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Highlights • Observations show that formation of sediment-laden sea ice occurs in coastal polynyas in winter. • Sea ice rafted sediments are a significant component of the Laptev Sea’s sediment budget. • No observational evidence for sediment entrainment into sea ice in mid-shelf polynyas at water depth greater than 20 m. Abstract Sea ice is an important vehicle for sediment transport in the Arctic Ocean. On the Laptev Sea shelf (Siberian Arctic) large volumes of sediment-laden sea ice are formed during freeze-up in autumn, then exported and transported across the Arctic Ocean into Fram Strait where it partly melts. The incorporated sediments are released, settle on the sea floor, and serve as a proxy for ice-transport in the Arctic Ocean on geological time scales. However, the formation process of sediment-laden ice in the source area has been scarcely observed. Sediment-laden ice was sampled during a helicopter-based expedition to the Laptev Sea in March/April 2012. Sedimentological, biogeochemical and biological studies on the ice core as well as in the water column give insights into the formation process and, in combination with oceanographic process studies, on matter fluxes beneath the sea ice. Based on satellite images and ice drift back-trajectories the sediments were likely incorporated into the sea ice during a mid-winter coastal polynya near one of the main outlets of the Lena River, which is supported by the presence of abundant freshwater diatoms typical for the Lena River phytoplankton, and subsequently transported about 80 km northwards onto the shelf. Assuming ice growth of 12 to 19 cm during this period and mean suspended matter content in the newly formed ice of 91.9 mg l-1 suggests that a minimum sediment load of 8.4x104 t might have been incorporated into sea ice. Extrapolating these sediment loads for the entire Lena Delta region suggests that at least 65% of the estimated sediment loads which are incorporated during freeze-up, and up to 10% of

Highlights • Observations show that formation of sediment-laden sea ice occurs in coastal polynyas in winter. • Sea ice rafted sediments are a significant component of the Laptev Sea’s sediment budget. • No observational evidence for sediment entrainment into sea ice in mid-shelf polynyas at water depth greater than 20 m. Abstract Sea ice is an important vehicle for sediment transport in the Arctic Ocean. On the Laptev Sea shelf (Siberian Arctic) large volumes of sediment-laden sea ice are formed during freeze-up in autumn, then exported and transported across the Arctic Ocean into Fram Strait where it partly melts. The incorporated sediments are released, settle on the sea floor, and serve as a proxy for ice-transport in the Arctic Ocean on geological time scales. However, the formation process of sediment-laden ice in the source area has been scarcely observed. Sediment-laden ice was sampled during a helicopter-based expedition to the Laptev Sea in March/April 2012. Sedimentological, biogeochemical and biological studies on the ice core as well as in the water column give insights into the formation process and, in combination with oceanographic process studies, on matter fluxes beneath the sea ice. Based on satellite images and ice drift back-trajectories the sediments were likely incorporated into the sea ice during a mid-winter coastal polynya near one of the main outlets of the Lena River, which is supported by the presence of abundant freshwater diatoms typical for the Lena River phytoplankton, and subsequently transported about 80 km northwards onto the shelf. Assuming ice growth of 12 to 19 cm during this period and mean suspended matter content in the newly formed ice of 91.9 mg l-1 suggests that a minimum sediment load of 8.4x104 t might have been incorporated into sea ice. Extrapolating these sediment loads for the entire Lena Delta region suggests that at least 65% of the estimated sediment loads which are incorporated during freeze-up, and up to 10% of

The large recurrent areas of open water and/or thin ice (polynyas) producing cold brine-enriched waters off the fast-ice edge are evident in the Laptev Sea in winter time. A number of abrupt positively correlated transitions in temperature and salinity were recorded in the bottom and intermediate layers at a mooring station in the West New Siberian (WNS) polynya in February-March 2008. Being in the range of -0.5 degrees C and -1.6 psu these changes are induced by horizontal motions across the polynya and correspond to temperature and salinity horizontal gradients in the range of 0.3-1.0 degrees C/10 km and 1.4-3.5 psu/10 km, respectively. The events of distinct freshening and temperature decrease coincide with a northward current off the fast-ice edge, while southward currents brought saltier and warmer waters at intermediate depths. We suggest that the observed transitions are connected to altering pycnocline depths across the polynya. The source of relatively fresher waters at the intermediate depths in polynya is supposed to originate from penetrative mixing of surface low salinity waters to intermediate water depth. Several forcing processes that could be responsible for a penetrative mixing through the density interface in polynya are discussed. These are penetrative convection and shear-driven mixing that originates from two-layer water dynamics and/or baroclinic tidal motions. The heavily ridged seaward fast-ice edge could produce an additional source of turbulent mixing even through a shear-free density interface due to the increased roughness at the ice-water interface

