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Abstract:The spatial distribution of precipitation is an important aspect of water-related research. The use of different interpolation schemes in the same catchment may cause large differences and deviations from the actual spatial distribution of rainfall. Our study analyzes different methods of spatial rainfall interpolation at annual, daily, and hourly time scales to provide a comprehensive evaluation. An improved regression-based scheme is proposed using principal component regression with residual correction (PCRR) and is compared with inverse distance weighting (IDW) and multiple linear regression (MLR) interpolation methods. In this study, the meso-scale catchment of the Fuhe River in southeastern China was selected as a typical region. Furthermore, a hydrological model HEC-HMS was used to calculate streamflow and to evaluate the impact of rainfall interpolation methods on the results of the hydrological model. Results show that the PCRR method performed better than the other methods tested in the study and can effectively eliminate the interpolation anomalies caused by terrain differences between observation points and surrounding areas. Simulated streamflow showed different characteristics based on the mean, maximum, minimum, and peak flows. The results simulated by PCRR exhibited the lowest streamflow error and highest correlation with measured values at the daily time scale. The application of the PCRR method is found to be promising because it considers multicollinearity among variables.

Depth profiles of total organic carbon (TOC) were measured in spring (2005) and winter (2006) in the South China Sea (SCS), the largest marginal sea adjacent to the North Western Pacific (NWP). Compared to TOC profiles in the NWP, excess TOC (3.2 +/- 1.1 mu mol kg(-1)) was revealed in the intermediate layer of the SCS at sigma(theta) similar to 27.2-27.6 (similar to 1000-1500 m). Below the depth of 2000 m, TOC concentrations were identical between the SCS and the NWP. Based on a one-dimensional steady state diffusion advection model constrained by potential temperature, we estimated a net TOC production rate of 0.12 +/- 0.04 mu mol kg(-1) yr(-1) to maintain this excess. A positive relationship between TOC and apparent oxygen utilization in the SCS deep water lent support to such a model-derived TOC production. This excess TOC in the out-flowing intermediate water may carry 3.1 +/- 2.1 Tg C yr(-1) of organic carbon out from the SCS and potentially into the deep open ocean. In light of the short residence time of the SCS deep water, the exported TOC was likely from the recently fixed organic carbon within the SCS. The export of such organic carbon, thereby less likely to return to the atmosphere may therefore contribute significantly to the carbon sequestration in the SCS.National Basic Research Program of China ; Ministry of Science and Technology [2009CB421200]; National Science Foundation of China (NSFC) [40821063, 90711005, 40490264

[1] During a spring intermonsoon cruise in 2004, depth profiles of total and particulate 234 Th in the upper 100 m were collected at 36 stations in the southern South China Sea (SCS), covering a surface area of $1.0 Â 10 6 km 2 . Thorium-234 was sampled by using a modified small-volume MnO 2 co-precipitation technique, which allows mapping the 234 Th distribution with a high spatial resolution. A stratified structure of 234 Th/ 238 U disequilibria was generally observed in the upper 100 m water column, suggesting that the euphotic zone of the southern SCS in this season can be separated into two layers: an upper layer with low export production rates and a lower layer with high export production rates. At the same time, we observed extensive zones of 234 Th excess within the euphotic layer, which is possibly due to intense remineralization of particulate matter. Particulate organic carbon (POC) export was estimated from a three-dimensional steady state model of Th ratio on suspended particles. The POC export for this region varied from a low of À10.7 ± 1.5 mmolC m À2 d À1 to a high of 12.6 ± 1.1 mmolC m À2 d À1 , with an average of 3.8 ± 4.0 mmolC m À2 d À1 . A negative flux of POC export is interpreted as the result of lateral input of particulate matter from nearby waters. Regional patterns in POC export show enhanced fluxes along the western and southern boundaries of the study region, and a ''tongue'' of low export extending northwestward from $7°N 116°E to $10°N 111°E. This geographic distribution is consistent with the overall surface circulation pattern of the southern SCS in this season.

Marine particles transport organic matter through the water column to the sediment where the organic matter can be buried. This pathway is one of the few natural removal mechanisms of CO 2 from the atmosphere over geological time. Picophytoplankton, major primary producers in the ocean, have until recently been thought unimportant regarding particle transport. Here we provide evidence that silicate is deposited on extracellular polymeric substance (EPS) associated with decomposing picophytoplankton. We also find that Si is enriched in a previously unexplored group of marine particles (called micro-blebs) from the deep-water column. The surprising similarity in morphology and composition between EPS-Si and micro-blebs suggests that EPS-Si may be a precursor of micro-blebs observed in the deep ocean. This previously unexplored source of silicon may be important to silicon cycling and may further enhance export of picophytoplankton to the deep ocean.