Eurasian ice sheets – Taymyr Peninsula 1998

 Project leader:

Christian Hjort, Department of Quaternary Geology, Lund University

The aim of the project

”Eurasian Ice Sheets” is a largely EU-financed project which, under the umbrella of the European Science Foundation’s programme QUEEN (Quaternary Environment of the Eurasian North), investigates the extent of glaciation, in time and space, in the Eurasian arctic. The geographical area covered by the project stretches from the Kola Peninsula eastwards to Taymyr, and the time frame principally targeted is the last glacial cycle, i.e. the last ea. 125 000 years. Emphasis is put on the situation during the last global glaciation maximum (LGM) ea. 20 000 years ago, as the basis for the contract with the EU is to delimit the extent of glaciation during the LGM and to study the growth of ice up to that time and the deglaciation process thereafter. This knowledge will be used as input into efforts to model global climate during the LGM, which represents the extreme cold end of the scale. These modelling results, in their turn, are vital for a reliable assessement of what path future climatic developments may take. The main problem so far hindering meaningful modelling of the global glacial climate in the vast arctic parts of Eurasia has been the unsolved conflict between two very different schools of glacial history. One school, the maximalists (e.g. Grosswald 1998), suggests that more or less the entire northern Eurasian coastal area, from the Atlantic to the Pacific, was covered by large ice sheets at the LGM. The other school, the minimalists (e.g. Velichko et al. 1997), argues that at that time glaciers were only found in some high arctic archipelagos, such as Svalbard and Franz Joseph Land, and in higher mountains. The minimalists also suggest that the northern coastal plains of Eurasia and the continental shelves (at that time dry due to the global eustatic lowering of sea-level at the LGM) should have been steppe tundras where, among other things, herds of mammoths roamed. A compromise hypothesis, e.g. that advocated by

Astakhov (1998), is that the maximum concept is probably geologically correct-but chlonologically wrong! According to this view the very large ice sheets either date from an earlier glacial cycle, in Europe called the Saale and more than 125 000 years old, or from the earliest part of the latest (Weichselian) glaciation. This would at least apply to the areas from Taymyr westwards. Due to lack of precipitation there were probably never any large ice sheets in eastern Siberia. The maximum ice sheets should thus predate any time which could effectively be dated with the 14C-method (up to ea. 35 000 years ago) and their age then has to be ascertained by other methods. This ”exten~ive but early glaciation- hypothesis” is in reality the theoretical takeoff position for the ”Eurasian Ice Sheets” project, and thus also for the SWEDARCTIC-based work on the Taymyr Peninsula.

Another part of the background for our work in 1998 was the SWEDARCTIC-assisted reconnaissance of central Taymyr in 1996, in cooperation with the Alfred Wegener Institute (Potsdam branch, Germany). From studies of marine and lacustrine sediments, including a large dating program using various methods, and from geomorphological evidence, it was concluded that there had been no glaciation in the Byrranga Mountains or in the areas south thereof since at least the early Weichselian (Moller et al., in press/1998). This conclusion is fully in line with that advocated by e.g. Astakhov (1998).

The 1998 fieldwork

The Quaternary field work on Taymyr in 1998 was carried out by three teams. One group (Moller, Bolshiyanov, Jansson and Schneider) travelled in two rubber boats and started out in those areas south of the Byrranga Mountains studied in 1996. They began in the southwestern part of the Taymyr Lake basin, revisiting important localities investigated in 1996. The two most important of these were the Ledyanaya Bay, with a marine sequence between 70 000 and 100 000 years old, and Cape Sahler, with lacustrine sediments documenting uninterrupted deposition between ea. 40 000-15 000 years ago, at a much higher lake level than today. New sites with marine and lacustrine sediments were found and investigated along the shores of the Taymyr Lake and in the Upper Taymyr River delta. The voyage then continued into the Lower Taymyr River, following this river downstream through the ”gaps” in the Byrranga Mountains and across the tundras north thereof, to the Fomina River junction just north of 76°N. From there they were picked up by a helicopter at the end of the field season. They had then travelled more than 700 km by boat, and traversed from the geologically older areas in the south, through the ”Isayeva Line” (see below), into the younger landscape on northern Taymyr, comparing the morphological and sedimentological differences between these two areas.

