Sea ice thickness measurement and its underside morphology analysis using radar penetration in the Arctic Ocean

Sea ice, as an important component of the Arctic climate system, has drawn significant sci-entific interest. Sea ice thickness and its morphology have dramatic impacts on ocean-atmos- phere-ice interactions[1—4], which directly affect the exchange proces…     

Investigations on distributions and fluxes of sea-air CO_2 of the expedition areas in the Arctic Ocean

揋reenhouse effect?causing global warming has been an important issue of studying climate change. In the latest 100 years, the earth surface temperature has been increased by about 0.4℃—0.8℃[1,2]. And this has been becoming a hotspot of the world[3,4]     

Changes in the dynamics/energetics of surface and internal tides in the White Sea on the coexistence of shore-fast and drifting ice covers

The results of modeling for _M2${\mathrm{M}}_2$ surface and internal tides in the White Sea are discussed. These results are obtained for the case when shore-fast and drifting ice covers are present concurrently. It is assumed that the interface between ice covers is of non-tidal origin (i.e., it is pre-assigned) and that ice rheology is viscous-elastic, representative of the low temperatures typical of winter conditions. Emphasis is placed on tidal energetics and, in particular, on the averaged (over a tidal cycle) values of the density and the dissipation rate of barotropic/baroclinic tidal energy. It is shown that in the White Sea, unlike in other marginal seas, the averaged (over a tidal cycle) and depth-integrated density of baroclinic tidal energy for the combined ice cover is much less than the same defined density of barotropic tidal energy. Similarly, the averaged and integrated (over the volume of the White Sea) rate of baroclinic tidal energy dissipation is much less than the same defined rate of barotropic tidal energy dissipation. The latter, in turn, is greater than for the shore-fast ice cover, but is smaller than for the drifting ice cover.     

New insights into the spatial variability of the surface water carbon dioxide in varying sea ice conditions in the Arctic Ocean

In the summer of 2005, continuous surface water measurements of fugacity of CO₂ (fCO₂^sw), salinity and temperature were performed onboard the IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. The aim was to investigate the importance of sea ice and river runoff on the spatial variability of fCO₂ and the sea–air CO₂ fluxes in the Arctic Ocean. Additional data was obtained from measurements of total alkalinity (A_T) by discrete surface water and water column sampling in the Canadian Arctic Archipelago (CAA), on the Mackenzie shelf, and in the Bering Strait. The linear relationship between A_T and salinity was used to evaluate and calculate the relative fractions of sea ice melt water and river runoff along the cruise track. High-frequency fCO₂^sw data showed rapid changes, due to variable sea ice conditions, freshwater addition, physical upwelling and biological processes. The fCO₂^sw varied between 102 and 678 μatm. Under the sea ice in the CAA and the northern Chukchi Sea, fCO₂^sw were largely CO₂ undersaturated of approximately 100 μatm lower than the atmospheric level. This suggested CO₂ uptake by biological production and limited sea–air CO₂ gas exchange due to the ice cover. In open areas, such as the relatively fresh water of the Mackenzie shelf and the Bering Strait, the fCO₂^sw values were close to the atmospheric CO₂ level. Upwelling of saline and relatively warm water at the Cape Bathurst caused a dramatic fCO₂^sw increase of about 100 μatm relative to the values in the CAA. At the southern part of the Chukchi Peninsula we found the highest fCO₂^sw values and the water was CO₂ supersaturated, likely due to upwelling. In the study area, the calculated sea–air CO₂ flux varied between an oceanic CO₂ sink of 140 mmol m⁻² d⁻¹ and an oceanic source of 18 mmol m⁻² d⁻¹. However, in the CAA and the northern Chukchi Sea, the sea ice cover prevented gas exchange, and the CO₂ fluxes were probably negligible at this time of the year. Assuming that the water was exposed to the atmosphere by total melting and gas exchange would be the only process, the CO₂ undersaturated water in the ice-covered areas will not have the time to reach the atmospheric CO₂ value, before the formation of new sea ice. This study highlights the value of using high-frequency measurements to gain increased insight into the variable and complex conditions, encountered on the shelves in the Arctic Ocean.     

