Blowing snow and sea ice surfaces as a source of polar sea salt aerosol (BLOWSEA)

大气中的小颗粒(称为气溶胶)起着几个关键作用。它们影响阳光向下表面的传输；它们影响云的形成，它们承载和加强重要的化学反应。当它们被存放在冰上时，它们会留下过去条件的记录，可以通过钻探冰芯来获取。海洋地区上空最重要的气溶胶成分是海盐气溶胶。在世界上大多数海洋上，这是由海浪中的气泡破裂造成的。然而，有强有力的证据表明，海盐气溶胶的另一个来源在极地地区很重要，而且最终来自海冰表面。这一来源的存在构成了一种拟议的方法的基础，该方法利用冰芯数据确定海冰范围在很长一段时间内的变化。此外，海盐气溶胶以及含盐的海冰表面是卤素化合物产生的宿主，而卤素化合物似乎在极地地区的氧化化学中起着关键作用。因此，重要的是要了解极地海盐气溶胶的来源，从而能够预测它们如何随气候变化和对气候的反馈。最近有人提出，这种极地海盐气溶胶的主要来源是含盐吹雪的升华。他们的想法是，海冰上的雪具有很高的盐度。当这些咸雪被动员起来吹雪时，从吹雪层(顶部)升华将允许在吹雪层上方形成海盐气溶胶，在吹雪停止后，它可以保持在空气中。最初的计算表明，这将提供一个强大的气溶胶来源(比同等区域的公海过程产生的气溶胶更多)。有人提出，这将对极地卤素化学产生强烈影响，并对较低纬度的卤素产生显著影响。然而，这是基于对相关参数的估计，因为没有来自这个来源的气溶胶产生的数据，也几乎没有关于海冰上吹雪的一般数据。在这里，我们建议利用一个非常难得的机会在冬季穿透南极海冰带，因为我们已经在德国破冰船Polarstein上分配了一次不同寻常的冬季巡航进入海冰带的空间。在这次巡航中，我们将能够证实吹来的雪海冰源的存在，并进行测量，提供一个可靠的源参数。这将通过测量海冰上的雪、吹雪本身和吹雪上方的气溶胶以及这些事件前后的情况来完成。测量将包括盐度、化学成分(查看每种介质中存在的溴的数量)、吹雪和气溶胶的数量和大小分布。通过将我们的数据与气象数据结合起来，并将它们与最近试图识别吹雪事件的卫星观测相比较，我们将能够估计整个南极海冰带上这个来源的海盐气溶胶的时空分布。这将使我们能够评估这种海盐(和卤素)来源与已提出的其他来源相比的重要性。然后，我们将使用现有的模型来评估这种来源对南极洲海盐沉积的重要性，从而使我们能够确定冰芯中的海盐如何与海冰范围相关。这为将定性的海冰替代物转变为定量的海冰替代物提供了可能性。还将利用模型重新评估这一来源对极地和全球卤素化学的重要性。总之，这项提议将首次有针对性地测量所需参数，以评估吹雪升华作为海盐来源的重要性，并量化其最相关的影响。

Small particles (known as aerosol) in the atmosphere play several critical roles. They affect the transmission of sunlight to the underlying surface; they affect the formation of clouds, and they host and enhance important chemical reactions. When they are deposited on ice they leave a record of past conditions that can be accessed by drilling ice cores. The most significant aerosol component over marine areas is sea salt aerosol. Over most of the world's oceans this is created by bubble bursting in sea spray. However there is strong evidence that another source of sea salt aerosol is important in the polar regions, and that this ultimately derives from the surface of sea ice. The existence of this source forms the basis for a proposed method using ice core data for determining changes in sea ice extent over long time periods. Additionally sea salt aerosol, along with salty sea ice surfaces, is the host for the production of halogen compounds which seem to play a key role in the oxidation chemistry of the polar regions. It is therefore important to understand the sources of polar sea salt aerosol and therefore to be able to predict how they may vary with, and feedback to, climate.It was recently proposed that the main source of this polar sea salt aerosol was the sublimation of salty blowing snow. The idea is that snow on sea ice has a significant salinity. When this salty snow is mobilised into blowing snow, sublimation from the (top of) the blowing snow layer will allow the formation of sea salt aerosol above the blowing snow layer, that can remain airborne after the blowing snow has ceased. First calculations suggested that this would provide a strong source of aerosol (greater than that from open ocean processes over an equivalent area). It was proposed that this would have a strong influence on polar halogen chemistry and a noticeable influence on halogens at lower latitudes. However, this was based on estimates of the relevant parameters as there were no data about aerosol production from this source, and almost no data about blowing snow over sea ice in general.Here we propose to take advantage of a very rare opportunity to penetrate the Antarctic sea ice zone during winter, as we have been allocated spaces on an unusual winter cruise into the sea ice zone on the German icebreaker Polarstern. During this cruise, we will be able to confrim that the blowing snow sea ice source exists, and make measurements that will provide a soundly-based parameterisation of the source. This will be done by making measurements of the snow on sea ice, of the blowing snow itself, and of aerosol above the blowing snow, as well as before and after such episodes. Measurements will include salinity, chemistry (looking at the amount of bromine present in each medium), and for blowing snow and aerosol, the amounts and size distributions.By combining our data with meteorological data, and by comparing them to satellite observations that have recently attempted to identify blowing snow episodes, we will be able to make estimates of the spatial and temporal distribution of sea salt aerosol from this source over the entire Antarctic sea ice zone. This will allow us to assess the importance of this source of sea salt (and of halogens) compared to others that have been proposed. We will then use existing models to assess how important such a source is to sea salt deposition in Antarctica, allowing us to determine how sea salt in ice cores is related to sea ice extent. This opens the possibility of turning a qualitative sea ice proxy into a quantitative one. Models will also be used to re-assess the importance of this source for halogen chemistry in the polar regions and globally.In summary this proposal will provide the first targeted measurements of the parameters needed to assess the importance of blowing snow sublimation as a source of sea salt, and to quantify its most relevant impacts.