When many people think about the ocean, they picture marine life such as whales, dolphins, sharks and coral reefs. But some of the most important creatures that play a huge role in our oceans are things that we can’t even see with the naked eye. These tiny architects of marine ecosystems are single celled organisms that drive chemical cycles that sustain life across the sea. One of the most important chemical cycles the ocean has to offer is the Nitrogen cycle. This process fuels the oceans largest and smallest creatures, from primary productivity to large scale marine mammals, it influences climate on a global scale as well, and at the center of it all are microbes and foraminifera – microscopic, single celled, shelled organisms.

Why should we care about Nitrogen in our oceans? Nitrogen is a huge deal in the marine ecosystem, phytoplankton that absorb and assimilate dissolved inorganic nitrogen (like nitrate NO₃⁻ and ammonium NH₄⁺) for photosynthesis form the base of the marine ecosystem food web. Too little nitrogen, and marine productivity slows down- too much (especially along coasts), and we see problems like eutrophication and oxygen dead zones, where excess nutrients fuel harmful algal blooms and oxygen depletion.

You may be wondering how Foraminifera plays into this. Foraminifera (or for short, Forams) are single celled organisms that build calcium carbonate shells and are best known (and used, in our purposes) for their fossil record: when forams die and fall to the seafloor they become part of the sediment. Scientists study sediment cores full of forams to reconstruct past climates. But in the present, forams are more than just fossil recorders. Some species of forams host nitrogen fixing bacteria, which can convert nitrogen gas (N₂) from the water into forms usable by other organisms, like ammonium (NH₄⁺). With this they help increase local nitrogen availability while supporting the growth of plankton and other small marine organisms.

The influence of foraminifera and microbes extends even further because of the role of nitrogen in climate regulation/change, nitrogen availability affects the growth of phytoplankton which plays a crucial role in the biological carbon pump. Phytoplankton use nitrogen to grow, and as they photosynthesize they absorb carbon dioxide from the atmosphere, so when plankton die or are consumed, some of that carbon which they contain, sinks to the deep ocean. This process removes CO₂ from the atmosphere for decades to centuries, helping to regulate Earth’s climate. Phytoplankton are not the only organisms that can leave behind traces of the nitrogen cycle, forams also do something similar; their calcium carbonate shells hold nitrogen isotopes from the environment which scientists can analyze in sediment cores to reconstruct how nitrogen levels (and by because of this, marine productivity) have changed over thousands to millions of years. This microfossil record helps researchers learn about past climate events such as glacial and interglacial periods.

Taken by Hunter Strong 7/9/2025 at University of Rhode Island – Bay Campus in the GSO lab. Imaged is the Foraminifera; Orbulina universa. This foram in specific was in a sediment core taken from the Mozambique Channel (site U1474D) in 2016 by a research expedition (Exp.361) – Cruise Info: https://iodp.tamu.edu/scienceops/expeditions/southern_african_climates.html