The base of our marine ecosystem

As I explore the complex systems that sustain life in our ocean, I look for the base of our marine ecosystem. Here I will outline a few of the routes that nutrients navigate on their travels into the depths of this planet we call home. Nitrogen fixation, phosphorus cycles, our impacts on these processes and of course, upwelling. Even though the nutrients that fuel the foundation of marine food webs can be broken down further into their chemical makeup, we will call nutrients, the base.

Nitrogen Fixation
Nitrogen fixation is one of the most important processes that occur on our planet. Nitrogen is the most abundant element in the air and it also feeds the organisms that form the base of marine ecosystems. Microorganisms convert Nitrogen into ammonium, nitrites and nitrates that can be used by plants and other organisms as food.Point being the aforementioned forms of nitrogen are now available for photosynthesis. This process happens in soil and in the ocean by a handful of organisms and it’s easy to get tangled in the seaweed trying to understand it. 

Phosphorus
Another fundamental nutrient is phosphorus. Weathering of rocks on land, releases phosphorus into rivers, which then transport this vital element to the ocean. The phosphorus then cycles the ecosystem through organisms from the simplest life forms to the largest on the planet.  It participates in a much longer cycle of sedimentation and migration over many millennia back to be weathered by rocks on land again.

Algae Blooms
Some of the world’s most biologically productive waters form near the outflows of large rivers as they meander from terrestrial watersheds into the ocean. The processes previously mentioned are increased by human activity, which can disturb the delicate balance required to maintain healthy ecosystems. These nutrients fuel photosynthetic organisms like phytoplankton which is an algae at the base of the ocean food web and produces nearly half of the atmosphere's oxygen. They only grow in surface waters up to a couple hundred meters because light cannot penetrate beyond these depths. Warm sunny seasons accelerate growth until nutrients are consumed entirely and then must be replenished. As organisms near the surface complete their life cycles, or perish, their remains, along with other organic particles, begin to sink. This descending shower of decaying organic matter, known as “marine snow”, carries with it the carbon and nutrients acquired during their growth. This is a vital part of the cycle  that contributes to transporting surface-derived nutrients deep into the ocean. These nutrients accumulate until ocean currents return them to the surface where they can fuel productivity once again. 

Upwelling
“Upwelling” is one of the main ways deep nutrients are pulled back to the surface of the ocean. Wind and strong air currents contribute greatly to this process. The massive volume of surface water that is displaced needs to be replaced with deep water because it leaves an area of low concentration, because of diffusion. Typically, it’s believed that mixing surface waters with the deep nutrient rich water is a physical process created by trade winds, storms, and tides. Another perspective considers the migrations of deep ocean organisms that (like krill who move through the water kicking their tiny legs ferociously) literally stampede to the surface every night to feed, shielded from predators by the darkness that they call home. These organisms may be incredibly small, but they undertake the greatest migration on the planet as millions of these tiny creatures create turbulence and drag water towards the surface. Specifically, Krill can proliferate in the frigid waters of Antarctica. Krill consume phytoplankton as their main source of food. Amazingly, Krill excretes waste that produces ammonium and iron which feeds phytoplankton completing a fascinating food chain. 

Looking beyond phytoplankton as the base of the marine food web, I realize the nearly unfathomable complexity and interdependence of the ecosystem. As I write this, I look out onto the Georgia Straight; below me depths nearing half a kilometer and the distance dissipates beyond a thick fog; every square inch of which is loaded with tiny living organisms. The largest animals on earth depend on these microorganisms to convert chemicals into forms available for microscopic sea plants to consume and feed the smallest animals on earth. The magic of this process is the byproduct, oxygen.