icebergs in the barents sea -...

Icebergs in the Barents Sea

Sveinung Løset, dr.ing., prof., vice-dean

Faculty of Engineering Science and Technology

Norwegian University of Science and Technology

Icebergs Icebergs –– requested data for design purposesrequested data for design purposes

1.1. Spatial and temporal distributionsSpatial and temporal distributions

2.2. Size and geometrySize and geometry

3.3. Drift speeds and patternsDrift speeds and patterns

4.4. Mechanical propertiesMechanical properties

Iceberg originIceberg origin

Iceberg bubblesIceberg bubbles

Flow

2-5 mm

20-200 µm

Air pressure

0.2-2 MPa

(After Nadreau, 1987)

Transformation from snow to iceTransformation from snow to ice

Grid size: 10 mm

Iceberg originIceberg origin

Franz Josephs Land , April 2005Franz Josephs Land , April 2005

Tabular bergs

Irregular bergs

Field campaigns:Field campaigns: ICEBASE 1987ICEBASE 1987IDAP 1988IDAP 1988--9292

Stereo aerial photography Stereo aerial photography →→ geometry and sizegeometry and size

Spotting by aircrafts Spotting by aircrafts →→ populationpopulation

Satellites images Satellites images →→ populationpopulation

Ground surveying Ground surveying →→ mechanical propertiesmechanical properties

Tracking of about 40 icebergs Tracking of about 40 icebergs →→ drift pattern/speeddrift pattern/speed

Iceberg shapesIceberg shapes

Tabular: Tilted Domed BlockyHorizont.

Irregular:

Rounded:

Pinnacled Pyramidal Drydock Tabular remnant

Subrounded Wellrounded

Iceberg sourcesIceberg sources

SvalbardSvalbard::Estimated iceberg/Estimated iceberg/bergybergy bits production rate is 1.3 bits production rate is 1.3 kmkm33/year/year

Franz Josef Land:Franz Josef Land:About 40 islands (most of them iceAbout 40 islands (most of them ice--capped) which include capped) which include about 2600 km of tideabout 2600 km of tide--water ice cliffswater ice cliffsMost islands are surrounded by deep waterMost islands are surrounded by deep waterEstimated iceberg/Estimated iceberg/bergybergy bits production rate is 3.0 bits production rate is 3.0 kmkm33/year of which 50 % is likely to drift into the BS /year of which 50 % is likely to drift into the BS

Iceberg traces, Spitsbergen Banks, 1988

Landsat image, 01.06.88

Spitsbergen Bank, 22.03.88

MV ’Lance’ (78 m long), upper-left side of berg

HHmaxmax = 43.5 m= 43.5 m

Tabular berg (BS)Tabular berg (BS)

12.1 mill. tons

Maximum sail height,1987Maximum sail height,1987

0

0,2

0,4

0,6

0,8

1

1,2

0 10 20 30 40 50

MAXIMUM SAIL HEIGHT (m)

PRO

BAB

ILIT

Y O

F EX

CEED (b)

Mass, 1987Mass, 1987

0

0,2

0,4

0,6

0,8

1

1,2

0 5000 10000 15000

MASS (1000 tonnes)

PRO

BAB

ILIT

Y O

F E

XCEE

D (b)0

5

10

15

20

25

30

35

100 2100 4100 6100 8100 10100 12100

MASS INTERVAL (1000 tonnes)

NUM

BER

OF

ICEB

ER

(a)

Geometry and sizeGeometry and size

2

4 ASpπ

=

LmaxWmaxHmax

Field surveys Field surveys -- 19871987

Analysis of stereo photos of 52 icebergs in the western BS:Analysis of stereo photos of 52 icebergs in the western BS:

Mean mass: 0.847 million tons; 14 % probability of encountering Mean mass: 0.847 million tons; 14 % probability of encountering an iceberg an iceberg with mass exceeding 1 million tonswith mass exceeding 1 million tons

HHmaxmax = 15.4 m, = 15.4 m, LLmaxmax = 118 m, = 118 m, WWmaxmax = 81 m, = 81 m, SS = 0.78= 0.78

HHmaxmax = 43.5 m of the highest iceberg; 6 % probability of encounterin= 43.5 m of the highest iceberg; 6 % probability of encountering an g an iceberg exceeding 30 miceberg exceeding 30 m

WWmaxmax is strongly correlated with the is strongly correlated with the LLmaxmax (correlation coefficient 0.95)(correlation coefficient 0.95)Total number of iceberg sightings: 180 in 3 field campaignsTotal number of iceberg sightings: 180 in 3 field campaigns

Biggest observed iceberg:Biggest observed iceberg:

Type:Type: TabularTabular

Geometry:Geometry: HHmaxmax = 12 m, = 12 m, LLmaxmax = 499 m, = 499 m, WWmaxmax = 253 m= 253 m

Mass:Mass: 6.35 million tons6.35 million tons

Location:Location: South of South of SvenskSvenskøøyaya

Surveys 1988Surveys 1988--9292

Year # Hmax (m) Lmax (m) Total iceberg mass(1000 tons)

1988 109 17.8 ± 7.1 101.8 ± 60.3 453.3 ± 738.81989 68 17.5 ± 7.2 83.4 ± 39.8 276.7 ± 306.71990 89 13.3 ± 6.1 84.9 ± 46.6 196.6 ± 244.31991 41 13.2 ± 5.0 83.1 ± 61.9 284.3 ± 516.91992 23 10.2 ± 3.8 104.2 ± 48.8 221.2 ± 219.4

1988-92 330 15.4 ± 6.9 92.3 ± 52.9 311.2 ± 512.2

Statistics (1988Statistics (1988--92)92)

