DOCSLIB.ORG

The Hydrography of the Mid-Latitude Northeast Atlantic Ocean I: the Deep Water Masses Hendrik M

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
The Hydrography of the Mid-Latitude Northeast Atlantic Ocean I: the Deep Water Masses Hendrik M Deep-Sea Research I 47 (2000) 757}788 The hydrography of the mid-latitude northeast Atlantic Ocean I: The deep water masses Hendrik M. van Aken* Netherlands Institute for Sea Research, P.O. Box 59, Den Burg/Texel, The Netherlands Received 22 December 1997; received in revised form 2 April 1999; accepted 7 September 1999 Abstract The circulation of the deep water masses in the mid-latitude northeast Atlantic Ocean was studied by analysis of the distributions of potential temperature, salinity, dissolved oxygen, phosphate, nitrate, and silicate. Pre-formed nutrients were used to allow a quantitative descrip- tion of the deep water masses, especially the Northeast Atlantic Deep Water, in terms of four local source water types: Iceland}Scotland Over#ow Water, Lower Deep Water, Labrador Sea Water, and Mediterranean Sea Water. Over the Porcupine Abyssal Plain between 2500 and 2900 dbar Northeast Atlantic Deep Water appears to be a mixture of mainly Iceland}Scotland Over#ow Water and Labrador Sea Water (&80%), with minor contributions of Lower Deep Water and Mediterranean Sea Water. When the Northeast Atlantic Deep Water re-circulates in the north-eastern Atlantic and #ows southwards towards the Madeira Abyssal Plain, contribu- tions of the former two water types of northern origin diminish to about 50% due to diapycnal mixing with the overlying and underlying water masses. The observed meridional and zonal trends of dissolved oxygen and nutrients in the Northeast Atlantic Deep Water appear to be caused both by diapycnal mixing with the underlying Lower Deep Water and by mineralization of organic matter. The eastward decrease of oxygen and increase of nutrients especially require considerable mineralization of organic matter near the European continental margin. At deeper levels (&4100 dbar), where the nutrient rich Lower Deep Water is found near the bottom, the meridional gradients of oxygen and nutrients are opposite to those found between 2500 and 2900 dbar. Diapycnal mixing cannot explain this change in gradients, which is therefore * Fax: 0031-0-222-319674. E-mail address: [email protected] (H.M. van Aken) 0967-0637/00/$- see front matter ( 2000 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 - 0 6 3 7 ( 9 9 ) 0 0 0 9 2 - 8 758 H.M. van Aken / Deep-Sea Research I 47 (2000) 757}788 considered to be a qualitative indication of ageing of the Lower Deep Water when it #ows northwards. A considerable part of the Iceland}Scotland Over#ow Water and the Lower Deep Water that enter the northeast Atlantic may be removed by deep upwelling in the Bay of Biscay and eastern Porcupine Plain. ( 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction In this paper we study the deep circulation in the mid-latitude northeast Atlantic Ocean by analysis of a data set of temperature, salinity, oxygen and nutrient observations from the 1980s and early 1990s, collected between 313 and 533N, and east of 213W (Fig. 1). We focus on the composition, circulation and modi"- cation of the North-East Atlantic Deep Water, characterized by a deep salinity maximum as it is observed over the Porcupine Abyssal Plain, and also of the underlying near bottom salinity minimum. We analyse the bio-geochemical properties for indications of ageing over the meridional succession of the Por- cupine Abyssal Plain, the Iberian Abyssal Plain, and the Madeira Abyssal Plain. These deep basins are separated by the Azores-Biscay Rise and by the Azores- Portugal Rise. We also study the composition of the deep water mass in terms of source water types from potential temperature H and salinity S, together with pre-formed nutrients. The zonal variation of the hydrographic properties is analysed by comparison with data from the Biscay Abyssal Plain, the West Iberian Margin, and the Seine Abyssal Plain. The hydrographic results are then discussed, and conclusions on the deep water mass of the northeastern Atlantic and its deep circulation and mixing are formulated. Part of the deep branch of the global thermohaline circulation passes through the northeastern basin of the North Atlantic Ocean (Dickson and Brown, 1994). Cold water from the Norwegian Sea #ows through the Faroe-Bank Channel and across the Iceland-Faroe Ridge into the Iceland Basin. During its descent from the sills between Iceland and Scotland into the deep Iceland Basin this water initially entrains warm and saline Sub-Polar Mode Water. At later stages in the Iceland Basin cold and less saline Labrador Sea Water (LSW) entering the eastern North Atlantic basins near the Charlie-Gibbs Fracture Zone at &523N (Talley and McCartney, 1982) is entrained as well as the overlying upper parts of