Sea-level budgets account for the contributions of processes driving sea-level change, but are predominantly focused on global-mean sea level and limited to the 20th and 21st centuries. Here we ...estimate site-specific sea-level budgets along the U.S. Atlantic coast during the Common Era (0-2000 CE) by separating relative sea-level (RSL) records into process-related signals on different spatial scales. Regional-scale, temporally linear processes driven by glacial isostatic adjustment dominate RSL change and exhibit a spatial gradient, with fastest rates of rise in southern New Jersey (1.6 ± 0.02 mm yr
). Regional and local, temporally non-linear processes, such as ocean/atmosphere dynamics and groundwater withdrawal, contributed between -0.3 and 0.4 mm yr
over centennial timescales. The most significant change in the budgets is the increasing influence of the common global signal due to ice melt and thermal expansion since 1800 CE, which became a dominant contributor to RSL with a 20th century rate of 1.3 ± 0.1 mm yr
.
A fundamental goal of the Earth Science community is to understand how perturbations on Earth's surface are preserved in the stratigraphic record. Recent Source to Sink (S2S) studies of the Waipaoa ...Sedimentary System (WSS), New Zealand, are synthesized herein to provide a holistic perspective of the processes that generate, transport and preserve sedimentary strata and organic carbon on the Waipaoa margin in the late Quaternary. Rapid uplift associated with subduction processes and weak sedimentary units have conspired to generate rapid rates of incision and erosion in the Waipaoa catchment since the Last Glacial Maximum (LGM). We show that although much of the sediment exported offshore during this time interval originated from valley excavation, a substantial portion emanated from hillslopes, mostly through deep-seated landslide and earthflow processes that were vigorous during periods of rapid fluvial incision just prior to the Pleistocene–Holocene transition. Lacustrine sediments deposited in naturally-dammed 7-ky-old Lake Tutira provide a record of Holocene environmental controls on upper catchment sedimentation in the WSS, with 1400 storms identified. Storm frequency is modulated by the waxing and waning of atmospheric teleconnections between the tropics and Antarctica. Furthermore, clear long-term changes in sediment yield are evident from the Lake Tutira record following human settlement as conversion to pasture is accompanied by a 3-fold increase in the long-term lake sediment accumulation rate.
Whereas there is ample evidence that Waipaoa River flood deposits are routinely deposited offshore in the sheltered confines of Poverty Bay, over the longer term, waves and currents subsequently resuspend and transport these deposits both landward (sandy fraction) and seaward (finer fraction). Thus, the timing of sediment supply to areas of net sediment accumulation is more often driven by wave events that are not associated with river flooding. Therefore, we conclude that asynchronicity of river-sediment delivery and of wave resuspension in most instances precludes the direct preservation of flood events in the stratigraphic record of the Waipaoa Shelf. Over the longer term, the sediment package preserved on the shelf and slope since the LGM can be explained in large measure by sequence-stratigraphic models forced by varying sea level and ongoing tectonic deformation of the margin. As sea level rose, sediment supply to the slope was reduced by about a factor of 5 due to shelf trapping. Despite this reduction, turbidites are found at similar frequency throughout the LGM–Present, as the dominant trigger appears to be subduction earthquakes, with large ones having a return interval of about 200±100years. Sediment-budget exercises that consider both modern (river discharge versus centennial accumulation rates) and post-LGM (terrestrial production versus offshore isopachs) mass balances indicate that about half of the total sediment production from the Waipaoa escapes the study area. Moreover, a coupled sediment transport-hydrodynamic model and observations of textural trends on the shelf indicate that a large fraction of the sediment is carried outside the study area along the shelf to the northeast by the river plume or by combined current/wave activity. Therefore, we conclude that the WSS is an open system with sediment escape from the present day through the LGM.
