Snow in the Gulf of Mexico

Funnel shaped sediment traps like this one are suspended just above the seafloor and left to collect deposits for several weeks at a time before being moved to a new location. Once retrieved (after a year or so) the collected sediments are subjected to biochemical analysis to provide a good view of what sank and when. Photo Credit: Uta Passow, UCSB.

Funnel shaped sediment traps like this one are suspended just above the seafloor and left to collect deposits for several weeks at a time before being moved to a new location. Once retrieved (after a year or so) the collected sediments are subjected to biochemical analysis to provide a good view of what sank and when. Photo Credit: Uta Passow, UCSB.

(From Winter 2015 Newsletter) It may not happen too often on land, but beneath the surface of the ocean, it’s a whole different story. As plants and animals living near the ocean’s surface die, they decay and fall to the seafloor in a natural phenomenon known as marine snow, which gets its name because the decaying material can look like fluffy white snowflakes as it drops. The formation and fall of marine snow is a common process in the Earth’s oceans and provides food for many deep-sea creatures who consume the decaying organic material on its way to the ocean floors and after it has settled. The amount of marine snow that makes it to the seafloor depends on a number of factors, but on average only 1-10% of the material formed at the top of the water column ends up on the bottom of the ocean without being consumed in shallower water. This sediment accumulates over millions of years into a layer of thick, muddy “ooze” that covers the ocean floor.

Researchers in the GoMRI program have been studying the effect of the Deepwater Horizon (DWH) event on the formulation and sedimentation of marine snow in the Gulf of Mexico for years. The Gulf of Mexico system is unique in that oil seeps are a common natural occurrence in the region and the system biota has already adapted to respond to small amounts of oil in the water column. However, a large, prolonged, release of oil such as the one associated with the DWH event has never been seen before and provides much area for further study. Dr. Uta Passow, a researcher at the University of California, Santa Barbara studies the formation and sedimentation of marine snow in the water column and serves as steering committee chair for a GoMRI funded inter-consortia working group on the topic. According to Dr. Passow, while initially many members of the general public and oil spill responders may only have been thinking of the spilled oil as “going up” through the water column and dispersing across the surface of the ocean, soon after the spill “people began realizing that a huge sedimentation event was also observed” and that it deserved scientific attention.

Dr. Passow uses sediment traps to determine several key characteristics of marine snow and oil aggregates. However, it was quickly realized that her trap work was only one piece of the puzzle. Other GoMRI researchers were focusing on marine oil snow through different perspectives, including experimental work and in situ observations. Thus, Dr. Passow and her colleagues, Dr. Jeff Chanton (FSU), Dr. Kendra Daily (USF) and Dr. David Hollander (USF) began working together to ensure that they were achieving a holistic picture of the rapidly sinking, marine oil snow sedimentation event that was observed after the spill. The first step, Dr. Passow states, was tackling the challenge of varying terminology across the different research disciplines.

“[The] first thing we noticed was that we have different terminology. I work with the water column and sediment traps, and marine snow is something which has been around for a very long time. Not associated with oil, but marine snow is a term which we all know and [the term] is characterized. We know a lot about marine snow. The people working on the seafloor, they call things floc, flocculent materials… and floc for me has a totally different meaning. [For me] floc is a special kind of marine snow, not just material that lands on the seafloor… That’s when we came up with this name.”

The name they developed to reconcile the well-established terminology in their respective fields, Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) was originally intended simply to be the name of their inter- consortia working group, but has come to characterize all studies on the processes involved with marine snow and its accumulation at the seafloor in relation to oil spills and various mitigation measures (e.g. the use of dispersants and in situ burning).

In October of 2013, researchers from six GoMRI consortia along with a number of experts not currently involved in GoMRI-funded research met in a collaborative MOSSFA workshop. The overarching goal of this workshop was threefold: to raise awareness of MOSSFA within the research and oil spill response community, to develop and discuss related concepts and plans for future research, and to forge connections between interested parties. Their discussion centered on several of the key questions involved in MOSSFA research such as: What is the extent of the oiled sediment layer? How does the presence of large amounts of oil and nutrient rich river sediments influence the formation of marine snow? Do common oil spill mitigation activities influence marine snow formation? And, what are the effects of the oiled sediments on deep water environments? Through two days of discussion and breakout groups, the MOSSFA researchers were able to begin answering these questions and identify areas where further information and research is needed.

The great success of the workshop can be measured by the numerous collaborations and sub-groups that have developed and continue to work together long after its close. “As a result of the workshop… people found each other and topics which need to be moved forward, and began working on them together,” Passow states. For example, Passow herself has been joining in on discussions with other organizations who are using sediment traps for research in the Gulf, including Woods Hole Oceanographic Institute and the US Geological Survey. This coordination is worthwhile, as the locations and timing of the traps differ from one study to the next. Their collective data can be used to broaden the overall understanding of the extent and thickness of the oil sediment layer, as well as inform sedimentation rates at varying distances from the DWH site.

Another important relationship formed from the workshop is collaboration between MOSSFA scientists and National Oceanographic and Atmospheric Administration (NOAA) modelers. It is widely believed among MOSSFA scientists that anywhere from 3-25% of the oil released during the spill was deposited on the seafloor as a result of marine snow sedimentation; however, this pathway was not considered in response strategies and is not included in the oil budget calculator for the DWH spill. GoMRI scientists have been in talks with Bill Lehr, a senior scientist at NOAA, discussing what information modelers would need to enable the integration of sedimentation into their models. In addition, during the 2014 Gulf of Mexico Oil Spill and Ecosystem Science Conference, a Town Hall event was held in which GoMRI scientists met with oil spill responders from NOAA and the US Coast Guard. They addressed ways that the MOSSFA theory could be included when using numerical models to predict the effects of spill response measures on the fate of spilled oil and to discuss the potential long- term contamination of benthic habitats and its impact on important benthic dependent fish species.

MOSSFA research continues to be an area of strong interest for GoMRI scientists, with researchers from multiple consortia involved in the work. Plans are underway for another inter-consortia workshop in the future and related publications are increasing in number, with several expected to be included in an upcoming issue of Deep Sea Research II (Discussed in more depth in this issue’s Notes from the Research Board Chair on Page 5). Dr. Passow summarizes the importance of their combined efforts well. “The impact of the oil on the open ocean ecosystem when it is disbursed and diluted at the top of the water column is very different from the impacts it has when it sinks and accumulates on the seafloor… We need to know where the oil is to learn how to keep the damage to a minimum for the whole ecosystem, and for that we need to understand all of the pathways involved” and those certainly include MOSSFA.

[Back to the Winter 2015 Newsletter]