Abstract The distributions of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in sediments are used as a proxy measurement to infer changes in past mean annual air temperatures (MAT). When applied to high resolution sedimentary sequences, measurement of brGDGT distributions is employed to reconstruct MAT at subdecadal time scales. In addition, brGDGT proxy estimates are also sometimes purported to be seasonally biased in environments where annual brGDGT production may not be constant during a seasonal cycle. The main aim of this study was to assess the occurrence of seasonality in the production and distribution of brGDGTs and the seasonality bias of the derived temperature proxy. For this purpose, we examined brGDGT distributions and brGDGT-derived MAT estimates in surface soils and settling/suspended particulate matter over one year, from two sites located in the same latitude but at different altitudes, in the Catalan Pyrenees, as well as at one site in southern Norway. These locations have marked seasonal temperature cycles, which were expected to maximize the possibility of detecting any seasonal bias in the production and compositions of brGDGTs. The results show that brGDGT abundance is heterogeneous and increases with soil humidity. The brGDGT distributions and some of the brGDGT-derived proxy measurements in soils are relatively stable throughout the year and do not change significantly in the suspended particulate matter in the river or settling particulate matter in traps. Our study shows that the impact of the seasonality of temperature on brGDGT distribution was absent in the soils studied, regardless of altitude or latitude on a catchment/regional scale. As soils are likely to contain a brGDGT signature which is representative of average environmental conditions in the catchment at least over decades, brGDGT proxy reconstructions derived from soil sources are more suitable to infer variability in environmental parameters over the same timescales (i.e. decades or longer). On shorter timescales (i.e. annual), sediment downcore variability in brGDGTs is likely to be related to changes derived from in situ production and sediment sources.

中文翻译：

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具有显着温度季节性的流域沉积物和土壤中的分支 G​​DGT 变异性

摘要 沉积物中支化甘油二烷基甘油四醚 (brGDGT) 的分布被用作替代测量来推断过去年平均气温 (MAT) 的变化。当应用于高分辨率沉积序列时，使用 brGDGT 分布的测量来重建次年代时间尺度的 MAT。此外，在年度 brGDGT 产量在季节性周期中可能不是恒定的环境中，brGDGT 代理估计有时也被认为具有季节性偏差。本研究的主要目的是评估 brGDGT 产生和分布中季节性的发生以及衍生温度代理的季节性偏差。为此，我们在一年多的时间内检查了表层土壤和沉降/悬浮颗粒物中的 brGDGT 分布和 brGDGT 衍生的 MAT 估计值，来自位于加泰罗尼亚比利牛斯​​山脉的两个位于同一纬度但海拔不同的地点，以及位于挪威南部的一个地点。这些位置具有显着的季节性温度循环，这有望最大限度地检测 brGDGT 的生产和组成中的任何季节性偏差。结果表明 brGDGT 丰度是异质的，并随着土壤湿度的增加而增加。土壤中的 brGDGT 分布和一些 brGDGT 衍生的代理测量值在全年相对稳定，并且在河流中的悬浮颗粒物或陷阱中的沉降颗粒物没有显着变化。我们的研究表明，无论集水区/区域尺度上的海拔或纬度如何，在所研究的土壤中都不存在温度季节性对 brGDGT 分布的影响。由于土壤可能包含 brGDGT 特征，该特征至少代表了流域中至少几十年来的平均环境条件，从土壤来源获得的 brGDGT 代理重建更适合推断相同时间尺度（即几十年或更长时间）内环境参数的变化. 在较短的时间尺度上（即每年），brGDGTs 中沉积物下核的变异性可能与来自原地生产和沉积物来源的变化有关。