Collaborative Re:Temporal resolution in benthic assemblages: assessing and modeling the roles of burial dynamics, seafloor type, and intrinsic factors using (un)natural experiments

协同Re：底栖生物群落的时间分辨率：利用（非）自然实验对埋藏动力学、海底类型和内在因素的作用进行评估和建模。芝加哥大学的苏珊·基德威尔克拉克·亚历山大斯基德韦海洋研究所的生物学家们越来越认识到，为了评估这些重要的生态系统是如何被人类活动改变的，需要从更长远的角度来看待沿海环境中物种的存在和丰富程度。在大多数地区，早在20世纪初定量调查和20世纪70年代联邦政府授权的生物监测出现之前就开始了。非常年轻的化石记录？也就是说，过去几十年、几百年甚至几万年的骨骼残骸，埋在沉积记录的上层几米内？提供一种有希望的方法，既可以重建文化/工业发展的整个历史中生态系统的变化，又可以获取对制定恢复目标至关重要的真正自然条件的信息。然而，为了自信地将这些地质上年轻的古生物学数据与传统的新生物学数据结合起来，我们需要了解生物信息是如何随着贝壳残骸的逐渐自然掩埋而改变的。过去20年的研究发现，软体动物的死亡组合（蛤壳和蜗牛壳）存在于最上层，风暴和动物搅拌的几厘米海床中，其中可能包括一些相当古老的贝壳（数千年历史，特别是在开放的大陆架上），但主要是在最近的（最近的）城市和沿海地区死亡的个体。一个世纪，尤其是最近几十年。因此，这一混合层的死亡集合显然是时间平均的，但最强烈的信号来自骨骼堆积的最后阶段，就像照片的时间曝光产生的运动物体的模糊轨迹，其最终位置被快照一样清晰地捕捉到。在这里，在美国国家科学基金会的资助下，我们将首次测试骨骼组合在多大程度上保持了这种时间分辨率，因为它们经历了更深、更永久的全新世沉积记录层的逐渐埋葬，在那里，组合不再被新的贝壳输入所刷新，而是受到不同的化学制度的影响。我们将利用对海底动物和南加州大陆架环境条件的广泛先验知识，对被认为控制骨骼积累的关键因素进行一系列观察实验，即：(1)壳材料的内在耐久性（重点关注六个关键的双壳类，壳矿物学和微观结构不同）；(2)沉积物积累的速率和类型（陆源泥浆和沙子）；(3)风暴和穴居动物混合沉积物的速率和深度，其中因子2和因子3使用放射性同位素方法进行量化。壳年龄将基于放射性碳校准的氨基酸外消旋定年，我们已经确定该方法在该地区效果良好。通过对长（3-4米）沉积岩心中一系列层位的贝壳进行测年，可以获得时间分辨率随埋藏变化的数据。我们将在帕洛斯弗迪斯大陆架上含有ddt的废水流出物的已知沉积物毒性梯度和历史上未受污染的海底采集这些岩心，提供一种“非自然”的方法。生物扰动效应试验。利用随机模拟和贝壳年龄频率分布的似然分析以及对实验结果的常规统计分析，本项目将确定决定贝壳保存的主要机制，这与生态保真度以及深时和近时化石记录中骨骼组合的时间分辨率有关。在更广泛的意义上，我们将开发和完善合并来自古生物学和新生物学来源的生物信息的协议，作为新兴的保护古生物学新领域的一部分。研究论文将在海洋生物和污染期刊上发表，而不仅仅是在地球科学期刊上发表，以促进科学整合。我们已经与几个负责环境管理的区域机构的科学家建立了合作关系，他们将通过现场会谈了解最新的研究成果。来自岩心的已存档的骨骼组合将为未来不同类型的研究（如形态学、年代学、同位素、分子）提供新的资源，特别是当与我们已经存档的过去（1970年代）和正在进行的(2003年？目前大陆架生物群落的调查和生物监测。该项目将为来自历史悠久的黑人机构（萨凡纳州立大学）的博士后学者和本科生和研究生助理提供实地和实验室经验。我们还将开发一个实验室练习，供当地高中和两年制或四年制大学使用，内容涉及南加州海洋水体的历史生态学以及沉积岩芯对环境和生态分析的作用。该地区有强烈的公众利益和政府对沿海环境质量的承诺，因此有良好的现有基础设施进行公众宣传。

Collaborative Re:Temporal resolution in benthic assemblages: assessing and modeling the roles of burial dynamics, seafloor type, and intrinsic factors using (un)natural experimentsSusan Kidwell, University of ChicagoClark Alexander, Skidaway Institute of OceanographyBiologists increasingly appreciate the need for longer term perspectives on the presence and abundance of species in coastal environments in order to evaluate how these important ecosystems have been altered by human activities, which in most areas began well before the advent of quantitative surveys in the early 20th century and federally mandated biomonitoring in the 1970s. Very young fossil records ? that is, skeletal remains from the last few decades, centuries, and tens of millennia, embedded within the upper few meters of the sedimentary record ? offer a promising means both of reconstructing changes in ecosystems over the full history of cultural/industrial development and of acquiring the information on truly natural conditions that is essential to developing restoration targets. However, to confidently merge these geologically young paleontological data with conventional neo-biological data, we need to understand how, if at all, biological information is altered with the progressive, natural burial of shelly remains. Research over the last 20 years finds that molluscan death assemblages (clam and snail shells) present within the uppermost, storm- and animal-stirred few centimeters of the seabed can include some fairly old shells (thousands of years old, especially on open continental shelves), but are strongly dominated by individuals that died during the last (most recent) ?urban? century and especially the last few decades. Death assemblages from this mixed layer are thus clearly time-averaged, but the strongest signal is from the final stages of skeletal accumulation, much like a photographic time-exposure