The large recurrent areas of open water and/or thin ice (polynyas) producing cold brine-enriched waters off the fast-ice edge are evident in the Laptev Sea in winter time. A number of abrupt positively correlated transitions in temperature and salinity were recorded in the bottom and intermediate layers at a mooring station in the West New Siberian (WNS) polynya in February-March 2008. Being in the range of -0.5 degrees C and -1.6 psu these changes are induced by horizontal motions across the polynya and correspond to temperature and salinity horizontal gradients in the range of 0.3-1.0 degrees C/10 km and 1.4-3.5 psu/10 km, respectively. The events of distinct freshening and temperature decrease coincide with a northward current off the fast-ice edge, while southward currents brought saltier and warmer waters at intermediate depths. We suggest that the observed transitions are connected to altering pycnocline depths across the polynya. The source of relatively fresher waters at the intermediate depths in polynya is supposed to originate from penetrative mixing of surface low salinity waters to intermediate water depth. Several forcing processes that could be responsible for a penetrative mixing through the density interface in polynya are discussed. These are penetrative convection and shear-driven mixing that originates from two-layer water dynamics and/or baroclinic tidal motions. The heavily ridged seaward fast-ice edge could produce an additional source of turbulent mixing even through a shear-free density interface due to the increased roughness at the ice-water interface

The large recurrent areas of open water and/or thin ice (polynyas) producing cold brine-enriched waters off the fast-ice edge are evident in the Laptev Sea in winter time. A number of abrupt positively correlated transitions in temperature and salinity were recorded in the bottom and intermediate layers at a mooring station in the West New Siberian (WNS) polynya in February-March 2008. Being in the range of -0.5 degrees C and -1.6 psu these changes are induced by horizontal motions across the polynya and correspond to temperature and salinity horizontal gradients in the range of 0.3-1.0 degrees C/10 km and 1.4-3.5 psu/10 km, respectively. The events of distinct freshening and temperature decrease coincide with a northward current off the fast-ice edge, while southward currents brought saltier and warmer waters at intermediate depths. We suggest that the observed transitions are connected to altering pycnocline depths across the polynya. The source of relatively fresher waters at the intermediate depths in polynya is supposed to originate from penetrative mixing of surface low salinity waters to intermediate water depth. Several forcing processes that could be responsible for a penetrative mixing through the density interface in polynya are discussed. These are penetrative convection and shear-driven mixing that originates from two-layer water dynamics and/or baroclinic tidal motions. The heavily ridged seaward fast-ice edge could produce an additional source of turbulent mixing even through a shear-free density interface due to the increased roughness at the ice-water interface

We present the prototype of a simplified photogrammetric system (HELicopter-borne Ice Observation System, HELIOS) and demonstrate how it can be used to document ground-based and airborne sea ice surveys. The aerial unit consists of a nadir-looking digital camera mounted on a gimbal, a GPS receiver and a computer. It is of low-cost and weight and is designed such that it withstands low temperatures, operates autonomously and fits to any standard helicopter skid. The accuracy of the georeferenced photographs is about ± 15 m for a flight height of 85 m, flight speed of 130 km/h and a GPS sampling rate of 4 Hz. Systematic errors arise from the GPS-based determination of the camera position, the pointing accuracy of the gimbal, and the camera alignment in flight direction. Because most sea ice mapping projects require lesser accuracies than conventional mapping standards (e.g. ≤ 0.5 m for a map scale of 1:600, ASPRS (1994)), HELIOS offers a broad range of applications. This includes the photogrammetric documentation of experimental sites as well as the verification of satellite-, and model-based estimates of sea ice and snow cover properties. Images taken simultaneously with other airborne observations provide a valuable tool to assess the accuracy of those measurements.

We present the prototype of a simplified photogrammetric system (HELicopter-borne Ice Observation System, HELIOS) and demonstrate how it can be used to document ground-based and airborne sea ice surveys. The aerial unit consists of a nadir-looking digital camera mounted on a gimbal, a GPS receiver and a computer. It is of low-cost and weight and is designed such that it withstands low temperatures, operates autonomously and fits to any standard helicopter skid. The accuracy of the georeferenced photographs is about ± 15 m for a flight height of 85 m, flight speed of 130 km/h and a GPS sampling rate of 4 Hz. Systematic errors arise from the GPS-based determination of the camera position, the pointing accuracy of the gimbal, and the camera alignment in flight direction. Because most sea ice mapping projects require lesser accuracies than conventional mapping standards (e.g. ≤ 0.5 m for a map scale of 1:600, ASPRS (1994)), HELIOS offers a broad range of applications. This includes the photogrammetric documentation of experimental sites as well as the verification of satellite-, and model-based estimates of sea ice and snow cover properties. Images taken simultaneously with other airborne observations provide a valuable tool to assess the accuracy of those measurements.

