March 28, 2008

How to unscrew a planet?

How many world leaders does it take to unscrew a light bulb? How about to unscrew a planet?

This week, Columbia University is hosting the fifth "State of the Planet" conference. Participants included UN visionaries like former UN Secretary General Kofi Annan as well as voices from the World Bank, corporations, and academia. I arrived early, fortified with coffee, and managed to sit near the front to witness both the clash and collaboration that sparked between these giants.

I was both inspired and frustrated by the discussions. Crucial issues were addressed: Poverty, Conflict, Health, Resource Management in the face of Climate Change. Big Problems met with Big Ideas. (I don't know how to convey the absolutely charged atmosphere, and emphasis on the importance of every word, except to capitalize.) Examples were given of both soaring successes and abysmal failures in aid to poor regions, especially Africa. The overall consensus seemed to be that definite progress is being made to improve health and sustainable growth, but that current efforts are not nearly enough. John McArthur of Columbia's Earth Institute, among others, repeatedly called for conversion of empty commitments to actions. McArthur further emphasized the massive difference that can be made by basic aid -- putting simple, fundamental tools "in the hands of those who need them." Food hand-outs were dismissed as temporary solutions, and the goal of jump-starting real growth from inside communities and within national infrastructures echoed throughout the day.

Many moments, I found myself absolutely on fire with hope. International conversations like these -- held under the conference's banner of "Real People, Real Places, Real Solutions" -- make possible truly international action. Also, the work of Jeff Sachs and other passionate advocates for positive change renewed my faith in the powers of reason and compassion, and reminded me that power itself does not necessarily eradicate those qualities from the hearts of those with influence. However. I was disturbed by The Economist's evening debate, weighing arguments for and against the proposition that "The United States will solve the climate change problem." (If you guffawed at the statement, you are not alone. 70% of the audience raised their hands firmly in the "Con" camp before the debate even began, myself included).

My concern is not with the statement, but with the climate problem misconceptions held by the debaters themselves!

FIRST: In this debate, the solution to "the climate change problem" was defined (implicitly) as simply creating cheap energy sources and decreasing the rate of atmospheric CO2 rise. Period, end of story. I had to tie my hands up in my scarf and take very deep and methodical breaths to keep from screaming "WHAT ABOUT EVERYTHING ELSE???" Don't get me wrong, I agree that carbon-budgeting, emissions reductions, and sustainable energy are absolutely crucial. Fundamental, in fact, to environmental health and the future of humanity. BUT. Their blatant disregard of issues such as deforestation and population was extremely short-sighted. Even in the 1980s, deforestation accounted for almost 20% of carbon emissions, and has been a growing problem. Ignorance of the TOTAL inputs and outputs of atmospheric CO2, and blindness towards the science behind our understanding of these fluxes, is fatal. Just as the net CO2-reduction from using many crop-based biofuels is now being slashed by research that finally takes into account the Big Picture (specifically, deforestation due to development of crop-fuels in tropical regions), these plans and "fixes" for this problem are doomed without a solid understanding of the WHOLE carbon cycle. Not to mention other greenhouse gases like methane. Policy and technology absolutely cannot ignore the complexity of the problem if we want to have any prayer at creating an effective response. ALSO -- the panel's complete neglect of the need to deal with IMPACTS of climate change as part of the solution was flat-out offensive. After all the insightful and urgent discussion during the day, I was taken aback. If the "climate change problem" is defined simply as an atmosphere and energy book-balancing problem, we are in big, big trouble. The potential benefits of lifestyle change (addressing the CONSUMPTION side of the carbon coin) were not mentioned either. Surely if the US is one of the greatest emitters, the Great Wasters of Resource, we have the largest capacity to make a difference by cutting back.