Distribution of ~(226)Ra in the Arctic Ocean and the Bering Sea and its hydrologic implications

The Arctic Ocean, the northernmost parts of the earth, covers the total surface area of 14.79 million square kilometers and amounts to only about 4% of global ocean surface area. Although its surface area is the smallest in the four major oceans, the Arct…     

Experimental observation on the characteristics of the near-surface turbulence over the Antarctic ice sheets during the polar day period

Based on the ultrasonic anemometer/thermometer data in the East Antarctic coastal area ice sheets ob-tained first by Chinese scientists, turbulent intensity, kinetic energy and sensible heat of turbulence, surface roughness height drag coefficient and normalized variation were calculated and analysed using the eddy-correlation method. The results show that the values of roughness height and drag coefficient are 4.3 X 10 m and 1.8x 10 -³, respectively. These turbulent parameters have apparent diurnal variations. Project supported by the National Natural Science Foundation of China (Grant No. 49675252).     

Characteristics of pCO_2 in surface water of the Bering Abyssal Plain and their effects on carbon cycle in the western Arctic Ocean

The global warming has obviously been causingthe Arctic sea ice shrinking and thinning during thelast 30 years, which would increase free ice waters andenhance biological productivity. These changes willimpact the source and sink of carbon in the ArcticOcean and subarctic waters as well as a feedback tothe global change[1—3]. The Chukchi Sea is located in the southwest ofthe western Arctic Ocean and the Bering Sea in thenorthwest of the North Pacific Ocean. Both seas are 1997—2001) and…     

Geothermal control on flow patterns in the Last Glacial Maximum ice sheet of Iceland

Because it is located both on the Mid‐Atlantic Ridge and on a mantle plume, Iceland is a region of intense tectonics and volcanism. During the last glaciation, the island was covered by an ice sheet approximately 1000 m thick. A reconstruction of the ice flow lines, based on glacial directional features, shows that the ice sheet was partly drained through fast‐flowing streams. Fast flow of the ice streams has been recorded in megascale lineations and flutes visible on the currently deglaciated bedrock, and is confirmed by simple mass balance considerations. Locations of the major drainage routes correlate with locations of geothermal anomalies, suggesting that ice stream activity was favoured by lubrication of the bed by meltwater produced in regions of high geothermal heat flux. Similar control of ice flow by geothermal activity is expected in ice sheets currently covering tectonically and volcanically active area such as the West Antarctic ice sheet. Copyright © 2000 John Wiley & Sons, Ltd.     

Export fluxes of biogenic matter in the presence and absence of seasonal sea ice cover in the Chukchi Sea

Drifting sediment traps were deployed at 9 stations in May-June (ice-covered conditions) and July-August (ice-free conditions) 2004 in the Chukchi Sea to investigate the variability in export fluxes of biogenic matter in the presence and absence of sea ice cover. Measurements of chlorophyll-a (Chl-a), particulate organic carbon (POC), particulate nitrogen (PN), phytoplankton, zooplankton fecal pellets, and the stable carbon isotope composition (δ¹³C) of the sinking material were performed along Barrow Canyon (BC) and a parallel shelf-to-basin transect from East Hanna Shoal (EHS) to the Canada Basin. POC export fluxes were similarly high in the presence (378±106 mg C m⁻² d⁻¹) and in the absence of ice cover (442±203 mg C m⁻² d⁻¹) at the BC stations, while fluxes were significantly higher in the absence (129±98 mg C m⁻² d⁻¹) than in the presence of ice cover (44±29 mg C m⁻² d⁻¹) at the EHS stations. The C/N ratios and δ¹³C values of sinking organic particles indicated that POC export fluxes on the Chukchi continental shelf were mostly composed of freshly produced labile material, except at the EHS stations under ice cover where the exported matter was mostly composed of refractory material probably advected into the EHS region. Chl-a fluxes were higher under ice cover than in ice-free water, however, relatively low daily loss rates of Chl-a and similar phytoplankton carbon fluxes in ice-covered and ice-free water suggest the retention of phytoplankton in the upper water column. An increase in fecal pellet carbon fluxes in ice-free water reflected higher grazing pressure in the absence of ice cover. Elevated daily loss rates of POC at the BC stations confirmed other indications that Barrow Canyon is an important area of carbon export to the basin and/or benthos. These results support the conclusion that there are large spatial and temporal variations in export fluxes of biogenic matter on the Chukchi continental shelf, although export fluxes may be similar in the presence and in the absence of ice cover in highly productive regions.     

