Icebergs in proglacial fjords serve as pupping, resting and molting habitat for some of the largest seasonal aggregations of harbor seals (Phoca vitulina richardii) in Alaska. One of the largest aggregations in Southeast Alaska occurs in Johns Hopkins Inlet, Glacier Bay National Park, where up to 2000 seals use icebergs produced by Johns Hopkins Glacier. Like other advancing tidewater glaciers, the advance of Johns Hopkins Glacier over the past century has been facilitated by the growth and continual redistribution of a submarine end moraine, which has limited mass losses from iceberg calving and submarine melting and enabled glacier thickening by providing flow resistance. A 15-year record of aerial surveys reveals (i) a decline in iceberg concentrations concurrent with moraine growth and (ii) that the iceberg size distributions can be approximated as power law distributions, with relatively little variability and no clear trends in the power law exponent despite large changes in ice fluxes over seasonal and interannual timescales. Together, these observations suggest that sustained tidewater glacier advance should typically be associated with reductions in the number of large, habitable icebergs, which may have implications for harbor seals relying on iceberg habitat for critical life-history events.

冰期前峡湾中的冰山是阿拉斯加一些最大的斑海豹 ( Phoca vitulina richardii ) 季节性聚集地的幼崽、休息和蜕皮栖息地。阿拉斯加东南部最大的聚集地之一位于冰川湾国家公园的约翰·霍普金斯湾，这里有多达 2000 只海豹在约翰·霍普金斯冰川产生的冰山上栖息。与其他前进的潮水冰川一样，约翰·霍普金斯冰川在过去一个世纪的前进是由海底末碛的生长和持续重新分布所促进的，它限制了冰山崩解和海底融化造成的质量损失，并通过提供流动阻力使冰川增厚。15 年的航空测量记录揭示了 (i) 冰山浓度下降与冰碛生长同时发生，以及 (ii) 冰山大小分布可近似为幂律分布，变化性相对较小，且幂律中没有明显的趋势尽管冰通量在季节和年际时间尺度上发生巨大变化，但仍呈指数变化。总之，这些观察结果表明，持续的潮水冰川前进通常应该与大型可居住冰山数量的减少有关，这可能对依赖冰山栖息地进行关键生活史事件的斑海豹产生影响。