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.

本数据集的元数据记录源自ASAC项目492，该项目的公开详情可通过下方链接查阅。基于所引用论文的摘要内容：研究人员将东南极洲麦克罗伯逊陆架两处全新世（Holocene）沉积岩芯（sediment core）GC1与GC2中的硅藻（diatom）组合，与该区域现代沉积硅藻组合进行了对比。冰山巷（Iceberg Alley，位于陆架外侧）的开阔海沉积（open marine deposition）始于距今超过10.7个碳十四千年（14C kyr BP）。以角毛藻（Chaetoceros）休眠孢子（resting spore）为主导的硅藻组合占比极高，这类孢子可指示冰架与/或海冰消融引发的水体层化，或是夏季海冰最大退缩时段。约距今7.5个碳十四千年时，海冰型硅藻组合得以沉积。该组合与现今麦克罗伯逊陆架表层沉积物中的硅藻组合高度相似，表明自彼时起，冰山巷附近海域长期存在海冰。然而，海冰型硅藻组合中夹有富含冕孢藻（Corethron）的沉积层，指示全新世中晚期出现了与气候适宜期相关的高生产力事件。

陆架内侧的尼尔森盆地（Nielsen Basin，GC2岩芯）的硅藻记录与GC1相比相对均一。距今超过5.6个碳十四千年之前，该区域存在冰川冰，其下方沉积了溶解型硅藻组合（dissolution diatom assemblage）。冰川消退后，短暂沉积了冰缘型硅藻组合（ice-edge diatom assemblage），随后形成与现今陆架海冰环境相似的沉积。GC2中未发现GC1中记录的全新世中晚期高生产力事件。

研究人员通过多元分析（multivariate analysis），从普里兹湾与麦克罗伯逊陆架的表层沉积物中识别出四类硅藻组合：沿海型硅藻组合以海冰硅藻为特征，包含脆边海束藻（Fragilariopsis curta）、棱角海束藻（F. angulata）、圆柱海束藻（F. cylindrus）以及膨胀拟菱形藻（Pseudonitzschia turgiduloides）；陆架型硅藻组合以开阔水域硅藻为特征，包含凯尔盖朗海束藻（Fragilariopsis kerguelensis）、光滑海链藻（Thalassiosira lenuginosa）、纤细海链藻期待变种（T. gracilis var. expecta）以及赖因博尔德三毛藻（Trichotoxin reinboldii）；达恩利角型硅藻组合同时包含海冰与开阔水域硅藻，但所有物种均体型硕大且硅质化程度极高。研究人员通过多元回归分析（multiple regression）明确了硅藻组合与已知环境变量之间的关联：沿海、陆架与远洋型硅藻组合与纬度、海冰分布及海流等生态条件存在显著相关性。达恩利角型硅藻组合被认为代表了经海流淘洗移除了体型更小、硅质化程度更低物种后的硅藻组合。

研究人员借助一段长352cm的短重力岩芯（gravity core）中的硅藻组合与沉积相数据，重建了东南极洲普里兹湾内侧过去21320个碳十四年（14C yr B.P.）的古沉积环境。在21320至11650个碳十四年之前，岩芯中发育致密冰碛岩（tillite）与混杂沉积（diamicton），硅藻壳（diatom frustule）罕见甚至缺失。这些数据表明，末次冰盛期期间，冰盖覆盖了该采样点。冰川消退后，11650至2600个碳十四年之前的时段内，开阔海环境下沉积了硅质泥质软泥。该阶段硅藻壳丰富且保存完好，南极海链藻（Thalassiosira antarctica）休眠孢子与脆边海束藻主导了硅藻组合。该组合指示当时的海冰时空分布范围小于现今的开阔海沉积环境。自2600个碳十四年之前至今，海冰与冰缘硅藻物种占比逐渐升高，指示新冰期（neoglacial）降温事件。现今普里兹湾海域每年有2-3个月海冰覆盖率不足10%，且近岸附近长期存在冰缘与/或多年海冰，该阶段的硅藻组合与现今普里兹湾的沉积组合高度相似。