Pelagic-Benthic Coupling in the Laptev Sea Affected by Ice Cover
C. Grahl l , A. Boetius 2 and E.-M. Nothigl
(1) Alfred-Wegener-Institutfiir Polar- und Meeresforschung, Postfach 120161, D 27515 Bremerhaven,
Germany
(2) Institutfiir Ostseeforschung, Postfach 301161, D 18112 RostockiWarnemiinde, Germany
Received I August 1997 and accepted in revised form 14 November 1997
Abstract - During two expeditions with RV Polarstern to the Laptev Sea (ARK IX/4 in
September/October 1993 and ARK XIII in July/August 1995), sediment samples were
collected from the continental shelf edge to the deep Arctic basins from water depths
between 37 m and 3831 m. Pigment concentrations in the surface sediments were
determined as a biomarker for the input of phytoplankton material by sedimentation
(Pfannkuche 1992). Furthermore, hydrolytic activities of the extracellular enzyme ~glucosidase in the sediments were measured as an indicator of microbial heterotrophic
activity linked to the availability of plankton detritus (Boetius and Lochte 1994).
In summer 1993, the eastern Laptev Sea was ice-free and the western section was icecovered. In contrast, in summer 1995, the shelf edge of the Laptev Sea was ice-free during
the whole summer and only the eastern part of the slope was ice-covered. However, in both
years, chlorophyll a equivalents (chlorophyll a + phaeopigments) and enzyme activities in
the surface sediments (0-1 em) decreased from the shelf edge to the bottom at the
continental slope more than 10fold with increasing water depth. Highest pigment
concentrations and microbial enzymatic activitiy was found at the shelf edge of the Eastern
Laptev Sea in summer 1993, in an area that had been crossed several times by the ice edge.
However, in general, variations in the ice cover during the Arctic summer seem to have a
lesser effect on phytodetritus deposition at the continental slope than water depth and/or
distance from the shelf area.
Introduction
Life at the bottom of the ocean mainly depends on the input of organic material from the
euphotic zone (Gage and Tyler, 1991). Depending on the climatic and hydrographic regimes in
an oceanic region, this food supply can be considered as a rain of organic material with little
variation or may be subject to strong seasonal events (Wefer, 1989). In polar regions, primary
productivity and thus the export of plant detritus to the seafloor is largely restricted to the
summer season when light is available and when the ice cover is receding. The relation between
pelagic and benthic processes in Arctic polar waters was summarized by Grebmeier and Barry
(1991). They found a direct impact of the input of organic material (influenced by variability in
hydrography, sea ice cover, light supply, and pelagic food web structure) on the abundance and
biomass of benthic communities. However, their Arctic studies were restricted to the shallow
shelf areas of the highly-productive Bering and Chukchi Seas. To date, little is known on
pelagic-benthic coupling in the Eastern Arctic Seas (East Siberian, Laptev, Kara Seas) which
are characterized by low nutrient concentrations and high ice coverage during summer.
The influence of water-depth, ice cover, and distance from the coast on the input of
phytoplankton detritus to the sediment was studied during two cruises to the Laptev Sea, ARK
IX/4 in 1993 (Flitterer, 1994) and ARK XIII in 1995 (Rachor, 1997). The data of the cruise in
1993 introduced new perspectives to the discussion of the factors controlling benthic microbial
activities and biomass in deep-sea sediments (Boetius et aI., 1996; Boetius and Damm, 1997;
Boetius, in press). Here data from the two expeditions are compared and implications for
pelagic-benthic coupling in the outer Laptev Sea are discussed. In our study, processes related
to pelagic-benthic coupling via transport of organic matter from the euphotic zone were
In: Kassens, H., H.A. Bauch,!. Dmitrenko, H. Eicken, H.-W. Hubberten, M. Melles, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999, 143-152.
C. Grahl l , A. Boetius 2 and E.-M. Nothigl
(1) Alfred-Wegener-Institutfiir Polar- und Meeresforschung, Postfach 120161, D 27515 Bremerhaven,
Germany
(2) Institutfiir Ostseeforschung, Postfach 301161, D 18112 RostockiWarnemiinde, Germany
Received I August 1997 and accepted in revised form 14 November 1997
Abstract - During two expeditions with RV Polarstern to the Laptev Sea (ARK IX/4 in
September/October 1993 and ARK XIII in July/August 1995), sediment samples were
collected from the continental shelf edge to the deep Arctic basins from water depths
between 37 m and 3831 m. Pigment concentrations in the surface sediments were
determined as a biomarker for the input of phytoplankton material by sedimentation
(Pfannkuche 1992). Furthermore, hydrolytic activities of the extracellular enzyme ~glucosidase in the sediments were measured as an indicator of microbial heterotrophic
activity linked to the availability of plankton detritus (Boetius and Lochte 1994).
In summer 1993, the eastern Laptev Sea was ice-free and the western section was icecovered. In contrast, in summer 1995, the shelf edge of the Laptev Sea was ice-free during
the whole summer and only the eastern part of the slope was ice-covered. However, in both
years, chlorophyll a equivalents (chlorophyll a + phaeopigments) and enzyme activities in
the surface sediments (0-1 em) decreased from the shelf edge to the bottom at the
continental slope more than 10fold with increasing water depth. Highest pigment
concentrations and microbial enzymatic activitiy was found at the shelf edge of the Eastern
Laptev Sea in summer 1993, in an area that had been crossed several times by the ice edge.
However, in general, variations in the ice cover during the Arctic summer seem to have a
lesser effect on phytodetritus deposition at the continental slope than water depth and/or
distance from the shelf area.
Introduction
Life at the bottom of the ocean mainly depends on the input of organic material from the
euphotic zone (Gage and Tyler, 1991). Depending on the climatic and hydrographic regimes in
an oceanic region, this food supply can be considered as a rain of organic material with little
variation or may be subject to strong seasonal events (Wefer, 1989). In polar regions, primary
productivity and thus the export of plant detritus to the seafloor is largely restricted to the
summer season when light is available and when the ice cover is receding. The relation between
pelagic and benthic processes in Arctic polar waters was summarized by Grebmeier and Barry
(1991). They found a direct impact of the input of organic material (influenced by variability in
hydrography, sea ice cover, light supply, and pelagic food web structure) on the abundance and
biomass of benthic communities. However, their Arctic studies were restricted to the shallow
shelf areas of the highly-productive Bering and Chukchi Seas. To date, little is known on
pelagic-benthic coupling in the Eastern Arctic Seas (East Siberian, Laptev, Kara Seas) which
are characterized by low nutrient concentrations and high ice coverage during summer.
The influence of water-depth, ice cover, and distance from the coast on the input of
phytoplankton detritus to the sediment was studied during two cruises to the Laptev Sea, ARK
IX/4 in 1993 (Flitterer, 1994) and ARK XIII in 1995 (Rachor, 1997). The data of the cruise in
1993 introduced new perspectives to the discussion of the factors controlling benthic microbial
activities and biomass in deep-sea sediments (Boetius et aI., 1996; Boetius and Damm, 1997;
Boetius, in press). Here data from the two expeditions are compared and implications for
pelagic-benthic coupling in the outer Laptev Sea are discussed. In our study, processes related
to pelagic-benthic coupling via transport of organic matter from the euphotic zone were
In: Kassens, H., H.A. Bauch,!. Dmitrenko, H. Eicken, H.-W. Hubberten, M. Melles, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999, 143-152.