acid) is marked with solid lines. Arsenic is marked by a cross in a circle, cadmium by a star, cobalt by a rhomb, chromium by a square, strontium by a circle, zirconium by a triangle and vanadium by a cross.
E and F. Concentrations of some trace metals vs. sediment depth. The level of arsenic at 38 cm down the core was below the detection limit, 3 ppm. For legend see text to Figs. 3C and D. Fifteen samples analysed with the "G-3" routine (sample leached with acid) from 4 lakes in the region give the following "background concentrations" in ppm of the total dry weight; arsenic minimum <3.0, "typical" (explained in the text) 3.5 and maximum 4.4, cadmium <1.0, 1.5 and 3.6, cobalt; 4.8, 11.4 and 21.8, chromium; 9.9, 22.9 and 55.4,strontium; 58.1, 84.8 and 140.0, vanadium; 32.4, 75.5 and105.0, and zirconium 2.2, 11.7 and 26.6.
5 THE RADIOCARBON CORRECTION FACTOR IN THE SEDIMENT OF LAKE BOECKELLA, ANTARCTIC PENINSULA
The radiocarbon correction factor in Lake Boeckella, Hope Bay (Fig. 1) is large at the sediment surface and, as indicated by some earlier results, possibly not constant throughout the core (Zale and Karlen 1989). This induces great uncertainty in the dating precision of the sediment of Lake Boeckella.The aim of the paper was to quantify the radio carbon correction factor in different parts of the sediment.A small part of the large Adélie penguin rookery in Hope Bay lies in the watershed of Lake Boeckella. The lake is therefore "polluted" with penguin remains and guano. The working hypothesis was that the guano is the main reason for the correction factor.Chemical analyses by ICP-AES of 32 elements, mostly metals, leached by acid from the sediment samples showed that most parts of the sediment of Lake Boeckella are significantly enriched in Ca, Cd, Cu, P, Sr and Zn compared to the background levels in the area. Statistical analyses showed good
13
direct correlation between these substances in the sediment.The background level was set to equal the mean level from the sediment of six reference lakes in the area, altogether 18 samples. Chemical and statistical analyses revealed that the enriched elements were strongly correlated to each other also in the 6 analysed penguin guano samples.Further chemical analyses, where the sediment was fully
dissolved in LiB09, showed that only Ca had a significantly higher concentration when all of the sample was analysed instead of only the portion dissolved in acid. This means that primary minerals were not the source of the enriched elements, but the penguin guano.Statistical analyses showed that Cu and P of the enriched
elements best described the penguin influence (penguin proxy) on the lake sediment (Fig. 6).Penguin proxy = ( ( ( Ap-Up)/Bp)+ ( ( ACu-UCu)/BCu) ) / 2where A = concentration
U = upper confidence limit of the background level.B = background level.
The sediment receives/received carbon from 4 main sources, from the bedrock surrounding/ground, from the penguin guano, from dissolved CC>2 tn the glacial meltwater, and from CO2 in the air. Only the "carbon from the air is considered to have an apparent age of zero.A mathematical model that uses the apparent age and amount
of carbon from the different sources and calculates the "true" radiocarbon age can then be constructed:a1=j1-(ln(((k1-c*<31-e*f1)*2(-1/h)+c*d1*2("g/h))/k1)/-i) (5)where a = "True" radiocarbon age in years BP.
c = Proportionality constant.d = Penguin proxy.e = Proportionality constant.f= Amount of minerogenic material in the sample
in per cent.g = Apparent age of the guano.h = Half life of radiocarbon, 5568 years.i = Proportionality constant, i = ln2/h.j = Radiocarbon age of the dated sample in years BP.k = Amount of carbon in the sample in per cent.1 = Apparent age of the autochtonous carbon in years.
The subscripts denote the sample number starting with the sample closest to the sediment surface.
14
S'o
cDCDCCD
□ L
Sediment depth (cm)
Fig. 6 . The penguin proxy versus sediment depth«
One equation is written for each of the 6 dated samples which make 10 unknown. Some of the unknowns are estimated by reasoning, others are assigned an arbitrary but reasonable value, so that only 6 unknowns remain and the model, i. e, the simultaneous equations, can be run.The apparent ages and the amounts of carbon from the diffe
rent sources are extensively discussed and different values are tested in the model. The result is used to recalculate the datings of Zale and Karlen (1989) (Fig. 7). The model showed that the correction factor in Lake Boeckella mainly depends on the amount of penguin guano in the sediment, the apparent age of the guano, and the amount of carbon in the sediment originating fom the bedrock. The supposedly "old“ meltwater from the glacier do not contribute to the correction factor nor does dissolved carbonates.The validity of the model is checked by comparing the
datings with the sedimentation curve independently dated by tephrochronology (Fig. 7) (Björck et al. 1991b).
