Figure 3. Comparison of upper water column temperature structure to the temperature estimate given by the U^k´₃₇ index determined in eight box core tops. Although a range of production scenarios describe the sediment data (shaded box represents range of U^k´₃₇ temperatures in core tops and possible depths of production in relation to annual variations in water-column temperature), the most plausible explanation involves alkenone synthesis near the sea surface with little seasonal bias. Dotted lines show high and low extremes.