SECOND: Using the word "solution" can be dangerous. It implies and end-point, a finish-line. Concrete, quantifiable goals are crucial -- of course! -- and setting limits on "carbon-costs" and CO2 ceilings is a necessary first step. BUT THIS IS A DYNAMIC PROBLEM, AND REQUIRES A DYNAMIC SOLUTION. Even if we reduce emissions, even if we manage to level off, we have ALREADY pushed the system far from equilibrium. I dedicate most of the hours in my day to understanding the climate system, and work with some of the sharpest minds in Earth Science. Despite heroic and olympian efforts across the globe, the scientific community can not predict the future with absolute certainty. However, we DO know that the system can change, and change FAST in response to the kinds of pressures civilization is exerting on the Earth. I am positive that if a solution to climate change is to be successful, it must be fully equipped to deal with rapid change -- appropriate adjustment of prices, infrastructure, and emissions standards at extremely short notice, coupled with a willingness to enforce completely new strategies should the need arise. We need a well-prepared group, perhaps a sort of mitigation militia, that has both the structure and the influence to deal with changes and problems as they arise -- creation of such a means of response needs to enter the conversation. This is not something we can fix with a wave of a magic technological device such as those hypothesized by Vinod Khosla, but is a problem we may have to parry for centuries.


May 24, 2006

Lake Tanganyika, Africa

In 34 days I will be stepping on a plane to Africa. Lightweight clothes, sunscreen, science books & relevant articles, camera, journal, malaria pills, and a really big hat ... I can't wait.

I've been thinking some more about my Nyanza project, and I may end up focusing more on the effects of deforestation than on climate change (although I suspect the two are, inevitably, related). Over the past 200 years, the northern part of Lake Tanganyika has been almost completely deforested. Runoff and erosion have increased, dumping sediment and excess nutrients into the lake. Since fish from Tanganyika supply almost half of the local population's protein needs, everyone is very concerned about lake health and productivity.

We will probably measure organic matter abundance over time to reconstruct productivity history, and look at sediment samples under a microscope to see how its composition and mineralogy change. Shifts in mineralogy can sometimes indicate a change in sediment source, and could help us understand how deforestation has altered erosion and transport in the region.

Fish depend on phytoplankton and other organisms in the water column, who in turn are strongly affected by sunlight and nutrient supply. Erosion can impact both: large amounts of fine-grained material can cloud lake waters, decreasing light penetration, and nitrogen and phosphorus washed from land (especially farmland) can cause algae blooms, etc. If we can compare changes in lake productivity and sediment type with the region's deforestation history over the past 200 years, then we might be better able to understand the relationship between land use change and lake health.

May 03, 2006

The Stable Isotope Story

I am now pretty convinced that climatic warming caused the whitings (calcite precipitation events) we see in Lake Erie! What made up my mind? And why should anybody care?

Stable isotope data was the key. It indicated that there were high levels of evaporation, high calcite precipitation rates, and high primary productivity.

Hold on -- what's a stable isotope? Good question, I'm glad you asked. Isotopes are "varieties" of elements: they all have the same number of protons, but a different number of neutrons. This means they behave almost the same, but not quite. Since they have different numbers of neutrons, isotopes have slightly different masses. This means that lighter isotopes will tend to evaporate more easily, and be preferred by organisms for use in photosynthesis, etc. For example, if lots of light oxygen isotopes are evaporating, then more heavy isotopes get left behind, making the water "heavier." We can measure the stable isotope composition of different materials (in this case, mud and shells) and compare it to an international standard to get a ratio. This ratio can help us figure out what was happening in the environment at the time!

It sounds like a bit of a stretch, I know. And it is true that different factors can cause the same change in an isotopic composition -- oxygen isotopic composition of lake water could be made really heavy by lots of evaporation, OR also by an influx of heavy water from another lake, or from precipitation, or groundwater ... so how do we know? Well, we can never really KNOW 100% (one of the frustrating things about trying to understand the past), but we can make a very good guess. It all comes back to that multi-proxy approach I was talking about in earlier entries. We use LOTS of variables, combined, to make a complete picture. Put it all together, and see what makes the most sense.