15
10000
CL03
%&g■eg
8 0 0 0 -
6000
4 0 0 0 -
2000-
BTi i » » i i r i i r i n t**! i i i i i i i i-q i i i r i i i i rp rrn~rtn~» | i i i i i i i i i0 50 100 150 200 250 3Ó0
Sediment depth (cm)
Fig. 7. Sediment depth vs. radiocarbon age in the sediment of Lake Boeckella. Dashed line from Zale and Karlen (1989) based on radiocarbon dates (crosses) minus a constant reservoir effect. Solid line based on the tehprochronology of Björck et al. (1991b). Tepra horizons are marked with stars. Datings"~as calculated with the model are marked with crossed circles.
Palaeoclimatic implications of the results are a revised deglaciation date at 6300 BP for Hope Bay and an implied long-term (5800 radiocarbon years) stability of the currents and watermasses around the tip of the Peninsula.6 CHANGES IN THE SIZE OF THE HOPE BAY ADÈLIE PENGUIN
ROOKERY AS INFERRED FROM LAKE BOECKELLA SEDIMENTFor thousands of years, Lake Boeckella, Hope Bay (Fig. 1) has been "polluted" by Adêlie penguins that nest in the watershed (Zale 1991b). The degree of "pollution" of the lake sediment has varied over time and is dependent on the size of the rookery. Zale (1991b) found, by statistical analysis, that the concentrations of copper and phosphorus were the elements most suitable to describe the penguin impact on the lake sediment, the so-called penguin proxy, and thereby the size of the rookery. The aim of this study was to make a more detailed analysis of the sediment and thereby obtain a more comprehensive picture of the rookery's changes in size and to find some of the reasons for it.Adélie penguins have a circumpolar distribution and are the the most polar of all penguins, except the emperor penguin (cf. Watson 1975, Yeates 1975, Croxall 1985, Trivelpiece et al. 1987b). They breed in large rookeries and their main prey is krill (Cambell and Lack 1985, Culik 1987).Eight one-cm samples from the 293 cm long Lake Boeckella sediment core were analysed for concentrations of P and Cu,
16
among other elements. The samples were leached with a 1:1 mixture of HNO3 and water in sealed PTFE containers in a microwave oven prior to analysis by ICP-AES. This "M-l" routine corresponds to the 10 "G-3" analyses performed earlier on one- and two-cm samples.The penguin proxy as a function of time indicates that
penguins have been continuously present on the shores of the lake since at least 5550 BP, with the exception of a period around 5300 BP (Fig. 8).Until man discovered Antarctica, climate was one of the
main factors regulating population size (Spellerberg 1975, Yeates 1975). However, very little is known about how climate and other environmental factors affect rookery size, and even less is known about the effect of these factors outside the breeding grounds (Oelke 1978).The penguin proxy was relatively low and fluctuating from the time when the first penguins appeared up to between 1250 and 850 BP (Fig. 8). There is no obvious correlation between a higher penguin proxy during that time and the regional climate (Fig. 8). The reason might be that climatic changes were not synchronous in the whole region and/or that different authors interpret the climatic signals differently.The penguin proxy increased dramatically from between 1250
and 850 BP till 50 BP (1900 AD). This coincided with a regional climatic deterioration (Fig. 8); active glaciers on James Ross Island (Rabassa 1983, 1987, Zale and Karlen 1989) and South Shetland Islands (Clapperton and Sugden 1986), and cold and arid climate on Livingston Island (Björck et al. 1991a).Sealing began immediately after Antarctica was discovered
in 1819 and in only a couple of years, the krill-feeding fur seals had become almost extinct (Laws 1985). However, calculations indicate that the amount of "surplus" krill was at least one order of magnitude too low to trigger a larger increase in the population of Adélies. Sealing is therefore considered a minor contributing reason for rookery growth in the 19th century.The penguin proxy decreased sharply from c. 1900 to 1973 (Fig. 8). This decrease coincided with man's growing interest in Antarctica and is considered to be the result of direct disturbance of the penguins of Hope Bay, changing the shape and location of the rookery, as well as the penguins' routes to the sea.However, censuses of the rookery size show a constant increase since 1945 (Fig. 8). This is considered to be a continuation of the rookery growth mirrored in the penguin proxy up to 1900 when man's activities in Hope Bay started to disturb the penguins. A contributing factor to the growth of the rookerys in recent years was probably the whaling which started in 1904 in the area and led to drastic decreases in the balean whale stock, making krill more abundant as predation decreased. This amount of extra food is considered to be the reason for the larger populations of krill-feeding penguins (Sladen 1964, Laws 1985, Shapley 1985) and seals (Beddington and May 1982, Busch 1985:212, Laws 1984) in many areas of Antarctica.
