Monthly Kachemak Bay report, November 2025
Summary
While sea-surface-temperatures in most parts of the Pacific remain anomalously warm, the warm-anomaly is not as ubiquitous or severe anymore as it was three months ago. Temperatures in Kachemak Bay are near the long-term mean again. Salinity in the inner bay was unseasonably high, where chlorophyll concentrations were low for the seasons, indicating an early onset of fall/winter conditions. Turbidity levels in deep water beyond 70 m were over 2 SD above the norm.
Conditions
After a missed month due to the shutdown of the federal government, Hans, Kris, and Ross conducted the KBL monthly survey on 18 November survey, which included T9 across the bay from the Homer Spit and the AlongBay transect. After a slightly warmer than normal September (approaching the 90th percentile), temperatures during the month leading up to this survey were close to the long-term seasonal mean (Figure 1). As is normal in Kachemak Bay, precipitation this fall was higher than during summer, but amounts in the month leading up to this survey were close to the long-term mean.
A complete set of up-to-date graphs can be found on the Google Drive: section plots and time sections.
Physical oceanography
Temperature
Recorded water temperatures during this survey ranged from a minimum of 6.9 °C at station AlongBay-10 (1 m depth), in the inner bay off Glacier Spit, to a maximum of 8.5 °C at AlongBay-1 (33 m depth) in the outer bay, off Seldovia. Throughout the bay, surface waters were cooler than deep water layers, especially in the inner bay. Deep water temperatures varied only slightly, but surface waters showed an area of cool water in the inner bay (Figure 2 (a)). The low salinity and high turbidity of this area indicated that this was due a plume of glacial outflow, most likely from nearby Grewingk Glacier.
The cross-bay transect of the Homer Spit (T9) was characterized by three distinct water masses of different temperatures: 1. cool waters at the northern end of the transect, especially near the surface (outflowing water from the inner bay, effectively air-cooled in shallow waters), 2. warmer water in the southern half of the transect (in-flowing oceanic water from the outer bay), and 3. warm waters pooling near the bottom (being denser than surface waters due to higher salinity, Figure 2 (b)). On a larger scale, satellite data showed a similar trend for sea surface temperatures, as observed here for Kachemak Bay, for Cook Inlet: warm waters from the Gulf of Alaska, gradually cooled, as they moved into the increasingly shallow waters of the upper inlet (Figure 3).
After a summer that was substantially warmer than the long-term mean (Figure 4, Figure 7, Figure 5), water temperatures were again closer normal values. Most values along both, the AlongBay, and T9 transects were within 0.5 standard deviations of the long-term mean (anomaly plots on the right: Figure 2 (a), Figure 2 (b)). While surface layers along T9 remained over 0.5 SD above normal (Figure 2 (b), also see Figure 5), deep waters were within 0.5 SD of normal, both in the AlongBay transect and in T9 (Figure 2 (a), Figure 2 (b), Figure 6).
Salinity
Salinity values ranged from 29.6 PSU at AlongBay-4 (4m depth) in the outer bay to 31.4 at AlongBay-5 (168m depth) in the outer bay. A salinity gradient maintained a stratified water column in much of Kachemak Bay (Figure 2 (a)), even though the differences in salinity were small compared to summer. In contrast to the summer months, there was no distinct pycnocline, but rather a smooth, gradual change from saltier deep waters to fresher surface waters. The fact that surface waters were fresher at the mouth of the bay than at the head, a reversal from the summer pattern, indicated that the fresher surface water originated less from local river/meltwater influx, but rather came from Cook Inlet (and ultimately the Alaskan Coastal Current). Mid-waters along T9 were saltier at the northern end of the transect and fresher in the southern part (Figure 2 (b)), also supported this hypothesis (currents are generally counter-clockwise in Kachemak Bay).
Since the beginning of the year, salinities at the mid-bay station T9-6 have been lower than the seasonal mean (Figure 8), particularly in waters below 25 m (Figure 7). This anomaly has reversed in September, deep waters being saltier than normal, and remained so into November. The anomaly section plots show that this anomaly at T9-6 was due to the inner bay being up to 1.5 SD saltier than expected (Figure 2 (a), Figure 2 (b)), suggesting that even though air temperatures in Homer were close to the long-term mean, freshwater influx had deminished unseasonally early.
Turbidity
While no areas of high turbidity were recorded during the survey, stations showed localized increased surface turbidity, visible both in the raw measurements and in the anomaly plot (Figure 2 (a)). These were likely due to plumes of glacier-fed streams entering the bay. Bottom waters also showed increased turbidity. Interestingly, turbidity near in deep waters over 100 m was over 2 standard deviations greater than the expected values, which is a substantial deviation from the norm.
Biological conditions
Phytoplankton
Chlorophyll concentrations were low throughout Kachemak Bay, showing no areas of concentrated activity (Figure 2 (a)). The highest concentration measured was 0.4 mg m^-3 at AlongBay-3 (2 m depth). Chlorophyll concentrations in the outer bay were near the long-term mean, but were over one standard deviation below in the inner bay (Figure 2 (b), Figure 9). Along with salinity values in the inner bay, fall appeared to have come early in the inner bay.
Wildlife
One late humpback whale was sighted.
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