Before I tell the Lake Erie isotopes story, one more piece of background:

We measured stable isotopes on two materials: mud and shells. The shells were made by fingernail clams, which are benthic organisms (ie, they live on the lake floor). The mud is not so easy to source, but since it was very fine-grained and calcitic, we had a hunch that it was precipitated out of the lake's upper waters (the fancy geologic word for this water layer is the "epilimnion." use it at a party, your friends will be impressed). Thus, we expect to see the shell isotopes telling us something about what was happening in the bottom waters, and the mud isotopes to tell us about the surface.

Here's what we found in the sedimentary record about 2,900 yrs ago:
1. Shells -- higher ratios of heavy Carbon (Carbon-13) to light Carbon (Carbon-12) (a "positive" trend), and higher ratios of heavy Oxygen (Oxygen-18) to light Oxygen (Oxygen-16).
2. Mud -- slight increase in Carbon 13/12 ratios, and lower ratios of Oxygen 18/16 (a "negative" trend).

What does it mean?

If you're not a geologist you're probably tired of reading this stuff by now, so I'll make is short and sweet as possible. Heavier Carbon isotopic compositions usually mean that there's a lot of photosynthesis going on -- lots of little phytoplankton sucking up the light isotope, leaving the heavy isotope behind in the water. So we have conclusion 1: lots of primary productivity.

Interpreting the oxygen is a bit trickier (hold on to your hats) ... when calcite precipitates out of water, it likes to use the light oxygen isotope, and tends to leave the heavy stuff behind. Evaporation (as we already talked about) also preferentially removes light oxygen, which also makes remaining water isotopically heavier. Nice story, does it fit? Yes! We see lighter oxygen ratios in the precipitated calcite (the mud) and heavier oxygen ratios in the shells (which reflect the composition of the water).

So climate was warmer, lake levels were lower, there was lots of calcite precipitation and lots of primary productivity.

Not a bad story, for a pile of mud.

April 20, 2006

Why Lake Erie is special

Lake Erie is by far the shallowest Great Lake: only 15 meters deep in the western basin, 20 meters in the central basin, and 64 in the eastern basin, as compared to the others, which are hundreds of meters deep. This means that Lake Erie is much more sensitive to changes -- like the littlest sibling who over-reacts to everything.

I think Lake Erie's shallow basins and resulting sensitivity are the reason that its sedimentary record (ie, mud) is different than those from other lakes in the region. We see whiting deposits (lots of fine-grained calcite) in Lake Erie and not Ontario, Huron, or the Finger Lakes because climate changes that happened in the region had a much stronger impact on Lake Erie than the others. Certain conditions are necessary for calcite precipitation (also called "whiting events" or "whitings"), and Erie was simply pushed over the edge, while the other lakes were more stable.

So where is this edge? How do we define it? And what pushed Lake Erie over this threshhold, inducing calcite precipitation? There are two possible interpretations.

CLIMATE
Warmer temperatures (jet stream shift?)increased water temperature, thus increasing CaCO3 saturation (ie, the point where water just can't hold any more dissolved ions).

LAKE LEVELS
The outlet sill eroded, lowering lake level, which increased Ca++ weathering from the shoreline, which increased CaCO3 saturation.

I like the climate explanation better, because I think temperature is the primary control on whitings, and lake level drops can't account for the degree of warming that is indicated by the other sediment properties. I also like the warm climate explanation because it is consistent with the increase in primary productivity (ie, more little green floaty organisms living, photosynthesizing, and dying) indicated by our stable isotopes. And finally (the icing on the cake), there have been several studies linking cyanobacteria abundance and whitings -- more cyanobacteria means more whitings (as described in previous entry). Altogether this seems to be a stronger interpretation, with lots of proxy data fitting together like puzzle pieces.

Of course I could be wrong. Before I officially root for this interpretation in my final paper (and in the article that we will hopefully publish!) I'm going to try to see if it's possible to quantitatively analyze how much a temperature change would have impacted cyanobacteria, and calcite solubility. In science, a self-consistent interpretation is good, but a self-consistent interpretation with numbers backing it up is better ...

