Biomarker and temperature and sea ice proxy data for TEX86 calibration in sediment core B997-316

Holocene paleoceanographic reconstructions along the North Iceland Shelf have employed a variety of sea surface temperature and sea ice proxies. However, these surface proxies tend to have a seasonal bias toward spring/summer and thus only provide a discrete snapshot of surface conditions during one season. Furthermore, sea surface temperature proxies can be influenced by additional confounding variables resulting in markedly different Holocene temperature reconstructions. Here, we expand Iceland's marine paleoclimate toolkit with TEX86 L: a temperature proxy based on the distribution of archaeal glycerol dibiphytanyl glycerol tetraether (GDGT) lipids. We develop a local Icelandic calibration from 21 surface sediment samples covering a wide environmental gradient across Iceland's insular shelves. Locally calibrated GDGT results demonstrate that (1) TEX86 L reflects winter subsurface (0-200 m) temperatures on the North Iceland Shelf and (2) our calibration produces more realistic temperature estimates with substantially lower uncertainty (S.E. ±4 °C) over global calibrations. We then apply this new calibration to a high‐resolution marine sediment core (last millennium) collected from the central NIS with age control constrained by 14C‐dated mollusks. To test the veracity of the GDGT subsurface temperatures, we analyze quartz and calcite wt% and a series of highly branched isoprenoid alkenes, including the sea ice biomarker IP25, from the same core. The sediment records demonstrate that the development of thick sea ice during the Little Ice Age warmed the subsurface due to winter insulation. Importantly, this observation reflects a seasonal component of the sea ice/ocean feedback to be considered for the nonlinear cooling of the Little Ice Age in and around Iceland.

冰岛北部陆架（North Iceland Shelf, NIS）的全新世（Holocene）古海洋重建研究已应用多种海表温度（sea surface temperature, SST）及海冰代用指标。然而，此类表层代用指标普遍存在春夏季季节性偏倚，仅能捕捉单一季节的表层环境离散快照。此外，海表温度代用指标易受额外混杂变量影响，致使全新世温度重建结果出现显著分歧。为此，本研究基于古菌甘油二烷基甘油四醚（archaeal glycerol dibiphytanyl glycerol tetraether, GDGT）脂类的分布特征，引入TEX86 L指标，以扩充冰岛海洋古气候研究的工具库。我们基于覆盖冰岛周边陆架广阔环境梯度的21个表层沉积物样品，建立了适配冰岛区域的本地化校准模型。经本地化校准的GDGT分析结果表明：其一，TEX86 L能够反映冰岛北部陆架的冬季次表层（0-200米）温度；其二，相较于全球校准模型，本研究的校准结果可生成更贴合实际的温度估算值，且不确定性大幅降低（标准误S.E. ±4℃）。随后，我们将该新校准模型应用于采自冰岛北部陆架中部的高分辨率海洋沉积物岩心——该岩心覆盖过去千年，其年代框架由14C测年的软体动物标本限定。为验证GDGT次表层温度数据的可靠性，我们对同一段岩心开展了石英、方解石重量百分比分析，以及一系列高支链类异戊二烯烯烃的检测，其中包含海冰生物标志物IP25。沉积物记录表明，小冰期（Little Ice Age）期间厚层海冰的发育通过冬季保温效应，使得次表层温度升高。值得注意的是，这一现象反映出海冰-海洋反馈的季节性分量，该分量在冰岛及周边区域小冰期的非线性降温研究中需予以考量。