Spectral gamma-ray measurements were carried out on eight cores collected in the Bransfield Strait at points distributed over a cross section connecting the South Shetland Islands (NW) and the Antarctic Peninsula (SE). These cores were acquired during the cruises OPERANTAR XXXIII, XXXIV, and XXXV, aboard the P/V Almirante Maximiano, from the Brazilian Navy, within the scope of the project “Use of Sedimentary and Biogeochemical Records as Indicative of Climate and Environmental Changes in the South Shetland Islands and Antarctic Peninsula”. The energy spectrum was measured in counts per period through a portable spectrometer which displays the total gamma-ray (total GR) counts, in addition to the individual concentrations of K (%), U (ppm), and Th (ppm), internally converted. The results, integrated with core sedimentological descriptions, enabled us to characterize the different geochemical environments and to recognize paleoenvironmental cycles and stratigraphic surfaces, proving to be a powerful tool for high-resolution stratigraphic studies. The Th/U and U/K ratios reveal six well-marked cycles (identified from A to F) interpreted as transitions from warm to cold periods. The increase in Th/U ratio was used as a proxy for higher clastic meltwater sedimentary input during warm periods, while the increase in U/K ratio indicates higher amounts of organic matter, and therefore higher U content, during cold periods, when clastic sedimentary input is smaller. The concomitant decrease in the Th/U ratio with the increase in the U/K ratio suggests a gradual change from a warm to a cold period. Otherwise, the gradual increase in the Th/U ratio and decrease in the U/K ratio indicates the transition from cold to warm periods. In addition, this study observed different behaviors between proximal and distal gamma-ray spectral logs.

中文翻译：

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基于伽马射线光谱的南极半岛布兰斯菲尔德盆地第四纪变暖和变冷趋势

光谱伽马射线测量是在布兰斯菲尔德海峡收集的八个岩心上进行的，这些岩心分布在连接南设得兰群岛 (NW) 和南极半岛 (SE) 的横截面上。这些岩心是在 OPERANTAR XXXIII、XXXIV 和 XXXV 航行期间，在“使用沉积物和生物地球化学记录作为气候和环境变化的指标”项目范围内从巴西海军的 P/V Almirante Maximiano 上获得的。南设得兰群岛和南极半岛”。能量谱是通过便携式光谱仪以每个周期的计数测量的，该光谱仪在内部显示总伽马射线（总 GR）计数，以及 K (%)、U (ppm) 和 Th (ppm) 的各个浓度转换。结果，结合岩心沉积学描述，使我们能够表征不同的地球化学环境并识别古环境旋回和地层表面，被证明是高分辨率地层研究的有力工具。Th/U 和 U/K 比率揭示了六个明显的周期（从 A 到 F）被解释为从温暖到寒冷时期的转变。Th/U 比率的增加被用作温暖时期碎屑融水沉积输入量较高的代表，而 U/K 比率的增加表明有机质含量较高，因此在寒冷时期碎屑沉积物沉积时 U 含量较高输入较小。Th/U 比值随着 U/K 比值的增加而降低，表明从温暖期到寒冷期的逐渐变化。除此以外，Th/U 比值的逐渐增加和 U/K 比值的减小表明从寒冷时期到温暖时期的转变。此外，这项研究观察到近端和远端伽马射线光谱日志之间的不同行为。