Exploring the deep biosphere in an intercontinental, brackish basin for the first time, and how the deep biosphere responds to environmental change.

海底生物圈是地球上最大的生命栖息地之一，但对地下微咸水沉积物中的微生物生命知之甚少。波罗的海是世界上最大的咸水水体之一。它的大陆流域面积很大(是盆地面积的四倍)，几千年来一直在不同的环境条件下积累沉积物，这些环境条件与冰川、海平面和海水进入门户门槛的变化有关。IODP 347考察队在这一地点获得了深层沉积物，这将使我们能够首次量化微咸水深层沉积物中的海底以下原核生物种群及其活动。这一点特别重要，因为最近有人提出，这些类型的浅水(约35米至451m)、也靠近陆地的高沉积速率沉积物应具有特别高的原核生物种群，因为这些因素被认为控制着全球海底以下生物圈的大小。这将是对这一假设的第一次检验。此外，关于环境条件的变化，包括新沉积沉积物的来源，如何影响深海海底人口，人们知之甚少。波罗的海深海沉积物是研究海底以下生物圈如何对环境变化作出反应的理想样本。这一点尤其重要，因为这些浅水沉积物可以加强气候变化(例如，增加二氧化碳和甲烷这两种强有力的温室气体的产生)或减缓气候变化(例如，能够保存沉积的有机物和/或加强甲烷的氧化)。我们还想弄清楚深层生物圈种群和活动是否代表淡水/陆地深层生物圈群落、海洋深层生物圈群落、两者的混合体，还是完全不同的东西。

The sub-seafloor biosphere is one of the largest habitats for life on Earth, but nothing is known about microbial life in subsurface brackish water sediments. The Baltic Sea is one of the largest brackish water bodies in the world. Its continental drainage area is large (four times the basin size) and it has been accumulating sediments for several thousands of years under varying environmental conditions linked to changes in glaciation, sea level and gateway thresholds for seawater ingress. IODP Expedition 347 has obtained deep sediments from this location which will enable us to quantify sub-seafloor prokaryotic populations and their activities for the first time in brackish water deep sediments. This is particularly important because it has recently been suggested that these type of shallow water (~35 m to 451 m), high sedimentation rate sediments that are also close to land, should have particularly high prokaryotic populations, as these factors are thought to control the size of sub-seafloor biosphere globally. This will be the first test of this hypothesis. In addition, little is known about how changes in environmental conditions, including the source of newly deposited sediments, affect deep sub-seafloor populations. The deep Baltic Sea sediments are ideal samples to investigate how the sub-seafloor biosphere responds to environmental change. This is particularly important as these shallow water sediments can either reinforce climate changed (e.g. enhanced production of the potent greenhouse gases carbon dioxide and methane) or mitigate climate change (e.g. enabling preservation of deposited organic matter and/or enhanced methane oxidation). We also want to find out whether deep biosphere populations and activities represent freshwater/terrestrial deep biosphere communities, marine deep biosphere communities, a mixture of both, or something completely different.