Holocene Spatiotemporal Redox Variations in the Southern Baltic Sea
Holocene Spatiotemporal Redox Variations in the Southern Baltic Sea
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DOI：
10.3389/feart.2021.671401
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发表时间：
2021-05-28
影响因子：
2.9
通讯作者：
Lyons, Timothy W.
中科院分区：
文献类型：
--
作者：
Hardisty, Dalton S.;Riedinger, Natascha;Lyons, Timothy W.
现代波罗的海的低氧条件因人类活动而加剧;然而，缺氧条件也在全新世自然盛行。很少有研究的特点，具体的古氧化还原条件（锰，铁，euxinic）和它们的频率在波罗的海南部的次盆地在这些古老的事件。在这里，我们应用一套同位素系统（Fe，Mo，S）和相关的元素代理（例如，铁形态，锰），以具体定义水柱氧化还原制度，通过波罗的海全新世在一个窗台近端到窗台远端样带（里尔带，博恩霍尔姆盆地，Landsort深）使用的综合大洋钻探计划远征347期间收集的样品。在靠近底梁的里尔带，有证据表明，在从Ancylus湖到Littorina海的过渡之后，大部分取心井段都存在缺氧的锰/铁条件，但没有明显的漂移到与全新世热极大期（HTM）或中世纪气候异常（MCA）事件相关的还原或缺氧条件。在Sill-远端南部次盆地，博恩霍尔姆盆地，铁的形态，孔隙水铁，和固相钼浓度和同位素数据的组合点锰/铁质条件在Ancylus湖-Littorina海过渡和HTM，但只有短暂的游览间歇性或弱缺氧条件在此期间。在波罗的海西部适当的子盆地，Landsort深，新的铁和硫同位素数据支持以前的钼同位素记录和铁形态的证据，两个不同的缺氧时期，但也表明，硫化物积累超过瞬态水平在很大程度上限制在沉积物-水界面。最后，从所有三个位置的综合数据表明，铁富集通常指示euxinia可能是最好的解释铁沉积氧化物的事件可能类似于定期入侵的含氧北海沃茨今天观察到的，随后形成黄铁矿硫化物孔沃茨。此外，从多个波罗的海南部盆地的钼同位素数据反对限制和广泛的缺氧条件，已证明在波罗的海和波的尼亚海在HTM或MCA。相反，类似于今天，每一个过去的波罗的海缺氧事件的特点是氧化还原条件，变得越来越减少与距离的窗台。
Low oxygen conditions in the modern Baltic Sea are exacerbated by human activities; however, anoxic conditions also prevailed naturally over the Holocene. Few studies have characterized the specific paleoredox conditions (manganous, ferruginous, euxinic) and their frequency in southern Baltic sub-basins during these ancient events. Here, we apply a suite of isotope systems (Fe, Mo, S) and associated elemental proxies (e.g., Fe speciation, Mn) to specifically define water column redox regimes through the Baltic Holocene in a sill-proximal to sill-distal transect (Lille Belt, Bornholm Basin, Landsort Deep) using samples collected during the Integrated Ocean Drilling Program Expedition 347. At the sill-proximal Lille Belt, there is evidence for anoxic manganous/ferruginous conditions for most of the cored interval following the transition from the Ancylus Lake to Littorina Sea but with no clear excursion to more reducing or euxinic conditions associated with the Holocene Thermal Maximum (HTM) or Medieval Climate Anomaly (MCA) events. At the sill-distal southern sub-basin, Bornholm Basin, a combination of Fe speciation, pore water Fe, and solid phase Mo concentration and isotope data point to manganous/ferruginous conditions during the Ancylus Lake-to-Littorina Sea transition and HTM but with only brief excursions to intermittently or weakly euxinic conditions during this interval. At the western Baltic Proper sub-basin, Landsort Deep, new Fe and S isotope data bolster previous Mo isotope records and Fe speciation evidence for two distinct anoxic periods but also suggest that sulfide accumulation beyond transient levels was largely restricted to the sediment-water interface. Ultimately, the combined data from all three locations indicate that Fe enrichments typically indicative of euxinia may be best explained by Fe deposition as oxides following events likely analogous to the periodic incursions of oxygenated North Sea waters observed today, with subsequent pyrite formation in sulfidic pore waters. Additionally, the Mo isotope data from multiple Baltic Sea southern basins argue against restricted and widespread euxinic conditions, as has been demonstrated in the Baltic Proper and Bothnian Sea during the HTM or MCA. Instead, similar to today, each past Baltic anoxic event is characterized by redox conditions that become progressively more reducing with increasing distance from the sill.