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Internal Waves on the Washington Continental Shelf  [PDF]
Matthew H. Alford,John B. Mickett,Shuang Zhang,Parker MacCready
Oceanography , 2012,
Abstract: The low-frequency oceanography of the Washington continental shelf has been studied in great detail over the last several decades owing in part to its high productivity but relatively weak upwelling winds compared to other systems. Interestingly, though many internal wave-resolving measurements have been made, there have been no reports on the region's internal wave climate and the possible feedbacks between internal waves and lower-frequency processes. This paper reports observations over two summers obtained from a new observing system of two moorings and a glider on the Washington continental shelf, with a focus on internal waves and their relationships to lower-frequency currents, stratification, dissolved oxygen, and nutrient distributions. We observe a rich, variable internal wave field that appears to be modulated in part by a coastal jet and its response to the region's frequent wind reversals. The internal wave spectral level at intermediate frequencies is consistent with the model spectrum of Levine (2002) developed for continental shelves. Superimposed on this continuum are (1) a strong but highly temporally variable semidiurnal internal tide field and (2) an energetic field of high-frequency nonlinear internal waves (NLIWs). Mean semidiurnal energy flux is about 80 W m–1 to the north-northeast. The onshore direction of the flux and its lack of a strong spring/neap cycle suggest it is at least partly generated remotely. Nonlinear wave amplitudes reach 38 m in 100 m of water, making them among the strongest observed on continental shelves of similar depth. They often occur each 12.4 hours, clearly linking them to the tide. Like the internal tide energy flux, the NLIWs are also directed toward the north-northeast. However, their phasing is not constant with respect to either the baroclinic or barotropic currents, and their amplitude is uncorrelated with either internal-tide energy flux or barotropic tidal forcing, suggesting substantial modulation by the low-frequency currents and stratification.
First record of a vagrant Commerson’s dolphin, Cephalorhynchus commersonii, at the southern African continental shelf  [cached]
P.J.N. de Bruyn,G.J.G. Hofmeyr,M.S. de Villiers
African Zoology , 2011,
Abstract: Commerson’s DolphinsCephalorhynchus commersonii are distributed in two disjunct populations, one around southern South America and the other around the sub-Antarctic Kerguelen Islands. These populations have been shown to be morphologically and genetically distinct and movement between the two populations is unlikely. We report on the sighting of a single specimen over the South African continental shelf on 13 November 2004. To our knowledge this is the first record of this species in South African waters and such a vast distance (over 4000 km) from the known distribution limits.
On instability and mixing on the UK Continental Shelf  [PDF]
Zhiyu Liu
Physics , 2015,
Abstract: The stability of stratified flows at locations in the Clyde, Irish and Celtic Seas on the UK Continental Shelf is examined. Flows are averaged over periods of 12-30 min in each hour, corresponding to the times taken to obtain reliable estimates of the rate of dissipation of turbulent kinetic energy per unit mass, $\varepsilon$. The Taylor-Goldstein equation is solved to find the maximum growth rate of small disturbances to these averaged flows, and the critical gradient Richardson number, $\textrm{Ri}_\textrm{c}$. The proportion of unstable periods where the minimum gradient Richardson number, $\textrm{Ri}_{\textrm{min}}$, is less than $\textrm{Ri}_\textrm{c}$ is about 35%. Cases are found in which $\textrm{Ri}_\textrm{c} <$ 0.25; 37% of the flows with $\textrm{Ri}_{\textrm{min}}<$ 0.25 are stable, and $\textrm{Ri}_\textrm{c}<$ 0.24 in 68% of the periods where $\textrm{Ri}_{\textrm{min}}<$ 0.25. Marginal conditions with 0.8 $<$ Ri$_{\textrm{min}}$$/$Ri$_\textrm{c}$ $<$ 1.2 occur in 30% of the periods examined. The mean dissipation rate at the level where the fastest growing disturbance has its maximum amplitude is examined to assess whether the turbulence there is isotropic and how it relates to the Wave-Turbulence boundary. It is concluded that there is a background level of dissipation that is augmented by instability; instability of the averaged flow does not account for all the turbulence observed in mid-water. The effects of a horizontal separation of the measurements of shear and buoyancy are considered. The available data do not support the hypothesis that the turbulent flows observed on the UK shelf adjust rapidly to conditions that are close to being marginal, or that flows in a particular location and period of time in one sea have stability characteristics that are very similar to those in another.
