Hydrographic Characteristics and Oceanic Heat Flux in the Upper Arctic Ocean over the Alpha Ridge Observed by the DTOP Platform in 2018 and 2021

In 2018 and 2021,the Drift-Towing Ocean Profilers(DTOP)provided extensive temperature and salinity data on the upper 120m ocean through their drifts over the Alpha Ridge north of the Canada Basin.The thickness and temperature maximum of Alaska Coastal Water(ACW)ranged from 20m to 40m and-1.5℃to-0.8℃,respectively,and the salinity generally maintained from 30.2 to 32.5.Comparison with World Ocean Atlas 2018’s climatology manifested a 40m-thick and warm ACW roughly ex-ceeding the temperature maximum by 0.4–0.5℃in June–August 2021.This anomalously warm ACW was highly related to the ex-pansion of the Beaufort Gyre in the negative Arctic Oscillation phase.During summer,the under-ice oceanic heat flux F_(w)^(OHF)was elevated,with a maximum value of above 25Wm^(-2).F_(w)^(OHF)was typically low in the freezing season,with an average value of 1.2Wm^(-2).The estimates of upward heat flux contributed by ACW to the sea ice bottom F_(w)^(OHF)were in the range of 3–4Wm^(-2)in June–August 2021,when ACW contained a heat content of more than 80MJm^(-2).The heat loss over this period was driven by a weak stratification upon the ACW layer associated with a surface mixed layer(SML)approaching the ACW core.After autumn,F_(w)^(OHF)was reduced(<2 Wm^(-2))except during rare events when it elevated F_(w)^(OHF)slightly.In addition,the intensive and widespread Ekman suction,which created a violent upwelling north of the Canada Basin,was largely responsible for the substantial cooling and thinning of the ACW layer in the summer of 2021.

Changes in area fraction of sediment-laden sea ice in the Arctic Ocean during 2000 to 2021

Sediment-laden sea ice plays an important role in Arctic sediment transport and biogeochemical cycles,as well as the shortwave radiation budget and melt onset of ice surface.However,at present,there is a lack of efficient observation approach from both space and in situ for the coverage of Arctic sediment-laden sea ice.Thus,both spatial distribution and long-term changes in area fraction of such ice floes are still unclear.This study proposes a new classification method to extract Arctic sediment-laden sea ice on the basic of the difference in spectral characteristics between sediment-laden sea ice and clean sea ice in the visible band using the MOD09A1 data with the resolution of 500 m,and obtains its area fraction over the pan Arctic Ocean during 2000−2021.Compared with Landsat-8 true color verification images with a resolution of 30 m,the overall accuracy of our classification method is 92.3%,and the Kappa coefficient is 0.84.The impact of clouds on the results of recognition and spatiotemporal changes of sediment-laden sea ice is relatively small from June to July,compared to that in May or August.Spatially,sediment-laden sea ice mostly appears over the marginal seas of the Arctic Ocean,especially the continental shelf of Chukchi Sea and the Siberian seas.Associated with the retreat of Arctic sea ice extent,the total area of sediment-laden sea ice in June-July also shows a significant decreasing trend of 8.99×10^(4) km^(2) per year.The occurrence of sediment-laden sea ice over the Arctic Ocean in June-July leads to the reduce of surface albedo over the ice-covered ocean by 14.1%.This study will help thoroughly understanding of the role of sediment-laden sea ice in the evolution of Arctic climate system and marine ecological environment,as well as the heat budget and mass balance of sea ice itself.

Contribution of Surface Waves to Sea Surface Temperatures in the Arctic Ocean

The aim of our study was to examine the contribution of surface waves from WAVEWATCH-III(WW3)to the variation in sea surface temperature(SST)in the Arctic Ocean.The simulated significant wave height(SWH)were validated against the products from Haiyang-2B(HY-2B)in 2021,obtaining a root mean squared error(RMSE)of 0.45 with a correlation of 0.96 and scatter index of 0.18.The wave-induced effects,i.e.,wave breaking and mixing induced by nonbearing waves resulting in changes in radiation stress and Stokes drift,were calculated from WW3,ERA-5 wind,SST,and salinity data from the National Centers for Environmental Prediction and were taken as forcing fields in the Stony Brook Parallel Ocean Model.The results showed that an RMSE of 0.81℃ with wave-induced effects was less than the RMSE of 1.11℃ achieved without the wave term compared with the simulated SST with the measurements from Argos.Considering the four wave effects and sea ice freezing,the SST in the Arctic Ocean decreased by up to 1℃ in winter.Regression analysis revealed that the SWH was linear in SST(values without subtraction of waves)in summer and autumn,but this behavior was not observed in spring or winter due to the presence of sea ice.The interannual variation also presented a negative relationship between the difference in SST and SWH.

