Sea level chnage

Dr. Arindam Sarkar , Department of Geography
Purash Kanpur Haridas Nandi College Website: https://pkhnm.ac.in/
Email ID: arindam.srkr1@gmail.com
Sea Level Change
Dr. Arindam Sarkar
Department of Geography
Purash Kanpur Haridas Nandi College
arindam.srkr1@gmail.com

Valentine Classification of Advancing and Retreating coast
Valentine's
Classification of
Coastal Contexts
(1952)
Identified coasts as
………
 Erosional or
Depositional
 Emerging or
Submerging coast

Scale and Process
Scale and Process of Sea Level Change
Eustatic  Global or large scale sea level change
caused by addition of large volume of water
into the ocean
Isostatic  Local scale sea level change caused by
uplift or submergence of land comparative to
the level of sea
Marine
Regression
 Impact associated with relative fall in sea
level
Marine
Transgression
 Impact associated with relative rise of sea
level

Eustatic Sea Level Change
 Decrease of global temperatures leads to more
precipitation occurring in the form of snow.
 Eventually this now turns to ice and so water is
stored on land rather than being returned to
ocean store.
 Consequently there is global fall of sea level.
 If global temperature subsequently rise,
glaciers retreat and ice melts causing a rise in
global sea level.

Eustatic
Sea Level Change

Isostatic Changes of sea level
Glacial Period
During a glacial period the weight of ice
sheets and glaciers adds weight to the earth
crust
 This causes the crust to sink lower into
the mantle rock beneath
 This results in an apparent rise in the
level of the sea
Interglacial Period
 At the end of the glacial period the ice
melts and weight is lost from the crust
 It causing it to slowly rise.
 The sea level will then appear to fall
Some places.
 At the east coast of Scotland are rising at
a rate of 7mm/year

Landforms associated with Marine Transgression
(Submergence landforms)
Ria Coast of Ferrol Fjords of Kenai

Landforms associated with Marine Regression
(Emergence landforms)
Raised
Beach
Turakirae
Head,
Wellington

Landforms associated with Marine Regression
(Emergence landforms)
Abandoned
Coastline
Britain’s abandoned
coastal area

Facts behind Sea Level Change:
 Rising and lowering of sea level is called sea level change.
 Two important events are associated with sea level change (Cooling
and Warming)
Global Cooling Global Warming
 Decrease of temperature
 Cooling in high latitude and high
altitude
 Evaporation in low latitude
 Sea level decrease in low latitude
 1° decrease of temperature causes
2m lowering of sea level
 Gradual increase of temperature
 Melting of glacier in the high
altitude and high latitude
 Water accumulation in low latitude
 Rise of sea level in low latitude
 Submergence of islands and
coastal area
 Conversion of marine ecology to
land ecology
Cycle of erosion

Causes of Sea Level Change
 Vertical Land Movement
 Isostatic adjustment
 Tectonic effect
 Sedimentation
 Human factor (Ground water and extraction of oil)
 Changes in level of ocean surface
 Glaciers
Ice sheets
 Ocean current
 Tidal behaviour
 Changes in hydrological cycle
 Expansion or contraction

Facts of contemporary sea level rise
 Sea level rises over 8 inches (23 cm) during 1880—present
 Sea level rises 3 inches in last 25 years
 Sea level rise rate is .13 inch (3.2 mm) per year
Major causes behind contemporary sea level rise
 Thermal expansion due to increase of sea surface temperature
 Melting of land-based ice (glaciers ice sheet)
Impact of sea level rise on drainage basin
 Reduce drainage basin area
 It brings greater aridity in the basin area
 It reduces run off in the basin area
Sea level change and related mechanism
 Rise of sea level-reduction of drainage basin are-greater aridity-reduction of runoff
 Fall of sea level- Enlarge drainage basin area 9downstream enlargement)-increase
drainage basin relief-increase the potential energy available in the landscape

Evidences from historical past (Geological age)
 The sea level fluctuation in Late Cenozoic caused major shifts in drainage area
and the periodic submergence of extensive drainage system in the relatively brief
interludes of high inter glacial sea level such as we are experie4ncing at the
present day (Summerfield,1991).
 Sea level fluctuation in Quaternary geological age leads lowering of base level
up to 100m during past 1Ma; large scale valley incision along the continental
margin has been promoted by this lower of base level. Successive erosion takes
palace with the formation of knick point and intensive down cutting.
 Valley aggregation has been laded buried of incised valley, huge sediment
carried by the perennial river due to rapid melting of high altitude glacier.
 Aggradations process is called as process of alluviation. Aggradation is a
geological term popularly used to represent the process of increase elevation of
land through rapid sedimentation by a dedicated river system.
 Aggradations occur when supply of sediment is greater than capacity to
transport.

