 Thank you Pat for the introduction and the systems for inviting me to talk as well as a big. Thank you to my PhD advisors Courtney Harris and Margie Friedrich at VIM as well as our collaborators for this project Katja Fennell Kevin Shue and Kristofra Buye The focus of this talk in my dissertation has been on coupling sediment transport processes specifically resuspension with biogeochemical dynamics and for this talk I'll be focusing on oxygen dynamics Oxygen is a critical component of marine ecosystems the and So the recent and recent decades the development of low oxygen areas and coastal environments has been met with a lot of resources being put in to Trying to limit the extent of these coastal hypoxic areas and so here you're looking at a Example from an online news article that showed That potted oxygen concentrations for the news or they're from Nancy Rabley's work from Lumcon And so these red areas are these low oxygen or hypoxic areas offshore of coastal Louisiana and the Mississippi Delta What's important for this talk is that these low oxygen areas develop near the seabed where sediment transport processes and resuspension can affect the biogeochemistry of the water So as an example of resuspension can affect the Vertical profiles of oxygen and nutrients in the water column which can affect their fluxes and to and out of the seabed And I'll come back to this idea later Additionally it but resuspension just by definition and trains organic matter as well as sediment into the water column and the Decomposition of this organic matter or remineralization of this organic matter can consume oxygen and then finally once the Organic matter is entrained into the water column. It can be transported around the system by currents And so this can cause spatial and temporal variability in oxygen dynamics As an example here, you're looking at observations from the Gironde estuary in France You're looking at a scatterplot of oxygen concentrations on the y-axis and suspended particulate matter concentrations on the x-axis And what you can see is that when you have these higher concentrations of suspended particulate matter you're getting a depletion of oxygen at this location in the estuary and the authors attribute part of this depletion to the Respension and transport of organic matter and the associated decomposition of that organic matter in the water column However, using point observations which are limited due to cost and technology constraints It can be hard to pull apart the relative roles of physical processes like resuspension From the role of biogeochemical processes like decomposition And so this motivates the development of a numerical modeling approach that can account for some of these processes and Previous modeling efforts have focused on Hydrodynamic coupling hydrodynamic models with sediment transport models. Here's an example I'm showing Rob Hellins model from the Gulf of Mexico as well as Kevin shoes model from the same location and They've previous efforts have also focused on hydrodynamic models being coupled to water combine geochemistry models And both of these types of models are well represented in the literature For these These water column by geochemistry models, although I'm showing a picture of chlorophyll here for the Gulf of Mexico they also are used to predict and Analyze oxygen dynamics However, and when they do incorporate seabed or sediment transport processes They typically do so as a bottom boundary condition for the model So that's the seabed water interface and they're typically based on relatively simple parameterizations and This can affect the model results for example in the Gulf of Mexico This can affect your estimates of hypoxic area by up to a hundred percent and other environments have also been to Shown to be affected by how you parametrize the seabed by geochemical processes at that seabed water interface And so this uncertainty further motivates the development of a model that can account for both sediment transport processes like the suspension as well as biogeochemical processes now for my Dissertation we started with a hydrodynamic model that ROMs or the regional ocean modeling system Which is well used within the research community. It's open source and community developed and Which is it's previously been coupled to the CSTMS Sediment transport model, which is also well used as well as water column by geochemistry models including the For this work in order to couple the biogeochemical and sediment transport processes We did this by adding a seabed biogeochemistry component based on the soda soda biogeochemistry model and this allowed us To account for processes including not only the deposition of organic matter to the seabed But also the storage of organic matter in the seabed and subsequent erosion back into the water column Depending on the hydrodynamic conditions of the environment Additionally once this organic matter could was reentrained into the water column it could be transported around the system based on the current Additionally by accounting by explicitly modeling the vertical profiles of Oxygen and nutrients throughout the water column as well as the seabed. We could account for seabed of oxy fluxes of oxygen through the seabed water interface and a more process-based approach and Additionally by incorporating the soda seabed biogeochemistry module. We could account for the This decomposition of organic matter in the seabed as well as other biogeochemical reactions And if you're interested in more about the model, this was just published in biogeosciences this year Okay, so for the remainder of the talk, I'm going to give you two examples of model implementations the first example it focuses on a location offshore of the Roan delta in France and so here the Roan River flows through France into the Gulf of Lyons in the Mediterranean Sea and Specifically we chose this particular location because of this fantastic observational data set Sub millimeter scale observations are really great data set and we work for this and we work The observations came from crystal Frabya's group at CNRS in France And I'll come back to that in a second, but So for this site we implemented a one-dimensional vertical model to represent their study location I'm going to show you a movie of the model results so you can get a feeling of how the model works and so And so here what I'm going to show you is you're looking at three profiles of seabed organic matter on the left nitrogen concentrations in the middle and oxygen concentrations on the right-hand side and In all three profiles this black dashed line at the surface indicates the seabed water interface And so you'll see it move up and down in response to cycles of erosion and deposition And then finally