Distribution of Pacific-origin water in the region of the Chukchi Plateau in the Arctic Ocean in the summer of 2003

The upper ocean thermohaline structures in the region of the Chukchi Plateauare analyzed with the hydrographic data collected by the Chinese National Arctic Research Expeditionin the summer of 2003. Three types of the Pacific-origin water were found in the upper ocean,Alaska Coastal Water (ACW), summer Bering Sea Water (sBSW) and winter Bering Sea Water (wBSW) areindicated by two maximums temperature and one minimum temperature, piling up from the upper to thelower respectively. The extreme warm ACW with a maximum temperature of 1.62℃ was found in thesouthwestern Canada Basin at a depth of about 50 m. A pathway of the ACW into the basin from itsadjacent area did not existed in the expedition period. So it is speculated that the extreme warmfeature of the ACW was formed locally in 2003. The relative weak ACW occurred to the east of theChukchi Cap and in the southern Chukchi Abyssal Plain. The latter one might originate from a warmdownwelling that existed in a small canyon at the shelf break of the Chukchi Sea. The sBSW withoutthe ACW was found only at the southwestern flank of the Chukchi Cap. The ACW and the sBSW were notfound in the northernmost station at 81°N,which indicates the north boundary of the upperPacific-origin water in the Canada Basin. The wBSW, which existed in all deep stations, was exactlyuniform at temperature. The difference of the core potential temperature of the wBSW in the deepregions is only 0.08℃.

Comparison of airsea fluxes of CO_(2) in the Southern Ocean and the western Arctic Ocean

The data were collected during Chinese Arctic and Antarctic Expeditions in the western Arctic Ocean and themarginal sea ice zone (MSIZ) of the Southern Ocean, respectively in the boreal summer from July to September of1999 and in the austral summer from December of 1999 to January of 2000. The concentrations of CO2 in surfacewater of the survey regions would mostly present lower than those in the atmosphere. A significant biologicaldriving force could also been observed in summer waters in both of the above oceans. Air to sea CO2 fluxes were alsocalculated to compare oceanic uptake capacity of CO2 in both oceans with the world oceans using Liss, Wanninkhof,and Jacobss methods. The averaged CO2 fluxes of air to sea in the western Arctic Ocean or in the MSIZ of theSouthern Ocean doubled that in the world oceans.

Isolation and phylogenetic assignation of actinomycetes in the marine sediments from the Arctic Ocean

Actinomycetes in five marine sediments collected from the Arctic Ocean atdepths of 43 to 3 050 m were cultivated using a variety of media. A total of 61 actinomycetecolonies with substrate mycelia only were observed, and no colonies with aerial mycelia wereobserved under aerobic conditions at 15℃. From these colonies, 28 were selected to representdifferent morphological types. Denaturing gradient gel electrophoresis (DGGE) was used to check thepurity of isolates and select representatives for subsequent sequencing. Phylogentic analyses basedon nearly full-length 16S ribosomal RNA gene (rDNA) sequences indicated that the actinomycetesisolated were accommodated within genus Rhodococcus of family Nocardiaceae, genus Dietzia of familyDietziaceae, genera Janibacter and Terrabacter of family Instrasporangiaceae and genera Kocuria andA nhrobacter of family Micrococcaceae. One of the strains (P27-24) from the deep-sea sediment atdepth of 3 050 m was found to be identical in 16S rDNA sequence(1474/1474) with theradiation-resistant Kocuria rosea ATCC 187~T isolated from air. More than half of the isolatesshowed the similarities ranging from 99.5% to 99.9% in 16S rDNA sequence to dibenzofran-degrading,butyl 2-ethylhexanoate-hydrolysising and nitrile-metabolizing actinomycetes. All the strainsisolated were psychrotolerant bacteria and grew better on the media prepared with natural seawaterthan on the media prepared with deionized water. Three of them (Dietzia sp. P27-10, Rhodococcus sp.S11-3 and Rhodococcus sp.P11-5) had an obligate growth requirement for salt, confirming that thesestrains are indigenous marine actinomycetes.

