Signals of watershed change preserved in organic carbon buried on the continental margin seaward of the Waipaoa River, New Zealand
Signals of watershed change preserved in organic carbon buried on the continental margin seaward of the Waipaoa River, New Zealand
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DOI：
10.1016/j.margeo.2013.10.007
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发表时间：
2013-12
期刊：
影响因子：
2.9
通讯作者：
E. Leithold;N. Blair;L. Childress;B. Brulet;M. Marden;A. Orpin;S. Kuehl;C. Alexander
中科院分区：
文献类型：
--
作者：
E. Leithold;N. Blair;L. Childress;B. Brulet;M. Marden;A. Orpin;S. Kuehl;C. Alexander
全新世沉积物埋藏在新西兰东北部的Waipaoa河向海的大陆架上，保存了陆地环境变化的地层记录。在这一地区的风暴，火山活动和人类干扰的特点，长期记录提供了一个机会，研究如何反映在埋在大陆边缘的有机碳（OC）的性质，这些变化。通过分析不同沉积组分（包括木炭、木材和粘土大小的分离物）的14 C含量和元素及稳定碳同位素组成获得的补充证据，表明，这些扰动导致动员的OC组件与变量存储历史的分水岭。木炭运输在现代怀保阿河和埋藏在近海沉积中心包括一个高度老化的组成部分，显然已经从土壤或冲积阶地中缓慢释放出来。在陶波火山爆发（1717 cal yr BP）和波利尼西亚人定居（约1717 cal yr BP）之后沉积的沉积物中，木炭组分年龄变得非常年轻。700 cal yr BP），两者都表示生物质燃烧。沉积在大陆架上的木本植物碎片和粘土结合OC的平均年龄也随时间而变化，在全新世中期和人类占领以来积累了较老的材料。沉积年龄大于平均值的木材碎片和粘土结合OC之间约5和3.6 kyr BP与证据的一段时间内增加风暴频率在该地区，并可能反映了增强交付的老年土壤和沉积岩动员从山坡通过泥石流和/或深层滑坡。同样，沉积较老的木材和粘土结合OC相称的第一次人为干扰约。700年前是一致的加速质量浪费由于森林砍伐。与此同时，在元素和稳定同位素组成的散装和粘土结合的OC埋在货架上的变化可能会反映增加海洋初级生产力和/或动员OC从土壤剖面的深层。从世纪中期开始，欧洲定居者对Waipaoa源头的森林砍伐被埋在近海的粘土相关OC年龄的急剧上升所证明。如今，深深的沟壑切入断裂的沉积基岩是河流沉积物和干酪根的主要来源，这一过程在沉积OC输送到邻近边缘的年龄上留下了印记。
Holocene sediments buried on the continental shelf seaward of the Waipaoa River, northeastern New Zealand, preserve a stratigraphic record of terrestrial environmental change. The well characterized, long-term record of storms, volcanism, and human disturbance in this region provides an opportunity to examine how such changes are reflected in the character of organic carbon (OC) buried on the continental margin. Complimentary evidence obtained from analyses of the14C content and the elemental and stable carbon isotopic composition of different sedimentary fractions, including charcoal, wood, and clay-sized isolates, indicates that these perturbations led to mobilization of OC components with variable storage histories in the watershed.Charcoal transported in the modern Waipaoa River and buried in offshore depocenters includes a highly aged component that has apparently been slowly released from storage in soil or alluvial terraces. The charcoal fraction ages become dramatically younger in sediments deposited after the Taupo volcanic eruption (1717 cal yr BP) and then Polynesian settlement (ca. 700 cal yr BP), both signaling biomass burning. The mean age of woody plant fragments and clay-bound OC deposited on the shelf also varies over time, with older material having accumulated in the middle Holocene and since human occupation. Deposition of older-than-average wood fragments and clay-bound OC between about 5 and 3.6 kyr BP correlates with evidence for a period of increased storm frequency in the region and may reflect the enhanced delivery of aged soil and sedimentary rock mobilized from hill slopes via earthflows and/or deep seated landslides. Similarly, the deposition of older wood and clay-bound OC commensurate with the first anthropogenic disturbance ca. 700 years ago is consistent with accelerated mass wasting due to deforestation. At the same time, a change in the elemental and stable isotopic composition of bulk and clay-bound OC buried on the shelf may reflect increased marine primary productivity and/or mobilization of OC from deep levels in soil profiles. Deforestation of the Waipaoa headwaters by European settlers beginning in the middle 19th century is evinced by a sharper rise in the age of clay associated OC buried offshore. Today, deep gully incision into fractured sedimentary bedrock is a major source of sediment and kerogen to the river, and this process has left its mark on the age of sedimentary OC delivered to the adjacent margin.