produces a somewhat blurry track of a moving object whose final position is captured with snapshot-like clarity. Here, with NSF funding, we will test for the first time the extent to which skeletal assemblages retain this level of temporal resolution as they undergo progressive burial into deeper, more permanent layers of the Holocene sedimentary record, where the assemblage is no longer refreshed by new shell input and is subject to different chemical regimes. We will leverage extensive prior knowledge of seafloor animals and environmental conditions on the southern California continental shelf to conduct a series of observational experiments on the key factors thought to control skeletal accumulation, namely (1) the intrinsic durability of shell material (focus on six key genera of bivalves, differing in shell mineralogy and microstructure), (2) rates and types of sediment accumulation (land-derived mud and sand, plus shell-rich seabeds deprived of sediment), and (3) rates and depths of sediment mixing by storms and burrowing animals, with factors 2 and 3 quantified using radioisotopic methods. Shell ages will be based on radiocarbon-calibrated amino-acid racemization dating, which we have already determined works well in this region. Data on how temporal resolution changes with burial will be generated by dating sets of shells from a series of horizons in long (3-4 m) sedimentary cores. We will take these cores at sites both along the known legacy gradient of sediment toxicity from DDT-charged wastewater effluents on the Palos Verdes shelf and from historically uncontaminated seafloors, providing an ?unnatural? experiment on the effects of bioturbation. Using stochastic simulations and likelihood analysis of shell-age frequency distributions as well as conventional statistical analysis of experimental results, this project will identify the dominant mechanisms that determine shell preservation, which is relevant to the ecological fidelity as well as the temporal resolution of skeletal assemblages in both the deep- and near-time fossil records. Of even broader implications, we will develop and refine protocols for merging biological information from paleontological and neo-biological sources, as part of the burgeoning new field of conservation paleobiology. Research papers will be published in marine biological and pollution journals rather than only earth science journals to promote scientific integration. We already have a cooperative relationship with scientists from several regional agencies charged with environmental management, who will be kept up to date with research results by talks on site. Archived skeletal assemblages from our cores will constitute a new resource for future studies of diverse types (e.g., morphology, sclerochronology, isotopes, molecules), particularly when combined with extensive mixed-layer death assemblages that we have already archived from past (1970s) and ongoing (2003 ? present) surveys and biomonitoring of living shelf communities. The project will provide field and lab experience for a post-doctoral scholar and for undergraduate and graduate student assistants drawn from an historically black institution (Savannah State). We will also develop a lab exercise for use in local high schools and 2-year or 4-year colleges on the historical ecology of the southern California marine bight and the power of sedimentary cores for environmental and ecological analysis. This region has strong public interest and governmental commitment to coastal environmental quality, and thus has a good existing infrastructure for public outreach.