Category Archives: Blog

Mesophotic reefs at the Amazon River mouth: an inconvenient truth

Did you know that there’s a reef near the mouth of the Amazon River?

Reefs off the Amazon River mouth at ~180 m depth, close to the Brazil-French Guiana border. They’re, thriving from abundant nutrients but with less light and more suspended sediment.

Our group has recently been involved in the study of the mesophotic reefs that are at the outer shelf where the Amazon River discharges into the Atlantic Ocean. Mesophotic means that the reef is composed of organisms that use photosynthesis to grow and organisms that don’t need light to grow.

Although evidence of a reef system in the region has been presented since the ‘70s, a simplistic view remained that the Amazon River plume prevented reef development. The existence of this reef system is now incontestable, due to results from scientific cruises performed in cooperation with the Brazilian Navy in 2014 and 2017, as well as with Greenpeace, in 2017 and 2018.

The  area is also facing potential threat from new oil & gas exploration, resulting in conflicting interests between environmental conservation and exploration of natural resources. Although oil companies themselves recognize the reef existence and its relevance, there have been unscrupulous people trying to convince the authorities and general public that the reef does not even exist (aka fake news).

Our mission is to better understand this reef system and how it survives so close to the Amazon River plume. The plume carries much suspended sediment, which decreases the light reaching the sea bed. We are working to understand the dynamics of suspended sediments of the Amazon River and the sedimentary and oceanographic mechanisms that enable this reef system to exist.

The Brazilian branch of the Sediment Dynamics Group

Nils and family at Drumheller Fountain, UW-Seattle

Nils outside the UFPA campus in Braganca.

 

 

 

 

 

 

 

Nils and his family have returned to Bragança, but they’re keeping in touch! Here’s his news on settling back into life and work in Brazil:

After spending one very pleasant and fruitful year at UW-Seattle, I’m back home in Bragança, Brazil where I work at the UFPA campus. Right now, the challenges for science are bigger than ever in Brazil, but the scientific tools I brought from UW are really helping me through. One major challenge is the drastic decrease in public funding for research for all disciplines and levels. I’m overcoming this impediment by taking advantage of all the data collected along the lower Amazon River, Tapajós and Xingu tributaries, as well as along the Brazilian Amazon mangrove belt and at the Amazon shelf. All this data is a result of large cooperative fieldwork efforts during the last five years. This backlog assures us long hours of data analysis at the lab and even more time trying to understand and publish the results. We have been making good progress so far, with the recent publication of papers in journals such as Estuarine, Coastal and Shelf Science; Earth Surface, Processes and Landforms; and Geochimica et Cosmochimica Acta. Several papers are under review as well and are coming out soon.

Stay tuned to our blog to hear more from Nils and get notifications for his upcoming publications!

Recent field work in Myanmar

The lab just finished a short, two-week trip to Myanmar. The primary goal of this trip was to discuss research with our Burmese colleagues. We participated in a conference at Yangon University, where we also heard presentations from American colleagues who have been working in the Gulf of Martaban.

Aaron preparing to discuss results with collaborators from VIMS and Yangon University

Next we presented our results at Pathein University, where we also led a data processing workshop and a short research trip on the Pathein River.

Filtering water samples doesn’t have to be boring!

We also managed to fit in two days of field work on the Yangon River with Myanmar Maritime University. During the winter period of dry weather, the river discharge decreases, and the amount of sediment in the water increases. During our previous trip, in March 2018, we measured as much as 15 grams of sediment per liter and our acoustic instruments didn’t work! This time, we came prepared for very high sediment concentrations. We were able to track the high concentrations during a full tidal cycle and also measure the river discharge. It’s very exciting to see such an extreme riverine environment!

Large vessels using the Yangon River. This one parked in the middle of our sampling location.

Improvised raft for measuring water flow.

Our Yangon River crew

Heading to the AGU Fall Meeting

It’s conference season again, and our lab is headed to Washington D.C. to meet and mingle with other scientists and students. Here is what we will be chatting about this time.