The aim of the second group (Hjort, Antonov, Alexandersson, Eriksson, Pavlov) was to document the genesis and age of the ”Isayeva Line”, also known as the North Taymyr Line. This is an icemarginal zone marking the southern boundary of an ice sheet coming from the Kara Sea and it was described by Isayeva (1984), amongst others. It was at the onset of the expedition the only possible candidate for a major LGM ice margin in this region. The work was done from two camps. The first was in the Barometric Lake area, where the ice margin had terminated into a deep ice dammed lake, roughly the size of Lake Vänern. The other camp was ea. 100 km to the northeast, at Bely Lake, where the ice had terminated on land, in an upslope situation.

The third group (Funder, Rydlevski, Seidenkrantz, Riazanova) worked along the coastal cliffs of the Kara Sea, i.e. well behind (up-glacier from) the Isayeva Line, where the sediments associated with the deglaciation after that stage ought to be found. Their first camp was north of the Leningradskaya estuary, in an area with mainly thick glaciolacustrine deposits. The second camp was on the Oskar Peninsula at the mouth of the Taymyr River, with both marine and glaciolacustrine sediments exposed.

Preliminary results

The major result expected from the field work is the geographical delimitation and absolute dating of the different glacial stages on central and northern Taymyr, especially the identification of the LGM ice margin, if it exists on what is presently dry land! Material for doing this, via 14C-, electron spin resonance and luminescence dating of plant material, marine shells and different types of sediments, has been collected, but that process has just started. The same applies to the paleontological ”dating” of marine and terrestrial sediments, via analysis of pollen, foraminifera, molluscs, etc. However, some other results are interesting enough:

1. There has long been speculation over why there are no high marine levels along most of the Siberian coasts, as elevated shorelines would be expected from isostatic readjustment of a land area downpressed by a recent load of ice. This pattern may be explained, at least partly, by one surprising result of this summer’s expedition that a very large part of the last ice-sheet is still there! Under only 0.5-1 m of till one finds the old glacier ice, exposed by landslides in hundreds of natural sections. Often it is penetrated by systems of younger ice wedges. If much of the ice is still there, only limited isostatic readjustment should have taken place, and the global eustatic rise of sea level after the LGM may always have exceeded the rise of land. That would mean a continuous marine transgression, with today’s shoreline constituting the postglacial marine limit.

 

2. The Kara Sea ice sheet, terminating at the Isayeva Line, was found to have dammed a large glacial lake, with its highest level reaching ea. 140 m above the present sea. The regional topography is such that this glacial lake could only have drained southwards, through the present narrow valley of the northflowing Taymyr River, where it cuts through the Byrranga Mountains. That would mean a drainage, via the Taymyr Lake basin, southeastwards to the Laptev Sea. Coarse fluvial sediments found in the narrowest part of the Taymyr River ”gap” through the mountains may be interpreted as illustrating this!

 

3. The widespread and well known ”marine sediments”, shell-bearing silts, deltas, etc., found inside (i.e. north of) the Isayeva Line (see e.g. Kind and Leonov 1982) often seem to consist of redeposited material, picked up and transported by the ice sheet when it moved southeast from the Kara Sea. These marine derived tills and the glaciolacustrine deltas contain two morphologically different types of redeposited marine shells, one thin-shelled population and a thick-shelled one. The latter, morphologically and specieswise, looks similar to shells found in situ in undisturbed marine sediments outside (i.e. south of) the Isayeva Line-e.g. at the Ledyanaya Bay in the Taymyr Lake (Moller et al. in press/ 1998).

 

4. There is, geomorphologically considered, a large difference between the ”fresh” glacial landscape inside the Isayeva Line and the well weathered formerly glaciated areas outside. This indicates a sizeable time difference between the two episodes of glaciation. The older southern area, which has a high glacioisostatically derived marine limit (ea. 110 m), seems to represent a time when the Kara Sea ice sheet reached south of the Byrranga Mountains (see e.g. Isayeva 1984, Astakhov 1998) and the minimum age of this event is the earliest Weichselian (Moller et al. in press/1998). As to the age of the Isayeva Line, representing the last major inundation of Taymyr by a Kara Sea ice sheet, we have to wait for the datings.

 

5. Several new localities exposing Cape Sabler-type sediments were found. These lacustrine sediments are rich in organic material, including mammoth and other mammalian remains, and span a time between ea. 40 000 and 15 000 years ago. Their regional occurrence and their altitude indicate the existence at that time of a paleoTaymyr Lake with a water level at 50-60 m a.s.l. (today it is only 5 m a.s.l. ) – during a period for which earlier investigators (e.g Kind and Leonov 1982, Grosswald 1998) have suggested a thick ice-sheet over the area.

The future

 The plan is to continue-and conclude-the field work on Taymyr in 1999, with a slightly smaller expedition than in 1998.