Anthropogenic iodine-129 in seawater along a transect from the Norwegian coastal current to the North Pole

Variation in the concentrations of iodine-129 (129I, T1/2=15.7 Myr), a low-level radioactive component of nuclear fuel waste, is documented in surface waters and depth profiles collected during 2001 along a transect from the Norwegian Coastal Current to the North Pole. The surface waters near the Norwegian coast are found to have 20 times higher 129I concentration than the surface waters of the Arctic Ocean. The depth profiles of 129I taken in the Arctic Ocean reveal a sharp decline in the concentration to a depth of about 300-500 m followed by a weaker gradient extending down to the bottom. A twofold increase in the 129I concentration is observed in the upper 1000 m since 1996. Based on known estimates of marine transient time from the release sources (the nuclear reprocessing facilities at La Hague, France, and Sellafield, UK), a doubling in the 129I inventory of the top 1000 m of the Arctic Ocean is expected to occur between the years 2001 and 2006. As 129I of polar mixed layer and Atlantic layer of the Arctic Ocean is ventilated by the East Greenland Current into the Nordic Seas and North Atlantic Ocean, further dispersal and increase of the isotope concentration in these regions will be encountered in the near future.     

Anthropogenic impact on the runoff of Russian rivers emptying into the Arctic Ocean

The effect of water consumption and reservoirs on the regime and water resources of Russian rivers emptying into the Arctic Ocean is discussed. The impact of reservoirs on the annual and seasonal runoff of regulated rivers is estimated. The transformation of this impact along the rivers down to their outlet sections is analyzed. Possible variants of the development of water management measures in Arctic river basins in the first quarter of the 21st century are considered.     

Iodine-129 concentrations in marginal seas of the north Pacific and Pacific-influenced waters of the Arctic Ocean

Water sampling during the 1993 IV Russian–US Joint Expedition to the Bering and Chukchi Seas (BERPAC) indicates that Pacific Ocean burdens of the long-lived radionuclide ¹²⁹I are relatively low in the Pacific-influenced Arctic, particularly compared to high latitude waters influenced by the North Atlantic. These low concentrations occur despite the presence of potential submerged anthropogenic sources in the East Sea (Sea of Japan), and in the northwest Pacific Ocean, east of the Kamchatka Peninsula. The concentration of ¹²⁹I entering the Arctic Ocean through Bering Strait, 0.7×10⁸ atoms kg⁻¹, is only slightly higher than observed in deep Pacific waters. Similar concentrations (0.44–0.76×10⁸ atoms kg⁻¹) measured in Long Strait indicate no significant transfer of ¹²⁹I eastward into the Chukchi Sea in the Siberian Coastal Current from the Siberian marginal seas to the west. However, the concentrations reported here are more than an order of magnitude higher than the Bering Strait input concentration estimated (1.0×10⁶ atoms kg⁻¹) from bomb fallout mass balances, which supports other existing evidence for a significant atmospheric deposition term for this radionuclide in surface ocean waters. Near-bottom water samples collected in productive waters of the Bering and Chukchi Seas also suggest that sediment regeneration may locally elevate ¹²⁹I concentrations, and impact its utility as a water mass tracer. As part of this study, two deep ¹²⁹I profiles were also measured in the East Sea in 1993–1994. The near-surface concentration of ¹²⁹I ranged from 0.12 to 0.31×10⁸ atoms kg⁻¹. The ¹²⁹I concentration showed a steady decrease with depth, although because of active deep water ventilation, the entire 3000 m water column exceeded natural concentrations of the radionuclide. Atom ratios of ¹²⁹I/¹³⁷Cs in the East Sea also suggest an excess of ¹²⁹I above bomb fallout estimates, also possibly resulting from atmospheric deposition ultimately originating from nuclear facilities.     

Reservoirs in the Drainage Basins of Russian Arctic Seas

Water Resources - The space and time distribution of reservoirs over the drainage basins of Arctic seas within Russian Federation territory and the main rivers flowing into the Arctic Ocean is...     

Tritium in the Arctic Ocean and East Greenland Current

High concentrations of tritium are found in the surface water of the Arctic Ocean (up to 50 TU) and in the East Greenland Current (up to 70 TU). These high tritium values are a direct result of atmospheric testing of nuclear weapons in the early 1960's. A box model with a time-dependent input of highly tritiated precipitation predicts that high tritium concentrations are to be expected in the surface layer of the Arctic Ocean and its various outflows. We suggest that a few tritium stations in the Arctic Ocean would provide a powerful analytical tool for assigning time scales to exchange processes.     