Atmospheric concentration characteristics and gas/particle partitioning of PCBs from the North Pacific to the Arctic Ocean

Polychlorinated biphenyls （PCBs） were measured in atmospheric samples collected from the North Pacific to the Arctic Ocean between July and September 2012 to study the atmospheric concentration characteris-tics of PCBs and their gas/particle partitioning. The mean concentration of 26 PCBs （vapor plus particulate phase） （∑PCBs） was 19.116 pg/m^3with a standard deviation of 13.833 pg/m^3. Three most abundant conge-ners were CB-28, -52 and -77, accounting for 43.0% to∑PCBs. The predominance of vapor PCBs （79.0% to∑PCBs） in the atmosphere was observed.∑PCBs were negative correlated with the latitudes and inverse of the absolute temperature （1/T）. The significant correlation for most congeners was also observed between the logarithm of gas/particle partition coefficient （logKp） and 1/T. Shallower slopes （from ∑0.15 to ∑0.46, average ∑0.27） were measured from the regression of the logarithm of sub-cooled liquid vapor pressures （logpoL） and logKP for all samples. The difference of the slopes and intercepts among samples was insignifi-cant （p〉0.1）, implying adsorption and/or absorption processes and the aerosol composition did not differ significantly among different samples. By comparing three models, the J-P adsorption model, the octanol/air partition coefficient （KOA） based model and the soot-air model, the gas/particle partitioning of PCBs in the Arctic atmosphere was simulated more precisely by the soot-air model, and the adsorption onto el-emental carbon is more sensitive than the absorption into organic matters of aerosols, especially for low-chlorinated PCB congeners.

Regional estimates of POC export flux derived from thorium-234 in the western Arctic Ocean

In order to elucidate the regional export variation of participate organiccarbon in the western Arctic Ocean, samples vertically integrated between 0 and 100 m depth orbetween 0 and 30 m/40 m depth were collected for total ^(234)Th measurements and those from 30 m/40m or 100 m depth were collected for paniculate ^(234)Th measurements during the Second ChineseArctic Expedition in July— September 2003. The removal fluxes and residence time of ^(234)Th in theupper water column were calculated by using irreversible steady-state scavenging model. The resultsshowed that, total ^(234)Th was deficit relative to its parent ^(238)U in the western Arctic Oceanexcept in the western Chukchi shelf and the slope regions around 160°W, indicating that scavengingand removal processes play an important role in element biogeochemical cycle in the Arctic Ocean. Inthe western Chukchi shelf and the slope regions around 160°W, total ^(234)Th was excess relativeto ^(238)U, ascribing to the horizontal input of ^(234)Th adsorbed by ice-rafted sediments.Thorium-234 removal fluxes decreased from the shelf to the deep ocean, while the residence time of^(234)Th increased from shelf to offshore, demonstrating that particle scavenging and removalprocesses are more active in the shelf regions. The estimated POC export fluxes from 40 m in theshelf regions and from 100 m in the slope and deep ocean varied between 1.6 and 27.5 mmol/(m^2·d),and between 1.8 and 14.4 mmol/(m^2·d), respectively. The averaged POC export fluxes over the entirewater column decreased from the shelf to the deep ocean, indicating that the Chukchi shelf is animportant region for organic carbon sequestration. The high ThE ratios (ratio of POC export fluxderived from ^(234)Th/^(238)U disequilibria to primary production) in the western Arctic Oceansuggested that the biological pump runs actively in high-latitudes.

A double-halocline structure in the Canada Basin of the Arctic Ocean

A year-round halocline is a particular hydrographic structure in the upperArctic Ocean. On the basis of an analysis of the hydrographic data collected in the Arctic Ocean, itis found that a double-halocline structure exists in the upper layer of the southern Canada Basin,which is absolutely different from the Cold Halocline Layer (CHL) in the Eurasian Basin. ThePacific-origin water is the primary factor in the formation of the double-halocline structure. Theupper halocline lies between the summer modification and the winter modification of thePacific-origin water while the lower halocline results from the Pacific-origin water overlying uponthe Atlantic-origin water. Both haloclines are all the year-round although seasonal and interannualvariations have been detected in the historical data.

