Controls on the onset and termination of past hypoxia in the Baltic Sea
Controls on the onset and termination of past hypoxia in the Baltic Sea
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DOI：
10.1016/j.palaeo.2017.11.012
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发表时间：
2018-01
期刊：
影响因子：
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通讯作者：
N. Papadomanolaki;N. Dijkstra;N. V. Helmond;M. Hagens;T. Bauersachs;U. Kotthoff;F. Sangiorgi;C. Slomp
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文献类型：
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作者：
N. Papadomanolaki;N. Dijkstra;N. V. Helmond;M. Hagens;T. Bauersachs;U. Kotthoff;F. Sangiorgi;C. Slomp
波罗的海是目前最大的海洋缺氧（O2< 2 mg L−1）“死亡区”，这是由于过去一个世纪以来人类活动造成的过量营养输入造成的。在全新世热极大期（HTM；早于现在的8-4 ka； BP）和中世纪气候异常期（MCA; 1.4-0.7 ka BP），波罗的海曾出现大面积缺氧。在这里，我们利用地球化学和海洋孢粉学数据研究了导致过去缺氧开始和结束的机制，这些数据来自于IODP远征347（站点M0063）期间从Landsort Deep获得的沉积物记录。鞭毛藻囊记录和基于tex86l的海面温度重建表明，在HTM缺氧间隔开始之前和开始期间，盐度和温度都有显著增加，强调了温度和盐度分层在提供有利于缺氧发生的条件方面的重要性。在HTM缺氧层段结束时，矿化度和温度均下降。相反，我们没有发现证据表明在MCA缺氧间隔期间表面盐度有显著变化，缺氧的开始和结束似乎主要是由温度变化驱动的。我们的研究结果表明，温度和盐度变化是波罗的海过去缺氧的关键驱动因素，这意味着持续的气候变化将推迟波罗的海从现代营养驱动的缺氧事件中恢复过来。
The Baltic Sea is currently the largest marine hypoxic (O2< 2 mg L− 1) ‘dead zone’ following excessive nutrient input from anthropogenic activities over the past century. Widespread hypoxia has previously developed in the Baltic Sea during the Holocene Thermal Maximum (HTM; 8–4 ka before present; BP) and the Medieval Climate Anomaly (MCA; 1.4–0.7 ka BP). Here we study the mechanisms that contributed to the onset and termination of this past hypoxia using geochemical and marine palynological data from a sediment record retrieved from the Landsort Deep during IODP Expedition 347 (Site M0063). Dinoflagellate cyst records and TEX86L-based sea surface temperature reconstructions indicate a major increase in salinity and temperature prior to and across the onset of the HTM hypoxic interval, underlining the importance of both temperature and salinity stratification in providing conditions conducive to the onset of hypoxia. Both salinity and temperature decline during the termination of the HTM hypoxic interval. In contrast, we find no evidence for significant changes in surface salinity during the MCA hypoxic interval and both the onset and termination of hypoxia appear to have been primarily driven by changes in temperature. Our results indicate that temperature and salinity changes were key drivers of past hypoxia in the Baltic Sea and imply that ongoing climate change will delay recovery from the modern, nutrient-driven hypoxic event in the Baltic Sea.