244
Andrew CLARKE
are considerably thicker, up to 2–3 km deep in areas of
the Canada Basin (Hunkins and Kutschale, 1967). All
the Plio–Pleistocene sediments examined have proved
to be sandy or silty lutites with a variable proportion of
gravel-sized clasts (Darby et al., 1989). Photographs,
however, reveal the presence of larger clasts, from
pebble to cobble size, which are usually not taken in
cores (see, for example, Hunkins et al., 1970). Clark
et al. (1980) classified the sediments into four types
based on the size frequency distribution of the <63 mm
fraction. The lithology of these sediments differed from
those in other ocean basins in the high proportion
(10–30%) of kaolinite and chlorite in the clay fraction
(<2 mm), together with the abundant detrital dolomite
and calcite in the coarser fractions.
The composition, mineralogy and physical characteristics of Arctic deep-sea sediments point to an important contribution from ice-rafted material. The overall
importance of ice-rafting is currently unquantified, but
the content of ice-rafted material in sediments of the
Arctic abyssal plain has been put at 60–70% (Darby
et al., 1989). Aeolian input is low.
Turbidity currents have been a major process for
sediment transport in the Arctic deep-sea basins. Their
importance is greater closer to the continental shelves,
but has probably been important over large areas.
Thus, the sediments in the Fram Basin have probably
originated from the Lena River, and have been carried
into the basin from the Kara and Laptev shelves
by turbidity currents. Similarly the Makarov Basin
contains turbidites from the East Siberian shelf, and the
Canada Basin sediment originated from the McKenzie
River region, and was carried by turbidity currents
(Weber, 1989). There is no evidence for significant
volumes of nonturbidite current-deposited sediments
in Arctic abyssal sediments, and the few existing
measures of rates of bottom currents in the Arctic deep
sea are all low (Galt, 1967).
Microfauna of Arctic deep-sea sediments
Relatively little is known of the microbial fauna or
meiofauna of the Arctic deep ocean. Darby et al.
(1989) reported organic-carbon contents for the Canada
Basin which decreased towards the centre of the basin.
The mean value (0.87% dry mass) was significantly
higher than in sediments of similar mineralogy from
the Atlantic and Pacific Oceans. Cranston (1997) found
organic content between 0.3 and 0.5% in the Makarov
Basin, with higher levels (1.2%) on the Lomonosov
Ridge and in the Amundsen Basin (1.0%). The low
hydrogen index (mg H/g C) and the high C/N atomic
ratios indicate that most of the organic matter in the
sediments of the Arctic deep sea is terrigenous material
(Stein et al., 1994; Stein, 1996; Fahl and Stein, 1997).
Such material typically has been extensively reworked
and consequently is of little nutritive value for benthic
organisms.
Concentrations of sediment-bound chlorophyll and
phaeopigments are very low (Boetius et al., 1996;
Soltwedel and Schewe, 1998). These data indicate that
the supply of phytodetritus to the benthos beneath
perennial ice cover is very low, and that advection
from areas of high production on the shelves is
minimal. Mean pigment concentrations were, however,
higher in the Amundsen Basin than in the Makarov
Basin (Soltwedel and Schewe, 1998). The limited data
thus suggest that, in the deep basins of the central
Arctic Ocean, organic matter input through the flux of
phytodetritus is extremely low and very patchy. A major
process contributing to the spatial heterogeneity may
be the production of organic matter in spatially restricted areas that are episodically ice-free, followed by
sedimentation of phytodetritus (Soltwedel and Schewe,
1998).
Bacterial numbers and biomass are also very low
in the central basins of the Arctic Ocean. Soltwedel
and Schewe (1998) reported 3.2–3.7×10
8 cells ml
−1 ,
equivalent to 5–6 mg C ml
−1 , in sediments from the
Amundsen and Makarov Basins. These data are somewhat higher than those reported by Kr¨ oncke et al.
(1994), but nevertheless indicate that bacterial biomass
in Arctic deep-sea sediments is very low. Soltwedel and
Schewe (1998) referred to the central Arctic deep-sea
basins as a benthic desert. Almost nothing appears to
be known of the non-bacterial microbial fauna or the
meiofauna of the central Arctic basins (Pfannkuche and
Thiel, 1987).