Estimation of vertical water and heat fluxes in the semi-confined aquifers in tokyo metropolitan area,japan

Groundwater circulation is known to be one of the agents responsible for the redistribution of geothermal energy by acting as a source or sink in the course of its movement through porous media. Heat transport in groundwater systems is considered to be a coupled process and the theory based on this was used to analyse temperature profiles of 30 thermally stable observation wells in a deep, semi-confined aquifer system in the Tokyo Metropolitan area. Vertical water fluxes in the semi-confined aquifers and the associated upward heat fluxes were estimated from a heat flux equation that describes convection and conduction processes of heat transport in one dimension. The vertical downward water fluxes in Shitamachi lowland, Musashino and Tachikawa terraces were 0.69.26.91 × 10^?9, 1.46-70.92 × 10^?9 and 2.61.2204 × 10^?9 m/s, respectively. A vertical upward water flux of 1.80-33.60 × 10^?9 m/s was estimated in Shitamachi lowland. The water flux generally decreased with increasing depth for observation wells which intercepted more than one semi-confining layer. The estimated upward heat fluxes for Shitamachi lowland, Musashino and Tachikawa terraces were 0.32-1.12, 0.49-1.21 and 1.00-11.62 W/m², respectively. The heat flux was highest in Tachikawa terrace where a major fault, the Tachikawa fault, is located. Generally, the estimated heat flux was higher in the semi-confining layers than in the aquifers. Areas with heat sources and sinks as well as groundwater flow patterns in the semi-confined aquifers were revealed by heat flux and temperature distributions in the study area.     

Distribution of <Superscript>226</Superscript>Ra in the Arctic Ocean and the Bering Sea and its hydrologic implications

Radium-226 (²²⁶Ra) activities were measured in the surface water samples collected from the Arctic Ocean and the Bering Sea during the First Chinese National Arctic Research Expedition. The results showed that ²²⁶Ra concentrations in the surface water ranged from 0.28 to 1.56 Bq/m³ with an average of 0.76 Bq/m³ in the Arctic Ocean, and from 0.25 to 1.26 Bq/m³ with an average of 0.71 Bq/m³ in the Bering Sea. The values were obviously lower than those from open oceans in middle and low latitudes, indicating that the study area may be partly influenced by sea ice meltwater. In the Bering Sea, ²²⁶Ra in the surface water decreased northward, probably as a result of the exchange between the ²²⁶Ra-deficient sea ice meltwater and the ²²⁶Ra-rich Pacific water. In the Arctic Ocean, ²²⁶Ra in the surface water increased northward and eastward. This spatial distribution of ²²⁶Ra reflected the variation of the ²²⁶Ra-enriched river component in the water mass of the Arctic Ocean. The vertical profiles of ²²⁶Ra in the Canadian Basin showed a concentration maximum at 200 m, which could be attributed to the inputs of the Pacific water or/and the bottom shelf water with high ²²⁶Ra concentration. This conclusion was consistent with the results from ²H, ¹⁸O tracers.     

Transport of water in frozen soil IV. Analysis of experimental results on the effects of ice content

Effects of ice content on the transport of water in frozen soil are studied experimentally and theoretically under isothermal conditions. A physical law, that the flux of water in unsaturated frozen soil is proportional to the gradient of total water content is proposed. Theoretical justification is made by the use of the two-phase flow theory. The experimental results are shown to support the proposed physical law. The results of this study are presented in two parts and this is the second paper describing the theoretical aspects of the study.     