 After end of ice age, during Holocene temperature rises frequently, that leads
spontaneously melting of high altitude glacier. Upstream water source of
perennial river increase. Stream power increase with increase of discharge of
channel. Leading with excessive carrying capacity of sediment load towards
downstream and deposited in the less sloped foothill area due to loss of energy
for sudden change of slope.
 Mississippi river is the best example of river aggregation.
 Mississippi valley has been produced by the deposition of huge glacially
derived sediment carried from upstream (North) enhanced by the melting of
Lauren tide ice sheet (glacier).
 Some result has been derived from several dynamic research work done on
terrace deposition in the lower Mississippi valley about phases of
sedimentation distribute with episodes of valley incision, which are associated
with fluctuation of sea level (rise and fall) in the Pleistocene age.
 Impact of Quaternary sea level change on drainage basin can be easily
explained through reference of Amazon river system.

 River Amazon was deeply entrenched during last glacial age, when sea level
was low but transformation has been observed in the lower starch of Amazon
river due to rise of sea level during past glacial age.
 But when sea level gets stabilized during Holocene age sediment behavior
has been changed, due to this wide low gradient flood plain has been spotted at
lower course of Amazon river.
 Frequent accumulation of sediment at the flood plain blocks mouth of the
tributaries of lower Amazon.
 When vertical movement of land is greater than sea and relative fluctuation
in sea observed then it has significant effect on drainage system and that also
depends on nature of crustal deformation. Here tectonic force and sea level
change both operating together.

Sea level change and river hydrostatic
consequences
 Fall of sea level-reduce water load on continental margin-flex upward.
 Rise of sea level maximize sediment load.
 Landward reversal of river course with less discharge and low coastal gradient
has been observed at Rhone and Nile river during Late Miocene. Because
desiccation of the Mediterranean sea cause flexural swarp of its NE and SE
margins.
 Major shift in drainage area and periodic submergence of extensive drainage
system due to frequent fluctuation of sea level has been observed in the Late
Cenozoic era.
 Effect of sea level change in drainage system in concentrated on its base level
of erosion.
 Shoreline migration is also an important impact of sea level change.
 Other related factor of shoreline migration are coastal geological configuration,
beach morphology etc.

 Sea level change spatially non-uniform in the globe
 Sea level affected by Geo-physical changes or process
 Local sea level observation connected with
 Ice age dynamics
 Dynamic topography
 Sediment fluxes
 Eustatic sea level is closely related to volume of ice as well as sate of water
Modelling of Sea Level Change
Modelling sea level change requires a gravitationally self- consistent model

 Gravity matter
Changes in gravity filed drive changes in the sea surface
 Solid earth matter
Glacial Isostatic adjustment is a significant component of projected sea level change over
the next century
Definition of sea level
Elevation difference between the sea surface equi-potential and the solid surface

 Modern Sea level models are built on the foundation of Ferrel and
Clark (1976)
 Gravitationally self consistence
 Deformable viscous-elastic earth
 Later model introduced
 Shoreline migration (Johnston, 1993)
 Earth rotation (Milne and Mitrovica, 1996,1998)
 Sediment redistribution (Dalca et al. 2013)
 Dynamic topography (Austermann and Mitrovica, 2015)
 Sea level change : Main fact from Model
 Changes in surface loading
 Crustal evolution
 Gravity field
 Earth rotation axis

Modelled Sea level response to ice and sediment loads are
governed by
 Spherically Symmetric
 Elastic lithosphere
 Density and elasticity profile ( PREM; Dziewonski and Anderson, 1981)
 Viscosity profile (VM2; Peltier, 2004)
 Discretized at spherical harmonic degree
Changes in ice loading produce spatially variable changes in sea
level
 input- ice thickness (Peltier, 2004)
 Output- sea level changes
This is a specific example of general principal
 All geophysical process produce spatially variable sea level change
 Shore line migration
 Sea level response to sediment distribution

Figure 1 shows the key
contributions to sea-
level changes at the
different operational
scales used in this paper.
The contribution of
glaciers, ice sheets and
land water storage
changes are calculated
using ofine models
forced with boundary
conditions derived from
climate model
projections (mainly
temperature and
precipitation), implying
that feedbacks between
freshwater flux and
ocean circulation are not
captured.

Sea level chnage

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