First up, our recent research in the Ayeyarwady Delta:

Andrea’s poster: Sedimentary Processes in the Tidal River to Estuarine Reach of the Ayeyarwady Delta (EP13C-2114)

Monday, 13:40 – 18:00 

Walter E Washington Convention Center Hall A-C (Poster Hall)

As the Ayeyarwady River approaches the Andaman Sea, it splits into multiple delta distributary channels, which together discharge >108 t/y of sediment. This study aims to understand: sediment retention and geomorphic variability through the lower distributaries, deltaic growth along mangrove shorelines, and sediment export to the coastal ocean.

Aaron’s Poster: Temporal variability in suspended-sediment dynamics within three distributaries of the Ayeyarwady Delta, Myanmar (EP13C-2113)

Monday, 13:40 – 18:00 

Walter E Washington Convention Center Hall A-C (Poster Hall)

The Ayeyarwady River is one of the largest sources of sediment to the global ocean. However, little is known about the timing, character, or routing of that sediment within the large Ayeyarwady Delta, which is building into the northern Andaman Sea. This study examines how the suspended loads of these distributaries vary spatially (along and between distributaries) and temporally (decennially, seasonally, fortnightly) using in-situ and remote-sensing approaches.

Later that afternoon, our recent research in Brazilian tidal channels:

Robin’s Talk: The Impacts of Channel Connectivity on Tidally-Driven Sediment Transport and Accumulation in a Mangrove Forest (OS14B-03)

Monday, 16:30 – 16:45

Walter E Washington Convention Center – 103AB

Mangrove forests provide many valuable ecosystem services, including wave- and tidal-energy dissipation, sediment accumulation, and substrate stabilization. But, their global extent is rapidly shrinking. Sediment cores and in-situ observations of water and sediment flux were obtained in two tidal channels near the Amazon River mouth to characterize how connectivity impacts tidally-driven sediment transport and accumulation in coastal mangrove forests.

Wrapping up our presentations, our research on the Elwha nearshore:

Hannah’s Talk: Nearshore benthic light attenuation due to sediment transport following dam removal on the Elwha River, WA: In-situ observations and statistical modeling (OS21B-08)

Tuesday, 09:45 – 10:00

Walter E Washington Convention Center – 103AB

The 2011–2014 removal of two dams from the Elwha River, WA provided an opportunity to study the sensitivity of a coastal ecosystem to a large-scale sediment input event. During the dam removal, >10 Mt of sediment was exported to the marine environment. Macroalgae, the primary habitat-forming species in the nearshore, disappeared from the region. Models were created to hindcast to light availability during the dam removal. Benthic light availability was found to be below the threshold for macroalgae growth, supporting the hypothesis that reduced light availability caused the mortality event.

Ocean Networks Canada Workshop: Seafloor collapse and submarine canyons

This month Ocean Networks Canada held a workshop in Victoria, BC focused on the “seabed and sediment in motion” at their observatory sites. They have cabled instruments on the seafloor that continually send data back to shore. The workshop focused on studies at two contrasting focus sites, one on the Fraser River delta, and the other in Barkley Canyon on the continental margin. Submarine canyons are dramatic features of continental margins throughout the world. They can be many kilometers deep and cut far into the shelf, like a Grand Canyon deep underwater. These canyons are hotspots of biological activity as well as conduits for sediment, nutrients, chemicals, and trash. Andrea Ogston attended the workshop to present collaborative research from Barkley Canyon and hear results from colleagues.

Map of a few of the instrumented ONC observatory sites in Barkley Canyon. Our margin off the west coast of the US/Canada is incised by numerous submarine canyons.

On the Fraser Delta, frequent mass failures of the seafloor and energetic gravity flows pose potential problems for the coastal port structures.  Dr. Gwyn Lintern, PGC, showed a dramatic data set from sensors that tumbled in a bottom flow recording velocities of 6-8 m/s, and eventually disconnected and disappeared!  In contrast, Barkley Canyon located off the coast of Vancouver Island has a very limited source of sediment at present, and dynamics are not as dramatic. However, Andrea Ogston showed two modes of particulate transport at ~1000 m water depth within the canyon axis:  1) relatively dense fine particles move down the canyon, carried by residual currents, and are at times pumped back up-canyon by tides, and 2) loose, fluffy phytodetritus (chunks of tiny organisms) from the surface ocean are mixed down into the canyon and during winter downwelling periods can be rapidly transferred to the deep ocean.  This winter process has the potential of adding significantly to the biological pump (which transports carbon to the deep sea). If you’re interested in reading more, check out Thomsen et al., 2017.