Anthropogenic transformations of the hydrological-ecological state of rivers in the Russian Arctic

The dynamics of time and space variations in the composition of the aquatic medium is estimated and correlated with the governing factors of anthropogenic impact. The role of anthropogenic component is shown to be determining in the formation of the hydrochemical regime in Russian Arctic rivers.     

Estimating the internal pressure gradient errors in a σ-coordinate ocean model for the Nordic Seas

Internal pressure gradient estimation is problematic in σ-coordinate ocean models and models based on more generalised topography following coordinate systems. Artificial pressure gradients in these models may create artificial flow. In recent literature, several methods for reducing the errors in the estimated internal pressure gradients are suggested. A basin with a bell-shaped seamount in the middle has often been applied as a test case. To supplement the findings from these more idealised experiments, the internal pressure gradient errors in a σ-coordinate ocean model for the Nordic Seas are discussed in the present paper. Three methods for estimating internal pressure gradients are applied in these experiments. The sensitivity of the results to the subtraction of background stratification and to the horizontal viscosity are also investigated. For the extended Nordic Seas case, basin scale modes dominate after a few days of simulation. The errors in the transports across some sections may be larger than 1 Sv (1 Sv = 10⁶ m³ s^− 1) in these studies with 16-km grid resolution. The order of magnitude of the errors in the transports of Atlantic water into the Nordic Seas is approximately 0.5 Sv or between 5 and 10 % of recent transport estimates based on measurements. The results do not indicate that the errors are generally reduced if the background stratification is subtracted when estimating internal pressure gradients in terrain following models. However, the results from the experiments initialised with the background stratification show that the erroneous flows may be reduced considerably by using more recent techniques for estimating internal pressure gradients, especially for higher values of horizontal viscosity.     

The Role of Sea Ice in the Coastal Zone Dynamics of the Arctic Seas

Data on the role of sea ice in the dynamics of the Arctic Basin coasts and floor is generalized and systematized.     

Anthropogenic Processes in Continental Waters of Arctic Regions and Criteria for Their Assessment

Development features of anthropogenic processes in continental waters in the Arctic Basin, including eutrophication, acidification, and toxic pollution, are characterized. The major changes in the ecosystems and the formation periods of hazardous situations are demonstrated. Criteria are suggested for the diagnostics of unfavorable processes and the need of more stringent water quality standards is substantiated.     

Analysis of trends in annual streamflow to the Arctic Ocean

There is increasing interest in the magnitude of the flow of freshwater to the Arctic Ocean due to its impacts on the biogeophysical and socio‐economic systems in the north and its influence on global climate. This study examines freshwater flow based on a dataset of 72 rivers that either directly or indirectly contribute flow to the Arctic Ocean or reflect the hydrologic regime of areas contributing flow to the Arctic Ocean. Annual streamflow for the 72 rivers is categorized as to the nature and location of the contribution to the Arctic Ocean, and composite series of annual flows are determined for each category for the period 1975 to 2015. A trend analysis is then conducted for the annual discharge series assembled for each category. The results reveal a general increase in freshwater flow to the Arctic Ocean with this increase being more prominent from the Eurasian rivers than from the North American rivers. A comparison with trends obtained from an earlier study ending in 2000 indicates similar trend response from the Eurasian rivers, but dramatic differences from some of the North American rivers. A total annual discharge increase of 8.7 km³/y/y is found, with an annual discharge increase of 5.8 km³/y/y observed for the rivers directly flowing to the Arctic Ocean. The influence of annual or seasonal climate oscillation indices on annual discharge series is also assessed. Several river categories are found to have significant correlations with the Arctic Oscillation, the North Atlantic Oscillation, or the Pacific Decadal Oscillation. However, no significant association with climate indices is found for the river categories leading to the largest freshwater contribution to the Arctic Ocean.     

Ice-induced seasonal variability of tidal constants in the Arctic Ocean

The results for three-dimensional (3D) winter and summer tidal flows in the homogeneous Arctic Ocean, obtained with the use of a modified version of the 3D finite-element hydrothermodynamic model QUODDY-4, are presented. It is shown that seasonal variability of the M₂ tidal constants (amplitudes and phases of tidal sea surface level elevations) in the Central and Canadian parts of the Arctic Ocean is less than the error in the predicted tidal sea surface level elevations. This means that the seasonal variability can be neglected at least as a first approximation. A different situation is encountered in the Siberian continental shelf, where seasonal changes of tidal amplitude are ±5 cm, while those of tidal phase vary from 15° to several tens of degrees.     