17
30 -
26 -
22 -*c£-I?s
13
t 8-e*3
i
-50 50 100 500 1000 4000 6000 Yaars BP2000 1950 1900 1850 Y*»r A0
RX-50 O 50 100 500 1000 2000 3000 4000 5000 6000 Y «ari BP
EI
Warm and humid
SO tOO 500 1000 2000
50 IOO 500 1000Cold and aridLI
-50 0 50 100 500 1000 2000 3000 4000 5000 6000 Y tar* BPSS1 — I— I— 1— Vtffi— I----1 F
2000 1950 1900 (850 Yaar AO
Fig. 8. The penguin proxy (squares) and number of penguins (circles) as a function of time. The number of penguins in 1903 is taken from estimates of Nordenskjöld et a_l. (1904) and Carlsson et al. (1990) and the later numbers of penguins are all from censuses; in 1945 by Conroy (1974), in 1955 by Novatti (1959), in 1963-64 by LeFeuvre (all in Cordier et al. 1983), in 1979-80 by Cordier et al. (1983) and in 1985 by Myrcha et al. (1987). The eight samples analysed in this paper and all 10 two-cm samples from Zale (1991b) are used. The LOI of the sediment of Hidden Lake on James Ross Island (dashed line) used as a proxy for climate (Redrawn from Zale and Karlen 1989). The LOI curve is strongly influenced by deglaciation sedimentation and processes before c. 3500 BP and is thus not a accurate climate proxy for that period. Note the nonlinear time-scale used for clarity.The climatic data in the lower part of the figure are from
James Ross Island (JRI) (Rabassa 1983, 1987, Zale and Karlen1989), Elephant Island (El) (Björck et al. 1991d), King George Island (KGI) (John 1972, Mäusbacher et al. 1989), Livingston Island (Li) (Björck et a].. 1991a) and from South Shetland Islands (SSI) (Clapperton and Sugden 1986).
18
ACKNOWLEDGEMENTSFirst of all I would like to thank; Wibjörn Karlen, Svante Björck and Christian Hjort for many stimulating and educative discussions both in the field and at home. Without them this thesis would not have been written.I would also like to thank; Alfred Wegener Institute for
Polar and Marine Research in Bremerhaven which organized the RV Polarstern Expedition ANT VI,Professor Sahrhage who led the Polarstern expedition in so successfully,SWEDARP, which organized the 1988/1989 expedition and supported me in many other ways,Professor Anders Karlqvist who led the SWEDARP expedition in a splendid way, the masters and crews, including the helicopter pilots
and mechanics, on both RV Polarstern and MS Stena Arctica who transported me safely and comfortably across stormy seas,Tommy Hammarström and Johan Delby who helped me to collect samples,Svante Björck, Kerstin Nordström and Anders Wasell who
cored the lakes with me,Svante Björck, Lars Brydsten, Mats Jansson, Kerstin
Nordström, Siv Olsson and Göran Skog who made valuable comments on various manuscripts,Nigel Rollison who made linguistic checks,The Swedish Natural Research Council, The Kempe Founda
tions, Gyllenstiernska Krapperupsstiftelse, Svenska Sällskapet för Antropologi och Geografi, Hierta-Retzius fonder and Stiftelsen Lars Hiertas Minne for funds,Antes Glas in Umeå for supplying equipment.REFERENCESBarsch, D. and Mäusbacher, R. 1986: New data on the relief
development of the South Shetland Islands, Antarctica. Interdiciplinary Science Review 11(2) :211-218.
Beddington, J. R. and May, R. 1982: The harvesting ofinteracting species in a natural ecosystem. Scientific American Vol. 247, nr. 5: 42-49.
Björck, S., Hjort, C., Ingoifsson, 0. and Skog, G. 1991a: Radiocarbon dates from the Antarctic Peninsula region - problems and potentials. Journal of Quaternary Science, 5, 61-72.
Björck, S., Sandgren, P. and Zale, R. 1991b: Late Hoi oc e ne tephrochronology of the northern Antarctic Peninsula. Quaternary Research 36:322-328.
Björck, S., Hakansson^ H., Za 1 R., Karlen, VK andLiedberg-Jönsson, B. 1991c: A late Holocene lake sediment sequence from Livingston Island, South Shetland Islands, with palaeoc1imatic implications. Antarctic Science, 3(1): 61-72.