the cold low salinity Lower Deep Water (LDW; van Aken and de Boer, 1995; van Aken and Becker, 1996). By this warm and cold entrainment the Iceland Scotland Over#ow Water (ISOW) is formed in the northern Iceland Basin. About 3.5 Sv (1 Sv "106 m3/s) ISOW passes south of Iceland (Saun- ders, 1996; van Aken and Becker, 1996). The characteristics of this water mass change considerably due to diapycnal mixing, which decreases its density, when this water proceeds further south to 523N, the latitude of the Charlie Gibbs Fracture Zone (van Aken and Becker, 1996). There a deep water mass is observed, characterized by a salinity maximum at about 2600 dbar between the low salinity cores of LSW and LDW (van Aken and Becker, 1996) and designated Northeast Atlantic Deep Water (NEADW). With a multi-stage H}S analysis Harvey and Theodorou (1986) derived H.M. van Aken / Deep-Sea Research I 47 (2000) 757}788 759 Fig. 1. The spatial distribution of the hydrographic stations with bio-geochemical data used in this study. At each station water samples with a potential temperature below 53C were collected. The symbols indicate the regional attribution of the stations to the di!erent deep basins and are explained in the legend. The water depth in m is indicated by isobaths. 760 H.M. van Aken / Deep-Sea Research I 47 (2000) 757}788 the presence of ISOW around the deep salinity maximum between 2000 and 2600 m in the southern Iceland Basin. They however did not pursue their analysis into the Porcupine Basin and further south. Lee and Ellett (1965) assumed that NEADW contains considerable amounts of ISOW. By analysis of salinity anomalies in the deep northeast Atlantic they were able to follow the NEADW core southwards to at least a latitude of 473W over the Porcupine Abyssal Plain. At that latitude the salinity signal due to the high salinity core of Mediterranean Sea Water prevented further identi"cation of the NEADW core. The abyssal water mass, LDW, is characterized by a low salinity and a low dissolved oxygen content, and especially by its high dissolved silica content (Mantyla and Reid, 1983; McCartney, 1992). This is assumed to be due to the contribution of Antarctic bottom Water (AABW) to the LDW when it enters the eastern Atlantic basins at the Vema Fracture zone near 103N (Mantyla and Reid, 1983; McCartney, 1992; Schmitz and McCartney, 1993). Throughout the north- eastern Atlantic Basin the LDW core can be recognized by a near bottom salinity minimum and a silica maximum. When the LDW meets the pure ISOW core in the Iceland Basin the ISOW has a higher potential density than the coldest LDW over the deep Porcupine Abyssal Plain. This forces LDW to overlie the ISOW core in the relatively shallow northern Iceland Basin (van Aken, 1995; van Aken and Becker, 1996). The low salinity LSW core is found at about 1850 dbar in the northern parts of the northeastern Atlantic basins, overlying the deep levels where NEADW and LDW are observed. A shallower high salinity Mediterranean Sea Water (MSW) core, which originates from over#ow near Gibraltar of sub-surface water from the Mediterranean Sea, is found at about 1000 dbar in the more southern parts of the northeastern Atlantic (Tsuchiya et al., 1992; Arhan et al., 1994). Due to diapycnal mixing of the NEADW core with the overlying water its salinity therefore may either increase or decrease, depending on the geographical location. Tsuchiya et al. (1992) have shown that near 203W the salinity minimum, characteristic for the LSW core, disappears south of 413N due to mixing with the saline MSW. This results in an increase of the salinity at NEADW levels south of that latitude. Arhan et al. (1994) have observed the same feature south of 453N near 153W. This e!ect limits the determination of the southward extent of the retraceable NEADW core in the northeastern Atlantic when one uses only a H}S analysis (Harvey and Theodorou, 1986; Harvey and Arhan, 1988). Broecker et al. (1985) tried to determine the #ushing in the deep northeastern Atlantic from northern sources by means of an analysis of dissolved oxygen and nutrients in the cold bottom layers with a potential temperature H(2.63C. Given the contrast between ISOW with low nutrient and relatively high oxygen concentrations and LDW with lower oxygen and high nutrient concentrations a northward decrease of nutrients and an increase of oxygen is expected if ISOW also contributes to the ventilation of the deep northeastern Atlantic. Broecker et al. (1985) did not "nd any evidence for a meridional trend above the scatter of the observations in the deep nutrient and oxygen concentrations south of the Charlie Gibbs Fracture Zone at 523. This led them to conclude that all ISOW leaves the northeastern Atlantic towards the H.M. van Aken / Deep-Sea Research I 47 (2000) 757}788 761 west through this gap in the Mid Atlantic Ridge and does not contribute to the deep water mass further to the south.
