Smithsonian at the Poles: Contributions to International Polar

TABLE 4. Mean PAR for each site for the period 26 July– 10
August (n � 1071 hourly measurements for each site) from
2004– 2006. Asterisks denote site means that are signifi cantly
different (p � 0.05) within years. Average surface PAR for the
same period is provided for reference.
Mean PAR (�mol m �2 s �1 )
Year W-1 E-1 DS-11 Surface
2004 15.3* 23.3 28.0 314.9
2005 28.3* 45.1* 59.2* 356.0
2006 23.3* 48.1 42.0 347.9
temperatures were about 2°C warmer in 2006 compared to
2004 and 2005, which was coincident with a 6– 7‰ drop in
surface and bottom water salinities in 2006. Decreased salinities
and pH in 2006 likely refl ect freshwater input from
the nearby Sagavanirktok River, which produced a distinct
brackish water layer to 4 m depths that was not evident in
2004 or 2005. Measurement of bottom salinity at depths
exceeding 6 m at various sites (data not reported here) indicate
that this brackish water layer seldom extended to
the seafl oor, sparing benthic organisms at depths greater
than 5 m exposure to widely fl uctuating salinities and temperatures.
However, vertical gradients in temperature and/
or salinity were apparent all three years, producing a clear
pycnocline.
Based on in situ frond length measurements made on
Laminaria solidungula plants in summers 2005 and 2006,
we were able to make new calculations of kelp biomass at
sites DS-11 (n � 226) and E-1 (n � 53). Areal biomass at
each site was calculated using a correlation coeffi cient between
basal blade dry weight (gdw) and basal blade length
(cm) developed for the Stefansson Sound Boulder Patch using
specimens collected between 1980 and 1984 (n � 912;
Figure 8). Biomass at DS-11 (>25% rock cover) ranged
from 5 to 45 gdw m �2 (mean 23 gdw m �2 ) compared to
a range of 0.5 to 2.7 gdw m �2 (mean 1.7 gdw m �2 ) at site
E-1 (10– 25% rock cover). Intermediate levels of biomass
were recorded at sites W-3 (10.1 gdw m �2 ) and E-3 (14.8
gdw m �2 ), both designated as sites with �25% rock cover
by Toimil (1980). The range in biomass at DS-11 is within
the estimates reported by Dunton et al. (1982). Estimates
of benthic biomass at sites in Stefansson Sound are critical
for calculation of realistic basin-wide benthic production
models in relation to changes in PAR.
Blade elongation in Laminaria solidungula displays
large spatial and temporal variability as refl ected in mea-
INTERANNUAL VARIABILITY IN LIGHT ATTENUATION 281
FIGURE 8. Correlation between basal blade dry weight (g) and basal
blade length (cm) in Laminaria solidungula.
surements from nine sites over the past decade (Figure 9).
In addition, mean blade growth at two sites, DS-11 and
E-1, made since 1977 and 1981, respectively, reveal some
interesting long-term interannual variations (Figure 10).
The two years of lowest growth (1999 and 2003) occurred
relatively recently and coincide with summers characterized
by intense storm activity that likely produced extremely
turbid water conditions resulting in extremely
FIGURE 9. Variation in annual growth in Laminaria solidungula
from 1996 to 2006 at sites occupied in the Stefansson Sound Boulder
Patch. Measurements are based on blade lengths of plants collected
between 2001 and 2006. Values are means � SE.