Ice shelf - ocean interaction in the cavity beneath the Amery Ice Shelf

---- Public Summary from Project ----Most of the snow falling on inland Antarctica drains via large ice streams and floating ice shelves to the sea where it lost by iceberg calving or as melt beneath the shelves. Ocean interaction beneath the shelves is complicated, and regions of basal refreezing as well as melt occur. These processes are important not only because they are a major component of the Antarctic mass budget, but because they also modify the characteristics of the ocean, influencing the formation of Antarctic Bottom Water which plays a major role in the global ocean circulation. The processes are sensitive to climate change, and shifts in ocean temperature or circulation near Antarctica could lead to the disappearance of all Antarctic ice shelves.The AmeryIce Shelf is the major embayed shelf in East Antarctica, and the subject of considerable previous ANARE investigation. Ocean interaction processes occurring beneath the shelf are only poorly understood, and this project will directly measure water characteristics and circulation in the cavity underneath the ice shelf, and the rates of melt and freezing on the bottom of the shelf. These measurements will be made through a number of access holes melted through the shelf. The project is closely linked with other projects investigating the circulation and interactions in the open ocean to the north of the shelf, and studies of the ice shelf flow and mass budget.There will be child records for each of the following data sets:AM01 and AM01 b boreholes* CTD profiles through water column* CTD annual records at selected depths* Ocean current profiles through water column* Temperature measurements through ice shelf and across ice-water interface* Small ice core samples* 0.5 m sea floor sediment core* Video footage of borehole walls (including marine ice) and sea floor benthos* GPS records of surface tidal motion* VideoAM02 borehole* CTD profiles through water column* CTD annual records at selected depths* Borehole diameter caliper profiles* Temperature measurements through ice shelf and across ice-water interface* 1.5 m sea floor sediment core* GPS records (surface elevation, ice motion) AM03 borehole* Aquadopp current meter data* Brancker thermistor data* Caliper data* FSI-CTD profile data* Drilling parameters data* Seabird MicroCAT CTD moorings at three depths in ocean cavity beneath the shelf* VideoAM04 borehole* Aquadopp current meter data* Brancker thermistor data* Caliper data* FSI-CTD profile data* Drilling parameters data* Seabird MicroCAT CTD moorings at three depths in ocean cavity beneath the shelf* VideoAM05 borehole* Aquadopp current meter data* Caliper data* FSI-CTD profile data* Drilling parameters data* Seabird MicroCAT CTD moorings in ocean cavity beneath the shelfAM06 borehole* Aquadopp current meter data* Caliper data* FSI-CTD profile data* Drilling parameters data* Seabird MicroCAT CTD moorings in ocean cavity beneath the shelfTaken from the 2008-2009 Progress Report:Progress Against Objectives:The work undertaken in the past 12 months has continued to relate chiefly to the first of our objectives - "quantify the characteristics and circulation of ocean water in the cavity beneath the Amery Ice Shelf". Data from the AMISOR project have provided the first record of a seasonal cycle of ice shelf-ocean interaction. After recovering the 2008 data we now have near-continuous oceanographic data from beneath the Amery at 3 different depths for 6, 6, 3, and 3 years from 4 different sites. Note that the instruments at AM01 and AM02 (6 annual cycles of data each) are no longer recording due to expiration of the onboard batteries (3-5 years expected life cycle). This allows us to investigate the "real" 3-D, seasonally varying, circulation and melt/freezing cycle beneath an ice shelf - rather than the steady state, simplified "2-D ice pump circulation" that has mostly been assumed previously.As much as 80% of the continental ice that flows into the Amery Ice Shelf from the Lambert Glacier basin is lost as basal melt melt beneath the southern part of the shelf, but a considerable amount of ice is also frozen onto the base in the north-western part of the shelf. These processes of melt and refreezing are due to a pattern of water circulation beneath the ice shelf which is driven by sea ice formation outside the front of the shelf. Our multi-year data from 4 sites beneath the Amery ice shelf show that there is a very strong seasonal cycle in the characteristics of the ocean water beneath the shelf, and strong interseasonal variability in this. The seasonal cycle is driven mostly by the seasonal cycle of sea ice formation and decay in Prydz Bay, and interseasonal variations are due to differences in the general ocean circulation, and in particular the upwelling of Circumpolar Deep Water onto the continental shelf in Prydz Bay. The melt and freeze processes beneath the ice shelf, also themselves modify the water characteristics.Taken from the 2009-2010 Progress Report:The AMISOR project drilled two new 600 m deep boreholes on the Amery Ice Shelf in 2009-10: the first on the marine ice flowline to enhance understanding of the re-freezing process beneath the shelf; and the second in a region of known interest with respect to circulation patterns in the ocean cavity below the shelf. Instrument deployments at both sites should provide valuable annual cycle data over the next 4-5 years.