Load more

Recommended publications
  • Respiration in the Mesopelagic and Bathypelagic Zones of the Oceans
    CHAPTER 10 Respiration in the mesopelagic and bathypelagic zones of the oceans Javier Arístegui1, Susana Agustí2, Jack J. Middelburg3, and Carlos M. Duarte2 1 Facultad de Ciencias del Mar, Universidad de las Palmas de Gran Canaria, Spain 2 IMEDEA (CSIC–UIB), Spain 3 Netherlands Institute of Ecology, The Netherlands Outline In this chapter the mechanisms of transport and remineralization of organic matter in the dark water-column and sediments of the oceans are reviewed. We compare the different approaches to estimate respiration rates, and discuss the discrepancies obtained by the different methodologies. Finally, a respiratory carbon budget is produced for the dark ocean, which includes vertical and lateral fluxes of organic matter. In spite of the uncertainties inherent in the different approaches to estimate carbon fluxes and oxygen consumption in the dark ocean, estimates vary only by a factor of 1.5. Overall, direct measurements of respiration, as well as − indirect approaches, converge to suggest a total dark ocean respiration of 1.5–1.7 Pmol C a 1. Carbon mass − balances in the dark ocean suggest that the dark ocean receives 1.5–1.6 Pmol C a 1, similar to the estimated respiration, of which >70% is in the form of sinking particles. Almost all the organic matter (∼92%) is remineralized in the water column, the burial in sediments accounts for <1%. Mesopelagic (150–1000 m) − − respiration accounts for ∼70% of dark ocean respiration, with average integrated rates of 3–4 mol C m 2 a 1, − − 6–8 times greater than in the bathypelagic zone (∼0.5 mol C m 2 a 1).
    [Show full text]
  • Chapter 5 Water Levels and Flow
    253 CHAPTER 5 WATER LEVELS AND FLOW 1. INTRODUCTION The purpose of this chapter is to provide the hydrographer and technical reader the fundamental information required to understand and apply water levels, derived water level products and datums, and water currents to carry out field operations in support of hydrographic surveying and mapping activities. The hydrographer is concerned not only with the elevation of the sea surface, which is affected significantly by tides, but also with the elevation of lake and river surfaces, where tidal phenomena may have little effect. The term ‘tide’ is traditionally accepted and widely used by hydrographers in connection with the instrumentation used to measure the elevation of the water surface, though the term ‘water level’ would be more technically correct. The term ‘current’ similarly is accepted in many areas in connection with tidal currents; however water currents are greatly affected by much more than the tide producing forces. The term ‘flow’ is often used instead of currents. Tidal forces play such a significant role in completing most hydrographic surveys that tide producing forces and fundamental tidal variations are only described in general with appropriate technical references in this chapter. It is important for the hydrographer to understand why tide, water level and water current characteristics vary both over time and spatially so that they are taken fully into account for survey planning and operations which will lead to successful production of accurate surveys and charts. Because procedures and approaches to measuring and applying water levels, tides and currents vary depending upon the country, this chapter covers general principles using documented examples as appropriate for illustration.