Regardless of what caused these whiting events, the fact remains: Lake Erie contains an extensive carbonate record that is absent in all the other lakes in the region. Since carbonate materials are extremely valuable for reconstructing past climates, I think these sediments will be key to understanding environmental changes in the Great Lakes/New York area.

April 12, 2006

Great Lakes Climate ... getting warmer?

I think my Lake Erie mud cores have recorded a warm/dry climate event that peaked about 3,000 years ago (see earlier entries for details). NOW I'm trying to figure out how this might influence or fit into the bigger regional picture. Was Lake Erie warm while other lakes were cool? That seems odd, but that's what data from some other research papers suggests. Here are some of my thoughts on the relationship/similarities/differences between Lake Erie and Lake Ontario.

McFadden's Ontario paper shows that carbonate precipitation drops and then essentially stops in the Neoglacial (the period between ~5200 to 250 years ago), and they interpret it to indicate cool/dry climate conditions. They also see a dramatic increase in diatoms (little floaty organisms made of silica), and a dramatic (fivefold) decrease in sedimentation rates (mud building up on the lake floor) during this period.

I'm not sure their data is actually documenting a cool period ... a couple ideas:

1) I think biology could actually be really important here. A study on whitings in Fayetteville Green Lake, NY (Thompson 1997) shows a really strong correlation between abundance of cyanobacteria and whiting events. Cyanobacteria blooms, coupled with warm conditions, seems to be initiating/intensifying calcite precipitation in Fayetteville Green lake more than any other factor. The paper talks about competition between cyanobacteria and diatoms -- says that diatoms need lots of nutrients but cyanobacteria (because of their shape/size, ability to absorb) can out-compete diatoms in oligotrophic conditions (because Green Lake is oligotrophic, cyanobacteria dominate and there are lots of whitings). In Lake Ontario, Mullins and Halfman said there was more wind, upwelling, and thus more nutrients in the Neoglacial -- so maybe diatoms out-competed the cyanobacteria there, and thus made it much more difficult for whitings to occur? No carbonate precipitation is associated with diatoms.

2) Maybe there were whitings, but the carbonate dissolved? Maybe oxygen levels were higher in the lake and there was more dissolution in the sediment Today Ontario mixes almost continuously from late fall to early spring (says McFadden). Is there more mixing in Ontario than in Erie? It's much deeper than Erie, so that doesn't seem quite right. Also magnetic susceptibility drops low and stays low during the Hypsithermal in Ontario -- since magnetic susceptibility is correlated with carbonate in Erie's central and eastern basins, could low mag. sus. could be evidence that there weren't whitings in Ontario?

3) Or, maybe McFadden is right, and it is a cool/dry period. What would make Ontario cool and Erie warm at the same time? Air masses/jet stream shifts?

Too many possibilities ... don't know if I can investigate them all! I almost wish I had more than 3 weeks of school left ... Almost.

April 05, 2006

Why should we care about lake mud? Part II


The Great Lakes hold 20% of the Earth’s surface fresh water, and are important natural and economic resources for the US and Canada. During the past several thousand years they have been strongly influenced by climate change and the evolving glacial landscape of the Great Lakes region. Lake Erie, the shallowest, has been very sensitive to environmental changes during its Holocene evolution and also to human influences during the modern era.

Lake level changes impact erosion rates; temperature shifts affect productivity and water chemistry; precipitation changes influence inflow from rivers and the Upper Great Lakes. Understanding these relationships and predicting future trends is important to maintaining these crucial natural resources. Also, understanding Lake Erie’s past climate is essential to predicting how the Great Lakes region will respond to both natural and human-induced climate change in the future.

