Klages Johann P, Kuhn Gerhard, Hillenbrand Claus-Dieter, Smith James A, Graham Alastair G C, Nitsche Frank O, Frederichs Thomas, Jernas Patrycja E, Gohl Karsten, Wacker Lukas
Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung, Marine Geosciences, Bremerhaven, Germany.
British Antarctic Survey, High Cross, Cambridge, United Kingdom.
PLoS One. 2017 Jul 25;12(7):e0181593. doi: 10.1371/journal.pone.0181593. eCollection 2017.
Precise knowledge about the extent of the West Antarctic Ice Sheet (WAIS) at the Last Glacial Maximum (LGM; c. 26.5-19 cal. ka BP) is important in order to 1) improve paleo-ice sheet reconstructions, 2) provide a robust empirical framework for calibrating paleo-ice sheet models, and 3) locate potential shelf refugia for Antarctic benthos during the last glacial period. However, reliable reconstructions are still lacking for many WAIS sectors, particularly for key areas on the outer continental shelf, where the LGM-ice sheet is assumed to have terminated. In many areas of the outer continental shelf around Antarctica, direct geological data for the presence or absence of grounded ice during the LGM is lacking because of post-LGM iceberg scouring. This also applies to most of the outer continental shelf in the Amundsen Sea. Here we present detailed marine geophysical and new geological data documenting a sequence of glaciomarine sediments up to ~12 m thick within the deep outer portion of Abbot Trough, a palaeo-ice stream trough on the outer shelf of the Amundsen Sea Embayment. The upper 2-3 meters of this sediment drape contain calcareous foraminifera of Holocene and (pre-)LGM age and, in combination with palaeomagnetic age constraints, indicate that continuous glaciomarine deposition persisted here since well before the LGM, possibly even since the last interglacial period. Our data therefore indicate that the LGM grounding line, whose exact location was previously uncertain, did not reach the shelf edge everywhere in the Amundsen Sea. The LGM grounding line position coincides with the crest of a distinct grounding-zone wedge ~100 km inland from the continental shelf edge. Thus, an area of ≥6000 km2 remained free of grounded ice through the last glacial cycle, requiring the LGM grounding line position to be re-located in this sector, and suggesting a new site at which Antarctic shelf benthos may have survived the last glacial period.
准确了解末次盛冰期（LGM；约26.5 - 19 cal. ka BP）时西南极冰盖（WAIS）的范围，对于以下几点至关重要：1）改进古冰盖重建；2）为校准古冰盖模型提供一个可靠的实证框架；3）确定末次冰期期间南极底栖生物可能的陆架避难所位置。然而，许多WAIS区域仍缺乏可靠的重建，特别是在外大陆架的关键区域，那里被认为是LGM冰盖的终止位置。在南极洲周围外大陆架的许多区域，由于末次盛冰期后的冰山冲刷，缺乏关于LGM期间是否存在陆冰的直接地质数据。这也适用于阿蒙森海中大部分外大陆架。在此，我们展示了详细的海洋地球物理和新的地质数据，记录了阿蒙森海湾区外陆架上古冰溪槽谷——阿伯特海槽深部约12米厚的一套冰川海洋沉积物序列。这套沉积物覆盖层的上部2 - 3米含有全新世和（前）末次盛冰期年龄的钙质有孔虫，结合古地磁年龄约束，表明自末次盛冰期之前很久，甚至可能自上一个间冰期以来，这里持续存在冰川海洋沉积。因此，我们的数据表明，此前确切位置不确定的末次盛冰期接地线，在阿蒙森海并非处处都到达陆架边缘。末次盛冰期接地线位置与距大陆架边缘内陆约100公里处一个明显的接地带楔形体的顶部重合。因此，在整个末次冰期循环中，面积≥6000平方公里的区域未被陆冰覆盖，这就需要重新确定该区域末次盛冰期接地线的位置，并表明这里是末次冰期期间南极陆架底栖生物可能存活的一个新地点。
