Browsing by Subject "ocean color"
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Item Open Access On the Horizontal Advection and Biogeochemical Impacts of North Atlantic Mode Waters and Boundary Currents(2007-07-26) Palter, Jaime BethUsing a combination of hydrographic data and the trajectories and profiles of isobaric floats, this dissertation evaluates the connections between remote regions in the North Atlantic. First, I establish that the production and advection of the North Atlantic Subtropical Mode Water (STMW) introduces spatial and temporal variability in the subsurface nutrient reservoir of the subtropical gyre. As the mode water is formed, its nutrients are depleted by biological utilization. When the depleted water mass is exported to the gyre, it injects a wedge of low-nutrient water into the upper layers of the ocean. Contrary to intuition, cold winters that promote deep convective mixing and vigorous mode water formation may diminish downstream primary productivity by altering the subsurface delivery of nutrients. Next, the source of elevated nutrient concentrations in the Gulf Stream is assessed. The historical hydrographic data suggest that imported water advected into the Gulf Stream via the tropics supplies an important source of nutrients to the Gulf Stream. Because the high nutrients are likely imported from the tropics, diapycnal mixing need not be invoked to explain the Gulf Stream's high nutrient concentrations, as had been previously hypothesized. Furthermore, nutrients do not increase along the length of the Stream, as would be expected with strong diapycnal mixing.Finally, profiling float data are used to investigate how the Labrador Sea Water enters the Deep Western Boundary Current, one of the primary pathways by which it exits the subpolar gyre. With the trajectories and profiles of an extensive array of P-ALACE floats I evaluate three processes for their role in the entry of Labrador Sea Water in the Deep Western Boundary Current (DWBC): 1) LSW is formed directly in the DWBC, 2) Eddies flux LSW laterally from the interior Labrador Sea to the DWBC, and 3) A horizontally divergent mean flow advects LSW from the interior to the DWBC. Each of the three processes has the potential to remove heat from the boundary current, and both the formation of LSW directly in the boundary current and the eddy heat flux are possible sources of interannual variability in the exported LSW product.Item Open Access Submesoscale Biophysical Interactions on the Gulf Stream: Eddies, Fronts, and New Observational Methods(2022) Gray, Patrick CliftonOur oceans are a key part of the Earth system, an underappreciated bastion of our carbon cycle, and the home of incredible biodiversity, yet marine ecosystems are extremely challenging to model with a range of feedbacks that are not understood. Particularly poorly understood are linkages between physics and biology at the submesoscale (horizontally O(0.1-10) km, vertically O(.1) km, temporally O(1) day) that could help explain broad scale properties in ocean biology. Persistent fronts of western boundary currents like the Gulf Stream are hotspots for submesoscale dynamics that may influence phytoplankton productivity and diversity with ramifications across marine ecosystems. In this dissertation I: 1) review the use of drones and ocean color remote sensing for observing biology at the submesoscale and below, and articulate a vision for addressing key observational needs with drones, 2) develop more robust methods for retrieving ocean color from drones, 3) integrate observations from new and existing sampling technologies to investigate phytoplankton enhancement and shifts in phytoplankton community composition on the Gulf Stream front, and 4) with a frontal eddy as a mesocosm investigate community composition in the eddy vs shelf and Gulf Stream water and then more broadly understand their impact on the marine ecosystem of the Gulf Stream and mid-Atlantic Bight. This work revealed seasonality contrasting that of the typical North Atlantic blooms, but more similar to Sargasso Sea water at this latitude with peak biomass in winter. We found shifting nutrient limitations and observed chlorophyll-a enhancement on the front in a large minority of samples with an indication of winter being more likely for enhancement. We speculate about linkages between this enhancement and ageostrophic circulation on the front but did not directly demonstrate this. Community composition shifts were present in all transects across the Gulf Stream front, though no consistent pattern emerged, with gradual shifts, step changes, and anomalies at the front. Finally the in-depth frontal eddy investigation revealed a different community, dominated by Prochlorococcus, and many optical indicators of a post-bloom shift to a microbial loop environment within the eddy. In summary the major goals of this work were to understand the interplay of ocean physics and marine ecosystems at the fine-scale. Towards this goal, I develop more robust methods for measuring ocean color from drones and then focus on the Gulf Stream, parsing out connections between the front and chl-a and biodiversity and then focus on a frontal eddy as a mesocosm for physical-ecological interactions and for their ecological impact on the mid-Atlantic Bight.