The Arctic deep-sea macrofauna
Whilst the fauna of the continental shelves of the Arctic
Ocean has become relatively well known through
the extensive work of biologists from Canada, North
America, Scandinavia and Russia, the abyssal fauna
remains little known (Paul and Menzies, 1974). Key
exploratory studies were the cruises of the Soviet
research vessels Sadko and Sedov between 1932 and
1938, Soviet studies of the central Arctic basin from
the Sedov in the period 1937 to 1940, and the work of
Andrew CLARKE
are considerably thicker, up to 2–3 km deep in areas of
the Canada Basin (Hunkins and Kutschale, 1967). All
the Plio–Pleistocene sediments examined have proved
to be sandy or silty lutites with a variable proportion of
gravel-sized clasts (Darby et al., 1989). Photographs,
however, reveal the presence of larger clasts, from
pebble to cobble size, which are usually not taken in
cores (see, for example, Hunkins et al., 1970). Clark
et al. (1980) classified the sediments into four types
based on the size frequency distribution of the <63 mm
fraction. The lithology of these sediments differed from
those in other ocean basins in the high proportion
(10–30%) of kaolinite and chlorite in the clay fraction
(<2 mm), together with the abundant detrital dolomite
and calcite in the coarser fractions.
The composition, mineralogy and physical characteristics of Arctic deep-sea sediments point to an important contribution from ice-rafted material. The overall
importance of ice-rafting is currently unquantified, but
the content of ice-rafted material in sediments of the
Arctic abyssal plain has been put at 60–70% (Darby
et al., 1989). Aeolian input is low.
Turbidity currents have been a major process for
sediment transport in the Arctic deep-sea basins. Their
importance is greater closer to the continental shelves,
but has probably been important over large areas.
Thus, the sediments in the Fram Basin have probably
originated from the Lena River, and have been carried
into the basin from the Kara and Laptev shelves
by turbidity currents. Similarly the Makarov Basin
contains turbidites from the East Siberian shelf, and the
Canada Basin sediment originated from the McKenzie
River region, and was carried by turbidity currents
(Weber, 1989). There is no evidence for significant
volumes of nonturbidite current-deposited sediments
in Arctic abyssal sediments, and the few existing
measures of rates of bottom currents in the Arctic deep
sea are all low (Galt, 1967).
Microfauna of Arctic deep-sea sediments
Relatively little is known of the microbial fauna or
meiofauna of the Arctic deep ocean. Darby et al.
(1989) reported organic-carbon contents for the Canada
Basin which decreased towards the centre of the basin.
The mean value (0.87% dry mass) was significantly
higher than in sediments of similar mineralogy from
the Atlantic and Pacific Oceans. Cranston (1997) found
organic content between 0.3 and 0.5% in the Makarov
Basin, with higher levels (1.2%) on the Lomonosov
Ridge and in the Amundsen Basin (1.0%). The low
hydrogen index (mg H/g C) and the high C/N atomic
ratios indicate that most of the organic matter in the
sediments of the Arctic deep sea is terrigenous material
(Stein et al., 1994; Stein, 1996; Fahl and Stein, 1997).
Such material typically has been extensively reworked
and consequently is of little nutritive value for benthic
organisms.
Concentrations of sediment-bound chlorophyll and
phaeopigments are very low (Boetius et al., 1996;
Soltwedel and Schewe, 1998). These data indicate that
the supply of phytodetritus to the benthos beneath
perennial ice cover is very low, and that advection
from areas of high production on the shelves is
minimal. Mean pigment concentrations were, however,
higher in the Amundsen Basin than in the Makarov
Basin (Soltwedel and Schewe, 1998). The limited data
thus suggest that, in the deep basins of the central
Arctic Ocean, organic matter input through the flux of
phytodetritus is extremely low and very patchy. A major
process contributing to the spatial heterogeneity may
be the production of organic matter in spatially restricted areas that are episodically ice-free, followed by
sedimentation of phytodetritus (Soltwedel and Schewe,
1998).
Bacterial numbers and biomass are also very low
in the central basins of the Arctic Ocean. Soltwedel
and Schewe (1998) reported 3.2–3.7×10
8 cells ml
−1 ,
equivalent to 5–6 mg C ml
−1 , in sediments from the
Amundsen and Makarov Basins. These data are somewhat higher than those reported by Kr¨ oncke et al.
(1994), but nevertheless indicate that bacterial biomass
in Arctic deep-sea sediments is very low. Soltwedel and
Schewe (1998) referred to the central Arctic deep-sea
basins as a benthic desert. Almost nothing appears to
be known of the non-bacterial microbial fauna or the
meiofauna of the central Arctic basins (Pfannkuche and
Thiel, 1987).
The Arctic deep-sea macrofauna
Whilst the fauna of the continental shelves of the Arctic
Ocean has become relatively well known through
the extensive work of biologists from Canada, North
America, Scandinavia and Russia, the abyssal fauna
remains little known (Paul and Menzies, 1974). Key
exploratory studies were the cruises of the Soviet
research vessels Sadko and Sedov between 1932 and
1938, Soviet studies of the central Arctic basin from
the Sedov in the period 1937 to 1940, and the work of