Biogeochemical Cycles and Mixing in Lake Baikal

作为地球表面存在的面积最大、深度最深、持续时间最长的淡水湖，贝加尔湖为西伯利亚东南部一个关键大陆遗址的古气候重建提供了无与伦比的机会。在此，我们建议完成现代湖泊及其支流的基本混合和生物地球化学特征的研究。这项研究将为破译贝加尔湖沉积古气候记录提供必要的基础。此外，将提供所需的基线数据，以确定贝加尔河流域人类活动扩大造成的扰动的性质和程度，并将确定流入北极的最重要河流之一叶尼塞河源水的化学调节。我们1988年6月探险的发现包括：1)推断出一种与温压不稳定性有关的独特机制，通过这种机制，这个最深的湖泊发生了混合，ıCarmack和Weiss，1991！2)根据氯氟化碳、氧气和营养物质的分布，确定了贝加尔湖8-10年的平均通气率，并确认贝加尔湖是高度贫营养化的，以硝酸盐为限制营养物质，ıWeiss等人，1991年！；3)湖泊中主要元素的循环始终以河流为主；通过温度异常已知并随后由潜水器观察到的热液活动不影响现代湖泊的化学成分；湖水方解石相不饱和，与湖泊沉积物中不存在方解石相一致；就蛋白石而言，湖水也是不饱和的，然而，高硅藻生产力确保了足够的降雨量，从而使沉积物中的硅质物质得以保存，这构成了硅的下沉；在次要元素中，只有BA在ıFalkner等人的湖中表现出非保守的行为，1991年！1991年7月对该湖进行了第二次探险，在此期间，建立了一种利用深水温度和氧气剖面来充分限制通风程度的方法。通过痕量金属清洁技术进行的采样已扩展到河流和湖泊周围的陆上温泉，以便更好地限制元素预算，并能够分析往往是人类活动影响的更敏感指标的微量元素。正在向国家科学基金会申请资金，以完成对这套样品的化学和同位素分析，并通过相互校准和与俄罗斯科学家正在进行的努力协调来扩大我们的观察范围。此外，还将举办一次研讨会，以整理、讨论和公布我们跨学科小组的研究结果，以便尽可能提供对现代湖泊的混合和生物地球化学的最完整的了解。

As the most voluminous, deepest and longest continually existing freshwater lake on the surface of the earth, Baikal presents unparalleled opportunity for paleo-climate reconstruction at a key continental site in southeastern Siberia. Here, it is proposed to complete our investigations of the fundamental mixing and biogeochemical characteristics of the modern lake and its tributaries. This study will provide groundwork essential for deciphering Baikal sedimentary paleo-climate records. In addition, baseline data needed to establish the nature and magnitude of perturbations caused by expanding human activities in the Baikal watershed will be contributed and the chemical conditioning of the source waters of the Yenisei, one of the most important rivers emptying into the Arctic, will be defined. Findings from our June, 1988 expedition include: 1) Deduction of a unique mechanism, related to thermobaric instabilities, by which mixing of this deepest of lakes occurs ıCarmack and Weiss, 1991!; 2) Determination, based on CFC, O2 and nutrient distributions, of an 8 to 10 year average rate of ventilation for the lake and confirmation that Baikal is highly oligotrophic with nitrate as the limiting nutrient ıWeiss et al., 1991!; 3) Cycling of major elements in the lake is dominated by riverine throughout; hydrothermal activity known by temperature anomalies and subsequently observed by submersible, does not impact the chemistry of the modern lake; lake waters are undersaturated with respect to calcite phases, consistent with lack of their occurrence in lake sediments; lake waters are also undersaturated with respect to opal, however, high diatom productivity assures a sufficient rain rate to result in the preservation of siliceous materials in sediments which constitute a sink for Si; of the minor elements, only Ba showed non-conservative behavior in the lake ıFalkner et al, 1991!. A second expedition to the lake was undertaken in July, 1991 during which a method by which to use deep water temperature and oxygen profiles to adequately constrain the extent of ventilation was established. Sampling, by trace-metal clean techniques was extended to rivers and land-based hot-springs surrounding the lake in order to better constrain elemental budgets and to allow analyses of trace elements which tend to be more sensitive indicators of impact by human activities. Funds are being requested from NSF to complete chemical and isotopic analyses of this sample suite and to extend our observations through intercalibration and coordination with ongoing efforts by Russian scientist. In addition, a workshop to collate, discuss and publish the findings of our interdisciplinary group will be held in order to provide the most complete understanding of mixing and biogeochemistry of the modern lake possible.