On Warm Waves and Melting Ice

I'm usually pretty good about getting a couple of posts up by the end of the week. Instead, I spent my July 4th holiday weekend doing what most Americans do to celebrate Independence Day: Slept in late, went to a BBQ, swam in a lake, and blew up thinks that sparkle. I also applied copious amounts of sunscreen while roasting in the summer heat, which gave me the inspiration for today's post.

A new study in Nature Geoscience takes a look at the melting of the ice sheets in relation to increasing ocean temperatures. Now, if you Google "ocean warming" or "increasing ocean temperatures" you are likely to just confuse yourself with a myriad of websites on both sides of the climate change debate (however, if you feel you must, I recommend looking at .edu sites and reading the actual research). I'm not writing today to debate the this-says-that-says and he-says-she-says of ocean warming itself. Let's just start with the fact that the ocean is not only acidifying due to increasing atmospheric carbon dioxide (CO2) but it is also warming. This warming is expected to cause changes in currents, changes in oxygen levels, shifts in plant and animal habitats, and sea level rise.

Since this study focuses on ice sheets let's jump right to that. The Greenland Ice Sheet (GIS...not to be confused with Geographic Information Systems) and the marine-based West Antarctic Ice Sheet (WAIS) have both recently undergone rapid mass loss that is not explainable by atmospheric warming only. So, well, why? First you need to picture what's going on here. Glaciers are like very very slow moving rivers of ice. Ice streams and outlet glaciers are channelized glaciers, they flow more rapidly than the surrounding body of ice, and they drain an ice sheet or ice cap. Tidewater glaciers are valley glaciers that flow far enough to reach out into the sea. The point at which a tidewater glacier floats free of its bed is called the grounding line. In Greenland the fjords are where outlet glaciers terminate and can reach several hundred meters depth at these grounding lines. Here is also where "warm and salty North Atlantic subtropical waters could penetrate from the shelf into the deep fjords, remain in the subsurface layer year-round and flush rapidly through local wind-driven circulation, thereby giving a ‘warm bath’ to the ice sheet." To date, most of the simulations and projections of melting polar ice have focused on the effects of atmospheric warming on the surface of the ice. This study focuses on this subsurface warming and how it is contributing to ice mass loss.

The scientists here used 19 state-of-the-art climate models to examine future ocean warming around the periphery of the ice sheets in response to increasing greenhouse-gas concentrations. Normally, the periphery of these ice sheets (GIS and WAIS) are kept cold by the currents that flow around them. In the Northern Hemisphere the East and West Greenland Current (EGC and WGC) keeps Greenland frozen, and in the Southern Hemisphere the Antarctic Circumpolar Current (ACC) combined with an upwelling of cold deep water keeps Antarctica frozen.

They found that, given a midlevel increase in greenhouse gasses, the ocean depths between 200 and 500 meters (650-1650 ft) will be warming 0.5 and 2°C, an average of 1°C (1.8°F), by 2100. However, the results for the two ice sheets studied were not the same. In Greenland the warming could be twice as much with the subsurface ocean temperatures increasing as much as 2°C (3.6°F). In Antarctica it could warm less, with only a 0.5°C (0.9°F) increase. Why such a difference? It is all due to those currents that I mentioned. Greenland receives warmer waters from the Gulf Stream. This warm water affects the exposed tidewater glaciers, melting them from underneath and causing the now unsupported tops to break off into the sea. Also, as the warm water melts the undersides of the glaciers the meltwater acts as a lubricant, speeding the glaciers' movement into the sea. Eventually, the glaciers will melt so much that they will not reach the sea. Antarctica has the ACC and the cold deep water upwellings to prevent, or at least slow, the warm water in the south. Unlike Greenland where the ice flows out into the sea, Antarctic ice is based on land that is already below sea level. This means that as the ice sheet melts the leading edge will continue to be underwater. Regardless of the differences between continents, the sea level is expected to rise by about 1 meter (~3ft) by the end of the century.

Looks like my inland Florida relatives will have beachfront property. Perhaps I should invest in a surfboard.

Here is the paper:
Jianjun Yin, et al. (2011) Different magnitudes of projected subsurface ocean warming around Greenland and Antarctica. Nature Geoscience: published online 03 July. (DOI: 10.1038/ngeo1189)

Learn more about glaciers here:
http://daac.gsfc.nasa.gov/geomorphology/GEO_9/GEO_CHAPTER_9.shtml
http://nsidc.org/glaciers/questions/types.html
http://www.homepage.montana.edu/~geol445/hyperglac/glossary.htm
http://www.fs.fed.us/r10/tongass/forest_facts/resources/geology/icefields.htm

and on this study...
http://www.msnbc.msn.com/id/43627029/ns/technology_and_science-science/
http://www.livescience.com/14892-warming-ocean-melting-ice-sheets.html
http://www.sciencedaily.com/releases/2011/07/110703133838.htm

The Aftermath of the Snowball

Our planet covered in ice from one pole to the other. Doesn't really seem possible does it? Well, a controversial hypothesis called Snowball Earth posits that our planet was indeed covered with a thick sheet of ice for a period of its history. This thick sheet of ice lasted for millions of years and may have occurred more than once. The most severe likely occurred around 750-580 million years ago.