Toward Improved Estimation of the Dynamic Topography and Ocean Circulation in the High Latitude and Arctic Ocean: The Importance of GOCE

The Arctic plays a fundamental role in the climate system and shows significant sensitivity to anthropogenic climate forcing and the ongoing climate change. Accelerated changes in the Arctic are already observed, including elevated air and ocean temperatures, declines of the summer sea ice extent and sea ice thickness influencing the albedo and CO₂ exchange, melting of the Greenland Ice Sheet and increased thawing of surrounding permafrost regions. In turn, the hydrological cycle in the high latitude and Arctic is expected to undergo changes although to date it is challenging to accurately quantify this. Moreover, changes in the temperature and salinity of surface waters in the Arctic Ocean and Nordic Seas may also influence the flow of dense water through the Denmark Strait, which are found to be a precursor for changes in the Atlantic meridional overturning circulation with a lead time of around 10 years (Hawkins and Sutton in Geophys Res Lett 35:L11603, 2008). Evidently changes in the Arctic and surrounding seas have far reaching influences on regional and global environment and climate variability, thus emphasizing the need for advanced quantitative understanding of the ocean circulation and transport variability in the high latitude and Arctic Ocean. In this respect, this study combines in situ hydrographical data, surface drifter data and direct current meter measurements, with coupled sea ice–ocean models, radar altimeter data and the latest GOCE-based geoid in order to estimate and assess the quality, usefulness and validity of the new GOCE-derived mean dynamic topography for studies of the ocean circulation and transport estimates in the Nordic Seas and Arctic Ocean.     

Cascading ocean basins: numerical simulations of the circulation and interbasin exchange in the Azov-Black-Marmara-Mediterranean Seas system

In this paper, we use the unstructured grid model SCHISM to simulate the thermohydrodynamics in a chain of baroclinic, interconnected basins. The model shows a good skill in simulating the horizontal circulation and vertical profiles of temperature, salinity, and currents. The magnitude and phases of the seasonal changes of circulation are consistent with earlier observations. Among the mesoscale and subbasin-scale circulation features that are realistically simulated are the anticyclonic coastal eddies, the Sebastopol and Batumi eddies, the Marmara Sea outflow around the southern coast of the Limnos Island, and the pathway of the cold water originating from the shelf. The superiority of the simulations compared to earlier numerical studies is demonstrated with the example of model capabilities to resolve the strait dynamics, gravity currents originating from the straits, high-salinity bottom layer on the shallow shelf, as well as the multiple intrusions from the Bosporus Strait down to 700 m depth. The warm temperature intrusions from the strait produce the warm water mass in the intermediate layers of the Black Sea. One novel result is that the seasonal intensification of circulation affects the interbasin exchange, thus allowing us to formulate the concept of circulation-controlled interbasin exchange. To the best of our knowledge, the present numerical simulations, for the first time, suggest that the sea level in the interior part of the Black Sea can be lower than the sea level in the Marmara Sea and even in some parts of the Aegean Sea. The comparison with observations shows that the timings and magnitude of exchange flows are also realistically simulated, along with the blocking events. The short-term variability of the strait transports is largely controlled by the anomalies of wind. The simulations demonstrate the crucial role of the narrow and shallow strait of Bosporus in separating the two pairs of basins: Aegean-Marmara Seas from one side and Azov-Black Seas from the other side. The straits of Kerch and Dardanelles provide sufficient interbasin connectivity that prevents large phase lags of the sea levels in the neighboring basins. The two-layer flows in the three straits considered here show different dependencies upon the net transport, and the spatial variability of this dependence is also quite pronounced. We show that the blocking of the surface flow can occur at different net transports, thus casting doubt on a previous approach of using simple relationships to prescribe (steady) outflow and inflow. Specific attention is paid to the role of synoptic atmospheric forcing for the basin-wide circulation and redistribution of mass in the Black Sea. An important controlling process is the propagation of coastal waves. One major conclusion from this research is that modeling the individual basins separately could result in large inaccuracies because of the critical importance of the cascading character of these interconnected basins.     

