March 30, 2003: Leg 3, Day #20

Steaming south. Sometimes you eat the bear—sometimes the bear eats you. 

The wind picked up again last night and though we hung around, hoping it would moderate, by midday it was clear that we had no chance for another dive in Carmen Basin. So we are steaming toward our next dive site, a little east of Cerralvo Island and a little west of Cerralvo Bank, where we made our first dive on the midwater leg of the Expedition. For lack of a better name, we are calling it Cerralvo Trough. It has the advantage of being the deepest spot close to La Paz, where we must be by 1600 hours tomorrow afternoon. Underway we have a following sea and the wind behind us, so it seems as though the R/V Western Flyer is really flying. She's the only one because the birds must be walking today. 

see that many familiar animals, like salps and larvaceans, live very much closer to the surface in the Gulf than they do back home. We think this is because the oxygen minimum zone comes so close to the surface here, that animals which are intolerant of low oxygen are squeezed upwards into a narrow band of water near the surface. 

This sort of pattern tells us that similar ecological niches must exist for salps and larvaceans in both places.  When these patterns are repeated again and again, we begin to think that maybe we are seeing a piece of the fundamental structure of midwater communities. We can also learn about the effects of certain environmental parameters, oxygen in this case. We see that salps and larvaceans are apparently displaced by low levels of oxygen, but we also see that other species, like the myctophid fishes and many small medusae, are not. 

Experimental manipulation is a traditional approach for conducting biological research. But in most cases, the ocean is just too big to manipulate, especially the deep parts. So in order to get that kind of information, we look for naturally occurring variations in the parameters we want to examine. To study the influence of oxygen, we go to the Gulf. To study the role of temperature, we go to the Antarctic, where the water column is virtually the same temperature from top to bottom. To study the impact of low productivity, we go out into the central Pacific Gyre. For this approach to work, it helps to have a reference standard, and for us that's Monterey Bay. 

Our plan is to begin our dive at 0400 hours tomorrow morning, dive until 1100 hours, and then head for the beach. Last communiqué tomorrow...  

Bruce Robison