Variability in the annual cycle of vertical particulate organic carbon export on Arctic shelves: Contrasting the Laptev Sea,Northern Baffin Bay and the Beaufort Sea

The ongoing regression of sea ice cover is expected to significantly affect the fate of organic carbon over the Arctic continental shelves. Long-term moored sediment traps were deployed in 2005–2006 in the Beaufort Sea, Northern Baffin Bay and the Laptev Sea to compare the annual variability of POC fluxes and to evaluate the factors regulating the annual cycle of carbon export over these continental shelves. Annual POC fluxes at 200 m ranged from 1.6 to 5.9 g C m⁻² yr⁻¹ with the highest export in Northern Baffin Bay and the lowest export over the Mackenzie Shelf in the Beaufort Sea. Each annual cycle exhibited an increase in POC export a few weeks before, during, or immediately following sea ice melt, but showed different patterns over the remainder of the cycle. Enhanced primary production, discharge of the Lena River, and resuspension events contributed to periods of elevated POC export over the Laptev Sea slope. High POC fluxes in Northern Baffin Bay reflected periods of elevated primary production in the North Water polynya. In the Beaufort Sea sediment resuspension contributed to most of the large export events. Our results suggest that the outer shelf of the Laptev Sea will likely sustain the largest increase in POC export in the next few years due to the large reduction in ice cover and the possible increase in the Lena River discharge. The large differences in forcing among the regions investigated reinforce the importance of monitoring POC fluxes in the different oceanographic regimes that characterize the Arctic shelves to assess the response of the Arctic Ocean carbon cycle to interannual variability and climate change.     

The simulation of heat and water exchange in the boreal spruce forest by the land-surface model SWAP

All previous versions of a physically based land-surface model SWAP have assumed for simplicity that vegetation is fully covered by snow during the cold season. Such assumption is reasonable only for the regions dominated by short vegetation or for warm climates where snow processes are absent. The major goals of this paper are (i) modification of the latest version of SWAP by incorporation of tall vegetation into the cold-season parameterizations to make the model applicable for simulating heat and water transfer within a boreal forest biome and (ii) validation of the modified version using the data from a forested catchment located in the boreal zone. Modification of SWAP required to parameterize radiative and turbulent exchange between the forest crown and forest floor, partitioning snowfall between interception by the canopy (in doing so, snow interception differs from rain interception) and falling to the ground, formation of snow cover on the forest crown and forest floor including snow accumulation (both in solid and liquid fractions), snow evaporation, and snowmelt. The advanced model was validated using a set of hydrometeorological data measured during 18 years (1966–1983) at the Tayozhniy catchment (covered by boreal spruce forest), Valdai, Russia. Simulations of annual and monthly snow/rain interception, daily runoff at the catchment outlet, snow density, snow depth, snow water equivalent, soil water storage in three layers (0–20, 0–50 and 0–100 cm), and monthly evapotranspiration from the catchment were compared with observations. Analysis of the results of validation shows that the new version of the model SWAP reproduces the heat and water exchange processes occurring in mid-latitude boreal forest quite reasonable.     

Simulating the exchanges of carbon dioxide, water vapor and heat over Changbai Mountains temperate broad-leaved Korean pine mixed forest ecosystem

A process-based ecosystem productivity model BEPS (Boreal Ecosystem Productivity Simulator) was updated to simulate half-hourly exchanges of carbon, water and energy between the atmosphere and terrestrial ecosystem at a temperate broad-leaved Korean pine forest in the Changbai Mountains, China. The BEPSh model is able to capture the diurnal and seasonal variability in carbon dioxide, water vapor and heat fluxes at this site in the growing season of 2003. The model validation showed that the simulated net ecosystem productivity (NEP), latent heat flux (LE), sensible heat flux (Hs) are in good agreement with eddy covariance measurements with an R2 value of 0.68, 0.86 and 0.72 for NEP, LE and Hs, respectively. The simulated annual NEP of this forest in 2003 was 300.5 gC/m2, and was very close to the observed value. Driving this model with different climate scenarios, we found that the NEP in the Changbai Mountains temperate broad-leaved Korean pine mixed forest ecosystem was sensitive to climate variability, and the current carbon sink will be weakened under the condition of global warming. Furthermore, as a process-based model, BEPSh was also sensitive to physiological parameters of plant, such as maximum Rubisco activity (Vcmax) and the maximum stomatal conductance (gmax), and needs to be carefully calibrated for other applications.     