Observed and modelled snow and ice thickness in the Arctic Ocean with CHINARE buoy data

Sea ice and the snow pack on top of it were investigated using Chinese National Arctic Research Expedition （CHINARE） buoy data. Two polar hydrometeorological drifters, known as Zeno ice stations, were deployed during CHINARE 2003. A new type of high-resolution Snow and Ice Mass Balance Arrays, known as SIMBA buoys, were deployed during CHINARE 2014. Data from those buoys were applied to investigate the thickness of sea ice and snow in the CHINARE domain. A simple approach was applied to estimate the average snow thickness on the basis of Zeno temperature data. Snow and ice thicknesses were also derived from vertical temperature profile data based on the SIMBA buoys. A one-dimensional snow and ice thermodynamic model （HIGHTSI） was applied to calculate the snow and ice thickness along the buoy drift trajectories. The model forcing was based on forecasts and analyses of the European Centre for Medium-Range Weather Forecasts （ECMWF）. The Zeno buoys drifted in a confined area during 2003-2004. The snow thickness modelled applying HIGHTSI was consistent with results based on Zeno buoy data. The SIMBA buoys drifted from 81. 1°N, 157.4°W to 73.5°N, 134.9°W in 15 months during 2014-2015. The total ice thickness increased from an initial August 2014 value of 1.97 m to a maximum value of 2.45 in before the onset of snow melt in May 2015; the last observation was approximately 1 m in late November 2015. The ice thickness based on HIGHTSI agreed with SIMBA measurements, in particular when the seasonal variation of oceanic heat flux was taken into account, but the modelled snow thickness differed from the observed one. Sea ice thickness derived from SIMBA data was reasonably good in cold conditions, but challenges remain in both snow and ice thickness in summer.

Organic carbon and nitrogen isotopes in surface sediments from the western Arctic Ocean and their implications for sedimentary environments

Surface sediments from the Chukchi Sea and adjacent arctic deep sea were investigated for organic carbon and nitrogen isotopes （in δ13Corg and δ15Norg） as well as biogeni＇c silica （BSiO2）. δ13Corg and δ15Norg values of surface sediments in the study area fall between the end-member values of marine and terrestrial organic matter from the surrounding lands and seas, their variations reflect the changes of marine productivity and terrestrial supply in the study area. BSiO2 shows a similar distribution pattern with δ13Corg and δ15Norg, and can be used as an indicator of marine productivity. In the central-west Chukchi Sea and the Chukchi Rise, sediments have higher δ13Corg, δ15Norg and BSiO2 values, indicating the region has high marine productivity influenced by the nutrient-rich branches of the Pacific waters. In the coastal zone off northwestern Alaska, δ13Corg and δ15Norg values become lighter, indicating a weakening marine productivity and an increasing terrigenous supply due to the effects of the least nutrient-rich branch of the Pacific waters. In the north and the northeast of the study area （including the Chukchi Plateau, the Canada Basin and the Beaufort shelf）, δ13Corg, δ15Norg and BSiO2 have the lowest values, and the terrigenous organic matter becomes dominant in surface sediments because this region has the longest ice-covered duration, the least nutrient-rich seawater and the increasing supply of terrestrial materials from the Mackenzie River and the northern Alaska under the action of the clockwise Beaufort gyre. Because the subarctic Pacific waters are continuously discharged into the central basin of the Arctic Ocean through the study area, the nutrient pool in the Chukchi Sea can be considered as a typical open system, the ratio of δ15Norg to BSiO2 content show some tracers that the level of nutrient utilization is contrary to nutrient supply and marine productivity formed in seawater.