We present the prototype of a simplified photogrammetric system (HELicopter-borne Ice Observation System, HELIOS) and demonstrate how it can be used to document ground-based and airborne sea ice surveys. The aerial unit consists of a nadir-looking digital camera mounted on a gimbal, a GPS receiver and a computer. It is of low-cost and weight and is designed such that it withstands low temperatures, operates autonomously and fits to any standard helicopter skid. The accuracy of the georeferenced photographs is about ± 15 m for a flight height of 85 m, flight speed of 130 km/h and a GPS sampling rate of 4 Hz. Systematic errors arise from the GPS-based determination of the camera position, the pointing accuracy of the gimbal, and the camera alignment in flight direction. Because most sea ice mapping projects require lesser accuracies than conventional mapping standards (e.g. ≤ 0.5 m for a map scale of 1:600, ASPRS (1994)), HELIOS offers a broad range of applications. This includes the photogrammetric documentation of experimental sites as well as the verification of satellite-, and model-based estimates of sea ice and snow cover properties. Images taken simultaneously with other airborne observations provide a valuable tool to assess the accuracy of those measurements.

This paper examines the role of atmospheric forcing in modifying the pathways of riverine water on the Laptev Sea shelf, using summer-to-winter hydrographic surveys from 2007 to 2009. Over the two consecutive winter seasons of 2007–2008 and 2008–2009 in the area of the winter coastal polynya, our data clearly link winter surface salinity fields to the previous summer conditions, with substantially different winter salinity patterns preconditioned by summer atmospheric forcing. In the summer of 2007, dominant along-shore westerly winds in the cyclonic regime force the Lena River runoff to flow eastward. In contrast, in the summer of 2008, dominant along-shore easterly winds over the East Siberian Sea and on-shore northerly winds over the Laptev Sea in the anticyclonic regime lock the riverine water in the vicinity of the Lena Delta. Over the coastal polynya area in the southeastern Laptev Sea these patterns precondition a surface salinity difference of 8–16 psu between the winters of 2008 and 2009. Overall, this indicates a residence time of at least half a year for riverine water on the Laptev Sea shelf. Future climate change associated with an enhanced summer cyclonicity over the eastern Arctic may turn more riverine water eastward along the eastern Siberian coast, resulting in weaker vertical density stratification over the Laptev Sea shelf, with possible impact on the efficiency of vertical mixing and polynya dense water production.

This paper examines the role of atmospheric forcing in modifying the pathways of riverine water on the Laptev Sea shelf, using summer-to-winter hydrographic surveys from 2007 to 2009. Over the two consecutive winter seasons of 2007–2008 and 2008–2009 in the area of the winter coastal polynya, our data clearly link winter surface salinity fields to the previous summer conditions, with substantially different winter salinity patterns preconditioned by summer atmospheric forcing. In the summer of 2007, dominant along-shore westerly winds in the cyclonic regime force the Lena River runoff to flow eastward. In contrast, in the summer of 2008, dominant along-shore easterly winds over the East Siberian Sea and on-shore northerly winds over the Laptev Sea in the anticyclonic regime lock the riverine water in the vicinity of the Lena Delta. Over the coastal polynya area in the southeastern Laptev Sea these patterns precondition a surface salinity difference of 8–16 psu between the winters of 2008 and 2009. Overall, this indicates a residence time of at least half a year for riverine water on the Laptev Sea shelf. Future climate change associated with an enhanced summer cyclonicity over the eastern Arctic may turn more riverine water eastward along the eastern Siberian coast, resulting in weaker vertical density stratification over the Laptev Sea shelf, with possible impact on the efficiency of vertical mixing and polynya dense water production.

