Preservation efficiencies and accumulation rates for biogenic silica and organic C, N, and P in high‐latitude sediments: The Ross Sea

Abstract

Rates of biogenic sediment accumulation (biogenic silica and organic C, N, and P) and pore water flux have been established for a variety of depositional environments in the Ross Sea. On the basis of 14C measurements in kasten cores, sediment accumulation rates ranged from 250 cm kyr−1 in the coastal basin of Granite Harbor to 1–2 cm kyr−1 in the shelf and slope environments of the northern and eastern Ross Sea. Burial of biogenic material was most rapid in the southwestern Ross Sea, where biogenic silica accumulation rates ranged from 2 to 31 g cm−2 kyr−1 and organic carbon accumulation rates ranged from 0.05 to 1.4 g cm−2 kyr−1. In the northern and eastern Ross Sea, biogenic silica and organic carbon accumulation rates typically equaled 0.02–0.03 g SiO2 cm−2 kyr−1 and 0.002–0.004 g C cm−2 kyr−1. Flux core measurements were used to estimate seabed regeneration rates for biogenic silica, organic carbon, and phosphorus. Pore water fluxes, in general, showed much less variability across the Ross Sea than did the biogenic accumulation rates. Pore water silicate fluxes in the study area ranged from 0.6 to 5.3 g SiO2 cm−2 kyr−1, whereas carbon fluxes ranged from 0.1 to 1.2 g C cm−2 kyr−1 and phosphate fluxes varied from −0.006 to 0.012 g P cm−2 kyr−1. Seabed preservation efficiencies were calculated for biogenic silica, organic carbon, and phosphorus by combining the solid‐phase and pore water data. The seabed preservation efficiencies for biogenic silica (1–86%) were greater than for organic carbon (1–71%) at all nine stations examined. The preferential preservation of biogenic silica relative to organic carbon also was apparent in Ross Sea sediments because the biogenic silica/organic carbon ratio in the material buried in the seabed generally was 2 times greater than the ratio in sediment particles arriving at the sediment‐water interface. Sediment accumulation rate correlated strongly with both the biogenic silica and the organic carbon preservation efficiency data. P preservation efficiencies remained relatively high (24–65%) even when the accumulation rates were low (1–2 cm kyr−1) because of the near‐zero phosphate fluxes out of the seabed. Of the total P in the seabed (0.04–0.09 wt. %), approximately 25% existed in the form of organic P. The total amount of biogenic silica accumulating on the Ross Sea shelf is ∼2.3 × 1012 g SiO2 yr−1, which is approximately an order of magnitude less than the Ledford‐Hoffman et al. [1986] estimate that was based on 210Pb chronologies. Biogenic silica accumulation rates in the southern, central, and western Ross Sea increased during the mid and late Holocene, reaching their maximum values during the past 500 to 1000 years.