Benthic Cycling of Biogenic Components of the Particulate Flux to the Sea Floor in the Southern Ocean in March and April, 1998 Book uri icon

abstract

  • We measured pore water profiles on depth scales of mm to tens of cm, using in situ and shipboard techniques, in order to quantify the cycling of biogenic materials at 7 sites at 170øW in the Southern Ocean. Sediment traps, deployed by Honjo et al., recorded time series of the particle flux at 1000m at 4 of these sites: AESOPS moorings MS-5 (Marginal Ice Zone), MS-4 (S. of the Polar Front), MS-3 (at the Polar Front), and MS-2 (N. of the Polar Front). Sedimentary recycling of biogenic silica and organic carbon was most rapid and variable at the three sites where a fluff layer was clearly visible on the sediment surface: site MS-4 and at the sediment sampling sites immediately south and north of MS- 4. Sedimentary carbonate dissolution occurred at all sites. It was slowest at the most southerly site, MS-5, at which the traps recorded the smallest CaCO3 rain, but showed no other trends. A comparison of sedimentary remineralization rates during the time period of our measurements with annually averaged particle rain rates from sediment traps shows several features. The largest apparent remineralization efficiencies were for biogenic silica: 100 +/- 30 \% at sites MS-5 and MS-4, 70 +/- 20\% at MS-3 and MS-2. The apparent remineralization efficiencies for Corg were lower: 65 +/- 20\% at site MS-5 and MS-4, and 30 +/- 10\% at MS-3 and MS-2. The values for CaCO3 were similar to those for Corg except at MS-5, where the sedimentary remineralization rate exceeded the annually averaged CaCO3 rain rate by a factor of 4.5. The low apparent remineralization efficiencies are not explained by high burial efficiencies. Rather, they must be explained either by remineralization at the sediment surface, not reflected in pore water profiles, or by temporal variability in sedimentary remineralization rates. Two factors point to the latter explanation in this region of extreme variability in rain rate to the sea floor. First, the highest apparent efficiencies were for biogenic silica, the component that is believed to react the most slowly in sediments. For that reason, its remineralization rate is expected to vary the least in response to variations in the particle rain rate. Second, apparent remineralization efficiencies were distinctly lower at the two northerly sites (MS-3 and MS-2) than at the two southerly sites. Although the sediment trap record ended about 50 days before our sampling, the record shows that the bloom arrived significantly earlier at the two northern sites, giving rise to the possibility that our measurements occurred later than peak rates at those sites, but closer in time to the peak rates and MS-5 and MS-4. We will determine reaction rate parameters from pore water and sediment data to examine whether they are consistent with short-term variability in sedimentary reaction rates.

publication date

  • January 2000