Projects

A time-series of iron and other micronutrients at Station ALOHA

The Hawaii Ocean Time-series program travels to Station ALOHA several times a year. Since late 2020, we have been tagging along to measure how iron, manganese and other metals vary over the seasonal cycle, and how quickly these micronutrients cycle through the ocean.

Recent measurements have suggested that humans contribute a large source of iron to the atmosphere, that then falls on the ocean. Our time series observations will determine how this anthropogenic source compares to the natural processes that add iron to the oceans, such as deposition of desert dust. 

This project was started by Ph.D. student Eleanor Bates. Check out Eleanorʻs first paper - published this summer in Global Biogeochemical Cycles!

Weʻre still figure out what the fate of iron ince it enters the oceans. In 2025, we started high-resolution sampling of sinking particles across the euphotic zone to help characterize the transformation of particles as they sink. This project is a part of a bigger collaboration called SUBSEA and is led by Post-Doc Alexis Floback.

Weʻre also starting to build records t understand the iron cycle before we started measuring it. Graduate student Kalena Genesis is leading a new study using archived deep-sea sediment trap samples that go back to the 1990s.

Investigating iron limitation with cultures, models, and natural gradients

There's more iron in a drop of blood than in a ton of seawater, but life in the oceans still requires iron, and many other scarce metals, to grow.

Phytoplankton and other microbes have evolved to minimize these requirements, but no one has figured out how to replace the crucial roles of iron in photosynthesis and respiration. 

By growing key phytoplankton in the lab, we can figure out how much iron these plankton need and assess if they can survive in harsh marine environments where iron is lowest. As part of this work, postdocs Logan Tegler and Nicole Travis are working to develop new techniques to assess iron deficiency in both lab-grown and wild plankton. 

Metal micronutrients in the Southern Ocean

Ocean life in the Southern Ocean is impacted by a unique combination of micronutrients. The metal manganese (Mn) - needed for effective photosynthesis - is abundant everywhere else in the global ocean, but found only in vanishingly low concentrations in the Antarctic. Other elements that are usually scarce, like zinc (Zn), are so abundant in the Southern Ocean that they may be toxic. How have phytoplankton adapted to these unique conditions? And what limits do these elements place on a changing Southern Ocean?

As part of the GEOTRACES GP17 project, we are working to understand the distribution and bioavailability of the Zn across the Southern Ocean and its impact on phytoplankton and ocean biogeochemistry. We are using voltammetry to measure the concentration of bioavailable Zn at ocean pH levels.

We are also growing Antarctic phytoplankton in the lab, in collaboration with Natalie Cohen (Skidaway Institute of Oceanography) to find out how these plankton adapted to high Zn and low Mn.

Recently, Nick worked with Alessandro Tagliabue (U. Liverpool) and Ben Twining (Bigelow Laboratory for Ocean Sciences) to test the expected impact of low Mn and high Zn on Southern Ocean phytoplankton using a state-of-the-art ocean model. You can read the paper here.

Exploring the ocean's cobalt cycle

Of all the elements required for life, cobalt is found at the lowest concentrations in the oceans. As a result, we're still learning about its sources and sinks, and how phytoplankton acquire cobalt from seawater. 

Building off of mapping efforts conducting by the GEOTRACES program, we are expanding the coverage of cobalt measurements across the globe to identify hotspots of cobalt sources to the ocean. This project is being led by UHM Undergraduate Researcher Stephanie Briones.

Based on the repeated observation of high cobalt in low oxygen waters, Nick and researcher Rhea Foreman tracked past changes in ocean oxygen levels, using cobalt stored in marine sediments as a proxy. You can read the paper here.

Lahaina Fire Response

Our lab group has been helping to measure metal inputs to Maui's coastal waters following the devastating fire in Lahaina in 2023. We are trying our best to give communities and other groups access to our data and to help interpret the results. So far, we have seen elevated copper, zinc, and lead, mostly coming from Lahaina harbor, but the levels of these contaminants have decreased since October 2023 and appear to be below EPA thresholds used to assess ecosystem health. This work was funded by a RAPID grant from the National Science Foundation.

Here is a presentation that UHM Professor and project leader Andrea Kealoha gave back in February describing our initial results. 

Here is a short write-up in Civil Beat from last spring about the relatively low metals found since the fire.

Anyone with concerns about metals can reach out to Prof. Nick Hawco over email at hawco@hawaii.edu.

Assessing the impacts of metal inputs from ocean alkalinity enhancement on coral reefs

Rising carbon dioxide in the atmosphere is driving ocean acidification, threatening the health of coral reefs worldwide. Ocean Alkalinity Enhancement (OAE) offers a way to locally mitigate acidification while enhancing the ocean’s capacity to absorb CO2, but the impacts of metal inputs from this technology is unknown. 

At the Hawai‘i Institute of Marine Biology (HIMB), we use flow through mesocosms that draw seawater directly from Kāne‘ohe Bay, creating near natural conditions to study corals. Here, we test different OAE treatments to understand how changes in seawater chemistry affect metal concentrations in the water and metal incorporation into coral and their symbiotic algae. This will help us evaluate both the risks and potential benefits of OAE for reef ecosystems.

Protein quantification to investigate nutrient limitation

In the oligotrophic ocean, productivity is often limited by nitrogen. The surface water is well stratified, and access to nitrate in the deep water is effectively blocked. Surface microbes use recycled nitrogen (tiny amounts of ammonium) or utilize diazotrophic strategies (abundant gaseous nitrogen) to sustain growth. One particularly abundant microbe in the mixed layer at Station ALOHA is the tiny cyanobacteria, Prochlorococcus, which is classically thought to be sustained mostly by ammonium.

Yet genomic and transcriptomic information shows that Prochlorococcus has the machinery to utilize a plethora of other forms of nitrogen (e.g. amino acids, urea, nitrite). What else is Prochlorococcus using at Station ALOHA? How does this tiny microbe fulfill its nitrogen needs? 

With the potential to "choose" from multiple nitrogen forms, how many  of each type of nitrogen transporter does Prochlorococcus embed in its limited cell membrane area?