Biogenic opal, carbonat concentrations and stable oxygen isotope ratios of foraminifera from sediment cores of the Southern Ocean@en

We present records of biogenic opal percentage and burial rate in 12 piston cores from the Atlantic and Indian sectors of the Southern Ocean. These records provide a detailed, quantitative description of changing patterns of opal deposition over the last 450 kyr. The striking regional coherence of these records suggests that dissolution in the deep sea and sediment pore waters does not obscure the surface productivity signal, and therefore these opal time series can be used in combination with other surface water tracers to make inferences about the chemistry and circulation of the Southern Ocean under different global climate conditions. Three broad depositional patterns can be distinguished. Northernmost records (39°-42°S latitude) are characterized by enhanced opal burial during glacial periods and strong 41 kyr periodicity. Records from cores just north of the present Antarctic Polar Front (46°-49°S) show even larger increases in opal burial rate during glacial intervals, but have variance concentrated in the 100 and 23 kyr bands. Southernmost records (51°-55°S) are completely out of phase with those to the north, with greatly reduced opal burial rates during glacial periods. Taken as a whole, the opal records show no evidence for the increased total Antarctic productivity predicted by recent geochemical models of atmospheric CO2 variability. The areal expansion of Southern Ocean sea ice over the present zone of high siliceous productivity provides one plausible explanation for the glacial-interglacial opal patterns. The excess silica not taken up in this zone during glacial periods would contribute to greater nutrient availability and thus higher productivity in the subantarctic region. However, local circulation changes may act to modify this basic signal, possibly accounting for the observed differences in the opal variance spectra.本研究提供了南大洋（Southern Ocean）大西洋与印度洋扇区12个活塞岩芯（piston cores）的生物成因蛋白石（biogenic opal）百分含量及埋藏速率数据集。该套记录可详细且定量地刻画过去450千年以来蛋白石沉积模式的演化过程。这些记录呈现出显著的区域一致性，表明深海与沉积物孔隙水中的溶解作用并未掩盖表层生产力信号，因此该套蛋白石时间序列可与其他地表水示踪剂结合，用于推演不同全球气候背景下南大洋的化学特征与环流模式。可区分出三类主要的沉积模式：最北端的记录（纬度39°S~42°S）以冰期阶段蛋白石埋藏速率升高及显著的41千年周期为特征；位于现今南极极锋（Antarctic Polar Front）北侧的岩芯记录（纬度46°S~49°S）在冰期时段的蛋白石埋藏速率增幅更为显著，但其方差集中于100千年与23千年频段；最南端的记录（纬度51°S~55°S）则与北部记录完全反相，冰期阶段的蛋白石埋藏速率大幅降低。整体而言，该套蛋白石记录未发现支持近期大气CO₂变化地球化学模型所预测的南极总生产力升高的证据。南大洋海冰在现今高硅质生产力海域的面积扩张，可为冰期-间冰期蛋白石沉积模式提供一种合理的解释。冰期时段该海域未被利用的过剩硅，会提升亚南极区域的养分可利用性，进而提高该区域的生产力。但局地环流变化可对这一基础信号进行改造，这或许可以解释观测到的蛋白石方差谱差异。