Snap back to reality. Whoop! There goes gravity…

March 2, 2009
Layer cake (Courtesy Wikimedia Commons)

Layer cake (predicted). (Courtesy Wikimedia Commons)

Consider a layer cake. How would you build a model that predicts the thickness of a 10 cm cube of frosting spread uniformly around the cake? If the cake is 10 cm tall and 30 cm in diameter (we’re hungry), then the frosting would contribute to a uniform “cake-level rise” of about 0.6 cm. Not particularly indulgent, but times are rough.

The layer-cake model could easily become a super-simplified, super-useless metaphor for models of melting ice sheets. Consider an ocean world with one continent, no atmosphere, just nothing at all. A ball of water, with a two-km thick ice cube at the South Pole, atop the continent. Bake at 60 degrees Celsius for 200 years.

Sea-level models are much more complex than our shopping guide for frosting. And they recently became more complicated.

A heated atmosphere is expected to melt ice sheets over a a longer period of time than you need to consider on a routine trip to the grocery store. Ice atop land runs off into the ocean, raising levels globally as the water works through the system. The Intergovernmental Panel on Climate Change’s Fourth Assessment Report (FAR) concluded that “the last time the polar regions were significantly warmer than present for an extended period (about 125,000 years ago), reductions in polar ice volume led to 4 to 6m of sea level rise.” (From IPCC FAR Working Group I, Summary for Policymakers, p 9, .pdf here.)

A paper in Science last month considers factors left out of modeling sea-level rise. The biggest factor is gravity. The 6,000-foot thick ice that covers much of Antarctica exerts great force on the surrounding ocean, so much so that if that gravity is redistributed, “sea level will actually fall within ~2000 km of the collapsing ice sheet and progressively increase as one moves further from this region.” If the West Antarctic sheet melts, its gravity disperses, too, releasing the water under its sway to rejoin the world’s oceans. A study published 30 years ago remarked on the ice sheet’s gravitational pull, and was then promptly forgotten. Jerry X. Mitrovica, Natalya Gomez, and Peter U. Clark build the observations into a new model of a melted world.

The authors estimate the effects of two other phenomena as well. The weight of ice transforms the ground beneath it, pressing bedrock farther down than it might otherwise “want” to be. Absent the ice sheet, this land might recoil, expelling water that would otherwise settle above it and move the Earth’s axis of rotation about a third of a mile, with its own influence on water sloshing about the seas.

Sea-level is notoriously difficult to model, and occurs over time periods long-enough to seem ridiculous if your primary diurnal concerns are more along the lines of buying frosting than creating a long-term national flood insurance program. But that’s the interesting thing about climate change, isn’t it? Models aren’t (neessarily) forecasts. They are specific predictions based on specific assumptions, a way to investigate how the Earth behaves based on our limited but ever-improving obervations.

New considerations suggest that sea levels could rise 30 percent higher than previously predicted if the West Antarctic ice sheet melts. (Courtesy CReSIS)

New considerations suggest that sea levels could rise 30 percent higher than previously predicted if the West Antarctic ice sheet melts. (Courtesy CReSIS)

Advertisements

Fish? In the ocean?

January 28, 2009
MYSTERY SOLVED? Flounder in seawater (below) show concentrations of calcium carbonate much higher than in fresh water.  (Courtesy Rod W. Wilson, Exeter University)

MYSTERY SOLVED? Flounder in seawater (below) show concentrations of calcium carbonate much higher than in fresh water. (Courtesy Rod W. Wilson, Exeter University)

Scientists from the U.S., U.K., and Canada and recently discovered an entire ocean in the belly of a fish.

Rod Wilson is an animal physiologist at the University of Exeter who, with Martin Grosell (U. Miami), has spent the last several years elucidating how fish make calcium carbonate in their intestines. Fish drink seawater rich in calcium and magnesium. It concentrates in their digestive tracks and  these ions, which fish might otherwise only use for kidney stones, meet up with carbonate ions.

