Greenland / Norwegian Seas / Eurasian Basin Model

by Gerhard Boenisch and Peter Schlosser

This page is under construction

The map shows the location of the Greenland, Icelandic and Norwegian Seas, and the Arctic Ocean.

The purpose of the intrduced simple box model is to calculate renewal times of the deep basins and to study variabilities in these renewal times.

Boenisch and Schlosser [1995] present a detailed description of the model. Here, we summarize the results.

A seperate inverse model is used to calculate the renewal time of the Canadian Basin

Box Division

For the model calculations, the area was devided into the Greenland Sea, the Norwegian Sea, and the Eurasian Basin of the Arctic Ocean. In the Greenland and Norwegian Seas, we distinguish between upper waters and deep waters, Norwegian Sea Surface Water (NSSW), Greenland Sea Upper Waters (GSUW), Norwegian Sea Deep Water (NSDW), and Greenland Sea Deep Water (GSDW). The Eurasian Basin shows strong vertical stratifications and Eurasian Basin Deep Water (EBDW) and Eurasian Basin Bottom Water (EBBW) are renewed from the Barents Sea (BS). The figure below shows a systematic view of the model. Exchange rates in Sv between the boxes are indicated.

Tracers

Temperature, salinity, tritium, 3He, the tritium/3He-age, CFC11, CFC12, the CFC11/CFC12-ratio, 85Kr, 39Ar, and 14C are used to calculate the exchange rates and renewal times.

Upper Waters

The figures show measurements and model simulations for the upper waters. GSUW is red, NSSW is green, and BS is blue. GSUW is a mixture of 80 % surface water and 20 % NSSW, delayed for 5 years. BS is a mixture of 99.8 % NSSW delayed for 3 years, and 0.2 % river runoff.
The tritium input functions are tuned to the observations.

For CFCs and 85Kr a 85 % equilibration rate with the atmosphere is assumed for BS and the surface water in the Greenland Sea.
This works well for the CFCs.
For 85Kr however, the model simulations are too low. But, since there is no reason to assume a different equilibration rate for 85Kr, the same equilibration rate as for the CFCs is applied.

The CFC model simulations are tuned to the measurements.

Reduction of deep water formation in the Greenland Sea

The figures show data and model simulations of CFC11, tritium, and the tr/3He-age in GSDW for deep water formation rates of

(1) 0.5 Sv between 1940 and 2000,
(2) 0.5 Sv between 1940 and 1980, 0.1 Sv between 1980 and 1993, and 0.5 Sv between 1993 and 2000,
(3) 0.5 Sv between 1940 and 1980 and 0.1 Sv between 1980 and 2000.

It is obvious that the data can only be verified by model simulations assuming a low deep water formation rate after 1980.

History of deep water formation in the Greenland Sea

The figures show model simulations and data for GSDW.
It is possible to reproduce the CFC measurements of the 1980s by a model simulation assuming a deep water formation rate of 0.5 Sv for the time period between 1975 and 1980 only (and 0.1 Sv before and afterwards). A model scenario like that, however, transports too little tritium into the deep basin of the Greenland Sea. Tritium reqires a deep water formation rate of 0.5 Sv for at least the time period between 1965 and 1980.
The 39Ar data, however, can not be verified by such a short period of high deep water formation rates. The 39Ar figures show GSDW in red, NSDW in green, EBDW in blue, and EBBW in purple.

Please note the extended time period of the model simulation to the left, 1900 to 2000 instead of 1940 to 2000 as regular.
The figure to the left shows the 39Ar values for a deep water formation rate of 0.5 Sv between 1910 and 1980 for the assumption that low deep water formation rates (0.1 Sv) are regular in the Greenland Sea. It would take several decades to raise the concentrations to the observed values.

Therefore, we can conclude that it is very likely that deep water formation rates were 0.5 Sv in the Greenland Sea for some decades prior to 1980.

Model simulations and measurements

For 3He a mantle component of 1 atom/cm2sec is assumed.

14C is only used as a steady state tracer in the model. The results depend on the assumed surface concentration and are summarized below (DELTA 14C in permille).

surface
NSDW
GSDW
EBDW
EBBW

-48
-64
-59
-70
-93

-55
-71
-66
-77
-100

These results are in good agreement with calculations in Schlosser et al. [1995] for the higher surface concentrations.

The model simulations usually describe the measurements quite well (within 2 sigma of the measurements). The only exception is 85Kr for which the assumed equilibration rate for the surface water in the Greenland Sea might be too low.

Renewal Times

The renewat times in years are summarized in the table below, the calculated deep water formation and exchange rates in the schematic view of the model at the beginning of the web page.

Period
NSDW total
GSDW surface
GSDW total
EBDW surface
EBDW total
EBBW surface
EBBW total

before 1980
22
34
17
226
62
740
290

1980-1993
31
170
28
226
77
740
290

Pubished in:

Bönisch, G., and P. Schlosser, Deep water formation and exchange rates in the Greenland/Norwegian seas and the Eurasian Basin of the Arctic Ocean derived from tracer balances, Progress in Oceanography, Vol. 35, 29-25, 1995

References

To GIN page
To Eurasion Basin page

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