Abstract Isfjorden, a broad Arctic fjord in western Spitsbergen, has shown significant changes in hydrography and inflow of Atlantic Water (AW) the last decades that only recently have been observed in the Arctic Ocean north of Svalbard. Variability and trends in this fjord’s climate and circulation are therefore analysed from observational and reanalysis data during 1987 to 2017. Isfjorden experienced a shift in summer ocean structure in 2006, from AW generally in the bottom layer to AW (with increasing thickness) higher up in the water column. This shift, and a concomitant shift to less fast ice in Isfjorden are linked to positive trends in the mean sea surface temperature (SST) and volume weighted mean temperature (VT) in winter (SSTw/VTw: 0.7 ± 0.1/0.9 ± 0.3 °C 10 yr−1) and summer (SSTS/VTS: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr−1). Hence, the local mean air temperature shows similar trends in winter (1.9 ± 0.4 °C 10 yr−1) and summer (0.7 ± 0.1 °C 10 yr−1). Positive trends in volume weighted mean salinity in winter (0.21 ± 0.06 10 yr−1) and summer (0.07 ± 0.05 10 yr−1) suggest increased AW advection as a main reason for Isfjorden’s climate change. Local mean air temperature correlates significantly with sea ice cover, SST, and VT, revealing the fjord’s impact on the local terrestrial climate. In line with the shift in summer ocean structure, Isfjorden has changed from an Arctic type fjord dominated by Winter Deep and Winter Intermediate thermal and haline convection, to a fjord dominated by deep thermal convection of Atlantic type water (Winter Open). AW indexes for the mouth and Isfjorden proper show that AW influence has been common in winter over the last decade. Alternating occurrence of Arctic and Atlantic type water at the mouth mirrors the geostrophic control imposed by the Spitsbergen Polar Current (carrying Arctic Water) relative to the strength of the Spitsbergen Trough Current (carrying AW). During high AW impact events, Atlantic type water propagates into the fjord according to the cyclonic circulation along isobaths corresponding to the winter convection. Tides play a minor role in the variance in the currents, but are important in the side fjords where exchange with the warmer Isfjorden proper occurs in winter. This study demonstrates that Isfjorden and its ocean climate can be used as an indicator for climate change in the Arctic Ocean. The used methods may constitute a set of helpful tools for future studies also outside the Svalbard Archipelago.

中文翻译：

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Isfjorden（斯瓦尔巴群岛）海洋气候和环流的变化和年代际趋势——欧洲北极气候变化的指标

摘要 Isfjorden 是斯匹次卑尔根岛西部广阔的北极峡湾，在过去几十年中，水文和大西洋水 (AW) 流入量已显示出显着变化，直到最近才在斯瓦尔巴群岛以北的北冰洋观察到这些变化。因此，根据 1987 年至 2017 年期间的观测和再分析数据分析了该峡湾气候和环流的变化和趋势。 伊斯峡湾在 2006 年经历了夏季海洋结构的转变，从普遍位于底层的 AW 到更高的 AW（随着厚度的增加）在水柱。这种转变以及随之而来的 Isfjorden 冰速较慢的转变与冬季平均海面温度 (SST) 和体积加权平均温度 (VT) 的积极趋势有关 (SSTw/VTw: 0.7 ± 0.1/0.9 ± 0.3 ° C 10 yr−1) 和夏季 (SSTS/VTS: 0.7 ± 0.1/0.6 ± 0.1 °C 10 yr−1)。因此，当地平均气温在冬季 (1.9 ± 0.4 °C 10 yr−1) 和夏季 (0.7 ± 0.1 °C 10 yr−1) 显示出相似的趋势。冬季 (0.21 ± 0.06 10 yr−1) 和夏季 (0.07 ± 0.05 10 yr−1) 体积加权平均盐度的积极趋势表明 AW 平流增加是 Isfjorden 气候变化的主要原因。当地平均气温与海冰覆盖、SST 和 VT 显着相关，揭示了峡湾对当地陆地气候的影响。顺应夏季海洋结构的转变，伊斯峡湾已从以冬季深部和冬季中度热盐对流为主的北极型峡湾，转变为以大西洋型水深部热对流为主的峡湾（Winter Open）。嘴巴和 Isfjorden 的 AW 指数表明，在过去十年中，AW 的影响在冬季很常见。北极和大西洋类型的水在河口交替出现，反映了斯匹次卑尔根极地流（携带北极水）相对于斯匹次卑尔根海槽流（携带 AW）的强度施加的地转控制。在高 AW 影响事件期间，大西洋类型的水根据与冬季对流相对应的等深线的气旋环流传播到峡湾。潮汐在洋流的变化中起次要作用，但在冬季与温暖的伊斯峡湾进行交换的侧峡湾中很重要。这项研究表明，伊斯峡湾及其海洋气候可以作为北冰洋气候变化的指标。所使用的方法可能构成一套有用的工具，用于未来也在斯瓦尔巴群岛以外的研究。