After a presentation and discussion of what can be done with the existing data on the Oceans Network Canada observatories, the workshop turned to needs and wants that could enable the next steps in the scientific discovery using the observatory data streams.  New, updated sensors and a reconfiguration of Barkley Canyon’s sensor array will be upcoming and will allow the scientific community to further explore the importance of the wintertime delivery of carbon to the deep sea.  Stay tuned for more on this exciting discovery!

Victoria BC at night during the ONC Seabed and Sediment in Motion Workshop

Show and Tell

People in earth science spend a lot of time thinking about the places we study. We work to understand how this mysterious place functions: we read papers, crunch equations, and scroll into satellite imagery. And then, with a van full of gear and a new set of questions, we drive until we find ourselves standing in that very place. It can be a powerful moment, and no one knows the feeling better than seasoned scientists. Chuck and Dave (both seasoned) are teaching a course this term, Rivers and Beaches, focused on giving students that duality. The class begins in a lecture hall, but students are soon out on field trips to the mountains, rivers, and beaches of the beautiful pacific northwest.

Students in this year’s class have now stayed up into the small hours of the night studying geology and oceanography for their midterm exam (today!), but they have also seen and touched these places. Last month, we traveled the length of the Nisqually river from its glacial headwaters to its salty estuary, tracking its transformation from rocky braided channels to gentle downstream meanders. Last week, the students were on a cruise of Puget Sound, testing classroom concepts by lowering CTD rosettes into the water and winching kasten cores out of the Sound’s muddy bed. Textbooks cannot offer the intuition and appreciation for these places and phenomena; building stronger students requires we show them, not simply tell.

It’s too early to tell who in the class will major in a geoscience, but we have one more trip to convince them, amongst the foggy mountains and sandy spits of the Olympic peninsula.

Dave and Chuck on the Nisqually river.

Dave discusses the consequences of a dam along the Nisqually river.

Hustle and bustle as students touch a Shipek sediment sample taken by the R/V Carson.

Observing texture on a 15×180 cm kasten core taken from Puget Sound (core bottom in the foreground).

Marine Sedimentary Processes Apprentices in the field

The Marine Sedimentary Processes Apprenticeship just finished a 5-day, field work marathon at the Elwha River! The MSP is an intensive, research-based class for undergraduate students focused on the evolution of the Elwha River following dam removal. Students take charge of a research question, collect data, and write a scientific paper from their results. They live at the Friday Harbor Labs and only take this class; it is an immersive experience.

This year students are investigating both the beach and the ocean near the mouth of the river. It’s incredible to be able to observe the evolution of this region since the dam removal. We used the brand new RV Carson to sample both the water and the seabed near the river.  After two days on the Carson, we moved on to the beach. We collected sediment from lagoons and sand dunes, and walked tens of miles to track the locations of logs on the beach.

The sun was shining the whole week making long field days fly by. Now it’s time to clean up, sleep, and get ready to process all of the data!

Anna and Hannah collect mud from a van veen with help from Carson crew members Loren and Tim

Liesl decked out in gear for sample collection

Brittney and Liesl collecting sediment cores in a lagoon

Students enjoying a sunny lunch on the beach

 

 

 

 

 

 

Students at the site of the former Elwha Dam

Hello, Goodbye!

This September is a bittersweet time for the Sed Lab. Nils’ sabbatical is coming to an end. He and his family will return to Brazil at the end of the month. At the same time, Andrea and Hannah will head to Friday Harbor Labs to teach the biannual Marine Sedimentary Processes Research Apprenticeship for the fall. But it’s not all goodbyes, we are also welcoming Evan, a new graduate student! Evan is joining us after finishing his BA at Carleton College (check out his bio on the freshly updated People Page). He will be diving straight into lab work with Aaron, processing samples from the Ayeyarwady.

