The Summer Sea Gets Skinny: 1980's to Summer 2002

The Summer Sea Gets Skinny: 1980's to Summer 2002

NASA and NOAA analysis reported that phytoplankton in the North Pacific Ocean in summer was about 30% less than it was 20 years ago, and more than 10% less in the North Atlantic. On the other hand, increases were observed in the northern Indian Ocean and equatorial regions. Fluctuations in plankton, the foundation of the food chain and the keystone of the carbon cycle, have a double ripple effect on the ecosystem and the climate.

The IPCC estimated that sea level could rise up to 88 cm by 2100, and the future of vulnerable coastal areas and islands became the focus of debate. Japanese observations also show a rise in average urban temperatures over the 100-year period from 1901 to 2000, with Tokyo showing a rise of 3 degrees Celsius. Global warming was no longer an abstraction, but a phenomenon that was manifested in our daily lives and in the ocean.

So what was happening in the ocean? The surface layer in summer tends to warm, and as the stratification strengthens, the supply of nutrients from the deep layer weakens. In the mid-latitude open ocean, the effect is a direct hit, leading to a decline in chlorophyll levels. On the other hand, in equatorial and monsoon-dominated areas, upwelling and changes in wind stress cause increases and decreases. Decadal-scale ocean fluctuations also overlap, and oceans that are decreasing and those that are increasing appear at the same time.

Related technologies were just reaching maturity. These include satellite ocean color observations to determine chlorophyll over a wide area, in-situ measurements using fluorescent meters on ships and mooring systems, physical observations using Argo floats and ocean buoys, and carbon flux estimation using sediment traps to capture sedimentation particles. The numerical models and data assimilation that link these data will redraw the entire picture from primary production to biological pumps.

The implications are heavy. Declining primary production casts a shadow over the food web from small planktonic organisms to higher order predators. Weakened fixation of carbon in the ocean will make it more difficult to manage concentrations on the atmospheric side. In addition to mitigating global warming, the human side of the ship must also be precise in steering the ship to protected areas, adjusting fisheries, and combating eutrophication on the coast. The question was how to face the slimming summer ocean by uniting observations, models, and on-the-ground wisdom.