The Seasonality of Physically Driven Export at Submesoscales in the Northeast Atlantic Ocean

Submesoscale dynamics O(1–100 km) are associated with enhanced vertical velocities and evolve on a time scale similar to that of biological production (hours to days). Here we consider an annual cycle of submesoscale dynamics and their relation to productivity and export in a small (20 × 20 km) region of the northeast Atlantic Ocean. In this region, a springtime bloom is initiated by restratification of the mixed layer in June, although intermittent shoaling of the mixed layer maintains phytoplankton populations throughout the year. An optical community index suggests a dominance of large species (e.g., diatoms) during spring and picophytoplankton during the winter. We review three types of submesoscale instabilities—mixed layer (baroclinic), gravitational, and symmetric—and consider the impact of each on export of fixed carbon out of the surface layer. Mixed layer instabilities can potentially export material out of the mixed layer during winter, although the vertical velocity across the base of the mixed layer is sensitive to the parameterization scheme. Symmetric instabilities, in contrast, provide a clear mechanism for rapid export out of the mixed layer. A crucial factor determining export potential is the strength of the pycnocline at the base of the mixed layer. Export production is sensitive to the degree of overlap that exists between intense submesoscale activity associated with deep mixed layers in the winter and high productivity associated with the spring restratification, meaning that physically driven export of fixed carbon will likely happen over a short time window during spring

Remote Sensing of Diatom Bloom Succession

Marine diatoms are major biogeochemical and ecological influencers that contribute to a large fraction of the carbon export and supplying fisheries (Falkowski 2015). The fluxes of carbon transfer to the food web or to the deep ocean vary according to the stage of a diatom bloom (Du Toit 2018). Stages can be determined using inherent optical properties that reflect their physiological state, such as the chlorophyll fluorescence to particulate backscattering ratio (ChlF/b(sub bp), Cetinic et al. 2015). Identifying the bloom stage can potentially improve biogeochemical models of carbon export and fishery management. However, it is not yet possible to adequately determine the stage of phytoplankton blooms using satellites. Satellite-derived remote sensing reflectance R(sub rs)() allow for remote identification of diatom blooms in the open ocean (Sathyendranath et al. 2004), and there are techniques to estimate the fluorescence quantum yield () that, when high, can indicate the nutrient limitation that often takes place when blooms start to senesce (Behrenfeld et al. 2009). The goal of this study is to use the ratio between the normalized fluorescence line height from R(sub rs)() (nFLH) and the particulate backscattering (b(sub bp)(443)) provided by satellites to identify exponentially growing and senescent diatom blooms from space

Physical Processes Leading to Export of Fixed Carbon Out of the Surface Ocean

The ocean sequesters carbon on long time scales by depositing it deep in the ocean, where it is no longer in contact with the atmosphere. This sequestration is also termed "carbon export", and is accomplished via a vertical flux of carbon into the interior of the ocean. Marine photosynthesis by phytoplankton, which consume carbon dioxide dissolved in the surface ocean and are transported to depth to be eventually remineralized or form sediments at the ocean surface, is a key component of this flux (the biological pump). This mechanism is primarily thought to occur via sinking of particulates. However, research over the past few decades has highlighted the role of instabilities at the "submesoscale", or 0.1--20 km, to induce large, O(100 m day-1) vertical velocities in the ocean. These vertical velocities can potentially subduct carbon from the surface ocean into the interior, where it would contribute to export. Observations of the ocean are, however, rarely made at scales which would detect these submesoscale instabilities. In this thesis, I use in situ observations from autonomous underwater vehicles, Seagliders, which make measurements in the upper 1000 m of the water column at horizontal scales of 1-3 km, to understand when and where submesoscale instabilities are present, and the extent to which they act to transport biologically fixed carbon out of the surface ocean. Three different types of instabilities are active in the surface mixed layer: baroclinic, gravitational, and symmetric. Each of these has potential to subduct material below the mixed layer; however, these instabilities are generally strongest during the winter, when biological production is at its minimum. An interesting exception is in southern Drake Passage, where interactions between the intense frontal system and the continental shelf result in subduction of water masses off the continental shelf during summer, when phytoplankton are photosynthesizing. In general, however, carbon export via submesoscale instabilities is expected to be largest during spring, when phytoplankton become more productive but conditions can still be ripe for submesoscale subduction. Scaling up these observations to the global ocean system is difficult because in situ observations at submesoscales are sparse. This thesis explores the ability of surface flux measurements, from reanalysis products and remote sensing measurements, to accurately depict carbon export via subduction processes by modeling the water profile in a one-dimensional model following Lagrangian floats in the ocean. This approach holds promise to advance the ultimate goal of determining the global effect of submesoscale-driven carbon export

Carbon Export Through Submesoscale instabilities: Combining in Situ and Satellite Products

No abstract availabl

Effects of Supplemental SoyPass in Forage-Based Diets Containing Distillers Grains on Performance of Growing Steers

