Evaluating Fluid Fluxes From Deep-Sea Seepage Habitats

The permanently dark deep-sea, located at oceanic water depths greater than 200 m, represents the largest potential habitat space on Earth. The physicochemical conditions of the planet’s largest biome are tightly coupled to the exchange of matter and energy from terrestrial and sea-floor end-members. In fact, global ocean and climate systems are significantly impacted by deep-sea processes. Seafloor vents and seeps appear to act as geologic exchange conduits, returning recycled materials to the hydrosphere to sustain another generation of life. Despite submarine seepage having control on global elemental cycling, it is estimated that less than 1% of the deep-sea has been mapped in detail sufficient to truly understand the spatial extent of regions of especially active material and energy exchange at regions of seafloor venting and seepage. Slow-flow discharge occurring at elevated temperatures (hydrothermal seepage) is suspected to exchange ~ 90% of the water required to balance heat budgets as compared to energetic vents. Deep-sea seepage occurring at ambient ocean temperatures (cold seeps), first discovered in the Gulf of Mexico, represents a second seepage environment where chemosynthetic primary production supports some of the most diverse biomes in the bathypelagic zones. However, methods and research directly applicable for understanding the rate of fluid discharge at low-flow submarine seepage sites are lacking, resulting in poorly constrained global chemical cycling estimates. This Dissertation provides a vertical exchange model designed to determine an effective fluid flux of porefluid from deep-sea environments. The vertical exchange model utilizes vertical distributions of aqueous 224Ra in porefluid recovered from regions impacted by hydrothermal and cold seepage and determines porefluid residence time related to radiogenic changes attributable to production and decay. The vertical exchange model is qualitatively tested whereby isotope proxy estimates confirm seepage in areas where seepage is indicated by ancillary evidence and suggest porefluid transport into the sediments best explains vertical isotope distributions observed for Control core. The vertical exchange model is applied to a hydrothermal site in Guaymas Basin to test whether spatial associations between microbial mats and seepage rates exist. We identify spatial relationships between subsurface temperature range and fluid flux where white colored microbial colonies exist; however, fluid flux appears unrelated to subsurface temperature range where orange filaments are found. Fluid flux estimates for sampled regions within both sites were observed to be similar despite the unique thermal source present only at Guaymas Basin. This work offers a novel approach to quantify fluid flow both into and out of the sediments across a variety of deep-sea habitats where seepage moderates the success of unique benthic ecosystems

Nearshore mixing and nutrient delivery along the western Antarctic Peninsula

The surface waters of the Southern Ocean play a key role in the global climate and carbon cycles by promoting growth of some of the world’s largest phytoplankton blooms. Several studies have emphasized the importance of glacial and sediment inputs of Fe that fuel the primary production of the Fe-limited Southern Ocean. Although the fertile surface waters along the shelf of the western Antarctic Peninsula (WAP) are influenced by large inputs of freshwater, this freshwater may take multiple pathways (e.g. calving, streams, groundwater discharge) with different degrees of water-rock interactions leading to variable Fe flux to coastal waters. During the summers of 2012–13 and 2013–14, seawater samples were collected along the WAP, near Anvers Island, to observe water column dynamics in nearshore and offshore waters. Tracers (223,224Ra, 222Rn, 18O, 2H) were used to evaluate the source and transport of water and nutrients in coastal fjords and across the shelf. Coastal waters are compared across two field seasons, with increased freshwater observed during 2014. Horizontal mixing rates of water masses along the WAP ranged from 110–3600 m2 s-1. These mixing rates suggest a rapid transport mechanism for moving meltwater offshore.ECU Open Access Publishing Support Fun

Groundwater discharge to the western Antarctic coastal ocean

Submarine groundwater discharge (SGD) measurements have been limited along the Antarctic coast, although groundwater discharge is becoming recognized as an important process in the Antarctic. Quantifying this meltwater path-way is important for hydrologic budgets, ice mass balances and solute delivery to the coastal ocean. Here, we estimate the combined discharge of subglacial and submarine groundwater to the Antarctic coastal ocean. SGD, including subglacial and submarine groundwater, is quantified along the WAP at the Marr Glacier terminus using the activities of naturally occurring radium isotopes (223Ra, 224Ra). Estimated SGD fluxes from a 224Ra mass balance ranged from (0.41 ± 0.14)×104 and (8.2 ± 2.3)×104m3 d−1. Using a salinity mass balance, we estimate SGD contributes up to 32% of the total freshwater to the coastal environment near Palmer Station. This study suggests that a large portion of the melting glacier may be infiltrating into the bedrock and being discharged to coastal waters along the WAP. Meltwater infiltrating as groundwater at glacier termini is an import-ant solute delivery mechanism to the nearshore environment that can influence biological productivity. More importantly, quantifying this meltwater pathway may be worthy of attention when predicting future impacts of climate change on retreat of tidewater glaciers

Constructing Water Budgets for a Coastal Stormwater Catchment to Examine Temporal Dynamics Between Urban Groundwater and Surface Runoff

It is well understood that urbanization results in changes to the hydrologic cycle, namely increasing surface runoff production rates. Precipitation falling on impervious areas is typically directed via a network of drainage pipes to detention reservoirs, a process shown to negatively impact aquifer recharge rates. Historically, urban hydrologists have focused primarily on surface processes with little consideration to subsurface implications of the urban water cycle. Here, we present an approach to construct long-term, high-resolution water budgets for a coastal stormwater catchment resolving surface runoff and groundwater fractions within the water body and associated source-specific fluid exports to the coastal ocean. We use the radiotracer 222Rn to delineate groundwater fraction within the reservoir, calculate direct precipitation inputs, and by difference, determine surface runoff contributions to the total water budget. By determining total output rates from Dogwood Swash, we also examine relative source outputs at both high- and low-resolution temporal scales from 2012 through 2013. While surface runoff constituted the majority of the water budget, both groundwater and surface runoff fractions varied by 36.5% suggesting the subsurface source to contribute significantly to the stormwater catchment fluid budget. However, long-term records indicate a decline in groundwater fraction (by 35%) and export (14%) from the system as aquifer residence times increased. Constructing water budgets for sub-basin tributaries within the larger Dogwood Swash drainage complex suggest reduced source water variability, lower groundwater fractions, and longer aquifer residence times with greater impervious surface area. Our approach to water budget construction may be applied to other environments providing the framework for source-specific material budgets. Such assessments could then be used by stormwater managers to best maintain desired ecosystem health in both urban streams and the coastal ocean