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The thickness of the pack ice is not the only thing that matters, though. Its topography is also important.
雖然浮冰塊的厚度不是唯一重要的事情。其地形也很重要。
This is the province of Jennifer Hutchings of Oregon State University. She is using GDP buoys to track the motion of the ice around the ship.
這是俄勒岡州立大學Jennifer Hutchings的所在省份。她正在利用全球漂流浮標項目的信號浮標追蹤船只周圍冰層的運動。
Though sea ice is solid, it is not rigid. It forms but a thin skin on the ocean—
海冰雖然是固體，但并不堅固。它在海洋上形成了一層薄薄的層——
varying in depth from around 30cm in summer to a couple of metres in winter—so is readily moved by wind and current.
其深度從夏季的30厘米左右到冬季的幾米不等——所以很容易隨著風和洋流移動。
As the ice moves it stretches and cracks in some places.
隨著冰層的移動，某些地方的冰層會伸展并裂開。
Large cracks formed in this way are called leads, because they are wide enough to "lead" a ship.
以這種方式形成的大裂縫被稱為引線，因為它們的寬度足以引導船只。
In other places, by contrast, movement makes the ice thicker.
相比在其他地方，移動使冰層變得更厚。
As individual panes of ice butt up against each other, they create ridges that can be metres high.
當一塊塊冰相互碰撞時，就會形成高達幾米的冰脊。
Dr Hutchings has not yet had a chance to process her data.
Hutchings博士還沒有機會處理她的數據。
But even from the ship's deck she has been able to watch leads opening and ridges forming around the vessel.
但即使是在甲板上，她也能看到引線在船體周圍的開口和隆起。
Her eyes and ears, as well as her instruments, tell her that this winter the ice has been particularly mobile—
她的眼睛和耳朵以及她的儀器都告訴她，這個冬天，冰的流動性特別大——
and has thus become particularly rough, with a surprising number of ridges.
因此變得特別粗糙，出現了數量驚人的冰脊。
These ridges may affect the rate at which the ice melts—but to complicate matters, this could happen in two opposing ways.
這些冰脊可能會影響冰融化的速度，但更復雜的是，這可能會以兩種相反的方式發生。
Ridges make ice thicker, and thicker ice melts more slowly.
冰脊讓冰層變得更薄，更厚的冰融化得更慢。
On the other hand, a ridge projects down into the sea as well as up into the air (Archimedes, again), so it may stir up water from below the surface.
另一方面，冰脊向下延伸到海里，也向上延伸到空中（又是阿基米德式的），所以它可能會從海面下激起海水。
Deep water is warmer than the surface layer, so this stirring would serve to increase melt rates.
深水比表層溫度高，所以這種跡象會加快融化速度。
Moreover, to add to the confusion, ridges are prone to having pieces of ice fall off them into the sea, to form small blocks known as brash.
此外，更讓人困惑的是，冰脊上的冰塊容易掉落到海里，形成碎冰。
This brash, having more surface area per unit volume than unbroken ice, melts faster.
這種冰的單位體積表面積比完整的冰大，融化速度也快。
Dr Hutchings's main observation, though, is a change in the ice's structure.
雖然Hutchings博士觀察的重點是冰層結構的變化。
Historically, this far north, where ice is always present in some form,
從歷史上看，在冰層一直存在的遙遠的北方，
winter is the time when it builds up as new layers are adding to existing floes, thickening them. In summer the ice then melts back a little.
冬天是冰層堆積的季節，因為新的冰層在原有的冰層上增加，使冰層變厚。到了夏天，冰就會融化一點。
But a core of the stuff remains from year to year and, over successive winters, more layers are added.
但物質中的核心年復一年被保存了下來，連續幾個冬天后，更多冰層疊加在了一起。
That forges what is known as multi-year perennial ice.
由此形成了多年的終年冰。
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