606
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
occur during few specific time intervals only (Figure 3). Accordingly, highest abundances are
recognized between 800-1000 a BP and between 1600-1900 a BP. Comparing the relative
abundances of individual species with the record of total test concentration clearly indicates that
T. clarkei is by far the dominant species during these intervals. All other species remain inferior
to T. clarkei and, moreover, never reach significant numbers even during other intervals.
Table 2: List of identified species from the investigated cores. Species names according to Hemleben et al.
(1989). Biogeographical distribution and stratigraphical first occurrence (FO) is based on Kipp (1976), Kennett
and Srinivasan (1983), Bolli and Saunders (1984), and Boltovskoy (1991). * biogeographical distribution
strongly depending on coiling direction.
Species
FOIBiogeography
Globigerina bulloides
Middle Miocene/subtropical-subpolar
Globigerinita glutinata
Late Oligocene/tropical-subpolar
Globoturborotalita tenella
Late Pliocene/tropical-temperate
Turborotalita clarkei
Late Miocene/tropical-temperate
Neogloboquadrina pachyderma * Late Miocene/subtropical-polar
Temporal variability on Lomonosov Ridge
The record from the Central Arctic Ocean consists essentially of a two-species assemblage with
N. pachyderma sin. being the dominant species (Figure 4). This species makes up 94-99 % of
all tests. The remainder proportion is due to N. pachyderma dex. A comparison of the test
concentrations of the two species indicates fairly good corresponding records throughout the
past 35 ka. In general, the two records show significantly reduced deposition of tests during the
last glaciation. The concentration of tests only begins to increase after the end of the
deglaciation, and reaches highest numbers in the later Holocene. Despite the good conformity
of the two records, the relative abundances reveal a less proportional relation between both
species. A comparatively strong dominance of N. pachyderma sin. is found between 15-20 ka,
i.e., during the last glacial maximum (LGM). During the deglacial phase (15-9 ka) this
dominance becomes less until relatively low values are noted between 6-8 ka. The midHolocene is marked by a significant shift at 3-4 ka although test concentrations steadily increase
already after about 7 ka.
Discussion
Origin of planktic foraminifera in Arctic sediments of Holocene age
The occurrence of unusually warm-water indicating planktic foraminifera in upper Holocene
sediments from the Laptev Sea shelf is intriguing in itself, but cannot be easily answered
considering the modern pathway of surface water flow in the Arctic Ocean. At present it is
difficult to reconcile the fact that these species from a tropical-temperate provenance can be
advected to the very shallow Laptev Sea shelf or that they have lived in this region during any
time of the Holocene. So far, species such as G. tenella or T. clarkei have not been reported
from areas such as the Nordic seas (e.g., Kellogg, 1984; Bauch, 1994) from where the main
mass of non-polar water masses is advected to the Arctic Ocean. On the other hand species such
as G. bulloides and G. glutinata may more likely invade the Laptev Sea via Atlantic derived
waters across the Barents Sea or along the Eurasian continental margin. A recent downcore
Land-Ocean Systems in the Siberian Arctic: Dynamics and History
occur during few specific time intervals only (Figure 3). Accordingly, highest abundances are
recognized between 800-1000 a BP and between 1600-1900 a BP. Comparing the relative
abundances of individual species with the record of total test concentration clearly indicates that
T. clarkei is by far the dominant species during these intervals. All other species remain inferior
to T. clarkei and, moreover, never reach significant numbers even during other intervals.
Table 2: List of identified species from the investigated cores. Species names according to Hemleben et al.
(1989). Biogeographical distribution and stratigraphical first occurrence (FO) is based on Kipp (1976), Kennett
and Srinivasan (1983), Bolli and Saunders (1984), and Boltovskoy (1991). * biogeographical distribution
strongly depending on coiling direction.
Species
FOIBiogeography
Globigerina bulloides
Middle Miocene/subtropical-subpolar
Globigerinita glutinata
Late Oligocene/tropical-subpolar
Globoturborotalita tenella
Late Pliocene/tropical-temperate
Turborotalita clarkei
Late Miocene/tropical-temperate
Neogloboquadrina pachyderma * Late Miocene/subtropical-polar
Temporal variability on Lomonosov Ridge
The record from the Central Arctic Ocean consists essentially of a two-species assemblage with
N. pachyderma sin. being the dominant species (Figure 4). This species makes up 94-99 % of
all tests. The remainder proportion is due to N. pachyderma dex. A comparison of the test
concentrations of the two species indicates fairly good corresponding records throughout the
past 35 ka. In general, the two records show significantly reduced deposition of tests during the
last glaciation. The concentration of tests only begins to increase after the end of the
deglaciation, and reaches highest numbers in the later Holocene. Despite the good conformity
of the two records, the relative abundances reveal a less proportional relation between both
species. A comparatively strong dominance of N. pachyderma sin. is found between 15-20 ka,
i.e., during the last glacial maximum (LGM). During the deglacial phase (15-9 ka) this
dominance becomes less until relatively low values are noted between 6-8 ka. The midHolocene is marked by a significant shift at 3-4 ka although test concentrations steadily increase
already after about 7 ka.
Discussion
Origin of planktic foraminifera in Arctic sediments of Holocene age
The occurrence of unusually warm-water indicating planktic foraminifera in upper Holocene
sediments from the Laptev Sea shelf is intriguing in itself, but cannot be easily answered
considering the modern pathway of surface water flow in the Arctic Ocean. At present it is
difficult to reconcile the fact that these species from a tropical-temperate provenance can be
advected to the very shallow Laptev Sea shelf or that they have lived in this region during any
time of the Holocene. So far, species such as G. tenella or T. clarkei have not been reported
from areas such as the Nordic seas (e.g., Kellogg, 1984; Bauch, 1994) from where the main
mass of non-polar water masses is advected to the Arctic Ocean. On the other hand species such
as G. bulloides and G. glutinata may more likely invade the Laptev Sea via Atlantic derived
waters across the Barents Sea or along the Eurasian continental margin. A recent downcore