16
Weferetal.
lated to upwelling and subsequent stratification
events (Emiliania sp.). Interannual variations may
be important in producing bloom conditions which
would dominate the supply of E. huxleyi to
sediments. The temperature fields during such
conditions may be atypical.
There are now several investigations which
provide indications as to what season and water
depth is documented by the alkenone temperature
estimates. Alkenone temperatures from 149 surface-sediment samples taken in the South Atlantic
have been compared to measured seasonal temperatures at various depths in the water column
(MUlier et al. 1998). The best correlation was observed using annual mean SST from 0-10 m water depth, deteriorating singificantly below 20 m
water depth. This study also showed that
seasonality of primary production and variations in
growth rate of the algae and nutrient availability
seem to have no strong effect on the U k '37 record
at least in open ocean environments. Applying a
global data set of core-tops (Fig. 8), the resulting
calibration of MUller et al. (1998) is almost identical to the linear relationship derived from culture
experiments of E. huxleyi (Prahl and Wakeham
1987). The standard error of estimate using the caliCore-top calibration of u~;
1.0
0.9
0.8
0,7
0.6
I"M
~
0.5
:::>
0.4
0.3
0.2
0.1
0.0
0
5
+
+
+
Pacific
D
+
o
Atlantic Ocean
Indian Ocean
()
Pacific Ocean
10
15
20
25
Annual mean SST, 0 m (DC)
30
Fig. 8. Relationships between Uk' 37 and annual mean SST (0 m water depth) for surface sediments from the global
ocean (60 0 N-60oS; U k ' 37 data based on literature and from MUller et al. (1998). From MUller et al. (I998).