Wintertime Expansion and Contraction of the Terra Nova Bay Polynya
161
34.5 PSU, roughly consistent with the salinity of Warm Core Water (WMCO) or
Low Salinity Shelf Water (LSSW) [45]. It follows that the total sait released into the
water column is:
^sait = Pi • (1-0.31) • (34.5 x 10’3) • YIce
(10)
where Ç, is the density of sea ice (0.95xl03 kg m 3) and the factor of 10'3 converts
grams per kilogram (PSU) into grams per gram [7], Roughly IxlO12 kg sait was
produced during the 4-month period in each of the 3 years with again the results
for 1989 being -10% higher than the other 2 years (Table 2).
The total volume of WMCO or LSSW converted to HSSW, which has a salinity
of 34.8 PSU [45], is given by
YsW -
Z Sait
Phssw (Shssw “ ^lssw) x 10 ’>
(H)
where pHSSVV is the density of HSSW (1030.45 kg m'3), Shssw is the salinity of
HSSW, and Slssvv is the salinity of LSSW and WMCO. Again the factor of 10’3 is
used to converts grams per kilogram (PSU) into grams per gram. Roughly
IxlO13 m3 HSSW is produced during this 4-month period. To convert WMCO
and LSSW to HSSW at a rate consistent with the observed ice production rate,
a transport of roughly 1 Sv is required during the winter months (Table 2). This
is comparable with estimâtes from recent current measurements in Terra Nova
Bay [46],
6 Summary
The original tenet of this study is that a simple polynya model, driven by in situ
heat flux data, could be used to estimate open water fraction at Terra Nova Bay.
The major finding of this study is that even for a nearly idéal situation, like Terra
Nova Bay, at best the model could explain only about 40% of the variance
observed in time-coincident microwave-derived ice concentration data. However,
in spite of not fully modeling fluctuations in open water fraction at Terra Nova
Bay, some insight into the dynamics of the polynya was obtained. Specifically it
was found that:
1. Both the longwave and sensible heat fluxes each explain roughly 15% of the
observed variance in satellite-derived open water fraction.
2. Fluctuations in both air température and wind speed contribute to changes in
the size of the Terra Nova Bay polynya; however, the contribution from the
wind speed is introduced as an amplification of the radiative flux terms.
3. The simple polynya models tested here did not adequately explain several
anomalously large polynya fluctuations that occurred during the three winters
studied. The polynya models studied here assumed that fluctuations in
polynya extent take place in response to local one-dimensional meteorological
forcing. The large unexplained fluctuations in polynya extent appeared to
161
34.5 PSU, roughly consistent with the salinity of Warm Core Water (WMCO) or
Low Salinity Shelf Water (LSSW) [45]. It follows that the total sait released into the
water column is:
^sait = Pi • (1-0.31) • (34.5 x 10’3) • YIce
(10)
where Ç, is the density of sea ice (0.95xl03 kg m 3) and the factor of 10'3 converts
grams per kilogram (PSU) into grams per gram [7], Roughly IxlO12 kg sait was
produced during the 4-month period in each of the 3 years with again the results
for 1989 being -10% higher than the other 2 years (Table 2).
The total volume of WMCO or LSSW converted to HSSW, which has a salinity
of 34.8 PSU [45], is given by
YsW -
Z Sait
Phssw (Shssw “ ^lssw) x 10 ’>
(H)
where pHSSVV is the density of HSSW (1030.45 kg m'3), Shssw is the salinity of
HSSW, and Slssvv is the salinity of LSSW and WMCO. Again the factor of 10’3 is
used to converts grams per kilogram (PSU) into grams per gram. Roughly
IxlO13 m3 HSSW is produced during this 4-month period. To convert WMCO
and LSSW to HSSW at a rate consistent with the observed ice production rate,
a transport of roughly 1 Sv is required during the winter months (Table 2). This
is comparable with estimâtes from recent current measurements in Terra Nova
Bay [46],
6 Summary
The original tenet of this study is that a simple polynya model, driven by in situ
heat flux data, could be used to estimate open water fraction at Terra Nova Bay.
The major finding of this study is that even for a nearly idéal situation, like Terra
Nova Bay, at best the model could explain only about 40% of the variance
observed in time-coincident microwave-derived ice concentration data. However,
in spite of not fully modeling fluctuations in open water fraction at Terra Nova
Bay, some insight into the dynamics of the polynya was obtained. Specifically it
was found that:
1. Both the longwave and sensible heat fluxes each explain roughly 15% of the
observed variance in satellite-derived open water fraction.
2. Fluctuations in both air température and wind speed contribute to changes in
the size of the Terra Nova Bay polynya; however, the contribution from the
wind speed is introduced as an amplification of the radiative flux terms.
3. The simple polynya models tested here did not adequately explain several
anomalously large polynya fluctuations that occurred during the three winters
studied. The polynya models studied here assumed that fluctuations in
polynya extent take place in response to local one-dimensional meteorological
forcing. The large unexplained fluctuations in polynya extent appeared to