    [Show full text]
  • National Hydrography Data Content Standard for Coastal and Inland Waterways Public Review Draft, January 2000
    FGDC Data Committee FGDC Document Number National Hydrography Data Content Standard for Coastal and Inland Waterways Public Review Draft, January 2000 NSDI National Spatial Data Infrastructure National Hydrography Data Content Standard for Coastal and Inland Waterways – Public Review Draft Bathymetric Subcommittee Federal Geographic Data Committee January 2000 Federal Geographic Data Committee i FGDC Data Committee FGDC Document Number National Hydrography Data Content Standard for Coastal and Inland Waterways Public Review Draft, January 2000 Established by Office of Management and Budget Circular A-16, the Federal Geographic Data Committee (FGDC) promotes the coordinated development, use, sharing, and dissemination of geographic data. The FGDC is composed of representatives from the Departments of Agriculture, Commerce, Defense, Energy, Housing and Urban Development, the Interior, State, and Transportation; the Environmental Protection Agency; the Federal Emergency Management Agency; the Library of Congress; the National Aeronautics and Space Administration; the National Archives and Records Administration; and the Tennessee Valley Authority. Additional Federal agencies participate on FGDC subcommittees and working groups. The Department of the Interior chairs the committee. FGDC subcommittees work on issues related to data categories coordinated under the circular. Subcommittees establish and implement standards for data content, quality, and transfer; encourage the exchange of information and the transfer of data; and organize the
    [Show full text]
  • Modeling Groundwater Rise Caused by Sea-Level Rise in Coastal New Hampshire Jayne F
    Journal of Coastal Research 35 1 143–157 Coconut Creek, Florida January 2019 Modeling Groundwater Rise Caused by Sea-Level Rise in Coastal New Hampshire Jayne F. Knott†*, Jennifer M. Jacobs†, Jo S. Daniel†, and Paul Kirshen‡ †Department of Civil and Environmental Engineering ‡School for the Environment University of New Hampshire University of Massachusetts Boston Durham, NH 03824, U.S.A. Boston, MA 02125, U.S.A. ABSTRACT Knott, J.F.; Jacobs, J.M.; Daniel, J.S., and Kirshen, P., 2019. Modeling groundwater rise caused by sea-level rise in coastal New Hampshire. Journal of Coastal Research, 35(1), 143–157. Coconut Creek (Florida), ISSN 0749-0208. Coastal communities with low topography are vulnerable from sea-level rise (SLR) caused by climate change and glacial isostasy. Coastal groundwater will rise with sea level, affecting water quality, the structural integrity of infrastructure, and natural ecosystem health. SLR-induced groundwater rise has been studied in coastal areas of high aquifer transmissivity. In this regional study, SLR-induced groundwater rise is investigated in a coastal area characterized by shallow unconsolidated deposits overlying fractured bedrock, typical of the glaciated NE. A numerical groundwater-flow model is used with groundwater observations and withdrawals, LIDAR topography, and surface-water hydrology to investigate SLR-induced changes in groundwater levels in New Hampshire’s coastal region. The SLR groundwater signal is detected more than three times farther inland than projected tidal flooding from SLR. The projected mean groundwater rise relative to SLR is 66% between 0 and 1 km, 34% between 1 and 2 km, 18% between 2 and 3 km, 7% between 3 and 4 km, and 3% between 4 and 5 km of the coastline, with large variability around the mean.