The penultimate deglaciation: High-resolution paleoceanographic evidence from a north–south transect along the eastern Nordic Seas

The penultimate termination has been studied with focus on oceanographic changes in the eastern Nordic Seas and the influence of these changes on the surrounding ice sheets and vice versa. Repeatedly, major changes in the strength of the Atlantic Meridional Overturning Circulation (AMOC) occurred during the studied interval. Times of strong overturning and increased heat transport northwards were of importance in triggering one minor and two major disintegration events. The two major disintegration events were separated by a deglacial pause, characterized by a strong AMOC. The same variability is seen throughout the eastern Nordic Seas, from the Faeroe–Shetland Channel in the south to the Fram Strait in the north. Some of the oceanographic changes occurring during the penultimate termination are comparable with changes seen through the last deglaciation. Reduced winter moisture flux and increased summer melting due to the present insolation forcing further amplified the rate of ice sheet disintegration. Calculated sea-level change through TII shows a mean change of 121 ± 4 m, 41 ± 16 m in the first step and 80 ± 13 m in the last step.     

Fine grid tidal modeling of the Yellow and East China Seas

A fine grid tidal modeling experiment is carried out in order to investigate the tidal regimes for major five tidal constituents, the nonlinear tidal phenomena in terms of M₄ and MS₄ generation, and the independent tide by the tide generating force in the Yellow and East China Seas (YECS). In this study a two-dimensional numerical model based upon a subgrid-scale (SGS) stress modeling technique is used with the tide generating force included. The model was validated with recently observed tide and current data. The calculated tidal charts for tidal elevation show a generally good agreement with existing ones, with more accurate feature of the M₂ cotidal chart in comparison with both the observed data and the existing tidal charts. A careful comparison of the computed diurnal amplitude with observations suggests that the diurnal constituents seem to be overdamped especially in the Kyunggi Bay region, for the case when quadratic bottom friction law is used.Propagation features of the M₄(MS₄) tides are discussed in the YECS, based upon the analyses of the observed and calculated results. The amphidromic system of the M₄ is quite complicated and one noticeable characteristic is that the propagation direction of the M₄ tidal wave along the west coast of Korean peninsula is opposite to that of the M₂ tidal wave. This result coincides with observations. The propagation feature of the MS₄ is almost similar to that of the M₄, but with lesser amplitude. The responses of the M₄ tidal features to momentum diffusion term and depth-dependent form of the friction coefficient are also discussed.It is also shown that when the independent tide (Defant, 1960) arising from tide generating force (TGF) coexists with tidal waves (co-oscillating tide) arising from external boundary forcing, the TGF tidal waves are dissipated and their amphidromes tend to move westward. This may be interpreted as a process whereby the incident and reflected TGF tidal waves are damped by co-oscillating tide arising from external force at open boundaries. The TGF amplitude is found to be up to 10 cm and 4 cm in the Kyunggi Bay for the M₂ and S₂ constituents while those for all diurnal constituents are less than 1 cm over the entire model domain.     

Analysis of Many-Year Variations in River Runoff into the Arctic Ocean

Statistical analysis of long-term hydrological observations has shown that the interannual variations in the total river runoff into the Arctic Ocean can be considered as a stationary process. Similar are the variations in the annual runoff of the Ob, Lena, and rivers of the northwestern Asia. However, some components of the total runoff into the Arctic Ocean feature distinct and fairly complicated disturbances in the homogeneity of runoff variations. For example, variations in the annual runoff of the Yenisei River have a distinct nonmonotonic trend: the runoff systematically decreased till the late 1950s and increased since the late 1960s. The rivers of the European part of the Arctic Ocean drainage basin featured a decrease in the amplitude of variations in runoff during the past decades. Rivers of the northwestern America and northeastern Asia featured a regular increase in the amplitude of runoff variations and their autocorrelation since the late 1960s.     

Modeled Stokes drift in the marginal ice zones of the Arctic Ocean

Ocean Dynamics - This study modeled Stokes drift in the marginal ice zone (MIZ) of the Arctic Ocean using WAVEWATCH III. Applying two viscoelastic and one empirical frequency-dependent...     

Climatic Change and the Dynamics of River Runoff into the Arctic Ocean

Time series of the river runoff into the Arctic Ocean over the period 1921–1999 are obtained through generalization of the available detailed hydrologic data on the drainage basin of the Arctic Ocean and estimates of the river runoff from areas in which no hydrometric observations have been made. Trends in the annual and seasonal river runoff from different parts of the basin are analyzed both for the entire period under study and for the last decades, which in the northern hemisphere are characterized by the most intense rise in air temperature. Potential future changes in the runoff of the main rivers of the basin and in the total river runoff into the ocean are discussed.