Title : Oceanography of marginal seas and the coastal zoneA marginal sea is a part of ocean partially enclosed by land such as islands, archipelagos, peninsulas or well marked indentation (Arabian Sea, Baltic Sea, Bay of Bengal, Bering Sea, Beaufort Sea, Black Sea, Gulf of California, Gulf of Mexico, Mediterranean Sea, Red Sea, Ross Sea, Weddell Sea, Barent Sea ….)The coastal zone is a region where interaction of the sea and land processes occurs …

Definitions (chapter 2.1)Oceanography is the study of the oceanGeophysics is the study of the physics of the Earth.Physical Oceanography is the study of physical properties and dynamics ofthe oceans. Geophysical Fluid Dynamics is the study of the dynamics of fluid motion onscales influenced by the rotation of the EarthHydrography is the preparation of charts describing oceandepths, currents, temperature, salinity and tides

Oceanography

GeophysicsPhysicalOceanography

Geophysical Fluid

Dynamics

Hydrography

Eras of Oceanographic Exploration (chapter 2.2 … revised)

• Era of (exploratory/discovery/sailorship) Surface Oceanography: Earliest times to 1873. The era is characterized by systematic collection of mariners’ observations of winds, currents, waves, temperature, and other phenomena observable from the deck of sailing ships.

• Era of early sub-surface scientific campaigns: 1873–1914 with wide range oceanographic campaigns later (1925–1940) characterized by detailed surveys of colonial areas

• Early contemporary oceanography: 1947–1956 (1958) . Characterized by long surveys using new “modern“ instruments and observational methods, At the same time the first basic theoretical understanding of ocean circulation was developed. This can be extended to include Era of International Cooperation: 1957–1978, during which the first multinational surveys of oceans and studies of oceanic processes were carried out .

• Era of modelling and (later) Earth system science 1969-present, Characterized by massive use of computer and numerical codes which have led to global studies of the interaction of biological, chemical, and physical processes in the ocean and atmosphere and on land

• Era of Satellites: 1978–present. Characterized by global surveys of oceanic processes from space.

Generalities on observations:Sampling Error (box in section 2.5)Sampling error is the largest source of error in the geosciences. It is caused by a set of samples not representing the population of the variable being measured. A population is the set of all possible measurements, and a sample is the sampled subset of the population. This has nothing to do with instrumental error a or precisionSampling error occurs also with an instrument with no error and infinite precisionTo determine if your measurement has a sampling error, you must first completely specify the problem you wish to study. This defines the population. Then, you must determine if the samples represent the population. Both steps are necessary. Oceanic samples rarely represent the population we wish to study. We always have sampling errors. instrument errors are due to the inaccuracy of the instrument. Sampling errors are due to a failure to make a measurement. Instrument error are related to the limitation of the observational instrument

(section 2.5)Accuracy is the difference between the measured value and the true value. Precision is the difference among repeated measurements. Linearity requires that the output of an instrument be a linear function of the inputErrors may be correlated with other variables unchecked of the problem.

Generalities on ocean size, longitude and latitudes.(chapter 3.2)Basins, continental shelves, slopes, canyons, plains, ridges, seamounts sills, trenches (chapter 3.3)

Aspect ratio of oceans𝛿 = 10−4

And Ridges, Seamounts, Sills, Trenches, Plains, Canyons, Sills…

From Introduction to Physical Oceanographyby Robert H. Stewart

Observations to produce ocean bottom maps

• Echo Sounders: maps of the ocean are mostly based on measurements made by echo sounders. The instrument transmits a burst of 10–30 kHz sound and listens for the echo from the sea floor (chapter 3.4). This can be very efficient when mapping a small portion of seafloor

o Limitation: at global scale the tracks are not well distributed and not sufficiently denseo Problem: The speed of sound waves depends on temperature, pressure and salinityo Solution: corrections are needed leading to a precision which is precision is typically 1%,

• Satellite Altimetry: Altimeters profile the shape of the sea surface along the satellite track. The mean shape of the sea surface follows at first approximation the geoid, that is a surface everywhere perpendicular to the local direction of gravity. Anomalies of mass distribution (seamounts, trenches, ridges) deform gravity and are mapped on geoid level. Note that many satellite passes are needed to obtain an average sea surface level (chapter 3.4) . Anomalies of the sea level represent immediately local gravity anomalies and only indirectly the topography of the seafloor (fig.3.12)

o Problem: The correspondence between the shape of the sea surface and the depth of the water depends on the characteristics of the sea floor.

o Solution: echo-sounders data are used to determine the regional relationships. Echo-sounders provide the large scale picture, satellite altimetry provides the details (see dataset of Smith and Sandwell , 1994 https://www.ngdc.noaa.gov/mgg/bathymetry/predicted/explore.HTML)

o Issue: the sea surface anomaly (sea surface topography or sea surface dynamic height) depends also on ocean currents

o Answer: transitional signals are cancelled by averaging over a long period. Residual mean anomalies are smaller than the signature of gravity anomaly

o Problem: The speed of EM waves depends on temperature, pressure and salinityo Solution: corrections are needed implying a precision which is typically 3-6cm

Sea floor mapping by ssea level gravity anomaly1Gal = 10-2m/s2 1mGal=10-5m/s2

g at the Earth’s surface has a value of about 9.8∙105mGalThe variation of g with level at the Earth’s surface is about 3.1∙10-1mgal/mTherefore a variation of 31mGal corresponds to a variation of 100m of levelHere it is shown how a map of the sea surface level (given as gravity anomaly) reveals the seafloor features (available at https://earthobservatory.nasa.gov/IOTD/view.php?id=87189 after Sandwell, D. et al. (2014) New global marine gravity model from CryoSat-2 and Jason-1 reveals buried tectonic structure. Science, 346 (6205), 65–67).The result combine the whole effect of the anisotropy of mass distribution of the Earths crust. ths

Sea floor bathymetry, Smith, W. H. F. , and D. T. Sandwell . 1997. Global sea floor topography from satellite altimetry and ship depth soundings. Science 277 5334 1956–1962.

3-6 -3 0

https://www.ngdc.noaa.gov/mgg/image/2minrelief.html

European Seas