on this bottom panel, you're looking at a time series of bed stress And so you're specifically want to note these three periods of large wave-induced bed stresses that will resuspend one to two centimeters of sediment in organic matter and so And so again as we go through these periods of erosion and deposition you'll you can see the profiles translate up and down and you can also see some Changes in the by the shape of the biogeochemical profiles and styles However, what you're going to notice for oxygen is that it's really hard to see these changes especially if they're small on small facial scales compared to the cycles of erosion and deposition So to look at these a bit closer And so this was the question one Can we represent these gradients and oxygen and the changes in the profiles? But also to what does that mean for oxygen dynamics? And so here to answer the first question is we plotted the model estimates of oxygen concentration In blue and then these really fine scale sub millimeter scale observations in red and Here I'm plotting results for two time periods for a quiescent period And then comparing that to a wrote an erosional period and what you're going to notice is that the In both cases the oxygen concentrations decrease as you go from the water column into the seabed and Then however, there's when you compared to the quiescent period the erosional time period It has a sharper gradient of oxygen at the seabed water interface. And so this occurs because the Here is a little schematic showing Before erosion you have an oxyc water column which is on top of the thin oxyc layer of the seabed Which overlies the anoxic portion of the seabed and so when you have a resuspension event you're in training that oxyc and suboxy Seabed into the water column which results in the anoxic portion of seabed being much closer to the oxyc water column increasing the diffusive gradient into the seabed and because of this Change in profile. Sorry, you increase the diffusive flux of oxygen into the seabed because there's a higher gradient of oxygen at that interface and in summary this matters because it's essentially increasing the sink of oxygen from that bottom water column where we care about the oxygen concentration and so Resuspensions essentially in is increasing the sink of oxygen from that bottom water column Now we're going to move from the seabed back into the water column and specifically I'm going to focus on the role of resuspended organic matter and how that affects oxygen dynamics there And so for this we implemented the couple or we implemented the model for the northern Gulf of Mexico So we started with previously published models from our colleagues Rob Hetlin's group at Texas A&M Sediment transport model that had previously been coupled to Rob's model from Kevin Chu at LSU as well as the What water column biogeochemistry model from Katja Fennel's group that I'd also previously been coupled to Rob's model And so for this project we implemented the model coupling which I talked about earlier Based on parameters from the one-dimensional seabed model from morons at all 2016 And then for the next couple of slides I'll be talking about results from Transacts offshore of the Chafalaya Bay. So here for those of you who aren't familiar with the Mississippi Delta and northern Gulf of Mexico. You have the Mississippi River which flows down this the Delta and into the Gulf of Mexico and then you also have a distributary that comes down the Chafalaya River into the Chafalaya Bay and And enters the Gulf of Mexico then So again, I'm going to show you a movie so you can get an idea about of the results So here what you're looking at is you're looking at transects offshore of the Chafalaya Bay So time out. Oh Okay, one minute So you're looking at transects offshore of a Chafalaya Bay where you're getting high concentrations of organic matter Near the seabed and that correlate Sorry here you're looking at oxygen concentration oxygen consumption due to the decomposition of that organic matter and then on the bottom you're going to see oxygen concentrations and Anywhere where you see these dark red colors you Indicating where hypoxia or these low oxygen areas are developing and so what you can see is that you're getting Episodically high concentrations due to resubstantion of organic matter and oxygen consumption and this somewhat correlates with decreases in oxygen concentration However to look at this in a little bit Without all the variability in the model run we're I'm going to show you time average results And so here what you're looking at is estimates on the left From the standard model run and then on the right hand side We're comparing the standard model run that included resubstantion with a sensitivity test without resubstantion And so the difference in those two model run gives you an estimate of the change In in this case organic matter due to resubstantion And so what these profiles are showing you is that you're getting higher organic matter concentrations near the seabed and much of that change is due to resubstantion and then Looking at the composition rate in addition to this area offshore You're getting a high Composition rates near the seabed where you're getting resubstantion organic matter And then this correlates with a decrease in oxygen consumption in these shallow environments And so finally I'm just to look at this these results one other way is we're looking at a map of oxygen Or sorry, we're looking at a map of the results instead of a transect and you can see this similar pattern So again, the standard model estimates are on the left and the change due to resubstantion is on the right and in areas where you're getting High organic matter concentrations much of which is due to resubstantion You're getting higher rates of decomposition and lower rates of oxygen Especially lower concentrations of oxygen, especially in these near shore areas And downstream with RiverMouse where you have a lot of organic matter being resubstant And so in conclusion we've developed a couple sediment transport by a geochemical model for coastal marine environments that was implemented for the Rhone Delta as well as the northern Gulf of Mexico the overall we Estimated that resubstantion increased fluxes of oxygen into the seabed and also increased the consumption of oxygen within that bottom layer of the Water column and then ongoing work includes implementing the model for the Chesapeake Bay and looking at the effects of light Attenuation in addition to the decomposition of organic matter. Thank you. Thank you, Julia okay, so moving on we will have a Short break a short break and but I want to go over a couple of things because when you come back You're not going to come back to this room You're going to