    [Show full text]
  • Dispersion in the Open Ocean Seasonal Pycnocline at Scales of 1–10Km and 1–6 Days
    FEBRUARY 2020 S U N D E R M E Y E R E T A L . 415 Dispersion in the Open Ocean Seasonal Pycnocline at Scales of 1–10km and 1–6 days a MILES A. SUNDERMEYER AND DANIEL A. BIRCH University of Massachusetts Dartmouth, North Dartmouth, Massachusetts JAMES R. LEDWELL Woods Hole Oceanographic Institution, Woods Hole, Massachusetts b MURRAY D. LEVINE, STEPHEN D. PIERCE, AND BRANDY T. KUEBEL CERVANTES Oregon State University, Corvallis, Oregon (Manuscript received 23 January 2019, in final form 14 November 2019) ABSTRACT Results are presented from two dye release experiments conducted in the seasonal thermocline of the 2 2 Sargasso Sea, one in a region of low horizontal strain rate (;10 6 s 1), the second in a region of intermediate 2 2 horizontal strain rate (;10 5 s 1). Both experiments lasted ;6 days, covering spatial scales of 1–10 and 1–50 km for the low and intermediate strain rate regimes, respectively. Diapycnal diffusivities estimated from 26 2 21 2 21 the two experiments were kz 5 (2–5) 3 10 m s , while isopycnal diffusivities were kH 5 (0.2–3) m s , with the range in kH being less a reflection of site-to-site variability, and more due to uncertainties in the background strain rate acting on the patch combined with uncertain time dependence. The Site I (low strain) experiment exhibited minimal stretching, elongating to approximately 10 km over 6 days while maintaining a width of ;5 km, and with a notable vertical tilt in the meridional direction. By contrast, the Site II (inter- mediate strain) experiment exhibited significant stretching, elongating to more than 50 km in length and advecting more than 150 km while still maintaining a width of order 3–5 km.
    [Show full text]
  • Article Is Available Gen Availability
    Hydrol. Earth Syst. Sci., 23, 1763–1777, 2019 https://doi.org/10.5194/hess-23-1763-2019 © Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. Oxycline oscillations induced by internal waves in deep Lake Iseo Giulia Valerio1, Marco Pilotti1,4, Maximilian Peter Lau2,3, and Michael Hupfer2 1DICATAM, Università degli Studi di Brescia, via Branze 43, 25123 Brescia, Italy 2Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Müggelseedamm 310, 12587 Berlin, Germany 3Université du Quebec à Montréal (UQAM), Department of Biological Sciences, Montréal, QC H2X 3Y7, Canada 4Civil & Environmental Engineering Department, Tufts University, Medford, MA 02155, USA Correspondence: Giulia Valerio ([email protected]) Received: 22 October 2018 – Discussion started: 23 October 2018 Revised: 20 February 2019 – Accepted: 12 March 2019 – Published: 2 April 2019 Abstract. Lake Iseo is undergoing a dramatic deoxygena- 1 Introduction tion of the hypolimnion, representing an emblematic exam- ple among the deep lakes of the pre-alpine area that are, to a different extent, undergoing reduced deep-water mixing. In Physical processes occurring at the sediment–water inter- the anoxic deep waters, the release and accumulation of re- face of lakes crucially control the fluxes of chemical com- duced substances and phosphorus from the sediments are a pounds across this boundary (Imboden and Wuest, 1995) major concern. Because the hydrodynamics of this lake was with severe implications for water quality. In stratified shown to be dominated by internal waves, in this study we in- lakes, the boundary-layer turbulence is primarily caused by vestigated, for the first time, the role of these oscillatory mo- wind-driven internal wave motions (Imberger, 1998).
    [Show full text]
  • Hydrographic Surveys Specifications and Deliverables
    HYDROGRAPHIC SURVEYS SPECIFICATIONS AND DELIVERABLES March 2019 U.S. Department of Commerce National Oceanic and Atmospheric Administration National Ocean Service Contents 1 Introduction ......................................................................................................................................1 1.1 Change Management ............................................................................................................................................. 2 1.2 Changes from April 2018 ...................................................................................................................................... 2 1.3 Definitions ............................................................................................................................................................... 4 1.3.1 Hydrographer ................................................................................................................................................. 4 1.3.2 Navigable Area Survey .................................................................................................................................. 4 1.4 Pre-Survey Assessment ......................................................................................................................................... 5 1.5 Environmental Compliance .................................................................................................................................. 5 1.6 Dangers to Navigation ..........................................................................................................................................