Insights into the coupling of upper ocean-benthic carbon dynamics in the western Arctic Ocean from an isotopic(^(13)C, ^(234)Th) perspective

The coupling of upper ocean-benthic carbon dynamics in the ice-free western Arctic Ocean （the Chukchi Sea and the Canada Basin） was evaluated during the late July-early September 2003 using natural stable （13C） and radioactive （238U-234Th） isotope tracers. POC export flux estimated from 234Th/238U disequilibria and dissolved CO2 concentration （[CO2（aq）]） pointed out that the strengthened biological pump in the Chukchi Shelf have significantly lowered [CO2（aq）] and altered the magnitude of isotopic （12C/13C） fractionation during carbon fixation in the surface ocean. Further, δ13C signatures of surface sediments （δ13Csed） are positively correlated to those of weighted δ13Cp0C in upper ocean （δ13Csed =13.64＋1.56xδ13Cpoc, r2=0.73, p〈0.01）, suggesting that the POC isotopic signals from upper ocean have been recorded in the sediments, partly due to the rapid export of particles as evidenced by low residence times of the highly particle-reactive 234Th from the upper water column. It is suggested that there probably exists an upper ocean-benthic coupling of carbon dynamics, which likely assures the sedimentary δ13C record an indicator of paleo-CO2 in the western Arctic Ocean.

The vertical structure of the atmospheric boundary layer over the central Arctic Ocean

The tropopause height and the atmospheric boundarylayer （PBL） height as well as the variation of inversion layer above the floating ice surface are presented using GPS （global position system ） radiosonde sounding data and relevant data obtained by Chinas fourth arctic scientific expedition team over the central Arctic Ocean （86°-88°N, 144°-170°W） during the summer of 2010. The tropopause height is from 9.8 to 10.5 km, with a temperature range between -52.2 and -54.10C in the central Arctic Ocean. Two zones of maximum wind （over 12 m/s） are found in the wind profile, namely, low- and upper-level jets, located in the middle troposphere and the tropopause, respectively. The wind direction has a marked variation point in the two jets from the southeast to the southwest. The average PBL height determined by two methods is 341 and 453 m respectively. These two methods can both be used when the inversion layer is very low, but the results vary significantly when the inversion layer is very high. A significant logarithmic relationship exists between the PBL height and the inversion intensity, with a correlation coefficient of 0.66, indicating that the more intense the temperature inversion is, the lower the boundary layer will be. The observation results obviously differ from those of the third arctic expedition zone （800-85° N）. The PBL height and the inversion layer thickness are much lower than those at 870-88° N, but the inversion temperature is more intense, meaning a strong ice- atmosphere interaction in the sea near the North Pole. The PBL structure is related to the weather system and the sea ice concentration, which affects the observation station.

Difference of planktonic ciliate communities of the tropical West Pacific, the Bering Sea and the Arctic Ocean

Ciliates are important components in planktonic food webs,but our understanding of their community structures in different oceanic water masses is limited.We report pelagic ciliate community characteristics in three seas:the tropical West Pacific,the Bering Sea and the Arctic Ocean.Planktonic ciliate abundance had"bimodal-peak","surface-peak"and"DCM(deep chlorophyll a maximum layer)-peak"vertical distribution patterns in the tropical West Pacific,the Bering Sea and the Arctic Ocean,respectively.The abundance proportion of tintinnid to total ciliate in the Bering Sea(42.6%)was higher than both the tropical West Pacific(7.8%)and the Arctic Ocean(2.0%).The abundance proportion of small aloricate ciliates(10–20μm size-fraction)in the tropical West Pacific was highest in these three seas.The Arctic Ocean had higher abundance proportion of tintinnids in larger LOD(lorica oral diameter)size-class.Proportion of redundant species increased from the Arctic Ocean to the tropical West Pacific.Our result provided useful data to further understand ecology roles of planktonic ciliates in different marine habitats.