On the freshening of the northwestern Weddell Sea continental shelf  [PDF]
H. H. Hellmer,O. Huhn,D. Gomis,R. Timmermann
Ocean Science Discussions (OSD) , 2010, DOI: 10.5194/osd-7-2013-2010
Abstract: We analysed hydrographic data from the northwestern Weddell Sea continental shelf of three austral winters (1989, 1997 and 2006) and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne) concentrations, indicating a significant input of glacial melt water. The comparison of the winter data at the tip of the Antarctic Peninsula, spanning a period of 17 years, shows a salinity decrease of 0.09 for the whole water column. We interpret this freshening as a reduction in salt input to the water masses being advected northward on the western Weddell Sea continental shelf. Possible causes for the reduced winter salinification are a southward retreat of the summer sea ice edge together with more precipitation in this sector. However, the latter might have happened in conjunction with an increase in ice shelf mass loss, counteracting an enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves.
On the freshening of the northwestern Weddell Sea continental shelf  [PDF]
H. H. Hellmer,O. Huhn,D. Gomis,R. Timmermann
Ocean Science (OS) & Discussions (OSD) , 2011, DOI: 10.5194/os-7-305-2011
Abstract: We analyzed hydrographic data from the northwestern Weddell Sea continental shelf of the three austral winters 1989, 1997, and 2006 and two summers following the last winter cruise. During summer a thermal front exists at ~64° S separating cold southern waters from warm northern waters that have similar characteristics as the deep waters of the central basin of the Bransfield Strait. In winter, the whole continental shelf exhibits southern characteristics with high Neon (Ne) concentrations, indicating a significant input of glacial melt water. The comparison of the winter data from the shallow shelf off the tip of the Antarctic Peninsula, spanning a period of 17 yr, shows a salinity decrease of 0.09 for the whole water column, which has a residence time of <1 yr. We interpret this freshening as being caused by a combination of reduced salt input due to a southward sea ice retreat and higher precipitation during the late 20th century on the western Weddell Sea continental shelf. However, less salinification might also result from a delicate interplay between enhanced salt input due to sea ice formation in coastal areas formerly occupied by Larsen A and B ice shelves and increased Larsen C ice loss.
Sub-National Island Jurisdictions as Configurations of Jurisdictional Powers and Economic Capacity: Nordic Experiences from land, Faroes and Greenland  [PDF]
Agneta Karlsson
Island Studies Journal , 2009,
Abstract: This paper is concerned with the relationship between jurisdictional powers and economic and innovative capacity in the context of sub-national island jurisdictions (SNIJs). The “jurisdictional powers thesis”, prominent in the present island studies debate, is confronted and discussed with reference to an empirical, comparative, study of the three Nordic SNIJs: the land Islands, the Faroe Islands and Greenland. The paper takes as its point of departure an ideal-type SNIJ which is characterized by a good match between jurisdictional powers and economic capacity; it then analyzes the three cases in terms of this ideal-type. Three different types of configurations emerge, representing three types of “deviations” from the ideal-type SNIJ; these are discussed in terms of their development potentialities.