The hydrography of the Laptev Sea is significantly influenced by river water and sea-ice processes, which are highly variable over the annual cycle. Despite of an estuarine structure the inner and outer shelf regions are decoupled at times as documented by the stability of a warm intermediate layer formed during summer below the Lena River plume. We demonstrate that a remnant of this warm layer is preserved below the fast ice until the end of winter, while only slightly farther to the north, offshore of the land fast ice in the polynya region, the pycnocline is eroded and no signature of this layer is found. The warm intermediate layer (WIL) formed during summer can be used as tracer for Laptev Sea shelf waters throughout the winter. There by, residence times of southern Laptev Sea waters can be estimated to be at least from summer to the end of winter/spring of the following year. (C) 2009 Elsevier Ltd. All rights reserved.

The hydrography of the Laptev Sea is significantly influenced by river water and sea-ice processes, which are highly variable over the annual cycle. Despite of an estuarine structure the inner and outer shelf regions are decoupled at times as documented by the stability of a warm intermediate layer formed during summer below the Lena River plume. We demonstrate that a remnant of this warm layer is preserved below the fast ice until the end of winter, while only slightly farther to the north, offshore of the land fast ice in the polynya region, the pycnocline is eroded and no signature of this layer is found. The warm intermediate layer (WIL) formed during summer can be used as tracer for Laptev Sea shelf waters throughout the winter. There by, residence times of southern Laptev Sea waters can be estimated to be at least from summer to the end of winter/spring of the following year. (C) 2009 Elsevier Ltd. All rights reserved.

The hydrography of the Laptev Sea is significantly influenced by river water and sea-ice processes, which are highly variable over the annual cycle. Despite of an estuarine structure the inner and outer shelf regions are decoupled at times as documented by the stability of a warm intermediate layer formed during summer below the Lena River plume. We demonstrate that a remnant of this warm layer is preserved below the fast ice until the end of winter, while only slightly farther to the north, offshore of the land fast ice in the polynya region, the pycnocline is eroded and no signature of this layer is found. The warm intermediate layer (WIL) formed during summer can be used as tracer for Laptev Sea shelf waters throughout the winter. There by, residence times of southern Laptev Sea waters can be estimated to be at least from summer to the end of winter/spring of the following year. (C) 2009 Elsevier Ltd. All rights reserved.

Historic data from the Russian-American Hydrochemical Atlas of Arctic Ocean together with data from the TRANSDRIFT II 1994 and TUNDRA 1994 cruises have been used to assess the spatial and inter-annual variability of carbon and nutrient fluxes, as well as air–sea CO2 exchange in the Laptev and western East Siberian Seas during the summer season. Budget computations using summer data of dissolved inorganic phosphate (DIP), dissolved inorganic nitrogen (DIN) and dissolved inorganic carbon (DIC) gives that the Laptev Sea shelf is a net sink of DIP and DIN of 2.5×106, 23.2×106 mol d−1, respectively, while it is a net source of DIC (excluding air–sea exchange) of 1249×106 mol d−1. In the East Siberian Seas the budget computations give 0.5×106, −11.4×106 and −173×106 mol d−1 (minus being a sink) for DIP, DIN, and DIC, respectively. In summers, the Laptev Sea Shelf is net autotrophic while the East-Siberian Sea Shelf is net heterotrophic, and both systems are weak net denitrifying. The Laptev Sea Shelf takes up 2.1 mmol CO2 m−2 d−1 from atmosphere, whereas the western part of the East-Siberian Sea Shelf loose 0.3 mmol CO2 m−2 d−1 to the atmosphere. The variability of DIP, DIN and DIC fluxes during summer in the different regions of the Laptev and East Siberian Seas depends on bottom topography, river runoff, exchange with surrounding seas and wind field.

Historic data from the Russian-American Hydrochemical Atlas of Arctic Ocean together with data from the TRANSDRIFT II 1994 and TUNDRA 1994 cruises have been used to assess the spatial and inter-annual variability of carbon and nutrient fluxes, as well as air–sea CO2 exchange in the Laptev and western East Siberian Seas during the summer season. Budget computations using summer data of dissolved inorganic phosphate (DIP), dissolved inorganic nitrogen (DIN) and dissolved inorganic carbon (DIC) gives that the Laptev Sea shelf is a net sink of DIP and DIN of 2.5×106, 23.2×106 mol d−1, respectively, while it is a net source of DIC (excluding air–sea exchange) of 1249×106 mol d−1. In the East Siberian Seas the budget computations give 0.5×106, −11.4×106 and −173×106 mol d−1 (minus being a sink) for DIP, DIN, and DIC, respectively. In summers, the Laptev Sea Shelf is net autotrophic while the East-Siberian Sea Shelf is net heterotrophic, and both systems are weak net denitrifying. The Laptev Sea Shelf takes up 2.1 mmol CO2 m−2 d−1 from atmosphere, whereas the western part of the East-Siberian Sea Shelf loose 0.3 mmol CO2 m−2 d−1 to the atmosphere. The variability of DIP, DIN and DIC fluxes during summer in the different regions of the Laptev and East Siberian Seas depends on bottom topography, river runoff, exchange with surrounding seas and wind field.