Phosphorus in the aerosols over oceans transported offshore from China to the Arctic Ocean: Speciation, spatial distribution, and potential sources

Atmospheric aerosol samples were collected from July to September 2008 onboard a round-trip cruise over the Eastern China Sea, Japan Sea, Western North Pacific Ocean, and the Arctic Ocean （31.1°N-85.18°N, 122.48°E-146.18°W）. Total phosphorus （TP） and total inorganic phosphorus （TIP） were analyzed. The organic phosphorus （OP） was calculated by subtracting TIP from TP. Average concentrations of TP in the East Asia, Western North Pacific and Arctic Ocean were 7.90±6.45, 6.87±6.66 and 7.13±6.76 ng.m^3, while TIP levels were 6.67±5.02, 6.07±6.58, and 6.23±5.96 along the three regions. TP and TIP levels varied considerably both spatially and temporally over the study extent. TIP was found to be the dominant species in most samples, accounting for 86.6% of TP on average. OP was also a significant fraction of TP due to the primary biogenic aerosol （PBA） contribution. The phosphorus in the atmospheric aerosol over the Arctic Ocean had a higher concentration than previous model simulations. Source apportionment analysis indicates that dust is an important phosphorus source which can be globally transported, and thus dust aerosol may be an important nutrient source in some remote regions.

Using genetic algorithms to calibrate a dimethylsulfide production model in the Arctic Ocean

The global climate is intimately connected to changes in the polar oceans. The variability of sea ice coverage affects deep-water formations and large-scale thermohaline circulation patterns. The polar radiative budget is sensitive to sea-ice loss and consequent surface albedo changes. Aerosols and polar cloud microphysics are crucial players in the radioactive energy balance of the Arctic Ocean. The main biogenic source of sulfate aerosols to the atmosphere above remote seas is dimethylsulfide (DMS). Recent research suggests the flux of DMS to the Arctic atmosphere may change markedly under global warming. This paper describes climate data and DMS production (based on the five years from 1998 to 2002) in the region of the Barents Sea (30–35°E and 70–80°N). A DMS model is introduced together with an updated calibration method. A genetic algorithm is used to calibrate the chlorophyll-a (CHL) measurements (based on satellite SeaWiFS data) and DMS content (determined from cruise data collected in the Arctic). Significant interannual variation of the CHL amount leads to significant interannual variability in the observed and modeled production of DMS in the study region. Strong DMS production in 1998 could have been caused by a large amount of ice algae being released in the southern region. Forcings from a general circulation model (CSIRO Mk3) were applied to the calibrated DMS model to predict the zonal mean sea-to-air flux of DMS for contemporary and enhanced greenhouse conditions at 70–80°N. It was found that significantly decreasing ice coverage, increasing sea surface temperature and decreasing mixed-layer depth could lead to annual DMS flux increases of more than 100% by the time of equivalent CO2 tripling (the year 2080). This significant perturbation in the aerosol climate could have a large impact on the regional Arctic heat budget and consequences for global warming.

Analysis of Wave Distributions Using the WAVEWATCH-III Model in the Arctic Ocean

In this work,we examined long-term wave distributions using a third-generation numerical wave model called WAVE-WATCH-III(WW3)(version 6.07).We also evaluated the influence of sea ice on wave simulation by using eight parametric switches.To select a suitable ice-wave parameterization,we validated the simulations from the WW3 model in March,May,September,and December 2017 against the measurements from the Jason-2 altimeter at latitudes of up to 60°N.Generally,all parameterizations ex-hibited slight differences,i.e.,about 0.6 m root mean square error(RMSE)of significant wave height(SWH)in May and September and about 0.9 m RMSE for the freezing months of March and December.The comparison of the results with the SWH from the European Centre for Medium-Range Weather Forecasts for December 2017 indicated that switch IC4_M1 performed most effec-tively(0.68 m RMSE)at high latitudes(60°-80°N).Given this finding,we analyzed the long-term wave distributions in 1999-2018 on the basis of switch IC4_M1.Although the seasonal variability of the simulated SWH was of two types,i.e.,‘U’and‘sin’modes,our results proved that fetch expansion prompted the wave growth.Moreover,the interannual variability of the specific regions in the‘U’mode was found to be correlated with the decade variability of wind in the Arctic Ocean.