Influence of terrestrial inputs on continental shelf carbon dioxide
L.-Q. Jiang,W.-J. Cai,Y. Wang,J. E. Bauer
Biogeosciences Discussions , 2012, DOI: 10.5194/bgd-9-9315-2012
Abstract: Air-sea carbon dioxide (CO2) fluxes have recently been reported for the US South Atlantic Bight (SAB), a low-latitude shallow continental shelf bordered landward by abundant salt marshes and rivers. In this study, influences of terrestrial inputs on sea surface partial pressure of CO2 (pCO2) in the SAB are quantified. After removing pCO2 variations due to the annual temperature cycle and air-sea gas exchange from the in situ pCO2, temperature and gas exchange corrected (TG-corrected) pCO2 is derived. Contributions from the river, marsh, and continental shelf to the TG-corrected pCO2 are then calculated. Findings show that CO2 contributions from the river [ΔpCO2(river)] are highest close to the coast and decrease with distance offshore. For example, ΔpCO2(river) was up to 30 μatm on the inner shelf but averaged only 0–3 μatm on the outer shelf during January and March 2005. CO2 contributions from salt marshes [ΔpCO2(marsh)] show similar spatial and seasonal distributions as ΔpCO2(river), with the magnitude of ΔpCO2(marsh) being about three times as high as that of ΔpCO2(river). CO2 contributions from within the shelf [ΔpCO2(shelf)] are highest among the three components. Compared to ΔpCO2(river) and ΔpCO2(marsh), ΔpCO2(shelf) show the smallest onshore-offshore gradients. Despite large uncertainties, this study clearly demonstrates the importance of terrestrial impacts on coastal ocean CO2distribution.
The staircase structure of the Southern Brazilian Continental Shelf  [PDF]
M. S. Baptista,L. A. Conti
Physics , 2008,
Abstract: We show some evidences that the Southeastern Brazilian Continental Shelf (SBCS) has a devil's staircase structure, with a sequence of scarps and terraces with widths that obey fractal formation rules. Since the formation of these features are linked with the sea level variations, we say that the sea level changes in an organized pulsating way. Although the proposed approach was applied in a particular region of the Earth, it is suitable to be applied in an integrated way to other Shelves around the world, since the analyzes favor the revelation of the global sea level variations.
Influence of terrestrial inputs on continental shelf carbon dioxide
L.-Q. Jiang, W.-J. Cai, Y. Wang,J. E. Bauer
Biogeosciences (BG) & Discussions (BGD) , 2013,
Abstract: The US South Atlantic Bight (SAB) is a low-latitude shallow continental shelf bordered landward by abundant salt marshes and rivers. Based on previously published data on sea surface partial pressure of carbon dioxide (pCO2) and new dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) data, a model analysis is presented to identify and quantify the contributions of various terrestrial carbon inputs on SAB sea surface pCO2. After removal of pCO2 variations due to annual temperature variability and air–sea gas exchange from the in situ pCO2, the temperature- and gas-exchange-corrected pCO2 (TG-corrected pCO2) is derived. Contributions from rivers, salt marshes, and the continental shelf to the TG-corrected pCO2 are then calculated. Our findings demonstrate that although additions of CO2 from within shelf waters (i.e., ΔpCO2(shelf)) were the greatest of the three components and underwent the largest seasonal changes, ΔpCO2(shelf) showed smaller onshore–offshore gradients than rivers and marshes. In contrast, CO2 contributions from river (ΔpCO2(river)) and salt marsh (ΔpCO2(marsh)) components were greatest closest to the coast and decreased with distance offshore. In addition, the magnitude of ΔpCO2(marsh) was about three-fold greater than ΔpCO2(river). Our findings also revealed that decomposition of terrestrial organic carbon was an important factor regulating the seasonal pattern of pCO2 on the inner shelf. Despite large uncertainties, this study demonstrates the importance of terrestrial inputs, in particular those from coastal wetlands, on coastal ocean CO2 distributions.
The Staircase Structure of the Southern Brazilian Continental Shelf
M. S. Baptista,L. A. Conti
Mathematical Problems in Engineering , 2009, DOI: 10.1155/2009/624861
Abstract: We show some evidences that the Southeastern Brazilian Continental Shelf (SBCS) has a devil's staircase structure, with a sequence of scarps and terraces with widths that obey fractal formation rules. Since the formation of these features is linked with the sea-level variations, we say that the sea level changes in an organized pulsating way. Although the proposed approach was applied in a particular region of the Earth, it is suitable to be applied in an integrated way to other shelves around the world, since the analyses favor the revelation of the global sea-level variations.
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