Biogeochemical Cycles and Mixing in Lake Baikal

贝加尔湖是地球表面面积最大、最深、最长的持续存在的淡水湖，为西伯利亚东南部一个重要的大陆遗址的古气候重建提供了无与伦比的机会。在此基础上，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。该研究将为贝加尔湖沉积古气候记录的破译提供必要的基础。此外，还将提供基线数据，以确定贝加尔湖流域不断扩大的人类活动所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的源水的化学条件。我们1988年6月考察的发现包括：1)推断出一种独特的机制，与温压不稳定有关，通过这种机制，这些最深的湖泊会发生混合ıCarmack和Weiss， 1991！2)根据CFC、O2和营养物分布确定贝加尔湖8 ~ 10年的平均通风量，确定贝加尔湖为高度寡营养湖泊，以硝酸盐为限制营养物ıWeiss et al., 1991！3)湖泊主要元素循环以河流为主；通过温度异常得知的热液活动，随后由潜水器观察到，并不影响现代湖泊的化学成分；湖水中方解石相不饱和，这与湖泊沉积物中方解石相的缺乏一致；相对于蛋白石，湖水也不饱和，然而，高硅藻生产力保证了足够的降雨率，从而在沉积物中保存硅质物质，构成硅的汇；在次要元素中，只有Ba在湖中表现出非保守行为ıFalkner et al ., 1991！1991年7月对该湖进行了第二次考察，在此期间建立了一种利用深水温度和氧气分布来充分限制通风程度的方法。利用微量金属清洁技术的取样已扩展到湖泊周围的河流和陆上温泉，以便更好地限制元素预算，并对往往是人类活动影响的更敏感指标的微量元素进行分析。正在请求国家科学基金会提供资金，以完成该样品组的化学和同位素分析，并通过与俄罗斯科学家正在进行的工作进行相互校准和协调来扩展我们的观察。此外，还将举办一个研讨会，整理、讨论和发表我们跨学科小组的研究成果，以便尽可能全面地了解现代湖泊的混合和生物地球化学。

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.