Seawater samples were collected in the water column of the Canda Basin and the Bering Sea from aboard the R/B Xue Long during August 1999. Activity concentrations of dissolved and particulate 234Th were measured using beta countion techniques to quantify the scavenging and residence time of 234Th and organic carbon export fluxes. Prinary production (PP)and bacterial production were also determined in the study areas through in situ incubation experiments. Singificant 234Th scavenging was observed in the upper 100m of the water column in both study ares. with up to 40% of 234Th defictit found at Bering Sea stations and -15% of 234Th defictit at the Canada Basin station. Measured PP decreased from -12.5μmol C/m3/hin in surface water to near zero at -100m depth. with an integrated PP of 3.83mmol C/m2/d in the Canada Basin. Bacterial production. on the other hand. was on the order of 2.0mmol C/m2/d. which is up to 52% fo the integrated PP. Particulate organic carbon (POC) export fluxes derived from 234Th/238U disequilibrium were -1mmol C/m2/d in the Canda Basin and -10mmol C/m2/d in the Bering Sea. with fluxes in the latter areaheing 5 to 10 times higher than those found in the Caada Basin. These expon fluxes correspond to a ThE ratio (the ratio of 234Th-derived POC export to primary production) of 0.23 for the Canada Basin and 0.7 for the Bering Sea. The highe ThE rations in the study areas suggest a decoupling of production and particulate export in the high-latiude ocean. Rations fo POC to particlate 234Th (μmol C/dpm) decreased consistertly with incerasing depth, suggestion that organic carbon is preferentially remineralized relative to 234Th. Interestigly, The profile of particulate 234Th in the Canada Basin showed a unique characteristic: particulate 234Th activeites increased with increasing depth. suggesting a contiuous scavenging of 234Th and a rapid settling rate of the particles.

Primary production, bacterial production, particulate organic carbon fluxes and organic carbon burial rates were quantified during the summer period of 1999 in the Arctic Ocean via 14C uptake, 3H uptake, 234Th/238U disequilibrium and 210Pbex dating, respectively. The integrated primary production in the water column was as high as 197mmolC/(m2

Seawater samples were collected in the water column from the Canada Basin aboard RV Xuelong in August 1999. Concentrations of d D, d 18O, nutrients (NO3-, PO43-, SiO32-) and dissolved oxygen were measured, along with hydrographic parameters (salinity and temperature). Our results showed that the upper layer of the water column was characterized by the occurrence of the upper halocline water (UHW) and the lower halocline water (LHW). The UHW was associated with a salinity of 33.1 (～150m depth) and maximums of nutrients, NO and PO*, whereas minimums of NO and PO* (PO*=PO3- + O2/175-1.95mmol/dm3) occurred at the depth of LHW (～300m depth). Two tracer systems, S-d 18O-PO* and S-d D-SiO3 2-, were used to estimate the fractions of the Atlantic water, Pacific water, river runoff and sea ice meltwater in water samples. Combined with the nutrient ratio NO/PO, it was suggested that the UHW was derived from the inflow of the Pacific water through the Bering Strait. These waters were modified to obtain the high salinity and nutrients in the Chukchi shelf or/and the east Siberian shelf. The LHW was maintained by inflow of the Atlantic water through Barents Sea and subsequent mixing with freshwater in the shelf region to produce the signals of NO and PO* minimums. In study basin, the river runoff signals were confined to water depths less than 300m and the fractions of river runoff decreased with the increasing depth. Water column inventories of river runoff and sea ice meltwater were calculated between the surface and 300m. The river runoff inventories in the Canada Basin were higher than those in other sea areas, suggesting that the Canada basin is a major storage region for Arctic river water. The sea ice meltwater signals suggested that the Canada Basin is a region of net sea ice formation and the inventories of net sea ice in the upper water column increasing from the south to the north.