Award: OCE-1842012

Kilauea Volcano on the island of Hawaii is one of the most active volcanoes on Earth. In May 2018, there was an explosive summit eruption and by early June, molten lava from the lower East Rift Zone inundated the town of Kapoho and entered the ocean. This rare event in the geologic history of the Hawaiian Islands presented a unique opportunity to investigate hydrothermal processes near the seawater-lava contact zone and to evaluate the impacts of volcanic aerosol and ash deposition on surrounding marine ecosystems. We mounted a 5-day oceanographic expedition in early July to investigate the lava-impacted zone, where remote satellite images predicted the presence of a large plume of phytoplankton (microscopic plants that produce food for the entire ocean ecosystem). A major goal of our expedition was to better understand how the lava flowing into the sea could fuel the growth of these phytoplankton. Initially, we hypothesized that the lava was supplying essential nutrients like iron and phosphorus to phytoplankton. However, lava is not known to contain another key nutrient essential for phytoplankton growth ? nitrogen. So we also proposed that a group of specialized microorganisms that can use atmospheric nitrogen gas might also be stimulated by lava nutrients, and thereby provide additional nitrogen necessary for phytoplankton growth. Once on site, we discovered that the nitrogen-gas-utilizing microbes were in very low abundance and the phytoplankton that were present appeared to be using nitrate, which is present in limiting concentrations in the ocean around Hawaii. Where was the nitrate coming from? Our results pointed to an unexpected source of nutrients ? the deep sea. Lava entering the coastal region quickly moved downslope into the deep waters that surround the island. The hot lava produced large buoyant plumes that moved nitrate- and phosphate-rich deep waters to the surface where they could be used for phytoplankton growth, with carbon and energy passed up to higher trophic levels, including fish. This previously unknown pathway to enhance photosynthesis in nutrient-poor environments served as a stimulus to conduct additional laboratory studies of lava-seawater interactions including geochemical studies of trace elements such as iron, nickel, copper, and zinc. Our scientific results provide new insight into how major geological events like volcanic eruptions, can influence, even stimulate, phytoplankton growth and production in ocean ecosystems. Our results captured considerable interest, and were widely distributed to the public via news articles, blogs, tweets, and numerous interviews that were conducted by expedition participants. Last Modified: 08/14/2020 Submitted by: David M Karl