Björck, S ., Malmer^ N., H_j 2E t-JL Ch ., Sandgren^ P ., Ingolf sson, Q ., W all en~7 B., Lewis Smithy R^ 1^ and Liedberg-Jons son, B. 1991d: Stratigaphic and paleocll- matic studies of a 5500-year-old moss bank on Elephant island, Antarctica. Arctic and A l p i n e Research23(4): 361-374.
Busch, B. C. 1985: The war against the seals. Alan Sutton, Gloucester, 374 pp.
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Campbell, B. and JL Lack, 1985: A dictonary of birds. T and AD Poyser, Calton, 570 pp.
Carlsson, 0., Lundgren^ S_̂ and Forsgren, M. 1990: Antarktis - i hela mänsklighetens intresse. Wiken, Höganäs 160pp.
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Cordier, J.-R., Mendez, A., Mougin^ J.-L. and Visbeck, G.1983: Les oiseaux de la baie de 1* E sper a ne e , Peninsula Antarctic (6 3°24'S. 5 6°59'W.). L'Oiseau et R. F. O.53:143-176.
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John, B. S. 1972: Evidence from the South Shetland Islands towards a glcial history of West Antarctica. In: Sugden, D. E. and Price, R. J. (eds.): Polar geomorphology, Inst, of British Geographers, 75-92.
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Matthies, D., Mäusbacher, R. and Stortzer, D. 1990: Deception Island tephra: a stratigraphical marker for limnic and marine sediments in Bransfield Strait area, Antarctica. Zentralblatt für Geologie und Paläontologie, Teil 1, No. 172, 153-165.
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tic lakes (King George Island). Zetschrift für Geomor phologie, N. F., 219-234.
Nordens jöld, O., Anders son± J_̂ G., Larsen C^ A^ and Skottsberg, C. 1904: Antarctic - två ar bland sydpolens isar. Del 2. Bonnier, Stockholm, 552 pp.
Novatti, R. 1959: Notas biologicas sobre el pingüin deAdelia. Contribucion del Instituto Antarctico Argentino, 38.
Oelke, H. 1978: Natürliche oder anthropogene Populations- feränderungen von Adél iepinguinen (Pygocelis ade]Liae) im Ross-Meer-Sektor. Journale von Ornitoiogie, 119(1):1-13 .
Rabassa, J. 1983: Stratigraphy of the glacigenic deposits inNorthern James Ross Island, Antarctic Peninsula. Inj_ Evenson, E., Schlächter, C. and Rabassa, J. (eds.J: Tills and related deposits, Balkema, Rotterdam, 329- 340.
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Rabassa, J. 1987: Drumlins and drumlinoid forms in NorthernJames Ross Island, Antarctic Peninsula. In: Menzies, J. and Rose, J. (eds.): Drumlin symposium. Balkema, Rotterdam, 267-288.
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Sladen, 1964: The distribution of the Adélie andchinstrap penguins. In: Carrick, R., Holdgate, M. and Prévost, J. (eds): Biologie Antarctique, Hermann,Paris, 359-365.
Spellerberg, I. F. 1970: Abandoned penguin rookeries near Cape Royds, Ross Island, Antarctica and C dating of penguin remains. New Zealand Journal of Science, 13:380-385.
Sugden, D. E. and Clapperton, C. M. 1986: Glacial history of the Antarctic Peninsula and South Georgia. South Afri can Journal of Science, 82:508-509.
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Tatur, A. and del Valle, R. 1989: Lake sediments in maritime Antarctic zone: A record of landscape and biota evolution. Abstract from the SIL congress in Munich, August 13-19, 1989.
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Watson, G. E. 1975: Birds of the Antarctic and Sub-Antarctic. American Geophysical Union, Washington, 350 pp.
Wasell, A. 1990: Diatom stratigraphy in the sediment of"Skua Lake", Horseshoe Island, Antarctica. 11th Int. Diatom Symposium. San Fransisco, August 1990. Abstract volume.
Yeates, G. W. 1975: Microclimate, climate and breedingsuccess in Antarctic penguins, In: Stonehouse, B. (ed), The biology of penguins, MacMillan, London, 397-409.
Zale, R. and Karlen, 1989: Lake sediment cores from the Antarctic Peninsula and surrounding islands. Geografis- ka Annaler 71A (3-4)-.211-220.
Zale R., 1991a: Chemical changes in the sediment of "SkuaLake", Horseshoe Island, Antarctic Peninsula, related to a marine/limnic transition. Presented at the IGCP- 274 symposium "Quaternary shorelines: evolution, processes and future changes" in La Plata, Argentina November 19-20, 1990. Submitted to Antarctic Science.
Zale, R. 1991b: The radiocarbon correction factor in the sediment of Lake Boeckella, Antarctic Peninsula. Submitted to Radiocarbon.
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