Spatial and temporal variability of POC in the northeast Subarctic Pacific |
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| Institution: | 1. School of Earth and Ocean Sciences, University of Victoria, Victoria, BC, Canada;2. School of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada;1. Department of Urology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California;2. Department of Radiology, Weill-Cornell School of Medicine, New York, New York;3. Department of Pathology, Duke University School of Medicine, Durham, North Carolina;1. Department of Urology, University of California, Los Angeles, CA;2. Department of Urology, Stanford University School of Medicine, Stanford, CA;3. Department of Biomedical Engineering, University of California, Los Angeles, CA;4. Center for Advanced Surgical and Interventional Technology, University of California, Los Angeles, CA;5. Department of Radiology, University of California, Los Angeles, CA;6. Department of Pathology, University of California, Los Angeles, CA;7. Biostatistics, University of California, Los Angeles, CA |
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| Abstract: | Particulate organic carbon (POC) concentrations from 0 to 1000 m were quantified in size-fractionated particulate matter samples obtained by the multiple unit large volume in situ filtration system (MULVFS) in 1996 and 1997 along the 1600 km long “line P” transect from continental slope waters near southern Vancouver Island to Ocean Station PAPA (OSP, 50°N, 145°W). Regression of in situ POC vs. beam attenuation coefficient, c, from a simultaneously deployed 1-m pathlength SeaTech transmissometer gave slope, intercept and r2 values of 6.15±0.19×10?5 m?1 (nmol C l?1)?1, 0.363±0.003 m?1, and 0.951 (n=145), respectively. This result agreed within several percent of calibrations obtained from two 2600-km-long transects of the equatorial Pacific in 1992 (Bishop, 1999). Data from other, more frequently deployed transmissometers were standardized against the 1-m instrument, and the combined optical data set was used to document POC variability at finer spatial and temporal scales than could be sampled directly using either conventional water bottle casts or MULVFS. Published bottle POC vs. c relationships show much more variability and remain problematic. Along the line P transect in the salinity-stratified upper 100 m, POC isolines shoaled from winter to summer in concert with seasonal stratification. At the same time, POC was progressively enriched in subeuphotic zone waters to depths greater than 500 m. Near-surface POC fields sampled in the winter time showed strong temporal POC variability over time scales of days as well as between years. POC concentrations at OSP in February 1996 were higher than those found at any other time of year. Less variability was found along line P in other seasons. In May 1996, kilometer-scale spatial variability of POC at OSP was small; dawn vs. dusk variations of c were used to calculate 0–100 m POC turnover times shorter than 6 d. Calculations also suggest that 25–50% of primary productivity was expressed as dissolved organic carbon at OSP in May 1996. |
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