---- 项目公开摘要 ----
降落至南极内陆的积雪，大多通过大型冰流（ice stream）与浮动冰架（ice shelf）汇入海洋，最终以冰山崩解（iceberg calving）或冰架底部融化的形式损失。冰架下方的海洋相互作用过程极为复杂，同时存在基底重冻（basal refreezing）与基底融化现象。这些过程不仅是南极质量平衡（Antarctic mass budget）的核心组成部分，还会改变海洋水团特性，进而影响南极底层水（Antarctic Bottom Water）的形成——而后者在全球海洋环流中扮演关键角色。此类过程对气候变化极为敏感，南极附近海域的水温或环流变化，可能导致所有南极冰架的消失。

埃默里冰架（Amery Ice Shelf）是东南极洲主要的海湾型冰架，也是澳大利亚国家南极研究探险队（ANARE）既往大量研究的对象。目前学界对冰架下方的海洋相互作用过程仍知之甚少，本项目将通过冰架上钻取的多个钻孔，直接测量冰架下方空腔内的海水特性与环流，以及冰架底部的融化与重冻速率。本项目与多项关联研究紧密结合：包括冰架北侧开阔海域的环流与相互作用研究，以及冰架流动与质量平衡相关研究。

本项目将为以下各数据集生成子记录：
AM01与AM01b钻孔
* 水柱CTD（Conductivity-Temperature-Depth，电导-温度-深度仪）剖面
* 选定深度的CTD年度连续记录
* 水柱海流剖面
* 冰架内部及冰水界面的温度测量数据
* 小型冰芯样品
* 0.5米长海底沉积物岩芯
* 钻孔壁（含海成冰）与海底底栖生物的视频影像
* 表面潮汐运动的GPS记录
* 视频数据

AM02钻孔
* 水柱CTD剖面
* 选定深度的CTD年度连续记录
* 钻孔直径Caliper测井剖面
* 冰架内部及冰水界面的温度测量数据
* 1.5米长海底沉积物岩芯
* GPS记录（表面高程、冰体运动）

AM03钻孔
* Aquadopp海流计数据
* Brancker热敏电阻数据
* Caliper测井数据
* FSI-CTD剖面数据
* 钻探参数数据
* 冰架下方海洋空腔内3个深度的Seabird MicroCAT CTD锚系观测数据
* 视频数据

AM04钻孔
* Aquadopp海流计数据
* Brancker热敏电阻数据
* Caliper测井数据
* FSI-CTD剖面数据
* 钻探参数数据
* 冰架下方海洋空腔内3个深度的Seabird MicroCAT CTD锚系观测数据
* 视频数据

AM05钻孔
* Aquadopp海流计数据
* Caliper测井数据
* FSI-CTD剖面数据
* 钻探参数数据
* 冰架下方海洋空腔内的Seabird MicroCAT CTD锚系观测数据

AM06钻孔
* Aquadopp海流计数据
* Caliper测井数据
* FSI-CTD剖面数据
* 钻探参数数据
* 冰架下方海洋空腔内的Seabird MicroCAT CTD锚系观测数据

--- 2008-2009年度进展报告 ---
#### 目标完成进展
过去12个月的工作主要围绕本项目的首要目标展开：「量化埃默里冰架下方空腔内的海水特性与环流」。埃默里冰架海洋研究项目（AMISOR）获取了首份冰架-海洋相互作用的季节性周期观测记录。在回收2008年的观测数据后，我们已在4个不同站点获得了埃默里冰架下方海域的连续海洋学观测数据，其中3组设备的观测时长分别为6年、6年、3年与3年。需注意的是，AM01与AM02钻孔处的观测设备（各自拥有6个年度数据周期）因板载电池耗尽（预期寿命3-5年）已停止记录。这使得我们得以研究冰架下方真实的三维、季节性变化环流与融化/重冻周期，而非此前多数研究中假设的稳态简化「二维冰泵环流」。

流入埃默里冰架的兰伯特冰川（Lambert Glacier）流域的大陆冰，多达80%在冰架南部区域以基底融化的形式损失，但冰架西北部区域也有大量冰体重冻于冰架底部。此类融化与重冻过程由冰架前缘外部的海冰形成所驱动的冰架下方海水环流模式所控制。我们在埃默里冰架下方4个站点获取的多年观测数据显示，冰架下方海水的特性存在极强的季节性周期，同时存在显著的季际变率。季节性周期主要由普里兹湾（Prydz Bay）的海冰形成与消融的季节性周期驱动，而季际变率则源于全球海洋环流的差异，尤其是绕极深层水（Circumpolar Deep Water）在普里兹湾陆架区的上涌现象。此外，冰架下方的融化与冻结过程本身也会改变海水的特性。

--- 2009-2010年度进展报告 ---
#### 项目进展
AMISOR项目于2009-2010年在埃默里冰架上钻取了2个新的600米深钻孔：第一个钻孔位于海成冰流线上，用于加深对冰架下方重冻过程的理解；第二个钻孔位于学界关注的冰架下方海洋环流模式重点研究区域。两个站点的仪器部署将在未来4-5年内提供宝贵的年度周期观测数据。