Stay tuned this fall to hear more from Nils as he continues to publish papers, from Chuck and Evan as they teach Rivers and Beaches, and from Andrea and Hannah in Friday Harbor as they guide students through research projects investigating the Elwha River.

The Sed Lab gathered on Nils’ porch this week for lab meeting.

 

Family Heirlooms in the Sediment Dynamics Lab

When you join academia, you join a family. Just like all other families, we have family heirlooms that get tucked away and rediscovered by younger generations. Stories are passed down, old photos are dug up, and memories are shared. Just a couple weeks ago, our lab group reorganized our shipping container that was packed full of old instruments. Tucked away in the back in an old wooden crate, we found some treasures – an old metal main brain and one of the earliest (dare we say world’s first?) nepholometers.

The main brain as it sits today. 

Dick Sternberg is my academic grandfather, my adviser’s adviser. He is a leader in the field of coastal sediment dynamics and pioneered studying the ocean with tripods – three legged metal frames that are outfitted with scientific instruments and deployed on the ocean floor. Back in the early 1970’s, his tripod was named R2D2.

Photograph of Dick’s tripod R2D2 (c. 1973) designed for remote operation on the continental shelf.

R2D2 spent many long days out on Washington’s continental shelf recording water temperature, pressure, salinity, turbidity, and even video. This tripod was a creature with a single brain – that central sphere in the photograph above was the main brain. The power supply for all of the instruments was in there; the camera was connected there; all of the data were logged on magnetic tape in there. The nepholometer we found is the big blue instrument strapped to the bottom of R2D2; it used to measure water turbidity.

Nowadays, our instruments are more sophisticated. They are smaller, smarter, and more powerful. Many of them can fit in the palm of your hand. They all have their own power supplies and data loggers. Gone are the days of one creature with a single brain. The tripods we use now are more like a community. Each instrument is self-sufficient, many with more power and memory than the entirety of R2D2. I wonder what students will think of them in a few decades when they are found tucked away in an old storage container for safe keeping.

Tripod deployed on the Eel River Shelf from 1995 – 2000.

Tripod deployed offshore the Elwha River beginning around 2010.

We also found boxes and boxes and boxes of bottom drifters stored in that old container. They were very simple, just bright pink plastic disks. These drifters were designed to track water currents near the seabed. Metal clamps would be added to the drifters until they were neutrally buoyant. After being deployed, the drifters would hover in the water column and drift wherever the current took them. Hours, days, weeks, even years would go by. Eventually, the drifters would wash up on a beach. Hopefully, a curious passerby would see the brightly colored drifter, pick it up, and call in to report their location – many drifters were labelled with contact information and advertised a $0.25 reward. These old drifters pale in comparison to our new instruments with GPS, buoyancy control, and velocity loggers. Still, they hold the title of adventure and suspense.

Research in the Caete Estuary

Offshore mud sources and mangrove development on the coast east of the Amazon River mouth

UFPA (Universidade Federal do Pará) and UW are collaborating on a project to study the tide-dominated estuaries and extensive mangrove plains east of the Amazon River mouth. In a recently submitted manuscript, we examined the Caeté estuary to understand how the longest mangrove belt in the world was built by rivers which don’t supply much mud to the coast. Instead, the Amazon river plume and its shelf deposits are the likely sources of mud to the Caeté and nearby estuaries.

Nils deploying equipment in a mangrove forest in the Caeté estuary.

In the Caeté, complex dynamics in suspended sediment concentrations are related to superimposed variations in rainfall and local fluvial discharge (landward end) and seasonal dynamics of the shelf (seaward end). During the dry season and transitional periods, the estuary is importing mud from the shelf. Tidal processes result in sediment accretion on mangrove mud-flats. During the rainy season, rainfall-related runoff and fluvial discharge increase. Suspended sediment is transported to the lower estuary, where flooded barrier-island trap sediment in a newly-formed back-barrier environment. Our results reinforce the concept that sediment-transport convergence and turbidity maxima are distinctive features of tide-dominated estuaries, and these features result in sediment entrapment. For tropical coasts, sediment trapped by the ETM can be buried in adjacent mangrove forests. Our results may also show that local fluvial sediment sources are of secondary relevance compared to offshore sources.