When an entire planet is covered in ice it is bound to have effects. A new(ish) paper in Nature takes a look at one of these effects and its relationship to life. But let's step back for a second...

Nutrients are chemicals that an organism needs to survive and grow, usually because they are vital to various metabolic and other bodily processes. What do we know about the kinds of nutrients that life needs to survive? Well, we know that life needs water (its inorganic but still counts), and if we're talking about a big melting ice sheet then we can check that one off our list. What about organic molecules? Sure. After all, we are organic and need building blocks, if you will, to help us live and grow. These building blocks, or nutrients, come in the form of carbohydrates, fats, and proteins (or amino acids), as well as various vitamins. Certain chemical elements are also important. These include carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur, calcium, etc. Of course, what type of organism you are will expand or narrow this list and vary the concentrations of these various nutrients.

The Nature paper zeros in on phosphorous. In most modern marine aquatic systems you will find that phosphorous and bioavailable nitrogen are the limiting factors. Usually when we are talking about nutrient limitations we're talking not about one being completely gone from the system but, rather, an imbalance of the nutrients. In the case of nitrogen and phosphorous you should see a nitrogen to phosphorous ratio of 16:1. It is generally thought that phosphorous limits productivity on a geologic timescale, and so it is particularly interesting to scientists to find the concentrations of this chemical over time.

In the aftermath of Snowball Earth, these researchers have found that the oceans were rich in phosphorus. Now, how in the world do you go about measuring that one? Well, these scientists looked at the rocks and sediments on the sea floor - about 700 samples of iron-oxide-rich rocks. They tracked phosphorus concentrations by analyzing the composition of iron-rich chemical precipitates which accumulated on the sea floor and took up phosphorus from the seawater. This analysis showed a spike in marine phosphorus levels in the mid-Neoproterozoic (from ~750 to ~635 million years ago). We know that the ice sheet melted right? Then it stands to reason that there was quite a bit of erosion and weathering going on at that time. These processes could explain the high concentrations of phosphorus in the seawater.

Let's take it another step, and link together what we know. Life likes phosphorus, there was lots of phosphorous in the seawater, therefore we should see more life in the oceans. Makes sense. Keep going. More life in the oceans means there's more oxygen production via photosynthesis, the oxygen is released into the atmosphere, atmospheric oxygen is available for other organisms. OK, good. Let's keep going. Oxygen is another of those molecules that life needs/likes, more oxygen availability, more animals using it and multiplying, throw in a little mutation and subsequent evolution, and bang! the emergence of more complex life on Earth.

Alright, alright, I agree, that's a lot of steps. Steps that all start at a single there-was-lots-of-phosphorus point. On their side, there is evidence that links marine phosphorus concentrations and the levels of atmospheric oxygen. And the authors aren't saying that this is definitely what happened. They are simply saying there was more oceanic phosphorus at that time and that it could have paved the way for the evolution of complex organisms and their diversification.

On a purely let's-look-at-the-chemicals level, until now scientists believed that the conditions of an iron-rich ocean would lead to low phosphorus levels. The fact that these researchers found the opposite after the Snowball Earth events is quite significant. We're talking about the finding of a possible nutrient driver behind one of the big explosions of life. Pretty neat.

Here's the source:
Planavsky, Noah J., Olivier J. Rouxel, Andrey Bekker, Stefan V. Lalonde, Kurt O. Konhauser, Christopher T. Reinhard, and Timothy W. Lyons (2010) The evolution of the marine phosphate reservoir. Nature: 467(7319): 1088 (DOI: 10.1038/nature09485)

Also:
http://www.nsf.gov/news/news_summ.jsp?cntn_id=117908
http://www.sciencedaily.com/releases/2010/10/101027133146.htm


(image from geos.ed.ac.uk)

The newest trend...ridiculous

A 265-ton glacier was imported from northern Sweden and whittled down to a 28 foot tall frozen landscape. The event? Karl Lagerfeld's inspiration for the Chanel Fall/Winter 2010 show.

Crazy.

Here's the story: http://www.inhabitat.com/2010/03/14/karl-lagerfeld-imports-a-265-ton-glacier-for-chanels-fashion-show/