Coccolithopohres and foraminifera are the 800-lb. plankton of the ocean carbon cycle. Their shells drop through the water column, perhaps packaged in bulk by copepods, transporting inorganic carbon to the deep ocean. It tends to dissolve below the lysocline, where the carbonate concentration of the water dips below favorable pH and pressure conditions for keeping it in tact. The problem with this picture is that scientists have long detected aberrations in alkalinity much higher than the lysocline at which calcite shells tend to dissolve. It’s been an oceanography mystery for decades.

Fish make a different kind of carbonate crystal than the phytoplankton — aragonite, which has a marked higher amount of magnesium. As a result of this difference in composition, aragonite dissolves higher in the water column than calcite.

Wilson presented this example of good piscine renal hygiene while visiting the University of Miami. The study was met with interest by Frank Millero, the distinguished marine chemistry scientist, who pointed out that Wilson and Grosell might have stumbled on to a clue to very big problem: Why scientists observed the effects of dissolving carbonate so much higher in the water column than expected from calcite.

The three of them teamed up to see if fish might be responsible for the mystery. The trick would be to estimate how much carbonate fish leave behind and then multiply it by the number of fish in the ocean, to arrive at a sense of just how much calcium carbonate the fish are producing. Easy.

How many fish are in the ocean? The typical answer you hear these days — “Not as many as there used to be” — was too imprecise. No one had calculated how many fish might be in the ocean! “That was a big surprise,” says physiologist Grosell. The team brought on Simon Jennings (U. East Anglia) and Villy Christensen, who contributed modeling estimates, figuring a total fish biomass in the vicinity of 900 million to 2 billion tons. That yielded a conservative range of 3 to 15 percent of all surface ocean calcium carbonate — originating in fish guts.

The findings were published in Science Jan. 16. Grosell marvels at the interdisciplinary approaches it took to surmise, in essence, the power of fish in the sea: The study couldn’t have happened without a marine chemist, fish physiologists, and ecosystems modelers. Grosell: “In hindsight, it’s like how could we have missed this?”


“Take that out of your mouth.”

October 21, 2008
Image courtesy Wikimedia Commons

Image courtesy Wikimedia Commons

Such is the cry of parents whose young children have an appetite for learning that is sometimes too literal. Over the last year or two we have seen an increase of stories about the effects of toxic plastics on human health, from fetal to adult. The scientist Jacques Monod once commented of genetics, “What’s true for e-coli is true for an elephant.” That goes for the effects of plastics, too.

Approximately no one should be surprised that the oceans absorb much of our chemical trash. Still, it was a useful and insightful exercise for Charles James Moore, of the Algalita Marine Research Foundation, to quantify just how much plastic the waters have absorbed – and by extension, the life within them. Moore finds that for two decades we have been flushing plastics out to sea faster than industry produces them for their infinite commercial use.

Bisphenol-A, singled out recently in several studies for harm to children, is just one chemical that seeps into marine ecosystems. Styrene, polycarbonates, UV stabilizers, non-stick coatings all break-down over time, but for the most part maintain their molecular integrity. When a foam coffee cup dematerializes to the four corners of the Earth, it doesn’t disappear, but soaks up other toxins before entering the food chain. Scientists have identified 267 species worldwide that ingest plastic debris, including albatross, fulmars, shearwaters, and petrels, which confuse plastic for food; 44 percent of seabird species; and sea turtles that munch on plastic bags and fishing line.

Moore identifies eight issues within the overall problem:

  • Macroscopic debris – diapers, syringes, etc – washes up on beaches, unsightly and potentially harmful.
  • Bags, lines, and other waste snares marine biota, “and kills through drowning, strangulation, dragging, and reduction of feeding efficiency.”
  • Some plastic debris looks like and weighs as much as food, but is only a toxic substitute.
  • Hydrocarbon-based synthetic compounds tend not to biodegrade. They can also provide a home to barnacles, worms, and other undesirables, and float them across the sea, where they become invasive species.
  • Many unprocessed plastics are shipped from suppliers to factories in the form of tiny resin pellets. At sea, these pellets and other plastic debris emit and absorb endocrine disrupters and other pollutants.
  • Debris falls through the water column and disrupts both benthic ecosystems and deep-sea deposition of CO2.
  • Coastal species see their nursery habitats poisoned by anthropogenic litter.
  • Plastic waste clogs ship intake ports and wraps propellers, costing time and money.

