70
c. Schiifer-Neth . K. Stattegger
the current system except for a strengthening of the East Greenland Current.
On the other hand, meltwaters from the European coast has severe effects. By
shifting the warm and salty inflow away from Britain over to Iceland, they can
spread over the whole GIN Seas, thereby stopping the deep water formation in
this region and pushing the circulation from its normal cyclonal-antiestuarine
into ananticyclonal-estuarine mode.
Our iceberg experiments extend these meltwater studies and address the
following questions: (i) Do icebergs cause circulation changes comparable to
those induced by continental meltwater runoff? (ii) Can Heinrich events be
simulated with SCINNA, and what are their consequences for the ocean circulation? (iii) Can the IRD deposits in Heinrich layers be correlated with distinct
iceberg source regions?
To summarize the results of numerous experiments with different regions
and intensities of iceberg input, we discuss here one study in which icebergs
were released at the coasts of Europe, Greenland, and Labrador. In this experiment, every 25th day, a huge iceberg of 300 m height and 5 km radius was
launched at each of the 32 locations marked by dots in Fig. 6. On average, this
amounts to a 0.29 Sv input of ice. For comparison, height estimates for the
glacial ice dome over the Barents Sea range from 1000 m (Peltier 1994) to
3400 m (Lambeck 1997). Taking 2000 m as a mean value [Saltzman and Verbitzky 1992; Eq. (8)] yields an ice mass of about 3 x 10 16 t, and a melting of
this mass over 2000 years would result in a meltwater input of almost 0.5 Sv.
The lifetime of the icebergs is highly variable, depending on water temperature. Icebergs entering warmer regions at about 50 N decay within 2-4 years,
whereas those transported to polar regions under freezing conditions may last
for some decades. Of course, the distribution of warmer and colder areas
changes with time, because the icebergs compose a heat sink that is not fixed
in space. After about 20 years, the model reaches a new steady state with almost all icebergs drifting to regions warm enough for complete melting, yielding a constant freshwater input of 0.25 Sv that is compensated for by the
boundary restoring zones.
4.2
Iceberg-Induced Circulation Changes
This new state is marked by distinctly decreased temperatures (Fig. 6, left)
reaching the freezing point in the Labrador Sea and at the coasts of Greenland
and Norway. The salinitiy is lowered to values of 30 psu in these regions (Fig. 6,
right), and in the central GIN Seas it drops by 0.8 to 34.2 psu. Most prominent
are the front from Norway to Iceland along 67 N and the cold low-salinity tongue pointing from Canada to Europe at 50 N.
The front corresponds to a strong westward current (Fig. 7, left) north of
Iceland. As a short cut of the GIN Seas cyclone (Fig. 4, left), this current isolates the GIN Seas very effectively from the warmer North Atlantic and feeds
an intensified East Greenland Current. In the Greenland Sea, the fomerly exist-
c. Schiifer-Neth . K. Stattegger
the current system except for a strengthening of the East Greenland Current.
On the other hand, meltwaters from the European coast has severe effects. By
shifting the warm and salty inflow away from Britain over to Iceland, they can
spread over the whole GIN Seas, thereby stopping the deep water formation in
this region and pushing the circulation from its normal cyclonal-antiestuarine
into ananticyclonal-estuarine mode.
Our iceberg experiments extend these meltwater studies and address the
following questions: (i) Do icebergs cause circulation changes comparable to
those induced by continental meltwater runoff? (ii) Can Heinrich events be
simulated with SCINNA, and what are their consequences for the ocean circulation? (iii) Can the IRD deposits in Heinrich layers be correlated with distinct
iceberg source regions?
To summarize the results of numerous experiments with different regions
and intensities of iceberg input, we discuss here one study in which icebergs
were released at the coasts of Europe, Greenland, and Labrador. In this experiment, every 25th day, a huge iceberg of 300 m height and 5 km radius was
launched at each of the 32 locations marked by dots in Fig. 6. On average, this
amounts to a 0.29 Sv input of ice. For comparison, height estimates for the
glacial ice dome over the Barents Sea range from 1000 m (Peltier 1994) to
3400 m (Lambeck 1997). Taking 2000 m as a mean value [Saltzman and Verbitzky 1992; Eq. (8)] yields an ice mass of about 3 x 10 16 t, and a melting of
this mass over 2000 years would result in a meltwater input of almost 0.5 Sv.
The lifetime of the icebergs is highly variable, depending on water temperature. Icebergs entering warmer regions at about 50 N decay within 2-4 years,
whereas those transported to polar regions under freezing conditions may last
for some decades. Of course, the distribution of warmer and colder areas
changes with time, because the icebergs compose a heat sink that is not fixed
in space. After about 20 years, the model reaches a new steady state with almost all icebergs drifting to regions warm enough for complete melting, yielding a constant freshwater input of 0.25 Sv that is compensated for by the
boundary restoring zones.
4.2
Iceberg-Induced Circulation Changes
This new state is marked by distinctly decreased temperatures (Fig. 6, left)
reaching the freezing point in the Labrador Sea and at the coasts of Greenland
and Norway. The salinitiy is lowered to values of 30 psu in these regions (Fig. 6,
right), and in the central GIN Seas it drops by 0.8 to 34.2 psu. Most prominent
are the front from Norway to Iceland along 67 N and the cold low-salinity tongue pointing from Canada to Europe at 50 N.
The front corresponds to a strong westward current (Fig. 7, left) north of
Iceland. As a short cut of the GIN Seas cyclone (Fig. 4, left), this current isolates the GIN Seas very effectively from the warmer North Atlantic and feeds
an intensified East Greenland Current. In the Greenland Sea, the fomerly exist-