Historic data from the Russian-American Hydrochemical Atlas of Arctic Ocean together with data from the TRANSDRIFT II 1994 and TUNDRA 1994 cruises have been used to assess the spatial and inter-annual variability of carbon and nutrient fluxes, as well as air–sea CO2 exchange in the Laptev and western East Siberian Seas during the summer season. Budget computations using summer data of dissolved inorganic phosphate (DIP), dissolved inorganic nitrogen (DIN) and dissolved inorganic carbon (DIC) gives that the Laptev Sea shelf is a net sink of DIP and DIN of 2.5×106, 23.2×106 mol d−1, respectively, while it is a net source of DIC (excluding air–sea exchange) of 1249×106 mol d−1. In the East Siberian Seas the budget computations give 0.5×106, −11.4×106 and −173×106 mol d−1 (minus being a sink) for DIP, DIN, and DIC, respectively. In summers, the Laptev Sea Shelf is net autotrophic while the East-Siberian Sea Shelf is net heterotrophic, and both systems are weak net denitrifying. The Laptev Sea Shelf takes up 2.1 mmol CO2 m−2 d−1 from atmosphere, whereas the western part of the East-Siberian Sea Shelf loose 0.3 mmol CO2 m−2 d−1 to the atmosphere. The variability of DIP, DIN and DIC fluxes during summer in the different regions of the Laptev and East Siberian Seas depends on bottom topography, river runoff, exchange with surrounding seas and wind field.

Sediment dynamics on the Laptev Sea shelf (Siberian Arctic), which is ice-covered for about 9 months a year, were studied for a I-year period. Two oceanographic bottom-mooring stations equipped with an Acoustic Doppler Current Profiler (ADCP) and a Conductivity Temperature Depth meter (CTD) were deployed on the eastern Laptev Sea shelf between August 1998 and September 1999. Thus, for the first time information on current, suspended particulate matter (SPM), and bottom temperature variations were provided throughout one seasonal cycle for a Siberian shelf sea. The data set indicates that during and shortly after the river-ice breakup (June-early July) sediment transport is dominated by riverine input and transport onto the eastern Laptev Sea shelf within the surface layer beneath the fast ice. Under ice-free conditions (mid-July to September), SPM is mainly trapped on the eastern Laptev Sea shelf SPM discharged by the Lena River is transported within the surface layer to the mid-shelf where it sinks through the water column into the bottom nepheloid layer only to be carried back onto the inner shelf again together with newly resuspended bottom material. On the inner shelf the material is partly transported back into the surface layer by turbid mixing and carried out onto the mid-shelf again. During freeze-up (October), SPM in the surface layer on the inner shelf is incorporated into newly formed ice and transported with the ice over the continental margin into the deep Arctic Ocean. Beneath the ice cover (November to June-July) SPM slowly sinks and sediment transport is of minor importance on the inner shelf. However, beneath the polynya, bottom material is resuspended during storm events and transported onto the inner shelf where it temporarily settles. The study suggests a quasi-estuarine sediment circulation on the eastern Laptev Sea shelf, especially during ice-free conditions, and sediment export dominated by ice rather than bottom transport

Based on hydrological data from 1979 to 1999 the average long-term salinity of the flaw polynya in the Eastern Laptev Sea is estimated. A new method to evaluate ice production based on hydrological rather than sea-ice observations is proposed. Average annual ice production in the polynya ranges between 3 and 4 m. The probability of convective mixing penetrating down to the seafloor is highest in the regions of the flaw polynya, but does not exceed 20% in the Eastern and 70% in the Western Laptev Sea. Conductivity-temperature-depth (CTD) measurements and observations of currents carried out in April-May 1999 allowed us to investigate the surface circulation along the margins of the Laptev Sea flaw polynya. The convective nature of the surface currents, with velocities measured as high as 62 cm/s, is discussed. Currents are most likely part of circulation cells, which arise as a result of brine rejection due to intensive ice formation in the polynya. It is shown that the spatial alignment of sea ice crystals in the marginal part of the polynya is most likely a consequence of the quasi-stationary cellular circulation

