Monday, January 18, 2010

Goodbye Adelie penguins, hello Fur seals

Today a fog enveloped us as we collected water samples. Snowflakes fell silently and disappeared as they met the smooth gray-green surface of the water. The world was just our boat and the gray cocoon surrounding us. Icebergs were ghostly in the distance, like more solid bits of cloud. The stillness was calm and strangely comforting even though we couldn't see further than 100m. Maybe this is how ships feel just before they hit the rocks in a fog.

It is surprising to know that although there is so much ice here, the west Antarctic Peninsula is warming more rapidly than anywhere else on earth. Looking out at the ice-mantled mountains makes me shiver involuntarily. I think of this place as a landscape out of equilibrium with the present climate, a relict of a previous time. If this climate existed anywhere without a history of cold temperatures and large ice volume, the ice wouldn’t be here. Put a different way, if you plopped down a glacier in Rhode Island, it would stick around for maybe a couple of months but it would eventually disappear. While it still existed, it would be a landscape out of equilibrium with the climate. I think that this is similar except that over all it is colder here than in Rhode Island so it will take longer for the ice to melt completely.

When Palmer Station was built in the 1970s, ships would sometimes be blocked by sea ice even in the summer. Now, there is never sea ice in the summer and soon there may be no sea ice. The sea ice extent has declined by 80% since the 1978-1986 average. Winter air temperatures have increased by 6C since 1950, five times the global average. In a general sense, the climate is shifting away from a cold polar regime to a relatively warm and moist maritime climate. Most of the evidence of climate change on the West Antarctic Peninsula presented in this post has been documented by LTER. Keep up the good work, LTER!

The changes in sea ice cover are driving changes throughout the food web. Sea ice, if it does not stick around all year, can actually help to increase phytoplankton productivy. These are the base of the marine ecosystem, because they photosynthesize. Just like plants, they convert sunlight and CO2 to water and sugars for other organisms to eat. These creatures need light, and they thrive in an stratified ocean. If the top layer is mixed around a lot by wave action, the phytoplankton get dunked deeper than light penetrates, and they have a hard time surviving. Sea ice is really great for these organisms, because as it melts it creates a cap of freshwater that floats on top of the saltier, denser seawater. The stabilizes the water column and makes the phytoplankton very happy because they can photosynthesize all day long, which is all the time in the summer. This was the situation at Palmer until recently and is one of the reasons that the coastal waters around Antarctica are some of the most productive in the world. However now there is too little sea ice to stratify the ocean and keep the phytoplankton in the photic zone. In addition, winds have been increasing over time, possibly in connection with climate change as well, which mixes the plankton even farther down into the dark. So phytoplankton productivity has been declining in the northern part of the West Antarctic Peninsula.

However, further south the story is different, which helps illustrate how the ecosystem interacts with the sea ice. On the southern end of the West Antarctic Peninsula, phytoplankton productivity is actually increasing. Previously the ocean there was covered with sea ice year-round, which put a serious damper on photosynthesis. Now as the water is ice-free during the summer but still stratified by melting sea ice, the phytoplankton are having a ball. However this may be a temporary boon as the southern peninsula begins to experience as much as ice loss as the Palmer area has had already.

But why do we care so much about phytoplankton? Well, these microscopic plants of the sea are eaten by zooplankton, the microscopic animals of the sea, which are eventually eaten by the not-so-microscopic animals of the sea, the penguins and whales and seals that we all love. And the effects of ecosystem reorganization have already been documented in fish, penguin and seal populations. The Antarctic Icefish (very good eating apparently) is no longer found near Palmer station because the water is too warm for it. The Antarctic Silverfish is also becoming more scarce, causing penguin diets to shift from about half fish and half krill to entirely krill. This puts the penguins at greater risk if the krill population collapses, which may happen. Krill (large zooplankton) are being replaced by salps, jelly-like creatures that cannot be eaten by the animals that eat krill.

As I mentioned in my post about penguins, the ice-dependent Adelie penguins are being replaced by sub-antarctic Gentoo and Chinstrap penguins. However, not to fear entirely for the Adelies yet, as they seem to be relocating southward, to Avian Island. This island is entirely covered with Adelie penguins, 65,000 pairs and growing. But where will they go as the warming pushes south? Eventually they will run out of room and this story may have a very bad ending.

The warming is very apparent here at Palmer station even without going out to count penguins for hours each day. The glacier behind the station is receding 30ft every year. The ice used to start right behind the buildings here but now there is a ¼ mile of bare rock exposed. You can even trace the melting of ice in the art displayed around the station. Oil paintings and watercolors painted over time unintentionally depict the rapid recession of the glacier. In previous years and decades, you could ski or snowmobile on the ice piedmont all the way to the base of the mountains eight miles away. Now we can only walk in a carefully roped-off area ½ mile in length because the ice is too unstable. The glacier has receded from small islands that used to be connected to mainland by ice, but are now surrounded by water. Some ice remains on the islands, but it is not connected to the main glacier so it is “dead,” just sitting there melting. It looks dirty and has deep cracks running through it. This image is particularly compelling to me because it reminds me of the glaciers I saw on Mt. Kilimanjaro that are also motionless, melting. More than what I have read in academic articles and the popular media, seeing the shocking effects of climate change in two places 9,000 miles apart makes me really feel what is happening to our planet.

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