SeascapeModeling has been on the road. Last week, Nick and I traveled to the RARGOM Gulf of Maine Symposium in St. Andrews, New Brunswick. We're now at the Society for Marine Mammalogists Biennial meeting in Quebec City. Nick and Dan presented various aspects of our copepod-right whale modeling work. I presented something completely different.
For the last several years, I've been sketching diagrams, scribbling equations, and filling spreadsheets trying to figure out whether whales are like trees, at least when it comes to carbon dioxide. Seriously. Yes, I know I need a life, but this is actually really neat. Here's how it goes:
Forests are an important reservoir of carbon on land. Through photosynthesis, trees take carbon dioxide out of atmosphere and turn it into tree (leaves, roots, and wood). When the carbon is locked up as tree it is no longer in the atmosphere, reducing the greenhouse effect. This is why businesses (at least in Europe) can get carbon credits by helping preserve forests. As a forest grows, more carbon is taken out of the atmosphere. Conversely, if a forests burns, the carbon gets released as carbon dioxide.
In the ocean, most of the photosynthesis takes place in single celled phytoplankton. These cells may live a few days or weeks, so they can't really store carbon. Instead, carbon in the ocean is stored in the bodies of larger organisms. As the largest and longest lived animals, whales act like the trees of ocean (minus the leaves). Whaling, like a forest fire, turned hundreds of years worth of whale-carbon and returned it to the atmosphere. Since industrial whaling stopped in the 1970s, most whale populations are now recovering and are storing more carbon.
Large fish, notably tuna and sharks, can similarly store carbon for many years. However, even including these species, the amount of carbon stored by marine vertebrates is small compared with the total amount of forest on land. But, whales (and large fish) have one more trick. Once a forest becomes mature, its ability to store carbon decreases. While there is an upper limit to how much carbon can be stored in living whale, whale populations can continue to export carbon as dead whales. Whales have few predators, so many of the whales that suffer "natural" deaths will sink to the bottom of the ocean. If the whale dies in deep water, its carbon will remain out of the atmosphere for thousands of years. The amount of dead whales is related to the total number of whales, so whaling reduced the size of this carbon "sink". By estimating the total decline in the mass of whales, assuming that whaling turned whales into carbon dioxide, and accounting for the lost "dead whale export potential", I calculated that the total carbon footprint of 100 years of whaling released an amount of carbon dioxide to the atmosphere equivalent to setting New England on fire. The full paper, (including equations!) is here.