Jökull - 01.01.2009, Síða 70

Hannesdóttir et al.
Figure 2. a. Bathymetry of Hestvatn, seismic profiles and core locations. Black lines indicate tracks of seis-
mic profiles, only white line profiles are shown in figures 3 and 4b. b. Multibeam bathymetric map of lake
floor of Hestvatn superimposed on the original bathymetric map to provide coverage in shallow water. Sub-
areal map published with permission from the National Land Survey of Iceland. – a. Dýptarkort Hestvatns
ásamt siglingalínum endurvarpsmælinga (gögn eftir hvítum línum er sýnd á myndum 3 og 4). Hvítir punktar
sýna staðsetningu kjarna sem teknir voru sumarið 2003. b. Fjölgeislamælingar af botni Hestvatns leiða í ljós
landslag á grunnum svæðum vatnsins. Kort birt með leyfi Landmælinga Íslands.
A detailed bathymetric map was compiled by
combining water depth calculations from the seismic
survey, and scanned and georectified bathymetric map
made with echo sounder measurements by the Hy-
drological Service Division of the Energy Authority
in Iceland (Rist, 1975). Isopach maps of the seismic
units were created by interpolation, both for the lake’s
two sub-basins and the whole lake. The number of
points varied depending on seismic unit (ranging from
1200 to 4600 points). The interpolation was limited
to areas of 180 m of the data points, with resulting
3 m grid cell spacing. Isopach maps for the lake’s
two sub-basins were created, as well as isopach maps
for the whole lake. Paleobathymetry maps were cre-
ated, subtracting sediment thickness from the modern
bathymetry. The mean thickness and volume for the
seismic units was calculated for the two sub-basins as
well as for the whole lake.
DOSECC’s GLAD200 core rig (http://www.-
dosecc.org/), equipped with ODP-style coring tools
was used to recover over 20 m long cores at 60 m
water depth in Hestvatn in the summer of 2003. Sedi-
ment cores from Hestvatn obtained in 1994 and 1995
(Harðardóttir et al., 2001a, 2001b) and the seismic
survey guided the selection of the new core sites. Four
new cores were obtained from Hestvatn, a set of du-
plicate cores from each sub-basin (Figure 2), with a
vertical offset of approximately 1.5 m (Table 1). Each
core segment is approximately 3 m long and 6.2 cm
in diameter. Additionally surface cores (Glew, 1991)
were recovered from each location, in order to retrieve
the water/sediment interface at the core sites. The
chronology of the cores is based on tephrochronology
and radiocarbon dating of marine molluscs (Table 2).
Seismic units are identified by comparison of the seis-
mic profiles and the core lithology.
70 JÖKULL No. 59