Radiolarian abundance of sediment core Y8

A high-resolution record of radiolarian faunal changes from Site Y8 south of the Subtropical Front (STF), offshore eastern New Zealand, provides insight into the paleoceanographic history of the last 265 kyrs. Quantitative analysis of radiolarian paleotemperature indicators and radiolarian-based sea surface temperature (SST) estimates reveal distinct shifts during glacial-interglacial (G-I) climate cycles encompassing marine isotope stages (MIS) 8-1. Faunas at Site Y8 are abundant and diverse and consist of a mixture of species typical of the subantarctic, transitional and subtropical zones which is characteristic of subantarctic waters just south of the STF. During interglacials, diverse radiolarian faunas have increased numbers of warm-water taxa (not, vert, similar 15%) while cool-water taxa decrease to not, vert, similar 11% of the assemblage. Warmest climate conditions occurred during MIS 5.5 and the early Holocene Climatic Optimum (HCO) at the onset of MIS 1 where SSTs reach maxima of 12.8 and 12.9 °C, respectively. This suggests that temperatures during the HCO were comparable to the Eemian, one of the warmest interglacial intervals of the Late Quaternary. Glacials are characterized by less diverse radiolarian faunas with cool-water taxa increasing to 49% of the assemblage. Coolest climate conditions occurred in MIS 4 and 2 where SSTs are reduced to 5.4 °C and 4.3 °C, respectively. Radiolarian faunal changes and SST estimates clearly identify major water masses and oceanic fronts in the offshore eastern New Zealand area. During warmest MIS 5.5 and early MIS 1 substantial influence of northern-sourced Subtropical Surface Water (STW) is evident at Site Y8. This implies southward incursions of STW around the eastern crest of Chatham Rise with the STF displaced towards higher latitudes and spinning off eddies as far south as Campbell Plateau. Additionally, increased flow of the Southland Current (SC) might have enhanced the local occurrence of warm-water radiolarians derived from the subtropical Tasman Sea. Coolest glacials are marked by a strong inflow of cool, southern-sourced waters at Site Y8 indicating a more vigorous flow along the Subantarctic Front (SAF).

取自新西兰东部近海副热带锋（Subtropical Front, STF）以南Y8站位的高分辨率放射虫动物群变化记录，为探究过去26.5万年的古海洋演化历史提供了关键依据。对放射虫古温度指标及基于放射虫的海表温度（sea surface temperature, SST）估算结果开展定量分析，结果揭示了涵盖海洋同位素阶段（marine isotope stages, MIS）8至1的冰期-间冰期（glacial-interglacial, G-I）气候旋回中的显著气候转变。Y8站位的放射虫动物群丰富且多样，由亚南极带、过渡带及亚热带典型物种混合构成，这一组合特征与副热带锋以南的亚极地水域典型特征相符。间冰期阶段，多样的放射虫动物群中暖水类群占比提升至约15%，而冷水类群占比则降至约11%。最温暖的气候条件出现在MIS 5.5期以及MIS 1初期的全新世气候适宜期（Holocene Climatic Optimum, HCO），此时海表温度分别达到12.8℃和12.9℃的峰值。这表明全新世气候适宜期的温度水平可与晚第四纪最温暖间冰期之一的埃姆间冰期相媲美。冰期阶段的放射虫动物群多样性较低，冷水类群占比升至49%。最寒冷的气候条件出现在MIS 4和MIS 2期，海表温度分别降至5.4℃和4.3℃。放射虫动物群变化与海表温度估算结果清晰识别出新西兰东部近海区域的主要水团与海洋锋面。在最温暖的MIS 5.5期与MIS 1早期，Y8站位显著受到北部源地副热带表层水（Subtropical Surface Water, STW）的影响。这意味着副热带表层水沿查塔姆海隆东脊向南入侵，副热带锋向高纬度偏移，并向南延伸至坎贝尔高原形成涡旋。此外，南兰洋流（Southland Current, SC）流量增强可能促进了源自亚热带塔斯曼海的暖水放射虫在当地的大量出现。最寒冷的冰期阶段则以Y8站位出现大量南部源地冷水团为特征，表明亚南极锋（Subantarctic Front, SAF）沿线的环流更为活跃。