    [Show full text]
  • Direct Observations of Along-Isopycnal Upwelling and Diapycnal Velocity at a Shelfbreak Front John A
    University of Rhode Island DigitalCommons@URI Graduate School of Oceanography Faculty Graduate School of Oceanography Publications 2004 Direct Observations of Along-Isopycnal Upwelling and Diapycnal Velocity at a Shelfbreak Front John A. Barth Dave Hebert University of Rhode Island See next page for additional authors Follow this and additional works at: https://digitalcommons.uri.edu/gsofacpubs Citation/Publisher Attribution Barth, J.A., D. Hebert, A.C. Dale, and D.S. Ullman, 2004: Direct Observations of Along-Isopycnal Upwelling and Diapycnal Velocity at a Shelfbreak Front. J. Phys. Oceanogr., 34, 543–565. doi: 10.1175/2514.1 Available at: https://doi.org/10.1175/2514.1 This Article is brought to you for free and open access by the Graduate School of Oceanography at DigitalCommons@URI. It has been accepted for inclusion in Graduate School of Oceanography Faculty Publications by an authorized administrator of DigitalCommons@URI. For more information, please contact [email protected]. Authors John A. Barth, Dave Hebert, Andrew C. Dale, and David S. Ullman This article is available at DigitalCommons@URI: https://digitalcommons.uri.edu/gsofacpubs/337 MARCH 2004 BARTH ET AL. 543 Direct Observations of Along-Isopycnal Upwelling and Diapycnal Velocity at a Shelfbreak Front* JOHN A. BARTH College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon DAVE HEBERT Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island ANDREW C. DALE College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon DAVID S. ULLMAN Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island (Manuscript received 18 November 2002, in ®nal form 2 September 2003) ABSTRACT By mapping the three-dimensional density ®eld while simultaneously tracking a subsurface, isopycnal ¯oat, direct observations of upwelling along a shelfbreak front were made on the southern ¯ank of Georges Bank.
    [Show full text]
  • Hydrographic Surveying Resources at ODOT
    Hydrographic Surveying Resources @ ODOT David Moehl, PLS, CH Project Surveyor, ODOT Geometronics What is hydrography? • Hydrography is the measurement of physical features of a water body. • Bathymetry is the foundation of the science of hydrography. • Hydrography includes not only bathymetry, but also the shape and features of the shoreline; the characteristics of tides, currents, and waves; and the physical and chemical properties of the water itself. What is bathymetry? • The name is derived from Greek: • Bathus = Deep • and Meton = Measure • Dictionary: “The measurement of the depths of oceans, seas, or other large bodies of water, also: the data derived from such measurement.” • Wikipedia: “is the underwater equivalent to topography.” • NOAA: “The study of the ‘beds’ or ‘floors’ of water bodies, including the ocean, rivers, streams, and lakes and currently means ‘submarine topography’.” Source: https://www.ngdc.noaa.gov The lost city of Atlantis? Source: Google Earth How do we measure water depths? • Manual How do we measure water depths? • Manual How do we measure water depths? • Manual How do we measure water depths? • Manual • Sound • Echosounders • Determines the depth by measuring the two way travel time of sound through the water • Different types of echosounders Singlebeam echosounders • This is the tool that ODOT utilizes • Benefits of this system: • Most affordable and widely used • Less ongoing training, software and maintenance costs • Useful for: • Cross section data acquisition for hydraulic modeling • Uniform topography
    [Show full text]
  • Geography, Hydrography and Climate 5
    chapter 2 Geography, hydrography and climate 5 GEOGRAPHY 2.1 Introduction This chapter defines the principal geographical characteristics of the Greater North Sea. Its aim is to set the scene for the more detailed descriptions of the physical, chemical, and biological characteristics of the area and the impact man’s activities have had, and are having, upon them. For various reasons, certain areas (here called ‘focus areas’) have been given special attention. 6 Region II Greater North Sea 2.2 Definition of the region 2.3 Bottom topography The Greater North Sea, as defined in chapter one, is The bottom topography is important in relation to its effect situated on the continental shelf of north-west Europe. It on water circulation and vertical mixing. Flows tend to be opens into the Atlantic Ocean to the north and, via the concentrated in areas where slopes are steepest, with the Channel to the south-west, and into the Baltic Sea to the current flowing along the contours. The depth of the North east, and is divided into a number of loosely defined Sea (Figure 2.1) increases towards the Atlantic Ocean to areas. The open North Sea is often divided into the about 200 m at the edge of the continental shelf. The relatively shallow southern North Sea (including e.g. the Norwegian Trench, which has a sill depth (saddle point) of Southern Bight and the German Bight), the central North 270 m off the west coast of Norway and a maximum depth Sea, the northern North Sea, the Norwegian Trench and of 700 m in the Skagerrak, plays a major role in steering the Skagerrak.