The distribution of dissolved and particulate trace metals (Fe, Mn, Cu, Ni, Zn, and Pb) was studied for the first time during the spring high flow period of the Lena River (Arctic Siberia). The results show that concentrations of dissolved metals in the river Lena during the spring high flow in June 1996 (spring freshet) were significantly higher than those reported for the rest of the year. For example the measured average concentration of dissolved Fe (6349 ± 2122 nM) during the high flow is approximately 7 times higher than previously published concentrations measured during the summer months. Dissolved Fe concentrations in the freshwater (salinity < 1) are positively correlated with the amount of suspended particulate matter (SPM) (p < 0.01), but negatively correlated with the Fe concentrations in SPM (p < 0.01). The data showed that the aluminium-normalized concentrations of particulate Fe, Mn, Pb, Ni, and Zn in the freshwater are negatively correlated with SPM. This suggests that the mobilization of metals from suspended particulate matter is the driving force for the observed high concentrations of dissolved Fe, Mn, Zn and Pb in the water of the Lena River during the spring freshet. During the high flow period in June about 35% of the total annual flow of the river Lena flows into the Laptev Sea. Previously published metal budgets for the river Lena that did not incorporate data from the spring high flow period, therefore, underestimate the fluxes of dissolved trace metals from the Siberian rivers to the Arctic Ocean. For instance, the estimated input of dissolved Fe in June 1996 is approximately 4.5 times higher than the average annual dissolved Fe input calculated on the basis of summer data. The results of this study demonstrate that the previous evaluations of the trace metal flux of the Lena river–which are based on data obtained from August to October–may underestimate the total riverine input of dissolved trace metals to the Arctic Ocean.

Sediment dynamics on the Laptev Sea shelf (Siberian Arctic), which is ice-covered for about 9 months a year, were studied for a I-year period. Two oceanographic bottom-mooring stations equipped with an Acoustic Doppler Current Profiler (ADCP) and a Conductivity Temperature Depth meter (CTD) were deployed on the eastern Laptev Sea shelf between August 1998 and September 1999. Thus, for the first time information on current, suspended particulate matter (SPM), and bottom temperature variations were provided throughout one seasonal cycle for a Siberian shelf sea. The data set indicates that during and shortly after the river-ice breakup (June-early July) sediment transport is dominated by riverine input and transport onto the eastern Laptev Sea shelf within the surface layer beneath the fast ice. Under ice-free conditions (mid-July to September), SPM is mainly trapped on the eastern Laptev Sea shelf SPM discharged by the Lena River is transported within the surface layer to the mid-shelf where it sinks through the water column into the bottom nepheloid layer only to be carried back onto the inner shelf again together with newly resuspended bottom material. On the inner shelf the material is partly transported back into the surface layer by turbid mixing and carried out onto the mid-shelf again. During freeze-up (October), SPM in the surface layer on the inner shelf is incorporated into newly formed ice and transported with the ice over the continental margin into the deep Arctic Ocean. Beneath the ice cover (November to June-July) SPM slowly sinks and sediment transport is of minor importance on the inner shelf. However, beneath the polynya, bottom material is resuspended during storm events and transported onto the inner shelf where it temporarily settles. The study suggests a quasi-estuarine sediment circulation on the eastern Laptev Sea shelf, especially during ice-free conditions, and sediment export dominated by ice rather than bottom transport

Based on hydrological data from 1979 to 1999 the average long-term salinity of the flaw polynya in the Eastern Laptev Sea is estimated. A new method to evaluate ice production based on hydrological rather than sea-ice observations is proposed. Average annual ice production in the polynya ranges between 3 and 4 m. The probability of convective mixing penetrating down to the seafloor is highest in the regions of the flaw polynya, but does not exceed 20% in the Eastern and 70% in the Western Laptev Sea. Conductivity-temperature-depth (CTD) measurements and observations of currents carried out in April-May 1999 allowed us to investigate the surface circulation along the margins of the Laptev Sea flaw polynya. The convective nature of the surface currents, with velocities measured as high as 62 cm/s, is discussed. Currents are most likely part of circulation cells, which arise as a result of brine rejection due to intensive ice formation in the polynya. It is shown that the spatial alignment of sea ice crystals in the marginal part of the polynya is most likely a consequence of the quasi-stationary cellular circulation