Simulation of energy and water balance in Soil-Vegetation-Atmosphere Transfer system in the mountain area of Heihe River Basin at Hexi Corridor of northwest China

Under the background of global water cycle, theregional water cycle systems of the arid inland regionsof northwest China are characterized by the fact thatthe area is composed of various relatively independentinland river basins, each of which is a system of inter-related climate, hydrology, water resources, ecologyand environment. An inland river basin consists of amountain area and the plain and basin area in front ofthe mountains. The vertical landscape zonality of aninland river basin can …     

Modelling and observation of hedgerow transpiration effect on water balance components at the hillslope scale in Brittany

Vegetation has a major influence on the water and energy balance of the earth's surface. In the last century, human activities have modified land use, inducing a consequent change in albedo and potential evapotranspiration. Linear vegetation structures (hedgerows, shelterbelts, open woodland, etc) were particularly abundant but have declined considerably over the past several decades. In this context, it is important to quantify their effect on water and energy balance both on a global scale (climate change and weather prediction) and on a local scale (soil column, hillslope and watershed). The main objective of this study was to quantify the effect of hedgerows on the water cycle by evaluating spatial and temporal variations of water balance components of a hillslope crossed by a hedgerow. Water flow simulation was performed using Hydrus‐2D to emphasize the importance of transpiration in the water balance and to evaluate water extraction from groundwater. Model validation was performed by comparing simulated and observed soil matrix potentials and groundwater levels. Hedgerow transpiration was calculated from sap flow measurements of four trees. Water balance components calculated with a one‐dimensional water balance equation were compared with simulations. Simulation runs with and without tree root uptake underlined the effect of hedgerow transpiration, increasing capillary rise and decreasing drainage. Results demonstrated that the spatial and temporal variability of water balance components was related to the hedgerow presence as well as to the meteorological context. The relations between transpiration, groundwater proximity and soil‐water availability determined the way in which water balance components were affected. Increased capillary rise and decreased drainage near hedges were related to the high transpiration of trees identified in this study. Transpiration reached twice the potential evapotranspiration when groundwater level and precipitation amounts were high. Water balance analysis showed that transpiration was a substantial component, representing 40% of total water output. These results may offer support for improving hydrological models by including the effect of land use and land cover on hydrological processes. Copyright © 2012 John Wiley & Sons, Ltd.     

Characteristics of <Emphasis Type="Italic">p</Emphasis>CO<Subscript>2</Subscript> in surface water of the Bering Abyssal Plain and their effects on carbon cycle in the

Characteristics of the pCO₂ distribution in surface water of the Bering Abyssal Plain and their relationships with the ambient hydrological conditions were discussed using variations of the partial pressure of CO₂ in surface water of the Bering Abyssal Plain and the Chukchi Sea. Data in this study are from a field investigation during the First Chinese National Arctic Research Expedition in 1999. Compared to the high productivity in the Bering Continental Shelf, much lower levels of chlorophyll a were observed in the Bering Abyssal Plain. The effect of hydrological factors on the pCO₂ distribution in surface seawater of the Plain in summer has become a major driving force and dominated over biological factors. The Plain also presents a High Nutrient Low Chlorophyll (HNLC). In addition, the pCO₂ distribution in the Bering Abyssal Plain has also been found to be influenced from the Bering Slope Current which would transform to the Anadyr Current when it inflows northwestward over the Plain. The Anadyr Current would bring a high nutrient water to the western Arctic Ocean where local nutrients are almost depleted in the surface water during the summer time. Resupplying nutrients would stimulate the growth of phytoplankton and enhance capacity of absorbing atmospheric CO₂ in the surface water. Otherwise, in the Bering Sea the dissolved inorganic carbon brought from freshwater are not deposited down to the deep sea water but most of them would be transported into the western Arctic Ocean by the Alaska Coastal Current to form a carbon sink there. Therefore, the two carbon sinks in the western Arctic Ocean, one carried by the Anadyr Current and another by the Alaska Costal Current, will implicate the western Arctic Ocean in global change.