Stable oxygen isotope records of different benthic foraminiferal species of core GeoB3004-1 from the western Arabian Sea

The stable isotope composition of one epifaunal and three infaunal benthic foraminiferal species of a sediment core from 1800 m water depth of the western Arabian Sea was determined to evaluate deepwater oxygenation, organic matter remineralization, and early diagenetic processes during the past 190,000 years. The d18O records reveal species-specific metabolic effects, susceptibility to changes in carbonate ion concentration, and supralysoclinal calcite dissolution. The foraminiferal d13C records reveal changes in the stable carbon isotope gradients of pore water dissolved inorganic carbon (d13CDIC) and in the microhabitat depth of infaunal species. Maximum d13CDIC offsets between bottom and pore waters ranged between mean values of 0.8 and 1.2% corresponding to estimates of deepwater oxygen concentration between approximately 1 and 2.7 ml/l. Intervals of improved deepwater oxygenation coincided with high benthic foraminiferal diversity and indicate the admixture of well-oxygenated deepwater masses during interglacials. During interglacial maxima the d13C difference between epifauna and shallow infauna indicates highest organic matter remineralization rates at times of maximum organic matter fluxes.

针对取自阿拉伯海西部水深1800米处的沉积岩芯，研究人员对其中1种表生底栖有孔虫（epifaunal benthic foraminifera）与3种内生底栖有孔虫（infaunal benthic foraminifera）的稳定同位素组成展开测定，以此评估过去19万年间的深水氧化作用、有机质再矿化过程以及早期成岩作用。δ¹⁸O（d18O）记录揭示了物种特异性代谢效应、对碳酸根离子浓度变化的敏感性，以及溶跃面上方方解石溶解现象。有孔虫δ¹³C（d13C）记录则反映了孔隙水溶解无机碳（d13CDIC）的稳定碳同位素梯度变化，以及内生有孔虫的微生境深度变化。底层水与孔隙水之间的最大d13CDIC差值介于0.8‰~1.2‰的平均区间，对应估算得到的深水氧浓度约为1~2.7 ml/l。深水氧化作用增强的时段与底栖有孔虫多样性升高的阶段相吻合，表明间冰期期间含氧充足的深水团发生了混合。在间冰期鼎盛阶段，表生有孔虫与浅栖内生有孔虫之间的δ¹³C差值表明，在有机质通量达到峰值的时期，有机质再矿化速率也达到最高水平。