SOURCE: Moore, Charles James. “Synthetic polymers in the marine environment: A rapidly increasing, long-term threat.” Environmental Research 108 (2008): 131-139.


“Equity in the Ecosystem”

September 22, 2008

A new report concludes that assigning individual property rights within the fishing industry staves off ecosystem collapse more frequently than other types of governance.

Management policies that assign catch rights to individuals may better stave off fishery collapse, according a report in Science. Christopher Costello, Steven D. Gaines, and John Lynham assembled a worldwide database of fisheries and catch statistics in 11,135 fisheries, from 1950 to 2003. By 2003, fisheries that have deployed “individual transferable quotas” collapse about half as frequently as fisheries that have no catch rights.

The impetus for the study came from the much-discussed 2006 study by Boris Worm et al, which predicted a collapse of all world fisheries by 2048. Costello, Gaines, and Lynham resolved that the community to date has focused on problems disproportionately to solutions. As a result, they happened upon inefficiencies in current management that might be rethought — in local ecololgical, economic, and social context. “The answer lies in the misalignment of incentives,” they write. “Even when management sets harvest quotas that could maximize profits, the incentives of the individual harvester are tyhpically inconsistent with profit maximazation for the fleet.”

Costello, Christopher, Steven D. Gaines, John Lynham. “Can Catch Shares Prevent Fisheries Collapse?” Science 321 (19 September 2008): 1678-1681.

See accompanying article, from which title of this post comes: Stokstad, Erik. “Privatization Prevents Collapse of Fish Stocks, Global Analysis Shows.” Science 321 (19 September 2008): 1619.


Fish trawl data points to global warming

July 1, 2008

Three University of Rhode Island oceanographers conclude from four decades of fishery data that rising temperatures are the primary cause for significant turnover in Narragansett Bay and Rhode Island Sound fish populations.

Weekly trawl surveys from two stations indicate that over 46 years these communities witnessed a transformation from vertebrates to invertebrates and from bottom-feeding fish to species that make a living higher in the water column. Collie et al posit several hypotheses: the effects of fishing, the abundance of chlorophyll, temperature change, and other climate factors, including the North Atlantic Oscillation. “Mounting evidence has revealed that even small increases in water temperature over extended periods of time can directly influence the species composition, distribution, and abundances of surrounding fish communities,” the authors write, citing observations from the English and Bristol Channels and similar studies in the northwest Atlantic. Temperature increases in these previously studied areas are consistent with the changes documented off Rhode Island: increasing numbers of squids, pelagic fish, bottom dwelling invertebrates.

If temperatures and other environmental factors have indeed driven these changes, the authors predict that the population may begin to more closely resemble warmer water estuaries, such as Delaware Bay and Chesapeake Bay.

The research rests on the valuable set of trawl-survey data. All but one month of the 564 studied had more than two surveys, and in 91 percent of the months three or more surveys were recorded. Twenty-five species made up 96 percent of the total haul (1.8 million animals over the 46 years).

The authors looked carefully at the fishing record to limit the potential influence human commercial activity has had on the transformation. They found “no strong correlations” between the population and the fishing activity. Fishing activity was overwhelmed by the climate signal: Sea surface temperature increased by 2 degrees C since 1959; fish species caught today prefer to swim in waters about 2 degrees C warmer than the water was in 1959. “That seems to be direct evidence of global warming,” Jeremy Collie said. “It’s hard to explain any other way.

Collie, Jeremy S., Anthony D. Wood, and H. Perry Jeffries. “Long-term shifts in species composition of a coastal fish community.” Canadian Journal of Fisheries and Aquatic Sciences. 65: 1352-1365: 2008.


Boesch and lessons learned from Louisiana and the Chesapeake

June 25, 2008

Boesch, D. F. (2006). “Scientific requirements for in the restoration of Chesapeake Bay and Coastal Louisiana.” Engineering 26(1): 6-26.

Here Donald Boesch analyzes two ostensibly ecosystem based management programs based on four broad principles that are generally considered key to an ecosystem-based approach: 1) integration of multiple ecosystem components; 2) sustainability as a goal; 3) precautionary approach; and 4) adaptive methodologies. These are all very broad concepts with potential for multiple interpretations, as the author notes. The challenge he raises is then how can scientific advancements help with the practical application of these concepts?