My senior thesis project investigates Lake Erie’s history by analyzing sediments deposited in the lake’s eastern basin during the Holocene (to about 3,500 years ago). Since changes in the physical, biological, and chemical proxies found in these lake sediments can be influenced by a variety of factors, clear identification of the primary factor or factors acting at the time of deposition is not always possible. However, good interpretations can be made based on a critical analysis of the combined data. In these Lake Erie sediments, we use a variety of proxies, looking at relationships between them to better understand the lake’s paleo-depositional environment.

How do we know when proxy changes happen? (Or, how do we date mud?)

Cores can be correlated by matching magnetic susceptibility peaks that appear in sediment across the central and eastern basins. Radiocarbon dates from above the magnetic susceptibility shift are out of stratigraphic order, indicating contamination or sediment re-working. An approximate age for the shift in our Station 23 sediment was estimated from 2900 14C yrs BP from immediately above and below the shift.

CONCLUSIONS (so far)

Multi-proxy data from a Lake Erie sediment core indicate a warm climate event, peaking at about 2900 14C years BP, followed by a period of greater climate variability.

Lake Erie’s climate record differs from New York lake records, potentially indicating high regional variability.

Understanding the response of Lake Erie to climate change is crucial to predicting and preparing for future changes. Because it has such a shallow basin, Lake Erie’s water levels are particularly sensitive to climate. As we continue to see shifts in regional and global temperatures, and as human impact on the Great Lakes increases, we need to prepare for major environmental consequences.

Lake level fluctuations will impact coastal wetlands, commercial shipping, pleasure boating, and beach erosion. Temperature and water chemistry changes will impact primary productivity, fisheries, and invasive organisms. Further high-resolution paleo-climate work needs to be done in order to address these concerns.


March 29, 2006

Why should we care about lake mud?

Some thoughts on my Lake Tanganyika research project:

The sediment deposited in Lake Tanganyika’s basin over the past several million years is largely composed of organic matter (Hartwell et al, 2002). Decaying algal remains, zooplankton excretions, and land-derived material all contribute to organic matter deposited in lakes, but the primary source is often phytoplankton biomass (Wetzel, 1975). Several physical and climatic factors influence the production, transport, deposition, and preservation of this organic matter, including: the degree of lake stratification, water temperature, oxygen levels, nutrient supply, and seasonal wind patterns. Understanding and quantifying these various influences in recent Lake Tanganyika sediment is important to paleoclimate studies, which attempt to reconstruct past environmental conditions based on the type and amount of organic matter present in ancient sediment. If we can better understand the factors determining sediment composition today, then we will be better able to understand regional and global climate changes recorded in the lake’s ~10 million year record.

Previous work has found that organic matter is a good paleo-indicator of depth, because it decreases with depth and has an almost inverse relationship to the amount of dissolved oxygen in the water (Jiminez, 2005). It is soluble in oxygenated water, so will tend to dissolve in shallow waters and will accumulate at higher rates as depth increases and oxygen levels decrease. Its presence or absence could help reconstruct paleo-oxycline levels.

However, the use of this proxy can be difficult because lakebed morphology also has a strong influence on organic matter abundances. In some places in Lake Tanganyika, terrestrial input is greater on sloped areas, which dilutes the organic matter (Hartwell et al, 2002). A quantitative understanding of slope on this proxy would be very useful.

Another difficulty with using organic matter as a paleoclimate proxy is that it also depends on seasonal winds and lake mixing depths. Oxygen levels do not decrease uniformly throughout the lake, but vary seasonally and with location. During the dry season, winds force surface currents northward; one model predicts that this will cause upwelling and high productivity in the southern part of the lake, which would lead to greater organic matter deposition. However, mixing reaches deeper in the southern lake and is predicted to cause high levels of organic matter dissolution (Tsuchida et al, 2002). Thus, factors such as seasonal winds and varying oxygen levels will also have to be taken into account when trying to understand the balance between productivity and preservation.

As climate is emerging as a major concern for the global community, studies such as this which enable high-resolution paleoclimate reconstruction are crucial. Lake Tanganyika contains an excellent record of past environmental changes, and could provide important information about the mechanisms of change on both regional and global scales.