Interaction of an anticyclonic eddy with sea ice in the western Arctic Ocean:an eddy-resolving model study

The dramatic decline of summer sea ice extent and thickness has been witnessed in the western Arctic Ocean in recent decades, which has motivated scientists to search for possible factors driving the sea ice variability. An eddy-resolving, ice-ocean coupled model covering the entire Arctic Ocean is implemented, with focus on the western Arctic Ocean. Special attention is paid to the summer Maskan coastal current （ACC）, which has a high temperature （up to 5℃ or more） in the upper layer due to the solar radiation over the open water at the lower latitude. Downstream of the ACC after Barrow Point, a surface-intensified anticyclonic eddy is frequently generated and propagate towards the Canada Basin during the summer season when sea ice has retreated away from the coast. Such an eddy has a warm core, and its source is high-temperature ACC water. A typical warm-core eddy is traced. It is trapped just below summer sea ice melt water and has a thickness about 60 m. Temperature in the eddy core reaches 2-3℃, and most water inside the eddy has a temperature over 1℃. With a definition of the eddy boundary, an eddy heat is calculated, which can melt 1 600 km2 of 1 m thick sea ice under extreme conditions.

Ice rafting history and paleoceanographic reconstructions of Core 08P23 from southern Chukchi Plateau, western Arctic Ocean since Marine Isotope Stage 3

Multiproxy investigations have been performed on Core 08P23 collected from the Chukchi Plateau, the western Arctic Ocean, during the Third Chinese National Arctic Expedition. The core was dated back to Ma-rine Isotope Stage （MIS） 3 by a combination of Accelerator Mass Spectrometric （AMS） carbon-14 dating and regional core correlation. A total of five prominent ice-rafted detritus （IRD） events were recognized in MIS 2 and MIS 3. The IRD sources in MIS 3 are originated from vast carbonate rock outcrops of the Canadian Arctic Archipelago and clastic quartz in MIS 2 may have a Eurasian origin. Mostδ18O andδ13C values of Neogloboquadrina pachyderma （sinistral） （Nps） in Core 08P23 are lighter than the average values of surface sediments. The lighterδ18O andδ13C values of Nps in the two brown layers in MIS 1 and MIS 3 were resulted from meltwater events; and those in the gray layers in MIS 3 were caused by the enhanced sea ice formation. Theδ18O values varied inversely withδ13C in MIS 2 indicate that the study area was covered by thick sea ice or ice sheet with low temperature and little meltwater, which prevented the biological productivity and sea-atmosphere exchange, as well as water mass ventilation. The covaried light values ofδ18O andδ13C in MIS 1 and MIS 3 were resulted from meltwater and/or brine injection.

Variation of diffuse attenuation coefficient of downwelling irradiance in the Arctic Ocean

The diffuse attenuation coefficient （Kd） for downwelling irradiance is calculated from solar irradiance data measured in the Arctic Ocean during 3rd and 4th Chinese National Arctic Research Expedition （CHINARE）, including 18 stations and nine stations selected for irradiance profiles in seawater respectively. In this study, the variation of attenuation coefficient in the Arctic Ocean was studied, and the following results were obtained. First, the relationship between attenuation coefficient and chlorophyll concentration in the Arctic Ocean has the form of a power function. The best fit is at 443 nm, and its determination coefficient is more than 0.7. With increasing wavelength, the determination coefficient decreases abruptly. At 550 nm, it even reaches a value lower than 0.2. However, the exponent fitted is only half of that adapted in low-latitude ocean because of the lower chlorophyll-specific absorption in the Arctic Ocean. The upshot was that, in the case of the same chlorophyll concentration, the attenuation caused by phytoplankton chlorophyll in the Arctic Ocean is lower than in low-latitude ocean. Second, the spectral model, which exhibits the relationship of attenuation coefficients between 490 nm and other wavelength, was built and provided a new method to estimate the attenuation coefficient at other wavelength, if the attenuation coefficient at 490 nm was known. Third, the impact factors on attenuation coefficient, including sea ice and sea water mass, were discussed. The influence of sea ice on attenuation coefficient is indirect and is determined through the control of enter- ing solar radiation. The linear relationship between averaging sea ice concentration （ASIC, from 158 Julian day to observation day） and the depth of maximum chlorophyll is fitted by a simple linear equation. In addition, the sea water mass, such as the ACW （Alaskan Coastal Water）, directly affects the amount of chlo- rophyll through taking more nutrient, and results in the higher attenuation coefficient in the layer of 30-60 m. Consequently, the spectral model of diffuse attenuation coefficient, the relationship between attenuation coefficient and chlorophyll and the linear relationship between the ASIC and the depth of maximum chlorophyll, together provide probability for simulating the process of diffuse attenuation coefficient during summer in the Arctic Ocean.