Radiocarbon dating of archived sediment cores in the Southeast Pacific from 1960 to 2000

There were likely large changes in Southeast (SE) Pacific Ocean biogeochemistry over the last glacial cycle as a consequence of coincident changes in dust flux, oxygenation, and latitudinal position of the Subantarctic and Antarctic Fronts. However, there are few available sediment core records with reliable chronologies for this time interval despite the large number of archived cores collected between the 1960s and 1990s. The apparent reason is that, except for sites in proximity to the South American continental margin, sedimentation rates are often lower than 1 cm/kyr and calcium carbonate is only well preserved on topographic highs. As part of a project to study past nitrogen fixation, we surveyed archived cores from the SE Pacific and selected the most promising for radiocarbon dating of the planktonic foraminiferal fraction.  While many cores have core tops were found to be older than detectable with radiocarbon, a number have core tops ages within the Holocene and sediment accumulation rates centering on 1.5 cm/kyr.

末次冰期旋回期间，东南太平洋（Southeast Pacific Ocean）的生物地球化学过程很可能发生了显著变化，其驱动因素为尘埃通量、氧化环境以及亚南极锋（Subantarctic Front）与南极锋（Antarctic Front）的纬度位置同步改变。尽管上世纪60至90年代采集了大量存档岩芯，但对应这一时间段、且具备可靠年代框架的沉积物岩芯记录却寥寥无几。究其缘由，除紧邻南美大陆边缘的站位外，其余站位的沉积速率通常低于1厘米/千年，且碳酸钙（calcium carbonate）仅在地形高地中得以良好保存。作为过去固氮作用（nitrogen fixation）研究项目的组成部分，我们对东南太平洋的存档岩芯开展了系统普查，并筛选出最具潜力的岩芯用于浮游有孔虫组分（planktonic foraminiferal fraction）的放射性碳定年（radiocarbon dating）。尽管多数岩芯的表层年龄已超出放射性碳测年的可检测范围，但仍有部分岩芯的表层年龄处于全新世（Holocene）范围内，且沉积堆积速率集中在1.5厘米/千年左右。