Jakobshavn ice margin reconstruction using lake sediments.
- a guide through the lake sediment coring component -

Goals:
1. To determine the timing of ice sheet retreat during the early/middle Holocene
2. To determine the timing of ice expansion at the onset of the Little Ice Age

Techniques:
1. Collect sediment cores from 'threshold' lake basins with 'on/off' glacier-sediment sequences
2. Radiocarbon dating of sediment contacts
3. Potentially use varves for high-resolution chronology and climate reconstructions

We cored a total of 6 lakes from three different camps (camps 2, 3, 4). No lakes were cored from camp 1.

Camp 2:

Goose Lake
08GOO-4 [ core log | core photo ]

Loon Lake
08LOO-1 [ core log | core photo ]

Raven Lake
08RAV-2 [ core log | core photo ]

Air photo showing the 1985 ice sheet margin and the three lakes cored from camp 1. The Little Ice Age ice position is
shown as the dashed white line. Based on the geometry of these three lake basins and the position of the ice sheet margin,
ice sheet meltwater ceased to feed Loon Lake the earliest (time unknown) and Goose Lake at some unknown time later;
meltwater still flows into Raven Lake. If the geometry of ice sheet advance was similar to ice sheet retreat, then we may
expect that melwater fed Raven Lake first, then Goose Lake, then Loon Lake during ice sheet expansion during the Little
Ice Age. The sedimentary sequences recovered suggest this pattern. Radiocarbon ages are pending.

Goose Lake, which is no longer glacier fed, is shown below. The Greenland Ice Sheet can be seen in the distance (on skyline).
The Little Ice Age moraine can also be seen as a large pile of unvegetated debris from the center to the right edge of this photo.
While near and at its Little Ice Age maximum position, the ice sheet created a large proglacial channel and delta, both of which
remain unvegetated today. The University at Buffalo campsite can be seen on the delta surface.

Raven Lake, shown below, still receives meltwater from the Greenland Ice Sheet. The Little Ice Age moraine occupies the right
side of this photograph, and Raven Lake is to the left. You can tell by its color, both in this image and the air photo above, that it
is still glacier fed. Raven Lake is the only lake that we collected sediment cores from that remains glacial fed today.

Camp 3:

Iceboom Lake
08ICE-3 [ core log | core photo ]
08ICE-4 [ core log | core photo ]
08ICE-5 [ core log | core photo ]
08ICE-6 [ core log | core photo ]

Lake Northsouthy
08NOR-3 [ core log | core photo ]

Below is a map of the area around Camp 3. Camp 3 is located on the northeastern shore of a lake we call "iceboom lake." We cored
2 lakes from this camp. We collected several cores from three different coring locations in Iceboom Lake. This lake, shown in this
AD 2000 Landsat image, does not receive ice sheet meltwater, and thus appears dark colored in this image. Below this image are
a series of air photographs from 1944, 1953, 1964, 1985, and this one from 2000. Iceboom lake receives ice sheet meltwater up to
sometime between 1964 and 1985. We also cored a lake that we call "lake northsouthy" (don't ask) that never received icesheet meltwater.
A third site that was a surprise find is a glacial lake that no longer exists that we call "glacial lake morten." This lake drained sometime
between 1985 and 2000.


1985:


1964:


1953:


1944:


Iceboom Lake. Photo view is across the lake to the east, with the Greenland Ice Sheet in the background. The lake received ice sheet meltwater
from two locations during the Little Ice Age (there were two inflows into this lake during the Little Ice Age). One of them is seen in this photograph
as the bedrock-floored, unvegetated channel in the left-center of the photograph on the opposite lake shore.



Stitched photograph of Glacial Lake Morten. The Little Ice Age margin is seen as a morainal bank or subaqueous moraine in the middle of the
left-most picture. The lake's outflow was at a fixed elevation at the far right side of the image. The ice dammed the lake when it abutted against
the left side of the bedrock ridge on the far side of this lake from where the photos were taken. Shorelines and deltas mark the former height of
the lake, and rills created since the lake drained expose thick sequences of laminated sediments (see next photo down).


Photograph from the floor of Glacial Lake Morten, which, as seen in the above images, drained sometime between 1985 and 2000.
The lake, which largely existed out in front of the Little Ice Age ice margin, was probably just a Little Ice Age feature. Even after
Iceboom Lake stopped receiving ice sheet meltwater, Glacial Lake Morten still persisted. You can see the tundra surface that
was buried when Glacial Lake Morten was initially dammed by the Greenland Ice Sheet. Radiocarbon dates from the uppermost
dead tundra will tell us when the lake formed. Varve counting the laminated sediments may allow us to more precisely determine
its duration.

Camp 4:

South Oval Lake
08SOV-1 [ core log | core photo ]
08SOV-4 [ core log | core photo ]

1985 air photo showing the lakes around camp #4. South Oval Lake is the southernmost of the pair of east-west oriented "oval-shaped" lakes
in the center of this image. Camp #4 was located at the eastern shore of South Oval Lake. The Little Ice Age margin of the Greenland Ice Sheet
is demarcated by the tonal shift in this image. The Greenland Ice Sheet position was half-way in North Oval Lake and just barely at the eastern
shore of South Oval Lake. Lakes in this image with bright halos around their shores indicate higher water levels during the Little Ice Age.

Photograph from the surface of South Oval Lake looking eastward toward the University at Buffalo camp, the Little Ice Age moraine, and the Greenland
Ice Sheet at the skyline. The tents were pitched on a Little Ice Age delta surface that was deposited a few meters above present lake level.