The organic matter associated with sediment as it moves from upland source to marine sink is a product of particle history, and provides a record of materials that have cycled over timescales of days to millions of years. The ubiquity of fossil Organic Carbon (OC) in both the terrestrial and marine realms of the Waipaoa attests both to the chronic nature of its source, crumbling mudstones further destabilized by land use, and its biogeochemical recalcitrance. Modern OC persists by virtue of its continual production along the S2S transit, and is buried and preserved within the adjacent marine depocenters. The Waipaoa contrasts with dispersal systems on wide, energetic shelves (e.g., the Amazon and Fly Rivers) where sediment is extensively refluxed in oxygenated overlying water resulting in the biogeochemical incineration of particulate OC. The Waipaoa, like other small mountainous rivers on active margins, exhibits a high riverine OC preservation efficiency (>50%) in its marine depocenters because of the relatively rapid, event-driven accumulation of sediment.
Urbanization and human-led development have increased more rapidly along shorelines and in coastal watersheds than inland regions over the past century. The result of major land use changes for both ...urban tracts and agriculture to serve the urban areas, as well as infrastructure development is increased runoff carrying sediments, nutrients, pollutants, pharmaceuticals, and toxins downstream to estuarine systems. The increased runoff levels are only the tip of the iceberg, with human development resulting in increased fecal bacteria from urbanization and excess nutrients from agriculture leading to harmful algal blooms. Estuaries act as a natural filter between land and sea, but have been overloaded by the influx of sediments and pollutants in recent decades. As a result, there have been a variety of impacts to estuarine ecosystems and water quality including increased sediment load, eutrophication, harmful algal blooms, fecal bacteria, as well as shellfish and fisheries declines. In some estuarine systems, the reduction in light penetration to the benthos has led to the loss of seagrasses. In others, seasonal hypoxia is a visible symptom of prolonged eutrophication. There is a need to augment long-term monitoring techniques with new technologies and data processing methods to better understand the current state of estuaries and work towards mitigating human impacts on estuarine ecosystems and water quality.
Barrier islands are found around the world and are important environmentally and economically. With accelerated sea level rise and relentless storms, their evolution is complex but important to ...understand, especially from a coastal planning and managing perspective. In this study, shoreline change estimates from aerial photography (1949, 1974, 2006), sedimentological and stratigraphic investigation, and analysis of geomorphic character were used to evaluate the hurricane response and decadal evolution of Ocracoke Island, NC. Between 1949 and 2006, the majority (> 65% of transects) of the entire island eroded at an average rate of-0.54 m/year. Cross-island width decreased by as much as 40% (180 m) over the period. Hurricane Isabel (2003) represented up to 23% of the long-term net change in some regions of the island. The rate of narrowing of Ocracoke Island appears to have increased in the last half century and is due to a combination of natural and anthropogenic factors. Isabel overwashed a total of 9% of the island based on aerial photographic analysis with an average deposit thickness of 0.24 m based on trench investigation. Assessment with the Storm Impact Scale showed a direct relationship between overwash and the pre-existing dune conditions, which had been affected by long-term erosion. Sedimentological signatures interpreted from cores show up to four distinct stacked overwash deposits, potentially dating back as fer as 1944. This multi-pronged analysis shows the complexity of barrier island evolution and highlights the necessity to examine and model a system response in four dimensions (i.e., spatially and with time).
Hurricane frequencies and intensities are expected to increase under warming climate scenarios, increasing potential to disrupt microbial communities from steady-state conditions and alter ecosystem ...function. This study shows the impact of hurricane season on microbial community dynamics within the barrier island system of Outer Banks, North Carolina. We found that the passage of two sequential energetic hurricanes in 2018 (Florence and Michael) were correlated with shifts in total and active (DNA and RNA) portions of bacterial communities but not in archaeal communities, and within surface waters but not within the sediment. These microbial community shifts were distinct from non-hurricane season conditions, suggesting significant implications for nutrient cycling in nearshore and offshore environments. Hurricane-influenced marine sites in the coastal North Atlantic region had lower microbial community evenness and Shannon diversity, in addition to increased relative abundance of copiotrophic microbes compared to non-hurricane conditions. The abundance of functional genes associated with carbon and nitrogen cycling pathways were also correlated with the storm season, potentially shifting microbial communities at offshore sites from autotroph-dominated to heterotroph-dominated and leading to impacts on local carbon budgets. Understanding the geographic- and system-dependent responses of coastal microbial communities to extreme storm disturbances is critical for predicting impacts to nutrient cycling and ecosystem stability in current and future climate scenarios.