Boesch starts with the idea that the real challenge for EBM is how to implement it in the field, and thus his focus on case studies in Louisiana and the Chesapeake. He then discusses how the four broad principles can be better applied to these cases through increased scientific input. For integration he points out that simulation models (run forward or backward) can be used to capture some key elements (e.g., the relationship between land use practices, runoff and nutrient loading in a bay), but that they still fail to provide a complete quantitative picture (e.g., we still can’t quantitatively connect nutrient loading in a bay to human health outcomes). Boesch notes that a major challenge here, from both the science and management sides, is that work (academic departments, journals, technical panels) tends to be fairly narrowly focused on one issue (e.g., toxic metals) rather than integrative from the start.

On the issue of sustainability, Boesch turns to “resilience” as a goal with perhaps a better chance of practical implementation. Invariably, this discussion raises the question of whether ecosystems have steady states that ecosystem properties (water quality, diversity, turnover, etc.) gravitate towards. My worry here is that it may be possible to note where an ecosystem has lost resilience (e.g., Louisiana in the 2005 hurricane season) or has declined to an undesirable state, but is it possible to design restoration with a particular resilient goal in mind?

Boesch notes that both in Louisiana and the Chesapeake the precautionary principle is mostly being applied in hindsight, focusing on the consequences of not reducing existing impacts rather than strictly on preventing future impacts.

On adaptive management Boesch importantly notes the difference between true adaptive management and “trial and error” management. In particular, a true adaptive management program must set explicit expectations and periodically monitoring how closely those expectations are being met, and make adjustments as necessary to bring expectations and reality closer. In responding to the recent blueprint for ocean research priorities in the US, several members of the Duke Nicholas School faculty and I pointed out the failure to explicitly differentiate adaptive management and “trial and error” as a weakness of the plan (available here). Boesch also points out the risk of being too reliant on predictive models in lieu of actual field data and monitoring in assessing the results of adaptive management.

Boesch offers five broad solutions for the scientific community, two of which are focused on institutions and norms in science and three focused on actual research areas. First, he argues that scientists should be more “solutions based”. This is always a tricky argument, given the institutional impediments (in funding, tenure granting and job candidate selection, for examples), but there are clearly both individual examples of people who have made this transition (e.g., Jane Lubchenco, Stuart Pimm) and institutional examples (Boesch points to the field of human health research). Second, Boesch calls for better bridging between science and management. I think many of the same institutional barriers apply here, especially with regard to training in most academic departments (if I may make a shameless plug here, the Nicholas School at Duke, to which I am a newcomer, seems to turn out a large number of well-trained scientists who end up in key marine management positions). Third, Boesch makes a plea for more predictive analyses, particularly with regard to thresholds of resilience in ecosystems. This seems like a particularly large (though important) task considering our current fairly basic understanding of resilience in ecosystems. Fourth, he argues for better scientific clarity on the issue of uncertainty and how to get beyond uncertainty as an impediment to progress. This is at the core of the science-politics interface with regard to the issue of climate change, as Stephen Schneider has often addressed. Finally, he calls for a more integrative approach to adaptive management including the direct comparison of different predictive models. This seems especially important in light of the ascendancy of Ecopath/Ecosim type models despite varying degrees of discomfort about the many assumptions that must be made in using them (sounds like a good topic for a debate here).


Babcock and Pikitch Seek Definition

June 25, 2008

By Sheril Kirshenbaum

Babcock, E. A. and E. K. Pikitch (2004). “Can we reach agreement on a standardized approach to ecosystem-based fishery management?” Bulletin of Marine Science 74(3): 685-692.

Unlike traditional single species fisheries management, ecosystem based management practices are brand new.  Thus the objectives, goals, and scientific methodology are not well defined to date.  For EBFM to move beyond single species management as the conceptual basis of US fisheries management, we must move from theory to a straightforward and convincing framework that is mutually agreed upon.  Inclusion of ecosystem values such as biodiversity and ecosystem function in fisheries management under US fisheries law will require the evolution of a consensus on a standardized, practical approach to EBM.