SoyPass was supplemented in two grass hay diets containing 20% or 35% wet distillers grains with solubles (WDGS) to analyze the effects on growing cattle performance. The SoyPass supplement replaced 0, 30, or 60% of dietary WDGS for a total of 6 treatments with a factorial design. Substituting SoyPass into the diet did not affect average daily gain (ADG) of calves; however, calves consuming the 35% WDGS diet gained 31% more than the 20% WDGS treatment calves. Dry matter intake (DMI) and feed to gain (F:G) increased linearly in the 35% WDGS diet with the inclusion of SoyPass. In the 20% WDGS diet, DMI and F:G were maximized when SoyPass replaced 30% of the WDGS and lowest when SoyPass replaced 60% of WDGS. Therefore, SoyPass can replace up to 60% of the WDGS in forage based diets containing 20% WDGS with no adverse effects on performance by appearing to supply needed lysine

The Seasonality of Physically Driven Export at Submesoscales in the Northeast Atlantic Ocean

Submesoscale dynamics O(1–100 km) are associated with enhanced vertical velocities and evolve on a time scale similar to that of biological production (hours to days). Here we consider an annual cycle of submesoscale dynamics and their relation to productivity and export in a small (20 × 20 km) region of the northeast Atlantic Ocean. In this region, a springtime bloom is initiated by restratification of the mixed layer in June, although intermittent shoaling of the mixed layer maintains phytoplankton populations throughout the year. An optical community index suggests a dominance of large species (e.g., diatoms) during spring and picophytoplankton during the winter. We review three types of submesoscale instabilities—mixed layer (baroclinic), gravitational, and symmetric—and consider the impact of each on export of fixed carbon out of the surface layer. Mixed layer instabilities can potentially export material out of the mixed layer during winter, although the vertical velocity across the base of the mixed layer is sensitive to the parameterization scheme. Symmetric instabilities, in contrast, provide a clear mechanism for rapid export out of the mixed layer. A crucial factor determining export potential is the strength of the pycnocline at the base of the mixed layer. Export production is sensitive to the degree of overlap that exists between intense submesoscale activity associated with deep mixed layers in the winter and high productivity associated with the spring restratification, meaning that physically driven export of fixed carbon will likely happen over a short time window during spring

An advective mechanism for Deep Chlorophyll Maxima formation in southern Drake Passage

We observe surface and subsurface fluorescence-derived chlorophyll maxima in southern Drake Passage during austral summer. Backscatter measurements indicate that the deep chlorophyll maxima (DCMs) are also deep biomass maxima, and euphotic depth estimates show that they lie below the euphotic layer. Subsurface, offshore and near-surface, onshore features lie along the same isopycnal, suggesting advective generation of DCMs. Temperature measurements indicate a warming of surface waters throughout austral summer, capping the winter water (WW) layer and increasing off-shelf stratification in this isopycnal layer. The outcrop position of the WW isopycnal layer shifts onshore, into a surface phytoplankton bloom. A lateral potential vorticity (PV) gradient develops, such that a down-gradient PV flux is consistent with offshore, along-isopycnal tracer transport. Model results are consistent with this mechanism. Subduction of chlorophyll and biomass along isopycnals represents a biological term not observed by surface satellite measurements which may contribute significantly to the strength of the biological pump in this region

An advective mechanism for Deep Chlorophyll Maxima formation in southern Drake Passage

We observe surface and subsurface fluorescence-derived chlorophyll maxima in southern Drake Passage during austral summer. Backscatter measurements indicate that the deep chlorophyll maxima (DCMs) are also deep biomass maxima, and euphotic depth estimates show that they lie below the euphotic layer. Subsurface, offshore and near-surface, onshore features lie along the same isopycnal, suggesting advective generation of DCMs. Temperature measurements indicate a warming of surface waters throughout austral summer, capping the winter water (WW) layer and increasing off-shelf stratification in this isopycnal layer. The outcrop position of the WW isopycnal layer shifts onshore, into a surface phytoplankton bloom. A lateral potential vorticity (PV) gradient develops, such that a down-gradient PV flux is consistent with offshore, along-isopycnal tracer transport. Model results are consistent with this mechanism. Subduction of chlorophyll and biomass along isopycnals represents a biological term not observed by surface satellite measurements which may contribute significantly to the strength of the biological pump in this region

Impact of Corn Silage Inclusion on Finishing Cattle Performance

Cattle fed high grain diets with little to no roughage are typically at greater risk for acidosis and reduced dry matter intake and average daily gain. An individual feeding study was conducted to compare different inclusions of corn silage used as a roughage source on finishing performance and liver abscess rate. Treatments consisted of 3 inclusions of corn silage at 0, 7.5 and 15% of the diet DM and a control treatment with 7.5% alfalfa. There were no differences for live animal performance or carcass characteristics. There were also no differences in liver abscess incidence. Feeding corn silage at 15% gave similar performance responses compared to 7.5% alfalfa. These data suggest that roughage is not required in a finishing diet when feeding individual animals

Evaluation of Protein from Distillers Grains in Finishing Diets on Nutrient Digestibility

A metabolism trial was conducted to evaluate protein from modified distillers grains plus solubles (MDGS) in finishing diets on nutrient digestibility and ruminal fermentation characteristics. Isolated protein from corn was not different than MDGS for dry matter, organic matter, or neutral detergent fiber digestibility. However, steers fed MDGS tended to have lower total tract organic matter digestibility compared to corn and protein from corn. Protein had greater total tract organic matter and starch digestibility than MDGS. Protein from corn did not contribute towards the lower digestibility of MDGS. Protein is more easily digestible than the other components in distillers grains plus solubles