    [Show full text]
  • Tides and Water Level Requirements for N.O.S Hydrographic Surveys
    International Hydrographic Review, Monaco, LXXVI(2), September 1999 TIDES AND WATER LEVEL REQUIREMENTS FOR N.O.S HYDROGRAPHIC SURVEYS by W. Michael G ib s o n and Stephen K. G i l l 1 Paper already presented at the HYDRO'99 Conference, Mobile, Alabama, USA, 27-29 April 1999. Abstract The Center for Operational Oceanographic Products and Services (CO-OPS) of the National Ocean Service (NOS) contributes to the NOAA Nautical Charting Program by establishing requirements for, and providing the critical water level data necessary to produce accurate depth measurements. CO-OPS efforts involve six main functional areas: 1) tide and water level requirement planning; 2) preliminary tidal zoning development; 3) water level station installation, operation and removal; 4) data quality control, processing, and tabulation; 5) tidal datum computation and tidal datum recovery; and 6) generation of water level reducers and final tidal zoning. For each functional area, CO-OPS maintains appropriate specifications and standard operating procedures under the umbrella of an overall Data Quality Assurance Plan (DQAP). The objective of this effort is to provide the tide and water level correction information necessary to reduce soundings to Chart Datum. The goal is to provide water level correction information that meets current error budgets for correctors to soundings. The total uncertainty in the water level corrections are derived from three main sources: 1) errors in the actual measurement of water level; 2) uncertainties in the computation of tidal datums based on short period observations and in the datum recovery process at historical locations; and 3) uncertainties in the application of tidal zoning within the survey area.
    [Show full text]
  • Chapter 5 Lecture
    ChapterChapter 1 5 Clickers Lecture Essentials of Oceanography Eleventh Edition Water and Seawater Alan P. Trujillo Harold V. Thurman © 2014 Pearson Education, Inc. Chapter Overview • Water has many unique thermal and dissolving properties. • Seawater is mostly water molecules but has dissolved substances. • Ocean water salinity, temperature, and density vary with depth. © 2014 Pearson Education, Inc. Water on Earth • Presence of water on Earth makes life possible. • Organisms are mostly water. © 2014 Pearson Education, Inc. Atomic Structure • Atoms – building blocks of all matter • Subatomic particles – Protons – Neutrons – Electrons • Number of protons distinguishes chemical elements © 2014 Pearson Education, Inc. Molecules • Molecule – Two or more atoms held together by shared electrons – Smallest form of a substance © 2014 Pearson Education, Inc. Water molecule • Strong covalent bonds between one hydrogen (H) and two oxygen (O) atoms • Both H atoms on same side of O atom – Bent molecule shape gives water its unique properties • Dipolar © 2014 Pearson Education, Inc. Hydrogen Bonding • Polarity means small negative charge at O end • Small positive charge at H end • Attraction between positive and negative ends of water molecules to each other or other ions © 2014 Pearson Education, Inc. Hydrogen Bonding • Hydrogen bonds are weaker than covalent bonds but still strong enough to contribute to – Cohesion – molecules sticking together – High water surface tension – High solubility of chemical compounds in water – Unusual thermal properties of water – Unusual density of water © 2014 Pearson Education, Inc. Water as Solvent • Water molecules stick to other polar molecules. • Electrostatic attraction produces ionic bond . • Water can dissolve almost anything – universal solvent © 2014 Pearson Education, Inc. Water’s Thermal Properties • Water is solid, liquid, and gas at Earth’s surface.
    [Show full text]