We crossed the equator on Sunday morning, the day we entered into PIPA. There is always a celebration of the event, crossing the line is a big thing for a sailor, for the first time in particular. Of course around the ship nothing changes, the same trade winds push us along, the same waves stretch into the horizon. Drawing lines into the high seas can seem like a funny business!
And on some level that is what PIPA is, a square patch of the ocean marked by lines drawn into the water. When we protect sensitive areas on land, understanding boundaries is easy. On this side of the fence big redwoods you mustn't touch, on this side a pasture for dairy cattle. The trees stay put, the situation is pretty stable.
Not so in the ocean. The ground is more than three miles below the ship and remains less known to us than the surface of Mars. No, what we really seek to protect here is in the shallow ocean, all the life that it nurtures and supports, from seabirds to tuna, from whales to the manta rays and the turtles. These are the iconic species of course, but in one way or the other their existence is predicated on an ocean ecosystem of plankton.
|A detail of a small lanternfish (Myctophid) from our meter net plankton tow this evening. |
These fish migrate up and down in the water column, spending the night feeding on
zooplankton close to the surface but at night swimming down up to 900 meters deep.
Plankton are those animals and single-celled algae that drift with the ocean currents. The phytoplankton, microscopic algae that photosynthesize, are the grass feeding this vast ocean savannah with its own equivalents of wildebeests and lions. One crucial problem with this metaphor exists, though. As ocean currents respect no boundaries, neither does all this oceanic life they transport. So what do those lines in the ocean really mean, then? What are we protecting here exactly?
Turns out you have to change your perspective here to include the notion that even in the ever flowing ocean there can be persistent hotspots of life that remain in the general location. These hotspot oases are fully aquatic, so water is of course not the limiting substance for growth here as it is in the desert. No, the limiting factors here are nutrients, mostly Nitrogen and Phosphorus (and Iron in the Equatorial Pacific) — the same resources we feed our terrestrial gardens! These hotspots tend to form wherever ocean currents act to bring these limiting resources to the sunlit surface ocean where their constant supply is needed to fuel the growth of the Phytoplankton.
Are there many such hotspots in PIPA? It turns out that the northern boundary of PIPA encompasses a portion of major ocean current called the Equatorial Undercurrent. This current is a product of our planetary climate system, persists over time, and is responsible for constantly pumping nutrients to the surface ocean. You could almost think of the northern fringes of PIPA as this lush rainforest at the edge of a savannah, a wall of green foliage. Today as we've been sailing through the tail end of this edge we’ve witnessed schools of tuna dashing after their pray, large flocks of seabirds following these feeding schools, and even a thresher shark lazily warming itself after a long dive, its long tail fin sticking out of the water as we sailed by.
We expect to find other such hotspots, aligned with seamounts and islands that act in concert with the currents to similarly help fertilize the surface ocean. We'll look for them as we sample, using our current meter to map the currents, our rosette water sampler to draw nutrient and chlorophyll samples, and our plankton nets to sample for the small fish and even smaller zooplankton, the necessary precursors for those big iconic species like sharks and dolphins to exist.
All of this means a lot of hard work of course, and once inside PIPA we’ve begun spending a lot more time on our sampling efforts. At night, the instrument and MOCNESS deployments have gone on from 9 pm to around 3:30 am. Daytime stations are shorter, from 10 to noon, though samples drawn during these stations keep the lab busy around the clock. Here the training we’ve done in the past two weeks really pays off — the students are an integral part of the lab workflow now. During our daily ships meetings we discuss aspects of our results and talk about the things to come.
Another short three weeks and we'll know much more about this aspect of PIPA. And with that I’ll sign off and head into the lab for our night station. We’ll catch some plankton, and I’ll include a picture of some of them with this post!