The distribution of dissolved and particulate trace metals (Fe, Mn, Cu, Ni, Zn, and Pb) was studied for the first time during the spring high flow period of the Lena River (Arctic Siberia). The results show that concentrations of dissolved metals in the river Lena during the spring high flow in June 1996 (spring freshet) were significantly higher than those reported for the rest of the year. For example the measured average concentration of dissolved Fe (6349 ± 2122 nM) during the high flow is approximately 7 times higher than previously published concentrations measured during the summer months. Dissolved Fe concentrations in the freshwater (salinity < 1) are positively correlated with the amount of suspended particulate matter (SPM) (p < 0.01), but negatively correlated with the Fe concentrations in SPM (p < 0.01). The data showed that the aluminium-normalized concentrations of particulate Fe, Mn, Pb, Ni, and Zn in the freshwater are negatively correlated with SPM. This suggests that the mobilization of metals from suspended particulate matter is the driving force for the observed high concentrations of dissolved Fe, Mn, Zn and Pb in the water of the Lena River during the spring freshet. During the high flow period in June about 35% of the total annual flow of the river Lena flows into the Laptev Sea. Previously published metal budgets for the river Lena that did not incorporate data from the spring high flow period, therefore, underestimate the fluxes of dissolved trace metals from the Siberian rivers to the Arctic Ocean. For instance, the estimated input of dissolved Fe in June 1996 is approximately 4.5 times higher than the average annual dissolved Fe input calculated on the basis of summer data. The results of this study demonstrate that the previous evaluations of the trace metal flux of the Lena river–which are based on data obtained from August to October–may underestimate the total riverine input of dissolved trace metals to the Arctic Ocean.

Based on hydrological data from 1979 to 1999 the average long-term salinity of the flaw polynya in the Eastern Laptev Sea is estimated. A new method to evaluate ice production based on hydrological rather than sea-ice observations is proposed. Average annual ice production in the polynya ranges between 3 and 4 m. The probability of convective mixing penetrating down to the seafloor is highest in the regions of the flaw polynya, but does not exceed 20% in the Eastern and 70% in the Western Laptev Sea. Conductivity-temperature-depth (CTD) measurements and observations of currents carried out in April-May 1999 allowed us to investigate the surface circulation along the margins of the Laptev Sea flaw polynya. The convective nature of the surface currents, with velocities measured as high as 62 cm/s, is discussed. Currents are most likely part of circulation cells, which arise as a result of brine rejection due to intensive ice formation in the polynya. It is shown that the spatial alignment of sea ice crystals in the marginal part of the polynya is most likely a consequence of the quasi-stationary cellular circulation

The distribution of dissolved and particulate trace metals (Fe, Mn, Cu, Ni, Zn, and Pb) was studied for the first time during the spring high flow period of the Lena River (Arctic Siberia). The results show that concentrations of dissolved metals in the river Lena during the spring high flow in June 1996 (spring freshet) were significantly higher than those reported for the rest of the year. For example the measured average concentration of dissolved Fe (6349 ± 2122 nM) during the high flow is approximately 7 times higher than previously published concentrations measured during the summer months. Dissolved Fe concentrations in the freshwater (salinity < 1) are positively correlated with the amount of suspended particulate matter (SPM) (p < 0.01), but negatively correlated with the Fe concentrations in SPM (p < 0.01). The data showed that the aluminium-normalized concentrations of particulate Fe, Mn, Pb, Ni, and Zn in the freshwater are negatively correlated with SPM. This suggests that the mobilization of metals from suspended particulate matter is the driving force for the observed high concentrations of dissolved Fe, Mn, Zn and Pb in the water of the Lena River during the spring freshet. During the high flow period in June about 35% of the total annual flow of the river Lena flows into the Laptev Sea. Previously published metal budgets for the river Lena that did not incorporate data from the spring high flow period, therefore, underestimate the fluxes of dissolved trace metals from the Siberian rivers to the Arctic Ocean. For instance, the estimated input of dissolved Fe in June 1996 is approximately 4.5 times higher than the average annual dissolved Fe input calculated on the basis of summer data. The results of this study demonstrate that the previous evaluations of the trace metal flux of the Lena river–which are based on data obtained from August to October–may underestimate the total riverine input of dissolved trace metals to the Arctic Ocean.

