Scott Benson, R/V John Martin in Monterey Bay. Last week, our coastal central California study area experienced a significant relaxation event. Relaxation of upwelling winds is the 'alter-ego' of upwelling waters, and local productivity is greatly influenced by the yin and yang interplay between upwelling and relaxation conditions.

If you were also on the water during the end of last week, you'd probably agree that conditions were exceptional: mirror-like seas and bright sunny skies. Thursday, 12 July, was one of the finest days for a local sea assignment that I've experienced in more than 10 years on the central California coast. As a result of the still air and cloudless skies, ocean surface temperatures soared by about 7 degrees Fahrenheit (4 degrees Celsius), particularly at the mouth of Monterey Bay, as offshore waters were able to approach the coast, unhindered by the effects of upwelling.

We were aboard the R/V John Martin on Thursday to to sample the surface jellyfish and have a look at how the leatherbacks' feeding areas are developing. (That's Moss Landing Marine Lab student Laurie Hall and I doing a jelly tow.) These are the leatherbacks that are near the end of their long swim from Indonesia. Despite the warm surface temperatures, water temperatures below the surface remain cool, a remnant of the strong northwest winds that occurred during the Spring and early Summer. That's when the winds induced the upwelling of cold waters that bring lots of nutrients from the depths.

We performed some trawls at the surface and at shallow depths, and some dip net sampling, collecting two species of jellyfish from the north end of Monterey Bay -- brown sea nettles (Chrysaora fuscesens), and the beautiful moon jellies (Aurelia labiata), which many of you have seen in the Monterey Bay Aquarium. Leatherback turtles eat both types, although the brown sea nettle seems to be the favorite item on the menu. The distribution of jellyfish was patchy and moon jellies dominated the assemblage. The largest aggregations were tucked inside north Monterey Bay in an area known as the "upwelling shadow" where waters are sheltered from northwest winds and residence time of the water entering Monterey Bay is the greatest. We call the brown-red water in the upwelling shadow and other central California retention areas "turtle muck" due to its turbidity and the likelihood of finding leatherbacks in such conditions. Here's Laurie displaying a sample from the turtle muck.

A few months ago, the jellyfish were only half-dollar size. The diameters of the jellyfish bells collected on Thursday were almost 12 inches (30 centimeters), as you can see below. (All photos were taken by Jim Harvey, a researcher at Moss Landing Marine Laboratories.)

If the upwelling-relaxation dance continues through early September, the jellyfish should continue to expand and attain bell diameters wider than 20 inches (50 centimeters), a good meal for a hungry leatherback. The habitat looks good, for July. The weather forecast is calling for some more wind and fog in the coming days. We'll have another look in early August with a plane and the R/V John Martin. In the meantime, this should be a good time to see what's happening at the other side of the Pacific, the origin of our reptile wanderers. And that's where I'm off to now. Next blog entry will come to you from Indonesia. SENT FROM HONG KONG AIRPORT.