Phytoplankton Distribution in Surface Samples and Cores from Prydz Bay and Long Fjord and its Relationship to Sea Level and Climatic Change

Metadata record for data from ASAC Project 492 See the link below for public details on this project.

From the abstracts of the referenced papers:

Diatom assemblages in two Holocene sediment cores (GC1 and GC2) from the Mac. Robertson Shelf, East Antarctica, are compared with modern sedimentary diatom assemblages from the same area. Open marine deposition commenced in Iceberg Alley (GC1), on the outer continental shelf, greater than 10.7 adj. 14C kyr BP. Chaetoceros resting spores, which may indicate water-column stabilsation from melting glacial and/or sea ice or the maximum summer sea-ice retreat, dominate the diatom assemblage. Approximately 7.5 adj. 14C kyr BP, a sea-ice diatom assemblage was deposited. This assemblage is similar to that being deposited in the surface sediments of the Mac. Robertson Shelf today and suggests that perennial sea ice has persisted in the vicinity of Iceberg Alley since that time. Interbedded within the sea-ice assemblage, however, are Corethron-rich sediment layers that suggest mid- to late-Holocene high-productivity events associated with a climatic optimum. The diatom record from Nielsen Basin (GC2), on the inner continental shelf, is relatively uniform compared to that in GC1. Glacial ice was present over the region c. greater than 5.6 adj. 14C kyr BP and a dissolution diatom assemblage was deposited beneath it. following ice retreat, an ice-edge diatom assemblage was deposited briefly before sea-ice conditions similar to that on the continental shelf today developed. There is no evidence in GC2 for the mid- to late-Holocene high-productivity events identified in GC1.

Four diatom assemblages are identified from the surface sediments of Prydz Bay and the Mac. Robertson Shelf using multivariate analysis. A coastal assemblage is characterised by the sea-ice diatoms Fragilariopsis curta, F. angulata, F. cylindrus and Pseudonitzschia turgiduloides. A continental shelf assemblage is characterised by the open-water diatoms Fragilariopsis kerguelensis, Thalassiosira lenuginosa, T. gracilis var. expecta and Trichotoxin reinboldii. The Cape Darnley assemblage contains both sea-ice and open-water diatoms, but all are characteristically large and heavily silicified. Multiple regression has been used to identify the relationships between the diatom assemblages and known environmental variables. There are strong correlations between the coastal, shelf and oceanic assemblages and ecological conditions, including latitude, sea-ice distribution and ocean currents. The Cape Darnley assemblage is thought to represent an assemblage from which the smaller and more lightly silicified species have been removed by current winnowing.

The palaeo-depositional environment of inner Prydz Bay, East Antarctica, has been reconstructed for the past 21,320 14C yr B.P., using diatom assemblages and sediment facies from a short, 352 cm long gravity core. Between 21,320 and 11,650 14C yr B.P., compact tillite and diamicton are present in the core, and diatom frustules are rare to absent. These data suggest that an ice sheet grounded over the site during the last glacial maximum. Following glacial retreat, siliceous muddy ooze was deposited, from 11,650 to 2600 14C yr B.P., in an open marine setting. During this stage, diatom frustules are abundant and well preserved, and Thalassiosira antarctica resting spores and Fragilariopsis curta dominate the assemblage. This assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today. Since 2600 14C yr B.P., sea-ice and ice-edge diatom species have become more abundant, and neoglacial cooling is inferred. The assemblage is similar to that forming currently in Prydz Bay, where sea-ice is absent (less than 10% cover) for 2-3 months of the year and permanent ice edge and/or multiyear sea ice remains in close proximity to the site.

ASAC项目492的数据集元数据记录，有关该项目的公开详情请参阅下方链接。

以下为参考文献论文摘要内容：

对东南极洲麦克罗伯逊陆架（Mac. Robertson Shelf）两处全新世（Holocene）沉积岩芯（GC1与GC2）中的硅藻组合，与该区域现代沉积硅藻组合开展对比分析。位于外大陆架的冰山航道（Iceberg Alley，GC1站位）的开阔海洋沉积始于距今10.7校正¹⁴C千年（adj. ¹⁴C kyr BP）之前。角毛藻（Chaetoceros）休眠孢子主导了该硅藻组合，这类孢子可指示冰川和/或海冰消融导致的水柱稳定，或是夏季海冰最大范围消退的信号。距今约7.5校正¹⁴C千年时，海冰型硅藻组合开始沉积。该组合与现今麦克罗伯逊陆架表层沉积物中的沉积组合特征相似，表明自该时期起，冰山航道附近区域长期存在海冰。但海冰型硅藻组合中夹有富角管藻（Corethron）沉积层，指示全新世中晚期出现了与气候最适宜期相关的高生产力事件。

位于大陆架内侧的尼尔森盆地（Nielsen Basin，GC2站位）的硅藻记录与GC1相比，相对均一。约距今5.6校正¹⁴C千年之前，该区域存在冰川冰，其下方沉积了溶解型硅藻组合。冰川消退后，在形成现今大陆架的海冰环境之前，曾短暂沉积过冰缘型硅藻组合。GC2岩芯中未发现GC1中所识别的全新世中晚期高生产力事件的相关证据。

通过多变量分析（multivariate analysis），从普里兹湾（Prydz Bay）与麦克罗伯逊陆架的表层沉积物中识别出四类硅藻组合。沿岸型硅藻组合以海冰硅藻曲脆杆藻（Fragilariopsis curta）、角脆杆藻（F. angulata）、圆柱脆杆藻（F. cylindrus）以及膨假拟菱形藻（Pseudonitzschia turgiduloides）为特征。大陆架型硅藻组合以开阔水域硅藻克氏脆杆藻（Fragilariopsis kerguelensis）、绒面海链藻（Thalassiosira lenuginosa）、纤细海链藻期望变种（T. gracilis var. expecta）以及伦氏三毛藻（Trichotoxin reinboldii）为特征。达恩利角（Cape Darnley）型硅藻组合同时包含海冰与开阔水域硅藻，但所有物种均体型较大且硅质化程度较高。研究通过多元回归分析，明确了硅藻组合与已知环境变量之间的关联。沿岸型、陆架型与大洋型硅藻组合与纬度、海冰分布及海流等生态环境条件存在显著相关性。达恩利角型硅藻组合被认为是经海流淘洗移除了体型较小、硅质化程度较低的物种后形成的组合。

研究依托一根长352cm的短重力岩芯（gravity core）中的硅藻组合与沉积相，重建了东南极洲普里兹湾内侧过去21320年碳十四年代的古沉积环境。在距今21320至11650年碳十四年代期间，岩芯中存在致密冰碛岩（compact tillite）与混杂堆积物（diamicton），硅藻壳（diatom frustules）极为稀少甚至缺失。这些数据表明，末次冰盛期（last glacial maximum）时冰盖覆盖了该站位区域。冰川消退后，在距今11650至2600年碳十四年代期间，该区域处于开阔海洋环境，沉积了硅质软泥（siliceous muddy ooze）。该阶段硅藻壳丰富且保存完好，南极海链藻（Thalassiosira antarctica）休眠孢子与曲脆杆藻主导了硅藻组合。该组合特征表明，当时的开阔海洋环境中海冰的时空分布范围小于现今。自距今2600年碳十四年代起，海冰与冰缘硅藻物种丰度上升，指示新冰期降温（neoglacial cooling）事件的发生。该硅藻组合与现今普里兹湾的沉积组合特征相似：该区域每年有2-3个月无海冰（海冰覆盖率低于10%），且站位附近常年存在冰缘或多年海冰。