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Regime Shifts and the Food Web

Recently scientists have uncovered a hidden yet massive ocean process in the Pacific Ocean. Every two or three decades, the region of the Pacific off the lower western United States does a major flip-flop between a positive (warm) and negative (cold) phase.


What do you like best about your profession?
Bill Peterson Peterson: “First and foremost, I have always found the ocean fascinating and this fascination began when I was a small child. Thus, I count myself lucky for being able to do fascinating science and to be paid to do it...”

See Bill Peterson's full Q&A »

Scientists call this pattern the Pacific Decadal Oscillation. The flip-flops are called regime shifts. Regime shifts have a great effect on the oceanic food web. For example, during the positive phase, like what occurred between the 1970s and 90s, warm surface waters thickened, essentially pushing the nutrient-rich deep water out of the reach of upwelling currents off the California coast. Without those essential nutrients reaching the sunlit layers, plant-like phytoplankton suffered causing grazers dependent on the phytoplankton (e.g. zooplankton like krill or euphasiids) to crash. This in turn, impacted the food web all the way up to the commercial fishes, seabirds and marine mammals.

During the negative phase, which is currently underway off the United States' west coast, the waters cool and zooplankton numbers rebound. Scientists suspect these regime shifts have been taking place in the Pacific for millennia. The sobering thought is that these shifts are now taking place in the context of rising global temperature. According to marine biologist, Bill Peterson, " this cool cycle will end... and it'll go into a warm cycle, but it won't be like the warm cycle that we had the last time, because we have this global warming going on all the time." Some researchers worry that rising temperatures atop these regime shifts could drive zooplankton numbers below a threshold so that their populations may not be able to recover.

Next: One Degree of Difference »


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