Sediment dynamics on the Laptev Sea shelf (Siberian Arctic), which is ice-covered for about 9 months a year, were studied for a I-year period. Two oceanographic bottom-mooring stations equipped with an Acoustic Doppler Current Profiler (ADCP) and a Conductivity Temperature Depth meter (CTD) were deployed on the eastern Laptev Sea shelf between August 1998 and September 1999. Thus, for the first time information on current, suspended particulate matter (SPM), and bottom temperature variations were provided throughout one seasonal cycle for a Siberian shelf sea. The data set indicates that during and shortly after the river-ice breakup (June-early July) sediment transport is dominated by riverine input and transport onto the eastern Laptev Sea shelf within the surface layer beneath the fast ice. Under ice-free conditions (mid-July to September), SPM is mainly trapped on the eastern Laptev Sea shelf SPM discharged by the Lena River is transported within the surface layer to the mid-shelf where it sinks through the water column into the bottom nepheloid layer only to be carried back onto the inner shelf again together with newly resuspended bottom material. On the inner shelf the material is partly transported back into the surface layer by turbid mixing and carried out onto the mid-shelf again. During freeze-up (October), SPM in the surface layer on the inner shelf is incorporated into newly formed ice and transported with the ice over the continental margin into the deep Arctic Ocean. Beneath the ice cover (November to June-July) SPM slowly sinks and sediment transport is of minor importance on the inner shelf. However, beneath the polynya, bottom material is resuspended during storm events and transported onto the inner shelf where it temporarily settles. The study suggests a quasi-estuarine sediment circulation on the eastern Laptev Sea shelf, especially during ice-free conditions, and sediment export dominated by ice rather than bottom transport

The Cenozoic sediments sampled in ODP Leg 104 on the Vøring Plateau show a distinct variability of the total organic carbon content (TOC) and the accumulation rates of TOC. Based on the geochemical and organic-petrographic characterization of the sedimentary organic matter (OM), the allochthonous and autochthonous proportion of the OM could be quantified.The results clearly demonstrate that high TOC percentages and TOC accumulation rates in Cenozoic sediment sections display a generally high input of allochthonous organic matter. Oxidized and partly well-rounded organic particles built up the main portion of OM within the Miocene, TOC-rich sediments. The most probable source of this oxidized OM are reworked sediments from the Scandinavian shelf. Changes in the input of these organic particles are to some degree correlative with sea-level changes.The Cenozoic accumulation of autochthonous OM is low and does not reveal a clear variation during the Miocene and early Pliocene. In spite of a high accumulation rate of biogenic opal during the Early Miocene, the accumulation rate of autochthonous TOC is low. The autochthonous particle assemblage is dominated by relatively inert OM, like dinoflagellate cysts. This points to an intensive biological and/or early diagenetic degradation of the marine OM under well oxidized bottom water conditions during the last 23 Myr. Nevertheless, a continuation of marine OM degradation during later stages of diagenesis cannot be excluded.A prominent dominance of allochthonous OM over autochthonous is documented with the beginning of the Pliocene. At 2.45 Ma the episodic occurrence of ice-rafted, thermally mature OM reflects the onset of the glacial erosion of Mesozoic, coal and black shale bearing sediments on the Scandinavian and Barents Sea shelves. The first occurrence of these, in view of the actual burial depth, thermally overmature OM particles is, therefore, a marker for the beginning of the strong Scandinavian glaciation and the adv

The Cenozoic sediments sampled in ODP Leg 104 on the Vøring Plateau show a distinct variability of the total organic carbon content (TOC) and the accumulation rates of TOC. Based on the geochemical and organic-petrographic characterization of the sedimentary organic matter (OM), the allochthonous and autochthonous proportion of the OM could be quantified.The results clearly demonstrate that high TOC percentages and TOC accumulation rates in Cenozoic sediment sections display a generally high input of allochthonous organic matter. Oxidized and partly well-rounded organic particles built up the main portion of OM within the Miocene, TOC-rich sediments. The most probable source of this oxidized OM are reworked sediments from the Scandinavian shelf. Changes in the input of these organic particles are to some degree correlative with sea-level changes.The Cenozoic accumulation of autochthonous OM is low and does not reveal a clear variation during the Miocene and early Pliocene. In spite of a high accumulation rate of biogenic opal during the Early Miocene, the accumulation rate of autochthonous TOC is low. The autochthonous particle assemblage is dominated by relatively inert OM, like dinoflagellate cysts. This points to an intensive biological and/or early diagenetic degradation of the marine OM under well oxidized bottom water conditions during the last 23 Myr. Nevertheless, a continuation of marine OM degradation during later stages of diagenesis cannot be excluded.A prominent dominance of allochthonous OM over autochthonous is documented with the beginning of the Pliocene. At 2.45 Ma the episodic occurrence of ice-rafted, thermally mature OM reflects the onset of the glacial erosion of Mesozoic, coal and black shale bearing sediments on the Scandinavian and Barents Sea shelves. The first occurrence of these, in view of the actual burial depth, thermally overmature OM particles is, therefore, a marker for the beginning of the strong Scandinavian glaciation and the adv