Ten or more years' worth of collected data is needed before beginning to analyze for climate change. Through monitoring, we hope to track natural changes in oceanographic conditions — such as the Pacific Decadal Oscillation — that occur over tens of years. In the short term, we are trying to understand the ocean's seasonal and inter-annual variability, as well as major factors that alter water quality.
Wintertime water temperatures tend to be about 4 degrees Celsius (39 degrees Fahrenheit); however during the winter of 2002-2003 the water temperature was 6 degrees Celsius (43 degrees Fahrenheit). This winter we found that the bay's temperatures were very similar — nearly 6 degrees Celsius. The water's temperature begins to rise in late March and continues rising at a rate of 1 degree Celsius per month until August.
Typical late summer water temperatures show much less variability than those of the winter, with the temperature in August and September measuring around 11 degrees Celsius (52 degrees Fahrenheit). Interestingly, the maximum and minimum temperatures do not occur at the same time as the maximum and minimum amounts of sunlight.
The maximum water temperature occurs later in the year because, even though there is less sunlight, there is still enough solar heat to continue warming the water. Water temperature does not begin to decrease until the nighttime cooling exceeds the daytime warming. Kachemak Bay's water temperatures begin decreasing in October and reach their minimum in January.
In August, pulses of warm, fresh water start entering Kachemak Bay on two-week intervals along its southern shore. The salinity and temperature structure of these pulses are consistent with what we know about the Alaska Coastal Current (ACC), which flows east to west along the Kenai Peninsula's outer coast. These pulses may be an indicator of the seasonal connection between Kachemak Bay and the Gulf of Alaska via the ACC.
While the salinity of deep water (greater than 15 meters or 50 feet) does not change much over the year, it does begin to decrease in late August and reaches a minimum in October. This minimum occurs at the same time as maximum rainfall. As rain then changes to snow, there is less freshwater input and by January the deep water salinity has risen to its normal value — around 31 parts per thousand. Similarly, the surface salinity decreases with the increased rainfall and may be as low as 15 ppt in October.
To learn more about the Kachemak Bay Research Reserve, please visit www.kbayrr.org.
Scott Pegau is a physical oceanographer and research coordinator with the Kachemak Bay Research Reserve.
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