Abstract Mars' polar layered deposits (PLD) are comprised of layers of varying dust-to-water ice volume mixing ratios (VMR) that are thought to record astronomically-forced climatic variation over Mars’ recent orbital history. Retracing the formation history of these layers by quantifying the sensitivity of polar rates of deposition to astronomical forcing may be critical for the interpretation of this record. Using a Mars global climate model (GCM), we investigate the sensitivity of annual polar water ice and dust surface deposition to a variety of obliquity and surface water ice source configurations at zero eccentricity that may provide a reasonable characterization of the evolution of the PLD during recent low-eccentricity epochs. The GCM employs a fully interactive dust lifting/transport scheme and accounts for dust-and-water physics coupling effects on the transport and deposition of water ice and dust. GCM results suggest that snowfall in the form of water ice-nucleated dust particles generally provides the greatest contribution to both water ice and dust deposition on the polar surfaces, suggesting that dust-and-water physics coupling is an important consideration in the modelling of PLD layer formation processes. Under a range of tested obliquities (15°–35°), predicted net annual accumulation rates range from −1 mm/yr to +14 mm/yr for water ice and from 0.005 to 0.57 mm/yr for dust. When these GCM-derived accumulation rates are ingested into an integration model that simulates polar accumulation of water ice and dust over five consecutive obliquity cycles (∼700 thousand years) during a low eccentricity epoch, select integration model simulations predict combined north polar water and dust accumulation rates that correspond to the observationally-inferred average growth rate of the north PLD (0.5 mm/yr) over its ∼5 million year formation history. These integration model simulation results are characterized by net water transfer from the south to the north polar region. In the north, a ∼230 m-thick deposit is accumulated over ∼700 thousand years. Three types of layers are produced per obliquity cycle: a ∼30 m-thick dust-rich (20–30% dust volume mixing ratio) layer that forms at high obliquity when both water ice and dust deposition rates are large, a ∼0.5 m-thick dust lag deposit (pure dust) that forms at low obliquity when net removal of water ice occurs, and two ∼10 m-thick dust-poor (∼3%) layers that separate the dust rich layers and form when obliquity is increasing or decreasing. The ∼30 m-thick dust-rich layer is reminiscent of a ∼30 m scale length feature derived from analysis of visible imagery of north PLD vertical structure. This work demonstrates the capability of obliquity variations to produce PLD stratigraphy reminiscent of observed PLD structure when water and dust deposition are interactively coupled.

中文翻译：

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火星PLD垂直结构形成对倾斜度的依赖

摘要 火星的极地层状沉积物 (PLD) 由不同的尘埃与水冰体积混合比 (VMR) 组成，被认为记录了火星近期轨道历史上天文强迫的气候变化。通过量化极地沉积速率对天文强迫的敏感性来追溯这些层的形成历史对于解释该记录可能至关重要。使用火星全球气候模型 (GCM)，我们研究了年度极地水冰和尘埃表面沉积对零偏心率下各种倾斜度和地表水冰源配置的敏感性，这可能为 PLD 的演变提供合理的表征。最近的低离心率时期。GCM 采用完全交互式的扬尘/运输方案，并考虑了尘埃和水物理耦合对水冰和尘埃的运输和沉积的影响。GCM 结果表明，以水冰成核尘埃颗粒形式的降雪通常对极地表面的水冰和尘埃沉积贡献最大，这表明尘埃和水物理耦合是 PLD 建模中的一个重要考虑因素层形成过程。在一系列测试倾角 (15°–35°) 下，预测的净年累积率范围为 -1 毫米/年至 +14 毫米/年（水冰）和 0.005 至 0.57 毫米/年（灰尘）。当这些 GCM 衍生的积累率被纳入一个积分模型中，该模型模拟了低偏心率时期五个连续倾斜周期（约 70 万年）内水冰和尘埃的极地积累，选择的积分模型模拟预测北极水和尘埃的组合累积速率对应于北 PLD 约 500 万年形成历史中观测推断的平均增长率（0.5 毫米/年）。这些整合模型模拟结果的特点是从南到北极地区的净水转移。在北部，约 230 米厚的矿床在约 70 万年的时间里积累。每个倾斜周期产生三种类型的层：约 30 米厚的富尘层（20-30% 的尘体积混合比），当水冰和尘土沉积率都很大时，在高倾角处形成，约 0.5 米厚的尘滞沉积物（纯尘）当发生净去除水冰时，低倾角形成，两个约 10 米厚的贫尘层（约 3%）将富尘层分开，并在倾角增加或减小时形成。约 30 m 厚的富尘层让人联想到从北 PLD 垂直结构的可见图像分析得出的约 30 m 尺度长度特征。这项工作证明了当水和灰尘沉积相互作用耦合时，倾角变化产生 PLD 地层的能力，使人联想到观察到的 PLD 结构。5 米厚的尘滞沉积物（纯尘）在发生水冰净去除时在低倾角形成，两层约 10 米厚的贫尘层（约 3%）将富含尘的层分开并在倾角时形成正在增加或减少。约 30 m 厚的富尘层让人联想到从北 PLD 垂直结构的可见图像分析得出的约 30 m 尺度长度特征。这项工作证明了当水和灰尘沉积相互作用耦合时，倾角变化产生 PLD 地层的能力，使人联想到观察到的 PLD 结构。5 米厚的尘滞沉积物（纯尘）在发生水冰净去除时在低倾角形成，两层约 10 米厚的贫尘层（约 3%）将富尘层分开并在倾角时形成正在增加或减少。约 30 m 厚的富尘层让人联想到从北 PLD 垂直结构的可见图像分析得出的约 30 m 尺度长度特征。这项工作证明了当水和灰尘沉积相互作用耦合时，倾角变化产生 PLD 地层的能力，使人联想到观察到的 PLD 结构。