The longer-term ecosystem impacts associated with a beach nourishment project conducted in 2014 were studied on an ocean beach on the Pea Island National Wildlife Refuge on North Carolina's Outer ...Banks. The unique nature of the project is tied to the study's duration, which spans nine years, and the venue, a national wildlife refuge where human-sourced confounding effects are minimal. Populations for five invertebrates: Emerita talpoida (the Atlantic Mole Crab), Donax variabilis (the Coquina Clam), Scolelepis squamata, Ocypode quadrata (the Atlantic Ghost Crab), and indigenous Amphipods were monitored seasonally over nine-years that asymmetrically straddled the 2014 nourishment event. Beach sediments were also monitored in concert with the biodata. Results show that the 2014 nourishment fill sands were finer than those native to the study area beach, however, reworking quickly brought the fill sands on the nourished beach into size parity with native sediments observed on a predefined control site.
Findings from this investigation fail to present evidence to suggest that any type of ephemeral species die-off occurred in association with the 2014 nourishment event. While die-offs are commonplace reported, such outcomes are not inevitable. Other investigators have documented ecosystem resilience against significant disturbances such as beach nourishment—this study appears to corroborate such findings, both at the system and species levels. Many argue that nourishment fill sand characteristics: their fit to the native sediment in terms of size and composition, and their application during construction, are the principal determinants driving the disturbance response and subsequent post-nourishment recovery. This study corroborates this fill-sand/recovery relationship but provides evidence to support a causation argument only circumstantially.
•Unique 9-year study of beach nourishment impact on National Wildlife Refuge beach.•Limited initial mortalities as a result of nourishment—no mass die-offs observed.•Immediate recovery observed for dominate E. talpoida and D. variabilis.•O. quadrata populations depressed for two or three seasons before recovery.•Limited impact attributed to close grain-size match between fill and native sands.
We report stratigraphic evidence of land‐level change and tsunami inundation along the Alaska‐Aleutian megathrust during prehistoric and historical earthquakes west of Kodiak Island. On Sitkinak ...Island, cores and tidal outcrops fringing a lagoon reveal five sharp lithologic contacts that record coseismic land‐level change. Radiocarbon dates, 137Cs profiles, computerized tomography scans, and microfossil assemblages are consistent with rapid uplift circa 290–0, 520–300, and 1050–790 cal yr B.P. and subsidence in A.D. 1964 and circa 640–510 cal yr B.P. Radiocarbon, 137Cs, and 210Pb ages bracketing a sand bed traced 1.5 km inland and evidence for sudden uplift are consistent with Russian accounts of an earthquake and tsunami in A.D. 1788. The mixed uplift and subsidence record suggests that Sitkinak Island sits above a nonpersistent boundary near the southwestern limit of the A.D. 1964 Mw 9.2 megathrust rupture.
Key Points
Mixed coseismic uplift and subsidence at edge of 1964 M 9.2 rupture since ~1 ka
First geologic evidence of the great 1788 earthquake and tsunami
Non‐persistent barrier to rupture important for tectonic and hazard models
Where the continent ends Paris, Paul J.; Walsh, J. P.; Corbett, D. Reide
Geophysical research letters,
16 December 2016, Letnik:
43, Številka:
23
Journal Article
Recenzirano
Odprti dostop
The Earth's continents and islands are bordered by shallow ocean plains that are arguably the most environmentally, economically, and politically important parts of the sea. Yet in spite of this, ...they remain poorly defined and understood. A quantitative approach is employed here to map and analyze these plains, or shelves. The Earth's ocean bathymetry was used to determine the continent‐ocean basin transition at ~1200 m and then parsed with a novel geospatial terrain classification concept/method borrowed from the field of image analysis: the geomorphic phonotype, or geomorphon. The technique is less subjective than visual interpretation and digitization and here illustrates that the ocean coastal plains are deeper, wider, and more steeply sloped than previously recognized. Their variable form is related to tectonics and latitude and ultimately affects function and habitat.
Key Points
We reexamine long‐standing geomorphic assumptions about the world's continental and insular shelves
A novel objective and reproducible method is employed in lieu of subjective interpretation to remap world's continental ocean shelves
Results indicate that overall, the world's continental shelves are wider, deeper, and steeper in slope than previously recognized
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 pathway 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 important 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.
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