Iceberg parameters: 3-parameter W eibull pdf

1

( ) expx xf xγ γγ ε ε

θ θ θ

− ⎡ ⎤− −⎛ ⎞ ⎛ ⎞= −⎢ ⎥⎜ ⎟ ⎜ ⎟⎝ ⎠ ⎝ ⎠⎢ ⎥⎣ ⎦

ε θ γ Rp = 50 yrs Rp = 100 yrsHmax 4.5 13.0 1.45 37.7 m 41.7 mLmax 44.9 74.4 0.83 432 m 516 m

NORWAY

SVALBARD

40ºE 60ºE20ºE

Sea surface currentSea surface current

Iceberg2 #3056 and #3057, autumn 1987Iceberg2 #3056 and #3057, autumn 1987

Iceberg drift (Newton’s 2. Law)

- Coriolis force

Fa,w - air and water form drag

Fr - wave radiation force

Fs - sea ice forcing

Fp - horizontal water pressure gradient force

0i

i a w r s pdm m fdt

= − × + + + + +V k V F F F F F

0 im f− ×k V

Drift patternDrift pattern

Thermal energy balanceThermal energy balance


Heat transfer equation:Heat transfer equation:

Ice parameters:

k –– thermal conductivitythermal conductivity

T -- temperaturetemperature

-- rate of mass exchange per rate of mass exchange per unit volumeunit volume

l -- latent heat of fusionlatent heat of fusion

ρ -- densitydensity

c -- specific heat capacityspecific heat capacity

kT ml cTii, + = ρ

UdV qdS rdV= +z z z

U (internal energy)

V (volume)

S (surface)

r (radiation)

q (flux)

m


WL

Temperature & deteriorationTemperature & deterioration

October 1, 1987

Oct 1 Jun 1

Metdata (Oct. 1987 – June 1988)Vertical slice

Air

tem

p. (°

C)

Win

d sp

eed

(m/s

)C

loud

cov

er

Time

Nov 1st, 1987 Dec 1st, 1987

Feb 1st, 1988Jan 1st, 1988

Temperature distributionTemperature distribution


The heat transfer coefficient to water is typically 150The heat transfer coefficient to water is typically 150--200 200 W/mW/m22°°C; about 15C; about 15--20 times higher than the one to air 20 times higher than the one to air =>=>undercut in the waterlineundercut in the waterline

Subsurface convection melt rate of 0.05Subsurface convection melt rate of 0.05--0.2 m/day per 0.2 m/day per °°C C of sea water/ice temperature difference.of sea water/ice temperature difference.

The subsurface of the berg does also melt for temperatures The subsurface of the berg does also melt for temperatures below the normal freezingbelow the normal freezing--point of fresh water, 0point of fresh water, 0°°C, due to C, due to salinity freezingsalinity freezing--point depression.point depression.

(After Nadreau, 1987)

NORWAY

SVALBARD

SVALBARD

Simulated tracks of 150 icebergs in the Barents Sea

Drift speeds of icebergsDrift speeds of icebergs

Mean value: 0.25 Mean value: 0.25 m/sm/s

From 3 a.m. 5th November 1987 a From 3 a.m. 5th November 1987 a pinnacledpinnacled iceberg was observed to iceberg was observed to drift with a mean drift speed of 1.13 drift with a mean drift speed of 1.13 m/sm/s for 31 hours. A maximum for 31 hours. A maximum speed of 1.38 speed of 1.38 m/sm/s was achieved towards the end of this periodwas achieved towards the end of this period

A strong tailwind acted on this iceberg during the extreme driftA strong tailwind acted on this iceberg during the extreme drift

The measured wind on The measured wind on HopenHopen showed a persistent wind speed of 13showed a persistent wind speed of 13--16 16 m/sm/s from the 5th of November to the 7th, with gusts of wind up to 3from the 5th of November to the 7th, with gusts of wind up to 32 2 m/sm/s

Summary (1): reconnaissance surveys 1987Summary (1): reconnaissance surveys 1987--9292

Argos buoy drift data confirm that Franz Joseph Land is the mainArgos buoy drift data confirm that Franz Joseph Land is the mainiceberg source for the BSiceberg source for the BS

Icebergs are probably the design environmental feature for produIcebergs are probably the design environmental feature for production ction facilities north of 74facilities north of 74ººN in the western BSN in the western BS

A maximum iceberg drift speed of 1.38 A maximum iceberg drift speed of 1.38 m/sm/s was recorded among 40 was recorded among 40 tracked bergstracked bergs

The biggest iceberg was encountered in 1987 with a mass of 6.4 The biggest iceberg was encountered in 1987 with a mass of 6.4 million tonsmillion tons

Summary (2): reconnaissance surveys Summary (2): reconnaissance surveys --19921992

Mean iceberg mass for the time period 1988Mean iceberg mass for the time period 1988--92: 0.311 million tons92: 0.311 million tons

Substantial inter annual variations in the iceberg population/maSubstantial inter annual variations in the iceberg population/mass with ss with 1988 as the most severe year in the 19871988 as the most severe year in the 1987--92 time period92 time period

In the time period 1970In the time period 1970--89, 1014 reconnaissance flights were 89, 1014 reconnaissance flights were performed in the BS and over 16000 icebergs were observed with tperformed in the BS and over 16000 icebergs were observed with the he largest monthly population in April. largest monthly population in April.

Cold Regions Science and Technology, Vol. 21 (2), pp. 105-115.

Journal of Geophysical Research, Vol.98, C6, pp. 10001-10012.

icebergs in the barents sea -...

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