(image: David Karl, UH)
The Earth’s oceans play integral roles in regulating global climate and supporting biodiversity. Our goal as marine scientists is to answer questions that broaden our understanding of the oceans role on Earth. An essential part of these efforts is providing context for our findings and communicating them to others. The goal of this blog is to not only share our excitement for the marine science, but provide insights into the inner workings of this far-out process of doing scientific research at sea. We may call it a cruise, but it’s nothing like a vacation with the Royal Caribbean. On this expedition, our sights are set on understanding the biological, chemical, and physical processes that ultimately control carbon production and export in the expansive North Pacific Subtropical Gyre.
The subtropical-gyre regions of the major ocean basins constitute the largest and most expansive ecosystems on earth, responsible for carbon fixation amounts on par with global rainforests. Gyre regions are nutrient-starved, but remain productive, complex, and richly diverse. There are hundreds of thousands of organisms in a droplet of seawater. Our understanding of what these organisms are doing, metabolically and interactively, is constantly being refined. At Station ALOHA we have a unique opportunity look to at how these organisms survive in a nutrient starved region of the ocean. We will use tools to measure the genes expressed, the organisms present, their size, and their chemical composition. This information helps assess the relative abundance of different organisms, what organisms can and are doing, and how their elemental composition scales with size. Moreover, these organisms are not self-sufficient, there are close relationships where organisms can trade resources to access elements critical to growth.
We can see the organisms in the water column using a number of methods, none of which involve sharks with laser beams on their heads, but many of which do involve lasers. Submersible instruments put in the water column shine lasers across a small window. As organisms and particles pass through that window and block the laser we can determine their size, shape, and depth (location). Traps, or open-floating trashcans, can also be used to collect dead, sinking particles and assess what amount of material from above falls into the abyss of the ocean and perhaps to the sediments. Together, these instruments assess the actively floating material and the sinking material. We can then measure the chemical compositions of the two and get further information about how and why different elements, like carbon, nitrogen, or phosphorus, move from the surface ocean to deeper waters when they aren’t recycled by nutrient-starved neighbors.
A number of approaches are used to help test the activity and speed at which organisms use elements in short-supply like nitrogen, phosphorus or iron. For instance, we will be using incubations to test how manipulating variables like: groups of organisms present, nutrient concentration(s), light, temperature, and carbon dioxide change the diversity of organisms present, their interactions, the elemental composition of the cells themselves, and ultimately the composition of the water. To trace the speed of elemental mobility, isotope additions to incubations track movement of elements between solution and particulate (living or dead organism) reservoirs given their unique character. Isotopes are elementally bigger and “easy” to measure as they move around. Combined, these approaches provide quantitative constraints on where and how fast elements channel between cells, the ocean, the atmosphere, and even the sediments.
Mobile and motile organisms, which are able to move without the help of ocean mixing, are an exciting and unique group that can move along and beyond physical, biological, and chemical barriers. For example, Station ALOHA is physically stratified with warm, nutrient-poor, clear water overlying cooler, nutrient-rich water with less available light. Organisms respond to this contrast by arranging themselves in the water according to what environment best suits their needs. Organisms which use photosynthesis to generate energy must remain in the light, while heterotrophs (organisms which eat others for energy) may have more flexibility. Mobile organisms, capable of swimming, may move into the deeper nutrient-rich waters to avoid nutrient stress and enhance their growth. This juxtaposition of environments, organismal needs, and traits presents a never-ending host of ecological and biological questions about how and why organisms live where they do.
The ocean’s role in regulating climate is closely tied to these systems. The living organisms we’re encountering and studying at sea are vessels to remove carbon from the atmosphere and lock it away in marine sediments, this in turn modulates climate. The delivery of biomass from the upper reaches of the ocean hinges upon physical, biological, and chemical reactions processes and interactions. Experiments at sea manipulate these variables and test responses to changes in things like nutrients and the subsequent biological interactions. Quantifying the biological and chemical processes present informs our understanding of how expansive gyre regions of the ocean sustain productive populations of organisms and how on a changing earth the ecology and biological productivity of this region might change.