Sea life's importance to the climate
Does the marine biosphere mix the ocean? A group of oceanographers led by W.K. Dewar of Florida State University argue that the swimming action of fish and other marine organisms may play a critical role in driving ocean currents. If true, large-scale over-fishing or the collapse of the marine food chain due to pollution or ocean acidification may cause significant changes in ocean currents--and Earth's climate.
Figure 1. Rainbow made From a sperm whale using his blowhole. Image taken June 17, 2006 in Kaikora, New Zealand by wunderphotographer jhfelder.
The Meridional Overturning Circulation (MOC) or Thermohaline Circulation is a well-known feature of the ocean circulation. In the Atlantic, the Gulf Stream current forms a portion of the MOC. Gulf Stream waters flow to the region near Greenland, where an input of fresh, denser water from melting ice and river run-off creates a downward flow of water that then moves southward along the ocean bottom towards the Equator. This deep water eventually returns to the surface in the mid-Atlantic to complete a cell of the MOC. Scientists have long thought that the energy needed to drive the MOC came from winds and tides--about two terrawatts of energy (Munk and Wunsch, 1998). However, Dewar et al. show that the mechanical energy added to the ocean by the swimming action of whales is about 1% of this total, and the swimming action of other marine organisms (primarily zooplankton) adds up to 50% of this total--one terrawatt of energy. While the authors admit that their calculations may have large errors, this research shows that marine life may have a heretofore unappreciated large impact on Earth's climate. Our climate is intimately connected to the sun, life on land, life in the ocean, and human activities in an incredibly complex web of interconnections. It is our challenge to understand this system, even as we change it and it changes of its own accord.
My next blog will be Thursday afternoon, when the new Dr. Bill Gray/Phil Klotzbach Atlantic hurricane season forecast will be released.
Dewar, W.K., R.J. Bingham, R.L. Iverson, D.P. Nowacek, L.C. St. Laurent, and P.H. Wiebe, 2006, "Does the marine biosphere mix the ocean?", Journal of Marine Research, 64, 541-561.
Munk, W., and C. Wunsch, 1998, "Abyssal recipes II: Energetics of tidal and wind mixing", Deep-Sea Res., 45, 1976-2009.